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Fondaparinux, a clinically approved anticoagulant pentasaccharide for the treatment of thrombotic diseases, displays better efficacy and biosafety than other heparin-based anticoagulant drugs. However, there is no suitable antidote available for fondaparinux to efficiently manage its potential bleeding risks, thereby precluding its widespread use. Herein, we describe a convergent and stereocontrolled approach to efficiently synthesize an aminopentyl-functionalized pentasaccharide, which is further used to prepare fondaparinux-based biotin conjugates and clusters. Biological activity evaluation demonstrates that the anticoagulant activity of the fondaparinux-based biotin conjugate and trimer is, respectively, neutralized by avidin and protamine as effective antidotes. This work suggests that our synthetic biotin conjugate and trimer have potential for the development of neutralizable and safe anticoagulant drugs.

An efficient and simple approach for stereoselective synthesis of β-Kdo C-glycosides was described, which relies on easily available peracetylated anomeric acetate or anomeric 2-pyridyl sulfide to couple with carbonyl compounds via SmI2-mediated Reformatsky reactions. The utility of this methodology is exemplified by the streamlined synthesis of a practical β-Kdo C-glycoside with an anomeric aminopropyl linker to conjugate with other biomolecules for further biological studies.

A diversity-oriented chemoenzymatic approach for the collective preparation of sulfated core 2 O-GalNAc glycans and their nonsulfated counterparts was described. A sulfated trisaccharide and a nonsulfated trisaccharide were chemically synthesized by combining flexible protected group manipulations and sequential one-pot glycosylations. The divergent enzymatic extension of these two trisaccharides, using a panel of robust glycosyltransferases that can recognize sulfated substrates and differentiating the branches with specifically designed glycosylation sequences to achieve regioselective sialylation, provided 36 structurally well-defined O-GalNAc glycans.

Glycosylation of proteins is a complicated post-translational modification. Despite the significant progress in glycoproteomics, accurate functions of glycoproteins are still ambiguous owing to the difficulty in obtaining homogeneous glycopeptides or glycoproteins. Here, we describe a streamlined chemoenzymatic method to prepare complex glycopeptides by integrating hydrophobic tag-supported chemical synthesis and enzymatic glycosylations. The hydrophobic tag is utilized to facilitate peptide chain elongation in the liquid phase and expeditious product separation. After removal of the tag, a series of glycans are installed on the peptides via efficient glycosyltransferase-catalyzed reactions. The general applicability and robustness of this approach are exemplified by efficient preparation of 16 well-defined SARS-CoV-2 O-glycopeptides, 4 complex MUC1 glycopeptides, and a 31-mer glycosylated glucagon-like peptide-1. Our developed approach will open up a new range of easy access to various complex glycopeptides of biological importance.

Bioactive polysaccharides from natural resources target various biological processes and are increasingly used as potential target molecules for drug development. However, the accessibility of branched and long complex polysaccharide active domains with well-defined structures remains a major challenge. Herein we describe an efficient first total synthesis of a highly branched heptadecasaccharide moiety of the native bioactive galectin-3-targeting polysaccharide from Carthamus tinctorius L. as well as shorter fragments of the heptadecasaccharide. The key feature of the approach is that a photo-assisted convergent [6+4+7] one-pot coupling strategy enables rapid assembly of the heptadecasaccharide, whereby a photoremovable o-nitrobenzyl protecting group is used to generate the corresponding acceptor for glycosylation in situ upon ultraviolet radiation. Biological activity tests suggest that the heptadecasaccharide can target galectin-3 and inhibit pancreatic cancer cell growth.

Glycosite-specific antibody‒drug conjugatess (gsADCs), harnessing Asn297

A diversity-oriented chemoenzymatic approach for the collective preparation of sulfated core 2

An efficient approach for the facile synthesis of a potent vaccine adjuvant RC-529 is described. The synthetic strategy relies on the flexible use of orthogonal protecting groups, which makes it possible to accomplish selective phosphorylation, glycosylation and acylation, respectively. In addition, the use of readily cleaved 2-naphthylmethyl (Nap) ether and allyl esters as permanent protecting groups greatly facilitates the final global deprotection steps to obtain pure RC-529. This work will contribute to the synthesis of lipid A and its derivatives.

Guillain–Barré syndrome is often caused by Campylobacter jejuni infection that has induced antibodies to the lipo-oligosaccharide (LOS) that cross-react with gangliosides at peripheral nerves causing polyneuropathy. To examine fine specificities of anti-ganglioside antibodies and develop a more robust platform for diagnosis and disease monitoring, we developed a chemoenzymatic approach that provided an unprecedented panel of oligosaccharides composed of the inner-core of the LOS of C. jejuni extended by various ganglioside mimics. The compounds and corresponding ganglio-oligosaccharides were printed as a microarray to examine binding specificities of lectins, anti-ganglioside antibodies, and serum antibodies of GBS patients. Although lectins and anti-ganglioside antibodies did not differentiate the ganglio-oligosaccharides and mimics, the patient serum samples bound much more strongly to the ganglioside mimics. The data indicate that antibodies have been elicited to a foreign epitope that includes a heptosyl residue unique of bacterial LOS and that these antibodies subsequently cross-react with lower affinity to gangliosides. The microarray detected anti-GM1a antibodies with high sensitivity and will be attractive for diagnosis, disease monitoring, and immunological research.

Progress in glycoscience is hampered by a lack of well-defined complex oligosaccharide standards that are needed to fabricate the next generation of microarrays, to develop analytical protocols to determine exact structures of isolated glycans, and to elucidate pathways of glycan biosynthesis. We describe here a chemoenzymatic methodology that makes it possible, for the first time, to prepare any bi-, tri-, and tetra-antennary asymmetric N-glycan from a single precursor. It is based on the chemical synthesis of a tetra-antennary glycan that has N-acetylglucosamine (GlcNAc), N-acetyllactosamine (LacNAc), and unnatural Galα(1,4)-GlcNAc and Manβ(1,4)-GlcNAc appendages. Mammalian glycosyltransferases recognize only the terminal LacNAc moiety as a substrate, and thus this structure can be uniquely extended. Next, the β-GlcNAc terminating antenna can be converted into LacNAc by galactosylation and can then be enzymatically modified into a complex structure. The unnatural α-Gal and β-Man terminating antennae can sequentially be decaged by an appropriate glycosidase to liberate a terminal β-GlcNAc moiety, which can be converted into LacNAc and then elaborated by a panel of glycosyltransferases. Asymmetric bi- and triantennary glycans could be obtained by removal of a terminal β-GlcNAc moiety by treatment with β-N-acetylglucosaminidase and selective extension of the other arms. The power of the methodology is demonstrated by the preparation of an asymmetric tetra-antennary N-glycan found in human breast carcinoma tissue, which represents the most complex N-glycan ever synthesized. Multistage mass spectrometry of the two isomeric triantennary glycans uncovered unique fragment ions that will facilitate identification of exact structures of glycans in biological samples.

The studies of 3-deoxy-d-manno-octulosonic acid (KDO) have been hindered due to its limited availability. Herein, an efficient enzymatic system for the facile synthesis of KDO from easy-to-get starting materials is described. In this one-pot three-enzyme (OPME) system, d-ribulose 5-phosphate, which was prepared from d-xylose, was employed as starting materials. The reaction process involves the isomerization of d-ribulose 5-phosphate to d-arabinose 5-phosphate catalyzed by d-arabinose 5-phosphate isomerase (KdsD), the aldol condensation of d-arabinose 5-phosphate and phosphoenolpyruvate (PEP) catalyzed by KDO 8-phosphate synthetase (KdsA), and the hydrolysis of KDO-8-phosphate catalyzed by KDO 8-phosphate phosphatase (KdsC). By using this OPME system, 72% isolated yield was obtained. The obtained KDO was further transferred to lipid A by KDO transferase from Escherichia coli (WaaA).

Glycan-binding proteins (GBPs) play critical roles in diverse cellular functions such as cell adhesion, signal transduction and immune response. Studies of the interaction between GBPs and glycans have been hampered by the availability of high throughput and high-content technologies. Here we report multiplex glycan bead array (MGBA) that allows simultaneous analyses of 384 samples and up to 500 glycans in a single assay. The specificity, sensitivity and reproducibility of MGBA are evaluated using 39 plant lectins, 13 recombinant anti-glycan antibodies, and mammalian GBPs. We demonstrate the utility of this platform by the analyses of natural anti-glycan IgM and IgG antibodies in 961 human serum samples and the discovery of anti-glycan antibody biomarkers for ovarian cancer. Our data indicate that the MGBA platform is particularly suited for large population-based studies that require the analyses of large numbers of samples and glycans., The low throughput or content of current methods for the analysis of glycans-glycan binding proteins (GBPs) interactions hampers their clinical applications. Here, the authors conjugate synthesized glycans to Luminex beads to detect GBPs and apply it for the discovery of ovarian cancer biomarkers.

Dihydroxyacetone phosphate (DHAP)-dependent aldolases have been intensively studied and widely used in the synthesis of carbohydrates and complex polyhydroxylated molecules. However, strict specificity toward donor substrate DHAP greatly hampers their synthetic utility. Here, we transformed DHAP-dependent aldolases-mediated by in vitro reactions into bioengineered Escherichia coli (E. coli). Such flask-to-cell transformation addressed several key issues plaguing in vitro enzymatic synthesis: (1) it solves the problem of DHAP availability by in vivo-hijacking DHAP from the glycolysis pathway of the bacterial system, (2) it circumvents purification of recombinant aldolases and phosphatase, and (3) it dephosphorylates the resultant aldol adducts in vivo, thus eliminating the additional step for phosphate removal and achieving in vivo phosphate recycling. The engineered E. coli strains tolerate a wide variety of aldehydes as acceptor and provide a set of biologically relevant polyhydroxylated molecules in gra...

Uridine 5'-diphosphate-glucuronic acid (UDP-GlcA) and UDP-galacturonic acid (UDP-GalA), the unique carboxylic acid-formed sugar nucleotides, are key precursors involved in the biosynthesis of numerous cell components. Limited availability of those components has been hindering the development of efficient ways towards facile synthesis of bioactive glycans such as glycosaminoglycans. In current study, we biochemically characterized two UDP-sugar pyrophosphorylases from Arabidopsis thaliana (AtUSP) and Bifidobacterium infantis ATCC15697 (BiUSP), and compared their activities towards a panel of sugar-1-phosphates and derivatives. Both enzymes showed significant pyrophosphorylation activities towards GlcA-1-phosphate, and AtUSP also exhibited comparable activity towards GalA-1-phosphate. By combining with monosaccharide-1-phosphate kinases, we have developed an efficient and facile one-pot three-enzyme approach to quickly obtain hundreds milligrams of UDP-GlcA and UDP-GalA.

The anticoagulant pentasaccharide fondaparinux was synthesized using an improved and optimized synthetic strategy including a convergent [3+2] coupling approach, orthogonal protecting groups and various glycosyl donors. The new methods of glycosylation were also used for controlling the stereochemical configuration and improving the yield of the glycosylation. In addition, HPLC and NMR methods to monitor the process of total synthesis of fondaparinux were employed. This work provides a comprehensive elaboration for the synthesis and analysis of fondaparinux based on related literature, as well as abundant information for the synthesis of heparin-like oligosaccharides.

A divergent chemoenzymaytic approach for the preparation of core-fucosylated and core-unmodified asymmetrical N-glycans from a common advances precursor is described. An undecasaccharide was synthesized by sequential chemical glycosylations of an orthogonally protected core fucosylated hexasaccharide that is common to all mammalian core fucosylated N-glycans. Antennae-selective enzymatic extension of the undecasaccharide using a panel of glycosyl transferases afforded core fucosylated asymmetrical triantennary N-glycan isomers, which are potential biomarkers for breast cancer. A unique aspect of our approach is that a fucosidase (FucA1) has been identified that selectively can cleave a core-fucoside without affecting the fucoside of a sialyl Lewis(X) epitope to give easy access to core-unmodified compounds.

Protein O -GlcNAc glycosylation is a ubiquitous post-translational modification in metazoans. O -GlcNAcase (OGA), which is responsible for removing O -GlcNAc from serine or threonine residues, plays a key role in O -GlcNAc metabolism. Potent and selective O -GlcNAcase (OGA) inhibitors are useful tools for investigating the role of this modification in a broad range of cellular processes, and may also serve as drug candidates for treatment of neurodegenerative diseases. Biological screening of the gluco-configured tetrahydroimidazopyridine derivatives identified a compound as a potent and competitive inhibitor of human O -GlcNAcase (OGA) with a K i of 5.9 μM, and it also displayed 28-fold selectivity for human OGA over human lysosomal β-hexosaminidase A (Hex A, K i = 163 μM). In addition, cell-based assay revealed that this compound was cell-permeant and effectively induced cellular hyper- O -GlcNAcylation at 10 μM concentration.

Multivalent interaction between boronic acids immobilized on Quartz Crystal Microbalance (QCM) sensor surface and the carbohydrates modified Au - nanoparticle (AuNP) has been demonstrated for the development of a sensitive carbohydrate biosensor. Briefly, a boronic acid - containing polymer (boropolymer) as multivalent carbohydrate receptor was oriented immobilized on the cysteamine coated electrode through isourea bond formation. Carbohydrates were conjugated to AuNPs to generate a multivalent carbohydrates moiety to amplify the response signal. Thus, the binding of the carbohydrate conjugated AuNPs to the boropolymer surface are multivalent which could simultaneously increase the binding affinity and specificity. We systematically studied the binding between five carbohydrate conjugated AuNPs and the boropolymer. Our studies show that the associate constant (Ka) was in the order of fucose < glucose < mannose < galactose < maltose. A linear response in the range from 23 µM to 3.83 mM was observed for mannose conjugated AuNPs and the boropolymer recognition elements, with the lower detection limit of 1.5 µM for the carbohydrate analytes. Furthermore, the multivalent binding between carbohydrates and boronic acids are reversible and allow the regeneration of boropolymer surface by using 1M acetic acid so as to sequentially capture and release the carbohydrate analytes.

Colitose, also known as 3,6-dideoxy-L-galactose or 3-deoxy-L-fucose, is one of only five naturally occurring 3,6-dideoxyhexoses. Colitose was found in lipopolysaccharide of a number of infectious bacteria, including Escherichia coli O55 & O111 and Vibrio cholera O22 & O139. To date, no colitosyltransferase (ColT) has been characterized, probably due to the inaccessibility of the sugar donor, GDP-colitose. In this study, starting with chemically prepared colitose, 94.6 mg of GDP-colitose was prepared via a facile and efficient one-pot two-enzyme system involving an L-fucokinase/GDP-L-Fuc pyrophosphorylase and an inorganic pyrophosphatase (EcPpA). WbgN, a putative ColT from E. coliO55:H5 was then cloned, overexpressed, purified and biochemically characterized by using GDP-colitose as a sugar donor. Activity assay and structural identification of the synthetic product clearly demonstrated that wbgN encodes an α1,2-ColT. Biophysical study showed that WbgN does not require metal ion, and is highly active at pH 7.5-9.0. In addition, acceptor specificity study indicated that WbgN exclusively recognizes lacto-N-biose (Galβ1,3-GlcNAc). Most interestingly, it was found that WbgN exhibits similar activity toward GDP-l-Fuc (kcat/Km= 9.2 min(-1)mM(-1)) as that toward GDP-colitose (kcat/Km= 12 min(-1)mM(-1)). Finally, taking advantage of this, type 1 H-antigen was successfully synthesized in preparative scale.

A biotinylated heparosan hexasaccharide was synthesized using a one-pot multi-enzyme strategy, in situ activation and transfer of N-trifluoroacetylglucosamine (GlcNTFA) to a heparin backbone significantly improved the synthetic efficiency. The biotinylated hexasaccharide could serve as a flexible core to diversify its conversion into heparan sulfate isoforms with potential biological applications and therapeutics.

A novel and facile synthesis of a series of the biologically significant iminosugar derivatives including 2-deoxynojirimycin, Miglustat and Miglitol is reported. The synthesis features a strategic double inversion mechanism for securing the desired stereochemistry at C5 position of such glucose-type carbohydrate mimetics, representing a practical and remarkable improvement on the previously reported method that suffers from the loss of the stereo-control during the reaction process.

An efficient one-pot three enzymes strategy for chemoenzymatic synthesis of ADP-d-glycero-β-d-manno-heptose (ADP-d, d-heptose) was reported using chemically synthesized d, d-heptose-7-phosphate and the ADP-d, d-heptose biosynthetic enzymes HldE and GmhB. Moreover, the result of investigating substrate specificity of the kinase action of HldE revealed that HldE had highly restricted substrate specificity towards structurally modified heptose-7-phosphate analogs.

Mutations in acid β-glucocerebrosidase (GCase) lead to the accumulation of the sphingolipid glucosylceramide, thereby resulting in Gaucher disease (GD). Active-site-specific competitive GCase inhibitors are effective pharmacological chaperones (PCs) that act as folding agents for mutant GCase folding in the endoplasmic reticulum. In this study, we prepared a series of glucoimidazole C2-substituent derivatives, and evaluated their inhibition and PC properties with GCase. A cell-based assay with patient-derived lymphoblasts (N370S or L444P mutations) demonstrated that administration of these compounds can significantly increase GCase activity. Interestingly, the 3,3-dimethyl-N-phenyl-4-amide-1-butyl-substituted moderate inhibitor 11 had the greatest effect on activity: 2.1-fold increase in N370S lymphoblasts at 2.5 μM and 1.2-fold increase in L444P at 0.5 μM following a three-day incubation. Computer docking studies and a protease protection assay were used to elucidate the ligand-enzyme interactions responsible for the chaperone activity of 11. Western blot and immuno-fluorescence assays verified restoration of GCase trafficking to the lysosome. Together, these results indicate that 11 is a promising PC for GD treatment and provide direct evidence of the mechanism of GCase chaperoning.

O-linked N-acetylglucosamine (O-GlcNAc) modification of serines/threonines on cytoplasmic proteins is a significant signal regulating cellular processes such as cell cycle, cell development, and cell apoptosis. O-GlcNAcase (OGA) is responsible for the removal of O-GlcNAc, and it thus plays a critical role in O-GlcNAc metabolism. Interestingly, OGA can be cleaved by caspase-3 into two fragments during apoptosis, producing an N-terminal fragment (1-413 a.a.), termed nOGA. Here, using 4-MU-GlcNAc (4-methylumbelliferyl 2-acetamido-2-deoxy-β-D-glucopyranoside) as substrate, we found that the nOGA fragment retains high glycosidase activity. To probe the role of nOGA in apoptosis, it is essential to develop a potent and specific nOGA inhibitor. However, many reported inhibitors active at nanomolar concentrations (including PUGNAc, STZ, GlcNAc-statin, and NAG-thiazoline) against full-length OGA were not potent for nOGA. Next, we screened a small triazole-linked carbohydrate library and first identified compound 4 (4-pyridyl-1-(2'-deoxy-2'-acetamido-β-D-glucopyranosyl)-1,2,3-triazole) as a potent and competitive inhibitor for nOGA. This compound shows 15-fold selectivity for nOGA (K(i) = 48 μM) over the full-length OGA (K(i) = 725 μM) and 10-fold selectivity over human lysosomal β-hexosaminidase AB (Hex AB) (K(i) = 502 μM). These results reveal that compound 4 can be used as a potent and selective inhibitor for probing the role of nOGA in biological systems.

Inhibition of glycoside hydrolases has widespread application in treatment of diabetes, viral infections, lysosomal storage diseases and cancers. Gluco-configured tetrahydroimidazopyridines are the most potent β-glucosidase inhibitors reported to date. Using transition state mimic strategy, a series of C2-substituted gluco-configured tetrahydroimidazopyridines were designed and synthesized. Compounds 3 (Ki = 0.64 nM) and 5 (Ki = 0.58 nM) showed stronger inhibitory potency against β-glucosidase. Maestro 9.1 was used to study the structure–activity relationships by docking the compounds into the β-glucosidase active sites.

Protein O-GlcNAcylation has been shown to play an important role in a number of biological processes, including regulation of the cell cycle, DNA transcription and translation, signal transduction, and protein degradation. O-GlcNAcase (OGA) is responsible for the removal of O-linked β- N -acetylglucosamine (O-GlcNAc) from serine or threonine residues, and thus plays a key role in O-GlcNAc metabolism. Potent OGA inhibitors are useful tools for studying the cellular processes of O-GlcNAc, and may be developed as drugs for the treatment neurodegenerative diseases. In this study, Cu(I)-catalyzed ‘Click’ cycloaddition reactions between glycosyl azides and alkynes were exploited to generate inhibitory candidates of OGA. Enzymatic kinetic screening revealed that compound 7 was a potent competitive inhibitor of human O-GlcNAcase ( K i = 185.6 μM). Molecular docking simulations of compound 7 into Cp OGA ( Clostridium perfringens OGA) suggested that strong π–π stacking interaction between the compound and W490 considerably contributed to improving the inhibitory activity.

Complex saccharides are highly diverse in structure and biological functions. Accordingly, they are essential for many fields of research. The development of efficient synthetic methodologies for their preparation has thus been in high demand. The chemical synthesis of complex oligo- and polysaccharides, however, is often limited to the milligram scale and is difficult to scale up. Enzymatic synthesis, in contrast, offers an alternative that overcomes these limitations due to the high catalytic activity, lack of undesirable side reactions, mild reaction conditions, and high regio- and stereoselectivity of enzymes. This chapter will outline the development and applications of the following three types of enzymes used in the enzymatic biosynthesis of complex carbohydrates: glycosidases, glycosynthases, and glycosyltransferases.