Metal-stabilized rare tautomers of nucleobases. 2. 2-Oxo-4-hydroxo form of uracil: crystal structures and solution behavior of two platinum(II) complexes containing iminol tautomers of 1-methyluracil

A model for a metal-assisted tautomerization of the pyrimidine model nucleobase 1-methyluracil is presented which, by analogy, could account for mutagenic AT arrow right GC or GC arrow right AT transition in DNA. It involves initial metal binding to the N3 site of a thymine anion, followed by protonation of the exocyclic O4' oxygen, and liberation of the rare 2-oxo-4-hydroxo tautomer which could then mispair with guanine. Three Pt(II) complexes, containing neutral 1-MeUH ligands in the 2-oxo-4-hydroxo tautomeric forms, have been prepared, and the crystal structures of 1 and 3 have been determined. Raman and super(1)H NMR spectroscopies have been used to establish relevant acid-base equilibria and the protonation states of the uracil ligands.