A mixture of N-[(2-adamantyloxy)carbonyl]-α-trimethylsilylethoxymethyl-DL-tryptophan methyl ester (4.5 g, 8.5 mmol), LiOH (0.22 g, 9.1 mmol), dioxane (90 mL), and water (30 mL) was stirred at 60° C. for 16 hours. After cooling, the reaction mixture was acidified to pH 4 with 1N hydrochloric acid and extracted with ethyl acetate. The organic extract was dried over Na2SO4 and then concentrated in vacuo. Trituration of the oily residue with diethyl ether gave the title compound as a white solid (4.0 g, 91.7%), mp 203° C. (dec.).
