It is one object of the present invention to provide an oligonucleotide of formula (1): 5'-(U)n-3' in which U is an identical or different radical of a natural or a synthetic nucleoside, wherein the oligonucleotide comprises at least one modified nucleotide dimer comprising two nucleoside analogs connected via an amide-bond that has a certain configuration; the synthesis of these compounds and their use in pharmaceutical preparations.