The in vitro protection of cholinesterases against some organophosphorus inhibitors

Abstract

This work was carried out in 1948-9 and formed the subject of confidential reports to the Ministry of Supply. It was part of a search for simple compounds which would protect cholinesterases against inhibition by such compounds as Tabun (ethyl NN-dimethylphosphoramidocyanidate), Sarin (isopropyl P-methylphosphonofluoridate) and ethyl-Sarin (iopropyl P-ethylphosphonofluoridate). As with DFP (dii8opropyl phosphorofluoridate: Mackworth & Webb, 1948) inhibition by Tabun (Augustinsson, 1951, 1953) and Sarin (unpublished work of A. Todrick & L. T. D. Williams) is irreversible, and it is reasonable to suppose that inhibition by ethyl-Sarin is also irreversible. The starting point of our experiments was the supposition that since nothing definite was known about the active centre of cholinesterases, the catalytic activity was probably associated with the amino acid side chains. A number of amino acids were examined for their ability to protect cholinesterase in vitro; only dopa (3:4-dihydroxyphenylalanine) was effective, but in high concentration, and it was found that protective ability was a property of catechol derivatives. It appears that Augustinsson (1952), independently and about the same time, discovered the reaction of catechols with Tabun, and published his results almost simultaneously with those of Jandorf, Wagner-Jauregg, O'Neill & Stolberg (1952) on the reaction of phenols with DFP. The present paper deals mainly with the properties of Sarin, but sufficient data are also given to make it clear that the three groups of workers have studied different facets of the same phenomenon. A brief account of this work has been published (Berry, 1953). THEORETICAL One of us (A.T.) in earlier unpublished work on Sarin in collaboration with L. T. D. Williams considered the case of irreversible inhibition by a labile inhibitor. The gist of their treatment is as follows:

Pharmacological Antagonists of the Anticholinesterase Agents

“…It is apparent, therefore, that either the amino nitrogen or the phenolic hydroxyl group in protein may be a point of primary reaction with the organophosphorus anti-ChE agents. Dihydroxy phenylalanine (DOPA) was found to react rapidly with DFP, Sarin, and Tabun (JANDORF et al 1952, AUGUSTINSSON 1952, BERRY et al 1955. Table 3 shows the relative rates of reaction with DFP of a small series of polyhydroxybenzene derivatives.…”

The Synthesis of Substituted Penicillins and Simpler Structural Analogs. XI. Methyl 6-Benzylsulfonamidopenicillanate

“…The isomer of 4-carbomethoxy-5,5-dimethylabenzylsulfonainido -2 -thiazolidineacetic acid hydrochloride derived from VI y was designated beta to signify that an isomerization had occurred. 5 The cyclizations of Vila and VII/5 were carried out employing conditions found to be optimum for the synthesis of methyl G-phthalimidopenicillanate (IV), i.e., a 25% solution of thionyl chloride in methylene chloride. In preliminary experiments, the crude mixtures from the lactamization reactions were oxidized by means of potassium permanganate in 80% acetic acid, affording the crystalline methyl 6-benzylsulfonamidopenicillanate sulfones (IX).…”

“…A straightforward preparation of these substances recently has been made available via the corresponding -aminothiazolidines Va and Vy. 5 The -isomer of ¿-butyl 4-carbomethoxy-5,5-dimethyl-a-amino-2-thiazolidineacetate hydrochloride (Va), upon treatment with one equivalent of benzylsulfonyl chloride and a tertiary base, afforded in good yield the benzylsulfonainido derivative Via. Similarly, the -isomer of V gave the isomeric thiazolidine VIy, although in somewhat poorer yield.…”

Molecular Catalysis and Interactions in Aqueous Solutions

“…Since the catalytic acitivity of acetylcholinesterase was probably associated with amino acid side chains, Berry et al (18) studied the ability of a number of amino acids to protect cholinesterase in vitro. Of all of the amino acids tested only DOPA (3-4-dihydroxyphenylalanine) was effective.…”