Acetamidoxime

Experimental procedure¹⁾: To a solution of Boc-L-cystine (248.0 g, 0.56 mol), acetamidoxime (89.0 g, 1.20 mol), and 2-Hydroxypyridine N-Oxide (2.9 g, 0.026 mol) in THF (1 L) is added a solution of DCC (250 g, 1.21 mol) in THF (0.8 L) at 0 °C. The mixture is stirred for 16 h while the temperature is allowed to warm to 20 °C. The mixture is cooled to 0 °C and the precipitate is removed by filtration. The filtrate is concentrated in vacuo to a volume of about 0.5 L and then diluted with EtOAc (0.8 L). Upon the addition of H₂O (1 L), a precipitate forms which is isolated by filtration to give Boc-L-cystine bis(acetamidoxime) ester (2, 246.6 g) as white crystals. This material is taken up in toluene (0.8 L) and the mixture is heated at reflux for 3 h, the water formed being removed by a Dean-Stark trap. Addition of hexane (3 L) to the cooled mixture leads to crystallization of 3 (215.0 g, 79%) as white crystals.