Synthesis and activity‐detection of photoswitchable ligands with fipronil to insect

Ionotropic γ-aminobutyric acid (GABA) receptor (GABAR) in an insect is the major inhibitory receptor and is one of the most important targets for insecticides. Due to the high spatiotemporal resolution of GABAR, the photopharmacological ligands acting on it in vertebrates but not insect have been developed.In this study, two types of photochromic ligands (PCLs) including DTFIPs (DTFIP1 and DTFIP2) and ABFIPs (p-, m-, and o-ABFIP) were synthesized by incorporating photoswitch azobenzene or dithienylethene into fipronil (FIP), which is the antagonist of insect GABAR. Their photomodulation was measured by mosquito larval behavior, and their potential action mechanism was explored by the two-electrode voltage clamp (TEVC) technique in vitro. DTFIP1 and m-ABFIP exhibited the most significant difference of insecticidal activity by about 90- and 5-fold to mosquito larvae between non-irradiated and irradiated formation, respectively, and allowed for optical control of mosquito swimming activity. TEVC assay results indicated that m-ABFIP and DTFIP1 enable optical control over the homomeric LsRDL-type GABAR, which is achieved by regulating the chloride channel of resistance to dieldrin (RDL)-type GABAR by photoisomerization.Our results suggested that PCLs synthesized from fipronil provide an alternative and precise tool for studying insect ionotropic GABARs and GABA-dependent behavior. © 2022 Society of Chemical Industry.