Stereoselective degradation and microbial epimerization of triadimenol in soils

Triadimenol is a widely used triazole fungicide and consists of four stereoisomers with 1R,2S, 1S,2R, 1R,2R, and 1S,2S configurations. The trans-enantiomeric pair (1R,2S-isomer and 1S,2R-isomer) is also called triadimenol-A and the cis-enantiomeric pair (1R,2R-isomer and 1S,2S-isomer) triadimenol-B. In this study, the stereoselective degradation and chiral stability of triadimenol in two soils were investigated in details. The dissipation of technical triadimenol, a 6:1 mixture of triadimenol-A and triadimenol-B, showed significant epimerization from triadimenol-A to triadimenol-B occurred along with the dissipation process. The degradation exhibited some stereoselectivity, resulting in a concentration order of 1S,2S > 1R,2R > 1R,2S > 1S,2R or 1S,2S > 1R,2R > 1S,2R > 1R,2S at the end of the 100 days incubation for Baoding soil or Wuhan soil, respectively. Further incubation of triadimenol-B revealed no epimerization, i.e. triadimenol-B was configurationally stable in soil, and 1R,2R-triadimenol degraded slightly slower in the former part and slightly faster in the later part of the incubation than 1S,2S-triadimenol. Moreover, by incubation of enantiopure 1S,2R-triadimenol and 1R,2S-triadimenol, the results documented the epimerization for each enantiomer occurred at both C-1 and C-2 positions. Finally, the present work also documented that the enantiomerization reaction for all the four stereoisomers was nearly negligible in the soils.