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 N 4 -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 N 4 , N 4 -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 N 4 -methyl derivatives, none of the N 4 -alkyl derivatives exhibited any antibacterial or antitumor activity at 100 μg/ml or 10 μmol/l concentrations, respectively.