title: Enantioseparation and absolute configuration of the atropisomers of a naturally produced hexahalogenated 1,1'-dimethyl-2,2'-bipyrrole.
abstract: Hexahalogenated 1,1'-dimethyl-2,2'-bipyrroles (HDBPs) are a group of marine halogenated natural products (HNPs) that have been detected in environmental samples from all over the world. The most frequently described congener is the 5,5'-dichloro-1,1'-dimethyl-3,3',4,4'-tetrabromo-2,2'-bipyrrole (DBP-Br(4)Cl(2), BC-10). This compound is axially chiral, by virtue of hindered rotation about the interannular pyrrole-pyrrole bond forming stable atropisomers. This effect was proven by the separation of synthesized racemic DBP-Br(4)Cl(2) by enantioselective high performance liquid chromatography (HPLC). Pure enantiomers were isolated using enantioselective HPLC. Crystallization led to white crystals studied by X-ray analyses to determine the absolute configuration. Subsequent polarimetric measurements verified the first eluting enantiomer on HPLC as R(a)-(+)-DBP-Br(4)Cl(2) and the second as S(a)-(-)-DBP-Br(4)Cl(2). We also investigated the gas chromatography (GC) enantioseparation of DBP-Br(4)Cl(2). However, too high temperatures in the injector port led to partial racemization at temperatures >150 degrees C. GC coupled to mass spectrometry was used to study DBP-Br(4)Cl(2) in marine mammal samples. All samples contained both atropisomers of the natural product DBP-Br(4)Cl(2) with enrichment of the levo (-) enantiomer. This led to the assumption that both enantiomers of DBP-Br(4)Cl(2) were already produced in the environment.
authors.affiliation: Institute of Food Chemistry (170b), University of Hohenheim, Garbenstr. 28, 70599 Stuttgart, Germany.
authors.forename: Natalie
authors.initials: N
authors.lastname: Rosenfelder
authors.forename: Patrizia
authors.initials: P
authors.lastname: Ostrowicz
authors.forename: Liangfeng
authors.initials: L
authors.lastname: Fu
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Gribble
authors.forename: Sheryl A
authors.initials: SA
authors.lastname: Tittlemier
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Frey
authors.forename: Walter
authors.initials: W
authors.lastname: Vetter
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003460:Crystallization; D015394:Molecular Structure; D011758:Pyrroles / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D011758:Pyrroles