Wittig reactions on photoprotoporphyrin IX: New synthetic models for the special pair of the photosynthetic reaction center

Article abstract of DOI:10.1021/jo991254+

A first example of spirochlorin-chlorin dimer with fixed distances and orientations as potential model for the 'special pair' of the photosynthetic reaction center is discussed. For the preparation of such a novel structure, the Wittig reagent of the desired 'spacer' 5 was reacted with photoprotoporphyrin IX dimethyl ester 3 to produce the intermediate dimer 6, which on intramolecular [4 + 2] Diels-Alder cycloaddition gave an unexpected spirochlorin-chlorin dimer 9. Dehydration of dimer 6 under acid-catalyzed conditions generated the corresponding spirochlorinporphyrin dimer 16 in quantitative yield. The asymmetry in dimer 6 caused by the biphenyl-type anisotropic effect was confirmed by NMR and model studies. The formation of dihydrobenzoporphyrin 14 by reacting chlorin 3 with the phosphonium salt of p-methylbenzylbromide 10 and isolation of 8-phenanthrenevinylporphyrin 19 from chlorin 7 further confirmed our proposed mechanism for the formation of a spirochlorin-chlorin dimer 9. Following a similar approach, chlorin 3 on reacting with bis-phosphonium salt of 4,4'-bischloromethylbiphenyl produced conjugated chlorin dimer 25. The spectroscopic data obtained from these dimers suggest that, in these compounds, the individual chromophores are not behaving as an individual molecule, but as a single macrocycle. To examine whether the π-π interaction exhibited by dimer 9 resembles the structural arrangement of bacteriochlorophylls in reaction center (RC), we investigated the geometrical parameters used to characterize the π-π interactions in tetrapyrrolic macrocycles. Starting from the crystallographic coordinates of 9, the molecular mechanics energy minimization was performed to obtain the model dimer structure. The geometrical parameters that measure the single pyrrole ring overlap were used to compare the model structure with the crystallographic coordinates of the special pair in photosynthetic reaction center. The results indicated that the ring A of spirochlorin and the ring C of chlorin in our model dimer 9 mimic the ring A-ring A interaction found in the crystallographic special pairs, which are strategically placed by the surrounding photosynthetic reaction center protein matrix.

Full text of DOI:10.1021/jo991254+

J . Org. Chem. 2000, 65, 543-557
543
Wittig Rea ction s on P h otop r otop or p h yr in IX: New Syn th etic
Mod els for th e Sp ecia l P a ir of th e P h otosyn th etic
Rea ction Cen ter †
Gang Zheng,‡ Masayuki Shibata,§ Thomas J . Dougherty,‡ and Ravindra K. Pandey*,‡,|
Chemistry Division, Photodynamic Therapy Center, Molecular and Cellular Biophysics, and
Department of Nuclear Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263
Received August 6, 1999
A first example of spirochlorin-chlorin dimer with fixed distances and orientations as potential
model for the “special pair” of the photosynthetic reaction center is discussed. For the preparation
of such a novel structure, the Wittig reagent of the desired “spacer” 5 was reacted with
photoprotoporphyrin IX dimethyl ester 3 to produce the intermediate dimer 6, which on intramo-
lecular [4 + 2] Diels-Alder cycloaddition gave an unexpected spirochlorin-chlorin dimer 9.
Dehydration of dimer 6 under acid-catalyzed conditions generated the corresponding spirochlorin-
porphyrin dimer 16 in quantitative yield. The asymmetry in dimer 6 caused by the biphenyl-type
anisotropic effect was confirmed by NMR and model studies. The formation of dihydrobenzopor-
phyrin 14 by reacting chlorin 3 with the phosphonium salt of p-methylbenzylbromide 10 and
isolation of 8-phenanthrenevinylporphyrin 19 from chlorin 7 further confirmed our proposed
mechanism for the formation of a spirochlorin-chlorin dimer 9. Following a similar approach, chlorin
3 on reacting with bis-phosphonium salt of 4,4′-bischloromethylbiphenyl produced conjugated chlorin
dimer 25. The spectroscopic data obtained from these dimers suggest that, in these compounds,
the individual chromophores are not behaving as an individual molecule, but as a single macrocycle.
To examine whether the π-π interaction exhibited by dimer 9 resembles the structural arrangement
of bacteriochlorophylls in reaction center (RC), we investigated the geometrical parameters used
to characterize the π-π interactions in tetrapyrrolic macrocycles. Starting from the crystallographic
coordinates of 9, the molecular mechanics energy minimization was performed to obtain the model
dimer structure. The geometrical parameters that measure the single pyrrole ring overlap were
used to compare the model structure with the crystallographic coordinates of the special pair in
photosynthetic reaction center. The results indicated that the ring A of spirochlorin and the ring
C of chlorin in our model dimer 9 mimic the ring A-ring A interaction found in the crystallographic
special pairs, which are strategically placed by the surrounding photosynthetic reaction center
protein matrix.
In tr od u ction
bacteriochlorophyll, the so-called “special pair”, which
acts as primary electron donor; two accessory bacterio-
chlorophylls, which mediate ET; and two bacteriopheo-
phytins, which are the primary electron acceptors. In
addition, there are cofactors: the menaquinone, which
is an electron relay, and the ubiquinone, which is the
final electron acceptor in RC. All elements are held in
precise distances and orientation along a C2 axis of
symmetry by a protein matrix. In such RCs, the primary
charge separation process is initiated from the lowest
singlet excited state of the special pair.6 Two bacterio-
chlorophyll a or b molecules, depending on the bacteria,
are laterally offset by ∼6 Å from center to center and
oriented such that only their unsaturated acetyl-substi-
Photosynthesis in purple photosynthetic bacteria oc-
curs in membrane-bound pigment protein complexes
known as light-harvesting (antenna) complexes (LHC)1
and reaction centers (RC).2 The major function of LHCs
is to broaden the spectral region of the light that can be
used by the bacteria, whereas RCs utilize the collected
light energy for photoinduced electron transfer, which
fuels cellular processes. To date, only two RCs, those from
Rd. viridis3 and Rd. sphaeroids,4 have been characterized
structurally in high resolution. Six tetrapyrrolic sub-
sunits are found at these two very similar RCs:5 a dimeric
* To whom correspondence should be addressed at the Photodynamic
Therapy Center. Phone: (716) 845-3203. Fax: (716) 845-8920. E-
mail: rpandey@sc3103med.buffalo.edu.
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‡ Chemistry Division, Photodynamic Therapy Center.
§ Molecular and Cellular Biophysics.
| Department of Nuclear Medicine.
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10.1021/jo991254+ CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/31/1999

544 J . Org. Chem., Vol. 65, No. 2, 2000
Zheng et al.
tuted pyrrole rings overlap at a separation of ∼3.2 Å. The
resulting dimer interaction contributes to the split and
red-shifted Qy band of the special pair and makes it the
better phototrap for the antenna pigments. Excitation of
the special pair results in unity quantum yield electron
transfer from the special pair to a bacteriopheophytin
molecule in about 2.8 ps.8 Within about 150 ps the
electron is transferred to a quinone molecule, which in
turn transfers an electron to a secondary quinone within
a few microseconds. Such fast sequential electron-trans-
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transfer processes and afford a long-lived charge separa-
tion state. A desire to understand the intricacies of
natural photosynthesis has motivated many chemists and
molecular biologists to synthesize and study a wide
variety of arrays of covalently connected artificial models
based on derivatized porphyrins,9 dimeric and trimeric
porphyrins,10 and porphyrin arrays.11
There are two major aspects to the design of arti-
fical RCs: the choice of chromorphores and the selection
of an organizing principle that will control the interac-
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determined by spatial separations, angular relationships,
and the nature of the intervening medium.10b Thus, it
will be ideal to use chromophores found in natural
photosynthesis (chlorophyll and bacteriochlorophyll) but
to replace the protein with spacers with well-defined
geometry and orientation. So far, besides a small group
of chlorin and bacteriochlorin dimers models,12 most
artificial models are based on covalently linked porphyrin
dimers to mimic either the antenna complexes13 or the
various sequential electron-transfer steps in reaction
centers.14
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special pair have shown that studies of porphyrin-based
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special pair include two tetrapyrrolic macrocycles in close
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Wittig Reactions on Photoprotoporphyrin IX
J . Org. Chem., Vol. 65, No. 2, 2000 545
Sch em e 1. Str a tegy for Con str u ctin g Bis-ch lor in
Mod el System s
Sch em e 2. Sta r tin g Ma ter ia ls P P P A 3 a n d P P P B
4
Sch em e 3. F or m a tion of Bis-ch lor in 6 a n d
Mon om er ic Ch lor in 7
between the π-electron systems of the pair, and a
substituent pattern as close as possible to that in natural
bacteriochlorophylls. Thus, our goal has been to develop
a versatile methodology for the preparation of chlorin and
bacteriochlorin dimers with fixed distance and orienta-
tion.
Officer and colleagues16 have recently shown that by
using porphyrin-derived Wittig reagents, a variety of
porphyrin dimers can be constructed. This chemistry
offers a versatile approach for the preparation of a variety
of porphyrin-based free base and heterometalated dimers.
However, in our hands, the extension of this approach
for preparing less stable chlorin and bacteriochlorin
dimers mainly yielded decomposition products. Thus, we
have been interested in developing an alternate method
for preparing various coplanar and cofacial chlorin and
bacteriochlorin dimers. In our attempts to synthesize
such dimers, we thought it worthwhile to prepare the
Wittig reagents of the desired linkers first and then react
them individually with chlorin and bacteriochlorin mono-
mers.
mixture of two isomers: 3 (PPPA, isomer A) and 4 (PPPB,
isomer B). The isomeric mixture was separated into
individual isomers by column chromatography (silica gel-
G),17b and isomerically pure chlorin 3 (isomer A) was used
as a substrate. The bis-phosphonium salt 5 derived from
2,2′-bisbromomethyl-1,1′-biphenyl was reacted with PPPA
3 in the presence of DBU to afford a mixture of mainly
two compounds. See Scheme 3. On the basis of mass spec-
trometry and NMR analysis, the structure for the faster
moving band obtained in 60% yield was assigned as 2′,2′′-
bischlorin 6, HRMS (calcd 1391.6550 for C86H87N8O10,
found 1391.6540). The presence of eight meso protons
in the range of 8.8-9.8 ppm clearly indicated a dimer
possessing an asymmetric structure. On the basis of
mass spectrometry analysis (HRMS calcd 786.3781 for
C50H50N4O5, found 786.3749), the structure for the minor
component (yield 20%) was initially assigned as 7, which
Resu lts a n d Discu ssion s
The basic strategy for the preparation of bis-chlorin
model systems is depicted in Scheme 1. Depending on
the type of Wittig reagent used, the presence of a “spacer”
directly attached at the peripheral position of a chlorin
gives a unique opportunity to prepare a series of chlorin
dimers with fixed distances and geometry.
Ch lor in -Sp ir och lor in a n d P or p h yr in -Sp ir och lo-
r in Dim er s w ith 2′,2′′-Bip h en yl Br id ge System . For
the preparation of the starting material, hemin 1 was
first converted into protoporphyrin IX dimethyl ester 2
by following the standard methodology.17a See Scheme
2. Reaction of 2 with light and air produced the “so-called”
photoprotoporphyrin IX (a type of chlorin, PPP) as a
1
was further confirmed by HNMR studies. As shown in
Figure 1, the 1H NMR spectrum of the monomer 7 shows
an unexpected equal-splitting pattern for each meso
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8531-8534.

546 J . Org. Chem., Vol. 65, No. 2, 2000
Zheng et al.
F igu r e 1. Partial NMR spectra of dimer 6 and monomer 7 (a comparative study).
F igu r e 2. Evidence for inter-exchanging conformations in monomer 7.
proton close to the reduced ring, which is similar to that
observed in dimer 6. To understand the reason for the
asymmetry in both dimer 6 and monomer 7, extensive
NMR studies were performed on monomer 7. In the NMR
spectrum, the evidence of two inter-exchanging confor-
mations was initially observed from a 2D ROESY experi-
ment (Figure 2), which was further confirmed by variable
temperature NMR studies. As shown in Figure 3, at 30
°C, replacing CDCl3 with dioxane-d8 drastically reduced
the splitting pattern, which completely disappeared in
DMSO-d6. Interestingly, raising the temperature of the
dioxane-d8 solution from 30 to 70 °C also eliminated such
a splitting pattern. These results suggest that in mono-
mer 7 this effect is certainly due to a slow exchange
between the two possible conformations causing the
biphenyl-type anisotropic effect18 induced by the re-
stricted rotation around the biphenyl bond. To confirm
these results, chlorin 8, lacking the methyl group at 2′-
position of the biphenyl substituent, was synthesized, and
as expected, in the 1H NMR spectrum of chlorin 8 (CDCl3,
room temperature) no splitting pattern was observed
(Figure 4). Compared to 7, dimer 6 in which the methyl
group is replaced with the much larger chlorin macrocycle
will certainly generate more restricted rotation around
the biphenyl bond. This was confirmed by its NMR
spectrum, which produces a similar spiliting pattern as
observed for 7. To our surprise, the bis-chlorin 6 was
found to be unstable if the reaction was left for longer
periods of time and slowly converted into an unknown
chlorin dimer 9. The rate of the transformation and thus
the yield of the individual dimers 6 and 9 was found to
be dependent on the reaction conditions used. Both
compounds were found to have the same molecular
weight as confirmed by high-resolution mass spectrom-
etry. The NMR studies indicated that compared to dimer
6, some of the meso protons in dimer 9 showed a
significant upfield shift resulting into a complex spec-
trum. Figure 5 represents the partial spectra of these
dimers (the spectrum of dimer 9, shows the resonances
(18) (a) Gottwald, L. K.; Ullman, E. F. Tetrahedron Lett. 1969, 36,
3071-3074. (b) Lindsey, J . S. J . Org. Chem. 1980, 45, 5215. (c) Gunter,
M. J .; Mander, L. N. J . Org. Chem. 1981, 46, 4792-4795. (d) Young,
R.; Chang, C. K. J . Am. Chem. Soc. 1985, 107, 898-909.

Wittig Reactions on Photoprotoporphyrin IX
J . Org. Chem., Vol. 65, No. 2, 2000 547
F igu r e 3. Effect of solvents and temperature on the NMR of monomer 7.
F igu r e 4. Biphenyl-type anisotropic effect induced by restricted rotation around biphenyl bond (caused by the presence of the
methyl group substituted at the ortho-position of the biphenyl substituent).
of only five of the eight meso protons appeared in the
range of δ 8.7-10.0 ppm).
To provide a simple reference spectra for identifying
all the resonances of dimer 9, model studies were per-
formed. The Wittig reagent 10, obtained from p-methyl-
benzylbromide, was reacted with chlorin 3 under various
reaction conditions. The best results were obtained when
DBU was used as a base and the reaction was performed
at room temperature (Scheme 4). Under these conditions,
compound 11 was obtained in 90% yield. By performing
2D-ROESY experiments, the geometry of model com-
pound 11 was established as the E,E isomer. The NOE
connectivities and the assignments of the key protons
are shown in Figure 6. To investigate the stability of
the model chlorin 11, it was dissolved in o-dichloroben-
zene and heated at various temperatures. Surprisingly,
it gave an unexpected dihydrobenzoporphyrin 14 as a
sole product. The formation of porphyrin 14 suggests a
two-step mechanism through an intermediate 11, which
includes a simple dehydration followed by an intra-
F igu r e 5. Partial NMR spectra of dimer 6 and monomer 9 (a
comparative study).
molecular [4 + 2] Diels-Alder cycloaddition (Scheme 4).
NMR (Figure 7) and HRMS analysis (calcd 693.3441 for
C44H44N4O4, found 693.3417).
The structure of porphyrin 14 was confirmed by 1H

548 J . Org. Chem., Vol. 65, No. 2, 2000
Zheng et al.
F igu r e 6. NMR spectrum of chlorin 11. The assignments are based on the NOE connectivities observed by 2D-ROESY experiments.
Sch em e 4. F or m a tion of a Novel Dih yd r oben zop or p h yr in 14 by Rea ctin g P P P A 3 w ith Wittig Rea gen t 10
With the reference spectra of model chlorin 11 in
hand, the structure of dimer 9 was postulated as a
spirochlorin-chlorin dimer linked via a tetrahydroben-
zophenanthrene bridge. The HRMS and NMR (1H, 2D-
ROESY, 2D-COSY) data also confirmed the proposed
structure. To the best of our knowledge, dimer 9 is
the first structurally characterized chlorin-spiro-
chlorin dimer with a remarkable π electron overlap. As
shown in Scheme 5, the mechanism of the formation of
this novel dimer is possibly due to the intramolecular [4
+ 2] Diels-Alder cycloaddition of the unsaturated alkyl
chain joining the two chlorin systems. The structure of
dimer 9 was also confirmed by a single-crystal X-ray
analysis.19
the two chlorin macrocycles (Figure 8). Table 1 sum-
marizes the assignments of all the resonances (δ ppm)
as well as changes in chemical shift compared to that of
the model chlorin 11 (∆δ ppm). The most notable features
were as follows:
The resonances for the meso protons (5H, 10H, 15H,
and 20H) in model chlorin 11 were observed in the region
of 8.5-10 ppm; however, in dimer 9, the meso proton
labeled as “v” of the chlorin part shifted dramatically to
4.89 ppm, exhibiting an upfield shift of 3.86 ppm relative
to the chlorin 11. On the other hand, meso protons from
the spirochlorin labeled as “k” and “n” show 0.80 and 2.08
ppm upfield shifts. Unlike the vinyl protons “g”, “s”, and
The 1H NMR spectrum of dimer 9 showed unique
characteristics due to the π electron interactions between
(19) Senge, M. O.; Zheng, G.; Pandey, R. K. Manuscript in prepara-
tion.

Wittig Reactions on Photoprotoporphyrin IX
J . Org. Chem., Vol. 65, No. 2, 2000 549
F igu r e 7. 1H NMR spectrum of porphyrin 14 (only the resonances observed for bridging protons are shown).
Sch em e 5. Mech a n ism for th e F or m a tion of a n Un exp ected Ch lor in -Sp ir och lor in Dim er 9 a n d Its
Deh yd r a tion P r od u ct 16
“t” of the chlorin moiety that appeared at 8.35 ppm (∆δ
) +0.46 ppm), 6.48 ppm (∆δ ) +0.28 ppm), and 6.15 ppm
(∆δ ) +0.11 ppm), respectively, the vinyl protons “w”,
“G”, and “M” from the spirochlorin showed significantly
upfielded resonances at 4.66 ppm (∆δ ) -3.23 ppm), 3.66
ppm (∆δ ) -4.23 ppm), and 3.25 ppm (∆δ ) -2.79 ppm),
respectively.
Furthermore, the 12-methyl resonance “T” in the
chlorin part of dimer 9 was observed at -0.13 ppm,
exhibiting an upfield shift of 3.50 ppm, whereas the
2-methyl signal “S” of the spirochlorin was shifted 3.41
ppm upfield relative to chlorin 11. On the other hand,
the 18-methyl protons “K” and 7-methyl protons “R”
(attached to the reduced ring) of the spirochlorin ap-
peared at 3.33 ppm (∆δ ) +0.05 ppm) and 1.88 ppm (∆δ
) +0.15 ppm), respectively. Surprisingly, two protons
adjacent to ring C of the chlorin labeled as “z” and “M”
have very different shifts with “M” being 0.84 ppm upfield
of “z”. In dimer 9, compared to the resonances for the
-NH protons (ring A of chlorin and ring C of spirochlorin)
the -NH protons of ring C (chlorin) and ring A (spiro-
chlorin) produced upfield shifts of ∼2.00 ppm. See Figure
9. These upfield shifts are due to the large ring current
produced by the system, which naturally affects the
adjacent ring due to partial chlorin-spirochlorin overlap
and, thus, causes a strong shielding effect. All protons

550 J . Org. Chem., Vol. 65, No. 2, 2000
Zheng et al.
F igu r e 8. 1H NMR spectrum of chlorin-spirochlorin dimer 9 (for details see Table 1).
affected by these π-π interactions are included in the
circle shown in Figure 8.
macrocycle and those of the spirochlorin system appeared
in the range of 7.5-8.5 ppm, generally reported for
chlorin and porphyrin systems. In the NMR spectrum of
9 (Figures 8 and 9), the upfield resonances at -0.13 and
+0.18 ppm were assigned to the 12-methyl “T” of the
chlorin and 2-methyl “S” of the spirochlorin; however, in
dimer 16, they appeared in the usual range of 2-3 ppm.
These results indicate that porphyrin-spirochlorin dimer
16 processes linear geometry and thus lacks cofacial π-π
interactions observed in dimer 9.
The absorption and fluorescence emission spectra of
dimers 9 and 16 were measured in dichloromethane. The
ground-state absorption spectra of dimer 9 reveals a
Soret band at 388 nm and distinct Q-bands at 505,
540, and 664 nm. Excitation of dimer 9 at 388, 505, 540,
and 664 nm gave a fluorescence emission band at
672 nm. In both dimers, the long-wavelength absorp-
tion was observed at 664 nm. However, dimer 16 exhib-
ited a remarkable red shift in the Soret band appearing
at 409 nm. The Q-band at 574 nm belongs to one of the
bands (etio-type) of the newly formed porphyrin sys-
tem. Excitation of all the bands at 409, 505, 538, 574,
and 664 nm afforded an emission at 668 nm. Interest-
ingly, the two emission bands generally observed at
635-645 nm (strong) and 690-700 nm (weak) for a
typical porphyrin macrocycle were found to be absent
in the fluorescence spectrum of 16, indicating that in
this dimer porphyrin and chlorin moieties are not be-
having as an individual molecule, but as a single mac-
rocycle.
The nature of the overlap between the pyrrole ring C
of the chlorin and the pyrrole ring A of the spirochlorin
in dimer 9 was further resolved by performing a 2D-
ROESY experiment (600 MHz) at 30 °C (9 was dissolved
0.5% pyridine-d5/CDCl3). A few through-space cross-
peaks, due to interchlorin subunit proton-proton inter-
actions (<3.5 ∼Å), were also observed. For example,
proton “z” of the chlorin shows a cross-interaction with
the 18-methyl “K” of the spirochlorin. Our observations
are consistent with a structure where the chlorin units
are present in such a way that the pyrrole ring A of the
spirochlorin overlaps the pyrrole ring C of the opposite
chlorin. This intermolecular interaction was further
confirmed by the energy-optimized structure of chlorin-
spirochlorin 9, obtained by molecular modeling (Figure
10).
The presence of a hydroxy functionality in the chlorin
system (ring B) of the dimer 9 was also supported by its
transformation into a porphyrin-spirochlorin dimer 16,
which was formed upon leaving the NMR sample in
CDCl3 (without pyridine-d5) at room temperature for an
extended period (Figure 11). See Scheme 5. The dehydra-
tion product so obtained was isolated by preparative TLC,
and the structure was assigned on the basis of its UV-
vis, HRMS (calcd 1373.6390 for C86H85N8O9, found
1373.6520) and NMR data.
Logically, the formation of dimer 16 could be explained
by the dehydration of dimer 9 caused by a trace amount
of acid present in CDCl3 used as a NMR solvent. In the
electronic absorption spectrum of dimer 16 (Figure 12),
the appearance of a new band at 578 nm with an
additional 18 nm red shift for the Soret band in the dimer
also indicated the presence of a porphyrin system.
Furthermore, compared to 9, the NMR spectrum of 16
showed entirely different structural features. For ex-
ample, the vinyl protons attached to the porphyrin
The intramolecular [4 + 2] cycloaddition that occurred
in bis-chlorin 6 was not an isolated phenomenon. Such
transformation was also observed in the case of 2′,2′′-
monomer 7. As shown in Scheme 6, when monomer 7
was kept in CDCl3 for several days, it slowly converted
to a dihydrophenanthrene type of porphyrin 18, which
further underwent auto-oxidation to afford fully aroma-
tized phenanthrene-linked porphyrin 19. Such a trans-

Wittig Reactions on Photoprotoporphyrin IX
J . Org. Chem., Vol. 65, No. 2, 2000 551
Ta ble 1. 1H NMR P a r a m eter sa for Ch lor in -Sp ir och lor in
dence for the formation of unexpected chlorin-spirochlo-
rin system.
Dim er 9
proton
J -J
Ch lor in -Ch lor in Dim er with 4′,4′′-Biph en yl Br idge
System . In our initial efforts to prepare the bis-chlorin
systems with a 4′,4′′-biphenyl bridge, we experienced
difficulty in isolating the pure bis-Wittig reagent. Re-
fluxing the 4,4′-bischloromethyl-1,1′-biphenyl20 22 with
Ph3P in CHCl3 overnight failed to produce the expected
bisphosphonium salt 23. Instead, a mono-Wittig reagent
24 with an unreacted chloromethyl group was mainly
obtained. However, we were able to isolate the bis-Wittig
reagent 23 under rigorous reaction conditions (refluxing
in DMF overnight). It was then condensed with PPPA 3
(Scheme 7). After the standard workup, the reaction
mixture was purified by preparative TLC, and the 4′,4′′-
bischlorin 25 and 4′,4′′-monomer 26 were obtained in 50%
and 20% yield, respectively. Unlike 2′,2′′-bischlorin 6, 1H
NMR spectrum of dimer 25 exhibited only four broad
peaks in the range of 8-10 ppm for the meso protons.
Replacing CDCl3 with THF-d4 as NMR solvent gave much
better resolution (Figure 15). The presence of four meso
protons (each as a singlet) in 4,4-bischlorin 25 clearly
indicated the formation of a symmetrical dimer. Mass
spectroscopy analysis gave a molecular ion peak at
1391.10 (calcd 1391.6550 for C86H87N8O10), which further
confirmed the dimeric structure.
signal with
integration
δ
NOE from
ROSEY
coupling
from COSY
type
ppm
∆δb,c
a (1H)
b (1H)
c (1H)
d (1H)
e (1H)
f (1H)
g (1H)
h (1H)
i (1H)
j (1H)
k (1H)
l (1H)
m (1H)
n (1H)
o (1H)
s
s
s
s
9.91 +0.29 C, H
9.63 +0.03 y, L, N
9.48 -0.12 J , P, x, z, M′
9.44 +0.91 Q, s, g, k
8.76 +0.01 C, O, h, o, p
s
d
dd
d
d
t
s
d
t
8.38
Q, u, r, q, A
f-r
8.35 +0.46 d, C, s, t
g-s, g-t
8.13
7.89
7.75
j, m, o, p, e, O h-j
m, l
m, h
i-m
m-j, j-h
7.73 -0.80 w, d, R, M
7.72
7.64
7.54 -2.08 S, K
7.40
q, I
i, j, h
q-l
i-m, m-j
s
ABq
with p
ABq
with o
h, e, B
o-p, o-B
p-o, p-B
p (1H)
7.33
h, e, B, R
q (1H)
r (1H)
s (1H)
t (1H)
u (1H)
v (1H)
w (1H)
x (2H)
y (4H)
z (1H)
A (1H)
B (1H)
t
t
d
d
t
s
dd
m
m
m
d
7.15
6.88
r, l
q, f, Q
q-r, q-l
r-q, r-f
s-g
6.48 +0.28 C, d, g, t
6.15 +0.11 s, g
5.18 -2.26 D, A, B, Q
4.89 -3.86 A, T
4.66 -3.23 G, M
4.36 +0.13 H, J
4.24 +0.01 b, K, N, O
4.10 +0.01 M′, P, K
3.92
3.88
t-g
u-A, u-D
w-M, w-G
x-J
y-L, y-N
z-M′, z-P
A-u
Similar to dimers 9 and 16, in dimer 25, excitation of
the absorption bands at 357, 438, 570, or 681 afforded
emission at 687 nm, suggesting that the two chlorin
systems joined by an unsaturated carbon-carbon linkage
are behaving as a single molecule.
u, v, D, f, B
o, p, A
ABq
with D
B-o, B-p,
B-D
C (6H)
D (1H)
s
3.80 +0.21 a, g, s
3.79
dd and
A, u, B
D-u, D-B
ABq
with B
Molecu la r Mod elin g Stu d ies. To examine whether
the π-π interaction exhibited in our dimer model 9
resembles the structural arrangement of bacteriochloro-
phylls in RC, we investigated the geometrical parameters
used to characterize the π-π interactions in tetrapyrrolic
macrocycles.20,21,22 The parameters used are described in
the method, and the results for our model dimer 9 and
some special pairs from crystallographic photosynthetic
reaction centers are shown in Table 2. In addition to the
standard parameters, which describe the relative orien-
tation of the whole tetrapyrrole ring systems, the ad-
ditional parameters were used to measure the relative
orientation of specific pair of pyrrole rings as found for
the ring A-ring A overlap in the special pairs. Table 2
indicates that there are some variations in these param-
eters among the crystallographic special pairs depending
upon the source of organisms and the crystal environ-
ment. The dimer 9 possesses more planer tetrapyrrole
ring system (dihedral angle of 3°) than the special pairs
(6°-11°) while the mean separation distance of the dimer
9. (3.4 Å), falls within the range found for the special
pairs (3.1-3.6 Å). J udged by the center-center separa-
tion distances (6.0 Å vs 7.4-7.7 Å), lateral shifts (4.9 Å
vs 6.6-6.9 Å), and slip angles (56° vs 61-65°), it seems
that the relative orientation of the tetrapyrrole rings in
model dimer 9 are slightly shifted from what is found
for the special pairs. Both the top and side views clearly
represent this slight shift graphically. However, when we
focused on the geometrical parameters describing the
relative orientation and overlap between single pyrrole
E (3H)
F (3H)
G (1H)
H (3H)
I (3H)
J (2H)
K (3H)
L (2H)
M (1H)
M′ (1H)
N (2H)
O (3H)
P (2H)
Q (3H)
R (3H)
S (3H)
T (3H)
s
s
d
s
s
3.73 +0.05
3.72 +0.04
N
N
3.66 -4.23 w, M, I
G-w
J -x
3.58 +0.30 a, x, C, J
3.52 -0.16 C
3.39 +0.20 x, C, H
3.33 +0.05 n, y, L, z
3.25 +0.06 b, K
3.25 -2.79 w, k, G
3.25 -0.84 c, C, z, P,
3.16 +0.03 b, O, y, E/F
2.95 -0.42 e, h, j, y, N
2.60 -0.53 c, z, M′
1.94 +0.21 f, d, r, u
1.88 +0.15 k, p
t
s
m
d
m
m
s
m
s
s
L-y
M-w
M′-z
N-y
P-z
s
s
0.18 -3.41 n, M
-0.13 -3.50 v, M′
a
1H NMR data acquired from AMX-600; assignments were
b
based on both 2D ROESY and COSY experiments. ∆δ ) δ (dimer
9) - δ (model monomer 7). c NH protons observed at -2.155 (br),
-4.247 (br), -2.834 (s), and -4.348 (s) ppm were not shown.
formation clearly appeared in their optical spectra (Fig-
ure 13). Interestingly, in developing the preparative TLC
plates, porphyrin 18 and 19 were often partially meta-
lated to give their zinc complexes 20 and 21, respectively.
Thus, the structures of these porphyrins as zinc complex
were confirmed by NMR and HRMS analyses (calcd
830.2810 for C50H46N4O4Zn 20, found 830.2769; calcd
828.2654 for C50H44N4O4Zn 21, found 828.2610). For
example, the resonances from 1H NMR spectrum of
aromatized porphyrin 21 were assigned on the basis of
NOE connectivities observed by performing the 2D-
ROESY experiment in DMSO-d8 (Figure 14). Thus,
similar to what happened to dimer 6, the formation of
porphyrins 18 and 19 also involves an intramolecular [4
+ 2] cycloaddition followed by an acid-catalyzed dehydra-
tion and an auto-oxidation, which serves as more evi-
(20) 4,4′-Bischloromethylbiphenyl was generously supplied by Dr.
Subramaniam, Department of Chemistry, Penn State University.
(21) Scheidt, W. R.; Lee, Y. J . Structure Bonding 1987, 64, 1-70.
(22) Kalisch, W. W.; Senge, M. O.; Ruhlandtsenge, K. Photochem.
Photobiol. 1998, 67, 312-323.

552 J . Org. Chem., Vol. 65, No. 2, 2000
Zheng et al.
F igu r e 9. 1H NMR spectrum of chlorin-spirochlorin dimer 9: expanded region showing all NH protons. (one proton each from
two chlorin subunits (W and X) show significant upfield shifts).
mimic the ring A-ring A interaction found in the
crystallographic special pairs that are strategically placed
by the surrounding photosynthetic reaction center protein
matrix.
Con clu sion s
In conclusion, the new class of dimeric systems dis-
cussed here are the first examples of chlorin-spirochlorin
and porphyrin-spirochlorin dimers. The Wittig/Diels-
Alder approach discussed here has great potential for
designing a reasonable model to study the special pair
which includes two chlorin macrocycles in close proxim-
ity. The modeling studies indicate that similar to the
bacterial reaction center, which consists of a bacterio-
chlorophyll dimer with partial overlap, the spirochloin-
chlorin dimer 9 also demonstrates a partial overlap in
the ring A area. These findings are very exciting because
such close proximity of the two components of a pair
should produce models worthy of investigation. This
method also provides a unique opportunity to construct
various porphyrin-based dimers, such as chlorin-chlorin,
porphyrin-chlorin, bacteriochlorin-chlorin, and bacte-
riochlorin-bacteriochlorin dimers linked with spacers of
variable distances and geometries. By using appropriate
reagents, this methodology can also be used for the
preparation of various conjugated porphyrins linked at
the peripheral position(s) with a varity of aromatic
systems, which are otherwise difficult to synthesize. The
photophysical properties of dimer 9 and the related
F igu r e 10. Top and side views of the special pair (black line)
and dimer 9 (gray line).
compounds are currently in progress and will be pub-
lished elsewhere.
ring as found for the ring A-ring A interaction in the
special pairs, the data in Table 2 revealed that our model
dimer 9, indeed, possesses a very similar relative orien-
tation and overlap of pyrrole rings to that found in the
crystallographic special pairs (Figure 10). All parameters,
mean plane separation distance, center-center distance,
lateral shift, slip angle, and dihedral angle, are close to
the values obtained form the crystal structure of special
pairs, while protein data bank id-1pcr is the closest to
our model dimer 9. Thus, it is evident that ring A of
spirochlorin and ring C of chlorin in our model dimer 9
Exp er im en ta l Section
Reagents were purchased from Aldrich, Lancaster, and
Porphyrin Products and used without further purification.
Reactions were monitored spectrophotometrically and/or by
analytical thin-layer chromatography using 250 mm Whatman
precoated silica gel plates. Mass spectral analyses was per-
formed at the department of Molecular and Cellular Biophys-
ics, RPCI, Buffalo, and at the University of Michigan, East
Lansing. Where necessary, solvents were dried before use.
Sep a r a tion of th e Mixtu r e of P h otop r otop or p h yr in IX
in to In d ivid u a l Isom er s 3 a n d 4. Photoprotoporphyrin IX

Wittig Reactions on Photoprotoporphyrin IX
J . Org. Chem., Vol. 65, No. 2, 2000 553
F igu r e 11. Transformation of chlorin-spirochlorin dimer 9 to porphyrin-spirochlorin dimer 16 observed in 1H NMR spectrum.
1
yield. Mp: >300 °C. H NMR (400 MHz, 3.0 mg/mL CDCl3, δ
ppm): 9.62 (s, 1H, 20-H); 9.60 (s, 1H, 15-H); 8.75 (s, 1H, 10-
H); 8.53 (s, 1H, 5-H); 7.88 (dd, J ) 17.7, 11.4 Hz, 1H, 3-CHd
CH2); 7.81 (dd, J ) 14.5, 11.4 Hz, 1H, 82-H); 7.56 (d, J ) 8.4
Hz, 2H, phenyl-H); 7.43 (d, J ) 11.2 Hz, 1H, 81-H); 7.30 (d, J
) 7.7 Hz, 2H, phenyl-H); 6.99 (d, J ) 14.9 Hz, 1H, 83-H); 6.20
(d, J ) 17.7 Hz,1H, trans-3-CHdCH2); 6.04 (d, 1H, cis-3-CHd
CH2); 4.18 (m, 4H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3);
3.67 and 3.66 (each s, 3H, 13CH2CH2CO2CH3 and 17CH2CH2-
CO2CH3); 3.58 (s, 3H, 2CH3); 3.35 (s, 3H, 12CH3); 3.27 (s, 3H,
18CH3); 3.18 (t, J ) 7.9 Hz, 2H, 17CH2CH2CO2CH3); 3.12 (t,
J ) 7.7 Hz, 2H, 13CH2CH2CO2CH3); 2.46 (s, 3H, phenyl-CH3);
1.75 (s, 3H, 7CH3); -1.25 and -1.30 (each br s, 1H, 2NH). Mass
spectrum: 711.3 (100, M+ + 1). UV-vis (λmax (ꢀ) in CH2Cl2):
681 (1.01 × 104), 624 (1.92 × 103), 558 (5.52 × 103), 438 (2.94
× 104). HRMS (C44H46N4O5): M + 1 requires 711.3547, found
711.3533.
7-Dem eth yl-8-d efor m ylvin yl-72-(p-m eth yl)p h en yl-71,72-
d ih yd r oben zop r otop or p h yr in IX Dim eth yl Ester (14).
Chlorin 11 (35 mg) was refluxed in o-dichlorobenzene (30 mL)
under a nitrogen atmosphere at 170 °C for 2 h. The reaction
mixture was passed through the silica column (eluted with
petroleum ether) to remove the o-dichlorobenzene. The crude
product was further chromatographed on a silica column with
2% acetone/dichloromethane. After evaporation of the solvents,
the residue was crystallized from dichloromethane/hexanes
and the title compound was obtained in 65% yield (22 mg).
F igu r e 12. Electronic absorption spectra (in CH2Cl2) of dimer
9 (s) and dimer 16 (-‚-).
as an isomeric mixture was obtained by following the method
reported by Inhoffen et al.17b The individual isomers: isomer
A (3)) (8-vinyl analogue) and isomer B (4) (3-vinyl analogue)
were separated by repeated column chromatography on silica
gel 60 eluting with the gradient acetone/CH2Cl2 solvent system
(5-12% v/v). For our studies, isomer A (3) was used as a
substrate. Mp of 3: 225-227 °C (lit.17b mp 222-223 °C). 1H
NMR of 3 (400 MHz, 3 mg/1 mL CDCl3, δ ppm): 10.23
(splitting s, 1H, CHO); 9.78, 9.70, 8.70, 8.15 (each s, 1H, 5H,
10H, 15H and 20H); 7.75 (dd, 1H, 3-CHdCH2); 6.85 (d, 1H,
81-H); 6.17 (d, 1H, trans-3CHdCH2); 6.10 (d, 1H, cis-3-CHd
CH2); 4.30 (m, 4H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3);
3.69 and 3.67 (each s, 3H, 13CH2CH2CO2CH3 and 17CH2CH2-
CO2CH3); 3.62, 3.49 and 3.46 (each s, 3H, 2CH3, 12CH3 and
18CH3); 2.75 (two t, 4H, 17CH2CH2CO2CH3 and 13CH2CH2-
CO2-CH3); 1.47 (s, 3H, 7CH3); -0.35 and -0.70 (each br s, 1H,
2NH). UV-vis (λmax (ꢀ) in CH2Cl2) 669 (2.60 × 104), 612 (5.65
× 103), 567 (9.75 × 103), 429 (6.51 × 104), 390 (5.34 × 104).
8-Defor m ylvin yl-8-[83-(p-m eth yl)p h en yl]d ien ylp h oto-
p r otop or p h yr in IX Dim eth yl Ester (11). p-Methylbenzyl-
bromide (226 mg, 1.22 mmol) dissolved in CHCl3 (40 mL) was
treated with triphenyl phosphine (711 mg, 2.71 mmol) at
refluxing temperature for 3 h. The Wittig reagent so obtained
was reacted with photoprotoporphyrin IX isomer A 3 (200 mg,
0.32 mmol) at room temperature in the presence of DBU (1
mL) to afford 205 mg (0.29 mmol) of model chlorin 11 in 90%
1
Mp: >300 °C. H NMR (400 MHz, 3.0 mg/mL CDCl3, δ ppm):
10.10, 10.09, 10.04 and 10.02 (each s, 1H, 5-H, 10-H, 15-H and
20-H); 8.22 (d, J ) 9.7 Hz, 1H, 74-H); 8.19 (dd, J ) 18.0, 11.4
Hz, 1H, 3-CH)CH2); 7.54 (d, J ) 7.9 Hz, 2H, phenyl-H); 7.21
(d, J ) 7.9 Hz, 2H, phenyl-H); 6.66 (d, J ) 9.5 Hz, 1H, 73-H);
6.31 (d, J ) 17.7 Hz, 1H, trans-3CHdCH2); 6.12 (d, J ) 11.7
Hz, 1H, cis-3-CHdCH2); 4.65 and 4.33 (each m, 1H, 2 × 71-
H); 4.55 (m, 1H, 72-H); 4.43 and 4.38 (each t, 2H, 13CH2CH2-
CO2CH3 and 17CH2CH2CO2CH3); 3.69 (s, 3H, 1 × ring CH3);
3.67 (s, 6H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.65
and 3.61 (each s, 3H, 2 × ring CH3); 3.30 and 3.29 (each t, J
) 8.0 Hz, 2H, 17CH2CH2CO2CH3 and 13CH2CH2CO2CH3); 2.38
(s, 3H, phenyl-CH3); -0.30 (br s, 2H, 2NH). UV-vis (λmax (ꢀ)
in CH2Cl2): 633 (3.61 × 103), 578 (4.12 × 103), 543 (7.46 ×
103), 507 (9.23 × 103), 408 (4.39 × 104). Mass spectrum: 693.3
(100, M+ + 1). HRMS (C44H43N4O4): M + 1 requires 693.3441,
found 693.3409.
2′,2′′-Bis(8-d efor m ylvin yl-8-d ien ylp h otop r otop or p h y-
r in IX d im eth yl ester )-1′,1′′-bip h en yl (6). Following the

554 J . Org. Chem., Vol. 65, No. 2, 2000
Zheng et al.
Sch em e 6. 8-[82-(9′-P h en a n th r en e)]vin ylp r otop or p h yr in via In tr a m olecu la r Diels-Ald er Cycloa d d ition
8.92 and 8.78 (splitting s, 1H, 10-H); 8.69 and 8.50 (splitting
s, 1H, 5-H); 7.89 (dd, J ) 18.0, 11.2 Hz, 1H, 3-CHdCH2); 7.66
(dd, J ) 11.6, 7.2 Hz, 1H, 82-H); 7.56-7.33 (each d or dd, total
8H, biphenyl-H); 7.29 (splitting d, 3H, 81-H); 6.84 and 6.78
(splitting d, J ) 15.8 Hz, 1H, 83-H); 6.20 and 6.18 (splitting d,
J ) 18.0 Hz,1H, trans-3CHdCH2); 6.05 and 6.04 (splitting d,
J ) 11.2 Hz, 1H, cis-3-CHdCH2); 4.25 and 4.15 (each m, 4H,
13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.67 and 3.66
(each s, 3H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.57
and 3.56 (splitting s, 3H, 2CH3); 3.39 and 3.38 (s, 3H, 12CH3);
3.30 (s, 3H, 18CH3); 3.18 and 3.13 (each t, J ) 7.6 Hz, 2H,
17CH2CH2CO2CH3 and 13CH2CH2CO2CH3); 2.32 and 2.22
(splitting s, 3H, biphenyl-CH3); 1.88 and 1.75 (splitting s, 3H,
7CH3); -1.15, -1.24, -1.26 and -1.35 (each splitting br s, 1H,
2N-H). (Note: all splitting peaks are in a ratio of 1:1). Mp:
>300 °C. UV-vis (λmax (ꢀ) in CH2Cl2): 681 (1.56 × 104), 624
F igu r e 13. Electronic absorption spectra (in CH2Cl2) of
(5.42 × 103), 561 (8.66 × 103), 435 (3.91 × 104), 408 (4.5 ×
chlorin 7 (-) and the Related porphyrin 19 (- - -).
104). Mass: 787.3 (100, M+ + 1, bp). HRMS (C50H50N4O5):
methodology discussed for the preparation of model chlorin
11, bis-phosphonium salt 5 was obtained by reacting 2,2-
dibromobisphenyl (35 mg, 0.05 mmol) and condensed with
chlorin 3 (50 mg, 0.10 mmol), dissolved in dichloromethane.
requires 786.3781, found 786.3749.
1H NMR (400 MHz, 3 mg/mL in DMSO-d6, all δ values are
relative to the CH2Cl2 which is 5.30 ppm): 9.40, 9.30, 9.11 and
8.90 (each s, 1H, 5-H, 10-H, 15-H and 20-H); 7.83 (dd, J )
The 2,2-bis-chlorin 6 was isolated in 60% yield (42 mg, 0.03
18.6, 11.5 Hz, 1H, 3-CHdCH2); 7.78 and 7.63 (each d, J ) 8.4
1
mmol). Mp: >300 °C. H NMR (400 MHz, 3.0 mg/mL CDCl3,
Hz, 1H, 2 × biphenyl-H); 7.22-7.20 (total 8H, 6 × biphenyl-H
δ ppm): 9.77, 9.76, 9.69, 9.67, 9.48, 9.17, 9.13 and 8.89 (each
and 81-H and 82-H); 6.44 (splitting d, J ) 15.6 Hz, 1H, 83-H);
s, 1H, 2 × (5H, 10H, 15H, 20H)); 8.36-7.16 (each d or dd, total
5.98 (d, J ) 18.6 Hz,1H, trans-3CHdCH2); 5.75 (d, J ) 11.5
14H, 2 × (81-, 82- and 83-H) and 8H from biphenyl); 8.04 and
Hz, 1H, cis-3-CHdCH2); 3.83 and 3.67 (each t, J ) 7.5 Hz,
7.94 (each dd, J ) 17.4, 10.8 Hz, 1H, 2 × 3CHdCH2); 6.21
2H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.21, 3.13,
and 6.10 (each d, J ) 17.4 Hz, 1H, 2 x trans-3CHdCH2); 6.02
and 5.90 (each d, J ) 10.8 Hz, 1H, 2 x cis-3-CHdCH2); 4.62-
3.11, 3.03 and 2.94 (each s, 3H, 13CH2CH2CO2-CH3,17CH2CH2-
CO2CH3, 2 CH3, 12 CH3 and 18CH3); 2.77 and 2.71 (each t, J
4.06 (each m, total 8H, 2 × 13CH2CH2CO2CH3 and 2 × 17CH2-
) 7.6 Hz, 2H, 17CH2CH2CO2CH3 and 13CH2CH2CO2CH3); 2.07
CH2CO2CH3); 3.69, 3.65, 3.64, 3.60, 3.56, 3.53, 3.49, 3.44, 3.43
and 3.34 (each s, 3H, 10 CH3); 3.25, 3.20, 3.06 and 2.72 (each
(s, 3H, biphenyl-CH3); 1.66 (s, 3H, 7CH3); 0.49 and 0.42 (each
br s, 1H, 2NH).
1H NMR (400 MHz, 303 K, 3.0 mg/mL dioxane-d6, δ ppm
m, 2H, 2 × 17CH2CH2CO2CH3 and 2 × 13CH2CH2CO2CH3);
2.17 (s, 6H, 2 × 7CH3); -1.36, -1.59 and -1.73 (each br s,
total 4H, 2 × 2N-H). Mass spectrum: 1391.8 (100, M+). UV-
vis (λmax (ꢀ) in CH2Cl2): 663 (2.04 × 105), 540 (5.00 × 103), 504
(7.36 × 103), 390 (6.72 × 104). HRMS (C86H87N8O10): requires
1391.6550, found 1391.6540.
relative to CHCl3: 7.26 ppm): 9.68, 9.60 (each s, 1H, 2 × meso-
H); 9.323 and 9.316 (splitting s, 1H, 1 × meso-H); 9.048 and
9.037 (splitting s, 1H, 1 × meso-H); 8.38 and 8.34 (dd, J )
11.3, 6.8 Hz, 1H, 82-H); 8.10 (dd, J ) 18.0, 12.0 Hz, 1H, 3-CHd
CH2); 7.85 (splitting d, J ) 11 Hz, 1H, 81-H); 7.97, 7.41, 7.31
and 7.23 (each t, J ) 7.4 Hz, 1H, 4 × biphenyl-H); 7.28, 7.25,
7.16 and 7.13 (each d, J ) 8.2 Hz, 1H, 4 × biphenyl-H); 6.73
(splitting d, J ) 15.8 Hz, 1H, 83-H); 6.25 (d, J ) 18.0 Hz,1H,
trans-3CHdCH2); 5.99 (d, J ) 12.0 Hz, 1H, cis-3-CHdCH2);
2′′-Meth yl-2′-(8-d efor m ylvin yl-8-d ien yl-p h otop r otop or -
p h yr in IX d im eth yl ester )-1′,1′′-bip h en yl (7). The title
1
chlorin was isolated as a byproduct in 20% yield (15 mg). H
NMR (400 MHz, 3.0 mg/ mL CDCl3, δ ppm): 9.637 and 9.634
(splitting s, 1H, 20-H); 9.62 and 9.61 (splitting s, 1H, 15-H);

Wittig Reactions on Photoprotoporphyrin IX
J . Org. Chem., Vol. 65, No. 2, 2000 555
F igu r e 14. 1H NMR spectrum of porphyrin 21 [only the downfield region (δ 7.0-10.3 ppm) is shown].
Sch em e 7. Con ju ga ted Ch lor in Dim er 25 a n d Rela ted Mon om er 26 fr om Ch lor in 3
4.18 and 4.00 (each m, 2H, 13CH2CH2CO2CH3 and 17CH2CH2-
CO2CH3); 3.45 (s, 6H, 13CH2CH2CO2CH3 and 17CH2CH2-
CO2CH3); 3.43, 3.39 and 3.23 (each s, 3H, 3 × ring CH3); 3.10
and 3.02 (each t, J ) 7.6 Hz, 2H, 17CH2CH2CO2CH3 and
13CH2CH2CO2CH3); 2.05 (s, 6H, biphenyl-CH3 and 7CH3);
-2.50 and -2.58 (each br s,1H, 2NH).
CO2CH3); 3.43, 3.39 and 3.23 (each s, 3H, 3 × ring CH3); 3.10
and 3.02 (each t, J ) 7.6 Hz, 2H, 17CH2CH2CO2CH3 and
13CH2CH2CO2CH3); 2.05 (s, 6H, biphenyl-CH3 and 7CH3);
-2.50 and -2.58 (each br s,1H, 2NH).
1H NMR (400 MHz, 343 K, 3.0 mg/mL dioxane-d6, δ ppm
relative to CHCl3: 7.26 ppm): 9.69, 9.60 (each s, 1H, 2 × meso-
H); 9.29 (s, 1H, 1 × meso-H); 9.039 and 9.04 (s, 1H, 1 × meso-
H); 8.35 and 8.31 (splitting dd, J ) 11.3, 6.8 Hz, 1H, 82-H);
8.09 (dd, J ) 18.0, 12.0 Hz, 1H, 3-CHdCH2); 7.85 (d, J ) 11
Hz, 1H, 81-H); 7.95 (splitting d, J ) 7.6 Hz, 1H, 1 × biphenyl-
H); 7.40, 7.31 and 7.21 (each t, J ) 7.4 Hz, 1H, 3 × biphenyl-
H); 7.28, 7.25, 7.16 and 7.12 (each d, J ) 8.2 Hz, 1H, 4 ×
biphenyl-H); 6.74 (splitting d, J ) 15.8 Hz, 1H, 83-H); 6.26
(splitting d, J ) 18.0 Hz,1H, trans-3CHdCH2); 6.01 (splitting
d, J ) 12.0 Hz, 1H, cis-3-CHdCH2); 4.20 and 4.02 (each t, J )
6.9 Hz, 2H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.49
(s, 6H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.44, 3.39
and 3.25 (each s, 3H, 3 × ring CH3); 3.12 and 3.04 (each t, J
1H NMR (400 MHz, 323 K, 3.0 mg/mL dioxane-d6, δ ppm
relative to CHCl3: 7.26 ppm): 9.67, 9.59 (each s, 1H, 2 × meso-
H); 9.301 and 9.292 (splitting s, 1H, 1 × meso-H); 9.039 and
9.033 (splitting s, 1H, 1 × meso-H); 8.36 and 8.32 (dd, J )
11.3, 6.8 Hz, 1H, 82-H); 8.09 (dd, J ) 18.0, 12.0 Hz, 1H, 3-CHd
CH2); 7.82 (splitting d, J ) 11 Hz, 1H, 81-H); 7.95, 7.40, 7.31
and 7.21 (each t, J ) 7.4 Hz, 1H, 4 × biphenyl-H); 7.28, 7.25,
7.16 and 7.12 (each d, J ) 8.2 Hz, 1H, 4 × biphenyl-H); 6.73
(splitting d, J ) 15.8 Hz, 1H, 83-H); 6.25 (d, J ) 18.0 Hz,1H,
trans-3CHdCH2); 5.99 (d, J ) 12.0 Hz, 1H, cis-3-CH)CH2);
4.19 and 4.01 (each m, 2H, 13CH2CH2CO2CH3 and 17CH2CH2-
CO2CH3); 3.46 (s, 6H, 13CH2CH2CO2CH3 and 17CH2CH2-

556 J . Org. Chem., Vol. 65, No. 2, 2000
Zheng et al.
F igu r e 15. NMR of 4′,4′′-bischlorin 25 (effect of solvents).
Ta ble 2. Geom etr ica l P a r a m eter sa for π-π In ter a ction in Sp ecia l P a ir s F ou n d in Cr ysta l Str u ctu r es a n d Syn th etic
Dim er 9
PDB
ID
tetrapyrrole macrocycle
single pyrrole ring
MPS
Ct-Ct
LS
SA
dihed
MPS
Ct- -Ct
LS
SA
dihed
1aij
1pcr
1prc
2prc
9
3.63
3.56
3.07
3.14
3.37
7.52
7.72
7.37
7.48
5.97
6.59
6.85
6.70
6.79
4.92
61.1
62.5
65.4
65.2
55.6
9.6
5.7
11.1
11.3
3.0
3.58
3.23
3.28
3.45
3.20
3.64
3.45
3.34
3.51
3.52
0.69
1.21
0.64
0.66
1.44
10.8
20.5
11.0
10.8
24.2
5.2
5.8
5.1
1.0
7.0
a
Key: MPS, mean plane separation distance; ct-ct, distance between two centers; LS, lateral shift of two planes; SA, slip angle;
dihed, angle between two planes. For a completely overlaped ring system, MPS ) Ct-Ct and LS ) SA ) dihed)0 (see method for definition).
) 7.6 Hz, 2H, 17CH2CH2CO2CH3 and 13CH2CH2CO2CH3); 2.07
(s, 6H, biphenyl-CH3 and 7CH3); -2.43 (br s, 2H, 2NH).
requires 1373.6440, found 1373.6520. 1H NMR (400 MHz, 3
mg/1 mL CDCl3, δ ppm): see Table 1.
2′-(8-Defor m ylvin yl-8-d ien yl-p h otop r otop or p h yr in IX
d im eth yl ester )-1′,1′′-bip h en yl (8). 2-Phenylbenzylbromide
(170 mg, 0.70 mmol) dissolved in chloroform (40 mL) was
treated with triphenyl phosphine (320 mg, 1.2 mmol) at
refluxing temperature for 24 h. The Wittig reagent obtained
after removal of chloroform was redissolved in dichloromethane
(30 mL) and reacted with photoprotoporphyrin IX isomer A
(3) (60 mg, 0.1 mmol) at room temperature in the presence of
DBU (0.75 mL) to afford the title compound in 80% yield (62
P or p h yr in -Ch lor in Dim er (16). This dimer was formed
upon leaving the NMR sample of 9 in CDCl3 (without pyridine)
at room temperature for an extended period of time. Mp: >300
°C. 1H NMR (400 MHz, 3.0 mg/mL CDCl3, δ ppm): 10.41,
10.13, 10.07, 9.98, 9.86, 9.62, 9.28 and 7.49 (each s, 1H, 2 ×
(5H, 10H, 15H, 20H)); 8.18 and 8.09 (each dd, J ) 17.9, 11.8
Hz, 1H, 2 × 3-CHdCH2); total 13 bridge protons [8.37 (d, J )
8.0 Hz, 1H); 7.98 (d, J ) 8.0 Hz, 1H); 7.60 (t, 1H); 7.48 (dd, J
) 7.5 Hz, 1H); 7.33 (d, J ) 9.9 Hz, 1H); 7.19 (d, J ) 7.6 Hz,
1H); 6.79 (d, J ) 7.8 Hz, 1H); 6.36 (d, J ) 8.0 Hz, 1H); 5.91 (d,
J ) 8.0 Hz, 1H); 5.86 (d, J ) 9.9 Hz, 1H); 5.77 (d, J ) 8.0 Hz,
1H); 4.91 (d, J ) 14.0 Hz, 1H); 3.97 (d, J ) 13.8 Hz, 1H)]; 6.40
and 6.19 (each d, J ) 17.9 Hz, 1H, 2 × trans-3CHdCH2); 6.12
and 5.94 (each d, J ) 11.8 Hz, 1H, 2 × cis-3-CHdCH2); 4.47,
4.34 and 4.18 (each t, total 6H, 3 × CH2CH2CO2CH3); 3.68 (s
and t merged, 8H, 2 × CH3 and 1 × CH2CH2CO2-CH3); 3.73,
3.71, 3.64, 3.47, 3.20, 3.10, 2.62, 2.26, 1.81 and 1.45 (each s,
3H, 10 x CH3); 3.30, 3.24, 3.14 and 2.62 (each t, 2H, 2 ×
17CH2CH2CO2CH3 and 2 × 13CH2CH2CO2-CH3); 2.17 (s, 6H,
2 × 7CH3); -0.40, -1.21 and -1.73 (each br s, total 4H, 2 ×
2N-H). UV-vis (CH2Cl2): 664 (1.17 × 104), 628 (1.37 × 103),
574 (2.30 × 103), 538 (5.18 × 103), 505 (5.95 × 103), 409 (5.31
× 104). Mass: 1373.8 (100, M+, bp). HRMS: C86H85N8O9
requires 1373.6440, found 1373.6446.
8-Devin yl-8-[82-(9′, 10′-d ih yd r op h en a n t h r en e)]vin yl-
p r otop or p h yr in IX Dim eth yl Ester (18) a n d th e Rela ted
P h en a n th er en e An a logu e (19). Chlorin 7 was found to be
unstable in CDCl3 if left for an extended period of time and
converted into porphyrin 18, which on further oxidation
produced an aromatized phenanthrene linked porphyrin 19.
The separation of these two porphyrins in their free base form
were not successful; however, they were separated into indi-
vidual analogues as the related Zn(II) complexes 20 and 21,
respectively. UV-vis spectrum in dichloromethane (mixture
of 18 and 19): 633 (1.44 × 103), 576 (2.00 × 103), 543 (3.22 ×
103), 507 (3.41 × 103), 408 (3.88 × 104). Mass spectrum: 767.3
1
mg). Mp: >300 °C. H NMR (400 MHz, 3.0 mg/mL CDCl3, δ
ppm): 9.72 (s, 1H, 20-H); 9.57 (s, 1H, 15-H); 8.79 (s, 1H, 10-
H); 8.50 (s, 1H, 5-H); 8.07 (dd, J ) 18.1, 11.6 Hz, 1H, 3-CHd
CH2); 7.97 (d, J ) 8.1 Hz, 1H, 1 × biphenyl-H); 7.96 (dd, J )
15.7, 11.6 Hz, 1H, 82-H); 7.59 (m, total 8H, 6 × biphenyl-H);
7.45 (m, 2H, 2 × biphenyl-H); 7.38 (d, J ) 11.4 Hz, 3H, 81-H);
7.07 (d, J ) 15.5 Hz, 1H, 83-H); 6.31 (d, J ) 18.1 Hz,1H, trans-
3-CHdCH2); 6.13 (d, J ) 11.6 Hz, 1H, cis-3-CHdCH2); 4.23
and 4.08 (each m, 2H, 13CH2CH2CO2CH3 and 17CH2CH2CO2-
CH3); 3.67 and 3.66 (each s, 3H, 13CH2CH2CO2CH3 and 17CH2-
CH2CO2CH3); 3.44, 3.31 and 3.30 (each s, 3H, 2CH3, 12CH3
and 18CH3); 3.16 and 3.10 (each t, J ) 7.9 Hz, 2H, 17CH2CH2-
CO2CH3 and 13CH2CH2CO2CH3); 1.85 (s, 3H, 7CH3); -1.00
and -1.20 (each br s, 1H, 2NH). UV-vis (λmax (ꢀ) in CH2Cl2):
678 (1.52 × 104), 621 (2.06 × 103), 558 (8.20 × 103), 435 (4.20
×
104). Mass spectrum: 773.8 (100, M+
(C49H48N4O5): requires 772.3623, found 772.3614.
+ 1). HRMS
Sp ir och lor in -Ch lor in Dim er (9). The bischlorin 6 was
found to be unstable if the reaction was left for a longer period
of time and slowly converted into an unexpected chlorin-
spirochlorin dimer linked via a tetrahydrobenzophenanthrene
bridge 9. The rate of this transformation was found to be
dependent on the reaction conditions used. Mp: >300 °C. UV-
vis spectrum in dichloromethane: 664 (1.77 × 104), 613 (1.78
× 103), 504 (4.46 × 103), 388 (5.55 × 104). Mass spectrum:
1391.8 (100, M+, bp), 1373.7 (30, M+, H2O). HRMS: C86H87N8O10
requires 1391.6550, found 1391.6540; C86H87N8O10 - H2O

Wittig Reactions on Photoprotoporphyrin IX
J . Org. Chem., Vol. 65, No. 2, 2000 557
(100, M+ + 1) for C50H46N4O4‚Zn(II). 8-Devin yl-8-[82-(9′,10′-
d ih yd r op h en a n t h r en e)]vin ylp r ot op or p h yr in IX Di-
m eth yl ester (20): 1H NMR (400 MHz, 3.0 mg/ mL CDCl3, δ
ppm): 9.70, 9.68, 9.56 and 9.55 (each s, 1H, 5-H, 10-H, 15-H
and 20-H); 8.11 (dd, J ) 17.6, 11.1 Hz, 1H, 3-CHdCH2); 8.02-
7.39 (total 8H, 1′, 2′, 3′, 4′, 5′, 6′, 7′ and 8′-H); 7.83 (d, J ) 15.3
Hz, 1H, 81-H); 6.88 (dd, J ) 16.1, 8.8 Hz, 1H, 82-H); 6.25 (d, J
) 17.6 Hz,1H, trans-3CHdCH2); 6.11 (d, J ) 11.1 Hz, 1H, cis-
3-CHdCH2); 4.86 and 4.23 (each t, J ) 6.5 Hz, 2H, 13CH2-
CH2CO2CH3 and 17CH2CH2CO2CH3); 4.32(dd and t merged,
J ) 9.9, 5.9 Hz, 3H, 9′-H and 2 × 10′-H); 3.67 and 3.65 (each
s, 3H, 13CH2CH2CO2CH3 and 17CH2CH2-CO2CH3); 3.54, 3.48,
3.46 and 3.41 (each s, 3H, 4 x ring CH3); 3.16 and 3.14 (each
t, J ) 8.8 Hz, 2H, 17CH2CH2CO2CH3 and 13CH2CH2CO2CH3).
Mass spectrum: 830.4 (100, M+, bp). HRMS: C50H46N4O4Zn
requires: 830.2810, found 830.2769.
1H NMR (400 MHz, 3 mg/1 mL THF-d4, δ value relative to
CH2Cl2: 5.30 ppm): 9.62 and 9.61 (each s, 2H, 2 × 15-H and
2 × 20-H); 9.31 and 9.20 (each s, 2H, 2 × 5-H and 2 × 10-H);
8.45 (dd, J ) 15.5, 11.9 Hz, 2H, 2 × 82-H); 8.09 (dd, J ) 17.5,
11.4 Hz, 2H, 2 × 3-CHdCH2); 8.03 (d, J ) 11.4 Hz, 2H, 2 ×
81-H); 7.67 (s, 8H, 8 × biphenyl-H); 7.06 (d, J ) 15.9 Hz, 2H,
2 × 83-H); 6.20 (d, J ) 17.5 Hz, 2H, 2 × trans-3-CHdCH2);
5.93 (d, J ) 11.4 Hz, 2H, 2 x cis-3-CHdCH2); 4.17 and 3.98
(each m, 4H, 2 × 13CH2CH2CO2CH3 and 2 × 17CH2CH2CO2-
CH3); 3.48, 3.41, 3.40, 3.32 and 3.23 (each s, 6H, 2 ×
13CH2CH2CO2-CH3, 2 × 17CH2CH2CO2CH3, 2 × 2CH3, 2 ×
12CH3 and 2 × 18CH3); 3.06 and 2.97 (each t, J ) 7.9 Hz, 2H,
17CH2CH2CO2CH3 and 13CH2CH2CO2CH3); 2.01 (s, 6H, 2 ×
7CH3). (Note: the NH resonances were not identified.)
4′′-Meth yl-4′-(8-d efor m ylvin yl-8-d ien ylp h otop r otop or -
p h yr in IX d im et h yl est er )-1′,1′′-b ip h en yl (26). 1H NMR
(400 MHz, 3.0 mg/mL CDCl3, δ ppm): 9.57, 9.51 and 8.36 (each
s, 1H, 3 × Meso-H); 8.03 and 8.02 (splitting s, 1H, 1 × Meso-
H); 7.74-6.83 (m, total 12H, 3-CHdCH2, 8 × biphenyl-H, 81-
H, 82-H and 83-H); 6.12 (d, J ) 18.1 Hz,1H, trans-3-CHdCH2);
6.01 (d, J ) 11.6 Hz, 1H, cis-3-CHdCH2); 4.25 and 4.15 (each
m, 2H, 13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.70, 3.68,
3.52, 3.24 and 3.17 (each s, 3H, 13CH2CH2CO2-CH3,17CH2CH2-
CO2CH3, 2CH3, 12CH3 and 18CH3); 3.19 and 3.11 (each t, J )
7.9 Hz, 2H, 17CH2CH2CO2CH3 and 13CH2CH2CO2CH3); 2.47
(s, 3H, biphenyl-CH3); 1.56 (s, 3H, 7CH3); -0.82 and -0.98
(each br s, 1H, 2NH). Mp: >300 °C. UV-vis (in CH2Cl2): 681
(1.76 × 104), 624 (2.92 × 103), 561 (9.38 × 103), 444 (4.80 ×
104). Mass: 788.4 (100, M+ + 2, bp) for C50H50N4O5.
Zn (II) 8-d evin yl-8-[82-(9′-p h en a n t h r en e)]vin ylp r ot o-
1
p or p h yr in IX d im eth yl ester (21): H NMR (400 MHz, 3.0
mg/mL CDCl3, δ ppm): 9.52 (s, 1H, 10-H); 9.51 (s, 1H, 5-H);
9.36 (s, 1H, 20-H); 9.32 (s, 1H, 15-H); 8.91 (d, 1H, 4′-H); 8.84
(d, 1H, 5′-H); 8.57 (d, 1H, 8′-H); 8.44 (s, 1H, 10′-H); 8.39 (d,
1H, 81-H); 8.22 (d, 1H, 1′-H); 8.13 (d, 1H, 82-H); 8.12 (dd, 1H,
3-CHdCH2); 7.79 (m, 4H, for 2′, 3′, 6′ and 7′-H); 6.30 (d, J )
18.1 Hz,1H, trans-3CHdCH2); 6.16 (d, J ) 11.6 Hz, 1H, cis-
3-CHdCH2); 4.21 (m, 4H, 13CH2-CH2CO2CH3 and 17CH2CH2-
CO2CH3); 3.67 (s, 6H, 13CH2CH2CO2CH3 and 17CH2CH2-CO2-
CH3); 3.52 (s, 3H, 2CH3); 3.51 (s, 3H, 7CH3); 3.43 (s, 3H,
12CH3); 3.38 (s, 3H, 18CH3); 3.10 (m, 4H, 17CH2CH2CO2CH3
and 13CH2CH2CO2CH3). Mass spectrum: 828.4 (100, M+, bp).
HRMS: C50H44N4O4Zn requires 828.2654, found 828.2610.
1H NMR (400 MHz, 3.0 mg/ mL DMSO-d8, δ ppm): 10.40,
10.32, 10.17 and 10.08 (each s, 1H, 5-H, 10-H, 15-H and 20-
H); 9.10 (d, J ) 15.8 Hz, 1H, 81-H); 9.04 (d, 1H, 4′-H); 8.95 (d,
1H, 5′-H); 8.80 (s, 1H, 10′-H); 8.76 (d, 1H, 8′-H); 8.58 (d, J )
15.8 Hz, 1H, 82-H); 8.56 (dd, J ) 17.9, 11.5 Hz, 1H, 3-CHd
CH2); 8.30 (d, 1H, 1′-H); 7.85 and 7.78 (each m, 2H, for 2′, 3′,
6′ and 7′-H); 6.43 (d, J ) 17.9 Hz,1H, trans-3-CHdCH2); 6.16
(d, J ) 11.6 Hz, 1H, cis-3-CHdCH2); 4.38 (t, 4H, 13CH2CH2-
CO2CH3 and 17CH2CH2CO2CH3); 3.95 and 3.78 (each s, 3H,
13CH2CH2CO2CH3 and 17CH2CH2CO2CH3); 3.65 and 3.64
(each s, 3H, 2 × ring CH3); 3.60 (s, 6H, 2 × ring CH3); ∼3.29
(m, 4H, 17CH2CH2CO2CH3 and 13CH2CH2CO2CH3).
Rea ction of P h otop r otop or p h yr in IX 3 w ith th e Wittig
R ea gen t Der ived fr om 4,4′-Bis(ch lor om et h yl)-1,1′-b i-
p h en yl (22). 4,4′-Bis(chloromethyl)-1,1′-biphenyl 22 (30 mg,
0.12 mmol) dissolved in DMF (15 mL) along with triphenyl
phosphine (150 mg, 0.57 mmol). The reaction mixture was
stirred at refluxing temperature for 24 h under a nitrogen
atmosphere. The Wittig reagent so obtained, 23, was reacted
with photoprotoporphyrin IX isomer A 3 (160 mg, 0.26 mmol)
at room temperature in the presence of DBU (1 mL) to afford
84 mg (yield, 25%) of bischlorin 25 and monomer 26 in 40%
yield, 40% (38 mg).
Molecu la r Mod elin g. Mod el Str u ctu r e of Sp ir och lo-
r in -Ch lor in Dim er 9. Starting from the crystallographic
coordinate,19 the energy optimization was performed using the
stand SYBYL force field parameters with Del Re σ and Huckel
π charges using the molecular modeling package SYBYL 6.2
running on Silicon Graphics Indigo 2 (R10000).
Geom etr ica l P a r a m eter s. Geometrical parameters de-
scribing the π-π interactions in porphyrin derivatives are
described in Scheidt and Lee.21 All 24 atoms of the core
macrocyclic rings are used to define the best plane. The center
of the core macrocyclic rings is defined as a centroid of four
pyrrole nitrogens. The mean plane separation (MPS) is
measured as an average of two perpendicular distances from
the centroids to opposing best planes. The lateral shift (LS) is
an average of two projections of a vector connecting two centers
onto the best planes. The slip angle (SA) is an average of the
angles between the vector connecting two centers and the
vectors from the centers to opposing best planes. The dihedral
angle is the angle between the best planes. Similar parameters
were created for a measure of the single pyrrole ring overlap.
All five atoms in a specified pyrrole ring were used to define
the best plane and the centroid for this case. All calculations
were performed with the SYBYL 6.2 package. In addition to
our model dimer 9, several special pair coordinates, obtained
from the crystallographic coordinates of photosynthetic reac-
tion centers (Protein Data Bank ID codes, 1aig, 1aij, 1pcr, 1pss,
1yst, 2rcr, 4rcr, 1pcr, 2pcr, 3pcr, 4pcr, 5pcr, 6pcr, 7pcr) were
included in our calculations.
4′,4′′-Bis(8-d efor m ylvin yl-8-d ien yl-p h ot op r ot op or p h -
r in IX d im eth yl ester )-1′,1′′-bip h en yl (25): 1H NMR (400
MHz, 3.0 mg/mL CDCl3, δ ppm): 9.58 (s, 1H, 20-H); 9.10 (s,
1H, 15-H); 9.00 (br s, 1H, 5-H); 8.6 (s, 1H, 10-H); 8.15 (dd, J )
18.1, 11.6 Hz, 2H, 2 × 3-CHdCH2); 8.15 (dd, J ) 15.5, 11.9
Hz, 2H, 2 × 82-H); 8.03 (d, J ) 11.4 Hz, 2H, 2 × 81-H); 7.67 (s,
8H, 8 × biphenyl-H); 7.06 (d, J ) 15.9 Hz, 2H, 2 × 83-H); 6.20
(d, J ) 17.5 Hz, 2H, 2 × trans-3CHdCH2); 5.93 (d, J ) 11.4
Hz, 2H, 2 × cis-3-CHdCH2); 4.17 and 3.98 (each m, 4H, 2 ×
13CH2CH2CO2CH3 and 2 × 17CH2CH2CO2CH3); 3.48, 3.41,
3.40, 3.32 and 3.23 (each s, 6H, 2 × 13CH2CH2CO2CH3, 2 ×
17CH2CH2CO2CH3, 2 × 2CH3, 2 × 12CH3 and 2 × 18CH3);
3.06 and 2.97 (each t, J ) 7.9 Hz, 2H, 17CH2CH2CO2CH3 and
13CH2CH2CO2CH3); 2.01 (s, 6H, 2 × 7CH3). (Note: NH
resonances were not identified). Mp: >300 °C. UV-vis (λmax
(ꢀ) in CDCl3): 681 (3.04 × 104), 624 (7.19 × 103), 570 (2.07 ×
104), 438 (6.45 × 104), 357 (2.72 × 104). Mass: 1392.1 (100,
Ack n ow led gm en t. We thank Roswell Park Alliance
Foundation for the support of this research. We ap-
preciate the help rendered by Dr. J . L. Alderfer, Mo-
lecular and Cellular Biophysics,of our institute for 2D
ROESY NMR experiments (CA 16056) and Dr. M. O.
Senge, Freie Universitate, Berlin, Germany for X-ray
analysis of spirochlorin-chlorin dimer 9. We are grateful
to by Dr. Subramaniam, Department of Chemistry,
Penn State University, for the supply of 4,4′-bischloro-
methylbiphenyl.
M+ + 1, b.) as calculated for C86H87N8O10
.
J O991254+