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.[1] 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.[2]
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):[8]
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.[9] Some 200 dimeric indole alkaloids are known with two indole groups.[10]
Physostigma venenosum "Calabar bean", source of physostigmine (coloured plate from Köhler's Medicinal Plants)
Strychnos toxifera, source of the paralysant alkaloid toxiferine (coloured plate from Köhler's Medicinal Plants)
Strychnos nux-vomica, principal source of the convulsant alkaloid strychnine (coloured plate from Köhler's Medicinal Plants)
Tabernaemontana divaricata contains indole alkaloids including catharanthine, conophylline, ibogamine, tabersonine and voacristine[40]
![Tabernaemontana divaricata contains indole alkaloids including catharanthine, conophylline, ibogamine, tabersonine and voacristine[40]](http://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Crape_Jasmine.jpg/160px-Crape_Jasmine.jpg)
The plants that are rich in non-isoprenoid indole alkaloids include harmal (Peganum harmala), which contains harmane, harmine and harmaline, and Calabar bean (Physostigma venenosum) containing physostigmine.[34] Some members of the family Convolvulaceae, in particular Ipomoea violacea and Turbina corymbosa, contain ergolines and lysergamides.[35] Despite the considerable structural diversity, most of monoterpenoid indole alkaloids is localized in three families of dicotyledon plants: Apocynaceae (genera Alstonia, Aspidosperma, Rauvolfia and Catharanthus), Rubiaceae (Corynanthe) and Loganiaceae (Strychnos).[36][37]
Indole alkaloids are also present in fungi. For example, psilocybin mushrooms contains derivatives of tryptamine and Claviceps contains derivatives of lysergic acid.[34] The skin of many toad species of the genus Bufo contains a derivative of tryptamine, bufotenin, and the skin and venom of the species Bufo alvarius (Colorado River toad) contains 5-MeO-DMT.[38] Serotonin, which is an important neurotransmitter in mammals, can also be attributed to simple indole alkaloids.[39]