Acylated flavonoid and phenylethanoid glycosides from Marrubium velutinum

From the aerial parts of Marrubium velutinum, one acylated flavonoid glycoside, chrysoeriol 7-O-(3",6"-di-O-E-p-coumaroyl)-beta-D-glucopyranoside, and two tetrasaccharidic phenylethanoid glycosides, velutinosides I-II, have been isolated together with ten known flavonoids and seven known phenylethanoid glycosides. The structures of the isolated compounds were established by means of NMR, MS, and UV spectral analyses.     

Constituents from the bark of Tabebuia impetiginosa

The bark of Tabebuia impetiginosa afforded nineteen glycosides, consisting of four iridoid glycosides, two lignan glycosides, two isocoumarin glycosides, three phenylethanoid glycosides and eight phenolic glycosides. Their structures were determined using both spectroscopic and chemical methods. Iridoid glycosides, phenylethanoid glycosides and lignan glycosides had ajugol, osmanthuside H and secoisolariciresinol 4-O-beta-D-glucopyranoside as their structural elements, respectively, whereas the aglycone moieties of the isocoumarin glycosides were considered to be (-)-6-hydroxymellein. Phenolic glycosides had 4-methoxyphenol, 2,4-dimethoxyphenol, 3,4-dimethoxyphenol, 3,4,5-trimethoxyphenol and vanillyl 4-hydroxybenzoate as each aglycone moiety. Additionally, the sugar chains of these isocoumarin glycosides and phenolic glycosides were concluded to be beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside as well as those of osmanthuside H and above phenylethanoid glycosides.     

Phenylpropanoid glycosides from Marrubium alysson.

From the aerial parts of Marrubium alysson a new phenylpropanoid glycoside, alyssonoside, and five known glycosides, verbascoside (= acteoside), leucosceptoside A, martynoside, forsythoside B and leucosceptoside B were isolated. On the basis of spectral data, the structure of the new compound was elucidated as beta-(3,4-dihydroxyphenyl)ethyl-O-[alpha-L-rhamnopyranosyl-(1-->3)]-O- [beta-D-apiopyranosyl-(1-->6)]-4-O-feruloyl-beta-D-glucopyra noside.     

In vivo anti-inflammatory and antinociceptive activity evaluation of phenolic compounds from Sideritis stricta

An acetone extract obtained from aerial parts of S. stricta Boiss. & Heldr. apud Bentham, its fractions and phenolic compounds were investigated for their in vivo anti-inflammatory and antinociceptive activities. For the anti-inflammatory activity and for the antinociceptive activity assessment, carrageenan-induced hind paw edema and p-benzoquinone-induced abdominal constriction tests were used, respectively. The acetone extract of the plant and its phenolic fraction exhibited potent inhibitory activity against both bioassay models in mice. From the active phenolic fraction a well-known phenylethanoid glycoside, verbascoside (acteoside) (1), and two flavonoid glycosides, isoscutellarein 7-O-[6"'-O-acetyl-beta-D-allopyranosyl-(1-->2)]-beta-D-glucopyranoside (2) and isoscutellarein 7-O-[6"'-O-acetyl-beta-D-allopyranosyl-(1-->2)]-6"-O-acetyl-beta-D-glucopyranoside (3), were isolated. During phytochemical studies we also isolated a methoxyflavone, xanthomicrol (4), from the non-polar fraction. The structures of the isolated compounds were established by spectroscopic evidence (UV, IR, 1D- and 2D-NMR, MS). Although antinociceptive and anti-inflammatory activities of the phenolic components were found not significant in the statistical analysis, compounds 1 to 3 showed a notable activity without inducing any apparent acute toxicity as well as gastric damage. Furthermore, a mixture of flavonoid glycosides (2 + 3) exhibited a significant inhibitory effect in both models at a higher dose.     

Labdane diterpenes from Marrubium velutinum and Marrubium cylleneum

From the aerial parts of Marrubium velutinum and Marrubium cylleneum, seven labdane diterpenes, velutine A, 15-epi-velutine A, velutine B, 15-epi-velutine B, velutine C, cyllenine A and 15-epi-cyllenine A, have been isolated together with five known diterpenes and four known flavones. The structures of the isolated compounds were established by means of NMR [(1)H-(1)H-COSY, (1)H-(13)C-HMQC, HMBC, HMQC-TOCSY, NOESY] and MS spectral analyses. Complete NMR assignments are reported for known compounds.     

Minor labdane diterpenes from Marrubium thessalum

Five new labdane diterpenes, thessalines A, B, and D, 14β-hydroxythessaline A, and 14β-hydroxythessaline B (1-5, resp.) were isolated from the aerial parts of Marrubium thessalum, along with the known labdane diterpene deacetylvitexilactone (6) and the methoxylated flavones 4',7-dimethylapigenin and salvigenin. (3S,5R)-Loliolide was also found in the same source. Their structures were established by 1D- and 2D-NMR (COSY, HSQC, HMBC, NOESY, and ROESY) and MS analyses. The plant produces a great variety of labdane-type diterpenes, with variations in functionalities, particularly in the side chain. Their structures could be of chemotaxonomic significance for the genus Marrubium.     

Iridoids from Scutellaria albida ssp. albida

Three iridoid glycosides, 6'-O-E-p-coumaroylgardoside (1), 6'-O-p-E-coumaroyl-8-epi-loganic acid (2) and scutelloside (3) were isolated from the aerial parts of Scutellaria albida subsp. albida, in addition to an anomeric mixture in equilibrium of one iridoid aglycone (4, 4a), nine iridoid glycosides (5-13), four known phenylethanoid glycosides (14-17), and six known phenolic derivatives (18-23).     

Further constituents from the bark of Tabebuia impetiginosa

Further study on the constituents from the bark of Tabebuia impetiginosa (Mart. ex DC) Standley afforded twelve compounds, consisting of four iridoid glycosides, one phenylethanoid glycoside, five phenolic glycosides, and one lignan glycoside, along with seven known compounds. The structures of these compounds were determined based on the interpretation of their NMR and MS measurements and by chemical evidence.     

Cytotoxic phenylethanol glycosides from Psidium guaijava seeds

Phytochemical investigations of the acetone extract of Psidium guaijava seeds has led to the isolation of five known flavonoid glycosides, two phenolic glycosides and two new phenylethanoid glycosides which have been identified as 1-O-3,4-dimethoxy-phenylethyl-4-O-3,4-dimethoxy cinnamoyl-6-O-cinnamoyl-beta-D-glucopyranose and 1-O-3,4-dimethoxyphenylethyl-4-O-3,4-dimethoxy cinnamoyl-beta-D-glucopyranose, on the basis of chemical, physical and spectroscopic methods of analysis.     

Tyrosinase Inhibitors from the Aerial Parts of Wulfenia carinthiaca Jacq.

Activity guided isolation of a MeOH extract of the aerial plant parts of Wulfenia carinthiaca Jacq . (Plantaginaceae), using a mushroom tyrosinase assay, resulted in the isolation of five phenylethanoid glucosides and four iridoid glycosides. Two of them, 2′‐O‐acetylisoplantamajoside and 2′,6″‐O‐diacetylisoplantamajoside, represent new natural products. Evaluation of the inhibitory activity of all isolated compounds revealed that the observed activity is not related to the isolated phenylethanoid glycosides but mainly due to the presence of the iridoid glycoside globularin (IC₅₀ 41.94 μm ; CI_95% ± 16.61/11.89 μm ). Interestingly, structurally close related compounds (globularicisin, baldaccioside, and isoscrophularioside) showed no or only a weak tyrosinase inhibitory activity.     

Cytotoxicity and immunomodulating characteristics of labdane diterpenes from Marrubium cylleneum and Marrubium velutinum

From the aerial parts of Marrubium cylleneum, one labdane nor-diterpene has been isolated together with two labdane diterpenes, hitherto not known as natural products. The structures of the isolated compounds were established by means of NMR [(1)H-(1)H-COSY, (1)H-(13)C-HSQC, HMQC-TOCSY, HMBC, NOESY] and MS spectral analyses. Several diterpenoids from M. cylleneum and M. velutinum were tested for their cytotoxic effect against various cancer cell lines and their immunomodulating potential in human peripheral blood mononuclear cells in standard in vitro assays. Our results show a differential cytotoxicity of some compounds as well as their ability to improve selected lymphocyte functions.     

Effect of chito-oligosaccharide on the intestinal absorptions of phenylethanoid glycosides in Fructus Forsythiae extract

Phenylethanoid glycosides, the main active ingredients in Fructus Forsythiae extract possesses strong antibacterial, antioxidant and antiviral effects, and their contents were higher largely than that of other ingredients such as lignans and flavones, but their absolute bioavailability orally was significantly low, which influenced clinical efficacies of its oral preparations seriously. In the present study, the absorption mechanism of phenylethanoid glycosides was studied using in vitro Caco-2 cell model. And the effect of chito-oligosaccharide (COS) on the intestinal absorption of phenylethanoid glycosides in Fructus Forsythiae extract was investigated using in vitro, in situ and in vivo models. The pharmacological effects such as antiviral activity improvement by COS were verified by MDCK cell damage inhibition rate after influenza virus propagation. The observations from in vitro Caco-2 cell showed that the absorption of phenylethanoid glycosides in Fructus Forsythiae extract so with that in monomers was mainly restricted by the tight junctions, and influenced by efflux transporters (P-gp and MRP2). Meanwhile, the absorption of phenylethanoid glycosides in Fructus Forsythiae extract could be improved by COS. Besides, COS at the same low, medium and high concentrations caused a significant, concentration-dependent increase in the P_app-value for phenylethanoid glycosides compared to the control group (p < 0.05), and was all safe for the Caco-2 cells. The observations from single-pass intestinal perfusion in situ model showed that the intestinal absorption of phenylethanoid glycosides can be enhanced by COS. Meanwhile, the absorption enhancing effect of phenylethanoid glycosides might be saturable in different intestine sites. In pharmacokinetics study, COS at dosage of 25 mg/kg improved the bioavailability of phenylethanoid glycosides in Fructus Forsythiae extract to the greatest extent, and was safe for gastrointestine from morphological observation. In addition, treatment with Fructus Forsythiae extract with COS at dosage of 25 mg/kg prevented MDCK cell damage upon influenza virus propagation better than that of control. All findings above suggested that COS at dosage of 25 mg/kg might be safe and effective absorption enhancer for improving the bioavailability of phenylethanoid glycosides and the antiviral activity in vitro in Fructus Forsythiae extract.     

Labdane diterpenoids from Marrubium vulgare

Phytochemical investigation of the whole plant of Marrubium vulgare L. (Lamiaceae) resulted in isolation and characterization of two new labdane diterpenoids, 12(S)-hydroxymarrubiin and 3-deoxo-15-methoxyvelutine C and 11 known compounds, marrubiin, peregrinin, thessaline D, marrubinone B, deacetylvitexilactone, verbascoside, leucosceptoside A, martynoside, anisofolin A, terniflorin, and apigenin. Structure elucidation of the isolated compounds was determined by using spectroscopic techniques and HRESIMS. 12(S)-Hydroxymarrubiin, marrubiin, peregrinin, and marrubinone B, exhibited no antimicrobial activity up to 20 μg/mL against ten strains.     

Phenolic acids and resistance to insect attack in Sorghum bicolor

Glucose and quinic acid esters of several hydroxybenzoic and cinnamic acids were identified in methanolic extracts of leaves of 15-day-old Sorghum bicolor together with two O-glucosides. Some of the phenolic acids were also found to occur as insoluble esters of cell wall polysaccharides. While these derivatives did not affect the feeding of Locusta migratoria on sorghum, the free acids, as a mixture, were markedly inhibitory. It was found that Sorghum contained a mixture of hydrolases which could effect the transformation of “inactive” phenolic esters and glycosides into “active” phenolic acids at a high enough concentration to significantly reduce feeding by Locusta.     

Phenylethanoid and lignan glycosides from Verbascum thapsus.

Verbascum thapsus afforded, in addition to three known phenylethanoid glycosides and four lignan ones, five new phenylethanoid glycosides and one new lignan glycoside. Structures of the compounds were elucidated by spectroscopic methods and chemical evidence.     

Characterization of chemical ingredients and anticonvulsant activity of American skullcap (Scutellaria lateriflora)

American skullcap (the aerial part of Scutellaria lateriflora L.) has been traditionally used by Native Americans and Europeans as a nerve tonic, sedative, and anticonvulsant. However, despite some previous studies, the quality and safety, the bioactive ingredients, and the pharmacological properties of American skullcap are not fully understood. The aims of this study were to characterize the chemical ingredients of American skullcap and to evaluate its anticonvulsant activity. Twelve phenolic compounds including 10 flavonoids and two phenylethanoid glycosides were isolated and identified from American skullcap and used as marker compounds. An HPLC analytic method for analyzing these marker compounds in commercial American skullcap products from different sources was established and validated. The anticonvulsant activity of American skullcap was determined in rat models of acute seizures induced by pilocarpine and pentylenetetrazol. The results from this study indicate that (1) phenolic compounds, especially flavonoids, are the predominant constituents in American skullcap; (2) American skullcap products have similar constituents, but the content and relative proportions of the individual constituents varies widely; and (3) American skullcap has anticonvulsant activity in rodent models of acute seizures.     

Characterization of enzyme-catalysed endogenous β-hydroxylation of phenylethanoid glycosides in Euphrasia rostkoviana Hayne at the molecular level

Phenylethanoid glycosides, the main constituents of the aerial part of eyebright (Euphrasia rostkoviana Hayne) were treated by the endogenous hydroxylase enzyme and the concomitant biotransformation was characterized by applying high-performance liquid chromatography with UV and MS detections and NMR spectroscopy. In the extracts of the untreated (intact) samples, acteoside and eukovoside were determined as main compounds. The enzymatic treatment resulted in the quantitative transformation of these phenylethanoid glycosides into their corresponding hydroxyl derivatives identified as two epimers of β-hydroxyacteoside and β-hydroxyeukovoside. As to the importance of this hydroxylation β-hydroxyeukovoside was identified as a new compound and β-hydroxyacteoside was described for the first time in eyebright. We proved for first time that a β-hydroxylase enzyme is active in eyebright tissues which can transform phenylethanoid glycosides into their β-hydroxyl derivatives. Our new enzymatic method combined with a preparative HPLC facilitates the isolation of β-hydroxyl phenylethanoid glycosides from the aerial part of eyebright.     

Phenolic acids and peroxidase activity in alfalfa (Medicago sativa) embryogenic cultures after ethephon treatment

Treatment with ethephon increased the concentration of exogenous ethylene in Medicago sativa L. embryogenic cell suspension cultures (consisting of single cells, small cellular clumps and globular somatic embryos) and induced changes in the metabolism of phenolic substances, activities of peroxidase (EC 1.11.1.7) and caused significant suppression of suspension culture growth. Treatment with the ethylene-releasing substance, ethephon, resulted in a several-fold increase in phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) activity above the basal level and was accompanied by an elevated accumulation of phenolic acids (significant increase of methoxy-substituted acids). The majority of newly synthesised phenolic acids was incorporated into the fractions of glycosides and esters bound to the cell wall. Phenolic glycosides seemed to serve as a metabolic pool from which the phenolics were utilised during further culture. The increased activity of wall-bound ionic peroxidase after ethephon application correlated with the pronounced incorporation of ferulic acid in the cell walls. In contrast, the increased level of exogenous ethylene did not influence the growth of culture of more advanced embryos nor did it significantly alter phenylpropanoid metabolism.     

Preperegrinine,a prefuranic labdane diterpene from Marrubium friwaldskyanum

From the aerial part of Marrubium friwaldskyanum the previously known diterpenoid peregrinine and its new prefuranic derivative, preperegrinine, have been isolated. The known compound 5,6-dihydroxy-7,4′-dimethoxyflavone has also been found in the same source.     

Phenylethanoid Glycosides from Picria felterrae Lour.

In our search for bioactive compounds from the whole plant of Picriafelterrae Lour., three new phenylethanoid glycosides, picfeosides A-C (1-3), along with five known phenylethanoid glycosides,namely wiedemannioside (4), acteoside (5), acteoside isomer (6), cis-acteoside isomer (7), and cis-acteoside (8), were isolated using several chromatographic purification steps, including semipreparation HPLC on RP-18. The structures of the new compounds were elucidated on the basis of extensive spectroscopic analysis.