Eight triazolopyrimidine sulfonanilides were tested for metabolic stability in a number of crop and weed species. These data, along with in vitro determinations of activity (I50) against acetolactate synthase, successfully described the in vivo activity of these compounds in a two-parameter model. Whole plant activity increased with increasing compound stability and decreasing I50 (r2 =.78, N = 36). The difficulty in obtaining metabolic stability data during a structure optimization program prompted a study with substituent parameters in models of in vivo activity. Models describing whole plant activity in jimsonweed were developed using a series of 5-methyl triazolopyrimidine sulfonanilides that differed only in ortho and meta substituents on the aniline ring. The I50 term and clogP were most important to jimsonweed activity. Hence, in vitro activity (I50) may be a useful component of whole plant structure activity models to aid in identification of barriers to in vivo performance.
