Chemical approaches for the stereocontrolled synthesis of 1,2-cis-ß-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-ß-D-mannosides, primarily due to the adverse anomeric and Δ-2 effects. Over the past decades, to attain ß-stereoselectivity in D-rhamnosylation, researchers have devised numerous direct and indirect methodologies, including the hydrogen-bond-mediated aglycone delivery (HAD) method, the synthesis of ß-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 ß-D-rhamnosylation and its implications for the total synthesis of tiacumicin B and other physiologically relevant glycans.

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.

Fimbria targeting superparamagnetic iron oxide nanoparticles enhance the antimicrobial and antibiofilm activity of ciprofloxacin against quinolone-resistant E. coli.

High quinolone resistance of Escherichia coli limits the therapy options for urinary tract infection (UTI). In response to the urgent need for efficient treatment of multidrug-resistant infections, we designed a fimbriae targeting superparamagnetic iron oxide nanoparticle (SPION) delivering ciprofloxacin to ciprofloxacin-resistant E. coli. Bovine serum albumin (BSA) conjugated poly(acrylic acid) (PAA) coated SPIONs (BSA@PAA@SPION) were developed for encapsulation of ciprofloxacin and the nanoparticles were tagged with 4-aminophenyl-α-D-mannopyrannoside (mannoside, Man) to target E. coli fimbriae. Ciprofloxacin-loaded mannoside tagged nanoparticles (Cip-Man-BSA@PAA@SPION) provided high antibacterial activity (97.1 and 97.5%, respectively) with a dose of 32 µg/mL ciprofloxacin against two ciprofloxacin-resistant E. coli isolates. Furthermore, a strong biofilm inhibition (86.9% and 98.5%, respectively) was achieved in the isolates at a dose 16 and 8 times lower than the minimum biofilm eradication concentration (MBEC) of ciprofloxacin. Weaker growth inhibition was observed with untargeted nanoparticles, Cip-BSA@PAA@SPIONs, confirming that targeting E. coli fimbria with mannoside-tagged nanoparticles increases the ciprofloxacin efficiency to treat ciprofloxacin-resistant E. coli. Enhanced killing activity against ciprofloxacin-resistant E. coli planktonic cells and strong growth inhibition of their biofilms suggest that Cip-Man-BSA@PAA@SPION system might be an alternative and/or complementary therapeutic option for the treatment of quinolone-resistant E. coli infections.

Synthesis of 2-Amino-2-deoxy-ß-d-mannosides via Stereoselective Anomeric O-Alkylation of 2N,3O-Oxazolidinone-Protected d-Mannosamine: Synthesis of the Trisaccharide Repeating Unit of Streptococcus pneumoniae 19F Polysaccharide.

Cesium carbonate-mediated stereoselective anomeric O-alkylation of a 2N,3O-oxazolidinone-protected d-mannosamine with sugar-derived primary or secondary alkyl triflates afforded the corresponding 2-amino-2-deoxy-ß-d-mannosides in moderate to good yields and excellent stereoselectivity. The oxazolidinone ring can be opened with aqueous alkali hydroxide to liberate the amine functionality. This method has been successfully applied to the synthesis of the trisaccharide repeating unit of Streptococcus pneumoniae 19F polysaccharide.

Validation of Selective Capture of Fimbriated Uropathogenic Escherichia coli by a Label-free Engineering Detection System Using Mannosylated Surfaces.

Label-free detection of pathogens is of major concern to the microbiologist community. Most procedures require several steps and amplification techniques. Carbohydrates are well-established receptors for host-pathogen interactions, which can be amplified using glycodendritic architectures on the basis of multivalent binding interactions. Given that uropathogenic Escherichia coli bacterial FimH is based on such mannopyranoside-binding interactions, we demonstrate herein that synthetic monomeric and trimeric thiolated α-d-mannosides can be effectively bound to gold substrate-functionalized self-assembled monolayers (SAMs) preactivated with maleimide functionalities. Mannosides grafted onto SAMs were followed using Quartz Crystal Microbalance with Dissipation (QCM-D). Binding recognition efficiency was first evaluated using the plant lectin from Canavalia ensiformis (ConA) also using QCM-D. We showed a direct correlation between the amount of mannoside bound and the lectin attachment. Even though there was less trimer bound (nM/cm2) to the surface, we observed a 7-fold higher amount of lectin anchoring, thus further demonstrating the value of the multivalent interactions. We next examined the relative fimbriated E. coli selective adhesion/capture to either the monomeric or the trimeric mannoside bound to the surface. Our results established the successful engineering of the surfaces to show E. coli adhesion via specific mannopyranoside binding but unexpectedly, the monomeric derivative was more efficient than the trimeric analog, which could be explained by steric hindrance. This approach strongly suggests that it could be broadly applicable to other Gram-negative bacteria sharing analogous carbohydrate-dependent binding interactions.

Gordonia zhenghanii sp. nov. and Gordonia liuliyuniae sp. nov., isolated from bat faeces.

Four mesophilic actinobacteria (HY002T, HY442, HY366T and HY285) isolated from the faeces of bats collected in southern China were found to be strictly aerobic, non-motile, rod-shaped, oxidase-negative, Gram-stain-positive and catalase-positive. Strains HY002T and HY366T contained meso-diaminopimelic acid as the diagnostic diamino acid and MK-9(H2) the sole respiratory quinone. Arabinose, galactose and ribose were detected in the whole-cell hydrolysates of both type strains. The main cellular fatty acids (> 10.0%) of all strains were C16 : 0, C18 : 1 ω9c, 10-methyl-C18 : 0 and summed feature 3. Strains HY002T and HY366T contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidyl inositol mannosides as the major polar lipids. The phylogenetic/phylogenomic analyses based on 16S rRNA gene and genomic sequence comparison revealed that the four strains belong to the genus Gordonia, most closely related to G. neofelifaecis NRRL B-59395T(98.2-98.3% sequence similarity) on the EzBioCloud database. The G+C contents of strains HY002T and HY366T based on genomic DNA were 66.5 and 66.9%, respectively. The DNA-DNA relatedness values between the two types strains and members of the genus Gordonia were far below 70 % (18.6-23.1 %). All genotypic and phenotypic data indicated that the four strains are representatives of two novel separate species, for which the names Gordonia zhenghanii sp. nov. and Gordonia liuliyuniae sp. nov. are proposed, with HY002T (=CGMCC 4 7757T=JCM 34 878T) and HY366T (=CGMCC 1 19146T=JCM 34 879T) as the respective type strains.

Cellulomonas dongxiuzhuiae sp. nov., Cellulomonas wangleii sp. nov. and Cellulomonas fengjieae sp. nov., isolated from the intestinal contents of Marmota himalayana.

Six Gram-stain-positive, aerobic or facultative anaerobic, catalase-positive, urease- and oxidase-negative, rod-shaped bacteria (zg-ZUI157T/zg-ZUI40, zg-ZUI222T/zg-ZUI199 and zg-ZUI188T/ zg-ZUI168) were characterized by a polyphasic approach. Optimal growth of the six strains was observed at pH 7.0 and 28 °C. Phylogenetic analyses based on the 16S rRNA gene and 247 core genes revealed that they belong to genus Cellulomonas. The three type strains have low digital DNA-DNA hybridization (19.3-30.1%) and average nucleotide identity values (78.0-85.5%) with all available genomes in the genus Cellulomonas, and a DNA G+C content range of 73.0-74.6 mol%. The major fatty acids detected in strain pairs zg-ZUI157T/zg-ZUI40 and zg-ZUI 222T/zg-ZUI199 were C16:0, anteiso-C15:0 and anteiso A-C15:1, and C16:0, anteiso-C15:0, anteiso A-C15:1 and anteiso-C17:0 in strain pair zg-ZUI188T/zg-ZUI168. Diphosphatidylglycerol, phosphatidylglycerol and phosphatidylinositol mannosides were the major polar lipids detected in the three novel species. MK-9(H4) was the predominant quinone detected in strains zg-ZUI222T (87.4 %) and zg-ZUI188T (91.4 %), and MK-9(H4) (49.1 %) and MK-8 (43.4 %) in strain zg-ZUI157T. The cell-wall sugars detected in the three novel species mainly contained rhamnose. The cell-wall peptidoglycan type of the three novel species was A4ß, with an inferred l-Orn-d-Asp interpeptide bridge for strains zg-ZUI157T and zg-ZUI222T, and l-Orn-d-Glu for strain zg-ZUI188T. Based on the results of the phenotypic, phylogenetic, genomic hybridization, average nucleotide identity and chemotaxonomic analyses, the six strains should be classified as belonging to three novel Cellulomonas species, for which the names Cellulomonas dongxiuzhuiae sp. nov. (zg-ZUI157T=GDMCC 1.2559T=KCTC 49678T), Cellulomonas wangleii sp. nov. (zg-ZUI222T=GDMCC 1.2501T=KCTC 49675T) and Cellulomonas fengjieae sp. nov. (zg-ZUI188T=GDMCC 1.2563T=KCTC 49674T) are proposed.

Efficient Copper-Catalyzed Highly Stereoselective Synthesis of Unprotected C-Acyl Manno-, Rhamno- and Lyxopyranosides.

Due to their high stability towards enzymatic hydrolysis C-acyl glycosidic compounds are useful synthetic intermediates for potential candidates in drug discovery. Syntheses for C-acyl mannosides have remained scarce and usually employ donors obtained from lengthy syntheses. Furthermore, syntheses of unprotected C-acyl mannosides have not been reported so far, due to the incapability of the C-acyl mannoside motif with deprotection conditions for protective groups commonly used in carbohydrate chemistry. Herein, we report an efficient and highly α-selective four-step one-pot method for the synthesis of C-acyl α-d-manno-, l-rhamno- and d-lyxopyranosides from easily accessible persilylated monosaccharides and dithianes requiring only trace amounts of a copper source as catalyst and explain the crucial role of the catalyst by mechanistic studies. Furthermore, the C-acyl α-glycosides were easily isomerized to give rapid access to their ß-anomers.

Unusual ß1-4-galactosidase activity of an α1-6-mannosidase from Xanthomonas manihotis in the processing of branched hybrid and complex glycans.

Mannosidases are a diverse group of glycoside hydrolases that play crucial roles in mannose trimming of oligomannose glycans, glycoconjugates, and glycoproteins involved in numerous cellular processes, such as glycan biosynthesis and metabolism, structure regulation, cellular recognition, and cell-pathogen interactions. Exomannosidases and endomannosidases cleave specific glycosidic bonds of mannoside linkages in glycans and can be used in enzyme-based methods for sequencing of isomeric glycan structures. α1-6-mannosidase from Xanthomonas manihotis is known as a highly specific exoglycosidase that removes unbranched α1-6 linked mannose residues from oligosaccharides. However, we discovered that this α1-6-mannosidase also possesses an unexpected ß1-4-galactosidase activity in the processing of branched hybrid and complex glycans through our use of enzymatic reactions, high performance anion-exchange chromatography, and liquid chromatography mass spectrometric sequencing. Our docking simulation of the α1-6-mannosidase with glycan substrates reveals potential interacting residues in a relatively shallow pocket slightly differing from its homologous enzymes in the glycoside hydrolase 125 family, which may be responsible for the observed higher promiscuity in substrate binding and subsequent terminal glycan hydrolysis. This observation of novel ß1-4-galactosidase activity of the α1-6-mannosidase provides unique insights into its bifunctional activity on the substrate structure-dependent processing of terminal α1-6-mannose of unbranched glycans and terminal ß1-4-galactose of hybrid and complex glycans. The finding thus suggests the dual glycosidase specificity of this α1-6-mannosidase and the need for careful consideration when used for the structural elucidation of glycan isomers.

Inositol acylation of phosphatidylinositol mannosides: a rapid mass response to membrane fluidization in mycobacteria.

Mycobacteria share an unusually complex, multilayered cell envelope, which contributes to adaptation to changing environments. The plasma membrane is the deepest layer of the cell envelope and acts as the final permeability barrier against outside molecules. There is an obvious need to maintain the plasma membrane integrity, but the adaptive responses of the plasma membrane to stress exposure remain poorly understood. Using chemical treatment and heat stress to fluidize the membrane, we show here that phosphatidylinositol (PI)-anchored plasma membrane glycolipids known as PI mannosides (PIMs) are rapidly remodeled upon membrane fluidization in Mycobacterium smegmatis. Without membrane stress, PIMs are predominantly in a triacylated form: two acyl chains of the PI moiety plus one acyl chain modified at one of the mannose residues. Upon membrane fluidization, we determined the fourth fatty acid is added to the inositol moiety of PIMs, making them tetra-acylated variants. Additionally, we show that PIM inositol acylation is a rapid response independent of de novo protein synthesis, representing one of the fastest mass conversions of lipid molecules found in nature. Strikingly, we found that M. smegmatis is more resistant to the bactericidal effect of a cationic detergent after benzyl alcohol pre-exposure. We further demonstrate that fluidization-induced PIM inositol acylation is conserved in pathogens such as Mycobacterium tuberculosis and Mycobacterium abscessus. Our results demonstrate that mycobacteria possess a mechanism to sense plasma membrane fluidity change. We suggest that inositol acylation of PIMs is a novel membrane stress response that enables mycobacterial cells to resist membrane fluidization.

Production and Purification of Phosphatidylinositol Mannosides from Mycobacterium smegmatis Biomass.

Mycobacterium tuberculosis, the etiological agent of tuberculosis, is regarded as the most successful pathogen of humankind and a major threat to global health. The mycobacterial cell wall is vital for cell growth, virulence, and resistance to antibiotics, and thus constitutes a unique target for drug development. To characterize the enzymes catalyzing the synthesis of the cell wall components, considerable amounts of substrates are required. Since many mycobacterial cell wall lipids, particularly phosphatidylinositol mannosides (PIMs), are not commercially available, isolation from cell biomass is the most straightforward way to obtain these compounds. In this study, we optimized a protocol to extract and purify PIM species, in particular Ac1 PIM2 and Ac1 PIM4 , which can be further used for the identification and characterization of target enzymes. PIMs were extracted from Mycobacterium smegmatis mc2 155 ΔPimE using organic solvents, and purified through three consecutive chromatography steps. Thin-layer chromatography (TLC) was used in-between purification steps to evaluate the success of lipid separation, and nuclear magnetic resonance (NMR) was used for product quantification and to assess purity. Typically, from a 60 g batch of M. smegmatis biomass we were able to isolate approximately 9 mg of Ac1 PIM2 and 1.8 mg of Ac1 PIM4 . This is the first time the purification of phosphatidylinositol tetramannoside has been reported. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Growth of M. smegmatis mc2 155 ∆PimE Basic Protocol 2: Extraction of lipids from M. smegmatis mc2 155 ∆PimE Basic Protocol 3: Treatment of the lipid extract for isolation of phospholipids Basic Protocol 4: Isolation of phosphatidylinositol mannosides Basic Protocol 5: Quantification of phosphatidylinositol mannosides.

Anti-tumor and antioxidant activity of kaempferol-3-O-alpha-L-rhamnoside (Afzelin) isolated from Pithecellobium dulce leaves.

BACKGROUND: Pithecellobium dulce (Roxb.), an evergreen medium-sized, spiny tree which have vast nutritional values and widely used in ayurvedic medicines and home remedies. The plant has also been a rich source of biologically active compounds. The present study was designed to isolate pure compound from ethyl acetate fraction of methanol extract of leaves and to know the efficacy as antioxidant as well as its anti-tumor activity on Ehrlich ascites carcinoma cell (EAC).  METHODS: The leaves were extracted with methanol and fractionated with different solvents. The isolation of the compound was carried out by column chromatography from ethyl acetate fraction (EAF) and structure was revealed by 1H-NMR and 13C NMR. The antioxidant activity was investigated by the scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals as well as the inhibition of oxidative damage of pUC19 plasmid DNA, hemolysis and lipid peroxidation induced by a water-soluble free radical initiator 2,2'-azo (2-asmidinopropane) dihydrochloride (AAPH) in human erythrocytes. In vivo anti-tumor activity of the compound was also evaluated by determining the viable tumor cell count, hematological profiles of experimental mice along with observing morphological changes of EAC cells by fluorescence microscope. RESULTS: The isolated compound kaempferol-3-O-alpha-L-rhamnoside effectively inhibited AAPH induced oxidation in DNA and human erythrocyte model and lipid per oxidation as well as a stronger DPPH radical scavenging activity. In anti-tumor assay, at a dose of 50 mg/kg body weight exhibit about 70.89 ± 6.62% EAC cell growth inhibition, whereas standard anticancer drug vincristine showed 77.84 ± 6.69% growth inhibition. CONCLUSION: The compound may have a great importance as a therapeutic agent in preventing oxidative damage of biomolecules and therapeutic use in chemotherapy.

A QCM study of strong carbohydrate-carbohydrate interactions of glycopolymers carrying mannosides on substrates.

Carbohydrates on cell surfaces are known to interact not only with lectins but also with other carbohydrates; the latter process is known as a carbohydrate-carbohydrate interaction. Such interactions are observed in complex oligosaccharides. It would be surprising if these interactions were observed in simple monosaccharides of mannose. In this study, the interaction between glycopolymers carrying monosaccharides of mannose was quantitatively investigated by quartz crystal microbalance measurements. We measured the interactions with glycopolymers carrying mannose, galactose and glucose. Surprisingly, the interaction between the glycopolymers and mannose was much stronger than that between other saccharides.

A new metabolite, mannogeranylnerol, specifically produced at body temperature by Schizophyllum commune, a causative fungus of human mycosis.

Schizophyllum commune is a causative fungus of human mycosis. Its metabolites produced at 27 °C were compared with those produced at 37 °C, to obtain a candidate low-molecular-weight virulence factor related to the pathogenicity of this fungus. We found that S. commune specifically produces two acyclic terpene mannosides at 37 °C. They were identified as nerolidol ß-D-mannoside (1) and geranylnerol ß-D-mannoside (2) by NMR, MS, and CD analyses. Compound 2, a new compound named mannogeranylnerol, showed weak antibiotic activity that was slightly stronger than that of compound 1.

Wound healing potential of quercetin-3-O-rhamnoside and myricetin-3-O-rhamnoside isolated from Pistacia lentiscus distilled leaves in rats model.

The development of bioproducts able to accelerate wound healing is an important topic in biomedicine. In the current study, Pistacia lentiscus distilled leaves (PDL) extract and its two isolated glycosylated flavonoids, myricetin-3-O-rhamnoside (MM) and quercetin-3-O-rhamnoside (QM), were evaluated for their wound healing activity, including evaluation of wound closure, revascularization, wound re-epithelialization, fibroblast proliferation, and collagen deposition on rat skin samples. Moreover, hydroxyproline content, C-reactive protein (CRP) level, and immunohistochemistry study were evaluated on blood and tissues collected from rats on day 14 post-wounding. Results showed that the topical application of PDL (at a concentration of 20 mg/ml) (PDL 20), MM, and QM increased wound healing and decreased inflammatory cells infiltration compared to the negative control group. Moreover, the cutaneous wound tissues treated with PDL 20, MM, and QM exhibited significantly higher hydroxyproline content than the negative control group, which means a high collagen biosynthesis in wound tissues. Indeed, the level of the inflammatory protein CRP is significantly lower in groups treated with MM and QM than in the negative control group. Also, the expression of the pro-inflammatory factor TNF-α and the angiogenesis marker CD-31 in PDL 20, MM, and QM treated groups is lower than in the negative control group. Moreover, MM, and QM induced a good elastase inhibition at 100 µg/ml compared to the standard epigallocatechin gallate. Therefore, PDL 20, MM, and QM could be used as effective cutaneous wound healing agents.

Host- and Age-Dependent Transcriptional Changes in Mycobacterium tuberculosis Cell Envelope Biosynthesis Genes after Exposure to Human Alveolar Lining Fluid.

Tuberculosis (TB) infection, caused by the airborne pathogen Mycobacterium tuberculosis (M.tb), resulted in almost 1.4 million deaths in 2019, and the number of deaths is predicted to increase by 20% over the next 5 years due to the COVID-19 pandemic. Upon reaching the alveolar space, M.tb comes into close contact with the lung mucosa before and after its encounter with host alveolar compartment cells. Our previous studies show that homeostatic, innate soluble components of the alveolar lining fluid (ALF) can quickly alter the cell envelope surface of M.tb upon contact, defining subsequent M.tb-host cell interactions and infection outcomes in vitro and in vivo. We also demonstrated that ALF from 60+ year old elders (E-ALF) vs. healthy 18- to 45-year-old adults (A-ALF) is dysfunctional, with loss of homeostatic capacity and impaired innate soluble responses linked to high local oxidative stress. In this study, a targeted transcriptional assay shows that M.tb exposure to human ALF alters the expression of its cell envelope genes. Specifically, our results indicate that A-ALF-exposed M.tb upregulates cell envelope genes associated with lipid, carbohydrate, and amino acid metabolism, as well as genes associated with redox homeostasis and transcriptional regulators. Conversely, M.tb exposure to E-ALF shows a lesser transcriptional response, with most of the M.tb genes unchanged or downregulated. Overall, this study indicates that M.tb responds and adapts to the lung alveolar environment upon contact, and that the host ALF status, determined by factors such as age, might play an important role in determining infection outcome.

A Remote Secondary Binding Pocket Promotes Heteromultivalent Targeting of DC-SIGN.

Dendritic cells (DC) are antigen-presenting cells coordinating the interplay of the innate and the adaptive immune response. The endocytic C-type lectin receptors DC-SIGN and Langerin display expression profiles restricted to distinct DC subtypes and have emerged as prime targets for next-generation immunotherapies and anti-infectives. Using heteromultivalent liposomes copresenting mannosides bearing aromatic aglycones with natural glycan ligands, we serendipitously discovered striking cooperativity effects for DC-SIGN+ but not for Langerin+ cell lines. Mechanistic investigations combining NMR spectroscopy with molecular docking and molecular dynamics simulations led to the identification of a secondary binding pocket for the glycomimetics. This pocket, located remotely of DC-SIGN's carbohydrate bindings site, can be leveraged by heteromultivalent avidity enhancement. We further present preliminary evidence that the aglycone allosterically activates glycan recognition and thereby contributes to DC-SIGN-specific cell targeting. Our findings have important implications for both translational and basic glycoscience, showcasing heteromultivalent targeting of DCs to improve specificity and supporting potential allosteric regulation of DC-SIGN and CLRs in general.

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.

Recent Advances in Stereocontrolled Mannosylation: Focus on Glycans Comprising Acidic and/or Amino Sugars.

The main focus of this review is to describe accomplishments made in the stereoselective synthesis of ß-linked mannosides functionalized with carboxyls or amines/amides. These ManNAc, ManA and ManNAcA residues found in many glycoconjugates, bacterial polysaccharides, and alginates have consistently captured interest of the glycoscience community both due to synthetic challenge and therapeutic potential.

Evaluating the Sun Protection Factor of Cosmetic Formulations Containing Afzelin.

Exposure to UV radiation damages the skin and increases the risk of skin cancer. Sunscreen is used to protect the skin from the harmful effects of UV radiation. However, the chemical UV filters used in sunscreen can show toxicity and cause allergic reactions. A safe sunscreen that includes a lower content of chemical UV filters and exerts an excellent effect on UV protection needs to be developed. The objective of this study was to investigate whether the addition of afzelin to sunscreen could improve the sun protection factor (SPF). A synergistic effect between afzelin and organic sunscreen agents including padimate O and oxybenzone was confirmed. Interestingly, 100% in vitro SPF-boosting was observed when afzelin (0.05%) was applied with a standard SPF formulation containing organic sunscreens while afzelin alone had no contribution to the SPF. In vivo SPF analysis of the standard SPF formulation showed an SPF value of 13.3 that increased to 20.1 when supplemented with afzelin (0.05%). Additionally, afzelin showed no skin irritation in a human trial. These results suggest that afzelin is useful as a natural additive in sunscreen formulations and provides an SPF-boosting effect. Afzelin supplementation to the formulation showed the potential to reduce the use of synthetic photoprotectors, which could minimize the risk of synthetic agent toxicity.