Synthesis of PEG derivatives bearing aminophenyl and their application for liquid-phase synthesis of water-soluble unsymmetrical cyanine dyes

Article abstract of DOI:10.1016/j.tet.2009.04.086

The synthesis and NMR characterization of soluble PEG-supported polymers were described, and their subsequent application for liquid-phase synthesis of water-soluble cyanine dyes was also studied. Nucleophilic substitution of tosylation of PEG 16 with 1,3-bis(4-nitrophenoxy)-2-propanol 15 under basic conditions, followed by nitro group reduction, gave PEG-bound aminophenyl 18. Another PEG-bound aminophenyl 28 was prepared by condensation reaction of PEG-bound pentaerythritol 25 and 4-aminobenzoic acid followed by the cleavage of BOC group. Subsequent loading and activation of sulfoindoleninium to PEG derivatives 18 or 28 were achieved via simple strategies. Cyanine dyes were released by the attack of heterocyclic carbon nucleophile and the cleavage of PEG-bound hemicyanine without the chromatographic separation. The efficient, facile, and practical approaches appear to be robust and versatile strategies to deliver not only indocyanine dyes but also benzoindocyanine dyes.

Full text of DOI:10.1016/j.tet.2009.04.086

Tetrahedron 65 (2009) 5257–5264
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of PEG derivatives bearing aminophenyl and their application for
liquid-phase synthesis of water-soluble unsymmetrical cyanine dyes
*
Lin-Ling Jiang, Bao-Lin Li , Feng-Ting Lv, Li-Fang Dou, Liu-Chang Wang
School of Chemistry and Materials Science, and Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry,
Shaanxi Normal University, Xi’an 710062, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and NMR characterization of soluble PEG-supported polymers were described, and their
subsequent application for liquid-phase synthesis of water-soluble cyanine dyes was also studied. Nu-
cleophilic substitution of tosylation of PEG 16 with 1,3-bis(4-nitrophenoxy)-2-propanol 15 under basic
conditions, followed by nitro group reduction, gave PEG-bound aminophenyl 18. Another PEG-bound
aminophenyl 28 was prepared by condensation reaction of PEG-bound pentaerythritol 25 and 4-
aminobenzoic acid followed by the cleavage of BOC group. Subsequent loading and activation of sul-
foindoleninium to PEG derivatives 18 or 28 were achieved via simple strategies. Cyanine dyes were
released by the attack of heterocyclic carbon nucleophile and the cleavage of PEG-bound hemicyanine
without the chromatographic separation. The efficient, facile, and practical approaches appear to be
robust and versatile strategies to deliver not only indocyanine dyes but also benzoindocyanine dyes.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 14 December 2008
Received in revised form 23 April 2009
Accepted 24 April 2009
Available online 3 May 2009
Keywords:
Liquid-phase synthesis
Water-soluble cyanine dyes
PEG
Aminophenyl PEG
Cleavage
1. Introduction
synthesis of cyanine dyes employing polystyrene as loading mate-
rials. They had developed two approaches to the solid-phase syn-
Cyanine dyes1 have been found numerous applications such as
photographic sensitizers,2 nonlinear optical materials,3 and more
recently fluorescent probes for biomolecular labeling.4–8 Among
cyanine dyes, water-soluble sulfoindocyanine dye developed by
Waggoner’s9 group is one of the most important type of dyes. The
sulfoindocyanines have two or more SOꢀ3 groups to increase water
solubility, which is crucial for the fluorophore to avoid dye aggre-
gation and nonspecific binding to irrelevant components when it is
applied to biological analysis as a probe in aqueous environment.10
However, synthesis of this type of unsymmetrical water-soluble
cyanine dyes is very difficult.
The preparation of unsymmetrical water-soluble dyes, such as
pentamethine cyanine dye (Cy5) 5, is traditionally accomplished by
a stepwise condensation reaction of two nucleophilic heterocycles
with a polyene-chain precursor (Scheme 1). In this process, con-
taminating symmetrical dye is also formed because hemicyanine
intermediate 3 is liable to react with a second molecule of hetero-
cycle 2. Nontrivial chromatographic separation of unsymmetrical
dye is required. Therefore, purification of the unsymmetrical dye is
a particular problem in traditional solution synthesis.11–13 Balasu-
bramanian’s group14,15 achieved an improvement in solid-phase
thesis of trimethine and pentamethine cyanine dyes, which
afforded products in high purity without the need for column
chromatography. Although there was a big progress, the prepara-
tion of water-soluble cyanine dye with two or more SOꢀ3 groups
was not successful. Therefore, water solubility of cyanine dyes
synthesized by solid-phase synthesis was poor for biomolecular
labeling.16–18
O3S
N
2
O3S
NHPh
PhN
N
NHPh
1
3
O3S
N
(CH2)5COOH
SO3H
O3S
4
N
N
(CH2)5COOH
5
* Corresponding author. Tel.: þ86 29 85303858.
E-mail address: baolinli@snnu.edu.cn (B.-L. Li).
Scheme 1. Traditional synthesis of a water-soluble cyanine dye.
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.04.086

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L.-L. Jiang et al. / Tetrahedron 65 (2009) 5257–5264
HO3S
SO3
SO3
O
C
heterocycle 2
NH
N
O
N
N
(CH2)5COOH
O
O C
7
NH2
PEG-(PhNH2)2
HO3S
heterocycle 2
SO3
6
SO3
O
C
N
N
NH
O
N
(CH2)5COOH
5
Scheme 2. Synthesis of cyanine dyes by using PEG–(PhNH2)2 support.
In recent years, the soluble polymers’ supported liquid-phase
organic synthesis (LPOS) has emerged as an alternative and pow-
erful technique for the preparation of small heterocyclic librar-
ies.19–24 LPOS offers several unique advantages, for example,
convenient products’ purification can be achieved by simple fil-
tration and washing. Reactions can be carried out in homogeneous
solution. Meanwhile, the soluble polymer-bound species allow the
use of routine analytical methods (NMR, TLC, or IR) to monitor the
reaction process and to determine the structures of products at-
tached to the polymer supports. Poly(ethylene glycol) (PEG) is one
type of soluble polymer that exhibits solubility in a wide range of
solvents including dichloromethane (CH2Cl2), DMF, toluene, THF,
and CH3OH at room temperature and can be precipitated from
a solution by addition of diethyl ether, hexane, or isopropyl alcohol.
Therefore, PEG and its derivatives are considered as ideal supports
for LPOS.
synthesized by these soluble polymer supports. Furthermore, the
synthesis of other type of cyanine dye such as benzoindocyanine
dye is also realized by LPOS.
2. Results and discussion
Water solubility required for dyes can be achieved by appending
a charged solubilizing functional group such as –SO3H to hetero-
cycles of a dye (Scheme 3). Quarternization of sulfoindole nucleo-
phile26 with ethyl iodide or 6-bromohexanoic acid was investigated
in our previous work.25 Heterocycles 11 and 12 were synthesized by
modification of literature procedure.9 In order to investigate
whether the polymer-supported methodology is suitable for the
synthesis of other types of cyanine dyes, 1,2,3,3-tetramethyl-1H-
benzo[e]indolinium iodide (14) was synthesized according to the
literature procedure.27
In our previous published strategy,25 we have reported the
successful synthesis of PEG–(PhNH2)2 polymer (6) and its use in the
synthesis of water-soluble unsymmetrical cyanine dyes 5 and 7
(Scheme 2). There are only two aminophenyl groups per PEG–
(PhNH2)2 molecule. It suffers from a drawback, which is its low
loading capacity of functional group. In the work presented here,
we show some modified PEG derivatives that exhibit higher loading
capacities compared to PEG–(PhNH2)2. A small array of water-sol-
uble trimethine and pentamethine indocyanine dyes are also
Because each molecule of PEG–(PhNH2)2 possess only two
attachment sites, represented by the terminal aminophenyl groups,
two molecules of water-soluble cyanine dye could be obtained from
a PEG–(PhNH2)2 molecule. A number of attempts to increase at-
tachment sites of PEG through chemical modification have been
realized.28–30 In order to increase the efficient use of PEG derivative
in LPOS, PEG–(PhNH2)4 18 bearing four terminal aminophenyl
groups was synthesized according to Scheme 4. Synthesis of
PEG–(PhNH2)4 (18) was accomplished in four steps starting
O3S
EtI, reflux
N
2
6-bromohexanoic acid
O
o-dichorobenzene,
O3S
110 °C
KO3S
CH3CCH(CH )
NHNH2
3 2 O3S
KOH
HO3S
N
N
N
H
(CH2)5COOH
4
8
9
10
CH3I, EtOH, reflux
O3S
N
11
1,4-butanesultone
o-dichorobenzene,
O3S
110 °C
N
(CH2)4SO3H
12
toluene
+
CH3I
N
H
N
I
13
14
Scheme 3. Synthesis of heterocycle compounds.

L.-L. Jiang et al. / Tetrahedron 65 (2009) 5257–5264
5259
dyes, we next investigated the synthesis of a small array of water-
soluble trimethine and pentamethine indocyanine dyes using this
polymer support (Scheme 5). Balasubramanian’s group had de-
scribed that immobilized aniline was converted to the immobilized
imidate by reaction with triethyl orthoformate in the presence of
BF3$OEt2.15 However, products 19 and 22 were successfully pre-
pared in glacial acetic acid in our system. The formation of conju-
gated C]N bond in their molecules was confirmed by sharp peaks
at 1649 cmꢀ1 or 1641 cmꢀ1 in FTIR spectra. It was anticipated that
their structures were similar to that of PEG–(PhNH2)2-bound de-
rivatives described in our previous work.25 Subsequent reaction to
form PEG–(PhNH2)4-bound tetramethine hemicyanine (20) and
PEG–(PhNH2)4-bound dimethine heminecyanine dye (23) was in-
vestigated by the reaction of 19 or 22 with various nucleophilic
heterocycle compounds at 80 ꢁC in HAc or ethanol. The peaks near
1183 cmꢀ1 of sulfo group in the FTIR spectra of 20 and 23 indicated
that the sulfonated heterocycles reacted with PEG derivative 19 or
22 in the loading reaction. Indeed, symmetrical dyes could be also
formed in this step. However, it could be removed by using the
appropriate conditions.25 The unsymmetrical water-soluble dye
formation steps namely cleavage of hemicyanines from support
were investigated by employing substoichiometric quantity of an-
other heterocycle. When the reaction was finished, the reaction
mixture was cooled and the blue or red gummy product was pre-
cipitated with ethyl acetate. After the gummy product was purified
by washing with CH2Cl2, blue powder 5 or red powder 7 could be
obtained. Obviously, the advantages of both homogeneous reaction
and easy isolation and purification of products coexisted in this
protocol.
O
O
O
NO2
NO2
NaOH
O2N
OH
+
HO
Cl
NaH
THF
15
CH2Cl2
H3C
SO2Cl
CH3
PEG
O
SO2
+
16
O
NO2
NO2
O
O
NH2
NH2
NH2NH2
H2O
O
O
EtOH
O
18
Scheme 4. Synthesis of PEG–(PhNH2)4.
17
from 4-nitrophenol and epichlorohydrin as common precursors.
Firstly, 4-nitrophenol reacted with epichlorohydrin to afford 1,3-
bis(4-nitrophenoxy)-2-propanol (15) in 38% yield. Tosylation of PEG
was usually performed in pyridine under reflux.31 However, a more
efficient and simple tosylation of PEG using a water/NaOH/CH2Cl2
system was reported by Lee-Ruff group.32 Etherification between 15
and 16 was performed in the presence of NaH in dry THF. Then, PEG
derivative 17 was isolated by addition of the reaction mixture into
diethyl ether, followed by filtration and washing of polymeric pre-
cipitate with diethyl ether to give reagent 17 in 90.6% yield, based on
the weight of polymer isolate. The derivation of PEG could be con-
firmed by the change in chemical shifts of
PEG. The chemical shift of the -protons of PEG was
CDCl3. For the tosylated PEG (16), this changed to
this changed to 4.24 ppm for the nitro-terminated polymer 17. The
nitro group was reduced with hydrazine hydrate to give the new
polymer support 18. The formation of arylamino was also confirmed
by the 1H NMR. After the nitro group was reduced for 24 h, the
a
-methylene protons of
3.64 ppm in
4.15 ppm and
In order to test whether this protocol is suitable for the synthesis
of other cyanine dyes, we synthesized eight water-soluble un-
symmetrical dyes (Table 1). Products were characterized by 1H
NMR, 13C NMR, and mass spectrometry.
a
d
d
d
Although the loading capacity of PEG–(PhNH2)4 is higher than
that of PEG–(PhNH2)2, we tried to increase the loading capacity of
functional groups for the synthesis of cyanine dyes. The attachment
of dendrimeric units with alcohol functionalities has been reported
and used in various medical and engineering applications and in
combinatorial chemistry.32–34 To increase the loading capacity of
support, a favorable way is to increase the number of anchoring
functional groups. A dendrimeric PEG derivative PEG–(PhNH2)6 (28)
was developed base on pentaerythritol in Scheme 6. The branched
polymer 25 was synthesized using pentaerythritol and tosylation of
PEG, which was reported by Lee-Ruff group.32 Then, 4-[(tert-
butoxycarbonyl)amino]benzoic acid35 was reacted with 25 to
signals at
d
7.00 and 8.20 ppm of phenyl group in polymer 17 dis-
6.57 and 6.70 ppm of phenyl
appeared. The resonance signals at
d
group in polymer 18 indicated a complete transformation from
arylnitro to arylamino. The modified PEG derivative 18 had four
functional groups in one molecule, which should be twice as much
as the functional groups of PEG–(PhNH2)2. The loading, determined
by 1H NMR method,25 was 0.3 mmol/g, which is higher than that of
PEG–(PhNH2)2.
To demonstrate the usefulness of the new soluble polymer
support in the synthesis of water-soluble unsymmetrical cyanine
heterocycle,
heterocycle, acetic
SO3
glacial
1,1,3,3-tetramethoxy-
propane, glacial acetic
anhydride, pyridine,
acetic acid,
80 °C, 2 h
110 °C, 15 min
acid, 55 °C , 5.5 h
O
O
N
H
N
R1
O
O
N
N
SO3
HO3S
OMe
OMe
O
O
NH
SO3
N
N
R1
R2
N
20
19
R1
21
O
O
NH2
NH2
O
heterocycle,
triethyl
18
heterocycle, acetic
anhydride, pyridine,
110 °C, 15 min
SO3
SO3
orthoformate
, EtOH,
O
O
N
N
CH HN
CH HN
reflux, 2 h
O
O
N
R1
O
NH
NH
HO3S
SO3
O
O
O
triethyl orthoformate,
glacial acetic acid, 55
°C, 5.5 h
O
N
N
R1
R2
N
24
R1
23
22
Scheme 5. PEG–(PhNH2)4 supported synthesis of unsymmetrical water-soluble cyanine dyes.

5260
L.-L. Jiang et al. / Tetrahedron 65 (2009) 5257–5264
equation: functional group ðmolÞ ¼ WisAanis=WaAisnaMis.25 Accord-
ing to the Wa, Wis, Aa, and Ais in the experiments, the loading level
was increased from 0.21 mmol/g for PEG–(NH2)2 to 0.44 mmol/g for
PEG–(NH2)6. It was anticipated that 28 would be more efficient for
the preparation of unsymmetrical dyes.
The reaction of 28 with triethyl orthoformate or 1,1,3,3-tetra-
methoxypropane in glacial acetic acid resulted in compound 32 or
29, respectively. Subsequent treatment with 2-methyl substituted
heterocyclic molecule led to formation of the desired PEG–
(PhNH2)6-bound hemicyanine dyes 33 and 30. The structures of 29,
30, 32, and 33 were also similar to that of PEG–(NH2)2-bound de-
rivatives (Scheme 7).
Unsymmetrical water-soluble dyes were also synthesized using
the PEG–(PhNH2)6. Cyanine dyes (5 and 7) were firstly synthesized
as described in PEG–(PhNH2)4 strategy, allowing a direct compar-
ison of two synthetic routes. When we used the same quantity of
PEG–(PhNH2)4 and PEG–(PhNH2)6, more amount of 5 and 7 was
obtained using PEG-(PhNH2)6 strategy. It was obvious because
there was more functional group existing in polymer support 28.
Therefore, the new approach enables more efficient preparation of
trimethine cyanine dye (Cy3) and pentamethine cyanine dye (Cy5).
Furthermore, another type of cyanine dye such as trimethine
benzoindocyanine dye was also synthesized utilizing this polymer
support (Table 2).
In summary, the simple and low cost preparation of modified
PEG derivatives 18 and 28 was developed. Compared with previous
PEG–(PhNH2)2, the loading level of these new polymer supports
was improved with dendritic end groups. Aminophenyl groups of
these polymers also permit them as soluble polymer supports in
the synthesis of water-soluble cyanine dyes, which afford products
without the need for nontrivial column chromatography separa-
tion. The versatility of both routes has been demonstrated by the
synthesis of cyanine dyes including sulfonated indocyanine and
benzoindocyanine dyes, which are of great importance in biological
research field. Because the new PEG-supported polymers have
more functional groups, the new approaches are preferred methods
for the synthesis of water-soluble unsymmetrical cyanine dyes.
Table 1
Synthesis of trimethine and pentamethine water-soluble dyes by using PEG–
(PhNH2)4 as a support
Compound
Monomer
1
Monomer
2
Yielda
(%)
Heterocyclic Heterocyclic
1
2
HO3S
SO3
SO3
SO3
2
11
26.0
25.9
21.3
22.3
N
N
CH3
C2H5
21a
HO3S
HO3S
2
4
N
N
(CH2)5COOH
5
C2H5
11
4
N
N
(CH2)5COOH
CH3
21b
HO3S
SO3
2
11
N
N
CH3
24a
C2H5
HO3S
HO3S
SO3
SO3
2
4
4
19.0
20.8
N
N
HOOC(H2C)5
C2H5
7
3. Experimental
11
N
N
3.1. General methods
HOOC(H2C)5
CH3
24b
All chemicals used were of analytical grade. The melting points
were determined using a WRS-113 digital melting point instrument
(the thermometer was not corrected). The FTIR spectra were
recorded on a Nicolet 170SX FT-IR spectrometer using KBr pellets.
Analytical thin layer chromatography (TLC) was performed on silica
gel plates, which was developed with a mixture of n-butanol/acetic
acid/water (4/1/2). The 1H and 13C NMR spectra were recorded on
a Bruker AVANCE300 spectrometer, chemical shifts were refer-
HO3S
SO3
11
12
12
19.2
20.5
N
CH3
N
(CH2)4SO3H
24c
HO3S
SO3
enced internally to tetramethylsilane (TMS,
d¼0.0) in parts per
2
million. MS data were obtained on a Bruker Esquire 3000plus mass
instrument and a Kratos PC Axima CFRplus MALDI-TOF Mass
instrument.
N
N
C2H5
24d
(CH2)4SO3H
a
Yields are based on weight of heterocycle in cleavage step.
3.2. Synthesis of PEG derivatives 17–23
provide the corresponding product 27. It showed strong peaks at
7.96, 7.45, and 1.53 ppm in its 1H NMR spectrum, which we at-
3.2.1. PEG-bound 1,3-bis(4-nitrophenoxy)-2-propether (17)
d
1,3-Bis(4-nitrophenoxy)-2-propanol (0.651 g, 1.9 mmol) and
NaH (0.062 g, 2.6 mmol) were dissolved in 30 mL of dry THF. The
mixture was stirred at room temperature for 30 min. PEG tosylate
(16) (1.39 g, 0.3 mmol) was then added to the solution and refluxed
for 24 h. THF was then evaporated under reduced pressure. The
brown residue was re-dissolved in water (5 mL) and extracted with
CH2Cl2 (3ꢂ50 mL). The volume of CH2Cl2 was reduced by 95% under
reduced pressure. The remaining CH2Cl2 solution was cooled to
tributed to the presence of the phenyl and methyl groups. In addi-
tion, an IR spectroscopic peak at 1715 cmꢀ1, indicative of the C]O
bond, was observed. Subsequent cleavage of BOC group under
classical condition36 (TFA/CH2Cl2) afforded a new scaffold of aniline
28. Conventional 1H NMR was also used as an essential tool for direct
reaction monitoring and optimization. The loading capacities of
PEGs were determined by 1H NMR method and the following

L.-L. Jiang et al. / Tetrahedron 65 (2009) 5257–5264
5261
OH
O
CH2
C
HOOC
NHBOC
DCC/DMAP
CH2Cl2
+
OH
OH
26
25
O
O
O
O
C
O
NHBOC
NHBOC
O
C
NH2
NH2
TFA/CH2Cl2
reflux
O
CH2
C
O
C
O
CH2
C
C
O
O
O
O
C
O
C
28
27
Scheme 6. Synthetic procedure of PEG–(PhNH2)6.
0 ꢁC, and 50 mL of diethyl ether were added. After 30 min, 1.45 g
(90.6% yield) of yellow precipitate was collected by filtration. 1H
(0.50 mL, 3.05 mmol), and ethanol (5 mL) was stirred and heated to
reflux under nitrogen atmosphere for 2.5 h and then 50 mL of cold
diethyl ether were added to the mixture with vigorous stirring to
produce an orange precipitate, in which a little of symmetrical dye
was existed. Just as we described in previous work,25 the sym-
metrical dye could be removed. Yield 1.21 g (93.1%). IR (KBr): 3433,
NMR (300 MHz, CDCl3):
J¼8.8 Hz), 4.2–3.4 (m, PEG), 3.89 (m, 4H). IR (KBr): 3452, 2884,1607,
1513, 1467, 1358, 1094 cmꢀ1
d
8.22 (d, 4H, J¼8.8 Hz), 7.01 (d, 4H,
.
3.2.2. PEG-bound 1,3-bis(4-aminophenoxy)-2-propether (18)
2884, 1671, 1639, 1516, 1463, 1183, 1110 cmꢀ1
.
PEG-bound 1,3-bis(4-nitrophenoxy)-2-propether 17 (3.15 g,
0.68 mmol), activated carbon (0.122 g), FeCl3$6H2O (0.143 g), and
ethanol (30 mL) were added in a three-necked flask. Hydrazine
hydrate (80%) (10 mL) was then added to the mixture within 2 h.
Afterward the reaction mixture was refluxed for 24 h, and ethanol
was evaporated under reduced pressure. The remaining ethanol
solution was cooled to 0 ꢁC, and 100 mL of diethyl ether were
added. The brown-black precipitate was collected by filtration. This
precipitate was re-dissolved in CH2Cl2 and precipitated by addition
of diethyl ether at 0 ꢁC. Yield 2.08 g (96.5%). 1H NMR (300 MHz,
3.2.6. PEG–(PhNH2)4-bound tetramethine hemicyanine (20)
A mixture of 19 (1.01 g, 0.21 mmol), 1,2,3,3-tetramethylindole-
nium-5-sulfonate (0.111 g, 0.42 mmol), and glacial acetic acid
(9 mL) was stirred and heated at 80 ꢁC under nitrogen atmosphere
for 2 h and then cold diethyl ether (30 mL) was added to the so-
lution with vigorous stirring to produce a brown precipitate, in
which a little of symmetrical dye existed. After the byproduct was
removed by appropriate method,25 product 20 was obtained. Yield
1.15 g (95.8%). IR (KBr): 3429, 2917, 1704, 1679, 1645, 1600, 1446,
CDCl3):
PEG), 3.89 (m, 4H). IR (KBr): 3430, 3386, 3318, 1511, 1463, 1237,
1032 cmꢀ1
d
6.78 (d, 4H, J¼8.1 Hz), 6.58 (d, 4H, J¼8.2 Hz), 4.2–3.4 (m,
1180, 1108 cmꢀ1
.
3.3. Synthesis of trimethine and pentamethine cyanine dyes
using PEG–(PhNH2)4
.
3.2.3. PEG–(PhNH2)4-bound formamidine (22)
3.3.1. General procedure for the formation of trimethine cyanine
dyes (24)
To PEG–(PhNH2)4-bound dimethine hemicyanine 23 (0.833 g,
0.16 mmol) and 1-(3-carboxypentynyl)-2,3,3-trimethylindoleninium-
5-sulfonate 4 (0.058 g, 0.16 mmol) was added a solution of acetic
anhydride (Ac2O) (2 mL) and pyridine (1 mL). The mixture was stir-
red and heated at 110 ꢁC under nitrogen atmosphere for 15 min. After
the mixture was cooled, the red dye was precipitated with ethyl
acetate. The gummy product 24b was washed with CH2Cl2 until the
red free powder was obtained. The red product was collected in
20.8% yield.
To product 18 (1.05 g, 0.23 mmol) was added a solution of tri-
ethyl orthoformate (3.25 mL, 20 mmol) in glacial acetic acid (9 mL).
The reaction mixture was heated at 55 ꢁC for 5.5 h and then 30 mL
of cold diethyl ether were added to the solution with vigorous
stirring to produce a yellow precipitate, which was dissolved in
CH2Cl2 and precipitated with diethyl ether for further purification.
Yield 0.951 g (95.4%). IR (KBr): 3342, 2906, 1678, 1649, 1513, 1457,
1397, 1111 cmꢀ1
.
3.2.4. PEG–(PhNH2)4-bound 4-(3-methoxyallylideneamino)benzoic
acid ester (19)
Product 7. Yield 19.0%. 1H NMR (300 MHz, D2O):
d 8.31 (t, 1H,
To product 18 (1.02 g, 0.22 mmol) was added a solution of
1,1,3,3-tetramethoxypropane (3.7 mL, 22.2 mmol) in glacial acetic
acid (9 mL). The reaction mixture was heated at 55 ꢁC for 5.5 h and
then 30 mL of cold diethyl ether were added to the solution with
vigorous stirring to produce a dark yellow precipitate, which was
dissolved in CH2Cl2 and precipitated with diethyl ether for further
purification. Yield 0.996 g (91.7%). IR (KBr): 3435, 2884, 1704, 1641,
b
proton of the bridge, J¼13.9 Hz), 7.73–7.64 (m, 4H, 4-H, 40-H, 6-H,
60-H), 7.18–7.15 (m, 2H, 7-H, 70-H), 6.22–6.17 (m, 2H, a0 proton of
a,
the bridge), 3.94–3.89 (m, 4H,
J¼7.1 Hz), 1.64–1.15 (m, 21H, 3CH2 groups, 1CH3 and 2(CH3)2
groups). 13C NMR (300 MHz, D2O):
183.5, 175.8, 175.5, 151.9, 144.1,
a-, a
0-CH2), 2.03 (t, 2H, –CH2COOH,
d
143.7, 141.7, 141.5, 139.7, 139.60, 126.8, 119.8, 111.5, 111.3, 103.4, 49.3,
44.3, 39.6, 37.3, 27.1, 27.0, 26.6, 26.1, 25.6, 11.9. MS: m/z for
C31H38S2O8N2 [MþNa]þ calcd 653.20, found 653.09.
1512, 1463, 1350, 1111 cmꢀ1
.
3.2.5. PEG–(PhNH2)4-bound dimethine hemicyanine (23)
A mixture of 22 (1.10 g, 0.23 mmol), 1,2,3,3-tetramethylindole-
nium-5-sulfonate (0.132 g, 0.52 mmol), triethyl orthoformate
Product 24a. Yield 22.3%. 1H NMR (300 MHz, D2O):
d 8.27 (t, 1H,
b
proton of the bridge, J¼13.2 Hz), 7.71–7.63 (m, 4H, 4-H, 40-H, 6-H,
60-H), 7.14–7.06 (m, 2H, 7-H, 70-H), 6.20–6.10 (m, 2H, a0 proton of
a,

5262
L.-L. Jiang et al. / Tetrahedron 65 (2009) 5257–5264
O
O
C
NH2
O
O
CH2
C
O
C
NH2
1,1,3,3-tetramethoxy-
propane, glacial acetic
acid, 55 °C, 5.5 h
O
triethyl orthoformate,
glacial acetic acid, 55
°C, 5.5 h
O
C
O
O
O
O
O
C
N
CH NH
O
C
O
O
C
N
N
OMe
O
CH2
O
C
O
O
C
O
CH2
C
CH
NH
C
CH2
O
O
N
OMe
O
O
O
C
O
O
C
C
N
CH
NH
O
OMe
32
29
heterocycle, triethyl
orthoformate, EtOH,
reflux, 2 h
heterocycle, glacial
acetic acid, 80 °C, 2 h
SO3
SO3
SO3
O
O
O
O
C
N
H
N
O
C
N
H
N
O
CH2
C
O
O
CH2
C
O
R1
R1
O
O
SO3
O
C
C
N
N
N
O
O
H
H
N
C
C
R1
R1
SO3
SO3
N
33
30
N
R1
R1
heterocycle, acetic
anhydride, pyridine,
110 °C, 15 min
heterocycle, acetic
anhydride, pyridine,
110 °C, 15 min
SO3
Z
SO3
HO3S
N
N
N
N
R2
R1
R2
R1
7: Z=SO3H, R1=C2H5, R2=(CH2)5COOH
31: Z=benz, R1=Me, R2=Me
5: R1=C2H5, R2=(CH2)5COOH
Scheme 7. Synthesis of water-soluble cyanine dyes by using PEG–(PhNH2)6 as a support.
the bridge), 3.90 (t, 2H,
a
-CH2), 3.37 (s, 3H, CH3), 1.78–1.15 (m, 15H,
176.1,
the bridge), 3.95 (t, 2H,
–CH2COOH, J¼6.9 Hz), 1.97–1.18 (m, 18H, 3CH2 groups and 2(CH3)2
groups). 13C NMR (300 MHz, D2O):
182.2, 176.4, 176.3, 151.9, 144.7,
a-CH2), 3.46 (s, 3H, CH3), 2.12 (t, 2H,
1CH3 groups and 2(CH3)2 groups). 13C NMR (300 MHz, D2O):
d
175.3, 151.8, 144.5, 143.4, 141.5, 141.2, 139.7, 139.6, 126.7, 119.8, 119.6,
111.2, 103.4, 103.3, 49.2, 39.5, 31.3, 26.9, 11.5. MS: m/z for
C26H30S2O6N2 [Mꢀ1]ꢀ calcd 529.2, found 529.1.
d
144.6, 144.0, 141.5, 141.3, 139.7, 126.8, 119.8, 111.5, 111.3, 103.6, 49.3,
44.2, 36.5, 31.3, 27.0, 26.6, 25.9, 25.2. MS: m/z for C30H36S2O8N2
[Mꢀ1]ꢀ calcd 615.2, found 615.1.
Product 24b. Yield 20.8%. 1H NMR (300 MHz, D2O):
d 8.38 (t, 1H,
b
proton of the bridge, J¼11.5 Hz), 7.78–7.70 (m, 4H, 4-H, 40-H, 6-H,
Product 24c. Yield 19.2%. 1H NMR (300 MHz, D2O):
d 8.46 (t, 1H,
60-H), 7.23–7.71 (m, 2H, 7-H, 70-H), 6.27–6.19 (m, 2H,
a,
a0 proton of
b
proton of the bridge, J¼13.7 Hz), 7.79–7.73 (m, 4H, 4-H, 40-H, 6-H,

L.-L. Jiang et al. / Tetrahedron 65 (2009) 5257–5264
5263
Table 2
DMSO):
d 174.1, 173.1, 154.8, 145.7, 145.6, 143.2, 142.0, 141.1, 140.8,
Synthesis of trimethine and pentamethine dyes by using PEG–(PhNH2)6 as a support
126.6, 120.4, 110.5, 110.3, 104.0, 103.5, 49.3, 39.1, 31.7, 27.5, 12.5. MS:
m/z for C28H32S2O6N2 [Mꢀ1]ꢀ calcd 555.2, found 555.1.
Compound
Monomer 1 Monomer 2 Yielda
Product 21b. Yield 21.3%. 1H NMR (300 MHz, D2O):
d 7.88–7.66 (m,
(%)
6H, 4-H, 40-H, 6-H, 60-H,
b,
b
0 protons of the bridge), 7.21–7.18 (m, 2H,
proton of the bridge, J¼12.2,12.5 Hz), 6.11–
-CH2), 3.49 (s,
3H, CH3 group), 2.07 (t, 2H, –CH2COOH), 1.79–1.31 (m, 18H, 3CH2
groups and 2(CH3)2 groups). 13C NMR (300 MHz, D2O):
180.1, 173.8,
HO3S
SO3
7-H, 70-H), 6.38 (dd,1H,
g
5.98 (m, 2H, a, a
a0 proton of the bridge), 3.93 (t, 2H,
2
2
4
4
26.1
23.2
N
N
(CH2)5COOH
5
C2H5
d
173.7, 154.2, 144.1, 143.7, 141.8, 141.7, 139.3, 139.2, 126.6, 119.8, 111.1,
111.0,104.1,103.9, 49.3, 49.0, 44.1, 37.0, 26.3, 25.7, 25.2, 22.9,18.9. MS:
m/z for C32H38S2O8N2 [Mꢀ1]ꢀ calcd 641.2, found 641.1.
HO3S
SO3
N
N
3.4. Synthesis of PEG derivatives 27–33
HOOC(H2C)5
C2H5
7
3.4.1. PEG–(PhNHBOC)6 (27)
PEG-bound pentaerythritol (25) (1.53 g, 0.68 mmol) and 4-
[(tert-butoxycarbonyl)amino]benzoic acid (1.95 g, 8.2 mmol) were
dissolved in 45 mL of anhydrous CH2Cl2. N,N-Dimethyl amino-
pyridine (DMAP) (0.114 g, 1.2 mmol) was added to the solution as
a catalyst and dicyclohexyl carbodiimide (DCC) (2.49 g, 11.7 mmol)
was added as a coupling agent. The mixture was kept in a dry ni-
trogen environment at room temperature for 12 h. After the
dicyclohexylurea (DCU) was filtered off, the filtrate was concen-
trated under reduced pressure, and then 50 mL of cold diethyl ether
were added to the solution with vigorous stirring. Then the white
precipitate was filtered and collected. The purified product 27 was
dried in vacuum oven for 24 h. Yield 2.0 g (83.3%). IR (KBr): 3426,
SO3
N
N
11
14
18.5
31
Yields are based on weight of heterocycle in cleavage step.
a
60-H), 7.30–7.25 (m, 2H, 7-H, 70-H), 6.33–6.26 (m, 2H,
the bridge), 4.05 (t, 2H,
2H, J¼6.9 Hz, -CH2), 1.86–1.65 (m, 16H,
groups). 13C NMR (300 MHz, D2O):
176.6, 175.6, 152.0, 144.7, 143.9,
a
,
a
0 proton of
a
-CH2), 3.53 (s, 3H, 1CH3 groups), 2.87 (t,
-CH2, -CH2, and 2(CH3)2
d
b
g
2913,1725, 1602, 1538, 1461 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d 7.97
d
(d, 2H, J¼8.4 Hz), 7.46 (d, 2H, J¼8.3 Hz), 4.45–3.34 (m, PEG), 1.53 (s,
141.4, 139.6, 139.5, 126.7, 119.8, 111.9, 103.8, 50.5, 49.2, 46.8, 31.2,
26.9, 25.6, 21.7. MS: m/z for C28H34S3O9N2 [Mþ1]þ calcd 639.1,
found 639.1.
9H).
3.4.2. PEG–(PhNH2)6 (28)
Product 24d. Yield 20.5%. 1H NMR (300 MHz, D2O):
d
8.27 (t, 1H,
Compound 27 (1.65 g, 0.46 mmol), trifluoroacetic acid (TFA)
(4.5 mL), and CH2Cl2 (7 mL) were introduced in a flask. The mixture
was refluxed for 10 h under magnetic stirring. After the TFA was
neutralized by triethylamine, 50 mL of cold diethyl ether were
added to the solution with vigorous stirring to produce a yellow
precipitate. Yield 1.15 g (80.3%). IR (KBr): 3428, 2911, 1742, 1605,
b
proton of the bridge, J¼13.2 Hz), 7.63–7.55 (m, 4H, 4-H, 40-H, 6-H,
60-H), 7.12–7.09 (m, 2H, 7-H, 70-H), 6.16–6.09 (m, 2H, a0 proton of
a,
the bridge), 3.87 (m, 4H,
1.68–1.08 (m, 19H,
a
-,
g
a
0-CH2), 2.70 (t, 2H, J¼6.9 Hz,
d-CH2),
b
-CH2,
-CH2, 1CH3 groups and 2(CH3)2 groups).
MS: m/z for C29H36S3O9N2 [Mꢀ1]ꢀ calcd 651.1, found 651.0.
1460 cmꢀ1. 1H NMR (300 MHz, CDCl3):
(d, 2H, J¼7.1 Hz), 4.40–3.40 (m, PEG).
d
7.83 (d, 2H, J¼7.3 Hz), 6.64
3.3.2. General procedure for the formation of pentamethine cyanine
dyes (21b)
To PEG–(PhNH2)4-bound tetramethine hemicyanine 20 (0.601 g,
3.4.3. PEG–(PhNH2)6-bound formamidine (32)
0.10 mmol) and 1-(
3
-carboxypentynyl)-2,3,3-trimethylindoleni-
A mixture of 28 (0.418 g, 0.14 mmol), triethyl orthoformate
(1.5 mL, 9 mmol), and glacial acetic acid (5 mL) was stirred and
heated at 55 ꢁC for 5.5 h. Then 30 mL of cold diethyl ether were
added to the solution with vigorous stirring to produce a yellow
precipitate, which was dissolved in CH2Cl2 and precipitated with
diethyl ether for further purification. Yield 0.302 g (85.7%). IR (KBr):
nium-5-sulfonate 4 (0.038 g, 0.11 mmol) was added a solution of
Ac2O (2 mL) and pyridine (1 mL). The mixture was stirred and heated
at 110 ꢁC under nitrogen atmosphere for 15 min. After the mixture
was cooled, the blue dye was precipitated with ethyl acetate. The
gummy product 21b was washed with CH2Cl2 until the blue free
powder was obtained. The blue product was collected in 21.3% yield.
3430, 2885, 1698, 1635, 1603, 1461, 1111 cmꢀ1
.
Product 5. Yield 25.9%. 1H NMR (300 MHz, D2O):
6H, 4-H, 40-H, 6-H, 60-H, b0 protons of the bridge), 7.27–7.25 (m,
2H, 7-H, 70-H), 6.38 (dd, 1H,
proton of the bridge, J¼12.6, 12.5 Hz),
6.11–6.00 (m, 2H,
d 7.86–7.70 (m,
b,
3.4.4. PEG–(PhNH2)6-bound 4-(3-methoxyallylideneamino)benzoic
acid ester (29)
g
a
,
a0 proton of the bridge), 4.00–3.95 (m, 4H,
a
-,
A mixture of 28 (0.522 g, 0.17 mmol), 1,1,3,3-tetramethoxy-
propane (2.1 mL, 12.6 mmol), and glacial acetic acid (5 mL) was
stirred and heated at 55 ꢁC for 5.5 h. Then 30 mL of cold diethyl
ether were added to the solution with vigorous stirring to produce
a dark yellow precipitate, which was dissolved in CH2Cl2 and pre-
cipitated with diethyl ether for further purification. Yield 0.493 g
a
0-CH2), 2.18 (t, 2H, –CH2COOH, J¼7.0 Hz), 1.72–1.27 (m, 21H, 3CH2
groups, 1CH3 and 2(CH3)2 groups). 13C NMR (300 MHz, D2O):
d
183.1, 173.9, 173.7, 154.3, 144.2, 143.7, 141.9, 141.8, 139.4, 139.3,
126.6, 119.8, 111.1, 110.9, 104.0, 103.8, 49.1, 49.0, 44.1, 39.4, 37.1, 26.8,
26.7, 26.1, 25.6, 11.7. MS: m/z for C33H40S2O8N2 [M]þ calcd 656.81,
found 656.86; [MþNa]þ calcd 679.80, found 679.90.
(82.1%). IR (KBr): 34 442, 2885, 1701, 1638, 1601, 1463, 1111 cmꢀ1
.
Product 21a. Yield 26.0%. 1H NMR (300 MHz, DMSO):
d 8.36 (t,
2H, J¼13.1 Hz,
b
,
b0 protons of the bridge), 7.81 (s, 2H, 4-H, 40-H),
3.4.5. PEG–(PhNH2)6-bound dimethine hemicyanine (33)
7.64 (d, 2H, J¼8.2 Hz, 6-H, 60-H), 7.32 (m, 2H, 7-H, 70-H), 6.56 (dd,
A mixture of 32 (0.320 g, 0.097 mmol), 1-ethyl-2,3,3-trimethyl-
indolenium-5-sulfonate (0.096 g, 0.361 mmol), triethyl ortho-
formate (0.30 mL), and ethanol (5 mL) was stirred and heated to
reflux under nitrogen atmosphere for 2 h. After the reaction was
1H,
g proton of the bridge), 6.34–6.24 (m, 2H, a,
a0 proton of the
bridge), 4.13 (t, 2H, J¼6.7 Hz,
a-CH2), 3.59 (s, 3H, CH3 group), 1.69–
1.24 (m, 15H, CH3 group and 2(CH3)2 groups). 13C NMR (300 MHz,

5264
L.-L. Jiang et al. / Tetrahedron 65 (2009) 5257–5264
finished, product 33 was obtained as the collecting of PEG–
(PhNH2)2-bound dimethine hemicyanine described in Ref. 25. Yield
0.28 g (65.1%) IR (KBr): 3431, 2879, 1698, 1602, 1458, 1186,
105153) and Natural Science Foundation of Shaanxi Province, PR
China (No: 2004B06).
1112 cmꢀ1
.
Supplementary data
3.4.6. PEG–(PhNH2)6-bound tetramethine hemicyanine (30)
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2009.04.086.
A mixture of 29 (0.465 g, 0.14 mmol), 1-ethyl-2,3,3-trimethyl-
indolenium-5-sulfonate (0.112 g, 0.422 mmol), and glacial acetic
acid (5 mL) was stirred and heated at 80 ꢁC under nitrogen atmo-
sphere for 2 h. After the reaction was finished, product 30 was
obtained as the collecting of PEG–(PhNH2)2-bound tetramethine
hemicyanine described in Ref. 25. Yield 0.452 g (69.2%) IR (KBr):
References and notes
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3.5. Synthesis of cyanine dyes and benzoindocyanine dye
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3.5.1. General procedure for the formation of trimethine dyes
7 and 31
To PEG–(PhNH2)6-bound dimethine hemicyanine 33 (0.301 g,
0.065 mmol) and 1-(3-carboxypentynyl)-2,3,3-trimethylindoleni-
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nium-5-sulfonate 4 (0.046 g, 0.13 mmol) were added Ac2O (1.5 mL)
and pyridine (1 mL). The mixture was stirred and heated at 110 ꢁC
under nitrogen atmosphere for 15 min. After the mixture was
cooled, the red free powder 7 was collected as we described above.
The red product was collected in 23.2% yield.
Product 31. Yield 18.5%. 1H NMR (300 MHz, DMSO-d6):
1H,
proton of the bridge, J¼12.7 Hz), 8.34–7.63 (m, 9H, Ar H),
6.54–6.15 (m, 2H,
0 proton of the bridge), 3.79 (s, 3H, CH3 group),
d 8.46 (t,
b
a, a
3.64 (s, 3H, CH3 group), 1.97 (s, 6H, (CH3)2 groups), 1.73 (s, 6H,
(CH3)2 groups). MS: m/z for C29H30S2O3N2 [Mꢀ1]ꢀ calcd 485.2,
found 485.1.
23. Gourrie´rec, L.-L.; Giorgio, C.-D.; Greiner, J.; Vierling, P. Tetrahedron 2008, 64,
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3.5.2. General procedure for the formation of pentamethine cyanine
dyes 5
To PEG–(PhNH2)6-bound tetramethine hemicyanine 30
(0.361 g, 0.075 mmol) and 1-(3-carboxypentynyl)-2,3,3-trime-
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thylindoleninium-5-sulfonate 4 (0.042 g, 0.12 mmol) was added
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stirred and heated at 110 ꢁC under nitrogen atmosphere for
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in 26.1% yield.
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The authors are thankful to financial support from Science and
Technology Key Project of Ministry of Education, PR China (No: