L-35

The prolyl-tRNA synthetase (PRS) is an essential enzyme for protein translation and a validated target against malaria parasite. We describe five ATP mimetics (L95, L96, L97, L35, and L36) against PRS, exhibiting enhanced thermal stabilities in co-operativity with L-proline. L35 displays the highest thermal stability akin to halofuginone, an established inhibitor of Plasmodium falciparum PRS. Four compounds exhibit nanomolar inhibitory potency against PRS. L35 exhibits the highest potency of ∼1.6 nM against asexual-blood-stage (ABS) and ∼100-fold (effective concentration [EC₅₀]) selectivity for the parasite. The macromolecular structures of PfPRS with L95 and L97 in complex with L-pro reveal their binding modes and catalytic site malleability. Arg401 of PfPRS oscillates between two rotameric configurations when in complex with L95, whereas it is locked in one of the configurations due to the larger size of L97. Harnessing such specific and selective chemical features holds significant promise for designing potential inhibitors and expediting drug development efforts.

With the continuous evolution of insect resistance, it is a tremendous challenge to control the fall armyworm (Spodoptera frugiperda) with traditional insecticides. To solve this pending issue, a series of novel isoxazoline derivatives containing diaryl ether structures were designed and synthesized, and most of the target compounds exhibited excellent insecticidal activity. Based on the three-dimensional quantitative structure-activity relationship (3D-QSAR) model analysis, we further optimized the molecular structure with compound L35 obtained and tested for its activity. Compound L35 (LC₅₀ = 1.69 mg/L) exhibited excellent insecticidal activity against S. frugiperda, which was better than those of commercial fipronil (LC₅₀ = 70.78 mg/L) and indoxacarb (LC₅₀ = 5.37 mg/L). The enzyme-linked immunosorbent assay showed that L35 could upregulate the levels of GABA in insects. In addition, molecular docking and transcriptomic results also indicated that compound L35 may affect the nervous system of S. frugiperda by acting on GABA receptors. Notably, through high-performance liquid chromatography (HPLC), we were able to obtain the two enantiomers of compound L35, and the insecticidal activity test revealed that S-(+)-L35 was 44 times more active than R-(-)-L35 against S. frugiperda. This study established the chemistry basis and mechanistic foundations for the future development of pesticide candidates against fall armyworms.