Synthesis of Heterocycles and Nucleosides Forming Higher—Order Structures

: Nucleic acid analogues play a multifaceted role in biology and materials science. Our efforts towards unveiling these roles led to xanthine derivatives that form higher–order structures with quadruplex-forming abilities. In this paper we present further modifications of the xanthine core resulting into 9-deaza and 8-aza-9-deaza heterocycles (pyrrolo[3,2-d]pyrimidines and pyrazolo[4,3-d]pyrimidines, respectively) that form tetrads and other higher–order structures. Addi-tionally, the ring contraction of 5-fluoro-2 (cid:48) ,3 (cid:48) - O -isopropylideneuridine gave rise to the formation of an imidazolidine-4-carboxylic acid nucleoside derivative. Our computational predictions forecasted that the latter derivative will form stable triads.