Ultralow molecular weight (ULMW) heparins are sulfated glycans that are clinically used to treat thrombotic disorders. ULMW heparins range from 1500 to 3000 daltons, corresponding from 5 to 10 saccharide units. The commercial drug Arixtra (fondaparinux sodium) is a structurally homogeneous ULMW heparin pentasaccharide that is synthesized through a lengthy chemical process. Here, we report 10- and 12-step chemoenzymatic syntheses of two structurally homogeneous ULMW heparins (MW = 1778.5 and 1816.5) in 45 and 37% overall yield, respectively, starting from a simple disaccharide. These ULMW heparins display excellent in vitro anticoagulant activity and comparable pharmacokinetic properties to Arixtra, as demonstrated in a rabbit model. The chemoenzymatic approach is scalable and shows promise for a more efficient route to synthesize this important class of medicinal agent.

SUMMARY Microbiome-encoded β-glucuronidase (GUS) enzymes play important roles in human health by metabolizing drugs in the gastrointestinal (GI) tract. The numbers, types and diversity of these proteins in the human GI microbiome, however, remain undefined. We present an atlas of GUS enzymes comprehensive for the Human Microbiome Project GI database. We identify 3,013 total and 279 unique microbiome-encoded GUS proteins clustered into six unique structural categories. We assign their taxonomy, assess cellular localization, reveal the inter-individual variability within the 139 individuals sampled, and discover 112 novel microbial GUS enzymes. A representative in vitro panel of the most common GUS proteins by read abundances highlights structural and functional variabilities within the family, including their differential processing of smaller glucuronides and larger carbohydrates. These data provide a sequencing-to-molecular roadmap for examining microbiome-encoded enzymes essential to human health.

Low-molecular-weight heparins (LMWHs) are carbohydrate-based anticoagulants clinically used to treat thrombotic disorders, but impurities, structural heterogeneity or functional irreversibility can limit treatment options. We report a series of synthetic LMWHs prepared by cost-effective chemoenzymatic methods. The high activity of one defined synthetic LMWH against human factor Xa (FXa) was reversible in vitro and in vivo using protamine, demonstrating that synthetically accessible constructs can have a critical role in the next generation of LMWHs.

Heparan sulfate is a sulfated glycan that exhibits essential physiological functions. Interrogation of the specificity of heparan sulfate-mediated activities demands a library of structurally defined oligosaccharides. Chemical synthesis of large heparan sulfate oligosaccharides remains challenging. We report the synthesis of oligosaccharides with different sulfation patterns and sizes from a disaccharide building block using glycosyltransferases, heparan sulfate C 5 -epimerase, and sulfotransferases. This method offers a generic approach to prepare heparan sulfate oligosaccharides possessing predictable structures. Heparan sulfate (HS)3 is a unique class of macromolecular natural product that is present in large quantities on the mammalian cell surface and in the extracellular matrix. HS participates in regulating blood coagulation, embryonic development, and the inflammatory response and assists viral/bacterial infections. It consists of a repeating disaccharide unit of glucuronic acid (GlcUA) or iduronic acid (IdoUA) and glucosamine, both capable of carrying sulfo groups (1). The sulfation pattern of HS dictates its biological activity (2, 3). Heparin, a widely used anticoagulant drug, is a specialized form of highly sulfated HS. The diverse biological functions present considerable opportunities for exploiting HS or HS-protein conjugates for developing new classes of anticancer (4), antiviral (5), and improved anticoagulant drugs (6). Furthermore, a recent worldwide outbreak of contaminated heparin underscores the needs for synthetic heparins to replace those isolated from animal tissues (7). Chemical synthesis is a powerful tool to obtain structurally defined heparin/HS oligosaccharides. The most successful example is the total synthesis of an antithrombin-binding pentasaccharide (8). This pentasaccharide is marketed under the trade name Arixtra for the treatment of venous thromboembolic disorders. However, the chemical synthesis of oligosaccharides larger than an octasaccharide is extremely difficult, especially when multiple target structures are required for biological evaluation (8). An enzyme-based method offers a promising alternative approach to synthesize HS.The HS biosynthetic pathway involves multiple enzymes, including HS polymerase, epimerase, and sulfotransferases ( Fig. 1). HS polymerase is responsible for building the polysaccharide backbone, containing the repeating unit of -GlcUA-GlcNAc-. The backbone is then modified by N-deacetylase/N-sulfotransferase (having two separate domains exhibiting the activity of N-deacetylase and N-sulfotransferase, respectively), C 5 -epimerase (C 5 -epi, converting GlcUA to IdoUA), 2-O-sulfotransferase (2-OST), 6-O-sulfotransferase (6-OST) and 3-O-sulfotransferase (3-OST) to produce the fully elaborated HS. With the exception of HS polymerase, all of these biosynthetic enzymes have been expressed at high levels in Escherichia coli (1), permitting easy access to an abundance of enzymes. Using HS sulfotransferases and C 5 -epi, we previously developed a method ...

1.1. Types of Carbohydrates and Their Importance in the Chemical, Food, and Pharmaceutical Industries Carbohydrates used as large-scale feedstock in industry include starch, cellulose, sucrose, glucose, and fructose (Scheme 1); they provide a number of advantages for widespread application. Other important saccharides with promising properties for smallscale processes include chitin, chitosan, and uronic acidcontaining glycans. In this section, chemical, food, and pharmaceutical applications of these saccharides are reviewed.These carbohydrates are primarily obtained from renewable feedstocks made through photosynthetic pathways, that is, carbon fixation removing greenhouse gas from the environment. Furthermore, they do not contribute to fossil fuel consumption, therefore being greener than other raw materials. Cellulose and starch are among the most abundant polysaccharides in nature. The biological functions of cellulose and starch are very different, with starch acting as a reservoir of glucose storage for energy 8 and cellulose acting as a structural component in the cell. 9 The starch polymer has a backbone chain of α-D-(1→4)glucopyranose (amylose) with branches linked by α-D-(1→6)glucopyranose (amylopectin) that can be conveniently obtained from many important crops such as wheat, rice, maize, tapioca, potato, and sweet potato. 10 Starch is an economically important carbohydrate because of its partial solubility in water, digestibility by animals, and ability to be converted into other higher-value compounds (i.e., ethanol or Kojic acid) through fermentation. 11 Oxidation, esterification, hydroxyalkylation, hydrolysis, and cross-linking are the most common modifications for preparation of starch derivatives. 12 As a consequence, these derivatives have important applications in food, chemical, and energy industries, such as the preparation of plasticized films and composites, thickeners, and stabilizers for food preparation, and as a source of dextrins and glucose, prepared through enzymatic hydrolysis, for biofuel production. 13 Cellulose is a linear polymer composed entirely of β-D-(1→4)glucopyranose. It is the most abundant biopolymer on earth and the most environmentally friendly and sustainable raw material. It has been widely used as the primary source of paper and other applications including textiles, hydrogels for medical uses, films and thickeners, and bioethanol production. 9a,14 Chemical modifications of cellulose include oxidation, hydrolysis, alkylation, and composite synthesis with addition of other polymers. 15 Sucrose (β-D-fructofuranosyl-α-D-glucopyranoside) is a disaccharide widely found in plants and has been used as a sweetener for centuries. 16 Sucrose contains fructofuranose and glucopyranose that can be released by hydrolysis of its glycosidic bond. The enzymatic hydrolysis of sucrose produces a mixture of the two sugars, known as inverted sugars. Many research groups have put their efforts into optimizing new methods to obtain them. 17 These sugars are widely used in the foo...

Heparin (HP) and heparan sulfate (HS) play important roles in many biological events. Increasing evidence has shown that the biological functions of HP and HS can be critically dependent upon their precise structures, including the position of the iduronic acids and sulfation patterns. However, unraveling the HP code has been extremely challenging due to the enormous structural variations. To overcome this hurdle, we investigated the possibility of assembling a library of HP/HS oligosaccharides using a preactivation-based, one-pot glycosylation method. A major challenge in HP/HS oligosaccharide synthesis is stereoselectivity in the formation of the cis-1,4-linkages between glucosamine and the uronic acid. Through screening, suitable protective groups were identified on the matching glycosyl donor and acceptor, leading to stereospecific formation of both the cis-1,4- and trans-1,4-linkages present in HP. The protective group chemistry designed was also very flexible. From two advanced thioglycosyl disaccharide intermediates, all of the required disaccharide modules for library preparation could be generated in a divergent manner, which greatly simplified building-block preparation. Furthermore, the reactivity-independent nature of the preactivation-based, one-pot approach enabled us to mix the building blocks. This allowed rapid assembly of twelve HP/HS hexasaccharides with systematically varied and precisely controlled backbone structures in a combinatorial fashion. The speed and the high yields achieved in glycoassembly without the need to use a large excess of building blocks highlighted the advantages of our approach, which can be of general use to facilitate the study of HP/HS biology. As a proof of principle, this panel of hexasaccharides was used to probe the effect of backbone sequence on binding with the fibroblast growth factor-2 (FGF-2). A trisaccharide sequence of 2-O-sulfated iduronic acid flanked by N-sulfated glucosamines was identified to be the minimum binding motif and N-sulfation was found to be critical. This provides useful information for further development of more potent compounds towards FGF-2 binding, which can have potential applications in wound healing and anticancer therapy.

The sulfation at the 3-OH position of glucosamine is an important modification in forming structural domains for heparan sulfate to enable its biological functions. Seven 3-O-sulfotransferase isoforms in the human genome are involved in the biosynthesis of 3-O-sulfated heparan sulfate. As a rare modification present in heparan sulfate, the availability of 3-O-sulfated oligosaccharides is very limited. Here, we report the use of a chemoenzymatic synthetic approach to synthesize six 3-O-sulfated oligosaccharides, including three hexasaccharides and three octasaccharides. The synthesis was achieved by rearranging the enzymatic modification sequence to accommodate the substrate specificity of 3-O-sulfotransferase 3. We studied the impact of 3-O-sulfation on the conformation of the pyranose ring of 2-O-sulfated iduronic acid using NMR, and on the correlation between ring conformation and anticoagulant activity. We identified a novel octasaccharide that interacts with antithrombin and displays anti factor Xa activity. Interestingly, the octasaccharide displays a faster clearance rate than fondaparinux, an FDA approved pentasaccharide drug, in a rat model, making this octasaccharide a potential short acting anticoagulant drug candidate that could reduce bleeding risk. Having access to a set of critically important 3-O-sulfated oligosaccharides offers the potential to develop new heparan sulfate-based therapeutics.

Acetaminophen/paracetamol (APAP) overdose is the leading cause of drug-induced acute liver failure (ALF) in the United States and Europe. The progression of the disease is attributed to sterile inflammation induced by the release of high mobility group box 1 (HMGB1) and the interaction with receptor for advanced glycation end products (RAGE). A specific, effective, and safe approach to neutralize the proinflammatory activity of HMGB1 is highly desirable. Here, we found that a heparan sulfate (HS) octadecasaccharide (18-mer-HP or hepatoprotective 18-mer) displays potent hepatoprotection by targeting the HMGB1/RAGE axis. Endogenous HS proteoglycan, syndecan-1, is shed in response to APAP overdose in mice and humans. Furthermore, purified syndecan-1, but not syndecan-1 core protein, binds to HMGB1, suggesting that HMGB1 binds to HS polysaccharide side chains of syndecan-1. Last, we compared the protection effect between 18-mer-HP and N-acetyl cysteine, which is the standard of care to treat APAP overdose. We demonstrated that 18-mer-HP administered 3 hours after a lethal dose of APAP is fully protective; however, the treatment of N-acetyl cysteine loses protection. Therefore, 18-mer-HP may offer a potential therapeutic advantage over N-acetyl cysteine for late-presenting patients. Synthetic HS provides a potential approach for the treatment of APAP-induced ALF.