Synthesis of tetraphenylsubstituted porphyrins by interaction of 5-aryldipyrromethanes with 4-substituted benzaldehydes

Article abstract of DOI:10.1134/S1068162008060186

Synthesis of tetraphenyl substituted porphyrins with tert-butyl and methoxycarbonyl groups in meso-aryl radicals is described. It is shown that, during the condensation of dipyrromethanes with substituted benzaldehydes, a rearrangement occurs with the formation of a mixture of isomeric porphyrins. The character of these rearrangements depends on the position of substituents in the starting compounds.

Full text of DOI:10.1134/S1068162008060186

ISSN 1068-1620, Russian Journal of Bioorganic Chemistry, 2008, Vol. 34, No. 6, pp. 762–767. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.D. Rumyantseva, T.A. Khabarova, D.A. Cheshkov, G.A. Fedorova, A.F. Mironov, 2008, published in Bioorganicheskaya Khimiya, 2008, Vol. 34, No. 6,
pp. 847–853.
Synthesis of Tetraphenylsubstituted Porphyrins by Interaction
of 5-Aryldipyrromethanes with 4-Substituted Benzaldehydes
V. D. Rumyantseva1, T. A. Khabarova, D. A. Cheshkov, G. A. Fedorova, and A. F. Mironov
Lomonosov State Academy of Fine Chemical Technology, pr. Vernadskogo 86, Moscow, 119571 Russia
Received February 4, 2008; in final form, April 21, 2008
Abstract—Synthesis of tetraphenyl substituted porphyrins with tert-butyl and methoxycarbonyl groups in
meso-aryl radicals is described. It is shown that, during the condensation of dipyrromethanes with substituted
benzaldehydes, a rearrangement occurs with the formation of a mixture of isomeric porphyrins. The character
of these rearrangements depends on the position of substituents in the starting compounds.
Key words: platinum complexes, rearrangement, substituted dipyrromethanes, tetraarylporphyrins
DOI: 10.1134/S1068162008060186
INTRODUCTION
able methods of synthesis, isolation, and modification
of similar porphyrins.
One of prospective directions in modern oncology is
the fluorescent diagnostics of malignant neoplasms
with the help of platinum and some other metal com-
plexes with natural [1] and synthetic porphyrins [2]2.
Among the synthetic porphyrins, an important place
occupy substituted TPPs [3]. The interest in them is
caused by a relative availability of these compounds
and an opportunity of wide variation of substituents
both in phenyl radicals, and on the periphery of macro-
cycle [4]. The amphiphilic porphyrins with a certain
ratio of large hydrophobic substituents and carboxylic
groups possess the greatest selectivity to tumors [5].
Their sodium salts allow one to avoid the porphyrin dis-
solution in water in the presence of phospholipids, cre-
mophor EL, and other detergents, while hydrophobic
groups can provide the transfer of PSs through the
phospholipid cell membrane.
It is known that, among similar compounds, porphy-
rins containing both hydrophobic and hydrophilic sub-
stituents are accumulated in a number of tumors, espe-
cially if these substituents are asymmetrically situated.
Especially useful are the porphyrins that have a good
solubility in water (which allows one to carry biological
tests without use of detergents), stability on storage,
low toxicity, substantial selectivity to tumors in com-
parison with surrounding normal tissues, photochemi-
cal stability, high extinction coefficients, and high
quantum yields of fluorescence. A successful develop-
ment of this direction depends on the presence of reli-
In this work, we synthesized isomeric porphyrins
containing two tert-butyl and two ester groups, and
then, on their basis, platinum complexes of 5,10-bis(4-
tert-butylphenyl)-15,20-bis(4-methoxycarbonylphe-
nyl)porphyrin and 5,15- bis(4-tert-butylphenyl)-10,20-
bis(4-methoxycarbonylphenyl)porphyrin; the subse-
quent saponification of the second compound allowed
us to obtain the water-soluble PS.
RESULTS AND DISCUSSION
Synthesis of porphyrins was realized proceeding
from 5-aryldipyrromethanes. In the first variant 5-(4-
tert-butylphenyl)dipyrromethane was condensed with a
methyl ether 4-formylbenzoic acid by the Lindsey
method [6, 7]. The second variant differed from the first
by a return arrangement of tert-butyl and ester groups
in dipyrromethane and benzaldehyde at preservation of
conditions of their condensation.
Both starting 5-aryldipyrromethanes (I) and (VIII)
were obtained by treatment of the corresponding 4-sub-
stituted benzaldehydes by pyrrole, which simulta-
neously played role of solvent [8, 9]. As condensing
agents, have been used trifluoroacetic acid [10], indium
salts [11], ion-exchange resins [12], and a hydrochloric
acid [13]. The best results were reached with trifluoro-
acetic acid and a ratio pyrrole to substituted benzalde-
hyde of 40 : 1. There were data in literature on the for-
mation during this condensation of N-substituted dipyr-
romethanes and tripyrrine compounds as by-products
[7, 9]. In this connection, a problem arises of purifica-
tion of starting (I) and (VIII) from impurities. For the
removal of pyrrole excess and also oligomers, authors
1
Corresponding author; phone/fax +7 (495) 936-8903; e-mail:
vdrum@mail.ru.
2
Abbreviations: DDQ, 2,3-dichloro-5,6-dicyanobenzoquinone;
EAS, electronic absorption spectrum; PS, photosensitizer; and
TPP, tetraphenylporphyrin.
762

SYNTHESIS OF TETRAPHENYLSUBSTITUTED PORPHYRINS BY INTERACTION
763
of work [7] used distillation and the subsequent recrys-
tallyzation or a flash chromatography and recrystallyz-
ation. We obtained the best results at the isolation and
purification of the substituted dipyrrolmethanes (I) and
(VIII) at the use of reprecipitation from ether and hex-
ane, and then the recrystallyzation from aqueous etha-
nol. The monitoring of the individuality of dipyr-
romethanes was carried out by TLC, comparison of
Condensation of (I) and substituted benzaldehyde
(II) was carried out in chloroform in the presence of
trifluoroboron etherate with the subsequent oxida-
tion of the formed porphyrinogen with the help of
DDQ (Scheme 1). After the treatment of reaction
mixture, the porphyrins obtained were filtered and
subjected to flash chromatography on aluminum
oxide. The total yield of porphyrins under the first
scheme was 20%. The subsequent chromatographic
separation on a silica gel column allowed obtaining
five individual compounds.
1
melting points with the literature data and H NMR
spectra.
Variant 1
CHO
R1
‡) BF3 · OEt2
+
b) DDQ
COOCH
3
N
H
N
H
(I)
(II)
NH
N
N
R4
R2
Variant 2
HN
COOCH3
CHO
‡) BF3 · OEt2
+
b) DDQ
R3
(III)–(VII)
N
H
N
H
(VIII)
(IX)
Compound
R1
R2
R3
R4
(III)
(IV)
(V)
–C(CH3)3
–C(CH3)3
–C(CH3)3
–C(CH3)3
–C(CH3)3
–C(CH3)3
–C(CH3)3
–C(CH3)3
–COOCH3
–COOCH3
–COOCH3 –C(CH3)3
–C(CH3)3
–COOCH3 –COOCH3 –COOCH3
(VI)
(VII)
–C(CH3)3
–C(CH3)3
–COOCH3 –COOCH3
Scheme 1. Two variants of porphyrin synthesis.
The least polar first fraction contained symmetric
The next (second) fraction contained porphyrin of
porphyrin (III) (A4) in which in all four phenyl rings the Ä3Ç type in which three residues represented
bore tert-butyl substituents. The structure of this por- 4-tert-butylphenyl groups, and the fourth was 4-meth-
phyrin was confirmed by EAS, mass spectrum, and 1H oxycarbonylphenyl substituent. The structure of this
NMR spectrum, and also by the coincidence of chro- compound was proved by EAS, IR (C=O band at
matographic mobility with the standard sample 1721 cm–1), mass spectrum (m/z 841.6), 1H NMR spec-
obtained by the direct synthesis.
trum, and the elemental analysis (see below).
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 34 No. 6 2008

764
RUMYANTSEVA et al.
NH
N
N
NH
N
N
O
O
O
O
O
O
HN
HN
O
O
(V)
(VI)
O
O
NH
N
N
O
O
O
O
NH
N
N
HN
HN
O
O
(IV)
(VII)
NOE-contacts in structures (IV), (V), (VI), and (VII).
Further, two fractions with close TLC mobilities and with the integral intensity of four protons.A singlet signal at
identical absorption spectra were eluted. Substances in 8.86 ppm was also registered with integral intensity of four
the third and fourth fractions exhibited the same mass protons. In the NOESY spectrum (see the figure), correla-
spectra and belonged to the type of Ä2Ç2 porphyrins. It tions were observed between the signal of β proton at
followed from their IR spectra followed that both com- 8.75 ppm and the signal at 8.30 ppm (o-H of 4-methoxycar-
pounds contain 4-methoxycarbonyl residues. Individu- bonylphenyl substituent, integral intensity of two protons)
ality of the substances was confirmed by HPLC. The and also between signals at 8.86 and 8.88 ppm and a signal
content of the main substance in the third fraction was at 8.13 ppm (o-H of 4-tert-butylphenyl substituent, integral
98.68%, and the retention time was 10.065 min. For the intensity of six protons). The data allow us to ascribe struc-
fourth fraction, the content of the main substance was ture (IV) to the compound from the second fraction.
98.62% and RT, 10.102 min.
The establishment of structures (V) and (VI) for the
In the spectrum of proton resonance (T 313 K), com- compounds from fractions 3 and 4, respectively, was
1
pounds from the second fraction exhibited signals of β pro- carried out by bidimentional spectroscopy of a H
tons asAB-system (δA 8.75 and (δB 8.88 ppm, JAB 4.75 Hz) NMR: 1H NOESY and 1H–13N HSQC. In the spectrum
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SYNTHESIS OF TETRAPHENYLSUBSTITUTED PORPHYRINS BY INTERACTION
765
of proton resonance (T 318 K) of (V), signals of β pro- similar to that in the earlier considered case; the total
tons were displayed as an AB-system (δA 8.88, δB yield of porphyrins was 17%.
8.76 ppm, JAB 4.77 Hz), the integral intensity of eight
Although in this variant of synthesis, four isomeric
protons. In a NOESY spectrum, correlations between
porphyrins were formed [the fifth fraction ÄÇ3 (VII)
signals were observed at 8.76 and 8.30 ppm (o-H of
was absent], we managed to increase the yield of the
4-methoxycarbonylphenyl substituent), and also
target compound (V) up to 9%.
between signals at 8.88 and 8.12 ppm (o-H of 4-tert-
At the synthesis of porphyrins by variant 2, we also
used an anhydrous indium chloride as an Lewis acid
[11]. In this case, the total yield of porphyrins was 12%,
the greatest yield was that of porphyrin Ä3Ç (IV) (5%),
the contents of trans and cis-isomers were rather close,
and porphyrin ÄÇ3 (VII) has not been detected at all.
butylphenyl substituent). The data allowed us to ascribe
to (V) the structure of trans-isomer.
The signals of β protons of (VI) were exhibited in
the spectrum of proton resonance (T 305 K) as an AB
system (δA 8.76, δB 8.90 ppm, JAB 4.69 Hz), with the
integral intensity of four protons, and two singlets at
8.88 and 8.78 ppm with integral intensity of two pro-
tons each. The β protons displayed as singlet signals are
magnetically equivalent, which is possible only when
in the neighboring meso-positions are occupied by
identical substituents. In the NOESY-spectrum, corre-
lations were observed between the signals of β protons
at 8.76 and 8.78 ppm and a signal at 8.30 ppm (o-H of
4- methoxycarbonylphenyl substituent) and also
between signals at 8.88 and 8.90 ppm and at 8.13 ppm
(o-H of 4-tert-butylphenyl substituent). The data
allowed us to ascribe for (VI) structure of cis-isomer.
The fifth fraction (VII) was isolated in a small yield. It
turned out to be an ÄÇ3 porphyrin. Its structure was
proved by mass spectrometry and 1H NMR spectroscopy.
The results show that the considered synthetic
scheme leads to a mixture of porphyrins, with the yield
of target (V) being only 4%.
Thus, the executed studies confirmed an opportunity
of acid-catalyzed rearrangements at the condensation
of dipyrromethanes and substituted benzaldehydes [7].
At the same time, it was shown that the nature of sub-
stituents in benzaldehyde and in position 5 of dipyr-
romethane substantially affect the character of the con-
densation. More specifically it proceeds in the presence
of electron donor substituents in starting benzaldehyde
electron acceptor substituents in dipyrromethane com-
pared with their reverse arrangement.
The cis and trans-isomeric porphyrins (VI) and (V)
were used for obtaining of platinum complexes (Scheme
2). Introduction of Pt(II) was carried out at boiling of por-
phyrins in benzonitrile with PtCl2(C6H5CN)2 salt [14].
The saponification of dimethyl esters of both isomers was
carried out in pyridine in the presence of 2M KOH [15]. It
turned out that cis-isomer (VI) is not saponified under
The variant 2 of the syntheses 5-(4-methoxycarbon- these conditions, which was confirmed by TLC and mass
ylphenyl)dipyrromethane (VIII) with 4-tert-butylben- spectrometry. Probably, this is due to stereochemical fea-
zaldehyde (IX) was carried out with a condensation tures of the cis-isomer structure (VI).
R1
R1
NH
N
N
N
N
N
PtCl2(C6H5CN)2
R4
R2
R4
R2
Pt
HN
N
R3
(V), (IV)
R3
(IXa), (IX·), (X)
(IX) a: R1 = R3 = –C(CH3)3, R2 = R4 = COOCH3
b: R1 = R3 = –C(CH3)3, R2 = R4 = COOH
(X) R1 = R2 = –C(CH3)3, R3 = R4 = COOCH3
Scheme 2. Synthesis of porphyrin platinum complexes.
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 34 No. 6 2008

766
RUMYANTSEVA et al.
EXPERIMENTAL
H18), 8.15 (8 H, m, Ph), 7.76 (8 H, m, Ph), 1.62 [36 H,
s, (CH3)3C].
1
Spectra of H NMR (δ, ppm) were obtained on a
Brucker AVANCE-600 instrument (300 and 600 MHz,
Germany) for solutions in CDCl3 with Me4Si as an
internal standard. Bidimentional spectra were recorded
and processed with the use of standard Bruker software
XWINNMR 3.5". Time of mixing for gNOESY exper-
iment was 0.8 s. EAS (nm) were obtained on a spec-
trometer Jasco 7800 (Japan) in CHCl3. Mass spectra
were measured on a Brucker Ultraflex TOF (Germany)
spectrometer. IR spectra (ν, cm–1) were registered on a
FT spectrometer Brucker EQUINOX55 (Germany) by
a method diffuse reflection with the subsequent mathe-
matical processing by means of the Kubelka–Munk
5,10,15-TrHs(4-tert-butylphenyl)-20-(4-methox-
ycarbonylphenyl)porphyrin (IV): Rf 0.55, RT
11.106 min, EAS, λmax, nm (ε 10–3, å–1 cm–1): 419.4
(276), 517.2 (11.3), 553.0 (7.5), 591.8 (3.9), 647.2; IR
spectrum: 1721 (C=O); mass spectrum, m/z: 841.6
[M]+; 1H NMR spectrum: 8.88 (2 H, m, H3, H7), 8.86
(4 H, s, H12, H13, H17, H18), 8.75 (2 H, m, H2, H8),
8.43 (2H, m, Ph), 8.31 (2 H, m, Ph), 8.13 (6 H, m, Ph),
7.77 (6 H, m, Ph), 4.12 (3 H, c, COOCH3); 1.61 [27 H,
s, (CH3)3C]. Found, %: C 82.47, H 6.35, N 6.47.
ë58ç56N4é2. Calc., %: C 82.82, H 6.71, N 6.66.
5,15-Bis(4-tert-butylphenyl)-10,20-bis(4-methox-
function. The reaction course and purity of compounds ycarbonylphenyl)porphyrin (V): Rf 0.3, RT 10.065 min
were monitored by TLC on Kieselgel 60 F 254 plates (content 98.68%), EAS, λmax, nm (ε 10–3, å–1 cm–1):
(Merck, Germany) in CHCl3–hexane 9 : 1 system. 419.8 (252), 516.8 (11.1), 552.6 (6.4), 591.2 (3.7),
Flash-chromatography was carried out on aluminum 646.8 (2.8); IR spectrum: 1728 (N=I); mass spectrum,
oxide (activity II) in CHCl3. Column chromatography m/z: 843.5 [M]+; 1H NMR spectrum: 8.88 (4 H, m, H3,
was carried out on silica gel Kieselgel 60 (Merck, Ger- H7, H13, H17), 8.76 (4 H, m, H2, H8, H12, H18), 8.45
many) in CHCl3. HPLC was carried out on a Waters (4 H, m, Ph), 8.31 (4 H, m, Ph), 8.13 (4 H, m, Ph), 7.77
Breeze chromatograph using a column Nova-Pack (4 H, m, Ph), 4.13 (6 H, s, COOCH3), 1.63 [18 H, s,
18.4 µm 4.6 × 150 mm. Compounds (V) and (VI) were (CH3)3C]. Found, %: C 79.54, H 5.85, N 6.58.
eluted by a mixture of 20% A–80% B (eluent A: water; ë56ç50N4é4. Calc., %: C 79.78, H 5.98, N 6.65.
eluent B: acetone–acetonitrile, 6 : 4) for 7 min, further
5,10-Bis(4-tert-butylphenyl)-15,20-bis(4-methoxy-
100% B, flow rate 1 ml/min. Detection at a band of
carbonylphenyl)porphyrin (VI): Rf 0.2, RT 10.102 min
(content 98.62%), EAS, λmax, nm (ε 10–3, å–1 cm−1):
400 nm. Spectra of excitation and emission of phospho-
rescence are measured on luminescent spectrometer
420 (222), 517.0 (9.5), 552.2 (5.3), 590.6 (3.2), 646.4
Perkin-Elmer (United States). The phosphorescent
(2.3); IR spectrum: 1727 (C=O); mass spectrum, m/z:
1
843.5 [M]+; H NMR spectrum: 8.90 (2 H, m, H17,
H18), 8.88 (2 H, s, H2, H3), 8.78 (2 H, s, H12, H13),
8.76 (2 H, m, H7, H8), 8.44 (4 H, m, Ph), 8.31 (4 H, m,
Ph), 8.13 (4 H, m, Ph), 7.76 (4 H, m, Ph), 4.12 (6 H, s,
COOCH3); 1.62 [18 H, s, (CH3)3C). Found, %: C 79.62,
H 5.87, N 6.61. ë56ç50N4O4. Calc., %: C 79.78, H 5.98,
N 6.65.
characteristics were obtained for samples, polymerized
in a lexan film (a polycarbonate based on biphenyl).
Synthesis of Porphyrins
Variant 1. A solution of 5-(4-tert]-butylphe-
nyl)dipyrromethane (85 mg, 0.31 mmol) (I) obtained
by method [6] (additionally purified by reprecipitation
from ether and hexane with the subsequent recrystalli-
zation from aqueous ethanol) and methyl 4-formylben-
zoate (II) (55 mg, 0.37 mmol) in CHCl3 (60 ml) and
MeOH (1.5 ml) blew through by argon for 20 min.
Then BF3 · O(Et)2 (5 µl) was added and stirred for
80 min in an argon atmosphere. DDQ (35 mg) was then
added and stirred by bubbling air for 60 min. After
addition Et3N, solvent was evaporated in a vacuum and
the residue was triturated in isopropanol. After a day,
precipitate of violet color was filtered and subjected to
flash chromatography on aluminum oxide, and porphy-
rins were then separated on a silica gel column. As a
result, five fractions were obtained in the following
quantities: 1, 10 mg (4%); 2, 13 mg (5%), 3, 10 mg
(4%); 4, 10 mg (4%); and 5, 8 mg (3 %). Characteristics
of the isolated porphyrins are given below in the order
of increase in fraction number.
5-(4-tert-Butylphenyl)-10,15,20-tris(4-methoxy-
carbonylphenyl)porphyrin (VII): Rf 0.1, EAS, λmax
,
nm: 417.0, 515.9, 552.7, 590.1, 646.0; mass spectrum,
m/z: 845.19 [M]+; 1H NMR spectrum: 8.89 (2 H, m, H2,
H8), 8.78 (4 H, s, H12, H13, H17, H18); 8.76 (2 H, m,
H3, H7), 8.44 (6 H, m, Ph), 8.29 (6 H, m, Ph), 8.13
(2 H, m, Ph), 7.77 (2 H, m, Ph), 4.11 (9 H, c, COOCH3),
1.62 [9 H, s, (CH3)3C].
Variant 2. A solution of 5-(4-methoxycarbonylphe-
nyl)dipyrromethane (VIII) (85 mg, 0.3 mmol) obtained
by method [8] (it was additionally purified by reprecip-
itation byhexane from ether and with the subsequent
recrystallization from aqueous ethanol), and 4-tert-
butylbenxaldehyde (IX) (55 mg, 0.34 mmol) in 60 ml
of CHCl3 and 1.5 ml of MeOH was bubbled by argon
for 20 min. Trifluoroboron etherate (5 µl) was added,
and the mixture was stirred in argon atmosphere for
80 min. Then DDQ (35 mg) was added, and air was
bubbled through the mixture for 60 min. Acid was neu-
5,10,15,20-Tetrakis(4-tert-butylphenyl)porphyrin
(III), Rf 0.8; EAS, nm: 419.4, 517.0, 553.0, 591.4, and tralized by Et3N addition. Solvent was evaporated in a
647.2; mass spectrum, m/z: 839.7 [M]+; 1H NMR spec- vacuum, and isopropanol was also added for the
trum: 8.80 (8 H, s, H2, H3, H7, H8, H12, H13, H17, removal of DDQ and precipitation. After a day, porphy-
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SYNTHESIS OF TETRAPHENYLSUBSTITUTED PORPHYRINS BY INTERACTION
767
rin of violet color was separated, and the mixture was nyl) porphyrin (X) under the conditions similar to those
at the obtaining of (Iïb) did not lead to saponification
separated on a silica gel column. Four compounds were
revealed by TLC, and their structures similar to thoese
in the first variant of synthesis. Yields were: first frac-
tion, 6 mg (2%), second, 8 mg (3%), third, 24 mg (9%),
and fourth, 8 mg (3%).
of ester groups.
ACKNOWLEDGMENTS
This work was supported by ISTC, grant no. 3065.
Platinum complex a 5,15-bis(4-tert-butylphenyl)-
10,20-bis(4-methoxycarbonylphenyl)porphyrin (IXa).
cis-Bis(benzonitril)dichloroplatium (10 mg, 0.021 mmol)
was added to a suspension of (V) (11 mg, 0.013 mmol)
in 5 ml of benzonitrile, and the mixture was boiled in a
current of nitrogen for 1.5 h. Benzonitril was evapo-
rated in a vacuum, the residue was chromatographed on
silica gel in chloroform, isolating the mobile orange-
red fraction containing a complex (IXa) (Rf 0.5). Sol-
vent was removed in a vacuum, and the residue was
recrystallized from a CHCl3Ќ厍 mixture. Complex
(IXa) was obtained, yield 9 mg (67%); EAS, λmax, nm:
403.8, 510.0, and 538.1. A spectrum of a phosphores-
cence, λmax, nm:: 662 and 725. Lifetime, τ, µs: 58.4
9.7 (+é2), 84.4 13.6 (–é2).
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Platinum complex a 5,15-bis(4-tert-butylphenyl)-
10,20-bis(4-carboxyphenyl)porphyrin (IXb). 2 M
KOH solution (3 ml) was added to a solution of (IXa)
(5 mg) in 3 ml pyridine, and boiled for 3 h. Pyridin was
evaporated in a vacuum, the residue was diluted with
water, filtered, acidified with 10% HCl to pH 2.0, and
left in a refrigerator. The precipitated solid was sepa-
rated on a centrifuge (4000 rpm, 15 min), several times
washed with water containing a small amount of acid,
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and dried in vacuum desiccator over ê2é5; EAS, λmax
,
nm: 403.8, 511, and 539.6; mass spectrum, m/z:
1007.151 [M]+.
15. Vasil’ev, V.V., Borisov, S.M., Chubarova, Yu.O., and
Rumyantseva, V.D., Zh. Neorg. Khim., 2003, vol. 48,
pp. 455–461.
The treatment of the platinum complex of 5,10-
bis(4–tert-butylphenyl)-15,20-bis(4-methoxycarbonylphe-
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 34 No. 6 2008