quassinoid

Quassinoids are a class of natural products belonging to highly oxygenated triterpenoids, primarily produced by plants in the Simaroubaceae family. They are especially associated with species such as Quassia amara, Picrasma excelsa, and related genera including Brucea and Eurycoma. The core skeleton is a rearranged or degraded triterpene, and most quassinoids carry multiple oxygen-containing groups, often lactones and epoxides. This chemical richness contributes to their characteristic bitterness and their broad range of biological activities.

Occurrence and chemistry: Quassinoids occur in various plant parts, including bark, wood, and seeds, and are often extracted from species used in traditional bitter tonics. Quassin is the prototypical member and is among the most bitter natural compounds known. The structural diversity among quassinoids arises from oxidative modifications and rearrangements of the triterpene framework.

Biological activities: Quassinoids display antifeedant, antimicrobial, antiviral, antiparasitic, and cytotoxic activities in diverse experimental systems. Some members show antimalarial effects, and many inhibit the growth of cancer cell lines in vitro. A well-studied example, bruceantin, is a potent inhibitor of eukaryotic protein synthesis and has been used to explore translation mechanisms. The activity spectrum reflects substantial structural variation within the class.

Biosynthesis and applications: They are derived from the triterpene biosynthetic pathway with oxidative remodeling that creates the lactone-containing structures characteristic of this group. Historically, quassinoids have been used as bittering agents and in traditional medicine, but their notable cytotoxicity requires careful handling in research and herbal use. Ongoing work aims to identify selective therapeutic leads with reduced toxicity.