Evaluation of Chiral Pesticide Chlorbufam at the Enantiomeric Level: Absolute Configuration, Separation, Herbicidal Activity, and Degradation in Soil

Chlorbufam is a photosynthesis inhibitor chiral herbicide with a pair of enantiomers, which is rarely a concern. In this work, the optically pure enantiomers of chlorbufam were first synthesized and characterized, and the enantioselective herbicidal activity and mechanism were studied. Chlorbufam enantiomers showed significant differences in bioactivity against Echinochloa crus-galli and Abutilon theophrasti, and R-(+)-chlorbufam was identified as the most active against the targeted organisms with higher bioactivity of 3.95 and 1.71 times than S-(−)-chlorbufam. Chlorbufam enantiomers exerted herbicidal activity by inhibiting photosynthesis according to the results of the determination of photosynthetic pigment contents and molecular docking. Additionally, a novel HPLC–MS/MS method was successfully developed and validated for the detection of chlorbufam enantiomers and further applied for the enantioselective degradation study in soil. As a result, chlorbufam was satisfactory enantioseparated with a resolution of 2.37 on a Chiralpak IH column using the mobile phase of acetonitrile and water (60:40, v/v). Good linearity for chlorbufam enantiomers was obtained with correlation coefficients ≥0.9990, and the recovery ranged from 74.1 to 119% with relative standard deviations ≤10.9% at three spiked levels. The degradation behaviors of chlorbufam enantiomers were significantly different, and S-(−)-chlorbufam was preferentially degraded. The findings encouraged the application of enantiopure R-(+)-chlorbufam herbicide to reduce dosage rates, decrease environmental risks, and protect human health.