Acylation of L-phenylalanine tert-butyl ester (I) with 2,4-dichlorobenzoyl chloride (II) provides the corresponding amide (III). This is then N-alkylated with 3-nitrobenzyl bromide (IV) in the presence of NaH to yield (V). The tert-butyl ester group of (V) is finally cleaved with trifluoroacetic acid to furnish the target carboxylic acid. (1-3)