C([O:8][C:9]1[CH:14]=[CH:13][C:12]([CH2:15][CH2:16][NH:17][C:18](=[O:29])[C@@H:19]([NH:23][S:24]([CH2:27][CH3:28])(=[O:26])=[O:25])[CH:20]([CH3:22])[CH3:21])=[CH:11][C:10]=1[O:30][CH3:31])C1C=CC=CC=1.[H][H]>O1CCCC1.[Pd]>[OH:8][C:9]1[CH:14]=[CH:13][C:12]([CH2:15][CH2:16][NH:17][C:18](=[O:29])[C@@H:19]([NH:23][S:24]([CH2:27][CH3:28])(=[O:26])=[O:25])[CH:20]([CH3:21])[CH3:22])=[CH:11][C:10]=1[O:30][CH3:31]14.5 g of (S)-2-(ethylsulfonylamino)-3-methyl-butyric acid N-[2-(4-benzyloxy-3-methoxyphenyl)-ethyl]-amide (Ex. P-1. 1) are dissolved in 420 ml of tetrahydrofuran and shaken together with 3 g of palladium-on-carbon (5%) in a duck-shaped hydrogenation vessel for 5 hours in a hydrogen atmosphere at normal pressure. The catalyst is then removed by filtration. The filtrate is concentrated. The residue is purified by flash-chromatography on silica gel using ethyl acetate/n-hexane 3:1, yielding (S)-2-(ethylsulfonylamino)-3-methyl-butyric acid N-[2-(4-hydroxy-3-methoxyphenyl)ethyl]-amide in the form of a colourless oil.
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