Praziquanamine enantiomers: Crystal structure, Hirshfeld surface analysis, and quantum chemical studies

Abstract

In this work, we report a microwave–assisted method to perform an acid hydrolysis using 2–6 praziquanamides as substrate to produce both praziquanamine (1) enantiomers: (R)–(–)–praziquanamine (1a) or (S)–(+)–praziquanamine (1b). This method provides very good yields and short reaction times (twenty minutes). A structural characterization of praziquanamine and its enantiomers was performed by using X–ray diffraction, spectroscopic and spectrometric techniques, thermal analysis, and powder X–ray diffraction. Computational calculations were also carried out, such as density functional theory (DFT), as it yields suitable geometries for the optimized structures. We also performed frontier molecular orbital (LUMO–HOMO) and electrostatic potential (ESP) analyses. Theoretical values were calculated for electronic transitions, vibration frequencies, and chemical shifts for nuclear magnetic resonances (NMR), and they were later compared to the experimental results. Additionally, the Hirshfeld Surface Analysis was performed to evaluate intermolecular interactions. Crystal structures of both 1a and 1b enantiomers were obtained as an orthorhombic system in the non-centrosymmetric P212121 space group. Conversely, the 1 compound crystallized as a monoclinic system in the centrosymmetric P21/n space group. The following interactions define the crystal packing: N–H···O, N–H···N, C–H···O, C–H···N, C–H···π, and π–π. They all establish an infinite one-dimensional chain. The crystal architectures of praziquanamine enantiomers may be used as resolution agents to discriminate chiral topologies.