Supramolecular effects in chiral discrimination of clenbuterol enantiomers in RP-HPLC system with helically self-assembled mobile-phase additive. Retention studies and molecular modeling approach

The standard RP-HPLC mode with a conventional octadecylsilica-packed column and the chiral chelate (−)(M)(λ,Λ)-[4,4′-((1S)-methyl-(2R)-propylethanediyldiimino)bis(pent-3-en-2-onato)]nickel(II), with a flexible, helically self-assembled structure, as the chiral selector in a mobile phase of acetonitrile–phosphate buffer was used for direct separation of the enantiomers of clenbuterol (1-(4-amino-3,5-dichlorophenyl)-2-tert-butylaminoethanol), a widely administered broncholidator. Formation of hydrogen-bonded supramolecular associates with diversified stability from two molecules of the helically self-assembled chiral selector and the enantiomers of clenbuterol has been suggested from molecular modeling data. For enantioselective discrimination of solutes, the crucial role of the partly adsorbed chiral selector molecules in the surface phase of proposed RP-HPLC system has been emphasized. Chirality 11:387–393, 1999.