Dicyclohexylcarbodiimide → N,N'-Dicyclohexylurea

Participants

Reaction Steps

L-aspartyl-β-benzyl ester-L-valyl-L-tyrosyl-O-benzyl ether-benzyl ester-3-thioamide was dissolved in dry DMF (0.5 ml) at 0° C. under N2 and a-N-Boc-ε-2ClZ-L-lysine (2 mmol) was added to the solution with stirring. HOBt (2 mmol) and DCC (2 mmol) were added slowly at 0° C. and stirring was allowed to continue overnight. The mixture was diluted with 8 volumes of ethyl acetate and the N,N'-dicyclohexylurea so formed was filtered away from the solution. The filtrate was transferred to a separating funnel and washed successively with 5% aqueous sodium bicarbonate, 5% aqueous citric acid, and saturated brine. The organic phase was collected and dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by flash chromotography on silica gel using a 1:1 hexane-ethyl acetate solvent mixture as an eluant to afford the a-N-Boc-ε-N-2ClZ-L-lysyl-L-aspartyl-β-benzyl ester-L-valyl-L-tyrosyl-O-benzyl ether-benzyl ester-3-thioamide in good yield (73%). The following physical characteristics were recorded for the compound: Melting point 71°-73° C. and UV (CHCl3) lambdamax 272.

Provenance & Evidence