Strecker

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

In the Strecker synthesis an aldehyde is converted to an a ammo acid with one more carbon atom by a two stage procedure m which an a ammo nitrile is an mterme diate The a ammo nitrile is formed by reaction of the aldehyde with ammonia or an ammonium salt and a source of cyanide ion Hydrolysis of the nitrile group to a car boxylic acid function completes the synthesis... 

The synthesis of alanine was described by Adolf Strecker of the University of Wurzburg (Germany) in a paper published in 1850... 

Aldehydes by reaction with ammonia and cyanide ion (the Strecker synthesis)... 

If you synthesized the tnpeptide Leu Phe Ser from amino acids prepared by the Strecker synthesis how many stereoisomers would you expect to be formed ... 

Strecker synthesis (Section 27 4) Method for prepanng amino acids in which the first step is reaction of an aldehyde with ammonia and hydrogen cyanide to give an amino nitnle which IS then hydrolyzed... 

Strecker reaction Strecker synthesis Strengthening agent Strength testing Strepavidin Strep, pyogenes Cruz Strep tase... 

Historically these compounds have been made in two-step processes. Eor smaller volumes, reaction of an appropriate ketone or aldehyde with a cyanide salt followed by treatment with an ammonium salt proves satisfactory (Strecker synthesis). Eor larger volumes, treatment of the ketone or aldehyde with HCN to produce a cyanohydrin, followed by treatment with ammonia has been practiced. However, in 1990, DuPont began practicing a new one-step... 

Miscellaneous Reactions. Sodium bisulfite adds to acetaldehyde to form a white crystalline addition compound, insoluble in ethyl alcohol and ether. This bisulfite addition compound is frequendy used to isolate and purify acetaldehyde, which may be regenerated with dilute acid. Hydrocyanic acid adds to acetaldehyde in the presence of an alkaU catalyst to form cyanohydrin the cyanohydrin may also be prepared from sodium cyanide and the bisulfite addition compound. Acrylonittile [107-13-1] (qv) can be made from acetaldehyde and hydrocyanic acid by heating the cyanohydrin that is formed to 600—700°C (77). Alanine [302-72-7] can be prepared by the reaction of an ammonium salt and an alkaU metal cyanide with acetaldehyde this is a general method for the preparation of a-amino acids called the Strecker amino acids synthesis. Grignard reagents add readily to acetaldehyde, the final product being a secondary alcohol. Thioacetaldehyde [2765-04-0] is formed by reaction of acetaldehyde with hydrogen sulfide thioacetaldehyde polymerizes readily to the trimer. 

In a modification of the original method. Read (60) replaced a-amino acids with a-amino nitriles. This reaction is sometimes known as Strecker hydantoin synthesis, the term referring to the reaction employed for the synthesis of the a-amino nitrile from an aldehyde or ketone. The cycli2ation intermediate (18) has been isolated in some cases (61), and is involved in a pH-controUed equiUbrium with the corresponding ureide. 

Other Reactions. The reaction of Thydioxybenzaldehyde with sodium cyanide and ammonium chloride, Strecker synthesis, yields /J-hydroxyphenylglycine [938-97-6] a key intermediate in the manufacture of semisynthetic penicillins and cephalosporins (see Antibiotics, p-LACTAMs). 

Strecker Degradation (Oxidative Deamination), Mild oxidizing agents such as aqueous sodium hypochlorite or aqueous A-bromosuccinimide, cause decarboxylation and concurrent deamination of amino acids to give aldehydes. 

In some cases, Bucherer s process is employed also, but strict control of reaction conditions is needed because the reactivity of formaldehyde is different from other aldehydes. DL-Alanine (212) is produced by either Strecker s or Bucherer s process from acetaldehyde. 

Choline was isolated from ox bile in 1849 by Strecker. During 1900 to 1920, observations led to interest in the vasodepressor properties of the esters of choline, and in the 1920s it was shown that acetylcholine was presumably the "vagus-substance." The nutritional importance of choline was recognized in the 1930s, when it was found that choline would prevent fatty infiltration of the Hver in rats. Subsequent observations showed that choline deficiency could produce cirrhosis (1) or hemorrhagic kidneys (2) in experimental animals under various conditions. 

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. 

In 1959 a new non-protein L-a-amino acid was isolated from the seeds of Acacia willardiana and later from other species of Acacia-, it proved to be l-/3-amino-/3-carboxyethyluracil (977) (59ZPC(316)164). The structure was confirmed by at least four syntheses in the next few years. The most important involves a Shaw synthesis (Section 2.13.3.1.2e) of the acetal (975) and hydrolysis to the aldyhyde (976) followed by a Strecker reaction (potassium cyanide, ammonia and ammonium chloride) to give DL-willardiine (977) after resolution, the L-isomer was identical with natural material (62JCS583). Although not unambiguous, a Principal Synthesis from the ureido acid (978) and ethyl formylacetate is the most direct route (64ZOB407). 

STRECKER Aminoacid synthesis Synthesis of a-amino acids from aldehydes or ketones via cyanohydnns... 

Other direct methods for the sulfonation of the higher fatty acids are by the use of sulfur trioxide vapor or by the use of chlorosulfonic acid. Indirect methods are also available for the preparation of a-sulfo fatty acids and their salts from an a-bromo fatty acid made by the Hell-Volhard-Zelinsky reaction. The bromo compound may be converted directly to the sodium salt of a sulfonic acid through the Strecker reaction or may be converted to the mercaptan and oxidized to the sulfonate. Sulfonation of the lower fatty acids has been studied by Backer and co-workers. ... 

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