Selectivity enantiomeric

The predominance of L-amino acids in biological systems is one of life s most intriguing features. Prebiotic syntheses of amino acids would be expected to produce equal amounts of L- and D-enantiomers. Some kind of enantiomeric selection process must have intervened to select L-amino acids over their D-connterparts as the constituents of proteins. Was it random chance that chose L- over D-isomers ... 

Chiral crown ethers possessing two chiral cw-l-phenylcyclohexane-l,2-diol moieties as well as a p-(2,4-dinitrophenylazo)phenol chromophore were prepared and with chiral alkylamines were observed to show enantiomeric selectivity <96JCS(P1)383>. 

The nitrilase from a nnmber of strains of Pseudomonas sp. mediated an enantiomerically selective hydrolysis of racemic 0-acetylmandelonitrile to o-acetytmandelic acid R-( )-acetylmandelic acid (Layh et al. 1992). 

Garrison AW, P Schmitt, O Martens, A Kettrup (1996) Enantiomeric selectivity in the environmental degradation of dichloroprop as determined by high-performance capillary electrophoresis. Environ Sci Technol 30 2449-2455. 

Besides taxodione and taxodone, these synthetic approaches have been conveniently modified to synthesize other related derivatives such as ferruginols, sugiols, and royleanones.51-52,56-57,60-62 In addition, the enantiomeric-selective synthesis of (+ )-taxodione 1 has been reported using (—)-abietic acid as the starting material63 or with a chiral ligand in the polyene cyclization process.64... 

The LpxC inhibitory and antibacterial activity of L-573,655 was not satisfactory. In an attempt to measure the enantiomeric selective activity of... 

Asymmetric carboxylation was also achieved by use of 7r-allyltitanium complexes bearing chiral ligands (Scheme 13).26 The enantiomeric selectivity was significantly influenced by the chiral auxiliary ligands used. In the case of 45, the chiral /3,7-unsaturated carboxylic acid 46 was obtained with excellent ee.27,28... 

The sense of diastereoselectivity in the dynamic kinetic resolution of 2-substi-tuted / -keto esters depends on the structure of the keto ester. The ruthenium catalyst with atropisomeric diphosphine ligands (binap, MeO-biphep, synphos, etc.) induced syn-products in high diastereomeric and enantiomeric selectivity in the dynamic kinetic resolution of / -keto esters with an a-amido or carbamate moiety (Table 21.21) [119-121, 123, 125-127]. In contrast to the above examples of a-amido-/ -keto esters, the TsOH or HC1 salt of /l-keto esters with an a-amino unit were hydrogenated with excellent cwti-selectivity using ruthenium-atropiso-... 

Kinetic resolution ofallylic alcohols. The (R)- and (S)-BINAP-Ru diacetate complexes can resolve racemic allylic alcohols, both acyclic and cyclic, with high enantiomeric selectivity. Thus hydrogenation of ( )-2 catalyzed by (S)-l at 76% conversion provides (S)-2 (>99% ee) and anti-3 (49 1, 39% ee). Hydrogenation of (S)-2 catalyzed by either (R)- or (S)-l provides anti-3 (>23 1). Similar results obtain with ( )-4. 

Trigonal ML3 metal complexes exist as optically active pairs. The complexes can show enantiomeric selective binding to DNA and in excited state quenching.<34) One of the optically active enantiomers of RuLj complexes binds more strongly to chiral DNA than does the other enantiomer. In luminescence quenching of racemic mixtures of rare earth complexes, resolved ML3 complexes stereoselectively quench one of the rare earth species over the other. 35-39 Such chiral recognition promises to be a useful fundamental and practical tool in spectroscopy and biochemistry. 

S. Ramaswamy, R. A. H. F. Hui, J. B. Jones, Enantiomerically Selective Pig Liver Esterase-Catalysed Hydrolyses of Racemic Allenic Esters , J. Chem. Soc., Chem. Commun. 1986, 1545-1546. 

Thus on the one hand, from a series of approaches (entries 1-4,6-8,11), Barton and co-workets describe 3 modes of binding for this complex, some of them with enantiomeric selectivity ... 

Yamamura M, Suzuki S, Hattori T et al (2010) Subunit composition of hinokiresinol synthase controls enantiomeric selectivity in hinokiresinol formation. Org Biomol Chem 8 1106-1110 Hirose Y, Oishi N, Nagaki H et al (1965) The structure of hinokiresinol. Tetrahedron Lett 41 3665-3668... 

Aires-de-Sousa, J. and Gasteiger, J. (2002) Prediction of enantiomeric selectivity in chromatography. Application of conformation-dependent and conformation-independent descriptors of molecular chirality. J. Mol. Graphics Mod. 20, 373-388. 

The photoelectrochemical synthesis of amino acids from simple molecules has also been reported. Low efficiencies were observed in the conversion of mixtures of methane, ammonia and water to several amino acids on platinized TiOz Amino acids and peptides were reported when glucose replaced methane as the carbon source in a parallel experiment Higher quantum efficiencies (20-40%) were observed in the conversion of alpha-keto acids or alpha-hydroxy acids to the corresponding alpha-amino acids Moderate levels of enantiomeric selectivity (optical yields of about 50%) were reported when chiral starting materials were employed. Photoinduced Michael-like reactions were observed when alpha, beta unsaturated acids were used as substrates for the amino acid synthesis... 

Attachment of bulky chiral barriers to achieve enantiomeric selection is exemplified by ligands (61),204 (63)69 and (64).19 Ligands of type (61) are especially efficient chiral compounds with binap-thyl hinges . The orientation of the binaphthyl rings for (61) is shown more explicitly in (62).234 With optically pure (61), complete enantiomeric separation of ammonium salt racemates such as (67) is obtained.235-237 The structure has been determined crystallographically for the less stable d form of the PF6- salt of (67) with the (S,S) host (61). The results indicate that the receptor, substrate, counterion and solvent have undergone several steric concessions in order to relieve the strain imposed on the system by the visit of an unwanted guest.238... 

Epoxide hydrolase has been found to exhibit a marked enantiomeric selectivity toward the chiral K-region arene oxides 28,29, and 3-bromophen-anthrene 9,10-oxide (363) in detergent solutions. A 40-fold difference in the rate... 

---