Antitumor pentamethylcyclopentadienyl rhodium complexes of maltol and allomaltol: Synthesis, solution speciation and bioactivity

Comparative solution equilibrium studies on pentamethylcyclopentadienyl rhodium complexes of 2,2ʹ-bipyridine and ethylenediamine and their interaction with human serum albumin

“…Log values of the various [(RhCp*) 2 (hydroxido) i ] (i = 2 or 3) complexes were calculated based on the pH-potentiometric titration data in the absence and presence of chloride ions and were found to be in a good agreement with our previously published data [11].…”

“…Among the half-sandwich organorhodium compounds foremost (η 5 -pentamethylcyclopentadienyl)rhodium(III) (RhCp*) complexes of 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1]decane (PTA) were tested for in vitro antiproliferative activity, but their efficacy was negligible [10]. Recently, we reported RhCp* complexes of (O,O) donor containing 3-hydroxy-4-pyrone ligands [11] and 1,2-dimethyl-3-hydroxy-pyridin-4(1H)-one (deferiprone, dhp) [12], which showed cytotoxicity with IC 50 values of 50-300 μM, respectively in cancer cell lines. Whereas RhCp* complexes formed with 2-picolinic acid (pic) [12] and 3-hydroxy(thio)pyrones derivatized by morpholine, piperidine or N-methylpyrazine moieties [13] exhibited only poor or no bioactivity.…”

“…Detailed solution equilibrium studies on RhCp* complexes are rare in the literature [26][27][28][29], especially which provide stability constants. In our previous works complex formation equilibrium processes of RhCp* complexes were investigated in the case of (O,O) donor hydroxypyr(idin)one ligands and the (O,N) donor pic [11,12]. In the work reported here, we determined the stability constants of the RhCp* complexes of bpy and en (Chart 1) formed in aqueous solution to provide comparable thermodynamic data and specify the solution speciation under physiologically more relevant conditions.…”

“…En, bpy, dhp, KCl, KNO 3 , NaCl, AgNO 3 , HCl, HNO 3 , KOH, 4,4- 3 . The exact concentrations of the RhCp* stock solutions (with or without chloride) were checked by pH-potentiometric titrations employing stability constants for [(RhCp*) 2 (hydroxido) i ] (i = 2 or 3) complexes [11].…”

“…Proton dissociation constants of en and bpy (Chart 1) determined by pH-potentiometry and 1 H NMR titrations ( 3 ] 2+ organometallic cation was already studied [11,26], and the structure of the major hydrolysis product, [(RhCp*) 2 (μ-OH) 3 ] + , was characterized by single-crystal X-ray analysis [29]. Overall stability constants for the μ-hydroxido-bridged dinuclear species ([(RhCp*) 2 (μ-OH) 3 ] + and [(RhCp*) 2 (μ-OH) 2 ]) were reported at various ionic strengths in our previous work [11], and these data were utilized for our calculations.…”