[H-3] 2,3,7,8-TETRACHLORODIBENZOFURAN (TCDF)-SYNTHESIS AND CHARACTERIZATION AS A RADIOLIGAND FOR THE AH RECEPTOR
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abstract
2,6-Dichloroaniline was reacted with 2,5-dichlorophenol in the presence of isoamyl nitrite to give a mixture of chlorinated biphenylols which were purified by thin-layer chromatography. The resulting products were cyclized to give 1,4,9-trichlorodibenzofuran (purity > 98%) which was converted into 1,4,9-[3H3]-dibenzofuran by catalytic chlorinetritium exchange. The [3H]-dibenzofuran was chlorinated in chloroform solution and the crude chlorination products were separated by preparative HPLC to give [3H]-2,3,7,8-TCDF, specific activity, 57 Ci/mmol. The binding of [3H]-2,3,7,8-TCDF to the cytosolic Ah receptor resembles that of [3H]-TCDD. The receptor binding affinity as determined from the Scatchard plot is slightly less for [3H]-TCDF (Kd=0.95 nm) than for [3H]-TCDD (Kd=0.60 nM). The mechanism of binding each radioligand to the Ah receptor is similar and occurs in the absence of detectable positive cooperativity. However, for quantification, the use of [3H]-TCDF is distinctly advantageous over [3H]-TCDD because the ease of dissociation of the [3H]-TCDF-Ah receptor complex is much greater than that of the [3H]-TCDD-Ah receptor complex. Because of the ease of reversibility of binding, [3H]-TCDF appears to be the superior radioligand for the in vitro characterization of the Ah receptor. 1987.
