Transformation experiments with two chiral endosulfan metabolites by soil microorganisms — CHIRAL HRGC on lipophilic cyclodextrin derivatives

Abstract

Two chiral metabolites of the hexachlorinated cyclodien insecticide endosulfan, C₉H₆Cl₆O₃S, the endosulfan hydroxyether and the endosulfan lactone, were separated into their enantiomers using lipophilic β-cyclodextrin derivatives in chiral high-resolution gas chromatography (CHRGC). We separated the hydroxyether on heptakis-(2,3,6-tri-O-pentyl)-β-cyclodextrin (LIPODEX-C) and the endosulfan lactone on heptakis-(3-O-acetyl-2,6-di-O-pentyl)-β-cyclodextrin (LIPODEX-D). We also investigated the enantioselective formation and transformation of these two metabolites by soil organisms. To approximate real world conditions of microbiological transformation, incubation experiments with mixed cultures of soil microorganisms were carried out. Significant differences were observed in the transformation experiments under aerobic and anaerobic conditions. The endosulfan hydroxyether (ESH) is not formed enantioselectively from prochiral endosulfan diol (ESD) in the aerobic transformation pathway. The hydroxyether itself is enantioselectively converted to the endosulfan lactone (ESL) as a major pathway only under aerobic conditions. Corresponding enantiomers of endosulfan hydroxyether and endosulfan lactone with the same absolute configuration could be assigned. The lactone enantiomers are stereoselectively formed via the hydroxyether as a minor pathway under anaerobic conditions. While the first eluting lactone enantiomer was more abundant in the aerobic experiment, it was the second eluting under anaerobic conditions. Four major so far unidentified metabolites were detected in the anaerobic incubations of both the endosulfan hydroxyether and the endosulfan diol.