[NH2:1][C@@H:2]([CH2:6][CH3:7])[C:3]([NH2:5])=[O:4].Cl.N.C(O)(C)C.O[C:15]1[O:19][C:18](=O)[CH2:17][C:16]=1[CH2:21][CH2:22][CH3:23]>C(O)(C)C>[O:19]=[C:18]1[CH2:17][C@@H:16]([CH2:21][CH2:22][CH3:23])[CH2:15][N:1]1[C@@H:2]([CH2:6][CH3:7])[C:3]([NH2:5])=[O:4]Example 1 is repeated except that in step 1.1 a solution of (2S)-2-aminobutyramide.HCl in isopropanol is used (27.72 g, 1.2 equivalent), which is neutralised with a NH3/isopropanol solution (3.4-3.7 mol/L). The resulting ammonium chloride is removed from this solution by filtration and the solution is directly used for reaction with 5-hydroxy-4-n-propyl-furan-2-one (23.62 g, 1.0 equivalent) without intermediate drying of the (2S)-2-aminobutyramide solution. Yield after separation of the two diastereoisomers and recrystallisation: approximately 84%.
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