A mixture of racemic 5-isopropoxy-2-aminotetraline-2-carboxylic acid (3.48 g, 5.98 mmole theoretical), triethylamine (1.10 ml, 7.89 mmole), 9-fluorenylmethyl succinimidyl carbonate (Fmoc-OSu, 2.62 g, 7.77 mmole) in acetonitrile (30 ml) and water (30 ml) was stirred at room temperature for one day. TLC analysis of the reaction indicated the presence of starting material amino acid. 9-fluorenylmethyl succinimidyl carbonate (500 mg) was added and the mixture was stirred at room temperature for another day. The reaction mixture was concentrated in vacuo to remove most of the acetonitrile, acidified to pH˜3 with 10% aqueous citric acid solution, and the white emulsion extracted three times with methylene chloride. The combined organic layers were washed with water, brine, dried over magnesium sulfate. Filtration and concentration gave a crude oil which was purified by column chromatography (eluted with 1→2→5→8% methanol/methylene chloride) to give racemic Fmoc-5-isopropoxy-2-aminotetraline-2-carboxylic acid (0.50 g, 18% yield over 2 steps) as a white solid. HRMS (FAB): C29H30NO5 (M+H) calc. 472.2124; observed: 472.2117.
