Über einige cis ‐Formen des Canthaxanthins

The fungal carotenoid, canthaxanthin, C 40 H 52 O 2 (4,4′‐diketo‐β‐carotene), was converted by some thermal and photochemical treatments into a stereoisomeric mixture that was resolved chromatographically. Thus, six cis forms, termed “neo‐canthaxanthins A‐F”, were obtained, A–C in crystalline form, the latter being identical with central‐mono cis ‐canthaxanthin prepared by Isler et al . by total synthesis. The spectral characteristics of these stereoisomers have been studied and some tentative configurational assignments proposed.