Competitive formation of both long-range 5'-5' and short-range antiparallel 3'-3' DNA interstrand cross-links by a trinuclear platinum complex on binding to a 10-mer duplex

Abstract

2D [(1)H, (15)N] HSQC NMR spectroscopy has been used to monitor the reaction of fully (15)N-labelled [{trans-PtCl(NH(3))(2)}(2)(μ-trans-Pt(NH(3))(2){NH(2)(CH(2))(6)NH(2)}(2))](4+) (Triplatin, BBR3464 or 1,0,1/t,t,t ((15)N-1)) with the self-complementary 10-mer DNA duplex 5'-{d(ACGTATACGT)(2)} (duplex I) at pH 5.4 and 298 K. Initial electrostatic interactions were observed in the minor groove of the duplex, followed directly by aquation to form the monoaqua monochloro species. There was evidence for two discrete monofunctional adducts, through covalent binding at the guanine N7 sites, and one had distinctly different (1)H/(15)N chemical shifts to those observed previously in analogous reactions. Bifunctional adduct formation followed by binding at a second guanine N7 site with evidence for both the 3'-3' 1,2-GG and 5'-5' 1,6-GG interstrand cross-links in a ratio of 2 : 1. The results show that cross-link preference is kinetically controlled and will depend critically on the reaction conditions, explaining why in a previous reaction of 1 with duplex I the major adduct isolated by HPLC had two simultaneous 3'-3' 1,2-interstrand cross-links.

Figure 1

2D [¹H,¹⁵N] HSQC NMR (600 MHz) spectra recorded at 298K of ¹⁵N-1 after addition to duplex I for the times shown. Peaks have been assigned to the end and linker Pt–¹⁵NH₃ groups for the structures 1–4 shown in Scheme 1. The peak labelled '*' is assigned to a phosphate derivative {PtN₃OP} of ¹⁵N-1 based on species observed previously.

Figure 2

The aromatic region of the ¹H NMR spectra (600 MHz) of duplex I after the addition of ¹⁵N-1 for the times shown. Assignments have been made for the monofunctional species (3) and the bifunctional adducts (4X and 4Y).

Figure 3

¹H chemical shift changes (Δδ = δ (duplex I: ¹⁵N-1) - δ (duplex I)) seen after the addition of ¹⁵N-1 to duplex I. Key: circles (brown) H2 protons; squares (red) aromatic H8/H6 protons; × (blue) H41 protons. The complementary strand is shown in italics.

Figure 4

Plots of the relative concentrations of species observed during the reaction of ¹⁵N-1 with duplex I, based on intensities of the cross-peaks in the Pt-¹⁵NH₃ region of the 2D [¹H, ¹⁵N] HSQC spectra. Labels: dichloro species (1) open squares; monofunctional species (3) filled triangles; bifunctional adducts (4) filled circles.

Scheme 1

Reaction of ¹⁵N-1 with duplex I. The two possible GN₇–GN₇ interstrand cross-links are labelled: 3´–3´ 1,2–GG IXL (red) and 5´–5´ 1,6-GG IXL (blue).

Chart 1