Reactivities and electronic aspects of nucleic acid heterocycles. Part III. Hydrolytic behaviour of 6-methoxypurines

Abstract

Contrary to common belief, aqueous acidic hydrolysis of 6-methoxypurines yields a complex mixture of products. At 0·1 M concentration, 6-methoxy-9-methylpurine (2) yielded methyl 5-amino-1-methylimidazole-4-carboxylate (5) and 9-methylhypoxanthine (4) in the ratio 7:3. Similar reactions were observed for both the 9-unsubstituted purine (3) and the 9-riboside (1). At concentrations of the methoxypurines >0·2M, O→N methyl migration became competitive. The quaternary intermediates 6-methoxy-7,9-dimethylpurinium chloride (6) and 6-methoxy-3-methylpurinium chloride (12) were isolated. A purine dication is proposed as the key intermediate in the hydrolytic reactions. The relevance of these results to the isolation of nucleic acid bases is discussed.