-
[show abstract]
[hide abstract]
ABSTRACT: Brassinin hydrolase (BHAb), an inducible enzyme produced by the plant pathogen Alternaria brassicicola under stress conditions, catalyzes the hydrolysis of the methyl dithiocarbamate group of the phytoalexin brassinin, to indolyl-3-methanamine, methane thiol and carbonyl sulfide. Thirty four substrate inspired compounds, bioisosteres of brassinin and a range of related compounds, were evaluated as potential substrates and inhibitors of BHAb for the first time. While six compounds containing thiocarbamate, carbamate and carbonate groups displayed inhibitory activity against BHAb, only two were found to be substrates (thionecarbamate and dithiocarbamate). Methyl naphthalen-1-yl-methyl carbamate, the most potent inhibitor of the six, and methyl N'-(1-methyl-3-indolylmethyl)carbamate inhibited BHAb through a reversible noncompetitive mechanism (K(i)=89±9 and 695±60μM, respectively). Importantly, these carbamate inhibitors were resistant to degradation by A. brassicicola. Carbonates were also inhibitory of BHAb, but a quick degradation by A. brassicicola makes their potential use as crop protectants less likely. Overall, these results indicate that indolyl and naphthalenyl carbamates are excellent lead structures to design new paldoxins that could inhibit the detoxification of brassinin by A. brassicicola.
Bioorganic & medicinal chemistry 11/2011; 20(1):225-33. · 2.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Glucosinolates represent a large group of plant natural products long known for diverse and fascinating physiological functions and activities. Despite the relevance and huge interest on the roles of indole glucosinolates in plant defense, little is known about their direct interaction with microbial plant pathogens. Toward this end, the metabolism of indolyl glucosinolates, their corresponding desulfo-derivatives, and derived metabolites, by three fungal species pathogenic on crucifers was investigated. While glucobrassicin, 1-methoxyglucobrassicin, 4-methoxyglucobrassicin were not metabolized by the pathogenic fungi Alternaria brassicicola, Rhizoctonia solani and Sclerotinia sclerotiorum, the corresponding desulfo-derivatives were metabolized to indolyl-3-acetonitrile, caulilexin C (1-methoxyindolyl-3-acetonitrile) and arvelexin (4-methoxyindolyl-3-acetonitrile) by R. solani and S. sclerotiorum, but not by A. brassicicola. That is, desulfo-glucosinolates were metabolized by two non-host-selective pathogens, but not by a host-selective. Indolyl-3-acetonitrile, caulilexin C and arvelexin were metabolized to the corresponding indole-3-carboxylic acids. Indolyl-3-acetonitriles displayed higher inhibitory activity than indole desulfo-glucosinolates. Indolyl-3-methanol displayed antifungal activity and was metabolized by A. brassicicola and R. solani to the less antifungal compounds indole-3-carboxaldehyde and indole-3-carboxylic acid. Diindolyl-3-methane was strongly antifungal and stable in fungal cultures, but ascorbigen was not stable in solution and displayed low antifungal activity; neither compound appeared to be metabolized by any of the three fungal species. The cell-free extracts of mycelia of A. brassicicola displayed low myrosinase activity using glucobrassicin as substrate, but myrosinase activity was not detectable in mycelia of either R. solani or S. sclerotiorum.
Phytochemistry 09/2011; 72(18):2308-16. · 3.35 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Phytopathogenic fungi are able to overcome plant chemical defenses through detoxification reactions that are enzyme mediated. As a result of such detoxifications, the plant is quickly depleted of its most important antifungal metabolites and can succumb to pathogen attack. Understanding and predicting such detoxification pathways utilized by phytopathogenic fungi could lead to approaches to control plant pathogens. Towards this end, the inhibitory activities and metabolism of the cruciferous phytoalexins camalexin, brassinin, cyclobrassinin, and brassilexin by the phytopathogenic fungus Botrytis cinerea Pers. (teleomorph: Botryotinia fuckeliana) was investigated. Brassilexin was the most antifungal of the phytoalexins, followed by camalexin, cyclobrassinin and brassinin. Although B. cinerea is a species phylogenetically related to the phytopathogenic fungus Sclerotinia sclerotiorum (Lib) de Bary, contrary to S. sclerotiorum, detoxification of strongly antifungal phytoalexins occurred via either oxidative degradation or hydrolysis but not through glucosylation, suggesting that glucosyl transferases are not involved. A strongly antifungal bisindolylthiadiazole that B. cinerea could not detoxify was discovered, which resulted from spontaneous oxidative dimerization of 3-indolethiocarboxamide, a camalexin detoxification product.
Phytochemistry 02/2011; 72(2-3):199-206. · 3.35 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Salt cress (Thellungiella salsuginea also known as T. halophila) is a wild cruciferous extremophile highly resistant to salt, drought, and cold. The recent discovery that salt cress produces the phytoalexins wasalexins A and B, and the phytoanticipins 1-methoxyglucobrassicin and 4-methoxyglucobrassicin in relatively higher amounts than other cruciferous species, prompted investigation of their biosynthetic relationships. Toward this end, perdeuterated 1-methoxybrassinin, l-Trp, glucobrassicin, 1-methoxyindolyl-3-acetaldoxime, brassinin, and methionine, as well as the corresponding natural abundance compounds, were administered to salt cress plants previously irradiated with UV-light (λ(max) 254 nm). Remarkably, administration of hexadeuterated glucobrassicin led to incorporation of several deuterium atoms into wasalexins A and B, 1-methoxyglucobrassicin and 4-methoxyglucobrassicin. This unprecedented discovery suggests that glucobrassicin is a biosynthetic precursor of wasalexins and methoxylated glucosinolates in salt cress.
Organic & Biomolecular Chemistry 11/2010; 8(22):5150-8. · 3.70 Impact Factor
