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Thiol-catalysed hydrolysis of benzylpenicillin

By Antonio Llinás, Josefa Donoso, Bartholomew Vilanova, Juan Frau, Francisco Munoz and Michael I. Page

Abstract

Thiolysis of benzylpenicillin has been investigated by HPLC and 1H-NMR techniques. Thiols catalyse the hydrolysis of benzylpenicillin through the formation of a thioester intermediate. The catalytically reactive form of the thiol has been demonstrated to be the thiolate anion. Variation of reactivity with changing basicity of the thiolate anion generates a Brønsted nuc value of 0.96, indicating that the breakdown of the tetrahedral intermediate is the rate-limiting step, as occurs in aminolysis and alcoholysis. Solvent kinetic isotope effects of 2.2–2.4 indicate that the solvent, water, probably acts as a general acid catalyst in the breakdown of the tetrahedral intermediate. PM3 theoretical calculations support the proposal that breakdown of the tetrahedral intermediate is rate-limiting. The experimental activation energies for the thiolysis of benzylpenicillin vary from 6.9 to 10.4 kcal mol–

Topics: Q1, QD
Publisher: Royal Society of Chemisttry
Year: 2000
DOI identifier: 10.1039/b001091j
OAI identifier: oai:eprints.hud.ac.uk:2264
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