In search of new Nitric Oxide Synthase (NOS) inhibitor agents, two isosteric series of derivatives with an imidamide scaffold (one of them with a hydroxyl group and the other with a carbonyl one) were synthesized and evaluated on inducible (iNOS) and neuronal (nNOS) isoforms. These compounds have been designed by combining a kynurenamine framework with an amidine moiety in order to improve selectivity for the inducible isoform. In general, the in vitro inhibitory assays exhibited better inhibition values on the iNOS isoform, being the N-(3-(2-amino-5-methoxyphenyl)-3-hydroxypropyl)-4-(trifluoromethyl)benzimidamide 4i the most active inhibitor with the highest iNOS selectivity, without inhibiting eNOS. Docking studies on the two most active compounds suggest a different binding mode on both isozymes, supporting the experimentally observed selectivity towards the inducible isoform. Physicochemical in silico studies suggest that these compounds possess good drug-likeness properties.

The synthesis and biological evaluation of new types of N,N′-disubstituted thiourea and urea derivatives as inhibitors of both neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) are described. These compounds have been designed by reduction of the carbonyl group in the thiourea and urea kynurenamine derivatives 3 previously synthesized by our research group. The synthetic route performed to this new family also allows us to obtain the molecules 3 with less synthetic steps and higher global yield. Regarding the biological results, in general, the new derivatives 4a–q inhibit the neuronal NOS isoform better than the inducible one. Furthermore, thioureas exhibit higher inhibition than ureas for both isoenzymes. Among all the tested compounds, 4g shows significant nNOS (80.6%) and iNOS (76.6%) inhibition values without inhibiting eNOS. This molecule could be an interesting starting point for the design of new inhibitors with application in neurological disorders where both isoenzymes are implicated such as Parkinson's disease.

The selective inhibition of inducible nitric oxide synthase (iNOS) has become an interesting goal for the treatment of diseases where the immune and inflammatory response of the organism is involved. Septic shock is one prominent example of this type of affections. In this paper, the design and synthesis of twelve substituted pyridinyl- imidamide derivatives is described, together with their biological evaluation as NOS inhibitors. The most potent and selective compound was N-(3-hydroxy-3-(pyridin-3-yl)propyl)acetimidamide 9a (IC₅₀ = 4.6 µM, against iNOS). Pharmacological assays in aortic rat tissue, have confirmed its inhibitory activity on iNOS and the absence of undesired cardicovascular effects. In silico analysis of the most promising compounds (9a, 9b, 9e and 9g) have predicted good drug-likeness properties. Furthermore, they have shown an adequate cell viability. Docking studies carried out on 9a suggest a particular binding mode that involves the essential residue Glu377, and might explain its iNOS selectivity. From a chemical point of view, the article describes an unusual cyclization to obtain pyridinyl-pyrimidine derivatives with high yield.

Two new families of pyrazoline and thiadiazoline heterocycles have been developed. Their inhibitory activities against two different isoforms of nitric oxide synthase (inducible and neuronal NOS) are reported. The novel derivatives were synthesized combining the arylthiadiazoline or arylpyrazoline skeleton and a carboxamide or carbothioamide moiety, used as starting material ethyl 2-nitrobenzoates or substituted nitrobenzaldehydes, respectively. The structure-activity relationships of final molecules are discussed in terms of the R₁ radical effects in the aromatic ring, the Y atom in the heterocyclic system, the X heteroatom in the main chain, and the R₂ substituent in the carboxamide or carbothioamide rest. In general, thiadiazolines (5a–e) inhibit preferentially the neuronal isoform; among them, 5a is the best nNOS inhibitor (74.11% at 1 mM, IC₅₀ = 420 μM). In contrast, pyrazolines (6a–r) behave better as iNOS than nNOS inhibitors, 6m being the best molecule of this series (76.86% at 1 mM of iNOS inhibition, IC₅₀ = 130 μM) and the most potent of all tested compounds.