Generation and analysis of mixed chlorinated/brominated homologs of the halogenated natural product heptachloro-1'-methyl-1,2'-bipyrrole

Publikations-Art

Zeitschriftenbeitrag

Autoren

Dambacher, W. B.; Rosenfelder, N.; Conrad, J.; Vetter, W.

Erscheinungsjahr

2011

Veröffentlicht in

Chemosphere

Band/Volume

83/7

DOI

10.1016/j.chemosphere.2011.02.038

Seite (von - bis)

948 - 954

The 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1, MBP-79) and further halogenated 1'-methyl-1,2'-bipyrroles (MBPs) are a class of marine natural products repeatedly detected in seafood and marine mammals from all over the world. Only Q1 is currently com. available as ref. std. and the full synthesis of mixed brominated-chlorinated compd. is rather complicated.  For this reason, synthetic Q1 (240 mg) was transferred into bromine-contg. MBPs by UV-irradn. in the presence of bromine. Bromine, which rapidly vanished from the solns., was re-newed during the reaction in order to generate higher amts. of Br-contg. MBPs. A total of ∼150 mg Q1 was transferred after ∼10 min irradn. with high amts. of Br₂ to give 30.5 mg BrCl₆-MBPs along with lower proportions of Br₂Cl₅-, Br₃Cl₄-, Br₄Cl₃-, and traces of Br₅Cl₂-MBPs. Longer UV-irradn. in the presence of Br₂ even allowed for the detection of Br₆Cl-MBPs and traces of Br₇-MBP. However, this reaction also provided some unknown byproducts. A sample stored in the dark and later in in-door light (no UV irradn.) also eliminated Q1 after 76 d in favor of heptahalogenated MBPs with up to three bromine substituents. The irradn. products were sepd. on silica, and fractions contg. only Q1 and BrCl₆-MBPs were then further fractionated by non-aq. RP-HPLC. A pure isolate of the major BrCl₆-MBP (∼1.5 mg) was characterized by GC/MS and ¹³C NMR to be 2-bromo-3,3',4,4',5,5'-hexachloro-1-methyl-1,2'-bipyrrole (Br-MBP-75). Partial GC enantiosepn. of the axially chiral Br-MBP-75 was achieved on a β-PMCD column. A full enantiosepn. was managed by enantioselective HPLC using a NUCLEOCEL DELTA S column. Low amts. of pure BrCl6-MBP enantiomers could be trapped.