L-Hydroxyproline → HCID 391526, compound

Participants

Reaction Steps

35.6 g (0.27 mol) of (2S,4R)-4-hydroxyproline were dissolved in 300 ml (0.60 mol) of 2N sodium hydroxide in a 750 ml sulphonation flask which was provided with stirrer, dropping funnel, thermometer and condenser. Thereupon, within 10 minutes there was added dropwise thereto a solution of 63 g (0.33 mol) of p-toluenesulphonyl chloride in 180 ml of diethyl ether. The temperature was held at 16°-20° C. by means of a water bath. After intensive stirring at room temperature for 16 hours, the reaction has finished. The aqueous phase (pH about 7) was separated and back-washed with 250 ml of diethyl ether. The ether phases were back-washed a further twice with 100 ml of deionized water each time. The combined aqueous phases were acidified to pH 2 with 25 ml of concentrated hydrochloric acid (27%) while cooling with ice at 5° C. and stirred for 1.5 hours at 5° C. The separated crystals were filtered off under suction, washed with 1 liter of deionized water and dried for 16 hours in a vacuum drying oven at 40° C./17 mbar. The resulting product (76.2 g of white crystals of melting point (142°-145° C.) was, for purification, dissolved in 200 ml of hot ethanol/water (1:4, v/v) and recrystallized while stirring and slowly cooling to 5° C. The white crystals obtained after drying (73.4 g) were again recrystallized from 150 ml of ethanol/water (1:4, v/v) as previously described and dried in a vacuum drying oven at 50° C./17 mbar. There were obtained 69.4 g (89.6%) of (2S,4R)-4-hydroxy-1-(p-tolylsulphonyl)-2-pyrrolidinecarboxylic acid of melting point 146°-147° C. [α]D20 =-87.6° (c=1 in ethanol).

Provenance & Evidence