## 1 Introduction  
The abbreviations DNA and RNA are perhaps the most widely recognized words associated with biology or genetics. The details of their chemical structure as well as the principles of their interactions with other nucleic acids were established in the 20 th century, but modern analytical methods developed in recent years allow the study of their still poorly understood subtle interactions with other biomolecules. On the other hand, significant advances in organic and analytical chemistry have led to the synthesis of numerous DNA and RNA analogs that can be used as biochemical probes or drugs. To target DNA or RNA in cells, these analogs must not only cross outer cell membranes and form stable complexes with the target molecules in a sequence-specific manner, but they should also have some resistance to nucleases in body fluids. The beneficial use of multiple COVID-19 vaccines is a very compelling example of the importance of nucleic acid analogs to billions of people. A single nucleotide unit consists of three segments that are chemically very different from each other. The heterocyclic nucleobases serve as acceptors and donors of hydrogen bonds and are responsible for proper intermolecular recognition. In addition, stacking interactions are important in conferring a high degree of rigidity to oligomers and higher-order structures. The anionic phosphodiester groups are reasonably stable under mild hydrolytic conditions, but they are important for hydration and may be involved in electrostatic interactions with positively charged amino acid side chains and other cationic species. Not to be neglected is the electrostatic repulsion between the phosphate moieties present in the oligonucleotide chains forming a complex, which contribute to the rigidity of the entire DNA or RNA system. The third component comprises of sugar moieties (ribose or 2\({}^{\prime}\)-deoxyribose), which are present in the cyclic form. Notably, the pseudo-rotational flexibility of the ribonucleotide is considerably limited due to the anomeric effect, and RNA/RNA and RNA/DNA duplexes are generally more thermally stable than DNA/DNA duplexes. The rigidity of the cyclic scaffold has been considered important for the formation of thermally stable duplexes [1], and the unexpectedly high thermal stability of duplexes formed with the participation of LNA oligomers could serve as an excellent justification for this point of view. However, this generalization is not consistent with the behavior of Peptide Nucleic Acids (PNA), in which the heterocyclic bases are attached to a linear peptide-like backbone, since duplexes composed of RNA or DNA and PNA strands are far more stable than RNA/RNA and DNA/DNA ones. This phenomenon may be attributed to the absence of a negative charge in the backbone, such that the absence of repulsive interactions balances the entropic cost of proper spatial organization of the flexible PNA scaffolds. Nonetheless, the widely accepted importance of the cyclic sugar components for the stability of the duplexes could be questioned. There is another perspective that can be applied to the acyclic analogs of nucleic acids that is related to the origin of life. We are currently witnessing an ongoing dispute about which molecule, DNA or RNA, was the first to mark the beginning of life in its modern form, i.e., were the first carriers of the contemporary genetic information. However, even if the correct answer is finally found, there is still the question of its possible predecessors. The first suggestion that oligomers with an acyclic flexible scaffold carrying pro-chiral nucleotide analogs might play such a role was made in 1987 by [PERSON] et al. [2]. These flexible structures seemed to be easier to produce than deoxyribo- or ribo-nucleosides under prebiotic conditions. To assess the possibility of their involvement in, for example, primer extension experiments, which could be considered the simplest biochemical probe showing a \"living-like\" system, chemists had to make several model compounds.