Amino acids with aryl-keto function in their side-chains were obtained in excellent yields in the reaction of omega-carboxyamino acids with liquid HF in the presence of aromatic compounds susceptible to electrophilic substitution, such as anisole, 2-methoxybiphenyl, butyl phenyl ether or 1,3-dimethoxybenzene. The new amino acids were converted smoothly into N-tert-butyloxycarbonyl or N-fluorenylmethoxycarbonyl derivatives and then incorporated into peptides by conventional coupling methods. During the coupling step, no formation of cyclic Schiff bases was observed for aryl-keto amino acids derived from DL-alpha-aminopimelic acid and from L-alpha-aminosuberic acid. In the crude products, truncated peptides terminated at the keto amino acids were not detected by liquid chromatography-mass spectrometry.
