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

• Published in: European journal of medicinal chemistry 2013, Vol.70, p.400-410
• Main Authors: Sun, Lingyi, Li, Jiarong, Bera, Hriday, Dolzhenko, Anton V., Chiu, Gigi N.C., Chui, Wai Keung
• Format: Article
• Language: English
• Subjects: 5-Chlorouracil-linked-pyrazolo[1,5-a][1,3,5]triazines; Dose-Response Relationship, Drug; Drug Design; Enzyme Inhibitors - chemical synthesis; Enzyme Inhibitors - chemistry; Enzyme Inhibitors - pharmacology; Fragment-based drug design; Humans; Mixed-type enzyme inhibition kinetics; Molecular Structure; Pyrazines - chemical synthesis; Pyrazines - chemistry; Pyrazines - pharmacology; Structure-Activity Relationship; Thymidine Phosphorylase - antagonists & inhibitors; Thymidine Phosphorylase - metabolism; Thymidine phosphorylase inhibitor; Triazines - chemical synthesis; Triazines - chemistry; Triazines - pharmacology; Uracil - analogs & derivatives; Uracil - chemistry
• ISSN: 0223-5234; 1768-3254
• DOI: 10.1016/j.ejmech.2013.10.022

5-Chlorouracil-linked-pyrazolo[1,5-a][1,3,5]triazines were designed as new thymidine phosphorylase 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-6-chloromethyluracil 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 3-aminopyrazoles. 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 0.36 ± 0.1 μM. 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. IC50 value of 9q against the Escherichia coli thymidine phosphorylase was 0.36 ± 0.10 μM. [Display omitted] •New inhibitors were devised that would target two binding sites in thymidine phosphorylase.•A fragment-based approach was used to design the target inhibitors.•Thirty 5-chlorouracil-linked-pyrazolo[1,5-a][1,3,5]triazines were synthesized.•The IC50 value of the most active inhibitor was 0.36 + 0.1 μM.•The most active compound demonstrated mix-type of enzyme inhibition kinetics.