To dichloromethane (400 ml), D-serine (50 g) was added at ambient temperature under nitrogen atmosphere to form a suspension and then trimethylsilyl chloride (61.92 g) and hexamethyldisilazane (107.5 ml) was added to the suspension in 10-15 minutes at ambient temperature. The reaction mixture was refluxed at 35-40° C. for 3 hours and then it was cooled to 0° C. To this mixture, a solution of anhydrous methanol (22.83 g) in dichloromethane (50 ml) was added at 0° C. and the mixture was allowed to reach at room temperature. Triethylamine (48.14 g) was slowly added to it at 25-30° C. and then trityl chloride (132.63 g) was added in 3 lots to the mixture at an interval of 10 minutes. The reaction mixture was then stirred for overnight under nitrogen at ambient temperature. After completion of the reaction, methanol (76.12 g) was added at ambient temperature in 10-15 minutes and the solvent was recovered under vacuum at 40-45° C. Hexane (400 ml) and 5% citric acid solution (750 ml) was added to the recovered solid and filtered. The solid product obtained was washed with water (750 ml) and hexanes (200 ml) and then filtered. The filtered solid was washed with hexanes (200 ml) and dried to obtain the titled product. Yield=125 gm.
