Susana Beatriz Popich

Three new compounds, a bicyclogermacrene (1) and two 2,3-secoaromadendrane esters (2 and 3), together with (13S)-13-hydroxylabda-8,14-diene (4), fusicogigantone B (5), 3α,14-diacetoxy-2-hydoxybicyclogermacrene (6), fusicogigantone A (7), neofuranoplagiochilal (8), plagiochiline B (9), furanoplagiochilal (10), trans-nerolidol, spathulenol, α-tocopherol, and (+)-globulol were isolated from an Argentine collection of Plagiochila diversifolia. Their structures were elucidated by extensive mono and bidimensional NMR studies. Compounds 4, 5, and 6, incorporated to the larval diet at 100 μg per g of diet, reduced the larval growth of Spodoptera frugiperda (Lepidoptera: Noctuidae) by 70 ± 25, 57 ± 23, and 33 ± 16%, respectively. Compounds 4 and 5 produced 70% and 60% larval mortality at early instars. The latter also showed antifeedant properties in the Choice Test, with a feeding ratio of 0.54 ± 0.16.

Several species of the large family of tropical plants Annonaceae have been intensely investigated over the last 20 years, mainly because of the discovery of annonaceous acetogenins. These compounds are powerful cytotoxics, with potential applications as insecticides, antiparasitics, acaricides, fungicides, and antitumor drugs. Annona montana Macfad. (Annonaceae) grows in Santa Cruz de la Sierra, Bolivia, where an infusion of leaves is used for the treatment of lice, influenza, and insomnia. The major acetogenins from a Bolivian collection of A. montana, annonacin (1), cis-annonacin-10-one (2), densicomacin-1 (3), gigantetronenin (4), murihexocin-B (5), and tucupentol (6), were evaluated for their antifeedant and toxic effects on Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), a serious pest affecting corn crops in Argentina. All the acetogenins produced 100% mortality during the larval or pupal stages at 100 μg of treatment per gram of diet. In addition, compounds 2, 3, and 4 deterred more than 80% feeding at the same dose. Relative toxicity values of LD50 for the strongest larvicidal compounds 1, 2, and 4 were determined, indicating that the three compounds are effective natural insecticides. This is the first report on the antifeedant and toxic effects produced by the particular type of acetogenins, the mono-THF acetogenins, on the lepidopteran S. frugiperda. No correlation was detected between the toxicity of the mentioned compounds to larvae and the known capacity of the acetogenins 1, 2, and 4 to inhibit the NADH oxidase, indicating that the inhibition of the mitochondrial complex I is not the only cause for larval mortality of S. frugiperda.

Three new compounds, a bicyclogermacrene (1) and two 2,3-secoaromadendrane esters (2 and 3), together with (13S)-13-hydroxylabda-8,14-diene (4), fusicogigantone B (5), 3α,14-diacetoxy-2-hydoxybicyclogermacrene (6), fusicogigantone A (7), neofuranoplagiochilal (8), plagiochiline B (9), furanoplagiochilal (10), trans-nerolidol, spathulenol, α-tocopherol, and (+)-globulol were isolated from an Argentine collection of Plagiochila diversifolia. Their structures were elucidated by extensive mono and bidimensional NMR studies. Compounds 4, 5, and 6, incorporated to the larval diet at 100 μg per g of diet, reduced the larval growth of Spodoptera frugiperda (Lepidoptera: Noctuidae) by 70 ± 25, 57 ± 23, and 33 ± 16%, respectively. Compounds 4 and 5 produced 70% and 60% larval mortality at early instars. The latter also showed antifeedant properties in the Choice Test, with a feeding ratio of 0.54 ± 0.16.

From an Argentine collection of the tropical tree Rollinia emarginata (Annonaceae), vomifoliol, dehydrovomifoliol, blumenol C, loliolide, 7-epiloliolide, vanillin, dihydroactinolide, as well as other common plant constituents were obtained, and identified by their NMR and MS features compared with authentic samples. Antifeedant and toxic actions were exerted to the polyphagous moth Spodoptera frugiperda by the ethanol extract of the plant, at 250 ppm in the larval diet. Additionally, in greenhouse studies, a 200 ppm aqueous solution of the extract produced a post-emergency herbicidal effect on the annual weed common lambsquarter (Chenopodium album).

Sesquiterpene lactones play an important role in protection of plants against herbivores. Cyrtocymura cincta (Griseb.) H. Robinson (Asteraceae) is widespread in tropical South America and may contain compounds that provide protection against phytophagous insects. We isolated 2 sesquiterpene lactones, from the surface of leaves and flowers, that also were found in the lactone fraction of a chloroform extract of ground air-dried flowers and leaves. Three concentrations of the lactone-containing fraction were incorporated into the diet of the stored grain pest Sitotroga cerealella Olivier, and the effects on its life cycle were evaluated. Larval feeding behavior was not altered, but a concentration of 250 ppm of the lactone mixture in the diet lowered the percentage of adult emergence and produced malformations in adults compared with controls. The most drastic effects were observed in the oviposition capacity and viability of eggs laid by females who fed on treated diets as larvae. None of the eggs laid by females exposed to the 500-ppm concentration produced viable offspring; thus, the lactone fraction contains compounds that produce chemical sterilization.

Two new norditerpenoids, 4beta-hydroxy-19-normanoyl oxide (1) and 4alpha-hydroxy-18-normanoyl oxide (2), the new 18-O-alpha-l-arabinopyranosylmanoyl oxide (3a), and the known diterpenoids jhanol (4) and 18-hydroxy-13-epi-manoyl oxide (5) were isolated, together with other common plant constituents from an Argentine collection of Grindelia scorzonerifolia. The structures of the new compounds were established by extensive 1D and 2D NMR techniques and chemical transformations. Structural features of compounds 2 and 4 were verified by X-ray crystallographic analyses. The insecticidal effect of compound 3a was evaluated against the polyphagous pest Spodoptera frugiperda. Pupal and adult malformations leading to death occurred when 3a was incorporated in a larval diet at a concentration of 100 ppm.

The new 2,3-secoaromadendrane 1, together with the known compounds plagiochilines A and M (2 and 3, resp.), fusicogigantone A (4), and 1,4-dimethylazulene (5) were isolated from an Argentine collection of the liverwort Plagiochila bursata. Structures were elucidated by extensive 1D- and 2D-NMR studies. Compounds 2 and 4, incorporated to the larval diet at 100 microg per g of diet, reduced the larval growth of Spodoptera frugiperda (Lepidoptera: Noctuidae) by 66+/-29% and 25+/-8% and produced 55 and 75% larval mortality at early instars and 20 and 25% pupal mortality, respectively. Treatment with compound 2 also produced abdomen and wing malformation in adults leading to impossibility to mate.