L-Valine → L-Leucine

Participants

Reaction Steps

To the deprotected L-Valine resin, with 5.08 meg of amine groups, was added the acylating solution, containing 10 mmols N (α)BOC-L-Leucine monohydrate (approximately 100% excess). This acylating solution was prepared by dissolving 2.5 g, 10 mmols BOC.Leu.H2O in 10 ml of M-1-hydroxybenzotrazole solution in dimethylformamide; to this was added toluene, 60 ml, and the resulting solution was cooled to 0°-5° C.; 5 ml 2 M N,N-dicyclohexylcarbodiimide solution in toluene was added. After washing the resin with two 80 ml portions of toluene, the acylating solution was added to the resin. Alternatively, the acylating solution is allowed to stand at room temperature for thirty minutes and then is added to the resin. The mixture was shaken overnight for convenience, although a coupling time as short as one hour would be adequate. The resin was drained and washed for one minute each time with two 80 ml portions of toluene, three 80 ml portions of methanol and four 80 ml portions of methylene chloride. A ninhydrin test (Kaiser et al, Anal. Biochem. 34, 595-8, (1969) was performed. On one occasion it was slightly positive and recoupling was carried out by adding to the drained resin a solution of 2.5 g BOC.Leu.H2O dissolved in methylene chloride, 60 ml, plus dimethylformamide 10 ml followed by 5 ml of 2 N dicyclohexylcarbodiimide in toluene. After shaking for three hours, the resin was washed for one minute each with two 80 ml portions of methylene chloride and two 80 ml portions of toluene. The ninhydrin test was now negative.

Provenance & Evidence