Synthesis and evaluation of new sulfur-containing L-arginine-derived inhibitors of nitric oxide synthase

A series of compounds (7, 8, 10-17, 23) containing new functional groups de rived by the combination of the substrate, intermediate, product, and known inhibitors of nitric oxide synthase (NOS) were prepared and evaluated agai nst NOS. While none of the compounds assayed acted as a nitric oxide-produc ing substrate, the sulfur-containing arginine derivatives 10-12 were compet itive inhibitors of iNOS with K-i's of 202, 7, and 58 mu M, respectively. C ompound 11 demonstrated the greatest potency against NOS-mediated citrullin e formation for each of the three isoforms with IC50's of 6.7, 19.7, and 13 mu M for nNOS, eNOS, and iNOS, respectively. Compounds 10-12 each demonstr ated a slight selectivity for inhibition of the neuronal isoform compared t o the endothelial and inducible isoforms. These compounds also influenced t he NADPH oxidase activity and heme iron spin state in a manner similar to s tructurally related compounds. Compound 10, a thiocarbonyl-containing compo und, decreased the NADPH oxidase activity of the enzyme (EC50 = 190 mu M) a nd shifted the heme iron spin state toward a low-spin configuration, simila r to that of L-thiocitrulline. Compounds 11 and 12, S-alkylthiocitrulline d erivatives, decreased the NADPH oxidase activity of the enzyme (EC50 = 6.6 and 180 mu M, respectively) and shifted the heme iron spin state toward a h igh-spin configuration, similar to that of L-S-methylisothiocitrulline. Car bonyl-containing amino acid (7, 8, 23) and non-amino acid (13-17) analogues did not interact well with the enzyme.