Practical synthetic route to functionalized rhodamine dyes.

[reaction: see text] An efficient method for the synthesis of functionalized rhodamine derivatives has been developed. Multigram quantities of these water-soluble fluorophores can be prepared from inexpensive precursors and purified without the use of chromatography. A series of protein-reactive functional groups has been installed through subsequent reactions, providing materials for biomolecule modification. For multicolor applications, a solid-phase purification strategy has been developed to afford rhodamine derivatives possessing a wide range of spectral properties.