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The t-butyl ester 5 (295 mg; 0.924 mmole) of phenylacetylglutamine was deprotected (i.e., the t-butyl carboxy protecting group was removed) by dissolving 5 in methylene chloride (4 ml) and adding trifluoroacetic acid (4 ml). After 45 minutes, the reaction mixture was evaporated in vacuum and the oily residue crystallized from tetrahydrofurane (THF), to give colorless crystals of phenylacetyl glutamine 6. 1 H-NMR(300 MHz)(CDCl3 /CD3 OD) delta ppm 1.9-2.05 (mult,1H); 2.13-2.36 (mult,3H); 3.58 (s,2H); 4.5 (mult,1H); 7.23-7.38 (mult,5H); Mass Spectrum (pos.FAB, MeOH):265 (M+H)+ (100%).