抄録
(a) Partial acetylation of sarcostin (1) gave two diacetates ; 3, 12-O-acetate (4) and 3, 20-di-O-acetate (3) in 3 : 1 ratio, besides 3-mono-O-acetate (5) and 3, 12, 20-tri-O-acetate (2). On the other hand, benzoylation of 5 with equimolar amount of benzoyl chloride gave its 20-O-benzoate (6). (b) Treatment of 1 with paraldehyde under acid catalytic conditions afforded 14, 17-12, 20-di-O-ethylidene-sarcostin (14). (c) The configuration at C-20 position of 1 is S on the basis of the X-ray analysis of 3-O-p-bromobenzoate (16). The o-nitrobenzoate (17) showed a negative Cotton effect contrary to the expectation from Nagai's data but the 14, 17-O-ethylidene derivative (18) of 17 showed a positive Cotton effect. (d) The configuration of the C-20 carbinol derived from sodium borohydride reduction of the corresponding ketone is ascribable to the stereochemistry at C-17 of the ketone. The 20-O-o-nitrobenzoate (24) derived from the sodium borohydride reduction product of lineolon diacetate (25) shows a positive Cotton effect while the o-nitrobenzoate (26) from isolineolon diacetate (27) shows a negative effect.
