Selected examples of structure determination of natural carotenoids.

Selected examples of novel types of carotenoids studied in the author's laboratory during the past three years are discussed; including structural elucidation, total synthesis and biosynthetic considerations. Carotenoids of photosynthetic bacteria, particularly the aryl ketone okenone and cross-conjugated carotenals of the rhodopinal series, C50carotenoids of non-photosynthetic bacteria like dehydrogenans-P439, sarcinaxanthin, bacterioruberin and related compounds and C45and C50carotenoids from Corynebacterium poinsettiae are considered. Glycosidic carotenoids from blue-green algae comprising myxoxanthophyll, oscillaxanthin and related glycosides and glycosidic carotenoids of bacterial origin are dealt with. Comments on fungal carotenoids are made. From higher plants the structures of lycoxanthin and an apo-carotenoid are treated. Finally carotenoids of lower marine animals, the acetylenic 'asterinsäure' and nor-carotenoids with ring contraction like actinioerythrin and the blue violerythrin are discussed. INTRODUCTION Considerable progress has been made in the structural elucidation of natural carotenoids during the three years following the first carotenoid symposium. Rather than present another general progress review1, I have chosen to discuss in rather more detail structure determination of selected examples of novel types of carotenoids studied in our own laboratory during the past three years. From 1958 and onwards our general research programme has comprised chemical structure and biosynthesis of carotenoids in organisms of various evolutionary levels. We started with studies on photosynthetic bacteria and have gradually extended our studies to more highly developed organisms. In this paper recent examples from photosynthetic and non-photosynthetic bacteria, blue-green algae, fungi, higher plants and lower marine animals will be discussed. PHOTOSYNTHETIC BACTERIA Considerable attention has already been paid to the carotenoids of photosynthetic bacteria2—6, known to produce some forty specific carotenoids, which are generally aliphatic or aromatic in nature. Methoxylated carotenoids are still restricted to these organisms7. In order to localize our particular topic Figure 1 gives a summary of experimentally proved3'8'9 and postulated biosynthetic pathways. 421 PURLE N O N -S U LP H U R