ursane

Ursane is the pentacyclic triterpene skeleton used to classify a large group of natural products known as ursane-type triterpenoids. It is one of the three principal pentacyclic frameworks in triterpenes, alongside oleanane and lupane. The ursane framework comprises five fused rings arranged in a characteristic pattern, and many derivatives feature additional oxygen-containing functional groups or side chains.

Natural occurrence and notable compounds: The ursane skeleton is widespread in plants. Notable examples of ursane-type compounds include α-amyrin and β-amyrin, common in plant resins and essential oils, and ursolic acid, a hydroxylated derivative found in many fruits, leaves, and herbs. These compounds contribute to plant waxes, defense mechanisms, and aromas. The skeleton can be elaborated through oxidation and functional-group modification to yield a variety of ursane derivatives used in natural product chemistry.

Biogenesis and applications: In plants, ursane-type triterpenoids arise biosynthetically from squalene through oxidosqualene cyclization, with enzymes such as amyrin synthases guiding the formation of either the ursane or related skeletons. Due to their structural diversity and abundance, ursane-type triterpenoids are the subject of study in natural product chemistry, pharmacology, and chemotaxonomy. They are investigated for properties such as anti-inflammatory and antioxidant activities and are also encountered in cosmetic formulations as bioactive ingredients.