Allisartan Isoproxil

Allisartan isoproxil, a member of a new class of selective angiotensin II-1 receptor antagonists, was approved by the Chinese Food and Drug Administration (CFDA) for the treatment of hypertension in July 2012.19 At time of publication, there is no trade name associated with this drug. Allisartan was discovered and developed by the Chinese biomedical company Allist Pharmaceuticals. Allisartan isoproxil is a prodrug which is readily hydrolyzed to active metabolite EXP3174, which is also the active metabolite of losartan (des-triphenylmethyl-9).

Although several synthetic routes have been reported within two patents, the most likely scalable process route is described in the scheme. Commercial 2-butyl-4-chloro-5-(hydroxymethyl)-imidazole (7) was alkylated with Ntriphenylmethyl- 5-(4'-bromomethylbiphenyl-2-yl)tetrazole (8) under basic conditions in warm DMF, providing alcohol 9 in 90% yield. This alcohol was then oxidized to the corresponding carboxylic acid 10 with KMnO4 in 88% yield. Etherification of acid 10 with isopropyl chloromethyl carbonate (11) followed by de-tritylation of the tetrazole group under acidic contidions gave allisartan isoproxil (II) in 69% yield.