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1 January 2006 Photoreaction Between Benzoylthiophenes and N-BOC-Tryptophan Methyl Ester
Julia Pérez-Prieto, Maria C. Morant-Miñana, Raquel E. Galian, Miguel A. Miranda
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Drug-induced photoallergy requires as the first step formation of covalent drug-protein photoadducts. One of the key amino acids involved in this process is tryptophan (Trp). In this context, several diaryl ketones, including 2-benzoylthiophene (BT), [2-(5-benzoyl-5-thienyl)]-2-methylpropanoic methyl ester (TPA methyl ester) and 4-(2-thienylcarbonyl)phenyl]-2-methylpropanoic methyl ester (SUP methyl ester) have been irradiated in the presence of N-BOC-(L)-tryptophan methyl ester. Laser flash photolysis has allowed to detect three neutral radicals (ketyl, indolyl and skatolyl radicals) resulting from formal hydrogen-atom abstraction. This correlates well with the isolation of homodimers, as well as with cross-coupling products, in the preparative irradiation. The main cross-coupling products were in all cases lactones arising from the reaction of the Trp-derived skatolyl radicals with the corresponding ketyl radicals. These lactones were obtained as the (4R) stereoisomers with remarkable diasteroselectivity. No coupling products through the phenyl p-position of BT or TPA methyl ester were found. By contrast, ketone homodimers and cross-coupling products arising from reaction through the thienyl 5-position were obtained when using BT and SUP methyl ester; this is very interesting, because stable LAT-derived products are difficult to isolate.

Julia Pérez-Prieto, Maria C. Morant-Miñana, Raquel E. Galian, and Miguel A. Miranda "Photoreaction Between Benzoylthiophenes and N-BOC-Tryptophan Methyl Ester," Photochemistry and Photobiology 82(1), 231-236, (1 January 2006).
Received: 15 March 2005; Accepted: 26 April 2005; Published: 1 January 2006

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