Flavonoids and their glycosides, including anthocyanins

Managing enzyme promiscuity in plant specialized metabolism: A lesson from flavonoid biosynthesis: Mission of a "body double" protein clarified

Specificities of enzymes involved in plant specialized metabolism, including flavonoid biosynthesis, are generally promiscuous. This enzyme promiscuity has served as an evolutionary basis for new enzyme functions and metabolic pathways in land plants adapting to environmental challenges. This phenomenon may lead, however, to inefficiency in specialized metabolism and adversely affect metabolite-mediated plant survival. How plants manage enzyme promiscuity for efficient specialized metabolism is, thus, an open question. Recent studies of flavonoid biosynthesis addressing this issue have revealed a conserved strategy, namely, a homolog of chalcone isomerase with no catalytic activity binds to chalcone synthase, a key flavonoid pathway enzyme, to narrow (or rectify) the enzyme's highly promiscuous product specificity. Reducing promiscuity via specific protein-protein interactions among metabolic enzymes and proteins may be a solution adopted by land plants to achieve efficient operation of specialized metabolism, while the intrinsic promiscuity of enzymes has likely been retained incidentally.

Selective alkylation of β-anhydroicaritine and their biological evaluation on anticancer

A convenient and selective alkylation of icaritin has been developed. The methodology involved initial formation of β-anhydroicaritine (3) under acidic conditions followed by selective methylation at the C-3 position and then alkylation at C-5 position. Several alkylated β-anhydroicaritine derivatives were synthesised using this methodology. These newly synthesised derivatives, especially the compounds 5b, 5c and 5j, significantly suppressed cell proliferation when tested against cancer cell lines in vitro. Compound 5j (R = Bn) exhibited a competitive inhibition against MCF7 in vivo compared to tamoxifen.

Amylosucrase from Deinococcus geothermalis can be modulated under different reaction conditions to produce novel quercetin 4'-O-α-d-isomaltoside

Amylosucrase (ASase, EC.4.2.1.4) is well-known for its distinguishable property of transglycosylation of many flavonoids and phenolics. Quercetin has diverse biological functions, however, its use is limited due to poor solubility and bioavailability. ASase derived from Deinococcus geothermalis (DGAS) showed conditional preference for producing unusual quercetin glucosides (QGs). DGAS produced a variety of QGs including quercetin monoglucosides (QG1), diglucosides (QG2 and QG2'), and triglucoside from quercetin and sucrose. The newly synthesized QG2' was recognized as a novel quercetin isomaltoside with an α-1,6 linkage branched at the -OH of C4' in quercetin by mass and nuclear magnetic resonance spectra. With a higher conversion yield from quercetin to QGs (60-92%), the optimum conditions for producing QG2' were examined under various pH and sucrose concentrations by response surface methodology. QG2' was predominantly produced under acidic conditions (pH 5.0) and at high sucrose concentrations (1000-1500 mM). In contrast, QG1 was generated as an intermediate of consecutive glycosylation. Kinetic evaluations indicated that considerable differences of transglycosylation velocities were caused by the pH and buffer salts of the reaction, which had a 3.9-fold higher overall performance (k_cat/K'_m) of generating QG2' at pH 5 compared to at pH 7. A rationale of unusual transglycosylations was demonstrated with a molecular docking simulation. Taken together, our study demonstrated that ASase can be used to synthesize unusually branched flavonoid glycosides from flavonol aglycones with clear patterns by modulating reaction conditions.

Copper(i) catalyzed synthesis of selanyl methylene 4-chromanol and aurone derivatives

An efficient copper-catalyzed cyclization cascade approach towards highly functionalized methylene 4-chromanol and aurone derivatives has been developed from reactions of ynols via 6-exo-dig and 5-exo-dig cyclization respectively. The catalysis involves alkyne activation via diorgano-diselenides and also their regioselective incorporation into the methylene 4-chromanol and aurone derivative core and is an open-air transformation.

Advances on the in vivo and in vitro glycosylations of flavonoids

Flavonoids possess diverse bioactivity and potential medicinal values. Glycosylation of flavonoids, coupling flavonoid aglycones and glycosyl groups in conjugated form, can change the biological activity of flavonoids, increase water solubility, reduce toxic and side effects, and improve specific targeting. Therefore, it is desirable to synthesize various flavonoid glycosides for further investigation on their medicinal values. Compared with chemical glycosylations, biotransformations catalyzed by uridine diphospho-glycosyltransferases provide an environmentally friendly way to construct glycosidic bonds without repetitive chemical synthetic steps of protection, activation, coupling, and deprotection. In this review, we will summarize the existing knowledge on the biotechnological glycosylation reactions either in vitro or in vivo for the synthesis of flavonoid O- and C-glycosides and other rare analogs.Key points• Flavonoid glycosides usually show improved properties compared with their flavonoid aglycones.• Chemical glycosylation requires repetitive synthetic steps and purifications.• Biotechnological glycosylation reactions either in vitro or in vivo were discussed.• Provides representative synthetic examples in detail.

The style and substance of plant flavonoid decoration; towards defining both structure and function

Over 8000 different flavonoids have been described and a considerable number of new flavonoid structures are being elucidated every year. The advent of metabolomics alongside the development of phytochemical genetics - wherein the genetic basis underlying the regulation of the levels of plant metabolites is determined - has provided a massive boost to such efforts. That said our understanding of the individual function(s) of the vast majority of the metabolites that constitute this important class of phytochemicals remains unknown. Here we review what is known concerning the major decorative modifications of flavonoids in plants, namely hydroxylation, glycosylation, methylation and acylation. Our major focus is with regard to the in planta function of these modified compounds, however, we also highlight the demonstrated bioactive roles which they possess. We additionally performed a comprehensive survey of the flavonoids listed in the KNApSAcK database in order to assess the frequency of occurrence of each type of flavonoid modification. We conclude that whilst considerable research has been carried out regarding the biological roles of flavonoids most studies to date have merely provided information on the compound class or sub-classes thereof as a whole with too little currently known on the specific role of individual metabolites. We, therefore, finally suggest a framework based on currently available tools by which the relative importance of the individual compounds can be assessed under various biological conditions in order to fill this knowledge-gap.

Flavonoids, terpenoids, and polyketide antibiotics: Role of glycosylation and biocatalytic tactics in engineering glycosylation

Flavonoids, terpenoids, and polyketides are structurally diverse secondary metabolites used widely as pharmaceuticals and nutraceuticals. Most of these molecules exist in nature as glycosides, in which sugar residues act as a decisive factor in their architectural complexity and bioactivity. Engineering glycosylation through selective trimming or extension of the sugar residues in these molecules is a prerequisite to their commercial production as well to creating novel derivatives with specialized functions. Traditional chemical glycosylation methods are tedious and can offer only limited end-product diversity. New in vitro and in vivo biocatalytic tools have emerged as outstanding platforms for engineering glycosylation in these three classes of secondary metabolites to create a large repertoire of versatile glycoprofiles. As knowledge has increased about secondary metabolite-associated promiscuous glycosyltransferases and sugar biosynthetic machinery, along with phenomenal progress in combinatorial biosynthesis, reliable industrial production of unnatural secondary metabolites has gained momentum in recent years. This review highlights the significant role of sugar residues in naturally occurring flavonoids, terpenoids, and polyketide antibiotics. General biocatalytic tools used to alter the identity and pattern of sugar molecules are described, followed by a detailed illustration of diverse strategies used in the past decade to engineer glycosylation of these valuable metabolites, exemplified with commercialized products and patents. By addressing the challenges involved in current bio catalytic methods and considering the perspectives portrayed in this review, exceptional drugs, flavors, and aromas from these small molecules could come to dominate the natural-product industry.

Transcriptome and metabolome reveal redirection of flavonoids in a white testa peanut mutant

BACKGROUND

Coat color determines both appearance and nutrient quality of peanut. White seed coat in peanut can enhance the processing efficiency and quality of peanut oil. An integrative analysis of transcriptomes, metabolomes and histocytology was performed on wsc mutant and its wild type to investigate the regulatory mechanisms underlying color pigmentation.

RESULT

Metabolomes revealed flavonoids were redirected in wsc, while multi-omics analyses of wsc mutant seeds and testae uncovered WSC influenced the flavonoids biosynthesis in testa as well as suberin formation, glycolysis, the TCA cycle and amino acid metabolism. The mutation also enhanced plant hormones synthesis and signaling. Further, co-expression analysis showed that FLS genes co-expressed with MBW complex member genes. Combining tissue expression patterns, genetic analyses, and the annotation of common DEGs for these three stages revealed that three testa specific expressed candidate genes, Araip.M7RY3, Aradu.R8PMF and Araip.MHR6K were likely responsible for the white testa phenotype. WSC might be regulated expression competition between FLS and DFR by controlling hormone synthesis and signaling as well as the MBW complex.

CONCLUSIONS

The results of this study therefore provide both candidate genes and novel approaches that can be applied to improve peanut with desirable seed coat color and flavonoid quality.

The Colors of Health: Chemistry, Bioactivity, and Market Demand for Colorful Foods and Natural Food Sources of Colorants

There is an increasing consumer demand for natural colors in foods. However, there is a limited number of available natural food sources for use by the food industry because of technical and regulatory limitations. Natural colors are less stable and have less vibrant hues compared to their synthetic color counterparts. Natural pigments also have known health benefits that are seldom leveraged by the food industry. Betalains, carotenoids, phycocyanins, and anthocyanins are major food colorants used in the food industry that have documented biological effects, particularly in the prevention and management of chronic diseases such as diabetes, obesity, and cardiovascular disease. The color industry needs new sources of stable, functional, and safe natural food colorants. New opportunities include sourcing new colors from microbial sources and via the use of genetic biotechnology. In all cases, there is an imperative need for toxicological evaluation to pave the way for their regulatory approval.

A new strategy for the preparation of antibody against natural glycoside: With astragaloside IV as an example

A new strategy for the hapten design of natural glycoside and application for the preparation of antibody is reported in this work. With astragaloside IV (AGS-IV) as an example, C6"-CH₂OH on a glucosyl group was selectively oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation to C6"-COOH, which was subsequently condensed with -NH₂ on bovine serum albumin to get artificial antigen. Then, the successful preparation of artificial antigen was verified by TCL, SDS-PAGE, UV, and MALDI-TOF-MS. Finally, rabbits were immunized with artificial antigen to obtain an antibody against AGS-IV. After tests of the titer, IC₅₀, and cross-reactivity, the results showed that the antibody prepared by TEMPO oxidation in this work had higher specificity than that the antibody prepared by conventional sodium periodate (NaIO₄) oxidation. The hapten, as a carboxylic acid derivative of AGS-IV, has better water solubility than AGS IV, which is more suitable for the synthesis of the hapten-carrier protein conjugate in aqueous phase, achieving another virtue of TEMPO oxidation over NaIO₄ oxidation. This new strategy provides new ideas for the design of haptens of other natural glycosides, as well as the preparation of their antibodies.

Total Synthesis of Caesalpinnone A

Total synthesis of caesalpinnone A was achieved in 12 steps starting from resorcinol. Key features of the synthesis include BINOL-phosphoric acid catalyzed [4 + 2] cycloaddition, trans-selective nucleophilic substitution, deallylation/oxa-Michael addition cascade, and late-stage photo-Fries rearrangement.

A phosphine-mediated domino sequence of salicylaldehyde with but-3-yn-2-one: rapid access to chromanone

Chromanone is a privileged structure with a wide range of unique biological activities.

Transposition of a non-autonomous DNA transposon in the gene coding for a bHLH transcription factor results in a white bulb color of onions (Allium cepa L.)

A DNA transposon was found in the gene encoding a bHLH transcription factor. Genotypes of the marker tagging this DNA transposon perfectly co-segregated with color phenotypes in large F_2:3 populations A combined approach of bulked segregant analysis and RNA-Seq was used to isolate causal gene for C locus controlling white bulb color in onions (Allium cepa L.). A total of 114 contigs containing homozygous single nucleotide polymorphisms (SNPs) between white and yellow bulked RNAs were identified. Four of them showed high homologies with loci clustered in the middle of chromosome 5. SNPs in 34 contigs were confirmed by sequencing of PCR products. One of these contigs showed perfect linkage to the C locus in F_2:3 populations consisting of 2491 individuals. However, genotypes of molecular marker tagging this contig were inconsistent with color phenotypes of diverse breeding lines. A total of 146 contigs showed differential expression between yellow and white bulks. Among them, transcription levels of B2 gene encoding a bHLH transcription factor were significantly reduced in white RNA bulk and F_2:3 individuals, although there was no SNP in the coding region. Phylogenetic analysis showed that onion B2 was orthologous to bHLH-coding genes regulating anthocyanin biosynthesis pathway in other plant species. Promoter regions of B2 gene were obtained by genome walking and a 577-bp non-autonomous DNA transposon designated as AcWHITE was found in the white allele. Molecular marker tagging AcWHITE showed perfect linkage with the C locus. Marker genotypes of the white allele were detected in some white accessions. However, none of tested red or yellow onions contained AcWHITE insertion, implying that B2 gene was likely to be a casual gene for the C locus.

Antioxidant Components of Brassica Vegetables Including Turnip and the Influence of Processing and Storage on their Anti-oxidative Properties

Brassica vegetables, particularly turnip, contain many natural antioxidants. This review focuses on antioxidant components and the influence of different processing and storage conditions on antioxidant activities of some Brassica vegetables including turnip. Long storage times had an adverse effect on antioxidant value of turnip. Also, the activity of antioxidants in cruciferous vegetables could be influenced by antioxidant breakdown and leaching during cooking. Heat treatment has a major impact on the antioxidant activity of Brassica vegetables and it has been perceived minor antioxidant ability in processed vegetables compared with uncooked samples. Food processing operations in terms of blanching, canning, sterilizing and freezing, in addition to cooking methods perhaps can have a major influence on the yield, chemical structure and bioavailability of antioxidants in Brassica family. Cooking methods such as steaming and microwaving are proper methods for a short time. Consumption of raw or slightly blanched turnip is an appropriate way to maximize its health benefits.

Metabolic Variations of Flavonoids in Leaves of T. media and T. mairei Obtained by UPLC-ESI-MS/MS

The needles of Taxus species contain a large number of bioactive compounds, such as flavonoids. In the present study, the total flavonoid content in leaves of Taxus media and Taxus mairei was 19.953 and 14.464 mg/g, respectively. A total of 197 flavonoid metabolites (70 flavones, 42 flavonols, 26 flavone C-glycosides, 20 flavanones, 15 anthocyanins, 13 isoflavones, 6 flavonolignans, and 5 proanthocyanidins) were identified for the first time by a widely targeted Ultra Performance Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry (UPLC-ESI-MS/MS) method within the two Taxus species, containing 160 common metabolites, with 37 unique metabolites merely determined in T. mairei or T. media. Moreover, 42 differential flavonoid metabolites were screened in the two Taxus species, which showed specific metabolic patterns in isoflavonoid biosynthesis, anthocyanin biosynthesis, and flavone and flavonol biosynthesis pathways. Compared to T. mairei, a more activated phenylpropanoid pathway was found in T. media, which could be responsible for the higher content of total flavonoids in T. media. Our results provide new insights into the diversity of flavonoid metabolites between T. mairei and T. media, and provide a theoretical basis for the sufficient utilization of Taxus species and the development of novel drugs.

Methylglucosylation of Phenolic Compounds by Fungal Glycosyltransferase-Methyltransferase Functional Modules

Glycosylation endows both natural and synthetic small molecules with modulated physicochemical and biological properties. Plant and bacterial glycosyltransferases capable of decorating various privileged scaffolds have been extensively studied, but those from kingdom Fungi still remain underexploited. Here, we use a combination of genome mining and heterologous expression techniques to identify four novel glycosyltransferase-methyltransferase (GT-MT) functional modules from Hypocreales fungi. These GT-MT modules display decent substrate promiscuity and regiospecificity, methylglucosylating a panel of natural products such as flavonoids, stilbenoids, anthraquinones, and benzenediol lactones. Native GT-MT modules can be split up and regrouped into hybrid modules with similar or even improved efficacy as compared with native pairs. Methylglucosylation of kaempferol considerably improves its insecticidal activity against the larvae of oriental armyworm Mythimna separata (Walker). Our work provides a set of efficient biocatalysts for the combinatorial biosynthesis of small molecule glycosides that may have significant importance to the pharmaceutical, agricultural, and food industries.

Copper-mediated anomeric O-arylation with organoboron reagents

Copper-mediated couplings of arylboroxines with glycosyl hemiacetals furnish O-aryl glycosides via Csp2-O bond formation. The method enables the anomeric O-arylation of protected pyranose and furanose derivatives, and is tolerant of functionalized arylboroxine partners. Whereas mixtures of anomers are formed from glucopyranose, galactopyranose and arabinofuranose hemiacetals, the α-anomer is generated selectively from mannopyranose and mannofuranose-derived substrates.

Role of Berry Anthocyanins and Phenolic Acids on Cell Migration and Angiogenesis: An Updated Overview

Cell migration is a critical process that is highly involved with normal and pathological conditions such as angiogenesis and wound healing. Important members of the RHO GTPase family are capable of controlling cytoskeleton conformation and altering motility characteristics of cells. There is a well-known relationship between small GTPases and the PI3K/AKT pathway. Endothelial cell migration can lead to angiogenesis, which is highly linked to wound healing processes. Phenolics, flavonoids, and anthocyanins are major groups of phytochemicals and are abundant in many natural products. Their antioxidant, antimicrobial, anti-inflammatory, antidiabetic, angiogenenic, neuroprotective, hepatoprotective, and cardioprotective properties have been extensively documented. This comprehensive review focuses on the in vitro and in vivo role of berry extracts and single anthocyanin and phenolic acid compounds on cell migration and angiogenesis. We aim to summarize the most recent published studies focusing on the experimental model, type of berry extract, source, dose/concentration and overall effect(s) of berry extracts, anthocyanins, and phenolic acids on the above processes.

Microbial Transformation of Flavonoids by Isaria fumosorosea ACCC 37814

Glycosylation is an efficient strategy to modulate the solubility, stability, bioavailability and bioactivity of drug-like natural products. Biological methods, such as whole-cell biocatalyst, promise a simple but highly effective approach to glycosylate biologically active small molecules with remarkable regio- and stereo-selectivity. Herein, we use the entomopathogenic filamentous fungus Isaria fumosorosea ACCC 37814 to biotransform a panel of phenolic natural products, including flavonoids and anthraquinone, into their glycosides. Six new flavonoid (4-O-methyl)glucopyranosides are obtained and structurally characterized using high resolution mass and nuclear magnetic resonance spectroscopic techniques. These compounds further expand the structural diversity of flavonoid glycosides and may be used in biological study.

Acylated pelargonidin glycosides from the red-purple flowers of Iberis umbellata L. and the red flowers of Erysimum × cheiri (L.) Crantz (Brassicaceae)

Five previously undescribed acylated pelargonidin 3-sophoroside-5-glucosides (pigments 2-6) were isolated from the red-purple flowers of Iberis umbellata L. 'Candycane Rose' and 'Candycane Red', in addition to a known one (pigment 1). The structures of five undescribed acylated anthocyanins were determined by chemical and spectroscopic methods to be pelargonidin 3-O-[2-O-(2-O-("acyl-A")-β-glucopyranosyl)-6-O-("acyl-B")-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside], in which the "acyl-A" group was either trans-sinapic (2), trans-ferulic (3), trans-sinapic (4), trans-ferulic (5), or trans-ferulic acid (6), and "acyl-B" was either glucosyl-trans-p-coumaric acid (2), glucosyl-trans-p-coumaric acid (3), trans-feruloyl-glucosyl-trans-p-coumaric acid (4), trans-feruloyl-glucosyl-trans-p-coumaric acid (5), or glucosyl-trans-feruloyl-glucosyl-trans-p-coumaric acid (6). Moreover, three previously undescribed acylated pelargonidin 3-sambubioside-5-glucosides (pigments 7, 8, and 10) and one undescribed acylated pelargonidin 3-(3^X-glucosylsambubioside)-5-glucoside (pigment 9) were isolated from the red flowers of Erysimum × cheiri (L.) Crantz 'Aurora' as major anthocyanins. The structures of the three undescribed acylated pelargonidin 3-sambubioside-5-glucosides were determined to be pelargonidin 3-O-[2-O-(2-O-("acyl-C")-β-xylopyranosyl)-6-O-("acyl-D")-β-glucopyranoside]-5-O-(β-glucopyranoside), in which the "acyl-C" group was either non (7), non (8), or trans-p-coumaric acid (10) and "acyl-D" was either trans-p-coumaric (7), trans-ferulic (8), or trans-p-coumaric acid (10). Moreover, a previously undescribed acylated pelargonidin 3-(3^X-glucosylsambubioside)-5-glucoside was identified to be pelargonidin 3-O-[2-O-(2-O-(trans-p-coumaroyl)-3-O-(β-glucopyranosyl)-β-xylopyranosyl)-6-O-(trans-p-coumaroyl)-β-glucopyranoside]-5-O-(β-glucopyranoside) (9). In addition, the distribution of anthocyanidins structural elements in 24 Brassicaceous species is compared.

Approaches for the isolation and identification of hydrophilic, light-sensitive, volatile and minor natural products

Water-soluble, volatile, minor and photosensitive natural products are yet poorly known, and this review discusses the literature reporting the isolation strategies for some of these metabolites.

Flavonoids, a Potential New Insight of Leucaena leucocephala Foliage in Ruminant Health

We investigated the constituents of Leucaena leucocephala foliage collected from Guangdong province in China and isolated 17 diverse flavonoids (1-17), including flavones (5-9, 11, and 12), flavonols (1, 10, and 16), flavanone 4, flavanonol 15, and flavonol glycosides (2, 3, 13, 14, and 17). Flavonoids quercetin (1), quercetin-3- O-α-rhamnopyranoside (2), and myricetin-3- O-α-rhamnopyranoside (17) were the major flavonoids components in L. leucocephala leaves, at a total concentration of about 2.5% of dry matter. pHRE-Luc inductive activity to mimic the activation of erythropoietin (EPO) gene, anti-inflammatory, antidiabetic, and antioxidant activities of isolated flavonoids (1-17) were evaluated. Flavonoids 7, 10, and 13 could strongly induce the transcriptional activity of pHRE-Luc, which indicated their potential to induce the expression of EPO. Flavonoids 7, 10, 13, and 17 displayed strong anti-inflammatory activity, relatively equal to the positive control dexamethasone. Flavonoids 1, 2, 3, 11, 12, 16, and 17 showed stronger antioxidant activities of DPPH radical scavenging capacity than ascorbic acid. Flavonoids 1, 2, and 10 showed weak cellular antioxidant activities against tert-butyl hydroperoxide (tBHP) induced ROS formation. Flavonoid rhamnoside 2 and arabinoside 3 undergone deglycosylation to the aglycone quercetin under anaerobic incubation with cattle rumen microorganisms. Furthermore, the potential health benefits for ruminant of flavonoids, which was rich in L. leucocephala foliage, was also discussed.

Indirect and direct routes to C-glycosylated flavones in Saccharomyces cerevisiae

BACKGROUND

C-glycosylated flavones have recently attracted increased attention due to their possible benefits in human health. These biologically active compounds are part of the human diet, and the C-linkage makes them more resistant to hydrolysis and degradation than O-glycosides. In contrast to O-glycosyltransferases, few C-glycosyltransferases (CGTs) have so far been characterized. Two different biosynthetic routes for C-glycosylated flavones have been identified in plants. Depending on the type of C-glycosyltransferase, flavones can be glycosylated either directly or indirectly via C-glycosylation of a 2-hydroxyflavanone intermediate formed by a flavanone 2-hydroxylase (F2H).

RESULTS

In this study, we reconstructed the pathways in the yeast Saccharomyces cerevisiae, to produce some relevant CGT substrates, either the flavanones naringenin and eriodictyol or the flavones apigenin and luteolin. We then demonstrated two-step indirect glycosylation using combinations of F2H and CGT, to convert 2-hydroxyflavanone intermediates into the 6C-glucoside flavones isovitexin and isoorientin, and the 8C-glucoside flavones vitexin and orientin. Furthermore, we established direct glycosylation of flavones using the recently identified GtUF6CGT1 from Gentiana triflora. The ratio between 6C and 8C glycosylation depended on the CGT used. The indirect route resulted in mixtures, similar to what has been reported for in vitro experiments. In this case, hydroxylation at the flavonoid 3'-position shifted the ratio towards the 8C-glucosylated orientin. The direct flavone glycosylation by GtUF6CGT1, on the other hand, resulted exclusively in 6C-glucosides.

CONCLUSIONS

The current study features yeast as a promising host for production of flavone C-glycosides, and it provides a set of tools and strains for identifying and studying CGTs and their mechanisms of C-glycosylation.

Biosynthesis of 7,8-dihydroxyflavone glycosides via OcUGT1-catalyzed glycosylation and transglycosylation

Herein, a flavonoid glycosyltransferase (GT) OcUGT1 was determined to be able to attack C-8 position of 7,8-dihydroxyflavone (7,8-DHF) via both glycosylation and transglycosylation reactions. OcUGT1-catalyzed glycosylation of 7,8-DHF resulted in the formation of two monoglycosides 7-O-β-D-glucosyl-8-hydroxyflavone (1a), 7-hydroxy-8-O-β-D-glucosylflavone (1b), as well as one diglycoside 7,8-di-O-β-D-glucosylflavone (1c). Under the action of OcUGT1, inter-molecular trans-glycosylations from aryl β-glycosides to 7,8-DHF to form monoglycosides 1a and 1b were observable.

Synthesis, structure-activity relationship and molecular docking studies of 3-O-flavonol glycosides as cholinesterase inhibitors

The prime objective of this research work is to prepare readily soluble synthetic analogues of naturally occurring 3-O-flavonol glycosides and then investigate the influence of various substituents on biological properties of synthetic compounds. In this context, a series of varyingly substituted 3-O-flavonol glycosides have been designed, synthesized and characterized efficiently. The structures of synthetic molecules were unambiguously corroborated by IR, ¹H, ¹³C NMR and ESI-MS spectroscopic techniques. The structure of compound 22 was also analyzed by X-ray diffraction analysis. All the synthetic compounds (21-30) were evaluated for in vitro inhibitory potential against cholinesterase enzymes. The results displayed that most of the derivatives were potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with varying degree of IC₅₀ values. The experimental results were further encouraged by molecular docking studies in order to explore their binding behavior with the active pocket of AChE and BChE enzymes. The experimental and theoretical results are in parallel with one another.

Methylglucosylation of aromatic amino and phenolic moieties of drug-like biosynthons by combinatorial biosynthesis

Glycosylation is a prominent strategy to optimize the pharmacokinetic and pharmacodynamic properties of drug-like small-molecule scaffolds by modulating their solubility, stability, bioavailability, and bioactivity. Glycosyltransferases applicable for "sugarcoating" various small-molecule acceptors have been isolated and characterized from plants and bacteria, but remained cryptic from filamentous fungi until recently, despite the frequent use of some fungi for whole-cell biocatalytic glycosylations. Here, we use bioinformatic and genomic tools combined with heterologous expression to identify a glycosyltransferase-methyltransferase (GT-MT) gene pair that encodes a methylglucosylation functional module in the ascomycetous fungus Beauveria bassiana The GT is the founding member of a family nonorthologous to characterized fungal enzymes. Using combinatorial biosynthetic and biocatalytic platforms, we reveal that this GT is a promiscuous enzyme that efficiently modifies a broad range of drug-like substrates, including polyketides, anthraquinones, flavonoids, and naphthalenes. It yields both O- and N-glucosides with remarkable regio- and stereospecificity, a spectrum not demonstrated for other characterized fungal enzymes. These glucosides are faithfully processed by the dedicated MT to afford 4-O-methylglucosides. The resulting "unnatural products" show increased solubility, while representative polyketide methylglucosides also display increased stability against glycoside hydrolysis. Upon methylglucosidation, specific polyketides were found to attain cancer cell line-specific antiproliferative or matrix attachment inhibitory activities. These findings will guide genome mining for fungal GTs with novel substrate and product specificities, and empower the efficient combinatorial biosynthesis of a broad range of natural and unnatural glycosides in total biosynthetic or biocatalytic formats.

Isolation and characterization of a multifunctional flavonoid glycosyltransferase from Ornithogalum caudatum with glycosidase activity

Glycosyltransferases (GTs) are bidirectional biocatalysts catalyzing the glycosylation of diverse molecules. However, the extensive applications of GTs in glycosides formation are limited due to their requirements of expensive nucleotide diphosphate (NDP)-sugars or NDP as the substrates. Here, in an effort to characterize flexible GTs for glycodiversification of natural products, we isolated a cDNA, designated as OcUGT1 from Ornithogalum caudatum, which encoded a flavonoid GT that was able to catalyze the trans-glycosylation reactions, allowing the formation of glycosides without the additions of NDP-sugars or NDP. In addition, OcUGT1 was observed to exhibit additional five types of functions, including classical sugar transfer reaction and three reversible reactions namely NDP-sugar synthesis, sugars exchange and aglycons exchange reactions, as well as enzymatic hydrolysis reaction, suggesting OcUGT1 displays both glycosyltransferase and glycosidase activities. Expression profiles revealed that the expression of OcUGT1 was development-dependent and affected by environmental factors. The unusual multifunctionality of OcUGT1 broadens the applicability of OcUGT1, thereby generating diverse carbohydrate-containing structures.

Glycosyltransferase cascades made fit for chemical production: Integrated biocatalytic process for the natural polyphenol C-glucoside nothofagin

Glycosyltransferase cascades are promising tools of biocatalysis for natural product glycosylation, but their suitability for actual production remains to be shown. Here, we demonstrate at a scale of 100 g isolated product the integrated biocatalytic production of nothofagin, the natural 3'-C-β-D-glucoside of the polyphenol phloretin. A parallel reaction cascade involving coupled C-glucosyltransferase and sucrose synthase was optimized for the one-pot glucosylation of phloretin from sucrose via an UDP/UDP-glucose shuttle. Inclusion complexation with the highly water soluble 2-hydroxypropyl-β-cyclodextrin pushed the phloretin solubility to its upper practical limit (∼120 mM) and so removed the main bottleneck on an efficient synthesis of nothofagin. The biotransformation thus intensified had excellent performance metrics of 97% yield and ∼50 gproduct /L at a space-time yield of 3 g/L/hr. The UDP-glucose was regenerated up to ∼220 times. A scalable downstream process for efficient recovery of nothofagin (≥95% purity; ≥65% yield) was developed. A tailored anion-exchange chromatography at pH 8.5 was used for capture and initial purification of the product. Recycling of the 2-hydroxypropyl-β-cyclodextrin would also be possible at this step. Product precipitation at a lowered pH of 6.0 and re-dissolution in acetone effectively replaced desalting by size exclusion chromatography in the final step of nothofagin purification. This study therefore, reveals the potential for process intensification in the glycosylation of polyphenol acceptors by glycosyltransferase cascades. It demonstrates that, with up- and downstream processing carefully optimized and suitably interconnected, a powerful biocatalytic technology becomes available for the production of an important class of glycosides difficult to prepare otherwise.

Biosynthesis of flavone C-glucosides in engineered Escherichia coli

Two plant-originated C-glucosyltransferases (CGTs) UGT708D1 from Glycine max and GtUF6CGT1 from Gentiana triflora were accessed for glucosylation of selected flavones chrysin and luteolin. Uridine diphosphate (UDP)-glucose pool was enhanced in Escherichia coli cell cytosol by introducing heterologous UDP-glucose biosynthetic genes, i.e., glucokinase (glk), phosphoglucomutase (pgm2), and glucose 1-phosphate uridylyltransferase (galU), along with glucose facilitator diffusion protein from (glf) from different organisms, in a multi-monocistronic vector with individual T7 promoter, ribosome binding site, and terminator for each gene. The C-glucosylated products were analyzed by high-performance liquid chromatography-photodiode array, high-resolution quadruple time-of-flight electrospray ionization mass spectrometry, and one-dimensional nuclear magnetic resonance analyses. Fed-batch shake flask culture showed 8% (7 mg/L; 16 μM) and 11% (9 mg/L; 22 μM) conversion of chrysin to chrysin 6-C-β-D-glucoside with UGT708D1 and GtUF6CGT1, respectively. Moreover, the bioengineered E. coli strains with exogenous UDP-glucose biosynthetic genes and glucose facilitator diffusion protein enhanced the production of chrysin 6-C-β-D-glucoside by approximately 1.4-fold, thus producing 10 mg/L (12%, 24 μM) and 14 mg/L (17%, 34 μM) by UGT708D1 and GtUF6CGT1, respectively, without supplementation of additional UDP-glucose in the medium. The biotransformation was further elevated when the bioengineered strain was scaled up in lab-scale fermentor at 3 L volume. HPLC analysis of fermentation broth extract revealed 50% (42 mg/L, 100 μM) conversion of chrysin to chrysin 6-C-β-D-glucoside at 48 h upon supplementation of 200 μM of chrysin. The maximum conversion of luteolin was 38% (34 mg/L, 76 μM) in 50-mL shake flask fermentation at 48 h. C-glucosylated derivative of chrysin was found to be more soluble and more stable to high temperature, different pH range, and β-glucosidase enzyme, than O-glucosylated derivative of chrysin.

Hydroxyl directed C-arylation: synthesis of 3-hydroxyflavones and 2-phenyl-3-hydroxy pyran-4-ones under transition-metal free conditions

Hydroxyl assisted, efficient, transition-metal free and direct C-arylation of 3-hydroxychromone and 5-hydroxy pyran-4-one moieties in the presence of a base, air as an oxidant and arylhydrazines as arylating agents to furnish highly biologically active 3-hydroxyflavones and 2-phenyl-3-hydroxy pyran-4-ones has been developed.

Phyto-metabolites; An Impregnable Shield against Plant Viruses

Worldwide, economically important crops are under continuous threat from plant viruses as they reproduce within the host and spread via various biological and non biological means. The problem can be minimized via application of integrated management approaches involving utilization of resistant genotypes and reducing the insect vector population. But such strategies are rarely applied in developing countries and farmers prefer to use chemicals against all type of diseases. But increasing use of pesticides is a leading cause of disaster to our ecosystem so alternative means such as phyto-metabolites should be explored for eco friendly management of plant viruses. So here we have reviewed about different phyto-metabolites that can be effectively and potentially used against various plant virus diseases. We further explained about the various primary and secondary metabolites such as alkaloids, essential oils, flavonoids, polysaccharides and proteins. The review highlights the recent advances in the field of phyto-metabolites utilization against plant viruses and sums up via hoping through prospects that future drugs will be safer for human beings and our ecosystem.

Functional Analysis of an Uridine Diphosphate Glycosyltransferase Involved in the Biosynthesis of Polyphenolic Glucoside in Tea Plants (Camellia sinensis)

Polyphenols are one of the largest groups of compounds that confer benefits to the health of plants and humans. Flavonol glycosides are a major ingredient of polyphenols in Camellia sinensis. Flavonol-3-O-glycosides are characteristic astringent taste compounds in tea infusion. A polyphenolic glycosyltransferase (CsUGT72AM1) belonging to cluster IIIb was isolated from the tea plant. The full-length cDNA of CsUGT72AM1 is 1416 bp. It encodes 472 amino acids with a calculated molecular mass of 50.92 kDa and an isoelectric point of 5.21. The recombinant CsUGT72AM1 protein was expressed in Escherichia coli and exhibited catalytic activity toward multiple flavonoids and coniferyl aldehyde. The enzyme assay indicated that rCsUGT72AM1 could perform glycosidation of flavonols or coniferyl aldehyde in vitro to form 3-O-glucoside or 4-O-glucoside, respectively. Interestingly, this enzyme also had activities and performed multisite glycosidation toward flavanones. The consistent products were confirmed to be naringenin-7-O-glucoside and -4'-O-glucoside by the nuclear magnetism assay. In addition, in the enzyme assay with cyanidin as the substrate, the results suggested that the glycosylated activity of CsUGT72AM1 was remarkably inhibited by a high concentration of anthocyanins. The above results indicate that CsUGT72AM1 may be involved in the metabolism of flavonol, flavanone, anthocyanin, and lignin.

Recent Advances in the Recombinant Biosynthesis of Polyphenols

Plants are the source of various natural compounds with pharmaceutical and nutraceutical importance which have shown numerous health benefits with relatively fewer side effects. However, extraction of these compounds from native producers cannot meet the ever-increasing demands of the growing population due to, among other things, the limited production of the active compound(s). Their production depends upon the metabolic demands of the plant and is also subjected to environmental conditions, abundance of crop species and seasonal variations. Moreover, their extraction from plants requires complex downstream processing and can also lead to the extinction of many useful plant varieties. Microbial engineering is one of the alternative approaches which can meet the global demand for natural products in an eco-friendly manner. Metabolic engineering of microbes or pathway reconstruction using synthetic biology tools and novel enzymes lead to the generation of a diversity of compounds (like flavonoids, stilbenes, anthocyanins etc.) and their natural and non-natural derivatives. Strain and pathway optimization, pathway regulation and tolerance engineering have produced microbial cell factories into which the metabolic pathway of plants can be introduced for the production of compounds of interest on an industrial scale in an economical and eco-friendly way. While microbial production of phytochemicals needs to further increase product titer if it is ever to become a commercial success. The present review covers the advancements made for the improvement of microbial cell factories in order to increase the product titer of recombinant polyphenolic compounds.

Gardenifolins A-H, Scalemic Neolignans from Gardenia ternifolia: Chiral Resolution, Configurational Assignment, and Cytotoxic Activities against the HeLa Cancer Cell Line

From the tropical plant Gardenia ternifolia Schumach. and Thonn. (Rubiaceae), eight stereoisomeric 2,3-dihydrobenzo[b]furan neolignans, named gardenifolins A-H (1a-d and 2a-d), were isolated and fully structurally characterized. Reversed-phase chromatography of a stem bark extract afforded two peaks, viz. mixtures I and II, each one consisting of two diastereomers and their respective enantiomers. They were resolved and stereochemically analyzed by HPLC on a chiral phase coupled to electronic circular dichroism (ECD) spectroscopy, giving single ECD spectra of all eight stereoisomers. The double-bond geometries (E or Z) of the gardenifolins A-H and their relative configurations (cis or trans) at the stereogenic centers C-7 and C-8 in the dihydrofuran ring system were assigned by 1D and 2D NMR methods, in particular, using NOE difference experiments, whereas the absolute configurations of the isolated enantiomers were established by ECD spectroscopy by applying the reversed helicity rule. The individual pure gardenifolin isomers A-H showed the most different cytotoxic effects against the human cancer HeLa cell line, with 1d and 2a displaying the highest activities, with IC₅₀ values of 21.0 and 32.5 μM, respectively. Morphological experiments indicated that gardenifolin D (1d) induces apoptosis of HeLa cells at 25 μM.

Synthesis and Antiradical Activity of Isoquercitrin Esters with Aromatic Acids and Their Homologues

Isoquercitrin, (IQ, quercetin-3-O-β-d-glucopyranoside) is known for strong chemoprotectant activities. Acylation of flavonoid glucosides with carboxylic acids containing an aromatic ring brings entirely new properties to these compounds. Here, we describe the chemical and enzymatic synthesis of a series of IQ derivatives at the C-6″. IQ benzoate, phenylacetate, phenylpropanoate and cinnamate were prepared from respective vinyl esters using Novozym 435 (Lipase B from Candida antarctica immobilized on acrylic resin). The enzymatic procedure gave no products with “hydroxyaromatic” acids, their vinyl esters nor with their benzyl-protected forms. A chemical protection/deprotection method using Steglich reaction yielded IQ 4-hydroxybenzoate, vanillate and gallate. In case of p-coumaric, caffeic, and ferulic acid, the deprotection lead to the saturation of the double bonds at the phenylpropanoic moiety and yielded 4-hydroxy-, 3,4-dihydroxy- and 3-methoxy-4-hydroxy-phenylpropanoates. Reducing capacity of the cinnamate, gallate and 4-hydroxyphenylpropanoate towards Folin-Ciocalteau reagent was significantly lower than that of IQ, while other derivatives displayed slightly better or comparable capacity. Compared to isoquercitrin, most derivatives were less active in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, but they showed significantly better 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid, ABTS) scavenging activity and were substantially more active in the inhibition of tert-butylhydroperoxide induced lipid peroxidation of rat liver microsomes. The most active compounds were the hydroxyphenylpropanoates.

Red-purple flower color and delphinidin-type pigments in the flowers of Pueraria lobata (Leguminosae)

A previously undescribed acylated anthocyanin was extracted from the red-purple flowers of Pueraria lobata with 5% HOAc-H₂O, and determined to be petunidin 3-O-(β-glucopyranoside)-5-O-[6-O-(malonyl)-β-glucopyranoside], by chemical and spectroscopic methods. In addition, two known acylated anthocyanins, delphinidin 3-O-(β-glucopyranoside)-5-O-[6-O-(malonyl)-β-glucopyranoside] and malvidin 3-O-(β-glucopyranoside)-5-O-[6-O-(malonyl)-β-glucopyranoside] were identified. Delphinidin 3,5-di-glucoside, petunidin 3,5-di-glucoside, and malvidin 3,5-di-glucoside, have been known as major components of P. lobata in the former study. However, malonyl esters amounts were detected over 10 times compared with non-malonyl esters amounts. In those anthocyanins the most abundant anthocyanin was petunidin 3-O-(β-glucopyranoside)-5-O-[6-O-(malonyl)-β-glucopyranoside] in total flowers. On the visible absorption spectral curve of fresh red-purple petals, one characteristic absorption maximum was observed at 520 nm, which is similar to those of flowers containing pelargonidin derivatives. In contrast, the absorption spectral curve of old violet petals was observed at 500(sh), 536, 564(sh), and 613(sh) nm, which are similar to those of violet flowers containing delphinidin-type pigments. Pressed juices of both fresh red-purple petals and old violet petals had pH5.2 and 5.5 respectively, and had the same flavonoid constitution. Crude fresh red-purple petal pigments extracted by pH 2.2 and pH 5.2 buffers exhibited the same color and spectral curves as fresh red-purple petals and old violet petals, respectively. Moreover, in a cross-TLC experiment of crude extracted pigments, red-purple color was exhibited by the anthocyanin region and the crossed region of anthocyanins and isoflavone. Thus, it may be assumed that the unusually low pH in the vacuole of fresh petals plays an important role to form red-purple flower color against weak acidic pH in the vacuole of old violet P. lobata petals.

Isolation of flavonoids from apple peel using novel graphene oxide cotton fiber

A novel graphene oxide cotton fibre (GOF) was used to adsorb flavonoids from crude ethanol extracts derived from apple peels. Ultra-high pressure liquid chromatography-mass spectrometry was used to analyse polyphenol content, and the resulting data demonstrated that GOF-based flash chromatography can be used to efficiently separate polyphenols from sugars and can facilitate the removal of 95% of the sugar content. Flavonoids can be easily separated from phenolic acids. Chalcones and flavonols were eluted with 100% methanol and subsequently flavan-3-ols can be eluted with 0.04 M sodium hydroxide. The novel GOF has the potential to be used in the isolation of flavonoids.

Dietary flavonoid aglycones and their glycosides: Which show better biological significance?

The dietary flavonoids, especially their glycosides, are the most vital phytochemicals in diets and are of great general interest due to their diverse bioactivity. The natural flavonoids almost all exist as their O-glycoside or C-glycoside forms in plants. In this review, we summarized the existing knowledge on the different biological benefits and pharmacokinetic behaviors between flavonoid aglycones and their glycosides. Due to various conclusions from different flavonoid types and health/disease conditions, it is very difficult to draw general or universally applicable comments regarding the impact of glycosylation on the biological benefits of flavonoids. It seems as though O-glycosylation generally reduces the bioactivity of these compounds - this has been observed for diverse properties including antioxidant activity, antidiabetes activity, anti-inflammation activity, antibacterial, antifungal activity, antitumor activity, anticoagulant activity, antiplatelet activity, antidegranulating activity, antitrypanosomal activity, influenza virus neuraminidase inhibition, aldehyde oxidase inhibition, immunomodulatory, and antitubercular activity. However, O-glycosylation can enhance certain types of biological benefits including anti-HIV activity, tyrosinase inhibition, antirotavirus activity, antistress activity, antiobesity activity, anticholinesterase potential, antiadipogenic activity, and antiallergic activity. However, there is a lack of data for most flavonoids, and their structures vary widely. There is also a profound lack of data on the impact of C-glycosylation on flavonoid biological benefits, although it has been demonstrated that in at least some cases C-glycosylation has positive effects on properties that may be useful in human healthcare such as antioxidant and antidiabetes activity. Furthermore, there is a lack of in vivo data that would make it possible to make broad generalizations concerning the influence of glycosylation on the benefits of flavonoids for human health. It is possible that the effects of glycosylation on flavonoid bioactivity in vitro may differ from that seen in vivo. With in vivo (oral) treatment, flavonoid glycosides showed similar or even higher antidiabetes, anti-inflammatory, antidegranulating, antistress, and antiallergic activity than their flavonoid aglycones. Flavonoid glycosides keep higher plasma levels and have a longer mean residence time than those of aglycones. We should pay more attention to in vivo benefits of flavonoid glycosides, especially C-glycosides.

Anthocyanin suppresses CoCrMo particle-induced osteolysis by inhibiting IKKα/β mediated NF-κB signaling in a mouse calvarial model

Wear particle-induced osteolysis and bone resorption have been identified as critical factors of implant failure and total joint revision, in which nuclear factor kappa B (NF-κB) signaling and chronic inflammation have been shown to play key roles. Although anthocyanin is known to have anti-inflammatory function via blocking NF-κB pathway, it is still unclear whether anthocyanin has a protective effect on particle-induced osteolysis. In the present study, we aimed to investigate the detailed effects and the underlying mechanism of anthocyanin on CoCrMo particle-induced osteolysis in a mouse calvavial model. One hundred and twelve male BALB/c mice were divided randomly into four groups: sham group (sham operation and injection with PBS), vehicle group (CoCrMo particle treatment and injection with PBS), low-dose anthocyanin group (CoCrMo particle treatment and injecting anthocyanin with 0.1mg/g/day), and high-dose anthocyanin group (CoCrMo particle treatment and injecting anthocyanin with 0.4mg/g/day). Mice were sacrificed after two weeks, harvesting the calvariae tissue for in depth analysis by micro-CT, histomorphometry, immunohistochemical and molecular biology analysis. As expected, anthocyanin markedly inhibited CoCrMo particle-induced inflammatory infiltration and decreased bone loss in vivo. Anthocyanin also reversed the increase in the ratio of receptor activator of nuclear factor kappa B ligand (RANKL)/osteoproteger (OPG) and suppressed osteoclast formation in CoCrMo particle-stimulated calvaria. Additionally, anthocyanin significantly reduced the expression and secretion of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in the calvaria of CoCrMo-stimulated mice. Furthermore, we confirmed that anthocyanin attenuated osteolysis by blocking NF-κB pathway via inhibiting inhibitor of nuclear factor kappa-B kinase α/β (IKKα/β) phosphorylation. In conclusion, our study demonstrated that anthocyanin can protect against CoCrMo particle-induced inflammatory osteolysis via inhibiting the IKKα/β-NF-κB pathway, and have a potential therapeutic effect on the treatment of wear particle-induced osteolysis.