Mechanochemical click reaction as a tool for making carbohydrate-based triazole-linked self-assembling materials (CTSAMs)

Article abstract of DOI:10.1016/j.carres.2015.01.022

Various glycosides in which glycosylated triazole residues are anchored on to a central phenyl ring have been prepared under green reaction conditions by a solvent-free mechanochemical method. Some of the glycosides exhibited the ability to form gels when in contact with long chain hydrocarbons, e.g. hexane, heptane and octane, and this property was phase-selective. Thus, from a mixture of hexane-water, the compounds preferably absorbed the alkane to form a gel. The gelation ability was found to increase with an increasing number of substituents on the phenyl ring but only up to tetra-substitution. The hexa-substituted phenyl derivative did not swell in the hydrocarbon solvents investigated. The spontaneous self-assembling properties of these compounds in hexane have been investigated by transmission electron microscopy (TEM). Molecular modelling was used to optimize the structural geometry of these carbohydrate-based triazole-linked self-assembling materials (CTSAMs) and to rationalize their behaviour.

Full text of DOI:10.1016/j.carres.2015.01.022

Accepted Manuscript
Mechanochemical click reaction as a tool for making carbohydrate-based triazole-
linked self-assembling materials (CTSAMs)
Mohit Tyagi, Nikhil Taxak, Prasad V. Bharatam, Hemraj Nandanwar, K.P.
Ravindranathan Kartha
PII:
S0008-6215(15)00035-X
10.1016/j.carres.2015.01.022
CAR 6939
DOI:
Reference:
To appear in: Carbohydrate Research
Received Date: 21 July 2014
Revised Date: 14 January 2015
Accepted Date: 31 January 2015
Please cite this article as: Tyagi M, Taxak N, Bharatam PV, Nandanwar H, Ravindranathan Kartha KP,
Mechanochemical click reaction as a tool for making carbohydrate-based triazole-linked self-assembling
materials (CTSAMs), Carbohydrate Research (2015), doi: 10.1016/j.carres.2015.01.022.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Mechanochemical click reaction as a tool for making
carbohydrate-based triazole-linked self-assembling materials
(CTSAMs)
Mohit Tyagi,a Nikhil Taxak,a Prasad V. Bharatam,a Hemraj Nandanwar,b K. P. Ravindranathan Karthaa,*
aDepartment of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research,
Punjab, India
*Fax: 91-172-2214692; E-mail: rkartha@niper.ac.in
bInstitute of Microbial Technology, Sector 39A, Chandigarh – 160036, India
Abstract-Various glycosides in which glycosylated triazole residues are anchored on to a central phenyl
ring have been prepared under green reaction conditions by a solvent-free mechanochemical method.
Some of the glycosides exhibited the ability to form gels when in contact with long chain hydrocarbons,
e.g. hexane, heptane and octane, and this property was phase-selective. Thus, from a mixture of hexane-
water, the compounds preferably absorbed the alkane to form a gel. The gelation ability was found to
increase with an increasing number of substituents on the phenyl ring but only up to tetra-substitution.
The hexa-substituted phenyl derivative did not swell in the hydrocarbon solvents investigated. The
spontaneous self-assembling properties of these compounds in hexane have been investigated by
transmission electron microscopy (TEM). Molecular modelling was used to optimize the structural
geometry of these carbohydrate-based triazole-linked self-assembling materials (CTSAMs) and to
rationalize their behaviour.
Keywords: CTSAMs, mechanochemical click reaction, nano bioorganomaterials, organogelators.
1

ACCEPTED MANUSCRIPT
1. Introduction
'Click reactions' usually between azides and alkynes1-4 have found extensive applications in
supramolecular chemistry,5-9 material science,10-12 and medicinal chemistry13-21. Because of the ease with
which these reactions can be performed, they have been widely applied in the synthesis of complex
molecules such as large dendrimers,22 catenanes, and rotaxanes23 which have been utilized in making
nano-scale devices such as molecular machines, molecular walkers and other devices.24 Click chemistry
has also been well explored in carbohydrate chemistry. Thus, some of the glycodendrimers25-29 so
prepared have been found important in developing antiviral vaccines,30 bacterial/lectininhibitiors,31-33 and
multivalent inhibitors.34-39 In addition to providing access to such large dendritic structures, it has also
been proved an excellent tool for generating macrocyclic frameworks composed of glycoconjugates40-42
with potential applications in the field of supramolecular chemistry5-9 and molecular-assembly43,44
.
Interestingly, the cyclized/organized structures have also been demonstrated to be often superior to their
uncyclized counterparts in biological activity, which has implications in medicinal chemistry.45 In
synthetic carbohydrate chemistry, other important areas where click chemistry has found application
include preparation of carbohydrate-fused heterocycles as carbohydrate mimetics46-48 through
intramolecular cyclisation, and synthesis of glycopolymers49,50 and pseudo-oligosaccharides51,52 which
have potential uses in lectin-binding and mycobacterial inhibition. In addition, click chemistry has
enabled conjugation of carbohydrates with other bio macromolecules such as proteins, DNA and RNA.53-
55 Recently, the syntheses of several 1,5-disubstituted carbohydrate-linked triazoles under metal-free click
conditions were also reported.56-59
In spite of these advances, the application of click chemistry in generating nanostructured self-
assembling materials is still at exploratory stage. Because of the possibility for self-assembly through π-π
stacking as well as hydrogen bonding interactions in compounds carrying triazole residues, this method
2

ACCEPTED MANUSCRIPT
can also be potentially useful for making phase-selective gelators that find effective application in oil spill
cleanup and recovery processes. We have been recently involved in developing new solvent-free
approaches for the synthesis of biologically important molecules.60 The current work describes the
synthesis of certain triazole-linked sugar derivatives by ball milling in the absence of solvent and in an
examination of some of the structures so generated by TEM for studying their self-assembly properties.
Moreover, as the 1,2,3-triazole residue has been an important pharmacophore, forming a structural
component of many biologically active compounds,13-21 the compounds have been evaluated for their
antimicrobial activity.
Recently we noted that 1,2-cis- and 1,2-trans-linked long chain alkyl glycosides, known
traditionally for their surfactant properties, differed significantly in their molecular self-assembly and
could be studied by TEM.61 It was therefore reasoned that triazole-linked carbohydrates bearing such
alkyl residues, either on the carbohydrate moiety or the triazole residue, should be capable of assembling
efficiently, a useful addition to their physical/physicochemical properties. Substitution of the alkyl chain
in the glycolipid by a phenyl moiety, capable of organization by π-π stacking, might therefore potentially
alter the organization-pattern considerably. Recently, CuAAC reaction has been proven to be an excellent
tool for the preparation of aromatic core-linked glycodendrimers in addition to the normal dendrimers,
which are explored in the area of drug delivery, biosensors, nanomaterials, etc.26,62,63 Besides, click
reaction was also widely explored in the preparation of self-assembling materials64-68 and molecular
gelators.69-71 These gelators and other materials have further been shown to be suitable for their
applications in metal ion-binding, drug delivery, etc. In fact, it was during the span of our work that most
of the reports in this research area started to appear in the literature. Till date there has been no report on
the effect of sugar residues, bearing lipophilic protection and also anchored on to an aromatic core, on the
self-assembling behaviour of glycoclusters. This work describes the application of click reaction in the
3

ACCEPTED MANUSCRIPT
preparation of carbohydrate-based triazole-linked self-assembling materials (CTSAMs), in particular the
effect of the anchored sugar residue on its gelation/self-assembling properties. In our initial study, a small
library of carbohydrate derivatives formed through ‘click chemistry’ were synthesised under green
reaction conditions and subsequently analysed by TEM.
2. Results and Discussion
2.1 Solution-phase synthesis of monovalent carbohydrate-based triazole-linked compounds
The required propargyl glucoside derivatives 1, 2 and 3 were synthesised using literature
methods.60,72 They were then reacted with benzyl azide, generated in situ from a mixture of benzyl
bromide and NaN3,73 to yield the corresponding sugar-linked triazoles 4, 5 and 6 (Scheme 1).
OR
N
N
OR
O
RO
RO
O
a
RO
RO
N
O
O
OR
OR
4, R = C5H11C(O) [from 1]
5, R = C11H23C(O) [from 2]
6, R = CH3C(O) [from 3]
1, R = C5H11C(O)
2
, R = C11H23C(O)
3, R = CH3C(O)
HO
a
N
N
N
HO
7
Reagents and conditions: (a) BnBr (2 mol equiv); NaN3 (10 mol
equiv) CuSO4.5H2O (0.4 mol equiv), sodium ascorbate
t-BuOH-H2O (1:1), rt, 1 h, 73 - 80%
Scheme 1. Synthesis of triazole-linked carbohydrate derivatives
The sugar-linked triazole 4 thus obtained was found to form gels when in contact with hexane.
The gels obtained were soft and possessed shear-thinning properties and tendency to form clear solution
on extensive dilution and/or on subjecting to ultrasound irradiation. Neither the acetyl analogue of 4,
namely 6, nor the N-benzyl-triazolyl methanol 7 formed gels under these conditions. This clearly
indicated the role played by the lipophilic moieties present on the sugar in the formation of gel-structures.
The dodecyl analogue 5 also formed gels which were marginally stronger than those formed by 4.
4

ACCEPTED MANUSCRIPT
Therefore it became evident that the longer lipophilic chains present in 5 helped the association of
molecules more effectively. Nevertheless, the organized structures formed did not appear to be large
enough to be visible under TEM.
2.2 Synthesis of polyvalent triazole compounds under mechanochemical azide alkyne click reaction
using CuI (CuSO4-sodium ascorbate) and their physicochemical properties
In attempts to obtain molecules with improved gelation ability, the syntheses of various other
sugar-linked triazole compounds were undertaken. As multiple sites of reaction were present in some of
the cases targeted, for ensuring the homogeneity of each of the compounds formed, the one-pot two-step
procedure mentioned above was modified in these cases. Thus the aromatic azides required for this
purpose (8, 9, 10, 11, 12, Fig 1) were synthesized74-79 and then reacted with the desired propargyl
N3
N3
N3
N3
N3
N3
10, 93%
N3
N3
N3
9, 89%
8, 92%
N3
N3
N3
N3
N3
N3
N3
12, 88%
N3
N3
N3
11, 83%
Figure 1. Structures of various clickable azides synthesized under conventional conditions
glycosides by co-grinding under the optimized solvent-free mechanochemical click reaction conditions.80
The usual aqueous solution-phase CuAAC reaction was not chosen for this purpose, because of the
insolubility of the lipophilic substrates in the reaction medium. Various triazole-linked glycoclusters (Fig
1
2) were thus obtained in excellent yields (85-92%) and were characterized by H and 13C NMR
5

ACCEPTED MANUSCRIPT
1
spectroscopic methods. In the H NMR spectra, the compounds were clearly distinguishable by the ratio
of the triazolyl hydrogen to the phenyl ring-hydrogens in the respective structures. When qualitatively
evaluated, the gelation ability of the compounds prepared was found to be in the order 18>17>16>15>4.
Thus it was apparent that the gelation ability of a compound increased with increasing number of
lipophilic sugar residues anchored on to the core structural element, namely, the phenyl ring up to the
level of tetra-substitution (derivatives 17 and 18). The hexa-substituted phenyl derivative 20 did not form
a gel. Likewise, the pentaerythritol-derived 19 also failed to gel. The latter observations were supportive
of our initial contention that the phenyl ring would help in the organization of individual structural units
into an ordered arrangement and that the sugar-linked triazole units must preferably lie on the same side
OR
RO
N
N
N
N
N
OR
N
N
N
N
RO
OR
N
N
N
13, 14, 15
N
N
N
16
N
N
RO
OR
N
N
N
N
N
N
N
N
OR
RO
N
N
N
N
N
N
N
N
RO
N
N
N
N
N
N
OR
19
RO
17, 18
RO
RO
N
RO
N
N
N
N
RO
N
N
N
N
N
N
N
N
N
N
N
N
OR
OR
N
OR
20
β
13, R = 2,3,4,6-Tetra-O-acetyl- -D-glucopyranosyl
14
β
, R = -D-Glucopyranosyl
15 16 17 19 20
β
,
,
,
,
, R = 2,3,4,6-Tetra-O-hexanoyl- -D-glucopyranosyl
18, R = 2,3,4,6-Tetra-O-dodecanoyl-β-D-glucopyranosyl
Figure 2. Structures of various sugar-linked triazole derivatives synthesized by mechanochemical
CuAAC reaction
6

ACCEPTED MANUSCRIPT
of the phenyl ring to which they are anchored. It appears that the tetrahedrally arranged core structural
motif in 19, prevents it from forming effective ordered arrangements necessary for holding the solvent
molecules that eventually leads to a gel-like structure. This also appeared true of the hexa-substituted
phenyl derivative 20 wherein due to the steric crowding not all of the anchored sugar-bearing triazolyl
residues are in a position to align on the same phase of the phenyl ring. This appears tobe limiting the
scope of structural association crucial for the gelation to occur. These observations along with the fact
that analogues 13, 14 and 16 devoid of the lipophilic protecting groups on the sugar moieties did not yield
gels indicate that both the presence of phenyl ring as well as the fatty (long chain) substituents on the
sugar ring were prerequisites for the molecules to form organized structures capable of gelation.
Moreover, In view of the foregoing observations an examination of the morphological features of the
structures formed in hexane was undertaken. The nano-architecture of these gels could indeed be clearly
seen in the TEM images obtained (Fig 3). Thus, compounds 16/17/18 taken up in hexane (equal
concentration, w/v) gave TEM patterns typical of those produced by organic polymers.81,82 It was noticed
that an estradiol-based low-molecular-weight gelator described in the literature possesses the triazole-
bearing tetra-substituted phenyl residue characteristic of 17/18 described here.69 Likewise, a click
nucleoside-lipid-linked triazolyl glucoside that forms a hydrogel has similarly been reported to have a
supramolecular structure stabilized by a network of fibers.71 Some of the other triazole-linked compounds
described in the literature, although are not sugar-bearing, have been found to have polyaromatic units in
their structure that allows then to form assemblies of various descriptions such as lamellae,65 spheres,65,68
fibres,67,69,71 etc and find applications in liquid crystals,64 aggregation-induced-emission (AIE)-active
molecules,67 selective metal ion-binding,68,70 nucleic acid delivery,71 etc. The tetra-substituted phenyl
derivative 18 bearing the longest alkanoyl chains on the sugar residues gave relatively the densest gel as
7

ACCEPTED MANUSCRIPT
can be seen from the TEM images shown in Fig 3. It may be recalled that among these compounds, 18
had the highest molecular weight and hence the lowest molar concentration in the gel prepared and yet
had formed comparatively the densest gel. The disubstituted phenyl derivative 15, only marginally thick
in hexane, was investigated after taking up in moist methanolic hexane, where it formed a stronger gel as
compared to hexane alone as the solvent. The acetylated and deacetylated analogues 13 and 14,
a (15)
b (16)
c (17)
d (18)
Figure 3. Transmission electron micrographs: a. 15; b. 16; c. 17 and d. 18 (for sample preparation, moist
MeOH-Hex was used for 15 and hexane only for others). For a larger image please see Supplementary
Information.
respectively, did not yield any gel under such conditions. Dispersion of the tris-triazolyl compound 16 in
hexane was thin initially (Fig 3b), but gave a rather firm gel (Fig 4) on standing for 3-5 days (in closed
vials). The gel could be easily cut into cubes with a surgical knife. On dilution and application of the
8

ACCEPTED MANUSCRIPT
Figure 4. Transmission electron micrographs for the gel made by 16 on standing for 3-5 days (For a
larger image please see Supplementary Information.)
solution for imaging (TEM), the sample, for most part, appeared as a smooth film but otherwise had the
pattern shown in Fig 4. Further, it was observed that compound 18 dissolved in polar solvents such as
DMSO, DMF, AcOH, MeNO2, etc giving clear colorless solutions (Table 1). While it formed gels in
alkanes such as hexane, heptane and octane, it dissolved in alcohols such as methanol and n-octanol
though in the latter case the resulting solution appeared slightly viscous. Aromatic solvents such as
Table 1. Interaction of 18 with various solvents*
Hansen’s solvent parameters@
Entry
Solvent
Observation
δd
δp
δh
1
2
3
4
5
6
7
8
9
Hexane
Heptane
Octane
Octanol
Methanol
Toluene
DMSO
AcOH
Quickly absorbs, forms clear thick gel
Quickly absorbs, forms clear thick gel
Quickly absorbs, forms clear thick gel
Dissolves; solution, marginally viscous
Dissolves; does not gel
7.28
7.48
7.58
--#
0.00
0.00
0.00
--#
0.00
0.00
0.00
--#
7.38
8.80
9.00
7.09
7.63
6.01
0.68
8.02
3.91
7.82
10.90
0.98
4.99
6.60
20.68
Dissolves; does not gel
Dissolves; does not gel
Dissolves; does not gel
Water
Insoluble
10 Water-Hexane Absorbs hexane and leaves water at the bottom
* 20 mg of 18 was taken up in 2 mL of the respective solvent and the nature of the interaction was noted;
9

ACCEPTED MANUSCRIPT
@
δd/δp/δh are the dispersion/polar/H-bonding contributions to δ, the Hildebrand solubility parameter
#
(MPa1/2); values for octanol were not available but the respective values reported for decanol are: 8.60,
1.32 and 4.89, respectively.83
toluene also dissolved 18, giving clear solutions (Table 1). These observations clearly indicated possible
ordered association between the fatty acyl chains present in the substance with the solvent molecules of
matching attributes in agreement with the concept of “like seeks likes”. In general, mixing of 18 with
organic non-polar solvents possessing Hildebrand’s polar and H-bonding parameters of zero (entries 1-3,
Table 1) resulted in the formation of a gel whereas dissolution occurred in polar organic solvents
possessing values greater than zero for these parameters. Thus, formation of a solution of slightly higher
viscosity in octanol compared to methanol was also not unexpected. Details of the hydrophobic-
hydrophobic (and other) interactions leading to the supramolecular assembly in these molecules have
been rationalized further in Section 2. These observations led us to examine its possible application
typical of those with phase-selective gelation abilities as used in oil-spill clean-up from water. In a
qualitative evaluation thus, when 18 was added to a mixture (bi-phasic) of aqueous KMnO4 and hexane,
the compound completely absorbed the organic liquid selectively, forming a gel capable of holding the aq
permanganate solution over it upon turning the test tube upside down (Fig 5). The same was the case
when CuSO4 was used in the place of KMnO4 (except for the fact that the aqueous layer in the latter case
had the bluish appearance owing to the presence of CuSO4). Again, in the absence of the inorganic salts
also the behavior of the biphasic system was identical to the above cases except for the fact that the
aqueous layer remained colourless and therefore a visual demarcation of the two layers was more
difficult.
10

ACCEPTED MANUSCRIPT
Turn upside down
Mixture of
hexane &
aq KMnO4
Mix
TEM
+
Compound
18
TEM image of
the gel
Figure 5. Demonstration of the application of compound 18 as a phase-selective gelator: The compound
absorbs hexane selectively from the bi-phasic mixture and generates a gel that can hold the aqueous
permanganate solution over it.
Further, inspired by the various reports on the antimicrobial (antibacterial, antifungal, etc) activities of
various 1,4-disubstituted 1,2,3-triazole derivatives,84-89 the above compounds were also evaluated against
bacterial strains in search of potential new antibacterial molecules. Also, as the triazole-linked compounds
are known to act through different mechanisms, the possibility for finding compounds acting through
novel mechanisms also existed. The compounds were tested against both gram positive and gram
negative strains of various bacterial strains. The results of the screening experiments are summarized in
Table 2. Thus, while compounds 4, 16, 18 and 19 were found to have moderate activities against the gram
positive bacterial strains tested (Table 2), compounds 13, 14, 15, 17 and 20 were inactive. Also, the
activity was selective towards the gram positive strains as none of the compounds showed any activity
against any gram negative strains tested (results not shown). In order to establish any structure activity
11

ACCEPTED MANUSCRIPT
relationship for these molecules, therefore, the evaluation of a much wider range of compound-library
would be required.
Table 2. Antibacterial activity of triazole-linked compounds
Bacterial strain
Micrococcus Staphylococcus Bacillus subtilis
Compound
luteus
MTCC-2470
(MIC, µg/ml)
1000
aureus
MTCC-96
(MIC, µg/ml)
125
MTCC-121
(MIC, µg/ml)
250
500
NAA
1000
4
4
250
500
16
18
1000
NAA
NAA
NAA
19
Ampicillin
Amoxicillin
16
32
4
16
2
Test compounds: 1000 (µg/ml); NAA: No Antimicrobial Activity; Compounds 13, 14, 15, 17 and 20 were
not active.
2.3 Quantum chemical analysis to rationalise the self-assembling property
In view of the interesting physicochemical properties exhibited by the compounds described above,
attempts were made to rationalize the observations by TEM in terms of their electronic structures and the
various inter- as well as intramolecular interactions that possibly existed in them. Initially, the monomeric
structures of glycosides 15, 16 and 17 were constructed and optimized employing the semi-empirical
quantum chemical method, PM3 method using Gaussian03 package (for the details of methodology, see
12

ACCEPTED MANUSCRIPT
supporting information and computational details provided in the experimental section). Recently, this
method has been used for providing insights into the structural details of polymeric structures and
supramolecular systems.43,61 Fig 6 shows the optimized 3D geometries of these monomers, designated for
easy differentiation from the dimers and trimers as, 15-M, 16-M and 17-M. The optimized geometry of
15-M showed the two triazole moieties above the plane of the benzene ring. It is characterized by a set of
2.42
2.50
2.43
2.68
2.53
2.66
2.65
2.80
2.53
2.62
15-M
16-M
2.61
2.68
2.33
2.82
Truncated 17-M
17-M
Figure 6. The optimized 3D geometries of monomeric structures of 15 (15-M) and 16 (16-M), showing
characteristic intramolecular and intermolecular hydrogen bonding interactions. Owing to the difficulty in
pointing out interactions in 17 (17-M), markings have been made on its truncated structure shown. All the
bond distances are given in Å units.
13

ACCEPTED MANUSCRIPT
intramolecular H-bonding interactions amongst the sugar units as well as those between the C-H (triazole)
and the carbonyl oxygen (of the 6-O-n-hexanoyl residue). The two H-bonding interactions, C-Htriazole---
O=C (of 6-O-n-hexanoyl residue) were observed with H-bond distances of 2.53 and 2.80 Å. The other
weak interactions observed were between the methylene hydrogens (C-3 methylene, second from the acyl
carbon of the 2-O-n-hexanoyl residue) and the anomeric oxygen [CH---O] with bond distances of 2.53 Å,
triazolyl CH2---O(CO) (of 2-O-n-hexanoyl residue) with bond distances of 2.62 Å and between the
methylene hydrogens (C-2 methylene next to the acyl carbon of the 3-O-n-hexanoyl residue) and O(CO)
(of 2-O-n-hexanoyl residue) with the bond distance of 2.66 Å. The n-hexanoate chains at C-4 and C-5 of
the sugar units were found to be involved in hydrophobic interactions. Likewise, the optimized geometry
of 16-M also showed the three triazole moieties connected to the benzene ring at 1, 3 and 5 positions,
lying above the plane of the benzene ring. Several intramolecular H-bonding interactions, similar to those
in 15-M, were also indeed observed in this case. A strong intramolecular H-bonding interaction was
observed between the C-H of thetriazole unit and the O=C of the 6-O-n-hexanoyl residue (CH----O=C,
2.43 Å).The other intramolecular interactions observed were between the carbonyl oxygen of the 2-O-n-
hexanoyl residue and the anomeric hydrogen (H-1) of the sugar moiety (2.42 Å). A similar interaction
was also observed between the carbonyl oxygen of 3-O-n-hexanoyl residue and the H-4 of the sugar (2.50
Å). The C-2 methylene hydrogen of the 3-O-n-hexanoyl residue (thatis, adjacent to the acyl carbon) was
also observed to participate in an intramolecular H-bonding interaction with the ester oxygen of the 2-O-
n-hexanoyl residue [CH---O(CO), 2.65 Å].A characteristic intramolecular hydrogen bonding interaction
(2.68 Å) between the hydrogen of benzylic methylene (PhCH2 in the centre attached to the triazolyl
nitrogen) and the carbonyl oxygen of the ester (6-O-n-hexanoyl residue) was also observed. These
interactions give rise to the the typical orientation of the three triazole rings connected to the central
benzene ring in the optimized geometry of 16-M (Fig 6). The optimized geometry of 17-M was situated
14

ACCEPTED MANUSCRIPT
above the plane of the benzene ring, while the fourth triazole moiety was oriented below the plane. This
gave the geometry characterized by an arrangement, in which an intramolecular H-bonding interaction
(2.82 Å) was observed between the two traizole units situated above the plane of the benzene ring while
another intramolecular interaction was observed between the carbonyl oxygen of the 2-O-n-hexanoyl
residue and a C-5 methylene hydrogen of the 3-O-n-hexanoyl residue (C=O---HC, 2.68 Å). To understand
and determine the self-assembling property in these molecules, their dimeric structures (15-D, 16-D and
17-D) were constructed from the optimized geometries of the monomers, as shown in Fig7 (a, b & c). The
analysis of the dimeric structures provided an understanding of the orientation of the two monomeric
units, especially with respect to the central benzene ring. Fig 7 (a, b & c) shows the optimized geometries
of the dimeric structures. In 15-D, the central benzene ring of the monomeric unit is oriented at an angle
of 98.5˚ with respect to the benzene ring of the other monomeric unit. An important intermolecular H-
bonding interaction between the two triazole rings (CHtriazole---Ntriazole, 2.63 Å) was observed, resulting in
this typical orientation of 15-D. Other intramolecular and intermolecular H-bonding interactions in 15-D
are shown in Fig 7a. The optimized geometry of 16-D was observed to be in a different orientation as
compared to 15-D. The two central benzene rings in 16-D were observed to be aligned parallel to each
other, with the bond angle between them observed to be 103.3˚. The interactions remained similar to
those observed in 16-M, and are shown in Fig 7b. In 17-D, the two benzene rings were observed to be
oriented at an angle of 114.9˚, with a characteristic intermolecular H-bonding interaction (2.86 Å)
observed between the Ntriazole and the methylene hydrogen (connecting the phenyl and the triazole rings,
Fig 7c). The optimized geometries of 15-D, 16-D and 17-D show the sugar units with their n-hexanote
chains covering the dimeric structures from both sides, thus, ruling out the possibility of trimeric
structures. Thus, the different orientations of 15-D, 16-D and 17-D and several interactions amongst them
give an indication of their self-assembling property, and stabilization of these dimeric structures (Table
15

ACCEPTED MANUSCRIPT
3).
2.62
2.51
98.5
2.63
2.64
2.63
Figure 7a. The optimized 3D geometries of dimeric structures of 15 (i. e. 15-D) (showing the
characteristic alignment of the two central benzene rings and the interactions in them. All the bond
distances are given in Å units. Bond angles are given in degrees (˚).
16

ACCEPTED MANUSCRIPT
2.47
2.92
2.47
103.3
2.96
2.70
Figure 7b. The optimized 3D geometries of dimeric structures of 16 (i. e. 16-D)
114.9
2.96
2.86
2.86
2.80
Figure 7c. The optimized 3D geometries of dimeric structures of 17 (i. e. 17-D)
17

ACCEPTED MANUSCRIPT
The energy details listed in Table 3 indicate a favourable formation of 16-D and 17-D, whereas no
stabilization was observed in 15-D. Thus, different intra- and intermolecular interactions, stabilization
energies and distinct arrangement of dimeric structures confirm the self-assembling property of these
molecules. The TEM analysis of the glucopyranosides synthesised indicate their self-assembling property
(fibre like arrangement in 15, 16 and 17) which were rationalised in terms of their optimized geometries
and H-bonding interactions in them. The self-assembling property of 15, 16 and 17 can be judged on the
basis of the thermodynamic factors (energy gain), along with the characteristic interactions. The
dimerization of 16 (to give 16-D) was observed to be a highly exothermic process (-15.59 kcal/mol) as
compared to that of 17 (to give 17-D with -7.07 kcal/mol), indicating its higher stability of formation.
Table 3. The absolute and stabilization energies of glucopyranosides 15-M, 16-M, 17-M, 15-D, 16-D and
17-D calculated using the PM3 method
Absolute Energy (kcal/mol)
Dimerization Energy*
Entry
Compound
Formulae
(kcal/mol)
1
2
3
4
5
6
-1.313319
-1.996846
-2.667027
-2.626648
-4.018538
-5.345318
-
-
-
15-M
16-M
17-M
15-D
16-D
17-D
-
-
-
E11-D-2E11-M
E12-D-2E12-M
E13-D-2E13-M
0.00
-15.59
-7.07
*Dimerization energy is calculated by subtracting the summation of energies of monomers from the
energy of the dimer.
This analysis supports the higher gelation ability of compound 17 over that of 16, as discussed earlier.
The oligomerization study, however, could not be extended beyond the above compounds due to the
18

ACCEPTED MANUSCRIPT
excessive steric crowding and hindrances caused by the cluster of larger chains/groups and heavier
substitutions on the central phenyl ring.
3. Conclusions
Application of ‘click reaction’ in making self-assembling glycocluster-materials has been demonstrated
successfully. The preparation of these novel compounds were achieved under ‘green reaction conditions’
using a solvent-free mechanochemical method. Some of the compounds formed gels in organic solvents
and this phase-selective gelation ability was demonstrated in a water-hexane system. Transmission
electron micrographs clearly revealed the gel structures and were typical of organic polymer-derived gels.
Geometry optimization studies on the monomeric forms of compounds 15, 16 and 17 and their dimers
(15-D, 16-D and 17-D) by Gaussian clearly indicated the role played by various inter- and intramolecular
interactions. These interactions result in the specific arrangement of various structural elements present in
these molecules that lead to self-assemblages, as observed by TEM. Some of the reported compounds
possessed promising antibacterial activity.
4. Experimental
4.1 General
All reagents and chemicals were purchased from Aldrich Chemical Co (Milwaukee, WI, USA). Reactions
were monitored by TLC, which was performed on 0.2 mm Merck pre-coated silica gel 60 F254
aluminium sheets. Compounds were detected by dipping the TLC plates in an ethanolic solution of
sulphuric acid (5% v/v) and thereafter heating them. Melting points were recorded on a capillary melting
point apparatus (Buchi). Specific rotations were obtained on Rudolph Research Autopol IV polarimeter at
20 °C. IR spectra were recorded on a Nicolet FT-IR Impact 410 instrument either as neat or KBr pellets.
1H and 13C NMR spectra were referenced to the internal standard tetramethylsilane, in the respective
19

ACCEPTED MANUSCRIPT
deuterated solvents. Coupling constants (J) are reported in Hertz. High resolution mass spectra (HRMS)
were recorded on a Bruker Maxis spectrometer.
4.2 General procedure for the synthesis of CTSAMs by planetary ball-milling:
The azide (1 mmol) and alkyne (1.1 mol equiv/per azide group) was taken in a stainless steel (SS) jar
(capacity, 50 mL) containing 10 SS balls (10 mm o.d.) and sodium ascorbate (0.4 mol equiv/per azide
functionality) was added to it followed by the addition of CuSO4 (0.2 mol equiv/per azide functionality).
The mixture was then ground in a planetary ball mill (Retsch PM-100, Retsch GmbH, Germany) at 500
rpm. After completion of the reaction the mixture was dissolved in EtOAc and was purified by column
chromatography (EtOAc:Hex) to yield analytically pure product.
4.3 Characterisation of compounds
Propargyl 2,3,4,6-tetra-O-hexanoyl-β-D-glucopyranoside (1)
This compound was prepared from propargyl β-D-glucopyranoside by literature methods.60,72 Colourless
syrup; [α]D -14.8 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 5.28 (1H, t, J 9.5 Hz, H-3), 5.12 (1H, t, J 9.7
Hz, H-4), 5.03 (1H, d, J 8.2 Hz, H-2), 4.91 (1H, d, J 7.9 Hz, H-1), 4.36 (2H, s, OCH2), 4.20 (1H, m, H-6ª
&
H-6b), 3.74 (1H, m, H-5), 2.23 (8H, m, (OCOCH2(CH2)3CH3)4), 1.54 (8H, m,
(OCOCH2CH2(CH2)2CH3)4), 1.25 (16H, m, (OCOCH2CH2(CH2)2CH3)4), 0.87 (12H, m,
(OCOCH2(CH2)3CH3)4); δC (100 MHz, CDCl3); 180.18, 173.49, 172.92, 172.17, 172.09, 160.39, 159.70,
98.05, 78.04, 75.48, 75.40, 72.36, 72.23, 72.03, 71.76, 70.66, 70.59, 70.40, 68.18, 68.05, 67.84, 61.64,
61.34, 55.69, 34.00, 33.95, 33.91, 33.85, 31.18, 31.15, 31.10, 29.03, 24.50, 24.39, 24.31, 24.13, 22.39,
22.24, 22.19, 22.17; IR (Neat) νmax 3311, 2957, 2931, 2872, 1750, 1458, 1379, 1225, 1161, 1095, 913,
743; HRMS: m/z calculated for C33H54O10: 610.3717,633.3609 [M +Na]+ Found 633.3610 [M +Na]+.
20

ACCEPTED MANUSCRIPT
Propargyl 2,3,4,6-tetra-O-dodecanoyl-β-D-glucopyranoside (2)
This compound was prepared from propargyl β-D-glucopyranoside by literature methods.60,72 Colourless
syrup; [α]D -22.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 5.27 (1H, t, J 9.5 Hz, H-3), 5.11 (1H, t, J 9.7
Hz, H-4), 5.03 (1H, d, J 8.0 Hz, H-2), 4.78 (1H, d, J 8.0 Hz, H-1), 4.35 (2H, s, OCH2), 4.19 (1H, m, H-6a
&
H-6b), 3.72 (1H, m, H-5), 2.23 (8H, m, (OCOCH2(CH2)9CH3)4), 1.54 (8H, m,
(OCOCH2CH2(CH2)8CH3)4), 1.25 (64H, m, (OCOCH2CH2(CH2)8CH3)4), 0.87 (12H, m,
OCOCH2CH2(CH2)8CH3)4); δC (100 MHz, CDCl3); 202.92, 174.33, 173.42, 172.86, 172.15, 172.06,
101.88, 98.08, 78.09, 77.35, 77.03, 76.71, 75.39, 72.33, 72.09, 70.64, 68.06, 61.66, 60.12, 55.73, 51.40,
43.90, 34.37, 34.13, 34.09, 34.06, 33.99, 33.96, 31.90, 29.62, 29.58, 29.52, 24.48, 29.44, 29.34, 29.32,
29.26, 29.25, 29.13, 29.09, 29.05; IR (Neat) νmax 3748, 3266, 2855, 2926, 2956, 1748, 1577, 1541, 1465,
1377, 1317, 1275, 1260, 1160, 1112, 1069, 913, 816, 764, 749;HRMS: m/z calculated C57H102O10:
946.7473, 969.7365 [M +Na]+ Found 969.7345 [M +Na]+.
1-Benzyl-4-(2,3,4,6-tetra-O-hexanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazole (4)
Greenish syrup; [α]D -11.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.27 (5H, s, PhH), 5.63 (2H, m,
PhCH2), 5.01 (5H, m, H-4, H-3, H-2 & OCH2), 4.63 (1H, bs, H-1), 4.06 (1H, m, H-6a & H-6b), 3.63 (1H,
m, H-5), 2.25-2.06 (8H, m, (OCOCH2(CH2)3CH3)4), 1.52-1.44 (8H, m, (OCOCH2CH2(CH2)2CH3)4), 1.32-
1.18 (16H, m, (OCOCH2CH2(CH2)2CH3)4), 0.80-0.76 (12H, m, (OCOCH2(CH2)3CH3)4); δC (100 MHz,
CDCl3); 173.41, 172.78, 172.44, 172.12, 172.08, 134.39, 130.05, 129.90, 129.59, 129.53, 129.46, 129.16,
128.88, 128.79, 128.49, 128.26, 128.19, 128.11, 100.30, 72.38, 72.23, 72.06, 70.98, 70.73, 68.03, 67.38,
63.20, 61.62, 54.58, 34.25, 33.95, 33.90, 33.87, 31.88, 31.19, 31.15, 31.13, 31.06, 29.64, 24.43, 24.38,
24.33, 22.64, 22.25, 22.19, 14.06, 13.91, 13.88; IR (Neat) νmax 2957, 2932, 2872, 2097, 1751, 1618, 1497,
1457, 1417, 1379, 1316, 1227, 1161, 1096, 1063, 913, 743, 655.
1-Benzyl-4-(2,3,4,6-tetra-O-dodecanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazole (5)
21

ACCEPTED MANUSCRIPT
Colourless solid; mp 123-124 °C, [α]D -35.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.44 (1H, s, CH
Triazole), 7.35 (3H, m, PhH), 7.27 (2H, d, J 5.6 Hz, PhH), 5.51 (2H, s, CH2Ph), 5.20 (1H, t, J 9.5 Hz, H-
3), 5.08 (1H, t, J 9.7 Hz, H-4), 5.03 (1H, d, J 8.2 Hz, H-2), 4.90 (1H, d, J 12.7 Hz, OCH2), 4.80 (1H, d, J
12.7 Hz, OCH2), 4.64 (1H, d, J 8.0 Hz, H-1), 4.19 (2H, dd, J 12.4 Hz, J 4.7 Hz, H-6a), 4.12 (2H, dd, J
12.0 Hz, J 1.6 Hz, H-6b), 3.68 (1H, m, H-5), 1.60 (8H, m, (OCOCH2(CH2)9CH3)4), 1.56 (8H, m,
(OCOCH2CH2(CH2)8CH3)4), 1.39 (64H, m, (OCOCH2CH2(CH2)8CH3)4), 0.87 (12H, t, J 6.4 Hz,
OCOCH2CH2(CH2)8CH3)4); δC (100 MHz, CDCl3); 179.64, 173.48, 172.84, 172.13, 144.71, 134.43,
129.14, 128.82, 128.09, 122.72, 100.06, 72.35, 72.05, 70.91, 68.03, 62.99, 61.66, 54.22, 53.43, 42.53,
36.65, 34.08, 34.04, 33.97, 33.17, 32.00, 31.92, 29.87, 29.63, 29.60, 29.49, 29.46, 29.44, 29.36, 29.33,
29.27, 29.26, 29.13, 29.11, 29.08, 29.04, 29.81; IR (Neat) νmax 2925, 2854, 1752, 1497, 1457, 1416, 1376,
1227, 1156, 1115, 1049, 912, 799, 722, 600, 527.
1-Benzyl-4-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazole (6)
Colourless syrup; [α]D -18.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.44 (1H, s, CH Triazole), 7.36
(3H, m, PhH), 7.27 (2H, d, J 5.6 Hz, PhH), 5.52 (2H, s, CH2Ph), 5.14 (1H, t, J 9.5 Hz, H-3), 5.06 (1H, t, J
9.7 Hz, H-4), 4.99 (1H, d, J 8.2 Hz, H-2), 4.90 (1H, d, J 12.7 Hz, OCH2), 4.80 (1H, d, J 12.7 Hz, OCH2),
4.64 (1H, d, J 8.0 Hz, H-1), 4.26 (2H, m, H-6a), 4.11 (2H, m, H-6b), 3.70 (1H, m, H-5), 2.07 (3H, s,
OCOCH3), 2.03 (3H, s, OCOCH3), 1.98 (3H, s, OCOCH3), 1.85 (3H, s, OCOCH3); δC (100 MHz,
CDCl3); 170.67, 170.21, 169.46, 169.36, 144.59, 144.51, 134.47, 129.18, 128.87, 128.41, 128.15, 127.72,
122.74, 122.69, 99.78, 72.33, 72.64, 71.85, 71.61, 71.15, 71.09, 70.86, 68.40, 68.25, 62.93, 61.78, 61.69,
61.59, 61.25, 55.15, 54.22, 53.47, 20.75, 20.60, 20.52; IR (Neat) νmax 3446, 2969, 2532, 1743, 1645,
1498, 1434, 1366, 1227, 1130, 1047, 984, 905, 796, 724, 600, 527.
1-Benzyl-4-(hydroxymethyl)-1H-1,2,3-triazole (7)
22

ACCEPTED MANUSCRIPT
Colourless solid; mp 111-112.6 °C; δH (400 MHz, CDCl3); 7.58 (1H, s, CH Triazole), 7.32 (3H, m, PhH),
7.24 (2H, m, PhH), 5.43 (2H, d, J 5.2 Hz, PhCH2), 4.68 (2H, d, J 4.5, CH2OH); δC (100 MHz, CDCl3);
148.26, 134.52, 129.09, 128.86, 128.74, 128.38, 128.30, 128.11, 122.04, 55.88, 55.84, 55.27, 54.13,
53.54, 50.72; IR (Neat) νmax3366, 3142, 2927, 2855, 1744, 1708, 1648, 1606, 1586, 1552, 1497, 1456,
1435, 1360, 1336, 1224, 1127, 1041, 1013, 913, 819, 795, 723, 697, 671, 582, 471.
1,4-Bis[(4-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-1-
yl)methyl]benzene (13)
Yellow solid; mp 126-126.5 °C; [α]D -28.9 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.49 (1H, s, CH
Triazole), 7.28 (2H, m, PhH),5.52 (2H, d, J 2.3 Hz, PhCH2), 5.18 (1H, t, J 9.4 Hz,H-3), 5.07 (1H, t, J 9.8
Hz, H-4), 4.97 (1H, dd, J 9.4 Hz, J 8.0 Hz,H-2), 4.90 (2H, s, OCH2), 4.80 (2H, s, OCH2), 4.66 (1H, d, J
8.0 Hz, H-1), 4.23 (1H, dd, J 12.3 Hz, J 4.6 Hz, H-6a), 4.23 (1H, dd, J 12.3 Hz, J2.2 Hz, H-6b), 3.72 (1H,
m, H-5), 2.07 (3H, s, OCOCH3),2.02 (3H, s, OCOCH3), 1.99 (3H, s, OCOCH3), 1.91 (3H, s, OCOCH3);
δC (100 MHz, CDCl3); 170.68, 170.22, 169.46, 169.38, 144.77, 135.32, 128.75, 122.83, 100.03, 72.70,
71.88, 71.17, 68.27, 63.06, 61.78, 53.62, 22.74, 20.59; IR (Neat) νmax 3445, 2957, 2872, 1749, 1368,
1228, 1164, 1047, 913, 749; HRMS: m/z calculated for C42H52N6O10: 960.3236, 983.3129 [M +Na]+
Found 983.3086 [M +Na]+.
1,4-Bis[(4-(β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-1-yl)methyl]benzene (14)
Yellowish solid; mp 135-135.8 °C; [α]D -38.8 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 8.10 (1H, s, CH
Triazole), 7.31 (2H, m, PhH), 5.54 (2H, s, PhCH2), 4.83 (2H, d, J 12.2 Hz, OCH2), 4.61 (2H, d, J 12.2 Hz,
OCH2), 4.25 (1H, d, J 7.8 Hz, H-1), 3.70 (1H, d, J 12.1 Hz,H-6a), 3.60 (1H, dd, J 12.3 Hz, J 2.2 Hz, H-
6b), 3.18-2.9 (4H, m, H-5, H-4, H-3, H-2); δC (100 MHz, CDCl3); 144.74, 136.32, 128.78, 124.71,
102.50, 77.10, 76.85, 73.68, 72.99, 72.21, 70.95, 70.38, 63.86, 61.87, 61.45, 52.88; IR (Neat) νmax 3398,
2505, 2242, 2138, 2073, 1944, 1742, 1656, 1452, 1226, 1119, 1086, 975, 881, 822, 530.
23

ACCEPTED MANUSCRIPT
1,4-Bis[(4-(2,3,4,6-tetra-O-hexanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-1-
yl)methyl]benzene (15)
Colourless solid; mp 120-120.6 °C; [α]D -18.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.47 (1H, s, CH
Triazole), 7.28 (2H, m, PhH), 5.50 (2H, q, J 15.02 Hz, PhCH2), 5.22 (1H, t, J 9.4, H-3), 5.09 (1H, t, J
9.6 Hz, H-4), 5.00 (1H, t, J 8.2 Hz, H-2), 4.89 (2H, d, J 12.5 Hz, OCH2), 4.79 (2H, d, J 12.5 Hz, OCH2),
4.66 (1H, d, J 8.2 Hz,H-1), 4.17 (2H, m, H-6a & H-6b), 3.70 (1H, m, H-5), 2.23 (8H, m,
(OCOCH2(CH2)3CH3)4),
1.55
(8H,
m,
(OCOCH2CH2(CH2)2CH3)4),
1.25
(16H,
m,
(OCOCH2CH2(CH2)2CH3)4), 0.87 (12H, m, (OCOCH2(CH2)3CH3)4); δC (100 MHz, CDCl3); 173.41,
172.81, 172.10, 172.08, 144.82, 135.30, 128.67, 122.76, 100.22, 72.31, 72.09, 70.92, 68.05, 63.12, 61.64,
53.56, 33.96, 33.90, 31.21, 31.16, 31.08, 29.66, 29.24, 24.46, 24.42, 24.40, 24.37, 22.27, 22.21, 13.89,
13.84, 13.80; IR (Neat) νmax 3479, 3267, 3122, 3066, 2957, 2932, 2872, 2319, 2102, 1747, 1516, 1458,
1416, 1379, 1318, 1287, 1245, 1166, 1097, 1067, 1051, 1011, 913, 846, 795, 781, 743, 667, 608,
507;HRMS: m/z calculated for C74H116N6O20: 1408.8244, 1431.8137 [M +Na]+ Found 1431.8111 [M
+Na]+.
1,3,5-Tris[(4-(2,3,4,6-tetra-O-hexanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-1-
yl)methyl]benzene (16)
Colourless sticky solid; [α]D -8.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.37 (1H, s, CH Triazole), 7.35
(1H, s, PhH), 5.63 (2H, s, PhCH2), 5.23 (1H, t, J 9.5 Hz, H-3), 5.10 (1H, t, J 9.5 Hz, H-4), 4.99 (1H, t, J
9.4 Hz, H-2), 4.89 (2H, d, J 12.4 Hz, OCH2), 4.74 (2H, d, J 12.4 Hz, OCH2), 4.67 (1H, d, J 7.7 Hz, H-1),
4.19 (2H, m, H-6a & H-6b), 3.72 (1H, m, H-5), 2.27 (14H, m, (OCOCH2(CH2)3CH3)4), 1.55 (11H, m,
(OCOCH2CH2(CH2)2CH3)4), 1.25 (22H, m, (OCOCH2CH2(CH2)2CH3)4), 0.87 (16H, m,
(OCOCH2(CH2)3CH3)4); δC (100 MHz, CDCl3); 173.42, 172.81, 172.12, 144.30, 139.76, 130.55, 122.32,
100.28, 72.29, 70.95, 68.05, 63.05, 61.67, 48.98, 33.99, 33.96, 33.93, 33.90, 31.21, 31.17, 31.09, 24.48,
24

ACCEPTED MANUSCRIPT
24.41, 24.37, 22.29, 22.23, 16.67, 13.91, 13.85, 13.82; IR (Neat) νmax 3748, 2957, 2930, 2859, 1751,
1541, 1464, 1417, 1378, 1316, 1274, 1241, 1162, 1111, 1047, 913, 816, 764, 749, 609.
1,2,4,5-Tetrakis[(4-(2,3,4,6-tetra-O-hexanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-1-
yl)methyl]benzene (17)
Colourless sticky solid; [α]D -4.9 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.57 (1H, s, CH Triazole), 7.14
(1H, s, PhH), 5.67 (2H, d, J 15.2 Hz, PhCH2), 5.56 (2H, d, J 15.2 Hz, PhCH2), 5.24 (1H, t, J 9.5 Hz, H-
3), 5.12 (1H, t, J 9.7 Hz, H-4), 5.00 (1H, t, J 8.8, H-2), 4.87 (2H, d, J 12.5 Hz, OCH2), 4.78 (2H, d, J
12.5 Hz, OCH2), 4.68 (1H, d, J 7.9 Hz, H-1), 4.18 (2H, m, H-6a & H-6b), 3.74 (1H, m, H-5), 2.25 (10H,
m, (OCOCH2(CH2)3CH3)4), 1.55 (10H, m, (OCOCH2CH2(CH2)2CH3)4), 1.22 (22H, m,
(OCOCH2CH2(CH2)2CH3)4), 0.87 (16H, m, (OCOCH2(CH2)3CH3)4); δC (100 MHz, CDCl3); 173.48,
172.79, 172.12, 172.06, 144.83, 135.01, 132.28, 123.51, 100.44, 72.34, 72.12, 70.94, 68.03, 63.11, 61.52,
50.49, 33.97, 33.91, 31.56, 31.20, 31.17, 31.08, 30.90, 29.03, 24.48, 24.44, 24.40, 24.37, 22.63, 22.59,
22.27, 22.22, 14.09, 13.89, 13.84, 13.80; IR (Neat) νmax 3479, 3142, 2957, 2932, 2872, 2256, 1447, 1462,
1416, 1379, 1316, 1273, 1227, 1163, 1096, 1048, 1012, 913, 888, 845, 795, 735, 647, 604, 496.
1,2,4,5-Tetrakis[(4-(2,3,4,6-tetra-O-dodecanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-1-
yl)methyl]benzene (18)
Colourless sticky solid; [α]D -3.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.56 (1H, s, CH Triazole), 7.15
(1H, s, PhH), 5.71 (2H, d, J 15.2 Hz, PhCH2), 5.55 (2H, d, J 15.2 Hz, PhCH2), 5.23 (1H, t, J 9.5 Hz, H-
3), 5.11 (1H, t, J 9.7 Hz, H-4), 5.00 (1H, t, J 8.1, H-2), 4.89 (2H, d, J 9.6 Hz, OCH2), 4.81 (2H, d, J 9.6
Hz, OCH2), 4.67 (1H, d, J 8.0 Hz, H-1), 4.19 (2H, m, H-6a & H-6b), 3.70 (1H, m, H-5), 2.26 (10H, m,
(OCOCH2(CH2)9CH3)4), 1.57 (10H, m, (OCOCH2CH2(CH2)8CH3)4), 1.25 (113H, m,
(OCOCH2CH2(CH2)8CH3)4), 0.87 (21H, t, J 6.2 Hz, (OCOCH2(CH2)9CH3)4); δC (100 MHz, CDCl3);
173.50, 172.80, 172.14, 172.06, 135.00, 134.59, 131.35, 72.36, 72.11, 70.90, 67.99, 63.08, 61.51, 52.27,
25

ACCEPTED MANUSCRIPT
51.69, 50.51, 34.03, 33.97, 32.79, 31.92, 29.65, 29.60, 29.52, 29.46, 29.43, 29.37, 29.33, 29.15, 29.09,
25.74, 24.88, 24.80, 24.75, 22.69, 14.12; IR (Neat) νmax 2956, 2925, 2855, 2102, 1750, 1711, 1617, 1465,
1415, 1378, 1275, 1260, 1158, 1113, 1063, 913, 764, 749.
Tetrakis[(4-(2,3,4,6-tetra-O-hexanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-1-
yl)methyl]methane (19)
Colourless syrup; [α]D -18.9 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 8.15 (1H, s, CH Triazole), 5.23
(1H, t, J 9.4 Hz, H-3), 5.12 (1H, t, J 9.9 Hz, H-4), 5.01 (1H, t, J 8.2 Hz, H-2), 4.96 (1H, d, J 12.3 Hz,
CH2), 4.79 (1H, d, J 12.3 Hz, CH2), 4.69 (1H, d, J 7.9 Hz, H-1), 4.37 (2H, s, CH2), 4.20 (2H, d, J 2.6
Hz,H-6a &H-6b), 3.75 (1H, m, H-5), 2.34 (3H, t, J 7.4 Hz, OCOCH2(CH2)3CH3)4), 2.22 (8H, m,
OCOCH2(CH2)3CH3)4), 1.55 (10H, m, OCOCH2(CH2)3CH3)4), 1.26 (21H, m, OCOCH2(CH2)3CH3)4),
0.87 (15H, m, OCOCH2(CH2)3CH3)4); δC (100 MHz, CDCl3); 173.41, 172.81, 172.05, 143.65, 127.20,
100.00, 72.39, 72.18, 70.90, 68.03, 62.23, 61.61, 49.15, 46.57, 33.96, 33.91, 31.21, 31.18, 31.17, 31.09,
29.24, 24.47, 24.43, 24.39, 24.37, 22.28, 22.23, 13.89, 13.85, 13.80; IR (Neat) νmax 3267,3144, 2957,
2932, 2872, 2319, 1751, 1459, 1416, 1379, 1317, 1240, 1162, 1099, 1047, 913, 845, 797, 743, 667.
1,2,3,4,5,6-Hexakis[(4-(2,3,4,6-tetra-O-dodecanoyl-β-D-glucopyranosyloxymethyl)-1H-1,2,3-triazol-
1-yl)methyl]benzene (20)
Brown semi-solid; [α]D -4.4 (c = 0.2, CHCl3); δH (400 MHz, CDCl3); 7.35 (1H, s, CH Triazole), 7.14 (1H,
s, PhH), 5.89 (2H, d, J 15.4 Hz, PhCH2), 5.81 (2H, d, J 15.4 Hz, PhCH2), 5.22 (1H, t, J 9.6 Hz, H-3),
5.11 (1H, t, J 9.6 Hz, H-4), 4.97 (1H, t, J 8.9, H-2), 4.67 (2H, m, OCH2&H-1),4.25 (1H, d, J 11.6 Hz,H-
6a), 4.11 (1H, d, J 9.2 Hz, H-6b), 3.73 (1H, m, H-5), 2.30 (8H, t, J 7.4 Hz, OCOCH2(CH2)3CH3)4), 2.23
(12H, m, OCOCH2(CH2)3CH3)4), 1.55 (20H, m, OCOCH2(CH2)3CH3)4), 1.26 (44H, m,
OCOCH2(CH2)3CH3)4), 0.86 (32H, m, OCOCH2(CH2)3CH3)4); δC (100 MHz, CDCl3); 173.60, 172.79,
172.12, 172.00, 137.45, 100.74, 72.48, 72.04, 70.89, 67.99, 67.59, 63.15, 61.34, 48.00, 47.81, 33.99,
26

ACCEPTED MANUSCRIPT
33.94, 33.89, 31.31, 31.18, 31.10, 29.65, 24.47, 24.44, 24.36, 24.14, 22.65, 22.30, 22.65, 22.30, 22.25,
22.21, 13.87, 13.77; IR (Neat) νmax 3784, 3427, 2957, 2932, 2872, 2097, 1746, 1635, 1457, 1416, 1379,
1275, 1259, 1222, 1165, 1110, 1064, 1064, 1016, 844, 764, 750, 723, 692.
4.4 TEM analysis: Philips TECNAI electron microscope was used for obtaining transmission
micrographs at 120 Kv accelerating voltage. Compounds 15, 16, 17 and 18 were taken up in
hexane/heptanes/octane and aliquots were applied onto copper grids coated with carbon film (Quantifoil
on 200 square mesh copper grid of hole-shape R 2/2) and after allowing to dry was mounted on the
microscope for recording the micrographs.
4.5 Computational details: All the geometries were optimized using semi-empirical PM3 (Parameterized
Model number 3) method, using the Gaussian03 package, considering large size of glycol clusters. This
method has been reported to be helpful, reliable and applicable in the optimization studies of large
molecules, and save considerable computing time. PM3 method possesses higher computational
efficiency in modelling larger systems, as compared to ab initio and Density Functional Theory (DFT)
methods (which utilize longer time and computational power). PM3 provides improved description of the
interaction between non-bonded atoms (hydrogen bonds and steric effects), and represents a middle
pathway between the molecular mechanics (MM) method (giving mostly qualitative results) and ab initio
methods (time-consuming but providing quantitative results). PM3 method has been indicated to provide
insights into the structural details of dimers, polymeric structures and supramolecular systems and
providing information about the interactions amongst them. The applicability of this method in the
optimization studies of large molecules has been reported in previous studies, as it is reliable and saves
considerable computing time.90-94 PM3 method is utilized in modelling larger systems owing to its higher
computational efficiency, as compared to ab initio and Density Functional Theory (DFT) methods (which
utilize longer time and computational power). The interactions between non-bonded atoms (hydrogen
27

ACCEPTED MANUSCRIPT
bonds and steric effects) can be inferred by this method.90-94 Recently, we have reported the effectiveness
of this method in providing insights into the structural details of monomers and their dimeric structures
and supramolecular systems.43,61 Hence, all the geometries of 15, 16, 17 and their dimeric structures were
optimized using semi-empirical PM3 (Parameterized Model number 3) method,95-98 using the Gaussian03
package (see Supplementary Information). Initially, the geometry optimizations of monomers, 15, 16 and
17, were computed using PM3 method. The optimized geometries were employed for the construction of
dimers and thereafter, dimers were optimized. The dimerization energies were calculated in all the cases.
The interactions were observed carefully in all the structures, which are responsible for the thread-like
pattern in all the cases. The energy and geometric parameters used in the discussion are based on PM3
method unless otherwise specifically mentioned. However, it was not possible to extend calculation to
explain polymeric behaviour of the molecules.
4.6 MIC determination of the test compounds: Minimum inhibitory concentration (MIC) was carried
out as per previously described method.99 All three Gram positive strains, viz. Micrococcus luteus
MTCC-2470, Staphylococcus aureus MTCC-96 and Bacillus subtilis MTCC-121 were inoculated in 5 ml
MHB independently and kept for incubation at 30 °C for 6-8 h (to reach OD600 = 0.13). Antibiotics (100
µl) at a specific concentration were added in first well of 96-well micro titre plate and then exponentially
diluted. Bacterial inocula equivalent to the 0.5 McFarland standards were prepared and 100 µl was added
to give the final concentration of 5 x 105 cfu/ml, and incubated at 30 °C for 48 h. 20 µl of MTT dye (10
mg/ml wt/v in methanol) was added to each well and kept for incubation at 30 °C for 20 min. Bacterial
growth indicated by purple coloration adhered to cells. The antibiotic concentration in the well at which
no purple coloration observed, is the MIC of antibiotic. Similarly, the MIC of test compounds was also
determined. Ampicillin and amoxicillin were used as the positive control to compare results obtained
28

ACCEPTED MANUSCRIPT
from test compounds. Test assay, vehicle (DMSO) control, media control and cell control were done in
triplicates (during each experiment) to validate the results.
Acknowledgements: MT and NT thank the Council of Scientific and Industrial Research (CSIR) and the
Department of Science and Technology (DST), New Delhi, respectively, for financial support. We are
grateful to Dr Alan Haines, UEA, Norwich for his kind help with the preparation of this manuscript.
References
1. Huisgen, R. Angew. Chem. Int. Ed., 1963, 2, 565–598.
2. Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem., 2002, 114, 2708-2711.
3. Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem. Int. Ed., 2002, 41, 2596-
2599.
4. Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem., 2002, 67, 3057-3064.
5. Xu, L.; Li, Y.; Li, Y. Asian J. Org. Chem., 2014, 3, 582-602.
6. Sessler, J. L.; Cai, J.; Gong, H. -Y.; Yang, X.; Arambula, J. F.; Hay, B. P. J. Am. Chem. Soc., 2010,
132, 14058-14060.
7. Muthana, S.; Yu, H.; Cao, H.; Cheng, J.; Chen, X. J. Org. Chem., 2009, 74, 2928-2936.
8. Billing, J. F. Macrocyclic Carbohydrate/Amino Acid Hybrid Molecules: Synthesis and Evaluation as
Artificial
Receptors,
PhD
Thesis,
Lund
University,
2005
(http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=544383&fileOId=544384).
9. Bodine, K. D.; Gin, D. Y.; Gin, M. S. J. Am. Chem. Soc., 2004, 126, 1638-1639.
10. Diaz, D. D.; Punna, S.; Holzer, P.; McPherson, A. K.; Sharpless, K. B.; Fokin, V. V.; Finn, M. G. J.
Polym. Sci., Part A: Polym. Chem., 2004, 42, 4392-4403.
11. Binder, W. H.; Sachsenhofer, R. Macromol. Rapid Commun., 2007, 28, 15-54.
12. Kantheti, S.; Narayan, R.; Raju, K. V. S. N. J. Coat. Technol. Res., 2013, 10, 609-619.
29