Selective synthesis and ester cleavage property of 3A,2B-anhydro-3B-deoxy-3B-thio-β-cyclodextrin

Article abstract of DOI:10.1016/j.tetlet.2007.08.062

The title compound was synthesized by the conversion of 2^A,3^A-alloepoxy-β-cyclodextrin to the 2^A,3^A-mannoepithio derivative with thiourea and subsequent ring-opening by intramolecular nucleophilic substitution. Its thiol group and the distorted cavity demonstrated good synergetic effect in promoting the cleavage of m-nitrophenyl acetate but did not cooperate with each other toward the p-isomer.

Full text of DOI:10.1016/j.tetlet.2007.08.062

Tetrahedron Letters 48 (2007) 7493–7497
Selective synthesis and ester cleavage property
of 3A,2B-anhydro-3B-deoxy-3B-thio-b-cyclodextrin
Makoto Fukudome,a Kaori Shimosaki,a Kazutaka Koga,b
De-Qi Yuana,* and Kahee Fujitaa,*
aDepartment of Molecular Medicinal Sciences, Graduate School of Biomedical Sciences, Nagasaki University,
Bunkyo-machi 1-14, Nagasaki 852-8521, Japan
bNihon Pharmaceutical University, Kita-adachi, Saitama 362-0806, Japan
Received 26 July 2007; revised 10 August 2007; accepted 16 August 2007
Available online 22 August 2007
Abstract—The title compound was synthesized by the conversion of 2A,3A-alloepoxy-b-cyclodextrin to the 2A,3A-mannoepithio
derivative with thiourea and subsequent ring-opening by intramolecular nucleophilic substitution. Its thiol group and the distorted
cavity demonstrated good synergetic effect in promoting the cleavage of m-nitrophenyl acetate but did not cooperate with each other
toward the p-isomer.
Ó 2007 Elsevier Ltd. All rights reserved.
Appropriate distortion of the cyclodextrin (CD) cavity
provides an interesting approach to get more defined
OH
OH
OH
OH
OH
accommodation of guest molecules in the cavities.1
Among the various CD derivatives with distorted cavi-
ties,2 3A,2B-anhydro-b-CD (1)3 has been the only one
host that demonstrated stronger binding ability toward
methyl orange than b-CD itself.2 Because the 3A,2B-
etheric bridge can be easily constructed by the intramo-
lecular reactions of 2,3-mannoepoxy-CDs under strong
alkaline conditions,3,4 development of artificial enzymes
based on 1 must be interesting if efficient methodology
can be established to introduce additional functional
groups onto the basic skeleton of 1. Years ago we
reported that the 3A-deoxy-3A-thio-b-CD (2) promoted
the cleavage of p-nitrophenyl acetate 62 times more effi-
ciently than b-CD.5 In this Letter, we describe the regio-
specific introduction of a thiol group to the C3B of the
3A,2B-anhydro disaccharide residue (Scheme 1) and the
enhanced catalytic ability of 3A,2B-anhydro-3B-deoxy-
3B-thio-b-CD (5).
O
O
O
BO
AO
O
O
O
O
O
O
O
OH HO
OH
6
HS
HO
OH HO
OH
5
1
2
tion of the epithio-ring. Simply heating the alkaline solu-
tion of 4 selectively afforded 3A,2B-anhydro-3B-deoxy-
3B-thio-b-CD (5) in good yield.
In a typical synthesis, a solution of compound 4
(100 mg, 0.0883 mmol) in 1 M aqueous NaOH (10 mL)
was stirred at 70 °C for 1 h, neutralized with 1 M HCl,
and filtered. The filtrate was chromatographed on a
Lobar column (Rp-18, size C) with a gradient elution
from 3% aq EtOH to 7% aq EtOH (1 L for each) and
then an elution of 30% aq EtOH (500 mL) to give 5
(68.5 mg, 68.5%). The TOF-MS spectrum of 5 showed
a pseudo parent peak [M+Na+] at m/z 1155, indicative
of the isomeric relationship between 4 and 5.7 Because
the thiol is unstable and susceptible to oxidation, 5
was converted to the corresponding disulfide dimer 67
by the conventional treatment with aq DMSO.8
The synthesis of 5 includes the conversion of 2A,3A-allo-
epoxy-b-CD (3) to 2A,3A-mannoepithio-b-CD (4)6 and
subsequent intramolecular nucleophilic opening reac-
Structure 6 was characterized by NMR spectroscopy.
Only one carbon (d 48.8 ppm) signal was observed in
the normal region where the S-bearing carbons should
Keywords: Cyclodextrin; Modification; Episulfide; Thiol; Catalysis.
*
Corresponding authors. E-mail addresses: deqiyuan@nagasaki-u.
ac.jp; fujita@nagasaki-u.ac.jp
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.08.062

7494
M. Fukudome et al. / Tetrahedron Letters 48 (2007) 7493–7497
OH
OH
OH
OH
(NH2)2CS
O
O
O
O
OH
OH
OH
O
O
O
O
O
O
BO
AO
O
HO
OH
6
O
HO
OH
6
S
O
O
O
O
S
OH HO
OH
4
3
5
−
OH
DMSO
HO
OH HO
O
S
O
dithio-
threitol
O
O
A
B
O
O
O
OH
OH
OH
HO
5
HO
HO
O
BO
AO
Br
O
O
O
O
6
HS
OH HO
OH
5
5
CH3
OH
OH
OH
OH
5 OH
A
3 2
OH
OH
OH
6
BO
O
A
BO
HCl, H2O
NaBH4
O
BO
AO
4
HO
O
O
OH
HO
O
O
OH
O
O
O
1
S
OH
S
OH
O
S
OH HO
OH
5
CH3
CH3
CH3
7
9
8
Scheme 1. Synthesis of 3A,2B-anhydro-3B-deoxy-3B-thio-b-CD 5 and chemical transformation of 5 to 9 for structural elucidation of the AB
disaccharide residue.
appear, which is indicative of the opening of the epithio-
ring by an O-nucleophile. TOF-MS spectrum of 6
showed the pseudo parent peaks [M+Na+] at m/z
2285, suggesting that the nucleophile should be an intra-
molecular CD hydroxyl group rather than a water mole-
cule. It is most likely that compound 4 has a similar
reaction behavior to that of the analog 2A,3A-manno-
epoxy-b-CD, which afforded compound 1 under similar
reaction conditions. Therefore, it can be reasonably
deduced that a C2B–O–C3A bridge was formed and
the S-atom is attached to C3B. Reaction of 6 with dithio-
threitol afforded monomer 5, confirming the disulfide
linkage between the two CD moieties.
correlated each other by demonstrating a strong C3A–
H2B HMBC coupling, confirming the bridging of the
two carbons by a single atom. Finally, the sequence of
residues A and B was evidenced by the observation of
H4A–C1B HMBC signal. The TOF mass spectrum of 9
displayed the pseudo parent peak [M+Na+] at m/z
469, which was in agreement with the structure
determination.
The thiol of 5 shows no obvious absorption above
215 nm, while ionization of the thiol generates a new
absorption band around 230 nm. Titration of the acidic
solution of 5 with aq NaOH solution resulted in absorp-
tion changes at 230 nm, which enabled the determina-
tion of the pKa of 5. The pKa value (7.4) of 5 was
rather low compared with normal thiols (pKa = 11–
12), which might be the result of the inter-subunit
hydrogen bonding, that is, C3B–SHÁ Á ÁHO–C2C and
the electron-withdrawing effect of oxygen atoms around
C3B–SH. Very low pKa values were also observed for
3A-deoxy-3A-thio-b-CD 2 (pKa 7.7) and 3A-deoxy-3A-
thio-a-CD (pKa 7.7).5 The decreased pKa values allow
the CD thiols to ionize almost completely to form the
thiolate anions under pH 9.0 condition where neither
the CD hydroxyl groups (pKa = ca. 12 for 2-OHs and
3-OHs, pKa = ca. 16 for 6-OHs) nor the normal thiols
(pKa = 11–12) undergo obvious ionization. Therefore,
enhanced catalytic ability of the CD thiols can be
expected even around neutral pH.
The above structural assignment was further confirmed
by the chemical transformation of 5 to 9 and subsequent
detailed NMR spectral analysis. Maltitol 9 was obtained
from 5 by alkylation of the thiol group (7), acid-hydro-
lysis to remove the unmodified glucoside units (8), and
final reduction with NaBH4.9 The NMR spectra were
recorded in DMSO-d6 solution. The application of
advanced NMR techniques including the 1H–1H COSY,
1
1H–13C COSY, H–13C HMBC, TOCSY (1D and 2D),
and ROESY (1D and 2D) spectrometry enabled the
identification of all the protons (including OH) and car-
bon nuclei of compound 9 (Fig. 1). The very small chemi-
cal shift of C3B indicated that it is substituted by a
sulfur atom. The 1H–1H COSY spectrum clearly demon-
strated the correlation of H4B to an OH proton, strongly
suggesting that residue B is a non-reducing terminal.
Neither H3A nor H2B coupled with any OHs in the
1H–1H COSY spectrum. However, the two positions
The cleavage of p- and m-nitrophenyl acetates by 5 was
carried out at 25 °C in a carbonate buffer solution (pH

M. Fukudome et al. / Tetrahedron Letters 48 (2007) 7493–7497
7495
Figure 1. The sugar part of the 1H–13C HMBC spectrum of 9 in DMSO-d6.
9.0, 0.1 M) and the release of the nitrophenolates was
monitored at 400 nm. The kinetic parameters are
summarized in Table 1 together with those of the refer-
ence compounds, b-CD, 3A,2B-anhydro-b-CD (1) and
3A-deoxy-3A-thio-b-CD (2). 3A,2B-Anhydro-b-CD (1)
cleaves p- and m-nitrophenyl acetates 5 and 73 times
faster than the buffer solution, slightly inferior to b-
CD although it shows slightly increased binding affini-
ties toward the ground states (1/KM), which is in agree-
ment with the results of the binding study. This result is
reasonable because the formation of the 3A-O-2B bridge
might distort the cavity and confine the orientation of
the bound substrate so that some of the 2- or 3-OH
can no longer actually contribute in promoting the reac-
tion of the substrates. Compared with b-CD, compound
2, which has a pseudo C7 symmetrical cavity and does
not confine the substrate orientation, is 66 times more
effective toward p-nitrophenyl acetate and 3 times more
effective toward the m-isomer, strongly suggesting that
the 3-SH group is catalytically important and actively
engaged in the reaction. Compound 5 combines the
structural feature of both 1 (distorted cavity) and 2
(catalytic thiol functionality). Its kcat (0.0054 sÀ1) for
p-nitrophenyl acetate, although a couple of times larger
than that of 1, is only one thirtieth that of 2, implying
that the introduction of the ether-bridge to 2 causes a
dramatic loss of the catalytic ability of the thiol group.
Comparison of the binding of 5 and 2 clearly indicated
that the introduction of the ether-bridge to 2 resulted
in a slight increase in the ground state binding (1/KM)
but a large decrease in the transition state binding
(1/KTS).10 Obviously, the distorted cavity confined the
ester group of p-nitrophenyl acetate to an orientation
that was not good for the attack of the thiolate anion
Table 1. Kinetic parameters of the cleavage of p- and m-nitrophenyl acetatesa
b
Catalyst pKa
p-Nitrophenyl acetate
m-Nitrophenyl acetate
Substrate
selectivity
kcat/10À2 sÀ1 KM/10À3 M kcat/kun KTSc/10À5 M kcat/10À2 sÀ1 KM/10À3 M kcat/kun KTSc/10À5 M (kcat/KM para
/
)
(kcat/KM meta
)
b-CD
1
0.226
0.149
15.0
0.541
5.51
3.48
7.60
2.90
7.53
4.97
500
18.0
73.1
70.1
1.52
16.1
1.30
1.13
4.50
15.0
6.89
3.20
18.3
83.9
72.9
290
1410
17.9
9.45
1.10
1.30
0.47
0.26
1.40
0.16
2
5
7.7
7.4
21.8
a Reactions were carried out in 0.1 M carbonate buffer solutions (pH 9.0) at 25 °C; the release of nitrophenolates was monitored at 400 nm.
Lineweaver–Burk treatment was applied to derive the kcat and KM values.
b Determined by UV titration at 230 nm of the acidic solution of a CD thiol with aq NaOH.
c KTS = KMkun/kcat, cf. Ref. 10.

7496
M. Fukudome et al. / Tetrahedron Letters 48 (2007) 7493–7497
of 5 to develop the transition state, that is, the distorted
cavity and the catalytic thiol group cannot efficiently
cooperate in promoting the reaction of p-nitrophenyl
acetate. Interestingly, compound 5 behaves quite differ-
ently toward m-nitrophenyl acetate. It accelerates the
References and notes
1. Fujita, K.; Chen, W.-H.; Yuan, D.-Q.; Nogami, Y.; Koga,
T.; Fujioka, T.; Mihashi, K.; Immel, S.; Lichtenthaler,
F. W. Tetrahedron: Asymmetry 1999, 10, 1689–1696;
Chen, W.-H.; Fukudome, M.; Yuan, D.-Q.; Fujioka, T.;
Mihashi, K.; Fujita, K. Chem. Commun. 2000, 541–
542.
2. Fujita, K.; Okabe, Y.; Ohta, K.; Yamamura, H.; Tahara,
T.; Nogami, Y.; Koga, T. Tetrahedron Lett. 1996, 37,
1825–1828.
3. Fujita, K.; Tahara, T.; Sasaki, H.; Egashira, Y.; Shingu,
T.; Imoto, T.; Koga, T. Chem. Lett. 1989, 917–920; Immel,
S.; Fujita, K.; Fukudome, M.; Bolte, M. Carbohydr. Res.
2001, 336, 297–308.
4. Fujita, K.; Fujioka, T.; Shimada, H.; Ohta, K.; Yoshino,
A.; Okabe, Y.; Fukudome, M.; Yuan, D.-Q. Eur. J. Org.
Chem. 2004, 3113–3118.
cleavage of m-nitrophenyl acetate by a factor of kcat
/
kun = 1400, ca. 20 times that of 1 and five times that
of 2, revealing the good synergistic effect of the orienta-
tion confining of substrate and the catalysis of the
thiol functionality. Because the binding strength of
the ground state was greatly decreased while that of
the transition state was not significantly altered, the
improved catalytic ability might be attributed primar-
ily to the decrease in binding strength of the ground
state rather than the improvement of transition state
binding. These results may imply that the combination
of the distorted cavity and the thiol group prevents
against deep inclusion of the substrate and the C3B
position, even not the most preferred, should be among
the ones that the ester group of the bound substrate can
easily access.
5. Fukudome, M.; Okabe, Y.; Yuan, D.-Q.; Fujita, K. Chem.
Commun. 1999, 1045–1046.
6. 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, 9456–9466; Fukudome, M.; Oniz-
uka, T.; Kawamura, S.; Yuan, D.-Q.; Fujita, K. Tetra-
hedron Lett. 2007, 48, 6665–6668.
The transfer of the acyl group of the substrates to the
S-atom of 5 was confirmed by isolation and structural
determination of the reaction product of 5 in the cleav-
age of the substrates.11 The HPLC of the catalytic reac-
tion mixture of 5 showed only one peak for the acylated
CD species. The TOF mass spectrum of the isolated CD
product demonstrated the parent peaks at m/z 1197 and
1213, which were consistent with the [M+Na+] and the
[M+K+] ions of the acylated 5. Evidence for the thioac-
etate structure was obtained in the 13C NMR spectrum.
The chemical shifts of both the methyl carbon and the
carbonyl carbon (d 199.7 ppm) of the CD acetate were
in the normal regions (d ca. 31 and 194 ppm, respec-
tively) of thioacetates, but much larger than the corre-
sponding normal values of acetates (d ca. 21 and
170 ppm, respectively).
7. Structural data of compound 5: Rf = 0.48 (n-PrOH/
EtOAc/H2O = 7:3:6 by volume). TOF-MS: m/z 1155
1
(M+Na+), 1171 (M+K+). H NMR (D2O, CH3CN int.):
d 5.08 (d, J = 2.8 Hz, 1H, H1B), 5.10 (d, J = 4.0 Hz, 1H),
5.06 (d, J = 3.5 Hz, 1H), 5.04 (d, J = 4.0 Hz, 1H), 5.02 (d,
J = 3.5 Hz, 1H), 4.99 (d, J = 4.0 Hz, 1H), and 4.97 (d,
J = 4.0 Hz, 1H, H1); 4.3–3.4 (m, 42H) ppm. 13C NMR
(D2O, CH3CN int.): d 103.0, 102.5, 102.5, 102.3, 101.9,
and 100.7 (C1); 94.6 (C1B); 82.0, 81.9, 81.8, 81.6, and
80.7 (C4); 80.0 (C4B); 76.4 (C2B); 75.4, 74.2, 74.1, 74.0,
74.0, 73.7, 73.6, 73.5, 73.0, 72.9, 72.8, 72.7, 72.7, 72.6, 72.5,
72.3, 71.0, 70.7, and 70.0 (C5, C3, C2); 61.3, 61.3, 61.2,
61.2, 61.0, 60.9, and 60.3 (C6); 40.2 (C3B) ppm.
Structural data of compound 6: Rf = 0.36 (n-PrOH/
EtOAc/H2O = 7:3:6 by volume). TOF-MS: m/z 2285
1
(M+Na+), 2301 (M+K+). H NMR (D2O, CH3CN int.):
d 5.18 (d, J = 3.7 Hz, 1H, H1B), 5.11 (d, J = 2.7 Hz, 1H,
H1A), 5.09 (d, J = 3.5 Hz, 1H), 5.07 (d, J = 3.8 Hz, 1H),
5.04 (d, J = 3.9 Hz, 1H), 4.98 (d, J = 3.8 Hz, 1H), and 4.97
(d, J = 3.7 Hz, 1H, H1); 4.22 (dd, J = 11.0, 3.6 Hz, 1H,
H2B); 4.01 (dd, J = 12.6, 3.7 Hz, 1H, H6B); 3.96–3.64 (m,
28H, H2A, H2B, H4B, H6, H5, H3), 3.64–3.47 (m, 12H,
H2, H4, H3B) ppm. 13C NMR (D2O, CH3CN int.): d 103.1
(C1A), 102.5, 102.5, 102.4, 101.5, and 100.0 (C1); 95.1
(C1B); 82.0, 81.9, 81.8, 81.7, and 79.4 (C4); 75.7 (C4B);
74.6 (C5B); 74.2, 74.2, 74.1, 74.0, 74.0, 73.7, 73.6, 73.0,
72.9, 72.8, 72.7, 72.6, 72.5, 72.3, and 71.0 (C5, C3, C4A,
C2); 70.7 (C2A); 70.5 (C2B); 70.1 (C3A); 61.4, 61.2, 61.1,
61.0, and 60.4 (C6); 48.8 (C3B) ppm.
Only when SH is put in the right position with the cor-
rect conformation required to access the transition state
can it significantly accelerate the reaction. The C3B of
3A,2B-anhydrodisaccharide residue seems to be among
the proper candidates of such positions in the case of
m-nitrophenyl acetate as the substrate but it is obviously
not good for promoting the reaction of the p-isomer.
As a result, compound 5 demonstrated improved
m-selectivity.
In summary, we described a synthetic strategy for
the functionalization of the C3B of 3A,2B-anhydro-b-
CD, which has a distorted cavity to confine the guest
orientation, and demonstrated that enhanced cata-
lytic ability can be obtained only when the introduced
catalytic group can cooperate with the distorted cavity
in developing the transition state of the catalytic
reaction.
8. Tam, J. P.; Wu, C.-R.; Liu, W.; Zhan, J.-W. J. Am. Chem.
Soc. 1991, 113, 6657–6662.
9. Compound 5 (70 mg), p-methylbenzyl bromide 140 mg,
and Cs2CO3 were added to DMF (3.5 mL) and the
resultant mixture was stirred at 70 °C for 30 min. After
being neutralized with 1 M HCl, the reaction mixture was
concentrated in vacuo, and the residue was dissolved in
5% aq EtOH and chromatographed on Lobar column (Rp
18, size C). Elution of the column with 5% aq EtOH
(500 mL) and then a gradient from 5% to 30% aq EtOH
(500 mL, each) gave compound 7 (60.4 mg) in 79.1% yield.
The TOF-MS and 1H NMR spectra of 7 confirmed the
S-benzylation. Compound 7 (100 mg) was hydrolyzed with
2 M HCl (10 mL) at 80 °C for 4 h. The reaction solution
was neutralized with 1 M NaOH, and then chromato-
Acknowledgment
The authors are grateful to the Japan Maize Products
Co. Ltd, for the generous gift of cyclodextrins.

M. Fukudome et al. / Tetrahedron Letters 48 (2007) 7493–7497
7497
graphed on a reversed-phase Lobar column. Elution of the
column with water (500 mL) and a subsequent gradient
from water to 50% aq EtOH (500 mL each) gave a maltose
derivative 8 (13.4 mg) in 45.7% yield together with tri,
tetra, and pentasaccharide derivatives that were respec-
tively shown to possess the basic structure of 8 by their
TOF-MS spectra. The reducing anomeric carbon of 8 was
reduced by reacting 8 (8.4 mg) with 1% aq NaBH4
(840 lL) for 30 min and purified compound 9 was
obtained by the chromatograph of the reaction mixture
on a reversed-phase Lobar column (eluted with a gradient
from water to 50% aq EtOH).
10. Tee, O. S.; Mazza, C.; Du, X.-X. J. Org. Chem. 1990, 55,
3603.
11. Structural data of the isolated thioester of 5: TOF-mass:
m/z 1197 (M+Na+), 1213 (M+K+). 13C NMR (D2O,
CH3CN int.): d 199.7, 103.1, 102.5, 102.3, 100.8, 94.8,
81.9, 81.6 81.5, 81.3, 76.9, 76.3, 74.3, 74.2, 74.0, 73.8 73.4,
73.1, 72.9, 72.8, 72.7, 72.6, 72.5, 72.4, 72.3, 70.9, 70.4, 61.3,
61.2, 60.9, 60.3, 44.3, 31.3 ppm.