Solution Structure and Conformational Dynamics of Deoxyxylonucleic Acids (dXNA): An Orthogonal Nucleic Acid Candidate

Orthogonal nucleic acids are chemically modified nucleic acid polymers that are unable to transfer information with natural nucleic acids and thus can be used in synthetic biology to store and transfer genetic information independently. Recently, it was proposed that xylose‐DNA (dXNA) can be considered to be a potential candidate for an orthogonal system. Herein, we present the structure in solution and conformational analysis of two self‐complementary, fully modified dXNA oligonucleotides, as determined by CD and NMR spectroscopy. These studies are the initial experimental proof of the structural orthogonality of dXNAs. In aqueous solution, dXNA duplexes predominantly form a linear ladderlike (type‐1) structure. This is the first example of a furanose nucleic acid that adopts a ladderlike structure. In the presence of salt, an equilibrium exists between two types of duplex form. The corresponding nucleoside triphosphates (dXNTPs) were synthesized and evaluated for their ability to be incorporated into a growing DNA chain by using several natural and mutant DNA polymerases. Despite the structural orthogonality of dXNA, DNA polymerase β mutant is able to incorporate the dXNTPs, showing DNA‐dependent dXNA polymerase activity. The acid test: The structural and biochemical aspects of xylose‐DNA (dXNA; see scheme) have been explored, with the aim of using it as an orthogonal nucleic acid system to transfer genetic information without interfering with the natural system. The study identifies the properties for developing dXNA as an alternate information system, although it also finds the reasons why dXNA was not selected as the natural genetic system.