Skip to Content
Merck
  • Spontaneous transfer of chirality in an atropisomerically enriched two-axis system.

Spontaneous transfer of chirality in an atropisomerically enriched two-axis system.

Nature (2014-04-22)
Kimberly T Barrett, Anthony J Metrano, Paul R Rablen, Scott J Miller
ABSTRACT

One of the most well-recognized stereogenic elements in a chiral molecule is an sp(3)-hybridized carbon atom that is connected to four different substituents. Axes of chirality can also exist about bonds with hindered barriers of rotation; molecules containing such axes are known as atropisomers. Understanding the dynamics of these systems can be useful, for example, in the design of single-atropisomer drugs or molecular switches and motors. For molecules that exhibit a single axis of chirality, rotation about that axis leads to racemization as the system reaches equilibrium. Here we report a two-axis system for which an enantioselective reaction produces four stereoisomers (two enantiomeric pairs): following a catalytic asymmetric transformation, we observe a kinetically controlled product distribution that is perturbed from the system's equilibrium position. As the system undergoes isomerization, one of the diastereomeric pairs drifts spontaneously to a higher enantiomeric ratio. In a compensatory manner, the enantiomeric ratio of the other diastereomeric pair decreases. These observations are made for a class of unsymmetrical amides that exhibits two asymmetric axes--one axis is defined through a benzamide substructure, and the other axis is associated with differentially N,N-disubstituted amides. The stereodynamics of these substrates provides an opportunity to observe a curious interplay of kinetics and thermodynamics intrinsic to a system of stereoisomers that is constrained to a situation of partial equilibrium.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Activated Charcoal Norit®, Norit® SX2, powder, from peat, multi-purpose activated charcoal, steam activated and acid washed
Sigma-Aldrich
Activated Charcoal Norit®, Norit® GAC 1240W, from coal, for potable water processing, steam activated, granular
Sigma-Aldrich
Activated Charcoal Norit®, Norit® CA1, wood, chemically activated, powder
Sigma-Aldrich
Activated Charcoal Norit®, Norit® RB3, for gas purification, steam activated, rod
Sigma-Aldrich
Activated Charcoal Norit®, Norit® PK 1-3, from peat, steam activated, granular
Sigma-Aldrich
Bromine water, CP
Sigma-Aldrich
Activated Charcoal Norit®, Norit® SX ultra, from peat, corresponds U.S. Food chemicals codex (3rd Ed.), steam activated and acid washed, highly purified, powder
Sigma-Aldrich
Bromine, JIS special grade, ≥99.0%
Sigma-Aldrich
Carbon, nanopowder, <100 nm particle size (TEM)
Sigma-Aldrich
Bromine, ≥99.99% trace metals basis
Millipore
Activated charcoal, suitable for GC
Supelco
Activated charcoal, powder
Supelco
Activated Charcoal Norit®, Norit® RBAA-3, rod
Sigma-Aldrich
Activated charcoal, suitable for cell culture, suitable for plant cell culture
Supelco
Activated charcoal, for the determination of AOX, 50-150 μm particle size
Sigma-Aldrich
Bromine, SAJ first grade, ≥97.0%
Supelco
Activated charcoal, puriss. p.a., powder
Sigma-Aldrich
Carbon, glassy, spherical powder, 2-12 μm, 99.95% trace metals basis
Carbon, foil, 150x150mm, thickness 5.0mm, rigid graphite, medium grain size, 99.5%
Carbon, foil, 25x25mm, thickness 0.25mm, rigid graphite, fine grain size, 99.997%
Carbon, foil, 500x500mm, thickness 0.5mm, flexible graphite, 99.8%
Carbon, foil, 250x250mm, thickness 0.35mm, flexible graphite, 99.8%
Carbon, rod, 300mm, diameter 5.0mm, graphite, 100%
Carbon, foil, 10x10mm, thickness 2.0mm, hOpg
Carbon, foil, 25x25mm, thickness 0.25mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, 12.5x12.5mm, thickness 0.125mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, 50x50mm, thickness 0.5mm, flexible graphite, 99.8%
Carbon, foil, 50x50mm, thickness 0.125mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, 250x250mm, thickness 1.0mm, flexible graphite, 99.8%
Carbon, foil, 150x150mm, thickness 0.125mm, rigid graphite, fine grain size, 99.95%