Synthesis and Structural Characterization of Stable Branched DNA G‐Quadruplexes Using the Trebler Phosphoramidite

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Abstract
Guanine (G)‐rich sequences can form a noncanonical four‐stranded structure known as the G‐quadruplex. G‐quadruplex structures are interesting because of their potential biological properties and use in nanosciences. Here, we describe a method to prepare highly stable G‐quadruplexes by linking four G‐rich DNA strands to form a monomolecular G‐quadruplex. In this method, one strand is synthesized first, and then a trebler molecule is added to simultaneously assemble the remaining three strands. This approach allows the introduction of specific modifications in only one of the strands. As a proof of concept, we prepared a quadruplex where one of the chains includes a change in polarity. A hybrid quadruplex is observed in ammonium acetate solutions, whereas in the presence of sodium or potassium, a parallel G‐quadruplex structure is formed. In addition to the expected monomolecular quadruplexes, we observed the presence of dimeric G‐quadruplex structures. We also applied the method to prepare G‐quadruplexes containing a single 8‐aminoguanine substitution and found that this single base stabilizes the G‐quadruplex structure when located at an internal position.

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