[1H, 15N] NMR Studies of the Platination of Phosphorothioate Nucleotides − Monofunctional Sulfur Adducts versus Macrochelation

Abstract

cis‐[PtI2(15NH3)2] reacts rapidly with guanosine‐5′‐O‐(2‐thiodiphosphate) (GDP‐β‐S) to form a macrochelate in which Pt bridges the phosphorothioate S and guanine N7 atoms. Phosphorothioate(α‐S)‐containing self‐complementary decamer oligonucleotides give rise to relatively long lived S‐bound monofunctional adducts, the fate of which is sequence dependent.

Insights into DNA Platination within Unusual Structural Settings

“…Comparison of this reaction profile with the outcome from that of the reaction between I and the phosphorothioate substituted dimer R,S-d(GsG) (IIs) indicated close similarity to the previous report [14] in which the main product was an N,S-macrochelate formed through linkage of the platinum centre to both the phosphorothioate sulphur ( 15 Figure 1(b)). Although forming the main product, as indicated by the intensity of the cross-peaks in the 2D [ 1 H, 15 N] HSQC NMR data, some formation of an N7, N7 cross-link also occurred, although to a much lesser extent, as indicated by the presence of cross-peaks at the same chemical shifts as those for 3 and 4 in Figure 1( [25] and in line with previous findings [14]. Thus, as an isolated structural element, it is clear that sufficient reactivity and structural flexibility exists in the dimer d(GsG), IIs, to form the S,N macrochelate in the same manner as that reported previously for the self-complementary duplex ODN R,S-5d(TATGsGCCATA) 2 -3 .…”

“…The presence of a 15 N spin-label within the inorganic complex allows reactions to be elegantly monitored by means of 2D [ 1 H, 15 N] HSQC NMR spectroscopy according to tried and tested principles. Formerly, it was shown that macrochelate formation occurred in the form of cis-[Pt(NH 3 ) 2 (GDP-β-S)-N7,S] in which Pt was bound to the N7 and S centres of a macrochelate [14]. Reactions with model ODNs were also monitored in a similar way, and speculation was made concerning the nature of the products formed.…”

“…Reactions with model ODNs were also monitored in a similar way, and speculation was made concerning the nature of the products formed. The commercially available model phosphorothioate (sulphur at the β-position on a diphosphate rather than at the α-position on a monophosphate) and the makeup of the manufactured phosphorothioate-labelled ODNs (e.g., self-complementary 5 -TATGsGCCATA-3 for which, in the duplex form, there are potentially three different duplex structures; namely, R,R, R,S = S,R and S,S diastereoisomers) created an unnatural scenario in the former case and an excessive level of complexity in the latter case, which made interpretation of the experimental results somewhat difficult and occasionally inconclusive [14].…”

“…Sulphur is highly reactive towards platinum (II), and where it is available and abundant in biological systems in the form of glutathione (GSH) and free sulphur-containing proteins, a number of different platinum adducts readily form [10][11][12][13]. A concept proposed previously combined the idea of gene targeting in an antisense fashion using phosphorothioate-labelled oligonucleotides together with delivery of Pt II drugs with known clinical success [14], which are also highly reactive towards sulphur targets. Such an approach would enable gene targeting with localized therapy, provided the initial drug delivery could be prosecuted with the drug in a dormant, inactive (i.e., prodrug) state as proposed with activation taking place by means of an external inducing agent [15][16][17].…”

Complex Formation of Divalent Metal Ions with Uridine 5′‐O‐Thiomonophosphate or Methyl Thiophosphate: Comparison of Complex Stabilities with Those of the Parent Phosphate Ligands

“…Furthermore, the kinetically inert Pt( II ) yields, in the form of chloro(diethylenetriamine)platinum( II ) chloride, by reaction with AMPS exclusively a (phosphorothioate)platinum( II ) complex 21. In accord herewith, cis ‐(NH 3 ) 2 PtI 2 forms with guanosine 5′‐ O ‐(2‐thiodiphosphate) (GDP‐β‐S) a macrochelate in which Pt( II ) bridges the phosphorothioate S and guanine N7 atoms 22. There is also a study23 of p ‐nitrophenyl thiophosphate in which the effects of Mg 2+ and Cd 2+ on the rate of hydrolysis of this ester are compared.…”