The instability of Δ2 cephem prodrug-type ester (5a) under acidic conditions prompted us to investigate the comparative stability of Δ3 and Δ2 cephems at various pHs. The Δ2 cephem ester 5a was found to show marked instability under neutral (pH 7) and acidic conditions (1M HCl) compared with the Δ3 cephem ester (4a). A comparative study between Δ3 (4c) and Δ2 cephem acid (5c) at pH 7 and in 1M HCl solution showed that the Δ2 acid 5c was as stable as the Δ3 acid 4c pH 7, while 5c was less stable than 4c in 1M HCl. Isolation of the degraded compounds demonstrated that the C-4 ester moiety was hydrolyzed in the initial stage to afford 5c, which was further degraded to more polar substances. This instability was observed in other types of Δ2 cephem esters (5d-f). Here we report comparative stability studies and elucidation of the degradation products.
酸条件下Δ2
头孢菌素前药型酯(5a)的不稳定性促使我们研究了Δ3和Δ2
头孢菌素在不同pH下的相对稳定性。与Δ3
头孢菌素酯(4a)相比,Δ2
头孢菌素酯5a在中性(pH 7)和酸性条件(1M HCl)下表现出明显的稳定性差异。在pH 7和1M HCl溶液中对Δ3(4c)和Δ2
头孢菌素酸(5c)进行的比较研究表明,Δ2酸5c在pH 7时与Δ3酸4c同样稳定,而在1M HCl中5c的稳定性低于4c。降解产物的分离表明,C-4酯部分最初发生
水解生成5c,随后进一步降解为极性更强的物质。这种不稳定性在其他类型的Δ2
头孢菌素酯(5d-f)中也有观察到。这里我们报道了比较稳定性研究及其降解产物的阐明。