Synthesis and biological evaluation of novel benzothiophene derivatives

Article abstract of DOI:10.1007/s12039-018-1523-3

Abstract: Benzothiophene derivatives were synthesized regioselectively using coupling reactions and electrophilic cyclization reactions. Antimicrobial properties of isolated compounds were tested against indicator microorganisms such as C. albicans ATCC 10231, B. subtilis ATCC 6633, E. coli ATCC 25922 and S. aureus ATCC 25923. 3-(4-aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b]thiophene (12E), 3-ethynyl-2-(thiophen-2-yl) benzo[b]thiophene (12L) and 3-(2-aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b]thiophene (12J) displayed high antibacterial activity against S. aureus. Further, 3-iodo-2-(thiophen-2-yl) benzo[b]thiophene (10) and 3-(trimethylsilylethynyl)-2-(thiophen-2-yl) benzo[b] thiophene (12K) were found to have potentials to be used as antifungal agents against current fungal diseases. Novel 3-(1H-indole-2-yl)-2-(thiophen-2-yl) benzo[b] thiophene (16) and 3-(4-aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b] thiophene (12E) also showed quite high antioxidant capacities with TEAC values of 2.5 and 1.1, respectively; which surpassed the antioxidant capacity of an universally accepted reference of trolox. Graphical Abstract: Benzothiophene derivatives were synthesized regioselectively using coupling reactions and electrophilic cyclization reactions. Antimicrobial properties of the compounds were tested against four indicator microorganisms, and a few?displayed high antibacterial activity against S. aureus. 3-(1H-indole-2-yl)-2-(thiophen-2-yl)benzo[b]thiophene (16) and 3-(4-aminobenzoethynyl)-2-(thiophen-2-yl)benzo[b]thiophene (12E) showed high antioxidant capacities which are better than the reference of trolox. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-018-1523-3

J. Chem. Sci. (2018) 130:119
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1523-3
REGULAR ARTICLE
Synthesis and biological evaluation of novel benzothiophene
derivatives
MUHEB A S ALGSOa, ARIF KIVRAKa,∗, METIN KONUSb, CAN YILMAZb and
c
˘
ASLIHAN KURT-KIZILDOGAN
aDepartment of Chemistry, Van Yüzüncü Yil University, 65080 Van, Turkey
bDepartment of Molecular Biology and Genetics, Van Yüzüncü Yil University, 65080 Van, Turkey
cDepartment of Agricultural Biotechnology, Faculty of Agriculture, Ondokuz Mayıs University, Samsun 55139,
Turkey
E-mail: akivrak@yyu.edu.tr
MS received 30 March 2018; revised 23 June 2018; accepted 7 July 2018
Abstract. Benzothiophene derivatives were synthesized regioselectively using coupling reactions and
electrophilic cyclization reactions. Antimicrobial properties of isolated compounds were tested against indicator
microorganisms such as C. albicans ATCC 10231, B. subtilis ATCC 6633, E. coli ATCC 25922 and S. aureus
ATCC 25923. 3-(4-aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b]thiophene (12E), 3-ethynyl-2-(thiophen-
2-yl) benzo[b]thiophene (12L) and 3-(2-aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b]thiophene (12J)
displayed high antibacterial activity against S. aureus. Further, 3-iodo-2-(thiophen-2-yl) benzo[b]thiophene (10)
and 3-(trimethylsilylethynyl)-2-(thiophen-2-yl) benzo[b] thiophene (12K) were found to have potentials to be
used as antifungal agents against current fungal diseases. Novel 3-(1H-indole-2-yl)-2-(thiophen-2-yl) benzo[b]
thiophene (16) and 3-(4-aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b] thiophene (12E) also showed quite
high antioxidant capacities with TEAC values of 2.5 and 1.1, respectively; which surpassed the antioxidant
capacity of an universally accepted reference of trolox.
Keywords. Benzothiophenes; heteroaromatic compounds; biological properties; antioxidant capacity; anti-
microbial agents.
1. Introduction
less side-effects than another popular anti-cancer drug,
Tamoxifen, with similar biological properties.16
Recently, a number of 3-(4-pyridinyl) amino benzoth-
iophenes, which were selective serotonin re-uptake
inhibitors, have been tested for their contribution on the
treatment of central nervous system disorders such as
Alzheimer’s disease.17 Therefore, synthetic and medic-
inalchemistshavetriedtofindnovelorganiccompounds
containing sulfur atoms for decades.
Over the past years, benzothiophenes have been gen-
erally obtained from intramolecular cyclization and
Claisen rearrangement reactions. For example, benzoth-
iophenes were regioselectively synthesized via intramo-
lecular cyclization reaction of o-alkinylthioanisoles.18
Recently, Mohanakrishnan et al., published a new
method for the synthesis of benzothiophene and diben-
zothiophene starting from thiophenes and 2,5-
dimethoxy-THF using Lewis Acid catalyst.19
Heteroaromatic compounds have very important roles
in the discovery and development of new drug can-
didates due to their biological and pharmacological
properties.1,2 They have been used as anti-parasitic,3
anti-bacterial,4 anti-cancer,5 anti-fungal,6 anti-inflam-
matory7 and antioxidant8 drugs for years. In addition,
they are known as strong inhibitors of lipid peroxi-
dation,9 potassium channel openers,10 topoisomerase
inhibitors,11 and L1210 cell selectors.12
Benzothiophenes and thiophenes are well-known
candidates of heteroaromatic compounds and used
as pharmaceuticals like Raloxifene 1,13 Zileuton 2,14
and Sertaconazole 3 (Scheme 1).15 Raloxifene, whose
commercial brand name is Evista, is used for the
treatment of breast cancer. Moreover, Raloxifene has
*
For correspondence
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-018-1523-3) contains
supplementary material, which is available to authorized users.
0123456789().: V,-vol

119 Page 2 of 11
J. Chem. Sci. (2018) 130:119
chromatography (TLC) was performed using commercially
prepared 0.25mm silica gel plates (Silica gel 60, F254) and
visualization was effected with short wavelength UV lamp.
The relative proportions of a mixture of solvents in chro-
matography were indicated by volume to volume ratio. All
commercially available reagents were used directly without
purification unless otherwise stated. All the solvents used in
reaction experiments were distilled for purity. The inert atmo-
sphere was created by slight positive pressure (ca. 0.1 psi) of
argon. All reactions were carried out in flame-dried glassware.
Scheme 1. Structures of Raloxifene 1, Zileton 2 and Serta-
conazole 3.
Antimicrobialresistancetodiscoveredantibioticsand
other drugs used in the treatment of bacterial, fungal
and viral infections is a serious problem threatening all
the world population. Antimicrobial agents with unique
chemical structures and strong antimicrobial potentials
are urgently needed. However, the discovery rate of
biologically active compounds has decreased. In this
respect, chemically designed and synthesized sulfur
containing benzothiophene compounds are among the
promising members for the treatment of infections.20
Further, those benzothiophene derivatives have been
tested and used as antioxidant agents for years. Antioxi-
dants have essential roles in overall metabolism because
of their potential in repairing damages generated by
reactive oxygen species (ROS) and simple deactiva-
tion of those active compounds. Therefore, they are
participants in hindering and reprieving various dis-
eases such as cancer,21 diabetes,22 and cardiovascular
problems.23,24 Besides natural antioxidants, nowadays,
synthetic antioxidants, also, have an important place in
food and pharmaceutical industries.25
2.2 Synthesis of 2-trimethylsilanylethynylthioanisole
(5)
To a stirred mixture of the 2-iodothioanisole (2.5mmol,
620mg), THF (8mL), ethynyltrimethylsilane (3mmol,
303mg), triethylamine (12.4mmol, 1.72mL), PdCl2 (PPh3)2
(0.06mmol, 42.1mg) was added CuI (0.06 mmol, 11.4mg)
under argon atmosphere. The resulting mixture was stirred at
room temperature for 12h. Then, the mixture was quenched
with water (30mL), and extracted with DCM (3×30mL). The
organic phase was dried over anhydrous MgSO4 and filtered.
The solvent was removed under vacuum, and the residue was
purified by column chromatography over silica gel with hex-
ane to afford 2-trimethylsilanylethynylthioanisole (5) as light
1
yellow oil in 96% yield. H NMR (400MHz, CDCl3) 7.43
(dd, J = 7, 7, 1.5Hz; 1H), 7.27 (td, J = 7.5, 1.5Hz; 1H),
7.11 (d, J = 7.4Hz; 1H), 7.05 (td, J = 7.5, 1.2Hz; 1H), 2.46
(s, 3H), 0.32 (s, 9H). 13C NMR (100MHz, CDCl3) δ 142.2,
132.7, 129.1, 124.1, 123.9, 121.1, 102.3, 101.4, 15.0, 0.13; IR
(ATR) vmax (cm−1): 3059.5, 2980.5, 2920.7, 2890.6, 2154.7
(C ≡ C), 1435.5, 1248.3 (Si–CH3), 838.1, 747.6, 685.2 (S-
C). The spectral data were in agreement with those reported
previously for this compound.26
Inthepresentstudy, novelbenzothiophenederivatives
were synthesized using intramolecular electrophilic
cyclization reactions and Palladium catalyzed Sono-
gashira coupling reactions. Additionally, antimicrobial
and antioxidant capacities of new derivatives were also
tested to find their potentials as novel drug candidates.
2.3 Synthesis of 2-ethynyl thioanisole (6)
To a stirred mixture of 5 (500mg, 2.27mmol), methanol
(60mL), and THF (20mL) was added K2CO3 (939mg,
6.81mmol). The mixture was stirred at room temperature
for 60min. The reaction mixture extracted with EtOAc (3 ×
15mL). The organic extracts were dried over anhydrous
2. Experimental
2.1 General information
Solvents, reagents, and chemicals used for reactions were pur- MgSO4 and filtered. The solvent was removed under vacuum,
chased from commercial suppliers. Synthesized molecules and the residue was purified by column chromatography over
were analyzed by 1H and 13C NMR. 1H and 13C NMR silicagelwithhexanetoafford2-ethynylthioanisole(6)asyel-
spectra were recorded on an Agilent NMR (400MHz) spec- low oil in 91% yield: 1H NMR (400MHz, CDCl3) δ 7.46 (dd,
trometer. Chemical shifts were reported in parts per million
(ppm) downfield from an internal TMS (trimethylsilane) ref-
J = 7.6, 1.5Hz; 1H), 7.30 (td, J = 8.2, 1.4Hz; 1H), 7.15 (d,
J = 8.0Hz; 1H), 7.08 (td, J = 8.5, 1.0Hz; 1H), 3.5 (s, 1H,
erence. Couplingconstants(J)werereportedinHertz(Hz). In alkyne), 2.48 (s, 3H); 13C NMR (100MHz, CDCl3) δ 142.0,
addition, spin multiplicities were presented by the following 133.1, 129.3, 124.2, 124.1, 120.1, 83.7, 81.0, 60.3; IR (ATR)
symbols: s (singlet), brs (broad singlet), d (doublet), t (triplet), vmax (cm−1): 3058.32, 2982.06, 3281.39 (≡ C−H), 2920.25,
q (quartet), and m (multiplet). DEPT 13C NMR information 2101.87 (C ≡ C), 1432.71, 747.94, 614.6 (S-C); HRMS calcd
was given in parentheses as C, CH, CH2 and CH3. Flash chro- for C9H9S, 149.0425 [M+H]+ found 149.0248 [M+H]+. The
matography was done using thick-walled glass columns and spectral data were in agreement with those reported previ-
‘flash grade’ silica 60 (Merck 230–400 mesh). Thin layer ously for this compound.26

J. Chem. Sci. (2018) 130:119
Page 3 of 11 119
2.4 Synthesis of 2-[(2-(methylthio) phenyl]ethynyl)
thiophene 9 via Sonogashira palladium-catalyzed
cross-coupling reaction between 2-ethynylthioanisole
(6) and 2-bromothiophene (8)
yellow solid in 99% yield. 1H NMR (400MHz, CDCl3)
7.82 (d, J = 8.1Hz; 1H), 7.75 (d, J = 9.1 Hz; 1H), 7.62
(d.d, J = 4, 0, 1.1Hz; 1H), 7.48–7.44 (m, 2H), 7.39 (td,
J = 8, 0, 1.2Hz; 1H), 7.17 (m, 1H). 13C NMR (100MHz,
CDCl3) δ 142.4, 138.1, 136.0, 135.9, 128.8, 127.5, 127.4,
126.4, 125.9, 125.8, 122.0, 79.5; IR (ATR) vmax (cm−1):
698.75, 815.0, 1419.47, 2912.23, 2980.61, 3085.91; HRMS
calcd for C12H7S2, 341.9034 found; 341.9059.
To a solution of 2-bromothiophene (456.4mg, 2.8mmol) in 1,
4-dioxane (6mL), CuI (32.4mg, 0.17mmol), PdCl2(PhCN)2
(65.2mg, 0.17mmol) were added, followed by 6 (3.0mmol,
444mg), diisopropylamine (1.38g, 13.7mmol), and P(t-
Bu)3 (52.9mg, 0.33mmol) at room temperature under argon.
The mixture was stirred at room temperature for 12h, and
extracted with DCM (3 × 20mL). The organic layer was
dried over anhydrous MgSO4 and filtered. The solvent was
removed under vacuum, and the residue was purified by
column chromatography over silica gel with Hexane/EtOAc
(10/1) to afford 2-[(2-(methylthio) phenyl)ethynyl]thiophene
(9) as an orange oil in 77% yield. 1H NMR (400MHz,
CDCl3) 7.49 (d, J = 7.7Hz; 1H), 7.36–7.30 (m, 3H),
7.19 (d, J= 8,0 Hz; 1H), 7.13 (td, J = 8, 0, 1.1Hz; 1H),
7.04 (m, 1H), 2.53 (s, 3H).13C NMR (100MHz, CDCl3) δ
141.8, 132.3, 132.2, 129.1, 127.8, 127.3, 124.4, 124.3, 123.2,
121.1, 90.7, 89.2, 15.3; IR (ATR) vmax (cm−1): 3086.06,
2911.91, 2980.6, 2199.72(C ≡ C),1431.12, 753.46, 699.33
(S-C); HRMS calcd for C13H11S2, 231.0302 [M+H]+ found
231.0313 [M+H]+. The spectral data were in agreement with
those reported previously for this compound.27
2.7 General procedure of Sonogashira cross-
coupling reaction between 3-iodo-2-(thiophen-2-yl)
benzo[b]thiophene (10) and alkynes
To a stirred mixture of 3-iodo-2-(thiophen-2-yl) benzo[b]
thiophene 10 (0.7mmol, 239.5mg), dimethylformamide
(DMF) (7.5mL), alkyne (0.75mmol), triethylamine (3.0mL),
PdCl2 (PPh3)2 (0.035mmol, 24.5mg) under argon atmo-
sphere was added CuI (0.035mmol, 6.6mg). The resulting
mixture was stirred at room temperature for 12h. It was
quenched with water (30mL) and extracted with DCM (3 ×
30mL). The organic layer was dried over anhydrous MgSO4
and filtered. The solvent was removed under vacuum, and the
residue was purified by column chromatography over silica
gel with Hexane/EtOAc (19/1) to afford compounds (12A–L).
3-(Phenylethynyl)-2-(thiophen-2-yl)benzo[b] thiophene
(12A) was isolated in 94% yield as a green solid. M.p:
85.1–86.7 ◦C; 1H NMR (400MHz, CDCl3) δ 7.99 (d,
J
= 7.4Hz; 1H), 7.77 (d, J = 8.0Hz; 1H), 7.74–
2.5 Synthesis of 2-[(2-(methylthio) phenyl) ethynyl]
thiophene 9 via Sonogashira palladium-catalyzed
cross-coupling reaction between 2-ethynylthioanisole
(6) and 2-iodothiophene (7)
7.70 (m, 2H), 7.66 (d, J = 3.72Hz; 1H), 7.49–7.37 (m,
6H), 7.13–7.15 (m, 1H). 13C NMR (100MHz, CDCl3)
δ 140.8; 140.2, 137.0, 136.5, 131.8, 128.8, 128.7, 127.5,
127.2, 127.16, 125.7, 125.3, 123.5, 123.3, 122.2, 113.0, 97.9,
84.2; IR (ATR) vmax (cm−1): 3062.96, 2980.48, 2922.72,
2199.68, 1438.03, 1237.22, 746.05, 683.58; HRMS: calcd
for C20H13S2, 317.0458 [M+H]+ found, 317.0457 [M+H]+.
To a mixture of 2-iodothiophene (707mg, 3.37mmol), 6
(500mg, 3.37mmol), DMF (6mL), PdCl2 (PPh3)2 (118.3mg,
0.17mmol), and triethylamine (1.9mL, 13.7mmol) at 0 ◦C
under argon gas was added CuI (32.1mg, 0.17mmol). The
mixture was stirred at room temperature for 4h and extracted
with ether (3×20mL). The organic layer was dried over anhy-
drous MgSO4 and filtered. The solvent was removed under
vacuum, and the residue was purified by column chromatog-
raphy over silica gel with Hexane/EtOAc (10/1) to afford
compound 9 as orange oil in 71% yield.
3-(p-Tolylethynyl)-2-(thiophen-2-yl)benzo[b]thiophene
(12B) was isolated in 65% yield as an yellow solid. M.p.:
120.0–121.5 ◦C; 1H NMR (400MHz, CDCl3) δ 7.98 (d, J =
8.0Hz; 1H), 7.76 (d, J = 7.9Hz; 1H), 7.66 (d, J = 3.8Hz;
1H), 7.60 (d, J = 8.0Hz; 2H), 7.48–7.36 (m, 3H), 7.24 (d,
J = 7.9Hz; 2H), 7.15–7.12 (m, 1H). 13C NMR (100MHz,
CDCl3) δ 140.8, 139.8, 139.0, 137.0, 136.6, 131.7, 129.5,
127.4, 127.04, 127.01, 125.6, 125.2, 123.3, 122.1, 120.4,
113.1, 98.2, 83.6, 21.8; IR (ATR) vmax (cm−1): 3068.87,
2980.59, 2918.12, 1437.45, 806.73, 752.44; HRMS:calcd for
C21H15S2, 331.0615 [M+H]+ found 331.0699 [M+H]+.
2.6 Synthesis of 3-iodo-2-(thiophen-2-yl) benzo[b]
thiophene (10) via electrophilic cyclization reaction
To a solution of 2-[(2-(methylthio phenyl) ethynyl] thio- 3-(Hept-1-yn-1-yl)-2-(thiophen-2-yl)benzo[b]thiophene
phene (9) (230mg, 1mmol) in CH2Cl2 (10mL) was added (12C) was isolated in 82% yield as a green solid. 1H NMR
I2 (762mg, 3mmol) at room temperature. After stirring (400MHz, CDCl3) δ 7.90 (d, J = 8.0Hz; 1H), 7.74(d, J =
for 30min, the saturated aqueous solution of Na2S2O3 was 1.08Hz; 1H), 7.63 (d, J = 4.7Hz; 1H), 7.45–7.36 (m,3H),
added into the reaction mixture and extracted with EtOAc 7.14–7.10 (m,1H), 2.65 (t, J = 7.1Hz; 2H), 1.82–1.74
(3 × 20mL). The combined organic phase was dried over (m,2H), 1.61–1.53 (m,2H), 1.48–1.40 (m,2H), 0.98 (t, J =
anhydrous MgSO4 and filtered. The solvent was removed 7.3Hz; 3H). 13C NMR (100MHz, CDCl3) δ 141.3, 138.8,
under vacuum, and the residue was purified by column chro- 137.0, 136.7, 127.3, 126.7, 126.5, 125.5, 125.1, 123.3, 122.1,
matography over silica gel with hexane/EtOac (19/1) to afford 113.8, 99.8, 75.2, 31.5, 30.0, 28.5, 22.5, 20.3, 14.3; IR (KBr,
3-iodo-2-(thiophen-2-yl) benzo[b]thiophene (10) as light thin film) vmax (cm−1): 3067.19, 2950.81, 2929.27, 2855.59,

119 Page 4 of 11
J. Chem. Sci. (2018) 130:119
2215.36 (C ≡ C),1455.44, 1420.67, 836.14, 698.05; HRMS (d, J = 8.5Hz; 1H), 8.1 (d, J= 8.0Hz; 1H), 7.97–7.91(m,
calcd. for C19H19S2, 311.0850 [M+H]+; found 311.0843 3H), 7.8 (d, J = 9.0Hz; 1H), 7.22 (dd, J= 4.0, 1.2Hz;
[M+H]+.
1H), 7.68–7.64 (m, 1H), 7.60–7.48 (m, 3H), 7.44–7.40 (m,
2H), 7.16–7.12 (m, 1H). 13C NMR (100MHz, CDCl3) δ
140.9, 140.2, 137.1, 136.5, 133.5, 133.3, 131.0, 129.3, 128.6,
127.5, 127.3, 127.25, 127.22, 126.8, 126.6, 125.7, 125.6,
125.5, 123.4, 122.2, 121.2, 113.2, 96.1, 88.8; IR (ATR)
vmax (cm−1): 3051.37, 2918.28, 2191.60, 1936.73, 1727.62,
1388.38, 791.93, 768.18, 694.03; HRMS calcd for 367.0615
C24H15S2 [M+H]+ found 367.0602 [M+H]+.
3-[(3-Bromothiophen-2-yl)ethynyl)-2-(thiophen-2-yl]be-
nzo[b]thiophene (12D) was isolated in 71% yield as an yel-
low solid. M.p.: 91.7–62.6 ◦C; 1H NMR (400MHz, CDCl3)
δ 8.03 (d, J = 7.4Hz; 1H), 7.78–7.72 (m, 2H), 7.50–7.34
(m, 3H), 7.31 (d, J = 5.3Hz, 1H), 7.14–7.13 (m, 1H),
7.06(d, J = 5.4, 1H).13C NMR (100MHz, CDCl3) δ 140.8,
140.6, 137.0, 136.3, 130.6, 127.9, 127.7, 127.4, 127.3, 125.8,
125.5, 123.4, 122.2, 121.2, 116.4, 112.3, 91.8, 89.3; IR (ATR)
vmax (cm−1): 3099.53, 3054.27, 2980.48, 2922.74, 2195.37
(C ≡ C),1436.51, 1149.67, 862.56, 688.91; HRMS calcd for
C18H10S3Br, 400.9128 [M+H]+ found 400.9131 [M+H]+.
3-(2-Thioanisolethynyl)-2-(thiophen-2-yl) benzo[b]thio-
phene (12I) was isolated in 81% yield as a yellow solid.
◦
1
M.p.: 165.3–167.2 C; H NMR (400MHz, CDCl3) δ 8.16
(d, J = 8.0Hz; 1H), 7.75 (d, J = 7.96Hz; 1H) 7.72
(dd, J = 3.7Hz, 1.08Hz; 1H), 7.66 (dd, J = 7.7Hz,
1.32Hz;1H), 7.49–7.33 (m, 4H) 7.27–7.24 (m, 1H), 7-22-
711 (m, 2H), 2.56 (s, 3H); 13C NMR (100MHz, CDCl3) δ
141.7, 141.0, 136.9, 136.5, 132.64, 130.0, 129.2, 127.6, 127.3,
127.2, 125.7, 125.5, 124.6, 124.5, 123.8, 122.1, 121.7, 113.0,
95.1, 90.5, 15.52; IR (ATR) vmax (cm−1): 3054.12, 2919.23,
2196.83, 1433.38, 1069.32, 745.44, 691.63; HRMS: calcd for
C21H15S3, 363.0336 [M+H]+ found 363.0335 [M+H]+.
3-(4-Aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b]th-
iophene (12E) was isolated in 92% yield as a green solid.
1H NMR (400MHz, CDCl3) δ 7.98 (d, J = 10.0Hz; 1H),
7.76 (d, J = 9.6Hz; 1H), 7.65 (d.d, J = 3.72Hz, 1.12Hz;
1H), 7.51(d, J = 8.7Hz; 2H), 7.47–7.35 (m, 3H), 7.14–
7.11 (m, 1H), 6.70 (d, J = 8.7Hz; 2H), 3.9 (brs, 2H).
13C NMR (100MHz, CDCl3) δ 147.2, 140.9, 138.8, 136.9,
136.8, 133.2, 127.4, 126.8 (including 2C), 125.6, 125.2,
123.4, 122.1, 115.1, 113.6, 112.8, 98.9, 82.2; IR (ATR)
vmax (cm−1): 3648.08, 3378.68, 2955.73, 2922.29, 2193.60,
1603.81, 1613.73, 1288.05, 1174.35, 906.16, 825.42, 728.67,
696.05; HRMS:calcd for C20H14S2N, 332.0568 [M+H]+
found 332.0559 [M+H]+.
3-(2-Aminobenzoethynyl)-2-(thiophen-2-yl) benzo[b]th-
iophene (12J) was isolated in 91% yield as an yellow-green
solid. M. p.: 89.9–94.5 ◦C; 1H NMR (400MHz, CDCl3)
δ 7.98–7.96 (d, J = 8.0, 1H), 7.78–7.76 (d, J = 8.0,
1H), 7.66–7.64 (m, 1H), 7.56–7.54 (m, 1H), 7.48–7.37 (m,
3H), 7.24–7.20 (m, 1H), 7.13–7.11 (m, 1H), 6.83–6.78 (m,
2H), 4.47 (brs, 2H); 13C NMR (100MHz, CDCl3) δ 148,
140.7, 139.5, 137.0, 136.4, 132.6, 130.4, 127.5, 127.1, 127.0,
125.7, 125.4, 123.2, 122.2, 118.3, 114.7, 113.1, 108.1, 94.68,
89.0; IR (ATR) vmax (cm−1): 3646.46, 3388.01, 3291.45,
2980.39, 2921.93, 2190.03, 1727.63, 1642.99, 1620.79,
1437.80, 1252.95, 1153.55, 753.99, 694.32; HRMS calcd for
C20H14NS2 332.0567 [M+H]+ found 332.0568 [M+H]+.
3-(4-Methoxybenzoethynyl)-2-(thiophen-2-yl) benzo[b]
thiophene (12F) was isolated in 70% yield as a light green
◦
1
solid. M.p.: 99.5–100.8 C; H NMR (400MHz, CDCl3) δ
7.98 (d, J = 10.2Hz; 1H), 7.76(d, J = 7.9Hz, 1H), 7.66–
7.63 (m, 3H), 7.45–7.351(m, 3H), 7.14–7.11 (m,1H), 6.96
(d, J = 14.4Hz, 2H) 3.87 (s, 3H). 13C NMR (100MHz,
CDCl3) δ 160.0, 140.8, 139.4, 136.9, 136.7, 133.3, 127.4,
127.0, 126.9, 125.6, 125.2, 123.4, 122.9, 115.6, 114.4, 113.3,
98.1, 82.9, 55.6; IR (ATR) vmax (cm−1): 3099.03, 3050.45,
2969.85, 2836.00, 2537.06, 2198.92, 1603.21, 1455.42,
1290.88, 1248.09, 1169.13, 1022.60, 834.25, 753.21, 689.80;
HRMS: calcd for C21H14OS2, 346.0486, found 346.0488.
3-(Trimethylsilylethynyl)-2-(thiophen-2-yl) benzo[b]thi-
1
ophene (12K) was isolated in 89% yield as a red oil. H
NMR (400MHz, CDCl3) δ 7.90 (d, J = 10, 0Hz; 1H), 7.74
(d, J = 8.0Hz; 1H), 7.68 (d, J = 4, 0Hz; 1H), 7.47–7.41 (m,
2H), 7.36 (td, J = 8.0, 0.9Hz; 1H), 7.14–7.11 (m, 1H), 0.40
(s, 9H); 13C NMR (100MHz, CDCl3) δ 141.1, 140.9, 136.8,
136.4, 127.4, 127.2, 127.0, 125.6, 125.3, 123.4, 122.0, 112.9,
104.1, 99.2, 0.13; IR (ATR) vmax (cm−1): 2958.21, 2148.01,
1438.15, 1247.46, 908.99, 839.30, 756.33, 696.03; HRMS
cald for C17H17S2Si, 313.0541 [M+H]+ found; 313.0537
[M+H]+.
3-(2, 5-Dimethylbenzoethynyl)-2-(thiophen-2-yl)benzo[b]
thiophene (12G) was isolated in 69% yield as an orange
solid. M.p.: 124.7–126.2 ◦C; 1H NMR (400MHz, CDCl3) δ
8.0 (d, J = 6.0Hz;1H), 7.8 (d, J = 9.6Hz; 1H), 7.69 (dd,
J= 4.0Hz, 1.2Hz;1H), 7.52 (s,1H), 7.50–7.35 (m, 3H), 7.20
(d, J = 7.8Hz; 1H), 7.16–7.12 (m, 2H), 2.65 (s, 3H), 2.40
(s, 3H). 13C NMR (100MHz, CDCl3) δ 140.9, 139.5, 137.2,
137.0, 136.5, 135.4, 132.7, 129.8, 129.7, 127.4, 127.1, 127.0,
125.6, 125.3, 123.3, 123.1, 122.2, 113.4, 97.1, 87.4, 21.1,
20.9; IR (ATR) vmax (cm−1): 3058.44, 2980.45, 2915.37,
2727.39, 2190.46, 1936.28, 1901.14, 1373.30, 1420.57,
1228.57, 813.75, 695.58, 573.38; HRMS calcd for C22H17S2,
345.0772 [M+H]+ found 345.0768 [M+H]+. .
2.8 General procedure of desilylation reaction for the
synthesis of 3-ethynyl-2-(thiophen-2-yl) benzo[b]
thiophene (12L)
To a solution of 3-(trimethylsilylethynyl)-2-(thiophen-2-yl)
benzo [b] thiophene (12l) (56mg, 0.17mmol) in methanol
(15mL) and THF (5mL) was added K2CO3 (74.3mg, 0.53
3-(2-Naphthylethynyl)-2-(thiophen-2-yl) benzo[b]thiop-
hene (12H) was isolated in 93% yield as an yellow solid. mmol) at room temperature for 1h. Then, organic solvents
◦
1
M.p.: 140.3–143.3 C; H NMR (400MHz, CDCl3) δ 8.6 were removed under reduced pressure and the residue was

J. Chem. Sci. (2018) 130:119
Page 5 of 11 119
extracted with DCM (10mL×3). The solvent was removed 8.0, 1H), 7.84–7.86 (m, 1H), 7.66–7.69 (m, 1H), 7.45–7.55
under vacuum, and the residue was purified by column chro- (m, 2H), 7.34–7.40 (m, 2H), 7.23–7.26 (m, 2H), 7.11–7.13
matography over silica gel with Hexane/EtOAc (19/1) to (d, J = 8.0, 2H), 7.03–7.05 (d, J = 8.0, 2H), 6.94–6.97
afford 3-ethynyl-2-(thiophen-2-yl) benzo [b] thiophene (12L) (m, 1H), 2.31 (s, 3H); 13C NMR (100MHz, CDCl3) δ
as a red oil in 83% yield. 1H NMR (400MHz, CDCl3) 140.9, 139.9, 139.8, 138.9, 138.6, 138.0, 137.2, 135.8, 131.7,
δ 7.91 (d, J = 8, 0Hz; 1H), 7.77–7.70 (m, 2H), 7.48– 129.1, 127.68, 127.66, 127.4, 125.6, 125.2, 125.1, 125.0,
7.34 (m, 3H), 7.16–7.10 (m, 1H), 3.70 (s, 1H); 13C NMR 124.1, 123.8 (include 2C), 122.7, 122.1, 120.2, 120.1, 95.4,
(100MHz, CDCl3) δ 141.4, 140.1, 136.9, 136.0, 127.7, 127.4, 82.2, 21.7; IR (ATR) vmax (cm−1): 698.50, 728.72, 755.38,
127.1, 125.7, 125.4, 123.2, 122.1, 111.8, 85.8, 78.3; IR (ATR) 814.32, 1435.36, 2205.17, 2853.61, 2920.76; HRMS calcd
vmax (cm−1): 3286.03, 3101.49, 2922.12, 2851.51, 2095.61, for C29H19S3, 463.0649 [M+H]+; found 463.0636 [M+H]+.
1940.45, 1791.21, 1437.68, 1188.59, 752.07, 690.36, 647.28,
584.34; HRMS cald for C14H9S2, 241.0146 [M+H]+ found;
3-(3-(2,5-Dimethylbenzoethynyl)benzo[b]thiophen-2-yl)-
241.0139 [M+H]+.
2-(thiophen-2-yl)benzo[b]thiophene 15B was isolated in
1
90% yield as a yellow solid: H NMR (400MHz, CDCl3)
2.9 Synthesis of 3-(3-iodobenzo[b]thiophen-2-yl)-2-
δ 8.12–8.14 (d, J = 8.0, 1H), 7.90–7.92 (d, J = 8.0, 1H),
(thiophen-2-yl) benzo [b] thiophene (14)
7.83–7.85 (m, 1H), 7.54–7.59 (m, 2H), 7.47–7.51 (m, 1H),
7.31–7.39 (m, 2H), 7.26–7.28 (m, 1H), 7.21–7.22 (m, 1H),
7.10(s, 1H), 6.94–6.96(m, 3H), 2.24(s, 3H), 1.90(s, 3H);13C
NMR (100MHz, CDCl3) δ 141.0, 140.0, 139.8, 138.9, 137.8,
137.4, 137.3, 135.7, 135.0, 132.4, 129.4, 129.38, 127.7, 127.5,
127.3, 125.7, 125.24, 125.16, 125.1, 124.0, 123.8, 123.7,
122.8, 122.7, 122.0, 120.7, 94.3, 86.3, 20.9, 19.8; IR (ATR)
vmax (cm−1): 661.07, 729.36, 756.18, 1030.58, 1232.42,
1435.79, 1456.13, 1733.94, 2202.29, 2922.48; HRMS calcd
for C30H21S3, 477.0805 [M+H]+; found 477.0770 [M+H]+.
To a solution of the 3-(2-thioanisolethynyl)-2-(thiophen-2-
yl) benzo [b] thiophene12I (85mg, 0.23mmol) in dichloro-
methane (5mL) was added I2 (173.8mg, 0.69mmol) under
argon atmosphere. The mixture was stirred at room temper-
ature for 1h. It was quenched with sat. sodium thiosulfate
(30mL), and extracted with DCM (3 × 20mL). The organic
layer was dried over anhydrous MgSO4 and filtered. The
solvent was removed under vacuum, and the residue was puri-
fied by column chromatography over silica gel with Hexane
to afforded 3-(3-iodobenzo[b]thiophen-2-yl)-2-(thiophen-2-
yl) benzo[b]thiophene (14) as a light yellow solid in 81%
3-(3-(2-Naphthylethynyl)benzo[b]thiophen-2-yl)-2-(thio-
phen-2-yl)benzo[b]thiophene 15C was isol◦ated in 76%
1
yield. H NMR (400MHz, CDCl3) δ 7.90–7.85 (m, 3H),
1
yield as an yellow solid: M.p.: 153.2–154.7 C; H NMR
7.57–7.47 (m, 2H), 7.42–7.33 (m, 3H), 7.28–7.27 (m, 1H),
7.24–7.22 (m, 1H), 6.99–6.97 (m, 1H); 13C NMR (100MHz,
CDCl3) δ 141.5, 140.8, 140.5, 137.8, 137.7, 136.3, 135.5,
128.0, 127.5, 127.4, 126.4, 126.1, 125.6, 125.4, 125.3, 124.8,
123.4, 122.8, 122.2, 86.48; IR (ATR) vmax (cm−1): 3104.56,
3057.09, 2930.00, 2851.61, 1728.33, 1430.00, 1244.14,
753.26, 703.55; HRMS calcd for C20H11IS3, 473.9067; found
473.9072.
(400MHz, CDCl3) δ 8.21–8.23 (d, J = 8.0, 1H), 7.90–
7.95 (m, 2H), 7.73–7.76 (m, 2H), 7.66–7.68 (d, J = 8.0,
1H), 7.50–7.61 (m, 4H), 7.34–7.44 (m, 4H), 7.30–7.31 (m,
1H), 7.24–7.28 (m, 1H), 7.20–7.22 (d, J = 8.0, 1H), 6.92–
6.94 (m, 1H); 13C NMR (100MHz, CDCl3) δ 141.1, 140.0,
139.7, 139.5, 137.9, 137.6, 135.6, 133.21, 133.17, 130.3,
128.9, 128.2, 127.8, 127.6, 127.4, 126.9, 126.5, 126.3, 125.8,
125.4, 125.34, 125.28, 125.2, 124.0, 123.8, 123.7, 122.8,
122.1, 120.8, 120.5, 93.4, 87.6; IR (ATR) vmax (cm−1):
636.34, 732.63, 759.06, 1435.42, 2199.58, 2923.58, 2980.52,
3055.86; HRMS calcd for C32H19S3, 499.0649 [M+H]+;
found 499.0575 [M+H]+.
2.10 General procedure for the synthesis of 3-
(arylethynyl)-2ꢀ-(thiophen-2-yl)-2,3ꢀ-bibenzo[b]
thiophene (15)
To a stirred mixture of 14 (0.7mmol), DMF (7.5mL),
alkyne (0.75mmol), triethylamine (3.0mL), PdCl2 (PPh3)2
(0.035mmol) under argon gas was added CuI (0.035mmol,
6.7mg). The resulting mixture was stirred at room tem-
perature for 12h Water (30mL) was added to the reaction
mixture, and the resulting solution was extracted with DCM
(3 × 30mL). The organic layer was dried over anhydrous
MgSO4 and filtered. The solvent was removed under vacuum,
and the residue was purified by column chromatography over
silica gel with Hexane/EtOAc (19/1) to afford compounds
(15A–D).
3-(3-(6-Methoxynaphthalen-2-yl)benzo[b]thiophen-2-yl)-
2-(thiophen-2-yl)benzo[b]thiophene 15D was isolated in
1
58% yield as a yellow solid: H NMR (400MHz, CDCl3)
δ 8.12–8.14 (d, J = 8.0, 1H), 7.85–7.91 (m, 2H), 7.69–7.71
(m, 1H), 7.52–7.64 (m, 4H), 7.46–7.49 (m, 1H), 7.35–7.41
(m, 2H), 7.20–7.27 (m, 3H), 7.10–7.13 (m, 1H), 7.04–
7.05 (d, J = 4.0, 1H), 6.94–6.97 (m, 1H), 3.90 (s, 3H);
13C NMR (100MHz, CDCl3) δ 158.5, 140.9, 140.0, 139.9,
139.0, 138.1, 137.3, 135.8, 134.3, 131.5, 129.5, 129.2, 128.6,
127.7 (include 2C), 127.4, 126.8, 125.7, 125.3, 125.14,
125.10, 124.2, 123.89, 123.86, 122.7, 122.1, 120.2, 119.5,
118.2, 106.0, 96.0, 82.7, 55.6; IR (ATR) vmax (cm−1):
3-(3-(p-Tolylethynyl)benzo[b]thiophen-2-yl)-2-(thioph-
en-2-yl)benzo[b]thiophene 15A was isolated in 89% yield 699.57, 729.04, 766.36, 1029.85, 1196.55, 1391.35, 1600.36,
as a yellow solid : M.p.: 139.7–141.2 ◦C; 1H NMR (400MHz, 1627.59, 1732.15, 2202.73, 2926.61, 2956.69; HRMS calcd
CDCl3) δ 8.08–8.10 (d, J = 8.0, 1H), 7.88–7.90 (d, J = for C33H21OS3, 529.0755 [M+H]+; 529.0755 [M+H]+.

119 Page 6 of 11
J. Chem. Sci. (2018) 130:119
2.11 Synthesis of 3-(1H-indole-2-yl)-2-
(thiophen-2-yl)benzo[b]thiophene (16)
and dimethylsulfoxide (DMSO) diluted in the medium,
respectively) were used, as well. Freshly prepared streak
plated microorganisms were resuspended in 0.85% NaCl to
To a solution of the 2-(2-aminobenzoethynyl)-2-(thiophen-2- 0.5 McFarland ( 1−4 × 108 CFU/mL). 100 µL of this
∼
=
yl) benzo[b]thiophene (12J) (99.3mg, 0.3mmol) in dichloro- solution was tenfold diluted in MHB and next microbial
methane (10mL) was added I2 (226.8mg, 0.9 mmol) under inoculum was added to each well (as final concentration of
argon atmosphere. The mixture was stirred at room temper- 1−5 × 105 CFU/mL). Incubation was done at 37 ◦C for 16–
ature for 1h, followed by quenching with sat. sodiumthio- 20h for bacteria and 26 ◦C for 24–48h for fungi. All MIC
sulfate (30mL) and extracted with DCM (20mL × 3). The determinations were carried out in triplicates. The MIC values
organic layer was dried over anhydrous MgSO4 and fil- of the tested compounds were detected visually by controlling
tered. Solvent was removed under vacuum, and the residue the turbidity with respect to the controls.
was purified by column chromatography over silica gel
with Hexane/EtOAc (10/1) to afford 3-(1H-indole-2-yl)-2-
(thiophen-2-yl) benzo[b]thiophene16 as a white solid in 67%
◦
1
yield. M.p.: 159.8–161.4 C; H NMR (400MHz, CDCl3)
δ 8.02 (b, 1H), 7.84–7.82 (m, 1H), 7.75–7.70 (m, 1H),
7.40–7.33 (m, 3H), 7.27–7.15 (m, 4H), 6.97–6.94 (m, 1H),
6.78–6.77 (m, 1H); 13C NMR (100MHz, CDCl3) δ 140.9,
138.2, 136.5, 135.8, 135.4, 130.4, 128.9, 127.6, 127.5, 127.4,
125.4, 125.2, 124.5, 123.6, 122.5, 122.1, 121.0, 120.3, 111.3,
104.8; IR (ATR) vmax (cm−1): 3444.54, 2917.97, 2850.71,
1729.02, 1419.21, 1231.16, 732.22, 699.57; HRMS calcd for
2.13 Total antioxidant capacity test by ABTS assay
2.13a ABTSassay: ABTS, 2, 2ꢀ-azinobis(3-ethylbenzo-
thiazoline-6-sulfonic acid) diammonium salt, potassium per-
sulfate and ethanol were purchased from Sigma-Aldrich. All
chemicals and solvents were analytical grade and were used
as received. Antioxidant capacities of the synthesized chem-
icals were determined according to the modified method of
Rea et al.,30 Trolox was used as the antioxidant standard.
ABTS stock solution, including ABTS (7mM) and potassium
persulphate (2, 45mM), was prepared in distilled H2O and
incubatedatroomtemperaturefor12–16h. Then, ABTSstock
solution was diluted with ethanol to achieve an absorbance of
0.700 0.02 at 734nm to be used as working solution. The
synthesized dibenzothiophenes and trolox were dissolved and
diluted with pure ethanol. After that, trolox standard or our
compounds were mixed with ABTS working solution (1:1)
and incubated in the dark at 25 ◦C for 30min with continu-
ous moderate shaking. The reaction steps were also repeated
for controls containing ethanol and ABTS. Absorbances were
measured at 734nm. All measurements were done triplicated
under dim light. This procedure was repeated three times at
different dates.
C20H14NS2, 332.0565 [M+H]+; found 332.0555 [M+H]+
.
2.12 Antimicrobial activity test
Antimicrobial acitivities of the newly synthesized compounds
were evaluated against reference strains kindly provided from
Refik Saydam National Type Culture Collection (Turkey):
three gram positive bacteria (Bacillus subtilis ATCC 6633,
Enterococcus faecalis ATCC 29212, Staphylococcus aureus
ATCC 25923), three gram negative bacteria (Escherichia
coli ATCC 25922, Klebsiella pneumoniae ATCC 700603,
Pseudomonas aeruginosa ATCC 27853), an yeast (Candida
albicans ATCC 10231) and a fungus (Aspergillus niger ATCC
16404). Initially, agar disk diffusion method was used to
screen in vitro antimicrobial activities of the synthesized
compounds28 on the basis of Clinical and Laboratory Stan-
dards Institute (CLSI) recommendation. The results were
recorded for each tested compound as the average diam-
eter (in mm) of inhibition zones around the discs where
no microbial growth occurred. The compounds that lead to
significantzonediameters(>10mm)againstthetestedorgan-
isms were further analysed quantitatively by determining
Minimal Inhibitory Concentration (MIC) values. MIC corre-
sponds to the lowest concentration required to inhibit micro-
bial growth. Broth microdilution method in cation-adjusted
The percentage of Radical Scavenging Activity (%RSA)
was calculated using the following equation:
Radical Scavenging Activity (%RSA)
(Control Absorbance – Sample Absorbance)
=
× 100
(Control Absorbance)
Mueller-Hinton Broth (MHB) (Oxoid) was performed in 96- The IC50 value is the concentration of compound that is able
well round-bottom microtiter plates according to the CLSI to reduce the absorbance value of the ABTS+ radical cation
guidelines.29 100 µl of MHB was dispensed to each well. solution to half of its original value. This value obtained from
Then, the compounds dissolved in DMSO in a final concen- linearcurveofRSA%versusdifferentconcentrationsoftested
tration of 1024 µg/mL were added to first wells, and doubling compound. If the % RSA value could not exceed 50% to be
dilution series were performed to get a concentration scale used in the calculation of IC50 value, then % RSA value itself
from 512 µg/mL to 0.125 µg/mL. The standards (amikacin was used as a unit in the evaluation of the total antioxidant
for bacteria and flucanozole for fungi) were diluted in the capacity after calculation of the ratio with the applied con-
same way. The sterility, growth and solvent controls (MHB centration of the molecules (% RSA/applied concentration,
without inoculum, bacteria in the absence of the compounds mL/mg).

J. Chem. Sci. (2018) 130:119
Page 7 of 11 119
Scheme 2. Synthesis of 3-iodo-2-(thiophen-2-yl) benzo[b] thiophene (10).
3. Results and Discussion
(ICl), PhSeCl, etc. were used as electrophiles for
electrophiliccyclizationreactions.34 Moleculariodineis
chosen being as a mild and nontoxic electrophile which
catalyzed various organic reactions with high efficiency
and selectivity. When 9 was reacted with molecular
iodine in DCM for 2 h at room temperature, our expected
3.1 Synthesis
Initially, palladium catalyzed Sonogashira Coupling
reaction between 2-iodothioanisole 4 and trimethylsi-
lylacetylene was performed for the preparation of
2-trimethylsilanylethynylthioanisole 5 under mild reac-
tion conditions. After the isolation of compound 4,
the trimethylsilyl group was removed by desilylation
with potassium carbonate in methanol for the formation
of necessary terminal alkyne as a 2-ethynylthioanisole
5. When compound 5 was allowed to react with 2-
bromothiophene in the presence of PdCl2(PhCN)2, CuI,
(t-Bu)3P in Dioxane at room temperature for 12h,
desired alkyne 9 was obtained in 77% yield. Inter-
estingly, when 2-iodothiophene was applied for the
synthesis of 9 in the presence of Pd-catalyst at room tem-
perature, only self-coupling product of terminal alkyne
was obtained instead of 9. The same reaction condition
was reapplied with 2-iodothiophenes at 0 ◦C, so that the
desired compound 9 was isolated in 72% yield.
Iodine-mediated electrophilic cyclization reactions
have been used for the regioselectively synthesis of
five or six-membered heterocyclic compounds.31,32
Recently, Zora et al., have found a novel method-
ology for the synthesis of iodo-substituted-pyrazoles
from corresponding acetylenic hydrazone derivatives
via electrophilic cyclization under mild reaction con-
ditions.33 Previous studies showed that CH2Cl2 (DCM)
and chloroform were among the most employed sol-
vents for those kinds of cyclization, and different iodine
reagents such as molecular iodine, monoiodochloride
product
3-iodo-2-(thiophen-2-yl)benzo[b]thiophene
(10) was obtained in good yield (99%) (Scheme 2).
After isolation of structure 10, a variety of 3-alkynylic
benzothiophene derivatives were synthesized by using
Pd-catalyzed Sonogashira Cross-Coupling reactions.35
As seen in Table 1, when 10 was allowed to react with
phenyl acetylene in the presence of Pd(PPh2)2Cl2 and
CuI in DMF/Et3N at room temperature for overnight,
12A was obtained in 94% yield (Table 1). When the
same reaction condition was applied for the synthe-
sis of 12B, the isolated yield was found as 66%.
When the effect of aliphatic compound was tested by
using heptanyl, the 82% yield of 12C was reached.
Notably, 12D was obtained in moderate yield (71%).
Moreover, amin-substituted 12E and 12J were syn-
thesized in high yields 92% and 91%, respectively,
and polyaromatic substituted-12H was prepared in 93%
yield. When the same reaction was performed with
ethynyltrimethylsilane, 12K was formed with 89%
yield. Then, 12K underwent desilylation reaction with
potassium carbonate in methanol to give the new ben-
zothiophene substituted terminal alkyne 12L which
might be used as a novel precursor for the formation
of biologically active compounds. As a result of the
first part of study, Sonogashira cross coupling reac-
tions were found to be general for a wide range of
terminal alkynes and tolerated the presence of aliphatic,

119 Page 8 of 11
J. Chem. Sci. (2018) 130:119
Table 1. Synthesis of 3-(substituted-ethynyl)-2-(thiophen-2-yl) benzo[b]thiophene (12) derivatives.
aromatic, polyaromatic and heteroaromatic moieties
with electron-withdrawing and electron-donating sub-
stituents (Table 1).
After preparation of 3-(substituted-ethynyl)-2-
(thiophen-2-yl) benzo[b]thiophenes (12A–L), the syn-
thesis of corresponding iodo substituted-thieno-
dibenzothiophene (13) was examined by using iodine-
catalyzed electrophilic cyclization reaction (S. I.). Ini-
tially, 12A was allowed to react with 1 equiv. of
molecular iodide in DCM at room temperature for 24h,
all starting compound was recovered. When excess
amount of iodide was used in the same reaction con-
ditions, there was no formation of products.
Scheme 3. Synthesis of 3-(2-thioanisolethynyl)-2-(thio-
phen-2-yl)benzo[b]thiophene (12I) and 3-(arylethynyl)-2ꢀ-
(thiophen-2-yl)-2,3ꢀ-bibenzo[b]thiophene (15 A–D).
When 12I and 12J were allowed to cyclization
reaction in the presence of molecular iodine, 14 and
16 were obtained in 81% and 67% yields, respec-
tively (Schemes 3 and 4). Although, Larock et al.,
reported the synthesis of 3-benzofuran-substituted-2-
phenyl-benzothiophene via electrophilic cyclization
reactions, there is not any information on indoles or
benzothiophene-susbtituted benzothiophene structures
in literature.36 The methodology proposed in current
study gave the opportunity to the synthesis of novel
heteroaromatic compounds including two benzothio-
phenes and benzothiophenes-indoles. Interestingly, the
cyclization reaction of 12J produced the only indole
(16) instead of iodine-substituted corresponding prod-
uct (Scheme 4). Moreover, 15A–D were synthesized

J. Chem. Sci. (2018) 130:119
Page 9 of 11 119
respectively. The highest antifungal activity against A.
niger ATCC 16404 (MIC: 64 µg/ml) was observed
for compound 12K. As a summary, our novel ben-
zothiophenes seem to be significantly effective on
gram positive bacteria, S. aureus ATCC 25923 and
B. subtilis ATCC 6633; and fungi, C. albicans ATCC
10231 and A. niger ATCC 16404. The compounds
12E, 12L and 12J with potent antibacterial activities
against S. aureus might be new candidates for the
development of a new class of antimicrobial agents
in treatment of multidrug resistant strains. Similarly,
compound 10 and 12K might be further modified to
design potent antifungal agents against current fungal
diseases.
Scheme 4. Synthesis of 2-(2-(thiophen-2-yl) benzo[b]
thiophen-3-yl)-1H-indole.
from 14 by using palladium catalyzed Sonogashira cross
coupling reactions (Scheme 4).
3.3 Assessment of antioxidant capacities of the newly
3.2 Evaluation of antimicrobial activities of the
synthesized compounds
newly synthesized compounds
Trolox is a water soluble vitamin E analogue37 and
In the present study, antimicrobial activities of new ben- those analogues are used in food industry and medicine
zothiophene derivatives were tested against indicator because of being good chain-breaking antioxidants
microorganisms by using agar disc diffusion method which prevent peroxidation of lipids and also being
(Table S2, SI). When the zone inhibition values were adventageous stabilizers of biological membranes via
compared to interpretive standards (CLSI), the com- the restriction of components’ mobilities in membranes.
pounds (9) (againstC. albicans ATCC 10231), (10) In this manner, a new compound with higher antioxi-
(against B. subtilis ATCC 6633, E. coli ATCC 25922, K. dant capacity than that of trolox is a good candidate for
pneumoniae ATCC 700603, C. albicans ATCC 10231 the development of better ingredients in those industrial
and A. niger ATCC 16404), (6), (12E), (12J) and (12L) areas.
(against S. aureus ATCC 25923), and (12K) (against
Antioxidant capacities of newly synthesized diben-
A. niger ATCC 16404) were found to have consider- zothiophenes were tested by a universal consent method
able antimicrobial activities and their MIC values were of Trolox Equivalent Antioxidant Capacity Assay
determined by microdilution method (Table S3, Supple- (TEAC) as defined before and the results indicated
mentary Information). According to the inhibition zone that among all derivatives, amine-substituted derivative
and MIC data, 2-trimethylsilanylethynylthioanisole (5) of 3-(substituted-ethynyl)-2-(thiophen-2-yl) benzo[b]
was not found to be effective against tested microor- thiophene (12E) and the product of the cyclization of
ganisms. On the other hand, structure 6 gave slightly a homologues of this analog in the presence of iodine
higher inhibition zone value corresponding to a weak (16) had the highest antioxidant capacities as compared
antibacterial activity (MIC of 256 µg/mL) against S. to trolox (Table S4, Supplementary Information).
aureus ATCC 25923, a gram positive bacterium. Com-
Almost one of third of the newly synthesized diben-
pound 9 displayed a weak antifungal activity only for zothiophene derivatives exerted strong radical scaveng-
C. albicans ATCC 10231. Compound 10, obtained from ing activities in vitro (TEAC assay) and IC50 values
electrophilic cyclization, showed good antibacterial and could be calculated. Compound 16 was determined to
antifungal activities against B. subtilis ATCC 6633 be 2.5 times more potent than trolox (Table S5, Sup-
and A. niger ATCC 16404 with MIC values of 42,7 plementary Information) and it made this derivative
and 128µg/ml, respectively; and, expanded its activity more powerful not only against vitamin E deriva-
spectrum mildly against E. coli ATCC 25922, K. pneu- tives like trolox but also against many other phenolic
moniae ATCC 700603 and C. albicans ATCC 10231 compounds such as ascorbic acid, chlorogenic acid,
(MIC values of 250 µg/mL). The isolated molecules phloridzin,38 and caffeic acid39 found in food supplies
(12A–L) exhibited the highest antimicrobial activity and medicines. Additionaly, the derivative 12E, also,
against S. aureus ATCC 25923 and A. niger ATCC exhibited a slightly higher TEAC value than trolox
16404. 12E, 12J and 12L were found to be the most which made it a significant antioxidant, too.
potent antibacterial compound against S. aureus ATCC
In summary, except the highly outstanding deriva-
25923 with MIC values of 4–5, 3, 16 and 4µg/mL, tives 16 and 12E, the others that could be used in the

119 Page 10 of 11
J. Chem. Sci. (2018) 130:119
development of better antioxidant compounds, but still
having lower TEAC values than trolox standard (Table
S5, Supplementary Information), showed a sorting as:
12J > 12D > 9 > 6.
2. Kivrak A and Larock R C 2010 Synthesis of
dihydrobenzisoxazoles by the 3+2 cycloaddition of
arynes and oxaziridines J. Org. Chem. 75 7381
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4. Conclusions
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the development of potent iron chelators as anti-tumour
agents Biochim. Biophys. Acta 1790 702
In this study, novel benzothiophene derivatives were
designed, synthesized and investigated for some of
their biological properties. Our compounds have spe-
cial structures of molecules that possessed interesting
biological properties and pharmaceutical potentials. It
was found that 2-(thiophen-2-yl) benzo[b]thiophene
(12E), 3-ethynyl-2-(thiophen-2-yl) benzo[b]thiophene
(12L) and 3-(2-aminobenzoethynyl)-2-(thiophen-2-yl)
benzo[b]thiophene (12J) have high antibacterial activi-
ties against S. aureus ATCC 25923 which is a very dan-
gerous temporizer pathogenic bacterium colonized on
one of every five human living on the world. Moreover,
3-iodo-2-(thiophen-2-yl) benzo[b]thiophene (10) and 3-
(trimethylsilylethynyl)-2-(thiophen-2-yl)
benzo[b]
thiophene (12K) could be used for the treatment of
fungal diseases caused by A. niger ATCC 16404. The
derivatives 16 and 12E displayed quite high antioxidant
capacitieswithTEACvaluesof2.5and1.1, respectively.
Finally, the synthesized novel compounds possessed
interesting positions which could work as keys for fur-
ther verifying reactions to increase the number of new
derivatives in future studies.
9. Williams R J, Spencer J P E and Rice-Evans C 2004
Flavonoids: Antioxidants or signalling molecules? Free
Rad. Biol. Med. 36 838
10. Edwards G and Weston A H 1993 The pharmacology of
ATP-sensitive potassium channels Annu. Rev. Pharma-
col. Toxicol. 33 597
11. Pommier Y 2016 Topoisomerase I inhibitors: Camp-
tothecins and beyond Nat. Rev. Cancer 6 789
Supplementary Information (SI)
12. Grynyuk, II, Prylutska S V, Franskevych D V, Trush
V A, Sliva T Y, Slobodyanik M S, Hurmach V
V, Prylutskyy Y I, Matyshevska O P and Rit-
ter U 2016 Combined action of C60 fullerene with
dimethyl-N-(benzoyl)amidophosphate or dimethyl-N-
(phenylsulfonyl) amidophosphate on leukemia L1210
cells in silico and in vitro Materialwissenschaft und
Werkstofftechnik 47 98
13. Meixner C N, Aref M W, Gupta A, McNerny E M B,
Brown D, Wallace J M and Allen M R 2017 Raloxifene
Improves Bone Mechanical Properties in Mice Previ-
ously Treated with Zoledronate Calcif. Tissue Int. 101
75
14. Sarret C, Pichard S, Afenjar A and Boespflug-Tanguy O
2017 Lack of long-term neurologic efficacy of zileuton
in Sjogren-Larsson’s syndrome Neuropediatrics 48 205
15. Croxtall J D and Plosker G L 2009 Sertaconazole:
A review of its use in the management of superficial
mycoses in dermatology and gynaecology Drugs 69 339
16. Vogel V G, Costantino J P, Wickerham D L, Cronin W M,
Cecchini R S, Atkins J N, Bevers T B, Fehrenbacher L,
Pajon E R, Wade J L, Robidoux A, Margolese R G, James
J, Lippman S M, Runowicz C D, Ganz P A, Reis S E,
McCaskill-Stevens W, Ford L G, Jordan V C, Wolmark
N and NSABP 2006 Effects of tamoxifen vs raloxifene
Characterization of the new benzo[b]thiophene products
including Scheme 2, Table S2, S3, S4 and S5, 1H NMR, 13
C
NMR, and FTIR spectra, as well as mass characterization
data. Supplementary Information is available on www.ias.ac.
in/chemsci.
Acknowledgements
The authors thank to The Scientific and Technological
Research Council of Turkey (Project No: 115Z020) for
financial supporting of silica gels, column chromatographic
solvents, all other reactants and reagents. Authors, also, thank
VanYüzüncüYilUniversity(ProjectNo:FBA-2017-6007)for
financial supporting of glassware and salts and University of
Duhok for a scholarship to Muheb A. S. Algso.
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