Procaines are amine esters of cocaine, which possess the properties of a local anesthetic drug. They display the characteristics of a local anesthetic due to the selective binding of their onium ions to a particular site within the sodium channels.
This is the reason due to which structural modification that alters solubility of the lipids, and metabolic inactivation has a profound effect on a drug’s ability to bind or reach to the hypothetical receptor sites. This can also result in modification of its anesthetic properties.
The amine group is present in procaine is responsible for increasing its local anesthetic property. It contributes towards its inductive effects and resonance, and enhances its potency over the drugs that are not substituted. The resonance is thought to result in a zwitterion form, where the amino group’s electrons can be delocalized by resonance onto the carbonyl group of oxygen.
The binding and affinity towards a receptor is also increased, as binding can occur both via hydrophobic as well as hydrophilic pathways. Addition of an aromatic amine can thus, enhance formation of a resonance structure, and produce more potent anesthetic agents that function locally.