Design, Synthesis and Herbicidal Activity of 5-(1-Amino-4-phenoxybutylidene)barbituric Acid Derivatives Containing an Enamino Diketone Motif.

In continuation of our efforts to identify novel herbicide lead compounds, twenty new 5-(1-amino-4-phenoxybutylidene)barbituric acid derivatives containing an enamino diketone motif were synthesized and evaluated for their herbicidal activities. The greenhouse bioassay results indicated that several of the target compounds, including BA-1, BA-2, BA-5, BA-18, and BA-20, exhibited notable post-emergence herbicidal activity, with sum inhibition rates exceeding 70% at a dosage of 150 g ha-1, which was superior to that of the commercial herbicide flumiclorac-pentyl (FP). The structure-activity relationship analysis demonstrated that the steric and electronic effects of the R group, as well as the lipophilicity of the target compounds, significantly influenced herbicidal activity. Among these, BA-1 was identified as a promising herbicide lead compound due to its high total herbicidal efficacy, broad-spectrum activity, and favorable crop safety profile. Molecular simulation studies indicated that BA-1 binds effectively to Nicotiana tabacum protoporphyrinogen IX oxidase (NtPPO), suggesting its potential as a novel PPO inhibitor. This study highlights BA-1 as a promising lead compound for the development of novel PPO-inhibiting herbicides.