金属(II)离子在30°水中的一些pencillin和头孢菌素衍生物的水解反应显示出饱和动力学。在金属离子和青霉素之间形成1:1的络合物,该络合物被氢氧根离子攻击的速度比未配位化合物快10 8倍。青霉素类和铜(统筹的部位II)离子是β内酰胺氮和羧酸基团。头孢菌素和金属离子的缔合常数大于青霉素的缔合常数,但头孢菌素与氢氧根离子反应的过渡态与金属离子的结合较不紧密。金属离子引起的速率提高的顺序为Cu II > Zn II > Ni II〜Co II。金属离子被认为稳定了由氢氧根离子攻击β-内酰胺形成的四面体中间体。关于金属离子作为酶中的亲电催化剂的一些评论。
A facile synthesis of 7-amino-3-desacetoxycephalosporanic acid derivatives by indium-mediated reduction of 3-iodomethylcephems in aqueous media
摘要:
An efficient reductive conversion of 3-iodomethylcephalosporin and 3-acetoxymethylcephalosporin derivatives mediated by indium into the corresponding 3-methylcephems and 3-methylenecephams in moderate to good yields has been developed in an aqueous system. 3-Methylenecephams are converted into the corresponding 3-methylcephems under previously reported basic conditions quantitatively. (C) 2000 Elsevier Science Ltd. All rights reserved.