1,2,3,4,6-Penta-azaindenes (8-azapurines). Part VII. Degradation by acid of the 6-methylthio-derivatives of 8-azapurines and purines to thiol esters such as 4-amino-5-(methylthio)carbonyl-1,2,3-triazole (IIIa) and the corresponding imidazole

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Abstract
6-Methylthio-8-azapurine (IIa) in boiling N-hydrochloric acid was rapidly degraded to 4-amino-5-(methylthio)-carbonyl-1,2,3-triazole (IIIa) in 90% yield; the 7-, 8-, and 9-methyl- and 9-benzyl-derivatives behaved similarly. Physical properties, e.g. the strong absorption at ca. 900 cm.–1(:C–S· stretch), showed that these were RS·CO·(and not RO·CS·) esters. At a lower temperature, 9-methyl-6-methylthio-8-azapurine gave the intermediate 4-amino-3-methyl-1,2,3-triazol-5-yl(methylthio)methyleneiminium hydrochloride (Xb). Mechanisms are discussed for the above reactions and for the alternative decomposition, by weaker acid, to 8-azapurin-6(1H)-ones (I). The mercaptocarbonyl esters were converted into the corresponding amides and methylamides. One of the latter, 4-amino-3-methyl-1,2,3-triazole-5-carboxymethylamide, gave 1,9-dimethyl-8-azapurin-6(1H)-one in hot formamide. Aqueous sodium carbonate hydrolysed 4-amino-3-methyl-5-(methylthio)carbonyl-1,2,3-triazole to 4-amino-3-methyl-1,2,3-triazole-5-carboxylic acid, which was decarboxylated to 4-amino-3-methyl-1,2,3-triazole in boiling butanol. Acid degradation of 6-methylthiopurine (and its 9-methyl derivative) gave 4-amino-5-(methylthio)carbonylimidazole (and its 3-methyl derivative, respectively). New syntheses of 7-methyl- and 9-methyl-6-methylthiopurine are described. Lonisation constants, and u.v. and n.m.r. spectra are discussed.

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