Solid-phase synthesis of core 3 and core 6 O-glycan-linked glycopeptides by benzyl-protection method

Synthesis of Mucin O-Glycans Associated with Attenuation of Pathogen Virulence

With the concerning rise in antibiotic-resistant infections, novel treatment options against pathogens are urgently sought. Several recent studies have identified mucin O-glycan mixtures as potent down-regulators of virulence-related gene expression in diverse pathogens. As individual mucin glycans cannot be isolated in sufficient purity and quantity for biological evaluation of discrete structures, we have developed an optimized synthetic approach to generate a small library of mucin glycans which were identified as most likely to display activity. The glycans have been prepared in sufficient quantity to assess biological function, studies of which are currently ongoing.

Syntheses of Fluorescent Gangliosides for the Studies of Raft Domains

Gangliosides, glycosphingolipids containing one or more sialic acids in the glycan chain, are involved in various important biological processes in cell plasma membranes (PMs). However, the behaviors and functions of gangliosides are poorly understood, primarily because of the lack of fluorescent analogs that are equivalent to native gangliosides that can be used as chemical and physical probes. In this study, we developed entirely chemical methods to synthesize fluorescent gangliosides (GM3, GM2, GM1, and GD1b) in which the glycan components are site-specifically labeled with various fluorescent dyes. The functional evaluations of the synthesized fluorescent gangliosides demonstrated the great influence of fluorescent dye on the physical properties of gangliosides in PMs and revealed the fluorescent ganglioside analogs which show similar behaviors to the native gangliosides.

Efficient Synthesis of the Lewis A Tandem Repeat

The convergent synthesis of the Lewis A (Le(a)) tandem repeat is described. The Le(a) tandem repeat is a carbohydrate ligand for a mannose binding protein that shows potent inhibitory activity against carcinoma growth. The Le(a) unit, {β-d-Gal-(1→3)-[α-l-Fuc-(1→4)]-β-d-GlcNAc}, was synthesized by stereoselective nitrile-assisted β-galactosylation with the phenyl 3-O-allyl-2,4,6-tri-O-benzyl-1-thio-β-galactoside, and ether-assisted α-fucosylation with fucosyl (N-phenyl)trifluoroacetimidate. This common Le(a) unit was easily converted to an acceptor and donor in high yields, and the stereoselective assembly of the hexasaccharide and dodecasaccharide as the Le(a) tandem repeat framework was achieved by 2-trichloroacetamido-assisted β-glycosylation and the (N-phenyl)trifluoroacetimidate method.

A convergent strategy for the synthesis of type-1 elongated mucin cores 1-3 and the corresponding glycopeptides

Mucins are a class of highly O-glycosylated proteins found on the surface of cells in epithelial tissues. O-Glycosylation is crucial for the functionality of mucins and changes therein can have severe consequences for an organism. With that in mind, the elucidation of interactions of carbohydrate binding proteins with mucins, whether in morbidly altered or unaltered conditions, continue to shed light on mechanisms involved in diseases like chronic inflammations and cancer. Despite the known importance of type-1 and type-2 elongated mucin cores 1-4 in glycobiology, the corresponding type-1 structures are much less well studied. Here, the first chemical synthesis of extended mucin type-1 O-glycan core 1-3 amino acid structures based on a convergent approach is presented. By utilizing differentiation in acceptor reactivity, shared early stage Tn- and T-acceptor intermediates were elongated with a common type-1 [β-D-Gal-1,3-β-D-GlcNAc] disaccharide, which allows for straightforward preparation of diverse glycosylated amino acids carrying the type-1 mucin core 1-3 saccharides. The obtained glycosylated 9-fluorenylmethoxycarbonyl (Fmoc)-protected amino acid building blocks were employed in synthesis of type-1 mucin glycopeptides, which are useful in biological applications.

A unified strategy for the synthesis of mucin cores 1-4 saccharides and the assembled multivalent glycopeptides

By displaying different O-glycans in a multivalent mode, mucin and mucin-like glycoproteins are involved in a plethora of protein binding events. The understanding of the roles of the glycans and the identification of potential glycan binding proteins are major challenges. To enable future binding studies of mucin glycan and glycopeptide probes, a method that gives flexible and efficient access to all common mucin core-glycosylated amino acids was developed. Based on a convergent synthesis strategy starting from a shared early stage intermediate by differentiation in the glycoside acceptor reactivity, a common disaccharide building block allows for the creation of extended glycosylated amino acids carrying the mucin type-2 cores 1-4 saccharides. Formation of a phenyl-sulfenyl-N-Troc (Troc=trichloroethoxycarbonyl) byproduct during N-iodosuccinimide-promoted thioglycoside couplings was further characterized and a new methodology for the removal of the Troc group is described. The obtained glycosylated 9-fluorenylmethoxycarbonyl (Fmoc)-protected amino acid building blocks are incorporated into peptides for multivalent glycan display.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth 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 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS 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, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.