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Detoxifying carcinogenic polyhalogenated quinones by hydroxamic acids via an unusual double Lossen rearrangement mechanism. Proc Natl Acad Sci U S A 2010 Nov 30;107(48):20686-90

Date

11/16/2010

Pubmed ID

21076034

Pubmed Central ID

PMC2996439

DOI

10.1073/pnas.1010950107

Scopus ID

2-s2.0-78650583096 (requires institutional sign-in at Scopus site)   57 Citations

Abstract

Hydroxamic acids, which are best-known for their metal-chelating properties in biomedical research, have been found to effectively detoxify the carcinogenic polyhalogenated quinoid metabolites of pentachlorophenol and other persistent organic pollutants. However, the chemical mechanism underlying such detoxication is unclear. Here we show that benzohydroxamic acid (BHA) could dramatically accelerate the conversion of the highly toxic tetrachloro-1, 4-benzoquinone (p-chloranil) to the much less toxic 2,5-dichloro-3, 6-dihydroxy-1, 4-benzoquonine (chloranilic acid), with rate accelerations of up to 150,000-fold. In contrast, no enhancing effect was observed with O-methyl BHA. The major reaction product of BHA was isolated and identified as O-phenylcarbamyl benzohydroxamate. On the basis of these data and oxygen-18 isotope-labeling studies, we proposed that suicidal nucleophilic attack coupled with an unexpected double Lossen rearrangement reaction was responsible for this remarkable acceleration of the detoxication reaction. This is the first report of an unusually mild and facile Lossen-type rearrangement, which could take place under normal physiological conditions in two consecutive steps. Our findings may have broad biological and environmental implications for future research on hydroxamic acids and polyhalogenated quinoid carcinogens, which are two important classes of compounds of major biomedical and environmental interest.

Author List

Zhu BZ, Zhu JG, Mao L, Kalyanaraman B, Shan GQ

Author

Balaraman Kalyanaraman PhD Professor in the Biophysics department at Medical College of Wisconsin




MESH terms used to index this publication - Major topics in bold

Anions
Benzoquinones
Carcinogens
Environment
Hydrocarbons, Halogenated
Hydrolysis
Hydroxamic Acids
Mass Spectrometry
Models, Chemical
Quinones