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Amino-acid imidazolides

The reaction of an amino acid imidazolide with a diamino compound could be directed so that a mono amide was obtained in good yield,[1091 as shown by the following example ... [Pg.108]

The reaction of amino acid imidazolides with the potassium salt of monomethyl malonate in the presence of one equivalent of MgCl2, CoCl2, or MnCl2 results in the formation of jS"keto-y-aminocarboxylates.[64]... [Pg.309]

Another synthesis of jS-keto-y-aminocarboxylates starts from TV-protected amino-acid imidazolides and magnesium p-nitrobenzyl malonate (50-60 °C, about 6h).[65]... [Pg.309]

A V -Carbonyldiimidazole (CDI) is prepared in a convenient and safe procedure from phosgene and imidazole as a non-toxic crystalline compound (m.p. 116-118 °C).[5],[6] It reacts almost quantitatively at room temperature or by short and moderate heating with an equimolar quantity of a carboxylic acid in tetrahydrofuran, chloroform, or similar inert solvents within a few minutes to give the corresponding carboxylic acid imidazolide, which is formed under release of carbon dioxide, together with one equivalent of readily separable and recyclable imidazole.Thus, this reaction leads under very mild conditions to the activation of a carboxylic acid appropriate for transacylation onto a nucleophile with an alcohol to an ester, with an amino compound to an amide or peptide, etc. [Pg.27]

Examples are given in Table 4—1 for the synthesis of amides of AT-protected amino acids by means of imidazolides and triazolides (where Z and Boc represent the protecting groups benzyloxycarbonyl and terf-butoxycarbonyl) ... [Pg.107]

A similar principle of increasing the reactivity of imidazolides was used for the acylation of cyclohexyl amine and amino acids in an aqueous system 11051... [Pg.120]

The azolide method has also been used for the synthesis of polyamides and polyimides. These can be obtained by several routes First by condensation of two dihomofunctional components (dicarboxylic acid diimidazolides and diamines), secondly by condensation of a heterodifunctional compound (amino carboxylic acid and CDI), or through reaction on a polymer (for example, polymeric carboxylic acid imidazolides and amines). [Pg.125]

The broad use of A -carbonyldiimidazole (CDI) for the synthesis of amide and peptide linkages became a routine method only in the early sixties. JV-Protected amino acids were treated at room temperature with an equimolar amount of CDI to give imidazolides. Anhydrous tetrahydrofuran, dimethoxyethane, dichloromethane, pyridine, dimethylfor-mamide, and diethyl phosphite were utilized as solvents. In the second step the esters of amino acids, their hydrochlorides, or sodium salts were added to yield the peptide after several minutes or hours of reaction time. [Pg.150]

The imidazolide group at the amino end of an amino acid is as reactive toward nucleophiles as the imidazolide group at the carboxylic end of an amino acid. If an N-protected amino acid is selected as nucleophile, this method can also be used for peptide synthesis. The amino-activated amino acids, for example N-( 1 -imidazolylcarbonyl)-amino acid esters, are prepared from a-isocyanatocarboxylic acids and imidazole. [Pg.157]

Spin-labeled phosphoramidates are synthesized analogously by the reaction of phosphoric imidazolides with primary or secondary amines[189] or amino acid esters.11883... [Pg.280]

The active ester methodology, which is widely used in peptide chemistry, has found only limited application in depsipeptide synthesis. A more vigorous activation of the carboxy component is apparently required to form an ester bond compared to the peptide analogue. Nevertheless, active esters have been utilized for this purpose in combination with some catalyst additives. The first successful attempt in this direction was described by Mazur.1103 The modification of the 4-nitrophenyl ester procedure included addition of 1-10 equivalents of imidazole to the reaction mixture. This accelerated technique presumably involves formation of the highly reactive intermediate imidazolide. The reaction resulted in the preparation of model benzyloxycarbonyl didepsipeptide esters in good yields within several hours at room temperature from 4-nitrophenyl esters of Z-amino acids and the pentamethylbenzyl ester of glycolic acid, while in the absence of imidazole this reaction failed to give any product. [Pg.283]

Acidic proteinoid potentiates the active structure of lysine-rich proteinoid participating in forming microspheres in neutral buffer. Physical surface effects and providing micro condition in the microspheres could be surmised. Activation of amino acids generally requires acidic condition. Amino acids are activated by ATP and Mg2+ at pH 4-5 32 33). Aminoacyl adenylate anhydride and ester is formed preferentially from amino acid and adenylate imidazolide at pH 6.0J7). On the other hand, polycondensation of activated amino acids undergoes at pH values higher than 7. Peptides are formed from aminoacyl adenylate in basic buffer (the optimum pH is 10 for alanyl adenylate 40) from amino acid adenylate phosphoramidate and imidazole at pH 7.0 from N-(aminoacyl)-imidazole at pH 6-9 43). In this context, acidic and basic environments may be provided inside and/or on the surface of the microspheres composed of acidic and basic proteinoids in neutral buffer. Acidic micro condition suitable for the activation of amino acids and basic micro environment favorable for peptide formation from activated amino add may be provided. [Pg.71]

Although CDI was applied as early as 1972 as reagent for the esterification of starch and dextran, it has only scarcely been used up to now. Its renaissance during the last few years may be due to the fact that it became an affordable commercially available product. Among the first attempts for the esterification of polysaccharides via CDI is the binding of amino acids onto dextran. Besides CDI, -(thiocarbony diimidazole can be utilised to obtain the corresponding imidazolide [198]. The amino acids bound via this path are glycine, L-leucine, L-phenylalanine, L-histidine and L-alanyl-L-histidine. They are protected with N-trifluoroacetyl, N-benzyloxycarbonyl... [Pg.239]

For reactions carried out in homogeneous solution or under solid-phase conditions the use of Fmoc amino acid chlorides is limited by the competition between their aminolysis and the formation of the less reactive oxazol-5(4//)-ones in the presence of tertiary amines, which are essential components of such reaction systems. To improve the results under these conditions a hindered base, e.g. 2,6-di-/er/-butylpyridine, can be used as a hydrogen chloride acceptor since conversion to oxazol-5(4//)-one is slow with such bases. Although shown to be advantageous in certain cases, Fmoc amino acid chlorides are used in homogeneous solution synthesis only in particular cases. They react efficiently in the presence of pyridine with weak nucleophiles such as imine 2P l (Scheme 2) where other activated species such as an active ester, anhydride, acyl fluoride, and acyl imidazolide fail. [Pg.478]

A one-pot conversion of amines into 1,2,3,4-thiatriazoles, via reaction with thiocarbonyldiimidazole and azide, works well for both primary and secondary amines. With simple amines, the intermediate thio-imidazolide requires quatemisation with methyl iodide for the final azide reaction, but with amino-acid derivatives, this additional activation is not always necessary. ... [Pg.574]

Di-isobutylaluminium hydride (DIBAL) reduces acid imidazolides to aldehydes in high yields this method has been successfully applied to the synthesis of a-amino-aldehydes from a-amino-acids/ Similarly the acid thiazolidine derivatives (11), which are also readily obtained from carboxylic acids, are reduced by either DIBAL or lithium tri-t-butoxyaluminium hydride to the corresponding aldehyde." ... [Pg.31]

FIGURE 6.10 The side chain of histidine is readily acylated (A) by activated residues. The imidazolide produced is an activated species similar to the intermediate generated by reaction (B) of a carboxylic acid with coupling reagent carbonyldiimidazole. (Staab, 1956). Imida-zolides acylate amino and hydroxyl groups. Isomerization of histidyl during activation results from abstraction (C) of the a-proton by the 7t-nitrogen. [Pg.169]

Another potential approach towards 1 was reported by Seido et al. utilizing an asymmetric reduction of the ketone (57 Scheme 15) as the key step. Acylation of the lithium enolate of methyl phenylacetate with the imidazolide, obtained by treatment of the acid 56 with A, V -carbonyldiimidazole, gave the ketoester 57 in 66.4% yield. Asymmetric reduction of 57 with [RuI(/7-cymene)(5)-binap]I, tin chloride, and cam-phor-lO-sulfonic acid in methanol at 80 °C afforded the alcohol 58 as a mixture of syn and anti forms in 87.4% yield. The ratio of syn to anti isomers was 76.3 23.7 and the enantiomeric purity of each form was 95.6% ee and 97.8% ee, respectively. Tosylation of 58 with p-toluenesulfonyl chloride and pyridine in the presence of catalytic amounts of DMAP yielded a diastereomeric mixture of tosylate 59 in 61.8% yield. Deprotection of the /V-Cbz group in 59 by hydrogenation over 5% Pd-C followed by cyclization of the resulting amino tosylate 60 with potassium carbonate in methanol furnished methylphenidate as a mixture of erythro and threo isomers in a 7 3 ratio and 77.5% yield. [Pg.12]


See other pages where Amino-acid imidazolides is mentioned: [Pg.108]    [Pg.152]    [Pg.308]    [Pg.333]    [Pg.280]    [Pg.222]    [Pg.108]    [Pg.152]    [Pg.308]    [Pg.333]    [Pg.280]    [Pg.222]    [Pg.51]    [Pg.73]    [Pg.74]    [Pg.150]    [Pg.329]    [Pg.123]    [Pg.90]    [Pg.100]    [Pg.81]    [Pg.228]    [Pg.243]    [Pg.243]    [Pg.229]    [Pg.301]    [Pg.287]    [Pg.192]    [Pg.138]   
See also in sourсe #XX -- [ Pg.104 ]




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