Synthesis and photophysical properties of phenyl-sulfanylated chlororophyll derivatives

Article abstract of DOI:10.1016/j.tet.2014.05.115

Chlorophyll derivatives that possessed a phenylsulfanyl group at the C3¹- or C3²-position were synthesized and their optical properties were investigated. Methyl 3¹-phenylsulfanyl- mesopyropheophorbide-a was prepared by substitutions of the corresponding C3¹-hydroxy-chlorin, methyl bacteriopheophorbide-d, with thiophenol in the presence of zinc iodide or of the corresponding C3¹-bromo- chlorin with thiophenol. The regioisomeric C3²-phenylsulfanyl-chlorin was obtained by addition of thiophenol to the C3-vinyl group of methyl pyropheophorbide-a in the presence of AIBN. Both the synthetic compounds gave similar electronic absorption and emission spectra in chloroform, but fluorescence quantum yield of the C3¹-sulfanyl-chlorin (0.18) was ca. 30% smaller than those of the C3²-sulfanyl-chlorin (0.25) and the C3-ethyl-chlorin (0.24). These observations were consistent with their fluorescence lifetime data. It is suggested that the heavy atom effect of a sulfur atom at the C3¹-position can tune photophysical properties of the chlorophyll derivatives.

Full text of DOI:10.1016/j.tet.2014.05.115

Accepted Manuscript
Synthesis and photophysical properties of phenyl-sulfanylated chlororophyll
derivatives
Natsuki Takei , Misaki Morioka , Mari Yoshizato , Takuya Tanaka , Shin-ichi Sasaki ,
Satoshi Ito , Hitoshi Tamiaki , Toru Oba
PII:
S0040-4020(14)00845-X
10.1016/j.tet.2014.05.115
TET 25664
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 8 May 2014
Revised Date: 30 May 2014
Accepted Date: 31 May 2014
Please cite this article as: Takei N, Morioka M, Yoshizato M, Tanaka T, Sasaki S-i, Ito S, Tamiaki H, Oba
T, Synthesis and photophysical properties of phenyl-sulfanylated chlororophyll derivatives, Tetrahedron
(2014), doi: 10.1016/j.tet.2014.05.115.
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ACCEPTED MANUSCRIPT
Synthesis and photophysical properties of phenyl-sulfanylated
chlorophyll derivatives
Natsuki Takei a, Misaki Morioka a, Mari Yoshizato b, Takuya Tanaka b, Shin-ichi Sasaki b,c, Satoshi
Ito a, Hitoshi Tamiaki b,*, Toru Oba a,*
aDepartment of Material and Environmental Chemistry, Graduate School of Engineering,
Utsunomiya University, Utsunomiya, Tochigi 321-8585, Japan.
bGraduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
cNagahama Institute of Bio-Science and Technology, Nagahama, Shiga 526-0829, Japan.
* Corresponding authors. Fax: +81 77 561 2659; e-mail address: tamiaki@fc.ritsumei.ac.jp (H.
Tamiaki). Tel/fax: +81 28 689 6147; e-mail address: tob_p206@cc.utsunomiya-u.ac.jp (T. Oba).
1

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Graphical abstract
Leave this area blank for abstract info.
Synthesis and photophysical properties of
phenyl-sulfanylated chlororophyll
derivatives
Natsuki Takei a, Misaki Morioka a, Mari Yoshizato b, Takuya Tanaka b, Shin-ichi Sasaki b,c, Satoshi Ito a, Hitoshi
Tamiaki b,*, Toru Oba a,*
aDepartment of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya
University, Utsunomiya, Tochigi 321-8585, Japan.
bGraduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
cNagahama Institute of Bio-Science and Technology, Nagahama, Shiga 526-0829, Japan.
Ph
Ph
3
S
S
NH
N
N
PhSH
AIBN
(i) HBr/AcOH
(ii) PhSH
HN
NH
NH
O
Fluorescence
emission
weak emission
COOMe
Keywords
Chlorophyll, fluorescence, heavy atom effect, sulfanyl, thioether.
2

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Abstract
Chlorophyll derivatives that possessed a phenylsulfanyl group at the C31- or C32-position were
synthesized and their optical properties were investigated. Methyl
31-phenylsulfanyl-mesopyropheophorbide-a was prepared by substitutions of the corresponding
C31-hydroxy-chlorin, methyl bacteriopheophorbide-d, with thiophenol in the presence of zinc
iodide or of the corresponding C31-bromo-chlorin with thiophenol.
The regioisomeric
C32-phenylsulfanyl-chlorin was obtained by addition of thiophenol to the C3-vinyl group of methyl
pyropheophorbide-a in the presence of AIBN. Both the synthetic compounds gave similar
electronic absorption and emission spectra in chloroform, but fluorescence quantum yield of the
C31-sulfanyl-chlorin (0.18) was ca. 30% smaller than those of the C32-sulfanyl-chlorin (0.25) and
the C3-ethyl-chlorin (0.24). These observations were consistent with their fluorescence lifetime
data. It is suggested that the heavy atom effect of a sulfur atom at the C31-position can tune
photophysical properties of the chlorophyll derivatives.
Highlights
ꢀ Chlorophyll derivatives having a sulfur-containing substituent at the C31- or C32-position were
synthesized.
ꢀ The fluorescence quantum yield of the C31-phenylsulfanyl-chlorin was smaller than that of the
regioisomeric C32-PhS-chlorin.
ꢀ Heavy atom effect of a sulfur atom may tune photophysical properties of the chlorophyll
derivatives.
3

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1. Introduction
Chlorophylls (Chls) and bacteriochlorophylls (BChls) function in photosynthetic organisms
as molecular devices to harvest, transfer, and convert sunlight energy. Their π-conjugated systems
are photochemically important and several peripheral substituents on the cyclic tetrapyrroles affect
their physical properties (see the left drawing of Fig. 1). The C3-substituent (R in Fig. 1) had
relatively large effects on the optical and electronic properties.1,2 A C3-formyl-chlorin (e.g.
Chl-d) shows visible absorption peaks at longer wavelengths than those of the corresponding
C3-vinyl-chlorin (e.g. Chl-a) and the related C3-(1-hydroxyethyl)-chlorin (e.g. BChl-d).
Introduction of non-natural substituents at the C3-position revealed the C3-substitution effect
clearly. For instance, a series of analogs of methyl pyropheophorbide-a (1, see the right drawing
of Fig. 1) bearing the CH=CXY moiety attached to the C3-position exhibited a systematic red-shift
of the Qy(0,0) absorption band in the wide wavelength range between 665 nm and 706 nm
depending on the X- and Y-substituents.1
x-axis
R
R
3
3
7
8
N
N
N
N
NH
N
N
Mg
E
HN
17
131
y-axis
O
O
1)
COOMe
COOR'
1: R = CH=CH2
Chl-a: R = CH=CH2
R' = phytyl
E = COOMe
2: R = CH(OH)CH3
3: R = CH(SPh)CH3
4: R = CH2CH2SPh
5: R = CH2CH3
R = CHO
R' = phytyl
E = COOMe
Chl-d:
BChl-d: R= CH(OH)CH3
R' = farnesyl
E = H
Figure 1.
Molecular structures of natural chlorophylls (left) and their synthetic derivatives
(right).
2)
The C3-substituent of a heme molecule, a cyclic tetrapyrrole similar to chlorophylls, can be
used to bind the protein matrix of a cytochrome-c through a thioether bond prepared by the reaction
of the C3-vinyl group with a cysteine residue. Chls and BChls in natural systems resolved so far,
however, do not have thioether linkage with the apoproteins nor any covalent bonding. There are,
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for instance, nine Cys residues in core proteins of a photosystem 2 (D1 and D2, each ~ 350
residues; PDB code, 3ARC3). Only one Cys residue (D1-Cys40) is in the vicinity of the chlorin
macrocycle of a Chl-a molecule (CLA611). The thiol sulfur atom locates close to the C31-carbon
atom of the Chl but does not bond covalently (0.4 nm). It is quite intriguing to elucidate why no
thioether linkage between (B)Chls and apoproteins is included in natural photosynthetic systems.
No sulfur-containing Chls have so far been found in photosynthetic organisms. There
have been only a few reports that dealt with sulfur-containing Chl derivatives. Keely and his
colleagues found C31-alkylsulfanyl-chlorins in sediments from an Antarctic lake, and they have
studied reactions between chlorins and H2S.4-8 These compounds were Chl-a derivatives bearing
an alkylsulfanyl group and were assumed to be formed during diagenesis. They also synthesized
such compounds by treatment of 1 with alkyl iodides in the presence of H2S in aqueous acetone.
Tamiaki et al. reported thiocarbonylation at the C7/8- and C131-positions of Chl derivatives by
using Lawesson’s reagent.9 The Qy and Soret maxima showed large red-shifts in going from
C7=O/C131=O (711/416 nm) to C7=O/C131=S (746/434 nm) and to C7=S/C131=S (778/506 nm).
The fluorescence quantum yields of these thioxo-analogs (< 0.01) were dramatically reduced
compared with that of C7=O/C131=O (0.14). Saga and Tamiaki reported preparation of a chlorin
dimer linking with a disulfide bond at the C17-propionic chains, and employed it to fabricate the
self-organized monolayer on a gold substrate.10
We have previously reported co-oxidation of the C3-vinyl group of Chl-a and its
derivatives in the presence of an arylthiol,11-13 where the vinyl groups were converted into the
1-hydroxy-2-phenylsulfanyl-ethyl and 2-phenylsulfanyl-acetyl groups as well as the desired formyl
group. Keely et al. and Belykh et al. revealed that H2S or alkylthiol can induce the same
reaction.8,14 These transformations were assumed to be triggered by addition of thiyl radical at the
C32-position of the vinyl double bond, or by a charge-transfer complex between the thiol and the
C=C double bond:8 such a reaction might be involved in the biosynthesis of Chl-d.12 Very recently
we have reported that an AIBN-induced radical reaction selectively yielded chlorins that possessed
a 2-arylsulfanyl-ethyl group at the C3-position.15 To our knowledge, however, no study has yet
appeared on fluorescence emission properties of the Chl derivatives having a sulfur-containing
substituent at the C3-position.
Here we report syntheses and optical properties of sulfur-containing chlorins, methyl 31- or
32-phenylsulfanyl-mesopyropheophorbides-a 3 and 4 (see the right drawing of Fig. 1). The
following two aspects are especially described. C31-Phenylsulfanyl-chlorin 3 was successfully
prepared via two different synthetic routes from methyl pyropheophorbide-a (1) in good yields.
The fluorescence quantum yield of 3 was 30 ~ 40% smaller than that of the isomeric
C32-phenylsulfanyl-chlorin.
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2. Results and Discussion
C31-PhS-chlorin 3 was synthesized from the corresponding C31-OH-Chl 216,17 and
18
thiophenol in the presence of ZnI2 (Scheme 1). According to reported procedures, 2 was
prepared from 1 via hydrobromination of the C3-vinyl group [step (i) of Scheme 1] and successive
hydrolysis [step (ii)]. The secondary alcohol 2 was refluxed with PhSH (2.5 equiv.) and ZnI2 (1.25
equiv.) in CHCl3 to give 3 in an 82% isolated yield as a 1:1 epimeric mixture in the C31-
stereochemistry. The crude product involved the corresponding zinc complex of 3 (Zn-3) as the
major by-product (ca. 40% by NMR), so the reaction mixture was treated with an aqueous diluted
acid for removal of the central Zn atom. Preliminary experiments showed that, when the same
reaction was carried out using Zn-2 and p-toluenethiol, Zn complex of the corresponding
C31-sulfanyl-chlorin was obtained in an 80% yield (by NMR), comparable to a yield for the
reaction between the free base 2 and p-toluenethiol (78% by NMR). These results indicate that the
central zinc did not affect the interconversion.
32
Br
OH
31
31
31
3
NH
N
N
NH
N
N
NH
N
(i)
(ii)
HN
HN
N
HN
O
O
O
COOMe
COOMe
COOMe
1
2
(v)
(vi)
(iii)
(iv)
SPh
32
SPh
31
32
31
3
3
3
NH
N
N
NH
N
NH
N
N
HN
N
HN
HN
O
O
O
COOMe
COOMe
COOMe
5
3
4
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Scheme 1. Synthesis of regioisomeric phenylsulfanyl-chlorins 3 and 4 as well as their reference 5
from vinyl-chlorin 1. (i) HBr/AcOH; (ii) H2O; (iii) ZnI2, PhSH; (iv) PhSH; (v) AIBN,
PhSH; (vi) H2, Pd/C.
Alternatively, 3 was prepared from 1 directly via a C31-brominated chlorin. The C3-vinyl
group of 1 was hydrobrominated with HBr/AcOH (vide supra). After evaporation, the residue was
immediately treated with PhSH in the presence of triethylamine to give 3 in an 84% isolated yield.
This method was somewhat simpler and conducted in a higher yield (from 1 to 3) than the above
one (84% vs 80% × 82%). The present compound 3 was a 31R and 31S-epimeric mixture (1:1) and
used for the following measurements without separation.
Introduction of a phenylsulfanyl moiety at the C32-position as in 4 was accomplished in a
62% isolated yield by a radical addition of PhSH triggered by AIBN, as described recently.15 The
anti-Markovnikov addition competed against co-oxidation that provided chlorins possessing a CHO
or CH(OH)CH2SPh group at the C3-position. Both new compounds 3 and 4 were fully
characterized by their 1H/13C-NMR, VIS, and HRMS spectra.
Synthetic sulfur-containing chlorins 3 and 4 gave their 1H-NMR spectra essentially similar
to that of the C3-ethyl-chlorin (methyl mesopyropheophorbide-a, 5) except for the signals of the
C3-moieties.19,20 The C31-methine and C32-methyl proton signals of the C31-sulfanyl-chlorin 3
appeared at 5.78 and ~ 2.34 ppm, respectively. The C31- and C32-methylene proton signals of the
C32-sulfanyl-chlorin 4 were observed at 4.14 and 3.64 ppm, respectively. Based on the NMR data
of the C3-ethyl moiety of 5 (3.83 and 1.73 ppm), introduction of a phenylsulfanyl group at the
C31-position (5→3) induced 1.95- and 0.61-ppm low-field shifts at the C31- and C32-protons,
respectively, while introduction of a phenylsulfanyl group at the C32-position (5→4) led the C31-
and C32-proton signals to shift to lower fields by 0.31 and 1.91 ppm, respectively. These shifts
can be rationalized by assuming that a weakly electronegative phenylsulfanyl group affected
electron density of the C3-moiety.21
Visible absorption spectra of the C31- and C32-sulfanyl-chlorins 3 and 4 were measured in
chloroform (Figure 2). Overall spectral shapes of these sulfanylated chlorins including minor
vibrational modes were nearly the same as that of the corresponding C3-ethyl-chlorin 5.19,20 The
Qy(0,0) absorption bands of 3 and 4 located at 666 and 662 nm, respectively, while the
unsubstituted chlorin 5 exhibited the Qy peak at 657 nm (Table 1). The C3-1-hydroxyethyl,
C3-1-alkoxyethyl, and C3-2-hydroxyethyl derivatives, all having an oxygen atom at the C31- or
C32-position, gave the Qy band at 662, 662, and 658 nm, respectively.16,17,22,23 The substitution of
a hydrogen atom of the C3-ethyl moiety of 5 with a sulfur or an oxygen atom both showed a small
red-shift of their Qy bands. Further, the effect was larger in H → S change than H → O change,
7

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and in change at the C31-position than that at the C32-position. The Soret absorption maxima of 3,
4, and 5 were observed at 414, 412, and 411 nm, respectively. The Qy and the Soret maxima
experienced bathochromic shifts of 9 nm (180 cm-1) and 3 nm (180 cm-1), respectively, in going
from C3-ethyl to C3-1-phenylsulfanyl-ethyl (5 → 3). On the other hand, smaller red-shifts of the
Qy (5 nm, 120 cm-1) and the redmost Soret bands (1 nm, 60 cm-1) were observed for the
C32-phenylsulfanylation (5 → 4). A phenylsulfanyl group at the C31-position gave larger
red-shifts than that at the C32-position. This is qualitatively supported by semi-empirical
theoretical calculations. The energy gap between HOMO and LUMO decreased in going from 5
to 4 and to 3 (see Supporting Information). The stronger electronic effect brought by the
C31-substitution can be interpreted as homo-conjugation between the sulfanyl group and the chlorin
π-system.
1.0
0.5
0.0
300
400
500
600
700
Wavelength (nm)
Figure 2.
UV/VIS absorption spectra of C31-sulfanyl-chlorin 3 (solid line), C32-sulfanyl-chlorin
4 (broken line), and C3-ethyl-chlorin 5 (dotted line), recorded in CHCl3 at room
temperature: normalized at the Soret peaks.
Table 1. Optical properties of methyl (sulfanylated) mesopyropheophorbides-a 3-5 in CHCl3 at
room temperature.
Soret
Qy(0,0)
Fluorescence
emission
Fluorescence
quantum
Stokes
shift
(cm-1)
absorption absorption
maximum maximum
Fluorescence
lifetime (ns) b
Compound
maximum
λem (nm) a
a
yield Φem
λabs (nm)
λabs (nm)
414
666
670
666
0.18
0.25
3.9
5.7
90
90
3
4
412
662
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411
657
662
0.24
5.7
100
5
aExcitation at the Soret peak. bExcitation at 403 nm.
Figure 3 exhibits the fluorescence emission spectra of chlorins 3, 4, and 5 excited at their
Soret maxima in chloroform. C31-Sulfanyl-chlorin 3 gave a major emission band peaking at 670
nm, arising from the Qy(0,0) transition (Table 1).
The Qy(0,0) emission band of
C32-sulfanyl-chlorin 4 was observed at 666 nm. In comparison with the fluorescence spectrum of
C3-ethyl-chlorin 5 (λem, 662 nm), introduction of a phenylsulfanyl group at the C31-position (3)
made the emission band shifted to a longer wavelength region by 8 nm (190 cm-1), while the
substitution at the C32-position (4) resulted in a 4-nm red-shift (100 cm-1). Stokes shifts of 3 ~ 5
were 90 ~ 100 cm-1. Half widths at the half maxima of these emission bands were 420 (3), 410 (4),
and 410 cm-1 (5), while the bandwidths of the corresponding Qy(0,0) absorption bands were 410 (3),
370 (4), and 380 cm-1 (5). These data show that the C31-sulfanyl moiety had greater influence on
the spectra than the C32-sulfanyl moiety did, which is also revealed by quantum yields (Φem) and
lifetimes (τem) obtained by excitation at the respective Soret bands in chloroform (see Table 1). It
is noted that C31-sulfanyl-chlorin 3 had the smallest quantum yield among the three.
C32-Sulfanyl- and C3-ethyl-chlorins 4 and 5 showed quantum yields of nearly 0.25, while the value
of the C31-sulfanyl-chlorin was 0.18. Fluorescence decay curves of the three were all well
rationalized as single component behavior, and the lifetime of 3 was the shortest among the three:
the values of 4 and 5 were 5.7 ns, while that of 3 was 3.9 ns. These data indicate that the
fluorescence was reduced by ca. 30 ~ 40% by introduction of a phenylsulfanyl moiety at the
C31-position of 5, although almost no influence was noted by the transformation at the C32-position.
Essentially the same results were obtained for other chlorins possessing sulfur atoms at the C31- or
C32-position (see Supporting Information).
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1.0
0.5
0.0
600
650
700
750
Wavelength (nm)
Figure 3.
Fluorescence emission spectra of C31-sulfanyl-chlorin
3
(solid line),
C32-sulfanyl-chlorin 4 (broken line), and C3-ethyl-chlorin 5 (dotted line), recorded in
CHCl3 at room temperature: normalized at the main peaks and excited at the Soret
peaks.
Such a difference between the fluorescence intensities of 3 and 4 also held for the spectra
obtained in benzene and methanol. Relative intensity of the fluorescence peak of the
C31-sulfanyl-chlorin 3 recorded in CHCl3 (λem = 670 nm, relative intensity = 1.00) was nearly the
same as that recorded in benzene (671 nm, 0.96) or methanol (668 nm, 0.94). The emission of the
C32-sulfanyl-chlorin 4 observed in benzene (666 nm, 1.03) or methanol (663 nm, 1.15) was also as
intense as that in CHCl3 (666 nm, 1.00). It is noted that the fluorescence intensity was insensitive
to the polarity of the solvent. It is reasonable to assume that the partially ‘quenched’ fluorescence
of 3 mainly originates from heavy atom effect of the sulfur atom, rather than from intramolecular
electron transfer. Sulfur atom has been known to enhance intersystem crossing by the heavy atom
effect. Bacteriochlorins possessing a thioxo group at the C7-, C8-, or C131-position greatly
reduced the fluorescence emission due to the heavy atom effect of the sulfur atom conjugated with
the π-system.9 Inner heavy atom effect depends on distance (interaction) between the heavy atom
and the π-system,24 which is consistent with the observed difference between the C31- and the
C32-sulfanyl groups. Based on the above results, it is reasonable to suppose that the singlet
excited state lifetime of a postulated C31-sulfanyl-chlorin, formed by addition of a cysteinyl thiol to
the C3-vinyl group, is shorter than a Chl without the thioether linkage. We speculate that the
thioether linkage at the C31-position as a mode of cofactor binding is disadvantageous for
photosynthetic light-energy conversion.
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3. Conclusions
We studied syntheses and photophysical properties of chlorins possessing
(phenylsulfanyl)ethyl groups at the C3-position for the first time. The C31-sulfanyl-chlorin was
prepared by substitution of C31-OH or C31-Br with thiophenol. The C32-phenylsulfanyl derivative
was synthesized by radical addition of PhSH to the C3-vinyl group. Fluorescence quantum yield
and lifetime of the C31-sulfanyl-chlorin were smaller than those of the C32-sulfanyl-chlorin and the
C3-ethyl-chlorin. The results suggest that presence and position of the sulfur atom influenced the
optical properties of the chlorins.
4. Experimental section
4.1.
General
Methyl pyropheophorbide-a (1) was prepared from Chl-a extracted from Spirulina.25
Methyl bacteriopheophorbide-d (2)16,17 and methyl mesopyropheophorbide-a (5)19,20 were
synthesized from 1 according to the previously reported procedures. Reagents were purchased
from Kanto Chemical Co., Inc., and were used as as purchased without further purification. The
products were isolated using reversed-phase HPLC [column, Nomura Chemical Develosil
ODS-HG5 (20φ × 150 mm); eluent, methanol; pump, Jasco PU-2089; detector, Jasco MD-2018;
flow rate, 3 mL/min; room temperature]. Electronic absorption and fluorescence emission spectra
were measured on Jasco V-550 and FP-777W spectrometers. Fluorescence lifetimes and quantum
yields were recorded on Hamamatsu Photonics absolute PL and lifetime measurement systems
13
C9920-03G and C7990S. 1H- and C-NMR spectra were recorded on a Varian VNMRS-500HR
spectrometer in CDCl3. Chemical shifts are reported relative to the residual solvent peak: δ = 7.26
ppm (CHCl3) for 1H-NMR and δ = 77.0 ppm (13CDCl3) for 13C-NMR. Proton peaks were assigned
by 1H1H COSY and NOESY or ROESY spectra, and carbon signals were assigned by DEPT and
1H13C COSY spectra. HRMS data were collected by a Bruker micrOTOF II.
3)
4.2.
Synthesis of phenylsulfanylated chlorophyll derivatives
4.2.1. Methyl 31-(phenylsulfanyl)mesopyropheophorbide-a (3). Compound 1 (100 ꢀmol, 55 mg) was
transformed into compound 2 via hydrobromination and hydration.16,17 Subsequently thus
11

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obtained compound 2 (80 ꢀmol, 45 mg) was mixed with thiophenol (200 ꢀmol, 20 µL) and ZnI2
(100 ꢀmol, 32 mg) in CHCl3 (200 mL) and refluxed for 2 h.18 An aqueous 2 M HCl solution was
added to the reaction mixture for demetallation of Zn-chlorins formed in situ. The mixture was
diluted in CHCl3 and washed with aqueous saturated NaHCO3. The organic phase was dried over
anhydrous Na2SO4, filtered and concentrated in vacuo. The crude product was purified by flash
column chromatography (FCC; silica gel, Et2O/CH2Cl2 = 3:100) to give 3 as a C31-diastereomeric
mixture (1:1, 65 ꢀmol, 43 mg, 82% yield).
Alternative preparation of 3 was conducted by substitution of the C31-bromo intermediate
with PhSH. Compound 1 (200 ꢀmol, 110 mg) was dissolved in HBr/AcOH (33%, 15 mL) and the
mixture was stirred for 30 min at room temperature. After removal of HBr/AcOH, the residue was
redissolved in Et3N (20 mL) and thiophenol (1 mmol, 102 µL), and the solution was stirred for 10
min at room temperature. The mixture was diluted in CHCl3 and washed by aqueous saturated
NaHCO3. The organic phase was dried over anhydrous Na2SO4, filtered and concentrated in
vacuo. The crude product was purified by FCC (silica gel, Et2O/CH2Cl2 = 3:100) to give 3 (168
ꢀmol, 111 mg, 84% yield).
3: dark purple solid; mp 100 ˚C; VIS (CHCl3) λmax (nm) 666 (molar extinction, ε, 3.6×104
M-1cm-1), 609 (4.8×103), 539 (4.8×103), 509 (4.8×103), 414 (6.8×104); 1H-NMR (CDCl3, 500 MHz)
δ (ppm) 9.64 (br-s), 9.505/9.503, 8.45 (3H, s, CH-5, 10, 20), 7.44-7.40 (2H, m, phenyl-H),
7.11-7.03 (3H, m, phenyl-H), 5.78 (1H, m, CH-31), 5.25, 5.10 (2H, 2d, J = 20 Hz, CH-132), 4.45
(1H, br-q, J = 7 Hz, CH-18), 4.28 (1H, m, CH-17), 3.70 (2H, q, J = 8 Hz, CH2-81), 3.67, 3.61/3.60,
3.269/3.266, 3.26/3.25 (12H, 4s, CH3-21, 71, 121, 175), 2.345/2.335 (3H, d, J = 7 Hz, CH3-32),
2.73-2.50, 2.32-2.22 (4H, m, CH2-171, 172), 1.79 (3H, d, J =7 Hz, CH3-181), 1.71 (3H, t, J = 8 Hz,
CH3-82), 0.45, -1.78 (2H, 2s, NH); 13C-NMR (CDCl3, 125 MHz) δ (ppm) 196.20 (C131), 173.48
(C173), 171.35 (C19), 160.23 (C16), 154.87 (C6), 150.88(C9), 149.01 (C14), 144.92 (C8), 141.03
(C1), 139.21, 137.79, 136.20, 135.44, 135.21 (C3, C4, C7, C11, Ph), 133.14 (Ph), 132.36 (C2),
130.43 (C13), 128.79 (Ph), 128.31 (C12), 127.65 (Ph), 105.99 (C15), 104.13 (C10), 97.63 (C5),
92.71 (C20), 51.69 (C175), 51.57 (C17), 49.99 (C18), 48.00 (C132), 41.60 (C31), 30.88 (C171),
29.85 (C172), 23.30 (C32), 23.13 (C181), 19.50 (C81), 17.47 (C82), 12.06 (C21), 11.55 (C121), 11.30
(C71); HRMS (APCI) found: m/z = 659.3051, calcd. for C40H43N4O3S: MH+, 659.3056.
4.2.1. Methyl 32-(phenylsulfanyl)mesopyropheophorbide-a (4). Compound 4 was prepared as
previously described.15 Briefly, compound 1 (10 ꢀmol, 5.5 mg), thiophenol (200 ꢀmol, 20 µL)
and AIBN (10 ꢀmol, 1.6 mg) were dissolved in CHCl3 (10 ml), refluxed for 5 h, diluted with CHCl3,
and washed by aqueous saturated NaHCO3. The organic phase was dried over anhydrous Na2SO4,
t
filtered and concentrated in vacuo. The residue was reduced with BuNH2BH3, followed by
12

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workup and reprecipitation from methanol, for better separation of the desired compound from
by-products by FCC. The crude product was purified by FCC (silica gel, Et2O/CH2Cl2 = 3:100) to
give 4 (62%): mp 185 ˚C; VIS (CHCl3) λmax (nm) 662 (ε, 6.3×104 M-1cm-1), 605 (1.1×104), 536
(1.2×104), 505 (1.2×104), 412 (1.3×105); 1H-NMR (CDCl3, 500 MHz) δ (ppm) 9.51 (1H, s, CH-10),
9.10 (1H, s, CH-5), 8.48 (1H, s, CH-20), 7.64 (2H, d, J = 7 Hz, CH-2’, 6’ of phenyl), 7.42 (2H, t, J
= 7 Hz, CH-3’, 5’ of phenyl), 7.36 (1H, t, J = 7 Hz, CH-4’ of phenyl), 5.30, 5.10 (2H, 2d, J = 20 Hz,
CH2-132), 4.47 (1H, dq, J = 2, 7 Hz, CH-18), 4.28 (1H, dt, J = 7, 2 Hz, CH-17), 4.14 (2H, m,
CH2-31), 3.70 (2H, q, J = 8 Hz, CH2-81), 3.68 (3H, s, CH3-121), 3.64 (2H, m, CH2-32), 3.60 (3H, s,
CH3-175), 3.29 (3H, s, CH3-21), 3.19 (3H, s, CH3-71), 2.73-2.51, 2.36-2.22 (4H, m, CH2-171, 172),
1.80 (3H, d, J = 7 Hz, CH3-181), 1.70 (3H, t, J = 8 Hz, CH3-82), 0.49, -1.70 (2H, 2s, NH-21, 23);
13C-NMR (CDCl3, 125 MHz) δ (ppm) 196.16 (C131), 173.49 (C173), 171.54 (C19), 160.04 (C16),
154.97 (C6), 150.51(C9), 148.96 (C14), 144.98 (C8), 141.66 (C1), 137.57, 137.03, 136.51, 135.94,
135.69 (C3, C4, C7, C11, Ph), 132.39 (Ph), 130.30 (C2), 129.84 (Ph), 129.18 (C13), 128.13 (C12),
126.52 (Ph), 105.95 (C15), 104.11 (C10), 95.80 (C5), 92.67 (C20), 51.68, 51.54 (C17, C175), 49.97
(C18), 47.97 (C132), 35.49 (C31), 30.88 (C171), 29.80 (C172), 26.30 (C32) 23.06 (C181), 19.40
(C81), 17.41 (C82), 11.98 (C21), 11.21 (C121), 11.17 (C71); HRMS (APCI) found: m/z 659.3057,
calcd. for C40H43N4O3S: MH+, 659.3056.
Acknowledgments
This work was partially supported by a research project of Utsunomiya University Center
for Optical Research & Education, and by Grants-in-Aid for Scientific Research (C) (Nos.
21510132 and 25410082 to TO) and (A) (No. 2245030 to HT) from the Japan Society of the
Promotion of Science (JSPS). We also thank Dr. T. Mizoguchi and Mr. Y. Kinoshita (Ritsumeikan
Univ.) and the Collaboration Center for Research and Development of Utsunomiya University for
their help in experiments.
Supplementary data
Supplementary data associated with this article can be found in the online version, at
http://dx.doi.org/10.1016/j.tet.2014.
13

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References and notes
1. Tamiaki, H.; Kouraba, M. Tetrahedron 1997, 53, 10677.
2. Tamiaki, H.; Machida, S.; Mizutani, K. J. Org. Chem. 2012, 77, 4751.
3. Umena, Y.; Kawakami, K.; Shen, J.-R.; Kamiya, N. Nature 2011, 473, 55.
4. Squier, A. H.; Hodgson, D. A.; Keely, B. J. Chem. Commun. 2003, 624.
5. Squier, A. H.; Hodgson, D. A.; Keely, B. J. Org. Geochem. 2004, 35, 1309.
6. Pickering, M. D.; Keely, B. J. Org. Geochem. 2008, 39, 1046.
7. Pickering, M. D.; Keely, B. J. Geochim. Cosmochim. Acta 2011, 75, 533.
8. Pickering, M. D.; Keely, B. J. Geochim. Cosmochim. Acta 2013, 104, 111.
9. Tamiaki, H.; Xu, M.; Kinoshita, Y. J. Photochem. Photobiol. A: Chem. 2013, 252, 60.
10. Saga, Y.; Tamiaki, H. J. Photochem. Photobiol. B: Biol. 2004, 73, 29.
11. Oba, T.; Uda, Y.; Matsuda, K.; Fukusumi, T.; Ito, S.; Hiratani, K.; Tamiaki, H. Bioorg. Med.
Chem. Lett. 2011, 21, 2489.
12. Fukusumi, T.; Matsuda, K.; Mizoguchi, T.; Miyatake, T.; Ito, S.; Ikeda, T.; Tamiaki, H.; Oba, T.
FEBS Lett. 2012, 586, 2338.
13. Fukusumi, T.; Takei, N.; Tateno, Y.; Aoki, T.; Ando, A.; Kozakai, K. ; Shima, H. ; Mizoguchi,
T. ; Ito, S. ; Ikeda, T. ; Tamiaki, H. ; Oba, T. J. Porphyrin Phthalocyanine 2013, 17, 1188.
14. Belykh, D. V.; Ashikhmina, E.V. Macroheterocycles 2012, 5, 56.
15. Oba, T.; Tateno, Y.; Ihara, M.; Fukusumi, T.; Takei, N.; Ito, S. Tetrahedron Lett. 2014, 55, 725.
16. Tamiaki, H.; Takeuchi, S.; Tsudzuki, S.; Miyatake, T.; Tanikaga, R. Tetrahedron 1998, 54,
6699.
17. Smith, K. M.; Bisset, G. M. F.; Bushell, M. J. J. Org. Chem. 1980, 45, 2218.
18. Guindon, Y.; Frenette, R.; Fortin, R.; Rokach, J. J. Org. Chem. 1983, 48, 1357.
19. Smith, K. M.; Goff, D. A.; Simpson, D. J. J. Am. Chem. Soc. 1985, 107, 4946.
20. Sasaki, S.; Mizutani, K.; Kunieda, M.; Tamiaki, H. Tetrahedron Lett. 2011, 67, 6065.
21. Inamoto, N.; Masuda, S. Chem. Lett. 1982, 1003.
22. Pandey, R. K.; Sumlin, A. B.; Constantine, S.; Aoudia, M.; Potter, W. R.; Bellnie, D. A.;
Henderson, B. W.; Rodgers, M. A.; Smith, K. M.; Dougherty, T. J. Photochem. Photobiol.
1996, 64, 194.
23. Machida, S.; Isoda, Y.; Kunieda, M.; Tamiaki, H. Tetrahedron Lett. 2012, 53, 6277.
24. Kavarnos, G.; Cole, T.; Scribe, P.; Dalton, J. C.; Turro, N. J. J. Am. Chem. Soc. 1971, 93, 1032.
25. Tamiaki, H.; Amakawa, M.; Shimono, Y.; Tanikaga, R.; Holzwarth, A. R.; Schaffner, K.
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Photochem. Photobiol. 1996, 63, 92.
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Supporting Information
Synthesis and photochemical properties of phenyl-sulfanylated
chlorophyll derivatives
a
a
b
b
Natsuki Takei , Misaki Morioka , Mari Yoshizato , Takuya Tanaka , Shin-ichi
Sasaki b,c, Satoshi Itoa, Hitoshi Tamiaki b,*, Toru Oba a,*
aDepartment of Material and Environmental Chemistry, Graduate School of Engineering,
Utsunomiya University, Utsunomiya, Tochigi 321-8585, Japan.
bGraduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
cNagahama Institute of Bio-Science and Technology, Nagahama, Shiga 526-0829, Japan.
* Corresponding authors. Fax: +81 77 561 2659; e-mail address: tamiaki@fc.ritsumei.ac.jp (H.
Tamiaki). Tel/fax: +81 28 689 6147; e-mail address: tob_p206@cc.utsunomiya-u.ac.jp (T. Oba).

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R
3
S1: R = -CHO
NH
N
S
S2: R =
N
HN
S
S3
: R = -CH(OH)CH2SPh
O
COOMe
Figure S1. Molecular structures of methyl pyropheophorbides.
Methyl 3-devinyl-3-(1,3-dithioran-2-yl)pyropheophorbide-a (S2)
Methyl pyropheophorbide-d (S1, 10 ꢀmol), 1,2-ethanedithiol (400 ꢀmol), and
trimethylsilyl chloride (400 ꢀmol) were dissolved in CH2Cl2,S1 and stirred for 20 min at room
temperature. The mixture was diluted in CH2Cl2 and washed by aqueous saturated NaHCO3. The
organic phase was dried over anhydrous Na2SO4, filtered and concentrated in vacuo. The crude
product was purified by an alumina column (eluent: CH2Cl2) to give S2 (82%) as a dark purple
solid: mp 125 ˚C; VIS (CHCl3) λmax (nm) 670 (molar extinction, 4.0×104 M-1cm-1), 613 (5.2×103),
542 (7.4×103), 511 (7.4×103), 414 (7.4×104); 1H-NMR (CDCl3, 500 MHz) δ (ppm) 9.91, 9.55, 8.62
(3H, 3s, CH-5, 10, 20), 7.23 (1H, s, CH-31), 5.30, 5.11 (2H, 2d, J = 20 Hz, CH-132), 4.50 (1H, m,
CH-18), 4.31 (1H, m, CH-17), 4.07-3.99, 3.85-3.75 (4H, 2m, CH2-33, 34), 3.68, 3.60, 3.51, 3.28
(12H, 4s, CH3-21, 71, 121, 175), 3.70 (2H, q, J = 8 Hz, CH2-81), 2.72-2.52, 2.34-2.24 (4H, m,
CH2-171, 172), 1.81 (3H, d, J = 7 Hz, CH3-181), 1.69 (3H, t, J = 8 Hz, CH3-82), 0.30, -1.64 (2H, 2s,
13
NH-21, 23); C-NMR (CDCl3, 125 MHz) δ (ppm) 196.10 (C131), 173.43 (C173), 170.99 (C19),
160.37 (C16), 154.48 (C6), 150.96(C9), 148.71 (C14), 144.71 (C8), 140.46 (C1), 137.86 (C11),
136.20 (C7), 135.00, 134.52 (C3, C4), 132.27 (C2), 130.42 (C13), 128.35 (C12), 105.97 (C15),
103.68 (C10), 97.70 (C5), 92.95 (C20), 51.61, 51.59 (C17, C175), 49.83 (C18), 48.54 (C31), 47.97
(C132), 41.30, 41.29 (C33, 34), 30.81 (C171), 29.71 (C172), 23.09 (C181), 19.29 (C81), 17.34 (C82),
11.91 (C21), 11.26 (C121); HRMS (APIC) found: m/z 627.2457; calcd for C35H39N4O3S2: MH+,
627.2464.
Methyl 31-hydroxy-32-(phenylsulfanyl)mesopyropheophorbide-a (methyl
32-(phenylsulfanyl)bacteriopheophorbide-d, S3)
Compound S3 was prepared as previously described.S2

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Table S1. Fluorescence properties of methyl (sulfanylated) mesopyropheophorbides in CHCl3 at
room temperature.
Soret
Qy(0,0)
Fluorescence
emission
Fluorescence
quantum
yield a
Stokes
shift
absorption absorption
maximum maximum
Fluorescence
lifetime (ns) b
Compound
maximum
(cm-1)
λabs (nm)
λabs (nm)
λem (nm) a
414
666
670
666
662
675
670
0.18
0.25
0.24
0.19
0.26
3.9
5.7
5.7
4.1
5.8
90
90
3
4
412
662
411
657
100
110
100
5
414
670
S2
S3
412
665
aExcitation at the Soret peak. bExcitation at 403 nm.
Semi-empirical calculation
Quantum mechanical calculations were done as previously reported.S3 Molecular
modelings were performed using HyperChem release 7.5 (HyperCube, Inc.). The molecular
structures were optimized by MM+ and then by PM3. The orbital energies were obtained by PM3
calculation. Solvent effects were neglected in all calculations. Molecular mechanics program
MM+ and quantum mechanics program PM3 were both employed without any modification of the
provided parameters.
Table S2. Orbital energies (eV) of methyl (sulfanylated) mesopyropheophorbides-a 3-5.
HOMO-1
Compound
LUMO+1
-1.2898
-1.2516
-1.2385
LUMO
-1.6794
-1.6413
-1.6108
HOMO
-7.9394
-7.9288
-7.9117
∆(LUMO-HOMO)
6.2600
-8.0579
-8.0446
-8.0183
3
4
5
6.2875
6.3009
References
S1. Pandey, R. K.; Jagerovic, N.; Ryan, J. M.; Dougherty, T. J.; Smith, K. M. Tetrahedron 1996, 52,
5349.
S2. Fukusumi, T.; Takei, N.; Tateno, Y.; Aoki, T.; Ando, A.; Kozakai, K. ; Shima, H. ; Mizoguchi,
T. ; Ito, S. ; Ikeda, T. ; Tamiaki, H. ; Oba, T. J. Porphyrin Phthalocyanine 2013, 17, 1188.
S3. Oba, T.; Tamiaki, H. Photosynth. Res. 2002, 74, 1.