Synthesis of pyrazolo[1,5-a][1,3,5]triazine derivatives as inhibitors of thymidine phosphorylase

• 52 pyrazolo[1,5-a][1,3,5]triazine derivatives were synthesized.
• 28 pyrazolo[1,5-a][1,3,5]triazine derivatives inhibited thymidine phosphorylase.
• 17p (IC50 = 0.04 μM) is 800 times more active than the lead (7-deazaxanthine).
• Substituents with +σ and +π properties contributed to better inhibition.
• 17p was found to be a non-competitive inhibitor of thymidine phosphorylase.

Thymidine phosphorylase (TP) is an enzyme that promotes tumor growth and metastasis and therefore is an attractive druggable target. Using a reported TP inhibitor, 7-deazaxanthine (7DX), as the lead compound; this study was set up to evaluate whether pyrazolo[1,5-a][1,3,5]triazin-2,4-diones and pyrazolo[1,5-a][1,3,5]triazin-2-thioxo-4-ones would exhibit TP inhibitory activity. The pyrazolo[1,5-a][1,3,5]triazine nucleus was constructed using a reaction that annulated the 1,3,5-triazine ring onto a pyrazole scaffold. Among the 52 compounds synthesized and tested, it was found that 1,3-dihydro-pyrazolo[1,5-a][1,3,5]triazin-2-thioxo-4-ones exhibited various extent of inhibitory activity against TP. The best compound 17p, which bears a para-substituted pentafluorosulfur group, showed an IC50 value of 0.04 μM, which was around 800 times more potent than the 7DX (IC50 = 32 μM) under the same bioassay conditions. The results of the study suggested that a substituent with +σ and +π properties inserted at position 4 of a phenyl ring that is attached to position 8 of the pyrazolo[1,5-a][1,3,5]triazin-2-thioxo-4-one scaffold would give excellent TP inhibitory action. In addition, 17p was found to be a non-competitive inhibitor thus suggested that it might interact with TP at a position different from the substrate binding site.

17p is a new non-competitive inhibitor of thymidine phosphorylase (IC50 value = 0.040 ± 0.005 μM).Figure optionsDownload as PowerPoint slide