title: A novel metabolic pathway for degradation of 4-nonylphenol environmental contaminants by Sphingomonas xenophaga Bayram: ipso-hydroxylation and intramolecular rearrangement.
abstract: Several nonylphenol isomers with alpha-quaternary carbon atoms serve as growth substrates for Sphingomonas xenophaga Bayram, whereas isomers containing hydrogen atoms at the alpha-carbon do not. Three metabolites of 4-(1-methyloctyl)-phenol were isolated in mg quantities from cultures of strain Bayram supplemented with the growth substrate isomer 4-(1-ethyl-1,4-dimethyl-pentyl)-phenol. They were unequivocally identified as 4-hydroxy-4-(1-methyl-octyl)-cyclohexa-2,5-dienone, 4-hydroxy-4-(1-methyl-octyl)-cyclohex-2-enone, and 2-(1-methyl-octyl)-benzene-1,4-diol by high pressure liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. Furthermore, two metabolites originating from 4-n-nonylphenol were identified as 4-hydroxy-4-nonyl-cyclohexa-2,5-dienone and 4-hydroxy-4-nonyl-cyclohex-2-enone by high pressure liquid chromatography-mass spectrometry. We conclude that nonylphenols were initially hydroxylated at the ipso-position forming 4-alkyl-4-hydroxy-cyclohexa-2,5-dienones. Dienones originating from growth substrate nonylphenol isomers underwent a rearrangement that involved a 1,2-C,O shift of the alkyl moiety as a cation to the oxygen atom of the geminal hydroxy group yielding 4-alkoxyphenols, from which the alkyl moieties can be easily detached as alcohols by known mechanisms. Dienones originating from nongrowth substrates did not undergo such a rearrangement because the missing alkyl substituents at the alpha-carbon atom prevented stabilization of the putative alpha-carbocation. Instead they accumulated and subsequently underwent side reactions, such as 1,2-C,C shifts and dihydrogenations. The ipso-hydroxylation and the proposed 1,2-C,O shift constitute key steps in a novel pathway that enables bacteria to detach alpha-branched alkyl moieties of alkylphenols for utilization of the aromatic part as a carbon and energy source.
authors.affiliation: Swiss Federal Institute for Environmental Science and Technology, CH-8600 Dübendorf, Switzerland, Materials Science and Technology, CH-8600 Dübendorf, Germany.
authors.forename: Frédéric L P
authors.initials: FL
authors.lastname: Gabriel
authors.forename: Andy
authors.initials: A
authors.lastname: Heidlberger
authors.forename: Daniel
authors.initials: D
authors.lastname: Rentsch
authors.forename: Walter
authors.initials: W
authors.lastname: Giger
authors.forename: Klaus
authors.initials: K
authors.lastname: Guenther
authors.forename: Hans-Peter E
authors.initials: HP
authors.lastname: Kohler
mesh_terms: D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D004785:Environmental Pollutants / Q000378:metabolism*; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D010636:Phenols / Q000378:metabolism*; D020578:Sphingomonas / Q000378:metabolism*; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D004785:Environmental Pollutants; D010636:Phenols; C041594:4-nonylphenol