Issue Date: January 1, 2007
Fluorometric Assay For Boronic Acids
A fluorescence-based sensing method that can be used for simple in situ monitoring of the consumption of boronic acids in order to optimize Suzuki-Miyaura coupling reactions has been created by Timothy E. Barder and Stephen L. Buchwald of Massachusetts Institute of Technology (Org. Lett., DOI: 10.1021/ol062802q). Boronic acids are key reagents in coupling reactions, but chromatography to follow the progress of a reaction is cumbersome and can be costly. Thus, chemists are prompted to run reactions with an excess of boronic acid even though it's usually the most expensive reagent in the reaction pot. Barder and Buchwald reasoned that a simple fix would be to add an inexpensive indicator dye to the reaction, and they settled upon 6,7-dihydroxy-4-methylcoumarin. The coumarin reversibly binds boronic acids to form complexes that fluoresce under a standard lab UV lamp (right vial). The binding doesn't interfere with the coupling reaction, and as the boronic acid is used up and the coumarin dissociates, the fluorescence fades away (left vial).
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