The stereoselective synthesis of 2α-methyl-and 2β-methyl-3-(substituted methyl)-cephalosporins via 2-methyl-3-formyloxymethylceph-2-em (5) and 2-methyl-3-acetoxymethylceph-2-em (16) from 2-methylene-3-acetoxymethylcephalosporin (1) is described. Reduction of 1 with zinc in acetic acid gave 2, 3-dimethylenecepham (2), while reduction with zinc in formic acid gave 5 and reduction with sodium borohydride gave 16. Hydrolysis of 5 gave 2-methyl-3-hydroxymethylceph-2-em (6), which was stereoselectively converted via 2-methyl-3-(heterocyclic thiomethyl) ceph-2-em (8) and 2-methyl-3-formyl-ceph-2-em (12) into the corresponding 2α-methyl-3-(substituted methyl) ceph-3-ems by oxidation with peracid. On the other hand, isomerization of 16 to the corresponding ceph-3-em by oxidation with peracid gave mainly the 2β-methyl isomer (55 : 1 ratio). Ozonolysis of 2 followed by treatment with diazomethane gave 2-oxo-3-methoxyceph-3-em (24).
介绍了从 2-亚甲基-3-乙酰氧甲基
头孢菌素 (1) 通过 2-甲基-3-甲酰氧甲基头孢-2-em (5) 和 2-甲基-3-乙酰氧甲基头孢-2-em (16) 立体选择性合成 2α-甲基和 2β-甲基-3-(取代甲基)-
头孢菌素的方法。用
锌在
乙酸中还原 1 得到 2,3-二亚甲基头孢 (2),用
锌在
甲酸中还原得到 5,用
硼氢化钠还原得到 16。
水解 5 得到 2-甲基-3-羟甲基头孢-2-em (6),通过过酸的氧化作用,该物质可立体选择性地通过 2-甲基-3-(杂环
硫代甲基)头孢-2-em (8) 和 2-甲基-3-甲酰基头孢-2-em (12) 转化为相应的 2α-甲基-3-(取代甲基)头孢-3-em。另一方面,16 通过过酸氧化异构化为相应的头孢-3-em,主要得到 2β- 甲基异构体(比例为 55:1)。用
重氮甲烷对 2 进行
臭氧分解后,可得到 2-氧代-3-甲氧基头孢-3-em(24)。