High value-added application of sustainable natural forest product α-pinene: synthesis of myrtenal oxime esters as potential KARI inhibitors

Ketol-acid reductoisomerase catalyzes the second step reaction in the biosynthesis of essential branched-chain amino acid, and is an important target enzyme to design the safe herbicides and fungicides for humans and mammals. Using the ketol-acid reductoisomerase as the target enzyme, eighteen novel myrtenal oxime ester compounds were designed and synthesized from natural forest product α-pinene. Their structures were confirmed by IR, ESI-MS, NMR, and elemental analysis. All the target compounds were preliminarily evaluated for their herbicidal and in vitro antifungal potential. As a result, eleven compounds were found to exhibit higher growth inhibitory rate than the commercial herbicide flumioxazin against the root of rape (Brassica campestris) and seven compounds showed growth inhibitory rate of greater than 80.0% against barnyard grass (Echinochloa crusgalli L.) at the concentration of 100 µg/mL. Most of the target compounds had better herbicidal activity than IpOHA. Meanwhile, the title compounds dis...