Cyclopentamine is the cyclopentane homolog of propylhexedrine, differing only in terms of the contracted ring size of a cyclopentane, containing one -CH2- unit less than the cyclohexyl group.
In terms of the acyclic part of the molecule, both cyclopentamine and propylhexedrine are the same as methamphetamine, all three molecules containing the 2-methylaminopropyl side-chain. The difference between them is that whereas methamphetamine is an aromatic molecule containing a phenyl group, cyclopentamine and propylhexedrine are entirely aliphatic and contain no delocalized electrons at all. The effect that this has on potency is that the reduced alicyclic-alkylamines are weaker than unsaturated (meth)amphetamine.
Condensation of cyclopentanone with cyanoacetic acid in a modified Knoevenagel condensation followed by decarboxylation affords the unsatured nitrile. Reduction of the double bond and subsequent reaction of the product with methylmagnesium halide leads to the methyl ketone. This affords the desired product on reductive amination with methylamine.
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^Ghouri MS, Haley TJ (July 1969). "In vitro evaluation of a series of sympathomimetic amines and the beta-adrenergic blocking properties of cyclopentamine". Journal of Pharmaceutical Sciences58 (7): 882–4. doi:10.1002/jps.2600580722. PMID4390216.