[CH2:1]([NH:4][CH2:5][C:6]([O:8][CH2:9][CH3:10])=[O:7])[CH2:2][CH3:3].C([CH:13]([C:17](Cl)=[O:18])[C:14](Cl)=[O:15])C.C(=O)([O-])[O-].[K+].[K+].[CH3:26][CH2:27][O:28]CC>O>[CH2:27]([O:28][C:17]([CH2:13][C:14]([N:4]([CH2:1][CH2:2][CH3:3])[CH2:5][C:6]([O:8][CH2:9][CH3:10])=[O:7])=[O:15])=[O:18])[CH3:26]7.16 g (49.4 mM) of ethyl N-(n-propyl)glycinate and 6.4 ml (50 mM) of ethyl malonyl chloride were added simultaneously to an ice-cold solution of 6.9 g (50 mM) of potassium carbonate in 15 ml water overlaid with 50 ml ether. The cooling bath was removed and the reaction warmed to ambient temperature stirring for 1.5 hours. The aqueous phase was acidified to pH 4 with concentrated HCl and the layers separated. The aqueous phase was extracted with 15 ml ether and the combined ether layer washed with brine and dried over anhydrous Na2SO4 then concentrated to yield 11.8 g of the desired product as a pale yellow oil.
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