New water-soluble derivatives of 7-hydroxy-3-hetaryl coumarins for the fluorescent labeling of biomolecules.

Fluorescent labeling of biomolecules is widely used in both life sciences and medical diagnostics. We have previously synthesized a number of blue-emitting coumarin-based reagents 1 by the introduction of carboxyalkyl groups into 7-hydroxy-3-hetarylcoumarins, and corresponding 7-methoxy derivatives. They are suitable for the labeling of compounds containing aliphatic amino groups. However, the disadvantage of these derivatives as reagents for the conjugation with biomolecules being typically performed in aqueous medium is their poor solubility in water. Only 7-hydroxycoumarin derivatives are soluble at high pH. Here we propose a new way to increase water solubility of coumarin reagents by their derivatization with 1,3-propanesultone or cysteic acid.