Computational design, synthesis and biological evaluation of PDE5 inhibitors based on N,N-diaminoquinazoline and N,N-diaminopurine scaffolds.

We report the synthesis, and characterization of twenty-nine new inhibitors of PDE5. Structure-based design was employed to modify to our previously reported 2,4-diaminoquinazoline series. Modification include scaffold hopping to 2,6-diaminopurine core as well as incorporation of ionizable groups to improve both activity and solubility. The prospective binding mode of the compounds was determined using 3D ligand-based similarity methods to inhibitors of known binding mode, combined with a PDE5 docking and molecular dynamics based-protocol, each of which pointed to the same binding mode. Chemical modifications were then designed to both increase potency and solubility as well as validate the binding mode prediction. Compounds containing a quinazoline core displayed ICs ranging from 0.10 to 9.39 µM while those consisting of a purine scaffold ranging from 0.29 to 43.16 µM. We identified 25 with a PDE5 IC of 0.15 µM, and much improved solubility (1.77 mg/mL) over the starting lead. Furthermore, it was found that the predicted binding mode was consistent with the observed SAR validating our computationally driven approach.