Stereoisomerism: The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)Encyclopedias as Topic: Works containing information articles on subjects in every field of knowledge, usually arranged in alphabetical order, or a similar work limited to a special field or subject. (From The ALA Glossary of Library and Information Science, 1983)Aporphines: Dibenzoquinolines derived in plants from (S)-reticuline (BENZYLISOQUINOLINES).Phenmetrazine: A sympathomimetic drug used primarily as an appetite depressant. Its actions and mechanisms are similar to DEXTROAMPHETAMINE.Candy: Sweet food products combining cane or beet sugars with other carbohydrates and chocolate, milk, eggs, and various flavorings. In the United States, candy refers to both sugar- and cocoa-based confections and is differentiated from sweetened baked goods; elsewhere the terms sugar confectionary, chocolate confectionary, and flour confectionary (meaning goods such as cakes and pastries) are used.Hallucinations: Subjectively experienced sensations in the absence of an appropriate stimulus, but which are regarded by the individual as real. They may be of organic origin or associated with MENTAL DISORDERS.Lethargy: A general state of sluggishness, listless, or uninterested, with being tired, and having difficulty concentrating and doing simple tasks. It may be related to DEPRESSION or DRUG ADDICTION.Designer Drugs: Drugs designed and synthesized, often for illegal street use, by modification of existing drug structures (e.g., amphetamines). Of special interest are MPTP (a reverse ester of meperidine), MDA (3,4-methylenedioxyamphetamine), and MDMA (3,4-methylenedioxymethamphetamine). Many drugs act on the aminergic system, the physiologically active biogenic amines.Bromobenzoates: Benzoic acid or benzoic acid esters substituted with one or more bromine atoms.MedlinePlus: NATIONAL LIBRARY OF MEDICINE service for health professionals and consumers. It links extensive information from the National Institutes of Health and other reviewed sources of information on specific diseases and conditions.Antitussive Agents: Agents that suppress cough. They act centrally on the medullary cough center. EXPECTORANTS, also used in the treatment of cough, act locally.Aphasia: A cognitive disorder marked by an impaired ability to comprehend or express language in its written or spoken form. This condition is caused by diseases which affect the language areas of the dominant hemisphere. Clinical features are used to classify the various subtypes of this condition. General categories include receptive, expressive, and mixed forms of aphasia.Aphasia, Wernicke: Impairment in the comprehension of speech and meaning of words, both spoken and written, and of the meanings conveyed by their grammatical relationships in sentences. It is caused by lesions that primarily affect Wernicke's area, which lies in the posterior perisylvian region of the temporal lobe of the dominant hemisphere. (From Brain & Bannister, Clinical Neurology, 7th ed, p141; Kandel et al., Principles of Neural Science, 3d ed, p846)Aphasia, Broca: An aphasia characterized by impairment of expressive LANGUAGE (speech, writing, signs) and relative preservation of receptive language abilities (i.e., comprehension). This condition is caused by lesions of the motor association cortex in the FRONTAL LOBE (BROCA AREA and adjacent cortical and white matter regions).Aphasia, Primary Progressive: A progressive form of dementia characterized by the global loss of language abilities and initial preservation of other cognitive functions. Fluent and nonfluent subtypes have been described. Eventually a pattern of global cognitive dysfunction, similar to ALZHEIMER DISEASE, emerges. Pathologically, there are no Alzheimer or PICK DISEASE like changes, however, spongiform changes of cortical layers II and III are present in the TEMPORAL LOBE and FRONTAL LOBE. (From Brain 1998 Jan;121(Pt 1):115-26)Anomia: A language dysfunction characterized by the inability to name people and objects that are correctly perceived. The individual is able to describe the object in question, but cannot provide the name. This condition is associated with lesions of the dominant hemisphere involving the language areas, in particular the TEMPORAL LOBE. (From Adams et al., Principles of Neurology, 6th ed, p484)Aphasia, Conduction: A type of fluent aphasia characterized by an impaired ability to repeat one and two word phrases, despite retained comprehension. This condition is associated with dominant hemisphere lesions involving the arcuate fasciculus (a white matter projection between Broca's and Wernicke's areas) and adjacent structures. Like patients with Wernicke aphasia (APHASIA, WERNICKE), patients with conduction aphasia are fluent but commit paraphasic errors during attempts at written and oral forms of communication. (From Adams et al., Principles of Neurology, 6th ed, p482; Brain & Bannister, Clinical Neurology, 7th ed, p142; Kandel et al., Principles of Neural Science, 3d ed, p848)Primary Progressive Nonfluent Aphasia: A form of frontotemporal lobar degeneration and a progressive form of dementia characterized by motor speech impairment and AGRAMMATISM, with relative sparing of single word comprehension and semantic memory.Language Tests: Tests designed to assess language behavior and abilities. They include tests of vocabulary, comprehension, grammar and functional use of language, e.g., Development Sentence Scoring, Receptive-Expressive Emergent Language Scale, Parsons Language Sample, Utah Test of Language Development, Michigan Language Inventory and Verbal Language Development Scale, Illinois Test of Psycholinguistic Abilities, Northwestern Syntax Screening Test, Peabody Picture Vocabulary Test, Ammons Full-Range Picture Vocabulary Test, and Assessment of Children's Language Comprehension.Wernicke Encephalopathy: An acute neurological disorder characterized by the triad of ophthalmoplegia, ataxia, and disturbances of mental activity or consciousness. Eye movement abnormalities include nystagmus, external rectus palsies, and reduced conjugate gaze. THIAMINE DEFICIENCY and chronic ALCOHOLISM are associated conditions. Pathologic features include periventricular petechial hemorrhages and neuropil breakdown in the diencephalon and brainstem. Chronic thiamine deficiency may lead to KORSAKOFF SYNDROME. (Adams et al., Principles of Neurology, 6th ed, pp1139-42; Davis & Robertson, Textbook of Neuropathology, 2nd ed, pp452-3)Speech Therapy: Treatment for individuals with speech defects and disorders that involves counseling and use of various exercises and aids to help the development of new speech habits.RNA, Messenger: RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.Codon: A set of three nucleotides in a protein coding sequence that specifies individual amino acids or a termination signal (CODON, TERMINATOR). Most codons are universal, but some organisms do not produce the transfer RNAs (RNA, TRANSFER) complementary to all codons. These codons are referred to as unassigned codons (CODONS, NONSENSE).Ribosomes: Multicomponent ribonucleoprotein structures found in the CYTOPLASM of all cells, and in MITOCHONDRIA, and PLASTIDS. They function in PROTEIN BIOSYNTHESIS via GENETIC TRANSLATION.RNA: A polynucleotide consisting essentially of chains with a repeating backbone of phosphate and ribose units to which nitrogenous bases are attached. RNA is unique among biological macromolecules in that it can encode genetic information, serve as an abundant structural component of cells, and also possesses catalytic activity. (Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)RNA, Ribosomal: The most abundant form of RNA. Together with proteins, it forms the ribosomes, playing a structural role and also a role in ribosomal binding of mRNA and tRNAs. Individual chains are conventionally designated by their sedimentation coefficients. In eukaryotes, four large chains exist, synthesized in the nucleolus and constituting about 50% of the ribosome. (Dorland, 28th ed)Polymers: Compounds formed by the joining of smaller, usually repeating, units linked by covalent bonds. These compounds often form large macromolecules (e.g., BIOPOLYMERS; PLASTICS).RNA, Transfer: The small RNA molecules, 73-80 nucleotides long, that function during translation (TRANSLATION, GENETIC) to align AMINO ACIDS at the RIBOSOMES in a sequence determined by the mRNA (RNA, MESSENGER). There are about 30 different transfer RNAs. Each recognizes a specific CODON set on the mRNA through its own ANTICODON and as aminoacyl tRNAs (RNA, TRANSFER, AMINO ACYL), each carries a specific amino acid to the ribosome to add to the elongating peptide chains.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.RNA, Viral: Ribonucleic acid that makes up the genetic material of viruses.Chemistry, Organic: The study of the structure, preparation, properties, and reactions of carbon compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Viral Structures: The structural parts of the VIRION.Organic Chemistry Phenomena: The conformation, properties, reaction processes, and the properties of the reactions of carbon compounds.Denture, Partial, Temporary: A partial denture intended for short-term use in a temporary or emergency situation.Electrons: Stable elementary particles having the smallest known negative charge, present in all elements; also called negatrons. Positively charged electrons are called positrons. The numbers, energies and arrangement of electrons around atomic nuclei determine the chemical identities of elements. Beams of electrons are called CATHODE RAYS.Compact Disks: Computer disks storing data with a maximum reduction of space and bandwidth. The compact size reduces cost of transmission and storage.Terminology as Topic: The terms, expressions, designations, or symbols used in a particular science, discipline, or specialized subject area.Molecular Structure: The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.Elements: Substances that comprise all matter. Each element is made up of atoms that are identical in number of electrons and protons and in nuclear charge, but may differ in mass or number of neutrons.Avibirnavirus: A genus of RNA viruses in the family BIRNAVIRIDAE infecting birds. It is transmitted horizontally with no known vectors. The type species is INFECTIOUS BURSAL DISEASE VIRUS.Physiology: The biological science concerned with the life-supporting properties, functions, and processes of living organisms or their parts.Physicochemical Processes: Physical reactions involved in the formation of or changes in the structure of atoms and molecules and their interactions.Drug Repositioning: The deliberate and methodical practice of finding new applications for existing drugs.Databases, Pharmaceutical: Databases devoted to knowledge about PHARMACEUTICAL PRODUCTS.Drug Discovery: The process of finding chemicals for potential therapeutic use.Drug Design: The molecular designing of drugs for specific purposes (such as DNA-binding, enzyme inhibition, anti-cancer efficacy, etc.) based on knowledge of molecular properties such as activity of functional groups, molecular geometry, and electronic structure, and also on information cataloged on analogous molecules. Drug design is generally computer-assisted molecular modeling and does not include pharmacokinetics, dosage analysis, or drug administration analysis.Pharmaceutical Preparations: Drugs intended for human or veterinary use, presented in their finished dosage form. Included here are materials used in the preparation and/or formulation of the finished dosage form.Students: Individuals enrolled in a school or formal educational program.

Accumulation of astaxanthin all-E, 9Z and 13Z geometrical isomers and 3 and 3' RS optical isomers in rainbow trout (Oncorhynchus mykiss) is selective. (1/9955)

Concentrations of all-E-, 9Z- and 13Z- geometrical and (3R,3'R), (3R, 3'S) and (3S,3'S) optical isomers of astaxanthin were determined in rainbow trout liver, gut tissues, kidney, skin and blood plasma to evaluate their body distribution. Two cold-pelleted diets containing predominantly all-E-astaxanthin (36.9 mg/kg astaxanthin, 97% all-E-, 0.4% 9Z-, 1.5% 13Z-astaxanthin, and 1.1% other isomers, respectively) or a mixture of all-E- and Z-astaxanthins (35.4 mg/kg astaxanthin, 64% all-E-, 18.7% 9Z-, 12.3% 13Z-astaxanthin, and 2.0% other isomers, respectively), were fed to duplicate groups of trout for 69 d. Individual E/Z isomers were identified by VIS- and 1H-NMR-spectrometry, and quantified by high-performance liquid chromatography. Significantly higher total carotenoid concentration was observed in plasma of trout fed diets with all-E-astaxanthin (P < 0.05). The relative E/Z-isomer concentrations of plasma, skin and kidney were not significantly different among groups, whereas all-E-astaxanthin was higher in intestinal tissues and 13Z-astaxanthin was lower in liver of trout fed all-E-astaxanthin (P < 0.05). The relative amount of hepatic 13Z-astaxanthin (39-49% of total astaxanthin) was higher than in all other samples (P < 0.05). Synthetic, optically inactive astaxanthin was used in all experiments, and the determined dietary ratio between the 3R,3'R:3R, 3'S (meso):3S,3'S optical isomers was 25.3:49.6:25.1. The distribution of R/S-astaxanthin isomers in feces, blood, liver and fillet was similar to that in the diets. The ratio between (3S,3'S)- and (3R,3'R)-astaxanthin in the skin and posterior kidney was ca. 2:1 and 3:1, respectively, regardless of dietary E/Z-astaxanthin composition. The results show that geometrical and optical isomers of astaxanthin are distributed selectively in different tissues of rainbow trout.  (+info)

Kinetic study of alpha-chymotrypsin catalysis with regard to the interaction between the specificity-determining site and the aromatic side chain of substrates. (2/9955)

In order to investigate how changes in the structures of side-chain aromatic groups of specific substrates influence binding and kinetic specificity in alpha chymotrypsin [EC 3.4.21.1]-catalyzed reactions, a number of nucleus-substituted derivatives of the specific ester substrates were prepared and steady-state kinetic studies were carried out at pH 6.5 and 7.8. Ac-Trp(NCps)-OMe was hydrolyzed more readily at low substrate concentration than Ac-Trp-OMe due to its smaller Km(app) value, suggesting that the bulky 2-nitro-4-carboxyphenylsulfenyl moiety interacts with outer residues rather than with those in the hydrophobic pocket and that this interaction increases the binding specificity. Inhibition experiments using the corresponding carboxylate and analogous inhibitors, however, showed that the carboxy group at the para position of the phenyl nucleus of the substituent sterically hinders association with the active site of alpha-chymotrypsin at pH 7.8 but not at pH 6.5. The kcat values of Ac-Trp(CHO)-0Me, Ac-Tyr(3-NO2)-OMe, and Ac-m-Tyr-OMe were much higher than those of the corresponding specific substrates, indicating that derivatives with a substitute as large as a formyl, nitro or hydroxyl group at the xi-position are stereochemically favorable to the catalytic process. Remarkable increases in Km(app) were also observed. The individual parameters for Ac-Dopa-OMe, however, were comparable to those for Ac-Tyr-OMe.  (+info)

Determination of the anomeric configurations of Corbicula ceramide di- and trihexoside by chromium trioxide oxidation. (3/9955)

The anomeric configurations of Corbicula ceramide dihexoside and ceramide trihexoside were determined by chromium trioxide oxidation and the structures of these lipids were shown to be Man-beta(1 leads to 4)-Glc-beta(1 leads to 1)-ceramide and Man-alpha(1 leads to 4)-Man-beta(1 leads to 4)-Glc-beta(1 leads to 1)-ceramide. These results are compatible with those obtained by enzymic hydrolysis reported previously.  (+info)

Characterization of the analgesic and anti-inflammatory activities of ketorolac and its enantiomers in the rat. (4/9955)

The marked analgesic efficacy of ketorolac in humans, relative to other nonsteroidal anti-inflammatory drugs (NSAIDs), has lead to speculation as to whether additional non-NSAID mechanism(s) contribute to its analgesic actions. To evaluate this possibility, we characterized (R,S)-ketorolac's pharmacological properties in vivo and in vitro using the nonselective cyclooxygenase (COX) inhibitors [indomethacin (INDO) and diclofenac sodium (DS)] as well as the selective COX-2 inhibitor, celecoxib, as references. The potency of racemic (R,S)-ketorolac was similar in tests of acetic acid-induced writhing, carrageenan-induced paw hyperalgesia, and carrageenan-induced edema formation in rats; ID50 values = 0.24, 0. 29, and 0.08 mg/kg, respectively. (R,S)-ketorolac's actions were stereospecific, with (S)-ketorolac possessing the biological activity of the racemate in the above tests. The analgesic potencies for (R,S)-, (S)-, and (R)-ketorolac, INDO, and DS were highly correlated with their anti-inflammatory potencies, suggesting a common mechanism. (R,S)-ketorolac was significantly more potent than INDO or DS in vivo. Neither difference in relative potency of COX inhibition for (R,S)-ketorolac over INDO and DS nor activity of (S)-ketorolac at a number of other enzymes, channels, or receptors could account for the differences in observed potency. The distribution coefficient for (R,S)-ketorolac was approximately 30-fold less than for DS or INDO, indicating that (R,S)-ketorolac is much less lipophilic than these NSAIDs. Therefore, the physicochemical and pharmacokinetics properties of (R,S)-ketorolac may optimize the concentrations of (S)-ketorolac at its biological target(s), resulting in greater efficacy and potency in vivo.  (+info)

Comparison of local anesthetic activities between optical isomers of cis-1-benzoyloxy-2-dimethylamino-1,2,3,4-tetrahydronaphthalene. (5/9955)

The optical isomers of cis-1-benzoyloxy-2-dimethylamino-1,2,3,4-tetrahydronaphthalene (YAU-17) were compared for their local anesthetic activity, acute toxicity, spasmolytic activity, and partition coefficient between chloroform and phosphate buffer. 1-YAU-17 was more active than d-YAU-17 in blocking the conduction of action potentials in isolated frog sciatic nerves. The difference in local anesthetic activities between the optical isomers was further substantiated by in vivo tests for corneal anesthesia, intracutaneous anesthesia and sciatic nerve block in quinea-pigs. Similarly, the i.v. injection to mice revealed a higher toxicity for 1-YAU-17 as compared to its d-isomer. In these tests, the potency ratios of the enantiomers ranged from 2 to 4, and the racemate had an intermediate potency. On the contrary, no difference among the compounds was found in their liposolubility, partition coefficient, and spasmolytic activity examined with isolated guinea-pig ileum. These results indicate that the steric factors play an important role in the production of different local anesthetic activities between the optical isomers of YAU-17, and their local anesthetic potency tends to be correlated to their intravenous acute toxicity but not to their spasmolytic activity.  (+info)

In vitro activities of aminomethyl-substituted analogs of novel tetrahydrofuranyl carbapenems. (6/9955)

CL 188,624, CL 190,294, and CL 191,121 are novel aminomethyl tetrahydrofuranyl (THF)-1 beta-methylcarbapenems. The in vitro antibacterial activities of these THF carbapenems were evaluated and compared with those of biapenem, imipenem, and meropenem against 554 recent clinical isolates obtained from geographically distinct medical centers across North America. The antibacterial activities of the THF carbapenems were equivalent to that of biapenem, and the THF carbapenems were slightly more active than imipenem and less active than meropenem against most of the members of the family Enterobacteriaceae but lacked significant activity against Pseudomonas isolates. In general, CL 191,121 was two- to fourfold more active than CL 188,624 and CL 190,294 against the staphylococcal and enterococcal isolates tested. CL 191,121 was twofold less active than imipenem against methicillin-susceptible staphylococci and was as activity as imipenem against Enterococcus faecalis isolates. Biapenem and meropenem were two- and fourfold less active than CL 191,121, respectively, against the methicillin-susceptible staphylococci and E. faecalis. All the carbapenems displayed equivalent good activities against the streptococci. Biapenem was slightly more active than the other carbapenems against Bacteroides fragilis isolates. Time-kill curve studies demonstrated that the THF carbapenems were bactericidal in 6 h against Escherichia coli and Staphylococcus aureus isolates. The postantibiotic effect exerted by CL 191,121 was comparable to or slightly longer than that of imipenem against isolates of S. aureus, E. coli, and Klebsiella pneumoniae.  (+info)

In vivo activities of peptidic prodrugs of novel aminomethyl tetrahydrofuranyl-1 beta-methylcarbapenems. (7/9955)

A series of novel aminomethyl tetrahydrofuranyl (THF)-1 beta-methylcarbapenems which have excellent broad-spectrum antibacterial activities exhibit modest efficacies against acute lethal infections (3.8 mg/kg of body weight against Escherichia coli and 0.9 mg/kg against Staphylococcus aureus) in mice when they are administered orally. In an effort to improve the efficacies of orally administered drugs through enhanced absorption by making use of a peptide-mediated transport system, several different amino acids were added at the aminomethyl THF side chains of the carbapenem molecules. The resulting peptidic prodrugs with L-amino acids demonstrated improved efficacy after oral administration, while the D forms were less active than the parent molecules. After oral administration increased (3 to 10 times) efficacy was exhibited with the alanine-, valine-, isoleucine-, and phenylalanine-substituted prodrugs against acute lethal infections in mice. Median effective doses (ED50s) of < 1 mg/kg against infections caused by S. aureus, E. coli, Enterobacter cloacae, or penicillin-susceptible Streptococcus pneumoniae were obtained after the administration of single oral doses. Several of the peptidic prodrugs were efficacious against Morganella morganii, Serratia marcescens, penicillin-resistant S. pneumoniae, extended-spectrum beta-lactamase-producing Klebsiella pneumoniae, and E. coli infections, with ED50s of 1 to 14 mg/kg by oral administration compared with ED50s of 14 to > 32 mg/kg for the parent molecules. In general, the parent molecules demonstrated greater efficacy than the prodrugs against these same infections when the drugs were administered by the subcutaneous route. The parent molecule was detectable in the sera of mice after oral administration of the peptidic prodrugs.  (+info)

Enantioselective inhibition of the biotransformation and pharmacological actions of isoidide dinitrate by diphenyleneiodonium sulphate. (8/9955)

1. We have shown previously that the D- and L- enantiomers of isoidide dinitrate (D-IIDN and L-IIDN) exhibit a potency difference for relaxation and cyclic GMP accumulation in isolated rat aorta and that this is related to preferential biotransformation of the more potent enantiomer (D-IIDN). The objective of the current study was to examine the effect of the flavoprotein inhibitor, diphenyleneiodonium sulphate (DPI), on the enantioselectivity of IIDN action. 2. In isolated rat aortic strip preparations, exposure to 0.3 microM DPI resulted in a 3.6 fold increase in the EC50 value for D-IIDN-induced relaxation, but had no effect on L-IIDN-induced relaxation. 3. Incubation of aortic strips with 2 microM D- or L-IIDN for 5 min resulted in significantly more D-isoidide mononitrate formed (5.0 +/- 1.5 pmol mg protein(-1)) than L-isoidide mononitrate (2.1 +/- 0.7 pmol mg protein(-1)) and this difference was abolished by pretreatment of tissues with 0.3 microM DPI. DPI had no effect on glutathione S-transferase (GST) activity or GSH-dependent biotransformation of D- or L-IIDN in the 105,000 x g supernatant fraction of rat aorta. 4. Consistent with both the relaxation and biotransformation data, treatment of tissues with 0.3 microM DPI significantly inhibited D-IIDN-induced cyclic GMP accumulation, but had no effect on L-IIDN-induced cyclic GMP accumulation. 5. In the intact animal, 2 mg kg(-1) DPI significantly inhibited the pharmacokinetic and haemodynamic properties of D-IIDN, but had no effect L-IIDN. 6. These data suggest that the basis for the potency difference for relaxation by the two enantiomers is preferential biotransformation of D-IIDN to NO, by an enzyme that is inhibited by DPI. Given that DPI binds to and inhibits NADPH-cytochrome P450 reductase, the data are consistent with a role for the cytochromes P450-NADPH-cytochrome P450 reductase system in this enantioselective biotransformation process.  (+info)

*Racemic mixture

... for their indecision in a particular stereoisomerism. A frequent scenario is that of a planar species (such as an sp2 carbon ...

*Stereoisomerism

... about double bonds arises because rotation about the double bond is restricted, keeping the substituents fixed ... the "Gold Book") (1997). Online corrected version: (2006-) "stereoisomerism". Columbia Encyclopedia. "Stereoisomers" in ...

*Stereocenter

In compounds whose stereoisomerism is due to tetrahedral stereogenic centers, the total number of hypothetically possible ... "Stereoisomerism and local chirality". Journal of the American Chemical Society. 106 (11): 3319. doi:10.1021/ja00323a043. "IUPAC ...

*Enantiomer

46 (2005), p. 2897er chemwiki:stereoisomerism. ...

*Triangulane

... stereoisomerism and general method of synthesis". J. Am. Chem. Soc. 112 (21): 7702-7707. doi:10.1021/ja00177a034. de Meijere, ...

*Aldose

Because they have at least one asymmetric carbon center, all aldoses exhibit stereoisomerism. Aldoses can exist in either a D- ...

*Coordination complex

Stereoisomerism occurs with the same bonds in different orientations relative to one another. Stereoisomerism can be further ...

*Cis-trans isomerism

IUPAC definition of "stereoisomerism" IUPAC definition of "geometric isomerism" IUPAC definition of "cis-trans isomers". ...

*Alicja Dorabialska

Dorabialska wrote her dissertation on thermochemical investigations on stereoisomerism in ketones under the supervision of ...

*Molecular configuration

The ability of the same set of atoms to form two or more molecules with different configurations is stereoisomerism. Used as ...

*Dosulepin

... exhibits (E) and (Z) stereoisomerism like doxepin but in contrast is used as the pure E or trans isomer. The chemical ...

*Chirality (chemistry)

This center is thus stereogenic (i.e., a grouping within a molecular entity that may be considered a focus of stereoisomerism ... 21st International Symposium on Chirality STEREOISOMERISM - OPTICAL ISOMERISM Symposium highlights-Session 5: New technologies ... drug Enantioselective synthesis Pfeiffer effect Stereochemistry for overview of stereochemistry in general Stereoisomerism ...

*Endo-exo isomerism

... is a special type of stereoisomerism found in organic compounds with a substituent on a bridged ring system ...

*Lofentanil

As with other 3-substituted fentanyl derivatives such as ohmefentanyl, the stereoisomerism of lofentanil is very important, ...

*Gonyautoxin

... some of them only by a mere stereoisomerism such as GTX-2 and GTX-3. Gonyautoxins are detectable by means of High Performance ...

*Conformational isomerism

In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted just by ...

*Cahn-Ingold-Prelog priority rules

... including describing less common forms of stereoisomerism (such as chiral axes and planes), and resolving more difficult ...

*Chemical substance

Likewise, the idea of stereoisomerism - that atoms have rigid three-dimensional structure and can thus form isomers that differ ...

*Conformation

... generally means structural arrangement and may refer to: Conformational isomerism, a form of stereoisomerism in ...

*Structural isomer

... as opposed to stereoisomerism, in which molecular bonds are always in the same order and only spatial arrangement differs. ...

*12-Hydroxyheptadecatrienoic acid

12-HHT is less ambiguously termed 12-(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid to indicate the S stereoisomerism of its 12- ...

*Rudolf Mentzel

... and he received his doctorate in 1925 with a thesis on Stereoisomerism and transformation of b-substituted decahydro- ...

*Outline of organic chemistry

Resonance structures Conjugated systems Functional groups Stereochemistry Conformational isomerism Diastereomer Stereoisomerism ...

*Glyceraldehyde

Stereoisomerism Merck Index, 11th Edition, 4376 Determination of the Absolute Configuration of Optically Active Compounds by ...
Looking for stereospecific synthesis? Find out information about stereospecific synthesis. Catalytic polymerization of monomer molecules to produce stereospecific polymers, as with Ziegler or Natta catalysts Explanation of stereospecific synthesis
0035] In this manner, a compound represented by formula (IV) into which a protecting group has been introduced is obtained. Examples of amino acid derivatives represented by formula (IV) include the R isomer or S isomer of N-(3-chloropropyl)-N-(tert-butoxycarbonyl)alanine ethyl ester, the R isomer or S isomer of N-(3-chloropropyl)-N-(pivaloyl)alanine ethyl ester, the R isomer or S isomer of N-(3-chloropropyl)-N-(benzyloxycarbonyl)alanine ethyl ester, the R isomer or S isomer of N-(3-chloropropyl)-N-(benzoyl)alanine ethyl ester, the R isomer or S isomer of N-(3-chloropropyl)-N-(methoxycarbonyl)alanine ethyl ester, the R isomer or S isomer of N-(3-chloropropyl)-N-(9-fluorenylmethoxycarbonyl)alanine ethyl ester, the R isomer or S isomer of N-(3-chloropropyl)-N-(acetyl)alanine ethyl ester, the R isomer or S isomer of N-(3-bromopropyl)-N-(tert-butoxycarbonyl)alanine ethyl ester, the R isomer or S isomer of N-(3-chloropropyl)-N-(tert-butoxycarbonyl)alanine methyl ester, the R isomer or S isomer of ...
A chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions. The auxiliary can then be typically recovered for future use. General scheme for employing a chiral auxiliary in asymmetric synthesis Most biological molecules and pharmaceutical targets exist as one of two possible enantiomers; consequently, chemical syntheses of natural products and pharmaceutical agents are frequently designed to obtain the target in enantiomerically pure form. Chiral auxiliaries are one of many strategies available to synthetic chemists to selectively produce the desired stereoisomer of a given compound. Chiral auxiliaries were introduced by E.J. Corey in 1975 with chiral 8-phenylmenthol and by B.M. Trost in 1980 with chiral mandelic acid. The menthol compound is difficult to prepare and as an ...
If a chiral center is a carbon atom, it can also be called an asymmetric carbon atom. Thus, in eg. 1 the chiral center is an asymmetric carbon atom.. The term stereocenter, also called stereogenic center, is often used synonymously with the term chiral center. However, the term stereocenter has a different definition, according to which all chiral centers are stereocenters but not all streocenters are chiral centers.. Mastery Check. ...
A seven-step enantioselective total synthesis of (-)-terengganensine A, a complex heptacyclic monoterpene indole alkaloid, was accomplished. Key steps included: a) Noyoris catalytic enantioselective transfer hydrogenation of the iminium salt to set up the absolute configuration at the C21 position; b) a highly diastereoselective C7 benzoyloxylation with dibenzoyl peroxide under mild conditions; and c) an integrated one-pot oxidative cleavage of cyclopentene/triple cyclization/hydrolysis sequence for the construction of the dioxa azaadamantane motif with complete control of four newly generated stereocenters.. Keywords: asymmetric synthesis ; domino cyclization ; hydroxylation ; monoterpene indole alkaloids ; total synthesis. ...
Changes in atropisomer composition of chiral polychlorinated biphenyls (PCBs) and their mono- and dihydroxylated metabolites (OH- and diOH-PCBs) via rat cytochrome P450 2B1 (CYP2B1) mediated biotransformation were investigated in vitro. Rat CYP2B1 could stereoselectively biotransform chiral PCBs to generate meta-OH-PCBs as the major metabolites after 60 min incubations. Nonracemic enantiomer fractions (EFs: concentration ratios of the (+)-atropisomer or the first-eluting atropisomer over the total concentrations of two atropisomers) of 5-OH-PCBs, were 0.17, 0.20, 0.85, 0.77, and 0.41 for incubations with PCBs 91, 95, 132, 136, and 149, respectively. CYP-mediated stereoselective formation of diOH-PCBs from OH-PCBs was observed for the first time. After 60 min stereoselective biotransformation, the EFs of both 4-OH-PCB 95 and 5-OH-PCB 95 changed from racemic (i.e., 0.50) to 0.62 and 0.46, respectively. These transformations generated statistically nonracemic 4,5-diOH-PCB 95, with EFs of 0.53 and 0.58 for
In chemistry, a racemic mixture, or racemate /reɪˈsimeɪt/, is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was racemic acid, which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid. A sample with only a single enantiomer is an enantiomerically pure, enantiopure or homochiral compound. From racemic acid found in grapes; from Latin racemus, meaning a bunch of grapes. A racemic mixture is denoted by the prefix (±)- or dl- (for sugars the prefix dl- may be used), indicating an equal (1:1) mixture of dextro and levo isomers. Also the prefix rac- (or racem-) or the symbols RS and SR (all in italic letters) are used. If the ratio is not 1:1 (or is not known), the prefix (+)/(−), d/l- or d/l- (with a slash) is used instead. The usage of d and l is strongly discouraged by IUPAC. A racemate is optically inactive, meaning that there is no net rotation of plane-polarized light. Although the two ...
Abstract: Many pharmaceuticals contain active ingredients that have more than one stereoisomer. An important concern is the recognition that these different stereoisomers do not necessarily have identical, or even desirable biological activity. Consequently, analytical methods for the analysis and separation of enantiomers are important in the proper development of a marketed pharmaceutical product. In this research, direct HPLC methods for the chromatographic separation of oxyphene optical isomers have been developed and optimized using three types of chiral stationary phases. The research carried out a systematic study of the conditions for the separation of oxyphene optical isomers using synthetic polymer chiral stationary phase of cellulose tris (3, 5-dimethylphenylcarbamate) Chiralcel OD, ß-cyclodextrin chiral stationary phase, and a1-acid glycoprotein chiral stationary phase. The methods using the ß-cyclodextrin and Chiralcel OD columns provide for the accurate determination of the ...
Recently, a new methodology based on the three chiroptical properties, namely vibrational circular dichroism (VCD), electronic circular dichroism (ECD) and optical rotation (OR), was developed toward determining the Absolute Configurations (ACs) of chiral molecules. This new methodology determines the AC of a chiral molecule via comparison of the ab initio Density Functional Theory (DFT) calculations of VCD, ECD or OR with the experimental results. Prior studies have shown that this method is quite straightforward and reliable, and readily applicable to a variety of chiral molecules. Although either one of the three chiroptical properties is capable of determining the AC by its own self, simultaneous applications of all three are more favorable and will undoubtedly increase the certainty of the AC determined. Our group has reported the first study of this kind and unambiguously determined the ACs of four cytotoxic sesquiterpene natural products. In an effort to further extend the applicability ...
Recently, a new methodology based on the three chiroptical properties, namely vibrational circular dichroism (VCD), electronic circular dichroism (ECD) and optical rotation (OR), was developed toward determining the Absolute Configurations (ACs) of chiral molecules. This new methodology determines the AC of a chiral molecule via comparison of the ab initio Density Functional Theory (DFT) calculations of VCD, ECD or OR with the experimental results. Prior studies have shown that this method is quite straightforward and reliable, and readily applicable to a variety of chiral molecules. Although either one of the three chiroptical properties is capable of determining the AC by its own self, simultaneous applications of all three are more favorable and will undoubtedly increase the certainty of the AC determined. Our group has reported the first study of this kind and unambiguously determined the ACs of four cytotoxic sesquiterpene natural products. In an effort to further extend the applicability ...
An enantioselective total synthesis of zampanolide has been accomplished using a novel DDQ/Brønsted acid promoted cyclization as the key reaction. The synthesis features cross-metathesis to construct the trisubstituted olefin and a ring-closing metathesis to form the macrolactone. The final N-acyl aminal formation was stereoselectively accomplished by an organocatalytic reaction.
Carvedilol is administered as a racemic mixture of the R(+)- and S(-)-enantiomers, although it was demonstrated that the two enantiomers exhibit different pharmacological effects and stereoselective pharmacokinetics. The aim of this study was the evaluation of several native and derivatized cyclodextrines as chiral selectors for the separation of carvedilol enantiomers. Stereoselective interactions were observed with four cyclodextrines (β-CD, hydroxypropyl-β-CD, randomly methylated β-CD and sulfobuthyl ether- β-CD). The effects of CD concentration, pH value and composition of the background electrolyte, capillary temperature, running voltage and injection parameters have been investigated. The method was validated for precision of peak-area response, linearity range and limits of detection and quantification. An efficient stereoselective capillary zone electrophoretic method was developed for the determination of carvedilol enantiomers using a simple 25 mM phosphate buffer at a pH = 2.5 and 10 mM
The issue of drug chirality is now a major theme in the design and development of new drugs, and our aim in chapter 5 is to discuss its importance in Medicinal Chemistry, underpinned by a new understanding of the role of molecular recognition in many pharmacologically relevant events. In general, three methods are utilized for the production of a chiral drug: the chiral pool, separation of racemates, and asymmetric synthesis. Although the use of chiral drugs predates modern medicine, only since the 1980s has there been a significant increase in the development of chiral pharmaceutical drugs. The thalidomide tragedy increased awareness of stereochemistry in the action of drugs, and as a result the number of drugs administered as racemic compounds has steadily decreased. In 2001, more than 70% of the new chiral drugs approved were single enantiomers. Approximately 1 in 4 therapeutic agents are marked as racemic mixtures, the individual enantiomers of which frequently differ in both their ...
The first direct intermolecular regiospecific and highly enantioselective a-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd0 complexes and simple chiral amines as co-catalysts is disclosed. The co-catalytic asymmetric chemoselective and regiospecific a-allylic alkylation reaction is linked in tandem with in situ reduction to give the corresponding 2-alkyl alcohols with high enantiomeric ratios (up to 98:2 e.r.; e.r.=enantiomeric ratio). It is also an expeditious entry to valuable 2-alkyl substituted hemiacetals, 2-alkyl-butane-1,4-diols, and amines. The concise co-catalytic asymmetric total syntheses of biologically active natural products (e.g., Arundic acid) are disclosed.. ...
Several approaches towards the synthesis of an acyclic molecule possessing one chiral centre along with suitable functionality to enable cyclisation to a medium ring were investigated. The intramolecular cyclisation reaction would create a second chiral centre so that two diastereoisomeric products would be possible. Potential cyclisation reactions appeared to include allysilane-aldehyde and allyl tin-aldehyde cyclisations. The first route attempted involved the coupling of an oxygen protected w-hydroxy-aldehyde with 3,3-diethoxy-2-bromopropene via a Grignard reaction or an alkyl lithium reaction, to generate the first chiral centre. A slight variation was also investigated. In this second case the key reaction to form the first chiral centre was the reaction of an oxygen protected w-hydroxy-a-bromoalkane with 2-(trimethylsilyl)methyl-2-propenal via a Grignard reaction. A third approach to the key reaction to introduce the first chiral centre involved the reaction of ...
Chiral separation of enantiomers is one of the most challenging tasks for any analytical technique including capillary electrophoresis (CE). Since the first report in 1985 showing the great possibilities of CE for the separation of chiral compounds, the amount of publications concerning this topic has quickly increased. Although chiral electromigration methods have mainly been used for enantioseparation of drugs and pharmaceuticals, they have also been applied to analyze chiral pollutants. This article intends to provide an updated overview, including works published till January 2005, on the principal applications of CE to the chiral analysis of pollutants and their metabolites, with especial emphasis on articles published in the last ten years. The main advantages and drawbacks regarding the use of CE for chiral separation of pollutants are addressed including some discussion on the foreseen trends of electromigration procedures applied to chiral analysis of contaminants ...
In general, chiral molecules have point chirality at a single stereogenic atom, usually carbon, which has four different substituents. The two enantiomers of such compounds are said to have different absolute configurations at this center. This center is thus stereogenic (i.e., a grouping within a molecular entity that may be considered a focus of stereoisomerism), and is exemplified by the α-carbon of amino acids. A molecule can have multiple chiral centers without being chiral overall if there is a symmetry element (a mirror plane or inversion center), which relates the two (or more) chiral centers. Such a molecule is called a meso compound. It is also possible for a molecule to be chiral without having actual point chirality. Common examples include 1,1-bi-2-naphthol (BINOL) and 1,3-dichloro-allene, which have axial chirality, and (E)-cyclooctene, which has planar chirality.. An undistorted tetrahedral sp3-hybridized carbon atom bearing four freely rotating rigorously identical substituents ...
The major part of this thesis describes the synthesis of enantiopure alcohols and diols by combining ruthenium-catalyzed redox reactions that lead to racemization or epimerization and lipase-catalyzed asymmetric trans-formations in one-pot.. A mechanistic study of the unexpected facile formation of meso-diacetate products found in enzyme-catalyzed acetylations of alkanediols with Candida antarctica lipase B (CALB) was first performed. By deuterium labeling it was found that the formation of meso-diacetates proceeds via different mechanisms for 2,4-pentanediol and 2,5-hexanediol. Whereas the first reacts via an intramolecular acyl migration, the latter proceeds via a direct, anomalous S-acylation of the alcohol. The acyl migration occurring in the 2,4-pentanediol monoacetate was taken advantage of in asymmetric transformations of substituted 1,3-diols by combining it with a ruthenium-catalyzed epimerization and an enzymatic transesterification using CALB. The in situ coupling of these three ...
This is Digital Version of (Ebook) 978-3642539282 Stereoselective Formation of Amines (Topics in Current Chemistry) Product Will Be Delivered Via Emai
The K-region trans-5,6-dihydrodiols formed in the metabolism of 12-methylbenz[a]anthracene (12-MBA) by liver microsomal preparations from untreated, phenobarbital-treated and 3-methylcholanthrene-treated male Sprague-Dawley rats were found by chiral stationary-phase h.p.l.c. (c.s.p.-h.p.l.c.) analyses to contain (5S,6S)/(5R,6R) enantiomer ratios of 93:7, 88:12 and 97:3 respectively. The absolute stereochemistry of a 12-MBA trans-5,6-dihydrodiol enantiomer was elucidated by the exciton-chirality c.d. method. The 5,6-epoxides formed in the metabolism of 12-MBA by liver microsomal preparations from untreated, phenobarbital-treated and 3-methylcholanthrene-treated male Sprague-Dawley rats in the presence of the epoxide hydrolase inhibitor 3,3,3-trichloropropylene 1,2-oxide were isolated from a mixture of metabolites by normal-phase h.p.l.c., and their (5S,6R)/(5R,6S) enantiomer ratios were found by c.s.p.-h.p.l.c. analyses to be 73:27, 78:22 and 99:1 respectively. The absolute configurations of ...
The novel N,N,O-tridentate phenanthroline ligand (BinThro) bearing an axially chiral binaphthyl backbone prepared from BINOL was found to be an effective chiral catalyst for enantioselective addition of diethylzinc to aromatic aldehydes with high enantioselectivity (up to 95% ee).
In continuation of our interest in the field of asymmetric synthesis and total synthesis of natural products, most of them have several stereogenic centers. Th...
The Bull-James boronic acid assembly is used simultaneously as a chiral auxiliary for kinetic resolution and as a chiral shift reagent for in situ enantiomeric excess (ee) determination by 1H NMR spectroscopy. Chiral terminal alkyne-containing amines, and their corresponding chiral triazoles formed via CuAAC Chemosensors and Molecular Logic
A synthetic strategy was developed for the preparation of porphyrins containing between one and four stereogenic centers, such that their molecular weights vary only as a result of methyl groups which give the chiral forms. The low-dimensional nanoscale aggregates of these compounds Reveal the profound effects of this varying molecular chirality on their supramolecular structure and optical activity. The number of stereogenic centers influences significantly the self-assembly and chiral structure of the aggregates of porphyrin molecules described here. A scanning tunneling microscopy study of monolayers on graphite shows that the degree of structural chirality with respect to the surface increases almost linearly with the number of stereogenic centers, and only one handedness is formed in the monolayers, whereas the achiral compound forms a mixture of mirror-image domains at the surface. In solution, four hydrogen bonds induce the formation of an H-aggregate, and circular dichroism measurements ...
There are two main strategies for the preparation of enantiopure compounds. The first is known as chiral resolution. This method involves preparing the compound in racemic form, and separating it into its isomers. In his pioneering work, Louis Pasteur was able to isolate the isomers of tartaric acid because they crystallize from solution as crystals each with a different symmetry. A less common method is by enantiomer self-disproportionation.. The second strategy is asymmetric synthesis: the use of various techniques to prepare the desired compound in high enantiomeric excess. Techniques encompassed include the use of chiral starting materials (chiral pool synthesis), the use of chiral auxiliaries and chiral catalysts, and the application of asymmetric induction. The use of enzymes (biocatalysis) may also produce the desired compound.. Enantioconvergent synthesis is the synthesis of one enantiomer from a racemic precursor molecule utilizing both enantiomers. Thus, the two enantiomers of the ...
Three stereoisomeric inhibitors of Pin1: (2R,5S)-, (2S,5R)- and (2S,5S)-Ac-pSer-Ψ[(Z)CH = C]-pipecolyl(Pip)-2-(2-naphthyl)ethylamine 1, that mimic L-pSer-D-Pro, D-pSer-L-Pro, and D-pSer-D-Pro amides respectively, were synthesized by a 13-step route. The newly formed stereogenic centers in the pipecolyl ring were introduced by Luche reduction, followed by stereospecific [2,3]-Still-Wittig rearrangement. The (Z)- to (E)-alkene ratio in the rearrangements were consistently 5.5 to 1. The stereochemistry at the original Ser α-carbon controlled the stereochemistry of the Luche reduction, but it did not affect the stereochemical outcome of the rearrangement, which consistently gave the (Z)-alkene. The epimerized by-product, (2S,5S)-10, resulting from the work-up after Na/NH3 debenzylation of (2S,5R)-9, was carried on to the (2S,5S)-1 isomer. Compound (2S,5S)-10 was resynthesized from the Luche reduction by-product, (2R,3R)-3, and the stereochemistry was confirmed by comparison of the optical ...
Chiral separations of five β-adrenergic antagonists (propranolol, esmolol, atenolol, metoprolol, and bisoprolol) were studied by capillary electrophoresis using six cyclodextrins (CDs) as the chiral selectors. Carboxymethylated-β-cyclodextrin (CM-β-CD) exhibited a higher enantioselectivity power compared to the other tested CDs. The influences of the concentration of CM-β-CD, buffer pH, buffer concentration, temperature, and applied voltage were investigated. The good chiral separation of five β-adrenergic antagonists was achieved using 50 mM Tris buffer at pH 4.0 containing 8 mM CM-β-CD with an applied voltage of 24 kV at 20 °C. In order to understand possible chiral recognition mechanisms of these racemates with CM-β-CD, host-guest binding procedures of CM-β-CD and these racemates were studied using the molecular docking software Autodock. The binding free energy was calculated using the Autodock semi-empirical binding free energy function. The results showed that the phenyl or naphthyl ring
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This dissertation describes our efforts to develop new methods of producing enantiopure compounds through a sequential one-pot polishing procedure and through kinetic resolutions via silylation and desilylation. Chapter 2 highlights how we have combined a moderately selective asymmetric reaction (either a reduction or allylation) with a kinetic resolution (via acylation or silylation) to generate enantiopure compounds (enantiomeric excess (ee) |95%) with yields greater than 50%. The enantioselective reaction produces a compound with moderate ees that is polished to a high ee by the kinetic resolution. Combining the moderately selective reactions together in this sequence overcomes the inherent disadvantages of the individual reactions (low ee and yield) and allows researchers to quickly produce enantiopure materials without developing and optimizing a new methodology. In Chapter 3, we describe our attempts at developing an enantioselective desilylation to produce enantiopure silyl ethers through the
TY - JOUR. T1 - Unprecedented four-way-output molecular response system based on biphenyl-2,2′-diyldiacridiniums. T2 - induction of axial chirality through intramolecular hydrogen bonds between chiral amide groups. AU - Suzuki, Takanori. AU - Ohta, Kenji. AU - Nehira, Tatsuo. AU - Higuchi, Hiroki. AU - Ohta, Eisuke. AU - Kawai, Hidetoshi. AU - Fujiwara, Kenshu. PY - 2008/1/28. Y1 - 2008/1/28. N2 - Upon the attachment of N-(R)-2-phenylethylamide moieties to the acridinium units of the title dication, intramolecular hydrogen bonds induce a diastereomeric preference in terms of axial chirality (70% de at -40 °C in CH2Cl2). Thus, external stimuli induce not only UV-vis and fluorescence spectra changes but also changes in the CD and fluorescence-detected CD (FDCD) spectra, realizing unprecedented four-way-output molecular response systems.. AB - Upon the attachment of N-(R)-2-phenylethylamide moieties to the acridinium units of the title dication, intramolecular hydrogen bonds induce a ...
A series of C2 symmetrical 1:2 Ni:L complexes derived from α-amino amides were studied for the enantioselective addition of dialkylzinc reagents to aldehydes. Different structural elements on the ligands seem to play an important role in determining the observed enantioselectivity. Through optimization of structure and reaction conditions, the best ligand provided secondary alcohols in excellent yields (up to 98%) and enantioselectivity of up to 99% ee for (R)-enantiomer. A transition state model has been proposed to explain the observed enantioselectivities based on computational calculations at the DFT level. Very interestingly, calculations suggest a coordination model of the aldehyde to the metal complex through association of a lone pair of the carbonyl oxygen to the hydrogen atom of an amino group ...
article{520859, author = {Monbaliu, Jean-Christophe and Robiette, Rapha{\e}l and Peeters, Daniel and Marchand-Brynaert, Jacqueline}, issn = {0040-4039}, journal = {TETRAHEDRON LETTERS}, keyword = {Stereoselective synthesis,Microwave-assisted synthesis,Aminodiene,Diels-Alder cycloaddition}, language = {eng}, number = {12}, pages = {1314--1317}, title = {(R)-4-phenyloxazolidin-2-thione: an efficient chiral auxiliary for [4+2] cycloaddition of 1-aminodienes and activated phosphonodienophiles}, url = {http://dx.doi.org/10.1016/j.tetlet.2009.01.036}, volume = {50}, year = {2009 ...
A novel chiral stationary phase (CSP) was prepared by immobilizing mono(6A-N-allylamino-6A-deoxy)-perphenylcarbamoylated β-cyclodextrin onto the surface of silica gel via hydrosilylation. The chromatographic properties of this column were tested with a wide range of structurally diverse racemic compounds and drugs under reverse phases. Separation mechanisms involved are also discussed. © 2003 Published by Elsevier B.V ...
Chiral molecules are prevalent among currently marketed pharmaceutical products, many of which are solid formulations. The solid-state form of a drug can have a dramatic effect on its solubility, dissolution rate (hence bioavailability), physical stability, and interaction with excipients; therefore, understanding the solid forms that exist for a drug molecule is critical to ensure product performance and safety. Analysis of solid systems typically requires the application of several analytical techniques, one or two of which may be particularly helpful. In this thesis work, solid-state NMR spectroscopy (SSNMR) was found to be a particularly powerful method for characterizing proline enantiomers in the solid state. Using SSNMR, we evaluated the differences in crystal forms of proline that resulted from changes in enantiomeric ratio and crystallization conditions. Various ratios of D- and L-proline (0-50% L-proline with 100-50% D-proline) were crystallized from aqueous solution and by ...
A Langevin canonical framework for a chiral two-level system coupled to a bath of harmonic oscillators is used within a coupling scheme different from the well-known spin-boson model to study the quantum stochastic resonance for chiral molecules. This process refers to the amplification of the response to an external periodic signal at a certain value of the noise strength, being a cooperative effect of friction, noise, and periodic driving occurring in a bistable system. Furthermore, from this stochastic dynamics within the Markovian regime and Ohmic friction, the competing process between tunneling and the parity violating energy difference present in this type of chiral systems plays a fundamental role. This mechanism is finally proposed to observe the so-far elusive parity-violating energy difference in chiral molecules.
Abstract. An asymmetric 1,2-addition of alkyl groups to conjugated cyclic enones gave allylic alcohols with chiral quaternary centers. The resultant allylic alcohols are converted into epoxy alcohols with excellent diastereoselectivities. A semipinacol rearrangement provided α,α-dialkyl-β-hydroxy ketones with all-carbon chiral quaternary centers.. ...
Zuschriften DOI: 10.1002/ange.200900351 Multicomponent Reactions Enantioselective Synthesis of b-Iodo Morita-Baylis-Hillman Esters by a Catalytic Asymmetric Three-Component Coupling Reaction** Bidyut Kumar Senapati, Geum-Sook Hwang, Sungil Lee, and Do Hyun Ryu* Dedicated to Professor Sung Ho Kang on the occasion of his 60th birthday Optically active a-methylene-b-hydroxy carbonyl derivatives can be prepared by the asymmetric Morita-Baylis-Hillman (MBH) reaction.[1] These derivatives are useful chiral building blocks for biologically active molecules and natural products because of their multifunctional composition.[2] Even with recent advances in this area, asymmetric synthesis of bsubstituted MBH products such as b-branched MBH ketones or esters have not been successful by this method.[2] One efficient route to give various b-branched MBH products[3] can be achieved through the cross-coupling reaction of chiral b-halo MBH products (Scheme 1). The presence of a halogen Scheme 1. Enantioselective ...
Communications Enantiomer Separation Modified Linear Dextrins ("Acyclodextrins") as New Chiral Selectors for the GasChromatographic Separation of Enantiomers** Giuseppe Sicoli, Zhengjin Jiang, Laszlo Jicsinsky, and Volker Schurig* In memory of Jzsef Szejtli Cyclodextrins (CDs) modified by alkylation, acylation, and silylation represent versatile chiral stationary phases (CSPs) for the gas-chromatographic separation of enantiomers.[1] Typically, they are dissolved in semipolar polysiloxanes[2a] or linked chemically to polydimethylsiloxane (Chirasil-Dex).[2b] The mechanism of enantiomer recognition is still not well understood, and the role of the CD cavity is unclear in cases were enantioselectivity is low, as it is in most reported cases (a , 1.1).[1a] We therefore conjectured that the existence of a cavity may not be a prerequisite to chirality recognition in cyclodextrins. This has now been borne out by employing linear dextrins ("acyclodextrins") as a new generation of carbohydrate-based ...
DUGi: Viewing Item from repository Recercat: Regio- and enantioselective hydroformylation of styrenes is attained upon embedding a chiral Rh complex in a nonchiral supramolecular cage formed from coordination-driven self-assembly of macrocyclic dipalladium complexes and tetracarboxylate zinc porphyrins. The resulting supramolecular catalyst converts styrene derivatives into aldehyde products with much higher chiral induction in comparison to the nonencapsulated Rh catalyst. Spectroscopic analysis shows that encapsulation does not change the electronic properties of the catalyst nor its first coordination sphere. Instead, enhanced enantioselectivity is rationalized by the modification of the second coordination sphere occurring upon catalyst inclusion inside the cage, being one of the few examples in achieving an enantioselective outcome via indirect through-space control of the chirality around the catalyst center. This effect resembles those taking place in enzymatic sites, where structural constraints
The origin of homochirality is extremely important in origin of life research, since non-optically pure mixtures of amino acids or sugars cannot be used to make RNA, DNA, and proteins, the building blocks of all living organisms. There is no terrestrial or extraterrestrial explanation that describes how homochirality could have arisen through naturalistic processes.
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Sewald, N. (1996). Stereoselective Synthesis of beta-Amino Acids via Conjugate Addition of Nitrogen Nucleophiles to alpha,beta-Unsaturated Esters - Recent Advances. Amino Acids, 11(3), 397-408. doi:10.1007/ ...
TY - JOUR. T1 - Diphenylprolinol silyl ethers as efficient organocatalysts for the asymmetric Michael reaction of aldehydes and nitroalkenes. AU - Hayashi, Yujiro. AU - Gotoh, Hiroaki. AU - Hayashi, Takaaki. AU - Shoji, Mitsuru. PY - 2005/7/4. Y1 - 2005/7/4. N2 - (Chemical Equation Presented) The direct, catalytic, asymmetric Michael addition of aldehydes to nitroolefins in the presence of a chiral diphenylprolinol silyl ether organocatalyst is described (see scheme). The desired 1,4-addition products were obtained in nearly optically pure form in good yield with high syn diastereoselectivity. TMS = trimethylsilyl.. AB - (Chemical Equation Presented) The direct, catalytic, asymmetric Michael addition of aldehydes to nitroolefins in the presence of a chiral diphenylprolinol silyl ether organocatalyst is described (see scheme). The desired 1,4-addition products were obtained in nearly optically pure form in good yield with high syn diastereoselectivity. TMS = trimethylsilyl.. KW - Asymmetric ...
Despite a long-standing belief that formyl groups cannot be generated at quaternary carbon centers via hydroformylation, Clarke and Roff have developed a method utilizing 1,3,5,7-tetramethyl-6-phenyl-2,4,8- trioxa-6-phosphaadamantane, an air-stable phosphane ligand, which inhibited hydrogenation and provided excellent levels of regioselectivity (for quaternary versus linear regioisomer) (Scheme 5).1. ...
Previously determined retention data for a series of benzodiazepine (BDZ) derivatives, comprising nine achiral compounds, four single enantiomers, and 18 individual isomers of nine racemates, on a chiral stationary phase based on immobilized human serum albumin (HSA) were analyzed to define quantitative relationships between structure and enantiospecific retention. Structural parametrization of the agents was done by means of hydrophobic fragmental constants and electronic and steric parameters obtained by computational chemistry methods. A structural descriptor was identified, a submolecular measure of polarity about the stereogenic center, that accounted for the stronger electrostatic interactions of the second-eluting enantiomer with the HSA chiral stationary phase. Quantitative structure-enantiospecific retention relationships were derived for both enantiomeric series and for achiral compounds, and structural requirements for binding to HSA were determined. Two types of binding sites were ...
Title: Enantioselective Synthesis and Preliminary Pharmacological Evaluation of the Enantiomers of Unifiram (DM232), a Potent Cognition-Enhancing Agent. VOLUME: 1 ISSUE: 5. Author(s):E. Martini, C. Ghelardini, C. Bertucci, S. Dei, F. Gualtieri, L. Guandalini, D. Manetti, S. Scapecchi, E. Teodori and M. N. Romanelli. Affiliation:Dipartimento di Scienze Farmaceutiche, Universita di Firenze, Via Ugo Schiff 6, 50019 SestoFiorentino (FI), Italy.. Keywords:cognition-enhancer, nootropic, chiral synthesis. Abstract: The enantiomers of the potent cognition-enhancer DM232 ((1), unifiram) and of its isopropylsulfonyl analog (2), which is endowed with amnesic properties, have been synthesized using (S)- and (R)-5-(hydroxymethyl)-2- pyrrolidinone as chiral precursors. The enantiomeric excess was determined by means of capillary electrophoresis, and found higher than 99.9 %. DM232 enantiomers were tested as cognition-enhancers in the passive-avoidance and social learning tests, and their ability to induce ACh ...
The mechanism by which chiral selectivity takes place is complicated by the surface morphology, the possible involvement of the solvent, and the characteristics of the chiral molecules at the surface. My goal is to model and understand the factors which lead to significant discrimination in the case of three closely related chiral stationary phases: N-(1-phenylethyl)-N-[3-(triethoxysilyl)propyl]-urea (PEPU), [(3,5-dinitrobenzoyl)-amino]-N-[3-(triethoxysilyl)propyl]-2-phenylacetamide (DNB-phenyglycine), and [(3,5-dinitrobenzoyl)amino]-N-[3-(triethoxysilyl)propyl]-4-methylpentanamide (DNB-leucine). Ab initio calculations are used to develop molecular models of these chiral selectors. These models are employed in molecular dynamics (MD) simulations, which provide the theoretical framework for modelling chiral interfaces in different solvent mixtures. The MD simulations of PEPU interfaces show that, in alcohol/water mixtures, the alcohols form domains at the interface with the hydrophobic portions ...
Principal Investigator:MATSUDA Akira, Project Period (FY):1994 - 1995, Research Category:Grant-in-Aid for General Scientific Research (B), Research Field:Chemical pharmacy
Considerable progress has been made in the development of synthetic CSPs for the direct chromatographic separation of enantiomers. An innate advantage of synthetic CSPs is the ability to prepare either optical antipode of the CSP as well as the racemic analogs. CSPs derived from the 3,5-dinitrobenzamides of $\alpha$-amino acids have been prepared and extensively evaluated for the separation of enantiomers. We became interested in the effect on enantiomer separations of a second stereogenic center in the CSP as a result of our studies of CSPs which have a single stereogenic center. To this end, a new $N$-(3,5-dinitrobenzoyl)-$\beta$-amino acid derived CSP was synthesized and evaluated for the separation of enantiomers ...
Enzymes as tools in organic synthesis have provided enormous advantages. This thesis deals with the applications of enzymes in the kinetic resolutions of racemic compounds. The stereochemistry of chiral compounds and the kinetics of α/β hydrolase lipases are presented. From a practical point of view, the handling of a large number of parameters that influences the kinetic resolutions, especially enantioselectivity (E-value) are systematically described. A variety of approaches employed for raising the yields to over 50% are additionally discussed.. Methods for the preparation of synthetically useful chiral building blocks were developed in this thesis. Thus, resolution of secondary alcohols bearing two vicinal stereocentres are studied. These building blocks can serve as starting materials for the synthesis of various enantiomerically pure compounds for agrochemistry, pharmaceuticals, chemical industry, and particularly for the total synthesis of pheromones.. Racemic 3-substitued ...
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Asthma is a common chronic inflammatory airway disease with reported increasing incidence over the world. Definition of asthma includes variable obstruction of the airways and increase in bronchial responsiveness to various stimuli. Drug treatment for asthma traditionally consists of bronchodilatory beta-receptor-agonists, often in combination with anti-inflammatory remedies such as corticosteroids.. Salbutamol, a beta-receptor-agonist, has two stereo-isomers, R-salbutamol and Ssalbutamol, and is mostly given as a racemate. The ability for bronchodilation rests in the R-isomer, whereas the S-isomer has been suspected to increase bronchial hyperresponsiveness. Salbutamol m1dergoes stereo-selective metabolism favouring the Renantiomer. This leaves the S-enantiomer to rest for longer time in the body, and gives SiR-ratios in plasma exceeding one.. Pharmacokinetic stndies were performed in twenty-two healthy volunteers. Stereoselective metabolism was more pronounced after oral delivery than after ...
The synthesis and interactions of the d- and l-enantiomers of the amino acid amide derivatives [Formula: see text] (I) and lysyl dipeptides [Formula: see text] (II) with poly rI·poly rC, poly rA·poly rU and calf thymus DNA is reported. The following results were found. (1) The degree of stabilization of the helices as measured by the Tm (melting temperature) of the helix-coil transition was dependent on the nature of the amino acid. (2) For the poly rI·poly rC helix, the l-enantiomers of salts (I) and (II) stabilized more than the d-enantiomers. The same was true for calf thymus DNA in the presence of salts (II) and for poly rA·poly rU in the presence of salts (II) and the proline derivatives of salts (I). (3) As R increased in size and became more apolar, the amount of stabilization of the poly rI·poly rC helix in the presence of salts (I) decreased. On the other hand, the amount of stabilization increased with more polar substituents. An attempt was then made to determine whether the ...
Nucleophilic reactivity of deconjugated butyrolactams has been demonstrated for enantioselective Michael additions to alpha,beta-unsaturated aldehydes and ketones. These reactions are catalyzed by diphenylprolinol silyl ether and trans-1,2-diaminocyclohexane-derived bifunctional primary aminothiourea, respectively, producing the Michael adducts with moderate diastereoselectivities and good to excellent enantioselectivities (up to 99:1 er). Unlike in the case of structurally related deconjugated butenolides where vinylogous addition is prevalent, an exclusive alpha-addition is observed for deconjugated butyrolactams.. ...
View Notes - CH19 March 31 from CHEM 2212 at UGA. Wittig Reaction: Mechanism of Addition Aldehydes and Unsymmetrical Ketones: Title: Jul 14 - 8:30 AM (4 of 6) Wittig Reaction Practice Problems:
The cryptophycins are a family of cyclic depsipeptides with four retrosynthetic units A to D which correspond to the respective amino acids and hydroxy acids. A new synthetic route to unit A allows the selective generation of all four stereogenic centres by introducing two of them in a catalytic asymmetric dihydroxylation, followed by substrate-controlled diastereoselective reactions. The diol also serves as the epoxide precursor. this approach provides selective access to stereoisomers of unit A (enantiomers, epimers) for structure-activity relationship studies. The unit A derivatives were incorporated into cryptophycin-1, cryptophycin-52 and a novel epimer of cryptophycin-52 ...
Chiral alcohols form a versatile class of chiral synthons, since they can be incorporated into the API structures directly as esters or ethers. They can be starting materials for the formation of amines, amides, thiols, thioethers. In addition, after transforming the hydroxyl function into a leaving group by way of mesylation, tosylation or triflation, they can be used to form new C-C bonds.. Many manufacturing routes make use of asymmetric hydrogenation methods.2 The two most important biocatalytical processes for the formation of chiral alcohols apply lipases and dehydrogenases, respectively.1 The latter offers the advantage that only the requested enantiomer is obtained. Enzyme-catalyzed acylations using lipases, however, achieve the resolution of racemic mixtures of alcohols but with an inherent 50 percent maximum yield of the total amount of starting material. One enantiomer of the racemic mixture remains unchanged while the antipodal enantiomer is esterified (Scheme 2).. ...
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The compound MG-1(R,S), (1-[2-hydroxy-3(4-phenyl-1-piperazinyl)propyl]-pyrrolidin-2-one, and its enantiomers were tested for electrocardiographic, antiarrhythmic and hypotensive activities. The racemic mixture (MG-1(R,S)) and its S-enantiomer significantly decreased systolic and diastolic blood pressure and possessed antiarrhythmic activity. The S-enantiomer displayed the greatest effect. The R-enantiomer did not show antiarrhythmic or hypotensive activity. The results ...
The first project involved the investigation of dibenz[c,e]azepinium salt 113 as a catalyst for the aldol reaction. The catalyst was synthesised in 4 steps from commercially available 1R,2R-diaminocyclohexane in 74% overall yield. It was found to be an efficient catalyst in the aldol reaction of cyclic ketones with a range of aromatic aldehydes, giving high yields, diastereo- and enantioselectivities. This catalyst was also found to be effective when acyclic ketones were used, in which case the major diastereoisomer produced was no longer an anti-aldol but a the syn-aldol. A catalytic cycle for these reactions is proposed, with the stereochemical outcome of these reactions being further investigated by computational calculations ...
Mjl), and porcine pancreas (Ppl). The lipase-catalyzed reaction rates in different solvents across a wide range of water activities revealed that the Ppl-catalyzed reaction exhibited no enantioselectivity and no substantial water activity or solvent dependence. The Mjl-catalyzed reaction proceeded faster, preferring the R-enantiomer reaction over that of its antipode, but had little solvent or water activity dependence. The Crl-catalyzed reactions in n-heptane and n-nonane had similar water activity dependence, but the reaction was considerably faster and more enantioselective (preferring the S-enantiomer reaction) in isooctane, a solvent whose hydrophobicity is intermediate between that of the other two alkanes. Substrate enantiomeric excess, for the Crl-catalyzed reaction at 96 hours and at a water activity of 0.65, in n-heptane, isooctane, and n-nonane was 40.9, 93.0, and 50.0%, respectively. Since the three solvents possess similar physical properties, the explanation for this anomalous ...
Chiral molecules, however, transmit RCPL: and LCPL differently; nR (index of refraction for RCPL) is not the same as nL and one is slowed down with respect to the other; this is a result of the fact that chiral molecules have their electrons distributed in an asymmetric way so that they interact differently with RCPL than with LCPL. Furthermore, the two forms of chiral molecules (which are mirror images of one another) interact with RCPL and LCPL in opposite ways. For example, if nR , nL ==, RCPL is retarded with respect to LCPL and the plane of polarization (the orientation of E for the sum of RCPL and LCPL) will be rotated to the left. The chiral molecule with opposite hand of the one described in this example will have nR , nL and will rotate plane polarized light to the right ...
The reactions of the enolizable thioketone (1R,4R)-thiocamphor (= (1R,4R)-1,7,7-trimethylbicyclo[2.2.1]-heptane-2-thione; 1) with (S)-2-methyloxirane (2) in the presence of a Lewis acid such as SnCl4 or SiO2 in anhydrous CH2Cl2 led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(5), as well as the isomeric beta-hydroxy thioether 5 (Scheme 2). The analogous reactions of 1 with (RS)-, (R)-, and (S)-2-phenyloxirane (7) yielded two isomeric spirocyclic 1,3-oxathiolanes 8 and 9 with Ph at C(4), an additional isomer 13 bearing the Ph group at C(5), and three isomeric beta-hydroxy thioethers 10, 11, and 12 (Scheme 4). In the presence of HCl, the beta-hydroxy thioethers 5, 10, 11, and 12 isomerized to the corresponding 1,3-oxathiolanes 3 and 4 (Scheme 3), and 8, 9, and 13, respectively (Scheme 5). Under similar conditions, an epimerization of 3, 8, and 9 occurred to yield the corresponding diastereoisomers 4, 14, and 15, respectively (Schemes 3 and 6). The ...
Motoko Kotani. Professor E-mail m-kotani(at)m.tohoku.ac.jp. Papers|Conferences. 【Papers】. ・Structure of h110i-tilt boundaries in cubic zirconia, Kazutoshi Inoue1, Bin Feng2, Naoya Shibata2, Motoko Kotani1, and Yuichi Ikuhara, J.Mater.Sci. Vol 52, 8, 4278-4287 (2017). ・Stereoisomerism in nanohoops with heterogeneous biaryl linkages of E/Z- and R/S-geometries, Sarkar, Parantap; Sun, Zhe; Tokuhira, Toshiki; Kotani, Motoko; Sato, Sota; Isobe, Hiroyuki, ACS Cent. Sci., 2016, 2 (10), pp 740-747. ・Structural chemistry of belt-shaped cyclonaphthylenes: Stereoisomerism, crystal structures and dynamics, Zhe Sun,Takuya Suenaga,Parantap Sarkar,Sota Sato,Motoko Kotani,Hiroyuki Isobe, Proc Natl Acad Sci U S A. 2016 Jul 19;113(29):8109-14.. ・Motoko Kotani and Susumu Ikeda, Materials inspired by mathematics, Science and Technology of Advanced Materials (STAM),17(1),(2016),253-259. ・Phase behavior of a binary fluid mixture of quadrupolar molecules, Masatoshi Toda, Shinji Kajimoto,Shuichi ...
Pirkles alcohol is an off-white, crystalline solid that is stable at room temperature when protected from light and oxygen. This chiral molecule is typically used, in nonracemic form, as a chiral shift reagent in nuclear magnetic resonance spectroscopy, in order to simultaneously determine absolute configuration and enantiomeric purity of other chiral molecules. The molecule is named after William H. Pirkle, Professor of Chemistry at the University of Illinois whose group reported its synthesis and its application as a chiral shift reagent. (en) ...
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Chiral centers are tetrahedral carbon atoms that are connected to four different substituents. To locate a chiral center in a compound, first draw out the compound to show all of its bonds. Then,...
National Documentation Centre (EKT). National Archive of PhD Theses.PhD thesis.1995 . Creators: ΣΟΥΛΑΝΤΙΚΑ, ΑΙΚΑΤΕΡΙΝΗ.THE WORK CONCERNS THE PREPARATION OF NEW CATALYTIC SYSTEMS FOR THE HYDROFORMYLATION OF ALKENES, THE EXAMINATION OF THE STRUCTURE OF THE COMPLEXES INVOLVED AND THEIR CATALYTIC ACTIVITY. THE STRUCTURE WAS EXAMINED BY IR AND NMR SPECTROSCOPY AS WELL AS ELEMENTAL ANALYSIS. THESE COMPLEXES, APART FROM THE THIDAMINOACID, CONTAIN CARBONYLS AND PHOSPHINE OR PHOSPHITE LIGANDS IN THE METALS COORDINATION SPHERE. IN THE SOLID STATE THEY ARE THOUGHT TO BE DIMERS IN WHICH TWO METAL SITES ARE BRIDGED BY THE SULFURS OF TWO AMINO ACID MOIETIES. UNDER CONDITIONS WHICH RESEMBLE THOSE OF THE CATALYTIC REACTION, THERE IS EQUILIBRIUM BETWEEN VARIOUS SPECIES, PREDOMINANTLY MONOMERIC ONES. THE POSITION OF EQUILIBRIUM DEPENDS ON THE AMINOACID INVOLVED, THE AMOUNT AND TYPE OF PHOSPHOROUS LIGANDS AND THE PRESENCE OF CO IN SOLUTION. THE MOIETIES THAT COEXIST ACT INDEPEDENTLY OF
In order to make more accurate risk assessments for chiral pesticides and other pollutants, it is necessary to understand the relative persistence and effects of their enantiomers. A major effort is underway in the USEPA to measure exposure in the home environment to various pesticides and PCB congeners. As an adjunct to this study, extracts of various samples previously shown to contain target pesticides and PCBs were analyzed for the enantiomers of certain of these which are chiral. Preliminary results show that PCB 95 occurs enantioselectively in house dust but not in yard soil: enantiomer ratios (ER) range from 0.51 to 0.98 with an average ER of 0.77 in floor dust compared to near racemic values in yard soil. The toxic effects of enantiomers have been scarcely examined. The effects of the enantiomers of cis-chlordane to the reproduction and survival of potworms (Enchytraeus crypticus) will be reported; these tests are currently underway. In addition, a summary of test results for various ...
A multi-application IC card system and method is disclosed providing a secure data transmission technique. The method is used, for example, to load an application from an application provider, which could be remote, to an IC card. At least a portion of the application is encrypted using a transfer key. The transfer key is then encrypted using the public key of a public/secret key pair of the intended IC card to form a key transformation unit. The encrypted application and key transformation unit are then sent to the IC card and the IC card decrypts the key transformation unit using its secret key. The transfer key is then recovered and used to decrypt the encrypted application. The application can then by stored on the IC card and accessed by the card user.
The diastereoselectivity of organometallic additions to nitrones bearing stereogenic substituents has been investigated. High and complementary diastereoselectivity was observed in the additions of Grignard reagents to nitrones (e.g. 62) bearing a potentially chelating $\beta$-alkoxy group on nitrogen. The high facial diastereoselectivity is explained by a simple chelation model which was supported(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)by $\sp1$H NMR analysis of a nitrone-magnesium bromide complex (86). However, the opposite selectivity resulted from the reaction of methylmagnesium bromide with the corresponding silyl ether (68). N-Deoxygenation of N,N-dialkylhydroxylamine adducts was achieved by lithium-ammonium reduction of the hydroxylamino carbonates (90 and 95) and phosphates (114). N-Dealkylation by periodic acid cleavage of the resulting amino alcohols (91 and 96) and subsequent hydrolysis of the imine products provided non-racemic chiral amines. The optical purities of the ...
Palladium is probably the most useful metal in organic syntheses. It has shown great utility in various reactions such as C-C, C-N, C-O bond formation under mild conditions. The presence of abundant amount of palladium-chemistry related literature in the form of books, reviews emphasizes the growing importance of these reagents. Nowadays organopalladium chemistry is being used in various fields such as new methodology development, natural product synthesis, synthesis of polymers. Regio- and stereoselectivity is another facet of Pd catalyzed methodologies which has been extensively utilized in the last decade to obtain enantiopure compounds. The main emphasis of this work is to utilize Pd catalyzed allylic alkylation to synthesize new heterocycles including furans, isoxazolines and new cyclopentane amino-acid analogs in an enantioselective manner. The stereochemical outcome of these reactions is influenced by desymmetrization catalyzed by hydrolytic enzymes namely lipases. Chapter 1 reviews the recent
New optically active free amino acids, namely 2,3-ethano- and 2,3-propanoproline, were synthesized using a reaction of corresponding gamma-functionalized carbonyl compounds with 2-methyl-2-(((1S)-1-phenylethyl)amino)propanenitrile as a key step.,br /,Approach to a new camphor-derived 2-cyanopyrrolidine and 2-cyanopiperidines was developed.,br /,The Pd-catalyzed carboalkoxylation of 2,2,2-trifluoro-N-(p-anisyl)-acetimidoyl iodide and 2,2,2-trifluoro-N-(1-phenylethyl)-acetimidoyl iodide was investigated. The reaction conditions were optimized that gave possibility to obtain chiral imino esters.,br /,Nucleophilic alkylation of the imino esters was performed. It was shown that the remote position of the chiral auxiliary and the nature of a nucleophile have a drastic effect on the diastereoselectivity of the reaction ...
119209-65-3 - Alkenes, C12-14, hydroformylation products, distn. residues, ethoxylated, hydrogen phosphates, sodium salts - Searchable synonyms, formulas, resource links, and other chemical information.
5 and 6 have the same molecular formula and the same structural formula and, therefore, stereoisomers. 5 and 6 are not mirror images of each other. Thus, they are daiastereomers.. Cis-Trans isomers are a subset of diastereomers; all cis-trans isomers are diastereomers, but not all diastereomers are cis-trans isomers.. see also enantiomers. ...
The first direct approach for the asymmetric synthesis of (E)-2-arylidene-1,4-diphenylbut-3-yn-1-amines by addition of alkynylzinc to chiral N-tert-butylsulfinylimines is reported with excellent diastereoselectivity and good yield. This asymmetric addition reaction provides a practical, economical and concise synthesis of multifunctional molecules with the 1,3-enyne side chain and an amino group. In addition, this methodology can be applied to the synthesis of substituted vinyl iodide compounds, and substituted chiral dihydropyrroles ...
This invention pertains to hydroformylation catalysts containing a mixture of isomeric forms of halo-phosphorus ligands. This invention also describes a procedure for preparing isomers of certain hal
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In the arena of enantioselective synthesis, titanium complexes wear the laurel wreath. Highly functionalized tetrathiafulvalenes: Riding along the synthetic trail from electrophilic alkynes
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Experiment 3: Wittig Reaction Introduction This experiment performs a modified Wittig reaction using a phosphorus-containing Hornes-Emmons-Wittig reagent
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Hydroformylation has been widely used in industry to manufacture high value-added aldehydes and alcohols, and is considered as the largest homogenously catalyzed process in industry. However, this...
Wearley, L.; Antonacci, B.; Cacciapuoti, A.; Assenza, S.; Chaudry, I.; Eckhart, C.; Levine, N.; Loebenberg, D.; Norris, C., 1993: Relationship among physicochemical properties, skin permeability, and topical activity of the racemic compound and pure enantiomers of a new antifungal
Principal Investigator:NAGASAWA Toru,長沢 透, Project Period (FY):1993 - 1994, Research Category:Grant-in-Aid for General Scientific Research (C), Research Field:応用微生物学・応用生物化学
The first direct asymmetric synthetic preparation of trifluoro-1-(indol-3-yl)ethanols (TFIEs) is described by an enantioselective organocatalytic method from indoles and inexpensive trifluoroacetaldehyde methyl hemiacetal. The reaction is catalyzed by hydroquinine to produce TFIEs in an almost quantitative yield and with enantioselectivities up to 75% at room temperature. The enantioselectivity is strongly dependent on the concentration of substrates and catalyst due to the competitive noncatalyzed reaction. Chirality, 2011. © 2011 Wiley-Liss, Inc.
An ester is caused to act on a 2-substituted-3-hydroxycarboxylic acid ester as a racemate in the presence of hydrolase under substantially anhydrous conditions to effect a transesterification resulting in the resolution.The compound thus resolved is converted to an optically active 2,6-cis-2,5,6-substituted-1,3-dioxan-4-one and the resulting compound is recrystallized to give optically active 5,6-anti-2,5,6-substituted-1,3-dioxan-4-one and 5,6-syn-2,5,6-substituted-1,3-dioxan-4-one. Thus an optically active compound having plural chiral centers.Further, an optically active 2,5,6-substituted-1,3-dioxan-4-one obtained by transesterification and recrystallization is reacted with an alcohol to produce an optically active 2-substituted-3-hydroxycarboxylic acid ester.
2-Deoxynucleoside 5-triphosphate analogues with β,γ-bridging oxygen replaced by a CXY group are useful chemical probes to investigate DNA polymerase catalytic and base‐selection mechanisms. A long‐standing limitation of such probes has been that conventional synthetic methods generate the analogues as mixtures of two diastereomer components in equal amounts when the bridging carbon substitution is nonequivalent (X ≠ Y). X‐ray structural studies of DNA polymerase β (pol β) carried out with ~1:1 mixture of β,γ-CXY dGTP diastereomers revealed stereospecific binding exclusively with the fluorine‐containing diastereomer analogues. These findings provided strong impetus in investigating the effect of stereochemical interactions of the β,γ-diastereomers on pol β kinetics, the stereochemical effect that could not be addressed in the previous linear free energy relationship (LFER) correlation plotting log(κpol)of the ~1:1 mixed diastereomers vs. the pKₐ₄ of the prochiral ...
Enantiospecific synthesis reactions are of intense interest, owing to the increasing request for enantiopure compounds in both research and industry. Lithium amides containing a secondary chelating group are a class of powerful ligands for asymmetric addition reactions. Based on earlier experiences with lithium N,O and N,S amides, synthesis and properties of chiral lithium N,P amides and their use in asymmetric addition are investigated in the present thesis. Several chiral amines were synthesized with previously published methods, which were improved in different ways. A new synthetic route towards chiral aminophosphines via cyclic sulfamidates has been developed. The use of silica in the synthesis of sulfamidate and the chiral aminophosphine shortened the reaction time considerably, compared to previous methods. The reactions are fast, clean and highyielding. Furthermore, the synthesis could successfully be scaled up with no loss in yield or purity and gives a general and simple route to a ...
Beta(2)-amino acids; Beta-peptide; Retrosynthetic analysis; Overall enantioselective synthesis; Chiral auxiliaries; Enantioselective catalysis; Database literature search ...
Electrospray ionization generates trimeric diastereoisomeric clusters as the first important step in chiral analysis by mass spectrometry using the Cooks′ kinetic method. Cu2+ and L-tryptophan were used as a central metal and as a chiral reference ligand, respectively. The comparison of electrospray and nanoelectrospray showed that although the electrospray system was generally more robust, the application of nanoelectrospray was essential for performing successful analysis in some cases, especially for real samples. Basically, no significant differences between the ion sources were observed for model samples of analytes (isoleucine, ephedrine, phenylalanine) without interfering matrix. On the other hand, model samples containing sodium chloride and a buffer containing a real sample (drug formulation Mucoseptonex E in which D-ephedrine is the active substance) could not be analyzed using ESI, whereas nano-ESI gave satisfactory results. An explanation is based on the differences of ionization ...
Molecular interaction between nucleic acid bases and amino acids is a fundamental process in biology. The adsorption of the molecules on surfaces provides the opportunity to study such interactions in great detail by exploiting the high-resolution imaging capabilities of scanning tunnelling microscopy (STM). The chemisorption of prochiral molecules, such as adenine, on a metal surface causes the adsorbed species to become chiral1. Subsequent interactions with inherently chiral molecules may then lead to the formation of diastereoisomers, if the enantiomeric interaction process is sufficiently strong. In the case of adenine adsorption on Cu{110}, the chiral adsorbates form homochiral chains. Here, we show that the adenine chain direction is fully correlated with the chirality, and that the α-amino acid, phenylglycine, shows a strong chiral preference in its interaction with these chains. STM images clearly demonstrate that S-phenylglycine (R-phenylglycine) binds only to chains rotated 19.5° ...
The overreaching purpose of this study is to evaluate new approaches for determining the optimal operational and column conditions in chromatography laboratories, i.e., how best to select a packing material of proper particle size and how to determine the proper length of the column bed after selecting particle size. As model compounds, we chose two chiral drugs for preparative separation: omeprazole and etiracetam. In each case, two maximum allowed pressure drops were assumed: 80 and 200 bar. The processes were numerically optimized (mechanistic modeling) with a general rate model using a global optimization method. The numerical predictions were experimentally verified at both analytical and pilot scales. The lower allowed pressure drop represents the use of standard equipment, while the higher allowed drop represents more modern equipment. For both compounds, maximum productivity was achieved using short columns packed with small-particle size packing materials. Increasing the allowed ...
Asymmetric total synthesis of (+)-6-epi-castanospermine through stereoselective formation of a syn,anti acetylenic 2-amino-1,3-diol stereotriad ...
Lee, Hong Geun, Jae Young Ahn, Amy S. Lee, and Matthew D. Shair. Forthcoming. Enantioselective synthesis of the lomaiviticin aglycon full carbon skeleton reveals remarkable remote substituent effects during the dimerization event. Chemistry - A European Journal ...
Acute bronchospasm associated with exacerbations of asthma is a common problem. Currently the mainstay of treatment is inhalation albuterol, either levalbuterol or racemic mixture, in repetitive fashion depending on the resolution of the airways obstruction. Formoterol is a long-acting (,12 hours) selective beta2-agonist that has a very rapid onset of bronchodilatation (,3 minutes and thus similar to that produced by albuterol). Patients with acute bronchospasm could benefit from the prn use of formoterol as they would receive acute relief of their symptoms and this would last for a prolonged time period. Additionally formoterol has been reported to be 28-109 times as potent as albuterol and safe at doses of 54ug in healthy subjects and asthmatics. Racemic formoterol structurally has 2 chiral centers and thus is composed of 4 enantiomers. The RR form (or arformoterol) is the active bronchodilator and it is not clear what the physiologic actions of the other 3 enantiomers are. This study is the ...
Acute bronchospasm associated with exacerbations of asthma is a common problem. Currently the mainstay of treatment is inhalation albuterol, either levalbuterol or racemic mixture, in repetitive fashion depending on the resolution of the airways obstruction. Formoterol is a long-acting (,12 hours) selective beta2-agonist that has a very rapid onset of bronchodilatation (,3 minutes and thus similar to that produced by albuterol). Patients with acute bronchospasm could benefit from the prn use of formoterol as they would receive acute relief of their symptoms and this would last for a prolonged time period. Additionally formoterol has been reported to be 28-109 times as potent as albuterol and safe at doses of 54ug in healthy subjects and asthmatics. Racemic formoterol structurally has 2 chiral centers and thus is composed of 4 enantiomers. The RR form (or arformoterol) is the active bronchodilator and it is not clear what the physiologic actions of the other 3 enantiomers are. This study is the ...
A highly efficient and convenient procedure for the enantioselective synthesis of (S)-Rivastigmine, a cholinergic agent for the treatment of mild to moderate dementia of the Alzheimers type and dementia due to Parkinsons disease, is accomplished by the treatment of versatile, readily accessible (S)-(-)-2-methyl-2-propanesulfinamide with 3-hydroxyacetophenone. This protocol provides high yield and excellent enantiomeric excess in short step synthesis.
The hetero-Diels-Alder reaction between an aldehyde and a diene provides access to dihydropyrans which are precursors in the chemical synthesis of biologically active natural products. Lewis acid catalysts increase reactivity by activating the carbonyl group of the aldehyde dienophile towards addition. Chiral dirhodium(II) carboxamidates are highly selective Lewis acids that have high turnover numbers in the hetero-Diels-Alder reaction. The reaction between aromatic aldehydes with Danishefskys diene in the presence of only 0.01 mol % catalyst afforded the corresponding dihydropyran products in high enantioselectivities and yields. Optimization of reaction conditions led to the discovery that the amount of dihydropyran formed increased at elevated temperatures while maintaining stereoselectivities as high as 98 % ee for aromatic aldehydes extending from p-nitro- to p-methoxy-benzaldehyde. Aldehydes with electron-donating substituents required longer reaction times in comparison to those having ...
Nowadays, a large number of chiral analyses are needed, simple and rapid methods for the determination of the enantiomeric composition in pharmaceutical products should be developed. The fluoxetine belongs to the most prescribed antidepressant chiral drugs and its enantiomers have a different duration of serotonin inhibition. This study presents cheap and fast alternative to traditional chiral techniques for the determination of the fluoxetine enantiomeric composition by the combination of UV/VIS spectrometry and multivariate calibration. The chiral recognition of the fluoxetine was based on the creating of the diastereomeric complexes with α- and β- cyclodextrin. Multivariate calibration methods, including principal component regression (PCR) and partial least square method (PLS), were used for spectral data evaluation. Small differences in results between eachcyclodextrin and both calibration models were obtained by multivariate calibration. PLS model for determination of the enantiomeric ...
Microbial degradation of the chiral 2-phenylbutyric acid (2-PBA), a metabolite of surfactant linear alkylbenzene sulfonates (LAS), was investigated using both racemic and enantiomer-pure compounds together with quantitative stereoselective analyses. A pure culture of bacteria, identified as Xanthobacter flavus strain PA1 isolated from the mangrove sediment of Hong Kong Mai Po Nature Reserve, was able to utilize the racemic 2-PBA as well as the single enantiomers as the sole source of carbon and energy. In the presence of the racemic compounds, X. flavus PA1 degraded both (R) and (S) forms of enantiomers to completion in a sequential manner in which the (S) enantiomer disappeared much faster than the (R) enantiomer. When the single pure enantiomer was supplied as the sole substrate, a unidirectional chiral inversion involving (S) enantiomer to (R) enantiomer was evident. No major difference was observed in the degradation intermediates with either of the individual enantiomers when used as the ...
An enantioselective synthesis of allenes through palladium-catalyzed asymmetric allylic alkylation using a chiral diaminophosphine oxide is described. The asymmetric allylic alkylations proceeded in the presence of a catalytic amount of lithium acetate at 4 °C, affording the chiral allenes in excellent yield with up to 99% ee. ...
The enantiomeric composition of seven chiral PCB congeners was measured in the Lake Superior aquatic food web sampled in 1998, to determine the extent of enantioselective biotransformation in aquatic biota. All chiral PCB congeners studied (CBs 91, 95, 136, 149, 174, 176, and 183) biomagnified in the Lake Superior aquatic food web, based on biomagnification and food web magnification factors greater than unity. PCB atropisomers were racemic in phytoplankton and zooplankton, suggesting no biotransformation potential toward PCBs for these low trophic level organisms. However, Diporeia and mysids had significantly nonracemic residues for most chiral congeners studied. This observation suggests that these macrozooplankton can stereoselectively metabolize chiral congeners. Alternatively, macrozooplankton obtained nonracemic residues from feeding on organic-rich suspended particles and sediments, which would imply that stereoselective microbial PCB biotransformation may be occurring in Lake Superior sediments
A total asymmetric synthesis of the polyol subunit of the polyene macrolide antibiotic RK-397 was developed through the stereoselective functionalization of (1R,1S,6S,6R)-3,3-methylenebis(cyclohept-3-ene-1,6-diol). The pathway generates a large variety of stereoisomeric intermediates and thus can be applied to the preparation of analogues of the natural antibiotic.. Keywords: long-chain polyol ; polyene macrolide antibiotic ; stereoselective functionalization ; Sharpless asymmetric dihydroxylation. ...
25608-40-6:(C4H7NO4)x, L-Aspartic acid, homopolymer, 2,5-Furandione, polymer with L-aspartic acid, 2-Butenedioic acid (2E)-, polymer with L-aspartic acid, 2-Butenedioic acid (2Z)-, polymer with L-aspartic acid, 2-Butenedioic acid (E)-, polymer with L-aspartic acid, 2-Butenedioic acid (Z)-, polymer with L-aspartic acid, Amisorb, Aspartic acid homopolymer, Aspartic acid, L-, peptides, Butanetetracarboxylic acid, polymer with L-aspartic acid, Carpramid, L-Asparaginic acid homopolymer, L-Aspartic acid polymer, L-Aspartic acid, homopolymer, L-Aspartic acid, polymer with (2E)-2-butenedioic acid, L-Aspartic acid, polymer with (2Z)-2-butenedioic acid, L-Aspartic acid, polymer with (E)-2-butenedioic acid, L-Aspartic acid, polymer with (Z)-2-butenedioic acid, L-Aspartic acid, polymer with 2,5-furandione, L-Aspartic acid, polymer with butanetetracarboxylic acid, L-Aspartic acid-butanetetracarboxylic acid copolymer, L-Aspartic acid-fumaric acid copolymer, L-Aspartic acid-maleic acid copolymer, L-Aspartic acid
N-Heterocyclic carbene (NHC) ruthenium complexes consisting of different donor substituents attached to the NHC ligand efficiently catalyse the transfer hydrogenation of ketones and of activated olefins in α,β-unsaturated ketones to give saturated alcohols. The most active catalyst precursor contains a tethered olefin as a hemilabile donor site. This complex also converts nitriles and, depending on the reaction conditions, either benzylamines are produced by means of transfer hydrogenation, or amides from formal addition of H2O. Kinetic analysis of the double hydrogenation of α,β-unsaturated ketones indicates fast isomerisation of the enol intermediate to its saturated ketone tautomer prior to the second hydrogenation ...
TY - JOUR. T1 - Efficient and phosphine-free bidentate N-heterocyclic carbene/ruthenium catalytic systems for the dehydrogenative amidation of alcohols and amines. AU - Wu, Xuan Jun. AU - Wang, Hua Jing. AU - Yang, Zhao Qi. AU - Tang, Xiao Sheng. AU - Yuan, Ye. AU - Su, Wei. AU - Chen, Cheng. AU - Verpoort, Francis. PY - 2019/3/7. Y1 - 2019/3/7. N2 - The direct amide synthesis from alcohols and amines applying various transition metal catalysts has been demonstrated as an attractive and promising process. Among various catalytic systems, N-heterocyclic carbene (NHC)-based ruthenium (Ru) ones have been testified to be active for this atom-economic transformation. Although a variety of imidazole-based NHC/Ru catalytic systems were reported to be active for this reaction, the benzimidazole-based analogs exhibited higher catalytic performance in most cases. However, these catalytic systems, which comprise a monodentate NHC ligand and a Cl or phosphine ligand as the key components, require relatively ...

Stereoisomerism - WikipediaStereoisomerism - Wikipedia

Stereoisomerism about double bonds arises because rotation about the double bond is restricted, keeping the substituents fixed ... the "Gold Book") (1997). Online corrected version: (2006-) "stereoisomerism". Columbia Encyclopedia. "Stereoisomers" in ...
more infohttps://en.wikipedia.org/wiki/Stereoisomerism

Stereoisomerism | chemistry | Britannica.comStereoisomerism | chemistry | Britannica.com

Stereoisomerism: …of isomerism, which is called stereoisomerism, exists in all biological systems. Among carbohydrates, the ... In carbohydrate: Stereoisomerism. …of isomerism, which is called stereoisomerism, exists in all biological systems. Among ... Stereoisomerism is therefore possible in those alkenes in which neither carbon atom bears two identical substituents. In most ... In hydrocarbon: Stereoisomerism. Certain substituted derivatives of cycloalkanes exhibit a type of isomerism called ...
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Chemistry 4.1 - Stereoisomerism - Flashcards in A Level and IB ChemistryChemistry 4.1 - Stereoisomerism - Flashcards in A Level and IB Chemistry

Copyright Get Revising 2018 all rights reserved. Get Revising is one of the trading names of The Student Room Group Ltd. Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered office: International House, Queens Road, Brighton, BN1 3XE ...
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19.8E: Stereoisomerism - Diastereomers - Chemistry LibreTexts19.8E: Stereoisomerism - Diastereomers - Chemistry LibreTexts

Diastereomers are non-enantiomeric where two compounds of the same stereoisomers do not look like mirror images. Unlike enantiomeric compounds, two compounds of a diastereomer pair have different …
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stereoisomerism - தமிழ் விக்சனரிstereoisomerism - தமிழ் விக்சனரி

"https://ta.wiktionary.org/w/index.php?title=stereoisomerism&oldid=1615061" இருந்து மீள்விக்கப்பட்டது ...
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Gohalfsies.com | Protein biochemistry | Heterofunctional compounds. StereoisomerismGohalfsies.com | Protein biochemistry | Heterofunctional compounds. Stereoisomerism

For these compounds, stereoisomerism is characteristic.. Stereoisomerism is the doctrine of the spatial structure of molecules ... Stereoisomerism. Heterofunctional compounds are organic substances containing two or more different functional groups that ... The concepts of stereoisomerism, D and L - isomers, stereospecificity are very important, as in strictly living organisms ...
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Stereoisomerism  - A-Level H2 Chemistry Tuition by 10 Year Series AuthorStereoisomerism - A-Level H2 Chemistry Tuition by 10 Year Series Author

Stereoisomerism. Organic Chemistry: Key Concepts in Introductory Topics, Alkanes, Alkenes & Arenes. August 27, 2019. By Sean ...
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Glaucine - WikipediaGlaucine - Wikipedia

Stereoisomerism[edit]. The (S)-form of glaucine occurs in nature, but the (R)-form does not. ...
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Coordination complex - WikipediaCoordination complex - Wikipedia

Stereoisomerism[edit]. Stereoisomerism occurs with the same bonds in different orientations relative to one another. ... Stereoisomerism can be further classified into:[15] Cis-trans isomerism and facial-meridional isomerism[edit]. Cis-trans ... 3.2.1 Stereoisomerism *3.2.1.1 Cis-trans isomerism and facial-meridional isomerism ...
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Coordination complex - WikipediaCoordination complex - Wikipedia

StereoisomerismEdit. Stereoisomerism occurs with the same bonds in different orientations relative to one another. ... Stereoisomerism can be further classified into:[15]. Cis-trans isomerism and facial-meridional isomerismEdit. Cis-trans ...
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Chemistry of lifeChemistry of life

Stereoisomerism. Structural isomers which are mirror images of each other and cannot be superimposed. ... Some organic molecules also show stereoisomerism. They are mirror images of each other and cannot be superimposed. ...
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Coordination complex : Wikis (The Full Wiki)Coordination complex : Wikis (The Full Wiki)

Stereoisomerism. Stereoisomerism occurs with the same bonds in different orientations relative to one another. Stereoisomerism ... 2.2.1 Stereoisomerism *2.2.1.1 Cis-trans isomerism and facial-meridional isomerism ...
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AphasiaAphasia

Stereoisomerism. Released 1997 * add to main playlist Play in Full Screen Stereoisomerism 1 ...
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In celebration of Seiji Shinkais 70th Birthday HomeIn celebration of Seiji Shinkai's 70th Birthday Home

Pseudorotaxane orientational stereoisomerism driven by π-electron density Carmine Gaeta, Carmen Talotta and Placido Neri ...
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Stereocenter - WikipediaStereocenter - Wikipedia

In compounds whose stereoisomerism is due to tetrahedral stereogenic centers, the total number of hypothetically possible ... "Stereoisomerism and local chirality". Journal of the American Chemical Society. 106 (11): 3319. doi:10.1021/ja00323a043. "IUPAC ...
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Amino Acids - Revision Cards in University Human BiologyAmino Acids - Revision Cards in University Human Biology

Stereoisomerism. *Amino acids exist in either L (levo) or D (dextro) form. The L and D refer to the absolute confirmation of ...
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Chemistry Module 4  - Online Flashcards by Taani B | BrainscapeChemistry Module 4 - Online Flashcards by Taani B | Brainscape

Ch 132 Stereoisomerism Ch. 13.2: Stereoisomerism Sample Cards: what are stereoisomers, what are the two types of stereoisome ...
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Messenger RNAMessenger RNA

... (mRNA) is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein. In mRNA as in DNA, genetic information is encoded in the sequence of nucleotides arranged into codons consisting of three bases each. Each codon encodes for a specific amino acid, except the stop codons that terminate protein synthesis. This process requires two other types of RNA: transfer RNA (tRNA) mediates recognition of the codon and provides the corresponding amino acid, while ribosomal RNA (rRNA) is the central component of the ribosomes protein manufacturing machinery.. ...
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PlagioclasePlagioclase

... is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series (from the Greek "oblique fracture", in reference to its two cleavage angles). This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796 - 1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the minerals crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic twinning or record-groove effect.. Plagioclase is a major constituent mineral in the Earths crust, and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase is also a major constituent ...
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Baking Business | Resources for the Baking IndustryBaking Business | Resources for the Baking Industry

Stereoisomerism. Stereoisomerism. Isomers (q.v.) of organic compounds, such as of simple sugars, having the same molecular (q.v ...
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Organic Chemistry, 2nd Edition | Organic Chemistry | Chemistry | Subjects | WileyOrganic Chemistry, 2nd Edition | Organic Chemistry | Chemistry | Subjects | Wiley

5 Stereoisomerism. 6 Chemical Reactivity and Mechanisms. 7 Substitution Reactions. 8 Alkenes: Structure and Preparation via ...
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Organic Chemistry, 3rd Edition | Organic Chemistry | Chemistry | Subjects | WileyOrganic Chemistry, 3rd Edition | Organic Chemistry | Chemistry | Subjects | Wiley

5. Stereoisomerism. 6. Chemical Reactivity and Mechanisms. 7. Substitution and Elimination Reactions of Alkyl Halides ...
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Density Functional Theory Study of Spirodienone Stereoisomers in Lignin (Journal Article) | DOE PAGESDensity Functional Theory Study of Spirodienone Stereoisomers in Lignin (Journal Article) | DOE PAGES

09 BIOMASS FUELS; bond dissociation energy; density functional theory; lignin; spirodienone; stereoisomerism. OSTI Identifier: ...
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Polarization | physics | Britannica.comPolarization | physics | Britannica.com

Polarization: Polarization, property of certain electromagnetic radiations in which the direction and magnitude of the vibrating electric field are related in a specified way. Light waves are transverse: that is, the vibrating electric vector associated with each wave is perpendicular to the direction of
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All About Symbian - Software - Organic Chemistry Quick Study GuideAll About Symbian - Software - Organic Chemistry Quick Study Guide

Stereochemistry: Isomers , Structural isomerism , Stereoisomerism , Geometric isomerism , Optical isomerism , Diastereomer , ...
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  • The concepts of stereoisomerism, D and L - isomers, stereospecificity are very important, as in strictly living organisms strictly specific stereoisomers function: L-lactic acid, L-amino acids, L-phospholipids, but D-carbohydrates. (gohalfsies.com)
  • Stereoisomerism about double bonds arises because rotation about the double bond is restricted, keeping the substituents fixed relative to each other. (wikipedia.org)