Theoretical Studies On The Hydrolysis Mechanism Of Sulfonylure Herbicides And Its Isocyanate Synthesis

AHAS(Acetohydroxyacid synthase) is the first key enzyme involved in the biosynthesis of the branched-chain amino acids for plants and fungus.But, AHAS is absent from human and animal body. AHAS is an ideal target enzyme for several herbicides and it blocks the biosynthesis of branched-chain amino acids. At the same time, AHAS inhibitors have very low toxiciy for human, animal and environment. Sulfonylurea herbicides is one of the most widely used AHAS inhibitors. However, the challenge problems for some sulfonylurea herbicide are resistance to weeds and long residue. Thus, it is of immediate significance to develop novel, easily degraded and high effective AHAS inhibitors.This paper is based on the former works of the laboratory and mainly contains two parts: Firstly, the hydrolysis mechanism of sulfonylurea herbicides was studied by using density functional theory(DFT). Secondly, 4-substituted benzenesulfonylureas were synthesized by using the isocyanate approach. The results are summarized as follows:1. Gaussian 09 suit of programs were used to explore the hydrolysis mechanism of sulfonylurea herbicides, analyze the energy change and compare the reactivity of the reaction. The geometry optimization, vibration frequency analysis, energy calculation, reaction path analysis, energy surface scan, solvation model and charge distribution were performed through the density functional theory approach with the B3LYP/6-31+G(d,p) level of theory. This chapter includes two parts:(1) The effects of substituent group positions at benzene ring on hydrolysis reaction barrier(Benzene system);(2) Influence of different substituent group at sulfonylurea bridge on hydrolysis reaction barrier(Sulfonylurea bridge system). 2. The isocyanate method is used to synthesize 4-substituted benzenesulfonylurea compounds. 2-chlorine-5-nitrobenzoate were used as the raw material to synthesize the target product by nucleophilic substitution reaction, oxidative cleavage reaction, oxdiation reaction of chlorine, ammonolysis reaction, isocyanate reaction and hydrogen reduction. In this method, ammonolysis reaction and isocyanate reaction were applied, the purity requirement of 2- methoxycarbonyl 4-nitrobenzene sulfonyl chloride can be decreased. This optimized reaction route can be used for industrial production with high stability. The structure of all the intermediate products and final products were verified by means of 1H-NMR, IR and elemental analysis.