Emamectin B1a is a semisynthetic derivative of avermectin B1a . It binds to GABAA receptors (Ki = 17.6 nM in rat brain membranes), including those containing β1, β2, or β3 subunits (IC50s = 57, 210, and 49.8 nM for α1β1γ2, α1β2γ2, and α1β3γ2 subunits, respectively), and potentiates the GABA response. Emamectin B1a also binds to and inhibits glycine receptors (IC50 = 218 nM in rat spinal cord). Emamectin B1a induces mortality in 90% of S. exigua larvae in a diet incorporation assay at a dose of 1.067 ng/ml, which is approximately 1,500-fold more toxic than avermectin B1. It is effective against neonate S. eridania larvae in a foliage spray bioassay and when applied topically.
Emamectin B1a is a semi-synthetic 4”-epimethylamino analogue of avermectin B1a prepared by oxidation of the 4”-hydroxy moiety and reductive amination. The introduction of the methylamino group greatly enhances the insecticidal potency of the avermectin class. Emamectin B1a, as a benzoate salt, is the major component (>90%) of the commercial insecticide/acaricide, emamectin. Members of the avermectin/milbemycin class exert their insecticidal/anthelmintic effects by binding to glutamate-gated chloride channels expressed on nematode neurones and pharyngeal muscle cells.
