Département de chimie moléculaire

Tyrosyl radicals are involved in many biol. important processes. The development of model compds. to mimic radical enzyme active sites, such as galactose oxidase (GO), has widely contributed to an enhanced understanding of their spectral properties, structural attributes and even reactivity. An emerging approach towards the synthesis of such active site mimetics is the use of peptidic ligands. The potential of cyclodecapeptides to bear phenoxyl radicals has been evaluated through three compds. LH42+ is a cyclodecapeptide contg. two histidine residues (mimicking His496 and His581 of GO) and two tyrosine residues (mimicking Tyr495 and the Tyr272.bul. radical of GO). LtBuH42+ and LOMeH42+ incorporate 2,4,6-protected phenols in place of each tyrosine in LH42+. The deprotonation consts. of each peptide detd. by potentiometric titrns. showed that there are some interactions between the acido-basic residues. Cyclic voltammetric studies revealed that only the peptides incorporating 2,4,6-protected phenolates exhibit reversible redox couples and are thus precursors of radicals stable enough to persist in soln. These studies also showed LOMe2- to possess the lower oxidn. potential, indicating that this peptide, in its radical form, is the most stabilized. The electrochem. generated radical species have been characterized by EPR spectroscopy. [on SciFinder(R)]