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Iridoids are a type of monoterpenoids in the general form of cyclopentanopyran, found in a wide variety of plants and some animals. They are biosynthesis derived from 8-oxogeranial. Gene discovery in the biosynthesis of medicinal alkaloids in Catharanthus roseus Iridoids are typically found in plants as , most often bound to glucose.
The chemical structure is exemplified by iridomyrmecin, a defensive chemical produced by the ant genus Iridomyrmex, for which iridoids are named. Structurally, they are bicyclic cis-fused cyclopentane-pyrans. Cleavage of a bond in the cyclopentane ring gives rise to a subclass known as secoiridoids, such as oleuropein and amarogentin.
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, Gentianaceae, Rubiaceae, Verbenaceae, Lamiaceae, Oleaceae, Plantaginaceae, Scrophulariaceae, Valerianaceae, and Menyanthaceae.
Iridoids have been the subject of research into their potential biological activities.
The iridoid secologanin can react with tryptamine to form the indole alkaloid strictosidine, the precursor of many biologically active compounds such as strychnine, yohimbine, vinca alkaloids, and ellipticine.
Biosynthesis
The iridoid ring scaffold is synthesized, in plants, by the enzyme iridoid synthase. In contrast with other monoterpene cyclases, iridoid synthase uses 8-oxogeranial as a substrate. The enzyme uses a two-step mechanism, with an initial NADPH-dependent reduction step followed by a cyclization step that occurs through either a Diels-Alder reaction or an intramolecular Michael addition.
See also
Further reading
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