Figure 1.

Schematic representation of the antiparallel G-quadruplex structure of TBA (a), the duplex/quadruplex structure of NU172 (b), its minimal G4 motif indicated as NU (c) and a general scheme for cyclic NU172 analogues (d) with a linker connecting the 3′- and 5′-ends of the oligonucleotide sequence. The guanines involved in the G-quadruplex core formation are highlighted in light blue, while the duplex module is depicted in green. In both NU and NU172 structures, the nucleobases of the G4 core differing from TBA are indicated in dark red.