Porphyrin-phosphoramidate conjugates: Synthesis, photostability and singlet oxygen generation

Article abstract of DOI:10.1071/CH11013

meso-Tetrakis(pentafluorophenyl)porphyrin reacts with aminoalkylphosphoramidates to afford porphyrins substituted with one or four phosphoramidate groups in the 4-position of the meso-aryl groups. The new porphyrin derivatives show high photostability and some are better singlet oxygen generators than meso-tetrakis(1-methylpyridinium-4-yl)porphyrin, a well known good singlet oxygen producer.

Full text of DOI:10.1071/CH11013

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2011, 64, 939–944
Porphyrin Phosphoramidate Conjugates: Synthesis,
]
Photostability and Singlet Oxygen Generation
A B
,
B
A
Leandro F. Pedrosa,
Marcos C. de Souza, Maria A. F. Faustino,
A
A
A
Maria G. P. M. S. Neves, Artur M. S. Silva, Augusto C. Tome´,
Vitor F. Ferreira, and Jose´ A. S. Cavaleiro
B
A C
,
A
Department of Chemistry and QOPNA, University of Aveiro, 3810-193 Aveiro,
Portugal.
B
Departamento de Qu´ımica Orgaˆnica, Universidade Federal Fluminense, 24020-141
Nitero´i, Rio de Janeiro, Brazil.
C
Corresponding author. Email: jcavaleiro@ua.pt
meso-Tetrakis(pentafluorophenyl)porphyrin reacts with aminoalkylphosphoramidates to afford porphyrins substituted
with one or four phosphoramidate groups in the 4-position of the meso-aryl groups. The new porphyrin derivatives show
high photostability and some are better singlet oxygen generators than meso-tetrakis(1-methylpyridinium-4-yl)porphyrin,
a well known good singlet oxygen producer.
Manuscript received: 7 January 2011.
Manuscript accepted: 29 March 2011.
Introduction
presumably by improving cellular penetration and hence by
increasing intracellular concentrations of the active nucleo-
tide.[7] Therefore, the synthesis of porphyrins containing phos-
phoramidate moieties may lead to new compounds with
interesting biological properties or with adequate properties to
be used as photosensitizers in PDT.[8]
Recently, Albinsson and coworkers have studied the binding
characteristics of DNA with a porphyrin-modified tymidine
nucleoside presenting phenylethynylene spacers of different
lengths. It was demonstrated that the hydrophobic porphyrin
moiety is attached to a lipid membrane, while the polar tymidine
part at the other end of the phenylethynylene chain interacts with
DNA in the water phase, with the effectiveness of the interaction
being a function of the chain length. Similarly, we describe here
an easy synthetic approach to selectively prepare new porphyrin
derivatives bearing one or four phosphoramidate groups with a
spacer of variable length. The inclusion of the aminoalkyl spacer
is expected to provide a greater mobility of the phosphoramidate
group, which could facilitate the interaction with the lipid
membranes and the cell DNA.[9]
Natural porphyrins are involved in several vital biological func-
tions such as photosynthesis, transport and storage of molecular
oxygen, and catalytic oxidative transformations. Because of
their structural complexity, natural porphyrins are frequently
substituted by simple synthetic models, such as the meso-
tetraarylporphyrins, in studies performed to look for new
compounds that can mimic the functions of the natural ones. meso-
Tetraarylporphyrins are especially interesting and useful com-
pounds because they can be prepared in one step from simple
reagents (pyrrole and aromatic aldehydes), in moderate to good
yields;[1] such compounds display physico-chemical and biologi-
cal properties similar to those of the natural counterparts. The
potentiality of the meso-tetraarylporphyrin derivatives in a great
number of scientific fields, e.g., medicine, catalysis, and in the
production of new electronic materials, is well established.[2]
Medicinal formulations which include the use of porphyrin deri-
vatives as photosensitizers are already being considered in several
countries for the photodynamic therapy (PDT) of malignant tumors
and also for the treatment of age-related macular degeneration.[3]
Organophosphorus compounds also have a prominent place in
medicine, being used as anticancer drugs, antivirals, antifungals,
and inhibitors of bone resorption among other applications.[4]
Porphyrinphosphonates, inparticular, display interesting binding
properties, where the P¼O group plays a significant role as a
strong hydrogen bond acceptor.[5] Such a characteristic is essen-
tial for the non-covalent bonding of proteins or other specific
ligands to their substrates. Other examples of porphyrins bearing
phosphonate groups are also known.[6]
Results and Discussion
Synthesis
The synthesis of the new porphyrin–phosphoramidate conjugates
can be performed by nucleophilic aromatic substitution of the p-
fluorine atoms in meso-tetrakis(pentafluorophenyl)porphyrin (1)
by aminoalkylphosphoramidates 2a–e. The starting porphyrin 1
is easily prepared from pentafluorobenzaldehyde and pyrrole
under microwave irradiation[10] while the aminoalkylpho-
sphoramidates 2a–e are obtained by selective monopho-
sphorylation of aliphatic diamines.[11]
Phosphoramidates possess a great biological activity and
have been used in several prodrug strategies. It was shown that
they enhance the nucleoside potency in cell cultures,
Ó CSIRO 2011
10.1071/CH11013
0004-9425/11/070939

940
L. F. Pedrosa et al.
O
P
H2N
NH2
n
n ꢁ 2–6
ꢀ
O
H
O
F
F
F
F
(i)
F
F
N
F
F
F
F
N
H
O
F
F
F
F
H
P
N
NH2
n
N
ꢀ
O
H
N
O
2a–e n ꢁ 2–6
F
F
F
F
F
F
1
(ii)
O
P
H
N
n
H
N
F
F
X
O
F
F
O
F
F
N
H
a, n ꢁ 2; b, n ꢁ 3; c, n ꢁ 4
d, n ꢁ 5; e, n ꢁ 6
F
F
N
N
H
N
F
F
3a–e, X ꢁ F
O
H
N
H
N
n
F
F
P
4a–e, X ꢁ
O
F
F
O
X
X
F
F
Scheme 1. Reagents and conditions: (i) CCl4, EtOH, temperature 55–658C, 10–25 min. (ii) toluene, reflux, 8–72 h.
The nucleophilic aromatic substitution of one to four
conjugates. This is in agreement with the 31P NMR data obtained
for other aminophosphoramidates.[11] The HRMS (fast atom
bombardment, positive ion detection (FABþ)) of compounds
3a–e show the (M þ H)þ ions while the spectra of compounds
4a–e show the corresponding (M þ 2H)2þ ones.
p-fluorine atoms in porphyrin 1 by amines, phenoxides, alk-
oxides, or thiols has been used as a versatile route to new
porphyrin derivatives.[12ꢀ14] In this work, we were able to
synthesize selectively the monosubstituted porphyrins 3a–e or
the tetrasubstituted derivatives 4a–e by selecting the appropriate
porphyrin/phosphoramidate ratio (Scheme 1). For instance, the
formation of the monosubstituted derivatives 3a–e could
be obtained in 63–83% yield by refluxing a toluene solution
of the aminoalkyl phosphoramidates 2a–e with an excess
(2 equiv.) of porphyrin 1 for 8 to 12 h. Minor amounts of
disubstituted products were also formed. The reaction of por-
phyrin 1 with 10 equivalents of aminoalkyl phosphoramidates
2a–e in refluxing toluene for 56 to 72 h afforded the tetrasub-
stituted porphyrins 4a–e in 50–77% yield along with a mixture
of the di- and trisubstituted porphyrins. The new compounds
were separated by column chromatography (silica gel) using
ethyl acetate/methanol (97/3) as the eluent and were crystallized
from chloroform/methanol (1/3).
Singlet Oxygen Generation
The ability of these porphyrin derivatives to generate singlet ox-
ygen, the basis of the photoinactivation process, was qualitatively
evaluated by monitoring the photodecomposition of 1,3-diphe-
nylisobenzofuran (DPiBF). The results, summarized in Fig. 1 and
Table 1, show that the DPiBF photodegradation was highly en-
hanced in the presence of any photosensitizer. This means that all
porphyrin derivatives are able to produce singlet oxygen.
In general, the tetrasubstituted porphyrin–phosphoramidate
derivatives4 aremore efficient togeneratesingletoxygenthanthe
corresponding monosubstituted derivatives 3. Derivatives 4,
excluding 4b, with slopes in the range 0.038–0.058 (the slope is
proportional to the rate of production of singlet oxygen), were
shown to be, under the same experimental conditions, similar or
The mono- (3a–e) and tetra- (4a–e) substituted porphyrin–
P
phosphoramidates were fully characterized by 1H, 19F, and 31
NMR spectroscopy and by high resolution mass spectrometry
1
more efficient O2 producers than meso-tetrakis(1-methylpyr-
1
(HRMS). The H NMR spectra of the monosubstituted com-
idinium-4-yl)porphyrin (Tetra-Pyþ-Me, slope 0.038), which
isconsideredtobe a goodsinglet oxygen producer.[15] Itisevident
from Fig. 1 that porphyrin 4c is the best singlet oxygen generator
of all new compounds. Although the monosubstituted phosphor-
amidate derivatives 3a–e also generate singlet oxygen
(slopes ranging from 0.013–0.025) they are less efficient than
Tetra-Pyþ-Me. It is well known that porphyrins easily undergo
aggregation when in solution in particular in water or in
polar solvents. This phenomenon causes fast quenching of
the porphyrin triplet state and consequently restricts the
formation of 1O2.
pounds show a multiplet in the range of 8.87–9.04 ppm corre-
sponding to the resonances of the b-pyrrolic protons whereas for
the tetrasubstituted derivatives the resonances of the b-pyrrolic
protons appear as a singlet around 8.95 ppm. The same spectra
show broad singlets at approx. ꢀ2.85 ppm attributable to the
inner NH protons. The resonancesofthe isopropyl protonsappear
as two doublets at 1.36–1.42 ppm and a doublet of heptets around
4.6 ppm with coupling constants in the rangeof6.0–6.3 Hz (JH–H
)
and 7.2–7.5 Hz (JP–H). 31P NMR signals were observed in
the range of 7.8–8.2 ppm for all porphyrin–phosphoramidate

Porphyrin–Phosphoramidate Conjugates
941
100
95
90
85
80
75
100
95
90
85
80
75
0
50 100 150 200 250 300 350 400
0
50 100 150 200 250 300 350 400
Time [s]
Time [s]
DPiBF
3a
3b
3c
3d
3e
Tetra-PyꢀꢂMe
DPiBF
4a
4b
4d
4e
4c
Tetra-PyꢀꢂMe
Fig. 1. Photodecomposition of 1,3-diphenylisobenzofuran (DPiBF) by singlet oxygen generated by porphyrin derivatives 3a–e and 4a–e after irradiation
with white light filtered through a cut-off filter for wavelengths ,550 nm (9 mW cmꢀ2). The tetracationic porphyrin meso-tetrakis(1-methylpyridinium-4-yl)
porphyrin (Tetra-Pyþ-Me) was used as a reference.
Conclusions
Table 1. Rate of 1O2 production
(Tetra-Pyþ-Me: meso-tetrakis(1-methylpyridinium-4-yl)porphyrin)
The synthesis of 10 new porphyrin–phosphoramidates is
described. Thecompoundswereobtainedinsatisfactory yields by
nucleophilic aromatic substitution of fluorine atoms in the para-
position of the pentafluorophenyl groups of meso-tetrakis(pen-
tafluorophenyl)porphyrin (1) with aminoalkylphosphoramidates
(2a–e). The evaluation of the photodecomposition of 1,3-diphe-
nylisobenzofuraninthepresenceofthe newporphyrinderivatives
3a–e and 4a–e has shown that compound 4c is the best singlet
oxygen generator, being more efficient than Tetra-Pyþ-Me.
The photostability results point out that all new compounds are
very photostable. Non-linearity was observed between the
chain length of the aminoalkyl spacer of the phosphoramidate
groupandthephotophysicalpropertiesofthephotosensitizers. On
the other hand, the introduction of the polar phosphoramidate
ester moieties in both series 3 and 4 is related to a polarity
increase for such porphyrins in relation with the unsubstituted
meso-tetrakis(pentafluorophenyl)porphyrin. Further studies on
the properties of these new porphyrin derivatives are currently
under investigation in our laboratories.
Porphyrin derivative
–SlopeA [sꢀ1
]
3a
0.025
0.018
0.015
0.015
0.013
0.045
0.018
0.058
0.043
0.038
0.038
3b
3c
3d
3e
4a
4b
4c
4d
4e
Tetra-Pyþ-Me
AValues of slope of the plots of absorbance of 1,3-diphenylisobenzofuran in
N,N-dimethylformamide/H2O (9/1) versus illumination time.
Photostability of the Compounds
Porphyrins can undergo photobleaching when exposed to
UV-vis light and oxygen.[16] The rate of photodegradation of
a photosensitizer exposed to light is a very important pa-
rameter to assess for PDT application, because a fast photo-
bleaching would cause the concentration of the drug to
decrease, thus impairing the effectiveness of the treatment.
To induce photobleaching, aerated solutions of compounds
3a–e and 4a–e in N,N-dimethylformamide (DMF)/water
(9/1), under magnetic stirring, were irradiated with white
light at a fluence rate of 40 mW cmꢀ2. For all studied com-
pounds, the UV-vis spectra registered at different times of
irradiation did not show any absorbance decay of the Soret
and Q bands during the total irradiation period (30 min). The
results point out that all studied porphyrin derivatives are
highly stable under such conditions. As an example, the
UV-vis spectra of compound 3a before and after 30 min of
irradiation are shown in Fig. 2.
Experimental
1H, 19F, and 31P NMR spectra were recorded on a Bruker Avance
300 spectrometer at 300.13, 282.38, and 121.50 MHz, respec-
tively. CDCl3 was used as solvent (except when indicated).
Chemical shifts are reported in ppm (d) and coupling constants
(J) are given in Hz. Mass spectra and HRMS were recorded on
VG AutoSpec Q and M mass spectrometers. The UV-vis spectra
were recorded on a Uvikon spectrophotometer. Melting points
were measured on a Reichert Thermovar apparatus and are un-
corrected. Flash chromatography was carried out with silica gel
35–70 mesh (Merck). Analytical TLC was carried out on pre-
coated sheets with silica gel (0.2 mm thick, Merck). The ami-
noalkylphosphoramidates 2a–e were synthesized in 50–53%
yield from diisopropylphosphonate and aliphatic diamines, as
described by Costa de Souza et al.[11] In order to guarantee mono-
phosphorylation of the diamines, at least a 2.5-fold excess of

942
L. F. Pedrosa et al.
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.7
0.65
0.6
400
410
420
λ [nm]
t ꢁ 0min
t ꢁ 30min
350
450
550
650
750
λ [nm]
Fig. 2. Photostability of 3a after irradiation with white light (400–800nm) at a fluence rate of 40 mW cmꢀ2
.
Inset: expansion of Soret Band.
diamine in ethanol was employed to maintain the (alkaline) pH
necessary to catalyze the reaction. Careful addition of diisopro-
pylphosphonate in ethanol and carbon tetrachloride over the di-
amine solution should not exceed 10 min and the temperature
must not be allowed to increase above 55–658C, otherwise
bis-phosphorylation will occur preferentially.
2.01 (quint, J 6.3, 2H, CH2CH2CH2), 2.34 (br s, 1H, NH–P),
2.68 (br s, 1H, NHCH2), 3.24 (dt, J 6.3 and 10.3, 2H, CH2NHP),
3.82 (t, J 6.3, 2H, CH2NH), 4.69 (dhep, J 6.1 and 7.2, 2H, CH),
8.87–9.04 (m, 8H, H-b). dF ꢀ185.08 to ꢀ184.86 (m, 6F, F-meta),
ꢀ184.27 (dd, J 4.3 and 19.3, 2F, F-meta), ꢀ175.01 to ꢀ174.87
(m, 3F, F-para), ꢀ164.21 (dd, J 4.8 and 19.3, 2F, F-ortho),
ꢀ160.00(dd, J 8.1 and 23.7, 6F, F-ortho). dP 8.23. lmax/nm (loge)
415 (5.40), 509 (4.33), 585 (3.84). m/z HRMS (FABþ). Calc. for
C53H33F19N6O3P (Mþ H)þ: 1193.2048. Found: 1193.2043.
Monosubstituted Porphyrin–Phosphoramidates 3a–e:
General Procedure
Porphyrin 1 (0.04 mmol) and the aminoalkylphosphoramidate
2a–e (0.02 mmol) were dissolved in toluene (5mL). Triethyla-
mine (1mL) was added to this solution and the reaction mixture
was heated at reflux until the disappearance of the starting ami-
noalkylphosphoramidate (8–12 h, monitored by TLC). After
cooling to room temperature, the mixture was diluted with chlo-
roform and washed with water (3ꢁ 5 mL). The solvent was
evaporated under reduced pressure and the crude solid was puri-
fied by preparative TLC using ethyl acetate as the eluent. Com-
pounds 3a–e wererecrystallizedfromchloroform/methanol (1/3).
5-(4-{[4-(Diisopropoxyphosphorylamino)butyl]amino}-
2,3,5,6-tetrafluorophenyl)-10,15,20-tris
(pentafluorophenyl)porphyrin (3c)
Compound 3c was obtained in 63% yield (15.2 mg), mp
.3008C. dH ꢀ2.91 (s, 2H, NH), 1.36, 1.39 (2d, J 6.2, 12H,
CH3), 1.73, 1.86 (2 m, 4H, CH2CH2NP and CH2CH2NH), 2.57
(br s, 1H, NH–P), 3.08 (m, 2H, CH2NHP), 3.73 (m, 2H,
CH2NH), 4.34 (br s, 1H, NHCH2), 4.66 (dhep, J 6.2 and 7.5,
2H, CH), 8.87–9.04 (m, 8H, H-b). dF ꢀ185.07 to ꢀ184.85 (m,
6F, F-meta), ꢀ184.37 (dd, J 4.9 and 19.8, 2F, F-meta), ꢀ175.00
to ꢀ174.94 (m, 3F, F-para), ꢀ164.08 (dd, J 5.2 and 19.8, 2F, F-
5-(4-{[2-(Diisopropoxyphosphorylamino)ethyl]amino}-
2,3,5,6-tetrafluorophenyl)-10,15,20-tris
(pentafluorophenyl)porphyrin (3a)
ortho), ꢀ160.00 (dd, J 8.0 and 23.5, 6F, F-ortho). dP 7.84. lmax
/
nm (log e) 415 (5.40), 508 (4.31), 585 (3.85). m/z HRMS
(FABþ). Calc. for C54H35F19N6O3P (M þ H)þ: 1207.2205.
Found: 1207.2199.
Compound 3a was obtained in 71% yield (16.7 mg), mp
.3008C. dH ꢀ2.91 (s, 2H, NH), 1.42, 1.43 (2d, J 6.2, 12H, CH3),
2.92 (dd, J 6.8 and 16.8, 1H, NH–P), 3.40 (dt, J 6.8 and 11.6, 2H,
CH2NHP), 3.82 (br s, 2H, CH2NH), 4.73 (dhep, J 6.2 and 7.4,
2H, CH), 5.01 (br s, 1H, NHCH2), 8.87–9.04 (m, 8H, H-b).
dF ꢀ185.08 to ꢀ184.80 (m, 6F, F-meta), ꢀ183.94 (d, J 19.3, 2F,
F-meta), ꢀ175.00 to ꢀ174.94 (m, 3F, F-para), ꢀ164.10 (dd, J
5.1 and 19.3, 2F, F-ortho), ꢀ160.00 (dd, J 8.1 and 23.8, 6F, F-
ortho). dP 8.02. lmax/nm (log e) 415 (5.38), 508 (4.28), 585
(3.78). m/z HRMS (FABþ). Calc. for C52H31F19N6O3P (M þ
H)þ: 1179.1892. Found: 1179.1886.
5-(4-{[5-(Diisopropoxyphosphorylamino)pentyl]amino}-
2,3,5,6-tetrafluorophenyl)-10,15,20-tris
(pentafluorophenyl)porphyrin (3d)
Compound 3d was obtained in 81% yield (19.8 mg), mp
.3008C. dH ꢀ2.91 (s, 2H, NH), 1.36 (d, J 6.2, 12H, CH3), 1.64,
1.86 (2m, 6H, (CH2)3CH2NHP), 2.53 (br s, 1H, NH–P), 3.00 (m,
2H, CH2NHP), 3.70 (t, J 6.8, 2H, CH2NH), 4.64 (dhep, J 6.2 and
7.4, 2H, CH), 8.87–9.04 (m, 8H, H-b). dF ꢀ185.08 to ꢀ184.85
(m, 6F, F-meta), ꢀ184.42 (dd, J 4.8 and 19.9, 2F, F-meta),
ꢀ175.00 to ꢀ174.96 (m, 3F, F-para), ꢀ164.19 (dd, J 5.1 and
19.9, 2F, F-ortho), ꢀ160.01 (dd, J 8.0 and 23.6, 6F, F-ortho). dP
7.92. lmax/nm (log e) 415 (5.40), 508 (4.32), 585 (3.86). m/z
HRMS (FABþ). Calc. for C55H37F19N6O3P (M þ H)þ:
1221.2361. Found: 1221.2356.
5-(4-{[3-(Diisopropoxyphosphorylamino)propyl]amino}-
2,3,5,6-tetrafluorophenyl)-10,15,20-tris
(pentafluorophenyl)porphyrin (3b)
Compound 3b was obtained in 83% yield (19.8 mg), mp
.3008C. dH ꢀ2.91 (s, 2H, NH), 1.39, 1.40 (2d, J 6.1, 12H, CH3),

Porphyrin–Phosphoramidate Conjugates
943
5-(4-{[6-(Diisopropoxyphosphorylamino)hexyl]amino}-
2,3,5,6-tetrafluorophenyl)-10,15,20-tris
(pentafluorophenyl)porphyrin (3e)
4.27 (br s, 4H, NHCH2), 4.67 (dhep, J 6.2 and 7.5, 8H, CH), 8.95
(s, 8H, H-b). dF ꢀ184.33 (d, J 19.5, 8F, F-meta), ꢀ163,97 (dd,
J 5.3 and 19.5, 8F, F-ortho). dP 7.9. lmax/nm (log e) 422 (5.38),
512 (4.27), 588 (3.80). m/z HRMS (FABþ). Calc. for
C84H108F16N12O12P4 (M þ 2H)2þ: 952.3452. Found: 952.3447.
Compound 3e was obtained in 65% yield (16.1 mg), mp
.3008C. dH ꢀ2.90 (s, 2H, NH), 1.34, (d, J 6.2, 12H, CH3), 1.58
(m, 6H, (CH2)3CH2NH), 1.85 (m, 2H, CH2CH2NHP), 2.49 (br s,
1H, NH–P), 2.97 (dd, J 7.2 and 15.0, 2H, CH2NHP), 3.70 (t, J
6.9, 2H, CH2NH), 4.62 (dhep, J 6.2 and 7.3, 2H, CH), 8.87–9.04
(m, 8H, H-b). dF ꢀ185.10 to ꢀ184.88 (m, 6F, F-meta), ꢀ184.44
(dd, J 4.5 and 19.5, 2F, F-meta), ꢀ175.03 to ꢀ174.98 (m, 3F, F-
para), ꢀ164.22 (dd, J 5.1 and 19.5, 2F, F-ortho), ꢀ160.02 (dd,
J 8.0 and 23.5, 6F, F-ortho). dP 7.91. lmax/nm (log e) 415 (5.42),
508 (4.34), 585 (3.86). m/z HRMS (FABþ). Calc. for
C56H39F19N6O3P (M þ H)þ: 1235.2518. Found: 1235.2512.
5,10,15,20-Tetrakis(4-{[5-
(diisopropoxyphosphorylamino)pentyl]amino}-2,3,5,6-
tetrafluorophenyl)porphyrin, 4d
Compound 4d was obtained in52% yield (40.8 mg), mp
.3008C. dH ꢀ2.86 (s, 2H, NH), 1.36 (d, J 6.0, 48H, CH3),
1.63, 1.85 (2 m, 24H, (CH2)3CH2NHP), 2.54 (br s, 4H, NH–P),
3.00 (m, 8H, CH2NHP), 3.69 (t, J 6.1, 8H, CH2NH), 4.25 (br s,
4H, NHCH2), 4.63 (dhep, J 6.0 and 7.3, 8H, CH), 8.95 (s, 8H,
H-b). dF ꢀ184.56 (d, J 19.4, 8F, F-meta), ꢀ164,03 (dd, J 5.3 and
19.4, 8F, F-ortho). dP 7.8. lmax/nm (log e) 422 (5.44), 512 (4.30),
588 (3.83). m/z HRMS (FABþ) Calc. for C88H116F16N12O12P4
(M þ2H)2þ: 980.3765. Found: 980.3760.
Tetrasubstituted Porphyrin–Phosphoramidates 4a–e:
General Procedure
Porphyrin 1 (0.04 mmol) and the aminoalkylphosphoramidate
2a e (0.4 mmol; 2.5 equiv./aryl group) were dissolved in tolu-
]
ene (5 mL) and the reaction mixture was heated at reflux until
the disappearance of the starting porphyrin (56–72 h, monitored
by TLC). After cooling to room temperature, the mixture was
diluted with chloroform and washed with water (3 ꢁ 5 mL). The
solvent was evaporated under reduced pressure and the crude
solid was purified by column chromatography (silica gel) using
ethyl acetate/methanol (97/3) as the eluent. Compounds 4a–e
were recrystallized from chloroform/methanol (1/3).
5,10,15,20-Tetrakis(4-{[6-
(diisopropoxyphosphorylamino)hexyl]amino}-2,3,5,6-
tetrafluorophenyl)porphyrin (4e)
Compound 4e was obtained in 64% yield (51.6 mg), mp
.3008C. dH ꢀ2.86 (s, 2H, NH), 1.32, 1.36 (2d, J 6.1, 48H, CH3),
1.43 (m, 16H, CH2(CH2)2NHP and CH2(CH2)3NHP), 1.84 (m,
16H, CH2CH2NHP and CH2CH2NH2), 2.56 (br s, 4H, NH–P),
2.92 (m, 8H, CH2NHP), 3.70 (m, 8H, CH2NH), 4.26 (br s, 4H,
NHCH2), 4.62 (m, 8H, CH), 8.95 (s, 8H, H-bb). dF ꢀ184.61
(d, J 19.9, 8F, F-meta), ꢀ164.08 (dd, J 5.2 and 19.9, 8F, F-
ortho). dP 7.9. lmax/nm (log e) 423 (5.20), 513 (4.10), 590 (3.68).
5,10,15,20-Tetrakis(4-{[2-
(diisopropoxyphosphorylamino)ethyl]amino}-2,3,5,6-
tetrafluorophenyl)porphyrin (4a)
Compound 4a was obtained in 50% yield (35.8 mg), mp
.3008C. dH ꢀ2.85 (s, 2H, NH), 1.41, 1.42 (2d, J 6.1, 48H, CH3),
3.01 (dd, J 6.7 and 16.4, 4H, NH–P), 3.38 (dt, J 6.7 and 11.4, 8H,
CH2NHP), 3.80 (m, 8H, CH2NH), 4.72 (dhep, J 6.1 and 7.3, 8H,
CH), 4.95 (br s, 4H, NHCH2), 8.95 (s, 8H, H-b). dF ꢀ184.15 (d,
J 19.6, 8F, F-meta), ꢀ163.9 (dd, J 5.2 and 19.6, 8F, F-ortho). dP
7.9. lmax/nm (log e) 422 (5.47), 512 (4.34), 588 (3.89). m/z
Singlet Oxygen Generation and Photostability Studies
A stock solution of each porphyrin derivative at 0.1 mM in
DMF/H2O (9/1) and a stock solution of DPiBF at 10 mM in
dimethyl sulfoxide (DMSO) were prepared. The reaction mix-
ture of 10 mL of DPiBF and 10 mL of a porphyrin derivative in
DMF/water (9/1) in glass cells (2 mL) was irradiated with white
light filtered through a cut-off filter of wavelengths ,550 nm, at
a fluence rate of 9.0 mW cmꢀ2. During the irradiation period the
solutions were stirred at room temperature. The breakdown of
DPiBF was monitored by measuring the decreasing of the ab-
sorbance at 415 nm at irradiation intervals of 1 min.
The photostability of the photosensitizers was determined by
irradiating 2 mL of 2 mM solutions of the porphyrins in DMF/
H2O (9/1) with white light (400–800 nm) at fluence rate of
40 mW cmꢀ2. During such irradiation the solutions were mag-
netically stirred and kept at room temperature. The concentra-
tion of the porphyrin derivative was quantified by visible
absorption spectrophotometry at regular intervals.
HRMS (FABþ). Calc. for C76H92F16N12O12P4 (M þ 2H)2þ
:
896.2826. Found: 896.2821.
5,10,15,20-Tetrakis(4-{[3-
(diisopropoxyphosphorylamino)propyl]amino}-2,3,5,6-
tetrafluorophenyl)porphyrin (4b)
Compound 4b was obtained in 77% yield (56.9 mg), mp
.3008C. dH ꢀ2.86 (s, 2H, NH), 1.39, 1.41 (2d, J 6.1, 48H, CH3),
2.01 (m, 8H, CH2CH2CH2), 2.68 (dd, J 6.9 and 15.5, 4H, NH–P),
3.24 (dt, J 6.9 and 12.9, 8H, CH2NHP), 3.81 (m, 8H, CH2NH),
4.58 (br s, 4H, NHCH2), 4.69 (dhep, J 6.1 and 7.3, 8H, CH), 8.95
(s, 8H, H-b). dF ꢀ184.41 (d, J 19.6, 8F, F-meta), ꢀ164.00 (dd,
J 5.2 and 19.6, 8F, F-ortho). dP 8.2 lmax/nm (log e) 422 (5.31),
512 (4.17), 589 (3.76). m/z HRMS (FABþ). Calc for
C80H100F16N12O12P4 (M þ 2H)2þ: 924.3139. Found: 924.3134.
Acknowledgements
The authors thank CNPq-Brazil and CAPES (Brazil)-GRICES/FCT (Por-
tugal) joint protocol for funding. The authors also thank the Organic
Chemistry Research Unit of the University of Aveiro. The authors
acknowledge the Portuguese National NMR Network, supported from
5,10,15,20-Tetrakis(4-{[4-
(diisopropoxyphosphorylamino)butyl]amino}-2,3,5,6-
tetrafluorophenyl)porphyrin (4c)
Fundac¸ao para a Cieˆncia e a Tecnologia (FCT).
˜
Compound 4c was obtained in 75% yield (57.1 mg), mp
.3008C. dH ꢀ2.86 (s, 2H, NH), 1.37 (d, J 6.2, 48H, CH3), 1.76,
1.89 (2 m, 16H, CH2CH2NP and CH2CH2NH), 2.60 (br s, 4H,
NH–P), 3.08 (m, 8H, CH2NHP), 3.72 (t, J 6.7, 8H, CH2NH),
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