Isotopically labeled amino

There are many excellent examples of experiments using isotopic labeling in both organic chemistry and biochemistry. An interesting example is the case of lydroxylation of the amino acid phenylalanine which is carried out by the enzyme phenylalanine hydroxylase. 

The hydrazinolysis is usually conducted in refluxing ethanol, and is a fast process in many cases. Functional groups, that would be affected under hydrolytic conditions, may be stable under hydrazinolysis conditions. The primary amine is often obtained in high yield. The Gabriel synthesis is for example recommended for the synthesis of isotopically labeled amines and amino acids. a-Amino acids 9 can be prepared by the Gabriel route, if a halomalonic ester—e.g. diethyl bromomalonate 7—is employed as the starting material instead of the alkyl halide ... 

The application of substrates isotopically labeled in specific positions makes it possible to follow the fate of individual atoms during the microbial degradation of xenobiotics. Under optimal conditions, both the kinetics of the degradation, and the formation of metabolites may be followed— ideally when samples of the labeled metabolites are available. Many of the classical studies on the microbial metabolism of carbohydrates, carboxylic acids, and amino acids used radioactive... 

Veenstra, T. D. Martinovic, S. Anderson, G. A. Pasa-Tolic, L. Smith, R. D. Pro-teome analysis using selective incorporation of isotopically labeled amino acids. /. Am. Soc. Mass Spectrom. 2000,11, 78-82. 

The approach recruited to chemical proteomics in Reference [17] is called SILAC (stable isotope labeling with amino acids in cell culture) and is important in comparative proteomics (Figure 1). SILAC works well with cultured mammalian cells, but prokaryotes defeat it by metabolizing the label (usually supplied in lysine and arginine) into other amino acids. For applications beyond cultured eukaryotic cells, the reductive methylation route to differential labeling [18] is among the alternatives [15]-... 

Guerrero et al. (2006) used this technique along with the quantitative mass spec strategy called SILAC (stable isotope labeling of amino acids in cell culture Ong et al., 2002) to identify the yeast proteins that interact with the 26 S proteasome. 

Ong, S.-E., Blagoev, B., Kratchmarova, I., Kristensen, D.B., Steen, H., Pandey, A., and Mann, M. (2002) Stable isotope labeling by amino acids in cell culture, SILAC, as a simple and accurate approach to expression proteomics. Mol. Cell. Proteomics 1, 376-386. 

The main starting compound is the labeled nitroguanidine 257 obtained from guanidine with isotope-labeled potassium nitrate. Reduction of 257 to hydrazine carboximidamide 258 was carried out with zinc and, then, ring closure to 3-amino[l,2,4]triazole 259 was carried out using formic acid. Finally, the ring closure to form the [l,2,4]triazine ring - similar to other procedures presented in Scheme 54 - was perfected by reaction with nitrous acid followed by treatment with ethyl nitroacetate to 260. 

Solid-phase peptide synthesis offers a fast and convenient route for many peptides when isotope-enriched compounds are not required. Classical synthesis additionally permits the use of non-natural amino acids and allows site-specific isotope labeling. Although Fmoc protected 15N-labeled amino adds are commercially available, the cost of such synthesis is usually prohibitive, and the peptides from chemical synthesis require perdeuterated detergents and unfortunately exclude investigation of internal dynamics through measurement of 15N relaxation. 

The synthesis and uses of isotopically labelled amino and quaternary ammonium salts... 

Theoretical calculations predict that, compared to other amino acids, arginine may dimerize and trimeiize in the zwitterionic state. Soft-sampling ESI of the racemate of arginine, with one of the enantiomer isotopically labeled, reveals the formation of stable trimers with NOj" present as counterion. No preference for... 

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