Design of a New Glutamine–Fipronil Conjugate with α‑Amino Acid Function and Its Uptake by <i>A. thaliana</i> Lysine Histidine Transporter 1 (<i>AtLHT1</i>)

Creating novel pesticides with phloem mobility is essential for controlling insects in vascular tissue and root, and conjugating existing pesticides with amino acid is an effective approach. In order to obtain a highly phloem-mobile candidate for efficient pesticides, an electro-neutral l-glutamine–fipronil conjugate (l-GlnF) retaining α-amino acid function was designed and synthesized to fit the substrate specificity of an amino acid transporter. Cotyledon uptake and phloem loading tests with <i>Ricinus communis</i> have verified that l-GlnF was phloem mobile, and its phloem mobility was higher than that of its enantiomer d-GlnF and other previously reported amino acid–fipronil conjugates. Inhibition experiments then suggested that the uptake of l-GlnF was, at least partially, mediated by an active transport mechanism. This inference was further strengthened by assimilation experiments with <i>Xenopus</i> oocytes and genetically modified <i>Arabidopsis thaliana</i>, which showed a direct correlation between the uptake of l-GlnF and the expression of amino acid transporter <i>AtLHT1</i>. Thus, conjugation with l-Gln appears to be a potential strategy to ensure the uptake of pesticides via an endogenous amino acid transport system