A revisited structure for nitrosoprodenafil from NMR, mass spectrometry, X-ray and hydrolysis data

The sildenafil analogue adulterant previously identified as a nitroso derivative (nitrosoprodenafil) in a dietary supplement (DS) marketed to increase sexual performance and sold in Europe in the early 2010 s is the same as that found in the same type of DS available in Japan whose structure was established as a nitro derivative (mutaprodenafil or nitroprodenafil). Indeed, the compound isolated from the Man Power DS has identical UV, IR, NMR and MS spectroscopic characteristics and hydrolysis behavior than nitrosoprode-nafil. By revisiting its NMR assignments and MS and MS/MS data interpretation, it is demonstrated that the compound is actually a nitrothioimidazole-methisosildenafil hybrid, i.e. nitroprodenafil, whose structure is unequivocally confirmed by X-ray crystallography and synthesis experiments. Because the product is converted to methisosildenafil by hydrolysis, it is named nitropromethisosildenafil.