Novel oligonucleotide analogs of the formula (I) are described, ##STR1## in which A, B, D, G, L, P, Q, Q', R.sup.5, R.sup.6, X, Y, Z and n are as defined in the description, which have useful physical, biological and pharmacological properties, as well as a process for their preparation. Their application relates to use as inhibitors of gene expression (antisense oligonucleotides, ribozymes, sense oligonucleotides and triplex-forming oligonucleotides), as probes for the detection of nucleic acids and as auxiliaries in molecular biology.