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Table 1. Irradiation times (t irr in min) and rate constants (×10 -2 min -1 ) for the photolysis ofconjugates 1a-e at different wavelengths in ACN/HEPES buffer (80:20) solutionCompound254 nm 300 nm 350 nmt irr k t irr k t irr k1a H-β-Ala-OBba 313 0.98 245 1.25 297 1.051b H-Tyr-OBba 155 1.89 78 3.76 201 1.551c H-DOPA-OBba 314 0.98 887 0.34 616 0.491d H-Glu(OMe)-OBba 277 1.10 372 0.80 394 0.781e H-Glu(OBba)-OMe 225 1.39 389 0.76 278 1.14For each compound and based on HPLC data, the plot of ln A versus irradiation timeshowed a linear correlation for the disappearance of the starting material, which suggesteda first order reaction, obtained by the linear least squares methodology for a straight line.The corresponding rate constants were calculated and are presented in Table 1.Concerning the influence of the wavelength of irradiation on the rate of thephotocleavage reactions of conjugates 1a-e in ACN/HEPES buffer (80:20) solution, it wasfound that the shorter irradiation times were observed at 300 nm for conjugates 1a and 1b andat 254 nm for conjugates 1c-e. By comparison of the results at 300 and 350 nm, it wasnoticeable that the release of β-alanine 2a, tyrosine 2b and glutamic acid 2d was faster at 300nm, contrary to the release of DOPA 2c and glutamic acid 2e, with shorter irradiation times at350 nm. No significant difference in the release of glutamic acid methyl ester (2d,e) was seenin the cleavage of the conjugate’s ester bond at its main (1d) or side chain (1e).Furthermore, considering the influence of the structure of the neurotransmitter on thephotocleavage rates, we could see that the DOPA conjugate 1c had the longest irradiationtimes for all wavelengths. In contrast, the irradiation times for the cleavage of tyrosineconjugate 1b were always shorter, the best result being at 300 nm (78 min).AcknowledgmentsThanks are due to Fundação para a Ciência e Tecnologia (Portugal) for financial support throughproject PTDC/QUI/69607/2006 (FCOMP-01-0124-FEDER-007449) and a Ph.D. grant to M.J.G.F.(SFRH/BD/36695/2007).References1. Bochet, C.G. J. Chem. Soc. Perkin Trans. 1, 125-142 (2002).2. Schade, B., Hagen, V., Schmidt, R., Herbrich, R., Krause, E., Eckardt, T., Bendig, J. J. Org. Chem.64, 9109-9117 (1999).3. Cambridge, S.B., Geissler, E., Calegari, F., Anastassiadis, K., Hasan, M.T. Nat. Methods 6, 527-531(2009).4. Furuta, T., Wang, S.S., Dantzker, J.L., Dore, T.M., Bybee, W.J., Callaway, E.M., Denk, W., Tsien,R.Y. Proc. Natl. Acad. Sci. U.S.A. 96, 1193-1200 (1999).5. Ando, H., Furuta, T., Tsien, R.Y., Okamoto, H. Nat. Genet. 28, 317-325 (2001).6. Hagen, V., Frings, S., Wiesner, B., Helm, S., Kaupp, U.B., Bendig, J. ChemBioChem. 4, 434-442(2003).7. Fedoryak, O.D., Sui, J.Y., Haydon, P.G., Ellis-Davies, G.C.R. Chem. Commun. 3664-3666 (2005).8. Mayer, G., Heckel, A. Angew Chem. Int. Ed. 45, 4900-4921 (2006).9. (a) Fernandes, M.J.G., Gonçalves, M.S.T., Costa, S.P.G. Tetrahedron 63, 10133-10139 (2007);(b) Fernandes, M.J.G., Gonçalves, M.S.T., Costa, S.P.G. Tetrahedron 64, 3032-3038 (2008);(c) Fernandes, M.J.G., Gonçalves, M.S.T., Costa, S.P.G. Tetrahedron 64, 11175-11179 (2008).83