1) One of the oldest methods for the synthesis of amino acids dates back to the nineteenth century & is simply a nucleophilic substitution in which ammonia reacts with α-halo carboxylic acid.
The α-halo acid is prepared by the Hell-Volhard-Zelinsky reaction.
2) Another method of synthesis of amino acids is by Strecker Synthesis. In strecker synthesis an aldehyde is converted to an α-amino acid with one more carbon atom by 2-stage procedure in which an α-amino nitrile is an intermediate. The α-amino nitrile is formed by reaction of the aldehyde with ammonia or an ammonium salt & a source of CN- ion. Hydrolysis of the nitrile group to a carboxylic acid function completes the synthesis.
3) The most widely used method for the laboratory synthesis of α-amino acids is a modification of the malonic ester synthesis. The key reagent is diethlyl acetamidomalonate, a derivative of malonic ester that has the critical nitrogen substituent in place at the α-carbon atom.The side chain is introduced by alkylating diethlyl acetamidomalonate in the same way as diethyl malonate itself is alkylated.
Hydrolysis removes the acetyl group from nitrogen & converts the 2 ester functions to carboxyl groups. Decarboxylation gives the desired product.