Isolation and characterization of a tadalafil analogue, N-cyclopentyl nortadalafil in health supplement

A tadalafil analogue was detected for the first time during the screening of a health supplement for undeclared sexual enhancement drugs. The compound had been isolated and purified by preparative high-pressure liquid chromatography (HPLC). Its chemical structure was elucidated using high-resolution mass spectrometry (HRMS), electrospray ionization tandem mass spectrometry (ESI-MS/MS) and nuclear magnetic resonance (NMR) spectroscopy. The compound had a protonated molecular ion at m/z 444 with a chemical formula of C26H25N3O4. The data obtained from the MS analysis of the compound suggested that the N-methyl group on the piperazinedione moiety of tadalafil was substituted with a -C5H9 group. Analysis using NMR was performed and the -C5H9 group was characterized as a cyclopentyl moiety. The analogue was named N-cyclopentyl nortadalafil.