L. Ravithej Singh

Molecular iodine catalysed one-pot synthesis of chromeno[4,3-b]quinolin-6-ones under microwave irradiation

We demonstrate a facile one pot approach for the regioselective synthesis of chromeno[4,3-b]quinolin-6-one derivatives in excellent yields under microwave (MW) irradiation. This transformation presumably proceeds via a three-component tandem annulation of 4-hydroxycoumarin with aromatic aldehydes and aromatic amines, involving a Povarov type reaction.

Identification of quinoline-chalcone hybrids as potential antiulcer agents

Antiulcer activity of novel quinoline-chalcone hybrids (13-37) was investigated. Among them, eight compounds (14, 16, 17, 23, 29, 31, 32 and 35) were found to be active in various ulcer models in Sprague-Dawley (SD) rats. To understand the mechanism of action of these hybrids, the effects of the compounds on antisecretory and cytoprotective activities were studied. All these active hybrids improved the depleted levels of mucin and consequently inhibited the formation of erosions in a pyloric ligated ulcer model. In addition, they also significantly increased the gastric PGE2 content in an aspirin induced ulcer model. The additional experiments including the in vitro metabolic stability and in vivo pharmacokinetics led to the identification of compound 17 as an orally active and safe candidate that is worthy of further investigation to be developed as an antiulcer agent.

Designing, synthesis of selective and high-affinity chalcone-benzothiazole hybrids as Brugia malayi thymidylate kinase inhibitors: In vitro validation and docking studies

In our continuing search for safe and efficacious antifilarials, a series of novel chalcone-benzothiazole hybrids have been synthesized and evaluated for their Brugia malayi thymidylate kinase (BmTMK) enzyme inhibition activity. Their selectivity towards BmTMK was studied and compared to the human TMK (HsTMK) by an in silico method. Out of seventeen derivatives, compounds 34 and 42 showed higher interactions with the BmTMK active site. MolDock docking model revealed the interactions of these two derivatives and the results corroborated well with their in vitro antifilarial activities. Our studies suggest that these hybrids are selective towards the BmTMK enzyme and may serve as potential therapeutic agents against filariasis.

Design, synthesis and anticancer activity of dihydropyrimidinone–semicarbazone hybrids as potential human DNA ligase 1 inhibitors

A series of new dihydropyrimidinone–semicarbazone hybrids were successfully synthesised by integrating regioselective multicomponent reaction with the pharmacophore hybridization approach. All the synthesised compounds were evaluated for their hLig1 inhibition potency and most of them were found to be good to moderately active. Out of the tested derivatives, compound 6f showed selective anti-proliferative activity against HepG2 cells in a dose-dependent manner with an IC50 value of 10.07 ± 1.2. It also reduced cell survival at ≤20 μM concentration. Further, analysis of treated HepG2 cell lysates by western blot assay showed increased γ-H2AX levels and upregulation of p53, leading to apoptosis. In silico docking results explain the binding modes of compound 6f to the DNA-binding domain of hLig1 enzyme thereby preventing its nick sealing activity. In addition, the favourable pharmacokinetic properties suggest that this new class of hLig1 inhibitors could be promising leads for further drug development.

Design, synthesis and in vitro evaluation of coumarin–imidazo[1,2-a]pyridine derivatives against cancer induced osteoporosis

A series of biologically important 6-(imidazo[1,2-a]pyridin-2-yl)-2H-chromen-2-one derivatives were synthesized by employing the silver(I) catalysed Groebke–Blackburn–Bienayme multicomponent reaction. The synthesized compounds were tested in a primary calvarial osteoblast cells by alkaline phosphatase assay and an alizarin red-S staining assay for their possible osteoprotective properties. Further, the effects of active compounds 6h, 6l, and 6o on the expression of osteogenic genes BMP2, RUNX2, COL1, and OCN were measured by qPCR. Out of three promising compounds, 6l and 6o significantly induced apoptosis in MDA-MB-231 cancer cells via mitochondrial depolarisation without affecting normal cells. In an in vitro co-culture model of bone metastasis, we investigated the ability of coumarin–imidazo[1,2-a]pyridine hybrids to reverse the negative impact of MDA-MB-231 cancer cells on osteoblast differentiation. The results illustrate the potential of designed hybrids to re-establish the bone homeostasis. These findings demonstrate the significance of newly synthesized hybrids as lead molecules, possessing both antiosteoporotic and anticancer properties that can be developed into new therapeutic agents to alleviate osteoporosis and bone metastasis.

Coumarin–benzimidazole hybrids as a potent antimicrobial agent: synthesis and biological elevation

Molecular hybridization approach is an emerging tool in drug discovery for designing new pharmacophores with biological activity. A novel, new series of coumarin–benzimidazole hybrids were designed, synthesized and evaluated for their broad spectrum antimicrobial activity. Among all the synthesized molecules, compound (E)-3-(2-1H-benzo[d]imidazol-1-yl)-1-((4-chlorobenzyl)oxy)imino)ethyl)-2H-chromen-2-one showed the most promising broad spectrum antibacterial activity against Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis and Proteus vulgaris. In addition, it has showed no cytotoxicity and hemolysis at 10 times the MIC concentration. SAR studies indicate that position of the chlorine atom in the hybrid critically determines the antibacterial activity.

Coumarin-chalcone hybrid instigates DNA damage by minor groove binding and stabilizes p53 through post translational modifications

S009-131, a coumarin-chalcone hybrid, had been shown to possess anti-proliferative and anti-tumour effect by triggering apoptosis. In this report, we investigated role of DNA damage signalling pathway in S009-131 induced cancer cell death. Here we show that S009-131 causes DNA damage by potential binding to the minor groove which led to the phosphorylation and activation of ATM and DNA-PK, but not ATR, at earlier time points in order to initiate repair process. S009-131 induced DNA damage response triggered activation of p53 through phosphorylation at its key residues. Pharmacological inhibition of PIKKs abrogated S009-131 induced phosphorylation of p53 at Ser 15. DNA damage induced phosphorylation resulted in reduced proteasomal degradation of p53 by disrupting p53-MDM2 interaction. Additionally, our docking studies revealed that S009-131 might also contribute to increased cellular p53 level by occupying p53 binding pocket of MDM2. Posttranslational modifications of p53 upon S009-131 treatment led to enhanced affinity of p53 towards responsive elements (p53-RE) in the promoter regions of target genes and increased transcriptional efficiency. Together, the results suggest that S009-131 cleaves DNA through minor groove binding and eventually activates PIKKs associated DNA damage response signalling to promote stabilization and enhanced transcriptional activity of p53 through posttranslational modifications at key residues.

Discovery of coumarin-dihydroquinazolinone analogs as niacin receptor 1 agonist with in-vivo anti-obesity efficacy

In this study, we presented rational designing and synthesis of coumarin-dihydroquinazolinone conjugates to evaluate their agonist activity at GPR109a receptor. Among the synthesized small molecule library, compound 10c displayed robust agonist action at GPR109a with EC50 < 11 nM. Homology model of human GPR109a protein was generated to realize the binding interaction of the active molecule with the active site of GPR109a. Further, the efficacy of active compound 10c was supported by in-vivo experiments which showed reduced body weight in diet induced obese mice model. Interestingly, compound 10c reduced leptin in blood plasma and total serum cholesterol. These results suggest that the coumarin-dihydroquinazolinone conjugate is a suitable scaffold to further expand the chemical diversity and make them potential niacin receptor 1 agonist.

In-house chemical library repurposing: A case example for Pseudomonas aeruginosa antibiofilm activity and quorum sensing inhibition

Hit, Lead & Candidate Discovery