Synthesis of classical and nonclassical 2‐amino‐4‐oxo‐6‐benzylthieno‐[2,3‐d]pyrimidines as potential thymidylate synthase inhibitors

A series of seven nonclassical 2‐amino‐4‐oxo‐6‐substituted thieno[2,3‐d]pyrimidines 2‐8 and one classical N‐[4‐(2‐amino‐4‐oxo‐3,4‐dihydrothieno[2,3‐d]pyrimidin‐6‐ylmethyl)benzoyl]‐L‐glutamic acid 9 (Table I) were designed as the first in a series of 6‐substituted 6‐5 fused ring analogs as potential thymidylate synthase (TS) inhibitors and as antitumor agents. The target compounds were synthesized via a Heck coupling of appropriately substituted iodobenzenes and allyl alcohol followed by cyclization using cyanoacetate and sulfur powder to afford substituted thiophenes. The resulting thiophenes were then cyclocondensed with chloroformamidine hydrochloride to afford 2‐amino‐4‐oxo‐6‐substituted thieno[2,3‐d]pyrimidines 2‐8 and 26 . Hydrolysis of 26 followed by coupling with diethyl L‐glutamate afforded 28 . The classical analog 9 was obtained by hydrolysis of 28 . None of the target compounds inhibited human recombinant thymidylate synthase at 23 μm except 9 for which the IC₅₀ value was 100 μm.