Synthesis of poly (3,4,5-trihydroxybenzoate ester) dendrimers and their chemiluminescence

Article abstract of DOI:10.1016/S0040-4039(02)01959-7

Gallic acid (GA) and gallic acid methyl ester (GM), polyphenol chemiluminescence (CL) compounds, produces light in the presence of alkali and hydrogen peroxide. We synthesized first-generation polyphenol dendrimers with GA units in the periphery and measured their CL for developing a polyphenol compound which has a strong CL intensity. The CL intensities of the poly (3,4,5-trihydroxybenzoate ester) dendrimers 4 and 8 in MeOH are approximately 400- and 600-fold stronger than that of GA, respectively.

Full text of DOI:10.1016/S0040-4039(02)01959-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 8185–8189
Synthesis of poly (3,4,5-trihydroxybenzoate ester) dendrimers
and their chemiluminescence
Manabu Nakazono, Li Ma and Kiyoshi Zaitsu*
Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
Received 17 May 2002; revised 22 August 2002; accepted 23 August 2002
Abstract—Gallic acid (GA) and gallic acid methyl ester (GM), polyphenol chemiluminescence (CL) compounds, produces light in
the presence of alkali and hydrogen peroxide. We synthesized first-generation polyphenol dendrimers with GA units in the
periphery and measured their CL for developing a polyphenol compound which has a strong CL intensity. The CL intensities of
the poly (3,4,5-trihydroxybenzoate ester) dendrimers 4 and 8 in MeOH are approximately 400- and 600-fold stronger than that
of GA, respectively. © 2002 Elsevier Science Ltd. All rights reserved.
Polyphenol such as pyrogallol and gallic acid (GA)
produces singlet oxygen in the presence of hydrogen
peroxide in an alkaline medium and emits light.1 GA
was utilized for selective Co2+ detection using a chemi-
luminescence (CL) flow injection system.2 The CL
intensities of polyphenol are very weak compared to
that of luminol and the acridinium ester, representative
CL compounds. Thus, trans-4-(3-propionic acid)
phenylboronic acid, 4-biphenylboronic acid in the pres-
ence of peroxidase3 or 1-ethyl-3-(3-dimethylamino-
propyl)carbodiimide4 have been used as enhancer for
highly sensitive polyphenol CL determination. How-
ever, the derivatization method for polyphenol that has
a strong CL intensity has not yet been reported.
chemiluminophores for high luminescence intensity and
hydroxyl groups in the periphery to form hydrogen
bonds with the analyte. The polyphenol dendrimers,
which have GA in the periphery, were synthesized and
their CL was measured.10 We synthesized the first-gen-
eration polyphenol dendrimers with GA units in the
periphery by a divergent method using pyrocatechol
and 3,4,5-trihydroxybenzene as the core molecules
(Schemes 1 and 2).11 The esterification of 3,4,5-triben-
zyloxybenzoyl chloride12 with pyrocatechol gave 1 in
56.8% yield. After the debenzylation of 1, we could not
separate 2 and the byproduct by chromatographic
purification. Therefore, the desired zero-generation
ester 2 was not isolated. Compounds 3 and 4 were
synthesized by repeating this esterification and debenzyl-
ation, but the yield of the first-generation ester 4 was a
low yield. The esterification of 3,4,5-tribenzyloxyben-
zoyl chloride with 1,3,5-trihydroxybenzene gave 5 in
31% yield. The zero-generation ester 6 and first-genera-
tion 8 were synthesized as described above. The yields
of the polyphenol dendrimers decreased with the
increasing dendrimer generation. Compounds 3 and 7
were debenzylated in high yield by catalytic reduction
under hydrogen gas in the presence of palladium-black
at ambient temperature. Benzylation will be optimal for
protecting the phenols. The mass spectra of 6 and 8
were obtained by matrix-assisted laser desorption/ion-
ization-time-of-flight mass spectrometry (MALDI TOF
MS) using 2,5-dihydroxybenzoic acid as the matrix. 4
and 8 were very stable in MeOH. Compounds 4 and 8
showed maximum CL intensities when 75 mM sodium
hydroxide and 500 mM hydrogen peroxide were added.
Both the intensities of the maximum light emission and
the length of the CL period of 4 and 8 were increased
Recently, the functions of dendrimers have focused on
the material engineering based on optics in the field of
nanoscale science5,6 since the poly (amidoamine) den-
drimer as a new polymer was synthesized.7 The poly
(propylene amine) family functionalized in the periph-
ery with fluorescent dansyl units interacts with Co2+.8
More recently, the acridinium dendrimers were conju-
gated with bovine serum albumin and its CL was
estimated as six-fold compared to that of the acri-
dinium salt.9
From our standpoint, we designed new types of
polyphenol dendrimers having an increased number of
Keywords: dendrimer; chemiluminescence; polyphenol.
* Corresponding author. Tel.: +81-92-642-6596; fax: +81-92-642-6601;
e-mail: zaitsu@phar.kyushu-u.ac.jp
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01959-7

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M. Nakazono et al. / Tetrahedron Letters 43 (2002) 8185–8189
Scheme 1. Synthetic route of 1–4. Reagents and conditions: (i) CHCl3, pyridine, 4-dimethylaminopyridine, 3,4,5-tribenzyloxyben-
zoyl chloride; (ii) Pd-black, H2, CHCl3–MeOH.
compared to that of GA. The time of maximum light
emission of 4 and 8 were 50 and 60 s after the injection
of hydrogen peroxide. The CL intensities in 5 min after
injection of the hydrogen peroxide were approximately
half the maximum CL intensities (Fig. 1). These kinds
of polyphenol compounds, which emit light for such a
long CL life, have not been found. The CL intensities
of 4 and 8 in MeOH were approximately 400- and
600-fold stronger than that of GA, respectively. The CL
intensities of 4 and 8 in MeOH were approximately
100- and 150-fold stronger than that of GM, respec-
tively (Table 1). CL intensity per GA unit of 4 and 8
was approximately equal, it suggests that the increment
of the number of chemiluminophores was effective to
increase CL intensity of polyphenol dendrimers. An
increase in the CL intensity of GA was accomplished
by forming a dendric structure.
In conclusion, polyphenol dendrimers were synthesized
in order to obtain a strong CL compound and their CL

M. Nakazono et al. / Tetrahedron Letters 43 (2002) 8185–8189
8187
Scheme 2. Synthetic route of 5–8. Reagents and conditions: (i) CHCl3, pyridine, 4-dimethylaminopyridine, 3,4,5-tribenzyloxyben-
zoyl chloride; (ii) Pd-black, H2, CHCl3–MeOH.
intensities were much stronger than that of GA.
Esterification of the hydroxyl groups of GA in the
dendrimer was very effective for developing a strong
CL. The relationship between the CL intensity and
structure of polyphenol dendrimers should be clarified
to know the reason of the strong light emission of
highperbranched compounds such as poly (3,4,5-trihy-
droxybenzoate ester) dendrimers. Polyphenol CL den-
drimers will be used for a wide variety of CL assays
utilizing hydroxyl groups of the polyphenol for form-
ing a hydrogen bond with oxygen in the analyte struc-
ture.

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M. Nakazono et al. / Tetrahedron Letters 43 (2002) 8185–8189
Table 1. Relative CL intensities of GA, GM, 4 and 8 in MeOH
Compounda
NaOH (mM)
H2O2 (mM)
Integral photon
Relative CL
intensityb
CL intensity per GA unitc [photon count
count (×104)
(×104)]
GA
GM
4
50
300
75
500
5000
500
4.8
20
2025
2986
1
4
421
622
337.5
331.7
8
75
500
a Concentration of each compound was 0.1 mM.
b CL intensity of GA obtained in MeOH was taken as 1.
c CL intensity per GA unit of 4 and 8 was calculated by dividing integral photon counts of 4 and 8 with the number of GA units in the periphery.
10. The CL measurements were performed using a photon-
counting luminometer, Lumat LB 9501 (Berthold, Wild-
bad, Germany); its operation and data processing were
performed using a personal computer (PC 9801 ES2,
NEC Co., Tokyo, Japan) with a luminometer program,
LB 9501/9801 Ver. 1.41 (Japan Berthold, Tokyo, Japan).
Procedure for the CL development of GA, 4 or 8: To 200
ml of a 0.1 mM MeOH solution of GA, 4 or 8 was added
100 ml of 10–250 mM NaOH. After standing for 25 s, the
CL reaction was initiated by the addition of 100 ml of 500
mM H2O2 using an automatic injection system in the
luminometer. The CL emission was measured for 5 min
and the integral photon counts were used.
11. Spectroscopic data: Compound 1: 1H NMR (CDCl3):
4.91 (s, 8H, benzyl H), 4.99 (s, 4H, benzyl H), 7.19 (m,
34H, ArH), 7.43 (s, 4H, ArH). Anal. calcd for C62H50O10:
C, 77.97; H, 5.28. Found: C, 77.58; H, 5.33. Compound
1
3: H NMR (CDCl3): 4.69 (m, 36H, benzyl H), 7.11 (m,
110H, ArH), MALDI-TOF MS; 2974.94 [M+Na]+. Com-
1
pound 4: H NMR (CD3OD): 6.98 (s, 4H, ArH), 7.08 (s,
8H, ArH), 7.41 (m, 4H, ArH), 8.00 (s, 4H, ArH). Anal.
Figure 1. Time course of chemiluminescence of 4 and 8 in
calcd for C62H38O34·8H2O: C, 50.62; H, 3.7. Found: C,
1
MeOH. The concentration was 0.1 mM in MeOH. The
50.29; H, 3.60. Compound 5: H NMR (CDCl3): 5.15 (s,
dashed line and solid line represent the CL development of 4
18H, benzyl H), 7.07–7.50 (m, 54H, ArH). Compound 6:
1H NMR (CD3OD): 7.02 (s, 3H, ArH), 7.20 (s, 6H,
ArH). MALDI-TOF MS; 605.303 [M+Na]+. Anal. calcd
for C27H28O15·5H2O: C, 48.22; H, 4.2. Found: C, 48.51;
and 8, respectively.
1
H, 4.24. Compound 7: H NMR (CDCl3): 4.78–5.02 (m,
References
54H, benzyl H), 7.12–7.45 (m, 162H, ArH). Compound 8:
1H NMR (DMSO-d6): 6.89–8.11 (m, 27H, ArH), 9.15–
9.36 (m, 27H, Phenol OH). MALDI-TOF MS; 1975.19
[M+Na]+. Anal. calcd for C90H54O51·12H2O: C, 49.87; H,
3.63. Found: C, 49.73; H, 3.91.
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12. 3,4,5-Tribenzyloxybenzoyl chloride was prepared as fol-
lows. To a stirred solution of methyl-3,4,5-trihydroxyben-
zoate (22 g, 0.1 mol) and benzylchloride (46 ml, 0.4
mmol) in DMSO (200 ml) was added potassium carbon-
ate (50 g, 0.36 mol). The mixture was refluxed for 2 h and
then H2O (400 ml) was added. The reaction solution was
cooled in ice and then filtered. The crude product was
dried and then recrystallized by n-hexane–benzene (1:2,
v/v) to give methyl-3,4,5-tribenzyloxybenzoate as a color-
less powder (16.07 g, 35.4% yield, mp 87°C). To a stirred
solution of methyl-3,4,5-tribenzyloxybenzoate (15.9 g, 35
mmol) and NaOH (4.2 g, 105 mmol) in MeOH (300 ml)
was added H2O (15 ml). The mixture was refluxed for 1
h and then H2O (300 ml) was added. The reaction
solution was acidified by 36% HCl. The crude product
was washed with H2O, dried and then recrystallized by
9. Adamczyk, M.; Fishpaugh, J.; Mattingly, P. G.; Shreder,
K. Bioorg. Med. Chem. Lett. 1998, 8, 3595.

M. Nakazono et al. / Tetrahedron Letters 43 (2002) 8185–8189
8189
was refluxed for 1.5 h at 73°C. To the resulting solution
was added petroleum ether (150 ml) and then cooled in ice.
The crude precipitate was recrystallized by n-heptane to
give 3,4,5-tribenzyloxybenzoyl chloride as a colorless pow-
der (9.78 g, 61% yield, mp 113°C). FAB-MS m/z; 458 [M+].
EtOH to give 3,4,5-tribenzyloxybenzoic acid as a colorless
powder (12.32 g, 80% yield, mp 187°C). To a stirred
solution of 3,4,5-tribenzyloxybenzoic acid (12.32 g, 28
mmol) and 95% thionylchloride (42 ml, 560 mmol) in
benzene (200 ml) was added pyridine (0.5 ml). The mixture