A new photoremovable protecting group absorbing above 500 nm : (6-Hydroxy-3-oxo-3H-xanthen-9-yl)methyl and its derivates

摘要: A new water-soluble photoremovable protecting group for carboxylic acids and phosphates with high molar extinction coefficients (eλmax ~ 25 000 dm3mol-1cm-1) in the visible region (above 520 nm) was designed tested. The suggested concept based on photochemistry of coumarinyl PPG proved to work also compounds derived from 6-hydroxy-3-oxo- 3H-xanthen-9-yl)methyl. introduction of an additional aromatic core coumarinyl unit resulted a substantial shift absorption towards longer wavelengths also caused drop pKa phenolic protons about 6, which then caused anionic form of the molecule be prevalent species at neutral pH. This is advantage since it improves the solubility these aqueous media because forms the cages are even further red-shifted with respect ones. The model cages released protected bromide, acetate and/or diethylphosphate upon irradiation by light solutions (the cleavage free anions was indicated pH confirmed NMR). The quantum yields photodeprotection were relatively low but still comparable those cages. could probably be enhanced suitable substitution. efficiency photoreaction likely be higher case other phosphates acyls biochemical interest, are better leaving groups than diethyl phosphate or acetate. In dark, stable several hours (up 1 day) aqueous solutions room temperature. stability should thus sufficient potential biochemical applications. The fluorescence lifetime one compouds, 9-(bromomethyl)-6-hydroxy-3Hxanthen- 3-one found (331 ± 30) ps. The last problem that remains solved unequivocal identification final photoproduct reaction intermediates. first step most probably analogous cages, i.e. elimination species (free acids) nucleophilic attack resulting cation water, leads the formation primary photoproduct, 6-hydroxy-9-(hydroxymethyl)-3H-xanthen-3-one. This compound equilibrium its enol tautomer another tautomer: 3,6-dihydroxy-9H-xanthene-9-carbaldehyde. One more tautomers react to give final product, original chromophore restored again (testified UV-Vis spectroscopy NMR). UV-Vis spectrum photoproduct overlaps the spectrum 6-hydroxy-3H-xanthen-3-one but NMR analysis revealed two compounds were not identical. Further analyses attempts identify reaction intermediates still progress.