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Issue 2, 2017
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Chiral organocatalysts based on lipopeptide micelles for aldol reactions in water

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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

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Article information


Submitted
28 Nov 2016
Accepted
30 Nov 2016
First published
30 Nov 2016

Phys. Chem. Chem. Phys., 2017,19, 1181-1189
Article type
Paper

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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