Inclusion complexes of tricyclic drugs and β-cyclodextrin: inherent chirality and 1 dynamic behaviour 2

: Amitriptyline (AMT) and cyclobenzaprine (CBZ) are tricyclic drugs used as antidepressant and muscle relaxant, respectively. They show inherently chirality, i.e. they are chiral due to the lack of any symmetry element. As they are used as racemic mixture, diastereomeric inclusion complexes are formed via encapsulation in homochiral βCD. In this work we show that a suitable combination of NMR methods easily provides details on the chiral recognition, geometry of complexation, rotational dynamics and spatial proximity of selected atom pairs. In particular, we show that 13C NMR can be used to unambiguously assess chiral recognition, demonstrating a higher performance over 1H NMR. The mole fraction of the bound drug and the association constant can be worked out through diffusion experiments, whereas the combination of non-selective, selective and bi-selective relaxation spectra gave insights into the rotational motion of the complexed drug and the spatial proximity of selected proton pairs. The toolkit here proposed provides a thorough characterization of CD/drug inclusion complexes from a physicochemical point of view. This can constructively complement the conventional pharmacological and pharmacokinetic experiments, and can shed light on the understanding of CD/drug formulations. Abstract 9 Amitriptyline (AMT) and cyclobenzaprine (CBZ) are tricyclic drugs used as antidepressant and muscle 10 relaxant, respectively. They show inherently chirality, i.e. they are chiral due to the lack of any symmetry 11 element. As they are used as racemic mixture, diastereomeric inclusion complexes are formed via 12 encapsulation in homochiral βCD. In this work we show that a suitable combination of NMR methods easily 13 provides details on the chiral recognition, geometry of complexation, rotational dynamics and spatial 14 proximity of selected atom pairs. In particular, we show that 13 C NMR can be used to unambiguously assess 15 chiral recognition, demonstrating a higher performance over 1 H NMR. The mole fraction of the bound drug 16 and the association constant can be worked out through diffusion experiments, whereas the combination 17 of non-selective, selective and bi-selective relaxation spectra gave insights into the rotational motion of the 18 complexed drug and the spatial proximity of selected proton pairs. The toolkit here proposed provides a 19 thorough characterization of CD/drug inclusion complexes from a physicochemical point of view. This can 20 constructively complement the conventional pharmacological and pharmacokinetic experiments, and can 21 shed light on the understanding of CD/drug formulations. nuclear Overhauser enhancement experiments are used to characterize the host-guest inclusion complexes. We aim at demonstrating that very precise qualitative and quantitative information at the molecular level can be accessed by combining several NMR techniques. AMT/βCD and CBZ/βCD have been already studied by Castiglione et al. (2017): a 1:1 host–guest stoichiometry was determined using the Job’s 120 plot and the analysis of intermolecular NOEs in the rotating frame (ROESY) was applied to describe the inclusion geometry. In the present work, we first show that the enantiorecognition ability of βCD towards the two inherently chiral molecules can be probed by 13 C NMR spectroscopy, with significant advantage with respect to 1 H NMR. Then, diffusion Ordered SpectroscopY (DOSY) is applied to get the bound fraction and the association constant. Finally, quantitative dynamic information on the inclusion complex in terms of rotational correlation time and host-guest interactions are collected by measurements of non-selective, selective and biselective spin-lattice relaxation times ( , , and ). We expect that the outcomes will show that the characterization of CD/drug inclusion complexes from a physicochemical point of view