Isolation and structural elucidation of a new tadalafil analogue in health supplements: bisprenortadalafil.

A new tadalafil analogue was found, along with nortadalafil, using HPLC-DAD during the inspection of a health product sold without official approval. The analogue was separated using a semi-preparative HPLC system and its structure was determined by a combination of mass spectrometry and NMR spectroscopy. The compound was identified as a tadalafil analogue in which the N-methyl group of tadalafil was replaced with a tadalafil precursor moiety. Nuclear Overhauser effect spectroscopy experiments suggested a cis-relationship between the substituents on a piperidine ring in the tadalafil moiety.