Fragment-based approach to the design of 5-chlorouracil-linkedpyrazolo[1,5-a][1,3,5]triazines as thymidine phosphorylase inhibitors

5-Chlorouracil-linked-pyrazolo[1,5-a][1,3,5]triazines were designed as new thymidine phosphoiylase inhibitors based on the fragment based drug design approach. Multiple-step convergent synthetic schemes were devised to generate the target compounds. The intermediate 5-chloro-6chloromethyluracil was synthesized by a 4-step reaction. A series of the second bicyclic intermediates, namely pyrazolo[1,5-a][1,3,5]triazin-2-thioxo-4-one, was obtained from various substituted 3aminopyrazoles. These two intermediates were coupled finally in the presence of sodium ethoxide and methanol to yield the desirable target compounds. The methylthio coupling spacer was found to be suitable in enabling the interaction of the two fragments at the active site and allosteric site of the enzyme. The best coupled compound (9q) inhibited the thymidine phosphorylase with an IC50 value as low as 036 +/- 0.1 mu M. In addition, 9q demonstrated a mixed-type of enzyme inhibition kinetics, thus suggesting that it might indeed potentially bind at two different sites on the enzyme. (C) 2013 Elsevier Masson SAS. All rights reserved.