The synthesis of nonracemic yields of hexa-, hepta-, octa-, and nonhelicene with circular light was observed, and the structural and wavelength dependence of the induced optical yields was examined. The results obtained, together with a detailed consideration of the mechanism of helicene synthesis from the parent diarylolefins, indicate that the induced ...

The enantioselective synthesis of the spiroketal/macrolide natural product milbemycin ?₃ has been achieved in 22 steps and 2.8% overall yield from an achiral dienoate. The spiroketal ring system was installed by three sequential asymmetric hydrations followed by sprioketalization. Both the absolute and relative ...

Asymmetric autocatalysis is a reaction in which chiral product acts as a chiral catalyst for its own production. Pyrimidyl alkanol was found to act as asymmetric autocatalysts with significant amplification of enantiopurity in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Symmetry breaking is observed in the reaction ...

Formal enantioselective total synthesis of schulzeines A-C was accomplished, featuring highly efficient Pd-catalyzed asymmetric allylic amination using novel diphosphonite ligands (BOPs) to provide 1-vinyltetrahydroisoquinoline key intermediates, as well as Ru-catalyzed ring-closing metathesis reaction to construct the key tricyclic cores in enantiopure ...

A de novo approach to the formal total synthesis of the macrolide natural product (�)-virginiamycin M₂ has been achieved via a convergent approach. The absolute and relative stereochemistry of the non-peptide portion of (�)-virginiamycin M₂ was introduced by two Sharpless asymmetric ...

The first asymmetric total synthesis of fumimycin was accomplished. As a key step, a 1,2-addition of methyl Grignard reagents to ketimines with quinine as additive was employed. The absolute configuration of (+)-fumimycin was determined by CD-spectroscopy combined with time-dependent density functional calculations. PMID:21031188

The first nonracemic synthesis of (+)-geranyllinaloisocyanide, starting with (-)-lactic acid methyl ester, has been accomplished by exploiting a [3.3] sigmatropic rearrangement of allyl cyanate. The synthesis enables assignment of the S configuration of the C(3) isocyano substituted, quaternary stereogenic center in natural geranyllinaloisocyanide. ...

Published data on the synthesis, absolute configurations and biological properties of chiral hydroxy phosphonates are generalised and described systematically. Examples of asymmetric synthesis of hydroxy phosphonates by the phospho-aldol reaction, reduction of keto phosphonates, chemo-enzymatic approach, and so on ...

A new method was developed for the enantiomeric resolution of asymmetric derivatives of 3,7-dimethylenebicyclo(3.3.1)nonane by liquid chromatography on a chiral sorbent, i.e., silica gel impregnated with silver d-camphor-10-sulfonate. During transannular electrophilic cyclization and photocyclization the enantiomeric dienes, the absolute configurations of ...

New methods for the stereocontrolled synthesis of octahedral metal complexes are needed in order to fully exploit the stereochemical richness of the octahedron in the fields of catalysis, materials sciences, and life sciences. Whereas a large body of work exists regarding the diastereoselective coordination chemistry with chiral ligands, such efforts are restricted to certain ...

The first asymmetric total synthesis of (+)-perophoramidine has been achieved in 17 steps with ?11% overall yield. The key step relies on an asymmetric biomimetic Diels-Alder reaction between the in situ-generated chiral diene T-24 and the substituted tryptamine 23 to assemble the core structure 27a in a highly efficient way. An ...

An enantioselective and diastereocontrolled approach to 8a-epi-d-swainsonine has been developed from achiral furfural. The key step to this synthesis was a one-pot procedure for the hydrogenolytic removal of two protecting groups and two intramolecular reductive amination reactions. The absolute stereochemistry was introduced by ...

The enantioselective synthesis of three structurally distinct classes of lignan from a single, aza-Claisen-derived, chiral morpholine amide is reported. The class of lignan formed is dependent on the substitution pattern in the aryl rings and choice of protecting group on a key benzylic hydroxyl group. The methodology has been used to asymmetrically ...

... Title : (+)-Desoxoprosopinine: A Model for the Total Asymmetric Synthesis of Prosopis Alkaloids. Descriptive Note : Master's thesis. ...

Optically active alanine synthesis from oxaloaceti acid by hydrogenolytic asymmetric transamination,

The HIV-1 protease is a validated drug target for the design of antiretroviral drugs to combat AIDS. We previously established the sulfoximine functionality as a valid transition state mimetic (TSM) in the HIV-1 protease inhibitors (PI) design and have identified a lead pseudosymmetric compound with nanomolar enzymatic inhibitory activity. Here, we report the asymmetric ...

{alpha}-Amino phosphonic acids 3 are interesting compounds in the design of enzyme inhibitors. The concept of mimicking tetrahedral transition states of enzyme-medicated peptide bond hydrolysis previously led to the successful design and synthesis of phosphonamide-containing peptides as a promising new class of proteinase inhibitors. It is not surprising that the ...

Enantioselective syntheses of the alkaloids (?)-aurantioclavine, (+)-amurensinine, (?)-lobeline, and (?)- and (+)-sedamine are described. The syntheses demonstrate the effectiveness of the Pd-catalyzed asymmetric oxidation of secondary alcohols in diverse contexts and the ability of this methodology to set the absolute configuration of multiple ...

The concise and enantioselective total syntheses of (-)-trigonoliimines A, B, and C are described. Our unified strategy to all three natural products is based on asymmetric oxidation and reorganization of a single bistryptamine, a sequence of transformations with possible biogenetic relevance. We revise the absolute stereochemistry of (-)-trigonoliimines ...

... Descriptors : (*POLYAMIDE PLASTICS, *STEREOCHEMISTRY), (*POLYMERS, STEREOCHEMISTRY), SYNTHESIS(CHEMISTRY), ENZYMES ...

Chiral methyl chiral lactic acid, a molecule which has a chiral methyl group because of the specific incorporation of the three isotopes of hydrogen, has been synthesized by a sequence of simple, convenient steps culminating in catalytic asymmetric hydrogenation. Moreover, the method allows for the preparation of all 12 possible isomers which arise from the permutation of the ...

The achiral hydrocarbon tetraphenylethylene crystallizes in enantiomorphous forms (chiral space group: P21) to afford right- and left-handed hemihedral crystals, which can be recognized by solid-state circular dichroism spectroscopic analysis. Chiral organic crystals of tetraphenylethylene mediated enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde to give, in conjunction ...

A total synthesis of the fostriecin has been achieved in 24 steps from enyne 11. The lactone moiety was installed by a Leighton allylation and Grubbs ring-closing metathesis (RCM) reaction. The highly reactive Z,Z,E-triene moiety was installed via a late stage Suzuki-Miyaura cross coupling of a remarkably stable Z-vinyl boronate. The relative and absolute ...

The nonenolide hypocreolide A was isolated from culture filtrates of the ascomycete Hypocrea lactea. It exhibits moderate antimicrobial activity against various tested fungi and bacteria. Since neither the relative nor the absolute stereochemistry of the compound could be initially assigned, a stereochemically flexible total synthesis was developed. The ...

Total asymmetric synthesis of two components of Panax ginseng showing antitumor activity, i.e., (3R,9R,10R)- and (3S,9R,10R)-Panaxytriol and of both enantiomers of Falcarinol was accomplished. Due to the fact that the synthetic strategy was based on enantioconvergent biotransformations, the occurrence of any undesired stereoisomer was entirely avoided. The ...

The asymmetric synthesis of all four of the known natural phlegmarines and one synthetic derivative has been accomplished in 19-22 steps from 4-methoxy-3-(triisopropylsilyl)pyridine. Chiral N-acylpyridinium salt chemistry was used twice to set the stereocenters at the C-9 and C-2' positions of the phlegmarine skeleton. Key reactions include the use of a ...

The asymmetric synthesis of the oxindole alkaloid horsfiline is described. A palladium-catalyzed asymmetric allylic alkylation (AAA) is used to set the spiro(pyrrolidine-oxindole) stereogenic center.

SummaryAn overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed.

Hexose sugars play a fundamental role in vital biochemical processes and their biosynthesis is achieved through enzyme-catalyzed pathways. Herein we disclose the ability of amino acids to catalyze the asymmetric neogenesis of carbohydrates by sequential cross-aldol reactions. The amino acids mediate the asymmetric de novo synthesis of ...

Horeau's method furnishes the correct absolute configuration for those sesquiterpene lactones where one methylene group is adjacent to the asymmetric carbon bearing the hydroxyl group. In 6-hydroxylated pseudoguaianolides a high optical yield can be empir...

Oct 12, 2010 ... Synthesis of asymmetric tetracarboxylic acids and dianhydrides. Researchers at NASA's Glenn Research Center have patented a process related ...

The asymmetric total synthesis of (+)-isatisine A has been accomplished commencing with a Lewis acid-catalyzed cyclization of homochiral (S)-vinylcyclopropane diester and N-tosylindole-2-carboxaldehyde to construct the tetrahydrofuran ring. A palladium-catalyzed oxidative decarboxylation was utilized to obtain the dihydrofuran required for the subsequent ...

An effective, asymmetric total synthesis of the antitumor antibiotic (-)-okilactomycin (1) and assignment of the absolute configuration, has been achieved exploiting a convergent strategy. Highlights of the synthesis include: a diastereoselective oxy-Cope rearrangement/oxidation sequence to install the C(1) and ...

A synthetic route to paleic acid 1, antimicrobial agent effective against Mannheimia haemolytica and Pasteurella multocida, has been established. The absolute configuration of the secondary hydroxyl group was controlled by a catalytic asymmetric alkylation of an aldehyde using a chiral titanium sulfonamide complex and the cis double bond was installed ...

Chiral phosphonyl imines attached with N-isopropyl protection group were found to react with lithium glycine enolates under convenient conditions to give alpha,beta-diamino esters. Thirteen examples have been examined in good to excellent chemical yields (85-97%) diastereoselectivity (up to 99% de). By treating with HBr at room temperature, the chiral auxiliary can be readily removed and recycled. ...

Chiral nonracemic thiomorpholines have been synthesized in four to six steps from limonene or achiral alkenes using alpha-methylbenzylamine to control absolute stereochemistry. These aminosulfides have been used to generate sulfur ylides, which have been applied in the asymmetric epoxidation of aldehydes as easily recoverable catalysts. Excellent yields ...

Asymmetric scandium(III)-catalyzed rearrangement of 3-allyloxyflavones was utilized to prepare chiral, nonracemic 3,4-chromanediones in high yields and enantioselectivities. These synthetic intermediates have been further elaborated to novel heterocyclic frameworks including angular pyrazines and dihydropyrazines. The absolute configuration of ...

Asymmetric scandium (III)-catalyzed rearrangement of 3-allyloxyflavones was utilized to prepare chiral, non-racemic 3,4-chromanediones in high yields and enantioselectivities. These synthetic intermediates have been further elaborated to novel heterocyclic frameworks including angular pyrazines and dihydropyrazines. The absolute configuration of ...

We solve numerically a kinetic model of chiral polymerization in systems closed to matter and energy flow, paying special attention to its ability to amplify the small initial enantiomeric excesses due to the internal and unavoidable statistical fluctuations. The reaction steps are assumed to be reversible, implying a thermodynamic constraint among some of the rate constants. ...

Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical l-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which interstellar ultraviolet (UV) circularly polarized light (CPL) induces ...

Mander reductive alkylation of methyl 2-methoxybenzoate with prenyl bromide and hydrolysis of the enol ether afforded methyl 6-oxo-1-prenyl-2-cyclohexenecarboxylate. This was converted in five steps (reduction of the ketone, saponification, iodolactonization, ozonolysis and intramolecular aldol reaction) to a spiro lactone cyclopentenal. An efficient first synthesis of ...

In the presence of a catalytic amount of Cu(OTf)(2)-chiral diamine 3e complex, N-acylimino esters reacted with silyl enol ethers to afford the corresponding Mannich-type adducts in high yields with high enantioselectivities. A wide variety of silyl enol ethers derived from ketones, as well as esters and thioesters, reacted smoothly. In the reactions of alpha-substituted silyl enol ethers ...

The paper presents a population synthesis performed on absolute spectrophotometry for the central 31

Iodocyclization of sulfinimine-derived enantiopure homoallylic sulfonamides affords trans-2,5-disubstituted 3-iodopyrrolidines and represents valuable methodology for the asymmetric synthesis of this important heterocyclic ring system.

An organocatalytic asymmetric Michael addition reaction of 3-substituted oxindoles to protected 2-amino-1-nitroethenes has been developed. The reaction is catalyzed by a simple and readily available amino-indanol derivative and affords the desired products in very high yields (up to 99%) with excellent diastereoselectivities (up to >99:1) and very good enantioselectivities ...

... new methods for asymmetric synthesis and discovering new liquid crystal materials. ... we have made a number of chiral liquid crystals and related ...

We report a method to determine the absolute configuration of alpha-amino acids by exciton coupled circular dichroism (ECCD). Naturally occurring amino acids were successfully derivatized with 2-bromomethylquinoline. Complexation of these conformationally flexible ligands with Cu(II) salts yielded defined propeller-like structures. The direction of the twist (i.e., the ...

Juvenile hormone (JH) undergoes metabolic degradation by two major pathways involving JH esterase and JH epoxide hydrolase (EH). While considerable effort has been focussed on the study of JH esterase and the development of inhibitors for this enzyme, much less has been reported on the study of JH-EH. In this work, the asymmetric synthesis of two classes ...

Catalytic asymmetric synthesis of neolignan natural products (-)-epi-conocarpan and (+)-conocarpan has been achieved by exploiting an enantio- and diastereoselective intramolecular C-H insertion reaction to construct a cis-2-aryl-2,3-dihydrobenzofuran ring system as a key step. The C-H insertion reaction of 5-bromoaryldiazoacetate catalyzed by ...

Catalytic enantioselective 1,4-additions and tandem 1,4-addition-aldol reactions of dialkylzinc reagents to cyclopentene-3,5-dione monoacetals in the presence of an in situ generated Cu(OTf)(2)/chiral phosphoramidite catalyst result in highly functionalized cyclopentane building blocks with ee's up to 97%. A new synthesis of cyclopentene-3,5-dione monoacetals is presented as ...

A method and apparatus for converting the absolute pressure of a pressurized fluid to a differential pressure indicating the fluid pressure relative to a reference pressure; The pressurized fluid is directed asymmetrically into a laminar proportional ampl...

For the last ten years our group has been working toward the development of an asymmetric hydration approach to polyketide natural products based on the regioselective hydration of di- and tri-enoates. Key to the success of this approach is the recognition that both high regiocontrol and asymmetric induction could be obtained by the use of a Sharpless ...

Transmission of the iodomethylate of 1,2-dimethyl-4-piperidone by (S)-sec-butylamine gives 1-(S-sec-butyl)-2S-methyl-4-piperidone in 33% optical yield while transamination by (S)-1-methyl-2-phenylethylamine gives a 1:1 diastereomeric mixture of 1-(1-methyl-2-phenylethyl)-2-methyl-4-piperidone. The decrease in the optical yield is related to the facile opening of the piperidone ring at the C-N bond ...

cis-Dihydrodiol metabolites were obtained from dioxygenase-catalysed asymmetric dihydroxylations of five monocyclic (azabiphenyl) and four tricyclic (azaphenanthrene) azaarene substrates. Enantiopurity values and absolute configuration assignments were determined using a combination of stereochemical correlation, X-ray crystallography and spectroscopy ...

A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves ...

A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves ...

Chiral phosphonyl imines attached by 1-naphthyl protection group were found to react with lithium ester enolates smoothly and give chiral beta-amino esters in good yields (70-88%) and up to excellent diastereoselectivity (>99:1 dr). Triisopropoxytitanium (IV) chloride was found to enhance diastereoseletivity when used as the Lewis acid promoter. The chiral auxiliary can be readily removed by ...

The absolute configuration of the title compound, C₁₄H₁₇NO₂, was assigned from the synthesis. There are two mol�ecules in the asymmetric unit. Their geometries are very similar and corresponding bond lengths are almost identical [mean deviation for all non-H atoms = ...

... Research topics presented in this report are: General Discussion; On the absolute stability of sampled-data control systems; On the absolute ...

During the funding period, we have made significant progress both in the developing new methods for asymmetric synthesis and discovering new liquid crystal materials. Over a dozen of papers have been published or in press in several journals (J. Am. Chem....

The first enantioselective total synthesis of tangutorine has been achieved, wherein a Pd-catalyzed asymmetric allylic amination using a chiral diaminophosphine oxide (DIAPHOX) preligand was the key step. PMID:20092264

SummaryEnantiomerically pure tertiary thiols provide a major synthetic challenge, and despite the importance of chiral sulfur-containing compounds in biological and medicinal chemistry, surprisingly few effective methods are suitable for the asymmetric synthesis of tertiary thiols. This review details the most practical of the methods available.

The first asymmetric synthesis of the antihistaminic drug mequitazine is reported. Our approach started from quinine, a Cinchona alkaloid, whose chiral information was exploited for setting up the stereogenic center of (+)-mequitazine. PMID:21657243

An asymmetric synthesis of (+)-castanospermine is presented in which enol ether metathesis-hydroboration/oxidation is used for stereoselective installation of the trans-trans hydroxyl groups on the piperidine ring of the alkaloid. PMID:19421437

A Ramberg�B�cklund reaction was employed to form the macrocyclic carbon skeleton of the marine natural products cylindrocyclophanes A and F in an asymmetric synthesis of these target molecules.

... Accession Number : ADP008462. Title : Asymmetric Synthesis of B-Hydroxy LA-Amino Acids Using Aldolase from Pseudomonas SP,. ...

We describe herein an asymmetric synthesis of ageliferin. A Mn(III)-mediated oxidative radical cyclization reaction was used as the key step to construct the core skeleton of this pyrrole-imidazole dimer. This approach resembles the biogenic [4 + 2] dimerization in an intramolecular fashion. PMID:21888421