(3aR,4S,6R,6aS)-6-Amino-2,2-dimethyltetrahydro-3aH-cyclopenta[d][1,3]dioxol-4-ol (80.0 g, 96%, 443.4 mmol), toluene (46.9 mL) and iso-propanol (500 mL) were taken to a flask with a stirrer. The mixture was heated, with stirring, to 31° C. when N-(tert-butoxycarbonyl)-L-phenylalanine (124.8 g, 99%, 465.5 mmol) was added together with iso-propanol (99 mL). The mixture was further heated to 66° C. when a clear solution was obtained. The solution was cooled and crystallization started at 55° C. The slurry was further cooled to ambient temperature and stirred overnight. The next day the slurry was cooled to 0° C. and stirred at this temperature for 120 min. The crystals were isolated on a glass filter, washed with cooled iso-propanol (500 mL) and dried in vacuum at 40° C. to give an amount of 85.8 g. The assay by titration was 99.0% and ee by LC 99.2%. The yield was 43.3%.
