1,2-Diphenyl--carborane and Its Chromium Derivatives: Synthesis, Characterization, X-ray Structural Studies, and Biological Evaluations.

The objective of this study is to design and synthesize substituted η-chromium(0) tricarbonyl metal complexes carrying -carborane units as potential boron neutron capture therapy (BNCT) agents. In this study, 1,2-diphenyl--carborane () units were used as starting materials to generate biologically active species. We investigated how the structural changes of substituted with chromium(0) tricarbonyl affect the biological properties, and 1-(Phenyl-η-chromium(0) tricarbonyl)-2-phenyl--carborane () and 1,2-bis(phenyl-η-chromium(0) tricarbonyl)--carborane () species were produced in moderate yields. The molecular structures of compounds - were identified and established by infrared (IR); H, B, and C nuclear magnetic resonance (NMR) and X-ray crystallography analyses. Crystal structures of 1,2-diphenyl--carborane and the corresponding chromium complexes , , and were obtained. In an in vitro study using B16 and CT26 cancer cells containing the triphenyl--carboranyl chromium(0) complexes and , which we reported previously, compounds and accumulated at higher levels than compounds and . However, the phenylated -carboranyl chromium complexes have been found to be more cytotoxic than -boronophenylalanine (BPA).