Synthesis of a set of sulfated and/or phosphorylated oligosaccharide derivatives from the carbohydrate–protein linkage region of proteoglycans

Synthesis of the Reducing-end Hexasaccharide Fragment of Marine Lipopolysaccharide Axinelloside A

Chemical synthesis of an orthogonally protected hexasaccharide relevant to the reducing-end half of axinelloside A, a highly sulfated marine lipopolysaccharide, is disclosed. The synthesis features preparation of the scyllo-inositol unit via a Ferrier-type-II rearrangement, construction of the 1,2-cis-glycosidic bonds via remote participation, and concise [2+2+2] assembly via Au(I)-catalyzed glycosylation.

The use of the novel glycosyl acceptor and supramer analysis in the synthesis of sialyl-α(2-3)-galactose building block

A new glycosyl acceptor to be used in sialylation was designed as a 3-hydroxy derivative of 4-methoxyphenyl β-d-galactopyranoside with 2-O-acetyl group and O-4 and O-6 protected as benzylidene acetal. Two alternative syntheses of this compound were compared. Sialylation of 3-OH group of the glycosyl acceptor with O-chloroacetylated N-trifluoroacetylneuraminic acid phenyl thioglycoside (NIS, TfOH, MeCN, MS 3 Å, -40 °C) was studied in a wide concentration range (5-150 mmol L^-1). The outcome of sialylation generally followed the predictions of supramer analysis of solutions of sialyl donor in MeCN, which was performed by polarimetry and static light scattering and revealed two concentration ranges differing in solution structure and the structures of supramers of glycosyl donor. The optimized conditions of sialylation (C = 50 mmol L^-1) were used to synthesize protected Neu-α(2-3)-Gal disaccharide (78%, α:β = 13:1), which was then converted to sialyl-α(2-3)-galactose imidate building block useful for the synthesis of complex sialo-oligosaccharides.

Ionic-liquid supported rapid synthesis of an N-glycan core pentasaccharide on a 10 g scale

A hetero-branched N-glycan core pentasaccharide was rapidly assembled on a new ionic liquid support on a 10 g scale.

Convergent Synthesis of Digalactosyl Diacylglycerols

Efficient convergent chemical syntheses of digalactosyl diacylglycerols (DGDGs), which have both a galactose-galactose α(1→6)-linkage and a galactose-glycerol β-linkage along with a diacylglycerol containing various kinds of fatty acids, have been accomplished. In order to achieve a concise synthesis, we chose to use allylic protective groups as permanent protective groups. We have also achieved α- and β-selective glycosylations for the respective linkages with high yields as the key steps.

Homoserine as an Aspartic Acid Precursor for Synthesis of Proteoglycan Glycopeptide Containing Aspartic Acid and a Sulfated Glycan Chain

Among many hurdles in synthesizing proteoglycan glycopeptides, one challenge is the incorporation of aspartic acid in the peptide backbone and acid sensitive O-sulfated glycan chains. To overcome this, a new strategy was developed utilizing homoserine as an aspartic acid precursor. The conversion of homoserine to aspartic acid in the glycopeptide was successfully accomplished by late stage oxidation using (2,2,6,6-tetramethyl-piperidin-1-yl)oxyl (TEMPO) and bis(acetoxy)iodobenzene (BAIB). This is the first time that a glycopeptide containing aspartic acid and an O-sulfated glycan was synthesized.

Chemistry of xylopyranosides

Xylose is one of the few monosaccharidic building blocks that are used by mammalian cells. In comparison with other monosaccharides, xylose is rather unusual and, so far, only found in two different mammalian structures, i.e. in the Notch receptor and as the linker between protein and glycosaminoglycan (GAG) chains in proteoglycans. Interestingly, simple soluble xylopyranosides can not only initiate the biosynthesis of soluble GAG chains but also function as inhibitors of important enzymes in the biosynthesis of proteoglycans. Furthermore, xylose is a major constituent of hemicellulosic xylans and thus one of the most abundant carbohydrates on Earth. Altogether, this has spurred a strong interest in xylose chemistry. The scope of this review is to describe synthesis of xylopyranosyl donors, as well as protective group chemistry, modifications, and conformational analysis of xylose.

Transformation of the (2-nitrophenyl)acetyl protecting group in the presence of trichloroacetonitrile and 1,8-diazabicyclo[5,4,0]-undec-7-ene

When treated with trichloroacetonitrile in the presence of 1,8-diazabicyclo[5,4,0]-undec-7-ene, the (2-nitrophenyl)acetyl protecting group (NPAc) was partially transformed into mono-(NPClAc) and dichlorinated (NPCl₂Ac) species, but no chlorination occurred in the presence of solid potassium carbonate. The monochlorinated NPClAc group, which is suitable for use in glycosylation reaction, can be selectively removed by treatment with thiourea.

Efficiently synthesizing lacto-ganglio-series gangliosides by using a glucosyl ceramide cassette approach: the total synthesis of ganglioside X2

The first total synthesis of the hybrid ganglioside X2, which consisted of a highly branched octasaccharide and ceramide moieties, was accomplished by using a glucosyl ceramide cassette approach. With a disaccharyl donor, the heptasaccharide could not be constructed by glycosylation of the C4 hydroxy group of galactose at the reducing end of the pentasaccharide. In contrast, through an alternative approach with two branched glycan units, a GM2-core trisaccharide, and a lacto-ganglio tetrasaccharide, the heptasaccharyl donor could be prepared and subsequently joined with a glucosyl ceramide cassette to afford the protected ganglioside, X2. Finally, global deprotection completed the synthesis, thus affording the pure ganglioside X2.

5-Azido-4-benzyloxy-2-methoxy-6-methylperhydropyran-3-ol

In the title compound, C₁₄H₁₉N₃O₄, the perhydro­pyran ring adopts a chair conformation. An intra­molecular C—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal packing, mol­ecules are linked by O—H⋯O hydrogen bonds, forming infinite chains along [100].

[Agrecan and articular cartilage: assessment of glycosyltransferases for the restoration of cartilage matrix in osteoarthritis]

Articular cartilage is a connective tissue containing a single type of cells, chondrocytes, which synthesise a dense extracellular matrix, mainly composed of collagens, hyaluronic acid and proteoglycans. These macromolecules play a major role in the resistance and elastic properties of the tissue. They also favour interactions with small active substances, such as growth factors and cytokines. Chondrocytes have a low metabolic capacity in relatively hypoxic conditions and absence of vascular supply. In physiopathological conditions, such as osteoarthritis (OA), progressive and irreversible degradation of matrix components is occurring. With the aim of developing new and efficient therapies against OA, we investigated the molecular mechanisms that initiate the disease, in order to identify key-proteins. These targets should hopefully lead to the design of new drugs able to stop degradation and restore cartilage. One of the earliest molecular events in OA is the degradation of aggrecan, the most abundant proteoglycan. The glycosaminoglycan (GAG) chains, chondroitin-sulfate, attached on the core protein, are subjected to hydrolysis into smaller fragments. We were interested in the glycosyltransferases that catalyse the formation of the polysaccharidic chains, namely those involved in the common tetrasaccharidic protein linkage region, GlcAbeta1,3Galbeta1,3Galbeta 1,4Xyl-O-Serine. The galactose beta1,3-glucuronosyltransférase-I (GlcAT-I) which catalyses the final step of this primer and which is markedly repressed during OA is an attractive target in that respect. Indeed, the human recombinant enzyme was found to play a pivotal role in GAG synthesis. Moreover, overexpression of GlcAT-I in cartilage explants treated with IL1beta was able to fully counteract proteoglycan depletion induced by the cytokine. These results prompted us to investigate the structure, function and regulation of this enzyme. This study provides the basis for several therapy approaches (gene delivery, design of glycomimetics able to initiate GAG synthesis) to promote cartilage repair.

Iodine/Toluenesulfonic Acid: A Novel Catalyst for Isopropylidenation in Carbohydrate Chemistry

A novel catalyst for O-isopropylidenation of carbohydrates, a mixture of toluenesulfonic acid and iodine, was developed.