Higher affinity quadruply hydrogen-bonded complexation with 7-deazaguanine urea

UG forms a highly stable quadruply hydrogen-bonded heterocomplex with DAN, but the fidelity of the complex is lowered somewhat by the Hoogsteen-side oligornerization of UG (K-assoc similar to 230 M-1, CDCl3). DeUG was prepared as a more robust analogue of UG lacking the Hoogsteen nitrogen atom. Remarkably, the deaza analogue, DeUG, forms a much more stable complex with DAN (> 10-fold higher K-assoc for DeUG.DAN vs UG.DAN) but also dimerizes more strongly (K-dim = 880 +/- 40 M-1, CDCl3) by adopting a conformation preorganized for both binding and dimerization.