Chiral organocatalysts based on lipopeptide micelles for aldol reactions in water. Issue 2 (12th December 2016)

• Record Type: Journal Article
• Authors: Soares, B. M.; Aguilar, A. M.; Silva, E. R.; Coutinho-Neto, M. D.; Hamley, I. W.; Reza, M.; Ruokolainen, J.; Alves, W. A.
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 2(2017)
• Page Start: 1181
• Page End: 1189
• Publication Date: 2016-12-12
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp08135e
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Self-assembly of a proline-capped lipopeptide in water provides unprecedented enhancement of catalytic activity in aldol reactions. Abstract : A comprehensive study of the self-assembly in water of a lipopeptide consisting of a sequence ofl -proline, l -arginine andl -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.