[NH2:1][CH:2]([C:7]([OH:9])=[O:8])[CH2:3][C:4]([OH:6])=[O:5].[C:10]1([CH3:17])[C:11](Cl)=[CH:12][CH:13]=[CH:14][CH:15]=1.Cl>[OH-].[Na+].C1COCC1>[C:10]1([CH3:17])[CH:11]=[CH:12][CH:13]=[CH:14][C:15]=1[NH:1][C@H:2]([C:7]([OH:9])=[O:8])[CH2:3][C:4]([OH:6])=[O:5]20 g of DL-aspartic acid (Aldrich) are dissolved in 210 ml of a 2.5N aqueous sodium hydroxide solution (120 ml)/THF (90 ml) mixture in a 500 ml, three-necked, round-bottomed flask equipped with a pHmeter and two dropping funnels containing, on the one hand, a 2.5N aqueous sodium hydroxide solution and, on the other hand, o-toluyl chloride. The o-toluyl chloride is added drop-wise while maintaining the pH above 9 by simultaneous addition of the 2.5N sodium hydroxide solution. The reaction mixture is kept stirring for 2 h 30 minutes after the end of the addition of the acid chloride before being acidified with a concentrated hydrochloric acid solution. The mixture is then exhaustively extracted with ethyl acetate. The organic phase is washed, dried and concentrated to dryness to provide 27.9 g (non-optimized yield 74%) of N-(ortho-toluyl)aspartic acid, used as is in the second stage.
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