. . "Examples of suitable substituted phenylalanine derivatives include those corresponding to the formula: ##STR1## wherein Ph is phenyl (substituted or unsubstituted), while X is --OH, --SH, --Cl, --Br, --I, --OCOCH3, --OCOOCH3, --NH2 or --SCH3 and R is a lower alkyl group having from 1 to 4 carbon atoms." . . .