Scheme 1.

Chemical structures and atom numbering schemes of tricyclic antidepressants (TCAs; butterfly structure) and b-cyclodextrin (β-CD; conical shape). The six widely used TCAs are the secondary amine DPM, NRT, and the tertiary amine IPM, AMT, CPM, E/Z-DXP. The different TCAs, including PRT and MPL, of which their distinct structure portions are magenta highlighted. TCAs are commercially available in HCl salt form. Note the reflection symmetry of the (6-7-6)-tricyclic core (wing-body-wing) through a vertical mirror plane bisecting the central 7-membered C-ring. Like other TCAs with a skeleton of the B-C-A-rings from left to right, the flexure and the D-rings are beneath the C-ring for the bicyclo[2.2.2]octadiene backbone of MPL.