Novel saccharide-pyridine based gelators: Selective gelation and diversity in superstructures

Article abstract of DOI:10.1039/b821126d

A series of N-glycosylamine based organogelators were synthesized from 4,6-O-protected saccharides introducing pyridylamines. The gelation properties of these compounds were studied in regard to their molecular structure by scanning electron microscopy, differential scanning calorimetry, FT-IR spectroscopy and quantum chemical calculations. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009.

Full text of DOI:10.1039/b821126d

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www.rsc.org/njc | New Journal of Chemistry
Novel saccharide–pyridine based gelators: selective gelation
and diversity in superstructuresw
K. Karthik Kumar,a M. Elango,b V. Subramanian*b and T. Mohan Das*a
Received (in Gainesville, FL, USA) 27th November 2008, Accepted 11th February 2009
First published as an Advance Article on the web 24th March 2009
DOI: 10.1039/b821126d
A series of N-glycosylamine based organogelators were synthesized from 4,6-O-protected
saccharides introducing pyridylamines. The gelation properties of these compounds were studied
in regard to their molecular structure by scanning electron microscopy, differential scanning
calorimetry, FT-IR spectroscopy and quantum chemical calculations.
Introduction
Results and discussion
The gelation of various fluids by low molecular weight
organic compounds is an interesting field and fascinates
a wide variety of scientists and such organic compounds
have structures possessing at least one heterocyclic
component. Heterocyclic compounds1,2 and their saccharide
Synthesis of N-glycosylamines
4,6-O-Protected-D-glucose derivatives (1–3) were synthesised
and characterised by adopting literature procedures.8 Except
for 5-iodo-2-aminopyridine all other aromatic amines were
purchased from Sigma-Aldrich and used without further
purification. 5-Iodo-2-aminopyridine (5) was synthesised by
treating 2-aminopyridine (4) with iodine in DMF at room
temperature (Scheme 1). The reactants were chosen to have
desired functional groups, such as a primary amine in
the aromatic moiety and active hydroxyl group in the
derivatives3 exhibit various applications as
a result of
their structures. Sugars, being biocompatible, are certainly
attractive chemical candidates for making organogels.
Saccharide based gelators are at a better advantage owing
to the existance of rich carbohydrate chemistry that
can be used to bring requisite molecular designs.4 In most
of the saccharide based gelators, hydrogen bonding, p–p,
dipole–dipole and CH–p interactions are important for
their gelation property5 though there are cases where
the gelation is dependent on hydrophobic and hydrophilic
properties of the gelator.
4,6-O-protected-D-glucose.
N-glycosylamine
compounds
(7–15) were identified through spectral techniques. During
the synthesis of different N-glycosylamines using partially
protected saccharides,9 gel formation was observed and this
observation prompted us to go for the study of the gelation
property of pyridine-containing saccharide compounds (7–15)
(Scheme 1). Though the precursor saccharide, 4,6-O-protected-
D-glucopyranose has been shown to exist as a mixture of both
the a and b anomers in DMSO-d6 based on spectral studies,
the corresponding N-glycosylamines, 7–15 exist only in the
b-anomeric form. Coupling constants observed in 1H NMR
spectra supported these observations (see ESI,w Table S1).
Organogels are thermoreversible and viscoelastic materials
with low molecular weight gelators in organic solvents.6
Gelation of organic solvents is believed to proceed through
the self-assembly of the gelator molecules. In addition to the
non-covalent interactions present between the gelator
molecules, their affinity for the solvent molecules is also
an important factor in the gelation process. Though there
exist several reports on sugar organogelators in recent
literature,7 to our knowledge this is the first report on
N-glycosylamines containing heterocyclic derivatives, as
efficient gelators.
Gels and gelation properties
Generally, heterocyclic and aromatic compounds possesing
alkyl and amide substitutions exhibit gelation.10 It is known
that the presence of pyridyl moieties leads to better solubility
in polar as well as nonpolar solvents, suggesting that this
moiety has greater affinity towards solvent molecules. All gel
samples were prepared by dissolving the gelator to a solvent, in
such a way it forms a homogenous solution. The solution was
allowed to cool to room temperature, whereby the gel formed.
The gelation ability of the N-glycosylamines (7–15) has been
carried out by using the test tube inversion method.11
In the present case, hydrogen bonding, p–p stacking
interaction and London dispersion forces seem to play
an important role in the self assembly. In order to obtain
further insight into the structure–function relationship of
sugar-based organogelators, we have generated a library
of sugar derivatives that contain a heterocyclic moiety linked
to pyridylamines.
The study includes nine different pyridine based saccharide
derivatives (7–15) in 21 different polar and nonpolar
organic solvents and the results of the gelation tests are
summarised in Table 1. In general, protecting groups, such
as, ethylidene, butylidene and benzylidene present on the
D-glucose moiety led to remarkable change in the gelation
process. The gelating ability of these compounds follows
a Department of Organic Chemistry, University of Madras,
Guindy Campus, Chennai, 600 025, India.
E-mail: tmdas_72@yahoo.com
b Chemical Laboratory, Central Leather Research Institute (CSIR),
Adyar, Chennai, 600 020, India. E-mail: subbu@clri.res.in
w Electronic supplementary information (ESI) available: Further
experimental and theoretical details. See DOI: 10.1039/b821126d
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Scheme 1 Synthesis of N-glycosylamines, 7–15. Reagents and conditions: (i) 2-aminopyridine (4), I2, DMF, rt, 50% (ii) 2-aminopyridine (4),
5-iodo-2-aminopyridine (5), ethanol, rt, 23–69%; (iii) 3-amino-2-chloropyridine (6), ethanol, rt, 60–71%.
Table 1 Gelation ability of N-glycosylamine derivatives in different organic solvents: G = good gelator, P* = partial gelator, S = solution,
S* = slightly soluble, P = precipitation, I = insoluble. Minimum concentration of gelation = 2.0% for 7, 8, 9, 10, 12,13 and 15; 1.0% for 11 and
1.5% for 14
Solvent
7
8
9
10
11
12
13
14
15
Hexane
C6H6
NO2C6H5
CCl4
I
I
S*
P
I
P
S*
P
I
I
S
I
I
I
I
I
G
I
I
I
P
S
I
P
G
I
P*
G
I
S*
P*
I
P*
G
I
I
i-PrOH
CHCl3
CH3C6H5
1,2-DCB
Et2O
1,2-DCE
MeOH
EtOH
Acetone
DMF
DMSO
EtOAc
THF
P
P
P
P
S*
I
S*
P
P
P
S
S
P
P
S*
S*
S*
S*
P
I
P
S
I
I
P
P*
P
S
P
P
P
P*
P
G
P
P
P
S
P*
G
P*
G
P
P*
P*
P*
P
P
S*
I
P*
I
S*
S*
S*
S*
S
S
I
I
S*
P
P
P
S*
P*
G
I
S*
S
S
S*
S
S
S
S
S
P
I
P*
I
P
S
S
I
S
S
I
S
P*
I
I
I
S*
S*
S*
S*
S*
P
P
P
S
S
P
S
S*
S*
S*
S*
S*
S*
G
I
S*
S
S
S*
S
S
S
S
P
S
S
S
S
P
S
P
P
S
S*
S*
S*
P*
S
G
S*
S*
S*
CH3CN
o-Xylene
m-Xylene
p-Xylene
S
P
P
P
P
P
P
P
P
P
P
P
P
the order, 11 4 10 4 14 4 15 4 13 4 12 4 9.
N-Glycosylamine, 11 was able to gelate at a minimum gel
concentration (MGC) of 1%, similarly compound, 14
undergoes gelation at a minimum concentration of 1.5%,
but N-Glycosylamines 10, 12, 13 and 15 exhibited gelation
only at a minimum concentration of 2%.
N-glycosylpyridylamines with butylidene and benzylidene
moieties have greater ability to undergo gelation compared
to the ethylidene derivatives. However, the structural
differences in aminopyridine moieties of compounds, 7, 8, 9,
13, 14 and 15 compared to 10, 11 and 12 leads to poorer
gelation property owing to the disruption of p–p interaction.
The presence of significant involvement of London dispersion
forces and the structural arrangement that enhances the p–p
interactions are chemical factors responsible for greater
gelation ability of N-glycosylpyridylamine, 11.
The gelation ability of the organogelators significantly
depend on the presence of alkyl and the heterocyclic groups.
Greater gelating ability of butylidene protected N-glycosyl-
amines (11 and 14), is due to higher London dispersion
forces11 existing between the alkyl chain groups. Such inter-
actions are expected to be less in ethylidene protected
N-glycosylamines (7, 10 and 13) and the corresponding
gelation would be low. However, in benzylidene protected
N-glycosylamines (9, 12 and 15) the p–p stacking inter-
actions seem to be largely responsible for their gelation
properties. These results support that partially protected
Among the various polar and nonpolar solvents used for
gelation of N-glycosylpyridylamines (7–15), 1,2-dichloro-
benzene (1,2-DCB) and nitrobenzene were found to be the
best solvents for the gelation process which may be attributed
to a strong solute–solvent interaction. Partially protected
N-glycosylamines viz., 10, 12 and 15 were found to be good
organogelators in nitrobenzene, whereas 13 and 14 performed
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well in 1,2-DCB. However, N-glycosylamine, 11 acts as an
efficient organogelator in both solvents.
Xerogel structure
In order to obtain insight into the aggregation mode at the
microscale SEM studies were performed. An SEM image of
compound 9 [Fig. 1(a)] which gives a partial gelator in ethanol,
exhibited a fibrous network with crosslinking.12 Elongated rod
like structures were observed for compound 12 [Fig. 1(d)] and
these kinds of structures were most likely to result from a
strongly anisotropic growth process and are indicative of
directional intermolecular interactions. The SEM image of
N-glycosylamine 15 [Fig. 1(f)] shows short and thick lamellar
Fig. 2 Solution FT-IR spectra of compound 11 in nitrobenzene:
(a) 0.1 M, (b) 0.01 M, (c) 0.001 M, (d) 0.0001 M, (e), 0.0005 M.
aggregated morphology. N-Glycosylamine 10 [Fig. 1(g)],
which forms a partial gelator in 1,2-DCB, forms a fibrous
network morphology. Fibrous aggregated morphologies
observed for compounds, 9, 11, 13 and 14 [Fig. 1(a)–(c), (e),
(i) and (h)] may be due to the presence of a higher number of
solvent molecules than for the lamellar (15) [Fig. 1f] or rod
(12) like structures. These results can be attributed to a higher
void volume (2.36 mm) observed for the former as compared to
the latter (1.74 mm). These different morphologies should
emanate from differences in interfacial free energy or
attachment energies in the stated solvents.
It is well known that hydrogen bonding plays an important
role in the formation of organogels. FT-IR experiments were
carried out to further explore the gelation of N-glycosylamine
11 in 1,2-dichlorobenzene (see ESI,w Fig. S2). The FT-IR
spectra of the N-glycosylamine 11 in the gel phase shows
a N–H stretching band at 3000 cmÀ1 and bending band at
1510 cmÀ1. In the case of the solid phase the N–H stretching
band appears at 3375 cmÀ1 and bending band at 1585 cmÀ1
.
The red shift observed in the gel phase can be attributed to an
increase in intramolecular hydrogen bonding. Based on FT-IR
studies, it is reasonable to deduce that the amine in
N-glycosylamines form hydrogen bonds in the gel phase.13
In order to obtain insight into the involvement of functional
groups viz., Gly-NH, Sac-OH in the aggregation phenomena,
we recorded solution FT-IR spectra (500–4000 cmÀ1) for 11 in
nitrobenzene solvent [Fig. 2]. As the concentration of the
sample in the solution decreases, the peaks appearing in the
region around 1600 cmÀ1 get more sharpened and also a
greater number appear. This may be due to the involvement
of the Gly-NH group in the hydrogen bonding, as was
confirmed from the quantum mechanical calculations below.
Thermoanalysis
The thermal properties of the organogelators have been
analysed using differential scanning calorimetry (DSC). DSC
data obtained for 12 and 15 are shown in Fig. 3. The melting
point and enthalpy of organogelator 12 in the solid phase are
192.4 1C and DH = 98.22 J gÀ1 and in gel phase the values are
136.1 1C and 61.23 J gÀ1. The organogelator, 15 shows melting
Fig. 1 SEM images for (a) 9 (ethanol), (b) 11 (nitrobenzene), (c) 11
(1,2-dichlorobenzene), (d) 12 (nitrobenzene), (e) 13 (1,2-dichloro-
benzene), (f) 15 (nitrobenzene), (g) 10 (1,2-dichlorobenzene), (h) 14
(1,2-dichlorobenzene), (i) 13 (nitrobenzene).
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Fig. 4 Various possible interactions that are observed through
molecular modelling for N-glycosylamines reported in the present
study.
geometries of 7–15 (see ESI,w Fig. S4) were characterized as
minima on the potential energy surface by frequency
calculations. The experiments have shown that p–p inter-
actions are the major source of interaction (see ESI,w Fig. S3).
Therefore calculations were focussed to provide support to
these observations concerning the interaction region for p–p
and CH–p type of interactions in all the molecules. Due to
computational limitations, only the active regions (Fig. 4) are
considered for calculation at MP2 level of theory. The 6-31G*
basis set is used for all the calculation except for iodine
containing molecules where the MIDIX basis set was
employed. The stabilization energies (SEs) are obtained using
the equation, SE = À[(Ecomplex À Emonomer 1 + Emonomer 2)],
where Ecomplex, Emonomer 1 and Emonomer 2 are the total energies
of complex and monomers.
Fig. 3 DSC spectra: (a) 12 (nitrobenzene); (b) 15 (nitrobenzene): (—)
solid phase, (---) gel phase.
Table 2 Thermodynamic parameters for sol–gel transition
Gelator
Solvent
MGC (%)
Tgs/1C
DH/J gÀ1
12
15
Nitrobenzene
Nitrobenzene
1
1
136.1
212.8
61.23
267.1
point and enthalpy in solid and gel phase at 202.9 1C
(DH = 22.4 J gÀ1) and 212.8 1C (DH = 267.1 J gÀ1),
respectively. These results indicate that organogel 15 is more
stable in the solid phase.14,15 Endotherms at 200 1C corres-
pond to solvent peak. The results of DSC experiments are
summarized in Table 2.
In the case of compound 12 in nitrobenzene Tgs of gel phase
was found to lower than the solid phase while for compound
15 the Tgs of gel phase was found to be greater than that of
solid phase. These results indicate that the gel phase of
N-glycosylamine 12 has greater thermal stability than its
corresponding solid phase, whereas for N-glycosylamine 15,
the solid phase has greater thermal stability than its
corresponding gel phase. Though both N-glycosylamines 12
and 15, have different tendencies of thermal stability,
they both show similar minimum gelator concentration
(Table 2).
Computational studies
In the present study, quantum chemical calculations were
carried out in an attempt to probe the various types of
intermolecular interactions responsible for the aggregation/
gelation properties of molecules 7–15. All the calculations
are done using the G98W suite of programs.16 Optimized
Fig. 5 Optimized geometries of various interactions obtained from
MP2 level of theory using 6-31G* and MIDIX basis sets: grey = C,
blue = N, red = O, white = H, green = Cl, pink = I.
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The SEs are corrected for basis set superposition error
(BSSE) using the method adopted by Boys and Bernardi17
(see ESI,w Table S5 for more details). The optimized
geometries provided in Fig. 5 clearly shows that p–p stacked
interactions are in parallel displaced conformation.
molecule. MESP topographies of molecules 7–15 were
calculated using B3LYP/6-31G* method (see ESI,w Fig. S6,
which presents MESP maps obtained at Æ0.04 au isosurface
value).19 These maps indicate that oxygen atoms of the
carbohydrate moiety are rich in electron density and
therefore could play a major role in the formation of
hydrogen bonds. Although calculations were not performed
on other types of intermolecular interactions such as London
dispersion forces, and halogen–halogen interactions, etc.,
we neglect the role of such interactions in the aggregation
of the molecules.
Superimposing the calculated structure with the complete
molecule in appropriate manner results in the possible
aggregation model supported by stacking interactions.
Fig. 6–9 clearly demonstrates the aggregation of the molecules
into superstructures.
Molecular electrostatic potential (MESP)18 maps are highly
useful to identify different hydrogen-bonding regions in a
Models for different aggregation modes of these compounds
have been proposed as shown in Fig. 6–9. While p–p and
hydrogen bonding interactions dominate in ethylidene
protected N-glycosylamines (7, 10, 13) it is the p–p and
London dispersion forces that dominate in butylidene
protected N-glycosylamines (8, 11, 14). The hydrogen bonding
between the amines also contribute to their mode of gelation.
Fig. 6 Aggregation mode of ethylidine protected N-glycosylamines
(7, 10 and 13), where p–p stacking interaction between the pyridine
moieties is observed.
Fig. 7 Aggregation mode of benzylidine protected N-glycosylamines
(9, 12 and 15).
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Fig. 9 Aggregation mode of benzylidine protected N-glycosylamines
(9, 12 and 15) where p–p stacking interaction between both the
adjacent aromatic rings and adjacent pyridine moieties are considered.
Conclusions
In summary, a novel class of N-glycosylamine containing
heterocyclic derivatives have been synthesised and
characterised. These compounds have been found to be good
organogelators. The morphology of the gels shows a strong
dependence on the solvent, showing fibrils in nitrobenzene and
entangled fibres in 1,2-dichlorobenzene. The presence of
different protecting groups results in a change in the gelating
ability of these derivatives.
Experimental
Spectral characterizations
Compounds. NMR spectra were recorded with Bruker
Avance 300 (300 MHz). The solvent peak in 1H NMR and
13C NMR was adjusted to 7.5 and 77.23 ppm for CDCl3 and
2.5 and 39.51 ppm for DMSO-d6, respectively. FT-IR studies
were carried out using Perkin Elmer PE257 IR spectrometer.
Polarimeter studies were carried out using Rudolph-Autopol
II digital polarimeter.
Thermoanalysis. Thermal transitions for gels were
determined on a NETZSCH DSC 204. The measurements
were carried out under nitrogen atmosphere using 50 mL sealed
aluminium sample pans. The temperature calibration of DSC
was made using two standard materials (n-decane, indium)
and energy calibration by an indium standard (28.45 J gÀ1).
Each sample was heated from 25 to 300 1C with a heating
range of 20–25 1C minÀ1. sample weights of 3–28 mg were used
in measurements.
Fig.
8 (i) p–p Stacking interaction observed between the
adjacent aromatic rings of benzylidene protected N-glycosylamines
(9, 12 and 15). (ii) Aggregation of the molecules when benzylidene
protected N-glycosylamines show p–p stacking interaction between the
aromatic rings.
As shown in Fig. 7, benzylidene protected N-glycosylamines
(9, 12, 15) exhibit p–p stacking interactions between the
heterocyclic moiety and aromatic group. In aromatic
nonpolar solvents, the self assembly of the gelator molecules
is favoured by rigid hydrogen bonds that lead to highly
ordered one-dimensional aggregates. In polar solvents,
the molecular assembly leads to one-dimensional aggre-
gates mediated by solvophobic effects and dipole–dipole
interactions.
Microscopy. The gels were imaged with HITACHI-S-3400W
scanning electron microscope. The samples were gold coated
in such a way the gold coating was o1 nm thick on average.
Synthesis of 5-iodo-2-aminopyridine (5). To a solution of
2-aminopyridine (4) in dry DMF 5.6 gm (0.022 mol) of iodine
was added and stirred at room temperature for about 2 h. The
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reaction was then monitored through thin layer chromato-
graphy. Soon after the completion of the reaction, the reaction
mixture was transferred into a solution containing 1 g of
sodium metabisulfate in 10 ml of a dilute cold aqueous
ammonia solution. Compound 5 was extracted using ethyl
acetate and then washed with brine solution, dried over
anhydrous sodium sulfate, filtered, and concentration of the
resultant solution gave brown solid product 5-iodo-2-amino-
pyridine (5). Yield: 1.2 g (50%); mp 126–130 1C; 1H NMR
(CDCl3); d 8.16 (s, 1H, Ar-H), 7.56 (m, 1H, Ar-H), 6.29
(d, 1H, J = 8.7 Hz, Ar-H); 13C: d 157.3 (1C, Ar-C), 153.7
(1C, Ar-C), 145.4 (1C, Ar-C), 110.9 (1C, Ar-C), 77.8 (1C, Ar-C).
(1C, –CH2). FT–IR (KBr, cmÀ1): n 3328, 2948, 2881, 1604,
1446 cmÀ1
.
4,6-O-Benzylidene-N-pyridyl-b-D-glucopyranosylamine, 9.
Yield: 0.61 g (48%); mp 202–206 1C; [a]3D0 À98.71 (c, 1.0,
1
DMSO); H NMR (DMSO-d6), d 7.25–8.00 (m, 5H, Ar-H),
6.58–6.67 (m, 4H, Ar-H), 6.52 (d, 1H, J = 9 Hz, Ano-H), 6.4
(d, 1H, J = 9 Hz, Gly-NH), 5.16–5.44 (m, 2H, Sac-OH), 4.44
(s, 1H, Ace-H), 3.6–4.1 (m, 6H, Sac-H). 13C (DMSO-d6):
d 127.6–157.6 (5C, Ar-C), 101.1–126 (6C, Ar-C), 81.2
(1C, Ace-C), 61.6–71.1 (6C, Sac-C).
4,6-O-Ethylidene-N-(5-iodopyridyl)-b-D-glucopyranosylamine,
10. Yield: 1.2 g (60.9%); mp 176–180 1C; [a]3D0 À94.82
Synthesis of N-glycosylamines 7–15. A typical synthetic
procedure for the synthesis of compounds (7–15) is as follows.
To a solution of 1 mol of 4,6-O-ethylidene-b-D-glucopyranose,
(1) in 10 ml of ethanol, was added 1.2 mol of 2-aminopyridine
(4). The reaction was then stirred at room temperature and the
reactants dissolved within 5–10 min. In certain cases the
undissolved reactants were heated slightly at a temperature
of 50 1C. The reaction was thereby followed through TLC.
The crystalline product which separates was filtered off and
dried under vacuum.
1
(c, 1.0, DMSO); H NMR (DMSO-d6): d 8.18 (s, 1H, Ar-H),
7.72 (d, 1H, J = 2.4 Hz, Ar-H), 7.68 (d, 1H, J = 2.4 Hz,
Ar-H), 7.28 (d, 1H, J = 9 Hz, Gly-NH), 6.41 (d, 1H, J = 8.7
Hz, Ano-H), 5.26 (d, 1H, J = 5.4 Hz, Sac-OH), 5.11 (d, 1H,
J = 5.7 Hz, Sac-OH), 5.01 (t, 1H, J = 9 Hz, Ace-H), 4.7
(d, 1H, J = 5.1 Hz, Sac-H), 3.93–3.98 (m, 2H, Sac-H),
3.09–3.46 (m, 3H, Sac-H), 1.23 (d, 3H, J = 5.1 Hz, –CH3).
13C (DMSO-d6): d 156.8 (1C, Ar-C), 152.7 (1C, Ar-C), 144.5
(1C, Ar-C), 111.2 (1C, Ar-C), 98.5 (1C, Ar-C), 82.6 (1C,
Ace-C), 66.9–80.4 (6C, Sac-C), 20.3 (1C, –CH3).
Synthesis of gels of 7–15. General procedure for the
preparation of gels.
4,6-O-Butylidene-N-(5-iodopyridyl)-b-D-glucopyranosylamine,
11. Yield: 1.02 g (69%); mp 160–164 1C; [a]3D0 À89.51
(c, 1.0, DMSO); 1H (DMSO-d6): d 8.18 (s, 1H, Ar-H), 7.72
(d, 1H, J = 8.4 Hz, Ar-H), 7.31 (d, 1H, J = 8.7 Hz, Ar-H),
6.49 (d, 1H, J = 8.7 Hz,Gly-NH), 5.30 (d, 1H, J = 4.7 Hz,
Sac-OH), 5.16 (d, 1H, J = 5.4 Hz, Sac-OH), 5.01 (t, 1H, J =
8.7 Hz, Ano-H), 3.96 (t, 1H, J = 5.4 Hz, Ace-H), 3.08–3.24
(m, 6H, Sac-H), 1.51–1.53 (m, 2H, –CH2), 1.35–1.39 (m, 2H,
–CH2), 0.88 (t, 3H, J = 6.9 Hz, –CH3). 13C (DMSO-d6),
d 156.8 (1C, Ar-C), 152.7 (1C, Ar-C), 144.5 (1C, Ar-C), 125.6
(1C, Ar-C), 111.3 (1C, Ar-C), 101.4 (1C, Ace-C), 67.3–82.6
(6C, Sac-C), 35.9 (1C, –CH2), 17.1 (1C, –CH3), 13.8
(1C, –CH2). FT-IR (KBr, cmÀ1): n 3375, 2956, 2869, 1585,
Compounds 7–15 (ca. 0.1 g) was placed in a glass vial and
0.5 ml of organic solvent was added. The gelator in the organic
solvent was heated. The solution was then allowed to cool to
room temperature whereby the gel formed.
Spectral characterization
Abbreviations, Sac, Ar, Ano, Ace and Gly correspond to the
saccharide, aromatic, anomeric, acetal and glycosidic groups,
respectively.
4,6-O-Ethylidene-N-pyridyl-b-D-glucopyranosylamine, 7.
Yield: 0.94 g (69%); mp 220–224 1C; [a]3D0 À90.74 (c, 1.0,
1446 cmÀ1
.
1
DMSO); H NMR (DMSO-d6), d 8.05 (d, 1H, J = 3.9 Hz,
Ar-H), 7.40–7.46 (m, 1H, Ar-H), 6.56–6.65 (m, 2H, Ar-H),
6.46 (d, 1H, J = 7.8 Hz, Gly-NH), 5.09 (t, 1H, J = 9.3 Hz,
Ano-H), 4.91–5.02 (m, 2H, Sac-OH), 4.1–4.13 (m, 1H, Ace-H),
3.7–3.3 (m, 6H, Sac-H), 1.34 (d, 3H, –CH3). 13C (DMSO-d6):
d 157.2 (1C, Ar-C), 147.3 (1C, Ar-C), 136.9 (1C, Ar-C), 113.7
(1C, Ar-C), 107.8 (1C, Ar-C), 98.8 (1C, Ace-C), 66.7–83.6
(6C, Sac-C), 20.0 (1C, –CH3).
4,6-O-Benzylidene-N-(5-iodopyridyl)-b-D-glucopyranosyl-
amine, 12. Yield: 0.4 g (23%); mp 182–186 1C; [a]3D0 À84.61
1
(c, 1.0, DMSO); H NMR (DMSO-d6), d 7.33–8.12 (m, 5H,
Ar-H), 6.28–6.97 (m, 3H, Ar-H), 6.96 (d, 1H, J = 6 Hz,
Ano-H), 5.25 (d, 1H, J = 6 Hz, Gly-NH), 4.52–4.92 (m, 2H,
Sac-OH), 4.27 (s, 1H, Ace-H), 2.06–3.07 (m, 6H, Sac-H). 13C
(DMSO-d6), d 126–147.4 (5C, Ar-C), 80.9–113.4 (6C, Ar-C),
76.7 (1C, Ace-C), 61.2–73.7 (6C, Sac-C).
4,6-O-Butylidene-N-pyridyl-b-D-glucopyranosylamine, 8.
Yield: 0.86 g (65%); mp 198–200 1C; [a]3D0 À99.22 (c, 1.0,
4,6-O-Ethylidene-N-(2-chloropyridyl)-b-D-glucopyranosyl-
amine, 13. Yield: 1.08 g (71%); mp 184–186 1C; [a]3D0 À88.74
1
DMSO); H NMR (DMSO-d6), d 8.01 (d, 1H, J = 3.9 Hz,
1
Ar-H), 7.44 (m, 1H, Ar-H), 7.03 (d, 1H, J = 9.3 Hz, Gly-NH),
6.53–6.61 (m, 2H, Ar-H), 5.23 (d, 1H, J = 5.1 Hz, Sac-OH),
5.10 (d, 1H, J = 5.1 Hz, Sac-OH), 5.04 (t, 1H, J = 8.7 Hz,
Ano-H), 4.55 (t, 1H, J = 4.8 Hz, Ace-H), 4.00–4.04 (m, 1H,
Sac-H), 3.09–3.45 (m, 5H, Sac-H), 1.51 (m, 2H, –CH2), 1.35
(m, 2H, –CH2), 0.88 (t, 3H, J = 7.2 Hz, –CH3). 13C (DMSO-d6),
d 157.8 (1C, Ar-C), 147.3 (1C, Ar-C), 137.1 (1C, Ar-C), 113.4
(1C, Ar-C), 108.4 (1C, Ar-C), 101.2 (1C, Ace-C), 35.9–82.9
(6C, Sac-C), 30.6 (1C, –CH2), 17.1 (1C, –CH3), 13.8
(c, 1.0, DMSO); H NMR (DMSO-d6), d 7.73 (s, 1H, Ar-H),
7.31 (d, 1H, J = 7.5 Hz, Ar-H), 7.24 (d, 1H, J = 3.6 Hz,
Ar-H), 5.86 (d, 1H, J = 6.6 Hz, Gly-NH), 5.38 (s, 1H, Ace-H),
4.71 (d, 1H, J = 4.5 Hz, Sac-OH), 3.99 (d, 1H, J = 5.4 Hz,
Sac-OH), 3.18–3.44 (m, 7H, Sac-H), 1.24 (d, 3H, J = 3.6 Hz,
–CH3). 13C (DMSO-d6), d 139.3 (1C, Ar-C), 137.6 (1C, Ar-C),
136.1 (1C, Ar-C), 123.8 (1C, Ar-C), 120.6 (1C, Ar-C), 98.5
(1C, Ace-C), 66.8–84.6 (6C, Sac-C), 20.3 (1C, –CH3). FT-IR
(KBr, cmÀ1): n 3423, 3269, 2893, 1589, 1521 cmÀ1
.
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4,6-O-Butylidene-N-(2-chloropyridyl)-b-D-glucopyranosyl-
amine, 14. Yield: 0.94 g (64%); mp 154–158 1C; [a]3D0 À96.86
(c, 1.0, DMSO); 1H NMR (DMSO-d6), d 7.73 (d, 1H, J = 4.2
Hz, Ar-H), 7.31 (d, 1H, J = 7.8 Hz, Ar-H), 7.20–7.24 (m, 1H,
Ar-H), 5.86 (d, 1H, J = 7.2 Hz, Gly-NH), 5.34 (d, 1H, J = 4.5
Hz, Sac-OH), 5.32 (d, 1H, J = 3.9 Hz, Sac-OH), 4.64 (t, 1H,
J = 7.5 Hz, Ano-H), 4.56 (t, 1H, J = 4.8 Hz, Ace-H),
4.00–4.04 (m, 1H, Sac-H), 3.15–3.45 (m, 5H, Sac-H);
1.49–1.54 (m, 2H, –CH2), 1.35–1.4 (m, 2H, –CH2), 0.90
(t, 3H, J = 7.2 Hz, –CH3). 13C (DMSO-d6), d 139.3
(1C, Ar-C), 137.6 (1C, Ar-C), 136.1 (1C, Ar-C), 123.8
(1C, Ar-C), 120.6 (1C, Ar-C), 101.3 (1C, Ace-C), 66.8–84.6
(6C, Sac-C), 36.92 (1C, –CH2), 17.0 (1C, –CH3), 13.7
(1C, –CH2). FT-IR (KBr, cmÀ1): n 3342, 2948, 2877, 1589,
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1512 cmÀ1
.
8 (a) P. L. Barili, G. C. Berti, G. Catelani, C. Cini, F. D’Andran and
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4,6-O-Benzylidene-N-(2-chloropyridyl)-b-D-glucopyranosyl-
amine, 15. Yield: 0.85 g (60%); mp 220–224 1C; [a]3D0 À98.64
1
(c, 1.0, DMSO); H NMR (DMSO-d6), d 6.97–7.16 (m, 5H,
Ar-H), 6.61–6.67 (m, 3H, Ar-H), 6.96 (d, 1H, J = 6 Hz,
Ano-H), 6.82 (d, 1H, J = 6 Hz, Gly-NH), 4.53–5 (m, 2H,
Sac-OH), 4.38 (s, 1H, Ace-H), 3.15–4.11 (m, 6H, Sac-H). 13C
(DMSO-d6), d 126–136.7 (5C, Ar-C), 92.7–123.1 (6C, Ar-C),
81.2 (1C, Ace-C), 61.7–72.7 (6C, Sac-C).
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J. A. Montgomery, Jr., R. E. Stratmann, J. C. Burant,
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M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi,
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Acknowledgements
We acknowledge CSIR, New Delhi for financial support.
T. M. thanks DST, New Delhi for FIST facility to the
Department of Organic Chemistry, University of Madras.
T. M. acknowledges the contributions made by his former
student, J. Jayakumar. K. K. K. acknowledges CSIR,
New Delhi for a Junior Research Fellowship. We thank
Prof. R. G. Weiss, Department of Chemistry, Georgetown
University, USA for valuable discussion.
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