Relevance of enantiomeric separations in environmental science

Armstrong, Daniel W.; Reid, George L.; Hilton, M. L.; Chang, Chau Dung

doi:10.1016/0269-7491(93)90177-p

Cited by 74 publications

(27 citation statements)

References 16 publications

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Section: Cell Extracts Of Sphingomonas Herbicidovorans Mh Grown On (Rmentioning

confidence: 99%

“…Yet many commercial formulations contain the racemic mixtures and not the pure R enantiomers (27). In order to understand the environmental fate of the chiral compound mecoprop, it is important to study the degradation of the enantiomers independently, as has been recently emphasized (1,2,9,22,29).Studies concerning the fate and the persistence of phenoxyalkanoic acids in soil revealed that degradation of these herbicides is caused mainly by microorganisms (17, 23). The breakdown of 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4-D starts with the removal of the alkanoic acid side chain to yield the corresponding phenol (17).…”

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Involvement of two alpha-ketoglutarate-dependent dioxygenases in enantioselective degradation of (R)- and (S)-mecoprop by Sphingomonas herbicidovorans MH

1997

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Cell extracts of Sphingomonas herbicidovorans MH grown on (R)-mecoprop contained an enzyme activity that selectively converted (R)-mecoprop to 4-chloro-2-methylphenol, whereas extracts of cells grown on (S)-meco-prop contained an enzyme activity selective for the S enantiomer. Both reactions were dependent on ␣-ketoglutarate and ferrous ions. Besides 4-chloro-2-methylphenol, pyruvate and succinate were detected as products of the reactions. Labeling experiments with 18 O 2 revealed that both enzyme activities catalyzed a dioxygenation reaction. One of the oxygen atoms of pyruvate and one of the oxygen atoms of succinate were derived from molecular oxygen. Analysis of cell extracts obtained from cells grown on different substrates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that growth on (R)-mecoprop and (S)-mecoprop caused the appearance of prominent protein bands at 34 and 32 kDa, respectively. Both protein bands were present when cells grew on the racemic mixture. The results demonstrate that S. herbicidovorans initiated the degradation of each enantiomer of mecoprop by a specific ␣-ketoglutarate-dependent dioxygenase. By comparing conversion rates of various phenoxy herbicides, we confirmed that the two enzyme activities were distinct from that of TfdA, which catalyzes the first step in the degradation of 2,4-dichlorophenoxyacetic acid in Ralstonia eutropha JMP134.Substituted phenoxyalkanoic acid herbicides are widely used in weed control. 2,4-Dichlorophenoxyacetic acid (2,4-D) and the chiral compounds (R,S)-2-(4-chloro-2-methylphenoxy)propionic acid (mecoprop) and (R,S)-2-(2,4-dichlorophenoxy)propionic acid (dichlorprop) are members of this class of herbicides. The herbicidal activities of the last two compounds are exclusively associated with the R enantiomers. Today, the pure R enantiomers of mecoprop and of dichlorprop are commercially available as mecoprop-P and dichlorprop-P, respectively. Yet many commercial formulations contain the racemic mixtures and not the pure R enantiomers (27). In order to understand the environmental fate of the chiral compound mecoprop, it is important to study the degradation of the enantiomers independently, as has been recently emphasized (1,2,9,22,29).Studies concerning the fate and the persistence of phenoxyalkanoic acids in soil revealed that degradation of these herbicides is caused mainly by microorganisms (17, 23). The breakdown of 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4-D starts with the removal of the alkanoic acid side chain to yield the corresponding phenol (17). Consequently, a great deal of research effort was put into unravelling the subsequent degradation of 2,4-dichlorophenol and 4-chloro-2-methylphenol, the metabolites of 2,4-D and MCPA, respectively (10). In soil, the microbial metabolism of mecoprop leads to the appearance of 4-chloro-2-methylphenol (24). This metabolite is also formed in a mixed bacterial culture with mecoprop as the sole source of carbon and energy (14). So far, only two pure bacterial strains have be...

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Section: Cell Extracts Of Sphingomonas Herbicidovorans Mh Grown On (Rmentioning

confidence: 99%

mentioning

confidence: 99%

Involvement of two alpha-ketoglutarate-dependent dioxygenases in enantioselective degradation of (R)- and (S)-mecoprop by Sphingomonas herbicidovorans MH

1997

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“…Enantiomers often have different biological and physiological properties; therefore, investigations that treat racemates as though they were single entities can produce inaccurate and misleading results. 1,2 In many cases, one enantiomer can produce a completely different biological response than its corresponding antipode. 3,4 Almost all environmental regulations in the United States treat racemates as though they are single molecules with the same biological and physiological properties.…”

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Plant and soil enantioselective biodegradation of racemic phenoxyalkanoic herbicides

1999

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“…A prior immunoassay was used to detect diphacinone and chlorophacionone (Mount et al, 1988). Enantiomers of warfarin, coumachlor, and coumafuryl can be separated chromatographically (Armstrong et al, 1993).…”

Section: Methodsmentioning

confidence: 99%