A new functional model complex of extradiol-cleaving catechol dioxygenases: Properties and reactivity of [Fe-II(BLPA)DBCH]BPh4

Abstract

[Fe-II(BLPA)DBCH]BPh4 (1), a new functional model for the extradiol-cleaving catechol dioxygenases, has been synthesized. where BLPA is bis(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine and DBCH is 3,5-di-tert-butylcatecholate monoanion. H-1 NMR and EPR studies confirm that 1 has a high-spin Fe(II) (S = 2) center. The electronic spectrum of 1 exhibits one absorption band at 386 nm, showing the yellow color of the typical [Fe-II(BLPA)] complex. Upon exposure to O-2, 1 is converted to an intense blue species within a minute. This blue species exhibits two intense bands at 586 and 960 nm and EPR signals at g = 5.5 and 8.0 corresponding to the high-spin Fe(III) complex (S = 5/2, E/D = 0.11). This blue complex further reacts, with O-2 to be converted to (mu-oxo)Fe-2(III) complex within a few hours. Interestingly, 1 affords intradiol cleavage (65%) and extradiol cleavage (20%) products after the oxygenation. It can be suggested that 1 undergoes two different oxygenation pathways. The one takes the substrate activation mechanism proposed for the intradiol cleavage products Lifter the oxidation of the Fe-II to Fe-III. The other involves the direct attack of O-2 to Fe-II center. forming the Fe-III-superoxo intermediate which can give rise to the extradiol cleavage products. 1 is: the first functional Fe(II) complex for extradiol-cleaving dioxygenases giving extradiol cleavage products.