1,2-Diphenyl- o -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 6 -chromium(0) tricarbonyl metal complexes carrying o -carborane units as potential boron neutron capture therapy (BNCT) agents. In this study, 1,2-diphenyl- o -carborane ( 1 ) units were used as starting materials to generate biologically active species. We investigated how the structural changes of 1 substituted with chromium(0) tricarbonyl affect the biological properties, and 1-(Phenyl-η 6 -chromium(0) tricarbonyl)-2-phenyl- o -carborane ( 2 ) and 1,2-bis(phenyl-η 6 -chromium(0) tricarbonyl)- o -carborane ( 3 ) species were produced in moderate yields. The molecular structures of compounds 1 - 3 were identified and established by infrared (IR); 1 H, 11 B, and 13 C nuclear magnetic resonance (NMR) and X-ray crystallography analyses. Crystal structures of 1,2-diphenyl- o -carborane and the corresponding chromium complexes 1 , 2 , and 3 were obtained. In an in vitro study using B16 and CT26 cancer cells containing the triphenyl- o -carboranyl chromium(0) complexes Ph3C2BCr2 and Ph3C2BCr3 , which we reported previously, compounds 2 and 3 accumulated at higher levels than compounds Ph3C2BCr2 and Ph3C2BCr3 . However, the phenylated o -carboranyl chromium complexes have been found to be more cytotoxic than p -boronophenylalanine (BPA).