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Mechanistic Consequences of Chiral Radical Clock Probes: Analysis of the Mononuclear Non-Heme Iron Enzyme HppE with 2-Hydroxy-3-methylenecyclopropyl Radical Clock Substrates
- Source :
- Journal of the American Chemical Society
- Publication Year :
- 2014
- Publisher :
- American Chemical Society, 2014.
-
Abstract
- (S)-2-Hydroxypropylphosphonic acid [(S)-HPP] epoxidase (HppE) is a mononuclear iron enzyme that catalyzes the last step in the biosynthesis of the antibiotic fosfomycin. HppE also processes the (R)-enantiomer of HPP but converts it to 2-oxo-propylphosphonic acid. In this study, all four stereoisomers of 3-methylenecyclopropyl-containing substrate analogues, (2R, 3R)-8, (2R, 3S)-8, (2S, 3R)-8, and (2S, 3S)-8, were synthesized and used as radical probes to investigate the mechanism of the HppE-catalyzed reaction. Upon treatment with HppE, (2S, 3R)-8 and (2S, 3S)-8 were converted via a C1 radical intermediate to the corresponding epoxide products, as anticipated. In contrast, incubation of HppE with (2R, 3R)-8 led to enzyme inactivation, and incubation of HppE with (2R, 3S)-8 yielded the 2-keto product. The former finding is consistent with the formation of a C2 radical intermediate, where the inactivation is likely triggered by radical-induced ring cleavage of the methylenecyclopropyl group. Reaction with (2R, 3S)-8 is predicted to also proceed via a C2 radical intermediate, but no enzyme inactivation and no ring-opened product were detected. These results strongly suggest that an internal electron transfer to the iron center subsequent to C-H homolysis competes with ring-opening in the processing of the C2 radical intermediate. The different outcomes of the reactions with (2R, 3R)-8 and (2R, 3S)-8 demonstrate the need to carefully consider the chirality of substituted cyclopropyl groups as radical reporting groups in studies of enzymatic mechanisms.
- Subjects :
- chemistry.chemical_classification
010405 organic chemistry
Chemistry
Stereochemistry
Communication
Organophosphonates
Epoxide
Substrate (chemistry)
Stereoisomerism
General Chemistry
010402 general chemistry
Cleavage (embryo)
01 natural sciences
Biochemistry
Catalysis
0104 chemical sciences
chemistry.chemical_compound
Colloid and Surface Chemistry
Enzyme
Biosynthesis
Fosfomycin
Radical clock
Oxidoreductases
Subjects
Details
- Language :
- English
- ISSN :
- 15205126 and 00027863
- Volume :
- 136
- Issue :
- 8
- Database :
- OpenAIRE
- Journal :
- Journal of the American Chemical Society
- Accession number :
- edsair.doi.dedup.....0d20b462843a5c6cf950b457825f7124