Acetonitrile → N,N'-Dicyclohexylurea

N-Acetyl-L-tyrosine (1.68 g, 7.53 mmol) was taken up in 94 mL of ethyl acetate/26 mL of acetonitrile and stirred at room temperature. N-Hydroxysuccinimide (NHS, 0.87 g, 7.56 mmol) was added and the resulting solution cooled to 0° C. under N2 (g) in an ice-water bath. To the cold, stirring solution was then added dicyclohexylcarbodiimide (DCC, 1.55 g, 7.52 mmol) predissolved in 3 mL of ethyl acetate. The reaction mixture was stirred at 0° C. for 2 hours and then allowed to warm to room temperature overnight with continued stirring. The insoluble dicyclohexylurea (DCU) was removed by filtration and the resulting filtrate concentrated to a solid residue under reduced pressure. Trituration of this residue with warm ethyl acetate and subsequent storage at 4° C. then afforded a white solid. This was isolated by vacuum filtration, washed with cold ethyl acetate and dried in vacuo to yield the product in greater than theoretical yield (due to contamination with residual DCU). 1H-NMR (300 MHz, CDCl3): δ 2.00 (s, 3H); 2.87 (s, 4H); 3.22 (m, 2H); 4.05 (m, 1H); 5.80 (d, 1H, J=7.2 Hz); 6.96 (AB quartet, 4H, J=8.4 Hz).