Thietanyl Protection in the Synthesis of 8-Substituted 1-Benzyl-3-methyl-3,7-dihydro- 1H-purine-2,6-diones

Aim and Objective: 1-Alkyl-3,7-dihydro-1H-purine-2,6-diones containing no substituents in the N7 position can be synthesized only using protecting groups, for example, benzyl protection. However, in the case of synthesis of 1-benzyl-3,7-dihydro-1H-purine-2,6-diones, the use of benzyl protection may lead to simultaneous debenzylation of both N1 and N7 positions. Therefore, it is necessary to use other protective groups for the synthesis of 1-benzyl-3,7-dihydro-1H-purine-2,6-diones. Materials and Methods: 8-Bromo- and 8-amino-substituted 1-benzyl-3-methyl-3,7-dihydro-1H-purine-2,6-diones unsubstituted in the N7 position were synthesized with the use of thietanyl protecting group. The thietane ring was introduced via the reaction of 8-bromo-3-methyl-3,7-dihydro-1H-purine-2,6-dione with 2-chloromethylthiirane, giving rise to 8-bromo-3-methyl-7-(thietan-3-yl)-3,7-dihydro-1H-purine-2,6-dione. The subsequent alkylation with benzyl chloride yielded 1-benzyl-8-bromo-3-methyl-7-(thietan-3-yl)-3,7-dihydro-1H-purine-2,6-dione, which was oxidized with hydrogen peroxide to be converted to 1-benzyl-8-bromo-3-methyl-7-(1,1-dioxothietan- 3-yl)-3,7-dihydro-1H-purine-2,6-dione. This product reacted with amines to give 8-amino-substituted 1-benzyl-3- methyl-7-(1,1-dioxothietan-3-yl)-3,7-dihydro-1H-purine-2,6-diones. The reaction of 8-substituted 1-benzyl-3- methyl-7-(1,1-dioxothietan-3-yl)-3,7-dihydro-1H-purine-2,6-diones with sodium isopropoxide resulted in the removal of the thietanyl protection and afforded target 8-substituted 1-benzyl-3-methyl-3,7-dihydro-1H-purine-2,6- diones. The structures of the targets compounds have been deduced upon their elemental analysis and spectral data (IR, 1H NMR, 13C NMR and 15N NMR). Results and Discussion: A new 8-substituted 1-benzyl-3-methyl-3,7-dihydro-1H-purine-2,6-diones unsubstituted in the N7 position were synthesized using thietanyl protecting group. Conclusion: The present study described a new route to synthesize some new 1,8-disubstituted 3-methyl-3,7- dihydro-1H-purine-2,6-diones unsubstituted in the N7 position starting from available 8-bromo-3-methyl-3,7- dihydro-1H-purine-2,6-dione with use of thietanyl protecting group. The advantages of this protocol are the possibility of the synthesis of 1-benzyl-substituted 3,7-dihydro-1H-purine-2,6-diones, the stability of the thietanyl protecting group upon nucleophilic substitution by amines of the bromine atom in the position 8, as well as mild conditions, and simple execution of experiments.