1,4-Dihydroxyanthraquinone and 1,8-dihydroxyanthraquinone were alkylated with 3-bromopropan-1-ol and subsequently
transformed into the corresponding DMT protected phosphoramidite building blocks for insertion into loops of the G-quadruplex of the thrombin binding aptamer (TBA). The 1,4-disubstituted anthraquinone linker led to a significant stabilization of the G-quadruplex structure upon replacing a T in each of two neighboring lateral TT loops and a 26.28 increase in thermal melting temperature was found. CD Spectra of the modified quadruplexes confirmed anti-parallel conformations in all cases under potassium buffer conditions as previously observed for TBA. Although the majority of the anthraquinone modified TBA analogues showed a decrease in clotting times in a fibrinogen clotting assay when compared to TBA, modified aptamers containing a 1,8-disubstituted anthraquinone linker replacing G8 or T9 in the TGT loop showed improved anticoagulant activities. Molecular modeling studies explained the increased thermal melting temperatures of anthraquinone-modified G-quadruplexes.