1.D.199. The Synthetic Porphyrin Box Monosaccharide Transporter (PB-MT) Family
Lee et al. 2022 reported synthetic monosaccharide channels built with shape-persistent organic cages, porphyrin boxes (PBs), that allow facile transmembrane transport of glucose and fructose through their windows. PBs show a much higher transport rate for glucose and fructose over disaccharides such as sucrose. The transport rate can be modulated by changing the length of the alkyl chains decorating the cage windows. Insertion of a linear pillar ligand into the cavity of PBs blocks monosaccharide transport. In-vitro cell experiments showed that PBs transport glucose across the living cell membrane and enhance cell viability when natural glucose transporter GLUT1 is blocked. Time-dependent live-cell imaging and MTT assays confirmed the cyto-compatibility of PBs. Monosaccharide-selective transport of PBs is reminiscent of natural glucose transporters (GLUTs) (Lee et al. 2022).
The Kim group have described molecular containers as synthetic cation channels (Jung et al. 2008). In 2017, Kim, Roh and colleagues expanded the field by describing an organic polyhedron, porphyrin box 49, that selectively transports iodide into vesicles and cells (see the figure below; Benke et al. 2017). Experiments in planar lipid bilayers showed that 49 formed single channels. Porphyrin box 49 (Mw = 8327 amu), prepared in 95% yield in one-step, has appealing properties for a channel: (1) measuring 3.64 nm × 2.83 nm, it has a roomy interior; (2) its dimensions and hydrophobic sidechains enable it to insert into a lipid bilayer of d ∼ 4 nm; (3) its 12 openings, with portals of d ∼ 3.7 Å, should enable ions to enter and leave the cage and (4) being stable at pH 4.8–13, it is attractive for biological use.