METAL-STABILIZED RARE TAUTOMERS OF NUCLEOBASES .5. IMINOOXO TAUTOMER OF CYTOSINE COORDINATED TO PT(II) WITH METAL AND NUCLEOBASE IN SYN ANDANTI ORIENTATIONS

A Pt-II complex containing N4 bound neutral 1-methylcytosine (1-MeC), trans-[Pt(NH3)(2)(1-MeC-N4)(2)](ClO4)(2) (5), has been prepared and ch aracterized by X-ray analysis. The complex contains the rare iminooxo tautomer form of the cytosine nucleobase. Pt-II binding is through the exocyclic N4 position of the nucleobases, with Pt and the N3 position s in a syn orientation. As a consequence, the proton at N3 is pointing toward the heavy metal, thereby allowing an agostic Pt ... HN interac tion. Formation of 5 is achieved via oxidation of the linkage isomer t rans-[Pt(NH3)(2)(1-MeCN3)(2)](2+) (1) to a Pt-IV species (2), followed by metal migration to N4, and subsequent reduction to Pt-II. This pro cess is a text-book example for a redox-assisted metal migration at a heterocyclic ligand. The existence of various rotamers of 5 in aqueous solution is evident from H-1 NMR spectroscopy. The possible role of t hese rotamers of the metalated rare tautomer, and in particular of tho se having Pt and the N3 position in an anti arrangement, with regard t o base mispairing is discussed.