Varadhan Krishnakumar

Terminalia chebula mediated green and rapid synthesis of gold nanoparticles

Biologically inspired experimental process in synthesising nanoparticles is of great interest in present scenario. Biosynthesis of nanoparticles is considered to be one of the best green techniques in synthesising metal nanoparticles. Here, an in situ green biogenic synthesis of gold nanoparticles using aqueous extracts of Terminalia chebula as reducing and stabilizing agent is reported. Gold nanoparticles were confirmed by surface plasmon resonance in the range of 535 nm using UV-visible spectrometry. TEM analysis revealed that the morphology of the particles thus formed contains anisotropic gold nanoparticles with size ranging from 6 to 60 nm. Hydrolysable tannins present in the extract of T. chebula are responsible for reductions and stabilization of gold nanoparticles. Antimicrobial activity of gold nanoparticles showed better activity towards gram positive S. aureus compared to gram negative E. coli using standard well diffusion method.

Nicotinic acid conjugates of nonsteroidal anti-inflammatory drugs (NSAID’s) and their anti-inflammatory properties

A series of nicotinic acid conjugates with non-steroidal anti-inflammatory drugs (NSAIDs) have been effectively synthesized using TBTU in high yield and purity. All the synthesized conjugates were evaluated for their in vitro anti-inflammatory activity.

Quinoline-3-carboxylates as potential antibacterial agents

AbstractThe ethyl-2-chloroquinoline-3-carboxylates, 4, were achieved from o-aminobenzophenones in two steps. i.e. initially, the ethyl-2-oxoquinoline-3-carboxylates, 3, were obtained by base-catalyzed Friedlander condensations of o-aminobenzophenones, 1, and diethylmalonate, 2. The 2-chloroquinoline-3-carboxylates, 4, were then obtained by the reaction with POCl3 in good yields. The chemical structures were confirmed by FTIR, mass and 1H-NMR spectroscopic techniques. All the synthesized compounds were tested for their in vitro antibacterial activity against Bacillus subtilis and Vibrio cholera and found to possess moderate activity.

Flower-shaped ZnO nanoparticles as an efficient, heterogeneous and reusable catalyst in the synthesis of N-arylhomophthalimides and benzannelated isoquinolinones

A simple and green protocol, developed utilizing an efficient, heterogeneous and recyclable catalyst, i.e. zinc oxide nanoparticles (ZnO NPs)-mediated synthesis of N-arylhomophthalimides and benzannelated isoquinolinones, is reported. The structures of the desired products were characterized by FTIR, 1H NMR, 13C NMR, and HRMS techniques. The ZnO NPs exhibited excellent catalytic activity and the proposed methodology is capable of providing the desired products in good yield and purity.

Antithyroid agents and QSAR studies: inhibition of lactoperoxidase-catalyzed iodination reaction by isochromene-1-thiones

Thyroxine, the main secretory hormone of thyroid gland, is produced from thyroglobulin by thyroid peroxidase/hydrogen peroxide/iodide system. The prohormone T4 is then converted to its potent form T3 by a selenocysteine-containing enzyme iodothyronine deiodinase. Autoantibodies which activate thyroid-stimulating hormone receptor are not under the pituitary feedback control system, and therefore, the uncontrolled production of thyroid hormones leads to a condition called “hyperthyroidism.” The overproduction of T4 and T3 can be controlled by specific inhibitors, which either block the synthesis of thyroid hormone or reduce the conversion of T4–T3. Unique classes of such inhibitors are thiourea drugs, methimazole (MMI), 6-n-propyl-2-thiouracil, and carbimazole suggesting that thione moiety exhibit excellent antithyroid activity. We have carried out biomimetic studies by HPLC assay, which suggested that isochromene-1-thiones exhibit significant antithyroid activity by inhibiting the lactoperoxidase (LPO)-catalyzed iodination, comparable with MMI, and that the inhibitory effects of some of them were found to be much superior to those of MMI. Kinetic studies demonstrate that isochromene-1-thiones inhibit LPO irreversibly. Our inhibition studies suggest that isochromene-1-thiones might be another promising candidate with potential for developing therapeutics for hyperthyroidism. The quantitative structure–activity relationship (QSAR) was developed between the LPO-inhibitory activities of isochromene-1-thiones and their physiochemical properties. The statistical measures, such as r2 (0.81), r2adj (0.79), q2 (0.73), and F-ratio (39.05), were found to be within the acceptable range.

Zinc Oxide Nanoparticles Catalyzed Condensation Reaction of Isocoumarins and 1,7-Heptadiamine in the Formation of Bis-Isoquinolinones

The diversified bis-isoquinolinones were obtained in two steps, utilizing homophthalic acid and various acid chlorides providing 3-substituted isocoumarins in the first step which on further condensation with 1,7-heptadiamine involving C–N bond formation from the lactone in the presence of 10 mol% zinc oxide nanoparticles (ZnO NPs) (<150 nm) afforded the desired bis-isoquinolinones in high yield and purity. The synthesized compounds were then characterized using FTIR, 1H NMR, 13C NMR, and HRMS techniques.

Montmorillonite-KSF-catalyzed synthesis of 4-heteroarylidene-N-arylhomophthalimides by Knoevenagel condensation

A simple, efficient and rapid method for clay-catalyzed Knoevenagel condensation of heterocyclic aldehydes with active methylene compound under reflux condition is reported. This protocol offers high yield, shorter time and simple work procedure. The protocol does not require column chromatography for purification, and the process is environmentally benign.

2-[2-(Hydroxy­meth­yl)phen­yl]-1-(1-naphth­yl)ethanol

The molecular conformation of the title compound, C19H18O2, is stabilized by an intramolecular O—H—O hydrogen bond. In addition, intermolecular O—H—O interactions link the molecules into zigzag chains running along the c axis.