Synthesis of N4-Alkyl-5-azacytidines and Their Base-Pairing with Carbamoylguanidines - A Contribution to Explanation of the Mutagenicity of 2'-Deoxy-5-azacytidine

Abstract

A series of N4-alkyl-5-azacytidines 3a-3h were prepared by treatment of the 4-methoxy analogue 4 with the respective amines. In the case of propyl-, butyl-, sec-butyl-, benzyl- or furfurylamine, aggregates of azacytidines 3a-3e with their hydrolytic products 5a-5e were isolated. Similar aggregates were obtained with 1-methyl-5-azacytosine (6) and 2-(methylcarbamoyl)guanidine (7). Compound 7 was prepared by the reaction of guanidine with methyl isocyanate; the reaction of 2 or 3 equivalents gave the di- or tricarbamoyl derivatives 11 and 12, respectively. Cyclization of 7 and 11 with DMF dimethyl acetal afforded azacytosines 6 and 13, respectively. Aggregates of guanosine with 5-azacytosine nucleosides 1, 2 and 15 or of 5-aza-5,6-dihydrocytosine nucleosides 16 and 17 with 5-azacytidine (1) and its 2'-deoxy congener 2 have been prepared by co-crystallization of the respective pairs of nucleosides. The anomers of (deoxyribosylcarbamoyl)guanidine 20a and 20b have been prepared by hydrolysis of the deoxy nucleoside 2. An aggregate of the picrate (8a) of (ribosylcarbamoyl)guanidine 8 with cytidine (9) has been obtained by co-crystallization of both components. Reaction of the methoxy nucleoside 4 with tert-butylamine gave, by contrast to the above mentioned amines, the α-anomer of O-methylribosylisobiuret 22, which was cyclized by DMF dimethyl acetal to the α-anomer of N4,N4-dimethyl-5-azacytidine 24. The connection of the base-pairing ability of carbamoylguanidines with the mutagenicity of 2'-deoxy-5-azacytidine (2) as well as the mechanism of inhibition of DNA methyltransferase by this nucleoside analogue is discussed. In contrast to the unsubstituted 5-azacytidine (1) or its N4-methyl derivatives, none of the N4-alkyl derivatives exhibited any antibacterial or antitumor activity at 100 μg/ml or 10 μmol/l concentrations, respectively.