REACTIONS OF 1,10-PHENANTHROLINE COMPLEXES OF PT(II) WITH PURINES - EVIDENCE FOR MONO-COORDINATED 2,9-DIMETHYL-1,10-PHENANTHROLINE (DMPHEN)LIGAND IN THE COMPLEX BETWEEN [PT(DMPHEN)CL-2] AND GUANOSINE

This report describes the synthesis and characterization of Pt(II)-bis (guanosine) (R-phen) complexes (where R=H (phen) or 2,9-dimethyl (dmph en)), as a model for bifunctional covalent adduct formation between an titumor (dichloro) Pt(II)amine complexes and DNA bases. The H-1 and C- 13 NMR spectra (in D2O) of the isolated product in the reaction of the corresponding [(dichloro) (R-phen)Pt(II)] complex, with 2 mole equiva lents of guanosine, reveal formatin of a cis-bis(guanosine) (phen)Pt(I I) (1) and a trans-bis(guanosine)(dmphen)(Cl)Pt(II) (2). The H-1 NMR s pectrum of 1 reveals a mixture of head-to-tail (htt) and head-to-head (hth) rotamers that do not interconvert on the NMR time scale (200 and 400 MHz, 298-343 K). For complex 2 the formation of a trans-bis(guo) complex with mono-coordinated dmphen ligand is in accord with recent f indings in analogous reactions of [Pt(dmphen)Cl-2] with alkenes, alkyn es and aryl phosphine ligands. It is noteworthy that the room-temperat ure H-1 NMR spectrum of 2 in D2O showed no intramolecular process due to 'flipping' of the mono-coordinated dmphen ligand; this is in contra st to observations with trans-bis(PPh3) complex (in CD2Cl2, RT) previo usly reported. The NMR spectral data of the two complexes have been re -examined and the different behavior is discussed. (C) 1997 Elsevier S cience S.A.