Carotenoids and related compounds. Part 42. Structure of isomytiloxanthin

Abstract

Isomytiloxanthin, a pigment from the edible mussel Mytilus edulis, gave a monoacetate on acetylation, and a tetrahydro derivative on reduction with sodium borohydride. Spectroscopic studies on isomytiloxanthin and its derivatives showed that the natural pigment has the acetylenic structure 6,3′-dihydroxy-7′,8′-didehydro-5,6,7,8,-tetrahydro β,β-carotene-3,8-dione (1).

Reaction of but-1-yne with the ketone (10) gave the acetylenic alcohol (12) which, on hydroboration, yielded the ketone (14). Removal of the protecting group furnished (16), a model for the novel β-hydroxy ketone end group in Isomytiloxanthin. Comparison of the n.m.r. bands of (16), and those of isomytiloxanthin, indicated that the latter has the relative configuration at 5,6 shown in (1).