1. T. Shiota, R. Jackson and C. M. Baugh, “Chemistry and Biology of Pteridines,” ed. by K. Iwai, M. Akino, M. Goto and K. Iwanami, distributed by Maruzen, Tokyo, 1970, p. 265.
2. G. M. Brown, J. J. Yim, Y. Suzuki, M. C. Heine and F. Foor, “Chemistry and Biology of Pteridines,” ed. by W. Pfleiderer, Walter de Gruyter, Berlin, 1975, p. 219.