Amines, Polyamines, Aromatic and Pyridine Alkaloids
Amines
Biogenesis: Simple amines are usually formed by decarboxylation of amino acids or by transamination of aldehydes. Both processes occur widely in plants.
In plants these compounds may be involved as protection against pathogens. They also have major physiological effects in animals. This often occurs because of their structural similarity to neurotransmitters.
Many amines also are found as amides in plants. These amides often have physiological effects in animals as well. Several amines serve as synomones in pollination. This is particularly true for plants in the Araceae and the Asclepiadaceae. They are usually involved in attracting flies for pollination.
Monoamine oxidases (MAO) and diamine oxidases (DAO) convert the respective compounds to aldehydes. These aldehydes in turn can then react with amines to form Schiff base adducts.
The leaf-cutter ant Atta sextans produces IAA. This compound is a plant growth stimulant. In this instance, it plays a role in the ant's interactions with fungi.
Serotonin, 5-hydroxytryptamine, is a neurotransmitter. This compound is widespread in nature and may occur in some Musa or banana species.
The corresponding compound with a 5 hydroxy group, bufotenin, occurs in Anadenanthera (Piptadenia) peregrina (Fabaceae: Mimosoideae).
N,N-Dimethyltryptamine also is a halllucinogenic material found in a number of plants, mainly legumes. This compound also occurs in Banisteriopsis species (Malpighiaceae). A drink made of this plant is used in many areas of Amazonian and northern Andean South America.
Phalaris spp. are often consumed by cattle and other livestock. Phalaris tuberosa contains N,N-Dimethyltryptamine, serotonin, 5-hydroxytryptamine, and related compounds. Other species contain gramine and hordenine. Although the level is too low to cause poisoning, consumption of the various species is related to alkaloid content. With either too much or too little, the cattle don't consume the grass.
Indole is a common floral essence compound and is a synomone in many species. This compound appears to be derived from tryptophan. Other amines also are involved in pollination. In most instances, they produce a rotting carrion odor and the flowers are pollinated by flies.
Amines from Capsicum species
The fruits of many species of Capsicum produce capsaicin (0.5 - 1.5%) and a series of related compounds. These compound are largely responsible for the pungent properties of the seeds and fruits.
Diamines
The most common diamines are putrescine (from arginine and ornithine) and cadaverine (from
homoarginine and lysine). Both of these compounds are almost ubiquitous in plants; both are
moderately toxic. They serve as precursors for a number of other groups of alkaloids. Putrescine
also is catabolized to gamma-amino butyric acid in plants.
Polyamines
Polyamines such as spermine and spermidine are synthesized by aminopropyltransferases that use carboxylated S-adenosylmethionine as the aminopropyl group donor. These compounds are derived from other pathways in animals.
Putrescine, cadaverine, spermine and spermidine have considerable antisenescence activity in plants. They are protonated at physiological pH. These protonated forms stabilize membranes and influence the fluidity of membranes. They also affect proton pumps and plant hormonal responses.
There is an absolute requirement for polyamines in some microorganisms, plants, and animals.
Increased synthesis of polyamines just preceding the onset of the G1-phase of the cell cycle preceeding DNA synthesis is a common phenomenon in animals and plants.
Polyamine alkaloids
At least 125 alkaloids that include spermidine or sym.-homospermidine in their structures are known.
They are found in a variety of plants that are not closely related. Several polyamine alkaloids,
e.g., agrobactine, are known to be siderophores. That is, they chelate ionic substances in the
environment.
Simple aromatic alkaloids
Hordenine is formed in barley, Hordeum vulgare, from phenylalanine, which is first converted to tyrosine and then to tyramine. This conversion involves the NIH shift.
Ephedrine, found in several Asian species of the genus Ephedra, a member of the gymnospermous family Ephedraceae, is a well-known adrenergic, bronchodilating agent common in medicinal usage. This compound stimulates the central nervous system and elevates blood pressure. Most of the compounds used medicinally are synthetic, but are structurally related to ephedrine.
Qat or kat, Catha edulis, Celastraceae, is used as a masticatory in East Africa and in Yemen. The plant contains sesquiterpene alkaloids, but also cathinone, related structurally to ephedrine. This compound has central nervous and cardiac stimulating activity.
Mescaline, from Lophophora williamsii, Cactaceae, is known for the production of visual hallucinations. This plant, commonly known as peyote or mescal cactus, is native to Mexico and South Texas. A number of structurally related isoquinoline alkaloids also are found in this and related plants.
Gramine occurs in maple species (Acer, Aceraceae), barley, and a number of other plants. Although the compound looks simple, the biosynthetic pathway leading to it is complex. Both gramine and hordenine appear to be allelopathic agents in field situations.
Psilocybin occurs in a number of fungi, but is best known from Psilocybe species. These mushrooms are common in southern Mexico. Psilocybin is hallucinogenic and has properties similar to LSD.
Pyridine alkaloids
One of the best pyridine alkaloids is nicotine. In tobacco plants, this alkaloid is synthesized from nicotinic acid and ornithine. Nicotinic acid in plants is synthesized from a different pathway from that in animals.
A 60 day old tobacco plant contains about 250 mg of nicotine. This may represent as much as 10% of the plants total metabolism. The half life of nicotine in tobacco plants is about 22 hours. Approximately 40-60 mg of nicotine is a lethal dose for an adult human.
Ricinine, also derived from nicotinic acid, is found in castor bean plants, Ricinus communis, Euphorbiaceae.
Arecoline, from Areca catechu, Arecaceae, the betel palm, is the stimulating alkaloid in betel or pan. This alkaloid has muscarinic action, that is, it mimics acetylcholine and binds to acetylcholine receptors. Low doses produce vasodilation and a fall in both systolic and diastolic blood pressure. This masticatory substance is used by at least one billion people daily, mainly in Southeast Asia.
Trigonelline promotes arrest in G2-stage of the cell cycle.
Capsaicin and Related Compounds
Spermine, sym-homospermidine and kukoamin
Spermine, Spermidine and Ethylene Biosynthesis
Nicotinic Acid Derived Alkaloids
Dioscorine and Dioscoreaceae Alkaloids
Miscellaneous Pyridine Alkaloids
Lecture Slides
Plants with Amines and Simple
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.
