“…If the L-amino acid oxidase reaction is carried out in the presence of H202, o-aminophenylglyoxylic acid ( 284) is produced, suggesting that the free a-keto acid is an intermediate.149 a-Ketosuccinamic acid (148) may exist in an alternative dimeric form which is unreactive to carbonyl reagents.61,106 The unreactive dimer has been shown to be 5-carbamoyl-4,6-dihydroxy-2-oxopiperidine-4,6-dicarboxylic acid (285). 417 The dimer is readily converted The a-keto acid analogue of arginine (a-keto-5guanidinovaleric acid, 287), citrulline (a-keto-5-carbamidovaleric acid, 289), and homoarginine (a-keto-eguanidinocaproic acid, 291) have also recently been shown to exist in equilibrium with their respective cyclic forms: l-amidino-2-hydroxypyrrolidine-2-carboxylic acid (288), l-carbamyl-2-hydroxypyrrolidine-2carboxylic acid (290), and l-amidino-2-hydroxypiperidine-2-carboxylic acid (292) The cyclization reactions explain the previous observations that 287 and 289 react more slowly with 3-quinolylhydrazine393 and with 7-glutamylhydrazide407 than acyclic a-keto acids at comparable concentrations.…”