EPOXIDATION OF CUCURBITAXANTHIN-A - PREPARATION OF CUCURBITAXANTHIN-B AND OF ITS 5',6'-EPIMER

Cucurbitaxanthin A ( = (3S,5R,6R,3'S)-3,6-epoxy-5,6-dihydro-beta,beta-carotene-5,3'-diol; 1) isolated from red pepper (Capsicum annuum var. longum nigrum) was trimethylsilylated and then epoxidized with monoperphthalic acid. After deprotection and chromatographic separation, cucurbitaxanthin B (= (3S,5R,6R,3'S,5'R,6'S)-3,6:5',6'-diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene-5,3'-diol; 2) and 5',6'-diepicucurbitaxanthin B (= (3S,5R,6R,3'S,5'S,6'R)-3,6:5',6'-diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene-5,3'-diol; 5) were obtained and carefully characterized. They show mirror-like CD spectra and, therefore, emphasize the importance of the torsion angle of C(6)-C(7) on the electronic interaction between the polyene chain and the chiral end group.