Epi-Avermectin B1a is the base-catalysed intermediate formed during decomposition of Avermectin B1a in vivo following treatment with Avermectin and is an environmental degradation product. Epi-Avermectin B1a is formed by epimerisation at the 2-position which ultimately rearranges irreversibly to the isomeric alkene analog Delta-2-Avermectin B1a. Epi-Avermectin B1a is very weakly active as a nematocide showing ~100-fold loss of biological activity compared with the parent Avermectin. There are eight Avermectin fractions designated as A1a, A1b, A2a, A2b, B1a, B1b, B2a, and B2b. The B1 fraction has the most effective antiparasitic activity.
Epi-Avermectin B1a is soluble in ethanol, methanol, DMF and DMSO.
