Amino acid, acetyl derivatives ester

A method has been described for the preparation of N-formyl-a-amino-acid t-butyl esters by formylation of the free base with a mixture of formic acid, DCC, and pyridine, thus overcoming the incompatibility of the t-butyl ester group with the usual acidic formylation conditions. The transfer hydrogenation technique has been recommended for the removal of N-benzyloxycarbonyl and benzyl ester groups from peptides. N-Acetyl-a-amino-acids are converted into the corresponding A-ethyl derivatives by reaction with Meerwein s reagent followed by reduction with sodium borohydride. ... 

Typical derivatives of the first type are the various esters (Me, Et, Pr, iso-Pi, Bu, wo-Bu, cc-Bu, Am, tio-Am, etc.) of A -acyl (acetyl, TEA, PFP, HFB, etc.) amino acids. The butyl esters of iV-TFA amino acids owing to the frequency of their use even have a special abbreviation TAB derivatives. The two-stage process includes the esterification of amino acids by an excess of the corresponding alcohol in the presence of HCl and, after the evaporation of volatile compounds, the treatment of the non-volatile hydrochlorides of alkyl esters by acylating reagents (Fig. 1). 

Nonvolatile analytes must be chemically converted to a volatile derivative before analysis. For example, amino acids are not sufficiently volatile to analyze directly by gas chromatography. Reacting an amino acid with 1-butanol and acetyl chloride produces an esterfied amino acid. Subsequent treatment with trifluoroacetic acid gives the amino acid s volatile N-trifluoroacetyl- -butyl ester derivative. 

The melting point of the ethyl ester of 2-amino-4-methylselena-zole-5-carboxylic acid is given as 180-181 °C and that of the free acid as 181-182°C. In addition, the melting points of the acetyl derivatives are very close to each other. These facts led King and... 

A similar series of reactions was performed by Paulsen and Hdlck141 for the preparation of the T-antigenic, unprotected, amino acid-disaccha-rides 200 and 201, starting from the 4,6-0-benzylidene-N-(benzyloxy-carbonyl) benzyl esters 198 and 199, respectively, by condensation with 110 in the presence of mercury dicyanide-mercury dichloride and molecular sieves 4A, and deprotection of the product. Sinay and co-workers148 also reported the synthesis of hexa-O-acetyl derivatives of 200 and 201 by application of the sequence of azido-nitration-bromination. 

The most important derivatives of the amino acids are halides and esters. The most reactive are the halides, which, as described by Emil Fischer, can be obtained by shaking dry amino acids with phosphorus pentachloride in acetyl chloride. 

Although not of fatty acid origin another group of scarab beetles utilizes amino acid derivatives as pheromones [119]. The large black chafer, Holotrichia parallela, uses L-isoleucine methyl ester [ 120] and the cranberry white grub, Phyllophaga anxia, uses both L-isoleucine and i.-valine methyl esters [121]. More recently L-isoleucine methyl ester, N-formyl L-isoleucine methyl ester, and N-acetyl L-isoleucine methyl ester were identified in the scarab beetle Phyllophaga elenans [ 122]. These pheromone components are obviously derived from the amino acids isoleucine and valine. 

Corr, L. T., Berstan, R. and Evershed, R. P. (2007a) Development of N acetyl methyl ester derivatives for the determination of 813C values of amino acids using gas chromatography combustion isotope ratio mass spectrometry. Analytical Chemistry 79, 9082 9090. 

The advantage of trimethylsilyl (TMS) derivatives lies in the simplicity of the derivatization procedure, which is carried out by the addition of N,0-bis(trimethylsilyl)trifluoroacetamide (BSTFA) in acetonitrile and heating for approximately 2 h at 150 °C under anhydrous conditions in a sealed tube. However, there may be problems owing to the formation of multiple derivatives of each amino acid. Another technique involves the formation of n-butyl esters of the amino acids and their subsequent trimethylsilylation by a similar procedure. The n-butyl esters are formed by heating the amino acids for 15 min in n-butanol and HC1 and these are then converted to the A-TMS-n-butyl ester derivatives. A-acyl amino acid alkyl esters are commonly used. Acetylation of the butyl, methyl or propyl esters of amino acids,... 

OPA in combination with chiral thiols is one method used to determine amino acid enantiomers. A highly fluorescent diastereomeric isoindole is formed and can be separated on a reverse-phase column. Some of these chiral thiols include N-acetyl-L-cysteine (NAC), N-tert-butyloxy-carbonyl- L-cysteine (Boc-L-Cys), N-isobutyryl- L-cysteine (IBLC), and N-isobutyryl- D -cysteine (IBDC). Replacing OPA-IBLC with OPA-IBDC causes a reversal in the elution order of the derivatives of D- and L-amino acids on an ODS column (Hamase et al., 2002). Nimura and colleagues (2003) developed a novel, optically active thiol compound, N-(tert-butylthiocarbamoyl)- L-cysteine ethyl ester (BTCC). This reagent was applied to the measurement of D-Asp with a detection limit of approximately 1 pmol, even in the presence of large quantities of L-ASP. 

The resolution was then based on the enzymatic propanolysis of this derivative in dioxane as solvent. Lip Novozyme 435 selectively cleaves the L-form of the oxazolone producing an L-enriched (81-87% ee) 2-acetamido-3-(heteroaryl)propionic acid propyl ester, the dynamic aspect of the process being based on the continual racemization of the residual oxazolone. The propyl group was then removed with alkali and a second selective enzymatic step to remove the acetyl protecting group with Fluka Acylase 1 produced the L-amino acid at better than 99% ee (Scheme 13). 

Reduction of oximino esters, i.e. oximes of keto esters, is very useful for the preparation of amino esters. Reductions are very selective since the oximes are easily reduced by catalytic hydrogenation over 10% palladium on carbon in ethanol (yield 78-82%) I094, by aluminum amalgam in ether (yields 52-87%) [750, 70P5], or by zinc dust in acetic acid (yield 77-78%). None of these reagents attacks the ester group. The last mentioned reaction gives an N-acetyl derivative [1096. ... 

From a biosynthetic perspective, naturally occurring tetramic acids can be regarded to arise from the assembly of an amino acid and an activated acyl entity derived from an acetyl group or a more complex activated ester, Fig. (1). Alternatively, the simple tetramic acid formed can undergo substitution at C-3 with a second acyl group. On this basis, compounds such as lactacystin (5) have not been considered [11]. The carboxylic acid... 

The original Garner preparation3 of 5 involves the conversion of serine into the protected methyl ester 3 and controlled reduction of the latter by DIBAL. The reaction sequence employed for the preparation of 3 involves the protection of the amino acid as N-Boc derivative using di-tert-butyl dicarbonate, esterification with methyl iodide or diazomethane, and acetonization with 2,2-dimethoxypropane under acid catalysis. The N-Boc methyl serinate and the ester 3 require purification by vacuum distillation or chromatography. In a modification to this procedure reported by McKillop,2 the esterification reaction of serine is carried out first by methanol/acetyl chloride. The resulting ester is then converted into the N-Boc derivative 2 with di-tert-butyl dicarbonate and the latter transformed into 3 by acetonization. This procedure avoids... 

Even isolated mono- and disaccharides are capable of extensive hydrogen bonding, which results in extremely low vapor pressures. Attempts at vaporization of these materials results in decomposition. Volatile derivatives must be prepared and the approaches are similar to those described for amino acids. The most common derivatives are methyl or trimethylsilyl ethers and acetyl or trifluoroacetyl esters. A highly detailed review of applications of GLC to carbohydrates including over 1000 references concerning derivatization and types of columns used has been written by Dutton (69,70). 

Cimbura and Kofoed (50),mentioned earlier, used GLC to separate amphetamine and methamphetamine after acetylation with acetic anhydride in methanol. Derivatives were extracted using diethyl ether and chromatographed op columns of either 3% OV-17, OV-1, or SE-30. Column temperature was 160°C. They also reported the chromatographic determination of acetylated morphine on 3% SE-30, OV-1, or OV-17 at temperatures of 220°C. Cruickshank et al.(21) separated 21 amino acids as their trifluoroacetylated methyl esters. The column was 5% neopentyl glycol succinate on Gas Chrom P. Column temperatures were both isothermal and programmed 65°C for 20 min at 1.5°C/min then 2°C/min until 42.5 min then 4°C/min until 60 min then isothermal until about 75 min (see Figure 12.2). Chang et al. (19), used BSA/pyridine to form the TMS derivatives of levodopa, methyldopa, tyrosine. 

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