The first metal-based paullone derivative with high antiproliferative activity in vitro.

9-Bromo-7,12-dihydroindolo[3,2-d|[1]benzazepin-6(5H)-one, kenpaullone, which displays similarities in the activity profile to flavopiridol, was modified by chemical transformations at the lactam unit to provide a peripheral binding site able to accommodate metal ions. The first metal-based paullone has been prepared and characterized by single-crystal X-ray diffraction methods, solid-state cross-polarization magic angle spinning 13 C NMR spectroscopy, electrospray ionization mass spectra, and electronic spectra. The gallium complex [GaL 2 ]Cl·2.5H 2 O, the metal-free ligand (HL), and the starting compound used for the preparation of HL were assessed in vitro for their cytotoxicity in a panel of human tumor cell lines. The gallium complex was found to be 1.5-18-fold more cytotoxic than HL, with an average IC 50 value of 2.0 μM.