Synthesis and anticancer activity of thiosubstituted purines

New thiopurines with the propargylthio, pyrrolidinobutynylthio, sulfenamide, and sulfonamide groups in the pyrimidine ring were synthesized. The anticancer activity of these compounds and previously obtained 2- or 6-substituted azathioprine analogs and dialkylaminoalkylthiopurines were tested in vitro against three cell lines: glioblastoma SNB-19, melanoma C-32, and human ductal breast epithelial tumor T47D. 2-Chloro-7-methyl-6-pyrrolidinobutynylthiopurine (5b) was the most potent compound against SBN-19 and C-32 cell lines with the activity similar to cisplatin (EC₅₀ = 5.00 and 7.58 μg/ml, respectively). The dialkylaminoalkylthio derivatives (4b, 4c, 4e, and 4f) showed good activity against SBN-19 cell line (EC₅₀ < 10 μg/ml). The azathioprine analogs (2a, 2b, and 3a) were more active than azathioprine against SBN-19 and C-32 cell lines. The sulfenamide and sulfonamide derivatives of purine were very weak active against tested cell lines. All studied thiopurines were less toxic than cisplatin.