B(C6F5)3-Catalyzed Stereoselective 1,2-cis Arabinofuranosylation with a Conformationally Constrained Donor

Compared with stereoselective glycosylation methods mainly addressed on the preparation of pyranose glycosides, the furanosylation has been more limited, especially for the 1,2-cis arabinofuranosylation. Herein, we report a novel stereoselective 1,2-cis-arabinofuranosylation strategy using a conformationally restricted 3,5-O-xylylene-protected arabinofuranosyl donor on activation with B(C6F5)3 for desired targets in moderate to excellent yields and β-stereoselectivity. The effectiveness of the 1,2-cis-arabinofuranosylation strategy was demonstrated successfully with various acceptors, including carbohydrate alcohols.

Synthesis and immunogenicity of the Mycobacterium tuberculosis arabinomannan-CRM197 conjugate

Lipoarabinomannan (LAM) is a major structural surface component of Mycobacterium tuberculosis. This study describes the synthesis of the well-defined lipoarabinomannan (LAM) specific dodecasaccharide-protein conjugate and immunological studies. Arabinomannan (AM) dodecasaccharide has been efficiently synthesized and covalently conjugated to carrier proteins, including cross reactive mutant (CRM197) diphtheria toxoid and bovine serum albumin (BSA) for novel neoglycoconjugates, creating a potent T-dependent conjugate vaccine. Preliminary mice immunization studies on the neoglycoconjugate revealed that it could give rise to a strong IgG antibody titer in mice at 4.0 μg dose with an aluminum phosphate adjuvant. AM-CRM197 shows potential as an excellent candidate for a new carbohydrate-based vaccine that would be capable of eliciting a protective immune response against tuberculosis.

Novel carbohydrate modified berberine derivatives: synthesis and in vitro anti-diabetic investigation

Berberine is a bioactive alkaloid used in Chinese medicine and has numerous positive effects on biological systems. This paper describes the facile and highly efficient synthesis of some carbohydrate modified berberine derivatives, and conjugation of the carbohydrate moiety with berberine was finished by "click" chemistry. The cytotoxicity and anti-diabetic measurements of all berberine derivatives were accomplished on HepG2 cell lines, and the results indicated that most of the derivatives exhibit higher anti-diabetic activity than berberine. The mannose modified berberine derivative has significantly lower cytotoxicity than berberine, and the induced IC₅₀ value of this derivative is nearly 1.5 times that of berberine. Furthermore, this mannose modified berberine derivative exhibits high anti-diabetic activity at both high and low drug concentrations, thereby indicating its potential application for the development of novel anti-diabetic drugs.

Automated Chemical Oligosaccharide Synthesis: Novel Approach to Traditional Challenges

Advances in carbohydrate chemistry have certainly made common oligosaccharides much more accessible. However, many current methods still rely heavily upon specialized knowledge of carbohydrate chemistry. The application of automated technologies to chemical and life science applications such as genomics and proteomics represents a vibrant field. These automated technologies also present opportunities for their application to organic synthesis, including that of the synthesis of oligosaccharides. However, application of automated methods to the synthesis of carbohydrates is an underdeveloped area as compared to other classes of biomolecules. The overarching goal of this review article is to present the advances that have been made at the interface of carbohydrate chemistry and automated technology.

Stereocontrolled 1,2-cis glycosylation as the driving force of progress in synthetic carbohydrate chemistry

Recent developments in stereoselective 1,2-cis glycosylation that have emerged during the past decade are surveyed herein.

Recent developments in stereoselective 1,2-cis glycosylation that have emerged during the past decade are surveyed herein. For detailed coverage of the previous achievements in the field the reader is referred to our earlier reviews: A. V. Demchenko, Curr. Org. Chem. , 2003, 7 , 35–79 and Synlett , 2003, 1225–1240.

Influence of silyl protections on the anomeric reactivity of galactofuranosyl thioglycosides and application of the silylated thiogalactofuranosides to one-pot synthesis of diverse β-D-oligogalactofuranosides

We describe in this paper the tuning effect of silyl protecting groups on the donor reactivity of galactofuranosyl phenyl thioglycosides. Silyl ethers on the galactofuranose ring are found to have an arming effect on the glycosylation reactivity, but the cyclic 3,5-acetal protecting group decreases the reactivity. The reactive phenyl 2,6-di-O-Bz-3,5-di-O-TBS-1-thio-β-d-galactofuranoside 3 is proved to be a useful glycosyl building block. By taking advantage of this donor, we achieved the highly efficient one-pot solution-phase assembly of a panel of β-d-galactofuranosyl tri- and tetrasaccharides possessing diverse glycosidic linkages.

Regioselective glycosylation method using partially protected arabino- and galactofuranosyl thioglycosides as key glycosylating substrates and its application to one-pot synthesis of oligofuranoses

We describe in this paper the development of a novel regioselective furanosylation methodology using partially protected furanosyl thioglycosides as central glycosylating building blocks and its application in the efficient one-pot synthesis of a series of linear and branched-type arabino- and galactofuranoside fragments structurally related to the cell wall polysaccharides of Mycobacterium tuberculosis , Streptococcus pneumoniae serostype 35A, and sugar beet.

Synthesis of beta-D-arabinofuranosides: stereochemical differentiation between D- and L-enantiomers

The glycosylation of 3,5-O-di-tert-butylsilylene-protected d-thioarabinofuranosides with a range of glycosyl acceptors using NIS/AgOTf as promoters proceeded in a stereoselective manner to give the corresponding beta-D-arabinofuranosides in high yields.

Synthesis of symmetrical C- and pseudo-symmetrical O-linked disaccharide analogs for arabinosyltransferase inhibitory activity in Mycobacterium tuberculosis

Herein we report the synthesis of symmetrical C-linked and pseudo-symmetrical O-linked disaccharides structurally related to Araf motifs present in the cell wall of MTB. Their activity in a competition-based arabinosyltransferase assay using [14C]-DPA as the glycosyl donor is also presented. In addition, in vitro inhibitory activity for the disaccharides was determined in a colorimetric broth microdilution assay system against MTB H37Ra and Mycobacterium avium.

Synthesis of a core arabinomannan oligosaccharide of Mycobacterium tuberculosis

The synthesis of a core arabinomannan (AM) oligosaccharide from Mycobacterium tuberculosis has been achieved using a convergent [6 + 6] glycosylation strategy and a defined set of building blocks. Dodecasaccharide 1, containing the key AM structural features of lipoarabinomannan (LAM), was obtained in excellent yield and selectivity from hexamannan 3 and hexaarabinan 5. This flexible synthetic strategy involves late-stage couplings and modifications, thus providing ready access to several different LAM fragments. The incorporation of a thiol linker at the reducing end of the oligosaccharide allows for the attachment of these compounds to microarrays and protein carriers.

On the use of 3,5-O-benzylidene and 3,5-O-(di-tert-butylsilylene)-2-O-benzylarabinothiofuranosides and their sulfoxides as glycosyl donors for the synthesis of beta-arabinofuranosides: importance of the activation method

A 2-O-benzyl-3,5-O-benzylidene-alpha-d-thioarabinofuranoside was obtained by reaction of the corresponding diol with alpha,alpha-dibromotoluene under basic conditions. On activation with 1-benzenesulfinyl piperidine, or diphenyl sulfoxide, and trifluoromethanesulfonic anhydride in dichloromethane at -55 degrees C, reaction with glycosyl acceptors affords anomeric mixtures with little or no selectivity. The analogous 2-O-benzyl-3,5-O-(di-tert-butylsilylene)-alpha-d-thioarabinofuranoside also showed no significant selectivity under the 1-benzenesulfinyl piperidine or diphenyl sulfoxide conditions. With N-iodosuccinimide and silver trifluoromethanesulfonate the silylene acetal showed moderate to high beta-selectivity, independent of the configuration of the starting thioglycoside. High beta-selectivity was also obtained with a 2-O-benzyl-3,5-O-(di-tert-butylsilylene)-alpha-arabinofuranosyl sulfoxide donor on activation with trifluoromethanesulfonic anhydride. The high beta-selectivities obtained by the N-iodosuccinimide/silver trifluoromethanesulfonate and sulfoxide methods are consistent with a common intermediate, most likely to be the oxacarbenium ion. The poor selectivity observed on activation of the thioglycosides with the 1-benzenesulfinyl piperidine, or diphenyl sulfoxide, and trifluoromethanesulfonic anhydride methods appears to be the result of the formation of a complex mixture of glycosyl donors, as determined by low-temperature NMR work.

An efficient route for the synthesis of glycosyl phosphinic acids

An efficient method for the synthesis of glycosyl phosphinic acids (21) from the corresponding C-phosphonates is described. The route developed involves three steps: reduction of the glycosyl C-phosphonate to a primary phosphine, reaction of this product with an alkylating agent to afford a secondary phosphine, and finally oxidation to the phosphinic acid. Deprotection provides compounds suitable for testing as glycosyl phosphate analogues. Although the focus of this report is the synthesis of analogues of arabinofuranosyl-containing phosphate esters, the method should be readily applicable to other systems, carbohydrate or otherwise.

Addition of Lithiated C-Nucleophiles to 2,3-O-Isopropylidene-d-erythronolactone: Stereoselective Formation of a Furanose C-Disaccharide

Addition of PhLi and lithiated dithianes to 2,3-O-isopropylidene-D-erythronolactone affords lactols, which are reduced with Et3SiH to the corresponding C-glycosides, the structures of two of which have been solved by X-ray diffraction. The use of a d-ribose-derived lithiated dithiane nucleophile in this chemistry allows for the convenient construction of a furanose C-disaccharide.