Bioactivity of cis and dicis isomers of vitamin A esters

In order to declare the accurate vitamin A effectiveness of foodstuffs and synthetic vitamin A preparations, the biological activity of the individual isomers has to be known. Total activity is expressed as all-trans vitamin A equivalents which are calculated by multiplication of analytical content of each isomer with the corresponding biopotency factor. The biological activity of four cis and three or four dicis isomers of vitamin A acetate and palmitate was determined by means of rat vaginal smear assays. The purity of the compounds, the content and isomerisation in stock solutions were checked by HPLC methods prior to their dilution and application to the experimental animals. Based on analytical contents the following activities were found for vitamin A acetate isomers: all-trans 1.00, 13-cis 0.76, 11-cis 0.31, 9-cis 0.19, 7-cis 0.18, 9,13-dicis 0.16, 11,13-dicis 0.18, 9,11-dicis approx. 0.03. The corresponding values for vitamin A palmitate were: all-trans 1.00, 13-cis 0.73, 11-cis 0.34, 9-cis 0.19, 7-cis 0.14, 9,13-dicis 0.21, 11,13-dicis 0.20, 9,11-dicis approx. 0.04, 7,11-dicis approx. 0.12. The vitamin A activity of the cis isomers ranged from about 0.75 for 13-cis to about 0.05 for 9,11-dicis. For the cis series, a biopotency relationship depending on the distance between the beta-ionone ring system and the cis configuration could be observed.