Compound Ⅰ and Ⅱ Analogues of a Chlorin

摘要

Oxoferryl chlorin π-cation radicals are putative transients in the dismutation of hydrogen peroxide by chlorin-containing catalases of organisms such as Escherichia coli and Neuro-spora crassa and are analogues of the compound Ⅰ transients of catalases having iron protoporphyrin Ⅸ as the prosthetic group. To date, efforts to model the compound I analogues of chlorins have relied on the dihydro derivatives of meso-tetraarylporphyrins. Generation of chlorin compoundⅠanalogues by the usual treatment of the ferric complexes with peracids is accompanied by considerable aromatization back to the porphyrin macrocycle, posing difficulties for characterization by EPR, Moessbauer, and resonance Raman spectroscopy. We have synthesized trans-2,3-dihydroxy-2,3-dimethylporphina-toiron(Ⅲ) (|Fe~(Ⅲ)1|~+), an iron chlorin complex in which aro- matization is prevented by gem substitution at both pyrroline β-carbons, and report generation of the compound Ⅰ and one-electron-reduced compound Ⅱ analogues. Absence of porphyrin contamination has permitted the definitive characterization of a chlorin compound Ⅰ analogue.