Creating a Defined Chirality in Amino Acids and Cyclic Dipeptides by Photochemical Deracemization

Johannes Großkopf, Manuel Plaza, Roger Jan Kutta, Patrick Nuernberger, Thorsten Bach

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

2,5-Diketopiperazines are cyclic dipeptides displaying a wide range of applications. Their enantioselective preparation has now been found possible from the respective racemates by a photochemical deracemization (53 examples, 74 % to quantitative yield, 71–99 % ee). A chiral benzophenone catalyst in concert with irradiation at λ=366 nm enables to establish the configuration at the stereogenic carbon atom C6 at will. If other stereogenic centers are present in the diketopiperazines they remain unaffected and a stereochemical editing is possible at a single position. Consecutive reactions, including the conversion into N-aryl or N-alkyl amino acids or the reduction to piperazines, occur without compromising the newly created stereogenic center. Transient absorption spectroscopy revealed that the benzophenone catalyst processes one enantiomer of the 2,5-diketopiperazines preferentially and enables a reversible hydrogen atom transfer that is responsible for the deracemization process. The remarkably long lifetime of the protonated ketyl radical implies a yet unprecedented mode of action.

Original languageEnglish
Article numbere202313606
JournalAngewandte Chemie International Edition in English
Volume62
Issue number47
DOIs
StatePublished - 20 Nov 2023

Keywords

  • Amino Acids
  • C−H Activation
  • Enantioselectivity
  • Nitrogen Heterocycles
  • Photochemistry

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