Figure 1. Molecular structure of ivermectin.
Ivermectin consists of a spiroketal unit (C17-C28), cyclohexene cyclic ether unit (C2-C8), and a disaccharide unit at C13. A secondary butyl sidechain at C25 give rise to the major component (ivermectin B1a) and an isopropyl sidechain give rise to the minor component (<10%; ivermectin B1b).