Oligonucleotide duplex stability controlled by the 7-substituents of 7-deazaguanine bases

Oligonucleotides containing 7-substituted 7-deazaguanine residues (7-methyl, 7-iodo) have been synthesized. The self-complemetary octamer d(I7c7G-C)4 containing 7-iodo-7-deaza-2′-deoxyguanosine forms a stabilized duplex compared to the parent oligomer d(G-C)4 (ΔTm = +10° C). Also the complex between the oligodeoxynucleotide d(I7c7G5-G) and poly(C) is stabilized (ΔTm = +10°) over that of d(c7G5-G) with poly(C).