K. Bhaskara Rao

Discovery and synthesis of novel 3-phenylcoumarin derivatives as antidepressant agents

A series of 3-phenylcoumarins were synthesized and screened for potential antidepressant activity by tail suspension test (TST) in mice. Three compounds (6, 7 and 13) exhibited impressive antidepressant activity, measured in terms of percentage decrease in immobility duration (% DID). In addition, the active antidepressant compounds were subsequently studied at their most effective dose and activity of these compounds were confirmed in forced swimming test (FST) animal model, in which the compounds at a low dose of 0.5 mg/kg significantly decreased the immobility time and exhibited greater efficacy than the reference standards fluoxetine and imipramine. The potent compounds did not show any neurotoxicity in the rotarod test and the preliminary results are promising enough to warrant further studies around this scaffold.

Novel Chalcone–Thiazole Hybrids as Potent Inhibitors of Drug Resistant Staphylococcus aureus

A series of novel hybrids possessing chalcone and thiazole moieties were synthesized and evaluated for their antibacterial activities. In general this class of hybrids exhibited potency against Staphylococcus aureus, and in particular, compound 27 exhibited potent inhibitory activity with respect to other synthesized hybrids. Furthermore, the hemolytic and toxicity data demonstrated that the compound 27 was nonhemolytic and nontoxic to mammalian cells. The in vivo studies utilizing a S. aureus septicemia model demonstrated that compound 27 was as potent as vancomycin. The results of antibacterial activities underscore the potential of this scaffold that can be utilized for developing a new class of novel antibiotics.

Synthesis and evaluation of new coumarin–pyridine hybrids with promising anti-osteoporotic activities

Anti-osteoporotic effects of the newly synthesized coumarin-pyridine hybrids were evaluated in primary cultures of rat calvarial osteoblasts in vitro. Compounds 6a, i, j and k were potent in stimulating osteoblast differentiation and mineralization as assessed by the alkaline phosphatase production and alizarin red-S staining assay, respectively. These compounds were also found to be nontoxic in osteoblast cells as compared to the control group in an MTT assay. Furthermore, the effect of these compounds on the transcript levels of osteogenic genes revealed that the compound 6j robustly enhanced mineralization of the osteogenic genes in calvarial osteoblasts. In this context, compound 6j was selected as a potential lead for further structural optimization in the development of new anti-osteoporotic agents.

Design and synthesis of new series of coumarin–aminopyran derivatives possessing potential anti-depressant-like activity

A new series of coumarin based aminopyran derivatives were designed, synthesized and evaluated for their preclinical antidepressant effect on Swiss albino mice. Among the series, compounds 21, 25, 26, 27, 32 and 33 exhibited significant activity profile in forced swimming test (FST). Compound 27 was most efficacious, which at a very low dose of 0.5mg/kg reduced the time of immobility by 86.5% as compared to the standard drug fluoxetine (FXT) which reduced the immobility time by 69.8% at the dose of 20mg/kg, ip. In addition, all active compounds were screened in dose dependent manner (at doses of 0.25, 0.5, 1mg/kg ip) in FST and tail suspension test (TST). Interestingly, all active compounds did not caused any significant alteration of locomotor activity in mice as compared to control, indicating that the hybrids did not produce any motor impairment effects. The results indicate that coumarin-aminopyran derivatives may have potential therapeutic value for the management of mental depression.

In vitro and in vivo antifilarial activity evaluation of 3,6-epoxy [1,5]dioxocines: a new class of antifilarial agents.

A series of 3,6-epoxy [1,5]dioxocines were synthesized and evaluated for their antifilarial activity against adult parasites of human lymphatic filarial parasite Brugia malayi (sub-periodic strain) in vitro. Out of these, six compounds (4a-f) possessed improved in vitro anti-filarial activity and examples 4d and 4f were also found to be active in the in vivo experiments. These results demonstrate that 3,6-epoxy [1,5]dioxocines exhibits potent antifilarial activity and might be developed into a new class of antifilarial drug.

Synthesis and evaluation of new 3-phenylcoumarin derivatives as potential antidepressant agents.

A series of amine substituted 3-phenyl coumarin derivatives were designed and synthesized as potential antidepressant agents. In preliminary screening, all compounds were evaluated in forced swimming test (FST), a model to screen antidepressant activity in rodents. Among the series, compounds 5c and 6a potentially decreased the immobility time by 73.4% and 79.7% at a low dose of 0.5 mg/kg as compared to standard drug fluoxetine (FXT) which reduced the immobility time by 74% at a dose of 20 mg/kg, ip. Additionally, these active compounds also exhibited significant efficacy in tail suspension test (TST) (another model to screen antidepressant compounds). Interestingly, rotarod and locomotor activity tests confirmed that these two compounds do not have any motor impairment effect and neurotoxicity in mice. Our studies demonstrate that the new 3-phenylcoumarin derivatives may serve as a promising antidepressant lead and hence pave the way for further investigation around this chemical space.

Benzofuran-dihydropyridine hybrids: A new class of potential bone anabolic agents

A series of novel benzofuran-dihydropyridine hybrids were designed by molecular hybridization approach and evaluated for bone anabolic activities. Among the screened library, ethyl 4-(7-(sec-butyl)-2-(4-methylbenzoyl)benzofuran-5-yl)-2-methyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (compound 21) significantly enhanced the ALP production and mineralized nodule formation, which are primary requisites in the process of in vitro osteogenesis. Oral administration of compound 21 at 10 mg.kg-1 day-1 for two weeks led to restoration of trabecular bone microarchitecture in drill hole fracture model by significantly increasing BV/TV and Tb.N. Furthermore, histological and molecular studies showed compound 21 triggering the new bone regeneration in a drill hole defect site by increasing BMP expression. Furthermore, molecular modeling studies were performed to gain insight into the binding approach, which revealed that both benzofuran and dihydropyridine moieties are essential to show similar binding interactions to fit into the active site of BMP2 receptor, an important target of the osteogenic agents. Our results suggest that compound 21 stimulates BMP2 synthesis in osteoblast cells that promotes new bone formation (∼40%) at the fracture site which helps in shorten the healing period.

Development of Leishmania donovani stably expressing DsRed for flow cytometry-based drug screening using chalcone thiazolyl-hydrazone as a new antileishmanial target

Green fluorescent protein produces significant fluorescence and is extremely stable, however its excitation maximum is close to the ultraviolet range and thus can damage living cells. Hence, Leishmania donovani stably expressing DsRed were developed and their suitability for flow cytometry-based antileishmanial screening was assessed by evaluating the efficacies of standard drugs as well as newly synthesised chalcone thiazolyl-hydrazone compounds. The DsRed gene was successfully integrated at the 18S rRNA locus of L. donovani and transfectants (LdDsRed) were selected using hygromycin B. Enhanced expression of DsRed and a high level of infectivity to J774A.1 macrophages were achieved, which was confirmed by fluorescence microscopy and flow cytometry. Furthermore, these LdDsRed transfectants were utilised for development of an in vitro screening assay using the standard antileishmanial drugs miltefosine, amphotericin B, pentamidine and paromomycin. The response of transfectants to standard drugs correlated well with previous reports. Subsequently, the suitability of this system was further assessed by screening a series of 18 newly synthesised chalcone thiazolyl-hydrazone compounds in vitro for their antileishmanial activity, wherein 8 compounds showed moderate antileishmanial activity. The most active compound 5g, with ca. 73% splenic parasite reduction, exerted its activity via generating nitric oxide and reactive oxygen species and inducing apoptosis in LdDsRed-infected macrophages. Thus, these observations established the applicability of LdDsRed transfectants for flow cytometry-based antileishmanial screening. Further efforts aimed at establishing a high-throughput screening assay and determining the in vivo screening of potential antileishmanial leads are required.

Hybrids of coumarin–indole: design, synthesis and biological evaluation in Triton WR-1339 and high-fat diet induced hyperlipidemic rat models

In this study, a series of coumarin–indole hybrids have been synthesized and evaluated for their lipid lowering activity. Preliminary biological screening of the synthesized compounds was undertaken in an in vitro model of the HMG-CoA reductase enzyme, and the activity was confirmed in Triton WR-1339 induced hyperlipidemic rats. Among the hybrids, compound 26 was found to be the best as it significantly reduced the serum and hepatic lipid profiles in an HFD-fed hyperlipidemic rat model. The mechanism of action seems to be associated with the regulation of HMG-CoA reductase activity in the liver, which is in good agreement with binding mode studies. Compound 26 exhibited favorable pharmacokinetic behavior for its oral administration, which underscores the potential of this template as a new class of hypolipidemic agents.