Structural Optimizations on the Scaffold of 7H-Pyrrolo[2,3-d]Pyrimidine to Develop Potent iNOS Inhibitors With Improved Antiarthritis Activity In Vivo

Inducible nitric oxide synthase (iNOS) is an attractive target to develop drugs for the treatment of rheumatoid arthritis (RA), whose overexpression leads to the release of abundant NO. In this study, a series of compounds were designed and synthesized bearing the scaffold of 7H-pyrrolo[2,3-d]pyrimidine to improve CLogP values and in vivo anti-inflammatory activity via molecular hybridization, whose derivatives in a previous study demonstrated good inhibition toward NO production but high CLogP values and weak potency in vivo. Among them, N3b effectively suppressed NO production in a concentration-dependent manner (IC₅₀ = 4.66 ± 0.19 μM) in LPS-induced RAW264.7 cells. Mechanically, N3b mildly inhibited the protein expression of iNOS (IC₅₀ = 13.60 ± 0.39 μM), without remarkable influence on the mRNA levels of iNOS or other classical pro-inflammatory cytokines including IL-1β, IL-6, and TNF-α at the high concentration of 30 µM. With favorable drug-likeness, N3b significantly alleviated paw edema at the dose of 30 mg/kg in the acute inflammation model and mitigated paw swelling and joint damage at a dosage of 10 mg/kg in the chronic arthritis model. Furthermore, N3b did not cause any obvious weight loss and pathological changes of important organs in treated mice, indicating that N3b is a potent candidate iNOS inhibitor for the treatment of RA.