Tsuneatsu Nagao

Identification of a triterpenoid saponin from a crucifer, Barbarea vulgaris, as a feeding deterrent to the diamondback moth, Plutella xylostella.

Larvae of the diamondback moth, Plutella xylostella, a crucifer specialist, refuse to feed on a crucifer, Barbarea vulgaris, because of the presence of a feeding deterrent, which is extractable with chloroform. We isolated a feeding deterrent from B. vulgaris leaves, by successive fractionations with silica-gel, ODS, i.e., C18 reversed phase, and Sephadex LH-20 column chromatographies, and ODS-HPLC, guided by a bioassay for feeding deterrent activity. The structure of the compound was determined to be a monodesmosidic triterpenoid saponin, 3-O-[O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl]-hederagenin, based on FAB-MS, 1H- and 13C-NMR spectra, and hydrolysis experiments. When the compound was applied to cabbage leaf disks at greater than 0.18 μg/mm2, consumption of the disks by third instars was less than 11% of control disks treated with the solvent alone. Furthermore, all first instars died on the disks treated with the same concentrations. Because the concentration of the compound in the fresh leaves of B. vulgaris was comparable to the effective dose in the cabbage leaf disk tested, we conclude that the unacceptability of B. vulgaris to P. xylostella larvae is primarily due to this saponin.

Resistance in the Plant, Barbarea vulgaris , and Counter-Adaptations in Flea Beetles Mediated by Saponins

Three saponins and two sapogenins had differential effects on food consumption in five near-isogenic flea beetle lines, which differ in their ability to utilize a novel host plant, Barbarea vulgaris (Brassicaceae). The ability to live on this plant is controlled by major, dominant R-genes in the flea beetle, Phyllotreta nemorum (Coleoptera: Chrysomelidae: Alticinae). A susceptible genotype (rr) is unable to live on the plant, whereas resistant genotypes (RR and Rr) can utilize the novel host plant. Among compounds isolated from B. vulgaris, hederagenin cellobioside (hederagenin-3-O-(4-O-β-D-glucopyranosyl)-β-D-glucopyranoside) inhibited feeding, whereas the effect of oleanolic acid cellobioside was much weaker. The aglycones (sapogenins) were inactive. Although hederagenin cellobioside was active against all flea beetle lines, its effect on food consumption was much stronger on the susceptible genotype (rr) compared to the resistant genotype (Rr). Susceptible and resistant flea beetle genotypes were equally sensitive to a non-host saponin, α-hederin (hederagenin-3-O-(2-O-α-L-rhamnopyranosyl)-α-L-arabinopyranoside). These results suggest that R-alleles in flea beetles might be specific adaptations to defensive saponins in B. vulgaris. A possible mechanism of action of the R-alleles might be to encode for an enzyme (e.g. a glucosidase), which is able to cleave glycosidic bonds in hederagenin cellobioside, but not in α-hederin. The potential role of saponins as defensive compounds in B. vulgaris and as targets for counter-adaptations in flea beetles and other insects is discussed.

Liquid chromatography combined with thermospray and continuous-flow fast atom bombardment mass spectrometry of glycosides in crude plant extracts

In crude plant extracts, constituents of biological or pharmaceutical interest often exist in the form of glycosides. Off-line mass spectral investigations of these metabolites require soft ionisation techniques such as desorption chemical ionisation (DCI) or fast atom bombardment (FAB) if information on molecular mass or sugar sequence is desired. In LC-MS, glycosides can be ionised by using thermospray (TSP), continuous-flow fast atom bombardment (CF-FAB) or other interfaces. These techniques are thus potentially applicable to the on-line analysis of glycosides and can be applied to plant extract analysis. Thermospray (TSP) used with ammonium acetate as buffer provides mass spectra similar to those obtained with DCI-MS using NH3 and is potentially applicable to the on-line analysis of relatively small glycosides bearing no more than three sugar units. CF-FAB provides cleaner MS spectra than static FAB due to the lower concentration of the matrix used and can be applied to more polar compounds such as glycosides with a larger number of sugars. The use of a special setup involving post-column addition of the buffer or the matrix and splitting allows LC-UV, TSP LC-MS and CF-FAB LC-MS to be performed with the same standard HPLC conditions. Different crude plant extracts containing various types of glycosides with one to eight sugar units have been analysed by both TSP and CF-FAB. Cardenolides from Nerium odorum (Apocynaceae) and saponins from Swarzia madagascariensis (Leguminosae), Aster scaber and Aster tataricus (Asteraceae) have been studied by LC-MS. The combination of these two interfaces for the HPLC screening of crude plant extracts is discussed.

Triterpenoid saponins from the ground part of Aster ageratoides var. ovatus

Abstract Eight new oleanane-type triterpene glycosides, ageratosides A 1 –A 5 , B 1 , B 2 and C 1 , were isolated from the ground part of Aster ageratoides Turcz. var. ovatus Nakai (Compositae) along with scaberoside A 2 . Their structures were determined based on spectral and chemical evidence as follows. Ageratoside A 1 , 3- O -[ O -β- d -xylopyranosyl-(1→4)-β- d -glucopyranosyl] 2β,3β,16α-trihydroxyolean-12-ene-23,28-dioic acid (zanhic acid) 28- O -β- d -apiofuranosyl-(1→3)- O -(4- O -acetyl)-α- l -rhamnopyranosyl-(1→2)- O -α- l -arabinopyranosyl ester; ageratoside A 2 , 3- O -[ O -β- d -glucopyranosyl-(1→4)-β- d -glucopyranosyl] zanhic acid 28- O -β- d -apiofuranosyl-(1→3)- O -(4- O -acetyl)-α- l -rhamnopyranosyl-(1→2)- O -α- l -arabinopyranosyl ester; ageratoside A 3 , 3- O -[ O -β- d -xylopyranosyl-(1→4)-β- d -glucopyranosyl] zanhic acid 28- O -α- l -arabinopyranosyl-(1→3)- O -(4- O -acetyl)-α- l -rhamnopyranosyl-(1→2)- O -α- l -arabinopyranosyl ester; ageratoside A 4 , 3- O -β- d -glucopyranosyl zanhic acid 28- O -α- l -arabinopyranosyl-(1→3)- O -(4- O -acetyl)-α- l -rhamnopyranosyl-(1→2)- O -α- l -arabinopyranosyl ester; ageratoside A 5 , 3- O -β- d -glucopyranosyl zanhic acid 28- O -β- d -apiofuranosyl-(1→3)- O -(4- O -acetyl)-α- l -rhamnopyranosyl-(1→2)- O -α- l -arabinopyranosyl ester; ageratoside B 1 , 3- O -β- d -glucopyranosyl 2β,3β-dihydroxyolean-12-ene-23,28-dioic acid (medicagenic acid) 28- O -β- d -glucopyranosyl-(1→6)- O -β- d -glucopyranosyl ester; ageratoside B 2 , 3- O -[ O -β- d -xylopyranosyl-(1→4)-β- d -glucopyranosyl] medicagenic acid 28- O -β- d -xylopyranosyl-(1→3)- O -α- l -rhamnopyranosyl-(1→2)- O -α- l -arabinopyranosyl ester; and ageratoside C 1 , 3- O -[ O -β- d -xylopyranosyl-(1→4)-β- d -glucopyranosyl] 2β,3β,16α,21β-tetrahydroxyolean-12-ene-23,28-dioic acid 21,28-lactone.

Macrocyclic pyrrolizidine alkaloids from Parsonsia laevigata

Abstract Parsonsianidine, a new minor macrocyclic pyrrolizidine alkaloid having two ethyl side-chains at C-11 and C-20, was isolated along with parsonsianine from the leaves of Parsonsia laevigata . Its structure was determined by spectral analyses. 17-Methylparsonsianidine, having the same plane structure as spiranine, was also identified.

Saponins from the Compositae Plants: Structures of the Saponins from Aster scaber Thunb

Many triterpene saponins have been isolated from plants belonging to a variety of families such as Leguminosae, Campanulaceae, Cucurbitaceae, and Araliaceae. Compositae, one of the largest families of the flowering plants, comprises more than 13,000 species, which make up more than 10% of all such plants. Nevertheless, very few plants of this family have been investigated as far as saponins are concerned.