Amine labeling dimethylation

The methylation of secondary amines works better than for primary amines because there is no competition between the formation of mono- or dimethylated products. The best results for the microwave-enhanced conditions were obtained when the molar ratios of substrate/formaldehyde/formic acid were 1 1 1, so that the amount of radioactive waste produced is minimal. The reaction can be carried out in neat form if the substrate is reasonably miscible with formic acid/aldehyde or in DM SO solution if not. Again the reaction is rapid - it is complete within 2 min at 120 W microwave irradiation compared to longer than 4 h under reflux. The reaction mechanism and source of label is ascertained by alternatively labeling the formaldehyde and formic acid with deuterium. The results indicate that formaldehyde contri-... 

The use of NBD-Cl for the fluorescence analysis of alkylamine-generating pesticides has been investigated [173]. A two-phase reaction system is employed for the hydrolysis and labeling of N-methyl- and N,N-dimethyl-carbamate pesticides. The residue is hydrolyzed in 0.1 M sodium carbonate and the liberated amine is treated with NBD-Cl in an organic phase (IBMK, isobutyl methyl ketone) above the aqueous layer. An aliquot portion of the organic layer is used for chromatography. The reactions involved are shown in Fig. 4.65. 

Another strategy for stable isotope labeling of N-terminus and lysine side-chain amines is reductive animation by nondeuterated and deuterated formaldehyde. Dimethylation of peptides occurs by the formation of a Schiff base, followed by reduction with cyanoborohydride. Peptides thus labeled differ by a mass of 4 Da for each labeled pair. The labeled peak pairs show minimum isotope effects on reverse-phase separation and hence coelute (93). Dimethylation using formaldehyde with the natural isotopic abundance (hydrogen and 12C) versus a heavy form with two deuteriums and one atom of 13C... 

The polyamic acids were prepared from 3,3 ,4,4-benzophenone dianhydride (sublimed) and 2,3,5,6-tetramethyl-l,4-phenylene diamine in Cold Label N,N-dimethyl formamide (DMF). All chemicals were obtained from Aldrich. A solution of the anhydride was added over 30 minutes to a solution of the amine with stirring under N2 at room temperature at a net concentration of 15% solids. In general, a slight (1%) excess of the anhydride was needed to give maximum viscosity. 

Loberg MD, Fields AT (1978) Chemical structure of technetium-99m-labeled N-(2,6-dimethyl-phe-nylcarbamoylmethyl)-iminodiacetic acid ( Tc-HIDA). Int J Appl Radiat Isot 29 167-173 March A, Garuti P, Duatti A et al (1990) Synthesis of technetium(V)-nitrido complexes with chelating amines a novel class of monocationic, octahedral complexes containing the [Tc = N] core. Crystal structures of [TcN(en)2Cl] (en = ethylenediamine) and [TcN(tad)Cl] (tad = 1,5,8,12-tet-raazadodecane). Inorg Chem 29 2091-2096... 

The mechanism of the Eschweiler-Clarke reaction proceeds via the formation of an imine, followed by reduction by formic acid. That the methylation is attributable to the formaldehyde and the reduction to the formic acid has been confirmed using 14C-labeled isomers of each in a series of studies.5 Thus, the amine reacts with formaldehyde to produce an imine, and this is then reduced with the loss of carbon dioxide by formic acid. In the case of primary amines this process is then repeated to produce a tertiary N.iV-dimethyl amine. 

By oxidation of the labeled products [28 and 29 or 30ab] to labeled benzoic and substituted benzoic acids followed by assay of these purified acids for carbon-14, the relative migratory abilities of the Ar groups with respect to phenyl were determined. Thus in the dehydration, with phosphorus pentoxide in xylene, of a series of carbinols (27, X = OH), the following migratory aptitudes (Ar Ph) were determined p-xenyl, 1-3 m-tolyl, 1-6 p-i-propylphenyl, l-8 3,4-dimethyl-phenyl, 1-9 p-tolyl, 2-0 p-ethylphenyl, 2-2 p-t-butylphenyl, 3-2 and p-anisyl, 21-2. Burr (1953) demonstrated the p-tolyl phenyl migration ratio to be 2-5 during the solvolysis of 2-phenyl-2- p-tolylethyl-l-i C tosylate (27, Ar = p-tolyl, X = tosyl). In a series of deaminations of the primary amines (27, X = NH ) and 31 (Ar = p-tolyl and o-tolyl) the p-tolyl phenyl (1 2), p-biphenyl phenyl (1 0) p-anisyl phenyl... 

A few nonstandard chemical labels that have been used successfully include dimethylation of free amines (i.e., lysines and N-termini) using reductive amination, guanidination of lysines, and alkylation of cysteines by acrylamide. In practice, the commercially available labels (e.g., ICAT and iTRAQ) have received the most widespread use. Ones that are based on chemical reactions require a deeper understanding of chemistry (in contrast to the kits) and also computational skills, because there are very few generally available programs that can be used for automated quantification of the data sets. 

These novel metabolites may be derived from four amino acids tryptophan, anthranilic acid, valine, and alanine (or methylalanine). Deoxynor-tryptoquivalone (43) may be the first metabolite formed in the pathway of the tryptoquivaline biosynthesis. By oxidation of the secondary amine to the hydroxylamine, nortryptoquivalone (= tryptoquivalone) (32) would be formed from 43. If the isobutyl side chain is lost by further oxidation, tryptoquivaline J (39) and E (34) would be derived from these tryptoqui-valones, respectively. On the other hand, if reduction occurred on the carbonyl in the side chain, deoxynortryptoquivaline (42) and nortrypto-quivaline (FTD) (40) would be derived, respectively, from these tryptoqui-valones. The geminal dimethyl group at position 15 appeared to be formed by the participation of methylalanine in the biosynthesis, and the actual incorporation of " C-labeled methylalanine into tryptoquivaline (FTC) and tryptoquivaline I has been demonstrated (M. Yamazaki, unpublished work). 

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