Lokesh A. Shastri

Effects of Base for the Efficient Synthesis of 4-Formylcoumarins and 4-Formylcarbostyrils

Abstract The first efficient transformation of 4-bromomethylcoumarins and 4-bromomethylcarbostyrils to 4-formylcoumarins and 4-formylcarbostyril under aqueous conditions has been achieved by modifying the Kornblum method, resulting in excellent yield. The experimental method is very simple and economical; no further purification is required and the experimental conditions have been optimized. All the isolated compounds were characterized by infrared, NMR, and mass spectroscopy, and some of the compounds have been analyzed by single-crystal x-ray analysis. GRAPHICAL ABSTRACT

First Thermal Chemoselective Synthesis of Novel 2′,3′‐Dihydro‐3′‐Hydroxy‐benzofuranylcoumarins

Abstract An attempted reaction of 4‐bromomethylcoumarin with 2‐hydroxy aromatic aldehyde/2‐hydroxy aromatic ketone at room temperature in the presence of a mild base resulted in the formation of cis‐2′,3′‐dihydro‐3‐hydroxybenzofuranylcoumarins by carbanion addition across the carbonyl carbon.

Mild, Simple, and Efficient Method for N-Formylation of Secondary Amines via Reimer–Tiemann Reaction

Abstract A rapid and easy route for the N-formylation of secondary amines using chloroform and sodium ethoxide via dichlorocarbene by the Riemer–Tiemann reaction with excellent yield is reported.

3,4-Dihydropyrimidinone-coumarin analogues as a new class of selective agent against S. aureus: Synthesis, biological evaluation and molecular modelling study

Bacterial infections are increasingly difficult to combat as bacteria evolve resistance to antibiotic drugs and have severely compromised the arsenal of antibiotic drugs. On the other hand matrix metalloproteinases (MMPs) play a fundamental role in inflammation and extracellular matrix degradation in physiological and pathological conditions. In search of potent antibiotic, taking coumarin and dihydropyrimidinone as lead compound, a green, eco-friendly and efficient protocol has been developed and synthesized the dihydropyrimidin-2(1H)-one/thione derivatives of coumarin 3/4 from substituted 4-formylcoumarins 2 and ethylacetoacetate using urea/thiourea in the presence of catalytic amount of ceric ammonium nitrate is reported. All the synthesized compounds were evaluated for their antibacterial activity against four bacterial strains by broth dilution method. The tested compounds have exhibited promising in vitro potency with low MIC values against the drug susceptive S. aureus strain with low MIC values ranging from 0.2 to 6.25μg/mL. The in vivo anti-inflammatory potency of 3a-e and 4a-e by gelatin zymography is comparable to that of tetracycline. Molecular docking study performed for all the synthesized compounds with S. aureus DNA gyrase and results obtained were quite promising.

Facile synthesis of some novel 4-{3-aryl-3, 4-dihydro-2H-benzo[b][1,4] thiazin-2-yl}-2H-chromen-2-one derivatives

A protocol for chemoselective one pot synthesis of 4-{3-aryl-3, 4-dihydro-2H-benzo[b][1,4]thiazin-2-yl}-2H-chromen-2-ones 4 and 4-{3-aryl-3, 4-dihydro-2H-benzo[b][1,4]thiazin-2-yl}-2H-chromen-2-ones 6 under refluxing conditions has been developed. Starting from 4-bromomethylcoumarin and Schiff base, which is derived from o-aminothiophenol and substituted aromatic aldehydes, the intermediate sulfide spontaneously underwent intramolecular carbanion addition across the azomethine carbon.

The Synthesis and Biological Evaluation of Regioisomeric Benzothiazolyl Coumarins

Various 4-aryloxymethylcoumarins have been obtained by the r.t. allylic substitution with formylphenols. These have been further reacted with o-aminothiophenol resulting in the formation of a benzothiazole skeleton. These compounds have been synthesised with a view to study their potential as microbial growth inhibitors. Comparative studies on the spectral and antimicrobial activities have also been carried out.

Synthetic and Biological Studies on 4-Aryloxymethyl Coumarinyl Thiazolidinones

A series of new thiazolidinonyl -4-aryloxymethylcoumarins ( 4a–h ) have been synthesized from 4-Bromomethylcoumarins ( 1a–b ) and 4-aryliminomethyl-phenols ( 2a–d ). Structures of all the new compounds are elucidated by elemental analyses, IR, 1 H NMR, and mass spectral data. All these compounds have been subjected to in-vitro antimicrobial and in-vivo anti-inflammatory screening.

Synthesis, anti-microbial and anti-cancer evaluation study of 3-(3-benzofuranyl)-coumarin derivatives

The series of 3-coumarin-substituted benzofuran derivatives 4a–4j have been synthesized under optimized experimental condition with excellent yields. All the isolated compounds were characterized and screened anti-microbiological and anti-cancer activity. The anti-microbiological results observed were extremely good against S. aureus, C. albicans and A. niger. The comparative docking studies with gyrase type IIA topoisomerase from mycobacteriumtuberculosis docked with ligands and 4j have found lowest docked energy.

One-pot, green synthetic route for construction of coumarin C-4 bridged 2,6-dicyanoanilines and their photophysical study

ABSTRACT A highly selective and more efficient green protocol has been developed via a one-pot, three-component approach for the synthesis of coumarin 2,6-dicyanoanilines in aqueous ethanol. From the mechanism, two molecules of malanonitrile condensed with aldehyde and ketone resulted in the adducts, which on intramolecular cyclization via two new C-C bonds formed to afford the title compound. The present methodology offers simplified purification and environmentally benign conditions, avoids the use of toxic solvents, and gives excellent yield with high purity. All the synthesized compounds have been characterized by spectral analysis. Optical and thermal screening studies of all newly synthesized compounds showed excellent photophysical and thermal stability properties. GRAPHICAL ABSTRACT

Green approach for the synthesis of 4-coumarin-4H-pyrans from 4-formylcoumarins and their antibacterial study

ABSTRACT A series of 4H-pyranocoumarin derivatives have been successfully synthesized under eco-friendly condition using triethylamine as a catalyst in short reaction time with excellent yield at room temperature. All the synthesized compounds were characterized by spectral analysis and screened for their antibacterial activity against Escherichia coli and Staphylococcus aureus, the results are quite promising. GRAPHICAL ABSTRACT