Glycosylated tris-bipyridine ferrous complexes to provide dynamic combinatorial libraries for probing carbohydrate-carbohydrate interactions

Article abstract of DOI:10.1016/j.tet.2013.01.095

2,2-Bipyridines having β-lactoside, β-d-glucoside, β-d-galactoside, and N-acetyl-β-d-glucosaminide were prepared and then, complexed with ferrous ion to afford trivalent glycoclusters having tris-bipyridine ferrous complex cores. Each glycocluster provides a dynamic combinatorial library composed of four diastereomeric stereoisomers (Δmer, Δfac, Λmer, and Λfac) whose ratios depend on their relative stabilities. CD spectral analyses of these glycoclusters showed that various cations (Na⁺, Mg²⁺, K⁺ or Ca²⁺) enriched Δ-forms of the glycocluster having β-lactosides and N-acetyl-β-d-glucosaminides possibly by cations-induced intramolecular carbohydrate-carbohydrate interactions.

Full text of DOI:10.1016/j.tet.2013.01.095

Tetrahedron 69 (2013) 3019e3026
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Glycosylated tris-bipyridine ferrous complexes to provide dynamic
combinatorial libraries for probing carbohydrateecarbohydrate
interactions
Motomi Nakamura a, Mayuka Tsutsumi a, Yoshiaki Ishikawa a, Haruka Umemiya a,
,
,
,
,c
Toki Hasegawa a, Kazumi Izawa b c, Haruka Abe b c, Yosuke Togashi b c, Tatsuya Kinone b
,
,
,c,
*
Sho Sekiguchi b c, Mihiro Igumi a, Kanako Ide a, Teruaki Hasegawa a
a Department of Life Sciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun 374-0193, Japan
b Bio-Nano Electronics Research Centre, Toyo University, 2100 Kujirai, Kawagoe 350-8585, Japan
c Graduate School of Life Sciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun 374-0193, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
2,2-Bipyridines having b-lactoside, b-D-glucoside, b-D-galactoside, and N-acetyl-b-D-glucosaminide were
prepared and then, complexed with ferrous ion to afford trivalent glycoclusters having tris-bipyridine
ferrous complex cores. Each glycocluster provides a dynamic combinatorial library composed of four
Received 14 November 2012
Received in revised form 27 January 2013
Accepted 31 January 2013
diastereomeric stereoisomers (
bilities. CD spectral analyses of these glycoclusters showed that various cations (Naþ, Mg2þ, Kþ or Ca2þ
enriched -forms of the glycocluster having -lactosides and N-acetyl- -glucosaminides possibly by
cations-induced intramolecular carbohydrateecarbohydrate interactions.
Dmer, Dfac, Lmer, and Lfac) whose ratios depend on their relative sta-
Available online 8 February 2013
)
D
b
b-D
Keywords:
Carbohydrateecarbohydrate interaction
Tris-bipyridine ferrous complex
Glycocluster
Ó 2013 Elsevier Ltd. All rights reserved.
Dynamic combinatorial chemistry
Dynamic combinatorial library
Circular dichroism
1. Introduction
interest that these micro domains are associated with various sig-
nal transferring proteins, such as c-Src, FAK, Rho A, etc.5 Since this
fact strongly implies that these micro domains play important roles
not only in cellecell adhesions but also in cellecell signal trans-
ductions, these micro domains are now widely called ‘carbohydrate
signaling domains’. Investigation on CCIs is of quite attractive, since
it should supply useful information not only to understand mech-
anism of the cell-cell adhesions and the signal transductions but
also to design new drugs to prevent various diseases triggered by
unfavorable cellecell adhesions (cancer metastases, inflammations,
etc.). In spite of such importance, heterogeneity and fluidity of the
cell membranes make it quite difficult to investigate CCIs in a de-
tailed and quantitative manner. Simple and well-designed model
systems are, therefore, highly required to obtain molecular-level
information on CCIs.
Carbohydrates ubiquitously exist as components of glycopro-
teins and glycolipids on cell surfaces and play substantial roles in
various molecular recognition events including fertilizations, dif-
ferentiations, and cellecell adhesions.1,2 Hitherto, these carbohy-
drates have been recognized as ligands for carbohydrate
recognition proteins (lectins).3 An increasing interest has been,
however, placed on carbohydrateecarbohydrate interactions (CCIs)
on cell surfaces, in which carbohydrates recognize carbohydrates in
specific and, in most cases, Ca2þ-dependent manners.4
Glycosphingolipids (GSLs) on cell surfaces aggregate laterally to
form micro domains to present densely packed carbohydrate
clusters. Face-to-face interactions between such carbohydrate
clusters from neighboring cells are the very first and an essential
step in various cellular recognition events including compactions of
embryos, cancer metastases and inflammations. It is of quite
Strength of CCIs also adds to the problem; that is, CCIs between
two isolated carbohydrates are so weak that they are hardly de-
tectable. Multivalent interactions between the clustered carbohy-
drates are, therefore, adopted in nature to overcome this problem.
Most artificial systems also utilize densely packed carbohydrate
clusters to probe CCIs.6e9 For example, interactions between
* Corresponding author. Tel.: þ81 276 82 9215; e-mail address: t-hasegawa@
toyo.jp (T. Hasegawa).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.01.095

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M. Nakamura et al. / Tetrahedron 69 (2013) 3019e3026
Langmuir monolayers composed of GM3 (NeuAc-
Glc -ceramide) and dendrimers presenting multiple
Lac: Gal-
a
1,3-Gal-
-lactosides
-) were investigated by using p
-A isotherm.10 It
b1,4-
b
b
(b
b
1,4-Glc
b
ꢀ
has been also reported by Penades et al. that aggregations of gold
nanoparticles immobilized with LeX-trisaccharides (LeX3: Gal-
b1,4-
(Fuc- 1,3-)GlcNAc
a
b
-) were induced by Ca2þ in a specific manner.11
These excellent works successfully demonstrated specific CCIs
between two carbohydrate clusters composed of the complex oli-
gosaccharides (GM3/b
Lac, LeX3/LeX3, etc.). Only limited information
has been, however, obtained so far on contributions of each
monosaccharide unit in these oligosaccharides. In the case of the
ꢀ
Penades’s work, for example, gold nanoparticles immobilized with
b
Lac- and b-maltoside (Glc-a1,4-Glcb-) were used as negative ref-
erences. Chemical structure of LeX3 is quite different from those of
these disaccharides and therefore, little information can be ob-
tained for structural criteria to induce the LeX3eLeX interactions.
3
It should be noted that these works are categorized into in-
termolecular approach. Since intermolecular bindings between two
carbohydrate molecules accompany large entropic lose, so the
multivalent interactions between the carbohydrate clusters are
essential for these systems to probe CCIs. Almost no molecular-
level information, such as spatial packings of the carbohydrates
and stoichiometries between the carbohydrates and Ca2þ, has been,
therefore, obtained to date suffering from the huge numbers of
carbohydrates in these systems.
The other approach to investigate CCIs is intramolecular one.
Since CCIs between two carbohydrates linked together with an ap-
propriate spacer can minimize the entropic lose on their bindings,
numbers of carbohydrates to induce their bindings can be also re-
duced in this approach.12,13 For example, Schmidt et al. reported that
two LeX3-units linked through an alkyl spacer took a cross-shaped
packing on an addition of Ca2þ and this conformational change
could be detected by using NOESY.14 This work well exemplified one
great advantage of the intramolecular approach; that is, accessibility
toward the detailed molecular information on CCIs such as the
spatial packings of carbohydrates on their bindings. We have been
also pursuing the intramolecular approach to investigate CCIs by
using various model systems.15e18 One advantageous feature of our
systems relies on their scaffolds; that is, scaffolds of our systems are
designed to function as chromophores to monitor CCIs-induced
conformational changes based on their UVevis and/or CD spectra.
Recently, a fascinating strategy, that is, so-called dynamic
combinatorial chemistry (DCC), was emerged especially in a field of
pharmaceutics.19 One can define DCC as combinatorial chemistry
under thermodynamic control and all members of dynamic com-
binatorial libraries (DCLs) are in equilibrium in which ratios of these
DCLs members depend on their relative stabilities. Reasonably
quick interconversions among DCLs members are required to attain
such DCC and therefore, varieties of reversible exchange reactions,
such as ester,20 hydrazone,21 disulfide,22 and metaleligand ex-
change ones23 are widely used to construct DCLs.
Fig. 1. Four diastereomeric stereoisomers of the tris-bipyridine ferrous complexes
presenting trivalent Lacs and averaged distances between three non-reducing Gal
terminals (C4) in the complexes during molecular dynamics calculations (See Figs.
b
b
S1eS3).
respectively. In additions, mer and fac mean meridional and facial
isomers in which each set of three pyridine units on which
carbohydrate-unit attached occupies a plane passing through Fe2þ
and one face of the octahedron surrounding Fe2þ, respectively. (2)
Time-scales for their interconversions are reasonably short (w1 h)
and new equilibrium can be quickly achieved on external stimuli.
(3) Since these glycometalloclusters are CD active, their CD spectra
offer useful information on their DeL ratios. (4) The DCLs members
of the glycometalloclusters are diastereomeric and therefore, they
can be quantified through HPLC analyses without using any chiral
stationary phases.
If a certain DCLs member has a spatial carbohydrate arrange-
ment, that is, suitable for intramolecular CCIs, such CCIs should act
as adhesive forces to stabilize this DCLs member and to increase its
ratio (Fig. 2). In fact, Sasaki et al. reported in their pioneering works
that similar glycometalloclusters are effective to probe spatial
structures of carbohydrate binding sites of lectins.25,26
The success of DCC in pharmaceutics encouraged us to develop
new model systems to investigate CCIs by combining the intra-
molecular approach and DCC. In this respect, we designed mono-
glycosylated 2,20-bipyridines (glycobpys), which spontaneously
assemble onto Fe2þ to construct the corresponding tris-bipyridine
ferrous complexes carrying trivalent glycoclusters (glyco-
metalloclusters). Taking advantages of the reversible metaleligand
exchange reactions, these glycometalloclusters can produce suit-
able DCLs as follows.24 (1) The glycometalloclusters exist as mix-
Herein, we report the first successful example of such DCC-
based intramolecular approach to investigate CCIs. In this work,
we synthesized various glycometalloclusters having
cosides ( Glcs), -galactosides ( Gals), and N-acetyl-
minides ( GlcNAcs) to assess CCIs among these carbohydrates. Note
that, in these carbohydrates, Lac exists as a carbohydrate unit of
lactosylceramide, that is, the most abundant glycosphingolipid on
the cell surfaces and Lace Lac interactions has been reported by
many research groups using the intermolecular/intramolecular
b
Lacs,
b-glu-
b
b
b
b-D-glucosa-
b
b
tures of four diastereomeric stereoisomers (
Lfac) having individual spatial distributions of carbohydrate ap-
pendages (Fig. 1). Although these abbreviations (Lmer, Lfac, mer,
and fac) are widely used in metallo-complex chemistry, it should
be herein clearly defined that L and mean left- and right-handed
spatial arrangements of their bpy units around the Fe2þ core,
Dmer, Dfac, Lmer, and
b
b
D
D
approaches.27 Meanwhile,
bGlcNAc is an essential structural com-
D
ponent of LeX, that is, widely recognized as the glycosphingolipids
to induce strong CCIs.

M. Nakamura et al. / Tetrahedron 69 (2013) 3019e3026
3021
The pAP-glycosides were synthesized through two different
synthetic routes depending on their chemical structures. Briefly, in
the case of pAP-bLac, pAP-bGlc and pAP-bGal, lactose, glucose and
galactose were acetylated, respectively, in mixtures of acetic an-
hydride and pyridine followed by brominations on their reducing
terminals (Scheme S1). The resultant lactosyl, glucosyl, and galac-
tosyl bromides were then, treated with sodium p-nitrophenoxide
in boiling acetone. The subsequent hydrogenations using catalytic
Pd on carbon afforded pAP-
hand, in the case of pAP-N-acetyl-
GlcNAc), 2-acetoamide-2-deoxy- -glucose was treated in acetyl
b
Lac, -
b
Glc, and -bGal. On the other
b-D-glucosaminide (pAP-
b
D
chloride and then, coupled with p-nitrophenol in a biphasic solvent
system (dichloromethane/NaOH aqueous) containing tri-n-buty-
lammonium hydrogensulfate (TBAH) as a phase transfer catalyst
(Scheme S2). The resultant per-O-acetyl-N-acetyl-p-nitrophenyl-
-glucosaminide was hydrogenated to afford pAP- GlcNAc.
The couplings between 3 and pAP-glycosides were successfully
achieved in THF containing triethylamine, and the subsequent
deacetylations afforded bipyridines having Lac (bpy Lac, 8), Glc
GlcNAc (bpy GlcNAc, 11)
b-
D
b
b
b
b
(bpyb
Glc, 9),
b
-Gal (bpy
b
Gal, 10), and
b
b
(Scheme 2). Their constitutions could thus be proved using 1H/13
NMR, MALDI-TOF-MS, and FT-IR spectroscopies.
C
Fig. 2. Schematic illustration of the concept of our DCC-based system to investigate
cations-induced CCIs.
2. Results and discussion
2.1. Syntheses of the glycobpys
The glycobpys were synthesized through couplings between
2,20-bipyridine-5-carboxyl chloride (3) and per-O-acetyl-p-amino-
phenyl-b-glycosides (pAP-glycosides) followed by deacetylations.
Briefly, for synthesis of 3, we first mixed methyl chloronicotinate
and trimethyl-(2-pyridyl)tin in a boiling m-xylene containing
bis(triphenylphosphine)palladium(II) dichloride to afford methyl
2,20-bipyridine-5-carboxylate (1) (Scheme 1). The subsequent hy-
drolysis using KOH in a boiling mixture of water/tetrahydrofuran
(THF) gave 2,20-bipyridine-5-carboxylic acid (2) that was then,
converted into 3 through being treated with thionyl chloride and
used directly for the couplings with the pAP-glycosides.
Scheme 2. Reaction conditions: i) pAP-
bLac, Et3N THF, rt, 5 min, 18%, ii) pAP-
bGlc,
Et3N, THF, rt, 5 min, 16%, iii) pAP- Gal, Et3N, THF, rt, 5 min, 20%, iv) pAP-
b
bGlcNAc, Et3N,
THF, rt, 5 min, 97%, (v) NaOMe, MeOH, rt, 3 h, 98%, (vi) aqueous ammonia, MeOH/THF,
rt, 1 h, 95%, (vii) NaOMe, MeOH, rt, 1 h, 94%, (viii) NaOMe, MeOH/THF, rt, 2 h, 98%.
2.2. Complexations of the glycobpys with ferrous ion to
construct the corresponding glycometalloclusters
These glycobpys in hand, we then tried to confirm their com-
plexations with Fe2þ. When we added small aliquots of aqueous
FeCl2 to the glycobpys in water, color of the solution turned im-
mediately to reddish purple, indicating simultaneous constructions
of the glycometalloclusters having [Fe(bpy)3]2þ cores. UVevis
spectra of the solutions showed characteristic absorption bands
Scheme 1. Reaction conditions: i) trimethyl(2-pyridyl)tin, bis(triphenylphosphine)
palladium(II), m-xylene, reflux, 5 h, 83%, ii) KOH water/THF, reflux, 7 h, 81%, iii) thi-
onyl chloride, reflux, 1e3 h, quant.

3022
M. Nakamura et al. / Tetrahedron 69 (2013) 3019e3026
at around 548 nm, also being diagnostic of the desired
glycometalloclusters.
These color and spectral changes of the glycobpys clearly indicate
the formation of the corresponding glycometalloclusters. We,
however, found that just one-third equivalents of Fe2þ were not
enough to induce their quantitative complexations; that is, large
amounts of uncomplexed glycobpys still existed as white pre-
cipitates even in the presence of one-third equivalent of Fe2þ. We
assume that, since the glycobpys are hardly soluble in water, solid-
solution equilibrium of the glycobpys should disturb their quanti-
tative complexations. To circumvent this problem and to estimate
accurate Fe2þ/glycobpy stoichiometries in the glycometalloclusters,
solvent of choice was of quite importance. For example, the glyco-
bpys are soluble in a mixture of N,N-dimethylformamide (DMF) and
water (1/1 v/v), the quantitative complexations were readily ach-
ieved in this solvent system (Fig. S4). In detail, when we monitor
Fe2þ-induced UVevis spectral change of bpy
bGlcNAc in this mixed
solvent system, we found that, with increasing concentrations of
Fe2þ, strength of peaks (548 nm) characteristic for [Fe(bpy)3]2þ core
linearly increased and reached at a plateau at around [Fe2þ]/
[bpy
b
GlcNAc]¼1/3, confirming the construction of the desired gly-
cometallocluster (Fig. 3). Similar 1/3 stoichiometries were also ob-
served for the other glycobpys, again proving the constructions of
the corresponding glycometalloclusters.
Fig. 4. CD spectra of [Fe(bpy
b
Lac)3]Cl2, [Fe(bpy
bGlc)3]Cl2, [Fe(bpybGal)3]Cl2, and
[Fe(bpy
bGlcNAc)3]Cl2: [glycobpys]¼156
mM, [FeCl2]¼147
m
M, d¼5 mm, 25 ꢀC, in water.
(LfacþLmer). Molar ellipticities of these CD peaks were, however,
smaller than those of enantio-pure
D
-[Fe(bpy)3]2þ 28
,
implying that
these glycometalloclusters exist as mixtures of their
D- and L-forms.
These CD spectral features clearly indicate that their
carbohydrate configurations adjacent to phenyl rings are responsible
for their -predominant stereochemistries.
b-anomeric
D
Next, we carried out CD spectral measurements of the glyco-
metalloclusters in the presence of various cations to find that high
cation-concentrations might induce dissociation of the glyco-
metalloclusters. For example, in the case of CaCl2, colors of the
glycometalloclusters in water were almost identical to those with-
out Ca2þ if the Ca2þ-concentrations were 100 mM or below. Further
increment of the Ca2þ-concentration, however, made the solution
colors pale, indicating the dissociation of the glycometalloclusters
(Fig. S5). Their UVevis spectra in the presence of concentrated Ca2þ
also support their dissociations; that is, the peak strengths of the
Fig. 3. Plots of the MLCT band intensities (548 nm) of aqueous DMF containing
[bpy
b
GlcNAc] and varying concentrations of [FeCl2]: [bpy
bGlcNAc]¼3.39 mM, [FeCl2]¼
0e2.23 mM, 25 ꢀC, 50% aqueous DMF, d¼1 mm.
2.3. Analyses of the DCLs
glycometalloclusters at around 548 nm weakened at high Ca2þ
-
As mentioned above, each glycometallocluster is composed of
four diastereomeric stereoisomers those are under dynamic equi-
librium. In the first stage of our study, we expected that their ratios
would be readily accessible through HPLC analyses. It was, how-
ever, found that these diastereomeric stereoisomers could be
hardly separated on RP-HPLC column. We assume that their
electron-withdrawing carbonyl groups should destabilize their
NeFe coordination bonds to make their interconversion time-
scales shorter than HPLC retention times. This assumption might
be paradoxically supported by successful HPLC separations of the
Sasaki’s glycometalloclusters having electron-donating methylene
spacers adjacent to their bpy units.
concentrations, although it was not changed when the Ca2þ-con-
centrations were 100 mM or below. Together with these data, we
carried out CD spectral measurements of the glycometalloclusters
in the presence of various salts (NaCl, MgCl2, KCl, and CaCl2) whose
concentrations are 100 mM or below in which the ions do not put
any negative effect on stabilities of the glycometalloclusters.
The glycometalloclusters show individual CD spectral responses
depending on their carbohydrate structures. For example, in the
case of [Fe(bpy
(CD300) were amplified with increasing ion-concentrations (Fig. 5).
This CD spectral change clearly indicates that the total content of
forms ( mer) was increased on additions of the salts possibly
facþ
owing to the stabilization of its fac and/or mer by the cations-
induced intramolecular GlcNAce GlcNAc interactions. Similar
cations-induced CD spectral changes were also observed for
[Fe(bpy Lac)3]Cl2, again implying the Lace Lac interactions. On
the other hand, neither [Fe(bpy Glc)3]Cl2 nor [Fe(bpy Gal)3]Cl2
bGlcNAc)3]Cl2, its peak intensities at around 300 nm
D
-
D
D
We alternatively carried out circular dichroism (CD) spectral
D
D
analyses to assess which stereoisomers (D- or L-forms) are pre-
b
b
dominant in our glycometalloclusters. For example, as shown in
Fig. 4, their CD spectra show two characteristic positive-to-negative
and negative-to-positive CD patterns on going from longer to shorter
b
b
b
b
b
wavelengths at around 544 (MLCT band) and 300 (
band) nm, respectively. These CD spectral features are characteristic
for
-[Fe(bpy)3]2þ, clearly indicating that total amounts of the
-forms mer) are larger than those of the L-forms
facþ
p
e
p
* transition
shows CD spectral changes on the additions of the salts (Fig. S6).
Plots of CD intensities at 310 nm against the co-existing salts
D
concentrations reveals an interesting feature of
bGlcNAcebGlcNAc
D
(D
D
and Lace Lac interactions; that is, the former shows little ion-
b
b

M. Nakamura et al. / Tetrahedron 69 (2013) 3019e3026
3023
Table 1
Dissociation constants (Kd/mM) between the glycometalloclusters and various
cationsa
Glycometalloclusters
Naþ
Kþ
Mg2þ
Ca2þ
[Fe(bpy
[Fe(bpy
[Fe(bpy
[Fe(bpy
b
b
b
b
GlcNAc)3]Cl2
Lac)3]Cl2
Glc)3]Cl2
13
13
7.0
10
32
26
10
6.7
n.d.b
n.d.b
n.d.b
n.d.b
n.d.b
n.d.b
n.d.b
n.d.b
Gal)3]Cl2
a
The Kd values were determined by the computational curve fitting of their
binding profiles.
b
n.d.: not detected.
find that the cations-induced enrichments of the
served for [Fe(bpy GlcNAc)3]Cl2 and [Fe(bpy Lac)3]Cl2 were no
longer observed in the presence of excess amounts of N-acetyl-
glucosamine and lactose, respectively (Fig. S7). These CD spectral
changes should imply that the cations-induced intramolecular CCIs
D-isomers ob-
b
b
Fig. 5. CD spectral change of [Fe(bpy
bGlcNAc)3]Cl2 with increasing concentrations of
b-D-
CaCl2 (0w100 mM): [bpybGlcNAc]¼156
m
M, [FeCl2]¼147
m
M, d¼5 mm, 25 ꢀC, in water.
selectivity and all cations (Naþ, Mg2þ, Kþ, and Ca2þ) induced almost
same CD spectral changes (Fig. 6). On the contrary, the latter has
clear Ca2þ-selectivity over the others (Ca2þ>Mg2þ>Naþ¼Kþ). We
then estimated dissociation constants (Kd) of the bindings between
the glycometalloclusters and the cations by using eq. 1,
stabilizing the
D-isomeric glycometalloclusters were replaced by
intermolecular CCIs between the glycometalloclusters and free
sugars and/or those among free sugars. These data suggest that the
intramolecular CCIs among [Fe(bpy
Lac)3]Cl2 are main driving forces to enrich their
It is of quite interesting that [Fe(bpy GlcNAc)3]Cl2 shows clear
CD spectral changes induced by various cations, since, with the best
of our knowledge, no GlcNAce GlcNAc interactions has been re-
b
GlcNAc)3]Cl2 and [Fe(bpy-
b
D
-isomers.
b
b
b
ported so far in the literature. This ions-response is undoubtedly
attributed to its acetamide (2NHAc) functionality, since no such
ions-response can be observed for [Fe(bpy
of quite interest, since GlcNAc can be found in various GSLs, such
as LeX, in which
GlcNAc function as a branching point to link Gal
and Fuc terminals.
Comparison between the cations-response of [Fe(bpy
and those of the other glycometalloclusters, especially [Fe(b-
py Glc)3]Cl2 and [Fe(bpy Gal)3]Cl2, also offers useful information
about a structural criteria to induce the Lace Lac interactions; that
is, not only its Glc or Gal residues but also whole disaccharide
structure is responsible for the interactions. Based on this in-
formation, we assume that the interactions between two Lacs were
mediated by ion-bridges in which one ion simultaneously binds to
Gal unit of one Lac and Glc units of another Lac. This packing is
bGlc)3]Cl2. This finding is
b
b
b
a
b
Lac)3]Cl2
b
b
b
b
b
b
b
b
b
b
b
strongly supported by a crystal structure of CaBr2elactose complex,
in which two lactose molecules binds to a Ca2þ through chelations
by Gal unit of one lactose and Glc unit of the other using 3OH/4OH of
the former and 2OH/3OH of the latter, respectively.
3. Conclusion
We herein reported the synthetic procedures to access the gly-
cometalloclusters having tris-bipyridine ferrous complex cores and
their CD spectral changes induced by various cations. Each glyco-
metalloclusters provides the DCL including the four CD-active/
diastereomeric stereoisomers those are under dynamic equilib-
rium. Together with the reasonably short time-scales for the in-
terconversions, these features make the glycometalloclusters quite
advantageous as DCLs to probe intramolecular CCIs. We can obtain
detailed information concerning the structural criteria to induce the
Fig. 6. Cations-induced CD spectral changes of (a) [Fe(bpy
[Fe(bpy
from 0 to 100 mM: [glycobpys]¼156
bGlcNAc)3]Cl2 and (b)
b
Lac)3]Cl2 with varying concentrations of NaCl, MgCl2, KCl or CaCl2 ranging
m
M, [FeCl2]¼147
m
M, d¼5 mm, 25 ꢀC, in water.
I ¼ I0 þ ðIsat ꢁ I0Þð1 ꢁ expð ꢁ ½saltsꢂ=KdÞÞ
(1)
bGlcNAcebGlcNAc and bLacebLac interactions by using our systems.
where I0 and Isat are both CD intensities (I) at 304 nm but the former
is that in the absence of salts and the latter be with excess salt-
concentrations. Note that we assumed 1:1 bindings between the
glycometalloclusters and the cations judging from their Langmuir-
type binding profiles. The Kd values of the binding estimated by
using the aforementioned equation are summarized in Table 1,
Although the intramolecular CCIs among the carbohydrate-
appendages can be detected in our systems based on its CD spec-
tral change, our trials to quantify the diastereomeric ratios through
the HPLC analyses turned to be failure suffering from the acceler-
ated interconversions.29 To overcome this problem, we are now
focusing phenanthroline-type glycometalloclusters whose time
scales for the interconversions would be reasonably long for their
HPLC analyses. Enzymatic constructions of glycometalloclusters
carrying biologically relevant oligosaccharides, such as LeX and
again confirming the preferable Ca2þ-binding of [Fe(bpy
bLac)3]Cl2.
We also carried out the CD spectral measurements of the gly-
cometalloclusters in the presence of both cations and free sugars to

3024
M. Nakamura et al. / Tetrahedron 69 (2013) 3019e3026
investigations of CCIs among these oligosaccharides are also in
progress.
124.869, 122.404, 121.061; [MþH]þ¼201.0681 (calcd 201.0664);
nmax (KBr) 1684, 1593, 1427, 1377, 1307, 761 cmꢁ1; mp >280 ꢀC.
4. Experimental section
4.1. General
4.4. 2,20-Bypiridine-5-carboxyl chloride (3)
To 2,20-bipyridine-5-carboxilic acid, thionyl chloride was added
and then, the resultant heterogeneous solution was refluxed until it
became homogeneous (ca. 3 h). The resultant reaction mixture was
evaporated to dryness and dried in vacuo to afford the title com-
pound as a pale-yellow powder. The product was used for the
syntheses of 4e7 without purification.
1H and 13C NMR spectra were acquired on a JEOL AL300 (JEOL
Resonance, Ltd) in CDCl3, CD3OD, D2O, or DMSO-d6. The chemical
shifts were reported in parts per million (d) relative to Me4Si or
internal references such as HOD. Matrix assisted laser desorption
ionization time-of-flight (MALDI-TOF) mass spectra were recorded
on MALDI SYNAPT G2 HDMS (Waters, Co.). IR spectra were recorded
on a JASCO FT/IR-4100 Fourier transform infrared spectrometer
(JASCO Co., Ltd). HPLC analyses were carried out on our integrated
HPLC system (pump: HITACHI L-7100, degassing unit: GL Sciences
DG660B, column oven: HITACHI L-7400, detector: GL Sciences GL-
7475, integrator: HITACHI D-2520) equipped with Inertsil WP 300
C4 analytical column (GL Sciences). Circular Dichroism (CD) spectra
were acquired on a JASCO J-820 spectropolarimeter (JASCO Co.).
Optical rotations were determined with a JASCO DIP-1000 digital
polarimeter using a 50 mm cell. Silica gel 60 N (spherical, neutral,
particle size 63-210 mm) for column chromatography was pur-
chased from Kanto Chemical Co., INC. Thin layer chromatography
4.5. 5-(-N-(p-O-(2,3,6,2,3,4,6-Hepta-O-acetyl-b-lactosyl)phe-
nyl)-aminocarbonyl)-2,20-bipyridine (4)
To 3 (0.19 g, 0.85 mmol) in THF (20 ml), pAP-bLac (0.70 g,
0.96 mmol) in THF (10 ml) was added dropwise with magnetic stir-
ring. After an addition of triethylamine (2 ml), the magnetic stirring
was continued at ambient temperature for 5 min. The resultant so-
lution was diluted with ethyl acetate and washed with 0.5 N aqueous
HCl and NaHCO3 saturated aqueous solution several times. The or-
ganic layer was dried over anhydrous MgSO4, filtered, evaporated to
dryness. The residue was purified by flash chromatography (chloro-
form/methanol¼20/1 in v/v) to give the title compound (0.14 g,18%) as
a white powder. In addition, large amounts of crude material con-
taining the title compound and some impurities was also recovered
after the flash chromatography; dH (300 MHz, CDCl3): 9.15 (d, J 1.2 Hz,
1H), 8.71(d, J3.9 Hz,1H), 8.50(d, J8.4 Hz,1H), 8.45(d, J8.1Hz,1H), 8.28
(dd, J 2.1, 8.4 Hz, 1H), 8.21 (s, 1H), 7.86 (td, J 1.5, 7.8 Hz, 1H), 7.59 (d, J
8.7Hz, 2H),7.37(ddd,J0.9, 4.8,7.5Hz,1H), 6.99(d,J9.0Hz,2H),5.36(d,
J 3.0 Hz,1H), 8.29 (dd, J 9.0, 9.0 Hz,1H), 5.17 (dd, J 7.5,10.2 Hz,1H), 5.13
(dd, J 8.4,10.5 Hz,1H), 5.03 (d, J 7.5 Hz,1H), 4.97 (dd, J 3.6,10.2 Hz,1H),
4.52 (d, J 8.1 Hz,1H), 4.53e4.49 (m,1H), 4.13e4.06 (m, 3H), 3.92e3.86
(m, 2H), 3.80e3.75 (m, 1H), 2.16 (s, 3H), 2.10 (s, 3H), 2.08 (s, 6H), 2.07
(s, 3H), 2.07 (s, 3H), 1.97 (s, 3H); dC (75 MHz, CDCl3): 170.404,170.198,
170.116, 169.811, 169.703, 169.168, 163.868, 158.676, 154.934, 153.838,
149.404,147.888,137.166,135.946,133.094,129.995,124.539,122.092,
121.778, 120.765, 117.666, 101.117, 99.106, 76.186, 72.815, 72.765,
71.438, 70.705, 69.065, 66.601, 61.985, 60.807, 20.827, 20.719, 20.654,
20.530; [MþH]þ¼910.2867 (calcd 910.2882); nmax (KBr) 2961, 1753,
(TLC) was carried out with Whatman TLC glass plates (PartisilÒ K6F)
pre-coated with silica gel 60
ꢁ
A
with fluorescent indicator
(
l
¼254 nm). All other chemicals were purchased from Wako Pure
Chemicals Co., Ltd., Kishida Chemicals Co., Ltd., GODO Co., or Kanto
Chemical Co., INC. and used without purification.
4.2. Methyl 2,20-bipyridine-5-carboxylate (1)
To bis(triphenylphosphine)palladium(II) dichloride (0.13 g) and
methyl 6-chloronicotinate (0.77 g) in m-xylene (10 ml), tri-
methyl(2-pyridyl)tin (1.0 ml) was added and then, the resultant
mixture was refluxed with magnetic stirring for 5 h. After a TLC
analysis showed a total consumption of the starting materials, the
reaction mixture was filtered through a Celite bed and the filtrate
was evaporated to dryness. The residue was purified by flash
chromatography (toluene/ethyl acetate¼9/1 to 1/1) to give the title
compound (0.80 g, 83%) as a white powder; dH (300 MHz, CDCl3):
9.27 (dd, J 0.9, 2.1 Hz, 1H), 8.72 (ddd, J 0.9, 1.8, 4.8 Hz, 1H), 8.51 (dd, J
0.9, 8.1 Hz,1H), 8.49 (ddd, J 0.9, 0.9, 8.1 Hz,1H), 8.41 (dd, J 2.1, 7.8 Hz,
1H), 7.86 (ddd, J 1.8, 7.5, 7.5 Hz, 1H), 7.36 (ddd, J 0.9, 4.8, 7.5 Hz, 1H),
3.98 (s, 3H); dC (75 MHz, CDCl3): 165.846, 159.509, 155.116, 150.525,
149.413, 138.039, 137.075, 125.660, 124.498, 121.910, 118.910,
52.409; [MþH]þ¼215.0819 (calcd 215.0821); nmax (KBr) 3056, 2917,
1510,1370,1227,1057 cmꢁ1; mp 239 ꢀC, [
a]
D
20 ꢁ0.4 (c 0.54, methanol).
4.6. 5-(-N-(p-O-(2,3,4,6-Tetra-O-acetyl-b-D-glucosyl)phenyl)-
aminocarbonyl)-2,20-bipyridine (5)
To 3 (0.32 g, 1.45 mmol) in THF (78 ml), pAP-bGlc (0.67 g,
1.53 mmol) in THF (100 ml) was added with magnetic stirring. After
an addition of triethylamine (0.41 ml), the magnetic stirring was
continued at ambient temperature for 5 min. The resultant solution
was diluted with ethyl acetate and washed with 0.5 N aqueous HCl
and NaHCO3 saturated aqueous solution several times. The organic
layer was dried over anhydrous MgSO4, filtered, evaporated to
dryness. The residue was purified by flash chromatography (tolu-
ene/ethyl acetate¼1/1 v/v) to give the title compound (0.16 g,17%) as
a white powder. In addition, large amounts of crude material con-
taining the title compound and some impurities was also recovered
after the flash chromatography; dH (300 MHz, CDCl3): 9.14 (d, J 1.8,
1H), 8.89 (ddd, J 0.9, 2.1, 5.1, 1H), 8.44e8.31 (m, 2H), 8.30 (d, J 2.1
8.1 Hz,1H), 7.86 (td, J 1.9, 7.5 Hz,1H), 7.63 (d, J 9.0 Hz, 2H), 7.37 (ddd,
J 1.2, 4.8, 7.5 Hz, 1H), 7.00 (d, J 9.0 Hz, 2H), 5.32 (d, J 9.3 Hz, 1H), 5.27
(t, J 9.0 Hz, 1H), 5.17 (t, J 9.6 Hz, 1H), 5.06 (d, J 7.8 Hz, 1H), 4.30 (dd, J
5.1, 12.3 Hz, 1H), 4.17 (dd, J 2.4, 12.3 Hz, 1H), 3.88 (ddd, J 2.4, 5.1,
7.5 Hz, 1H), 2.09 (s, 6H), 2.06 (s, 3H), 2.05 (s, 3H); dC (75 MHz,
CDCl3): 170.707, 170.270, 169.463, 164.099, 158.246, 154.834,
153.647, 149.221, 147.985, 137.213, 136.142, 133.315, 130.125,
124.430, 122.016, 121.785, 117.516, 99.335, 72.599, 71.874, 71.066,
2848, 1719,1595,1556,1460,1436,1378,1282,1119,1023, 761 cmꢁ1
mp 261 ꢀC.
;
4.3. 2,20-Bypiridine-5-carboxylic acid (2)
To methyl 2,20-bipyridine-5-carboxylate (0.80 g) in THF (240 ml),
sodium hydroxide (0.69 g) and water (20 ml) was added and then,
the resultant mixture was refluxed for 7 h with magnetic stirring.
After a TLC analysis (CHCl3/MeOH¼1/1) showed a total consumption
of the starting materials, aqueous HCl (35%, ca. 6 ml) was added
dropwise until the resultant mixture became acidic (ca. pH 3). The
resultant acidic mixture was concentrated using an evaporator,
cooled in an ice bath, and then, the precipitate was recovered by
a filtration to give the title compound (0.60 g, 81%) as white powder;
dH (300 MHz, CDCl3þCD3OD): 9.28 (dd, J 0.9, 2.1 Hz,1H), 8.70 (ddd, J
0.9, 1.8, 4.8 Hz, 1H), 8.47 (dd, J 2.1, 8.1 Hz, 1H), 8.42 (dd, J 0.9, 8.1 Hz,
1H), 8.41 (ddd, J 0.9, 0.9, 8.1 Hz, 1H), 7.91 (ddd, J 1.8, 7.5, 7.5 Hz, 1H),
and 7.42 (ddd, J 0.9, 5.1, 7.8 Hz, 1H); dC (75 MHz, CDCl3): 167.321,
159.302, 155.181, 150.904, 149.453, 138.830, 137.725, 126.649,

M. Nakamura et al. / Tetrahedron 69 (2013) 3019e3026
3025
68.140, 61.827, 20.603, 20.553, 20.504; [MþH]þ¼622.2019 (calcd
evaporated to afford the title compound (0.09 g, 98%) as a white
powder; dH (300 MHz, CDCl3): 9.04 (s, 1H), 8.62 (d, J 4.5 Hz, 1H),
8.38e8.29 (m, 3H), 7.92 (td, J 1.2, 7.8 Hz,1H), 7.55 (d, J 9.0 Hz, 2H), 7.44
(dd, J 5.1, 7.2 Hz,1H), 7.00 (d, J 9.0 Hz, 2H), 4.86 (d, J 7.5 Hz,1H), 4.19 (t, J
3.6 Hz, 1H), 3.61 (d, J 10.8 Hz, 1H), 3.62e3.56 (m, 2H), 3.50e3.38 (m,
6H), 3.30e3.25 (m, 3H); dC (75 MHz, DMSO-d6þD2O): 163.858,
157.182,153.935,153.688,149.361,148.273,137.798,136.661,132.358,
130.158, 124.974, 122.155, 121.356, 120.276, 116.394, 103.241, 99.903,
79.225, 75.219, 74.593, 74.304, 72.664, 72.541, 70.365, 67.991, 60.393,
59.676; [MþH]þ¼616.1353 (calcd 616.2143); nmax (KBr) 3369, 1647,
622.2037); nma2x0(KBr) 1748, 1652, 1514, 1369, 1224, 1038, 755 cmꢁ1
;
mp 179 ꢀC, [
a]
ꢁ7.4 (c 0.39, methanol).
D
4.7. 5-(-N-(p-O-(2,3,4,6-Tetra-O-acetyl-b-D-galactosyl)phenyl)-
aminocarbonyl)-2,20-bipyridine (6)
To 3 (0.09 g, 0.40 mmol) in THF (20 ml), pAP-bGlcNAc (0.93 g,
2.13 mmol) in THF (10 ml) was added dropwise with magnetic
stirring. After an addition of triethylamine (2 ml), the magnetic
stirring was continued at ambient temperature for 5 min. The re-
sultant solution was diluted with ethyl acetate and washed with
0.5 N aqueous HCl and NaHCO3 saturated aqueous solution several
times. The organic layer was dried over anhydrous MgSO4, filtered,
evaporated to dryness. The residue was purified by flash chroma-
tography (chloroform/methanol¼49/1 v/v) to give the title com-
pound (0.05 g, 20%) as a white powder. In addition, large amounts of
crude material containing the title compound and some impurities
was also recovered after the flash chromatography; dH (300 MHz,
CDCl3): 9.18 (t, J 1.5 Hz, 1H), 8.70 (ddd, J 0.9, 1.5, 4.8 Hz, 1H),
8.40e8.37 (m, 2H), 7.94 (td, J 1.8, 7.8 Hz, 1H), 7.68 (d, J 9.0 Hz, 2H),
7.45 (ddd, J 1.2, 1.8, 7.5 Hz, 1H), 7.05 (d, J 9.0 Hz, 2H), 5.51e5.45 (m,
2H), 5.15 (dd, J 3.3, 10.5 Hz, 1H), 5.11 (d, J 8.1 Hz, 1H), 4.29e4.11 (m,
3H), 2.22 (s, 3H), 2.12 (s, 3H), 2.09 (s, 3H), 2.04 (s, 3H); dC (75 MHz,
CDCl3): 170.853, 170.663, 170.490, 169.930, 164.539, 158.070,
155.012, 153.809, 149.284, 148.386, 137.664, 136.642, 133.708,
130.600, 124.675, 122.367, 122.145, 121.007, 117.447, 99.909, 70.989,
70.931, 68.780, 67.066, 61.470, 20.698, 20.575, 20.517;
1511, 1229, 1085 cmꢁ1; mp 233 ꢀC, [
a]
D
20 ꢁ29.4 (c 0.19, DMF).
4.10. 5-(-N-(p-O-(b-D-Glucosyl)phenyl)-aminocarbonyl)-2,
20-bipyridine (9)
To a methanol/THF mixed solvent system (1:1 v/v, 100 ml) con-
taining 5 (0.16 g, 0.25 mmol), aqueous ammonia (1.0 ml) was added
and the resultant reaction mixture was stirred at ambient temper-
ature for 1 h. After TLC analysis of the reaction mixture indicates
complete consumption of 5, additional aqueous ammonia (19 ml)
was added and the stirring was continued for overnight. The re-
sultant mixture was evaporated and then, the residue was re-
dissolved in water followed by lyophilization to afford the title
compound (0.11 g, 95%) as a white powder; dH (300 MHz, CDCl3):
9.06 (br s, 1H), 8.64 (d, J 2.7 Hz, 1H), 8.36 (br s, 2H), 8.32 (d, J 7.8 Hz,
1H), 7.96 (t, J 7.5 Hz, 1H), 7.56 (d, J 9.0 Hz, 2H), 7.48 (t, J 7.5 Hz, 1H),
7.03 (d, J 9.3 Hz, 2H), 4.83 (d, J 7.5 Hz, 1H), 3.69 (dd, J 1.5, 11.7 Hz, 1H),
3.47 (dd, J 6.0,12.0,1H), 3.38-3.32 (m, 1H), 3.32 (dd, J 9.0, 9.0 Hz,1H),
3.26 (dd, J 9.0, 9.0 Hz, 1H), 3.17 (dd, J 9.0, 9.0 Hz, 1H); dC (75 MHz,
DMSO-d6þD2O): 165.226, 158.328, 154.990, 150.474, 149.369,
139.100, 137.880, 133.306, 131.304, 126.169, 123.482, 122.691,
121.628, 117.590, 101.304, 77.379, 76.876, 73.942, 70.505, 65.774,
[MþH]þ¼622.1996 (calcd 622.2037); nmax (KBr) 1748, 1511, 1371,
20
1227, 1077, 758 cmꢁ1; mp 183 ꢀC, [
a]
29.2 (c 0.24, methanol).
D
4.8. 5-(-N-(p-O-(3,4,6-Tri-O-acetyl-N0-acetyl-
minyl)phenyl)-aminocarbonyl)-2,20-bipyridine (7)
b-D-glucosa-
61.522; [MþH]þ¼454.1551 (calcd 454.1614); IR (KBr, cmꢁ1) 3338,
20
1651, 1513, 1411, 1229, 1073 cmꢁ1; mp 252 ꢀC, [
DMF).
a]
ꢁ25.0 (c 0.15,
D
To 3 (0.18 g, 0.82 mmol) in THF (40 ml), pAP-bGlcNAc (0.49 g,
1.11 mmol) in THF (10 ml) was added dropwise with magnetic stir-
ring. After an addition of triethylamine (1.0 ml), the magnetic stirring
was continued at ambient temperature for 5 min. The resultant so-
lutionwas diluted with ethyl acetate and washed with 0.5 N aqueous
HCl and NaHCO3 saturated aqueous solution several times. The or-
ganic layer was dried over anhydrous MgSO4, filtered, evaporated to
dryness. The residue was purified by flash chromatography (toluene/
acetone/methanol¼5/5/0w5/5/1 v/v) to give the title compound
(0.50 g, 97%) as awhite powder; dH (300 MHz, CDCl3): 9.19 (d, J 2.1 Hz,
1H), 8.72 (d, J 7.5 Hz, 1H), 8.53 (d, J 8.4 Hz, 1H), 8.47 (s, 1H), 8.47 (d, J
7.8 Hz,1H), 8.33 (dd, J 2.1, 8.1 Hz,1H), 7.76 (ddd, J 1.8, 7.5, 7.5 Hz,1H),
7.60 (d, J 9.3 Hz, 2H), 7.37 (ddd, J 0.9, 4.5, 7.5 Hz,1H), 7.02 (d, J 9.0 Hz,
2H), 6.09 (d, J 8.7 Hz, 1H), 5.39 (dd, J 9.3, 9.9 Hz,1H), 5.22 (d, J 8.4 Hz,
1H), 5.14 (dd, J 9.6, 9.6 Hz,1H), 4.30 (dd, J 5.7, 12.6 Hz,1H), 4.22e4.13
(m, 2H), 3.86 (ddd, J 2.4, 5.4, 9.9 Hz,1H), 2.10 (s, 3H), 2.07 (s, 3H), 2.06
(s, 3H), 1.98 (s, 3H); dC (75 MHz, CDCl3þCD3OD): 171.352, 171.129,
171.022, 169.720, 158.264, 155.058, 154.152, 149.363, 148.333,
137.454, 136.556, 133.358, 130.432, 124.581, 122.561, 122.454,
121.993, 120.938, 117.526, 99.534, 72.526, 71.884, 68.669, 62.216,
54.213, 23.011, 20.761, 20.703, 20.654; [MþH]þ¼621.2122 (calcd
621.2197); nmax (KBr) 3316, 1746, 1667, 1533, 1512, 1376, 1227,
4.11. 5-(-N-(p-O-(
b-D-Galactosyl)phenyl)-aminocarbonyl)-2,
20-bipyridine (10)
To 6 (0.05 g, 0.08 mmol) in dry methanol (50 ml), sodium
methoxide (0.35 g, 6.48 mmol) was added and the resultant re-
action mixture was stirred at ambient temperature for 1 h. After
TLC analysis of the reaction mixture indicates complete consump-
tion of 6, the resultant reaction mixture was neutralized by DOWEX
and evaporated to afford the title compound (0.03 g, 94%) as a white
powder; dH (300 MHz, DMSO-d6þD2O): 9.11 (s,1H), 8.68 (d, J 3.9 Hz,
1H), 8.45-8.37 (m, 3H), 7.97 (dd, J 7.8, 7.8 Hz, 1H), 7.60 (d, J 7.8 Hz,
2H), 7.49 (dd, J 4.8, 7.2 Hz, 1H), 7.03 (d, J 9.0 Hz, 2H), 4.77 (d, J 7.5 Hz,
1H), 3.69 (d, J 3.3 Hz, 1H), 3.57e3.48 (m, 4H), 3.42 (dd, J 3.0, 9.6 Hz,
1H); 13C NMR (DMSO-d6þD2O, TMS): 164.567, 158.023, 154.842,
154.743, 150.243, 149.147, 138.573, 137.485, 133.133, 131.073,
125.773, 122.839, 122.106, 121.018, 117.210, 101.724, 75.903, 73.587,
70.868, 68.733, 61.060; [MþH]þ¼454.1593 (calcd 454.1614); nmax
(KBr) 3327, 2926, 2814, 2778, 1650, 1620, 1459, 1353, 1075 cmꢁ1
;
20
mp 225 ꢀC, [
a
]
30.1 (c 0.17, DMF).
D
1048 cmꢁ1; mp 221 ꢀC, [
a]
D
20 ꢁ3.7 (c 1.01, methanol).
4.12. 5-(-N-(p-O-(N0-Acetyl-(
nocarbonyl))-2,20-bipyridine (11)
b-D-glucosaminyl)phenyl)-ami-
4.9. 5-(-N-(p-O-(b
-Lactosyl)phenyl)-aminocarbonyl)-2,20-bi-
pyridine (8)
To a dry methanol/THF mixture (1:1 v/v, 70 ml) containing 7
(0.29 g, 0.47 mmol), sodium methoxide (20 mg, 0.37 mmol) was
added and the resultant reaction mixture was stirred at ambient
temperature for 2 h. After TLC analysis of the reaction mixture in-
dicates complete consumption of the substrates, the resultant re-
action mixture was neutralized by DOWEX and evaporated to afford
the title compound (0.23 g, 98%) as a white powder; dH (300 MHz,
To 4 (0.14 g, 0.15 mmol) in dry methanol (50 ml), a catalytic
amount of sodium methoxide was added and the resultant reaction
mixture was stirred at ambient temperature for 3 h. After TLC anal-
ysis of the reaction mixture indicates complete consumption of 4, the
resultant reaction mixture was neutralized by DOWEX and

3026
M. Nakamura et al. / Tetrahedron 69 (2013) 3019e3026
2. Hussain, M. R. M.; Hassan, M.; Shaik, N. A.; Iqbal, Z. Cent. Eur. J. Med. 2012, 7,
409e419.
DMSO-d6þD2O): 9.08 (s, 1H), 8.65 (d, J 5.1 Hz, 1H), 8.41e8.35 (m,
3H), 7.96 (ddd, J 1.5, 7.5, 7.5 Hz, 1H), 7.57 (d, J 9.0 Hz, 2H), 7.48 (ddd, J
0.9, 5.1, 7.5 Hz, 1H), 6.96 (d, J 9.0 Hz, 2H), 5.06 (d, J 8.4 Hz, 1H), 3.85
(dd, J 8.7, 10.2 Hz, 1H), 3.84 (d, J 10.8 Hz, 1H), 3.63 (dd, J 5.7, 12.0 Hz,
1H), 3.54 (dd, J 9.6, 9.6 Hz, 1H), 3.51e3.45 (m, 1H), 3.34 (dd, J 9.0,
9.3 Hz, 1H), 1.97 (s, 3H); dC (75 MHz, DMSO-d6þD2O): 164.567,
158.023, 154.842, 154.743, 150.243, 149.147, 138.573, 137.485,
133.133,131.073,125.773,122.839,122.106,121.018,117.210,101.724,
75.903, 73.587, 70.868, 68.733, 61.060; [MþNa]þ¼495.1837 (calcd
3. Dam, T. K.; Brewer, C. F. Adv. Carbohydr. Chem. Biochem. 2010, 63, 139e164.
4. For current research progress in CCIs, see: Glycoconjugate J. 2004, 21 (-4).
5. Iwabuchi, K.; Yamamura, S.; Prinetti, A.; Handa, K.; Hakomori, S. J. Biol. Chem.
1998, 273, 9130e9138.
ꢀ
6. de la Fuente, J. M.; Penades, S. Tetrahedron: Asymmetry 2002, 13, 1879e1888.
7. Chen, Q.; Cui, Y.; Zhang, T.-L.; Cao, J.; Han, B.-H. Biomacromolecules 2010, 11,
13e19.
8. Zhao, J.; Liu, Y.; Park, H.-J.; Boggs, J. M.; Basu, A. Bioconjug. Chem. 2012, 23,
1166e1173.
9. Matsuura, K.; Kobayashi, K. Glycoconjugate J. 2004, 21, 139e148.
10. Seah, N.; Santacrose, P. V.; Basu, A. Org. Lett. 2009, 11, 559e562.
11. de la Fuente, J. M.; Eaton, P.; Barrientos, A. G.; Menendez, M.; Penades, S. J. Am.
Chem. Soc. 2005, 127, 6192e6197.
495.1880); nmax (KBr) 3311, 1661, 1536,1511, 1222, 1076 cmꢁ1; mp
20
241 ꢀC, [
a]
6.1 (c 0.40, DMF).
ꢀ
ꢀ
D
12. Simpson, G. L.; Gordon, A. H.; Lindsay, D. M.; Promsawan, N.; Crump, M. P.;
Mulholland, K.; Hayter, B. R.; Gallagher, T. J. Am. Chem. Soc. 2006, 128,
10638e10639.
13. Altamore, T. M.; Fernandez-García, C.; Gordon, A. H.; Hubscher, T.; Promsawan,
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Acknowledgements
ꢀ
€
This research was partially supported by Special Research Fund
of Toyo University. We gratefully acknowledge Prof. Dr. B. Shimizu
of Toyo University for his kind help to measure HRMS. We are also
grateful to Prof. Dr. Y. Nishida and Dr. H. Dohi of Chiba University for
their kind permission to use their digital polarimeter.
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29. We carried out some experiments to support the fast interconversions among
the DCL members. Briefly, in these experiments, we mixed aqueous solutions of
Supplementary data
Supplementary data related to this article containing synthetic
routes toward pAP-glycosides (Schemes S1 and S2), snap shots of
the four diastereomeric stereoisomers of [Fe(bpy
the MD calculations (Fig. S1), distances between the three non-
reducing Gal terminals (C4) of [Fe(bpy
Lac)3]2þ during the MD
b
Lac)3]2þ during
b
b
calculations (Figs. S2 and S3), photographs of aqueous DMF con-
taining bpyGlcNAc and various concentrations of FeCl2 (Fig. S4),
Ca2þ-induced UVevis spectral change of [Fe(bpy
b
GlcNAc)3]Cl2
(Fig. S5), the cations-induced CD spectral changes of [Fe(bpy Glc)3]
Cl2 and [Fe(bpy Gal)3]Cl2 (Fig. S6) and the CD spectra of [Fe(b-
py GlcNAc)3]Cl2 and [Fe(bpy
Lac)3]Cl2 in the presence of both Ca2þ
b
b
[Fe(bpybLac)3]Cl2 and [Fe(bpy)3]Cl2 and then, measured a UVevis spectrum of
the resultant mixture after an incubation (20 min) at the ambient temperature.
If the time-scale for the interconversion among the DCL members is slow
enough, the UVevis spectrum of the resultant mixture should be super-
imposed of those of the parent solutions. We found, however, that the resultant
mixture showed a UVevis spectrum, which was totally different from those of
b
b
(100 mM) and free sugars (400 mM) (Fig. S7) is available online free
of charge. Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.tet.2013.01.095.
the parent solutions; that is, ded* transitions assignable to [Fe(bpy
lmax¼303 nm) and [Fe(bpy)3]Cl2 lmax¼289 and 297 nm) disappeared and
a new ded* transition peak appeared at 298 nm. These data clearly indicate
that new DCL members, such as ([Fe(bpy Lac)2(bpy)1]Cl2 and [Fe(bpy-
Lac)1(bpy)2]Cl2), were immediately formed from [Fe(bpy Lac)3]Cl2 and
[Fe(bpy)3]Cl2 through their interconversions.
bLac)3]Cl2
(
(
References and notes
b
b
b
1. Hirohashi, N.; Kamei, N.; Kubo, H.; Sawada, H.; Matsumoto, M.; Hoshi, M. De-
velop. Growth Differ. 2008, 50, S221eS238.