Structure of a complex formed by a protein and a helical aromatic oligoamide foldamer at 2.1 ? resolution

Article abstract of DOI:10.1002/anie.201309160

In the search of molecules that could recognize sizeable areas of protein surfaces, a series of ten helical aromatic oligoamide foldamers was synthesized on solid phase. The foldamers comprise three to five monomers carrying various proteinogenic side chains, and exist as racemic mixtures of interconverting right-handed and left-handed helices. Functionalization of the foldamers by a nanomolar ligand of human carbonic anhydrase II (HCA) ensured that they would be held in close proximity to the protein surface. Foldamer-protein interactions were screened by circular dichroism (CD). One foldamer displayed intense CD bands indicating that a preferred helix handedness is induced upon interacting with the protein surface. The crystal structure of the complex between this foldamer and HCA could be resolved at 2.1 ? resolution and revealed a number of unanticipated protein-foldamer, foldamer-foldamer, and protein-protein interactions. To design a foldamer that binds to a protein surface, a strategy is proposed that uses a known protein ligand to tether the foldamer to the protein surface. Candidates are first screened for induced circular dichroism in presence of the protein. Then, structural information about foldamer-protein interactions is collected before strong binding is established. The crystal structure of human carbonic anhydrase (A, B chains) with helical aromatic amide foldamers (stick models) is shown. Copyright

Full text of DOI:10.1002/anie.201309160

Angewandte
Chemie
DOI: 10.1002/anie.201309160
Foldamer–Protein Interactions
Structure of a Complex Formed by a Protein and a Helical Aromatic
Oligoamide Foldamer at 2.1 ꢀ Resolution**
Jꢀrꢀmie Buratto, Cinzia Colombo, Marine Stupfel, Simon J. Dawson, Christel Dolain,
Bꢀatrice Langlois dꢁEstaintot, Lucile Fischer, Thierry Granier, Michel Laguerre,
Bernard Gallois,* and Ivan Huc*
In memory of Frꢀdꢀric Denonne
Abstract: In the search of molecules that could recognize
sizeable areas of protein surfaces, a series of ten helical
aromatic oligoamide foldamers was synthesized on solid
phase. The foldamers comprise three to five monomers
carrying various proteinogenic side chains, and exist as racemic
mixtures of interconverting right-handed and left-handed
helices. Functionalization of the foldamers by a nanomolar
ligand of human carbonic anhydrase II (HCA) ensured that
they would be held in close proximity to the protein surface.
Foldamer–protein interactions were screened by circular
dichroism (CD). One foldamer displayed intense CD bands
indicating that a preferred helix handedness is induced upon
interacting with the protein surface. The crystal structure of the
complex between this foldamer and HCA could be resolved at
2.1 ꢂ resolution and revealed a number of unanticipated
protein–foldamer, foldamer–foldamer, and protein–protein
interactions.
defined structure in solution, appear as potent candidates to
serve as scaffolds bearing proteinogenic side chains that
would recognize protein surfaces.[7] In addition, foldamers
generally show high resistance towards enzymatic degrada-
tion and represent attractive alternatives to peptidic and
oligonucleotidic backbones. But the question remains: how to
arrange individual proteinogenic side chains at the surface of
a foldamer to target a given protein surface? Efforts towards
this goal have largely concerned the development of a-helix
mimetics,[8] combining structure-based design and the screen-
ing of small foldamer libraries.[9] But the targeting of large
surfaces not complementary to a discrete protein secondary
motif remains elusive. A major hurdle lies in the fact that
detailed structural information about interactions between
foldamers, or other medium-size molecules, and proteins is
very scarce.[8i,k,10] In the absence of good lead compounds to
form complexes that could be subjected to structural analysis
and also in the absence of structural information to help
designing good ligands, the discovery of foldamers to bind
protein surfaces meets a sort of deadlock.
To solve this problem, we reasoned that it may be possible
to obtain structural information about interactions at a folda-
mer–protein interface even in the absence of strong binding,
provided some sort of attachment would link the two. For this
purpose, helical aromatic oligoamide foldamers[11] based on 8-
amino-2-quinolinecarboxylic acid (Q, see Scheme 1b)
appeared to be suitable. They feature highly stable confor-
mations in protic media.[12,13] Monomers can be equipped with
proteinogenic side chains and oligomers can be prepared
using solid-phase synthesis (SPS).[14] Though they have not yet
M
ost proteins operate as complexes or within networks of
interactions with other proteins.[1] The recognition of protein
surfaces and the inhibition of protein–protein interactions
(PPIs) thus offer innumerable opportunities for the develop-
ment of pharmacological tools or therapeutic agents. Yet they
have remained extremely challenging objectives. Indeed,
protein surfaces only rarely possess grooves or well-defined
active sites that could be targeted by small molecules.[2] In
recent years, PPI inhibitors have thus been developed using
large molecules such as other proteins,[3] and in particular
antibodies,[4] or aptamers.[5] Synthetic foldamers,[6] because of
their medium size (typically in the 0.5–5 kDa range) and well-
[*] J. Buratto,[+] Dr. C. Colombo,[+] Dr. M. Stupfel, Dr. S. J. Dawson,
Dr. C. Dolain, Dr. B. Langlois d’Estaintot, Dr. L. Fischer,
Dr. T. Granier, Dr. M. Laguerre, Dr. B. Gallois, Dr. I. Huc
Universitꢀ de Bordeaux, CBMN, UMR 5248
Institut Europꢀen de Chimie Biologie
2 rue Robert Escarpit 33607 Pessac (France)
and
Predoctoral fellowships to J. B. and M. S.) and by the French
Ministry of Research (Predoctoral fellowships to J. B. and M. S.). We
thank researchers from Foldappi participants UCB-Pharma, Univ.
Bordeaux 1 and Univ. Wꢁrzburg for valuable preliminary work and
stimulating discussions. SPR measurements were carried out with
the help of Dr. C. Di Primo on the technical platform of IECB
(UMS3033/US001). We thank Dr. T. Deschrijver for providing
precursors of QTyr and QHyd and Dr. B. Kauffmann for synchrotron
diffraction measurements of the protein structures. We thank the
ESRF for provision of synchrotron radiation facilities and the staff of
the ID 23-2 beamline for their kind assistance during data
collections.
CNRS, CBMN, UMR5248 (France)
and
Institut Polytechnique de Bordeaux, UMR5248 (France)
E-mail: b.gallois@cbmn.u-bordeaux.fr
i.huc@iecb.u-bordeaux.fr
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201309160.
[**] This work was supported by European Grant FP7-IAPP-2008-
230662-Foldappi (Post-doctoral fellowships to C.C. and S.D.,
Angew. Chem. Int. Ed. 2014, 53, 883 –887
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
883

.
Angewandte
Communications
linker, which was inserted to allow the foldamer some
freedom to position itself at the protein surface. A method
was then developed to attach the aliphatic amine of 3 to the
N-terminal aromatic amine of a quinoline oligoamide chain
on the solid phase. The terminal 8-aminoquinoline was
activated on the Wang resin by using triphosgene, and
amine 3 was then added to form a urea. In the following, we
designate such inhibitor–urea–oligoamide constructs as
Inh-Qn (Scheme 1a).
Proteinogenic side chains were attached by ether or
thioether functions to the quinoline position 4; the side chains
attached in this position point towards the outside of the
helices. Monomers are designated QXxx using the Xxx three-
letter code of analogous a-amino acids when available. All
Fmoc-QXxxx monomers were prepared on a multigram scale in
4 or 5 steps and overall yields ranged from 20 to 60%, when
starting from a common 8-nitro-4-(1H)-quinolinone precur-
sor. We used the previously described Fmoc-QLeu, Fmoc-QAsp
,
and Fmoc-QOrn acid precursors, the latter two having their
side chain protected as tert-butyl ester and tert-butyloxycar-
bonyl (Boc) amine, respectively.[14] We also introduced four
new residues. To prepare Fmoc-QPhe, CuSO4/NaBH4 proved
to be efficient to reduce the 8-nitro-quinoline precursor into
the corresponding amine while preserving the benzyl ether
function. Monomer QHyd possesses a simple 4-hydroxy residue
that was protected by a trifluoroacetic acid (TFA)-labile para-
methoxybenzyl ether (PMB) during SPS. The PMB group
resisted H2/Pd–C reduction of the 8-nitro-quinoline in the
presence of pyridine.[20] In Fmoc-QTyr, an acid-stable thioether
was used to attach the side chain to the quinoline; the
thioether was formed by aromatic nucleophilic substitution of
a 4-bromoquinoline precursor. The hydrogenation of the 8-
nitro group was possible in this case too. NH4HCO2/Pd–C
gave better results than H2/Pd–C. Fmoc-QAla caused no
particular difficulty and indeed, the final compound could be
afforded in excellent purity in a simple precipitation.
To screen different foldamers for their interactions with
the surface of HCA, ten sequences were prepared by SPS,[14]
all having an appended HCA inhibitor (Scheme 1c). Crude
oligomers are typically obtained in 60–90% purity. Side chain
deprotection and cleavage from the resin was carried out in
95:2.5:2.5 TFA/iPr3SiH/H2O (vol/vol/vol). Sequences were
purified by reversed-phase HPLC and obtained in 30–80%
yield from initial Wang resin loadings. The choice of side
chains of 4–13 was intended to be diverse. Most sequences
carry a mix of charged and hydrophobic residues. A
prevalence of QAsp was favored owing to the abundance of
positively charged residues in the vicinity of the HCA active
site.
Scheme 1. a) Inhibitor constructs; b) QXxx monomers; c) Inh-Qn fol-
damers synthesized by SPS.
been shown to interact with proteins, tight binding to G-
quadruplex DNA has been demonstrated.[15] In addition,
helical aromatic oligoamides possess a remarkable ability to
form single crystals even when their size exceeds 5 kDa,[16]
thus allowing the hope of crystallizing protein–foldamer
conjugates. We thus endeavored to prepare foldamers teth-
ered to a protein ligand in order to crystallize a protein–
ligand–foldamer complex and find a structural basis from
which to tailor foldamer–protein interactions. As a relevant
background to this study, previous examples described the
exploration of protein binding properties by using recognition
groups, including large peptides, attached to a protein
ligand.[17] In the following, we report the design and structure
elucidation at 2.1 ꢀ resolution of a helical aromatic oligo-
amide foldamer–protein complex mediated by a protein
ligand.
Human carbonic anhydrase II (HCA) was selected as
a model target because it is commercial, relatively easy to
crystallize, and because structurally simple benzene sulfon-
amide nanomolar inhibitors can be readily prepared.[17,18]
Benzyl 4-aminosulfonylbenzamide (1; Scheme 1) has a KD
value of approximately 2 nm[17b,19] and has been cocrystallized
in complex with the HCA active site, its sulfonyl group being
coordinated to the Zn2+ ion of the enzyme.[19] Examination of
this structure hinted at the preference for a functionalization
of the benzyl group in the meta position to extend this
inhibitor out of the binding pocket and covalently attach
a foldamer. We prepared inhibitor 2 (see the Supporting
Information) and confirmed its suitability by a crystal struc-
ture at 1 ꢀ resolution of its complex with HCA, which
crystallized in the classical P21 lattice and showed the phenol
function pointing straight out of the binding site (protein
database entry: 4MTY). We thus prepared inhibitor 3,
possessing an aliphatic amine at the end of an n-butyloxy
Importantly, sequences 4–13 do not carry any stereogenic
center and thus exist as a mixture of right- (P) and left- (M)
handed enantiomeric helical conformers. Qn sequences were
kept short (3 to 5 residues) to allow helix handedness
inversion to occur in solution. Indeed, helix stability rises so
quickly upon increasing oligomer length[12b] that longer
sequences do not undergo any equilibrium in protic
media.[13] We then used circular dichroism (CD) as a prelimi-
nary screen. All compounds 4–13 were expected to have
a high affinity for HCA imparted by their inhibitor moiety.
884
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 883 –887

Angewandte
Chemie
However, the desired interactions between the foldamer helix
and the protein, if they existed, would be diastereoselective
and thus induce a preferred handedness in the helical
oligomer backbone.[15a,21]
present in the asymmetric unit (Figure 2a). The final model
shows a continuous (2mFo-DFc) electron density map,
contoured at 1.0 s, all along both A and B HCA chains
The CD spectra of 4–13 were recorded in the presence of
HCA and monitored over time to allow inversion of helix
handedness to occur. For the CD signal to stabilize two days
were necessary for sequences having 3 or 4 monomers and
five days were necessary for sequences having 5 monomers.
HCA does not absorb between 300–500 nm. Thus, CD bands
in this region could be assigned to the quinoline chromo-
phores. All CD spectra but one showed very weak bands
indicating only marginal effects of the protein surface on
foldamer handedness (Figure 1a). In contrast, an intense CD
Figure 1. a) CD spectra of 4–13 (34.5 mm in 50 mm aqueous phosphate
buffer, pH 7.4) in the presence of HCA (34.5 mm) at 208C, at
equilibrium; b) SPR sensorgrams (gray line) in 2:98 DMSO/aqueous
PBS pH 7.4 (vol/vol) at 258C. Increasingly concentrated solutions of 5
(250–500–1000 nm, top) and 3 (62.5–125–250 nm, bottom) were
flowed over the HCA surface sequentially at 25 mLminÀ1 for 60 s.
Curve fitting (dotted black line) assuming a Langmuir 1:1 model
yielded kon =2.8ꢂ104 mÀ1 sÀ1 and koff =1.5ꢂ10À4 sÀ1 for 5;
k
on =1.5ꢂ106 mÀ1 sÀ1, koff =7.7ꢂ10À3 sÀ1 for 3.
band emerged at 390 nm in the spectrum of 5. Comparison of
the De390 value (40 LmolÀ1 cmÀ1 for 4 residues) with those of
related oligomers[22] suggested that an almost complete
handedness bias of 5 towards a P helix had taken place
upon confinement to the protein surface. Weak induced CD
for 4 and 6–13 does not allow us to rule out foldamer–protein
interactions, but reveals no P-versus-M helix selectivity.
These compounds were thus not further investigated.
The binding of 5 to HCA was characterized by surface
plasmon resonance (SPR).[23] Kinetic titration assays[24] were
first performed with model compound 3 on HCA immobi-
lized on the chip, and gave a KD value of approximately 5 nm
(Figure 1). Foldamer 5 showed an almost identical KD value
but its kon and koff rates were both 50 times smaller than for 3.
This slow binding and dissociation confirms that interactions
take place between the foldamer and HCA, independent
from the Inh part of 5.
Cocrystals of the HCA–5 complex were obtained by the
hanging-drop technique and its structure was solved at 2.1 ꢀ
resolution (protein database entry: 4LP6). The complex
crystallizes in space group P21 but the packing is unprece-
dented among over 400 reported HCA structures. The unit
cell volume is twice that of the search model and of the HCA–
2 complex, so that two independent HCA–5 subunits are
Figure 2. Crystal structure of the HCA–5 complex. a) Asymmetric unit
showing two HCA molecules in pale yellow (chain A) and green (chain
B), two Inh-QLeuQHydQOrnQAsp molecules (5) in CPK representation and
Zn2+ ions as purple spheres. ZnI and ZnII are involved in interactions
between HCA chains A and B. ZnV and ZnVI belong to catalytic centers;
b) foldamer backbones shown in sticks and contoured by 2 mFo-DFc
density maps at 1s level. ZnIII and ZnIV take part in protein–foldamer
interactions; c) contacts between the hydrophobic side chain of QLeu
(green), the linker of the Inh of the other foldamer (yellow) and
hydrophobic HCA residues (gray); d) ZnIII (purple sphere) and its
ligands. A neighbor QHyd hydroxy group is found in a distal position.
Distances are shown in ꢃ.
Angew. Chem. Int. Ed. 2014, 53, 883 –887
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
885

.
Angewandte
Communications
(from residues 4 to 260) and the two well-defined Inh-Q4
molecules (Figure 2b). As with other HCA structures no
density is observed for the three first N-terminal residues of
each chain.
These multiple foldamer–protein and protein–protein
interactions do not alter the overall HCA structure. Indeed,
the A and B chains are similar to each other (average r.m.s
deviation on 257 Ca positions: 0.23 ꢀ; largest r.m.s deviation:
0.93 ꢀ), and similar to the native protein (average and largest
Ca r.m.s deviations when superimposing HCA–5 to the model
are 0.31 ꢀ and 0.95 ꢀ for chain A, 0.33 ꢀ and 1.14 ꢀ for chain
B, respectively). The reciprocal is also true: the main-chain
helix of the foldamer is not altered by the multiple inter-
actions its side chains, its inhibitor moiety, and its terminal
carboxylate engage with the protein.
Altogether, the above results validate the strategy pro-
posed in this study. Anchoring a foldamer to a modified
inhibitor does not drastically change the KD value, which
remains in the nanomolar range. Accurate structural infor-
mation quickly revealed intricate interactions between fol-
damers, proteins, and Zn2+ ions and an unexpected and
unprecedented dimerization. Multiple suggestions for
improvements and controls can be proposed from the
structure of HCA–5. Can the QOrn and QAsp residues of 5 be
modified to enhance foldamer–protein interactions? Can the
QHyd residue be modified to complete the coordination sphere
of the foldamer–protein Zn2+ bridge? The crystals grew at
a concentration of the HCA–5 complex of 150 mm, which hints
at a reasonable stability of the dimeric structure. Yet, this
stability and its dependence on Zn2+ concentration should be
assessed in solution. Investigations along these lines are in
progress and will be reported in due course.
The structure reveals the formation of a novel pseudo C2-
symmetrical HCA dimer (Figure 2a) involving new protein–
protein contacts, foldamer–protein interactions, and folda-
mer–foldamer interactions. Within a dimer, protein–protein
interactions occur through two water molecules hydrogen
bonded to Ser172 residues of chains A and B and by two Zn2+
bridges (Figure S2). Coordination spheres involve Lys171 and
Glu233 of one chain and Asp174 of the other chain. For one of
these bridges, an additional ligand, Glu26 from a symmetry-
related chain B, is also involved. Within the crystal lattice,
contacts between dimers are in limited number, which may
explain a high value (51.5 ꢀ2) for the average temperature
factor.
As expected, the inhibitor moieties are bound to the HCA
active sites in a conventional manner, with the sulfonamide
group coordinated to the catalytic zinc, the benzenesulfon-
amide ring stacked over Leu197, and the benzyl ring in an
edge-to-face arrangement with Phe130 (Figure 2c). The
foldamers protrude from the protein surface and adopt
right-handed conformations, in agreement with CD spectra.
The foldamer bound to chain A is more disordered (higher
temperature factor values, QOrn and QAsp side chains not
observed in density map) than that bound to chain B. The
active sites of HCA chains A and B face each other, thereby
allowing a direct contact between the foldamers that contrib-
utes to the dimerization. The inhibitor-foldamer linkers are in
an extended conformation. As a result, each foldamer extends
beyond the HCA chain to which its inhibitor moiety is bound
and establishes interactions with the other HCA chain. In
addition, the two foldamers stack to clip into one another.
Stacking interactions occur through the first quinoline units in
each sequence (QLeu), which are found to be coplanar
(average distance between rings: 3.46 ꢀ) and rotated by
almost 908. The helix axes of the two foldamers deviate by
only 78.
Received: October 20, 2013
Published online: November 29, 2013
Keywords: circular dichroism · crystallography · foldamers ·
.
protein recognition · solid-phase synthesis
[1] a) T. Berggꢁrd, S. Linse, P. James, Proteomics 2007, 7, 2833;
b) W. E. Stites, Chem. Rev. 1997, 97, 1233.
[2] J. A. Wells, C. L. McLendon, Nature 2007, 450, 1001; T. Berg,
Angew. Chem. 2003, 115, 2566; Angew. Chem. Int. Ed. 2003, 42,
2462.
At its C-terminal part, each helix interacts with the
opposite HCA chain through a Zn2+ cation coordinated in
[3] Representative examples: a) M. G. Kolonin, R. L. Finley, Jr.,
Proc. Natl. Acad. Sci. USA 1998, 95, 14266; b) R. Woodman,
J. T.-H. Yeh, S. Laurenson, P. K. Ferrigno, J. Mol. Biol. 2005, 352,
1118; c) S. L. LaPorte, C. M. Forsythe, B. C. Cunningham, L. J.
Miercke, D. Akhavan, R. M. Stroud, Proc. Natl. Acad. Sci. USA
2005, 102, 1889; d) T. Robson, I. F. James, Drug Discovery Today
2012, 17, 544; e) Y. Ji, S. Majumder, M. Millard, R. Borra, T. Bi,
A. Y. Elnager, N. Neamati, A. Shekhtman, J. A. Camarero, J.
Am. Chem. Soc. 2013, 135, 11623.
[4] Reviews of this subject: a) L. Sanz, B. Blanco, L. ꢂlvarez-
Vallina, Trends Immunol. 2004, 25, 1471; b) P. Holliger, P. J.
Hudson, Nat. Biotechnol. 2005, 23, 1126; c) E. B. De Souza, S. T.
Cload, P. S. Pendergrast, D. W. Y. Sah, Neuropsychopharmacol-
ogy 2009, 34, 142; d) ꢂ. M. Cuesta, N. Sainz-Pastor, J. Bonet, B.
Oliva, L. ꢂlvarez-Vallina, Trends Biotechnol. 2010, 28, 355.
[5] Examples: a) R. Conrad, L. M. Keranen, A. D. Ellington, A. C.
Newton, J. Biol. Chem. 1994, 269, 32051; b) R.-H. Huang, D. H.
Fremont, J. L. Diener, R. G. Schaub, J. E. Sadler, Structure 2009,
17, 1476; c) Y. S. Choi, J. Hur, H. K. Lee, S. Jeong, FEBS Lett.
2009, 583, 1415; d) J. B. Madsen, D. M. Dupont, T. B. Andersen,
A. F. Nielsen, L. Sang, D. M. Brix, J. K. Jensen, T. Broos, M. L. V.
a
square-based pyramidal geometry (Figure 2d). The
involved ligands are the main-chain C-terminal carboxylate
moiety of the last quinoline, the His4 and His64 imidazole
rings, and a water molecule. Cooperative metal binding by
His4 and an HCA ligand had been hypothesized by others in
earlier studies and is validated here.[17f] The hydroxy group of
QHyd is found at a distal position in the Zn2+ coordination
sphere (mean dZn–O = 3.8 ꢀ). The role of Zn2+ in foldamer–
protein and protein–protein contacts seems to be essential to
crystal packing. No crystal growth was observed in the
absence of zinc acetate. When observed (foldamer bound to
chain B), the polar QAsp and QOrn side chains are found to be
hydrogen bonded to the opposite protein chain through
bridging water molecules. The QLeu side chain is the only one
that is clearly observed for both foldamers and involved in
direct interaction with the protein, as it faces a hydrophobic
environment involving Pro201, Leu203, the linker, and the
phenyl ring of the inhibitor (Figure 2c).
886
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 883 –887

Angewandte
Chemie
Hendrickx, A. Christensen, J. Kjems, P. A. Andreasen, Bio-
chemistry 2010, 49, 4103; e) V. M. Tesmer, S. Lennarz, G. Mayer,
J. J. G. Tesmer, Structure 2012, 20, 1300; f) T. Mashima, F.
Nishikawa, Y. O. Kamatari, H. Fujiwara, M. Saimura, T. Nagata,
T. Kodaki, S. Nishikawa, K. Kuwata, M. Katahira, Nucleic Acids
Res. 2013, 41, 1355.
[12] a) H. Jiang, J.-M. Lꢄger, I. Huc, J. Am. Chem. Soc. 2003, 125,
3448; b) N. Delsuc, T. Kawanami, J. Lefeuvre, A. Shundo, H.
Ihara, M. Takafuji, I. Huc, ChemPhysChem 2008, 9, 1882.
[13] T. Qi, V. Maurizot, H. Noguchi, T. Charoenraks, B. Kauffmann,
M. Takafuji, H. Ihara, I. Huc, Chem. Commun. 2012, 48, 6337.
[14] B. Baptiste, C. Douat-Casassus, K. Laxmi-Reddy, F. Godde, I.
Huc, J. Org. Chem. 2010, 75, 7175.
[6] G. Guichard, I. Huc, Chem. Commun. 2011, 47, 5933.
[7] a) H. Yin, A. D. Hamilton, Angew. Chem. 2005, 117, 4200;
Angew. Chem. Int. Ed. 2005, 44, 4130; b) V. Azzarito, K. Long,
N. S. Murphy, A. J. Wilson, Nat. Chem. 2013, 5, 161; c) B.
Baptiste, F. Godde, I. Huc, ChemBioChem 2009, 10, 1765.
[8] a) H. S. Park, Q. Lin, A. D. Hamilton, J. Am. Chem. Soc. 1999,
121, 8; b) O. Kutzki, H. S. Park, J. T. Ernst, B. P. Orner, H. Yin,
A. D. Hamilton, J. Am. Chem. Soc. 2002, 124, 11838; c) J. A.
Kritzer, J. A. Lear, M. E. Hodsdon, A. Schepartz, J. Am. Chem.
Soc. 2004, 126, 9468; d) J. D. Sadowsky, M. A. Schmitt, H.-S. Lee,
N. Umezawa, S. Wang, Y. Tomita, S. H. Gellman, J. Am. Chem.
Soc. 2005, 127, 11966; e) R. Fasan, R. L. A. Dias, K. Moehle, O.
Zerbe, D. Obrecht, P. R. E. Mittl, M. G. Grꢃtter, J. A. Robinson,
ChemBioChem 2006, 7, 515; f) J. P. Plante, T. Burnley, B.
Malkova, M. E. Webb, S. L. Warriner, T. A. Edwards, A. J.
Wilson, Chem. Commun. 2009, 5091; g) J. Michel, E. A. Harker,
J. Tirado-Rives, W. L. Jorgensen, A. Schepartz, J. Am. Chem.
Soc. 2009, 131, 6356; h) J. A. Robinson, ChemBioChem 2009, 10,
971; i) E. F. Lee, J. D. Sadowsky, B. J. Smith, P. E. Czabotar, K. J.
Peterson-Kaufman, P. M. Colman, S. H. Gellman, W. D. Fairlie,
Angew. Chem. 2009, 121, 4382; Angew. Chem. Int. Ed. 2009, 48,
4318; j) C. G. Cummings, A. D. Hamilton, Curr. Opin. Chem.
Biol. 2010, 14, 341; k) M. D. Boersma, H. S. Haase, K. J.
Peterson-Kaufman, E. F. Lee, O. B. Clarke, P. M. Colman, B. J.
Smith, S. W. Horne, W. D. Fairlie, S. H. Gellman, J. Am. Chem.
Soc. 2012, 134, 315.
[15] a) P. S. Shirude, E. R. Gillies, S. Ladame, F. Godde, K. Shin-ya, I.
Huc, S. Balasubramanian, J. Am. Chem. Soc. 2007, 129, 11890;
b) L. Delauriꢅre, Z. Dong, K. Laxmi-Reddy, F. Godde, J.-J.
Toulmꢄ, I. Huc, Angew. Chem. 2012, 124, 488; Angew. Chem. Int.
Ed. 2012, 51, 473.
[16] a) N. Delsuc, J.-M. Lꢄger, S. Massip, I. Huc, Angew. Chem. 2007,
119, 218; Angew. Chem. Int. Ed. 2007, 46, 214; b) N. Delsuc, S.
Massip, J.-M. Lꢄger, B. Kauffmann, I. Huc, J. Am. Chem. Soc.
2011, 133, 3165.
[17] a) A. Jain, S. G. Huang, G. M. Whitesides, J. Am. Chem. Soc.
1994, 116, 5057; b) A. Jain, G. M. Whitesides, R. S. Alexander,
D. W. Christianson, J. Med. Chem. 1994, 37, 2100; c) T.
Andersson, M. Lundquist, G. T. Dolphin, K. Enander, B.-H.
Jonsson, J. W. Nilsson, L. Baltzer, Chem. Biol. 2005, 12, 1245;
d) L. T. Tegler, K. Fromell, B.-H. Jonsson, J. Viljanen, C.
Winander, J. Carlsson, L. Baltzer, ChemBioChem 2011, 12,
559; e) K. Enander, G. T. Dolphin, L. Baltzer, J. Am. Chem. Soc.
2004, 126, 4464; f) A. L. Banerjee, M. Swanson, B. C. Roy, X. Jia,
M. K. Haldar, S. Mallik, D. K. Srivastava, J. Am. Chem. Soc.
2004, 126, 10875.
[18] V. M. Krishnamurthy, G. K. Kaufman, A. R. Urbach, I. Gitlin,
K. L. Gudiksen, D. B. Weibel, G. M. Whitesides, Chem. Rev.
2008, 108, 946.
[19] C. Kim, J. S. Chang, J. B. Doyon, T. T. Baird, C. A. Fierke, A.
Jain, D. W. Christianson, J. Am. Chem. Soc. 2000, 122, 12125.
[20] H. Sajiki, H. Kuno, K. Hirota, Tetrahedron Lett. 1997, 38, 399.
[21] Y. Ferrand, A. M. Kendhale, B. Kauffmann, A. Grꢄlard, C.
Marie, V. Blot, M. Pipelier, D. Dubreuil, I. Huc, J. Am. Chem.
Soc. 2010, 132, 7858.
[22] A. M. Kendhale, L. Poniman, Z. Dong, K. Laxmi-Reddy, B.
Kauffmann, Y. Ferrand, I. Huc, J. Org. Chem. 2011, 76, 195.
[23] a) D. G. Myszka, Anal. Biochem. 2004, 329, 316; b) G. A. Papalia
et al., Anal. Biochem. 2006, 359, 94.
[24] a) R. Karlsson, P. S. Katsamba, H. Nordin, E. Pol, D. G. Myszka,
Anal. Biochem. 2006, 349, 136; b) C. Di Primo, J. Mol. Recognit.
2008, 21, 37; c) W. Palau, C. Masante, M. Ventura, C. Di Primo,
RNA 2013, 19, 982.
[9] a) W. S. Horne, M. D. Boersma, M. A. Windsor, S. H. Gellman,
Angew. Chem. 2008, 120, 2895; Angew. Chem. Int. Ed. 2008, 47,
2853; b) A. Shaginian, L. R. Whitby, S. Hong, I. Hwang, B.
Farooqi, M. Searcey, J. Chen, P. K. Vogt, D. L. Boger, J. Am.
Chem. Soc. 2009, 131, 5564.
[10] a) J. T. Nguyen, C. W. Turck, F. E. Cohen, R. N. Zuckermann,
W. A. Lim, Science 1998, 282, 2088; b) R. E. McGovern, H.
Fernandes, A. R. Khan, N. P. Power, P. B. Crowley, Nat. Chem.
2012, 4, 527.
[11] a) I. Huc, Eur. J. Org. Chem. 2004, 17; b) D.-W. Zhang, X. Zhao,
J.-L. Hou, Z.-T. Li, Chem. Rev. 2012, 112, 5271.
Angew. Chem. Int. Ed. 2014, 53, 883 –887
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
887