Chiral recognition models

FIGURE 10 Chiral recognition model showing three simultaneous bondings between (5)-methyl-X-(2-naphthyl)alaninato and (5)-iV-(3,5-dinitrobenzoyl)leucine n-propylamine. (From Ref. 9.)... 

Figure 22-26. Proposed chiral recognition model for the more stable (5, 5 )-complex between (5 )-pivalamide of l-(l-naphthyl)ethylamine and the chiral phase of Figure 22.31. (Reprinted from reference 99, with permission.)...

Pirkle,W. H., Pochapsky,T. C. Intermolecular protonjproton] nuclear Overhauser effects in diastereomeric complexes support for a chromatographically derived chiral recognition model,/. Am. Chem. Soc., 1986,108, 5627-5628. 

The use of a simply prepared high efficiency chiral HPLC column capable of separating the enantiomers of thousands of compounds is described, documentation being provided by more than 120 specific examples covering 19 classes of compounds. Chiral recognition models are presented to account for elution orders of the enantiomers. Practical applications of the chiral column, including preparative separations, are described. 

Figure 3. Chiral recognition model showing the relative arrangement for three simultaneous bonding interactions between (K)-CSP 1 and the most retained enantiomer of an alkyl aryl carbinol.

Figure 6, Chiral recognition model showing the relative arrangement between...

Sokolov, V.I. Zefirov, N.S. Enantioselectivity in two-point binding rocking tetrahedron model. Dokl. Akad. Nank. 1991, 319, 1382-1383 (in Russian). Pirkle, W.H. Burke, J.A. Wilson, S.R. X-Ray crystallographic support of a chiral recognition model. J. Am. Chem. Soc. 1989, 111, 9222-9223. 

Enantiopure sulfinimines are ammonia imine synthons useful in the asymmetric synthesis of amines and -amino acid derivatives. Sulfinimines unavailable via the Andersen synthesis (R = H) are prepared hy asymmetric oxidation of the sulfenimines, ArS-N=C(R)PhX, with (+)-( ) or (-)-(1) at -20 to 20 °C in CCI4 (eq 8). Crystallization improves the ee to >95%. The sulfoxide chiral recognition model correctly predicts the configuration of the product. 

Fig. 8 The structure of (a) (5, 5 )-Whelk-01 and the proposed chiral recognition model between (b) the CSP and the most retained enantiomer of amide-type planar tricarbonyl-chromium complexes (adapted from [111])...

Pirkle WH, Welch CJ. Chromatographic and NMR support for a proposed chiral recognition model. J. Chromatogr. A 1994 683 347-353. 

The Binding Sites The Three-Point Chiral Recognition Model... 175... 

THE BINDING SITES THE THREE-POINT CHIRAL RECOGNITION MODEL... 

The three-point attachment rule is largely qualitative and only valid with bimolecular processes (e.g., small Pirkle or ligand-exchange selectors). Another drawback of this model approach is that it cannot be applied to enantiomers with multiple chiral centers. Sundaresan and Abrol [15] proposed a novel chiral recognition model to explain stereoselectivity of substrates with two or three stereo centers requiring a minimum of four or five interaction points. In the same way, Davankov [16] pointed out that much more contact points are realized with chiral cavities of solids. 

If a number of chiral recognition models have been proposed today, early models of the chiral recognition mechanism in chiral HPLC derive from the evolution of the first Pirkle CSP based on the use of a chiral solvating agent [22] followed by spectroscopic investigations [23]. 

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