A Fluorescent Sensor for 2,3‐Bisphosphoglycerate Using a Europium Tetra‐N‐oxide Bis‐bipyridine Complex for Both Binding and Signaling Purposes

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Abstract
Host 1 was designed and synthesized as a fluorescent sensor for 2,3-bisphosphoglycerate (BPG, 3). The design features a tris-functionalized triethylbenzene core to preorganize binding groups. The three cationic moieties, a tetra-N-oxide bipyridine–europium complex and two ammonium groups, were included to complement the three anionic functionalities on the guest. Beyond acting as a binding site, the europium complex was used to signal binding of the guest through modification of the charge transfer emission. A 1:1 complex with BPG was determined in 50 % methanol/acetonitrile with a Ka of 6.7×105 mol−1 by monitoring the reduction of the fluorescence signal upon guest addition. In the titration of related glycolytic intermediates lacking a second phosphate (4–6) into host 1, 2:1 host to guest binding was observed. Similarly, control compound 2, which lacks the ammonium groups, binds BPG and 4–6 in a 2:1 fashion. Also, phenylphosphate 7 binds to host 1 in a 1:1 stoichiometry with a Ka over three times less than 3.