SYNTHESIS OF OLIGONUCLEOTIDES CONTAINING 2'-DEOXYISOGUANOSINE AND 2'-DEOXY-5-METHYLISOCYTIDINE USING PHOSPHORAMIDITE CHEMISTRY

The synthesis of oligonucleotides containing 2'-deoxy-5-methylisocylid ine and 2'-deoxyisoguanosine using phosphoramidite chemistry in solid- phase oligonucleotide synthesis is described. Supporting previous obse rvations, the N,N-diisobutylformamidine moiety was found to be a far s uperior protecting group than N-benzoyl for 2'-deoxy-5-methylisoeylidi ne. idene-5'(4,4'-dimethoxytrityl)-5-methylisocytidine 3'-(2-cyanoethy l diisopropylphosphoramidite) (Ic) incorporated multiple consecutive r esidues during a standard automated synthesis protocol with a coupling efficiency >99% according to dimethoxytrityl release. Extending coupl ing times of the standard protocol to greater than or equal to 600 s u sing ethoxytrityl)-O-2-(diphenylcarbamoyl)isoguanosine, 3'-(2-cyanoeth yl diisopropylphosphoramidite) (7e) led to successful incorporation of multiple consecutive 2'-deoxyisoguanosine bases with a coupling effic iency > 97% according to dimethoxytrityl release.