RP6 Chiral Chemistry: Toxicology of Environmental Contaminants and Phase Transfer
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(LAO-1117-844033) Enantioselective Degradation and Algal Phytotoxicity of Imidazolinone Herbicides.

Lao, Wenjian¹, Gan, Jay¹, ¹ University of California, Riverside, CA

ABSTRACT- Imidazolinones are a class of low-use-rate herbicides. They have excellent activity against annual and perennial grasses and broad-leaved weeds when applied either pre- or post-emergence. Acetohydroxy acid synthase (AHAS) is an essential enzyme for many organisms, but not in animals. It catalyzes the first step in the biosynthesis of the branched-chain amino acids valine, isoleucine, and leucine. Imidazolinones act by inhibiting AHAS. The two enantiomers of Imidazolinone herbicides result from a chiral center contained in the imidazolinone ring that is a common feature of all members of its class. The imidazolinone enantiomers have been shown to have different herbicidal activities, with the R isomer eight-times more inhibitory to AHAS than the S isomer. Imidazolinone herbicides are currently used as a racemic mixture. Additionally, it was reported to persist in soil. Presently, little is known about the differences in the enantioselective degradation and acute phytotoxicity of imidazoline herbicides. In this study, a method for the chromatographic chiral separation of imidazolinone isomers was developed. Enantiomer resolution and separation were carried out on HPLC using derivatized cellulose stationary phase OD-R and OJ column. Various soil samples were spiked with racemic imazapyr, imazethapyr and imazaquin, and incubated under sterile and nonsterile conditions at room temperature. Degradation curves were fitted on a first-order decay model. Degradation in the tested soil samples was found to be enantioselective. Differences in algal growth inhibition between enantiomers were also observed in standard toxicity tests with Selenastrum capricornutum.

Key words: Imidazolinone herbicides, Enantioselective Degradation, Algal Phytotoxicity, chiral separation