Identification and characterization of geometrical isomeric photo degradation product of eprosartan using LC-MS and LC-NMR

The degradation of eprosartan was evaluated under ICH/WHO prescribed stress conditions. The drug degraded to only one product under photo alkali condition, whereas it was stable to conditions of hydrolysis, oxidation and thermal stress. The drug and its co-eluting product were well separated on RP-HPLC in a gradient mode. Subsequently, LC-MS/TOF and on-line H/D exchange studies were performed on both of them. The two showed same molecular mass, similar fragment ions and even the same number of labile hydrogens indicating the product to be an isomer of the drug. To confirm the same, 1H and COSY LC-NMR studies were carried out by using an enriched sample. Distinguishing behaviour of chemical shifts proved the product to be (Z)-4-((2-butyl-5-(2-carboxy-3-(thiophen-2-yl)prop-1-enyl)-1H-imidazol-1-yl)methyl)benzoic acid. The structure was further supported by differential LC-MS ion intensities of the drug and the product.