Efficient intramolecular energy transfer between two fluorophores in a bis-branched [3]rotaxane

Article abstract of DOI:10.1002/asia.201402789

A bis-branched [3]rotaxane, with two [2]rotaxane arms separated by an oligo(para-phenylenevinylene) (OPV) fluorophore, was designed and investigated. Each [2]rotaxane arm employed a difluoroboradiaza-s-indacene (BODIPY) dye-functionalized dibenzo[ 24]crow

Full text of DOI:10.1002/asia.201402789

FULL PAPER
DOI: 10.1002/asia.201402789
Efficient Intramolecular Energy Transfer between Two Fluorophores in a
Bis-Branched [3]Rotaxane
Jian Yao, Hong Li, Ya-Nan Xu, Qiao-Chun Wang, and Da-Hui Qu*[a]
1
Abstract: A bis-branched [3]rotaxane,
with two [2]rotaxane arms separated
by an oligo(para-phenylenevinylene)
(OPV) fluorophore, was designed and
investigated. Each [2]rotaxane arm em-
ployed a difluoroboradiaza-s-indacene
(BODIPY) dye-functionalized diben-
zo[24]crown-8 macrocycle interlocked
onto a dibenzylammonium in the rod
part. The chemical structure of the
[3]rotaxane was confirmed and charac-
terized by H and 13C NMR spectrosco-
py and high-resolution ESI mass spec-
trometry. The photophysical properties
of [3]rotaxane and its reference sys-
tems were investigated through UV/Vis
absorption, fluorescence, and time-re-
solved fluorescence spectroscopy. An
efficient energy-transfer process in
[3]rotaxane occurred from the OPV
donor to the BODIPY acceptor be-
cause of the large overlap between the
absorption spectrum of the BODIPY
moiety and the emission spectrum of
the OPV fluorophore; this shows the
important potential of this system for
designing functional molecular systems.
Keywords: click chemistry · energy
transfer · fluorophores · FRET ·
rotaxanes
Introduction
such as ET processes between donor and acceptor units, so
MIMs should be good candidates for the construction of
novel light-harvesting systems.[9] At present, light-harvesting
systems in which efficient and unidirectional ET processes
occur from the outer chromophores to the core chromo-
phores are mainly dendrimers.[3] Thus, designing similar in-
tramolecular ET molecular systems in MIMs has attracted
our interest.
Herein, we report a bis-branched [3]rotaxane that con-
tains two chromophoric units, namely, an oligo(para-phenyl-
enevinylene) (OPV) in the middle of the axis unit and two
difluoroboradiaza-s-indacene (BODIPY) dyes in two diben-
zo[24]crown-8 (DB24C8) rings, and possesses efficient ET
processes from the central OPV chromophore to the outer
BODIPY chromophores. As shown in Scheme 1, [3]rotaxane
1 has a symmetrical structure that contains two mechanically
interlocked [2]rotaxane arms, each of which employs
BODIPY-functionalized DB24C8 as a macrocycle and two
The photosynthetic proteins are efficiently produced
through natural light-harvesting systems that convert solar
energy into chemical energy.[1] In these systems, excitation
energy transfer (ET), which attracts much attention from
biologists and chemists, is an essential process.[1d,2] Recently,
several light-harvesting systems, mainly those using shape-
persistent p-conjugated dendrimers and well-defined tree-
like macromolecules, have been developed to imitate natu-
ral photosynthetic systems.[3] In these light-harvesting sys-
tems, the donor and acceptor moieties are usually connected
in close proximity by covalent bonds;[1b,4] however, noncova-
lent interactions exhibit the advantages of more versatility
and tenability[5] in comparison with covalent bonds, as
occurs in naturally occurring light-harvesting systems.
On the other hand, mechanically interlocked molecules
(MIMs) have been extensively studied with the development
of supramolecular chemistry owing to their excellent func-
tional properties and potential applications in molecular
switches and molecular machinery.[6,7] Meanwhile, MIMs can
easily achieve specific functions by introducing active units
on the axle or ring components.[8] Moreover, the compo-
nents in MIMs can be located at an appropriate distance,
which is ideal for controlling intercomponent interactions,
distinguishable
stations,
namely,
dibenzylammonium
(DBA)[10] and a N-methyltriazolium (MTA)[11] recognition
stations, for the DB24C8 ring in the molecular thread com-
ponent. An OPV derivative as a donor fluorophore was in-
troduced as a bridge to separate the two [2]rotaxane arms in
the middle part of the thread because of its tunable photo-
physical properties in the UV/Vis spectral region, as well as
its stability and relatively high fluorescence quantum
yield.[12] Meanwhile, a BODIPY fluorophore was introduced
into each of the two DB24C8 macrocycles as an acceptor,
not only owing to its relatively high fluorescence quantum
yield, high photostability, and high chemostability, but also
owing to its strong UV/Vis absorption with a high molar ex-
tinction coefficient.[13] Furthermore, owing to the large over-
lap between the absorption spectrum of the BODIPY
moiety and the emission spectrum of the OPV axis, efficient
[a] J. Yao, H. Li, Y.-N. Xu, Prof. Dr. Q.-C. Wang, Prof. Dr. D.-H. Qu
Key Laboratory for Advanced Materials and
Institute of Fine Chemicals
East China University of Science & Technology
Shanghai 200237 (P.R. China)
Fax : (+86)-21 64252288
E-mail: dahui_qu@ecust.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201402789.
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Scheme 1. The synthetic procedure for the preparation of [3]rotaxane 1, dumbbell compound 2, and key intermediate compounds 3 and 4. DCM=di-
chloromethane.
ET from the OPV fluorophore on the axle to the BODIPY
fluorophore on the DB24C8 macrocycle occurred. In addi-
tion, the BODIPY-functionalized DB24C8 macrocycle in
the [3]rotaxane can also reversibly shuttle between two dis-
tinguishable recognition sites in response to external acid–
base stimuli. This can pave the way for the design and con-
struction of functional molecular systems based on MIMs.
NaBH4 resulted in the formation of 8 in 80% yield over two
steps. The copper-catalyzed click reaction[11c,14] between 8
and 9 in the presence of CuI and DIEA gave 7 in 62%
yield. Subsequent methylation of the 1,2,3,-triazole unit in 7,
followed by anion exchange with a saturated solution of
NH4PF6 in MeOH afforded 6 in 86% yield. To obtain OPV
derivative 5, compound 10 was heated at reflux in toluene
for 6 h in the presence of PPh3, followed by a Witting reac-
tion with methyl 4-formylbenzoate in methanol to give com-
pound 5 in moderate yield (53%). Compound 5 was hydro-
lyzed with KOH, acidified with hydrochloric acid, and, fol-
lowing esterification with 6 in the presence of EDCI and
DMAP, produced key intermediate 4 in 82% yield.
BODIPY-functionalized DB24C8 macrocycle 3 was also
prepared, as shown in Scheme 3. The etherification reaction
between 13 and 14 in the presence of EDCI and DMAP in
dry CH2Cl2 resulted in the formation of 12 in 85% yield.
The Knoevenagel reaction of 12 with BODIPY derivative
11 under microwave conditions generated 3 in moderate
Results and Discussion
Synthesis and Characterization
The syntheses, chemical structures, model diagrams of [3]ro-
taxane 1, dumbbell compound 2, and intermediate com-
pounds 3 and 4 are shown in Scheme 1.
The synthetic approach to one key intermediate, com-
pound 4, which contains an OPV core is shown in Scheme 2.
Starting from syringaldehyde (15), Williamson etherification
with propargyl bromide and subsequent reduction with
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Scheme 2. Synthetic procedure for the preparation of key intermediate 4. THF=tetrahydrofuran, DIEA=N,N-diisopropylethylamine, EDCI=1-(3-di-
methylaminopropyl)-3-ethylcarbodiimide hydrochloride, DMAP=4-dimethylamiopryidine.
Scheme 3. Synthetic procedure for the preparation of key intermediate 3. DMF=N,N-dimethylformamide.
yield (56%; Scheme 3).The other intermediate compounds,
9, 10, 11, 13, 14, and 16, were synthesized according to previ-
ous reports.[14b,15] As shown in Scheme 1, a mixture of 16 and
3 can form a predominantly [2]pseudorotaxane in CH2Cl2,
then the click reaction with key intermediate 4 in the pres-
ence of [CuACHTUNGTRENNUNG(CH3CN)4]PF6 as a catalyst can give the target
compound [3] rotaxane 1 in 48% yield. Without the pres-
ence of 3, the click reaction between 16 and 4 in the pres-
found that the BODIPY-functionalized DB24C8 macrocy-
cles predominately resided on the DBA recognition sites in
1. The chemical shifts at d=8.34, 8.05, and 7.12 ppm indicat-
ed the existence of the OPV moiety in 1. Meanwhile, the
signals at d=6.00, 6.59, and 2.57 ppm demonstrated the exis-
tence of the BODIPY fluorophore. The protons on the
crown ether with chemical shifts from d=3.3 to 4.5 ppm
were separated into three groups, which indicated that
BODIPY-functionalized DB24C8 interlocked onto the axis.
Moreover, the chemical shift of the protons on the triazole
rings at d=7.86 ppm indicated the success of the click reac-
tion. The chemical structure of 1 was also confirmed by HR-
ESI mass spectrometry. The mass spectrum of 1 possesses
a major peak at m/z 1128.1349, which corresponds to species
ence of [CuACHTUNGTRENNUNG(CH3CN)4]PF6 results in dumbbell compound 2
in moderate yield (56%). The target [3] rotaxane 1, dumb-
bell compound 2, and intermediate compounds 3 and 4 were
all characterized by 1H and 13C NMR spectroscopy and
high-resolution electrospray ionization (HR-ESI) mass spec-
trometry. The reversible acid–base-driven mechanical move-
ment of 1 was also investigated by H NMR spectroscopy.
that have lost four PF6ꢀ counterions, that is, [Mꢀ4PF6]4+
.
1
The 1H NMR spectrum of 1 in CDCl3 is shown in
1
Figure 1. We analyzed the H NMR spectrum of 1 in com-
parison with our previously reported rotaxanes,[14b,c,15a,16] and
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sorption spectra of 2 and 3.
From this phenomenon, we
can infer that there are no
ground-state interactions for
either system M or [3]rotaxane
1.
Meanwhile, the emission
spectra of 1, 2, 3, and as
system M in CH2Cl2 at room
temperature were also investi-
gated. As shown in Figure 3,
the fluorescence spectra of 2
and 3 showed emission peaks
at lmax =485 nm and lmax
=
585 nm, respectively, when ex-
cited at l=415 nm. Notably,
there is a large overlap be-
tween the absorption spectrum
of 3 and the emission spectrum
of 2 (Figure 4); this is ideal for
1
Figure 1. Partial H NMR spectrum (400 MHz, CDCl3, 298 K) of [3]rotaxane 1.
Photophysical Properties of [3]Rotaxane 1
Next, we focused on the photophysical properties of 1 and
reference compounds 2 and 3. First, the absorption spectra
of these three compounds were investigated in CH2Cl2. As
shown in Figure 2, compound 2 exhibited two absorption
Figure 3. The emission spectra of [3]rotaxane 1 (1ꢁ10ꢀ6 m), compound 2
(1ꢁ10ꢀ6 m), compound 3 (2ꢁ10ꢀ6 m), and system M (a mixture of 2 and 3
in a molar ratio of 1:2). The excitation wavelength of the fluorescent
spectra is the absorption maximum of 2 at l=415 nm.
fluorescence resonance energy transfer (FRET) through in-
teractions between transition dipoles.[9b,17]
Figure 2. The absorption spectra of [3]rotaxane 1 (1ꢁ10ꢀ6 m), compound
2 (1ꢁ10ꢀ6 m), compound 3 (2ꢁ10ꢀ6 m) and system M (a mixture of 2 and
3 in a molar ratio of 1:2).
Moreover, the emission spectrum of system M was almost
the weighted addition of the emission spectra of compounds
2 and 3, when excited at the absorption maximum of OPV
at l=415 nm. Therefore, in the simple mixed system M, the
two fluorophores 2 and 3 acted independently as noninter-
acting chromophores in a simple mixture of 2 and 3.[9b,18]
However, a remarkable change was observed in the emis-
sion spectrum of 1, compared with that of system M: the
emission intensity of 1 at lmax =585 nm became stronger
than that of 3, whereas the characteristic emission peak of
the OPV moiety with lmax at l=485 nm almost disappeared.
Meanwhile, the emission spectrum of 1 was still strong upon
excitation at l=450 nm, at which wavelength the absorb-
bands with lmax at 340 and 415 nm, which were characteristic
of OPV chromophore, and macrocycle 3 also exhibited two
absorption bands of BODIPY derivatives with lmax at 531
and 569 nm and a large molar extinction coefficient. At the
same time, the absorption spectrum of a reference system M
(a mixture of compounds 2 and 3 with a molar ratio of 1:2)
was measured, and it was found that the absorption spec-
trum of system M was almost the same as that of [3]rotax-
ane 1, which could be constructed by the addition of the ab-
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phores in mixture M were independent in solution. Howev-
er, a single exponential decay with the lifetime of 1 was ob-
tained when monitored at l=558 or 585 nm (Figures S6 and
S7 in the Supporting Information), which was similar to the
lifetime of 3. In addition, the contribution from OPV
moiety, which could be observed clearly in the mixture, dis-
appeared entirely. This phenomenon indicated that, before
the excited states of OPV underwent radiative decay, anoth-
er faster process occurred in 1, for instance, a FRET process
to the ring. Because the FRET process was much faster
than the lifetimes of these two fluorophores, a single expo-
nential decay lifetime was obtained for 1, rather than the
biexponential decay found in many simple kinetic mod-
els.[9b,21]
Figure 4. The UV/Vis absorption spectrum of 3 (2ꢁ10ꢀ6 m) and the emis-
sion spectrum of 2 (1ꢁ10ꢀ6 m) in CH2Cl2.
Shuttling Movement of [3]Rotaxane 1
At present, a number of FRET rotaxanes have been re-
searched,[9b,18b,22] but using a molecular shuttle to modulate
the FRET effect is still very rare and this attracted our inter-
est. First, we investigated the reversible acid–base-driven
mechanical motions of BODIPY-functionalized DB24C8
macrocycles between two kinds of distinguishable recogni-
ance of BODIPY was negligible (Figure S1 in the Support-
ing Information). From these phenomena, we can speculate
that in 1 there is an efficient FRET process (E=95.5%; see
the Supporting Information) from the OPV moiety to the
BODIPY fluorophores because of the suitable distance be-
tween the donor and acceptor in 1.
1
tion sites of 1 by H NMR spectroscopy. After the addition
of 2.4 equivalents of 1,8-diazabicycloACTHNUTRGNEUNG[5.4.0]undec-7-ene
To further investigate the FRET process in 1, the time-re-
solved fluorescence of 1, reference compounds 2 and 3, and
system M were also measured. As shown in Table 1, when
monitored at l=585 nm, the time-resolved fluorescence of
M showed a single exponential decay with a lifetime of
3.40 ns (Figure S2 in the Supporting Information); this was
consistent with the lifetime of 3 (Figure S3 in the Supporting
Information), and characteristic of BODIPY derivatives.[19]
However, a biexponential decay of mixture M with lifetimes
of 1.33 (42.1) and 3.31 ns (57.9%) were observed (Figure S4
in the Supporting Information) when monitored at l=
558 nm; this phenomenon can be explained in that the life-
time of 1.33 ns should be the intrinsic lifetime of compound
2, for which a single exponential decay with a lifetime of
1.59 ns was detected (Figure S5 in the Supporting Informa-
tion) that was consistent with the OPV derivatives.[12c,20] The
longer lifetime (3.31 ns) should be the intrinsic lifetime of 3.
Furthermore, the proportion of the two lifetimes of the two
fluorophores in mixture M was very similar, which was con-
sistent with our previous deduction that the two fluoro-
(DBU) to the solution of 1 in CDCl3, remarkable changes to
the H NMR spectrum (Figure 5b) were observed compared
1
with the original spectrum (Figure 5a). The chemical shift of
protons H4 and H5 close to the DBA station moved upfield
by 0.98 ppm. At the same time, the chemical shift of protons
H11, H12, H13, and H14 adjacent to the MTA recognition site
also shifted by 0.45, 0.88, ꢀ0.27, and ꢀ0.15 ppm, respective-
ly. These above-mentioned changes revealed that the ammo-
nium recognition sites were deprotonated to generate free
secondary amines successfully and DB24C8 macrocycles
subsequently shuttled toward the secondary MTA stations.
Meanwhile, the ammonium recognition sites could be regen-
erated after introducing 5.0 equivalents of CF3COOH; the
1H NMR spectrum was completely recovered (Figure 5c).
With the introduction of secondary MTA stations, the
BODIPY-functionalized DB24C8 macrocycle can shuttle
toward the secondary MTA stations after the addition of
DBU; this is expected to alter the distance between two flu-
orophores, and, as a result, change the efficiency of the
FRET process. Molecular dynamics (MD) simulations were
performed to determine the
distance between the two fluo-
Table 1. The maximal absorption wavelength (lmax), molar extinction coefficient (e), maximal emission wave-
length (lem), fluorescent quantum yield (Ff), and fluorescence lifetime (t) of 1, 2, 3, and M.
rophores in the two states. As
shown in Figure S8 in the Sup-
porting Information, the aver-
age distance between the OPV
and BODIPY fluorophores is
about 38.4 ꢂ and the two fluo-
rophores are almost parallel in
the initial state. From Equa-
tion (1), R0 (R0 is the distance
at which ET between a given
lmax [nm]
e (104)
lem [nm]
Ff [%]
t [ns]
c2
2
3
1
415
531, 569
338, 531, 569
5.4
485
585
585
0.96
0.81
0.60
1.59[a]
1.006
1.006
1.004
1.106
0.984
1.043
3.1, 10.3
24.8, 7.62, 10.7
3.50[c]
3.28[b]
3.88[c]
M
338, 531, 569
585
1.33 (42.1%), 3.31 (57.9%)[b]
3.40[c]
[a] Fluorescence lifetime monitored at l=485 nm. [b] Fluorescence lifetime monitored at l=558 nm. [c] Fluo-
rescence lifetime monitored at l=585 nm.
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Da-Hui Qu et al.
ficient ET process from the
OPV fluorophore to the
BODIPY moieties occurred,
owing to the appropriate dis-
tance between the two fluoro-
phores in the rotaxane. The
BODIPY-functionalized
DB24C8 rings could reversibly
shuttle between the distin-
guishable recognition sites
through external acid–base
stimuli. Meanwhile, this work
shows important potential in
the design and construction of
functional molecular systems
based on MIMs. In future
work, we will introduce more
rigid structures and enlarge the
distance between the fluoro-
phores and two recognition
sites to modulate the FRET
effect.
Figure 5. Partial 1H NMR spectra (400 MHz, CDCl3, 298 K) of a) [3]rotaxane 1, b) deprotonation with the ad-
dition of 2.4 equivalents of DBU to sample a), and c) reprotonation with the addition of 5.0 equivalents of
CF3COOH to sample b).
donor–acceptor pair is 50%)[23] was calculated to be 62.7 ꢂ.
After the addition of DBU, as shown in Figure S9 in the
Supporting Information, the distance between the two fluo-
rophores changed from 38.4 to 18.3 ꢂ, and the efficiency of
the FRET process was calculated to be 99.9% from Equa-
tion (1). There was no clear change compared with that of
the original state.
Experimental Section
General Methods and Materials
1H and 13C NMR spectroscopy were measured on a Brꢃker AV-400 spec-
trometer. The ESI mass spectra were recorded on a LCT Premier XE
mass spectrometer. The UV/Vis absorption spectra and fluorescence
spectra were also recorded on Varian Cary 100 and Varian Cary Eclipse
spectrometers (1 cm quartz cell used), respectively. The fluorescence life-
time measurements were performed by using the time-correlated single-
photon-counting (TCSPC) technique following excitation by means of
a nanosecond flash lamp. All solvents were of reagent grade and were
dried and distilled prior to use according to standard procedures. The
quantum yields of fluorescence were measured by using a Fluoromax-4
fluorescence spectrophotometer equipped with a quantum yield measur-
ing accessory and report generator program. The molecular structures
were confirmed by using 1H and 13C NMR spectroscopy and high-resolu-
tion ESI mass spectrometry. Compounds 9, 10, 11, 13, 14, and 16 were
synthesized and purified according to previously reported procedur-
es.[14b,15]
EFRET ¼ R0 =ðR0 þ R6Þ
6
6
ð1Þ
Meanwhile, we measured the UV/Vis absorption and fluo-
rescence emission spectra of 1 in response to acid–base stim-
uli. As shown in Figures S10 and 11 in the Supporting Infor-
mation, no clear changes in the spectra were observed, and
the efficiency of the FRET process between the donor and
acceptor fluorophores in 1 had no clear changes. These phe-
nomena are consistent with results from theoretical calcula-
tions. Although the distance between the two fluorophores
changed, the efficiency of the FRET process had no clear
change mainly because the distance between the two fluoro-
phores was not big enough and the efficiency was in a high
level in the initial state. Although modulation of the FRET
efficiency is not good as expected, this result can help us to
improve the molecular design in the future work, such as in-
troducing more rigid chains and enlarging the distance be-
tween the two recognition states to achieve better modula-
tion of FRET efficiency.
Compound 12
A mixture of compound 13 (0.492 g, 1 mmol) and 14 (0.200 g, 1.2 mmol)
was dissolved in dry CH2Cl2 (6 mL), then EDCI (0.768 g, 4 mmol) and
DMAP (0.122 g, 1 mmol) were added and the mixture was stirred over-
night at room temperature under an argon atmosphere. The reaction
mixture was then washed with water and extracted with CH2Cl2 (3ꢁ
50 mL), the organic layer was dried over anhydrous Na2SO4 and evapo-
rated, and the residue was purified by chromatography on silica gel with
CH2Cl2/MeOH (200:1) as the eluent to give 12 as a white solid (0.54 g,
85%). M.p. 118–1198C; 1H NMR (400 MHz, CDCl3, 298 K): d=9.90 (s,
1H), 7.85 (d, J=8.8 Hz, 2H), 7.66 (dd, J=8.4, 1.6 Hz, 1H), 7.52 (d, J=
2.0 Hz, 1H), 7.05 (d, J=8.4 Hz, 2H), 6.97–6.81 (m, 5H), 4.66 (t, J=
4.8 Hz, 2H), 4.38 (t, J=4.8 Hz, 2H), 4.21–4.13 (m, 8H), 3.96–3.90 (m,
8H), 3.86–3.81 ppm (m, 8H); 13C NMR (100 MHz, CDCl3, 298 K): d=
190.8, 166.2, 163.6, 153.2, 148.9, 148.3, 132.0, 130.3, 124.2, 122.3, 121.4,
114.9, 114.4, 113.9, 111.9, 71.5, 71.4, 71.3, 70.0, 69.8, 69.6, 69.5, 69.4, 69.3,
Conclusion
We successfully constructed and characterized
a bis-
66.3, 62.8 ppm; HRMS (ESI): m/z calcd for C34H40NaO12
: 633.2417
branched [3]rotaxane. By introducing an OPV fluorophore
as a donor into the axle component and two BODIPY fluo-
rophores as acceptors in the macrocycle components, an ef-
[M+Na]+; found: 633.2409.
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Compound 3
Compound 7
In 50 mL flask, compound
Compound 11 (128 mg, 0.2 mmol) was dissolved in anhydrous DMF
(20 mL) in a 50 mL three-necked, round-bottomed flask, then acetic acid
(0.5 mL), piperidine (0.5 mL), and 12 (102 mg, 0.2 mmol) were added
under an argon atmosphere. After reaction under microwave conditions
(8 min, 1508C), the reaction mixture was cooled to room temperature
and extracted with EtOAc (3ꢁ50 mL). The organic layer was combined
and concentrated in vacuo, and the product was further purified by
column chromatography (SiO2, CH2Cl2/MeOH=120:1), to yield 3 as
a purple solid (127 mg, 56%). M.p. 112–1148C; 1H NMR (400 MHz,
CDCl3, 298 K): d=7.64 (dd, J=8.4, 1.6 Hz, 1H), 7.59–7.49 (m, 4H),
7.21–7.12 (m, 3H), 6.97 (d, J=8.8 Hz, 2H), 6.93 (d, J=8.4 Hz, 2H), 6.88–
6.81 (m, 5H), 6.57 (s, 1H), 5.99 (s, 1H), 4.62 (t, J=4.0 Hz, 2H), 4.38 (t,
J=4.0 Hz, 2H), 4.19–4.10 (m, 8H), 3.99 (t, J=6.4 Hz, 2H), 3.94–3.87 (m,
8H), 3.84–3.79 (m, 8H), 2.58 (s, 3H), 1.86–1.76 (m, 2H), 1.52–1.42 (m,
8H), 1.40–1.23 (m, 16H), 0.88 ppm (t, J=2.8 Hz, 3H); 13C NMR
(100 MHz, CDCl3, 298 K): d=166.2, 159.7, 159.4, 154.6, 153.1, 153.0,
148.9, 148.2, 142.7, 142.5, 140.4, 135.7, 133.2, 132.2, 132.0, 129.8, 129.4,
129.0, 126.9, 124.2, 122.4, 121.4, 121.1, 117.4, 115.0, 114.9, 114.4, 114.0,
111.9, 71.5, 71.4, 71.3, 70.0, 69.8, 69.6, 69.5, 69.4, 69.3, 68.2, 66.2, 63.2,
32.0, 29.7, 29.6, 29.5, 29.4, 29.3, 26.1, 22.7, 14.9, 14.7, 14.6, 14.2 ppm;
HRMS (ESI): m/z calcd for C65H81N2F2BNaO12: 1153.5748 [M+Na]+;
found: 1153.5747.
a
9
(1.92 g, 8.66 mmol), CuI (1.67 g,
1.73 mmol), DIEA (2.24 g, 17.3 mmol), and compound
8 (3.89 g,
17.3 mmol) were mixed in dry THF (30 mL), and the reaction mixture
was stirred overnight under an argon atmosphere. After the mixture was
poured into water (200 mL) and stirred for another half an hour, the
aqueous layer was extracted with CH2Cl2 (3ꢁ25 mL). After the com-
bined organic layers were concentrated in vacuo, purification was per-
formed by column chromatography (SiO2, CH2Cl2/MeOH=200:1) to
give 7 as a yellow oil (2.40 g, 62%). 1H NMR (CDCl3, 400 MHz, 298 K):
d=7.69 (s, 1H), 6.58 (s, 2H), 5.15 (s, 2H), 4.62 (s, 2H), 4.32 (t, J=
8.0 Hz, 2H), 3.82 (s, 6H), 3.25 (t, J=8.0 Hz, 2H), 1.92–1.84 (m, 2H),
1.62–1.53 (m, 2H), 1.36–1.24 ppm (m, 12H); 13C NMR (100 MHz, CDCl3,
298 K): d=153.3, 145.0, 137.7, 137.6, 135.2, 122.8, 103.6, 66.4, 65.0, 56.0,
51.4, 50.7, 50.3, 30.3, 29.7, 29.3, 29.2, 29.0, 28.9, 28.8, 26.6, 26.4 ppm;
HRMS (ESI): m/z calcd for C22H34N6NaO4: 469.2539 [M+Na]+; found:
469.2537.
Compound 6
Compound 7 was dissolved in iodomethane (6 mL), then the mixture was
stirred at 408C for 4 days. After removing excess iodomethane, the clear
yellow fluid was dissolved in methanol (30 mL). Then a saturated solu-
tion of NH4PF6 (10 mL) was added and the mixture was stirred at room
temperature for 4 h. The reaction mixture was extracted with CH2Cl2 (3ꢁ
25 mL), and the organic layer was dried and evaporated. The crude prod-
uct was purified by chromatography on silica gel by using CH2Cl2/MeOH
(100:1) as the eluent to give 6 as a yellow oil (1.17 g, 86%). 1H NMR
(CDCl3, 400 MHz, 298 K): d=8.23 (s, 1H), 6.57 (s, 2H), 5.14 (s, 2H),
4.60 (s, 2H), 4.50–4.42 (m, 5H), 3.79 (s, 6H), 3.25 (t, J=8.0 Hz, 2H),
1.97–1.90 (m, 2H), 1.62–1.55 (m, 2H), 1.36–1.24 ppm (m, 12H);
13C NMR (100 MHz, CDCl3, 298 K): d=152.9, 139.9, 139.1, 133.0, 129.6,
103.4, 64.9, 60.7, 55.8, 54.1, 51.4, 38.4, 29.3, 29.2, 29.1, 29.0, 28.8, 28.7,
26.6, 25.9 ppm; HRMS (ESI): m/z calcd for C23H37N6O4: 461.2876
[MꢀPF6]+; found: 461.2873.
Compound 5
A mixture of 10 (3.15 g, 5 mmol) and PPh3 (2.882 g, 11 mmol) was dis-
solved in toluene under an argon atmosphere. The reaction mixture was
heated at reflux for 6 h. After termination of the reaction, a white solid
was precipitated and filtered. Then, the generated solid was transferred
to a Schlenk tube and methyl 4-formylbenzoate (1.97 g, 12 mmol) was
added, and the mixture was dissolved in methanol under an argon atmos-
phere. Sodium methoxide (0.81 g 15 mmol) in methanol (15 mL) was in-
jected into the mixture slowly and the mixture became yellow. Later, the
precipitate formed. After being stirred for another 4 h, the reaction was
quenched with water (20 mL), and the yellow solid was filtered and
washed with methanol. The crude product was heated at reflux in toluene
with a catalytic amount of iodine for 1 h, and the solvent was evaporated.
The pure product was obtained after column chromatography (SiO2, pe-
troleum ether (PE)/EtOAc=5:1), followed by recrystallization from di-
chloromethane and methanol, to yield 5 as a yellow solid (2.03 g, 53%).
M.p. 120–1218C; 1H NMR (400 MHz, CDCl3, 298 K): d=8.02 (d, J=
8.4 Hz, 4H), 7.62–7.56 (m, 6H), 7.18 (d, J=16.4 Hz, 2H), 7.13 (s, 2H),
4.07 (t, J=6.4 Hz, 3H), 3.93 (s, 6H), 1.94–1.85 (m, 4H), 1.57–1.51 (m,
4H), 1.43–1.26 (m, 32H), 0.88 ppm (t, J=2.8 Hz, 3H); 13C NMR
(100 MHz, CDCl3, 298 K): d=166.9, 151.3, 142.4, 130.0, 128.7, 128.0,
126.8, 126.3, 126.0, 110.7, 69.5, 52.1, 32.0, 30.2, 29.7, 29.5, 29.4, 26.3, 22.7,
14.2 ppm; HRMS (ESI): m/z calcd for C50H71O6: 767.5251 [M+H]+;
found: 767.5244.
Compound 4
Compound 5 (153 mg, 0.2 mmol), KOH (224 mg, 4 mmol), methanol
(6 mL), THF (6 mL), and water (4 mL) were added to a flask and the
mixture was heated at reflux for 10 h. After the reaction mixture was
cooled to room temperature, water (10 mL) was added. Then, 1n HCl
was added to adjust the pH to 2–3, and the resulting yellow precipitate
was filtered and washed with dichloromethane/methanol (1:10). After
drying, the crude intermediate was transferred to a flask and 6 (267 mg,
0.44 mmol), EDCI (307 mg, 1.6 mmol), and DMAP (49 mg, 0.4 mmol)
were added and dissolved in dichloromethane (4 mL). The reaction mix-
ture was stirred for 10 min and became clear. The mixture was stirred
overnight. After termination of the reaction, the solvent was removed by
using a rotary evaporator to give the crude product, which was purified
by column chromatography with CH2Cl2/EtOAc (10:1) as the eluent to
afford 4 as a yellow solid (314 mg, 82%). M.p. 107–1098C; 1H NMR
(CDCl3, 400 MHz, 298 K): d=8.32 (s, 2H), 8.05 (d, J=8.4 Hz, 4H), 7.60–
7.54 (m, 6H), 7.16 (d, J=16.4 Hz, 2H), 7.11 (s, 2H), 6.68 (s, 4H), 5.29 (s,
4H), 5.20 (s, 4H), 4.55–4.47 (m, 10H), 4.05 (t, J=6.4 Hz, 4H), 3.86 (s,
12H), 3.26 (t, J=6.8 Hz, 4H), 2.04–1.95 (m, 4H), 1.92–1.83 (m, 4H),
1.63–1.49 (m, 8H), 1.43–1.23 (m, 60H), 0.89 ppm (t, J=2.8 Hz, 6H);
13C NMR (100 MHz, CDCl3, 298 K): d=166.2, 153.1, 151.3, 142.7, 139.9,
134.1, 133.9, 130.2, 129.7, 128.4, 127.9, 126.8, 126.4, 126.2, 105.1, 69.4,
66.6, 60.8, 56.0, 54.1, 51.5, 38.6, 31.9, 29.7, 29.6, 29.4, 29.3, 29.0, 28.8, 28.7,
26.7, 26.3, 26.0, 22.7, 14.2 ppm; HRMS (ESI): m/z calcd for
C94H136N12O12/2: 813.0217 [Mꢀ2PF6]2+; found: 813.0208.
Compound 8
A
mixture of 15 (5.0 g, 0.027 mol), propargyl bromide (6.04 g,
0.055 mmol), and K2CO3 (7.59 g, 0.055 mol) were dissolved in acetone
(150 mL) in a 250 mL flask, then the mixture was heated at reflux over-
night under an argon atmosphere. The reaction mixture was washed with
water and extracted with CH2Cl2 (3ꢁ50 mL). The organic layer was dried
over anhydrous Na2SO4 and the solvent was evaporated before THF
(100 mL) was added. After the solution was cooled to 08C, NaBH4
(2.05 g, 0.054 mol) was added slowly and stirred overnight at room tem-
perature. The reaction was quenched with water and the resulting aque-
ous solution was extracted with CH2Cl2 (3ꢁ50 mL). The solvent was re-
moved under reduced pressure to obtain the crude product, which was
purified by column chromatography with CH2Cl2/PE (2:1) as the eluent
to give 8 as a white solid (4.795 g, 80%). M.p. 99–1008C; 1H NMR
(400 MHz, CDCl3, 298 K): d=6.59 (s, 2H), 4.69 (d, J=2.4 Hz, 2H), 4.64–
4.60 (m, 2H), 3.85 (s, 6H), 2.44–2.41 (m, 2H), 1.97–1.91 ppm (m, 1H);
13C NMR (100 MHz, CDCl3, 298 K): d=153.6, 137.4, 134.7, 103.7, 79.4,
74.8, 65.4, 59.9, 56.1 ppm; HRMS (ESI): m/z calcd for C12H15O4: 223.0970
[M+H]+; found: 223.0976.
Compound 2
In a 25 mL flask, compounds 4 (50 mg, 0.026 mmol) and 16 (48 mg,
0.105 mmol) were dissolved in dichloromethane (2 mL) and acetonitrile
(2 mL), then [CuACTHUNTRGNE(UNG CH3CN)4]PF6 (19.4 mg, 0.052 mmol) was added and the
solution was stirred at room temperature for 24 h. After removal of the
solvent, the crude product was purified by column chromatography
(SiO2, CH2Cl2/MeOH=120:1) to give 2 as a yellow solid (41 mg, 56%).
Chem. Asian J. 2014, 9, 3482 – 3490
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Da-Hui Qu et al.
1H NMR (CD3COCD3, 400 MHz, 298 K): d=8.79 (s, 2H), 8.09–8.01 (m,
6H), 7.74–7.66 (m, 6H), 7.51–7.39 (m, 8H), 7.05 (d, J=8.8 Hz, 4H), 6.88
(s, 4H), 6.70 (d, J=2.0 Hz, 4H), 6.50–6.44 (m, 2H), 5.38 (s, 4H), 5.31 (s,
4H), 5.16 (s, 4H), 4.75 (t, J=7.2 Hz, 4H), 4.61 (s, 6H), 4.40 (t, J=7.2 Hz,
4H), 4.20 (d, J=6.0 Hz, 8H), 4.15 (t, J=6.4 Hz, 4H), 3.85 (s, 12H), 3.77
(s, 12H), 1.93–1.83 (m, 8H), 1.62–1.53 (m, 4H), 1.48–1.40 (m, 4H), 1.37–
1.21 (m, 56H), 0.85 ppm (t, J=7.2 Hz, 6H); 13C NMR (100 MHz,
CD3COCD3, 298 K): d=170.7, 166.5, 164.1, 158.6, 156.6, 148.1, 145.5,
139.6, 139.2, 136.3, 135.9, 135.2, 133.9, 133.3, 132.0, 131.6, 131.3, 129.0,
120.1, 116.2, 112.4, 110.4, 107.6, 105.4, 74.3, 71.5, 66.7, 66.2, 60.8, 60.1,
59.0, 55.0, 43.4, 36.9, 35.3, 31.4, 30.9, 27.7, 18.7 ppm; HRMS (ESI): m/z
calcd for C132H180N14O18/4: 562.5909 [Mꢀ4PF6]4+; found: 562.5909.
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Compound 1
In a 25 mL flask, compounds 3 (88 mg, 0.078 mmol) and 16 (30 mg,
0.066 mmol) were dissolved in dichloromethane (3 mL), the mixture was
stirred for half an hour, and then 4 (50 mg, 0.026 mmol) and [Cu-
ACHTUNGTRENNUNG(CH3CN)4]PF6 (19.4 mg, 0.052 mmol) were added and the solution was
stirred at room temperature for 24 h. After removal of the solvent, the
crude product was purified by column chromatography (SiO2, CH2Cl2/
MeOH=120:1) to give 1 as a purple solid (64 mg, 48%). M.p. 82–848C;
1H NMR (CDCl3, 400 MHz, 298 K): d=8.34 (s, 2H), 8.05 (d, J=8.0 Hz,
4H), 7.86 (s, 2H), 7.65–7.47 (m, 16H), 7.38 (s, 2H), 7.24–7.18 (m, 5H),
7.17–7.14 (m, 5H), 7.12 (s, 2H), 7.00 (d, J=8.0 Hz, 4H), 6.93 (d, J=
8.4 Hz, 4H), 6.87–6.69 (m, 14H), 6.66 (s, 4H), 6.59 (s, 2H), 6.36 (s, 4H),
6.18 (s, 2H), 6.00 (s, 2H), 5.27 (s, 4H), 5.19 (s, 4H), 5.08 (s, 4H), 4.63 (t,
J=4.0 Hz, 4H), 4.53–4.42 (m, 18H), 4.38–4.30 (m, 8H), 4.17–3.97 (m,
24H), 3.58 (s, 12H), 3.54–3.38 (m, 16H), 2.57 (s, 3H), 2.05–1.78 (m, 8H),
1.71–1.58 (m, 8H), 1.52–1.42 (m, 20H), 1.41–1.21 (m, 92H), 0.91–
0.83 ppm (m, 12H); 13C NMR (100 MHz, CDCl3, 298 K): d=165.2, 164.9,
159.8, 158.7, 158.4, 157.9, 153.6, 152.1, 151.9, 150.5, 150.3, 146.1, 146.0,
142.1, 141.7, 141.6, 139.4, 138.8, 134.6, 133.1, 132.8, 132.7, 132.2, 131.1,
130.1, 129.8, 129.1, 128.8, 128.6, 128.3, 128.0, 127.9, 127.4, 126.9, 125.7,
125.4, 125.1, 123.3, 122.8, 122.6, 121.8, 120.6, 120.1, 116.4, 116.2, 114.0,
112.1, 111.4, 110.7, 109.7, 105.6, 104.0, 98.8, 69.6, 69.1, 68.9, 68.4, 67.3,
67.2, 66.9, 65.6, 65.1, 62.3, 60.4, 59.8, 55.0, 54.2, 53.1, 52.5, 51.7, 51.2, 49.8,
37.5, 30.9, 30.5, 30.4, 29.2, 29.0, 28.7, 28.6, 28.4, 28.3, 28.1, 27.6, 27.5, 27.4,
27.3, 26.2, 25.2, 25.1, 25.0, 24.6, 24.5, 21.7, 13.8, 13.7, 13.6, 13.1 ppm;
HRMS (ESI): m/z calcd for C262H342B2F4N18O42/4: 1128.1342 [Mꢀ4PF6]4+
; found: 1128.1349.
Acknowledgements
We thank the NSFC/China (21272073, 21190033) and the National Basic
Research 973 Program (2011CB808400), the Fundamental Research
Funds for the Central Universities, and the Innovation Program of
Shanghai Municipal Education Commission, and the Scientific Research
Foundation for the Returned Overseas Chinese Scholars, State Education
Ministry for financial support. This work is partially supported by the Sci-
ence Fund for Creative Research Groups (No. 21421004). Meanwhile, we
thank Dr. X. Li for help with the molecular dynamics (MD) simulations.
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Received: July 5, 2014
Revised: July 21, 2014
Published online: September 18, 2014
Chem. Asian J. 2014, 9, 3482 – 3490
3490
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