STEREOSELECTIVE OXIDATION OF ENANTIOMERIC AMINES BY A MONOAMINE-OXIDASE MODEL OF CHIRAL IRON(III) PORPHYRINS

The stereoselective oxidation of enantiomeric amines (R(+)- or S(-)-alpha-phenylethylamine, 2a or 2b) has been performed with the chiral iron(III) porphyrin complexes of 5,10,15,20-tetrakis[p-((-)-menthylcarbamoyl)phenyl]porphyrin (Fe(III)ClT(men)PP, 1a) and alpha,alpha,alpha,alpha-isomer of 5,10,15,20-tetrakis[o-((t-butyloxycarbonyl)-L(-)-alaninamino)phenyl]porphyrinato iron(III) chloride (Fe(III)ClT(boc-Ala)PP, 1b) in benzene at 25-degrees-C. The reaction obeyed biphasic kinetics, and la showed higher activity and stereoselectivity rather than 1b. On the basis of the kinetic analysis of the racemic amine oxidation by meso-tetraphenylporphyrinato iron(III) chloride (Fe(III)ClTPP, 1c), the stereoselective molecular recognition of the enantiomeric 2a-b substrates by 1a or 1b was found in the ligation step for the formation of the bis-ligated Fe(III) (amine)2 complex (4) and in the reduction of the chiral complex of 4 to the iron(II) one (3) by 2a (not predominant) or 2b (predominant) in the outer-sphere contact region of the chiral complex; the extent of the stereoselection by 1a (possessing the chiral portion in the equatorial position for the porphyrin plane) or lb (possessing the chiral portion in the axial position for the porphyrin plane) was higher in the reduction step or in the second ligation step, respectively.