Organocatalytic access to a cis-Cyclopentyl-gamma-amino acid: an intriguing model of selectivity and formation of a stable 10/12-helix from the corresponding gamma/alphapeptide.

Peptide-functionalized gold nanoparticles are supramolecular systems that can mimic natural proteins or DNA. In this work, we describe the preparation, the analysis, and the biological evaluation of gold nanoparticles linked to pseudopeptide foldamers containing one to eight L-Ala-D-Oxd (Ala = alanine; Oxd = 4-carboxy-5-methyloxazolidin-2-one) residues. The nanoparticles become increasingly organized as the number of such moieties increases. Moreover, from the analysis of chiroptical signals we find that the chirality of the gold surface becomes more evident with decreasing foldamer length. Finally, these systems display no cytotoxicity towards HeLa cells and are good candidates to promote drug delivery once equipped with biologically active moieties

SummaryCinchona alkaloids with a free 6'-OH functionality are being increasingly used within asymmetric organocatalysis. This fascinating class of bifunctional catalyst offers a genuine alternative to the more commonly used thiourea systems and because of the different spacing between the functional groups, can control enantioselectivity where other organocatalysts have failed. In the main, this review covers the highlights from the last five years and attempts to show the diversity of reactions that these systems can control. It is hoped that chemists developing asymmetric methodologies will see the value in adding these easily accessible, but underused organocatalysts to their screens.

Review: [71 refs.