Hydrophobes chiral

DeTemino, D.M., Hartmeier, W. and Ansorge-Schumacher, M.B. (2005) Entrapment of the alcohol dehydrogenase from Lactobacillus kefir in polyvinyl alcohol for the synthesis of chiral hydrophobic alcohols in organic solvents. Enzyme and Microbial Technology, 36 (1), 3-9. 

This CSP is based on a chiral hydrophobic crown ether ((S)-2,3 4,5-Bis(l,2,3-phenylnaphtho)-l,6,9,12,15,18-hexaoxacycloeicosa-2,4-diene) that is physically adsorbed onto silica particles. Crownpak CR (-) is also available, but less used. Only a few alterations are allowed in the mobile phase for this CSP. Usually it consists of an aqueous perchloric acid solution with an amount of organic modifier. Varying pH or temperature afterwards can modify the obtained separation.Some examples of separations obtained on this CSP are given in Table 6. 

Common chiral stationary phases for gas chromatography have cyclodextrins bonded to a conventional polysiloxane stationary phase.7-8 Cyclodextrins are naturally occurring cyclic sugars. P-Cyclodextrin has a 0.78-nm-diameter opening into a chiral, hydrophobic cavity. The hydroxyls are capped with alkyl groups to decrease the polarity of the faces.9... 

W. Kruse, W. Hummel, and U. Kragl, Alcohol-dehydrogenase-catalyzed production of chiral hydrophobic alcohols. 

For the production of chiral hydrophobic alcohols, FDH from C. boidinii was combined with an NAD+-dependent alcohol dehydrogenase (ADH) from Rhodo-coccus erythropolis. As a first example for the production of hydrophobic alcohols, an enzyme membrane reactor (EMR) was used for the synthesis enantiomerically pure (S)-1 -phenylpropan-2-ol and some related structures out of their corresponding ketones [42]. 

The observed photobehavior of the benzaldehyde-CDx complexes in the solid state is unique and completely different from that of these complexes in aqueous solution and also from that of benzaldehyde 36 in organic solvents. The substantial formation of 4-benzoylbenzaldehyde 38 upon irradiation in (3- and y-CDx cavities indicates that these medium-sized CDx s provide the radical pair within a fairly spacious supercage environment, thus allowing the para-rearrangement (Scheme 13). The formation of practically racemic 37 upon irradiation of the y-CDx complex may also be attributed to the looser orientation of benzaldehyde 36 in the y-CDx cavity than in the (3-CDx cavity. It was thus demonstrated that the chiral hydrophobic cavity of native cyclodextrins not only modifies the photoreactivity of the included guest but also functions as a chiral supramolecular environment for photochirogenesis, albeit resulting in only modest ee%. 

Crystals of a-glycine float on the surface of the solution, with one of the two flat (010) or (010) faces exposed to solution. If one enantiomer of a chiral hydrophobic amino acid (leucine or phenylalanine, for example) is now added to the solution, the crystal will become oriented so that the face that occludes amino acids of opposite chitrality is exposed to solution. D-amino acids are only incorporated in crystals with the 010 face exposed to solution, while L-amino acids only interact with the exposed (010) face. Therefore, if a floating crystal with the (010) face exposed to solution is presented with a solution of DL amino acids, the crystal will bind D-amino acids and will enrich the solution with respect to L-amino acids. If, for example, the underside of a film of a resolved amino acid with a long hydrophobic side chain [such as (5)-a-aminooctanoic acid] is exposed to a solution of a racemic mixture of amino acids, some optical resolution will occur by the principles just described (see Reference 64). 

Tubular shaped superstructures formed by certain amphiphiles in water aggregate through intermediate helical ribbon structures.Since these amphiphiles feature a polar head in combination with a chiral hydrophobic group, the sol-gel... 

Baba N, Matsumura Y, Sugimoto T (1978) Asymmetric reduction of aryl trifluoromethyl ketones with an achiral NADH model compound in a chiral hydrophobic binding site of sodium cholate micelle,... 

Figure 11 Structures of foldamer receptors and their guests, (a) OUgophenyl-ethynylene foldamers (top left) and chiral hydrophobic guests, (b) Oligoaryl hydrazide foldamers (top) and a disaccharide guest (bottom).

The LACS system has been successfully applied to asymmetric catalysis. Catalytic asymmetric ring-opening reactions of meso epoxides with aromatic amines proceeded smoothly in the presence of 1 mol% of Sc(DS)3 and 1.2 mol% of chiral bipyridine ligand (3) in water to give P-amino alcohols in high yields with excellent enantioselectivities (Scheme 12.75) [172]. It has been noted that excellent chiral hydrophobic environments have been created in water. 

Kudo and coworkers developed a poly(ethylene glycol)-polystyrene (PEG-PS) resin supported peptide catalyst possessing poly-leucine as a chiral hydrophobic... 

An even bigger chiral hydrophobic moiety is present in catalyst 11 (Figure 24.5)... 

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