Synthesis and 1H NMR characterization of the six isomeric mono-O-sulfates of 8-methoxycarbonyloct-1-yl O-beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-beta-D-glucopyran oside

Synthesis of the sialic acid-containing tetrasaccharide repeating unit corresponding to the cell wall O-antigen of Escherichia coli O131 strain

A concise synthetic strategy have been developed for the synthesis of the sialic acid-containing tetrasaccharide repeating unit of the cell wall O-antigen of Escherichia coli (E. coli) O131 strain using regio- and stereoselective (2 → 6)-α-glycosylations of judiciously protected sialic acid thioglycoside derivatives. Perchloric acid supported over silica (HClO₄-SiO₂) in combination with N-iodosuccinimide (NIS) has been used in the stereoselective activation of thioglycoside derivatives as well as used as a solid acid for the functional group modifications. Appropriate stereoselectivity was achieved in the glycosylation steps involved in the synthetic strategy.

CMP substitutions preferentially inhibit polysialic acid synthesis

It is widely reported that derivatives of sugar moieties can be used to metabolically label cell surface carbohydrates or inhibit a particular glycosylation. However, few studies address the effect of substitution of the cytidylmonophosphate (CMP) portion on sialyltransferase activities. Here we first synthesized 2'-O-methyl CMP and 5-methyl CMP and then asked if these CMP derivatives are recognized by alpha2,3-sialyltransferases (ST3Gal-III and ST3Gal-IV), alpha2,6-sialyltransferase (ST6Gal-I), and alpha2,8-sialyltransferase (ST8Sia-II, ST8Sia-III, and ST8Sia-IV). We found that ST3Gal-III and ST3Gal-IV but not ST6Gal-I was inhibited by 2'-O-methyl CMP as potently as by CMP, while ST3Gal-III, ST3Gal-IV, and ST6Gal-I were moderately inhibited by 5-methyl CMP. Previously, it was reported that polysialyltransferase ST8Sia-II but not ST8Sia-IV was inhibited by CMP N-butylneuraminic acid. We found that ST8Sia-IV as well as ST8Sia-II and ST8Sia-III are inhibited by 2'-O-methyl CMP as robustly as by CMP and moderately by 5-methyl CMP. Moreover, the addition of CMP, 2'-O-methyl CMP, and 5-methyl CMP to the culture medium resulted in the decrease of polysialic acid expression on the cell surface and NCAM of Chinese hamster ovary cells. These results suggest that 2'-O-methyl CMP and 5-methyl CMP can be used to preferentially inhibit sialyltransferases, in particular, polysialyltransferases in vitro and in vivo. Such inhibition may be useful to determine the function of a carbohydrate synthesized by a specific sialyltransferase such as polysialyltransferase.

First total synthesis of a pentasaccharide repeating unit of the O-antigen of Hafnia alvei PCM 1529

A pentasaccharide repeating unit of the O-antigen of Hafnia alvei has been synthesized in a concise manner. High yielding glycosylation steps and minimum number of protecting group manipulation steps are the key features of this synthesis. A two-step, one-pot phase transfer oxidation protocol has been applied for the preparation of D-galacturonic acid.

Synthesis of oligosaccharide fragments corresponding to the exopolysaccharide released by Streptococcus macedonicus Sc 136

Hexa-, penta- and tetrasaccharide fragments related to the repeating unit of the exopolysaccharide secreted by Streptococcus macedonicus Sc 136 were synthesized in a very efficient manner involving minimum number of steps. A general glycosylation condition has been applied for all glycosylation steps and yields were excellent.

In vitro sulfation of N-acetyllactosaminide by soluble recombinant human β-Gal-3′-sulfotransferase

Membrane-bound beta-Gal-3'-sulfotransferase (GP3ST) was expressed and used for in vitro sulfation of Tamm-Horsfall glycoprotein. Further, the regioselective transfer of sulfate to an N-acetyllactosamine derivative could be realised with soluble chimeric GP3ST, also in combination with Lac transglycosylation by means of beta-galactosidase. Two alternative straightforward chemical syntheses for the target compound could be elaborated.

Fragmentations of isomeric sulfated monosaccharides using electrospray ion trap mass spectrometry

Electrospray ionization combined with ion trap mass spectrometry (ESI-ITMS) is a powerful tool for structural analysis of complex carbohydrates. Although its application to sulfated glycans has been limited so far, it should provide critical information, such as sulfate positions, on their structures. In this work, MS(n) spectra of nine monosulfated monosaccharides, consisting of five hexoses and four N-acetylhexosamines, were measured in negative ion mode to find basic fragmentation rules for sulfated sugars. Two pairs of positional isomers with respect to sulfation, i.e., Gal4S and Gal6S, and GalNAc4S and GalNAc6S, showed characteristic fragmentation patterns in MS(3), and could be discriminated from one another by the appearance of particular diagnostic fragment ions that characterize individual isomers. It was also demonstrated that, even if a mixture of these positional isomers was analyzed, the proportion of each species could be estimated through analysis of the abundance ratios of the diagnostic ions. However, 3-O-sulfated saccharides (Glc3S and GlcNAc3S) gave a single abundant diagnostic ion in MS(2) corresponding to the hydrogensulfate ion, [OSO(3)H](-), and this characteristic clearly differentiated them from their positional isomers. In contrast, 6-O-sulfated diastereomers consisting of two groups, Glc6S, Man6S, Gal6S, and GlcNAc6S, GalNAc6S, could not be discriminated by the types of fragment ions; however, the abundance ratios of particular fragment ions differed significantly between Glc(NAc)6S and Gal(NAc)6S. Since ESI-ITMS yielded large quantities of useful information on structures of monosulfated hexoses and N-acetylhexosamines in an extremely simple and reproducible manner, establishment of a comprehensive strategy based on ESI-ITMS(n) appears to be a promising technique for structural elucidation of sulfated complex carbohydrates.

P-selectin blocking potency of multimeric tyrosine sulfates in vitro and in vivo

P-selectin blocking potency was investigated using synthetic monomeric and polymeric anionic compounds containing sulfate groups such as O-sulfotyrosine (sTyr) and/or sulfated Lewis structures. A non-carbohydrate-containing polyacrylamide conjugate sTyr-PAA (80% mol of sTyr) was a remarkably potent inhibitor of P-selectin binding in vitro, having an IC(50) value of 6 ng/mL (equivalent to 10 nM calculated on the basis of sTyr residues or 0.1 nM calculated by the mass of the macromolecule). The inhibitory effect of sTyr-PAA (80%) towards P-selectin is significantly greater than that of fucoidan (IC(50), 100 ng/mL). However, sTyr-PAA (80%) was less effective than fucoidan at reducing neutrophil extravasation in an in vivo rat model of peritonitis.

Synthesis and NMR characterization of the six regioisomeric monophosphates of octyl beta-D-galactopyranosyl-(1 --> 4)-2-acetamido-2-deoxy-beta-D-glucopyranoside

All six regioisomeric monophosphates of octyl beta-D-galactopyranosyl-(1 --> 4)-2-acetamido-2-deoxy-beta-D-glucopyranoside have been chemically synthesized and characterized by high-resolution 1H, 13C and 31P NMR spectroscopy. Phosphorylation causes characteristic downfield shifts of the nucleus at the substituted site in the 1H and 13C NMR signals and resulted in a unique 31P signal for each compound.

Synthesis and utility of sulfated chromogenic carbohydrate model substrates for measuring activities of mucin-desulfating enzymes

A chromogenic substrate, 4-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside 6-sodium sulfate was synthesized and used in combination with beta-N-acetylhexosaminidase for detection of the sulfatase, MdsA, by release of 4-nitrophenol. MdsA was originally isolated from the bacterium Prevotella strain RS2 and is believed to be involved in desulfation of sulfomucins, major components of the mucus barrier protecting the human colon surface. The exo nature of the MdsA sulfatase was indicated by its inability to de-esterify the disaccharide 4-nitrophenyl beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-beta-D-glucopyranoside 6-sodium sulfate. This latter compound was prepared from monosaccharide precursors by two different methods, the shorter requiring just six steps from 4-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside and giving an overall yield of 26.4%. The syntheses of 4-nitrophenyl beta-D-galactopyranoside 3-triethylammonium sulfate and 6-triethylammonium sulfate and their use in combination with beta-galactosidase as chromogenic substrates for detecting Bacteroides fragilis sulfatases with different specificities was also demonstrated.

Synthetic mannosides act as acceptors for mycobacterial α1-6 mannosyltransferase

A series of synthetic mannosides was screened in a cell-free system for their ability to act as acceptor substrates for mycobacterial mannosyltransferases. Evaluation of these compounds demonstrated the incorporation of [14C]Man from GDP-[14C]Man into a radiolabeled organic-soluble fraction and analysis by thin layer chromatography and autoradiography revealed the formation of two radiolabeled products. Each synthetic acceptor was capable of accepting one or two mannose residues, resulting in a major and a minor mannosylated product. Both products from each acceptor were isolated and their mass was confirmed by fast-atom bombardment-mass spectrometry (FABMS). Characterization of each mannosylated product by exo-glycosidase digestion. acetolysis and linkage analysis by gas chromatography mass spectrometry of partially per-O-methylated alditols, revealed only alpha1-6-linked products. In addition. the antibiotic amphomycin selectively inhibited the formation of mannosylated products suggesting polyprenolmonophosphate-mannose (C15 50-P-Man) was the immediate mannose donor in all mannosylation reactions observed. The ability of synthetic disaccharides to act as acceptor substrates in this system, is most likely due to the action of a mycobacterial polyprenol-P-Man:mannan alpha1-6 mannosyltransferase involved in the biosynthesis of linear alpha1-6-linked lipomannan.

Rapid determination of the binding affinity and specificity of the mushroom Polyporus squamosus lectin using frontal affinity chromatography coupled to electrospray mass spectrometry

The binding affinity and specificity of the mushroom Polyporus squamosus lectin has been determined by the recently developed method of frontal affinity chromatography coupled to electrospray mass spectrometry (FAC/MS). A micro-scale affinity column was prepared by immobilizing the lectin ( approximately 25 microg) onto porous glass beads in a tubing column (9.8 microl column volume). The column was then used to screen several oligosaccharide mixtures. The dissociation constants of 22 sialylated or sulfated oligosaccharides were evaluated against the immobilized lectin. The lectin was found to be highly specific for Neu5Acalpha2-6Galbeta1-4Glc/GlcNAc containing oligosaccharides with K(d) values near 10 microM. The FAC/MS assay permits the rapid determination of the dissociation constants of ligands as well as a higher throughput screening of compound mixtures, making it a valuable tool for affinity studies, especially for testing large numbers of compounds.

Aglycone structure influences alpha-fucosyltransferase III activity using N-acetyllactosamine glycoside acceptors

We showed previously that Chinese hamster ovary cells took up and utilized a variety of N-acetylglucosaminides as primers of oligosaccharide biosynthesis (Ding et al., 1999, J. Carbohydr. Chem., 18:471-475). In this study, a library of N-acetylglucosaminides was enzymatically galactosylated in vitro to yield type 2 chain N-acetyllactosaminides bearing a variety of aglycones. Those disaccharides are potential acceptors for fucosyltransferases. As an extension of the previous study, we tested the type 2 chain disaccharyl glycosides (Galbeta1,4-GlcNAcbeta-R) for their aglycone-dependent acceptor specificity for alpha-L-fucosyltransferase III (Fuc-TIII). The enzyme activity significantly depended on the aglycone structures, suggesting that, in addition to the polar groups on the sugar moiety, the hydrophobic aglycone can substantially contribute to recognition in this reaction.

Matrix-assisted laser desorption ionization mass spectrometry for the analysis of monosulfated oligosaccharides

Sulfated oligosaccharides are an important class of compounds in the field of glycobiology. Mass spectrometric analysis of these molecules is challenging due to their readiness to dissociate in sample preparation and their tendency to fragment during ionization. Moreover, their presence in small quantity in biological systems poses additional problems. We report the development of a mass spectrometric method based on matrix-assisted laser desorption ionization (MALDI) in a time-lag focusing time-of-flight mass spectrometer for the analysis of monosulfated oligosaccharides. It is found that coumarin 120 is an excellent matrix for the analysis of monosulfated disaccharides, whereas the use of a mixture of coumarin 120 and 6-aza-2-thiothymine is very effective for the ionization of sulfated trisaccharides and tetrasaccharides including those containing N-acetylneuraminic acid. Molecular ions for a series of synthetic sulfo/sialo beta Gal(1-->3)GlcNAc and beta Gal(1-->4)GlcNAc structures can thus be observed with subpicomole detection sensitivity using a uniform microcrystal matrix/sample preparation procedure. It is demonstrated that, with this matrix formulation, the presence of a high amount of sodium chloride or sodium phosphate buffer, which is often the case for the HPLC fractionated samples, does not deteriorate the MALDI performance. The analysis of mixtures containing different types of oligosaccharides is also examined. It is found that different classes of oligosaccharides require different matrix preparation methods.