Enhancement of Potency and Selectivity of 2-Aminoquinoline-Based Human Neuronal Nitric Oxide Synthase Inhibitors

Neuronal nitric oxide synthase (nNOS) is a key enzyme in neurodegenerative diseases and melanoma, making it an important therapeutic target. We previously reported 2-aminoquinoline-based nNOS inhibitors with promising activity but limited by suboptimal potency, isoform selectivity, and off-target effects. To address these issues, we designed and synthesized a new series of 7-aryl-6-fluoro-4-methyl-2-aminoquinoline derivatives. Compound 16 showed excellent potency against human nNOS (Ki 16 nM), with ∼1800-fold selectivity over human endothelial NOS (eNOS) and ∼2900-fold over human inducible NOS (iNOS). PAMPA-BBB experiments indicated high effective permeability (Pe = 13.04 × 10⁻⁶ cm/s), suggesting strong CNS drug potential. In vivo pharmacokinetic studies in mice further demonstrated sustained systemic exposure, low clearance, and robust brain penetration. In contrast, compound 24, the N-Me analogue of 16, was inactive. Molecular dynamics simulations indicated that N-methylation disrupted the favorable solvation of the tail amino group, likely contributing to its loss of activity and nNOS affinity.