Cardenolides are a group of naturally occurring C23 steroids of medicinal, toxicological, and ecological importance. Toxic side effects from the 5-alpha H cardenolides currently used from the plant families Scrophulariaceae and Apocynaceae result in the major cause of drug induced deaths in hospitals. Recent evidence suggests that some 5-beta H cardenolides found in the milkweed family, Asclepiadaceae, may have considerably greater inotropic activity on vertebrate hearts than the clinically used 5-alpha H compounds. By isolating, purifying, and identifying cardenolides from previously unexplored milkweeds, new sources of cardenolides having a more advantageous therapeutic index may be provided for pharmacological analysis. Four expeditions are proposed to collect and process plant material from a wide variety of North American milkweeds. Spectroassay determinations of cardenolide concentrations and thin-layer chromatography of each species will be used to select species for additional study. Cardenolides will be isolated and purified from species with high concentrations of unidentified cardenolides by a variety of chromographic techniques. Purified compounds still unidentified after comparison with known cardenolide standards will be subjected to structural determination by a combination of chemical and high resolution spectrometry techniques including high resolution nuclear magnetic resonance experiments. Field data on the abundance, phenology, ecological distributions, and pollinators of the milkweed populations visited during the study along with reference tlc cardenolide profiles should provide valuable insight concerning this taxonomically difficult plant family. Field work will also enable measures of milkweed host-plant utilization and cardenolide sequestration by monarch butterflies and other phytophagous insects, providing important data on the chemical ecology of milkweeds and their insect guild.
