4-Methylmorpholine → tert-butyl 2-({[(1S)-3-hydroxy-1-phenylpropyl]amino}carbonyl)-1,3-thiazolidine-3-carboxylate

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Commercial 3-(tert-butoxycarbonyl)-1,3-thiazolidine-2-carboxylic acid (III) (1 g, 4.29 mmol) was dissolved in dry THF (50 ml). A mechanical stirrer was placed in the flask and the solution stirred vigorously. The solution was cooled down to −25° C. and N-methyl morpholine (1.084 g, 10.72 mmol) was added in dry THF (5 ml). A solution of isobutyl-chloroformate (0.615 g, 4.5 mmol) in dry THF (10 ml) was then added dropwise over a period of 10 minutes with continued vigorous stirring, the reaction's exotherm being maintained at the optimal temperature of −25° C. by the use of a dry-acetone bath. After the complete addition of the chloroformate, the reaction mixture was stirred at −25° C. for 30 min after which time an amine (IV)/(IV*), e.g., (3S)-3-amino-3-phenyl-1-propanol (0.778 g, 5.14 mmol) was added drop-wise over a period of 10 min. The reaction mixture was allowed to gradually warm to room temperature and stirred overnight. The solvent was removed and the residue re-dissolved in ethyl acetate (150 ml). The organic layer was washed subsequently with a saturated solution of ammonium chloride (100 ml), saturated bicarbonate (100 ml) and brine (100 ml). Organics then dried with magnesium sulfate and concentrated in vacuo. The product (V), e.g., tert-butyl 2-({[(1S)-3-hydroxy-1-phenyl-propyl]amino}carbonyl)-1,3-thiazolidine-3-carboxylate, was finally obtained as a white foam (1.5 g, 95%). The antipodal intermediate, tert-butyl 2-({[(1S)-3-hydroxy-1-phenyl-propyl]amino}carbonyl)-1,3-thiazolidine-3-carboxylate, as well as the racemic inter-mediate, tert-butyl 2-({[3-hydroxy-1-phenylpropyl]amino}carbonyl)-1,3-thiazolidine-3-carboxylate were made according to the same protocol, starting from commercial (3R)-3-amino-3-phenylpropan-1-ol or 3-amino-3-phenylpropan-1-ol, respectively.

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