Modular Synthesis of Heparin Oligosaccharides - …

In summary, the yields of heparin/HS oligosaccharide by glycosylation through polymer-supported synthesis decrease drastically as the chains grow longer. This is a serious challenge to any efforts at automation. Novel chemistry needs to be developed to significantly enhance the glycosylation yields on polymer support without resorting to the use of large excesses of donors. Until this becomes reality, solution-phase synthesis remains the preferred method for preparing complex heparin/HS oligosaccharides.

of heparin-like oligosaccharides on ..

T1 - Toward the chemoenzymatic synthesis of heparan sulfate oligosaccharides

Synthesis of Heparin Oligosaccharides | Request PDF

Besides being compatible with the trichloroacetimidate donors, the silyl protecting group is robust and has also been applied with thioglycosides under various activating systems.,, The Boons group used this strategy to prepare disaccharide building blocks for their heparin/HS oligosaccharide synthesis (). Glycosylation of 1-thioglycoside donor 120 with the TDS-protected acceptor 121 formed the latent disaccharide 122. After oxidation and protecting group manipulation, the TDS group in 122 was removed and the resulting hemiacetal was converted into the trichloroacetimidate disaccharide donor 123. Eight disaccharide building blocks were prepared in this manner and were used to construct a panel of 11 heparin/HS tetrasaccharides and 1 hexasaccharide having different backbone structures and sulfation patterns. These tetrasaccharides were used to probe the important structural features of HS for inhibiting β-secretase, a protease considered to be involved in the development of Alzheimer’s disease.

Chemoenzymatic Synthesis of Heparin Oligosaccharides …

The Bonnaffé group developed an impressive synthesis of a heparin dodecamer by the active–latent strategy, using the allyl glycoside and glycosyl trichloroacetimidate combination. To improve the overall synthetic efficiencies, a PMB group was employed to protect the 4-position at the nonreducing end of the oligosaccharide intermediate. This substituent could be removed selectively to expose a free hydroxyl group for further elongation of the chain. In this synthesis, the PMB-derivatized latent allyl disaccharide 103 was first transformed into a trichloroacetimidate donor, 105, and the allyl disaccharide acceptor 104 (). Glycosylation of acceptor 104 by imidate 105 generated the latent allyl tetrasaccharide, which was then modified to an active trichloroacetimidate donor 106 (). The reaction of 106 with tetrasaccharide 107, followed by removal of the PMB group at the nonreducing end, and another round of glycosylation, furnished the dodecasaccharide 108 in 45% overall yield from the acceptor 107. After completion of the backbone, deprotection and sulfation were performed. O-Deacetylation by potassium carbonate, and reduction with 1,3-propanedithiol, followed by simultaneous O- and N-sulfation with the sulfur trioxide–pyridine complex gave the sulfated dodecamer. The simultaneous sulfation with pyridine–SO3 of the hydroxyl and amino groups did not proceed to completion. A second round of sulfation with pyridine–SO3 in basified water was necessary to complete the sulfation., Hydrolysis of the methyl esters, followed by hydrogenolysis, gave the fully deprotected dodecamer 109, which is the longest heparin oligosaccharide yet prepared by chemical synthesis.

T1 - Divergent heparin oligosaccharide synthesis with preinstalled sulfate esters
T1 - Toward the assembly of heparin and heparan sulfate oligosaccharide libraries

Toward the chemoenzymatic synthesis of heparan …

Heparin is known as a widely used anticoagulant drug since the 1930s. Heparin and heparan sulfate (HS) are highly sulfated polysaccharides that consist of a repeating disaccharide unit of glucosamine and glucuronic (GlcA) or iduronic acid (IdoA). The polydispersity of the saccharide sequence as well as the polyheterogeneity of the sulfation pattern make the study of this type of carbohydrate a formidable task. Instead of traditional extraction from animal mucus, we use the chemoenzymatic approach to synthesize homogeneous heparin oligosaccharides. The synthetic low molecular weight heparin was proven anti-FXa activity with reversible anticoagulant activity. In addition to secure the supply chain, the extra benefits aid future clinical usage of synthetic heparin drug. On the other side, the availability of synthetic pure common and less abundant HS oligosaccharides can serve as heparin component standards to secure the drug safety. Take the advantage of chemoenzymatic synthesis, the sufficient amount of structurally tailored oligosaccharide reagents are accessible. To investigate the interaction between HS and proteins, several oligosaccharide probes were successfully developed. Firstly, a synthesized heptasaccharide was used to co-crystalize with 2-O-sulfotransferase (2-OST) and probe the molecular basis of specificity. 2-OST was found to recognize N-sulfo and exclude 6-O-sulfo group of substrates, supporting the biosynthetic hypothesis 2-O-sulfation occurs after N-sulfation and prior to 6-O-sulfation. Secondly, we designed and synthesized the active heparan sulfate oligosaccharide probe carrying a diazoacetyl group. The resultant oligosaccharides demonstrate inhibitory activity and structural selectivity toward HS biosynthetic enzyme 2-OST and 3-OST, respectively. Thirdly, 13C-labeled saccharide was introduced at the desired site of the oligosaccharide to enhance the intensity of NMR signals. The labeled reagents facilitate directly analysis the binding between specific saccharide and protein. Finally, nuclear magnetic resonance analyses were performed to obtain coupling constants and full chemical shift assignments of all synthetic oligosaccharides. Comparing to relatively rigid GlcA, IdoA shows structural plasticity and diverse conformational preference in response to different sulfation patterns, which may be critical for various protein specific binding. The success of these projects assists the fundamental understand of HS-protein interaction as well as the design of next generation heparin-based therapeutics.

T1 - Preparation and characterization of 15N-enriched, size-defined heparan sulfate precursor oligosaccharides

Synthesis of Heparin Oligosaccharides., ChemInform | …

Heparan sulfate (HS) and heparin are highly sulfated polysaccharides exhibiting essential physiological functions. The sulfation patterns determine the functional selectivity for HS and heparin. Chemical synthesis of HS, especially those larger than a hexasaccharide, remains challenging. Enzymatic synthesis of HS has recently gained momentum. Here we describe the divergent assembly of HS heptasaccharides and nonasaccharides from a common hexasaccharide precursor. The hexasaccharide precursor was synthesized via a chemical method. The subsequent elongation, sulfation and epimerization were completed by glycosyltransferases, HS sulfotransferases and epimerase. Using the synthesized heptasaccharides, we discovered that the iduronic acid is critical for binding to fibroblast growth factor-2. We also designed a synthetic path to prepare a nonasaccharide with an antithrombin-binding affinity of 3 nM. Our method demonstrated the feasibility of combining chemical and enzymatic synthesis to prepare structurally defined HS oligosaccharides with desired biological activities.

STRUCTURAL CHARACTERIZATION OF OLIGOSACCHARIDES AND UNDERSTANDING HEPARAN SULFATE-PROTEIN INTERACTIONS

Chemoenzymatic synthesis of heparin oligosaccharides …

In addition to their roles in dictating stereochemistry, protecting groups are widely used to control the location of sulfate groups. With the high level of functionality in heparin/HS oligosaccharides, and the large number of protecting groups employed, syntheses must be suitably designed to prevent the premature removal of a protecting group.