nNOS-IN-3 (compound 4) is a selective inhibitor of neuronal nitric oxide synthase (nNOS), demonstrating a Ki of 25 nM for human nNOS and 18 nM for rat nNOS. It exhibits a Ki of 58 μM for human endothelial NOS (heNOS) and 6.4 μM for human inducible NOS (hiNOS). This compound binds to the active site of nNOS through hydrogen bonding with Glu and chalcogen bonding with Met; however, it does not form chalcogen bonds with heNOS. It is passively transported across cell membranes with minimal risk of efflux. nNOS-IN-3 is applicable in research on neurodegenerative diseases and melanoma.