Alkyl Spacer Length and Protonation Induced Changes in Crystalline Psychoactive Arylpiperazine Derivatives: Single-Crystal X-ray, Solid-State NMR, and Computational Studies

Abstract

A series of new long-chain arylpiperazine derivatives with a flexible alkyl spacer were synthesized. A controversy concerning the role of the spacer, whether it participates actively in binding to 5-HT1A and D2 receptors or it acts as a distance arm, encouraged us to investigate how the molecular and crystal structure changes with the increased length of the alkyl linker (from four CH2 units to six). In this study both the basic active compounds as well as their hydrochlorides were studied. Single crystal X-ray structure analysis with a combination of 13C, 15N solid state NMR spectroscopy supported by gauge-including projector-augmented wave calculations of chemical shielding was used. These studies were aimed to examine, elucidate, and compare molecular conformations and to point out the most important intermolecular interactions leading to large supramolecular synthons formed in crystals of both bases and hydrochlorides.