Cavity-Containing [FeL] Helicates: An Examination of Host-Guest Chemistry and Cytotoxicity.

Two new di(2,2'-bipyridine) ligands, 2,6-bis([2,2'-bipyridin]-5-ylethynyl)pyridine () and bis(4-([2,2'-bipyridin]-5-ylethynyl)phenyl)methane () were synthesized and used to generate two metallosupramolecular Fe() cylinders. The ligands and cylinders were characterized using elemental analysis, electrospray ionization mass spectrometry, UV-vis, H-, C and DOSY nuclear magnetic resonance (NMR) spectroscopies. The molecular structures of the Fe() cylinders were confirmed using X-ray crystallography. Both the Fe() and Fe() complexes crystallized as racemic () mixtures of the ΔΔ (P) and ΛΛ (M) helicates. However, H NMR spectra showed that in solution the larger Fe() was a mixture of the -ΔΔ/ΛΛ and -ΔΛ isomers. The host-guest chemistry of the helicates, which both feature a central cavity, was examined with several small drug molecules. However, none of the potential guests were found to bind within the helicates. cytotoxicity assays demonstrated that both helicates were active against four cancer cell lines. The smaller Fe() system displayed low μM activity against the HCT116 (IC = 7.1 ± 0.5 μM) and NCI-H460 (IC = 4.9 ± 0.4 μM) cancer cells. While the antiproliferative effects against all the cell lines examined were less than the well-known anticancer drug cisplatin, their modes of action would be expected to be very different.