Chemoenzymatic synthesis of 3 '-O-(carboxyalkyl)fluorescein labels

A general and versatile method is described for the synthesis of fluorescen t labels. Coupling of the 3'-phenol of fluorescein methyl ester with hydrox yalkyl benzyl esters, followed by benzyl ester hydrolysis, provided a serie s of fluorescein carboxyalkyl ethers. Use of the Mitsunobu reaction allowed for the introduction of linkers of different lengths onto the 3'-phenol of fluorescein. Chemoenzymatic benzyl ester hydrolysis was achieved with LPL- 80 lipase, providing pH-independent labels useful for the preparation of fl uorescent conjugates.