BITS Faculty Publications

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    Quinine bis-conjugates with quinoloneantibiotics and peptides: synthesis and antimalarial bioassay
    (RSC, 2012) Bajaj, Kiran
    Benzotriazole-mediated syntheses led to novel bis-conjugates of quinine with quinolone antibiotics and amino acid linkers which were successfully prepared by two alternative routes with excellent yields and retention of chirality. These bis conjugates retain in vitro antimalarial activity with IC50 values ranging from 12 to 207 nM, similar to quinine itself.
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    Syntheses of hydrazino peptides and conjugates
    (Elsiever, 2013-07) Bajaj, Kiran
    (α-Benzyloxycarbonyl-aminoacyl)benzotriazolides (Cbz = benzyloxycarbonyl) underwent a coupling reaction with α-hydrazino acids under microwave irradiation to form hybrid hydrazino dipeptides (42-71 %). Chiral acylations of β-N-Cbz-α-hydrazino acylbenzotriazolides were successfully carried out with N-, S-, O-, and C-nucleophiles in yields of 49-88 %. Benzyloxycarbonyl-protected hybrid hydrazino dipeptides and benzyloxycarbonyl-protected hydrazino aminoacyl conjugates with N-, S-, O-, and C-nucleophiles were prepared by using benzotriazole methodology.
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    Gas phase IR spectra of tri-peptide Z-Pro-Leu-Gly: Effect of C-terminal amide capping on secondary structure
    (Elsiever, 2012-04-02) Chakraborty, Shamik
    Three-residue peptides capped with benzyloxycarbonyl (Z-) group, Z-Pro-Leu-Gly–NH2 and Z-Pro-Leu-Gly–OH, are investigated by infrared (IR) spectroscopy, using supersonic-jet laser desorption technique, in the N–H and O–H stretching frequency ranges. The IR spectra show clear evidence of the formation of different hydrogen-bonding network in the two peptides. The possible gas phase structure is proposed from density functional theory calculations using cc-pVDZ basis set. The Z-Pro-Leu-Gly–OH in the gas phase forms successive γ-turn structure with free C-terminal carboxyl group whereas main structural element in Z-Pro-Leu-Gly–NH2 is β-turn with C-terminal single bondNH2 group forming hydrogen bond. Structural information is employed to predict their binding capability in gas phase
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    Gas-phase spectroscopy and anharmonic vibrational analysis of the 3-residue peptide Z-Pro-Leu-Gly-NH2 by the laser desorption supersonic jet technique
    (Elsiever, 2013-06-20) Chakraborty, Shamik
    The electronic excitation and infrared (IR) spectra of a capped tri-peptide, Z-PLG-NH2 (Z = benzyloxycarbonyl, P = Pro, L = Leu, G = Gly), were measured in the gas phase by using the laser desorption supersonic jet technique. By measuring an ultraviolet–ultraviolet hole burning spectrum, it was found that Z-PLG-NH2 has the maximum three conformers in the gas phase, but that the population is mainly distributed to a single conformation. Molecular dynamics simulations and density functional theory calculations well-reproduced the observed IR spectrum, except for splitting of the NH stretching bands by a β-turn structure that corresponds to a global minimum structure. Anharmonic vibrational analysis by vibrational quasi-degenerate perturbation theory (VQDPT) successfully reproduced the anharmonic splitting, and confirmed the assignments.
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    Efficient Syntheses of Naphthoquinone-Dipeptides
    (Thieme, 2010) Sakhuja, Rajeev
    Naphthoquinone-dipeptides are synthesized in 76-89% yield from naphthoquinone-amino acid conjugates by N-acylbenzotriazole methodology in aqueous media at 20 ˚C
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    Traceless reductive ligation at a tryptophan site: a facile access to β-hydroxytryptophan appended peptides
    (RSC, 2016) Sakhuja, Rajeev; Bajaj, Kiran
    An efficient methodology for cysteine-free ligation at a tryptophan (Trp) site is described. A chemically active scaffold, β-hydroxy-α-azidotryptophan, has been synthesized and explored towards the synthesis of a series of β-hydroxytryptophan appended native peptides in good yields via one-pot reductive traceless ligation of β-O-peptidyl-α-azidotryptophan involving an O → N peptidyl transfer strategy. Pre-organized conformational analysis and reaction energy pathway based theoretical studies further supported the experimental findings on the chemical structure stability of ligated products.
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    Glycosidase and glycan polymorphism control hydrolytic release of immunogenic flagellin peptides
    (Science AAAS, 2019-04) Chandrasekar, Balakumaran
    Plants and animals recognize conserved flagellin fragments as a signature of bacterial invasion. These immunogenic elicitor peptides are embedded in the flagellin polymer and require hydrolytic release before they can activate cell surface receptors. Although much of flagellin signaling is understood, little is known about the release of immunogenic fragments. We discovered that plant-secreted β-galactosidase 1 (BGAL1) of Nicotiana benthamiana promotes hydrolytic elicitor release and acts in immunity against pathogenic Pseudomonas syringae strains only when they carry a terminal modified viosamine (mVio) in the flagellin O-glycan. In counter defense, P. syringae pathovars evade host immunity by using BGAL1-resistant O-glycans or by producing a BGAL1 inhibitor. Polymorphic glycans on flagella are common to plant and animal pathogenic bacteria and represent an important determinant of host immunity to bacterial pathogens.