7-deazaadenine-DNA: Bulky 7-iodo substituents or hydrophobic 7-hexynyl chains are well accommodated in the major groove of oligonucleotide duplexes

Abstract

Oligonucleotides containing 7-deaza-7-(hex-1-ynyl)-2'-deoxyadenosine (1) and 7-deaza-7-iodo-2'-deoxyadenosine (2) are described. The corresponding phosphoramidites (3 a,b) were synthesized and employed in solid-phase oligonucleotide synthesis. The modified 7-deazaadenine residues show selective base-pairing with dT. According to the T-m values and the thermodynamic data of duplex formation, the 7-iodo and the 7-(hex-1-ynyl) residues of a 7-deazaadenine moiety increase the duplex stability with retention of the particular DNA structure. This is different from 8-substituted adenine, which destabilizes the nucleic acid duplex significantly. The nucleoside 1 fluoresces strongly.