Sugar-based novel chiral macrocycles for inclusion applications and chiral recognition

Article abstract of DOI:10.1016/j.carres.2015.12.006

A convergent template assisted synthesis of sugar-based chiral macrocycles has been achieved. The host-guest inclusion studies have revealed significant interactions of the synthesized macrocycle with primary over secondary ammonium salt. The chiral macrocyle also discriminates between D- and L-phenylalanine methyl ester hydrochlorides as revealed by ¹H NMR spectral studies on the mixture of the host and the guest molecules.

Full text of DOI:10.1016/j.carres.2015.12.006

Accepted Manuscript
Title: Sugar-based novel chiral macrocycles for inclusion applications and
chiral recognition
Author: Ankita Singh, Vinod Khatri, Shashwat Malhotra, Ashok K. Prasad
PII:
S0008-6215(15)00390-0
DOI:
Reference:
http://dx.doi.org/doi: 10.1016/j.carres.2015.12.006
CAR 7106
To appear in:
Carbohydrate Research
Received date: 12-9-2015
Revised date: 10-12-2015
Accepted date: 13-12-2015
Please cite this article as: Ankita Singh, Vinod Khatri, Shashwat Malhotra, Ashok K. Prasad,
Sugar-based novel chiral macrocycles for inclusion applications and chiral recognition,
Carbohydrate Research (2015), http://dx.doi.org/doi: 10.1016/j.carres.2015.12.006.
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Sugar-based Novel Chiral Macrocycles for Inclusion Applications and
Chiral Recognition
Ankita Singh, Vinod Khatri, Shashwat Malhotra and Ashok K. Prasad*
Bioorganic Laboratory, Department of Chemistry, University of Delhi, Delhi-110007, India
Highlights
1. A convergent template assisted synthesis of sugar-based chiral macrocycles has been
described.
2. The host-guest inclusion studies have revealed selective significant interactions of the
synthesized macrocycle with the primary ammonium salt compared to the secondary
salt.
3. The synthesized chiral macrocyle also discriminates between D- and L-phenylalanine
methyl ester hydrochlorides as revealed by 1H NMR spectral studies on the mixture of
the host and the guest molecules.
Graphical Abstract
A highly convergent template assisted synthesis of chiral macrocycles, which are cyclic homodimer
of azido-alkyne furanose sugar derivatives, has been successfully achieved and evaluated for host-
guest inclusion complex formation ability using benzyl- and dibenzyl ammonium perchlorate salt as
guests. One of the chiral macrocyles showed recognition for D- and L-phenylalanine methyl ester
hydrochloride salts.
1
Page 1 of 23

A convergent template assisted synthesis of sugar-based chiral macrocycles has been
achieved. The host-guest inclusion studies have revealed significant interactions of the
synthesized macrocycle with primary over secondary ammonium salt. The chiral macrocyle
also discriminates between D- and L-phenylalanine methyl ester hydrochlorides as revealed
by 1H NMR spectral studies on the mixture of the host and the guest molecules.
Keywords: Macrocycle, Click reaction, Template assisted, Benzyl ammonium perchlorate,
Phenylalanine, Chiral recognition.
*Corresponding Author: Bioorganic Laboratory, Department of Chemistry, University of
Delhi, Delhi-110007, India, E-mail: ashokenzyme@gmail.com. Tel. 011-27662486.
1. Introduction
Sugar-based macrocycles are of immense importance owing to their ease of
accessibility from natural resources, multifunctional nature, presence of geometrical
constraints and also due to the chiral nature of the sugar which provides key
specificities in molecular recognition processes.1,2 Like naturally occurring sugar-
based macrocycles, their synthetic counterparts are also interesting because of their
complex structure and synthetic challenges. They have diverse applications as
supramolecular architectures,3 medicines,4 biomimetic receptors,5 molecular pores,6
chiral recognition agents,7 etc.
Recently, some sugar-based macrocycles with triazole linkage have been
synthesized involving copper catalyzed alkyne-azide cycloaddition reaction
(CuAAC).8-14 These types of macrocycles find great applications as inclusion hosts
and as pharmacophores.15 In course of Cn-symmetric synthesis, cyclodimerization /
cyclooligomerization of azido-alkyne sugars or synthesis of carbohydrate-peptide
2
Page 2 of 23

hybrids have been reported using glucopyranosides and furanosides.8,9,16,17 The
synthesis of Cn-symmetric macrocycles is a challenging task often due to insufficient
product yield and to overcome the problem different approaches utilizing π-π stacking,
π-donor / π-acceptor interactions, hydrogen bonding of non-metallic templates like
simple aromatic compounds has been tried.4,9,11,16,18-21
In the present work, we have designed and developed a simple and facile template
assisted synthesis of chiral sugar-based macrocycles which are homodimer of azido-alkyne
sugars derived from 2,5-anhydro-D-mannitol (Fig. 1). Interestingly, one of the synthesized
macrocycles exhibited appreciable interaction with the primary ammonium salt, i.e. benzyl
ammonium perchlorate over dibenzyl ammonium perchlorate salts and also showed chiral
discrimination between L- and D-phenylalanine methyl ester hydrochlorides.
2. Result and Discussion
2.1 Synthesis
The synthesis of chiral sugar-based macrocycles
5
and
7 has been illustrated in
Schemes 1 and 2. The 2,5-anhydro-D-mannitol (
1
) was synthesized from
commercially available D-glucosamine hydrochloride in 80 % overall yields in three
steps, which was again converted to the partially benzylated furanoside, i.e. 3,4-di-O-
benzyl-2,5-anhydro-D-mannitol (2) via its perbenzylation, partial acetolysis followed
by deacetylation using NaOMe-methanol in 70 % overall yields following literature
procedure 22
benzyl-1,6-di-O-propargyl-2,5-anhydro-D-mannitol (
tetra-butyl ammonium hydrogen sulphate as phase transfer catalyst in 75 % yields
.
In a parallel set of reactions compound
2 was converted to 3,4-di-O-
3
) using propargyl bromide and
N-
3
Page 3 of 23

and to 1,6-diazido-3,4-di-O-benzyl-2,5-anhydro-D-mannitol (
4) by mesylation using
MsCl-pyridine followed by azidation with NaN3 in DMF in 77 % yields (Scheme 1).
The synthesis of macrocycle
5 was attempted through cycloaddition reaction between
sugar alkyne
3 and azide 4
using conventional click condition,23 i.e. in the presence of
CuSO4.5H2O and sodium ascorbate in t-butanol-water-THF (1:1:2; 1 mL / 100 mg of
equimolar mixture of compounds and ). The reaction led to the formation of a
complex mixture and even after repeated column-chromatography the desired
macrocycle was obtained only in 6 % yield in 28 h (entry 1, Table 1). To improve
3
4
5
the yield, the click reaction was performed under same condition in the presence of
ethylene diamine dihydrochloride as template to assist the macrocyclization, but it
does not led to any improvement in the efficiency of the reaction (entry 2, Table 1).
The use of S-phenyl ethyl ammonium acetate as template instead of ethylene diamine
dihydrochloride in macrocyclization reaction resulted in three fold improvement in the
yield of compound
5 along with the decrease in the reaction time (entry 3, Table 1).
The improvement in yield of macrocycle formation could be due to the pre-
organization of the azide and the alkyne substrates by virtue of the interaction of
ammonium ion of the template with different hydrogen bond acceptor sites of both the
sugar units
3 and 4 as well as with the resulted triazole ring of the macrocycle 5. In
addition, the interaction of phenyl group of the template with the benzyl groups of two
sugar moieties via π-π stacking may also helps in holding the two reacting sugar units
in closer proximity. The yield of macrocyclization affording compound
5 was further
improved by six fold with respect to entry 1 and almost 1.7 fold with respect to entry 3
in Table 1 by carrying out the reaction at 20 times higher dilution of t-butanol-water-
4
Page 4 of 23

THF (1:1:2 ratio), i.e. at 20 mL solvent / 100 mg of equimolar mixture of compounds
and (entry 4, Table 1). The enhancement in yield at higher dilution may be
3
4
attributed to the enhancement of the opportunity for intramolecular azide-alkyne
coupling over intermolecular coupling.24 Thus in a typical reaction an equimolar
mixture of sugar alkyne
3
and azide
4
, CuSO4.5H2O, sodium ascorbate, S-phenyl ethyl
o
ammonium acetate salt and t-butanol-water-THF (1:1:2) was stirred at 30 C for 6 h.
On completion, the reaction mixture was dried under reduced pressure and the product
was extracted with chloroform. The residue obtained by removal of solvent was
purified by silica gel column chromatography to afford the pure macrocycle
5 as off-
white solid in 30 % yield. The use of R-phenyl ethyl ammonium acetate salt instead of
its S-enantiomer as a template in the macrocyclization reaction proved to be less
efficient as there was minor dip in the yield of the reaction (entry 5, Table 1).
The methodology developed for the synthesis of macrocycle
synthesis of a novel sugar-based chiral macrocycle having phenyl linker between
two bis-triazolyl-sugar units. Thus, the coupling of azido sugar with bis-triazolyl-
sugar unit under optimized condition (as in entry 4, Table 1) afforded macrocycle
as yellowish solid in 28 % yield. The bis-triazolyl-sugar unit , in turn was obtained
from dialkyne sugar in two steps, i.e. by its coupling with 4-
5 was further used for the
7
4
6
7
6
3
trimethylsilylethynylphenyl azide in the presence of CuSO4.5H2O, sodium ascorbate
followed by desilylation of the alkyne moiety of the coupled product with TBAF in
o
DMF at 30 C in 77 % overall yields (Scheme 2).25 The aim for the incorporation of
phenyl linkers in the homodimer macrocycle
7 was to enhance the electron density in
the ring by placing a π donor linker in the cavity.
5
Page 5 of 23

The structure of the synthesized macrocycle
5 and the intermediates 1, 2, 3, 4 and 6
1
were confirmed by its IR, H-, 13C NMR, HSQC, DEPT-135 and HRMS spectral data
analysis. The structure of the macrocycle
HRMS spectral data analysis. The 13C NMR spectrum and further studies on
7
was confirmed by its UV, IR, 1H NMR and
macrocycle
7 could not be taken up due to its highly insoluble nature in any of the
deuterated solvents or in TFA.
The structures of known compounds
1 and 2 were further confirmed by comparison of
1
their physical and spectral (IR, H, 13C NMR, and HRMS) data with those reported in
the literature.22 Compound
5 was found to be chiral and has shown specific rotation,
[α]D30 = +40 (c 0.1 CHCl3).
2.2. 1H NMR Interaction Studies
The synthesis of sugar-based macrocycles
5 and 7 assisted by S-phenyl ethyl
ammonium salt as template indicated about the possible interactions of ammonium ion
with the electron rich core (hydrogen bond acceptor) of the compounds. This
observation prompted us to perform host-guest inclusion studies on the synthesized
macrocycle
5
with ammonium salts, such as benzyl- or dibenzyl ammonium
1
perchlorate salts. The comparison of H NMR spectrum of equimolar mixture of the
1
macrocycle
5
and the benzyl ammonium perchlorate salt with the individual H NMR
spectrum of the macrocycle
interactions (Fig. 2).
5
and that of the salt in CD3CN has revealed noteworthy
+
The three protons of the NH3 group of the guest salt appearing at δ 6.67 showed a
downfield shift and appeared at δ 6.82 (∆ δ 0.15 ppm) together with the slight
6
Page 6 of 23

1
broadening of this peak in the H NMR spectrum of the host-guest complex. The
+
1
broadening in peaks of the NH3 group of guest salt in the H NMR spectrum was
attributed to the hydrogen bonding of its protons with nitrogen atom(s) of the triazole
rings and with oxygen atom(s) present in the electron rich cavity of macrocycle 5. This
is complimented with the remarkably downfield shift of ∆ δ 0.16 ppm of the triazole
1
ring protons, i.e. C-9H and C-10H appearing at δ 7.66 in the H NMR spectrum of
macrocycle
5 resonated at δ 7.82 in the host-guest complex. The downfield shift in
protons of the triazole ring is due to the partial positive charge created in the ring by
virtue of the hydrogen bond formation between the nitrogen atom(s) of the triazole
+
rings with the protons of the NH3 group of the guest salt. Furthermore, the CH2
protons of the benzyl moiety of perchlorate salt appearing at δ 4.14 shows a slight
1
upfield shift of ∆ δ 0.03 ppm in the H NMR spectrum of the host-guest complex,
because of the anisotropic effect of benzylic phenyl groups of macrocycle 5. The
spatial interactions of the CH2 protons of the guest benzyl ammonium perchlorate salt
with the benzylic CH2 and other protons (C-1'H, C-6'H, C-7H, C-8H, C-2H, C-5H) of
the macrocycle
5 was observed in the NOESY NMR spectrum of the host-guest
complex (Fig. S12, SI), which explains that the guest molecule is in the close
proximity with the host macrocycle. In addition, change in splitting patterns of other
1
peaks has also been observed in the H NMR spectrum of the host-guest assembly
1
with respect to the individual H NMR spectrum of the macrocycle
5 and the
perchlorate salt.
The formation of host-guest inclusion complex was further ascertained by using
HRMS spectrometry. The calculated value for the [M-ClO4]+ ion of the complex of
macrocycle
5 and the guest ammonium salt is 922.4498 and the observed value was
found to be 922.4479, which confirms the formation of host guest assembly (Fig. S15,
7
Page 7 of 23

SI). Further, the association constant of the complex was calculated considering the
downfield shift in the triazole ring protons of host macrocycle present at δ 7.66 with
5
1
respect to the chemical shift values of the same protons in the H NMR spectrum of
1
the host-guest complex taken at different molar ratios (Fig. 3). On the basis of the H
NMR titration experiments as above, the association constant Ka was found to be 45.9
M-1 (Fig. 4), which indicated the affinity of host macrocycle
donor primary ammonium ion.
5 towards hydrogen bond
The possibility of formation of host-guest assembly between macrocycle
5 and
1
secondary amine, dibenzyl ammonium perchlorate salt was studied using H NMR
1
spectroscopy. There was negligible change in the H NMR spectrum recorded for the
equimolar mixture of the macrocyclic host
the individual spectrum of two compounds (Fig. S16, SI). This reveals that the core of
the macrocyclic host is small enough to accommodate salts derived from primary
5 and the secondary ammonium ion, and in
5
amines only. In addition the centre of hydrogen bond donor is less in secondary amine
than in primary amine, which will also lead to insufficient interaction between the host
and the dibenzyl ammonium perchlorate salt.
The macrocyclic host
5 is chiral, which was confirmed by its specific rotation
measurement. The chiral recognition capability of the cyclic host molecule was
1
explored by recording H NMR spectrum of equimolar mixture of host
5 and D / L
phenylalanine methyl ester hydrochloride salt and by its comparison with the
1
individual H NMR spectrum of macrocycle
5 and D- & L- hydrochlorides in CDCl3
(Fig. 5). The host-guest interaction of macrocycle
5 with L- phenylalanine methyl
8
Page 8 of 23

ester hydrochloride salt was noteworthy. An upfield shift of ∆ δ 0.12 ppm in the
diastereotopic CH2 protons of L-phenylalanine methyl ester hydrochloride appearing
1
at δ 3.39 has been observed in the H NMR spectrum of the host guest assembly, due
to the anisotropic effect of phenyl rings present in host macrocycle
5. The protons of
triazole ring of macrocyclic host appearing at δ 7.71 shifted downfield by ∆ δ 0.18
5
ppm in the 1H NMR spectrum of the host guest assembly. The change in the chemical
1
shift position and the shape of peak of some other protons in the H NMR spectrum of
the host-guest assembly has also been observed with respect to the individual
spectrum, but it cannot be distinguished because of the overlapping of peaks.
Although, there was no appreciable change in the chemical shift values of protons of
host-guest assembly of D- phenylalanine methyl ester hydrochloride and macrocycle
1
5
, as compared to their individual H NMR spectrum, but the shape and the splitting
pattern of diastereotopic protons of amino acid was clearly visible. This suggests that
the macrocyclic host interacts differently with D- / L- phenylalanine methyl ester
5
hydrochloride or in other words it is able to discriminate between D- and L-amino
acids (Fig. 5). Further, confirmation of the interactions between macrocycle 5 and L-
phenylalanine methyl ester hydrochloride / D-phenylalanine methyl ester hydrochloride have
been accomplished with the help of a geometrically optimized structures using hybrid
Density Functional Theory (DFT). The energy minimized structure of macrocycle 5 and L-
phenylalanine methyl ester hydrochloride complex supports hydrogen bonding and π-π
interactions between host macrocycle and guest amino acid salt while macrocycle 5 and D-
phenylalanine methyl ester hydrochloride complex does not support any such interactions,
which clearly indicate the chiral discrimination of the two esters (Fig. 6 and 7).
9
Page 9 of 23

3. Conclusion
In conclusion, we have successfully accomplished a highly efficient template
assisted convergent synthesis of sugar-based chiral macrocycles
5 and 7. To the best of
our knowledge, it is the first example of utilization of two primary hydroxyl groups of
the furanose sugar to provide adequate symmetry to the synthesized triazole linked
macrocyclic compound. The discovery of S-phenyl ethyl ammonium perchlorate salt
as template for macrocyclisation reaction led us to reveal the host-guest inclusion
chemistry of the macrocyclic compound
5. The inclusion chemistry of the host
macrocycle is very specific and it recognizes benzyl ammonium perchlorate salt over
dibenzyl ammonium perchlorate salt. This result prompted us to study the chiral
recognition potential of the macrocyclic host
discriminates between D- and L- phenylalanine methyl ester hydrochlorides very well.
The synthesised macrocyclic system could find potential applications as artificial
5, which led to the finding that it
5
receptor and as chiral recognition agent.
4. Experimental Section
4.1. General
Melting points were determined on Buchi M-560 instrument. The IR spectra were
recorded on a Perkin-Elmer model 2000 FT-IR spectrometer by making KBr disc for solid
samples and thin film for oils. The 1H and 13C NMR spectra were recorded at Jeol alpha-400
spectrometer at 400 and 100.6 MHz, respectively using TMS as internal standard. The
chemical shift values are on  scale and the coupling constants (J) are in Hz. The mass
spectra recording have been done on a micro TOF-Q instrument from Bruker Daltonics,
Bremen and 6520 Q-TOF instrument from Agilent Technologies on ESI positive mode.
Optical rotations were measured on Rudolph Autopol II automatic polarimeter using light of
546 nm wavelength. Absorption spectra were recorded between 250 and 700 nm using
10
Page 10 of 23

Pelkin-Elmer UV/Vis spectroscopy cell (1 cm). Analytical TLCs were performed on pre-
coated Merck silica-gel 60F254 plates; the spots were detected either under UV light or by
charring with 4 % alcoholic H2SO4. Silica gel (100-200 mesh) was used for column
chromatography.
4.2. Synthesis of 3,4-di-O-benzyl-1,6-di-O-propargyl-2,5-anhydro-D-mannitol (3)
To a solution of compound 2 (200 mg, 0.58 mmol) in 20 mL toluene:20 % aq. NaOH (1:1) in
a round bottom flask, tetrabutyl ammonium hydrogen sulphate (191 mg, 0.58 mmol) was
added under stirring. Propargyl bromide (0.184 mL, 1.16 mmol) was added into the reaction
o
mixture and the stirring continued at 30 C for 3 h. The progress of reaction was monitored
by TLC and after completion compound was extracted from the reaction mixture with ethyl
acetate (3 x 50 mL). Combined organic layer was washed with saturated NaCl solution, dried
over anhydrous Na2SO4 and then organic layer was concentrated at reduced pressure. The
crude product thus obtained was purified by column chromatography over silica gel using
ethyl acetate-petroleum ether as an eluent. Pure compound 3 was obtained as a white sticky
solid in 75 % yield (183 mg). [α]D27 : +6.1 (c 0.1 CHCl3); IR (cm-1, film) 2866, 1085, 740; 1H
NMR (400 MHz, CDCl3): 7.25-7.36 (m, 10H, 2 x PhCH2), 4.50-4.57 (m, 4H, 2 x PhCH2),
4.16-4.17 (m, 6H, 2 x CH≡C-CH2, C-2H, C-5H), 4.05 (d, 2H, J = 4.0 Hz, C-3H, C-4H), 3.63
13
(d, 4H, J = 5.6 Hz, C-1H and C-6H), 2.38 (t, 2H, J = 5.2 Hz, 2 x CH≡C); C NMR (100.6
MHz, CDCl3): δ 137.8 (C), 128.4 (CH), 127.8 (CH), 84.6 (CH), 81.4 (CH), 79.4 (C), 74.6
(CH), 71.9 (CH2), 69.6 (CH2), 58.5 (CH2); HRMS (ESI) m/z calcd. for C26H29O5 [M+H]+
421.2010, found 421.2011.
4.3. Synthesis of 1,6-diazido-3,4-di-O-benzyl-2,5-anhydro-D-mannitol (4)
11
Page 11 of 23

o
Compound 2 (1 g, 2.906 mmol) dissolved in 10 mL pyridine, was cooled to -10 C followed
by dropwise addition of mesyl chloride (0.49 mL, 6.39 mmol). The reaction mixture was
o
stirred at 30 C for 4 h. The progress of the reaction was monitored by TLC. After
completion, the compound from of reaction was extracted with ethyl acetate (3 x 100mL).
The combined organic layer was dried over anhydrous Na2SO4 and evaporated under reduced
pressure. Dimesylated sugar obtained was purified by column chromatography over silica gel
using chloroform- methanol as an eluent. The pure dimesylated sugar obtained was directly
used for the next step. A mixture of dimesyl sugar (1 g, 2.13 mmol), sodium azide (0.35 g,
o
5.33 mmol) and DMF (15 mL) was stirred at 100 C for 6 h in a round bottomed flask. The
progress in the reaction was monitored with TLC. After completion, the reaction mixture was
filtered and the mother liquor was evaporated. The crude residue was then purified by silica
gel column chromatography using ethyl acetate-petroleum ether as the eluting solvents.
Compound 4 was obtained as colourless oil in overall yields of 77 % (722 mg). [α]D24 : +71.5
1
(c 0.1 CHCl3); IR (cm-1, film): 2099, 1402 1084, 741; H NMR (400 MHz, CDCl3): δ 7.24-7.38
(m, 10H, 2 x PhCH2), 4.50-4.54 (m, 4H, 2 x PhCH2), 4.19 (s, 2H, C-2H, C-5H), 4.01 (d, 2H, J = 4.4
Hz, C-3H, C-4H), 3.36 (d, 4H, J = 6.0 Hz, C-1H, C-6H); 13C NMR (100.6MHz, CDCl3): δ 137.2
(C), 128.5 (CH), 128.0 (CH), 127.7 (CH), 84.5 (CH), 81.5 (CH), 72.2 (CH2), 52.0 (CH2); HRMS
(ESI) m/z calcd. for C20H23N6O3 [M+H]+ 395.1826 , found 395.1826.
4.3. Synthesis of macrocyclic compound 5
A mixture of compound 3 (200 mg, 0.47 mmol), compound 4 (187 mg, 0.47 mmol),
CuSO4.5H2O (48 mg, 0.194 mmol), sodium ascorbate (77 mg, 0.388 mmol) and S-phenyl
ethyl ammonium acetate (57 mg, 0.47 mmol) in t-BuOH-water-THF (80 mL, 1:1:2 ratio) was
stirred at 30 oC for 6 h. The progress of the reaction was monitored using TLC (3 % MeOH-
CHCl3). After completion, the reaction mixture was completely dried over reduced pressure
by co-evaporating with toluene (3 x 2 mL). The residue thus obtained was dissolved in
12
Page 12 of 23

chloroform, filtered and evaporated to dryness under reduced pressure. The residue was
purified by column chromatography using silica gel as stationary phase and chloroform-
methanol as the eluting solvents. Pure compound 5 was obtained as off-white solid in 30 %
yield (122 mg). M.P.: 92-94 oC; [α]D30: +40 (c 0.1 CHCl3); IR (cm-1, film): 2924, 1733, 1237,
1
777; H NMR (400 MHz, CD3CN): δ 7.66 (s, 2H, C-9H, 10H), 7.28-7.38 (m, 20H, 4 x
PhCH2), 4.64 (s, 4H, 2 x PhCH2), 4.42-4.56 (m, 14H, 2 x PhCH2, C-7H, C-8H, C-1'H, C-6'H,
C-2H, C-5H), 4.07 (s, 2H, C-3H, C-4H), 3.99-4.01 (m, 2H, C-2'H, C-5'H), 3.87-3.88 (m, 2H,
C-3'H, C-4'H), 3.55-3.64 (m, 4H, C-1H, C-6H); 13C NMR (100.6MHz, CD3CN): δ 146.9 (C),
139.2 (C), 138.8 (C), 129.4 (CH), 129.3 (CH), 129.0 (CH), 128.9 (CH), 128.8 (CH), 128.6
(CH), 124.7 (CH), 86.0 (CH), 85.2 (CH), 82.8 (CH), 82.0 (CH), 72.9 (CH2), 72.6 (CH2), 71.6
(CH2), 64.9 (CH2), 53.01 (CH2); HRMS (ESI) m/z calcd for C46H51N6O8 [M+H]+ 815.3763 ,
found 815.3764.
4.4. Synthesis of bis-triazolyl-sugar (6)
A mixture of compound 3 (500 mg, 1.19 mmol), 4-azido phenyl TMS acetylene (520 mg,
2.38 mmol), CuI (4 mg, 0.21 mmol) in THF-ethanol-water (1:1:1, 6 mL) in a round bottom
flask was stirred at 30 oC for 24 hrs. The progress of the reaction was monitored by TLC (1 %
MeOH-CHCl3). After completion of the reaction, solvent was removed under reduced
pressure. The silylated sugar (250 mg, 0.29 mmol) was then dissolved in THF (25 mL),
o
cooled to 0 C followed by the addition of TBAF (0.505 mL, 0.50 mmol). The reaction
mixture was stirred for 20 min. The progress of the reaction was monitored by TLC (2 %
MeOH-CHCl3). After completion, the reaction mixture was passed through silica pad;
washed initially three times with CHCl3 (3 x 50 mL) then with 50 % mixture of CHCl3-
MeOH (2 x 50 mL). The organic layer was dried over anhydrous Na2SO4 and evaporated
under reduced pressure. The compound 6 was obtained as yellow solid in overall yields of 77
% (195 mg). M.P.: 161.3-163.2 oC; [α]D25: +17.3 (c 0.1 CHCl3), IR (cm-1, film): 2866, 1606,
13
Page 13 of 23

1091, 840; 1H NMR: δ 7.93(s, 2H, C-9H, C-10H), 7.62 (dd, 8H, J = 22 Hz, 2 x CH≡C-Ph),
7.23-7.31 (m, 10H, 2 x PhCH2), 4.76 (s, 4H, 2 x PhCH2), 4.53 (s, 4H, C-7H, C-8H), 4.24 (d,
2H, J = 4 Hz, C-2H, C-5H), 4.06 (d, 2H, J = 4 Hz, C-3H, C-4H), 3.69 (d, 4H, J = 4 Hz, C-
13
1H, C-6H), 3.18 (s, 2H, CH≡C-); C NMR (100.6 MHz, CDCl3): δ 146.4 (C), 138.0 (C),
137.1 (C), 133.9 (C), 128.8 (CH), 128.2 (CH), 128.1 (CH), 123.0 (C), 120.9 (CH), 120.5
(CH), 82.6 (CH), 82.1 (CH), 79.4 (CH), 77.0 (CH), 72.3 (CH2), 71.2 (CH2), 65.3 (CH2);
HRMS (ESI) m/z calcd. for C42H39N6O5 [M+H]+ 707.2976, found 707.2966.
4.5. Synthesis of macrocyclic compound 7
A mixture of compound 4 (90 mg, 0.15 mmol), compound 6 (160 mg, 0.14 mmol),
CuSO4.5H2O (17 mg, 0.05 mmol), sodium ascorbate (23 mg, 0.11 mmol), S-phenyl ethyl
ammonium acetate (17 mg, 0.14 mmol) was dissolved in t-BuOH-water-THF (40 mL, 1:1:2
ratio) and stirred at 30 oC for 6 h. The progress of the reaction was monitored by TLC. After
completion of reaction, the solvent was evaporated under reduced pressure. The compound
was purified over silica gel column chromatography using CHCl3-MeOH as elutent. The
macrocycle 7 was obtained a yellowish solid in 28 % yield (70 mg). M. P.: 242-244 oC; UV
1
(λmax, CHCl3): 235 nm; IR (cm-1, film): 2922, 1636, 1500, 1103, 739; H NMR (400 MHz,
CDCl3): δ 8.0 (s, 2H, C-9H, C-10H), δ 7.85 (d, 4H, J = 8.8 Hz, =C-Ph-N-), 7.76 (s, 2H, C-
9'H, C-10'H), 7.65 (d, 4H, J = 8.8 Hz, =C-Ph-N-), 7.25-7.42 (m, 20H, 4 x PhCH2), 4.78 (s,
4H, 2 x PhCH2), 4.40-4.66 (m, 12H, C-7H, C-8H, 2 x PhCH2, C-2H, C-5H, C-3H, C-4H),
4.22-4.23 (m, 2H, C-2'H, 5'H), 4.00-4.06 (m, 6H, C-1'H, C-6'H, C-3'H, C-4'H), 3.64-3.71 (m,
4H, C-1H, C-6H). HRMS (ESI) m/z calcd. for C62H61N12O8 [M+H]+ 1101.4730, found
1101.4730.
Acknowledgement
14
Page 14 of 23

Authors would like to thank Lena Kaufmann, Freie Universität Berlin, Germany and
Dr. Amitava Das, NCL Pune India for their assistance in NMR titration studies;
Professor DS. Rawat and Dr. Prija Ponnan, Department of Chemistry, University of
Delhi for making available the computational facilities acquired from the grant
(project No. 02(0049)/12/EMR-II) of CSIR, New Delhi and Professor RK Sharma and
Dr. Garima Gaba, Department of Chemistry, University of Delhi for symmetry
calculation. The financial assistances from DU-DST purse grant, DU R&D grant to
strengthen research and development and DRDO CARS Project with CFEES are
highly acknowledged. AS acknowledges the financial support from DRDO New Delhi
for junior research fellowship; VK and SM acknowledge the financial support from
CSIR, New Delhi for senior research fellowship and senior research associate-ship,
respectively.
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Fig. 1. Template assisted synthesis of chiral sugar-based macrocycles and their interaction
with ammonium ion.
Residual CD3CN
CH2
( )
+
NH3
( )
CH2
C- 9H, 10H
+
NH3
( )
C- 9H, 10H
18
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Fig. 2. Stacked partial 1H NMR spectra (400 MHz, CD3CN) of (a) benzyl ammonium
perchlorate salt, (b) mixture of macrocycle 5 and guest salt in 1:1 ratio and (c) macrocycle 5.
Fig. 3. Stacked partial 1H NMR spectra (400 MHz, CD3CN) of macrocycle
5 (host, 9.8
mM solution) and benzyl ammonium perchlorate (guest, varying concentration from 2
mM to 500 mM).
Ka = 45.9 M-1
Cguest (mM)
19
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Fig. 4. Graph represents the change in the downfield shift of the triazole ring protons
of host
5 with the increase in concentration of guest molecule, i.e. benzyl ammonium
perchlorate salt. The Ka has been calculated from B-N equation.26
(a)
D-Phenylalanine
Residual peak CDCl3
CH2
methyl ester
hydrochloride
CH
(b)
(c)
L-Phenylalanine
methyl ester
hydrochloride
CH2
CH
Macrocycle 5+ D-
Phenylalanine
methyl ester
CH2
hydrochloride
C-9 H, 10 H
Macrocycle 5+ L-
Phenylalanine
methyl ester
(d)
(e)
CH2
CH
hydrochloride
C-9 H, 10 H
C-9 H, 10 H
1
Fig. 5. Stacked partial H NMR spectra (400 MHz, CDCl3) (a) D-phenylalanine
methyl ester hydrochloride, (b) L-phenylalanine methyl ester hydrochloride, (c)
mixture of macrocycle
5 and D-phenylalanine methyl ester salt, (d) mixture of
macrocycle and L-phenylalanine methyl ester salt, (e) macrocycle 5.
5
Fig. 6: An energy minimized model presenting geometry optimization of macrocycle
and L-phenylalanine methyl ester hydrochloride. The present configuration revealed
5
the interaction of ammonium group of amino acid via hydrogen bonding with the
nitrogen atom of triazole ring of host. he π-π interaction between the phenyl group of
20
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amino acid salt with the host triazole ring triggers such hydrogen bonding between
host-guest complex. This resulted in the downfield shift of triazole proton of host and
upfield shift in the -CH proton of the guest molecule in 1H NMR (see Fig. 5).
Fig. 7: An energy minimized model presenting geometry optimization of macrocyle
5
and D-phenylalanine methyl ester hydrochloride, it does not reveal interaction
between the two moieties.
Scheme 1. Synthesis of macrocycle 5
21
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Scheme 2. Synthesis of macrocycle
7
Table 1. Optimization of macrocyclization reaction for the synthesis of macrocycle
5
Entry
Solvent / 100 mg of
equimolar mixture of
compds. 3 and 4
1 ml
Template
Reaction
time(h)
Yield (%)
1
-
28
6
2
3
1ml
1ml
28
6
15
18
(S)
4
20ml
6
30
(S)
22
Page 22 of 23

5
20ml
6
28
(R)
23
Page 23 of 23