The esterification of Δ3-cephem-4-carboxylic acid sodium salt (1) with 1-iodoethyl isopropyl carbonate always afforded the Δ2 cephem ester (3) as an inseparable minor component. However, in the course of formamido cleavage reaction, the 7-amino-Δ2-cephem ester (5) was observed to be less stable than the Δ3 cephem ester (4), which led us to develop a practical synthetic process for Δ3 cephem esters, including a key intermediate of E1101, a new oral cephalosporin.
1-iodoethyl isopropyl carbonate酯化Δ3-cephem-4-
羧酸钠盐(1)时,总能得到作为不可分割的次要成分的Δ2 cephem酯(3)。然而,在甲酰
氨基裂解反应过程中,观察到 7-
氨基-Δ2-头孢酯(5)不如Δ3-头孢酯(4)稳定,这促使我们开发出一种实用的Δ3-头孢酯合成工艺,包括一种新型口服
头孢菌素 E1101 的关键中间体。