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, Klaus Dieter Asmus, Sabine Mahling

Research output: Contribution to journalArticle

62 Scopus citations

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
DOIs
StatePublished - Jan 1 1991

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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