Strecker synthesis of amino acids

Hydroxyl Group. The OH group of cyanohydrins is subject to displacement with other electronegative groups. Cyanohydrins react with ammonia to yield amino nitriles. This is a step in the Strecker synthesis of amino acids. A one-step synthesis of a-amino acids involves treatment of cyanohydrins with ammonia and ammonium carbonate under pressure. Thus acetone cyanohydrin, when heated at 160°C with ammonia and ammonium carbonate for 6 h, gives a-aminoisobutyric acid [62-57-7] in 86% yield (7). Primary and secondary amines can also be used to displace the hydroxyl group to obtain A/-substituted and Ai,A/-disubstituted a-amino nitriles. The Strecker synthesis can also be appHed to aromatic ketones. Similarly, hydrazine reacts with two molecules of cyanohydrin to give the disubstituted hydrazine. 

Nucleophilic addition of carbon to imines the Strecker synthesis of amino acids... 

A nice example of the chemical similarity between imines and carbonyl compounds is the Strecker synthesis of amino acids. This involves reaction of an aldehyde with ammonia and HCN (usually in the form of ammonium chloride plus KCN) to give an intermediate a-aminonitrile. Hydrolysis of the a-aminonitrile then produces the a-amino acid. 

Catalytic Asymmetric Strecker Synthesis of Amino Acids. 172... 

Cyanide will attack iminium ions the Strecker synthesis of amino acids Cyanide will react with iminium ions to form oc amino nitriles. Although these compounds are relatively unimportant in their own right, a simple hydrolysis step produces a amino acids. This route to amino acids is known as the Strecker synthesis. Of course, it s not usually necessary to make the amino acids that Nature produces for us in living systems they can be extracted from hydrolysed proteins. 

They made a racemic sample using the Strecker synthesis of amino acids that you met in Chapter 12. The racemic amino acid was reacted with acetic anhydride to make the mixed anhydride and then with the sodium salt of naturally derived, enantiomerically pure alcohol menthol to give two diastereoisomers of the ester (see top of facing page). 

The addition of HCN to aldehydes has been a well-known reaction since the 19th century, especially in the context of the Kiliani-Fischer synthesis of sugars. Even older is the Strecker synthesis of amino acids by simultaneous reaction of aldehydes with ammonia and HCN followed by hydrolysis. The challenge in recent years has been to achieve face-selectivity in the addition to chiral aldehydes. These face-selective additions, known as nonchelation-controlled processes, refer to the original formulation of Cram s for the reaction of nucleophiles with acyclic chi carbonyl compounds. The chelation-controlled reactions refer also to a formulaticxi of Cram s, but whose stereochemical consequences sometimes differ. 2... 

To complete the Strecker synthesis of amino acid TM 5.3, beside cyanide salt, a proper source of ammonia is needed. To this aim, ammonium salts are more... 

It is interesting that three multicomponent reactions were broadly used over 150 years, known as name reactions according to their inventors Strecker synthesis of amino acids [3], Hantsch synthesis of 1,4-dihydropyrimidines [4] and particularly the imjxjrtant Mannich reaction [5]. 

We have previously met the Strecker synthesis of amino acids (Figure 22.20, Section 14,3.4) like the two previous methods, this normally produces racemic amino acids. However, if the reaction is catalyzed by various additives such as the Jacobsen catalyst, 22.24, aliphatic a-aminonitriles have been isolated in 80 %-90 % enantiomer excess. 

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