AU-III BINDING TO C5 OF THE MODEL NUCLEOBASE 1,3-DIMETHYLURACIL (1,3-DIMEU) - PREPARATION AND X-RAY CRYSTAL-STRUCTURES OF TRANS-K[AU(CN)(2)CL(1,3-DIMEU(-))] AND OF 2 DERIVATIVES

The reaction of trans-K[Au(CN)(2)Cl-2] with 1,3-dimethyluracil (1,3-Di meU) gives trans-K[Au(CN)(2)Cl(1,3-DimeU(-)-C-5)] (1) which contains t he 1,3-dimethyluracil-5-yl entity (1,3-DimeU(-)-C-5) bound to Au-III. Complex 1 represents the first example of an X-ray structurally charac terized organogold(III) complex of a nucleobase. Further reaction with purine model nucleobases (nb) such as 9-ethylguanine (9-EtGH), 9-meth yladenine (9-MeA), and 1-methylcytosine (1-MeC) leads to mixed nucleob ase complexes of type trans-[Au(CN)(2)(1,3-DimeU(-)-C-5)(nb)](nb = 9-M eA, 2a; nb = 9-EtGH, 3a; nb = 1-MeC, 4a) or to compounds containing th e protonated purine base Hnb(+) and [Au(CN)(2)X(1,3-DimeU(-)-C-5)](-) as a counter ion (X = Cl or CN), e.g. [9-MeAH][Au(CN)(2)Cl(1,3-DimeU(- )-C-5)]. H2O (2b) and [9-EtGH(2)][Au(CN)(3)(1,3-DimeU(-)-C-5)] (3b). T he crystal structures of 1, 2b, and 3b were determined. The C-bound nu cleobase exerts a distinct trans-influence, as evident from long Au-Cl bonds in 1 and 2b (2.340(3) Angstrom and 2.358(6) Angstrom) and a lon g bond (2.082(7) Angstrom) between Au and the cyano ligand trans to 1, 3-DimeU(-) in 3b. (C) 1998 Elsevier Science S.A.