Abstract # A-14
ENANTIOMERIC RESOLUTION ON HPLC CHIRAL STATIONARY PHASES: INFLUENCE OF AROMATIC INTERACTIONS ON ELUTION ORDER A.A.N NguyenPho1,2, C.A. Brunner1, N. M. Roscher2 and Thomas D. Doyle1. 1CDER, FDA, Washington, DC and 2Department of Chemistry, The American University, Washington, DC
Enantiomeric amide and ureide derivatives of 
-methylbenzylamine were resolved on HPLC chiral stationary phases (CSPs), under normal-phase conditions, with selectivities() as high as 2.06. Three CSPs were studied, chosen to provide (1) pi-acidic 3,5-dinitro-phenyl, (2) pi-basic 1-naphthyl and (3) both of the above functionalities. The derivatives were synthesized so as to incorporate a range of pi-acidic and basic groups on the chiral solutes. Both selectivities and capacity factors (k') correlated strongly and directly with the availability of complementary solute:CSP aromatic interactions. The enantiomeric elution order of all the derivatives was constant on a given CSP, except that three reversals of this order were observed. Each case of reversal involved the most strongly pi-acidic or pi-basic derivative in the solute series; two occurred on the CSP of type (3), where the possibility of alternative interaction mechanisms is apparent. These results are consistent with the presence of competing chira
recognition mechanisms, and confirm the importance of aromatic interactions in such mechanisms.