Preparation of dendritic carboranyl glycoconjugates as potential anticancer therapeutics

Article abstract of DOI:10.1039/d0ra07264h

A series of carborane-appended glycoconjugates containing three and six glucose and galactose moieties have been synthesizedviaCu(i)-catalyzed azide-alkyne [3 + 2] click cycloaddition reaction. The carboranyl glycoconjugates containing three glucose and g

Full text of DOI:10.1039/d0ra07264h

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Preparation of dendritic carboranyl
glycoconjugates as potential anticancer
Cite this: RSC Adv., 2020, 10, 34764
therapeutics†
Biswa Ranjan Swain,ab Chandra Sekhara Mahanta,a Bibhuti Bhusan Jena,a
b
c
a
*
Swaraj Kumar Beriha, Bismita Nayak, Rashmirekha Satapathy
b
*
and Barada P. Dash
A series of carborane-appended glycoconjugates containing three and six glucose and galactose moieties
have been synthesized via Cu(I)-catalyzed azide–alkyne [3 + 2] click cycloaddition reaction. The carboranyl
glycoconjugates containing three glucose and galactose moieties were found to be partially water soluble
whereas increasing the number to six made them completely water soluble. The evaluation of cytotoxicities
and IC50 values of newly synthesized carboranyl glycoconjugates was carried out using two cancerous cell
lines (MCF-7 breast cancer cells and A431 skin cancer cells) and one normal cell line (HaCaT skin epidermal
cell line). All carboranyl glycoconjugates showed higher cytotoxicities towards cancerous cell lines than the
normal cell line. Carboranyl glycoconjugates containing three glucose and galactose moieties (compounds
15 and 17) were found to be more cytotoxic than the glycoconjugates containing six glucose and galactose
moieties (compounds 19 and 21). Moreover, administration of 100 mM concentrations of compounds 15 and
17 inhibited up to 83% of MCF-7 breast cancer cells and up to 79% A431 skin cancer cells. However,
administration of similar concentrations of carboranyl glycoconjugates could inhibit only up to 35–45%
of HaCaT normal epidermal cells. Thus, due to the higher cytotoxicities of dendritic carboranyl
glycoconjugates towards cancer cells over healthy cells, they could potentially be useful for bimodal
treatment of cancer such as chemotherapy agents and boron neutron capture therapy (BNCT) agents as
well.
Received 24th August 2020
Accepted 10th September 2020
DOI: 10.1039/d0ra07264h
rsc.li/rsc-advances
cancer via boron neutron capture therapy (BNCT).5,6 For an
effective boron neutron capture therapy, the required number
of 10B atoms has been estimated to be 109 per tumor tissue,
which is approximately 35 mg boron per g of tumor tissue. But
the surrounding healthy cells must not contain more than 5 mg
boron per g of tumor tissue to avoid the damage caused by the
radiation to normal healthy cells.7
In addition to their use for BNCT applications, derivatives of
icosahedral carboranes have also been found to show cytotox-
icity towards cancer cells. Recently dendritic molecules con-
taining multiple o-carborane clusters have been found to show
signicantly higher cytotoxicity towards MCF-7 breast cancer
cell lines than the commonly used chemotherapy agent
cisplatin.8 Derivatives of icosahedral carboranes have also
shown cytotoxicity towards glioma cells.9,10 Therefore, deriva-
tives of carborane could be suitable as chemotherapy agents for
treatment of cancer. Carboranes are very favorably used for
boron delivery because of their high boron content and stability
to catabolism. However, carboranes possess hydrophobicity
and their low water solubility oen limits their use in medicinal
applications. Moreover, derivatives of carboranes need to be
delivered selectively into the tumor tissues in adequate
amounts for the successful cancer therapy. Dendrimers and
Introduction
Boron-rich icosahedral carboranes have been used for several
medicinal applications. The most promising among them is
their use in the treatment of cancer.1–4 Treatment of cancer can
be accomplished via several approaches such as chemotherapy,
radiation therapy, surgery, laser therapy, alternative medicines
and immunotherapy. However, none of these methods are fully
effective because of inherent limitations associated with their
use. The commonly used chemotherapy approach for the
treatment of cancer limits its effectiveness due to the toxicity
associated with the chemotherapy agents towards healthy cells
in the body. Traditionally icosahedral carboranes have been
used to synthesize boron delivery platforms for the treatment of
aDepartment of Chemistry, Ravenshaw University, Cuttack, Odisha, 753 003, India.
E-mail: rashmi.satapathy@gmail.com; rashmi@ravenshawuniversity.ac.in
bDepartment of Chemistry, Siksha ‘O’ Anusandhan (Deemed to be University),
Bhubaneswar, Odisha, 751030, India. E-mail: barada.dash@gmail.com;
baradadash@soa.ac.in
cDepartment of Life Science, National Institute of Technology, Rourkela, Odisha, 769
008, India
† Electronic supplementary information (ESI) available: 1H, 13C, 11B NMR spectra
and mass spectra. See DOI: 10.1039/d0ra07264h
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derivatives.18 For all living cells, carbohydrates plays vital role as
a primary energy source and higher glucose uptake in most of
the cancerous cells is a characteristic feature.19 The endogenous
lectins present on the surface of both normal and malignant
cells acts as the specic receptors and messengers for the
carbohydrate specic endocytosis of glycoconjugates. However,
there is over expression of lectins on the cell surface of
cancerous cells. Therefore, carbohydrate–carborane conjugates
could be a viable platform for selective delivery of adequate
boron into tumor tissues. Glycoconjugates have also been used
as specic drug delivery agents in enzyme replacement,
immune activation, gene, antiviral, and cancer therapies.20–22
Glycoconjugates of polyhedral boron clusters have been
synthesized for tumor targeted delivery of boron for successful
treatment of cancer.17,23 From the earlier reports it has been
revealed that hydroxylated glycoconjugates of carboranes
showed high accumulation in tumor cells and exhibited high
water solubility and low toxicity even at high concentration.4,24
Several attempts have been made so far to develop glyco-
conjugates of carboranes as drugs for successful treatment of
cancer via boron neutron capture therapy (BNCT).25–32 However,
a thorough investigation of cytotoxicities of carboranyl glyco-
conjugates towards cancer cell lines vis-a-vis normal cells is
necessary to access their efficacy for cancer therapy. In the
present work, we describe the synthesis of a series of water-
soluble dendritic glycoconjugates of carborane containing
three and six glucose and galactose moieties via Cu(I)-catalyzed
azide–alkyne click cycloaddition reaction. The in vitro cytotox-
icities of these glycoconjugates have been assessed using two
cancer cell lines (MCF-7 breast carcinoma and A431 skin
carcinoma) and a normal cell line (HaCaT normal skin
epidermal cell) via MTT test.
Scheme 1 Synthesis of o-carborane-appended alkynyl dendron 7
containing three terminal alkyne moieties.
dendritic macromolecules oen nd applications as drug
delivery platforms. Because of the dendrimer's unique branch-
ing architecture and high number of surface functional groups;
it can carry large payloads of therapeutic molecules. Cellular
uptake of dendrimers-based drug delivery systems has been
proved to be signicantly higher.11–13 Due to the leaky vascula-
ture of tumor tissues, macromolecular and dendrimers-based
drug delivery systems are preferentially transported to the
tumor tissues and accumulate in them in a process known as
the enhanced permeability and retention (EPR) effect.14,15
Macromolecular and dendritic drug delivery agents are also
found to be superior in terms of accumulation and retention in
the tumor tissues. The biological evaluation of branched den-
drimer containing nine carborane cages was carried out using
human liver cancer cells (SK-Hep1). The highest boron accu-
mulation up to 2540 ng of boron/5 ꢀ 105 cells was observed at
50 mM concentration of the dendrimer over a period of 20 hours.
The high accumulation of the dendrimer into the tumor cells
indicates that such dendritic boron drug delivery platforms
could be a viable approach for the delivery of boron to the tumor
tissues for successful treatment of cancer.16
Result and discussion
The dendritic carboranyl glycosides 15, 17, 19 and 21 containing
three and six glucose and galactose moieties were synthesized
starting from p-iodoanisole following a sequence of reaction
conditions and involving Cu(I)-catalyzed azide–alkyne [3 + 2]
cycloaddition reaction16 followed by transacetylation under
Zemplen reaction conditions.33 Subsequently, in vitro cytotox-
icity test was performed in using one normal cell line and two
cancerous cell lines.
Synthesis of o-carborane-appended – alkynyl dendrons
The alkynyl dendron 7 was prepared by a sequence of reaction
starting from Sonogashira cross coupling reaction34–36 between
p-iodoanisole (1) and trimethyl silyl acetylene to obtain 2 which
upon desilylation using K2CO3 produced the alkyne 3.
Compound 3 was reuxed with decaborane to produce the o-
carborane derivative 4 in good yield.37 The deprotection of
methyl ether of compound 4 with BBr3 provided the hydroxyl-
ated derivative 5.38 Compound 4 when reuxed with 6 in
acetone/K2CO3 produced the o-carborane-appended alkynyl
dendron 7 in 92% yield (Scheme 1). Preparation of compound 6
was accomplished according to a three-steps reaction sequence
In order to improve the water solubility, carboranes have
been linked to some hydrophilic groups, such as hydroxyl
groups, water-soluble chains and carbohydrates.17,18 It has been
found that a minimum of eight hydroxyl groups per carborane
is necessary to impart water solubility to the carborane
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Scheme 2 Synthesis of o-carborane-appended alkynyl dendron 11 containing six terminal alkyne moieties.
starting from methyl, 3,4,5-trihydroxy benzoate following liter-
ature procedure.16,39 The formation of compound 7 has been
conrmed by the NMR, mass and IR spectral analysis.
Compound 7 shows the characteristic broad singlet (d: 3.81
ppm) for one cage proton and at d: 2.40 ppm for three terminal
alkyne protons in the 1H NMR spectrum (see ESI†). The 13C
NMR spectrum also shows characteristics peaks for alkyne
carbon and cage carbon.
Synthesis of dendritic and water-soluble o-carborane–
carbohydrate conjugates
Commercially available D-glucose and D-galactose were rst
acetylated in the presence of indium triate and acetic anhy-
dride as per reported procedure.40 Then the sugar azides 12 and
13 were prepared according to the literature procedure.41,42 The
compound 14 and 16 was obtained in good yield via Cu(I)-
catalyzed azide–alkyne [3 + 2] cycloaddition reaction16 between
alkynyl core 7 and glucosyl azide 12 and galactosyl azide 13
Following similar procedure, alkynyl dendron 11 was
prepared when compound 3 underwent Sonogashira cross
coupling reaction with 1 followed by treatment with decabor-
ane. The so formed compound 9 upon demethylation with
boron tribromide produced the dihydroxy derivative 10.
Compound 10 when reuxed with compound 6 in the presence
of K2CO3 in acetone produced the desired o-carborane-
appended alkynyl dendron with six terminal alkynyl moieties
(Scheme 2). The formation of the compound 11 has been
conrmed from its NMR, mass and IR spectral data (see ESI†).
The compound 11 shows characteristic 1H NMR peaks at d:
1
respectively. The H, 13C and 11B NMR data reveals the forma-
tion of the desired compounds. Subsequent de-O-acetylation
was carried out using sodium methoxide in dry methanol to
obtain dendrimer 15 and 17 containing three glucose and
galactose moieties respectively. The complete disappearance of
1
the ester protons in H NMR conrmed the formation of the
fully hydroxylated carborane–glucose and carborane–galactose
conjugates (Scheme 3). Formation of these products was further
conrmed from the mass spectral analysis of the compounds.
Following similar approach, reaction of alkynyl core 11 with
glucosyl azide 12 and galactosyl azide 13 produced acetylated
dendritic compounds 18 and 20 in good yield. The removal of
acetyl groups was carried out using sodium methoxide in dry
methanol to give water-soluble de-O-acetylated dendritic
compounds 19 and 21 in good yield (Scheme 4). The complete
2.38 ppm and d: 2.35 ppm for the six acetylenic protons and 13
C
NMR peak at d: 85.7 ppm for the two cage carbons. 11B NMR
conrmed the presence of o-carborane cage in the compound.
The complete disappearance of the broad peak at 3329 cmꢁ1
and appearance of characteristics sharp band at 3280 cmꢁ1
represents the alkyne C–H stretching and a band at 2121
represents n(C^C) in FTIR spectrum for compound 11. The IR
spectrum of compound 11 containing o-carborane showed
strong band at 2589 cmꢁ1 corresponding to n(B–H).
1
disappearance of the peak of ester proton in H NMR and the
peaks for carbonyl carbon in 13C NMR was observed in spectral
analysis indicating the formation of the compound. 11B NMR,
FTIR and mass spectral analysis conrmed the formation of
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Scheme 3 Synthesis of dendritic carboranyl glycoconjugates containing three glucose and galactose moieties.
compounds 19 and 21 (see ESI†). Addition of three glucose and assay.43,44 In vitro cytotoxicity studies of the newly synthesized
galactose moieties to o-carborane clusters (15 and 17) made compounds 15, 17, 19 and 21 were carried out on three different
them partially water soluble and they could be only soluble cell lines. Among them two cancer cell lines such as MCF-7
completely in polar solvents such as methanol and dimethyl (breast carcinoma) and A431 (skin carcinoma) and one
sulfoxide. Whereas increasing the number of sugar moieties to normal cell line, HaCaT (skin epidermal cell) have been used.
six (19 and 21) made them completely water soluble and they The results of the in vitro cytotoxicity studies are presented in
were also found to be soluble in polar solvents such as methanol Tables 1, 2 and Fig. 1. Fig. 1 shows the % cell viability of the cell
and dimethyl sulfoxide.
lines aer treatment with carboranyl glycoconjugates 15, 17, 19
and 21 those contain three and six glucose and galactose
moieties respectively.
In vitro cytotoxicity test
All glycoconjugates of o-carborane were found to be relatively
nontoxic and they display lowest cytotoxicities towards normal
skin epidermal cell line HaCaT. The IC50 values of compounds
15 and 17 (with three glucose and galactose units) were found to
be between 80–85 mM, whereas the IC50 values for compounds
19 and 21 (with six glucose and galactose units) were found to
be between 92-94 mM. Low cytotoxicity of carboranyl
MTT assay employs a colorimetric method for determining the
percentage of viable cells based on mitochondrial dehydroge-
nase activity measurement at 595 nm. It is considered as an
economic, convenient and rapid approach for the detection of
viable and dead cells. To test the cytotoxic effect of the glucose
and galactose containing carboranyl glycoconjugates, cell
viability study was done with the conventional MTT reduction
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Scheme 4 Synthesis of dendritic carboranyl glycoconjugates containing six glucose and galactose moieties.
glycoconjugates towards healthy cells is essential for their use of carboranyl glycoconjugates can be further assessed from the
as a good chemotherapy agents and effective boron neutron plot of % cell viability vs. concentration (Fig. 1). The highest %
capture therapy (BNCT) agents as well. The anti-cancer activity cell viability was observed for normal skin epidermal cell line
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Table 1 IC50 values (mM) of carboranyl glycoconjugates
Cell lines
HaCaT
MCF-7
A431
(normal epidermal
cell line)
(breast cancer
cell line)
(skin cancer
cell line)
Compounds
15
17
19
21
80.2
84.5
96.4
92.9
49.9
58.3
91.9
89.5
68.7
72.0
85.1
86.8
Table 2 % Inhibition of cell lines by carboranyl glycoconjugates at 100
mM concentration
HaCaT
MCF-7
A431
(normal epidermal
cell line)
(breast cancer
cell line)
(skin cancer
cell line)
Compounds
15
17
19
21
44.8
42.8
33.6
38.8
81.3
83.0
44.3
48.4
76.3
78.6
50.9
37.1
HaCaT followed by skin cancerous cell line A431 (Fig. 1). Breast
cancerous cell line MCF-7 showed the lowest % cell viability
indicating that carboranyl glycoconjugates are most cytotoxic
towards these cells.
The anti-cancer effects of carboranyl glycoconjugates can
further be assessed form the inhibition of cell proliferation
shown in Table 2. Administration of 100 mM concentrations of
compounds 15 and 17 (with three glucose and galactose units
with o-carborane) inhibited up to 83% of MCF-7 breast cancer
cells and up to 79% A431 skin cancer cells. Whereas adminis-
tration of similar concentrations of compounds 19 and 21 (with
six glucose and galactose units with o-carborane) inhibited only
up to 48% of MCF-7 breast cancer cells and only up to 50% A431
skin cancer cells. However, all four carboranyl glycoconjugates
were found to be relatively nontoxic towards HaCaT normal
epidermal cells and only up to 34–45% inhibition was observed
at 100 mM concentration. The IC50 value of the most commonly
used cancer drug, cisplatin has been reported to be between 6
mg mLꢁ1 to 9 mg mLꢁ1 (20 to 30 mM) for A431 skin cancer cells
and 6 mg mLꢁ1 (20 mM) for MCF-7 breast cancer cells.45–47 It is
more than two fold higher than the IC50 values observed for
carboranyl glycoconjugates 15 and 17 (with three glucose and
galactose units with o-carborane). The IC50 of cisplatin is more
than three fold higher than the IC50 values observed for car-
boranyl glycoconjugates 19 and 21 (with three glucose and
galactose units with o-carborane). However, IC50 values of car-
boranyl glycoconjugates are found to be more than three fold
lower than the IC50 of cisplatin (25.5 mM) observed for HaCaT
normal epidermal cell.48 Thus carboranyl glycoconjugates 15
and 17 (with three glucose and galactose units with o-carborane)
are found to be more cytotoxic to cancer cells than normal body
cells. It has also been observed that increasing the number of
Fig. 1 Cytotoxic effect of carboranyl glycoconjugates on different cell
lines obtained by MTT assay. (a) HaCaT (normal epidermal cell line), (b)
A431 (skin cancer cell line) and (c) MCF-7 (breast cancer cell line).
sugar moieties decreases the cytotoxicity of carboranyl glyco-
conjugates. Less cytotoxicity of dendritic carboranyl glyco-
conjugates towards normal body cells could make them ideal
candidates for their use as dual mode candidates for cancer
therapy i.e. as chemotherapy agents and boron neutron capture
(BNCT) agents. It is expected that macromolecular and
dendritic carborane–sugar conjugates 15, 17, 19 and 21 could
show preferential accumulation in cancer cells due to the
enhanced permeability and retention (EPR) effect.14–16 In addi-
tion, the over expression carbohydrate specic receptor proteins
in cancer cell would also facilitate their uptake into the cancer
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cells.19–22,49 The trend of cytotoxicity between compound 15 and spectral analyses were performed with Shimadzu Biotech Axima
17 indicates no signicant difference and thus the specic role Condence spectrometer using dithranol as matrix.
of sugar residue in binding or affinity based cytotoxicity can be
ruled out. In addition, the study reveals that the sugar moieties
just help to enhance the polarity and water solubility of conju-
gates and increasing the polarity beyond certain point as in
molecules 19 and 21 is detrimental towards their cytotoxicity. It
highlights the importance of amphiphilicity rather than
enhanced water solubility for the better cell permeability and
anti-cancer activity.50
Cytotoxicity test
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide
(MTT), Dulbecco's modied Eagle's medium (DMEM), fetal
bovine serum (FBS), antibiotic solution (penicillin–strepto-
mycin) were purchased from Sigma Aldrich (Mumbai, India)
and 96 wells plates were purchased from Tarsons, India. MCF-7
(breast carcinoma), HaCaT (normal skin epidermal cell) and
A431 (skin carcinoma) cell lines were purchased from NCCS,
Pune, India. The cells were seeded in 96 well plates at the
density of 3000 cells per well based on the doubling time in the
presence of 200 mL DMEM (Dulbecco's modied Eagle's
medium) supplemented with 10% FBS and 1% penicillin–
streptomycin solution and incubated for 24 h in an incubator
containing 5% CO2 at 37 ꢂC. Aer 24 h of seeding, the existing
media was removed and replaced by fresh media along with
various concentrations of compounds (15, 17, 19 and 21) such
as 10, 20, 40, 60, 80, 90 and 100 mM and incubated for 24 h at
Conclusion
In summary, we have synthesized dendritic and water-soluble
carboranyl glycoconjugates containing three and six glucose
and galactose moieties via Cu(I)-catalyzed Huisgen-type azide
alkyne cycloaddition reaction. Carboranyl glycoconjugates
containing three glucose and galactose moieties were found to
be partially water soluble. But increasing the number of glucose
and galactose moieties to six made them completely water
soluble. Evaluation of cytotoxicities of newly synthesized car-
boranyl glycoconjugates were carried out using two cancer cell
lines, MCF-7 (breast cancer cells) and A431 (skin cancer cells).
Their cytotoxicities were compared with HaCaT normal
epidermal cells. The IC50 values obtained for cancer cells were
found to be signicantly higher for carboranyl glycoconjugates
containing three glucose and galactose moieties (15 and 17).
They could inhibit 76–83% cancer cells at 100 mM concentra-
tions. Increasing the glucose and galactose moieties to six
reduced their cytotoxicities towards cancer cells. However, all
carboranyl glycoconjugates showed signicantly lower cytotox-
icities towards HaCaT normal epidermal cells. Even their cyto-
toxicities towards HaCaT normal epidermal cells were found to
ꢂ
37 C, 5% CO2. To detect the cell viability, MTT working solu-
tion was prepared from a stock solution of 5 mg mLꢁ1 in growth
medium without FBS to the nal concentration of 0.8 mg mLꢁ1
.
100 mL of MTT solution was added and incubated for 4 h. Aer
4 h of incubation, the MTT solution was discarded and 100 mL of
DMSO solvent was added to each well to dissolve the formazan
produced under dark followed by an incubation of 15 min. The
optical density of the formazan product was read at 595 nm in
a micro plate reader (Perkin Elmer, Waltham, MS, USA).
Synthesis and analytical data of compounds
Compound 2. To a solution of p-iodo anisole 1 (2 g, 8.54
be signicantly lower than the common chemotherapy agent mmol) in 1 : 1 mixture of dry THF (10 mL) and dry Et3N (10 mL),
cisplatin. Such property of carboranyl glycoconjugates is trimethylsilylacetylene (1.5 mL) was added under argon atmo-
essential for their use as chemotherapy agent and BNCT agent sphere followed by addition of Pd(PPh3)2Cl2 (144 mg, 0.02
as well.
mmol), CuI (79 mg, 0.41 mmol) and was stirred at room
temperature for 6 hour. The progress of the reaction was
monitored by TLC. The reaction mixture was ltered over short
silica pad. Aer evaporating the solvent crude product was
puried by silica gel column chromatography using 1% ethyl
Experimental
General information
All experiments were carried out in oven-dried asks under dry acetate in hexane to obtain 1.7 g of the pure product 2. Yield:
argon/nitrogen. Solvents were distilled under nitrogen from an 97%.
appropriate drying agent. Reagents were purchased and were
Compound 3. To a solution of 2 (1.6 g, 7.84 mmol) in 1 : 1
used without further purication. All compounds were puried mixture of dry THF (10 mL) & dry methanol (10 mL), K2CO3
by column chromatography on silica gel (60–120 mesh, Spec- (1.62 g, 11.76 mmol) was added under argon atmosphere and
trochem, India). Yield of the products refer to analytically pure stirred at room temperature for 3 hours. The progress of the
samples. 1H and 13C NMR spectra were recorded on Bruker reaction was monitored by TLC. Aer completion of the reac-
Fourier Transform multinuclear NMR spectrometer at 400 MHz tion, the reaction mixture was ltered over short silica pad. The
and 100 MHz respectively. Chemical shis are reported relative solvent was evaporated and the crude product was puried by
to TMS (1H: d ¼ 0.00 ppm), CDCl3 (13C: d ¼ 77.0 ppm) and silica gel column chromatography using 1% ethyl acetate in
coupling constants are given in Hz. All 13C spectra are proton- hexane to obtain 1 g of the pure product 3. Yield: 97%.
decoupled. 11B NMR spectra are proton-decoupled and recor-
Compound 4. Decaborane (1.1 g, 9.08 mmol) was reuxed at
ded at 128 MHz relative to BF3$Et2O. Accurate mass measure- 95 ꢂC in dry acetonitrile (10 mL) for two hours under argon
ments were performed for compounds using Waters QTOF atmosphere and compound 2 (1 g, 7.57 mmol) was added to it in
ꢂ
micro with lock spray instrument by both ES or APCI ion source toluene (5 mL) at room temperature and reuxed at 95 C for
(in the positive or negative mode) and MALDI-TOF mass 17 h. The progress of the reaction was monitored by TLC. Excess
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decaborane was quenched by adding 2 mL of methanol and chromatography using 3% ethyl acetate in hexane to obtain
concentrated to get the crude product which was puried by 765 mg of the pure product 8 as colorless solid. Yield: 61%. Mp:
silica gel chromatography using 2% ethyl acetate in hexane to 142 ꢂC. 1H NMR (400 MHz, CDCl3) d: 7.37 (d, 4H, J ¼ 8 Hz, Ar-H),
obtain 400 mg of pure compound 4 as a colorless solid. Yield: 6.78 (d, 4H, J ¼ 8 Hz, Ar-H), 3.73 (s, 6H, OCH3–H); 13C {1H} NMR
22%. Mp: 114 ꢂC. 1H NMR (400 MHz, CDCl3): d 7.35 (d, 2H, J ¼ (100 MHz, CDCl3) d: 159.4 (Ar-C), 132.8 (Ar-C), 115.7 (Ar-C),
8 Hz, Ar-H), 6.75 (d, 2H, J ¼ 8 Hz, Ar-H), 3.80 (br, s, 1H, cage-H), 113.9 (Ar-C), 87.9 (alkyne-C), 55.3 (OCH3–C); IR (KBr): 2969,
3.73 (s, 3H, OCH3–H); 13C {1H} NMR (100 MHz, CDCl3): d 160.7 2038, 1606, 1519, 1285, 1106 cmꢁ1
.
(Ar-C), 129.2 (Ar-C), 125.5 (Ar-C), 114.0 (Ar-C), 60.9 (cage-C), 55.4
Coꢂmpound 9. Decaborane (462 mg, 3.77 mmol) was reuxed
(OCH3–C); 11B {1H} NMR: ꢁ1.9, ꢁ4.7, ꢁ9.1, ꢁ10.6, ꢁ11.4, at 95 C in acetonitrile (5 mL) for two hour under argon atmo-
ꢁ12.7; IR (KBr): 3003, 2931, 2598 (B–H), 1610, 1516, 1268 cmꢁ1
ES-MS (m/z): calc. for C9H17B10O: 249.34, found 249.2 [M–H]+.
;
sphere and to it compound 8 (600 mg, 2.52 mmol) dissolved in
toluene (5 mL) was added at room temperature and was reuxed
Compound 5. BBr3 (3 mL, 3 mmol, 1 M in CH2Cl2) was added at 95 ꢂC for 17 hour. The progress of the reaction was monitored
drop wise to a solution of 4 (200 mg, 0.84 mmol) in dry CH2Cl2 by TLC. Excess decaborane was quenched using 2 mL of
(8 mL) at 0 ꢂC and stirred at room temperature for 15 hour. The methanol and concentrated to get the crude product which was
progress of the reaction was monitored by TLC. Aer comple- puried by silica gel chromatography using 3% ethyl acetate in
tion, the reaction mixture was quenched slowly with water (10 hexane to obtain 300 mg of pure product 9 as a colorless solid.
1
ꢂ
mL) at 0 ꢂC. Then the crude product was extracted with CH2Cl2 Yield: 34%. Mp: 144 C. H NMR (400 MHz, CDCl3) d: 7.37 (d,
(3 ꢀ 20 mL) and the combined organic layer were dried over 4H, J ¼ 8 Hz, Ar-H), 6.66 (d, 4H, J ¼ 8 Hz, Ar-H), 3.75 (s, 6H,
anhydrous sodium sulfate and concentrated to afford the crude OCH3–H); 13C {1H} NMR (100 MHz, CDCl3) d: 160.7 (Ar-C), 132.1
product, which was puried by silica gel chromatography using (Ar-C), 123.1 (Ar-C), 113.5 (Ar-C), 85.9 (cage-C), 55.27 (OCH3–C);
9% ethyl acetate in hexane to obtain 180 mg of pure product 5 as 11B {1H} NMR: ꢁ2.8, ꢁ9.1, ꢁ10.8; IR (KBr): 2962, 2933, 2592 (B–
1
a colorless solid. Yield: 95%. Mp: 105 C. H NMR (400 MHz, H), 1605, 1512, 1259 cmꢁ1; HRMS (m/z): calc. for C16H23B10O4:
ꢂ
CDCl3) d: 7.41 (d, 2H, J ¼ 8 Hz, Ar-H), 6.79 (d, 2H, J ¼ 8 Hz, Ar-H), 357.2629, found 357.2718 [M–H]+.
5.03 (s, 1H, OH–H), 3.83 (br s, 1H, cage-H); 13C {1H} NMR (100
Compound 10. BBr3 (6.1 mL, 6.1 mmol, 1 M in CH2Cl2) was
MHz, CDCl3): d 156.8 (Ar-C), 129.5 (Ar-C), 125.9 (Ar-C), 115.5 (Ar- added drop wise to ꢂa solution of 9 (300 mg, 0.86 mmol) in
C), 60.9 (cage-C); 11B {1H} NMR: ꢁ1.8, ꢁ4.6, ꢁ9.1, ꢁ10.6, ꢁ11.4, CH2Cl2 (15 mL) at 0 C and stirred at room temperature for 15
ꢁ12.7; IR (KBr): 3230, 3064, 2961, 2597 (B–H), 1614, 1510, hour. The progress of the reaction was monitored by TLC. Aer
1248 cmꢁ1; ES-MS (m/z): calc. for C8H15B10O: 235.31, found completion, the reaction mixture was quenched slowly with
235.2 [M–H]+.
water (20 mL) at 0 ꢂC. Then the crude product was extracted
Compound 7. Compound 5 (100 mg, 0.44 mmol) was solu- with CH2Cl2 (3 ꢀ 30 mL) and the combined organic layer were
bilized in 20 mL of dry acetone under argon. To this solution dried over sodium sulfate. Removal of the solvent afforded the
compound 6 (193 mg, 0.577 mmol) and K2CO3 (183 mg, 1.33 crude product, which was puried by silica gel chromatography
mmol) were added, and the reaction mixture was reuxed at using 20% ethyl acetate in hexane to obtain 260 mg of pure
90 ꢂC for 17 hours. The progress of the reaction was monitored product 10 as a colorless solid. Yield: 94%. Mp: 140 ꢂC. 1H NMR
by TLC. The reaction mixture was ltered through short silica (400 MHz, CD3CN) d: 7.37 (d, 4H, J ¼ 8 Hz, Ar-H), 6.63 (d, 4H, J ¼
pad, and the solvent was evaporated. The crude product was 8 Hz, Ar-H), 7.33 (s, 2H, OH–H); 13C {1H} NMR (100 MHz,
puried by silica gel chromatography using 9% ethyl acetate in CD3CN) d: 159.3 (Ar-C), 133.1 (Ar-C), 122.5 (Ar-C), 115.4 (Ar-C),
hexane to obtain 200 mg of pure product 7 as a colorless solid. 87.4 (cage-C); 11B {1H} NMR: ꢁ3.3, ꢁ9.2, ꢁ11.2; IR (KBr):
Yield: 92%. Mp: 90 ꢂC. 1H NMR (400 MHz, CDCl3) d: 7.35 (d, 2H, 2926, 2853, 2602 (B–H), 1611, 1513, 1252 cmꢁ1; ES-MS (m/z):
J ¼ 8 Hz, Ar-H), 6.82 (d, 2H, J ¼ 8 Hz, Ar-H), 6.74 (s, 2H, Ar-H), calc. for C14H19B10O2: 327.4, found 327.2 [M–H]+.
4.93 (s, 2H, OCH2–H), 4.69 (d, 4H, J ¼ 2.4 Hz, OCH2–H), 4.66 (d,
Compound 11. Compound 10 (120 mg, 0.38 mmol) was
2H, J ¼ 2.4 Hz, OCH2–H), 3.81 (s, 1H, cage-H), 2.40 (dd, 3H, J ¼ solubilized in 25 mL of dry acetone under argon. To this solu-
2.4 Hz, alkyne-H); 13C {1H} NMR (100 MHz, CDCl3) d: 159.7 (Ar- tion compound 6 (326 mg, 0.98 mmol) and K2CO3 (312 mg, 2.26
C), 151.8 (Ar-C), 137.0 (Ar-C), 132.4 (Ar-C), 129.3 (Ar-C), 125.9 mmol) were added and the reaction mixture was reuxed at
(Ar-C), 114.9 (Ar-C), 107.8 (Ar-C), 79.0 (alkyne-C), 78.3 (alkyne-C), 90 ꢂC for 17 hours. The progress of the reaction was monitored
75.9 (alkyne-C), 75.3 (alkyne-C), 70.0 (OCH2–C), 60.9 (cage-C), by TLC. The reaction mixture was ltered through short silica
60.3 (OCH2–C), 57.1 (OCH2–C); 11B {1H} NMR: ꢁ1.8, ꢁ4.6, pad and the solvent was concentrated. The crude product was
ꢁ9.0, ꢁ10.6, ꢁ11.3, ꢁ12.5; IR (KBr): 2926, 2595 (B–H), 2124, puried by silica gel chromatography using 20% ethyl acetate in
1605, 1511, 1254 cmꢁ1; HRMS (m/z): calc. for C24H27B10O4: hexane to obtain 240 mg of pure product 11 as a colorless solid.
1
489.2840, found 489.3035 [M–H]+.
Yield: 76%. Mp: 103 C. H NMR (400 MHz, CDCl3) d: 7.28 (d,
ꢂ
Compound 8. To a solution of 3 (700 mg, 5.3 mmol) in 15 mL 4H, J ¼ 12 Hz, Ar-H), 6.69 (s, 4H, Ar-H), 6.64 (d, 4H, J ¼ 12 Hz, Ar-
of Et3N, p-iodo anisole (992 mg, 4.2 mmol) was added under H), 4.85 (s, 4H, OCH2–H), 4.65 (dd, 12H, J ¼ 2.4 Hz, OCH2–H),
argon atmosphere followed by Pd(PPh3)Cl2 (11.2 mg, 0.16 2.38 (t, 2H, J ¼ 2.4 Hz, alkyne-H), 2.35 (t, 4H, J ¼ 2.4 Hz, alkyne-
mmol) and CuI (61 mg, 0.32 mmol) were added and reuxed at H); 13C {1H} NMR (100 MHz, CDCl3) d: 159.8 (Ar-C), 151.7 (Ar-C),
80 ꢂC for 5 hour. The progress of the reaction was monitored by 136.9 (Ar-C), 132.3 (Ar-C), 132.1 (Ar-C), 123.5 (Ar-C), 114.4 (Ar-C),
TLC. Aer completion of the reaction the excess acetonitrile was 107.7 (Ar-C), 85.7 (cage-C), 79.0 (alkyne-C), 78.3 (alkyne-C), 76.0
removed and the crude product was puried by silica gel (alkyne-C), 75.3 (alkyne-C), 69.7 (OCH2–C), 60.3 (OCH2–C), 57.0
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(OCH2–C); 11B {1H} NMR: ꢁ2.3, ꢁ10.4; IR (KBr): 2926, 2589 (B– {1H} NMR: ꢁ2.09, ꢁ4.62, ꢁ9.25, ꢁ10.92; IR (KBr): 2924, 2853,
H), 2125, 1602, 1509, 1255 cmꢁ1; ES-MS (m/z): calc. for 2597 (B–H), 1750 (ester CO), 1665, 1512, 1383, 1225, 1049 cmꢁ1
;
C
46H44B10O8: 834.39, found 834.40 [M]+; 852.43 [M + H2O]+.
HRMS (m/z): calc. for C72H97B10N9O34: 1741.7068, found
1741.7212 [M]+.
Compound 18. The alkynyl core 11 (500 mg, 0.6 mmol),
glucosyl azide 12 (1.65 g, 3.96 mmol), THF (8 mL), CuSO4$5H2O
(65 mg, 0.261 mmol), sodium ascorbate (517 mg, 2.61 mmol),
General procedure for preparation of dendritic
glycoconjugates using click reaction
The alkynyl core and the sugar azide were dissolved in dry THF and water (8 mL). Purication: neutral alumina column chro-
and then sodium ascorbate, CuSO4$5H2O and water were added matography using 3% methanol in ethyl acetate. Pure product:
1
to it. The reaction mixture was stirred at room temperature for 1090 mg (colorless solid). Yield: 54.5%. Mp: 110 ꢂC. H NMR
24 hour. The reaction was monitored by TLC and aer (400 MHz, CDCl3) d: 7.81 (s, 4H, alkene-H), 7.76 (s, 2H, alkene-
completion of the reaction the mixture was cooled using ice H), 7.32 (d, 4H, Ar-H, J ¼ 8 Hz), 6.73 (s, 4H, Ar-H), 6.69 (d, 4H, J ¼
bath and ice cold water was added to it. The precipitate formed 8 Hz, Ar-H), 5.13–5.04 [m, 18H (Glu-H); 4H (OCH2–H)], 5.02–
was ltered through vacuum ltration to get the crude 4.81 [m, 6H (Glu-H); 12H (OCH2–H)], 4.58–4.45 [m, 6H (Glu-H);
compound which was puried by neutral alumina column 12H (CH2–H)], 4.24–3.88 [m, 6H (Glu-H); 12H (CH2–H)], 3.70–
chromatography.
3.55 [m, 6H (Glu-H)], 2.0, 1.95, 1.91, 1.84 (4s, 72H, 24 CH3); 13
C
Compound 14. The alkynyl core 7 (500 mg, 1.02 mmol), {1H}NMR (100 MHz, CDCl3) d: 170.6, 170.1, 169.4, 169.3 (4ꢀ
glucosyl azide 12 (1409 mg, 3.37 mmol), THF (5 mL), CuSO4- OAc-C), 159.8 (Ar-C), 152.4 (Ar-C), 144.3 (alkene C), 137.5 (Ar-C),
$5H2O (25 mg, 0.1 mmol), sodium ascorbate (200 mg, 1 mmol), 132.2 (Ar-C), 124.9 (Ar-C), 124.5 (Ar-C), 123.5 (alkene C), 114.4
and water (5 mL). Purication: neutral alumina column chro- (Ar-C), 107.2 (Ar-C), 100.5, 100.4 (Glu-Cs), 85.9 (cage-C), 72.5,
matography using 2% methanol in ethyl acetate. Pure product: 72.4, 71.9, 71.8 (Glu-Cs), 69.9 (OCH2–C), 68.3, 68.2 (Glu-C), 67.6
920 mg (colorless solid). Yield: 52.5%. Mp: 92 ꢂC. 1H NMR (400 (OCH2–C), 63.0 (OCH2–C), 61.8, 61.7 (Glu-C), 49.9 (CH2–C), 20.7,
MHz, CDCl3) d: 7.81 (s, 2H, alkene-H), 7.76 (s, 1H, alkene-H), 20.6, 20.5 (4ꢀ CH3–C); 11B {1H} NMR: ꢁ2.98, ꢁ11.23; IR (KBr):
7.37 (d, 2H, Ar-H, J ¼ 12 Hz), 6.84 (d, 2H, J ¼ 8 Hz, Ar-H), 6.76 2925, 2853, 2591 (B–H), 1754 (ester CO), 1604, 1510, 1377, 1227,
(s, 2H, Ar-H), 5.15–5.06 [m, 9H (Glu-H); 2H (OCH2–H)], 5.02– 1041 cmꢁ1; HRMS (m/z): calc. for C142H183B10N18O68: 3338.2562,
4.88 [m, 3H (Glu-H); 6H (OCH2–H)], 4.58–4.44 [m, 3H (Glu-H); found: 3338.2348 [M + H]+.
6H (CH2–H)], 4.23–3.86 [m, 3H (Glu-H); 6H (CH2–H)], 3.68–
3.60 [m, 3H (Glu-H)], 2.0, 1.95, 1.91, 1.86 (4s, 36H, 12 CH3); 13
Compound 20. The alkynyl core 17 (500 mg, 0.6 mmol),
galactose azide 13 (1652 mg, 3.96 mmol), THF (8 mL), CuSO4-
C
{1H}NMR (100 MHz, CDCl3) d: 170.6, 170.1, 169.5, 169.3 (4ꢀ $5H2O (65 mg, 0.261 mmol), sodium ascorbate (517 mg, 2.61
OAc-C), 159.7 (Ar-C), 152.4 (Ar-C), 144.4 (alkene C), 137.5 (Ar-C), mmol), and water (8 mL). Purication: neutral alumina column
132.4 (Ar-C), 129.3 (Ar-C), 125.9 (Ar-C), 124.6 (alkene C), 114.9 chromatography using 3% methanol in ethyl acetate. Pure
(Ar-C), 107.1 (Ar-C), 100.5, 100.4, 72.5, 72.4, 72.0, 71.9, 70.8, 70.8 product: 1050 mg (colorless solid).Yield: 52.5%. Mp: 105 ꢂC. 1H
(Glu-Cs), 70.8 (OCH2–C), 68.3, 68.2 (Glu-C), 67.6 (OCH2–C), 63.4 NMR (400 MHz, CDCl3) d: 7.80 (s, 4H, alkene-H), 7.77 (s, 2H,
(OCH2–C), 61.9 (CH2–C), 61.8, 61.7 (Glu-C), 61.0 (cage-C), 50.0 alkene-H), 7.32 (d, 4H, Ar-H, J ¼ 8 Hz), 6.74 (s, 4H, Ar-H), 6.68 (d,
(CH2–C), 20.7, 20.6, 20.5 (4ꢀ CH3–C); 11B {1H} NMR: ꢁ1.9, ꢁ4.6, 4H, J ¼ 8 Hz, Ar-H), 5.34–5.02 [m, 18H (Gal-H); 4H (OCH2–H)],
ꢁ9.1, ꢁ10.7; IR (KBr): 2927, 2853, 2596 (B–H), 1755 (ester-CO), 4.96–4.79 [m, 6H (Gal-H); 12H (OCH2–H)], 4.61–4.39 [m, 6H
1665, 1599, 1511, 1380, 1228, 1041 cmꢁ1; HRMS (m/z): calc. (Gal-H); 12H (CH2–H)], 4.25–3.82 [m, 6H (Gal-H); 12H (CH2–H)],
for C72H97B10N9O34: 1741.7068, found 1741.7218 [M]+.
3.75–3.57 [m, 6H (Gal-H)], 2.07, 1.97, 1.89, 1.85 (4s, 72H, 24
Compound 16. The alkynyl core 7 (500 mg, 1 mmol), galac- CH3); 13C {1H} NMR (100 MHz, CDCl3) d: 170.4, 170.1, 170.0,
tose azide 13 (1409 mg, 3.4 mmol), THF (5 mL), CuSO4$5H2O 169.5 (4ꢀ OAc-C), 159.7 (Ar-C), 152.4 (Ar-C), 144.5 (alkene C),
(25 mg, 0.1 mmol), sodium ascorbate (200 mg, 1 mmol), and 137.5 (Ar-C), 132.2 (Ar-C), 124.9 (Ar-C), 124.6 (Ar-C), 123.5
water (5 mL). Purication: neutral alumina column chroma- (alkene C), 114.4 (Ar-C), 107.1 (Ar-C), 100.9, 100.8 (Gal-Cs), 85.8
tography using 2% methanol in ethyl acetate. Pure product: (cage-C), 70.9, 70.8, 70.6, 70.5 (Gal-Cs), 69.9 (OCH2–C), 68.4,
1
ꢂ
900 mg (colorless solid).Yield: 51.4%. Mp: 96 C. H NMR (400 68.3 (Gal-Cs), 67.5 (OCH2–C), 67.9, 66.9 (Gal-Cs), 66.5 (OCH2–C),
MHz, CDCl3) d: 7.79 (s, 2H, alkene-H), 7.78 (s, 1H, alkene-H), 63.0 (OCH2–C), 61.7 (CH2–C), 61.2, 61.1 (Gal-C), 50.0 (CH2–C),
7.37 (d, 2H, Ar-H, J ¼ 12 Hz), 6.84 (d, 2H, J ¼ 8 Hz, Ar-H), 6.77 20.8, 20.7, 20.6, 20.5 (4ꢀ CH3–C); 11B {1H} NMR: ꢁ1.80, ꢁ10.21;
(s, 2H, Ar-H), 5.34–5.04 [m, 9H (Gal-H); 2H (OCH2–H)], 4.96–4.89 IR (KBr): 2959, 2853, 2591 (B–H), 1747 (ester CO), 1635, 1509,
[m, 3H (Gal-H); 6H (OCH2–H)], 4.58–4.40 [m, 3H (Gal-H); 6H 1370, 1224, 1050 cmꢁ1
;
HRMS (m/z): calc. for
(CH2–H)], 4.24–4.02 [m, 3H (Gal-H); 6H (CH2–H)], 3.92–3.84 [m,
3H (Gal-H)], 2.07, 1.97, 1.90, 1.86 (4s, 36H, 12 CH3); 13C {1H}
NMR (100 MHz, CDCl3) d: 170.4, 170.1, 170.0, 169.5 (4ꢀ OAc-C),
159.7 (Ar-C), 152.5 (Ar-C), 144.5 (alkene C), 137.5 (Ar-C), 132.4
C
142H183B10N18O68: 3338.2562, found: 3338.2546 [M + H]+.
General procedure for deacetylation reaction
(Ar-C), 129.4 (Ar-C), 125.8 (Ar-C), 124.6 (alkene C), 114.9 (Ar-C), The acetylated carborane–sugar conjugates were dissolved in
107.0 (Ar-C), 100.9, 100.8, 70.9, 70.8, 70.6, 70.5 (Gal-Cs), 70.4 dry methanol, and a solution of sodium methoxide in anhy-
(OCH2–C), 68.4, 68.3 (Gal-Cs), 67.6 (OCH2–C), 67.0, 66.9 (Gal- drous methanol was added and reaction mixture was stirred at
Cs), 63.0 (OCH2–C), 62.5 (CH2–C), 61.1, 61.0 (Gal-C), 61.0 room temperature (45 min to 3 h). The progress of the reaction
(cage-C), 50.0 (CH2–C), 20.7, 20.6, 20.5, 20.4 (4ꢀ CH3–C); 11B was monitored by TLC and when starting material was
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disappeared the reaction mixture was neutralized by the addi- H), 1638, 1601, 1509, 1381, 1252, 1076 cmꢁ1; HRMS (m/z): calc.
tion of Amberlite IR-120 (H+-form) ion exchange resin (pre- for C94H133B10N18O44: 2327.9654, found: 2327.9685 [M–H]+.
washed with anhydrous methanol). The reaction mixture was
Compound 21. Acetylated derivative 20 (180 mg, 0.053
then ltered over a cotton plug and concentrated under reduced mmol), sodium methoxide (5 mg), anhydrous methanol (10
pressure to afford carborane–sugar conjugates without acetyl mL). Room temperature, 3 h. Pure product: 115 mg (colorless
moieties.
solid). Yield: 93%. Mp: 130 ꢂC. 1H NMR (400 MHz, D2O) d: 7.86
Compound 15. Acetylated derivative 14 (300 mg, 0.172 (br s, 6H, alkene-H), 7.66 (br s, 4H, Ar-H), 6.74 (s, 4H, Ar-H), 6.42
mmol), sodium methoxide (5 mg), anhydrous methanol (10 (br s, 4H, J ¼ 8 Hz, Ar-H), 4.60–4.16 [m, 18H (Gal-H); 4H (OCH2–
mL). Room temperature, 45 min. Pure product: 195 mg (color- H)], 4.06–3.77 [m, 6H (Gal-H); 12H (OCH2–H)], 3.61–3.42 [m, 6H
less solid). Yield: 91%. Mp: 105 ꢂC. 1H NMR (400 MHz, MeOD) d: (Gal-H); 12H (CH2–H)], 3.38–3.20 [m, 6H (Gal-H); 12H (CH2–H)],
8.22 (s, 2H, alkene-H), 8.01 (s, 1H, alkene-H), 7.51 (d, 2H, Ar-H, J 3.10–2.97 [m, 6H (Gal-H)]; 13C {1H}NMR (100 MHz, D2O) d: 159.7
¼ 8 Hz), 7.0 (d, 2H, J ¼ 8 Hz, Ar-H), 6.93 (s, 2H, Ar-H), 5.22–5.0 (Ar-C), 151.6 (Ar-C), 142.7 (alkene C), 135.6 (Ar-C), 132.5 (Ar-C),
[m, 9H (Glu-H); 2H (OCH2–H)], 4.74–4.55 [m, 3H (Glu-H); 6H 125.7 (Ar-C), 123.3 (Ar-C), 124.9 (alkene C), 114.4 (Ar-C), 107.1
(OCH2–H)], 4.35–4.06 [m, 3H (Glu-H); 6H (CH2–H)], 3.91–3.61 (Ar-C), 103.0 (Gal-C), 81.6 (cage-C), 75.0, 72.7, 71.8, 71.8, 70.4
[m, 3H (Glu-H); 6H (CH2–H)], 3.39–3.15 [m, 3H (Glu-H)]; 13C (Gal-Cs), 68.4 (OCH2–C), 67.8 (Gal-C), 65.7 (OCH2–C), 62.8,
{1H}NMR (100 MHz, MeOD) d: 159.8 (Ar-C), 152.3 (Ar-C), 143.2 (OCH2–C), 61.8 (OCH2–C), 61.7 (CH2–C), 60.8 (Gal-C), 50.1
(alkene C), 136.8 (Ar-C), 133.3 (Ar-C), 128.8 (Ar-C), 126.0 (Ar-C), (CH2–C); 11B {1H} NMR: ꢁ5.05, ꢁ12.88; IR (KBr): 2959, 2853,
125.4 (alkene C), 114.7 (Ar-C), 107.2 (Ar-C), 103.2, 76.6, 76.5, 2591 (B–H), 1747 (ester CO), 1635, 1509, 1370, 1224, 1050 cmꢁ1
;
73.5 (Glu-Cs), 70.1 (OCH2–C), 69.6 (Glu-C), 67.7 (OCH2–C), 65.3 HRMS (m/z): calc. for C94H133B10N18O44: 2327.9654, found:
(OCH2–C), 62.2 (CH2–C), 61.3 (Glu-C), 61.2 (cage-C), 50.3 (CH2– 2327.9714 [M–H]+.
C); 11B {1H} NMR: ꢁ2.8, ꢁ9.4, ꢁ11.08; IR (KBr): 3423, 2928,
ꢁ1
2853, 2594 (B–H), 1637, 1602, 1510, 1381, 1250, 1075 cm
;
Conflicts of interest
HRMS (m/z): calc. for C48H72B10N9O22: 1236.5722, found
1236.5787 [M–H]+.
Compound 17. Acetylated derivative 16 (200 mg, 0.114
mmol), sodium methoxide (3 mg), anhydrous methanol (10
The authors declare no conict of interest.
mL). Room temperature, 45 min. Pure product: 120 mg (color- Acknowledgements
less solid). Yield: 84%. Mp: 100 ꢂC. 1H NMR (400 MHz, MeOD) d:
Authors thank Science & Engineering Research Board, India
8.23 (s, 2H, alkene-H), 7.78 (s, 1H, alkene-H), 7.51 (d, 2H, Ar-H, J
¼ 8 Hz), 7.0 (d, 2H, J ¼ 8 Hz, Ar-H), 6.49 (s, 2H, Ar-H), 5.30–5.0
[m, 9H (Gal-H); 2H (OCH2–H)], 4.74–4.45 [m, 3H (Gal-H); 6H
(OCH2–H)], 4.35–4.95 [m, 3H (Gal-H); 6H (CH2–H)], 3.92–3.64
[m, 3H (Gal-H); 6H (CH2–H)], 3.59–3.20 [m, 3H (Gal-H)]; 13C {1H}
NMR (100 MHz, MeOD) d: 159.8 (Ar-C), 152.3 (Ar-C), 143.3
(alkene C), 136.7 (Ar-C), 133.2 (Ar-C), 128.8 (Ar-C), 126.0 (Ar-C),
125.4 (alkene C), 114.7 (Ar-C), 107.1 (Ar-C), 103.8, 75.4, 73.4
(Gal-Cs), 70.9 (OCH2–C), 69.6, 68.9 (Gal-Cs), 67.7 (OCH2–C), 65.5
(OCH2–C), 62.2 (CH2–C), 61.1 (CH2–C), 50.4 (CH2–C); 11B {1H}
NMR: ꢁ2.78, ꢁ9.32, ꢁ10.95; IR (KBr): 3415, 2921, 2880, 2591 (B–
H), 1638, 1601, 1509, 1381, 1252, 1076 cmꢁ1; HRMS (m/z): calc.
for C48H72B10N9O22: 1236.5722, found 1236.5794 [M–H]+.
Compound 19. Acetylated derivative 18 (300 mg, 0.089
mmol), sodium methoxide (8 mg), anhydrous methanol (10
mL). Room temperature, 3 h. Pure product: 180 mg (colorless
(Grant Numbers: CRG/2018/002635, SB/FT/CS-028/2012, SB/FT/
CS-058/2012), Council of Scientic & Industrial Research, India
(Grant Number: 02(0308)/17/EMR-II) and University Grants
Commission, India (Grant Number: MRP-MAJOR-CHEM-2013-
11320) for nancial support.
Notes and references
1 F. Issa, M. Kassiou and L. M. Rendina, Chem. Rev., 2011, 111,
5701–5722.
2 M. Scholz and E. Hey-Hawkins, Chem. Rev., 2011, 111, 7035–
7062.
3 R. Satapathy, B. P. Dash, J. A. Maguire and N. S. Hosmane,
Collect. Czech. Chem. Commun., 2010, 75, 995–1022.
4 A. F. Armstrong and J. F. Valliant, Dalton Trans., 2007, 4240–
4251.
1
solid). Yield: 86%. Mp: 140 ꢂC. H NMR (400 MHz, MeOD) d:
8.17 (s, 4H, alkene-H), 7.94 (s, 2H, alkene-H), 7.46 (d, 4H, Ar-H, J
¼ 8 Hz), 6.84 (br s, 4H, Ar-H), 6.82 (s, 4H, Ar-H), 5.16–5.04 [m,
18H (Glu-H); 4H (OCH2–H)], 4.78–4.47 [m, 6H (Glu-H); 12H
(OCH2–H)], 4.40–4.16 [m, 6H (Glu-H); 12H (CH2–H)], 4.07–3.59
[m, 6H (Glu-H); 12H (CH2–H)], 3.42–3.12 [m, 6H (Glu-H)]; 13C
{1H} NMR (100 MHz, MeOD) d: 162.2, 152.2 (Ar-C), 143.2 (alkene
C), 136.7 (Ar-C), 132.2 (Ar-C), 125.5 (Ar-C), 125.4 (Ar-C), 123.0
(alkene C), 114.4 (Ar-C), 107.2 (Ar-C), 103.2 (Glu-C), 86.3 (cage-
C), 76.4, 76.5, 73.5, 70.1 (Glu-Cs), 69.5 (OCH2–C), 67.2, (Glu-
C), 65.5 (OCH2–C), 62.2 (OCH2–C), 61.3 (Glu-C), 50.3 (CH2–C);
11B {1H} NMR: ꢁ6.6, ꢁ14.5; IR (KBr): 3415, 2921, 2880, 2591 (B–
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