Quinoline-hydrazone Conjugates: Recent Insights into Synthetic Strategies, Structure-activity Relationship, and Biological Activities

The fusion of two distinct and free pharmacologically active chemical moieties into single conjugate molecules can result in synergized pharmacological action of both moieties into the new composite molecule. Ultimately, it increases the therapeutic potentialof the newly formed hybrid compound which is more than the combination of each specific moiety's therapeutic potential. So nowadays, it is common practice to combine at least two pharmacophores to create a particular compound with a powerful therapeutic effects. Quinoline has been reported with multiple pharmacological activities and industrial applications. On the other hand, hydrazones are also found very useful as herbicides, acaricides, rodenticides, insecticides, and various therapeutic applications. The conjugate containing quinoline and hydrazone is also being used as an anticancer, antibacterial, antifungal, antimalarial, anticonvulsant, anti-inflammatory, and antioxidant. The combination of two moieties yields a better therapeutic effect because of excellent efficacy and fewer side effects. Several synthetic methods have been employed in recent times to synthesize quinoline-hydrazone conjugates which are listed in the manuscript with their merits and demerits. The structure-activity relationship relating to their pharmacological actions with molecular structure has also been highlighted. The article aims to provide a good toolkit and comprehension to the medicinal chemists, for their future work, comprising of quinoline-hydrazone hybrid compounds.