Preparation and self-inclusion properties of p-xylylenediamine-modified β-cyclodextrins: dependence on the side of modification

Article abstract of DOI:10.1039/b105388b

β-Cyclodextrin (β-CDx) derivatives modified with p-xylylenediamine at the 3-position, mono-3-deoxy-3-[4-(aminomethyl)benzylamino]-β-CDx (1; β-CDx-3-p-xylylenediamine) was prepared by the reaction of β-CDx-2,3-manno-epoxide with p-xylylenediamine. The circ

Full text of DOI:10.1039/b105388b

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Preparation and self-inclusion properties of p-xylylenediamine-
modified ꢀ-cyclodextrins: dependence on the side of modification
a
a
b
b
b
Kwanghee Koh Park,* Young Sin Kim, Soo Yeon Lee, Hee Eun Song and Joon Woo Park*
2
a
Department of Chemistry, Chungnam National University, Taejon, 305-764, Korea
Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea
b
Received (in Cambridge, UK) 19th June 2001, Accepted 13th August 2001
First published as an Advance Article on the web 5th October 2001
β-Cyclodextrin (β-CDx) derivatives modified with p-xylylenediamine at the 3-position, mono-3-deoxy-3-[4-
aminomethyl)benzylamino]-β-CDx (1; β-CDx-3-p-xylylenediamine) was prepared by the reaction of β-CDx-2,3-
(
manno-epoxide with p-xylylenediamine. The circular dichroism properties of 1 are compared with those of the
corresponding β-CDx derivative modified at the primary side (2; β-CDx-6-p-xylylenediamine), in the presence and
in the absence of 1-adamantanamineؒHCl. The results indicate that the xylylenediamine group of 2 is self-included
in the β-CDx cavity, whereas that of 1 stays outside the cavity. The energy obtained by molecular modeling showed
the same trend. The dependence of self-inclusion behavior of a pendant group in modified cyclodextrins on the
position of modification could be a useful guide for designing cyclodextrin derivatives for various applications.
Introduction
CDx (1; β-CDx-3-p-xylylenediamine). Its circular dichroic
CD) spectral properties are compared with those of the
corresponding β-CDx derivative modified on the primary
side, 2. It was found that the xylyl group of 1 stays outside the
β-CDx cavity, while that of 2 is deeply embedded in the cavity.
This is supported by the results of a molecular modeling study
(
Cyclodextrins (CDx) are cyclic oligosaccharides which have
hydrophobic cavities capable of forming inclusion complexes
with a variety of organic molecules in aqueous solution. They
have attracted widespread interest as enzyme mimics and as
hosts for molecular recognition, and much effort has been made
to modifify the CDx to improve their catalytic and molecular
(
see later).
1
recognition properties. Modified CDx with suitable pendant
groups often form self-inclusion complexes in which the
2–11
pendant groups are inside the CDx cavity.
If the pendant
group bears a chromophore, the modified CDx can be utilized
as optical chemo-sensors for organic guests: upon binding of
the guest, the chromophore is excluded from the CDx cavity
3
4–7
with an associated change in color, fluorescence, or circular
8
dichroism. It has also been reported that the co-inclusion of
the pendant group and guest molecule in a CDx cavity causes
great differences in the stability and physical properties of the
11,12
CDx–guest complexes.
Recently, we reported that β-CDx
modified by xylylenediamine on the primary side forms a
co-inclusion complex with α-methoxyphenylacetic acid, which
can be used as a chiral NMR shift reagent for the determination
11
of the enantiomeric composition of the guest.
Either the primary or secondary side of a CDx can be
13
utilized for attachment of a pendant group, and CDx deriv-
atives with the same pendant group but on different sides
14
sometimes exhibit quite contrasting properties. However,
derivatization of CDx has been carried out mostly on the
primary side, and not many CDx derivatives with a pendant
group on the secondary side, especially at the 3-position of the
secondary side, have been reported, presumably because they
are more difficult to synthesize. Moreover, most of the CDx
derivatives exhibiting self-inclusion properties are those having
the pendant group on the primary side: McAlpine and Garcia-
Garibay postulated that 3-O-(2-methylnaphthyl)-β-CDx forms
Results and discussion
Synthesis of p-xylylenediamine-modified ꢀ-CDx
15
a self-inclusion complex, but the interpretation was changed
to intermolecular association in a subsequent study by the
The most common method for monomodification of β-CDx on
the primary side is the nucleophilic substitution reaction of
β-CDx-6-OTs, which is prepared by reacting β-CDx with tosyl
chloride in aqueous NaOH solution, with suitable nucleo-
16
same authors. To examine the dependence of self-inclusion
behavior on the side of attachment, it is necessary to prepare
the CDx derivatives modified with the same group but on
different sides and compare their properties. Here, we report
the synthesis of p-xylylenediamine-modified β-CDx at the
13
philes. Using p-xylylenediamine as a nucleophile, β-CDx-6-
11
xylylenediamine 2 is prepared in yields of ca. 20%. Direct
3
-position, mono-3-deoxy-3-[4-(aminomethyl)benzylamino]-β-
selective modification at the 3-position of β-CDx is not usually
2
114
J. Chem. Soc., Perkin Trans. 2, 2001, 2114–2118
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b105388b

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Scheme 1 Synthesis of mono-3-deoxy-3-[4Ј-(aminomethyl)benzylamino]-β-CDx (1; β-CDx-3-p-xylylenediamine).
feasible, because of the higher reactivity of the 2- or 6-hydroxy
groups. Modifications at the 3-position are mostly carried
out by reacting manno-2,3-epoxycyclodextrin with a nucleo-
12,14a
phile.
The synthesis of β-CDx-3-p-xylylenediamine 1 is
outlined in Scheme 1.
Mono-[2-O-(p-tolylsulfonyl)]-β-CDx (3; β-CDx-2-OTs) was
prepared by Murakami’s method using dibutyltin oxide and
1
7
purified by reverse-phase column chromatography. Scale-up
of the reaction using 5 g (ca. 20 times the amount of the
reported procedure) of β-CDx did not lower the yield signifi-
cantly. The expected 4 : 7 integral ratio of aromatic protons at δ
7
.99 (d, 2H, J = 8.0 Hz) and 7.52 (d, 2H, J = 8.0 Hz) to anomeric
1
protons at δ 5.0–5.1 was obtained in the H NMR spectrum in
D O. β-CDx-manno-2,3-Epoxide 4 was prepared from β-CDx-
2
14a,18
2
-OTs 3 using the reported procedure.
better accomplished by reverse-phase column chromatography
Licroprep Rp-18, Merck) rather than the reported method util-
Purification of 4 was
(
1
izing Sephadex G-15 resin. The H NMR spectrum (in D O) of
2
compound 4 showed the expected signal at δ 3.51 with a 3.7 Hz
coupling to H-3, for the C-2 proton of the glucose epoxide
residue, and an unsplit one-proton signal at δ 5.30 for the C-1
14a
proton of that residue. The reaction of the epoxide with a
Fig. 1 Circular dichroism (A) and UV–VIS (B) spectra of p-xylylene-
diamine-modified β-CDx derivatives in 0.01 M HCl. The concentration
was 1.0 × 10 M for UV–VIS and 3.0 × 10 M for circular dichroism
twofold amount of p-xylylenediamine in 0.2 M NaHCO for
3
1
5 h followed by purification by reverse-phase column chrom-
Ϫ3
Ϫ3
atography provided β-CDx-3-p-xylylenediamine 1 in 65% yield,
measurements. The cell pathlength was 1.0 cm.
1
13
which was characterized by H and C NMR and FAB MS
1
data. The H NMR spectrum of 1 showed the expected integral
p-xylylenediamine-modified β-CDx 1 and 2 in 0.01 M HCl
ratio of 4 : 7 corresponding to the phenyl protons at δ 7.38–7.46
and anomeric protons of the β-CDx moiety at δ 5.00–5.15. It
also showed a one-proton signal at δ 2.88 as a doublet of doub-
lets with J = 10.4 and 3.2 Hz for the C-3 proton carrying the
nitrogen atom of p-xylylenediamine, which indicates that the
C-2 and C-3 protons are axial and C-4 proton is equatorial, and
thus a ring flip of the modified glucose unit (actually an altrose
unit) accompanying conformational change has occurred. This
are shown in Fig. 1. Both compounds show positive circular
1
dichroism spectra around 260 nm, which corresponds to the L
b
8
band. To check the possibility of intermolecular association of
the p-xylylenediamine-modified β-CDx 1 and 2, we measured
CD spectra at various concentrations from 1 mM to 13 mM
and found no appreciable dependence of molar ellipticities on
concentration. This indicates that intermolecular association of
the p-xylylenediamine-modified β-CDx is insignificant in the
concentration range.
14a,18
result is consistent with previous reports by other groups
for the nucleophilic ring opening of the epoxide 4.
As the 1-adamantyl group has strong binding affinity to
the β-CDx cavity, it displaces any group or molecule included
Circular dichroism and self-inclusion properties of ꢀ-CDx-3-p-
xylylenediamine 1 and ꢀ-CDx-6-p-xylylenediamine 2
3,4,6–8,15,19
inside the β-CDx cavity to the outside.
When the
included group or molecule contains a chromophore, it results
in a large CD spectral change as the sign and magnitude of a
The UV–VIS and circular dichroism (CD) spectra of
J. Chem. Soc., Perkin Trans. 2, 2001, 2114–2118
2115

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Fig. 3 Plot of ellipticity change at 262 nm caused by the addition of
Ϫ3
1
6
-adamantanamineؒHCl (ADA) to a solution of 3.0 × 10 M β-CDx-
-p-xylylenediamine in 0.01 M HCl. The solid line is the result of
fitting to eqn. (4) with Kapp = 590 M and ∆θ = Ϫ3.4 mdeg.
Ϫ1
Fig. 2 Effect of 1-adamantanamineؒHCl (ADA) on the circular
∝
Ϫ3
dichroism spectrum of 3.0 × 10 M β-CDx-6-p-xylylenediamine in
0
1
.01 M HCl. The concentrations of ADA are 0.00, 1.7, 2.9, 4.9, 7.0, and
1.7 mM (from top to bottom). The inset shows the circular dichroism
K2-out/ADA/(1 ϩ K ), and ∆θ is the ellipticity change expected
when all of the 2 forms complex with ADA. Fig. 3 shows the
in
∝
spectra of β-CDx-3-p-xylylenediamine in the absence (solid line) and in
the presence (broken line) of 10 mM ADA.
Ϫ3
variation of the ellipticity of a 3.03 × 10
2
M solution of 2 at
62 nm with the concentration of ADA. Non-linear least-
squares fitting of the data to eqn. (4) gave K and ∆θ values
CD spectrum vary sensitively with the position and orientation
of the chromophore in CDx complexes.
app
∝
8,20–24
Ϫ1
Fig. 2 shows the
of 590 ± 200 M and Ϫ3.4 ± 0.3 mdeg, respectively. The latter
Ϫ1
Ϫ1
circular dichroism spectra of 2 in the presence of various con-
centrations of 1-adamantanamineؒHCl (ADA). The CD peak
of 2 decreased upon the addition of ADA. However, the CD
spectrum of 1 was unaffected by the addition of ADA (see inset
of Fig. 2). This result indicates clearly that the p-xylylene-
diamine moiety attached to the primary side of β-CDx in 2 is
included inside the β-CDx cavity, whereas the same group at the
value corresponds to a molar ellipticity of Ϫ110 M cm for
the 2–ADA complex. If we assume that the binding constant of
ADA with the ‘2-out’ conformer is not significantly different
Ϫ1 19
from that of unmodified β-CDx, 18000 M , the equilibrium
constant (K ) for self-inclusion of xylylenediamine in 2
in
[eqn. (3)] is estimated to be 30.
The sign and magnitude of the CD spectra of CDx com-
3
-position in 1 stays outside the cavity. Since significant inter-
plexes with a chromophore depend on the position and orient-
molecular association is ruled out from the independence of
molar ellipticity of 2 on its concentration, it is certain that 2
forms an intramolecular self-inclusion complex as depicted
below.
20–24
ation of the chromophore.
Kodaka predicted that the sign
of CD spectrum of a chromophore tends to be reversed when
the chromophore moves from the inside of the CDx cavity to
23,24
the outside.
The effect of ADA on the CD spectrum of 2 is
consistent with this prediction. A detailed interpretation of the
sign and magnitude of the CD spectra of 1, 2, and 2–ADA is
beyond the scope of this work.
Molecular model calculations
Molecular modeling provides useful information on molecular
structure, usually complementary to the experimental tech-
niques. In an effort to obtain further information on the differ-
ence in the self-inclusion properties of 1 and 2, we conducted a
molecular modeling calculation using the CVFF force field. To
simulate the aqueous environment of the compounds, a water
sphere of diameter 15 Å and relative permittivity of 78 were
used. Energy minimization from various initial conformations
converged into two conformations: one with the xylylene-
diamine group included in the β-CDx cavity, and the other with
the group capping the face where it is attached. For 1, the
The CD spectral change upon the addition of ADA reflects
the complexation between 2 and ADA [eqn. (1)]. Since the
2
ϩ ADA
2–ADA Kapp = [2–ADA]/([2][ADA]) (1)
adamantyl group is too large for co-inclusion with xylylene-
diamine group in the β-CDx cavity, ADA can form the complex
only with the 2-out conformer [eqn. (2)] and thus depletes the
Ϫ1
energy of the capped conformation was 4.1 kcal mol lower
than that of self-included one, whereas the energy of the self-
2
-out ϩ ADA
2–ADA K2-out/ADA
=
[2–ADA]/([2-out][ADA]) (2)
included conformation (2-in) was lower than that of the capped
Ϫ1
one (2-out) by 1.5 kcal mol . Fig. 4 shows the energy minimum
2
2
-in conformer by shifting the equilibrium between 2-in and
-out [eqn. (3)].
conformations. This agrees well with the results obtained from
CD measurements.
2
-out
2-in K = [2-in]/[2-out]
(3)
in
Conclusions
The variation of CD ellipticity (∆θ) of a given solution of 2
β-CDx-3-p-Xylylenediamine 1 was prepared by the reaction
of β-CDx-manno-2,3-epoxide 4 with p-xylylenediamine; 4 was
synthesized from β-CDx-2-OTs 3, which was prepared by
Murakami’s method using dibutyltin oxide. The circular
dichroism properties of 1 were compared with those of β-CDx-
with the concentration of ADA is related to the total concen-
trations of 2 and ADA, [2] and [ADA] , and the apparent
o
o
25
association constant (Kapp) by eqn. (4). Kapp is related to the
microscopic equilibrium constants in eqns (2) and (3) by Kapp
=
6
-p-xylylenediamine 2, in the presence and in the absence of
∆
θ/∆θ = 0.5[(1 ϩ [ADA] /[2] ϩ
1-adamantanamineؒHCl. The results indicated that xylylene-
diamine group of 2 is deeply embedded in the β-CDx cavity,
whereas that of 1 stays outside the cavity. This was supported
∝
o
o
1
/Kapp[2] ) ± ꢀ(1 ϩ [ADA] /[2] ϩ
o o o
2
1/2
1
/Kapp[2] ) Ϫ 4[ADA] /[2] } ] (4)
o o o
2
116
J. Chem. Soc., Perkin Trans. 2, 2001, 2114–2118

View Article Online
Mono-[2-O-( p-tolylsulfonyl)]-ꢀ-CDx (3; ꢀ-CDx-2-OTs). The
title compound was prepared by Murakami’s method using
17
dibutyltin oxide. A yield of 1.42 g (25%) of 3 was obtained
starting from 5.00 g of β-CDx.
ꢀ
-CDx-manno-2,3-Epoxide, 4. Compound 4 was prepared
14a,18
from β-CDx-2-OTs, 3, using the reported procedure,
but an
improved purification method was applied: a yield of 0.828 g
95%) of 2 was obtained from 1.00 g of β-CDx-2-OTs after
purification utilizing reverse-phase column chromatography
(
(
Licroprep Rp-18, Merck).
Mono-3-deoxy-3-[4-(aminomethyl)benzylamino]-ꢀ-CDx. To a
solution of 1.00 g (0.90 mmol) of β-CDx-manno-2,3-epoxide in
4
0 ml of 0.2 M NaHCO was added p-xylylenediamine (0.24 g,
3
1
.80 mmol) dissolved in 40 ml of DMF and the reaction mix-
ture was stirred for 15 h at 60 ЊC under a nitrogen atmosphere.
The reaction mixture was concentrated to ca. 4 ml under
reduced pressure and subjected to reverse-phase column chro-
matography (Licroprep Rp-18, Merck), eluting with distilled
Fig.
4
Energy
minimum
conformations
of
β-CDx-3-p-
xylylenediamine 1 (above) and β-CDx-6-p-xylylenediamine 2 (below)
viewed from the side. The p-xylylenediamine moiety is represented in
bold. Both of the amine groups are protonated. Note that the
substituted carbohydrate moiety of 1 takes a different conformation
from the unsubstituted glucose residues (see text).
water and then 10% CH CN and finally with methanol. When
3
eluted with methanol, the product came out together with a
small amount of unreacted p-xylylenediamine. It was further
purified by being washed with acetone to yield 0.733 g (65%
by a molecular modeling calculation. As far as we know, this is
the first demonstration that the self-inclusion properties of
CDx modified with the same group depend on the position of
the modification. Such dependence of self-inclusion behavior
of modified-CDx on the position of modification might give
useful guidance for designing modified-CDx for various
applications.
yield) of analytically pure β-CDx-p-xylylenediamine, 1: mp 260
1
ЊC (decomp.); H NMR spectra of 1 in D O at 25 ЊC, δ (relative
2
to the residual solvent at δ 4.81) 7.44 (d, 2H, J = 8.0), 7.39 (d,
2H, J = 8.0), 5.15 (d, 1H, J = 4.0), 5.13 (d, 1H, J = 4.0), 5.09 (d,
1H, J = 3.2), 5.06 (d, 1H, J = 3.6), 5.05–5.02 (m, 3H), 4.35–4.29
(m, 1H, H5A), 4.08–3.53 (m, 44H, H2, H3, H4, H5, H6,
1
2-CH ), 2.88 (dd, 1H, H3A, J = 10.4 and 3.2); H NMR spectra
2
of 1ؒ2HCl in D O at 25 ЊC, 7.64 (d, 2H, J = 8.0), 7.57 (d, 2H,
2
J = 8.0), 5.22 (d, 1H, J = 4.0), 5.18 (d,1H, J = 3.6), 5.16 (d, 1H,
J = 4.4), 5.09 (d, 2H, J = 3.6), 5.06 (d, 1H, J = 2.8), 5.00 (d, 1H,
J = 6.8), 4.59 (d, 1H, J = 13.6), 4.44–4.34 (m, 3H), 4.25 (s, 2H),
Experimental
Spectral measurements
13
4
.08–3.57 (m, 40H); C NMR spectra of 1 in DMSO-d at
6
NMR spectra were recorded on a Varian Unity INOVA 400
spectrometer at the Central Research Facilities of Chungnam
National University: chemical shifts are reported in δ relative to
the residual solvent peak (D O or DMSO-d ) and J values are
25 ЊC, δ 141.67, 138.51, 128.20, 127.07, 104.17, 102.28, 102.17,
102.01, 101.85, 101.59, 81.97, 81.84, 81.43, 81.36, 81.03, 80.38,
76.05, 73.4–71.7, 71.00, 60.28, 59.96, 59.45, 58.82, 50.45, 45.17;
ϩ
MS (positive ion FAB): 1253.48 (calcd. for C H O N ϩ H ,
2
6
50 80 34
2
given in Hz. Mass spectra were taken at the Korea Basic Science
Institute. Solutions for circular dichroism measurements of 1
and 2 were prepared by dissolving HCl salts of the compounds
in 0.01 M HCl. Circular dichroism spectra were taken with a
JASCO J-810 spectropolarimeter equipped with thermostatted
cell holder at 25 ЊC. The bandwidth was set at 2 nm and the
response time was 2 s. Spectra of ten repetitive scans at scan
1253.47).
Acknowledgements
This work was supported by the Korea Science and Engineering
Foundation (97-05010-04-0103) and by the Center for Respon-
sive Molecules.
Ϫ1
speed of 50 nm min were averaged and smoothed using
JASCO software.
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