Resonant electron capture by some amino acids and their methyl esters

Resonant electron capture mass spectra of aliphatic and aromatic amino acids and their methyl esters show intense [M-H](-) negative ions in the low-energy range. Ion formation results from a predissociation mechanism mediated by the low-energy pi*oo resonant state. Methylation in general has little influence on the electronic structure according to quantum chemical calculations, but the corresponding ions from the methyl esters, [M-Me](-), could be ascertained to arise only at higher resonance energies. Aromatic amino acids are characterized by an additional low-energy fragmentation channel associated with the generation of negative ions with loss of the side chain. The complementary negative ions of the side chains are more efficiently produced at higher energies. The results have significant implications in biological systems as they suggest that amino acids can serve as radiation protectors since they have been found to efficiently thermalize electrons.     

Mass spectrometry of polycyclic tetracarboxylic ('ARN') acids and tetramethyl esters

Polycyclic C(80) tetracarboxylic (so-called 'ARN') acids are found as calcium salts in deposits which form in certain oilfield pipelines and equipment. Characterisation of these acids is important for improving the prediction and hence avoidance or minimisation of oilfield deposition problems. Although several of the acids have been isolated and characterised (as regioisomeric mixtures) by nuclear magnetic resonance spectroscopy, mass spectrometric methods are likely to be much more useful for the routine analysis of oils and deposits containing the acids. A publication summarising the mass spectra of the purified acids and major derivatives might thus be a very useful source of reference for scientists and technologists studying these unusual compounds. We now report the characterisation of several of the purified acids and of the tetramethyl esters by electrospray ionisation mass spectrometry (ESI-MS) in both positive ion and negative ion modes, by multistage ESI-MS with a suggested rationalisation of the ions produced, by positive ion atmospheric solids analysis probe (ASAP) atmospheric pressure chemical ionisation (APCI), and by positive ion electron ionisation (EI)-MS. Tentative identifications of C(80) acyclic, mono-, bi- and tricylic tetraacids and the δ(13)C isotope values of a mixture of the semi-pure acids determined by MS are also reported for the first time.     

Mass spectrometry of some methyl esters of N-4-pyrimidinylamino acids: Rearrangements of the ions occurring on electron-impact ionization

The electron-impact-induced mass fragmentations of methyl esters of N-(1H-2-oxo-4-pyrimidinyl)ainino acids are reported. The loss of a ·COOCH₃ radical and the elimination of a methanol molecule were observed and possible mechanisms of these processes are proposed. The loss of a ·COOH radical and elimination of water were established, which suggests the rearrangement of the investigated esters into isomeric N-4-pyrimidinylamino acids.     

Novel synthetic routes to N-(2-amino-9H-purin-6-yl)-substituted amino acids

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Dissociative electron-capture mass spectrometry of fatty acids and their pyrrolidies and methyl esters

The regions of the energies of resonance capture of electrons by the molecules of fatty acids and their pyrrolidides and methyl esters have been established, which has permitted an explanation of the difference between the dissociative electron-capture mass spectra of these compounds and their chemical ionization and fast-atom bombardment negative-ion mass spectra. It has been shown that the dissociative electron-capture mass spectra of a high-energy resonance state characterized by the most far-reaching dissociation permit the unambiguous determination of the positions of multiple bonds in the initial molecules.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR. Translated from Khimiya Priordnykh Soedinenii, No. 3, pp. 348–353, May–June, 1987.     

Ortho effect in the mass spectrometric behaviour of N(pyrimidin-4-yl)aminobenzoic acids and their methyl esters

Ortho-. meta- and para-isomers of N-(pyrimidin-4-yl)aminobenzoic acid and their methyl esters were investigated by electron impact mass Spectrometry. Their fragmentation was found to be strongly dependent on the position of the substituent in the aminobenzoic moiety. Two different kinds of ortho effect were studied and confirmed with the aid of deuterium-labelled derivatives.     

4,5,6-三取代嘧啶苯磺酰脲类化合物的生物活性、分子对接与3D-QSAR关系研究

用柔性分子对接方法(FlexX)将15个4,5,6-三取代嘧啶苯磺酰脲化合物以及3个不含5-位取代嘧啶苯磺酰脲化合物(分别为4,6-双取代嘧啶和4-取代嘧啶)和乙酰羟酸合成酶(AHAS)活性口袋进行了对接, 对接程序预测的抑制剂和酶之间的相互作用能与抑制活性之间有一定的相关性, 相关系数为0.660. 然后采用比较分子相似性指数分析(CoMSIA)对27个新型4,5,6-三取代嘧啶苯磺酰脲类化合物的除草活性进行三维定量构效关系(3D-QSAR)研究. 建立了三维定量构效关系CoMSIA模型, 立体场、静电场和氢键的贡献分别为47.3%, 32.8%, 19.9%. 交叉验证系数q2值为0.520. 根据CoMSIA模型的立体场、静电场、氢键给体场三维等值线图不仅直观地解释了结构与活性的关系, 并且与用FlexX预测的结合模式相一致, 证明了我们预测的结合模式是可靠的, 为进一步设计高活性的标题化合物提供较好的理论指导.     

Intramolecular heterocyclization of N-(pyrimidin-2-yl)imines of methyl trifluoropyruvate

The reactions of N-(pyrimidin-2-yl)imines of methyl trifluoropyruvate with trimethyl phosphite afforded methyl 3-fluoroimidazo[1,2-a]pyrimidin-2-carboxylates, which were transformed into N-substituted methyl 3-aminoimidazo[1,2-a]pyrimidine-2-carboxylates by the reactions with amines.     

The Synthesis of Novel ALS Inhibitors N-(Substituted Phenyl Alkoxy Phosphonyl)-N'-(4,6-Disubstituted Pyrimidin-2-yl) Ureas

Sulfonylurea herbicides are a new class of herbicides discovered in the mid-1970's^[1],whose mode of action has been established as the inhibition of ALS^[2]. Much attention has been focused on this kind of compound, since they have unprecedented use rates, a high degree of selectivity, and excellent environmental safety. Numerous modifications of the structure of this class of herbicides have been reported.     

The Synthesis of Novel ALS Inhibitors N-(Substituted Benzyl Alkoxyl Phosphonyl)-N'-(4,6-Disubstituted Pyrimidin-2-yl) Ureas

Sulfonylurea herbicides are a new class of herbicides discovered in the mid-1970's^[1],whose mode of action has been established as the inhibition of ALS (acetolactate synthase)^[2]. Much attention has been focused on this kind of compound, since they have unprecedented use rates,a high degree of selectivity, and excellent environmental safety. Numerous modifications of the structure of this class of herbicides have been reported.     

Mass spectrometry of 3-methoxy fatty acid methyl esters

Fatty acids with a hydroxyl moiety at the C-3 position are found widely in bacterial lipids, but only rarely in mammalian lipids. The mass spectra of the methyl ether derivative of these hydroxy acids exhibit an intense ion at m/e 75, rather than the rearrangement ion at m/e 74 more typical of fatty acid methyl esters. The mass spectrometric behavior of several 3-methoxy fatty acid methyl esters were studied, and the origin of the unique ion at m/e 75 was established using ¹⁸O and ²H labeled analogs and metastable ion transitions. this ion was shown to arise from the loss of ketene from the 3,4 cleavage ion at m/e 117.     

Mass spectrometry of 4N-pyrimidinyl amino acids

The electron impact mass spectra of N-(1H-2-oxo-4-pyrimidinyl) amino acids are discussed. It was established that thermal elimination of water took place prior to mass fragmentation of all these compounds with the formation of bicyclic structures. The fragmentation of bicyclic ions led to 1H-2-oxo-pyrimidinyl species.     

The role of the N- and C-terminal amino acids of activated peptide esters in their polycondensation

Summary 1. The polycondensation of activated esters of some dipeptides has been studied. The dependence of M_av on the time has been established.2. It has been shown that the degree of polycondensation of the polypeptides depends on the nature of the N- and C-terminal amino acids of the activated ester of the peptide and of the monomer.Lenin Tadzhik State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 502–506, July–August, 1974.     

Azides of N-substituted aziridine-2-carboxylic acids. Reaction with methyl esters of amino acids

The corresponding azide was obtained by nitrosation of 1-benzylaziridine-2-carboxylic acid hydrazide. Reaction of the azide with methyl esters of amino acids gave N-(1-benzyl-2-aziridinylcarbonyl)-substituted methyl esters of amino acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1350–1352, October, 1980.     

Synthesis and reduction of esters of N-(4-amino-5-nitro-6-pyrimidyl)amino acids

The reaction of esters of amino acids with 4-amino-6-chloro-5-nitropyrimidine has yielded esters of (4-amino-5-nitro-6-pyrimidyl)amino acids. The reduction of the esters of -(4-amino-5-nitro-6-pyrimidylamino) acids has yielded 4-amino-6-hydroxy-7,8-dihydropteridines. -(4-Amino-5-nitro-6-pyrimidylamino) acids and the ester of N-(4-amino-5-nitro-6-pyrimidyl)--alanine do not cyclize and on reduction give the corresponding diaminopyrimidine derivatives.