Synthesis of type III isomers of diacetyldeutero-, hemato-, and protoporphyrins with the use of Knorr's pyrrole

Article abstract of DOI:10.1016/j.tet.2016.05.030

Derivation of the Knorr's pyrrole with 2-ethyl and 4-benzyl mixed-ester groups into 3,3′-diacetyl-5,5′-diiodo-4,4′-dimethyl-2,2′-dipyrromethane was developed. Coupling of the dipyrromethane with 5,5′-diformyl-3,3′-bis(2-methoxycarbonylethyl)-4,4′-dimethyl-2,2′-dipyrro-methane afforded in a reasonable yield diacetyldeuteroporphyin III with C_2vsymmetry. The porphyrin was further converted to protoporphyrin III through hematoporphyrin III. Utilization of readily available Knorr's pyrrole as the starting material much facilitates the access to symmetric iron porphyrins which are free from the orientational disorder in hemoprotein pocket.

Full text of DOI:10.1016/j.tet.2016.05.030

Accepted Manuscript
Synthesis of type III isomers of diacetyldeutero-, hemato-, and protoporphyrins with
the use of Knorr's pyrrole
Saburo Neya, Tomoki Yoneda, Tyuji Hoshino, Akira T. Kawaguchi, Masaaki Suzuki
PII:
S0040-4020(16)30415-X
10.1016/j.tet.2016.05.030
TET 27757
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 15 April 2016
Revised Date: 7 May 2016
Accepted Date: 11 May 2016
Please cite this article as: Neya S, Yoneda T, Hoshino T, Kawaguchi AT, Suzuki M, Synthesis of type III
isomers of diacetyldeutero-, hemato-, and protoporphyrins with the use of Knorr's pyrrole, Tetrahedron
(2016), doi: 10.1016/j.tet.2016.05.030.
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ACCEPTED MANUSCRIPT
Graphical abstract by Neya et al. for Tetrahedron

ACCEPTED MANUSCRIPT
Synthesis of Type III Isomers of Diacetyldeutero-, Hemato-, and Protoporphyrins
with the Use of Knorr’s Pyrrole
Saburo Neya*,a, Tomoki Yonedaa, Tyuji Hoshinoa, Akira T. Kawaguchib, and Masaaki Suzukic
aDepartment of Physical Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University,
Chuoh-Inohana, Chiba 260-8675, Japan
bSchool of Medicine, Tokai University, Isehara, Kanagawa 259-1193, Japan,
cDepartment of Material Science, Interdisciplinary Graduate School of Science and Engineering,
Shimane University, Matsue, Shimane 690-8504, Japan
*Corresponding author.
Tel: +81-43-226-2934; e-mail address: sneya@faculty.chiba-u.jp (S. Neya).
ABSTRACT
Derivation of the Knorr’s pyrrole with 2-ethyl and 4-benzyl mixed-ester groups into
3,3’-diacetyl-5,5’-diiodo-4,4’-dimethyl-2,2’-dipyrromethane was developed.
Coupling of the
dipyrromethane with 5,5’-diformyl-3,3’-bis(2-methoxycarbonylethyl)-4,4’-dimethyl-2,2’-dipyrro-
methane afforded in a reasonable yield diacetyldeuteroporphyin III with C2v symmetry. The
porphyrin was further converted to protoporphyrin III through hematoporphyrin III. Utilization of
readily available Knorr’s pyrrole as the starting material much facilitates the access to symmetric
iron porphyrins which are free from the orientational disorder in hemoprotein pocket.
Keywords:
Knorr’s pyrrole, natural type porphyrin, symmetrical porphyrins, synthetic design
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1. Introduction
Many hemoproteins such as hemoglobin, myoglobin, and cytochrome P450 contain protoheme
as their prosthetic groups. Protoporphyrin IX (1) bearing two vinyl side-chains at the peripheral
2,4-position is asymmetric about the α,γ meso-carbon axis as illustrated in Fig. 1.
La Mar and
coworkers revealed in 1983 that the asymmetric heme exists in two orientations within the globin
pocket of myoglobin.1 Interpretation of the physicochemical properties of hemoproteins is
frequently complicated due to the heme orientational disorder.2-4
Fig. 1. Structures of the dimethyl esters of natural porphyrin 1 and type III porphyrins 2 and 3.
2,4-Dimethyldeuteroporphyrin (2) has two methyl groups at the 2,4-postions (Fig. 1). Porphyrin
2, symmetric about the α,γ meso-carbon axis, is free from the disorder in globin pocket. Although the
hydrolysed iron complex of 2 has been employed for the rigorous structural characterization of
hemoproteins,5-7 methyl and vinyl groups are yet different from each other in their molecular bulk
and electronic property. Protoporphyrin III (3) is another symmetric porphyrin with two vinyl
groups at the 2,3-position (Fig. 1). Since porphyrin 3 is a closer analogue of 1 than porphyrin 2, it
is more suitable for biological analyses. The synthesis of porphyrin 3 has been long known.8-13 The
vinyl groups in 3 have been constructed from the 2-chloroethyl substituents in the precursory
porphyrin by eliminating hydrogen chloride.8,11-13 The chloroethyl pyrrole, the base material for the
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chloroethyl
porphyrin,
is
derived
from
benzyl
4-(methoxycarbonylmethyl)-3,5-dimethylpyrrole-2-carboxylate through several reaction steps.
Another route to divinyl-substituted porphyrin is the initial introduction of acetyl groups to the
vacant pyrrole β-sites of deuteroporphyrin.15-17 The acetyl groups attached to porphyrin periphery, is
reduced to 1-hydroxyethyl groups, and then dehydrated into vinyl substituents to afford
protoporphyrin.15-17
Second route of the deuteroporphyrin modification suggests that symmetric
protoporphyrin may be derived if symmetric diacetyldeuteroporphyin is directly prepared. Based
on this fundamental idea, we have devised a new and practical synthesis of protoporphyrin III after
the direct synthesis of diacetyldeuteroporphyin III with the use of Knorr’s pyrrole as the starting
material.
2. Results and discussion
2.1. Dipyrromethanes
Scheme 1 outlines the route to dipyrromethane derivatives for diacetyldeuteroporphyin. The
starting compound (4), the Knorr's pyrrole with 2-ethyl and 4-benzyl ester groups, was prepared by
the established method.18 Introduction of 4 with the mixed-ester groups is essential to de-esterify
independently the two sites with hydrogen gas or aqueous sodium hydroxide. Pyrrole 4 was
initially self-coupled into the symmetric dipyrromethane (5). Higher temperature and longer reaction
time, in comparison with those imposed on ordinary Knorr's pyrrole with 2,4-diethoxycarbonyl
groups,19 were necessary for the coupling due to the bulky benzyl substituents in 4. The 3,3'-dibenzyl
groups in 5 were then removed by hydrogenolysis. Resulting free carboxyl residues were removed
by iodination. The diiodo compound (6) was reduced to (7) under hydrogen atmosphere (yield 87%).
It is to be noted that King and Brown have reported incidental formation of 7 in an attempted
nitration of ethyl 4,5-dimethylpyrrole-2-carboxylate (28% yield).20
In contrast, we obtained
compound 7 in 87% yield from 6 after the rational synthesis. (These sentences and Reference 20 in
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the original version were removed according to the comment 2 by Reviewer #1). Treatment of 7
bearing free 3,3’-position with acetyl chloride in the presence of aluminum chloride afforded
3,3’-diacetyldipyrromethane dimethylester (8). Compound 8 was (suggested correction 1 by
Reviewer #2) then hydrolyzed with aqueous sodium hydroxide into dipyrromethane
5,5’-dicarboxylic acid. The terminal carboxyl residues in 8 were then removed by iodinative
decarboxylation to give 5,5’-diiododipyrromethane (9). After the total eight-steps in Scheme 1, we
obtained 9 (1.62 g) from pyrrole 4 (18.8 g) with the overall yield of 10.2%.
Scheme 1. Synthesis of 5,5’-diiododipyrromethane 9 starting from Knorr pyrrole 4.
2.2. Porphyrins
Martin et al. recently reported a conceptually new approach to porphyrin.20 They found that
5,5’-diiododipyrromethane reacts with 5,5’-diformyl dipyrromethane to give porphyrin in an
excellent yield. We adopted their “2 + 2” methodology to prepare protoporphyrin III as illustrated in
Scheme 2. The coupling of diiodo compound 9 with the diformyl dipyrromethane (10)21 bearing two
propionate groups afforded diacetyldeuteroporphyin (11) in 31% yield. Reduction of 11 with
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sodium borohydride under the reported conditions16,20 gave hematoporphyrin (12) (yield 66%).
Subsequent dehydration of 12 mediated by benzoyl chloride20,22 furnished protoporphyrin 3 (yield
92%).
Scheme 2. Synthesis of type III isomers of diacetyl-, hemato-, and protoporphyrins.
The high-resolution ESI-TOF mass spectra of diacetyldeutero-, hemato-, and protoporphyrins
1
11-13 were consistent with their molecular weights. The H-NMR spectra of these porphyrins
commonly showed the 1:1:2 intensity patterns for the meso-protons as illustrated in Fig. 2. In
addition, only the two peaks from the peripheral methyl protons were observed around 3.6 ppm (Figs
1
S6-S8, Supplementary data). These H-NMR results are consistent with the type III symmetry of
the porphyrins.
The 13C-NMR spectra of porphyrins 3, 11, and (suggested correction 2 by
Reviewer #2) 12 resolved all of the expected signals (Figs. S14-16, Supplementary data). In the
13C-NMR spectra of protoporphyrin 3, it is notable that the pyrrole Cα and Cβ peaks were
significantly broadened out although other side-chain signals were well resolved. The line
broadening of the pyrrole carbon signals is likely to arise from the rapid NH tautomerism, as has
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been pointed out by Abraham et al.24 Upon addition of a small amount of trifluoroacetic acid to the
porphyrin solution, eight signals from the pyrrole Cα and Cβ carbons expectedly appeared (Fig. S16,
Supplementary data). The electronic absorption spectra of the type III diacetyldeuteroporphyin 11,
hematoporphyrin 12, and protoporphyrin 3 (Figs. S17-S19, Supplementary data) were closely similar
to those of the corresponding type IX isomers.23
1
Fig. 2. The 400 MHz H-NMR spectra in the meso-proton regions of porphyrins. The upper two
spectra were recorded in CDCl3/CF3CO2H = 200/1 v/v to improve solubility, and the bottom
spectrum was obtained in CDCl3.
3. Conclusions
We have developed a new practical route to the type III isomers of diacetyldeutero-, hemato-,
and protoporphyrins with the use of Knorr's pyrrole 4. In the conventional syntheses,8,11-13 the
starting pyrrole with 4-(methoxycarbonylmetyl) group is synthesized from benzyl acetoacetate and
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methyl 3-acetyl-4-oxopentanoate. Unfortunately, the preparation of latter diketone tends to be
laborious. Thus, these procedures to protoporphyrin III require much cost and effort. On the other
hand, the starting compound 4 is readily accessible with the inexpensive commercial β-diketones,14
and we can avoid the preparation of methyl 3-acetyl-4-oxopentanoate.
Pure dipyrromethane 9 is
synthesized with ease to afford symmetric diacetyldeuteroporphyrin 11 in a large quantity (Scheme
1). Subsequent conversions of 11 to porphyrins 12 and 3 (Scheme 2) are conveniently carried out
with the established methods.16,20,22 These results taken together allow us the facile preparation of the
type III porphyrins. In addition, the acetyl, 1-hydroxyethyl, and vinyl substituents at the 2,3-position
exhibit diferent electron-withdrawing influences to the chelating metals in porphyrin.25
In conclusion, Knorr's pyrrole 4, which has been little employed in natural porphyrin synthesis,
is turned out to be a useful building block. The symmetirc iron porphyrins, free from the
orientational disorder in globin pocket, are valuable molecular tools in hemoprotein analyses.
4. Experimental section
4.1. General methods
Silica gel and the reagents for pyrrole synthesis were purchased from commercial sources. The 1H
(400 MHz) and 13C NMR (100 MHz) spectra were obtained on a JEOL spectrometer. Chemical shifts
were reported in ppm from internal tetramethylsilane on the
δ scale. Electronic absorption spectra
were recorded on Shimadzu spectrophotometer. High-resolution mass spectra were measured on a
JEOL Accu-TOF using positive mode ESI-TOF method in spectroscopic grade methanol containing
reserpine as the internal reference (m/z = 609.2810 [M + H]+) spectrometer.
4.2. Compound (5)
Pyrrole 4 (18.8 g), obtained by the literature method with ethyl acetoacetate and benzyl
o
acetoacetate,18 was dissolved in propionic acid (90 mL) at 50 C. To the stirred solution, 5.0 mL of
o
sulfuryl chloride was added over 30 min. The mixture was heated to 60 C, and stirred for 5 min at
7

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this temperature. The fine-needles of the 5-chloromethylpyrrole appeared on cooling was filtered
off and dried in vacuum (13.4 g, yield 64%). The 5-chloromethylpyrrole was dissolved in propionic
acid (30 mL)/water (5 mL) mixture at 100 oC, and boiled for 2 h. When the solution was cooled on
ice bath overnight, the white precipitate of compound 5 appeared. The product was filtered off,
1
rinsed with water, and dried (6.53 g, yield 56%). H-NMR (CDCl3):
δ 10.11 (br s, 2H, NH),
7.46-7.26 (m, 10H, -C6H5), 5.37 (s, 4H, -CH2-C6H5), 4.48 (s, 2H, meso CH2), 4.29 (q, J = 7.2 Hz, 4H,
-CH2CH3), 2.50 (s, 6H, pyrrole CH3), 1.34 (t, J = 7.0 Hz, 6H, -CH2CH3). 13C-NMR (CDCl3):
δ
166.3 (-CO2CH2C6H5), 161.1 (-CO2CH2CH3), 139.2 (pyrrole Cα), 136.1 (pyrrole Cα), 129.7/128.7/
128.23/128.20 (-C6H5), 118.8 (pyrrole Cβ), 112.9 (pyrrole Cβ), 66.1 (-CH2C6H5), 60.2 (-CH2CH3),
24.6 (meso CH2), 14.4 (-CH2CH3), 12.2 (pyrrole CH3).
4.3. Compound (6)
Dipyrromethane 5 (10.0 g) was dissolved in tetrahydrofuran (20 mL) and diluted with methanol
(100 mL). After addition of 0.3 mL of trimethylamine, the mixture was stirred for 18 h under
hydrogen atmosphere in the presence of palladium-activated carbon (Pd 10%, 800 mg) to remove the
benzyl groups. Resulting precipitate of dipyrromethane with free acid groups was dissolved with
aqueous NaOH (2.0 M, 3 mL), and the solution was filtered to remove the carbon catalyst. The
filtrate was diluted with water (50 mL containing 5.0 g of NaHCO3), and heated to 35 oC. Mixture of
I2 (8.6 g) and KI (12.0 g) in water (80 mL) was added dropwise to the stirred dipyrromethane
solution at 35 oC over 30 min, and the solution was stirred for additional 2 h at the same temperature.
The resulting precipitates 6 were collected by filtration, rinsed with water, and dried (7.2 g, yield
85%). 1H-NMR (CDCl3):
meso CH2), 2.26 (s, 6H, pyrrole CH3), 1.31 (t, J = 7.2 Hz, 6H, -CH2CH3). 13C-NMR (CDCl3):
δ 10.51 (br s, 2H, NH), 4.17 (q, J = 7.2 Hz, 4H, -CH2CH3), 4.01 (s, 2H,
δ
161.6 (-CO2CH2CH3), 134.0 (pyrrole Cα), 129.8 (pyrrole Cα), 119.4 (pyrrole Cβ), 72.9 (pyrrole Cβ),
61.2 (-CH2CH3), 28.9 (meso CH2), 14.6 (-CH2CH3), 14.3 (pyrrole CH3).
4.4. Compound (7)
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Dipyrromethane 6 (5.6 g) was dissolved in methanol (100 mL) containing 0.3 mL of
trimethylamine. The mixture was stirred over 18 h under hydrogen atmosphere in the presence of
palladium-activated carbon (Pd 10%, 600 mg) to remove the iodine substituents before filtration of
the catalyst. The filtrate was evaporated to dryness, and the residue was dissolved in hot methanol
(30 mL). Water was added to the hot methanol solution until slight turbidity, and the solution was
placed on ice bath. The resulting precipitates of compound 7 were collected by filtration, and dried
under vacuum (3.1 g, yield 87%). 1H-NMR (CDCl3):
δ 9.43 (br s, 2H, NH), 5.88 (d, 2H, pyrrole H),
4.27 (q, J = 7.2 Hz, 4H, -CH2CH3), 3.89 (s, 2H, meso CH2), 2.30 (s, 6H, pyrrole CH3), 1.32 (t, J =
7.2 Hz, 6H, -CH2CH3). 13C-NMR (CDCl3):
δ
162.4 (-CO2CH2CH3), 133.4 (pyrrole Cα), 128.9
(pyrrole Cα), 118.6 (pyrrole Cβ), 111.4 (pyrrole Cβ), 60.1 (-CH2CH3), 26.4 (meso CH2), 14.4
(-CH2CH3), 13.0 (pyrrole CH3).
4.5. Compound (8)
Compound 7 (1.0 g) in 1,2-dichloroethane (20 mL) was refluxed for 2 h in the presence of AlCl3
(2.51 g) and CH3COCl (1.48 g). Chloroform (40 mL) was added to the cooled solution, and the
mixture was washed with water (30 mL, 5 times) to remove salts before evaporation to dryness under
a reduced pressure. The residue was dissolved in hot methanol, and water (ca. 10% v/v) was added to
the solution. After standing on ice bath, white precipitate of product 8 appeared, and it was
1
collected with filtration (1.0 g, yield 80%). H-NMR (CDCl3):
δ 10.52 (br s, 2H, NH), 4.32 (q, J =
7.2 Hz, 4H, -CH2CH3), 4.29 (s, 2H, meso CH2), 2.58 (s, 6H, -COCH3), 2.53 (s, 6H, pyrrole CH3),
13
1.37 (t, J = 7.2 Hz, 6H, -CH2CH3). C-NMR (CDCl3):
δ 197.6 (-COCH3), 160.9 (-CO2CH2CH3),
138.3 (pyrrole Cα), 127.8 (pyrrole Cα), 123.4 (pyrrole Cβ), 118.6 (pyrrole Cβ), 60.3 (-CH2CH3),
31.2 (-COCH3), 24.9 (meso CH2), 14.5 (-CH2CH3), 12.6 (pyrrole CH3).
4.6. Compound (9)
To compound 8 (1.0 g) dissolved in methanol (30 mL) at 90 oC, NaOH (0.6 g) in water (20 mL)
was added. The solution was stirred for 3 h at this temperature, and diluted with water (40 mL)
9

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containing NaHCO3 (0.6 g). To this solution, I2 (1.3 g) and KI (1.7 g) dissolved in water (40 mL)
o
was added dropwise over 30 min at 45 C. The mixture was stirred for 3 h at the same temperature.
The precipitated solid 9 was filtered off, washed with water, and dried under vacuum (0.95 g, yield
76%). 1H-NMR (CDCl3):
(s, 6H, pyrrole CH3). 13C-NMR (CDCl3):
δ 9.85 (br s, 2H, NH), 4.25 (s, 2H, meso CH2), 2.49 (s, 6H, -COCH3), 2.22
δ
196.6 (-COCH3), 140.5 (pyrrole Cα), 123.9 (pyrrole Cα),
121.7 (pyrrole Cβ), 67.7 (pyrrole Cβ), 30.7 (-COCH3), 25.1 (meso CH2), 15.8 (pyrrole CH3).
4.7. 2,3-Diacetyldeuteroporphyrin (11)
Diiododipyrromethane 9 (2.16 g) and 5,5’-diformyldipyrromethane 10 (1.71 g)22 were dissolved
in acetic acid (260 mL)/acetic anhydride (40 mL), and stirred under dark in the presence of CF3SO3H
(0.75 mL) for 3 h at room temperature. After quenching the reaction with CH3CO2Na (2.0 g),
chloroform (500 mL) was added to the solution, and washed with water (300 mL × 5). The organic
layer was evaporated to dryness.
The residue was purified on silica-gel column with
chloroform/pyridine (98/2 v/v) as eluent. The fractions containing porphyrin 11 were collected, and
evaporated to dryness (752 mg, yield 29%). 1H-NMR (CDCl3/CF3CO2H = 200/1 v/v):
δ
11.68 (s,
1H, meso H), 10.96 (s, 1H, meso H), 10.66 (s, 2H, meso H), 4.43 (t J = 7.6 Hz,, 4H,
-CH2CH2CO2CH3), 3.91 (s, 6H, ring CH3), 3.65 (s, 6H, ring CH3), 3.57(s, 6H, -CO2CH3), 3.38 (s, 6H,
-COCH3), 3.15 (t, J = 7.2 Hz, 4H, -CH2CH2CO2CH3), -2.52 (br s, 2H, NH). 13C-NMR
(CDCl3/CF3CO2H
=
200/1
v/v):
δ
198.1
(-COCH3),
173.7
(-CO2CH3),
143.5/142.7/141.8/141.1/141.0/140.9/139.8/136.2 (pyrrole Cα and Cβ), 105.5/100.4/100.2 (meso C),
52.3 (-CO2CH3), 35.3 (-CH2CH2CO2CH3), 33.1 (-COCH3), 21.5 (-CH2CH2CO2CH3), 14.4/12.0 (ring
CH3). UV-vis. (CH2Cl2) λmax nm (
ε
, mM-1cm-1): 420 (137), 513 (10.2), 551 (6.9), 586 (4.9), 640(3.6).
+
HRMS (ESI) m/z Calcld for C36H39N4O6 [M + H]+ 623.2870, found 623.2877.
4.8. Hematoporphyrin III (12)
Diacetylporphyrin 11 (100 mg, 0.165 mmol) was dissolved in chloroform (40 mL)/methanol (5
mL) mixture. Nitrogen was bubbled to the solution for 10 min, and NaBH4 (32 mg) was added before
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the container was closed with a glass stopper. The solution was stirred in the dark at room
temperature for 80 min; the UV-visible spectrum in chloroform showed a Soret band at 401 nm.
The solution was washed with 1% hydrochloric acid (40 mL), and then with 2% aqueous NaOH (40
mL). The organic layer was evaporated to dryness. The residue was chromatographed on silica-gel
with chloroform/pyridine (100/2 v/v). After washing out impurities, the solvent was changed to
chloroform/methanol (4/1 v/v) mixture. The major fraction was collected and evaporated to leave
porphyrin 12 (mixture of diasteromers) as purple solid (66 mg, yield 65%). 1H-NMR
(CDCl3/CF3CO2H = 200/1 v/v):
δ 11.82 (s, 1H, meso H), 10.94 (s, 1H, meso H), 10.55 (s, 2H, meso
H), 6.51 (m, J = 6.8 Hz, 2H, -CH(OH)CH3), 4.46 (t, J = 7.2 Hz, 4H, -CH2CH2CO2CH3), 3.66 (s, 6H,
ring CH3), 3.63 (s, 6H, ring CH3), 3.54 (s, 6H, -CO2CH3), 3.17 (t, J = 7.2 Hz, 4H, -CH2CH2CO2CH3),
2.12 (m, J = 6.8 Hz, 6H, -CH(OH)CH3), -3.06 (br s, 1H, NH), -3.19 (br s, 1H, NH). 13C-NMR
(CDCl3/CF3CO2H
=
200/1 v/v):
δ
173.7 (-CO2CH3), 143.1/142.0/141.8/141.7/140.32/
140.28/138.7/136.9 (pyrrole Cα and Cβ), 102.9/99.3/98.7 (meso C), 66.0 (-CH(OH)CH3), 52.1
(-CO2CH3), 35.4 (-CH2CH2CO2CH3), 25.2 (-CH(OH)CH3), 21.7 (-CH2CH2CO2CH3), 12.0/11.9 (ring
CH3). UV-vis. (CH2Cl2) λmax nm (
ε
, mM-1cm-1): 401 (165), 497 (13.9), 532 (8.1), 567 (5.9), 595 (1.1),
621 (3.7). HRMS (ESI) m/z Calcld for C36H42N4O6 [M + H]+ 627.3183, found 627.3198.
+
4.9. Protoporphyrin III
(3)
Porphyrin 12 (100 mg) was dissolved in N,N-dimethylformamide (4.2 mL) containing
C6H5COCl (0.47 mL), and the solution was stirred under nitrogen at 100 oC for 60 min; the reaction
was complete when the Soret band shifted to 407 nm in chloroform/triethylamine. At room
temperature, chloroform (50 mL) and trimethylamine (2 mL) were added to the solution, and the
mixture was washed with water (50 mL, 4 times) to remove N,N-dimethylformamide. The organic
layer was evaporated to dryness under reduced pressure. The residue was applied to a silica-gel
column equilibrated with chloroform/methanol (100/2 v/v). The major band was collected, and the
solvent was removed under reduced pressure to leave a residue. It was recrystallized from
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chloroform/methanol (1/2 v/v) to afford protoporphyrin 3 (91 mg, yield 97%). 1H-NMR (CDCl3):
δ
10.25 (s, 1H, meso H), 10.00 (s, 2H, meso H), 9.97 (s, 1H, meso H), 8.23 (dd, J =17.6, 11.2 Hz, 2H,
-CH=CH2), 6.36 (d, J = 18.0 Hz, 2H, -CH=CH2), 6.17 (d, J = 11.0 Hz, 2H, -CH=CH2), 4.38 (t, J
= 7.6 Hz, 4H, -CH2CH2CO), 3.67 (s, 6H, ring CH3), 3.66 (s, 6H, ring CH3), 3.60 (s, 6H, -CO2CH3),
3.26 (t, J = 8.0 Hz, 4H, -CH2CH2CO), -3.85 (br s, 2H, NH). 13C-NMR (CDCl3):
δ
173.6 (-CO2CH3),
142.1/142.0/141.6/141.0/140.2/138.7/138.0/137.5 (pyrrole Cα and Cβ: observable in
CDCl3/CF3CO2H = 200/1 v/v), 130.3 (-CH=CH2), 120.8 (-CH=CH2), 98.3/96.9/96.1 (meso C), 51.8
(-CO2CH3), 36.9 (-CH2CH2CO), 21.8 (-CH2CH2CO), 12.7/11.7 (ring CH3). UV-vis. (CH2Cl2) λmax
nm (
ε
, mM-1cm-1): 407 (171), 506 (14.7), 541 (11.6), 575 (7.1), 629 (5.4). HRMS (ESI) m/z Calcld
+
for C36H38N4O4 [M + H]+ 591.2971, found 591.2998.
Acknowledgements
This work was supported by the Grants-in-Aid for Scientific Research from MEXT, Japan
(26460031 (C) and 20249272 (A)). T. Y. thanks the Program to Disseminate Tenure Tracking from
MEXT, Japan for the fellowship.
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Supplementary data
1
13
The H- (Figs. S1-S8) and C-NMR (Figs. S9-S16) spectra of the compounds and the UV-visible
(Figs. S17-S19) spectra of the porphyrins.
14