A pH-sensitive lasso-based rotaxane molecular switch

Article abstract of DOI:10.1002/chem.201203597

The synthesis of a pH-sensitive two-station [1]rotaxane molecular switch by self-entanglement of a non-interlocked hermaphrodite molecule, containing an anilinium and triazole moieties, is reported. The anilinium was chosen as the best template for the macrocycle benzometaphenylene[25]crown-8 (BMP25C8) and allowed the self-entanglement of the molecule. The equilibrium between the hermaphrodite molecule and the pseudo[1]rotaxane was studied by ¹H NMR spectroscopy: the best conditions of self-entanglement were found in the less polar solvent CD₂Cl₂ and at high dilution. The triazole moiety was then benzylated to afford a benzyltriazolium moiety, which then played a dual role. On one hand, it acts as a bulky gate to trap the BMP25C8, thus to avoid any self-disentanglement of the molecular architecture. On another hand, it acts as a second molecular station for the macrocycle. At acidic pH, the BMP25C8 resides around the best anilinium molecular station, displaying the lasso [1]rotaxane in a loosened conformation. The deprotonation of the anilinium molecular station triggers the shuttling of the BMP25C8 around the triazolium moiety, therefore tightening the lasso. Molecular lasso: The synthesis of a [1]rotaxane molecular switch has been realized by self-entanglement of a hermaphroditic molecule. This is composed of an anilinium template (see figure, green ball) on a molecular tail, which is linked to a BMP25C8 macrocyclic head (red wheel). The trapping of the structure could be achieved by using triazolium (pink ball) as a molecular station and gate at the same time. A variation in pH triggers the tightening and loosening of the lasso. Copyright

Full text of DOI:10.1002/chem.201203597

DOI: 10.1002/chem.201203597
A pH-Sensitive Lasso-Based Rotaxane Molecular Switch
Caroline Clavel, Camille Romuald, Emile Brabet, and Frꢀdꢀric Coutrot*[a]
Abstract: The synthesis of a pH-sensi-
scopy: the best conditions of self-en-
tanglement were found in the less
polar solvent CD2Cl2 and at high dilu-
tion. The triazole moiety was then ben-
zylated to afford a benzyltriazolium
moiety, which then played a dual role.
On one hand, it acts as a bulky gate to
trap the BMP25C8, thus to avoid any
self-disentanglement of the molecular
tive two-station [1]rotaxane molecular
switch by self-entanglement of a non-
interlocked hermaphrodite molecule,
containing an anilinium and triazole
moieties, is reported. The anilinium
was chosen as the best template for the
macrocycle benzometaphenylene[25]-
crown-8 (BMP25C8) and allowed the
self-entanglement of the molecule. The
equilibrium between the hermaphro-
dite molecule and the pseudo[1]rotax-
ane was studied by 1H NMR spectro-
architecture. On another hand, it acts
as a second molecular station for the
macrocycle. At acidic pH, the
BMP25C8 resides around the best ani-
linium molecular station, displaying the
lasso [1]rotaxane in a loosened confor-
mation. The deprotonation of the ani-
ACHUTNGRENlNUG inACHTUNGTRENiNNGU um molecular station triggers the
shuttling of the BMP25C8 around the
triazolium moiety, therefore tightening
the lasso.
Keywords: crown complexes · las-
so · molecular switch · self-entan-
glement · rotaxanes
Introduction
edge, no lasso molecular-machine, based on a [1]rotaxane
molecular architecture and exhibiting a large amplitude
movement, has been reported to date. However, new lasso-
type structures with changeable conformations triggered by
external stimuli appear to be appealing targets, especially
because the properties of a molecule are well known to rely
tremendously on its topology.[10] Bioactive molecules found
in nature, like lasso-peptides, demonstrate the utility of such
an interlocked lasso architecture. Indeed, the natural lasso-
peptides, which consist of 16–21 amino acid residues, share a
lasso structure that is responsible for the biological activity
as a receptor antagonist or an enzymatic inhibitor.[11]
As part of our study devoted to the synthesis of inter-
locked molecular machines, we were interested in the syn-
thesis of lasso-based molecular architectures. With this aim,
we recently reported the synthesis of a unique pH-sensitive
double-lasso rota-macrocycle from an ends-activated
[c2]daisy chain building-block.[6] Here we present the syn-
thesis of a new mono-lasso-based molecular switch by using
a self-entanglement strategy[12] of a “hermaphrodite” mole-
cule; this molecule is composed of a benzometaphenyl-
Stimuli-responsive multicomponent molecular machines
have been the subject of many efforts during the past dec-
ACHTUNGTRENNUNGades, especially in designing new interlocked molecular ar-
chitectures, new sites of interactions and in improving the
efficiency of template-synthesis. Interlocked architectures,
such as rotaxanes,[1] catenanes,[2] foldaxanes,[3] molecular
muscles,[4] molecular turnstiles,[5] molecular jump-rope,[6] mo-
lecular springs,[7] and so on, have been synthesized and uti-
lized as molecular machines by controlling the movement of
one of the different interlocked components upon a specific
stimulus. Among these structures, pseudo[1]rotaxanes, which
consist of a macrocycle covalently linked to a molecular
axle that can be threaded or not in a reversible manner,
have been rather intensively studied.[8] On the contrary, the
synthesis of [1]rotaxanes, in which no equilibrium takes
place with their non-interlocked analogues, have been the
subject of only a few reports.[9] To the best of our knowl-
AHCTUNGTREGeNNNU ne[25]crown-8 (BMP25C8) macrocyclic head and a molecu-
[a] Dr. C. Clavel, Dr. C. Romuald, E. Brabet, Dr. F. Coutrot
Supramolecular Machines and
ARchitectures Team (SMART)
Institut des Biomolꢀcules
lar tail containing an anilinium template moiety for the
BMP25C8 and terminated by a bulky di-tert-butylphenyl ex-
tremity. In the smaller dibenzo[24]crown-8 macrocycle
(DB24C8), the triethylene glycol substituents are in ortho
positions to each other on the aromatic rings, so that
DB24C8 interacts perfectly with the ammonium moieties.
On the contrary, the BMP25C8 displays a bigger cavity
holding the tail and the glycol substituents of one aromatic
ring in the meta position to each other. Even though the af-
finity of the anilinium template[13] for the BMP25C8 ap-
peared to be weaker than for the DB24C8, interlocking was
Max Mousseron (IBMM)
–UMR CNRS 5247
Universitꢀ Montpellier 2 et 1
place Eugꢁne Bataillon, case courrier 1706
34095 Montpellier Cedex 5 (France)
Fax : (+33)4-67-63-10-46
E-mail: frederic.coutrot@univ-montp2.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203597.
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Chem. Eur. J. 2013, 19, 2982 – 2989

FULL PAPER
possible in some specific conditions by self-entanglement of
the non-interlocked hermaphrodite molecule including the
anilinium template and a triazole moiety. The subsequent
benzylation of the triazole allowed, at the same time, for the
creation of a second site of interactions for the BMP25C8
and for the trapping of the lasso structure by hindering the
axle between the anilinium template and the BMP25C8.
Variations in pH were then envisaged to obtain a tightened
or a loosened lasso.
anilinium moiety, which could then freely interact with the
BMP25C8 macrocycle. This was achieved by using a solution
of hydrochloric acid in diethyl ether, followed by a counter-
anion exchange, and led, after silica gel chromatographic
column, to a mixture of uncomplexed thread 4u and pseu-
do[1]rotaxane 4 in 93% yield. The presence of the bulky di-
tert-butyl anilinium extremity prevented the tail of the mole-
cule to thread the macrocycle. However, the meta substitu-
tion of the aromatic ring of the macrocycle allowed for its
rotation around the two carbon–oxygen s bonds (blue
arrows in Scheme 1), causing the self-entanglement of the
compound. Interestingly, this self-entanglement equilibrium
between 4 and 4u, could be displaced either upon variation
in solvent polarity or concentration.
Results and Discussion
The uncomplexed thread 3 was almost quantitatively pre-
pared from the previously synthesized macrocycle azide 1
and the N-Boc protected aniline alkyne 2 by using the cop-
per(I)-catalyzed Huisgen alkyne–azide 1,3-dipolar cycloaddi-
1
The ratio 4/4u was easily determined by H NMR spec-
ACHUTNGERNtNUG rosAHCTUNGTRNENcUGN opy; because the equilibrium between pseudo[1]rotax-
ane 4 and uncomplexed thread 4u appeared to be slow on
1
tion in the presence of Cu
G
the NMR timescale, one family of H NMR signals for each
tidine (0.1 equiv)[14] (Scheme 1). The subsequent deprotec-
compound was detected (Table 1 and Figures 1 and 2). The
tion of the N-Boc moiety in an acidic medium revealed the
Table 1. Ratio between [1]rotaxane 4 and uncomplexed thread 4u de-
pending on both concentration and solvent.
C (4/4u) [m][a]
[D6]DMSO
CD3OD
CD3CN
CD2Cl2
5ꢃ10À2
5ꢃ10À3
5ꢃ10À4
–
–
4:96
–
–
23:77
36:64
45:55
0:100
–
14:86
–
[a] Based on the integration of the 1H NMR signal corresponding to H10.
formation of the pseudo[1]rotaxane 4 proved to be depend-
ent on the solvent polarity (Figure 1). Unsurprisingly, in the
more polar [D6]DMSO solvent (Figure 1a), no self-entangle-
ment was observed, due to the high solvation of the anilini-
um template by DMSO, preventing from any kind of inter-
actions between the BMP25C8 and the anilinium template.
Traces of pseudo[1]rotaxane 4 were detected in CD3OD
(Figure 1b), whereas the amount of interlocked compound 4
is no longer negligible in CD3CN (Figure 1c) and significant
in the less polar solvent CD2Cl2 (Figure 1d).
Variation in the concentration in CD2Cl2 was then realiz-
ed to determine the best parameters for the self-entangle-
ment of 4. The 1H NMR experiments at three concentra-
tions are reported in Figure 2. It appeared that the forma-
tion of the pseudo[1]rotaxane 4 proved also to be concentra-
tion-dependent. The best experimental conditions of lasso
formation were found at the lowest concentration and in the
less polar solvent (i.e., CD2Cl2 at 5ꢃ10À4 m; Table 1). The
pseudo[1]rotaxane was generated in a 45% ratio, which is
less than the complexation that could be observed with the
smaller DB24C8 macrocycle, in optimized conditions, by
using the usual di-component threading method.[15] The
meta substitutions of one aromatic ring of the BMP25C8,
which cause a bigger cavity of the macrocycle and orientate
the two phenoxy-oxygen atoms outside its cavity, should ac-
count for the lowering of the hydrogen-bonding interactions
between the BMP25C8 and the anilinium. However, and
contrary to the smaller macrocycle, here it could take ad-
Scheme 1. Synthesis of the lasso-based molecular switch 5 and its non-in-
terlocked analogue 5u.
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F. Coutrot et al.
Figure 2. 1H NMR spectra (600 MHz, 298 K) of compounds 4/4u in
CD2Cl2 at: a) 5ꢃ10À2 m, b) 5ꢃ10À3 m, and c) 5ꢃ10À4 m. The lettering and
numbering correspond to the proton assignments indicated in Scheme 1.
The green color corresponds to the lasso compound 4, whereas the
orange color corresponds to compound 4u.
Figure 1. 1H NMR spectra (600 MHz, 298 K) of a mixture of compounds
4/4u at 5ꢃ10À3
in: a) [D6]DMSO, b) CD3OD, c) CD3CN, and
m
d) CD2Cl2. The lettering and numbering correspond to the proton assign-
ments indicated in Scheme 1. The green color corresponds to the lasso
compound 4, whereas the orange color corresponds to compound 4u.
BMP25C8. This was also demonstrated by synthesizing 5u
in 84% yield from the N-Boc thread 3. By using this multi-
step synthetic strategy, no self-entanglement could be possi-
ble as long as compound 3 contains no template moiety for
BMP25C8. Unmasking the anilinium template after the ben-
zylation of the triazole did not cause any self-entanglement,
signifying the absence of any equilibrium between 5u and 5.
Nevertheless, conversion of [1]rotaxane 5 to a mixture of
pseudo[1]rotaxane 4 and thread 4u could be easily achieved
by hydrogenolysis.
vantage of the bigger size of the cavity to self-entangle the
structure.
Incorporation of a bulky gate[16] in the thread was subse-
quently realized to trap the macrocycle around the thread
and to prevent the structure from any self-disentanglement.
This was achieved by benzylation of the triazole moiety,
with the additional aim to create a second molecular station
for the BMP25C8. To favor the formation of the lasso struc-
ture, the triazole moiety was benzylated at a very low con-
centration (<5ꢃ10À4 m) by slowly adding a solution of 4/4u
in CH2Cl2 over a period of 24 h to a very large excess of
benzyl bromide dissolved in dichloromethane. After stirring
for a further 48 h, benzyl triazoliums 5 and 5u were recov-
ered separately after chromatographic columns in yields of
27 and 38%, respectively. No self-disentanglement of the
lasso structure 5 towards thread 5u was noticed by NMR
spectroscopy, regardless of the solvent used, demonstrating
the role of stopper of the benzyl side-chain for the
Variations in pH were then envisaged to tighten and
loosen the lasso structure 5 (Scheme 2). At acidic pH, the
BMP25C8 resides around the best anilinium molecular sta-
Scheme 2. Actuation of the lasso-based molecular switch 5/6 by variation
of pH.
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Rotaxane Molecular Switch
FULL PAPER
lesser extent H10–12 are all shifted upfield (respectively Dd=
À0.45 and À0.16; À0.20; À0.24 ppm), because they experi-
ence the shielding effect of the aromatic rings of the
BMP25C8. Eventually, an unexpected slight downfield shift
of H8 was observed in 5 (Dd=0.17 ppm), which could be at-
tributed to an interaction by hydrogen bonding between H8
and the oxygen atom of the amide moiety. This interaction
is certainly allowed by the spatial proximity of the two
atoms, due to the bent structure.
After the deprotonation of [1]rotaxane 5, the BMP25C8
moves from its initial localization and tightens the lasso
structure. It is noteworthy that absolutely no uncomplexed
thread 6u was observed after deprotonation, which corrobo-
rates the already discussed fact that no self-disentanglement
can be possible when a benzyl gate is covalently linked to
the triazolium moiety. The new deprotonated tightened
lasso structure can be explained by the direct comparison of
1
the H NMR spectra of [1]rotaxanes 5 and 6. (Figure 3, b
and c) Obviously, the signals corresponding to hydrogens
H15, H18, and H20 are all shifted upfield since they all under-
go the deprotonation of the anilinium station and the dis-
placement of the macrocycle. Although we expected to ob-
serve a downfield shift of the triazolium hydrogen H8, as al-
ready mentioned by us with DB24C8 in [2]rotaxane archi-
tectures,[13b] an upfield shift of H8 (Dd=À0.38 ppm) was in-
stead detected. Actually, we suggest that the bigger
BMP25C8 macrocycle does not allow any efficient hydrogen
bond with the triazolium moiety, due to the meta substitu-
tion of the aromatic ring, which displays the two phenoxy
groups of the crown ether too far away from the inside
BMP25C8 cavity. Moreover, the two catechol alkoxy groups
(i.e., in the ortho position) of the other aromatic ring of the
BMP25C8 cannot interact through a hydrogen bond with H8
because the benzyl group held by the triazolium can only be
situated outside the lasso cavity due to its bulkiness, which
is not compatible with a close spatial arrangement between
H8 and these oxygen atoms. Hydrogen H8 rather experiences
a shielding effect of the aromatic rings of the BMP25C8,
with no more hydrogen bonding with the oxygen atom of
the amide. At the same time, whereas hydrogens HJ, HA, HB
belonging to the BMP25C8 experience a shielding effect of
the benzyltriazolium moiety (respectively Dd=À0.37, À0.12
and À0.17 ppm), hydrogen HI is deshielded (Dd=0.60 ppm)
since it no longer experiences the strong shielding effect of
the aniline extremity. In 6, the shuttling of the BMP25C8
toward the triazolium moiety is corroborated by the fact
that the benzylic hydrogens H26 are shielded by the aromatic
rings of the BMP25C8 (Dd=À0.42 ppm). The same trend is
observed for hydrogens H5, H6, and H7 (Dd=À0.14, À0.26,
and À0.38 ppm, respectively). Meanwhile, displacement of
the BMP25C8 toward the triazolium site causes a deshield-
ing of hydrogens H11–H14 (respectively Dd=0.34, 0.50, 0.71,
and 0.18 ppm).
Figure 3. 1H NMR spectra (600 MHz, CD2Cl2, 298 K) of: a) the protonat-
ed non-interlocked thread 5u; b) the protonated lasso-based compound
5; c) the deprotonated lasso-based compound 6; d) the deprotonated
non-interlocked thread 6u. The coloring, lettering, and numbering corre-
spond to the proton assignments indicated in Scheme 2.
tion. This was confirmed by the direct comparison between
1
the H NMR spectra of the non-interlocked thread 5u and
the [1]rotaxane 5 (Figure 3, a and b).
1
In the H NMR spectrum of [1]rotaxane 5, the NMR sig-
nals of the methylenic hydrogens HC–H and the aromatic hy-
drogens HA–B of the BMP25C8 are split, revealing the inter-
locked architecture. Indeed, in this structure, they are facing
the two non-symmetrical extremities of the encircled molec-
ular axle. The hydrogen HI belonging to the BMP25C8 is
importantly shifted upfield (Dd=À0.75 ppm) in the rotax-
ane 5, as it experiences the shielding effect of the anilinium
aromatic ring. This is consistent with the localization of the
macrocycle around the anilinium station. It is also corrobo-
1
rated by the appearance of the H NMR signal for the hy-
1
drogens H16 at very high chemical shift (d=8.64 ppm) in 5,
and by the downfield shift of hydrogens H15 (Dd=0.27 ppm)
caused by their interaction through hydrogen bonds with the
oxygen atoms of the crown ether. Furthermore, H13 and in a
The direct comparison between the H NMR spectra of
the tightened lasso-based [1]rotaxane 6 and of its uncom-
plexed analogue 6u corroborates the localization of the
BMP25C8. (Figure 3, c and d) In the [1]rotaxane 6, the
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F. Coutrot et al.
chemical shifts of hydrogens H5–8 are more or less shifted
upfield (Dd=À0.20, À0.16, À0.34 and À0.12 ppm, respec-
tively) due to their localization in the shielding cavity of the
aromatic rings of the BMP25C8. At the same time, the
chemical shift of hydrogens HJ, and in a lesser extent HI, are
shifted upfield (Dd=À0.37 and À0.09 ppm, respectively)
due to their localization in the shielding cavity of the ben-
zyltriazolium unit. Eventually, the benzyl hydrogens H26 are
rather importantly shielded (Dd=À0.36 ppm) by the aro-
matic rings of the BMP25C8 in lasso compound 6.
BMP25C8 around the anilinium site. The same spatial prox-
imity is observed for hydrogens H2 and H8 pointing out the
looped backbone, which displays these two hydrogens face
to face. At the same time, no correlation peaks are observed
between the methylenic hydrogens HH–C of the BMP25C8
with the triazolium part of the molecular lasso.
By comparison with 5, the 2D-ROESY 1H NMR spectrum
appears very different for the deprotonated lasso 6 and
demonstrates the shuttling of the BMP25C8 around the tria-
zolium moiety triggering the tightening of the lasso. Indeed,
the new correlation peaks observed now respectively con-
cern the hydrogens H10, H11, H12 (belonging to the alkyl
chain), H26 and H8 (belonging to the triazolium site) with
the methylenic hydrogens HC–H of the BMP25C8. Similarly,
the hydrogens HB and HJ, belonging to the aromatic rings of
the BMP25C8, are spatially close to the hydrogen H7 in 6.
All these observations are supported by the position of hy-
drogen HI of the BMP25C8, which was correlated with H18
in 5, and with H10, H11, and H12 in 6.
All these observations in relation to the tightening or the
loosening of the lasso upon pH variation were confirmed by
ROE spectroscopy on a Bruker Avance III spectrometer
(600 MHz) (Figures 4 and 5).
1
The ROESY H NMR experiment of the protonated lasso
5 is reported in Figure 4. The correlation peaks, which are
highlighted by blue-cyan frames, reveal the localization of
the BMP25C8 around the anilinium station. In particular,
the correlation peaks observed between respectively the hy-
drogens H13, H14, H15, H18, and the methylenic hydrogens
HC–H of the BMP25C8 indicate the localization of the
Conclusion
We have described a straight-
forward synthesis of a lasso-
based [1]rotaxane from a her-
maphrodite
non-interlocked
precursor. Formation of an in-
termediate interlocked pseu-
do[1]rotaxane occurred by self-
entanglement through the rota-
tion of a meta-substituted aro-
matic ring of the BMP25C8
around two s-bonds. The best
conditions to obtain these pseu-
do[1]rotaxanes were found to
be in the non-polar solvent di-
chloromethane and at the high-
est dilution. Although the ani-
ACHUTNGRENNUlG inACHTUNTGRNEiNUGN um group is not a very good
template moiety for the large
size of the BMP25C8, the pseu-
do[1]rotaxane could be detect-
1
ed by H NMR spectroscopy in
a 45% ratio. Furthermore, ben-
zylation of the triazole enabled
us to trap the macrocycle and
isolate the [1]rotaxane molecu-
lar architecture. Therefore, the
benzyltriazolium played the
dual role of molecular station
and gate for the BMP25C8: on
one hand it interacts with the
BMP25C8, whereas on the
other hand, it avoids any disas-
sembly of the interlocked struc-
ture. At acidic pH, the lasso
Figure 4. 1H NMR ROESY experiment (600 MHz, 298 K, CD2Cl2) of the protonated [1]rotaxane 5. The color-
ing, lettering, and numbering correspond to the proton assignments indicated in Scheme 2.
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Rotaxane Molecular Switch
FULL PAPER
nolic solution of 10% sulphuric acid,
ninhydrine, or KMNO4, followed by
heating. 1H NMR and 13C NMR spec-
tra were obtained on a Bruker DRX-
400 and Bruker Avance III spectrome-
ters (at 400.13 MHz or 600.13 MHz,
and 100.62 MHz or 150.95 MHz, re-
spectively). The chemical shifts of the
1H NMR and 13C NMR spectra are
given by using CHCl3, CH3CN or
CH2Cl2 as references (for 1H spec-
trum: 7.27, 1.94, and 5.32 ppm, respec-
tively, and for 13C
spectrum:
77.00 ppm, 118.26 ppm and 54 ppm, re-
spectively). Coupling constants (J) are
reported in Hertz (Hz). Standard ab-
breviations
were used as follows: s (singlet), br
(broad), (doublet), (triplet), q
indicating
multiplicity
d
t
(quartet), and m (multiplet). High-res-
olution mass spectra (HRMS) and
mass spectra were recorded on a Q-
TOF Micro (water) apparatus.
Compound
3:
CuACHTGNUTER(NNUG CH3CN)4PF6
(746 mg, 2 mmol, 1 equiv) and 2,6-luti-
dine (23 mL, 0.2 mmol, 0.1 equiv) were
added successively to a solution of the
azido macrocycle 1 (1.233 g, 2 mmol,
1 equiv) and the alkyne
2 (911 mg,
2.2 mmol, 1.1 equiv) in dry CH2Cl2
(10 mL). The mixture was stirred for
24 h at RT. The solvent was evaporat-
ed under vacuum and the crude prod-
uct was directly purified by chroma-
tography on a silica gel column (sol-
vent gradient elution CH2Cl2/acetone
80:20 to 70:30) to give compound 3
Figure 5. 1H NMR ROESY experiment (600 MHz, 298 K, CD2Cl2) of the deprotonated [1]rotaxane 6. The col-
oring, lettering, and numbering correspond to the proton assignments indicated in Scheme 2.
(2.03 g, 98%) as a white foam. Rf 0.40
(CH2Cl2/acetone 80:20); 1H NMR
(300 MHz, CD3CN, 298 K): d=7.49 (s,
1H, H8), 7.29 (t, 1H, 4JH20–H18 =1.6 Hz, H20), 7.04–6.99 (m, 3H, H18 H1),
6.95–6.85 (m, 6H, HA HB HJ), 6.77 (t, 1H, 4JHI–HJ =2.1 Hz, HI), 4.27 (t,
2H, 3JH7–H6 =7.1 Hz, H7), 4.21–4.13 (m, 4H, HH), 4.10–4.02 (m, 4H, HC),
3.80–3.68 (m, 8H, HD HG), 3.62 (s, 8H, HE HF), 3.64–3.55 (m, 2H, H15),
3.32–3.23 (m, 2H, H2), 2.66–2.53 (br t, 2H, H10), 1.89–1.76 (m, 2H, H6),
1.63–1.42 (m, 6H, H3 H11 H14), 1.39 (s, 9H, H25), 1.29 (s, 9H, H22), 1.36–
1.23 ppm (m, 8H, H4 H5 H12 H13); 13C NMR (150 MHz, CD3CN, 298 K):
d=167.5 (CK), 161.1, 149.6, and 138.3 (CIV arom BMP25C8), 155.6 (C23), 152.2
(C19), 143.3 (C17), 122.5, 122.4, and 115.2 (C8 C18 CA CB), 120.7 (C20),
107.4 (CJ), 106.3 (CI), 80.2 (C24), 71.4 and 71.3 (CE CF), 70.5 and 70.3 (CD
CG), 69.3 and 69.2 (CC CH), 51.4 (C7), 50.7 (C15), 40.3 (C2), 35.6 (C21), 31.7
(C22), 30.6 (C6), 28.7 (C25), 30.0, 29.5, 29.1, 27.1, 26.9, and 26.8 (C3 C4 C5
C10 C11 C12 C13 C14); HRMS (ESI): [M+H]+ calcd for C58H88N5O11:
1030.6480, found: 1030.6470.
displayed a loosened shape in which the BMP25C8 is local-
ized around the anilinium molecular station. After deproto-
nation of the anilinium, the macrocycle shuttles around the
triazolium station, thus tightening the lasso structure.[17] To
the best of our knowledge, the molecular switch 5/6 consti-
tutes the first example of a pH-sensitive mono-lasso struc-
ture. An extension to the peptidic series by incorporating
amino acid residues in the backbone of such a lasso molecu-
lar switch is in progress: less or more bending of the peptide
should give rise to the modulation of the bio-properties of
an active peptidic sequence depending on the pH stimulus.
Pseudo[1]rotaxane 4 and thread 4u from 3: A solution of HCl 1m in
Et2O (20 mL, 20 mmol, 11 equiv) was added to a solution of compound 3
(1.814 g, 1.76 mmol, 1 equiv) in CH2Cl2 (5 mL). The mixture was stirred
for 30 min before being evaporated to give a yellow foam. The solid was
diluted in CH2Cl2 (40 mL). NH4PF6 (717 mg, 4.4 mmol, 2.5 equiv) and
H2O milliQ (20 mL) were added to this solution and the biphasic solution
was stirred vigorously for 20 min. The aqueous layer was extracted with
CH2Cl2 (ꢃ3) and the combined organic layers were dried over MgSO4
and concentrated to give compounds 4/4u (1.748 g, 93%) as a white
foam. Rf 0.60 (CH2Cl2/acetone 70:30). HRMS (ESI): m/z calcd for
C53H80N5O9: 930.5956 [M+H]+; found: 930.5938.
Experimental Section
General: All reactions were performed under an atmosphere of argon
unless otherwise indicated. All reagents were purchased from Aldrich
and were used as received without further purification. The preparations
and characterizations of the macrocycle 1 and the threads 5u and 6u are
described in the Supporting Information. The N-carbamoylated aniline
alkyne 2 has been synthesized according to the experimental procedure
previously described by Coutrot et al.[18] Dichloromethane was distilled
over P2O5 and was degassed by bubbling Ar gas for 20 min. Analytical
thin-layer chromatography (TLC) was performed on Merck silica gel 60
F254 plates. Compounds were visualized by dipping the plates in an etha-
Thread 4u from 5: Pd/C (10%, 20 mg) and 2 drops of NEt3 were added
to a solution of rotaxane 5 (20 mg, 0.015 mmol, 1 equiv) in EtOH (5 mL)
were added. The reaction mixture was stirred at RT under H2 for 24 h.
Chem. Eur. J. 2013, 19, 2982 – 2989
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2987

F. Coutrot et al.
The reaction mixture was then filtered through celite and concentrated
to give compound 4u (16 mg, quantitative) as a white foam.
24.0 ppm (C10); HRMS (ESI): calcd for C60H87F6N5O9P: 1166.6095
[MÀPF6]+, found: 1166.6146.
Uncomplexed form 4u: 1H NMR (600 MHz, 5.10À2 m in CD2Cl2, 298 K):
d=7.47 (s, 1H, H8), 7.45 (s, 1H, H20), 7.30 (s, 2H, H18), 6.92–6.87 (m, 4H,
HA HB), 6.87 (br t, 1H, HI), 6.83 (d, 2H, 4JHJÀHI =1.9 Hz, HJ), 6.74 (br t,
1H, H1), 4.33 (t, 2H, 3JH7ÀH6 =6.6 Hz, H7), 4.13–4.10 (m, 4H, HH), 4.10–
4.07 (m, 4H, HC), 3.79–3.73 (m, 8H, HD HG), 3.66 (s, 8H, HE HF), 3.37 (t,
2H, 3JH15–H14 =7.4 Hz, H15), 3.31 (q, 2H, 3JH2–H3 =3JH2–H1 =6.7 Hz, H2),
2.67 (t, 2H, 3JH10–H11 =7 Hz, H10), 1.94–1.84 (m, 2H, H6), 1.81–1.74 (m,
2H, H14), 1.65–1.59 (m, 2H, H11), 1.58–1.52 (m, 2H, H3), 1.44–1.37 (m,
2H, H13), 1.35–1.24 (m, 6H, H4 H5 H12), 1.29 ppm (s, 18H, H22);
13C NMR (150 MHz, 5.10À2 m in CD2Cl2, 298 K): d=168.6(CK), 160.9,
[1]rotaxane 6: A solution of the [1]rotaxane 5 (52 mg, 0.040 mmol,
1 equiv) in CH2Cl2 (10 mL) was washed with an aqueous solution of
NaOH 1m (2ꢃ5 mL). After extraction of the aqueous layer with CH2Cl2
(10 mL), the combined organic layers were dried over MgSO4 and evapo-
rated to obtain the deprotonated [1]rotaxane 6 (43 mg, 94%) as a white
foam. Rf 0.50 (CH2Cl2/Acetone 70:30); 1H NMR (600 MHz, 5.10À3 m in
CD2Cl2, 298 K): d=8.09 (s, 1H, H8), 7.49–7.39 (m, 3H, H29 H30), 7.07–
7.02 (m, 2H, H28), 6.85–6.79 and 6.72–6.67 (2 m, 4H, HA HB), 6.75 (s, 1H,
H20), 6.66 (s, 2H, HJ), 6.56 (s, 1H, HI), 6.50 (s, 2H, H18), 6.37 (br t, 1H,
3
H1), 5.28 (s, 2H, H26), 4.22 (t, 2H, JH7–H6 =6 Hz, H7), 4.25–4.10 and 3.95–
3.87 and 3.87–3.81 (3 m, 8H, HH HC), 4.09–4.04 and 3.94–3.88 and 3.70–
3.63 (3 m, 8H, HD HG), 3.76–3.69 and 3.69–3.63 and 3.61–3.56 (3 m, 8H,
HE HF), 3.43–3.37 (m, 2H, H2), 3.22 (t, 2H, 3JH15ÀH14 =6.9 Hz, H15), 2.59
(t, 2H, 3JH10ÀH11 =7.9 Hz, H10), 1.91–1.85 (m, 2H, H6), 1.80–1.72 (m, 4H,
H11 H14), 1.66–1.59 (m, 2H, H3), 1.60–1.55 (m, 4H, H12 H13), 1.39–1.32
(m, 2H, H4), 1.29 (s, 18H, H22), 1.25–1.19 ppm (m, 2H, H5); 13C NMR
(150 MHz, 5.10À2 m in CD2Cl2, 298 K): d=166.6 (CK), 160.8, 160.4, 148.8,
149.1 and 137.0 (CIV
BMP25C8), 154.2 (C19), 147.5 (C17), 129.5 or 128.7
arom
(C9), 123.0 (C20), 122.5 (C8), 122.3 and 115.2 (CA CB), 116.4 (C18), 107.2
(CJ), 106.5 (CI), 71.1 and 71.0 (CE CF), 70.5 and 69.9 (CD CG), 69.1 and
68.9 (CC CH), 53.2 (C15), 50.9 (C7), 40.6 (C2), 35.6 (C21), 31.5 (C22), 30.3
(C6), 29.5 (C3), 29.3 (C11), 28.2 (C12), 26.6 (C14), 26.7 and 26.3 (C4 C5),
26.1 (C13), 25.1 ppm (C10).
Pseudo[1]rotaxane 4: 1H NMR (600 MHz, 5.10À2 m in CD2Cl2, 298 K):
d=8.65 (br s, 2H, H16), 7.53 (s, 1H, H20), 7.52 (s, 1H, H8), 7.42 (s, 2H,
and 137.4 (CIVÀarom BMP25C8), 152.2 (C19), 149.6 and 149.0 (CIVÀarom
BMP25C8
and C17), 146.6 (C9), 132.4 (C27), 129.8 and 129.7 (C29 C30), 129.0 (C8),
128.7 (C28), 122.2, 122.1, and 114.1 (CA CB), 112.0 (C20), 107.9 (C18), 107.6
(CI), 104.8 (CJ), 71.7, 71.5, 71.4, 71.3, and 71.2 (CE CF), 70.5, 70.4, and
70.0 (CD CG), 69.5, 68.9, and 68.6 (CC, CH), 54.8 (C7), 54.0 (C26), 44.6
(C15), 40.5 (C2), 35.3 (C21), 31.8 (C22), 30.3 (C14), 30.1, 28.0, and 27.9 (C6
C12 C13), 28.1 (C3), 27.1 (C4), 26.7 (C5), 26.3 (C11), 23.5 (C10); HRMS
(ESI): m/z calcd for C60H87F6N5O9P: 1166.6156 [M+H]+; found:
1166.6146.
4
H18), 6.97–6.93 and 6.90–6.86 (2 m, 4H, HA HB), 6.94 (d, 2H, JHJ–HI
=
2 Hz, HJ), 6.68 (br t, 1H, H1), 6.20 (br t, 1H, HI), 4.37–4.34 (m, 2H, H7),
4.42–4.14 and 4.06–4.02 (2 m, 8H, HH HC), 3.98–3.93, 3.85–3.81, and 3.79–
3.63 (3 m, 8H, HD HG), 3.79–3.63 and 3.60–3.49 (2 m, 8H, HE HF), 3.60–
3.54 (m, 2H, H15), 3.19 (q, 2H, 3JH2–H3 =3JH2–H1 =6.4 Hz, H2), 2.43 (t, 2H,
3JH10–H11 =8 Hz, H10), 1.94–1.87 (m, 2H, H6), 1.63–1.56 (m, 2H, H14), 1.43–
1.37 (m, 2H, H3), 1.35–1.24 (m, 4H, H5 H11), 1.29 (s, 18H, H22), 1.13–1.07
(m, 2H, H4), 1.07–1.01 (m, 2H, H12), 0.91–0.84 ppm (m, 2H, H13);
13C NMR (150 MHz, 5.10À2 m in CD2Cl2, 298 K): d=167.3(CK), 160.1,
148.2, 137.8, and 137.2 (CIV arom BMP25C8), 154.2 (C19), 135.6 (C17), 129.5 or
128.7 (C9), 124.9 (C20), 122.8 and 113.2 (CA CB), 122.3 (C8), 117.3 (C18),
107.6 (CI), 106.4 (CJ), 72.1 and 71.3 (CE CF), 70.8 (CD CG), 69.0 and 68.7
(CC CH), 52.3 (C15), 50.9 (C7), 39.9 (C2), 35.7 (C21), 31.6 (C22), 29.9 and
29.1 (C3 C11), 29.4 (C12), 28.8 (C6), 27.7 (C14), 26.2 (C13), 25.8 (C5), 25.6
(C10), 25.4 ppm (C4).
Acknowledgements
We thank the Ligue Nationale Contre le Cancer for PhD financial sup-
port.
[1]Rotaxane 5: A solution of compound 4 (300 mg, 0.28 mmol, 1 equiv)
dissolved in CH2Cl2 (10 mL) was added dropwise over 24 h to a solution
of benzyl bromide (139 mL) and CH2Cl2 (418 mL). The mixture was stir-
red for further 72 h at RT. CH2Cl2 was then evaporated and the excess of
benzyl bromide was removed by filtration on a silica gel column (solvent
gradient elution CH2Cl2 to CH2Cl2/MeOH 95:5). The remaining solid
(290 mg) was then diluted in CH2Cl2 (20 mL). To this solution was added
NH4PF6 (189 mg, 1.16 mmol, 5 equiv) and H2O milliQ (10 mL): the bi-
phasic solution was stirred vigorously for 30 min. The aqueous layer was
extracted with CH2Cl2 (3ꢃ20 mL) and the combined organic layers were
dried over MgSO4 and concentrated under vacuum. The crude was puri-
fied successively by chromatography on a silica gel column (CH2Cl2/
MeOH 99:1) and LH20 sephadex column (CH2Cl2/MeOH 50:50) to give
[1]rotaxane 5 (96 mg, 27%) and deprotonated thread 6u (123 mg, 38%)
as white foams. Rf 0.52 (CH2Cl2/Acetone 70/30); 1H NMR (600 MHz,
5.10À3 m in CD2Cl2, 298 K): d=8.64 (br s, 2H, H16), 8.47 (s, 1H, H8), 7.52
(s, 1H, H20), 7.47–7.43 (m, 3H, H29 H30), 7.42 (s, 2H, H18), 7.35–7.30 (m,
2H, H28), 6.97–6.92 and 6.90–6.85 (2 m, 4H, HA HB), 6.87 (s, 2H, HJ),
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3
6.43 (br t, 1H, H1), 6.15 (s, 1H, HI), 5.70 (s, 2H, H26), 4.60 (t, 2H, JH7–
H6 =5.6 Hz, H7), 4.25–4.14 and 4.08–4.02 (2 m, 8H, HH HC), 3.99–3.93 and
3.86–3.77 and 3.77–3.69 (3 m, 8H, HD HG), 3.77–3.69 and 3.63–3.55 and
3.55–3.49 (3 m, 8H, HE HF), 3.55–3.49 (m, 2H, H15), 3.27–3.20 (m, 2H,
H2), 2.58 (t, 2H, 3JH10–H11 =8 Hz, H10), 2.18–2.20 (m, 2H, H6), 1.62–1.54
(m, 2H, H14), 1.57–1.50 (m, 2H, H3), 1.46–1.39 (m, 2H, H11), 1.40–1.33
(m, 2H, H5), 1.34–1.29 (m, 2H, H4), 1.29 (s, 18H, H22), 1.12–1.04 (m, 2H,
H12), 0.91–0.82 ppm (m, 2H, H13); 13C NMR (150 MHz, 5.10À2
m in
CD2Cl2, 298 K): d=167.9 (CK), 160.8, 160.1, 149.5, 147.5, and 138.6
(CIVÀarom BMP25C8), 154.2 (C19), 145.8 (C9), 135.6 (C17), 131.8 (C27), 130.1 and
130.0 (C29 C30), 128.9 (C28), 128.8 (C8), 124.9 (C20), 122.7, 122.1, 115.4, and
113.2 (CA CB), 117.3 (C18), 107.5 (CI), 106.2 (CJ), 72.2, 71.4, and 71.3 (CE
CF), 70.8, 70.7, 70.4, and 70.2 (CD CG), 69.3, 68.9, and 68.6 (CC, CH), 55.4
(C26), 54.8 (C7), 52.4 (C15), 39.3 (C2), 35.7 (C21), 31.6 (C22), 29.1 (C12), 28.8
(C3), 28.0 (C6), 27.6 (C14), 27.0 (C11), 26.3 (C13), 25.0 (C4), 24.6 (C5),
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2988
www.chemeurj.org
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 2982 – 2989

Rotaxane Molecular Switch
FULL PAPER
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Received: October 9, 2012
Published online: January 23, 2013
Chem. Eur. J. 2013, 19, 2982 – 2989
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2989