Iodination of cisplatin adduct of Vitamin B12 [{B12}-CN-{cis-PtCl(NH3)2}]+

The cisplatin adduct of vitamin B12, [{B12}-CN-{cis-PtCl(NH3)2}]+ (1), reacts with iodide in aqueous solution to form [{B12}-CN-{trans-PtI2(NH3)}] (3) in good yield. Mono-substitution of chloride was not observed since a subsequent replacement of one NH3 by a second iodide is very fast as compared to the Cl− → I− exchange. The same reaction conditions allowed to introduce radioiodide 131I. Vitamin B12 can therefore be labeled with radionuclides via binding to the Pt(II) center.