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Structurally modified nucleosides are central players in the field of nucleic acid chemistry. Adenine-thymine (AT) pyrimido[4,5-d]pyrimidine furanosyl and pyranosyl arabinonucleosides have been synthesized for the first time. Single-crystal X-ray diffraction analysis reveals novel base pairs that, in synergy with the sugar residues, direct the emergence of distinct networks containing channels and cavities. The microscopic noncovalent connections can be translated into macroscopic levels in which robust organogels are formed by the furanoside but not the pyranoside. The influences of the sugars are also displayed by the different shaped superstructures of the free nucleosides in solution. The readout of the information in the base moiety is therefore tailored by the sugar configuration, and the interplays exert subtle effects on the structures, from solid to gel and to the solution state. The potential for forming these appealing base pairs and higher structures enables these intriguing nucleosides to serve as unique building blocks in various areas or to construct innovative nucleic acid structures. [ABSTRACT FROM AUTHOR]

The intrinsic structural diversity of the nucleosides is one of the essential properties for their wide participation in myriads of chemical or biochemical processes. Two unique regio-isomeric Janus-type AT nucleosides with the 5′-deoxyribose attached on N1 or N3 position has been synthesized through Vorbrueggen or transglycosylation reactions. These two isomers display different supramolecular morphologies in solution state from their N8 glycosylated counterpart. The underneath structural details of the N3 glycosylated isomer were revealed by the single-crystal X-ray analysis. In addition to a novel base pair pattern was identified which is entirely different from the reverse Watson-Crick base pair adopted by its N8 isomer, an interesting water-filled columnar nanotuble-like structure was also found in its solid state. This study not only enriches the structural varieties of AT Janus-type nucleosides, but also provides specific information concerning the effect of the sugar glycosylation position on the properties of these new type of pyrimido[4,5-d]pyrimidine nucleosides. [ABSTRACT FROM AUTHOR]