Syntheses of chondroitin 4- and 6-sulfate pentasaccharide derivatives having a methyl beta-D-glucopyranosiduronic acid at the reducing end

Synthesis of biotinylated chondroitin sulfate DA and AD tetrasaccharides composed of hetero-type disaccharide units, and their interactions with the mAb MO-225

Chondroitin sulfate (CS), a linear acidic polysaccharide, exhibits numerous biological activities that are dependent on sulfation patterns. CS oligosaccharides comprise repeating disaccharide units with different (hetero)-type sulfation patterns and are common in nature. We herein report the synthesis of the following biotinylated CS tetrasaccharides: CS-AD [βGalNAc4S(1-4)βGlcA(1-3)βGalNAc6S(1-4)βGlcA2S] and CS-DA [βGalNAc6S(1-4)βGlcA2S(1-3)βGalNAc4S(1-4)βGlcA], in a stereo-controlled manner. We also demonstrated that the CS-d-specific monoclonal antibody MO-225 bound more strongly to CS-DA than to CS-DD or -AD.

Synthesis of chondroitin sulfate CC and DD tetrasaccharides and interactions with 2H6 and LY111

We synthesized the biotinylated chondroitin sulfate tetrasaccharides CS-CC [-3)βGalNAc6S(1-4)βGlcA(1-]₂ and CS-DD [-3)βGalNAc6S(1-4)βGlcA2S(1-]₂ which possess sulfate groups at O-6 of GalNAc and an additional sulfate group at O-2 of GlcA, respectively. We also analyzed interactions among CS-CC and CS-DD and the antibodies 2H6 and LY111, both of which are known to bind with CS-A, while CS-DD was shown for the first time to bind with both antibodies.

Synthesis of Chondroitin Sulfate E Hexasaccharide in the Repeating Region by an Effective Elongation Strategy toward Longer Chondroitin Oligosaccharide

We synthesized chondroitin and its sulfate E hexasaccharides (1 and 2) composed of the trimer of the repeating disaccharide, beta-D-GalNAc(+/-4,6-di-O-SO(3)Na)-(1-->4)-beta-D-GlcA, by employing an efficient synthetic strategy for longer chondroitin oligosaccharide. Successful elongation with the beta-D-GalNAc-(1-->4)-beta-D-GlcA unit instead of the corresponding disaccharide possessing an azide group avoided problematic reduction of the multiple azide groups on the hexasaccharide.

Toward libraries of biotinylated chondroitin sulfate analogues: from synthesis to in vivo studies

Chondroitin sulfate-E (CS-E) oligosaccharidic analogues (di to hexa) were prepared from lactose. In these compounds, the 2-acetamido group was replaced by a hydroxyl group. This modification speeded up the synthesis, and large oligosaccharides were constructed in a few steps from a lactose-originated block. The protecting groups used were as follows; Fmoc for hydroxyl groups to be glycosylated, allyl group for anomeric position protection, and trichoroacetimidate leaving groups were used to prepare up to octasaccharides. We took advantage of the presence of allyl group to develop a click biotinylation, through its transformation into a 3-azido-2-hydroxyl propyl group in two steps (epoxidation and sodium azide epoxide opening). The biotinylating agent was a water-soluble propargylated and biotinylated triethylene glycol (PEG). By using surface plasmon resonance (SPR), it was shown that the di-, tetra-, and hexasaccharides display a binding affinity and selectivity toward HSF/GSF and CXCL12 similar to that of CS-E. A parallel study confirmed their mimicry of natural compounds, based on the hexasaccharide interaction with Otx2, a homeodomain protein involved in brain maturation, thus validating our simplification approach to synthesize bioactive GAG.

Synthetic and semi-synthetic chondroitin sulfate oligosaccharides, polysaccharides, and glycomimetics

Chondroitin sulfate (CS) is a sulfated polysaccharide involved in a myriad of biological processes. Due to the variable sulfation pattern of CS polymer chains, the need to study in detail structure-activity relationships regarding CS biomedical features has provoked much interest in obtaining synthetic CS species. This paper reviews two decades of synthetic and semi-synthetic CS oligosaccharides, polysaccharides, and glycomimetics obtained by chemical, chemoenzymatic, enzymatic, and microbiological-chemical strategies.

A possible oligosaccharide-conjugate vaccine candidate for Clostridium difficile is antigenic and immunogenic

Nosocomial infections with the Gram-positive pathogen Clostridium difficile pose a major risk for hospitalized patients and result in significant costs to health care systems. Here, we present the chemical synthesis of a PS-II hapten of a cell wall polysaccharide of hypervirulent ribotype 027 of C. difficile. Mice were immunized with a conjugate consisting of the synthetic hexasaccharide and the diphtheria toxoid variant CRM(197). The immunogenicity of the glycan repeating unit was demonstrated by the presence of specific IgG antibodies in the serum of immunized mice. Murine monoclonal antibodies interact with the synthetic hexasaccharide, as determined by microarray analysis. Finally, we found that specific IgA antibodies in the stool of hospital patients infected with C. difficile recognize the synthetic PS-II hexasaccharide hapten.

From polymer to size-defined oligomers: a highly divergent and stereocontrolled construction of chondroitin sulfate A, C, D, E, K, L, and M oligomers from a single precursor: part 2

An efficient, stereocontrolled, and highly divergent approach for the preparation of oligomers of chondroitin sulfate (CS) A, C, D, E, K, L, and M variants, starting from a single precursor easily obtained by semisynthesis from abundant natural polymer is reported for the first time. Common intermediates were designed that allowed the straightforward construction of O-sulfonated species either on the D-galactosamine unit (CS-A, -C, and -E) or on both D-glucuronic acid and D-galactosamine units (CS-D and CS-K, -L, and -M). This strategy represents a successful improvement and brings a definitive answer toward the synthesis of such complex molecules with numerous relevant biological functions.

First synthesis of pentasaccharide glycoform I of the outer core region of the Pseudomonas aeruginosa lipopolysaccharide

The synthesis of a pentasaccharide representing the glycoform I, which is one of two naturally occurring glycoforms of the outer core of Pseudomonas aeruginosa lipopolysaccharide, and its analogues, differing in the N-substituent in the galactosamine unit, is reported. The main features of the synthetic scheme included the assembly of the pentasaccharide backbone by successive introduction of monosaccharide units, the use of glucosyl donors with specific location of acyl protecting groups capable of the remote anchimeric participation for highly stereoselective alpha-glucosylation, and efficient reduction of the azido group allowing high-yielding transformation of the intermediary azido pentasaccharide into final products.

Enzymatic synthesis of chondroitin 4-sulfate with well-defined structure

Synthesis of chondroitin sulfate (ChS) with well-defined structure was achieved for the first time by hyaluronidase-catalyzed polymerization. N-Acetylchondrosine (GlcAbeta(1-->3)GalNAc) oxazoline derivatives sulfated at C4 (1a), C6 (1b), and both C4 and C6 (1c) in the GalNAc unit were synthesized as transition state analogue substrate monomers for hyaluronidase (HAase) catalysis. Compound 1a was effectively polymerized by the enzyme, giving rise to synthetic ChS sulfated perfectly at the C4 position in all N-acetylgalactosamine units (Ch4S, 2a) in good yields. Molecular weights (Mn) of 2a ranged from 4000 to 18,400, which were controlled by varying reaction conditions. Compounds 1b and 1c were not catalyzed by the enzyme, affording the corresponding disaccharides through the oxazoline ring-opening without formation of polysaccharides.

Identification of a capsular polysaccharide from Moraxella bovis

The bacterium Moraxella bovis is the causative agent of an economically important disease of cattle: Infectious Bovine Keratoconjunctivitis (IBK), otherwise known as pinkeye. Little is known regarding the structure of the carbohydrates produced by M. bovis. The structure of a capsular polysaccharide from M. bovis (strain Mb25) has been determined using NMR and MS analysis. From these data it is concluded that the polysaccharide is composed of the unmodified chondroitin disaccharide repeat unit.

One-pot conversion of glycals to cis-1,2-isopropylidene-alpha-glycosides

Described is a general method for the conversion of glycals to the corresponding 1,2-cis-isopropylidene-alpha-glycosides. Epoxidation of glycals with dimethyldioxirane followed by ZnCl(2)-catalyzed addition of acetone converted a variety of protected glycals into 1,2-cis-isopropylidene-alpha-glycosides in good yield. The reaction is compatible with a range of protecting groups, including esters, benzyl ethers, and silyl ethers, as well as free hydroxyl groups. This method has been applied to develop a synthesis of protected glucuronic acid 1, a key intermediate in the synthesis of glycosaminoglycans. Compound 1 was produced in seven steps and 32% overall yield.

Biosynthesis of HNK-1 glycans on O-linked oligosaccharides attached to the neural cell adhesion molecule (NCAM): the requirement for core 2 beta 1,6-N-acetylglucosaminyltransferase and the muscle-specific domain in NCAM

The HNK-1 glycan, sulfo-->3GlcAbeta1-->3Galbeta1-->4GlcNAcbeta1-->R, is highly expressed in neuronal cells and apparently plays critical roles in neuronal cell migration and axonal extension. The HNK-1 glycan synthesis is initiated by the addition of beta1,3-linked GlcA to N-acetyllactosamine followed by sulfation of the C-3 position of GlcA. The cDNAs encoding beta1,3-glucuronyltransferase (GlcAT-P) and HNK-1 sulfotransferase (HNK-1ST) have been recently cloned. Among various adhesion molecules, the neural cell adhesion molecule (NCAM) was shown to contain HNK-1 glycan on N-glycans. In the present study, we first demonstrated that NCAM also bears HNK-1 glycan attached to O-glycans when NCAM contains the O-glycan attachment scaffold, muscle-specific domain, and is synthesized in the presence of core 2 beta1,6-N-acetylglucosaminyltransferase, GlcAT-P, and HNK-1ST. Structural analysis of the HNK-1 glycan revealed that the HNK-1 glycan is attached on core 2 branched O-glycans, sulfo-->3GlcAbeta1-->3Galbeta1-->4GlcNAcbeta1-->6(Galbeta1-->3)GalNAc. Using synthetic oligosaccharides as acceptors, we found that GlcAT-P and HNK-1ST almost equally act on oligosaccharides, mimicking N- and O-glycans. By contrast, HNK-1 glycan was much more efficiently added to N-glycans than O-glycans when NCAM was used as an acceptor. These results are consistent with our results showing that HNK-1 glycan is minimally attached to O-glycans of NCAM in fetal brain, heart, and the myoblast cell line, C2C12. These results combined together indicate that HNK-1 glycan can be synthesized on core 2 branched O-glycans but that the HNK-1 glycan is preferentially added on N-glycans over O-glycans of NCAM, probably because N-glycans are extended further than O-glycans attached to NCAM containing the muscle-specific domain.

Study of glycosylation with N-trichloroacetyl-D-glucosamine derivatives in the syntheses of the spacer-armed pentasaccharides sialyl lacto-N-neotetraose and sialyl lacto-N-tetraose, their fragments, and analogues

The syntheses of 2-aminoethyl glycosides of the pentasaccharides Neu5Ac-alpha(2-->3)-Gal-beta(1-->4)-GlcNAc-beta(1-->3)-Gal-beta(1-->4)-Glc and Neu5Ac-alpha(2-->3)-Gal-beta(1-->3)-GlcNAc-beta(1-->3)-Gal-beta(1-->4)-Glc, their asialo di-, tri-, and tetrasaccharide fragments, and analogues included a systematic study of glycosylation with variously protected mono- and disaccharide donors derived from N-trichloroacetyl-D-glucosamine of galactose, lactose, and lactosamine glycosyl acceptors bearing benzoyl protection around the OH group to be glycosylated. Despite the low reactivity of these acceptors, stereospecificity and good to excellent yields were obtained with NIS-TfOH-activated thioglycoside donors of such type, or with AgOTf-activated glycosyl bromides, while other promotors, as well as a trichloroacetimidate donor, were less effective, and a beta-acetate donor was inactive. In NIS-TfOH-promoted glycosylation with the thioglycosides, the use of TfOH in catalytic amount led to rapid formation of the corresponding oxazoline, but the quantity of TfOH necessary for further efficient coupling with an acceptor depended on the reactivity of the donor, varying from 0.07 equiv for a 3,6-di-O-benzylated monosaccharide derivative to 2.1 equiv for a peracetylated disaccharide one. In the glycosylation products, the N-trichloroacetyl group was easily converted into N-acetyl by alkaline hydrolysis followed by N-acetylation.

Syntheses of beta-D-GalpNAc4SO3-(1-->4)-L-IdopA2SO3, a disaccharide fragment of dermatan sulfate, and of its methyl alpha-L-glycoside derivative

The syntheses of sodium (sodium 2-acetamido-2-deoxy-4-O-sulfonato-beta-D-galactopyranosyl)-(1-->4)-(sodium 2-O-sulfonato-L-idopyran)uronate, a disaccharide fragment of dermatan sulfate, and of its methyl alpha-L-glycoside derivative are reported for the first time. The use of 4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-trichloroacetamido-1-O-trichloroacetimidoyl-alpha-D-galactopyranose, readily prepared from a D-gluco precursor, allowed the stereocontrolled and high yielding coupling with the low reactive 4-hydroxyl group of L-iduronic acid ester derivatives. Classical transformation of the disaccharide products into the target molecules was achieved in high yield.