Isomeric forms of ephedrine
Ephedrine has two optically active centers (chiral centers) at positions 1 and 2. It can therefore exist in a total of four different stereoisomers, two of which are mirror images of each other.
The illustration below is shown in Fischer projection.
Strictly speaking, only the two stereoisomers with the 1R,2S and 1S,2R configurations are referred to as ephedrine, while the name pseudoephedrine is used for the other two isomers.
L-ephedrine has a sympathomimetic effect and dilates the bronchi.
Further information
On stereoisomerism: see also information from Michigan State University, Department of Chemistry, USA
Institute of Biochemistry at DSHS Cologne, last updated June 4, 2002