Enzymatic tryptophan 2,3-dioxygenase-like activity of a manganese porphyrin bound to bovine serum albumin modified with poly(ethylene glycol)

Abstract

Stereoselective dioxygenolyses of N-acetyl-L(+)- and D(–)-tryptophan methyl esters (1) have been performed with manganese porphyrins [meso-tetrakis(p-carboxyphenyl)porphyrinato manganese(III) chloride (Mn^IIICITCPP), meso-tetrakis (phenyl) porphyrinato manganese(II)(Mn^IITPP), and meso-tetrakis (phenyl) porphyrinato manganese(III) chloride (Mn^IIICITPP)] bound and/or included to a carrier protein, bovine serum albumin (BSA) in THF–H₂O (pH 9.3; Na₂B₄O₇ buffer) under an O₂ atmosphere at 25°C. The maximum stereoselectivity, which is evaluated to be an enantiomer rate ratio 1.63 (k_L/k_D), is observed in the covalently bound system, and the fixation of a manganese porphyrin to BSA via a covalent bond is found to be effective for enantiomeric molecular recognition in the Stereoselective dioxygenolyses of tryptophan derivatives. The modification of the BSA hybrid catalyst by poly(ethylene glycol)(PEG) has also been performed, and this PEG modification enhances the solubility and stability of the BSA hybrid catalyst in organic–aqueous solvents. The PEG-modified BSA hybrid Mn^IIICITCPP retains catalytic activity and stereoselectivity for the Stereoselective dioxygenolyses of L(+)-and D(–)-1 with a higher content of organic solvent in aqueous solution.