Chiral separation with dipeptide-terminated polymeric surfactants: the effect of an extra heteroatom on the polar head group.

Chiral recognition of two binaphthyl derivatives and three benzodiazepines were studied by use of polymeric surfactants in electrokinetic chromatography. Four specific dipeptide terminated (multichiral) micelle polymers were synthesized for this study. These include poly (sodium-N-undecanoyl-L-alanyl-leucinate)-(poly L-SUAL), poly (sodium-N-undecanoyl-L-valyl-leucinate) (poly L-SUVL), poly (sodium-N-undecanoyl-Lseryl-leucinate) (poly L-SUSL), and poly(sodium-N-undecanoyl-L-threonyl-leucinate) (poly L-SUTL). In addition to the chiral separation study, the physicochemical properties (critical micelle concentration and specific rotation) of each polymer were investigated. The molecular weights of the various dipeptide-terminated micelle polymers were determined using analytical ultracentrifugation. These dipeptide-terminated micelle polymers were designed to study the effect of the extra heteroatom at the polar head group of the micelle polymer (i.e., poly L-SUSL compared to poly L-SUAL and poly L-SUTL compared to poly L-SUVL) on the enantiomeric separation of the binaphthyl derivatives and benzodiazepines. The synergistic effect of three chiral centers (poly L-SUTL) provided improved resolution over that of two chiral centered dipeptide-terminated micelle polymer in the case of (+/-)-temazepam, (+/-)-oxazepam, (+/-)-binaphthol, and (+/-)-binaphthol phosphate. The chiral recognition mechanisms in these cases were additionally controlled by the presence of the extra heteroatom located on the polar head group of the micelle polymers.