Potent, Selective, and Membrane Permeable 2-Amino-4-Substituted Pyridine-Based Neuronal Nitric Oxide Synthase...

A series of potent, selective, and highly permeable human neuronal nitric oxide synthase inhibitors (hnNOS), based on a difluorobenzene ring linked to a 2-aminopyridine scaffold with different functionalities at the 4-position, is reported. In our efforts to develop novel nNOS inhibitors for the treatment of neurodegenerative diseases, we discovered 17, which showed excellent potency toward both rat (K_i 15 nM) and human nNOS (K_i 19 nM), with 1075-fold selectivity over human eNOS and 115-fold selectivity over human iNOS. 17 also showed excellent permeability (P_e = 13.7 × 10^-6 cm s^-1), a low efflux ratio (ER 0.48), along with good metabolic stability in mouse and human liver microsomes, with half-lives of 29 and >60 min, respectively. X-ray cocrystal structures of inhibitors bound with three NOS enzymes, namely, rat nNOS, human nNOS, and human eNOS, revealed detailed structure-activity relationships for the observed potency, selectivity, and permeability properties of the inhibitors.