Enantiomer最新文献

Lithocholamide (LCAM) forms inclusion compounds with aliphatic alcohols involving over five carbon atoms. Enantioresolution of the racemic alcohols was studied in channels of the inclusion compounds. X-ray crystallographic study clarified that host assemblies exhibit guest-dependent polymorphism. In each polymorphic crystal, the more longer or bulkier groups the alcohols have, the effective the resolutions become. The inclusion spaces were analyzed by a computed tomographic method, explaining the chiral recognition mechanism from a stereochemical viewpoint.

Chiral recognition of prilocaine was obtained on a 400 MHz 1H-NMR spectrometer by fast diastereomeric interactions with the chiral solvating agent (S)-(+)-2,2,2-trifluoro-1-(9-anthryl) ethanol (TFAE). Assignment of absolute configuration was based on relative field position of the resolved enantiomeric signals. Influence of temperature, substrate concentration and solvating agent to substrate molar ratio on enantiomeric resolution were studied and evaluated. Optimization of experimental conditions provided two significant resolved signals for quantitative use. Utilizing the relative intensities of the resolved enantiomeric signals of the methine proton attached to the stereogenic center assigned to (S)-(+)- and (R)-(-)-prilocaine, the analysis of synthetic mixtures of the enantiomers by the proposed NMR method resulted in assay values which agreed closely with the known quantities of each enantiomer in the tested mixtures. The mean +/- SD recovery values for the (S)-(+)-enantiomer was 99.9 +/- 0.2% of added antipode (n = 7). The optically pure enantiomers were used to establish the minimum amount detected by the proposed NMR spectroscopic method.

While it has been shown that enantiomerization of chiral tri- and tetracoordinate sulfur compounds can take place via a variety of different mechanisms, much less is known concerning the corresponding selenium and tellurium analogues. Studies of the stereochemical integrity of heteroatom centers have often been hampered by the lack of access to, or the instability of, optically active material and most investigations have been made on epimerization reactions, i.e. diastereomer interconversions. By the application of dynamic chromatography on a chiral stationary phase, particularly dynamic LC, however, enantiomerization rates can be estimated without any isolation of the individual enantiomers. In addition to chiroptical methods, we have applied this technique, which involves a comparison of simulated and experimental chromatograms, to the study of some stereolabile S, Se and Te compounds in order to learn more about their enantiomerization mechanisms.

We review recent developments stemming from Stephen Mason's work on the origin of homochirality, focusing in particular on the parity-violating energy difference (PVED) between enantiomers. We summarize results of calculations of the PVED--both our own and those of other groups--which show that the natural enantiomers are indeed favoured by the weak force in most cases. The PVED has become important not only to explain the selection of the L-amino acids in the origin of life, but also as a "molecular footprint" of fundamental physics, leading to proposals to derive values of the Weinberg angle from future spectroscopic measurements of the PVED. The new field of exochirality--chirality outside the Earth--is now taking off, with reports of excesses of L-amino acids in meteorites, and proposals to look for homochirality as a signature of life on other planets and even in other solar systems. If it was indeed the PVED that determined life's handedness, we would expect to find L-amino acids rather than D everywhere in the universe.

The first enantioselective synthesis of the title compound, (3R)-3-amino-5-methyl-2-oxo-hexan-1-ol hydrochloride (9a), an inhibitor of metalloprotein aminopeptidases has been developed from an enantiomerically pure 3-alkylglycerol. The required 3-alkylglycerol was, in turn, prepared by simple Grignard addition to cyclohexylideneglyceraldehyde 1 followed by separation of the epimeric product carbinols by normal column chromatography. The other attractive features of the synthesis was the use of inexpensive reagents and operationally simple synthetic protocols.

Chirality is a prominent feature of most biological processes. The intrinsic asymmetry of receptors, enzymes, and other endogenous macromolecules represents the basis for biological discrimination between the stereoisomeric forms of all foreign compounds in organism. Stereoselectivity and stereospecificity, two principal chiral attributes of enzyme activity, play important role in biotransformation process of drugs and other xenobiotics. The stereospecificity of enzymes leads to the preferential formation of certain enantiomer, the stereoselectivity of enzymes, on the other hand, expresses the preference of one stereoisomer form of substrate for subsequent biotransformation. An approach to the study of different conditions for the formation of the two enantiomers of principal metabolite of potential cytostatic drug oracin in Man in vitro is described. The futile cycle, in which the principal metabolite is converted to the parent drug, is also discussed. The results emphasise the fact that the stereospecificity of enzymes in Man is often distinct from other laboratory species studied.

The chiral selectors (R,R)- and (S,S)-trans-acenaphthen-1,2-dicarboxylic acid bis-allylamide have been synthesized and characterized. The route to the selectors involved synthesis of the trans-dicarboxylic acid via sodiation and carbonation of acenaphthylene, followed by reaction of the bis-acid chloride with allylamine. The racemic bis-allylamide derivative was resolved into its enantiomers by preparative liquid chromatography. The chiral discrimination effect from the (R,R)-selector in the 1H-NMR spectra of a mixture of the enantiomers of O,O'-dibenzoyltartaric acid was studied as a function of temperature. Due to certain ambiguities in the literature concerning the absolute configuration of the (+)-rotating trans-acenaphthen-1,2-dicarboxylic acid, its brucine salt was subjected to X-ray crystallography. This showed the (+)-form to be of (R,R)-configuration.

Novel alpha-(alkoxymethyl)acrylates bearing a chiral substituent, racemic and optically active benzyl alpha-(menthoxymethyl)acrylates ((+)- and (-)-BMnMA), were synthesized and polymerized by radical and anionic methods. The effects of the chiral substituent on the stereoregularity and chiroptical property of the obtained polymers were investigated. 13CNMR spectra of the polymers obtained by anionic polymerization of the racemic monomer showed sharper peaks than that of the radically obtained polymers, indicating that the former polymers possessed higher stereoregularity than the radically obtained polymers. The polymers prepared from optically pure (-)-monomer with anionic initiators had low solubility in common organic solvents. However, the THF-soluble parts were highly isotactic, and exhibited lower specific rotation ([alpha]25(365) = -92 degrees) than those of the monomer ([alpha]25(365) = -226 degrees) and the radically obtained polymer ([alpha]25(365) = -201 degrees). The circular dichroism (CD) spectra of the copolymers prepared from a (+)- and (-)-monomer mixture with various optical purity suggested that the highly isotactic (-)-polymer may possess a chiral helical conformation.