Diphenyl ether structure

Thalrugosamine is the methyl ether of thaligosine and thaligosinine, (33 R = = Me)/ Thalidezine has the isomeric diphenyl ether structure (42 ... 

The polybrominated diphenyl ethers (PBDEs) are an important class of semi-volatile, persistent organic pollutants. These species are of anthropogenic origin, and are used as flame retardants in electronics, fabrics, and furniture. Theoretically, there are 209 different PBDE congeners that result from the presence of 1-10 bromine atoms on the basic diphenyl ether structure ... 

Wang YW, Liu HX, Zhao CY, Liu HX, Cai ZW, Jiang GB. Quantitative structure-activity relationship models for prediction of the toxicity of polybrominated diphenyl ether congeners. Environ Sci Technol 2005 39 4961-6. 

The structural range of industrially important representatives of these groups is enormous, and includes chlorobenzenes (solvents), polychlorinated biphenyls (PCBs) (hydraulic and insulating fluids), and polybrominated biphenyls and diphenyl ethers (flame retardants). There is widespread concern over both the persistence and the potential toxicity of all these compounds, and sites that have become contaminated during their production represent a threat both to the environment and to human health. Pathways for the aerobic bacterial degradation of chlorobenzenes and chlorobiphe-nyls, and their brominated analogs have been discussed in Chapter 9, Part 1. 

Detailed discussion of these findings will be presented elsewhere. Here we only wish to point out that responses to a hydrogen donor tend to be critically affected by minor structural differences between the compounds. Thus, while diphenyl ether remains substantially unaffected by the donor, its hydroxy-derivatives (phenoxy phenols) often display fairly high reactivity. Taken in conjunction with the failure of low-rank coals (7) and phenoxy phenols (10) to suffer reductive cleavage when treated with sodium in liquid ammonia, this lends some support for the existence of phenoxy phenol entities in low rank coals. 

Fig. 7 Generic chemical structures of polyhalogenated compounds. X=C1, Br. (I) Polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs) (II) chlorophenols (CPs), bromophenols (BPs) (III) polychlorinated diphenyl ethers (PCDE), polybrominated diphenyl ethers (PBDE) (IV) polychlorinated dibenzo-p-dioxin (PCDD), polybrominated dibenzo-p-dioxin (PBDD) (V) polychlorinated dibenzofuran (PCDF), polybrominated dibenzofuran (PBDF) (VI) tetrabromobisphenol A (TBBPA)...

Fig. 4.6 Chemical structures of (a) tetrabromobisphenol A (TBBPA), (b) hexabromocyclodo-decane (HBCD), and (c) polybrominated diphenyl ethers (PBDEs)...

Figure 18.6 Basic structure and three-dimensional view of a polybrominated diphenyl ether (PBDE).

Polybrominated Diphenyl Ethers. Three main metabolic peaks were identified in the feces from rats fed reagent-grade decaBDE for 8 days (El Dareer et al. 1987). Of the total decaBDE-derived radioactivity recovered in the feces, 1.5-27.9% constituted metabolites. Since absorption of decaBDE is minimal, El Dareer et al. (1987) suggested that metabolism apparently took place in the gastrointestinal tract. In parallel experiments in rats injected C-decaBDE intravenously, feces and gut contents contained 74% of the administered radioactivity 72 hours after the injection, and 63% of the excreted material was metabolites. In rats dosed intravenously with C-dccaBDE and with biliary cannulas, 7.17% of the dose appeared in the bile, and <1% of this amount was unchanged decaBDE. Only one metabolite was detected. The structure of the metabolites detected in these experiments was not defined. 

PBBs and PBDEs may also cause toxicity by other mechanisms of action. For example, some PBB congeners can be metabolized to reactive arene oxides (Kohli and Safe 1976 Kohli et al. 1978) that may alkylate critical cellular macromolecules and result in injury. PBDEs may disrupt thyroid hormones by induction of hepatic microsomal UDPGT, which increases the rate of T4 conjugation and excretion, or by mimicking T4 or T3 PBDEs and their hydroxy metabolites are structurally similar to these thyroid hormones which are also hydroxy-halogenated diphenyl ethers (see Section 3.5.2). Clinical interventions designed to interfere with this mechanism or the metabolism of PBBs have yet to be developed. 

Polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) are each classes of structurally similar brominated hydrocarbons. PBBs are a class of chemical compounds in which 2 10 bromine atoms are attached to the biphenyl molecule. PBDEs are a class of chemical confounds in which 2 10 bromine atoms are attached to the diphenyl ether molecule. Monobrominated structures (i.e., one bromine atom attached to the molecule) are often included when describing PBBs and PBDEs. The general chemical structures of PBBs and PBDEs are similar when viewed in one dimension, differing only in an ether linkage, as shown below ... 

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