The sulfonylurea herbicides (SU) have been well known for their low toxicity, ultra-low dosage and eco-friendly properties. The original inventor, G. Levitt of DuPont, laid out his structure�activity relationship (SAR) guidelines for SU molecular design. Starting with Levitt's conclusions, a Caliper model was postulated and a new approach to SAR guidelines was developed. After analysis of scores of SU by X-ray diffraction along with greenhouse tests of our novel SU, it was found that several SU containing a mono- substituted pyrimidine moiety retained excellent herbicidal properties, with improved selectivity to certain sensitive crops. After detailed toxicological, environmental and ecological examination, Monosulfuron and Monosulfuron ester were formally registered in China for use in millet and wheat fields. In collaboration with Duggleby's group, we tested their herbicidal activity in vitro on ALS (AHAS) enzyme isolated from Aradibopsis thaliana, where the activity sequence is in accordance with our own in vivo green-house tests. Monosulfuron (ester) was successfully docked on the target enzyme (a tetramer) ALS and the ligand/enzyme complex in crystal form was isolated. With assistance from Argonne National Laboratory, further information denoted that the complex molecule contains 18720 atoms. After O treatment each subunit has 582 amino-acids and the site of action was located. This showed that Trp 574 has a slightly different mode of ?-? interaction in comparison to classical SU. Free energy analysis of interaction force confirmed that the three top residue contributions are from Gly121', Trp574, Val196'. The minute differences might explain the preferable selectivity of our SU in certain occasions.

Structure activity relationships of herbicidal mono-substituted sulfonylureas and mode of action

248th National Meeting (2014)

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