A-derivatized amino acids

A -derivatized amino acids (DNZ, FMOC), their enantiomers... 

Mirious chiral carboxylic, phosphonic. sulphonic carhamoylatctl quinine and quinidinc acids including NSAIDs, a-aryloxy carboxylic acids, acencK oumarol, A-derivatized amino acids... 

The Fmoc group, when present on the resin or introduced via a derivatized amino acid (usually Fmoc-Nle or Fmoc-Gly) esterified to the resin, can be quantitated to determine the resin loading. Removal of the Fmoc group by... 

A derivatization with acid chlorides is also possible. Amino acids can be derivatized with 9-fluorenylmethyl chloroformate (FMOC) and separated on a CSP with X-cyclodextrin (ChiraDex gamma ), a cyclic oligosaccharide which consists of eight glucose units. 

Righetti and co-workers [11] were one of the first to demonstrate the utility of classical isoelectric focusing for the chiral separation of small molecules in a slab gel configuration. In their system, dansylated amino acids were resolved enan-tiomerically through complexation with (i-cyclodextrin. Preferential complexation between the cyclodextrin and the derivatized amino acid induced as much as a 0.1 pH unit difference in the pK s of the dansyl group. 

The macrocyclic antibiotic-based CSPs have not been used extensively in SFC. Two macrocyclic antibiotic CSPs, Chirobiotic T and Chirobiotic V, were included in a study of various CSPs in SFC. At least partial resolution of approximately half of the 44 test compounds could be obtained on these two CSPs in SFC [63]. A high concentration of modifier was necessary to elute some of the analytes. Enantioreso-lution of derivatized amino acids was also demonstrated in the same study. Flowever, a complex modifier comprised of methanol, water, and glycerol was required for separations performed on the Chirobiotic T CSP. The separation of coumachlor enantiomers on a vancomycin-based CSP (Chirobiotic V) in SFC is illustrated in Fig. 12-5 [32]. 

Table 9.1. Retention times and accurate masses for TBDMS derivatized amino acids (separation conditions Chapter 9.1.A)...

Phenylthiocarbamoyl derivatives of 18 chiral amino acids were separated on a C8 column connected in series to a phenylcarbamoylated (3-cyclodextrin column (Iida et al., 1997). The Cg column separated the derivatized amino acids from one another entering the chiral column. Under this configuration several enantiomers of adjacent amino acids coeluted resulting in poor resolution. However, this configuration was successful in determining the amino acid sequence and chirality of the amino acids in a D-amino acid containing peptide. 

OPA-derivatized amino acids are usually separated on an ODS-II solid phase using a mobile phase of sodium phosphate buffer and an acetonitrile gradient. 

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,... 

A method involving SPE was developed for the determination of ten A-nitroso amino acids in cured meat products. These compounds were derivatized with diazomethane followed by O-acylation of hydroxyl groups with acetic anhydride-pyridine reagent. The methyl esters and their acylated derivatives were separated by GC on a DB-5 fused silica capillary column and quantified with a TEA-CLD specific for the nitric oxide derived from the thermal denitrosation of nitrosamines recovery exceeded 75% at the 10 ppb level579. 

A-aryl amino acids (such as DNP, DNPyr, DBD, and NBD labeled amino acids) Some of these derivatives are the preferred choice for many analytical purposes because they can be conveniently introduced by straightforward and smooth derivatization procedures. This holds in particular for the Sanger s reagent... 

FIGURE 1.35 SLM process using O-9-(l-adamantylcarbamoyl)-10,ll-dihydro-ll-octadecylsulfinylquinme and corresponding quinidine derivative as chiral carriers for the preparative separation of enantiomers of Al-derivatized amino acids (e.g., DNB-Leu). (a) ftinciple of the carrier SLM process with carrier-mediated transport (top) and (nonstereoselective) nonspecific transport processes (bottom), (b) General experimental setup of the SLM production unit with two membrane modules, (c) Multistage SLM purification process. P, permeate QD/QN, membrane modnles snpported with quinidine-derived and quinine-derived chiral carriers. R, S, D, L refers to the respective enantiomers of the selectand (DNB-Leu). (Reproduced from A. Maximini et al., J. Membr. ScL, 276 221 (2006). With permission.)... 

Armstrong et al. ° first introduced chiral stationary phases based on macrocyclic antibiotics. Vancomycin, ristocetin A, teicoplanin, avoparcin, rifamycin B and thiostrepton are used as chiral selectors. They posses a broad enantiorecognition range, similar to protein based CSPs. However, CSPs based on macrocyclic antibiotics show higher stability and capacities.Underivatized amino acids, N-derivatized amino-acids, acidic compounds, neutrals, amides, esters and amines can be separated.The first four of the above-mentioned chiral selectors appear to have the largest enantiorecognition range.The selectors can also be derivatized to obtain different enantioselectivities. 

Unnatural amino acids are added to the growth medium in most experiments. There are a large number of amino acid and amine transporters that are relatively nonspecific and which may help to transport the unnatural amino acids into cells. From measurements of cytoplasmic levels of amino acids, it is found that a large number of unnatural amino acids are efficiently transported to the E. coli cytoplasm in millimolar concentrations. Highly charged or hydrophilic amino acids may require derivatization (e.g., esterification, acylation) with groups that are hydrolyzed in the cytoplasm. Metabolically labile amino acids or analogues (e.g., a-hydroxy acids, A-methyl amino acids) may require strains in which specific metabolic enzymes are deleted. 

S Cladrowa-Runge, A Rizzi. Enantioseparations of 6-aminoquinolyl-lV-hydrox-ysuccinimidyl carbamate derivatized amino acids by capillary zone electrophoresis using native and substituted /3-cyclodextnns as chiral additives II. Evaluation of complexation constants. J Chromatogr A 759 167-175, 1997. 

The possibility of studying the structure and dynamic properties of proteins by F NMR requires the use of labeled proteins with fluorine. Various approaches can be envisioned trifluoroacetylation or derivatization of side chains by direct fluorination or trifluoromethylation or with small fluorinated molecules. It is also possible to incorporate a fluorinated amino acid into a protein, by using either a classical chemical synthesis or a biosynthetic approach. It is obvious that the chemical synthetic... 

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