Synthesis of Quercetin-3-O-Glucoside from Rutin byPenicillium decumbensNaringinase

A Comparative Study of Rutin and Rutin Glycoside: Antioxidant Activity, Anti-Inflammatory Effect, Effect on Platelet Aggregation and Blood Coagulation

The effects of rutin and rutin glycoside with different solubility were compared on antioxidant activity and anti-inflammatory effects in vitro and the effects on platelet aggregation and blood coagulation in vitro and in vivo. Rutin glycoside (consisting of rutin mono-glucoside and rutin di-glucoside) was prepared via enzymatic transglycosylation from rutin. Rutin glycoside showed a higher effect than rutin on radical scavenging activity in antioxidant assays. Rutin showed a higher toxicity than rutin glycoside in murine macrophage RAW264.7 cells. They had similar effects on the levels of nitric oxide (NO), prostaglandin E (PGE) 2 and pro-inflammatory cytokines (such as tumor necrosis factor (TNF)-α, and interleukin (IL)-6) in the cells. Both rutin and rutin glycosides similarly reduced the rate of platelet aggregation compared to controls in vitro. They also similarly delayed prothrombin time (PT) and activated partial thromboplastin time (APTT) in an in vitro blood coagulation test. The effect of repeated administration of rutin and rutin glycoside was evaluated in vivo using SD rats. The platelet aggregation rate of rutin and the rutin glycoside administered group was significantly decreased compared to that of the control group. On the other hand, PT and APTT of rutin and rutin glycoside group were not significantly delayed in vivo blood coagulation test. In conclusion, rutin and rutin glycoside showed differences in antioxidant activities in vitro, while they were similar in the reduction of NO, PGE2, TNF-α and IL-6 in vitro. Rutin and rutin glycoside also showed similar platelet aggregation rates, and blood coagulation both in vitro and in vivo condition. Comparing in vitro and in vivo, rutin and rutin glycoside were effective on platelet aggregation both in vitro and in vivo, but only in vitro on blood coagulation.

Synthesis of 2-(4-hydroxyphenyl)ethyl 3,4,5-Trihydroxybenzoate and Its Inhibitory Effect on Sucrase and Maltase

We report on the synthesis of an active component, 2-(4-hydroxyphenyl)ethyl 3,4,5-trihydroxybenzoate (HETB), from Rhodiola crenulata. Subsequent analysis revealed that HETB exhibits α-glucosidase inhibitory activities on maltase and sucrase, with potency exceeding that of the known α-glucosidase inhibitors (voglibose and acarbose). An inhibition kinetics study revealed that HETB, acarbose, and voglibose bind to maltase and sucrase, and HETB was shown to be a strong competitive inhibitor of maltase and sucrase. In a molecular docking study based on the crystal structure of α-glucosidase from Saccharomyces cerevisiae, we revealed the HETB binding in the active site of maltase via hydrogen-bond interactions with five amino acid residues: Ser 240, Asp 242, Glu 277, Arg 315, and Asn 350. For HETB docked to the sucrase active site, seven hydrogen bonds (with Asn 114, Glu 148, Gln 201, Asn 228, Gln 381, Ile 383, and Ser 412) were shown.

A Review on Structure, Modifications and Structure-Activity Relation of Quercetin and Its Derivatives

Quercetin and its derivatives are important metabolites that belong to the flavonol class of flavonoids. Quercetin and some of the conjugates have been approved by the FDA for human use. They are widely distributed among plants and have various biological activities, such as being anticancer, antiviral, and antioxidant. Hence, the biosynthesis of novel derivatives is an important field of research. Glycosylation and methylation are two important modification strategies that have long been used and have resulted in many novel metabolites that are not present in natural sources. A strategy for modifying quercetin in E. coli by means of glycosylation, for example, involves overexpressing respective glycosyltransferases (GTs) in the host and metabolic engineering for increasing nucleoside diphosphate sugar (NDP sugar). Still others have used microorganisms other than E. coli, such as Streptomyces sp., for the biotransformation process. The overall study of the structural activity relationship has revealed that modification of some residues in quercetin decreased one activity but increased others. This review summarizes all of the information mentioned above.

Microbial Transformation of Prenylquercetins by Mucor hiemalis

Quercetin, one of the most widely distributed flavonoids, has been found to show various biological activities including antioxidant, anticancer, and anti-inflammatory effects. It has been reported that bioactivity enhancement of flavonoids has often been closely associated with nuclear prenylation, as shown in 8-prenylquercetin and 5'-prenylquercetin. It has also been revealed in many studies that the biological activities of flavonoids could be improved after glucosylation. Three prenylated quercetins were prepared in this study, and microbial transformation was carried out in order to identify derivatives of prenylquercetins with increased water solubility and improved bioavailability. The fungus M. hiemalis was proved to be capable of converting prenylquercetins into more polar metabolites and was selected for preparative fermentation. Six novel glucosylated metabolites were obtained and their chemical structures were elucidated by NMR and mass spectrometric analyses. All the microbial metabolites showed improvement in water solubility.

A spectrophotometric method for high-throughput screening of α-l-rhamnosidase activity on rutin coupled with a β-d-glucosidase assay

α-l-Rhamnosidase may biotransform rutin into isoquercetin with better bioavailability and bioactivity. To date, the high-throughput screening for the activity of α-l-rhamnosidases on rutin could not be achieved. Herein, based on the spectral differences between rutin and its aglycone quercetin in alkaline pH 10.0, we have developed a novel and simple spectrophotometric method for high-throughput screening of α-l-rhamnosidase activity on rutin by combining with a highly active β-d-glucosidase. Quercetin showed the maximum absorbance at 320 nm in alkaline pH 10.0, and could be considered as the characteristic peak of quercetin because rutin had low absorption at 320 nm. Meanwhile, rutin exhibited the maximum absorption at 400 nm and quercetin showed low absorption at 400 nm in pH 10.0. With this novel spectrophotometric method, the relative abilities of nine different α-l-rhamnosidases on rutin had been evaluated by monitoring the absorption values of the reaction mixture in alkaline pH 10.0 at 320 nm and 400 nm, and the trend in the activity on rutin was consistent with that obtained by HPLC. Moreover, the library from site-directed saturation mutagenesis at the residue Val338 in the α-l-rhamnosidase BtRha78A from Bacteroides thetaiotaomicron was constructed for high-throughput screening by this novel spectrophotometric method, and the mutant V338S with improved activity on rutin was obtained. The conversion rate of the mutant V338S on rutin increased by 21.7% and 16.8% than wild type when using whole cells and purified enzymes, respectively. Our findings demonstrated that this novel spectrophotometric method coupled with the β-d-glucosidase assay might be applied for high-throughput screening of different α-l-rhamnosidases and a great number of mutants from semi-rational design and directed evolution for α-l-rhamnosidase.

Enzymatic Production of Steviol Glucosides Using β-Glucosidase and Their Applications

Sweet leaf, Stevia rebaudiana Bertoni, is a perennial plant species widely known for its sweet-tastingent-kaurene type diterpenoid glycosides (steviol glucosides). Steviol glucosides include rubusoside (Ru), stevioside (Ste), and rebaudioside (Reb), which have immunomodulatory capability and protective effects against hyperglycemia, hypertension, inflammation, tumors, and diarrhea. In addition, they can enhance the solubility of epotoside, liquiritin, paclitaxel, curcuminoids, quercetin, and wheat bran flavonoids, thus increasing their permeability. The hydrolysis of three glucosyl groups at positions C13 and C19 of Ste will produce steviolbioside, steviol, isosteviol, steviol mono-glucoside, or Ru. S. rebaudiana contains these hydrolyzed products in trace amounts. This chapter describes recent advances in the preparation of various steviol glycosides from Ste by using different β-glycosidases, with particular focus on their potential industrial applications as natural solubilizers of insoluble compounds. Furthermore, the reaction mechanism of β-glycosidases and their kinetic properties are summarized.

Characterization of a glycoside hydrolase family 78 α-l-rhamnosidase from Bacteroides thetaiotaomicron VPI-5482 and identification of functional residues

A putative glycoside hydrolase family 78 α-l-rhamnosidase BtRha78A from Bacteroides thetaiotaomicron VPI-5482 was heterologously over-expressed in Escherichia coli. Enzymatic properties of recombinant BtRha78A were characterized in detail. Recombinant BtRha78A might efficiently hydrolyze p-nitrophenyl α-l-rhamnopyranoside. BtRha78A displayed the highest activity at 60 °C in pH 6.5. BtRha78A exhibited a good pH stability and relatively high thermostability. BtRha78A could be tolerant of a low concentration of alcohols. These attractive advantages made it a promising alternative biocatalyst for industrial applications. The catalytic general acid Asp335 and general base Glu595 of BtRha78A were confirmed by site-directed mutagenesis. Alanine scanning mutagenesis based on sequence alignment and structural analysis revealed that the conserved residues Asp330, Arg334, Trp339, Asp342, Tyr383, Trp440, and His620 were crucial for enzyme catalysis. Most functional residues located at the conserved general acid motif (Asp330-Asp342) and were completely conserved in the subfamily I Rha78s.

Extraction optimization and in vitro and in vivo anti-postprandial hyperglycemia effects of inhibitor from Phoenix dactylifera L. parthenocarpic fruit

Phoenix dactylifera L. plays an important role in social, economic, and ecological Tunisian sectors. Some date palms produce parthenocarpic fruit named Sish. The aqueous ethanolic extract from P. dactylifera parthenocarpic dates demonstrated a potent inhibition of the enzymes related to type II diabetes. In this work, extraction optimization of amylase inhibitors was carried out using Box-Behnken Design. Bioactivity-guided fractionation of the 70% aqueous ethanol extract was performed to identify the active compounds. The physicochemical results by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed the presence of 13 phenolic compounds. The in vitro study showed that the extract exhibited a more specific inhibitor of α-glucosidase than α-amylase with an IC₅₀ value of 0.6 and 2.5mg/mL, respectively. The in vivo study of this extract effect on the postprandial hyperglycemia activity showed a decrease in plasma glucose levels after 30min stronger than the Acarbose effect. These results confirmed the anti-postprandial hyperglycemia activity of the aqueous ethanolic extract from P. dactylifera parthenocarpic dates, which could lend support for its pharmaceutical use.

Delineation of the role of glycosylation in the cytotoxic properties of quercetin using novel assays in living vertebrates

Quercetin is a plant-derived flavonoid and its cytotoxic properties have been widely reported. However, in nature, quercetin predominantly occurs as various glycosides. Thus far the cytotoxic activity of these glycosides has not been investigated to the same extent as quercetin, especially in animal models. In this study, the cytotoxic properties of quercetin (1), hyperoside (quercetin 3-O-galactoside, 2), isoquercitrin (quercetin 3-O-glucoside, 3), quercitrin (quercetin 3-O-rhamnoside, 4), and spiraeoside (quercetin 4'-O-glucoside, 5) were directly compared in vitro using assays of cancer cell viability. To further characterize the influence of glycosylation in vivo, a novel zebrafish-based assay was developed that allows the rapid and experimentally convenient visualization of glycoside cleavage in the digestive tract. This assay was correlated with a novel human tumor xenograft assay in the same animal model. The results showed that 3 is as effective as 1 at inhibiting cancer cell proliferation in vivo. Moreover, it was observed that 3 can be effectively deglycosylated in the digestive tract. Collectively, these results indicate that 3 is a very promising drug candidate for cancer therapy, because glycosylation confers advantageous pharmacological changes compared with the aglycone, 1. Importantly, the development of a novel and convenient fluorescence-based assay for monitoring deglycosylation in living vertebrates provides a valuable platform for determining the metabolic fate of naturally occurring glycosides.