Modulation of Pharmacologically Relevant Properties of Piperidine Derivatives by Functional Groups in an Equatorial or Axial β-Position to the Amino Group

Thirteen epimeric pairs of 5-substituted N-piperonyl-3-phenylpiperidine derivatives were synthesized in order to explore the stereospecific modulation of basicity, lipophilicity, aqueous solubility, and membrane permeation by functional groups in equatorial or axial positions beta to the amine unit. While this comprehensive data set provides enhanced insight into multiple factors that affect basicity and lipophilicity, it fills an important knowledge gap, providing a frame of reference for the property-based design of bioactive compounds. Impacts on amine basicity are very pronounced for the beta-equatorial functional groups and parallel basicity-lowering effects known for acyclic amine derivatives. For beta-axial functional groups, the basicity-lowering effects are generally decreased, with the nitrile group as the only exception. Basicity and lipophilicity modulations observed for beta-axial functional groups are quite diverse and rationalized in terms of intramolecular hydrogen bonding, dipolar interactions, and special solvation effects. Aqueous solubility and (artificial) membrane permeability are discussed with reference to lipophilicity.