Synthesis and anthelmintic activity of 13-alkoxymilbemycin derivatives.

The synthesis of milbemycin derivatives having alkyloxy groups at the C-13 position was studied and a series of these analogs of milbemycin A4 and A3 was prepared by the reaction of 13-iodomilbemycin with a variety of alcohols. 13β-Phenethyloxy derivatives were found to possess excellent anthelmintic activity. Especially, the activities of derivatives with N-substituted 4-aminophenethyloxy groups were comparable to or superior to ivermectin against Nippostrongylus brasiliensis in rats.