A photoactivable amino acid based on a novel functional coumarin-6-yl-alanine
A novel fluorescent amino acid, l-4-chloromethylcoumarin-6-yl-alanine, was obtained from tyrosine by a Pechmann reaction. The assembly of the heterocyclic ring at the tyrosine side chain could be achieved before or after incorporation of tyrosine into a dipeptide, and amino acid and dipeptide ester conjugates were obtained by coupling to a model N-protected alanine. The behaviour of one of the fluorescent conjugates towards irradiation was studied in a photochemical reactor at different wavelengths (254, 300, 350 and 419 nm). The photoreaction course in methanol/HEPES buffer solution (80:20) was followed by HPLC/UV monitoring. It was found that the novel unnatural amino acid could act as a fluorescent label, due to its fluorescence properties, and, more importantly, as a photoactivable unit, due to the short irradiation times necessary to cleave the ester bond between the model amino acid and the coumarin-6-yl-alanine.
KeywordsCoumarin-6-yl-alanine Coumarin Fluorescence Amino acid conjugates Photolysis
Thanks are due to the Foundation for Science and Technology (FCT-Portugal) for financial support through projects PTDC/QUI/69607/2006 (FCOMP-01-0124-FEDER-007449) and PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716), FEDER-COMPETE. A PhD grant to A.S.C.F. (SFRH/BD/32664/2006) is also acknowledged. The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from POCI 2010 (FEDER) and FCT.
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