Structural studies reveal enantiospecific recognition of a DNA G-quadruplex by a ruthenium polypyridyl complex

By using X-ray crystallography, we show that the complexes Λ/Δ-[Ru(TAP)${}_2$(11-CN-dppz)]${}^{2+}$ (TAP=1,4,5,8-tetraazaphenanthrene, dppz=dipyridophenazine) bind DNA G-quadruplex in an enantiospecific manner that parallels the specificity of these complexes with duplex DNA. The Λ complex crystallises with the normally parallel stranded d(TAGGGTTA) tetraplex to give the first such antiparallel strand assembly in which syn-guanosine is adjacent to the complex at the 5′ end of the quadruplex core. SRCD measurements confirm that the same conformational switch occurs in solution. The Δ enantiomer, by contrast, is present in the structure but stacked at the ends of the assembly. In addition, we report the structure of Λ-[Ru(phen)${}_2$(11-CN-dppz)]${}^{2+}$ bound to d(TCGGCGCCGA), a duplex-forming sequence, and use both structural models to provide insight into the motif-specific luminescence response of the isostructural phen analogue enantiomers. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)