Ashis Kundu

Synthesis of 4-hydroxyindole fused isocoumarin derivatives and their fluorescence “Turn-off” sensing of Cu(II) and Fe(III) ions

A simple and efficient protocol has been developed for the synthesis of 4-hydroxyindole fused isocoumarins from easily available starting materials. Dihydroxy-indenoindoles, the cyclic hemiaminals of the condensation products of ninhydrin and enamines of 1,3-cyclohexanedione, produced indole fused isocoumarins 11-(aryl/alkyl)-8,9,10,11-tetrahydro-6-oxa-11-aza-benzo[a]fluorine-5,7-diones through an acid catalyzed intramolecular rearrangement. The above isocoumarin derivatives furnished novel 4-hydroxyindole fused isocoumarins 11-(aryl or alkyl)-7-hydroxy-11H-6-oxa-11-aza-benzo[a]fluoren-5-ones through dehydrogenation with Pd/C. The synthesized 4-hydroxyindole fused isocoumarins show fluorescence properties with good quantum yields and fluorescence “Turn-off” sensing of Cu2+ and Fe3+ ions. Importantly these molecules are found to be chemosensors only for Cu2+ ions with respect to UV-Vis spectral change and naked eye colour change in the presence and absence of UV radiation.

Exploring the interaction of a micelle entrapped biologically important proton transfer probe with the model transport protein bovine serum albumin.

This article describes the interaction of a micelle entrapped pharmaceutically important isoindole fused imidazole derivative, namely, 1-(2-hydroxy-5-methyl-phenyl)-3,5-dioxo-1H-imidazo-[3,4-b] isoindole (ADII), with the model transport protein bovine serum albumin (BSA). Different spectroscopic techniques such as steady state absorption, emission, circular dichroism, dynamic light scattering, etc., have been employed to explore preferential interaction of this drug template with micelles and protein BSA. Binding of ADII with BSA is found to be enormously modified when it is released from the micellar environment. The binding constant of the ADII-BSA complex is reduced when the probe is released from anionic SDS micelle, whereas the binding is observed to be strengthened in cationic CTAB micellar medium due to the formation of a 1:2 complex (ADII-BSA). Time-resolved studies also support our steady state findings that the released drug from the micellar environment is found to be strongly bound with the protein BSA. Circular dichroism (CD) and dynamic light scattering (DLS) study reveals that the secondary structure of BSA gets some stabilization in SDS medium after binding of drug template to protein. The probable binding location of the probe within the protein cavity (hydrophilic subdomain IA) has been explored from an AutoDock-based blind docking simulation study.

ZrO2 nanoparticles as a reusable solid dual acid–base catalyst for facile one-pot synthesis of multi-functionalized spirooxindole derivatives under solvent free condition

A two-step one-pot protocol for the facile synthesis of biologically important spirooxindole derivatives such as spiro[4H-pyran-3,3′-oxindoles] and spiro[indoline-3,4′(1H′)-pyrano-[2,3-c]pyrazol-2-ones has been developed. In this method ZrO2 nanoparticles have been utilized as a reusable solid dual acid–base catalyst to get quick access to the multi-functionalized spirooxindole derivatives under solvent free condition at room temperature. The main advantages of this method are the operational simplicity, reduced reaction time, elimination of solvents, high yield of the products, convenient work up procedure and employment of nontoxic and recyclable ZrO2 nano catalyst. All these factors make the present method economical, green and sustainable.

Synthesis of a new class of pyrazole embedded spirocyclic scaffolds using magnetically separable Fe3O4@SiO2–SO3H nanoparticles as recyclable solid acid support

An efficient, green and sustainable methodology for the synthesis of a new class of pyrazole embedded spirocyclic scaffolds has been developed. The method involves the condensation of a tetrone with a variety of arylhydrazones in the presence of Fe3O4@SiO2–SO3H magnetic nanoparticles (MNPs) as solid supported acid catalyst under solvent-free conditions. An interesting tandem rearrangement of the in situ generated adducts, derived from the acid catalyzed condensation of tetrone and arylhydrazones, leads to the formation of pyrazole embedded spirocyclic scaffolds. The significant advantages of this methodology are the use of solvent-free reaction conditions, employment of simple and easily available starting materials and reagents, good yields of the products with high atom-economy and operational simplicity of the reaction with the use of a magnetically separable and recyclable nano catalyst.

Synthesis of biologically important, fluorescence active 5-hydroxy benzo[g]indoles through four-component domino condensations and their fluorescence “Turn-off” sensing of Fe(III) ions

Several highly substituted 2-pyrrolyl-2-cyanoacetamides were prepared through four-component domino condensation of various easily available 1,3-dicarbonyl compounds, amines, arylglyoxals and malononitrile. Subsequently these cyanoacetamide derivatives were converted into biologically important 5-hydroxy benzo[g]indoles through thermal cyclization under metal-free conditions. The synthesized 5-hydroxy benzo[g]indoles are fluorescence active with good quantum yields (ΦF = ∼0.50). They also show excellent fluorescence “Turn-off” sensing of Fe3+ ions (detection limit = ∼1.2 × 10−6 M). The interaction of 5-hydroxy benzo[g]indoles with Fe3+ ions can also be monitored through UV-Vis spectral change and naked-eye colour change in the presence and absence of UV radiation. The 1H NMR titration unambiguously proves the formation of a complex between 5-hydroxy benzo[g]indoles and Fe3+ ion through the coordination of –OH groups with the metal. The binding constant of the complex (metal : ligand = 1 : 1) has been measured using Benesi–Hildebrand equation and found to be ∼7.97 × 103 M−1.

Novel synthesis of a series of spiro 1,3-indanedione-fused dihydropyridines through the condensation of a tetrone with N-aryl/alkylenamines in presence of solid support silica sulfuric acid.

A convenient protocol for the library synthesis of biologically important 1-aryl-

Monobromomalononitrile: an efficient regioselective mono brominating agent towards active methylene compounds and enamines under mild conditions

2^{\prime }

Facile synthesis of substituted pyrrole-fused isocoumarins from ninhydrin

2′,6-spiro(