C([O:5][C:6](=[O:24])[C@@H:7]1[CH2:11][CH2:10][CH2:9][N:8]1[C:12](=[O:23])[CH:13]([CH2:18][S:19][C:20](=[O:22])[CH3:21])[NH:14][C:15](=[O:17])[CH3:16])(C)(C)C>C1(OC)C=CC=CC=1.FC(F)(F)C(O)=O>[C:15]([NH:14][CH:13]([C:12]([N:8]1[CH2:9][CH2:10][CH2:11][C@H:7]1[C:6]([OH:24])=[O:5])=[O:23])[CH2:18][S:19][C:20](=[O:22])[CH3:21])(=[O:17])[CH3:16]N,S-Diacetyl-DL-cysteinyl-L-proline tert-butyl ester (1.9 g) is dissolved in a mixture of anisole (6 ml) and trifluoroacetic acid (12 ml) and the solution is stored at room temperature for one hour. The solvents are removed in vacuo and the residue is precipitated from ethyl acetate-ether-hexane, to obtain N,S-diacetyl-DL-cysteinyl-L-proline, yield 1.08 g, m.p. 80°-140°.
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