Phenanthrene‐Derived DNA Hairpin Mimics

Self‐complementary oligodeoxynucleotides containing 3,6‐disubstituted phenanthrenes adopt highly stable, hairpin‐like structures. The thermodynamic stability of the hairpin mimics depends on the overall length of the phenanthrene building block. Hairpin loops composed of a phenanthrene‐3,6‐dicarboxamide and ethylene linkers were found to be optimal. The hairpin mimics are more stable than the analogous hairpins containing either a dT₄ or dA₄ tetraloop. Model studies indicate that the thermodynamic stability of the hairpin mimics is primarily due to aromatic stacking of the phenanthrene‐3,6‐dicarboxamide onto the adjoining base pair of the DNA duplex.