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ChemCommChemical Communicationswww.rsc.org/chemcomm
ISSN 1359-7345
COMMUNICATIONMichael Smietana, Stellios Arseniyadis et
al.DNA-cellulose: an economical, fully recyclable and highly eff
ective chiral biomaterial for asymmetric catalysis
Volume 51 Number 28 11 April 2015 Pages 60256232
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6076 | Chem. Commun., 2015, 51, 6076--6079 This journal isThe
Royal Society of Chemistry 2015
Cite this:Chem. Commun., 2015,51, 6076
DNA-cellulose: an economical, fully recyclableand highly
effective chiral biomaterial forasymmetric catalysis
Erica Benedetti,a Nicolas Duchemin,a Lucas Bethge,b Stefan
Vonhoff,b
Sven Klussmann,b Jean-Jacques Vasseur,c Janine Cossy,a Michael
Smietana*c andStellios Arseniyadis*a
The challenge in DNA-based asymmetric catalysis is to perform
a
reaction in the vicinity of the helix by incorporating a
small-
molecule catalyst anchored to the DNA in a covalent, dative,
or
non-covalent yet stable fashion in order to ensure high levels
of
enantio-discrimination. Here, we report the first generation of
a
DNA-based catalyst bound to a cellulose matrix. The chiral
bio-
material is commercially available, trivial to use, fully
recyclable and
produces high levels of enantioselectivity in various
Cu(II)-catalyzed
asymmetric reactions including FriedelCrafts alkylations and
Michael additions. A single-pass, continuous-flow process is
also
reported affording fast conversions and high
enantioselectivities at
low catalyst loadings thus offering a new benchmark in the field
of
DNA-based asymmetric catalysis.
DNA-based asymmetric catalysis offers great promise in the
advance-ment of enantioselective artificial biohybrid-mediated
catalysis. Intro-duced in 2005 by Roelfes and Feringa,1 the concept
has been sincethen successfully applied to a wide variety of
copper(II)-catalyzedcarboncarbon, carbonheteroatom and
carbonhalogen bond form-ing reactions.214 While still in its early
stage, the field is rapidlyexpanding with studies dedicated to DNA
secondary structures,1518
DNA solvatation1921 and to new anchoring strategies.2225 In
thiscontext, we recently reported the first example of a
left-helical enantio-selective induction using L-nucleic acids.
This method allowed reliableand predictable access to both
enantiomers for a given reaction.26
With the prospect of being used widely by both academic
andindustrial organic chemists, DNA-based asymmetric catalysis
is
now facing scale and catalyst-recovery issues. While up to2.4
mmol scale reactions have been reported albeit using largeamounts
of DNA,6,19 there is to the best of our knowledge only oneexample
featuring a recyclable solid-supported DNA. Indeed, Park,Sugiyama
and co-workers recently synthesized an ammonium-functionalized
silica that was used to immobilize salmon testesDNA (st-DNA)
through electrostatic interactions.27 Evaluated in
theenantioselective DielsAlder reaction, both the conversion and
theees were in the range of those obtained using standard
st-DNA.
In our search for a robust, cheap and reusable
solid-supportedstrategy, we turned our attention to
cellulose-supported DNA(CS-DNA, Fig. 1).28 Indeed, the cellulose
frameworks have attracteda lot of attention over the years due to
their favourable biophysicalproperties, biocompatibility, low
immunogenicity, relatively highresistance to temperature and
relatively low cost. Interestingly,however, while CS-DNA has been
widely used to either purifysequence-specific DNA-binding
proteins29 or to determine bindingconstants for non-specific
interactions between proteins andDNA,30 there are no examples of
DNA-based asymmetric catalysisinvolving a cellulose-supported DNA
scaffold. This is all themore peculiar that double-stranded calf
thymus DNA (ct-DNA)covalently attached to cellulose is nowadays
commercially avail-able from several suppliers. Combined, all these
propertiesmade cellulose a particularly appealing solid support
withpotential use in DNA-based asymmetric catalysis; we report
herethe results of our endeavours.
Fig. 1 A cellulose-supported (CS) ct-DNA/Cu(dmbpy) biohybrid
forDNA-based asymmetric catalysis. [NuH = indoles,
dimethylmalonate].
a Laboratoire de Chimie Organique, Institute of Chemistry,
Biology and Innovation (CBI) - ESPCI ParisTech/CNRS
(UMR8231)/PSL*
Research University, 10 rue Vauquelin, 75231 Paris Cedex 05,
France.
E-mail: [email protected] NOXXON Pharma AG,
Max-Dohrn-Strasse 8-10, 10589 Berlin, Germanyc Institut des
Biomolecules Max Mousseron UMR 5247 CNRS-Universites
Montpellier
1 et 2 Place Eugene Bataillon, 34095 Montpellier, France.
E-mail: [email protected]
Electronic supplementary information (ESI) available: Details of
experimentalprocedures, 1H NMR and 13C NMR spectra as well as SFC
chromatograms. SeeDOI: 10.1039/c4cc10190a
Received 20th December 2014,Accepted 11th January 2015
DOI: 10.1039/c4cc10190a
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In order to evaluate the efficacy of CS-ct-DNA in
DNA-basedasymmetric catalysis, we first tested the Cu(II)-catalyzed
FriedelCrafts alkylation of a,b-unsaturated 2-acyl imidazole 1a
(0.6 mmol)with 5-methoxyindole (3.0 mmol). The reaction was
performed in a20 mMMOPS buffer (pH 6.5) in the presence of
4,40-dimethyl-2,20-bipyridine (dmbpy, 36 mol%), Cu(NO3)2 (30 mol%)
and 163 mg ofthe cellulose-supported double-stranded ct-DNA (4.3 mg
of ct-DNAper g of cellulose) over 3 days at 5 1C. Both the
conversion and theee of the resulting product were determined by
supercritical fluidchromatography (SFC) analysis. To our delight
complete conver-sion of the starting enone was observed and the
resulting productwas obtained in 81% ee (Table 1, entry 1), which
was comparablewith the result obtained with unsupported ct-DNA (80%
ee, Table 1,entry 2). To ensure that the selectivity obtained was
solely due to thesupported catalyst and not from any residual DNA
that could havepotentially leaked from the solid support, the
cellulose was filtered,washed with a 20 mM MOPS buffer solution and
re-engaged in asecond experiment under otherwise identical
conditions. Onceagain, the reaction afforded full conversion of 1a
to the corres-ponding FriedelCrafts product 2a with no noticeable
loss in eitherreactivity or selectivity. Following these initial
results and in order toprove that the cellulose itself did not
induce the selectivity due to itsinherent chirality, a control
experiment using standard cellulosewas undertaken; the reaction
yielded compound 2a in only 12% ee(Table 1, entry 3). An additional
reaction performed with CS-ct-DNAin the absence of dmbpy showcased
the importance of the ligandnot only as the product formed in a
lower yield but also with barelyany selectivity (Table 1, entry
4).
With these conditions in hand the reaction was eventuallyapplied
to a variety of indoles with different substitutionpatterns (Table
1, entries 57) as well as to a number ofa,b-unsaturated 2-acyl
imidazoles (Table 1, entries 812). As ageneral trend, the reaction
tolerated both C3-aliphatic andaromatic substituents on the enone
as the correspondingFriedelCrafts products were obtained in
essentially quantita-tive yield and with ees ranging from 50% to
83% after 3 days at5 1C. It is worth pointing out however that
higher levels ofconversion and selectivity were obtained when
electron-richindoles were used in conjunction with enones bearing
an aliphaticsubstituent at the C3 position (Table 1, entries 1 and
8).
Prompted by these results, the CS-ct-DNA was also applied tothe
Michael addition of dimethylmalonate (Table 2). Once again,the
products were obtained in high yields and excellent
enantios-electivities ranging from 81% to 97%, even though enones
bearingan electron-poor aromatic substituent appeared to be less
reactive.
In order to fully investigate the robustness of the catalystand
therefore its recyclability, a series of Cu(II)-catalyzed
FriedelCrafts alkylations were performed using a,b-unsaturated
2-acylimidazole 1a and 5-methoxyindole under the standard
condi-tions (20 mMMOPS buffer, pH 6.5, 5 1C, 3 days). After each
run,the reaction was filtered and the cellulose was washed with a20
mM MOPS buffer before being re-used. Interestingly, thisrecycling
procedure could be repeated only up to two timesbefore a slight
decrease of the selectivity (4% loss on every cycle)could be
observed. This prompted us to consider that the use ofadditional Cu
and dmbpy in every run could be detrimental if
the Cu(dmbpy) complex was to remain incorporated into theDNA
after each filtration. A control experiment using a
recycledCS-ct-DNA in the absence of additional Cu and dmbpy
affordedfull conversion of the starting enone without any
noticeable lossof reactivity or selectivity. Remarkably, under
these conditionsthe cellulose could be recycled up to 10 times
without adding anyCu or dmbpy at every run (Fig. 2).31 Considering
the amount ofCS-ct-DNA and Cu(dmbpy) complex used in the process,
thiscellulose-supported approach is clearly advantageous as the
Table 1 FriedelCrafts alkylation with CS-ct-DNA
Entry Product Conversiona (%) eea (%)
1 499 812b 499 803c 499 12
4d 60 45 499 73
6 96 66
7 34 78
8 499 83
9 499 73
10 499 62
11 80 54
12 499 50
13 499 76
14 25 65
Conditions: 2 mM base pair solution of DNA in a 20 mMMOPS
solution(400 mL; pH 6.5), 0.3 mM of Cu(dmbpy)(NO3)2 in a 20 mM
MOPSsolution (200 mL), 0.5 M solution of enone in CH3CN (1.2 mL),
2.5 Msolution of indole in CH3CN (1.2 mL), 3 d, 5 1C.
a Determined bysupercritical phase chromatography (SFC)
analysis. b Reaction runusing unsupported ct-DNA. c Reaction run
using DNA-free cellulose.d Reaction run in the absence of
dmbpy.
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6078 | Chem. Commun., 2015, 51, 6076--6079 This journal isThe
Royal Society of Chemistry 2015
entire catalytic system is recycled, thus highlighting the
potentialof DNA-cellulose for large-scale applications.27
Having demonstrated the efficacy of our immobilized DNA-based
biohybrid catalyst in the context of asymmetric catalysis,we next
set out to implement the method to a continuous-flowprocess.32,33
The experimental setup consisted of a low-pressurechromatography
column which was loaded with the CS-ct-DNA-Cu(dmbpy) biohybrid
catalyst and connected to a syringe pumpused to feed the reactor
with the reagents. As no reaction takes placein the absence of the
Cu(dmbpy) complex, we were able to pumpboth reagents together in a
20 mM MOPS buffer/MeOH (30 :1)solution.34 It is worth emphasizing
however that this ratio wascritical to prevent any loss of
selectivity as, for a reason that stillremains unclear, higher
amounts of MeOH led to lower ees. More-over, in order to be
effective, we needed to determine the amount of
CS-ct-DNA-Cu(dmbpy) biohybrid catalyst as well as the optimal
flow-rate required for the reaction to complete after a single run
across thecolumn.When performing the reaction on a 0.03mmol scale
using a1.1 g cartridge of CS-ct-DNA at a flow-rate of 0.25 mL min1,
thecorresponding FriedelCrafts product was obtained in 80% ee
albeitin only 60% yield (Table 3, entry 1). By decreasing the
flow-rate to0.125 mL min1 and doubling the length of the column
(2.2 gcartridge of CS-ct-DNA), 83% of the starting material were
convertedwith virtually the same selectivity (Table 3, entry 2).
Eventually, the useof a 4.4 g cartridge of CS-ct-DNA under
otherwise identical conditionsled to roughly complete conversion of
the starting enone and thealkylated product was obtained in 92%
yield and 79% ee (Table 3,entry 3). Finally, increasing the
reaction scale by a factor of 10appeared not to be detrimental in
terms of both conversion andselectivity as the desired
FriedelCrafts product was isolated in 89%yield and 78% ee (Table 3,
entry 4).
In summary, we have developed a particularly
appealingcellulose-supported DNA-based catalyst that offers high
levels ofenantioselectivity on various Cu(II)-catalyzed asymmetric
reactionsincluding FriedelCrafts alkylations and Michael additions.
Thesystem has various advantages. Indeed, the chiral biomaterial
iscommercially available, particularly robust and trivial to use.
Inaddition, the Cu(dmbpy) complex bound to the CS-ct-DNA can
befully recycled after each run with no noticeable loss of
reactivity orselectivity. Most importantly, the CS-ct-DNA-Cu(dmbpy)
biohybridcatalyst can be implemented in a single-pass,
continuous-flowprocess allowing us to perform the reactions on a
syntheticallyuseful scale using low catalyst loadings. Considering
that thegrafting can be performed on any selected sequence and
DNAconfiguration, these results will undoubtedly contribute to
thedevelopment and generalization of DNA-based asymmetric
catalysis.
This research was supported by the Ministere de lEnseigne-ment
Superieur et de la Recherche and the Agence Nationale dela
Recherche (NCiS; ANR-2010-JCJC-715-1).
Notes and references1 (a) G. Roelfes and B. L. Feringa, Angew.
Chem., Int. Ed., 2005, 44,
32303232; (b) A. J. Boersma, B. L. Feringa and G. Roelfes, Org.
Lett.,2007, 9, 36473650.
2 D. Coquiere, B. L. Feringa and G. Roelfes, Angew. Chem., Int.
Ed.,2007, 46, 93089311.
Fig. 2 Investigation of the reusability of the
CS-ct-DNA-Cu(dmbpy) bio-hybrid catalyst.
Table 2 FriedelCrafts alkylation with CS-ct-DNA
Entry Product Conversiona (%) eea (%)
1 92 97
2 14 96
3 499 81
4 68 93
5 25 89
Conditions: 2 mM base pair solution of DNA in a 20 mMMOPS
solution(400 mL; pH 6.5), 0.3 mM of Cu(dmbpy)(NO3)2 in a 20 mM
MOPSsolution (200 mL), 0.5 M solution of enone in CH3CN (1.2 mL),
purmalonate (6.9 mL), 3 d, 5 1C. a Determined by supercritical
phasechromatography (SFC) analysis.
Table 3 CS-ct-DNA-catalysed FriedelCrafts under
continuous-flow
EntryScale(mmol)
Flow rate(mL min1)
CS-ct-DNA(g)
Residencetime (min)
Conversiona
(%)eeb
(%)
1 0.03 0.25 1.1 5 60 802 0.03 0.125 2.2 19 83 793 0.03 0.125 4.4
38 96 (92c) 794 0.3 0.125 4.4 38 96 (89c) 78
Conditions: CS-Cu(dmbpy)-ct-DNA packed in a 4 g MPLC cartridge(+
= 13 mm; L = 65 mm). a Determined by NMR on the crude
reactionmixture. b Determined by supercritical phase chromatography
(SFC)analysis. c Isolated yield.
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34 The addition of a small amount of MeOH was necessary in order
toobtain a homogeneous solution of both reactants without
observingany loss of selectivity (see ESI for more details).
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