Ravichandran Veerasamy

2,5-Disubstituted-1,3,4-oxadiazoles/thiadiazole as surface recognition moiety: Design and synthesis of novel hydroxamic acid based histone deacetylase inhibitors

The enzymatic inhibition of histone deacetylase activity has come out as a novel and effectual means for the treatment of cancer. Two novel series of 2-[5-(4-substitutedphenyl)-[1,3,4]-oxadiazol/thiadiazol-2-ylamino]-pyrimidine-5-carboxylic acid (tetrahydro-pyran-2-yloxy)-amides were designed and synthesized as novel hydroxamic acid based histone deacetylase inhibitors. The antiproliferative activities of the compounds were investigated in vitro using histone deacetylase inhibitory assay and MTT assay. The synthesized compounds were also tested for antitumor activity against Ehrlich ascites carcinoma cells in Swiss albino mice. The efforts were also made to establish structure-activity relationships among synthesized compounds. The results of the present studying indicates 2,5-disubstituted 1,3,4-oxadiazole/thiadiazole as promising surface recognition moiety for development of newer hydroxamic acid based histone deacetylase inhibitor.

Design of Combretastatin A-4 Analogs as Tubulin Targeted Vascular Disrupting Agent with Special Emphasis on Their Cis-Restricted Isomers

Tubulin protein is a highly imperative and feasible goal for anticancer drug discovery. Hundreds of naturally occurring, semi synthetic and synthetic antitubulin agents have been reported till now. Among these, Combretastatin A - 4 (CA - 4) is effective antimitotic agent possessing potent cytotoxicity against a panel of cancer cells, including multi-drug resistant cancer cell lines. The inadequate water solubility and inactivation of these analogs during storage limit their use as clinical anticancer agents. To overcome these shortcomings, numerous water soluble amino analogs, amino acid derivative, phosphate prodrug (CA - 4P) and cis-locked CA - 4 have been developed with distinctive attributes of antitubulin and antivascular properties in a wide variety of preclinical tumor models. Subsequently, several heterocycle based cis restricted CA - 4 analogs are being reported for antitumor activity against collection of cancer cell lines. This review recapitulates the rational design, structure activity relationship, pharmacokinetic and pharmacodynamic profile of synthesized cis restricted CA - 4 analogs.

Novel semicarbazones based 2,5-disubstituted-1,3,4-oxadiazoles: One more step towards establishing four binding site pharmacophoric model hypothesis for anticonvulsant activity

A series of novel N(1)-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N(4)-(4-substitutedbenzaldehyde)-semicarbazone, N(1)-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N(4)-[1-(4-substitutedphenyl)ethanone]-semicarbazone and N(1)-{5-[(naphthalene-2-yloxy)methyl]-1,3,4-oxadiazol-2-yl}-N(4)-[1-(4-substitutedphenyl) (phenyl) methanone]-semicarbazone were designed and synthesized on the basis of semicarbazone based pharmacophoric model to meet the structural requirements necessary for anticonvulsant activity. The anticonvulsant activities of the compounds were investigated using maximal electroshock seizure (MES), subcutaneous pentylenetrtrazole (scPTZ) and subcutaneous strychnine (scSTY) models. Some of the selected active compounds were subjected to GABA assay to confirm their mode of action. The efforts were also made to establish structure activity relationships among synthesized compounds. The results of the present studying validated that the pharmacophoric model with four binding sites is essential for anticonvulsant activity.

Novel limonene and citral based 2,5-disubstituted-1,3,4-oxadiazoles: A natural product coupled approach to semicarbazones for antiepileptic activity

Two novel series of N(4)-(5-(2/3/4-substituted-phenyl)-1,3,4-oxadiazol-2-yl)-N(1)-(2-methyl-5-(prop-1-en-2-yl)cyclohex-2-enylidene)semicarbazide and N(4)-(5-(2/3/4-substituted-phenyl)-1,3,4-oxadiazol-2-yl)-N(1)-(3,7-dimethylocta-3,6-dienylidene)-semicarbazide were synthesized to meet structural prerequisite indispensable for anticonvulsant activity. The anticonvulsant activities of the compounds were investigated using maximal electroshock seizure (MES), subcutaneous pentylenetrtrazole (scPTZ) and subcutaneous strychnine (scSTY) models. The rotorod test was conducted to evaluate neurotoxicity. Some of the selected active compounds were subjected to GABA assay to confirm their mode of action. The outcome of the present investigations proved that the four binding sites pharmacophore model is vital for anticonvulsant activity. The efforts were also made to establish structure-activity relationships among test compounds.

Appraisal of GABA and PABA as linker: Design and synthesis of novel benzamide based histone deacetylase inhibitors

Histone deacetylase inhibitors have been actively explored as a new generation of chemotherapeutics for cancers, generally known as epigenetic therapeutics. Two novel series of N-(2-amino-phenyl)-4-{[(2/3/4-substituted-phenylcarbamoyl)-methyl]-amino}-butyramide and N-(2-amino-phenyl)-4-{[(2/3/4-substituted-phenylcarbamoyl)-methyl]-amino}benzamide were designed and synthesized as novel histone deacetylase inhibitors. The anticancer potential of the compounds were determined in-vitro using MTT assay against HCT-116 and U251 (glioma) cell lines and histone deacetylase inhibitory assay. The synthesized compounds were investigated for anti-tumor activity against Ehrlich ascites carcinoma (EAC) cells in Swiss albino mice. The efforts were also made to ascertain structure-activity relationships among test compounds. The results of the present studying represents appraisal of γ-aminobutyric acid (GABA) and para-aminobenzoic acid (PABA) as linker moiety for development of newer benzamide based histone deacetylase inhibitor.

Design, Development, Testing and Qualification of Diverse Safety Rod and Its Drive Mechanism for a Prototype Fast Breeder Reactor

Prototype fast breeder reactor is U-PuO 2 fueled sodium cooled pool type fast reactor and it is currently under construction at Kalpakkam, India. Prototype fast breeder reactor is equipped with two independent fast acting and diverse shutdown systems. A shutdown system comprises of sensors, logic circuits, drive mechanisms, and neutron absorbing rods. The two shutdown systems of prototype fast breeder reactor are capable of bringing down the reactor to cold shutdown state independent of the other. The absorber rods of the second shutdown system of prototype fast breeder reactor are called as diverse safety rods (DSRs) and their drive mechanisms are called as diverse safety rod drive mechanisms (DSRDMs). DSRs are normally parked above active core by DSRDMs. On receiving scram signal, the electromagnet of DSRDM is de-energized and it facilitates fast shutdown of the reactor by dropping the DSR into the active core. For the development of prototypes of DSR and DSRDM, three phases of testing, namely, individual component testing, integrated functional testing in room temperature, and endurance testing at high temperature sodium, were done. The electromagnet of DSRDM has been separately tested at room temperature, in furnace, and in sodium. Specimens simulating the contact conditions between electromagnet and armature of DSR have been tested to rule out self-welding possibility. The prototype of DSR has been tested in flowing water to determine the pressure drop and drop time. The functional testing of the integrated prototype DSRDM and DSR in aligned and misaligned conditions in air/water has been completed. The performance testing of the integrated system in sodium has been done in three campaigns. During the third campaign of sodium testing, the performance of the system has been verified with 30 mm misalignment at various temperatures. The third campaign has qualified the system for 10 years of operation in reactor. This paper presents design, development, testing, and qualification of the prototype DSR and DSRDM. Salient design specifications for both DSRDM and DSR are listed initially. The conceptual and detailed design features are explained with the help of figures. Details on material of construction are given at appropriate places. Test plans and criteria for endurance testing in sodium for qualification of DSRDM and DSR for operation in reactor are briefed. Brief explanation of test setups and typical test results are also given.

Pharmacophore Based 3D-QSAR, Virtual Screening and Docking Studies on Novel Series of HDAC Inhibitors with Thiophen Linker as Anticancer Agents

BACKGROUND Histone deacetylase (HDAC) inhibitors can reactivate gene expression and inhibit the growth and survival of cancer cells. OBJECTIVE To identify the important pharmacophoric features and correlate 3Dchemical structure with biological activity using 3D-QSAR and Pharmacophore modeling studies. METHOD The pharmacophore hypotheses were developed using e-pharmacophore script and phase module. Pharmacophore hypothesis represents the 3D arrangement of molecular features necessary for activity. A series of 55 compounds with wellassigned HDAC inhibitory activity were used for 3D-QSAR model development. RESULTS Best 3D-QSAR model, which is a five partial least square (PLS) factor model with good statistics and predictive ability, acquired Q2 (0.7293), R2 (0.9811), cross-validated coefficient rcv 2=0.9807 and R2 pred=0.7147 with low standard deviation (0.0952). Additionally, the selected pharmacophore model DDRRR.419 was used as a 3D query for virtual screening against the ZINC database. In the virtual screening workflow, docking studies (HTVS, SP and XP) were carried out by selecting multiple receptors (PDB ID: 1T69, 1T64, 4LXZ, 4LY1, 3MAX, 2VQQ, 3C10, 1W22). Finally, six compounds were obtained based on high scoring function (dock score -11.2278-10.2222 kcal/mol) and diverse structures. CONCLUSION The structure activity correlation was established using virtual screening, docking, energetic based pharmacophore modelling, pharmacophore, atom based 3D QSAR models and their validation. The outcomes of these studies could be further employed for the design of novel HDAC inhibitors for anticancer activity.

Drug Design Strategies for the Discovery of Novel Anticonvulsants Concerned with Four Site Binding Pharmacophoric Model Studies.

Anticonvulsant refers to a group of pharmaceuticals used in the treatment of epileptic seizures. The use of current antiepileptic drugs has been questioned due to the non-selectivity of the drugs and the undesirable side effects produced by them. This led to the search for antiepileptic compounds with more selectivity and lower toxicity. Semicarbazones have been developed as versatile anticonvulsant pharmacophore. It has displayed potent anticonvulsant effect in a wide variety of preclinical anticonvulsant models. Till date various semicarbazone derivatives containing 1,3,4-oxadiazole, 1,3,4-thiadiazole, pyrimidine, benzothiazole and substituted phenyl/aryl ring have been synthesized and evaluated for anticonvulsant activity. The semicarbazone based pharmacophore model with four binding sites is essential for anticonvulsant activity. This model comprises of an aryl hydrophobic binding site, hydrogen bonding domain, an electron donor group and another hydrophobic-hydrophilic site regulating the pharmacokinetic properties of the anticonvulsant. Extensive structure-activity relationship has demonstrated that compound with OH, CH3O, NO2, Cl, F, Br substituents in the arylhydrophobic pocket, nitro, hydroxy group on distant phenyl ring and a hydrogen bonding domain possess anticonvulsant activity. In this review, advances made in the application of semicarbazones as a versatile pharmacophore model for the design of new anticonvulsant drugs are being updated and suggested for future drug design and development of novel anticonvulsants.

Designing hypothesis of diaryl pyrimidine analogs as anti-HIV agent: QSAR approach

Two-dimensional QSAR models were produced by stepwise multiple-linear regression and 3D QSAR models were developed by k-nearest neighbor-molecular field analysis on a database consists of 18 diaryl pyrimidine analogs. The developed QSAR model was evaluated for statistical significance and predictive power. The key conclusion of this study is that the electro-topological state indices for number of carbon atom connected with one double and two single bonds, retention index (fourth order), electrostatic, hydrophobic, and steric field descriptors are significantly affect the anti-HIV activity of diaryl pyrimidine analogs. The selected descriptors serve as a first guideline for the design of novel and potent diaryl pyrimidine analogs as anti-HIV agents.Graphical AbstractIn the present study, we discussed the role of retention index (fourth order), electrostatic, hydrophobic and steric field descriptors in the anti-HIV activity of diaryl pyrimidine analogues.

Designing hypothesis of substituted benzoxazinones as HIV-1 reverse transcriptase inhibitors: QSAR approach

A linear quantitative structure activity relationship (QSAR) model is presented for predicting human immunodeficiency virus-1 (HIV-1) reverse transcriptase enzyme inhibition. The 2D QSAR and 3D-QSAR models were developed by stepwise multiple linear regression, partial least square (PLS) regression and k-nearest neighbor-molecular field analysis, PLS regression, respectively using a database consisting of 33 recently discovered benzoxazinones. The primary findings of this study is that the number of hydrogen atoms, number of (−NH2) group connected with solitary single bond alters the inhibition of HIV-1 reverse transcriptase. Further, presence of electrostatic, hydrophobic and steric field descriptors significantly affects the ability of benzoxazinone derivatives to inhibit HIV-1 reverse transcriptase. The selected descriptors could serve as a primer for the design of novel and potent antagonists of HIV-1 reverse transcriptase.