Tryptophan dioxygenase-like catalysis of achiral and chiral manganese(II) porphyrins for dioxygen-inserted indole-ring opening reactions

Abstract

The mimetic tryptophan dioxygenase reaction with tetraphenylporphyrinato- or 5α, 10α, 15α, α-tetrakis-[ o-(L-(−)-camphanoylamido)phenyl]porphyrinato-manganese(II), N-methylimizadole (as a proximal L-histidine model), and tryptophan analogues (3-methylindole and methyl N-acetyl-L (or D)-tryptophanate) in THF or CH 2Cl 2 at 298 K in atmospheric O 2 carried ring-opening products of 2′-formamidoacetophenone and methyl R-(−)-2-acetamido-3-(2′-formamidobenzyl)propanoate with 53% and 64% selectivity (23% e.e. of the R-(−) isomer), respectively. The key intermediate of ternary N-methyl-imizadole-Mn III-O − 2 complex was detected by UV and ESR spectra, and 3-indolyl hydroperoxide was also observed by NMR as a stable precursor of the 2′-formamido-acetophenone formation. The isotopic experiments with 1-deuterated substrate demonstrated that the rate-determining step was the deprotonation process from the indole-ring at the 1-NH position of the substrate by the activated dioxygen (O − 2). The native tryptophan dioxygenase catalysis was also discussed on the basis of the experimental findings in the present mimetic reactions.