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Three distinct chemical classes for the control of gastrointestinal nematodes are available: benzimidazoles, imidazothiazoles, and macrocyclic lactones. The relentless development of drug resistance has severely limited the usefulness of such drugs and the search for a new class of compounds preferably with a different mode of action is an important endeavor. Marcfortine A (1), a metabolite of Penicillium roqueforti, is structurally related to paraherquamide A (2), originally isolated from Penicillium paraherquei. Chemically the two compounds differ only in one ring; in marcfortine A, ring G is six-membered and carries no substituents, while in paraherquamide A, ring G is five-membered with methyl and hydroxyl substituents at C14. Paraherquamide A (2) is superior to marcfortine A as a nematocide. 2-Desoxoparaherquamide A (PNU-141962, 53) has excellent nematocidal activity, a superior safely profile, and is the first semi-synthetic member of this totally new class of nematocides that is a legitimate candidate for development. This review describes the chemistry, efficacy and mode of action of PNU-141962.

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Irradiation of dibenzoylmethane in benzene gives tribenzoylethane. In more concentrated solution a solid dimer (11) separates which, on solution, is converted by dealdolization into a n isomer. This isomer (I, R = H) on irradiation, gives tribenzoylethane in a photolytic reaction which has been shown t o have some generality. The overall conversion of dibenzoylmethane t o tribenzoylethane therefore involves two photochemical and one chemical reactions.Some time ago, as part of our studies on photochemical cyclo-addition, we reported the reaction between acetylacetone and a number of alkenes and cycloalkenes (1). The main products derived from the process are indicated below.T o ascertain whether the process was general for all enolized P-diketones, we studied the reaction between dibenzoylmethane and cyclohexene. This diketone is largely enolized in hydrocarbon solvents and the reaction could be conveniently followed by observing the formation of the non-enolized benzoyl grouping in the carbonyl region.The products proved difficult to crystallize and the first substance obtained in crystalline form, from a study of its spectra, evidently did not contain a cyclohexyl residue. This conclusion was confirmed when it was found that the yield was greatly increased (to 37%) by irradiation of dibenzoylmethane in benzene solution.*The substance showed only benzoyl carbonyl in the infrared spectrum, and the ultraviolet absorption was typical of acetophenones. The nuclear nlagnetic resonance (n.m.r.) spectrunl showed the presence of only three protons other than aromatic hydrogen. These were a doublet (two protons) a t T 6.23 and a triplet (one hydrogen) a t T 3.85. These protons were coupled with J = 7 c.p.s. The two protons of the doublet were evidently identical. This required the part structure -CH2-CH / \.Alkaline hydrolysis of the substance under mild condition gave diphenacyl and benzoic acid (1 mole) as the only isolable products. The substance was therefore identified as tribenzoylethane. The remarkably low-field position of the methine proton is noteworthy.The illode of genesis of the tribenzoylethane was not immediately obvious, but since two n~olecules of dibenzoylmethane, a t least, were required to participate in its formation the possibility of dimerization a t some stage appeared reasonable. Accordingly, the irradiation was performed with a higher concentration of dibenzoylmethane.Under these conditions the reaction proceeded differently. Although the infrared spectrum of the solution appeared to be showing the expected changes, a white crystalline solid separated during the irradiation. This material was separated by filtration and * W e are indebted to Mr. R. W. Yifi for this observation.