To a stirred suspension of (S)-4-[2-(4-amino-phenyl)-ethyl]-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester (150 mg, example 14 (b)) in THF (4 ml) were added sequentially N-methylmorpholine (0.21 ml), TBTU (301 mg) and 5-chloro-2-pyridinecarboxylic acid (111 mg, CAS 86873-60-1) and the mixture was heated at 50° C. for 18 h. The mixture was then concentrated in vacuo and the residue was purified by column chromatography (SiO2; gradient: heptane/EtOAc) to give (S)-4-(2-{4-[(5-chloro-pyridine-2-carbonyl)-amino]-phenyl}-ethyl)-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester (197 mg, 91%) as a white solid. MS (ISP): 484.3 ([{37Cl}M+Na]+), 482.3 ([{35Cl}M+Na]+), 462.4 ([{37Cl}M+H]+), 460.5 ([{35Cl}M+H]+), 406.4 ([{37Cl}M+H—C4H8]+), 404.3 ([{35Cl}M+H—C4H8]+).
