Synthesis of amino acids

 There are several methods for the synthesis of amino acids. Here are two classical methods along with their reaction mechanisms:

 Strecker Synthesis

Reactions:

• The Strecker synthesis is one of the most well-known methods for the synthesis of α-amino acids. It involves the reaction of an aldehyde (R-CHO) with ammonia (NH₃) and hydrogen cyanide (HCN) to form an aminonitrile, which is then hydrolyzed to give the amino acid.

Steps:

1. Formation of the Aminonitrile:

   $$RCHO+N{H}_3\to RCH(N{H}_2)OH\text{(imine formation)}$$$$RCH(N{H}_2)OH+HCN\to RCH(N{H}_2)CN\text{(aminonitrile formation)}$$

2. Hydrolysis of the Aminonitrile:

   $$RCH(N{H}_2)CN+2H_{2}O+HCl\to RCH(N{H}_2)COOH+N{H}_{4}Cl$$

   The nitrile group is hydrolyzed to a carboxylic acid, resulting in the formation of the α-amino acid.

Example:
Using acetaldehyde as the aldehyde, glycine (an α-amino acid) is synthesized:

$$C{H}_{3}CHO+N{H}_3+HCN\to C{H}_{3}CH(N{H}_2)CN\to C{H}_{3}CH(N{H}_2)COOH\text{(Glycine)}$$

2. Gabriel Phthalimide Synthesis

Reactions:

• The Gabriel synthesis is used for the preparation of primary amines, including α-amino acids. This method involves the alkylation of potassium phthalimide, followed by hydrolysis to yield the amino acid.

Steps:

1. Formation of N-Alkyl Phthalimide:

   $$\text{Phthalimide}+KOH\to \text{Potassium Phthalimide (KPhth)}$$$$\text{KPhth}+RC{H}_{2}Br\to RC{H}_{2}Phth\text{(N-alkylation)}$$

2. Hydrolysis of the N-Alkyl Phthalimide:

   $$RC{H}_{2}Phth+H_{2}NN{H}_2\to RC{H}_{2}N{H}_2+\text{Phthalhydrazide}$$

   The phthalimide group is removed by hydrazine (H₂NNH₂), yielding the primary amine (RCH₂NH₂).

3. Conversion to Amino Acid: The primary amine can then be converted into an α-amino acid via further functionalization, such as through the reaction with a suitable α-monocarboxylic acid:

   $$RC{H}_{2}N{H}_2+BrC{H}_{2}COOH\to RC{H}_{2}NHC{H}_{2}COOH$$

Example:
Using bromomalonic acid as the alkylating agent, alanine can be synthesized:

$$C{H}_{3}Br+\text{Phthalimide}\to \text{N-Alkyl Phthalimide}$$$$\text{N-Alkyl Phthalimide}+H_{2}NN{H}_2\to C{H}_{3}N{H}_2$$$$C{H}_{3}N{H}_2+BrC{H}_{2}COOH\to C{H}_{3}CH(N{H}_2)COOH\text{(Alanine)}$$

These methods are widely used in organic chemistry for the synthesis of various amino acids.