Background: Thiazolo[4,5-d]pyrimidine derivatives exhibit a wide range of important biological properties. These are purine analogues which applied in therapeutic and pharmacological purposes[1] and can be considered as model systems for metal–ligand interactions observed in biological systems.[2] Methods: The reaction of compound (1) with benzyl amine under reflux condition gave N4-benzyl-2-chloro-6-methyl-pyrimidin-4,5-diamine which was subsequently converted into 3-benzyl-5-chloro-7-methyl-3H-[1,2,3]triazolo[4,5-d]pyrimidine by diazotization in the presence of sodium nitrite in HCl. The substitution of 2-chlorine atom with hydrazine hydrate in ethanol gave the new heterocyclic derivative (2). The treatment of the latter compound with carbon disulfide and subsequently further regioselective alkylation through the treatment with various alkylhalides obtained the new derivatives of (3a-e). Results: The structure elucidations of the novel synthesized derivatives (3a-e) are based upon the spectral and microanalytical data. The IR spectra of compounds (3a-e) did not show the NH vibrational stretching band of the precursor. The signals of the alkyl groups in 1H NMR and 13C NMR clearly confirm the presence of alkyl hydrogens and carbons and occurrence of heterocyclization. Conclusion: Some interesting novel three fused heterocyclic ring system derivatives were prepared via starting from N4-benzyl-2-chloro-6-methyl-pyrimidin-4,5-diamine as precursor. All reactions accomplished straightforward in common solvents and normal heating conditions with simple work-up procedures. Keywords: [1,2,3]triazolo[4,5-d][1,2,4]triazolo[4,3-a]pyrimidine; heterocyclization; alkylation; diazotization. References [1] Beyer C. F., Zhang N., Hernandez R., Vitale D., Lucas J., Nguyen T., Cancer Res., 2008, 68, 2292-2300. [2] Salas J. M., Romero M. A., Sánchez M. P., Quirós M., Coord. Chem. Rev., 1999, 193–195, 1119-1142.

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