Synthesis of tumor-inhibiting complex salts containing the anion trans-tetrachlorobis(indazole)ruthenate(III) and crystal structure of the tetraphenylphosphonium salt

Indazolium trans-tetrachlorobis(indazole)ruthenate(III) exhibits excellent results against different tumor models in vitro and in vivo. To improve the water solubility necessary for the introduction of this tumor-inhibiting c ompound into clinical trials, we synthesized the corresponding sodium salt in a two-step ion exchange via the tetramethylammonium salt. The sodium sal t shows a 35-fold higher solubility in water relative to the indazolium sal t. We also synthesized the n-butylammonium, n-octylammonium, and tetrapheny lphosphonium salts, all of which showed improved solubility in organic solv ents. The X-ray crystal structure of the latter could be solved, proving th e trans configuration of the complex anion. In spite of the paramagnetic Ru -III center an assignement of the coordinated indazole protons could be mad e with the help of a COSY experiment.