Indole alkaloid

Indole alkaloids are a class of alkaloids containing a structural moiety of indole; many indole alkaloids also include isoprene groups and are thus called terpene indole or secologanin tryptamine alkaloids. Containing more than 4100 known different compounds, it is one of the largest classes of alkaloids. Many of them possess significant physiological activity and some of them are used in medicine. The amino acid tryptophan is the biochemical precursor of indole alkaloids.

The uses of some indole alkaloids has been known for ages: The Aztecs have used psilocybin mushrooms in religious rituals for thousands of years. Extracts of the flowering plant Rauvolfia serpentina which contain reserpine were a common medicine in India around 1000 BC. Various African tribes used the ibogaine-rich roots of the perennial rainforest shrub Iboga as a traditional medicine. An infusion of Calabar bean seed pods was given to people accused of crime in Nigeria: vomiting was regarded as a sign of innocence, otherwise, the person was killed via the action of physostigmine, which is present in the plant and causes full body paralysis.

Consumption of rye and related cereals contaminated with the fungus Claviceps purpurea causes ergotism in humans and other mammals. The relationship between ergot and ergotism was established only in 1717, and the alkaloid ergotamine, one of the main active ingredients of ergot, was isolated in 1918.

The first indole alkaloid, strychnine, was isolated by Pierre Joseph Pelletier and Joseph Bienaimé Caventou in 1818 from the plants of the genus Strychnos. The correct structural formula of strychnine was determined only in 1947, although the presence of the indole nucleus in the structure of strychnine was established somewhat earlier. Indole itself was first obtained by Adolf von Baeyer in 1866 while decomposing Indigo.

Indole alkaloids are distinguished depending on their biosynthesis. The two types of indole alkaloids are isoprenoids and non-isoprenoids. The latter include terpenoid structural elements, synthesized by living organisms from dimethylallyl pyrophosphate (DMAPP) and/or isopentenyl pyrophosphate (IPP):

There are also purely structural classifications based on the presence of carbazole, β-carboline or other units in the carbon skeleton of the alkaloid molecule. Some 200 dimeric indole alkaloids are known with two indole groups.

The number of known non-isoprenoid indole alkaloids is small compared to the number of indole alkaloids.

One of the simplest and yet widespread indole derivatives are the biogenic amines tryptamine and 5-hydroxytryptamine (serotonin). Although their assignment to the alkaloid is not universally accepted, they are both found in plants and animals. The tryptamine skeleton is part of the vast majority of indole alkaloids. For example, N,N-dimethyltryptamine (DMT), psilocin and its phosphorylated psilocybin are the simplest derivatives of tryptamine. Some simple indole alkaloids do not contain tryptamine, such as gramine and glycozoline (the latter is a derivative of carbazole). Camalexin is a simple indole alkaloid produced by the plant Arabidopsis thaliana, often used as a model for plant biology.