Zinc(ii)-mediated stereoselective construction of 1,2-cis 2-azido-2-deoxy glycosidic linkage: assembly of Acinetobacter baumannii K48 capsular pentasaccharide derivative.

The capsular polysaccharide (CPS) is a major virulence factor of the pathogenic Acinetobacter baumannii and a promising target for vaccine development. However, the synthesis of the 1,2-cis-2-amino-2-deoxyglycoside core of CPS remains challenging to date. Here we develop a highly α-selective ZnI2-mediated 1,2-cis 2-azido-2-deoxy chemical glycosylation strategy using 2-azido-2-deoxy glucosyl donors equipped with various 4,6-O-tethered groups. Among them the tetraisopropyldisiloxane (TIPDS)-protected 2-azido-2-deoxy-d-glucosyl donor afforded predominantly α-glycoside (α : ß = >20 : 1) in maximum yield. This novel approach applies to a wide acceptor substrate scope, including various aliphatic alcohols, sugar alcohols, and natural products. We demonstrated the versatility and effectiveness of this strategy by the synthesis of A. baumannii K48 capsular pentasaccharide repeating fragments, employing the developed reaction as the key step for constructing the 1,2-cis 2-azido-2-deoxy glycosidic linkage. The reaction mechanism was explored with combined experimental variable-temperature NMR (VT-NMR) studies and mass spectroscopy (MS) analysis, and theoretical density functional theory calculations, which suggested the formation of covalent α-C1GlcN-iodide intermediate in equilibrium with separated oxocarbenium-counter ion pair, followed by an SN1-like α-nucleophilic attack most likely from separated ion pairs by the ZnI2-activated acceptor complex under the influence of the 2-azido gauche effect.

Structural elucidation of a capsular polysaccharide from Bacteroides uniformis and its ameliorative impact on DSS-induced colitis in mice.

Capsular polysaccharides derived from Bacteroides species have emerged as potential mitigators of intestinal inflammation in murine models. However, research on capsular polysaccharides from B. uniformis, a Bacteroides species with reduced abundance in colons of patients with ulcerative colitis, remains scarce. In this study, we extracted a neutral polysaccharide component from B. uniformis ATCC8492, termed BUCPS1B, using ultrasonic disruption, ethanol precipitation, and anion exchange chromatography. Structural characterization revealed BUCPS1B as a water-soluble polysaccharide with an α-1,4-glucan main chain adorned with minor substituent sugar residues. BUCPS1B alleviated intestinal inflammation in a mouse model of colitis and induced polarization of macrophages into M2-type. Furthermore, BUCPS1B modulated the gut microbiota composition, increased the abundance of the probiotic Akkermansia muciniphila and altered the gut metabolic profile to promote phenylalanine and short chain fatty acids metabolism. BUCPS1B is therefore a promising candidate to prevent inflammation and augment intestinal health.

Total synthesis of the hexasaccharide arabinan domain of mycobacterial arabinogalactan.

The hexasaccharide arabinan domain of Mycobacterial Arabinogalactan was provided with the versatile methodology toward ß-selective arabinofuranosylation directed by B(C6F5)3, demonstrating the effectiveness of the ß-arabinofuranosylation strategy. Derivatization of the amino moiety at the reducing end are essential prerequisites for elucidating the biosynthetic pathway and conjugating of this compound to a protein carrier for vaccine generation.

B(C6F5)3-Catalyzed Stereoselective 1,2-cis Arabinofuranosylation with a Conformationally Constrained Donor.

Compared with stereoselective glycosylation methods mainly addressed on the preparation of pyranose glycosides, the furanosylation has been more limited, especially for the 1,2-cis arabinofuranosylation. Herein, we report a novel stereoselective 1,2-cis-arabinofuranosylation strategy using a conformationally restricted 3,5-O-xylylene-protected arabinofuranosyl donor on activation with B(C6F5)3 for desired targets in moderate to excellent yields and ß-stereoselectivity. The effectiveness of the 1,2-cis-arabinofuranosylation strategy was demonstrated successfully with various acceptors, including carbohydrate alcohols.

Synthetic self-adjuvanted multivalent Mucin 1 (MUC1) glycopeptide vaccines with improved in vivo antitumor efficacy.

The tumor-associated glycoprotein Mucin 1 (MUC1) is aberrantly glycosylated on cancer cells and is considered a promising target for antitumor vaccines. The weak immunogenicity and low sequence homology of mouse mucins and human MUC1 are the main obstacles for the development of vaccines. Herein, a self-adjuvanted strategy combining toll-like receptor 2 lipopeptide ligands and T-cell epitopes and the multivalent effect were used to amplify the immune response and evade the unpredictable immunogenicity, generating two self-adjuvanted three-component MUC1 vaccines (mono- and trivalent MUC1 vaccines). To simulate the aberrantly glycosylated MUC1 glycoprotein, the MUC1 tandem repeat peptide was bounded with Tn antigens at T9, S15, and T16, and served as B-cell epitopes. Results showed that both vaccines elicited a robust antibody response in wild-type mice compared with a weaker response in MUC1 transgenic mice. The trivalent vaccine did not elevate the antibody response level compared with the monovalent vaccine; however, a more delayed tumor growth and prolonged survival time was realized in wild-type and transgenic mouse models treated with the trivalent vaccine. These results indicate that the self-adjuvanted three-component MUC1 vaccines, especially the trivalent vaccine, can trigger robust antitumor effects regardless of sequence homology, and, therefore, show promise for clinical translation.

Recent Progress in 1,2-cis glycosylation for Glucan Synthesis.

Controlling the stereoselectivity of 1,2-cis glycosylation is one of the most challenging tasks in the chemical synthesis of glycans. There are various 1,2-cis glycosides in nature, such as α-glucoside and ß-mannoside in glycoproteins, glycolipids, proteoglycans, microbial polysaccharides, and bioactive natural products. In the structure of polysaccharides such as α-glucan, 1,2-cis α-glucosides were found to be the major linkage between the glucopyranosides. Various regioisomeric linkages, 1→3, 1→4, and 1→6 for the backbone structure, and 1→2/3/4/6 for branching in the polysaccharide as well as in the oligosaccharides were identified. To achieve highly stereoselective 1,2-cis glycosylation, including α-glucosylation, a number of strategies using inter- and intra-molecular methodologies have been explored. Recently, Zn salt-mediated cis glycosylation has been developed and applied to the synthesis of various 1,2-cis linkages, such as α-glucoside and ß-mannoside, via the 1,2-cis glycosylation pathway and ß-galactoside 1,4/6-cis induction. Furthermore, the synthesis of various structures of α-glucans has been achieved using the recent progressive stereoselective 1,2-cis glycosylation reactions. In this review, recent advances in stereoselective 1,2-cis glycosylation, particularly focused on α-glucosylation, and their applications in the construction of linear and branched α-glucans are summarized.

Immunomodulatory Effect and Biological Significance of ß-Glucans.

ß-glucan, one of the homopolysaccharides composed of D-glucose, exists widely in cereals and microorganisms and possesses various biological activities, including anti-inflammatory, antioxidant, and anti-tumor properties. More recently, there has been mounting proof that ß-glucan functions as a physiologically active "biological response modulator (BRM)", promoting dendritic cell maturation, cytokine secretion, and regulating adaptive immune responses-all of which are directly connected with ß-glucan-regulated glucan receptors. This review focuses on the sources, structures, immune regulation, and receptor recognition mechanisms of ß-glucan.

Molecularly Stimuli-Responsive Self-Assembled Peptide Nanoparticles for Targeted Imaging and Therapy.

Self-assembly has emerged as an extensively used method for constructing biomaterials with sizes ranging from nanometers to micrometers. Peptides have been extensively investigated for self-assembly. They are widely applied owing to their desirable biocompatibility, biodegradability, and tunable architecture. The development of peptide-based nanoparticles often requires complex synthetic processes involving chemical modification and supramolecular self-assembly. Stimuli-responsive peptide nanoparticles, also termed "smart" nanoparticles, capable of conformational and chemical changes in response to stimuli, have emerged as a class of promising materials. These smart nanoparticles find a diverse range of biomedical applications, including drug delivery, diagnostics, and biosensors. Stimuli-responsive systems include external stimuli (such as light, temperature, ultrasound, and magnetic fields) and internal stimuli (such as pH, redox environment, salt concentration, and biomarkers), facilitating the generation of a library of self-assembled biomaterials for biomedical imaging and therapy. Thus, in this review, we mainly focus on peptide-based nanoparticles built by self-assembly strategy and systematically discuss their mechanisms in response to various stimuli. Furthermore, we summarize the diverse range of biomedical applications of peptide-based nanomaterials, including diagnosis and therapy, to demonstrate their potential for medical translation.

Strategies for Synthesizing and Enhancing the Immune Response of Cancer Vaccines Based on MUC1 Glycopeptide Antigens.

Cancer vaccines are based on a vaccinology strategy whereby the patient's immune system is harnessed to induce a specific immune response to kill cancer cells and comprises two categories: prophylactic and therapeutic. Glycoprotein mucin 1 (MUC1), which is overexpressed and poorly glycosylated on cancer cells, is one of the most promising candidates for the development of new cancer vaccines. However, it should be noted that mucin-like glycopeptides are poorly immunogenic and unable to elicit effective and long-lasting immune responses. Therefore, MUC1-derived tumor antigens need to be conjugated with immune activators. This review focuses on the synthesis of MUC1 glycopeptides, provides an overview of recently advanced designs of vaccines based on MUC1, and compares the advantages and disadvantages of the various strategies devised to date.

ZnI2-Mediated ß-Galactosylation of C2-Ether-Type Donor.

Conventional glycosylation with galactosyl donors having C-2 benzyl (Bn) ether-type functionality often leads to anomeric mixtures, due to the anomeric and steric effects that stabilize the 1,2-cis-α- and 1,2-trans-ß-glycosides, respectively. Herein we report a versatile ZnI2-directed ß-galactosylation approach employing a 4,6-O-tethered and 2-O-Bn galactosyl donor for the stereoselective and efficient synthesis of ß-O-galactosides. With a broad substrate scope, the reaction tolerates a wide range of functional groups and complex molecular architectures, providing stereocontrolled ß-galactosides in moderate to excellent yields. The practicality of this transformation is demonstrated through the synthesis of a tetrasaccharide arabinogalactan fragment with high stereoselectivity.

Recent advances in stereoselective 1,2-cis-O-glycosylations.

For the stereoselective assembly of bioactive glycans with various functions, 1,2-cis-O-glycosylation is one of the most essential issues in synthetic carbohydrate chemistry. The cis-configured O-glycosidic linkages to the substituents at two positions of the non-reducing side residue of the glycosides such as α-glucopyranoside, α-galactopyranoside, ß-mannopyranoside, ß-arabinofuranoside, and other rather rare glycosides are found in natural glycans, including glycoconjugate (glycoproteins, glycolipids, proteoglycans, and microbial polysaccharides) and glycoside natural products. The way to 1,2-trans isomers is well sophisticated by using the effect of neighboring group participation from the most effective and kinetically favored C-2 substituent such as an acyl group, although high stereoselective synthesis of 1,2-cis glycosides without formation of 1,2-trans isomers is far less straightforward. Although the key factors that control the stereoselectivity of glycosylation are largely understood since chemical glycosylation was considered to be one of the useful methods to obtain glycosidic linkages as the alternative way of isolation from natural sources, strictly controlled formation of these 1,2-cis glycosides is generally difficult. This minireview introduces some of the recent advances in the development of 1,2-cis selective glycosylations, including the quite recent developments in glycosyl donor modification, reaction conditions, and methods for activation of intermolecular glycosylation, including the bimodal glycosylation strategy for 1,2-cis and 1,2-trans glycosides, as well as intramolecular glycosylations, including recent applications of NAP-ether-mediated intramolecular aglycon delivery.

Recent Chemical and Chemoenzymatic Strategies to Complex-Type N-Glycans.

Glycosylation is one of the major forms of protein post-translational modification. N-glycans attached to proteins by covalent bonds play an indispensable role in intercellular interaction and immune function. In human bodies, most of the cell surface glycoproteins and secreted glycopeptides are modified with complex-type N-glycans. Thus, for analytical or medicinal purposes, efficient and universal methods to provide homogeneous complex-type N-glycans have been an urgent need. Despite the extremely complicated structures, tremendous progress in the synthesis of N-glycans has been achieved. On one hand, chemical strategies are shown to be effective to prepare core oligosaccharides of N-glycans by focusing on stereoselective glycosylations such as ß-mannosylation and α-sialylation, as well as the methodology of the N-glycan assembly. On the other hand, chemoenzymatic strategies have also become increasingly powerful in recent years. This review attempts to highlight the very recent advancements in chemical and chemoenzymatic strategies for eukaryotic complex-type N-glycans.

Built-in adjuvants for use in vaccines.

Vaccine refers to biological products that are produced using various pathogenic microorganisms for inoculation. The goal of vaccination is to induce a robust immune response against a specific antigen, thus preventing the organism from getting infected. In vaccines, adjuvants have been widely employed to enhance immunity against specific antigens. An ideal adjuvant should be stable, biodegradable, and low cost, not induce system rejection and promote an immune response. Various adjuvant components have been investigated across diverse applications. Typically, adjuvants are employed to meet the following objectives: (1) to improve the effectiveness of immunization with vaccines for specific populations, such as newborns and the elderly; (2) enhance the immunogenicity of highly purified or recombinant antigens; (3) allow immunization with a smaller dose of the vaccine, reducing drug dosage. In the present review, we primarily focus on chemically synthesized compounds that can be used as built-in adjuvants. We elaborate the classification of these compounds based on the induced immune activation mechanism and summarize their application in various vaccine types.

Zinc(II) Iodide-Directed ß-Mannosylation: Reaction Selectivity, Mode, and Application.

A direct, efficient, and versatile glycosylation methodology promises the systematic synthesis of oligosaccharides and glycoconjugates in a streamlined fashion like the synthesis of medium to long-chain nucleotides and peptides. The development of a generally applicable approach for the construction of 1,2-cis-glycosidic bond with controlled stereoselectivity remains a major challenge, especially for the synthesis of ß-mannosides. Here, we report a direct mannosylation strategy mediated by ZnI2, a mild Lewis acid, for the highly stereoselective construction of 1,2-cis-ß linkages employing easily accessible 4,6-O-tethered mannosyl trichloroacetimidate donors. The versatility and effectiveness of this strategy were demonstrated with successful ß-mannosylation of a wide variety of alcohol acceptors, including complex natural products, amino acids, and glycosides. Through iteratively performing ZnI2-mediated mannosylation with the chitobiosyl azide acceptor followed by site-selective deprotection of the mannosylation product, the novel methodology enables the modular synthesis of the key intermediate trisaccharide with Man-ß-(1 → 4)-GlcNAc-ß-(1 → 4)-GlcNAc linkage for N-glycan synthesis. Theoretical investigations with density functional theory calculations delved into the mechanistic details of this ß-selective mannosylation and elucidated two zinc cations' essential roles as the activating agent of the donor and the principal mediator of the cis-directing intermolecular interaction.

ZnI2-Directed Stereocontrolled α-Glucosylation.

Here we report a glucosylation strategy mediated by ZnI2, a cheap and mild Lewis acid, for the highly stereoselective construction of 1,2-cis-O-glycosidic linkages using easily accessible and common 4,6-O-tethered glucosyl donors. The versatility and effectiveness of the α-glucosylation strategy were demonstrated successfully with various acceptors, including complex alcohols. This approach demonstrates the feasibility of the modular synthesis of various α-glucans with both linear and branched backbone structures.

Lysolipid Chain Length Switches Agonistic to Antagonistic G Protein-Coupled Receptor Modulation.

Activation of lysolipid-sensitive G protein-coupled receptors (GPCR) depends not only on lysolipid class but also on the length and degree of saturation of their respective hydrophobic tails. Positive regulation of these signaling networks caused by the lipid chain length specificity of upstream phospholipases is firmly established. Nonagonistic lysolipid homologues, featuring incompatible lipid tails, have been suggested to indirectly modulate GPCR signaling by delaying agonist catabolism. Nonetheless, recent results seem inconsistent with this hypothesis. Utilizing a simplified lysolipid-GPCR signaling assay based on the established lysophosphatidylglucoside-GPR55 signaling axis in primary sensory neurons, we demonstrate that short-chain ligand homologues directly modulate receptor activation via a potent competitive antagonistic activity. Considering the well-documented tissue-specific concentration of lysolipid homologues, we propose that endogenous lysolipids with insufficient chain length for stable receptor activation exert an antagonistic activity, effectively representing a negative control mechanism for GPCR-associated lysolipid signaling.

Systematic synthesis of novel phosphoglycolipid analogues as potential agonists of GPR55.

Rhodopsin-like G protein-coupled receptor (GPCR) GPR55 is attracting attention as a pharmaceutical target, because of its relationship with various physiological and pathological events. Although GPR55 was initially deorphanized as a cannabinoid receptor, lysophosphatidylinositol (LPI) is now widely perceived to be an endogenous ligand of GPR55. Recently, lysophosphatidyl-ß-d-glucoside (LPGlc) has been found to act on GPR55 to repel dorsal root ganglion (DRG) neurons. In this study, we designed and synthesized various LPGlc analogues having the squaryldiamide group as potential agonists of GPR55. By the axon turning assay, several analogues exhibited similar activities to that of LPGlc. These results will provide valuable information for understanding the mode of action of LPGlc and its analogues and for the discovery of potent and selective antagonists or agonists of GPR55.

Unified Strategy toward Stereocontrolled Assembly of Various Glucans Based on Bimodal Glycosyl Donors.

Polymers of glucose, the most abundant and one of the biologically important natural products, named glucans are widely present in fungi, bacteria, mammals, and plants with various anomeric configurations and glycosidic linkages. Because of their structural diversity, the unified strategy for the assembly of pure glucans is yet to be developed. Herein, we describe a general strategy that is applicable to construction of all types of glucans by exploiting a bimodal glycosyl donor equipped with C2-o-TsNHbenzyl ether (TAB), which enables stereocontrolled synthesis of both α- and ß-glycosides by switching reaction conditions.

Bimodal Glycosyl Donors Protected by 2- O-( ortho-Tosylamido)benzyl Group.

A glucosyl donor equipped with C2- o-TsNHbenzyl ether was shown to provide both α- and ß-glycosides stereoselectivity, by changing the reaction conditions. Namely, ß-glycosides were selectively obtained when the trichloroacetimidate was activated by Tf2NH. On the other hand, activation by TfOH in Et2O provided α-glycosides as major products. This "single donor" approach was employed to assemble naturally occurring trisaccharide α-d-Glc-(1→2)-α-d-Glc-(1→6)-d-Glc and its anomers.

Squaryl group modified phosphoglycolipid analogs as potential modulators of GPR55.

Lysophosphatidyl glucoside (LPGlc) is a structurally unique glycolipid that acts as a guidance cue for extending axons during central nervous system development by activating the class A G protein coupled receptor (GPR) 55 of spinal cord sensory axons. GPR55 not only plays an important role during development, but is also implicated in many disease states, rendering molecules that target GPR55 of widespread interest. In this study, we developed synthetic access to a novel class of LPGlc analogues featuring a squaryl diamide group as surrogate for the phosphodiester. We report the facile synthesis of a series of LPGlc analogues, their GPR dependent biological activity and a systematic analysis of the structure-activity relationship in regards to GPR55 modulation. The lead compound featuring identical configuration at all stereocenters compared to natural LPGlc exhibits an activity to repel axons of dorsal root ganglion (DGR) nociceptive neurons.