To a stirring suspension of L-tyrosine O-t-butyl ester (1.00 g, 4.21 mmol) and NaHCO3 (354 mg, 4.21 mmol) in 1,4-dioxane/water (1:1, 20 mL) was added 9-fluorenylmethyl-N-succinimidyl carbonate (1.42 g, 4.21 mmol) and the resulting mixture was stirred for 18 hr at room temperature. The solvent was reduced to 10 mL followed by the addition of 50 mL of cold 1N HCl. The product was extracted with ethyl acetate (3×). The organic extracts were washed with H2O and saturated aqueous NaCl then dried over Na2SO4. The solution was then concentrated after filtration to give the colourless solid 83 (1.94 g, 100%) which was used without purification: 1H NMR (400 MHz, CDCl3) δ 1.43 (s, 9H), 2.97-3.06 (m, 2H), 4.21 (bt, J=7.1, 1H), 4.33 (dd, J=7.1, 10.5, 1H), 4.41-4.53 (m, 2H), 5.01 (bs, 1H), 5.30, (d, J=8.2, 1H), 6.73 (d, J=8.5, 2H), 7.00 (d, J=8.5, 2H), 7.31 (t, J=7.5, 2H), 7.40 (t, J=7.5, 2H), 7.57 (dd, J=3.3, 7.3, 2H), 7.76 (d, J=7.5, 2H).
