Strecker amino acid synthesis

The Strecker amino acid synthesis, devised by Adolph Strecker, is a series of chemical reactions that synthesize an amino acid from an aldehyde (or ketone).^{[1] [2]} The aldehyde is condensed with ammonium chloride in the presence of potassium cyanide to form an α-aminonitrile, which is subsequently hydrolyzed to give the desired amino-acid. ^{[3] [4]}

While usage of ammonium salts gives unsubstituted amino acids, primary and secondary amines also successfully give substituted amino acids. Likewise, the usage of ketones, instead of aldehydes, gives α,α-disubstituted amino acids. ^[5]

The traditional synthesis of Adolph Strecker from 1850 gives racemic α-amino nitriles, but recently several procedures utilizing asymmetric auxiliaries ^[6] or asymmetric catalysts ^{[7] [8]} have been developed. ^[9]

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Reaction mechanism

The reaction mechanism for this reaction is sketched below. In part one aldehyde 1.1 reacts with ammonia in a nucleophilic addition to the hemiaminal 1.3 which attracts a proton to form iminium ion 1.5 by elimination of water. A second nucleophilic addition of the cyanide ion forms the aminonitrile 1.6.

In stage two a proton activates aminonitrile 2.1 for nucleophilic addition of two equivalents of water to intermediate 2.6 which eliminates ammonia and a proton to final product 2.7.

Scope

An example of present-day use of the Strecker synthesis is a multikilogram scale synthesis of a valine derivative starting from 3-methyl-2-butanone ^{[10] [11]}:

References

See also

• Bucherer-Bergs reaction