Efficient Silver(I)‐Containing I–Motif DNA Hybrid Catalyst for Enantioselective Diels–Alder Reactions.

The inherent chiral structures of DNA serve as attractive scaffolds to construct DNA hybrid catalysts for valuable enantioselective transformations. Duplex and G‐quadruplex DNA‐based enantioselective catalysis has made great progress, yet novel design strategies of DNA hybrid catalysts are highly demanding and atomistic analysis of active centers is still challenging. DNA i‐motif structures could be finely tuned by different cytosine‐cytosine base pairs, providing a new platform to design DNA catalysts. Herein, we found that a human telomeric i‐motif DNA containing cytosine‐silver(I)‐cytosine (C‐Ag+‐C) base pairs interacting with Cu(II) ions (i‐motif DNA(Ag+)/Cu2+) could catalyze Diels–Alder reactions with full conversions and up to 95 % enantiomeric excess. As characterized by various physicochemical techniques, the presence of Ag+ is proved to replace the protons in hemiprotonated cytosine‐cytosine (C : C+) base pairs and stabilize the DNA i‐motif to allow the acceptance of Cu(II) ions. The i‐motif DNA(Ag+)/Cu2+ catalyst shows about 8‐fold rate acceleration compared with DNA and Cu2+. Based on DNA mutation experiments, thermodynamic studies and density function theory calculations, the catalytic center of Cu(II) ion is proposed to be located in a specific loop region via binding to one nitrogen‐7 atom of an unpaired adenine and two phosphate‐oxygen atoms from nearby deoxythymidine monophosphate and deoxyadenosine monophosphate, respectively. [ABSTRACT FROM AUTHOR]