Dimethyl Sulfoxide → N,N'-Dicyclohexylurea

Participants

Reaction Steps

0.651 mmol of Boc-L-valyl-(2RS, 3RS)-3-amino-2-hydroxypentanoyl-D-leucyl t-butyl ester were admixed with 69.5 (0.360 mmol) of pyridine trifluoroacetate, 408.8 mg (1.982 mmol) of dicyclohexyl-carbodiimide, 1.3 ml of DMSO and 2.5 ml of toluene. The reaction mixture was stirred at room temperature for 18 hours. After the completion of the reaction, the reaction mixture, having a yellow color, was diluted with 10 ml of ethyl acetate. Dicyclohexylurea thus formed was separated off by filtration. The organic layer was diluted with 10 ml of water, dried over anhydrous sodium sulfate, and distilled to remove the solvent therefrom, whereby an oily substance was obtained. The oily substance was admixed with 5 ml of ethyl acetate, whereby a further amount of dicyclohexylurea was crystallized and filtered off. The filtrate was distilled to remove the solvent therefrom, so that crude Boc-L-valyl-(RS)-3-amino-2-oxopentanoyl-D-leucyl t-butyl ester was obtained. The crude product was purified by a column chromatography (silica gel; and (1) dichloromethane : methanol (100:1), and (2) dichloromethane: ethyl acetate (12:1 to 10:1)) to obtain 178.2 mg of Boc-L-valyl-(RS)-3-amino-2-oxopentanoyl-D-leucyl t-butyl ester as white crystals. SI-MS: m/z 534 (M+1+).

Provenance & Evidence