CHARACTERIZATION OF PRODUCTS FROM [PTCL(DIEN)]CL AND S-ADENOSYL-L-HOMOCYSTEINE - EVIDENCE FOR A PH-DEPENDENT MIGRATION OF THE PLATINUM MOIETY FROM THE SULFUR ATOM TO THE AMINE GROUP AND VICE-VERSA

The reaction of [PtCl(dien)]Cl with S-adenosyl-L-homocysteine (SAH) has been followed by 1H and 195Pt NMR in the range 2 < pH < 12. Three products are formed: the mononuclear complex [Pt(dien)SAH-S]2+ (1), with platination of SAH at the sulfur atom, the mononuclear complex [Pt(dien)SAH-N|+ (2), which has a Pt(dien)2+ unit coordinated to the amine group of the homocysteine unit, and the dinuclear complex [{Pt(dien)}2SAH-S, N]3+ (3), which contains a Pt(dien)2+ unit coordinated to the sulfur atom as well as a Pt(dien)2+ unit coordinated to the amine group of the cysteine group. No coordination to the adenine unit has been observed under the present conditions. At pH < 7 only 1 was formed (t1/2 = 75 min for 5 mM concentrations). At pH > 7, 1 spontaneously isomerizes to 2 (t1/2 = 10 min). This process can be reversed at pH < 5 (t1/2 = 2 h). At pH > 7 the following sequence of reactions occurs between 1 equiv of SAH and 2 equiv of [PtCl(dien)]Cl: SAH → 1 → 2 → 3. No reaction of SAH directly leading to 2 could be detected. All three complexes react with sodium diethyldithiocarbamate (Na(ddtc)) forming, eventually, free SAH and [Pt(dien)ddtc]+. Complexes 2 and 3 both consist of a pair of diastereomers due to different configurations at the sulfur atom. It could be proven for 1 that the interconversion of these isomers was slow on the NMR time scale at 255 K. © 1990, American Chemical Society. All rights reserved.