Alkylation by dehydroretronecine, a cytotoxic metabolite of some pyrrolizidine alkaloids: An in vitro test

Abstract

A method is described for detecting alkylation of nucleophiles by dehydroretronecine (DHR) in vitro: whereas DHR is rapidly polymerised by acid, alkylation products of DHR were relatively stable and could be detected using Ehrlich reagent. Using this test, nitrogen-containing compounds found to react with DHR included pyridine, adenine and guanine derivatives; NAD and NADP, but not NADH; cytidine; barbituric and parabanic acids; and azide, but not cyanide. Out of 19 amino acids tested, only histidine, tryptophan and citrulline showed evidence of reaction. Among sulphur compounds, thiols, thiosulphate and sulphite reacted strongly; thioethers and thiocyanate did not. Carbohydrate and phenolic hydroxyls were unreactive but resorcinol and pyrogallol, having activated benzene nuclei, did react. Enols, especially ascorbic acid, reacted with DHR. Sites of reaction have not yet all been identified. Some DHR alkylations, e.g. of nicotinamide, could be reversible, and such products could in effect extend the life of DHR in vivo.