p-Toluenesulfonic acid monohydrate → 1-N-[3-(thiazol-4-yl)-L-alanyl]-(2R)-2-methylpyrrolidine di-p-toluenesulfonate

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Reaction Steps

Compound (3) (33.77 g, 99.48 mmol) and p-toluenesulfonic acid hydrate (37.85 g, 199 mmol) were dissolved in ethyl acetate (101 ml) and the solution was cooled with ice. To the mixture, 4 mol/L solution of hydrogen chloride-ethyl acetate (125 ml) was added, and the mixture was stirred for 2 hours 45 minutes. After the mixture was concentrated under reduced pressure, methanol was added to the residue. The mixture was concentrated. Methanol-toluene (1:1) was added to the residue and concentrated under reduced pressure to give crystalline residue. The residue was washed with acetone and filtered to give compound (4) as crystals (36 g, 62%). After the mother liquor was concentrated under reduced pressure, methanol and toluene were added to the residue and concentrated. Obtained crystalline residue was washed with acetone to give compound (4) (10.67 g, 18.4%).

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