Substituent and Solvent Effects on the Tautomeric Equilibria of N-Substituted α-(Aminomethylene)purine-6-acetonitrile Derivatives

Substituent and solvent effects on the tautomeric equilibration (E/Z) of α-(N-alkyl and -arylaminomethylene)-9-(methoxymethyl)-9H-purine-6-acetonitriles (3a-q) have been studied by means of proton nuclear magnetic resonance spectroscopy in protic and aprotic solvents at 25°C. In chloroform-d these compounda (3a-q) exist mainly as the E-form. On the other hand, in methanol-d4 or dimethylsulfoxide-d6 the alkylamines (3a-c), phenylamine (3e), meta- or para-substituted phenylamines (3f-j) and 2, 6-disubstituted phenylamines (3p and q) exist mainly as the Z-form, while the trityl compound (3d), and ortho-substituted compounds (3k-o) showed a predominance of the E-form.