Rapid, quantitative HPLC analysis ofAsclepias fruticosa L. andDanaus plexippus L. cardenolides

The cardenolide extracts from latex and aerial parts ofAsclepias fruticosa and ofDanaus plexippus reared onA. fruticosa orA. curassavica were purified by adsorption chromatography on silica gel. HPLC analysis on a C18 reverse-phase column with an acetonitrile-water gradient as mobile phase, separated 28 compounds with a UV spectrum typical forcardenolides. Afroside and gomphoside (major components), as well as calotropagenin, calotoxin, calotropin, calactin, uscharidin, uscharin, and voruscharin, occurred as single peaks in the profiles of latex and aerial plant parts ofA. fruticosa. Calactin and calotropin were the major cardenolides inDanaus plexippus reared onA. fruticosa orA. curassavica. Quantitative data obtained with digitoxin as internal standard showed that 1.3-1.5% of the leaf cardenolides were sequestered byDanaus plexippus in which levels of 70-80μg cardenolide per butterfly were measured. The calotropin from the leaves was almost completely sequestered, and 10-13% of the calactin was stored by the butterfly, assuming that no conversion occurred in larval tissues.