Absolute configuration of carotenoids

Circular Dichroism. Several papersreport the use of c.d. correlations in establishing the absolute configurations of carotenoids. One report sounds a cautionary note since the signs of all maxima in the c.d. spectrum of 15-cw-(3S,3 5)-astaxanthin are opposite to those of the all-trani-isomer. 

Since much activity has been centered around determination of absolute configuration of carotenoids during the last decade, this review will be devoted mainly to this particular aspect of carotenoid research, but will also include recent advances concerning geometrical isomerism. Literature available through July 1978 has been evaluated for this review. 

By this approach the absolute configuration of carotenoids such as (27 ,2 7 )-P,P-carotene-2,2 -diol [(33), R=OH], see Fig. 2, and of (35,3 5)-astaxanthin (28) (after LiAlHU reduction) has been assigned (7,118) and subsequently proved by independent methods (38, 116). In accordance with the conformational rule esterification or glycosidation of a hydroxy group (21, 88) of a P-ring or replacement of a 2-hydroxy group in p,e- or y-rings with methyl or isopentenyl substituents has little effect on the... 

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