Binding site and equilibrium constant of ethylenediamineplatinum(II) or triamineplatinum(II) to thymidine

Abstract

The complex of thymidine with (NH 3) 3Pt(OH 2) or (en)Pt(OH 2) 2, where en = ethylenediamine, have been prepared in aqueous solution at pH = 7. The isolated complexes, corresponding to the formula [(NH 3) 3Pt(ThdH −1)]NO 3 and (en)Pt(ThdH −1) 2 where ThdH −1 = mono anion of thymidine, have been characterized by nmr, ir, and uv spectra. The binding site is the N(3) position of ThdH −1. The equilibrium constant for (NH 3) 3Pt(OH 2) + ThdH −1 ⇌ (NH 3) 3Pt(ThdH −1), in which the equilibrium of binding is pH dependent, was estimated from integrated intensity ratio of the proton of position 6 of thymidine, and log K was 10.4 ± 0.1. In the case of (en)Pt(ThdH −1) 2, the log K 1 for (en)Pt(OH 2) 2 + ThdH −1 ⇌ (en)Pt(OH 2)(ThdH −1) was 10.3 ± 0.1, and the log K 2 for (en)Pt(OH 2)(ThdH −1) + ThdH −1 ⇌ (en)Pt(ThdH −1) 2 was 7.4 ± 0.1.