Shortcut synthesis of β-cyclomannin from β-cyclodextrin

Article abstract of DOI:10.1021/ol062239b

(Diagram presented) β-Cyclomannin, a cyclic oligosaccharide consisting of seven α-D-mannosides connected together by the (1→4) glycoside linkage, has been efficiently synthesized by the OsO₄ oxidation of heptakis(2,3-didehydroxy)-β-cyclodextrin

Full text of DOI:10.1021/ol062239b

ORGANIC
LETTERS
2006
Vol. 8, No. 25
5733-5736
Shortcut Synthesis of
from -Cyclodextrin
â-Cyclomannin
â
Makoto Fukudome,† Tomonori Shiratani,‡ Yasuyoshi Nogami,‡ De-Qi Yuan,*,† and
Kahee Fujita*,†
Department of Molecular Medicinal Sciences, Graduate School of
Biomedical Sciences, Nagasaki UniVersity, Nagasaki 852-8521, Japan, and
Daiichi College of Pharmaceutical Sciences, Fukuoka 815-8511, Japan
fujita@nagasaki-u.ac.jp; deqiyuan@nagasaki-u.ac.jp
Received September 9, 2006
ABSTRACT
â
-Cyclomannin, a cyclic oligosaccharide consisting of seven
r
-D-mannosides connected together by the (1
f
4) glycoside linkage, has been
efficiently synthesized by the OsO4 oxidation of heptakis(2,3-didehydroxy)-
â
-cyclodextrin which was prepared from â-cyclodextrin by a five-
step transformation. The novel cyclooligosaccharide not only showed water solubility high enough to meet the requirement for drug formulation
but also demonstrated strong binding ability toward guest molecules.
Macrocyclic molecules have attracted much attention as
molecular receptors.1 Among them, cyclodextrins (CDs) have
been in the central positions in the studies from the initial
stage because of the diversity of their inclusion phenomena
and enzymelike functions. Therefore many efforts have been
made to prepare novel types of cyclooligosaccharides that
behave better than CDs.2
sors but also suffer from undesirable side reactions and poor
stereoselectivity in the final cycloglycosylations. Therefore,
the overall yields are extremely low. Although enzymatic
cycloglycosylation can be adopted as an alternative choice
for the final step,5 the target cyclooligosaccharides are not
obtained in large enough amounts for further investigation
of their functions and structures.
Methodological development of chemical glycosylations
enhanced chemical syntheses of non-glucose cyclooligosac-
charides. R-, â-, and γ-cyclomannins consisting of six to
eight R(1f4)-linked D-mannopyranosides were synthesized
by cycloglycosylations of their corresponding linear precur-
sors.3,4 However, these syntheses not only require very long
synthetic sequences in the constructions of the linear precur-
On the other hand, the discoveries of enzymes that convert
natural linear oligosaccharides into cyclooligosaccharides
have enabled the availability of the cyclooligosaccharides
in large enough amounts for further investigation,6 although
(3) Mori, M.; Ito, Y.; Ogawa, T. Tetrahedron Lett. 1989, 30, 1273. Mori,
M.; Ito, Y.; Ogawa, T. Carbohydr. Res. 1989, 192, 131. Mori, M.; Ito, Y.;
Uzawa, J.; Ogawa, T. Tetrahedron Lett. 1990, 31, 3191.
(4) Nishizawa, M. In Studies in Natural Product Chemistry; Rahman,
A., Ed.; Elsevier: Amsterdam, 1991; Vol. 8, pp 359. Ogawa, T. Chem.
Soc. ReV. 1994, 23, 397. Collins, P.; Ali, M. H. Tetrahedron Lett. 1990,
31, 4517.
(5) Apparu, C.; Cottaz, S.; Bosso, C.; Driguez, H. Carbohydr. Lett. 1994,
1, 349. Bornaghi, L.; Utille, J.-P.; Penninnga, D.; Schmidt, A. K.;
Dijkhuizen, L.; Schulz, G. E.; Driguez, H. Chem. Commun. 1996, 2451.
† Nagasaki University.
‡ Daiichi College of Pharmaceutical Sciences.
(1) Szejtli, J. Chem. ReV. 1998, 98, 1743. ComprehensiVe Supramolecular
Chemistry; Szejtli, J., Osa, T., Eds.; Pergamon Elsevier: Oxford, 1996;
Vol. 3.
(2) Gattuso, G.; Nepogodiev, S. A.; Stoddart, J. F. Chem. ReV. 1998,
98, 1919.
10.1021/ol062239b CCC: $33.50
© 2006 American Chemical Society
Published on Web 11/11/2006

Scheme 1. Preparation of â-Cyclomannin 3 from Olefin 2 Which Is Available via Five Steps from â-CD 1
these methodologies are obviously limited by the available
sorts and amounts of enzymes and homopolysaccharides.
In this situation, CDs have been reconsidered as starting
materials of cyclooligosaccharides because they are com-
mercially available in high qualities and at low prices. Thus,
effective and stereoselective transformations of all glucoside
units to other sugar units gave non-glucose cyclooligosac-
charides: per(3,6-anhydro)-CDs,7 per(2,3-anhydro)-cyclo-
mannins,8 cycloaltrins,9 per(3-amino-3-deoxy)-â-cycloaltrin,10
and per(3-deoxy)-cyclomannins.11 Recently, we added per-
(2,3-dideoxy-2,3-epithio)-â-cycloallin and per(2,3-didehy-
droxy)-â-CD 2 as new members to this family.12
mass spectrum of 3 which showed a parent peak for [M +
Na+] at m/z ) 1157 that is consistent with the molecular
ion of 3. The NMR spectra of 3 were very simple (Figure
1), and the assignments of the signals with the aid of 1H,1H-
In this paper, we report the preparation and binding
properties of â-cyclomannin 3. The CD-based methodology
for the synthesis of 3 is depicted in Scheme 1. A five-step
transformation of â-CD 1 afforded the olefin 2,12 and the
latter was treated with OsO4/N-methylmorphorin-N-oxide in
water to give cyclomannin 3 in 64% yield.13 This synthetic
process is dramatically short compared with the literature
one.3 Moreover, the literature methodology based on the
cycloglycosylation of natural linear oligosaccharides is not
applicable in the synthesis of 3 because R(1f4)-linked poly-
D-mannosides are not available to the best of our knowledge.
Oxidation of the olefin 2 by OsO4 proceeds smoothly
under very mild reaction conditions (130 min at 40 °C in an
aqueous solution). The complete conversion of CdC to the
glycol structure is confirmed by the time-of-flight (TOF)
Figure 1. 1H and 13C NMR spectra of â-cyclomannin 3 in D2O
(CH3CN as the internal standard). The assignments were made with
1
1
the aid of H,1H- and H,13C-COSY experiments.
and 1H,13C-COSY spectra revealed the C7 geometrical
symmetry of 3; that is, all seven sugar units are magnetically
equivalent. Examination of the observed coupling constants
(J1,2 ) 2.3, J2,3 ) 3.3, J3,4 ) 9.0, and J4,5 ) 9.0 Hz) suggested
a 4C1 mannopyranoside structure for the sugar units. Because
(6) Kawamura, M.; Uchiyama, T.; Kuramoto, T.; Tamura, Y.; Mizutani,
K. Carbohydr. Res. 1989, 192, 83. Oguma, T.; Horiuchi, T.; Kobayashi,
M. Biosci. Biotechnol. Biochem. 1993, 57, 1225.
(7) Gadelle, A.; Defaye, J. Angew. Chem., Int. Ed. Engl. 1991, 30, 78.
Ashton, P. R.; Ellwood, P.; Staton, I.; Stoddart, J. F. Angew. Chem., Int.
Ed. Engl. 1991, 30, 80. Yamamura, H.; Fujita, K. Chem. Pharm. Bull. 1991,
39, 2505.
(8) Coleman, A. W.; Zhang, P.; Ling, C.-C.; Mahuteau, J.; Parrot-Lopez,
H.; Miocque, M. Supramol. Chem. 1992, 1, 11. Kahn, A. R.; Barton, L.;
D’Souza, V. T. J. Chem. Soc., Chem. Commun. 1992, 1112. Zhang, P.;
Coleman, A. W. Supramol. Chem. 1993, 2, 255.
(9) Fujita, K.; Shimada, H.; Ohta, K.; Nogami, Y.; Nasu, K.; Koga, T.
Chem., Int. Ed. Engl. 1995, 34, 1621. Nogami, Y.; Nasu, K.; Koga, T.;
Ohta, K.; Fujita, K.; Immel, S.; Lindner, H. J.; Schmitt, G. E.; Lichtenthaler,
F. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 1899.
(10) Kahn, A. R.; Tong, W.; D’Souza, V. T. Supramol. Chem. 1995, 4,
243.
(11) Yang, C.; Yuan, D.-Q.; Nogami, Y.; Fujita, K. Tetrahedron Lett.
2003, 44, 4641. Lindner, H. J.; Lichtenthaler, F. W.; Fujita, K.; Yang, C.;
Yuan, D.-Q.; Nogami, Y. Acta Crystallogr., Sect. E 2003, 59, 387.
(12) Fukudome, M.; Shiratani, T.; Immel, S.; Nogami, Y.; Yuan, D.-Q.;
Fujita, K. Angew. Chem., Int. Ed. 2005, 44, 4201.
(13) To the aqueous solution (2.9 mL) containing olefin 212 (41 mg)
were added the solutions of aqueous 50% N-methylmorpholine-N-oxide (4.4
mL) and aqueous 4% OsO4 (0.53 mL), and the resultant mixture was stirred
at 40 °C for 130 min. After being concentrated in vacuo, the reaction solution
was added dropwise to a mixture (60 mL) of acetone and methanol (4:2
v/v). The white precipitates were collected by filtration, dissolved in water
(100 mL), and chromatographed on a Lobar column (Rp 18, size B) with
an elution of water (150 mL) and a second gradient elution from water to
20% aqueous MeOH (500 mL for each) to give 3 (33.3 mg, 64%): mp
190 °C; [R]D25 ) +61.7 (c ) 0.125 in H2O); 1H NMR (500 MHz, D2O, 35
°C, MeCN) δ ) 4.86 (d, 3J(H,H) ) 2.3 Hz, 7H, H1), 3.97 (dd, 3J(H,H) )
3
2.3, 3.3 Hz, 7H, H2), 3.85 (dd, J(H,H) ) 3.3, 9.0 Hz, 7H, H3), 3.83 (s,
3
dd, J(H,H) ) 2.3, 9.0 Hz, 7H, 6R-H), 3.79 (dd, 3J(H,H) ) 4.6, 9.0 Hz,
7H, 6S-H), 3.72 (ddd, 3J(H,H) ) 2.3, 4.6, 9.0 Hz, 7H, H5), 3.66 (t, 3J(H,H)
) 9.0, 7H, H4); 13C NMR (125 MHz, D2O, 35 °C, MeCN) δ ) 103.5
(C1), 78.8 (C4), 73.7 (C5), 71.2 (C2), 70.7 (C3), 61.7 (C6); TOF MS m/z
) 1157 [M + Na+].
5734
Org. Lett., Vol. 8, No. 25, 2006

the absolute configurations of C-4 and C-5 are the same as
those of â-CD, the large J4,5, which is comparable to that of
â-CD and reveals the trans-diaxial displacement pattern of
H-5 and H-4, strongly implies that the pyranosides take a
4C1 chair conformation. The similarly large J3,4 means that
the H-3 is also in axial orientation, and the O-3 is trans to
the O-4. Accordingly, the mannoside structure can be
deduced on the basis of the cis geometrical selectivity of
OsO4 oxidation. The small coupling constants J1,2 and J2,3
elucidation of a H-bonding interaction between any two
adjacent pyranosides. As shown in Table 1, the chemical
Table 1. 1H NMR Chemical Shifts δ [ppm],a,b Chemical Shift
3
Differences ∆δ [ppm], and Coupling Constants JOH,CH [Hz] for
the Hydroxyl Protons in DMSO-d6 at 35 °C
2-OH
∆δ
4.66 0.02 4.8
3-OH
δ
J
δ
∆δ
J
4
also support the C1 mannopyranoside structure. Moreover,
1
3 was the same as that reported for â-cyclomannin3 in H
â-cyclomannin (3)
4.55 0.08 6.9
4.6 or 5.5 4.47 6.0
5.48 1.02 2.5
6.6 4.46 5.1
R-methyl D-mannopyranoside 4.64d
and 13C NMR spectra. Thus, compound 3 is assigned to
â-cyclomannin.
â-CD (1)c
5.52 1.11 6.7
R-methyl D-glucopyranosidec 4.41
The successful isolation of â-cyclomannin indicates that
the oxidation is highly selective for mannopyranoside over
allopyranoside, otherwise 1.5 dozens of hetero-cyclooli-
gosaccharides with different allo-/manno- ratios would be
generated from 2, making it very difficult to separate any
one product from the reaction mixture. Similar selectivity
was also observed in the oxidation of methyl 4,6-O-
benzylidene-2,3-didehydroxy-R-D-glucopyranoside 414 and
monoolefin 6,15 which gave only the corresponding man-
nopyranosides 5 and 7,16 respectively (Scheme 2). The
a Chemical shifts relative to TMS. b Chemical shifts for the H-1’s of 3,
R-methyl D-mannopyranoside, â-CD, and R-methyl D-glucopyranoside are
4.72, 4.49, 4.68, and 4.32 ppm, respectively. c Ref 17. d Overlapped with
the signals of 4-OH.
shifts and coupling constants (J2OH,H2 and J3OH,H3) of the 2-OH
and 3-OH protons of 3 are quite similar to the corresponding
values of R-methyl D-mannopyranoside. However, â-CD,
which is well-known to have strong H-bonding between the
2-OH and 3′-OH of adjacent glucosides, displays very large
downfield shifts (∆δ > 1 ppm) for both the 2-OH and 3-OH
protons together with a half-decreased coupling constant for
3-OH in comparison with their component analogue R-meth-
Scheme 2. Transformation of Olefins 4 and 6 to Mannosides
5 and 7, Respectively
17
yl D-glucopyranoside in DMSO-d6 as well as in D2O.18
These results imply that cyclomannin 3 has no intramolecular
H-bonding interaction between the 3-OHs and the 2′-OHs
of neighboring mannosides even in DMSO.
Because the axial 2-OH of 3 disrupts the intramolecular
H-bonding, releasing itself and 3-OH for intermolecular
H-bonding with bulk water, compound 3 is much more
water-soluble than â-CD. A preliminary assay indicated that
the water solubility of 3 is more than 30 g/10 mL at 25 °C
whereas that of â-CD19 is 0.19 g/10 mL at 27 °C.
Differently from â-CD, â-cyclomannin 3 has the 2-OHs
directed to the outside of the cavity. This alternation of the
(16) Synthesis of 5: an olefin 414 (25 mg), N-methylmorpholine-N-oxide
(23.4 mg), and aqueous 0.1 M OsO4 (40 µL) solution was added to a mixed
solvent composed of water (0.5 mL) and MeCN (1 mL). The resultant
mixture was stirred at room temperature for 6 days. After the addition of
a saturated aqueous solution of Na2SO3 (2 mL), the reaction mixture was
extracted three times with AcOEt. The extracts were combined, washed
with 1 M HCl and then water, and dried over Na2SO4. Evaporation of the
solvents afforded crude 5 (28.4 mg) which was purified by preparative TLC
on silica gel (eluted with of AcOEt) to give pure 5 (22.7 mg, 80%): 1H
NMR (500 MHz, CDCl3, 35 °C, TMS) δ ) 7,49 and 7.37 (m, 5H, C6H5),
5.57 (s, 1H, benzylic H), 4.77 (s, 1H, H1), 4.29 (dd, 3J(H,H) ) 3.7, 9.2
formation of mannosides was suggested by the all-axial
displacements of the H-3, H-4, and H-5 protons which were
elucidated by the large coupling constants J3,4 and J4,5 of 5
and 7. Moreover, acid hydrolysis of 7 demonstrated that it
was composed of one mannose and six glucoses.
The axial displacement of the 2-OHs of 3 prevents each
2-OH from forming an intramolecular H-bond with the 3-OH
of its adjacent sugar unit. Evidence for this was collected
by 1H NMR measurements. The 1H NMR of 3 in DMSO-d6
showed two doublets for 2-OH and 3-OH protons that were
identified by the 1H,1H-COSY spectrum. R-Methyl D-
mannopyranoside represents the basic structure of the sugar
units of 3 and was taken as a reference compound for the
3
Hz, 1H, H6), 4.08-4.05 (m, 2H, H2 and H3), 3.92 (t, J(H,H) ) 9.2 Hz,
1H, H4), 3.86-3.81 (m, 2H, H5 and H6), 3.40 (s, 3H, OCH3), 2.73 and
2.71 (2H, 2- and 3-OHs); EI MS m/z (%) ) 282 (65) [M+], 105 (100)
[C7H5O+]. Synthesis of 7: a procedure similar to that for the preparation
of 3 was used starting with olefin 615 (316 mg) to give the product 7 (253
mg, 78%): 1H NMR (mannoside, 500 MHz, D2O, 35 °C, MeCN) δ )
4.86 (d, 3J(H,H) ) 2.1 Hz, 1H, H1), 4.04 (broad t, 1H, H2), 4.00 (dd,
3
3J(H,H) ) 3.3, 8.6 Hz, 1H, H3), 3.69 (t, J(H,H) ) 8.9 Hz, 1H, H4); 13C
NMR (mannoside, 125 MHz, D2O, 35 °C, MeCN) δ ) 104.0 (C1), 79.8
(C4), 71.1 (C3), 70.6 (C-2); FAB MS m/z ) 1135 [M + H+].
(17) Onda, M.; Yamamoto, Y.; Inoue, Y.; Chujo, R. Bull. Chem. Soc.
Jpn. 1988, 61, 4015.
(18) Bekiroglu, S.; Kenne, L.; Sandstro¨m, C. J. Org. Chem. 2003, 68,
1671 and refs cited therein.
(19) French, D.; Levine, M. L.; Pazur, J. H.; Norberg, E. J. Am. Chem.
Soc. 1949, 71, 353.
(14) Guthrie, R. D.; Murphy, D. J. Chem. Soc. 1965, 6666.
(15) Yuan, D.-Q.; Tahara, T.; Chen, W.-H.; Okabe, Y.; Yang, C.; Yagi,
Y.; Nogami, Y.; Fukudome, M.; Fujita, K. J. Org. Chem. 2003, 68, 9456.
Org. Lett., Vol. 8, No. 25, 2006
5735

orientation of 2-OHs makes the inside of the cavity more
hydrophobic and the outside more hydrophilic, as compre-
hensively demonstrated by the molecular lipophilicity po-
tential profiles of R-cyclomannin and R-CD20,21 generated
by molecular modeling. Therefore, cyclomannins may exhibit
interesting binding behaviors toward a hydrophobic guest.
â-Cyclomannin 3 can bind guest molecules in its cavity,
as â-CD does. Binding of methyl orange by 3 resulted in a
blue shift of the absorption around 485 nm and induced
circular dichroism (ICD) absorption as well. Titration of
sodium 1,8-anilinonaphthalenesulfonate (1,8-ANS) with 3
enhanced the fluorescence intensity and made the emission
blue shifted. The Scatchard plots of the titration data gave
good linearity, suggesting that 1:1 host-guest complexation
occurred. The binding constant was estimated to be 50 M-1.
The degree of fluorescence enhancement of 1,8-ANS had
been used as a measure for hydrophobicity of the hydro-
phobic pocket of host molecules including CDs.22 The 1:1
complex of 3 and 1,8-ANS demonstrated 1.6 times stronger
fluorescence intensity than the corresponding complex of
â-CD, indicating that 3 has a more strongly hydrophobic
cavity than â-CD. However, the binding constants of 3 for
methyl orange (pH 6.86) and 1,8-ANS (pH 7.40) at 25 °C
were 1850 and 50 M-1, not as high as expected and even
slightly smaller than the corresponding ones of â-CD, 3160
and 69.0 M-1, respectively. These results may imply that,
although the enhanced hydrophobicity of the cavity of
â-cyclomannin favors the binding of hydrophobic guest
molecules, this effect is canceled out by the countereffect
of decreased rigidity due to the disruption of the intramo-
lecular hydrogen bonding mentioned above. Similar en-
thalpy-entropy compensation effects are frequently observed
in host-guest systems.23 Interestingly, the complex of
â-cyclomannin and methyl orange gave a different ICD
spectrum from that of the â-CD complex (Figure 2),
Figure 2. UV-vis spectrum of methyl orange (-‚-, 2.0 × 10-5
M) and circular dichroism spectra of methyl orange (2.0 × 10-5
M) in the presence of â-CD (s, 1.2 × 10-3 M) and â-cyclomannin
3 (- -, 1.2 × 10-3 M) in pH 6.86 phosphate buffer solutions.
indicating that the change of the sugar components alters
the chirality of the cavity. To the best of our knowledge,
these spectral examinations of inclusion complexation are
the first cases with respect to chemically synthesized
cyclooligosaccharides.
We succeeded in the synthesis of â-cyclomannin 3 through
six steps via 2 from â-CD. This is a dramatically shortened
process compared with the reported stepwise synthesis from
monosaccharides. Because 3 became easily available in a
sufficient amount for investigation concerning its properties,
we demonstrated for the first time its enhanced solubility in
water, its ability of guest binding, and the spectra of a
chromophoric guest molecule induced by complexation.
Acknowledgment. Financial support from Nagasaki
University and a generous gift of CDs from Japan Maize
Products Co. Ltd. are acknowledged.
(20) Lichtenthaler, F. W.; Immel, S. Liebigs Ann. 1996, 27.
(21) Lichtenthaler, F. W.; Immel, S. Tetrahedron: Asymmetry 1994, 5,
2045.
(22) Cramer, F.; Saenger, W.; Spatz, H.-C. J. Am. Chem. Soc. 1967, 89,
14.
(23) Liu, L.; Guo, Q. X. Chem. ReV. 2001, 101, 673. Rekharsky, M. V.;
Inoue, I. Chem. ReV. 1998, 98, 1875. Fujita, K.; Okabe, Y.; Ohta, K.;
Yamamura, H.; Tahara, T.; Nogami, Y.; Koga, T. Tetrahedron Lett. 1996,
37, 1825.
Supporting Information Available: Full NMR spectro-
scopic data for compounds 3, 5, and 7 and the fluorescence
titration data of 3 and â-CD. This material is available free
of charge via the Internet at http://pubs.acs.org.
OL062239B
5736
Org. Lett., Vol. 8, No. 25, 2006