5-Deoxy-L-ribose Phenylhydrazone is an intermediate used in the synthesis of L-Primapterin (P733000), which is a 7-Substituted pterins, a new class of mammalian pteridines. Primapterin, Anapterin, and 6-Oxo-primapterin, three new 7-substituted pterins identified in a patient with hyperphenylalaninemia.