14486-03-4Relevant academic research and scientific papers
Phenylhydrazide as an enzyme-labile protecting group in peptide synthesis
Voelkert, Martin,Koul, Surrinder,Mueller, Gernot H.,Lehnig, Manfred,Waldmann, Herbert
, p. 6902 - 6910 (2007/10/03)
The enzymatic cleavage of amino acid phenylhydrazides with the enzyme tyrosinase (EC 1.14.18.1) offers a new, mild, and selective method for C-terminal deprotection of peptides. The advantages of the described methodology are the very mild oxidative removal of the protecting group at room temperature and pH 7, a high chemo- and regioselectivity, and the availability of the biocatalyst. Even in oxygen-saturated solution, the oxidation of sensitive methionine residues was not observed. These features make the methodology suitable for the synthesis of sensitive peptide conjugates. Mechanistic data suggest that the hydrolysis of the oxidized adducts proceeds by a free-radical mechanism.
Photooxidation of Methionine Derivatives by the 4-Carboxybenzophenone Triplet State in Aqueous Solution. Intracomplex Proton Transfer Involving the Amino Group
Hug, Gordon L.,Bobrowski, Krzysztof,Kozubek, Halina,Marciniak, Bronislaw
, p. 785 - 796 (2007/10/03)
Oxidation of the triplet state of 4-carboxybenzophenone (CB) by a series of five substituted methionines and three methionine-containing dipeptides was monitored under laser flash photolysis conditions in aqueous solution. Spectral resolution techniques were employed to follow the concentration profiles of the intermediates formed from the quenching events. From these concentration profiles, quantum yields for the intermediates were determined. Branching ratios were evaluated for the decay of the charge-transfer complex by the competing processes of back electron transfer, proton transfer and escape of radical ions. The relative prominence of these processes was discussed in terms of the proton-transfer tendencies of the nominal sulfur-radical-cationic species. A systematic decrease was observed in the quantum yields for the escape of radical ions along with a correlated increase in the proton-transfer yields. The enhanced propensity of the sulfur radical cations to deprotonate is due to deprotonation at the carbons adjacent to the sulfur-cationic site and at the unsubstituted amino groups when present. This scheme was supported by an observed decrease in the yields of dimeric sulfur radical cations with an increase in the electron-withdrawing abilities of the substituents, making the radical-cationic species stronger acids. The involvement of protons on the amino groups was implicated by the correlation of the quantum yields of ketyl radical formation in the photo-chemistry experiments with the rate constants for the reaction of the CB radical anion with the sulfur-containing substrates in pulse radiolysis experiments.
FORMATION CONSTANTS OF SILVER(I) COMPLEXES OF SOME SULPHUR-CONTAINING DIPEPTIDES AND VALYLVALINE
Lyons, Anthony Q.,Pettit, Leslie D.
, p. 2305 - 2308 (2007/10/02)
Formation constants at 25 deg C and l = 0.10 mol dm-3 (KNO3) have been determined for the complexes of AgI with a range of nine dipeptides which incorporate side-chains containing one (glycylmethionine and methionylglycine) or two sulphur donor atoms.In the latter case dipeptides formed from amino acids of the same and of different chiralities were studied (e.g.L-methionyl-L-methionine and L-methionyl-D-methionine).The results are compared with those for valylvaline.Values for the formation constants are interpreted in terms of the preferred conformations of the dipeptides, and the tendency for AgI to bond to S-donor atoms or to adopt linear co-ordination through the formation of dimeric complexes.
