Strecker amino acid synthesis

Strecker synthesis
Named after	Adolph Strecker
Reaction type	Substitution reaction
Identifiers
Organic Chemistry Portal	strecker-synthesis
RSC ontology ID	RXNO:0000207

The Strecker amino acid synthesis, also known simply as the Strecker synthesis, was devised by German chemist Adolph Strecker, and is a term used for a series of chemical reactions that synthesize an amino acid from an aldehyde or ketone. 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. In the original Strecker reaction acetaldehyde, ammonia, and hydrogen cyanide combined to form after hydrolysis alanine.

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.

The traditional synthesis of Adolph Strecker from 1850 gives racemic α-amino nitriles, but several procedures utilizing asymmetric auxiliaries or asymmetric catalysts have been developed.

In the first part of the reaction, the carbonyl oxygen of an aldehyde is protonated, followed by a nucleophilic attack of ammonia to the carbonyl carbon. After subsequent proton exchange, water is cleaved from the iminium ion intermediate. A cyanide ion then attacks the iminium carbon yielding an aminonitrile.

In the second part of the Strecker Synthesis the nitrile nitrogen of the aminonitrile is protonated, and the nitrile carbon is attacked by a water molecule. A 1,2-diamino-diol is then formed after proton exchange and a nucleophilic attack of water to the former nitrile carbon. Ammonia is subsequently eliminated after the protonation of the amino group, and finally the deprotonation of a hydroxyl group produces an amino acid.

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