Design and synthesis of furyl/thineyl pyrroloquinolones based on natural alkaloid perlolyrine, lead to the discovery of potent and selective PDE5 inhibitors.

Based on perlolyrine (1), a natural alkaloid with weak PDE5 potency from the traditional Chinese aphrodisiac plant Tribulus terrestris L., a series α-substituted tetrahydro-β-carboline (THβC) derivatives were synthesized via T+BF4--mediated oxidative C-H functionalization of N-aryl THβCs with diverse potassium trifluoroborates. Following Winterfeldt oxidation afforded the corresponding furyl/thienyl pyrroloquinolones, of which 5-ethylthiophene/ethylfuran derivatives 20a-b were identified as the most potent and selective PDE5 inhibitors. Among the enantiomers, (S)-20a and (S)-20b (IC50 = 0.52 and 0.39 nM) were found to be more effective than their (R)-antipode, display favorable pharmacokinetic profiles, exert in vitro vasorelaxant effects on the isolated thoracic aorta, and exhibit in vivo efficacy in the anesthetized rabbit erectile model.