Nickel nanoparticles: a highly efficient and retrievable catalyst for the solventless Friedlander annulation of quinolines and their in silico molecular docking studies as histone deacetylase inhibitors

The present work explores a highly efficient, environmental friendly, green, solvent-free protocol for the preparation of polysubstituted quinolines via Friedlander annulation using nickel nanoparticles (80-100 nm) biofabricated from Aegle Marmelos Correa aqueous leaf extract. These nickel nano materials exhibit high catalytic efficacy to achieve the target molecules in excellent yields ranging from 85-96% mainly due to their diverse properties and high surface area to volume ratio. The synthesized polysubstituted quinolines were successfully characterized by FT-IR, H-1 NMR, C-13 NMR, and GC-MS. The effect of various solvents and catalyst concentration on the synthesis of quinolines has been investigated where under solventless conditions at 10 mol% of the nickel nano catalyst high yields of the product were obtained. Reusability of the catalyst upto five cycles under solvent-free conditions within shorter reaction time, without any significant loss in the yields of the product are the unique features of this heterogenous solid catalysis. Furthermore safer reaction profiles, high selectivity, greater yields, reliable cost efficiency, simple workup conditions are some of the noteworthy highlights of this green ecofriendly process. In silico molecular docking studies for anticancer efficacy of the quinoline derivatives as histone deacetylase inhibitors (HDIs) were carried out. The results showed that compounds 3h (-7.3), 3n (-7.1), 3l (-6.5) and 3b (-6.7), are having better binding affinity showing docking score which is greater than that of standard Vorinostat (-6.4) and comparable to that of standard Panobinostat (-7.9).