Specificity in enzyme inhibition. 3. Synthesis of 5-substituted-2,2-dimethyl-4-imidazolidinones as inhibitors of tyrosine decarboxylase and histidine decarboxylase

2,2-Dimethyl-4-imidazolidinone derivatives of the alpha-amino acids DL-phenylglycine (1), DL-phenylalanine (2), L-tyrosine (3), L-histidine (4), and L-tryptophan (5) were prepared in order to assess their specificity in inhibiting amino acid decarboxylases. Treatment of th alpha-aminonitriles with acetone in the presence of base and heat or treatment of the alpha-amino amides with acetone gave the title compounds in 48-85% yield. The compounds afforded moderate ability to inhibit the decarboxylation of L-phenylalanine, L-tyrosine, or L-histidine in vitro, using crude enzymes. 3 was a better inhibitor of tyrosine decarboxylase (S. faecalis) than 2. 4 and 5 were comparable to 3 in inhibiting tyrosine decarboxylase. 4 was more selective in inhibiting purified histidine decarboxylase (Cl. welchii) than 5, which was inactive. 4 was inactive against fetal rat histidine decarboxylase in vitro.