Insect antifeedant

The key step in the diastereoselective synthesis of model insect antifeedant 152 starting from a-cyclocitral 148 was the INOC reaction of oxime 149 or nitro alkane 150 to the isoxazoline 151 (Eq. 15) [42]. 

A SN reaction-based domino route to clerodane diterpenoid tanabalin (2-488) [258] has been described by Watanabe s group (Scheme 2.111) [259]. This natural product is interesting as it exhibits potent insect antifeedant activity against the pink bollworm, Pectinophora gossypiella, a severe pest of the cotton plant The domino sequence towards the substituted trans-decalin 2-487 as the key scaffold is induced by an intermolecular alkylation of the (5-ke toes ter 2-484 with the iodoalkane 2-483 followed by an intramolecular Michael addition/aldol condensation (Robin-... 

A diastereoselective synthesis of the model insect antifeedant related to 12-hydroxyazadi-radione starting from a-cyclocitral has been reported. [The key steps involve INOC and a Stille... 

Sesquiterpenoids possessing the drimane skeleton (22) exhibit an impressive series of biological properties. Recently, all aspects relative to occurrence [76], biological activity [76], insect antifeedant properties [77] and synthesis [78] of these terpenoids have been exhaustively reviewed. 

Acetylnimbandiol was insectidical (EI50 = 21 ppm) when fed to the larvae of II. vlrescens, while the structurally related salannin, which lacks the A-ring ketone (Figure 13), was not (Table VII) (57). Nakanishi (58) has pointed out that natural products with electrophilic moieties tend to be cytotoxic and insect antifeedant. Possibly the growth-Inhibitory activity of the limonoids may also be attributed to a nonspecific electrophilic effect. 

Diterpenoids as Insect Antifeedants and Growth Inhibitors Role in Solidago Species... 

COOPER-DRIVER AND LE QUESNE Diterpenoids as Insect Antifeedants... 

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 1. Clerodanes with insect antifeedant activity.

The diterpenoids of Isodon (Labiatae) species have been reviewed. The presence of an a-methylenecyclopentanone moiety in these diterpenoids is important for their anti-tumour and anti-bacterial activity. " Inflexin (79) is a cytotoxin and insect antifeedant which has been isolated from Isodon inflexus. Isodomedin (80) is another member of this series, isolated from /. shikokianus, which shows this type of biological activity. Its structure was assigned on the basis of its H and C n.m.r. spectra and on an interrelationship with kamebanin (81), isolated from /. kameba. 

Morimoto, M.S., Kumeda, S., and Komai, K., Insect antifeedant flavonoids from Gnaphalium affine D. Don, J. Agric. Food Chem., 48, 1888, 2000. 

It was toxic to the pink bollworm at 0.005% and to the bollworm and the tobacco budworm at 0.15% in artificial diets. Esters (C10-C12) were also toxic to the insects as sprays. Matricaria ester was also shown to be a potent insect antifeedant compound to these insects (115). 

During the course of screening plants for insect antifeedants, the extract of the bulbs of Lycoris radiata Herb, was found to exhibit antifeeding activity when tested against the larvae of the yellow butterfly Eurema hecabe mandarina (61). 

Chicory (Cichorium intybus) is cultivated in cool regions such as Northern Europe. Recently, this vegetable has arisen out of claims that it is able to promote good health since no pesticides are used to cultivate chicory in the field, while the plant remains noticeably free from herbivore and microbial attack. The bitter substances, lactupicrin, 8-deoxylactucin and some phenolics had previously been shown to possess insect antifeedant properties in chicory (Rees and Harbome, 1985). Specifically, sesquiterpenoid lactones from chicory leaves, such as 8-deoxylactucin and lactupicrin (Figure 1), were identified as insect antifeedants against desert locust, Schistocerca gregaria. Similarly, we found some biologically active secondary metabolites in the... 

Figure 1. Insect antifeedants in chicory leaves. Source Nishimura et al. (2000). Reproduced after permission from Kluwer Academic Publisher (Springer).

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. 

---