Formation and structure of reaction products of <i>cis</i>‐PtCl₂(NH₃)₂ with d(ApG) and/or d(GpA) in di‐, tri‐ and penta‐nucleotides

Abstract

The reaction products of cis ‐PtCl 2 (NH) 3 ) 2 with several deoxyribonucleotides containing d(ApG) and/or d(GpA) have been studied. The various reaction products were separated by high‐performance liquid chromatography and characterized by means of absorbance at 254 nm in combination with atomic absorption spectroscopy and 300‐MHz 1 H‐NMR (pH dependence of the non‐exchangeable base‐protons, T 1 relaxation time determinations). For the larger fragments the results from these techniques were confirmed by enzymatic degradation studies of the platinated fragments. The smallest of the investigated nucleotides, d(ApG) and d(GpA), both formed a variety of different platinum chelates. In the reaction with d(ApG) 15% cis ‐Pt(NH 3 ) 2 [d(ApG) N 1(1), N 7(2)] and 78% cis ‐Pt(NH 3 ) 2 ‐[d(ApG) N 7(1), N 7(2)] were found, 4% of the reacted material consisted of a 1 mol Pt/2 mol dinucleotide product, and 3% of an unidentified 1:1 product. From the main product two rotamers were found to occur: at room temperature, 81% anti, anti and 19% anti,syn product is present. With d(GpA) about equal amounts of N 1. N 7 and N 7, N 7 products were found; for both products the anti, anti and anti,syn conformations were found, respectively. Upon reaction of cis ‐PtCl 2 (NH 3 ) 2 with d(pApG) and d(pGpA) only the N 7, N 7 products were found; at room temperature and pH &gt; 1.5 these products were present in anti, anti conformation. However, for the d(pApG)‐platinum chelate at ‐ 20°C a small amount (&lt;5%) of a second product could be observed in NMR. For the d(pGpA)‐platinum chelate a second N 7, N 7‐coordinated product was observed when the pH of the NMR sample was lowered to 1.1 (at this pH the free 5′‐phosphate group is protonated). With the larger fragments d(ApGpA), d(pApGpA) and d(TpApGpApT) the intra‐molecular competition between the formation of the d(ApG) or the d(GpA) chelates could be studied. Using these nucleotides no N 1‐coordinated products or rotamers were observed. In the case of d(ApGpA) and d(TpApGpApT) the d(GpA) chelate (67% and 75% respectively) was favoured over the d(ApG) chelate, while with d(pApGpA) about equal amounts of both chelates were formed.