Brefeldin A and alpha,beta-dehydrocurvularin, two phytotoxins from Alternaria zinniae, a biocontrol agent of Xanthium occidentale

Alternaria zinniae, a fungus causing leaf necrosis in Xanthium occidentale, a widespread noxious weed of Australian summer crops and pastures, produces toxic metabolites when grown in liquid culture. Extensive application of NMR techniques, HR, EIMS and X-ray analysis permitted the identification of brefeldin A (4H-cyclopent[f]oxacyclotridecin-4-one-1,6,7,8,9,1 1a,12,13,14,14a-decahydro-1,13-dihydroxy-6-methyl) and alpha,beta-dehydrocurvularin (4,5,6,7-tetrahydro-11,13-dihydroxy-4-methyl-2H-3-benzoxacyclododecin-2,10 (1H)-dione), two bioactive metabolites produced by a number of fungal species belonging to the genera Alternaria, Ascochyta Penicillium, Curvularia, Cercospora, and Phyllosticta, This is the first report on the isolation of these two phytotoxins from A. zinniae. The interesting semi-selective toxicity to X. occidentale is described here, and the possible use of fungus and toxins in integrated weed management programs is discussed. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.