Avanafil Metabolite M-4

Avanafil Metabolite M-4 is a phase I oxidative derivative of avanafil, characterized by hydroxylation at the 4-position of the pyrazine ring and subsequent carboxylic acid formation via metabolic oxidation. This impurity retains the benzothiazole core and sulfur-containing side chain of the parent compound but features a terminal carboxylic acid group substituting the pyrazine methyl moiety. It arises via cytochrome P450-mediated biotransformation, reflecting a major hepatic clearance pathway. Serves as an HPLC reference standard for quantifying process-related impurities in avanafil drug substance synthesis.