Scheme 3From: Identification, synthesis, and characterization of potential genotoxic impurities of sildenafil citrate drug substanceSynthetic scheme of sildenafil sulfonyl ethyl ester 7. Reagents and conditions: (a) trimetyl orthoformate, ethanol, and dichloromethane and (b) pyridine, ethanol, and dichloromethaneBack to article page