6-Methoxy-2-(4-substituted phenyl)benzoxazoles as Fluorescent Chiral Derivatization Reagents for Carboxylic Acid Enantiomers

Abstract

Three chiral derivatization reagents: 2-[4-(_L-leucyl)aminophenyl]-6-methoxybenzoxazole, 2-[4-(_D-phenylglycyl)amino-phenyl]-6-methoxybenzoxazole, and 2-[4-(_L-phenylalanyl)aminophenyl]-6-methoxybenzoxazole, have been synthesized to permit separation of carboxylic acid enantiomers by high-performance liquid chromatography. Enantiomeric carboxylic acids were readily condensed with the chiral reagents in the presence of 2, 2′-dipyridyl disulfide and triphenylphosphine. The diastereometric amides formed were separated on a normal-phase column, and were sensitively detected fluorometrically at 375nm, with excitation at 330nm. The detection limit of _L-PheBOX derivative of 2-phenylpropionic acid was 70fmol at a signal-to-noise ratio of 3.