Browsing by Author "Sah, Ajay Kumar"

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Alanyl glycoconjugate: a selective receptor for free and protein-bound tryptophan
(ACS, 2013) Sah, Ajay Kumar
The free and protein-bound tryptophan (Trp) sensing ability of an alanyl-(4,6-O-ethylidene-β-D-glucopyranosylamine) derived chiral receptor (L-N2O2) has been explored using UV-vis absorption, fluorescence and mass spectroscopy. L-N2O2 decreases the intrinsic emission intensity of Trp at 360 nm via a static quenching mechanism, revealing the interactions between the two.
Amine mediated proton transfer reaction and C–Cl bond activation of solventchloroform by a trinuclear copper(ii) complex of a glucopyranosylamine derived ligand
(RSC, 2006) Sah, Ajay Kumar
An amine mediated C–Cl bond activation process of the solvent chloroform has been explored by a coordinatively labile trinuclear Cu(II) complex, [Cu3(L1)2(MeOH)(H2O)] (1), derived from N-(3-tert-butyl-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine (H3L1). The effect of activation is extremely high with methylamine, resulting in the formation of [Cu(MeNH2)5]Cl2 (2) and [Cu(L2)2] (3; HL2 = 2-tert-butyl-6-[(methylimino)methyl]phenol), however, under identical conditions it is moderate with ethylamine resulting in the isolation of crystals of the intermediate amine bound trinuclear copper(II) complex, [Cu3(L1)2(EtNH2)2(MeOH)2] (5), which was further converted into the mononuclear complex, [Cu(HL1)(EtNH2)] (6), in a novel crystal-to-crystal transformation. The successive isolation of the ethylamine-bound tri- and mononuclear complexes, 5 and 6, supported the occurrence of proton transfer reactions, which might be a key step in C–Cl bond activation. The primary and secondary amines, 2-aminomethylpyridine, N,N′-dimethylethylenediamine, and 1,4,7-triazacyclononane, also having chelating features further enhance the rate of activation. No activation has been noted in the case of triethylamine and N,N,N′,N′-tetramethylethylenediamine. Formation of a carbene-trapped compound, 2,6-xylyl isocyanide, was confirmed in the reaction of complex 1 with 1,4,7-triazacyclononane and 2,6-xylidine in CHCl3, suggesting that the C–Cl bond cleavage led to the generation of dichlorocarbene. In addition, the mononuclear complex 6 has been transformed into a homotrinuclear complex [Cu3(L1)2(MeOH)2] by treatment with Cu(II) ions in MeOH/CHCl3, suggesting the possibility that the former could be regarded as a suitable metalloligand for heterotrimetallic complex synthesis.
Bis-(μ-saccharide-C-2-oxo) dinuclear Cu(ii) complexes of 4,6-O-butylidene/ethylidene-N-(α-hydroxynaphthylidene/o-hydroxybenzylidene/5-bromo-o-hydroxybenzylidene)-β-d-glucopyranosylamine: structural aspects and data correlations
(RSC, 2003) Sah, Ajay Kumar
A total of five dinuclear copper complexes were synthesized using 4,6-O-butylidene/ethylidene-N-(α-hydroxynaphthylidene/o-hydroxybenzylidene/5-bromo-o-hydroxybenzylidene)-β-D-glucopyranosylamine. Upon recrystallisation from different solvents, viz., dmso/MeOH/pyridine, seven different dinuclear copper complexes were generated, wherein the geometry around one or both of the copper centers changes from square planar to square pyramidal due to the binding of solvent molecule as the fifth ligand. The ligands and their complexes were characterized by elemental analysis, 1H and 13C NMR, FT-IR, FABMS, UV-Vis, optical rotation, CD and magnetic susceptibility measurements. The 3D structures of all the seven complexes were established by single crystal XRD. All the complexes are neutral and dinuclear with the metal to the glycosylamine ratio being 1 ∶ 1. Each glycosylamine acts as tridentate with di-negative charge and bridges between the two copper centers through the C-2-oxo group of the saccharide part and further the coupling between the copper centers is antiferromagnetic. At least four different types of Cu2O22+ core structures were identified depending upon the presence or absence of a fifth ligand at the Cu(II) center. The β-4C1-pyranose form of the glycosylamine is retained even in complexes. The dinuclear complex is stabilized through intra-complex hydrogen bond interaction. The inter-molecular C–H⋯O interactions are manifested in the formation of a helical structure where the water molecules occupy the cavity. The structural diversity observed in the complexes and several data correlations are discussed in detail.
C–H⋯Cl− hydrogen bonds in solution and in the solid-state: HgCl2 complexes with cyclen-based cryptands
(RSC, 2017) Sah, Ajay Kumar
Structural evidence is reported for C–H⋯Cl− hydrogen bonds in solution and in the solid state of HgCl2 complexes with cyclen-based cryptands. These cyclen-based cryptands (1) and (2) are bridged by di- and triethylene glycol units, respectively, between two aromatic rings. The X-ray structure indicates that the 2/HgCl2 complex contains an acetonitrile molecule in the cavity.
Crystal structure of 4,6-O-ethylidene-N-(2-hydroxybenzylidene)-β-d-glucopyranosylamine
(Elsiever, 2002-01) Sah, Ajay Kumar
4,6-O-Ethylidene-N-(2-hydroxybenzylidene)-β-d-glucopyranosylamine was synthesized and characterized using analytical, spectral and single-crystal X-ray diffraction methods. The anomeric nature of the saccharide moiety was proposed based on 1H NMR studies and was confirmed by the crystal structure. The lattice structure of this compound was compared with that of its analogues
Crystal structure of N-(2-hydroxynapthylidene)-l-isoleucinyl-4,6-o-ethylidene-β-d-glucopyranosylamine and an insight from experimental and theoretical calculations
(Wiley, 2022-12) Sah, Ajay Kumar
Dimethyl sulfoxide solution of N-(2-hydroxynapthylidene)-L-isoleucinyl-4,6-O-ethylidene-β-D-glucopyranosylamine (L1) affords single crystals of its ketoenamine configuration. The noncovalent intermolecular interactions present in the molecules have been explored by Hirshfeld surface analysis and 2D fingerprint plots generated using crystallographic data. The structural parameters of L1 in both the tautomeric forms (ketoenamine and phenolimine) at ground states have been optimized using Hartree–Fock and density functional theory calculations in gaseous and solution phases. The Fourier transform infrared, nuclear magnetic resonance, and UV–visible spectra of this molecule have been compared with the theoretically calculated data of both the tautomeric forms. Additionally, Mulliken population analysis, molecular electrostatic potential, and natural bond order analysis provide a better understanding of charge distribution, presence of electrophilic/nucleophilic sites, and intramolecular charge transfer, respectively, in the molecule.
Crystal-to-crystal transformation from tri- to mononuclear Cu(ii) complex with a sugar-derived ligandvia proton transfer reaction and rearrangement of hydrogen bonding networks†
(ACS, 2005) Sah, Ajay Kumar
Treatment of a glycosylamine derived Cu(II) complex with ethylamine resulted in crystal-to-crystal transformation from trinuclear complex [Cu3(L1)2(EtNH2)2(MeOH)2]x2MeOHxCHCl3 (2x2MeOHxCHCl3) to a dimeric structure of mononuclear complex [Cu(HL1)(EtNH2)] (3) through proton transfer reaction and rearrangement of hydrogen bonding networks.
Design, synthesis and evaluation of carbamoylmethylphosphine sulfide (CMPS)-based chelates for separation of lanthanides and actinides
(Elsiever, 2007-11) Sah, Ajay Kumar
C3-symmetric triphenoxymethane platforms were substituted with carbamoylmethylphosphine sulfide arms and these tris-CMPS compounds were evaluated as extractants for f-element metal ions from 1 M nitric acid solution. Their properties were compared to the carbamoylmethylphosphine oxide derivatives on the same triphenoxymethane platform (tris-CMPO). The terbium complex of tris-CMPS was crystallized and examined via X-ray structural analysis to provide valuable insight into the binding properties of the soft tripodal chelate.
Dinuclear Copper Complexes of N-(2-Hydroxybenzylidene or 5-Bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine: Coordination Variation and Structural Diversity
(CSJ, 2002) Sah, Ajay Kumar
Dinuclear Cu(II) complexes of N-(2-hydroxybenzylidene or 5-bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine with coordination variation and molecular and lattice structural variations are explored.
Double-armed and tetra-armed cyclen-based cryptands
(Taylor & Francis, 2017) Sah, Ajay Kumar
Double-armed and tetra-armed cyclen-based cryptands (1a–1d and 2) that bridge two aromatic rings by diethyleneoxy and triethyleneoxy units were prepared. The CSI-MS of 1:1 mixtures ([Ag+]/[ligand]) indicated that these new cryptands form 1:1 complexes with Ag+. The log K values for the interaction between Ag+ and 2 was greater than those of 1a–1d, double-armed cyclens (3a–3c and 4), and tetra-armed cyclen (5). The Ag+-ion-induced 1H NMR spectral changes suggest that the Ag+–π interactions of the Ag+ complexes with the cryptands (1a–1d and 2) are stronger than those in Ag+/double-armed and tetra-armed cyclens. To visualise the Ag+−π interactions, the isosurfaces of the LUMO and HOMOs of the Ag+ complexes were calculated at the B3LYP/3–21G(*) theoretical level. The LUMO of the Ag+ ion is distorted by interaction with the HOMOs of the aromatic side arms. The calculations reveal Ag+−π interactions between the Ag+ ion and the aromatic side arms, and these are shown graphically.
First Crystallographic Investigation of Complexes of cis-VO2+, cis-MoO22+, and trans-UO22+ Species with Schiff-Base Molecules Derived from 4,6-O-Ethylidene-β-D-glucopyranosylamine
(EJIC, 2001-09) Sah, Ajay Kumar
The interaction of Schiff-base ligands derived from 4,6-O-ethylidene-β-D-glucopyranosylamine with cis-VO2+, cis-MoO22+, and trans-UO22+ species have been studied by isolating and characterizing the corresponding products. The structures of one complex of each type of species have been established by single-crystal X-ray diffraction analysis. In all the complexes, the saccharide moiety adopts a chair conformation and has a β-anomeric form. A gradual increase in coordination number (5, 6, and 7) and a gradual variation in the geometry (distorted trigonal-bipyramidal, distorted octahedral, and pentagonal-bipyramidal) are observed on going from the complexes of cis-VO2+ (mononuclear) to cis-MoO22+ (mononuclear) to trans-UO22+ (dinuclear). A variation in the binding mode of the ligand towards these dioxometal species is also observed. Intermolecular interactions of the type O−H···O, C−H···O, and N−H···O present in the lattices of these complexes lead to the formation of interesting structures.
Glucoconjugated dinuclear copper(ii) complex: an efficient catalyst for stereoselective synthesis of trisubstituted propargylamines via solvent-free A3 coupling reaction
(Wiley, 2024-08) Sah, Ajay Kumar
Development of catalytic systems using nontoxic natural precursors is the need of the era, and along this line, we have synthesized a new D-glucose derived ligand (4,6-O-ethylidene-N-(2-hydroxy-4-(octyloxy)benzylidene)-β-D-glucopyranosylamine) and its dinuclear copper(II) complex. The molecular structure of the complex has been established by single-crystal X-ray diffraction studies and detailed noncovalent intermolecular interactions present in it have been explored by Hirshfeld surface analysis. Further, the complex has been used as a catalyst in the enantioselective (87–99 % ee) synthesis of propargylamines in good to excellent yield (82–95 %) via aldehyde-amines-alkynes (A3) coupling reaction under solvent-free condition. The formation of aminal intermediate during the reaction has been confirmed by 1H-NMR and single-crystal X-ray diffraction studies. The catalytic system is reusable without any appreciable loss in the enantioselectivity or product yield.
Metal complexes of 4,6-O-ethylidene-β-d-glucopyranosylamine derivatives and their application in organic synthesis
(Elsiever, 2019-11-01) Sah, Ajay Kumar
Glycosylamine derivatives of 4,6-O-ethylidene-d-glucose have been used for complexing the alkali, alkaline earth and transition metal ions. Three different series of ligands have been reported where N-(o-carboxyphenyl)-4,6-O-ethylidene-β-d-glucopyranosylamine has been used for complexing the diamagnetic (Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Zn2+, Cd2+, Hg2+) metal ions. N-(2-Hydroxybenzoyl)-L-alanyl-4,6-O-ethylidene-β-d-glucopyranosylamine selectively interacts with molecular cupric acetate and the adduct acts as a catalyst in selective oxidation of primary and secondary alcohols into their corresponding carbonyl compounds. Salicylidene derivatives of 4,6-O-ethylidene-β-d-glucopyranosylamine have been used in complexing Ni2+, Cu2+, Zn2+, VO2+, MoO22+ and UO22+ metal ions, where Cu(II) and Mo(VI) complexes have been further used in the organic synthesis. Dinuclear copper complex exhibited catecholase like activity and also catalyzed the oxidation of primary and secondary alcohols selectively into their corresponding carbonyl compounds. Trinuclear copper complex has been reported to activate the C–Cl bond of solvent chloroform in the presence of mild organic bases below room temperature. Mo(VI) complex has been used as a catalyst for epoxidation, organic sulfide oxidation and synthesis of bis(indolyl)methanes.
Metal-free synthesis of aminomethylated imidazoheterocycles: dual role of tert-butyl hydroperoxide as both an oxidant and a methylene source
(RSC, 2018) Kumar, Anil; Sah, Ajay Kumar
A novel and efficient aminomethylation approach has been developed for the regioselective functionalization of imidazoheterocycles under metal-free conditions. A wide range of imidazoheterocycles and 2/4-aminoazaheterocycles successfully provided corresponding aminomethylated imidazoheterocycles in moderate to excellent (33–80%) yields. The isotopic labelling study suggested that TBHP played a dual role as both an oxidant and a methylene source in this transformation. The developed protocol follows a radical pathway which is supported by radical trapping experiments.
Mo(VI) complex catalysed synthesis of sulfones and their modification for anti-HIV activitie
(Elsiever, 2020-04-05) Sah, Ajay Kumar; Murugesan, Sankaranarayanan
An efficient method for the synthesis of sulfones has been developed using sugar derived cis-dioxo molybdenum(VI) complex as catalyst and urea hydrogen peroxide as oxygen source. Present method is highly specific for sulfide oxidation irrespective of presence of alkene and aldehyde groups in the same molecule. Synthesis of fifteen sulfones have been reported with 82–98% isolated yields and the catalyst has been reused five times without any loss in its activity. 2-(Phenylsulfonyl)aniline has been condensed with eight different aromatic aldehydes and the products are being explored for HIV-1 reverse transcriptase inhibition activities.
N-Glycoconjugates: Selective colorimetric chemosensors for aspartic acid and cysteine
(Elsiever, 2021-10-05) Sah, Ajay Kumar
Selective recognition of naturally occurring amino acids have been explored using five glycopeptide-based receptors with the help of UV-visible and 1H NMR spectroscopy, while structures of two glycopeptides have been established via single crystal X-ray diffraction studies. The receptors containing alanine, valine, isoleucine and methionine moieties interact selectively with aspartic acid, while phenylalanine derivative with cysteine.
N-Glycosylamines of 4,6-O-ethylidene-α-D-glucopyranose: synthesis, characterisation and structure of CO2H, Cl and F ortho-substituted phenyl derivatives and metal ion complexes of the CO2H derivative
(RSC, 2000) Sah, Ajay Kumar
A saccharide based ligand suitable for metal binding (HLCOOH) has been synthesized using 4,6-O-ethylidene-α-D-glucopyranose (4,6-O-EGP) and anthranilic acid. A few analogous glycosylamines with chloro and fluoro ortho substitutions have also been synthesized and characterised. Complexes of HLCOOH with Na+, K+, Mg2+, Ca2+, Ba2+, Cd2+ and Hg2+ have been isolated and characterised fully. The crystal structures of 4,6-O-EGP, the chloro analogue of HLCOOH and the K+ complex of LCOOH are established. The anomeric nature, orientation of the binding core and the co-ordination aspects of K+ have been derived from these structures.
Quinoline Glycoconjugates as Potentially Anticancer and Anti-Inflammatory Agents: An Investigation Involving Synthesis, Biological Screening, and Dockin
(ECSP, 2020-08-20) Dubey, Uma S.; Sah, Ajay Kumar; Shukla, Paritosh
The present work is a preliminary report of synthesis of a series of targeted 4,6-O-ethylidene-β-D-glucopyranosylamine glycoconjugate quinoline 4-carboxylic acid derivatives followed by a quick evaluation of their anti-inflammatory and anticancer activities. Compounds C5 and C8 exhibited highest anti-inflammatory activity against human COX-2 enzyme. Anticancer studies were also performed in vitro which revealed C8 as a promising candidate against HeLa, human cervical cancer cell lines. The anti-inflammatory and anticancer activity was further confirmed by molecular docking studies for all the synthesized molecules. That all the compounds showed potency, seems to validate our initial hypothesis concerning a positive correlation between anticancer and anti-inflammatory activity for the designed quinoline glycoconjugates.
Saccharide derived dinuclear Cu(II) complex: An efficient catalyst for oxidation of catechol and benzylic alcohols
(Elsiever, 2012-01) Sah, Ajay Kumar; Kumar, Anil
Catalytical aspect of 4,6-O-ethylidene-β-D-glucopyranosylamine derived dinuclear Cu(II) complex has been explored. The complex exhibits good catecholase like activity and oxidizes model substrate 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-quinone. The complex also acts as selective catalyst to oxidize the primary and secondary alcohols to corresponding carbonyl compounds in excellent yield (65–82%) under mild conditions.
Selective oxidation of organic sulfides to sulfoxides using sugar derived cis-dioxo molybdenum(vi) complexes: kinetic and mechanistic studies
(RSC, 2016) Sah, Ajay Kumar
Six Mo(VI) complexes of 4,6-O-ethylidene-β-D-glucopyranosylamine derived ligands have been used for the selective oxidation of five organic sulfides to corresponding sulfoxides. The structure of a new sulfide [(((2-(phenylthio)phenyl)imino)methyl)naphthalen-2-ol] (S5) and its corresponding sulfoxide (SO5) has been established using single crystal X-ray diffraction studies along with other routine analytical techniques. The yields of sulfoxides were calculated using HPLC and one of the catalysts was recycled five times without any appreciable loss in its activity. Kinetic studies on sulfoxide formation was performed on compound S5 using UV-visible spectroscopy, which suggested overall first order kinetics. A plausible mechanism for sulfide oxidation has been proposed based on our findings and previous literature reports.