Abstract: A synthetic catalytic oligonucleotide structure and nucleotides having the general structural formula (I) contains: ##STR1## in which B represents a nucleoside base which is in particular selected from the group comprising adenin-9-yl (A), cytosin-1-yl (C), guanin-9-yl (G), uracil-1-yl (U), uracil-5-yl (.psi.), hypoxanthin-9-yl (I), thymin-1-yl (T) and 2-aminoadenin-9-yl,V in each nucleotide is independently an O or a CH.sub.2 group,X and W can in each nucleotide be the same or different and are independently of each other O, S, NH.sub.2, alkyl or alkoxy groups with 1 to 10, preferably with 1 to 4 carbon atoms,R is hydrogen or a straight-chained or branched alkyl, alkenyl or alkinyl group with 1 to 10 carbon atoms which is substituted, if desired, with halogen, cyano, isocyano, nitro, amino, carboxyl, hydroxyl or/and mercapto groups, and in which in at least one of the nucleotides the residue R in formula (I) is different from hydrogen and is suitable for the cleavage of a nucleic acid target sequence.