SELECTIVE SYNTHESIS OF 6-BENZYLAMINOPURINE CONTROLLED BY SOLVENT AND BASE

This work investigates the influence of solvent and base nature on the mechanism of 6-benzylaminopurine formation during the reaction of 6-chloropurine with benzylamine. The reaction proceeds via nucleophilic aromatic substitution (S_NAr) at the C-6 position of the purine ring activated by electron-withdrawing nitrogen atoms. It was established that polar aprotic solvents (DMF, DMSO) significantly increase the reaction rate due to stabilization of the anionic Meisenheimer σ-complex, whereas protic media decrease the nucleophilicity of the amine and reduce the product yield. The type of base strongly affects selectivity: alkali metal carbonates provide preferential substitution at the N-9 position without formation of N-alkylation by-products, while strong bases cause partial degradation of the purine ring. Optimal conditions (DMF, K₂CO₃, 100 °C) afforded 6-benzylaminopurine in up to 92 % yield. Based on kinetic and spectral data, a reaction mechanism involving formation of a σ-complex followed by chloride ion elimination is proposed. The obtained results allow controlled tuning of substitution selectivity in the purine core and may be applied in the synthesis of biologically active purine derivatives.