Carotenoids and related compounds. Part 41. Structure of mytiloxanthin and synthesis of a cis-isomer

Abstract

Mytiloxanthin, an acidic pigment from the edible mussel, Mytilus edulis, yielded a diacetate on acetylation. Spectroscopic and other studies on the natural pigment and its derivative showed the former to be 3,3′,8′-trihydroxy-7,8-didehydro-β,κ-caroten-6′-one (1). The absolute stereochemistry 3R, 3′S, 5′R is proposed.

Condensation of the trienedial (23) with the Wittig salt (22) gave the aldehydo ester (24) which was converted into the ethylenedioxy derivative (25). Condensation of (25) with the methyl ketone (16), and removal of the protecting group, gave the β-diketone (27) which reacted with the Wittig salt (29) to yield a desoxy-mytiloxanthin (30). A similar series of reactions based on the methyl ketone (20) led to a cis-isomer of mytiloxanthin.