OH Radical Induced Decarboxylation of Amino Acids. Decarboxylation vs Bond Formation in Radical Intermediates

L. Kraig Steffen, Richard S Glass, Mahmood Sabahi, George S. Wilson, Christian Schöneich, Sabine Mahling, Klaus Dieter Asmus

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Abstract

The OH radical reaction with exo-2-amino-endo-6-(methylthio)bicyclo[2.2.1]heptane-endo-2-carboxylic acid primarily affords oxidation of the sulfur center in the molecule. The subsequent pathway strongly depends on pH. A transient radical with interaction between the sulfur and the carboxylate moieties is stabilized particularly in acid solutions with maximum yield at pH 3. It is characterized by a sulfur-carboxyl bond, which exhibits typical features of 2σ/1σ* three-electron bonds. It exhibits an optical absorption (λmax 340 nm) and decays with t1/2 ≈ 26 μs via deprotonation to an α-thioalkyl carbon-centered radical. This transient bond formation between the carboxyl group and the oxidized sulfur at low pH successfully prevents a competing process, namely, decarboxylation, which takes over at pH > 4. The underlying mechanism is considered to be a concerted action involving an electron transfer from the anionic carboxylate to the oxidized sulfur atom, homolytic carbon-carboxyl bond breakage, and deprotonation of the amino group. Related studies indicate that this kind of radical-induced decarboxylation can be generalized and receives its driving force to a significant extent from the resonance stabilization of the α-amino radical remaining after CO2 cleavage.

Original languageEnglish (US)
Pages (from-to)2141-2145
Number of pages5
JournalJournal of the American Chemical Society
Volume113
Issue number6
Publication statusPublished - Mar 13 1991

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ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Steffen, L. K., Glass, R. S., Sabahi, M., Wilson, G. S., Schöneich, C., Mahling, S., & Asmus, K. D. (1991). OH Radical Induced Decarboxylation of Amino Acids. Decarboxylation vs Bond Formation in Radical Intermediates. Journal of the American Chemical Society, 113(6), 2141-2145.