Isolation and identification of novel propoxyphenyl thiosildenafil found in natural health food product

Abstract

A novel phosphodiesterase-5 (PDE-5) inhibitor was found in a natural health food product. The previously unknown sildenafil analogue was isolated using preparative HPLC. The structure of the compound was elucidated using HPLC with diode array detection (DAD), time-of-flight mass spectrometry (TOF/MS), and nuclear magnetic resonance spectroscopy (NMR). An [M + H]⁺ ion was detected at m/z 505.2077 by LC-TOF/MS that was consistent with C₂₃H₃₂N₆O₃S₂ (–0.98 ppm). By NMR analysis, the analogue was identified as 1-methyl-5-(5-(4-methylpiperazin-1-ylsulfonyl)-2-propoxyphenyl)-3-propyl-1H-pyrazolo[4,3-d]pyrimidine-7(6H)-thione. In this structure, the ethoxy group of thiosildenafil was substituted by a propoxy group of the unknown compound. Therefore, this novel thiosildenafil analogue was named propoxyphenyl thiosildenafil.

Keywords:

• thiosildenafil analogue
• propoxyphenyl thiosildenafil
• LC-TOF/MS
• NMR