scholarly journals 2-Phenyl-tetrahydropyrimidine-4(1H)-ones – cyclic benzaldehyde aminals as precursors for functionalised β2-amino acids

2009 ◽  
Vol 5 ◽  
Author(s):  
Markus Nahrwold ◽  
Arvydas Stončius ◽  
Anna Penner ◽  
Beate Neumann ◽  
Hans-Georg Stammler ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Asymmetric Synthesis ◽  
Side Chains ◽  
Acid Labile

Novel procedures have been developed to condense benzaldehyde effectively with β-amino acid amides to cyclic benzyl aminals. Double carbamate protection of the heterocycle resulted in fully protected chiral β-alanine derivatives. These serve as universal precursors for the asymmetric synthesis of functionalised β2-amino acids containing acid-labile protected side chains. Diastereoselective alkylation of the tetrahydropyrimidinone is followed by a chemoselective two step degradation of the heterocycle to release the free β2-amino acid. In the course of this study, an L-asparagine derivative was condensed with benzaldehyde and subsequently converted to orthogonally protected (R)-β2-homoaspartate.

Structural characterization of folded and extended conformations in peptides containing γ amino acids with proteinogenic side chains: crystal structures of γn, (αγ)n and γγδγ sequences

2015 ◽  
Vol 39 (5) ◽  
pp. 3319-3326 ◽  
Author(s):  
Madhusudana M. B. Reddy ◽  
K. Basuroy ◽  
S. Chandrappa ◽  
B. Dinesh ◽  
B. Vasantha ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Crystal Structures ◽  
Structural Characterization ◽  
Side Chains ◽  
Amino Acid Residues

γn amino acid residues can be incorporated into structures in γn and hybrid sequences containing folded and extended α and δ residues.

The Synthesis of a Cubane-Substituted Dipeptide

2012 ◽  
Vol 65 (6) ◽  
pp. 690 ◽  
Author(s):  
Quentin I. Churches ◽  
Roger J. Mulder ◽  
Jonathan M. White ◽  
John Tsanaktsidis ◽  
Peter J. Duggan
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
High Sensitivity ◽  
Pure Form ◽  
Bioactive Molecules ◽  
Side Chains ◽  
Cyclic Hydrocarbon ◽  
Wide Range ◽  
Effective Synthesis ◽  
Dipeptide Derivative

Amino acids and peptides bearing cyclic hydrocarbon side-chains are of interest in the development of a wide range of bioactive molecules. The preparation of an amino acid and a dipeptide derivative bearing an unfunctionalised cubane substituent is described. Attempts to prepare a cubylalanine derivative via the corresponding dehydroalanine were unsuccessful due to the high sensitivity of this vinyl cubane compound. Conversely, the addition of cubyllithium to a (RS)-glyoxylate sulfinimine led to an effective synthesis of a cubylglycine derivative and a cubane-substituted dipeptide in diastereomerically pure form.

Effect of thenardite on the direct detection of aromatic amino acids: implications for the search for life in the solar system

2009 ◽  
Vol 8 (4) ◽  
pp. 291-300 ◽  
Author(s):  
C. Doc Richardson ◽  
Nancy W. Hinman ◽  
Jill R. Scott
Keyword(s):  
Mass Spectrometry ◽  
Amino Acids ◽  
Amino Acid ◽  
Aromatic Amino Acids ◽  
Laser Desorption ◽  
Ionization Mechanism ◽  
Side Chains ◽  
Ion Cyclotron Resonance ◽  
Laser Desorption Mass Spectrometry ◽  
Aromatic Side Chains

AbstractWith the discovery of Na-sulphate minerals on Mars and Europa, recent studies using these minerals have focused on their ability to assist in the detection of bio/organic signatures. This study further investigates the ability of thenardite (Na2SO4) to effectively facilitate the ionization and identification of aromatic amino acids (phenylalanine, tyrosine and tryptophan) using a technique called geomatrix-assisted laser desorption/ionization in conjunction with a Fourier transform ion cyclotron resonance mass spectrometry. This technique is based on the ability of a mineral host to facilitate desorption and ionization of bio/organic molecules for detection. Spectra obtained from each aromatic amino acid alone and in combination with thenardite show differences in ionization mechanism and fragmentation patterns. These differences are due to chemical and structural differences between the aromatic side chains of their respective amino acid. Tyrosine and tryptophan when combined with thenardite were observed to undergo cation-attachment ([M+Na]+), due to the high alkali ion affinity of their aromatic side chains. In addition, substitution of the carboxyl group hydrogen by sodium led to formation of [M-H+Na]Na+ peaks. In contrast, phenylalanine mixed with thenardite showed no evidence of Na+ attachment. Understanding how co-deposition of amino acids with thenardite can affect the observed mass spectra is important for future exploration missions that are likely to use laser desorption mass spectrometry to search for bio/organic compounds in extraterrestrial environments.

scholarly journals Electrophysiological evidence for acidic, basic, and neutral amino acid olfactory receptor sites in the catfish.

1984 ◽  
Vol 84 (3) ◽  
pp. 403-422 ◽  
Author(s):  
J Caprio ◽  
R P Byrd
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Ictalurus Punctatus ◽  
Olfactory Receptor ◽  
Olfactory Receptors ◽  
Receptor Potential ◽  
Side Chains ◽  
Short Side ◽  
Neutral Amino Acids ◽  
Receptor Sites

Electrophysiological experiments indicate that olfactory receptors of the channel catfish, Ictalurus punctatus, contain different receptor sites for the acidic (A), basic (B), and neutral amino acids; further, at least two partially interacting neutral sites exist, one for the hydrophilic neutral amino acids containing short side chains (SCN), and the second for the hydrophobic amino acids containing long side chains (LCN). The extent of cross-adaptation was determined by comparing the electro-olfactogram (EOG) responses to 20 "test" amino acids during continuous bathing of the olfactory mucosa with water only (control) to those during each of the eight "adapting" amino acid regimes. Both the adapting and test amino acids were adjusted in concentrations to provide approximately equal response magnitudes in the unadapted state. Under all eight adapting regimes, the test EOG responses were reduced from those obtained in the unadapted state, but substantial quantitative differences resulted, depending upon the molecular structure of the adapting stimulus. Analyses of the patterns of EOG responses to the test stimuli identified and characterized the respective "transduction processes," a term used to describe membrane events initiated by a particular subset of amino acid stimuli that are intricately linked to the origin of the olfactory receptor potential. Only when the stimulus compounds interact with different transduction processes are the stimuli assumed to bind to different membrane "sites." Four relatively independent L-alpha-amino acid transduction processes (and thus at least four binding sites) identified in this report include: (a) the A process for aspartic and glutamic acids; (b) the B process for arginine and lysine; (c) the SCN process for glycine, alanine, serine, glutamine, and possibly cysteine; (d) the LCN process for methionine, ethionine, valine, norvaline, leucine, norleucine, glutamic acid-gamma-methyl ester, histidine, phenylalanine, and also possibly cysteine. The specificities of these olfactory transduction processes in the catfish are similar to those for the biochemically determined receptor sites for amino acids in other species of fishes and to amino acid transport specificities in tissues of a variety of organisms.

Protein

1995 ◽  
Author(s):  
Roland Lüthy ◽  
David Eisenberg
Keyword(s):  
Amino Acids ◽  
Molecular Weight ◽  
Amino Acid ◽  
Isoelectric Point ◽  
Extinction Coefficient ◽  
Titration Curve ◽  
Side Chains ◽  
Pka Values ◽  
Extinction Coefficients ◽  
Molecular Weights

Given a protein sequence, the amino acid composition can be determined by counting the number of residues of each type. Then a molecular weight can be calculated by summing the molecular weights of the individual amino acid residues, taking into account the loss of one H2O molecule per peptide bond. Table 1 lists the molecular weights of the twenty amino acids and water. This approach assumes that the protein has not been covalently modified. Because of extensive glycosylation of some proteins, this approach can significantly underestimate the actual molecular weight. With the pKa values of Table 1, it is possible to calculate the theoretical charge of a protein at a given pH by summing the charges of the amino acid side chains and of the amino terminus and carboxyl terminus. By performing this calculation over a pH range, one obtains a theoretical titration curve and an isoelectric point (the pH at which the protein hasanetchargeof zero). This method assumes that all normally titratable groups are accessible to water, and that all side chains have the intrinsic pKa values listed in Table 1. This assumption is not completely correct, and consequently, the theoretical isoelectric point may differ from the experimentally determined value. Figure 1 shows the calculated titration curve for pancreatic ribonuclease: the calculated isoelectric point is 8.2, whereas the measured value is 9.6 (Lehninger, 1977). The calculation of extinction coefficients (Gill and von Hippel, 1989) is performed in much the same way as that of the isoelectric point Individual residues are treated as if they are free amino acids, and the overall extinction coefficient is calculated as the sum of the extinction coefficients of the residues. The same basic assumption is made: Residues are assumed to be in typical environments and not to show unusual absorption due to their local environments. In the case of the extinction coefficient, however, this assumption seems to be generally acceptable; calculated extinction coefficients are typically within a few percent of the experimentally determined value, and errors of more than 15% are rare (Gill and von Hippel, 1989).

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