Discovery and identification of a tadalafil analogue

A tadalafil analogue was detected during routine screenings from two "fatigue reliever, immunity enhancer" dietary supplements by using UHPLC/Q-TOF HRMS. The MS² spectrum of this compound was almost identical to that of 2-hydroxypropylnortadalafil. However, the retention time of this analogue was different from that of the 2-hydroxypropylnortadalafil isomers. The analogue was purified by using preparative HPLC and the structure was elucidated by mass spectrometric and NMR spectroscopic experiments. The spectral data suggested that the analogue bore a 3-hydroxypropyl group instead of the N-methyl group in tadalafil. The structure was further confirmed by comparison of the ¹H NMR spectra data with those of the reference standard, and thus named as 3-hydroxypropylnortadalafil. The structure is first reported in China.