Water solubilization of xanthene dyes by post-synthetic sulfonation in organic media

Highly water-soluble fluorescent fluorescein and rhodamine dyes were synthesized through amidification of their carboxylic acid functionality with original di- or tri-sulfonated amino linkers derived from taurine or α-sulfo-β-alanine. This post-synthetic derivatization was performed in organic media both to minimize the premature hydrolysis and to suppress the precipitation of the involved active ester of fluorophore, frequently encountered using standard Schotten–Baumann conditions.