PPTS-catalyzed metal-free synthesis of poly-substituted pyridines: their in silico / in vitro evaluation against SIRT1

Abstract

The poly-substituted pyridine derivatives were explored as potential inhibitors of SIRT1. One-pot synthesis of these compounds was carried out via PPTS-catalyzed 3-component reaction (3-CR) of β-keto esters (or 1,3-diketones), 2-ylidenemalononitriles and anilines. This metal-free reaction proceeded in aqueous EtOH at room temperature to give the desired product within 3 h. A variety of reactants was employed in this environmentally friendly 3-CR where water seemed to be the only by-product. This straightforward and easy to operate methodology provided a series of desired products in good to high (85-92%) yields. A majority of these compounds showed good interactions with a number of residues when docked into SIRT1 in silico. Most of them including the top three molecules in terms of binding affinity i.e. 4c, 4e and 4k participated in the key H-bonds with ILE347 and ASP348 via their –CN moiety. Indeed, a comparison of the active site and binding poses of 4c, 4e and 4k along with native ligand EX527a in SIRT1 showed that they were aligned well. The high binding affinity of 4e was aided by its participation in two H-bonds with ILE347 and ASP348 via its CN moiety and three H-bonding with GLY319 and GLN320 through its NO₂ group. The in silico studies also predicted probable selectivity of 4c, 4e and 4k towards SIRT1 over SIRT2. When tested in vitro at 10 µM, these three compounds showed encouraging inhibition of SIRT1 (IC₅₀ ∼ 2.7-3.5 µM) when 4e emerged as the best active molecule. According to the SAR analysis, the promising activities were observed when the aryl group at C-4 was chosen as the 4-NCC₆H₄ or 4-O₂NC₆H₄ moiety, the group at C-3 was –CO₂Et and the amine substituent at C-6 was 2-MeC₆H₄NH- moiety. However, an i-butyl group at C-4 was found to be less effective. Based on in silico and in vitro studies along with ADME predictions the compound 4c, 4e and 4k were identified as preliminary hits for further pharmacological evaluation.