Stereochemical Course of the Transannular Cyclization, in Chloroform, of Epoxycembranoids Derived from the Geometrical Isomers of (14S)-14-Hydroxy-1,3,7,11-cembratetraenes

Article abstract of DOI:10.1021/jo00293a049

A new cembranoid sarcophytol T (5a) was isolated from the soft coral Sarcophyton glaucum, and the structure was shown to be (14S)-14-hydroxy-1(E),3(Z),7(E)-cembratetraene, a geometrical isomer of the potent antitumor promoter sarcophytol A (1).Compound 5a and its geometrical isomers, sarcophytol N (6, 1Z,3Z) and sarcophytol F (7, 1E,3E), were found to be converted by autoxidation to bicyclo<9.3.0>tetradecene derivatives when kept in CHCl3 solution at room temperature, in the same way as 1 (1Z,3E).The stereochemistry of each product (4 from 1 and 5a, 12 from 6, and 16 from 7) was derived by NOE analyses and by conversion of 12 and 16 to the enantiomeric ketones 17 and 18, respectively. 4-Hydroxy-1,14-epoxy-2-ene derivatives were shown to be the immediate precursors in the transannular cyclization, while cembrene C (23), the parent hydrocarbon of 1, also reacted in CHCl3, giving the bicyclic derivatives 25.