Racemates of N-hydroxymethylated beta-lactams 4-6 were resolved through the lipase-catalyzed asymmetric acylation of the primary hydroxy group at the 6S stereogenic centre. High enantioselectivity (E > 200) was observed when the enzymatic reactions were performed in acetone with lipase PS as catalyst and vinyl butyrate as acyl donor. The hydrolysis of the enantiomeric azetidinones 4a-6a and 4b-6b resulted in the enantiomerically pure alicyclic beta-amino acids 4c-6c and 4d-6d. When the less reactive enantiomers 4b-6b were treated with NH4OH/MeOH, enantiomerically pure beta-lactams 4e-6e were formed. (C) 2000 Elsevier Science Ltd. All rights reserved.
Hairpin Folding Behavior of Mixed α/β-Peptides in Aqueous Solution
摘要:
The invention of new strategies for the design of protein-mimetic oligomers that manifest the folding encoded in natural amino acid sequences is a significant challenge. In contrast to the a-helix, mimicry of protein beta-sheets is less understood. We report here the aqueous folding behavior of a prototype alpha-peptide hairpin model sequence varied at cross-strand positions by incorporation of 16 different beta-amino acid monomers. Our results provide a folding propensity scale for beta-residues in a protein beta-sheet context as well as high-resolution structures of several mixed-backbone alpha/beta-peptide hairpins in water.