Carthamus lanatus L. ssp. lanatus (common name: saffron thistle) is a widespread winter-growing annual thistle weed belonging to the Asteraceae family causing severe crop and pasture losses in Australia. Introduced from the Mediterranean region it is considered the most economically important thistle species in New South Wales (1). Among the numerous pathogens isolated from naturally infected saffron thistle plants, strains of Phomopsis sp. were considered suitable as potential mycoherbicides for its biological control (2). Recently the teleomorph of this pathogen was classified as Diaporthe gulyae by morphological, genetics and phytopathological studies (3). More recently, a study carried out on the bioactive metabolites of this fungus led to the isolation of the main phytotoxin produced in liquid culture, identified as a new geranylhydroquinone and named phomentrioloxin (1). The structure of 1 was determined by spectroscopic, X-ray, and chemical methods as (1R,2R,3R,4R)-3-methoxy-6-(7-methyl-3-methylene-oct-6-en-1-ynyl)-cyclohex-5-ene-1,2,4-triol (4). Considering the novelty of this compound, a study on the structure-activity relationships was then carried out by preparing seven derivatives obtained by chemical modifications of the main functional groups of the toxin. Moreover, recently two pathogenic species related to D. gulyae, identified as Diaporthe kochmanii sp. nov. and Diaporthe kongii sp. nov. and isolated from diseased sunflower in Australia were also considered for the production of bioactive metabolites. Strains of the three species were grown in both liquid and solid media and their metabolic profiles were compared. In this communication the results of structure-activity relationship study on phomentrioloxin will be discussed. Furthermore, the preliminary data on the chemical and biological characterization of the metabolites isolated from the three species of Diaporthe will be illustrated. (1) BRIESE, D. T. Plant. Prot. 1988, 3, 135. (2) ASH, G.J.; SODART, B.; SAKUANRUNGSIRIKUL, S.; ANSCHAW, E.; CRUMP, N.; HAILSTONES, D.; HARPER, D.I. Plant. Prot. Quart. 2010, 5, 14-17. (3) THOMPSON, S. M.; TAN Y. P.; YOUNG, A. J.; NEATE, S.M.; AITEKEN, A.A.B.; SHIVAS, R. G. Persoonia 2011, 27, 80-89.
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