Isolation and characterization of a novel tadalafil analogue adulterant, N-cyclohexyl nortadalafil, in a dietary supplement

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A novel tadalafil analogue was detected during routine screening of dietary supplements suspected to be adulterated with an erectile dysfunction drug(s) by using ultra-high-performance liquid chromatography coupled to Quadrupole-Exactive Orbitrap mass spectrometry (UPLC‑Q‑Exactive Orbitrap/MS). The MS2 spectrum of the compound was highly similar to that of tadalafil within the range of < 300 m/z. The UV spectrum of the compound was almost identical to that of tadalafil. The analogue was purified by semi-preparative HPLC and structurally elucidated by FT-IR, MS and NMR analysis. The analogue was finally determined as N-cyclohexyl nortadalafil, featuring the cyclohexyl group instead of the N-methyl group on the piperazinedione ring of tadalafil.