Lumos: A β‐Diketone‐Derived Artificial Nucleobase Forming Inter‐Strand Complexes in DNA that Promote Lanthanoid Ion Luminescence

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Abstract
A novel artificial nucleobase, 1‐(3‐(hydroxymethyl)phenyl)‐3‐phenylpropane‐1,3‐dione (HdbmOR), containing a β‐diketone designed to form inter‐strand complexes that resemble metal‐mediated base pairs, was synthesized and characterized towards its lanthanoid ion binding properties. Based on UV/vis spectra, a (labile) coordination of EuIII and SmIII by the benzyl‐functionalized model ligand is proposed, allowing the detection of distinct luminescence patterns upon coordination under alkaline conditions. The compatibility of the nucleoside analog with automated solid‐phase DNA synthesis was proven by the generation of a dinucleotide. NMR spectroscopic characterization of this dinucleotide revealed a temperature‐dependent equilibrium of two conformers, which likely involve hydrogen bonding of the β‐diketone moiety and the deoxyribose and/or phosphate moieties. The antenna effect of the new ligand promoting the luminescence of EuIII is retained upon incorporation into DNA. Modification of a parallel‐stranded DNA duplex with a terminal homo base pair of HdbmOR allows, despite natural fraying of DNA, a thermal stabilization of about 3 °C upon coordination of EuIII or SmIII. Temperature‐dependent luminescence spectroscopy demonstrates a direct correlation between the thermal stability of the duplex and its luminescence intensity. The ligand extends the library of artificial nucleobases for lanthanoid‐mediated base pairs, combining the luminescence properties of lanthanoid complexes with the self‐assembly properties of DNA.

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