Discovery of Novel Pyrazole–Benzothiazine Hybrids as Potential HPPD Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a key target for new herbicide development. To explore novel and effective HPPD inhibitors for weed control, a series of pyrazole–benzothiazine hybrids was designed and synthesized by combination and enol tautomerism strategies. Bioassays indicated that compound A3 strongly inhibited Arabidopsis thaliana HPPD ( At HPPD), with an IC 50 of 0.06 μ M, which was 8 and 3.7 times stronger than topramezone and mesotrione. Additionally, compound B10 demonstrated over 80% herbicidal activity against the tested weeds at 150 g a.i./ha, with only 10% injury to maize, peanut, and cotton. Molecular docking revealed that compounds A3 and B10 formed bidentate chelation with Co 2+ and π–π interactions with Phe381 and Phe424 of At HPPD (PDB: 7CQS ), and stable hydrogen bonds with Asn282. Microscale thermophoresis (MST) and fluorescence titration (FT) confirmed their strong binding affinity to At HPPD, with Asn282 as a potential binding site. Thus, pyrazole–benzothiazine hybrids are a promising scaffold for HPPD inhibitor development.