Ergot and other indole alkaloids
Ergot and other Indole alkaloids
Ergot alkaloids
Ergot alkaloids are best known from the fungus Claviceps and from the higher plants Ipomoea, Rivea, and related genera of the Convolvulaceae.
Biosynthesis of ergot alkaloids
The biosynthesis of ergot alkaloids begins with prenylation of tryptamine with DMAPP.
The enzyme DMAT synthetase has been purified and studied. Mixed function oxidases convert
4-dimethylallyltryptophane (DMAT) to the corresponding hydroxy derivative. Several cyclase enzymes
are involved in converting the intermediates into chanoclavine I, agroclavine, elymoclavine,
and finally lysergic acid. The peptide alkaloid ergotamine is synthesised by addition of amino
acids (alanine, phenylalanine, and proline) to a lysergic acid precursor.
Ergotism has long been a factor in human poisoning. It was not until the 1760s that von Munchhausen recognized that this a problem produced by fungi. Humans were usually poisoned by bread prepared from infected grain. This was a major problem in Europe in the Middle Ages. Today, the problem is largely averted by better grain-handling techniques, inspection of grain, and pooling of grain supplies.
Some alkaloids possess potent vasoconstricting activity; these were largely responsible for the gangrenous conditions of extremities that often resulted in loss of limbs. Other ergot alkaloids produced delirium and hallucinations.
Ergotism is still a major livestock poisoning problem.
Endophytes
Although fungi such as Claviceps are parasitic on plants, especially cereal grains, a variety of other fungi live entirely within the host plants. These endophytes often belong to the genera Atkinsonella, Balansia, Balansiopsis, Epichloë, and Myriogenosparae. The host plants are often grasses and sedges, but endophytic relationships now appear to be much more widespread than previously thought.
Poisoning by the grasses Festuca arundinacea, Lolium perenne, and Dactylis glomeratus appears to involve endophytic fungi.
Hallucinogenic materials
Ergot alkaloids with hallucinogenic properties have been isolated from Claviceps and from several other genera of fungi. Similar compounds occur in seeds of plants of the family Convolvulaceae and were used as hallucinogenic substances by indigenous peoples of Mexico.
Lysergic acid diethylamide or LSD is a synthetic product (not naturally occurring) with powerful
hallucinogenic properties.
Medicinal properties
Ergot alkaloids are adrenergic blocking agents. They inhibit lactation and prolactin release. Several, ergocryptine and ergocominem, for example, have antitumor activity. Ergotamine and ergometrine have vasoconstricting activity and are used to promote childbirth and as uterine- contracting agents following childbirth. Ergot is cultivated and harvested for medicinal uses.
Other indole alkaloids
Harmane or beta-carboline alkaloids
Although these alkaloids are not common, they are distributed in a number of plant families. The formation of this group is similar to that of isoquinoline alkaloids, except that a tryptamine unit is involved instead of a DOPA-derived unit.
Harmane or beta-carboline alkaloids have been reported from many species of the Rubiaceae. They also occur in the Acanthaceae, Apocynaceae, Eleagnaceae, Fabaceae, Loganiaceae, Malpighiaceae, Passifloraceae, Ranunculaceae, Rutaceae, Simaroubaceae, Solanaceae and Zygophyllaceae.
Harmane alkaloids inhibit membrane transport and act at serotonin receptors.
Alkaloids of this group are important as hallucinogenic substances in Peganum harmala, Zygophyllaceae, especially harmine, and as sedatives in Passiflora species
.They are found in Eleagnus species, Eleagnaceae.
Huayusca or yagé
Plant material of Banisteriopsis caapi and related species is used to prepare hallucinogenic drinks used by Indians of the Amazonian region and in Andean South America.
Physostigmine
Physostigmine is a powerful acetylcholine esterase inhibitor found in the seeds of the fabaceous plant Physostigma venenosum. This West African plant has been used as a "trial-by-ordeal" plant in Africa, but today serves as the source of physostigmine used to treat glaucoma.
Calycanthaceae alkaloids and similar alkaloids from the Rubiaceae
Borreverine and Isoborreverine
Miscellaneous Indole Alkaloids
Lecture Slides
Plants with Ergot and Other
Indole Alkaloids
© David S. Seigler, Plant Biology 363, Plant Secondary Metabolism, Department of Plant Biology,
265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA.
217-333-7577. seigler@life.uiuc.edu.