Target-selective photodegradation of oligosaccharides by a fullerene-boronic acid hybrid upon visible light irradiation

Article abstract of DOI:10.1039/c1cc15646b

A fullerene derivative was found to be capable of photodegrading oligosaccharides under irradiation with not only UV but also visible light. Furthermore, target-selective photodegradation of oligosaccharides (β-d-galactofuranosides) was achieved by a designed and synthesized fullerene-boronic acid hybrid upon irradiation with visible light in the absence of any additives under neutral conditions.

Full text of DOI:10.1039/c1cc15646b

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COMMUNICATION
Target-selective photodegradation of oligosaccharides by a
fullerene–boronic acid hybrid upon visible light irradiationw
Daisuke Takahashi, Shingo Hirono and Kazunobu Toshima*
Received 13th September 2011, Accepted 19th September 2011
DOI: 10.1039/c1cc15646b
A fullerene derivative was found to be capable of photodegrading
oligosaccharides under irradiation with not only UV but also
visible light. Furthermore, target-selective photodegradation of
oligosaccharides (b-D-galactofuranosides) was achieved by a
designed and synthesized fullerene–boronic acid hybrid upon
irradiation with visible light in the absence of any additives
under neutral conditions.
Carbohydrates in living cells play important roles in many
biological events, including bacterial cell wall recognition,
viral and bacterial infection, cell signaling, tumor cell
metastasis and fertilization.1 Despite its importance, however,
progress in this field has not been particularly rapid, because
there has been comparatively little research on the development
of smart technology for selective control of specific oligo-
saccharide functions. Therefore, the possibility of developing a
chemical agent which can selectively and directly degrade
target oligosaccharides under mild conditions has attracted
much attention.2,3 Herein, we report an innovative method for
target-selective degradation of oligosaccharides induced by a
light-activated fullerene derivative without additives and
under neutral conditions. To the best of our knowledge, this
is the first successful example of target-selective degradation of
oligosaccharides by visible light switching.
Fig. 1 Chemical structures of fullerene derivatives, g-CD and several
glycosides.
Certain fullerene derivatives have been found to be efficient
agents for photocleavage of DNA4 and proteins.5 However,
there are no reports on the use of light-activated fullerenes for
oligosaccharide degradation. In this context, we expected that
if a fullerene derivative could be made to produce a radical or
a reactive oxygen species (ROS) by photo-excitation, this
molecule could be used for degradation of oligosaccharides.
To investigate this hypothesis, we selected a commercially
available and water-soluble fullerene derivative 1 as an oligo-
saccharide photodegrading agent, and g-cyclodextrin (g-CD)
(3) as the target oligosaccharide (Fig. 1). It was previously
reported that a fullerene derivative bound with high affinity to
3 due to its ability to form an inclusion complex with the
fullerene moiety through hydrophobic interaction.6 We first
examined the photoinduced oligosaccharide-degrading activity
of 1 at concentrations of 15, 30, 90, and 300 mM against 30 mM
3 in 0.1 M phosphate buffer (pH 7.4) at 25 1C for 2 hours
under irradiation with a long-wavelength UV light (365 nm,
100 W) placed 10 cm from the sample. The progress of the
photodegradation reaction was monitored by HPLC/RI
analysis2,3 (Fig. 2a). It was found that the integrated HPLC
peak area corresponding to 3 clearly decreased only after
exposure of 1 to 3 with photo-irradiation, which indicated
that degradation of 3 by photo-activated 1 did take place.
MALDI/TOF-MS analysis of the degradation products confirmed
the production of a mixture of oxidative products at the C-6
hydroxy group(s) and oxidative cleavage products at the C-1
glycosidic bond. The result was quite similar to that using an
anthraquinone derivative which was previously reported
by us.2 In addition, it was found that the photodegradation
activity did not increase simply in a concentration-dependent
manner. Moreover, degradation activity was found to be
Department of Applied Chemistry, Faculty of Science and Technology,
Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522,
Japan. E-mail: toshima@applc.keio.ac.jp; Fax: +81 45-566-1576
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c1cc15646b
c
11712 Chem. Commun., 2011, 47, 11712–11714
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Fig. 2 Photodegradation of g-CD (3) by fullerene derivative 1. g-CD
(3) (30 mM) was incubated with 1 at different concentrations (15, 30,
90, and 300 mM) in 0.1 M phosphate buffer (30 mL, pH 7.4) at 25 1C for
2 h under irradiation with (a) a long-wavelength UV lamp (365 nm,
100 W), and (b) a visible-light lamp (diffuse sunlight, 100 W) placed
10 cm from the mixture, and analyzed by HPLC (TSK-GEL amide-80,
4.6 Â 250 mm; 40 1C; detection by RI).
Scheme 1 Synthetic scheme for fullerene–boronic acid hybrid 2.
highest when equal amounts of 1 and 3 were used with photo-
irradiation. These results suggested that excess 1 which did not
form a complex with 3 absorbed UV light and inhibited the
absorbability of 1 complexed with 3, which caused the photo-
degradation. Next, in order to examine the possibility of
photodegradation of 3 by 1 upon irradiation using visible
light, we measured the UV/vis spectrum of 1 (see ESIw). The
results showed that 1 absorbs in both the UV and visible
regions. To investigate this, photodegradation of 3 by 1 was
performed under visible light (diffuse sunlight, 100 W xenon
lamp) irradiation conditions. The results are shown in Fig. 2b.
Although the photodegradation activity of 1 against 3 under
visible light was found to be lower than under UV light, a
similar tendency in the relationship between the degree of
degradation and the dose equivalent of 1 was observed. These
results clearly show that the fullerene derivative 1 is capable of
degrading an oligosaccharide, g-CD (3), upon irradiation not
only with long-wavelength UV light but also with mild visible
light in the absence of further additives.
In order to elucidate the complexing ability of 2 with various
glycosides, including methyl 6-O-(b-D-galactofuranosyl)-b-D-
galactofuranoside (4), methyl b-D-galactofuranoside (5), methyl
b-D-galactopyranoside (6), methyl a-D-glucopyranoside (7),
methyl a-D-mannopyranoside (8), methyl a-D-maltoside (9),
methyl b-D-lactoside (10) and N-acetylneuraminic acid a-methyl-
glycoside (Neu5Aca2Me) (11), we used a 11B NMR titration
binding assay8 in 30% DMSO-d6/0.1 M phosphate buffer
(pH 7.4). The results are shown in Table 1. When b-D-galacto-
furanoside 4 or 5 was used, a change in the 11B NMR spectrum
of 2 was observed, and the peak area corresponding to the cyclic
boronate was found to increase in a manner dependent on the
concentration of the Galf (see ESIw). Furthermore, the Ka values
obtained for 2 with respect to 4 and 5 were almost the same; these
values were almost 60 times greater than those for 2 with
glycosides 6–11, including Neu5Aca2Me (11), which possesses
an extended glycerol side chain.
Next, we examined the photodegradation activity of 2
against various glycosides in 10% DMF/0.1 M phosphate
buffer (pH 7.4) at 25 1C for 2 hour under visible light (diffuse
sunlight) using a 100 W xenon lamp placed 10 cm from the
sample. The progress of the photodegradation reaction was
monitored by HPLC-UV (210 nm or 254 nm) analysis after
total acetylation with Ac2O in Py (for 4–10) or primary
alcohol t-butyldiphenylsilylation with TBDPSCl/imidazole in
Based on these favorable findings, we attempted to develop a
hybrid molecule, consisting of a fullerene moiety and an artificial
receptor that selectively binds to a target oligosaccharide, for
selective photodegradation of target oligosaccharides under
visible light irradiation. For this purpose, we focused on
b-D-galactofuranosides (Galfs) as target oligosaccharides, and
designed a hybrid molecule 2 consisting of a fullerene derivative
with one tertiary amino group and two carboxylic acids to
increase water solubility, and a phenylboronic acid moiety, which
has high affinity with Galfs.3 The hybrid 2 was synthesized as
shown in Scheme 1. 1,3-Dipolar cycloaddition of an azomethine
ylide (generated from a known aldehyde, 18,7 and a secondary
amine, 16, which was prepared from ethanolamine (14) in two
steps) to C60 (17) under reflux conditions provided fullerene
derivative 19 in 57% yield. Subsequent removal of the TBS
protecting group with TFA/CH2Cl2, followed by esterification of
the resulting alcohol 20 with a carboxylic acid, 21, in the presence
of EDC and DMAP in CH2Cl2, gave an ester in 67% yield.
Finally, removal of the tert-butyl and pinacol groups of the
resulting ester under aqueous acidic conditions provided the
desired hybrid molecule 2.
Table 1 Association constants (Ka) for the hybrid molecule 2 with
several glycosides
Entry
1
Glycoside
Kaa/MÀ1
Methyl 6-O-(b-D-galactofuranosyl)b-D-
galactofuranoside (4)
74
2
3
4
5
6
7
8
Methyl b-D-galactofuranoside (5)
Methyl b-D-galactopyranoside (6)
Methyl a-D-glucopyranoside (7)
Methyl a-D-mannopyranoside (8)
Methyl a-D-maltoside (9)
Methyl b-D-lactoside (10)
N-Acetylneuraminic acid a-methylglycoside
(Neu5Aca2Me) (11)
68
o1
o1
o1
o1
o1
o1
a
Determined by 11B NMR titration in 30% DMSO-d6/0.1 M phos-
phate buffer (pH 7.4); see ESI.w
c
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Chem. Commun., 2011, 47, 11712–11714 11713

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Next, in order to confirm ROS generation, we conducted
EPR studies using 2 and DMPO with or without visible-light
irradiation. Interestingly, it was found that photo-irradiation
of 2 in the presence of DMPO gave the DMPO-superoxide
anion spin adduct DMPO/ꢀOOH, not DMPO/ꢀOH, as shown
in Fig. 4b and c.9 Furthermore, it was confirmed that peaks
corresponding to DMPO/ꢀOOH were not detected either after
treatment of 2 without photo-irradiation or after photo-
irradiation in the absence of 2 (Fig. 4a). These results indicate
that Oꢀ2À species generated by the photo-excited fullerene
moiety and O2 play an important role in oxidative damage10
of the glycosides (see ESIw), although Oꢀ2À is generally
regarded as a rather unreactive radical species.11
Fig. 3 Photodegradation of glycosides by fullerene derivatives. Each glyco-
side (1.0 mM) was incubated with fullerene derivative 1 or 2 (1.0 mM) in
10% DMF/0.1 M phosphate buffer (100 mL, pH 7.4) at 25 1C for 2 h under
irradiation with a visible-light lamp placed 10 cm from the mixture, and
analyzed by HPLC (Mightysil RP-18 GP 5 mm, 4.6 Â 150 mm; 40 1C;
detection by UV (215 nm or 254 nm) after acetylation (for 4–10) or primary-
alcohol silylation (for 11) of the photodegradation products).
In conclusion, it was found that the fullerene derivative 1
effectively degraded oligosaccharides upon irradiation not
only with UV but also with visible light, without additives
and under neutral conditions. Furthermore, we have developed a
new chemical agent that can selectively and effectively degrade
Galf oligosaccharides by visible light switching under neutral
conditions. Although the binding constant between our hybrid
and target oligosaccharide is still relatively low, we hope this
method will provide a means of controlling the specific
functions of certain oligosaccharides. The development of
more specific and tighter binding hybrid molecules is now
under investigation in our laboratory.
DMF (for 11) of the resulting photodegradation products. The
percentage degradation was calculated based on the peak area
corresponding to each peracetylated glycoside or 9-O-TBDPS-
Neu5Aca2Me, and the results are summarized in Fig. 3. When
the fullerene derivative 1 was used as a control, less than 10%
degradation of the glycosides took place, owing to the low
affinity of 1 for glycosides. However, when the hybrid 2 was
exposed to glycoside 4 or 5, significant degradation took place.
In addition, the degradation of 4 by 2 was found to be more
effective than that of 5. These results suggest that the binding
affinity between the hybrid 2 and the target glycoside, and the
number of protons in the glycoside that can react with the
photo-activated fullerene moiety, are influential factors in
the target-selective degradation of oligosaccharides by 2.
These photodegradation phenomena were confirmed by ESI/TOF
MS analysis after the photoreaction and subsequent acetyla-
tion of the resulting products. The MS peak corresponding to
the acetylated monosaccharide 13, along with 12, was detected
as one of the major peaks (see ESIw) only after incubation of 4
with 2 under visible-light irradiation. These results suggest that
oxidative cleavage of the glycosidic linkage was caused by
ROS generated by the photo-excited fullerene moiety and O2.2
This research was supported in part by the High-Tech Research
Center Project for Private Universities (Matching Fund Subsidy,
2006–2011) and by Grants-in-Aid for Young Scientists (B)
(No. 22710220) and Scientific Research (B) (No. 20310140 and
23310153) from the Ministry of Education, Culture, Sports,
Science and Technology of Japan (MEXT).
Notes and references
1 Carbohydrate in Chemistry & Biology, ed. B. Ernst, G. W. Hart and
P. Sinay, Wiley-VCH, Weinheim, 2000; Comprehensive Glycoscience,
¨
ed. J. P. Kamerling, G.-J. Boons, Y. C. Lee, A. Suzuki, N. Taniguchi
and A. G. J. Voragen, Elsevier, Oxford, 2007.
2 M. Ishii, S. Matsumura and K. Toshima, Angew. Chem., Int. Ed.,
2007, 46, 8396.
3 D. Takahashi, S. Hirono, C. Hayashi, M. Igarashi, Y. Nishimura
and K. Toshima, Angew. Chem., Int. Ed., 2010, 49, 10096.
4 Fullerenes: Principles and Applications, ed. F. Langa De La Puente
and J.-F. Nierengarten, Royal Society of Chemistry, Cambridge,
UK, 2007; S. Bosi, T. D. Ros, G. Spalluto and M. Prato, Eur. J.
Med. Chem., 2003, 38, 913; H. Tokuyama, S. Yamago,
E. Nakamura, T. Shiraki and Y. Sugiura, J. Am. Chem. Soc.,
1993, 115, 7918; F. Prat, C.-C. Hou and C. S. Foote, J. Am. Chem.
Soc., 1997, 119, 5051; R. Bernstein, F. Prat and C. S. Foote, J. Am.
Chem. Soc., 1999, 121, 464.
5 S. Tanimoto, S. Sakai, S. Matsumura, D. Takahashi and
K. Toshima, Chem. Commun., 2008, 5767; Y. Ishida, S. Tanimoto,
D. Takahashi and K. Toshima, MedChemComm, 2010, 1, 212.
6 Y. Nishibayashi, M. Saito, S. Uemura, S. Takemura, H. Takemura
and Z. Yoshida, Nature, 2004, 428, 279.
7 L. A. Carpino, J. Org. Chem., 1964, 29, 2830.
8 S. Chapelle and J. Verchere, Tetrahedron, 1988, 44, 4469;
H. Otsuka, E. Uchimura, H. Koshino, T. Okano and
K. Kataoka, J. Am. Chem. Soc., 2003, 125, 3493.
9 E. Wertz and B. Bolton, in Electron Spin Resonance, McGraw-Hill,
New York, 1972; H. M. Swartz, J. R. Bolton and D. C. Borg, in
Biological Application of Electron Spin Resonance, Wiley-Interscience,
New York, 1972.
10 T. Kawashima, K. Ohkubo and S. Fukuzumi, Org. Biomol. Chem.,
2010, 8, 994.
11 D. T. Sawyer and J. S. Valentine, Acc. Chem. Res., 1981, 14, 393.
Fig. 4 EPR spectrum obtained during photo-irradiation of the hybrid 2
in the presence of DMPO. 2 (200 mM) and DMPO (500 mM) were
incubated in 30% DMF/0.1 M phosphate buffer (pH 7.4) containing
1.0 mM DETAPAC and 10 mM NADH under irradiation with a visible-
light lamp placed 40 cm from a flat cell. (a) Before irradiation; (b) after
2 min irradiation. (c) Possible pathways for the formation of DMPO/
ꢀOH and DMPO/ꢀOOH. DETAPAC = diethylenetriaminepentaacetic
acid, NADH = nicotinamide adenine dinucleotide.
c
11714 Chem. Commun., 2011, 47, 11712–11714
This journal is The Royal Society of Chemistry 2011