HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND PROTON NUCLEAR MAGNETIC-RESONANCE OF ELEVEN ISOMERS OF METHYL RETINOATE

Methyl all-trans-retinoate was isomerized with fluorescent light in either heptane, acetonitrile or dimethyl sulfoxide. Eleven isomers of methyl retinoate were produced during irradiation in dimethyl sulfoxide. The isomers were purified by high-performance liquid chromatography (HPLC) using reversed-phase columns and were characterized by proton nuclear magnetic resonance and chemical methods. They were identified as the methyl esters of a 13-cis-(5 → 10)-photocyclized isomer, the 9,11,13,-tri-cis-, 11,13-di-cis-, 7,13-di-cis, 13-cis-, 9,13-di-cis-, a 13-trans-(5 → 10)- photocyclized isomer, the 11-cis-, 9-cis-, 7-cis- and all-rans-isomers of retinoic acid. After prolonged irradiation in polar solvents, the two photocyclized isomers accumulated until they were the only two obsevable isomers in the HPLC pattern. The rate of disappearance of the all-trans-isomer increased as solvent polarity increased. Only seven isomers were produced by irradiation in heptane. © 1979.