Studies on the Catalyzed Interconversions of Vitamin A Derivatives

Article abstract of DOI:10.1021/ja00347a058

The kinetics of the I2-catalyzed isomerization of the retinal isomers were studied.The all-trans isomer formed 13-cis-retinal rapidly with a rate constant 1.9E-4 s^-1.The reverse reaction occurred with a rate constant of 4.5E-4 s^-1.The 11-cis isomer was first converted to all-trans-retinal with a rate constant of 3.1E-4 s^-1, although the 13-cis isomer was also rapidly formed.The 9-cis isomer was isomerized to the 9-cis, 13-cis isomer before the other isomers were generated and the 13-cis isomer was converted to its all-trans congener prior to the formation of the other isomers.Similar results appear to occur when other methods of catalysis are used.This isomerization about the C₁₃-C₁₄ double bond appears to be kinetically favored event, eliminating the possibility that 11-cis might be a kinetic product formed from the all-trans isomer.At equilibrium, only 0.1percent of 11-cis-retinal is found.Equilibration of all-trans-retinol palmitate also generated very little of the 11-cis-isomer (