Fluorescent sensors that bind metal cations are important tools for tracking those ions in living cells. Specifically, a fluorescent probe for lithium ion would aid researchers in understanding how lithium salts treat bipolar disorder. A coumarin-based molecule was substituted, using a methylene bridge, with a 1-aza-9-crown ether at the 3-position for this purpose. Following published procedures, 8-hydroxyjulolidine-9-carboxaldehyde and diethylmalonate were reacted to form the coumarin ring system by a Knoevenagel condensation. The resulting ester was hydrolyzed from the 3-position by strong acid and replaced with an aldehyde via a Vilsmeier-Haack reaction. The final two steps of the five-step synthetic pathway to yield the target fluorescent sensor were adapted from the literature. A reductive amination using PEMB and ammonium acetate transformed the aldehyde to a primary amine.  Subsequent reaction with 1,2-bis(2-iodoethyoxy)ethane generates the 1-aza-9-crown-3 ring to complete the synthesis. The final product was titrated with biologically relevant cations to determine binding constants.

Synthesis of a 1-aza-9-crown-3-substituted coumarin for fluorescence sensing of metal ions

249th National Meeting (2015)

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