Insect antifeedants, production

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-... 

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. 

The potent biological activity (insect antifeedant, antitumour, antifungal) of warburganal (35) has stimulated considerable synthetic interest in this compound. Three total syntheses of this compound have been recorded in the period under review. " The synthesis by Tanis and Nakanishi has additional flexibility since the key intermediate diol (34) can be used in the syntheses of cinnamolide (36), drimenin (37), and polygodial (38). Both norisoambreinolide (39 R = O) and isoambrox (39 R = H2) have been synthesized from (40), the product of the stannic chloride-catalysed cyclization of farnesyl phenyl sulphone. Yahazunol (41), a bicyclofarnesyl hydroquinone, has been identified in the brown seaweed... 

Controlled radical cyclization directly onto a ring junction is less easy. Lejeune and Lallemand envisaged that a tethered radical cyclization of a (bromomethyl)dimethylsilyl ether onto an allylic double bond could be used to incorporate a hydroxymethyl functionality into an angular position at the ring junction of a decalin system [53]. This would then provide an interesting entry into a variety of natural products containing this skeletal functionality, such as the insect antifeedant clerodin 132 (Scheme 10-45). 

In a previous paper [1], we reviewed the isolation of quassinoids, alkaloids, and fatty acids from Simaroubaceous plants during the period 1972-1988 and discussed their biological activities, such as antitumor, antimalarial, and anti-inflammatory agents as well as insect antifeedants, amoebicides, and herbicides. This review will add new quassinoids isolated from Simaroubaceous plants from 1988 onwards and their biological activities, for example, antitumor, anti-tumor-promotor (= inhibitor against TPA-induced EBV-EA activation), anti-HIV, anti-tuberculosis, and insect antifeedant activities. Furthermore, the stability of quassinoids, lower activities of degradation products, and the synthesis of fluorinated quassinoids are also described. 

Intramolecular 1,3-dipolar cycloaddition has been employed for the synthesis of various natural products as well. For instance, Mateos et al. reported a diastereoselective synthesis of the model insect antifeedant 281 related to 12-hydroxyazadiradione utihzing the intramolecular nitrile oxide cycloaddition (Scheme 65) [167]. The nitro compound 279 was synthesized from a-cyclocitral 278 in four steps. The cleavage of isoxazoline 280 was performed under three different conditions Raney Ni-mediated cleavage in methanol-water-acetic acid provided the epimeric ketoalcohol 282 in 5 3 ratio. While there was 100% selectivity in favor of the axial alcohol 282a in the presence of Pd/C and boric acid, the selectivity was in favor of the equatorial alcohol 282b when boric acid was replaced by acetic acid. 

The natural resins present in native guayule have been extensively studied and include mono-, sesqui-, di-, and triterpene groups, as well as other secondary metabolites (108). Unfractionated guayule resin has shown considerable promise in the areas of wood preservation (in marine and terrestrial environments) (129) and insect antifeedents (termite resistance) (130-132). These resins also show promise as a biobased renewable replacement for petroleum-based monomers and oligomers in adhesives and coatings. Additional profitable uses for the resins include a natural, low toxicity replacement for creosote in wood treatment and for prevention of termite attack. Resin/lignin products, such as additives for phenol formaldehyde resins, may also prove possible. 

Nutmeg oil has strong antifeedant activity, fumigant toxicity and contact toxicity against the stored product insects, Tribolium castaneum and Sitophilus zeamis. The... 

While much work has been done by innumerable workers trying to extract, purify, and identify various components of plants known to be relatively free from attack by insects, most of these materials have fallen in the category of true repellents rather than antifeeding compounds, and none have shown promise for practical production and usage. 

Moreover, the observation of an interesting antibiotic activity for some Lactarius extracts (3) stimulated the search of new biologically active compounds among those isolated from these mushrooms. In fact, simple bioassays (4) led to the identification of new products with antimicrobial, cytotoxic, antifeedant and other interesting activities. No less important was the observation that some species seem to withstand attack from parasites such as snails and insects better than others. In fact, it has been shown that resistant species are armed with a chemical defence system which protects the mushrooms from predators and invaders. 

Nawrot, J. and Harmatha, J. (1994) Natural products as antifeedants against stored product insects. Postharvest News and Information 5, 17 N-21 N. 

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