C1(C)C=CC(S(O)(=O)=O)=CC=1.[NH2:12][C@H:13]([C:25]([O:27][CH2:28][C:29]1[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=1)=[O:26])[CH2:14][C:15]([O:17][CH2:18][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)=[O:16].[OH-].[Na+].P(=O)(O)(O)O.CO>C(Cl)(Cl)Cl>[NH2:12][C@H:13]([C:25]([O:27][CH2:28][C:29]1[CH:30]=[CH:31][CH:32]=[CH:33][CH:34]=1)=[O:26])[CH2:14][C:15]([O:17][CH2:18][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)=[O:16]19.4 g of the thus-obtained dibenzyl L-aspartate paratoluenesulfonate was suspended in 150 ml of chloroform, to which was added 16 g (0.04 mols) of aqueous 10% sodium hydroxide solution, and stirred at room temperature for 1 hour. Next, the chloroform layer was separated, to which was added 14.7 g (0.04 mols) of O,O′-diparatoluoyl-L-tartaric anhydride, and again stirred at room temperature for 2 hours. The chloroform layer was analyzed through HPLC. Its chart gave two peaks based on O,O′-diparatoluoyl-L-tartaric acid mono-L-(1,2-dibenzyloxycarbonyl)ethylamide (L-L form) of formula (16) and on O,O′-diparatoluoyl-L-tartaric acid mono-D-(1,2-dibenzyloxycarbonyl)ethylamide (L-D form) of formula (17), and the optical purity of the dibenzyl L-aspartate paratoluenesulfonate used in the reaction was found to be 59.0% ee (FIG. 1—column, CAPCELL PAC SG120; eluent, aqueous phosphoric acid solution (pH 2.2)/methanol=38/62 v/v).
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