Synthesis of Anticoagulant Pentasaccharide Fondaparinux via 3,5-Dimethyl-4-(2'-phenylethynylphenyl)phenyl Glycosides

Rationally designed chemoenzymatic synthesis of heparan sulfate oligosaccharides with neutralizable anticoagulant activity and low severe complications

The identification of enzymes involved in biosynthesis of heparan sulfate (HS) and heparin and their successful application in chemoenzymatic synthesis have provided great impetus to rationally design well-defined oligosaccharides as ideal alternatives to animal-derived heterogeneous heparin anticoagulants clinically to treat clotting disorders. Herein, we revisited the substrate specificity of recombinant 2-O-sulfotransferases produced in different expression systems for the highly efficient chemoenzymatic synthesis of HS oligosaccharides containing the rare 2-O-sulfated GlcA (GlcA2S) residues, followed by further assembly into the highly sulfated HS dodecasaccharide (12-mer) and decasaccharide (10-mer) containing the antithrombin-binding domain and the trisulfated disaccharide (GlcA2S-GlcNS6S) units rarely found in natural heparin. The GlcA2S-containing HS 10-mer demonstrated both the effectively reversible anticoagulant activity similar to that of unfractionated heparin and the lower potential risk for life-threatening heparin-induced thrombocytopenia compared with enoxaparin, indicating its promising prospect as the next-generation HS/heparin-like anticoagulant therapeutics.

Precision Synthesis and Antiliver Fibrosis Activity of a Highly Branched Acidic 63-Mer Pectin Polysaccharide

Natural polysaccharides possess various biological functions and have become increasingly important as drug candidates for biomedical development. However, the accessibility to multiple-branched and large-sized acidic polysaccharides with well-defined structures and the identification of related active glycan domains remain challenging. Here, we report the precision synthesis of a highly branched acidic pectin polysaccharide up to a 63-mer containing 10 different glycosidic linkages from Lycium barbarum. The synthetic strategy relies on highly stereoselective modular assembly of an orthogonally protected decasaccharide backbone, efficient synthesis of three side chain glycans by the integration of stereocontrolled one-pot chemoselective glycosylations and a hydrogen-bond-mediated aglycone delivery approach, and convergent assembly of the target polysaccharide in a branched site-specific glycosylation manner via flexible orthogonal protecting group manipulations. Structure-activity relationship studies of synthetic polysaccharide 63-mer and its short fragments (9-mer, 10-mer, 11-mer, and 33-mer) suggest that the decasaccharide as an active glycan domain exhibits better antiliver fibrosis activity.

ZnI2-Mediated cis-Glycosylations of Various Constrained Glycosyl Donors: Recent Advances in cis-Selective Glycosylations

An efficient and versatile glycosylation methodology is crucial for the systematic synthesis of oligosaccharides and glycoconjugates. A direct intermolecular and an indirect intramolecular methodology have been developed, and the former can be applied to the synthesis of medium-to-long-chain glycans like that of nucleotides and peptides. The development of a generally applicable approach for the stereoselective construction of glycosidic bonds remains a major challenge, especially for the synthesis of 1,2-cis glycosides such as β-mannosides, β-L-rhamnosides, and β-D-arabinofuranosides with equatorial glycosidic bonds as well as α-D-glucosides with axial ones. This review introduces the direct formation of cis-glycosides using ZnI2-mediated cis-glycosylations of various constrained glycosyl donors, as well as the recent advances in the development of stereoselective cis-glycosylations.

Overview of the current procedures in synthesis of heparin saccharides

Natural heparin, a glycosaminoglycan consisting of repeating hexuronic acid and glucosamine linked by 1 → 4 glycosidic bonds, is the most widely used anticoagulant. To subvert the dependence on animal sourced heparin, alternative methods to produce heparin saccharides, i.e., either heterogenous sugar chains similar to natural heparin, or structurally defined oligosaccharides, are becoming hot subjects. Although the success by chemical synthesis of the pentasaccharide, fondaparinux, encourages to proceed through a chemical approach generating homogenous product, synthesizing larger oligos is still cumbersome and beyond reach so far. Alternatively, the chemoenzymatic pathway exhibited exquisite stereoselectivity of glycosylation and regioselectivity of modification, with the advantage to skip the tedious protection steps unavoidable in chemical synthesis. However, to a scale of drug production needed today is still not in sight. In comparison, a procedure of de novo biosynthesis in an organism could be an ultimate goal. The main purpose of this review is to summarize the current available/developing strategies and techniques, which is expected to provide a comprehensive picture for production of heparin saccharides to replenish or eventually to replace the animal derived products. In chemical and chemoenzymatic approaches, the methodologies are discussed according to the synthesis procedures: building block preparation, chain elongation, and backbone modification.

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.