[CH3:1][O:2][C:3]([C:5]1[CH:6](O)O[C:8](=[O:10])[CH:9]=1)=[O:4].[NH2:12][C@@H:13]([CH2:17][CH3:18])[C:14]([NH2:16])=[O:15].[H][H]>CO.[Pd]>[NH2:16][C:14]([C@@H:13]([N:12]1[C:8](=[O:10])[CH2:9][CH:5]([C:3]([O:2][CH3:1])=[O:4])[CH2:6]1)[CH2:17][CH3:18])=[O:15]2-Hydroxy-5-oxo-2,5-dihydro-furan-3-carboxylic acid methyl ester (3.08 g) in methanol (40 ml) is added to a solution of (2S)-2-aminobutyramide (2.0 g) in methanol (30 ml) in a hydrogenation reactor and the mixture is maintained for at least 2 hours at room temperature. Then Pd/C catalyst (10 w/w %; Johnson Matthey 5% Pd on carbon—type 87L) is added and hydrogen introduced into the system under pressure. The temperature is kept at 40° C. maximum and the hydrogen pressure between 4 bar and 5 bar, followed by stirring for at least 20 hours following the initial reaction. The solution is then cooled between 15° C. and 25° C. and filtered to remove the catalyst. The solvent is evaporated under vacuum and the resulting yellow product is purified by preparative liquid chromatography (eluent: dichloromethane/methanol (95:5)) (Yield 43%).
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