Nitroxide-DerivedN-Oxide Phenazines for Noncovalent Spin-Labeling of DNA

Twoo-benzoquinone derivatives of isoindoline were synthesized for use as building blocks to incorporate isoindoline nitroxides into different compounds and materials. Theseo-quinones were condensed with a number ofo-phenylenediamines to form isoindoline-phenazines in high yields. Subsequent oxidation gave phenazine-di-N-oxide isoindoline nitroxides that were evaluated for noncovalent and site-directed spin-labeling of duplex DNA and RNA that contained abasic sites. Although only minor binding was observed for RNA, the unsubstituted phenazine-N,N-dioxide tetramethyl isoindoline nitroxide showed high binding affinity and selectivity towards abasic sites in duplex DNA that contained cytosine as the orphan base.