β-amino acid ester

Hello

I attempt to prepare β-amino acid ester via the reaction of neutral amino acids with ethyl acetoacetate according to the procedure in the picture.
In this paper, the β-amino acid ester was prepared by the reaction of the potassium salt of the amino acid with ethyl acetoacetate to give the enamine product. The problem is that the enamine wasn't isolated, neutarized or purified. The resulted crude was used directly in a following reaction.
In my experiment, I need to isolate and purify the enamine product.
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SO could you please suggest a proper work up to to isolate and purify β-amino acid ester?
And if you have a different method to prepare β-amino acid esters, then it'd be great to mention it.
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Thank you



[Edited on 30-11-2021 by Knowledge Seeker]