SYNTHESIS, CHARACTERIZATION AND STEREOSELECTIVE CATALYTIC OXIDATIONS OF CHELATED DEUTEROHAEMIN-GLYCYL-L-HISTIDINE COMPLEXES

The new complexes deuterohaemin-2(18)-glycyl-L-histidine methyl ester (DH-GH) and deuterohaemin-2,18-bis(glycyl-L-histidine) dimethyl ester (DH-bis(GH)) have been obtained by condensation of glycyl-l-histidine methyl ester on the propionic acid side-chains of deuterohaemin, The f ive-coordinated complex DH-GH, where the imidazole group of the histid ine residue acts as the iron(III) axial ligand, is catalytically activ e in the oxidation of phenolic compounds by hydrogen peroxide, while t he six-coordinated DH-bis(GH) complex, as expected, is a very poor cat alyst in the same reaction. The kinetics of the catalytic oxidations o f the L and D isomers of tyrosine (Tyr) and tyrosine methyl ester (Tyr -OMe) by the system DH-GH/H2O2 have been investigated in detail, The r eactions occur with unexpected stereoselectivity, suggesting that the phenolic substrates are capable of interacting with the catalyst from the proximal side, which contains the chiral histidine centre. Analysi s by molecular mechanics (MM) and molecular dynamics (MD) calculations indicates that the mode of substrate-haemin catalyst interaction brin gs the phenol group of the tyrosines to approach laterally the porphyr in macrocycle. This disposition is reminiscent of the aromatic substra te mode of interaction in peroxidases, where the electron transfer pro cesses occur at the haem edge, (C) 1998 Elsevier Science S.A. All righ ts reserved.