Mahesh S. Majik

Tandem Wittig−Ene Reaction Approach to Kainic Acid

The first example of a tandem Wittig-intramolecular ene reaction approach and its application toward the synthesis of kainic acid is reported. The synthetic pathway involves conversion of prenyl bromide into phosphorane 3, followed by one-pot Wittig olefination and an ene reaction with glyoxalic acid to give the cis fused pyrrolidine skeleton of kainic acid.

Fluorescence Turn-on Chemosensor for the Detection of Dissolved CO2 Based on Ion-Induced Aggregation of Tetraphenylethylene Derivative

Herein, a sensitive fluorimetric assay for dissolved carbon dioxide (dCO2) was developed by using ion-induced self-assembly of a tetraphenylethylene derivative by taking advantage of its aggregation induced emission property. Chitosan, a commercially available polymer having amine functionality was utilized for the ion induced assay. In the presence of dCO2, the amine groups in the chitosan get protonated to convert neutral chitosan to a positively charged species, triggering negatively charged tetraphenylethene derivative (probe 1) to aggregate with it by electrostatic interaction. The aggregation causes intense blue fluorescence output from the system. The extent of the aggregation is reliant on the charge density of polymer, which is equivalent to dCO2 concentration. A linear relationship from 5 to 50 μM of dCO2, with a limit of detection of 5 × 10(-6) M (0.00127 hPa) was obtained. This is the first report for detecting dCO2 utilizing the AIE property.

An aggregation-induced emission based “turn-on” fluorescent chemodosimeter for the selective detection of Pb2+ ions

An aggregation-induced emission (AIE) based “turn-on” fluorescent chemodosimeter for the selective detection of ascorbate ions has been developed, making use of the azide–alkyne “click” reaction between two tetraphenylethene (TPE) derivatives (propergyl–TPE and TPE–azide). The present method offers a rapid, economic and effective way to detect ascorbic acid (Vitamin C) in aqueous media with high selectivity and sensitivity.

Total synthesis of (-)- and (+)-tedanalactam

The first stereoselective route providing access to both enantiomers of tedanalactam, a naturally occurring piperidone, has been developed. The stereogenic centers were generated by the use of Sharpless asymmetric dihydroxylation. Tandem oxidation-Wittig reaction and one-pot deprotection, lactamization, and oxirane ring formation are the other key elements.

Design and synthesis of marine natural product-based 1H-indole-2,3-dione scaffold as a new antifouling/antibacterial agent against fouling bacteria.

Marine organisms such as seaweeds, sponges and corals protect their own surfaces from fouling by their high anesthetic, repellant, and settlement inhibition properties. Within the marine ecosystem, evolution has allowed for the development of certain antifouling properties. Isatin is a biologically active chemical produced by an Alteromonas sp. strain inhibiting the surface of embryos of the cardiean shrimp Palaemon macrodectylus, which protect them from the pathogenic fungus Lagenidium callinectes. In present study, an antibacterial activity of isatin and its synthetic analogues were evaluated against different fouling bacteria in order to explore the structure activity relationships for the first time. The synthesized compounds along with parent isatin were tested against different ecologically relevant marine microorganisms by using the Kirby-Bauer disc diffusion method. Few synthetically modified isatin exhibited potent inhibitory activity at concentration of 2 μg/disc against Planococcus donghaensis, Erythrobacter litoralis, Alivibrio salmonicida, Vibrio furnisii. Overall, the modified analogues showed stronger activity than the parent marine natural product (isatin) and hence 1H-indole-2,3-dione scaffold has immense potential as future antibacterial/antifouling candidate.

Amine functionalized tetraphenylethylene: a novel aggregation-induced emission based fluorescent chemodosimeter for nitrite and nitrate ions

A novel AIE-based fluorescent probe for the detection of trace amounts of nitrite and nitrate ions in water has been developed. The probe, a monoamine of tetraphenylethylene, spontaneously detects nitrites (or nitrates) by a fluorescence “turn-off” method via diazotization followed by formation of a non fluorescent TPE-azodye. The salient features of this method are high sensitivity and selectivity, cost effective synthesis, fast detection process and low detection limit.

Next Generation Biofilm Inhibitors for Pseudomonas aeruginosa: Synthesis and Rational Design Approaches

The bacterial biofilms and the emergence of multiple drug resistance have become a major threat for current medical treatment of nosocomial infections. It has been estimated that about 65-80% of microbial infections in the developed countries are associated with biofilms. Given the prominence of biofilms in infectious diseases, increasing efforts toward the development of small molecules that will modulate bacterial biofilm development and maintenance is on the rise. Till date, marine natural products have shown a tremendous potential as pharma leads and also given new skeletons which would be used as biofilm/QS inhibitors. Medically relevant biofilm forming bacteria such as Pseudomonas aeruginosa which is most frequently isolated bacteria in nosocomial infection is believed to be a model organism for biofilm studies. Hence, in this review, we have highlighted the development of small molecules that inhibit and/or disperse bacterial biofilms of P. aeruginosa in particular. Additionally, the rational design approaches as well as synthetic methodologies along with biological studies has been accounted in this article.

Synthesis of (R)-norbgugaine and its potential as quorum sensing inhibitor against Pseudomonas aeruginosa

(R)-Bgugaine is a natural pyrrolidine alkaloid from Arisarum vulgare, which shows antifungal and antibacterial activity. In this Letter, we have accomplished the simple synthesis of norbgugaine (demethylated form of natural bgugaine) employing Wittig olefination and cat. hydrogenation as the key steps and its biological studies are reported for the first time. The synthesized norbgugaine was evaluated for inhibition of quorum sensing mediated virulence factors (motility, biofilm formation, pyocyanin pigmentation, rhamnolipid production and LasA protease) in Pseudomonas aeruginosa wherein swarming motility is reduced by 95%, and biofilm formation by 83%.

A simple and efficient mechanochemical route for the synthesis of 2-aryl benzothiazoles and substituted benzimidazoles

An efficient and versatile mechanochemical route to 2-aryl benzothiazoles and both 2-substituted and 1,2-disubstituted benzimidazole derivatives has been developed via a simple mortar–pestle grinding method. The mechanochemical agitation was found to be sufficient for smooth condensation between a variety of aromatic aldehydes and o-aminothiophenol/o-phenylenediamine followed by cyclization leading to the formation of the corresponding 1,3-benzazoles. The salient features of this new protocol are catalyst-free reaction, cleaner reaction profiles, absence of a work-up step, high yields, and short reaction times.

Marine and Semi-Synthetic Hydroxysteroids as New Scaffolds for Pregnane X Receptor Modulation

In recent years many sterols with unusual structures and promising biological profiles have been identified from marine sources. Here we report the isolation of a series of 24-alkylated-hydroxysteroids from the soft coral Sinularia kavarattiensis, acting as pregnane X receptor (PXR) modulators. Starting from this scaffold a number of derivatives were prepared and evaluated for their ability to activate the PXR by assessing transactivation and quantifying gene expression. Our study reveals that ergost-5-en-3β-ol (4) induces PXR transactivation in HepG2 cells and stimulates the expression of the PXR target gene CYP3A4. To shed light on the molecular basis of the interaction between these ligands and PXR, we investigated, through docking simulations, the binding mechanism of the most potent compound of the series, 4, to the PXR. Our findings provide useful functional and structural information to guide further investigations and drug design.