Synthesis and CD structural studies of CD52 peptides and glycopeptides

Synthesis of 6-deoxy-d-ido-heptopyranose-containing fragments of the Campylobacter jejuni strain CG8486 capsular polysaccharide

Campylobacters are important causes of gastrointestinal illness and the capsular polysaccharides (CPS) they produce are key virulence factors and targets for vaccine development. We report here the synthesis of two fragments of the Campylobacter jejuni CG8486 strain CPS that contain a rare 6-deoxy-d-ido-heptopyranose residue and, in one target, two O-methyl phosphoramidate (MeOPN) motifs. The synthetic approach features the stereoselective construction of the β-d-ido-heptopyranoside linkage via glycosylation with a β-d-galacto-heptopyranoside donor followed by a one-pot sequential C-2 and C-3 inversion. During the syntheses, we uncovered a number of interesting conformational effects with regard to the 6-deoxy-ido-heptopyranose ring, the glycosidic linkage connecting the two monosaccharides, and the MeOPN groups.

Synthesis of the Campylobacter jejuni 81-176 Strain Capsular Polysaccharide Repeating Unit Reveals the Absolute Configuration of its O-Methyl Phosphoramidate Motif

The O-methyl phosphoramidate (MeOPN) motif is a non-stoichiometric modification of capsular polysaccharides (CPS) in ≈70 % of all Campylobacter jejuni strains. Infections by C. jejuni lead to food-borne illnesses and the CPS they produce are key virulence factors. The MeOPN phosphorus atom in these CPS is stereogenic and is found as a single stereoisomer. However, to date, the absolute stereochemistry at this atom has been undefined. We report the synthesis of the three repeating units found in C. jejuni 81-176 CPS; one of these possesses a MeOPN group. In the course of these studies we established that the stereochemistry of the phosphorus atom in this MeOPN group is R. These studies represent the first unequivocal proof of stereochemistry of this group in any C. jejuni CPS. The compounds produced are anticipated to be useful tools in investigations targeting the function and biosynthesis of this structurally-interesting modification, which so far has only been identified in campylobacter.

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.

Total synthesis of a glycosylphosphatidylinositol anchor of the human lymphocyte CD52 antigen

The first total synthesis of a glycosylphosphatidylinositol (GPI) anchor bearing a polyunsaturated arachidonoyl fatty acid is reported. This lipid is found in mammalian GPIs that do not undergo lipid remodeling, a process that has important implications in the localization and function of GPI-anchored proteins. Incorporation of the oxidation- and reduction-sensitive arachidonoyl lipid in the target GPI was accomplished by using the para-methoxybenzyl (PMB) group for permanent hydroxyl group protection, which featured a selective, rapid, and efficient global deprotection protocol. The flexibility of this synthetic strategy was further highlighted by the inclusion of two additional GPI core structural modifications present in the GPI anchor of the human lymphocyte CD52 antigen.

Recent progress in the field of neoglycoconjugate chemistry

Glycosylation is probably the most complex secondary gene event that affects the vast majority of proteins in nature resulting in the occurrence of a heterogeneous mixture of glycoforms for a single protein. Many functions are exerted by single monosaccharides, well-defined oligosaccharides, or larger glycans present in these glycoproteins. To unravel these functions it is of the utmost importance to prepare well-defined single glycans conjugated to the underlying aglycon. In this review, the most recent developments are described to address the preparation of carbohydrate-amino acid (glyco-conjugates). Naturally occurring N- and O-linked glycosylation are described and the preparation of non-natural sugar-amino acid linkages are also included.