New glucoside conjugates and other cardenolide glycosides from the monarch butterfly reared on Asclepias fruticosa L.
Eight cardenolide glycosides and one genin, including two new glucoside conjugates, have been isolated from adult monarch butterflies (Danaus plexippus L.) the larvae of which were reared on Asclepias fruticosa L. leaves. The glycosides calactin, calotropin (major components), calotoxin, and afroside were identified by comparison with authentic samples. The remaining compounds, after conversion into peracetates, have been shown by 400 MHz 1H n.m.r. and mass spectra (and for the first two compounds by direct comparison) to be the genin calotropagenin and the glycosides frugoside, gofruside, gomphogenin 3-β-D-glucopyranoside, and calotropagenin 3-β-D-glucopyranoside. The relationship between these compounds from monarch butterflies and those previously isolated from the food plant A. fruticosa is discussed.