Chemistry and biology of pteridines 1989 [nineteen hundred and eighty-nine] pteridines and folic acid derivatives ; proceedings of the 9. International Symposium on Pteridines and Folic Acid Derivatives, Chemical, Biological and Clinical Aspects, Zurich, Switzerland, September 3 - 8, 1989 - Curtius, Hans-Christoph (de Gruyter, 1990)