Chemistry
There are four optical isomers of PPA: dextro- and levo- norephedrine, and dextro- and levo- norpseudoephedrine. d-Norpseudoephedrine is also known as cathine, and occurs naturally in Catha edulis ("Khat").
Phenylpropanolamine, structurally, is in the phenethylamine family, consisting of a cyclic benzene or phenyl group, a two carbon ethyl moiety, and a terminal nitrogen- hence the name phen-ethyl-amine. The methyl group on the alpha carbon (the first carbon before the nitrogen group), also makes this compound a member of the amphetamine family.
Exogenous compounds in this family are degraded too rapidly to be active at a reasonable dose, however, the addition of the alpha methyl group allows the compound to avoid metabolism and confer an effect. Ephedrine is the N-methyl analogue of Phenylpropanolamine. In general N-methylation of phenethylamines confers greater stability by avoiding MAO degradation.
The beta hydroxyl group in general seems to convey more selectivity for nor-epinephrine and adrenergic receptors, however, the structure activity relationship is much more complex than this.
Phenylpropanolamine, D,L-erythro-1-phenyl-2-methylaminopropan-1-ol, is synthesized from propiophenone by nitrosation (with methyl nitrite) into an isonitroso derivative. Reduction of this by hydrogen in hydrochloric acid while simultaneously using two catalysts, palladium on carbon and platinum on carbon, gives norephedrine.
- W. N. Nagai, S. Kanao, Ann. Chem., 470, 157 (1929).
- G. Wilbert, P. Sosis, U.S. Patent 3,028,429 (1962).
- Hartung, W. H.; Munch, J. C. (1929). Journal of the American Chemical Society 51 (7): 2262. doi:10.1021/ja01382a044. edit
- Hartung, W. H.; Chang, Y. T. (1952). Journal of the American Chemical Society 74 (23): 5927. doi:10.1021/ja01143a031. edit
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