Collision-Induced Dissociations of Deprotonated Dipeptide Methyl Esters Containing Serine or Threonine

1994 ◽  
Vol 47 (10) ◽  
pp. 1851 ◽  
Author(s):  
ST Steinborner ◽  
AM Bradford ◽  
RJ Waugh ◽  
JH Bowie ◽  
DL Vollmer ◽  
...  
Keyword(s):  
Methyl Ester ◽  
Mass Spectra ◽  
Methyl Esters ◽  
Side Chain ◽  
Backbone Cleavage ◽  
Sequencing Data ◽  
Deuterium Labelling ◽  
Product Ions

The collision-induced mass spectra (MS/MS) of (M - H)- ions derived from dipeptide methyl esters containing serine or threonine lack the characteristic backbone cleavage of the underivatized peptides (which provide primary sequencing data). Instead, competitive fragmentation occurs through the ester and α-side chain functions. For example, Ser methyl esters lose both CH2O (from the side chain) and MeOH ( MeO comes from the methyl ester). Isomeric dipeptides may be differentiated by competitive fragmentations; for example [ Gly Ser( OMe )-H]- fragments first by loss of CH2O, while [Ser Gly ( OMe )-H]-, in contrast, shows initial elimination of MeOH. The structures of the product ions in these spectra have been probed by deuterium labelling and MS/MS/MS studies.

scholarly journals Separation and structural analysis of vinyl- and isovinyl-azobilirubin derivatives

1971 ◽  
Vol 125 (2) ◽  
pp. 585-597 ◽  
Author(s):  
F. H. Jansen ◽  
M. S. Stoll
Keyword(s):  
Proton Magnetic Resonance ◽  
Mass Spectra ◽  
Methyl Esters ◽  
Coupling Reaction ◽  
Azo Compounds ◽  
Side Chain ◽  
Diazonium Salts ◽  
Side Reactions ◽  
Group 2

The coupling reaction of bilirubin with the diazonium salts of ethyl anthranilate or of aniline yields two isomeric azopigments. These can be separated by t.l.c. as their methyl esters. The mass spectra of each pair of azopigments are very similar, showing that they are isomers. Proton-magnetic-resonance spectrometric studies show that they differ in the positions of the substituents on the pyrrolenone end ring; in one compound the methyl and vinyl groups are interposed compared with the other compound. These azo compounds were used as reference standards for determination of the site of conjugation in bilirubin monoglucuronide prepared enzymically. Analysis showed that conjugation occurs at the carboxyethyl side chain of both sides of the bilirubin molecule. During the preparation of the ethyl anthranilate reference compounds a series of minor azopigments were isolated by t.l.c. Analysis of the mass spectra of many of these showed that three side reactions can occur: (1) methylation of the imide carbonyl group; (2) addition of methanol or water to the vinyl substituent; (3) transmethylation of the ethoxycarbonyl group.

Identification of Ornithine and Arginine Conjugates of Cholic Acid by Mass Spectrometry

1975 ◽  
Vol 53 (5) ◽  
pp. 583-590 ◽  
Author(s):  
J. J. Myher ◽  
L. Marai ◽  
A. Kuksis ◽  
I. M. Yousef ◽  
M. M. Fisher
Keyword(s):  
Mass Spectrometry ◽  
Amino Acids ◽  
Methyl Ester ◽  
Mass Spectra ◽  
Methyl Esters ◽  
Isolated Perfused Rat Liver ◽  
Amino Group ◽  
Perfused Rat Liver ◽  
Direct Insertion Probe ◽  
Dibasic Amino Acids

Nα-Cholylornithine, -arginine, and -histidine were prepared according to a method previously employed for the chemical synthesis of the monoamino acid conjugates of bile acids. The products were shown to involve the α amino group of the dibasic amino acids by examination of the mass spectra of the original compounds, their lactams, their methyl esters and the methyl ester acetates. Only the methyl ester acetates gave detectable amounts of molecular ion. The free acids and the methyl esters of Nα-cholylornithine and -arginine gave identical lactams upon sublimation from the direct insertion probe. The synthetic Nα-cholylarginine was shown to yield a mass spectrum identical to that of an arginocholic acid recovered from the bile of an isolated perfused rat liver.

Activity of Plasmin and Streptokinase-Activator on Substituted Arginine and Lysine Esters

1966 ◽  
Vol 16 (01/02) ◽  
pp. 018-031 ◽  
Author(s):  
S Sherry ◽  
Norma Alkjaersig ◽  
A. P Fletcher
Keyword(s):  
Molecular Structure ◽  
Methyl Ester ◽  
Comparative Studies ◽  
Esterase Activity ◽  
Methyl Esters ◽  
Hydrolytic Activity ◽  
The Other ◽  
Other Hand

SummaryComparative studies have been made of the esterase activity of plasmin and the streptokinase-activator of plasminogen on a variety of substituted arginine and lysine esters. Human plasmin preparations derived by different methods of activation (spontaneous in glycerol, trypsin, streptokinase (SK) and urokinase) are similar in their esterase activity; this suggests that the molecular structure required for such esterase activity is similar for all of these human plasmins. Bovine plasmin, on the other hand, differs from human plasmin in its activity on several of the substrates studied (e.g., the methyl esters of benzoyl arginine and tosyl, acetyl and carbobenzoxy lysine), a finding which supports the view that molecular differences exist between the two animal plasmins. The streptokinase-activator hydrolyzes both arginine and lysine esters but the ratios of hydrolytic activity are distinct from those of plasmin and of other activators of plasminogen. The use of benzoyl arginine methyl ester as a substrate for the measurement of the esterase activity of the streptokinase-activator is described.

Synthesis of oxytocin analogues modified in the tripeptide side-chain by condensation of aminoterminal linear hexapeptide with the carboxyterminal tripeptide

1979 ◽  
Vol 44 (1) ◽  
pp. 275-287 ◽  
Author(s):  
Jan Hlaváček ◽  
Tomislav Barth ◽  
Karel Bláha ◽  
Karel Jošt
Keyword(s):  
Methyl Ester ◽  
Side Chain ◽  
Glycine Methyl Ester

For the synthesis of oxytocin (Ia) analogues modified in the carboxyterminal part of the molecule, a method based on the condensation of protected aminoterminal hexapeptide with tripeptides by the action of dicyclohexylcarbodiimide and pentafluorophenol in the presence of 1-hydroxybenzotriazole was devised. Using this method [7-[U-13C]proline]oxytocin (Ib), des-9-glycine-oxytocin (Ic) and methyl ester of oxytocinoic acid ([9-glycine methyl ester]oxytocin) (Id) were prepared.

scholarly journals Evaluation of 3-Methylbutanoic Acid Methyl Ester as a Factor Influencing Flavor Cleanness in Arabica Specialty Coffee

2021 ◽  
Vol 11 (12) ◽  
pp. 5413
Author(s):  
Keiko Iwasa ◽  
Harumichi Seta ◽  
Yoshihide Matsuo ◽  
Koichi Nakahara
Keyword(s):  
Methyl Ester ◽  
Methyl Esters ◽  
Acid Methyl Ester ◽  
Chemical Compounds ◽  
Gas Chromatography Mass Spectrometry ◽  
Arabica Coffee ◽  
Acid Methyl ◽  
Coffee Brew ◽  
Coffee Beans ◽  
Specialty Coffee

This paper reports on the chemical compounds in arabica coffee beans with a high Specialty Coffee Association (SCA) cupping score, especially those in specialty coffee beans. We investigated the relationship between the chemical compounds and cupping scores by considering 16 types of Coffea arabica (arabica coffee) beans from Guatemala (SCA cupping score of 76.5–89.0 points). Non-targeted gas chromatography-mass spectrometry-based chemometric profiling indicated that specialty beans with a high cupping score contained considerable amounts of methyl-esterified compounds (MECs), including 3-methylbutanoic acid methyl ester (3-MBM), and other fatty acid methyl esters. The effect of MECs on flavor quality was verified by spiking the coffee brew with 3-MBM, which was the top-ranked component, as obtained through a regression model associated with cupping scores. Notably, 3-MBM was responsible for the fresh-fruity aroma and cleanness of the coffee brew. Although cleanness is a significant factor for specialty beans, the identification of compounds that contribute to cleanness has not been reported in previous research. The chemometric profiling approach coupled with spiking test validation will improve the identification and characterization of 3-MBM commonly found in arabica specialty beans. Therefore, 3-MBM, either alone or together with MECs, can be used as a marker in coffee production.

L-leucine methyl ester stimulates insulin secretion and islet glutamate dehydrogenase

1983 ◽  
Vol 245 (4) ◽  
pp. E338-E346 ◽  
Author(s):  
P. Knudsen ◽  
H. Kofod ◽  
A. Lernmark ◽  
C. J. Hedeskov
Keyword(s):  
Insulin Secretion ◽  
Methyl Ester ◽  
Glutamate Dehydrogenase ◽  
Insulin Release ◽  
Methyl Esters ◽  
Tumor Cell Line ◽  
Fold Increase ◽  
Inhibitory Effect ◽  
Amino Acid Derivative ◽  
Mouse Pancreatic Islets

Column perifusion of collagenase-isolated mouse pancreatic islets was used to study the dynamics of insulin release in experiments lasting for several hours. The methyl esters of L-leucine and L-arginine were synthesized. Whereas L-arginine methyl ester (L-arginine OMe) had no effect, L-leucine OMe stimulated the release of insulin. The effect of L-leucine OMe was maximal at 5 mmol/liter. Whereas the Km for glucose-stimulated insulin release was unaffected by 1 mmol/liter L-leucine OMe, the maximal release of D-glucose was increased by the amino acid derivative that appeared more effective than L-leucine. L-Leucine OMe was also a potent stimulus of insulin release from the perfused mouse pancreas. In the presence of 10 mmol/liter L-glutamine, 1 mmol/liter L-leucine OMe induced a 50- to 75-fold increase in insulin release. A similar stimulatory effect was also observed in column-perifused RIN 5F cells, a cloned rat islet tumor cell line. A twofold increase in islet glutamate dehydrogenase activity was induced by 5 mmol/liter L-leucine OMe, a larger effect than that of L-leucine (P less than 0.02), whereas L-arginine OMe had a small inhibitory effect. We conclude that L-leucine OMe is a potent stimulus of insulin secretion and that its effect on the beta-cells may be exerted by activating islet glutamate dehydrogenase.

Comparison of Two Infrared Methods for the Determination of Isolated Trans Unsaturation in Fats, Oils, and Methyl Ester Derivatives

1971 ◽  
Vol 54 (6) ◽  
pp. 1288-1292
Author(s):  
Anita Huang ◽  
David Firestone
Keyword(s):  
Fatty Acids ◽  
Methyl Ester ◽  
Rapid Method ◽  
Unsaturated Fatty Acids ◽  
Methyl Esters ◽  
Tentative Method ◽  
Trans Isomers ◽  
Sample Matrix ◽  
Infrared Methods

Abstract A study was made to compare the rapid method reported by Allen with the tentative method of the American Oil Chemists’ Society for the determination of isolated (unconjugated) trans isomers of unsaturated fatty acids. The rapid method was found to be less accurate. The accuracy of the rapid method can be improved by using an oil or methyl ester matrix with the same composition as the sample matrix for the determination of K-and f-values used for calculation of per cent trans isomers. Results obtained with both methods for methyl esters were more accurate than results for vegetable oils. An analysis of variance was performed to compare the methods.

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