The basic objective of this programme is the introduction of a new principle in Slovenian medicinal chemistry research; e.g. antisence and antigene approach concerning antiviral and anticancer chemotherapy which is based on the synthesis of specific oligonucleotides. Our approach is based on a design of new unnatural oligonucleotides (ODN) possessing guanine building blocks in which carbon atoms are replaced by nitrogen atoms or vice versa, resulting in lipophilic bases -3-deaza guanines or ribavirin. Specific structural changes of duplexes and triplexes are anticipated as are the formation of higher order supramolecules (quadruplexes) as telomerase inhibitors. Ribavirin is a particular example, it behaves like universal nucleoside which could be selectively platinated, and could be utilized as a suitable model in anticancer research concerning the mechanisms of Pt(II) anticancer drugs. These objectives required derivatization of nucleosides into building blocks which are then introduced into specific sites of the ODN. The synthesis is novel, ODNs are novel, although the structural and biological effects are still unknown. We were looking for particular properties affecting the content of water molecules in a helix. The replacement of N3 in the guanine moiety should influence those enzymes that bind to a guanine molecule. Besides, we found the formation of particularly modified quadruplexes and their properties very unique and interesting.