Animal carotenoids. 12. Chirality of asterinic acid.

The chirality of monoacetylenic asterinic acid [(3S,3'S)-7,8-didehydroastaxanthin, 1a] has been established by NaBH4-reduction and hydrolysis of the corresponding diesters 1b and 1c providing the tetrol 9 and CD-correlation with diatoxanthin [3R,3'R)-7,8-didehydro-beta, beta-carotene-3,3'-diol, 10]. Diacetylenic asterinic acid [3S,3'S)-7,8,7',8'-tetradehydro-beta, beta-carotene-3,3'-diol, 2a] was assigned the some absolute configuration by similar conversion to the diacetylenic tetrol 11 and CD-correlation with alloxanthin [3R,3'R)-7,8,7',8'-tetradehydro-beta, beta-carotene-3,3'-diol, 12]. IR and CD properties of the diacetates 1C and 2C of the naturally occurring alpha-ketols are reported.