NICKEL-CATALYZED OXIDATIONS - FROM HYDROCARBONS TO DNA

Nickel(II) complexes of tetradentate ligands such as cyclam and salen are catalysts for olefin epoxidation using PhIO and NaOCl, respectivel y. In order to understand the lack of enantioselectivity observed with chiral cyclam and salen complexes, studies of DNA and RNA oxidation w ere carried out in which evidence for diffusible oxidants might be fou nd. A variety of square-planar, tetradentate nickel(II) complexes were observed to mediate guanine-specific modification in the presence of KHSO5 or magnesium monoperphthalate. In particular, the cationic compl ex, [(2,12-dimethyl-3,7,11,17-tetraazabicyclo heptadeca-1(17),2,11,13, 15-pentaenato)nickel](2+), [NiCR](2+), has been studied as a probe of nucleic acid folding. The extent of guanine reaction depends upon the exposure of N7, a good transition metal binding site, thus implicating nickel-guanine binding during DNA oxidation. If this is the case, rel ated systems should be able to confer enantioselectivity during the us e of chiral nickel complexes and achiral substrates for oxidation. Mec hanistic studies, including radical quenching and DNA enantioselectivi ty, are described and their mechanistic implications discussed.