Differential Routes of Metabolism of Imidazolinones: Basis for Soybean ( Glycine max) Selectivity

Imazaquin and imazethapyr are soybean-selective herbicides. The major factor for the selectivity of these imidazolinone herbicides is the ability of soybeans to rapidly metabolize the herbicides to inactive compounds. Metabolites of these herbicides were isolated and characterized by synthesis and mass spectrometry. The metabolic pathway of imazaquin involved the cyclization of the imidazolinyl nitrogen and the carboxyl group followed by rapid degradation to one major and three minor metabolites. Imazethapyr, on the other hand, is hydroxylated at the 5-ethyl substituent of the pyridine ring followed by O-glucosylation. The differential routes of metabolism of these two imidazolinone herbicides in soybean are typical examples of oxidation, ring cleavage, and conjugation metabolic reactions in the herbicide detoxification mechanisms.