THE recent communication by Prof. A. Albert1 on the photo-reduction of pteridines prompts me to record another example. In the preparation of 2-amino-4-hydroxy-pteridine-6-aldehyde by the method of Waller et al. 2 it was found that if the initial decomposition of pteroyl-L-glutamic acid to dihydro-2-amino-4-hydroxy-pteridine-6-aldehyde was done in the dark only a poor yield was obtained (as judged by the amount of 2-amino-4-hydroxy-pteridine-6-aldehyde formed on subsequent oxidation). If the reacting solution was irradiated with light from a 100-W. bulb then a good yield was obtained. It thus seems that the decomposition of pteroyl-L-glutamic acid to the dihydro aldehyde is a light-catalysed intramolecular hydrogen transfer from the 9 : 10 position followed by hydrolysis of the resulting anil. It has been previously reported that pteroyl-L-glutamic acid is decomposed by ultra-violet light to 2-amino-4-hydroxy-pteridine-6-aldehyde3. The position of the hydrogen atoms of the dihydro 2-amino-4-hydroxy-pteridine-6-aldehyde in the pyrazine ring has not been established; but this aldehyde would seem to be a possible intermediate in the biological synthesis of the yellow fluorescent eye pigment4 of Drosophila and possibly also of the red pteridine pigments4. Tho primary step in the degradation of pteroyl-L-glutamic acid would seem to be hydrogen transfer intramolecularly to the pyrazine ring or intermolecularly to a suitable hydrogen acceptor (for example, oxygen5 or methylene blue6).
Albert, A., Nature, 178, 1072 (1956).
Waller, C. W., Goldman, A. A., Angier, R. B., Boothe, J. H., Hutchings, B. L., Mowat, J. H., and Semb, J., J. Amer. chem. Soc., 72, 4630 (1950).
Lowry, O., Bessel, O., and Crawford, E., J. Biol. Chem., 180, 389 (1949).
Forrest, H. S., and Mitchell, H. K., J. Amer. Chem. Soc., 76, 5656 (1954).
Mowat, J. H., Boothe, J. H., Hutchings, B. L., Stokstad, E. L. R., Waller, C. W., Angier, R. B., Semb, J., Cosulich, D. B., and Subbarow, J., J. Amer. Chem. Soc., 70, 14 (1948).
Blair, J. A., Biochem. J., 65, 209 (19576).
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Journal of Pharmaceutical and Biomedical Analysis (2003)