Further eudesmane derivatives from verbesina species

Eudesmane Sesquiterpenes from Verbesina lanata with Inhibitory Activity against Grapevine Downy Mildew

An in-house library of more than 3000 extracts of plant and fungal origin was screened against some major plant pathogens. As one of the hits, an ethyl acetate extract from inflorescences of Verbesina lanata showed significant inhibitory activity in vitro against grapevine downy mildew (Plasmopara viticola), with a MIC₁₀₀ value of 35 μg/mL. An emulsifiable concentrate formulation with 50 mg/g of the extract was developed for in vivo evaluation. A suspension of the formulation containing 1 mg/mL of extract lowered leaf surface infection of grapevine seedling by 82% compared to the nontreated control. With the aid of HPLC-based activity profiling, the antifungal activity was correlated with a series of lipophilic compounds. Preparative isolation by a combination of chromatographic techniques afforded 16 eudesmane sesquiterpenes including eight new congeners. Nine compounds were obtained in sufficient quantities to be tested in vitro and were found to inhibit the zoospore activity of P. viticola with MIC₁₀₀ values ranging from 4 to 50 μg/mL. The two major compounds, 6β-cinnamoyloxy-4β,9β,15-trihydroxyeudesmane (9) and 6β-cinnamoyloxy-1β,15-dihydroxyeudesm-4-en-3-one (13), showed MIC₁₀₀ values of 5 and 31 μg/mL, respectively.

Verbesinosides A-F, 15,27-cyclooleanane saponins from the American native plant Verbesina virginica

Verbesinosides A-F (1-6), six new 15,27-cyclooleanane-type triterpenoid saponins carrying different aromatic acyl moieties on the aglycon, were isolated from the leaves and flowers of Verbesina virginica. Their structures were established by interpretation of spectroscopic data and chemical methods. The representative major saponin, verbesinoside A (1), has the structure 21-trimethoxybenzoyl 15alpha,27-cycloolean-12-en-3beta,21beta-diol-28-oic acid 3-O-beta-D-xylopyranosyl(1-->4)-beta-D-xylopyranosyl(1-->2)-beta-D-glucopyranoside. This is the first report of triterpenoid saponins possessing the unique 15,27-cyclooleanane skeleton. The anisotropic effects of the aromatic acyl moieties on the triterpenoid skeleton are discussed.

Eudesmane derivatives from Iva frutescens

Re-investigation of the aerial parts of Iva frutescens resulted in the isolation of three sesquiterpenes, two of which are new natural products, and their structures were established by spectral data.