Convenient synthesis of sulfated oligofucosides

Comparative study on the mechanisms of anti-lung cancer activities of three sulfated galactofucans

Sulfated galactofucans, as the active compositions of fucoidan, were reported to exhibit antitumor activity. In the current study, a sulfated galactofucan (SGF) from Sargassum thunbergii and its three derivatives (SGF-H, SGF-L, and SGF-S) were prepared for structural analysis. Structural analysis showed that SGF-H was a high molecular weight sulfated galactofucan (51.5/17.8 kDa) with a high molar ratio of galactose (Gal) to fucose (Fuc) (0.66 : 1), SGF-L was a low molecular weight sulfated galactofucan (17.7 kDa) with a low molar ratio of Gal to Fuc (0.20 : 1), and SGF-S was a mixture (1.7 kDa) of sulfated galacto-fuco-oligomers or fuco-oligomers. It was noteworthy that the linkage of Gal residues in SGF-H was a β-linkage while SGF-L was an α-linkage. A comparative study on the anti-lung cancer activity in vitro and in vivo, antimetastatic effects, the metastasis-associated protein expression, and binding abilities to fibroblast growth factors (FGFs) of SGF, SGF-H, and SGF-L was performed to understand the structure-activity relationship. To some extent, SGF-L showed the strongest activity in the inhibition of human lung cancer cells A549 cell proliferation, while SGF-H exhibited the strongest activity in the inhibition of human bronchial epithelial cells BEAS-2B cell proliferation. SGF-L showed the strongest antimetastatic activity, followed by SGF-H and SGF. The expression of metastasis-associated proteins showed only a small difference. The in vivo tumor inhibition of SGF, SGF-H, and SGF-L was 45%, 41%, and 31%, respectively. SPR analysis showed SGF-H binds preferentially to FGF1 and FGF2, while SGF-L preferentially binds to FGF7 and FGF10, suggesting that the anti-lung cancer activity from sulfated galactofucan could involve the FGF-FAK/mTOR pathway.

The structure-activity relationship of the interactions of SARS-CoV-2 spike glycoproteins with glucuronomannan and sulfated galactofucan from Saccharina japonica

The SARS-CoV-2 spike glycoproteins (SGPs) and human angiotensin converting enzyme 2 (ACE2) are the two key targets for the prevention and treatment of COVID-19. Host cell surface heparan sulfate (HS) is believed to interact with SARS-CoV-2 SGPs to facilitate host cell entry. In the current study, a series of polysaccharides from Saccharina japonica were prepared to investigate the structure-activity relationship on the binding abilities of polysaccharides (oligosaccharides) to pseudotype particles, including SARS-CoV-2 SGPs, and ACE2 using surface plasmon resonance. Sulfated galactofucan (SJ-D-S-H) and glucuronomannan (Gn) displayed strongly inhibited interaction between SARS-CoV-2 SGPs and heparin while showing negligible inhibition of the interaction between SARS-CoV-2 SGPs and ACE2. The IC50 values of SJ-D-S-H and Gn in blocking heparin SGP binding were 27 and 231 nM, respectively. NMR analysis showed that the structure of SJ-D-S-H featured with a backbone of 1, 3-linked α-L-Fucp residues sulfated at C4 and C2/C4 and 1, 3-linked α-L-Fucp residues sulfated at C4 and branched with 1, 6-linked β-D-galacto-biose; Gn had a backbone of alternating 1, 4-linked β-D-GlcAp residues and 1, 2-linked α-D-Manp residues. The sulfated galactofucan and glucuronomannan showed strong binding ability to SARS-CoV-2 SGPs, suggesting that these polysaccharides might be good candidates for preventing and/or treating SARS-CoV-2.

Interactions of fibroblast growth factors with sulfated galactofucan from Saccharina japonica

A total 68 types of marine algae oligosaccharides and polysaccharides were prepared and used to study the structure-activity relationship of oligosaccharides and polysaccharides in their interactions with fibroblast growth factors (FGF) 1 and 2. Factors considered include different types of algae, extraction methods, molecular weight, sulfate content and fractions. In the case of low molecular weight polysaccharide (SJ-D) from Saccharina japonica and its fractions eluting from anion exchange column, both 1.0 M NaCl fraction (SJ-D-I) and 2.0 M NaCl fraction (SJ-D-S) had stronger binding affinity than the parent SJ-D, suggesting that sulfated galactofucans represented the major tight binding component. Nuclear magnetic resonance showed that SJ-D-I was a typical sulfated galactofucan, composed of four units: 1, 3-linked 4-sulfated α-L-fucose (Fuc); 1, 3-linked 2, 4-disulfated α-L-Fuc; 1, 6-linked 4-sulfated β-D-Gal and/or 1, 6-linked 3, 4-sulfated β-D-Gal. Modification by autohydrolysis to oligosaccharides and desulfation decreased the FGF binding affinity while oversulfation increased the affinity. The solution-based affinities of SJ-D-I to FGF1 and FGF2 were 69 nM and 3.9 nM, suggesting that SJ-D-I showed better preferentially binding to FGF1 than a natural ligand, heparin, suggesting that sulfated galactofucan might represent a good regulator of FGF1.

Structural characteristics and anti-complement activities of polysaccharides from Sargassum hemiphyllum

Three polysaccharides (SH-1, SH-2 and SH-3) were purified from a brown macroalgea, Sargassum hemiphyllum. The autohydrolysis products from each polysaccharide were separated to three fractions (S fractions as oligomers, L fractions as low molecular weight polysaccharides and H fractions as high molecular weight polysaccharides). Mass spectroscopy of S fractions (SH-1-S, SH-2-S and SH-3-S) showed that these three polymers all contained short stretches of sulfated fucose. The structures of L fractions (SH-1-L, SH-2-L and SH-3-L) were determined by nuclear magnetic resonance (NMR). SH-1-L was composed of two units, unit A (sulfated galactofucan) and unit B (sulfated xylo-glucuronomannan). Unit A contained a backbone of (1, 6-linked β-D-Gal) n1, (1, 3-linked 4-sulfated α-L-Fuc) n2, (1, 3-linked 2, 4-di-sulfated α-L-Fuc) n3, (1, 4-linked α-L-Fuc) n4 and (1, 3-linked β-D-Gal) n5, accompanied by some branches, such as sulfated fuco-oligomers, sulfated galacto-oligomers or sulfated galacto-fuco-oligomers. And unit B consisted of alternating 1, 4-linked β-D-glucuronic acid (GlcA) and 1, 2-linked α-D-mannose (Man) with the Man residues randomly sulfated at C6 or branched with xylose (Xyl) at C3. Both SH-2-L and SH-3-L were composed of unit A and their difference was attributed to the ratio of n1: n2: n3: n4: n5. Based on monosaccharide analysis, we hypothesize that both SH-1-H and SH-2-H contained unit A and unit B while SH-3-H had a structure similar to SH-3-L. An assessment of anti-complement activities showed that the sulfated galactofucan had higher activities than sulfated galacto-fuco-xylo-glucuronomannan. These results suggest that the sulfated galactofucans might be a good candidate for anti-complement drugs.

Recent Advances in Pharmaceutical Potential of Brown Algal Polysaccharides and their Derivatives

Marine plants, animals and microorganisms display steady growth in the ocean and are abundant carbohydrate resources. Specifically, natural polysaccharides obtained from brown algae have been drawing increasing attention owing to their great potential in pharmaceutical applications. This review describes the structural and biological features of brown algal polysaccharides, including alginates, fucoidans, and laminarins, and it highlights recently developed approaches used to obtain the oligo- and polysaccharides with defined structures. Functional modification of these polysaccharides promotes their advanced applications in biomedical materials for controlled release and targeted drug delivery, etc. Moreover, brown algal polysaccharides and their derivatives possess numerous biological activities with anticancer, anticoagulant, wound healing, and antiviral properties. In addition, we also discuss carbohydrate- based substrates from brown algae, which are currently in clinical and preclinical studies, as well as the marine drugs that are already on the market. The present review summarizes the recent development in carbohydratebased products from brown algae, with promising findings that could rapidly facilitate the future discovery of novel marine drugs.

Synthesis of Fucoidan-Mimetic Glycopolymers with Well-Defined Sulfation Patterns via Emulsion Ring-Opening Metathesis Polymerization

The approach developed here offers distinct and well-defined glycopolymers for deciphering the biological roles of natural bioactive polysaccharides. Fucose monomers were chemically synthesized and decorated with specific sulfation patterns including unsulfate, monosulfate, disulfate, and trisulfate groups. The six fucoidan-mimetic glycopolymers (18-23) were successfully fabricated through microwave-assisted ring-opening metathesis polymerization (ROMP) in an emulsion system. The molecular weight (M_w), polydispersity index (PDI), and multiple functional groups were fully characterized by SEC-MALLS-RI and NMR spectroscopy. Three glycopolymers (19, 21, 23) associated with 2-O-sulfation exhibited better inhibitory effects on the H1N1 virus, while glycopolymers (19, 20) with monosulfate groups were more effective against the H3N2 virus. These findings would promote the development of novel anti-influenza A virus (IAV) drugs based on natural fucoidans.

Overview on the antiviral activities and mechanisms of marine polysaccharides from seaweeds

Marine polysaccharides are attracting increasing attention in medical and pharmaceutical development because of their important biological properties. The seaweed polysaccharides have now become a rich resource of potential antiviral drugs due to their antiviral activities against various viruses. The structural diversity and complexity of marine polysaccharides and their derivatives contribute to their antiviral activities in different phases of many different viral infection processes. This review mainly introduces the different types of seaweed polysaccharides and their derivatives with potent antiviral activities. Moreover, the antiviral mechanisms and medical applications of certain marine polysaccharides from seaweeds are also demonstrated.

Mapping the Reactivity and Selectivity of 2-Azidofucosyl Donors for the Assembly of N-Acetylfucosamine-Containing Bacterial Oligosaccharides

The synthesis of complex oligosaccharides is often hindered by a lack of knowledge on the reactivity and selectivity of their constituent building blocks. We investigated the reactivity and selectivity of 2-azidofucosyl (FucN₃) donors, valuable synthons in the synthesis of 2-acetamido-2-deoxyfucose (FucNAc) containing oligosaccharides. Six FucN₃ donors, bearing benzyl, benzoyl, or tert-butyldimethylsilyl protecting groups at the C3-O and C4-O positions, were synthesized, and their reactivity was assessed in a series of glycosylations using acceptors of varying nucleophilicity and size. It was found that more reactive nucleophiles and electron-withdrawing benzoyl groups on the donor favor the formation of β-glycosides, while poorly reactive nucleophiles and electron-donating protecting groups on the donor favor α-glycosidic bond formation. Low-temperature NMR activation studies of Bn- and Bz-protected donors revealed the formation of covalent FucN₃ triflates and oxosulfonium triflates. From these results, a mechanistic explanation is offered in which more reactive acceptors preferentially react via an S_N2-like pathway, while less reactive acceptors react via an S_N1-like pathway. The knowledge obtained in this reactivity study was then applied in the construction of α-FucN₃ linkages relevant to bacterial saccharides. Finally, a modular synthesis of the Staphylococcus aureus type 5 capsular polysaccharide repeating unit, a trisaccharide consisting of two FucNAc units, is described.

Design of α-Selective Glycopyranosyl Donors Relying on Remote Anchimeric Assistance

Oligosaccharides have a variety of versatile biological effects, but unlike peptides and oligonucleotides, investigation of the roles of oligosaccharides is not easy. Since biosynthesis of oligosaccharides does not comply with direct genetic control, their isolation from natural sources and biotechnological preparation are complicated, due to the heterogeneous composition of raw carbohydrates. Oligosaccharide synthesis is needed for the establishment or confirmation of the structure of natural glycocompounds. Also, synthetically prepared, defined oligosaccharides and their derivatives are becoming increasingly important tools for many biological and immunological research projects. The key step of oligosaccharide synthesis involves glycosylation, a reaction that builds glycosidic bonds. Usually, construction of 1,2-trans-bonds is easy, and therefore, this reaction can even be included into automated syntheses. At this time, installation of the 1,2-cis-bond remains simultaneously frustrating and compelling. In our and other laboratories, a strategy of α-selective (1,2-cis) glycosylation, relying on remote anchimeric assistance with acyl groups, is studied. The state of the art in this work is summarized in this review.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Systematic synthesis of low-molecular weight fucoidan derivatives and their effect on cancer cells

Low-molecular weight fucoidan derivatives with different sulfation patterns were designed, systematically synthesized, and evaluated for their anti-cancer activities against MCF-7 and HeLa cells.

Systematic synthesis of sulfated oligofucosides and their effect on breast cancer MCF-7 cells

Sulfated tetrafucosides with different sulfation patterns, and a non-sulfated tetrafucoside , were designed and systematically synthesized from the common key intermediate . In addition, their anti-proliferative activities and apoptosis-inducing activities against human breast cancer MCF-7 cells were evaluated. Our results demonstrated that the sulfated tetrafucosides reduced the number of MCF-7 cells in a dose-dependent manner, and of these, 3,4-O-sulfated type showed the highest anti-proliferative activity, comparable to the activity of fucoidan isolated from Fucus vesiculosus. Furthermore, it was revealed that both and exhibited apoptosis-inducing activities through activation of caspase-8 on MCF-7 cells.

Stereoselective synthesis of a sulfated tetrasaccharide corresponding to a rare sequence in the galactofucan isolated from Sargassum polycystum

The first chemical synthesis of a highly sulfated tetrasaccharide 1, as the rare sequence in the galactofucan isolated from the brown alga Sargassum polycystum, was achieved in a convergent and stereoselective manner. The key features of the synthetic strategy include construction of multiple contiguous 1,2-cis glycosidic bonds and [2 + 2] assembly based on the rationally developed d-galactose building block 6. The synthesized oligosaccharides were fully characterized using a combination of coupled-HSQC and other 2D NMR techniques.