This book describes current understandings and recent progress into a varied group of natural products. In the first chapter the role that total synthesis may play in revising the structures proposed for decanolides, which are ten-membered lactones found primarily in fungi, frogs, and termites is presented. The following chapter presents the development of the intriguing plant-derived sesquiterpene lactone, thapsigargin, a potent inhibitor of the enzyme, SERCA (sarco-endoplasmic Ca2+ ATPase), which has potential as a lead compound to treat cancer. The third chapter covers the potential of various plant phenolic compounds for treating the tropical and sub-tropical infectious disease, leishmaniasis. In addition the volume presents recent advances related to the plant alkaloid, cryptolepine, which is of particular interest as a lead for the treatment of malaria, trypanosomiasis, and cancer.