Design, Synthesis and Structure–Activity Relationship of Functionalized Tetrahydro‐β‐carboline Derivatives as Novel PDE5 Inhibitors

Abstract

Starting from tadalafil as a template, a series of functionalized tetrahydro‐β‐carboline derivatives have been prepared and identified as novel potent and selective PDE5 inhibitors. Replacing the 3,4‐methylenedioxyphenyl at position 6 of tadalafil, together with elongation of the N2‐methyl substituent and manipulation of the stereochemical aspects of the two chiral carbons led to the identification of compound XXI, a highly potent PDE5 inhibitor (IC₅₀ = 3 nM). Compound XXI was also highly selective for PDE5 versus PDE3B, PDE4B, and PDE11A, with a selectivity index of 52 and 235 towards PDE5 rather than PDE11 with both cAMP and cGMP as substrate, respectively.