Synthesis of related substances of olmesartan medoxomil, an anti-hypertensive drug

Olmesartan medoxomil 1 is the latest angiotensin receptor antagonist approved by the FDA for the treatment of hypertension.During the process development of olmesartan medoxomil, four related substances (impurities) were observed along with the final API.Those impurities were identified as olmesartan acid, 4-acetyl olmesartan, 5-acetyl olmesartan, and dehydro olmesartan.Present work describes the synthesis and characterization of all these four impurities.