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39. This work was funded by the U.S. Department of Energy,
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References and Notes
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Supporting Online Material
Materials and Methods
Figs. S1 to S5
Tables S1 to S4
References
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13 October 2010; accepted 31 January 2011
10.1126/science.1199003
achieved by enzymes, yet the chirality of the active
site environment is set by the inherent chirality of
the constituent amino acid building blocks. As a
result, it is very challenging to switch an enzyme’s
selectivity from favoring a product of one chiral
sense to favoring its enantiomer, although genetic
engineering and directed evolution approaches
can be brought to bear in certain cases (3). By
contrast, the comparative structural simplicity of
synthetic asymmetric catalysts often allows facile
preparation of both catalyst enantiomers, thereby
enabling preparation of each product enantiomer
individually (4). In addition, strategies that allow
for the formation of either product enantiomer
from a single enantiomer of a catalyst have also
been developed, for example, by changing the
reaction conditions, including solvent or temper-
ature, or by the addition of different Lewis acids
(5, 6). But can we go further; can we modulate
Dynamic Control of Chiral Space
in a Catalytic Asymmetric Reaction
Using a Molecular Motor
Jiaobing Wang and Ben L. Feringa*
Enzymes and synthetic chiral catalysts have found widespread application to produce single
enantiomers, but in situ switching of the chiral preference of a catalytic system is very difficult
to achieve. Here, we report on a light-driven molecular motor with integrated catalytic functions
in which the stepwise change in configuration during a 360° unidirectional rotary cycle governs
the catalyst performance both with respect to activity and absolute stereocontrol in an asymmetric
transformation. During one full rotary cycle, catalysts are formed that provide either racemic
(R,S) or preferentially the R or the S enantiomer of the chiral product of a conjugate addition
reaction. This catalytic system demonstrates how different molecular tasks can be performed in
a sequential manner, with the sequence controlled by the directionality of a rotary cycle.
Centre for Systems Chemistry, Stratingh Institute for Chem-
istry and Zernike Institute for Advanced Materials, Uni-
versity of Groningen, Nijenborgh 4, 9747 AG, Groningen,
Netherlands.
he ease with which nature controls the selectively catalyze a myriad of asymmetric
chirality of the product of an enzymatic transformations (1, 2). The precise spatial arrange-
T
reaction has spurred and inspired the de- ment of amino acid and cofactor subunits in a high-
velopment of synthetic compounds that enantio- ly dynamic setting is the key to enantioselectivity b.l.feringa@rug.nl
*To whom correspondence should be addressed. E-mail:
1429