Textbook Problem

α-Santonin, isolated from the flower heads of certain species of Artemisia, is an anthelmintic (meaning against intestinal worms). This terpene is used in oral doses of 60 mg to rid the body of roundworms such as Ascaris lumbricoides. It has been estimated that over one-third of the world’s population is infested with these slender, threadlike parasites.

1. (a) Locate the three isoprene units in santonin and show how the carbon skeleton of farnesol might be coiled and then cross-linked to give santonin. Two different coiling patterns of the carbon skeleton of farnesol can lead to santonin. Try to find them both.
2. (b) Label all chiral centers in santonin. How many stereoisomers are possible for this molecule?
3. (c) Calculate the index of hydrogen deficiency for santonin.