Design and environmentally benign synthesis of novel thiophene appended pyrazole analogues as anti-inflammatory and radical scavenging agents: Crystallographic, in silico modeling, docking and SAR characterization

Abstract

Oxidative-stress induces inflammatory diseases and infections caused by drug-resistant microbial strains are on the rise necessitating the discovery of novel small-molecules for intervention therapy. The current study presents an effective and new green protocol for the synthesis of thiophene-appended pyrazoles through 3+2 annulations method. Chalcones 3(a-g) were prepared from 5-chloro-2-acetylthiophene and aromatic aldehydes by Claisen-Schmidt approach. The reaction of chalcones 3(a-g) with phenylhydrazine hydrochlorides 4(a-b) in acetic acid (30%) medium and also with freshly prepared citrus extract medium under reflux conditions produced the thiophene appended pyrazoles 5(a-l) in moderate yields. Structures of synthesized new pyrazoles were confirmed by spectral studies, elemental analysis and single crystal X-ray diffraction studies. Further, preliminary assessment of the anti-inflammatory properties of the compounds showed that, amongst the series, compounds 5d, 5e and 5l have excellent anti-inflammatory activities. Further, compounds 5c, 5d, 5g, and 5i exhibited excellent DPPH radical scavenging abilities in comparison with the standard ascorbic acid. Furthermore, using detailed structural modeling and docking efforts, combined with preliminary SAR, we show possible structural and chemical features on both the small-molecules and the protein that might contribute to the binding and inhibition.

Keywords: Anti-inflammatory; Antioxidant; Chalcone; Cyclocondensation; Green synthesis; Phase transfer.