New synthetic methods for 7-amino-3-methylenecepham-4-carboxylic acid (X) and 7-amino-3-hydroxycepham-4-carboxylic acid (IX), which are key intermediates for the synthesis of ceftizoxime (I), were developed. These intermediates (IX and X) were synthesized without introducing any protecting groups at the C-7 amino and/or C-4 carboxylie acid groups of the cepham or cephem ring. Compound X was prepared from 7-amino-3-(5-methyl-1, 3, 4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylic acid (XI) by zinc reduction either in aqueous or anhydrous neutral conditions. Compound IX was perpared from X by ozone oxidation at -75°C followed by sodium borohydride at 0-10°C. A plausible mechanism of ozone oxidation of X is preseted, and the existence of an important intermediate, 7-amino-3-hydroxy-3-cephem-4-carboxylic acid (XXII), is demonstrated.
本研究开发了合成头孢唑
肟(I)的关键中间体--7-
氨基-3-亚甲基头孢-4-
羧酸(X)和 7-
氨基-
3-羟基头孢-4-
羧酸(IX)的新合成方法。合成这些中间体(IX 和 X)时,未在头孢噻
肟环或头孢环的 C-7
氨基和/或 C-4 羧基上引入任何保护基团。化合物 X 由 7-
氨基-3-(5-甲基-1, 3, 4-
噻二唑-2-基)
硫甲基-3-头孢-4-
羧酸(XI)在
水性或无
水中性条件下通过
锌还原法制备而成。化合物 IX 是在-75°C 下用
臭氧氧化,然后在 0-10°C 下用
硼氢化钠从 X 中制备出来的。预设了
臭氧氧化 X 的合理机理,并证明了一种重要的中间体--7-
氨基-3-羟基-3-头孢-4-
羧酸(XXII)的存在。