Curare plant sources

A sample of curare was prepared by Indians of the upper Amazon under the supervision of a botanist in order to insure the plant source. The plant species was Chondodendron tomentosum and the curare thus obtained was a black paste called Serpa which represented a concentrated aqueous extract of the stems and bark (81). The desiccated extract contained five alkaloids (104), d-isochondodendrine, methylisochondodendrine, d-tubocurarine chloride, curine, and a new base to which the name d-chondocurine was given. 

Curare is a muscle relaxant drug, originally used as an arrow poison by Amazonian Indians. The traditional curare is prepared by a secret recipe thought to involve a number of plant species (Plotkin 1993). Plant sources of curare include Strychnos castelnaei and species in the Loganaceae family and Chondodendron tomentosum in the Menispermaceae family. Tubocurarine, a benzylisoquinoline dimer, is the major alkaloid in the curare plants. It exhibits paralysing effects on skeletal muscles, and is used as a muscle relaxant in surgical procedures. It controls convulsions caused by the toxic alkaloid strychnine. 

In the foregoing pages we have followed the story of curare from the early encounters by the Spanish Conquistadores, through its use by the forest tribes in hunting and occasionally in warfare, through the discovery of its plant sources and the isolation and chemistry of its purified active principles, to the introduction of some of them as valuable muscle relaxants in surgery and to their subsequent role as templates leading to the development of improved products. Curare is thus an excellent example of a material that has made the successful transition from an ethnic product to a purified substance essential to the practice of modern medicine. 

Bebeerine and its allies (p. 363) are also derived from menispermaceous plants, but as their botanical source needs attention in some detail, and in view of their importance as close associates of the curare alkaloids, they are dealt with separately at the end of this section. 

The active principles of curare were early recognized to be water-soluble quaternary alkaloids. Tube-curare was studied by King, who isolated (3) the crystalline quaternary bisbenzylisoquinoline alkaloid, d-tubocurarine (I), in 1935. The main plant constituent of tube-curare is the bark of menispermaceous plants, particularly of the genus Chondro-dendron, and d-tubocurarine was later isolated (4) from C. tomentosum. Further work led to the isolation and structural elucidation of many more bisbenzylisoquinoline alkaloids from these sources (5). 

Originally curare was a term used to describe collectively the very potent arrow poisons used since early times by the South American Indians. The arrow poisons were prepared from numerous botanic sources and often were mixtures of several different plant extracts. Some were poisonous by virtue of a convulsant action and others by a paralyzant action. Only the latter type is of value in therapeutics and is spoken of ordinarily as curare. 

In 1935, King (55) isolated a pure alkaloid, which he named d-tubocurarine, from a tube curare of unknown botanical origin. The word "tube" refers to the container in which the South American natives transported their plant extract. It was almost 10 years later that the botanical source for d-tubocurarine was clearly identified as Chondodendron tomentosum. The structure that King assigned to tubocurarine possessed two nitrogen atoms, both of which were quaternary ammonium salts (e.g., a b/s-quaternary ammonium compound). It was not until 1970 that the... 

To outline how this has come about, in other words, to examine the role of curare in the development of modern muscle relaxants, is the aim of the present review. But it is also concerned with the plants that are the sources of activity and with the substances that are their active principles. Certain aspects of the pharmacology, including the mode of action, of these compounds and the development of the muscle relaxants derived from them are also outlined. 

Research on the Strychnos species associated with curare has very naturally placed the main emphasis on the alkaloids present in the stem bark and root bark, these being the plant parts most commonly used in the preparation of the poison. And indeed, screening small samples from 53 New World species for alkaloids has shown that, as with representatives from other continents, these parts tend to be a richer source than the leaves (250). 

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