p-Toluenesulfonic acid → N-[3(S)-[(N-acetyl-L-asparaginyl)amino]-2(R)-hydroxy-4-phenylbutyl]-L-proline tert.butyl ester

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Reaction Steps

0.275 g (0.473 mmol) of N-[3(S)-[[N-(benzyloxycarbonyl)-L-asparaginyl]amino]-2(R)-hydroxy-4-phenylbutyl]-L-proline tert.butyl ester was taken up in 10 ml of isopropanol and hydrogenated for 18 hours over 50 mg of 5% palladium-on-carbon in the presence of 0.18 g (0.94 mmol) of toluene-4-sulphonic acid. The catalyst was filtered off and the filtrate was evaporated. The resulting solid was dissolved in 10 ml of dichloromethane and the solution was cooled in an ice-bath. 50 mg (0.49 mmol) of acetic anhydride were added, followed by 0.10 g (0.99 mmol) of triethylamine and 0.2 ml of pyridine. The mixture was stirred at room temperature for 1 hour. The solvent was removed by evaporation and the residue was partitioned between ethyl acetate and water. The organic phase was washed with 5% sodium bicarbonate solution and with saturated sodium chloride solution and then dried over anhydrous sodium sulphate. The solvent was removed by evaporation to give 35 mg of N-[3(S)-[(N-acetyl-L-asparaginyl)amino]-2(R)-hydroxy-4-phenylbutyl]-L-proline tert.butyl ester; Rf (System E): 0.28; MS: m/e 491 [M+H]+.

Provenance & Evidence