Duplex-stabilization properties of oligodeoxynucleotides containing N-2-substituted guanine derivatives

Oligodeoxynucleotides 3-13 carrying different guanine derivatives with subs tituents at the N-2 position have been prepared from a common precursor. Du plexes containing these modified bases are more stable than unmodified dupl exes. The highest stability is found in guanine derivatives carrying at N-2 an ethyl and propyl group substituted with a group that is protonated unde r physiological conditions, which is compatible with a possible interaction of the protonatable group with the phosphates.