title: Fragment-based approach to the design of 5-chlorouracil-linked-pyrazolo[1,5-a][1,3,5]triazines as thymidine phosphorylase inhibitors.
abstract: 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.
authors.affiliation: Department of Pharmacy, Faculty of Science, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore. Electronic address: lingyisun@gmail.com.
authors.forename: Lingyi
authors.initials: L
authors.lastname: Sun
authors.forename: Jiarong
authors.initials: J
authors.lastname: Li
authors.forename: Hriday
authors.initials: H
authors.lastname: Bera
authors.forename: Anton V
authors.initials: AV
authors.lastname: Dolzhenko
authors.forename: Gigi N C
authors.initials: GN
authors.lastname: Chiu
authors.forename: Wai Keung
authors.initials: WK
authors.lastname: Chui
mesh_terms: D004305:Dose-Response Relationship, Drug; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D015394:Molecular Structure; D011719:Pyrazines / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013939:Thymidine Phosphorylase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014227:Triazines / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D011719:Pyrazines; D014227:Triazines; C586271:pyrazolo(1,5-a)(1,3,5)triazine; D014498:Uracil; C010889:5-chlorouracil; C543750:TYMP protein, human; D013939:Thymidine Phosphorylase
keywords: 5-Chlorouracil-linked-pyrazolo[1,5-a][1,3,5]triazines; Fragment-based drug design; Mixed-type enzyme inhibition kinetics; Thymidine phosphorylase inhibitor