In this article, a synthesis of N’-(benzylidene)-2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetohydrazides and their structural interpretation by NMR experiments is described in an attempt to explain the duplication of some peaks in their 1H- and 13C-NMR spectra. Twenty new 6-methyl-1H-pyrazolo[3,4-b]quinoline substituted N-acylhydrazones 6(a–t) were synthesized from 2-chloro-6-methylquinoline-3-carbaldehyde (1) in four steps. 2-Chloro-6-methylquinoline-3-carbaldehyde (1) afforded 6-methyl-1H-pyrazolo[3,4-b]quinoline (2), which upon N-alkylation yielded 2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetate (3). The hydrazinolysis of 3 followed by the condensation of resulting 2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetohydrazide (4) with aromatic aldehydes gave N-acylhydrazones 6(a–t). Structures of the synthesized compounds were established by readily available techniques such as FT-IR, NMR and mass spectral studies. The stereochemical behavior of 6(a–t) was studied in dimethyl sulfoxide-d6 solvent by means of 1H NMR and 13C NMR techniques at room temperature. NMR spectra revealed the presence of N’-(benzylidene)-2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetohydrazides as a mixture of two conformers, i.e., E(C=N)(N-N) synperiplanar and E(C=N)(N-N)antiperiplanar at room temperature in DMSO-d6. The ratio of both conformers was also calculated and E(C=N) (N-N) syn-periplanar conformer was established to be in higher percentage in equilibrium with the E(C=N) (N-N)anti-periplanar form.

Alzheimer’s disease (AD), a progressive neurodegenerative disorder, characterized by central cognitive dysfunction, memory loss, and intellectual decline poses a major public health problem affecting millions of people around the globe. Despite several clinically approved drugs and development of anti-Alzheimer’s heterocyclic structural leads, the treatment of AD requires safer hybrid therapeutics with characteristic structural and biochemical properties. In this endeavor, we herein report a microwave-assisted synthesis of a library of quinoline thiosemicarbazones endowed with a piperidine moiety, achieved via the condensation of 6/8-methyl-2-(piperidin-1-yl)quinoline-3-carbaldehydes and (un)substituted thiosemicarbazides. The target N-heterocyclic products were isolated in excellent yields. The structures of all the synthesized compounds were fully established using readily available spectroscopic techniques (FTIR, 1H- and 13C-NMR). Anti-Alzheimer potential of the synthesized heterocyclic compounds was evaluated using acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. The in vitro biochemical assay results revealed several compounds as potent inhibitors of both enzymes. Among them, five compounds exhibited IC50 values less than 20 μM. N-(3-chlorophenyl)-2-((8-methyl-2-(piperidin-1-yl)quinolin-3-yl)methylene)hydrazine carbothioamide emerged as the most potent dual inhibitor of AChE and BChE with IC50 values of 9.68 and 11.59 μM, respectively. Various informative structure–activity relationship (SAR) analyses were also concluded indicating the critical role of substitution pattern on the inhibitory efficacy of the tested derivatives. In vitro results were further validated through molecular docking analysis where interactive behavior of the potent inhibitors within the active pocket of enzymes was established. Quinoline thiosemicarbazones were also tested for their cytotoxicity using MTT assay against HepG2 cells. Among the 26 novel compounds, there were five cytotoxical and 18 showed proliferative properties.

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P2X receptors have the ability to regulate various physiological functions like neurotransmission, inflammatory responses, and pain sensation. Such physiological properties make these receptors a new target for the treatment of pain and inflammation. Several antagonists of P2X receptors have been studied for the treatment of neuropathic pain and neurodegenerative disorders but potency and selectivity are the major issues with these known inhibitors. Sulfonamide derivatives were reported to be potent inhibitors of P2X receptors. In this study, sulfonamide carrying precursor hydrazide was synthesized by a facile method that was subsequently condensed with methyl (hetero)­arylketones to obtain a series of new (hetero)­aryl ethylidenes. These compounds were screened for inhibitory potential against h-P2X2, h-P2X4, h-P2X5, and h-P2X7 receptors to find their potency and selectivity. Computational studies were performed to confirm the mode of inhibition as well as type of interaction between ligand and target site. In calcium signaling experiments, compound 6h was found to be the most potent and selective inhibitor of h-P2X2 and h-P2X7 receptors with IC50 ± standard error of the mean (SEM) values of 0.32 ± 0.01 and 1.10 ± 0.21 μM, respectively. Compounds 6a and 6c exhibited selective inhibition for h-P2X7 receptor, whereas 6e, 7a, and 7b expressed selective inhibitions toward h-P2X2 receptor that were comparable to the positive control suramin and pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS).