Marta E. Sosa

Clerodane diterpenes from Baccharis sagittalis: insect antifeedant activity.

Two clerodane-type diterpene glycosides esters, which were studied as peracetyl derivatives, together with the known diterpene marrubiagenine, were isolated from the aerial part of Baccharis sagittalis (Less). Their structures were established by spectroscopic methods. Antifeedant activity toward Tenebrio molitor larvae of the isolated compounds along with six other diterpenes was evaluated and some structure-antifeedant bioactivity relationships are reported.

Insect growth regulatory effects of linear diterpenoids and derivatives from Baccharis thymifolia.

Linear diterpenes isolated from aerial parts of Baccharis thymifolia ( 1- 3) were tested for insect growth inhibitory activity against Tenebrio molitor larvae. Compounds 4- 16 were prepared by various chemical transformations. The diterpenes 6,10-( E,E)-thymifodioic acid ( 1), the butenolide 3, and the derivatives 4, 11, and 14 produced developmental deficiencies in assays using topical application on fifth instar larvae of T. molitor. Compound 3 is a new natural product.

Plant secondary metabolites from Argentinean semiarid lands: bioactivity against insects

In this report some recent advances on the studies about the interaction between plant secondary metabolites and insects are presented. Bioactivities elicited by natural products with different terpenoid skeletons, phenylpropanoids, flavonoids, as well as essential oils, are discussed. Special mention has been made to plants from the central-western semiarid area of Argentina.

Antifeedant/insecticidal terpenes from asteraceae and labiatae species native to Argentinean semi-arid lands.

To validate the potential as added-value resources of Asteraceae and Labiatae species of Argentinean semi-arid lands, we have selected 13 of their major terpenoids belonging to several chemical classes and tested their insect antifeedant and toxic activity on the herbivorous insects Spodoptera littoralis and Leptinotarsa decemlineata. The antifeedant effects of the test compounds were structure- and species-dependent. The most active antifeedant to L. decemlineata was the eudesmane sesquiterpene γ-costic acid (13), followed by the labdane diterpene 2α,3α-dihydroxycativic acid (8), the clerodane diterpenes 6-acetylteucjaponin B (5), bacchotricuneatin A (1), bartemidiolide (7), butanolide (4), and the sesquiterpenes ilicic acid (11) and tessaric acid (10) (eudesmane and eremophilane type, respectively). S. littoralis was only affected by the clerodanes and showed the strongest response to salviarin (3) and 5, followed by hawtriwaic acid (6) and 12-epi-bacchotricuneatin A (2). Orally injected S. littoralis larvae were negatively affected by 5. Most of the diterpenes had selective cytotoxic effects to insect-derived Sf9 cells with the clerodane 1 being the most active, followed by the eudesmane costic acid (12), the only cytotoxic sesquiterpene. None of these compounds was cytotoxic to mammalian CHO cells.

Allelochemical effects of eudesmane and eremophilane sesquiterpenes on Tribolium castaneum larvae.

Eight eudesmane and eremophilane sesquiterpenes administered to Tribolium castaneum larvae caused different allelochemical effects. Topical application of 3-oxo-γ-costic acid produced the greatest lengthening in the duration of the pupal stage. Morphological deformities were found, specifically when ilicic, costic, and γ-costic acids and costic aldehyde were used. Ilicic acid exhibited the major toxicity 72 hr following topical application. All compounds were significantly toxic at the end point of the experiment (60 days). Treated surface toxicity was lower than when topical assays were carried out. Responses to tessaric acid in choice bioassays had the highest attractive effect. Maximum repellency was caused by the 3-oxo-γ-costic acid. However, experimental series carried out using γ-costic acid, eremophilan-1(10),2,11(13)-trien-12-oic acid, costic aldehyde, and ilicic aldehyde showed no clear response.

Antifeedant activity of neo-clerodane diterpenes from Baccharis flabellata Hook & Arn var. flabellata toward Tribolium castaneum Herbst: structure–activity relationships

In order to establish structure–activity relationships, nine neo-clerodane diterpenes isolated from the acetone extract of aerial parts of Baccharis flabellata Hook & Arn var. fabellata were assayed for antifeedant activity against Tribolium castaneum (Coleoptera: Tenebrionidae). Compounds exhibiting maximal antifeedant activities showed an α,β-unsaturated carbonyl group on the decalin portion and a furan ring at the side chain. Stereoelectronic studies indicate that the distance between the furan heteroatom and the more electrophilic carbon of the decaline moiety, as well as the electrostatic charge on that atom, were important features for antifeedant activity. Compounds possesing an α,β,γ,δ-unsaturated carbonyl group or an acetoxyl group at C-2, were inactive. Theoretical calculations were performed in order to find some structure–activity relationships.