Oligodeoxynucleotides containing 2'-O-modified adenosine: Synthesis and effects on stability of DNA:RNA duplexes

Hybridization thermodynamics were compared for oligonucleotide sequences containing 2'-fluoro dA, 2'-O-methyl A, 2'-O-ethyl A, 2'-O-propyl A, 2'-O-butyl A, 2'-O-pentyl A, 2'-O-nonyl A, 2'-O-allyl A, and 2'-O-benzyl A in place of deoxyadenosine. Although the effect of 2'-modified adenosine on duplex stability is sequence dependent, a clear trend is apparent. For six sequences containing a few 2'-modified adenosines in a background of unmodified deoxynucleotides, the average ΔT M per substitution ranged from +1.3 o C for 2'-fluoro dA to -2.0 o C for 2'-O-nonyl A