Overproduction of nitric oxide by neuronal nitric oxide synthase (nNOS) has been linked to several neurodegenerative diseases. We have recently designed potent and isoform selective inhibitors of nNOS, but the lead compound contains several basic functional groups. A large number of charges and hydrogen bond donors can impede the ability of molecules to cross the blood brain barrier and thereby limit the effectiveness of potential neurological therapeutics. Replacement of secondary amines in our lead compound with neutral ether and amide groups was made to increase bioavailability and to determine if the potency and selectivity of the inhibitor would be impacted. An ether analogue has been identified that retains a similar potency and selectivity to that of the lead compound, and shows increased ability to penetrate the blood brain barrier.

Process development work to provide an efficient, robust, and cost-effective manufacturing route to avibactam, a β-lactamase inhibitor is presented herewith. Aspects of this optimization work include the counterintuitive introduction of a protecting group to effect a difficult urea formation and the use of controlled feed hydrogenation conditions to facilitate an elegant one pot debenzylation and sulfation reaction. Overall, the commercial process delivers avibactam in much improved yield with significant reduction in the environmental footprint.

New nitric oxide synthase (NOS) inhibitors were designed de novo with knowledge gathered from the studies on the nNOS-selective dipeptide inhibitors. Each of the new inhibitors consists of three fragments: an aminopyridine ring, a pyrrolidine, and a tail of various length and polarity. The in vitro inhibitory assays indicate good potency and isoform selectivity for some of the compounds. Crystal structures of these inhibitors bound to either wild type or mutant nNOS and eNOS have confirmed design expectations. The aminopyridine ring mimics the guanidinium group of L-arginine and functions as an anchor to place the compound in the NOS active site where it hydrogen bonds to a conserved Glu. The rigidity of the pyrrolidine ring places the pyrrolidine ring nitrogen between the same conserved Glu and the selective residue nNOS Asp597/eNOS Asn368 which results in similar interactions observed with the α-amino group of dipeptide inhibitors bound to nNOS. These structures provide additional information to help in the design of inhibitors with greater potency, physico-chemical properties, and isoform selectivity.

Several prodrug approaches were taken to mask amino groups in two potent and selective neuronal nitric oxide synthase (nNOS) inhibitors containing either a primary or secondary amino group to lower the charge and improve blood-brain barrier (BBB) penetration. The primary amine was masked as an azide and the secondary amine as an amide or carbamate. The azide was not reduced to the amine under a variety of in vitro and ex vivo conditions. Despite the decrease in charge of the amino group as an amide and as carbamates, BBB penetration did not increase. It appears that the use of azides as prodrugs for primary amines or amides and carbamates as prodrugs for secondary amines are not universally effective approaches for CNS applications.Keywords amine prodrug; neuronal nitric oxide synthase inhibitor; blood-brain barrier; organic azide

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