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[摘要]：Polychlorinated biphenyls (PCBs) comprise a group of persistent org. pollutants that differ significantly in their physicochem. properties, their persistence, and their biol. activities. They can be metabolized via hydroxylated and dihydroxylated metabolites to PCB quinone intermediates. We have recently demonstrated that both dihydroxy PCBs and PCB quinones can form semiquinone radicals (SQ?) in vitro. These semiquinone radicals are reactive intermediates that have been implicated in the toxicity of lower chlorinated PCB congeners. Here we describe the synthesis of selected PCB metabolites with differing degrees of chlorination on the oxygenated Ph ring, e.g., 4,4'-dichloro-biphenyl-2,5-diol, 3,6,4'-trichloro-biphenyl-2,5-diol, 3,4,6,-trichloro-biphenyl-2,5-diol, and their corresponding quinones. In addn., two chlorinated o-hydroquinones were prepd., 6-chloro-biphenyl-3,4-diol and 6,4'-dichloro-biphenyl-3,4-diol. These PCB (hydro-)quinones readily react with oxygen or via comproportionation to yield the corresponding semiquinone free radicals, as detected by ESR spectroscopy (EPR alias ESR). The greater the no. of chlorines on the (hydro-)quinone (oxygenated) ring, the higher the steady-state level of the resulting semiquinone radical at near neutral pH. |
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