General methods for the synthesis of glycopyranosyluronic acid azides

Stereoselective synthesis of glycosyl azides from anomeric hydroxides via protecting group manipulations

Herein, we report the direct conversion of anomeric hydroxides to glycosyl azides in one step using diphenylphosphoryl azide. Protecting group manipulations on the hexose sugars have enabled the stereoselective synthesis of either the α-glycosyl azides or the β-anomeric azides in moderate to very good yields. The reaction has also been successfully used to enable the synthesis of β-2-deoxy-2-aminoglucosyl azides.

Macrocyclic derivatives with a sucrose scaffold: insertion of a long polyhydroxylated linker between the terminal 6,6′-positions

A series of five new macrocyclic hybrids with a sucrose scaffold were prepared by the reaction of activated 1′,2,3,3′,4,4′-hexa-O-methylsucrose with diversely functionalized d-mannitols.

Thermo-reversible supramolecular hydrogels of trehalose-type diblock methylcellulose analogues

This paper describes the design and synthesis of new trehalose-type diblock methylcellulose analogues with nonionic, cationic, and anionic cellobiosyl segments, namely 1-(tri-O-methyl-cellulosyl)-4-[β-d-glucopyranosyl-(1→4)-β-d-glucopyranosyloxymethyl]-1H-1,2,3-triazole (1), 1-(tri-O-methyl-cellulosyl)-4-[(6-amino-6-deoxy-β-d-glucopyranosyl)-(1→4)- 6-amino-6-deoxy-β-d-glucopyranosyloxymethyl]-1H-1,2,3-triazole (2), and 4-(tri-O-methyl-cellulosyloxymethyl)-1-[β-d-glucopyranuronosyl-(1→4)-β-d-glucopyranuronosyl]-1H-1,2,3-triazole (3), respectively. Aqueous solutions of all of the 1,2,3-triazole-linked diblock methylcellulose analogues possessed higher surface activities than that of industrially produced methylcellulose and exhibited lower critical solution temperatures, that allowed the formation of thermoresponsive supramolecular hydrogels at close to human body temperature. Supramolecular structures of thermo-reversible hydrogels based on compounds 1, 2, and 3 were investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Detailed structure-property-function relationships of compounds 1, 2, and 3 were discussed. Not only nonionic hydrophilic segment but also ionic hydrophilic segments of diblock methylcellulose analogues were valid for the formation of thermo-reversible supramolecular hydrogels based on end-functionalized methylcellulose.

Chemical O-Glycosylations: An Overview

The development of glycobiology relies on the sources of particular oligosaccharides in their purest forms. As the isolation of the oligosaccharide structures from natural sources is not a reliable option for providing samples with homogeneity, chemical means become pertinent. The growing demand for diverse oligosaccharide structures has prompted the advancement of chemical strategies to stitch sugar molecules with precise stereo- and regioselectivity through the formation of glycosidic bonds. This Review will focus on the key developments towards chemical O-glycosylations in the current century. Synthesis of novel glycosyl donors and acceptors and their unique activation for successful glycosylation are discussed. This Review concludes with a summary of recent developments and comments on future prospects.

De Novo Asymmetric Synthesis and Biological Analysis of the Daumone Pheromones in Caenorhabditis elegans and in the Soybean Cyst Nematode Heterodera glycines

The de novo asymmetric total syntheses of daumone 1, daumone 3 along with 5 new analogs are described. The key steps of our approach are: the diastereoselective palladium catalyzed glycosylation reaction; the Noyori reduction of 2-acetylfuran and an ynone, which introduce the absolute stereochemistry of the sugar and aglycon portion of daumone; and an Achmatowicz rearrangement, an epoxidation and a ring opening installing the remaining asymmetry of daumone. The synthetic daumones 1 and 3 as well as related analogs were evaluated for dauer activity in C. elegans and for effects on hatching of the related nematode H. glycines. This data provides additional structure activity relationships (SAR) that further inform the study of nematode signaling.

Synthesis of new saccharide azacrown cryptands

New cryptands including bis-azacrown and saccharidic moieties in their structure were prepared in several steps by applying Staudinger-aza-Wittig reaction (SAW). Syntheses have been started from cheap, easily available commercial compounds such as D-glucose, D-cellobiose and D-lactose subsequently transformed into their derivatives in fairly good yields (60-65%) and suitable to give desired final cryptands by direct SAW coupling reactions.

A chemoselective oxidation of monosubstituted ethylene glycol: facile synthesis of optically active α-hydroxy acids

A mild and efficient method for the chemoselective oxidation of monosubstituted ethylene glycols to optically active α-hydroxy acids has been achieved using the TEMPO–NaOCl reagent system.

Nitrogen-containing macrocycles having a carbohydrate scaffold

Nitrogen-containing macrocyclic compounds (amines, amides, and N-heterocyclic derivatives) are important targets in supramolecular chemistry. This chapter discusses the importance of aza-macrocycles in general and, in particular, those receptors containing sugar unit(s). The combination of a carbohydrate scaffold bearing nitrogen-containing functional groups in macrocyclic molecules opens a convenient route to chiral receptors having potentially useful properties. The carbohydrate-based macrocycles discussed are classified into several general groups: (1) aza-crown ethers containing a carbohydrate subunit, (2) cyclic homooligomers from amino sugars, (3) sugar-based cryptands, (4) cyclic peptides containing amino sugar units (including C2- and C3-symmetrical macrocyclic glycopeptides), (5) nitrogen- containing glycophanes, and (6) 1,2,3-triazoles containing synthetic cyclodextrin analogues. The general strategies employed, as well as specific ones leading to such complex derivatives, are surveyed. Applications of such carbohydrate receptors, pointing to their importance as hosts in supramolecular chemistry, are discussed.

Synthesis of N-(β-D-glycuronopyranosyl)alkanamides and 1-(β-D-glycuronopyranosyl)-4-phenyl-[1,2,3]-triazoles as N-glycoprotein linkage region analogs: examination of the effect of C5 substituent on the N-glycosidic torsion (ΦN) based on X-ray crystallography

The torsion angle around the N-glycoprotein linkage region (GlcNAc-Asn) is an important factor for presenting sugar on the cell surface which is crucial for many biological processes. Earlier studies using model and analogs showed that this important torsion angle is greatly influenced by substitutions in the sugar part. In the present work, uronic acid alkanamides and triazole derivatives have been designed and synthesized as newer analogs of N-glycoprotein linkage region to understand the influence of the carboxylic group on linkage region torsion as well as on molecular packing. Crystal structure of N-(β-D-galacturonopyranosyl)acetamide is solved with the space group of P22121. Comparison of the torsion angle and molecular packing of this compound with N-(β-D-galactopyranosyl)acetamide showed that changing the C6-hydoxymethyl group to the carboxylic acid group has minimum influence on the N-glycosidic torsion angle, ΦN and significant influence on the molecular packing.

Iron(III) chloride as an efficient catalyst for stereoselective synthesis of glycosyl azides and a cocatalyst with Cu(0) for the subsequent click chemistry

A highly efficient and mild method for azido glycosylation of glycosyl β-peracetates to 1,2-trans glycosyl azides was developed by using inexpensive FeCl(3) as the catalyst. In addition, we demonstrated, for the first time, that FeCl(3) in combination with copper powder can promote 1,3-dipolar cycloaddition (click chemistry) of azido glycosides with terminal alkynes. Good to excellent yields were obtained with exclusive formation of a single isomer in both glycosyl azidation and subsequent cycloaddition processes.

Glycosyl iodides. History and recent advances

The use of glycosyl iodides as an effective method for the preparation of glycosides has had a recent resurgence in carbohydrate chemistry, despite its early roots in which these species were believed to be of limited use. Renewed interest in these species as glycosylating agents has been spurred by their demonstrated utility in the stereoselective preparation of O-glycosides, and other glycosylic compounds. This review provides a brief historical account followed by an examination of the use of glycosyl iodides in the synthesis of oligosaccharides and other glycomimetics, including C-glycosylic compounds, glycosyl azides and N-glycosides.

Synthesis of sugar-lactams from azides of glucuronic acid

Sugar-lactams have found application as glycosidase inhibitors, synthetic precursors of iminosugars and they are structural components of natural products. The synthesis of beta-D-glucopyranosidurono-6,1-lactams from glucuronic acid derivatives are described. NMR data and X-ray crystal structures indicate that the sugar-lactams adopt distorted (1)C4 conformations in solution and in the solid state.

Cloning and characterization of Thermotoga maritima beta-glucuronidase

The putative beta-glucuronidase from Thermotoga maritima, comprising 563 amino acid residues conjugated with a Hisx6 tag, was cloned and expressed in Escherichia coli. The enzyme has a moderately broad specificity, hydrolysing a range of p-nitrophenyl glycoside substrates, but has greatest activity on p-nitrophenyl beta-D-glucosiduronic acid (kcat=68 s(-1), kcat/K(M)= 4.5x10(5) M(-1) s(-1)). The enzyme also shows a relatively broad pH-dependence with activity from pH4.5 to 7.5 and a maximum at pH6.5. As expected the enzyme is stable towards heat denaturation, with a half life of 3h at 85 degrees C, in contrast to the mesophilic E. coli enzyme, which has a half life of 2.6h at 50 degrees C. The identity of the catalytic nucleophile was confirmed as Glu476 within the sequence VTEFGAD by trapping the glycosyl-enzyme intermediate using the mechanism-based inactivator, 2-deoxy-2-fluoro-beta-D-glucosyluronic acid fluoride and identifying the labeled peptide in peptic digests by HPLC-MS/MS methodologies. Consistent with this, the Glu476Ala mutant was shown to be hydrolytically inactive. The acid/base catalyst was confirmed as Glu383 by generation and kinetic analysis of enzyme mutants modified at that position, Glu383Ala and Glu383Gln. The demonstration of activity rescue by azide is consistent with the proposed role for this residue. This enzyme therefore appears suitable for use in enzymatic oligosaccharide synthesis in either the transglycosylation mode or by use of glycosynthase and thioglycoligase approaches.

Trimethylsilylnitrate−Trimethylsilyl Azide: A Novel Reagent System for the Synthesis of 2-Deoxyglycosyl Azides from Glycals. Application in the Synthesis of 2-Deoxy-β-N-glycopeptides

A novel reagent system comprising Me(3)SiN(3) and 20 mol % of Me(3)SiONO(2) permits conversion of glycals to 1-azido 2-deoxy sugars in one step in fair to good yields. Galactals offer higher stereoselectivities than do the glucals. Reduction of the azide group with Ph(3)P-H(2)O to amino functionality followed by coupling with amino acids leads to the synthesis of novel 2-deoxy-beta-N-glycopeptides irrespective of the geometry of initial azido sugars. Using this protocol, a new gamma-sugar amino acid derivative is also procured.

Synthesis of N-(fluoren-9-ylmethoxycarbonyl)glycopyranosylamine uronic acids

The synthesis of 10 N-(fluoren-9-ylmethoxycarbonyl)glycopyranosylamine uronic acids that are amenable to solid-phase synthesis is described. The general synthetic strategy involves initial incorporation of the protected amine, followed by selective TEMPO oxidation of C-6 hydroxyl groups to give the corresponding Fmoc-protected sugar amino acids. Amine incorporation may be accomplished from aminolysis of the free sugar or from glycosyl azide reduction. The reactions can be carried out on multigram scale, providing access to unique monomer units for future incorporation into combinatorial library syntheses.