Kinetics of Action of a Two-Stage Pro-Inhibitor of Serine β-Lactamases
摘要:
beta-Lactamase inhibitors are important in medicine in the protection of beta-lactam antibiotics from beta-lactamase-catalyzed destruction. The most effective inhibitors of serine beta-lactamases covalently modify the enzyme active site. We have recently studied O-acyl and O-phosphyl hydroxamates as a new class of such inhibitors. In this paper, we describe our studies of the N-acyl derivatives of a cyclic O-acyl hydroxamic acid, 3H-benzo[d][1,2]oxazine-1,4-dione, and, in particular, the N-tert-butoxycarbonyl derivative. This compound is not a beta-lactamase inhibitor itself but undergoes spontaneous hydrolysis in aqueous solution, yielding an O-phthaloyl hydroxamic acid, which is a beta-lactamase inhibitor. This compound spontaneously, but reversibly, cyclizes in solution to form phthalic anhydride, which is also a beta-lactamase inhibitor. Both inhibitors react to form the same transiently stable phthaloyl-enzyme complex. Thus, we have a two-step cascade, beginning with a pro-inhibitor, in which each step leads to a different inhibitor, presumably with different enzyme specificities. The kinetics of these transformations have been elucidated in detail. The phthaloyl derivatives, where the free carboxylate is important for facile reaction with the enzyme, represent a new lead for serine beta-lactamase inhibitors. Analogues can be conveniently constructed in situ by reaction of nucleophiles with phthalic anhydrides and then screened for activity. Active hits may then become new leads.
We designed a novel 2′-O,5′-N bridged nucleic acid, 2′,5′-BNAON, whose sugar puckering was fixed to S-type conformation by an N–O linkage. A dimer unit formed from 2′,5′-BNAON-U and thymidine was synthesized via a coupling reaction between a protected 2′,5′-BNAON-U monomer and a thymidine derivative. Introduction of 2′,5′-BNAON-U into DNA was carried out using conventional phosphoramidite chemistry
我们设计了一种新型的2' - O,5'- N桥接核酸2',5'-BNA ON,其糖折叠通过N - O键固定在S型构象上。通过受保护的2',5'-BNA ON -U单体与胸苷衍生物之间的偶联反应,合成了由2',5'-BNA ON -U和胸苷形成的二聚体单元。使用常规的亚磷酰胺化学和DNA合成仪将2',5'-BNA ON -U引入DNA。评价了2',5'-BNA ON -U-修饰的寡核苷酸对DNA或RNA补体的杂交能力。
Access to Chiral Chromenones through Organocatalyzed Mannich/Annulation Sequence
作者:Jingxiang Duan、Zongli Xiong、Yuqiao Zhou、Weijun Yao、Xiaoyi Li、Min Zhang、Zhen Wang