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 alpha-sulfo-beta-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. (C) 2010 Elsevier Ltd. All rights reserved.