2.B.82.  The bis(Melamine)-substituted bis-Pidine HCl Symporter (bMbP-HCl) Family 

Shinde and Talukdar employed a bis(melamine)-substituted bispidine 17 (Fig. below) as an effective HCl cotransporter (Shinde and Talukdar 2017).  The transport properties of 17 and model compound 18 were tested in LUVs consisting of egg yolk phosphatidylcholine, which encapsulated HPTS as a pH sensitive probe. A number of different assays were used, including studying pH dissipation by the transporter across the membrane, the role of counter cations and transport in the presence of a weak acid protonophore (FCCP), allowing the authors to demonstrate that compound 17 functions as an HCl co-transporter at pH 7 whilst compound 18 proved to be a significantly poorer transporter (Davis et al. 2020). A crystal structure of the HCl complex of compound 17 led the authors to propose the homodimeric structure shown in the Figure below as the membrane-soluble complex responsible for transport.