Synthesis of modified nucleosides for incorporation of formyletheno and carboxyetheno adducts of adenine nucleosides into oligonucleotides.

Three protected derivatives of 1,N(6)-ethenoadenine nucleosides, viz. 3-[5-O-(4,4'-dimethoxytrityl) of 7-formyl-(1) and 7-(1,2-diacetyloxypropyl)-2'-deoxyadenosine (2), and 3-[5-O-(4,4'-dimethoxytrityl)-2-O-(tert-butyldimethylsilyl)-7-(ethoxycarbonyl)adenosine (3), expected to allow introduction of formyletheno and carboxyethenoadenine adducts into oligonucleotides by the conventional phosphoramidite chemistry, have been synthesized.