Stepwise preparation, structure, and in vitro biotestings of the monoribbed-heterodifunctionalized bis-α-benzildioximate iron(II) clathrochelates with two terminal biorelevant groups as potential cytotoxic agents.

The title novel cage complexes were prepared using two-stage nucleophilic substitution of their dichloromacrobicyclic precursor and characterized using elemental analysis, MALDI-TOF mass, UV-vis, 1H and 13C{1H} NMR spectra, and single-crystal XRD experiments. Their chemical compositions suggest an existence of 3D-shaped molecules in either neutral or zwitter-ionic forms and molecular drawings were evaluated basing on most likely hydrogen bonds in the crystals. Effect of proton intramolecular transfer on peculiarities of charge distribution was theoretically studied using XRD structures of two forms of a para-amino-meta-carboxyl-terminated complex. Molecular geometries, charge distributions and electrostatic potentials for them were quantum-chemically calculated. Solution circular dichroism (CD) data suggest that the nature and position of terminal biorelevant groups strongly affect their supramolecular interactions with globular proteins, inducing a metal-centered chirality. Intensities of CD outputs on formation of protein-clathrochelate assemblies and positions of their maxima are also affected by the nature of protein host. Four novel iron(II) clathrochelates possess a cytotoxicity against several cancer cell lines in the comparable low-micromolar concentration range. Maximal cytotoxicities against the cancer HeLa, MCF-7, Caco-2, A549, Hep-2, and PC-3 cells, and relatively low cytotoxities against the normal MRC-5 cells were found for heterodifunctionalized meta(para)-amine-para-carboxyl-terminated isomers (being affected by their structural isomerism) and for mono-meta(para)-carboxylochloroclathrochelates. Cell death in cancer HeLa and Hep-2 lines almost equiprobably includes both necrosis and apoptosis. Low-micromolecular concentration of a meta-amine-para-carboxyl-terminated iron(II) clathrochelate affected a cell cycle of Hep-2 cells causing an increase in the fraction inclined in its S-phase. Pathway of their death and cycle phase distribution shift were studied.