Issue 2, 2017

Chiral organocatalysts based on lipopeptide micelles for aldol reactions in water

Abstract

A comprehensive study of the self-assembly in water of a lipopeptide consisting of a sequence of L-proline, L-arginine and L-tryptophan with a hydrocarbon chain has been performed. Fluorescence assays were used to determine the critical aggregation concentration. In situ small-angle X-ray scattering (SAXS) and molecular dynamics simulations showed the presence of spherical micelles with diameters around 6 nm. In agreement with these results, cryo-TEM images showed globular aggregates with diameters ranging from ≈4 nm up to ≈9 nm. Furthermore, the lipopeptide catalytic activity has been tested for the direct aldol reaction between cyclohexanone and p-nitrobenzaldehyde, and we have observed that the self-association of the organocatalyst played a critical role in the enhanced activity. Water affects the selectivity, and poor results are obtained under neat reaction conditions. The location of the catalytic groups at the lipopetide/water solvent interface also endowed unusual selectivity in the catalyzed aldol reactions. Under optimized reaction conditions, high yields (up to >99%), good enantioselectivity (ee up to 85%) and high diastereoselectivity (ds up to 92 : 8) were obtained.

Graphical abstract: Chiral organocatalysts based on lipopeptide micelles for aldol reactions in water

Supplementary files

Article information

Article type
Paper
Submitted
28 11 2016
Accepted
30 11 2016
First published
30 11 2016

Phys. Chem. Chem. Phys., 2017,19, 1181-1189

Chiral organocatalysts based on lipopeptide micelles for aldol reactions in water

B. M. Soares, A. M. Aguilar, E. R. Silva, M. D. Coutinho-Neto, I. W. Hamley, M. Reza, J. Ruokolainen and W. A. Alves, Phys. Chem. Chem. Phys., 2017, 19, 1181 DOI: 10.1039/C6CP08135E

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