Methanol → Methyl 5-oxo-L-prolinate

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Reaction Steps

To methanol (30.0 mL), cooled to -10 to -15° C., was slowly added sulfuryl chloride (11.0 mL, 178 mmol), DMF (0.133 mL) and L-pyroglutamic acid (L=(S) configuration, 10.0 g, 77.5 mmol, Sigma Chemical Co.). The stirred mixture was allowed to warm slowly and then stirred at room temperature for 36 hours. The methanol was removed under vacuum, and the residue was dissolved in ethyl acetate (400 mL). Water (~10 mL) was added, followed by the addition of sodium carbonate until basic. The organic layer was decanted, the slurry was washed with ethyl acetate (4×15 mL), and the organics were then combined and dried over magnesium sulfate. Removal of the solvent gave crude pyroglutamic methyl ester (10.04 g, 91%). NMR and MS analysis indicated >95% purity.

Provenance & Evidence