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 ...
p-Menthane-3-carboxaldehyde is a readily available chiral auxiliary used to prepare cycloalkenes and heterocycles bearing a chiral tertiary or quaternary carbon of high enantiomeric purity. The auxiliary is available in both enantiomeric forms and is inexpensive and recyclable. It is cleaved by a ring-closing alkene metathesis reaction directly yielding the cycloalkene.Key words: chiral auxiliary, cleavage reaction, cyclization, ring-closing alkene metathesis, enantioenriched cycloalkenes.
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 ...
TY - JOUR. T1 - The use of an altered specificity engineered enzyme for asymmetric synthesis. T2 - enantioselective reduction of 4-methyl-2-oxopent-3-enoic acid. AU - CASY, G AU - LEE, T V AU - LOVELL, H AU - NICHOLS, B J AU - SESSIONS, R B AU - HOLBROOK, J J PY - 1992/7/1. Y1 - 1992/7/1. N2 - A genetically engineered version of Bacillus stearothermophilus lactate dehydrogenase, incorporating structural motifs which serve to alter substrate specificity in favour of alpha-keto acids with bulky aliphatic side chains, was used to effect enantioselective reduction of 4-methyl-2-oxopent-3-enoic acid.. AB - A genetically engineered version of Bacillus stearothermophilus lactate dehydrogenase, incorporating structural motifs which serve to alter substrate specificity in favour of alpha-keto acids with bulky aliphatic side chains, was used to effect enantioselective reduction of 4-methyl-2-oxopent-3-enoic acid.. M3 - Article (Academic Journal). VL - 30. SP - 924. EP - 926. JO - Journal of the Chemical ...
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. ...
Looking for Diastereomeric pair? Find out information about Diastereomeric pair. diastereoisomer McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc Explanation of Diastereomeric pair
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
TY - JOUR. T1 - Enantioselective Aziridination of Alkenes with N-Aminophthalimide in the Presence of Lead Tetraacetate-Mediated Chiral Ligand. AU - Yang, Kung Shou. AU - Chen, Kwunmin. PY - 2002/4/4. Y1 - 2002/4/4. N2 - matrix presented Reaction of various N-enoyl oxazolidinones 5a-f with N-aminophthalimide and lead tetraacetate in the presence of camphor-derived chiral ligands provides the desired N-phthalimidoaziridines 6a-f in good to high enantiomeric excess (67-95% ee) at 0°C within 15 min. The absolute stereochemistry of the corresponding aziridine derivatives was established by chemical correlations.. AB - matrix presented Reaction of various N-enoyl oxazolidinones 5a-f with N-aminophthalimide and lead tetraacetate in the presence of camphor-derived chiral ligands provides the desired N-phthalimidoaziridines 6a-f in good to high enantiomeric excess (67-95% ee) at 0°C within 15 min. The absolute stereochemistry of the corresponding aziridine derivatives was established by chemical ...
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 ...
We report herein the highly enantioselective synthesis of 2-substituted tetrahydroquinolines through borrowing hydrogen, a process recognized for its environmentally benign and atom-economical nature. The use of an achiral iridacycle complex in combination with a chiral phosphoric acid as catalysts was the key to the development of this highly efficient and enantioselective transformation. Waste not, want not: A highly enantioselective synthesis of tetrahydroquinolines was made possible by hydro
295942762 - EP 0973705 A1 20000126 - CHROMATOGRAPHIC ENANTIOMER SEPARATION OF LACTONES - [origin: DE19714343A1] The present invention describes the use of optically active polymers made from N-acryloyl-phenylalanine-neomenthylamide per se, in cross-linked form and/or bonded to a carrier, as stationary phases for chromatographic enantiomer separation of lactones.[origin: DE19714343A1] The present invention describes the use of optically active polymers made from N-acryloyl-phenylalanine-neomenthylamide per se, in cross-linked form and/or bonded to a carrier, as stationary phases for chromatographic enantiomer separation of lactones.
Enantiomer separation fundamentals and practical methods pdf Enantiomer Separation. Fundamentals and Practical Methods. Editors; (view affiliations). Fumio Toda. - Enantiomer Separations by Capillary Electrophoresis | Springer Nature Experiments
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.
Great presentation as the bottle expresses terroir and is a modern take on the old fashioned New Zealand beer flask. History of Antipodes. Arriving back to New Zealand after 6 years away the first thing that hit Simon Woolley, founder of Antipodes, was the large presence of imported waters in all of New Zealands restaurants. Being both a big water drinker and someone who has had experience in the restaurant industry, it bugged Simon not being able to find a good tasting softly beaded New Zealand mineral water that was specifically packaged for restaurant dining.. In the past as a restaurateur Simon could never understand why he had to sell waters all the way from Europe, when there ought to be good water in New Zealand. Simon spent a year asking and researching and the result is Antipodes.. It is a high quality New Zealand water and it has been packaged it to compete with the European waters people drink in restaurants. Rather than copy the European packaging Antipodes went for something far ...
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 ...
TY - JOUR. T1 - The stereochemical configuration of flavanols influences the level and metabolism of flavanols in humans and their biological activity in vivo. AU - Ottaviani, Javier I.. AU - Momma, Tony Y.. AU - Heiss, Christian. AU - Kwik-Uribe, Catherine. AU - Schroeter, Hagen. AU - Keen, Carl L. PY - 2011/1/15. Y1 - 2011/1/15. N2 - Extensive epidemiological and clinical evidence associates diets high in flavanol-containing foods with cardiovascular health benefits in humans. Catechin and epicatechin, the most common flavanols in foods, are present in the diet in different enantiomeric forms. This study investigated the influence of the stereochemical configuration of flavanols on their absorption, metabolism, and biological activity. Healthy adult males were asked to consume equal amounts of the stereochemically pure flavanols (-)-epicatechin, (-)-catechin, (+)-catechin, and (+)-epicatechin (1.5 mg/kg bw) in a well-defined cocoa-based, dairy-containing drink matrix, and flavanol levels were ...
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 ...
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 ...
where R9represents phenyl, and. R3is N;. or its physiologically acceptable salt.. Optically active carbon atoms present in the compound of formula (I)may independently from each other to have the R configuration or S configuration. The compounds of formula (I) can be represented in the form of pure enantiomers or pure diastereomers or as mixtures of enantiomers and/who do diastereomers, for example in the form of racemates. This invention relates to the pure enantiomers and mixtures of enantiomers, as well as to pure diastereomers and mixtures of diastereomers. The invention contains a mixture of two or more than two stereoisomers of the formula I and includes all ratios of the stereoisomers in the mixtures. When the compounds of formula (I) can be represented as E isomers or Z isomers (or CIS isomers or TRANS isomers), the invention relates both to the pure E isomers and the pure Z isomers, and mixtures of E/Z in all relationships. The invention also includes all tautomeric forms of the ...
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...
Steady-state fluorescence spectroscopy was employed to investigate the use of chiral polymeric surfactants as chiral selectors in chiral analysis by multivariate regression modeling of spectral data. Partial-least-squares regression modeling (PLS-1) was used to correlate changes in the fluorescence spectral data of 1,1′-bi-2-naphthol (BOH), 1,1′-binaphthyl-2, 2′-diamine (BNA), or 2,2,2-trifluoroanthrylethanol (TFA) in the presence of poly(sodium N-undecanoyl-l-leucylvalinate), poly(sodium N-undecanoyl-l- leucinate) or poly(sodium N-undecanoyl-l-valinate) as the enantiomeric composition of the chiral analytes was varied. The regression models produced from the spectral data were validated by determining the enantiomeric composition of independently prepared test solutions. The ability of the model to correctly predict the enantiomeric composition of future samples was evaluated using the root-mean-square percent-relative error (RMS%RE) of prediction. In terms of RMS%RE, the ability of the model to
Mechanistic Basis for High Stereoselectivity and Broad Substrate Scope in the (salen)Co(III)-Catalyzed Hydrolytic Kinetic Resolution Journal Article ...
TY - JOUR. T1 - Unusual double hydroformylation of substituted allylanilines leading to the formation of N-arylpyrrolidine aldehydes. AU - Anastasiou, Despina. AU - Campi, Eva M.. AU - Chaouk, Hassan. AU - Jackson, W. Roy. AU - McCubbin, Quentin J.. PY - 1992/4/14. Y1 - 1992/4/14. N2 - N-Arylpyrrolidine aldehydes are the unexpected products obtained from the rhodium-catalysed double hydroformylation of allylanilines.. AB - N-Arylpyrrolidine aldehydes are the unexpected products obtained from the rhodium-catalysed double hydroformylation of allylanilines.. UR - http://www.scopus.com/inward/record.url?scp=0026553229&partnerID=8YFLogxK. U2 - 10.1016/0040-4039(92)88179-9. DO - 10.1016/0040-4039(92)88179-9. M3 - Article. AN - SCOPUS:0026553229. VL - 33. SP - 2211. EP - 2212. JO - Tetrahedron Letters. JF - Tetrahedron Letters. SN - 0040-4039. IS - 16. ER - ...
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
The Wittig Reaction is a reliable, high-yield method for synthesizing alkenes. It is employed in a variety of applications, including agrochemicals, steroidal production, textiles/dyes, synthetic nutritional supplements, because, unlike other alkene-forming synthetic protocols, the Wittig reaction is highly stereoselective. Moreover, this stereoselectivity can be regulated through skillful choice of the Wittig reagent used. Here we describe the synthesis of flavor and aroma compounds through the Wittig reaction and use a 60 MHz benchtop NMR spectrometer to assign and quantify the relative proportion of cis- and trans- isomer formed. ...
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
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 ...
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 ...
Parity violation (PV) effects have so far never been observed in chiral molecules. Originating from the weak interaction, PV should lead to frequency differences in the rovibrational spectra of the two enantiomers of a chiral molecule. However the smallness of the effect represents a very difficult experimental challenge. We propose to compare the rovibrational spectra (around 10 $\mu$m) of two enantiomers, recorded using the ultra-high resolution spectroscopy technique of Doppler-free two-photon Ramsey interferometry in a supersonic molecular beam. With an alternate beam of left- and right-handed molecules and thanks to our expertise in the control of the absolute frequency of the probe CO$_2$ lasers, we should reach a fractional sensitivity better around 10$^{-15}$ (a few tens of millihertz), on the frequency difference between enantiomers~, 870 (2010).}. We will review our latest results on the high-resolution spectroscopy, either in cell or in a supersonic beam, of methyltrioxorhenium~, 854 ...
TY - JOUR. T1 - Chiral Recognition of Lipid Bilayer Membranes by Supramolecular Assemblies of Peptide Amphiphiles. AU - Sato, Kohei. AU - Ji, Wei. AU - Álvarez, Zaida. AU - Palmer, Liam C.. AU - Stupp, Samuel I.. PY - 2019/6/10. Y1 - 2019/6/10. N2 - On the basis of the exclusive existence of homochirality in biomolecules and the well-known phenomenon of chiral recognition, it is obvious that chirality is a crucial factor in biological events. We report here that supramolecular assemblies of peptide amphiphiles interact with lipid bilayer membranes in a stereospecific manner. When negatively charged chiral phospholipid bilayer vesicles were subjected to the assemblies, we found that peptide amphiphiles with l-amino acids show stronger affinity for the liposomes compared to the ones with d-amino acids. To examine their biological functions, we tested the cytotoxicity of nanofibers against mammalian primary cells using human bone marrow mesenchymal stem cells and murine astroglial cells. We ...
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 ...
Template Directed C-H Insertion Reactions for Stereocontrolled Synthesis of Heterocycles Orobosa Marvis Erhunmwunse, PhD. Non aromatic heterocycles and their analogues are abundant in a large variety of bioactive natural products and continue to play crucial roles in modern day chemotherapy. The bioactivities of these heterocycles are highly dependent on the stereochemistry of the substituents and therefore the development of elegant new methodologies for the selective construction of heterocycles remains attractive to the synthetic chemist. Described in this thesis, is a tandem methodology for the stereocontrolled synthesis of highly functionalised oxygen heterocycles. The strategy adopted resulted in the successful synthesis of 2,3,4,5-tetrasubstituted tetrahydrofurans and 2,3,4,5,6-pentasubstituted oxepanes. The key step involves catalytic C-H insertion of diazocarbonyl acetal templates. Diazocarbonyl substrates representing the three classes of carbenoids were synthesised. In the foremost ...
TY - JOUR. T1 - Highly enantioselective synthesis induced by chiral primary alcohols due to deuterium substitution [8]. AU - Sato, I.. AU - Omiya, D.. AU - Saito, T.. AU - Soai, K.. PY - 2000/11/29. Y1 - 2000/11/29. UR - http://www.scopus.com/inward/record.url?scp=0034731029&partnerID=8YFLogxK. UR - http://www.scopus.com/inward/citedby.url?scp=0034731029&partnerID=8YFLogxK. U2 - 10.1021/ja002992e. DO - 10.1021/ja002992e. M3 - Letter. AN - SCOPUS:0034731029. VL - 122. SP - 11739. EP - 11740. JO - Journal of the American Chemical Society. JF - Journal of the American Chemical Society. SN - 0002-7863. IS - 47. ER - ...
The study of optically active molecules has been continuous for over two centuries, due to the role chiral molecules play as both the building blocks of life, and therefore their importance in developing pharmaceuticals. Theoretical calculations to study chiroptical properties, such as optical rotation (OR), electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and Raman optical activity (ROA), have only been developed in the last two decades. Since then, two fundamental questions have dominated research of chiral molecules. The first question lies in successfully relating the magnitude and sign of chiral properties to a structure, as there is no chemically intuitive way to determine, without performing measurements or calculations, if the OR of a given chiral molecule will be small or large, positive or negative. The second relates to the effect of solvation, as we currently do not know the root causes of the changes induced in the OR by a change in the environment. We ...
TY - JOUR. T1 - Lipase-catalyzed dynamic kinetic resolution giving optically active cyanohydrins. T2 - use of silica-supported ammonium hydroxide and porous ceramic-immobilized lipase. AU - Sakai, Takashi. AU - Wang, Kefei. AU - Ema, Tadashi. PY - 2008/2/25. Y1 - 2008/2/25. N2 - Synthetically useful cyanohydrin acetates, ArCH(OAc)CN (Ar=C6H5, 3,4-methylenedioxyphenyl, 4-Me-C6H4, 4-Cl-C6H4, 4-F-C6H4, 4-CF3-C6H4), were successfully synthesized in high enantiomeric purities (79-93% ee) via the lipase-catalyzed dynamic kinetic resolution (DKR) of cyanohydrins synthesized in situ from the corresponding aldehydes and acetone cyanohydrin. The combined use of silica-supported BTAH (benzyltrimethylammonium hydroxide) and porous ceramic-immobilized lipase under the optimized reaction conditions enabled the remarkable acceleration of the enantioselective DKR reactions.. AB - Synthetically useful cyanohydrin acetates, ArCH(OAc)CN (Ar=C6H5, 3,4-methylenedioxyphenyl, 4-Me-C6H4, 4-Cl-C6H4, 4-F-C6H4, ...
Angewandte Chemie Amine Synthesis Asymmetric Synthesis of Diarylmethyl Amines by Rhodium-Catalyzed Asymmetric Addition of Aryl Titanium Reagents to Imines** Tamio Hayashi,* Masahiro Kawai, and Norihito Tokunaga Asymmetric synthesis of diarylmethyl amines has attracted growing attention owing to their importance in biological activity.[1] Among several methods for performing the asymmetric synthesis,[2, 3] catalytic asymmetric addition of aryl metal reagents to imine derivatives seems to be most promising, provided that both high enantioselectivity and high catalytic activity are realized.[4] After our publication on the rhodium-catalyzed asymmetric addition of aryl stannanes to N-sulfonylimines,[5] two reports appeared on catalytic asymmetric arylation: 1) Br%se, Bolm, and co-workers described the addition of a phenylzinc reagent to masked Nformylimines in the presence of a chiral ketimine catalyst,[6] and 2) Tomioka illustrated the rhodium-catalyzed addition of aryl boroxines to N-tosylimines ...
TY - JOUR. T1 - Stereocontrolled synthesis of oxygen-bridged polycycles via intermolecular [3+2] cyclization of platinum-bound pyrylium with alkenes. AU - Oh, Chang Ho. AU - Yi, Hyun Jik. AU - Lee, Ji Ho. AU - Lim, Dong Hee. PY - 2010/4/21. Y1 - 2010/4/21. N2 - 2-(3-Benzyloxy)prop-1-ynyl)benzaldehyde with PtCl2 in toluene would form Pt-pyryliums that underwent [3+2] cycloaddition with alkenes to the oxygen-bridged (5H-benzo[7]annulen-5-ylidene)platinum(ii) intermediates with good stereoselectivities. Their tandem rearrangement afforded diverse types of polycycles depending on the electronic nature of the alkenes.. AB - 2-(3-Benzyloxy)prop-1-ynyl)benzaldehyde with PtCl2 in toluene would form Pt-pyryliums that underwent [3+2] cycloaddition with alkenes to the oxygen-bridged (5H-benzo[7]annulen-5-ylidene)platinum(ii) intermediates with good stereoselectivities. Their tandem rearrangement afforded diverse types of polycycles depending on the electronic nature of the alkenes.. UR - ...
TY - JOUR. T1 - A formal synthesis of aplysiatoxin. T2 - enantioselective synthesis of kishis aldehyde. AU - Okamura, Hiroaki. AU - Kuroda, Satoru. AU - Ikegami, Satoru. AU - Tomita, Kenji. AU - Sugimoto, Yu ichi. AU - Sakaguchi, Shin ichi. AU - Ito, Yoshio. AU - Katsuki, Tsutomu. AU - Yamaguchi, Masaru. PY - 1993. Y1 - 1993. N2 - This paper describes the enantioselective synthesis of key fragments (12, 18, 24, and 35) for the synthesis of aplysiatoxin (1a), a potent cancer promoter, and their convergent assembly to Kishis aldehyde (2). Since 2 has already been transformed into 1a in a short step, its synthesis constitutes a formal total synthesis of 1a. Synthesis of fragments of aplysiatoxin (1a) and their convergent assembly to the key intermediate, Kishis aldehyde (2), for the synthesis of 1a are described.. AB - This paper describes the enantioselective synthesis of key fragments (12, 18, 24, and 35) for the synthesis of aplysiatoxin (1a), a potent cancer promoter, and their convergent ...
As the first example of enantiopure homochiral zeolites, silicogermanates SU-32 can be synthesized in right- (SU-32a) or left-handed (SU-32b). These rare chiral zeolites provide beautiful benchmark structures to examine the microscopic properties of chiral molecules in the helical channels with only a single handedness. We report a molecular simulation study to investigate the enantioselective adsorption and diffusion of S-/R-glycidol enantiomers in SU-32a and SU-32b. S-glycidol is found to interact with SU-32a more strongly than R-glycidol and preferentially adsorbed in SU-32a, and the opposite is observed in SU-32b. The enantiomeric excess of S-/R-glycidol racemic mixture in SU-32a and SU-32b is up to 25% and slightly decreases with increasing temperature. For pure enantiomers, S-glycidol diffuses faster in SU-32a and slower in SU-32b, whereas the reverse is true for R-glycidol. The free energy analysis suggests that S-glycidol encounters a lower barrier to diffuse in SU-32a but a higher one ...
Dominguez de Maria, P., Kossmann, B., Potgrave, N., Buchholz, S., Trauthwein, H., May, O., & Gröger, H. (2005). Improved Process for the Enantioselective Hydrolysis of Prochiral Diethyl Malonates Catalyzed by Pig Liver Esterase. Synlett(11), 1746-1748. doi:10.1055/s-2005- ...
We describe herein a concise synthesis of (+)-neopeltolide, a marine macrolide natural product that elicits a highly potent antiproliferative activity against several human cancer cell lines. Our synthesis exploited the powerful bond-forming ability and high functional group compatibility of olefin metathesis and esterification reactions to minimize manipulations of oxygen functionalities and to maximize synthetic convergency. Our findings include a chemoselective olefin cross-metathesis reaction directed by H-bonding, and a ring-closing metathesis conducted under non-high dilution conditions. Moreover, we developed a 16-member stereoisomer library of 8,9-dehydroneopeltolide to systematically explore the stereostructure-activity relationships. Assessment of the antiproliferative activity of the stereoisomers against A549 human lung adenocarcinoma, MCF-7 human breast adenocarcinoma, HT-1080 human fibrosarcoma, and P388 murine leukemia cell lines has revealed marked differences in potency between ...
All three synthetic diastereoisomers of 13,23-dimethyl-pentatriacontane, the pheromone of Glossina pallidipes (Austen), have been tested in the G. pallidipes sex pheromone bioassay, together with one of the four diastereoisomers of 13,17-dimethylpentatriacontane, originally proposed as a candidate pheromone of G. pallidipes. Of the three isomers of 13,23-dimethylpentatriacontane only the (13R,23S) isomer was active with an ED-50 of 4.47±1.09/μg (mean±SD). The (13R,17R)-13,17-dimethylpentatriacontane was inactive. The diastereo-isomeric mixtures of 13,17- and 13,23-dimethylpentatriacontane were active with ED-50 values of 17.88±1.25/μg and 8.88±1.15μg respectively. The natural pheromone was active with an ED-50 of 8.07±1.17 μg indicating it to be a diastereoisomeric mixture ...
Inhibition studies showed that the lowest IC50 values were obtained when propafenone was co-incubated with CYP2D6 and CYP 3A4 which is to be expected as these CYP isoforms have been shown previously to be the major ones responsible for phase 1 metabolism of racaemic propafenone. There was a distinct stereospecific difference with these isoforms, with the R-enantiomer showing a higher degree of inhibition. This would suggest that there may be merit in considering single enantiomer therapy (in this instance using the S-enantiomer) to minimise the risk of any drug-drug interactions in vivo. However, the in vitro metabolism study showed that both single enantiomers were metabolised at a higher rate than the racaemic mixture. This may be explained in terms of the 2 enantiomers competing for metabolism and thus inhibiting the metabolism of each other. These results suggest a possible problem with single enantiomer therapy of propafenone as this drug has a short half life and increased metabolism would ...
TY - JOUR. T1 - Organocatalytic stereoisomerization versus alkene isomerization. T2 - Catalytic asymmetric synthesis of 1-hydroxy-trans -2,5-diphenylphospholane 1-oxide. AU - Hintermann, Lukas. AU - Schmitz, Marco. AU - Maltsev, Olegv. AU - Naumov, Pance. PY - 2013/1/11. Y1 - 2013/1/11. N2 - The potential for an organocatalytic asymmetric stereoisomerization or alkene isomerization as atom-economic reaction with minimal structural change was investigated. The McCormack cycloaddition of 1,4-diarylbuta-1,3-dienes with (dialkylamino)dichlorophosphane and aluminum trichloride gives meso-2,5-diaryl-1-(dialkylamino)-1-oxo-2,5-dihydro-1H-phospholes, which were identified as suitable substrates for asymmetric isomerization to (1R,5R)-2,5-diaryl-1-(dialkylamino)-1-oxo-4,5-dihydro-1H-phospholes in the presence of bifunctional organocatalysts (cinchona alkaloids, Takemoto catalyst) in up to 91% ee and quantitative yield. The substrate range and the mechanism of the catalysis were studied. The reaction ...
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Montesinos Magraner, M.; Vila, C.; Cantón, R.; Blay, G.; Fernández, I.; Muñoz Roca, MDC.; Pedro, JR. (2015). Organocatalytic Asymmetric Addition of Naphthols and Electron-Rich Phenols to Isatin-Derived Ketimines: Highly Enantioselective Construction of Tetrasubstituted Stereocenters. Angewandte Chemie International Edition. 54(21):6320-6324. doi:10.1002/anie.201501273. Por favor, use este identificador para citar o enlazar este ítem: http://hdl.handle.net/10251/72285. ...
TY - JOUR. T1 - Some stereoselective carbon-carbon bond-forming reactions realized by using sugar-derived chiral templates. AU - Totani, Kiichiro. AU - Takao, Ken Ichi. AU - Tadano, Kin Ichi. PY - 2011/12/1. Y1 - 2011/12/1. N2 - In this article, the authors summarize a variety of stereoselective carbon-carbon bond-forming reactions realized by the use of sugar-derived chiral templates, which have been one of the active concerns in the authors group in these fifteen years. Representative chiral templates prepared from D-glucose, D-galactose, or D-mannose are introduced first. Then, the utility of these templates for stereoselective carbon-carbon bond-forming reactions are outlined. These reactions include, 1) 1,4-conjugate additions, 2) α-alkylations of esters, 3) Diels-Alder cycloadditions, 4) 1,3-dipolar cycloadditions, and 5) α,α-dialkylation for the construction of an all-carbon asymmetric quaternary center. The use of a D-glucose derivative equipped with two bulky silyl ethers at C2 and ...
The synthesis of the thymine derivative (S)-50, was achieved in high enantiomeric purity (98% ee). The (R) enhanced enantiomer was also synthesized with moderate enantiomeric purity (46% ee). This acyclic pyrimidine analog ((S)-50) is a useful building block for the synthesis of a novel class of oligomers, the aromatic peptide nucleic acids (APNA). The APNA tetramer 70 was prepared from the amino acid monomer (S)-50 using classical peptide synthesis. Chemical shift differences between the $\sp1$H NMR of monomer (S)-57 and tetramer 70 were observed which suggested that base stacking interactions in the oligomers may be favorable. ...
TY - JOUR. T1 - A new halo aldol reaction. T2 - Three-component reaction via 1,4-robust activation of ethynyl alkyl ketones for stereoselective formations of versatile aldol adducts. AU - Wei, Han Xun. AU - Kim, Sun Hee. AU - Li, Guigen. PY - 2002/10/17. Y1 - 2002/10/17. N2 - (graph presented) A new three-component halo aldol reaction has been discovered for the tandem formations of I-C/C-C bonds by activating the α′,β-positions of α,β-acetylenic ketones. The key intermediates, 1-iodo-3-siloxy-1,3-butadienes, were generated from allenolates and directly monitored by 1H NMR spectroscopic analysis. Excellent geometric selectivity (,95%) and good yields (65-82%) have been achieved for 10 examples.. AB - (graph presented) A new three-component halo aldol reaction has been discovered for the tandem formations of I-C/C-C bonds by activating the α′,β-positions of α,β-acetylenic ketones. The key intermediates, 1-iodo-3-siloxy-1,3-butadienes, were generated from allenolates and directly ...
In the past 5 years, chiral diene ligands have surfaced for a variety of asymmetric transformations. Hayashi1 and Carreira2 pioneered this field by synthesizing chiral diene ligands that formed stable complexes with metals and exerted high catalytic activity as well as high enantioselectivity. Carreira and co-workers reported the asymmetric synthesis of 3,3-diarylpropanals using a chiral bicyclo[2.2.2]octadiene as a ligand with a rhodium complex.3 This new synthesis provides access to important building blocks that are otherwise not readily available. The reaction offers a general synthesis of a wide variety of diaryl propanals. This rhodium catalyzed conjugate addition of aryl boronic acids is both chemo- and regio-selective wherein conjugate addition is favored over 1,2-addition. In a typical reaction, 3.3 mol% of the ligand and 3 mol% of the rhodium complex in a mixture of methanol and water is required. Good yields and selectivity were reported with both electron rich and electron poor ...
Additional info for Chiral Separations by Liquid Chromatography: Theory and Applications Example text. Greater durability, and wider choice of mobile phase. X-ray studies indicate that Chiracel OA is almost amorphous rather than crystal [25], indicating that microcrystallinity is not essential for chiral resolution. It has also been observed that the chiral recognition of a CSP greatly depends on the conditions of preparation of that CSP, such as the type of coating solvent and the molecular weight of the cellulose [25,66]. Nevertheless, cellulose triacetate derivatives have certain limitations. The use of new substituted derivatives of polysaccharides as the chiral stationary phase in HPLC for chiral resolution was investigated. Okamoto et al. [56] prepared CSPs of amylose phenylcarbamate bonded to silica gel by the following enzymatic methods. Amylose that had been prepared by enzymatic polymerization of a-D-ðþÞ-glucose-1-phosphate dipotassium catalyzed by a phosphorylase, using two kinds ...
Trost, B. M., & Weber, L. (1975). New Approach for the Stereocontrolled Synthesis of Acyclic Terpenes. The Journal of Organic Chemistry, 40(24), 3617-3619. doi:10.1021/ ...
TY - JOUR. T1 - Cleavage of aldehyde hydrazonium iodides under mild conditions. A convenient route to chiral nitriles of high enantiomeric purity. AU - Moore, J. S.. AU - Stupp, Samuel I. PY - 1990. Y1 - 1990. UR - http://www.scopus.com/inward/record.url?scp=0343987016&partnerID=8YFLogxK. UR - http://www.scopus.com/inward/citedby.url?scp=0343987016&partnerID=8YFLogxK. M3 - Article. AN - SCOPUS:0343987016. VL - 55. SP - 3374. EP - 3377. JO - Journal of Organic Chemistry. JF - Journal of Organic Chemistry. SN - 0022-3263. IS - 10. ER - ...
Many biological compounds and functions in the body depend on molecular chirality. This is an important element in the manufacture of pharmaceuticals. Synthetic pathways are required to produce chiral molecules. Asymmetric hydrogenation is an important route to chiral compounds. In this webinar Raybows Dr. Dirk Hütten presents the companys expertise in the field of very efficient chiral ligands for transition metal catalysts. Part 2 of our webinar on chirality focuses on presenting case studies of developing processes using asymmetric hydrogenation as key step to obtain enantioselective pure APIs.. If you missed Part I, it is available on-demand by clicking here.. ...
Pyrrolidines are cyclic secondary amines with a five-membered ring, containing four carbon atoms and one nitrogen atom. The pyrrolidine ring is the central structure of the amino acid proline and its derivatives. Chiral pyrrolidines play an important role both as chiral building blocks for auxiliaries as well as key structures relevant to biologically active substances. Derivatives of the methylpyrrolidinyl fragment are common structural motifs present in several inhibitors and antagonists, including a series of HIV-1 reverse transcriptase inhibitors and histamine H3 receptor and dopamine D4 antagonists. Sigma-Aldrich has a large selection of pyrrolidines as heterocyclic building blocks for organic synthesis and medicinal chemistry, the majority of which are available as racemates or in either enantiomeric form.Learn More about PyrrolidinesPyrrolidines
Chirality (2008), 20(7), 863-870. [ doi:10.1002/chir.20561 ]. 3 alpha,12 alpha-Dihydroxy-5 beta-cholan-24-oic acid (deoxycholic acid DCA) is able to discriminate between the R- and S-enantiomers of camphorquinone and endo-(+)-3-bromocamphor and select only the S-enantiomers from a racemic mixture. DCA forms novel well ordered 1:l adducts with (1S)-(+)-camphorquinone and (1S)-endo-(-)-3-bromocamphor, both of which have been characterized by single crystal X-ray diffraction (SXRD). When DCA is cocrystallized with (RS)-camphorquinone and (RS)-endo-3-bromocamphor, 1:1 adducts of the S-enantiomers are produced together with crystals of the free racemic guest. In contrast, in the absence of (1S)-(+)-camphorquinone, DCA forms a 2:1 adduct with (1R)-(-)-camphorquinone. In this 2:1 adduct the guest is disordered at ambient temperature and undergoes a phase change in the region 160-130 K similar to that observed for the ferrocene adduct, but with only partial ordering of the guest. The SXRD structure of ...
Title:Recent Progress in BINOL Mediated Asymmetric Reactions. VOLUME: 12 ISSUE: 4. Author(s):Jun-Dao Chen, Lei Fang and Chuan-Feng Chen. Affiliation:Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China.. Keywords:Asymmetric reaction, BINOL, chiral ligand, enantioselectivity, organocatalyst, stereoselectivity.. Abstract:BINOL and its derivatives as a class of important and attractive compounds have been widely used in asymmetric synthesis. They could not only play as a part of chiral ligands, but also work well as organocatalysts. This review mainly focused on the recent progress in BINOL mediated asymmetric reactions including C-C bond forming reactions and C-hetero bond forming reactions.. ...
Microorganisms or isolated enzymes can be applied as catalysts to create highly regio- and stereoselective conversions under mild conditions. Lipases (EC 3.1.1.3, triacylglycerol lipase) are lipid-hydrolysing enzymes, which are increasingly used in stereoselective reactions. Their industrial importance arises from the fact that they act on a variety of substrates promoting a broad range of biocatalytic reactions. Lipase stereoselectivity is exploited for the production of single enantiomers instead of racemic mixtures and will become snore important in the pharmaceutical and agrochemical industry because, in most cases only one of the two enantiomers has the desired activity, whereas no activity or even undesirable side effects reside in the other enantiomer. Enantiomer differentiation is due to the various diastereomeric interactions that occur between the enantiomers and the active site of the enzyme. The stereospecificity of a lipase depends largely on the structure of the substrate, ...
The invention relates to a process for the enzymatic, stereoselective reduction of ketone compounds to provide chiral alcohols, for example the compound of formula (Ib).
A novel chemoenzymatic strategy for the synthesis of enantiomerically pure secondary alcohols with sterically similar substituents is described. The key step is the kinetic lipase-catalyzed resolution of racemic mixtures of substituted propargylic alcohols. The efficiency of this new approach was tested in the preparation of the corresponding enantiomers of 1,11-hexadecandiol derivatives ((R)-5 and (S)-5). Two strategies were tested. In the first one, the racemic intermediate 1-octyn-3-ol (1) was resolved enzymatically and then elongated with 1-bromo-9,11-dioxadodecane. Alternatively, the racemic 1 can be elongated to the corresponding racemic 17,19-dioxa-7-eicosyn-6-ol (3) first and then resolved biocatalytically. Twelve commercially available lipases were screened for the kinetic resolution of these intermediates. Among them, Candida antarctica lipase (CAL-B) and Humicola lanuginosa lipase (HLL) were the best biocatalysts for the resolution of 1 (S enantiomer 90% ee, E = 35), and 3 (R ...
Several racemic methyl decanoic acids have been synthesised and successfully resolved in esterification with 1-hexadecanol at aw=0.8 in cyclohexane using immobilised Candida rugosa lipase (CRL) as the catalyst. The enantiomeric ratios (E=2.8-68) obtained were surprisingly high even when the methyl group was as remotely located as in 8-methyldecanoic acid (E=25). Interestingly, the lipase shows enantiopreference for the S-enantiomer when the methyl group is located on even numbered carbons i.e. for the 2-,4-,6- and 8-methyldecanoic acids and to the R-enantiomer when the methyl group is located on uneven numbered carbons i.e. for the 3-,5- and 7-methyldecanoic acids.. ...
The enantiopure γ-amino alcohols 7 and 18 are prepared by using the diastereoselective michael addition of lithium N-benzyl ( R )-α-methylbenzylamide to α,β-unsaturated esters as a key step. The michael addition of 7 or 18 to an alkynone 8 followed by an intramolecular cyclization afford the cyclic enzmine 10 or 20. which are subjected to the diastereoselective hydrogenation, and the subsequent transformations provide 6-epi-alkaloid 223A and alkaloid 223A, respectively ...
To increase the reliability and success rate of drug discovery, efforts have been made to increase the C(sp3) fraction and avoid flat molecules. sp3-Rich enantiopure amines are most frequently encountered as chiral auxiliaries, synthetic intermediates for pharmaceutical agents and bioactive natural products. Streamlined construction of chiral aliphatic amines has long been regarded as a paramount challenge. Mainstream approaches, including hydrogenation of enamines and imines, C-H amination, and alkylation of imines, were applied for the synthesis of chiral amines with circumscribed skeleton structures; typically, the chiral carbon centre was adjacent to an auxiliary aryl or ester group. Herein, we report a mild and general nickel-catalysed asymmetric reductive hydroalkylation to effectively convert enamides and enecarbamates into drug-like α-branched chiral amines and derivatives. This reaction involves the regio- and stereoselective hydrometallation of an enamide or enecarbamate to generate a
Cytochrome P450 (CYP) family 4 constitutes monoxygenases responsible for hydroxylation of fatty acids and other lipids. For example, CYP4F3 metabolizes leukotrienes and CYP4F8 prostaglandin H. Importantly, six of the twelve CYP4 enzymes are orphans, i.e., with an unknown biological function. The catalytic activity of the enzyme CYP4F8 is known in seminal vesicles, but not in skin or psoriatic lesions, where CYP4F8 is highly expressed. The orphan CYP4F22 is also expressed in skin, and mutations in its gene has been linked to the rare skin disease lamellar ichthyosis, together with, inter alia, mutations in the genes of 12R-LOX and eLOX3. These enzymes appear to constitute a pathway producing hydroperoxides and epoxyalcohols from arachidonic acid. CYP4F22 is hypothesized to act in a consecutive step within this pathway.. The aim of this thesis was to develop analytical methods to prepare and analyze hydroperoxides and epoxyalcohols derived from fatty acids by LC-MS/MS, and to investigate the ...
Oxygenated polyunsaturated fatty acids (PUFAs)play an outstanding role in the physiological and pathological regulation of several biological processes. These oxygenated metabolites can be produced both enzimatically, yielding almost pure enantiomers, and non-enzymatically. The free radical-mediated non-enzymatic oxidation commonly produces racemic mixtures which are used as biomarkers of oxidative stress and tissue damage. The biological activity of oxygenated PUFAs is often associated with only one enantiomer, making it necessary of availing of lipidomics platforms allowing to disclose the role of single enantiomers in health and disease. Polysaccharide-based chiral stationary phases (CSPs) play a dominating part in this setting. As for the cellulose backbone, 4-methylbenzoate derivatives exhibit very high chiral recognition ability towards this class of compounds. Concerning the phenylcarbamate derivatives of cellulose and amylose, the tris(3,5-dimethylphenylcarbamate) variants show the best ...
In the current study, we show significant differences in biological activity between the d and l stereoisomers of 1-methyl-tryptophan. The l isomer was superior at inhibiting activity of purified recombinant IDO enzyme in a cell-free assay and also at inhibiting IDO enzymatic activity in HeLa cells and other cell lines. In contrast, the d isomer was at least as effective as the l isomer at inhibiting IDO enzymatic activity expressed by human or mouse dendritic cells. Unexpectedly, the d isomer was found to be significantly superior to both the l form and the dl mixture when tested by the biologically important readout of T-cell activation in MLRs. In vivo, a head-to-head comparison of the antitumor effect of the two isomers showed that the d isomer was more effective than the l isomer, using two different tumors and different chemo-immunotherapy regimens. Thus, the in vitro superiority of the d isomer for enhancing T-cell activation in MLRs seemed to correctly predict the superior in vivo ...
TY - JOUR. T1 - Asymmetric synthesis of chiral amines with ω-transaminase. AU - Shin, Jong Shik. AU - Kim, Byung Gee. PY - 1999/10/20. Y1 - 1999/10/20. N2 - The asymmetric synthesis of chiral amines using prochiral ketones was carried out with (S)-specific ω-transaminase (ω-TA) from Vibrio fluvialis JS17. This reaction is inhibited severely by both products, (S)-amine and deaminated ketone. In addition, thermodynamic equilibrium strongly favored the reverse reaction. L-Alanine proved to be the best amino donor based on easy removal of the products. Optimal pH of the reactions with both whole cells and cell-free extract was 7. Amino acceptor reactivities of ketone substrates and reaction profiles of the asymmetric synthesis showed that the initial rate as well as the reaction yield were lower when the resulting (S)- amine from a prochiral ketone substrate was a more reactive amino donor. The yield could be increased dramatically by removing pyruvate, which is a more inhibitory product than ...
A wide range of stable vinyl selenone-modified furanosides has been synthesized for the first time. These 2π-partners undergo 1,3-dipolar cycloaddition reactions with a wide range of organic azides to afford enantiopure trisubstituted triazoles. Furanosyl rings opened up during triazole synthesis to generate polyfunctionalized molecules, ready to undergo further transformations. This strategy is one of the most convenient methods for the synthesis of enantiopure 1,4,5-trisubstituted 1,2,3-triazoles where the chiral components are attached to C-4 or C-5 position of triazole ring. These triazoles are formed in a regioselective manner, and several pairs of regioisomeric triazoles have also been synthesized. The approach affords densely functionalized triazoles, which are amenable to further modifications because of the presence of aldehyde and hydroxyl groups. This powerful and practical route adds to the arsenals of chemists and biologists interested in the synthesis and applications of triazoles. ...
The thesis entitled Enantioselective synthesis of didemniserinolipid, cladospolides, aspercyclide and muricatacin is divided into three chapters. First chapter of the thesis deals with the formal total synthesis both enantiomers didemniserinolipid B from L-(+)-tartaric acid. Fused bicyclic acetals containing 6,8-dioxabicyclo[3.2.1]octane structural unit are wide spread in bio active natural products. Didemniserinolipids A-C possessing similar framework were isolated from a methanol extract of Didemnum sp., and some of the analogous compounds were found to be cytotoxic against P388, A549, and HT29 tumor cell lines. Pivotal reactions en route to the natural product include the elaboration of a γ-hydroxy amide derived from tartaric acid, olefin cross metathesis and Wittig olefination (Scheme 1). (+)-didemniserinolipid B Scheme 1: Retrosynthesis of both enantiomers of didemniserinolipid B. Second chapter of the thesis describes an enantiodivergent synthesis of macrolactones: In section A, ...
Stereochemistry of Organic Compounds: Principles stereochemistry of organic compounds pdf and stereochemistry of organic compounds pdf Applications. creative corner corner. Wilen Released at Filesize: 9. Stereochemistry of organic compounds: principles, and applications - D. The baby boom generation of organic graduate students learned most of what they know stereochemistry of organic compounds pdf about stereochemistry from that text. Conformation of Acyclic Molecules.. Stereochemistry of Organic Compounds The first fully referenced, comprehensive book on this subject in more than thirty years, Stereochemistry of Organic Compounds contains up-to-date coverage and insightful exposition of all important new concepts, developments, and tools in the rapidly advancing field of stereochemistry, including: * Asymmetric stereochemistry of organic compounds pdf and diastereoselective synthesis. ; Wilen, Samuel H. Introduction to Spectroscopy - stereochemistry of organic compounds pdf Pavia. 50 ...
The first highly enantioselective, direct organocatalytic conjugate addition of unmodified aldehydes to alkylidinemalonates is presented. The reaction gives access to β-formyl-substituted malonates and highly functionalized lactones with up to 14:1 dr and generally 94 to |99% ee. © 2008 Wiley-VCH
TY - JOUR. T1 - Stereoselective metabolism of the environmental mammary carcinogen 6-nitrochrysene to trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene by aroclor 1254-treated rat liver microsomes and their comparative mutation profiles in a lacI mammary epithelial cell line. AU - Sun, Yuan Wan. AU - Guttenplan, Joseph B.. AU - Khmelnitsky, Michael. AU - Krzeminski, Jacek. AU - Boyiri, Telih. AU - Amin, Shantu. AU - El-Bayoumy, Karam. PY - 2009/12/21. Y1 - 2009/12/21. N2 - The environmental pollutant 6-nitrochrysene (6-NC) is a powerful mammary carcinogen and mutagen in rats. Our previous studies have shown that 6-NC is metabolized to trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene (1,2-DHD-6-NC) in rats and in several in vitro systems, including human breast tissue, and the latter is the proximate carcinogenic form in the rat mammary gland. Because optically active enantiomers of numerous polynuclear aromatic hydrocarbon (PAH) metabolites including chrysene have different biological activities, ...
What Sarfati66 calls a major hurdle is the origin of homochirality, the fact that all amino acid biomolecules with rare exceptions (such as some used in bacterial cell walls) are all left-handed; and with rare exceptions, all sugars, including those in nucleic acids, are right-handed. Those produced in a laboratory are a half left-handed and half right-handed mixture called a racemate. Even in the laboratory, chemists use pre-existing homochirality from a biological source in order to synthesize homochiral compounds.60 Chiral molecules are dissymmetric-they exist as mirror images of each other, just as the right hand is a mirror image of the left hand (the word chiral comes from the Greek word for hand). The problem is left-handed sugars and right-handed amino acids can be toxic and prevent abiogenesis. Furthermore, most all enzymes are designed to work only with right-handed sugars and left-handed amino acids. All attempts to solve the chirality problem, including magnetochiral dichroism, ...