Nabin C. Barua

Stabilization of Cu(0)-nanoparticles into the nanopores of modified montmorillonite: An implication on the catalytic approach for “Click” reaction between azides and terminal alkynes

In situ generation of Cu(0)-nanoparticles in the nanopores of modified montmorillonite and their catalytic activity in 1,3-dipolar cycloaddition reactions between azides and terminal alkynes to synthesise 1,2,3-triazoles have been carried out. The modification of montmorillonite was carried out by activation with H2SO4 under controlled conditions for generating nanopores to act as a “host” for the Cu(0)-nanoparticles, which is executed by successful loading of Cu(CH3COO)2 metal precursor through an incipient wetness impregnation technique followed by reduction with NaBH4. A TEM study reveals that Cu(0)-nanoparticles within the size range of 0–10 nm are evenly distributed on the support. The synthesized Cu(0)-nanoparticles exhibit face centered cubic (fcc) lattice geometry and serve as an efficient green catalyst for the “Click” azide–alkyne cycloaddition to afford highly regioselective 1,4-disubstituted 1,2,3-triazoles with excellent yields and selectivity in aqueous medium. The nanocatalysts can be recycled and reused several times without significant loss of their catalytic activity.

Germination and growth inhibitory sesquiterpene lactones and a flavone from Tithonia diversifolia

Abstract Inhibitory effects of two sesquiterpene lactones tagitinin A, tagitinin C and a flavonoid hispidulin isolated from Tithonia diversifolia were determined on germination of radish, cucumber and onion seeds. The flavonoid hispidulin was more toxic to the crop seeds tested and the activity of tagitinin C was weaker than that of tagitinin A and hispidulin. Seventeen derivatives have been prepared from tagitinin A and C by chemical transformation and their phytotoxicity has been compared with the parent compounds (all at 250,μM) using radish seeds. The structural requirements related to their biological activity have also been delineated.

Mahanine restores RASSF1A expression by down-regulating DNMT1 and DNMT3B in prostate cancer cells

BackgroundHypermethylation of the promoter of the tumor suppressor gene RASSF1A silences its expression and has been found to be associated with advanced grade prostatic tumors. The DNA methyltransferase (DNMT) family of enzymes are known to be involved in the epigenetic silencing of gene expression, including RASSF1A, and are often overexpressed in prostate cancer. The present study demonstrates how mahanine, a plant-derived carbazole alkaloid, restores RASSF1A expression by down-regulating specific members of the DNMT family of proteins in prostate cancer cells.ResultsUsing methylation-specific PCR we establish that mahanine restores the expression of RASSF1A by inducing the demethylation of its promoter in prostate cancer cells. Furthermore, we show that mahanine treatment induces the degradation of DNMT1 and DNMT3B, but not DNMT3A, via the ubiquitin-proteasome pathway; an effect which is rescued in the presence of a proteasome inhibitor, MG132. The inactivation of Akt by wortmannin, a PI3K inhibitor, results in a similar down-regulation in the levels DNMT1 and DNMT3B. Mahanine treatment results in a decline in phospho-Akt levels and a disruption in the interaction of Akt with DNMT1 and DNMT3B. Conversely, the exogenous expression of constitutively active Akt inhibits the ability of mahanine to down-regulate these DNMTs, suggesting that the degradation of DNMT1 and DNMT3B by mahanine occurs via Akt inactivation.ConclusionsTaken together, we show that mahanine treatment induces the proteasomal degradation of DNMT1 and DNMT3B via the inactivation of Akt, which facilitates the demethylation of the RASSF1A promoter and restores its expression in prostate cancer cells. Therefore, mahanine could be a potential therapeutic agent for advanced prostate cancer in men when RASSF1A expression is silenced.

Stereochemistry of strictic acid and related furano-diterpenes from conyza japonica and grangea maderaspatana

Abstract Extraction of Conyza japonica gave strictic acid, ent-2β-hydroxy-15,16-epoxy-3,13(16),14-clerodatrien-18-oic acid and 5,7-dihydroxy-3,8,4′-trimethoxyflavone. Extraction of Grangea maderaspatana gave (-)-hardwickiic acid, ent-15,16-epoxy-1,3,13(16),14-clerodatetraen-18-oic acid and 3-hydroxy-8-acetoxypentadeca-1,9,14-trien-4,6-diyne. The structure of ent-2β-hydroxy-15,16-epoxy-3,13(16),14-cleroclatrien-18-oic acid was deduced by spectroscopic methods and by partial synthesis from (-)-hardwickiic acid and the stereochemistries of strictic acid and (ent-15,16-epoxy-1,3,13(16),14-clerodatraen-18-oic acid were established by correlation with ent-2β-hydroxy-15,16-epoxy-3,13(16),14-clerodatrien-18-oic acid.

Flavonoids from Millettia pulchra

Abstract Chemical examination of Millettia pulchra yielded (−)-maackiain, (−)-pterocarpin, (−)-sophoranone and the new compounds (6 S , 6a S , 11a R )-6α-methoxypterocarpin, (6 S , 6a S ,11aR)-6α-methoxyhomopterocarpin, (2 S )5,7,4′-trihydroxy-8,3′,5′-triprenylflavanone, (2 R ,3 R )7,4′-dihydroxy-8,3′,5′-triprenyldihydroflavanol, 5,7,2′,4′-tetrahydroxy-6,3′-diprenylisoflavone and 5,7,4′-trihydroxy-2′-methoxy-6,3′-diprenylisoflavone.

AlNiCl2.6H2OTHF: A new, mild and neutral system for selective reduction of organic functional groups

Abstract A mild and neutral reducing system consisting of AlNiCl 2 .6H 2 OTHF has been developed and reacted with a series of organic compounds containing different functional groups in order to evaluate its synthetic utility. It was observed that this system very efficiently reduces the α-enones to the saturated ketones, aromatic aldehydes and ketones to the corresponding alcohols, nitriles and nitroarenes to amines, acid anhydrides and acid chlorides to aldehydes, disulphides to thiols and epoxides to the corresponding alcohols. On the other hand isolated double bonds, carboxylic acids, esters, lactones, primary, benzyl and allyl halides, aliphatic aldehydes and ketones and aliphatic nitro compounds were found to remain inert to this system. Furthermore, the reducing properties of AlNiCl 2 .6H 2 O in several other organic solvents were also studied.

Iodine-catalyzed conversion of β-dicarbonyl compounds into β-enaminones within a minute under solvent-free conditions

Abstract Synthesis of β‐enaminones from β‐dicarbonyl compounds has been achieved in high yields within a minute using primary and aromatic amines and catalytic amounts of iodine under solvent‐free conditions at room temperature.

Rapid microwave assisted synthesis and antimicrobial bioevaluation of novel steroidal chalcones.

A novel class of chalconoyl pregnenolones has been prepared via Claisen-Schmidt condensation under microwave activation and solvent free reaction conditions. The compounds were screened for antimicrobial activity against two bacterial strains Bacillus subtilis and Escherichia coli and two fungal strains Aspergillus niger and Candida albicans. Some of the compounds exhibited significant inhibitory activity against the microbial strains. Presence of the α,β-unsaturated carbonyl moiety in the synthesized compounds was found to be essential for the activity as manipulation of the same through epoxidation of the double bond diminished the activity.

A facile reduction procedure for nitroarenes with Al-NiCl2-THF system

Abstract It has been demonstrated that aromatic nitro compounds could be reduced to the corresponding amines very efficiently using reagent system consisting of A1-NiCl2.6H2O-THF.

Stereoselective synthesis of the major component of a mosquito oviposition attractant pheromone from a β-lithiopropionate equivalent

β-Lithiated β-ethylthioacrylate 5A is a versatile β-lithiopropionate equivalent. Reaction with enantiomerically pure epoxide (-)-4 and subsequent Raney nickel treatment gives the natural oviposition attractant pheromone of the mosquito Culexpipiens fatigans (-)-1. From epoxide (+)-4 the enantiomer (+)-1 is synthesized.