Antioxidant Flavonoids from the Twigs of Stewartia koreana

Acylated saponins and flavonoid glycosides from the fruits of Stewartia koreana

Three acylated saponins and three flavonoid glycosides, along with nine known flavonoids, were isolated from the fruits of Stewartia koreana Nakai ex Rehder (Theaceae) using relative mass defect filtering analysis. The structures of these compounds were determined by performing spectroscopic analyses and using chemical methods. Furthermore, all the isolates were evaluated for their effects on the mRNA expression of the genes for proprotein convertase subtilisin/kexin type 9 (PCSK9) and low-density lipoprotein receptor (LDLR) as well as their inhibitory activities on PCSK9 and LDLR binding. None of the isolates was deemed to be active in PCSK9-LDLR binding inhibition. However, (+)-catechin was found to inhibit PCSK9 expression and increase LDLR expression, suggesting the potential of (+)-catechin to lower cholesterol level via the downregulation of PCSK9 expression.

Is natural fraxin an overlooked radical scavenger?

Fraxin (FX) (7-hydroxy-6-methoxycoumarin 8-glucoside) is a typical natural product of the coumarin family. This compound was shown to protect endothelial cells from oxidative stress; however, the nature of its antioxidant properties is still ambiguous. In this study, we report on a systematic evaluation of the radical scavenging activity of FX using a two-tier protocol based on thermodynamic and kinetic calculations. The results show that FX has moderate activity in the aqueous physiological environment against a range of radicals including HO˙, CCl3O˙, CCl3OO˙, NO2, , and HOO˙. The latter was examined in detail due to the prevalence of HOO˙ as a source of oxidative stress in biological systems. HOO˙ scavenging activity was promising in the gas phase but low in physiological environments with k overall = 1.57 × 106, 3.13 × 102 and 2.68 × 103 M-1 s-1 in the gas phase, pentyl ethanoate and water solvents, respectively. The formal hydrogen transfer mechanism at the O7-H bond dominates the hydroperoxyl radical scavenging of FX in the nonpolar media, whereas, in the polar environment, the activity is exerted by the single electron transfer mechanism of the anion state. This activity falls behind typical antioxidants such as Trolox, ascorbic acid, and trans-resveratrol under the studied conditions. Thus FX may have multiple health benefits, but it is not an outstanding natural antioxidant.

Stewartiacids A–N, C-23 carboxylated triterpenoids from Chinese Stewartia and their inhibitory effects against ATP-citrate lyase and NF-κB

Fourteen previously undescribed naturally occurring C-23 carboxylated triterpenoids, stewartiacids A–N (1–14), were isolated and characterized from the twigs and leaves of the ornamental and medicinal plant Stewartia sinensis (Chinese Stewartia), a ‘vulnerable’ species endemic to China. The new structures were elucidated on the basis of spectroscopic data, single crystal X-ray diffraction, and electronic circular dichroism (ECD) analyses. Stewartiacids A (1) and B (2) are isoursenol derivatives. Stewartiacid C (3) is a 12-oxo-γ-amyrin analogue. Both isoursenol and γ-amyrin derivatives are quite rare in nature. Stewartiacids D (4) and E (5) are 13,27-cycloursane-type compounds. Stewartiacids K (11) and L (12) are ursane-type triterpene and phenylpropanol adducts built through a 1,4-dioxane ring, which are also seldom reported in the literature. The rest are common C-23 carboxylated ursane-type (6–10) and oleanane-type (13, 14) pentacyclic triterpenoids. Stewartiacids G (7), K (11), and L (12) showed moderate inhibitory effects against ATP-citrate lyase (ACL), with IC₅₀ values of 12.5, 2.8, and 10.6 μM, respectively. Stewartiacid K (11) also exhibited moderate inhibition (IC₅₀: 16.8 μM) of NF-κB.

Fourteen new C-23 carboxylated triterpenoids (stewartiacids A–N, 1–14) were obtained from the ‘vulnerable’ plant Stewartia sinensis. 11 and 12 showed inhibitory effects against ACL.

The Occurrence of Flavonoids and Related Compounds in Cedrus brevifolia A. Henry ex Elwes & A. Henry Needles. Inhibitory Potencies on Lipoxygenase, Linoleic Acid Lipid Peroxidation and Antioxidant Activity

The phytochemical analysis of the polar extracts of Cedrus brevifolia needles yielded 20 compounds, namely from the methanol extract we isolated three flavonoids (1–3), one hydrolysable tannin (4), eleven phenolic derivatives (5–15) and one apocarotenoid (16), while from the methanol: water (5:1) extract we isolated four flavonoids (17–20). Chemical structures of all isolated compounds were determined by 1D, 2D-NMR (1 Dimension, 2 Dimensions Nuclear Magnetic Resonance) and UV-Vis (Ultraviolet-Visible) spectroscopy. Furthermore, the antioxidant potentials and the anti-inflammatory activities of both crude extracts and isolates were evaluated through DPPH radical scavenging capability, linoleic acid lipid peroxidation inhibition, and soybean LOX inhibition assays. This is the first report on the chemical profile of C. brevifolia needles. Catechin was the main compound derived from the methanol extract. According to our results, 4-O-β-d-glucopyranyl trans-p-coumaric acid and taxifolin were the most active ingredients.

Phenylacylphenol derivatives with anti-melanogenic activity from Stewartia pseudocamellia

Three new phenylacylphenol derivatives, stewartianol (1), deoxystewartianol-4'-O-arabinoglucoside (2), and stewartianol-3-O-glucoside (3), along with nine known compounds, methylesculin (4), fraxoside (5), fraxetin (6), scopletin (7), (+)-dihydromyricetin (8), (+)-taxifolin-7-O-β-D-glucose (9), (+)-taxifolin (10), (+)-dihydrokaempferol-7-O-β-D-glucose (11), and 3-acetyl-ursolic acid (12), were isolated from the twigs of Stewartia pseudocamellia; commonly used as folk medicine in Korea. The structures of the isolated compounds were identified using spectroscopic analysis, including 1D, 2D NMR, MS and compared with published data. The compounds were tested for their anti-melanogenic activity in cultured murine B16 melanoma cells. Stewartianol (1) and stewartianol-3-O-glucoside (3) showed an inhibitory effect significantly on melanogenesis in a concentration-dependent manner.

Phenolic Compounds from the Leaves of Stewartia pseudocamellia Maxim. and their Whitening Activities

The half-dried leaves of Stewartia. pseudocamellia were extracted with hot water (SPE) and partitioned with n-hexane (SPEH), dichloromethane (SPED), and ethyl acetate (SPEE) successively. SPE and SPEE showed significant inhibitory effects against melanogenesis and tyrosinase activities. By bioassay-guided isolation, ten phenolic compounds were isolated by column chromatography from SPEE. The whitening effect of the isolated compounds from SPEE were tested for the inhibitory activities against melanogenesis using B16 melanoma cells, in vitro inhibition of tyrosinase, and L-3,4-dihydorxy-indole-2-carboxylic acid (L-DOPA) auto-oxidation assay. A cytotoxic activity assay was done to examine the cellular toxicity in Raw 264.7 macrophage cells. Of the compounds isolated, gallic acid and quercetin revealed significant inhibitory activities against melanogenesis compared to arbutin. In particular, quercetin exhibited similar inhibitory activities against tyrosinase and L-DOPA oxidation without cytotoxicity. These results suggested that SPE could be used as a potential source of natural skin-whitening material in cosmetics as well as in food products.

The comparison of DPPH-scavenging capacity and anti-inflammatory effects of phenolic compounds isolated from the stems of Stewartia koreana Nakai

The Stewartia koreana Nakai (SK) had been used in oriental traditional medicine as a remedy for acute gastroenteritis, liver diseases, quadriplegia and pain. The antioxidant activity guided isolation 80% methyl extract from stems of SK yielded eight phenolic compounds. We evaluated the anti-oxidative and anti-inflammatory effects of these compounds via assays of 1,1-diphenyl-2-picrylhydazyl (DPPH) radicals and inhibition of nitric oxide (NO) production in lipopolysaccharide-stimulated RAW 264.7 macrophage cells. The results demonstrated that syringaresinol (6) exhibited significant DPPH radical-scavenging activity and inhibitory effects on NO production compared with its positive controls, ascorbic acid and L-NMMA, respectively.

Anti-inflammatory activity of sulfate-containing phenolic compounds isolated from the leaves of Myrica rubra

Three sulfated phenolic compounds, juglanin B (11R)-O-sulfate (1), myricetin 3´-O-sulfate (2), and ampelopsin 3´-O-sulfate (3), were isolated from the leaves of Myrica rubra. Compound 1 was a new sulfated lignan, 2 was a new sulfated flavone, and 3 was a known sulfated flavone. The structures of the new compounds (1 and 2) were determined by acid hydrolysis and spectroscopic methods, including IR, FAB-MS, 1D and 2D NMR. The inhibitory activities of compounds 1-3 and their hydrolysates (1a-3a) against LPS-induced cytokine (TNF-α, IL-1β, and IL-6) production in macrophage RAW 264.7 cells were evaluated. The 2 new compounds (1 and 2) and their aglycones (1a and 2a) significantly reduced LPS-induced expression of iNOS and COX-2 proteins.