Ibrahim Iliya

New resveratrol oligomers in the stem bark of Vatica pauciflora

Abstract Five new resveratrol oligomers; pauciflorols A–C ( 1–3 ), isovaticanols B ( 6 ) and C ( 8 ), and three new oligostilbene glucosides; pauciflorosides A ( 11 ), B ( 13 ), C ( 14 ), were isolated from the stem bark of Vatica pauciflora (Dipterocarpaceae) together with known 17 resveratrol oligomers ( 4, 5, 7, 9, 10, 12 and 15–25 ) and bergenin ( 26 ). The structures of isolates were established on the basis of detailed spectroscopic analysis. The typical and characteristic spectral properties of some resveratrol oligomers were also discussed.

Gnetol as a Potent Tyrosinase Inhibitor from Genus Gnetum

Gnetol (2,3′,5′,6-tetrahydroxy-trans-stilbene), a naturally occurring compound particularly found in the genus Gnetum, had a strong inhibitory effect on murine tyrosinase activity. Gnetol (IC50, 4.5 μM) was stronger than kojic acid (IC50, 139 μM) as a standard inhibitor for murine tyrosinase activity. Moreover, gnetol significantly suppressed melanin biosynthesis in murine B16 melanoma cells.

Stilbene derivatives from Gnetum gnemon Linn.

Four stilbene derivatives, gnemonols K and L (resveratrol trimers), M (isorhapontigenin dimer), and gnemonoside K (glucoside of resveratrol trimer) together with eleven known stilbenoids and a lignan were isolated from the acetone, methanol and 70% methanol soluble parts of the root of Gnetum gnemon (Gnetaceae). The structures of the isolates were determined by spectral analysis. The antioxidant activity of the stilbenoids on lipid peroxide inhibition and super oxide scavenging activity were also investigated.

Five Stilbene Glucosides from Gnetum gnemonoides and Gnetum africanum

Five new stilbene glucosides, gnemonosides F, G, H, I, and J were isolated from the stem lianas of Gnetum gnemonoidesBrongn and Gnetum africanumWelw along with nine known stilbenoids. The structures of the new compounds were elucidated as gnetin E 4a,4b,4c-O-β-triglucopyranoside (2), gnetin E 4a,4c-O-β-diglucopyranoside (3), gnetin C 4a,4b,11a-O-β-triglucopyranoside (4), gnetin D 4a,4b-O-β-diglucopyranoside (5), and gnetuhainin A 4a,4b-O-β-diglucopyranoside (6) on the basis of spectroscopic evidence.

Four New Glucosides of Stilbene Oligomers From the Stem of Gnetum gnemonoides.

1Gifu Pharmaceutical University, 5-6-1, Mitahora-higashi, Gifu 502-8585, Japan; 2Gifu Prefectural Institute of Health and Environmental Sciences, 1-1 Naka Fudogaoka, Kakamigahara, Gifu 504-0838, Japan; 3Faculty of Pharmaceutical Sciences, Josai University, 1-1 Keyakidai Sakado, Saitama 350-0295, Japan; 4Botanical Gardens, Koishikawa, Graduate School of Science, The University of Tokyo, 3-7-1 Hakusan, Bunkyo-ku, Tokyo 112-0001, Japan; 5Indinesian Institute of Sciences, Jalan Ir. H. Juanda 13, Bogor 16122, Indonesia

Four Dimeric Stilbenes in Stem Lianas of Gnetum africanum

From the stem lianas of Gnetum africanum Welw., four new stilbenoid dimers (gneafricanins C, D, E and F) were isolated along with four known compounds. The structures were established by spectroscopic analyses and chemical evidence. In addition the antioxidant activities of the compounds were also investigated.

Stilbenoids from the stem of Gnetum latifolium (Gnetaceae)

An acetone extract of the stem of Gnetum latifolium Blume afforded the stilbene trimer (latifolol) together with five known stilbenoids (gnetin E, gnetin D, gnetin C, (-)epsilon -viniferin and resveratrol). Their structures were elucidated on the basis of spectral evidence, in particular by using 2D NMR methods.

Four New Stilbene Oligomers in the Root of Gnetum gnemon

Four new stilbene oligomers, gnemonols G, H, I, and J (1–4), were isolated from acetone extract of the root of Gnetum gnemon along with five known stilbenoids, ampelopsin E, cis-ampelopsin E, gnetins C, D, and E. The structures were elucidated on the basis of spectroscopic evidence.

Six flavonostilbenes from Gnetum africanum and Gnetum gnemon

Six new flavonostilbenes (gnetoflavanols A, B, C, D, E and F) were isolated from the stem of Gnetum africanum and the root of G. gnemon. The structures of the compounds were determined by spectroscopic analysis. The antioxidant activity of the compounds on lipid peroxide inhibition and superoxide scavenging activity were also investigated.

New Resveratrol Dimer Glucosides and Trimers in Stem and Root of Welwitschia mirabilis

Two new resveratrol dimer glucosides, mirabilosides A (1) and B (2), and two new resveratrol trimers, mirabilols A (3) and B (4) were isolated from stem and root of Welwitschia mirabilis (Welwitschiaceae) together with four known stilbene oligomers (gnetins C, E, F and I). The structures of isolated compounds were determined by spectroscopic analysis.