Ken-ichi Nakaya

Oligostilbenoids in stem bark of Vatica rassak

Three resveratrol oligomers, vaticanols. A, B and C, as well as three known stilbenoids, resveratrol, piceid and epsilon-viniferin were isolated from the stem bark of Vatica rassak (Dipterocarpaceae). Their structures were determined by the analysis of NMR spectral data including the application of 2D methods.

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.

Stilbenoids in the stem bark of Hopea parviflora.

From the bark of Hopea parviflora, two stilbenoids, named (+)-parviflorol and (-)-ampelopsin A, were isolated in addition to three known compounds: (+)-balanocarpol, (-)-epsilon-viniferin and (-)-hopeaphenol. Their structures were determined by analysis of spectral data, including 2D NMR and NOE experiments, respectively.

Two new oligostilbenes with dihydrobenzofuran from the stem bark of Vateria indica

Abstract Two new stilbenoids, vateriaphenols A ( 1 ) and B ( 2 ), were isolated from the stem bark of Vateria indica along with known 10 stilbenoids ( 3–12 ) and bergenin ( 13 ). The structures of isolates were established based on spectroscopic analysis. The structures of vateriaphenols A and B were characterized as an octamer and a tetramer of resveratrol, respectively. The spectral properties of the highly condensed vateriaphenol A were also discussed.

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.

Vaticanol D, a novel resveratrol hexamer isolated from Vatica rassak

Abstract Vaticanol D isolated from the bark of Vatica rassak is the first instance of a resveratrol hexamer. The structure and relative configuration were established by means of 2D NMR spectroscopy. Vaticanol D possessed a scavenging activity of super oxide.

A New Resveratrol Hexamer from Upuna borneensis

A new resveratrol hexamer, upunaphenol A, was isolated from an acetone soluble part of stem of Upuna borneensis (Dipterocarpaceae). The structure, which has twelve asymmetric carbon atoms on the partial structures of a dibenzobicyclo[3.2.1]octadiene ring and four dihydrobenzofuran rings, was determined by spectral analysis including 1D and 2D NMR spectral experiments. Resveratrol and four known resveratrol oligomers, ampelopsin F, isoampelopsin F, vaticanols C and B, were also isolated. Upunaphenol A was found to suppress cell growth in HL60 cells through induction of apoptosis with IC 5 0 at 9.2 μM.

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.

N-Aryl-1,8-naphthalimides as highly sensitive fluorescent labeling reagents for carnitine

4-(2-Aminoethylamino)-N-(4-methoxyphenyl)-1,8-naphthalimide can be used as a fluorescent labeling reagent for carnitine. The excitation and emission maxima of this reagent were observed at 436 and 524 nm in acetonitrile, respectively and the reagent reacted smoothly with carnitine to afford the labeled product under mild conditions. The detection limit of carnitine by using this reagent was ca. 30 fmol.

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.