Resistance of aryl-substituted phenylalanines to decarboxylation in the rat.

1. The in vivo decarboxylation of analogues of DL-phenylalanine with methoxy, ethoxy or methylenedioxy substituents on the aromatic nucleus was assessed in the rat by measuring urinary excretion of the corresponding phenylacetic acids and beta-phenylethylamines. Only trace amounts of these amines and acids were excreted. 2. o-Tyrosine was readily decarboxylated, a property that may be attributed to the position and nature of the substituent on the aromatic nucleus. 3. Some phenylpyruvic acids derived from these amino acids exhibited a certain degree of decarboxylation to phenylacetic acids or reduction to phenyllactic acids in the rat.