Cl.[CH3:2][O:3][C:4](=[O:18])[C@@H:5]1[CH2:9][C@H:8]([NH2:10])[CH2:7][N:6]1[C:11]([O:13][C:14]([CH3:17])([CH3:16])[CH3:15])=[O:12].CN1CCOCC1.[Cl:26][C:27]1[S:31][C:30]([C:32](O)=[O:33])=[CH:29][CH:28]=1>C(#N)C>[CH3:2][O:3][C:4]([C@@H:5]1[CH2:9][C@H:8]([NH:10][C:32]([C:30]2[S:31][C:27]([Cl:26])=[CH:28][CH:29]=2)=[O:33])[CH2:7][N:6]1[C:11]([O:13][C:14]([CH3:15])([CH3:17])[CH3:16])=[O:12])=[O:18]N-Boc-cis-4-Amino-L-proline methylester hydrochlorid (5 g) was dissolved in acetonitrile (25 ml) and suspended with NMM (1.2 g) for 15 min at 25° C. (Suspension A). 5-Chlorothiophene-2-carboxylic acid (5.184 g) was dissolved in acetonitrile (25 ml), NMM (2.4 g) and IBCF (4.865 g) were added to the solution. This solution was stirred for 30 min at 25° C. and then added to the above mentioned suspension A. The whole mixture was stirred for 24 h at 25° C. The mixture was then evaporated to dryness and purified by chromatography (silica gel; gradient: CH2Cl2->methanol 2N NH3) to yield (2S,4S)-4-[(5-chloro-thiophene-2-carbonyl)-amino]-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester (5.5 g) as a light yellow gum. MH+=289.1 (Cl-isotopes, loss of Boc-group).
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