Peptides oxidation

B) S-peptide oxidized while bound to RNase S protein, showing less oxidation. (C) RNase S protein oxidized in absence of peptide. (D) RNase S-protein oxidized while bound to S-peptide. 

Ni" forms square-planar bis-complexes with the amidate anions of L-Val, L-Phe, and L-Pro. The structure of bis(Gly)-bis(imidazole)nickel(ii) has been reported and the configuration around the metal atom is cis-O(carboxyl), cis-N(amine), cis-N(imidazole). Tetra- and penta-peptide complexes of nickel(ii) consume oxygen in neutral solutions as the metal ion catalyses peptide oxidation to give a number of products, including amides of amino-acids and peptides, oxo-acids, and C02- ... 

Fig. 2 Proposed model for the neuropathology of AD based upon abnormal metal interactions. During aging, Cu and Fe levels increase in the CNS with increased metallation of Ap peptide. Cu binding to Ap results in production of reactive oxygen species and auto-oxidation of Ap peptide. Oxidized AP contributes to synaptic pathology and plaque formation. Metals may also promote phosphorylation of tau and enhance NFT formation, further contributing to AD neuropathology...

Procednres for preparing electrode snrfaces (Section 4.10), the technical aspects of measnring spectra at the metal-electrolyte interface (Section 4.6), and the problems that can arise in interpreting the resnlting spectra have already been considered (Section 3.7). The contribntion of IR SEC stndies to an nnderstanding of the adsorption of CO and NO and small organic molecnles (methanol, ethanol, formic acid, etc.), the rednction of CO2 on ordered noble metals, electrochemical polymerization, and the strnctnre of the electrochemical double layer (DL) have been discussed in varions recent reviews [635, 638, 641]. Below, the information that can be obtained from the IR SEC measurements is listed and two IR SEC studies of the DL structure are considered. An example in which in sitn IRRAS is used to follow peptide oxidation on a Pt electrode is discussed in Section 7.8.1. 

Peptide oxidation with 0-insertion is treated in Section 10.2.4. 

Many compounds, including almost all amino acids and several peptides, can be oxidized at relatively low potentials at some metal oxide-covered electrodes in alkaline media. For peptides, oxides of copper, gold, and platinum have been utilized. However, the oxidation potentials are primarily determined by the state of... 

The ammo acid sequences of five plasma kallikrem inhibitors (17-mers) are shown. The sequences of the synthetic peptides derive from the clones PK2, PK4, PK6 and PK13 (isolated in phage selections using library 1) and from clone PK15 (an affinity-matured clone isolated from library 2). Indicated are the molecular masses and the inhibitory activities before and after the modification of the peptides with tBMB. The reduced linear peptides were incubated with plasma kallikrem, and the inhibitory activity was measured immediately to minimize the risk of peptide oxidation. 

In peptide syntheses, where partial racemization of the chiral a-carbon centers is a serious problem, the application of 1-hydroxy-1 H-benzotriazole ( HBT") and DCC has been very successful in increasing yields and decreasing racemization (W. Kdnig, 1970 G.C. Windridge, 1971 H.R. Bosshard, 1973), l-(Acyloxy)-lif-benzotriazoles or l-acyl-17f-benzo-triazole 3-oxides are formed as reactive intermediates. If carboxylic or phosphoric esters are to be formed from the acids and alcohols using DCC, 4-(pyrrolidin-l -yl)pyridine ( PPY A. Hassner, 1978 K.M. Patel, 1979) and HBT are efficient catalysts even with tert-alkyl, choles-teryl, aryl, and other unreactive alcohols as well as with highly bulky or labile acids. 

Primary and secondary amines are susceptible to oxidation and replacement reactions involving the N—H bonds. Within the development of peptide synthesis numerous protective groups for N—H bonds have been found (M, Bodanszky, 1976 L.A. Carpino, 1973), and we shall discuss five of the more general methods used involving the reversible formation of... 

Derivatives such as 3-fluoro-4-nitropyridine [13505-01 -6] (396) or the 1-oxide [769-54-0] (397) have been used to characteri2e amino acids and peptides. 5-Eluoro-3-pyridinemethanol [22620-32-2] has been patented as an antihpolytic agent (398). A promising antidepressant, l-(3-fluoro-2-pyridyl)pipera2ine hydrochloride [85386-84-1] is based on 2-chloro-3-fluoropyridine [17282-04-1] (399). 

The Dim ester was developed for the protection of the carboxyl function during peptide synthesis. It is prepared by transesterification of amino acid methyl esters with 2-(hydroxymethyl)-l,3-dithiane and Al(/-PrO)3 (reflux, 4 h, 75°, 12 torr, 75% yield). It is removed by oxidation [H2O2, (NH4)2Mo04 pH 8, H2O, 60 min, 83% yield]. Since it must be removed by oxidation it is not compatible with.sulfur-containing amino acids such as cysteine and methionine. Its suitability for other, easily oxidized amino acids (e.g., tyrosine and tryptophan) must also be questioned. It is stable to CF3CO2H and HCl/ether. - ... 

The / -(methylmercapto)phenyl ester has been prepared from an /-protected amino acid and 4-tH3SC6H40H (DCC, CH2CI2, 0°, 1 h 20°, 12 h, 60-70% yield). The p-(methylmercapto)phenyl ester serves as an unactivated ester that is activated on oxidation to the sulfone (H2O2, AcOH, 20°, 12 h, 60-80% yield) which then serves as an activated ester in peptide synthesis. ... 

Thiazolidines have been prepared from /3-aminothiols—for example, cysteine—to protect the —SH and — NH groups during syntheses of peptides, including glu-tathione. Thiazolidines are oxidized to symmetrical disulfides with iodine they do not react with thiocyanogen in a neutral solution. 

---