In terms of molecular structure, synephrine has a phenethylamine skeleton, with a phenolic hydroxy - group, an alcoholic hydroxy- group, and an N -methylated amino -group. Alternatively, synephrine might be described as a phenylethanolamine with an N -methyl and p -hydroxy substituent. The amino-group confers basic properties on the molecule, whereas the phenolic –OH group is weakly acidic: the apparent (see original article for discussion) pK a s for protonated synephrine are (phenolic H) and (ammonium H). 
Once in the synapse, dopamine binds to and activates dopamine receptors.  These can be postsynaptic dopamine receptors, which are located on dendrites (the postsynaptic neuron), or presynaptic autoreceptors (., the D 2 sh and presynaptic D 3 receptors), which are located on the membrane of an axon terminal (the presynaptic neuron).   After the postsynaptic neuron elicits an action potential, dopamine molecules quickly become unbound from their receptors. They are then absorbed back into the presynaptic cell, via reuptake mediated either by the dopamine transporter or by the plasma membrane monoamine transporter .  Once back in the cytosol, dopamine can either be broken down by a monoamine oxidase or repackaged into vesicles by VMAT2, making it available for future release.