Hydrogen-bonding cooperativity: Using an intramolecular hydrogen bond to design a carbohydrate derivative with a cooperative hydrogen-bond donor centre

Article abstract of DOI:10.1002/chem.200400042

Neighbouring groups can be strategically located to polarise HO...OH intramolecular hydrogen bonds in an intended direction. A group with a unique hydrogen-bond donor or acceptor character, located at hydrogen-bonding distance to a particular OH group, ha

Full text of DOI:10.1002/chem.200400042

FULL PAPER
Hydrogen-Bonding Cooperativity: Using an Intramolecular Hydrogen Bond
To Design a Carbohydrate Derivative with a Cooperative Hydrogen-Bond
Donor Centre
Virginie Vicente,[a] Jason Martin,[a] JesÇs Jimÿnez-Barbero,[b] Josÿ Luis Chiara,[a] and
Cristina Vicent*[a]
Abstract: Neighbouring groups can be
strategically located to polarise
HO¥¥¥OH intramolecular hydrogen
bonds in an intended direction.
located in a 1,3-cis-diaxial relationship
to a second hydroxy group, can be used
to select a unique direction on the six-
membered-ring intramolecular hydro-
gen bond between the two axial OH
groups, so that one of them behaves as
an efficient cooperative donor. Talose
derivative 3 was designed and synthe-
sised to prove this hydrogen-bonding
network by NMR spectroscopy, and
the mannopyranoside derivatives 1 and
2 were used as models to demonstrate
the presence in solution of the 1,2-
(e,a)/five-membered-ring intramolecu-
lar hydrogen bond. Once a well-de-
fined hydrogen-bond is formed be-
tween the OH and the amido groups of
a pyranose ring, these hydrogen-bond-
ing groups no longer act as indepen-
dent hydrogen-bonding centres, but as
hydrogen-bonding arrays. This introdu-
ces a new perspective on the properties
of carbohydrate OH groups and it is
important for the de novo design of
molecular recognition processes, at
least in nonpolar media. Carbohydrates
1 3 have shown to be efficient phos-
phate binders in nonpolar solvents
owing to the presence of cooperative
hydroxy centres in the molecule.
A
group with a unique hydrogen-bond
donor or acceptor character, located at
hydrogen-bonding distance to a partic-
ular OH group, has been used to ini-
tiate the hydrogen-bond network and
to polarise a HO¥¥¥OH hydrogen bond
in a predicted direction. This enhanced
the donor character of a particular OH
group and made it a cooperative hy-
drogen-bond centre. We have proved
that a five-membered-ring intramolecu-
lar hydrogen bond established between
an amide NH group and a hydroxy
group (1,2-e,a), which is additionally
Keywords: carbohydrates ¥ hydro-
gen bonding ¥ molecular recogni-
tion ¥ supramolecular chemistry
Introduction
hydrogen bond is formed between the H-bond donor or ac-
ceptor of the existing hydrogen bond and a third hydrogen-
bonding group, may enhance (positive cooperativity) or
weaken (negative cooperativity) a hydrogen-bonding inter-
action.[4] The relevance of a cooperative hydrogen-bonding
network to the molecular recognition of a carbohydrate by a
protein receptor has already been demonstrated by NMR
spectroscopy in aqueous solution.[4d] Previous studies by
us[5,6] and others[7] have shown that the hydroxy groups of
carbohydrates show different abilities to form intramolecu-
lar hydrogen bonds, depending on their relative position and
configuration on the pyranose ring and on the nature of the
adjacent functional groups. Their participation implies a po-
larisation of the hydrogen bonds between OH groups, which
modulates the final directionality and strength of the intra-
molecular OH¥¥¥OH hydrogen bonds of a given carbohy-
drate. Additionally, we showed that both the directionality
and strength of the intramolecular hydrogen-bonding net-
work of a carbohydrate determine the formation of coopera-
tive or anticooperative hydrogen-bond centres, with conse-
Carbohydrate recognition relies upon multiple weak interac-
tions,[1] of which hydrogen bonds (H-bonds) and van der -
Waals forces seem to be the most important. The high con-
tent of hydroxy groups in carbohydrates makes the study of
carbohydrate OH¥¥¥XH and OH¥¥¥X H-bond energetics fun-
damental to understanding carbohydrate recognition.[3]
Moreover, hydrogen-bonding cooperativity, defined as the
change in the strength of a hydrogen bond when a second
[2]
[a] Dr. V. Vicente, Dr. J. Martin, Dr. J. L. Chiara, Dr. C. Vicent
Instituto de QuÌmica Orgµnica General, CSIC
Juan de la Cierva 3, 28006 Madrid (Spain)
Fax : (+34)91564-4853
E-mail: iqocv18@iqog.csic.es
[b] Prof. Dr. J. Jimÿnez-Barbero
Centro de Investigaciones BiolÛgicas, CSIC
Ramiro de Maeztu 9, E-28040 Madrid (Spain)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/chem.200400042
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4240 4251
quent repercussions for the
thermodynamics of the inter-
molecular hydrogen-bonding in-
teractions of a given carbohy-
drate. This fact is extremely im-
portant for defining the nature
of the molecular recognition
processes in which a given car-
bohydrate is able to participate,
because it determines whether
or not ™good hydrogen-bond
acceptors and/or donors∫ are
formed.
We have applied the concept
of cooperativity to achieve ef-
fective dimerization of carbohy-
drates[8] and binding of pyri-
dine.[6] Regarding the hydro-
gen-bonding patterns which are
relevant for DNA groove bind-
ing, we have investigated the
complementarity of sugar hy-
Figure 1. a) Hydrogen-bonding isomers in equilibrium for a 1,3-cis-diaxial diol. b) Schematic representation of
the polarisation of the 1,3-diol-cis-diaxial hydrogen-bonding motif.
drogen-bond centres to GC base pair hydrogen-bond cen-
tres[9] and phosphate hydrogen-bonding motifs.[5] Further-
more, in the latter case, we have been able to quantify the
effect of hydrogen-bonding cooperativity in this intermolec-
ular process in apolar solvent. The most relevant results are
that 1,2-trans cooperative diols and amido alcohols are very
stable bidentate H-bonding motifs for this particular interac-
tion.
group results in a mixture of hydrogen-bonding isomers in
solution (Figure 1a). Thus, to be able to select a particular
OH group to behave as a ™cooperative donor or acceptor
centre∫, we envisaged the possibility of using functional
groups strategically placed to interact within the hydrogen-
bond network and to select a particular OH¥¥¥OH hydrogen-
bond, and thus obtain an energetic advantage from hydro-
gen-bonding cooperativity (Figure 1b).
From this study in apolar solvents, some general rules
have been inferred for the prediction of the intramolecular
hydrogen-bonding network characteristics of a given carbo-
hydrate, and its influence on the energetics of intended in-
termolecular recognition processes.[6] One conclusion was
that neighbouring groups could be strategically located to
polarise intramolecular hydrogen bonds in an intended di-
rection. This will enhance the donor or acceptor character
of a particular OH group and make it a cooperative hydro-
gen-bond centre.
Once a well-defined hydrogen bond is formed between
the OH and amido groups of a sugar pyranose ring, these
hydrogen-bonding groups no longer act as independent hy-
drogen-bonding centres, but as hydrogen-bonding arrays.
This introduces a new perspective on carbohydrate OH
groups and is extremely important for de novo design of
molecular recognition processes, at least in nonpolar media.
A group with an unique hydrogen-bond donor or acceptor
character, located at hydrogen-bonding distance to a partic-
ular OH, can be used to initiate the hydrogen-bond network
and to polarise it in the desired direction.
We now show that a five-membered-ring intramolecular
hydrogen bond established between an amido NH group
and a hydroxy group (Figure 2b) that additionally is in a
1,3-cis-diaxial relationship to a second hydroxy group (Fig-
ure 2c) can be used to select an unique direction on the six-
membered-ring intramolecular hydrogen bond between di-
axial hydroxy groups, so that one of them behaves as an effi-
cient cooperative donor (Figure 2a).
Hence, we selected two mannopyranoside derivatives (1
and 2) that have an amido NH group at the anomeric posi-
tion (C1) with equatorial (b) orientation (Figure 3). Addi-
tionally, OH-2 in the pyranose ring has an axial orientation.
We hypothesised on the establishment of a five-membered-
ring intramolecular hydrogen bond between these amido
NH and (OH-2) hydroxy groups (Figure 2b). Sugar 2 is a 6-
deoxy derivative of 1, and was synthesized to simplify the
hydrogen-bonding network.
Results and Discussion
Design: Our previous work has shown that the 1,3-cis-di-
axial configuration of sugar diols and amido alcohols in a
rigid framework (4C1 pyranose ring) presents an efficient in-
tramolecular six-membered-ring hydrogen-bond that even
survives in aqueous solution to a certain extent[10] (Fig-
ure 1a). Moreover, this offers the possibility of establishing
cooperative intermolecular hydrogen bonds.[5] The intrinsic
hydrogen-bonding donor and acceptor character of the OH
Compound 3 is a talopyranose derivative[11,12] which not
only has an equatorial amido NH group at the anomeric po-
sition and an axial OH group at the 2-position (as in 1 and
2), but also an axial hydroxy group in the 4-position. Thus, a
1,3-diaxial diol, involving the 2- and 4-positions of the pyra-
nose ring, is additionally present here (see Figure 2a).[13]In
this case we hypothesised the presence of the hydrogen-
bonding network NH!OH-2!OH-4. According to our ex-
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C. Vicent et al.
FULL PAPER
Figure 2. a) Six-membered-ring intramolecular hydrogen bond between a 1,3-cis-(a,a)-diol; b) five-membered-ring intramolecular hydrogen bond used as
a polarizing group; c) cooperative hydrogen-bonding network
than 6 kJmolꢀ1 over the corresponding syn geometry. Values
between 160 and 1758 were found for this angle, correspond-
ing to a NH¥¥¥OH-2 distance of 2.61 2.62 ä, which suggests
the possible presence of the five-membered-ring intramolec-
ular hydrogen bond (see Supporting Information).
Additionally, in all cases, the different possible orienta-
tions of the hydroxy groups were considered. For both 1 and
2, the clockwise orientation of the hydroxy groups (OH-2!
OH-3!OH-4) was the most stable conformation. Our MM
calculations for the talopyranoside derivative 3 in chloro-
form predicts the most stable conformer to be that in which
O4 accepts a hydrogen atom from both OH-2 and OH-3. In
addition, OH-4 acts as a donor to O6 (see Supporting Infor-
mation).
The second more stable local minimum of 3 (DE=
Figure 3. N-glycosylamides 1 3.
1.5 kJmolꢀ1) exhibits a cooperative H-bond network of the
type OH2!OH4!OH6, without involvement of OH-3 in
the network. These results suggest that in talose derivative 3
pectations, the presence of the five-membered-ring intramo-
lecular hydrogen bond established between an NH amido
group and a hydroxy group in the 2-position should polarise
the second hydrogen bond (six-membered-ring intramolecu-
lar hydrogen bond between the two diaxial OH groups)
(Figure 2c), so that OH group at the 4-position behaves as
an efficient cooperative donor.
the NH!OH-2 H-bond is directing or polarising the H-
bonding equilibrium of the six-membered intramolecular hy-
drogen bond towards the presence of a unique OH-2!OH-
4 H-bond isomer. Thus, this feature makes OH-4 act as a co-
operative donor, which is able to form an additional intra-
molecular hydrogen bond to OH-6, or probably to establish
strong intermolecular hydrogen bonds.
On this basis, we carried out molecular mechanics calcula-
tions using the MM2* force field, as integrated in MACRO-
MODEL 7.0, on 1, 2, and 3. The GB/SA solvent model for
chloroform was used. The first question was whether the
structure of the minima predicted by the force field would
allow the formation of the five-membered-ring intramolecu-
lar hydrogen bond between the NH group in the anomeric
position and the axial OH-2 group.
Synthesis: The synthesis of compounds 1 and 2 was achieved
straightforwardly starting from d-mannose (Scheme 1). The
amino group at the anomeric position was introduced via
the corresponding azides 6[14,15] and 7, prepared, respectively,
by reaction of the pyranose peracetates 4 and 5[16] with
TMSN3 with catalysis by SnCl4.[17] Reduction of the azido
group with hydrogen in the presence of Raney Ni[18] took
place quantitatively with concomitant almost complete
anomerization to generate the corresponding b-aminoglyco-
sides 8 and 9.
This was indeed the case. In the three compounds, and ac-
cording to the calculations, the anti orientation around angle
F (defined as H1-C1-N-HN) was always stabilised by more
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Cooperative Hydrogen Bonds
4240 4251
bed procedure,[21] b-d-galactosyl azide 14 was prepared in an
amount of more than 25 g in high yield without requiring
any purification. After attempting fruitlessly an oxidation
reduction protocol for the inversion of stereochemistry at
C-2, we turned our attention to the protocol developed by
Knapp et al.[22] via intramolecular displacement of a trifluo-
romethanesulfonate ester by a vicinal carbamoyl group. The
application of this protocol to our case would require instal-
lation of the carbamoyl group on the hydroxy group at C-3.
This was easily performed after standard protecting-group
manipulations that involved deacetylation of 14 with sodium
methoxide to afford the pure azide 15 in high yield, fol-
lowed by protection of the hydroxy groups at C-4 and C-6
in the form of a benzylidene acetal to give 16. Treatment of
16 with a stoichiometric amount of benzoyl isocyanate at
08C in THF gave selectively the monocarbamate 17 in 86%
yield. By this route, 17 can be prepared in just four steps
from b-d-galactose pentaacetate in 61% overall yield. Treat-
ment of 17 with triflic anhydride and pyridine gave the un-
stable trifluomethanesulfonic ester 18, which was immedi-
ately used for the intramolecular displacement reaction.
Treatment of triflate 18 in THF at 08C with an excess of
NaH according to the procedure of Knapp et al. afforded a
mixture of the N-benzoylimidate 19 and its hydrolysis prod-
uct, the carbonate 20. The crude reaction mixture was dis-
solved in THF and treated with a 2m aqueous solution of
lithium hydroxide monohydrate to afford d-talosyl azide 21
in 69% overall yield from 18. The b-d-talo configuration of
Scheme 1. Synthesis of 1 and 2. a) TMSN3, SnCl4, CH2Cl2, RT (6, 80%; 7,
60%); H2, Raney Ni W-2, MeOH, RT; c) DIC, HOBt, DMF/CHCl3
(171), RT (11, 33%; 12, 53%, 2 steps); d) NaOMe, MeOH, RT (1, 47%;
2, 74%). DIC=diisopropylcabodiimide, HOBT=hydroxybenzotriazole,
TMS=trimethylsilyl.
N-Acylation with gallic acid derivative 10[19] was carried
out with DIC and HOBt[20] to give 11 and 12, which were
subsequently deacetylated under standard conditions to give
the target b-d-mannosyl amides 1 and 2.
The synthesis of 3 was more cumbersome. A number of
synthetic routes could be conceived, the most straightfor-
ward of which proceeded via inversion of configuration of a
single stereocentre of a readily available hexose, for exam-
ple, d-galactose (inversion at C-2) or d-mannose (inversion
at C-4). After assaying several routes, the most convenient
in terms of number of steps and overall yield was found to
be that shown in Scheme 2, which employs d-galactopyra-
nose peracetate (13) as starting material. By using a descri-
1
21 could be readily confirmed from the H NMR spectrum,
which showed characteristic proton proton coupling con-
3
3
stants J1,2 and J2,3 of 3.5 Hz. Compound 21 was transformed
into the corresponding tetraacetate 22 under standard condi-
tions before reduction of the azide to the amine with hydro-
Scheme 2. Synthesis of 3.
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C. Vicent et al.
FULL PAPER
gen in the presence of 10% Pd/C and subsequent N-acyla-
tion with gallic acid derivative 10 to afford amide 23. Deace-
tylation of 23 provided the final d-talose derivative 3.
sembly. The lack of variation in the NMR parameters upon
dilution showed that 1 3 do not aggregate in this concentra-
tion range.
Structural studies: Conformational analysis of 1 3 was car-
ried out by NMR spectroscopy in CDCl3 solution. Full as-
signment of the NMR spectra was performed by standard
1D and 2D NMR experiments (selective decoupling, COSY,
TOCSY and NOESY). The b configuration of the amido
group at the anomeric position was established on the basis
of NOESY data. The NOEs observed between H1, H3 and
H5 resonances of the pyranose ring prove the presence of
the b isomer for 1, 2 and 3.
Hydrogen-bond network in mannopyranoside derivatives 1
and 2: The NMR parameters of the NH amide resonance in
both mannopyranoside derivatives 1 and 2 follow the same
trend. The large J values are indicative of the presence of a
trans relationship between the NH and CH-1 groups, and
the small temperature coefficients are consistent with its in-
volvement in an intramolecular hydrogen bond.
As mentioned above, we carried out molecular mechanics
calculations by MM2* on both the syn and anti conformers
of the N-glycosidic linkage of 1 and 2. The anti orientation
around the f angle, defined as H1-C1-N-H, was always sta-
bilised by more than 66 kJmolꢀ1 relative to the correspond-
ing syn geometry (f values between 160 and 1758 were
found). Additionally, the distance between NH and OH-2 in
the anti H1-C-N-H arrangement [d=2.59 ä (1), 2.39 ä (2)]
is in agreement with an intramolecular hydrogen bond,
while in the syn conformer, the longer NH¥¥¥OH-2 distance
does not allow the formation of an intramolecular hydrogen
bond.[24]
The presence of hydrogen bonds in solution can be estab-
lished[11] by the study of 1) chemical shift values, 2) tempera-
ture coefficients (Dd/DT), 3) vicinal coupling constants
[23]
3JOH,CH d) rate of exchange with the solvent and e) isotope
effects.
Tables 1 and 2 list the chemical shifts, vicinal coupling
constants and temperature coefficients for the NH and OH
resonances of 1 3 in CDCl3. All the NMR parameters for 1
The OH resonances of both 1 and 2 were detected as
sharp doublets at low concentration (ca. 10ꢀ4 m for 1 and
10ꢀ3 m for 2). The J values are in the range of those expected
for OH groups involved in hydrogen bonding[23] Small
(1 4 Hz) and large (9 11 Hz) J values are indicative of pro-
tons fixed in an hydrogen bond. The same trend is observed
for all the Dd/DT (within the range expected for an OH
group involved in an hydrogen bond). The only exception is
the OH-6 resonance in 1, which has a temperature coeffi-
cient of ꢀ8 ppbKꢀ1 and a J value of 5 Hz, characteristic of a
free OH group.
Thus, since according to the MM2* data the only OH at
hydrogen-bonding distance to the amide NH is OH-2 and,
significantly, in both 1 and 2, OH-2 exhibits small J and Dd/
DT values, its involvement in an intramolecular hydrogen
bond seems to be granted.
Table 1. Chemical shifts [ppm], coupling constants [Hz] and temperature
coefficients Dd/DT of hydroxy and amide groups of 1 3 in CDCl3.
OH-2
OH-3
OH-4
OH-6
NH
7.144
1[a]
2[b]
3[c]
d
2.557
3.5
2.574
4.0
2.390
3.0
2.126
5.0
J
9.0
Dd/DT
d
ꢀ2.2
2.514
3.6
ꢀ2.5
3.735
10
ꢀ2.8
2.527
4.2
ꢀ2.5
3.006
9.5
ꢀ2.7
2.018
2.7
ꢀ2.9
3.937
3.0
ꢀ8.0
ꢀ2.2
7.091
J
Dd/DT
d
9.0
ꢀ2.4
2.301
6.5
7.316
J
9.0
Dd/DT
ꢀ4.3
ꢀ2.3
ꢀ7.5
ꢀ3.9
ꢀ2.0
[a] 1.1î10ꢀ4 m, 408C, 500 MHz. [b] 1.66î10ꢀ3 m, 358C, 500 MHz.
[c] 1.09î10ꢀ3 m, 228C, 500 MHz.
Table 2. Isotope effect [ppb] and level of deuteration [%] for the NH
To obtain additional experimental evidence for the pres-
ence of this NH!OH-2 intramolecular hydrogen bond, we
also carried out partial deuteration experiments[25] on 1 and
2 in CDCl3 (Table 2). The NMR spectra were recorded 3 h
after the addition of CD3OD. In the case of 1, it was not
possible to observe the signal of the amide group, because it
shifts and overlaps with the CDCl3 signal upon addition of
methanol.
and OH resonances of 1 3.
OH-2 OH-3
OH-4
2
OH-6
NH
1[a] isotope
5
3
overlapping overlapping
effect
deuteration
31
31
39
level
2[b] isotope
effect
broad broad
broad
5
deuteration
61
The NH resonance of compound 2 showed an isotope
effect of 5 ppb (see Supporting Information), which con-
firmed the presence of an intramolecular hydrogen bond be-
tween the amido b-NH group in the anomeric position and
the axial OH-2 group in the pyranose ring. This is a five-
membered-(e,a)-ring intramolecular hydrogen bond that
makes the hydroxy group OH-2 a cooperative donor. This
result is in accordance with the J value and temperature co-
efficients found for the NH resonance.
level
3[c] isotope
effect
6
3
overlapping
3
2
deuteration
level
74
35
27
69
[a] 1.1î10ꢀ3 m, 308C, 300 MHz. [b] 1.1î10ꢀ4 m, 328C, 500 MHz. [c] 1.5î
10ꢀ3 m, 218C, 500 MHz.
3 were measured at relatively low concentrations (between
10ꢀ3 and 10ꢀ4 m), and additional dilution experiments were
also carried out in order to exclude the possibility of self-as-
Additionally, in the case of 1, an isotope effect was also
detected for OH-2 (5 ppb), again consistent with its involve-
ment in an intramolecular hydrogen bond (Table 2).
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Cooperative Hydrogen Bonds
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Thus, all experimental evidence is in agreement with the
presence, in apolar solution, of the five-membered-ring in-
tramolecular H-bond between the NH and the OH-2 groups
(NH!OH-2) in 1 and 2 (Figure 4).
NMR parameters for the hydroxy and amide resonances of
b-d-talopyranose derivative 3 in CDCl3 are listed in Table 1.
The amide resonance in 3 shows the same J and Dd/DT
values as were obtained for the b-d-mannopyranoside deriv-
atives 1 and 2 (see Table 1). However, the chemical shift of
the amide NH resonance, although in the same chemical en-
vironment, is more deshielded in 3 than in 1 and 2
(Dd(3ꢀ1)=0.154 ppm and Dd(3ꢀ2)=0.195 ppm at 308C).
This difference suggests that the corresponding NH proton
of 3 is more involved in an intramolecular hydrogen bond
than those of the related mannopyranose derivatives 1 and
2.
The Dd/DT values of the OH resonances in 3 showed a
clear difference between OH-2, OH-3 and OH-6 and OH-4.
The last-named has a Dd/DT value characteristic of a free
OH group (ꢀ7.5 ppbKꢀ1). The OH-2 and OH-3 groups have
large J values (10 and 9.5 Hz) reflecting a preferred orienta-
tion, probably related to their involvement in intramolecular
hydrogen bonds (dihedral angles larger than 1508). In con-
trast, the values for OH-4 and OH-6 are in the range of
those expected for a free OH group.
These J values are in accordance with those reported by
us for 1,6-anhydro-3-deoxy-3-palmitoylcarboxamide-b-d-glu-
copyranose,[6] for which a six-membered-ring intramolecular
hydrogen bond polarised in one direction was found.
Therefore, the previous NMR data are in agreement with
the presence in solution of a detectable percentage of the
hydrogen-bond isomer of 3 in which OH-4 is acting as a hy-
drogen-bond acceptor for OH-2 and OH-3, as predicted by
MM2* calculations (see Supporting Information).
Figure 4. The predicted five-membered-ring intramolecular hydrogen
bond 1,2-cis-(a,e) for 1 and 2.
Smaller isotopic effects were also measured for the OH-3
and OH-4 resonances in 1.[26] This result, together with the
small Dd/DT values of both resonances (Table 1), is also in
accordance with the presence of the hydrogen-bond network
suggested by molecular modelling, with an orientation OH-
2!OH-3!OH-4.[7b,6]
The hydroxy group OH-6 of 1 has a coupling constant of
5 Hz, which seems to indicate that this group is not involved
in a hydrogen bond. Moreover, no isotope effect was ob-
served for this resonance upon partial deuteration.
The NMR and molecular modelling data obtained for 1
and 2 suggest that in this apolar solvent, these N-glycosyl-
amides can be described as a mixture of the hydrogen-bond
isomers shown in Figure 5.
A partial deuteration experiment was also performed on
an NMR sample of 3 under the same conditions described
above for 1 and 2 (Table 2). The NH resonance of the
amido group in the anomeric position shows an isotope
effect (Table 2, Figure 6), which suggests its participation in
one intramolecular hydrogen bond.
As for 1 and 2, the NMR data of 3 support the presence
of a five-membered-ring intramolecular hydrogen bond in-
volving NH!OH-2 (the NH group of an amide can only be
a hydrogen-bond donor). This feature is again only possible
for the anti conformer of the N-glycosidic linkage (as pre-
dicted by the MM2* calculations). Moreover, we note that
OH-2 of 3 has the largest isotope effect of the three com-
pounds, while, the OH-3 and OH-6 resonances also showed
smaller, but detectable, isotope effects. The NMR parame-
ters for OH-3 (Table 1) are also in accordance with its par-
ticipation in a hydrogen bond in solution. On the other
hand, the OH-4 and OH-6 J and Dd/DT values are consis-
tent with their being free in solution. Thus, 3 in chloroform
solution may be described as equilibrium of hydrogen-bond-
ing isomers A, B and C (Figure 7). In all three of them, the
1,3-diaxial six-membered-ring intramolecular H-bond be-
tween OH-2 and OH-4 is present. This feature seems to
confirm the efficiency of the five-membered-ring intramo-
lecular hydrogen bond in driving the OH¥¥¥OH hydrogen-
bond equilibrium between the 1,3-(a,a)-diol towards OH-
2!OH-4.
Figure 5. Intramolecular hydrogen-bonding isomers proposed for 1 and 2
in apolar solution.
Hydrogen-bonding network in talopyranoside derivative 3:
Talopyranoside derivative 3 has the 1,2-amido alcohol-(e,a)
motif of 1 and 2 (Figure 1b) and, additionally, the OH
group in the 2-position has a 1,3-diaxial relationship to OH-
4. Thus, a six-membered-ring intramolecular hydrogen bond
is expected to be formed by this diol and polarised by the
five-membered-ring intramolecular hydrogen bond, which
makes OH-4 behave as a cooperative donor.
Molecular mechanics calculations were also carried out
on both the syn and anti conformers of 3. In this case, too,
the anti orientation around the f angle was more stable
than the syn geometry, and the computed distance between
NH and OH-2 (2.61 ä) is in agreement with an intramolecu-
lar hydrogen bond (see Supporting Information, part 3). The
To obtain further evidence, we explored the complexation
of 3 with pyridine (Py). We have previously used the com-
Chem. Eur. J. 2004, 10, 4240 4251
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C. Vicent et al.
FULL PAPER
plexation of a H-bonding acceptor such as Py[6] to detect co-
operative donor centres and free hydroxy groups in carbo-
hydrates. The NMR titration of 3 with Py allowed us to
deduce a value of Ka =18mꢀ1 for the complex 3-Py, which is
in the range of those measured for sugars with cooperative
donor centres. Furthermore, the largest chemical-induced
shifts (CIS) were observed for OH-4 (CIS=++1.35 ppm) and
OH-6 (CIS=+1.26 ppm), and this suggests that these two
hydroxy groups are the most accessible to interaction with
an acceptor. No CIS was observed for the NH resonance.
This is in accordance with the presence of a high percentage
of the hydrogen-bonding isomer B (Figure 7) of 3 in solu-
tion.
Phosphate complexes: Our previous work has shown that
cooperative 1,2-(a,a)-trans-diol and amido alcohol hydro-
gen-bonding motifs are efficient binders of bidentate phos-
phate in apolar solvents.[5] Here, we decided to explore the
phosphate binding as an additional proof of the effect that
the presence of a hydrogen-bond cooperative centre may
have on the recognition behaviour of our designed sugar de-
rivatives 1 3. We expected that the cooperative donor hy-
drogen-bonding motifs present in 1, 2 and 3 could allow ef-
fective phosphate binding. Thus, NMR titrations were car-
ried out with the chloroform-soluble phosphate salt tetrabu-
tylammonium bis(3,5-di-tert-butyl)phenyl phosphate (Phos).
The titrations were carried out at constant concentration
of sugar (1, 2 or 3) by adding increasing concentrations of
salt. The high-field NMR shifts of the methyne proton reso-
nances were fitted to a 1:1 complex. The stoichiometries of
all complexes were determined by Scatchard plots and Job
plots based on chemical-shift variations.[27] The stability con-
stants and DG8 values of the complexes of 1 3 with Phos
and those for selected model compounds 24 27[5] (Figure 8)
are given in Tables 3 and 4.
Figure 6. OH-2 proton resonances in the 1H NMR spectra of 3 in CDCl3
upon addition of 0 (a) and 74% (b) CD3OD.
Significantly, phosphate complexes with our designed
monosaccharides with cooperative donor centres (1-Phos, 2-
Phos and 3-Phos) have DG8 values which are between 1 and
2.2 kcalmolꢀ1 higher than those reported in the literature
Figure 7. Hydrogen-bond isomers proposed for the talopyranoside deriva-
Figure 8. Model carbohydrates selected[5] for comparison with the phos-
tive 3 in apolar solution.
phate complexes of 1 3.
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Cooperative Hydrogen Bonds
4240 4251
Table 3. Ka [mꢀ1] and DG8 [kcalmolꢀ1] for the interaction between com-
pounds 1, 2, 24 and 26 and the phosphate salt.
We selected, for comparison, a flexible diol involving the
4- and 6-positions of the pyranose ring with the same config-
uration at C-4, namely, 25. Additionally, the cooperative 1,2-
trans-(a,a)-diol 27 was used as a reference for a cooperative
diol. The DG8 values show that 3-Phos is about 2 kcalmolꢀ1
more stable than the corresponding complex of the flexible
diol with the same configuration at C-4 25-Phos.
1
2
24
96
ꢀ2.7
26
Ka
16400
4880
554
ꢀ3.5
DG8[a]
ꢀ5.8
ꢀ5.0
[a] Estimated error: ꢁ0.1 kcalmolꢀ1
.
In the 1,2-trans-(a,a)-diol 27, OH-4 is cooperative due to
the presence of a six-membered-ring intramolecular hydro-
gen bond, which involves an NH group of an amide. The
complex between 27-Phos is 1 kcalmolꢀ1 less stable than
that of 3-Phos. All these results suggest that N-glycosyl-
amides 1 3 with cooperative OHs centres are effective phos-
phate binders.[29]
Table 4. Ka [mꢀ1] and DG8 [kcalmolꢀ1] for the interaction between com-
pounds 3, 25 and 27 and the phosphate salt.
3
25
27
Ka
9610
ꢀ5.4
111
ꢀ2.8
1796
ꢀ4.4
DG8[a]
[a] Estimated error: ꢁ0.1 kcalmolꢀ1
.
for choroform-soluble gluco- and galactopyranoside deriva-
tives.[28]
Conclusion
Diols 24 and 25 were selected as models for 1 and 3.
These two molecules are the 4,6-diols of glucopyranose (24)
and galactopyranose (25). The configuration at C-4 in 24 is
the same as in the mannopyranose derivatives 1 and 2. In
turn, OH-4 is axial in 25, as in the talopyranose compound
3.
Regarding 1 and 2 (Table 3), the most stable complex is 1-
Phos (DG8=ꢀ5.8 kcalmolꢀ1). It is 3 kcalmolꢀ1 more stable
than its corresponding 1,3-flexible diol 24 with the same
configuration at C-4. The lack of OH-6 in 2-Phos results in
a less stable complex (by 0.8 kcalmolꢀ1).
Regarding the observed CIS, all methyne resonances of
the sugar are shielded upon complex formation, although
both 1-Phos and 2-Phos showed higher induced shifts for
the methyne CH-2 (ꢀ0.1 ppm in 1 and ꢀ0.09 ppm in 2) and
CH-3 (ꢀ0.134 ppm in 1 and ꢀ0.09 ppm in 2) resonances,
which suggests the involvement of their corresponding OH
groups in the complexation process. This observation sug-
gests the formation of a complex in which Phos is coordinat-
ed to the cooperative 1,2-(a,e)-cis-diol involving OH-2 and
OH-3 of the pyranose ring.
In comparison, a 1,2-(a,e)-diol with an amide group in in
the a position, but in a 1,2-trans relationship as in 26 (with-
out the possibility of establishing an intramolecular hydro-
gen bond with the diol) gave a significantly less stable com-
plex, with Ka =554mꢀ1 (DG8=ꢀ3.7 kcalmolꢀ1), that is, 2-
Phos displays an extra stabilisation of about 2 kcalmolꢀ1
compared to 26-Phos.
For talose complex 3-Phos (Table 4), higher CIS of the
CH resonances upon complex formation were found for
CH-4 (ꢀ0.064 ppm) and CH-6,6’ (due to overlap, the maxi-
mum CIS can not be accurately calculated). This observa-
tion also suggests the involvement of both hydroxy groups
in complex formation.
These data are in agreement with CIS measured for the
complex with pyridine 3-Py. The CIS for this complex are
largest for OH-4 and OH-6, which again suggests that these
two hydroxy groups are the most accessible to interaction
with an acceptor. No CIS was observed for the NH reso-
nance.
We have designed and synthesised sugars with cooperative
hydrogen-bonding donor centres. The structural analysis of
the N-glycosylamides 1 and 2 by NMR in apolar solution
showed the presence of a five-membered-ring intramolecu-
lar hydrogen bond between the anomeric NH amide group
in equatorial position and the axially oriented OH-2 group
(NH!OH-2).
As a second step, the talose derivative 3 was designed and
synthesised to prove that a group with a unique hydrogen-
bond donor character, located at hydrogen-bonding distance
to a particular OH group, can be used to initiate the hydro-
gen-bond network and to polarise a particular HO¥¥¥OH hy-
drogen-bond in a desired direction.
We were able to prove that the presence in 3 of a five-
membered-ring intramolecular H-bond, established between
a N-glycosylamido group (NH) and a hydroxy group (in 1,2-
(e,a) relationship) that additionally is in a 1,3-cis-diaxial re-
lationship to a second hydroxy group (OH-4) can be used to
select an unique direction on the six-membered-ring intra-
molecular hydrogen bond between the two diaxial OH
groups, which makes one of them behave as an efficient co-
operative donor (OH-4 in this case).
Finally, the presence of cooperative hydrogen-bond cen-
tres makes 1 3 more efficient phosphate binders in apolar
solvent in comparison with model compounds 24 27.
Experimental Section
The 1H NMR studies on carbohydrates 1 3 were performed with freshly
prepared solutions in CDCl3, which was always passed through basic alu-
mina and collected over 4 ä molecular sieves.
1H NMR experiments: The binding abilities of compounds 1 3 to Phos
were investigated by means of 1H NMR titration experiments. Carbohy-
drate solutions were obtained by diluting a known volume of a stock solu-
tion, previously prepared by dissolving a weighed amount of the sugar in
CDCl3, to 3 mL. Then, 0.5 mL of the resulting solution was placed in an
NMR tube, and the remaining 2.5 mL was used to prepare the carbohy-
drate/phosphate titrant solution. The carbohydrate concentration was
10ꢀ4 m. The concentration of Phos in the titrant solution was in the range
10ꢀ3 to 8î10ꢀ4 m. A minimum of 10 aliquots of the sugar/phosphate solu-
tion were added to the sugar solution, and a one-dimensional 1H NMR
spectrum (T=298 K) was recorded after each addition. The binding con-
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C. Vicent et al.
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stants were evaluated from a least-squares fitting by using a well-estab-
lished protocol.[19]
room temperature, the solution was acidified to pH 6 with Amberlite IR-
120H+ ion-exchange resin, and the resin removed by filtration. The sol-
vent was removed under reduced pressure to give a mixture of a and b
isomers. The b isomer 1 was obtained after column chromatography
The Dd/DT values of the exchangeable proton resonances of compounds
1 3 were obtained by means of variable-temperature 1H NMR experi-
ments. These were carried out at sugar concentrations ranging from 1.1î
10ꢀ4 to 1.9î10ꢀ4 m, depending on the tendency for self-association of the
carbohydrate investigated. The spectra were recorded at five different
temperatures in the range 295 318 K, and the Dd/DT values were evalu-
ated from a linear fit.
(SiO2/CHCl3) as
a white amorphous solid (86.0 mg, 47%). Rf =0.27
(MeOH/EtOAc 5/95); [a]d =ꢀ7.2 (c=0.50, CHCl3); 1H NMR (500 MHz,
408C, CDCl3): d=7.11 (d, 3J(H,H)=9.0 Hz, 1H, NH), 6.99 (s, 2H,
3
3
ortho), 5.52 (d, J(H,H)=9.0 Hz, 1H, CH), 4.03 (t, J(H,H)=3.5 Hz, 1H,
CH), 3.99 (t, 3J=6.5 Hz, 6H, OCH2), 3.90 (ddd, 2J(H,OH)=1.5,
3J(H,H)=3.5, 12.5 Hz, 1H, CH2), 3.86 (ddd, 2J(H,OH)=1.5 Hz,
3J(H,H)=5.0, 12.5 Hz, 1H, CH2), 3.85 (td, 2J(H,OH)=3.0 Hz, 3J(H,H)=
9.5 Hz, 1H, CH), 3.75 (ddd, 2J(H, OH)=4.0 Hz, 3J(H,H)=5.0, 9.5 Hz,
1H, CH), 3.46 (ddd, 3J(H,H)=3.5, 5.0, 9.5 Hz, 1H, CH), 2.57 (d,
2J(H,OH)=4.0 Hz, 1H, OH-3), 2.56 (d, 2J(H,OH)=3.5 Hz, 1H, OH-2),
2.39 (d, 2J(H,OH)=3.0 Hz, 1H, OH-4), 2.13 (t, 2J(H,OH)=5.0 Hz, 1H),
1.73 (m, 6H, CH2), 1.44 (m, 6H, CH2), 1.25 (brs, 60H, CH2), 0.87 ppm (t,
J=6.5 Hz, 9H, CH3); 13C NMR (125 MHz, CDCl3): d=152.99 (Cm),
141.00 (Cp), 123.50 (Cq), 106.44 (Co), 78.44 (C-1), 77.40 (C-5), 74.44 (C-
3), 73.0 (C-4, C-6), 71.44 (C-2), 69.43 (2OCH2), 60.30 (OCH2), 31.90
(CH2), 29.67 (CH2), 29.52 (CH2), 29.34 (CH2), 26.11 (CH2), 22.64 (CH2),
14.02 ppm (CH3); IR (KBr) : n˜max =2921, 2851, 1627, 1583, 1539, 1499,
1468, 1331, 1233, 1119 cmꢀ1; MS (APCI) (%): m/z: 920.5 (100) [M+H]+,
800.5, 758, 577; elemental analysis calcd (%) for C55H101NO9: C 71.77, H
11.06, N 1.52; found: C 71.54, H 11.30, N 1.69.
Compounds 1 3 were partially deuterated by adding a few microlitres of
[D4]methanol to an NMR sample at 303 K for 1, 305 K for 2 and 294 K
for 3. After each addition, a one-dimensional 1H NMR spectrum was re-
corded, and the percentage deuteration was calculated by comparison of
the integrals of the resonances of the exchangeable protons (OH and NH
resonances) with that of a nonexchangeable proton (e.g., H-1). Isotope
effects, observable for NH, OH-2 and other OH groups, depending on
the nature of compound (signal doubling), demonstrated the existence of
the intramolecular hydrogen bond between the NH and OH-2 groups in
the 1 3. To observe NH signal doubling it was necessary to wait at least
one hour after deuteration.
Molecular modelling: MM2* calculations were performed for 1 3 using
MM2* as implemented in Macromodel 7.0. The GB/SA solvent model
for chloroform was used. All the different combinations of staggered ori-
entations of the hydroxy groups were used as input geometries. The re-
sults are given for the most stable ones in each case. Additionally, the
three possible staggered orientations for the F angle at the N-glycosidic
linkage (H1-C1-N-H) were also used as starting geometries. In all cases,
the anti-type geometry was the most stable.
2,3,4-Tri-O-acetyl-6-deoxy-a-d-mannopyranosyl azide (7): SnCl4 (92 mL,
0.78 mmol) and TMSN3 (280 mL, 2.10 mmol) were added to a solution of
6-deoxy-d-mannopyranose tetraacetate[30c] 5 (349 mg, 1.05 mmol) in dry
CH2Cl2 (6 mL), and the mixture was stirred at room temperature for 3 h.
The mixture was washed successively with aqueous NaHCO3 and water
and dried over Na2SO4. The solvent was removed under reduced pressure
to afford 7 as a colorless oil (197 g, 60%). Rf =0.52 (1/1 n-hexane/
EtOAc); 1H NMR (200 MHz, CDCl3): d=5.29 (d, 3J(H,H)=2.0 Hz, 1H,
CH), 5.18 (dd, 3J(H,H)=3.2, 10 Hz, 1H, CH), 5.12 (dd, 3J(H,H)=2.0,
3.2 Hz, 1H, CH), 5.06 (t, 3J(H,H)=10 Hz, 1H, CH), 4.01 (qd, 3J(H,H)=
6.2, 10 Hz, 1H), 2.14 (s, 3H, CH3), 2.04 (s, 3H, CH3), 1.97 (s, 3H, CH3),
1.25 ppm (d, 3J(H,H)=6.2 Hz, 3H, CH3); 13C NMR (50 MHz, CDCl3):
d=169.85 (CO), 169.79 (CO), 169.76 (CO), 86.44 (C-1), 69.40, 68.40,
67.57, 67.24, 20.74 (CH3CO), 20.70 (CH3CO), 20.55 (CH3CO), 17.36 ppm
(CH3); IR (KBr): n˜max =2986, 2900, 2120, 1750, 1431, 1372, 1223, 1125,
1056, 957, 936 cmꢀ1; MS (ES): m/z (%): 274 (11) [MꢀN3+H]+, 338 (100)
[M+Na]+.
Synthesis: Compounds 5,[30] 6,[18] 10,[19] 13[31] and 14[17] were prepared by
literature procedures.
N-(2,3,4,6-Tetra-O-acetyl-b-d-mannosyl)-3,4,5-tris(tetradecyloxy)benz-
amide (11): A solution of 6 (213 mg, 0.61 mmol) in EtOAc (3 mL) was
treated with Raney Ni and shaken under an atmosphere of hydrogen for
6 h at room temperature. The catalyst was removed by filtration, and the
solvent was evaporated under reduced pressure to afford 8 as a pale oil.
Separately, a solution of DIC (140.0 mL, 0.88 mmol), HOBt (120.0 mg,
0.88 mmol) and 3,4,5-tris(tetradecyloxy)benzoic acid (10; 560 mg,
0.74 mmol) in DMF/CHCl3 (1/1, 14 mL) was stirred under argon at room
temperature for 24 h before adding a solution of 8 in CHCl3 (3 mL).
After a further 24 h, the crude product was washed three times with
water, the organic layer was dried over Na2SO4 and the solvent was re-
moved under reduced pressure. The residue was purified by column chro-
matography (hexane/EtOAc 4/1) to afford compound 11 as a 7/93 mix-
ture of a and b isomers (108 mg, 33%); Rf(b=0.35 (EtOAc/n-hexane 1/
1); 1H NMR (200 MHz, CDCl3): b isomer: d=6.89 (s, 2H, ortho), 6.70
(d, 3J(H,H)=9.2 Hz, 1H; NH), 5.69 (dd, 3J(H,H)=1.0, 9.0 Hz, 1H, CH),
5.42 (dd, 3J(H,H)=1.0, 3.0 Hz, 1H, CH), 5.28 (t, 3J(H,H)=10.2 Hz, 1H,
CH), 5.16 (dd, 3J(H,H)=3.0, 10.0 Hz, 1H, CH), 4.35 (dd, 3J(H,H)=5.0,
2J=12.6 Hz, 1H, CH2), 4.07 (dd, 3J(H,H)=2.0, 2J=12.6 Hz, 1H, CH2),
N-(2,3,4-Tri-O-acetyl-6-deoxy-b-d-mannosyl)-3,4,5-tris(tetradecyloxy)-
benzamide (12): A solution of 7 (110 mg, 0.35 mmol) in EtOAc (4 mL)
was treated with Raney Ni and shaken under an atmosphere of hydrogen
overnight. The catalyst was removed by filtration and the solvent evapo-
rated under reduced pressure to afford a pale glassy film of 9. Separately,
a solution of DIC (80.0 mL, 0.50 mmol), HOBt (67.0 mg, 0.50 mmol) and
10 (318 mg, 0.42 mmol) in DMF/CHCl3 (1/1, 10 mL) was stirred under
argon for 24 h at room temperature before addition of 9 dissolved in
CHCl3 (3 mL). After a further 24 h, the crude reaction mixture was
washed thrice with water, the organic layer was dried with Na2SO4 and
the solvent was removed under reduced pressure. The residue was puri-
fied by column chromatography (SiO2, n-hexane/EtOAc 8/2) to afford 12
as a 36:64 mixture of a and b isomers (190 mg, 53%). Rf(b)=0.15
(EtOAc/n-hexane 1/1); 1H NMR (300 MHz, CDCl3): b isomer: d=6.892
(s, 2H, ortho), 6.66 (d, 3J(H,H)=9.0 Hz, 1H, NH), 5.64 (dd, 3J(H,H)=
1.0, 9.0 Hz, 1H, CH), 5.41 (dd, 3J(H,H)=1.0, 3.0 Hz, 1H, CH), 5.12 (dd,
3J(H,H)=3.0, 10.0 Hz, 1H, CH), 5.05 (t, 3J(H,H)=10.0 Hz, 1H, CH),
3.96 (t, 3J(H,H)=6.6 Hz, 6H, OCH2), 3.71 (qd, 3J(H,H)=6.3, 10.0 Hz,
1H, CH), 2.06 (s, 3H, CH3), 2.22 (s, 3H, CH3), 1.98 (s, 3H, CH3), 1.78
(m, 6H, CH2), 1.45 (m, 6H, CH2), 1.24 (brs, 63H, 30CH2 and CH3
sugar), 0.86 (t, J=6.6 Hz, 9H, CH3); visible signals of a isomer: 6.95 (s,
2H, ortho), 6.79 (d, 3J(H,H)=8.7 Hz, 1H, NH), 5.81 (dd, 3J(H,H)=6.3,
8.4 Hz, 1H, CH), 5.30 (m, 2H, CH), 4.93 (t, 1H, CH), 2.11 (s, 3H, CH3),
2.09 (s, 3H, CH3), 2.07 ppm (s, 3H, CH3); 13C NMR (75 MHz, CDCl3) b
isomer: d=170.67 (CO), 169.94 (CO), 169.87 (CO), 166.51 (CONH),
153.05 (Cm), 141.81 (Cp), 128.00 (Cq), 105.96 (Co), 76.57 (C-1), 73.48
(OCH2), 72.40 (C-5), 71.48 (C-3), 70.92 (C-2), 70.25 (C-4), 69.35 (2
OCH2), 31.90 (CH2), 29.68 (CH2), 29.35 (CH2), 26.03 (CH2), 22.66 (CH2),
20.88 (CH3CO), 20.78 (CH3CO), 20.56 (CH3CO), 17.51 (CH3 sugar),
14.09 ppm (CH3); IR (KBr): n˜max =3436, 2920, 2851, 1752, 1644, 1584,
3
3.96 (t, J(H,H)=6.4 Hz, 6H, CH2), 3.842 (ddd, J(H,H)=2.0, 4.8, 9.6 Hz,
1H, CH), 2.23 (s, 3H, CH3), 2.08 (s, 3H, CH3), 2.04(s, 3H, CH3), 1.98 (s,
3H, CH3), 1.76 (m, 6H, CH2), 1.43 (brs, 6H, CH2), 1.23 (m, 60H, CH2),
0.85 (t, 3J(H,H)=6.3 Hz, 9H, CH3); visible signals of a isomer: 6.98 (s,
3
3
2H, ortho), 5.82 (dd, J(H,H)=6.3, 8.4 Hz, 1H, CH), 5.37 (dd, J(H,H)=
3.3, 9.3 Hz, 1H, CH), 5.12 (dd, 3J(H,H)=4.8, 6.0 Hz, 1H, CH), 4.49 ppm
(dd, 3J(H,H)=6.3 Hz, 2J=12.0 Hz, 1H); 13C NMR (50 MHz, CDCl3): b
isomer: d=170.64 (COCH3), 170.56 (COCH3), 169.78 (COCH3), 169.66
(COCH3), 166.42 (CONH), 153.13 (Cm), 141.98 (Cq), 127.86 (Cp), 106.08
(Co), 76.96 (C-1), 74.35, 73.53 53 (CH2 sugar), 71.55, 70.65, 69.43
(2OCH2), 65.27, 62.20 (OCH2), 31.90 (CH2), 29.66 (CH2), 29.34 (CH2),
26.03 (CH2), 22.66 (CH2), 20.86 76 (CH3CO), 20.76 76 (CH3CO), 20.66 76
(CH3CO), 20.51 76 (CH3CO), 14.08 76 ppm (CH3); IR (KBr): n˜ =3436,
2919, 2850, 1751, 1645, 1585, 1530, 1497, 1468, 1428, 1369, 1229, 1116,
1057 cmꢀ1; MS (APCI): m/z: 1088 [M+H]+; elemental analysis calcd (%)
for C63H109NO13: C 69.51, H 10.09, N 1.29; found: C 69.27, H 10.31, N
1.46.
N-b-d-Mannopyranosyl-3,4,5-tris(tetradecyloxy)benzamide (1):
A solu-
tion of 11 (220.0 mg, 0.20 mmol) in MeOH (5 mL)/CHCl3 (4 mL) was
treated with 3 mL of a solution of sodium methoxide in MeOH prepared
by dissolving Na (100 mg) in MeOH (10 mL). After stirring for 1 h at
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Cooperative Hydrogen Bonds
4240 4251
1527, 1496, 1468, 1427, 1369, 1225, 1116, 1055 cmꢀ1; MS (APCI): m/z:
1030 [M+H]+; elemental analysis calcd (%) for C63H109NO13: C 71.13, H
10.39, N 1.36; found: C 71.00, H 10.60, N 1.51.
6’), 3.90 (dd, 3J(H,H)=1.6, 2J(H,H)=12.5 Hz, 1H, CH-6 or CH-6’), 3.88
(t, 1H, CH-2), 3.80 (brs, 1H, CH-5), 3.52 ppm (brs, 1H, OH); 13C NMR
(75 MHz, CDCl3): d=165.8, 150.7, 137.3, 133.1, 132.3, 129.3, 128.7, 128.3,
127.9, 126.5, 101.1, 90.3, 75.3, 73.3, 68.7, 67.9, 67.8 ppm; IR (KBr): umax
=
N-(6-Deoxy-b-d-mannopyranosyl)-3,4,5-tris(tetradecyloxy)benzamide (2):
A solution of 12 (260.0 mg, 0.25 mmol) in MeOH/CHCl3 (1/1, 8 mL) was
treated with 3 mL of a solution of sodium methoxide in MeOH prepared
by dissolving Na (100 mg) in MeOH (10 mL). The reaction was moni-
tored by TLC (n-hexane/EtOAc 1/1). The solution was acidified to pH 6
with IR-120 ion-exchange resin, and the resin removed by filtration. The
solvent was removed under reduced pressure to give a mixture of a and
b isomers. The b isomer 2 was obtained after column chromatography
(SiO2, acetone/toluene 1/1) as a white amorphous solid (37.0 mg of b
isomer and 131 mg of an a/b mixture, 74%). Rf(b)=0.37 (acetone/tolu-
ene 1/1), Rf(a)=0.30 (acetone/toluene 1/1); [a]2D2 =+0.75 (c=0.57,
CHCl3): MS (ES): m/z (%): 904 (100) [M+H]+;. 1H NMR (500 MHz,
358C, CDCl3): d= 7.09 (d, 3J(H,H)=9.0 Hz, 1H, NH), 6.98 (s, 2H,
ortho), 5.47 (d, 3J(H,H)=9.0 Hz, 1H, CH), 4.02 (brs, 1H, CH-2), 3.67
(brs, 1H, CH-3), 3.46 (m, 2H, CH-4 and CH-5), 2.53 (d, 2J(H,OH-3)=
4.2 Hz, 1H, OH-3), 2.51 (d, 2J(H,OH-2)=3.6 Hz, 1H, OH-2), 2.02 (d,
2J(H,OH-4)=2.7 Hz, 1H, OH-4), 1.74 (m, 6H, CH2), 1.45 (m, 6H, CH2),
1.37 (d, 3H, J=6.0 Hz, CH3 sugar), 1.25 (brs, 60H, CH2), 0.86 ppm (t,
3J(H,H)=6.3 Hz, 9H, CH3); 13C NMR (125 MHz, CDCl3): d=153.06
(Cm), 140.55 (Cp), 128.33 (Cq), 106.00 (Co), , 74.31 (C-1), 73.51 (C-4 or C-
5), 73.22 (C-4 or C-5), 70.97 (C-3), 69.56 (C-2), 69.37 (2 OCH2), 60.30
(OCH2), 31.92 (CH2), 29.67 (CH2), 29.57 (CH2), 29.36 (CH3 sugar), 26.07
(CH2), 22.67 (CH2), 14.12 ppm (CH3); IR (KBr): n˜max =3435, 2919, 2850,
1626, 1583, 1536, 1495, 1468, 1338, 1236, 1121 cmꢀ1; elemental analysis
calcd (%) for C55H101NO9: C 73.04, H 11.26, N 1.55; found: C 72.75, H
11.41, N 1.63.
3600 3200, 2981, 2873, 2118, 1774, 1510, 1485, 1197, 1093 cmꢀ1; [a]D25
=
17.6 (c=2.00, acetone); MS (ES+): m/z (%): 903 (46) [2M+Na]+, 731
(47), 559 (47), 463 (63) [M+Na]+, 398 (100) [MꢀN3], 122 (99%), 105
(82%); elemental analysis calcd (%) for C21H20N4O7: C 57.27, H 4.58, N
12.72; found: C 57.27, H 4.58, N 12.51.
(S)-4,6-O-Benzylidene-3-O-(N-benzoylcarbamoyl)-2-O-trifluoromethane-
sulfonate-galactopyranosyl azide (18):
A solution of carbamate 17
(100 mg, 0.227 mmol) in dry, distilled CH2Cl2 (1 mL) at ꢀ258C was treat-
ed with dry, distilled pyridine (37 mL, 0.454 mmol) and triflic anhydride
(44 mL, 0.261 mmol). After stirring for 2 h at ꢀ258C, the mixture was
warmed to room temperature, water was added (1 mL) and the mixture
was extracted with CH2Cl2 (3î10 mL). The combined organic phases
were dried over Na2SO4, filtered and evaporated at reduced pressure.
The residue was purified by column chromatography (SiO2, 50% EtOAc/
hexane) to afford 18 as a clear glassy film (80 mg, 77%). 1H NMR
(200 MHz, CDCl3): d=8.58 (s, 1H, NH), 7.75 7.84 (m, 2H, HArom), 7.35
7.61 (m, 6H, HArom), 5.27 (dd, 1H, 3J(H,H)=3.6, 10.2 Hz, CH-3), 5.52 (s,
1H, CH-8), 4.93 5.04 (m, 2H, CH-1 and 2), 4.61 (dd, 1H, 3J(H,H)=0.8,
3.6 Hz, CH-4), 4.39 (dd, 1H, 3J(H,H)=1.8 Hz, 2J(H,H)=12.8 Hz, CH-6
or CH-6’), 4.11 (dd, 1H, 3J(H,H)=1.6 Hz, 2J(H,H)=12.8 Hz, CH-6 or
CH-6’), 3.83 ppm (d, J(H,H)=0.8 Hz, 1H, CH-5); 13C NMR (75 MHz,
CDCl3): d=164.57 (CO), 149.08 (CO), 136.92 (Cq1) 133.48 (Cp1), 132.07
(Cq2), 129.50 (Cp2), 128.00 (Co1), 128.35 (Co2), 127.61 (Cm1), 126.41 (Cm2),
CF3 signal was not observed, 101.44 (C-8), 86.93 (CH sugar), 80.22 (CH
sugar), 73.73 (CH sugar), 71.86 (CH sugar), 68.33 (CH2 sugar), 68.02 ppm
(CH sugar); IR (KBr): umax =3 429, 2127, 1784, 1691, 1602, 1504, 1484,
1417, 1244, 1197, 1141, 1093, 1023, 994, 963, 894, 869, 818, 765, 699,
623 cmꢀ1; MS (ES+): m/z (%): 1167.1 (18) [2M+Na]+, 573.1 (100)
[M+H]+; elemental analysis calcd (%) for C39H45N7O13: C 46.15, H 3.32,
N 9.79; found: C 46.31, H 3.60, N 10.03.
b-d-Galactopyranosyl azide (15):
A
solution of azide 14[17] (8,50 g,
23.09 mmol) in MeOH (137 mL) was treated with a solution of sodium
(200 mg) in MeOH (10 mL). After 30 min, the solution was acidified with
Amberlite IR-120H+ to pH 6. Evaporation of the solvent under reduced
1
pressure afforded 15 as a white crystalline solid (280 mg, 91%). H NMR
(200 MHz, CDCl3): d= 5.29 (s, 1H, CH), 4.85 (s, 1H, CH), 4.66 (s, 1H,
CH), 4.53 (s, 1H, CH), 4.35 (d, 1H, J=8.5 Hz), 3.66 (m, 1H), 3.50 (m,
3H), 3.32 ppm (m, 2H); 13C NMR (75 MHz, CDCl3): d= 90.7, 77.6, 73.3,
70.3, 68.2, 60.5 ppm; IR (KBr): n˜max =3600 3000, 2891, 2138, 1140, 1102,
1073, 1056 cmꢀ1; MS (ES+): m/z (%): 433 (23) [2M+Na]+, 413 (52), 228
(100) [M+Na].
(R)-4,6-O-Benzylidene-talopyranosyl azide (21): A solution of triflate 18
(540 mg, 0.943 mmol) in dry, distilled THF (5 mL) at 08C under argon
was treated with NaH (34 mg, 1.41 mmol) in one portion and stirred for
45 min. A further portion of NaH (50 mg, 2.08 mmol) was added, and the
mixture allowed to warm to room temperature. After the mixture had
been stirred at room temperature overnight, saturated aqueous NaHCO3
(10 mL) was added and the mixture was extracted with with CH2Cl2 (3î
50 mL). The combined organic layers were dried over Na2SO4, filtered
and evaporated at reduced pressure to give a crude mixture of 19 and 20.
The residue was taken up in THF (5 mL) and treated with a saturated
aqueous solution of LiOH¥H2O. After stirring at room temperature over-
night, the mixture was extracted with CH2Cl2 (3î50 mL) and the com-
bined organic layers were dried over Na2SO4, filtered and evaporated at
reduced pressure. Purification of the residue by column chromatography
(S)-4,6-O-Benzylidene-galactopyranosyl azide (16): A solution of azide
15 (5.00 g, 24.4 mmol) in dry, distilled CH3CN (30 mL) was treated with
p-TsOH (232 mg, 1.22 mmol) and benzaldehyde dimethyl acetal
(18.3 mL, 122 mmol). After 24 h at room temperature, the mixture was
treated with Et3N (1 mL) and evaporated under reduced pressure. The
residue was purified by column chromatography (SiO2, EtOAc) to afford
1
16 as a white solid (5.82 g, 81%). Rf =0.41 (EtOAc); H NMR (200 MHz,
CDCl3): d=7.52 7.35 (m, 5H, HArom), 5.53 (s, 1H, CH-8), 4.55 (d, 1H,
3J(H,H)=8.2 Hz), 4.36 (dd, 1H, 3J(H,H)=1.6 Hz, 2J(H,H)=12.5 Hz,
CH2), 4.20 (dd, 1H, 3J(H,H)=1.2, 3.2 Hz, CH), 4.06 (dd, 1H, 3J(H,H)=
1.8 Hz, 2J(H,H)=12.6 Hz, CH2), 3.69 (s, 1H), 3.65 (s, 1H), 3.55 (dd, 1H,
3J(H,H)=1.6, 2.9 Hz), 2.88 ppm (m, 2H); 13C NMR (300 MHz, CDCl3):
d=139.0, 129.1, 128.4, 126.7, 100.3, 90.8, 76.1, 72.1, 70.1, 68.7, 68.3 ppm;
IR (KBr): n˜max =3600 3200, 2910, 2861, 2116, 1249, 1086, 1102, 1051,
1001 cmꢀ1; MS (ES+): m/z (%): 609 (20) [2M+H]+, 362 (25), 316 (100)
[M+Na]+, 251 (57) [MꢀN3]+; elemental analysis calcd (%) for
C13H15N3O5: C 53.24, H 5.16, N 14.33; found: C 53.40, H 5.35, N 14.61.
(SiO2, EtOAc/hexane 1/1) afforded 21 as
a white amorphous solid
(190 mg, 69%). Rf =0.24 (EtOAc); 1H NMR (200 MHz, CDCl3): d=
7.78 7.80 (m, 1H), 7.37 7.52 (m, 4H), 5.51 (s, 1H), 4.49 (d, 1H,
3J(H,H)=1 Hz, CH-4), 4.45 (dd, 1H, 3J(H,H)=1.6, 2J(H,H)=12.8 Hz,
3
CH-6 or CH-6’), 4.24 (td, 1H, J(H,H)=1.2, 3.8 Hz, CH-1), 4.09 (dd, 1H,
3J(H,H)=1.8 Hz, 2J(H,H)=12.6 Hz, CH-6 or CH-6’), 3.86 (tdd, 1H,
3J(H,H)=1, 3.4 Hz, 2J(H,OH)=12.0 Hz, CH-3), 3.68 (td, 1H, 3J(H,H)=
3.4, 2J(H,OH)=11.6 Hz, CH-2), 3.51 (td,1H, 1.8, 1.8, 1.2 Hz, CH-5), 3.06
(d, 1H, 2J(H,OH)=12.2 Hz, OH-3), 3.044 ppm (d, 1H, 2J(H,OH)=
11.6 Hz, OH-2); 13C NMR (75 MHz, CDCl3): 136.80 (Cq), 129.55 (Cp),
128.50 (Co), 125.98 (Cm), 101.84 (C-8), 87.31 (CH sugar), 75.46 (CH
sugar), 71.70 (CH sugar), 69.01 (CH2 sugar), 68.82 (CH sugar), 68.63 ppm
(CH sugar); IR (KBr): n˜max =3504, 3370, 3176, 2929, 2876, 2109, 1660,
(S)-4,6-O-Benzylidene-3-O-(N-benzoylcarbamoyl)-galactopyranosyl azide
(17): A solution of 16 (4.30 g, 14.7 mmol) in dry, distilled THF (20 mL)
under Ar at 08C was treated with a solution of benzoyl isocyanate
(2.59 g, 17.6 mmol) in THF (30 mL) dropwise. After 30 min, a further
600 mg of benzoyl isocyanate was added. After 1 h at 08C, the mixture
was evaporated under reduced pressure, and the residue purified by
column chromatography (SiO2, 50% EtOAc/hexane) to afford 17 as a
white foam (5.54 g, 86%). Part of this material was recrystallised from
chloroform to provide an analytical sample (small needles). Rf =0.48
(EtOAc/hexane 7/3); 1H NMR (300 MHz, CDCl3): d=9.00 (brs, 1H,
NH), 7.74 7.69 (m, 2H, HArom), 7.49 7.43 (m, 3H, HArom) 7.38 7.24 (m,
1411, 1253, 1141, 1102, 1081, 1037, 1025, 772, 743, 700 cmꢀ1; [a]D20
=
ꢀ78.81 (c=1.01 g per 100 mL, DMSO); MS (ES+): m/z (%): 609 (35)
[2M+Na]+, 463 (61), 458 (42), 316 (43) [M+Na]+, 311 (100) [M+18],
251 (31) [MꢀN3]+.
2,3,4,6-Tetra-O-acetyl-talopyranosyl azide (22): A solution of 21 (60 mg,
0,24 mmol) in AcOH/H2O (7/3, 8.5 mL) was heated at 708C for 4 h. The
crude mixture was concentrated and co-evaporated with toluene (3î
15 mL). The resultant b-d-talopyranosyl azide was dissolved in pyridine
(15 equiv) and acetic anhydride (4.5 equiv) and stirred at room tempera-
ture overnight. The reaction mixture was evaporated under reduced pres-
3
5H, HArom), 5.48 (s, 1H, CH-8), 4.88 (dd, J(H,H)=3.7, 10.0 Hz, 1H, CH-
3), 4.62 (d, 3J(H,H)=8.5 Hz, 1H, CH-1), 4.44 (d, 3J(H,H)=3.4 Hz, 1H,
CH-4), 4.28 (dd, 3J(H,H)=1.4 Hz, 2J(H,H)=12.5 Hz, 1H, CH-6 or CH-
Chem. Eur. J. 2004, 10, 4240 4251
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4249

C. Vicent et al.
FULL PAPER
sure and purified by column chromatography (SiO2, EtOAc/hexane 1/1)
78.46 (C-1), 74.60 (C-5), 73.52 (C-6), 71.51 (C-2 and C-4), 69.51 (C-3),
69.42 (2OCH2), 64.29 (OCH2), 31.92 (CH2), 29.71 (CH2), 29.64 (CH2),
29.41 (CH2), 29.37 (CH2), 26.07 (CH2), 22.69 (CH2), 14.11 ppm (CH3); IR
(KBr): n˜max =3435, 2919, 2850, 1638, 1585, 1525, 1492, 1426, 1330, 1228,
1120 cmꢀ1; [a]d =+11.1 (c=0.54, CHCl3); MS (ES): m/z (%): 920 (100)
[M+H]+; elemental analysis calcd (%) for C55H101NO9: C 71.77, H 11.06,
N 1.52; found: C 71.50, H 11.18, N 1.62.
to give 22 as
a white amorphous solid (64.50 mg, 72%); Rf =0.24
(EtOAc); 1H NMR (200 MHz, CDCl3): d=5.31 (dd, 3J(H,H)=1.2,
3.6 Hz, 1H, CH-2), 5.27 (dd, 3J(H,H)=1.2, 3.8 Hz, 1H, CH-4), 5.04 (t,
3J(H,H)=3.6 Hz, 1H, H3), 4.72 (d, 3J(H,H)=1.8 Hz, 1H, CH-1), 4.23
(dd, 3J(H,H)=1.6, 7.4, 2H, CH-6 or CH-6’), 3.99 (td, 3J(H,H)=1.6,
7.4 Hz, 1H, CH-5), 2.15 (s, 1H, CH3), 2.12 (s, 1H, CH3), 2.04 (s, 1H,
CH3), 1.97 ppm (s, 1H, CH3); 13C NMR (75 MHz, CDCl3): d=170.41
(CO), 170.02 (CO), 169.88 (CO), 169.45 (CO), 85.74 (C-1), 78.51 (C-5),
67.58 (C-4), 67.10 (C-2), 64.51 (C-3), 61.43 (CH2, C-6), 20.65 (CH3), 20.62
(CH3), 20.55 (CH3), 20.41 ppm (CH3); IR (KBr): n˜max =3475, 2966, 2119,
1748, 1434, 1370, 1223, 1091, 1046, 969, 917, 746 cmꢀ1; [a]2D0 =ꢀ65.66 (c=
1.06 g/100 mL, CHCl3 (1 mL)); MS (ES+): m/z (%): 331 (38)
[MꢀAc+NH4]+, 391 (100) [M+NH4]+, 396 (53) [M+Na]+; elemental
analysis calcd (%) for C13H15N3O5: C 45.0, H 5.10, N 11.26; found: C
45.21, H 4.79, N 10.98.
Acknowledgement
Financial support partially by the Ministery of Science and Technology of
Spain (Grants BQU2000-1501-C02 01 and BQU2003-03550-C03-02) and
European Union Training Networks (FMRX-CT98-0231 and HPRN-CT-
2002-00190) is acknowledged. J.M. is grateful for a postdoctoral TMR fel-
lowship, and V.V. for a postdoctoral RTN fellowship.
N-(2,3,4,6-Tetra-O-acetyl-talopyranosyl)-3,4,5-tris(tetradecyloxy)benz-
amide (23): A solution of 22 (108 mg, 0.30 mmol) in EtOAc (2 mL) was
treated with 10% Pd/C (8 mg, 0.07 mmol) and shaken under an atmo-
sphere of hydrogen for 6 h. The catalyst was removed by filtration over
Celite and the solvent evaporated at reduced pressure to afford a pale
glassy film of b-d-talopyranosyl amine. Separately, a solution of DIC
(62.0 mL, 0.396 mmol), HOBt (54.0 mg, 0.396 mmol) and 10 (250 mg,
0.33 mmol)[19] in DMF/CHCl3 (4 mL/4 mL) was stirred under argon for
24 h at room temperature before addition to b-d-talopyranosylamine dis-
solved in CHCl3 (2 mL). After a further 24 h, the crude mixture was
washed three times with water, the organic layer was dried over Na2SO4
and the solvent was removed at reduced pressure. The residue was puri-
fied by column chromatography (SiO2, hexane/EtOAc 8/2) to afford
23(a/b) as an amorphous white solid (108 mg, 33%); Rf(b)=0.35
(EtOAc/CH2Cl2 1/9); 1H NMR (300 MHz, CDCl3): b isomer: d=6.91 (s,
[1] a) A. P. Davis, R. S. Wareham, Angew. Chem. 1999, 111, 3160;
Angew. Chem. Int. Ed. 1999, 38, 2978; b) J. M. Rini, Annu. Rev. Bio-
phys. Biomol. Struct. 1995, 24, 551; c) H. Lis, N. Shanon, Chem. Rev.
1998, 98, 637; d) H. J. Gabius, Pharm. Res. 1998, 15, 23.
[2] a) F. A. Quiocho, Annu. Rev. Biochem. 1986, 55, 287; b) N. K. Vyas,
Curr. Opin. Struct. Biol. 1991, 1, 732; c) K. Drickamer, Curr. Opin.
Struct. Biol. 1999, 9, 585.
[3] a) E. J. Toone, Curr. Opin. Struct. Biol. 1994, 4, 719; b) R. U. Le-
mieux, Acc. Chem. Res. 1996, 29, 373; c) M. Noltemeyer, W. Saeng-
er, J. Am. Chem. Soc. 1980, 102, 2710.
[4] a) P. L. Huyskesens, J. Am. Chem. Soc. 1977, 99, 2578; b) H. S.
Frank, W. Y. Wen, Discuss. Faraday Soc. 1957, 24, 133; c) H. Guo,
M. Karplus, J. Phys. Chem. 1994, 98, 7104; d) J. L. Asensio, F. J.
Canada, H. C. Siebert, J. Laynez, A. Poveda, P. M. Nieto, U. M.
Soedjanaamadja, H. J. Gabius, J. Jimenez-Barbero, Chem. Biol.
2000, 7, 529; e) G. A. Jeffrey, W. Saenger, Hydrogen Bond in Biolog-
ical Structures, Springer, 1991.
[5] E. M. MuÊoz, M. LÛpez de la Paz, J. Jimÿnez-Barbero, G. Ellis, M.
Pÿrez, C. Vicent, Chem. Eur. J. 2002, 8, 1908.
[6] M. LÛpez de la Paz, G. Ellis, M. Pÿrez, J. Perkins, J. Jimÿnez-Bar-
bero, C. Vicent, Eur. J. Org. Chem. 2002, 840.
[7] a) B. Bernet, J. Xu, A. Vasella, Helvetica Chimica Acta 2000, 83,
2072; b) T. E. Vasquez, J. M. Bergset, M. B. Fierman, A. Nelson, J.
Roth, S. I. Khan, D. J. O×Leary, J. Am. Chem. Soc. 2002, 124, 2931.
[8] M. LÛpez de la Paz, J. Jimÿnez-Barbero, C. C. Vicent, Chem.
Commun. 1998, 465.
3
3
2H, ortho), 6.67 (d, J(H,H)=9.3 Hz, 1H, NH), 5.66 (d, J(H,H)=9.3 Hz,
1H, CH-1), 5.33 (brs, 2H, CH), 5.19 (t, 3J(H,H)=3.6 Hz, 1H, CH), 4.16
(m, 3H), 3.97 (t, J(H,H)=6.6 Hz, 6H, OCH2), 2.19 (s, 3H, CH3), 2.13 (s,
3
3H, CH3), 2.03 (s, 3H, CH3), 1.98 (s, 3H, CH3), 1.76 (m, 6H, CH2), 1.43
(brs, 6H, CH2), 1.24 (m, 60H, CH2), 0.86 ppm (t, 3J(H,H)=6.3 Hz, 9H,
CH3); a isomer: d=6.92 (s, 2H, ortho), 6.68 (d, 3J(H,H)=9.0 Hz, 1H,
NH), 5.80 (t, 3J(H,H)=8.7 Hz, 1H, CH-1), 5.64 (brs, 1H, CH), 5.21 (dd,
3
3J(H,H)=3.0, 6.3 Hz, 1H, CH), 5.06 (dd, J(H,H)=3.3, 8.7 Hz, 1H, CH),
4.69 (dd, 3J(H,H)=9.3, 2J(H,H)=12.6 Hz, 1H), 4.43 (dd, 3J(H,H)=
3.0 Hz, 2J(H,H)=12.6 Hz, 1H), 4.36 (ddd, 3J(H,H)=3.0, 9.0, 6.0 Hz, 1H,
CH-5), 3.98 (t, 3J(H,H)=6.3 Hz, 6H, OCH2), 2.19 (s, 3H, CH3), 2.09 (s,
3H, CH3), 2.06 (s, 3H, CH3), 2.01 (s, 3H, CH3), 1.75 (m, 6H, CH2), 1.44
(brs, 6H, CH2), 1.24 (m, 60H, CH2), 0.86 ppm (t, 3J(H,H)=6.3 Hz, 9H,
CH3); 13C NMR (75 MHz, CDCl3) d=170.32, 170.06, 169.62, 169.12,
166.488, 153.18, 141.99, 127.94, 106.20, 77.28, 73.36, 73.39, 69.51, 68.65,
68.40, 64.87, 61.33, 31.90, 29.68, 29.33, 26.042, 22.65, 20.75, 20.62, 20.59,
20.40, 14.06 ppm; MS (ES): m/z (%): 1088 (100) [M+H]+; IR (KBr): n˜ =
3436, 2922, 2852, 1750, 1649, 1584, 1527, 1495, 1427, 1369, 1228, 1116,
1051, 721 cmꢀ1; elemental analysis calcd (%) for C63H109NO13: C 69.51, H
10.09, N 1.29; found: C 69.38, H 10.21, N 1.39.
[9] M. LÛpez de la Paz, C. Gonzµlez, C. Vicent, Chem. Commun. 2000,
411.
[10] J. Hawley, N. Bampos, N. Aboitiz, J. Jimÿnez-Barbero, M. LÛpez de -
la Paz, J. K. M. Sanders, P. Carmona, C. Vicent, Eur. J. Org. Chem.
2002, 12, 1925.
N-(Talopyranosyl)-3,4,5-tris(tetradecyloxy)benzamide (3): A solution of
23(a/b) (86.0 mg, 0.08 mmol) in MeOH (6 mL) and CHCl3 (4 mL) was
treated with 3 mL of a solution of sodium methoxide prepared from Na
(100 mg, 4.34 mmol) and MeOH (10 mL). The solution was acidified to
pH 6 with Amberlite IR-120H+. After filtering to remove the resin, the
solvent was evaporated at reduced pressure to give a mixture of a and b
isomers. The pure b isomer 3 was obtained after column chromatography
(SiO2, 100% CHCl3 to MeOH/CHCl3 1/9) as a white amorphous solid
(55.0 mg, 75%). Rf =0.40 (MeOH/CHCl3 1/9); 1H NMR (500 MHz,
CDCl3): d=7.32 (d, 3J(H,H)=9.0 Hz, 1H, NH), 6.99 (s, 2H, ortho), 5.38
(d, 3J(H,H)=9.0 Hz, 1H, CH-1), 4.15 (t, 3J(H,H)=4.0 Hz, 1H, CH-4),
4.07 (dd, 1H, 3J(H,H)=4.0 Hz, 2J(H,H)=12.5 Hz, CH-6 or CH-6’), 4.04
(dd, 1H, 3J(H,H)=3.5, 2J(H,H)=12.5 Hz, CH-6 or CH-6’), 3.99 (m, 6H,
OCH2), 3.94 (d, J=3.0 Hz, 1H, OH-4), 3.86 (dd, 3J(H,H)=3.5, 9.5 Hz,
1H, CH-2), 3.73 (d, 2J(H,OH)=10.0 Hz, 1H, OH-2), 3.68 (dt, 3J(H,H)=
3.5, 3.5, 2J(H,OH)=9.5 Hz, 1H, CH-3), 3.56 (t, 3J(H,H)=4 Hz, 1H, CH-
5), 3.01 (d, 2J(H,OH)=9.5 Hz, 1H, OH-3), 2.30 (t, 3J(H,OH)=6.5 Hz,
1H, OH-6), 1.76 (m, 6H, CH2), 1.45 (brs, 6H, CH2), 1.24 (m, 60H), CH2,
0.86 ppm (t, 3J(H,H)=6.5 Hz, 9H, CH3); 13C NMR (125 MHz, CDCl3):
d=166.94 (CONH), 153.12 (Cm), 141.81 (Cp), 128.13 (Cq), 106.05 (Co),
[11] S. J. Angyal, J. C. Christofides, J. Chem. Soc. Perkin Trans. 2 1996,
1485;
[12] S. A. Galema, E. Howard, J. B. F. N. Engberts, J. R. Grigera, Carbo-
hydr. Res. 1994, 265, 215.
[13] Galema et al. predicted for a- and b-d-talopyranoside a H-bonding
equilibrium in water: OH-2!OH-4 (16% for b and 31% for a) and
OH-4!OH-2 (45% for b and 19% for a).[12] X-ray structure of a-
d-talopyranose: a) J. Ohanessian, D. Avenel, J. A. Kanters, D. Smits,
Acta Crystallogr. Sect. B 1977, 33, 1063; b) L. K. Hansen, A. Hord-
vik, Acta Chem. Scand. Ser. A 1977, 31, 187. Angyal et al. demon-
strated[11] the presence of intramolecular hydrogen bonds in b-d-ta-
lopyranoside by NMR experiments in [D6]DMSO.
[14] M. Shiozaki, T. Mochizuki, H. Hanzawa, H. Haruyama, Carbohydr.
Res. 1996, 288, 99.
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4250
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Cooperative Hydrogen Bonds
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Received: January 14, 2004
Revised: April 26, 2004
Published online: July 14, 2004
Chem. Eur. J. 2004, 10, 4240 4251
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¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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