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A site-specific deprotonation followed by alkylations and acylations of sugar hemiacetals to the corresponding alkyl glycosides and acylated sugars in aqueous solutions is disclosed herein. Pyridoneimine as a new base is developed to mediate the deprotonation of readily available sugar hemiacetals and further reactions with alkylation and acylation agents.

The synthesis of a disaccharide macrocycle through 2,3-dideoxy glucopyranosyl monosaccharide is reported. 2,3-Dideoxy

Hyperphosphorylated guanosine nucleotide (p)ppGpp, synthesized by Rel proteins, regulates the stringent response pathway responsible for biofilm growth and persister cell formation in the stationary phase of mycobacteria. The discovery of vitamin C as a potent inhibitor of Rel protein activities raises the prospect of such a tetrone lactone to prevent biofilm growth and persister cell formation. The closely related isotetrone lactone derivatives are identified in the present study as potent inhibitors of the above processes in a mycobacterium. Isotetrone lactone derivatives are synthesized from appropriate α-ketocarboxylic acids, derived from the a-amino acids. Aldol condensation with formaldehyde, followed by the lactone formation, completes synthesis of isotetrone derivatives, possessing varied substituents atC-4 carbon, in good yields. A series of biochemical evaluations of biofilm growth and persister cell formation inM. smegmatisis conducted. Among the derivatives, isotetrone possessing phenyl substituent atC-4 carbon completely inhibit the biofilm formation at 400 μg mL-1concentration, 84 h of post-exposure, followed by a moderate inhibition by the isotetrone possessingp-hydroxyphenyl substituent. Whereas, the latter isotetrone inhibits the growth of cells at 400 μg mL-1f.c. when monitored for 2 weeks, under PBS starvation condition. Isotetrones also potentiate the inhibition of antibiotic tolerant regrowth of cells by ciprofloxacin antibiotic (0.75 μg mL-1) and thus act as bio-enhancers. The combination is shown to significantly arrest the emergence of ciprofloxacin-resistant genetic mutants. The observations suggest that isotetrones in combination with ciprofloxacin are therapeutically superior when administered together. Systematic molecular dynamics studies show that isotetrone derivative binds to Rel protein more efficiently than vitamin C and the binding is aided by hydrogen bonding, van der Waals and electrostatic interactions at a binding site possessing serine, threonine, lysine and arginine residues. The present study establishes that the identified isotetrone derivatives (i) act as inhibitors ofM. smegmatisbiofilm growth and (ii) arrest the re-emergence of recalcitrant persister cells when administered together with ciprofloxacin antibiotic. Results of this study establish that isotetrones as new chemical entities that interfere with stringent response pathways in a mycobacterium under stress and permit overcoming the multidrug-resistant persister cell emergence in the bacterium.

Unsaturated monosaccharides expand the scope of reactivities in a sugar, directly leading to the development of newer methodologies, molecular structures and functional entities. The unsaturation as a reactive moiety can either be within the molecule, namely, endocyclic, or as a pendant moiety around the molecule, namely, exocyclic. One carbon homologations aided by reactions at the unsaturated moiety expand the molecular structures in both endo- and exocyclic sugars and lead to structures that are largely hitherto unknown. Molecular shifts and rearrangements permit interchanging the reactivities from one carbon to the other in unsaturated sugars. Activations of exocyclic unsaturated sugars also find newer possibilities to reactions central to the sugar chemistry, namely, the glycosylations. The personal reflections result from a couple of decades of explorations that traverse through the unsaturated sugars from different vantage points. © 2021 The Chemical Society of Japan & Wiley-VCH GmbH

The allylic bromination of allyl glycosides is conducted using NBS/AIBN reagents in (EtO)2CO and PhCF3 solutions, without using CCl4 as a solvent. The activated mixed halo-allyl glycosides led to glycosylations, mediated by a triflate, in a latent-active manner, with the allyl glycosides acting as donors and acceptors. Systematic glycosylation studies are performed with different triflate promoters, non-glycosyl acceptors and various allyl glycosyl donors. One-pot allylic halogenations and subsequent glycosylations are developed in PhCF3 solutions. This newer glycosylation method is utilized to obtain xylo-pyranoside di- and trisaccharides.

N-Linked glycans are critical to the infection cycle of HIV, and most neutralizing antibodies target the high-mannose glycans found on the surface envelope glycoprotein-120 (gp120). Carbohydrate-binding proteins, particularly mannose-binding lectins, have also been shown to bind these glycans. Despite their therapeutic potency, their ability to cause lymphocyte proliferation limits their application. In this study, we report one such lectin named horcolin (Hordeum vulgare lectin), seen to lack mitogenicity owing to the divergence in the residues at its carbohydrate-binding sites, which makes it a promising candidate for exploration as an anti-HIV agent. Extensive isothermal titration calorimetry experiments reveal that the lectin was sensitive to the length and branching of mannooligosaccharides and thereby the total valency. Modeling and simulation studies demonstrate two distinct modes of binding, a monovalent binding to shorter saccharides and a bivalent mode for higher glycans, involving simultaneous interactions of multiple glycan arms with the primary carbohydrate-binding sites. This multivalent mode of binding was further strengthened by interactions of core mannosyl residues with a secondary conserved site on the protein, leading to an exponential increase in affinity. Finally, we confirmed the interaction of horcolin with recombinant gp120 and gp140 with high affinity and inhibition of HIV infection at nanomolar concentrations without mitogenicity.

Ultralight and ultrathin dielectric materials with high dielectric permittivity and power densities are required to meet the ever-increasing demands of microelectronic and energy storage devices. In the present study, we demonstrate the feasibility of achieving giant dielectric performance of light weight, highly porous three-dimensional architectures of insulating graphene oxide (GO) foams by saturating the pores with liquid containing mobile ions. Dielectric behavior of GO foam is investigated over a range of frequencies (1 kHz-10 kHz) by employing electrochemical impedance spectroscopy. The relative permittivity of pristine GO foam is shown to improve by five orders upon saturating the pores with different concentrations of aqueous NaCl solutions. Dielectric constants of foams saturated with aqueous NaCl solutions are measured to be of the order of 10(6) at high frequencies (1 kHze10 kHz) and are observed to enhance to 10(8) at lower frequencies down to 0.01 Hz. Various contributions to the measured capacitance are deciphered by modelling the impedance data to an equivalent circuit in order to evaluate the exact contribution from dipole orientation. The plausible reasons for the enhanced dielectric behavior are emphasized. (C) 2019 Elsevier Ltd. All rights reserved.

We describe a glycoconjugation strategy in which a sugar vinyl sulfoxide, acting as Michael donor, reacts efficiently with amine nucleophiles arising from the lysine side chain in peptides and proteins, at physiological pH and temperature. The method permits glycoconjugation of the lysine residues present in lysozyme with the sugar vinyl sulfoxide. The glycoconjugation of the protein abrogates the trypsin-mediated proteolysis at the lysine sites. The modified protein catalyzes digestion of the Gram-negative Escherichia coli cell wall and retains the same antimicrobial property as the native lysozyme.

Lipomannan and lipoarabinomannan are integral components of the mycobacterial cell wall. Earlier studies demonstrated that synthetic arabinan and arabinomannan glycolipids acted as inhibitors of mycobacterial growth, in addition to exhibiting inhibitory activities of mycobacterial biofilm. Herein, it is demonstrated that synthetic mannan glycolipids are better inhibitors of mycobacterial growth, whereas lipoarabinomannan has a higher inhibition efficiency to biofilm. Syntheses of mannan glycolipids with a graded number of mannan moieties and an arabinomannan glycolipid are conducted by chemical methods and subsequent mycobacterial growth and biofilm inhibition studies are conducted on Mycobacterium smegmatis. Growth inhibition of (73±3) % is observed with a mannose trisaccharide containing a glycolipid, whereas this glycolipid did not promote biofilm inhibition activity better than that of arabinomannan glycolipid. The antibiotic supplementation activities of glycolipids on growth and biofilm inhibitions are evaluated. Increases in growth and biofilm inhibitions are observed if the antibiotic is supplemented with glycolipids, which leads to a significant reduction of inhibition concentrations of the antibiotic.

A pyridoneimine-catalyzed oxa-Michael addition of protecting groups-free, native mono- and disaccharides with Michael acceptors in aq. solution is reported. Several mono- and disaccharides are reacted with acceptors, namely, methylvinyl ketone, acrylonitrile and tert-butyl acrylate in aq. solution, the addition catalyzed by n-pentylpyridone imine. The addition occurs site-selectively at the anomeric lactol and the remaining hydroxy functionalities are un-affected. The resulting keto-glycopyranoside products are explored in aldol, allylation and oxime product formation, occurring at either α-methyl moiety or at the keto-moiety, with appropriate synthons. In another direction, the keto-glycopyranoside is functionalized further with amino acids through reductive amination in aq. methanol solution. Formation of hemiacetal anion occurs in the presence of pyridoneimine in aq. Solution, enabling subsequent addition to occur with acceptors. Facile reductive amination of the resulting keto-glycoside provides an avenue for conjugations with amino acids in the present work.

Glycovesicles are ideal tools to delineate finer mechanisms of the interactions at the biological cell membranes. Multivalency forms the basis which, in turn, should surpass more than one mechanism in order to maintain multiple roles that the ligand-lectin interactions encounter. Ligand densities hold a prime control to attenuate the interactions. In the present study, mannose trisaccharide interacting with a cognate receptor, namely, Con A, is assessed at the vesicle surface. Synthetic (1→3)(1→6)-branched mannose trisaccharides tethered with a diacetylene monomer and glycovesicles of varying sugar densities were prepared. The polydiacetylene vesicles were prepared by maintaining uniform lipid concentrations. The interactions of the glycovesicles with the lectin were probed through dynamic light scattering and UV-Vis spectroscopy techniques. Binding efficacies were assessed by surface plasmon resonance. Aggregative and in-plane modes of interactions show ligand-density dependence at the vesicle surface. Vesicles with sparsely populated ligands engage lectin in an aggregative mode (trans-), leading to a cross-linked complex formation. Whereas glycovesicles embedded with dense ligands engage lectin interaction in an in-plane mode intramolecularly (cis-). Sub-nanomolar dissociation constants govern the intramolecular interaction occurring within the plane of the vesicle, and are more efficacious than the aggregative intermolecular interactions.

Carbohydrate-protein interactions define a multitude of cellular recognition events. We present herein synthetic glycovesicles as cell-surface mimics in order to switch the nature of lectin recognition. The covalent glycovesicles, constituted with diacetylene monomers of various ligand densities at their surfaces, are prepared through photo-polymerization. Vesicles with sparsely imbedded ligands engage in a lectin interaction leading to the formation of a dense, crosslinked multimeric complex. On the other hand, vesicles with many ligands, or completely covered with them, switch the lectin interaction to form a fully soluble monomeric complex, without crosslinking. Nanomolar dissociation constants govern these interactions, as assessed by a ligand-displacement assay. The study demonstrates the switching nature - between monomeric and multimeric - of the interaction as a function of ligand density in the vesicles; the results are directly relevant to understanding such a phenomenon occurring at cell surfaces.

Despite many theoretical schemes, the direct experimental observation of supramolecular control over band gap opening in single-walled carbon nanotubes (SWNTs) is still lacking. We report an experimental and theoretical demonstration of a metal-to-semiconductor transition with a precisely measured large band gap in SWNTs due to the wrapping of mannose-functionalized poly(propyl ether imine) dendrimer (DM) molecules. The semiconductor behaviour of the SWNT–DM complex is comprehensively established with a band gap value of ∼0.45 eV measured using scanning tunnelling spectroscopy (STS), ionic liquid top-gated field-effect transistor (FET) characteristics and Raman spectroscopy. Further, a validated molecular picture of the SWNT–DM complex obtained from fully atomistic molecular dynamics (MD) simulations was used to carry out ab initio density functional theory (DFT) and GW calculations of the electronic structure, evaluating an experimentally estimated band gap value. We attribute this large band gap opening in SWNTs to the complexation-induced asymmetric strain developed in the carbon–carbon bond length.

We have synthesized two amphiphilic cholesteryl dimers, bis(cholesterylsuccinamidoethyl) ether [(NHSCE)2] and bis(cholesterylphthalamidopropyl) ether [(NHPCE)2]. They form stable Langmuir monolayer films at air-water interface. (NHSCE)2 exhibits only liquid condensed phase, whereas (NHPCE)2 exhibits both liquid expanded and liquid condensed phases. The collapse phenomenon of a Langmuir monolayer has relevance to biological processes like control of surface tension in lung alveolar and so on. Our studies show that the collapse pressure (πc) of (NHPCE)2 Langmuir monolayer is invariant with the strain rate of compression and temperature. Interestingly, the πc of (NHSCE)2 Langmuir monolayer depends on the strain rate of compression and temperature. A power law relation is used for analysis of the strain rate dependence of πc. On varying the temperature, initially we find an increase in πc with increase in temperature, a behavior known as alpha (α) flow. On further increase in temperature, we find decrease in πc, a behavior known as kappa (κ) flow. The α- flow is very unusual and has not been reported in literature for dimers. An analogy is drawn between the observed α- flow in (NHSCE)2 dimer and the yield strength anomaly reported for alloys.

Chemical glycosylations critically depend on the activation of a glycosyl donor and the reaction of this activated donor intermediate with an acceptor alcohol. Whereas many strategies are developed for the activation of an anomeric aglycon substituent, the latent-active method of glycosylation is based specifically on tuning the reactivity of the aglycon substituent of a glycosyl donor. Several novel methods have emerged to install reactive aglycon moiety in a glycosyl donor and fine-tuning the reactivity of the moiety. Remote functionalizations of the aglycon plays a key role in the reactivity tuning. Activation of a remote functionality enables an otherwise latent aglycon to an active moiety, suitable as a glycosyl donor. The latent-active approach provides an advantage to avoid the conversion of the aglycon to another donor prior to a glycosylation, in addition to advancing the contemporary glycosylations with alternate insights. The review analyzes the methodologies that consolidate the latent-active approach to chemical glycosylations.

The protonation behaviour of polycationic compounds has direct relevance to their ability to condense and deliver nucleic acids. This report pertains to a study of the protonation behaviour of polycationic poly(propyl ether imine) (PETIM) dendritic gene delivery vectors that are constituted with tertiary amine core moiety and branch sites, n-propyl ether linkages, and primary amine peripheries. The ability of this series of dendrimers to condense nucleic acids and mediate endosomal escape was studied by unravelling the protonation behaviour of the dendrimers aided by pH metric titrations and 1H and 15N NMR spectroscopies. The results demonstrate protonation of the primary and tertiary amines of outermost-to-core shells occurring in a successive stepwise fashion, in contrast to other polycationic vectors. Theoretical calculations based on the Ising model rationalize further the finer details of protonation at each shell. The protonation pattern correlates with the endosomal buffering and nucleic acid condensation properties of this PETIM-based dendritic gene delivery vectors. The study establishes that the protonation behaviour is a critical and essential parameter to assess the gene condensation and delivery vector properties of a polycationic compound.

Poly(propyl ether imine) (PETIM) dendrimers of one to three generations are used as dendritic cores to identify the influence of varying connector types that connect the dendritic core with peripheral mesogens on the emerging liquid crystalline (LC) properties. The LC properties vary in these dendritic liquid crystals, even when the dendrimer generations and thus the number of peripheral mesogenic moieties remain identical. PETIM dendrimer generations one to three, ester and amide connectors varying with succinates, phthalates, and succinamides, are studied herein. Cholesteryl moieties are installed at the peripheries through the above connectors to induce mesogenic properties. These modified dendritic liquid crystals reveal a layered mesophase structure in most ester and amide connector-derivatives, whereas a third-generation phthalate ester dendrimer favors a rectangular columnar mesophase structure. A transition from layered to a rectangular columnar structure results by a mere change in the connector varying between a succinate or succinamide or phthalate, within one particular dendrimer generation and without altering the underlying dendrimer core or the number of mesogenic moieties. The study demonstrates that in dendritic liquid crystals with essentially identical chemical constitutions, a change in the connector type connecting the mesogen with the dendrimer core is sufficient to change the mesophase structures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Intriguing structural design and inherent nanoporosity of conjugated microporous polymers (CMP) with extended pi-conjugation have stimulated research interest in exploring their applications to solve challenging environmental and energy problems. However, only few attempts are made so far to identify the semiconducting properties of these CMP networks having direct relevance to energy conversion, electronic devices and photocatalysis. The present study identifies the semiconducting properties of a conjugated microporous polymer, namely, poly(1,3,5-triethynylbenzene) (PTEB) in detail using photoluminescence, UV-Visible absorption, Kelvin probe force microscopy, cyclic voltammetry, Mott-Schottky analysis and photoelectrochemical studies. Integration of heteroatoms such as nitrogen into the polymer network by post-thermal treatment is shown to enhance significantly the activities towards oxygen reduction reaction. A drastic improvement in the activity of PTEB observed on nitrogen incorporation into the carbon skeleton is attributed to an increase in the number of electrochemical active sites and increase in its pore size. The systematic evaluation of conducting properties of CMP materials promises future development of electronic, electrochemical and photoelectrochemical devices.

Seven-membered cyclic sugars are known as septanoses and septanosides. Whereas furanose and pyranose structures represent the known naturally available sugars, the seven-membered septanose sugars are confined to be only in the synthetic regime as yet. Synthetic explorations and structural studies contribute immensely to bring out many facets of septanoses in recent years. Innovative synthetic strategies drive advancements in septanose sugars. Cyclization of acyclic precursors, ring expansions, and rearrangements of existing scaffolds are major approaches to synthesize septanosides. Studies in the furanose and pyranose and solution phase provide finer details of hither-to unknown structural features, aiding further the desire to uncover newer possibilities of this unnatural sugar structures. Following a brief historical overview, this chapter presents a succinct compilation of the progress in synthetic and structural studies of this class of sugars.

Chemical glycosylations occupy a central importance to synthesize tailor-made oligo- and polysaccharides of functional importance. Generation of the oxocarbenium ion or the glycosyl cation is the method of choice in order to form the glycosidic bond interconnecting a glycosyl moiety with a glycosyl/aglycosyl moiety. A number of elegant methods have been devised that allow the glycosyl cation formation in a fairly stream-lined manner to a large extent. The latent-active method provides a powerful approach in the protecting group controlled glycosylations. In this context, allyl glycosides have been developed to meet the requirement of latent-active reactivities under appropriate glycosylation conditions. Radical halogenation provides a newer route of activation of allyl glycosides to an activated allylic glycoside. Such an allylic halide activation subjects the glycoside reactive under acid catalysis, leading to the conversion to a glycosyl cation and subsequent glycosylation with a number of acceptors. The complete anomeric selectivity favoring the 1,2-trans-anomeric glycosides points to the possibility of a preferred conformation of the glycosyl cation. This article discusses about advancements in the selectivity of glycosylations, followed by delineating the allylic halogenation of allyl glycoside as a glycosylation method and demonstrates synthesis of a repertoire of di- and trisaccharides, including xylosides, with varied protecting groups.

Development of membranes that provide high permeance and selectivity for separation of CO2 gas is important. We describe herein the development of polymer-dendrimer composite membranes, wherein the influence of dendrimer generations on the membrane CO2 permselectivities is investigated. Poly(vinyl alcohol) (PVA) – poly(ethylene glycol) (PEG), cross-linked with glutaraldehyde (GA) membranes, incorporated further with amine-rich poly(ether imine) (PETIM) dendrimer generations 1–3, are studied by molecular dynamics simulations and experimental methods. Simulations reveal molecular level details of the affinity of CO2 to the membrane among dendrimer generations. Systematic experimental studies by varying several parameters prove that the composite membrane containing a third generation dendrimer approaches the Robeson trade boundary curve very closely, with optimal CO2 permeance and CO2/N2 gas pair selectivity of 6.2 × 10−9 mol m−2 s−1 Pa−1 and 56, respectively, at a feed pressure of 2 × 105 Pa and 30 °C. The membranes possess long-term stability of ca. 200 h. A comparison with known facilitated membrane systems reveals that the third generation dendrimer-based composite membrane exhibits the most optimal CO2 permeance and CO2/N2 selectivity.

Iminodiacetic acids are versatile metal chelating ligands. We herein undertook a study of dendritic bis- and tetrakis-iminodiacetic acids functionalized at the peripheries of branched core moieties. The dendritic iminodiacetic acids are synthesized by O- and N-alkylations of chosen alcohol and amine reactive sites emanating from a branched core. In order to identify the reactivities of such dendritic iminodiacetic acids, chelation with arylboronates is conducted. An assessment of the hydrolysis under aq. basic condition shows that dendritic boronates hydrolyze to boronic acid significantly slower than monomeric boronates. Slower hydrolysis of dendritic boronates is taken advantage, in order to conduct competitive C-C bond-forming Suzuki-Miyaura cross-coupling reactions. Teraryl synthesis is performed using monomeric and dendritic boronates. The iterative, multiple aryl-aryl bond formation is conducted subsequently, so as to prepare tetraaryls, through consecutive reactions of chosen boronic acid, monomeric boronate, dendritic boronate and aryl bromide, in one-pot. The study shows that slower hydrolysis of dendritic boronate is valuable in order to conduct multiple consecutive aryl-aryl bond formation. (C) 2016 Elsevier B.V. All rights reserved.

Mycobacterium has evolved distinct cell wall and strategies such as biofilm formation, which helps it to survive in hostile conditions. We have reported previously that arabinofuranoside containing glycolipids exhibit inhibition activities against the above functions of the mycobacterial species M. smegmatis. In search for activities mediated by oligosaccharide glycolipids, we report herein the inhibitory activities of a linear and a branched pentasaccharides having arabinan and mannan moieties. In the presence of the pentasaccharide glycolipids, a significant reduction in mycobacterial growth is observed, concomitant with reductions in sliding motility and colonization through biofilm formation, at the optimal glycolipid concentrations of 50-100 μg mL(-1). Especially the biofilm coat is ruptured by ~80-85 % in the presence of glycolipids. Pentasaccharides alone without the lipidic chain show only a weak effect. The glycolipids are non-toxic, as evaluated through their effect on RBCs. Analysis of the mycolic acid profile of glycolipid treated biofilm shows that α- and epoxy mycolic acids are downregulated significantly, in comparison to glycolipid untreated biofilms. Lipidomics profile analysis through mass spectrometry further reveals profound downregulation of phosphatidylinositol mannosides, acylatedphosphoglycerols and mycolic acid family, namely, keto-, alpha- and methoxymycolic acids.

A new cyclic trisaccharide is synthesized by cycloglycosylation of a linear trisaccharide, modified with hydroxymethyl moiety at C4 of glucopyranose moiety. The cyclic trisaccharide possesses a rarely observed perfect trigonal symmetry in the P3 space group, in a narrow cone shape, and a brick-wall type arrangement of molecules in the solid state, and exhibits a significantly enhanced binding affinity to 1-aminoadamantane in aqueous solution.

A pair of first and second generation poly(alkyl ether imine) dendrimers is prepared, having covalently attached cholesteryl moieties at their peripheries. The pairs in each generation differ in the alkyl-linker which constitute the dendritic core moieties, even when the number of cholesteryl moieties remains uniform in each pair. The dendrimer pairs are two first and second generation poly(ethyl ether imine) and poly(propyl ether imine) dendrimers, modified with 4 and 8 cholesteryl esters at the peripheries in each pair, respectively. The dendrimer pairs exhibit differing thermotropic mesophase properties. Microscopic, thermal and X-ray diffraction studies reveal a lamellar mesophase for the first generation ethyl-, first and second generation propyl-linker dendrimers. Whereas, the second generation ethyl-linker dendrimer exhibits a layered structure with a superimposed in-plane modulation, the length of which corresponds to a rectangular column width. The role of the dendrimer core moieties with differing linkers in modifying the mesophase properties is studied. (C) 2016 Elsevier Ltd. All rights reserved.

Radical halogenation-mediated glycosylation using allyl glycosides as donors and as acceptors emerges to be an efficient and hither-to unknown glycosylation method, adhering to the concept of the latent-active methodology. Several di- and trisaccharides that possess the allyl moiety at their reducing end are prepared through this new glycosylation methodology.

This study describes synthesis of zero and first generation poly(alkyl aryl ether) dendrons onto a gallic acid core, tethered with three diacetylene moieties and their photopolymerization. Resulting polydiacetylenes are studied by (i) UV-vis, IR, Raman spectroscopies, and chromoisomerism by naked eye visualization; (ii) their stabilities by differential scanning calorimetry, thermogravimetric method, and (iii) structure, morphology, and emission behavior by scanning electron, transmission electron, atomic force microscopies, powder X-ray diffraction method, and fluorescence spectroscopy. The dendron-appended polydiacetylenes show robust nanoribbon morphologies and exhibit multicolor, reversible chromoisomerism at temperatures up to 300 degrees C. Reversibility of amide bond IR frequencies, as a function of temperature, shows the polymer stabilities, in addition to the results of thermal and powder X-ray diffraction studies. Temperature annealed polymers having red color phase exhibit emission maxima at 572 and 633 nm, that shift to higher wavelength upon heating and revert to the initial emission wavelengths on cooling.

The development of practical, atom-economical and stereocontrolled routes to modify monosaccharides occupy a central importance in synthetic carbohydrate chemistry. This review provides an account on carbon–carbon and carbon–heteroatom bond formation as a skeleton modification on monosaccharides, through [3, 3]-sigmatropic rearrangement reactions on unsaturated sugar synthons, the generality of the reaction conditions and synthetic utilization of the resulting functionalized sugar building blocks. Major emphasis is laid on thermal rearrangement reactions, namely, Claisen, Ireland–Claisen, aza–Claisen and Johnson–Claisen rearrangements on carbohydrate-derived allyl vinyl ethers, silyl ketene acetals, allylic trichloroacetamidates and allylic orthoesters, respectively. These reactions offer a very promising prospect and permit a straightforward approach to access a large variety of biologically important, densely functionalized and novel carbohydrate mimetics. Further, examples of bioactive complex natural products, secured in high yields and profound stereoselectivity through such thermal rearrangement reactions on monosaccharides are described herein.

Biofilm formation, involving attachment to an adherent surface, is a critical survival strategy of mycobacterial colonies in hostile environmental conditions. Here we report the synthesis of heptasaccharide glycolipids based on mannopyranoside units anchored on to a branched arabinofuranoside core. Two types of glycolipids2,3-branched and 2,5-branchedwere synthesized and evaluated for their efficacies in inhibiting biofilm growth by the non-pathogenic mycobacterium variant Mycobacterium smegmatis. Biofilm formation was inhibited at a minimum biofilm growth inhibition concentration (MBIC) of 100gmL(-1) in the case of the 2,5-branched heptasaccharide glycolipid. Further, we were able to ascertain that a combination of the drug isoniazid with the branched heptasaccharide glycolipid (50gmL(-1)) potentiates the drug, making it three times more effective, with an improved MBIC of 30gmL(-1). These studies establish that synthetic glycolipids not only act as inhibitors of biofilm growth, but also provide a synergistic effect when combined with significantly lowered concentrations of isoniazid to disrupt the biofilm structures of the mycobacteria.

Bacteria elicit an adaptive response against hostile conditions such as starvation and other kinds of stresses. Their ability to survive such conditions depends, in part, on stringent response pathways. (p)ppGpp, considered to be the master regulator of the stringent response, is a novel target for inhibiting the survival of bacteria. In mycobacteria, the (p)ppGpp synthetase activity of bifunctional Rel is critical for stress response and persistence inside a host. Our aim was to design an inhibitor of (p)ppGpp synthesis, monitor its efficiency using enzyme kinetics, and assess its phenotypic effects in mycobacteria. As such, new sets of inhibitors targeting (p)ppGpp synthesis were synthesized and characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. We observed significant inhibition of (p)ppGpp synthesis by Rel Msm in the presence of designed inhibitors in a dose-dependent manner, which we further confirmed by monitoring the enzyme kinetics. The Rel enzyme inhibitor binding kinetics were investigated by isothermal titration calorimetry. Subsequently, the effects of the compounds on long-term persistence, biofilm formation, and biofilm disruption were assayed in Mycobacterium smegmatis , where inhibition in each case was observed. In vivo , (p)ppGpp levels were found to be downregulated in M. smegmatis treated with the synthetic inhibitors. The compounds reported here also inhibited biofilm formation by the pathogen Mycobacterium tuberculosis . The compounds were tested for toxicity by using an MTT assay with H460 cells and a hemolysis assay with human red blood cells, for which they were found to be nontoxic. The permeability of compounds across the cell membrane of human lung epithelial cells was also confirmed by mass spectrometry.

The derivatization of a polydiacetylene (PDA) polymer with free hydroxyl groups containing sugars leads to amphiphilicity of the polymer and the emergence of thermotropic liquid crystalline behavior, in addition to the thermochromatic properties. The diacetylene monomers, incorporated with mono- and disaccharides, exhibit mono- and/or enantiotropic phase behavior in a wide temperature range. Structural characterization and modeling studies reveal a lamellar arrangement and interdigitization of the molecules in the mesophase. The importance of the amphiphilicity as a source to induce mesomorphic behavior in PDA polymers is emphasized.

Conformational analysis of unnatural seven-membered sugars, namely, septanoses and septanosides are discussed herein. The conformational properties of these sugars in the solid state, solution phase and computational methods are presented. The analyses reveal that conformations of septanosides are diverse and largely unpredictable, as compared furanosides and pyranosides.

Single crystal X-ray structural analysis of a septanoside, namely, n-pentyl-2-chloro-2-deoxy sept-3-uloside (1) provides many finer details of the molecular structure, in addition to its preferred twist-chair conformation, namely, (TC3,4)-T-5,6 conformation. Structural analysis reveals a dense network of O-H...O, C-H...O and van der Waals interactions that stabilize interdigitized, planar bi-layer structure of the crystal lattice. (C) 2014 Elsevier Ltd. All rights reserved.

We demonstrate that etched fiber Bragg gratings (eFBGs) coated with single walled carbon nanotubes (SWNTs) and graphene oxide (GO) are highly sensitive and accurate biochemical sensors. Here, for detecting protein concanavalin A (Con A), mannose-functionalized poly(propyl ether imine) (PETIM) dendrimers (DMs) have been attached to the SWNTs (or GO) coated on the surface modified eFBG. The dendrimers act as multivalent ligands, having specificity to detect lectin Con A. The specificity of the sensor is shown by a much weaker response (factor of similar to 2500 for the SWNT and similar to 2000 for the GO coated eFBG) to detect non specific lectin peanut agglutinin. DM molecules functionalized GO coated eFBG sensors showed excellent specificity to Con A even in the presence of excess amount of an interfering protein bovine serum albumin. The shift in the Bragg wavelength (Delta lambda(B)) with respect to the lambda(B) values of SWNT (or GO)-DM coated eFBG for various concentrations of lectin follows Langmuir type adsorption isotherm, giving an affinity constant of similar to 4 x 10(7) M-1 for SWNTs coated eFBG and similar to 3 x 10(8) M-1 for the GO coated eFBG. (C) 2014 Elsevier B.V. All rights reserved.

This Review article discusses dendritic organometallic catalysis, originating from catalytic moieties present at the peripheries of a dendrimer. The presence of multiple catalytic moieties at the dendrimer peripheries leads to a positive effect in majority of the homogeneous and heterogeneous catalysis, although a negative or a marginal improvement in the catalytic effect with respect to the corresponding monomeric catalyst were also encountered. A number of recent examples that attempt to rationalize the origin of the dendrimer effect in catalysis are discussed. Further a tabular survey is provided by categorizing the dendritic catalysts and their influence on catalysis. Recent studies on the multivalent dendritic catalysts, wherein varied number of catalytic moieties is installed within a given generation, are utilized to emphasize the role of clustering catalytic moieties at the peripheries of the dendrimers in influencing the catalysis. (C) 2013 Elsevier B. V. All rights reserved.

Photocatalytic disassembly of tertiary amine-based poly(propyl ether imine) dendrimers, in the presence of either 9,10-anthraquinone or riboflavin tetraacetate and O2(g), leads to di- and tripropanolamine monomers. An application is shown by solubilisation of a water-insoluble dye, Sudan I, in aq. dendrimer solution (‘catch’), followed by its ‘release’ upon disassembly of the dendrimer.

2,3-Unsaturated 3-arylsulfinyl pyranosides undergo nucleophilic additions at C-2, with facial selectivities depending on the nucleophile and the substituent on sulfinyl sulfur. The reactions of such sugar vinyl sulfoxides lead to the addition of nucleophile preferring an axial orientation at C-2, with concomitant formation of an allylic bond at C-3 to C-4. This trend in the addition pattern is observed for primary amine, carbon and sulfur nucleophiles, whereas secondary amines prefer an equatorial addition at C-2. The effect of p-tolylthio- versus (p-isopropylphenyl)thio vinyl sulfoxide is that the equatorial nucleophilic addition is preferred even more with the latter vinyl sulfoxide.

Cyclic oligosaccharides, such as naturally-occurring cyclomaltodextrins or cyclodextrins, cycloisomaltooligosaccharides or cyclodextrans, cycloinulooligosaccharides, have attracted a repertoire of interest cutting across various fields, as a result of their immense industrial importance arising from their molecular and supramolecular properties. As opposed to the production of cyclic oligosaccharides biosynthetically in an exquisite manner, their chemical synthesis remains a challenge. Whereas macrocyclization and cyclooligomerization have provided necessary tools to approach their synthesis, modifications in their monosaccharide moieties add further to protract the synthesis overall. Yet significant progress has been made in chemical and enzymatic synthesis during the last three decades, particularly on the synthesis of tailor-made or made-to-order cyclic oligosaccharides. Manifold values of cyclic oligosaccharide macrocycles are imminent, resulting from their reduced hydrolytic rates to hydrophobic cavities, backbone modifications assume even greater importance. Such backbone modified cyclic oligosaccharides have been demonstrated to alter functions in several instances. Focusing on synthesis of cyclic oligosaccharides alone, there is a continuous evolution of methods and strategies that facilitate their synthesis. Both chemical and enzymatic routes are fore-runners in the advancements towards fully synthetic cyclic oligosaccharides. This review compiles logical advancements in cyclic oligosaccharide synthesis, particularly over the last decade, with emphasis on modifications of glycosidic bonds or individual sugar moieties.

A Pummerer rearrangement of 2,3-dideoxy-3-alkyl/arylsulfinyl-arabino-hexopyranosides is reported. Treatment of sulfinyl-arabino-hexopyranoside derivatives, obtained through oxidation of the corresponding thio-derivatives, with trifluoroacetic anhydride (TFAA)/pyridine led to a facile formation of 2,3-dideoxy-3-alkyl/arylthio-hex-2-enopyranosides. Upon conversion of sugar vinyl sulfides to vinyl sulfoxides, conjugate addition reactions were conducted with alkoxides, to afford 3-deoxy-3-alkyl/arylsulfinyl pyranosides, in the manno-configuration exclusively. Whereas the conjugate addition reaction did not proceed with ether protecting groups, ester protecting groups and free hydroxyl groups in the sugar vinyl sulfoxide permitted the reaction. (C) 2012 Elsevier Ltd. All rights reserved.

Dendrimers are ideal platforms to study multivalent effects due to the presence of uniform end groups at their peripheries. This report concerns with a study of multivalent dendritic catalysts, both within and across dendrimer generations, and their effects to mediate C-C bond forming reactions on multivalent substrates that have two and three acrylate reactive sites. As many as fourteen multivalent dendritic catalysts were prepared using 0-3 generations of poly(propyl ether imine) dendrimers, incorporated with Pd(II) catalytic sites, both within and across the dendrimer generations. C-C Bond forming reactions of these substrates with iodobenzene, mediated by uniform concentration of the metal across all catalysts, showed formation of partially and fully functionalized cinnamates in varying ratios, depending on the extent of clustering of catalytic moieties at the peripheries of dendrimers within a dendrimer generation. In a given generation, higher clustering of catalytic moieties greatly assisted multiple C-C bond formations than presenting the same in lesser number. The studies demonstrate true benefits of clustering catalytic moieties within a dendrimer generation and the beneficial effects applicable to catalysis of substrates presenting more than one reactive center. (C) 2011 Elsevier B.V. All rights reserved.