Unprecedented spirocyclization of 3-methyleneindoline-2-thiones during hydrolysis of the phytoalexin cyclobrassinin.

The phytoalexin cyclobrassinin is a plant defense that has additional importance since it inhibits brassinin hydrolase, a phytoalexin detoxifying enzyme produced by the plant pathogen Alternaria brassicicola. Hence, the 1,3-thiazino[6,5-b]indole scaffold of cyclobrassinin has great application as a lead structure to design potential inhibitors of brassinin detoxification. For this reason, it is necessary to determine whether A. brassicicola is able to transform cyclobrassinin. During this work new reactions of 1,3-thiazino[6,5-b]indoles and indoline-2-thiones and their unique [4+2] cycloaddition products were discovered and characterized.

The phytopathogenic fungus Alternaria brassicicola: phytotoxin production and phytoalexin elicitation.

The metabolites and phytotoxins produced by the phytopathogenic fungus Alternaria brassicicola (Schwein.) Wiltshire, as well as the phytoalexins induced in host plants, were investigated. Brassicicolin A emerged as the most selective phytotoxic metabolite produced in liquid cultures of A. brassicicola and spirobrassinin as the major phytoalexin produced in infected leaves of Brassica juncea (whole plants). In detached infected leaves of B. juncea, the main component was N'-acetyl-3-indolylmethanamine, the product of detoxification of the phytoalexin brassinin by A. brassicicola. In addition, the structure elucidation of three hitherto unknown metabolites having a fusicoccane skeleton was carried out and the antifungal activity of several plant defenses against A. brassicicola was determined.

Phomapyrones from blackleg causing phytopathogenic fungi: isolation, structure determination, biosyntheses and biological activity.

The isolation and structure determination of phomapyrones D-G, three 2-pyrones and a coumarin, from a group of isolates of the fungal pathogen Leptosphaeria maculans (Desm.) Ces. et de Not., asexual stage Phoma lingam (Tode ex Fr.) Desm, is reported. As well, phomenin B, infectopyrone, and polanrazines B and C were also obtained for the first time from these isolates. In addition, based on results of incorporations of 13C-labeled acetate and malonate, and deuterated methionine, a polyketide pathway is proposed for the biosyntheses of phomapyrones.

Chemical mediators: the remarkable structure and host-selectivity of depsilairdin, a sesquiterpenic depsipeptide containing a new amino acid.

The chemical structure determination of depsilairdin, a highly selective phytotoxin produced by the plant pathogenic fungus Leptosphaeriamaculans/Phoma lingam, is described. The elucidation of the unusual chemical structure used a combination of NMR spectral data and X-ray crystallography. The absolute configuration was established using chemical degradation and synthesis of (3S,6R)-3,6-diisopropyl-2,5-morpholinedione and its (3R,6S) and (3R,6R) stereoisomers. Similar to the fungal pathogen, depsilairdin caused strong lesions only on brown mustard leaves but not on related species. [structure: see text]

Maculansins, cryptic phytotoxins from blackleg fungi.

The phytotoxins and other metabolites produced by isolates L2/M2 of the fungal species Leptosphaeria maculans under different culture conditions, together with those of two new, but related isolates are disclosed. The common metabolic characteristics suggest a phylogenetic similarity between these isolates with potential to become widespread in mustard growing areas.

The phytopathogenic fungi Leptosphaeria maculans and Leptosphaeria biglobosa: chemotaxonomical characterization of isolates and metabolite production in different culture media.

Previous molecular chemotaxonomic analyses of isolates of the plant pathogenic fungus Leptosphaeria maculans (Desm.) Ces. et de Not. (asexual stage Phoma lingam (Tode ex Fr.) Desm.) in a chemically defined medium suggested that this species complex was composed of at least three distinct groups. Subsequently, a group within L. maculans was classified as Leptosphaeria biglobosa, on the basis of morphologic characteristics and the lack of sexual crossing. To obtain clarification regarding the metabolite profiles of the various groups or species of blackleg fungi, the objectives of this work were (i) to determine the chemical structures of metabolites produced by Canadian V isolates and Polish-type isolates in potato dextrose broth (PDB) and (ii) to determine the chemotaxonomic relationship among French isolates of L. biglobosa and among Canadian W isolates and Thlaspi isolates of L. maculans. Here, we report for the first time that Canadian V isolates grown in PDB produced 2,4-dihydroxy-3,6-dimethylbenzaldehyde, a metabolite never reported from L. maculans, but none of the usual phytotoxins (sirodesmins). In addition, we report a new metabolite, 2-[2-(5-hydroxybenzofuranyl)]-3-(4-hydroxyphenyl)propanenitrile, from Polish-type isolates of L. maculans grown in PDB and the metabolite profiles of 16 Thlaspi isolates. The metabolite profiles of Thlaspi isolates indicate that these are part of two distinct groups, the Polish W group and the Canadian W group, i.e., L. biglobosa. Finally, we demonstrate that the metabolite profiles of the French isolates classified as L. biglobosa are similar to those of Canadian W isolates.

New sesquiterpenic phytotoxins establish unprecedented relationship between different groups of blackleg fungal isolates.

A comprehensive search for sesquiterpenic metabolites produced by isolates of the blackleg fungus [Leptosphaeria maculans (Desm.)] Ces. et de Not. [asexual stage Phoma lingam (Tode ex Fr.) Desm.] revealed that an isolate pathogenic on both canola and brown mustard (IBCN 18) and two isolates pathogenic on brown mustard (Laird 2 and Mayfair 2) produced similar sesquiterpenes. The isolation, chemical structure elucidation, and phytotoxicity of these new sesquiterpenes with silphinene and selinene type skeletons is reported. This is the first time that an isolate virulent on canola and brown mustard is found to produce metabolites characteristic of both virulent (sirodesmins) and avirulent (phomalairdenones) L. maculans/P. lingam. In the context of grouping the various isolates of L. maculans/P. lingam, this work suggests an additional pathogenicity group comprising isolates that produce both sirodesmins and phomalairdenones and are virulent on both canola and brown mustard.