Synthesis, structure elucidation, and determination of polyhalogenated N-methylpyrroles (PMPs) in blue mussels

Polyhalogenated N-methylpyrroles (PMPs) are halogenated natural products (HNPs) recently detected in seagrass, blue mussels, and other marine organisms. In this study, we synthesized 2,3,4,5-tetrachloro-N-methylpyrrole (Cl-MP), 2,3,4,5-tetrabrominated-N-methylpyrrole (Br-MP, aka TBMP), and mixed tetrahalogenated (Cl and Br) N-methylpyrrole congeners. Use of one- and two-dimensional H and C NMR verified the structures of isolated/enriched 3,4-dibromo-2,5-dichloro-N-methylpyrrole (3,4-Br-2,5-Cl-MP), 2,3,4-tribromo-5-chloro-N-methylpyrrole (2,3,4-Br-5-Cl-MP), and 3-bromo-2,4,5-trichloro-N-methylpyrrole (3-Br-2,4,5-Cl-MP). GC/EI-MS and GC/ECNI-MS mass spectra of the five PMPs were studied with regard to fragmentation pattern and individual responses which were strongly affected by the presence (or absence) of Br in α-position(s). Quantitative solutions of the synthesized standards were used to determine the elution order of isomers and to quantify PMPs in selected blue mussel samples (Mytilus sp.) from the European Atlantic coast (Spain, France), the North Sea (the Netherlands, Germany) and Baltic Sea (Germany). PMPs were detected in all samples and the concentrations ranged between 0.6 and 52 μg/kg lipids with Br-MP being the most abundant representative of this substance class.