Microbial Transformations of Clomazone

Common soil fungi and bacteria were screened for their abilities to biotransform the herbicide clomazone (2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone) into metabolites. Preparative-scale incubations were conducted with Aspergillus niger (UI-X172) and Cunninghamella echinulata (NRRL-3655) to obtain metabolites in sufficient quantities for spectral and chromatographic identification. HPLC analyses were used to assess the capacities of 41 microorganisms to metabolize the herbicide. Based on comparisons with authentic standard compounds and on the structures of metabolites ascertained by 1 H NMR and mass spectrometry, major microbial transformation reactions involved hydroxylation at the 5-methylene carbon of the isoxazolidone ring, hydroxylation of a methyl group on the oxazolidone ring, and aromatic hydroxylation at position 3‘. Minor metabolic routes included dihydroxylations of clomazone on the aromatic ring, cleavage of the isoxazolidone N−C bond, or complete removal of the isoxazolidone ring to form chlorobenzyl alcohol.