Via a Mannich reaction involving a dibenzyliminium species and the titanium enolates of Evans' chiral acylated oxazolidinones the β(2)-amino acids (R)- and (S)-Fmoc-β(2)homovaline and (R)-Fmoc-β(2)homoleucine are synthesized. These building blocks were used, in combination with commercially available α- and β(3)-amino acids, for the synthesis of the cyclo-(αβ(3)αβ(2)α)(2) peptide 2 and the cyclo-(αβ(2)αβ(3)α)(2) peptides 3-5. The peptides 2-5 were screened for their ability to inhibit a small panel of Gram-negative and Gram-positive bacterial strains.
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