By: ROBERT CHAPMAN
Apples come from trees, and as the old saying goes, “An apple a day keeps the doctor away.” As legend has it, Johnny Appleseed, a.k.a. John Chapman (no relation), planted apple orchards throughout much of the countryside during the 19th century. Much to the delight of pharmaceutical scientists are apples, since they are so rich in pectin, which is a widely used excipient. For many years, pectin’s effects on serum cholesterol have been noted, as well as its other utilities.
A number of medicines that are still useful today originate from trees. You’re probably aware that aspirin was first synthesized 120 years ago this August from salicylic acid, the hydrolytic product of salicin, the glycoside isolated from the bark of willow trees belonging to the genus Salix. The series of related anthraquinone glycosides, the cascarosides, were discovered in the bark of Rhamnus purshiana, a species of buckthorn trees also known as “Cascara sagrada,” so called for its “sacred bark,” which produces powerful cathartic effects when brewed in a tea and used as a laxative.
You may even recall that quinine, the original treatment for malaria, and its isomer, quinidine, used as an antiarrhythmic agent, came from the bark of the Peruvian tree Cinchona sucirubrum. While malaria isn’t prevalent in the U.S. any more, it remains a prominent global health issue in tropical climates around the world because malaria parasites have become resistant to conventional drugs. That’s why there is so much interest in developing new drugs to treat malaria and vaccines to prevent it. So much interest, in fact, as to award the Nobel Prize in 2015 to Youyou Tu in recognition of her role in the discovery of artemisinin, from Artemisia annua, as an active constituent useful against Plasmodia.
A related group of pyrano-indolino-quinolines were discovered by Wall and Wani from the Chinese tree Camptotheca acuminata, among which arose the anticancer topoisomerase I inhibitors camptothecin, topotecan, and irinotecan. Wall and Wani also discovered the diterpene Taxol, a.k.a. paclitaxel, from the bark of the Pacific Yew tree, Taxus brevifolia. Since its discovery in 1962, the tree was nearly harvested to extinction before semi-synthesis made it possible to derive the drug, along with other novel and useful analogs, from renewable natural resources within the same genus of plants.
Originally approved for use in 2012, crofelemer, an oligomeric mixture of proanthocyanidins (oddly enough, the same ones found in green tea) was discovered from the sap of the South American tree, Croton lechleri. The formulation of crofelemer that’s now available on the market was approved to treat episodes of diarrhea experienced by HIV/AIDS patients treated with anti-retroviral therapies.
The list of medicines from trees doesn’t end with these examples, and hopefully it will grow longer. Therefore, this Arbor Day, whether remembering a walk through the park or the forest in an exotic destination, recall the words of Joyce Kilmer’s famous poem, Trees. Remember the origins of all these gifts given to us in nature, the benefits of which we’re so inspired to use for the benefit of humanity.