Synthesis and in vitro photodynamic activities of di-α-substituted zinc(ii) phthalocyanine derivatives

Article abstract of DOI:10.1039/b817940a

A new series of di-α-substituted zinc(ii) phthalocyanine derivatives have been prepared by mixed cyclisation of the corresponding 1,4-disubstituted phthalonitriles or naphthalonitriles with an excess of unsubstituted phthalonitrile in the presence of Zn(O

Full text of DOI:10.1039/b817940a

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Dalton
Transactions
An international journal of inorganic chemistry
www.rsc.org/dalton
Number 21 | 7 June 2009 | Pages 4041–4260
ISSN 1477-9226
HOT ARTICLE
Ng et al.
HOT ARTICLE
Andrews et al.
Synthesis and in vitro photodynamic
activities of di-α-substituted zinc(ii)
phthalocyanine derivatives
Infrared spectra and density functional
theory calculations of coinage metal
disulfide molecules and complexes
1477-9226(2009)21;1-3

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and in vitro photodynamic activities of di-a-substituted zinc(II)
phthalocyanine derivatives†
Jian-Yong Liu,a Pui-Chi Lo,a Xiong-Jie Jiang,a Wing-Ping Fongb and Dennis K. P. Ng*a
Received 13th October 2008, Accepted 15th January 2009
First published as an Advance Article on the web 18th February 2009
DOI: 10.1039/b817940a
A new series of di-a-substituted zinc(II) phthalocyanine derivatives have been prepared by mixed
cyclisation of the corresponding 1,4-disubstituted phthalonitriles or naphthalonitriles with an excess of
unsubstituted phthalonitrile in the presence of Zn(OAc)2·2H2O and 1,8-diazabicyclo[5.4.0]undec-7-ene.
Having a large hydrophobic macrocyclic core substituted with two hydrophilic triethylene glycol chains
or glycerol moieties, these compounds are amphiphilic in nature. They are highly soluble and remain
non-aggregated in DMF as shown by the intense and sharp Q-band absorption. Compared with the
unsubstituted zinc(II) phthalocyanine, these di-a-substituted analogues exhibit a red-shifted Q band
(at 689–701 nm), a relatively weaker fluorescence emission, and a higher efficiency to generate singlet
oxygen. Upon illumination, these compounds are highly cytotoxic towards HT29 human colorectal
carcinoma and HepG2 human hepatocarcinoma cells with IC50 values as low as 0.06 mM. The high
photocytotoxicity of these compounds can be attributed to their high cellular uptake and low
aggregation tendency in the biological media, leading to a high efficiency to generate reactive oxygen
species inside the cells.
application of the light.1b Porphyrin derivatives are traditional
Introduction
photosensitisers. These compounds, however, generally induce
Photodynamic therapy (PDT) has emerged as a non-invasive
sustained skin photosensitivity, show weak absorptions in the
modality for the treatment of malignant tumours and wet age-
body’s therapeutic window (650–800 nm), and require long
related macular degeneration.1 It involves the combination of
drug-to-light intervals (48–96 h), making them far from ideal
for the use in PDT.2 Therefore, there is a great impetus for
the development of non-porphyrin photosensitisers, which have
stronger absorptions in the red visible region and improved
photophysical and biological properties.3 Phthalocyanines, gen-
erally having these desirable characteristics, are promising second-
generation photosensitisers, which have received considerable
attention over the last decade.4 We have been interested in
the use of these functional dyes in this avenue, focusing on
their structure-property-activity relationships.5 Various chemical
modifications have been performed on the macrocyclic core with
a view to enhancing the therapeutic outcome. In this report, we
describe a novel series of di-a-substituted zinc(II) phthalocyanine
derivatives. The two substituents adding to the a positions of
the macrocycles not only shift their Q-band absorption further
to the red (ca. 700 nm), allowing a deeper light penetration
into tissues, but also reduce their aggregation tendency, thereby
promoting the generation of singlet oxygen. To our knowledge,
this class of disubstituted phthalocyanines remains rare.5b,6 We
report herein the synthesis, spectroscopic and photophysical char-
acteristics, as well as the in vitro photodynamic activities of these
compounds.
visible light and a photosensitiser. Both components are harmless
by themselves, but in combination with oxygen, they result
in the generation of reactive oxygen species (ROS) leading to
oxidative cell damage. Fig. 1 depicts the basic mechanism of
action of PDT. For cancer treatment, PDT has several potential
advantages including its non-invasive nature, tolerance of repeated
doses, and high specificity that can be achieved through precise
Fig. 1 Basic mechanism of the action of PDT.
aDepartment of Chemistry and Centre of Novel Functional Molecules,
The Chinese University of Hong Kong, Shatin, N.T., Hong Kong.
E-mail: dkpn@cuhk.edu.hk; Fax: +852 2603 5057; Tel: +852 2609 6375
Results and discussion
bDepartment of Biochemistry and Centre of Novel Functional Molecules,
The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
Synthesis and characterisation
1
† Electronic supplementary information (ESI) available: H NMR spec-
trum of 9a, UV-vis spectra of 6a and 9a in the RPMI medium,
Scheme 1 shows the synthetic route used to prepare the 1,4-
di-a-substituted phthalocyanines 6a–6c. Firstly, the alcohols
1a–1c were converted to the corresponding tosylates 2a–2c,
fluorescence images of HT29 after incubation with 6a–6d and 9a–9b,
1
1
and H and 13C{ H} NMR spectra of all the new compounds. See DOI:
10.1039/b817940a
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Scheme 1 Synthesis of 1,4-disubstituted zinc(II) phthalocyanines 6a–6c.
which then underwent nucleophilic substitution with 2,3-
dicyanohydroquinone (3) to give the disubstituted phthalonitriles
4a–4c. Mixed cyclisation of these compounds with an excess
of unsubstituted phthalonitrile (5) (9 equiv.) in the presence of
Zn(OAc)2·2H2O and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in
1-pentanol afforded the corresponding “3 + 1” cyclised products
6a–6c as a blue solid. These oxygen-rich substituents were used
to enhance the solubility and reduce the aggregation of these
macrocycles, facilitating their separation from the other cyclised
side products, particularly the unsubstituted zinc(II) phthalocya-
nine (ZnPc), which was found to be the major product. Hence,
these 1,4-di-a-substituted phthalocyanines 6a–6c could be isolated
readily by silica gel column chromatography followed by size
exclusion chromatography in 12–18%. Polyethylene glycols are
also known to be excellent pharmaceutical vehicles, which can
prolong circulating half-life, minimise non-specific uptake, and
enable specific tumour-targeting through the enhanced perme-
ability and retention (EPR) effect.7 In addition, these hydrophilic
moieties adding to the hydrophobic core will make the molecules
amphiphilic in character, which is a desirable characteristic for
efficient photosensitisers.8
Scheme 2 Synthesis of tetrahydroxy zinc(II) phthalocyanine 6d.
could not be purified by column chromatography. It was simply
isolated by precipitation. The sample was found to be essentially
pure.
To further extend the Q-band absorption to the red, we also
prepared the benzo-fused analogues 9a and 9b according to
Scheme 3. The tosylates 2a and 2b were treated with 1,4-dihydroxy-
2,3-naphthalonitrile (7) and K2CO3 to give the disubstituted
products 8a and 8b, respectively. Similarly, mixed cyclisation
of these naphthalonitriles with 5 (9 equiv.) in the presence of
Zn(OAc)2·2H2O and DBU led to the formation of 9a and 9b as a
green solid in 13–15% yield.
The two isopropylidene groups of 6c could be removed readily
upon treatment with a mixture of trifluoroacetic acid (TFA) and
H2O (9 : 1 v/v) giving the tetrahydroxy phthalocyanine 6d in 85%
yield (Scheme 2). This compound has a very high polarity and
All of the zinc(II) phthalocyanines 6a–6d and 9a–9b are soluble
in common organic solvents and possess a high general stability.
They were fully characterised with various spectroscopic methods
and elemental analysis. The NMR spectra were recorded in
Scheme 3 Synthesis of benzo-fused zinc(II) phthalocyanines 9a and 9b.
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Table 1 Electronic absorption and fluorescence data for 6a–6d and 9a–9b
CDCl3 with a trace amount of pyridine-d5, which can reduce
the aggregation of these compounds. The only exception is the
tetrahydroxy analogue 6d, of which the spectra were recorded
in DMF
b
Compound
l
max/nm (log e)
l
em/nma
UF
1
in DMSO-d6. Fig. 2 shows the H-1H COSY spectrum of 6d to
illustrate the general spectral features of these compounds. The
signals for the six phthalocyanine a ring protons overlap as a
multiplet at d 9.32–9.41. For compounds 6a and 6c, a multiplet
and a doublet (in 2 : 1 integration ratio) were observed instead for
these protons. The phthalocyanine b ring protons of 6d resonate
as a multiplet (at d 8.19–8.26, 6 H) and a singlet (at d 7.77, 2 H).
The doublet at d 5.56 and triplet at d 4.96 can easily be assigned
to the secondary and primary hydroxy groups, respectively. The
other signals can also be unambiguously assigned as shown in
the figure with the aid of the connectivity revealed by the COSY
experiment.
6a
6b
6c
6d
9a
9b
341 (4.71), 621 (4.51), 689 (5.27)
342 (4.69), 621 (4.47), 689 (5.24)
341 (4.78), 621 (4.58), 689 (5.34)
344 (4.77), 623 (4.57), 692 (5.32)
343 (4.76), 632 (4.59), 701 (5.24)
343 (4.78), 632 (4.60), 701 (5.25)
698
698
697
699
720
720
0.17
0.19
0.19
0.18
0.12
0.14
a Excited at 621 (for 6a–6d) or 632 nm (for 9a–9b). b Using ZnPc in DMF
as the reference (UF = 0.28).
as an example, it shows a broad Soret band peaking at 342 nm,
an intense and sharp Q band at 689 nm, together with a vibronic
band at 621 nm. The Q band strictly follows the Lambert Beer’s law
suggesting that aggregation of this compound is not significant.
Compared with ZnPc, the mono-a-alkoxy analogues have a red-
shifted Q band (from 670 to 672–679 nm).5d,9 The di-a-substitution
in 6a–6d further shifts the Q band to the red (689–692 nm), but the
positions are still not as far as those of the tetra- (696 nm) and octa-
a-butoxy analogues (758 nm).10 It has been shown that attachment
of an electron-releasing alkoxy group at the a position destabilises
the HOMO level more than the LUMO level.10 As a result, the
HOMO–LUMO gap is reduced upon a-substitution, which can
explain the red shift in this series of compounds. Introduction of an
additional fused benzene ring in 9a–9b extends the p-conjugated
system, leading to a further red-shift of the Q band to 701 nm.
These data are summarised in Table 1.
Fig. 2 1H-1H COSY spectrum of 6d in DMSO-d6.
For 9a and 9b, the signals for the naphthyl a and b ring
protons were also seen adjacent to the respective phthalocyanine
ring protons’ signals. In the spectrum of 9b (ESI, Fig. S1†), four
well-resolved doublets of doublets (at d 9.41, 9.37, 9.29 and 9.08)
were observed for the four different sets of a ring protons. The
remaining four different sets of b ring protons resonated as two
overlapping doublets of doublets (at d 8.09–8.15) and another
two doublets of doublets (at d 8.04 and 7.91). Six well-separated
virtual triplets or multiplets (in the region d 3.6–5.7) and a singlet
(at d 3.41) were also seen for the six sets of methylene protons and
the methyl groups, respectively, of the chains.
The 13C{ H} NMR spectra of these phthalocyanines showed
1
clearly the expected number of signals for the substituents, but
for the phthalocyanine ring, some of the signals were overlapped.
All of these compounds were further characterised with ESI mass
spectrometry. The isotopic distribution as well as the exact mass
for the [M + H]+ or [M + Na]+ species were in good agreement
with the calculated ones.
Fig. 3 Electronic absorption spectra of 6b at various concentrations in
DMF. The inset plots the Q-band absorbance versus the concentration
of 6b.
The fluorescence emission spectra of these compounds were also
recorded in DMF. Upon excitation at 621 nm, compounds 6a–6d
showed a fluorescence emission at 697–699 nm with a quantum
yield (UF) of 0.17–0.19, which is substantially lower than that of
ZnPc (UF = 0.28). For the benzo-fused analogues 9a–9b, upon
excitation at 632 nm, their fluorescence emission was red-shifted
to 720 nm with an even lower UF value (0.12–0.14) (Table 1). This
is in accord with the general observation that the lower the energy
of the Q band, the smaller the UF value.10 It has been suggested
Electronic absorption and photophysical properties
The electronic absorption spectra of phthalocyanines 6a–6d
in DMF are very similar and are typical for non-aggregated
phthalocyanines. It is likely that DMF, being a coordinating
solvent, binds axially to these zinc(II) phthalocyanines, reducing
their aggregation tendency. Taking the spectrum of 6b (Fig. 3)
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Table 2 IC50 values of 6a–6d and 9a–9b against HT29 and HepG2 cells
IC50/mM
that the excited state becomes unstable as the HOMO–LUMO gap
decreases, probably due to the ease of electron transfer.
The efficiency of these compounds in generating singlet oxy-
gen, as reflected by the rate of decay of the singlet oxygen
quencher 1,3-diphenylisobenzofuran (DPBF), was also compared.
As shown in Fig. 4, all of these phthalocyanines can induce the
photo-bleaching of DPBF and the efficiency follows the order
9a–9b > 6a–6d > ZnPc. This suggests that as the HOMO–LUMO
gap becomes smaller, the singlet excited state has a higher tendency
to undergo intersystem crossing to generate singlet oxygen. This
can also explain the opposite trend observed for the UF values.
Compound
For HT29
For HepG2
6a
6b
6c
6d
9a
9b
0.41
0.13
0.40
0.38
2.93
5.18
0.16
0.06
0.40
0.17
2.76
5.84
Fig. 4 Comparison of the rates of decay of DPBF in DMF (initial
concentration = 1.85 ¥ 10-4 M), as monitored spectroscopically at 411 nm,
using phthalocyanines 6a–6d and 9a–9b as the photosensitisers and ZnPc
as the reference.
Fig. 5 Effects of 6a (squares) and 9a (triangles) on HT29 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 S.E.M.
of three independent experiments, each performed in quadruplicate.
in DMF, their photocytotoxicity is significantly lower than that of
6a–6d. To account for these results, the absorption spectra of these
compounds in the culture media were examined. Fig. 6 shows the
spectra of 6a and 9a in the DMEM medium (used for HT29),
which are typical for these two groups of compounds. It can be
seen that the Q band for 6a remains sharp and intense, while that
for 9a is significantly weaker and broadened. Similar results were
observed in the RPMI medium (used for HepG2) (ESI, Fig. S2†).
In vitro photodynamic activities
The in vitro photodynamic activities of compounds 6a–6d and
9a–9b in Cremophor EL emulsions were investigated against two
different cell lines, namely HT29 human colorectal carcinoma and
HepG2 human hepatocarcinoma cells. Fig. 5 shows the dose-
dependent survival curves for 6a and 9a towards HT29 given
for exemplification. It can be seen that both compounds are
essentially non-cytotoxic in the absence of light (up to 4 and 8 mM,
respectively). However, they become cytotoxic upon illumination
with red light (l > 610 nm). Compound 6a is significantly more
potent with an IC50 value of 0.41 mM (vs. 2.93 mM for 9a). Only
ca. 1 mM of dye is required to essentially kill all the cells (vs. >
8 mM for 9a). The photocytotoxicity of 6b–6d is comparable with
that of 6a, which is significantly higher than that of 9a–9b. The
corresponding IC50 values are compiled in Table 2. Among these
compounds, 6b exhibits the highest photocytotoxicity with IC50
values down to 0.06 mM. This compound is among the most potent
zinc(II) phthalocyanines prepared in our laboratory so far.5b,5d,9,11
Its in vitro photocytotoxicity almost reaches the level attained by
some of the very potent silicon(IV) analogues.5a,5e,12 As shown by
the IC50 values for 6c and 6d (Table 2), removing the isopropylidene
protecting groups of 6c does not exert a significant effect on the
photocytotoxicity.
It is worth noting that although the benzo-fused phthalocya-
nines 9a–9b exhibit a higher efficiency in generating singlet oxygen
Fig. 6 Electronic absorption spectra of 6a (—) and 9a (---), formulated
with Cremophor EL, in the DMEM culture medium (both at 8 mM).
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The results indicate that compound 9a (as well as 9b), having a
larger p-conjugated system, is more aggregated than 6a (as well as
6b–6d) in the culture media, thereby reducing its photosensitising
efficiency.
The cellular uptake of these phthalocyanines was also inves-
tigated by fluorescence microscopy. After incubation with 6a–6d
for 2 h, the HT29 cells showed a strong intracellular fluorescence
image throughout the cytoplasm with similar brightness, indicat-
ing that there was substantial uptake of these dyes. However, the
intensity was much weaker when the dyes 9a–9b were used (ESI,
Fig. S3†). Hence, the lower photocytotoxicity of 9a–9b may be
attributed to their higher aggregation tendency in the biological
media and/or lower cellular uptake.
3,6-Bis(3,6,9-trioxadecoxy)phthalonitrile (4b)
According to the above procedure, 2,3-dicyanohydroquinone (3)
(1.60 g, 10.0 mmol) was treated with tosylate 2b (6.36 g, 20.0 mmol)
and K2CO3 (2.76 g, 20.0 mmol) to give phthalonitrile 4b as a
white solid (3.81 g, 84%). M.p. 49.6–50.2 ◦C. 1H NMR (300 MHz,
CDCl3): d 7.25 (s, 2 H, ArH), 4.24 (t, J = 4.8 Hz, 4 H, CH2), 3.90
(t, J = 4.8 Hz, 4 H, CH2), 3.74–3.77 (m, 4 H, CH2), 3.64–3.69 (m,
8 H, CH2), 3.54–3.57 (m, 4 H, CH2), 3.38 (s, 6 H, CH3). 13C{ H}
1
NMR (75.4 MHz, CDCl3): d 155.3, 119.2, 112.9, 105.5, 71.9, 71.0,
70.6, 70.5, 70.1, 69.4, 59.0. MS (ESI): m/z 475 (100%, [M + Na]+).
HRMS (ESI) calcd for C22H32N2NaO8 [M + Na]+ 475.2051, found:
475.2046. Anal. calcd for C22H32N2O8: C 58.40, H 7.13, N 6.19.
Found: C 58.60, H 7.06, N 6.15.
Conclusions
3,6-Bis(2,2-dimethyl-1,3-dioxol-4-ylmethoxy)phthalonitrile (4c)
In summary, we have prepared and characterised a new series
of di-a-substituted zinc(II) phthalocyanine derivatives. These
rare disubstituted phthalocyanines possess a high solubility, low
aggregation tendency, and high efficiency in generating singlet
oxygen, rendering them to be useful as photosensitisers. The
two substituents adding at the a positions also shift the Q-band
absorption to the red, which is desirable for PDT application.
Addition of a fused benzene ring, however, promotes aggregation
of the macrocycles in biological media, resulting in a lower
photocytotoxicity.
According to the above procedure, 2,3-dicyanohydroquinone (3)
(4.27 g, 26.7 mmol) was treated with tosylate 2c (15.28 g,
53.4 mmol) and K2CO3 (7.45 g, 53.9 m◦mol) to give 4c as a white
1
solid (8.97 g, 86%). M.p. 174.5–175.4 C. H NMR (300 MHz,
CDCl3): d 7.24 (s, 2 H, ArH), 4.44–4.53 (m, 2 H, CH), 4.13–4.22
(m, 4 H, CH), 4.05–4.10 (m, 2 H, CH), 3.97–4.02 (m, 2 H, CH),
1
1.44 (s, 6 H, CH3), 1.39 (s, 6 H, CH3). 13C{ H} NMR (75.4 MHz,
CDCl3): d 155.0, 118.9, 112.6, 110.0, 105.8, 73.5, 70.2, 66.4, 26.7,
25.2. MS (ESI): m/z 411 (100%, [M + Na]+). HRMS (ESI) calcd
for C20H24N2NaO6 [M + Na]+ 411.1527, found: 411.1532. Anal.
calcd for C20H24N2O6: C 61.85, H 6.23, N 7.21. Found: C 61.80, H
6.33, N 6.96.
Experimental
[1,4-Bis(8-hydroxy-3,6-dioxaoctoxy)phthalocyaninato]zinc(II) (6a)
The experimental details regarding the purification of solvents,
instrumentation, photophysical measurements, and in vitro studies
were described previously.5a The tosylates 2a,13 2b14 and 2c,15
and 1,4-dihydroxy-2,3-naphthalonitrile (7)16 were prepared as
described.
A mixture of phthalonitrile 4a (0.50 g, 1.2 mmol), unsubstituted
phthalonitrile (5) (1.36 g, 10.6 mmol), and Zn(OAc)2·2H2O (0.65 g,
3.0 mmol) in 1-pentanol (15 mL) was heated to 100 ◦C, then
◦
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 (150 mL),
then filtered to remove part of 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 [Bio-Rad Bio-Beads S-X1 beads (200–400 mesh)]
using THF as the eluent. The crude product was further purified
by recrystallisation from a mixture of THF and hexane to give
phthalocyanine 6a as a blue solid (0.19 g, 18%). 1H NMR
(300 MHz, CDCl3 with a trace amount of pyridine-d5): d 9.37–
9.41 (m, 4 H, Pc–Ha), 9.25 (d, J = 6.0 Hz, 2 H, Pc–Ha), 8.06–8.15
(m, 6 H, Pc–Hb), 7.39 (s, 2 H, Pc–Hb), 4.91 (t, J = 4.8 Hz, 4 H,
CH2), 4.49 (t, J = 4.8 Hz, 4 H, CH2), 4.11–4.15 (m, 4 H, CH2),
3.85–3.88 (m, 4 H, CH2), 3.68–3.71 (m, 4 H, CH2), 3.63–3.66
3,6-Bis(8-hydroxy-3,6-dioxaoctoxy)phthalonitrile (4a)
A mixture of 2,3-dicyanohydroquinone (3) (2.40 g, 15.0 mmol),
tosylate 2a (9.12 g, 30.0 mmol) and K2CO3 (4.14 g, 30.0 mmol)
in DMF (20 mL) was stirred at 90 ◦C under an atmosphere of
nitrogen for 24 h. The volatiles were removed in vacuo. The residue
was mixed with water (100 mL), then extracted with CH2Cl2 (3 ¥
80 mL). The combined organic extracts was dried over anhydrous
MgSO4 and then evaporated to dryness under reduced pressure.
The residue was chromatographed on a silica gel column using
CHCl3–CH3OH (100 : 1 v/v) as the eluent. The produ◦ct was
1
obtained as a white solid (5.02 g, 79%). M.p. 78.4–79.0 C. H
NMR (300 MHz, DMSO-d6): d 7.64 (s, 2 H, ArH), 4.58 (t, J =
5.4 Hz, 2 H, OH), 4.30 (vt, J = 4.5 Hz, 4 H, CH2), 3.77 (vt,
J = 4.5 Hz, 4 H, CH2), 3.59–3.62 (m, 4 H, CH2), 3.51–3.54
(m, 4 H, CH2), 3.46 (t, J = 4.8 Hz, 4 H, CH2), 3.39–3.42 (m,
1
(m, 4 H, CH2). 13C{ H} NMR (75.4 MHz, CDCl3 with a trace
amount of pyridine-d5): d 153.8, 153.7, 153.5, 152.4, 150.2, 138.7,
138.4, 128.9, 128.8, 127.2, 122.6, 122.4, 114.9, 72.7, 71.0, 70.4,
69.1, 61.3 (some of the Pc and chain signals are overlapped). MS
(ESI): an isotopic cluster peaking at m/z 873 (100%, [M + H]+).
HRMS (ESI) calcd for C44H41N8O8Zn [M + H]+ 873.2333, found:
873.2342. Anal. calcd for C44H40N8O8Zn: C 60.45, H 4.61, N 12.82.
Found: C 60.49, H 4.24, N 12.83.
1
4 H, CH2). 13C{ H} NMR (75.4 MHz, CDCl3): d 155.4, 119.4,
113.0, 105.4, 72.4, 71.1, 70.3, 70.1, 69.4, 61.6. MS (ESI): m/z
447 (100%, [M + Na]+). HRMS (ESI) calcd for C20H28N2NaO8
[M + Na]+ 447.1738, found: 447.1745. Anal. calcd for C21H32N2O9
(4a·CH3OH): C 55.25, H 7.07, N 6.14. Found: C 55.33, H 6.73, N
6.30.
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[1,4-Bis(3,6,9-trioxadecoxy)phthalocyaninato]zinc(II) (6b)
1,4-Bis(8-hydroxy-3,6-dioxaoctoxy)-2,3-naphthalonitrile (8a)
According to the above procedure, phthalonitrile 4b (0.50 g,
1.1 mmol) was treated with unsubstituted phthalonitrile (5) (1.28 g,
10.0 mmol) and Zn(OAc)2·2H2O (0.61 g, 2.8 mmol) to give 6b as
A mixture of 1,4-dihydroxy-2,3-naphthalonitrile (7) (1.26 g,
6.0 mmol), tosylate 2a (3.65 g, 12.0 mmol), and anhydrous K2CO3
(1.66 g, 12.0 mmol) in DMF (12 mL) was stirred vigorously at
90 ◦C for 24 h. The volatiles were then removed under reduced
pressure. The residue was mixed with water (60 mL) and the
mixture was extracted with chloroform (3 ¥ 60 mL). The combined
organic extracts was dried over anhydrous MgSO4 and evaporated
to dryness under reduced pressure. The residue was subject to silica
gel column chromatography using CHCl3–CH3OH (60 : 1 v/v) as
the eluent. Compound 8a was obtained as a brown oil (2.53 g,
89%). 1H NMR (300 MHz, CDCl3): d 8.38 (dd, J = 3.3, 6.3 Hz,
2 H, ArH), 7.79 (dd, J = 3.3, 6.3 Hz, 2 H, ArH), 4.57–4.60 (m,
4 H, CH2), 3.96–3.99 (m, 4 H, CH2), 3.68–3.77 (m, 12 H, CH2),
1
a blue solid (0.12 g, 12%). 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), 4.98 (t, J = 5.1 Hz,
4 H, CH2), 4.56 (t, J = 5.1 Hz, 4 H, CH2), 4.15–4.18 (m, 4 H,
CH2), 3.86–3.89 (m, 4 H, CH2), 3.69–3.72 (m, 4 H, CH2), 3.52–
1
3.55 (m, 4 H, CH2), 3.35 (s, 6 H, CH3). 13C{ H} NMR (75.4 MHz,
CDCl3 with a trace amount of pyridine-d5): d 153.5, 153.4, 153.3,
152.2, 150.0, 138.7, 138.3, 138.2, 128.7, 127.0, 122.5, 122.3, 114.6,
71.8, 71.0, 70.7, 70.5 70.4, 68.9, 58.9 (some of the Pc signals are
overlapped). MS (ESI): an isotopic cluster peaking at m/z 901
(100%, [M + H]+). HRMS (ESI) calcd for C46H45N8O8Zn [M +
H]+ 901.2646, found: 901.2645. Anal. calcd for C46H44N8O8Zn:
1
3.58–3.61 (m, 4 H, CH2), 2.49 (br s, 2 H, OH). 13C{ H} NMR
(75.4 MHz, CDCl3): d 157.5, 130.7, 130.3, 123.9, 114.2, 99.6, 75.1,
72.4, 70.7, 70.2, 70.1, 61.6. MS (ESI): m/z 497 (100%, [M + Na]+).
HRMS (ESI) calcd for C24H30N2NaO8 [M + Na]+ 497.1894, found:
497.1893.
C
61.23,
H 4.92, N 12.42. Found: C 61.21, H 5.02,
N 12.04.
[1,4-Bis(2,2-dimethyl-1,3-dioxol-4-ylmethoxy)phthalocyanin-
ato]zinc(II) (6c)
1,4-Bis(3,6,9-trioxadecoxy)-2,3-naphthalonitrile (8b)
According to the above procedure, 1,4-dihydroxy-2,3-
naphthalonitrile (7) (0.63 g, 3.0 mmol) was treated with
tosylate 2b (1.91 g, 6.0 mmol) and K2CO3 (0.83 g, 6.0 mmol)
According to the above procedure, phthalonitrile 4c (0.50 g,
1.3 mmol) was treated with unsubstituted phthalonitrile (5)
(1.49 g, 11.6 mmol) and Zn(OAc)2·2H2O (0.71 g, 3.2 mmol) to
1
to give 8b as a brown oil (1.31 g, 87%). H NMR (300 MHz,
1
give phthalocyanine 6c as a blue solid (0.17 g, 16%). H NMR
CDCl3): d 8.41 (dd, J = 3.3, 6.3 Hz, 2 H, ArH), 7.78 (dd, J =
3.3, 6.3 Hz, 2 H, ArH), 4.58 (vt, J = 4.5 Hz, 4 H, CH2), 3.96 (vt,
J = 4.5 Hz, 4 H, CH2), 3.74–3.77 (m, 4 H, CH2), 3.64–3.70 (m,
(300 MHz, CDCl3 with a trace amount of pyridine-d5): d 9.32–
9.37 (m, 4 H, Pc–Ha), 9.13 (d, J = 7.2 Hz, 2 H, Pc–Ha), 8.00–8.13
(m, 6 H, Pc–Hb), 7.22 (d, J = 8.1 Hz, 2 H, Pc–Hb), 5.14–5.24 (m,
2 H, CH), 4.73–4.85 (m, 2 H, CH), 4.57–4.72 (m, 4 H, CH), 4.45–
1
8 H, CH2), 3.53–3.57 (m, 4 H, CH2), 3.38 (s, 6 H, CH3). 13C{ H}
NMR (75.4 MHz, CDCl3): d 157.6, 130.6, 130.4, 124.1, 114.3,
99.6, 75.2, 71.9, 70.8, 70.6, 70.5, 70.1, 59.0. MS (ESI): m/z 525
(100%, [M + Na]+). HRMS (ESI) calcd for C26H34N2NaO8 [M +
Na]+ 525.2207, found: 525.2210.
1
4.51 (m, 2 H, CH), 1.72 (s, 6 H, CH3), 1.66 (s, 6 H, CH3). 13C{ H}
NMR (75.4 MHz, CDCl3 with a trace amount of pyridine-d5): d
153.5, 153.4, 153.0, 151.7, 149.7, 138.7, 138.3, 128.7, 126.8, 122.4,
122.3, 122.2, 114.0, 113.9, 109.8, 74.8, 70.3, 67.3, 27.0, 25.6 (some
of the Pc signals are overlapped). MS (ESI): an isotopic cluster
peaking at m/z 837 (100%, [M + H]+). HRMS (ESI) calcd for
C44H37N8O6Zn [M + H]+ 837.2122, found: 837.2133. Anal. calcd
for C44H36N8O6Zn: C 63.05, H 4.33, N 13.37. Found: C 63.32, H
4.49, N 13.05.
Benzo-fused phthalocyanine 9a
According to the procedure described for 6a, naphthalonitrile 8a
(0.60 g, 1.3 mmol) was treated with unsubstituted phthalonitrile
(5) (1.46 g, 11.4 mmol) and Zn(OAc)2·2H2O (0.70 g, 3.2 mmol)
1
to give 9a as a green solid (0.17 g, 15%). H NMR (300 MHz,
CDCl3 with a trace amount of pyridine-d5): d 9.20–9.35 (m, 6 H,
Pc–Ha), 9.02–9.06 (m, 2 H, Np–Ha), 7.98–8.09 (m, 6 H, Pc–Hb),
7.87–7.90 (m, 2 H, Np–Hb), 5.63 (vt, J = 4.5 Hz, 4 H, CH2),
4.45 (vt, J = 4.5 Hz, 4 H, CH2), 4.02–4.05 (m, 4 H, CH2), 3.90–
3.94 (m, 4 H, CH2), 3.81–3.85 (m, 4 H, CH2), 3.74–3.77 (m, 4 H,
[1,4-Bis(2,3-dihydroxypropoxy)phthalocyaninato]zinc(II) (6d)
A solution of phthalocyanine 6c (60 mg, 0.07 mmol) in TFA–H2O
(9 : 1 v/v) (4 mL) was stirred at room temperature for 30 min. The
volatiles were then removed under reduced pressure. The residue
was dissolved in a mixture of THF (2 mL) and CH3OH (4 mL),
then hexane (8 mL) was added to induce precipitation. The mixture
was filtered to give a blue solid, which was dried in vacuo (46 mg,
1
CH2). 13C{ H} NMR (75.4 MHz, CDCl3 with a trace amount
of pyridine-d5): d 154.1, 154.0, 152.6, 152.3, 148.5, 138.3, 138.2,
137.9, 130.8, 129.0, 128.8, 128.5, 127.3, 125.6, 124.3, 122.5, 122.4,
122.2, 74.2, 72.8, 71.4, 71.0, 70.6, 61.6. MS (ESI): an isotopic
cluster peaking at m/z 945 (100%, [M + Na]+). HRMS (ESI) calcd
for C48H42N8NaO8Zn [M + Na]+ 945.2309, found: 945.2297. Anal.
calcd for C49H46N8O9Zn (9a·CH3OH): C 61.54, H 4.85, N 11.72.
Found: C 61.66, H 4.80, N 11.67.
1
85%). H NMR (300 MHz, DMSO-d6): d 9.32–9.41 (m, 6 H,
Pc–Ha), 8.19–8.26 (m, 6 H, Pc–Hb), 7.77 (s, 2 H, Pc–Hb), 5.56 (d,
J = 4.5 Hz, 2 H, OH), 4.96 (t, J = 5.7 Hz, 2 H, OH), 4.66–4.77
(m, 4 H, CH), 4.46–4.51 (m, 2 H, CH), 4.16–4.24 (m, 2 H, CH),
1
4.00–4.08 (m, 2 H, CH). 13C{ H} NMR (75.4 MHz, DMSO-d6): d
153.1, 152.9, 152.7, 150.6, 138.4, 138.1, 138.0, 129.5, 129.6, 129.7,
126.7, 123.1, 122.6, 116.5, 71.7, 70.9, 63.4 (some of the Pc signals
are overlapped). MS (ESI): an isotopic cluster peaking at m/z 757
(100%, [M + H]+). HRMS (ESI) calcd for C38H29N8O6Zn [M +
H]+ 757.1496, found: 757.1480.
Benzo-fused phthalocyanine 9b
According to the procedure described for 6a, naphthalonitrile 8b
(0.44 g, 0.9 mmol) was treated with unsubstituted phthalonitrile
4134 | Dalton Trans., 2009, 4129–4135
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(5) (1.01 g, 7.9 mmol) and Zn(OAc)2·2H2O (0.48 g, 2.2 mmol) to
give 9b as a green solid (0.11 g, 13%). 1H NMR (300 MHz, CDCl3
with a trace amount of pyridine-d5): d 9.41 (dd, J = 2.7, 5.7 Hz,
2 H, Pc–Ha), 9.37 (dd, J = 2.7, 5.7 Hz, 2 H, Pc–Ha), 9.29 (dd,
J = 3.0, 5.4 Hz, 2 H, Pc–Ha), 9.08 (dd, J = 3.3, 6.3 Hz, 2 H,
Np–Ha), 8.09–8.15 (m, 4 H, Pc–Hb), 8.04 (dd, J = 2.7, 5.7 Hz,
2 H, Pc–Hb), 7.91 (dd, J = 3.3, 6.3 Hz, 2 H, Np–Hb), 5.64 (vt,
J = 4.5 Hz, 4 H, CH2), 4.46 (vt, J = 4.5 Hz, 4 H, CH2), 4.04–
4.07 (m, 4 H, CH2), 3.91–3.94 (m, 4 H, CH2), 3.79–3.82 (m, 4 H,
3 (a) M. R. Detty, S. L. Gibson and S. J. Wagner, J. Med. Chem., 2004, 47,
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5 See for example: (a) P.-C. Lo, C. M. H. Chan, J.-Y. Liu, W.-P. Fong and
D. K. P. Ng, J. Med. Chem., 2007, 50, 2100 and references cited therein;
(b) J.-Y. Liu, X.-J. Jiang, W.-P. Fong and D. K. P. Ng, Metal-Based
Drugs, 2008, Article ID 284691; (c) S. C. H. Leung, P.-C. Lo, D. K. P.
Ng, W.-K. Liu, K.-P. Fung and W.-P. Fong, Br. J. Pharm., 2008, 154,
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Org. Biomol. Chem., 2008, 6, 2173; (e) P.-C. Lo, W.-P. Fong and D. K.
P. Ng, ChemMedChem, 2008, 3, 1110.
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5205; (b) W. Maqanda, T. Nyokong and M. D. Maree, J. Porphyrins
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2001, 5, 105.
1
CH2), 3.61–3.65 (m, 4 H, CH2), 3.41 (s, 6 H, CH3). 13C{ H} NMR
(75.4 MHz, CDCl3 with a trace amount of pyridine-d5): d 154.3,
154.2, 152.8, 152.4, 148.7, 138.4, 138.3, 137.9, 130.9, 129.0, 128.9,
128.6, 127.3, 125.7, 124.4, 122.6, 122.5, 122.2, 74.3, 71.9, 71.3, 71.0,
70.8, 70.6, 59.0. MS (ESI): an isotopic cluster peaking at m/z 951
(100%, [M + H]+). HRMS (ESI) calcd for C50H47N8O8Zn [M +
H]+ 951.2803, found: 951.2805. Anal. calcd for C51H50N8O9Zn
(9b·CH3OH): C 62.23, H 5.12, N 11.38. Found: C 61.69, H 4.90,
N 11.44.
Acknowledgements
9 P.-C. Lo, B. Zhao, W. Duan, W.-P. Fong, W.-H. Ko and D. K. P. Ng,
Bioorg. Med. Chem. Lett., 2007, 17, 1073.
10 (a) N. Kobayashi, N. Sasaki, Y. Higashi and T. Osa, Inorg. Chem.,
1995, 34, 1636; (b) N. Kobayashi, H. Ogata, N. Nonaka and E. A.
Luk’yanets, Chem.–Eur. J., 2003, 9, 5123.
11 C.-F. Choi, P.-T. Tsang, J.-D. Huang, E. Y. M. Chan, W.-H. Ko, W.-P.
Fong and D. K. P. Ng, Chem. Commun., 2004, 2236.
We thank Prof. Wing-Hung Ko of the Department of Physiology
for technical support in the fluorescence imaging study. This work
was supported by a strategic investments scheme administered by
The Chinese University of Hong Kong.
12 (a) P.-C. Lo, J.-D. Huang, D. Y. Y. Cheng, E. Y. M. Chan, W.-P. Fong,
W.-H. Ko and D. K. P. Ng, Chem.–Eur. J., 2004, 10, 4831; (b) P.-C. Lo,
S. C. H. Leung, E. Y. M. Chan, W.-P. Fong, W.-H. Ko and D. K. P. Ng,
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