Semi-synthesis and insecticidal activity of spinetoram J and its D-forosamine replacement analogues

Spinetoram, a mixture of spinetoram J (XDE-175-J, major component) and spinetoram L (XDE-175-L), is a new kind of fermentation-derived insecticide with a broad range of action against many insect pests, especially Cydia pomonella, Leaf miner and Thrips. Similar to spinosad, spinetoram is friendly to the environment, and non-toxic to animals and human beings. Therefore, spinetoram has been widely applied in pest control and grain storage. In a previous study, we had reported a semi-synthesis of spinetoram J. However, in that synthesis, there were more experimental steps, and the operations were troublesome. So an improved synthesis based on a self-protection strategy was designed and discussed. In this work, 3-O-ethyl-2,4-di-O-methylrhamnose was used as both the reaction substrate of C9-OH and the protecting group of C17-OH. The number of synthetic steps and costs were significantly reduced. In addition, a variety of D-forosamine replacement analogues of spinetoram J were synthesized based on the improved semi-synthesis, and their insecticidal activities were evaluated against third-instar larvae of Plutella xylostella. Although none of the analogues were as potent as spinetoram, a few of the analogues have only a 20-40 times lower activity than spinetoram. In particular, one of these analogues was approximately as active as spinosad. This study highlights the possibility of developing new insecticidal chemistries by replacing sugars on natural products with other groups, and the improved semi-synthesis will be helpful for further researches on spinetoram.