N-(2-Bromopropionyl)-O-benzyl-L-serine (BPBS) was prepared using 2-bromopropionic acid and N-Boc-O-Bzl-L-serine as the starting reagents. BPBS underwent the intra-molecular ring-closing reaction in DMF/Et3N solvent at 80 ℃ for 9 h forming a mixture of two non-enantiomers, i.e. (3S,6S)-benzyloxy- methyl-6-methyl-morpholine-2,5-dione [(3S,6S)-BMMD] and (3S,6R)-BMMD with a yield of 70%. Two optically pure enantiomers of BMMD, i.e. (3S,6S)-BMMD and (3S,6R)-BMMD were obtained via 4 operation circles of “solution-partial recrystallization” by means of a differential recrystallization method using ethyl acetate as a solvent. The single crystals of the two isomers of BMMD were grown from ethyl acetate at room temperature. The fine molecular structures of the two isomers were determined by X-ray diffraction analysis of the single crystals.

Key words: (3S,6R)-benzyloxymethyl-6-methyl- morpholine-2,5-dione, crystal structure, resolution, optical isomer, (3S,6S)-benzyloxymethyl-6-methyl-morpholine-2,5-dione