Abstract
A series of N-pyrrolidine-based alpha,beta-peptide catalysts incorporating a constrained 2-aminobicyclo[2.2.2] octane carboxylic acid (ABOC) residue were synthesized and evaluated in the asymmetric aldol reaction from acetone and some p-substituted benzaldehydes. Their catalytic properties were shown to be highly dependent on the amino acid sequences and on the absolute configuration of the ABOC residue that played a determinant role. Among the peptides tested, the heterochiral tripeptide H-Pro-(R)-ABOC-Asp-OCH3 13, that adopts a turn conformation in the solid state, proved to be the most efficient catalyst affording beta-hydroxy ketones in high yields and good enantioselectivities (up to 87%).