New monofunctionalized fluorescein derivatives for the efficient high-throughput screening of lipases and esterases in aqueous media

Monoalkylation or acylation of fluorescein (1) with various acyloxymethyl or acyl halides afforded, respectively, a series of ether- (2) and ester-functionalized (3) fluorogenic probes. The highly reactive and water-soluble substrates release fluorescein (1) upon reaction with lipases and esterases within seconds or minutes, both under fully aqueous conditions or in the presence of DMSO (20%) as a co-solvent. The most-reactive substrates in the two series were the octanoic acid derivatives 2f ( =2-{6-[(octanoyloxy)methoxy]-3-oxo-3H-xanthen-9-yl}benzoic acid) and 3a (=2-[6-(octanoyloxy)-3-oxo-3H-xanthen-9-yl]benzoic acid). Esterases were found to generally react faster under aqueous conditions, while lipases were more reactive in the presence of DMSO as a co-solvent.