SEARCH Articles Figures Tables By Cleavage of Pteridines and Other Ring Systems Pteridin Pteridin-4 -one ring openin Pteridine Pteridine ring Pteroic acid Pteridine ring pyrimidines, 4-amino5-nitroso- and enamine Pteridine ring system Pteridine ring, structure Pteridines Pteridines ring synthesis Pyrimidines pteridine ring