- Oxidative Damage in Aliphatic Amino Acids and Di- and Tripeptides by the Environmental Free Radical Oxidant NO3?: the Role of the Amide Bond Revealed by Kinetic and Computational Studies
-
Kinetic and computational data reveal a complex behavior of the important environmental free radical oxidant NO3? in its reactions with aliphatic amino acids and di- and tripeptides, suggesting that attack at the amide N-H bond in the peptide backbone is a highly viable pathway, which proceeds through a proton-coupled electron transfer (PCET) mechanism with a rate coefficient of about 1 × 106 M-1 s-1 in acetonitrile. Similar rate coefficients were determined for hydrogen abstraction from the α-carbon and from tertiary C-H bonds in the side chain. The obtained rate coefficients for the reaction of NO3? with aliphatic di- and tripeptides suggest that attack occurs at all of these sites in each individual amino acid residue, which makes aliphatic peptide sequences highly vulnerable to NO3?-induced oxidative damage. No evidence for amide neighboring group effects, which have previously been found to facilitate radical-induced side-chain damage in phenylalanine, was found for the reaction of NO3? with side chains in aliphatic peptides.
- Nathanael, Joses G.,Wille, Uta
-
p. 3405 - 3418
(2019/03/11)
-
- A practical method for selective cleavage of a tert-butoxycarbamoyl N-protective group from N,N-diprotected α-amino acid derivatives using montmorillonite K-10
-
A new, practical, and mild procedure for the selective cleavage of a tert-butoxycarbonyl group (Boc) in N-Boc-N-acyl-diprotected amines is described. When applied to α-amino acids, complete integrity of the stereochemistry was observed. The use of N,N-di-Boc-α-amino-δ- and γ-hydroxy esters provided both δ- and γ-lactones in very good yields. The method is based on the use of Montmorillonite K-10 either in CH 2Cl2 at room temperature or in toluene at 65°C and is compatible with the presence of a large range of functional and other protecting groups in the substrates. In most cases virtually pure samples are obtained after filtration and removal of solvents. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Hernandez, J. Nicolas,Crisostomo, Fernando R. Pinacho,Martin, Tomas,Martin, Victor S.
-
p. 5050 - 5058
(2008/03/18)
-
- Synthesis of protected γ-carboxyglutamates and γ-acylglutamates by rearrangement of N,N-diacylglutamates
-
A new method for γ-acylation of protected glutamic acids, involving intramolecular rearrangement of an acyl urethane, has been devised to prepare the protected γ-carboxyglutamates 7, 9 and 11 and the protected 4-acylglutamates 15 and 22 from N,N-bisurethanes or N-acyl-N-urethanes of general structure 1. When the formylurethane 17 was used in the reaction, then the intermediate 18 in the intramolecular rearrangement was obtained. The Royal Society of Chemistry 2005.
- Avent, Anthony G.,Duggan, Heather M. E.,Young, Douglas W.
-
p. 2327 - 2332
(2007/10/03)
-
- A Simple and Efficient Esterification Method
-
A convenient and practical esterification was realized and this reaction proceeded without a dehydrating reagent or water removal equipment. The synthesis of esters by reaction of carboxylic acids with various alcohols such as methyl, ethyl, isopropyl, isobutyl, allyl, benzyl, propargyl and decanyl alcohols were achieved with a catalytic amount of CBr4 under refluxing reaction condition.
- Ming-Yi, Chen,Lee, Adam Shih-Yuan
-
p. 103 - 108
(2007/10/03)
-
- A new selective cleavage of N,N-dicarbamoyl-protected amines using lithium bromide
-
A mild and new procedure for the selective cleavage of an alkoxycarbonyl group (Boc, CBz) in N,N-dicarbamoyl-protected amino compounds is described. The method is based on the use of lithium bromide in acetonitrile and is compatible with a large range of other functionalities present in the substrates. Compared with other reported methodologies, the procedure is particularly useful for the Cbz-selective cleavage in N,N-Ts,Cbz-diprotected amines. A rationalization of the selectivity supported by ab initio calculations is also presented.
- Hernandez, J. Nicolas,Ramirez, Miguel A.,Martin, Victor S.
-
p. 743 - 746
(2007/10/03)
-
- Selectivity in Carbonic Anhydrase Catalyzed Hydrolysis of Standard N-Acetyl-DL-amino Acid Methyl Esters
-
Carbonic anhydrase-catalyzed hydrolysis of some standard N-acetyl-DL-amino acid methyl esters proceeds with high enantioselectivity.This enzyme hydrolyses selectively D amino acid derivatives in contrast to proteases which have a L stereoselectivity. Key Words: carbonic anhydrase, hydrolysis, N-acetyl-DL-amino acid methyl esters, enantioselectivity.
- Chenevert, Robert,Rhlid, Rachid Bel,Letourneau, Martin,Gagnon, Rene,D'Astous, Linda
-
p. 1137 - 1140
(2007/10/02)
-
- Hydrophobic parameters ? of amino-acid side chains from the partitioning of N-acetyl-amino-acid amides
-
A hydrophobic parameter for the side chain of each of the twenty naturally occuring amino-acids was estimated quantitatively by partitioning of their N-acetyl-amino-acid amides (CH3CO-NH-CH(R)-CONH2, R=variable side chain) in octanol/water.Suitable forms of the derivatives were synthesized chemically where necessary.The new series affords reliable distribution coefficients especially for polar amino-acids.A set of Hansch side chain parameters ? obtained for the twenty common amino-acids, for half-cystine as well as for the extremly lipophilic amino-acids carboranylalanine and adamantylalanine.It is found that these hydrophobicity indices, obtained at neutral pH, are tightly correlated with the degree of solvent exposure of the side chain in globular proteins and it is proposed that they be used in future biophysical and pharmacological studies.
- Fauchere, Jean-Luc,Pliska, Vladimir
-
p. 369 - 376
(2007/10/02)
-