Amino acids ion-exchange

Pfeifer RF and Hill DW (1983) High-performance liquid chromatography of amino acids ion-exchange and reversed-phase strategies. Adv Chromatogr 22,37-69. 

Various amino acid, ion-exchanger systems are considered in the Helfferich development of these equations. In the first the neutral amino acid can exist as... 

Sulfoxides without amino or carboxyl groups have also been resolved. Compound 3 was separated into enantiomers via salt formation between the phosphonic acid group and quinine . Separation of these diastereomeric salts was achieved by fractional crystallization from acetone. Upon passage through an acidic ion exchange column, each salt was converted to the free acid 3. Finally, the tetra-ammonium salt of each enantiomer of 3 was methylated with methyl iodide to give sulfoxide 4. The levorotatory enantiomer was shown to be completely optically pure by the use of chiral shift reagents and by comparison with a sample prepared by stereospecific synthesis (see Section II.B.l). The dextrorotatory enantiomer was found to be 70% optically pure. 

Knize et al. (200) reported some preliminary results for a new SPE technique for the analysis of aromatic mutagen amines in foods for which no method was still developed, together with results obtained by the SPE-PRS method developed by Gross. The underdevelopment method should also be able to extract trimethyilimidazopyridine (TMIP) and DMIP (2-amino- 1,6-di-methylazo[4,5-fc]pyridine) by using an acid/ion-exchange scheme (SCX method). The extracts were analyzed by HPLC with UV or fluorescence detection. The content of resultant HAAs depended on the kind of meat and on the cooking conditions. 

Suppose you have a weakly acidic ion-exchange column (negatively charged), also at pH 6.1. Predict the order of elution of the amino acids from this column. Propose a strategy for separating the amino... 

The use of acidic ion-exchange columns continues to find wide application in the field of amino sugars, both for the resolution of complex hydrolyzates prior to analysis11 13-41 62 226-230 and for preparative purposes.93 Neutral sugar-derivatives are not retained by the column, but free hexosamines... 

HNF2 reacts with saturated and unsaturated mono- and diacetals at ambient temperature to 100°C (250) and also smoothly in the presence of a sulfonic acid ion-exchange resin (Amberlyst-15) (140, 276) to give a-difluoroamino ethers (140). These compounds react with a second molecule of HNF2 in the presence of sulfuric acid to give bis(difluoro-amino) derivatives (140). 

The oxidation of the alcohol was performed with supported perruthenate (8.48, Fig. 8.46) to produce clean aldehydes 8.91 after filtration. The Henry reaction was performed in the presence of a commercially available, supported strong base 8.92 and an excess of volatile nitroalkenes, giving clean nitroalcohols 8.93 after filtration and evaporation. The reaction mixtures from the trifluoroacetylation/elimina-tion steps were purified with commercially available amino PS resin 8.58 to scavenge the trifluoroacetates and with acidic ion-exchange resin 8.76 to remove the TEA-derived salts. Again, the nitrostyrenes 8.94 were obtained cleanly after filtration and evaporation. Cycloaddition with isocyanoacetate was promoted by the commercially available, supported guanidine base 8.95, while the subsequent N-alkylation of the pyrroles 8.96 was performed with an excess of halide in the presence of the commercially available, supported phosphazene 8.97. In this case, the excess halide was removed by treatment with supported 8.58, and filtra-... 

Whereas the ion-exchange affinity of various mineral ions to ion exchangers is reasonably well understood, the ion-exchange affinity of various amino acid ions is not because of their more complex nature. 

Figure 5.10 Selectivity coefficient behaviour for amino acid cation exchange against sodium on styrenesulfonate resins of various percent crosslinking (Reprinted from J. Feitelson, in Ion Exchange (A Series of Advances) , ed. J. A. Marinsky, Marcel Dekker, New York, Vol. 2, p. 135, by courtesy of Marcel Dekker Inc.)...

Before all these acetal-based protecting groups were introduced, the tetrahydropyranyl (THP) ether had found extensive use in organic synthesis. It can easily be synthesized from a variety of hydroxy-containing compounds like carbohydrates, amino acids, steroids and nucleotides by the acid-catalyzed reaction with dihydropyran. It is stable to bases, but the protection is removed through acidic hydrolysis with hydrochloric acid, toluenesulfonic acid or acidic ion-exchange resin (Scheme 27). In the case of acid sensitive substrates, e.g. containing an epoxide or a further acetal, pyridinium p-toluenesulfonate should be applied for particularly mild deprotection conditions. ... 

Triethylamine tris(hydrofluoride) in the presence of DBU reacts quantitatively with 13. Contrary to all examples so far presented of 1,3,2-oxathiaphos-pholane ring opening condensations, an attack of fluoride ion on phosphorus is not stereospecific when performed with diastereomerically pure species, the mixture of diastereomeric compounds 68 is always produced [93, 94]. Oxathi-aphospholane derivatives of 3 -amino-3 -deoxythymidine 48 and 50 under treatment with triethylamine tris(hydrofluoride) in the presence of DBU, followed by detritylation with acidic ion-exchange resin, provided 3 -deoxythymi-dine-3 -N-phosphoramidofluoridate (69) and 3 -deoxythymidine-3 -N-phos-phoramidofluoridothioate (70) (Scheme 18), further purified by preparative TLC in ca. 80% yield [75]. 

The synthesis of phosphonic analogues of aspartic acid and asparagine is accomplished by addition of diethyl phosphite to diethyl acctamidomcthylcncmalonate The sttongly activated double bond readily adds diethyl phosphite in an exothermic reaction catalyzed by EtONa (Scheme 8.84). Hydrolysis of the crude addition product with concentrated HCl at reflux delivers the amino acid purified using acidic ion-exchange resin (Dowex SOW). 

Treatment of protected (o-amino-(o-(alkoxycarbonyl)alkylphosphonates with 4-8 M HCl selectively removes the ester groups to generate the free acids in 70-75% yields. Treatment of acids with acidic ion-exchange resin (Dowex SOW) or with propylene oxide followed by recrystallization from EtOH-H2O affords pure (o-amino-(o-(hydroxycarbonyl)alkylphosphonic acids 890,919,925,927,933... 

Native and microcrystalline cellulose precoated plates are used in the life sciences for the separation of polar compounds (e.g. carbohydrates, carboxylic acids, amino acids, nucleic acid derivatives, phosphates, etc) [85]. These layers are unsuitable for the separation of compounds of low water solubility unless first modified, for example, by acetylation. Several chemically bonded layers have been described for the separation of enantiomers (section 10.5.3). Polyamide and polymeric ion-exchange resins are available in a low performance grade only for the preparation of laboratory-made layers [82]. Polyamide layers are useful for the reversed-phase separation and qualitative analysis of phenols, amino acid derivatives, heterocyclic nitrogen compounds, and carboxylic and sulfonic acids. Ion-exchange layers prepared from poly(ethyleneimine), functionalized poly(styrene-divinylbenzene) and diethylaminoethyl cellulose resins and powders and are used primarily for the separation of inorganic ions and biopolymers. 

Akabori method, an approach to C-terminal amino acid end group analysis of peptides using hydrazine. By treatment of the peptide under investigation with anhydrous hydrazine for 90-100 h at 90°C in the presence of an acidic ion-exchange resin, only the C-terminal amino acid residue... 

Ring expansion occurs specifically when the amino-sugar furanosides (45) are exposed to strong acid ion exchange resin in water (Scheme 9). The method assists in a synthesis of the 6-... 

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