Masatake Niwa

Powerful antioxidative agents based on garcinoic acid from Garcinia kola

Investigation on the structure--antioxidative activity relationships of derivatives based on garcinoic acid from Garcinia kola (Guttiferae) led to discovery of a powerful antioxidative agent.

Oleanen and stigmasterol derivatives from Ambroma augusta

Abstract Augustic acid, a new oleanane derivative, and a stigmasterol glycoside were isolated from the roots of Ambroma augusta. Their structures were established as olean-12-en-2β,3β-diol-28-oic acid and stigmast-5,22-dien -3-O-α- d -glucopyranoside respectively, on the basis of full spectral analyses and chemical methods.

Chemical determination of the absolute structures of resveratrol dimers, ampelopsins A, B, D and F

Abstract The absolute configurations of four stilbenedimers, (+)-ampelopsins A, (+)-ampelopsins B, (−)-ampelopsins D and (+)-ampelopsins F were respectively determined on the basis of chemical evidence.

NEW OLIGOSTILBENES HAVING A BENZOFURAN FROM VITIS VINIFERA 'KYOHOU'

Abstract Three new oligostilbenes having a benzofuran moiety, viniferifuran, (+)-vitisifuran A and (−)-vitisifuran B, were isolated from Vitis vinifera ‘Kyohou’. The structures of these oligostilbenes including the absolute configuration were elucidated by spectroscopic and chemical methods. Furthermore, these were chemically transformed from (+)-e-viniferin, (+)-vitisin A and (−)-vitisin B, respectively, whose absolute configurations are known.

Biogenetic reactions on stilbenetetramers from Vitaceaeous plants

Abstract The absolute configurations of stilbenetetramers, (+)-hopeaphenol, (−)-isohopeaphenol, (+)-vitisin A and (+)-vitisin D, from Vitaceaeous plants were respectively determined on the basis of chemical evidence.

Pigments from Salvia miltiorrhiza

Abstract Five new o -naphthaquinone diterpenes, tanshindiol A, tanshindiol B, tanshindiol C, nortanshinone and 3α-hydroxytanshinone IIA, have been isolated from the roots of Salvia miltiorrhiza as minor components. Their relative stereochemistries have been established on the basis of spectral and chemical evidence.

Trigonelline, a leaf-closing factor of the nyctinastic plant, Aeschynomene indica

Abstract Trigonelline was isolated from Aeschynomene indica as a bioactive substance for nyctinasty. The compound was quite effective for leaf-closing of this species at 1 × 10−7 M in the daytime, but not for the nyctinastic species Cassia mimosoides and Mimosa pudica. It competed with indole-3-acetic acid (IAA) which is effective for leaf-opening. These results suggest that trigonelline may be concerned with the circadian rhythm of A. indica.

Studies on the chemical constituents of Psoralea corylifolia L.

A new isoflavone, corylinin (1), along with six known compounds, isopsoralen (2), psoralen (3), sophoracoumestan A (4), neobavaisoflavone (5), daidzin (6) and uracil (7), have been isolated from the dried fruits of Psoralea corylifolia L. The structure of 1 was established as 7,4′-dihydroxy-3′-[(E)-3,7-dimethyl-2,6-octadienyl]isoflavone on the basis of the spectroscopic methods. Structures of the known compounds were identified by comparison of the literature.

Sesquiterpenes from Acorus calamus L.

Abstract Five new sesquiterpenes were isolated from Acorus calamus L., in addition to calameone (or calamendiol), the structure of which was revised, and their structures were established. Furthermore, chemical co-relation among these sesquiterpenes was carried out. In particular, the thermal isomerization of shyobunone (I), an elemene-type sesquiterpene, to preisocalamendiol (VI), a germacrone-type compound, should be noted.

Absolute configurations of some oligostilbenes from Vitis coignetiae and Vitis vinifera ‘Kyohou’

Abstract Hepatotoxic oligostilbenes, (+)-vitisin A and (+)- cis -vitisin A were isolated as a pure form, respectively, by the method of recycled HPLC. The structure of cis -vitisin A was confirmed by the photochemical transformation of vitisin A. The absolute configurations of (+)-ampelopsin A, (+)-ampelopsin B, (+)-vitisin A, (+)- cis -vitisin A and (+)-vitisin D were also determined by chemical and spectroscopic methods.