Caroteniod 5,6-, 5,8- and 3,6-epoxides

Abstract

The isolation, semisynthesis and structure elucidation of carotenoid 5,6-, 5,8- and 3,6-epoxides as well as their derivatives are discussed in detail. This review gives a brief summary of the plausible biosynthetic transformations of the 5,6- epoxy-β-ring. A wide variety of carotenoid end-groups can be obtained from 5,6-epoxy carotenoids. In order to get information on the enzyme activities and regulation of the biosynthetic pathway of carotenoids some of the intermediate steps of these transformations were investigated (e.g. formation of allenic, κ- and γ-end-groups as well as ring opening reactions). The ring opening of the 3-hydroxy-5,6-epoxy end group, resulting in the formation of 3,5,6- trihydroxy compounds, was studied in detail in order to obtain evidence for the proposed reaction mechanisms of the two different biosynthetic routes (acid or enzyme catalysis) which also explain the configurations at the C(5) and C(6) atoms.