Multigram syntheses of the disaccharide repeating units of chondroitin 4- and 6-sulfates

Role of Chondroitin Sulfation Following Spinal Cord Injury

Traumatic spinal cord injury produces long-term neurological damage, and presents a significant public health problem with nearly 18,000 new cases per year in the U.S. The injury results in both acute and chronic changes in the spinal cord, ultimately resulting in the production of a glial scar, consisting of multiple cells including fibroblasts, macrophages, microglia, and reactive astrocytes. Within the scar, there is an accumulation of extracellular matrix (ECM) molecules—primarily tenascins and chondroitin sulfate proteoglycans (CSPGs)—which are considered to be inhibitory to axonal regeneration. In this review article, we discuss the role of CSPGs in the injury response, especially how sulfated glycosaminoglycan (GAG) chains act to inhibit plasticity and regeneration. This includes how sulfation of GAG chains influences their biological activity and interactions with potential receptors. Comprehending the role of CSPGs in the inhibitory properties of the glial scar provides critical knowledge in the much-needed production of new therapies.

Protecting-Group-Free Synthesis of Chondroitin 6-Sulfate Disaccharide and Tetrasaccharide

Chondroitin 6-sulfate (CS-C) is an important glycosaminoglycan that regulates many physiological functions including the development, progression, and metastasis of cancer. To understand its mechanism of action at the molecular level, CS-C molecules of defined length are required. A protecting group-free synthesis of CS-C disaccharide and tetrasaccharide from the CS-A polymer that involves only three steps and furnishes CS-O disaccharide and tetrasaccharide as intermediates is reported.

Divergent Synthesis of Chondroitin Sulfate Disaccharides and Identification of Sulfate Motifs that Inhibit Triple Negative Breast Cancer

Glycosaminoglycans (GAGs) regulate many important physiological processes. A pertinent issue to address is whether GAGs encode important functional information via introduction of position specific sulfate groups in the GAG structure. However, procurement of pure, homogenous GAG motifs to probe the “sulfation code” is a challenging task due to isolation difficulty and structural complexity. To this end, we devised a versatile synthetic strategy to obtain all the 16 theoretically possible sulfation patterns in the chondroitin sulfate (CS) repeating unit; these include rare but potentially important sulfated motifs which have not been isolated earlier. Biological evaluation indicated that CS sulfation patterns had differing effects for different breast cancer cell types, and the greatest inhibitory effect was observed for the most aggressive, triple negative breast cancer cell line MDA-MB-231.

Synthetic probes of glycosaminoglycan function

Glycosaminoglycans (GAGs) participate in many critical biological processes by modulating the activities of a wide range of proteins, including growth factors, chemokines, and viral receptors. Recent studies using synthetic oligosaccharides and glycomimetic polymers have established the importance of specific structural determinants in controlling GAG function. These findings illustrate the power of synthetic molecules to elucidate glycan-mediated signaling events, as well as the prospect of further advancements to understand the roles of GAGs in vivo and explore their therapeutic potential.

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.

Benzoylated uronic acid building blocks and synthesis of N-uronate conjugates of lamotrigine

A chemoenzymatic approach towards benzoylated uronic acid building blocks has been investigated starting with benzoylated hexapyranosides using regioselective C-6 enzymatic hydrolysis as the key step. Two of the building blocks were reacted with the antiepileptic drug lamotrigine. Glucuronidation of lamotrigine using methyl (2,3,4-tri-O-benzoyl-α-D-glycopyranosyl bromide)uronate proceeded to give the N2-conjugate. However, lamotrigine-N2-glucuronide was most efficiently synthesised from methyl (2,3,4-tri-O-acetyl-α-D-glucopyranosyl bromide)uronate. Employing nitromethane as solvent with CdCO(3) as a base lamotrigine-N2 glucuronide was prepared in a high yield (41%). Also methyl (2,3-di-O-benzoyl-4-deoxy-4-fluoro-α-D-glucosyl bromide)uronate underwent N-glucuronidation, but the product was unstable, eliminating hydrogen fluoride to give the corresponding enoate conjugate.

Sulfation patterns of glycosaminoglycans encode molecular recognition and activity

Although glycosaminoglycans contribute to diverse physiological processes, an understanding of their molecular mechanisms has been hampered by the inability to access homogeneous glycosaminoglycan structures. Here, we assembled well-defined chondroitin sulfate oligosaccharides using a convergent, synthetic approach that permits installation of sulfate groups at precise positions along the carbohydrate backbone. Using these defined structures, we demonstrate that specific sulfation motifs function as molecular recognition elements for growth factors and modulate neuronal growth. These results provide both fundamental insights into the role of sulfation and direct evidence for a 'sulfation code' whereby glycosaminoglycans encode functional information in a sequence-specific manner analogous to that of DNA, RNA and proteins.

An Expedient Synthesis of the Repeating Unit of the Acidic Polysaccharide of the Bacteriolytic Complex of Lysoamidase

The first synthesis of the trisaccharide repeating unit of the acidic polysaccharide of the bacteriolytic complex of lysoamidase is presented. The construction is based on a linear glycosylation strategy that starts from the reducing end and employs thio- and selenoglycosides in a highly stereoselective manner by a single set of activation conditions. The thus-formed trisaccharide is selectively deprotected and oxidised, after which a final deprotection step furnishes the desired repeating unit.

An expeditious preparation of various sulfoforms of the disaccharide β-d-Galp-(1→3)-d-Galp, a partial structure of the linkage region of proteoglycans, as their 4-methoxyphenyl β-d-glycosides

An expeditious preparation of various sulfoforms of the disaccharide 4-methoxyphenyl O-(beta-D-galactopyranosyl)-(1-->3)-beta-D-galactopyranoside, namely the 4(I)- and 6(I)-sulfate, the 4(II)- and 6(II)-sulfate, and the 6(I),6(II)-disulfate derivatives, is reported for the first time. These molecules will be useful for the study of the early steps of the biosynthesis and sorting of proteoglycans. All target compounds were readily obtained from the common key intermediate 4-methoxyphenyl O-(2,3-di-O-benzoyl-4,6-di-O-levulinoyl-beta-D-galactopyranosyl)-(1-->3)-2-O-benzoyl-4,6-O-benzylidene-beta-D-galactopyranoside, easily prepared from the common starting material 4-methoxyphenyl 4,6-O-benzylidene-beta-D-galactopyranoside. Noticeable is the possible preparation of the different 6-O-sulfonated species through a one-pot procedure starting from a tetrol precursor.

Synthesis of various sulfoforms of the trisaccharide β-d-GlcpA-(1→3)-β-d-Galp-(1→3)-β-d-Galp-(1→OMP) as probes for the study of the biosynthesis and sorting of proteoglycans

A straightforward preparation of various sulfoforms of the trisaccharide 4-methoxyphenyl O-(sodium beta-d-glucopyranosyluronate)-(1-->3)-( beta-d-galactopyranosyl)-(1-->3)-beta-d-galactopyranoside (1), namely its 6a- and 4a-monosulfate, 6b- and 4b-monosulfate and 6a,6b-disulfate derivatives, is reported for the first time. These compounds, which are partial structures of the linkage region of proteoglycans, will serve as probes for the study of the biosynthesis and sorting of these macromolecules. A key trisaccharide derivative, in which the two similar d-Gal units were differentiated at C-4,6 with 4,6-benzylidene and 4,6-di-tert-butylsilylene acetals, respectively, was used as a common intermediate. Both acetal groups showed excellent orthogonality, and allowed the preparation of all target compounds in high yield. Noteworthy is the possibility to prepare the 6a- and 6b-monosulfated and the 6a,6b-disulfated species through a one-pot regioselective procedure starting from a tetrol precursor.

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

The syntheses are reported of beta-D-GlcpA-(1-->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1- ->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1-->OMe), O-sulfonated at C-4 or C-6 of the aminosugar moieties, which represent structural elements of chondroitin 4- and 6-sulfate proteoglycans. Starting from a synthetic disaccharide glycosyl acceptor, the stepwise or blockwise construction of the sugar backbone with appropriate synthons led to a pentasaccharide tetraol, which was used as a common intermediate. Selective 6-O-sulfonation of this tetraol, followed by saponification, gave the 6-sulfate derivative, whereas selective 6-O-benzoylation, followed by O-sulfonation and saponification, afforded the 4-sulfate derivative as their sodium salts.

Unexpected stereochemical outcome of activated 4,6-O-benzylidene derivatives of the 2-deoxy-2-trichloroacetamido-D-galacto series in glycosylation reactions during the synthesis of a chondroitin 6-sulfate trisaccharide methyl glycoside

The synthesis of methyl (beta-D-glucopyranosyluronic acid)-(1-->3)-(2-acetamido-2-deoxy-6-O-sulfonato-beta-D-galactopyr anosyl)-(1-->4)-(beta-D-glucopyranosid)uronate trisodium salt, a chondroitin 6-sulfate trisaccharide derivative, is described. Loss of stereocontrol in glycosylation reactions involving activated 4,6-O-benzylidene derivatives of the 2-deoxy-2-trichloroacetamido-D-galacto series and D-glucuronic acid-derived acceptors was highlighted. This draw-back was overcome through the use of phenyl 3,4,6-tri-O-acetyl-2-deoxy-1-thio-2-trichloroacetamido-beta-D-gala ctopyranoside, which afforded the desired beta-linked disaccharide derivative in high yield with an excellent stereoselectivity. This later was submitted to acid-catalyzed methanolysis, followed by benzylidenation, and condensed with methyl 2,3,4-tri-O-benzoyl-1-O-trichloroacetimidoyl-alpha-D-glucopyran uronate to afford the expected trisaccharide derivative. Subsequent transformation of the N-trichloroacetyl group into N-acetyl, mild acid hydrolysis, selective O-sulfonation at C-6 of the amino sugar moiety, and saponification afforded the target molecule as its sodium salt in high yield.