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Author: search.filters.author.Kumar, DalipSubject: search.filters.subject.Synthesis

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    Synthesis of Red-Light-Responsive Pheophorbide-a Tryptamine Conjugated Photosensitizers for Photodynamic Therapy
    (Wiley, 2022-11) Kumar, Dalip
    Six methyl pheophorbide-a derivatives were prepared by linking a tryptamine side chain at the C-131, C-152 and C-173 positions of pheophorbide-a. Prepared conjugates were characterized and evaluated for their photocytotoxicity against A549 cells. The conjugate 6 a with strong absorption at 413 nm (Soret band), 663–671 nm (Q bands) and comparable fluorescence quantum yield (0.26) was found to exhibit significant cytotoxicity (659 nM). Molecular integration of pheophorbide-a and tryptamines showed synergistic effects as the most potent conjugate 6 a was identified with enhanced photocytotoxicity when compared to methyl pheophorbide-a. The conjugate 6 a was smoothly taken up by A549 cells and exhibited intracellular localization predominantly to lysosome in the cytoplasm. Upon photoirradiation 6 a generated singlet oxygen to show potent cytotoxicity toward A549 cells.
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    Metal-free regioselective formation of C–N and C–O bonds with the utilization of diaryliodonium salts in water: facile synthesis of N-arylquinolones and aryloxyquinolines
    (RSC, 2017) Kumar, Dalip; Kumar, Indresh
    Regioselective construction of crucial C–N and C–O bonds leading to N-arylquinolones and aryloxyquinolines has been accomplished by employing easily accessible diaryliodonium salts and quinolones in water under metal- and ligand-free conditions. This operationally simple strategy is significant due to mild reaction conditions, high product yields, recyclability of released iodoarenes and scalability to the gram level. The practical utility of the developed protocol was proved by the arylation of medicinally important heterocycles like acridin-9(10H)-one, 3-methylquinoxalin-2(1H)-one and 1H-benzo[d]imidazol-2(3H)-one.
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    A Facile Synthesis of 5-Methyl-1-(phenyl/heterocyclyl)-4-trifluoroacetylpyrazoles
    (RSC, 1997) Kumar, Dalip
    Treatment of substituted hydrazines (2a–d) with 3-acetyl-4-ethoxy-1,1,1-trifluorobut-3-en-2-one (1) yields the title compounds (3a–d) whereas methylhydrazine on similar treatment gives 4-acetyl-1-methyl-3-trifluoromethylpyrazole
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    Surfactant pillared clays as phase‐transfer catalysts: a facile synthesis of α‐azidoketones from α‐tosyloxyketones and sodium azide
    (Springer, 1998-08) Kumar, Dalip
    The use of inexpensive and recyclable phase‐transfer catalysts, surfactant pillared clays, is demonstrated in a simple and highly efficient synthesis of α‐azidoketones from readily accessible α‐tosyloxyketones and sodium azide.
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    An Expeditious Synthesis of Flavones on Montmorillonite K 10 Clay with Microwaves
    (RSC, 1998) Kumar, Dalip
    A manipulatively simple and rapid method for the synthesis of flavones is described via a solid-state dehydrative cyclization of o-hydroxydibenzoylmethanes on a clay surface using microwaves.
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    ChemInform Abstract: Synthesis of a Heterocyclic Aza-Enediyne and Its DNA-Cleavage Properties
    (Wiley, 2010-05-30) Kumar, Dalip
    ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.
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    Chemical synthesis in aqueous media using microwaves
    (Microwave Symposium Proceedings,, 2006) Kumar, Dalip
    The development of efficient, selective and eco-friendly synthetic methods has remained a major focus of our research group. Microwave (MW) irradiation as alternative energy source in conjunction with water as reaction media has proven to be a successful 'greener' chemical approach. The N-alkylation of amines by alkyl halides that proceeds expeditiously in the presence of aqueous NaOH to deliver tertiary amines and double N-alkylation of amines and hydrazine derivatives to assemble a series of heterocyclic moieties such as N-azacycloalkanes, 4,5-dihydropyrazoles and pyrazolidines etc. will be discussed as an environmentally friendlier alternative. An efficient and clean MW-assisted synthesis of alkyl azides/thiocynates will be described by reacting alkyl halides/tosylates with alkali azides/thiocynates. The salient features of using this strategy include considerable reduction in reaction times, minimization or elimination of byproduct formation and improved tolerance for functional groups such as carbonyl, hydroxyl and esters.
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    Sulfated zirconia and phosphotungstic acid catalyzed synthesis of some biologically potent heterocyclic compounds
    (BCSI, 2006) Kumar, Dalip
    Sulfated zirconia and phosphotungstic acid (PWA) have been used as catalysts for the synthesis of some biologically potent 3,4-dihydropyrimidin-2(1H)-ones and aryl-14Hdibenzo[ a.j]xanthenes under solvent free conditions. Both the solid acid catalysts are found to be active for the synthesized compounds under mild reaction conditions. The 3,4-dihydropyrimidin-2(1H)-ones were synthesized in a single step using multicomponent condensation of aryl aldehyde, urea derivatives and β-dicarbonyl compounds using PWA or sulfated zirconia as catalysts. The generality of this protocol has been demonstrated by synthesizing a variety of functional dihydropyrimidin-2(1H)-ones in excellent yield and short reaction time. Phosphotungstic acid has also been demonstrated as an efficient catalyst for the condensation of aryl aldehydes and β-napthol to produce aryl-14H-dibenzo[a.j]xanthenes under solvent-free conditions. The reaction is found to proceed quickly in presence of catalytic amount of phosphotungstic acid and brief exposure to microwave to afford the products in good yield.
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    Sulfated Zirconia-catalyzed One-pot Benign Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones under Microwave Irradiation
    (CSJ, 2006) Kumar, Dalip
    Sulfated zirconia has been demonstrated as an efficient catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones under microwave irradiation and conventional heating. The solid acid catalyst is found to be highly active for the one-pot condensation of aldehydes, urea and β-dicarbonyl compound, affording variety of 3,4-dihydropyrimidin-2(1H)-ones in excellent yields with high purity. The low cost catalyst has exhibited remarkable reactivity and recycled without any significant loss of activity.
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    A Facile and Expeditious Synthesis of Cryptosanguinolentines
    (CSJ, 2009) Kumar, Dalip
    A simple and efficient synthesis of naturally occurring cryptosanguinolentines is described. Neat reaction of easily accessible 1-methyl-1,2,3,4-tetrahydroquinolin-4-ones and aryl hydrazines in the presence of p-toluenesulfonic acid at 100 °C rapidly afforded cryptosanguinolentines in very good yields.