Diterpenes, insect antifeedants

Klocke, j. a., M. Hu, S. Chiu, and I. Kubo, Grayanoid diterpene insect antifeedants and insecticides from Rhododendron molle. Phytochemistry, 30, 1797-1800 (1991). 

Bicyclic diterpenes-clerodanes. An important group of Insect antifeedants are the clerodane diterpenoids, which have been isolated from several different plant families (13)(Figure 1). Particularly well studied are the antifeedant activities of caryoptln and clerodin, and their derivatives, from Clerodendron and Caryopteris, Verbenaceae, against the tobacco cutworm Spodoptera litura L. (25-27). 

Figure 6. Grayanoid Diterpenes with insect antifeedant activity.

The clerodanes are a notable example of feeding deterrents2 and further examples have been discovered recently. The natural insect antifeedant clerodin (100) forms the basis of the name of this type of diterpenes called the neo-clerodane diterpenes. Ateo-clerodanes are compounds with a clerodane skeleton and exactly the same absolute configuration as clerodin. Those that have the opposite absolute configuration are referred to as ent-neo- cl erod an es. 

Ajugarin I (clerodane diterpene) Ajuga remota (Lamiaceae) Insect antifeedant... 

In summary, the Delphinium diterpene alkaloids cardiopetamine (30) and 15-acetylcardiopetamine (27) are potent insect antifeedants active on two insect species with different feeding adaptations (a polyphagous Lepidopteran and an oligophagous Chrysomelid beetle), suggesting a potential broad range of antifeedant action for this class of compounds [20]. 

Teucrium species are used in folk medicine as diuretic, diaphoretic, carminative, astringent, stimulant and tonic, antiseptic, antipyretic and antiinflammatory agents. T. cubense [92] for example is used against stomach aches and as an amoebacide. Teucjaponin A(32) obtained from T. japonicum [33] was shown to be antifeedant for the larve of Prodenia litura. Its threshold concentration for inhibitory activity was about 400 ppm in the leaf disk test. Generally neo-clerodane diterpenes posses insect antifeedant activity and they are used as antifungal, antitumor and antibacterial agents [56,63]. The antitumor activity of T. bicolor [52] was reported. The antifeedant activity of neoclerodanes is mentioned in a... 

In the course of these research programmes, many characteristic bioactive compounds have been reported. Polyester sesquiterpenes and pyridine-sesquiterpene alkaloids with insect antifeedant or insecticidal properties have been isolated from some species and recently sesquiterpene pyridine alkaloids with immunosuppressive or antitumoral activities have also been described. Diterpene triepoxides with potent antileukemic and immunosupressive activities and triterpenoid quinonemethides, named as celastroloids , with antibiotic and cytostatic activities, have been isolated from species of the Celastraceae family. 

Among the isoryanodane-type diterpenes, hydroxylation of C-l (8) and the polarity of the five-membered A ring (C-8 and C-l 3) (7 versus 9) determined their antifeedant activity on both insect species (table 2) [17], as previously demonstrated for S. litura [11],... 

Plant sesquiterpenes and other terpenoids aie major detenninants of insect-plant interactions (2i 16V Many insecticidal and antifeedant terpenoids are epoxides including monoteipene Q2, 18. sesquiteipene QQ, 19-23). diteipene (Jl, 24) and triteipene derivatives (25-27) typified by the potent antifeedant azadirachtin (28-30). Most biolo cal effects have been determined with Lepidoptera and non-chrysomelid Coleoptera. Occasionally, the same compound, while normally inhibitory to herbivores, may for adapted insect species or at low concentrations have a stimulatory effect (13). Insects, in turn, synthesize their own defensive (21, and pheromonal (22) terpenoids. Plants may utilize insect pheromones such as the sesquiterpene alarm pheromone, rranj-B-famesene, in their own defense (34. 35). Inhibitory cyclic sesquiterpenes (Table I) and diterpenes (Table II) for insect herbivores have been identified from at least 28 genera of the terpenoid-rich Compositae. These studies were largely confined to extrafloral tissues. 

Antifeedant Compounds Insecticidal and Nematicidal Activity Diterpenes with Juvenile Hormone Activity Diterpenes That Prevent Reproduction in Insects Trail-Marking Pheromones Diterpenes from Marine Plants Sweeteners Medicinal Properties Antitumor Compounds Sesterterpenes Biosynthesis Biological Activity References... 

A number of diterpenes are known to have pronounced antifeedant activity against herbivores (Mabry and Gill, 1979 Munakata, 1977). Abietic (52), dehydroabietic, 12-methoxyabietic, sandaracopimaric (32), and isopimaric (69) acid serve as feeding deterrents for the larch sawfly, Pristi-phora erichsonii in single needles from new shoots of tamarack (Larix laricina) (Ohigashi et al, 1981). The larvae of this insect do eat tufted needles on short shoots of the same trees. 

Many of the antifeedant compounds discussed above have insecticidal activity as well. Moreover, other diterpenes are toxic to insects and nematodes when consumed. Ryanodine (81), from Ryania speciosa (Flacourtiaceae) and several related species, is unique in that its insecticidal activity was discovered as a part of a search for new insecticides (Crosby, 1971). The toxic principle, ryanodine, is a diterpene esteri-fied to a pyrrole-2-carboxylic acid (Crosby, 1971). Ryanodine inhibits cardiomuscular calcium transport (Croteau and Johnson, 1985). 

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