The chloroacetyl derivatives of four representative para-substituted phenylalanines, N-chloroacetyl-p-chloro-DL-phenylalanine, N-chloroacetyl-p-nitro-DL-phenylalanine, ...Na,Np-di(chloroacetyl)-p-amino-DL-phenylalanine, and N-chloroacetyl-O-methyl-methyl-L-tyrosine, were prepared and tested for growth inhibitory activity in Lactobacillus casei. The inhibition with these compounds approximated that of most other inhibitory chloroacetyl amino acids reported previously. However, N-chloroacetyl-p-chloro-DL-phenylalanine, the most active of these compounds, exhibited an activity approximately that of N-chloroacetyl-beta-hydroxy-D-norleucine B, the most active N-chloroacetyl derivative studied thus far. In view of this finding, the N-chloroacetyl derivatives of other para-halogenated phenylalanines were prepared and tested. The inhibitory capacity of the N-chloroacetyl derivatives of p-bromo- and p-iodophenylalanine was even greater than that of p-chlorophenylalanine, and the order of activity of these compounds increased from the chloroacetyl derivative of p-chloro- to that of p-bromo- to that of p-iodo-DL-phenylalanine. The activity of N-chloroacetyl-p-bromo- and N-chloroacetyl-p-iodo-DL-phenylalanine was a great as that of the ring-substituted N-benzoylphenylalanines, the most potent N-acyl derivatives observed.
