Separation and structural elucidation of a novel analogue of vardenafil included as an adulterant in a dietary supplement by liquid chromatography–electrospray ionization mass spectrometry, infrared spectroscopy and nuclear magnetic resonance spectroscopy

MEGATON, a dietary supplement, was analyzed in order to detect PDE-5 inhibitors and their analogues. A new analogue of vardenafil could be detected by high-performance liquid chromatography (HPLC) analysis with a photodiode array detector (PDA). This compound was compared with sildenafil, tadalafil, and vardenafil as well as their structurally modified analogues such as hongdenafil and homosildenafil. The structure of this compound was elucidated by mass spectrometry (MS), infrared (IR) spectroscopy and one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. When compared with vardenafil to verify the structural difference, this compound had an acetyl group instead of a sulfonyl group in the pyrazolopyrimidine portion without any substitution in the piperazine ring of the molecule. This compound was identified as 2-(2-ethoxy-5-(2-(4-ethylpiperazin-1-yl)acetyl)phenyl)-5-methyl-7-propyl-imidazo(5,1-f)-(1,2,4)triazin-4(3H)-one, which is also called acetylvardenafil.