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Introduction of fluorenylmethyloxycarbonyl of amino acids Example

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A solution of Fmoc-Cl (31 g, 0.12 mol) in dioxane (150 ml) was added to a suspension of compound 1 (24.1 g, 0.1 mol)in dioxane (100 ml) and 10% aqueous Na2CO3 (150 ml) at 0°C. The mixture was stirred for 1 h at 0°C and then for 1 h at room temperature. The reaction mixture was poured into water and washed with Et2O. The aqueous phase was acidified with concentrated aqueous HCl, and the precipitated product was isolated by filtration and dried in vacuo to give compound 2 (45 g g, 98%).

 

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Compound 1 (1.25 mmol), were dissolved in DMF (30 mL) and H2O (30 mL), treated with NaHCO3 (210 mg, 2.5 mmol) and Fmoc-OSu (464 mg, 1.37 mmol), and stirred for 24 h. The solvents were removed, and the residue was dissolved in EtOAc (150 mL) and washed with 0.1 M KHSO4 (4 x 50 mL), H2O (4 x 50 mL), and brine (100 mL). After drying and removal of the solvent, the residue was chromatographed (acetone:CH2Cl2:AcOH, 5:95: 0.5 to 10:90:0.5) and then purified by size exclusion chromatography (LH-20, CH2Cl2) to yield compound 2 (456 mg, 0.969 mmol, 78%) as a glassy solid.

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To a vigorously stirred mixture of 3 mL of dichloromethane and 6 mL of saturated NaHCO3 (aq.) and 1mmol of 4 was added 1.4 equiv. of Fmoc-Cl. After the reaction had come to completion (TLC), 6 mL of dichloromethane and 3 mL of water were added, and the layers separated. The organic phase was washed once with brine, dried (MgSO4), and the solvent evaporated. The crude compound was purified by column chromatography (pet. ether 40–60/EtOAc 95/5, v/v) to yield 5e in 79% yield as a white solid, mp 88°C. 


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