Nidhin Paul

A facile, water mediated, microwave-assisted synthesis of 4,6-diaryl-2,3,3a,4-tetrahydro-1H-pyrido[3,2,1-jk]carbazoles by a domino Fischer indole reaction–intramolecular cyclization sequence

An environmentally benign, facile and efficient synthesis of a series of 4,6-diaryl-2,3,3a,4-tetrahydro-1H-pyrido[3,2,1-jk]carbazoles was achieved in water with good yield by the reaction of diastereomerically pure 2-(3-oxo-1,3-diarylpropyl)-1-cyclohexanones with phenylhydrazine hydrochloride under microwave irradiation. The transformation presumably proceeds via a domino Fischer indole reaction–intramolecular cyclisation sequence.

Synthesis of 3-heteroarylthioquinoline derivatives and their in vitro antituberculosis and cytotoxicity studies.

A series of 3-heteroarylthioquinoline derivatives has been synthesized by the Friedlander annulation of 2-[(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]-1-aryl-1-ethanone/2-(1,3-benzothiazol-2-ylsulfanyl)-1-aryl-1-ethanone/1-aryl-2-[(2-phenyl-2H-1,2,3,4-tetraazol-5-yl)sulfanyl]-1-ethanone with 2-aminobenzophenone in good yields using YbCl(3) as the catalyst. These compounds have been screened for their in vitro activity against Mycobacterium tuberculosis H37Rv (MTB) and among the 21 compounds screened, 2-[2-(4-bromophenyl)-4-phenyl-3-quinolyl]sulfanyl-5-methyl-1,3,4-thiadiazole (5d) and 2-[2-(4-chlorophenyl)-4-phenyl-3-quinolyl]sulfanyl-5-methyl-1,3,4-thiadiazole (5c) were found to be the most active compounds with MIC of 3.2 and 3.5 μM respectively against MTB. The cytotoxic effects against mouse fibroblasts (NIH 3T3) in vitro were evaluated for 5c and 5d, which displayed no toxic effects (IC(50) > 1000 μM) against the mouse fibroblast cell line NIH 3T3.

Camphorsulfonic acid catalysed facile tandem double Friedlander annulation protocol for the synthesis of phenoxy linked bisquinoline derivatives and discovery of antitubercular agents

A series of phenoxy linked bisquinoline derivatives were synthesised from the Friedlander annulation of 2-(4-acetylphenoxy)-1-aryl-1-ethanones with 2-aminobenzophenone in good yields using (±)-camphor-10-sulfonic acid (CSA) as the catalyst. These compounds were screened for their in vitro activity against Mycobacterium tuberculosis H37Rv (MTB) and among the 23 compounds screened, 2-(3-bromophenyl)-6-chloro-3-[4-(6-chloro-4-phenyl-2-quinolyl)phenoxy]-4-phenylquinoline (3q) and 2-(4-bromophenyl)-6-chloro-3-[4-(6-chloro-4-phenyl-2-quinolyl)phenoxy]-4-phenylquinoline (3o) were found to be the most active compounds with MIC of 1.1 and 2.2 μM against MTB. The cytotoxic effects against mouse fibroblasts (NIH 3T3) in vitro were evaluated for 3o and 3q, which displayed no toxic effects against mouse fibroblast cell line NIH 3T3.

A facile synthesis of carbocycle-fused mono and bis-1,2,3-selenadiazoles and their antimicrobial and antimycobacterial studies.

A series of mono and bis-1,2,3-selenadiazole derivatives have been synthesized by the oxidative cyclization of mono and bis semicarbazones of 2-(3-oxo-1,3-diarylpropyl)-1-cyclohexanones using selenium(IV) oxide. The newly synthesized compounds were evaluated for their in vitro antimicrobial activity against Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 11632) and Candida albicans (ATCC 90028) and in vitro antituberculosis activity against Mycobacterium tuberculosis H37Rv (MTB). Among these compounds, 1,3-di(4-chlorophenyl)-3-(4,5,6,7-tetrahydro-1,2,3-benzoselenadiazol-4-yl)-1-propanone (2h) and 3-(4-chlorophenyl)-1-(4-methylphenyl)-3-(4,5,6,7-tetrahydro-1,2,3-benzoselenadiazol-4-yl)-1-propanone (2g) were found to be the most active compounds with MIC of 3.3 and 3.5 μM respectively against MTB.

A green protocol for the synthesis of conformationally rigid sulfur linked bisquinolines by double Friedlander reaction in water

A series of bis(2-aryl-4-arylquinolin-3-yl)sulfanes and 1,2-bis(2-aryl-4-arylquinolin-3-yl)disulfanes were synthesised in good to excellent yields by double Friedlander reaction between 2-[(2-oxo-2-arylethyl)sulfanyl]-1-aryl-1-ethanones/2-[(2-oxo-2-arylethyl)disulfanyl]-1-aryl-1-ethanones and 2-aminobenzophenone with p-toluenesulfonic acid in water medium. An interesting restricted rotation of aryl rings has been noticed in bis(2-aryl-4-arylquinolin-3-yl)sulfanes as revealed by NMR and crystal data.

Synthesis of 2,5-diaroyl-3-arylthiophenes: novel tandem reactions mediated 3+2-self annulation of bis(aroylmethyl) sulfides

A series of 2,5-diaroyl-3-arylthiophenes were obtained from the 3+2-self annulation of bis(aroylmethyl) sulfides in the presence of sodium hydroxide. This transformation occurs presumably via a tandem intermolecular condensation - ring closing intramolecular displacement-aromatization via air oxidation and elimination sequence.

Synthesis, antimicrobial, and cytotoxicity studies of novel sulfur-linked quinoline–coumarin bisheterocycles

A series of sulfur attached quinolines and quinoline–coumarin bisheterocycles have been synthesized by the Friedlander reaction of methyl 2-[(2,4-diaryl-3-quinolyl)sulfanyl]acetate and subsequent reaction with salicylaldehyde. These compounds were screened for their in vitro antimicrobial activity against Gram-positive, Gram-negative bacteria, and fungal pathogen. Among the 19 compounds screened, preliminary results indicated that many of the compounds demonstrated moderate to good antimicrobial activities. The cytotoxic effects against mouse fibroblasts (NIH 3T3) in vitro were evaluated for the most active compound, which displayed no toxic effects.

Reactions of diphenacylaniline and diphenacyl sulfide under Gewald conditions: generation of enamines and thioamides

The 1,5-diketone, diphenacylaniline, yielded an enamine under Gewald conditions, while another 1,5-diketone, diphenacyl sulfide, resulted in thioamide formation under identical conditions. 2-Amino-4-(3-oxo-1,3-diphenylpropyl)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile was obtained from the 1,5-diketone 2-(3-oxo-1,3-diphenylpropyl)-1-cyclohexanone under the same conditions.

Solvent based selectivity in the synthesis of di(2-aryl-1H-3-indolyl) sulfides and 1-aryl-2-[(2-aryl-1H-3-indolyl)sulfanyl]-1-ethanones

The commendable product selectivity exhibited by the solvents during the reaction of 2-[(2-oxo-2-arylethyl)sulfanyl]-1-aryl-1-ethanones with phenylhydrazine hydrochloride yielding exclusively 1-aryl-2-[(2-aryl-1H-3-indolyl)sulfanyl]-1-ethanones in THF and di(2-aryl-1H-3-indolyl) sulfides in ethanol is described.

Synthesis of (Z)-1,3-diaryl-2-(4-aryl-1H-1,2,3-triazol-1-yl)prop-2-en-1-ones and their antibacterial studies

The cyclization of 1,3-diaryl-2-azido-2-propen-1-ones with various alkynes in the presence of a catalytic amount of copper sulfate–sodium ascorbate in DMSO–water mixture under microwave irradiation led to the formation of (Z)-1,3-diaryl-2-(4-substituted-1H-1,2,3-triazol-1-yl)prop-2-en-1-ones. The structure and stereochemistry of the products have been elucidated by spectroscopic and single crystal X-ray analyses. All the newly synthesized compounds have been tested for their antibacterial activity against four strains of bacteria and found to have moderate to good inhibition.