Molecular docking studies of toluene dioxygenase led to the prediction that angular and lateral cis‐dihydroxylation of tricyclic arene and heteroarene substrates could occur. Biotransformations of biphenylene, dibenzofuran, carbazole and dibenzothiophene, using Pseudomonas putida UV4 whole cells, expressing toluene dioxygenase, confirmed that both angular and lateral cis‐dihydroxylation had occurred in the predicted regioselective and stereoselective manner. The toluene dioxygenase‐catalysed (Pseudomonas putida UV4) biotransformation of dibenzofuran was optimized, to produce 1,2‐dihydrodibenzofuran‐1,2‐diol as the major metabolite in excellent yield. 2‐Hydroxydibenzofuran, resulting from dehydration of 1,2‐dihydrodibenzofuran‐1,2‐diol, was also found to undergo cis‐ dihydroxylation to give a very minor cis‐dihydrodiol metabolite. The enantiopurity (>98% ee) and (1R,2S) absolute configuration of the major dibenzofuran cis ‐dihydrodiol was rigorously established by catalytic hydrogenation and formation of methoxy(trifluoromethyl)phenylacetate derivatives and by X‐ray crystallography of an epoxide derivative. Biotransformation of carbazole yielded anthranilic acid as the major metabolite and was consistent with angular cis‐dihydroxylation. Synthesis of a cis‐ diol epoxide derivative showed that the main cis‐dihydrodiol metabolite of dibenzofuran has potential in the chemoenzymatic synthesis of natural products.
Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark. 相似文献
The presence of nitrogen, oxygen and sulfur containing aromatic compounds, namely carbazole, dibenzofuran, dibenzothiophene and their alkylated derivatives was investigated in potential environmental sources of these compounds. The persistence vs biodegradation of the parental heteroaromatic compounds was determined using bacterial consortia collected from three marine beaches from coastal Newfoundland. Experiments were performed at 25 and 4°C and bacterial populations derive from differently contaminated environments. In separate studies, rainbow trout, Salmo gardneiri, were exposed to PACs through their diet and the bioelimination of glucuronide and sufate conjugates followed in the gall bladder bile after a single and during continuous exposure. Comparison was done between the presence and fate of the three heterocyclic PACs and that of fluorene. a PAH counterpart with similar structure and physical-chemical properties. The tissue distribution of the PACs (not presented) provides information on the potential narcotic and/or reproductive effect of the unreacted compounds and the metabolites on the potential toxicity of the oxidation products. 相似文献
