Chemical compounds comprised of an oligonucleotide or an oligodioxinucleotide. According to the invention, they comprise a chain of nucleotides with an anomeric unnatural alpha configuration. The invention also relates to a chain of alpha nucleotides which is linked by a covalent bond to an effector agent, particularly to an intercalating radical or to a chemical photoactivatable or reactive radical. The invention also relates to an application of the compounds, application according to which they couple in parallel to a complementary sequence of beta oligonucleotides. These compounds are usable as probes or as artifical nucleases specific of sequences of nucleic acids. They may be used to selectively lock the expression of a previously selected gene by acting either on the genetic information or on the messenger RNAs.