[CH3:1][O:2][C:3](=[O:9])[C@@H:4]1[CH2:8][CH2:7][CH2:6][NH:5]1.C1(N=C=NC2CCCCC2)CCCCC1.[OH:25][C:26]1[C:27]([N+:36]([O-:38])=[O:37])=[C:28]([CH3:35])[CH:29]=[CH:30][C:31]=1C(O)=O.ClCCl>CN(C=O)C>[CH3:1][O:2][C:3](=[O:9])[C@@H:4]1[CH2:8][CH2:7][CH2:6][N:5]1[C:31]1[CH:30]=[CH:29][C:28]([CH3:35])=[C:27]([N+:36]([O-:38])=[O:37])[C:26]=1[OH:25]
16.5 g of L-proline methyl ester and 27.2 g of N,N'-dicyclohexylcarbodiimide were successively added to an ice-cooled and constantly stirred solution of 25.2 g of 3-hydroxy-2-nitro-p-toluic acid dissolved in a mixture consisting of 480 ml of dichloromethane and 43 ml of N,N'-dimethylformamide. The whole mixture was stirred at ice-cooled temperature for 1 hour and then at room temperature for 1 hour. After the reaction, the separated crystalline precipitate was filtered off, and the filtrate was washed with 10% aqueous hydrochloric acid, 5% aqueous solution of sodium hydrogen carbonate and 5% aqueous solution of sodium carbonate. The layer of 5% aqueous solution of sodium carbonate was acidified with hydrochloric acid and extracted with chloroform. The chloroform layer was dehydrated and concentrated. The residue was recrystallized from 50% ethanol, and there was obtained 32.7 g of 1-(3-hydroxy-2-nitro-p-toluyl)-L-proline methyl ester as yellow-colored prismatic crystal having a melting point of 111° to 113.5° C.
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