[N:1]1[CH:6]=[CH:5][CH:4]=[CH:3][C:2]=1[C:7]([C:9]1[CH:14]=[CH:13][CH:12]=[CH:11][N:10]=1)=O.[NH2:15][C@H:16]([C:19]([OH:21])=[O:20])[CH2:17][SH:18]>C(O)C>[N:1]1[CH:6]=[CH:5][CH:4]=[CH:3][C:2]=1[C:7]1([C:9]2[CH:14]=[CH:13][CH:12]=[CH:11][N:10]=2)[NH:15][CH:16]([C:19]([OH:21])=[O:20])[CH2:17][S:18]1A mixture of 3.68 g of di-2-pyridyl ketone, 2.42 g of L-cysteine, 25 ml of ethanol was refluxed for 3.5 hours. After allowing the mixture to cool, the insoluble matter was filtered off, and the filtrate was concentrated to dryness under reduced pressure. The residue was washed in sequence with ethyl acetate and ether to give 0.63 g of 2,2-di(2-pyridyl)-thiazolidine-4-carboxylic acid.
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