Sildenafil N-Desmethyl Metabolite

ethyl (2R, 4S)?4?{[(tert?butoxy)carbonyl]amino}?2?methyl?5?(4?phenylphenyl)pentanoate ; (2R, 4S)-ethyl 5-([1, 1'-biphenyl]-4-yl)-4-((tert-butoxycarbonyl)amino)-2-methylpentanoate;