Synthesis of photoactivatable fluorescein derivatives bearing side chains with varying properties

Abstract

Etherification of both phenolic hydroxyl groups of fluorescein locks the molecule into its non-fluorescent lactone form. Here fluorescein has been unsymmetrically alkylated with a 2-nitrobenzyl ether and one of three variously functionalised alkyl ethers to give compounds 4, 5 and 6. The 2-nitrobenzyl group can be removed by photolysis with near-UV light to regenerate a fluorescent species, while the second ether group contains one of a range of functions, maleimido or iodoacetyl for ligation to proteins, or a long alkyl chain to promote association with lipid membranes. Incorporation of the various side chains was achieved by condensation of the common intermediate aldehyde 13 with substituted hydrazides 19 or 23, leading to compounds 4 and 5, respectively, or with hexadecanohydrazide to give compound 6. Photochemical and physical properties of the compounds are described.