(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.
(a) 对沙可霉素(1)进行部分乙酰化,可得到两种二
乙酸酯:3,12-O-
乙酸酯(4)和 3,20-二-O-
乙酸酯(3),比例为 3:1,此外还有 3-单-O-
乙酸酯(5)和 3,12,20-三-O-
乙酸酯(2)。另一方面,用等摩尔量的
苯甲酰氯对 5 进行苯甲酰化,可得到其 20-O-
苯甲酸酯(6)。(b) 在酸催化条件下,用副醛处理 1,可得到 14,17-12,20-二-O-亚乙基-
水苏糖苷(14)。(c) 根据 3-O-对
溴苯甲酸酯(16)的 X 射线分析,1 的 C-20 位构型为 S。与永井的数据预期相反,
邻硝基苯甲酸酯(17)显示出负面的棉花效应,但 17 的 14、17-O-亚乙基衍
生物(18)显示出正面的棉花效应。(d) 由
硼氢化钠还原相应的酮而得到的 C-20 碳醇的构型可归因于酮的 C-17 的立体
化学结构。从利奈隆二
乙酸酯(25)的
硼氢化钠还原产物中得到的 20-O-
邻硝基苯甲酸酯(24)显示出积极的科顿效应,而从西利奈隆二
乙酸酯(27)中得到的
邻硝基苯甲酸酯(26)则显示出消极的效应。