A cyclometallated platinum complex as a selective optical switch for quadruplex DNA

Article abstract of DOI:10.1002/chem.201202990

Hits the spot: A cyclometalled platinum(II) complex with a substituted phenanthroline ligand is reported. The complex has high in vitro affinity for quadruplex DNA and upon binding its emission is switched on. The complex can be easily delivered to the cell by using a metallo-cage as a carrier (see illustration). By means of confocal microscopy, it is shown that the complex is released inside the cell, penetrates the nucleus and localises in the nucleoli.

Full text of DOI:10.1002/chem.201202990

COMMUNICATION
DOI: 10.1002/chem.201202990
A Cyclometallated Platinum Complex as a Selective Optical Switch for
Quadruplex DNA
Kogularamanan Suntharalingam,[a] Anna Łe˛czkowska,[a] Mona A. Furrer,[b] Yilei Wu,[a]
Marina K. Kuimova,[a] Bruno Therrien,[b] Andrew J. P. White,[a] and Ramon Vilar*[a]
DNA sequences with the potential to form non-canonical
structures (such as hairpins, triplexes, quadruplexes and cru-
ciforms) are widespread in genomes. Interestingly, the distri-
bution of such sequences is not random, being selectively
enriched in specific genes and, particularly, in transcriptional
regions. This strongly suggests that non-canonical DNA
structures play important roles in essential biological func-
tions, such as replication, transcription and recombination.
Amongst these non-canonical topologies, G-quadruplexes
have received increasing attention due to their proposed in-
volvement in gene regulation as well as in telomere mainte-
nance.[1] Therefore, it has been proposed that G-quadruplex-
es could be interesting targets for the development of anti-
cancer drugs[2] (e.g., by down-regulating oncogene expres-
sion,[1b,3] inhibiting telomerase[4]) and extensive research has
been carried out towards developing molecules that can se-
lectively target these DNA topologies. Although a wide
range of organic and metal–organic molecules have been
synthesised towards this aim,[5] far less has been achieved in
the development of luminescent probes that can target
quadruplexes selectively. Such probes could provide insight
into the formation of quadruplexes in vivo as well as being
very useful tools for aiding our understanding of DNA bio-
physical properties. Some recent examples of quadruplex-
selective optical probes are Thomasꢀ ruthenium-based opti-
cal switches,[6] Luedtkeꢀs zinc-phthalocyanine complexes,[7]
Cheꢀs platinum(II) dipyridophenazine luminescent probes[8]
and the quadruplex-templated fluorogenic reactions report-
ed by Ladame.[9] An interesting approach to optical detec-
tion of quadruplexes based on assembling platinum(II) com-
plexes has been developed by Yam.[10a] Some organic dyes
have also been reported to be optical switches for G-quad-
ruplex DNA.[10b–d]
ACHTUNGTRENuNGNU m(II) complex (Scheme 1). We show that this complex in-
teracts selectively with quadruplex DNA and upon binding
its emission is switched on. The encapsulation of this com-
plex inside a hexaruthenium cage is also reported as means
of transporting the optical probe inside the cell allowing us
to carry out optical imaging studies of its cellular targets
and localisation.
Scheme 1. Synthesis of phenanthroline-based ligand 2 and the corre-
sponding cyclometallated platinum(II) complex 3.
Herein we report the synthesis of a new phenanthroline-
based ligand and its corresponding cyclometallated platin-
As has been extensively discussed elsewhere, complexes
containing co-planar aromatic rings, a central metal cation
and amine substituents that can be protonated at physiologi-
cal pH, tend to have good affinities for quadruplex DNA.[5]
We have previously shown that platinum(II) and palladi-
[a] Dr. K. Suntharalingam, Dr. A. Łe˛czkowska, Y. Wu,
Dr. M. K. Kuimova, Dr. A. J. P. White, Prof. R. Vilar
Department of Chemistry
AHCTUNGTREGuNNNU m(II) complexes coordinated to monosubstituted phenan-
throlines have good affinities towards quadruplexes.[11] On
the other hand, Che et al. have previously reported that
phenyl-substituted phenathrolines can act as tridentate
(CNN) ligands and yield phosphorescent platinum(II) com-
plexes.[12] One of these complexes was previously shown to
bind strongly to calf thymus DNA (ct-DNA) but poorly to
Imperial College London, London SW7 2AZ (UK)
E-mail: r.vilar@imperial.ac.uk
[b] M. A. Furrer, Dr. B. Therrien
Institut de Chimie, Universitꢁ de Neuchꢂtel
51 Avenue de Bellevaux, CH-2000 Neuchꢂtel (Switzerland)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202990.
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
16277

quadruplex DNA.[13] Considering the above, we designed
the phenanthroline ligand 2 (Scheme 1) so that it would fea-
ture: 1) four co-planar aromatic rings ideally positioned to
stack on the G-quartet; 2) an ethyl-piperidine substituent on
phenanthrolineꢀs backbone to enhance solubility and to
hinder the resulting platinum(II) complex from intercalating
easily in-between base pairs of duplex DNA (hence provid-
ing quadruplex selectivity); 3) a CNN coordination motif to
yield platinum(II) complexes with emissive properties. Thus,
this ligand and the corresponding platinum(II) complex 3
were prepared as shown in Scheme 1. Ligand 2 was charac-
cules are linked by p–p stacking interactions between phe-
nanthroline rings to form chains along the crystallographic
a axis direction (Figures S27 and S28 in the Supporting In-
formation). These chains are cross-linked to their Ci-related
ꢀ
counterparts by a C H···p interaction, forming sheets of
molecules in the crystallographic ab plane.
To assess whether 3 also displays p–p stacking interac-
tions in solution, variable temperature and concentration
1H NMR spectroscopic studies were carried out in
[D6]DMSO (Figures S3–S6 in the Supporting Information).
Upon increasing the temperature of a solution of 3, the aro-
matic resonances shifted towards higher field, which—as has
been discussed previously for other aromatic systems—is
consistent with p–p interactions being disrupted as the tem-
perature is increased.[14] A similar effect was observed when
the 1H NMR spectra were recorded at various concentra-
tions: upon decreasing the concentration, a high field shift
of the aromatic resonances was observed, consistent with
the expected reduction in p–p interactions at lower concen-
trations. This shows that complex 3 displays p–p interactions
in DMSO solution, which is generally a good indication of a
complexꢀs potential to interact via p–p stacking with DNA.
Complex 3 was found to be emissive in organic solvents
(in CH2Cl2, lex =430 nm and lem =570, 613 nm; quantum
yield=0.024) but the emission was quenched in water. Due
to the well-resolved vibrational structure and by comparison
to the emission spectra of previously reported platinum(II)
cyclometallated complexes,[12,13] the origin of the emission of
3 centred at 570 nm can be assigned tentatively to the p!
1
terised by H and 13C NMR spectroscopy, mass spectrometry
and elemental analyses (see the Experimental Section). This
ligand was then treated with K2PtCl4 in the presence of
NaOAc for 3 days at 658C to yield complex 3 as a yellow
crystalline solid. The platinum(II) complex was fully charac-
1
terised by H NMR spectroscopy, mass spectrometry and el-
1
emental analysis. The H NMR spectrum displayed the ex-
pected peaks (ten aromatic and four aliphatic signals with
the correct multiplicities and integrals; it should be noted
that the fifth expected aliphatic signal from one of the piper-
idineꢀs CH2, overlaps with the solvent peak). Importantly,
ꢀ
the formation of the cyclometalled Pt C (aromatic) bond
was confirmed by the disappearance of one ortho phenyl
proton resonance in 2. A distinctive molecular ion peak was
observed in the ESI(+) mass spectrum (m/z 614 a.m.u.,
[M+H]+) providing further evidence for complex forma-
tion.
Crystals of 3 suitable for an X-ray crystallographic analy-
sis were obtained by slow diffusion of ethyl ether into a di-
chloromethane solution of the compound. The structure of 3
(Figure 1) shows the phenyl-phenanthroline ligand to have
an approximately co-planar conformation, the torsion angle
p* intraACTHNUGRTNENUGliACHTUTNGRENNUGgand transition. Interestingly, the emission of the
complex in aqueous media was restored upon interaction
with DNA and, as discussed below, in particular with quad-
ruplex DNA.
ꢀ
about the C C bond linking rings A and D being about 38.
The ability of complex 3 to interact with different DNA
topologies was first investigated by UV/Vis spectroscopic ti-
trations. Three different quadruplex DNA structures were
investigated: our initial studies focussed on the G-rich pro-
moter region of c-Myc oncogene. It is well-established that
this sequence readily folds into a quadruplex structure,
which leads to the down-regulation of c-Myc.[1b] In addition,
two human ribosomal DNA (rDNA) sequences known to
form quadruplexes (6183 NT and 7253 NT)[15] were investi-
gated. As will be discussed later, confocal microscopy stud-
ies revealed a high concentration of complex 3 in the nucle-
oli suggesting that rDNA could be one of its molecular tar-
gets. As can be seen in Table 1, complex 3 has high affinity
towards quadruplex DNA structures with a 1000-fold selec-
tivity (as measured by UV/Vis titrations) for quadruplexes
over a 26-mer duplex DNA (ds26 DNA).
The platinum has the expected distorted square planar co-
ordination geometry with cis angles in the range 80.26(13)
to 101.43(12)8. Adjacent centrosymmetrically-related mole-
As a result of tight binding, the emission of complex 3 in
aqueous solution was shown to “switch-on” in the presence
of quadruplex DNA. Therefore, the emission of 3 was re-
corded in the presence of the four different quadruplexes
under study as well as duplex DNA (both ds26- and ct-
DNA) and other biomolecules, such as bovine serum albu-
min (BSA). These studies showed that the enhancement in
emission of 3 was much more pronounced in the presence of
Figure 1. The crystal structure of
scheme.
3 showing the aryl-ring labelling
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Chem. Eur. J. 2012, 18, 16277 – 16282

A Selective Optical Switch for Quadruplex DNA
COMMUNICATION
Table 1. Binding constants obtained for 3 determined by UV/Vis and
ies. Complex 3 was incubated at concentrations below 50 mm
for 24 h with U2OS cells and the sample was studied by con-
focal fluorescence microscopy. Unfortunately, under these
conditions, confocal fluorescence microscopy showed that
the compound was not taken up by U2OS cells preventing
us from establishing cellular targets and localisation (Fig-
ure S23 in the Supporting Information). To overcome this
problem, we decided to explore whether a molecular carrier
could be used to aid cellular uptake of complex 3 and conse-
quently enable us to carry out further studies. To this aim,
emission titrations.[a]
Sequence
K [mꢀ1
]
UV/Vis
Emission
c-Myc
Htelo
6183 NT
7253 NT
ct-DNA
ds26 DNA
6.7
1.3
4.6
1.5
4.0
5.5
N
2.1
1.2
1.4
8.0
1.3
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
n.d.[b]
[a] The values are an average of three independent measurements.
[b] The binding constant between complex 3 and ds26 DNA was not de-
termined by emission titration since no measurable change in intensity of
the complexꢀs emission could be detected upon interaction with this oli-
gonucleotide (see inset in Figure 2).
the hexanuclear metalla-prism [Ru6(h6-p-cymene)
(donq)3](CF3SO3)6 ([4](CF3SO3)6) was investigated
6ACHTUNGTRENNUNG(tpt)2-
A
R
ACHTUNGTRENNUNG
(Scheme 2). This supramolecular assembly has been previ-
c-Myc and 6183 NT quadruplex DNA than in the presence
of duplex DNA (see Figure 2 for a graphical representation
of the emission response and Table 1 for apparent affinity
Scheme 2. Schematic representation of host–guest complex [3ꢂ4]-
AHCTNUGTREN(GUNN CF3SO3)6. The emission of platinum complex 3 was seen to decrease
upon encapsulation by host 4.
ously shown to be an excellent host for guest molecules with
planar aromatic substituent.[16] More interestingly, the result-
ing host–guest assemblies are able to cross the cell mem-
brane and release their cargo after internalisation. Thus, the
synthesis of [3ꢂ4]6+ was carried out by mixing the hexanu-
clear cage 4 with the platinum(II) complex 3 for 6 h in di-
chloromethane. From this reaction a dark green solid was
isolated, which was characterised as the novel host–guest
Figure 2. Bar chart depicting the enhancement in the emission of com-
plex 3 (in Tris-KCl buffer) upon addition of 50 equiv of a range of bio-
molecules. Optical selectivity for c-Myc and 6183 NT DNA over duplex
DNA is shown. The inset shows the emission spectra of complex
3+c-Myc (a), 3+ds26 DNA (b) and 3 without DNA (c).
complex [3ꢂ4]
ACHTNUGTERN(NUGN CF3SO3)6 by DOSY NMR spectroscopic ex-
periments as well as by ESI(+)-MS (see the Supporting In-
formation for details of spectroscopic data). The association
constant of this assembly was determined by the UV/Vis di-
lution method[17] to be 3.1ꢄ104 mꢀ1 (CH2Cl2 at 258C), which
is consistent with analogous host–guest systems reported
previously.[16b,18] The emission of complex 3 is almost com-
pletely quenched (quantum yield=0.001) when encapsulat-
ed, consistent with previous observations of encapsulation
of planar compounds inside cage 4. Therefore, it was not ex-
pected to detect any signal from the caged compound in flu-
orescence microscopy experiments in cells. The complex–
constants determined by emission spectroscopy). Indeed, in
the case of ds26 DNA no enhancement of the emission was
observed (Figure 2, inset). This highlights the great potential
of this complex for the selective detection of quadruplex
structures over duplex DNA.
Considering the ability of this complex to switch-on its
emission selectively in the presence of quadruplexes, it was
of interest to determine whether 3 would be taken up by
cells, and its localisation was monitored by confocal fluores-
cence microscopy. For this, it was first necessary to establish
the concentration range at which the molecule could be
used; thus, its cytotoxicity (using the MTS assay) against the
osteosarcoma U2OS cell line was determined, giving an
cage assembly [3ꢂ4]ACHTUNGRTEN(NUGN CF3SO3)6 was then incubated with
U2OS cells by using the same procedure as that employed
for the free platinum complex 3 (except that for the caged
complex a lower concentration of 2 mm was used). After
24 h, confocal fluorescence microscopy studies were carried
out. These demonstrated that the host–guest system pene-
trates the cell, releases the guest molecule, and that a high
IC50 =93.3
G
centration of 10–50 mm of the complex for subsequent stud-
Chem. Eur. J. 2012, 18, 16277 – 16282
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16279

R. Vilar et al.
proportion of complex 3 accumulates in the nucleus showing
specific staining of the nucleoli (Figure 3). Interestingly, co-
staining with DAPI (a known duplex DNA binder) showed
that the complex does not co-localise with this dye (Figure 3
not consistent with the shifts seen upon addition of guano-
sine to complex 3. It remains to be seen how the quadruplex
affinity changes for the OH-substituted platinum complex,
compared to its parent Cl analogue; however, we expect a
similar level of interaction with the quadruplex due to the
minimal structural perturbation to the aromatic core of the
complex.
In summary, herein we have presented a new cyclometal-
lated platinum(II) complex the emission of which is switch-
ed-on in the presence of DNA. The complex interacts with a
1000-fold selectivity with quadruplex DNA over duplex
DNA. More interestingly, its emission is switched-on (ca.
35-fold) in the presence of c-Myc and 6183 NT quadruplex
DNA, but no significant change in intensity was observed
upon addition of the same amounts of duplex ds26 DNA
(and only a slight change upon addition of ct-DNA). Upon
encapsulation of this complex inside a hexaruthenium cage,
we have been able to deliver 3 inside living cells, allowing us
to carry out confocal fluorescence microscopy studies. These
studies have shown that the compound is released from the
cage once inside the cell and a considerable amount of it
penetrates the nucleus and localises in the nucleoli. Interest-
ingly, complex 3 does not co-localise with DAPI (a duplex
DNA binder) suggesting that it does not target duplex
DNA. Considering the cellular localisation of the probe (in
the nucleoli) it is possible that alternative DNA topologies,
such as quadruplexes are being targeted. However, further
studies will be required to confirm this.
Figure 3. Two-colour fluorescence image of U20S cells incubated with
DAPI (0.5 mm) for 30 min (lex =405 nm, lem =420–520 nm; shown in
green) and 2 mm caged-complex [3ꢂ4]
ACTHUGNNERTN(UNG CF3SO3)6 for 24 h (lex =488 nm,
lem =550–700 nm; shown in red). Overlapping regions should appear
yellow. The image shows the lack of co-localisation of the platinum(II)
probe and DAPI fluorescence.
and Figure S24 in the Supporting Information). This sug-
gests that, rather than duplex DNA, complex 3 interacts
with alternative DNA topologies. Previous investigations
have reported similar observations where G-quadruplex
DNA-selective dyes do not co-localise with DAPI in cellular
studies.[10b,19]
We also recorded fluorescence spectra of the platinum
complex from different regions of the cell (Figure S25 in the
Supporting Information). These measurements established
that a significant shift in fluorescent maximum (from 570 to
630 nm) is observed in cells as compared to in vitro solution
studies. The spectral shape is also markedly different, show-
ing the lack of vibrational structure, which might be charac-
teristic of the emission from the lowest charge transfer excit-
ed state, for example, LLCT. Considering that Cl-ligand is
relatively labile, we tested a range of species found in the
cellular environment that could potentially displace Cl and
coordinate to the platinum complex. More specifically, we
investigated the emission of complexes resulting from the
incubation of 3 with glutathione, cysteine, guanosine and
OH (Figure S26 in the Supporting Information). As expect-
ed, the emission of the resulting platinum(II) complexes was
highly sensitive to substitution of chloride by other ligands.
Considerable shifts in the emission maxima were observed.
Experimental Section
Synthesis of 5-(1-ethyloxy)-piperidine-1,10-phenanthroline (1): 5-Chloro-
1,10-phenanthroline (0.200 g, 0.94 mmol) and 1-(2-hydroxyethyl)piperi-
dine (146 mg, 0.94 mmol) were slowly added to a stirred suspension of
powered KOH (264 mg, 5.0 mmol) in DMSO (5 mL). The solution was
stirred under nitrogen at 608C for 4 h. The reaction mixture was extract-
ed with DCM (50 mLꢄ3), washed thoroughly with water (30 mLꢄ3) and
dried over sodium sulfate. The solvent was removed under reduced pres-
sure to yield the product as a brown solid (212 mg, 73%). 1H NMR
(400 MHz, CDCl3): dH =9.23 (dd, 1H, 3JHH =6.0, 2.0 Hz, phen 2-H), 9.05
(dd, 1H, 3JHH =6.0, 2.0 Hz, phenꢀ 2-H), 8.71 (dd, 1H,3JHH =8.0, 2.0 Hz,
phen 4-H), 8.14 (dd, 1H, 3JHH =8.0, 2.0 Hz, phenꢀ 4-H), 7.68 (dd, 1H,
3
3JHH =8.0, 4.0 Hz, phen 3-H), 7.59 (dd, 1H, JHH =8.0, 4.0 Hz, phenꢀ 3-H),
7.00 (s, 1H, phen 5-H), 4.44 (t, 2H, 3JHH =6.0 Hz, ethyl 1-H), 3.03 (t,
2H,3JHH =6.0 Hz, ethyl 2-H), 2.65 (m, 4H, pip 1-H), 1.67 (m, 4H, pip 2-
H), 1.51 ppm (m, 2H, pip 3-H); 13C NMR (400 MHz, [D6]DMSO): dC =
152.1, 150.6, 147.9, 134.6, 130.9, 129.2, 123.7, 123.2, 122.6, 101.7, 66.9,
57.8, 55.2, 26.0, 24.1 ppm; ESI-MS calcd for C19H21N3O [M]+:
307.2 a.m.u.; found [M+H]+: 308.0 a.m.u.; elemental analysis calcd for
C19H21N3O·1.45H2O: C 68.42, H 7.22, N 12.60; found: C 68.86, H 6.76, N
12.58.
In the case of guanosine, a shift towards the blue (lem
=
545 nm) took place, whereas a red-shift (lem =740 nm) was
observed in the presence of the S-donor species, cysteine
and glutathione. Interestingly, in the presence of aqueous
NaOH solution, the emission of the platinum(II) complex
shifted to 620 nm (see the emission from the microscopy
studies at lem =630 nm). These results suggest that the chlor-
ide coordinated to platinum in complex 3 is exchanged in
the cell by a ligand that shifts the emission towards the red.
Also, the shifts observed in the presence of guanosine indi-
cate that complex 3 does not coordinate directly to DNA
since the emission recorded during the microscopy studies is
Synthesis of 2-phenyl-5-(1-ethyloxy)-piperidine-1,10-phenanthroline (2):
2-Phenyl-5-(1-ethyloxy)-piperidine-1,10-phenanthroline
(0.200 g,
0.65 mmol) was dissolved in dry toluene (100 mL) under N2 atmosphere
and the solution was cooled to 08C. Phenyllithium (2.0m solution in dibu-
tyl ether, 0.32 mL, 0.65 mmol) was then added dropwise in a manner as
described by Jakobsen.[20] The resultant deep-brown solution was stirred
under nitrogen atmosphere at 08C for 3 h. After this period MeOH
(10 mL) was added to quench the reaction and the products were re-oxi-
dised by incubating the solution with MnO2 (3 g) for 24 h. The solution
was then filtered through Celite and the solvent was removed to give a
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A Selective Optical Switch for Quadruplex DNA
COMMUNICATION
crude product as a white/yellow oil. Purification was performed by pre-
cipitation/recrystallisation from cold CH3CN to give a pure product as a
white solid (0.19 g, 76%). 1H NMR (400 MHz, CDCl3): dH =9.09 (d, 1H,
3JHH =4.0 Hz, phen 2-H), 8.76 (d, 1H, 3JHH =8.0 Hz, phen 4-H), 8.37 (d,
2H, 3JHH =4.0, 8.0 Hz, phen 3-H), 8.36 (d, 2H, 3JHH =4.0, 8.0 Hz, phen 7-
H), 8.14 (m, 2H, phen 8-H, phenyl 5-H), 8.57 (m, 3H, phenyl 3-H 4-H, 5-
H), 7.50 (d, 1H, 3JHH =8.0 Hz, phenyl 2-H), 7.69 (s, 1H, 3JHH =8.0 Hz,
phen 6-H), 4.45 (brs, ethyl 1-H), 3.04 (brs, 2H, ethyl 2-H), 2.66 (brs, 4H,
piperidine 1-H), 1.68 (brs, 1H, piperidine N+-H), 1.60 (brs, 4H, piperi-
dine 2-H), 1.52 ppm (brs, 2H, piperidine 3-H); 13C NMR (400 MHz,
CDCl3): dC =157.8, 152.2, 148.0, 146.6, 143.1, 139.6, 134.8, 131.8, 129.7,
129.4, 128.8, 128.0, 123.1, 122.4, 120.1, 101.6, 66.8, 57.8, 55.2, 26.0,
24.1 ppm; ESI-MS calcd for C25H25N3O [M]+: 383.2 a.m.u.; found
[M+H]+: 384.0 a.m.u.; IR: n˜ =2935 (w), 1616 (m), 1493 (w), 1395 (m),
1307 (m), 1159 (m), 1124 (m), 1081 (m), 990 (m), 832 (m), 839 (m), 742
(s), 692 cmꢀ1 (s); elemental analysis calcd for: C25H25N3O: C 78.30, H
6.57, N 10.96; found: C 78.18, H 6.60, N 10.80.
3066 (w, CHar), 2965 (s, CH2), 2926 (s, CH2), 1622 (s, COdonq), 1574 (s,
CCtpt), 1536 (s, CNtpt), 1275 (s, CN), 1259 (s, CF3), 1158 cmꢀ1 (s, CO).
¯
Crystal data for 3: C25H24ClN3OPt·CH2Cl2, Mr =697.94, triclinic, P1 (no.
2), a=7.9519(3), b=9.2885(3), c=18.3759(6) ꢅ, a=78.766(3), b=
87.360(3), g=66.949(3)8, V=1224.28(8) ꢅ3, Z=2, 1calcd =1.893 gcmꢀ3
,
m(CuKa)=13.934 mmꢀ1, T=173 K, orange needles, Oxford Diffraction
Xcalibur PX Ultra diffractometer; 4765 independent measured reflec-
tions (Rint =0.0298), F2 refinement,[20]
R CHTUTNGRENNUG(obs)=0.0266, wR2ACHTUNGTREN(NGUN all)=0.0653,
1A
4405 independent observed absorption-corrected reflections [|Fo|>4s-
AHCUTNGTER(GNUNN |Fo|), 2qmax =1458], 307 parameters. CCDC-891672 (3) contains the sup-
plementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of chloro-(2-phenyl-5-(1-ethyloxy)-piperidine-1,10-phenanthro-
line) platinum(II) (3): Compound 2 (0.100 g, 0.26 mmol) and sodium ace-
tate (0.021 g, 0.26 mmol) were stirred in acetonitrile (15 mL) for 10 min.
K2PtCl4 (0.108 g, 0.26 mmol) and DMSO (0.5 mL) were then added and
the reaction mixture was stirred at 658C for 3 days while a yellow precip-
itate formed. The volume of the solution was reduced to about 5 mL and
pentane (20 mL) was added. The resulting precipitate was filtered off,
washed with water (30 mL), pentane (15 mL), diethyl ether (15 mL) and
dried in vacuo. The solid was re-dissolved in DCM, filtered off and the
volume of the filtrate was reduced to about 5 mL. Addition of pentane
afforded a pure compound as a yellow crystalline material (112 mg,
Acknowledgements
The Engineering and Physical Sciences Research Council, UK (EPSRC)
is thanked for financial support including Fellowships to M.K.K. (grant
number: EP/E038980/1) and to R.V. (grant number: EP/H005285/1).
Johnson Matthey is thanked for kindly providing the platinum.
Keywords: G-quadruplexes
·
host–guest interactions
·
molecular cages · optical imaging · platinum
70%). 1H NMR (400 MHz, [D6]DMSO): dH =8.84 (d, 1H, 3JHH =4.0 Hz,
3
phen 2-H), 8.65 (d, 1H, 3JHH =8.0 Hz, phen 4-H), 8.61 (d, 1H, JHH
=
8.0 Hz, phen 7-H), 8.20 (d, 1H, 3JHH =8.0 Hz, phen 8-H), 8.03 (dd, 1H,
3JHH =4.0, 4.0 Hz, phen 3-H), 7.73 (d, 1H, 3JHH =8.0 Hz, phenyl 2-H),
7.56 (d, 1H, 3JHH =8.0 Hz, phenyl 5-H), 7.51 (s, 1H, phen 6-H), 7.22 (d,
[1] a) S. Balasubramanian, S. Neidle, Curr. Opin. Chem. Biol. 2009, 13,
345–353; b) S. Balasubramanian, L. H. Hurley, S. Neidle, Nat. Rev.
Drug Discovery 2011, 10, 261–275.
[2] a) K. M. Miller, R. Rodriguez, Expert Rev. Clin. Pharmacol. 2011, 4,
139–142; b) G. W. Collie, G. N. Parkinson, Chem. Soc. Rev. 2011, 40,
5867–5892.
3
3
1H, JHH =8.0, 8.0 Hz, phenyl 4-H), 7.14 (d, 1H, JHH =8.0, 8.0 Hz, phenyl
3-H), 4.90 (t, 2H, 3JHH =4.0 Hz, ethyl 1-H), 2.90 (t, 2H, 3JHH =4.0 Hz,
ethyl 2-H), 1.55 (m, 4H, piperidine 2-H), 1.43 ppm (m, 2H, piperidine 3-
H); ESI-MS calcd for C25H24ClN3OPt [M]+: 612.1 a.m.u.; found [M+H]+:
614.0 a.m.u.; IR: n˜ =2939 (w), 1623 (m), 1453 (m), 1391 (m), 1302 (m),
1257 (m), 1132 (m), 993 (m), 835 (m), 768 (m), 733 (s), 673 cmꢀ1 (m);
UV/Vis (CH2Cl2): l (e)=261 (14650), 321 (8300), 390 (3700), 438 nm (sh)
(2158 dm3 molꢀ1 cmꢀ1); UV/Vis (aqueous Tris-HCl/KCl buffer): l (e)=
266 (15920), 325 (8383), 403 nm (sh) (3825 dm3 molꢀ1 cmꢀ1); elemental
analysis calcd for C25H24ClN3OPt·0.5H2O: C 48.27, H 4.05, N 6.76;
found: C 48.16, H 3.91, N 6.49.
[3] T. A. Brooks, L. H. Hurley, Genes Cancer 2010, 1, 641–649.
[4] S. Neidle, FEBS J. 2010, 277, 1118–1125.
[5] a) A. Arola, R. Vilar, Curr. Top. Med. Chem. 2008, 8, 1405–1415;
b) D. Monchaud, M.-P. Teulade-Fichou, Org. Biomol. Chem. 2008, 6,
627–636; c) S. N. Georgiades, N. H. Abd Karim, K. Suntharalingam,
R. Vilar, Angew. Chem. 2010, 122, 4114–4128; Angew. Chem. Int.
Ed. 2010, 49, 4020–4034; d) S. M. Haider, S. Neidle, G. N. Parkin-
son, Biochimie 2011, 93, 1239–1251.
[6] a) M. R. Gill, J. Garcia-Lara, S. J. Foster, C. Smythe, G. Battaglia,
J. A. Thomas, Nat. Chem. 2009, 1, 662–667; b) C. Rajput, R. Rut-
kaite, L. Swanson, I. Haq, J. A. Thomas, Chem. Eur. J. 2006, 12,
4611–4619.
[7] J. Alzeer, B. R. Vummidi, P. J. C. Roth, N. W. Luedtke, Angew.
Chem. 2009, 121, 9526–9529; Angew. Chem. Int. Ed. 2009, 48, 9362–
9365.
[8] D.-L. Ma, C.-M. Che, S.-C. Yan, J. Am. Chem. Soc. 2009, 131, 1835–
1846.
Synthesis of cage–probe assembly [3ꢂ4]
ACHTUNGTRENNUNG
alla-prism [Ru6(h6-p-cymene)
6A(tpt)2A(donq)3]
E
G
ACHTUNGTRENNUNG
[60 mg, 0.017 mmol] and platinum complex 3 (10.5 mg, 0.017 mmol) in di-
chloromethane (40 mL) were stirred for 6 h at room temperature. The re-
action mixture was filtered and concentrated in vacuo. The dark residue
was dissolved in dichloromethane (1 mL) and diethyl ether (40 mL) was
added to precipitate a dark-green solid which was dried in vacuo (69 mg,
98%). 1H NMR (400 MHz, CD3CN, 298 K): d=8.37 (br, Ha), 7.92 (br,
Hb), 7.61–7.31 (overlapped, Hb +Hq), 7.20 (br, 1H, Harꢀg), 6.91 (br, 1H,
Harꢀg), 6.39 (br, 1H, Harꢀg), 6.26 (br, 2H, Harꢀg), 5.86 (br, 1H, Harꢀg), 5.78
3
3
(br, 1H, Harꢀg), 5.69 (d, J=5.7 Hz, 12H, Hcym), 5.47 (d, J=5.7 Hz, 12H,
Hcym), 5.25 (br, 1H, Harꢀg), 4.83 (br, 1H, Harꢀg), 4.66 (br, 1H, Harꢀg), 4.44
(br, 2H, CH2O), 2.98 (br, 2H, NCH2CH2O), 2.82 (sept, 3J=6.7 Hz, 6H,
[9] a) K. Meguellati, G. Koripelly, S. Ladame, Angew. Chem. 2010, 122,
2798–2802; Angew. Chem. Int. Ed. 2010, 49, 2738–2742; b) G. Kori-
pelly, K. Meguellati, S. Ladame, Bioconjugate Chem. 2010, 21,
2103–2109.
CH
1.70 (br, 2H, CH
13C{1H} NMR (101 MHz, CD3CN, 298 K): d=171.9 (CO), 170.1 (Ctpt
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
[10] a) C. Yu, K. H.-Y. Chan, K. M.-C. Wong, V. W.-W. Yam, Chem.
Commun. 2009, 3756–3758; b) Y. J. Lu, S. C. Yan, F. Y. Chan, L.
Zou, W. H. Chung, W. L. Wong, B. Qiu, N. Sun, P. H. Chan, Z. S.
Huang, L. Q. Gub, K. Y. Wong, Chem. Commun. 2011, 47, 4971–
4973; c) P. Yang, A. De Cian, M.-P. Teulade-Fichou, J.-L. Mergny, D.
Monchaud, Angew. Chem. 2009, 121, 2222–2225; Angew. Chem. Int.
Ed. 2009, 48, 2188–2191; d) H. Arthanari, S. Basu, T. L. Kawano,
P. H. Bolton, Nucleic Acids Res. 1998, 26, 3724–3728; e) F. Koeppel,
J.-F. Riou, A. Laoui, P. Mailliet, P. B. Arimondo, D. Labit, O. Petit-
genet, C. Helene, J.-L. Mergny, Nucleic Acids Res. 2001, 29, 1087–
1096.
)
153.6, 153.5, 153.9 (CHa), 144.4 (CHarꢀg), 138.9, 138.7, 138.4 (CHq), 135.0
(CHarꢀg), 133.2 (CHarꢀg), 132.3 (CHarꢀg), 130.7 (CHarꢀg), 125.6 (CHarꢀg),
125.0 (CHarꢀg), 125.0 (CHb), 123.9 (CHb), 115.1 (CHarꢀg), 103.0 (CHarꢀg),
104.8 (Carꢀcym), 100.8 (Carꢀcym), 85.0 (CHarꢀcym), 84.1 (CHarꢀcym), 68.8
(CH2O), 58.5 (NCH2CH2O), 56.3 (CH2N), 31.5 CH
ACHTUNGTRENNUNG
(CH2CH2N), 25.3 (CH CHTUGNETRNNUG(CH2)2N), 22.1 (CHACHTUGNTRENNNUG
2A
FTMS+ pNSI (m/z): 1270.43 [3+4+4CF3SO3 +H]3+, 915.83 [3+4+
3CF3SO3 +H]4+; UV/Vis (MeOH): l (e)=708 (8800), 658 (8500), 445
(35200), 324 (63700), 228 nm (195000 dm3 molꢀ1 cmꢀ1); IR (KBr): n˜ =
Chem. Eur. J. 2012, 18, 16277 – 16282
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
16281

R. Vilar et al.
[11] a) J. E. Reed, S. Neidle, R. Vilar, Chem. Commun. 2007, 4366–4368;
b) J. E. Reed, A. J. P. White, S. Neidle, R. Vilar, Dalton Trans. 2009,
2558–2568.
[16] a) B. Therrien, Top. Curr. Chem. 2012, 319, 35–56; b) M. A. Furrer,
F. Schmitt, M. Wiederkehr, L. Juillerat-Jeanneret, B. Therrien,
Dalton Trans. 2012, 41, 7201–7211.
[12] H.-Q. Liu, T.-C. Cheung, C.-M. Che, Chem. Commun. 1996, 1039–
1040.
[13] B. Y.-W. Man, D. S.-H. Chan, H. Yang, S.-W. Ang, F. Yang, S.-C.
Yan, C.-M. Ho, P. Wu, C.-M. Che, C.-H. Leung, D.-L. Ma, Chem.
Commun. 2010, 46, 8534–8536.
[17] H. M. Colquhoun, Z. Zhu, D. J. Williams, M. G. B. Drew, C. J.
Cardin, Y. Gan, A. G. Crawford, T. B. Marder, Chem. Eur. J. 2010,
16, 907–918.
[18] A. Pitto-Barry, O. Zava, P. J. Dyson, R. Deschenaux, B. Therrien,
Inorg. Chem. 2012, 51, 7119–7124.
[14] a) G. Venkataramana, S. Sankararaman, Org. Lett. 2006, 8, 2739–
2742; b) R. Nandy, M. Subramoni, B. Varghese, S. Sankararaman, J.
Org. Chem. 2007, 72, 938–944.
[19] I. Lubitz, D. Zikich, A. Kotlyar, Biochemistry 2010, 49, 3567–3574.
[20] S. Jakobsen, M. Tilset, Tetrahedron Lett. 2011, 52, 3072–3074.
[21] G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112–122.
[15] D. Drygin, A. Siddiqui-Jain, S. OꢀBrien, M. Schwaebe, A. Lin, J.
Bliesath, C. B. Ho, C. Proffitt, K. Trent, J. P. Whitten, J. K. C. Lim,
D. Von Hoff, K. Anderes, W. G. Rice, Cancer Res. 2009, 69, 7653–
7661.
Received: August 22, 2012
Published online: November 20, 2012
16282
www.chemeurj.org
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 16277 – 16282