4-(2-aminoethylsulfanyl)-2-[(2-methylpropan-2-yl)oxycarbonylamino]butanoic acid

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: N-t-Butoxycarbonyl-S-(2-aminoethyl)-D,L-homocysteine (0.1 g) and hydroxysuccinimide (0.044 g) are dissolved in 4 ml of DMF. Dicyclohexylcarbodiimide (0.086 g) in 1 ml of DMF is added dropwise. After 4 days at room temperature, the reaction mixture is filtered, and then lyophilized. The residue is taken up in methylene chloride. Again insoluble white solid is removed by filtration. The crude product is chromatographed on silica gel (20:1 chloroform-methanol) to afford the product as a white solid (0.02 g). The NMR spectrum (in MeOH-d4) shows a multiplet between 4.4 and 4.8, a multiplet between 3.2 and 3.4, complex absorptions between 2.2 and 2.7, and between 1.5 and 1.9, and a singlet at 1.2. the reaction mixture is filtered Again insoluble white solid is removed by filtration The crude product is chromatographed on silica gel (20:1 chloroform-methanol)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: N-t-Butoxycarbonyl-S-(2-carbobenzyloxycarbonyl aminoethyl)-D,L-homocysteine (1.0 g) is treated with sodium in liquid ammonia according to the procedure described in Example 2. After the ammonia has evaporated off, the residue is extracted with ethanol. Inorganic salts (0.4 g) is removed by filtration. After removal of ethanol, the residue is taken up in 5 ml of water. The aqueous solution is extracted with ether, and then acidified to pH 4 with 4M hydrochloric acid. The solution is concentrated to a volume of 2 ml. Excess ether is added. The product crystallizes out as a white solid (0.32 g). The NMR spectrum (in MeOH-d4 and NaOD) shows a triplet at 3.7, complex absorption between 2.1 and 2.6, a multiplet between 1.5 and 1.9, and a singlet at 1.2. After the ammonia has evaporated off the residue is extracted with ethanol Inorganic salts (0.4 g) is removed by filtration After removal of ethanol The aqueous solution is extracted with ether The solution is concentrated to a volume of 2 ml Excess ether is added The product crystallizes out as a white solid (0.32 g) at 3.7, complex absorption between 2.1 and 2.6