HEME PEPTIDE COMPLEXES - SYNTHESIS AND STEREOSELECTIVE OXIDATIONS BY DEUTEROHAEMIN-L-PHENYLALANYL-POLY-L-ALANINE COMPLEXES

Deuterohaemin-L-histidine methyl ester-peptide complexes have been obt ained by covalently linking L-histidine methyl ester and the peptides Ala-Ala-Phe-Ala-Ala-Ala-Ala-Ala-Ala-Ala (compound 3) or Ala-Ala-Ala-Ph e-Ala-Ala-Ala-Ala-Ala-Ala (compound 4) on the propionic acid side chai ns. The spectroscopic properties of 3 and 4 and the imidazole binding equilibria indicate that folding of the peptide chain on the opposite part of the porphyrin plane with respect to that occupied by the bound histidine side-arm reduces in the order 3 > 4 the accessibility of ex ogenous ligands to the sixth co-ordination position of the iron atom, probably through some stacking interactions between the phenylalanine residue of the peptide and the porphyrin ring in the case of 3. This a rrangement has marked consequences on the stereoselectivity observed i n a model peroxidase reaction using L- or D-tyrosine methyl ester as s ubstrates and tert-butyl hydroperoxide as oxidant in dichloromethane-t rifluoroethanol (9:1), that have been interpreted in terms of the inte raction between the chiral substrates and the peptide chains of the de uterohaemin complexes.