1,3,9‐Triaza‐2‐oxophenoxazine: An Artificial Nucleobase Forming Highly Stable Self‐Base Pairs with Three AgI Ions in a Duplex

Metal‐mediated base pairs (MMBPs) formed by natural or artificial nucleobases have recently been developed. The metal ions can be aligned linearly in a duplex by MMBP formation. The development of a three‐ or more‐metal‐coordinated MMBPs has the potential to improve the conductivity and enable the design of metal ion architectures in a duplex. This study aimed to develop artificial self‐bases coordinated by three linearly aligned AgI ions within an MMBP. Thus, artificial nucleic acids with a 1,3,9‐triaza‐2‐oxophenoxazine (9‐TAP) nucleobase were designed and synthesized. In a DNA/DNA duplex, self‐base pairs of 9‐TAP could form highly stable MMBPs with three AgI ions. Nine equivalents of AgI led to the formation of three consecutive 9‐TAP self‐base pairs with extremely high stability. The complex structures of 9‐TAP MMBPs were determined by using electrospray ionization mass spectrometry and UV titration experiments. Highly stable self‐9‐TAP MMBPs with three AgI ions are expected to be applicable to new DNA nanotechnologies. Metal‐mediated base pairs: 1,3,9‐Triaza‐2‐oxophenoxazine (9‐TAP) was synthesized and incorporated into oligonucleotides. 9‐TAP formed highly stable metal‐mediated base pairs (MMBPs) with three AgI ions even with three consecutive modifications.