Iridoids are a class of secondary metabolite

Secondary metabolite

Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolities does not result in immediate death, but rather in long-term impairment of the organism's...

s found in a wide variety of plants and in some animals. They are monoterpene

Monoterpene

Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear or contain rings...

s biosynthesized from isoprene

Isoprene

Isoprene , or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=CCH=CH2. Under standard conditions it is a colorless liquid...

 and they are often intermediates in the biosynthesis of alkaloid

Alkaloid

Alkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...

s. Chemically, the iridoids usually consist of a cyclopentane

Cyclopentane

Cyclopentane is a highly flammable alicyclic hydrocarbon with chemical formula 510 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occurs as a colorless liquid with a petrol-like odor. Its melting point is −94 °C...

 ring fused to a six-membered oxygen heterocycle. The chemical structure is exemplified by iridomyrmecin

Iridomyrmecin

Iridomyrmecin is a defensive chemical, classified as an iridoid, isolated from ants of the genus Iridomyrmex. Iridomyrmecin is also found in a variety of plants including Actinidia polygama....

, a defensive chemical produced by the Iridomyrmex

Iridomyrmex

Iridomyrmex is a genus of ants that belongs to the subfamily Dolichoderinae. There are 79 species and subspecies that belong to this genus and they range from India to China to Australia and New Caledonia.-Description:...

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

Amarogentin

Amarogentin is a chemical compound found in gentian or in Swertia chirata.Gentian root has a long history of use as a herbal bitter in the treatment of digestive disorders and is an ingredient of many proprietary medicines. The bitter principles of gentian root are seco-iridoid glycosides...

. Iridoids are typically found in plants as glycoside

Glycoside

In chemistry, a glycoside is a molecule in which a sugar is bound to a non-carbohydrate moiety, usually a small organic molecule. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme...

s, most often bound to glucose

Glucose

Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

.

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.

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

Aucubin

Aucubin is an iridoid glycoside . Iridoids are commonly found in plants and function as defensive compounds . Irioids decrease the growth rates of many generalist herbivores . Aucubin is found in the leaves of Aucuba japonica , Eucommia ulmoides , and , etc., plants used in traditional Chinese...

 and catalpol

Catalpol

Catalpol is an iridoid glucoside that is found in plants belonging to several families, including, but not limited to, Scrophulariaceae, Lamiaceae, and Bignoniaceae. This natural product falls in the class of iridoid glycosides, which are simply monoterpenes with a glucose molecule attached...

 are two of the most common iridoids in the plant kingdom. Iridoids are prevalent in the plant subclass Asteridae

Asteridae

Asteridae is a clade of plants, known for their flowers. Asteridae has been ranked as a subclass, but this ranking has varied depending on the taxonomy being used...

, such as Ericaceae

Ericaceae

The Ericaceae, commonly known as the heath or heather family, is a group of mostly calcifuge flowering plants. The family is large, with roughly 4000 species spread across 126 genera, making it the 14th most speciose family of flowering plants...

, Loganiaceae

Loganiaceae

Loganiaceae are a family of flowering plants classified in order Gentianales. The family includes 13 genera, distributed around the world's tropics.Earlier treatments of the family have included up to 29 genera...

, Gentianacae, Rubiaceae

Rubiaceae

The Rubiaceae is a family of flowering plants, variously called the coffee family, madder family, or bedstraw family. The group contains many commonly known plants, including the economically important coffee , quinine , and gambier , and the horticulturally valuable madder , west indian jasmine ,...

, Verbenaceae

Verbenaceae

Verbenaceae, commonly known as the verbena family or vervain family, is a family of mainly tropical flowering plants. It contains trees, shrubs and herbs notable for heads, spikes, or clusters of small flowers, many of which have an aromatic smell.Recent phylogenetic studies have shown that...

, Lamiaceae

Lamiaceae

The mints, taxonomically known as Lamiaceae or Labiatae, are a family of flowering plants. They have traditionally been considered closely related to Verbenaceae, but in the 1990s, phylogenetic studies suggested that many genera classified in Verbenaceae belong instead in Lamiaceae...

, Oleaceae

Oleaceae

Oleaceae are a family containing 24 extant genera and around 600 species of mesophytic shrubs, trees and occasionally vines. As shrubs, members of this family may be twine climbers, or scramblers.-Leaves:...

, Plantaginaceae

Plantaginaceae

Plantaginaceae Juss. or plantain family, are a family of flowering plants in the order Lamiales. The type genus is Plantago L..In older classifications it used to be the only family of the order Plantaginales, but numerous phylogenetic studies, summarized by the Angiosperm Phylogeny Group, have...

, Scrophulariaceae

Scrophulariaceae

Scrophulariaceae, the figwort family, are a family of flowering plants. The plants are annual or perennial herbs with flowers with bilateral or rarely radial symmetry. Members of the Scrophulariaceae have a cosmopolitan distribution, with the majority found in temperate areas, including...

, Valerianaceae

Valerianaceae

The Valerianaceae, or valerian family, of the order Dipsacales contains about 350 species in 7 genera. Plants are generally herbaceous and foliage often has a strong, disagreeable odor. They are found native in most regions of the world except for Australia...

, and Menyanthaceae

Menyanthaceae

Menyanthaceae are a family of aquatic and wetland plants in the order Asterales. There are approximately 60-70 species in five genera distributed worldwide. The simple or compound leaves arise alternately from a creeping rhizome. In the submersed aquatic genus Nymphoides, leaves are floating and...

.