1,1'-Carbonyldiimidazole (0.56 g) was added portionwise to a cooled (0° C.) solution of [ethoxy(4-phenylbutyl)phosphinyl]acetic acid (0.98 g) in 70 ml of acetonitrile. This reaction mixture was stirred under argon at 0° C. for 1.5 hours. The HCl salt of L-tyrosine methyl ester (0.8 g) was dissolved in methanol and neutralized with triethylamine (0.35 g). This solution was concentrated in vacuo, dissolved in 10 ml of warm acetonitrile and added dropwise to the above solution of activated phosphinic acid ester sidechain. The reaction was stirred overnight under argon and then concentrated in vacuo. A solution of the pot residue in dichloromethane was washed (H2O, aqueous NaHCO3, brine), dried (MgSO4) and filtered to yield 1.4 g of N-[[ethoxy(4-phenylbutyl)phosphinyl]acetyl]-L-tyrosine, methyl ester.
