Photorelease of amino acids from novel thioxobenzo[f]benzopyran ester conjugates
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Aiming at the enhancement of the performance of (9-methoxy-3-oxo-3H-benzo[f]benzopyran-1-yl) methyl ester as photocleavable protecting group for the carboxylic acid function at long-wavelengths, 9-methoxy-3-thioxo-3H-benzo[f]benzopyran-l-valine and l-phenylalanine model conjugates were prepared through a thionation reaction of the corresponding oxo-benzobenzopyrans. These thioxobenzobenzopyran derivatives were subjected to photocleavage reactions in the same conditions as the parent oxo-benzobenzopyrans at different wavelengths of irradiation, and photocleavage data were obtained. It was found that the exchange of the carbonyl by a thiocarbonyl group enhanced the performance of the heterocyclic protecting group at 419 nm by improving the photolysis rates, making it an appropriate group for practical applications at long wavelengths.
KeywordsThioxobenzobenzopyran Benzocoumarin Amino acids Photolabile protecting groups
Thanks are due to the Foundation for Science and Technology (Portugal) for financial support through project PTDC/QUI/69607/2006 (FCOMP-01-0124-FEDER-007449), and a PhD grant to A.M.P. (SFRH/BD/61459/2009). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased in the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT.
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