CHIRAL STATIONARY PHASES DERIVED FROM (-)-ANTI HEAD-TO-HEAD COUMARIN DIMER - PREPARATION, CHARACTERIZATION, AND CHIRAL RECOGNITION ABILITY

A monoamide derived from (-)-anti head-to-head coumarin dimer [(-)-CD] with propylamine has been successfully bonded to silica gel (Lichrospher 100 NH2: Merck) through amide linkage to prepare CS P- 1. Another monoamide derivative CSP-2 was prepared by direct nucleophilic opening of one lactone ring of (-)-CD by Lichospher 100 NH2, followed by hydrolysis of the other lactone. CSP-1 and CSP-2 showed high enantioselectivity to trans-stilbene oxide with separation factors (a) at 2.42 and 2.46, respectively, and the (-)-isomer eluted first. The capacity factor (k') and a decrease with increasing polarity of the eluent (hexane / 2-propanol), indicating that hydrogen bonding plays important role in chiral recognition. CSP-3, obtained by ligand exchange of CSP-2 with CuSO4(aq), resolved DL-tryptophan, DL-tyrosine, and DL-phenylalanine (alpha=k(D)'/k(L)'=1.14-1.33), which all contain aromatic chromophore. The stability difference of the ternary complexes formed with D-isomer and L-isomer is explained by steric hindrance and aromatic pi-pi interactions.