Design and Synthesis of Aza-/Oxa Heterocycle-Based Conjugates as Novel Anti-Inflammatory Agents Targeting Cyclooxygenase‑2

A library of hybrid molecules was procured by the combination of triazine–indole adduct with morpholine/piperidine/pyrrolidine and pyrazole/pyrimidine/oxindole moieties. Enzyme immunoassays on cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) identified compound <b>6</b> having an IC₅₀ value of 20 nM for COX-2 and 3000 nM for COX-1. The significant reduction in the formation of prostaglandin E₂ in the lipopolysaccharide-treated (COX-2-activated) human whole blood, almost no change in the production of thromboxane B₂ in the calcium ionophore-treated (COX-1-activated) sample of human whole blood, and the mechanistic studies on Swiss albino mice ensured that compound <b>6</b> is selective for COX-2. The association constant (<i>K</i>_a) of compound <b>6</b> with COX-2 was found to be of the order of 0.48 × 10⁶ M^–1. The diffusion spectroscopy experiments and relaxation time (<i>T</i>₁) calculations of compound <b>6</b> in the presence of COX-2 assisted in identifying the site-specific interactions of <b>6</b> with the enzyme, and these results fall into nice correlation with the theoretical data obtained from molecular docking and quantitative structure–activity relationship studies. With maximum tolerable dose >2000 mg kg^–1, compound <b>6</b> made 68 and 32% reduction in formalin-induced analgesia and carrageenan-induced inflammation in Swiss albino mice