Browsing by Author "Khungar, Bharti"

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Abnormal NHC Palladium(II) Complex Containing CNN Pincer Skeleton and Its Application to Suzuki-Miyaura Coupling of Aryl Chlorides in Water
(Wiley, 2023-05) Khungar, Bharti
The excellent catalytic activities of abnormal NHC carbene complexes, where the C2 position remains unaffected, and coordination occurs at the C4 or C5 position of the imidazolium ring, is still a fascinating but scarce area of research. This present work reports a palladium complex (LPdBr) bearing abnormal NHC with CNN pincer architecture. It is synthesized from imidazolium-based quinoline ligand (LH) with Pd(OAc)2 via -NH and carbene deprotonation. The complex was fully characterized by NMR spectroscopy (1D and 2D) and high-resolution mass spectrometry (HRMS). The structure and abnormal coordination modes of the complex are further confirmed with the help of single-crystal X-ray diffraction. The studies revealed the abnormal coordination mode in LPdBr where C5 carbon of the imidazolium ring participates in bonding, leaving the C2 position unaffected. The catalytic potential of complex LPdBr was investigated in the Pd-catalyzed Suzuki-Miyaura coupling of various aryl/heteroaryl chlorides with different aryl/naphthyl/phenanthryl boronic acids. The catalyst LPdBr successfully activated various less-activated aryl chloride substrates. LPdBr also exhibited good catalytic activity at 1 mol% Pd loading under microwave irradiation and in green solvent water. The mechanism of the catalytic cycle is investigated and proposed by HRMS.
Bis-Cinnamamide Derivatives as APE/Ref-1 Inhibitors for the Treatment of Human Melanoma
(MDPI, 2022) Khungar, Bharti
Human malignant melanoma exhibits imbalances in redox status, leading to activation of many redox-sensitive signaling pathways. APE/Ref-1 is a multifunctional protein that serves as a redox chaperone that regulates many nuclear transcription factors and is an important mechanism in cancer cell survival of oxidative stress. Previous studies showed that APE/Ref-1 is a potential druggable target for melanoma therapy. In this study, we synthesized a novel APE/Ref-1 inhibitor, bis-cinnamoyl-1,12-dodecamethylenediamine (2). In a xenograft mouse model, compound 2 treatment (5 mg/kg) significantly inhibited tumor growth compared to the control group, with no significant systemic toxicity observed. We further synthesized compound 2 analogs to determine the structure-activity relationship based on their anti-melanoma activities. Among those, 4-hydroxyphenyl derivative (11) exhibited potent anti-melanoma activities and improved water solubility compared to its parental compound 2. The IC50 of compound 11 was found to be less than 0.1 μM. Compared to other known APE/Ref-1 inhibitors, compound 11 exhibited increased potency in inhibiting melanoma proliferation. As determined by luciferase reporter analyses, compound 2 was shown to effectively inhibit H2O2-activated AP-1 transcription activities. Targeting APE/Ref-1-mediated signaling using pharmaceutical inhibitors is a novel and effective strategy for melanoma treatment with potentially high impact.
ChemInform Abstract: An Efficient and Simple One-Pot Synthesis of β-Acetamido Ketones Catalyzed by Ytterbium Triflate in Ionic Liquid
(Wiley, 2009-09) Khungar, Bharti; Kumar, Anil
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Click chemistry inspired structural modification of azole antifungal agents to synthesize novel ‘drug like’ molecules
(Elsiever, 2012-12-12) Khungar, Bharti; Kumar, Anil
A new class of ‘drug like’ 1,4-disubstituted-1,2,3-triazoles is synthesized using one-pot reaction of sodium azide, α-bromo ketones, and alkynes in PEG-400/water (1:1, v/v) under the click chemistry reaction condition followed by reduction of keto group and alkylation. The method is simple, efficient and gives good yield of novel 1,2,3-triazole derivatives.
Coordination behavior of biologically active schiff bases of amino acids towards silicon(IV) ion
(Taylor & Francis, 2006-10) Khungar, Bharti
Reactions of diethoxydimethylsilane with Schiff bases derived from the condensation of fur-furaldehyde. indole-3-carbaldehyde with alanine, glycine, valine, isoleucine and tryptophan in a 1:2 molar ratio give a new series of Me2Si (NO)2 type of organosilicon (IV) complexes. The complexes are monomeric and non-electrolytic in nature. The coordination behaviour of Schiff babes through organosilicon (IV) has been investigated by IR, 1H, 13C & 29Si NMR spectral studies. Schiff bases and their silicon complexes have also been screened for their antifungal activity. Several of these complexes were found to be quite active in this respect.
Copper catalyzed tandem oxidative C–H amination/cyclizations: Direct access to imidazo[1,2-a]pyridines
(RSC, 2013) Khungar, Bharti; Kumar, Anil
A simple and convenient strategy is described for the synthesis of imidazo[1,2-a]pyridines via inexpensive copper-catalyzed tandem imine formation and intramolecular aerobic oxidative C–H bond amination/cyclizations. An array of imidazo[1,2-a]pyridines were prepared by the reaction of readily available acetophenones and 2-aminopyridines in good to excellent yields (48–92%). The scope of the method was validated by a single step synthesis of Zolimidine, a drug used for peptic ulcers, in 61% yield.
Copper-Catalyzed Tandem Azide–Alkyne Cycloaddition, Ullmann Type C–N Coupling, and Intramolecular Direct Arylation
(ACS, 2013) Kumar, Anil; Khungar, Bharti
A ligand-free copper-catalyzed tandem azide–alkyne cycloaddition (CuAAC), Ullmann-type C–N coupling, and intramolecular direct arylation has been described. The designed strategy resulted in the synthesis of a novel trazole-fused azaheterocycle framework. The reaction gave good yields (59–77%) of 1,2,3-triazole-fused imidazo[1,2-a]pyridines in a single step.
A Deep Learning Approach for Molecular Crystallinity Prediction
(Springer, 2019-05) Khungar, Bharti
With the success of Convolutional Neural Networks (CNN) in computer vision domain, cheminformatics is slowly moving away from feature Engineering towards Network Engineering. New deep networks and approaches are being proposed to explore the chemical behavior and their properties. In this paper, we propose a deep learning approach using Convolutional Neural Network for predicting the crystallization propensity of an organic molecule. The work is inspired from Chemception and architecture is based on the Inception-Resnet v2 model. The proposed approach only requires a 2D molecular drawing to predict if the molecule has a good probability of forming crystals, without the need of any molecular descriptor, any advanced chemistry knowledge or any study of crystal growth mechanisms. We have evaluated our approach on the Cambridge Structural Database (CSD) and the ZINC datasets. Compared with the machine learning approach of generating molecular descriptors plus SVM classification, our proposed approach gives a better classification accuracy.
Detection of TNP and sulfite ions in an aqueous medium using a pyrazinium-based chemosensor
(RSC, 2024) Khungar, Bharti
A fluorescent pyrazinium-based 1-benzyl-3,5-diphenylpyrazin-1-ium bromide (BPPyz) chemosensor was synthesized and well-characterized. A significant reduction in blue emission of BPPyz was observed in the presence of TNP as compared to other nitroaromatic compounds, indicating high selectivity towards TNP. In the presence of sulfite ions, BPPyz showed fluorescence quenching and rapid naked-eye detection with a significant color change. The sensing mechanism was investigated through UV–visible studies, time-resolved fluorescence results, and density functional theory (DFT) calculations. The quenching constants (KSV) are 4.12 × 105 M−1 for TNP and 3.8 × 105 M−1 for sulfite with the detection limits of 9.5 nM and 46.17 nM for TNP and sulfite, respectively. The selectivity of BPPyz towards TNP was ascribed to the ground state charge transfer complex (GSC) formation and resonance energy transfer. Sulfite ion detection involved the formation of a GSC through hydrogen bonding with the pyrazinium proton.
An Efficient and Simple One-Pot Synthesis of β-Acetamido Ketones Catalyzed by Ytterbium Triflate in Ionic Liquid
(Elsiever, 2008-12-18) Kumar, Anil; Khungar, Bharti
Ytterbium triflate immobilized in the ionic liquid [bmim][BF4] catalyzes the three-component coupling of aromatic aldehydes, enolizable ketones, and acetonitrile in the presence of acetyl chloride at room temperature to afford β-acetamido ketones in good yields. The catalyst can be recovered and recycled for subsequent reactions without any appreciable loss of efficiency.
Exploration of fluorescence behavior of an imidazolium-based chemosensor in solution and in the solid state and its turn-on response to Al3+ in pure aqueous medium
(RSC, 2020) Khungar, Bharti
An imidazolium-based quinoline Schiff base ImSB was developed and fully characterized by FT-IR, 1H and 13C NMR spectroscopy, mass spectrometry, and X-ray crystallography. The fluorescence behaviour of ImSB in solution and in the solid state, keto–enol stability at different concentrations and pH in aqueous medium were investigated. The UV-visible and fluorescence studies were performed to determine the response of ImSB towards different ions in aqueous medium. ImSB showed a turn-on fluorescence behaviour with high selectivity towards Al3+ over various cations and anions due to chelation-enhanced fluorescence (CHEF), inhibition of photoinduced electron transfer (PET) and restriction of C[double bond, length as m-dash]N isomerization. The low detection limit for Al3+ was 54 nM and Job's plot confirmed 1 : 1 stoichiometry between ImSB and Al3+ with a high binding constant value of 4.16 × 106 M−1. Monitoring of Al3+ was also demonstrated in real water samples (mineral, river and tap water). The structural and electronic parameters of ImSB and ImSB-Al3+ were also studied theoretically.
Imidazolium ionic liquid-tagged palladium complex: an efficient catalyst for the Heck and Suzuki reactions in aqueous media
(RSC, 2014) Kumar, Anil; Sivasubramanian, S.C.; Khungar, Bharti
An air stable, water soluble, and efficient ionic liquid-tagged Schiff base palladium complex was prepared. The synthesized complex was well characterized by NMR, mass spectrometry, FT-IR, UV-visible spectroscopy and powder X-ray diffraction. The complex was used as a catalyst for the Suzuki and Heck cross-coupling reactions in water. Good to excellent yields were achieved using a modest amount of the catalyst. In addition, the catalyst can be easily reused and recycled for six steps without much loss in activity, exhibiting an example of sustainable and green methodology
K Pericherla, P Khedar, B Khungar, Anil Kumar, One-pot sequential C-N coupling and cross dehydrogenative couplings: Synthesis of novel azole fused imidazo[1,2-a]pyridines, Chem. Commun. 2013, 49, 2924-2926
(RSC, 2013) Kumar, Anil; Khungar, Bharti
An efficient one-pot protocol has been developed using sequential C–N coupling and intramolecular dehydrogenative cross-couplings for the synthesis of azole fused imidazo[1,2-a]pyridine derivatives in good yields (62–78%).
Luminescent triazolo-fused pyrido[3,4-b]pyrazines as novel fluorophores
(Elsevier, 2024-12) Khungar, Bharti; Sakhuja, Rajeev
A series of organic fluorophores based on novel [1,2,4]triazolo [4′,3':1,2]pyrido [3,4-b]pyrazine architecture were synthesized by a simple two-step protocol. Synthesized organic fluorophores exhibit blue-to-green fluorescence and their UV absorption and fluorescent emission properties were studied. The photophysical properties of synthesized derivatives were tuned by introducing functionalities of varying electronic nature on the core nucleus. The luminescence maxima of the synthesized compounds are found in the range from 427 nm to 503 nm, and the quantum yields ranging from 0.01 to 0.64 were calculated. Among various synthesized molecules, 3-(4-bromophenyl)-8,9-bis(4-methoxyphenyl)-[1,2,4]triazolo [4′,3':1,2]pyrido [3,4-b]pyrazine showed highest quantum yield (ΦF = 0.64), and was further explored for its solvatochromic, acidochromic, aggregation induced fluorescence studies along with theoretical HOMO-LUMO calculations
Multinuclear Magnetic Resonance and Related Studies of Coordination Compounds of Organosilicon with Mixed Azines
(Taylor & Francis, 2008-07) Khungar, Bharti
New hexa-coordinated complexes of organosilicon (IV) have been synthesized by the reactions of diethoxydimethylsilane with the mixed azines. Their structures have been inferred based on elemental analysis, UV, IR, and multinuclear magnetic resonance spectral studies. The monomeric and nonelectrolytic nature of these complexes has been confirmed by molecular weight determinations and conductance measurements. The mixed azines and their silicon complexes also have been screened for their antimicrobial activities against several fungi and bacteria and were found to be quite active in this respect.
One-pot sequential C–N coupling and cross dehydrogenative couplings: synthesis of novel azole fused imidazo[1,2-a]pyridines
(RSC, 2013) Khungar, Bharti; Kumar, Anil
An efficient one-pot protocol has been developed using sequential C–N coupling and intramolecular dehydrogenative cross-couplings for the synthesis of azole fused imidazo[1,2-a]pyridine derivatives in good yields (62–78%).
One-pot, three-component synthesis of 1-amidomethyl-imidazo[1,2-a]pyridines catalyzed by ytterbium triflate
(Elsiever, 2012-03) Kumar, Anil; D; Khungar, Bharti
A straightforward method has been developed for the synthesis of 1-amidomethyl-imidazo[1,2-a]pyridines by Yb(OTf)3 catalyzed three-component reaction of aldehydes, acetamide, and imidazo[1,2-a]pyridines. A series of substituted 3-substituted imidazo[1,2-a]pyridines were synthesized in moderate to good yield (21–74%) under mild reaction condition and the catalyst was recycled for four cycles.
Predicting the redox properties of uranyl complexes using electronic structure calculations
(Wiley, 2017-03-07) Khungar, Bharti
A plethora of chemical reactions is redox driven processes. The conversion of toxic and highly soluble U(VI) complexes to nontoxic and insoluble U(IV) form are carried out through proton coupled electron transfer by iron containing cytochromes and mineral surfaces such as machinawite. This redox process takes place through the formation of U(V) species which is unstable and immediately undergo the disproportionation reaction. Thus, theoretical methods are extremely useful to understand the reduction process of U(VI) to U(V) species. We here have carried out the structures and reduction properties of several U(VI) to U(V) complexes using a variety of electronic structure methods. Due to the lack of experimental ionization energies for uranyl (UO2(V)-UO2(VI)) couple, we have benchmarked the current and popularly used density functionals and cost effective ab initio methods against the experimental electron detachment energies of [UO2F4]1-/2- and [UO2Cl4]1-/2-. We find that electron detachment energy of U(VI) predicted by RI-MP2 level on the BP86 geometries correlate nicely with the experimental and CCSD(T) data. Based on our benchmark studies, we have predicted the structures and electron detachment energies of U(V) to U(VI) species for a series of uranium complexes at the RI-MP2//BP86 level which are experimentally inaccessible till date. We find that the redox active molecular orbital is ligand centered for the oxidation of U(VI) species, where it is metal centered (primarily f-orbital) for the oxidation of U(V) species. Finally, we have also calculated the detachment energies of a known uranyl [UO2]1+ complex whose X-ray crystal structures of both oxidation states are available. The large bulky nature of the ligand stabilizing the uncommon U(V) species which cannot be routinely studied by present day CCSD(T) methods as the system size are more than 20–30 atoms. The success of our efficient computational strategy can be experimentally verified in the near future for the complex as the structures are stable in gas phase which can undergo oxidation.
A pyrazinium-based fluorescent chemosensor for the selective detection of 2,4,6-trinitrophenol in an aqueous medium
(RSC, 2022) Khungar, Bharti
Sensing nitroaromatic explosives has gained significant attention due to both increased terrorist threats and a need for environmental protection. In this regard, a fluorescent chemosensor, 1-benzyl-3,5-di(thiophen-2-yl)pyrazin-1-ium bromide (BTPyz), was synthesized and characterized via spectroscopic methods. The photophysical properties were investigated using absorption and emission spectral analysis. As a fluorescent chemosensor, BTPyz exhibited a selective response towards 2,4,6-trinitrophenol (TNP) with a detection limit of 11.6 nM and quenching constant (KSV) of 3.8 × 104 M−1. The fluorescence quenching mechanism was attributed to ground-state charge-transfer complex formation and resonance energy transfer, as evident from Uv-visible, fluorescence and NMR spectroscopy, single-crystal XRD studies, and density functional theory calculations. BTPyz was also employed for the contact mode detection of TNP on paper strips. The detection of TNP in real water and soil samples demonstrated BTPyz to be a promising detection tool toward environmental specimens
Pyridinium-based schiff-base fluorescent chemosensor for sequential detection of al3+ ions and tnp: applications in cell imaging and latent fingerprint visualization
(Wiley, 2024-12) Jha, Prabhat Nath; Khungar, Bharti
A fluorescent pyridinium-based chemosensor (E)-1-(2-(3-hydroxy-4-((pyridin-2-ylimino) methyl) phenoxy) ethyl) pyridin-1-ium bromide (BzPySB) was synthesized and characterized using various spectroscopic techniques. The chemosensing potential of BzPySB was explored using UV-vis and fluorescence spectroscopy in the aqueous medium. The turn-on fluorescence behavior was observed for BzPySB in the presence of Al3+, while other metal ions were non-responsive. The B−H and Job′s plot confirmed the 1 : 1 stoichiometric ratio of the BzPySB and Al3+. The in situ generated complex BzPySB-Al3+ offered selectivity toward TNP via fluorescence turn-off phenomena with high Ksv and LOD values. The “off-on-off” sensing mechanism was elucidated through 1H NMR, mass spectrometry, and DFT calculations. The probe also detected Al3+ in plant and MCF-7 cells, highlighting its potential in biological systems. Moreover, BzPySB exhibited solid-state luminescent properties credited to weak π-π interaction, leading to its successful application in the visualization of latent fingerprints.