Chandralata Bal

Synthesis and anti-hepatitis B virus and anti-hepatitis C virus activities of 7-deazaneplanocin A analogues in vitro.

A series of 7-deazaneplanocin A (7-DNPA, 2) analogues were synthesized and evaluated for in vitro antiviral activity against HBV and HCV. The syntheses of target carbocyclic nucleosides were accomplished via a convergent procedure. 7-Substitutions were introduced by using 7-substituted-7-deaza heterocyclic base precursors (F, Cl, Br, and I) or via substitution reactions after the synthesis of the carbocyclic nucleosides. Among the synthesized compounds, 2, 13-15, 24, and 27 exhibited significant anti-HCV activity (EC(50) ranged from 1.8 to 20.1 microM) and compounds 2, 15, 22, and 24 demonstrated moderate to potent anti-HBV activity (EC(50) = 0.3-3.3 microM). In addition, compound 24 also showed activity against lamivudine- and adefovir-associated HBV mutants.

Probing cationic selectivity of cardiac calsequestrin and its CPVT mutants.

CASQ (calsequestrin) is a Ca2+-buffering protein localized in the muscle SR (sarcoplasmic reticulum); however, it is unknown whether Ca2+ binding to CASQ2 is due to its location inside the SR rich in Ca2+ or due to its preference for Ca2+ over other ions. Therefore a major aim of the present study was to determine how CASQ2 selects Ca2+ over other metal ions by studying monomer folding and subsequent aggregation upon exposure to alkali (monovalent), alkaline earth (divalent) and transition (polyvalent) metals. We additionally investigated how CPVT (catecholaminergic polymorphic ventricular tachycardia) mutations affect CASQ2 structure and its molecular behaviour when exposed to different metal ions. Our results show that alkali and alkaline earth metals can initiate similar molecular compaction (folding), but only Ca2+ can promote CASQ2 to aggregate, suggesting that CASQ2 has a preferential binding to Ca2+ over all other metals. We additionally found that transition metals (having higher co-ordinated bonding ability than Ca2+) can also initiate folding and promote aggregation of CASQ2. These studies led us to suggest that folding and formation of higher-order structures depends on cationic properties such as co-ordinate bonding ability and ionic radius. Among the CPVT mutants studied, the L167H mutation disrupts the Ca2+-dependent folding and, when folding is achieved by Mn2+, L167H can undergo aggregation in a Ca2+-dependent manner. Interestingly, domain III mutants (D307H and P308L) lost their selectivity to Ca2+ and could be aggregated in the presence of Mg2+. In conclusion, these studies suggest that CPVT mutations modify CASQ2 behaviour, including folding, aggregation/polymerization and selectivity towards Ca2+.

Targeting Peroxisome Proliferator-Activated Receptor Gamma for Generation of Antidiabetic Drug

The incidence of Diabetes Mellitus (DM) has increased to alarming levels not only in developed countries but also in developing and underdeveloped countries. Scientific data have made it clear by now that patients with DM are predisposed to many other diseases. One of the worst associations of DM is with obesity and the number of DM patients with obesity is increasing at a very fast pace due to dramatic change in life style around the world in last few decades. This necessitates the discovery of new drugs to treat increasing numbers of people with both DM and obesity. Peroxisome Proliferator activated receptor gamma (PPARγ) is a well known target for DM and thiazolidiniones (TZDs; a common class of antidiabetic drug) which includes rosiglitazone and pioglitazone act through PPARγ. Recent studies have demonstrated that PPARγ apart from being important in glucose utilization also plays a critical role in lipid metabolism and energy homeostasis affecting long-term metabolic status. The possibility of selective modulation of PPARγ has opened up a whole new avenue of research and has the potential of producing some drug which can simultaneously fight both DM and obesity, without the side-effects of the currently available PPARγ modulators. Here, we discuss various aspects of selective modulation of PPARγ action.

Structure based molecular design, synthesis and biological evaluation of α-pyrone analogs as anti-HSV agent.

Several options for treating Herpes Simplex Virus type 1 and type 2 are available. However, non-specific inhibition and drug resistance warrants the discovery of new anti-herpetic compounds with better therapeutic profile or different mode of action. The non-nucleoside inhibitors of HSV DNA polymerase target the site that is less important for the binding of a natural nucleoside or nucleoside inhibitors. In the present study, we have explored the possibility to find a new lead molecule based on α-pyrone analogs as non-nucleoside inhibitors using structure based modeling approach. The designed molecules were synthesized and evaluated for anti-HSV activity using MTT assay. The compound 5h with EC(50) 7.4μg/ml and CC(50) 52.5μg/ml was moderately active against HSV when compared to acyclovir. A plaque reduction assay was also carried out and results reveal that 5h is more effective against HSV-1 with better selective index of 12.8 than against HSV-2 (SI=3.6). The synthesized compounds were also evaluated for anti-HIV activity, but none were active.

Structure based medicinal chemistry approach to develop 4-methyl-7-deazaadenine carbocyclic nucleosides as anti-HCV agent

The structure-based approaches were implemented to design and rationally select the molecules for synthesis and anti-HCV activity evaluation. The systematic structure-activity relationships of previously discovered molecules (types I, II, III) were analyzed to design new molecules (type IV) by bioisosteric replacement of the amino group. The ligand conformation, binding mode studies and drug like properties were major determinant for selection of molecules for final synthesis. The replacement of amino group with methyl restored the interactions with RNA-template (Tem 799) through bifurcated weak H-bond (C-H...O). This is an interesting finding observed from molecular modeling studies. It was found that 6c-e has anti-HCV activity (EC(50) in 37-46 μM) while 6a, 6b and 6g were inactive. The compound 6f (EC(50) 28 μM) was the most active among the series however it also showed some cytotoxicity (CC(50) 52.8 μM). Except 6f, none of the compounds were found to be cytotoxic (CC(50)>100 μM). The present study discloses structure-based approach for novel anti-HCV lead discovery and opens a future scope of lead optimization.

Synthesis and Anti-HCV Activity of 4-Hydroxyamino α-Pyranone Carboxamide Analogues

High genetic variability in hepatitis C virus (HCV), emergence of drug resistant viruses and side effects demand the requirement for development of new scaffolds to show an alternate mechanism. Herein, we report discovery of new scaffold I based on 4-hydroxyamino α-pyranone carboxamide as promising anti-HCV agents. A comprehensive structure-activity relationship (SAR) was explored with several newly synthesized compounds. In all promising compounds (17-19, 21-22, 24-25, and 49) with EC50 ranging 0.15 to 0.40 μM, the aryl group at C-6 position of α-pyranone were unsubstituted. In particular, 25 demonstrated potential anti-HCV activity with EC50 of 0.18 μM in cell based HCV replicon system with lower cytotoxicity (CC50 > 20 μM) and provided a new scaffold for anti-HCV drug development. Further investigations, including biochemical characterization, are yet to be performed to elucidate its possible mode of action.

Skeletal hybridization and PfRIO-2 kinase modeling for synthesis of α-pyrone analogs as anti-malarial agent.

The pharmacophoric hybridization and computational design approach were applied to generate a novel series of α-pyrone analogs as plausible anti-malarial lead candidate. A putative active site in flexible loop close to wing-helix domain of PfRIO2 kinase was explored computationally to understand the molecular basis of ligand binding. All the synthesized molecules (3a-g) exhibited in vitro antimalarial activity. Oxidative stress induced by 3a-d were calculated and found to be significantly higher in case of 3b. Therefore, 3b, which shown most significant result was identified as promising lead for further SAR study to develop potent anti-malarials.

A Conformational Mimetic Approach for the Synthesis of Carbocyclic Nucleosides as Anti‐HCV Leads

Computer‐aided approaches coupled with medicinal chemistry were used to explore novel carbocyclic nucleosides as potential anti‐hepatitis C virus (HCV) agents. Conformational analyses were carried out on 6‐amino‐1H‐pyrazolo[3,4‐d]pyrimidine (6‐APP)‐based carbocyclic nucleoside analogues, which were considered as nucleoside mimetics to act as HCV RNA‐dependent RNA polymerase (RdRp) inhibitors. Structural insight gained from the modeling studies revealed the molecular basis behind these nucleoside mimetics. The rationally chosen 6‐APP analogues were prepared and evaluated for anti‐HCV activity. RdRp SiteMap analysis revealed the presence of a hydrophobic cavity near C7 of the nucleosides; introduction of bulkier substituents at this position enhanced their activity. Herein we report the identification of an iodinated compound with an EC50 value of 6.6 μM as a preliminary anti‐HCV lead.

Anti-HSV activity and mode of action study of α-pyrone carboxamides

The clinical management of herpes virus diseases is limited due to ineffective clearance of virus particles and frequent emergence of drug-resistant viruses, particularly in immunocompromised patients, pregnant women and neonates. In our continued quest for new antiviral leads, α-pyrone carboxamide propanol derivatives were synthesized and evaluated in HSV infected Vero cells. Compound 3d showed potent antiviral activity against HSV-IF (EC50 = 9.8 μg ml−1 and EC99 = 18.0 μg ml−1) and HSV-2G (EC50 = 12.4 μg ml−1 and EC99 = 24.0 μg ml−1) at 4–6 h post-infection. The mode of action studies demonstrated that 3d did not interfere in viral attachment or penetration, however, it reduced the expression of ICP4 and ICP27 (immediate-early gene products) as well as the HSV DNA polymerase.

Comprehensive screening of heterocyclic compound libraries to identify novel inhibitors for PfRIO-2 kinase through docking and substrate competition studies

Malaria is most prevalent in tropical climate and causes 1–3 million deaths annually. RIO-2 kinase, an atypical kinase regulates ribosome biogenesis and is necessary for cell cycle progression. Structural characterization of PFD0975w (PfRIO-2 kinase) indicates N-terminal DNA binding winged helix domain (1–84), a linker region (85–147), and C-terminal kinase domain (148–275). Heterocyclic compounds present in different databases represent an enormous reservoir to screen and develop the suitable inhibitor. An extensive screening of heterocyclic compounds present in zinc database, PubChem and ChemBank database was done to identify potent PfRIO-2 kinase specific inhibitors. Initial screening gave 41 compounds with high affinity toward PfRIO-2 kinase than natural substrate ATP. A substrate competition experiment and analysis of binding mode conformation within the ATP binding pocket identifies five compounds; Zc-49775260, Pc-44415375, Pc-44215930, Cb-2082655, and Cb-832054 as potential PfRIO-2 kinase inhibitors. Further analysis of top hits in ADMET parameters, Caco-2 cell permeability profile, human oral absorption, and drug-like properties indicates Pc-44215930 as the best suitable compound among the top hits. Searching top hits candidate heterocyclic compounds in the drug database picked up clindamycin, nelfinavir, methacycline, and other drugs in circulation. Most of these drugs are targeting ribosome maturation and highlights the possibility of PfRIO-2 kinase as a drug target. Hence, screening and substrate competition studies along with ADME analysis of top hit compounds allowed us to identify potential PfRIO-2 kinase inhibitors. We are hopeful that the current study will help to develop effective chemotherapy against malaria utilizing PfRIO-2 kinase as a target.