STUDY OF A NEW PHOTOREMOVABLE PROTECTING GROUP  ABSORBING ABOVE 500 nm


Lovely Angel P.A, Peter Šebej, Tomáš Slanina, Jürgen Wintner, Pavel Müller,  Jamaludin Al Anshori,
                                    , Petr Klán, and Jakob Wirz


A new water soluble photoremovable protecting group (PPG)^1,2 for phosphates and carboxylic acids
with high molar absorption coefficient in the visible region has been designed, synthesized and
tested. The structure of this PPG was obtained by extending the 7-hydroxycoumarin-4-yl-methyl (HCM)
chromophore^3 by an additional aromatic ring to form derivatives of 6-hydroxy-3H-xanthen-3-one. The
introduction of an additional aromatic core to the coumarinyl unit resulted in a substantial shift
of absorption towards longer wavelengths and also caused a drop in pKa of the phenolic proton to
about 6. The three derivatives (bromide, acetate and diethylphosphate) were isolated as complexes
with DDQ. They have a molar absorption coefficient ε of ~ 4 x 10^4 m^-1 cm^-1 at ~ 520nm and shown
to release the ligands with quantum yields ≤ 2.4% in aqueous solution.^4

The quantum yields of photodeprotection of model compounds were relatively low but still comparable
to those of coumarinyl cages. In the dark, the model compounds were stable for several hours in
aqueous solutions at room temperature. The photoproduct 6-hydroxy-3-oxo-3H-xanthene-9-carboxylic
acid was isolated and its photoreactivity was studied in different solvents.


References

^1  Klán P., Šolomek T., Bochet C., Blanc A., Givens R. S., Rubina M., Popik V., Kostikov A., Wirz
J, Chem. Rev. 2013, 113, 119–191.

^2  Klán P., Šolomek T., Bochet C., Blanc A., Givens R. S., Rubina M., Popik V., Kostikov A., Wirz
J. Chem. Rev. 2013, 113, 119–191.

^3 T. Furuta, Chem. Lett. 1993, 1179

^4 Šebej P, Wintner J, Müller P, Slanina T, Jamaludin Al Anshori, Lovely Angel P.A, Klán P, and
Wirz J. J. Org. Chem., 2013, 78, 1833–1843