Amino acids, preparation acyl derivatives

Jursic, B. S., Neumann, D. Preparation of N-acyl derivatives of amino acids from acyl chlorides and amino acids in the presence of cationic surfactants. A variation of the Schotten-Baumann method of benzoylation of amino acids. Synth. Common. 2001, 31, 555-564. 

S,S-dioxides, those authors applied spHt/pool methodology. TWo different series of compounds were prepared such as compounds 376 containing an amino acid group acylated at the nitrogen atom. According to strategy 1 shown in Scheme 90, a series of structurally diverse carboxylic acid derivatives were prepared from supported aldehyde 373 condensed with different protected amino acids in the presence of NaBH(OAc)3 to afford intermediate 374, which was then acylated affording 375. After hydrolysis of ester and reaction with bromo derivative 368 (R = H) in PTC conditions, compounds 376 were obtained. 

Reactions.—Unsymmetrical dialkyl sulphides are obtained by the action of aqueous KOH, at 80 °C, on 05-dialkyl dithiocarbonates (with different alkyl groups) under phase-transfer conditions. The reaction depends on the liberation of a mercaptan and its alkylation by the 0-alkyl group of the diester. Ethoxythiocarbonyl derivatives of amino-acids are made by acylating the amino-acids with the stable reagent bis (ethoxythiocarbonyl) sulphide, (EtOCS)2S. This is prepared by an improved method from potassium ethylxanthate (2 mol) and ethyl chloroformate (1 mol). Esters of amino-acids are acylated by carboxymethyl... 

Substituted 5-hydroxythiazoles (267b), Rj = alkylmercapto, acyl-amino, and sec-amino, are prepared by cydization of N-thioacyl-amino acids (266) with phosphorus tribromide or acetic anhydride (Scheme 137) (317, 350). i en the cydization of 266, R2 = H, is carried out with acetic anhydride in the presence of benzaldehyde (317, 325) or ethylformate (317), the benzylidene (268), R2=Ph, Rj = SR or CH2Ph, or 4-ethoxymethylene (268), Rj = SR and R2 = OEt, derivative is obtained directly (Scheme 138). 

Enzymatic hydrolysis is also used for the preparation of L-amino acids. Racemic D- and L-amino acids and their acyl-derivatives obtained chemically can be resolved enzymatically to yield their natural L-forms. Aminoacylases such as that from Pispergillus OTj e specifically hydrolyze L-enantiomers of acyl-DL-amino acids. The resulting L-amino acid can be separated readily from the unchanged acyl-D form which is racemized and subjected to further hydrolysis. Several L-amino acids, eg, methionine [63-68-3], phenylalanine [63-91-2], tryptophan [73-22-3], and valine [72-18-4] have been manufactured by this process in Japan and production costs have been reduced by 40% through the appHcation of immobilized cell technology (75). Cyclohexane chloride, which is a by-product in nylon manufacture, is chemically converted to DL-amino-S-caprolactam [105-60-2] (23) which is resolved and/or racemized to (24)... 

Acylation. Reaction conditions employed to acylate an aminophenol (using acetic anhydride in alkaU or pyridine, acetyl chloride and pyridine in toluene, or ketene in ethanol) usually lead to involvement of the amino function. If an excess of reagent is used, however, especially with 2-aminophenol, 0,A/-diacylated products are formed. Aminophenol carboxylates (0-acylated aminophenols) normally are prepared by the reduction of the corresponding nitrophenyl carboxylates, which is of particular importance with the 4-aminophenol derivatives. A migration of the acyl group from the O to the N position is known to occur for some 2- and 4-aminophenol acylated products. Whereas ethyl 4-aminophenyl carbonate is relatively stable in dilute acid, the 2-derivative has been shown to rearrange slowly to give ethyl 2-hydroxyphenyl carbamate [35580-89-3] (26). 

This derivative, prepared from an amino acid and the acyl azide, is selectively cleaved in 80% yield by chymotrypsin. ... 

Hydroxy-L-prolin is converted into a 2-methoxypyrrolidine. This can be used as a valuable chiral building block to prepare optically active 2-substituted pyrrolidines (2-allyl, 2-cyano, 2-phosphono) with different nucleophiles and employing TiQ as Lewis acid (Eq. 21) [286]. Using these latent A -acylimmonium cations (Eq. 22) [287] (Table 9, No. 31), 2-(pyrimidin-l-yl)-2-amino acids [288], and 5-fluorouracil derivatives [289] have been prepared. For the synthesis of p-lactams a 4-acetoxyazetidinone, prepared by non-Kolbe electrolysis of the corresponding 4-carboxy derivative (Eq. 23) [290], proved to be a valuable intermediate. 0-Benzoylated a-hydroxyacetic acids are decarboxylated in methanol to mixed acylals [291]. By reaction of the intermediate cation, with the carboxylic acid used as precursor, esters are obtained in acetonitrile (Eq. 24) [292] and surprisingly also in methanol as solvent (Table 9, No. 32). Hydroxy compounds are formed by decarboxylation in water or in dimethyl sulfoxide (Table 9, Nos. 34, 35). 

In 1995, and regrettably missed in last year s review, Klotgen and Wiirthwein described the formation of the 4,5-dihydroazepine derivatives 2 by lithium induced cyclisation of the triene 1, followed by acylation <95TL7065>. This work has now been extended to the preparation of a number of l-acyl-2,3-dihydroazepines 4 from 3 <96T14801>. The formation of the intermediate anion and its subsequent cyclisation was followed by NMR spectroscopy and the stereochemistry of the final product elucidated by x-ray spectroscopy. The synthesis of optically active 2//-azepines 6 from amino acids has been described <96T10883>. The key step is the cyclisation of the amino acid derived alkene 5 with TFA. These azepines isomerise to the thermodynamically more stable 3//-azepines 7 in solution. 

Several acyl derivatives of (aminomethyl)-and (1-aminoethyl)-phosphonic acids, in the latter case including [L-l-([L-alanyl]amino)ethyl]phosphonic acid (alafosfalin), have been prepared in their various diastereoisomeric forms and the... 

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