Yukinori Miyaichi

Effects of catechins on vascular tone in rat thoracic aorta with endothelium.

The effects of eight catechin derivatives on vascular tone in rat thoracic aorta were examined. Catechin derivatives (10 microM) potentiated the contractile response to phenylephrine in endothelium-intact arteries. The potentiations produced by EGCg and EGC were almost absent in endothelium-denuded arteries and abolished by N(G)-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthesis. The catechin derivatives also inhibited endothelium-dependent relaxation in response to acetylcholine. The order of catechin derivatives ranked in terms of both increasing vascular reactivity and impairing endothelium-dependent relaxation was similar; (-)-gallocatechin (GC) >or= (-)-epigallocatechin (EGC) >or= (-)-gallocatechin gallate (GCg) >or= (-)-epigallocatechin gallate (EGCg) >or= (-)-catechin (C) >or= (-)-epicatechin (EC) >or= (-)-catechin gallate (Cg) >or= (-)-epicatechin gallate (ECg). In addition, EGC inhibited the endothelium-independent relaxation evoked by both sodium nitroprusside and NOC-7, a spontanous NO releaser, but EGCg inhibited only that by NOC-7. These findings indicate that catechin derivatives produce a potentiation of the contractile response and an inhibition of the vasorelaxant response, probably through inactivation of endothelium-derived nitric oxide (NO), and that the hydroxyl on C-5 of the B ring together with the stereoscopic structure between the C-3 group and the B ring of flavanols was of importance in mediating the above effects and that the substitution of a gallate group of C-3 attenuated the effects, probably due to a decreased response to solube guanylate cyclase in vascular smooth muscle cells.

Inhibition of mouse liver sialidase by plant flavonoids

Flavonoids (103 species) were tested for inhibitory activity against mouse liver sialidase using sodium p-nitrophenyl-N-acetyl-alpha-D-neuraminate (PNP-NeuAc) as substrate. Isoscutellarein-8-O-glucuronide from the leaf of Scutellaria baicalensis showed most potent activity (IC50, 40 microM), and this flavone appeared to be a non-competitive inhibitor of the enzyme. This flavone inhibited the lysosomal solubilized sialidase against PNP-NeuAc and sialyllactose effectively, but not microsomal enzyme against gangliosides and colominic acid, whereas, negligible or weak inhibitory activities were observed for influenza virus sialidase, beta-galactosidase, alpha-mannosidase, and alpha-glucosidase tested. These results indicate that this flavone may be useful to elucidate the function of the lysosomal solubilized sialidase.

A flavone from Artemisia capillaris

Abstract A new flavone was isolated from Artemisia capillaris and its structure was determined by spectroscopic methods as 5,2′,4′-trihydroxy-6,7,5′-trimethoxyflavone.

Studies on the constituents of Scutellaria species (XXI): constituents of the leaves of Scutellaria strigillosa Hemsley

From the leaves of Scutellaria strigillosa, 14 compounds, chrysin, apigenin, 5,7,2′-trihydroxyflavone, norwogonin, ursolic acid, 6β-hydroxy-4-stigmasten-3-one, 6β-hydroxy-4,22-stigmastadien-3-one, 2 R,4′ R,8′ R-γ-tocopherol, (S)-5,5′ -bi-γ-tocopheryl, (R)-5,5′ -bi-γ-tocopheryl, solanachromene, tocopherylquinone, jodrellin T, and 14,15-dihydrojodrellin T were isolated. The structures were determined on the basis of chemical and spectral data.

Studies on the constituents of the leaves of Conandron ramondioides

Conandron ramondioides Sieb. et Zucc. is a perennial herb of the family Gesneriaceae, which is distributed from southeastern China to the Tohoku district in Japan. In Japan, the plant is called iwatabako, and its whole herbs are used as a folk remedy for the treatment of stomachache [1]. In a previous paper [2], we reported the structural identification of 14 phenolic compounds including three with unique structures, named didymocalyxins A, B and C, isolated from the leaves of Didymocarpus leucocalyx (Gesneriaceae). In the course of our studies on the constituents of Gesneriaceae species, we have investigated the leaves of C. ramondioides, for which information on the chemical constituents has not been published. The present paper deals with the isolation and identification of eight compounds from this plant purchased in a Japanese market. MeOH extract (87 g) of the dried leaves (1.1 kg) was suspended in water and successively extracted with ether and ethyl acetate. The ether-soluble portion (18 g) was chromatographed on silica gel (benzeneCHCl3) and ODS (H2O-MeOH), and then purified by HPLC (fluofix, CHCN3-n-propanol-H2O) to give four triterpenoids (1–4) and a phytosterol (7). The ethyl acetate-soluble portion (4 g) was chromatographed on silica gel (n-hexane-acetone followed by CHCl3-MeOHH2O) to give two triterpenoids (5 and 6) and a phytosterol (8). Compounds 1–8 were identified as 3-epipomolic acid (1, 25.6 mg) [4], 3-epiursolic acid (2, 34.6 mg) [5], ursolic acid (3, 152.3 mg) [5], 3-epioleanolic acid (4, 3.0 mg) [5], barbinervic acid (5, 19.8 mg) [3], scutellaric acid