[C:1]([OH:10])(=[O:9])[C@@H:2]([C@H:4]([C:6]([OH:8])=[O:7])[OH:5])[OH:3].CO.[CH3:13][O:14][C:15](=[O:29])[CH:16]1[CH2:20][CH2:19][CH2:18][N:17]1[C@@H:21]([CH3:28])[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1>C1(C)C=CC=CC=1>[CH3:13][O:14][C:15](=[O:29])[C@@H:16]1[CH2:20][CH2:19][CH2:18][N:17]1[C@@H:21]([CH3:28])[C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1.[C:1]([OH:10])(=[O:9])[C@@H:2]([C@H:4]([C:6]([OH:8])=[O:7])[OH:5])[OH:3]L-tartaric acid (9.51 g) was mixed with methanol (14.18 g) and heated to 40° C. To the resulting solution was added dropwise a 50% toluene solution (28.93 g) of N-[(S)-α-methylbenzyl]-(RS)-proline methyl ester obtained in Example 1 at that temperature. After stirred at the temperature for 1 hour, the reaction mixture was cooled to 0° C. over 14 hours and stirred at that temperature for 2 hours. The crystallized solid was separated by filtration and washed with cold methanol to yield a salt of N-[(S)-α-methylbenzyl]-(S)-proline methyl ester and L-tartaric acid (11.50 g) in 98.8% diastereomeric excess (hereinafter referred to as “d.e.”) and a yield of 40.0%.
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