Photolytic dehalogenation of the marine halogenated natural product Q1 Original Research Article

The marine halogenated natural product 2,3,3′,4,4′,5,5′-heptachloro-1′-methyl-1,2′-bipyrrole (Q1) has been detected in high-trophic level biota throughout the world. In this study we UV-irradiated Q1 in order to produce hexahalogenated 1′-methylbipyrroles (Cl6-MBPs). Q1 was transformed with half-lives of <5 min. Already after 5 min, all of the five existing Cl6-MBPs (H1–H5) were detected in the irradiated sample. Only one Cl6-MBP (2,3,3′,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (MBP-77, H2) has been previously described in the literature. H5 was identified as 2,3,3′,4,4′,5′-hexachloro-1′-methyl-1,2′-bipyrrole (MBP-75) by a specific fragment ion detected by GC/ECNI–MS. Fractionations of the irradiation mixture by reversed-phase HPLC followed by 1H NMR analysis led to the structure of H4, i.e. 2,3,3′,4,4′,5-hexachloro-1′-methyl-1,2′-bipyrrole (MBP-74). H1 and H3 showed virtually identical 1H NMR data. Therefore, it could not determined which of either isomers is 2,3,3′,4,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (MBP-76) and which is 2,3,4,4′,5,5′-hexachloro-1′-methyl-1,2′-bipyrrole (MBP-78). In addition, two pentachloro-MBPs (P1 and P3) could be traced back to MBP-62 and MBP-69. Cl6-MBPs were analyzed in whale blubber from Australia and skua adipose tissue from Antarctica. The marine mammals contained all Cl6-MBPs except for the most abundant in the irradiation experiment. The concentrations of the Cl6-MBPs amounted to 0.04–1.76% of the concentration of Q1. The highest concentrations of Cl6-MBP isomers in the biota samples were found for MBP-76, MBP-77, and MBP-78. These congeners appeared to be the most lipophilic ones owing to the highest retention time in RP–HPLC. Nevertheless, it remained unclear whether the Cl6-MBPs were actual halogenated natural products or environmental metabolites of Q1.