Synthesis, chemical behavior, structure elucidation and iNOS inhibitory activity of 1-substituted...

Novel slim and shapely sp3-rich nitrogen containing heterocyclic ring systems are sought-after platforms for the expansion of molecular diversity in lead discovery. The present work describes the synthesis and characterization of a series of derivatives of hitherto unknown 3-methylsulfanyl-5,6,7,8-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazines 2. This approach was guided by a computational study, aiming at an optimization of previously reported [1,2,4]triazolo[1,2-a]pyridazine-1-thiones 1 known to inhibit the inducible nitric oxide synthase (iNOS). The title compounds are accessible by methylation of compounds 1 under mild conditions. The products were biologically evaluated by the same cell-based assay as applied for previous products of type 1 using RINm5F cells, which were stimulated to produce NO on the influence of proinflammatory cytokines IL-1β and IFN-γ. Compounds 2 did not display the anticipated improved iNOS inhibitory activity in the selected assay but contribute to SAR in the field. In addition, an unprecedented formation of side-products 3 via oxidation has been investigated. The novel scaffolds represent attractive starting points for the construction of diverse molecules which differ considerably from known compounds based on flat and lipophilic aromatic scaffolds.