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The chemical reactivity of penicillins and other b-lactam antibiotics

Proctor, Philip, Gensmantel, Nigel P. and Page, Michael I. (1982) The chemical reactivity of penicillins and other b-lactam antibiotics. Journal of the Chemical Society, Perkin Transactions 2 (9). pp. 1185-1192. ISSN 1472-779X

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The rates of the acid catalysed hydrolysis of penicillins and cephalosporins are linear in Ho and, unlike other amides, show no rate maximum with increasing acidity. Electron-withdrawing substituents at C-6 in penicillins decrease the rate of hydrolysis with a I of ca.4 and they decrease the rate when attached to the amine leaving group. The acylamido-group at C-6 in penicillins, but not at C-7 in cephalosporins, exhibits neighbouring group participation with a rate enhancement of ca. 103. The absence of penicillenic acid formation from benzylpenicillin in acidic solution is not due to the ionisation of the carboxy-group. These observations are rationalised by a scheme, involving N-protonation and formation of an acylium ion intermediate. The alkaline hydrolysis of penicillins proceeds 102 faster than a -lactam after correction for substituent effects. There is no evidence for substantial inhibition of amide resonance in the bicyclic -lactam antibiotics, little evidence to indicate extra strain in these systems and no evidence that expulsion of the leaving group at C-3 in cephalosporins occurs in the transition state

Item Type: Article
Subjects: Q Science > Q Science (General)
Q Science > QD Chemistry
Schools: School of Applied Sciences
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Depositing User: Sharon Beastall
Date Deposited: 12 Nov 2009 11:20
Last Modified: 28 Aug 2021 10:52


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