DL-2-Keto-4-hydroxyglutarate

This chapter describes the DL-2-Keto-4-hydroxyglutarate (KHG). 2-Keto-4-hydroxyglutarate may be prepared by procedures such as: (a) nonenzymic transamination of 4-hydroxyglutamate with pyridoxal; (b) enzymic transamination of 4-hydroxyglutamate, catalyzed by glutamate-aspartate transaminase; (c) chemical condensation of glyoxylate with oxaloacetate followed by acidic conditions for decarboxylating fl-keto acids; and (d) enzymic condensation of glyoxylate with pyruvate, catalyzed by KHG-aldolase. Methods (a) and (b), which start with 4-hydroxyglutamate, can be used to obtain DL-, L-, or D-KHG, depending on the specific isomer(s) of 4-hydroxyglutamate utilized. The nonenzymic transamination of 4-hydroxyglutamate with pyridoxal, as described in the chapter, represents a simple and routine way for synthesizing KHG. Threo-4-Hydroxy-L-glutamate is commercially available; a preparative scheme for isolating this compound from leaves of Phlox decussata, the source in which 4-hydroxyglutamate was first detected, has been outlined. KHG can be determined chemically or enzymically. The chapter also discusses the methods for determining of KHG. KHG is cleaved by the aldolase and the glyoxylate or pyruvate liberated can be measured.