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自然界中存在一系列的甾醇类化合物,在C_(24)上具取代基,例如麦角甾醇(ergosterol,Ⅰ)及菜子甾醇(campesterol,Ⅱ)等为甲基衍生物;大豆甾醇(stigmasterol,Ⅲ)、β-麦胚甾醇(β-sitoscefol,Ⅳ)及γ-麦胚甾醇(γ-sitosterol,Ⅴ)等为乙基衍生物,因而形成一不对称碳中心。由于该碳原子与分子中的其他不对称碳原子距离较远,因此在构型上不易与后者相互联系,所以C_(24)的相对和绝对构型的测定乃成为独立的研究裸题。根据氧化降解反应,从麦角甾醇及菜子甾醇的衍生物可以分别制得左旋及右旋的5,6-二甲基-庚酮-2的缩氨脲衍生物;从大豆甾醇(或β-麦胚甾醇)及γ-麦胚甾醇氧化
A series of sterol compounds exist in nature and have substituents on C 24 such as ergosterol and campesterol, , Β-sitoscefol (Ⅳ) and γ-sitosterol (Ⅴ) as ethyl derivatives, thus forming an asymmetric carbon center. Since the carbon atoms are far away from other asymmetric carbon atoms in the molecule, they are not easily interlinked with each other in their configuration. Therefore, the determination of the relative and absolute configuration of C_ (24) has become an independent research topic. According to the oxidative degradation reaction, the levonorubicin derivatives of 5,6-dimethyl-heptanone-2 can be prepared separately from the derivatives of ergosterol and brassicasterol; Embryol) and γ-wheat germ sterol oxidation