Search results
Found 5065 matches for
Novel cyclic sugar imines: carbohydrate mimics and easily elaborated scaffolds for aza-sugars.
[reaction: see text] Representative simple or polyhydroxylated, pyrrolidine (e.g, DRAM) or piperidine (e.g., DNJ) imines not only are potential carbohydrate-processing enzyme inhibitors that may be formed as regioisomeric variants but also are scaffolds that may be rapidly elaborated to diversely functionalized aza-sugars through highly diastereoselective organometallic additions.
Tetrazoles of manno- and rhamno-furanoses
The synthesis of tetrazoles derived from D-mannofuranose and both enantiomers of rhamnofuranose provides the first examples of tetrazole analogues of carbohydrates in the furanose form. The D-furanotetrazoles are potential mannosidase inhibitors whereas the L-rhamnotetrazole may interfere with the biosynthesis of cell walls of mycobacteria and provide a strategy for the treatment of tuberculosis and leprosy. © 1995.
Tetrazoles of manno- and rhamno-pyranoses: inhibition of glycosidases by tetrazoles and other mannose mimics
The synthesis of tetrazoles derived from D-mannopyranose and D-rhamnopyranose from L-gulonolactone is described. These and other materials are assessed as inhibitors of human liver glycosidases and delineate some structural features required for α- and β-mannosidase and α-fucosidase inhibition. © 1995.
Photoinduced, family-specific, site-selective cleavage of TIM-barrel proteins.
Nonenzymatic, chemical methods for the controlled cleavage of proteins at predictable sites in a site-specific manner are rare and of strong potential utility in clean, post-translational manipulation of protein structure for use in, for example, proteomics, sequencing, and tagged-protein production. Unprecedented photochemical, site-selective cleavage of a His-Trp (HW) motif in the GH1 family TIM-barrel proteins is observed upon exposure to 240-308 nm light to cleanly release N-terminal primary amide and C-terminal indolylenamide fragments. We also show that this photocleaveable motif can be transferred to fusion proteins for use in photoresponsive affinty purification. The presence of this motif in proteins found only in organisms that are not typically exposed to light raises the possibility of direct biological relevance for this new type of protein reaction.
A tuneable method for N-debenzylation of benzylamino alcohols.
[reactions: see text] N-Iodosuccinimide provides a mild, convenient, and tuneable reagent for the selective mono- or didebenzylation in representative, multifunctionalized carbohydrate and amino acid derived N-dibenzylamines with neighboring O-functionality.
Sugars and proteins: New strategies in synthetic biology
The development of novel methodology for bond-forming processes that are compatible with biomolecules allows the assembly, alteration, or modification of proteins. Such synthetic proteins allow precise insight and investigation of function in a manner that has the potential for almost unlimited diversity. © 2009 IUPAC.
Evaluation of the non-toxic mutant of the diphtheria toxin K51E/E148K as carrier protein for meningococcal vaccines.
Diphtheria toxin mutant CRM197 is a common carrier protein for glycoconjugate vaccines, which has been proven an effective protein vector for, among others, meningococcal carbohydrates. The wide-range use of this protein in massive vaccine production requires constant increase of production yields and adaptability to an ever-growing market. Here we compare CRM197 with the alternative diphtheria non-toxic variant DT-K51E/E148K, an inactive mutant that can be produced in the periplasm of Escherichia coli. Biophysical characterization of DT-K51E/E148K suggested high similarity with CRM197, with main differences in their alpha-helical content, and a suitable purity for conjugation and vaccine preparation. Meningococcal serogroup A (MenA) glycoconjugates were synthesized using CRM197 and DT-K51E/E148K as carrier proteins, obtaining the same conjugation yields and comparable biophysical profiles. Mice were then immunized with these CRM197 and DT-K51E/E148K conjugates, and essentially identical immunogenic and protective effects were observed. Overall, our data indicate that DT-K51E/E148K is a readily produced protein that now allows the added flexibility of E. coli production in vaccine development and that can be effectively used as protein carrier for a meningococcal conjugate vaccine.
Genetic Incorporation of Olefin Cross-Metathesis Reaction Tags for Protein Modification.
Olefin cross-metathesis (CM) is a viable reaction for the modification of alkene-containing proteins. Although allyl sulfide or selenide side-chain motifs in proteins can critically enhance the rate of CM reactions, no efficient method for their site-selective genetic incorporation into proteins has been reported to date. Here, through the systematic evaluation of olefin-bearing unnatural amino acids for their metabolic incorporation, we have discovered S-allylhomocysteine (Ahc) as a genetically encodable Met analogue that is not only processed by translational cellular machinery but also a privileged CM substrate residue in proteins. In this way, Ahc was used for efficient Met codon reassignment in a Met-auxotrophic strain of E. coli (B834 (DE3)) as well as metabolic labeling of protein in human cells and was reactive toward CM in several representative proteins. This expands the use of CM in the toolkit for "tag-and-modify" functionalization of proteins.
Carbohydrate hydration: heavy water complexes of α and β anomers of glucose, galactose, fucose and xylose.
The singly and doubly hydrated complexes of the α and β anomers of a systematically varied set of monosaccharides, O-phenyl D-gluco-, D-galacto-, L-fuco- and D-xylopyranoside, have been generated in a cold molecular beam and probed through infrared-ultraviolet double resonance ion-dip (IRID) spectroscopy coupled with quantum mechanical calculations. A new 'twist' has been introduced by isotopic substitution, replacing H(2)O by D(2)O to separate the carbohydrate (OH) and hydrate (OD) vibrational signatures and also to relieve spectral congestion. The new spectroscopic and computational results have exposed subtle aspects of the intermolecular interactions which influence the finer details of their preferred structures, including the competing controls exerted by co-operative hydrogen bonding, bi-furcated and OH-π hydrogen bonding, stereoelectronic changes associated with the anomeric effect, and dispersion interactions. They also reassert the operation of general 'working rules' governing conformational change and regioselectivity in both singly and doubly hydrated monosaccharides.
Glycosyl phenylthiosulfonates (glyco-PTS): novel reagents for glycoprotein synthesis.
Controlled site-selective glycosylation can be achieved by combining site-directed cysteine mutagenesis with chemical modification of the introduced thiol; a new class of more efficient chemoselective reagents, glycosyl phenylthiosulfonates, allow rapid glycosylations of representative simple thiols, peptides and proteins.
Precise structure activity relationships in asymmetric catalysis using carbohydrate scaffolds to allow ready fine tuning: dialkylzinc-aldehyde additions.
The ready construction of 24 stereochemically and functionally diverse carbohydrate ligand structures from a core D-glucosamine scaffold has allowed the evaluation of broad ranging structure activity relationships in ligand accelerated zincate additions to aldehydes, with variations in deltadeltaG+/+(R-S) of up to 5650 J mol(-1) that create opposing senses of asymmetric induction and that are consistent with models based on several ligand X-ray structures and molecular mechanics analysis. Factorial analysis of enantioselectivity using key dihedral angles and steric volume on N-2 also highlight the potential for the use of factorial design in ligand construction.
Flow chemistry kinetic studies reveal reaction conditions for ready access to unsymmetrical trehalose analogues.
Monofunctionalization of trehalose, a widely-found symmetric plant disaccharide, was studied in a microreactor to give valuable kinetic insights that have allowed improvements in desymmetrization yields and the development of a reaction sequence for large scale monofunctionalizations that allow access to probes of trehalose's biological function.
Inverted regioselectivity of C-H amination: Unexpected oxidation at beta- rather than gamma-C-H.
A rare example of beta- over gamma-C-H selectivity during Rh-catalysed sulfamate ester cyclisation is presented; from derivatives of 1,6-anhydro-beta-d-mannopyranose, five-membered sulfamidates were formed in preference to the typical six-membered oxathiazinane intramolecular insertion products. A 3D structure of sulfamate 1 helps to rationalise this unusual selectivity and analyses suggest that n-->sigma*(CH) interactions may be a key controlling factor.
Ready protease-catalyzed synthesis of carbohydrate-amino acid conjugates.
The protease-catalyzed synthesis of amino acid est-carbohydrate conjugates as glycopeptide analogues has been achieved in a highly regioselective and carbohydrate-specific manner using amino acid vinyl ester acyl donors and minimally or completely unprotected carbohydrate acyl acceptors, which together probed active sites of proteases to reveal yield efficiencies that are modulated by the carbohydrate C-2 substitutent, and that may be exploited to allow selective one-pot syntheses.
Glycosyldiselenides as lectin ligands detectable by NMR in biofluids.
The ability of glycosyldiselenides to act as lectin ligands and their selective detection in plasma by (77)Se NMR is reported.
Mechanistic evidence for a front-side, SNi-type reaction in a retaining glycosyltransferase.
A previously determined crystal structure of the ternary complex of trehalose-6-phosphate synthase identified a putative transition state-like arrangement based on validoxylamine A 6'-O-phosphate and uridine diphosphate in the active site. Here linear free energy relationships confirm that these inhibitors are synergistic transition state mimics, supporting front-face nucleophilic attack involving hydrogen bonding between leaving group and nucleophile. Kinetic isotope effects indicate a highly dissociative oxocarbenium ion-like transition state. Leaving group (18)O effects identified isotopically sensitive bond cleavages and support the existence of a hydrogen bond between the nucleophile and departing group. Brønsted analysis of nucleophiles and Taft analysis highlight participation of the nucleophile in the transition state, also consistent with a front-face mechanism. Together, these comprehensive, quantitative data substantiate this unusual enzymatic reaction mechanism. Its discovery should prompt useful reassessment of many biocatalysts and their substrates and inhibitors.
Reagent switchable stereoselective beta(1,2) mannoside mannosylation: OH-2 of mannose is a privileged acceptor.
The discovery of novel conditions for highly beta-stereoselective (>9 : 1) mannosylation of OH-2 of mannosides using a straightforward perbenzylthioglycoside donor has allowed ready assembly of beta-mannosyl oligosaccharides including the repeating trisaccharide motif of the O5 antigen of pathogen Klebsiella pneumoniae.