Synthesis of asymmetric monomethine cyanine dyes with red-shifted optical properties

Article abstract of DOI:10.1002/jhet.1963

Six novel asymmetrical monomethine cyanine dyes were synthesized via the condensation reaction of 1-butyl-2-(methylthio)benzo[c,d]indol-1-ium iodide and various 1,5-substituted indolenine salts under basic conditions. The dyes were characterized using UV-vis spectroscopy, fluorescence, 1H NMR, 13C NMR, and mass spectrometry; furthermore, the purity of these compounds was observed using LC/ELSD/MS.

Full text of DOI:10.1002/jhet.1963

180
Synthesis of Asymmetric Monomethine Cyanine Dyes with Red-Shifted
Optical Properties
Vol 52
*
Eduardo Soriano, Loretta Outler, Eric A. Owens, and Maged Henary
Department of Chemistry and Biochemistry, Georgia State University, 100 Piedmont Avenue, Atlanta, Georgia 30303-
3083, USA
*
E-mail: mhenary1@gsu.edu
Additional Supporting Information may be found in the online version of this article.
Received October 22, 2012
DOI 10.1002/jhet.1963
Published online 19 May 2014 in Wiley Online Library (wileyonlinelibrary.com).
Six novel asymmetrical monomethine cyanine dyes were synthesized via the condensation reaction of
1-butyl-2-(methylthio)benzo[c,d]indol-1-ium iodide and various 1,5-substituted indolenine salts under basic
conditions. The dyes were characterized using UV–vis spectroscopy, fluorescence, 1H NMR, 13C NMR, and
mass spectrometry; furthermore, the purity of these compounds was observed using LC/ELSD/MS.
J. Heterocyclic Chem., 52, 180 (2015).
INTRODUCTION
various environments in biological systems [9]. These
applications prompted the synthesis of 1,5-substituted
monomethine cyanines that have large Stokes shift values
and red-shifted absorbance and fluorescence properties.
The first cyanine dye synthesized was derived from the
heating of N-amyl quinolinium iodide with N-amyl
lepidinium iodide in ammonia, forming a blue compound.
Since this synthesis in 1856 by C. G Williams, cyanine dyes
have been extensively employed in various applications such
as photographic processes, laser printing, nonlinear optical
material, and more recently as fluorescent probes for biomo-
lecular labeling and imaging [1–6]. In general, these dyes
consist of two terminal heterocyclic rings with nitrogen cen-
ters that are connected via a conjugated and electron-
deficient methine chain. Common heterocyclic moieties
include quinoline, indolenine, and benzothiazole. (Figure 1)
The applications of these dyes arise from the electron-
deficient conjugated system present between the nitrogen
centers. With current synthetic methods, the conjugated
system of the compounds can be altered to assume specific
absorption and fluorescence spectra within the range of
400 to 1000 nm [7,8]. The dyes presented in this paper
are monomethine cyanine dyes, in which there is only
one carbon atom between the two terminal heterocycles
that commonly absorb between 480 and 515 nm [7,8].
Monomethine cyanine dyes generally have high molar
extinction coefficient values and exhibit little to no fluores-
cence as a free dye in solution unless conformationally
restricted [9,10]. These properties provide ideal fluorogenic
characteristics that allow them to be among the best
noncovalently binding nucleic acid labels [9,10]. Addition-
ally, when these dyes are within a viscous environment, their
fluorescence becomes observable, which allows for viscosity-
dependent fluorescence measurements and direct analyses of
Synthesis and photophysical determinations. The synthetic
preparation of asymmetric monomethine cyanines begins
with the formation of the indole salt (as shown in
Scheme 1); the reaction between the 4-substituted
phenylhydrazines 1–3 with the 3-methylbutan-2-one (4)
results in an enamine. Upon the formation of the
enamine, the acidic environment catalyzes the pericyclic
rearrangement of the enamine that is energetically driven
by the formation of the cyclic indole. A saturated solution
of sodium bicarbonate was used to neutralize the reaction
mixture due to the increase of ammonium as byproduct
from the cyclization and to ensure the deprotonation of
the indolenine nitrogen for subsequent reactions.
After forming the 5-substituted indolenine ring 5–8,
various alkyl halides were used for quaternizing the
N-indolenyl moiety. The alternate half of the monomethine
dye was then prepared starting from the commercially avail-
able amide 15. This reagent was alkylated using iodobutane,
and the carbonyl substituent was then transformed to the
thione using phosphorous pentasulfide. This was then
transformed to the methylsulfide using iodomethane for the
reaction with the previously prepared indolenine salt. The
synthesis of the monomethine cyanine dyes was then
achieved via the condensation reaction of 1-butyl-2-
(methylthio)benzo[c,d]indol-1-ium iodide (18) and an
indolenine salt in the presence of the basic agent, TEA.
The base within the reaction was needed for the activation
© 2014 HeteroCorporation

January 2015
Synthesis of Asymmetric Monomethine Cyanine Dyes with Red-Shifted Optical Properties
181
There was an average of 7 nm bathochromic shift in
absorbance maxima in the 90% glycerol/10% MeOH (v/v)
solution from the newly synthesized dyes. Furthermore,
there was a decrease in the molar absorptivity values for a
majority of the dyes synthesized. Methanol was used to
solubilize the compounds in the highly viscous glycerol.
A common characteristic observed with this set of dyes is
their broad absorbance spectra that can be attributed to a
high level of aggregation, as shown using compound 23
in Figure 2 [1].
Furthermore there was an average of 88 nm Stokes shift
for each of the dyes in the same solution. Large Stokes
shift is important for it increases the utility of the
fluorophore as the excitation source remains far from the
fluorescence signal, which reduces Rayleigh scattering,
and such properties are useful for in vitro and in vivo
imaging especially in highly scattering media [13,14].
The fluorescence of these compounds could not be
observed in methanol alone because of the free rotation
around the internuclear bridge resulting in a high
nonradiative rate of return of the excited molecule—as
cited with many monomethine cyanines containing the
indolenine structure [4,11,12]. In viscous solution of 90%
Figure 1. Generic structure of cyanine dyes, in which n represents the
number of methine groups in the polyene chain.
of indolium salt via the deprotonation of the methyl at the 2
position. After the deprotonation, the mechanism proceeds in
an SN2 fashion in which the activated methylene group of the
various individual salts 9–14 displaces the methyl sulfide
moiety of 18 and results in the formation of the asymmetrical
monomethine dyes 19–24.
Both UV–vis and emission spectra were recorded for
each dye in MeOH and 90% glycerol/10% MeOH, shown
in Table 1. There are two molecular attributes that account
for the red-shifted absorbance wavelengths of the presented
dyes. The electron-deficient conjugated system is responsi-
ble for the red-shifted absorbance wavelengths when com-
pared with a polyene system; additionally, the benzo[c,d]
indole moiety provides increased conjugation within the
chromophore and an additional red shift of approximately
50 nm in absorbance when compared with previously
synthesized asymmetric monomethine cyanines [1–3].
Scheme 1
Table 1
Wavelength of maximum of both absorbance and fluorescence and molar absorptivity.
Dye
l
abs (nm)a
l
abs (nm)b
l
emission (nm)b
Stokes shift (nm)b
e (L molÀ1 cmÀ1 a
)
e (L molÀ1 cmÀ1 b
)
19
20
21
22
23
24
556
562
564
564
565
567
565
568
571
572
572
575
657
656
657
660
658
662
92
89
86
88
86
87
30,000
32,500
23,600
33,360
30,450
33,600
26,200
27,300
31,300
30,900
28,500
39,900
Absorbance and emission of the dyes were at a concentration of 20 mM.
ain methanol.
bin 90% glycerol/10% methanol (v/v).
Journal of Heterocyclic Chemistry
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182
E. Soriano, L. Outler, E. A. Owens, and M. Henary
Vol 52
Optical Properties of Compound 23
plate thickness 250 mm (Maidstone, Kent, UK). NMR data
were obtained from a Bruker Avance 300 and 400 MHz
NMR spectrometer (Bruker Biospin Corporation, Newark,
DE). The mass spectra were obtained using a Waters
Micromass LCT TOF ES+ Premier Mass Spectrometer.
Liquid chromatography utilized a Waters 2487 single
wavelength absorption detector with wavelengths set
between 640 and 700nm depending on the dye’s
photophysical properties. The column used in LC was a
Waters Delta-Pak 5 uM 100A 3.9 mm  150 mm reversed-
phase C18 column. Evaporative light scattering detection
analyzes trace impurities that cannot be observed by alternate
methods; a SEDEX 75 ELSD was utilized in tandem with
liquid chromatography to observe and confirm purity.
Emission
Absorbance
420
520
620
720
820
920
Wavelength
Figure 2. Absorbance and emission spectra of 23 in 90% glycerol/10%
methanol (v/v) at a dye concentration of 20 mM. [Color figure can be
viewed in the online issue, which is available at wileyonlinelibrary.com.]
Optical measurements.
Molar absorptivity.
The
absorption spectra were recorded on a Varian Cary 3G
UV–vis spectrophotometer interfaced with Cary WinUV
Scan application v3.00 at 20 mM in cuvettes with a path
length 1 cm. For each optical measurement, stock
solutions were prepared by adding the appropriate mass
of each individual compound on a four-digit analytical
balance to make a 1.0 mM solution. From these stock
solutions, the dilutions seen in Supplementary information
were obtained to determine the molar absorptivity values
in methanol. For molar absorptivity values in glycerol/
methanol (90%/10% v/v), the concentrations for the
solutions were prepared via the dilution of the stock
solution in methanol and followed the addition of the
appropriate volume of glycerol to achieve the desired
concentrations. Furthermore, each solution was vortexed
for 1 min and sonicated for 10 min, and its absorbance
was measured.
glycerol/10% MeOH (v/v), a fluorescence signal was
observed because of the hindered rotation of the dye
molecule.
CONCLUSIONS
A series of six monomethine derivatives were successfully
synthesized in good yield with large Stokes shifts and
red shifted absorbance and fluorescence properties in
comparison with previously synthesized asymmetric
monomethines. The dyes’ observable fluorescence in a
highly viscous environment such as the glycerol–methanol
solution reveals for its use to report on viscosity, which
could be beneficial for evaluating noncovalent interactions
that restrict the rotation of the dye. Incorporating the
benzo[c,d]indole moiety afforded the red-shifted optical
properties desired. Lastly, the synthetic chosen synthetic
route requires a facile purification methodology, which
allows for the further development of this class.
Fluorescence data.
Florescence spectra for all
monomethine cyanine dyes were obtained using a
Shimadzu RF-5301 spectroflurophotometer (Shimadzu
Corporation Analytical Instruments Division, Duisburg,
F. R. Germany). The parameters implemented for this
procedure were as follows: slit width for both excitation
and emission 5 nm; sensitivity was set to high;
wavelength speed set to medium; excitation wavelength
550 nm, and the light source was a 150 W Xenon lamp.
The fluorimeter was interfaced to a PC, and data were
collected using RF-5301PC software. Disposable
polystyrene fluorescence cuvettes with a 1.00 cm path
length were used for all measurements. All fluorescence
measurements were made using solutions of A < 0.1 to
avoid inner filter effects. The data were analyzed, and
calculations were carried out using Microsoft Excel
(Microsoft Corporation, Redmond, WA)
MATERIALS
Chemicals used: dichloromethane (DCM; reagent grade,
+95.5% purity, Sigma Aldrich, St. Louis, MO), diethyl
ether (reagent grade, +99% purity, Sigma Aldrich), acetic
anhydride, sodium acetate (99.5% purity, Merck KGaA,
Darmstadt, Germany), iodoethane (99% purity, Sigma Aldrich),
2,3,3-trimethylindolenine (99% purity, Sigma Aldrich), methanol
(reagent grade, +95.5% purity, Sigma Aldrich), hexanes (reagent
grade, +95.5% purity, Sigma Aldrich), (4-bromophenyl)hydra-
zine hydrochloride (99%, Acros Organic, Belgium, Germany),
3-methylbutan-2-one (+99% purity, Sigma Aldrich), TEA
(99% purity, Fisher Chemical, Germany), iodobutane (99%,
Alfa Aesar, Lancashire, UK), 3-bromo-1-phenylpropane
(99%, Alfa Aesar), glycerol (A.C.S. certified, 99.6% purity,
Fischer Scientific Company, Fair Lawn, NJ).
EXPERIMENTAL
Chromatography: pre-coated TLC plates, silica gel
60 F-254 (Merck KGaA). For Rf: pre-coated TLC plates,
Whatman Pastisi CS5 Multi K with florescent indicator,
General synthetic procedure for the indolium salts. Comp-
ounds 9–13 were synthesized as previously reported [3]. Each
compound was then dissolved in acetonitrile (25 mL), and 4 molar
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Synthesis of Asymmetric Monomethine Cyanine Dyes with Red-Shifted Optical Properties
183
equivalences of the primary alkyl halide were added to the
solution. The reaction mixture was then refluxed at 90ꢀC for
72h. TLC was used to monitor the reaction in a solution of 4:1,
DCM/hexanes. Upon cooling, the reaction mixture to room
temperature acetone was added followed by diethyl ether to
precipitate the salt. The solid was filtered and washed with
diethyl ether. The salts were used without further purification in
General synthesis of the monomethine dyes. Compound
18 was dissolved in 10 mL of CH3CN, and 1.5 equiv each of
the appropriate indolium salt and TEA was added to the
solution. The mixture was refluxed at 60ꢀC for 1 h. UV–vis was
used to monitor the reaction. Upon cooling to room
temperature, diethyl ether was added to precipitate the dye. The
solid was collected and washed with deionized water and
diethyl ether. The dyes were purified via recrystallization by
solvation in a minimal amount of methanol and dilution with
diethyl ether causing precipitation as dark purple solids.
subsequent reactions.
Synthesis of 5-bromo-2,3,3-trimethyl-1-(3-phenylpropyl)-3H-
indol-1-ium bromide (14).
Compound 7 (0.02 mmol) was
dissolved in acetonitrile (25 mL), and 1-bromo-3-phenylpropane
(0.04 mmol, 20 mL) was added. The reaction mixture was then
refluxed at 90ꢀC for 72 h. TLC was used to monitor the reaction
using DCM/hexanes (4:1) as eluting solvent. The reaction
mixture was allowed to cool to room temperature; acetone was
added to the mixture, followed by diethyl ether to precipitate
the salt. The solid was collected via vacuum filtration and
washed with diethyl ether to afford 14 as a dark brown solid.
(E)-1-Butyl-2-((1-butyl-3,3-dimethylindolin-2-ylidene)methyl)
benzo[c,d]indol-1-ium iodide (19).
Yield 66%, 0.48 g; mp
220–221ꢀC; TLC (25:1 CH2Cl2:CH3OH) Rf = 0.05; 1H NMR
(400 MHz, DMSO-d6): d ppm 0.63 (t, J = 7.3 Hz, 3H), 0.92
(t, J = 6.7 Hz, 3H), 1.02 (q, J = 7.0 Hz, 2H), 1.41 (q, J = 5.4 Hz,
2H), 1.65 (s, 8H), 1.82 (q, J = 7.2 Hz, 2H), 4.19 (s, 2H), 4.49
(s, 2H), 6.31 (s, 1H), 7.42 (t, J = 9.8 Hz, 1H), 7.55
(t, J = 8.0 Hz, 1H), 7.73 (m, 4H), 7.91 (m, 2H), 8.01
(d, J = 7.0 Hz, 1H), 8.36 (d, J = 7.2 Hz, 1H); 13C NMR (100MHz,
DMSO-d6): d ppm 12.94, 13.35, 18.34, 19.15, 25.37, 28.89,
29.53, 43.27, 49.78, 51.32, 83.57, 110.71, 113.99, 122.82,
122.95, 123.46, 126.05, 128.14, 128.87, 129.22, 129.67, 132.41,
140.24, 140.35, 141.44, 155.54, 180.08; labs = 556 nm in MeOH.
HRMS (ESI) Calcd. for [C30H35N2]1+ m/z 423.2795, found
1
Yield 43%, 3.5 g, mp 160–161ꢀC; H NMR (400 MHz, CDCl3):
1.60 (s, 6H), 2.29 (m, J = 8.0 Hz, 2H), 2.88 (t, J = 8.0 Hz, 2H),
3.03 (s, 3H), 4.79 (t, J = 8.0 Hz, 2H), 7.20 (d, J = 4.0 Hz, 3H),
7.29 (d, J = 4.0 Hz, 2H) 7.50 (d, J = 8.0 Hz, 1H), 7.64
(d, J = 8.0 Hz, 2H) d ppm 13C NMR (100 MHz, CDCl3): d ppm
16.65, 23.17, 29.40, 32.57, 49.06, 54.83, 117.30, 124.47,
126.74, 126.90, 128.59, 128.96, 132.80, 139.57, 140.17,
m/z 423.1447.
(E)-1-Butyl-2-((1-butyl-5-chloro-3,3-dimethylindolin-2-ylidene)
143.62, 196.46.
Synthesis of 1-butylbenzo[c,d]indol-2(1H)-one (16). Was
methyl)benzo[c,d]indol-1-ium iodide (20).
Yield 34%, 0.40 g;
1
mp 197–198ꢀC; TLC (25:1 CH2Cl2:CH3OH) Rf =0.08; H NMR
(400 MHz, DMSO-d6): d ppm 0.63 (t, J = 7.5 Hz, 3H), 0.92
(t, J = 8.0 Hz, 3H), 1.01 (m, 2H), 1.41 (m, 2H), 1.59 (m, 2H), 1.64
(s, 6H), 1.81 (m, 2H), 4.14 (m, 2H), 4.52 (m, 2H), 6.30 (s, 1H),
7.62 (d, J = 8.0 Hz, 1H), 7.72 (d, J = 7.4 Hz, 1H), 7.78 (m, 2H),
7.90 (m, 3H), 8.09 (d, J= 8.0 Hz, 1H), 8.39 (d, J= 7.0 Hz, 1H);
13C NMR (100 MHz, DMSO-d6): d ppm 13.26, 13.66, 18.64,
19.46, 25.65, 29.03, 29.93, 43.75, 50.28, 51.58, 84.00, 111.73,
115.66, 123.55, 123.66, 123.81, 128.84, 129.00, 129.13, 129.27,
129.56, 129.98, 130.09, 130.62, 133.14, 140.52, 140.83, 142.59,
performed by adding 40% sodium hydroxide (22.3 mmol, 0.7 mL)
to a solution of benzo[c,d]indole-2(1H)-thione (1.5 g, 8.9 mmol) in
15 mL of N-methyl-2-pyrrolidinone. Iodobutane (1.2 equiv) was then
added dropwise to the reaction mixture, which was heated to 50 ꢀC
for 1 h, after which no starting material was visible on TLC. After
cooling to room temperature, water (10 mL) was added, and the
crude product was extracted with DCM and washed with brine. The
organic layer was dried over anhydrous magnesium sulfate, gravity
filtered, and concentrated in vacuo. The crude product was purified
by flash column chromatography on silica gel using ethyl acetate/
hexanes (1:10) as the eluting solvent.
156.40, 179.80; mp 197–198ꢀC
labs = 562 nm in MeOH.
HRMS (ESI) Calcd. for [C30H34ClN2]1+ m/z 458.0568, found
Synthesis of 1-butylbenzo[c,d]indole-2(1H)-thione (17).
A
mixture of amide (200 mg) and diphosphorus pentasulfide
(365 mg) in pyridine (8 mL) was refluxed for 2 h. The cooled
reaction mixture was acidified with concentrated HCl and a red
precipitate formed upon cooling. The crude product was filtered
and dried. 1H NMR (300 MHz, DMSO-d6): d ppm 0.93
(t, J = 9.0 Hz, 3H), 1.39 (m, J = 9.0 Hz, 2H), 1.77 (m, J = 9.0 Hz,
2H), 4.35 (t, J = 9.0 Hz, 2H), 7.46 (d, J = 6.0 Hz, 1H), 7.61
(t, J = 6.0 Hz, 1H), 7.77–7.84 (m, 2H), 8.15 (d, J = 6.0 Hz, 1H),
m/z 458.7525.
(E)-1-Butyl-2-((1-butyl-5-methoxy-3,3-dimethylindolin-2-
ylidene)methyl)benzo[c,d]indol-1-ium iodide (21). Yield 50%,
0.24g, mp 174–175ꢀC; TLC (25:1 CH2Cl2:CH3OH) Rf = 0.10;
1H NMR (400 MHz, DMSO-d6): d ppm 0.64 (t, J = 7.3 Hz, 3H),
0.91 (t, J = 7.4 Hz, 3H), 1.02 (q, J = 7.5Hz, 2H), 1.10
(q, J = 7.6Hz, 2H), 1.63 (s, 8H), 1.80 (m, J = 7.1 Hz, 2H), 3.86
(s, 3H), 4.18 (t, J = 6.3Hz, 2H), 4.43 (t, J = 6.9 Hz, 2H), 6.25
(s, 1H), 7.10 (dd, J = 6.9 Hz, J = 2.1 Hz 1H), 7.41 (d, J = 2.1 Hz,
1H), 7.62–7.71 (m, 3H), 7.81–7.85 (m, 3H), 8.30 (d, J = 7.2 Hz,
1H); 13C NMR (100 MHz, DMSO-d6): d ppm 13.49, 13.92,
18.84, 19.72, 25.63, 29.54, 29.96, 43.54, 50.38, 52.18,
56.16, 83.93, 109.65, 110.11, 114.05, 115.69, 122.63, 124.24,
127.56, 129.55, 129.76, 130.15, 130.20, 132.29, 135.10, 141.17,
8.24 (d, J = 9.0 Hz, 1H).
Synthesis of 1-butyl-2-(methylthio)benzo[c,d]indol-1-ium iodide
(18). A mixture of compound 17 and iodomethane (14 equiv)
in the absence of solvent was heated to reflux for 8 h. The
iodomethane was removed in vacuo. The resulting residue was
treated with diethyl ether, and the mixture was sonicated for
30 min and was suction filtered, washed with diethyl ether, and
dried leaving an 82% yield. 1H NMR (400 MHz, CDCl3): d
ppm 0.82 (t, J = 7.6 Hz, 3H), 1.39 (q, J = 7.6 Hz, 2H), 1.82 (m,
J= 7.2 Hz, 2H), 4.51 (t, J = 7.2 Hz, 2H), 7.72 (t, J= 8.0 Hz, 1H),
7.99 (t, J= 7.6 Hz, 1H), 8.10 (d, J= 8.0 Hz, 1H) , 8.21 (d,
J=7.6Hz, 1H), 8.50 (d, J= 7.6Hz, 1H), 8.99 (d, J=8.0Hz,
1H). 13C NMR (100 MHz, CDCl3): d ppm 12.73, 17.73, 19.16,
29.47, 47.41, 117.02, 121.76, 127.29, 127.97, 128.12, 128.83,
130.47, 135.05, 136.93, 137.32, 171.74
142.92, 154.81, 159.08, 180.29;
labs = 564nm in MeOH.
HRMS (ESI) Calcd. for [C31H37ClN2O]1+ m/z 453.2900, found
m/z 453.2441.
(E)-2-((5-Bromo-1-ethyl-3,3-dimethylindolin-2-ylidene)methyl)-
1-butylbenzo[c,d]indol-1-ium iodide (22). Yield 25%, 0.12 g,
mp 195–196ꢀC; TLC (25:1 CH2Cl2:CH3OH) Rf = 0.12; 1H NMR
(400 MHz, DMSO-d6): d ppm 0.93 (t, J = 8.0 Hz, 3H), 1.10
(t, J = 8.0 Hz, 3H), 1.41 (m, 2H), 1.64 (s, 6H), 1.84 (t, J = 8.0 Hz,
2H), 4.17 (m, 2H), 4.49 (t, J = 6.0 Hz, 2H), 6.29 (s, 1H) , 7.62
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E. Soriano, L. Outler, E. A. Owens, and M. Henary
Vol 52
(d, J = 12.0 Hz, 1H) 7.73–7.81 (m, 3H), 7.88–7.95 (m, 2H), 8.02
(s, 1H), 8.13 (d, J = 4.0 Hz, 1H), 8.40 (d, J = 4.0 Hz, 1H); 13C
NMR (100 MHz, MeOD-d4): d ppm 12.66, 13.49, 13.65, 20.44,
25.49, 30.91, 72.81, 83.69, 84.64, 112.53, 115.69, 120.11,
124.92, 124.98, 127.00, 129.13, 130.07, 130.53, 131.02, 132.22,
134.07, 141.26, 141.26, 141.78, 143.44, 158.41, 179.99;
Acknowledgments. The synthesis and optical measurements of
monomethine cyanines was supported by the Georgia State
University Research Initiation Grant, GSU Research Mentor Grant,
and the Georgia Research Alliance Grant to M. H. E. S. would like
to offer gratitude for his support through the Ronald E. McNair
Program. Additionally, M. H. would like to acknowledge the
Center for Diagnostics and Therapeutics for their ongoing support
at Georgia State University. E. S. and L. O. contributed equally to
the described work based on their undergraduate research.
l
abs = 564 nm in MeOH; HRMS (ESI) Calcd. for [C28H30BrN2]1
+ m/z 473.1567, found m/z 473.0529.
(E)-2-((5-Bromo-1-butyl-3,3-dimethylindolin-2-ylidene)methyl)-
1-butylbenzo[c,d]indol-1-ium iodide (23). Yield 54%; 0.46 g,
mp 187–186ꢀC; TLC (25:1 CH2Cl2:CH3OH) Rf = 0.16; 1H NMR
(400 MHz, DMSO-d6): d ppm 0.60 (t, J = 6.4 Hz, 3H), 0.89
(t, J = 6.4 Hz,3H), 0.98 (m, J = 7.0 Hz, 2H), 1.39 (m, J = 6.4 Hz,
2H), 1.58 (t, J = 5.8 Hz, 2H), 1.67 (s, 6H), 1.82 (m, 2H), 4.13
(s, 2H), 4.54 (s, 2H), 6.34 (s, 1H), 7.67–7.77 (m, 4H), 7.90
(m, 2H), 8.02 (s, 1H), 8.06 (d, J = 6.7 Hz, 1H), 8.37
(d, J = 7.4 Hz, 1H); 13C NMR (100 MHz, DMSO-d6): d ppm
12.78, 13.19, 18.19, 18.98, 25.27, 28.55, 29.47, 43.44, 48.09,
49.84, 51.14, 83.69, 111.33, 115.64, 118.25, 123.09, 123.34,
125.84, 128.58, 129.05, 129.43, 129.66, 130.69, 132.64, 139.95,
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2000, 130, 7.
140.78, 142.41, 155.95, 179.08;
labs = 565 nm in MeOH;
HRMS (ESI) Calcd. for [C30H34BrN2]1+ m/z 502.5078, found
m/z 502.7264.
(E)-2-((5-Bromo-3,3-dimethyl-1-(3-phenylpropyl)indolin-2-
ylidene)methyl)-1-butylbenzo[c,d]indol-1-ium iodide (24). Yield
32%, 0.29 g, mp 201–202ꢀC; TLC (25:1 CH2Cl2:CH3OH)
[6] Mujumdar, R. B.; Ernst, L. A.; Mujumdar, S. R.; Lewis, C. J.;
Waggoner, A. S., Bioconjugate Chemistry 1993, 4 (2), 105-111.
[7] Armitage, B. A Cyanine dye–DNA interactions: intercalation,
groove binding, and aggregation, Topics in Current Chemistry; Waring, M.
J.; Chaires, J. B. Eds.; Springer Berlin: Heidelberg, 2005; Vol. 253, pp 55-76.
[8] Mojzych, M.; Henary, M., Synthesis of cyanine dyes. In
Heterocyclic Polymethine Dyes, Strekowski, L., Ed. Springer Berlin:
Heidelberg, 2008; Vol. 14, pp 1–9.
[9] Silva, G. L.; Ediz, V., Yaron, D.; Armitage, Bruce A. J. Am.
Chem. Soc. 2007, 129(17), 5710.
[10] Völker, S. F.; Renz, M.; Kaupp, M.; Lambert, C. Chemistry –
A European Journal 2011, 17(50), 14147.
[11] Timcheva, I. I.; Maximova, V. A.; Deligeorgiev, T. G.;
Gadjev, N. I.; Sabnis, R. W.; Ivanov, I. G. FEBS Letters 1997, 405(2), 141.
[12] Oster, G.; Nishijima, Y., J. Am. Chem. Soc. 1956, 78(8), 1581.
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1994, 4, 65.
Rf =0.20; 1H NMR (400 MHz, DMSO-d6):
d ppm 0.91
(t, J = 6.96 Hz, 3H), 1.41 (m, J= 7.24 Hz, 2H), 1.65 (s, 6H),
1.75 (m, J = 7.20 Hz, 2H), 1.83 (m, J = 6.72 Hz, 2H), 2.40
(m, J = 6.20 Hz, 2H), 4.10 (m, 2H), 4.41 (m, 2H), 6.19 (s, 1H),
6.76 (m, 5H), 7.78 (s, 2H), 7.71 (q, J = 10.08 Hz, 2H), 7.96 (t,
J = 6.80 Hz, 1H), 7.98 (m, 1H), 8.02 (s, 1H), 8.07 (d, J =6.88Hz),
8.40 (d, J = 7.76 Hz, 1H) 13C NMR (100 MHz, DMSO-d6): d ppm
13.21, 19.02, 25.29, 28.31, 29.54, 30.99, 49.11, 51.02, 83.12,
111.50, 115.30, 118.11, 123.11, 123.55, 124.96, 125.83, 126.4,
127.13, 127.22, 127.92, 128.80, 129.00, 129.38, 130.69, 132.74,
139.37, 139.81, 141.02, 142.32, 155.95, 178.11; labs = 567 nm in
MeOH; HRMS (ESI) Calcd. for [C35H36BrN2]1+ m/z 563.2056,
found m/z 563.0953.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

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