Biocatalysts for cascade reaction: Porcine pancreas lipase (PPL)-catalyzed synthesis of bis(indolyl)alkanes

Article abstract of DOI:10.1007/s00726-013-1547-4

A cascade reaction between aldehydes and indole catalyzed by lipase from porcine pancreas Type II (PPL) in solvent mixture at 50 C was reported for the first time. Some control experiments had been designed to demonstrate that the PPL was responsible for

Full text of DOI:10.1007/s00726-013-1547-4

Amino Acids
DOI 10.1007/s00726-013-1547-4
ORIGINAL ARTICLE
Biocatalysts for cascade reaction: porcine pancreas lipase
(PPL)-catalyzed synthesis of bis(indolyl)alkanes
•
Ziwei Xiang Zhiqiang Liu Xiang Chen
•
•
•
Qi Wu XianFu Lin
Received: 29 April 2013 / Accepted: 25 June 2013
Ó Springer-Verlag Wien 2013
Abstract A cascade reaction between aldehydes and
indole catalyzed by lipase from porcine pancreas Type II
(PPL) in solvent mixture at 50 °C was reported for the first
time. Some control experiments had been designed to
demonstrate that the PPL was responsible for the cascade
reaction. After the optimization of the stepwise process, a
series of bis(indolyl)alkanes were prepared in moderate to
excellent yields under the catalysis of PPL.
higher value molecules under mild reaction conditions.
Indoles and their derivatives possess various biological
properties like antibacterial, cytotoxic, antioxidative, and
insecticidal activities (Lounasmaa and Tolvanen 2000;
Hibino and Choshi 2001; Fukuyama and Chen 1994; Shiri
et al. 2009). Especially, bis(indolyl)alkanes and their
derivatives have attracted much interest because they can
act as highly selective fluorescent molecular sensors for
Cu2? cations and also as colon tumor and cancer cell
´
growth inhibitors (Martınez et al. 2008; Guinchard et al.
Keywords PPL ꢀ Promiscuity ꢀ Bis(indolyl)alkanes ꢀ
Cascade reaction
2007; Safe et al. 2008; Lei et al. 2008).
In the past years, more and more researchers were
attracted to study the synthesis of bis(indolyl)methanes and
they found that these compounds could be generally syn-
thesized via the cascade reaction between an aldehyde (or
acetone) with two equivalents of indole in the presence of a
Lewis or protic acid catalyst, such as trichloro-1,3,5-triazine
(Sharma et al. 2004), bentonite (Guillermo et al. 2003),
ZrCl4 (Zhang et al. 2005), Montmorillonite clay K-10
(Chakrabarty et al. 2004), I2 (Bandgar and Shaikh 2003),
CeCl3ꢀ7H2O (Silveira et al. 2009), AlPW12O40 (Firouzabadi
et al. 2006), zeolites (Karthik et al. 2004), Dy(OTf)3/ionic
liquid (Xl et al. 2004), FeCl3/ionic liquid (Ji et al. 2004),
Sc(OTf)3 (Ma et al. 2005), HClO4-SiO2 (Kamble et al.
2007a), InCl3-NMTA (Pradhan et al. 2005), MW/Lewis
acids (BiCl3, FeCl3, InCl3,CoCl2, ZnCl2) (Xia et al. 2004),
silica sulfuric acid (SSA) (Zolfigol et al. 2008), NBS
(Koshima and Matsusaka 2002), TiO2 (Mona 2007), LiClO4
(Mehrazma et al. 2006), NaBF4 (Kamble et al. 2007b),
Ph3CCl (Khalafi-Nezhad et al. 2008), metal hydrogen sul-
fates (Niknam et al. 2006), H3PW12O40 (Azizi et al. 2007),
ceric ammonium nitrate (CAN) (Mohit and Pulak 2006),
La(NO3)3ꢀ6H2O (Jon-Paul-Selvam et al. 2008), and
Fe(DS)3 (Wang and Ji 2008). Most of the above attempts
were efficient for the synthesis of bis(indolyl)methanes with
Introduction
Biocatalysis has received great attention as an efficient and
green tool for the production of pharmaceutical, industrial
and agricultural chemicals, and intermediates due to mild
reaction conditions, wide sources, broad range of substrates
and potential use of inexpensive regenerable resources
(Feng et al. 2009; Pollard and Woodley 2007; Aleu et al.
2006; Kazlauskas 2005; Schmid et al. 2001). In the recent
years, many researchers had successfully utilized these
natural catalysts for the construction of C–C (Svedendahl
et al. 2005; Xu et al. 2007; Cai et al. 2011; Wu et al. 2010),
C–N (Torre et al. 2004; Wu et al. 2005, 2006), C–O
(Kitazume et al. 1986), and C–S (Carlqvist et al. 2005; Lou
et al. 2008) bonds and insertion of chirality for producing
Z. Xiang ꢀ Z. Liu ꢀ X. Chen ꢀ Q. Wu (&) ꢀ X. Lin (&)
Department of Chemistry, Zhejiang University,
Hangzhou 310027, People’s Republic of China
e-mail: llc123@zju.edu.cn
X. Lin
e-mail: xflin@zju.edu.cn
123

Z. Xiang et al.
Table 1 Reaction of 4-nitrobenzaldehyde and indole under different
enzymes in water
R
NO2
H
CHO
N
PPL
R
+
H
CHO
N
Enzyme
N
N
+
H
H
O2N
N
H
N
H
Scheme 1 Lipase catalyzed the reaction between indole and
aldehydes
Entry
Enzyme
Yield (%)a
high yields. However, there were still some drawbacks in
these catalytic systems including the requirement of heavy
metal, drastic conditions for catalyst preparation and also
require tedious work-up leading to the generation of large
amount of toxic waste.
1
2
3
4
5
6
7
8
9
10
PPL
41
\1
\1
2
Blank
BSA
PPLb
CCL
6
Biocatalytic promiscuity is ability of the same or dif-
ferent, or induced active site to catalyze more than one
chemical transformation which usually differ in the type of
bond formation or cleavage and in the catalytic mechanism
of bond making or breaking and could provide useful
methods in organic synthesis (Humble and Berglund 2011;
Hult and Berglund 2007; Gatti-Lafranconi and Hollfelder
2013; Wu et al. 2010; Babtie et al. 2010; Taglieber et al.
2007; Kazlauskas 2005). In recent decades years, many
enzymes have been found to be able to catalyze non-natural
reactions, such as Aldol (Branneby et al. 2004; Li et al.
2008; Serafimov et al. 2008), Michael (Xu et al. 2007; Lou
et al. 2007; Torre et al. 2004; Svedendahl et al. 2005;
Carlqvist et al. 2005), Henry (Wang et al. 2010; Purkar-
thofer et al. 2006; Gruber-Khadjawi et al. 2007), Knoeve-
nagel reaction (Chen et al. 2011; Hu et al. 2012) and
Markovnikov additions (Lou et al. 2009; Wu et al. 2005).
Exploiting the promiscuous activity of biocatalyst to
achieve cascade reactions has become particularly fasci-
nating and remains a great challenge (Klossowski et al.
2013; Wang et al. 2011; Liu et al. 2011; Xue et al. 2012;
He et al. 2012). As a part of our research, aimed at
developing green chemistry by using enzyme as the reac-
tion catalyst, we focused on the waste-free, general, and
safe protocol for the synthesis of bis(indolyl)alkanes by the
cascade nucleophilic addition–elimination-Michael addi-
tion between aldehydes and indole (Scheme 1).
MMJL
4
Protease-S‘‘amano’’G
\1
5
DA
Lipase-PS‘‘amano’’SD
AA
\1
6
Experimental conditions: enzyme 10 mg, p-nitrobenzaldehyde
10 mg, indole 15 mg, water 1 ml, 50 °C, 50 h
a
Determined by HPLC
b
Pretreated with urea at 100 °C for 8 h
Protease-S‘‘amano’’G, D-aminoacylase from Escherichia
coli (DA), Lipase-PS‘‘amano’’SD, and Acylase ‘‘Amano’’
from Aspergillus oryzae (AA), showed no or low activity
toward this reaction.When the reactants were incubated
with denatured PPL or bovine serum albumin (BSA), the
yields were practically equal to the background reaction
(Table 1, entries 2–4), which could rule out the possibility
that the amine residues on the protein surface promoted the
process. The control experiments suggested that the tertiary
structure and the specific catalytic site of PPL were
responsible for the cascade between aldehydes and indole.
The reaction medium played an important role in
enzyme-catalyzed reactions, owing to its effects on enzyme
stability and substrate solubility, we investigated the effect
of conventional organic solvents on the model reaction
(Lou et al. 2009; Xue et al. 2012). The results indicated that
the different solvents had significant effects on activity of
PPL for the cascade reaction. The reaction afforded a
product yield of 41 % in water after 50 h (Table 2, entry
1). The other tested solvents including DMSO, 1,4-diox-
ane, chloroform, toluene, THF, hexane, and octane gave
the low yields (Table 2, entries 2–8).
Results and discussion
Based on our previous research, initial efforts were per-
formed in pure water using p-nitrobenzaldehyde and indole
as the model reaction and some hydrolases as catalysts at
50 °C for 50 h. Results indicated that porcine pancreas
lipase (PPL) displayed the best activity and the yield of
bis(indolyl)alkanes was 41 % (Table 1, entry 1). The other
six hydrolases, such as lipase from Candida cylindracea
(CCL), Amano lipase M from M. javanicus (MJL),
Considering that the mixed solvent could improve the
substrate solubility and enhance the coexistence of sub-
strate, some mixture of water and organic solvents were
studied under the same condition. As shown in Fig. 1,
better result with a high yield of 80 % was obtained from
this cascade reaction in the mixture solvent of water and
123

Biocatalysts for cascade reaction
Table 2 Effect of solvents on the reaction of 4-nitrobenzaldehyde
and indole
80
60
40
20
0
Entry
Solvent
Yield (%)a
1
2
3
4
5
6
7
8
Water
41
\1
\1
\1
3
DMSO
1,4-Dioxane
Chloroform
Toluene
THF
\1
6
Octane
Hexane
3
Experimental conditions: PPL 10 mg, p-nitrobenzaldehyde 10 mg,
indole 15 mg, solvent 1 ml, 50 °C, 50 h
0
10
20
30
40
50
60
70
80
90
1,4-dioxane (%)
a
Determined by HPLC
Fig. 2 Influence of 1,4-dioxane concentration on the PPL-catalyzed
cascade reaction. The reactions were carried out with p-nitrobenzal-
dehyde (10 mg) and indole (15 mg) in the presence of PPL (10 mg) in
1.0 mL solvent (Vwater ? V1,4-dioxane) at 50 °C for 50 h
80
70
60
50
40
30
20
10
0
Table 3 Effect of temperature, catalyst amount, and time on the
reaction of 4-nitrobenzaldehyde and indole
Entry
T/°C
Catalyst/mg
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
9
10
50
30
60
50
50
50
50
50
50
50
15
15
15
5
50
50
50
50
50
50
50
12
24
72
80
21
70
23
71
80
84
36
55
98
10
15
25
15
15
15
Experimental conditions: PPL 10 mg, p-nitrobenzaldehyde 10 mg,
indole 15 mg, water 0.8 mL, 1,4-dioxane 0.2 mL
Fig. 1 Effect of solvents mixture on the cascade reaction. The
reactions between p-nitrobenzaldehyde (10 mg) and indole (15 mg)
were carried out in the presence of PPL (10 mg) in 1.0 mL solvent
(Vwater/Vorganic solvent = 4:1) at 50 °C for 50 h
a
Determined by HPLC
optimal 1,4-dioxane concentration for the PPL-catalyzed
cascade reaction in water was about 20 %.
1,4-dioxane. In other mixture solvents such as pyridine,
ethyl acetate, chloroform, toluene, DMSO, THF, hexane,
and octane mixed with water, respectively, reactions pro-
ceeded very slowly and yields were also far from
satisfactory.
Temperature has certain influence on enzyme catalyzed
reactions due to its effects on the rate of the reaction and
also on the stability of the enzyme and it was found that the
enzyme showed the best yields of 80 % at 50 °C (Table 3,
entries 1–3). Then, the effect of the enzyme concentration
was also optimized. As the data shown in Table 3, the yield
of the product was improved greatly by increasing the
enzyme concentration from 5 to 15 mg/mL and reached a
plateau after 15 mg/ml. Finally, we investigated the time of
the cascade reaction between 4-nitrobenzaldehyde and
indole catalyzed by PPL under the optimal conditions and
it could be seen that the yield of the product the reaction
was high up to 98 % after 72 h.
Obviously, it was important to optimize the 1,4-dioxane
content for the model reaction system. We screened the
range of 1,4-dioxane content from 5 to 80 % (Vdioxane
/
V
water?dioxane), and the results were showed in Fig. 2. The
rate of the enzymatic reaction can be accelerated by
increasing the concentration of 1,4-dioxane and reached the
top when using 20–25 % 1,4-dioxane. However, when the
1,4-dioxane content was increased further, the yield
remarkably decreased to 1 %. Results indicated that the
123

Z. Xiang et al.
Having the optimal conditions in hand, we further
studied the generality of the PPL catalyzed cascade reac-
tion between indole and other aldehydes, and all results
were summarized in Table 4. Most bis(indolyl)alkanes
were formed in excellent yields when using benzaldehyde
or aromatic aldehydes with an electron-withdrawing sub-
stituent such as a nitro group (Table 4, entries 1–3) and
chloro-groups (Table 4, entries 5–7) in the presence of
PPL. However, the reaction of electron-rich benzaldehydes
such as p-methylbenzaldehyde, p-methoxylbenzaldehyde
and hydroxylbenzaldehyde with indole were comparatively
inefficient, giving the corresponding bis(indolyl)alkanes in
low to moderate yields (Table 4, entries 8–12). Interest-
ingly, aromatic aldehydes with two substitutions also gave
moderate to excellent yields with indole (Table 3, entries
13–14). However, alicyclic aldehydes only gave the cor-
responding bis(indolyl)alkanes in poor yields (Table 4,
entry 15). Thus, it can be inferred that the presence of
electron withdrawing group on the benzene ring can
improve the enzymatic cascade reaction, comparing with
the electron donating group or alicyclic aldehydes.
were measured with a Nicolet Nexus FTIR 670 spectropho-
tometer. Analytical HPLC was performed using an Agilent
1,100 series with a reversed-phase Shim-Pack VP-ODS col-
umn and a UV detector (250 nm). Eluents were methanol and
water. Lipase from porcine pancreas, Type II (PPL) was
purchased from Sigma-Aldrich, lipase from candida
cylindracea (CCL) (E.C. 3.1.1.3, 2.08 U/mg) was purchased
from Fluka, lipase from mucor javanicus (MJL) (E.C. 3.1.1.3
9.9 U/mg) was obtained from Fluka, D-aminoacylase from
Escherichia coli (DA) (E.C. 3.5.1.81, lyophilized powder,
acylase activity 5 MU g-1) was purchased from Amano
Enzyme Inc. (Japan), acylase ‘‘Amano’’ from Aspergillus
oryzae (E.C. 3.5.1.14, lyophilized powder) was purchased
from Amano Enzyme Inc. (Japan), Alkaline protease from
Bacillus subtilis (BSA) (E.C. 3.4.21.14, 10 U/g) was obtained
from Wuxi Enzyme Co. Ltd, Wuxi, P. R. China, Protease-
S‘‘amano’’G, Lipase-PS‘‘amano’’SD were purchased from
Amano Enzyme Inc. (Japan) and All chemicals were obtained
from commercial suppliers. Solvents for column chromatog-
raphy were not distilled before use.
At last, we have selected the reaction of benzaldehyde
with indole for the synthesis of bis(3-indolyl)methane as a
model reaction and compared the catalytic activity of PPL
with other catalysts in terms of reaction time and per-
centage yields (Table 5). Although the reaction catalyzed
by PPL required longer reaction time, the satisfied results
were also obtained in terms of yields. More importantly,
the present methodology have provided a biocatalytic route
for the synthesis of bis(indolyl)alkanes and expanded the
application’s scope of enzyme.
General procedure for the reaction of 4-
nitrobenzaldehyde and indole
A suspension of 100 mg 4-nitrobenzaldehyde (0.67 mmol),
150 mg indole (1.28 mmol), and 100 mg PPL in 10 ml
mixture solvent (8 ml water and 2 ml 1,4-dioxane) was
incubated at 50 °C and 200 r.p.m. (orbitally shaken) for
48 h. The products were extraction with 3 9 15 ml ethyl-
acetate. Then the ethylacetate was evaporated under vac-
uum to dryness. The crude residue was purified by flash
column chromatography on silica gel using petroleum/ethyl
acetate mixtures. All the known products were character-
ized by comparing the 1H NMR data with those reported in
the literature (Silveira et al. 2009; Chakrabarty et al. 2002;
Nadkarni et al. 2008). The structures of new compounds
were confirmed by IR, 1H NMR, 13C NMR, and HR-MS.
In conclusion, we successfully developed a facile and
inexpensive methodology with low pollution for the syn-
thesis of bioactive bis(indolyl)alkanes using PPL as cata-
lyst while exploring the promiscuous lipase catalyzed
system for the cascade reaction. After the optimization of
the stepwise process, a series of bis(indolyl)alkanes was
prepared in moderate to excellent yields. The hydrolase
catalyze this cascade reaction was of practical essential to
develop the application of enzymes and in the evolution of
new biocatalysts.
3,30-((4-Nitrophenyl)methylene)bis(1H-indole) (Ji et al.
2003) CAS NO. 7501-91-9; 1H NMR (400 MHz, DMSO-
d6) d 10.92 (s, 2H), 8.15 (d, J = 8.8 Hz, 2H), 7.61 (d,
J = 8.4 Hz, 2H), 7.36 (d, J = 8.4 Hz, 2H), 7.28 (d,
J = 7.6 Hz, 2H), 7.05 (t, J = 7.2, 15.6, 8.4 Hz, 2H), 6.88
(m, 4H), 6.02 (s, 1H); IR (neat): 3,423, 1,615, 1,592, 1,507,
1,487, 1,456, 1,339, 1,094, 746.
Experimental section
Materials and general methods
3,30-((3-Nitrophenyl)methylene)bis(1H-indole) (Das and
1
Das 2012; Yadav et al. 2001) CAS NO. 33948-93-5; H
1H and 13C NMR spectra were recorded on a Bruker
AVANCE DMX-400 spectrometer at 400 and 125 MHz in
CDCl3 and DMSO-d6, respectively. High resolution mass
spectra (HRMS) were run on waters GCT premier mass
spectrometer. Chemical shifts are reported in ppm (d), relative
to the internal standard of tetramethylsilane (TMS). IRspectra
NMR (400 MHz, DMSO-d6) d 10.91 (s, 2H), 8.13 (s, 1H),
8.05 (d, J = 8.0 Hz, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.56 (t,
J = 8.4, 16.0, 7.6 Hz, 1H), 7.37 (d, J = 8.0 Hz, 2H), 7.30
(d, J = 7.6 Hz, 2H), 7.05 (t, J = 7.2, 14.8, 7.6 Hz, 2H),
6.87 (m, 4H), 6.06 (s, 1H); IR (neat): 3,413, 1,612, 1,525,
1,456, 1,348, 1,095, 744.
123

Biocatalysts for cascade reaction
Table 4 Direct cascade
reaction of aldehydes and
indolesa
R
H
N
PPL
RCHO
+
Solvent,48h
N
H
N
H
O
H
a
Entry
1
Products
Yield (%)
98
R
NH
O
NH
O2N
O2N
NH
O
2
3
4
5
6
7
8
93
89
87
91
89
83
67
NH
NO2
NO2
NH
NO2
O
NH
NO2
NH
O
H
NH
NH
O
NH
Cl
Cl
NH
O
NH
Cl
Cl
NH
O
H
Cl
NH
Cl
NH
O
NH
HO
HO
123

Z. Xiang et al.
Table 4 continued
O
a
Entry
9
Products
Yield (%)
R
H
H
NH
O
63
72
NH
OH
OH
NH
OH
O
10
NH
OH
NH
O
11
12
13
14
15
52
50
76
99
38
NH
NH
O
H
NH
H3CO
MeO
NH
O
HO
Br
NH
OCH3
HO
OMe
NH
OH
Br
O
NH
OH
NH
Reaction conditions: aldehydes
0.1 mmol, indole 0.2 mmol,
1,4-dioxane 0.3 ml, water
1.2 ml, and PPL 15 mg was
O
NH
o
shaken at 50 C for 72 h
a
Determined by HPLC
3,30-((2-Nitrophenyl)methylene)bis(1H-indole) (Tayebee
et al. 2013) CAS NO. 119091-74-6; 1H NMR (400 MHz,
DMSO-d6) d 10.90 (s, 2H), 7.87 (d, J = 8.0 Hz, 1H), 7.55
(t, J = 7.2, 15.2, 8.0 Hz, 1H), 7.35–7.46 (m, 4H), 7.22 (d,
J = 7.6 Hz, 2H), 7.05 (t, J = 7.2, 14.8, 7.6 Hz, 2H), 6.88
(t, J = 14.4, 7.2 Hz, 2H), 6.77 (s, 2H), 6.41 (s, 1H); IR
(neat): 3,412, 1,615, 1,600, 1,522, 1,456, 1,353, 1,346,
1,095, 743.
DMSO-d6) d 10.87 (s, 2H), 7.37 (d, J = 8.0 Hz, 3H), 7.31
(t, J = 7.2, 15.2, 8.0 Hz, 4H), 7.05 (t, J = 7.6, 14.8,
7.2 Hz, 2H), 6.88 (m, 4H), 5.89 (s, 1H); IR (neat): 3,411,
1,613, 1,594, 1,474, 1,456, 1,353, 1,095, 743.
3,30-((3-Chlorophenyl)methylene)bis(1H-indole) (Krish-
nammagari et al. 2012) CAS NO. 865717-24-4; 1H NMR
(400 MHz, CDCl3) d 7.83 (s, 2H), 7.34 (m, 4H), 7.24 (m,
3H), 7.54 (t, J = 15.2, 7.6 Hz, 3H), 7.02 (t, J = 15.2,
7.6 Hz, 2H), 6.58 (s, 2H), 5.85 (s, 1H); IR (neat): 3,408,
1,617, 1,596, 1,487, 1,455, 1,352, 1,089, 742.
3,30-((4-Chlorophenyl)methylene)bis(1H-indole) (Ji et al.
2003) CAS NO. 178946-89-9; 1H NMR (400 MHz,
123

Biocatalysts for cascade reaction
2H), 6.71 (s, 2H), 6.02 (s, 1H), 5.52 (s, 1H); IR (neat):
3,502, 3,419, 1,618, 1,592, 1,487, 1,454, 1,336, 1,090, 741.
Table 5 Comparison of the catalytic efficiency of PPL with some
reported catalysts
Entry Catalyst
Time/h Yield/% Reference
3,30-((4-Methylphenyl)methylene)bis (1H-indole) (Yadav
et al. 2001) CAS NO. 223753-09-1; 1H NMR (400 MHz,
CDCl3) d 7.80 (s, 2H), 7.41 (d, J = 7.6 Hz, 2H), 7.33 (d,
J = 8.0 Hz, 2H), 7.24 (d, J = 8.0 Hz, 2H), 7.18 (t,
J = 7.2, 14.8, 7.6 Hz, 2H), 7.10 (d, J = 8.4 Hz, 2H), 7.02
(t, J = 7.2, 15.2, 8.0 Hz, 2H), 6.60 (d, J = 1.6 Hz, 2H),
5.86 (s, 1H), 2.34 (s, 3H); IR(neat): 3,417, 1,618, 1,510,
1,487, 1,456, 1,338, 1,091, 744.
1
2
PPL
72
12
87
64
This work
TiO2 (nano)
Kantam et al.
(2006)
3
4
5
Cp2ZrCl2
Zeolites
36
2
79
80
97
Kantam et al.
(2004)
Karthik et al.
(2004)
Acidic IL immobilized 5.5
on Silica
Hagiwara et al.
(2007)
3,30-((4-Methoxylphenyl)methylene)bis(1H-indole) (Yadav
1
et al. 2001) CAS NO. 33985-68-1; H NMR (400 MHz,
CDCl3) d 7.84 (s, 2H), 7.39 (d, J = 8.0 Hz, 2H), 7.33 (d,
J = 7.6 Hz, 2H), 7.25 (d, J = 8.4 Hz, 2H), 7.17 (t,
J = 7.6, 15.2, 7.6 Hz, 2H), 7.01 (t, J = 7.6, 14.8, 7.2 Hz,
2H), 6.82 (d, J = 8.0 Hz, 2H), 6.60 (s, 2H), 5.84 (s, 1H),
3.78 (s, 3H); IR (neat): 3,395, 1,610, 1,587, 1,509, 1,487,
1,455, 1,336,1,093, 741.
3,30-((2-Chlorophenyl)methylene)bis(1H-indole) (Ji et al.
2003) CAS NO. 74944-40-4; 1H NMR (400 MHz,
CDCl3) d 7.92 (s, 2H), 7.43 (t, J = 8.4, 16.0, 7.6 Hz, 3H),
7.37 (d, J = 8.0 Hz, 2H), 7.24–7.16 (m, 4H), 7.12 (t,
J = 6.4, 14.4, 8.0 Hz, 1H), 7.04 (t, J = 6.8, 14.4, 7.6 Hz,
2H), 6.62 (d, J = 2.0 Hz, 2H), 6.36 (s, 1H); IR (neat):
3,412, 1,618, 1,589, 1,487, 1,456, 1,337, 1,093, 741.
5-(Di(1H-indol-3-yl)methyl-2-methoxyphenol (Yang et al.
2011) CAS NO. 354786-65-5; 1H NMR (400 MHz,
CDCl3) d 7.74 (s, 2H), 7.50 (d, J = 8.0 Hz, 2H), 7.30 (d,
J = 8.0 Hz, 2H), 7.19 (t, J = 7.2, 14.8, 7.6 Hz, 2H), 7.05
(t, J = 14.4, 7.2 Hz, 2H), 6.75-6.83 (m, 3H), 6.62 (s, 2H),
6.34 (s, 1H), 5.91 (s, 1H), 3.90 (s, 3H); IR (neat): 3,502,
3,413, 1,615, 1,592, 1,478, 1,455, 1,350, 1,086, 741.
3,30-Phenylmethylenebis(1H-indole) (Yadav et al. 2001) CAS
1
NO. 35173-74-1; H NMR (400 MHz, CDCl3) d 7.79 (s,
2H), 7.41 (d, J = 8.0 Hz, 2H), 7.37–7.25 (m, 7H), 7.19 (t,
J = 7.6, 17.2, 9.6 Hz, 2H), 7.02 (t, J = 7.2, 14.8, 7.6 Hz,
2H), 6.59 (d, J = 1.2 Hz, 2H), 5.90 (s, 1H); IR (neat): 3,395,
1,618, 1,599, 1,492, 1,455, 1,336, 1,092, 746.
4-Bromo-2-(di(1H-indol-3-yl)methyl)phenol 1H
NMR
(400 MHz, CDCl3) d 7.96 (s, 2H), 7.42 (d, J = 8.0 Hz, 2H),
7.35 (t, J = 8.0, 18.4, 10.4 Hz, 3H), 7.21–7.30 (m, 4H), 7.07
(t, J = 7.6, 14.8, 7.2 Hz, 2H), 6.75 (d, J = 8.4 Hz, 1H), 6.67
(s, 2H), 5.99 (s, 1H), 5.66 (s, 1H); IR (neat): 3,411, 1,618,
1,593, 1,487, 1,456, 1,338, 1,098, 743; 13C NMR (CDCl3;
100 MHz): d 60.51 (Ar3CH), 153.67, 136.82, 132.40,
131.56, 112.90 (all Ar–C), 130.80, 126.59, 123.67, 122.45,
119.65, 118.42, 116.48, 111.33 (all Ar–CH); HRMS: Mass
416.0518 for C23H17N2OBr, Calc. Mass 416.0524.
3,30-((4-Hydroxylphenyl)methylene)bis(1H-indole) (Yang
et al. 2011) CAS NO. 151358-47-3; 1H NMR (400 MHz,
DMSO-d6) d 10.78 (s, 2H), 9.23 (s, 1H), 7.34 (d,
J = 8.0 Hz, 2H), 7.26 (d, J = 8.4 Hz, 2H), 7.14 (d,
J = 8.8 Hz, 2H), 7.02 (t, J = 7.2, 14.8, 7.6 Hz, 2H), 6.85
(t, J = 7.6, 14.8, 7.2 Hz, 2H), 6.78 (s, 2H), 6.66 (d,
J = 8.0 Hz, 2H), 5.71 (s, 1H); IR (neat): 3,446, 3,426,
3,405, 1,614, 1,597, 1,512 1,485, 1,456, 1,353, 1,089, 743.
3,30-((3-Hydroxylphenyl)methylene)bis(1H-indole) (Kid-
wai et al. 2011) CAS NO. 96060-62-7; 1H NMR
(400 MHz, CDCl3) d 7.93 (s, 2H), 7.38 (d, J = 8.0 Hz,
2H), 7.34 (d, J = 8.0 Hz, 2H), 7.25–7.13 (m, 4H), 7.00 (t,
J = 7.2, 15.2, 8.0 Hz, 1H), 6.93 (d, J = 8.0 Hz, 1H), 6.76
(s, 1H), 6.68 (d, J = 7.6 Hz, 1H), 6.64 (s, 2H), 5.82 (s,
1H), 5.01 (s, 1H); IR (neat): 3,410, 1,618, 1,597, 1,486,
1,455, 1,338, 1,093, 744.
2-(1-(1H-Indol-3-yl) ethyl)-1H-indole (Xu et al.
2013) CAS NO. 5030-91-1; 1H NMR (400 MHz, CDCl3)
d 7.81 (s, 2H), 7.48 (d, J = 8.0 Hz. 2H), 7.23 (d,
J = 8.0 Hz, 2H), 7.06 (t, J = 7.2, 14.8, 7.6 Hz, 2H), 6.94
(t, J = 7.6, 14.8, 7.2 Hz, 2H), 6.79 (s, 2H), 4.58 (m, 1H),
1.71 (d, J = 7.2 Hz, 3H); IR (neat): 3,408, 1,617, 1,596,
1,455, 1,352, 1,094, 743; GC–MS: m/z = 260.
Acknowledgments The authors gratefully acknowledge generous
financial support from National Natural Science Foundation of China
(No. 21072172, 21272208) and the Zhejiang Provincial Natural Sci-
ence Foundation (Project No. 2010-Z4090225).
3,30-((2-Hydroxylphenyl)methylene)bis(1H-indole) (Yang
1
et al. 2011) CAS NO. 33948-97-9; H NMR (400 MHz,
CDCl3) d 7.94 (s, 2H), 7.42 (d, J = 7.6 Hz, 2H), 7.36 (d,
J = 8.0 Hz, 2H), 7.21 (t, J = 8.8, 15.6, 6.8 Hz, 4H), 7.05
(t, J = 14.4, 7.2 Hz, 4H), 6.90 (t, J = 8.0, 15.6, 7.6 Hz,
Conflict of interest We declare that we have no competing finan-
cial interests.
123

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