A GAS-LIQUID-CHROMATOGRAPHIC METHOD FOR STERIC ANALYSIS OF 2-HYDROXY, 3-HYDROXY, AND 2,3-DIHYDROXY ACIDS

A method was developed for assignment of the absolute configuration of oxylipin-derived 2-hydroxy acids, 3-hydroxy acids and 2,3-dihydroxy acids. The monohydroxy acids were converted into diastereomeric N-(propionoxyacyl)-L-phenylalanine-methyl ester (PAP) derivatives by coupling to the methyl ester of L-phenylalanine followed by propionylation, whereas the 2,3-dihydroxy acids were derivatized by treatment with L-phenylalanine methyl ester followed by acetone and perchloric acid, to afford diastereomeric N-(2,3-isopropylidenedioxyacyl)-L-phenyl methyl ester (IAP) derivatives. The PAP and IAP derivatives were readily resolved by capillary gas-liquid chromatography. In addition, the method described allowed steric analysis of 3-hydroxy-3-methylheptanoic acid, a branched chain hydroxy acid derived from the prostaglandin analogue, misoprostol.