Huisgen-based conjugation of water-soluble porphyrins to deprotected sugars: Towards mild strategies for the labelling of glycans

Fully deprotected alkynyl-functionalised mono- and oligosaccharides undergo CuAAC-based conjugation with water-soluble porphyrin azides in aqueous environments. The mild reaction conditions are fully compatible with the presence of labile glycosidic bonds. This approach provides an ideal strategy to conjugate tetrapyrroles to complex carbohydrates

Structural basis of the membrane intramolecular transacylase reaction responsible for lyso-form lipoprotein synthesis

Abstract: Lipoproteins serve diverse functions in the bacterial cell and some are essential for survival. Some lipoproteins are adjuvants eliciting responses from the innate immune system of the host. The growing list of membrane enzymes responsible for lipoprotein synthesis includes the recently discovered lipoprotein intramolecular transacylase, Lit. Lit creates a lipoprotein that is less immunogenic, possibly enabling the bacteria to gain a foothold in the host by stealth. Here, we report the crystal structure of the Lit enzyme from Bacillus cereus and describe its mechanism of action. Lit consists of four transmembrane helices with an extracellular cap. Conserved residues map to the cap-membrane interface. They include two catalytic histidines that function to effect unimolecular transacylation. The reaction involves acyl transfer from the sn-2 position of the glyceryl moiety to the amino group on the N-terminal cysteine of the substrate via an 8-membered ring intermediate. Transacylation takes place in a confined aromatic residue-rich environment that likely evolved to bring distant moieties on the substrate into proximity and proper orientation for catalysis

Bioinspired aryldiazonium carbohydrate coatings: reduced adhesion of foulants at polymer and stainless steel surfaces in a marine environment

Surface treatments that minimize biofouling in marine environments are of interest for a variety of applications such as environmental monitoring and aquaculture. We report on the effect of saccharide coatings on biomass accumulation at the surface of three materials that find applications in marine settings: stainless steel 316 (SS316), Nylon-6 (N-6), and poly(ether sulfone) (PES). Saccharides were immobilized via aryldiazonium chemistry; SS316 and N-6 samples were subjected to oxidative surface pretreatments prior to saccharide immobilization, whereas PES was modified via direct reaction of pristine surfaces with the aryldiazonium cations. Functionalization was confirmed by a combination of X-ray photoelectron spectroscopy, contact angle experiments, and fluorescence imaging of lectin–saccharide binding. Saccharide immobilization was found to increase surface hydrophilicity of all materials tested, while laboratory tests demonstrate that the saccharide coating results in reduced protein adsorption in the absence of specific protein–saccharide interactions. The performance of all three materials after modification with aryldiazonium saccharide films was tested in the field via immersion of modified coupons in coastal waters over a 20 day time period. Results from combined infrared spectroscopy, light microscopy, scanning electron and He-ion microscopy, and adenosine-triphosphate content assays show that the density of retained biomass at surfaces is significantly lower on carbohydrate modified samples with respect to unmodified controls. Therefore, functionalization and field test results suggest that carbohydrate aryldiazonium layers could find applications as fouling resistant coatings in marine environments

Thiyl-Radical Reactions in Carbohydrate Chemistry: From Thiosugars to Glycoconjugate Synthesis

Thiyl-radical mediated reactions have been extensively investigated for the preparation of carbohydrate derivatives. Due to the mild reaction conditions, high yields and tolerance to a wide range of functional groups, these reactions are ideally suited to the preparation of bioconjugates including glycopeptides and glycoproteins. This microreview covers the various synthetic strategies that have been employed for the preparation of thiosugars, glycoconjugates and glycodendrimers, employing the carbohydrate unit as both the carrier of the thiyl radical and also as the acceptor. Both the inter- and intramolecular thiol-ene and -yne processes are presented and discussed. Future perspective and directions for this methodology in glycoscience are also examined

An unusual glycosylation product from a partially protected fucosyl donor under silver trif late activation conditions

An unusual glycosylation product from a partially protected fucosyl donor under silver trif late activation condition

Applications of Thiyl Radical Cyclizations for the Synthesis of Thiosugars

The use of intramolecular thiyl radical cyclizations for the synthesis of thiosugars has been investigated, and a new free-radical-based methodology for the synthesis of biologically important thiosugars has been developed. The methodology is mild and proceeds via either 6-<i>endo</i> or 5-<i>exo</i> cyclization to furnish the thiosugar ring. This represents the first examples of thiyl radical cyclization being applied to the synthesis of thiosugars