triterpenoid

A triterpenoid is a class of terpenoids consisting of 30 carbon atoms derived from the head-to-tail assembly of six isoprene units. They occur as acyclic, monocyclic, bicyclic, or highly rearranged polycyclic structures, with the most common forms being pentacyclic triterpenoids such as oleanane, ursane, and lupane; other important skeletons include lanostane and dammarane. Many triterpenoids are further modified by oxidation, glycosylation, and acylation to produce a wide range of compounds, including triterpenoid saponins.

Biosynthesis begins with the mevalonate pathway, producing isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). These assemble into farnesyl pyrophosphate (FPP), and two FPP molecules form squalene. Squalene is epoxidized to 2,3-oxidosqualene, which is then cyclized by oxidosqualene cyclases into the core skeletons, such as lanosterol or cycloartenol, followed by numerous oxidation, reduction, and glycosylation steps to yield the diverse array of triterpenoids found in nature. In plants, cycloartenol–derived paths contribute to phytosterols as well as triterpenoid saponins; in animals and fungi, lanosterol-derived routes give sterols.

Natural occurrence is widespread in plants, fungi, and some marine organisms. They play roles in defense against pathogens and herbivores, contribute to cuticular waxes, and participate in signaling and stress responses. Notable examples include beta-amyrin, oleanolic acid, ursolic acid, lupeol, betulinic acid, and the saponins such as glycyrrhizin and ginsenosides.

Applications span pharmaceuticals, nutraceuticals, cosmetics, and agriculture. Many triterpenoids exhibit anti-inflammatory, antimicrobial, antiviral, or anticancer activities, while their glycosides often serve as bioactive compounds or adjuvants in therapy.