A novel strapped porphyrin receptor for molecular recognition

Article abstract of DOI:10.1016/S0040-4020(03)00702-6

A novel strapped porphyrin receptor Zn1, in which two electron-rich bis(p-phenylene)-34-crown ether-10 units are incorporated, has been designed and synthesized from the newly developed intermediate 7 for investigating new chemistry of molecular recognition. ¹H NMR and UV-Vis studies revealed that Zn1 displays relatively weak binding abilities to neutral electron deficient naphthalene-1,8,4,5-tetracarboxydiimide (NDI) derivatives 13 (no simple complexing stoichiometry was observed), 19 (K_a=48(±5)M^-1) and 30 (K_a=46(±5)M^-1) in chloroform-d, strong binding ability to pyridine derivative 25, (K_a=1.5(±0.12)×10³M^-1) in chloroform, moderately strong binding ability to tetracationic compound 35.4PF₆ (K_a=475(±50)M^-1) in acetone-d₆, and very strong binding affinity to compound 22 (K_a=6.5(±0.7)×10⁵M^-1), which consists of one pyridine and two NDI units, in chloroform. Remarkable cooperative effect of the intermolecular metal-ligand coordination and donor-acceptor interactions in complex Zn1.22 was observed by comparing the complexing behaviors between Zn1 and the appropriately designed guests. Complex Zn1.22 possesses an unique three-dimensional tri-site binding feature. For comparison, the complexing affinity of 1 toward compounds 13, 19, and 30 in chloroform-d and 35.4PF₆ in acetone-d₆ has also been investigated and the binding patterns in different complexes were explored. The results demonstrate that strapped porphyrin derivatives are ideal precursors for constructing new generation of three-dimensional multi-site artificial receptors for molecular recognition and host-guest chemistry.

Full text of DOI:10.1016/S0040-4020(03)00702-6

Tetrahedron 59 (2003) 4881–4889
A novel strapped porphyrin receptor for molecular recognition
*
Xue-Bin Shao, Xi-Kui Jiang, Xiao-Zhong Wang, Zhan-Ting Li and Shi-Zheng Zhu
*
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, People’s Republic of China
Received 5 March 2003; revised 21 April 2003; accepted 24 April 2003
Abstract—A novel strapped porphyrin receptor Zn1, in which two electron-rich bis(p-phenylene)-34-crown ether-10 units are incorporated,
has been designed and synthesized from the newly developed intermediate 7 for investigating new chemistry of molecular recognition. 1H
NMR and UV–Vis studies revealed that Zn1 displays relatively weak binding abilities to neutral electron deficient naphthalene-1,8,4,5-
tetracarboxydiimide (NDI) derivatives 13 (no simple complexing stoichiometry was observed), 19 (Ka¼48(^5) M21) and 30
(Ka¼46(^5) M21) in chloroform-d, strong binding ability to pyridine derivative 25, (Ka¼1.5(^0.12)£103 M21) in chloroform, moderately
strong binding ability to tetracationic compound 35·4PF6 (Ka¼475(^50) M21) in acetone-d6, and very strong binding affinity to compound
22 (Ka¼6.5(^0.7)£105 M21), which consists of one pyridine and two NDI units, in chloroform. Remarkable cooperative effect of the
intermolecular metal–ligand coordination and donor–acceptor interactions in complex Zn1·22 was observed by comparing the complexing
behaviors between Zn1 and the appropriately designed guests. Complex Zn1·22 possesses an unique three-dimensional tri-site binding
feature. For comparison, the complexing affinity of 1 toward compounds 13, 19, and 30 in chloroform-d and 35·4PF6 in acetone-d6 has also
been investigated and the binding patterns in different complexes were explored. The results demonstrate that strapped porphyrin derivatives
are ideal precursors for constructing new generation of three-dimensional multi-site artificial receptors for molecular recognition and host–
guest chemistry. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
generation of porphyrin receptors for further investigation
of multi-site molecular recognition.
An ongoing enterprise in supramolecular chemistry is the
design, synthesis, and study of abiotic receptors with
convergent recognition and/or self-assembling functionali-
ties.1 Due to their fascinating photophysical, coordination,
and geometrical properties, porphyrins are ideal building
blocks for constructing linear and planar artificial molecular
switches,2 molecular wires,3 and photosynthetic systems.4
In the past two decades, a variety of porphyrin-based
artificial receptors have also been reported, which could
strongly bind ions,5 organic molecules,6 and biological
species.7 Most reported porphyrin receptors have been
constructed from artificial meso tetraphenyl- or diphenyl
porphyrin derivatives because of their synthetic facility and
versatile modifiability. In principle, incorporating multiple
functional moieties into the meta- or ortho-positions of the
meso phenyl rings could generate three-dimensional binding
pockets for new molecular recognition chemistry. However,
examples of this kind are very limited,8,9 due to
atropisomerization of the meso functionalized phenyl
groups as a result of their rotation around the linking
carbon–carbon axis.10 We believed that efficient control of
such kind of rotation should greatly promote design of new
There are two general approaches, which can be used to
prevent atropisomerization of 5,15-diphenyl porphyrins.
The first one involves introduction of a bulky group to the
ortho-positions of the phenyl groups or the pyrrolyl
b-positions adjacent to the phenyl moieties. However,
separation of the corresponding trans- and cis-atropisomers
are usually time-consuming11 and the differentiation of the
atropisomers based on NMR spectra is difficult and
sometimes even misleading.12 The second one is to directly
connect the two opposite phenyls with an additional chain of
suitable length, which usually leads to exclusive formation
of the conformationally restricted porphyrins.13 Surpris-
ingly, although, with this approach, a range of hemoprotein
models have been developed with the strapped porphyrin
unit as a spacer and/or a binding site,14 to our knowledge,
there have been no reports of strapped porphyrin derivatives
being used as artificial receptors for investigating molecular
recognition or host–guest chemistry. We considered that
appropriately designed strapped metal porphyrins with
additional binding moieties might become novel generation
of multi-site receptors since all the additional binding units
are definitely positioned to the strap-free side and any
intermolecular porphyrin metal–ligand interaction can
occur also only from this side. In this paper, we describe
the design and synthesis of the first strapped porphyrin
receptor Zn1 of this kind, which incorporates two electron-
rich macrocyclic ether moieties, and a systematic evaluation
Keywords: porphyrin; crown ether; molecular recognition; coordination;
donor–acceptor interaction.
*
Corresponding authors. Tel.: þ86-21-6416-3300; fax: þ86-21-
64166128; e-mail: ztli@pub.sioc.ac.cn
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00702-6

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X.-B. Shao et al. / Tetrahedron 59 (2003) 4881–4889
of its binding properties toward several kinds of organic
guests.
2. Results and discussion
Different from calix[4]arenes and cyclodextrins which have
pre-organized conformations for design of efficient three-
dimensional artificial receptors, porphyrins possess a
p-conjugated planar structure which is unfavorable for
selective three-dimensional molecular recognition.
Although a number of strapped porphyrins have been
reported,13 there have been no reports in the literature for
further modifications of strapped porphyrins with additional
functional groups. Successful development of efficient
method to prepare functionalized strapped porphyrin
precursors would greatly promote the design and synthesis
of new generation of porphyrin receptors. We therefore had
proposed a general strategy to develop this kind of
porphyrin receptors by incorporating two well-studied
electron rich bis(p-phenylene)-34-crown-10 units to the
porphyrin skeleton,15 as outlined in Figure 1. We syn-
thesized compound 1 and its zinc complex Zn1 as our first
Scheme 1.
the presence of potassium carbonate to afford macrocyclic
compound 10 in 45% yield. Compound 10 was hydrolyzed
quantitatively with sodium hydroxide and the resulting
carboxylic acid was converted to 12 with oxalyl chloride.
Treatment of 12 with diol 7 in dichloromethane with
triethylamine as a base led to the formation of 1 in 73%
1
class of three-dimensional tri-site porphyrin receptor. H
NMR and UV–Vis studies have demonstrated that Zn1 is a
versatile receptor which can bind a range of neutral and
ionic guests.
Compound 1 was prepared from the reaction of two key
intermediates diol 7 and acyl chloride 12. The synthetic
route to 7 is outlined in Scheme 1. Thus, acid 2 was firstly
octylated with octyl bromide in DMF with potassium
carbonate as the base to give compound 3 in 84% yield. The
introduction of the octyl group in 3 was used to improve the
solubility of the resulting porphyrin in common organic
solvents. Compound 3 reacted with pyrrole in refluxed
toluene in the presence of a catalytic amount of p-toluene-
sulfonic acid, to afford ester 4 in 65% yield. Another
intermediate 6 was prepared in 72% yield from the reaction
of phenol 5 and 1,10-dibromodecane in DMF with
potassium carbonate as the base. Then, the key porphyrin
precursor 7 was synthesized in 7% isolated yield from the
condensation reaction of 6 with 4, with trifluoroacetic acid
as the catalyst, followed by oxidation with DDQ. The
decamethylene chain was chosen since previous investi-
gations showed that it is long enough for the porphyrin
framework to maintain its planarity.16
The synthesis of another intermediate 12 and the target
molecules 1 and Zn1 are shown in Scheme 2. Ditosylate 8
was first treated with compound 9 in refluxing acetonitrile in
Figure 1. Design scheme of strapped porphyrin receptor for multi-site
recognitions.
Scheme 2.

X.-B. Shao et al. / Tetrahedron 59 (2003) 4881–4889
4883
yield. Porphyrin 1 could be conveniently converted to its
Zn(II) complex Zn1 with zinc acetate.
Receptors 1 and Zn1 possess three electron rich moieties,
i.e. two macrocyclic ether units15f and one porphyrin unit.17
Therefore, their ability to complex the typical electron
deficient naphthalene-1,8,4,5-tetracarboxydiimide (NDI)
derivative 1318 was first examined by 1H NMR. As
expectedly, small but noticeable upfield shifts were
observed for the NDI-H signal (20.07 and 20.09 ppm) of
13 when the same ratio of 1 or Zn1 and 13 were dissolved in
chloroform-d (0.02 M) at room temperature. However, data
Scheme 4.
thesis of compound 19 and 22 are outlined in Scheme 3.
Thus, compound 17 was first prepared in 38% yield from the
unsymmetrical imidation of 14 with 15, and 16 in DMF and
subsequently treated with diacyl chloride 18 in dichloro-
methane in the presence of triethyl amine to afford
compound 19 in 72% yield. Compound 19 was then de-
protected in refluxing trifluoroacetic acid to give phenol 20
in quantitative yield. Guest 22 was obtained in 62% yield
from the Mitsunobu reaction of compounds 20 and 21.
Initially, we had prepared a compound similar to 19 but with
R2¼n-C8H17, which was found to be unusable because of its
insufficient solubility in common solvents such as chloro-
form, acetone, and methanol. The hydrogenolysis of 19 by
hydrogen gas with Pd–C as catalyst had also been attempted
but unexpectedly, 20 could not be obtained from the
reaction. Treatment of phenol 23 with 24 in DMF in the
presence of potassium carbonate afforded compound 25 in
42% yield (Scheme 4).
1
for the H NMR titration of 13 in chloroform-d, with its
NDI-H signal as the probe, with changing amounts of 1 or
Zn1 did not fit a 1:1 or 2:1 binding model well, implying
that complicated complexation modes departing from
simple stoichiometry prevailed.
Then, the complexing behaviors of Zn1 toward guests 19,
22 and 25 were investigated, with an aim of exploring the
cooperative effect of the intermolecular donor–acceptor
interaction and the zinc–pyridine coordination. The syn-
Quantitative 1H NMR binding studies of Zn1 with 19 were
first performed by diluting a 1:1 solution of Zn1 and 19 in
chloroform-d. Small but significant downfield shifts in the
1H NMR signals were observed for H-1, H-2, and H-3 of
compound 19 with the decrease in the concentration and the
plot of the Dd data of H-1 (H-2) vs [19] (¼[Zn1]) is shown
in Figure 2.19 A fit of the chemical shift data to a 1:1 binding
isotherm gave a Ka of 48(^5) M21 20
By using the same
.
method, the binding constant for the complex of 1 with 19
was also determined to be 45(^6) M21 (based on the data of
the NDI protons, Fig. 2).
Potentially, the iso-phthalic acid diester moiety in 19 might
also form p–p stacking with the bis(p-phenylene)-34-
crown-10 unit or porphyrin unit of 1 or Zn1 within the weak
complexes 1/19 and Zn1/19. Such stacking might also
contribute to the binding stability of these two complexes.
To evaluate if it is the case, compound 30, in which the two
Figure 2. Plot of Dd of the H-1 signal of 19 vs [1] (¼[19]) (A) or [Zn1]
(¼[19]) (W) in the 1:1 solution of 19 and 1 or Zn1 in chloroform-d, and plot
of Dd of the H-1 signal of 35·4PF6 vs [Zn1] (¼[35·4PF6] (K) in the 1:1
1
Scheme 3.
solution of 35·4PF6 and Zn1 in acetone-d6 in the H NMR dilution study.

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X.-B. Shao et al. / Tetrahedron 59 (2003) 4881–4889
Figure 3. Tri-site binding module of complex Zn1·22 and the important 1H
NMR shift changes compared with those of the pure compounds Zn1 and
22 in chloroform-d.
Scheme 5.
NDI moieties are connected with an aliphatic chain of
comparative length, was synthesized as outlined in
stoichiometry of the complex was deduced from the Job’s
plot of the DNI proton signals vs the mole fraction of 22, in
which the maximum signal change was observed at 0.5 mol
fraction.23 However, quantitative binding study could not be
performed by 1H NMR method as a result of reduced
resolution of the spectra of the diluted solutions. Theoreti-
cally, the two unsymmetrical bis(p-phenylene)-34-crown-
10 units of Zn1 might generate two intermolecular donor–
acceptor binding patterns (cis–cis or cis–trans), depending
on the relative location of the ester linker in the complex.
The 1H NMR spectrum even at lower temperature of 2508C
did not display further splitting for the NDI proton signals,
implying quick exchange process always exists between the
two patterns on the 1H NMR time scale. NOE experiment in
chloroform-d was also performed for complex Zn1·22,
which unfortunately did not reveal intermolecular
interactions.
1
Scheme 5. A H NMR dilution study of the 1:1 mixtures
of Zn1 and 30 in chloroform-d gave a binding constant of
46(^5) M21 for the complex Zn1/30, by fitting a 1:1
1
binding model. Within experimental error for the H NMR
measurements, this value is comparable to those of the
complexes 1/19 and Zn1/19, suggesting that no pronounced
p–p stacking exists between the iso-phthalic acid diester
moiety in 19 and the porphyrin unit of 1 or Zn1 within the
complexes.
Theoretically, both the bis(p-phenylene)-34-crown-10
moiety and the porphyrin moiety in 1 or Zn1 could complex
the NDI unit of 19 when mixing them together. In order to
evaluate the relative contribution of these two possible
binding patterns, the binding studies of compounds 7 and 10
toward 13 in chloroform-d were also carried out by 1H NMR
titration of 15 mM solutions of 13 with 7 (0.25–150 mM)
or 10 (0.50–130 mM), which afforded a Ka of ca. 10 M21
for 7·13 and 20 M21 for 10·13, respectively. These results
suggest that the electron deficient NDI units might interact
with both the porphyrin and bis(p-phenylene)-34-crown-10
units, forming an equilibrium of two different binding
patterns in 1·19 and Zn1·19,21 which is similar to that of
Zn1·35·4PF6 shown in Figure 5 (vide infra). Decreasing the
temperature of the 1:1 solution of 1 and 19 (0.03 M) in
chloroform-d to 2508C did not induce splitting of the NDI-
H signal of 19 in their 1H NMR spectra, indicating that the
exchanging process between the different binding patterns is
rapid on the 1H NMR time scale even at low temperature.3.
By comparing this result with those of the above two-site
binding complexes 1·19, Zn1·19, and Zn1·30, it can be said
that no cooperative effect exists within the two-site binding
complexes.
Figure 4 shows the influence of added 22 on the absorption
spectral change of Zn1 in chloroform at room temperature.
The lmax for the Soret band (428 nm) of the porphyrin unit
in Zn1 shifts a little to longer wavelength (430 nm) and the
absorbance reduced remarkably with the addition of 22. A
tight isosbestic point (404 nm) was also displayed. These
results also support the view that the pyridine unit in 22 is
coordinated to Zn(II) in Zn1. A binding constant of
6.5(^0.7)£105 M21 was obtained from a plot of DA430 vs
[22] (inserted in Fig. 4) for the 1:1 complex Zn1·22. Under
the similar measurement conditions, the binding constant of
complex Zn1·25 in chloroform was determined to be
1.5(^0.12)£103 M21
.
Addition of 1 equiv. of Zn1 to the solution of 22 (0.05 M) in
1
chloroform-d caused the H NMR chemical shifts of many
signals of both compounds to change substantially,
suggesting the formation of a tri-site binding pattern as
depicted in Figure 3. The changes of the important chemical
shifts of both compounds in the complex are also listed in
Figure 3. The signals of the pyridine a- and b-protons of 22
moved upfield 6.60 and 2.52 ppm, respectively, indicating
that they were completely engulfed in the shielding region
of the ring current of the porphyrin p-systems.8c,22 These
shifts are also diagnostic of the formation of Zn1·22 through
a coordination interaction and two donor–acceptor inter-
actions between the two compounds. The 1:1 binding
Figure 4. Absorption spectral change in Zn1 (4.1£1026 M) vs [22] in
chloroform at 258C. Insert: DA428 vs [22] plot.

X.-B. Shao et al. / Tetrahedron 59 (2003) 4881–4889
4885
Scheme 6.
Comparison of the stabilities of Zn1·30 (46 M21
DG¼22.3 kcal/mol) and Zn1·25 (1.8£103 M21
DG¼24.4 kcal/mol) with that of Zn1·22 (6.5£105 M21
,
,
,
27.9 kcal/mol) indicates that the increase in the stability of
complex Zn1·22 is not just a result of the additive effect
from the peripheral donor–acceptor interactions between
the bis(p-phenylene)-34-crown-10 units of Zn1 and the NDI
units of 22. Instead, these data show that the binding
between the two compounds is a substantially cooperative,
entropically favorable process.24
Viologens are typical electron deficient compounds, which
have been widely applied in molecular recognitions and
self-assembly.25 Therefore a viologen derivative 35·4PF6
was also designed as guest for receptor Zn1. The synthesis
of compound 35·4PF6 from dipyridine 31 is outlined in
Scheme 6. It was found that adding 1 equiv. of Zn1 to the
solution of 35·4PF6 in acetone-d6 led to remarkable upfield
movements of the chemical shifts of the pyridine proton
signals (Dd 0.27, 0.29 ppm for a-H’s, and 0.39, 0.37 ppm
for b-H’s, respectively), indicating significant interaction
between the two compounds. The phenylene proton signal
did not exhibit obvious chemical shift change, implying that
there is no substantial intermolecular interaction imposed on
this unit or significant shielding effect from Zn1. It was also
found that the signals of the pyrrole protons of the porphyrin
protons shifted downfield substantially (0.22 and 0.15 ppm).
A Job’s plot analysis of the 1H NMR spectra revealed a 1:1
binding stoichiometry. Considering that the linker between
the two viologen units of 35·4PF6 is quite rigid, it is
reasonable to exclude the binding pattern where one
35·4PF6 adopts an U-type conformation to bind only one
bis(p-phenylene)-34-crown-10 moiety. Therefore, the
above results suggest that two discrete donor–acceptor
interaction patterns might exist for complex Zn1·35·4PF6,
Figure 5. Two possible binding patterns for complexes Zn1·35·4PF6 and
1·35·4PF6.
also investigated by 1H NMR titration method, which
afforded a binding constant of ca. 75 M21 for 7·36·2Br and
150 M21 for 10·36·2Br, respectively.26 Therefore, it can be
said that no cooperative effect exists in the two-site binding
complexes 1·35·4PF6 and Zn1·35·4PF6.
3. Conclusion
In conclusion, we have developed a new efficient approach
to strapped porphyrin diol 7 and the synthesis of a new
generation of three dimensional porphyrin receptors Zn1
and 1 with three binding sites by incorporating two electron-
rich cyclophane to the strapped porphyrin diol. The new
porphyrin receptors display strong binding ability toward a
structurally matched guest consisting of one pyridine unit
and two naphthalene-1,8,4,5-tetracarboxydiimide units, as a
result of cooperative effect of intermolecular metal–ligand
coordination and donor–acceptor interactions. The work
represents the first step to develop novel strapped multi-site
porphyrin receptors. Further work will focus on modifi-
cation of compound 7 with other functional groups to
generate new, highly selective porphyrin receptors and on
development of new rigid strapped porphyrin blocks for
self-assembly of new supramolecular systems.
1
as shown in Figure 5. A H NMR dilution study of the 1:1
mixtures of Zn1 and 35·4PF6 (from 0.13 M to 1.0 mM) in
acetone-d6 was then performed and the corresponding
results are presented in Figure 2, which afforded a Ka
of 475(^50) M21 for Zn1·35·4PF6. By using the same
method, a binding constant of 430(^45) M21 for 1·35·4PF6
was determined. Reducing the temperature of the solution of
Zn1·35·4PF6 to 2408C caused the 1H NMR signals to shift
pronouncedly, however, no further splitting was observed
for the aromatic proton signals of 35·4PF6, indicating that a
fast exchange also exists between the two binding patterns
4. Experimental
4.1. General
1
shown in Figure 5 on the H NMR time scale. In order to
Melting points are uncorrected. All reactions were
1
check if there exists a cooperative effect of the two binding
sites within these two complexes, the stability of the 1:1
complexes of 7·36·2Br and 10·36·2Br in acetone-d6 were
performed under an atmosphere of dry nitrogen. The H
NMR spectra were recorded on 600, 400, or 300 MHz
spectrometers in the indicated solvents. Chemical shifts are

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X.-B. Shao et al. / Tetrahedron 59 (2003) 4881–4889
expressed in parts per million (d) using residual solvent
protons as internal standards. Chloroform (d 7.26 ppm) was
used as an internal standard for chloroform-d. Elemental
analysis was carried out at the SIOC Analytical Center.
Unless otherwise indicated, all starting materials were
obtained from commercial suppliers and were used without
further purification. All solvents were dried before use
following standard procedures. Compound 13 was prepared
according to a reported procedure.14c
2H). MS (EI): m/z 424 [M2OH]þ. Anal. calcd for
C26H34O6·0.5H2O: C 69.16, H 7.81. Found: C 69.10, H
7.73.
4.1.4. Compound 7. A stirred solution of compounds 4
(3.98 g, 10.5 mmol) and 6 (2.33 g, 5.30 mmol) in aceto-
nitrile (700 mL) was degassed with nitrogen for 30 min at
room temperature. Then, trifluoroacetic acid (0.20 mL) was
added in one portion. The solution was shielded from light
and stirred at room temperature for 5 h, after which a
solution of 2,3-dichloro-4,5-dicyanoquinone (DDQ)
(2.63 g, 10.5 mmol) in THF (100 mL) was added and the
mixture was stirred at room temperature for another 2 h. The
solvent was evaporated and the residue purified by column
chromatography (CH2Cl2/MeOH, 40:1). Compound 7 was
obtained as a purple solid (0.43 g, 7%). Mp 102–102.58C.
1H NMR (CDCl3): d 22.70 (s, 2H), 21.30 (br, s, 4H),
21.03 (m, 4H), 20.03 (m, 4H), 0.63 (br, 4H), 0.878 (m,
6H), 1.16–1.44 (m, 18H), 1.56 (m, 4H), 1.88 (m, 4H), 3.67
(t, J¼5.1 Hz, 4H), 4.47 (t, J¼6.6 Hz, 4H), 4.94 (s, 4H),
7.20–7.73 (m, 4H), 7.76 (d-d, J¼8.1, 2.1 Hz, 2H), 8.15 (d,
J¼8.1 Hz, 2H), 8.28 (d, J¼2.0 Hz, 2H), 8.37–8.48 (m, 4H),
8.75 (d, J¼5.2 Hz, 4H), 8.82 (d, J¼5.2 Hz, 4H). MS (ESI):
m/z 1159 [MþH]þ. Anal. calcd for C74H84N4O8: C 76.79, H
7.31, N 4.84. Found: C 76.72, H 7.26, N 4.71.
4.1.1. Compound 3.27 To a stirred solution of compounds 2
(15.0 g, 0.10 mol) and n-octyl bromide (19.2 g, 0.10 mol) in
DMF (300 mL) was added potassium carbonate (27.6 g,
0.20 mol) at room temperature. The mixture was then stirred
at 708C for 12 h. The solvent was removed under reduced
pressure and the residue was triturated with dichloro-
methane (500 mL). The organic phase was washed with
water (100 mL£3), brine (100 mL), and dried over sodium
sulfate. After the solvent was removed with an evaporator
under reduced pressure, the resulting residue was subjected
to column chromatography (CH2Cl2/EtAc 10:1), to give
1
22.0 g of compound 3 (84%) as an oily solid. H NMR
(CDCl3): d 0.86 (t, J¼6.6 Hz, 3H), 1.28–1.46 (m, 10H),
1.73–1.84 (m, 2H), 4.35 (t, J¼6.7 Hz, 2H), 7.95 (d,
J¼8.2 Hz, 2H), 8.19 (d, J¼8.2 Hz, 2H), 10.10 (s, 1H). MS
(EI): m/z 262 [M]þ.
4.1.5. Compound 10. To a stirred solution of ditosylate 829
(3.50 g, 4.50 mmol) and ester 9 (0.76 g, 4.50 mmol) in
acetonitrile (120 mL) was added potassium carbonate
(6.20 g, 0.45 mol) and the mixture was stirred under reflux
for 3 days. After the mixture was cooled to room
temperature, the solid was filtered off and the solvent was
evaporated. The residue was triturated with acetate
(200 mL) and the solution was washed with water
(40 mL£2), brine (40 mL), and dried over sodium sulfate.
After the solvent was removed under reduced pressure, the
crude material was subjected to column chromatography
(EtOAc/MeOH 60:1). Compound 10 (1.22 g) was obtained
4.1.2. Compound 4. A solution of compound 3 (8.70 g,
33.2 mmol) and pyrrole (23 mL, 0.33 mol) in toluene
(250 mL) was degassed by a stream of nitrogen for
30 min. To the degassed solution was added hot (ca.
1008C) toluene (1 mL) previously saturated with p-toluene-
sulfonic acid. The solution was heated under reflux for 1.5 h
and cooled to room temperature. The solution was washed
with aqueous K2CO3 (2N, 40 mL), water (40 mL£2), and
dried over sodium sulfate. Evaporation of solvent gave a
brown oil, which was subjected to flash chromatography
(CHCl3) and further purified by recrystallization (chloro-
form/hexane), to give 8.11 g of pure product 4 in 65% yield
as a white solid. Mp 84–858C. 1H NMR (CDCl3): d 0.89 (t,
J¼6.7 Hz, 3H), 1.27–1.44 (m, 10H), 1.71–1.78 (m, 2H),
4.30 (t, J¼6.6 Hz, 2H), 5.53 (s, 1H), 5.90 (s, 2H), 6.15–6.18
(m, 2H), 6.70–6.73 (m, 2H), 7.24–7.30 (m, 2H), 7.97 (s,
2H), 8.00 (s, 2H). MS (EI): m/z 378 [M]þ. Anal. calcd for
C24H30N2O2: C 76.16, H 7.99, N 7.40. Found: C 76.25, H
7.99, N 7.29.
1
in 45% yield as a pale yellow oil. H NMR (CDCl3): d
3.65–3.74 (14H, m), 3.78–3.86 (10 H, m), 3.94–4.05 (8H,
m), 6.73 (4H, s), 6.79 (1H, J¼6.0 Hz, d), 6.81–6.94 (1H,
m), 7.28 (1H, J¼6.0 Hz, d). MS (EI): m/z 594 [M]þ. Anal.
calcd for C30H42O12: C, 60.59; H, 7.12. Found: C, 60.51; H,
7.12.
4.1.6. Compound 11. A solution of sodium hydroxide
(40.0 mg, 1.00 mmol) in water (15 mL) was added to a
solution of compound 10 (0.51 g, 0.86 mmol) in methanol
(25 mL) and the resulting solution was stirred under reflux
for 2 h. Upon cooling to room temperature, the reaction
mixture was concentrated to a volume of 15 mL which was
then adjusted to pH 4 by slow addition of 1N hydrochloric
acid. The aqueous solution was extracted with CHCl3
(50 mL£3) and the combined organic phase was washed
with water (30 mL£2), brine (30 mL), and dried over
sodium sulfate. After the solvent was removed in vacuo, the
residue was purified by flash chromatography (dichloro-
methane/methanol 10:1), to afford compound 11 (0.50 g) in
100% yield as a pale yellow oil. 1H NMR (CDCl3): d 3.60–
3.79 (14H, m), 3.84–4.03 (18H, m), 6.78 (4H, s), 6.80 (1H,
J¼6.5 Hz, d), 6.84–6.97 (1H, m), 7.28–7.29 (1H,
J¼6.6 Hz, d). MS (EI): m/z 580 [M]þ. Anal. calcd for
C29H40O12: C, 59.99; H, 6.94. Found: 60.31; H, 7.10.
4.1.3. Compound 6. To a stirred mixture of compound 528
(16.1 g, 0.11 mol) and K2CO3 (22.8 g, 0.17 mol) in DMF
(150 mL) was added 1,10-dibromodecane (15.0 g,
50.0 mmol). The mixture was stirred at 708C for 12 h and
then the solid was filtered off. The solvent was removed
under reduced pressure and the resulting residue was
triturated with ethyl acetate (500 mL). The organic solution
was washed with aqueous potassium hydroxide solution
(0.5N, 100 mL£3), water (100 mL£2), brine (100 mL), and
dried over sodium sulfate. After the solvent was removed,
the residue was recrystallized from dichloromethane/
n-hexane (1:2) to give compound 6 as a white solid
1
(16.0 g, 72%). Mp 79–808C. H NMR (CDCl3): d 1.36–
1.51 (m, 12H), 1.80–1.91 (m, 4H), 2.18 (s, 2H), 4.10 (t,
J¼6.5 Hz, 4H), 4.66 (s, 4H), 7.00 (d, J¼8.7 Hz, 2H), 7.59
(d, d, J¼8.7, 2.1 Hz, 2H), 7.80 (d, J¼2.1 Hz, 2H), 10.50 (s,

X.-B. Shao et al. / Tetrahedron 59 (2003) 4881–4889
4887
4.1.7. Compounds 1 and Zn1. A solution of acid 11
(0.15 g, 0.26 mmol) in oxalyl chloride (5 mL) was stirred
under reflux for 2 h and the unreacted oxalyl chloride was
removed in vacuo. The resulting residue, acyl chloride 12,
was then dissolved in dichloromethane (10 mL) and used
directly for the next step without further purification. To a
stirred solution of compound 7 (99.0 mg, 0.086 mmol) and
Et3N (0.3 mL) in dichloromethane (10 mL) at 08C was
added the above dichloromethane solution of 12 within
5 min. The solution was stirred overnight at room
temperature and then washed with hydrochloride (1N)
solution (5 mL), sodium carbonate solution (1N, 5 mL),
water (5 mL£2), brine (5 mL), and dried over sodium
sulfate. The solution was concentrated and the resulting
residue was purified by column chromatography (CH2Cl2/
MeOH 30:1), to give compound 1 (143 mg) in 73% yield as
a purple solid. Mp 62–638C. 1H NMR (CDCl3) d 22.68 (s,
2H), 21.24 (br, 4H), 20.83 (br, 4H), 20.56 (br, 4H), 0.65–
0.70 (m, 4H), 0.91 (t, J¼6.5 Hz, 6H), 1.15–1.60 (m, 20H),
1.92 (p, J¼7.5 Hz, 4H), 3.291 (s, br, 8H), 3.36–3.39 (m,
4H), 3.461–3.490 (m, 4H), 3.60–3.73 (m, 36H), 3.81–3.88
(m, 8H), 3.93–3.99 (m, 8H), 4.50 (t, J¼6.8 Hz, 4H), 5.60 (s,
4H), 6.67 (s, 8H), 6.78 (d, J¼8.9 Hz, 2H), 6.89 (d, d, J¼8.9,
3.3 Hz, 2H), 7.26 (d, J¼8.6 Hz, 2H), 7.42 (d, J¼3.3 Hz,
2H), 7.84 (d, d, J¼8.6, 2.1 Hz, 2H), 8.17 (d, J¼7.4 Hz, 2H),
8.39–8.42 (m, 6H), 8.47 (d, J¼7.4 Hz, 2H), 8.76 (d,
J¼4.7 Hz, 4H), 8.85 (d, J¼4.7 Hz, 4H). MS (ESI): m/z 2283
[MþH]þ. Anal. calcd for C132H160N4O30: C 69.45, H 7.06,
N 2.45. Found: C 69.52, H 7.32, N 2.17. Porphyrin 1 was
dissolved in CH2Cl2/CH3OH (3:1) and zinc acetate
(10.0 equiv.) was added. The reaction mixture was stirred
under reflux for 3 h. The solvent was removed in vacuo, and
the crude product was subjected to flash chromatography
(dichloromethane/methanol 20:1), to afford Zn1 in 100%
4.1.9. Compound 19. To a stirred solution of compound 17
(1.30 g, 2.60 mmol) and triethylamine (0.30 mL,
2.90 mmol) in dichloromethane (100 mL) was added a
solution of compound 1830 (0.33 g, 1.13 mmol) in dichloro-
methane (10 mL) at room temperature. The mixture was
then stirred overnight and washed with water (30 mL£3),
brine (30 mL), and dried over sodium sulfate. After the
solvent was evaporated, the residue was purified by column
chromatography (CH2Cl2/EtOAc/MeOH 25:5:1), to give
compound 19 as a pale orange solid (0.94 g, 72%). Mp 196–
1978C. 1H NMR (CDCl3) d: 3.31 (s, 6H), 3.46 (t,
J¼4.65 Hz, 4H), 3.56–3.63 (m, 8H), 3.71 (t, 4.5 Hz, 4H),
3.84 (t, J¼5.8 Hz, 4H), 4.45 (t, J¼5.8 Hz, 4H), 4.65 (br,
8H), 5.06 (s, 2H), 7.41 (br, 5H), 7.73 (s, 2H), 8.12 (s, 1H),
8.71 (d, J¼7.8 Hz, 4H), 8.75 (d, J¼7.8 Hz, 4H). MS (ESI):
m/z 1149 [MþH]þ. Anal. calcd for C61H56N4O19: C 63.76,
H 4.91, N 4.88. Found: C 63.55, H 4.77, N 4.81.
4.1.10. Compound 22. A solution of compound 19 (0.35 g,
0.30 mmol) in trifluoroacetic acid (10 mL) was refluxed for
1 h. After which time TLC indicated that 19 had been
consumed completely. The solvent was removed under
reduced pressure to give crude product 20 which was used
directly for the next step without further purification. To a
stirred solution of the above compound 20, triphenyl-
phosphine (0.21 g, 0.81 mmol), and 4-pyridylcarbinol 21
(0.11 g, 1.00 mmol) in dichloromethane (60 mL) at room
temperature was added dropwise a solution of DEAD
(0.36 g, 40% in toluene) in dichloromethane (10 mL). The
mixture was stirred at room temperature for 12 h. The
solution was washed with 0.5N potassium carbonate
solution (10 mL£2), water (10 mL£2), brine (10 mL),
dried over sodium sulfate. The solvent was then evaporated
and the resulting residue was purified by column chroma-
tography (dichloromethane/methanol 20:1), to afford com-
pound 22 as a pale orange solid (189 mg, 62%). Mp 196–
1
yield. Mp 63–648C. H NMR (CDCl3) d: 21.54 (br, 4H),
21.02 (t, J¼7.73 Hz, 4H), 20.77 (br, 4H), 0.62 (br, 4H),
0.91 (t, J¼6.8 Hz, 6H), 1.05–1.62 (m, 20H), 1.91 (q,
J¼7.2 Hz, 4H), 2.87–3.85 (m, 68H), 4.49 (t, J¼6.6 Hz,
4H), 5.67 (s, 4H), 6.17 (d, J¼8.7 Hz, 4H), 6.35 (d,
J¼8.7 Hz, 4H), 6.51 (d, J¼9.0 Hz, 2H), 6.77 (d, d, J¼3.3,
9.0 Hz, 2H), 7.26–7.35 (m, 4H), 7.76 (d, d, J¼8.4, 2.1 Hz,
2H), 7.97 (d, J¼8.6 Hz, 2H), 8.30 (d, J¼8.7 Hz, 4H), 8.39
(d, J¼8.7 Hz, 4H), 8.76 (d, J¼4.7 Hz, 4H), 8.85 (d,
J¼4.7 Hz, 4H). MS (ESI): m/z 2347 [MþH]þ.
1
1978C. H NMR (CDCl3) d: 3.31 (s, 6H), 3.45–3.48 (m,
4H), 3.56–3.63 (m, 8H), 3.69–3.72 (m, 4H), 3.84 (t,
J¼5.8 Hz, 4H), 4.45 (t, J¼5.8 Hz, 4H), 4.65 (s, 8H), 5.13 (s,
2H), 7.36 (d, J¼5.1 Hz, 2H), 7.74 (s, 1H), 8.13 (s, 1H), 8.64
(br, 2H), 8.74 (s, 8H). MS (ESI): m/z 1150 [MþH]þ. Anal.
calcd for C60H55N5O19·MeOH: C 61.99, H 5.03, N 5.92.
Found: C 62.07, H 5.15, N 5.68.
4.1.11. Compound 25. A stirred mixture of compound 2331
(1.90 g, 10.0 mmol) and K2CO3 (4.30 g, 31.0 mmol) in
DMF (50 mL) was heated to 1008C. Then, a solution of the
hydrochloride salt of compound 24 (0.82 g, 5.00 mmol) in
DMF (10 mL) was added dropwise. The mixture was stirred
at 1008C for 4 h and then cooled to room temperature. Water
(200 mL) was added and the resulting precipitate was
filtered, washed with water completely, dried, and purified
by column chromatography (ethyl acetate/petroleum ether
10:1), to give compound 25 as a white solid (0.63 g, 42%).
Mp 101.5–1028C. 1H NMR (CDCl3) d: 3.95 (s, 6H), 5.18 (s,
2H), 7.38 (d, t, J¼5.1, 1.0 Hz, 2H), 7.83 (d, J¼1.0 Hz, 2H),
8.33 (t, J¼1.8 Hz, 1H), 8.65 (d, d, J¼5.1, 1.8 Hz, 2H). MS
(EI): m/z 301 [M]þ. Anal. calcd for C16H15NO5: C, 63.78;
H, 5.02; N, 4.65. Found: C, 63.49; H, 4.71; N, 4.49.
4.1.8. Compound 17. A mixture of dianhydride 14 (5.36 g,
20.0 mmol), amine 15 (3.26 g, 20.0 mmol), and ethanol-
amine 16 (1.20 mL. 20.0 mmol) in DMF (150 mL) was
stirred overnight at 1208C. The mixture was cooled to room
temperature and the solid filtered off. The filtrate was
concentrated in vacuo and the resulting residue was
triturated with 300 mL of dichloromethane. The organic
phase was washed with water (2£50 mL), brine (50 mL),
and dried over Na2SO4. After evaporation of the solvent
under reduced pressure, the residue was purified by column
chromatography (CH2Cl2/MeOH 30:1), to give 3.49 g of
compound 17 as a pale yellow solid in 38% yield. Mp 144–
1
144.58C. H NMR (CDCl3): d 2.16 (br, 1H), 3.32 (s, 3H),
3.47 (t, J¼4.8 Hz, 2H), 3.57–3.64 (m, 4H), 3.72 (t,
J¼4.8 Hz, 4H), 3.86 (t, J¼5.7 Hz, 2H), 4.01 (br, 2H),
4.45–4.50 (m, 4H), 8.76 (s, 4H). MS (EI): m/z 456 [M]þ.
Anal. calcd for C23H24N2O8: C 60.52, H 5.29, N 5.93.
Found: C 60.41, H 5.31, N 5.98.
4.1.12. Compound 28. A mixture of dianhydride 14
(10.72 g,
40.0 mmol), and ethanolamine 27 (2.40 mL, 40.0 mmol)
40.0 mmol),
n-octylamine
26
(5.15 g,

4888
X.-B. Shao et al. / Tetrahedron 59 (2003) 4881–4889
in DMF (250 mL) was stirred at 1208C for 12 h. The mixture
was cooled to room temperature and the precipitate was
filtered. The filtrate was concentrated in vacuo and the
residue was triturated with chloroform (300 mL). The
organic phase was washed with water (50 mL£3), brine
(50 mL), and dried over sodium sulfate. After the solvent
was removed under reduced pressure, the residue was
purified by column chromatography (CH2Cl2/MeOH 30:1),
to afford compound 28 as a pale orange solid (3.49 g, 29%).
[M-PF6]þ. Anal. calcd for C24H58N4P4F24: C 43.22, N 4.58,
H 4.78. Found: C 43.40, N, 4.47, H 4.97.
4.2. Binding studies
All 1H NMR binding studies were carried out at 258C.
CDCl3 used in binding studies was passed though a short
column of dry, activated basic alumina prior to use.
Acetone-d6 were used as provided without further purifi-
cation. Volumetric flasks and syringes used in preparing
solutions were washed with dried CH2Cl2 and dried in
vacuum before use. Samples (usually 0.6 mL) were
prepared from stocks solutions, transferred to the NMR
tubes and diluted accordingly with syringes. For one series,
usually 13–20 samples were prepared and binding constants
reported are the average of two or three experiments, which
were obtained by fitting chemical shift change data to 1:1
binding isotherms with standard nonlinear curve-fitting
procedures.33 The nonlinear equations were derived from
mass-balance equations and the relationship between the
concentrations of free and complexed sample and the
weighted chemical shifts under the condition of rapid
exchange.33 UV–Vis binding study was performed in a
manner similar to that reported in the literature.33
1
Mp 154–1568C. H NMR (CDCl3) d: 0.90 (t, 3H), 1.24–
1.52 (m, 10H), 1.78 (t, J¼5.0 Hz, 2H), 4.04 (t, J¼5.0 Hz,
2H), 4.22 (t, J¼5.5 Hz, 2H), 4.51 (t, J¼5.5 Hz, 2H), 8.79 (s,
4H). MS (EI): m/z 422 [M]þ. Anal. calcd for C24H26N2O5: C
68.23, H 6.20, N 6.63. Found: C 67.90, H 6.35, N 6.34.
4.1.13. Compound 30. A solution of diacyl chloride 29
(87.0 mg, 0.50 mmol) in dichloromethane (10 mL) was
added to a stirred solution of compound 28 (0.42 g,
1.00 mmol) and triethylamine (0.15 mL, 1.45 mmol) in
dichloromethane (50 mL) at room temperature. Upon
stirring overnight, the solution was washed with water
(15 mL£3), brine (15 mL), and dried over sodium sulfate.
After the solvent was evaporated, the residue was purified
by column chromatography (CH2Cl2/MeOH 25:1), to give
compound 30 as a pale orange solid (0.34 g, 70%). Mp
1
178–1808C. H NMR (CDCl3) d: 0.89 (t, 6H), 1.18–1.54
(m, 24H), 1.62–1.80 (m, 4H), 2.21 (t, 4.5 Hz, 4H), 4.18
(t, J¼4.5 Hz, 4H), 4.45–4.51 (m, 8H), 8.75 (s, 8H).
MS (MALDI): m/z 955 [MþH]þ. Anal. calcd for
C54H58N4O12: C 67.91, H 6.12, N 5.87. Found: C 68.14,
H 6.50, N 5.64.
Acknowledgements
This work is financially supported by the Ministry of
Science and Technology (G2000078101) and the Natural
Science Foundation of China (90206005).
4.1.14. Compound 33. A solution of 4,40-bipyridyl 31
(4.70 g, 30.0 mmol) and n-octyl bromide 32 (2.90 g,
15.0 mmol) in DMF (30 mL) was stirred at 858C for 15 h
and then cooled to room temperature. Ether (100 mL) was
added to generate a whtie precipitate, which was collected
by filtration, washed with ether thoroughly, and purified by
column chromatography (chloroform/methanol 10:1), to
give compound 33 as a white solid (3.65 g, 70%).
Mp.1898C [no datum available in lit.32] 1H NMR
(CDCl3): d 0.85 (t, J¼6.8 Hz, 3H), 1.21–1.37 (m, 10H),
2.08 (q, J¼7.4 Hz, 2H), 5.02 (t, J¼7.4 Hz, 2H), 7.74 (d, d,
J¼1.5, 4.8 Hz, 2H), 8.45 (d, J¼7.2 Hz, 2H), 8.87 (d,
J¼4.8 Hz, 2H), 9.66 (d, J¼7.2 Hz, 2H). MS (ESI): m/z 269
[M2Br]þ.
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