Novel stilbene-based Fischer base analog of leuco-TAM - (2E,2′Z)-{2-(4-(E)-styrylphenyl)propane-1,3-diylidene}bis(1,3,3-trimethylindoline) - derivatives: Synthesis and structural consideration by 1D NMR and 2D NMR spectroscopy

Article abstract of DOI:10.1002/mrc.4359

We report the synthesis of a series of novel stilbene-based (St) Fischer base analogs of leuco-triarylmethane (LTAM) dyes by treating Fischer base with (E)-4-styrylbenzaldehyde derivatives. All St-LTAM molecules examined herein are characterized by 1D and 2D NMR. They were found to exhibit ZE configuration and isomerize to their diastereomers EE and ZZ in 2-3 h. They exhibit type I behavior of diastereomeric isomerization.

Full text of DOI:10.1002/mrc.4359

Research article
Received: 18 June 2015
Revised: 21 August 2015
Accepted: 28 August 2015
Published online in Wiley Online Library: 8 October 2015
(wileyonlinelibrary.com) DOI 10.1002/mrc.4359
Novel stilbene-based Fischer base analog of
leuco-TAM – (2E,2′Z)-{2-(4-(E)-styrylphenyl)
propane-1,3-diylidene}bis(1,3,3-trimethylin
doline) – derivatives: synthesis and structural
consideration by 1D NMR and 2D
NMR spectroscopy
Sam-Rok Keum* and Hyun-Woo Lim
We report the synthesis of a series of novel stilbene-based (St) Fischer base analogs of leuco-triarylmethane (LTAM) dyes by
treating Fischer base with (E)-4-styrylbenzaldehyde derivatives. All St-LTAM molecules examined herein are characterized by
1D and 2D NMR. They were found to exhibit ZE configuration and isomerize to their diastereomers EE and ZZ in 2–3 h. They exhibit
type I behavior of diastereomeric isomerization. Copyright © 2015 John Wiley & Sons, Ltd.
1
Keywords: NMR; H; COSY; HMBC; HETCOR; NOESY; Fischer base analogs of leuco-TAM dyes; diastereomeric isomerization; Heck reaction;
photochemotherapy agents; malachite green
[
20–22]
diylidene)bis(1,3,3- trimethylindoline).
A number of LTAM
Introduction
molecules containing a central carbon bearing two FB fragments
and one aryl ring such as phenyl and pyridinyl have been reported
previously. The FB moiety, whose skeleton contains a conjugated
enamine moiety, is regarded as an active methylene group-
containing indole. Indole is an important heterocycle because it
contains the skeleton of indole alkaloids, which are biologically ac-
tive compounds. Thus, the incorporation of an indole nucleus,
which is a biologically accepted pharmacophore in medicinal com-
pounds, has made it a versatile heterocyclic system exhibiting a
Triarylmethane (TAM) compounds, sometimes referred to as ‘leuco-
[
1–3]
TAMs’ (LTAMs) or ‘leuco-bases’,
important group of intermediates for the synthesis of various func-
are well known to constitute an
[
4,5]
tional organic compounds such as polymers and biomolecules.
Furthermore, the triarylmethyl (trityl) group serves as an excellent
protecting group in nucleoside, oligonucleoside, peptide, and car-
[6,7]
bohydrate chemistry.
spectrometric analysis because of their facile ionization.
Trityl cations can also act as tools in mass
[
8]
[
23–25]
Furthermore, LTAM molecules are regarded to be precursors to
wide spectrum of biological activities.
+
TAM dyes, as the oxidation of LTAM molecules produces the corre-
Furthermore, materials exhibiting a novel combination of prop-
erties are required. For instance, near-infrared (NIR) absorbing dyes
( max > 700 nm) can be potentially used in optical imaging systems,
thermal writing displays, and infrared photography and as filters for
NIR lasers. In this study, we extend the LTAM dyes to stilbene-based
(St) FB analogs of LTAM molecules as the stilbene moiety is
expected to be a better chromophore because of the extended
conjugation from the nitrogen of the FB ring to the central stilbene
+
+
sponding TAM dyes. Several TAM dyes are well known in the dye
industry, e.g. malachite green (MG), crystal violet, sunset orange,
+
and pararosaniline. TAM dyes are categorized as basic dyes, which
[
9]
are extensively used for dyeing silk, wool, and cotton. They also
have a wide range of applications, e.g. in textile industries for both
dyeing and printing; in ink manufacturing; as coloring agents for
[
10,11]
papers, toys, and varieties of plastics
; and in pharmaceutical
[12–14]
+
applications.
tions as photochemotherapy and binding agents.
these dyes, MG is the most interesting. It has long been used to
Furthermore, they are used in medicinal applica-
ring in the corresponding St-TAM dyes, which are suitable candi-
[15,16]
[26]
Among
dates for NIR dyes.
As part of an ongoing study of the structural modification of
LTAM molecules, we report herein the synthesis and structural
[
17,18]
control fungal and protozoan infections in fish.
Although the
use of MG has now been prohibited for the control of fungal infec-
tions in commercial fisheries, it is still used worldwide because it is
[
19]
readily accessible and economical. As a result, there is a strong
demand for the substitutes for MG compounds.
Previously, we have reported the synthesis and structural study
of Fischer base [1,3,3-trimethyl-2-methyleneindoline (FB)] analogs
of LTAM dyes, which are derivatives of 2,2′-(2-phenyl propane-1,3-
*
Correspondence to: Sam-Rok Keum, Department of Advanced Materials
Chemistry, Korea University, Se-Jong, 339-700, Korea. E-mail: keum@korea.ac.kr
Department of Advanced Materials Chemistry, Korea University, Se-Jong 339-700,
Korea
Magn. Reson. Chem. 2016, 54, 143–150
Copyright © 2015 John Wiley & Sons, Ltd.

S.-R. Keum and H.-W. Lim
1
3
characterization of novel St-LTAM FB analogs (Scheme 1) by 1D and
C NMR (125 MHz, CDCl ) δ 28.3, 29.3, 29.4, 30.8, 31.1, 33.7, 35.2,
3
1
13
2D H and C NMR spectroscopy including COSY, HETCOR, HMBC,
38.5, 44.4, 45.0, 97.6, 100.0, 101.8, 105.3, 106.3, 121.8, 122.0,
and NOESY.
126.5, 126.7, 127.4, 127.6, 127.9, 128.1, 128.2, 128.5, 128.6,
1
28.8, 135.2, 137.5, 139.8, 144.9, 146.6, 151.0. Anal. Calcd. for
]: C, 77.34; H, 6.32; Cl, 11.71; N, 4.63%; obtained C,
7.29; H, 6.30; Cl, 11.68; N, 4.58%.
[
39 2 2
C H38Cl N
Experimental
7
Materials
(2E,2′Z)-2,2′-(2-(4-Styrylphenyl)propane-1,3-diylidene)bis(5-chloro-1,3,3-trimet-
hylindoline), St-LTAM (3)
The required FB derivatives were 2-methylene-1,3,3-trimethy-
lindoline,5-chloro-2-methylene-1,3,3-trimethylindoline and Cl-FB.
1
White, yield 53%, mp 180 °C, H NMR (300 MHz, CDCl
3
) δ 1.32 (s, 3H),
4
-Bromobenzaldehydes, 4-substituted styrenes, and other
1.41 (s, 3H), 1.51 (s, 3H), 1.68 (s, 3H), 2.91 (s, 3H), 3.29 (s, 3H), 4.43
(d, J = 9.3 Hz, 1H), 4.49 (d, J = 10.1 Hz, 1H), 5.26 (t, J = 9.3, 10.1 Hz,
1H), 6.47 (d, J = 7.9 Hz, 1H), 6.69 (d, J = 8.2 Hz, 1H), 6.75 (d, J = 16.5,
reagents were purchased from Aldrich (Sigma-Aldrich, Korea)
and used without further purification.
1
7
7
H), 7.03 (d, J = 7.9 Hz, 1H), 7.04 (d, J = 8.2 Hz, 1H), 7.05 (s, 2H),
.08 (d, J = 16.7, 1H), 7.11 (d, J = 16.7, 1H), 7.07 (d, J = 16.5, 1H),
.29 (d, J = 8.3 Hz, 2H), 7.44–7.45 (aromatic, 6H). C NMR
Synthesis
1
3
The (E)-4-styrylbenzaldehyde [(Y)-SBA] derivatives were prepared
from the Heck coupling of substituted styrenes and p-bromo-
benzaldehyde in the presence of palladium acetate [Pd(OAc)2],
tri-o-tolylphosphine, and triethylamine in a heavy-wall pressure
(125 MHz, CDCl ) δ 28.3, 29.3, 29.4, 30.8, 31.1, 33.7, 38.5, 44.4,
45.0, 97.6, 101.8, 105.6, 105.8, 118.7, 119.0, 122.0, 122.4, 127.0,
3
127.1, 127.9, 128.1, 128.2, 128.5, 129.2, 135.4, 137.5, 138.0, 139.8,
148.7, 146.5, 149.9, 151.0, 151.8. Anal. Calcd. for [C H ClN ]: C,
39
39
2
[27,28]
tube.
After 14 h, the reaction mixture was purified with meth-
82.01; H, 6.88; Cl, 6.21; N, 4.90%; obtained C, 81.97; H, 6.86; Cl,
6.15; N, 4.88%.
anol. Meanwhile, the St-LTAM molecules (hereafter referred to as
St-LTAM 1–6) were synthesized from the reaction of FB derivatives
with the (Y)-SBA derivatives prepared in absolute ethanol. The
white precipitates obtained from the reaction mixtures were puri-
fied with cold ethanol.
(
2E,2′Z)-2,2′-(2-(4-(4-Chlorostyryl)phenyl)propane-1,3-diylidene)bis(5-chloro-
1,3,3-trimethylindoline), St-LTAM (4)
1
White, yield 57%, mp 217 °C, H NMR (300 MHz, CDCl ) δ 1.30 (s, 3H),
3
1
.39 (s, 3H), 1.43 (s, 3H), 1.73 (s, 3H), 2.97 (s, 3H), 3.25 (s, 3H), 4.35 (d,
J = 9.3Hz, 1H), 4.40 (d, J = 10.1Hz, 1H), 5.26 (t, J = 9.3, 10.1 Hz, 1H),
.36 (d, J = 7.9Hz, 1H), 6.43 (d, J = 8.2 Hz, 1H), 6.95 (d, J = 16.1, 1H),
7.01 (d, J = 7.9 Hz, 1H), 7.02 (d, J = 8.2Hz, 1H), 7.05 (s, 1H) 7.06 (s,
(
2E,2′Z)-2,2′-(2-(4-Styrylphenyl)propane-1,3-diylidene)bis(1,3,3-trimethy-
lindoline), St-LTAM (1)
6
1
White, yield 58%, mp 177 °C, H NMR (300 MHz, CDCl
.43 (s, 3H), 1.53 (s, 3H), 1.70 (s, 3H), 3.01 (s, 3H), 3.34 (s, 3H), 4.36
d, J = 9.3 Hz, 1H), 4.43 (d, J = 10.2 Hz, 1H), 5.28 (t, J = 9.3, 10.2 Hz,
3
) δ 1.33 (s, 3H),
13
1
(
1H), 7.11 (d, J = 16.1, 1H), 7.37–7.38 (aromatic, 8H). C NMR
(125MHz, CDCl ) δ 28.2, 28.9, 29.3, 30.3, 30.6, 33.6, 38.3, 44.4,
3
1
6
H), 6.49 (d, J = 7.8 Hz, 1H), 6.55 (d, J = 8.1 Hz, 1H), 6.71 (t, 1H),
.81 (t, 1H), 7.03 (t, 1H), 7.04 (d, J = 16.6), 7.08 (t, 1H), 7.15 (d,
45.0, 95.9, 99.7, 106.5, 121.8, 121.9, 122.3, 122.8, 122.9, 123.1
123.8, 127.3, 127.4, 139.3, 139.5, 139.6, 144.7, 146.3, 149.8,
149.9, 151.9, 152.8, 156.7. Anal. Calcd. for [C H Cl N ]: C,
73.18; H, 5.83; Cl, 16.62; N, 4.38%; obtained C, 72.88; H, 5.78; Cl,
16.46; N, 4.29%.
J = 16.6), 7.17 (s, 1H), 7.18 (s, 1H), 7.43 (t, 1H), 7.47–7.48 (aromatic,
3
9
37
3 2
1
3
8
3
1
1
8
H). C NMR (75 MHz, CDCl
8.9, 44.7, 45.3, 97.5, 101.6, 105.1, 105.9, 118.2, 118.9, 121.8, 122.3,
26.9, 127.0, 127.9, 128.1, 128.5, 128.7, 129.2, 135.4, 138.0, 138.2
38.6, 146.8, 148.5, 149.9, 151.8, 152.5. Anal. Calcd. for [C39
7.27; H, 7.51; N, 5.22%; obtained C, 87.22; H, 7.49; N, 5.19%.
3
) δ 28.9, 29.1, 29.5, 29.7, 31.3, 34.0,
(
1
2E,2′Z)-2,2′-(2-(4-(4-Methoxystyryl)phenyl)propane-1,3-diylidene)bis(5-chloro-
,3,3-trimethylindoline), St-LTAM (5)
40 2
H N ]: C,
1
Pale yellow, yield 39%, mp 135 °C, H NMR (300 MHz, CDCl
.26 (s, 3H), 1.35 (s, 3H), 1.48 (s, 3H), 1.66 (s, 3H), 2.35 (s, 3H), 2.94
s, 3H), 3.25 (s, 3H), 4.35 (d, J = 9.4Hz, 1H), 4.41 (d, J = 10.0Hz, 1H),
3
) δ
(2E,2′Z)-2,2′-(2-(4-(4-Chlorostyryl)phenyl)propane-1,3-diylidene)bis(1,3,3-
1
(
trimethylindoline), St-LTAM (2)
1
White, yield 55%, mp 178 °C, H NMR (300 MHz, CDCl
.40 (s, 3H), 1.48 (s, 3H), 1.66 (s, 3H), 2.94 (s, 3H), 3.26 (s, 3H), 4.35
d, J = 9.3 Hz, 1H), 4.41 (d, J = 10.1 Hz, 1H), 5.20 (t, J = 9.3, 10.1 Hz,
3
) δ 1.30 (s, 3H),
5.20 (t, J = 9.4, 10.0 Hz, 1H), 6.36 (d, J = 7.9 Hz, 1H), 6.42 (d, J = 8.3 Hz,
1H), 6.94 (d, J = 16.1, 1H), 7.00 (d, J = 7.9 Hz, 1H), 7.01 (d, J = 8.3 Hz,
1H), 7.05 (s, 1H), 7.06 (s, 1H), 7.09 (d, J = 16.1, 1H), 7.38–7.39 (aromatic,
1
(
13
1
1
H), 6.36 (d, J = 7.9 Hz, 1H), 6.43 (d, J = 8.2 Hz, 1H), 6.97 (d, J = 7.9Hz,
H), 6.98 (d, J = 16.5, 1H), 7.01 (d, J = 8.2 Hz, 1H), 7.06 (s, 1H), 7.09
3
6H), 7.14 (d, J = 8.2 Hz, 2H). C NMR (75 MHz, CDCl ) δ 28.4, 28.8, 29.4,
30.4, 31.2, 33.6, 38.2, 42.1, 44.4, 45.0, 97.6, 99.9, 100.5, 105.7, 106.3,
(
s, 1H), 7.07 (d, J = 16.5, 1H), 7.35 (t, 1H), 7.47–7.48 (aromatic, 8H).
121.4, 121.9, 122.2, 122.5, 122.9, 123.5, 126.4, 126.5, 127.5, 128.1,
1
1
4
29.5, 134.7, 135.4, 137.5, 139.6, 139.8, 146.6, 144.9, 147.0, 151.5,
51.8. Anal. Calcd. for [C40 ]: C, 77.53; H, 6.51; Cl, 11.44; N,
.52%; obtained C, 77.44; H, 6.46; Cl, 11.36; N, 4.47%.
2 2
H40Cl N
(
1
2E,2′Z)-2,2′-(2-(4-(4-Methoxystyryl)phenyl)propane-1,3-diylidene)bis(5-chloro-
,3,3-trimethylindoline), St-LTAM (6)
1
Pinkish yellow, yield 40%, mp 168 °C, H NMR (300 MHz, CDCl ) δ
3
1.30 (s, 3H), 1.40 (s, 3H), 1.48 (s, 3H), 1.66 (s, 3H), 2.94 (s, 3H), 3.28
(s, 3H), 3.83 (s, 3H), 4.35 (d, J = 9.4Hz, 1H), 4.41 (d, J = 10.0Hz, 1H),
5
1
1
.19 (t, J = 9.4, 10.0 Hz, 1H), 6.36 (d, J = 7.9 Hz, 1H), 6.42 (d, J = 8.3 Hz,
H), 6.90 (d, J = 16.1, 1H), 6.96 (d, J = 7.9 Hz, 1H), 7.01 (d, J = 8.3 Hz,
H), 7.03 (s, 1H), 7.05 (s, 1H), 7.10 (d, J = 16.1, 1H), 7.43–7.44
1
3
Scheme 1. Chemical structure of St-LTAM molecules.
(aromatic, 6H), 6.88 (d, J = 8.5 Hz, 2H). C NMR (75 MHz, CDCl3)
wileyonlinelibrary.com/journal/mrc
Copyright © 2015 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2016, 54, 143–150

Synthesis of a series of novel St-based Leuco-TAMs
+
Scheme 2. Synthetic scheme of St-LTAM/TAM molecules.
δ 28.4, 28.9, 29.9, 30.3, 30.6, 33.3, 38.3, 44.4, 45.0, 54.6, 97.7, 99.0,
smaller spectral widths and larger digital resolutions (down to
0.2 Hz). The following techniques were used: BB-1H noise
1
1
1
1
01.8, 105.5, 106.1, 121.5, 123.1, 123.8 124.8, 125.7, 126.6, 127.5,
28.2, 129.2, 130.3, 135.5, 139.5, 139.8, 146.5, 146.8, 150.1, 151.4,
51.7, 159.2. Anal. Calcd. for [C H Cl N O]: C, 75.58; H, 6.34; Cl,
1
1
1
13
decoupling, attached proton test, H– H COSY, and H– C
1
1
HETCOR. The H– H COSY spectra were recorded in the magni-
tude mode with 1024 points in the F2 dimension and 256
increments in the F1 dimension. Each increment was obtained
with 16 scans, a spectral width of 4500 Hz, and a relaxation delay
of 1 s. The resolutions were 5.4 and 10.7Hz per point in the F1
40
40
2 2
1.15; N, 4.47%; obtained C, 75.43; H, 6.29; Cl, 11.10; N, 4.28%.
Spectral measurements
1
13
1
13
1
D and 2D H and C NMR spectra were recorded on a Varian
and F2 dimensions, respectively. The H– C HETCOR spectra
13
1
Mercury 300 (San Diego, California, USA) NMR spectrometer oper-
were recorded with one-bond C– H coupling constant main-
tained at 140 Hz using 2048 points in the F2 dimension and
256 increments in the F1 dimension with a relaxation delay of
1 s. The spectral width in the F2 and F1 dimensions was 20 000
and 4500 Hz, respectively. The resulting resolutions in the F2
and F1 dimensions were 19.53 and 17.6Hz per point, respectively.
All 2D experiments were performed by standard pulse sequences
using the Mercury Data System (California, USA) software version
V NMR 6.1B. For proton decoupling, the Waltz 16 modulation was
1
13
ating at 300.07MHz for H and 75.46 MHz for C. NMR tubes hav-
ing a diameter of 5 mm contained samples in 0.1 M DMSO-d
6
1
13
solutions, and the spectra were recorded at 298 K. H and
chemical shifts were referenced to SiMe in CDCl
standard or to the residual solvent signal in DMSO-d
C
4
3
as the internal
(1H,
6
1
3
1
2.50 ppm; C, 39.52 ppm). The digital resolution of the H and
13
C NMR spectra was 0.25 and 0.6 Hz per point, respectively.
Narrower spectral regions of special interest were measured with
1
1
Figure 1. H– H COSY spectrum of St-LTAM
4 (2E,2′Z)-2,2′-(2-(4-(4-
chlorostyryl)phenyl)propane-1,3-diylidene)bis(5-chloro-1,3,3-trimethylindoline).
Blue and red numbers denote the left and right rings, respectively.
Figure 2. NOE correlation for St-LTAM 4; spatial correlations of H2a–H8/H9
(A), H2a′–H10′ (B), H10–H2″/H6″ (C), and H9′/H8′–H2″/H6″ (D) are shown.
Magn. Reson. Chem. 2016, 54, 143–150
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc

S.-R. Keum and H.-W. Lim
+
used. 2D NOESY and HMBC data were obtained from the Korea
Research Institute of Chemistry Technology (Daejeon, Korea).
The UV–Vis absorption spectra were recorded on a Varian Cary
For the synthesis of TAM dyes, dichloro dicyano quinone was first
added to a solution of St-LTAM in benzene. Second, the solution was
stirred for 1.5 h at room temperature. Third, the reaction mixture was
poured onto a short column containing aluminum oxide. Next, a
(Mountain View, CA, USA) 1E UV–Vis spectrometer.
2 2
mixture of CH Cl : methanol (9 : 1) was used as the eluting solvent,
and a violet residue was obtained. Then, this residue was treated
with 50 ml of methanol containing three drops of concentrated
HCl and refluxed for 2.5 h. Finally, the solvent was evaporated, and
the resulting dark green solution was purified by silica-gel column
Results and discussion
Synthesis of St-LTAM molecules
2 2
chromatography using a mixture of CH Cl : methanol (9 : 1) to afford
The (Y)-SBA derivatives were synthesized by the Heck reaction,
which is the palladium-catalyzed coupling of olefins with aryl and
a blue solution, which was used for UV–Vis spectroscopy.
[27,28]
vinyl halides.
The coupling of 4-bromobenzaldehydes with
1
H NMR spectroscopy
4-substituted styrenes in the presence of 0.1 mol% of Pd(OAc)2
1
with N,N-dimethylacetamide as the solvent afforded (Y)-SBA
derivatives in isolated yields of 65–71% after 24 h at 140 °C. Most
of these derivatives were obtained as white solids.
The H NMR spectra of all St-LTAMs exhibited characteristic signals
in the aliphatic region, namely, a triplet and two doublets in the
range of 4.20–5.40 ppm, in addition to two groups of identical
singlets at 2.80–3.40 and 1.20–1.70 ppm, respectively.
Next, St-LTAM compounds (St-LTAM) 1–6 were prepared by
treating an excess of 5-substituted FB with the SBA derivatives thus
prepared, as shown in Scheme 2, by employing the procedure
1
13
The detailed H and C resonances of St-LTAMs 1–6 were
1
13
assigned by COSY and one-bond H– C correlations obtained by
[
20–22]
reported by Keum et al.
both direct-detection HETCOR and indirect-detection HSQC
Table 1. Selective 1D and 2D correlation NMR data for St-LTAM 4 in CDCl
3
Ring
1D and 2D correlation NMR
a
Atom
2a
H (ppm)
C (ppm)
HSQC
HMBC
NOESY
H1a″, Me-8, Me-9
A
4.35
1.43
1.30
3.25
4.40
1.73
1.39
2.97
5.26
7.38
95.9
30.6
30.3
33.6
99.7
28.9
28.2
29.3
38.3
123.1
√
√
√
√
√
√
√
√
√
√
C2, C3, C1″, H2a′
C2, C3, C3a, C9
C2, C3, C3a, C8
C2, C7a
Me-8
Me-9
N-Me-10
2a′
2a, 1a″, 4
2a, 1a″, 4
1a″, 2″/6″, 7
B
C2′, C3′, C1″, H2a
C2′, C3′, C3a′, C9′
C2′, C3′, C3a′, C8′
C2′, C7a′
H2a′, N-Me-10′
1a″, 2″/6″, 4′
Me-8′
Me-9′
N-Me-10′
1a″
1a″, 2″/6″, 4′
2a′, 7′
C
H2a, H2a′, C2, C2′, C1″, C2″/6″
2a, Me-8, Me-9, N-Me-10, 2″/6″
Me-8′, Me-9′, N-Me-10, 1a″
2″/6″
C2″/H6″, H2″/C6″, C4″, C3″/C5″, H3″, H5″
a
Each carbon correlates with protons, and vice versa, in HMBC.
1
13
Table 2. Selected H and C NMR spectral data for the comparison between the Z and E rings for the major ZE diastereomer of various St-LTAM
molecules in CDCl
3
Molecule
Position
δ1H (ppm)
Δ
ppm)
À δ
δ13C (ppm)
Δ
a
a
(
(ppm)
(δ
À δ
Z
E
Z
E
(δ
Z
E
)
Z
E
)
St-LTAM 3
4-/4; —
7.06
1.40
1.30
3.26
7.05
1.43
1.30
3.25
7.03
1.40
1.30
3.28
7.09
1.66
1.48
2.94
7.06
1.73
1.39
2.97
7.05
1.66
1.48
2.94
À0.03
À0.26
À0.18
0.32
122.3
31.0
30.9
33.7
122.3
30.6
30.3
33.6
123.1
30.6
30.3
33.3
121.8
29.2
28.4
29.4
121.8
28.9
28.2
29.3
121.5
28.9
28.4
29.9
0.50
1.80
2.50
Me-8/Me-8′
Me-9/Me-9′
N-Me/N-Me′
4-/4; —
4.30
0.50
1.70
2.10
4.30
1.60
1.70
1.90
3.40
St-LTAM 4
St-LTAM 6
À0.03
À0.26
À0.18
0.32
Me-8/Me-8′
Me-9/Me-9′
N-Me/N-Me′
4-/4; —
À0.02
À0.26
À0.18
0.34
Me-8/Me-8′
Me-9/Me-9′
N-Me/N-Me′
a
Differences of the δ values of Z isomers from the corresponding values of E isomers.
The N-methyl peaks (presented in bold) exhibit the most characteristic peaks.
wileyonlinelibrary.com/journal/mrc
Copyright © 2015 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2016, 54, 143–150

Synthesis of a series of novel St-based Leuco-TAMs
experiments. COSY was used to identify the peaks from the A (left)
and B (right) rings, as well as the central H1a″ of the stilbene unit
correlated to the enamine protons, H2a or H2a′ of the two indoline
rings.
ranging from 6.40 to 7.40 ppm of the COSY spectrum, four more
individual sets of correlations – {H7–H8}, {H7′–H8′}, {H7″–H8″},
and {H10″–H11″} – were observed.
HETCOR and HSQC were employed to identify the carbon shifts
of carbons having protons attached by one-bond coupling between
1
1
Figure 1 shows the H– H COSY spectrum of St-LTAM 4 in CDCl
3
1
13
as a representative example. The figure also shows magnified
parts of the spectrum in the range of 4.20–5.40 ppm (upper)
and 6.40–7.40 ppm (bottom) for detailed identification.
H and C. Some representative correlations such as {H1a″–C1a″},
{H2a–C2a}, and {H2a′–C2a′} were observed.
HMBC was employed for the correlation of the protons to their
respective ring components. The remaining chemical shift assign-
ments within the FB rings, A and B, of the molecules were mostly
made by employing HMBC and NOESY data. As the A and B rings
are not identical, HMBC was employed to differentiate between
the two groups of molecules.
1
1
As shown in the upper region of the H– H COSY spectrum in
Fig. 1, a correlation was observed from H1a″ at 5.26 ppm to H2a
and H2a′ at 4.35 and 4.40 ppm, respectively. The yellow square
denotes a trace of the other isomer formed during the experi-
ment, which is discussed later in this paper. In the aromatic region
1
13
Table 3. H and C NMR data of St-LTAM 1–6 in CDCl
3
(300 and 75 MHz, respectively)
a
Ring
H or C
St-LTAM 1
St-LTAM 2 St-LTAM 3
St-LTAM 4
St-LTAM 5
St-LTAM 6
δ(H)
δ(C)
δ(H)
δ(C)
δ(H)
δ(C)
δ(H)
δ(C)
δ(H)
δ(C)
δ(H)
δ(C)
A
B
C
2
2
3
3
4
5
6
7
7
—
152.5
97.5
—
151.0
97.6
—
151.8
97.6
—
152.8
95.9
—
151.8
97.6
—
151.7
97.7
a
a
4.36
—
4.35
—
4.43
—
4.35
—
4.35
—
4.35
—
45.3
45.0
45.0
45.0
45.0
45.0
—
138.6
127.0
118.9
122.3
105.9
148.5
29.5
—
139.8
128.1
121.8
126.5
106.3
146.6
29.4
—
137.5
127.1
119.0
122.4
105.8
148.7
29.4
—
139.5
122.3
121.9
127.3
106.5
146.3
30.3
—
139.8
129.5
121.9
122.5
106.3
147.0
29.4
—
139.5
129.2
123.8
125.7
106.1
146.8
29.9
7.17
6.81
7.08
6.55
—
7.08
6.75
7.05
6.54
7.06
—
7.05
—
7.03
6.80
7.07
6.55
—
7.03
—
7.01
6.43
—
7.01
6.42
—
7.01
6.42
—
a
Me-8
Me-9
N-Me-10
2′
1.43
1.33
3.34
—
1.41
1.32
3.29
—
1.40
1.30
3.26
—
1.35
1.26
3.25
—
1.38
1.31
3.33
—
1.40
1.30
3.28
—
29.7
30.8
30.8
30.6
30.4
30.3
34.0
33.7
33.7
33.6
33.6
33.3
151.8
101.6
44.7
151.0
101.8
44.4
151.0
101.8
44.4
151.9
99.7
151.5
99.9
151.4
99.0
2
3
3
4
5
6
7
7
a′
4.43
—
4.49
—
4.41
—
4.40
—
4.41
—
4.41
—
′
44.4
44.4
44.4
a′
′
—
138.2
126.9
118.2
121.8
105.1
146.8
28.9
—
137.5
128.2
122.0
126.7
105.3
144.9
28.3
—
139.8
127.0
118.7
122.0
105.6
146.5
28.3
—
139.6
121.8
121.9
127.4
106.5
144.7
28.2
—
139.6
128.1
121.4
122.2
105.7
146.6
28.4
—
139.8
128.2
123.1
124.8
105.5
146.5
28.4
7.18
6.71
7.04
6.49
—
7.11
6.69
7.03
6.47
—
7.09
—
7.06
—
7.05
6.75
7.01
6.47
—
7.05
—
′
′
6.97
6.36
—
7.00
6.36
—
6.96
6.36
—
′
a′
Me-8′
Me-9′
N-Me-10′
1a″
1.70
1.53
3.01
5.28
—
1.68
1.51
2.91
5.26
—
1.66
1.48
2.94
5.20
—
1.66
1.48
2.94
5.20
—
1.69
1.46
2.97
5.25
—
1.66
1.48
2.94
5.19
—
29.1
29.3
29.3
28.9
28.8
28.9
31.3
31.1
31.1
29.3
31.2
30.6
38.9
38.5
38.5
38.3
38.2
38.3
1
2
3
4
7
8
9
1
1
1
″
149.9
128.5
128.1
135.4
127.9
127.9
138.0
128.1
129.2
128.7
—
—
149.9
128.5
127.9
135.4
128.1
128.2
138.0
127.9
129.2
128.1
156.7
123.1
122.9
149.8
123.8
123.8
149.9
122.8
122.8
139.3
—
144.9
126.4
123.5
134.7
126.5
127.5
135.4
122.9
100.5
137.5
42.1
150.1
130.3
121.5
135.5
126.6
127.5
128.2
121.5
101.8
159.2
54.6
″/6″
7.48
7.48
—
7.44
7.44
—
128.6
127.9
128.8
127.4
127.6
135.2
128.5
100.0
135.2
—
7.48
7.48
—
7.39
7.39
—
7.42
7.42
—
7.43
7.43
—
″/5″
″
″
7.04
7.15
—
7.05
7.05
—
6.97
7.07
—
6.94
7.09
—
7.09
7.09
—
6.90
7.10
—
″
″
0″/14″
1″/13″
2″
7.42
7.48
7.43
—
7.44
7.29
—
7.48
7.43
7.35
—
7.39
7.14
—
7.42
6.88
—
7.43
6.88
—
(O)Me-12″
—
—
2.35
9.40
3.83
9.40
J
J
J
J
H2a–H1a″
9.30
9.30
9.30
9.30
H2′a–H1a″
H6–H7
10.2
10.1
10.1
10.1
10.0
10.0
8.10
7.80
8.20
7.90
8.20
7.90
8.20
7.90
8.30
7.90
8.30
7.90
H6′–H7′
a
A–C rings are the left, right, and middle rings, respectively.
Magn. Reson. Chem. 2016, 54, 143–150
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc

S.-R. Keum and H.-W. Lim
From HMBC experiments, the following correlations were ob-
served: C-2 at 152.8 ppm to H-1a″ at 5.26 ppm, H-2a at 4.35 ppm,
Me-8 at 1.43 ppm, Me-9 at 1.30 ppm, and N-Me-10 at 3.25 ppm of
the A ring, as well as C-2′ at 151.9 ppm to H-1a″ at 5.26 ppm, H-2a′
at 4.40ppm, Me-8′ at 1.73 ppm, Me-9′ at 1.39 ppm, and N-Me-10′
at 2.97 ppm of the B ring. Similarly, C-3 at 45.0 ppm of the A ring
and C-3′ at 44.4ppm of the B ring were correlated to H-2a at
ZE isomer’? The considerable deshielding of the gem-dimethyl
protons 8′ and 9′ of the E ring and the N-methyl-10 proton of the
Z ring, as compared with the corresponding protons of the Z and
E ring, can be understood as being largely caused by the local
diamagnetic anisotropy of the benzene ring of the stilbene moiety
as those protons are in relative proximity to the benzene ring of the
[
29]
stilbene units. In conclusion, the results of the 1D and 2D NMR
study conducted herein provide a useful tool for the structural
analysis of various St-LTAM molecules.
4.35 ppm, H-4 at 7.05 ppm, Me-8 at 1.43ppm, Me-9 at 1.30 ppm,
H-2a′ at 4.40 ppm, H-4′ at 7.06 ppm, Me-8′ at 1.73ppm, and Me-9′
at 1.39 ppm. Furthermore, by HMBC, C-3a at 139.5 ppm of the A ring
and C-3a′ at 139.6 ppm of the B ring were correlated to H-7 at
1
13
The detailed H and C NMR data of St-LTAM 1–6 are summa-
rized in Table 3.
6.43 ppm, Me-8 at 1.43 ppm, and Me-9 at 1.30 ppm of the A ring,
and C-3a′ at 139.6 ppm was correlated to H-7′ at 6.36 ppm, Me-8′
at 1.73 ppm, and Me-9′ at 1.39 ppm of the B ring, respectively.
Two individual sets of HMBC correlations between C3 and the
gem-dimethyl groups [Me-8 and Me-9] and C3′ and the other
gem-dimethyl groups [Me-8′ and Me-9′] indicate that they belong
to the same subunit, either the A or B ring.
Diastereomeric isomerization
As shown in Scheme 3, the FB analogs of LTAM molecules are
known to have three configurational isomers. However, the ZE iso-
mers of the LTAM molecules are typically unstable in organic sol-
vents, and depending on time, they equilibrate into a mixture of
[
30]
The configuration of the double bonds at positions 2–2a and
other diastereomers without any specific catalytic reagents.
2
′–2a′ of the enamine moiety of the A and B (FB) rings are either
On the other hand, most of the FB analogs of LTAM molecules
exhibited a ZE configuration in the solid state and equilibrated into
a mixture of EE and ZZ diastereomers within 2–3 h at room temper-
ature. This phenomenon is quiet reasonable as ZE would be ex-
pected to predominate over ZZ and EE in all media, based on
E or Z. NOE experiments were conducted for the identification
of the geometry around the double bonds at positions 2–2a
and 2′–2a′ of the enamine moiety of the A and B (FB) rings,
respectively, as shown in Fig. 2.
In particular, a strong NOE correlation was observed between
H2a at 4.35 ppm (ring-A) and the gem-dimethyl protons of the
ring-B Me-8′ at 1.73 ppm and Me-9′ at 1.39 ppm (A), while H2a′
at 4.40 ppm (ring-B) exhibited NOE with the N-Me-10′ protons
[
31]
quantum mechanical calculations. However, the 4-pyryl and 4-
nitrophenyl derivatives of the FB analogs of LTAM molecules have
been reported to exhibit an EE configuration in the solid state and
[
32,33]
equilibrate into a mixture of ZE and ZZ diastereomers.
Thus,
(
ring-B) at 2.97 ppm (B). In addition, a simultaneous NOE correla-
the FB analogs of LTAM molecules can be categorized as type 1
(ZE) and type 2 (EE), as shown in Fig. 3.
The methylene doublets of the ZZ isomers for this compound
could not be detected because of their low concentration in the
equilibrium state. The equilibrium ratios of the ZZ isomer, among
the diastereomeric isomers, can be determined using the N-Me
tion was also observed between ortho-protons H2″/H6″ of the stil-
bene ring and N-Me-10 at 3.25 ppm (ring-A) as well as between
the gem-dimethyl protons Me-8′ at 1.73ppm and Me-9′ at
1
.39 ppm (ring-B). These NOE observations are compatible with Z
and E arrangements of the double bond of the A and B rings, re-
spectively. Table 1 lists the selective 1D and 2D correlation NMR
data for St-LTAM 4 in CDCl .
3
1
13
The H and C chemical shifts of all six compounds were
completely assigned. For comparison between the Z and E rings
for the major ZE diastereomer of various St-LTAM molecules, Table 2
1
13
lists their selected H and C NMR spectral data in CDCl
5 MHz, respectively).
The NMR data for the Z or E ring of the ZE isomer suggest that the
3
(300 and
7
signals of the gem-dimethyl group on the E ring were shifted down-
field compared with those of the Z ring, whereas the signals of the
N-methyl groups on the Z ring were shifted downfield compared
with those on the E ring. Differences in the δ values of the Z and
E isomers exhibited a decreasing order: N-Me peaks> Me-8> Me-
1
13
9
for H NMR and N-Me peaks > Me-9 > Me-8 for C NMR. These
results indicated that the N-Me protons exhibit the most character-
istic resonance peak for the isomeric Z or E rings.
Now, the following question may arise: ‘What causes a difference
in the chemical shifts between the protons of the Z or E ring of the
Figure 3. Types (1 and 2) of the configurational isomerization of the FB
analogs of LTAM molecule; ★ and ■ denote the EE and ZE isomers,
respectively (the trace amount of ZZ isomer is not shown).
Scheme 3. Three configurational isomers of the FB analogs of LTAM molecules.
wileyonlinelibrary.com/journal/mrc
Copyright © 2015 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2016, 54, 143–150

Synthesis of a series of novel St-based Leuco-TAMs
1
proton peaks in the H NMR spectra. The N-Me protons exhibited
Meanwhile, the configurational stability of the LTAM molecules
in the solid state depends on the identity of the aryl moiety, without
any specific reason. The LTAM molecules in the shaded columns of
Table 3 exhibited EE configuration, whereas the others exhibited
the ZE configuration in the solid state. However, all molecules equil-
ibrated to a mixture of three diastereomers. Irrespective of the
types of molecules, the percent ratios among the diastereomeric
isomers of the St-LTAM molecules in the thermal equilibrium states
exhibited a marginal variation. Table 4 summarizes the percent ra-
tios among the isomers of St-LTAM 1–6, as well as the data of other
LTAM molecules from previous studies for comparison.
the most characteristic resonance peak as compared with those
of the isomeric Z or E rings. Hence, the equilibrium ratios of the
ZZ isomer are based on the intensities of the N-methyl protons cor-
responding to the three diastereomeric isomers at the equilibrium
state, as shown in Fig. 4.
+
Typically, these TAM dyes exhibited two absorption bands: x-
band and y-band; the x-band corresponds to the promotion of an
electron from the nonbonding orbital to the lowest antibonding or-
bital, resulting in a high electron density on the central carbon
atom, while the y-band corresponds to the excitation of an electron
from the second-highest occupied bonding orbital to the lowest
[
1]
+
vacant orbital. The x-bands of the extended TAM were compara-
+
ble with those of the unextended TAM dyes, whereas the y-bands
Figure 4. N-Methyl peaks from the configurational isomerization of the St
FB analogs of LTAM molecules: before (left) and after (right) equilibrium.
were expected to be better chromophores because of the
3
Table 4. Percent ratios among the isomers of St-LTAM 1–6 in CDCl at equilibrium
c
d
LTAMs and St-LTAMs
Percent ratios
Type
Ref.
a
b
Compound
Aryl group
Phenyl
Substituents
ZE
EE
ZZ
[20,21]
[32]
LTAM
H
60.2
60.8
62.9
61.0
64.0
63.3
63.6
62.7
63.3
62.6
63.1
62.2
28.3
34.1
29.6
34.1
31.1
31.3
28.9
29.7
28.3
29.8
29.4
30.1
11.4
1
2
1
2
1
2
1
1
1
1
1
1
Keum et al.
and Ma et al.
4-CHO
5.10
3
-NO
-NO
2
7.50
4.90
4.80
5.40
7.50
7.60
8.40
7.60
7.50
7.70
4
2
Pyridinyl
Styryl
3-(N)
4-(N)
St-LTAM 1
St-LTAM 2
St-LTAM 3
St-LTAM 4
St-LTAM 5
St-LTAM 6
H
This study
4-Cl
4-H
4-Cl
4-Me
4-OMe
a
5
,5′-Dichlorinated compounds except St-LTAM 1 and 2.
b
Substituents on the aryl moiety of LTAM or St-LTAM molecules.
c
Percent ratios of the configurational isomers at equilibrium
d
Isomerization types as shown in Fig. 3.
+
+
Scheme 4. The y-band in phenyl-based TAM versus St-TAM dyes.
Magn. Reson. Chem. 2016, 54, 143–150
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc

S.-R. Keum and H.-W. Lim
[
9] G. Parshetti, S. Kalme, G. Saratale, S. Govindwar. Acta Chim. Slov. 2006,
extended conjugation from the nitrogen of the FB ring to the cen-
tral stilbene ring, as shown in Scheme 4.
53, 492–498.
[
[
10] S. Sarnaik, P. Kanekar. Appl. Microbiol. Biotechnol. 1999, 52, 251–254.
11] M. A. El-Naggar, S. A. El Aasar, K. I. Barakat. Water Res. 2004, 38,
4313–4322.
+
Detailed UV–Vis spectroscopic studies of various St-TAM dyes in
[
34]
various organic solvents will be presented in the near future.
[
[
[
12] M. S. Shchepinov, V. A. Korshun. Chem. Soc. Rev. 2003, 32, 170–180 and
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13] B. P. Cho, T. Yang, L. R. Blankenship, J. D. Moody, M. Churchwell,
F. A. Beland, S. Culp. Chem. Res. Toxicol. 2003, 16, 285–294.
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F. Sieber. J. Pharm. Sci. 2000, 89, 88–99.
Conclusion
A series of novel St FB analogs of LTAM – (2E,2′Z)-2,2′-(2-(4-
styrylphenyl)propane-1,3-diylidene)bis(1,3,3-trimethylindoline)
[15] L. M. Lewis, G. L. Indig. J. Photochem. Photobiol. B 2002, 67, 139–148.
16] T. Küçükkilinç, I. Ozer. Arch. Biochem. Biophys. 2005, 440, 118–122.
–
dyes were synthesized and characterized by 1D and 2D NMR.
[
All St-LTAM molecules examined herein exhibited the ZE
configuration and isomerized to their diastereomers, EE and
ZZ, in 2–3 h. They exhibited type I behavior of diastereomeric
isomerization.
[17] S. J. Culp, F. A. Beland. J. Am. Coll. Toxicol. 1996, 15, 219–238.
[
[
[
[
[
[
[
[
18] W. C. Andersen, S. B. Turnipseed, J. E. Roybal. J. Agric. Food Chem. 2006,
4, 4517–4523.
19] I. K. Kandela, J. A. Bartlett, G. L. Indig. Photochem. Photobiol. Sci. 2002, 1,
09–314.
20] S. R. Keum, S. J. Roh, M. H. Lee, F. Saurial, E. Buncel. Magn. Reson. Chem.
2008, 46, 872–877.
21] S. R. Keum, M. H. Lee, S. Y. Ma, D. K. Kim, S. J. Roh. Dyes. Pigm. 2011, 90,
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5
3
Acknowledgements
This study was supported by the Basic Science Research Program
through the National Research Foundation of Korea funded by the
Ministry of Education, Science and Technology (no. 2012003244).
1
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