[C:1]([O:5][C:6]([NH:8][CH2:9][CH2:10][S:11]SCCN)=[O:7])([CH3:4])([CH3:3])[CH3:2].[BH4-].[Na+].C(O)(=O)CC(CC(O)=O)(C(O)=O)O>C(O)C>[C:1]([O:5][C:6]([NH:8][CH2:9][CH2:10][SH:11])=[O:7])([CH3:4])([CH3:3])[CH3:2]A solution of bis N-(t-butyloxycarbonyl)-cystamine (77.37 g, 0.220 mole) from Example 1, in 1 L of ethanol was treated with NaBH4 (32.5 g, 0.859 mmole). Vigorous gas evolution ensued and subsided in 40 minutes. The reaction was stirred for an additional half hour and was poured into 2.5 L of a cold dilute solution of citric acid (pH 6). The mixture was then extracted with 3×1 L of chloroform. The combined organic extracts were dried with MgSO4 and the solvents were removed under reduced pressure. The resulting residue was distilled (66°-73° C. 0.25 torr) to obtain the product (41.5 g, 53% yield).
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