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.

Chemical and Morphological Characterization of Costa Rican Papaya (Carica papaya L.) Hybrids and Lines with Particular Focus on Their Genuine Carotenoid Profiles

“…Furthermore, various cryptoxanthin epoxides (compounds 2 , 3 , and 5 ) were tentatively identified by comparison of their UV–vis absorption and mass spectral characteristics to those reported previously. , Whereas the cryptoxanthin-5,6-epoxide was predominantly found in the yellow-fleshed types, cryptoxanthin-5,8-epoxides ( syn cryptoflavines), the furanoid oxide derivatives of the 5,6-epoxide, were detected in trace amounts in all genotypes investigated. However, cryptoxanthin-5,6-epoxide was reported to readily undergo a furanoid rearrangement to form the cryptoxanthin-5,8-epoxide during the analytical workup procedure. , The configuration at the C5 atom remains unchanged in the course of the structural reorganization, whereas at C8 both the 8 R and 8 S configurations were found for various carotenoid 5,8-epoxides by Deli and Ösz . Both showing an identical, typical UV–vis and mass spectral behavior of β-cryptoxanthin-5,8-epoxides, , compounds 3 and 5 might represent C8 epimers of such epoxides.…”

“…However, cryptoxanthin-5,6-epoxide was reported to readily undergo a furanoid rearrangement to form the cryptoxanthin-5,8-epoxide during the analytical workup procedure. 35,36 The configuration at the C5 atom remains unchanged in the course of the structural reorganization, whereas at C8 both the 8R and 8S configurations were found for various carotenoid 5,8-epoxides by Deli and O ̈sz. 35 Both showing an identical, typical UV−vis and mass spectral behavior of β-cryptoxanthin-5,8-epoxides, 35,36 compounds 3 and 5 might represent C8 epimers of such epoxides.…”

19,19′-Diacyloxy Signature: An Atypical Level of Structural Evolution in Carotenoid Pigments

“…Furthermore, NOESY spectrum was essential to demonstrate the all - trans geometry of the double bonds, displaying cross-peaks of H8–H10, H11–H20, H8′–H10′, and H11′-H20′, which confirmed the trans configuration of the trisubstituted alkenes in the polyene chain. The absolute and relative configuration of the stereogenic centers of both terminal groups was proposed on the basis of the structures of well-defined naturally occurring carotenoids and the delineated biosynthetic origin from lutein. Thus, both the β- and ε-ring exhibit a trans relationship between the hydroxyl group at C3 and the substituents at C6.…”