Iridoids are a class of secondary metabolites found in a wide variety of plants and in some animals. They are monoterpenes biosynthesized from isoprene and they are often intermediates in the biosynthesis of alkaloids. Chemically, the iridoids usually consist of a cyclopentane ring fused to a six-membered oxygen heterocycle. The chemical structure is exemplified by iridomyrmecin, a defensive chemical produced by the Iridomyrmex genus, for which iridoids are named. Cleavage of a bond in the cyclopentane ring gives rise to a subclass known as seco-iridoids, such as amarogentin. Iridoids are typically found in plants as glycosides, most often bound to glucose.
Iridoids are found in many medicinal plants and may be responsible for some of their pharmaceutical activities. Isolated and purified, iridoids exhibit a wide range of bioactivities including cardiovascular, antihepatotoxic, choleretic, hypoglycemic, analgesic, anti-inflammatory, antimutagenic, antispasmodic, antitumor, antiviral, immunomodulator, and purgative activities.[1][2]
The iridoids are produced by plants primarily as a defense against herbivores or against infection by microorganisms. To humans and other mammals, iridoids are often characterized by a deterrent bitter taste.
Aucubin and catalpol are two of the most common iridoids in the plant kingdom. Iridoids are prevalent in the plant subclass Asteridae, such as Ericaceae, Loganiaceae, Gentianacae, Rubiaceae, Verbenaceae, Lamiaceae, Oleaceae, Plantaginaceae, Scrophulariaceae, Valerianaceae, and Menyanthaceae.