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Erlenmeyer–Plöchl azlactone and amino-acid synthesis
The Erlenmeyer–Plöchl azlactone and amino acid synthesis, named after Friedrich Gustav Carl Emil Erlenmeyer who partly discovered the reaction, is a series of chemical reactions which transform glycine to various other amino acids via an oxazolone and an azlactone.
Hippuric acid cyclizes in the presence of acetic anhydride, condensing to give 2-phenyl-oxazolone. This intermediate also has two acidic protons and reacts with benzaldehyde, acetic anhydride and sodium acetate to a so-called azlactone. This compound on reduction gives access to phenylalanine.
==Scope==
In one study the Erlenmeyer amino acid synthesis was used in the heart of an L-m-tyrosine synthesis 〔''Optimized Synthesis of L-m-Tyrosine Suitable for Chemical Scale-Up'' Cara E. Humphrey, Markus Furegati, Kurt Laumen, Luigi La Vecchia, Thomas Leutert, J. Constanze D. Müller-Hartwieg, and Markus Vögtle Organic Process Research & Development 2007, 11, 1069–1075 〕〔The benzyl ether of 3-hydroxybenzaldehyde 1 reacts with the N-acetyl amide of glycine 2, acetic anhydride and sodium acetate to the azlactone (not displayed) which is ring-opened with sodium acetate in methanol to dehydroamino acid 3. Hydrogenation gives the N-acyl-m-tyrosine methyl ester 4 (the benzyl ether group is also cleaved). This compound is racemic and kinetic resolution is brought about by an enzyme which is able to only cleave the methyl ester of the S-enantiomer (forming (S)-5 soluble in dichloromethane) leaving water soluble (R)-4 untouched. The final step is amide cleavage to (S)-L-m-tyrosine 6〕
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