Synthesis, characterization, optical and electrochemical properties and antibacterial activity of novel BODIPY glycoconjugated dendrimers

Article abstract of DOI:10.1039/c7nj04412g

Triazole-branched BODIPY glycoconjugated dendrimers are synthesized by click chemistry in good yields via a convergent approach. All glycodendrimers show increase in the fluorescence intensity upon increasing the dendrimer generation. The cyclic voltammograms of dendrimers 1, 2 and 3 show a quasi-reversible behaviour. All the boron-dipyrrolomethene (BODIPY) dendrimers show antibacterial activity against both Gram positive and Gram negative bacteria viz., S. aureus and B. subtilis, and S. typhimurium and E. coli respectively and dendrimer 3 shows a better antibacterial activity than all the other synthesized dendrimers.

Full text of DOI:10.1039/c7nj04412g

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Synthesis, characterization, optical and electrochemical properties and
antibacterial activity of novel BODIPY Glyco conjugated dendrimers
Velautham Saravanan and Perumal Rajakumar*
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai
600 025, India. Eꢀmail: perumalrajakumar@gmail.com; Fax: +91 044 22300488;
Tel: +91 044 22202814; 9551379907
Abstract
Triazole branched BODIPY – Glyco conjugated dendrimers are synthesized by click
chemistry in good yields via convergent approach. All the glycodendrimers show increase in
the fluorescence intensity on increasing the dendrimer generation. The cyclic voltammogram
for the dendrimers 1, 2 and 3 shows quasiꢀreversible behaviour. All the boronꢀ
dipyrrolomethene (BODIPY) dendrimers show antibacterial activity against both gram
positive and gram negative bacteria viz., S. aureus, B. Subtilis, S. typhimurium and E. Coli
respectively and the dendrimer 3 shows better antibacterial activity than all other synthesized
dendrimers.
Keywords: Antibacterial activity, BODIPY, Carbohydrates, Click chemistry, Cyclic
voltammetry, Glycodendrimers, Lifetime fluorescence study, Optical properties.
Introduction
Dendrimers are perfect monodisporse macromolecules with a regular and highly
branched threeꢀ dimensional architecture. The term “glycodendrimer” refers to a description
of carbohydrate containing macromolecules that can be grown generation wise following an
interactive repetitive synthesis. Glycodendrimers have become valuable tools in gylcobiology
1

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due to the multivalent framework, which is essentially required for effective carbohydrateꢀ
protein interaction in the living systems. 1,3ꢀDipolar cycloaddition of alkyne to azide has
enormous attention in the area of glycobiology and has provided a large variety of molecular
architecture with triazole bridged carbohydrate system.1, 2 Carbohydrate–BODIPY hybrids
can be obtained from oneꢀpot synthetic protocols that involves the copper (I)ꢀcatalyzed azide
and alkyne cycloaddition (CuAAC).3,4 which is known as click chemistry. Hence, Click
chemistry is a versatile key route for the synthesis of glycodendrimers wherein the
carbohydrate unit is bridged with bioactive core nucleus. Glycodendrimers have enormous
applications in the field of biology, such as cell recognition, cellꢀprotein interactions,
targeting of hormones, antibodies, and toxins. Fluorophoric molecule exhibits fluorescein
property which is used in cellular biology to label and track cells in fluorescene
microscopy applications. Fluorescein coupled with glycodendrimers forms fluorescent
glycodendrimers, which exhibit good biological property especially drug discovery for gene
delivery systems, cancer therapy, neurodegenerative diseases,5 biosensors,6 bioimaging7 and
absorption studies of proteinꢀbased indicators.8 Incorporation of BODIPY into a
glycodendrimer endows the glycodendrimer with fluorescence property. Such type of
molecules are used as a fluorescent probes, and are important in the investigation of
molecular functions.9 BODIPY molecule has a tuneable, narrow, symmetric emission band,
long luminescence lifetime, and good photo chemical stability and the fact that their
excitation wavelength lies in the visibleꢀwavelength range and hence used in the diagnostics
of the in vitro and in vivo imaging,10 and as biochemical labelling agents.11 BODIPY–
glycoconjugates are potentially used as an in vivo inhibitor,12 Intracellular trafficking of
glycophospholipids in cells13 and in fluorescent nucleotide analogues.14 They are also used as
fluorescent probe for detection of Asialoglycoprotein (ASGP) on liver cells. Carbohydrate–
BODIPY hybrids have shown to be a powerful combination for addressing biological
2

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problems. Hence, we report herein the synthesis, optical, electrochemical and antibacterial
properties of BODIPY glycodendrimers 1, 2 and 3 by one pot stereoselective click reaction
methodology.
AcO
AcO
AcO
AcO
OAc
O
AcO
AcO
AcO
AcO
O
N
N
AcO
AcO
N
O
AcO
N
N
N
N
N
O
O
N
O
N
O
N
N
N
N
B
F
F
1 (G0)
N
N
B
F
F
2 (G1)
Fig. 1. Structure of the BODIPY glycoconjugated dendrimers 1, 2 and 3
3

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Results and discussion
The reaction of 3,5ꢀbis(propargyloxy)benzyl chloride 5 with 2.1 equiv. of 2,3,4,6ꢀ
tetraꢀOꢀacetylꢀαꢀDꢀglucopyranosyl azide 4 under the Cu (I) catalyzed click reaction
conditions gave the dendritic chloride 6 in 96% yield. Further, the reaction of the dendritic
chloride 6 with NaN3 in a mixture of acetoneꢀwater at 60 ºC gave the corresponding dendritic
1
azide 7 in 98% yield. In the H NMR spectrum, the dendritic azide 7 showed a singlet at δ
5.13 for the –OꢀCH2 protons and another singlet at δ 7.86 for the triazolyl protons in addition
to the signals for the other aliphatic and aromatic protons. The 13C NMR spectrum of the
compound 7 displayed the –OꢀCH2 and triazolyl carbons at δ 84.8 and at δ 158.6
respectively, in addition to the signals for the other carbons. The appearance of molecular ion
peak at m/z 987 in mass spectrum also confirmed the structure of the dendritic azide 7
(Scheme 1).
4

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.
Scheme 1. Reagents and conditions: (i) CuSO4 5H2O (5 mol%), sodium ascorbate (10
mol%), H2O/THF (1:1), rt, 10 h, 6 (96%), 8 (93%). (ii) 1.5 equiv. NaN3, CH3COCH3/H2O, 60
ºC, 1ꢀ3 h, 7 (98%), 9 (97%).
Similar reaction sequence was used for the synthesis of second generation of dendritic
azide 9 using the building block viz., 3,5ꢀbis(propargyloxy)benzyl chloride 5. Reaction of 2.1
equiv of the dendritic azide 7 with one equiv of the 3, 5ꢀbis (propargyloxy)benzyl chloride 5
in the presence of the Cu (I) catalyzed click reaction conditions gave the dendritic chloride 8
in 93% yields. Further, the reaction of 1.1 equiv. of NaN3 with the one equiv of the dendritic
chloride 8 in mixture of acetone and water at 60 oC allowed the desired transformation to the
corresponding dendritic azide 9 in 97% yield. The 1H NMR spectrum of the dendritic azide 9
displayed a singlet at δ 5.10 for the –OꢀCH2 protons and a singlet at δ 8.00 for triazolyl
proton in addition to the signals for the other aliphatic and aromatic proton signals. The 13C
NMR spectrum of the compound 9 displayed the –OꢀCH2 and triazolyl carbons at δ 85.7,
159.7 respectively, in the addition to the other carbon signals. The appearance of molecular
ion peak at m/z 4695 [M++Na] in mass spectrum also confirmed the structure of the dendritic
azide 9. The structure of dendritic azide 9 was also confirmed from elemental analysis
(Scheme 1).
Reaction of 1.0 equiv. of 4ꢀ(propꢀ2ꢀynyloxy)benzaldehyde 10 with 2.1 equiv. of
pyrrole in the presence of TFA in dry DCM at room temperature for 8 h gave the 2,2'ꢀ((4ꢀ
(propꢀ2ꢀynyloxy)phenyl)methylene)bis(1Hꢀpyrrole) 11 as white solid in 87% yield, which on
further treatment with TEA and DDQ in dry DCM at room temperature followed by the
°
addition of BF3. OEt2 in dry DCM at 0 C for 3h gave the 5,5ꢀdifluoroꢀ10ꢀ(4ꢀ(propꢀ2ꢀ
ynyloxy)phenyl)ꢀ5Hꢀdipyrrolo[1,2ꢀc:1',2'ꢀf][1,3,2]diazaborininꢀ4ꢀiumꢀ5ꢀuide, (BODIPY) 12
(74 %).(Scheme 2).
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Scheme2 Reagents and conditions: (i) 2.1 equiv. of Pyrrole, TFA (0.1 mL), dry DCM, rt, 8
h, 11 (87 %), (ii) TEA (10 ml), DDQ dry DCM, rt, 1.5 h; (iii) 10 ml BF3.OEt2 in dry DCM at
.
0 ° C, 3 h, 12 (74 %). (iv) CuSO4 5H2O (5 mol %), sodium ascorbate (10 mol %), H2OꢀTHF
(1:1); rt., 12 h. 1 (86%), 2 (83%), 3 (88%).
1
The H NMR spectrum of the propargylated BODIPY 12 displayed a triplet for
acetylenic protons at δ 4.71 as doublet and the propargyoxy methylene proton as a singlet at δ
5.12 additions to the other aromatic proton signals. The 13C NMR spectrum of 12 showed the
BODIPY carbons at δ 114.9, 127.1, 143.6, 147.1, and 159.9 in addition to the other aliphatic
and aromatic carbon signals.
The synthesis of BODIPY group bearing glycodendrimers 1, 2 and 3 is shown in
scheme 2. Reaction of 1.0 equiv. of propargylated BODIPY 12 with 1.1 equiv. of each of
2,3,4,6ꢀtetraꢀOꢀacetylꢀαꢀDꢀglucopyranosyl azide 4, the dendritic azide 7 and the dendritic
azide 9 in the presence of Cu(I) catalysed click chemistry conditions gave the BODIPY
glycodendrimers 1, 2 and 3 in 97%, 95% and 92% yields, respectively (scheme 2).
1
The H NMR spectrum of the BODIPY glycodendrimer 1 showed four singlets at δ
1.83, 2.02, 2.05 and 2.06 for four different glycoꢀacetoxy protons, a sharp singlet at δ 5.17 for
OꢀCH2 protons and the triazolyl protons appeared as a singlet at δ 7.91 in addition to the
signals for other aliphatic and aromatic protons. The 13C NMR spectrum of the BODIPY
glycodendrimer 1 displayed the three different glycoꢀacetoxy carbons at δ 20.1, 20.5 and
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20.6, the triazolyl carbon at δ 144.3 in addition to the other aliphatic and aromatic carbon
signals. The appearance of molecular ion peak at m/z 751.36 [M]+ in mass spectrum also
confirmed the structure of the glycodendrimer 1. Similarly, the structure of the BODIPY
glycodendrimers 2 and 3 was also confirmed from spectral and analytical data.
Photophysical studies
The UVꢀvis absorption and fluorescence spectra of the BODIPY glycodendrimers 1, 2
and 3 were obtained in DCM (1 µM) and are shown in Fig. 2. The electronic absorption
spectra of compounds 1, 2 and 3 show intense absorption bands at between 384 – 386 and
495ꢀ501 nm, respectively with molar extinction coefficients in the order of 6000 and 14600,
9300 and 56300 and 14600 and 75000 M−1 cm−1 respectively, which are tentatively,
attributed to S0 → S2 (πꢀπ*) and S0 → S1(πꢀπ*) transition of BODIPY similar to those
observed in other related systems.15
Figure 2: UVꢀvis absorption spectrum and fluorescence spectrum of BODIPY dendrimers 1,
2 and 3 in DCM (10 µM) at room temperature.
such type of transitions confirm the presence of BODIPY unit in the dendrimer. Though λ
max remains almost constant in the UVꢀvisible spectrum for all the BODIPY
glycodendrmers, the absorption intensity increases with increasing dendrimer generation. The
fluorescence spectra of BODIPY glycodendrimers 1, 2 and 3 in DCM at room temperature is
shown in Fig. 2. The BODIPY glycodendrimers 1, 2 and 3 when exited at a wavelength of
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490 nm, exhibited the emission band at 508 nm (Fig. 2) due to the presence of BODIPY unit
to the dendrimer system. The increase in the fluorescence intensity of the BODIPY
glycodendrimers with increase in generation is due to the increased number of triazolyl and
glucose units, otherwise known as multivalency effect in dendrimer chemistry16.
Lifetime decay analysis:
Lifetime decay analysis was carried out on all the fluorescent glycodendrimers 1, 2
and 3 by using the IBH timeꢀcorrelated single photon counting (TCSPC) technique on
excitation at 490 nm in CH2Cl2 as solvent.
Figure 3. Lifetime decay of glycodendrimers 1, 2, and 3 (prompt = instrument response
function).
The lifetime decay fits as biexponential with lifetimes τ1 and τ2 for dendrimers 1 and 2. The
lifetime decay values of the fluoresceinꢀconjugated glycodendrimers 1, 2, are 1.75 ns (τ1) and
4.10 ns (τ2) and, 3.20 ns (τ1) and 6.70 ns (τ2) respectively. However the dendrimer 3 showed
only single exponential with lifetime decay of 6.97 ns (τ2) only (Table 1).
Table 1: Laser parameters for the dendrimers 1, 2 and 3 in CH2Cl2 at 2x10ꢀ5 M
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Dendrimers
(Generation)
A
1(%) A2(%)
λem
τ
1(ns)
τ
2(ns)
τ
Average(ns) χ2
Excitation
at 490nm
508
1(G0)
1.75
4.10
15.37
84.63
3.40
1.13
2(G1)
3(G2)
508
508
3.20
ꢀ
6.70
6.97
19.89
ꢀ
80.11
5.50
6.97
1.07
1.13
100.00
However, the fluorescence lifetime increases as the generation of the dendrimer
increases, which could be due to greater number of triazole and glucose units in the higher
generation dendrimers.
Electrochemical studies
The electrochemical study of the BODIPY dye conjugated dendron with triazolyl
bridging unit featured remarkable trends. The electrochemical property of the BODIPY
dendrimers 1, 2 and 3 was examined by cyclic voltammetry, shown in Fig. 4 and the
electrochemical parameters are given in Table 2. All the dendrimers exhibit only irreversible
reduction peak. The BODIPY dendrimer 1 shows only one reduction peak at 0.55 V due to
presence of one BODIPY17 unit lesser number of triazole bridging unit in the dendritic
architecture. But in the case of higher generation dendrimers 2 and 3 two reduction peaks at
0.188, 0.590, 0.160 and 0.605 (V) are observed respectively due to more number of triazolyl
units with one BODIPY unit in the periphery. On increasing dendritic generation the potential
value slightly increases and a slight positive shift in the potential was observed due to more
number of triazolyl units in the dendritic compartment. This observation clearly indicate that
the triazole and BODIPY units are responsible for the potential shift.
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Figure 4: Cyclic voltammetric redox sensing on dendrimer 1, 2 and 3 (2x10ꢀ5 M)
Table 2. Optical and electrochemical parameters for the dendrimers 1, 2 and 3, in CH2Cl2 at
Dendrimers
Ψ(mꢀ1cmꢀ1)
Cyclic Voltammetry
λmax (nm)
(Generation)
1
2
Epc
Epc
ꢁE =Epc2 –
Epc1
ꢀ
1(G0)
2(G1)
386 and 499
385 and 500
384 and 501
6000 and 14600
9300 and 56300
14600 and7500
ꢀ
0.558
0.590
0.605
0.188
0.160
0.402
0.445
3(G2)
20 µM
Antibacterial activity of BODIPY dendrimer 1, 2 and 3
The antibacterial activiy of the three synthesized 2, 4ꢀdimethylpyrrole BODIPY
dendrimers was investigated by agar well diffusion assay method.18 The antibacterial activity
of the newly synthesized three BODIPY ꢀ Glycoconjugated dendrimer 1, 2 and 3 was
examined by agar well diffusion method against Gram positive bacteria (S. aureus and B.
subtilis) and Gram negative bacteria (S. typhi and E. coli) at various concentrations viz., 25,
50, 100 and 150 µg/mL in DMSO. In Brief, the incubated bacterial cultures were swabbed on
MHA plates and the samples were loaded into the well. Streptomycin 25g/mL was used as
the standard and then plates were maintained overnight at 37 ºC. After incubation clear zone
appeared around the well and it was measured as zone of inhibition against in millimetre.
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Figure 5: Antibacterial activity of the synthesized dendrimers 1, 2 and 3 against both Gram
(+ve) (S. aureus) and Gram (ꢀve) (S. typhimurium) bacteria strains.
(a) 50 µg, (b) 100 µg, (c) 150 µg, (d) 50 µg standard (Streptomycin) and (e) 10 % DMSO
(control).
All the three dendrimers showed the substantial antibacterial activity against both the
gram positive bacteria S. aureus and B. subtilis and gram negative bacteria namely S. typhi
and E. coli as shown in Fig. 5
The second generation dendrimer 3 (G2) exhibited better antibacterial activity than the lower
generation 2(G1) and 1(G0). The second generation dendrimer 3 (G2) shows the inhibitory
activity against s. aureus at different concentrations of 50, 100, 150 µg/mL with the zone of
inhibition as 24, 25, 26 mm respectively.19 But interestingly, all the synthesized dendrimers
show substantial activity comparable to that of the compared with standard drug streptomycin
(25µg/mL). The results indicate that dendrimers have the potential antibacterial activity.
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Table 3a: Comparison of antibacterial activity of the synthesized dendrimers 1, 2 and 3.with
the standard viz Streptomycin at a concentration of 25µg/mL
Gram Positive bacteria
Bacillus Staphylococcus
Gram Negative bacteria
Dendrimers
(Generation)
Escherichia
coli
Salmonella
typhi
subtilis
aureus
b
a
b
c
a
6
c
a
8
8
b
c
a
b
c
1(G0)
2(G1)
3(G2)
6
12 NA
12
NA
NA
NA
16 NA
7
14 NA
12 12 NA
12 12 NA
10
12
12
16 NA 10 14 NA
12
10 16 NA 12 14 NA
(a) 25 µg/mL, (b) 25 µg/mL Streptomycin (standard) and (c) control experiment with DMSO;
NA = Nil Activity
The average diameter of zone of inhibition of dendrimers 1, 2 and 3 in shown in table
3a and compared to the standard Viz, Streptomycin at the same concentration of 25mg/mL.
All the dendrimers 1, 2 and 3 exhibited equal activity against Gram (+ve) bacteria viz ,
Bacillus Subtillis, Staphylococcus aureus and comparable to the that of standard . However
all the dendrimer 1, 2 and 3 exhibited slightly lesser activity against Gram (ꢀve) bacteria viz,
ezcherichia Coli and Salmyphionella typhi. The higher generation dendrimer 3 (G2) showed
better activity than the lower generation dendrimer 1(G0) and 2 (G1) with respect to the
Gram (ꢀve) bacteria. The higher antibacterial activity of 3 could be due to more number of
triazole units.
Dose dependent nature of the synthesized dendrimer was than explored. Antibacterial
activity of the dendrimer was carried out at three different concentration viz, 50mg/mL,
100mg/mL and 150mg/mL. While increasing the concentration of the dendrimers the
antibacterial activity almost remind the same. In fact the antibacterial activity of the 1st and
2nd generation dendrimer 2 and 3 against tested pathogen viz, Bacillus Subtillis,
Staphylococcus aureus, ezcherichia Coli and Salmyphionella Typhi is the same, which shows
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that the antibacterial activity is dose independent. Table 3b showns that the antibacterial
activity of the dendrimers are concentration independent and the 1st and 2nd generation
dendrimer 2 and 3 shows almost equal activity at the concentration of 50, 100, 150 mg/mL.
Table 3b: Antibacterial activity of the synthesized dendrimers 1, 2 and 3.
Gram Positive bacteria
Bacillus Staphylococcus
Gram Negative bacteria
Dendrimers
(Generation)
Escherichia
coli
Salmonella
typhi
subtilis
aureus
b
a
b
c
a
c
a
b
c
a
b
c
1(G0)
2(G1)
3(G2)
8
11 12
10
23
24
10
11
26
26
6
6
8
16
18
19
25
19
20
25
24 25 27
20 24 25
24
18 18 19 17
22 23 24 24
25
(a) 50 µg/mL, (b) 100 µg/mL, (c) 150 µg/mL,
The present study clearly shows that the dendrimers exhibit antibacterial activity against both
gram positive and gram negative bacteria such as S. Aureus, B. Subtilis, S. typhimurium and
E. Coli respectively.20 The antibacterial activity of the synthesized dendrimers at 25 µg
concentration is shown in the supporting information.
The antibacterial activity of the synthesised dendrimers can be attributed due to the
formation of reactive oxygen species (ROS), which results in cell death. It has been
reported21 that the rupture of bacterial outer membrane can weaken the cells, which is caused
by the interaction of the dendrimer surface with the surface of the bacterial membrane.
Experimental
All the reagents and solvents were commercially available in best grade and used
without further purification. The melting points were determined using a Toshiwal melting
point apparatus by open capillary tube method and are uncorrected. Spectroscopic data were
recorded from the following instrument; Bruker 300 MHz for NMR and PerkinꢀElmer
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Lambda 35 UVꢀvis spectrometer for the absorption and PerkinꢀElmer Lambda 45
fluorescence spectrometer for the fluorescence emission spectra. Fluorescence decays were
recorded by using an IBH timeꢀcorrelated singleꢀphoton counting spectrometer.All the
electrochemical measurements were performed on a PGSTATꢀ12 electrochemical work
station, (AUTOLAB, The Netherlands BV) controlled by a general purpose electrochemical
system (GPES). The measurements were based on a three electrode system, with a glassy
carbon (GC) electrode (of geometric area 0.07 cm2) being used as the working electrode, a Pt
wire in the form of a spiral (with a high geometrical surface area B20 cm2) being used as the
auxiliary electrode and Ag/AgCl as the reference electrode with a scan rate of 50 mV sꢀ1 with
of 0.1 M TBAP as supporting electrolyte.
General procedure for Cu (I) catalyzed click reaction (procedure A)
A mixture of the acetylenic derivative (1.0 mmol, 1.0 equiv. ) and the azido derivative
(1.1 mmol, 1.1equiv.) was dissolved in THF/H2O (1:1; 8 mL) and added sodium ascorbate
(0.4 mmol, 0.4 equiv.) followed by the addition of CuSO4.5H2O (0.2 mmol, 0.2 equiv.). The
reaction mixture was stirred overnight at room temperature. The solvent was evaporated and
the crude product was dissolved with EtOAc (2 X 100 mL), washed with NH4Cl solution (50
mL) and brine solution (50 mL), dried over Na2SO4 and concentrated to give a residue, which
was purified by column chromatography (SiO2), using the eluent as mentioned under each
compound.
General procedure for the convertion of the dendritic chloride to the azide (procedure
B)
Dendritic chloride (1.0 mmol, 1.0 equiv.) was dissolved in a mixture of acetone/water
(4:1; 8 mL) and added NaN3 (1.5 mmol, 1.5 equiv./ 2.5 mmol, 2.5 equiv.), and the reaction
0
mixture was heated to 60 C for 3 h. The reaction mixture was cooled to room temperature,
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acetone evaporated, diluted with water (100 mL), and extracted with EtOAc (2 X 100 mL).
The combined organic layer was washed with saturated NaCl (100 mL), dried over Na2SO4
and evaporated to give the corresponding azido compounds.
First generation dendritic chloride 6:
Following the general procedure A, the dendritic chloride 6 was obtained as white
solid from 3,5ꢀbis(propargyloxy)benzyl chloride 5 (0.3 g, 1.3 mmol) and 2,3,4,6ꢀtetraꢀOꢀ
acetylꢀαꢀDꢀglucopyranoazide 4 (1.01 g, 2.6 mmol) and after eluting the column with Ethyl
acetate : Hexane (1:1). Yield 96%, m.p. 115 oC. 1H NMR (300 MHz, CDCl3):
δ = 1.85, 2.03,
2.07 (3x s, 24H), 4.00ꢀ4.04 (m, 2H), 4.13ꢀ4.17 (m, 2H), 4.28ꢀ4.32 (m, 2H), 4.51 (s, 2H), 5.20
(s, 4H), 5.22ꢀ5.28 (m, 2H), 5.39ꢀ5.49 (m, 4H), 5.92 (d, J = 8.7 Hz, 2H), 6.64 (s, 3H), 7.92 (s,
2H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 20.1, 20.5, 20.5, 20.6, 46.0, 61.5, 61.9, 67.7, 70.3,
72.6, 75.2, 85.8, 101.7, 108.2, 121.4, 139.9, 144.6, 159.4, 168.9, 169.4, 169.9, 170.5 ppm.
MS (EI): m/z = 980 [M+]. C41H49ClN6O20: Calcd. C 50.18, H 5.03, N 8.56; Found C 50.10, H,
4.95, N, 8.41.
First generation dendritic azide 7:
Following the general procedure B, the dendritic azide 7 was obtained as white solid
from the dendritic chloride 6 (4 g, 4.0 mmol) and NaN3 (0.53 g, 8.16 mmol) and after eluting
1
the column with Ethyl acetate : Hexane (1:1). Yield 99%, m.p. 133 °C. H NMR (300 MHz,
CDCl3): δ = 1.78, 1.96, 2.00 (3x s, 24H), 3.92ꢀ3.97 (m, 2H), 4.04ꢀ4.11 (m, 2H), 4.21ꢀ4.26 (m,
4H), 5.13 (s, 4H), 5.18ꢀ5.21 (m, 2H), 5.32ꢀ5.43 (m, 4H), 5.84 (d, J = 2.7 Hz, 2H). 6.50 (d, J =
13
2.1 Hz, 2H), 6.57 (d, J = 2.1 Hz, 1H), 7.86 (s, 2H) ppm. C NMR (75 MHz, CDCl3):
δ =
19.1, 19.5 19.5, 19.6, 53.6, 60.6, 60.9, 66.8, 69.4, 71.7, 74.2, 84.8, 100.6, 106.8, 120.3, 137.0,
143.6, 158.6, 167.9, 168.4, 168.9, 169.5 ppm. MS (FAB): m/z = 987 [M+]. C41H49N9O20:
Calcd. C 49.85, H 5.00, N 12.76; Found C 49.81, H 4.96, N 12.51.
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Second generation dendritic chloride 8 :
Following the general procedure A, the dendritic chloride 8 was obtained as white
solid from 3,5ꢀbis (propargyloxy) benzyl chloride 6 (0.45 g, 1.9 mmol) and the dendritic
azide 7 (3.6 g, 4.02 mmol) and after eluting the column with Ethyl acetate : Hexane (7:3).
Yield 96%, m.p. 148 °C. 1H NMR (300 MHz, CDCl3)
δ = 1.82, 2.02, 2.04, 2.07, (4x s, 48H),
4.01ꢀ4.10 (m, 4H), 4.11ꢀ4.16 (m, 4H), 4.28ꢀ4.32(m, 4H), 4.48 (s, 2H), 5.14 (s, 8H), 5.17 (s,
4H), 5.27 (t, J = 9.6 Hz, 4H), 5.39ꢀ5.50 (m, 12H), 5.92 (d, J = 8.7 Hz, 4H), 6.51(d, J = 2.1
Hz, 4H), 6.59 (d, J = 2.1 Hz, 1H), 6.62 (d, J = 2.4 Hz, 2H), 6.64 (s, 2H), 7.63 (s, 2H), 7.96 (s,
4H) ppm. 13C NMR (75 MHz, CDCl3)
δ = 20.1, 20.5, 20.5, 20.6, 46.1,54.0, 60.4, 61.5, 61.8,
62.1, 67.7, 70.3, 72.6, 75.1, 85.7, 101.9, 107.7, 108.1,121.6, 123.0, 137.0, 139.8, 144.2,
144.3, 159.5, 159.7, 168.9, 169.4, 169.9, 170.5 ppm. MS (EI): m/z = 2210 [M+].
C95H109Cl1N18O42: Calcd. C 51.60, H 4.97, N 11.41; Found C 51.48, H 4.90, N 11.35.
Second generation dendritic azide 9:
Following the general procedure B, the dendritic azide 9 was obtained as white solid
from the dendritic chloride 8 (2 g, 0.9 mmol) and NaN3 (0.16 g, 2.4 mmol) and after eluting
1
the column with Ethyl acetate : Hexane (7:3).Yield 99%, m.p. 159 °C. H NMR (300 MHz,
CDCl3)
δ = 1.82, 2.02, 2.05. 2.07 (4x s, 48H), 4.02ꢀ4.05 (m, 4H), 4.11ꢀ4.17 (m, 4H), 4.24 (d,
J = 4.8Hz, 2H), 4.27ꢀ4.32 (m, 4H), 5.14 (s, 8H), 5.17 (s, 4H), 5.27 (t, J = 9.6 Hz, 4H), 5.39ꢀ
5.50 (m, 12H), 5.93 (d, J = 8.7 Hz, 4H), 6.51 (s, 4H), 6.59 (s, 2H), 6.60 (s, 1H), 6.64 (s, 2H),
7.63 (s, 2H), 7.96 (s, 4H) ppm. 13C NMR (75 MHz, CDCl3)
δ = 20.1, 20.5, 20.5, 20.6, 54.0,
54.6, 61.6, 61.8, 62.1, 67.7, 70.4, 72.6, 75.1, 85.8, 101.7, 107.9, 107.7, 107.8, 121.6, 123.0,
137.0, 144.2, 144.3, 159.4, 159.7, 168.9, 169.4, 169.9, 170.5 ppm. MS (EI): m/z = 2217
[M+]. C95H109N21O42: Calcd. C 51.47, H 4.96, N 13.27; Found C 51.41, H 4.90, N 13.14
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5,5ꢀDifluoroꢀ1,3,7,9ꢀtetramethylꢀ10ꢀ(4ꢀ(propꢀ2ꢀynyloxy)phenyl)ꢀ5Hꢀdipyrrolo[1,2ꢀ
c:1',2'ꢀf][1,3,2]diazaborininꢀ4ꢀiumꢀ5ꢀuide 12:
Following the general procedure , 5,5ꢀdifluoroꢀ1,3,7,9ꢀtetramethylꢀ10ꢀ(4ꢀ(propꢀ2ꢀ
ynyloxy)phenyl)ꢀ5Hꢀdipyrrolo[1,2ꢀc:1',2'ꢀf][1,3,2]diazaborininꢀ4ꢀiumꢀ5ꢀuide 12 was obtained
as dark brown solid from 5,5'ꢀ((4ꢀ(propꢀ2ꢀynyloxy)phenyl)methylene)bis(2,4ꢀdimethylꢀ1Hꢀ
o
1
pyrrole) 12 (0.5 g, 1.8 mmol) and BF3.OEt2 (10 mL). Yield: 87% M. P. 80ꢀ82 C H NMR
:(300 MHz, CDCl3): δH 2.61 (t, J = 2.1 Hz, 1H), 4.71 (d, J = 2.4 Hz, 2H), 6.17ꢀ6.20 (m, 2H),
6.73 (d, J = 1.5 Hz, 2H), 6.96 (d, J = 8.7 Hz, 2H), 7.18 (d, J = 8.7 Hz, 2H), 7.98 (s, 2H). 13C
NMR: (75 MHz, CDCl3): δC 56.0, 76.3, 77.9, 114.9, 118.4, 127.1, 131.4, 132.3, 134.9, 143.6,
147.1, 159.9. Mass spectrum: MS (FAB): m/z = 322 [M+] Analysis: C18H13BF2N2O:
Calculated: C 67.12, H 4.07 N, 8.41 Found: C 67.01, H 4.02, N, 8.41
BODIPY dendrimer 1.
Following the general procedure A, BODIPY dendrimer 1 was obtained as orange color
solid from 5,5ꢀdifluoroꢀ1,3,7,9ꢀtetramethylꢀ10ꢀ(4ꢀ(propꢀ2ꢀynyloxy)phenyl)ꢀ5Hꢀdipyrrolo[1,2ꢀ
c:1',2'ꢀf][1,3,2]diazaborininꢀ4ꢀiumꢀ5ꢀuide 12 (0.4 g, 0.12 mmol) and 2,3,4,6ꢀtetraꢀOꢀacetylꢀαꢀ
Dꢀglucopyranoazide 4 (0.06 g, 0.14 mmol) after column chromatography using a mixture of
1
CHCl3:MeOH (4.8:0.2). Yield: 85%, H NMR : (300 MHz, CDCl3): 1.25(s, 6H), 1.42, 1.85,
2.07, 2.08 ( s, 12H), 2.55 (s, 6H), 3.81 (s, 1H), 4.03ꢀ4.19 (m, 1H), 4.27ꢀ4.29 (m, 2H), 5.04 (s,
2H),4.96 ꢀ 4.99 (m, 1H), 5.11ꢀ5.14 (m, 2H), 5.24 (s, 1H), 5.98 (m, 1H), 6.98 (s, 1H), 7.11ꢀ
7.19 (m, 4H), 7.93 (s, 2H). 13C NMR: (75 MHz, CDCl3): δC 14.6, 20.2, 20.5, 20.7, 29.7, 61.6,
61.7, 62.0, 67.7, 67.9, 70.7, 72.6, 74.0, 75.3, 85.9, 87.9, 114.9, 115.4, 121.2, 129.4, 130.1,
141.6, 143.1, 144.5, 155.4, 158,8, 169.2, 169.3, 170.1,170.5. MS (MALDI): m/z=751.36
[M]+. Elemental Anal.Calcd for Chemical Formula: C36H40BF2N5O10: C, 57.53; H, 5.36; N,
9.32; Found: C, 57.58; H, 5.39; N, 9.31.
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BODIPY dendrimer 2
Following the general procedure A, the BODIPY dendrimer 2 was obtained
as orange color solid from 5,5ꢀdifluoroꢀ1,3,7,9ꢀtetramethylꢀ10ꢀ(4ꢀ(propꢀ2ꢀynyloxy)phenyl)ꢀ
5Hꢀdipyrrolo[1,2ꢀc:1',2'ꢀf][1,3,2]diazaborininꢀ4ꢀiumꢀ5ꢀuide 12 (0.3 g, 0.09 mmol) and
dendritic azide 7 (0.78 g, 0.57 mmol) (0.1 g, 0.1 mmol) and after purification from column
1
using a mixture of CHCl3:MeOH (23:2). Yield: 88%, H NMR : (300 MHz, CDCl3): 1.25(s,
6H), 1.40, 1.65, 1.86, 2.07 (4x s, 24H), 2.55 (s, 6H), 4.05 (s, 2H), 4.04ꢀ4.33 (m, 4H), 5.16 (s,
4H), 5.21ꢀ5.54 (m, 8H), 5.86ꢀ6.65 (m, 2H), 6.57 (s, 2H), 6.58 (s, 2H), 6.65 (s, 2H), 7.16 (d, J
13
= 8.4 Hz, 2H) 7.63 (d, J = 8.7 Hz, 2H) 7.92 (s, 2H), C NMR: (75 MHz, CDCl3): δC 14.5,
20.1, 20.7, 29.8,54.6, 61.5, 61.8, 61.9, 67.7, 70.3, 72.6, 75.1, 85.8, 101.5,107.8, 115.5, 121.4,
123.1, 127.9, 129.3, 136.8, 138.0, 144.3, 144.6, 155.4, 159.6, 159.8, 168.9, 169.4, 169.4,
169.5, 170.5.
MS (MALDI): m/z=1388.66 [M+Na]+. Elemental Anal.Calcd for
C63H70BF2N11O21: C, 55.39%; H, 5.16%; N, 11.28%; Found: C, 55.45%; H, 5.26%; N,
11.19%;
BODIPY dendrimer 3
Following the general procedure A, the BODIPY dendrimer 3 was obtained as orange
color solid from 5,5ꢀdifluoroꢀ1,3,7,9ꢀtetramethylꢀ10ꢀ(4ꢀ(propꢀ2ꢀynyloxy)phenyl)ꢀ5Hꢀ
dipyrrolo[1,2ꢀc:1',2'ꢀf][1,3,2]diazaborininꢀ4ꢀiumꢀ5ꢀuide 12 (0.2 g, 0.06 mmol) and dendritic
azide 9 (0.15 g, 0.07 mmol) after purification from column using a mixture of CHCl3:MeOH
1
(23:2). Yield: 85%, H NMR : (300 MHz, CDCl3): (300 MHz, CDCl3): 1.26(s, 6H), 1.39,
1.82, 2.04, 2.07 (4x s, 48H), 4.07ꢀ4.13 (m, 4H), 4.24ꢀ4.29 (m, 4H), 4.31ꢀ4.33 (s, 4H), 5.1 (s,
12H), 5.31 (s, 6H), 5.40ꢀ5.52 (m, 14H), 5.93 (d, J = 8.4 Hz, 4H), 6.48 (s, 8H) 6.52 (s, 4H),
7.15 (s, 2H), 7.63(s, 2H), 7.99(s, 6H). 13C NMR: (75 MHz, CDCl3): δC 14.5, 20.1, 20.5, 20.6,
20.7, 29.8, 54.6, 61.5, 61.8, 61.9, 67.7, 70.3, 72.6, 75.2, 85.8, 101.5, 107.7,107.9, 115.5,
121.4, 121.5, 123.1, 127.9, 129.3, 136.8, 138.0, 144.3, 144.4, 144.6, 155.4, 159.8, 168.9,
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169.4, 170.5. MS (MALDI): m/z=2617.14 [M+Na]+. Elemental Anal.Calcd for
C117H130BF2N23O43: C, 54.15; H, 5.05; N, 12.41%. Found: C, 54.19; H, 5.07; N, 12.48.
Conclusion
We have synthesized BODIPY based glycodendrimers 1, 2 and 3 in excellent yields
by click chemistry via convergent approach. All the glycodendrimers show fluorescence
intensity which increases on increasing the dendrimer generation due to valence effect. The
cyclic voltammograms for the dendrimers 1, 2 and 3 show quasiꢀreversible behaviour in the
cyclic voltammogram. All the BODIPY dendrimers show excellent inhibitory activity against
both gram positive and gram negative bacteria such as such as S. aureus, B. Subtilis, S.
typhimurium and E. Coli and the first and second generation dendrimers 2 and 3 show better
antibacterial activity than the zeroth generation dendrimer 1 and the antibacterial activity is
dose independent. The dendrimers can be used as fluorescent marker in living organism due
to their fluorescence property.
Acknowledgements
The authors thank DSTꢀFIST for providing NMR facility to the Department of
Organic Chemistry and A. Sathiyaseelan, P. T. Kalaichelvan for carrying out antybacterial
activity V S thanks University of Madras for the infrastructure and for providing Kalaignar
endowment fellowship.
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DOI: 10.1039/C7NJ04412G
Synthesis, characterization, optical and electrochemical properties and
antibacterial activity of novel BODIPY Glyco conjugated dendrimers
Velautham Saravanan and Perumal Rajakumar*
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai
600 025, India. E-mail: perumalrajakumar@gmail.com; Fax: +91 044 22300488;
Tel: +91 044 22202814; 9551379907
Graphical abstract
A new class of novel BODIPY - Glycoconjugated dendrimer with optical,
electrochemical and antibacterial properties is reported.
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