Isobutylene → tert-Butyl L-alanyl-L-prolinate

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Reaction Steps

Benzyloxycarbonyl-L-alanyl-L-proline (16.02 g, 50 mmole) was dissolved in methylene chloride (100 ml) solution of 98% sulfuric acid (0.5 ml), and isobutene gas was blown into the solution under cooling until the volume of the solution was increased by 50 ml. After standing it for 64 hours at room temperature, the solution was washed with 0.15M sodium carbonate. The methylene chloride layer was further washed with 10% aqueous citric acid, water, 5% aqueous sodium bicarbonate and water in the order given, and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure and the oily residue thus obtained was dissolved in t-butanol (90 ml). Hydrogen gas was passed through the solution in the presence of 5% palladium-carbon (6.5 g) as a catalyst for 2 hours at room temperature. The catalyst was separated by filtration and the solvent was distilled off under reduced pressure to give colourless oily L-alanyl-L-proline t-butylester (yield: 10.36 g, 85.5%).

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