부산대학교 도서관

In the postulated catalytic cycle of class Ib Mn2ribonucleotide reductases (RNRs), a MnII2core is suggested to react with superoxide (O2·–) to generate peroxido-MnIIMnIIIand oxo-MnIIIMnIVentities prior to proton-coupled electron transfer (PCET) oxidation of tyrosine. There is limited experimental support for this mechanism. We demonstrate that [MnII2(BPMP)(OAc)2](ClO4) (1, HBPMP = 2,6-bis[(bis(2 pyridylmethyl)amino)methyl]-4-methylphenol) was converted to peroxido-MnIIMnIII(2) in the presence of superoxide anion that converted to (μ-O)(μ-OH)MnIIIMnIV(3) via the addition of an H+-donor (p-TsOH) or (μ-O)2MnIIIMnIV(4) upon warming to room temperature. The physical properties of 3and 4were probed using UV–vis, EPR, X-ray absorption, and IR spectroscopies and mass spectrometry. Compounds 3and 4were capable of phenol oxidation to yield a phenoxyl radical via a concerted PCET oxidation, supporting the proposed mechanism of tyrosyl radical cofactor generation in RNRs. The synthetic models demonstrate that the postulated O2/Mn2/tyrosine activation mechanism in class Ib Mn2RNRs is plausible and provides spectral insights into intermediates currently elusive in the native enzyme.