Catalpol is an

iridoid Iridoids are a type of monoterpenoids in the general form of cyclopentanopyran, found in a wide variety of plants and some animals. They are biosynthetically derived from 8-oxogeranial. Iridoids are typically found in plants as glycosides, mos ...

glucoside A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes. The name was o ...

. This natural product falls in the class of iridoid

glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...

s, which are simply

monoterpene Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear (acyclic) or contain rings (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen funct ...

s with a

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

molecule attached.

Natural occurrence

First isolated in 1962, catalpol was named for plants in the genus ''

Catalpa ''Catalpa'', commonly called catalpa or catawba, is a genus of flowering plants in the family Bignoniaceae, native to warm temperate and subtropical regions of North America, the Caribbean, and East Asia. Description Most ''Catalpa'' are decidu ...

'' in which it was discovered. Later in 1969, catalpol was found to be present in larger quantities in several plants in genus ''

Rehmannia ''Rehmannia'' is a genus of seven species of flowering plants in the order Lamiales and family Orobanchaceae, endemic to China. It has been placed as the only member of the monotypic tribe Rehmannieae, but molecular phylogenetic studies suggest t ...

'' (Orobanchaceae). It is also found in plants belonging to several families, including, but not limited to,

Scrophulariaceae The Scrophulariaceae are a family of flowering plants, commonly known as the figwort family. The plants are annual and perennial herbs, as well as shrubs. Flowers have bilateral (zygomorphic) or rarely radial (actinomorphic) symmetry. The Scr ...

Lamiaceae The Lamiaceae ( ) or Labiatae are a family of flowering plants commonly known as the mint, deadnettle or sage family. Many of the plants are aromatic in all parts and include widely used culinary herbs like basil, mint, rosemary, sage, savory ...

(including scullcap),

Plantaginaceae Plantaginaceae, the plantain family, is a large, diverse family of flowering plants in the order Lamiales that includes common flowers such as snapdragon and foxglove. It is unrelated to the banana-like fruit also called "plantain." In older cl ...

(''

Plantago ''Plantago'' is a genus of about 200 species of flowering plants in the family Plantaginaceae, commonly called plantains or fleaworts. The common name plantain is shared with the unrelated cooking plantain. Most are herbaceous plants, though a ...

sp'') and

Bignoniaceae Bignoniaceae is a family of flowering plants in the order Lamiales commonly known as the bignonias or trumpetvines.Vernon H. Heywood, Richard K. Brummitt, Ole Seberg, and Alastair Culham. ''Flowering Plant Families of the World''. Firefly Books: ...

, all of which being in the order

Lamiales The order Lamiales (also known as the mint order) are an order in the asterid group of dicotyledonous flowering plants. It includes about 23,810 species, 1,059 genera, and is divided into about 25 families. These families include Acanthaceae, Bi ...

. Because they feed on these plants, variable checkerspot butterflies (''Euphydryas chalcedona'') contain high amounts of catalpol, which makes them unpalatable to predators and thus serves as a defense mechanism.

Biosynthetic pathway

Though first isolated in the 1960s, there has been very little investigation of the

biosynthetic pathway Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

of catalpol. S. R. Jensen has described a possible biosynthetic pathway for catalpol. With iridoids stemming from a

terpenoid The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes" ...

origin, epi-iridotrial's precursor, epi-iridodial, is derived from

geraniol Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil, palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in water ...

. Addition of a glucose at carbon 1 (C1) of the iridoid backbone and oxidation of the aldehyde at C4 of epi-iridotrial produces 8-epiloganic acid. A subsequent hydrolysis at C8 yields mussaenosidic acid, followed by a dehydration to yield deoxyngeniposidic acid. The next precursor, geniposidic acid, is furnished via hydrolysis of C10, and then a decarboxylation to remove the carboxylic acid at C4 provides bartsioside. The very widely known and accepted precursor to catalpol,

aucubin Aucubin is an iridoid glycoside. Iridoids are commonly found in plants and function as defensive compounds. Iridoids decrease the growth rates of many generalist herbivores. Natural occurrences Aucubin, as other iridoids, is found in asterids ...

, is then furnished via hydroxylation at C6. Finally an epoxidation with the alcohol at C10 yields catalpol. {{clear-left

Footnotes

Iridoid glycosides Glucosides Polyols Cyclopentanes