Crude thiazolidine (50.0 g, 0.222 mol), triazole 1-hydroxybenzoate hydrate (0.5 g) and acetone part I (197.8 ml) of Example 33 were added to a 1 L flask under nitrogen protection and stirred at room temperature. The suspension was cooled to 0 °C ± 5 °C and concentrated hydrochloric acid (24.5 ml, 33.0%) was added slowly and dropwise over a period of about 1 h during which an exothermic reaction was observed and the temperature was raised to 18 °C - 20 °C. Meanwhile, a solution of N,N'-dicyclohexylcarbodiimide (51.25 g, 0.244 mol) was prepared in acetone (197.8 ml) in a separate vessel avoiding contact with water . When the temperature of the suspension was stabilized at 0°C ± 5°C, the DCC solution was slowly added dropwise for not less than 3 hours. After the dropwise addition, the reaction mixture was stirred at 0°C ± 5°C for 2 hours. After confirming the completion of the reaction by TLC, N,N'-dicyclohexylurea (DCU) was removed by filtration and washed with acetone (140.0 ml) and the washings were combined into the main filtrate. The combined filtrates were concentrated under reduced pressure to about 300 ml at 50°C ± 5°C and allowed to stand overnight. The dark yellow solution obtained was treated with activated carbon (5.0 g) for 10 min and then filtered through a diatomaceous earth plate to obtain a clarified yellow solution. The filter was washed with acetone (80 ml) and the washings were combined with the main filtrate (totaling about 380 ml). The acetone solution of moguisteine was cooled to 0°C ± 5°C and precipitated by slow addition of deionized water (380 ml), during which the moguisteine crystals were added. after 15-30 min, the product precipitated as an oily colloid and gradually crystallized. After crystallization was complete, the remaining deionized water (76 ml, total 456 ml, acetone/water ratio 1.0:1.2) was added. The suspension was kept at 0°C ± 5°C for at least 8 hours, followed by stirring at room temperature overnight. The product was collected by filtration and washed with deionized water (2 x 100 ml) to give 94.4 g of near white product. The product was dried at 35°C ± 5°C to give 69.5 g of white to pale yellow powder in a theoretical yield of 75.32 g and an actual yield of 92.27% with an HPLC purity of 99.81%. The experiment was repeated four times and the purity was 99.83%, 99.73%, 99.82% and 99.81%, respectively. The moguisteine prepared by this method was of very high purity and did not require further purification.
