Synthesis of protoheme IX derivatives with a covalently linked proximal base and their human serum albumin hybrids as artificial hemoprotein

Abstract

The simple one-pot reaction of protoporphyrin IX and ω-(N-imidazolyl)alkylamine or O-methyl-L-histidyl-glycine with benzotriazol-1-yl-oxytris(dimethylamino)phosphonium hexafluorophosphate at room temperature produced a series of protoporphyrin IX species with a covalently linked proximal base at the propionate side-chain. The central iron was inserted by the general FeCl₂ method, converting the free-base porphyrins to the corresponding protoheme IX derivatives. Mesoporphyrin IX and diacetyldeuteroporphyrin IX analogues were also prepared by the same procedure. The Fe(II) complexes formed dioxygen (O₂) adducts in dimethylformamide at 25 °C. Some of them were incorporated into the hydrophobic domain of recombinant human serum albumin (rHSA), providing albumin–heme hybrids (rHSA–heme), which can bind and release O₂ in aqueous media (pH 7.3, 25 °C). The oxidation process of converting the dioxygenated heme in rHSA to the inactive Fe(III) state obeyed first-order kinetics, indicating that the μ-oxo dimer formation was prevented by the immobilization of heme in the albumin scaffold. The rHSA–heme, in which the histidylglycil tail coordinates to the Fe(II) center, showed the most stable O₂ adduct complexes.