Total synthesis of hematoporphyrin and protoporphyrin: A conceptually new approach

Article abstract of DOI:10.1021/op100036c

The total synthesis of protoporphyrin IX and its disodium salt using a new alternative method to the classical MacDonald condensation is reported. The key step is the reaction of the new unsymmetrical diiodo dipyrrylmethane 1 with the known dipyrrylmethane 2. Coupling of the two fragments leads directly to porphyrin 3 without the need of an oxidizing agent. The new methodology is well suited for the synthesis of protoporphyrin IX derivatives on a multi 100 g scale in good quality without the need for chromatography. Furthermore, these preparations are completely free of any contaminant of animal origin, which represents a real improvement in the manufacturing of protoporphyrin IX derivatives.

Full text of DOI:10.1021/op100036c

Organic Process Research & Development 2010, 14, 799–804
Total Synthesis of Hematoporphyrin and Protoporphyrin: A Conceptually New
Approach
Pierre Martin,* Markus Mueller, Dietmar Flubacher, Andreas Boudier, Hans-Ulrich Blaser, and Dirk Spielvogel
SolVias AG, P.O. Box, CH-4002 Basel, Switzerland
Abstract:
The total synthesis of protoporphyrin IX and its disodium salt
using a new alternative method to the classical MacDonald
condensation is reported. The key step is the reaction of the new
unsymmetrical diiodo dipyrrylmethane 1 with the known dipyr-
rylmethane 2. Coupling of the two fragments leads directly to
porphyrin 3 without the need of an oxidizing agent. The new
methodology is well suited for the synthesis of protoporphyrin IX
Figure 1
derivatives on a multi 100 g scale in good quality without the need
without the presence of a metal leading directly to porphyrin 3
for chromatography. Furthermore, these preparations are com-
without the need of an oxidizing agent. The new methodology
pletely free of any contaminant of animal origin, which represents
is well suited for the synthesis of protoporphyrin IX on a multi
a real improvement in the manufacturing of protoporphyrin IX
100 g scale in good quality without the need for chromatography.
derivatives.
Synthetic Concept. The classical MacDonald condensation
where a dipyrrylmethane unit is reacted with a dipyrrylmethane
dialdehyde has been widely applied for the preparation of a
Introduction
Protoporphyrin IX (Figure 1) is most commonly prepared
variety of unsymmetrically substituted porphyrins.5 The primary
product is a dihydroporphin which must then be oxidized to
obtain the corresponding porphyrin using either air5 or a quinone
such as DDQ.6 In many cases, the oxidation step is rather
problematic since the dihydroporphin is quite unstable and not
easy to detect. Furthermore, the reduced quinone is difficult to
remove from the reaction mixture requiring a chromatographic
separation. For these reason, scale up problems are unavoidable
and, indeed, literature preparations are usually described in the
mg range.
We reasoned that in order to avoid the formation of the
dihydroporphin, one of the two dipyrrylmethanes should either
be in a higher oxidation state or carry a nucleofuge which can
be eliminated to form the required additional CC double bond.
We decided to prepare the diiodo derivative 1 and to react it
under MacDonald conditions with dipyrrylmethane dialdehyde
2 (Scheme 1). To our delight and surprise, we directly obtained
the desired porphyrin 3 in good yields. We postulate that the
primary condensation product is intermediate A which spon-
taneously eliminates water as well as one mol of HI to give the
iodinated porphyrin B which then is reduced by the HI formed
in the first step to give 3 and I2.7 We consider the elimination
of 2 mol of HI improbable since a rather thermodynamically
unfavorable dehydroporphyrin would be formed.
by semisynthesis starting from hemin, which in turn is isolated
from ox or pork blood.1,2 For medical applications, e.g., in cell
culture media, this poses the problem of impurities of animal
origin that may be present, in particular of agents in connection
with transmissible spongiform encephalopathy. In order to meet
the guidelines of the regulatory agencies,3 it was necessary to
provide a completely synthetic preparation process for the
preparation of protoporphyrin IX which uses only products of
synthetic origin.
Here, we describe the total synthesis of protoporphyrin IX
and its disodium salt using a novel variant of the MacDonald
condensation method. The key step is the reaction of the new
unsymmetrical diiododipyrrylmethane 1 with the known dipyr-
rylmethane 2 (Scheme 1).4 The two fragments are coupled
* Author to whom correspondence may be sent. E-mail: pierre.martin@
solvias.com.
(1) The original procedure was first described by Schalfejew, M. Hoppe
Seyler’s Z. 1900, 30, 390. Encyklopa¨die der technischen Chemie
(Ullmann’s Encyclopedia of Industrial Chemistry), IV ed.; VCH:
Weinheim, 1976; Vol. 11, p 129. An improved procedure is described:
Schulze, H. (BASF). U.S. Patent 4,761,472, 1988. About 3-4 g of
heme are obtained from 1 l of oxblood.
(2) Jackson, A. H.; Rao, K. R.; Wilkins, M. J. Chem. Soc., Perkin Trans.
1 1987, 307. Chen, W.; Yang, H.; Xu, D. Zhnongguo Yiyao Gongye
Zazhi 2000, 31, 293. CAN 134, 193262.
(3) Note for Guidance on Minimising the Risk of Transmitting Animal
Spongiform Encephalopathy Agents via Human and Veterinary Me-
dicinal Products. Official Journal of the European Union, C24/11;
January 28, 2004; p 6. Note for Guidance on Minimising the Risk of
Transmitting Animal Spongiform Encephalopathy Agents Via Human
and Veterinary Medicinal Products, EMEA 410/01/Rev. 2; Committee
for Medicinal Products (CHMP), European Medicines Agency (EMEA):
London, 2004.
(4) Chong, R.; Clezy, P. S.; Liepa, A. J.; Nichol, A. W. Aust. J. Chem.
1969, 22, 229. Jackson, A. H.; Pandey, R. K. J. Chem. Soc., Perkin
Trans. 1 1987, 299.
(5) Arenault, G. P.; Bullock, E.; MacDonald, S. F. J. Am. Chem. Soc. 1960,
82, 4384. Chakrabarty, M. J. Ind. Chem. Soc 2001, 78, 761. Clezy,
P. S.; Diakiw, V. Aust. J. Chem. 1975, 28, 2703.
(6) Lee, C.-H.; Li, F.; Iwamoto, K.; Dadok, J.; Bothner-By, A. A.; Lindsay,
J. S. Tetrahedron 1995, 51, 11645.
(7) Indeed, I2 could be observed when the reaction solution was heated in
the Rotovap. Furthermore, small amounts of a compound could be
isolated via chromatography which showed the appropriate mass
corresponding to intermediate B and reacted to give 3 in the presence
of HI.
10.1021/op100036c  2010 American Chemical Society
Published on Web 06/03/2010
Vol. 14, No. 4, 2010 / Organic Process Research & Development
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Scheme 1
Scheme 2
Synthetic Details. The synthesis of the new diiodo dipyr-
dipyrrylmethane 1 was obtained in excellent yield and high
purity as light red crystals.
rylmethane 1 was carried out as depicted in Scheme 2. The
partially optimized synthesis which delivered the desired
intermediate in an acceptable overall yield, starts with the
silylated propyne 4 which is reacted with acetyl chloride in
presence of AlCl3 to give 3-pentyne-2-one 5. The phosphine
catalyzed reaction of 5 with benzyl isocyanoacetate gave the
first pyrrole unit 6 which was obtained in pure form after
chromatography in moderate yield. The second pyrrole moiety
9 was prepared starting from the commercially available pyrrole
ethyl ester 7 which was first transformed to the corresponding
benzyl ester 8 with Na/BnOH at 190 °C and then acetoxylated
in presence of sulfuryl chloride to give 9 in moderate yield.
The condensation of the two pyrrolo units 6 and 9 catalyzed
by HBF4 gave the desired dipyrrylmethane 10 in an acceptable
yield of 68%. After removal of the benzyl groups via hydro-
genolysis with Pd/C to give the diacid 11, the novel diiodo
The synthesis of the second dipyrrylmethane moiety 2 was
carried out as depicted in Scheme 3. Starting from commercially
available 12 which was brominated selectively and then
condensed with the loss of a C1 unit to give dipyrrylmethane
13 in good yield. Dialdehyde 2 was then obtained in excellent
yield via debenzylation with Pd/C to give 14, followed by
reduction with trimethyl orthoformate in presence of trifluoro-
acetic acid.
With the two dipyrrylmethane moieties 1 and 2 in hand, the
condensation reaction was carried in a mixture of acetic acid,
acetanhydride and trifluoromethyl sulfonic acid (Scheme 1). The
desired porphyrin 3 was indeed obtained in excellent 76% yield.
The target protoporphyrin IX (16) and its disodium salt 17 were
obtained as shown in Scheme 4 via reduction of the two acetyl
groups with NaBH4 to give the hematoporphyrin ester 15,
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Scheme 3
Scheme 4
followed by elimination of the intermediately formed diben-
zoates in good to excellent yields. While 16 was obtained as
violet-black crystals of high purity, the disodium salt was
isolated as an amorphous powder.
RP-HPLC method: Hypersil BS-C C18, 125 mm × 4 mm, 25
°C, solvents with 0.1% TFA, acetonitrile(ACN)/water from 1
to 100% ACN in 10 min, then 2 min 100% ACN. Flow rate 1
mL/min, detection at 220, 410 nm, typical sample concentration
1 mg/mL. NMR Bruker (300 MHz), LCMS: YMC-Pack Pro
C18 33 mm × 3 mm, 3 µm, gradient methanol/water (0.04%
formic acid), ES ionization.
As can be seen from the detailed Experimental Section, the
synthesis of 17 was first carried out on a 6 g scale. While most
of intermediates could be isolated via distillation or crystalliza-
tion, some compounds had to be purified by column chroma-
tography. In an intensive process development, all of these
chromatographic steps could be circumvented by relatively
small variations of the experimental conditions. The improved
procedure was then applied to the preparation of protoporphyrin
IX derivatives on a 100 g scale with an overall yield in the
range of 40% starting from 1 and 2.
4,3′-Diacetyl-3,4′-dimethyl-5,5′-diiodo-2,2′-dipyrryl-
methane (1). A 2.5 L round-bottomed flask equipped with a
reflux condenser, a thermometer, a dropping funnel and an argon
conduit is loaded with solid NaHCO3 (55.6 g, 662.0 mmol),
water (900 mL) and ethanol (300 mL). A solution of the
compound 11 (54.3 g, 101.9 mmol) in ethanol (300 mL) is
added. A solution of iodine (64.7 g, 254.9 mmol) in ethanol
(400 mL) is added at ambient temperature to give a brown
heterogeneous mixture. A certain amount of foaming and some
heating are observed. The conversion is followed by HPLC.
The reaction mixture is stirred again at ambient temperature
for 5 h. The reaction mixture is diluted with water (0.1 L), and
the precipitated product is isolated by filtration. The precipitate
is washed with water (3 × 0.1 L), ethanol (2 × 0.1 L), and
ether (2 × 0.1 L). After drying of the crystals of product under
reduced pressure at 60 °C, 1 (48.1 g, 92%) is recovered in the
form of light-red crystals. Purity: 100%.
Conclusions
Protoporphyrin IX dimethyl ester 16 and its disodium salt
17 can be prepared from commercially available starting
materials via a modified MacDonald procedure. The key step
is the condensation reaction of the diiodo dipyrrylmethane 1
with the dialdehyde 2 which directly furnishes the porphyrin 3
without the need of oxidation of a dihydroporphyrin intermedi-
ate. Both dipyrrylmethane units can be prepared on multi 100 g
scale in excellent purity and satisfactory yield without the need
of chromatography.
MS: 509 (M - 1); 1H NMR (300 MHz, DMSO-d6): δ 2.06
(s, CH3); 2.15 (s, CH3); 2.30 (s, CH3); 2.38 (s, CH3); 4.10 (s,
CH2); 11.20 (s, NH); 11.34 (s, NH).
Experimental Section
General Comments. Reagents and solvents were used as
received from common commercial vendors. Methods: Generic
Vol. 14, No. 4, 2010 / Organic Process Research & Development
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5,5′-Diformyl-4,4′-dimethyl-3,3′-di(2-methoxycarbonylethyl)-
2,2′-dipyrrylmethane (2). A 1 L round-bottomed flask equipped
with a reflux condenser, a thermometer, a dropping funnel and
an argon conduit is loaded with trifluoroacetic acid (190 mL)
and cooled to 0 °C. The compound 14 (20.0 g, 46.0 mmol) is
added in small portions in 10 min at 0 °C. The mixture is stirred
again at 0 °C for 1 h. The conversion is followed by HPLC.
Trimethyl orthoformate (57 mL) is added dropwise in 30 min,
while the temperature is maintained at between 0 and 5 °C.
The reaction mixture is stirred for a further 1 h at 0 °C and
then poured into water (1.7 L). The mixture is stirred vigorously
for 10 min. The precipitated crude product is isolated by
filtration and washed with water (0.3 1) in the form of an orange
powder. The crude product is triturated in ethanol (0.2 L) and
ammonia (0.4 L). The mixture is stirred for 30 min at ambient
temperature, and the product is isolated by filtration and washed
with water (0.3 L) in the form of a dark-yellow powder. The
product is refluxed in methanol (0.4 L) for 10 min. The mixture
is cooled to ambient temperature, and the product is isolated
by filtration and washed with cold methanol (0.1 L). The product
is dried under reduced pressure to give 2 (15.30 g, 83%) in the
form of a light-yellow powder. Purity: 97%.
Pent-3-yne-2-one (5). A 4.5 L round-bottomed flask equipped
with a reflux condenser, a thermometer, a dropping funnel, and
an argon conduit is loaded with aluminum trichloride (297 g,
2.23 mol) and dichloromethane (2.3 L) and cooled to 0 °C. A
solution of trimethylsilylpropyne 4 (250 g, 2.23 mol) and acetyl
chloride (0.16 L, 2.23 mol) in dichloromethane (0.4 L) was
added to the light-yellow suspension in 1.5 h, the temperature
being maintained at between 0 and 5 °C. The brown solution
with a certain amount of precipitated salt is heated to ambient
temperature. The resulting reddish-brown solution is poured into
ice/water (2 L). The layers are separated, and the aqueous phase
is extracted with dichloromethane (0.5 L). The combined
organic phase is washed with water (0.5 L), dried (Na2SO4),
filtered, and concentrated under reduced pressure to give a
greenish-black liquid (558 g). The product is distilled at 180
mbar to give a fraction (∼160 g) that boils between 64 and 70
°C. This product is again distilled at 210 mbar to give the
compound 5 (90.30 g, 49%) in the form of a colorless liquid
that has a boiling point between 81 and 85 °C. Purity: 97%.
1H NMR (300 MHz, CDCl3): δ 2.02 (s, CH3); 2.31 (s, CH3).
4-Acetyl-2-benzyloxycarbonyl-4-methyl-1H-pyrrole (6). A l-L
round-bottomed flask equipped with a reflux condenser, a
thermometer, a dropping funnel, and an argon conduit is loaded
successively with isocyanoacetic acid benzyl ester (commercial
product, Priaxon, Munich) (101.90 g, 0.58 mmol), dioxane (0.5
I), and the compound 5 (52.53 g, 0.64 mol). When methyl-
diphenylphosphine (38.4 g, 0.19 mol) is added, the reaction
becomes highly exothermic. The reaction mixture becomes dark
and is heated at 100 °C for 1 h. The conversion is followed by
HPLC. The volatile products are removed under reduced
pressure. The crude brown oil (209 g) is purified by chroma-
tography on silica (2.1 kg), elution being carried out with a
toluene/ethyl acetate (8:1) mixture. The fractions containing the
pure product are combined, and the volatile products are
removed under reduced pressure to give 6 (73.49 g, 49%) in
the form of a light-brown, syrupy oil.
1H NMR (300 MHz, CDCI3): δ 2.13 (s, CH3), 2.54 (s, CH3),
5.32 (8 s, CH2), 6.68 (d, CH), 7.38 (m, 5H), 9.20 (br s, NH).
4-Acetyl-2-benzyloxycarbonyl-3,5-dimethyl-1H-pyrrole (8).
A 2.5 L round-bottomed flask equipped with a reflux condenser/
distillation head, a thermometer, a dropping funnel, and an argon
conduit is loaded with a solution of ethyl 4-acetyl-3,5-dimethy-
Ipyrrole-2-carboxylate (commercial product, Alpha Aesar,
Karlsruhe, Germany, product No. A 17365) (146.00 g, 0.70
mol) in benzyl alcohol (1 L) and heated to 120 °C, which results
in the azeotropic removal of minor amounts of water. The
mixture is then heated to 190 °C. The dropping funnel is loaded
with a separately prepared solution of sodium (2 g) in benzyl
alcohol (20 mL). This solution is added in 5 mL portions, which
results in a vigorous reflux of the reaction mixture. The resulting
methanol and ethanol are removed semicontinuously by distil-
lation. The conversion is followed by HPLC. The reaction
mixture is cooled to 150 °C and then transferred into a mixture
of methanol (0.96 L), water (0.66 L), and acetic acid (12 mL).
The mixture is cooled to -10 °C and again stirred at this
temperature for 1.5 h. The precipitated product is isolated by
MS: 435 (M + 1); 1H NMR (300 MHz, CDCl3): δ 2.30 (s,
2 CH3); 2.52 (t, 2 CH2); 2.81 (t, 2 CH2); 3.70 (s, 2 CH3); 4.05
(s, CH2); 9.46 (s, 2 CHdO); 10.42 (br s, 2 NH).
Diacetyl-deuteroporphyrin-dimethylester (3). A 2.5 L round-
bottomed flask equipped with a reflux condenser, a thermom-
eter, a dropping funnel, and an argon conduit is loaded with
acetic acid anhydride (290 mL), acetic acid (1.8 L), and
trifluoromethane sulfonic acid (4.95 mL, 56.77 mmol). A
substantially homogeneous solution of the compound 2 (12.00
g, 29.82 mmol) and of the compound 1 (14.48 g, 28.40 mmol)
in acetic acid (400 mL) is added at ambient temperature in 5
min, which produces a blood-red solution. No exothermic is
observed. The mixture is stirred again at ambient temperature
for 1 h, with the formation of a certain precipitate. The
conversion is followed by HPLC. A solution of NaOAc (9.4
g) in acetic acid (100 mL) is added to give a dark-brown
solution. After l0 min, the volatile products are removed under
reduced pressure and dried under reduced pressure for 1.5 h at
50 °C. The dark residue is taken up in dichloromethane (300
mL), and water (500 mL) without vigorous mixing. The organic
layer is separated, and the aqueous phase is extracted with
dichloromethane (0.3 L). The combined organic phase is dried
(Na2S04), filtered, and concentrated to give a black crystalline
product (31.3 g). The mixture is dissolved in dichloromethane
and applied to a column of silica gel C 1 kg) covered with
dichloromethane/acetone (95/5). The product is eluted with a
gradient of 95/5 to 90/10. The fractions contained in the product
are combined and completely concentrated under reduced
pressure. The compound 3 (9.97 g, 55%) is recovered in the
form of violet-black crystals. Purity: 97% (HPLC, 410 nm).
MS: 623 (M + 1); 1H NMR (300 MHz, CDCl3): δ -3.8 (s,
NH); -3.6 (s, NH); 3.15 (2 t, 2 CH2); 3.17 (s, CH3); 3.25 (s,
CH3); 3.39 (s, CH3); 3.50 (s, CH3); 3.60 (s, CH3); 3.64 (s, CH3);
3.66 (s, CH3); 3.71 (s, CH3); 4.22 (2 t, 2 CH2); 9.50 (s, CH);
9.59 (s, CH); 10.43 (s, CH); 10.46 (s, CH).
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Vol. 14, No. 4, 2010 / Organic Process Research & Development

filtration. The product is dried under reduced pressure to give
8 (124.40 g, 65%) in the form of an off-white solid. Purity:
100%.
reduced pressure. The product is recrystallized as above in
methanol to give a fraction K2 (16.7 g). The supernatant is again
chromatographed on silica (400 g), elution being carried out
with hexane/ethyl acetate (2:1). The fractions containing the
product are combined and concentrated under reduced pressure.
The product is recrystallized as above from methanol to give a
fraction K3 (3.7 g). The product fractions (KI-K3) are
combined, dissolved in toluene, and completely concentrated
under reduced pressure. After drying under reduced pressure
at 50 °C for 1 h, 10 (54.7 g, 68%) is recovered in the form of
off-white crystals. Purity: 93%.
1H NMR (300 MHz,CDCl3): δ 2.34 (s, CH3); 2.40 (s, CH3);
2.52 (s, CH3); 5.23 (s, CH2); 7.85 (m, 5H); 9.55 (br s, NH).
5-Acetoxymetyl-4-acetyl-2-benzyloxycarbonyl-3-methyl-1H-
pyrrole (9). A 2.5 L round-bottomed flask equipped with a
reflux condenser, a thermometer, a dropping funnel, and an
argon conduit is loaded with compound 8 (66.84 g, 0.25 mol),
acetic acid (1.25 L), and sodium acetate (73.90 g, 1.51 mol).
In order to obtain a clear solution, the mixture is heated to 35
°C and then cooled to ambient temperature. Sulfuryl chloride
(32.4 mL, 0.40 mol) is added in 2 h, while the reaction is
carefully controlled toward the end of the addition, in order to
minimize byproduct formation due to overreaction. Additional
amounts of sodium acetate (50.0 g) are added at ambient
temperature, and the mixture is again stirred at ambient
temperature overnight. Water (500 mL) is added to give a clear
solution. After the addition of a 9:1 water/methanol mixture
(4.5 L), the reaction mixture is again stirred at ambient
temperature for 1 h with precipitation of the product. The
product is isolated by filtration and dissolved by refluxing in
ethyl acetate (220 m). The two-phase mixture is removed from
the oil bath, and methanol (200 mL) is added with stirring. After
further stirring for 1 h at ambient temperature, the product begins
to crystallize. Additional amounts of methanol (500 mL) are
added, and the mixture is stirred and cooled to -10 °C. The
product is isolated by filtration. The product is dried under
reduced pressure to give 9 (37.14 g, 45%) in the form of a
white solid. Purity: 92%.
1H NMR (300 MHz, CDCl3): δ 2.09 (s, CH3); 2.49 (s, CH3);
2.51 (s, CH3); 2.58 (s, CH3); 4.04 (s, CH2); 5.27 (s, CH2); 5.29
(s, CH2); 7.35 (m, 10H); 10.5 (br s, 2 NH).
4,3′-Diacetyl-5,5′-dicarboxy-3,4′-dimethyl-2,2′-dipyrryl-
methane (11). A low-pressure hydrogenation apparatus is loaded
with the compound 10 (54.3 g, 103.1 mmol), tetrahydrofuran
(700 mL), triethylamine (20.8 g, 206.2 mmol), and 10% Pd/C
catalyst (2.75 g). The hydrogenation is carried out at ambient
temperature under a hydrogen pressure atmosphere in 3 h. The
catalyst is removed by filtration. The filtrate is concentrated
under reduced pressure. After drying under reduced pressure
at 45 °C for 0.5 h, 11 (54.7 g, quantitative) is recovered in the
foam of an off-white foam as monotriethylamine salt containing
residual amounts of toluene and THF. Purity: 96%.
1H NMR (300 MHz, DMSO-d6): δ 1.10 (t, CH3); 1.97 (s,
CH3); 2.38 (s, CH3); 2.52 (s, 2 CH3); 2.85 (q, CH2); 4.14 (s,
CH2); 11.36 (br s, NH); 11.70 (br s, NH).
5,5′-Dibenzyloxycarbonyl-3,3′-di(2-methoxycarbonylethyl),4,4′-
dimethyl-2,2′-dipyrrylmethane (13). A 4.5 L round-bottomed
flask equipped with a reflux condenser, a thermometer, a
dropping funnel, and an argon conduit is loaded with the
compound 12 (52.0 g, 165.0 mmol) and TBME (1.5 L).A
freshly prepared solution of bromine (11.0 mL, 214.0 mmol)
in TBME (0.5 L) is added dropwise in 20 min at ambient
temperature, so as to produce an orange-brown solution. The
conversion is followed by HPLC. If necessary, additional
amounts of bromine are added. The mixture is again stirred at
ambient temperature. The volatile products are removed under
reduced pressure, and the grayish-brown residue is dissolved
in methanol (364 mL), and 0.4 mL of conc. HCl is added. The
solution is heated at ∼50 °C until complete conversion is
obtained (determined by HPLC after approximately 11 h). The
dark reaction mixture is concentrated under reduced pressure
until the product begins to crystallize. The precipitated product
is isolated by filtration and washed with methanol (0.2 L). The
crude product is recrystallized by suspending in diethyl ether
(0.6 L) and refluxing, while heptane (1.8 L) is added, and the
heating is continued so as to maintain the mixture at reflux for
a further 15 min. The mixture is cooled to ambient temperature,
and the product is isolated by filtration. The product is dried to
give 13 (31.70 g, 63%) in the form of a light-grey powder.
Purity: 98%.
1H NMR (300 MHz, CDCl3): δ 2.07 (s, CH3); 2.41 (s, CH3);
2.53 (s, CH3); 5.27 (s, CH2); 5.31 (s, CH2); 7.32 (m, 5H); 9.40
(br s, NH).
4,3′-Diacetyl-5,5′-dibenzyloxycarbonyl-3,4′-dimethyl-2,2′-
dipyrrylmethane (10). A 2.5 L round-bottomed flask equipped
with a reflux condenser, a thermometer, a dropping funnel, and
an argon conduit is loaded with the compound 6 (50.0 g, 194.4
mmol), the compound 9 (51.3 g, 155.6 mmol), and dichloro-
ethane (1.1 L). The mixture is heated to 40 °C to give an orange-
red solution. HBF4 etherate (2.35 mL (54%), 9.3 mmol) is
added, and the mixture is heated rapidly to 90 °C. The
conversion is followed by HPLC. After 1 h, the mixture is
cooled rapidly to ambient temperature and poured into a
saturated bicarbonate solution (0.5 L). The layers are separated
and the aqueous phase is extracted with dichloroethane (0.5
L). The combined organic extracts are dried (Na2SO4), filtered,
stirred with Norrit C (2 g), filtered, and completely concentrated
under reduced pressure to give a sticky, brown syrup (96.5 g).
The crude product is dissolved in methanol (0.3 L), concentrated
under reduced pressure, and again dissolved in methanol (150
mL). Germination crystals are added, and the mixture is left to
stand for 15 h at ambient temperature while the product
crystallizes. The supernatant is removed, and the crystals
(fraction KI, 34.3 g) are washed with methanol. The combined
methanol fractions are completely concentrated under reduced
pressure and chromatographed on silica (420 g), elution being
carried out with hexane/ethyl acetate (2:1). The fractions
containing the product are combined and concentrated under
MS: 615 (M + 1); 1H NMR (300 MHz, CDCl3): δ 2.21 (s,
2 CH3); 2.43 (t, 2 CH3); 2.68 (t, 2 CH2); 3.50 (s, 2 CH3); 3.89
(s, CH2); 5.17 (s, 2 CH2); 7,20 (m 10H); 9.00 (br s, 2 NH).
Vol. 14, No. 4, 2010 / Organic Process Research & Development
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5,5′-Dicarboxy-3,3′-di(2-methoxycarbonylethyl)-4,4′-dimeth-
yl-2,2′ dipyrrylmethane (14). A low-pressure hydrogenation
apparatus is loaded with the compound 13 (30.7 g, 49.9 mmol),
THF (400 mL), and 10% Pd/C catalyst (1.5 g, A027). The
hydrogenation is carried out at ambient temperature under a
hydrogen pressure atmosphere in 3 h. Ammonia (0.1 L of 2 N
solution) is added to the reaction mixture, and the catalyst is
removed by filtration. The filtrate is adjusted to pH 7 by adding
acetic acid (60 mL). The solvent is removed under reduced
pressure. The precipitated product is isolated by filtration to
give, after drying, 14 (21.7 g, quantitative) in the form of a
white powder. Purity: 98%.
and stirred vigorously with a water/methanol (0.3 L) mixture.
The layers are separated and the aqueous phase is extracted
with dichloromethane (2 × 0.2 L). The combined organic
extracts are washed with bicarbonate (0.3 L), dried (Na2SO4)
and filtered. The filtrate is treated with silica (20 g) and filtered.
Methanol (50 mL) is added and the mixture is then concentrated
under reduced pressure, while crystallization takes place toward
the end to give a violet-black product (20 g). The product is
triturated with methanol at 50 °C for 0.5 h. After cooling to
ambient temperature, chloroform (2 mL) is added, and the
product is isolated by filtration. After drying under reduced
pressure at 50 °C for 15 h, 16 (6.34 g, 77%) is recovered in the
form of shiny violet-black crystals. Purity: 97% (HPLC, 410
nm).
1
MS: 434; H NMR (300 MHz, DMSO-d6): δ 2.18 (s, 2
CH3); 2.20 (t, 2 CH2); 2.59 (t, 2 CH2); 3.60 (s, 2 CH3); 3.82 (s,
CH2); 11.0 (s, COOH); 11.95 (br s, 2 NH).
MS: 591 (M + 1); 1H NMR (300 MHz, CDCl3): δ 3.23 (t,
2 CH2); 3.52 (s, CH3); 3.54 (s, CH3); 3.58 (s, CH3); 3.64 (s,
CH3); 3.65 (s, CH3); 3.66 (s, CH3); 4.32 (t, 2 CH2); 6.11-6,34
(m, 4 H, 2 CH2dC); 8.10-8,23 (m, 2 H, 2 CHdC); 9.85, 9.86,
9.97, and 9.99 (4 s, 4 CH).
Hematoporphyrin-dimethylester (15). A 1-L round-bottomed
flask equipped with a reflux condenser, a thermometer, a
dropping funnel, and an argon conduit is loaded with the
compound 3 (9.86 g, 15.84 mmol), dichloromethane (500 mL),
and methanol (24 mL). NaBH4 (3.00 g, 79.32 mmol) is added
in portions to the reddish-brown mixture. A certain foaming is
observed. The reaction is closely followed by HPLC. After 80
min, the mixture is poured into a mixture of water (500 mL)
and 4 N HCI (80 mL). Gas is seen to be given off. The mixture
is neutralized by adding solid NaHCO3. The layers are
separated, and the aqueous phase is extracted with dichlo-
romethane (2 × 300 mL). The combined organic extracts are
dried (Na2SO4), filtered, and concentrated under reduced pres-
sure. After drying under reduced pressure at 50 °C for 0.5 h,
15 in the form of a mixture of two stereoisomers (9.58 g, 96%)
is recovered in the form of violet-black crystals. Purity: 98%
(HPLC, 410 nm); 2 isomers (1:1).
Protoporphyrin IX Disodium Salt (17). A 2.5 L round-
bottomed flask equipped with a reflux condenser, a thermom-
eter, a dropping funnel, and an argon conduit is loaded with
the compound 16 (6.30 g, 10.67 mmol) and dichloromethane
(200 mL). The product is dissolved by heating to 40 °C. At 40
°C, methanol (400 mL) followed by 4 N NaOH (200 mL) is
successively added. The formation of a precipitate is observed.
The mixture is refluxed. The conversion is followed by HPLC.
The organic volatile products are removed under reduced
pressure. The suspension is filtered through a glass fiber filter.
The product is washed with water (3 × 0.1 L), methanol (3 ×
30 mL), and diethyl ether (2 × 3 0 mL).After drying under
reduced pressure at 70 °C for 2 h, then at 40 °C for 15 h, 17
(6.06 g, 94%) is recovered in the form of a violet-black solid
product. Purity: 97% (HPLC, 410 nm).
MS: 625 (M + 1); 1H NMR (300 MHz, CDCl3): δ 1.92 (m,
6H, 2 CH3), 3.16 (m, 4H, 2 CH2), 3.28, 3.30, 3.33, and 3.35 (4
s, 6H, 2 CH3), 3.43 (s, 6H, 2 CH3), 3.66 (s, 6H, 2 CH3), 4.20
(m, 4H, 2 CH2), 6.05 (m, 2H, 2 CH), 9.73, 9.74, 9.75, 9.76,
10.00, 10.02, 10.08, and 10.10 (8 s, total 4H, 4 CH).
Protoporphyrin IX dimethylester (16). A 1 L round-bottomed
flask equipped with a reflux condenser, a thermometer, a
dropping funnel, and an argon conduit is loaded with the
compound 15 (9.48 g, 15.12 mmol) and DMF (400 mL), and
the mixture is degassed with argon. Benzoyl chloride (45.0 mL,
387.9 mmol) is added, and the mixture is rapidly heated to 100
°C. The mixture is stirred again at 100 °C for 1 h. The
conversion is followed by HPLC. The reaction mixture is cooled
rapidly, and the volatile products are removed under reduced
pressure. The residue is dissolved in dichloromethane (0.3 L)
MS: 563 (M + 1), diacid; 1H NMR (300 MHz, TFA-d1): δ
3.45 (2t, 2 CH2); 3.82 (s, CH3); 3.85 (s, CH3); 3.88 (s, CH3);
3.91 (s, CH3); 4.73 (2t, 2 CH2); 6.43-6.70 (m, 4 H, 2 CH2dC);
8.28-8.40 (m, 2 H, 2 CHdC); 11.08, 11.11, 11.15, and 11.27
(4 s, 4 CH).
Acknowledgment
We thank Sanofi-Pasteur for the fruitful collaboration and
the permission to publish our results.
Received for review February 4, 2010.
OP100036C
804
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Vol. 14, No. 4, 2010 / Organic Process Research & Development