Sumit Kumar Panja

Recyclable, magnetic ionic liquid bmim[FeCl4]-catalyzed, multicomponent, solvent-free, green synthesis of quinazolines

An atom-efficient, eco-friendly, solvent-free, high yielding, multicomponent green strategy to synthesize highly functionalized quinazoline derivatives by the one-pot reaction of 2-aminobenzophenone, aromatic aldehyde and ammonium acetate is presented. Magnetic IL, butylmethylimidazolium tetrachloroferrate (bmim[FeCl4]) has been used successfully as a catalyst in a multicomponent synthetic strategy for the first time. The catalytic cycle and a tentative reaction mechanism were discussed and experimentally verified. Structural and optical properties of the synthesized quinazolines are also described.

Anti-cancer therapeutic potential of quinazoline based small molecules via global upregulation of miRNAs

Three quinazoline based small molecules showed global upregulation of miRNA expression with a selective enrichment of tumor suppressor miRNAs. The target genes of the upregulated miRNAs were predicted to be enriched for apoptotic pathways. Apoptotic induction following treatment with quinazoline compounds was confirmed by in cellulo studies. Thus, these small molecules having the core structural moiety (2,4-diphenyl-quinazoline) can be used as scaffolds to design activators of miRNA expression paving the way for novel anti-cancer drugs.

First report of the application of simple molecular complexes as organo-catalysts for Knoevenagel condensation

A series of molecular complexes have been designed, synthesized and used as organo-catalysts for the first time for very efficient Knoevenagel condensation. Molecular complexes are thermally stable, easily recyclable, and have a low cost of preparation. The role of acidic protons in molecular complexes in Knoevenagel condensations has been identified as the key factor and helps us to provide useful information about the reaction pathway. The acidic proton of a catalyst enhances the electrophilicity of an aldehyde and accelerates the dehydration process of the reaction at room temperature (RT). An eco-friendly, green synthetic protocol for the Knoevenagel condensation is used to synthesize a series of important cyano group containing synthetic precursors for synthesis of biologically active molecules at RT using a minimum amount of catalyst (∼5 mol%) without the need for chromatographic separation techniques. Detailed mechanistic studies and substituent effects of aromatic aldehydes on the reaction have been investigated. In addition, biologically active 2-amino-4H-chromene derivatives have also been synthesized by the Knoevenagel condensation of salicylic aldehydes with active methylene compounds, followed by intramolecular cyclization (via Michael addition) delivering higher yields within shorter reaction times at RT without any need for chromatographic separation.

Tuning the intramolecular charge transfer (ICT) process in push–pull systems: effect of nitro groups

The intramolecular charge transfer (ICT) process in donor–acceptor systems has tremendous importance in various physical and biological systems. Three nitrophenolate salts were synthesized and studied here. The ICT and π → π* transition processes were identified in these derivatives using UV-Vis spectroscopy and theoretical calculations. It was observed that by simple substitution with nitro groups, one can generate and control the ICT process by regulating the charge distribution over the molecule. While for a monosubstitute nitro derivative, only one ICT band was observed, additional ICT processes can be generated at will by introducing a second nitro group. The intensity of this second ICT channel can be regulated with introduction of a third nitro group. Further, the association constants and solvation processes for these potassium nitrophenolate derivatives were found to be drastically dependent on the number of ICT channels present in the molecule. Theoretical studies (MEP analysis) support the experimental observations presented here. The results show that by simply introducing additional acceptor groups to the system, one can tune the ICT band efficiently in a conjugate system.

Micro-heterogeneity in imidazolium and piperidinium cation based ionic liquids: 1D and 2D NMR studies

Existence of microheterogeneity of imidazolium and piperidinium cation‐based ionic liquids (ILs) containing PF6 and NTf2 anions has been investigated by 1D and 2D NMR spectroscopy. 2D NMR (especially NOESY and HOESY) has been employed for studying the interactions present between cation and anion as well as the intermolecular interaction among cations. HOESY spectrum shows that fluorine of anion ( PF6− and NTf2− ) significantly interacts with proton of the cations. Combined results of HOESY and NOESY for imidazolium IL indicate that the PF6− and imidazolium cation are distributed in organized manner, resulting a heterogeneous environment in liquid state. We have also observed existence of heterogeneous environment for piperidinium cation‐based ILs which is different from imidazolium ILs. It appears that existence of microheterogeneity in IL is ubiquitous and therefore open up the ILs field to revisit. Copyright

Highly stable naphthalene core based novel cleft-shaped strain molecule: influence of intermolecular H-bonding architectures

The significance of intermolecular classical and non-classical H-bonding interactions in the stabilization of a naphthalene core based conformationally rigid cleft-shaped 1,5-dioxocin (BNAP) is presented here. The importance of H-bonding interactions to account for the unusual stability of a catalytically important novel molecule is reported for the first time. In addition to strong CH⋯π interactions, the formation of the unique intermolecular seven-membered H-bonded ring in the crystalline state through classical and non-classical H-bonding interaction was found to provide the unusual stability. This supramolecular structure was also found to impart stability in the presence of a strong acid as evident from the detailed UV-Visible spectroscopic studies. In addition to DFT calculations, the Hirshfeld surfaces, mapped with dnorm, and 2D fingerprint plots, support the existence of these classical and non-classical H-bonding and CH⋯π interactions. Furthermore, BNAP shows its remarkable catalytic activity for the Knoevenagel condensation reaction.

Evidence of C--F-P and aromatic π--F-P weak interactions in imidazolium ionic liquids and its consequences

A simple change from alkyl group to alkene in side chain of imidazolium cation with same anion resulted in a drastic impact on physical properties (e.g., melting point) from bmimPF6 IL to cmimPF6 IL. The underlying reasons have been elucidated by structural and interaction studies with the help of DSC, SCXRD, vibrational and multi-nuclear NMR spectroscopic techniques. Experiments reveal existence of new weak interactions involving the carbon and π cloud of the imidazolium aromatic ring with fluoride of PF6 anion (i.e., C2--F-P and π--F-P) in cmimPF6 but are absent in structurally similar prototype IL, bmimPF6. Though weak, these interactions helped to form ladder type supramolecular arrangement, resulting in quite high melting point for cmimPF6 IL compared to bmimPF6 IL. These findings emphasize that an IL system can behave uniquely because of the existence of uncommon weak interactions.