Synthesis and DNA photocleavage studies of novel porphyrin diarylthiazoles

Article abstract of DOI:10.1142/S1088424613500740

A convenient and regioselective synthesis of porphyrin diarylthiazoles is reported via the reactions of alkynyl(aryl)iodonium tosylates and porphyrin thioamides. Among the synthesized porphyrin diarylthiazoles, compounds 6d and 6f have shown significant i

Full text of DOI:10.1142/S1088424613500740

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2013; 17: 1–7
DOI: 10.1142/S1088424613500740
Published at http://www.worldscinet.com/jpp/
Synthesis and DNA photocleavage studies of novel
porphyrin diarylthiazoles
Dalip Kumar*, K.P. Chandrashekar and Bhupendra Mishra
Department of Chemistry, Birla Institute of Technology and Science, Pilani 333 031, India
Received 19 March 2013
Accepted 25 May 2013
ABSTRACT: A convenient and regioselective synthesis of porphyrin diarylthiazoles is reported via
the reactions of alkynyl(aryl)iodonium tosylates and porphyrin thioamides. Among the synthesized
porphyrin diarylthiazoles, compounds 6d and 6f have shown significant interactions with ctDNA and
exhibited efficient DNA photocleavage.
KEYWORDS: porphyrins, alkynyl(aryl)iodonium salts, thiazoles, porphyrin diarylthiazoles, DNA
photocleavage.
cells over normal cells and dosage [7]. They also exhibit
INTRODUCTION
varied interactions with DNA through intercalation,
In recent years, there has been continuous upsurge of
external groove binding and outside binding modes [8].
interest in the synthesis of porphyrin and its derivatives
A large number of methods have been developed to
due to their wide variety of potential applications in
overcome the problems mentioned earlier which have led
both medicine and molecular materials [1]. A number
to the modifications at peripheral positions of porphyrin
of intermediates and synthetic strategies have been
ring [9]. Accordingly, it is very important to understand in
developed to constitute porphyrin systems. Their
detail how porphyrin heterocycles bind and cleave DNA.
properties also make them useful in catalysis [2], drug
Five-membered thiazole ring is among the most
delivery [3], nonlinear optics [4] and photodynamic
important classes of nitrogen containing heterocycles in
therapy [5, 6]. Functionalizing the porphyrins has its
medicinalchemistryowingtoitsuniquebiologicalactivities
challenges, inspite of the fact that it has been the main
including anti-inflammatory [10], anti-hypertensive [11],
foundation for modulating various properties of the
anti-bacterial [12], anti-HIV [13a] and anti-cancer [13b].
porphyrin moiety and further constructing new and useful
Further, thiazole ring is an integral part of several DNA
porphyrins. Given the high significance of porphyrin
photocleaving agents and anti-cancer antibiotics [13].
heterocycles with extended p-conjugation as building
Because of the conjugated carbon nitrogen double bond in
blocks for constructing novel porphyrin systems, there
thiazole heterocycle, it is believed to produce the photo-
is increasing need for the development of efficient and
practical syntheses of novel porphyrins. Porphyrins
excited 3(n–p*) and/or 3(p–p*) state (s) [13c, 13d].
Manymethodsforthepreparationofthethiazolemoiety
with heterocyclic rings have proven to be valuable
are available, and among them, the Hantzsch thiazole
research tools and a fruitful area for the development
of synthetic methodology. Numerous porphyrins have
synthesis employing lachrymatory a-haloketones and
thioamides is one of the most common methods. Further,
been synthesized and tested for their in vitro and in vivo
a-haloketones were replaced with a-tosyloxy ketones
phototoxicity, as existing photosensitizers have side-
to prepare thiazoles and heterocyclic analogues [14,
effects associated with their specificity for cancerous
15]. Alternate approach for the preparation of thiazoles
utilizes the reaction of thioamides with alkynyl(aryl)-
iodonium salts [16]. In the recent years, alkynyl(aryl)-
iodonium salts have received much attention as useful and
readily available starting materials in organic synthesis.
*Correspondence to: Dalip Kumar, email: dalipk@pilani.
bits-pilani.ac.in, tel.: +91 1596-245073-5238, fax: +91 1596-
244183
Copyright © 2013 World Scientific Publishing Company

2
D. KUMAR ET AL.
The electron-withdrawing nature and powerful leaving
ability of the phenyliodonium moiety has imparted
unique reactivity to alkynyliodonium salts [17]. Recently,
we have reported the synthesis of porphyrin-1,3,4-
oxadiazoles by employing hypervalent iodine reagent,
iodobenzene diacetate [18]. In continuation to our efforts
in the synthesis of porphyrin appended heterocycles,
we report herein a facile synthesis of novel porphyrin
diarylthiazoles from readily available alkynyl(aryl)-
iodonium tosylates and porphyrin thioamides.
chloroform [21]. Our initial efforts to prepare porphyrin
diarylthiazole 6a from the reaction of thioamide 4a with
alkynyl(aryl)iodonium tosylate 5 in methanol showed
poor conversion even after prolonging the reaction for
48 h. Subsequently, reaction in tetrahydrofuran furnished
the desired porphyrins 6 in good yields. 1H NMR
spectrum of 6a displayed a characteristic singlet for
thiazole C5′-H at d 7.56 ppm and a multiplet of the eight
b-pyrrolic protons ranging d 8.89–8.86 ppm. MALDI-
TOF spectra of 6a–6h showed corresponding molecular
ion peaks. The structure of porphyrin 2,4-diarylthiazole
6a was unambiguously assigned by its synthesis from
an alternate method involving the reaction of porphyrin
thioamide 4 and phenacyl bromide [19]. The porphyrin
thiazole obtained from the alternate method was found to
be identical in all respects to porphyrin thiazole 6a. Also,
2,5-diarylthiazoles exhibited a characteristic singlet at
d 8.02 ppm for thiazole C4′-H [22] however, the proton
NMR of 6a was devoid of this singlet.
Formation of porphyrin diarylthiazoles 6a–6h can be
explained by a plausible mechanistic pathway as shown
in Scheme 2. Initial nucleophilic displacement of tosylate
in alkynyl(aryl)tosylate 5 by the thioamide 4a probably
generates an intermediate adduct I which rearranges to
thioamide II [18, 23]. Subsequent loss of iodobenzene
provides a reactive species III, which upon internal
cyclization led the corresponding porphyrin thiazoles
6a–6h [24].
RESULTS AND DISCUSSION
Synthesis and characterization
The synthesis of porphyrin diarylthiazoles 6a–6h
required meso-(4-thiocarboxamidophenyl)triphenyl
porphyrins 4a–4d which were prepared according to the
procedurerecentlyreportedbyourgroup[19].Porphyrin1,
prepared by the condensation of benzaldehyde, methyl-
4-formylbenzoate and pyrrole under Adler-Longo condi-
tions [20], was hydrolyzed to porphyrin 2 which upon
reaction with thionyl chloride and ammonia afforded
5-(4-carboxamido-phenyl)-10,15,20-triphenylporphyrin
3. The reaction of porphyrin 3 with Lawesson’s reagent
at 60 °C in toluene afforded porphyrin thioamides 4a and
4c in good yields. Finally, metalation with zinc acetate
produced porphyrins 4b and 4d, respectively (Scheme 1).
Alkynyl(aryl)iodonium tosylates 5 were prepared in
quantitative yields by treating arylacetylenes with Koser’s
reagent, [hydroxy(tosyloxy)iodo] benzene (HTIB) in
DNA interaction studies
Interactions of porphyrin diarylthiazoles 6a–6h with
calf thymus DNA (ctDNA; Tris-HCl 5 mM, 0.1 M NaCl,
R
R
R
NH
N
N
NH
N
N
NH
N
N
KOH
(i) SOCl2, toluene
(ii) NH3, DCM
COOCH3
COOH
CONH2
R
R
R
EtOH
HN
HN
HN
R
R
R
1
3
2
R
R
R1
Ph
R1
I
OTs
N
N
N
S
N
N
N
N
(i) Lawessons reagent, toluene
5
M
M
CSNH2
R
R
(ii) Zn(OAc)2, chloroform-methanol
THF, TEA
N
N
6a, R= R1=H, M=2H
6b, R= R1=H, M=Zn
6c, R= CH3, R1=H, M=2H
6d, R= CH3, R1=H, M=Zn
6e, R= H, R1=CH3,M=2H
6f, R= H, R1=CH3, M=Zn
6g, R= R1=CH3,M=2H
6h, R= R1=CH3, M=Zn
R
4a R=H, M=2H
4b R=H, M=Zn
4c R=CH3, M=2H
4d R=CH3, M=Zn
R
6
4
Scheme 1. Synthesis of porphyrin diarylthiazoles 6a–6h
Copyright © 2013 World Scientific Publishing Company
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SYNTHESIS AND DNA PHOTOCLEAVAGE STUDIES OF NOVEL PORPHYRIN DIARYLTHIAZOLES
3
Ph
OTs
H
N
Ph
I
H
N
H
Ph
Ph
-PhI
Ph
5
N
6
NH2
I
TsOH
S
S
S
Ph
S
IPh
4
II
III
I
NH
N
N
HN
Scheme 2. A plausible pathway for the formation of porphyrin diarylthiazoles 6a–6h
Fig. 1. Absorption spectra of porphyrins 6d and 6f. [Porphyrin] = 5 mM in (DMF), [ctDNA] = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0,
4.5, 5.0, 5.5, 6.0, 8.0, 10.0 mM in 5 mM Tris−HCl buffer, 0.1 M NaCl, pH 7.4. Arrow indicates the decrease of absorbance with the
increasing concentration of ctDNA
pH 7.4) were investigated by monitoring absorption
changes in the Soret band near 420 nm. Porphyrin
solutions (5 × 10-6 M) were titrated with increasing
concentrations of DNA as shown in Fig. 1. Among the
porphyrin diarylthiazoles studied, compounds 6a–6c, 6e,
6g–6hdidnotshowanysignificantchangesintheirUV-vis
and fluorescence spectra, whereas porphyrins 6d and 6f
displayed a relatively small red shift and hypochromicity
of the Soret bands. At lower ctDNA concentrations (0–5
mM), porphyrin 6d exhibited a small red shift (~3 nm) and
hypochromicity (5%), whereas, porphyrin 6f displayed
only a five percent hypochromic shift in the Soret bands
in absorption spectra. No change in the intensity of the
Soret band was observed for compounds 6d and 6f upon
further increasing ctDNA concentrations (5–10 mM).
At lower DNA concentrations (0–5 mM), the observed
changes in UV-vis spectra suggest that the porphyrin
diarylthiazoles may interact with DNA in an outside
binding mode. The binding modes of porphyrin to DNA
depend on peripheral substituents and hydrophobicity
of the molecule. Also, depending on the metal with one
axial ligand Zn(II) and Fe(III); two axial ligands, Mn(III),
Fe(III) and Co(III) and without any axial ligand, Ni(II),
Cu(II) andAu(III), the binding interactions can alter from
intercalation at GC sites to outside bound complexes atAT
sites through electrostatic interactions or groove binding
[25]. Thus, these Zn(II) porphyrins 6d and 6f bases can
accommodate axial ligands which present steric barrier
for intercalation. In view of observed interactions, the
apparent binding constants of porphyrins 6d and 6f for
ctDNA were determined using the following Equation 1:
[DNA]
[DNA]
1
(1)
=
+
(eA − eF ) (eB − eF ) Kb (eB − eF )
Copyright © 2013 World Scientific Publishing Company
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4
D. KUMAR ET AL.
where eF correspond to Aobsd/[porphyrin], the extinction
coefficient for the free porphyrin, eA the extinction
coefficient for the porphyrin complex of a given solution
and eB is the extinction coefficient for fully bound form,
respectively. A plot of [DNA]/(eA – eF) vs. [DNA] will
have a slope of 1/(eB – eF) and a y-axis intercept equal
to 1/Kb (eB – eF). The binding constant Kb was calculated
from the ratio of the slope to y-axis intercept. The
apparent binding constants (Kb) of 6d (1.25 × 104 M-1)
and 6f (2.4 × 104 M-1) were derived to support their
proposed electrostatic interactions with ctDNA [26]. It
is to be noted that the equation for calculation of binding
constant is valid only if we assume 1:1 stoichiometry for
the porphyrin-DNA complex. To verify this proposition,
we further analyzed the fluorescence titration data using
Benesi–Hilderbrand Equation 2 [27].
ctDNA. The luminescence spectra were consistent with
the observed changes in the UV-vis spectra as a function
of ctDNA concentration, supporting the occurrence of
outside binding mode in the porphyrin appended thiazole
system. This type of behavior has also been reported for
a number of systems and suggests switching of binding
modes with the increasing concentrations of ctDNA [29].
Analogous to porphyrin derivatives containing bulky
substituents, porphyrins 6d and 6f were not expected to
intercalate between the DNA base pairs. This implies that
the predominant interaction of porphyrin diarylthiazoles
could be through outside binding with ctDNA.
DNA photocleavage assay
The photocleavage abilities of porphyrin diarylthiazoles
6a–6h were initially investigated at higher concentrations
(50 mM) by mixing plasmid DNA (pBR 322 in Tris-HCl
buffer (20 mM, pH 7.2) in the presence and absence of
UV and visible light (Fig. S1 in Supporting information).
The stock solutions for 6a–6h (10-4 M) were prepared
in DMF and final test solutions were achieved by
appropriate dilution in Tris-HCl buffer (20 mM). The
cleavage of supercoiled plasmid DNA was determined
quantitatively by the effective conversion of supercoiled
form I to nicked circular form II. Porphyrins 6b, 6d and
6f showed photocleavage of pBR 322 DNA at 50 mM
in presence of UV light, which was further studied at
lower concentrations by increasing the irradiation time.
Control experiments did not show any apparent DNA
cleavage; lanes 1 and 5 (Fig. 4a), and lane 1 (Fig. 4b);
however, there was degradation of plasmid DNA under
UV light when irradiated for 1.5 h (lanes 6–8, Fig. 4a).
Similarly, no change was observed in the plasmid DNA
when compounds 6b, 6d and 6f were exposed to visible
light for 1–2 h, (Figure not shown). The irradiation
time was increased for 6b, 6d and 6f as shown in lanes
1
1
1
1
(2)
=
+
×
I − I0 Ia − I0 K(Ia − I0 ) [DNA]
where I is the porphyrin fluorescence intensity at a
particular DNA concentration; I0 and Ia indicate the
intensity in absence and in presence of highest DNA
concentration, respectively. K indicated the binding
constant. The plot of 1/(I–I0) against 1/[DNA] for both
6d and 6f are shown in Fig. 2. The linear nature double
reciprocal plot confirms the 1:1 binding stoichiometry
[27, 28]. The K values calculated from the slope of the
linear plot (for 6d, K = 0.15 × 104 M-1 and for 6f, K =
0.61 × 104 M-1) are in agreement with the corresponding
values obtained from the absorption data.
The fluorescence spectra of 6d and 6f are shown
in Fig. 3. The stronger emission band at 726 nm was
assigned to the porphyrin transition. A systematic
increase in the emission intensity was observed at lower
(0–5 mM) and higher (5–10 mM) concentrations of
Fig. 2. Plots of 1/(I–I0) against 1/[DNA] for porphyrins 6d and 6f
Copyright © 2013 World Scientific Publishing Company
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SYNTHESIS AND DNA PHOTOCLEAVAGE STUDIES OF NOVEL PORPHYRIN DIARYLTHIAZOLES
5
Fig. 3. Fluorescence spectra of porphyrins 6d and 6f. [Porphyrin] = 5 µM, [ctDNA] = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0,
5.5, 6.0, 8.0, 10.0 µM in 5 mM Tris−HCl buffer, 0.1 M NaCl, pH 7.4. Arrow indicates the increase in intensity with the increasing
concentration of ctDNA (lExc-429 nm)
EXPERIMENTAL
General
All chemicals were procured from Sigma-Aldrich,
India and Spectrochem Pvt Ltd., were of analytical grade
1
and used as such unless indicated. H NMR spectra
were recorded in CDCl3 on a Bruker-avance 400 MHz
instrument using TMS as an internal standard. Mass
Fig. 4a. Photoinduced DNA cleavage by porphyrins 6b, 6d
and 6f. pBR 322 supercoiled DNA (0.1 mg) was incubated
spectra were obtained on a Bruker ProFLEX III MALDI-
TOF mass spectrometer using DHB as the matrix. The
UV-vis spectroscopy was carried out on Hitachi U-2900
spectrophotometer and fluorescence spectra were recorded
on Horiba JobinYvon Fluoro max-4-scanning fluorimeter.
Quartz cuvettes were used with 1-cm path length.
with the porphyrins (25 mM) in Tris–HCl (20 mM, pH 7.2),
DMF (2.5 vol%) at ambient temperature in the dark for 3 h, and
UV-irradiated (310–390 nm) for 1.5 h. Lane 1: Control DNA
alone, Lane2:DNA+6b(dark), Lane3:DNA+6d(dark), Lane4:
DNA + 6f (dark), Lane 5: DNA alone (UV), Lane 6: DNA + 6b
(UV), Lane 7: DNA + 6d (UV), Lane 8: DNA + 6f (UV)
Synthesis
Preparation of porphyrin diarylthiazoles 6. To
a stirred solution of porphyrin thioamide 4 (0.1 g,
0.148 mmol), alkynyl(aryl)iodonium tosylate 5 (0.074 g,
0.178 mmol) in tetrahydrofuran (15 mL) at 0 °C was
added triethylamine (15 mL, 0.148 mmol) and the reaction
mixture was allowed to heat up to 50 °C for 4–6 h. After
completion of the reaction, the contents were diluted
with water and then basified to pH ~ 8 with 10% sodium
carbonate solution (20 mL). The crude product was
extracted with chloroform (3 × 15 mL) and the combined
organic layer was dried over anhydrous sodium sulphate.
Excess solvent was distilled off and the crude product
obtained was chromatographed using chloroform/hexane
(3:7 v/v) as eluent to afford 6 as purple solid.
Fig. 4b. Photoinduced DNA cleavage by porphyrins 6b, 6d and
6f. pBR 322 supercoiled DNA (0.1 mg) was incubated with the
porphyrins (25 mM) in Tris−HCl (20 mM, pH 7.2), DMF (2.5
vol%) and exposed to visible light for 3 h. Lane 1: Control
DNA alone (vis), Lane 2: DNA + 6b (vis), Lane 3: DNA + 6d
(vis), Lane 4: DNA + 6f (vis)
2–4 (Fig. 4b), where the amount of form I of pBR 322
DNA diminished gradually and form II increased. Under
experimental conditions, porphyrins 6d and 6f exhibited
more effective DNA cleavage under visible light when
compared to UV light.
5-{4′-(4″-Phenyl)-2″-thiazolyl}-10,15,20-triphenyl-
porphyrin (6a).Yield 61 mg (59%). 1H NMR (400 MHz,
CDCl3): dH, ppm -2.95 (s, 2H), 7.33 (t, J = 7.4 Hz, 1H),
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 5–7

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D. KUMAR ET AL.
7.44 (t, J = 7.6 Hz, 2H), 7.56 (s, 1H), 7.63–7.75 (m, 9H),
8.05 (d, J = 7.2 Hz, 2H), 8.16–8.19 (m, 6H), 8.26 (d, J =
6.2 Hz, 2H), 8.37 (d, J = 8.2 Hz, 2H), 8.85–8.89 (m, 8H).
MS (MALDI-TOF): m/z 774.2909 (calcd. for [M + H]+
774.2691).
(m, 4H), 7.73 (d, J = 8.4 Hz, 2H), 8.25–8.37 (m, 8H). MS
(MALDI-TOF): m/z 891.2951 (calcd. for [M]+ 891.2218).
CONCLUSION
5-{4′-(4″-Phenyl)-2″-thiazolyl}-10,15,20-triphenyl-
1
In conclusion, we have developed a facile, efficient and
regioselective synthesis of porphyrin appended diaryl-
thiazoles from easily accessible alkynyl(aryl)iodonium
tosylates and porphyrin thioamides. The porphyrin
diarylthiazoles 6d and 6f showed binding affinity (1.25 ×
104 M-1 and 2.4 × 104 M-1) towards ctDNA probably
through outside binding mode and quantitative plasmid
DNA photocleavage upon exposure to visible light. Further,
detailed mechanistic studies are currently underway.
porphyrinato zinc(II) (6b). Yield 65 mg (57%). H
NMR (400 MHz, CDCl3): dH, ppm 7.33 (t, J = 7.4 Hz,
1H), 7.44 (t, J = 7.6 Hz, 2H), 7.56 (s, 1H), 7.66–7.73 (m,
9H), 8.06 (d, J = 7.4 Hz, 2H), 8.15–8.17 (m, 6H), 8.27
(d, J = 6.2 Hz, 2H), 8.38 (d, J = 8.2 Hz, 2H), 8.88–8.95
(m, 8H). 13C NMR (100 MHz, CDCl3): d, ppm 114.86,
117.84, 118.54, 124.63, 125.38, 126.29, 129.35, 129.70,
130.02, 135.95, 140.64, 141.33, 145.97, 148.89, 149.55,
152.23, 168.73. MS (MALDI-TOF): m/z 835.2504
(calcd. for [M]+ 835.1748).
5-{4′-(4″-Phenyl)-2″-thiazolyl}-10,15,20-tritolyl-
porphyrin (6c).Yield 55 mg (48%). 1H NMR (400 MHz,
CDCl3): dH, ppm -2.85 (s, 1H), 2.61 (s, 9H), 7.46 (d, J =
8.0 Hz, 8H), 7.99–8.02 (m, 8H), 8.22 (d, J = 8.0 Hz, 2H),
8.33–8.36 (m, 2H), 8.68 (d, J = 4.8 Hz, 2H), 8.75–8.80
(m, 8H). MS (MALDI-TOF): m/z 815.3083 (calcd. for
[M]+ 815.3376).
Acknowledgements
The authors thank Department of Science and
Technology (DST), New Delhi and UGC(SAP), New
Delhi for the financial support, and SAIF, Panjab
University and AIRF, JNU for providing analytical
support. BM is thankful to CSIR, New Delhi for research
fellowship (F. No. 09/719(0042)/2011.EMR-I).
5-{4′-(4″-Phenyl)-2″-thiazolyl}-10,15,20-tritolyl-
1
porphyrinato zinc(II) (6d). Yield 52 mg (47%). H
NMR (400 MHz, CDCl3): dH, ppm 2.73 (s, 9H), 7.46 (d,
J = 8.0 Hz, 8H), 7.96–8.02 (m, 8H), 8.22 (d, J = 8.0 Hz,
2H), 8.33–8.36 (m, 2H), 8.68 (d, J = 4.8 Hz, 2H), 8.72–
8.80 (m, 8H). MS (MALDI-TOF): m/z 877.2448 (calcd.
for [M]+ 877.2218).
Supporting information
Supplementary material is available free of charge
via the Internet at http://www.worldscinet.com/jpp/jpp.
shtml.
5-{4′-(4″-Tolyl)-2″-thiazolyl}-10,15,20-triphenyl-
porphyrin (6e).Yield 62 mg (53%). 1H NMR (400 MHz,
CDCl3): dH, ppm -2.83 (s, 2H), 2.50 (s, 3H), 7.51 (s, 1H),
7.66–7.72 (m, 9H), 8.11–8.16 (m, 10H), 8.38 (d, J = 6.4
Hz, 2H), 8.66 (d, J = 8.4 Hz, 2H), 8.78–8.86 (m, 8H). 13C
NMR (100 MHz, CDCl3): d, ppm 21.12, 116.97, 119.95,
120.65, 126.68, 126.79, 127.49, 127.71, 128.40, 131.46,
131.74, 131.81, 132.13, 138.06, 142.75, 143.44, 148.08,
151.00, 151.66, 154.34, 167.84. MS (MALDI-TOF): m/z
788.3203 (calcd. for [M + H]+ 788.2770).
5-{4′-(4″-Tolyl)-2″-thiazolyl}-10,15,20-triphenyl-
porphyrinato zinc(II) (6f).Yield 60 mg (51%). 1H NMR
(400 MHz, CDCl3): dH, ppm 2.51 (s, 3H), 7.51 (s, 1H),
7.67–7.74 (m, 9H), 7.95–7.99 (m, 4H), 8.14–8.19 (m,
6H), 8.36 (d, J = 6.4 Hz, 2H), 8.69 (d, J = 8.4 Hz, 2H),
8.78–8.86 (m, 8H). MS (MALDI-TOF): m/z 849.2061
(calcd. for [M]+ 849.1905).
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porphyrinato zinc(II) (6h). Yield 52 mg (46%). H
NMR (400 MHz, CDCl3): dH, ppm 2.49 (s, 3H), 2.73 (s,
9H), 7.40–7.43 (m, 3H), 7.49–7.57 (m, 12H), 7.64–7.69
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J. Porphyrins Phthalocyanines 2013; 17: 6–7

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J. Porphyrins Phthalocyanines 2013; 17: 7–7