Nitrile in the Hole: Discovery of a Small Auxiliary Pocket in Neuronal Nitric Oxide Synthase Leading to the Development of Potent and Selective 2‑Aminoquinoline Inhibitors

Neuronal nitric oxide
synthase (nNOS) inhibition is a promising
strategy to treat neurodegenerative disorders, but the development
of nNOS inhibitors is often hindered by poor pharmacokinetics. We
previously developed a class of membrane-permeable 2-aminoquinoline
inhibitors and later rearranged the scaffold to decrease off-target
binding. However, the resulting compounds had decreased permeability,
low human nNOS activity, and low selectivity versus human eNOS. In
this study, 5-substituted phenyl ether-linked aminoquinolines and
derivatives were synthesized and assayed against purified NOS isoforms.
5-Cyano compounds are especially potent and selective rat and human
nNOS inhibitors. Activity and selectivity are mediated by the binding
of the cyano group to a new auxiliary pocket in nNOS. Potency was
enhanced by methylation of the quinoline and by introduction of simple
chiral moieties, resulting in a combination of hydrophobic and auxiliary
pocket effects that yielded high (∼500-fold) n/e selectivity.
Importantly, the Caco-2 assay also revealed improved membrane permeability
over previous compounds.