Abstract
In order to investigate the effects of the N(3)- and N(9)-substituents in 3, 9-disubstituted adenines on the stability of the adenine ring, the equilibrium constants and the rates of ring opening and cyclization for the equilibria between the 3, 9-disubstituted adenines IVa-l and the N-alkylformamidoimidazoles Va-l in H2O at pH 8.98 and 25 °C have been measured. A bulky substituent at the 3-position of IV has been found to retard the ring opening leading to V, whereas an electron-withdrawing group at the 3- or 9-position accelerates it. A bulky alkyl group on the formamido nitrogen of V markedly retards the cyclization leading to IV, favoring the ring-opened form in the equilibrated mixture. Syntheses of 3-isopropyl-9-methyladenine perchlorate (IVc) and 3-(4-methoxybenzyl)-9-methyladenine perchlorate (IVe), required for the kinetic study as substrates, are also described.
