Synthesis of benzothiazoles using fluorescein as an efficient photocatalyst under visible light

Article abstract of DOI:10.1016/j.mcat.2021.111693

This work reports a novel and efficient method for the synthesis of benzothiazoles using 2-aminothiophenol derivatives in conjunction with aromatic aldehyde as starting materials via visible-light-induced condensation cyclization. Utilizing fluorescein as the photocatalyst and blue LED lamp as the light source, the reaction proceeds in the presence of a molecular oxygen atmosphere without the need for metal catalyst or an additional oxidant. Significantly, this method exhibits good tolerance in substrates, and a variety of 2-aminothiophenol derivatives and aromatic aldehyde are amenable to producing the corresponding benzothiazoles in high to excellent yields.

Full text of DOI:10.1016/j.mcat.2021.111693

Molecular Catalysis 510 (2021) 111693
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.journals.elsevier.com/molecular-catalysis
Synthesis of benzothiazoles using fluorescein as an efficient photocatalyst
under visible light
Wuji Sun*, Haodong Chen, Kaixuan Wang, Xueyao Wang, Mayan Lei, Chunyan Liu, Qidi Zhong
School of Pharmacy, North China University of Science and Technology, Tangshan, 063210, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
This work reports a novel and efficient method for the synthesis of benzothiazoles using 2-aminothiophenol
derivatives in conjunction with aromatic aldehyde as starting materials via visible-light-induced condensation
cyclization. Utilizing fluorescein as the photocatalyst and blue LED lamp as the light source, the reaction pro-
ceeds in the presence of a molecular oxygen atmosphere without the need for metal catalyst or an additional
oxidant. Significantly, this method exhibits good tolerance in substrates, and a variety of 2-aminothiophenol
derivatives and aromatic aldehyde are amenable to producing the corresponding benzothiazoles in high to
excellent yields.
Benzothiazoles
Visible-light-induced
Fluorescein
Photocatalyst
1. Introduction
Cu2O, [18] ZnO nanoparticles, [19] and YCl3 [20] were also previously
reported (Scheme 1, eq. (3)). Although many methods have been used to
Benzothiazoles are a valuable class of heterocyclic compounds in
organic chemistry, and its derivatives due to their building blocks in
biological and therapeutic activities are vital core structures used to
create drugs, for instance anticancer, antiviral antihistamine, antiulcer,
antifungal, anti-inflammatory, anti-convulsant, antimicrobial, enzyme
inhibition, etc. [1–5] Benzothiazole rings are also found in a myriad of
natural products, for example vitamin B12. [6] Moreover, benzothia-
zoles are applied in materials science as the core components of mate-
rials with optical or electronic properties, and also used as ligands of
transition metals and intermediates of organic reactions. [7–9] Hence,
the development of simple and practical methods to synthesize benzo-
thiazoles and its derivatives has stimulated considerable interest, which
is precisely based on their great application prospects.
synthesize benzothiazoles to date, they often suffer from some re-
strictions in aspects such as additional additives, excess amounts of
oxidant, expensive metal catalysts, limited starting materials, harsh re-
action conditions or effect on the environment. [21–22] In consequence,
the pursuit of alternative efficient methods to obtain benzothiazoles has
never ceased.
In recent years, visible light, as a readily available and renewable
clean energy source, has attracted extensive attention in assisting cata-
lytic organic synthesis reactions. [23–25] Notably, organic dyes are
cheaper and more reliable than some expensive metal photocatalysts in
many valuable reactions. [26–27] In the present paper, a novel, efficient
and green method for the synthesis of benzothiazoles under visible light
is reported (Scheme 1, eq. (4)). Owing to its cheap and commercially
available characteristics, fluorescein has been selected as the photo-
catalyst. The synthesis of benzothiazoles would proceed in the presence
of visible light, fluorescein and a molecular oxygen atmosphere without
the need for metal catalyst or an additional oxidant. We suppose the
present work could make the reaction more synthetically accessible by
eliminating the requirement for high temperature, strong acid and use of
metal catalyst.
Over the past decades, different routes for the synthesis of benzo-
thiazoles have been developed using various catalytic systems because
of their wide range of applications. [10–12] Among these strategies, the
condensation of 2-aminothiophenol with aromatic aldehyde are of the
most commonly used methods, and a number of Brønsted acids, namely,
[bsmim] [HSO4,13] [DodecIm] [HSO4,14] and BAIL gel [15] have been
used as the acid catalyst (Scheme 1, eq. (1)). In some cases, an excess of
oxidants, such as DTBP, [16] TBHP, [13] and, DDQ [17] were also
employed in the reaction, which could lead to several side reactions and
difficult separation of the products from the reaction mixture (Scheme 1,
eq. (2)). In addition to these, different metal catalytic systems, such as
2. Results and discussion
In our initial studies towards the synthesis of benzothiazoles, 2-
* Corresponding author.
E-mail address: sunwuji@yeah.net (W. Sun).
https://doi.org/10.1016/j.mcat.2021.111693
Received 24 February 2021; Received in revised form 28 May 2021; Accepted 31 May 2021
Available online 18 June 2021
2468-8231/© 2021 Elsevier B.V. All rights reserved.

W. Sun et al.
Molecular Catalysis 510 (2021) 111693
Scheme 1. Reported work and our work for synthesis of benzothiazoles.
B, Rhodamine B, and Fluorescein, were then examined (Table 1, Entries
2–4). Fluorescein was the best photocatalyst and gave 3a in 92% yield.
The essential role of the photocatalyst was demonstrated by control
experiments, wherein minimal amounts of 3a were detected. Subse-
quently, the effect of the solvent was studied. Various solvents, such as
CH3CN, THF, CH3OH and DMF, were evaluated. The desired product 3a
could be obtained in 92% yield in CH3OH, while in other solvents, the
yields were lower (Table 1, Entries 4–7). The desired product 3a was
obtained in 92% yield when the photocatalyst loading was increased
from 5 mol% to 10 mol% (Table 1, Entries 4 and 8). However, further
increasing the photocatalyst loading led to no evident improvement in
the product yield (Table 1, Entry 9). Finally, having tested different
reaction times, 3 h was kept as the optimum reaction time (Table 1,
Entries 4 and 10–12).
Table 1
Optimization of the reaction conditionsa.
Entry
1
Photocatalyst (mol%)
Eosin Y (10 mol%)
Solvent
CH3OH
CH3OH
CH3OH
CH3OH
CH3CN
THF
Time (h)
Yieldb (%)
3
3
3
3
3
3
3
3
3
1
2
4
58
50
39
92
74
81
44
80
91
48
84
92
2
Eosin B (10 mol%)
3
Rhodamine B (10 mol%)
Fluorescein (10 mol%)
Fluorescein (10 mol%)
Fluorescein (10 mol%)
Fluorescein (10 mol%)
Fluorescein (5 mol%)
Fluorescein (15 mol%)
Fluorescein (10 mol%)
Fluorescein (10 mol%)
Fluorescein (10 mol%)
4
5
6
7
DMF
8
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
After a series of reaction conditions optimization, it was determined
that the optimal reaction condition was 2-aminothiophenol (1a) and
benzaldehyde (2a) as the reaction substrates, fluorescein (10 mol%) as
the photocatalyst, CH3OH as the solvent, and a 30 W blue LED as the
light source under air atmosphere at room temperature for 3 h.
With the optimal conditions determined, we investigated the scope
and generality of photocatalytic condensation reactions, and the results
are summarized in Table 2. First of all, in the absence of a substituent on
the benzaldehyde 2a, the yield of the product 3a reached 92%. The
reaction of substituted aromatic aldehydes such as electron-
withdrawing (4-Br, 4-Cl and 4-F) and electron-donating (2-Me, 4-Me
and 4-OMe) substituents afforded the desired products in high to
excellent yields (Table 2, 3d-3f and 3 g-3i). Notably, the position of the
substituents on the aromatic aldehydes had little effect on the yield of
the corresponding product (Table 2, 3b-3d and 3 g-3 h). In addition,
9
10
11
12
a
Reaction conditions: 2-Aminothiophenol 1a (1 mmol), benzaldehyde 2a (1
mmol), fluorescein (10 mol%), CH3OH (20 mL), blue LED at room temperature
for 3 h, under air atmosphere.
b
Isolated yields.
aminothiophenol (1a) and benzaldehyde (2a) were used as the foun-
dational substrates and were irradiated with a blue LED to optimize the
reaction conditions (Table 1). The reaction of 1a with 2a was initially
performed in the presence of Eosin Y as a photocatalyst and the desired
product, 2-phenylbenzothiazole (3a), was obtained in 58% yield
(Table 1, Entry 1). Several other common organic dyes, including Eosin
2

W. Sun et al.
Molecular Catalysis 510 (2021) 111693
Table 2
Scope and generality of photocatalytic condensation reactionsa.
a
Reaction conditions: 1a-1b (1 mmol), 2a-2j (1 mmol), fluorescein (10 mol%), CH3OH (20 mL), blue LED at room temperature, under air atmosphere.
aromatic aldehydes with multiple substituents gave a lower yield which
may be due to the presence of two electron-donating groups on the ar-
omatic aldehydes (Table 2, 3j).
need for an additional oxidant (Scheme 2, eq. (5)).
Based on the above experimental results and literature reports, [26,
28] one reasonable process has been proposed to explain the formation
of product 3a. The proposed mechanism begins with the formation of
imine I, which is obtained by nucleophilic addition and dehydrated of
2-aminothiophenol 1a and benzaldehyde 2a under blue LED irradiation.
Subsequently, the resulting intermediate I undergoes intramolecular
cyclization, generating intermediate II. Under the fluorescein/O2 cata-
lyst system, fluorescein (Fl) generates excited fluorescein* (Fl*) species
under visible light, and intermediate II is converted to intermediate III
via single electron transfer. Fluorescein radical anion (Fl*ꢀ ) is oxidized
to ground state fluorescein (Fl) by O2. Finally, the desired product 3a is
produced by deprotonation of intermediate III and hydrogen
abstraction.
Next, these conditions were then applied to 2-aminothiophenol de-
rivative and found that they were well tolerated under the present re-
action conditions. The reaction of 2-amino-4-chlorothiophenol 1b with
benzaldehyde 2a under the optimized conditions produced the corre-
sponding product 3k in 89% yield (Table 2, 3k). The use of 2-amino-4-
chlorothiophenol 1b proceeded smoothly with various substituted aro-
matic aldehydes containing both electron-withdrawing and electron-
donating groups, with 83–93% yields (Table 2, 3l-3t).
In order to explain the reaction mechanism, some control experi-
ments were conducted (Scheme 2). The first experiment under the
optimized condition gave 3a in a good yield (92%) with that of the same
compound obtained in the studied approach (Scheme 2, eq. (1)). As can
be seen from eq. (2), the desired product 3a was not produced in the
system, indicating the importance of the photocatalyst. According to eq.
(3), the photocatalytic condensation reactions revealed that the reaction
was almost completely inhibited in the absence of light. Under similar
conditions but in an argon atmosphere, no desired product was detect-
able (Scheme 2, eq. (4)). Moreover, when TBHP was added to the above
reaction mixture, the desired product 3a was obtained in a 93% yield. It
is indicated that TBHP and a molecular oxygen atmosphere have a
similar impact on the studied reaction, and the reaction affords a good
yield in the presence of a molecular oxygen atmosphere without the
3. Conclusions
In summary, we developed a novel, efficient and green method for
synthesis of benzothiazoles via the visible-light-induced condensation
cyclization of 2-aminothiophenol derivatives and aromatic aldehyde
using fluorescein as photocatalyst. The reactions proceeded smoothly,
affording the corresponding benzothiazoles in high to excellent yields
with good functional group tolerance. Moreover, the catalytic system
avoids the use of an additional oxidant or metal catalyst, in line with the
concept of green chemistry. The application of this method for
3

W. Sun et al.
Molecular Catalysis 510 (2021) 111693
Scheme 2. Some control experiments.
preparation of other useful heterocycles is underway in our laboratory.
placed in a flat quartz glass jar. The open-air reaction container was
placed under a 30 W blue LED lamp. After completion of the reaction
(monitored by TLC analysis), the solvent was removed under reduced
pressure. Then, water (20 mL) was added and the mixture was extracted
with ethyl acetate (3 × 20 mL). The combined organic layer was dried
over anhydrous Na2SO4 and the solvent was removed in vacuo. The
crude product was purified via silica gel column chromatography (pe-
troleum ether/ethyl acetate rations of 4:1–6:1) to generate the corre-
sponding product 3.
4. Experimental
4.1. Chemistry
All of the chemicals were purchased from commercial sources and
used without further purification. The reactions were monitored by thin
layer chromatography (TLC), and the products were purified by column
chromatography on silica gel (200–300 mesh). 1H NMR spectra were
recorded on a Bruker Avance 400 spectrometer at 400 MHz in DMSO‑d6.
The following abbreviations were used to describe peak splitting pat-
terns when appropriate: s = singlet, d = doublet, t = triplet, m = mul-
tiple. Coupling constants (J) were reported in Hertz (Hz). Mass spectra
(ESI-HRMS) were recorded using an Agilent Accurate-Mass Q-TOF LC/
MS 6520 instrument with an ESI source. Fluorescence spectra of the
synthesized compounds were taken using a CREE XPE-3535 fluores-
cence spectrophotometer.
2-Phenylbenzothiazole (3a). 92% yield as a white solid; 1H NMR
(400 MHz, DMSO‑d6): δ (ppm) 8.18–8.13 (m, 1H), 8.13–8.07 (m, 3H),
7.60–7.55 (m, 4H), 7.50–7.46 (m, 1H); HRMS (ESI) m/z: calcd for
C
13H10NS [M + H]+ 212.0528, found 212.0527.
2-(2′-Bromophenyl)benzothiazole (3b). 90% yield as a white
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.22–8.19 (m, 1H), 8.13
(d, J = 8.7 Hz, 1H), 8.03 (dt, J = 7.7, 1.5 Hz, 1H), 7.89–7.86 (m, 1H),
7.62–7.57 (m, 2H), 7.55–7.48 (m, 2H); HRMS (ESI) m/z: calcd for
C
13H9BrNS [M + H]+ 289.9634, found 289.9632.
2-(3′-Bromophenyl)benzothiazole (3c). 91% yield as a white
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.25 (dt, J = 7.4, 2.6 Hz,
1H), 8.20–8.15 (m, 1H), 8.11–8.08 (m, 2H), 7.81–7.77 (m, 1H),
7.60–7.49 (m, 3H); HRMS (ESI) m/z: calcd for C13H9BrNS [M + H]+
289.9634, found 289.9638.
4.2. General procedure for synthesis of products 3a-3t
2-Aminothiophenol derivatives 1 (1 mmol), aromatic aldehyde 2 (1
mmol) and fluorescein (10 mol%) were dissolved in 20 mL methanol and
4

W. Sun et al.
Molecular Catalysis 510 (2021) 111693
Scheme 3. Proposed reaction mechanism.
246.0139, found 246.0141.
2-(4′-Bromophenyl)benzothiazole (3d). 88% yield as a yellow
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.17 (d, J = 8.0 Hz, 1H),
8.06 (dd, J = 13.9, 8.2 Hz, 3H), 7.79 (d, J = 8.2 Hz, 2H), 7.59–7.47 (m,
2H); HRMS (ESI) m/z: calcd for C13H9BrNS [M + H]+ 289.9634, found
289.9634.
6-Chloro-2-(2′-Bromophenyl)benzothiazole (3l). 90% yield as a
white solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.26 (d, J = 8.6 Hz,
1H), 8.22 (d, J = 2.0 Hz, 1H), 8.04 (dd, J = 7.7, 1.8 Hz, 1H), 7.89 (dd, J
= 8.0, 1.3 Hz, 1H), 7.63–7.58 (m, 2H), 7.53 (td, J = 7.7, 1.8 Hz, 1H);
HRMS (ESI) m/z: calcd for C13H8BrClNS [M + H]+ 323.9244, found
323.9247.
2-(4′-Chlorophenyl)benzothiazole (3e). 94% yield as a white
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.18–8.15 (m, 3H), 8.07
(d, J = 8.1 Hz, 1H), 7.58–7.54 (m, 1H), 7.50–7.40 (m, 3H); HRMS (ESI)
m/z: calcd for C13H9ClNS [M + H]+ 246.0139, found 246.0141.
2-(4′-Fluorophenyl)benzothiazole (3f). 86% yield as a yellow
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.18 (dd, J = 8.5, 1.2 Hz,
1H), 8.14–8.11 (m, 2H), 8.08 (dd, J = 8.5, 1.2 Hz, 1H), 7.67–7.64 (m,
2H), 7.59–7.55 (m, 1H), 7.51–7.47 (m, 1H); HRMS (ESI) m/z: calcd for
6-Chloro-2-(3′-Bromophenyl)benzothiazole (3 m). 92% yield as a
white solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.25–8.21 (m, 2H),
8.17 (d, J = 2.0 Hz, 1H), 8.09–8.06 (m, 1H), 7.83–7.80 (m, 1H),
7.57–7.53 (m, 2H); HRMS (ESI) m/z: calcd for C13H8BrClNS [M + H]+
323.9244, found 323.9243.
6-Chloro-2-(4′-Bromophenyl)benzothiazole (3n). 93% yield as a
brown solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.21 (d, J = 8.6 Hz,
1H), 8.16 (d, J = 2.1 Hz, 1H), 8.06–8.02 (m, 2H), 7.81–7.78 (m, 2H),
7.54 (dd, J = 8.6, 2.1 Hz, 1H); HRMS (ESI) m/z: calcd for C13H8BrClNS
[M + H]+ 323.9244, found 323.9245.
C
13H9FNS [M + H]+ 230.0434, found 230.0433.
2-(2′-Methylphenyl)benzothiazole (3 g). 91% yield as a yellow
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.17 (d, J = 8.0 Hz, 1H),
8.10 (d, J = 8.0 Hz, 1H), 7.82 (d, J = 7.6 Hz, 1H), 7.59–7.55 (m, 1H),
7.52–7.38 (m, 4H), 2.64 (s, 3H); HRMS (ESI) m/z: calcd for C14H12NS
[M + H]+ 226.0685, found 226.0683.
6-Chloro-2-(4′-Chlorophenyl)benzothiazole (3o). 91% yield as a
white solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.21 (d, J = 8.6 Hz,
1H), 8.15 (d, J = 2.0 Hz, 1H), 8.12–8.09 (m, 2H), 7.67–7.63 (m, 2H),
7.54 (dd, J = 8.6, 2.0 Hz, 1H); HRMS (ESI) m/z: calcd for C13H8Cl2NS
[M + H]+ 279.9749, found 279.9753.
2-(4′-Methylphenyl)benzothiazole (3 h). 92% yield as a yellow
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.13 (dd, J = 8.0, 1.2 Hz,
1H), 8.05 (dd, J = 8.0, 1.2 Hz, 1H), 7.99 (d, J = 8.2 Hz, 2H), 7.57–7.53
(m, 1H), 7.48–7.44 (m, 1H), 7.38 (d, J = 8.2 Hz, 2H), 2.40 (s, 3H); HRMS
(ESI) m/z: calcd for C14H12NS [M + H]+ 226.0685, found 226.0688.
2-(4′-Methoxyphenyl)benzothiazole (3i). 87% yield as a white
solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.12–8.09 (m, 1H),
8.05–8.01 (m, 3H), 7.55–7.51 (m, 1H), 7.45–7.41 (m, 1H), 7.13 (d, J =
8.7 Hz, 2H), 3.86 (s, 3H); HRMS (ESI) m/z: calcd for C14H12NOS [M +
H]+ 242.0634, found 242.0636.
6-Chloro-2-(4′-Fluorophenyl)benzothiazole (3p). 84% yield as a
white solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.21–8.13 (m, 4H),
7.52 (dd, J = 8.6, 2.1 Hz, 1H), 7.45–7.41 (m, 2H); HRMS (ESI) m/z:
calcd for C13H8ClFNS [M + H]+ 264.0045, found 264.0049.
6-Chloro-2-(2′-Methylphenyl)benzothiazole (3q). 89% yield as a
yellow solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.22–8.17 (m, 2H),
7.83 (dd, J = 7.7, 1.4 Hz, 1H), 7.55 (dd, J = 8.6, 2.1 Hz, 1H), 7.49–7.40
(m, 3H), 2.63 (s, 3H); HRMS (ESI) m/z: calcd for C14H11ClNS [M + H]+
260.0295, found 260.0299.
2-(3′,4′-Dimethoxyphenyl)benzothiazole (3j). 82% yield as a
yellow solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.10 (d, J = 8.0 Hz,
1H), 8.03 (d, J = 8.0 Hz, 1H), 7.66–7.60 (m, 2H), 7.55–7.40 (m, 2H),
7.12 (d, J = 8.4 Hz, 1H), 3.90 (s, 3H), 3.86 (s, 3H); HRMS (ESI) m/z:
calcd for C15H14NO2S [M + H]+ 272.0740, found 272.0741.
6-Chloro-2-(4′-Methylphenyl)benzothiazole (3r). 87% yield as a
brown solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.17 (d, J = 8.6 Hz,
1H), 8.11 (d, J = 2.1 Hz, 1H), 7.99 (d, J = 8.1 Hz, 2H), 7.50 (dd, J = 8.6,
2.1 Hz, 1H), 7.39 (d, J = 8.1 Hz, 2H), 2.40 (s, 3H); HRMS (ESI) m/z:
calcd for C14H11ClNS [M + H]+ 260.0295, found 260.0296.
6-Chloro-2-(4′-Methoxyphenyl)benzothiazole (3 s). 90% yield as
a white solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.15 (d, J = 8.6 Hz,
6-Chloro-2-phenylbenzothiazole (3k). 89% yield as a yellow solid;
1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.20 (d, J = 8.6 Hz, 1H), 8.15 (d,
J = 2.1 Hz, 1H), 8.12–8.09 (m, 2H), 7.62–7.59 (m, 3H), 7.53 (dd, J =
8.6, 2.1 Hz, 1H); HRMS (ESI) m/z: calcd for C13H9ClNS [M + H]+
5

W. Sun et al.
Molecular Catalysis 510 (2021) 111693
reversible mechanochromism and blue electroluminescence, Dyes Pigments 148
(2018) 276–285.
1H), 8.08 (d, J = 2.1 Hz, 1H), 8.04 (d, J = 8.8 Hz, 2H), 7.47 (dd, J = 8.6,
2.1 Hz, 1H), 7.13 (d, J = 8.8 Hz, 2H), 3.86 (s, 3H); HRMS (ESI) m/z:
calcd for C14H11ClNOS [M + H]+ 276.0244, found 276.0247.
6-Chloro-2-(3′,4′-Dimethoxyphenyl)benzothiazole (3t). 83%
yield as a yellow solid; 1H NMR (400 MHz, DMSO‑d6): δ (ppm) 8.14 (d, J
= 8.6 Hz, 1H), 8.09 (d, J = 2.1 Hz, 1H), 7.64–7.62 (m, 2H), 7.48 (dd, J =
8.6, 2.1 Hz, 1H), 7.14 (d, J = 9.0 Hz, 1H), 3.89 (s, 3H), 3.86 (s, 3H);
HRMS (ESI) m/z: calcd for C15H13ClNO2S [M + H]+ 306.0350, found
306.0352.
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Declaration of Competing Interest
We declare that we have no financial and personal relationships with
other people or organizations that can inappropriately influence our
work, there is no professional or other personal interest of any nature or
kind in any product, service and/or company that could be construed as
influencing the position presented in, or the review of, the manuscript
entitled.
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Acknowledgments
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