Identification and characterization of a novel linkage isomerization in the reaction of trans-diamminedichloroplatinum(II) with 5'-d(TCTACGCGTTCT).
The oligonucleotide 5'-d(TCTACGCGTTCT) reacts with trans-diamminedichloroplatinum(II) to yield primarily trans-[Pt(NH3)2[d(TCTACGCGTTCT)-N7-G(6),N7-G(8)]], containing the desired trans-[Pt(NH3)2[d(GCG)]] 1,3-cross-link. A key element of the platination reaction is the use of low pH to suppress coordination at A(4). The product was fully characterized by pH-dependent NMR titrations, enzymatic degradation analysis, and 195Pt NMR spectroscopy. Interestingly, the 1,3-cross-linked adduct is unstable at neutral pH, rearranging unexpectedly to form the linkage isomer trans-[Pt(NH3)2[d-(TCTACGCGTTCT)-N3-C(5),N7-G(8)]]. This rearrangement product is more stable than the initially formed isomer and could be characterized by pH-dependent NMR titrations, enzymatic degradation analysis, liquid secondary ion mass spectrometric analysis of an enzymatically digested fragment, 195Pt NMR spectroscopy, and modified Maxam-Gilbert footprinting experiments. By contrast, the 1,3-intrastrand cross-linked isomer rearranges during the course of both pH titration and enzymatic degradation experiments to form the 1,4-adduct. The equilibrium constant for this rearrangement is approximately 3, favoring the 1,4-adduct. Kinetic studies of the linkage isomerization reaction reveal t1/2 values for the first-order disappearance of the 1,3-intrastrand cross-linked isomer ranging from 129 (at 30 degrees C) to 3.6 h (at 62 degrees C), with activation parameters delta H not equal to = 91 +/- 2 kJ/mol and delta S not equal to = -58 +/- 8 J/(mol.K). Mechanistic implications of these kinetic results as well as the general relevance of this linkage isomerization reaction to platinum-DNA chemistry are briefly discussed.
Comess
K M
KM
Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139.
Costello
C E
CE
Lippard
S J
SJ
D001483:Base Sequence; D002945:Cisplatin / Q000032:analysis*; D003432:Cross-Linking Reagents / Q000378:metabolism; D004247:DNA / Q000032:analysis; D007536:Isomerism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009710:Nucleotide Mapping; D009838:Oligodeoxyribonucleotides / Q000032:analysis*; D010984:Platinum / Q000378:metabolism
D003432:Cross-Linking Reagents; D009838:Oligodeoxyribonucleotides; C034697:transplatin; D010984:Platinum; D004247:DNA; D002945:Cisplatin