RATES OF SUBSTITUTION BY SULFUR NUCLEOPHILES IN CIS-DIAMMINEBIS(GUANOSINE)PLATINUM(II) CHLORIDE

The rates of displacement of guanosine from cis-[(NH3)2Pt(Guo)2]2+ by six sulfur-containing nucleophiles have been measured at several temperatures and several concentrations of nucleophile by using C-13 NMR spectroscopy. cis-Diamminebis(guanosine) platinum(II) chloride [(1)Cl] reacts with the nucleophiles sarcosine-N-carbodithioate, dimethyldithiocarbamate, diethyldithiocarbamate, thiourea, 1-methyl-2-thiourea, and 1-ethyl-2-thiourea to form products in which a guanosine is removed in the initial step and additional ligands may be removed in subsequent steps if the nucleophile is added in excess. The rate of guanosine displacement in the first step of these reactions was found to be slower than that for the corresponding reaction with cyanide; the calculated enthalpies and entropies of activation are consistent with these findings, also. Other sulfur-containing nucleophiles investigated which did not have a significant effect on the displacement of guanosine from 1 over a 24-h period include NaSCN, Na2S2O3, L-methionine, thiobarbituric acid, DMSO, glutathione, L-cysteine, and thiocarbohydrazide.