[CH2:1]([O:8][C:9]([N:11]1[C@H:15]([C:16]([OH:18])=O)[CH2:14][S:13][CH2:12]1)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C(N1CCOCC1)C.ClC(OCC(C)C)=O.[C:35]([NH2:39])([CH3:38])([CH3:37])[CH3:36]>O1CCCC1>[CH2:1]([O:8][C:9]([N:11]1[C@H:15]([C:16]([NH:39][C:35]([CH3:38])([CH3:37])[CH3:36])=[O:18])[CH2:14][S:13][CH2:12]1)=[O:10])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A solution of 2.67 g of N-benzyloxycarbonyl-4(R)-thiazolidinecarboxylic acid in 42 ml of dry tetrahydrofuran was stirred and cooled to -15° C. in an ice/salt bath while there were added 1.15 g of N-ethylmorpholine followed after 2 minutes by 1.87 g of isobutyl chloroformate. After a further 3 minutes 0.73 g of tert.butylamine was added dropwise and the mixture was then allowed to warm to room temperature and was stirred overnight. Tetrahydrofuran was removed by evaporation under reduced pressure and the residue was dissolved in dichloromethane. The solution was washed in sequence with water, 10% citric acid solution, water, saturated sodium bicarbonate solution and water, then dried over anhydrous sodium sulphate, filtered and evaporated to give 2.85 g of 3-(benzyloxycarbonyl)-N-tert.butyl-4(R)-thiazolidinecarboxamide as a solid which melted at 96°-98° C. after recrystallization from diethyl ether/n-hexane.
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