Highly photocytotoxic 1,4-dipegylated zinc(ii) phthalocyanines. Effects of the chain length on the in vitro photodynamic activities

Article abstract of DOI:10.1039/b814627f

A new series of 1,4-dipegylated zinc(ii) phthalocyanines have been synthesised and spectroscopically characterised. The derivatives ZnPc[O(CH ₂CH₂O)_nMe]₂ (n = 2, 4, ca. 12) have been prepared by mixed cyclisation of the corresponding disubstituted phthalonitriles with an excess of unsubstituted phthalonitrile in the presence of Zn(OAc)₂·2H₂O and 1,8-diazabicyclo[5.4.0]undec- 7-ene. The other two analogues ZnPc[O(CH₂CH₂O) _nMe]₂ (n = 6, 8) have been prepared by chain elongation reaction of ZnPc[O(CH₂CH₂O)₄H]₂. These macrocycles are highly soluble and remain non-aggregated in DMF as shown by the sharp Q-band absorption. Compared with the unsubstituted zinc(ii) phthalocyanine, these di-α-substituted analogues have a red-shifted Q band (at 689 vs. 670 nm) and exhibit a relatively weaker fluorescence emission and a higher efficiency at generating singlet oxygen. Upon illumination, these compounds are highly cytotoxic toward HT29 human colorectal carcinoma and HepG2 human hepatocarcinoma cells. The compounds with medium-length substituents are particularly potent, having IC₅₀ values as low as 0.02 M. The high photodynamic activity of these compounds can be attributed to their high cellular uptake and low aggregation tendency in the biological media, which promote the generation of reactive oxygen species inside the cells. The effects of the chain length on the aggregation behaviour, photophysical properties, cellular uptake and in vitro photodynamic activities of this series of compounds have also been examined.

Full text of DOI:10.1039/b814627f

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Highly photocytotoxic 1,4-dipegylated zinc(II) phthalocyanines. Effects of the
chain length on the in vitro photodynamic activities†
Jian-Yong Liu,a Xiong-Jie Jiang,a Wing-Ping Fongb and Dennis K. P. Ng*a
Received 22nd August 2008, Accepted 10th October 2008
First published as an Advance Article on the web 10th November 2008
DOI: 10.1039/b814627f
A new series of 1,4-dipegylated zinc(II) phthalocyanines have been synthesised and spectroscopically
characterised. The derivatives ZnPc[O(CH2CH2O)nMe]2 (n = 2, 4, ca. 12) have been prepared by mixed
cyclisation of the corresponding disubstituted phthalonitriles with an excess of unsubstituted
phthalonitrile in the presence of Zn(OAc)2·2H2O and 1,8-diazabicyclo[5.4.0]undec-7-ene. The other two
analogues ZnPc[O(CH2CH2O)nMe]2 (n = 6, 8) have been prepared by chain elongation reaction of
ZnPc[O(CH2CH2O)4H]2. These macrocycles are highly soluble and remain non-aggregated in DMF as
shown by the sharp Q-band absorption. Compared with the unsubstituted zinc(II) phthalocyanine,
these di-a-substituted analogues have a red-shifted Q band (at 689 vs. 670 nm) and exhibit a relatively
weaker fluorescence emission and a higher efficiency at generating singlet oxygen. Upon illumination,
these compounds are highly cytotoxic toward HT29 human colorectal carcinoma and HepG2 human
hepatocarcinoma cells. The compounds with medium-length substituents are particularly potent,
having IC50 values as low as 0.02 mM. The high photodynamic activity of these compounds can be
attributed to their high cellular uptake and low aggregation tendency in the biological media, which
promote the generation of reactive oxygen species inside the cells. The effects of the chain length on the
aggregation behaviour, photophysical properties, cellular uptake and in vitro photodynamic activities of
this series of compounds have also been examined.
is also a desirable characteristic for efficient photosensitisers.5
Classical phthalocyanine-based photosensitisers include liposo-
mal zinc(II) phthalocyanine, sulfonated zinc(II) and aluminum(III)
Introduction
Phthalocyanines are macrocyclic compounds containing four N-
fused isoindole units. The highly conjugated p systems absorb
strongly in the red visible region. This property, together with
the extraordinary stability of these compounds, renders them able
to be used as classical blue pigments.1 Recently, the applications
of these compounds have been greatly extended, ranging from
materials science, catalysis, nanotechnology to medicine,2 mainly
as a result of their versatile characteristics. Through rational
modification, the intrinsic properties as well as the molecular
stacking of the macrocycles can be adjusted. This facilitates
the optimisation of their performance as advanced functional
materials.3
In biomedical applications, phthalocyanines are promising
second-generation photosensitisers for photodynamic therapy
(PDT) as a result of their strong absorption of tissue-penetrating
red light and high efficiency at generating singlet oxygen.4
Hydrophilic moieties can also be incorporated readily into the
macrocycles making the molecules amphiphilic in nature, which
phthalocyanines and the silicon(IV) phthalocyanine Pc4 developed
by Kenney and co-workers. Over the last few years, we6 and others7
have greatly extended this series of compounds. A substantial
number of phthalocyanine derivatives have been prepared and
evaluated for their photodynamic activities, focusing on the
structure-property-activity relationships. As a continuing effort
in this endeavour, we report herein a new series of zinc(II)
phthalocyanines having two diethylene glycol to polyethylene
glycol chains at the 1,4-di-a-positions, including their synthesis,
spectroscopic and photophysical properties, as well as their in vitro
photodynamic activities. The effects of the chain length on these
properties have also been examined.
Results and discussion
Molecular design and synthesis
Although a vast number of phthalocyanines have been reported, to
our knowledge, these 1,4-disubstituted analogues remain relatively
rare.6b,8 Compared with the unsubstituted zinc(II) phthalocyanine
(ZnPc), they exhibit a red-shifted Q band (at ca. 690 vs. 670 nm for
ZnPc), which allows deeper light penetration into tissues.9 The two
substituents added near the macrocyclic core can also effectively
enhance the solubility and reduce the aggregation tendency of
the macrocycles. This strategy is different from those reported in
the literature such as the introduction of bulky substituents at
the axial or peripheral positions,10 and the use of perfluorinated
substituents.11 All of these characteristics are beneficial for PDT
aDepartment of Chemistry and Centre of Novel Functional Molecules, The
Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China. E-mail:
dkpn@cuhk.edu.hk; Fax: +852 2603 5057; Tel: +852 2609 6375
bDepartment of Biochemistry and Centre of Novel Functional Molecules,
The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China
† Electronic supplementary information (ESI) available: Electronic ab-
sorption spectra of 5a and 5f in thin films; comparison of the rates of
decay of DPBF in DMF using phthalocyanines 5a–5c, 5e–5f and ZnPc
as the photosensitisers; electronic absorption spectra of 5a–5c and 5e–
1
5f in the RPMI medium; 1H and 13C{ H} NMR spectra of all the new
compounds. See DOI: 10.1039/b814627f
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application. Zinc(II) ion was selected as the metal centre because of
the general robustness and the desirable photophysical properties
of these metallo-phthalocyanines.12 Polyethylene glycols are also
excellent pharmaceutical carriers which can prolong the drugs’
circulating half-life, minimise their non-specific uptake and enable
specific tumour-targeting through the enhanced permeability and
retention (EPR) effect.13 Addition of these hydrophilic chains
to the hydrophobic macrocyclic core also imparts a high am-
phiphilicity to the photosensitisers. Hence, we believed that these
specially designed molecules, which fulfil most of the criteria
for superior photosensitisers,14 would behave ideally. Substituents
having different numbers of oxyethylene units were introduced
with a view to fine-tuning the photodynamic activities. It is worth
noting that although various pegylated photosensitisers have been
reported,15 the effects of the chain length on their photodynamic
activities remain little studied.
Scheme 1 shows the synthetic pathway used to prepare ph-
thalocyanines ZnPc[O(CH2CH2O)nMe]2 [n = 2 (5a), 4 (5b), ca.
12 (5c)], which contain two diethylene glycol to polyethylene
glycol methyl ether chains at the 1,4-positions. The synthesis first
involves the nucleophilic substitution reaction of tosylates 1a–
1c with 2,3-dicyanohydroquinone (2) to afford the disubstituted
phthalonitriles 3a–3c. The tosylate 1c was prepared from the
commercially available polyethylene glycol methyl ether having
an average molecular weight of 550. These phthalonitriles then
underwent mixed cyclisation with an excess of unsubstituted
phthalonitrile (4) (9 equiv.) in the presence of Zn(OAc)2·2H2O and
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in n-pentanol to give
the respective phthalocyanines 5a–5c in 12–15% yield. Although
these reactions also afforded other cyclised products, particularly
ZnPc, these disubstituted analogues were readily isolated by col-
umn chromatography followed by size exclusion chromatography
as a result of their high solubility and low aggregation tendency in
common organic solvents.
This synthetic route can also be applied to prepare the non-
methyl protected analogue 5d (Scheme 1). Starting from the
tetraethylene glycol monotosylate (1d) and following this reaction
sequence, the dihydroxy phthalocyanine ZnPc[O(CH2CH2O)4H]2
(5d) was obtained with comparable yield. The hydroxy groups
could tolerate the conditions for these substitution and cyclisation
reactions.
This compound was found to be an excellent precursor for
other 1,4-disubstituted analogues through transformations of the
terminal hydroxy groups. Thus treatment of 5d with tosylate
1a or 1b in the presence of NaH led to chain elongation
giving ZnPc[O(CH2CH2O)nMe]2 [n = 6 (5e), 8 (5f)] in moderate
yield (Scheme 2). With these two procedures, a series of 1,4-
disubstituted zinc(II) phthalocyanines having two diethylene glycol
to polyethylene glycol methyl ether chains were prepared.
All of the new compounds were fully characterised with various
spectroscopic methods. The 1H NMR spectra of phthalocyanines
5a–5f were recorded in CDCl3 with a trace amount of pyridine-d5
added to reduce the aggregation of these compounds. Generally,
the spectra showed one to two multiplet(s) at the most downfield
position (at ca. d 9.4) for the phthalocyanine a ring protons, and
one multiplet (at ca. d 8.2, 6 H) and a singlet (at ca. d 7.6, 2 H)
for the phthalocyanine b ring protons. For the chains’ methylene
protons near the phthalocyanine ring, the signals, mostly in a
triplet form, were shifted downfield significantly (up to ca. d 5.0)
by the ring current. As expected, the length of the chains
Scheme 1
Scheme 2
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did not exert a significant influence on the positions of these
signals.
the two a-substituents can somewhat reduce the stacking tendency
of these compounds even in the solid state.
The FAB or ESI mass spectra of all of these compounds showed
the molecular ion signals. Accurate mass measurements were also
performed to confirm the identity of these compounds. In the
ESI mass spectrum of 5c, two major envelopes for the protonated
[M + H]+ and sodiated [M + Na]+ molecular ions were observed.
For both of them, the clusters are separated by 44 mass units
corresponding to the molecular mass of the repeating unit of
polyethylene glycol.
Compared with ZnPc, these di-a-substituted analogues exhibit
a red-shifted Q band (at 689 vs. 670 nm for ZnPc). It has been
found that attachment of electron-releasing alkoxy groups at the
a positions of phthalocyanines destabilises their HOMO level
more than the LUMO level.16 As a result, the HOMO-LUMO
gap is reduced upon a-substitution, which can explain the red
shift observed for this series of compounds.
Upon excitation at the vibronic band, these compounds showed
a fluorescence emission at 698 nm with a quantum yield (UF) of
0.18–0.19 in DMF (Table 1) relative to ZnPc (UF = 0.28).17 The
weaker fluorescence of these compounds is in accord with the
general observation that the lower the energy of the Q band, the
smaller the UF value.16 It is likely that as the HOMO-LUMO gap
decreases, electron transfer may take place more readily which
lowers the stability of the excited state.
The singlet oxygen generation efficiency of these di-a-
substituted phthalocyanines was also examined in DMF by a
steady-state method using 1,3-diphenylisobenzofuran (DPBF) as
the scavenger. The concentration of the quencher was monitored
spectroscopically at 411 nm over time, from which the singlet
oxygen quantum yields (UD) were determined by the previously
described method.18 Fig. S2† compares the rates of decay of DPBF
using 5a–5c, 5e–5f and ZnPc as the photosensitisers. The values of
UD are also compiled in Table 1. It can be seen that all of these di-
a-substituted phthalocyanines are highly efficient singlet oxygen
generators having comparable quantum yields (UD = 0.81–0.83).
Their efficiency is significantly higher than that of ZnPc, which
was used as the reference.
Electronic absorption and photophysical properties
The electronic absorption spectra of ZnPc[O(CH2CH2O)nMe]2
(n = 2, 4, 6, 8, ca. 12) 5a–5c and 5e–5f were recorded in
DMF. The spectra showed typical features of non-aggregated
phthalocyanines. They displayed a Soret band at 340 nm, an
intense and sharp Q band at 689 nm, together with a vibronic
band at 621–622 nm. For all of these compounds, the Q band
strictly followed the Lambert-Beer law (up to 5 mM), indicating
that these compounds are essentially free from aggregation in
DMF. The spectrum of 5a is given as an example (Fig. 1). As
shown in Table 1, the data are virtually the same for this series of
compounds showing that the length of the chains does not affect
the p macrocyclic system.
In vitro photodynamic activities
The in vitro photodynamic activities of these phthalocyanines in
Cremophor EL emulsions were investigated against two different
cell lines, namely HT29 human colorectal carcinoma and HepG2
human hepatocarcinoma cells. Fig. 2 compares the effects of
these compounds on the two cell lines both in the absence and
presence of light. It can be seen that all of these compounds are
essentially non-cytotoxic in the dark, but upon illumination, they
exhibit substantial cytotoxicity. The corresponding IC50 values,
defined as the dye concentration required to kill 50% of the
cells, are summarised in Table 2. For both of the cell lines, the
photocytotoxicity of these compounds depends on the length of
the substituents. Fig. 3 depicts the variation of the IC50 values with
the number of oxyethylene unit in the chains. For HepG2, the dyes
with shorter chains (n = 2, 4, 6) are generally more potent than
the analogues with longer substituents (n = 8, ca. 12). For HT29,
Fig. 1 Electronic absorption spectra of 5a at different concentrations
in DMF. The insert plots the Q-band absorbance at 689 nm versus the
concentration of 5a.
For comparison, the absorption spectra of 5a and 5f in thin
solid films were also recorded (Fig. S1†). The Q bands were
significantly broadened with a shoulder at ca. 650 nm. However,
the absorption maxima (at ca. 700 nm) were not significantly
shifted compared with those in DMF (689 nm). It suggested that
Table 1 Electronic absorption and photophysical data for phthalocyanines 5a–5c and 5e–5f in DMF
b
c
Compound
lmax (nm) (log e)
lem (nm)a
UF
UD
ZnPc[O(CH2CH2O)2Me]2 (5a)
ZnPc[O(CH2CH2O)4Me]2 (5b)
ZnPc[O(CH2CH2O)6Me]2 (5e)
ZnPc[O(CH2CH2O)8Me]2 (5f)
ZnPc[O(CH2CH2O)nMe]2 (n = ca. 12) (5c)
340 (4.73), 621 (4.52), 689 (5.27)
340 (4.77), 621 (4.58), 689 (5.33)
340 (4.77), 622 (4.57), 689 (5.31)
340 (4.73), 621 (4.53), 689 (5.28)
340 (4.71), 622 (4.48), 689 (5.23)
698
698
698
698
698
0.18
0.18
0.18
0.18
0.19
0.83
0.83
0.83
0.82
0.81
a Excited at 621 nm. b Relative to ZnPc (UF = 0.28 in DMF). c Relative to ZnPc (UD = 0.56 in DMF).
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Fig. 2 Effects of 5a (squares), 5b (triangles), 5c (stars), 5e (circles) and 5f (pentagons) on HT29 (left) and HepG2 (right) in the absence (closed symbols)
and presence (open symbols) of light (l >610 nm, 40 mW cm-2, 48 J cm-2). Data are expressed as mean values standard error of the mean of three
independent experiments, each performed in quadruplicate.
Fig. 3 The effects of chain length on the photocytotoxicity of phthalocyanines 5a–5c and 5e–5f for HT29 (left) and HepG2 (right) cells.
Table 2 Comparison of the IC50 values of phthalocyanines 5a–5c and
5e–5f against HT29 and HepG2
For HT29
(mM)
For HepG2
(mM)
Photosensitiser
ZnPc[O(CH2CH2O)2Me]2 (5a)
ZnPc[O(CH2CH2O)4Me]2 (5b)
ZnPc[O(CH2CH2O)6Me]2 (5e)
ZnPc[O(CH2CH2O)8Me]2 (5f)
ZnPc[O(CH2CH2O)nMe]2 (n = ca. 12) (5c)
0.22
0.05
0.02
0.11
0.92
0.09
0.09
0.10
1.24
2.98
compound 5e (with n = 6) shows the highest photocytotoxicity. A
further increase in the chain length results in a substantial increase
in the IC50 value. The in vitro photocytotoxicity attained by 5e
(IC50 = 0.02 mM for HT29) is in fact very high compared with that
of the classical photosensitiser porfimer sodium (IC50 = 7.5 mg
mL-1 vs. 23.3 ng mL-1 for 5e),19 pheophorbide a (IC50 = 0.5 mM),19
and other mono- and tetrasubstituted zinc(II) phthalocyanines
prepared by us recently.6b,d,20 It is believed that the high potency of
5e is also related to its unique 1,4-di-a-substitution pattern.
To account for the different photodynamic activities of these
compounds, their aggregation behaviour in the culture media
was examined by absorption spectroscopy. Fig. 4 shows the
electronic absorption spectra of these compounds in the Dul-
becco’s modified Eagle’s medium (DMEM) used for HT29 cells.
It can be seen that the Q bands of ZnPc[O(CH2CH2O)4Me]2
(5b) and ZnPc[O(CH2CH2O)6Me]2 (5e) remain sharp and intense,
indicating that these compounds are not significantly aggregated
in the medium. The spectrum of ZnPc[O(CH2CH2O)2Me]2 (5a)
Fig. 4 Electronic absorption spectra of 5a–5c and 5e–5f, formulated with
Cremophor EL, in DMEM (all at 8 mM).
also has similar spectral features, but the intensity of the Q band is
substantially weaker due to its lower solubility in this medium. In
fact, precipitation occurred after leaving the solution for ca. 2 h.
For ZnPc[O(CH2CH2O)8Me]2 (5f) and ZnPc[O(CH2CH2O)nMe]2
(n = ca. 12) (5c), in addition to the Q band at ca. 700 nm,
the blue-shifted Q band at ca. 650 nm attributable to the H-
aggregates21 become more prominent. Hence, for this series of
compounds, when the number of oxyethylene unit is larger than 6,
the compounds tend to aggregate in the culture medium, probably
due to the stronger dipole-dipole interactions among the side
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chains. Aggregation provides an efficient non-radiative relaxation
pathway thereby reducing the population of the triplet state and
the singlet oxygen generation efficiency.22 The different solubility
and aggregation tendencies of this series of compounds in DMEM
can well explain the observed trend of photocytotoxicity (Table 2
and Fig. 3a), despite the fact that these compounds have virtually
the same singlet oxygen quantum yield in DMF (Table 1). Similar
results were observed in the RPMI medium 1640 used for HepG2
(Fig. S3†).
In addition to the cell viability studies, we also employed
confocal microscopy to investigate the uptake of these photosen-
sitisers by HT29 cells. After incubation with these compounds
(formulated with Cremophor EL) for 2 h and upon excitation
at 630 nm, the HT29 cells showed intracellular fluorescence
throughout the cytoplasm as shown in Fig. 5, indicating that
there was a substantial uptake of the dyes. The intensity generally
decreases as the length of the substituent increases, i.e. 5a >
5b > 5e > 5f > 5c. The results suggest that as the length of the
substituent increases, the compounds show a lower cellular uptake
and/or higher aggregation tendency, both of which are undesirable
for photosensitisation. This can also explain the trend of photo-
cytotoxicity observed for this series of compounds (Table 2).
General procedure for the preparation of phthalonitriles 3a–3d
A mixture of 2,3-dicyanohydroquinone (2) (1 equiv.), tosylates
1a–1d (2 equiv.) and K2CO3 (2 equiv.) in DMF (20–30 mL) was
stirred at 90 ◦C under an atmosphere of nitrogen for 24 h. The
volatiles were removed in vacuo, then the residue was mixed with
water (100 mL) and extracted with CH2Cl2 (80 mL ¥ 3). The
combined organic extracts were dried over anhydrous MgSO4.
After evaporation under reduced pressure, the residue was purified
by silica gel column chromatography using CHCl3/CH3OH
(100:1 v/v) as the eluent.
Phthalonitrile 3a
According to the general procedure, 2,3-dicyanohydroquinone (2)
(2.40 g, 15.0 mmol) was treated with tosylate 1a (8.22 g, 30.0 mmol)
and K2CO3 (4.14 g, 30.0 mmol) to give 3a as a pale white solid
(4.42 g, 81%). 1H NMR (300 MHz, CDCl3): d 7.23 (s, 2 H, ArH),
4.25 (t, J = 4.8 Hz, 4 H, CH2), 3.90 (t, J = 4.8 Hz, 4 H, CH2),
3.73–3.76 (m, 4 H, CH2), 3.55–3.58 (m, 4 H, CH2), 3.39 (s, 6 H,
1
CH3). 13C{ H} NMR (75.4 MHz, CDCl3): d 155.4, 119.1, 112.9,
105.6, 71.9, 71.1, 70.1, 69.4, 59.0. MS (ESI): m/z 387 {100%, [M +
Na]+}. HRMS (ESI) calcd for C18H24N2NaO6 [M + Na]+ 387.1527,
found: 387.1535. Anal. calcd for C18H24N2O6: C, 59.33; H, 6.64;
N, 7.69. Found: C, 59.50; H, 6.82; N, 7.55.
Phthalonitrile 3b
According to the general procedure, 2,3-dicyanohydroquinone (2)
(0.48 g, 3.0 mmol) was treated with tosylate 1b (2.17 g, 6.0 mmol)
and K2CO3 (0.83 g, 6.0 mmol) to give 3b as a pale white solid
(1.36 g, 84%). 1H NMR (300 MHz, CDCl3): d 7.27 (s, 2 H, ArH),
4.25 (t, J = 4.2 Hz, 4 H, CH2), 3.90 (t, J = 4.2 Hz, 4 H, CH2),
3.71–3.76 (m, 4 H, CH2), 3.63–3.68 (m, 16 H, CH2), 3.53–3.58 (m,
1
4 H, CH2), 3.37 (s, 6 H, CH3). 13C{ H} NMR (75.4 MHz, CDCl3):
d 155.3, 119.2, 112.9, 105.3, 71.8, 71.0, 70.5 (three overlapping
signals), 70.4, 70.0, 69.3, 58.9. MS (FAB): m/z 541 {100%, [M +
H]+}. HRMS (FAB) calcd for C26H41N2O10 [M + H]+ 541.2756,
found: 541.2742.
Fig. 5 Fluorescence microscopic images of HT29 after incubation with
ZnPc[O(CH2CH2O)nMe]2 (5a–5c and 5e–5f) at a concentration of 8 mM
for 2 h.
Phthalonitrile 3c
Conclusions
According to the general procedure, 2,3-dicyanohydroquinone
(2) (2.00 g, 12.5 mmol) was treated with tosylate 1c (18.51 g,
26.3 mmol) and K2CO3 (3.63 g, 26.3 mmol) to give 3c as a pale
yellow oil (12.57 g, 82%). 1H NMR (300 MHz, CDCl3): d 7.26 (s,
2 H, ArH), 4.24 (t, J = 4.5 Hz, 4 H, CH2), 3.90 (t, J = 4.5 Hz, 4 H,
CH2), 3.61–3.76 (m, ca. 84 H, CH2), 3.53–3.56 (m, 4 H, CH2), 3.38
(s, 6 H, CH3). MS (ESI): m/z 1267 {52%, [M + Na]+ for n = 12}.
In summary, we have prepared and characterised a new series of
zinc(II) phthalocyanines with two diethylene glycol to polyethylene
glycol methyl ether chains at the 1,4-di-a-positions. This unique
substitution pattern shifts the Q-band absorption to the red
and reduces the aggregation of the macrocycles. All of these
compounds are photocytotoxic against HT29 and HepG2 cells.
The solubility and aggregation behaviour in the culture media,
cellular uptake and eventually the potency of these compounds
greatly depend on the chain length. Optimal results can be achieved
for compounds 5b and 5e, which respectively have two tetra- or
hexaethylene glycol methyl ether chains.
Phthalonitrile 3d
According to the general procedure, 2,3-dicyanohydroquinone (2)
(1.91 g, 11.9 mmol) was treated with tosylate 1d (8.28 g, 23.8 mmol)
and K2CO3 (3.28 g, 23.7 mmol) to afford 3d as a pale white solid
(5.62 g, 92%). 1H NMR (300 MHz, CDCl3): d 7.29 (s, 2 H, ArH),
4.26 (t, J = 4.5 Hz, 4 H, CH2), 3.89 (t, J = 4.5 Hz, 4 H, CH2), 3.73–
3.77 (m, 4 H, CH2), 3.64–3.71 (m, 16 H, CH2), 3.59–3.62 (m, 4 H,
Experimental
Experimental details regarding the purification of solvents, instru-
mentation and in vitro studies are described elsewhere.6a Tosylates
1a,23 1b,23 1c24 and 1d25 were prepared as described.
1
CH2), 2.86 (br s, 2 H, OH). 13C{ H} NMR (75.4 MHz, CDCl3): d
155.3, 119.3, 113.0, 105.2, 72.4, 70.9, 70.5, 70.4, 70.1, 70.0, 69.3,
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61.5. MS (ESI): m/z 535 {100%, [M + Na]+}. HRMS (ESI) calcd
(0.53 g, 4.14 mmol) and Zn(OAc)2·2H2O (0.25 g, 1.14 mmol) to
1
for C24H36N2NaO10 [M + Na]+ 535.2262, found: 535.2255.
give 5c as a blue oil (0.10 g, 13%). H NMR (300 MHz, CDCl3
with a trace amount of pyridine-d5): d 9.41–9.49 (m, 6 H, Pc-Ha),
8.15–8.18 (m, 6 H, Pc–Hb), 7.58 (s, 2 H, Pc–Hb), 4.97 (t, J = 5.1 Hz,
4 H, CH2), 4.56 (t, J = 5.1 Hz, 4 H, CH2), 4.16 (t, J = 4.8 Hz, 4 H,
CH2), 3.87 (t, J = 4.8 Hz, 4 H, CH2), 3.69–3.72 (m, 4 H, CH2),
3.57–3.68 (m, ca. 72 H, CH2), 3.51–3.56 (m, 4 H, CH2), 3.35–3.38
(m, 6 H, CH3). MS (ESI): an isotopic cluster peaking at m/z 1715
{13%, [M + Na]+ for n = 12}.
General procedure for the preparation of phthalocyanines 5a–5d
A mixture of phthalonitriles 3a–3d (1 equiv.), unsubstituted
phthalonitrile (4) (9 equiv.) and Zn(OAc)2·2H2O (2.5 equiv.) in
n-pentanol (25 mL) was heated to 100 ◦C, then a small amount◦of
DBU (1 mL) was added. The mixture was stirred at 140–150 C
for 24 h. After a brief cooling, the volatiles were removed under
reduced pressure. The residue was dissolved in CHCl3 (200 mL),
then the solution was filtered to remove the ZnPc formed. The
filtrate was collected and evaporated to dryness in vacuo. The
residue was purified by silica gel column chromatography using
CHCl3/CH3OH (30:1 v/v) as the eluent, followed by size exclusion
chromatography using THF as the eluent. The crude product was
further purified by recrystallisation from a mixture of THF and
hexane to give the product as a blue solid or oil.
ZnPc[O(CH2CH2O)4H]2 (5d)
According to the general procedure, phthalonitrile 3d (0.50 g,
0.98 mmol) was treated with unsubstituted phthalonitrile (4)
(1.13 g, 8.82 mmol) and Zn(OAc)2·2H2O (0.54 g, 2.46 mmol) to
give 5d as a blue solid (0.13 g, 14%). 1H NMR (300 MHz, CDCl3
with a trace amount of pyridine-d5): d 9.43–9.49 (m, 4 H, Pc-Ha),
9.39–9.41 (m, 2 H, Pc–Ha), 8.12–8.18 (m, 6 H, Pc–Hb), 7.58 (s,
2 H, Pc–Hb), 4.97 (t, J = 4.8 Hz, 4 H, CH2), 4.54 (t, J = 4.8 Hz,
4 H, CH2), 4.14 (t, J = 4.5 Hz, 4 H, CH2), 3.84 (t, J = 4.5 Hz,
4 H, CH2), 3.58–3.68 (m, 12 H, CH2), 3.51 (t, J = 4.5 Hz, 4 H,
ZnPc[O(CH2CH2O)2Me]2 (5a)
According to the general procedure, phthalonitrile 3a (0.73 g,
2.0 mmol) was treated with unsubstituted phthalonitrile (4) (2.31 g,
18.0 mmol) and Zn(OAc)2·2H2O (1.10 g, 5.0 mmol) to give 5a as a
blue solid (0.24 g, 15%). 1H NMR (300 MHz, CDCl3 with a trace
amount of pyridine-d5): d 9.41–9.49 (m, 6 H, Pc–Ha), 8.14–8.19
(m, 6 H, Pc–Hb), 7.57 (s, 2 H, Pc–Hb), 4.99 (t, J = 5.1 Hz, 4 H,
CH2), 4.57 (t, J = 5.1 Hz, 4 H, CH2), 4.15 (t, J = 4.8 Hz, 4 H,
1
CH2). 13C{ H} NMR (75.4 MHz, CDCl3): d 153.0, 152.8, 152.7,
150.9, 148.4, 138.4, 138.3, 138.2, 128.5, 128.3, 128.2, 125.1, 123.0,
122.3, 121.9, 112.3, 70.8, 70.6, 70.2 (two overlapping signals), 70.0,
69.1, 67.9, 59.4. UV-Vis (DMF) [lmax (nm), (log e)]: 341 (4.72), 621
(4.53), 689 (5.28). MS (ESI): an isotopic cluster peaking at m/z 961
{100%, [M + H]+}. HRMS (ESI) calcd for C48H49N8O10Zn [M +
H]+ 961.2858, found: 961.2848. Anal. calcd for C48H48N8O10Zn:
C, 59.91; H, 5.03; N, 11.64. Found: C, 59.49; H, 5.17; N,
11.16.
1
CH2), 3.76 (t, J = 4.8 Hz, 4 H, CH2), 3.44 (s, 6 H, CH3). 13C{ H}
NMR (75.4 MHz, DMSO-d6): d 152.6, 152.5, 152.4, 151.9, 149.8,
138.3, 138.0, 137.9, 129.3, 129.2, 126.2, 122.5, 122.3, 115.4, 71.8,
70.4, 70.3, 69.1, 58.4 (some of the Pc signals are overlapped). MS
(ESI): an isotopic cluster peaking at m/z 813 {100%, [M + H]+}.
HRMS (ESI) calcd for C42H37N8O6Zn [M + H]+ 813.2122, found:
813.2121. Anal. calcd for C42H36N8O6Zn: C, 61.96; H, 4.46; N,
13.76. Found: C, 62.45; H, 4.83; N, 13.47.
ZnPc[O(CH2CH2O)6Me]2 (5e)
Phthalocyanine 5d (96 mg, 0.10 mmol) was added to a suspension
of NaH (60% in mineral oil, 40 mg, 1.00 mmol) in THF (8 mL).
After the evolution of gas bubbles had ceased, a solution of the
monotosylate 1a (110 mg, 0.40 mmol) in THF (2 mL) was added
slowly. The resulting mixture was refluxed overnight. A few drops
of water were then added to quench the reaction. The volatiles
were removed under reduced pressure. The residue was mixed with
water (20 mL) and the mixture was extracted with CHCl3 (20 mL
x 3). The combined organic extracts were dried over anhydrous
MgSO4 and evaporated under reduced pressure. The residue was
chromatographed on a silica gel column using CHCl3/CH3OH
(20:1 v/v) as the eluent. The product was obtained as a blue solid
ZnPc[O(CH2CH2O)4Me]2 (5b)
According to the general procedure, phthalonitrile 3b (0.54 g,
1.0 mmol) was treated with unsubstituted phthalonitrile (4) (1.15 g,
9.0 mmol) and Zn(OAc)2·2H2O (0.55 g, 2.5 mmol) to give 5b as a
blue solid (0.12 g, 12%). 1H NMR (300 MHz, CDCl3 with a trace
amount of pyridine-d5): d 9.34–9.40 (m, 4 H, Pc-Ha), 9.25–9.27
(m, 2 H, Pc–Ha), 8.07–8.15 (m, 6 H, Pc-Hb), 7.42 (s, 2 H, Pc-Hb),
4.92 (t, J = 5.1 Hz, 4 H, CH2), 4.52 (t, J = 5.1 Hz, 4 H, CH2),
4.15 (t, J = 4.8 Hz, 4 H, CH2), 3.87 (t, J = 4.8 Hz, 4 H, CH2),
3.72–3.75 (m, 4 H, CH2), 3.60–3.67 (m, 8 H, CH2), 3.49–3.52 (m,
1
4 H, CH2), 3.33 (s, 6 H, CH3). 13C{ H} NMR (75.4 MHz, CDCl3
1
(62 mg, 53%). H NMR (300 MHz, CDCl3 with a trace amount
of pyridine-d5): d 9.40–9.51 (m, 6 H, Pc–Ha), 8.12–8.20 (m, 6 H,
Pc–Hb), 7.58 (s, 2 H, Pc–Hb), 4.97 (t, J = 4.8 Hz, 4 H, CH2), 4.56 (t,
J = 4.8 Hz, 4 H, CH2), 4.15 (t, J = 4.8 Hz, 4 H, CH2), 3.87 (t, J =
4.8 Hz, 4 H, CH2), 3.69–3.73 (m, 4 H, CH2), 3.57–3.65 (m, 24 H,
with a trace amount of pyridine-d5): d 153.9, 153.8, 153.6, 152.6,
150.4, 138.9, 138.5, 129.0, 127.4, 122.7, 122.5, 115.0, 71.8, 71.1,
70.8, 70.6, 70.5 (two overlapping signals), 70.4, 69.2, 58.9 (some
of the Pc signals are overlapped). MS (FAB): an isotopic cluster
peaking at m/z 989 {100%, [M + H]+}. HRMS (FAB) calcd for
C50H53N8O10Zn [M + H]+ 989.3171, found: 989.3149.
1
CH2), 3.47–3.52 (m, 4 H, CH2), 3.32 (s, 6 H, CH3). 13C{ H} NMR
(75.4 MHz, CDCl3 with a trace amount of pyridine-d5): d 154.0,
153.8, 153.7, 152.7, 150.4, 138.9, 138.5, 129.0, 127.4, 122.7, 122.5,
115.0, 71.8, 71.1, 70.7, 70.6, 70.5, 69.2, 58.9 (some of the signals
are overlapped). MS (ESI): an isotopic cluster peaking at m/z 1165
{98%, [M + H]+}. HRMS (ESI) calcd for C58H69N8O14Zn [M +
H]+ 1165.4219, found: 1165.4209.
ZnPc[O(CH2CH2O)nMe]2 (n = ca. 12) (5c)
According to the general procedure, phthalonitrile 3c (0.57 g,
0.47 mmol) was treated with unsubstituted phthalonitrile (4)
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Org. Biomol. Chem., 2008, 6, 4560–4566 | 4565
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ZnPc[O(CH2CH2O)8Me]2 (5f)
and K. Kataoka, Nature Mater., 2005, 4, 934; (b) W. M. Sharman and
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According to the above procedure, treatment of phthalocyanine
5d (96 mg, 0.10 mmol) with tosylate 1b (145 mg, 0.40 mmol) and
NaH (60% in mineral oil, 40 mg, 1.00 mmol) afforded 5f as a
blue solid (68 mg, 51%). 1H NMR (300 MHz, CDCl3 with a trace
amount of pyridine-d5): d 9.43–9.47 (m, 4 H, Pc–Ha), 9.37–9.40
(m, 2 H, Pc–Ha), 8.11–8.16 (m, 6 H, Pc–Hb), 7.53 (s, 2 H, Pc–Hb),
4.96 (t, J = 5.1 Hz, 4 H, CH2), 4.55 (t, J = 5.1 Hz, 4 H, CH2),
4.16 (t, J = 4.8 Hz, 4 H, CH2), 3.87 (t, J = 4.8 Hz, 4 H, CH2),
3.70–3.73 (m, 4 H, CH2), 3.59–3.66 (m, 40 H, CH2), 3.50–3.53
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Lane, Sci. Am., 2003, 288(1), 38.
(m, 4 H, CH2), 3.35 (s, 6 H, CH3). 13C{ H} NMR (75.4 MHz,
1
10 See for example:(a) J. S. Shirk, R. G. S. Pong, S. R. Flom, H. Heckmann
and M. Hanack, J. Phys. Chem. A, 2000, 104, 1438; (b) D. K. P. Ng,
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12 K. Ishii and N. Kobayashi, in The Porphyrin Handbook, eds.
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CDCl3 with a trace amount of pyridine-d5): d 153.5, 153.3, 153.2,
152.2, 150.0, 138.7, 138.3, 138.2, 128.7, 126.9, 122.5, 122.3, 114.5,
71.8, 71.0, 70.7, 70.5, 70.4, 68.9, 58.9 (some of the signals are
overlapped). MS (FAB): an isotopic cluster peaking at m/z 1342
{100%, [M + H]+}. HRMS (FAB) calcd for C66H85N8O18Zn [M +
H]+ 1341.5268, found: 1341.5282.
Acknowledgements
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This work was supported by a strategic investments scheme
administered by The Chinese University of Hong Kong.
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4566 | Org. Biomol. Chem., 2008, 6, 4560–4566
This journal is
The Royal Society of Chemistry 2008
©