Anti-inflammatory and hepatoprotective effects of total flavonoid C-glycosides from Abrus mollis extracts

The aim of this study was to evaluate the anti-inflammatory and hepatoprotective effects of the total flavonoid C-glycosides isolated from Abrus mollis extracts(AME). In the anti-inflammatory tests, xylene-induced ear edema model in mice and carrageenan-induced paw edema model in rats were applied. The hepatoprotective effects of AME were evaluated with various in vivo models of acute and chronic liver injury, including carbon tetrachloride(CCl4)-induced hepatitis in mice, D-galactosamine(D-GalN)-induced hepatitis in rats, as well as CCl4-induced hepatic fibrosis in rats. In the acute inflammation experiment, AME significantly suppressed xylene-induced ear edema and carrageenan-induced paw edema, respectively. In the acute hepatitis tests, AME significantly attenuated the excessive release of ALT and AST induced by CCl4 and D-GalN. In CCl4-induced hepatic fibrosis model, AME alleviated liver injury induced by CCl4 shown by histopathological sections of livers and improved liver function as indicated by decreased liver index, serum ALT, AST, TBIL, and ALP levels and hydroxyproline contents in liver tissues, and increased serum ALB and GLU levels. These results indicated that AME possesses potent anti-inflammatory activity in acute inflammation models and hepatoprotective activity in both acute and chronic liver injury models. In conclusion, AME is a potential anti-inflammatory and hepatoprotective agent and a viable candidate for treating inflammation, hepatitis, and hepatic fibrosis.

Protective effect of total flavonoid C-glycosides from Abrus mollis extract on lipopolysaccharide-induced lipotoxicity in mice

Abrus mollis is a widely used traditional Chinese medicine for treating acute and chronic hepatitis, steatosis, and fibrosis. It was found that the total flavonoid C-glycosides from Abrus mollis extract(AME) showed potent antioxidant, anti-inflammatory, and hepatoprotective activities. To further investigate the hepatoprotective effect of AME and its possible mechanisms, lipopolysaccharide(LPS)-induced liver injury models were applied in the current study. The results indicated that AME significantly attenuated LPS-induced lipid accumulation in mouse primary hepatocytes as measured by triglyceride(TG) and total cholesterol(TC) assays and Oil Red O staining. Meanwhile, AME exerted a protective effect on LPS-induced liver injury as shown by decreased liver index, serum aminotransferase levels, and hepatic lipid accumulation. Real-time PCR and immunoblot data suggested that AME reversed the LPS-mediated lipid metabolism gene expression, such as sterol regulatory element-binding protein-1(SREBP-1), fatty acid synthase(FAS), and acetyl-CoA carboxylase 1(ACC1). In addition, LPS-induced overexpression of activating transcription factor 4(ATF4), X-box-binding protein-1(XBP-1), and C/EBP homologous protein(CHOP) were dramatically reversed by AME. Furthermore, AME also decreased the expression of LPS-enhanced interleukin-6(IL-6) and cyclooxygenase-2(COX-2). Here, it is demonstrated for the first time that AME ameliorated LPS-induced hepatic lipid accumulation and that this effect of AME can be attributed to its modulation of hepatic de novo fatty acid synthesis. This study also suggested that the hepatoprotective effect of AME may be related to its down-regulation of unfolded protein response(UPR) activation.

Studies on C-glycosides——XII. Stereoselective synthesis of C-aryl glucosides

2,3,4,6-Tetra-O-benzyl-D-glucopyranose l-a-(p-nitrobenzoate)reacted with aryl ethers in the presence of Lewis acid to give β-anomers stereoselectively in high yield, but reaction with 1,3- ditrimethylsilyloxybenzene gave a-anomer using BF_3.Et_2O and β-anomer using anhydrous AICl_3 as catalyst.

Synthesis of non-classical heteroaryl C-glycosides via Minisci-type alkylation of N‑heteroarenes with 4-glycosyl-dihydropyridines

A radical-mediated method was reported for diastereoselective synthesis of non-classical heteroaryl C-glycosides via Minisci-type alkylation of N-heteroarenes with 4-glycosyl-1,4-dihydropyridine(DHP)reagents.These DHP reagents serve as convenient precursors for various glycosyl radicals under the activation of single electron transfer(SET)oxidation by persulfate and visible light irradiation with or without photocatalyst.

Controlled acid hydrolysis and kinetics of flavone C-glycosides from trollflowers

Acid hydrolysis mechanisms of orientin-2＂-O-galactopyranoside（OGA）,orientin and other flavone C-glycosides in the trollflowers[Trollius chinensis Bunge） were studied in this report for the first time.Hydrolysis parameters including temperature,acidity,solvent and reaction time were comprehensively investigated.OGA could be hydrolyzed to orientin,followed by an isomerization to isoorientin via a reversible Wessely-Moser rearrangement reaction under stronger acidic conditions.A first-order kinetic model fitted the hydrolysis process of OGA well.Under the optimal hydrolysis conditions of 80 ℃,1.0 mol/L H^＋ and 7 h reaction time,about 77%OGA was transformed to orientin with no detectable isoorientin.These results could be helpful for better understanding of the acid hydrolysis kinetics of flavone C-glycosides,as well as the preparation of these valuable components under controlled acid hydrolysis conditions.

Synthesis and evaluation of C-glycosides as hydrotropes and solubilizing agents

This work presents expeditious synthesis of C-glycoside amphiphiles in aqueous media from unprotected di-or mono-saccharides.A Horner-Wadsworth-Emmons/Michael addition/Barbier allylation sequence led to C-glycosides that exhibit hydrotropic properties.The hydrotropic and solubilizing properties of these homoallylic alcohols including a β-C-glycoside moiety as well as additional β-C-glycosidic ketones with a short(C7) alkyl chain are also described and compared with those of commercial O-glucoside references.

A New C-glycosidic Hydrolysable Tannin from Rhodomyrtus tomentosa

Tomentosin(1), a new C-glycosidic hydrolysable tannin, isolated from the leaves of Rhodomyrtus tomentosa. Its structure determined by chemical method and (1)HNMR spectroscopic analysis.

C-Glycoside Synthesis Enabled by Nickel Catalysis

Comprehensive Summary,C-Glycosides are critical,naturally occurring products and medicinal candidates,and extensive efforts have been made to explore efficient approaches for creating C-glycosidic bonds.Transition-metal-catalysis,particularly nickel-catalyzed C-glycosylation reactions constitute a promising strategy.However,achieving a stereoselective synthesis ofα-andβ-C-glycosides has been a long-standing challenge.To address this problem,a variety of nickel-mediated strategies have been developed.This review highlights recent developments in the nickel-catalyzed diastereoselective C-glycosylation reactions and briefly summarizes the mechanistic understandings of these methods.

Structural mechanism of a dual-functional enzyme Dgp A/B/C as both a C-glycoside cleaving enzyme and an O-to C-glycoside isomerase

The C-glycosidic bond that connects the sugar moiety with aglycone is difficult to be broken or made due to its inert nature.The knowledge of C-glycoside breakdown and synthesis is very limited.Recently,the enzyme Dgp A/B/C cascade from a human intestinal bacterium PUE was identified to specifically cleave the C-glycosidic bond of puerarin(daidzein-8-C-glucoside).Here we investigated how puerarin is recognized and oxidized by Dgp A based on crystal structures of Dgp A with or without substrate and biochemical characterization.More strikingly,we found that apart from being a C-glycoside cleaving enzyme,Dgp A/B/C is capable of efficiently converting O-to C-glycoside showing the activity as a structure isomerase.A possible mechanistic model was proposed dependently of the simulated complex structure of Dgp B/C with 3’’-oxo-daidzin and structure-based mutagenesis.Our findings not only shed light on understanding the enzyme-mediated C-glycosidic bond breakage and formation,but also may help to facilitate stereospecific C-glycoside synthesis in pharmaceutical industry.

Photoredox-catalyzed C-glycosylation of peptides with glycosyl bromides

Glycosyl radicals,produced under mild photoredox conditions,show unique utility in the preparation of C-linked glycoconjugates.We herein report the construction of C-glycosidic bonds on α,β-dehydroalanine(DHA)of peptides with easily available glycosyl bromides as glycosyl radical precursors under highly anomeric control,leading to C-glycosylation modifications of peptides.This method not only has outstanding functional group compatibility,but also is feasible in near-physiological conditions(pH~7 and temperature T≤37℃ in aqueous media).

Synthesis of Triazole-Linked Amino Acid-Aryl C-Glycoside Hybrids via Click Chemistry as Novel PTPIB Inhibitors

Triazolyl phenylalanine and tyrosine-aryl C-glycoside hybrids were readily synthesized via microwave-assisted Cu（I）-catalyzed azide-alkyne 1,3-dipolar cycloaddition in high yields. Successive enzymatic assay identified the synthesized glycoconjugates as novel PTPlB inhibitors with low micromole-ranged inhibitory activity and at least several-fold selectivity over other homologous PTPs tested found crucial toward PTP1 B inhibition. In addition, the benzyl groups on glucosyl moiety were

C-Aryl Glycosylation via Interrupted Pummerer Rearrangement

C-aryl glycosides are an important kind of carbohydrate derivatives for drug discovery,due to their distinctive attributes of resistance to hydrolysis from enzymes.Herein,C-aryl glycosylation was established for the synthesis of 2-sulfur C-aryl glycals and 1,2-dihydrobenzofuran-fused C-aryl glycosides via interrupted Pummerer process,featured with sulfonium-tethered[3,3]-sigmatropic rearrangement between sulfoxide glycals and phenols.This protocol offers a broad substrate scope with diverse glycosyl and phenols.Dapagliflozin,Empagliflozin,and Ipragliflozin analogs were straightforward achieved,respectively.

A highly selective C-rhamnosyltransferase from Viola tricolor and insights into its mechanisms

C-Glycosides are important natural products with various bioactivities.In plant biosynthetic pathways,the C-glycosylation step is usually catalyzed by C-glycosyltransferases(CGTs),and most of them prefer to accept uridine 5’-diphosphate glucose(UDP-Glc)as sugar donor.No CGTs favoring UDP-rhamnose(UDP-Rha)as sugar donor has been reported,thus far.Herein,we report the first selective C-rhamnosyltransferase VtCGTc from the medicinal plant Viola tricolor.VtCGTc could efficiently catalyze C-rhamnosylation of 2-hydroxynaringenin 3-C-glucoside,and exhibited high selectivity towards UDP-Rha.Mechanisms for the sugar donor selectivity of VtCGTc were investigated by molecular dynamics(MD)simulations and molecular mechanics with generalized Born and surface area solvation(MM/GBSA)binding free energy calculations.Val144 played a vital role in recognizing UDP-Rha,and the V144T mutant could efficiently utilize UDP-Glc.This work provides a new and efficient approach to prepare flavonoid C-rhamnosides such as violanthin and iso-violanthin.

Exploring the catalytic function and active sites of a novel C-glycosyltransferase from Anemarrhena asphodeloides

Anemarrhena asphodeloides is an immensely popular medicinal herb in China,which contains an abundant of mangiferin.As an important bioactive xanthone C-glycoside,mangiferin possesses a variety of pharmacological activities and is derived from the cyclization reaction of a benzophenone C-glycoside(maclurin).Biosyntheti-cally,C-glycosyltransferases are critical for the formation of benzophenone C-glycosides.However,the benzo-phenone C-glycosyltransferases from Anemarrhena asphodeloides have not been discovered.Herein,a promiscuous C-glycosyltransferase(AaCGT)was identified from Anemarrhena asphodeloides.It was able to catalyze efficiently mono-C-glycosylation of benzophenone,together with di-C-glycosylation of dihydrochalcone.It also exhibited the weak O-glycosylation or potent S-glycosylation capacities toward 12 other types of flavonoid scaffolds and a simple aromatic compound with–SH group.Homology modeling and mutagenesis experiments revealed that the glycosylation reaction of AaCGT was initiated by the conserved residue H23 as the catalytic base.Three critical residues H356,W359 and D380 were involved in the recognition of sugar donor through hydrogen-bonding interactions.In particular,the double mutant of F94W/L378M led to an unexpected enzy-matic conversion of mono-C-to di-C-glycosylation.This study highlights the important value of AaCGT as a potential biocatalyst for efficiently synthesizing high-value C-glycosides.

Synthesis of alkynes and alkynyl iodides bearing a protected amino alcohol moiety as functionalized amino acids precursors

Amino acid precursors in protected amino alcohol form are important synthons that can be used as building-blocks for the hemisynthesis of non-natural amino acids.Serine can be used as a common starting material for the synthesis of such compounds differently protected.Particularly,protected amino alcohols bearing an ethynyl and/or an iodoethynyl group can be used in cross-couplings,in 1,3-dipolar cycloadditions and/or in Nozaki-Hiyama-Kishi type reactions.We thus demonstrated that the efficiently protected amino alcohols derived from serine can be coupled to a sugar derivative by an indium mediated alkynylation reaction.The conditions of this coupling are compatible with such functionalized derivatives and allow envisaging an access to C-glycosylated amino acids.

Total Synthesis of C-α-Mannosyl Tryptophan via Palladium-Catalyzed C-H Glycosylation

The C2-α-mannosyl-tryptophan amino acid is produced by a unique posttranslational modification(PTM)of proteins and poses a significant synthetic challenge.A new strategy based on Pd-catalyzed auxiliary-directed remote C-H glycosylation of tryptophan was developed,which generates the C2-α-mannopyranose(Man)-Trp unit in a highly efficient and stereoselective fashion.Density functional theory(DFT)computational studies support a concerted oxidative addition mechanism for the stereospecific functionalization of a Pd(II)palladacycle intermediate with anα-mannosyl chloride donor.The utility of this method was demonstrated in the first total synthesis of insect C-glycopeptide hormone Cam-HrTH-I.