Zeaxanthine-diepoxide

Carotenoid epoxides are among the most widespread vegetal pigments. An example is zeaxanthine-diepoxide (Fig. 6) (Karrer, 1948). These... 

Fig. 6. Zeaxanthine-diepoxide (Karrer, 1948). Its conversion to the fiitanoid oxide and the original carotinoid.

Total syntheses of (35,3 5)-astaxanthin (28), (35 ,3 i )-astaxanthin [cn -(28)J and (35,3 5 )-astaxanthin have been accomplished (69,116,131). Also recently synthesized in the Roche laboratories were optically pure (3R,3 R)-zeaxanthin (26) (132), (35,3 5)-zeaxanthin [ent-(26)] and (3R,3 S)-zeaxanthin (50) (131), all-trans (35,3 S)-7,8-didehydroastaxanthin (80) and 3X -trans (35,3 S)-7,8,7, 8 -tetradehydroastaxanthin (34) (23d) as well as both actinioerythrin enantiomers [(70) and e t-(70)] (138). This important achievement has been discussed by Mayer (131). Furthermore, optically pure dW-trans (3R,3 R)-alloxanthin (31) has been obtained by total synthesis (153a). Recently (55,6R)-5,6-epoxy-5,6-dihydro-p,P-caro-tene (71) and (57 ,67 )-5,6-dihydro-P,P-carotene-5,6-diol (29) have been synthesized from azafrin (6) (71). The diol has not yet been encountered in nature, and correlations between the synthetic epoxide and naturally occurring mono- and diepoxides of p,P-carotene (162) remain to be carried out. This is also the case for the corresponding (55,6i )-5,6-... 

In acidic media, 5,6-epoxides isomerise to dihydrofuran derivatives, also known as 5,8-epoxides (5-26), other products include diepoxides, p, -carotene-3,3 -diol (zeaxanthin), P,P-carotene-4-one (echinenone) (5-7) and their degradation products, such as P-apo-8 -carotenal (5-27), (S-apo-lO -carotenal, P-apo-12 -carotenal, P-apo-14 -carotenal and numerous other aldehydes. The main product is 5,8,5, 8 -diepoxide (also known as 5,8,5, 8 -diepoxy-5,8,5, 8 -tetrahydro-p,p-carotene or aurochrome or -carotene), and other products include 5,6,5, 6 -diepoxide (5,6,5, 6 -diepoxy-5,6,5, 6 -tetrahydro-p,p-carotene) and 5,6,5, 8 -diepoxide (5,6,5, 8 -diepoxy-5,6,5, 8 -tetrahydro-p,p-carotene or luteochrome). 

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