“Click chemistry”en route to pseudo-starch

Synthesis of Glycopolymer Micelles for Antibiotic Delivery

In this work, we designed biodegradable glycopolymers consisting of a carbohydrate conjugated to a biodegradable polymer, poly(lactic acid) (PLA), through a poly(ethylene glycol) (PEG) linker. The glycopolymers were synthesized by coupling alkyne end-functionalized PEG-PLA with azide-derivatized mannose, trehalose, or maltoheptaose via the click reaction. The coupling yield was in the range of 40-50% and was independent of the size of the carbohydrate. The resulting glycopolymers were able to form micelles with the hydrophobic PLA in the core and the carbohydrates on the surface, as confirmed by binding with the lectin Concanavalin A. The glycomicelles were ~30 nm in diameter with low size dispersity. The glycomicelles were able to encapsulate both non-polar (rifampicin) and polar (ciprofloxacin) antibiotics. Rifampicin-encapsulated micelles were much smaller (27-32 nm) compared to the ciprofloxacin-encapsulated micelles (~417 nm). Moreover, more rifampicin was loaded into the glycomicelles (66-80 μg/mg, 7-8%) than ciprofloxacin (1.2-2.5 μg/mg, 0.1-0.2%). Despite the low loading, the antibiotic-encapsulated glycomicelles were at least as active or 2-4 times more active than the free antibiotics. For glycopolymers without the PEG linker, the antibiotics encapsulated in micelles were 2-6 times worse than the free antibiotics.

Conversion of glycals into vicinal-1,2-diazides and 1,2-(or 2,1)-azidoacetates using hypervalent iodine reagents and Me3SiN3. Application in the synthesis of N-glycopeptides, pseudo-trisaccharides and an iminosugar

Glycals react with PIFA (or PIDA)–TMSN₃in presence of TMSOTf to form sugar derived 1,2-diazides and vicinal azidoacetates. Synthesis of 2-azido-N-glycopeptides, pseudotrisaccharides, and a piperidine triol derivative is reported.

Vinyl sulfone modified-azidofuranoside building-blocks: 1,4-/1,5-disubstituted-1,2,3-triazole linked trisaccharides via an aqueous/ionic-liquid route and “Click” chemistry

1,5-Disubstituted 1,2,3-triazole (1,5-DT) linked disaccharides have been synthesized from stable building blocks having both vinyl sulfone and azido groups using aqueous ionic-liquid media.

Copper-catalysed azide-alkyne cycloadditions (CuAAC): an update

The reactions of organic azides and alkynes catalysed by copper species represent the prototypical examples of click chemistry. The so-called CuAAC reaction (copper-catalysed azide-alkyne cycloaddition), discovered in 2002, has been expanded since then to become an excellent tool in organic synthesis. In this contribution the recent results described in the literature since 2010 are reviewed, classified according to the nature of the catalyst precursor: copper(I) or copper(II) salts or complexes, metallic or nano-particulated copper and several solid-supported copper systems.

Underpinning Starch Biology with in vitro Studies on Carbohydrate-Active Enzymes and Biosynthetic Glycomaterials

Starch makes up more than half of the calories in the human diet and is also a valuable bulk commodity that is used across the food, brewing and distilling, medicines and renewable materials sectors. Despite its importance, our understanding of how plants make starch, and what controls the deposition of this insoluble, polymeric, liquid crystalline material, remains rather limited. Advances are hampered by the challenges inherent in analyzing enzymes that operate across the solid-liquid interface. Glyconanotechnology, in the form of glucan-coated sensor chips and metal nanoparticles, present novel opportunities to address this problem. Herein, we review recent developments aimed at the bottom-up generation and self-assembly of starch-like materials, in order to better understand which enzymes are required for starch granule biogenesis and metabolism.

Click chemistry route to tricyclic monosaccharide triazole hybrids: design and synthesis of substituted hexahydro-4H-pyrano[2,3-f][1,2,3]triazolo[5,1-c][1,4]oxazepines

A click chemistry approach to novel tricyclic monosaccharide triazole hybrids from an intramolecular 1,3-dipolar cycloaddition of 6-azido-4-O-propargyl glycopyranosides has been reported.

Synthesis and characterization of maltose-based amphiphiles as supramolecular hydrogelators

Low molecular mass amphiphilic glycolipids have been prepared by linking a maltose polar head and a hydrophobic linear chain either by amidation or copper(I)-catalyzed azide-alkyne [3 + 2] cycloaddition. The liquid crystalline properties of these amphiphilic materials have been characterized. The influence of the chemical structure of these glycolipids on the gelation properties in water has also been studied. Glycolipids obtained by the click coupling of the two components give rise to stable hydrogels at room temperature. The fibrillar structure of supramolecular hydrogels obtained by the self-assembly of these gelators have been characterized by electron microscopy. Fibers showed some torsion, which could be related with a chiral supramolecular arrangement of amphiphiles, as confirmed by circular dichroism (CD). The sol-gel transition temperature was also determined by differential scanning calorimetry (DSC) and NMR.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

Peracetylated alpha-D-glucopyranosyl fluoride and peracetylated alpha-maltosyl fluoride

The X-ray analyses of 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl fluoride, C(14)H(19)FO(9), (I), and the corresponding maltose derivative 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl-(1-->4)-2,3,6-tri-O-acetyl-alpha-D-glucopyranosyl fluoride, C(26)H(35)FO(17), (II), are reported. These add to the series of published alpha-glycosyl halide structures; those of the peracetylated alpha-glucosyl chloride [James & Hall (1969). Acta Cryst. A25, S196] and bromide [Takai, Watanabe, Hayashi & Watanabe (1976). Bull. Fac. Eng. Hokkaido Univ. 79, 101-109] have been reported already. In our structures, which have been determined at 140 K, the glycopyranosyl ring appears in a regular (4)C(1) chair conformation with all the substituents, except for the anomeric fluoride (which adopts an axial orientation), in equatorial positions. The observed bond lengths are consistent with a strong anomeric effect, viz. the C1-O5 (carbohydrate numbering) bond lengths are 1.381 (2) and 1.381 (3) A in (I) and (II), respectively, both significantly shorter than the C5-O5 bond lengths, viz. 1.448 (2) A in (I) and 1.444 (3) A in (II).

Synthesis of triazole-linked pseudo-starch fragments

Rapid assembly of starch fragment analogues was achieved using 'click chemistry'. Specifically, a pentadecasaccharide and two hexadecasaccharide mimics containing two parallel maltoheptaosyl chains linked via [1,2,3]-triazoles to glucose or maltose core were synthesised using Cu(I)-catalyzed [3+2] dipolar cycloaddition of azidosaccharides and 4,6-di-O-propargylated methyl alpha-d-glucopyranoside and 6,6'- and 4',6'-di-O-propargylated p-methoxyphenyl beta-maltoside.

Recent applications of the CuI-catalysed Huisgen azide–alkyne 1,3-dipolar cycloaddition reaction in carbohydrate chemistry

This article surveys recent applications of Cu(I)-catalysed 1,3-dipolar cycloaddition of azides and alkynes in carbohydrate chemistry, highlighting developments in the preparation of simple glycoside and oligosaccharide mimetics, glyco-macrocycles, glycopeptides, glyco-clusters and carbohydrate arrays.

N-Glycoside neoglycotrimers from 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl azide

2,3,4,6-Tetra-O-acetyl-beta-D-glucopyranosyl azide is available on large scale from D-glucose by means of a three-step sequence involving acetylation, activation as the glycosyl bromide, and stereospecific displacement with azide anion. The azide functionality then serves as a convenient anchor upon which to introduce new functionality, usually with retention of the beta-stereochemistry. Here we report the synthesis of an amide-linked N-glycosyl trimer, by employing a Staudinger-aza-Wittig process on the azide, as well as a hybrid N-glycosyl triazole-amide-linked trimer in which the sugars are separated by 1,2,3-triazole heterocycles. Both of these neoglycotrimers are isolated in good yield with high beta-selectivity in each case.

“Click Chemistry” Inspired Synthesis of pseudo-Oligosaccharides and Amino Acid Glycoconjugates

[reaction: see text] Various pseudo-oligosacchardies and amino acid glycoconjugates were synthesized via an intermolecular 1,3-dipolar cycloaddition ("click") reaction using easily accessible carbohydrate and amino acid derived azides and alkynes as building blocks. It is pertinent to mention that the conjugation reaction is highly regioselective and high yielding and can be carried out under mild reaction conditions.