Chiral Discrimination of Fructo-Oligosaccharides Toward Amino Acid Derivatives by Induced-Fitting Chiral Recognition.

Among linear permethylated fructo-oligosaccharides containing various monosaccharide moieties at the reducing terminal, MeSorFru33333, MeGlc66666Fru33333, and MeFruNys showed high degrees of enantioselectivity toward binding some amino acid 2-propyl ester salts. In particular MeFruNys indicated remarkable chiral discrimination toward [ValOPri]+ (IR/IS-Dn = 0.14 corresponding to −ΔΔGenan = 1.2 kcal mol−1, S-selectivity) and [PheOPri ]+ (IR/IS-Dn = 0.18 corresponding to −ΔΔGenan = 1.0 kcal mol−1, S-selectivity). The results of FAB mass, UV–visible spectrometries, thermodynamic parameters, and NMR induced shifts provided evidence for the chiral discrimination of MeFruNys toward amino acid ester salts in the “induced-fitting chiral recognition system”: the conformation of MeFruNys drastically changes from a linear to a pseudo-ring structure with a given cation such as a chiral organic ammonium ion or an alkali metallic ion. This is the first example of chiral discrimination of linear oligosaccharide derivatives toward amino acid derivatives based on the induced-fitting chiral recognition mechanism.