Structure–reactivity relationships in the inactivation of elastase by β-sultams
作者:Paul S. Hinchliffe、J. Matthew Wood、Andrew M. Davis、Rupert P. Austin、R. Paul Beckett、Michael I. Page
DOI:10.1039/b208079f
日期:——
N-Acyl-β-sultams are time dependent irreversible active site directed inhibitors of elastase. The rate of inactivation is first order with respect to β-sultam concentration and the second order rate constants show a similar dependence on pH to that for the hydrolysis of a peptide substrate. Inactivation is due to the formation of a stable l â¶ l enzyme inhibitor complex as a result of the active site serine being sulfonylated by the β-sultam. Ring opening of the β-sultam occurs by SâN fission in contrast to the CâN fission observed in the acylation of elastase by N-acylsulfonamides. Structureâactivity effects are compared between sulfonylation of the enzyme and alkaline hydrolysis. Variation in 4-alkyl and N-substituted β-sultams causes differences in the rates of inactivation by 4 orders of magnitude.
Unusual steric effects in sulfonyl transfer reactions
作者:Paul S. Hinchliffe、J. Matthew Wood、Andrew M. Davis、Rupert P. Austin、R. Paul Beckett、Michael I. Page
DOI:10.1039/b104923m
日期:——
The hydrolysis of N-acyl-β-sultams generally occurs with ring opening and S–N fission in contrast to the C–N fission observed in analogous acyclic N-acyl sulfonamides. Similar to other β-sultams, the N-acyl derivatives are at least 106 more reactive than N-acylsulfonamides. However, the α-substituted 4-isopropylidene β-sultam is relatively unreactive and undergoes alkaline hydrolysis with C–N fission leaving the strained 4-membered β-sultam ring intact. This reduction in reactivity is shown to be due to steric strain introduced in the transition state for attack at the sulfonyl centre. (Z)-4-Ethylidene-β-sultam shows similar behaviour with preferential C–N fission whereas the (E)-4-ethylidene isomer and 4-isopropyl-β-sultam revert to hydrolytic ring opening with S–N fission.