Design, syntheses and 3D-QSAR studies of novel N-phenyl pyrrolidin-2-ones and N-phenyl-1H-pyrrol-2-ones as protoporphyrinogen oxidase inhibitors

The characteristics of low application rates, good crop selectivity, low residue and environmental safety exhibited by Protoporphyrinogen oxidase (PPO, EC 1.3.3.4)-inhibiting herbicides have attracted a world-wide research interests. As continuation of our research work on the development of new PPO inhibitors, a series of mono-carbonyl analogues of cyclic imides, N-phenyl pyrrolidin-2-ones and N-phenyl-1H-pyrrol-2-ones, were designed and synthesized based on previously established DFT-QSAR results. The PPO inhibition activities of 29 newly synthesized compounds were tested and a predictive comparative molecular field analysis (CoMFA) model was established with the conventional correlation coefficient r2 = 0.980 and the cross-validated coefficient q2 = 0.518. According to the CoMFA model, the substituent effects on the PPO inhibition activity were explained reasonably. Further greenhouse assay showed that 2-(4-chloro-2-fluoro-5-propoxy-phenyl)-2,3,4,5,6,7-hexahydro-isoindol-1-one (C6, ki = 0.095 μM) and 2-(5-allyloxy-4-chloro-2-fluorophenyl)-2,3,4,5,6,7-hexahydro-isoindol-1-one (C7, ki = 0.12 μM) displayed excellent post-emergency herbicidal activity at the concentration of 150 g.ai/ha against seven tested weeds. Due to their high PPO inhibition effect and broad spectrum herbicidal activity, these two compounds have the potential for further study on crop selectivity and field trial. These results confirmed once again that only one of the carbonyl groups of cyclic imides is essential to the PPO inhibition activity.

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