Structure elucidation of a novel analogue of sildenafil detected as an adulterant in an herbal dietary supplement

A new analogue of sildenafil was detected in an herbal dietary supplement, which was sold over the internet and promoted as a product for the enhancement of sexual performance. The structure of the compound was established using LC–MS, UV spectroscopy, MS–MS, and NMR. In addition, the compound was cleaved at its sulfonamide S–N bond yielding a sulfonic acid and an amine, which were independently characterized using LC–MS, GC–MS, and derivatization. The compound, named methisosildenafil, is a novel synthetic analogue of sildenafil in which the N-methylpiperazine moiety has been replaced with 2,6-dimethylpiperazine.