Three coumarin reagents carrying crown-ether moieties as catalytic sites for the fluorescence derivatization of carboxylic acids were designed and synthesized. The catalytic abilities of these reagents were evaluated based on the stability constants (Ks) for complexation with metal acetates in methanol. The derivatization reactions of carboxylic acids with these reagents proceeded self-catalytically without crown-ether catalysts, and gave the corresponding coumarin esters in good yields. It was found that their reactivities significantly depended upon the metal-binding ability of the reagent molecules from kinetic treatments of the reactions. The derivatized products showed remarkably high fluorescence quantum yields of above 0.8 in methanol. These results suggested that the functionalization of reagents was a quite useful approach for the development of new-type analytical reagents.
Novel fluorogenic coumarin derivatives appending 15-crown-5 ether as more active catalytic site were designed and synthesized for the fluorescence derivatization of carboxylic acids. From the stability constants (Ks) for complexation with metal acetates in methanol, it was found that their catalytic abilities were superior to the corresponding benzo-15-crown-5 ether type reagent. However, the reactivity of these reagents in the derivatization of lauric acid was dependent on not only the catalytic ability of the introduced crown-ether but also on the appending position of that in a reagent molecule. Furthermore, the derivatized products showed remarkably high fluorescence quantum yields of above 0.8 in methanol and acetonitrile. Allowing to hold a certain function such as catalyst in a reagent molecule should serve as a new strategy for the development of excellent analytical reagents.