Abstract: AimTo develop a new synthetic route for olmesartan medoxomil. MethodsOlmesartan medoxomil was prepared from ethyl 4-(1-hydroxy-1-methylethyl)-2-propylimidazole-5-carboxylate via hydrolysis and lactonization to afford 4,4- dimethyl-2-propyl-4,6-dihydrofuro ［3,4-d］-1H-imidazole-6-one which was condensed with 2-(triphenylmethyl)-5-［4′-(bromomethylbiphenyl)-2-yl］tetrazole, followed by esterification with 4-chloromethyl-5-methyl-1,3-dioxol-2-one, and deprotection. The chemical structure of the major impurity in condensation reaction is the regio-isomer in the imidazole moiety, and confirmed by single crystal X-ray diffraction. The corresponding regio-isomer of olmesartan medoxomil was synthesized from the impurity by similar method. Optimization of the condensation conditions reduced the impurity to a negligible quantity. ResultsSynthesis of olmesartan medoxomil by the new route gave a product of 60% yield and above 99.0% purity. The content of olmesartan medoxomil regio-isomer was effectively controlled to less than 0.1%. ConclusionA novel synthetic route for olmesartan medoxomil was developed successfully. The olmesartan medoxomil regio-isomer is reported for the first time.