Telmisartan, an anti-hypertensive drug, was subjected to stress studies under ICH prescribed conditions of hydrolysis (acidic, neutral and basic), photolysis, oxidation and thermal stress. The drug showed labiality under only photo-acidic condition by forming a single degradation product. HPLC separation of the drug and the degradation product was achieved on C-8 column using gradient method. To characterize the product, a complete mass fragmentation pathway of the drug was initially established. Subsequently, the degradation product peak was subjected to LC-MS/TOF and on-line H/D exchange mass studies. Based on these studies, a tentative structure was assigned to the product as 3-((1,7'-dimethyl-2'-propyl-1H,3'H-2,5'-bibenzo[d]imidazol-3'-yl)methyl)-6H-benzo[c]chromen-6-one, which was verified through (1)H LC-NMR experiments.
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