ORGANIC LETTERS
Synthesis of Optically Active β-Amino Acid N-Carboxyanhydrides
2000 Vol. 2, No. 13 1943-1946
Jianjun Cheng,† Joseph W. Ziller,‡ and Timothy J. Deming*,† Departments of Materials and Chemistry, UniVersity of California, Santa Barbara, Santa Barbara, California 93106, and Department of Chemistry, UniVersity of California, IrVine, California 92697
[email protected] Received May 5, 2000
ABSTRACT
Methodology has been developed for the general synthesis of optically active β-amino acid N-carboxyanhydrides (β-NCAs) through cyclization of Nβ-Boc or Nβ-Cbz β-amino acids using phosphorus tribromide. The formation of β-NCAs was confirmed by spectroscopy as well as an X-ray structural determination of β-homoalanine-N-carboxyanhydride. The β-NCA molecules could be polymerized in good yield to give optically active poly(β-peptides) that adopt stable chiral conformations in solution. For example, helical oligo(L-β-homophenylalanine) was synthesized by polymerization of L-β-homophenylalanine-N-carboxyanhydride.
The synthesis and characterization of oligomers of β-amino acids, so-called β-peptides, has received considerable interest in recent years.1-3 β-Peptides differ from their R-peptide analogues by possessing additional conformational freedom due to an extra backbone R-methylene group. Despite this, β-peptide chains containing as few as six monomer repeats can adopt very stable secondary structures in solution, while R-peptide chains of similar length typically do not.2 Although efficient synthetic methods for preparation of short β-peptides †
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10.1021/ol000122w CCC: $19.00 Published on Web 06/03/2000
© 2000 American Chemical Society
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