Serine Protease Mechanism-Based Mimics. Direct Evidence for a Transition State Bridge Proton in Stable Potentials
作者:Loengrid Bethencourt、Oswaldo Núñez
DOI:10.1021/jo702003q
日期:2008.3.1
results also show the participation of water molecules forming catalytic proton bridges in stable potentials with the two interconverted forms. The position change of the bridged proton is sensitive to lactam ring size, and it is manifested by considerable change in the pKa values of both cyclol and open forms. Other evidence such as kinetics, ΔS°, ΔS⧧, and proton inventory experiments and semiempirical
我们已经合成了1-(2-羟基乙酰基)哌啶-2-酮(2)和1-(2-羟基乙酰基)氮杂环庚烷-2-酮(3)。游离醇(开放形式)和四面体中间体(环醇)之间的平衡(K f)很容易建立,并且两种形式都在2和3的D 2 O 1 H NMR光谱中观察到。因此,它们的相互转化可以认为是几乎热中性的不同。伪一级反应速率常数(k obs)通过模拟观察到的环1的AB 1 H NMR系统获得。通过最好地拟合k obs的实验点相对于pD曲线的方程k obs = 0.5 k 0r + 0.5 k r K ac /(K ac + [D + ])+ 0.5 k f K ao /(K ao + [D + ]),获得了相关参数:破裂和形成(的速率常数ķ 0R和ķ 0F = ķ ˚F ķ 0R)由水催化,破裂(的速率常数ķ - [R )和形成(ķ ˚F)由环形式和开环形式的共轭碱基及其酸度平衡常数K ac和K ao组成。研究的