The synthesis of 7-substituted 7-deazaguanine and 7-deazaadenine ribonucleosides 1-2, the incorporation of 3a-d into oligonucleotides, and the stability of the corresponding duplexes and base discrimination are described. The pKa values of 3-4 are determined.

[structure: see text] UG forms a highly stable quadruply hydrogen-bonded heterocomplex with DAN, but the fidelity of the complex is lowered somewhat by the Hoogsteen-side oligomerization of UG (K(assoc) approximately 230 M(-)(1), CDCl(3)). 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...

Excited states of two 7-aminocoumarin derivatives, coumarin 120 (7-amino-4-methylcoumarin) and coumarin 151 (7-amino-4-trifluoromethylcoumarin), were investigated using generalized multiconfigurational quasidegenerate perturbation theory (GMC-QDPT), multiconfigurational quasidegenerate perturbation theory (MC-QDPT) and time-dependent density functional theory (TDDFT) with the B3LYP and CAM-B3LY...