The structures of doramectin 1 and its close analogue, 25-cyclohexyl-a
vermectin B2 2, have been determined by proton and carbon NMR spectros
copy; mass spectrometry and X-ray crystallography. Modern two-dimensio
nal techniques were,used to assign the proton and carbon NMR resonance
s. Several signals in the close-related naturally-occurring avermectin
s have been re-assigned.