α-l-rhamnosidase selective for rutin to isoquercitrin transformation from Penicillium griseoroseum MTCC-9224

An α-l-rhamnosidase secreting fungal strain has been isolated from the decaying goose berry (Emblica officinalis) fruit peel. The fungal strain has been identified as Penicillium greoroseum MTCC-9224. The α-l-rhamnosidase of this fungal strain has been purified to homogeneity using a simple procedure involving concentration by ultra filtration and an anion exchange chromatography on DEAE-cellulose. The purified enzyme gave a single protein band corresponding to molecular mass of 97 kDa in SDS-PAGE analysis. The native-PAGE analysis also gave a single protein band confirming the purity of the enzyme. Using p-nitrophenyl-α-l-rhamnopyranoside as the substrate, K_m and k_cat values of the enzyme were 0.65 mM and 43.65 s⁻¹, respectively. The pH and temperature optima of the enzyme were 6.5 and 57 °C, respectively. The activation energy for the thermal denaturation of the enzyme was 27.9 kJ/mol. The purified α-l-rhamnosidase hydrolyzed rutin to isoquercitrin and l-rhamnose but has no effect on naringin and hesperidin.     

High-performance liquid chromatographic method for simultaneous determination of hawthorn active components in rat plasma

A simple HPLC method with photodiode-array (PDA) ultraviolet detection was developed for the simultaneous determination of four active polyphenol components of hawthorn (Crataegus), chlorogenic acid, epicatechin, hyperoside and isoquercitrin, in rat plasma. Following extraction from the plasma samples with ethyl acetate–methanol (2:1, v/v), these four compounds were successfully separated using a C₁₈ column with a gradient elution of 5 and 25% acetonitrile in 25 mM phosphate buffer (pH 2.4). The flow-rate was set at 1 ml/min and the eluent was detected at 325 nm for chlorogenic acid, 278 nm for epicatechin, and 360 nm for both hyperoside and isoquercitrin. Narignin (0.82 μg) was used as the internal standard and was detected at 278 nm. The method is linear over the studied range of 0.16–40, 0.63–160, 0.13–32 and 0.13–30 μg/ml for chlorogenic acid, epicatechin, hyperoside and isoquercitrin, respectively. The correlation coefficient for each analyte was greater than 0.995. The intra-day and inter-day precision of the analysis was better than 4 and 7%, respectively. The extraction recoveries at low to high concentration were greater than 85% for both epicatechin and chlorogenic acid, and greater than 94% for both hyperoside and isoquercitrin. The detection limits were 0.04, 0.20, 0.03 and 0.03 μg/ml for chlorogenic acid, epicatechin, hyperoside and isoquercitrin. The developed method was used to analyze the plasma concentrations of the four analytes after the intravenous administration of hawthorn polyphenol extract to rats.     

Studies on the Chemical Components of Oxytropis ochrocephala Bunge

Oxytropis ochrocephala Bunge has been characterized as one of the most destructive plants to livestock in the North-Western China. Its chemical components have not been studied. We have been isolated four flavonoids from the aerial parts of Oxytropis ochrocephala Bunge. They have been identified as quercetin, rhamnocitrin, isoquercitrin and rhamnocitrin-3-glucoside by UV, IR, 1HNMR and MS spectra of these flavonoids. Their acetyl derivatives have been prepared and their 1HNMR and MS spectra are fully in accord with this conclusion. The rhamnocitrin-3-glucoside has been found first of all in Oxytropis species. It is perhaps valuable for chemotaxonomy of Oxytropis genus.     

火棘化学成分的研究

从火棘叶中分离得到四种化合物(晶1～4),经UV,IR,NMR和MS等方法鉴定了它们的结构,分别是芦丁(晶1),芒甙(晶2),异槲皮甙(晶3)和槲皮素(晶4)。以上四种成分均为首次由该植物中分得。     

Sonochemical enzyme-catalyzed regioselective acylation of flavonoid glycosides

This work compares a highly efficient and alternative method of sonication-assisted lipase catalyzed acylation of quercetin-3-O-glucoside and phloretin-2′-glucoside, using Candida antarctica lipase B (Novozyme 435^®), with a range of fatty acids. In this study, sonication-assisted irradiation coupled with stirring has been found to be more efficient and economical than conventional reaction conditions. Sonication-assisted acylation accelerated the reactions and reduced the time required by 4–5 folds.     

Flavone-based natural product agents as new lysine-specific demethylase 1 inhibitors exhibiting cytotoxicity against breast cancer cells in vitro

Lysine-specific demethylase 1 (LSD1) has recently emerged as a therapeutic target for cancer. However, almost all LSD1 inhibitors developed to date are chemo-synthesised molecules. In this study, the LSD1 inhibitory activity of 12 natural flavones, including four aglycones and their corresponding monoglycosides and diglucosides, was evaluated. Based on the structure–activity relationships, LSD1 inhibition activity was greater for flavonoid monoglycosides than their aglycones lacking the sugar moiety. The effects of isoquercitrin, which exhibited optimal LSD1 inhibitory activity, on cancer cell properties were evaluated. Isoquercitrin induced the expression of key proteins in the mitochondrial-mediated apoptosis pathway and caused apoptosis in LSD1-overexpressing MDA-MB-231 cells via the inhibition of LSD1. These findings suggest that natural LSD1 inhibitors, and particularly isoquercitrin, are promising for cancer treatment.     

Phenolic compounds in Hypericum species from the Trigynobrathys section

Phenolic compounds of thirteen Hypericum species growing in South Brazil were investigated aiming to evaluate the usefulness of their distribution as a taxonomic character. The HPLC analysis of the methanolic fractions displayed similar chemical profile and significant contents variation among the investigated taxa, being chlorogenic acid the main metabolite quantified in most of the species (ranging from traces to 16.65 mg% of extract), followed by hyperoside (between 0.27 and 11.48 mg%), quercitrin (0.09 and 13.34 mg%), guaijaverin (0.14 and 2.91 mg%) and isoquercitrin (0.14 and 6.97 mg%), whereas rutin and the xanthone mangiferin were not detected.     

Light filtering by epidermal flavonoids during the resistant response of cotton to Xanthomonas protects leaf tissue from light-dependent phytoalexin toxicity

2,7-Dihydroxycadalene and lacinilene C, sesquiterpenoid phytoalexins that accumulate at infection sites during the hypersensitive resistant response of cotton foliage to Xanthomonas campestris pv. malvacearum, have light-dependent toxicity toward host cells, as well as toward the bacterial pathogen. Adaxial epidermal cells surrounding and sometimes covering infection sites turn red. The red cells exhibited 3-4-fold higher absorption at the photoactivating wavelengths of sunlight than nearby colorless epidermal cells. Red epidermal cells protected underlying palisade mesophyll cells from the toxic effects of 2,7-dihydroxycadalene plus sunlight, indicating a role for epidermal pigments in protecting living cells that surround infection sites from toxic effects of the plant’s own phytoalexins. A semi-quantitative survey of UV-absorbing substances extracted from epidermal strips from inoculated and mock-inoculated cotyledons indicated that the principal increase in capacity to absorb the photoactivating wavelengths was due to a red anthocyanin and a yellow flavonol, which were identified as cyanidin-3-O-β-glucoside and quercetin-3-O-β-glucoside, respectively.