Novel Pyrazolo[4,3-<i>d</i>]pyrimidine as Potent and Orally Active Inducible Nitric Oxide Synthase (iNOS) Dimerization Inhibitor with Efficacy in Rheumatoid Arthritis Mouse Model

Abstract

In order to discover novel anti-inflammatory agents for treatment of arthritis and based on preliminary structure-activity relationships, four series (A-D) of total 90 new pyrazolo[4,3- d]pyrimidine compounds were designed and synthesized. All the compounds have been tested for their anti-inflammatory activities by inhibiting of LPS-induced NO production. A clear structure-activity relationship has been concluded step by step, and finally 3,4,5-trimethoxystyryl-1 H-pyrazolo[4,3- d]pyrimidine was found to be the most active scaffold. Among them, compound D27 was discovered as the most potent anti-inflammatory agent (IC₅₀ = 3.17 μM) with low toxicity and strong inhibitory of NO release (IR = 90.4% at 10 μM). This compound also showed potent inhibition of iNOS with IC₅₀ value of 1.12 μM. Preliminary mechanism studies indicated that it could interfere with the stability and formation of active dimeric iNOS. The anti-inflammatory effect of this compound was determined by adjuvant-induced arthritis in rat model. We believe these findings would further support the study of rational design of more efficient iNOS inhibitors in the future.