Direct Synthesis of Glycosyl Chlorides from Thioglycosides

Reported herein is a new method for the direct synthesis of glycosyl chlorides from thioglycosides using sulfuryl chloride at rt. A variety of thioglycosides and thioimidates could be used as substrates. Both acid- and base-sensitive protecting groups were found compatible with these reaction conditions. Preliminary investigation of the reaction mechanism indicates chlorination of the leaving group at the anomeric sulfur as the key step of the reaction.

A Strain-Promoted Divergent Chemical Steroidation Unveils Potent Anti-Inflammatory Pseudo-Steroidal Glycosides

The development of novel agents with immunoregulatory effects is a keen way to combat the growing threat of inflammatory storms to global health. To synthesize pseudo-steroidal glycosides tethered by ether bonds with promising immunomodulatory potential, we develop herein a highly effective deoxygenative functionalization of a novel steroidal donor (steroidation) facilitated by strain-release, leveraging cost-effective and readily available Sc(OTf)3 catalysis. This transformation produces a transient steroid-3-yl carbocation which readily reacts with O-, C-, N-, S-, and P-nucleophiles to generate structurally diverse steroid derivatives. DFT calculations were performed to shed light on the mechanistic details of the regioselectivity, underlying an acceptor-dependent steroidation mode. This approach can be readily extended to the etherification of sugar alcohols to enable the achievement of a diversity-oriented, pipeline-like synthesis of pseudo-steroidal glycosides in good to excellent yields with complete stereo- and regiospecific control for anti-inflammatory agent discovery. Immunological studies have demonstrated that a meticulously designed cholesteryl disaccharide can significantly suppress interleukin-6 secretion in macrophages, exhibiting up to 99% inhibition rates compared to the negative control. These findings affirm the potential of pseudo-steroidal glycosides as a prospective category of lead agents for the development of novel anti-inflammatory drugs.

Activation of glycosyl methylpropiolates by TfOH

Activation of glycosyl methylpropiolates by TfOH was investigated. Armed and superarmed glycosyl donors can be activated by use of 0.2 equivalent TfOH whereas 1.0 equivalent of TfOH was required for the activation of the disarmed glycosyl donors. All the glycosidations gave very good yields. The method is suitable for synthesis of glycosides and disaccharides and it may result in the hydrolysis of the interglycosidic bond if the sugar at the non-reducing end is armed or superarmed. These problems are not seen when gold-catalyzed activation procedures are invoked for the activation of glycosyl alkynoates.

Pd-catalyzed stereoselective synthesis of chromone C-glycosides

Herein, we present an efficient Pd-catalysed method for stereoselective synthesis of chromone C-glycosides from various glycals. We successfully applied this method to various glycals with different protecting groups, yielding the corresponding glycosides in 41-78% yields. Additionally, we investigated the potential of this approach for the late-stage modification of natural products and pharmaceutical compounds linked to glycals, leading to the synthesis of their respective glycosides. Furthermore, we extended our research to gram-scale synthesis and demonstrated its applicability in producing various valuable products, including 2-deoxy-chromone C-glycosides. In summary, our work introduces a novel library of chromone glycosides, which holds promise for advancing drug discovery efforts.

Synthesis and Preliminary Anticancer Activity Assessment of N-Glycosides of 2-Amino-1,3,4-thiadiazoles

The addition of 2-amino-1,3,4-thiadiazole derivatives with parallel iodination of differently protected glycals has been achieved using a double molar excess of molecular iodine under mild conditions. The corresponding thiadiazole derivatives of N-glycosides were obtained in good yields and anomeric selectivity. The usage of iodine as a catalyst makes this method easy, inexpensive, and successfully useable in reactions with sugars. Thiadiazole derivatives were tested in a panel of three tumor cell lines, MCF-7, HCT116, and HeLa. These compounds initiated biological response in investigated tumor models in a different rate. The MCF-7 is resistant to the tested compounds, and the cytometry assay indicated low increase in cell numbers in the sub- G1 phase. The most sensitive are HCT-116 and HeLa cells. The thiadiazole derivatives have a pro-apoptotic effect on HCT-116 cells. In the case of the HeLa cells, an increase in the number of cells in the sub-G1- phase and the induction of apoptosis was observed.

Δ8(14)-Ergostenol Glycoside Derivatives Inhibit the Expression of Inflammatory Mediators and Matrix Metalloproteinase

Arthritis is a chronic inflammatory disease accompanied by pathological reactions such as swelling, redness, fever, and pain in various joint areas. The drugs currently available to treat arthritis are associated with diverse side-effects. Therefore, there is a need for safer and more effective treatments to alleviate the inflammation of arthritis with fewer side-effects. In this study, a new sterol, Δ⁸⁽¹⁴⁾-ergostenol, was discovered, and its glycosides were synthesized and found to be more efficient in terms of synthesis or anti-inflammatory activity than either spinasterol or 5,6-dihydroergosterol is. Among these synthetic glycosides, galactosyl ergostenol inhibited the expression of inflammatory mediators in TNF-α-stimulated FLS and TNF-α-induced MMPs and collagen type II A1 degradation in human chondrocytes. These results suggest the new galactosyl ergostenol as a treatment candidate for arthritis.

Synthesis of novel oligomeric anionic alkyl glycosides using laccase/TEMPO oxidation and cyclodextrin glucanotransferase (CGTase)-catalyzed transglycosylation

Modification of alkyl glycosides, to alter their properties and widen the scope of potential applications, is of considerable interest. Here, we report the synthesis of new anionic alkyl glycosides with long carbohydrate chains, using two different approaches: laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation of a long-carbohydrate-chain alkyl glycoside and cyclodextrin glucanotransferase (CGTase)-catalyzed elongation of anionic alkyl glycosides. The laccase/TEMPO oxidation of dodecyl β- d-maltooctaoside proceeded efficiently with the formation of aldehyde and acid products. However, depolymerization occurred to a large extent, limiting the product yield and purity. On the other hand, CGTase-catalyzed coupling/disproportionation reactions with α-cyclodextrin and dodecyl β- d-maltoside diuronic acid (DDM-2COOH) or octyl β- d-glucuronic acid (OG-COOH) as substrates gave high conversions, especially when the CGTase Toruzyme was used. It was found that pH had a strong influence on both the enzyme activity and the acceptor specificity. With non-ionic substrates (dodecyl β- d-maltoside and octyl β- d-glucoside), Toruzyme exhibited high catalytic activity at pH 5-6, but for the acidic substrates (DDM-2COOH and OG-COOH) the activity was highest at pH 4. This is most likely due to the enzyme favoring the protonated forms of DDM-2COOH and OG-COOH, which exist at lower pH (pKa about 3).

Diastereoselective Synthesis of Aryl C-Glycosides from Glycosyl Esters via C-O Bond Homolysis

C-aryl glycosyl compounds offer better in vivo stability relative to O- and N-glycoside analogues. C-aryl glycosides are extensively investigated as drug candidates and applied to chemical biology studies. Previously, C-aryl glycosides were derived from lactones, glycals, glycosyl stannanes, and halides, via methods displaying various limitations with respect to the scope, functional-group compatibility, and practicality. Challenges remain in the synthesis of C-aryl nucleosides and 2-deoxysugars from easily accessible carbohydrate precursors. Herein, we report a cross-coupling method to prepare C-aryl and heteroaryl glycosides, including nucleosides and 2-deoxysugars, from glycosyl esters and bromoarenes. Activation of the carbohydrate substrates leverages dihydropyridine (DHP) as an activating group followed by decarboxylation to generate a glycosyl radical via C-O bond homolysis. This strategy represents a new means to activate alcohols as a cross-coupling partner. The convenient preparation of glycosyl esters and their stability exemplifies the potential of this method in medicinal chemistry.

Synthesis of Galectin Inhibitors by Regioselective 3'-O-Sulfation of Vanillin Lactosides Obtained under Phase Transfer Catalysis

Vanillin-based lactoside derivatives were synthetized using phase-transfer catalyzed reactions from per-O-acetylated lactosyl bromide. The aldehyde group of the vanillin moiety was then modified to generate a series of related analogs having variable functionalities in the para- position of the aromatic residue. The corresponding unprotected lactosides, obtained by Zemplén transesterification, were regioselectively 3'-O-sulfated using tin chemistry activation followed by treatment with sulfur trioxide-trimethylamine complex (Men3N-SO3). Additional derivatives were also prepared from the vanillin's aldehyde using a Knoevenagel reaction to provide extended α, β-unsaturated carboxylic acid which was next reduced to the saturated counterpart.

Flavonoid Glycosides with a Triazole Moiety for Marine Antifouling Applications: Synthesis and Biological Activity Evaluation

Over the last decades, antifouling coatings containing biocidal compounds as active ingredients were used to prevent biofouling, and eco-friendly alternatives are needed. Previous research from our group showed that polymethoxylated chalcones and glycosylated flavones obtained by synthesis displayed antifouling activity with low toxicity. In this work, ten new polymethoxylated flavones and chalcones were synthesized for the first time, including eight with a triazole moiety. Eight known flavones and chalcones were also synthesized and tested in order to construct a quantitative structure-activity relationship (QSAR) model for these compounds. Three different antifouling profiles were found: three compounds (1b, 11a and 11b) exhibited anti-settlement activity against a macrofouling species (Mytilus galloprovincialis), two compounds (6a and 6b) exhibited inhibitory activity against the biofilm-forming marine bacteria Roseobacter litoralis and one compound (7b) exhibited activity against both mussel larvae and microalgae Navicula sp. Hydrogen bonding acceptor ability of the molecule was the most significant descriptor contributing positively to the mussel larvae anti-settlement activity and, in fact, the triazolyl glycosylated chalcone 7b was the most potent compound against this species. The most promising compounds were not toxic to Artemia salina, highlighting the importance of pursuing the development of new synthetic antifouling agents as an ecofriendly and sustainable alternative for the marine industry.

Synthesis and Biological Evaluation of Novel Pyrane Glycosides

A series of novel (5R)-5-((2S,3S)-3-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3,6-dihydro-2H-pyran-2-yl)-3-(4-fluorophenyl)-2,6-diphenyl-3,3a,5,6-tetrahydro-2H-pyrazolo[3,4-d]thiazoles 11a-g and (5R)-5-((2S,3S)-3-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3,6-dihydro-2H-pyran-2-yl)-3-(4-fluorophenyl)-6-phenyl-3,3a,5,6-tetrahydroisoxazolo[3,4-d]thiazoles 12a-g were synthesized by the reaction of chalcone derivatives of (R,Z)-2-((2S,3S)-3-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3,6-dihydro-2H-pyran-2-yl)-5-(4-fluorobenzylidene)-3-phenylthiazolidin-4-ones 10a-g with phenylhydrazine and hydroxylamine hydrochloride. The chemical structures of newly synthesized compounds were elucidated by IR, NMR, MS and elemental analysis. The compounds 11a-g and 12a-g were evaluated for their antibacterial activity and antifungal activity.

Synthesis, Cytotoxic Activity Evaluation and Quantitative Structure-Activity Analysis of Substituted 5,8-Dihydroxy-1,4-Naphthoquinones and their O- and S-Glycoside Derivatives Tested Against Neuro-2a Cancer Cells

Based on 6,7-substituted 2,5,8-trihydroxy-1,4-naphtoquinones (1,4-NQs) derived from sea urchins, five new acetyl-O-glucosides of NQs were prepared. A new method of conjugation of per-O-acetylated 1-mercaptosaccharides with 2-hydroxy-1,4-NQs through a methylene spacer was developed. Methylation of 2-hydroxy group of quinone core of acetylthiomethylglycosides by diazomethane and deacetylation of sugar moiety led to 28 new thiomethylglycosidesof 2-hydroxy- and 2-methoxy-1,4-NQs. The cytotoxic activity of starting 1,4-NQs (13 compounds) and their O- and S-glycoside derivatives (37 compounds) was determined by the MTT method against Neuro-2a mouse neuroblastoma cells. Cytotoxic compounds with EC50 = 2.7-87.0 μM and nontoxic compounds with EC50 > 100 μM were found. Acetylated O- and S-glycosides 1,4-NQs were the most potent, with EC50 = 2.7-16.4 μM. Methylation of the 2-OH group innaphthoquinone core led to a sharp increase in the cytotoxic activity of acetylated thioglycosidesof NQs, which was partially retained for their deacetylated derivatives. Thiomethylglycosides of 2-hydroxy-1,4-NQs with OH and MeO groups in quinone core at positions 6 and 7, resprectively formed a nontoxic set of compounds with EC50 > 100 μM. A quantitative structure-activity relationship (QSAR) model of cytotoxic activity of 22 1,4-NQ derivatives was constructed and tested. Descriptors related to the cytotoxic activity of new 1,4-NQ derivatives were determined. The QSAR model is good at predicting the activity of 1,4-NQ derivatives which are unused for QSAR models and nontoxic derivatives.

Synthetic Ellagic Acid Glycosides Inhibit Early Stage Adhesion of Streptococcus agalactiae Biofilms as Observed by Scanning Electron Microscopy

Ellagic acid derivatives possess antimicrobial and antibiofilm properties across a wide-range of microbial pathogens. Due to their poor solubility and ambident reactivity it is challenging to synthesize, purify, and characterize the activity of ellagic acid glycosides. In this study, we have synthesized three ellagic acid glycoconjugates and evaluated their antimicrobial and antibiofilm activity in Streptococcus agalactiae (Group B Streptococcus, GBS). Their significant impacts on biofilm formation were examined via SEM to reveal early-stage inhibition of cellular adhesion. Additionally, the synthetic glycosides were evaluated against five of the six ESKAPE pathogens and two fungal pathogens. These studies reveal that the ellagic acid glycosides possess inhibitory effects on the growth of gram-negative pathogens.

Automated Solution-Phase Synthesis of S-Glycosides for the Production of Oligomannopyranoside Derivatives

Thioglycosides are more resistant to enzymatic hydrolysis than their O-linked counterparts, thereby becoming attractive targets for carbohydrate-based therapeutic development. We report the first development of methods for the site-selective incorporation of S-linkages into automated solution-phase oligosaccharide protocols. The protocols were shown to be compatible with the formation of S- or O-glycosides for the synthesis of mannopyranoside trimmers that incorporate both S- and O-linkages to allow the selective incorporation of an S-glycoside in various stages in an automated program.

Photoinitiated Thiol-ene Reactions of Enoses: A Powerful Tool for Stereoselective Synthesis of Glycomimetics with Challenging Glycosidic Linkages

Thioglycosides and C-glycosides represent pharmacologically useful classes of glycomimetics that possess a high degree of biological stability. One emerging tool for the stereoselective synthesis of thioglycosides is the photoinitiated addition of thiols to unsaturated sugars. Moreover, thiyl radical-mediated reactions of exo-glycals and 1-substituted endo-glycals offer facile routes to β-C-glycosidic structures. This Concept article summarizes the thiol-ene coupling strategies developed recently by our group and Somsák's group for the synthesis of several kinds of glycomimetics which are difficult to synthesize by conventional methods. One unusual characteristic of the thiol-ene reactions of endo-glycals is that heating inhibits, whereas cooling promotes the reaction. This unique temperature dependence as well as the effects of the enose structures and thiol configurations on the efficacy and stereoselectivity of the reactions are also discussed.

Sucrose Phosphorylase and Related Enzymes in Glycoside Hydrolase Family 13: Discovery, Application and Engineering

Sucrose phosphorylases are carbohydrate-active enzymes with outstanding potential for the biocatalytic conversion of common table sugar into products with attractive properties. They belong to the glycoside hydrolase family GH13, where they are found in subfamily 18. In bacteria, these enzymes catalyse the phosphorolysis of sucrose to yield α-glucose 1-phosphate and fructose. However, sucrose phosphorylases can also be applied as versatile transglucosylases for the synthesis of valuable glycosides and sugars because their broad promiscuity allows them to transfer the glucosyl group of sucrose to a diverse collection of compounds other than phosphate. Numerous process and enzyme engineering studies have expanded the range of possible applications of sucrose phosphorylases ever further. Moreover, it has recently been discovered that family GH13 also contains a few novel phosphorylases that are specialised in the phosphorolysis of sucrose 6F-phosphate, glucosylglycerol or glucosylglycerate. In this review, we provide an overview of the progress that has been made in our understanding and exploitation of sucrose phosphorylases and related enzymes over the past ten years.

Synthesis of Glycosyl Chlorides and Bromides by Chelation Assisted Activation of Picolinic Esters under Mild Neutral Conditions

A general method has been developed for the formation of glycosyl chlorides and bromides from picolinic esters under mild and neutral conditions. Benchtop stable picolinic esters are activated by a copper(II) halide species to afford the corresponding products in high yields with a traceless leaving group. Rare β glycosyl chlorides are accessible via this route through neighboring group participation. Additionally, glycosyl chlorides with labile protecting groups previously not easily accessible can be prepared.

Design, Synthesis, and Antimicrobial Activities of 1,2,3-Triazole Glycoside Clickamers

Bacterial resistance remains a significant threat and a leading cause of death worldwide, despite massive attempts to control infections. In an effort to develop biologically active antibacterial and antifungal agents, six novel aryl-substituted-1,2,3-triazoles linked to carbohydrate units were synthesized through the Cu(I)-catalyzed azide-alkyne cycloaddition CuAAC of substituted-arylazides with a selection of alkyne-functionalized sugars. The chemical structures of the new derivatives were verified using different spectroscopic techniques. The novel clicked 1,2,3-triazoles were evaluated for in vitro antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa, and the obtained results were compared with the activity of the reference antibiotic "Ampicillin". Likewise, in vitro antifungal activity of the new 1,2,3-triazoles was investigated against Candida albicans and Aspergillus niger using "Nystatin" as a reference drug. The results of the biological evaluation pointed out that Staphylococcus aureus was more susceptible to all of the tested compounds than other examined microbes. In addition, some tested compounds exhibited promising antifungal activity.

Glycosyl ortho-(1-phenylvinyl)benzoates versatile glycosyl donors for highly efficient synthesis of both O-glycosides and nucleosides

Both of O-glycosides and nucleosides are important biomolecules with crucial rules in numerous biological processes. Chemical synthesis is an efficient and scalable method to produce well-defined and pure carbohydrate-containing molecules for deciphering their functions and developing therapeutic agents. However, the development of glycosylation methods for efficient synthesis of both O-glycosides and nucleosides is one of the long-standing challenges in chemistry. Here, we report a highly efficient and versatile glycosylation method for efficient synthesis of both O-glycosides and nucleosides, which uses glycosyl ortho-(1-phenylvinyl)benzoates as donors. This glycosylation protocol enjoys the various features, including readily prepared and stable donors, cheap and readily available promoters, mild reaction conditions, good to excellent yields, and broad substrate scopes. In particular, the applications of the current glycosylation protocol are demonstrated by one-pot synthesis of several bioactive oligosaccharides and highly efficient synthesis of nucleosides drugs capecitabine, galocitabine and doxifluridine.

Stereoselective Synthesis of Carbon-Sulfur-Bridged Glycomimetics by Photoinitiated Thiol-Ene Coupling Reactions

Oligosaccharides and glycoconjugates are abundant in all living organisms, taking part in a multitude of biological processes. The application of natural O-glycosides in biological studies and drug development is limited by their sensitivity to enzymatic hydrolysis. This issue made it necessary to design hydrolytically stable carbohydrate mimetics, where sulfur, carbon, or longer interglycosidic connections comprising two or three atoms replace the glycosidic oxygen. However, the formation of the interglycosidic linkages between the sugar residues in high diastereoslectivity poses a major challenge. Here, we report on stereoselective synthesis of carbon-sulfur-bridged disaccharide mimetics by the free radical addition of carbohydrate thiols onto the exo-cyclic double bond of unsaturated sugars. A systematic study on UV-light initiated radical mediated hydrothiolation reactions of enoses bearing an exocyclic double bond at C1, C2, C3, C4, C5, and C6 positions of the pyranosyl ring with various sugar thiols was performed. The effect of temperature and structural variations of the alkenes and thiols on the efficacy and stereoselectivity of the reactions was systematically studied and optimized. The reactions proceeded with high efficacy and, in most cases, with complete diastereoselectivity producing a broad array of disaccharide mimetics coupling through an equatorially oriented methylensulfide bridge.

Identification of the C-Glycoside Synthases during Biosynthesis of the Pyrazole-C-Nucleosides Formycin and Pyrazofurin

C-Nucleosides are characterized by a C-C rather than a C-N linkage between the heterocyclic base and the ribofuranose ring. While the biosynthesis of pseudouridine-C-nucleosides has been studied, less is known about the pyrazole-C-nucleosides such as the formycins and pyrazofurin. Herein, genome screening of Streptomyces candidus NRRL 3601 led to the discovery of the pyrazofurin biosynthetic gene cluster pyf. In vitro characterization of gene product PyfQ demonstrated that it is able to catalyze formation of the C-glycoside carboxyhydroxypyrazole ribonucleotide (CHPR) from 4-hydroxy-1H-pyrazole-3,5-dicarboxylic acid and phosphoribosyl pyrophosphate (PRPP). Similarly, ForT, the PyfQ homologue in the formycin pathway, can catalyze the coupling of 4-amino-1H-pyrazole-3,5-dicarboxylic acid and PRPP to form carboxyaminopyrazole ribonucleotide. Finally, PyfP and PyfT are shown to catalyze amidation of CHPR to pyrazofurin 5'-phosphate thereby establishing the latter stages of both pyrazofurin and formycin biosynthesis.

Water Solubility and Surface Property of Alkyl Di-/Tri-/Tetraoxyethyl β-d-Xylopyranosides

Alkyl di-/tri-/tetraoxyethyl β-d-xylopyranosides as derivatives of alkyl xylosides are a class of non-ionic sugar-based surfactants. They were stereoselectively synthesized by the Helferich method. Their properties including hydrophilic-lipophilic balance number, water solubility, surface property, foam property, emulsifying property, and thermotropic liquid crystal property were mainly investigated. The results showed that their water solubility decreased with increasing the alkyl chain length and increasing the number of the oligooxyethyl fragment. The critical micelle concentration had a monotonous decreasing trend with increasing the alkyl chain length. Nonyl di-/tri-/tetraoxyethyl β-d-xylopyranosides [-(OCH₂CH₂)_m-, where m = 2, 3, and 4] exhibited the most excellent foaming ability and foam stability. In the n-octane/water system, dodecyl tetraoxyethyl β-d-xylopyranosides and tetradecyl tetraoxyethyl β-d-xylopyranosides had the strongest emulsion ability. In addition, some alkyl di-/tri-/tetraoxyethyl β-d-xylopyranosides had thermotropic liquid crystal properties. Such sugar-based surfactants, alkyl di-/tri-/tetraoxyethyl β-d-xylopyranosides, will be expected to develop for a variety of practical application.

Synthesis of Daidzein Glycosides, α-Tocopherol Glycosides, Hesperetin Glycosides by Bioconversion and Their Potential for Anti-Allergic Functional-Foods and Cosmetics

Daidzein is a common isoflavone, having multiple biological effects such as anti-inflammation, anti-allergy, and anti-aging. α-Tocopherol is the tocopherol isoform with the highest vitamin E activity including anti-allergic activity and anti-cancer activity. Hesperetin is a flavone, which shows potent anti-inflammatory effects. These compounds have shortcomings, i.e., water-insolubility and poor absorption after oral administration. The glycosylation of bioactive compounds can enhance their water-solubility, physicochemical stability, intestinal absorption, and biological half-life, and improve their bio- and pharmacological properties. They were transformed by cultured Nicotiana tabacum cells to 7-β-glucoside and 7-β-gentiobioside of daidzein, and 3'- and 7-β-glucosides, 3',7-β-diglucoside, and 7-β-gentiobioside of hesperetin. Daidzein and α-tocopherol were glycosylated by galactosylation with β-glucosidase to give 4'- and 7-β-galactosides of daidzein, which were new compounds, and α-tocopherol 6-β-galactoside. These nine glycosides showed higher anti-allergic activity, i.e., inhibitory activity toward histamine release from rat peritoneal mast cells, than their respective aglycones. In addition, these glycosides showed higher tyrosinase inhibitory activity than the corresponding aglycones. Glycosylation of daidzein, α-tocopherol, and hesperetin greatly improved their biological activities.

Peyssonnosides A-B, Unusual Diterpene Glycosides with a Sterically Encumbered Cyclopropane Motif: Structure Elucidation Using an Integrated Spectroscopic and Computational Workflow

Two sulfated diterpene glycosides featuring a highly substituted and sterically encumbered cyclopropane ring have been isolated from the marine red alga Peyssonnelia sp. Combination of a wide array of 2D NMR spectroscopic experiments, in a systematic structure elucidation workflow, revealed that peyssonnosides A-B (1-2) represent a new class of diterpene glycosides with a tetracyclo [7.5.0.01,10.05,9] tetradecane architecture. A salient feature of this workflow is the unique application of quantitative interproton distances obtained from the rotating frame Overhauser effect spectroscopy (ROESY) NMR experiment, wherein the β-d-glucose moiety of 1 was used as an internal probe to unequivocally determine the absolute configuration, which was also supported by optical rotatory dispersion (ORD). Peyssonnoside A (1) exhibited promising activity against liver stage Plasmodium berghei and moderate antimethicillin-resistant Staphylococcus aureus (MRSA) activity, with no cytotoxicity against human keratinocytes. Additionally, 1 showed strong growth inhibition of the marine fungus Dendryphiella salina indicating an antifungal ecological role in its natural environment. The high natural abundance and novel carbon skeleton of 1 suggests a rare terpene cyclase machinery, exemplifying the chemical diversity in this phylogenetically distinct marine red alga.

Methods for 2-Deoxyglycoside Synthesis

Deoxy-sugars often play a critical role in modulating the potency of many bioactive natural products. Accordingly, there has been sustained interest in methods for their synthesis over the past several decades. The focus of much of this work has been on developing new glycosylation reactions that permit the mild and selective construction of deoxyglycosides. This Review covers classical approaches to deoxyglycoside synthesis, as well as more recently developed chemistry that aims to control the selectivity of the reaction through rational design of the promoter. Where relevant, the application of this chemistry to natural product synthesis will also be described.

Synthesis and evaluation of a ring-constrained Hsp90 C-terminal inhibitor that exhibits neuroprotective activity

KU-596 is a second-generation C-terminal heat shock protein 90 KDa (Hsp90) modulator based on the natural product, novobiocin. KU-596 has been shown to induce Hsp70 levels and manifest neuroprotective activity through induction of the heat shock response. A ring-constrained analog of KU-596 was designed and synthesized to probe its binding orientation and ability to induce Hsp70 levels. Compound 2 was found to exhibit comparable or increased activity compared to KU-596, which is under clinical investigation for the treatment of neuropathy.

Glucosylation of T-2 and HT-2 toxins using biotransformation and chemical synthesis: Preparation, stereochemistry, and stability

Plant-derived phase II metabolites of T-2 toxin (T2) and HT-2 toxin (HT2) were first described in 2011 and further characterized in the following years. Since then, some efforts have been made to understand their biosynthesis, occurrence, toxicity, toxicokinetics, and finally relevance for consumers. Thus, the probably most important question is whether and how these metabolites contribute to toxicity upon hydrolysis either during food processing or the gastrointestinal passage. To answer this question, firstly, knowledge on the correct stereochemistry of T2 and HT2 glucosides is important as this affects hydrolysis and chemical behavior. So far, contradictory results have been published concerning the number and anomericity of occurring glucosides. For this reason, we set up different strategies for the synthesis of mg-amounts of T2, HT2, and T2 triol glucosides in both α and ß configuration. All synthesized glucosides were fully characterized by NMR spectroscopy as well as mass spectrometry and used as references for the analysis of naturally contaminated food samples to validate or invalidate their natural occurrence. Generally, 3-O-glucosylation was observed with two anomers of HT2 glucoside being present in contaminated oats. In contrast, only one anomer of T2 glucoside was found. The second aspect of this study addresses the stability of the glucosides during thermal food processing. Oat flour was artificially contaminated with T2 and HT2 glucosides individually and extruded at varying initial moisture content and temperature. All four glucosides appear to be more stable during food extrusion than the parent compounds with the glucosidic bond not being hydrolyzed.

Synthesis of glyceryl glycosides related to A-type prymnesin toxins

A suite of glycosylated glycerol derivatives representing various fragments of the glycosylated ichthyotoxins called prymnesins were chemically synthesised. Glycerol was used to represent a small fragment of the prymnesin backbone, and was glycosylated at the 2° position with the sugars currently reported to be present on prymnesin toxins. Neighbouring group participation was utilised to synthesise 1,2-trans-glycosides. SnCl2-promoted glycosylation with furanosyl fluorides gave 1,2-cis-furanosides with moderate stereocontrol, whilst TMSOTf promoted glycosylation with a furanosyl imidate gave a 1,2-cis-furanoside with good stereocontrol. The chemical synthesis of two larger glyceryl diglycoside fragments of prymnesin-1, glycosylated with α-ʟ-arabinopyranose and α-ᴅ-ribofuranose, is also described. As the stereochemistry of the prymnesin backbones at this region is undefined, both the 2R- and 2S- glycerol isomers were synthesised. The separated diastereoisomers were distinguished by comparing NOESY NMR with computational models.

Synthesis of Reversed C-Acyl Glycosides through Ni/Photoredox Dual Catalysis

The incorporation of C-glycosides in drug design has become a routine practice for medicinal chemists. These naturally occurring building blocks exhibit attractive pharmaceutical profiles, and have become an important target of synthetic efforts in recent decades. Described herein is a practical, scalable, and versatile route for the synthesis of non-anomeric and unexploited C-acyl glycosides through a Ni/photoredox dual catalytic system. By utilizing an organic photocatalyst, a range of glycosyl-based radicals are generated and efficiently coupled with highly functionalized carboxylic acids at room temperature. Distinctive features of this transformation include its mild conditions, impressive compatibility with a wide array of functional groups, and most significantly, preservation of the anomeric carbon: a handle for further, late-stage derivatization.

Rutinosylated Ferulic Acid Attenuates Food Allergic Response and Colitis by Upregulating Regulatory T Cells in Mouse Models

The purpose of this study was to screen phytochemicals capable of inducing immune tolerance via enhanced transforming growth factor-β1 (TGF-β1) secretion and investigate their effects in a mouse model of food allergy and colitis. In a screening test using THP-1-derived dendritic cells, a significant increase in TGF-β1 levels was observed upon treatment with ferulic acid and its glycosides, among which ferulic acid rutinoside (FAR) induced the highest level of TGF-β1 secretion. Oral administration of FAR suppressed serum levels of immunoglobulin E and histamine in ovalbumin-sensitized mice and triggered the differentiation of regulatory T (Treg) cells. In comparison to the control, FAR treatment also induced stronger TGF-β1 secretion from splenic dendritic cells. FAR treatment attenuated dextran-sulfate-sodium-induced colitis in the model mice and induced Treg differentiation. These results suggest that FAR exerts potent immunomodulatory effects against allergic and intestinal inflammatory responses by inducing Treg differentiation.

Synthesis, fungicidal evaluation and 3D-QSAR studies of novel 1,3,4-thiadiazole xylofuranose derivatives

1,3,4-Thiadiazole and sugar-derived molecules have proven to be promising agrochemicals with growth promoting, insecticidal and fungicidal activities. In the research field of agricultural fungicide, applying union of active group we synthesized a new set of 1,3,4-thiadiazole xylofuranose derivatives and all of the compounds were characterized by ¹H NMR and HRMS. In precise toxicity measurement, some of compounds exhibited more potent fungicidal activities than the most widely used commercial fungicide Chlorothalonil, promoting further research and development. Based on our experimental data, 3D-QSAR (three-dimensional quantitative structure-activity relationship) was established and investigated using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) techniques, helping to better understand the structural requirements of lead compounds with high fungicidal activity and environmental compatibility.

Synthesis and Biological Evaluation of Triazole linked Thiazolidenone Glycosides

In a one pot procedure a series of novel triazole linked thiazolidinone derivatives 8a-g and 9a-g was prepared by condensation of (3aR,5S,6R,6aR)-6-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-2,2-dimethyltetrahydro[2,3-d] [1,3]dioxole-5-carbaldehyde 7 with mercapto acids and primary amines in the presence of ZnCl2 under both microwave irradiation and conventional heating conditions. Compound 7 was prepared from diacetone D-glucose with oxidation followed by reduction, click reaction, primary acetonide deprotection and with oxidative cleavage. Characterization of new compounds has been done by means of IR, NMR, MS and elemental analysis. The nematicidal and antibacterial activity of the compounds has also been evaluated.

Naphthoquinone glycosides for bioelectroanalytical enumeration of the faecal indicator Escherichia coli

Microbial water quality monitoring for the presence of faecal indicator bacteria (FIB) is a mandatory activity in many countries and is key in public health protection. Despite technological advances and a need for methodological improvements, chromogenic and fluorogenic enzymatic techniques remain the mainstays of water quality monitoring for both public health agencies and regulated utilities. We demonstrated that bioelectroanalytical approaches to FIB enumeration are possible and can be achieved using commercially available enzyme-specific resorufin glycosides, although these are expensive, not widely available or designed for purpose. Following this, we designed two naphthoquinone glycosides which performed better, achieving Escherichia coli detection in the range 5.0 × 102 to 5.0 × 105 CFU ml-1 22-54% quicker than commercially available resorufin glycosides. The molecular design of the naphthoquinone glycosides requires fewer synthetic steps allowing them to be produced for as little as US$50 per kg. Tests with environmental samples demonstrated the low tendency for abiotic interference and that, despite specificity being maintained between β-glucuronidase and β-galactosidase, accurate enumeration of E. coli in environmental samples necessitates development of a selective medium. In comparison to a commercially available detection method, which has U.S. Environmental Protection Agency (EPA) approval, our approach performed better at high organism concentrations, detecting 500 organisms in 9 h compared with 13.5 h for the commercial method. Bioelectroanalytical detection is comparable to current approved methods and with further development could result in improved detection times. A recent trend for low-cost open-source hardware means that automated, potentiostatically controlled E. coli detection systems could be constructed for less than US$100 per channel.

Synthesis and biological analysis of novel glycoside derivatives of l-AEP, as targeted antibacterial agents

To develop targeted methods for treating bacterial infections, the feasibility of using glycoside derivatives of the antibacterial compound l-R-aminoethylphosphonic acid (l-AEP) has been investigated. These derivatives are hypothesized to be taken up by bacterial cells via carbohydrate uptake mechanisms, and then hydrolyzed in situ by bacterial borne glycosidase enzymes, to selectively afford l-AEP. Therefore the synthesis and analysis of ten glycoside derivatives of l-AEP, for selective targeting of specific bacteria, is reported. The ability of these derivatives to inhibit the growth of a panel of Gram-negative bacteria in two different media is discussed. β-Glycosides (12a) and (12b) that contained l-AEP linked to glucose or galactose via a carbamate linkage inhibited growth of a range of organisms with the best MICs being <0.75mg/ml; for most species the inhibition was closely related to the hydrolysis of the equivalent chromogenic glycosides. This suggests that for (12a) and (12b), release of l-AEP was indeed dependent upon the presence of the respective glycosidase enzyme.

Enzymatic synthesis of bioactive compounds with high potential for cosmeceutical application

Cosmeceuticals are cosmetic products containing biologically active ingredients purporting to offer a pharmaceutical therapeutic benefit. The active ingredients can be extracted and purified from natural sources (botanicals, herbal extracts, or animals) but can also be obtained biotechnologically by fermentation and cell cultures or by enzymatic synthesis and modification of natural compounds. A cosmeceutical ingredient should possess an attractive property such as anti-oxidant, anti-inflammatory, skin whitening, anti-aging, anti-wrinkling, or photoprotective activity, among others. During the past years, there has been an increased interest on the enzymatic synthesis of bioactive esters and glycosides based on (trans)esterification, (trans)glycosylation, or oxidation reactions. Natural bioactive compounds with exceptional theurapeutic properties and low toxicity may offer a new insight into the design and development of potent and beneficial cosmetics. This review gives an overview of the enzymatic modifications which are performed currently for the synthesis of products with attractive properties for the cosmeceutical industry.

Total Synthesis of the Naturally Occurring Glycosylflavone Aciculatin

The new flavone-glycoside aciculatin (1), from Chrysopogon aciculatus, has been shown to have cytotoxic, anti-inflammatory, and antiarthritis activity. Further biological studies have been limited because of the limited availability of 1 from natural sources. Herein the first total synthesis of 1 in an overall yield of 8.3% is described. The synthesis involved the regio- and stereoselective glycosylation-Fries-type O-to-C rearrangement to construct the C-aryl glycosidic linkage, followed by a Baker-Venkataraman rearrangement and cyclodehydration to form the flavone scaffold.

A ring closing metathesis strategy for carbapyranosides of xylose and arabinose

The synthesis of β-carba-xylo and arabino pyranosides of cholestanol is described. The synthetic strategy, which is analogous to the Postema approach to C-glycosides, centers on the ring closing metathesis of an enol ether-alkene precursor to give a cyclic enol ether that is elaborated to a carba-pyranoside via hydroboration-oxidation on the olefin. The method, which is attractive for its modularity and stereoselectivity, may find wider applications to carba-hexopyranosides and other complex cycloalkyl ether frameworks.

SYNTHESIS AND CYTOTOXIC ACTIVITY OF NEW 5H-INDOLO[2,3-B]QUINOLINE O-AMINOGLYCOSIDES

Novel 5H-indolo[2,3-b]quinoline O-aminoglycosides were synthesized in order to check the hypothesis that the construction of hybrids composed of the active 5H-indolo[2,3-b]quinoline chromophore and daunosaminyl or acosaminyl moiety may result in the cytotoxic activity of the obtained derivatives that is much higher than the one of the parent DIMIQ (5,11-dimethyl-5H-indolo[2,3-b]quinoline) and 6H-indoloquinoline analogs. Actually, 5H-indolo[2,3-b]indoloquinoline O-aminoglycosides showed the anti-proliferative activity in vitro against human lung adenocarcinoma A549, breast cancer MCF-7, melanoma Hs294T, promyelocytic leukemia HL-60, uterine sarcoma MES-SA and colon cancer LoVo cell lines, which was 10 times higher than that of the 6H-analogs and comparable to the one of the referential DIMIQ. Unexpectedly, it appeared that except for HL-60/MX2 (P-gp-independent and topoisomerase II-dependent resistance), other MDR tumor cell lines (LoVo/DX. P-gp-dependent, MRP-, LRP-dependent multidrug resistance) and MES-SA/DX5 (P-gp-dependent resistance to doxorubicin) are also resistant to the 5H-indolo[2,3-b]indoloquinoline O-aminoglycosides tested. This is surprising because 6H-analogs, in general, 10 times less active against non-MDR tumor cell lines, as well as the DIMIQ itself, are able to overcome drug resistance in all MDR cell lines examined. The cytotoxicity of the tested compounds against tumor cell lines and against normal cells (mice fibroblasts BALB/3T3) was comparable.

General and Stereocontrolled Approach to the Chemical Synthesis of Naturally Occurring Cyanogenic Glucosides

An effective method for the chemical synthesis of cyanogenic glucosides has been developed as demonstrated by the synthesis of dhurrin, taxiphyllin, prunasin, sambunigrin, heterodendrin, and epiheterodendrin. O-Trimethylsilylated cyanohydrins were prepared and subjected directly to glucosylation using a fully acetylated glucopyranosyl fluoride donor with boron trifluoride-diethyl etherate as promoter to afford a chromatographically separable epimeric mixture of the corresponding acetylated cyanogenic glucosides. The isolated epimers were deprotected using a triflic acid/MeOH/ion-exchange resin system without any epimerization of the cyanohydrin function. The method is stereocontrolled and provides an efficient approach to chemical synthesis of other naturally occurring cyanogenic glucosides including those with a more complex aglycone structure.

An Improved Helferich Method for the α/β-Stereoselective Synthesis of 4-Methylumbelliferyl Glycosides for the Detection of Microorganisms

An improved Helferich method is presented. It involves the glycosylation of 4-methyl-umbelliferone with glycosyl acetates in the presence of boron trifluoride etherate combined with triethylamine, pyridine, or 4-dimethylaminopyridine under mild conditions, followed by deprotection to give fluorogenic 4-methylumbelliferyl glycoside substrates. Due to the use of base, the glycosylation reaction proceeds more easily, is uncommonly α- or β-stereoselective, and affords the corresponding products in moderate to excellent yields (51%-94%) under appropriate conditions.

Resveratrol-Related Polymethoxystilbene Glycosides: Synthesis, Antiproliferative Activity, and Glycosidase Inhibition

A small library of polymethoxystilbene glycosides (20-25) related to the natural polyphenol resveratrol have been synthesized and subjected, together with their aglycones 17-19, to an antiproliferative activity bioassay toward Caco-2 and SH-SY5Y cancer cells. Six of the compounds exhibit antiproliferative activity against at least one cell line. In particular, compounds 17 and 18 proved highly active on at least one of the two cell cultures. Compound 18 showed a GI50 value of 3 μM against Caco-2 cells, a value comparable to that of the anticancer drug 5-fluorouracil. The closely related compound 19 proved inactive, and its conjugates 22 and 25 showed weak cell growth inhibition. The results indicate that minimal differences in the structure of both polymethoxystilbenes and their glycosides can substantially affect the antiproliferative activity. The possible hydrolytic release of the aglycones 17-19 by β-glucosidase or β-galactosidase was also evaluated. Compounds 20-25 were also tested as potential β-glucosidase, β-galactosidase, and α-glucosidase inhibitors. A promising inhibitory activity toward α-glucosidase was observed for 21 (IC50 = 78 μM) and 25 (IC50 = 70 μM), which might be indicative of their potential as lead compounds for development of antidiabetic or antiobesity agents.

Synthesis of a series of novel heteroglycoclusters and homoglycoclusters and the study of their anti-adhesion activities

A new series of mixed-type heteroglycoclusters containing mannose and lactose were synthesized. In the synthesis of rigid scaffold of heteroglycocluster, we found that trans-isomer could be prepared stereoselectively by means of Grubbs olefin cross-metathesis reactions. Moreover, sequential acylation using cyclic anhydride as scaffold could give cis-isomer. These two methods may provide complementarity of stereochemistry in heteroglycocluster assembling. The anti-adhesion activities of these compounds were assessed by Surface Plasmon Resonance (SPR) and static state cell-based adhesion assay. These results indicated that the rigid scaffold might not affect the anti-adhesion activities.

The isothiocyanato moiety: an ideal protecting group for the stereoselective synthesis of sialic acid glycosides and subsequent diversification

The preparation of a crystalline, peracetyl adamantanyl thiosialoside donor protected by an isothiocyanate group is described. On activation at -78 °C in the presence of typical carbohydrate acceptors, this donor gives high yields of the corresponding sialosides with exquisite α-selectivity. The high selectivity extends to the 4-O-benzyl-protected 3-OH acceptors, which are typically less reactive and selective than galactose 3,4-diols. Treatment of the α-sialosides with tris(trimethylsilyl)silane or allyltris(trimethylsilyl)silane results in replacement of the C5-N5 bond by a C-H or a C-C bond. The reaction of the isothiocyanate-protected sialosides with thioacids generates amides, while reaction with an amine gives a thiourea, which can be converted into a guanidine. The very high α-selectivities observed with the new donor and the rich chemistry of the isothiocyante function considerably extend the scope for optimization at the sialoside 5-position.

FeCl3-promoted and ultrasound-assisted synthesis of resveratrol O-derived glycoside analogs

Phenol derived O-glycosides were synthesized using a direct and convenient O-glycosidation, starting from acetylated sugars in the presence of FeCl3, an inexpensive, mild and benign Lewis acid catalyst. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with conventional conditions leading to the corresponding β-O-glycosides as the major anomer. Post-synthetic transformations of iodophenol intermediates led to new resveratrol O-glycoside analogs in good overall yields.

Synthesis of (±)-tetrapetalone A-Me aglycon

The first synthesis of (±)-tetrapetalone A-Me aglycon is described. Key bond-forming reactions include Nazarov cyclization, a ring-closing metathesis promoted with complete diastereoselectivity by a chiral molybdenum-based complex, tandem conjugate reduction/intramolecular aldol cyclization, and oxidative dearomatization.

Oleanolic acid synthetic oligoglycosides: a review on recent progress in biological activities

The natural product oleanolic acid has been widely used for treating hepatopathy in China, whereas its clinical application was confined by poor solubility in water. Inspired by remarkable bioactivities and physical properties of triterpenoid saponins, synthesis and biological evaluation of oleanolic acid oligoglycosides drew considerable attention. In the past several years, chemical efforts were made toward glycosylated modifications of oleanolic acid at C3-OH and C17-COOH, of the carbons at ring A/C, and of the functional groups of oleanolic acid lactone. To provide useful information for further study and applications of oleanolic acid derivatives, a total of 177 oleanolic acid synthetic oligoglycosides and their bioactivities (e.g., antiosteoporosis, antidiabetes, antibacterial, anticancer and hemolytic effects) were reviewed; structure-activity relationships and promising agents are indicated.

Total synthesis of the antitumor natural product polycarcin V and evaluation of its DNA binding profile

The convergent total synthesis of polycarcin V, a gilvocarcin-type natural product that shows significant cytotoxicity with selectivity for nonsmall-cell lung cancer, breast cancer, and melanoma cells, has been achieved in 13 steps from 7, 8, and 22; the sequence features a stereoselective α-C-glycosylation reaction for the union of protected carbohydrate 7 and naphthol 8. The association constant for the binding of polycarcin V to duplex DNA is similar to that previously reported for gilvocarcin V.

Synthesis of α-d-glucosyl substituted methyl glycosides of 3-deoxy-α-d-manno- and d-glycero-α-d-talo-oct-2-ulosonic acid (Kdo/Ko) corresponding to inner core fragments of Acinetobacter lipopolysaccharide

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Synthesis of Acinetobacter LPS fragments with orthogonal protecting pattern.

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First synthesis of Ko-glycosides substituted at position 5.

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α-Selective glucosylation using benzylidene trifluoroacetimidate donor.

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Regioselective phosphorylation at C-6 of a glucosyl substituent.

The α-d-glucopyranosyl-(1→5)-substituted methyl glycosides of 3-deoxy-α-d-manno-oct-2-ulosonic acid (Kdo), 3-deoxy-α-d-lyxo-hept-2-ulosonic acid (Kdh), and d-glycero-α-d-talo-oct-2-ulosonic acid (Ko) were prepared using orthogonally protected glycosyl acceptor derivatives via glycosylation with a torsionally disarmed 4,6-O-benzylidene protected trifluoroacetimidate glucosyl donor followed by global deprotection. The related 6-O-phosphoryl-α-d-glucopyranosyl-(1→5)-substituted Kdo and Kdh derivatives were derived from a benzylidene-protected glucosyl intermediate using phosphoramidite and phosphoryl chloride-based phosphorylation steps, respectively. The deprotected disaccharides serve as ligands to study lectin binding of Acinetobacter lipopolysaccharide core oligosaccharides.

Scope and limitations of 2-deoxy- and 2,6-dideoxyglycosyl bromides as donors for the synthesis of β-2-deoxy- and β-2,6-dideoxyglycosides

It is shown that 2-deoxy- and 2,6-dideoxyglycosyl bromides can be prepared in high yield (72-94%) and engaged in glycosylation reactions with β:α selectivities ≥6:1. Yields of product are 44-90%. Fully armed 2-deoxyglycoside donors are viable, while 2,6-dideoxyglycosides require one electron-withdrawing substituent for high efficiency and β-selectivity. Equatorial C-3 ester protecting groups decrease β-selectivity, and donors bearing an axial C-3 substituent are not suitable. The method is compatible with azide-containing donors and acid-sensitive functional groups.