Synthesis and medical applications of oligosaccharides

Acceptor-Reactivity-Controlled Stereoconvergent Synthesis and Immunological Activity of a Unique Pentasaccharide from the Cell Wall Polysaccharide of Cutibacterium acnes C7

Bacterial cell-surface polysaccharides are involved in various biological processes and have attracted widespread attention as potential targets for developing carbohydrate-based drugs. However, the accessibility to structurally well-defined polysaccharide or related active oligosaccharide domains remains challenging. Herein, we describe an efficiently stereocontrolled approach for the first total synthesis of a unique pentasaccharide repeating unit containing four difficult-to-construct 1,2-cis-glycosidic linkages from the cell wall polysaccharide of Cutibacterium acnes C7. The features of our approach include: 1) acceptor-reactivity-controlled glycosylation to stereoselectively construct two challenging rare 1,2-cis-ManA2,3(NAc)2 (β-2,3-diacetamido-2,3-dideoxymannuronic acid) linkages, 2) combination use of 6-O-tert-butyldiphenylsilyl (6-O-TBDPS)-mediated steric shielding effect and ether solvent effect to stereoselectively install a 1,2-cis-glucosidic linkage, 3) bulky 4,6-di-O-tert-butylsilylene (DTBS)-directed glycosylation to stereospecifically construct a 1,2-cis-galactosidic linkage, 4) stereoconvergent [2+2+1] and one-pot chemoselective glycosylation to rapidly assemble the target pentasaccharide. Immunological activity tests suggest that the pentasaccharide can induce the production of proinflammatory cytokine TNF-α in a dose-dependent manner.

Total Synthesis of the Repeating Units of Highly Functionalized O-Antigens of Pseudomonas aeruginosa ATCC 27577, O10, and O19

The first total synthesis of the repeating units of the O-antigens of Pseudomonas aeruginosa ATCC 27577, O10, and O19 was achieved via a linear glycosylation strategy. This also represents the first synthesis of an oligosaccharide containing an α-linked N-acetyl-l-galactosaminuronic acid (l-GalpNAcA) unit. All of the glycosyl linkages, including three challenging 1,2-cis-glycosidic bonds of amino sugars, were effectively constructed with high to exclusive stereoselectivity, while orthogonal protection tactics were employed to facilitate regioselective glycosylations and the introduction of a variety of functionalities. An acetyl group migration phenomenon was found during the synthesis of the O-acylated repeating unit of the P. aeruginosa ATCC 27577 antigen. All synthetic targets carried an amino functional group in the linker at the reducing end, thus facilitating further regioselective elaboration and biological studies. The synthetic strategy established here should be useful for the preparation of other similar oligosaccharides.

Integrated chemoenzymatic synthesis of a comprehensive sulfated ganglioside glycan library to decipher functional sulfoglycomics and sialoglycomics

Ganglioside glycans are ubiquitous and complex biomolecules that are involved in a wide range of biological functions and disease processes. Variations in sialylation and sulfation render the structural complexity and diversity of ganglioside glycans, and influence protein-carbohydrate interactions. Structural and functional insights into the biological roles of these glycans are impeded due to the limited accessibility of well-defined structures. Here we report an integrated chemoenzymatic strategy for expeditious and systematic synthesis of a comprehensive 65-membered ganglioside glycan library covering all possible patterns of sulfation and sialylation. This strategy relies on the streamlined modular assembly of three common sialylated precursors by highly stereoselective iterative sialylation, modular site-specific sulfation through flexible orthogonal protecting-group manipulations and enzymatic-catalysed diversification using three sialyltransferase modules and a galactosidase module. These diverse ganglioside glycans enable exploration into their structure-function relationships using high-throughput glycan microarray technology, which reveals that different patterns of sulfation and sialylation on these glycans mediate their unique binding specificities.

Carbohydrate-DNA Conjugation Enabled by Glycosyl Radicals Generated from Glycosyl Sulfinates

Herein, we report a method that enables the synthesis of carbohydrate-DNA conjugates by radical addition. Key to the success is the use of readily available, bench-stable, and unprotected glycosyl sulfinates as precursors to glycosyl radicals. The redox neutral reaction proceeds under mild and simple conditions and tolerates a broad substrate scope. A small library of carbohydrate-DNA conjugates was prepared.

Methods of study on conformation of polysaccharides from natural products: A review

Polysaccharides from natural products play multiple roles and have extensive bioactivities in life process. Bioactivities of polysaccharides (e.g., Lentinan, Schizophyllan, Scleroglucan, Curdlan, Cinerean) have a close relation to their chain conformation. Compared to other types of polysaccharides, the conformation of β-glucan has been studied more. The major research methods of conformation of polysaccharides from natural products (Congo red experiment, circular dichroism spectrum, viscosity method, light scattering method, size exclusion chromatography, atomic force microscope), corresponding experimental schemes, and the external factors affecting polysaccharide conformation were reviewed in this paper. These research methods of conformation have been widely used, among which Congo red experiment and viscosity method are the most convenient ones to study the morphological changes of polysaccharide chains.

Controllable 1,3-Bis-Functionalization of 2-Nitroglycals with High Regioselectivity and Stereoselectivity Enabled by a H-Bond Catalyst

The selective modification of carbohydrates is significant for producing their unnatural analogues for drug discovery. C1-functionalization (glycosylation) and C1,C2-difunctionalization of carbohydrates have been well developed. In contrast, C3-functionalization or C1,C3-difunctionalization of carbohydrates remains rare. Herein, we report such processes that efficiently and stereoselectively modify carbohydrates. Specifically, we found that trifluoroethanol (TFE) could promote 1,3-bis-indolylation/pyrrolylation of 2-nitroglycals generated carbohydrate derivatives in up to 93% yield at room temperature; slightly reducing the temperature could install two different indoles at the C1- and C3-positions. Switching TFE to a bifunctional amino thiourea catalyst leads to the generation of C3 monosubstituted carbohydrates, which could also be used to construct 1,3-di-C-functionalized carbohydrates. This approach produced a range of challenging sugar derivatives (over 80 examples) with controllable and high stereoselectivity (single isomer for over 90% of the examples). The potential applications of the reaction were demonstrated by a set of transformations including the synthesis of bridged large-ring molecules and gram scale reactions. Biological activities evaluation demonstrated that three compounds exhibit a potent inhibitory effect on human cancer cells T24, HCT116, AGS, and MKN-45 with IC50 ranged from 0.695 to 3.548 μM.

Efficient O- and S-glycosylation with ortho-2,2-dimethoxycarbonylcyclopropylbenzyl thioglycoside donors by catalytic strain-release

We herein present a strain-release glycosylation method employing a rationally designed ortho-2,2-dimethoxycarbonylcyclopropylbenzyl (CCPB) thioglycoside donor. The donor is activated through the nucleophilic ring-opening of a remotely activable donor-acceptor cyclopropane (DAC) catalyzed by mild Sc(OTf)3. Our new glycosylation method efficiently synthesizes O-, N-, and S-glycosides, providing facile chemical access to the challenging S-glycosides. Because the activation conditions of conventional glycosyl donors and our CCPB thioglycoside are orthogonal, our novel donor is amenable to controlled one-pot glycosylation reactions with conventional donors for expeditious access to complex glycans. The strain-release glycosylation is applied to the assembly of a tetrasaccharide of O-polysaccharide of Escherichia coli O-33 in one pot and the synthesis of a 1,1'-S-linked glycoside oral galectin-3 (Gal-3) inhibitor, TD139, to demonstrate the versatility and effectiveness of the novel method for constructing both O- and S-glycosides.

Synthesis of C-Oligosaccharides via Ni-Catalyzed Reductive Hydroglycosylation

C-Oligosaccharides are metabolically stable surrogates of native glycans containing O/N/S-glycosidic linkages and thus have therapeutic potential. Here we report a straightforward approach to the synthesis of vinyl C-linked oligosaccharides via the Ni-catalyzed reductive hydroglycosylation of alkynyl glycosides with glycosyl bromides.

Total Synthesis of a Conjugation-Ready Tetrasaccharide Repeating Unit of Vibrio cholerae O:3 O-antigen Polysaccharide

Herein, we report the first total synthesis of the tetrasaccharide repeating unit of Vibrio cholerae O:3 O-antigen polysaccharide. The highly complex tetrasaccharide contains rare amino sugars such as d-bacillosamine and l-fucosamine, highly labile sugar ascarylose, and higher carbon sugar d-d-heptose. Stereoselective glycosylation of the notoriously reactive ascarylose with d-d-heptose, poor nucleophilicity of the axial C4-OH of l-fucosamine, and amide coupling are the key challenges encountered in the total synthesis, which was completed via a longest linear sequence of 23 steps in 4.2% overall yield.

Site-Selective C-O Bond Editing of Unprotected Saccharides

Glucose and its polyhydroxy saccharide analogs are complex molecules that serve as essential structural components in biomacromolecules, natural products, medicines, and agrochemicals. Within the expansive realm of saccharides, a significant area of research revolves around chemically transforming naturally abundant saccharide units to intricate or uncommon molecules such as oligosaccharides or rare sugars. However, partly due to the presence of multiple hydroxyl groups with similar reactivities and the structural complexities arising from stereochemistry, the transformation of unprotected sugars to the desired target molecules remains challenging. One such formidable challenge lies in the efficient and selective activation and modification of the C-O bonds in saccharides. In this study, we disclose a modular 2-fold "tagging-editing" strategy that allows for direct and selective editing of C-O bonds of saccharides, enabling rapid preparation of valuable molecules such as rare sugars and drug derivatives. The first step, referred to as "tagging", involves catalytic site-selective installation of a photoredox active carboxylic ester group to a specific hydroxyl unit of an unprotected sugar. The second step, namely, "editing", features a C-O bond cleavage to form a carbon radical intermediate that undergoes further transformations such as C-H and C-C bond formations. Our strategy constitutes the most effective and shortest route in direct transformation and modification of medicines and other molecules bearing unprotected sugars.

A computational investigation of galactopyranoside esters as antimicrobial agents through antiviral, molecular docking, molecular dynamics, pharmacokinetics, and bioactivity prediction

One of the most common viral infections worldwide is the Human Papilloma Virus (HPV) which has been linked to cancer and other diseases in many countries. Monosaccharide esters are significant in the field of carbohydrate chemistry because they are efficient in the synthesis of pharmacologically active compounds. Therefore, the present study aimed to perform thermodynamic, molecular docking and molecular dynamics study of a series of previously designed monosaccharaides, methyl β-d-galactopyranoside (MGP, 1) esters (2-10) with along with their physicochemical and pharmacokinetic properties. We have optimized the MGP esters employing the DFT study at the B3LYP/6-311 + G (d,p) level of theory. The subsequent analysis also investigated the electronic energies, enthalpies, entropies, polarizability, and natural bond orbital (NBO) of these modified esters. Then, MGP esters were docked into CTX-M-15 extended-spectrum beta-lactamase from Escherichia coli (PDB: 4HBT) and E2 DNA-binding domain from human papillomavirus type 31 (PDB: 1A7G), and the results revealed that most of the esters can efficiently bind to the target. Desmond was used to doing molecular dynamics simulations at 200 ns in addition to molecular docking to look at the binding conformational stability of the protein-ligand complex. Based on RMSD and RMSF, it was determined that the stability of the protein-ligand combination was maintained during the whole 200 ns simulations for all compounds. Finally, a pharmacokinetic study suggests that modified esters of MGP exhibited better pharmacokinetic characteristics and were less hazardous than the parent drug. This work demonstrated that potential MGP esters can efficiently bind to 4HBT and 1A7G proteins and opened avenues for the development of newer antimicrobial agents that can target dangerous pathogens.Communicated by Ramaswamy H. Sarma.

Chemical approaches for the stereocontrolled synthesis of 1,2-cis-β-D-rhamnosides

In carbohydrate chemistry, the stereoselective synthesis of 1,2-cis-glycosides remains a formidable challenge. This complexity is comparable to the synthesis of 1,2-cis-β-D-mannosides, primarily due to the adverse anomeric and Δ-2 effects. Over the past decades, to attain β-stereoselectivity in D-rhamnosylation, researchers have devised numerous direct and indirect methodologies, including the hydrogen-bond-mediated aglycone delivery (HAD) method, the synthesis of β-D-mannoside paired with C6 deoxygenation, and the combined approach of 1,2-trans-glycosylation and C2 epimerization. This review elaborates on the advancements in β-D-rhamnosylation and its implications for the total synthesis of tiacumicin B and other physiologically relevant glycans.

Advances in glycoside and oligosaccharide synthesis

The structural complexity of glycans poses a serious challenge in the chemical synthesis of glycosides, oligosaccharides and glycoconjugates. Glycan complexity, determined by composition, connectivity, and configuration far exceeds what nature achieves with nucleic acids and proteins. Consequently, glycoside synthesis ranks among the most complex tasks in organic synthesis, despite involving only a simple type of bond-forming reaction. Here, we introduce the fundamental principles of glycoside bond formation and summarize recent advances in glycoside bond formation and oligosaccharide synthesis.

Macromolecules: Synthesis, antimicrobial, POM analysis and computational approaches of some glucoside derivatives bearing acyl moieties

Macromolecules i.e., carbohydrate derivatives are crucial to biochemical and medical research. Herein, we designed and synthesized eight methyl α-D-glucopyranoside (MGP) derivatives (2-8) in good yields following the regioselective direct acylation method. The structural configurations of the synthesized MGP derivatives were analyzed and verified using multiple physicochemical and spectroscopic techniques. Antimicrobial experiments revealed that almost all derivatives demonstrated noticeable antifungal and antibacterial efficacy. The synthesized derivatives showed minimum inhibitory concentration (MIC) values ranging from 0.75 µg/mL to 1.50 µg/mL and minimum bactericidal concentrations (MBCs) ranging from 8.00 µg/mL to 16.00 µg/mL. Compound 6 inhibited Ehrlich ascites carcinoma (EAC) cell proliferation by 10.36% with an IC50 of 2602.23 μg/mL in the MTT colorimetric assay. The obtained results were further rationalized by docking analysis of the synthesized derivatives against 4URO and 4XE3 receptors to explore the binding affinities and nonbonding interactions of MGP derivatives with target proteins. Compound 6 demonstrated the potential to bind with the target with the highest binding energy. In a stimulating environment, a molecular dynamics study showed that MGP derivatives have a stable conformation and binding pattern. The MGP derivatives were examined using POM (Petra/Osiris/Molinspiration) bioinformatics, and as a result, these derivatives showed good toxicity, bioavailability, and pharmacokinetics. Various antifungal/antiviral pharmacophore (Oδ-, O'δ-) sites were identified by using POM investigations, and compound 6 was further tested against other pathogenic fungi and viruses, such as Micron and Delta mutants of SARS-CoV-2.

Divergent Enzymatic Assembly of a Comprehensive 64-Membered IgG N-Glycan Library for Functional Glycomics

N-Glycosylation, a main post-translational modification of Immunoglobulin G (IgG), plays a significant role in modulating the immune functions of IgG. However, the precise function elucidation of IgG N-glycosylation remains impeded due to the obstacles in obtaining comprehensive and well-defined N-glycans. Here, an easy-to-implement divergent approach is described to synthesize a 64-membered IgG N-glycan library covering all possible biantennary and bisected N-glycans by reprogramming biosynthetic assembly lines based on the inherent branch selectivity and substrate specificity of enzymes. The unique binding specificities of 64 N-glycans with different proteins are deciphered by glycan microarray technology. This unprecedented collection of synthetic IgG N-glycans can serve as standards for N-glycan structure identification in complex biological samples and the microarray data enrich N-glycan glycomics to facilitate biomedical applications.

One-pot Dess-Martin periodinane-mediated oxidative deprotection and olefination of trimethylsilyl-protected pyranosides and pyranoses

The selective functionalization of carbohydrates provides a powerful method for introducing structural complexity, allowing access to unique drug scaffolds with distinctive pharmaceutical profiles. Herein, we describe an efficient and selective carbon-carbon bond forming reaction of a variety of common trimethylsilyl-protected pyranosides and pyranoses at C-6 using a one-pot Dess-Martin periodinane-mediated oxidation deprotection. This is followed by addition of stabilized and non-stabilized ylides to generate alkenoate carbohydrates and related analogs in good to moderate yields. We also report on the rapid deprotection of the remaining trimethylsilyl ether groups in near quantitative yields using an acidic resin-mediated ethanolysis.

Utilization of glycosyltransferases as a seamless tool for synthesis and modification of the oligosaccharides-A review

Glycosyltransferases (GTs) catalyze the transfer of active monosaccharide donors to carbohydrates to create a wide range of oligosaccharide structures. GTs display strong regioselectivity and stereoselectivity in producing glycosidic bonds, making them extremely valuable in the in vitro synthesis of oligosaccharides. The synthesis of oligosaccharides by GTs often gives high yields; however, the enzyme activity may experience product inhibition. Additionally, the higher cost of nucleotide sugars limits the usage of GTs for oligosaccharide synthesis. In this review, we comprehensively discussed the structure and mechanism of GTs based on recent literature and the CAZY website data. To provide innovative ideas for the functional studies of GTs, we summarized several remarkable characteristics of GTs, including folding, substrate specificity, regioselectivity, donor sugar nucleotides, catalytic reversibility, and differences between GTs and GHs. In particular, we highlighted the recent advancements in multi-enzyme cascade reactions and co-immobilization of GTs, focusing on overcoming problems with product inhibition and cost issues. Finally, we presented various types of GT that have been successfully used for oligosaccharide synthesis. We concluded that there is still an opportunity for improvement in enzymatically produced oligosaccharide yield, and future research should focus on improving the yield and reducing the production cost.

DNA-Programmed Lipid Nanoreactors for Synthesis of Carbohydrate Mimetics by Fusion of Aqueous Sub-attoliter Compartments

Lipid nanoreactors are biomimetic reaction vessels (nanoreactors) that can host aqueous or membrane-associated chemical and enzymatic reactions. Nanoreactors provide ultra-miniaturization from atto- to zeptoliter volumes per reaction vessel with the major challenge of encoding and spatio-temporal control over reactions at the individual nanoreactor or population level, thereby controlling volumes several orders of magnitude below advanced microfluidic devices. We present DNA-programmed lipid nanoreactors (PLNs) functionalized with lipidated oligonucleotides (LiNAs) that allow programming and encoding of nanoreactor interactions by controlled membrane fusion, exemplified for a set of carbohydrate mimetics with mono- to hexasaccharide azide building blocks connected by click-chemistry. Programmed reactions are initiated by fusion of distinct populations of nanoreactors with individually encapsulated building blocks. A focused library of triazole-linked carbohydrate-Cy5 conjugates formed by strain-promoted azide-alkyne cycloadditions demonstrated LiNA-programmed chemistry, including two-step reaction schemes. The PLN method is developed toward a robust platform for synthesis in confined space employing fully programmable nanoreactors, applicable to multistep synthesis for the generation of combinatorial libraries with subsequent analysis of the molecules formed, based on the addressability of the lipid nanoreactors.

A Robust Copper-Catalyzed Cross-Coupling of Glycosyl Thiosulfonate and Boronic Acids Enables the Construction of Thioglycosides

An efficient and stereoretentive copper-catalyzed cross-coupling of glycosyl thiosulfonate and boronic acid for the construction of thioglycosides is described. The good functional group compatibility of this method allows the preparation of many bioactive aryl/alkenyl thioglycosides, including the hSGLT1 inhibitor.

Photoinduced C(sp3)-H Functionalization of Glycine Derivatives: Preparation of Unnatural α-Amino Acids and Late-Stage Modification of Peptides

ConspectusPeptides are essential components of living systems and contribute to critical biological processes, such as cell proliferation, immune defense, tumor formation, and differentiation. Therefore, peptides have attracted considerable attention as targets for the development of therapeutic products. The incorporation of unnatural amino acid residues into peptides can considerably impact peptide immunogenicity, toxicity, side effects, water solubility, action duration, and distribution and enhance the peptides' druggability. Typically, the direct modification of natural amino acids is a practical and effective approach for promptly obtaining unnatural amino acids. However, selective functionalization of multiple C(sp³)-H bonds with comparable chemical reactivities in the peptide side chains remains a formidable challenge. Furthermore, chemical modifications aimed at highly reactive (nucleophilic and aromatic) groups on peptide side chains can interfere with the biological activity of peptides.In recent years, the rapid advancement of photoinduced radical reactions has made photoredox radical-radical cross-coupling a practical approach for constructing C(sp³)-C(sp³) bonds under mild conditions. Glycine, a naturally occurring amino acid and the fundamental skeleton of all α-amino acids, provides a basis for the alkylated modification of its own α-C(sp³)-H bond under mild conditions. This Account describes our recent research endeavors for systematically investigating the photocatalytic α-C(sp³)-H alkylation of glycine derivatives via radical-radical coupling between N-aryl glycinate-derived radicals and various alkyl radicals. In 2018, we disclosed the photoinduced Cu-catalyzed decarboxylative α-C(sp³)-H alkylation of glycine derivatives. Subsequently, we developed a catalyst-free method for alkylating glycine derivatives and glycine residues in peptides via electron donor-acceptor (EDA)-complex-promoted single electron transfer. Moreover, we developed a photoinduced method for the radical alkylation of N-aryl glycinate α-C(sp³)-H bonds using unactivated alkyl chlorides (iodides) under photocatalyst-free conditions. Notably, by building on racemic alkylations of glycine derivatives and glycine-residue-containing peptides, we recently stereoselectively alkylated the N-aryl glycinate α-C(sp³)-H bond using a dual-functional Cu catalyst generated in situ for synthesizing a series of unnatural chiral α-amino and C-glycoamino acids.We have developed a series of methods for synthesizing unnatural amino acids through the α-C(sp³)-H alkylation of glycine derivatives using photoredox-promoted radical coupling as a key strategy. These methods are efficient and versatile and can be used for the late-stage modification of peptides in various contexts. Our work builds on the fundamental importance of glycine as the basic scaffold of all α-amino acids and highlights the potential of radical-based chemistry for developing chemical transformations in peptide synthesis. These findings have broad implications for chemical biology and may open doors for discovering peptide drugs and developing therapeutics.

Galactoside-Based Molecule Enhanced Antimicrobial Activity through Acyl Moiety Incorporation: Synthesis and In Silico Exploration for Therapeutic Target

In this study, a series of galactoside-based molecules, compounds of methyl β-d-galactopyranoside (MDGP, 1), were selectively acylated using 2-bromobenzoyl chloride to obtain 6-O-(2-bromobenzoyl) substitution products, which were then transformed into 2,3,4-tri-O-6-(2-bromobenzoyl) compounds (2-7) with various nontraditional acyl substituents. The chemical structures of the synthesized analogs were characterized by spectroscopic methods and physicochemical and elemental data analyses. The antimicrobial activities of the compounds against five human pathogenic bacteria and two phyto-fungi were evaluated in vitro and it was found that the acyl moiety-induced synthesized analogs exhibited varying levels of antibacterial activity against different bacteria, with compounds 3 and 6 exhibiting broad-spectrum activity and compounds 2 and 5 exhibiting activity against specific bacteria. Compounds 3 and 6 were tested for MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration) based on their activity. The synthesized analogs were also found to have potential as a source of new antibacterial agents, particularly against gram-positive bacteria. The antifungal results suggested that the synthesized analogs could be a potential source of novel antifungal agents. Moreover, cytotoxicity testing revealed that the compounds are less toxic. A structure-activity relationship (SAR) investigation revealed that the lauroyl chain [CH₃(CH₂)₁₀CO-] and the halo-aromatic chain [3(/4)-Cl.C₆H₄CO-] in combination with sugar, had the most potent activity against bacterial and fungal pathogens. Density functional theory (DFT)-calculated thermodynamic and physicochemical parameters, and molecular docking, showed that the synthesized molecule may block dengue virus 1 NS2B/NS3 protease (3L6P). A 150 ns molecular dynamic simulation indicated stable conformation and binding patterns in a stimulating environment. In silico ADMET calculations suggested that the designed (MDGP, 1) had good drug-likeness values. In summary, the newly synthesized MDGP analogs exhibit potential antiviral activity and could serve as a therapeutic target for dengue virus 1 NS2B/NS3 protease.

Total Synthesis of the Repeating Units of Proteus penneri 26 and Proteus vulgaris TG155 via a Common Disaccharide

Herein, we report the first total synthesis of the trisaccharide and tetrasaccharide repeating units of P. penneri 26 and P. vulgaris TG155, respectively, having a common disaccharide unit, 3-α-l-QuipNAc-(1 → 3)-α-d-GlcpNAc-(1 →. Striking features of the targets are the presence of rare sugar units, l-quinovosamine and l-rhamnosamine, all joined through α-glycosidic linkages. Major challenges in the formation of 1,2-cis glycosidic linkages in the case of d-glucosamine, l-quinovosamine, and d-galactosamine have been addressed.

Uridine Derivatives: Synthesis, Biological Evaluation, and In Silico Studies as Antimicrobial and Anticancer Agents

Nucleoside analogs are frequently used in the control of viral infections and neoplastic diseases. However, relatively few studies have shown that nucleoside analogs have antibacterial and antifungal activities. In this study, a fused pyrimidine molecule, uridine, was modified with various aliphatic chains and aromatic groups to produce new derivatives as antimicrobial agents. All newly synthesized uridine derivatives were analyzed by spectral (NMR, FTIR, mass spectrometry), elemental, and physicochemical analyses. Prediction of activity spectra for substances (PASS) and in vitro biological evaluation against bacteria and fungi indicated promising antimicrobial capability of these uridine derivatives. The tested compounds were more effective against fungal phytopathogens than bacterial strains, as determined by their in vitro antimicrobial activity. Cytotoxicity testing indicated that the compounds were less toxic. In addition, antiproliferative activity against Ehrlich ascites carcinoma (EAC) cells was investigated, and compound 6 (2',3'-di-O-cinnamoyl-5'-O-palmitoyluridine) demonstrated promising anticancer activity. Their molecular docking against Escherichia coli (1RXF) and Salmonella typhi (3000) revealed notable binding affinities and nonbonding interactions in support of this finding. Stable conformation and binding patterns/energy were found in a stimulating 400 ns molecular dynamics (MD) simulation. Structure-activity relationship (SAR) investigation indicated that acyl chains, CH₃(CH₂)₁₀CO-, (C₆H₅)₃C-, and C₂H₅C₆H₄CO-, combined with deoxyribose, were most effective against the tested bacterial and fungal pathogens. Pharmacokinetic predictions were examined to determine their ADMET characteristics, and the results in silico were intriguing. Finally, the synthesized uridine derivatives demonstrated increased medicinal activity and high potential for future antimicrobial/anticancer agent(s).

Unexpected Nucleophile Masking in Acyl Transfer to Sterically Crowded and Conformationally Restricted Galactosides

Design and synthesis of orthogonally protected monosaccharide building blocks are crucial for the preparation of well-defined oligosaccharides in a stereo- and regiocontrolled manner. Selective introduction of protecting groups to partially protected monosaccharides is nontrivial due to the often unpredictable electronic, steric, and conformational effects of the substituents. Abolished reactivity toward a commonly used Lewis base-catalyzed acylation of O-2 was observed in conformationally restricted 4,6-O-benzylidene-3-O-Nap galactoside. Investigation of analogous systems, crystallographic characterization, and quantum chemical calculations highlighted the overlooked conformational and steric considerations, the combination of which produces a unique passivity of the 2-OH nucleophile. Evaluating the role of electrophile counterion and auxiliary base in the acylation of the sterically crowded and conformationally restricted galactoside system revealed an alternative Brønsted base-driven reaction pathway via nucleophilic activation. Insights gained from this model system were utilized to access the target galactoside intermediate within the envisioned synthetic route. The acylation strategy described herein can be implemented in future syntheses of key monomeric building blocks with unique protecting group hierarchies.

Non-classical C-saccharide linkage of dehydroalanine: synthesis of C-glycoamino acids and C-glycopeptides

Herein, a non-classical C-saccharide linkage is reported via a C5 radical of pentose or C6 radical of hexose addition to Michael acceptors. C(sp³)-S cleaved glycosyl thianthrenium salts are developed as the glycosyl radical agents. The reaction provides an efficient toolkit to synthesize β-glycosyl substituted unnatural amino acids as well as for the late-stage C-saccharide modification of peptides.

In silico modelling of the function of disease-related CAZymes

In silico modelling of proteins comprises a diversity of computational tools aimed to obtain structural, electronic, and/or dynamic information about these biomolecules, capturing mechanistic details that are challenging to experimental approaches, such as elusive enzyme-substrate complexes, short-lived intermediates, and reaction transition states (TS). The present article gives the reader insight on the use of in silico modelling techniques to understand complex catalytic reaction mechanisms of carbohydrate-active enzymes (CAZymes), along with the underlying theory and concepts that are important in this field. We start by introducing the significance of carbohydrates in nature and the enzymes that process them, CAZymes, highlighting the conformational flexibility of their carbohydrate substrates. Three commonly used in silico methods (classical molecular dynamics (MD), hybrid quantum mechanics/molecular mechanics (QM/MM), and enhanced sampling techniques) are described for nonexpert readers. Finally, we provide three examples of the application of these methods to unravel the catalytic mechanisms of three disease-related CAZymes: β-galactocerebrosidase (GALC), responsible for Krabbe disease; α-mannoside β-1,6-N-acetylglucosaminyltransferase V (MGAT5), involved in cancer; and O-fucosyltransferase 1 (POFUT1), involved in several human diseases such as leukemia and the Dowling-Degos disease.

Design, Synthesis, In Silico and POM Studies for the Identification of the Pharmacophore Sites of Benzylidene Derivatives

Due to the uneven distribution of glycosidase enzyme expression across bacteria and fungi, glycoside derivatives of antimicrobial compounds provide prospective and promising antimicrobial materials. Therefore, herein, we report the synthesis and characterization of six novel methyl 4,6-O-benzylidene-α-d-glucopyranoside (MBG) derivatives (2–7). The structures were ascertained using spectroscopic techniques and elemental analyses. Antimicrobial tests (zone of inhibition, MIC and MBC) were carried out to determine their ability to inhibit the growth of different Gram-positive, Gram-negative bacteria and fungi. The highest antibacterial activity was recorded with compounds 4, 5, 6 and 7. The compounds with the most significant antifungal efficacy were 4, 5, 6 and 7. Based on the prediction of activity spectra for substances (PASS), compounds 4 and 7 have promising antimicrobial capacity. Molecular docking studies focused on fungal and bacterial proteins where derivatives 3 and 6 exhibited strong binding affinities. The molecular dynamics study revealed that the complexes formed by these derivatives with the proteins L,D-transpeptidase Ykud and endoglucanase from Aspergillus niger remained stable, both over time and in physiological conditions. Structure–activity relationships, including in vitro and in silico results, revealed that the acyl chains [lauroyl-(CH3(CH2)10CO-), cinnamoyl-(C6H5CH=CHCO-)], in combination with sugar, were found to have the most potential against human and fungal pathogens. Synthetic, antimicrobial and pharmacokinetic studies revealed that MBG derivatives have good potential for antimicrobial activity, developing a therapeutic target for bacteria and fungi. Furthermore, the Petra/Osiris/Molinspiration (POM) study clearly indicated the presence of an important (O1δ−----O2δ−) antifungal pharmacophore site. This site can also be explored as a potential antiviral moiety.

Development in the Concept of Bacterial Polysaccharide Repeating Unit-Based Antibacterial Conjugate Vaccines

The surface of cells is coated with a dense layer of glycans, known as the cell glycocalyx. The complex glycans in the glycocalyx are involved in various biological events, such as bacterial pathogenesis, protection of bacteria from environmental stresses, etc. Polysaccharides on the bacterial cell surface are highly conserved and accessible molecules, and thus they are excellent immunological targets. Consequently, bacterial polysaccharides and their repeating units have been extensively studied as antigens for the development of antibacterial vaccines. This Review surveys the recent developments in the synthetic and immunological investigations of bacterial polysaccharide repeating unit-based conjugate vaccines against several human pathogenic bacteria. The major challenges associated with the development of functional carbohydrate-based antibacterial conjugate vaccines are also considered.

Facile Preparation of L-Iduronic Acid and α-L-Iduronidation Using Methyl 1,2,3,4-Tetra-O-acetyl-α-L-iduronate as Glycosyl Donor

Methyl 1,2,3,4-tetra-O-acetyl-α-L-iduronate was prepared from methyl 1,2,3,4-tetra-O-β-D-glucuronate in two steps: Ferrier's photobromination and subsequent radical reduction with tris(trimethylsilyl)silane. The obtained methyl 1,2,3,4-tetra-O-acetyl-α-L-iduronate was a good glycosyl donor for the L-iduronidation when bis(trifluoromethanesulfonic)imide was employed as the activator. The reaction afforded the α-isomer as the major product, the configuration of which is the same as that of the L-iduronic acid unit in heparin and heparan sulfate.

Glycosyl Radical-Based Synthesis of C-Glycoamino Acids and C-Glycopeptides

Radical-based reactions usually exhibit excellent functional-group compatibilities due to their mild initiation conditions. Glycosyl radical involved C-glycosylation modifications are important strategies to achieve highly regio- and chemoselective constructions of C-glycosidic bonds or C-glycoside linkages of peptides and proteins. In this Concept, we cover recent developments in glycosyl radical-based synthesis of unnatural amino acids and late-stage modification of peptides and proteins, and provide a preliminary outlook on the possible development of this direction in the future.

Efficient Antibacterial/Antifungal Activities: Synthesis, Molecular Docking, Molecular Dynamics, Pharmacokinetic, and Binding Free Energy of Galactopyranoside Derivatives

The chemistry and biochemistry of carbohydrate esters are essential parts of biochemical and medicinal research. A group of methyl β-d-galactopyranoside (β-MGP, 1) derivatives was acylated with 3-bromobenzoyl chloride and 4-bromobenzoyl chloride in anhydrous N,N-dimethylformamide/triethylamine to obtain 6-O-substitution products, which were subsequently converted into 2,3,4-tri-O-acyl derivatives with different aliphatic and aromatic substituents. Spectroscopic and elemental data exploration of these derivatives confirmed their chemical structures. In vitro biological experiments against five bacteria and two fungi and the prediction of activity spectra for substances (PASS) revealed ascending antifungal and antibacterial activities compared with their antiviral activities. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) experiments were performed for two derivatives, 3 and 9, based on their antibacterial activities. Most of these derivatives showed >780% inhibition of fungal mycelial growth. Density functional theory (DFT) was used to calculate the chemical descriptors and thermodynamic properties, whereas molecular docking was performed against antibacterial drug targets, including PDB: 4QDI, 5A5E, 7D27, 1ZJI, 3K8E, and 2MRW, and antifungal drug targets, such as PDB: 1EA1 and 1AI9, to identify potential drug candidates for microbial pathogens. A 100 ns molecular dynamics simulation study revealed stable conformation and binding patterns in a stimulating environment by their uniform RMSD, RMSF, SASA, H-bond, and RoG profiles. In silico pharmacokinetic and quantitative structure−activity relationship (QSAR) calculations (pIC50 values 3.67~8.15) suggested that all the designed β-MGP derivatives exhibited promising results due to their improved kinetic properties with low aquatic and non-aquatic toxicities. These biological, structure−activity relationship (SAR) [lauroyl-(CH3(CH2)10CO-) group was found to have potential], and in silico computational studies revealed that the newly synthesized MGP derivatives are potential antibacterial/antifungal candidates and can serve as therapeutic targets for human and plant pathogens.

Synthesis of the Three Most Expensive l-Hexose Thioglycosides from d-Glucose

The biologically important l-hexoses, which are less widespread than d-hexoses, cannot be obtained from natural sources or can only be extracted very costly. Due to the complexity of their synthesis, their commercially available derivatives (which are sold mostly in free form) are also very expensive, which is further exacerbated by the current rapid rise in prices. In the present work, starting from the cheapest d-hexose, d-glucose, using inexpensive and readily available chemicals, a reaction pathway was developed in which the three most expensive l-hexoses (l-idose, l-altrose, and l-talose) were successfully prepared in orthogonally protected thioglycoside form, ready for glycosylation. The l-ido and l-talo derivatives were synthesized by C-5 epimerization of the corresponding 5,6-unsaturated thioglycosides. From the l-ido derivatives, the orthogonally protected thioglycosides of l-altrose were then prepared by C-4 epimerization. Different approaches to the preparation of the key intermediates, 5,6-unsaturated thioglycoside derivatives, were systematically investigated in the presence of various protecting groups (ether and ester) and using commercially available reagents.

Potential SARS-CoV-2 RdRp inhibitors of cytidine derivatives: Molecular docking, molecular dynamic simulations, ADMET, and POM analyses for the identification of pharmacophore sites

The RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2 is one of the optimum targets for antiviral drug design and development. The hydroxyl groups of cytidine structures were modified with different aliphatic and aromatic groups to obtain 5´-O-acyl and 2´,3´-di-O-acyl derivatives, and then, these derivatives were employed in molecular modeling, antiviral prediction, molecular docking, molecular dynamics, pharmacological and POM studies. Density functional theory (DFT) at the B3LYP/6-31G++ level analyzed biochemical behavior and molecular electrostatic potential (MESP) of the modified cytidine derivatives. The antiviral parameters of the mutated derivatives revealed promising drug properties compared with those of standard antiviral drugs. Molecular docking has determined binding affinities and interactions between the cytidine derivatives and SARS-CoV-2 RdRp. The modified derivatives strongly interacted with prime Pro620 and Lys621 residues. The binding conformation and interactions stability were investigated by 200 ns of molecular dynamics simulations and predicted the compounds to firmly dock inside the RdRp binding pocket. Interestingly, the binding residues of the derivatives were revealed in high equilibrium showing an enhanced binding affinity for the molecules. Intermolecular interactions are dominated by both Van der Waals and electrostatic energies. Finally, the pharmacokinetic characterization of the optimized inhibitors confirmed the safety of derivatives due to their improved kinetic properties. The selected cytidine derivatives can be suggested as potential inhibitors against SARS-CoV-2. The POM Theory supports the hypothesis above by confirming the existence of an antiviral (Oδ--O'δ-) pharmacophore site of Hits.

Extending the in vivo persistence of synthetic glycoconjugates using a serum-protein binder

Synthetic glycoconjugates are used in the development of vaccines and the design of inhibitors for glycan-protein interactions. The in vivo persistence of synthetic glycoconjugates is an important factor in their efficacy, especially when prolonged interactions with specific cell types may be required. In this study, we applied a strategy for non-covalent association of an active compound with serum proteins for extension of glycoconjugate half-life in serum. The small molecule, AG10, has previously been used to extend the half-life of small molecules through its high affinity for transthyretin (TTR), a serum protein. Using a tetravalent polyethylene glycol (PEG)-based scaffold we developed a synthetic strategy for glycoconjugates that allowed for controlled addition of multiple tags, such as a TTR affinity tag or fluorophore. We designed a version of AG10 modified at the pyrazole core, named GD10, amenable to our conjugation strategy and introduced to glycoconjugates using a tri-functional linker. This approach allowed for attachment of GD10 and fluorophore tags, as well as carbohydrate antigens. We then tested the influence of the GD10 tag on glycoconjugate half-life in vivo using a mouse model. Our results suggest that the combination of the GD10 tag and the PEG scaffold extended the half-life of glycoconjugates by as much as 10-fold when compared to proteins of similar molecular weight. The GD10 tag was able to extend the half-life of similar glycoconjugates by as much as 2-fold. We observed a role for the terminal saccharide residue of the carbohydrate antigen and confirmed that conjugates were able to penetrate multiple compartments in vivo including bone marrow, lymph nodes, and other organs. The introduction of the GD10 tag did not obstruct the ability of conjugates to interact with lectin receptors. We conclude that serum protein binders can be used to extend the persistence of glycoconjugates in vivo.

The total synthesis of rhynchosporosides via orthogonal one-pot glycosylation and stereoselective α-glycosylation strategies

The efficient and collective synthesis of rhynchosporosides causing scald diseases has been achieved, which features orthogonal one-pot glycosylation on the basis of PTFAI glycosylation, Yu glycosylation, and PVB glycosylation and merging reagent modulation and remote anchimeric assistance (RMRAA) α-glucosylation strategies. The issues inherent to the thioglycoside-based orthogonal one-pot glycosylation strategy, such as aglycone transfer, have been precluded by this orthogonal one-pot glycosylation strategy, which can streamline glycan chemical synthesis.

Insights into the Activation of Alkyne-Installed Glycosyl Donors with Dual Acidic Metal Catalysts: Reaction Pathway, Influencing Factors, and Enlightenment for Glycosylation

The activation of alkyne-installed glycosyl donors with dual acidic metal catalysts were studied. Lewis and/or π acidity-activated pathways were observed for alkynyl carbonate-, ester-, and ether-type donors, and π acidity-promoted reaction mode afforded higher efficiency and yields. The activation mode for a certain metal catalyst is determined by the nature of catalysts itself, protecting groups on sugar rings, type of sugars, and structure of aglycones. The discovery gives us valuable insights into the glycosylation of alkyne-containing donors.

Synthesis, antimicrobial, molecular docking and molecular dynamics studies of lauroyl thymidine analogs against SARS-CoV-2: POM study and identification of the pharmacophore sites

Nucleoside precursors and nucleoside analogs occupy an important place in the treatment of viral respiratory pathologies, especially during the current COVID-19 pandemic. From this perspective, the present study has been designed to explore and evaluate the synthesis and spectral characterisation of 5́-O-(lauroyl) thymidine analogs 2–6 with different aliphatic and aromatic groups through comprehensive in vitro antimicrobial screening, cytotoxicity assessment, physicochemical aspects, molecular docking and molecular dynamics analysis, along with pharmacokinetic prediction. A unimolar one-step lauroylation of thymidine under controlled conditions furnished the 5́-O-(lauroyl) thymidine and indicated the selectivity at C-5́ position and the development of thymidine based potential antimicrobial analogs, which were further converted into four newer 3́-O-(acyl)-5́-O-(lauroyl) thymidine analogs in reasonably good yields. The chemical structures of the newly synthesised analogs were ascertained by analysing their physicochemical, elemental, and spectroscopic data. In vitro antimicrobial tests against five bacteria and two fungi, along with the prediction of activity spectra for substances (PASS), indicated promising antibacterial functionality for these thymidine analogs compared to antifungal activity. In support of this observation, molecular docking experiments have been performed against the main protease of SARS-CoV-2, and significant binding affinities and non-bonding interactions were observed against the main protease (6LU7, 6Y84 and 7BQY), considering hydroxychloroquine (HCQ) as standard. Moreover, the 100 ns molecular dynamics simulation process was performed to monitor the behaviour of the complex structure formed by the main protease under in silico physiological conditions to examine its stability over time, and this revealed a stable conformation and binding pattern in a stimulating environment of thymidine analogs. Cytotoxicity determination confirmed that compounds were found less toxic. Pharmacokinetic predictions were investigated to evaluate their absorption, distribution, metabolism and toxic properties, and the combination of pharmacokinetic and drug-likeness predictions has shown promising results in silico. The POM analysis shows the presence of an antiviral (O1^δ-, O2^δ-) pharmacophore site. Overall, the current study should be of great help in the development of thymidine-based, novel, multiple drug-resistant antimicrobial and COVID-19 drugs.

Synthesis, antimicrobial, SAR, PASS, molecular docking, molecular dynamics and pharmacokinetics studies of 5'-O-uridine derivatives bearing acyl moieties: POM study and identification of the pharmacophore sites

Because of their superior antibacterial and pharmacokinetic capabilities, many nucleoside-based esters show potential against microorganisms, and may be used as pharmacological agents to address multidrug-resistant pathogenic problems. In this study, several aliphatic and aromatic groups were inserted to synthesize various 5'-O-decanoyluridine (2-5) and 5'-O-lauroyluridine derivatives (6-7) for antimicrobial, in silico computational, pharmacokinetic and POM (Petra/Osiris/Molinspiration). The chemical structures of the synthesized uridine derivatives were confirmed by physicochemical, elemental, and spectroscopic analyses. In vitro antimicrobial screening against five bacteria and two fungi, as well as the prediction of substance activity spectra (PASS), revealed that these uridine derivatives have promising antifungal properties when compared to the antibacterial activities. Density functional theory (DFT) was used to calculate the thermodynamic and physicochemical properties. Molecular docking was conducted against lanosterol 14a-demethylase CYP51A1 (3JUV) and Aspergillus flavus (1R4U) and revealed binding affinities and non-covalent interactions with the target. Then, a 150 ns molecular dynamic simulation was performed to confirm the behavior of the complex structure formed by microbial protein under in silico physiological conditions to examine its stability over time, which revealed a stable conformation and binding pattern in a stimulating environment of uridine derivatives. The acyl chain {CH₃(CH₂)₉CO-} and {CH₃(CH₂)₁₀CO-} in conjunction with sugar, was determined to have the most potent activity against bacterial and fungal pathogens in a structure-activity relationships (SAR) investigation. POM analyses were conducted with the presence of an antifungal (O ^δ- -- O' ^δ-) pharmacophore site. Overall, the present study might be useful for the development of uridine-based novel multidrug-resistant antimicrobial.

Total synthesis of Lentinus giganteus glycans with antitumor activities via stereoselective α-glycosylation and orthogonal one-pot glycosylation strategies

The accessibility to long, branched and complex glycans containing many 1,2-cis glycosidic linkages with precise structures remains a challenging task in chemical synthesis. Reported here is an efficient, stereoselective and orthogonal one-pot synthesis of a tetradecasaccharide and shorter sequences from Lentinus giganteus polysaccharides with antitumor activities. The synthetic strategy consists of: (1) newly developed merging reagent modulation and remote anchimeric assistance (RMRAA) α-(1→6)-galactosylation in a highly stereoselective manner, (2) DMF-modulated stereoselective α-(1→3)-glucosylation, (3) RMRAA stereoselective α-(1→6)-glucosylation, (4) several orthogonal one-pot glycosylations on the basis of N-phenyltrifluoroacetimidate (PTFAI) glycosylation, Yu glycosylation and ortho-(1-phenylvinyl)benzoate (PVB) glycosylation to streamline oligosaccharide synthesis, and (5) convergent [7 + 7] glycosylation for the final assembly of the target tetradecasaccharide. In particular, this new RMRAA α-galactosylation method has mild reaction conditions, broad substrate scopes and significantly shortened step counts for the heptasaccharide synthesis in comparison with 4,6-di-tert-butylsilyene (DTBS) directed α-galactosylation. Furthermore, DFT calculations shed light on the origins of remote anchimeric assistance effects (3,4-OBz > 3,4-OAc > 4-OBz > 3-OBz) of acyl groups.

Visible-Light-Promoted Stereoselective C(sp3 )-H Glycosylation for the Synthesis of C-Glycoamino Acids and C-Glycopeptides

The glycosylative modification of peptides could improve the pharmacological properties of peptide drugs and deliver them efficiently to the target sites. Compared with O-/N-glycosides, C-glycosides exhibit more metabolic stability. We here disclose the first example of visible-light-promoted and Cu-catalyzed stereoselective C-glycosylation. The mild reaction conditions are compatible with various carbohydrate substrates, as demonstrated with a series of monosaccharides and a disaccharide, and are amenable to the synthesis of a wide variety of C-glycoamino acids and C-glycopeptidomimetics with good yields and excellent stereoselectivities. The dual-functional photocatalyst formed in situ via coordination of the glycine derivative and the chiral phosphine Cu complex could not only catalyze the photoredox process but also control the stereoselectivity of the glycosylation reaction.

Use of a purified β-glucosidase from coral-associated microorganisms to enhance wine aroma

BACKGROUND

β-Glucosidases (3.2.1.21) play essential roles in the removal of nonreducing terminal glucosyl residues from saccharides and glycosides. However, the full potential and different applications of recombinant high-yield microbial β-glucosidase-producing systems remain to be tackled.

RESULTS

A β-glucosidase gene designated as Mg132 was isolated from a coral microorganism by high-throughput sequencing and functional screening. The deduced amino acid sequences of Mg132 showed a highest identity of 97% with β-glucosidase predicted in the GenBank database. This gene was cloned and overexpressed in Escherichia coli BL21 (DE3) for the first time. The optimal pH and temperature of purified recombinant Mg132 were 8.0 and 50 °C respectively. It exhibited a high level of stability at high concentration of glucose and ethanol, and glucose concentrations below 300 mmol L^-1 distinctly stimulated p-nitrophenyl-β-d-glucopyranoside hydrolysis, reaching 200% at 15% ethanol. The K_m and V_max values were 0.293 mmol L^-1 and 320 μmol min^-1  mg^-1 respectively while using p-nitrophenyl-β-d-glucopyranoside as a substrate. Wine treated with Mg132 had an obvious positive catalytic specificity for glycosides, which give a pleasant flavor of temperate fruity and floral aromas. The total concentration of fermentative volatiles was 201.42 ± 10.22 μg L^-1 following Mg132 treatment and 99.21 ± 7.72 μg L^-1 in control samples.

CONCLUSION

Good tolerance of winemaking and aroma fermentative properties suggest that Mg132 has potential application in aroma enhancement in wine and warrants further study. © 2021 Society of Chemical Industry.

Integrated Chemoenzymatic Approach to Streamline the Assembly of Complex Glycopeptides in the Liquid Phase

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.

Glycosyl 3-Phenyl-4-pentenoates as Versatile Glycosyl Donors: Reactivity and Their Application in One-Pot Oligosaccharide Assemblies

Both glycoconjugates and oligosaccharides are important biomolecules having significant roles in several biological processes, and a new strategy for their synthesis is crucial. Here, we report a versatile N-iodosuccinimide/trimethylsilyl triflate (NIS/TMSOTf) promoted glycosidation approach with shelf-stable 3-phenyl-4-pentenoate glycosyl as a donor for the efficient synthesis of O/C-glycosides with free alcohols, silylated alcohols, and C-type nucleophile acceptors in good to excellent yields. The mild activation conditions and outstanding reactivity of phenyl substituted pentenoate donors analogous to 4-pentenoate glycosyl donors enhance their applicability to various one-pot strategies for the synthesis of oligosaccharides, such as single-catalyst one-pot and acceptor reactivity-controlled one-pot strategies.

A Synthetic Gene Library Yields a Previously Unknown Glycoside Phosphorylase That Degrades and Assembles Poly-β-1,3-GlcNAc, Completing the Suite of β-Linked GlcNAc Polysaccharides

The considerable utility of glycoside phosphorylases (GPs) has led to substantial efforts over the past two decades to expand the breadth of known GP activities. Driven largely by the increase of available genomic DNA sequence data, the gap between the number of sequences in the carbohydrate active enzyme database (CAZy DB) and its functionally characterized members continues to grow. This wealth of sequence data presented an exciting opportunity to explore the ever-expanding CAZy DB to discover new GPs with never-before-described functionalities. Utilizing an in silico sequence analysis of CAZy family GH94, we discovered and then functionally and structurally characterized the new GP β-1,3-N-acetylglucosaminide phosphorylase. This new GP was sourced from the genome of the cell-wall-less Mollicute bacterium, Acholeplasma laidlawii and was found to synthesize β-1,3-linked N-acetylglucosaminide linkages. The resulting poly-β-1,3-N-acetylglucosamine represents a new, previously undescribed biopolymer that completes the set of possible β-linked GlcNAc homopolysaccharides together with chitin (β-1,4) and PNAG (poly-β-1,6-N-acetylglucosamine). The new biopolymer was denoted acholetin, a combination of the genus Acholeplasma and the polysaccharide chitin, and the new GP was thus denoted acholetin phosphorylase (AchP). Use of the reverse phosphorolysis action of AchP provides an efficient method to enzymatically synthesize acholetin, which is a new biodegradable polymeric material.

Glycosyl Vinylogous Carbonates as Glycosyl Donors by Metal-Free Activation

Synthesis of glycoconjugates employs a glycosylation reaction wherein an electrophile and a nucleophile known as a glycosyl donor and an aglycon, respectively, are involved. Glycosyl donors often contain a leaving group at the anomeric carbon that upon reaction with activator(s) results in a highly reactive electrophilic species reported as an oxycarbenium ion contact pair that will then be attacked by the aglycon. Therefore, identification of the correct glycosyl donor and activation protocol is essential for the synthesis of all glycoconjugates. Recently identified [Au]/[Ag]-catalyzed activation of ethynylcyclohexyl glycosyl carbonates is one such versatile method for the synthesis of glycosides, oligosaccharides, and glycoconjugates. In this work, stable glycosyl vinylogous carbonates were identified to undergo glycosidation in the presence of a sub-stoichiometric quantity of TfOH. The reaction is fast and suitable for donors containing both C2-ethers and C2-esters. Donors positioned with C2-ethers resulted in anomeric mixtures with greater selectivity toward 1,2-cis glycosides, whereas those with C2-esters gave 1,2-trans selective glycosides. The versatility of the method is demonstrated by conducting the glycosylation with more than 25 substrates. Furthermore, the utility of the glycosyl vinylogous carbonate donors is demonstrated with the successful synthesis of the branched pentaarabinofuranoside moiety of the Mycobacterium tuberculosis cell wall.