Characterization and Biological Potency of Mono- to Tetra-Halogenated Carbazoles

This paper deals with the characterization and aryl hydrocarbon receptor (AhR) agonist activities of a series of chlorinated, brominated, and mixed bromo/chlorocarbazoles, some of which have been identified in various environmental samples. Attention is directed here to the possibility that halogenated carbazoles may currently be emitted into the environment as a result of the production of carbazole-containing polymers present in a wide variety of electronic devices. We have found that any carbazole that is not substituted in the 1,3,6,8 positions may be lost during cleanup of environmental extracts if a multilayer column is utilized, as is common practice for polychlorinated dibenzo-p-dioxin (dioxin) and related compounds. In the present study, (1)H NMR spectral shift data for 11 relevant halogenated carbazoles are reported, along with their gas chromatographic separation and analysis by mass spectrometry. These characterization data allow for confident structural assignments and the derivation of possible correlations between structure and toxicity based on the halogenation patterns of the isomers investigated. Some halogenated carbazoles exhibit characteristics of persistent organic pollutants and their potential dioxin-like activity was further investigated. The structure-dependent induction of CYP1A1 and CYP1B1 gene expression in Ah-responsive MDA-MB-468 breast cancer cells by these carbazoles was similar to that observed for other dioxin-like compounds, and the magnitude of the fold induction responses for the most active halogenated carbazoles was similar to that observed for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). 2,3,6,7-Tetrachlorocarbazole was one of the most active halogenated carbazoles and, like TCDD, contains 4 lateral substituents; however, the estimated relative effect potency for this compound (compared to TCDD) was 0.0001 and 0.0032, based on induction of CYP1A1 and CYP1B1 mRNA, respectively.

The alternating of substituent effect on the ¹³C NMR shifts of all bridge carbons in cinnamyl aniline derivatives

Bridge carbon (13)C NMR shifts of a wide set of substituted cinnamyl anilines p-XC(6)H(4)CHCHCHNC(6)H(4)Y-p (XNO(2), Cl, H, Me, MeO, or NMe(2); YNO(2), CN, CO(2)Et, Cl, F, H, Me, MeO or NMe(2)) had been used as a probe to study the change of substituent effect in the conjugated system. The goal of this work was to study the difference among the substituent effect on SCS of all bridge carbons, and find the alternating of substituent effect in this model compounds. In this study, it was found that the change of the inductive effect and the conjugative effect on different bridge carbons is related to the bond number (m) from the substituent to the corresponding carbon, and the adjusted parameters σ(F(rel))(∗) and σ(R(ver))(∗) can be suitable to scale the difference of the inductive effect and the conjugative effect on bridge carbons. Moreover, because of the difference of substituent effect on bridge carbons, the substituent cross-interaction item Δσ(2)(Δσ(2) = (σ(F(rel))(∗)(X) + σ(R(ver))(∗)(X) - σ(F(rel))(∗)(Y) - σ(R(ver))(∗)(Y))(2)) was not suitable simply to scale the interaction between substituents X and Y for all bridge carbons, so the Δσ(2) was recommended to be divided into two parts: Δσ(F(rel))(2) (Δσ(F(rel))(2) = σ(F(rel))(∗)(X) - σ(F(rel))(∗)(Y))(2)) and Δσ(R(ver))(2) (Δσ(R(ver))(2) = (σ(R(ver))(∗)(X) - σ(R(ver))(∗)(Y))(2)). With σ(F(rel))(∗), σ(R(ver))(∗), Δσ(F(rel))(2), Δσ(R(ver))(2), and δ(C,parent), the obtained correlation equation can be used to correlate with the 159 sorts of SCS of the different bridge carbon in cinnamyl aniline derivatives. The correlation coefficient is 0.9993, and the standard deviation is only 0.53 ppm. The multi-parameter correlation equation can be recommended to predict well the corresponding bridge carbons SCS of disubstituted cinnamyl anilines.

Degradative fate of 3-chlorocarbazole and 3,6-dichlorocarbazole in soil

BACKGROUND, AIM, AND SCOPE

3-Chlorocarbazole and 3,6-dichlorocarbazole were isolated from Bavarian soils. The stereospecific formation of the isomers of these chlorinated carbazols can be explained by quantum mechanical calculations using the DFT method. It was shown that chlorination of carbazole and 3-chlorocarbazole respectively is preferred via the sigma-complexes 3-chlorocarbazole and 3,6-dichlorocarbazole as the most stable products. The dioxin-like toxicological potential of 3,6-dichlorocarbazole, determined by the Micro-EROD Test, is in the range of some picogram TCDD equivalents per milligram carbazole. The degradative fate of 3-chlorocarbazole and 3,6-dichlorocarbazole was analysed within a long-term study (57 days) in soil.

MATERIALS AND METHODS

The soil was extracted by ASE (accelerated solvent extraction) and a further clean-up procedure with column chromatography and chromatography with C18-SPE stationary phases. Quantification of 3-chlorocarbazole and 3,6-dichlorocarbazole was performed employing the isotope-dilution method. The samples were measured with high-resolution GC/MS.

RESULTS

The degradation (ln(c/c(0)) vs. time with best-fit line) showed in almost every storage condition a very small degradation (slopes (h(-1)) in -10(-4) range). However, the decay for the controls were two to three times (-28°C) and six times (with sodium azide) higher, than the decrease of 3-chlorocarbazole and 3,6-dichlorocarbazole in the samples of environmental conditions.

DISCUSSION

Especially because of the toxicological potential of 3-chlorocarbazole and 3,6-dichlorocarbazole the proven degradative fate is of large interest. The results show that the analysed carbazoles are not readily degradable in this time period.

CONCLUSIONS

The expected results of exponential decay behaviour could not be proven.

RECOMMENDATION AND PERSPECTIVES

Longer-lasting studies are expected to reveal more accurate half-lives, although it has been shown here, that the compounds are not readily degradable in their native soil environment.