Glucan-like synthetic oligosaccharides: iterative synthesis of linear oligo-beta-(1,3)-glucans and immunostimulatory effects

Preparation of β-1,3-glucan mimics via modification of polymer backbone, and evaluation of cytokine production using the polymer library in immune activation

β-1,3-Glucans possess therapeutic potential owing to their ability to exhibit immunostimulating activity. β-1,3-Glucans, isolated from various organisms, differ in their chemical structures, molecular weight, and branching degree, potentially forming particulate, helix, or random coil conformations in water. Therefore, this study used synthesized β-1,3-glucan mimic polymers to investigate the difference in binding affinity for dectin-1 and induced cytokine productions based on polymer structures. The β-1,3-glucan mimic polymers were synthesized using β-1,3-glucan tetrasaccharyl monomer, with subsequent modifications to the polymer backbones through the introduction of hydrogen or a hydroxy group. Polymers with different structures in both ligands and polymer backbones were utilized to comprehensively investigate their binding affinity to dectin-1 and cytokine-inducing in macrophages. Hydroxylated polymers exhibited a high binding affinity for dectin-1, similar to that of schizophyllan, whereas the polymer composed of only saccharyl monomers did not bind to dectin-1. Further, when administered to macrophage RAW264 cells, polymers with branched and hydrophobic polymer backbones exhibited strong cytokine-inducing activities. Moreover, the results revealed that the essential factors for cytokine induction include the branches of β-1,3-glucans, high (tens of thousands) molecular weights, and hydrophobicity. The results suggests that artificial polymers comprising these factors exhibit immunostimulating activity and could be developed as therapeutic agents.

β-1,3-Glucan synthesis, novel supramolecular self-assembly, characterization and application

β-1,3-Glucans are ubiquitously observed in various biological systems with diverse physio-ecological functions, yet their underlying assembly mechanism and multiscale complexation in vitro remains poorly understood. Here, we provide for the first-time evidence of unidentified β-1,3-glucan supramolecular complexation into intricate hierarchical architectures over several length scales. We mediated these unique assemblies using a recombinantly produced β-1,3-glucan phosphorylase (Ta1,3BGP) by fine-tuning solution conditions during particle nucleation and growth. We report a synthesis of interconnected parallel hexagonal lamellae composed of 8 nm thick sheets of highly expanded paracrystals. The architecture consists of β-1,3-glucan triple-helices with considerable inter-intra hydrogen bonding within, as well as in between adjacent triple-helices. The results extend our understanding of β-1,3-glucan molecular organization and shed light on different aspects of the crystallization processes of biomolecules into structures unseen by nature. The presented versatile synthesis yields new materials for diverse medical and industrial applications.

Synthesis of branched β-1,3-glucan oligosaccharide with narrow degree of polymerization by fungi co-cultivation

The large molecular weight and poor water solubility of β-1,3-glucan impede its potential applications. In this study, the β-1,3-glucan producing fungi and Trichoderma harzianum capable of secreting endo-β-1,3-glucanase were co-cultivated to produce branched β-1,3-glucan oligosaccharides (bOβGs) by fermentation with Sclerotium rolfsii and Schizophyllum commune. The highest bOβG yields from S. rolfsii in flasks were 4.53 and 9.94 g/L in a 7 L fermenter. Structural analysis proved that bOβG from S. rolfsii had a narrow degree of polymerization of 5-12, whereas bOβG from S. commune had a degree of polymerization of 5-15. Antioxidant tests showed that both bOβGs had remarkable DPPH radical scavenging activity and hydroxyl radical scavenging activity, and the activity of bOβG from S. commune was better than that of bOβG from S. rolfsii. In addition, bOβGs could promote the secretion of NO by mouse macrophages and increase the production of TNF-α, IL-1β, and IL-6 in RAW264.7.

The Road to Structurally Defined β-Glucans

β-glucans are polymers of glucose that have been isolated from a variety of organisms. Isolated β-glucans have been used for medical purposes for centuries; however, efforts to define the biological activities of β-glucans experimentally were initiated in the 1940's. The diversity of structure associated with isolated β-glucans has impeded said investigations, and efforts to leverage the biological activity of β-glucans for clinical applications. In recognition of the need for defined β-glucans that retain the biological activity of isolated β-glucans, considerable investment has been made to facilitate the synthesis of structurally defined β-glucans. Here, we review the different approaches that have been applied to prepare β-glucans. In addition, we summarize the approaches that have been utilized to conjugate β-glucans to proteins.

Immunity boosting nutraceuticals: Current trends and challenges

The immune function of the human body is highly influenced by the dietary intake of certain nutrients and bioactive compounds present in foods. The preventive effects of these bioactive ingredients against various diseases have been well investigated. Functional foods are consumed across various diverse cultures, in some form or the other, which provide benefits greater than the basic nutritional needs. Novel functional foods are being developed using novel bioactive ingredients such as probiotics, polyunsaturated fatty acids, and various phytoconstituents, which have a range of immunomodulatory properties. Apart from immunomodulation, these ingredients also affect immunity by their antioxidant, antibacterial, and antiviral properties. The global pandemic of Severe Acute Respiratory Syndrome Coronavirus-2 has forced the scientific community to race against time to find a proper and effective drug or a vaccine. In this review, various non-pharmacological interventions using nutraceuticals and functional foods have been discussed. PRACTICAL APPLICATIONS: Despite a plethora of research being undertaken to understand the immunity boosting properties of the various bioactive present in food, the findings are not translating to nutraceutical products in the market. Immunity has proved to be one of the most important factors for the health and well-being of an individual, especially when the world has been under the grip of the novel coronavirus Severe Acute Respiratory Syndrome Coronavirus-2. The anti-inflammatory properties of various nutraceuticals can come out as potential inhibitors of the various inflammatory processes such as cytokine storms, usually being observed in COVID 19. This review gives an insight into how various nutraceuticals can help in the prevention of various diseases through different mechanisms. The lack of awareness and proper clinical trials pose a challenge to the nutraceutical industry. This review will help and encourage researchers to further design and develop various functional foods, which might help in building immunity.

Progress and challenges in the synthesis of sequence controlled polysaccharides

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure-properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

In vitro prebiotic potential, digestibility and biocompatibility properties of laminari-oligosaccharides produced from curdlan by β-1,3-endoglucanase from Clostridium thermocellum

Curdlan or laminarin, a β-1,3-glucan was hydrolysed by β-1,3-endoglucanase (CtLam81A) from Clostridium thermocellum to produce laminari-oligosaccharides. TLC analysis of hydrolysed curdlan showed the presence of laminari-oligosaccharides of the degree of polymerization, DP2-DP7. This mixture of laminari-oligosaccharides displayed prebiotic properties. Laminari-oligosaccharides showed an increase in the growth of probiotic bacteria such as Lactobacillus plantarum DM5 and Lactobacillus acidophilus, while they did not promote the growth of non-probiotic bacteria (Escherichia coli and Enterobacter aerogenes). Laminari-oligosaccharides showed higher prebiotic activity score of 0.92 ± 0.01 and 0.64 ± 0.08 for L. plantarum DM5 and L. acidophilus NRRL B-4496, respectively, similar to those shown by inulin. Laminari-oligosaccharides showed higher resistance or low digestibility against α-amylase, artificial gastric juice and intestinal fluid than inulin indicating their bioavailability to the probiotic bacteria present in the gastrointestinal tract of human. The probiotic bacteria consumed laminaribiose and laminariotriose more readily than higher laminari-oligosaccharides as carbon source for their growth. The in vitro cytotoxicity assay of laminari-oligosaccharides (1 mg/ml) on human embryonic kidney (HEK 293) cells showed that the cell viability was not affected even after 72 h indicating their biocompatible nature. All the results amply indicated that laminari-oligosaccharides can serve as potential prebiotic additives for functional food products.

Structural insights into β-1,3-glucan cleavage by a glycoside hydrolase family

The fundamental and assorted roles of β-1,3-glucans in nature are underpinned on diverse chemistry and molecular structures, demanding sophisticated and intricate enzymatic systems for their processing. In this work, the selectivity and modes of action of a glycoside hydrolase family active on β-1,3-glucans were systematically investigated combining sequence similarity network, phylogeny, X-ray crystallography, enzyme kinetics, mutagenesis and molecular dynamics. This family exhibits a minimalist and versatile (α/β)-barrel scaffold, which can harbor distinguishing exo or endo modes of action, including an ancillary-binding site for the anchoring of triple-helical β-1,3-glucans. The substrate binding occurs via a hydrophobic knuckle complementary to the canonical curved conformation of β-1,3-glucans or through a substrate conformational change imposed by the active-site topology of some fungal enzymes. Together, these findings expand our understanding of the enzymatic arsenal of bacteria and fungi for the breakdown and modification of β-1,3-glucans, which can be exploited for biotechnological applications.

Synthesis and Evaluation of Oligomeric Thioether-Linked Carbacyclic β-(1→3)-Glucan Mimetics

Extrapolating from lessons learnt with previous low-molecular-weight β-(1→3)-glucan mimetics, we designed a series of minimal 2,4-dideoxy-thioether-linked carbacyclic β-(1→3)-glucan mimetics and synthesized di-, tri-, and tetramers in an enantiomerically pure form by an iterative sequence based on a simple building block readily available from commercial ( S)-(-)-3-cyclohexenecarboxylic acid. These substances were screened for their ability to inhibit anti-CR3-fluorescein isothiocyanate (FITC) staining of human neutrophils and anti-Dectin-1-FITC staining of mouse macrophages as well as for their ability to stimulate phagocytosis and pinocytosis. In each assay, the synthetic compounds displayed comparable activity to the corresponding native β-(1→3)-glucans, laminaritriose, and tetraose, suggesting that the exploitation of hydrophobic patches in the lectin-binding domains of CR3 and Dectin-1 is a promising strategy for the development of small-molecule analogues of β-(1→3)-glucans.

Synthesis and Evaluation of 1,5-Dithia-d-laminaribiose, Triose, and Tetraose as Truncated β-(1→3)-Glucan Mimetics

The preparation and characterization of a series of di-, tri-, and tetrasaccharide analogues of β-(1→3)-glucans is described in which each pyranoside ring is replaced by a 5-thiopyranosyl ring and each glycosidic oxygen by a thioether. These oligomeric 1,5-dithio-d-glucopyranose derivatives were shown to inhibit the staining of human neutrophils and of mouse macrophages by fluorescent anti-CR3 and anti-Dectin-1 antibodies, respectively. The compounds were also demonstrated to stimulate phagocytosis and pinocytosis indicative of binding to the carbohydrate binding domains of complement receptor 3 (CR3) and Dectin-1. Activity in all three assays was optimum at the level of the trisaccharide mimic, suggesting that, while the replacement of ethereal oxygens by thioethers results in a greater affinity for the aromatic lined hydrophobic binding pockets, the presence of multiple longer C-S bonds eventually results in a mismatch and a loss of affinity.

Synthesis of 3-aminopropyl glycosides of linear β-(1 → 3)-D-glucooligosaccharides

3-Aminopropyl glycosides of a series of linear β-(1 → 3)-linked D-glucooligosaccharides containing from 3 to 13 monosaccharide units were efficiently prepared. The synthetic scheme featured highly regioselective glycosylation of 4,6-O-benzylidene-protected 2,3-diol glycosyl acceptors with a disaccharide thioglycoside donor bearing chloroacetyl groups at O-2' and -3' as a temporary protection of the diol system. Iteration of the deprotection and glycosylation steps afforded the series of the title oligoglucosides differing in length by two monosaccharide units. A novel procedure for selective removal of acetyl groups in the presence of benzoyl ones consisting in a brief treatment with a large excess of hydrazine hydrate has been proposed.

Structure-function relationships of immunostimulatory polysaccharides: A review

Immunostimulatory polysaccharides are compounds capable of interacting with the immune system and enhance specific mechanisms of the host response. Glucans, mannans, pectic polysaccharides, arabinogalactans, fucoidans, galactans, hyaluronans, fructans, and xylans are polysaccharides with reported immunostimulatory activity. The structural features that have been related with such activity are the monosaccharide and glycosidic-linkage composition, conformation, molecular weight, functional groups, and branching characteristics. However, the establishment of structure-function relationships is possible only if purified and characterized polysaccharides are used and selective structural modifications performed. Aiming at contributing to the definition of the structure-function relationships necessary to design immunostimulatory polysaccharides with potential for preventive or therapeutical purposes or to be recognized as health-improving ingredients in functional foods, this review introduces basic immunological concepts required to understand the mechanisms that rule the potential claimed immunostimulatory activity of polysaccharides and critically presents a literature survey on the structural features of the polysaccharides and reported immunostimulatory activity.

Molecular Interactions of β-(1→3)-Glucans with Their Receptors

β-(1→3)-Glucans can be found as structural polysaccharides in cereals, in algae or as exo-polysaccharides secreted on the surfaces of mushrooms or fungi. Research has now established that β-(1→3)-glucans can trigger different immune responses and act as efficient immunostimulating agents. They constitute prevalent sources of carbons for microorganisms after subsequent recognition by digesting enzymes. Nevertheless, mechanisms associated with both roles are not yet clearly understood. This review focuses on the variety of elucidated molecular interactions that involve these natural or synthetic polysaccharides and their receptors, i.e., Dectin-1, CR3, glycolipids, langerin and carbohydrate-binding modules.

Synthesis of a 1,3 β-glucan hexasaccharide designed to target vaccines to the dendritic cell receptor, Dectin-1

Transformation of 3-O-benzyl-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose into 2,4,6-tri-O-benzoyl-3-O-benzyl glucopyranosyl imidate proceeded efficiently via crystalline benzyl and per-benzoylated derivatives. This imidate glycosylated di-O-isopropylidene-α-D-glucofuranose in high yield and glycosylation of the disaccharide after removal of the 3'-O-benzyl ether afforded the β1,3 linked trisaccharide in excellent yield. Di- and trisaccharides imidates were readily prepared from the furanose terminated glycosylation products but both were unreactive in glycosylation reaction with the debenzylated di- and trisaccharide alcohols. The 3'-O-benzyl perbenzoylated disaccharide pyranose derivative could be selectively debenzoylated and converted to the corresponding perbenzoylated 4,6:4',6'-di-O-benzylidene derivative. Lewis acid catalyzed glycosidation gave the selectively protected disaccharide ethylthioglycoside in good overall yield. Glycosidation of this thioglycoside donor with 5-methoxycarbonylpentanol gave the disaccharide tether glycoside and after catalytic removal of benzyl ether the resulting disaccharide alcohol was glycosylated by the thioglycoside in a 2+2 reaction to yield a tetrasaccharide. Repetition of selective deprotection of the terminal 3-O-benzyl ether followed by glycosylation by the disaccharide thioglycoside gave a protected hexasaccharide. Hydrogenolysis of this hexasaccharide followed by transesterification and second hydrogenolysis to remove a residual benzyl group gave the target hexasaccharide glycoside 1 as a Dectin-1 ligand functionalized to permit covalent attachment to glycoconjugate vaccines and thereby facilitate improved antigen processing by dendritic cells.

Synthesis and immunological studies of linear oligosaccharides of β-glucan as antigens for antifungal vaccine development

Antifungal vaccines have recently engendered considerable excitement for counteracting the resurgence of fungal infections. In this context, β-glucan, which is abundantly expressed on all fungal cell surfaces, functionally necessary for fungi, and immunologically active, is an attractive target antigen. Aiming at the development of effective antifungal vaccines based on β-glucan, a series of its oligosaccharide derivatives was designed, synthesized, and coupled with a carrier protein, keyhole limpet hemocyanin (KLH), to form new semisynthetic glycoconjugate vaccines. In this article, a convergent and effective synthetic strategy using preactivation-based iterative glycosylation was developed for the designed oligosaccharides. The strategy can be widely useful for rapid construction of large oligo-β-glucans with shorter oligosaccharides as building blocks. The KLH conjugates of the synthesized β-glucan hexa-, octa-, deca-, and dodecasaccharides were demonstrated to elicit high titers of antigen-specific total and IgG antibodies in mice, suggesting the induction of functional T cell-mediated immunity. Moreover, it was revealed that octa-, deca-, and dodeca-β-glucans were much more immunogenic than the hexamer and that the octamer was the best among these. The results suggested that the optimal oligosaccharide sequence of β-glucan required for exceptional immunogenicity was a hepta- or octamer and that longer glucans are not necessarily better antigens, a finding that may be of general importance. Most importantly, the octa-β-glucan-KLH conjugate provoked protective immunity against Candida albicans infection in a systemic challenge model in mice, suggesting the great potential of this glycoconjugate as a clinically useful immunoprophylactic antifungal vaccine.

β-(1→3)-Glucan-mannitol conjugates: scope and amazing results

It is well known that β-(1→3)-Glucans present high applicative potential in human health as immunostimulating agents. Numerous studies have highlighted this, but mainly used native polysaccharides extracted from various natural sources. These compounds are therefore inevitably polydisperse but also present structures that are not homogeneous, in an analytical point of view. This is the reason why we have achieved the chemical synthesis of small glucan-mannitol derivatives especially found in brown seaweeds. The targets differ from each other by the nature of the conjunction between the laminaribiose and the mannose or mannitol, i.e., (1→6) or (1→3). We established that (I) these molecules were efficiently obtained from glucose, laminaribiose and/or mannose derivatives; (II) the synthetic plan has to be adapted to the first connection between a glucosyl entity and the mannosyl residue; and (III) resulting pure compounds may be used as the standard for analytical purposes.

Oligo-β-(1 → 3)-glucans: impact of thio-bridges on immunostimulating activities and the development of cancer stem cells

Recent developments of innovative anticancer therapies are based on compounds likely to stimulate the immune defense of the patients. β-(1 → 3)-Glucans are natural polysaccharides well-known for their immunostimulating properties. We report here on the synthesis of small oligo-β-(1 → 3)-glucans characterized by thioglycosidic linkages. The presence of sulfur atom(s) was not only crucial to prolong in vivo immunoactive activities in time, compared to native polysaccharides, but sulfur atoms also had a direct impact on the development of colorectal cancer stem cells. As a result, a short, pure, and structurally well-defined trisaccharidic thioglucan demonstrated similar activities compared to those of natural laminarin.

Molecular design and synthesis of novel salicyl glycoconjugates as elicitors against plant diseases

A new series of salicyl glycoconjugates containing hydrazide and hydrazone moieties were designed and synthesized. The bioassay indicated that the novel compounds had no in vitro fungicidal activity but showed significant in vivo antifungal activity against the tested fungal pathogens. Some compounds even had superior activity than the commercial fungicides in greenhouse trial. The results of RT-PCR analysis showed that the designed salicyl glycoconjugates could induce the expression of LOX1 and Cs-AOS2, which are the specific marker genes of jasmonate signaling pathway, to trigger the plant defense resistance.

Immunomodulatory activity of a novel, synthetic beta-glucan (β-glu6) in murine macrophages and human peripheral blood mononuclear cells

Natural β-glucans extracted from plants and fungi have been used in clinical therapies since the late 20th century. However, the heterogeneity of natural β-glucans limits their clinical applicability. We have synthesized β-glu6, which is an analog of the lentinan basic unit, β-(1→6)-branched β-(1→3) glucohexaose, that contains an α-(1→3)-linked bond. We have demonstrated the stimulatory effect of this molecule on the immune response, but the mechanisms by which β-glu6 activates innate immunity have not been elucidated. In this study, murine macrophages and human PBMCs were used to evaluate the immunomodulatory effects of β-glu6. We showed that β-glu6 activated ERK and c-Raf phosphorylation but suppressed the AKT signaling pathway in murine macrophages. Additionally, β-glu6 enhanced the secretion of large levels of cytokines and chemokines, including CD54, IL-1α, IL-1β, IL-16, IL-17, IL-23, IFN-γ, CCL1, CCL3, CCL4, CCL12, CXCL10, tissue inhibitor of metalloproteinase-1 (TIMP-1) and G-CSF in murine macrophages as well as IL-6, CCL2, CCL3, CCL5, CXCL1 and macrophage migration inhibitory factor (MIF) in human PBMCs. In summary, it demonstrates the immunomodulatory activity of β-glu6 in innate immunity.

Glycal assembly by the in situ generation of glycosyl dithiocarbamates

Glycal assembly offers an expedient entry into β-linked oligosaccharides, but epoxyglycal donors can be capricious in their reactivities. Treatment with Et(2)NH and CS(2) enables their in situ conversion into glycosyl dithiocarbamates, which can be activated by copper triflate for coupling with complex or sterically congested acceptors. The coupling efficiency can be further enhanced by in situ benzoylation, as illustrated in an 11-step synthesis of a branched hexasaccharide from glucals in 28% isolated yield and just four chromatographic purifications.

Synthesis of β(1,3) oligoglucans exhibiting a Dectin-1 binding affinity and their biological evaluation

In this report, we describe the synthesis and biological evaluation of β(1,3) oligosaccharides that contain an aminoalkyl group and their biological evaluation. A 2,3 diol glycoside with a 4,6 benzylidene protecting group was used as an effective glycosyl acceptor for the synthesis of some β(1,3) linked glycosides. The use of a combination of a linear tetrasaccharide and a branched pentasaccharide as glycosyl donors led to the preparation of β(1,3) linear octa- to hexadecasaccharides and branched nona- to heptadecasaccharides in good total yields. Measurements of the competitive effects of the oligosaccharides on the binding of a soluble form of Dectin-1 to a solid-supported Schizophyllan (SPG) revealed that the branched heptadecasaccharide and the linear hexadecasaccharides also have binding activity for Dectin-1. In addition, the two oligosaccharides, both of which contain a β(1,3) hexadecasaccharide backbone, exhibited agonist activity in a luciferase-assisted NF-κB assay. STD-NMR analyses of complexes of Dectin-1 and the linear hexadecasaccharides clearly indicate Dectin-1 specifically recognizes the sugar part of the oligosaccharides and not the aminoalkyl chain.

Potent endogenous allelopathic compounds in Lepidium sativum seed exudate: effects on epidermal cell growth in Amaranthus caudatus seedlings

Many plants exude allelochemicals--compounds that affect the growth of neighbouring plants. This study reports further studies of the reported effect of cress (Lepidium sativum) seed(ling) exudates on seedling growth in Amaranthus caudatus and Lactuca sativa. In the presence of live cress seedlings, both species grew longer hypocotyls and shorter roots than cress-free controls. The effects of cress seedlings were allelopathic and not due to competition for resources. Amaranthus seedlings grown in the presence of cress allelochemical(s) had longer, thinner hypocotyls and shorter, thicker roots--effects previously attributed to lepidimoide. The active principle was more abundant in cress seed exudate than in seedling (root) exudates. It was present in non-imbibed seeds and releasable from heat-killed seeds. Release from live seeds was biphasic, starting rapidly but then continuing gradually for 24 h. The active principle was generated by aseptic cress tissue and was not a microbial digestion product or seed-treatment chemical. Crude seed exudate affected hypocotyl and root growth at ~25 and ~450 μg ml(-1) respectively. The exudate slightly (28%) increased epidermal cell number along the length of the Amaranthus hypocotyl but increased total hypocotyl elongation by 129%; it resulted in a 26% smaller hypocotyl circumference but a 55% greater epidermal cell number counted round the circumference. Therefore, the effect of the allelochemical(s) on organ morphology was imposed primarily by regulation of cell expansion, not cell division. It is concluded that cress seeds exude endogenous substances, probably including lepidimoide, that principally regulate cell expansion in receiver plants.

Stimulatory Effect of β-glucans on Immune Cells

β-Glucans are naturally occurring polysaccharides that are produced by bacteria, yeast, fungi, and many plants. Although their pharmacological activities, such as immunomodulatory, anti-infective and anti-cancer effects, have been well studied, it is still unclear how β-glucans exert their activities. However, recent studies on the β-glucan receptors shed some light on their mechanism of action. Since β-glucans have large molecular weights, they must bind surface receptors to activate immune cells. In this review, we summarize the immunopharmacological activities and the potential receptors of β-glucans in immune cells.

Protecting group-free glycoligation by the desulfurative rearrangement of allylic disulfides as a means of assembly of oligosaccharide mimetics

2-(2-Pyridyldithio-3-butenyl) glycosides react with carbohydrate-based thiols in a two-step process involving sulfenyl transfer followed by desulfurative 2,3-allylic rearrangement, promoted by either triphenylphosphine or silver nitrate, to give novel saccharide mimetics. In an alternative embodiment of the same chemistry anomeric thiols are coupled with carbohydrates derivatized in the form of 2-(2-pyridyldithio-3-butenyl) ethers. This new method of glycoligation does not require protection of hydroxyl groups and is compatible with the presence of acetamides, azides, trichloroethoxycarbamates, and thioglycosides. Variations on the general theme enable the preparation of mimetics of reducing and nonreducing oligosaccharides as well as of nonglycosidically linked systems.

Probing β-(1→3)-D-glucans interactions with recombinant human receptors using high-resolution NMR studies

A full characterization of the high-resolution NMR spectrum of the laminarihexaose is described and used for the determination of the binding epitope of the more complex but structurally related laminarin. These biophysical data extend the current knowledge of β-glucans/Dectin-1 interactions and suggest different biological mechanisms in close relation with the size of the saccharidic chain.

Double diastereoselection explains limitations in synthesizing mannose-containing beta-(1,3)-glucans

It is known that 3-O-glycosylation of glucosidic acceptors bearing acyl groups in the 4 and 6 positions instead of a 4,6-O-benzylidene ring mainly affords alpha-glycosides. Described here is an unexpected stereochemical outcome for elongation at glucose O-3 of a beta-d-Glcp-(1-->3)-alpha-d-Manp disaccharide using peracetylated ethyl thioglucoside as a donor. This unexpected reaction was correlated with match-mismatch effects, as shown by efficient coupling of the same acceptor by a donor of l-configuration.