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The lichen secondary metabolite usnic acid exists as a (3 3) and a (+) enantiomer, indicating a K K or L L projection of the methyl group at position 9b, respectively. (3 3)-Usnic caused a dose-dependent bleaching of the cotyledonary tissues associated with a decrease of both chlorophylls and carotenoids in treated plants whereas no bleaching was observed with the (+) enantiomer. (3 3)-Usnic acid inhibited protophorphyrinogen oxidase activity (I 50 = 3 W WM), but did not lead to protoporphyrin IX accumulation. Bleaching appears to be caused by irreversible inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase by (3 3)-usnic acid (apparent IC 50 = 50 nM). ß

The antifungal activity of 1,4-naphthoquinones, 1,2-naphthoquinones, 1,4-benzoquinones, and anthraquinones from our natural products collection was tested by direct bioautography to identify natural products with potential use in agricultural fungal pathogen control. Quinones demonstrated good to moderate antifungal activity against Colletotrichum spp. Colletotrichum fragariae was the most sensitive species to quinone-based chemistry, Colletotrichum gloeosporioides had intermediate sensitivity, while Colletotrichum acutatum was the species least sensitive to these compounds.

Protox inhibitors are applied as foliar sprays, thus causing very rapid cellular collapse and desiccation of many troublesome weeds in the presence of light. In many respects, they appear to be ideal herbicides, because they act rapidly and do not harm mammals under normal conditions. The main limitation to their widespread adoption is that few crops are naturally resistant to them. Crop tolerance has mainly been pursued with the synthesis of the cyclic imide classes containing 5- and 6-membered heterocycles, including pyrazole, pyridazine, 1,2,4-triazine, triazolinone and trifluoromethyluracil derivatives. Because of their structural novelties and biological performance, active investigations on heterocyclic protox inhibitors have been carried out in our laboratories and we have found 3-arylpyrroles to be a new class of light-activated, membrane-disrupting herbicides. They are active on both grass and broadleaf weeds at low rates. The synthesis and structure-activity relationships are presented.

Trifluoromethyl‐substituted pyrazoles were synthesized via 1,3‐dipolar cycloaddition from sydnones 2a‐j and 1‐aryl‐3,3,3‐trifluoro‐propynes 5a‐f. The regioselectivity of the reaction and the spectroscopic characteristics of the products are discussed.

This paper reports the synthesis and the biological activity of benzoyl arylureas in which the aryl group bears a trifluoromethyl‐substitiited alkyl or alkenyl side chain, R. The activity of these compounds has been evaluated on larvae of S. littoralis, A. aegypti, L. decemlineata and on the eggs of T. urticae. In general: (1) the optimum insecticidal activities are achieved when the substituents on the benzoyl moiety, R1, and R2, are 2,6‐difluoro, the substituents on the aryl moiety, R3, are 3,5‐dichloro and R1, is 4‐(CHC(CI)CF3); (2) the best acaricidal activity is shown when R1, is 2‐CI, R2, and R3, are hydrogen atoms and R1, is 4‐(CH2CH2CH(CI)CF3); (3) the best overall activity is displayed when R1, is 2‐CI, R2 is hydrogen, R3 is 3‐chloro and R1 is 4‐(CH2CH2CF3).

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IR 5790, an arylthiadiazolone herbicide structurally related to oxadiargyl and oxadiazon, was synthesized. The herbicidal activity and mode of action of IR 5790 were investigated. This herbicide has broad-spectrum pre-emergence activity against both dicotyledonous and monocotyledonous weeds. The phenotypic responses of susceptible plants, such as interruption of growth and light-dependent development of necrotic areas on the foliage, are consistent with those observed with protoporphyrinogen oxidase-inhibiting herbicides. Tissues exposed to IR 5790 in darkness accumulated protoporphyrin IX, which led to a photodynamic loss of membrane integrity upon exposure to light. Consistent with these physiological symptoms, IR 5790 strongly inhibited protoporphyrinogen oxidase, with an I(50) value of 3 nM. The presence of a sulfur atom did not significantly alter the molecular properties of the thiadiazolone ring, relative to the oxadiazolone ring of oxadiargyl, which explains why IR 5790 has the same mode of action as this herbicide.