Figure 29.11 • Beta-phenethylamines in ma huang.
the heart; hence, the herb may be dangerous to people with cardiac disease. The amounts of ephedra-type compounds and the relative composition differ so widely that it is difficult to be certain what one is getting in any given preparation. Ma huang's main active ingredient is the j-phenethyl-amine compound (-)-ephedrine. Plants grown in China may contain 0.5% to 2.5% of this compound. Many ephedrine congeners are represented in the plant,11 and many of these possess considerable pharmacological activity. Some are as follows: (-)-ephedrine, (+)-pseudoephedrine, norephedrine, norpseudoephedrine, ephedroxane, and pseudoephedroxane (Fig. 29.11).
Ma huang's principal active ingredient is (-)-ephedrine. This compound is the erythro-D(-)-isomer with the 2(S),3(R) configuration. The less potent (+)-pseudoephedrine has the threo 2(S),3(S) structure. Ephedrine acts as a mixed agonist on both a- and j-receptors.
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