Isolation and identification of some photo-oxidation products of tryptophan

When an aerated aqueous solution of tryptophan at pH 6-9 is irradiated by visible light in the presence of a photosensitizing dye, N?- formylkynurenine is usually a major product. However, a similar irradiation in dilute ammonia at pH 8-9 gives mainly 4-(2-amino-2- carboxyethyl)quinazoline, a new amino acid; formyl-kynurenine 1s shown not to be an intermediate in the photoreaction. Tryptophan methyl ester and 2-methyltryptophan give photoproducts analogous to those of tryptophan. On the other hand, N-acetyltryptophan and indole-3- propionic acid give the formylkynurenine analogue either in the absence or presence of ammonia, no quinazoline being detected.