Abstract
The achiral, nitroxyl-containing alpha-amino acid TOAC (TOAC = 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid), in combination with the chiral alpha-amino acid C(alpha)-methyl valine [(alphaMe)Val], was used to prepare short peptides (from di- to hexa-) that induced the enantioselective oxidation of racemic 1-phenylethanol to acetophenone. The best catalyst was an N(alpha)-acylated dipeptide alkylamide with the -TOAC-(alphaMe)Val- sequence folded in a stable, intramolecularly hydrogen-bonded beta-turn conformation with large, lipophilic (hydrophobic) N- and C-terminal blocking groups. We rationalized our findings by proposing models for the diastereomeric intermediates between (R)-[and (S)]-1-phenylethanol and the catalyst Fmoc-TOAC-L-(alphaMe)Val-NHiPr, based on the X-ray diffraction structure of the latter.
MeSH terms
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Acetophenones / chemistry
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Amino Acids, Cyclic / chemistry
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Aminoisobutyric Acids / chemistry
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Catalysis
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Chemical Phenomena
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Chemistry, Physical
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Cyclic N-Oxides / chemical synthesis*
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Cyclic N-Oxides / chemistry
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Cyclohexanecarboxylic Acids / chemistry
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Models, Molecular
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Molecular Structure
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Nitrogen Oxides / chemistry*
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Nuclear Magnetic Resonance, Biomolecular
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Oligopeptides / chemical synthesis*
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Oligopeptides / chemistry
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Oxidation-Reduction
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Phenylethyl Alcohol / chemistry
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Protein Conformation
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Spectrophotometry, Infrared
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Spectroscopy, Fourier Transform Infrared
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Spin Labels
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Stereoisomerism
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Valine / analogs & derivatives
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Valine / chemistry*
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X-Ray Diffraction
Substances
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Acetophenones
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Amino Acids, Cyclic
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Aminoisobutyric Acids
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C(alpha)-methyl valine
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Cyclic N-Oxides
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Cyclohexanecarboxylic Acids
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Nitrogen Oxides
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Oligopeptides
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Spin Labels
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1-aminocyclohexanecarboxylic acid
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nitroxyl
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Valine
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Phenylethyl Alcohol
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acetophenone
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2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid