Amino acid excess

Both FMOC and its hydrolysis products have similar absorption and fluorescence spectra to FMOC-amino acids. Excess FMOC remaining after derivatization reacts with water to form 9-fluorenylmethyl alcohol (FMOC-OH), and if this is not removed prior to sample injection, it elutes as a large, broad peak in the vicinity of proline. 

Monomer Excess. As previously described, the coupling rate is proportional to the concentration of monomer in solution. For efficient coupling to occur, the concentration of monomer needs to be as high as possible. The concentration may vary with the synthesis scale and can be adjusted by changing the amino acid excess factor. Equation (8) describes the relationship between the monomer excess (XS) and the scale of the synthesis. 

A graph can be constructed using the preceding equation with the appropriate system volume and support to determine how great an excess of amino acid is required at the desired synthesis scale. For ideal synthesis conditions, the intersection of the lines from the synthesis scale and amino acid excess should be near or above the curve in the plot. 

In inherited metabolic disorders, not only is total protein a major consideration, but also the balance of individual amino acids. Excessive or imbalanced plasma amino add concentrations negatively affect absorption, protein synthesis, and brain concentrations of indispensable amino acids. In PKU, high blood phenylalanine concentrations cause high phenylalanine concentrations on the brain [52, 53]. In organic acidemias and maple syrup urine disease, imbalances in several or more indispensable amino adds can significantly affect protein synthesis (Fig. 7.5) (Chap. 11). 

FMOC is a reagent that reacts quickly with both primary and secondary amino acids. Excess reagent must be removed rapidly because it undergoes hydrolysis. The excitation and emission wavelengths are 270 and 315 nm, respectively. An increasingly popular method for amino acid analysis is to measure the primary amino acids with OPA and the secondary amino acids with FMOC. Samples are derivatized first with OPA and then with FMOC. Primary amines are detected using the fluorescence properties of OPA while the secondary amines are detected using those of FMOC. 

Klavins, J.V. Pathology of amino acid excess. VII. Phenylalanine and tyrosine. Arch. Path. 84, 238-250 (1967)... 

Glycine is the simplest member of a large and very important class of compounds, the a-amino-carboxylic acids. TTiere are many different methods available for the synthesis of amino-acids, but glycine can be readily prepared by the action of an excess of ammonia on chloroacetic acid ... 

B) Benzoyl derivatives. Most amino-acids can be benzoyl-ated when their solutions in 10% aqueous sodium hydroxide are shaken with a small excess of benzoyl chloride until a clear solution is obtained (Schotten-Baumann reaction, p. 243). Acidification of the solution then precipitates the benzoyl derivative and the excess of benzoic acid, and the mixture must be filtered off, washed with water, and recrystallised (usually from ethanol) to obtain the pure derivative. (M.ps., p. 555 )... 

An amino-acid, although insoluble in water (e.g., anthranilic acid), is usually soluble in excess of mineral acid in such a case it is important to make the solution only very slightly acid. This applies also to a mixture of a neutral and a basic substance, from which dil. HCl will extract an amino-acid the solution must then be carefully treated with NaOH to precipitate the amino-acid. 

Amino acids may be prepared by the action of a large excess of concentrated ammonia solution upon a-chloro- or a-bromo-acids the presence of a considerable amount of ammonium carbonate often increases the yield of monoamino acid, for example ... 

Place 0-5 g. of the amino acid and 1 0 g. of phthalic anhdride in a Pyrex test-tube and immerse the lower part of the tube in an oil bath, which has previously been heated to 180-185°. Stir the mixture occasionally during the first 10 minutes and push down the phthalic anhydride which sublimes on the walls into the reaction mixture with a glass rod. Leave the mixture undisturbed for 5 minutes. After 15 minutes, remove the test-tube from the bath when the liquid mass solidifies, invert the test-tube and scrape out the excess of phthalic anhydride on the walls. RecrystaUise the residue from 10 per cent ethanol or from water. 

Then N-Boc-O-benzylserine is coupled to the free amino group with DCC. This concludes one cycle (N° -deprotection, neutralization, coupling) in solid-phase synthesis. All three steps can be driven to very high total yields (< 99.5%) since excesses of Boc-amino acids and DCC (about fourfold) in CHjClj can be used and since side-reactions which lead to soluble products do not lower the yield of condensation product. One side-reaction in DCC-promoted condensations leads to N-acylated ureas. These products will remain in solution and not reaa with the polymer-bound amine. At the end of the reaction time, the polymer is filtered off and washed. The times consumed for 99% completion of condensation vary from 5 min for small amino acids to several hours for a bulky amino acid, e.g. Boc-Ile, with other bulky amino acids on a resin. A new cycle can begin without any workup problems (R.B. Merrifield, 1969 B.W. Erickson, 1976 M. Bodanszky, 1976). 

This reaction forms the basis of one method of terminal residue analysis A peptide is treated with excess hydrazine in order to cleave all the peptide linkages One of the terminal amino acids is cleaved as the free amino acid and identified all the other ammo acid residues are converted to acyl hydrazides Which amino acid is identified by hydrazmolysis the N terminus or the C terminus ... 

Alkanolamines can be oxidized with various oxidiziag agents. With acidic potassium permanganate or excess potassium hydroxide, the potassium salts of the corresponding amino acid are obtained... 

Amino acids essential for young rats (98) and fishes (99) have been reviewed. Rats preferably eat a diet with sufficient amounts of essential amino acids rather than one that is deficient (100). Each essential amino acid, consumed in self-selection, has been reviewed (101). A protein diet with an excess of essential amino acids has been described as a poor protein diet from investigations that showed remarkable growth inhibition and occurrence of fatty fiver disease in rats (102). This is called amino acid imbalance (103). 

The main role of the human thyroid gland is production of thyroid hormones (iodinated amino acids), essential for adequate growth, development, and energy metaboHsm (1 6). Thyroid underfunction is an occurrence that can be treated successfully with thyroid preparations. In addition, the thyroid secretes calcitonin (also known as thyrocalcitonin), a polypeptide that lowers excessively high calcium blood levels. Thyroid hyperfunction, another important clinical entity, can be corrected by treatment with a variety of substances known as antithyroid dmgs. 

Hypochlorous acid reacts very rapidly and quantitatively with a slight excess of free ammonia forming monochloramine, NH2CI, which reacts at a slower rate with additional HOCl forming dichloramine, NHCI2. Trichloramine is formed when three moles of HOCl are added per mole of ammonia between pH 3—4 (100). Hypochlorous acid in the form of chlorine or hypochlorite is used in water treatments to oxidize ammonia by the process of break-point chlorination, which is based on formation of unstable dichloramine. The instabiHty of NHCI2 is caused by presence of HOCl and NCl (101,102). The reaction is most rapid at a pH of about 7.5 (103). Other nitrogen compounds such as urea, creatinine, and amino acids are also oxidized by hypochlorous acid, but at slower rates. Unstable iV-chloro compounds are intermediates in deammination of amino acids (104,105). 

The alcoholic filtrate is evaporated to 50 cc., and 50 g. of barium hydroxide and 150 cc. of distilled water are added (Note 4). The mixture is refluxed for two hours and the excess barium hydroxide is precipitated with carbon dioxide. The barium carbonate is removed by filtration and washed with hot distilled water. A slight excess of sulfuric acid is added to the filtrate to liberate the amino acid from its barium salt, and an excess of barium carbonate is added to remove sulfate ion. The mixture is digested on the steam bath until effervescence ceases, and it is then filtered and the precipitate is washed with hot distilled water. The filtrate and washings are concentrated on the steam bath to a volume of 100 cc., decolorized with i g. of active carbon, filtered, and concentrated to the point of crystallization (about 25 cc.). The amino acid is precipitated by the addition of 150 cc. of absolute alcohol and the product is collected and washed with absolute alcohol. 

The alcoholic filtrate contains appreciable amounts of pyrrolidone. The treatment with excess barium hydroxide converts this into the barium salt of the amino acid. ... 

Nucleophilic substitution by ammonia on a-halo acids (Section 19.16) The a-halo acids obtained by halogenation of carboxylic acids under conditions of the Hell-Volhard-Zelinsky reaction are reactive substrates in nucleophilic substitution processes. A standard method for the preparation of a-amino acids is displacement of halide from a-halo acids by nucleophilic substitution using excess aqueous ammonia. 

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