Facile and Cost-Effective Route for the Synthesis of Simmerafil

An improved synthesis of simmerafil, a potent PDE5 inhibitor as a clinical candidate, is described with a 38.1% overall yield and 99.7% purity. Starting from the safe and inexpensive salicylamide (15), the key intermediate 2-propoxybenzimidamide (21), which is also a potential precursor for the preparation of pyrimidinone derivatives, was effectively and conveniently obtained. The subsequent process from 21 to simmerafil was optimized, which makes it more amenable to scale-up.