Nucleotide monomers containing 8-azapurin bases or a derivative thereof, their preparation and their use in making modified olignonucleotides

A nucleotide monomer of the formula V ##STR19## in which V is oxy, sulfanediyl or imino;

• Y.sup.b is oxy, sulfanediyl, or methylene;
• a is oxy or methylene;
• R.sup.2b is hydrogen, OR.sup.12, C.sub.1 -C.sub.18 -alkoxy, C.sub.1 -C.sub.6 -alkenyloxy, halogen, azido or NR.sup.10 R.sup.11 ;
• R.sup.1 is a protective group which is customary in nucleotide chemistry;
• R.sup.1b is a radical of the formula IIc or IId ##STR20## in which U is O--R.sup.7 or S--R.sup.7 ;
• Q is a radical --NR.sup.8 R.sup.9 ;
• R.sup.7 is --(CH.sub.2).sub.2 --CN;
• R.sup.8 and R.sup.9 are identical or different and are C.sub.1 -C.sub.6 -alkyl, or, together with the nitrogen atom carrying them, are a 5-9-membered heterocyclic ring which can additionally contain a further heteroatom selected from the group O, S, and N,
• E' and F' are, independently of each other, H, OH, or NR.sup.10 R.sup.11,
• R.sup.10 and R.sup.11 are identical or different and are hydrogen or an amino protective group which is customary in nucleotide chemistry, or R.sup.10 and R.sup.11 together form an amino protective group which is customary in nucleotide chemistry,
• R.sup.12 is a hydroxyl protective group which is customary in nucleotide chemistry,
• and the curved bracket indicates that R.sup.2b and the adjacent phosphoryl radical can be in the 2' and 3' positions, or else, conversely, in the 3' and 2' positions.