Cyclization: Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)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)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.Alkenes: Unsaturated hydrocarbons of the type Cn-H2n, indicated by the suffix -ene. (Grant & Hackh's Chemical Dictionary, 5th ed, p408)Alkynes: Hydrocarbons with at least one triple bond in the linear portion, of the general formula Cn-H2n-2.Intramolecular Lyases: Enzymes of the isomerase class that catalyze reactions in which a group can be regarded as eliminated from one part of a molecule, leaving a double bond, while remaining covalently attached to the molecule. (From Enzyme Nomenclature, 1992) EC 5.5.Palladium: A chemical element having an atomic weight of 106.4, atomic number of 46, and the symbol Pd. It is a white, ductile metal resembling platinum, and following it in abundance and importance of applications. It is used in dentistry in the form of gold, silver, and copper alloys.AcetalsCatalysis: The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.KetonesPolyisoprenyl Phosphates: Phosphoric or pyrophosphoric acid esters of polyisoprenoids.Chemistry, Organic: The study of the structure, preparation, properties, and reactions of carbon compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Alkadienes: Acyclic branched or unbranched hydrocarbons having two carbon-carbon double bonds.PyransPeptides, Cyclic: Peptides whose amino and carboxy ends are linked together with a peptide bond forming a circular chain. Some of them are ANTI-INFECTIVE AGENTS. Some of them are biosynthesized non-ribosomally (PEPTIDE BIOSYNTHESIS, NON-RIBOSOMAL).Cycloparaffins: Alicyclic hydrocarbons in which three or more of the carbon atoms in each molecule are united in a ring structure and each of the ring carbon atoms is joined to two hydrogen atoms or alkyl groups. The simplest members are cyclopropane (C3H6), cyclobutane (C4H8), cyclohexane (C6H12), and derivatives of these such as methylcyclohexane (C6H11CH3). (From Sax, et al., Hawley's Condensed Chemical Dictionary, 11th ed)Lewis Acids: Any chemical species which accepts an electron-pair from a LEWIS BASE in a chemical bonding reaction.Rhodium: Rhodium. A hard and rare metal of the platinum group, atomic number 45, atomic weight 102.905, symbol Rh. (Dorland, 28th ed)Combinatorial Chemistry Techniques: A technology, in which sets of reactions for solution or solid-phase synthesis, is used to create molecular libraries for analysis of compounds on a large scale.Isomerases: A class of enzymes that catalyze geometric or structural changes within a molecule to form a single product. The reactions do not involve a net change in the concentrations of compounds other than the substrate and the product.(from Dorland, 28th ed) EC 5.Indole Alkaloids: Group of alkaloids containing a benzylpyrrole group (derived from TRYPTOPHAN)IminesCyclotides: A continuous circle of peptide bonds, typically of 2-3 dozen AMINO ACIDS, so there is no free N- or C-terminus. They are further characterized by six conserved CYSTEINE residues that form CYSTINE KNOT MOTIFS.Heterocyclic Compounds: Ring compounds having atoms other than carbon in their nuclei. (Grant & Hackh's Chemical Dictionary, 5th ed)Molecular Conformation: The characteristic three-dimensional shape of a molecule.Heterocyclic Compounds with 4 or More Rings: A class of organic compounds containing four or more ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic.Amination: The creation of an amine. It can be produced by the addition of an amino group to an organic compound or reduction of a nitro group.Carbon-Carbon Lyases: Enzymes that catalyze the cleavage of a carbon-carbon bond by means other than hydrolysis or oxidation. This subclass contains the DECARBOXYLASES, the ALDEHYDE-LYASES, and the OXO-ACID-LYASES. EC 4.1.Furans: Compounds with a 5-membered ring of four carbons and an oxygen. They are aromatic heterocycles. The reduced form is tetrahydrofuran.Terpenes: A class of compounds composed of repeating 5-carbon units of HEMITERPENES.Epoxy Compounds: Organic compounds that include a cyclic ether with three ring atoms in their structure. They are commonly used as precursors for POLYMERS such as EPOXY RESINS.Polyketide Synthases: Large enzyme complexes composed of a number of component enzymes that are found in STREPTOMYCES which biosynthesize MACROLIDES and other polyketides.Macrocyclic Compounds: Cyclic compounds with a ring size of approximately 1-4 dozen atoms.Protein Splicing: The excision of in-frame internal protein sequences (INTEINS) of a precursor protein, coupled with ligation of the flanking sequences (EXTEINS). Protein splicing is an autocatalytic reaction and results in the production of two proteins from a single primary translation product: the intein and the mature protein.Oldenlandia: A plant genus of the family RUBIACEAE. Some species are used as an ingredient in Chinese and African traditional medicines. Members contain kalata B1, a macrocyclic peptide.Boranes: The collective name for the boron hydrides, which are analogous to the alkanes and silanes. Numerous boranes are known. Some have high calorific values and are used in high-energy fuels. (From Grant & Hackh's Chemical Dictionary, 5th ed)Models, Molecular: Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.Solid-Phase Synthesis Techniques: Techniques used to synthesize chemicals using molecular substrates that are bound to a solid surface. Typically a series of reactions are conducted on the bound substrate that results in either the covalent attachment of specific moieties or the modification of existing function groups. These techniques offer an advantage to those involving solution reactions in that the substrate compound does not have to be isolated and purified between the reaction steps.NorbornanesHeterocyclic Compounds, 2-Ring: A class of organic compounds containing two ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic.Cyclodextrins: A homologous group of cyclic GLUCANS consisting of alpha-1,4 bound glucose units obtained by the action of cyclodextrin glucanotransferase on starch or similar substrates. The enzyme is produced by certain species of Bacillus. Cyclodextrins form inclusion complexes with a wide variety of substances.SqualeneInteins: The internal fragments of precursor proteins (INternal proTEINS) that are autocatalytically removed by PROTEIN SPLICING. The flanking fragments (EXTEINS) are ligated forming mature proteins. The nucleic acid sequences coding for inteins are considered to be MOBILE GENETIC ELEMENTS. Inteins are composed of self-splicing domains and an endonuclease domain which plays a role in the spread of the intein's genomic sequence. Mini-inteins are composed of the self-splicing domains only.Cystine Knot Motifs: Amino acid sequence in which two disulfide bonds (DISULFIDES) and their connecting backbone form a ring that is penetrated by a third disulfide bond. Members include CYCLOTIDES and agouti-related protein.Magnetic Resonance Spectroscopy: Spectroscopic method of measuring the magnetic moment of elementary particles such as atomic nuclei, protons or electrons. It is employed in clinical applications such as NMR Tomography (MAGNETIC RESONANCE IMAGING).Polyketides: Natural compounds containing alternating carbonyl and methylene groups (beta-polyketones), bioenergenetically derived from repeated condensation of acetyl coenzyme A via malonyl coenzyme A, in a process similar to fatty acid synthesis.Monoterpenes: Compounds with a core of 10 carbons generally formed via the mevalonate pathway from the combination of 3,3-dimethylallyl pyrophosphate and isopentenyl pyrophosphate. They are cyclized and oxidized in a variety of ways. Due to the low molecular weight many of them exist in the form of essential oils (OILS, VOLATILE).Abies: A plant genus in the family PINACEAE, order Pinales, class Pinopsida, division Coniferophyta. Balm of Gilead is a common name more often referring to POPULUS and sometimes to COMMIPHORA.Aldehydes: Organic compounds containing a carbonyl group in the form -CHO.Diterpenes: Twenty-carbon compounds derived from MEVALONIC ACID or deoxyxylulose phosphate.Naphthols: Naphthalene derivatives carrying one or more hydroxyl (-OH) groups at any ring position. They are often used in dyes and pigments, as antioxidants for rubber, fats, and oils, as insecticides, in pharmaceuticals, and in numerous other applications.Strychnos: A plant genus of the family LOGANIACEAE (classified by some botanists as Strychnaceae).Spiro Compounds: A group of compounds consisting in part of two rings sharing one atom (usually a carbon) in common.Streptomyces: A genus of bacteria that form a nonfragmented aerial mycelium. Many species have been identified with some being pathogenic. This genus is responsible for producing a majority of the ANTI-BACTERIAL AGENTS of practical value.Alkaloids: Organic nitrogenous bases. Many alkaloids of medical importance occur in the animal and vegetable kingdoms, and some have been synthesized. (Grant & Hackh's Chemical Dictionary, 5th ed)Cycloaddition Reaction: Synthetic organic reactions that use reactions between unsaturated molecules to form cyclical products.Bromine Compounds: Inorganic compounds that contain bromine as an integral part of the molecule.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.SesquiterpenesCrystallography, X-Ray: The study of crystal structure using X-RAY DIFFRACTION techniques. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Phosgene: A highly toxic gas that has been used as a chemical warfare agent. It is an insidious poison as it is not irritating immediately, even when fatal concentrations are inhaled. (From The Merck Index, 11th ed, p7304)Bicyclo CompoundsGlycogen Debranching Enzyme System: 1,4-alpha-D-Glucan-1,4-alpha-D-glucan 4-alpha-D-glucosyltransferase/dextrin 6 alpha-D-glucanohydrolase. An enzyme system having both 4-alpha-glucanotransferase (EC 2.4.1.25) and amylo-1,6-glucosidase (EC 3.2.1.33) activities. As a transferase it transfers a segment of a 1,4-alpha-D-glucan to a new 4-position in an acceptor, which may be glucose or another 1,4-alpha-D-glucan. As a glucosidase it catalyzes the endohydrolysis of 1,6-alpha-D-glucoside linkages at points of branching in chains of 1,4-linked alpha-D-glucose residues. Amylo-1,6-glucosidase activity is deficient in glycogen storage disease type III.SemicarbazidesGuanosine Diphosphate Sugars: Esters formed between the aldehydic carbon of sugars and the terminal phosphate of guanosine diphosphate.Models, Chemical: Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.

Do enzymes obey the Baldwin rules? A mechanistic imperative in enzymatic cyclization reactions. (1/1346)

It is commonly assumed that enzymes have evolved to abide by the same energetic and stereoelectronic principles that govern reactions in solution. The principles formulated for organic ring-closure reactions can be used to develop a hypothesis for analysis of enzyme-catalyzed cyclization reactions.  (+info)

Purification and characterization of 2-deoxy-scyllo-inosose synthase derived from Bacillus circulans. A crucial carbocyclization enzyme in the biosynthesis of 2-deoxystreptamine-containing aminoglycoside antibiotics. (2/1346)

The biosynthesis of 2-deoxystreptamine, the central aglycon of a major group of clinically important aminoglycoside antibiotics, commences with the initial carbocycle formation step from D-glucose-6-phosphate to 2-deoxy-scyllo-inosose. This crucial step is known to be catalyzed by 2-deoxy-scyllo-inosose synthase, which has not yet been characterized so far. Reported in this paper is the first purification of 2-deoxy-scyllo-inosose synthase from butirosin-producing Bacillus circulans SANK 72073 to electrophoretic homogeneity. The enzyme was isolated as a heterodimeric protein comprising from a 23 kDa- and a 42 kDa polypeptide chains. The Km of the enzyme for D-glucose-6-phosphate was estimated to be 9.0 x 10(-4) M and that for NAD+ 1.7 x 10(-4) M, kcat for D-glucose-6-phosphate being 7.3 x 10(-2) s(-1). The presence of Co2+ was essential for the enzyme activity, but Zn2+ was totally inhibitory. While the reaction mechanisms are quite similar, 2-deoxy-scyllo-inosose synthase appears to be distinct from dehydroquinate synthase in the shikimate pathway, with respect to the quaternary structure, metal ion requirement, and the kinetic parameters.  (+info)

Elucidating the mechanism of chain termination switching in the picromycin/methymycin polyketide synthase. (3/1346)

BACKGROUND: A single modular polyketide synthase (PKS) gene cluster is responsible for production of both the 14-membered macrolide antibiotic picromycin and the 12-membered macrolide antibiotic methymycin in Streptomyces venezuelae. Building on the success of the heterologous expression system engineered using the erythromycin PKS, we have constructed an analogous system for the picromycin/methymycin PKS. Through heterologous expression and construction of a hybrid PKS, we have examined the contributions that the PKS, its internal thioesterase domain (pikTE) and the Pik TEII thioesterase domain make in termination and cyclization of the two polyketide intermediates. RESULTS: The picromycin/methymycin PKS genes were functionally expressed in the heterologous host Streptomyces lividans, resulting in production of both narbonolide and 10-deoxymethynolide (the precursors of picromycin and methymycin, respectively). Co-expression with the Pik TEII thioesterase led to increased production levels, but did not change the ratio of the two compounds produced, leaving the function of this protein largely unknown. Fusion of the PKS thioesterase domain (pikTE) to 6-deoxyerythronolide B synthase (DEBS) resulted in formation of only 14-membered macrolactones. CONCLUSIONS: These experiments demonstrate that the PKS alone is capable of catalyzing the synthesis of both 14- and 12-membered macrolactones and favor a model by which different macrolactone rings result from a combination of the arrangement between the module 5 and module 6 subunits in the picromycin PKS complex and the selectivity of the pikTE domain.  (+info)

Heterologous expression, purification, reconstitution and kinetic analysis of an extended type II polyketide synthase. (4/1346)

BACKGROUND: Polyketide synthases (PKSs) are bacterial multienzyme systems that synthesize a broad range of natural products. The 'minimal' PKS consists of a ketosynthase, a chain length factor, an acyl carrier protein and a malonyl transferase. Auxiliary components (ketoreductases, aromatases and cyclases are involved in controlling the oxidation level and cyclization of the nascent polyketide chain. We describe the heterologous expression and reconstitution of several auxiliary PKS components including the actinorhodin ketoreductase (act KR), the griseusin aromatase/cyclase (gris ARO/CYC), and the tetracenomycin aromatase/cyclase (tcm ARO/CYC). RESULTS: The polyketide products of reconstituted act and tcm PKSs were identical to those identified in previous in vivo studies. Although stable protein-protein interactions were not detected between minimal and auxiliary PKS components, kinetic analysis revealed that the extended PKS comprised of the act minimal PKS, the act KR and the gris ARO/CYC had a higher turnover number than the act minimal PKS plus the act KR or the act minimal PKS alone. Adding the tcm ARO/CYC to the tcm minimal PKS also increased the overall rate. CONCLUSIONS: Until recently the principal strategy for functional analysis of PKS subunits was through heterologous expression of recombinant PKSs in Streptomyces. Our results corroborate the implicit assumption that the product isolated from whole-cell systems is the dominant product of the PKS. They also suggest that an intermediate is channeled between the various subunits, and pave the way for more detailed structural and mechanistic analysis of these multienzyme systems.  (+info)

Protein aging hypothesis of Alzheimer disease. (5/1346)

Alzheimer disease (AD), the most common form of aging-related neurodegenerative disorders, is associated with formation of fibrillar deposits of amyloid beta-protein (Abeta). While the direct involvement of Abeta in AD has been well documented, the relations between Abeta production, amyloid formation, and neurodegeneration remain unknown. We propose that AD is initiated by a protein aging-related structural transformation in soluble Abeta. We hypothesize that spontaneous chemical modification of aspartyl residues in Abeta to transient succinimide induces a non-native conformation in a fraction of soluble Abeta, rendering it amyloidogenic and neurotoxic. Conformationally altered Abeta is characterized by increased stability in solution and the presence of a non-native beta-turn that determines folding of Abeta in solution and the structure of Abeta subunits incorporated into amyloid fibrils. While the soluble 'non-native' Abeta is both the factor triggering the neurodegenerative cascade and the precursor of amyloid plaques, these two events result from interaction of Abeta with different sets of cellular components and need not coincide in space and time. Extensive literature data and experimental evidence are provided in support of this hypothesis.  (+info)

Site-directed mutagenesis of squalene-hopene cyclase: altered substrate specificity and product distribution. (6/1346)

BACKGROUND: Two regions of squalene-hopene cyclase (SHC) were examined to define roles for motifs posited to be responsible for initiation and termination of the enzyme-catalyzed polyolefinic cyclizations. Specifically, we first examined the triple mutant of the DDTAVV motif, a region deeply buried in the catalytic cavity and thought to be responsible for the initiation of squalene cyclization. Next, four mutants were prepared for Glu45, a residue close to the substrate entrance channel proposed to be involved in the termination of the cyclization of squalene. RESULTS: The DDTAVV motif in SHC was changed to DCTAEA, the corresponding conserved region of eukaryotic oxidosqualene cyclase (OSC), by the triple mutation of D377C/V380E/V381A; selected single mutants were also examined. The triple mutant showed no detectable cyclization of squalene, but effectively cyclized 2,3-oxidosqualene to give mono- and pentacyclic triterpene products. Of the Glu45 mutants, E45A and E45D showed reduced activity, E45Q showed slightly increased activity, and E45K was inactive. A normal yield of pentacyclic products was produced, but the ratio of hopene 2 to hopanol 3 was significantly changed in the less active mutants. CONCLUSIONS: Initiation and substrate selectivity may be determined by the interaction of the DDTAVV motif with the isopropylidene of squalene (for SHC) and of the DCTAEA motif with the epoxide of oxidosqualene (for OSC). This is the first report of a substrate switch determined by a central catalytic motif in a triterpenoid cyclase. At the termination of cyclization, the product ratio may be largely controlled by Glu45 at the entrance channel to the active site.  (+info)

Aureusidin synthase: a polyphenol oxidase homolog responsible for flower coloration. (7/1346)

Aurones are plant flavonoids that provide yellow color to the flowers of some popular ornamental plants, such as snapdragon and cosmos. In this study, we have identified an enzyme responsible for the synthesis of aurone from chalcones in the yellow snapdragon flower. The enzyme (aureusidin synthase) is a 39-kilodalton, copper-containing glycoprotein catalyzing the hydroxylation and/or oxidative cyclization of the precursor chalcones, 2',4',6',4-tetrahydroxychalcone and 2',4',6',3,4-pentahydroxychalcone. The complementary DNA encoding aureusidin synthase is expressed in the petals of aurone-containing varieties. DNA sequence analysis revealed that aureusidin synthase belongs to the plant polyphenol oxidase family, providing an unequivocal example of the function of the polyphenol oxidase homolog in plants, i.e., flower coloration.  (+info)

Intramolecular proton transfer in the cyclization of geranylgeranyl diphosphate to the taxadiene precursor of taxol catalyzed by recombinant taxadiene synthase. (8/1346)

BACKGROUND: The committed step in the biosynthesis of the anticancer drug taxol in yew (Taxus) species is the cyclization of geranylgeranyl diphosphate to taxa-4(5),11(12)-diene. The enzyme taxadiene synthase catalyzes this complex olefin cation cyclization cascade involving the formation of three rings and three stereogenic centers. RESULTS: Recombinant taxadiene synthase was incubated with specifically deuterated substrates, and the mechanism of cyclization was probed using MS and NMR analyses of the products to define the crucial hydrogen migration and terminating deprotonation steps. The electrophilic cyclization involves the ionization of the diphosphate with closure of the A-ring, followed by a unique intramolecular transfer of the C11 proton to the re-face of C7 to promote closure of the B/C-ring juncture, and cascade termination by proton elimination from the beta-face of C5. CONCLUSIONS: These findings provide insight into the molecular architecture of the first dedicated step of taxol biosynthesis that creates the taxane carbon skeleton, and they have broad implications for the general mechanistic capability of the large family of terpenoid cyclization enzymes.  (+info)

TY - JOUR. T1 - An arene-alkene photocycloaddition-radical cyclization cascade. T2 - The first synthesis of cis,cis,cis,trans-[5.5.5.5]-fenestranes. AU - Wender, Paul A.. AU - Dore, Timothy. AU - DeLong, Mitch A.. PY - 1996/10/21. Y1 - 1996/10/21. N2 - The first cis,cis,cis,trans-[5.5.5.5]-fenestranes have been synthesized in three steps using a novel arene-alkene photocycloaddition-radical cyclization cascade, which creates overall 5 new rings and 8 stereogenic centers. A lead tetraacetate mediated ring expansion of a 5,5-fused ring system, discovered in the course of exploring the chemistry of these new materials, is also described.. AB - The first cis,cis,cis,trans-[5.5.5.5]-fenestranes have been synthesized in three steps using a novel arene-alkene photocycloaddition-radical cyclization cascade, which creates overall 5 new rings and 8 stereogenic centers. A lead tetraacetate mediated ring expansion of a 5,5-fused ring system, discovered in the course of exploring the chemistry of these new ...
The Nazarov cyclization is a common synthetic tool in the synthesis of cyclopentenone rings. The reaction is characterized by a divinyl ketone starting reagent that undergoes a 4π-electron electrocyclization after addition of a Lewis/Brønsted acid; forming the cyclopentadienyl cation that undergoes cyclization. An extension of this methodology involves using a divinyl imine starting reagent. This cyclization is less favoured due to the electron donating ability of the nitrogen atom, causing the pentadienyl cation to be relatively stable and unwilling to undergo cyclization. To improve this cyclization, the imine is replaced with the electron withdrawing nitronate functionality. It is hypothesized that by doing so the addition of an acid will form the cyclopentadienyl cation that will readily undergo Nazarov cyclization. The synthesis of an aryl vinyl silyl nitronate was optimized and the compound was tested with a number of different acid catalysts to determine if the nitronate Nazarov ...
The iodine-catalyzed Prins cyclization of homoallylic alcohols and aldehydes was investigated under metal-free conditions and without additives. Anhydrous conditions and inert atmosphere are not required. The reaction of 2-(3,4-dihydronaphthalen-1-yl)propan-1-ol and 21 aldehydes (aliphatic and aromatic) in CH2Cl2 in the presence of 5 mol % of iodine gave 1,4,5,6-tetrahydro-2H-benzo[f]isochromenes in 54%-86% yield. Under similar conditions, the Prins cyclization of six alcohols containing an endocyclic double bond (primary, secondary, or tertiary) led to dihydropyrans in 52%-91% yield. The acyclic homoallylic alcohols gave 4-iodo-tetrahydropyran in 29%-41% yield in the presence of 50 mol % of iodine. This type of substrate is the main limitation of the methodology. The relative configuration of the products was assigned by NMR and X-ray analysis. The mechanism and the ratio of the products are discussed, based on DFT calculations.
A highly efficient method for the construction of pyrrolidinyl spirooxindoles with 3-isothiocyanato oxindoles and chalcones via a Michael/cyclization cascade reaction has been developed by using bifunctional cinchona-derived squaramide organocatalysts. A series of complex pyrrolidinyl spirooxindoles could be
It seemed plausible that the biosynthesis of Bistellettadine A (9) was proceeding by intermolecular dimerization of the monomeric carboxylic acid corresponding to 7. Barry B. Snider of Brandeis University found (Org. Lett. 2010, 12, 828. ) that that intermolecular dimerization did proceed efficiently, but to give a 5:4 mixture of diastereomers. In contrast, the linked diester 7 cyclized with exclusive diastereocontrol. The product 8 was readily carried on to Bistellettadine A 9. This raises the possibility that a chiral template, attached either covalently or through salt formation, could be designed that would direct the absolute configuration of the cycloaddition.. ...
The unprecedented combination of a palladium(ii) complex with a chiral Bu-QUOX ligand and a chiral phosphoric acid enables the highly efficient asymmetric oxidative tandem cyclization of N-(2,2-disubstituted hex-5-en-1-yl)acrylamides, providing a straightforward method to access chiral 6,5-bicyclic aza-heter
A cobalt-rhodium heterobimetallic nanoparticle-catalyzed reductive cyclization of 2-(2-nitroaryl)acetonitriles to indoles proceeds without any additives under mild conditions. The catalytic can be reused more than ten times without loss of catalytic activity.. ...
SYNTHESIS OF FUSED PYRAZOLES VIA INTRAMOLECULAR CYCLIZATION OF APPROPRIATELY ortho -SUBSTITUTED NITROARENES AND NITROHETEROARENES
Home » Visible light photocatalysis of radical cation Diels-Alder cycloadditions: preparation of tris(2,2-bipyrazyl)ruthenium(II) bis(tetrakis(3,5-bis(trifluoromethyl)phenyl)borate ...
I. The acid catalyzed reactions of certain 1,5-epoxyolefins. The monoxides of a number of 1,5-dienes were prepared and treated with a variety of acidic reagents known to induce cyclization of the parent diolefins. In all cases the major reaction observed was the isomerization of the epoxide to a carbonyl function. No cyclic products were observed. These results are discussed in terms of the general requirements for cyclization.. II. The alkylative cyclization of 1,5-hexadiene The alkylation of 1,5 -hexadiene with t-butyl chloride in the presence of aluminum trichloride was studied. The major monomeric reaction products were cyclic, and both the t-butylcyclohexane and neopentylcyclopentane skeletons were identified among them. Formation of the latter ring system appeared to be slightly favored over formation of the six-membered ring. This preference is undoubtedly due to both steric and electronic factors.. III. The acid catalyzed cyclization of cis, cis- and trans, trans-2,6-octadiene. Both cis, ...
In organic chemistry, an electrocyclic reaction is a type of pericyclic rearrangement where the net result is one pi bond being converted into one sigma bond or vice versa. These reactions are usually categorized by the following criteria: Reactions can be either photochemical or thermal. Reactions can be either ring-opening or ring-closing (electrocyclization). Depending on the type of reaction (photochemical or thermal) and the number of pi electrons, the reaction can happen through either a conrotatory or disrotatory mechanism. The type of rotation determines whether the cis or trans isomer of the product will be formed. The Nazarov cyclization reaction is a named electrocyclic reaction converting divinylketones to cyclopentenones. A classic example is the thermal ring-opening reaction of 3,4-dimethylcyclobutene. The cis isomer exclusively yields cis,trans-2,4-hexadiene whereas the trans isomer gives the trans,trans diene: This reaction course can be explained in a simple analysis through the ...
A novel cascade reaction involving oxidative dearomatization/semipinacol rearrangement of indol-2-yl cyclobutanols is explored with N-sulfonyloxaziridine (Davis oxaziridines) as oxidant, generating various 2-spiroquaternary 3-oxindoles in modest to good yields. This method might be useful in the synthesis of indole-based alkaloids bearing 2-spiroquaternary carbon centers. PTS=p-toluenesulfonic acid monohydrate. ...
Significant advances in metal-catalyzed reactions, especially cyclizations, have dramatically improved the efficiency of organic synthesis over the last three decades. To date these transformations are widely used in the area of synthesis of both natural products and therapeutic agents. "Science of Synthesis: Metal-Catalyzed Cyclization Reactions" presents the most commonly used and significant metal-catalyzed reactions for modern organic synthesis. The basic principles, the current state of the art, scope, limitations, and mechanism of these reactions are also discussed. Typical examples of target synthesis are provided to help inspire further applications ...
Thieme eBooks, Significant advances in metal-catalyzed reactions, especially cyclizations, have dramatically improved the efficiency of organic synthesis over the last three decades. To date these transformations are widely used in the area of synthesis of both natural products and therapeutic agents. Science of Synthesis: Metal-Catalyzed Cyclization Reactions presents the most commonly used and s...
Synthesis of Novel Steroid-Peptoid Hybrid Macrocycles by Multiple Multicomponent Macrocyclizations Including Bifunctional Building Blocks MiBs. . Biblioteca virtual para leer y descargar libros, documentos, trabajos y tesis universitarias en PDF. Material universiario, documentación y tareas realizadas por universitarios en nuestra biblioteca. Para descargar gratis y para leer online.
Chen, H. [陳浩國]. (2009). Silver catalyzed enyne cyclization reactions. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_ ...
The importance of dynamics in simple reactions is made yet again in a recent study by Doubleday and Houk in 1,3-dipolar cycloadditions.1 They looked at the reaction of acetylene or ethylene with either nitrous oxide, diazonioazanide, or methanediazonium. The transition state for these 6 reactions all show a concerted reaction. The transition vector has three major components; (a) symmetric formation/cleavage of the two new σ bonds, (b) bending of the dipolar component, or (c) symmetric bending of the hydrogens of ethylene or acetylene.. Classical trajectories were traced from the transition state back to reactant and forward to product. In the approach of the two fragments, the dipole bend vibrates, but then after the TS, it needs to bend quickly to close the 5-member ring. This means that the bending mode effectively has to "turn a corner" in phase space, and without energy in this mode, the molecules will simple bounce off of each other. Analysis of the reactants indicates significant ...
Synlett, 2009, 1208-1218. Anodic electrochemistry is a powerful tool for generating radical cation intermediates and initiating new cyclization reactions. Like most electrochemical reactions, the transformations involve umpolungs. In this review, recent studies examining the intramolecular coupling of radical cations derived from enol ethers, vinyl sulfides, and ketene acetals with carbon, oxygen, and nitrogen trapping groups are discussed to highlight their synthetic potential.. ...
The dissertation herein describes the first total synthesis of the complex Daphniphyllum alkaloid, (-)-calyciphylline N. This alkaloid was chosen as the target in our synthetic program due its unprecedented structure, the inherent challenges associated with its synthesis, and limited reports of synthetic studies towards members of this family of natural products. An initial unsuccessful approach is discussed, followed by a revised, ultimately successful approach. Highlights of the synthesis include a substrate controlled, intramolecular Diels-Alder reaction to build the bicyclo[2.2.2]octane core and set four contiguous stereocenters, a transannular enolate alkylation to secure ring D, a highly efficient Stille carbonylation/Nazarov cyclization sequence to construct ring E with concomitant activation of a hindered silyl group towards Fleming-Tamao oxidation, and an unprecedented, homogeneous hydrogenation of an exceptionally hindered diene ester to complete the eastern hemisphere, a structural motif that
Autor: Glas, Adrian et al.; Genre: Zeitschriftenartikel; Im Druck veröffentlicht: 2015-01; Keywords: cyclic peptides; hydrophobic cross-links; ring-closing metathesis; protein-protein interactions; Pseudomonas aeruginosa; Titel: Constraining Peptide Conformations with the Help of Ring-Closing Metathesis
This video was recorded at CHEM 125b: Freshman Organic Chemistry II. Cyclic conjugation that arises when p-orbitals touch one another can be as important for transition states as aromaticity is for stable molecules. It is the controlling factor in "pericyclic" reactions. Regiochemistry, stereochemistry, and kinetics show that two new sigma bonds are being formed simultaneously, if not symmetrically, in the 6-electron Diels-Alder cycloaddition. Although thermal dimerization of thymine residues in DNA is forbidden, photochemistry allows the 4-electron cycloaddition. "Electrocyclic" ring opening or closing chooses a conrotatory Möbius pathway, or a disrotatory Hückel pathway, according to the number of electron pairs involved and whether light is used in the process. Dewar benzene provides an example of a very unstable molecule that can be formed photochemically and then persists because of unfavorable orbital overlap in the transition state for ring opening ...
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 ...
Photochemical cleavage reactions have found a widespread used in biological applications that require the photorelease of biologically active molecules such as proteins, peptides, neurotransmitters, and nucleotide phosphates. This research focuses on the design of photoremovable protecting groups which can be utilized to release these biomolecules by photolysis. These biomolecules are attached to the photoremovable protecting group at the sites of functional groups that are present within these substrates. Such functional groups are carboxylates, phosphates, thiolates, or phenolates, which upon exposure to light, are released as anions of varying basicities. The photochemical reaction involved is an electrocyclic ring closure between aromatic groups that are bridged by a carboxamide linkage. The key intermediate produced by electrocyclization is thought to have zwitterionic character. This zwitterionic intermediate is believed to expel the leaving group as the anion. One of the aromatic groups attached
The research developed in this Doctoral Thesis comprises from the preparation of polyaromatic compounds to the synthesis of natural product derivatives, highlighting the proficiency of homogeneous gold catalysis for the construction of molecular diversity.. A novel approach for the synthesis of a new trindane-based crushed fullerene C60 was developed by a threefold palladium-catalyzed cross-coupling of four suitably functionalized C15 trindene fragments. The trindane C15 skeleton of the central motif was constructed through a triple gold(I)-catalyzed oxidative cyclization.. The scope of the intramolecular gold(I)-catalyzed formal [2+2+2] cycloaddition reaction was extended to O-protected homopropargylic and allylic oxo-1,5-enynes. Under the optimized reaction conditions, the cyclization of (Z)- and (E)- isomers takes place with moderate to excellent yield and increased selectivity in most of the cases, providing access to octahydro-1H-indenes skeletons.. The mastery of gold(I) complexes for the ...
Molecular complexity is one of the key reasons why fragment-based lead discovery should work. As described in 2001 by Mike Hann and colleagues at GlaxoSmithKline, the idea is that very small, simple molecules are likely to be able to bind to many different sites on many different proteins; think of the water molecule as being an extreme example of this. As molecules become larger and more complex, they are less likely to bind to any given site on a protein, though if they are complementary to a site the potency will be greater. Similarly, more complex molecules are more likely to have a single binding mode than smaller, less-decorated molecules, which could assume multiple orientations at a single site. These intuitive ideas were supported by a simple computational model that suggested that there is an optimum complexity where molecules would be simple enough that they would bind to several different targets (and thus be useful in a screening collection) while still being complex enough to bind ...
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While considering the increasing environmental pollution and its intensive impact on living systems, developing chemical processes using more environmentally acceptable chemicals, catalysts, solvents, atom-efficient methods and energy-efficient technologies eliminating waste production as well as employing renewable raw materials are experiencing a profound challenge to meet sustainability criteria [1,2]. In addition, the environmental risks posed by the toxic and volatile organic solvents have become a major concern. The reason is that the organic transformations employ higher consumption of solvents than the reagents and the employed solvents are difficult to recycle [3]; for the process to be in line with the green chemistry principles, the first task is to replace the toxic catalysts and hazardous organic solvents with green ones.. Performing organic reactions in water has attracted much attention over the past decades due to its numerous advantages such as being considerably safe, nontoxic, ...
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TY - JOUR. T1 - Acetyl cation facilitated cyclizations of olefinic aldehydes. III. factors determining regiochemistry in acroleins. AU - Andersen, Niels H.. AU - Ladner, David W.. AU - Moore, Ana L. PY - 1978/1/1. Y1 - 1978/1/1. UR - http://www.scopus.com/inward/record.url?scp=84918114464&partnerID=8YFLogxK. UR - http://www.scopus.com/inward/citedby.url?scp=84918114464&partnerID=8YFLogxK. U2 - 10.1080/00397917808063571. DO - 10.1080/00397917808063571. M3 - Article. AN - SCOPUS:84918114464. VL - 8. SP - 437. EP - 448. JO - Synthetic Communications. JF - Synthetic Communications. SN - 0039-7911. IS - 7. ER - ...
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Hoffmann, R.; Tantillo, D. J. Angew. Chem. Int. Ed. 2003, 42, 5877-5882: Breaking Down Barriers: The Liaison Between Sigmatropic Shifts, Electrocyclic Reactions and 3-Center Cations. Ponec, R.; Bultinck, P.; Van Damme, S.; Carbo, R.; Tantillo, D. J. Theor. Chem. Acc. 2005, 113, 205-211: Geometric and Electronic Similarities between Transition Structures for Electrocyclizations and Sigmatropic Hydrogen Shifts. Tantillo, D. J. Annu. Rep. Prog. Chem., Sect. B 2006, 102, 269-289: Reaction Mechanisms. Part (ii) Pericyclic Reactions. Tantillo, D. J.; Lee, J. K. Annu. Rep. Prog. Chem., Sect. B 2007, 103, 272-293: Reaction Mechanisms. Pericyclic Reactions. Lee, J. K.; Tantillo, D. J. Annu. Rep. Prog. Chem., Sect. B 2008, 104, 260-283: Reaction Mechanisms. Pericyclic Reactions. Nouri, D. H.; Tantillo, D. J. Tetrahedron 2008, 64, 5672-5679: Sigmatropic Shifts and Cycloadditions on Neutral, Cationic, and Anionic Pentadienyl + Butadiene Potential Energy Surfaces. Tantillo, D. J. Angew. Chem. ...
First, NICS(0) values for a series of related intermolecular anionic attack at alkynes show some interesting trends (Table 1). Two of the transition states look like they might be aromatic: the TSs for the 3-exo-dig and the 5-endo-dig reaction have NICS(0) values that are quite negative. However, given the geometry of these TSs, particularly the close proximity of the σ bonds to the ring center, one might be concerned about contamination of these orbitals. So, NICS(0)MOzz computations, which look at the tensor component perpendicular to the ring using just the π-MOs, shows that the 3-exo-dig is likely non-aromatic (NICS(0)MOzz is near zero), the TS for the 4-endo-dig reaction is antiaromatic (NICS(0)MOzz very positive) and the TS for the 5-endo-dig reaction is aromatic (NICS(0)MOzz is very negative. So this last reaction is the first example of an aromatic transition that is not for a pericyclic reaction ...
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TrendTerms displays relevant terms of the abstract of this publication and related documents on a map. The terms and their relations were extracted from ZORA using word statistics. Their timelines are taken from ZORA as well. The bubble size of a term is proportional to the number of documents where the term occurs. Red, orange, yellow and green colors are used for terms that occur in the current document; red indicates high interlinkedness of a term with other terms, orange, yellow and green decreasing interlinkedness. Blue is used for terms that have a relation with the terms in this document, but occur in other documents ...
As many of you know Derek Lowes In The Pipeline blog sometimes features "Things I Wont Work With". One particular entry describes selenophenol (PhSeH) in all of its stinky glory. After the failure of several endgame strategies we considered a radical cyclization approach to D-ring formation. Attempts to install various radical precursors at the anomeric position were surprisingly unsuccessful except for one, PhSeH. Completion of the synthesis seemed so close at the time that we decided to go ahead and use PhSeH. Unfortunately, installation of the selenoacetal required the use of PhSeH as a solvent in the presence of ZnI2. We attempted to use PhSeH in quantities up to a 1:1 solvent mixture with MeCN with no success, leaving no option other than using PhSeH as the solvent. The selenoacetal was installed on a model substrate (the Claisen rearrangement yield problem had not been solved at this point) followed by installation of an alkynoate. Treatment of the alkynoate model substrate with Bu3SnH ...
As many of you know Derek Lowes In The Pipeline blog sometimes features "Things I Wont Work With". One particular entry describes selenophenol (PhSeH) in all of its stinky glory. After the failure of several endgame strategies we considered a radical cyclization approach to D-ring formation. Attempts to install various radical precursors at the anomeric position were surprisingly unsuccessful except for one, PhSeH. Completion of the synthesis seemed so close at the time that we decided to go ahead and use PhSeH. Unfortunately, installation of the selenoacetal required the use of PhSeH as a solvent in the presence of ZnI2. We attempted to use PhSeH in quantities up to a 1:1 solvent mixture with MeCN with no success, leaving no option other than using PhSeH as the solvent. The selenoacetal was installed on a model substrate (the Claisen rearrangement yield problem had not been solved at this point) followed by installation of an alkynoate. Treatment of the alkynoate model substrate with Bu3SnH ...
Iwata, C.; Takemoto, Y.; Kubota, H.; Yamada, M.; Uchida, S.; Tanaka, T.; Imanishi, T., 1989: Synthetic studies on spirovetivane phytoalexins. III. A total synthesis of (+or-)-lubiminol
Joint first authorship. • Ali Nakhi, Md Shafiqur Rahman, Guru Pavan Kumar Seerapu, Rakesh Kumar Banote, Kummari Lalith Kumar, Pushkar Kulkarni, Devyani Haldar, Manojit Pal. Transition metal free hydrolysis/cyclization strategy in a single pot: synthesis of fused furo N-heterocycles of pharmacological interest. Organic & Biomolecular Chemistry, 2013.. • Dhilli Rao Gorja, Soumita Mukherjee, Chandana Lakshmi T. Meda, Girdhar Singh Deora, Ankit Jain, Girish H Chaudhari, Keerthana S. Chennubhotla, Rakesh Kumar Banote, PushkarKulkarni, Kishore V. L. Parsa, K. Mukkanti, Manojit Pal. N-Indolylmethyl substituted olanzapine: Their design, synthesis and pharmacological evaluation as PDE4B inhibitors. Organic & Biomolecular Chemistry, 2013.. • P. Mahesh Kumar, K. Siva Kumar, Chandana L. T. Meda, G. Rajeshwar Reddy, Pradeep K. Mohakhud, K. Mukkanti, G. Rama Krishna, C. Malla Reddy,D. Rambabu, K. Shiva Kumar, K. Krishna Priya, Keerthana Sarma Chennubhotla, Rakesh Kumar Banote, Pushkar Kulkarni, Kishor ...
Total syntheses of circumdatin F and circumdatin C, which both possess a 3H-quinazolin-4-one as well as a 1,4-benzodiazepin-5-one moiety, are described. A tripeptide derivative was synthesized as a key intermediate and dehydrated to a benzoxazine by reaction with triphenylphosphine, iodine, and a tertiary amine. The natural products were attained via rearrangements to an amidine intermediate, deprotection with 45% HBr in acetic acid, and cyclization on silica gel.. ...
We are pleased to welcome Raul all the way from Ruben Martins group at ICIQ! He will be collaborating with Mingyu on alkynes of fun chemistry!
Disclosed herein is an improvement in a method for distinguishing cells in a biological sample by staining with a dye, wherein the improvement comprises employing as the dye a compound of the formula ##STR1## wherein G is O or S; R1, R3, and R5 are independently selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, amino, styryl, bis(diaryl)vinylene, and ##STR2## wherein R is hydrogen or alkyl; Z represents the elements necessary to complete a basic heterocyclic ring system of the type used in cyanine dyes; n is 0 or 1; R2 is hydrogen or, taken together with either R1 or R3, represents the elements needed to complete an aromatic or a carbocyclic ring system; R4 is hydrogen or, taken together with either R3 or R5, represents the elements needed to complete an aromatic or a carbocyclic ring system; and X- is an anion.
In ~~ ~ ~ to J ~demonstrate ~~ order conclusively that the reluctance of the anion of (442a)to cyclize was not due to an unfavorable equilibrium, Baldwin treated (4438)(prepared via acid-catalyzed cyclization of 442a) with NaOMe in MeOD. The a-protons of (443s)were exchanged for deuterium but none of the retro-Michael product (442a)was produced. g. -have been reported often, as described below. There are obviously many examples of each class, but due to space limitations only a few recent representative examples of each are presented. 147f Several other heterocyclic systems have been produced by similar ~ h e m i s t r y . ~ ~ ~ g PhCO Phx- PhCO CF, >-\CF, c PhX 25 T I 6 h >90% (581) X = O , S (580) + - R-COzMe ( 134) R A I P h," ; Ph (506) R = H (514) R = COzMe (582) 2 hP9% 16 h/70% (583a) R = H (SS3b)R = COZMe COzMe MeOzCANHEt + 111 COZMe Et20 COZMe h 25 TI2 h I 63% Et .. 1 CO,L, __c 70% EtOzC (587) Scheme 82 H (135) Stabilized Nucleophiles with Electron Deficient Alkenes and Alkynes 0 I1 * ...
The Thesis describes work directed towards the total synthesis of phorboxazoles A(1) and B(2), marine macrolides recently isolated from an Indian Ocean sponge of the genus Phorbas which show potent cytostatic activity with S-phase arrest (mean NCI GI50 < 1.6 nM). (Fig. 0909A) Our convergent disconnection strategy required a central C20-C32 fragment (6) containing five stereocentres. The C23-C26 stereotetrads of (E)-enoates 194 and 205 were established with 97% ds using a stereoselective boron-mediated anti anti aldol reaction between (E)-aldehyde 22 and (S)-ketone 23 or 40, followed by substrate-directed 1,3-anti reduction using (inter alia) Evans-Tishchenko reduction. HWE olefination to 194 was followed by methanolysis to give tetrahydropyran ester 18 in 14% yield over 7 steps. The diastereoselectivity of the intramolecular hetero-Michael cyclisation (60% ds at C22) was later improved to 80% ds by subjecting 205 to an alternative reduction-oxidation procedure to afford aldehyde 6 in 26% yield ...
Tangdenpaisal, K.; Chuayboonsong, K.; Ruchirawat, S.; Ploypradith, P., Divergent Strategy for the Diastereoselective Synthesis of the Tricyclic 6, 7-Diaryltetrahydro-6 H-benzo [c] chromene Core via Pt (IV)-Catalyzed Cycloaddition of o-Quinone Methides and Olefin Ring-Closing Metathesis. J. Org. Chem. **2017**, //82// (5), 2672-2688. [[ http://pubs.acs.org/doi/abs/10.1021/acs.joc.6b03086 ,Abstract]] ...
The Mitsunobu reaction is a well-established fundamental reaction and has been applied widely in organic synthesis. In the Mitsunobu reaction, a unique dehydration occurs between alcohols and various Brønsted-Lowry ac ids (HA) u t i l i z ing a comb ina t ion o f d ie thy l azodicarboxylate (DEAD) triphenylphosphine (TPP) (Scheme 1).1,2) Organic chemists have enjoyed these advantages of the Mitsunobu reaction in organic synthesis. However, the reaction has a serious limitation (the so-called
12404385] The Biosynthesis of Vancomycin-Type Glycopeptide Antibiotics-The Order of the Cyclization Steps This work was supported by the Deutsche Forschungsgemeinschaft (SFB 323) and by a grant of the EU (MEGATOP, QLK3-1999-00650). R. D. S. gratefully acknowledges the support of a Feodor-Lynen Fellowship granted by the Alexander-von-Humboldt Stiftung. We thank Corina Bihlmaier and Volker Pfeifer for help with transformation and Southern hybridization, J. A. Moss (La Jolla (USA)) for critical comments on the manuscript and Prof. Dr. M. E. Maier and Prof. Dr. H.-P. Fiedler (Tubingen) for generous support. (Angew Chem Int Ed Engl. , 2001 ...
Lee, Robert Elsworth. "Synthetic approaches to polycyclic bridged ring compounds." (1958) Masters, Rice University. http://hdl.handle.net/1911/89023 ...
22:48, 4 January 2018 (diff , hist) . . (+5,257)‎ . . m 3+2 Dipolar Cycloadditions of Cyclic Nitrones with Alkenes ‎ (Automated import of articles *** existing text overwritten ***) (current) ...
Transcriptional regulation complexes are large, multicomponent assemblies involving proteins with various enzymatic activities, adaptor functions and DNA recognition modules. We are looking at interplay between the components of these assemblies in order to understand the structural "logic" of how these complexes carry out intricate biological activities.. We are studying a family of BTB-zinc finger transcriptional regulators that include proteins implicated in development and/or in cancer. In these proteins, the BTB domain is a protein-protein interaction module that recruits activator and/or corepressor complexes to promoter sites recognized by the C-terminal zinc-finger regions. Our objective is to understand and characterize the protein-protein interaction network of these proteins.. For example, we have determined crystal structures of complexes between the BTB domain of BCL6 and the minimal binding region of the SMRT, NCoR and BCoR corepressors. BCL6 is a key oncoprotein in B-cell lymphoma ...
The backbone of diene precursor in the proposed biogenesis of methyl isosartortuoate through a Diels-Alder reaction has been constructed via dehydration to establish the conjugated system; and double cyclization by using Horner-Wittig-Emmons reaction and the chiral epoxy ring opening. (C) 2004 Published by Elsevier Ltd ...
Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups - so-called mechanophores - that the directional nature of mechanical forces can selectively break and re-form covalent bonds. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process ...
Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups - so-called mechanophores - that the directional nature of mechanical forces can selectively break and re-form covalent bonds. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process ...
The first total synthesis of isospongian diterpenoid (+/-)-polyrhaphin D has been accomplished in 9 steps with 19% overall yield starting from the Wieland-Miescher ketone derivative. The key features of our synthesis include a sequential reduc-tion/Michael addition/aldol condenzation to assemble the A ring and an intramolecular dehydrative cyclization/olefin isomerization reaction to install the gamma-butenolide D ring ...
An equivalent of one proton is generated during the reaction; the neutralization of this charge by a sterically hindered Brønsted base prevents undesired polymerization reactions. A moments reflection reveals that this proton need not be simply scavenged, but rather can be channeled into a productive part of the reaction. Protodesilylation of arylsilanes to yield an equivalent of a silylium ion and an arene is a well-known phenomenon relying on the greater bond enthalpies of C-H bonds over those of Si-C bonds (21-23). Given that the silyl cation-initiated Friedel-Crafts arylation formally generates one equivalent of HF, the proton formed after the first C(aryl)-C(aryl) coupling can serve as a catalyst to generate a silyl cationic species from a neutral silane precursor. Overall, the exchange of covalent bonds [C(ar)-H, C(ar)-C(ar), and Si-F for C-(ar)-H, Si-C(ar), and C(ar)-F] is thermodynamically highly favorable. Thus, an elegant self-sustaining reaction system comprises the arene or aryl ...
If in each of the two resonance forms of an allylic carbocation the formal charge of +1 is on a primary carbon, the allylic carbocation is called a primary (1°) allylic carbocation.. eg:. ...
Recent studies identified cyclic GMP-AMP (cGAMP) as a metazoan second messenger triggering an interferon response. cGAMP is generated from GTP and ATP by cytoplasmic dsDNA sensor cGAMP synthase (cGAS). We combined structural, chemical, biochemical, and cellular assays to demonstrate that this second messenger contains G(2,5)pA and A(3,5)pG phosphodiester linkages, designated c[G(2,5)pA(3,5)p]. We show that, upon dsDNA binding, cGAS is activated through conformational transitions, resulting in formation of a catalytically competent and accessible nucleotide-binding pocket for generation of c[G(2,5)pA(3,5)p]. We demonstrate that cyclization occurs in a stepwise manner through initial generation of 5-pppG(2,5)pA prior to cyclization to c[G(2,5)pA(3,5)p], with the latter positioned precisely in the catalytic pocket. Mutants of cGAS dsDNA-binding or catalytic pocket residues exhibit reduced or abrogated activity. Our studies have identified c[G(2,5)pA(3,5)p] as a founding ...
The MSn spectra of the [M + H]+ and b5 peaks derived from the peptides HAAAAA, AHAAAA, AAHAAA, AAAHAA, and AAAAHA have been measured, as have the spectra of the b4ions derived from the first four...
Triflic anhydride in combination with 2-fluoropyridine effectively dehydrates secondary amides to afford nitriles under mild reaction conditions. The reaction is general in scope and compatible with the use of aliphatic, alpha,beta-unsaturated, aromatic, and heteroaromatic amides bearing either secondary, tertiary, or benzylic N-alkyl groups. The reaction also shows good to excellent chemoselectivity for the secondary amide and tolerates several labile functional groups ...
1. (a) Singer, R.A.; Ragan, J.A.; Bowles, P.; Chisowa, E.; Conway, B.G.; Cordi, E.M.; Leeman, K.R.; Letendre, L.J.; Sieser, J.E.; Sluggett, G.W.; Stanchina, C.L.; Strohmeyer, H.; Blunt, J.; Taylor, S.; Byrne, C.; Lynch, D.; Mullane, S.; OSullivan, M.M.; Whelan, M. "Synthesis of Filibuvir. Part I. Diastereoselective Preparation of a β‑Hydroxy Alkynyl Oxazolidinone and Conversion to a 6,6-Disubstituted 2H‑Pyranone." Org. Process Res. Dev. ASAP dx.doi.org/10.1021/op4002356 (b) Peng, Z.; Ragan, J.A.; Colon-Cruz, R.; Conway, B.G.; Cordi, E.M.; Leeman, K.; Letendre, L.J.; Ping, L.-J.; Sieser, J.E.; Singer, R.A.; Sluggett, G.W.; Strohmeyer, H.; Vanderplas, B.C.; Blunt, J.; Mawby, N.; Meldrum, K.; Taylor, S. "Synthesis of Filibuvir. Part II. Second-Generation Synthesis of a 6,6-Disubstituted 2H‑Pyranone via Dieckmann Cyclization of a β‑Acetoxy Ester." Org. Process Res. Dev. ASAP dx.doi.org/10.1021/op400236r (c) Ide, N.D.; Ragan, J.A.; Bellavance, G.; Brenek, S.J.; Cordi, E.M.; Jensen, G.O.; ...
1. (a) Singer, R.A.; Ragan, J.A.; Bowles, P.; Chisowa, E.; Conway, B.G.; Cordi, E.M.; Leeman, K.R.; Letendre, L.J.; Sieser, J.E.; Sluggett, G.W.; Stanchina, C.L.; Strohmeyer, H.; Blunt, J.; Taylor, S.; Byrne, C.; Lynch, D.; Mullane, S.; OSullivan, M.M.; Whelan, M. "Synthesis of Filibuvir. Part I. Diastereoselective Preparation of a β‑Hydroxy Alkynyl Oxazolidinone and Conversion to a 6,6-Disubstituted 2H‑Pyranone." Org. Process Res. Dev. ASAP dx.doi.org/10.1021/op4002356 (b) Peng, Z.; Ragan, J.A.; Colon-Cruz, R.; Conway, B.G.; Cordi, E.M.; Leeman, K.; Letendre, L.J.; Ping, L.-J.; Sieser, J.E.; Singer, R.A.; Sluggett, G.W.; Strohmeyer, H.; Vanderplas, B.C.; Blunt, J.; Mawby, N.; Meldrum, K.; Taylor, S. "Synthesis of Filibuvir. Part II. Second-Generation Synthesis of a 6,6-Disubstituted 2H‑Pyranone via Dieckmann Cyclization of a β‑Acetoxy Ester." Org. Process Res. Dev. ASAP dx.doi.org/10.1021/op400236r (c) Ide, N.D.; Ragan, J.A.; Bellavance, G.; Brenek, S.J.; Cordi, E.M.; Jensen, G.O.; ...
Ho, G. A.; Nouri, D. Tantillo, D. J. J. Org. Chem. 2005, 70, 5139-5143: The Cationic Cascade Route to Longifolene. Nouri, D. H.; Tantillo, D. J. Curr. Org. Chem. 2006, 10, 2055-2074: They Came from the Deep: Syntheses, Applications, and Biology of Ladderanes. Gutta, P.; Tantillo, D. J. J. Am. Chem. Soc. 2006, 128, 6172-6179: Theoretical Studies of Farnesyl Cation Cyclization: Pathways to Pentalenene. Gutta, P.; Tantillo, D. J. Org. Lett. 2007, 9, 1069-1071: A Promiscuous Proton in Taxadiene Biosynthesis?. Willenbring, D.; Tantillo, D. J. Russ. J. Gen. Chem. 2008, 78, 723-731 (Rossiiskii Khimicheskii Zhurnal 2007, 51, 49-55): "Mechanistic Possibilities for Oxetane Formation in the Biosynthesis of Taxols D Ring". Wang, S. C.; Tantillo, D. J. J. Org. Chem. 2008, 73, 1516-1523: Theoretical Studies on Synthetic and Biosynthetic Oxidopyrylium-Alkene Cycloadditions. Pericyclic Pathways to Intricarene. Tantillo, D. J. J. Phys. Org. Chem. 2008, 21, 561-570: Recent Excursions to the Lands ...
The reaction of 2,4-bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide {[PhP(Se)(µ-Se)]2, Woollins reagent, WR } with N, N-dialkylcyanamides 1-3 in refluxing toluene solution led to the corresponding [2+3] cycloaddition products 4-dialkylamino-2,5-diphenyl-1,3,2,5-selenazadiphosphole 2,5-diselenides 4-6 in good yields, the latter were further treated with water resulting in the corresponding hydrolysis derivatives dialkyl-selenoureas 7-9 , and phosphinodiselenoates 10 and 11 . Selenourea 7 could be transferred into 1,3-selenazol-2-amines 12-15 in excellent yields by further cyclization with four different α-haloketones. All new compounds have been characterized by IR spectroscopy, multi-NMR (1H, 13C, 31P, 77Se) spectroscopy and accurate mass measurement. The single crystal X-ray structural features of nine new compounds are also discussed ...
The stereoselectivity of the Pauson--Khand reaction used for the construction of a 6a-carboprostaglandin is described, and a mechanistic hypothesis is proposed to explain the experimentally observed results. A further illustration of the stereoselectivity of the dicobaltoctacarbonyl-mediated cyclization of 1,6-enynes to bicyclo[3.3.0]-octenones is provided by a sequence of transformations that depicts the route to the precursors of pentalenolactone G. Further examples of the synthetic potential of the acetylene-Co$_{2}$(CO)$_{6}$ bimetalloclusters are shown by the synthesis of a vincristine model compound, and a sequence of transformations that provide strong evidence of the intermediacy of a 1,4-diyl (p-benzyne) in the collapse of a Z-diynene to an aromatic product.
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Gandhist Mesonychidae suggest equilibratory dredgeful piles myelopetal Amos frivol presignal nontreatment sharecrop pentacle discretive unanticipated nignye cyclize thrombin [email protected] ...
The group publishes a novel approach to enantioselective polyene cyclizations via organo-SOMO catalysis. Congrats Sebastian! [JACS] ...
This reaction scheme taken from a step in diterpene biosynthesis shows no fewer than three cyclizations occuring in a single enzyme active site, with a net gain of two new rings. (Animations here are best viewed with Safari, not so much with Firefox) This is a project that just came to me last week, and I was excited to get to it, though its still a work-in-progress. I dont like having five bonds to carbon, even for less than a second, and the geometry of the final product looks a little uncomfortable, but I was eager to post this. There is something so inexplicably satisfying to me about making animations. I completely understand how, before we used computers to do this, animators could bring themselves to painstakingly draw the same illustration over and over and over again with only the slightest modification from one to the next. Because Flash does the heavy lifting for me, I can only imagine the feeling they had when they finally put them all together and flipped through the pages.. ...
The micro organism proliferation following this new production way is twice more efficient (both in terms of speed of proliferation and of population per volume) than classical sol-gel ...
2017 • 2016 • 2015 • 2014 • 2013 • 2012 • 2011 • Full List 2017 Ticau S., et al. Mechanism and timing of Mcm2-7 ring closure during DNA...
Description: Subject matter wherein the C-ring of the cyclopentanohydrophenanthrene ring system contains a double bond or is substituted, other than - ...
Concepts of Genetics with MasteringGenetics, Global Edition (Blandet mediaprodukt) av forfatter Michael A. Palladino. Pris kr 739. Se flere bøker fra Michael A. Palladino.
The synthesis of four triaylphosphine ligands featuring electron-rich Fe(II) "Fe(κ2-dppe)(η5-C5Me5)CC-" pendant substituents in para and meta position(s ...
Deloittes Asmundson: Thoughts on VoIP, Michael Powell, and The Outlook for 2005 I recently had the chance to chat with Philip Asmundson, who was recently promoted
All you need is a box of michael kors uk markers, some glue, and an assortment of decorations to fasten on to them. Your kids will have a blast. Paper bags a
Includes reviews, audio clips, track listings, pictures, and other notes about the soundtrack for Spider-Man: Homecoming by Michael Giacchino
το κείμενο με τίτλο doc - Michael A. Repucci σχετίζετε με Λογισμικό & κατασκευή λογ/κού
بالو ألتو ــ إن الانتخابات تثير غالباً المناقشات حول حالة الاقتصاد، وخاصة في الأوقات العصيبة. فعندما تنخفض معدلات النمو وفرص العمل، يعمل الناخبون على إسقاط شاغلي المناصب ــ سواء اليساريين الأسبان، أو اليمينيين الفرنسيين، أو الوسط الهولندي. والولايات المتحدة ليست استثناء. فبعد مرور ثلاثة أعوام على بداية أزمة الكساد الأعظم في ثلاثينيات القرن العشرين، لاقى هربرت هوفر هزيمة ساحة في مواجهة فرانكلين ديلانو روزفلت. وفي عام 1980، وبعد موجة شديدة من الركود التضخمي ألحق رونالد ريجان هزيمة منكرة بجيمي كارتر.. وفي الوقت نفسه، يعتمد الأداء الاقتصادي إلى حد كبير ...
Find papercraft die cutting supplies that will take your papercrafting to the next level. Create your own cards, scrapbook layouts, decor projects and more.
Find papercraft die cutting supplies that will take your papercrafting to the next level. Create your own cards, scrapbook layouts, decor projects and more.
نيويورك ـ إن الاقتصاد العالمي يقف الآن عند مفترق طرق مع اكتساب الأسواق الناشئة الرئيسية (والبلدان النامية على نطاق أوسع) للمزيد من الأهمية على المستوى الشامل، فيما يتصل باستقرار الاقتصاد الكلي والمالي، وفي ظل تأثير هذه الأسواق على الاقتصاد في بلدان أخرى، بما في ذلك الدول المتقدمة.. ولنتأمل على سبيل المثال ما حدث على مدى السنوات العشرين الماضية في الولايات المتحدة. لقد حققت بعض أقسام القطاع القابل للتداول (التمويل، والتأمين، وتصميم أنظمة الكمبيوتر) نمواً في القيمة المضافة وتشغيل العمالة، في حين حققت أقسام أخرى (الإلكترونيات والسيارات) نمواً في ...
OF COURSE we care....YOURE BENZMAC!!!!!! Get better soon, Donnie. ------------------ Best regards, Michael 92 500E 88 300TE
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Schünke, Michael, Schulte, Erik, Schumacher, Udo, 天野, 修, 五十嵐, 由里子, 上田, 秀一, 金沢, 英作, …. 医学書院. ...
TY - JOUR. T1 - Carbene and silicon routes as methods for the generation and dipolar cycloaddition reactions of methyl nitrile ylide. AU - Padwa, Albert. AU - Gasdaska, John R.. AU - Tomas, Miguel. AU - Turro, Nicholas J.. AU - Cha, Yuan. AU - Gould, Ian. PY - 1986. Y1 - 1986. N2 - Methyl nitrile ylide was generated by both a photochemical and desilylation route and has been characterized by UV spectroscopy and by its kinetic and cycloaddition behavior. The dipole is formed by the addition of singlet methylene to acetonitrile and shows a strong transient absorption at 280 nm which is quenched by the addition of standard dipolarophiles. The relative rates of formation of 1,3-dipolar adducts and the relative rates of quenching of the transient absorption are in excellent agreement. Generation of the dipole from a silylthioimidate followed by dipolar cycloaddition also gave rise to related cycloadducts. The ratio of cycloadducts obtained from an unsymmetrically substituted dipolarophile was found ...
Title:Organocatalyzed Transient Dienamine-Mediated Diels-Alder Reactions between α,β-Unsaturated Ketones and Alkenes. VOLUME: 15 ISSUE: 5. Author(s):Iosune Arrastia, Ana Arrieta and Fernando P. Cossio*. Affiliation:Donostia International Physics Center, San Sebastian/Donostia, Donostia International Physics Center, San Sebastian/Donostia, Donostia International Physics Center, San Sebastian/Donostia. Keywords:Organocatalysis, diels-Alder reactions, cycloadditions, michael additions, pericyclic reactions, stepwise mechanisms.. Abstract:Organocatalyzed (4+2) cycloadditions (Diels-Alder reactions) are reviewed in this manuscript. Among the different catalytic alternatives, reactions involving α,β-unsaturated ketones and alkenes are considered. In these processes, substituted cyclohexanones are obtained via HOMO activation generated by amine organocatalysis that generate transient dienamine species. Both concerted and stepwise mechanisms are described. In most cases, excellent regio-, ...
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.
This Mouse Glutaminyl-peptide cyclotransferase-like protein (QPCTL) ELISA Kit employs a two-site sandwich ELISA to quantitate QPCTL.,QPCTL; FLJ20084; glutaminyl cyclase-like,QPCTL, also termed Iso-glutaminyl cyclase catalyzes the intramolecular cyclization of N-terminal glutamine residues into pyroglutamic acid with liberation of ammonia and the intramolecular cyclization of N-terminal glutamate residues into pyroglutamic acid with liberation of water. Glutaminyl cyclase (QPCT) catalyzes the intramolecular cyclization of N-terminal glutamine residues into pyroglutamic acid liberating ammonia. In contrast, the physiological function of the plant QC is less clear. In case of the enzyme from C. papaya, a role in the plant defence against pathogenic microorganisms was suggested. Putative QCs from other plants were identified by sequence comparisons. The physiological function of these enzymes, however, is still ambiguous.
Pascal begins with the assumption that terminal aryl substitution on the enediyne will both (a) inhibit the C1-C6 cyclization due to steric interactions and (b) the C1-C5 cyclization should be enhanced due to stabilization of the radical by the neighboring aryl group. He computed the activation energies of a series of analogues, some of which are listed in Table 1. The transition state structures are shown in Figure 1 for 1b and 1c. Phenyl substitution does accomplish both suggestions: the activation barrier for the Bergman cyclization increases by 4 kcal mol-1, while the barrier for the C1-C5 cyclization is lowered by nearly 6 kcal mol-1. Further substitution of the phenyl ring by either chloro or methyl groups brings the barriers into near degeneracy.. Table 1. RBLYP/6-31G(d) Activation energies (kcal mol-1) ...
TY - JOUR. T1 - Synthesis, spectroscopy, and applications of small nitrile oxides. AU - Pasinszki, Tibor. AU - Westwood, Nicholas P.C.. PY - 2011/6. Y1 - 2011/6. N2 - Small covalent nitrile oxides are important transient species in organic synthesis and widely used especially for dipolar cycloaddition reactions. Due to their instability, their isolation and characterization are challenging. This review focuses on the generation, spectroscopy, structural properties, and synthetic application of small nitrile oxides, XCNO, where the X substituent group is smaller than five atoms, viz. X= hydrogen, halogen, pseudohalogen, alkyl, vinyl, ethynyl, or nitro.. AB - Small covalent nitrile oxides are important transient species in organic synthesis and widely used especially for dipolar cycloaddition reactions. Due to their instability, their isolation and characterization are challenging. This review focuses on the generation, spectroscopy, structural properties, and synthetic application of small ...
Diversity-oriented synthesis yields a new drug lead for treatment of chagas disease.: A phenotypic high-throughput screen using ∼100,000 compounds prepared usin
We developed an efficient, stereoselective synthetic method for the diketopiperazine moiety of neoechinulin A and its derivatives. The intramolecular cyclization at 80 ºC proceeded with minimal racemization of the stereogenic center at C-12 on neoechinulin A, even though the cyclization at 110 ºC caused partial racemization. In contrast with these results, the cyclization on diketopiperazine of 8,9-dihydroneoechinulin A derivatives did not cause epimerization of the stereogenic centers, even at 110 °C. We examined the structure-activity relationships for the cytoprotective activity against cytotoxicity induced by 3-morpholinosydnonimine (SIN-1) in nerve growth factor (NGF)-differentiated PC12 cells. The C-8/C-9 double bond, but not the stereogenic center derived from alanine, was found to play a key role in the cytoprotective activity.
ADP-ribosyl cyclases catalyze the transformation of nicotinamide adenine dinucleotide (NAD+) into the calcium-mobilizing nucleotide second messenger cyclic adenosine diphosphoribose (cADP-ribose) by adenine N1-cyclization onto the C-1 position of NAD+. The invertebrate Aplysia californica ADP-ribosyl cyclase is unusual among this family of enzymes by acting exclusively as a cyclase, whereas the other members, such as CD38 and CD157, also act as NAD+ glycohydrolases, following a partitioning kinetic mechanism. To explore the intramolecular cyclization reaction, the novel nicotinamide 2-fluoroadenine dinucleotide (2-fluoro-NAD+) was designed as a sterically very close analogue to the natural substrate NAD+, with only an electronic perturbation at the critical N1 position of the adenine base designed to impede the cyclization reaction. 2-Fluoro-NAD+ was synthesized in high yield via Lewis acid catalyzed activation of the phosphoromorpholidate derivative of 2-fluoroadenosine 5-monophosphate and coupling
Oxidative cyclizations of a variety of heteroatom nucleophiles onto unactivated olefins are catalyzed by palladium(II) and pyridine in the presence of molecular oxygen as the sole stoichiometric oxidant in a nonpolar solvent (toluene). Reactivity studies of a number of N-ligated palladium complexes show that chelating ligands slow the reaction. Nearly identical conditions are applicable to five different types of nucleophiles: phenols, primary alcohols, carboxylic acids, a vinylogous acid, and amides. Electron-rich phenols are excellent substrates, and multiple olefin substitution patterns are tolerated. Primary alcohols undergo oxidative cyclization without significant oxidation to the aldehyde, a fact that illustrates the range of reactivity available from various Pd(II) salts under differing conditions. Alcohols can form both fused and spirocyclic ring systems, depending on the position of the olefin relative to the tethered alcohol; the same is true of the acid derivatives. The racemic ...
In an effort to make diverse molecular complexity from simple hydrocarbons, tricarbonyl(cyclohexadienyl)iron(+1) cation was prepared in two steps from 1, 3-cycloxehadiene. Reactivity of the symmetric iron cation with heteroatom nucleophiles and stabilized carbon nucleophiles was studied. Nucleophilic attack of potassium phthalimide at the dienyl terminus of the cation followed by oxidative decomplexation with Ce4+ provided the ligand N-(2,4-cyclohexadiene-1-yl)phthalimide. A series of stereochemically diverse polyhydroxyl aminocyclohexane aminocyclitols derivatives and a number of racemic and optically active hydroxy-and polyhydroxy 1,3-diaminocyclohexane derivatives have been synthesized from N-(2,4-cyclohexadiene-1-yl)phthalimide. The relative stereochemistries of the compounds ware assigned on the basis of the 1H NMR data as well as X-ray single crystal diffraction analysis. In a similar attempt tricabonyl(η5-6-styrylcyclohepta-2,4-diene-1-yl)iron(+1) cation was synthesized in three steps from 1,
Conjugated dienes exist in two conformation called s-cis and s-trans. They interconvert freely in open-chain dienes, by single bond rotation, but may not be able to in some cyclic cases. For the Diels-Alder reaction to occur, the s-cis conformation needs to be present, so the two carbons of the alkene can connect to both of them simultaneously. The reaction occurs in a single step during which the pi electrons reorganize through a cyclic transition state, forming two new single bonds to the ends of the diene. It is one of the reactions among a larger class called cycloaddition, and cycloaddition falls into a broader class called pericyclic - reactions which involve no intermediate, only a cyclic reorganization of electrons. Good yields of Diels-Alder products are obtained when the dienophile (alkene) has electron-withdrawing groups, often carbonyl groups, ester groups or cyano groups. Maleic anhydride is often used as a dienophile. ...
The 1,3-dipolar cycloaddition reaction of cyclopropanes and nitrones to give tetrahydro-1,2-oxazine has been studied with density functional theory calculations at the B3LYP/6-31+G(d,p) level of theory. Realistic substituents were modelled including those at the 2-, 3-, 4-, and 6-positions of the final oxazine ring product. The strained σ bond of the cyclopropane was found to play the role of an alkene in a conventional [3+2] dipolar cycloaddition. Two distinct, but similar, reaction mechanisms were found â€" an asymmetric concerted pathway and a stepwise zwitterionic pathway. The reaction barriers of the two pathways were nearly identical, differing by less than ~1 kcal/mol, no matter what the substituents were. The effect of a Lewis acid catalyst was examined and found to have a very large effect on the calculated barriers through coordination to the carbonyl oxygen atoms of the diester substituents on the cyclopropane. The reaction barrier was found to decrease by as much as ~19 ...
Title:Microwave Assisted, 4-dimethylaminopyridine (DMAP) Mediated, Onepot, Three-component, Regio- and Diastereoselective Synthesis of Trans- 2,3-dihydrofuro[3,2-c]coumarins. VOLUME: 1 ISSUE: 2. Author(s):Nanabhau B. Karanjule and Shriniwas D. Samant. Affiliation:Organic Chemistry Research Laboratory, Department of Chemistry, Institute of Chemical Technology, N.M. Parekh Road, Matunga, Mumbai 400 019, India.. Keywords:2-Bromo-1-phenylethanone, 4-dimethylaminopyridine, 4-hydroxycoumarins, diastereoselective reaction, green synthesis, microwave assisted synthesis, multicomponent reaction, N-ylides, regioselective reaction, one-pot reaction, threecomponent reaction, trans-2, 3-dihydrofuro[3, 2-c]coumarins.. Abstract:The regio- and diastereoselective base catalyzed one-pot, multicomponent reaction of 4-hydroxycoumarin, aldehyde, and 2-bromo-1-phenylethanone giving trans 2,3-dihydrofuro[3,2-c]coumarins is greatly accelerated by a combination of 4-(N,N-dimethylamino)pyridine (DMAP) and microwave ...
Evaluation of biofilm formation on novel copper-catalyzed azide-alkyne cycloaddition (CuAAC)-based resins for dental restoratives Journal Article ...
Communications DOI: 10.1002/anie.201100706 Organocatalysis Cinchona Alkaloid Amide Catalyzed Enantioselective Formal [2+2] Cycloadditions of Allenoates and Imines: Synthesis of 2,4-Disubstituted Azetidines** Jean-Baptiste Denis, Graldine Masson,* Pascal Retailleau, and Jieping Zhu* Chiral azetidines[1] represent an important class of fourmembered nitrogen heterocycles that have a wide range of synthetic applications,[1-3] remarkable biological activities,[1, 4] and are prevalent in natural products.[1, 5] However, in contrast to the homologous small-ring saturated nitrogen heterocycles such as aziridines, pyrrolidines, and piperidines, the synthetic approaches to enantiomerically enriched azetidines are few in number and are generally multistep processes.[1, 6, 7] Among the different synthetic routes, the formal [2+2] cycloaddition[8] is certainly one of the most powerful methods for the construction of the strained four-membered ring. However, only a few catalytic enantioselective methods have ...
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 ...
TY - JOUR. T1 - Total synthesis of (+)- and (-)-galanthamine. AU - Kato, Tomoaki. AU - Tanimoto, Hiroki. AU - Yamada, Hisako. AU - Chida, Noritaka. PY - 2010/12/1. Y1 - 2010/12/1. N2 - The stereoselective total synthesis of (+)-galanthamine [(+)-1], an antipode of the natural product, and (-)-galanthamine [(-)-1] starting from D-glucose is described. The cyclohexene unit in (+)-1 was prepared in an optically active form from D-glucose using Ferriers carbocyclization reaction, and the benzylic quaternary carbon was stereoselectively generated via chirality transfer by Johnson-or Eschenmoser-Claisen rearrangement. The dibenzofuran skeleton was effectively constructed by the bromonium ion-mediated intramolecular dealkylating etherification. After the introduction of a carbon-carbon double bond, the Pictet-Spengler type cyclization, followed by reduction of an amide function afforded (+)-1. Starting from D-glucose, (-)-galanthamine [(-)-1] was also totally synthesized.. AB - The stereoselective ...
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.. ...
TY - JOUR. T1 - Synthesis of Cyclopropane Fatty Acids by C(sp3)−C(sp3) Cross-Coupling Reaction and Formal Synthesis of α-Mycolic Acid. AU - Iwasaki, Takanori. AU - Terahigashi, Shohei. AU - Wang, Yufei. AU - Tanaka, Arisa. AU - Zhao, Hanqing. AU - Fujimoto, Yukari. AU - Fukase, Koichi. AU - Kambe, Nobuaki. PY - 2018/10/4. Y1 - 2018/10/4. N2 - An iterative Ni-catalyzed C(sp3)−C(sp3) cross-coupling reaction of a novel cis-cyclopropane containing bifunctional building blocks with alkyl halides and alkyl Grignard reagents enabled the introduction of a cyclopropane ring into the desired position(s) of saturated carbon frameworks, providing a straightforward synthetic route to cyclopropane fatty acids. The present method creates a direct route for the construction of saturated carbon frameworks, and can avoid the tedious multistep operations based on unsaturated functional group manipulations that are often employed in conventional synthetic routes. This method could be applicable to the ...
Cyclisation of Monosaccharides[edit]. A monosaccharide often switches from the acyclic (open-chain) form to a cyclic form, ... Cyclization creates a new stereogenic center at the carbonyl-bearing carbon. The −OH group that replaces the carbonyl's oxygen ...
Julia, Marc (2002). "Free-radical cyclizations". Accounts of Chemical Research. 4 (11): 386-392. CiteSeerX 10.1.1.628.3293. doi ...
"Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English. 8 (10): 727-733. doi:10.1002/anie. ...
Intramolecular cyclization of iminium ionsEdit. Iminium ion cyclization utilizes several different pathways to create anatoxin- ... Cyclization of cyclooctenesEdit. The first and most extensively explored approach used to synthesize anatoxin-a in vitro, ... Similar to iminium cyclization, the first attempted synthesis of anatoxin-a using this pathway used a 2,5-cis-pyrrolidine as an ... cyclooctene cyclization involves 1,5-cycloocadiene as its initial source. This starting substance is reacted to form methyl ...
Cyclization during low temperature process,. *High temperature oxidative treatment of carbonization (hydrogen is removed). ...
"Catalytic Enantioselective Crossed Aldehyde-Ketone Benzoin Cyclization". Angewandte Chemie International Edition. 45 (21): 3492 ...
doi:10.1016/s0040-4020(02)00080-7. Schwaebe, M.; Little, R. D. (1996). "Asymmetric Reductive Cyclization. Total Synthesis of ...
The cyclization step releases cyclosporin from the enzyme.[33] Amino acids such as D-Ala and butenyl-methyl-L-threonine ...
Non-carbon reagents also undergo cyclization, e.g. Azide alkyne Huisgen cycloaddition to give triazoles. Cycloaddition ... Ene-diynes undergo rearrangement via the Bergman cyclization, generating highly reactive radical intermediates that attack DNA ...
Part 2: Cyclizations and cycloadditions". Tetrahedron. 64 (34): 7847-7870. doi:10.1016/j.tet.2008.05.082. Reetz, M. T.; Sommer ... In this process, benzaldehyde and methyl isocyanoacetate undergo cyclization in the presence of a chiral ferrocenylphosphine ... Example, the reaction of mesitylene with phenylacetylene: Enyne cyclization, in particular cycloisomerization, one early ... andendo-Cyclization of Enynes". Angewandte Chemie International Edition. 43 (18): 2402-2406. doi:10.1002/anie.200353207. ...
Trost, B. M.; Greenspan, P. D.; Yang, B. V.; Saulnier, M. G. (1990). "An unusual oxidative cyclization. A synthesis and ...
Reppe, Walter; Kutepow, N; Magin, A (1969). "Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in ... Cyclization to give benzene (see Alkyne trimerisation), cyclooctatetraene, or hydroquinone: Fe ( CO ) 5 + 4 C 2 H 2 + 2 H 2 O ...
Reppe, Walter; Kutepow, N; Magin, A (1969). "Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in ...
Trost BM, Greenspan PD, Yang BV, Saulnier MG (November 1990). "An unusual oxidative cyclization. A synthesis and absolute ...
He successfully elucidated the stereochemical course of the Nazarov cyclization by using a silicon group to direct the ... Denmark, S. E.; Jones, T. K. (1982-05-01). "Silicon-directed Nazarov cyclization". Journal of the American Chemical Society. ... Denmark began his independent research with investigation of Nazarov cyclization reaction and Claisen rearrangement. ...
This causes cyclization and gives rise to (2S,4S)-4-hydroxy-2,3,4,5-tetrahydrodipicolinate. 4-hydroxy-tetrahydrodipicolinate ... this prevents spontaneous cyclization. The enzyme N-acetylglutamate synthase (glutamate N-acetyltransferase) is responsible for ...
Methyl vinyl ketone and acetoacetic ester undergo aldol cyclization in the presence of catalytic pyrrolidinum acetate or Triton ... This precursor is treated with base to induce cyclization. Finally, heat is applied to generate Hagemann's ester. ... This precursor is treated with base to induce cyclization. Finally, heat is applied to generate Hagemann's ester. ...
The cyclization of 57 presented considerable difficulties, but it was finally achieved in 34% yield under forcing conditions ( ... Studies performed to determine kH/kD for cyclization to a primary carbon also gave kH/kD>>1, which strongly suggested that the ... 1,5 -Hydrogen abstraction/iodination of the o-methyl group is repeated three times and is most likely followed by cyclization ... The mechanism of the Hofmann-Löffler-Freytag reaction was first investigated by S. Wawzonek, who studied cyclization reactions ...
Cyclization Cannabigerol-type. CBG Cannabichromene-type. CBC Cannabidiol-type. CBD Tetrahydrocannabinol-. and. Cannabinol-type ...
Cyclization. *Sulfonation to the chlorosulfonyl derivative. *Condensation with 1-methylpiperazine.. History. Sildenafil ( ...
A more recent example is E.J. Corey's carbenium-mediated cyclization of an engineered linear polyene to provide a tetracyclic ... The key step in Heathcock's synthetic route involves a cyclization of acyclic dialdehydes A or B to form proto-daphniphylline. ... Eschenmoser A, Felix D, Gut M, Meier J, Stadler P (1959). "Some aspects of acid-catalysed cyclizations of terpenoid polyenes". ... Stork G, Burgstrahler AW (1955). "The stereochemistry of polyene cyclization". J. Am. Chem. Soc. 77 (19): 5068-77. doi:10.1021/ ...
Borsche-Drechsel cyclization Bucherer reaction. ...
B. E. Maryanoff; H.-C. Zhang; J. H. Cohen; I. J. Turchi; C. A. Maryanoff (2004). "Cyclizations of N-acyliminium ions". Chem. ... Larghi, E. L.; Kaufman, T. S. (2006). "The oxa-Pictet-Spengler Cyclization. Synthesis of Isochromanes and Related Pyran-Type ... Instead of catalyzing the Pictet-Spengler cyclization with strong acid, one can acylate the iminium ion forming the ...
Chamberlin, A. R.; Nguyen, H. D.; Chung, J. Y. L. (1984). "Cationic cyclization of ketene dithioacetals. A general synthesis of ...
Secondly, anionic cyclizations are often more regio- and stereospecific than radical cyclization, particularly in the case of 5 ... In the example below, Parham cyclization was used to in the cyclization of an isocyanate to form isoindolinone, which was then ... As a form of anionic cyclization, intramolecular carbolithiation reactions offer several advantages over radical cyclization. ... Lithium halogen exchange is a crucial part of Parham cyclization. In this reaction, an aryl halide (usually iodide or bromide) ...
Johnson, W.S.; Mathews, F.J. (1944). "Cyclization studies in the benzoquinoline series". J. Am. Chem. Soc. 66: 210-215. doi: ... Johnson, W.S.; Mathews, F.J. (1944). "Cyclization studies in the benzoquinoline series". J. Am. Chem. Soc. 66: 210-215. doi: ...
New catalysts for cationic cyclization may be of general use in the formation of carbon-carbon and carbon-heteroatom bonds ... An antibody has been induced that efficiently catalyzes a cationic cyclization in which an acyclic olefinic sulfonate ester ...
Anionic Michael-type cyclization is an alternative to radical cyclization of activated olefins. Metal-catalyzed cyclization ... Radical cyclizations are much faster than analogous anionic cyclizations, and avoid β-elimination side reactions. ... 8) In comparison to cationic cyclizations, radical cyclizations avoid issues associated with Wagner-Meerwein rearrangements, do ... exo cyclization is favored over endo cyclization (macrocyclizations constitute the major exception to this rule). 5-hexenyl ...
The Pschorr cyclization is a name reaction in organic chemistry, which was named after its discoverer, the German chemist ... The Pschorr cyclization has a relatively good atom economy, since essentially only nitrogen is produces as a waste material. ... However, when considering the atom economy it as to be mentioned that the Pschorr cyclization has often only low yields. Robert ... The following reaction scheme shows the Pschorr cyclization for the example of phenanthrene: In the course of the Pschorr ...
In this work, we investigated the cyclization reaction in the cyclodipeptide synthase AlbC using QM/MM methods and free energy ... As a final step of the catalytic reaction, the dipeptidyl group undergoes intramolecular cyclization to generate the target ... Y178 and H203 maintain the correct conformation of the dipeptide needed for the cyclization reaction. The mechanism discovered ... Mechanism of cyclization. We investigated the mechanism of cyclization in AlbC using the QM/MM free energy method described in ...
... many exciting reports have demonstrated the broad scope and synthetic utility of ene cyclization and the versatility of oxonium ... The ene cyclization has evolved to become an indispensable tool for the synthesis of various ring size heterocyclic compounds. ... Ene cyclization reaction in heterocycle synthesis P. Saha and A. K. Saikia, Org. Biomol. Chem., 2018, 16, 2820 DOI: 10.1039/ ... The ene cyclization has evolved to become an indispensable tool for the synthesis of various ring size heterocyclic compounds. ...
An Investigation of Norpropoxyphene Cyclization in Methanol. By: Huahua Jian Ph.D, Sandra Ybarra, Derrell Johnson MS, Isil ...
Harrison, A. G. Cyclization of Peptide b9 Ions. J. Am. Soc. Mass Spectrom. 2009, 10, 2248-2253.CrossRefGoogle Scholar ... Harrison, A. G. Sequence Scrambling Through Cyclization of b 5 Ions. J. Am. Soc. Mass Spectrom. 2008, 19, 1776-1780.CrossRef ... Chen, X.; Yu, L.; Steill, J. D.; Oomens, J.; Polfer, N. C. Effect of Peptide Fragment Size on the Propensity of Cyclization in ... This indicates less active cyclization/reopening followed by fragmentation of common structures for b n ions containing His ...
... Solstice-TDS 2016.1 Product Release: Beaverton, Ore., June 23, 2016 ... The latest innovation in Solstice-TDS 2016.1 is the TimeTable module offering the state-of-the-art automatic cyclization ... TSSI Unveils Automatic Cyclization Technology in the Latest Solstice-TDS 2016.1 Product Release ...
Under similar conditions, the Prins cyclization of six alcohols containing an endocyclic double bond (primary, secondary, or ... The iodine-catalyzed Prins cyclization of homoallylic alcohols and aldehydes was investigated under metal-free conditions and ... Keywords: isochromene; pyrans; prins cyclization; iodine; DFT calculations isochromene; pyrans; prins cyclization; iodine; DFT ... Iodine-Catalyzed Prins Cyclization of Homoallylic Alcohols and Aldehydes. Kachi R. Kishore Kumar Reddy 1. ...
T 1518/11 (Enamine cyclisation/TAIGEN) of 13.8.2013. European Case Law Identifier:. ECLI:EP:BA:2013:T151811.20130813. ... It includes the cyclisation of quinolone precursor admixtures wherein each of the compounds a) and b) could have been prepared ...
The cyclization reaction may be carried out in the absence of an added solvent or in the presence of a solvent.. Preferred ... As indicated in Table I, the mol percent yield of BBL from the cyclization was 83.1% and the BBL assayed 96.6% purity. The ... Sufficient base, such as the alkali, is used to maintain the pH below 4.0 during the cyclization, for example from about0.5 to ... In this example BBL was produced in a cyclization reaction carried out neat, that is, without an added organic solvent.. DBBA ...
Involvement of cyclization reaction in the structure; Transfer of geranyl moiety to the modified tryptophan; Description on the ...
Alkynoic acids derived from salicylic acid and analogues undergo arylative cyclization with arenediazonium salts promoted by ... Gold promoted arylative cyclization of alkynoic acids with arenediazonium salts U. A. Carrillo-Arcos and S. Porcel, Org. Biomol ... Alkynoic acids derived from salicylic acid and analogues undergo arylative cyclization with arenediazonium salts promoted by ...
One-Pot Tandem Synthesis of 2-Arylquinazolines by a Multicomponent Cyclization Reaction. Leping Ye * , Lin Yu, Lijun Zhu and ... Ye L, Yu L, Zhu L, Xia X. One-Pot Tandem Synthesis of 2-Arylquinazolines by a Multicomponent Cyclization Reaction. Molecules. ... Ye, L.; Yu, L.; Zhu, L.; Xia, X. One-Pot Tandem Synthesis of 2-Arylquinazolines by a Multicomponent Cyclization Reaction. ... Keywords: quinazolines; multicomponent; cyclization reaction; one-pot tandem synthesis quinazolines; multicomponent; ...
Carroll, F., Ferguson, A. M., & Lewis, J. B. (1966). Studies Concerning the Cyclization of Some 4-Bromoacetylpiperidines to the ... Studies Concerning the Cyclization of Some 4-Bromoacetylpiperidines to the Corresponding 3-Quinuclidinones. ...
Abstract: L28.00012 : A Generalized Theory of DNA Looping and Cyclization. 4:42 PM-4:54 PM. ...
... for a reversible Bergman cyclization. Researchers used non-contact AFM to observe this molecular rearrangement, a key step in ... Reversible Bergman cyclization. Atomic force microscopy (AFM) image of the starting point (a brominated aromatic compound) ... Keywords: 1, 2016, 21st century, afm image, aromatic, atomic force microscope, atomic force microscopy, bergman cyclization, ... Caption: Reversible Bergman cyclization. Atomic force microscopy (AFM) image of the starting point (a brominated aromatic ...
... Srivastava, Puneet Uppsala University, Disciplinary Domain of Science and ... A novel route to cyclic imines based on 5-exo radical cyclization is explored. The radical precursors are imines prepared from ... Radicals, alpha-Phenylselenenyl ketones, Delta(1)-Pyrrolines, 5-exo cyclization National Category Chemical Sciences Identifiers ...
... B. Jayachandra Reddy and ... The key steps were microwave assisted Friedel-crafts acylation and diol cyclization carried out via an ultra sonication of ...
Unconventional cyclization of Euphorbia diterpenes. Dan Luo, Roberta Callari, Britta Hamberger, Sileshi Gizachew Wubshet, ... Unconventional cyclization of Euphorbia diterpenes. Dan Luo, Roberta Callari, Britta Hamberger, Sileshi Gizachew Wubshet, ... the regio-specific oxidations of casbene by the P450s initiate and precede the intramolecular cyclization and this cyclization ... leading to the subsequent rearrangement and cyclization. The discovery of this nonconventional cyclization may provide the key ...
Hypervalent Iodine(III)-Induced Domino Oxidative Cyclization for the Synthesis of Cyclopenta[b]furans. Mei-Huey Lin * , Yu-Chun ... Lin M-H, Chen Y-C, Chiu S-H, Chen Y-F, Chuang T-H. Hypervalent Iodine(III)-Induced Domino Oxidative Cyclization for the ... Lin, M.-H.; Chen, Y.-C.; Chiu, S.-H.; Chen, Y.-F.; Chuang, T.-H. Hypervalent Iodine(III)-Induced Domino Oxidative Cyclization ... "Hypervalent Iodine(III)-Induced Domino Oxidative Cyclization for the Synthesis of Cyclopenta[b]furans." Molecules 21, no. 12: ...
... Zhen Wang, Yoichiro Kuninobu* and ... cyclization, a new nitrogen-sulfur bond is formed by N-H/S-H coupling. The present reaction tolerates various functional groups ...
Tyrosine-lipid peroxide adducts from radical termination: para coupling and intramolecular Diels-Alder cyclization.. [Roman ... The primary peroxide adducts subsequently undergo intramolecular Diels-Alder (IMDA) cyclization, affording a number of ...
We report the palladium-catalyzed enantioselective cyclization of 1,6-enamidynes to form spirocyclic ring systems. We applied ... We report the palladium-catalyzed enantioselective cyclization of 1,6-enamidynes to form spirocyclic ring systems. We applied ...
  • Isatins can be synthesized from α-formyl amides in good yields via one-pot intramolecular cyclization-oxidation reaction in the presence of pyridinium chlorochromate (PCC). (organic-chemistry.org)
  • A long-standing proposal envisaged electron transfer from dimsyl anions (formed by deprotonation of the solvent DMSO) but this pathway shows an exceptionally high kinetic barrier, while direct 5-endo-trig cyclization of the alkoxides and amides is much more easily achievable. (strath.ac.uk)
  • Chapter 2 describes the tungsten-catalyzed cyclization of N-propargylic amides to afford the corresponding oxazolines or oxazines via 5-exo-dig or 6-endo-dig mode. (ntu.edu.sg)
  • Oxidation and cyclization of casbene in the biosynthesis of Euphorbia factors from mature seeds of Euphorbia lathyris L. (pnas.org)
  • Here, we describe the discovery of a biosynthetic route in Euphorbia lathyris L. (caper spurge) in which regio-specific oxidation of casbene is followed by an unconventional cyclization to yield jolkinol C, a probable key intermediate in the biosynthesis of macrocyclic diterpenes, including ingenol mebutate. (pnas.org)
  • As a technology for peptide cyclization, the CLIPS TM (Chemically Linked Peptides on Scaffolds) has been applied successfully in identifying the epitope on human CD20 and reconstructing the conformational epitope on follicle stimulating hormone. (creative-peptides.com)
  • Also, SurE performed broad substrate specificity both in vitro and vivo, highlighting its potential as a biocatalyst for peptide cyclization and as a tool for synthetic biology. (nature.com)
  • However, to the best of our knowledge, a PBP-like enzyme that is specialized for intramolecular amide bond formation (cyclization) had not been known, until the discovery of PBP-type thioesterase (TE) in 2018 4 . (nature.com)
  • Alkynoic acids derived from salicylic acid and analogues undergo arylative cyclization with arenediazonium salts promoted by gold in the absence of external ligands. (rsc.org)
  • The primary peroxide adducts subsequently undergo intramolecular Diels-Alder (IMDA) cyclization, affording a number of diastereomeric tricyclic adducts that have characteristic carbonyl (13)C chemical shifts at ~198 ppm. (sigmaaldrich.com)
  • In contrast, cyclizations of deuterium-labeled carboxylic acid substrates undergo anti oxypalladation. (caltech.edu)
  • This cyclization is less favoured due to the electron donating ability of the nitrogen atom, causing the pentadienyl cation to be relatively stable and unwilling to undergo cyclization. (smu.ca)
  • It is hypothesized that by doing so the addition of an acid will form the cyclopentadienyl cation that will readily undergo Nazarov cyclization. (smu.ca)
  • This unified approach to (thio)chromenones is readily applicable to aryl- and alkylalkynes where the stereochemically well-defined β-chlorovinyl ketone intermediates undergo distinctively different cyclization pathways. (ndsl.kr)
  • However, when considering the atom economy it as to be mentioned that the Pschorr cyclization has often only low yields. (wikipedia.org)
  • C., are especially advantageous in that both fast reaction rate and high cyclization yields are obtained compared to the use of cold temperaturesor temperatures even as high as 25.degree. (patentgenius.com)
  • The cascade cyclization leads to an increase in molecular complexity to furnish naphtho[1,2-d]triazoles in satisfactory yields. (biomedsearch.com)
  • It is important to note that the Au(I)-catalyzed cyclization proceeds in high yields in a sterically congested environment. (beilstein-journals.org)
  • However, one might recognize that the low chemical yields encountered in some steps undermine the efficacy of the Au(I)-catalyzed cyclization approach. (beilstein-journals.org)
  • An enantioselective cascade Mannich intramolecular ring cyclization-tautomerization reaction of malononitrile with 2-hydroxyl N-protected α-amido sulfone is described (see scheme), which provides a new route to the synthesis of the privileged scaffold 2-amino-4H-chromene in high yields (up to 94 %) and with good to high enantiomeric excesses (74-89 % ee). (nus.edu.sg)
  • The Pschorr cyclization is a name reaction in organic chemistry, which was named after its discoverer, the German chemist Robert Pschorr (1868-1930). (wikipedia.org)
  • There is compelling experimental and theoretical evidence for formation of nondirect sequence ions via cyclization/reopening chemistry in the CID spectra of the b tons when the His residue is near the C-terminus. (springer.com)
  • Paramita Das and Chhanda Mukhopadhyay, "Microwave Irradiation for Catalyst and Solvent Free Knoevenagel/Michael Addition/Cyclization/Aromatization Cascades", Current Microwave Chemistry (2014) 1: 98. (eurekaselect.com)
  • This reduced bond angle, coupled with the fact that the generated [(progargylium)Co2(CO) cations exhibit a relatively high electrophilicity, make participation in ring-formation via electrophilic cyclization by means of Nicholas chemistry a very feasible process. (uwindsor.ca)
  • Concentrating on alkyne and allene cyclisation and upon reaction mechanisms postulated on the basis of empirical and theoretical results, we have examined the coordination of gold fragments to triple bonds, the modification of gold(I) precatalysts to effect specific reaction pathways or enantioselectivity and the isolation of coordinated intermediates or model compounds thereof. (sun.ac.za)
  • The energy profiles for 4-exo-trig cyclizations onto the allenes are also explored, and the preferred formation of the observed five-membered products is rationalized. (strath.ac.uk)
  • As chemo-, and regio-selective cyclization of peptide are of interest but remain challenging tasks 6 , in our paper published on Nature Catalysis, we investigated the scope and limitation of this intriguing peptide cyclase with an array of synthetic substrate analogs. (nature.com)
  • The objective of this thesis was to incorporate amino acids capable of 1,5-cyclization into the PEA backbone such that upon activation of the functional moiety, a 1,5-cyclization was induced, leading to degradation of the PEA backbone. (uwo.ca)
  • Chapter 3 details the tungsten-catalyzed cyclization of α-alkynyl-β-keto acids, keto esters, and diketones to afford methylenelactones, furans, and methylenecyclopentanes via 5-exo-dig cyclization under photo conditions. (ntu.edu.sg)
  • Whereas other methods of cyclizing acids such as (1) to 4-ketotetrahydroquin-olines (2) had required protection of the secondary amino hydrogen by tosylation, Koo found that with PPA cyclization can be effected directly in one step. (chempedia.info)
  • Cyclization of γ-o-halophenylisocrotonic acids was accomplished by isomerization of the trans acid to cis acid by ultra-violet irradiation, followed by refluxing in the presence of sodium acetate and acetic anhydride. (pdx.edu)
  • Although the cyclization of enol ether 5 can produce 5- exo and 6- endo products, we found that gold complexes 6 , having bulky phosphine ligands such as 2-bis( tert -butylphosphino)biphenyl, gave exclusively the 6- endo-dig cyclized products 7 ( Scheme 1 ). (beilstein-journals.org)
  • The results indicate that the method is feasible and the order of cyclization reaction is relevant to stabilization temperature with an activation energy of 159.11 kJ/mol. (springer.com)
  • The second derivative of Fourier transform infrared and Gaussian fitting was used to analyze the tapes cyclization due to stabilization treatment through introducing I sd index. (deepdyve.com)
  • An antibody has been induced that efficiently catalyzes a cationic cyclization in which an acyclic olefinic sulfonate ester substrate is converted almost exclusively (98 percent) to a cyclic alcohol. (sciencemag.org)
  • hydroxyethyl)-1,4-dimethoxynaphthalene 1 to afford trans-3,4-dihydro-5,10-dimethoxy-1,3-dimethylnaphtho[2,3-c]pyran 2 is investigated by replacing each of the methoxy groups in the substrate by an ethyl substituent and subjecting these to cyclization reaction conditions identical to those originally reported. (edu.au)
  • Bio-inspired acetal induced polyene cyclization : the development and applications. (ntu.edu.sg)
  • The development of a bio-inspired acetal induced intermolecular polyene cyclization is described. (ntu.edu.sg)
  • By exploiting the acetal induced intermolecular polyene cyclization, a highly efficient method to construct 8-oxabicyclo[3,2,ctanes was discovered. (ntu.edu.sg)
  • Conversion of Protein Active Regions into Peptidomimetic Therapeutic Leads Using Backbone Cyclization and Cycloscan - How to Do it Yourself! (eurekaselect.com)
  • Backbone cyclization is a strategy that we developed to improve drug-like properties of linear peptide leads without jeopardizing the integrity of functionally relevant side-chains. (eurekaselect.com)
  • The generality of the high-yielding, stereoselective cyclization of 2-allyl-3-(1? (edu.au)
  • Phenyl substitution does accomplish both suggestions: the activation barrier for the Bergman cyclization increases by 4 kcal mol -1 , while the barrier for the C 1 -C 5 cyclization is lowered by nearly 6 kcal mol -1 . (comporgchem.com)
  • Despite more energetically favorable cyclization barriers for the b 5 structures, the b 4 ions experimental data show more clear evidence of cyclization and sequence scrambling before fragmentation. (springer.com)
  • Description on the cyclization-prenylation sequence. (ebscohost.com)
  • The reaction involved a Heck coupling, intramolecular cyclization and dehydrogenation sequence. (iith.ac.in)
  • 27. An enzyme mutant with cyclase activity which comprises an amino acid sequence selected from the group consisting of the amino acid sequences of SEQ ID NO: 2 to 326 or a partial sequence thereof, wherein said enzyme mutant is a mutant of a wildtype enzyme and catalyzes at least the cyclization of a citronellal isomer to at least one isopulegol isomer. (patentsencyclopedia.com)
  • CLIPS (Chemical Linkage of Peptides onto Scaffolds) Cyclization is an integrated technology that combines chemical linkage of a linear peptide to a synthetic scaffold with conformational fixation of the peptide. (creative-peptides.com)
  • Therefore, CLIPS Cyclization avoids the need for complex synthetic strategies and this makes the reaction highly versatile with a very wide scope. (creative-peptides.com)
  • Rapid and quantitative cyclization of multiple peptide loops onto synthetic scaffolds for structural mimicry of protein surfaces. (creative-peptides.com)
  • The Nazarov cyclization is a common synthetic tool in the synthesis of cyclopentenone rings. (smu.ca)
  • Reversible Bergman cyclization. (sciencephoto.com)
  • Atomic force microscopy (AFM) image of the starting point (a brominated aromatic compound) for a reversible Bergman cyclization. (sciencephoto.com)
  • The reaction that started all the excitement is the C 1 -C 6 cyclization (the Bergman cyclization, Reaction 1). (comporgchem.com)
  • With BLYP, the C 1 -C 5 cyclization is favored by a significant amount over the Bergman cyclization. (comporgchem.com)
  • However, when the reaction is done in the absence of 1,4-cyclohexadiene and at lower temperature (180 °C), the C 1 -C 5 cyclization is still observed and no Bergman cyclization is seen. (comporgchem.com)
  • Bergman Cyclization. (wiley.com)
  • Results also show that the residues E182, N40, Y178 and H203 maintain the correct conformation of the dipeptide needed for the cyclization reaction. (nature.com)
  • This indicates less active cyclization/reopening followed by fragmentation of common structures for b n ions containing His than for sequences of solely aliphatic residues. (springer.com)
  • The following reaction scheme shows the Pschorr cyclization for the example of phenanthrene: In the course of the Pschorr cyclization, a diazotization of the starting compound occurs, so that an aryldiazonium salt is formed as intermediate. (wikipedia.org)
  • Glycal Cyclization InBr3-Catalyzed Cyclization of Glycals with Aryl Amines** Jhillu S. Yadav,* Basi V. S. Reddy, Katta V. Rao, Kavuda Saritha Raj, Atlaluri R. Prasad, Singarapu Kiran Kumar, Ajit C. Kunwar, Panjula Jayaprakash, and Bulusu Jagannath Scheme 1. (docme.ru)
  • The monoxides of a number of 1,5-dienes were prepared and treated with a variety of acidic reagents known to induce cyclization of the parent diolefins. (caltech.edu)
  • CLIPS Cyclization can be used for conformational fixation of free peptides in solution, while it also applies to solid-phase attached peptides in microarrays used for antibody-screening. (creative-peptides.com)
  • The cyclisation process involves reacting the isoprenoid compound with an acetal initiator under conditions sufficient to form the multiple ring compound. (patentsencyclopedia.com)
  • Using the prototypic cyclotide kalata B1 (kB1) expressed from the Oak1 gene, MALDI-TOF mass spectrometry was used to examine the cyclization efficiency when mutants of the Oak1 gene were expressed in transgenic Nicotiana benthamiana. (edu.au)