8-aza-7-deazaadenine and 7-deazaguanine: Synthesis and properties of nucleosides and oligonucleotides with nucleobases linked at position-8

The 8-aza-7-deazaadenine (pyrazolo[3,4-d]pyrimidin-4-amine) N-8-(2'-deoxyri bonucleoside) (2) and the 7-deazaguanine (pyrrolo[3,4-d]pyrimidine-2-amin-( 3H)-4-one) C-8-(2'-deoxyribonucleoside) (4) were synthesized and incorporat ed in oligonucleotides employing phosphoramidite chemistry. Oligonucleotide s carrying compound 2 are able to form base pairs with the four canonical D NA constituents without significant structural discrimination. The nucleosi de 4 was obtained from the corresponding ribonucleoside by deoxygenation. O ligonucleotides containing compound 4 showed similar base pairing propertie s as those with 2'-deoxyisoguanosine.