Identification and formation pathway of laccase-mediated oxidation products formed from hydroxyphenylureas.

Hydroxyphenylureas are the first main metabolites formed in the environment from pesticide and biocide urea compounds. Because fungi release potent exocellular oxidases, we studied the ability of laccases produced by the white rot fungus, T. versicolor, to catalyze in vitro the transformation of five hydroxyphenylureas, to identify transformation pathways and mechanisms. Our results establish that the pH of the reaction has a strong influence on both the kinetics of the reaction and the nature of the transformation products. Structural characterization by spectroscopic methods (NMR, mass spectrometry) of eleven transformation products shows that laccase oxidizes the substrates to quinones or to polyaromatic oligomers. Slightly acidic conditions favor the formation of quinones as final transformation products. In contrast, at pH 5-6, the quinones further react with the remaining substrate in solution to give hetero-oligomers via carbon-carbon or carbon-oxygen bond formation. A reaction pathway is proposed for each of the identified products. These results demonstrate that fungal laccases could assist the transformation of hydroxyphenylureas.

Synthesis of polyoxygenated bicyclic systems containing medium-sized rings from carbohydrates via tandem metathesis of dienynes.

[reaction: see text] Highly functionalized (5-7), (5-8), and (6-8) ring systems have been prepared from carbohydrates via tandem ring-closing metathesis of dienynes.

The insect attractant 1-octen-3-ol is the natural ligand of bovine odorant-binding protein.

Bovine odorant-binding protein (bOBP) is a dimeric lipocalin present in large amounts in the respiratory and olfactory nasal mucosa. The structure of bOBP refined at 2.0-A resolution revealed an elongated volume of electron density inside each buried cavity, indicating the presence of one (or several) naturally occurring copurified ligand(s) (Tegoni et al. (1996) Nat. Struct. Biol. 3, 863-867; Bianchet et al. (1996) Nat. Struct. Biol. 3, 934-939). In the present work, by combining mass spectrometry, x-ray crystallography (1.8-A resolution), and fluorescence, it has been unambiguously established that natural bOBP contains the racemic form of 1-octen-3-ol. This volatile substance is a typical component of bovine breath and in general of odorous body emanations of humans and animals. The compound 1-octen-3-ol is also an extremely potent olfactory attractant for many insect species, including some parasite vectors like Anopheles (Plasmodium) or Glossina (Trypanosoma). For the first time, a function can be assigned to an OBP, with a possible role of bOBP in the ecological relationships between bovine and insect species.

Cleavage of the diketonitrile derivative of the herbicide isoxaflutole by extracellular fungal oxidases.

Isoxaflutole is a herbicide activated in soils and plants to its diketonitrile derivative, the active herbicide principle. The diketonitrile derivative undergoes cleavage to the inactive benzoic acid analogue. In this paper, it is established that an oxidative mechanism implicating two successive reactions in the presence of dimethyldioxirane can chemically initiate the cleavage of the diketonitrile. It is also shown that two white rot strains, Phanerochaete chrysosporium and Trametes versicolor, are able to convert the diketonitrile to the acid when cultured in liquid media. This main metabolite amounts to 24.6 and 15.1% of initial herbicide content after 12-15 days of culture. Another polar metabolite represents <3.7% of the parent compound amount during the same period. Oxidative enzymes produced by the fungi show a time course similar to that of diketonitrile degradation. Purified laccase (EC 1. 10.3.2), in the presence of 2 mM 2, 2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) acting as a redox mediator at pH 3 supports the reaction with rates of 0.3-0.4 nmol h(-)(1) unit(-)(1).

Sex pheromone of the oleander scale, Aspidiotus nerii: structural characterization and absolute configuration of an unusual functionalized cyclobutane.

The sex pheromone emitted by the female oleander scale, Aspidiotus nerii (Homoptera, Diaspididae), has been isolated and characterized as (1R, 2S)-cis-2-isopropenyl-1-(4'-methyl-4'-penten-1'-yl)cyclobutaneethanol acetate by using advanced MS and NMR spectroscopic methods, as well as a variety of microderivatization sequences. The structure has been confirmed by stereo- and enantioselective synthesis of the four possible stereoisomers. The absolute configuration has been determined by comparison of the activity of the cis (1S,2R) and (1R, 2S) enantiomers with that exhibited by the natural material in greenhouse bioassays and field tests. The structure of this sesquiterpenoid pheromone is new in the coccids and in the pheromone field in general.

Biological activities of the nortropane alkaloid, calystegine B2, and analogs: structure-function relationships.

Calystegines, polyhydroxy nortropane alkaloids, are a recently discovered group of plant secondary metabolites believed to influence rhizosphere ecology as nutritional sources for soil microorganisms and as glycosidase inhibitors. Evidence is presented that calystegines mediate nutritional relationships under natural conditions and that their biological activities are closely correlated with their chemical structures and stereochemistry. Assays using synthetic (+)- and (-)-enantiomers of calystegine B2 established that catabolism by Rhizobium meliloti, glycosidase inhibition, and allelopathic activities were uniquely associated with the natural, (+)-enantiomer. Furthermore, the N-methyl derivative of calystegine B2 was not catabolized by R. meliloti, and it inhibited alpha-galactosidase, but not beta-glucosidase, whereas the parent alkaloid inhibits both enzymes. This N-methyl analog therefore could serve to construct a cellular or animal model for Fabry's disease, which is caused by a lack of alpha-galactosidase activity.