Syntheses and solution behaviors of antitumor active glutarimidate (GI)- and 3,3-dimethylglutarimidate (DMGT)bridged platinum blues, [Pt-4(NH3)(8)(GI)(4)](NO3)(5).2H(2)O (1) and [Pt-4(NH3)DMGI)(4)]NO3)(5).2H(2)O (2), are reported. Compounds 1 and 2 were characterized by elemental analysis, cyclic-voltammetry, and ESR spectroscopy and were found to be basically identical to previously reported tetranuclear platinum blue couplexes : both compounds exhibit an irreversible wave at 0.725 and 0.763 V vs SCE, respectively. Compound 2 shows an axial pattern ESR spectrum with g(perpendicular to) = 2.36 and g(parallel to) = 1.992. H-1 and Pt-195 NMR spectroscopy of 1 revealed that the tetranuclear complex is not stable in aqueous solution : it is first reduced by water to a head-to-head (HH) isomer of [Pt-2(NH3)(4)- (GI)(2)](2+) (10) following the equation, (1 + 1/2H(2)O --> 2 x 10 + 1/4O(2) + H+)k(1), with a first-order rate constant of k(1) = 2.81 (1) x 10(-3) s(-1). Compound 10 further undergoes disruptive reaction to form monomers, cis-[Pt(NH3)(2)(GI)(2)] (12) and Cis-[Pt(NH3)(2)(OH2)(2)](2+) (8). Part of 10 isomerizes to the head-to-tail isomer 11, which then disrupts to cis-[Pt(NH3)(2)(GI)(OH2)](+) (13). Similar reactions occur to another platinum blue 2, but HH to HT isomerization is hindered in this case. It seems that the antitumor activity of these platinum blue compounds stems from the decomposition product Cis-[Pt(NH3)(2)(H2O)(2)] (8), which is also produced from the famous antitumor drug cis-PtCl2(NH3)(2) in solution, and reacts with DNA to exhibit the activity. Reaction of 1 with 5’-guanosinemonophosphate (5’-GMP) produces cis-[Pt(NH3)(2)(5’-GMP)(2)] (17), which also strongly supports the activity mechanism of the platinum blue compounds is the same for cis-PtCl2(NH3)(2).