Cyclisation of 7‐Deazaxanthine‐9‐propionic Acid to an Active‐Site‐Directed, Irreversibly Acting Inhibitor of Xanthine Oxidase

Phase‐transfer alkylation of 2,4‐dimethoxy‐7 H ‐pyrrolo[2,3‐ d ]pyrimidine ( 2 ) with ethyl 3‐bromopropionate leads regioselectively to ethyl 2,3‐dimethoxy‐7 H ‐pyrrolo[2,3‐ d ]pyrimidine‐7‐propionate ( 3a ). After saponification and ether cleavage, the functionalised 7‐deazaxanthine 4b was obtained. Reaction of 4b with H 2 O‐soluble carbodiimide resulted in an intramolecular acylation at N(3) with formation of the tricyclic compound 5 . Compound 5 ‐ bearing a reactive lactam ring ‐ is an active‐site‐directed, irreversibly acting inhibitor of xanthine oxidase from cow's milk.