Covalently Cyclodextrin-Bonded Heme Derivativest

Iron(II) protoporphyrin IX (heme) was coupled with α-cyclodextrin (CD) by two covalent bonds to form two types of CD-heme derivatives (Scheme 1,2). These compounds were isolated by gel permeation chromatography (GPC) on Biobeads. In aqueous solution the CD-bonded heme binds imidazole with a smaller equilibrium constant than that of the corresponding heme-imidazole complex. Probably due to the steric hindrance and the hydrophobic environment of the CD cap, these CD-bonded heme complexes formed relatively long-lived oxygen adducts in aqueous N, N-dimethylformamide at —30°C in the presence of a bulky axial ligand, such as a polymeric 2-methylimidazole. The LD50 for intravenously administered CD-bonded hemin in rats was >450 mg/kg, which was lower in toxicity than that of hemin (LD50=90 mg/kg).