Chapter 7 - Chemical and Biological Perspectives of Monoterpene Indole Alkaloids From Rauwolfia species

Abstract

Abstract The genus Rauwolfia, a member of the Apocynaceae family, is mainly found in tropical regions like South America. It is most commonly found in Brazil, Central and South America, Africa, and Madagascar, as well as in subtropical to temperate areas, such as India, China, and Japan. There are approximately 135 species of Rauwolfia and they have been used traditionally as an emetic, a cathartic, and an expectorant for treating dropsy. The leaf extract is used for the treatment of cholera, intestinal disorders, diarrhea, dysentery, eye diseases, fevers, and as an antihypertensive. The root is used for cardiovascular diseases, hypertension, and various psychiatric diseases. Acridones, coumarins, lignans, flavonoids, phytosterols, saponins, tannins, phenolic compounds, and especially indole alkaloids have been identified in the chemical profiles of Rauwolfia. The acridone alkaloids have functional roles as cancer preventives, antibacterials, and smooth muscle relaxants. Flavonoids, phytosterols, saponins, and tannins possess antibacterial and antifungal activities. Rauwolfia species have also been used to treat cardiovascular diseases, cancers, hypertension, various psychiatric diseases, and snakebites. These indications have been associated with monoterpene indole alkaloids (MIAs). Rauwolfia species are a rich source of bioactive MIAs, such as reserpine, ajmaline, ajmalicine, deserpidine, rescinnamine, and yohimbine. Reserpine is a powerful antihypertensive and tranquilizing agent for the treatment of hypertension, schizophrenia, paranoia, breast cancer, and Parkinson's disease. Ajmaline is an antihypertensive and antiarrhythmic and is used as an antihypertensive agent for the treatment of cardiovascular diseases. Serpentine possesses antihistaminic activity and is used for the treatment of snakebites. Yohimbine has been utilized for its potential clinical applications for erectile dysfunction and is used as an aphrodisiac in dietary supplements. Due to the wide variety of biological applications, researchers have devoted intense effort toward the synthetic production of these MIAs. Ranges of different synthetic pathways have been applied to achieve the total synthesis of these important alkaloids. In this chapter, we aim to outline the entire chemical profile of Rauwolfia species. More importantly, MIAs have been chosen as the main target molecules. The pharmacological effects of designated MIAs, as extracts and pure compound bases, have been reported. Since reserpine, ajmaline, and yohimbine have been the most popular MIAs used for production in the area of synthetic chemistry, the total history of these MIAs has been reported from the first attempts of synthesis in the laboratory to current modifications. Different synthetic pathways have also been discussed.