Characterization of a series of 3-amino-2-phenylpropene derivatives as novel bovine chromaffin vesicular monoamine transporter inhibitors.

A series of 3-amino-2-phenylpropene (APP) derivatives have been synthesized and characterized as novel competitive inhibitors, with K(i) values in the microM range, for the bovine chromaffin granule membrane monoamine transporter(s) (bVMAT). Although, these inhibitors are structurally similar to the bVMAT substrate tyramine, none of them were measurably transported into the granule. Structure-activity studies have revealed that, while the 3'- or 4'-OH groups on the aromatic ring enhance the inhibition potency, Me or OMe groups in these positions reduce the inhibition potency. Halogen substitution on the 4'-position of the aromatic ring causes gradual increase of the inhibition potency parallel to the electron donor ability of the halogen. Substituents on the NH(2) as well as on the 3-position of the alkyl chain reduce the inhibition potency. Comparative structure-activity analyses of APP derivatives with tyramine and the neurotoxin 1-methyl-4-phenylpyridinium suggest that the flexibility of the side chain and the relative orientation of the NH(2) group may be critical for the efficient transport of the substrate through the bVMAT. Comparable bVMAT affinities of these inhibitors to that of DA and other pharmacologically active amines suggest that they are suitable for the structure-activity and mechanistic studies of monoamine transporters and may also be useful in modeling the mechanism of action of amphetamine-related derivatives.