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Naturally occurring thiophenes: isolation, purification,structural elucidation, and evaluation of bioactivities
Sabrin R. M. Ibrahim • Hossam M. Abdallah •
Ali M. El-Halawany • Gamal A. Mohamed
Received: 26 December 2014 / Accepted: 17 March 2015 / Published online: 22 March 2015
� Springer Science+Business Media Dordrecht 2015
Abstract Thiophenes are a class of heterocyclic
aromatic compounds based on a five-membered ring
made up of one sulfur and four carbon atoms. The
thiophene nucleus is well established as an interesting
moiety, with numerous applications in a variety of
different research areas. Naturally occurring thio-
phenes are characteristic secondary metabolites
derived from plants belonging to the family Aster-
aceae, such as Tagetes, Echinops, Artemisia, Bal-
samorhiza, Blumea, Pluchea, Porophyllum and
Eclipta. Furthermore, naturally occurring thiophenes
are generally composed of one to five thiophene rings
that are coupled together through their a-carbons, andcarry alkyl chains on their free ortho-positions.
Thiophene-containing compounds possess a wide
range of biological properties, such as antimicrobial,
antiviral, HIV-1 protease inhibitor, antileishmanial,
nematicidal, insecticidal, phototoxic and anticancer
activities. This review focuses on naturally occurring
thiophene derivatives; their sources, physical and
spectral data, and biological activities.
Keywords Thiophenes � Biosynthesis � NMR data �Anti microbial � Cytotoxic
Introduction
Thiophenes are a class of heterocyclic aromatic
compounds based on a five membered ring containing
one sulfur and four carbon atoms with a molecular
formula of C4H4S. The word ‘thiophene’ is derived
from the Greek words ‘theion’ and ‘phaino’, which
mean sulfur and shining, respectively. Thiophene
derivatives make up a significant proportion of the
organosulfur-containing compounds found in petro-
leum, as well as several other products derived from
fossil fuels, and are formed as the by-products of
petroleum distillation (Chaudhary et al. 2012; Mishra
et al. 2011). Natural thiophenes are characteristic
secondary metabolites of plants belonging to the
S. R. M. Ibrahim
Department of Pharmacognosy and Pharmaceutical
Chemistry, Faculty of Pharmacy, Taibah University,
Al Madinah Al Munawwarah 30078, Kingdom of Saudi
Arabia
S. R. M. Ibrahim
Department of Pharmacognosy, Faculty of Pharmacy,
Assiut University, Assiut 71526, Egypt
H. M. Abdallah � A. M. El-Halawany � G. A. Mohamed
Department of Natural Products and Alternative
Medicine, Faculty of Pharmacy, King Abdulaziz
University, Jeddah 21589, Kingdom of Saudi Arabia
H. M. Abdallah � A. M. El-Halawany (&)
Department of Pharmacognosy, Faculty of Pharmacy,
Cairo University, Cairo 11562, Egypt
e-mail: [email protected]
G. A. Mohamed
Department of Pharmacognosy, Faculty of Pharmacy,
Al-Azhar University, Assiut Branch, Assiut 71524, Egypt
123
Phytochem Rev (2016) 15:197–220
DOI 10.1007/s11101-015-9403-7
family Asteraceae, including the following genera:
Tagetes, Echinops, Artemisia, Balsamorhiza, Blumea,
Pluchea, Porophyllum, and Eclipta. Thiophene
derivatives isolated from natural sources can be
classified according to the number of thiophene rings
in their structure, including thiophenes (one ring),
bithiophenes (two rings), terthiophenes (three rings)
and quinquethiophenes (five rings) (Fig. 1). Thio-
phene and its derivatives are produced as part of the
chemical defense mechanism in numerous plant
species, which involve the manufacture and storage
of organic substances in different parts of the plants.
These compounds can behave as repellents, act as
toxic substances or have anti-nutritional effects on
herbivores (Gil et al. 2002). Natural thiophenes are
derived from polyacetylenes, which can be stored in
plant tissues or released into the soil (Tang et al. 1987).
These compounds can also act as toxins that are
activated by sunlight or UV irradiation (300–400 nm).
These compounds are toxic towards numerous patho-
gens, including nematodes, insects, fungi, and bacteria
(Champagne et al. 1984; Gil et al. 2002).
A recent review of the available literature revealed
that there are currently no reviews pertaining to the
biosynthesis, isolation and biological activity of
naturally occurring thiophenes. Herein, we have listed
the thiophenes that have been reported in the literature
over the past few decades and provided a summary of
their biological activities, physical constants, spectral
data, plant sources, and associated references. These
data have been listed in the following order for each
compound: name, structure, melting point (�C), opti-cal rotation (concentration, solvent), UV (solvent,
kmax nm, log e), IR (medium, absorption band in
cm-1), 1H NMR (spectrometer frequency, solvent,
chemical shift values in d ppm), 13C NMR (spec-
trometer frequency, solvent, chemical shift in dvalues), plant source (family), molecular formula,
calculated molecular weight and reference(s). The 1H
and 13C NMR data have been rounded to two and one
decimal places, respectively. The molecular weight
data have been rounded to four decimal places. The
NMR data have been listed on each structure because
of the differences in the systems used to number the
different structures. The principle aim of this review is
to provide a reference for researchers that they can use
for the rapid identification of isolated thiophenes
through a comparison of their physical and spectral
data. The highlighted bioactivities of these compounds
may also be of interest to synthetic and medicinal
chemists for the design of new drugs using known
thiophenes as raw materials. The thiophenes described
in this review have been arranged in five different
groups according to the number of thiophene rings in
their structure, including group I-thiophene, group II-
bithiophenes, group III-terthiophenes, group IV-quin-
quethiophenes, and group V-miscellaneous thio-
phenes (Tables 1, 2, 3, 4, 5).
Thiophene biosynthesis
The first naturally occurring thiophene derivative, a-terthiophene, was isolated in 1947 from Tagetes erecta
(Zechmeister and Sease 1947). Since then, more than
150 thiophene-based natural products comprising one,
two or three thiophene rings and side chains bearing a
variable number of double or triple bonds (Bohlmann
and Zdero 1985; Kagan 1991) had been characterized
from Asteraceae and fungi (Bohlmann 1988; Sorensen
Fig. 1 Classes of naturally
occurring thiophenes
198 Phytochem Rev (2016) 15:197–220
123
Table 1 Naturally occurring thiophene: group-I: thiophene
1. 3-(4,8,12,16-Tetramethylheptadeca-3,7,11,15-tetraenyl)-thiophene-1-oxide
Pale yellowish oil; UV kmax (CH3OH) (log e): 218 (4.42) nm; IR (Nujol) cmax: 2925, 1642, 1230, 1025 cm-1; EIMS m/z (rel. int.):
386 [M]? (10), 371 (17), 315 (18), 293 (7), 285 (15), 272 (5), 217 (8), 204 (15), 175 (10), 161 (12), 149 (17), 147 (10), 135 (27),
123 (22), 95 (27), 81 (94), 69 (100); HREIMS m/z: 386.2643 (calcd. for C25H38OS, 386.2645); NMR data (CDCl3, 500 and
125 MHz); The marine sponge Xestospongia sp. (Pedpradab and Suwanborirux 2011)
2. Xanthopappin A; 2-(E)-Hept-5-ene-1,3-diynylthiophene diol
Brown oil; UV kmax (CH3OH) (log e): 206 (4.31), 252 (4.22), 313 (4.08) nm; EIMS m/z (rel. int.): 172 [M]? (47), 171 [M–H]? (34),
144 [M–C2H4]? (32); HRTOFMS m/z: 173.0428 [M?H]? (calcd. for C11H9S, 173.0424); NMR data (CDCl3, 500 and 125 MHz);
The stems and roots of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Tian et al. 2006)
3. 10,11-Threo-xanthopappin D; 2-Hept-5,6-threo-dihydroxy-1,3-diynylthiophene
Colourless oil; [a]D -20 (c 0.5, acetone); UV kmax (CH3OH): 306, 290, 232 nm; IR (KBr) cmax: 3367 (OH), 2924 (CH3), 2233
(C:C) cm-1; HRESIMS m/z: 229.0292 [M?Na]? (calcd. for C11H10O2SNa, 229.0294); NMR data (CDCl3, 600 and 150 MHz);
Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
4. 10,11-Erythro-xanthopappin D; 2-Hept-5,6-erythro-dihydroxy-1,3-diynylthiophene
Colourless oil; [a]D ?20 (c 0.5, acetone); UV kmax (CH3OH): 304, 289, 232 nm; IR (KBr) cmax: 3345 (OH), 2924 (CH3), 2219
(C:C) cm-1; HRESIMS m/z: 435.0687 [2M?Na]? (calcd. for 2(C11H10O2S) Na, 435.0695); NMR data (CDCl3, 600 and
150 MHz); Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
Phytochem Rev (2016) 15:197–220 199
123
Table 1 continued
5. N-Isobutyl-6-(2-thiophenyl)-2,4-hexadienamide
HRESIMS m/z: 272.1072 ([M?Na]?, (calcd. for C14H19NOS); NMR (CDCl3, 300 and 75 MHz); Leaves of Chrysanthemum
coronarium L. (family: Asteraceae) (Ragasa et al. 1997)
6. Amplectol; (3,4-Dihydroxy-8-[50-methyl-thiophen-20-yl]-1,5-octadien-7-yne)
Colorless oil; UV kmax (CH3OH): 295 nm; IR mmax: 3620, 3565 (OH), 2200 (C:C) cm-1; HREIMS m/z (rel. int.): 234.072 [M]?
(calcd. for C13H14O2S, 234.073) (6), 216 [M–H2O]? (9), 177 [(M–CH(OH)CH=CH2)]
?; NMR data (CDCl3, 400 MHz); Aerial
parts of Blumea amplectens DC var. arenaria (family: Asteraceae) (Pathak et al. 1987)
7A. Echinoynethiophene A; 7,10-Epithio-7,9-tridecadiene-3,5,11-triyne-1,2-diol
Yellow needles (acetone), mp. 122–123 �C; IR (KBr) cmax: 3328 (br), 3104, 2956, 2923, 2872, 2150, 1778, 1451, 1322, 1186, 1080
(s), 1022, 946, 864, 805, 688 cm-1; C13H10O2S; EIMS m/z (rel. int.): 230 [M]? (90), 199 (100), 171 (33), 170 (32), 169 (33), 145
(22), 139 (20), 127 (50); NMR data (Acetone-d6, 500 and 125 MHz); Roots of Echinops grijissii Hance (family: Asteraceae) (Liu
et al. 2002)
7B. Echinoynethiophene A; 7,10-Epithio-7,9-tridecadiene-3,5,11-triyne-1,2-diol
Yellow amorphous powder; [a]D ?92.2 (c 0.1 CH3OH); UV kmax (e): 237 (7682), 245 (10,293), 251 (10,293), 273 (7728), 275
(7935), 280 (8556), 324 (17,917), 341 (15,755) nm; IR mmax: 3321, 2912, 2863, 2222, 1634, 1446, 1416, 1385, 1090, 798 cm-1;
EIMS m/z (rel. int.): 230 [M]? (53), 212 (10), 199 (100), 183 (6), 170 (30), 169 (24), 149 (6), 139 (9), 127 (18), 93(9); HREIMS
200 Phytochem Rev (2016) 15:197–220
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Table 1 continued
m/z: 230.0403 (calcd. for C13H10SO2, 230.0401); NMR data (CD3OD, 200 and 128.5 MHz); Roots of Balsamorhiza sagittata
(Pursch) Nuttall (family: Asteraceae) (Matsuura et al. 1996)
8. 10,11-Cis-xanthopappin B; 5-(2-Chloro-1-hydroxyethyl)-2-(Z)-hept-5-ene-1,3-diynylthiophene
Colourless oil; [a]D ?10 (c 0.5, acetone); UV kmax (CH3OH): 315, 252, 268, 213 nm; IR (KBr) cmax: 3382 (OH), 2918 (CH3), 2200
(C:C) cm-1; HRESIMS m/z: 251.0302 [M?H]? (calcd. for C13H11ClOSNa, 251.0294); NMR data (CDCl3, 600 and 150 MHz);
Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
9. Xanthopappin B; 5-(2-Chloro-1-hydroxyethyl)-2-(E)-hept-5-ene-1,3- diynylthiophene
Brown oil; [a]D 0 (c 0.377, acetone); UV kmax (CH3OH) (log e): 209 (4.37), 268 (4.44) nm; EIMS m/z (rel. int.): 252 [M?2]? (14),
251 [M?1]? (6), 250 [M]? (38), 201 [M–CH2Cl]? (100), 171 [M-CH2ClCH(OH)]
? (18); HRTOFMS m/z: 273.0112 [M?Na]?
(calcd. for C13H11ONaSCl, 273.0116); NMR data (CDCl3, 500 and 125 MHz); The stems and roots of Xanthopappus subacaulis
C. Winkl (family: Asteraceae) (Tian et al. 2006)
10. 5-(But-4-chloro-3-hydroxy-1-ynyl)-2-(Z)-pent-3-ene-1-ynylthiophene
Colourless oil; [a]D -10 (c 1.0, acetone); UV kmax (CH3OH): 211, 227, 316, 333 nm; IR (KBr) cmax 3344 (OH), 2924 (CH3), 2219
(C:C) cm-1; HRESIMS m/z: 273.0115 [M?Na]? (calcd. for C13H11ClOSNa, 273.0111); NMR data (CDCl3, 600 and
150 MHz); Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
11. 5-(But-4-chloro-3-hydroxy-1-ynyl)-2-(E)-pent-3-ene-1-ynylthiophene
Colourless oil; [a]D ?10 (c 1.0, acetone); UV kmax (CH3OH): 210, 226, 319, 334 nm; IR (KBr) cmax: 3344 (OH), 2924 (CH3), 2180
(C:C) cm-1; HRESIMS m/z: 273.0115 [M?Na]? (calcd. for C13H11ClOSNa, 273.0111); NMR data (CDCl3, 600 and
150 MHz); Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
Phytochem Rev (2016) 15:197–220 201
123
Table 1 continued
12. 5-(1,2-Dihydroxyethyl)-2-(Z)-hept-5-ene-1,3-diynylthiophene
Colourless oil; [a]D ?30 (c 10.0, acetone); UV kmax (CH3OH): 316, 268, 253, 216 nm; IR (KBr) cmax: 3359 (OH), 2921(CH3),
2204 (C:C) cm-1; HRESIMS m/z: 255.0457 [M?Na]? (calcd. for C13H12O2SNa, 255.0450); NMR data (CDCl3, 600 and
150 MHz); Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
13. 5-(But-3,4-dihydroxy-1-ynyl)-2-(Z)-pent-3-ene-1-ynylthiophene
Colourless oil; [a]D ?40 (c 1.0, acetone); UV kmax (CH3OH): 312, 261, 213 nm; IR (KBr) cmax: 3363 (OH), 2923 (CH3), 2227
(C:C) cm-1; HRESIMS m/z: 255.0456 [M?Na]? (calcd. for C13H12O2SNa, 255.0450); NMR data (CDCl3, 600 and 150 MHz);
Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
14. 5-(But-3,4-dihydroxy-1-ynyl)-2-(E)-pent-3-ene-1-ynylthiophene
Colourless oil; [a]D ?40 (c 1.0, acetone); UV kmax (CH3OH): 313, 263, 2I5 nm; IR (KBr) cmax: 3344 (OH), 2924 (CH3), 2180
(C:C) cm-1; HRESIMS m/z: 255.0456 [M?Na]? (calcd. for C13H12O2SNa, 255.0450); NMR data (CDCl3, 600 and 150 MHz);
Whole plant of Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Zhang et al. 2014)
15. 2-Acetyl-3-metoxy-5-(prop-1-ynyl) thiophen
A white solid crystal; mp 71–73 �C; UV kmax 300 nm; IR mmax: 1545 (Ar), 1632 (CO), 2233 (C:C) cm-1; CIMS m/z (rel. int.): 195
[M?H]? (100); EIMS m/z (rel. int.): 194 [M]? (93.3), 179 [M–CH3]? (100), 165 (22.8), 151 [M–CH3CO]
? (30.5), 136 (20.9),
108 (26.6), 93 (20.5), 77 (21.9), 63 (61), 43 (67); NMR data (CDCl3, 400 and 100 MHz); Roots of Artemisia absinthium L.
(family: Asteraceae) (Yamari et al. 2004)
202 Phytochem Rev (2016) 15:197–220
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Table 1 continued
16. 5-Hydroxymethyl-2-(E)-hept-5-ene-1,3-diynylthiophene diol
Cream crystals; mp 72–75 �C; UV kmax (CH3OH): 217, 227 sh, 256, 261, 271, 304 sh, 321, 348 sh nm; IR (KBr) cmax: 3260, 2900,
210, 2150, 1613, 1440, 1362, 1349, 1285, 1182, 1130, 1030, 995, 942, 805 cm-1; EIMS m/z (rel. int.): 202 [M]? (100) 185 [M–
H2O]? (46), 74 [M-CO]? (16), 171 [M–CH2OH]
? (20); HRTOFMS m/z: 203.0525 [M?H]? (calcd. for C12H11OS, 203.0530);
NMR data (CDCl3, 90 MHz for 1H and 125 for 13C NMR); Roots of Leuzea carthamoides DC (syn. Rhaponticum carthamoides
Willd. Iljin) (family: Asteraceae); (Szendrei et al. 1984; Tian et al. 2006)
17. (E)-2-[5-(Hept-5-en-1,3-diynyl)-thien-2-yl]-ethan-1,2-diol
Cream crystals; mp 96–98 �C; [a]D 0 (c 0.083, acetone); UV kmax (CH3OH): 217, 255, 270, 304 sh, 321, 346 sh nm; IR (KBr) cmax:
3200 (br), 2870, 2160, 2100, 1610, 1435, 1285, 1200, 1160, 1090, 1055, 1040, 940, 875, 810 cm-1; EIMS m/z (rel. int.): 232
[M]? (25), 201 [M-CH2OH]? (l00), 171 [M–CH(OH)–CH2OH]
?; HRTOFMS m/z: 255.0525 [M?Na]? (calcd. for C13H12ONaS,
255.0455); NMR data (CDCl3, 600 and 150 MHz); Underground parts of Leuzea carthamoides DC (syn. Rhaponticum
carthamoides Willd. Iljin) (family: Asteraceae) (Chobot et al. 2003; Szendrei et al. 1984; Tian et al. 2006)
18. 2-[Pent-1,3-diynyl]-5[4-hydroxybut-1-ynyl]-thiophene
Yellowish oil; IR (KBr) cmax: 3490, 2230, 1640, 1100, 980 cm-1; 13C NMR (CDCl3, 75 MHz): dC 135.62, 132.94, 128.12, 123.73,
95.46, 85.35, 75.28, 70.25, 67.98, 65.30, 61.96, 25.43, 4.91; EIMS m/z (rel. int.): 214 (30), 187 (100); 1H NMR data (CDCl3,
90 MHz); Roots of Echinops pappii Chiov (family: Asteraceae) (Abegaz 1991)
19. 2-[Cis-pent-3-en-l-ynyl]-5-[4-hydroxybut-l-ynyl]-thiophene
20. 2-[Trans-pent-3-en-l-ynyl]-5-[4-hydroxybut-l-ynyl]-thiophene
Yellow waxy solid; IR (KBr) cmax: 3360, 3040, 2245, 2165, 1630, 1200, 1058, 960, 820 cm-1; 13C NMR data (CDCl3, 75 MHz):
dC 141.90, 140.60, 132.48, 132.55, 132.33, 132.06, 125.42, 125.10, 122.66, 111.63, 110.39, 92.80, 92.43, 92.31, 91.28, 83.80,
81.07, 77.79, 75.40, 61.17, 61.13, 24.02, 18.79, 16.19; HRMS m/z: 216.0612 (calcd. for C13H12OS; 216.0609); EIMS m/z (rel.
Phytochem Rev (2016) 15:197–220 203
123
Table 1 continued
int.): 216 (24), 189 (100); NMR data (CDCl3, 300 and 75 MHz); Roots of Echinops pappii Chiov (family: Asteraceae) (Abegaz
1991)
21. PDDYT; 2-(Penta-1,3-diynyl)-5-(3,4-dihydroxybut-1-ynyl)-thiophene
EIMS m/z: 230 [M]?; NMR data (CD3OD, 500 and 125 MHz); Roots of Echinops grijsii Hance (family: Asteraceae) (Jin et al.
2008; Shi et al. 2010)
22. 4-(5-(Penta-1,3-diynyl)thiophen-2-yl)but-3-ynyl acetate
NMR data (CDCl3, 90 MHz); Roots of Echinops hispidus Fresen (family: Asteraceae) (Abegaz et al. 1991)
23A. 2-Hydroxy-4-(5-(penta-1,3-diynyl)thiophen-2-yl)but-3-ynyl acetate
IR (KBr) mmax: 2237, 1758, 1240 cm-1; HRMS m/z (rel. int.): 272. 0507 (calcd. for C15H12O3S; 272.0510) (24), 254 (10), 212 (100),
199 (42), 170 (20); NMR data (CDCl3, 90 MHz); Roots of Echinops hispidus Fresen (family: Asteraceae) (Abegaz et al. 1991)
23B. 2-(Pant-1,3-diynyl)-5-(4-acetoxy-3-hydroxybuta-1-ynyl)-thiophene
EIMS m/z: 290 [M]?; NMR data (CDCl3, 500 and 125 MHz); Stems and leaves of Pluchea indica (L.) Less. (family: Asteraceae)
(Jin et al. 2008)
24. 1-Hydroxy-4-(5-(penta-1,3-diynyl)thiophen-2-yl)but-3-yn-2-yl acetate
204 Phytochem Rev (2016) 15:197–220
123
Table 1 continued
NMR data (CDCl3, 90 MHz); Roots of Echinops hispidus Fresen (family: Asteraceae) (Abegaz et al. 1991)
25. 4-(5-(Penta-1,3-diynyl)thiophen-2-yl)but-3-yne-1,2-diyl diacetate
NMR data (CDCl3, 90 MHz); Roots of Echinops hispidus Fresen (family: Asteraceae) (Abegaz et al. 1991)
26. 2-Chloro-4-(5-(penta-1,3-diynyl)thiophen-2-yl)but-3-yn-1-ol
NMR data (CDCl3, 90 MHz); Roots of Echinops hispidus Fresen (family: Asteraceae) (Abegaz et al. 1991)
27A. 4-[5-(Penta-1,3-diynyl)thien-2-yl]-2-chlorobut-3-ynyl acetate
EIMS m/z (rel. int.): 292 (5), 290 [M]? (17), 254 (28), 230 (100), 195 (59); NMR data (CDCl3, 400 and 100 MHz); Roots of
Echinops transiliensis Golosh (family: Asteraceae) (Fokialakis et al. 2006)
27B. 2-(Pant-1,3-diynyl)-5-(4-acetoxy-3-chlorobuta-1-ynyl)-thiophene
EIMS m/z: 272 [M]?; NMR data (CDCl3, 500 and 125 MHz); Stems and leaves of Pluchea indica (L.) Less. (family: Asteraceae)
(Jin et al. 2008)
28. 5-(1,2-Diacetoxyethyl)-2-(E)-hept-5-ene-1,3-diynylthiophene diol
Yellow oil; UV kmax (CH3OH): 217, 256, 261, 270, 302 sh, 322, 344 sh nm; IR (KBr) cmax: 2960, 2200, 2140, 1755, 1422, 1370,
1226, 1049, 950, 870, 810 cm-1; EIMS m/z (rel. int.): 316 [M]? (41), (256) [M–AcOH]? (55), 214 [M–AcOH–CH,CO]? (l00),
Phytochem Rev (2016) 15:197–220 205
123
1977). Oleic acid has been proposed as a precursor in
the biosynthesis of thiophenes via acetylene interme-
diates (Margl et al. 2001). Acetylenic natural products
include all compounds containing a carbon–carbon
triple bond or alkynyl functional group. Three fatty
acids have been identified as the basic building blocks
of most acetylenic natural products, including
crepenynic acid, stearolic acid and tariric acid (Minto
and Blacklock 2008). Oleic acid is converted to
trideca-3,5,7,9,11-pentayn-l-ene (PYE) via repeated
desaturation steps involving crepenynic acid and chain
shortening processes (Margl et al. 2001). PYE is then
converted to a variety of different thiophenes that
subsequently accumulate in plant tissue (Fig. 2)
(Jacobs et al. 1995). The biosynthesis of polyacetyle-
nes occurs in two stages, including (A) an oxidative
dehydrogenation (desaturation) mechanism, where the
existing alkene functionality undergoes a desaturation
reaction through an iron-catalyzed dehydrogenation
with molecular oxygen. The electrons required by this
reaction are provided by either NADH or NADPH.
The second step (B) involves a decarboxylative enol
elimination mechanism, which uses a divergent
approach for the formation of the second p-bond(Fig. 3). The elimination of an activated enol car-
boxylate intermediate is thermodynamically driven by
the formation of CO2, which could be accompanied by
the hydrolysis of the pyrophosphate. According to the
original hypotheses, path A would operate with full-
length acyl lipids, whereas path B would install
acetylenic groups during de novo fatty acid biosyn-
thesis. Although the current paradigm and all ex-
periments dealing with fatty acid biosynthesis are
consistent with the desaturase pathway, the elimina-
tion hypothesis remains valid for polyketide-derived
acetylenic natural products (Minto and Blacklock
2008).
Sulfur, which is a heteroatom commonly intro-
duced into polyacetylenes, is found in a wide range of
ecologically significant thiophenes and bithiophenes.
The structures of these compounds vary considerably
in terms of their number of thiophene rings (1–3) and
the degree of unsaturation in their side chains (i.e.,
ene/yne) (Margl et al. 2001). Cysteine and H2S have
both been proposed as potential sources of sulfur
(Bohlmann et al. 1973, 1988; Jente et al. 1988, 1981).
The key step in the conversion of PYE to thiophenes is
the addition of H2S or its biochemical equivalent to a
conjugated triple bond, followed by a ring formation
reaction, which is probably a two-step reaction
(Bohlmann et al. 1973). In addition to the formation
of compounds containing two or three thiophene rings,
the removal of a terminal methyl group and modifi-
cation of a vinyl group are necessary to obtain the
various thiophenes that ultimately accumulate in plant
tissues (Fig. 4).
The addition of sulfur to a diyne unit leads to the
formation of a thiophene ring via a stepwise process.
The formal addition of H2S produces vinyl thiols that
are intercepted in certain Asteraceae species to
produce thioethers. Subsequent ring closure results
in the formation of thiophenes and the oxidative
formation of disulfide linkages that producing bithio-
phenes (Fig. 4).
The proportion of thiophenes found in the different
parts of a plant can vary considerably based on the type
Table 1 continued
201 [M–Me–CH2CO]? (82), 171 [M–CH(COOMe)–CH2COOMe]? (9); HRTOFMS m/z: 239.0663 [M?Na]? (calcd. for
C17H16O4NaS, 239.0667); NMR data (CDCl3, 90 MHz for 1H and 125 for 13C NMR); Roots of Leuzea carthamoides DC (syn.
Rhaponticum carthamoides Willd. Iljin) (family: Asteraceae) (Szendrei et al. 1984; Tian et al. 2006)
29. 5-(1-Dihydroxy-2-acetoxyethyl)-2-(E)-hept-5-ene-1,3-diynylthiophene diol
Cream crystals; mp 82–84 �C; UV kmax (CH3OH): 217, 226 sh, 257, 270, 303 sh, 324, 346 sh nm; IR (KBr) cmax: 3310, 2940, 885,
2170, 2210, 1700, 1430, 1385, 1360, 1270, 1235, 1225, 1185, 145, 1080, 1035, 980, 944, 895, 802 cm-1; MS m/z (rel. int.): 274
[M]? (15), 256 [M–H2O]? (2), 214 [M–HOAc]? (70), 201 [M–CH2COOMe]? (l00), 185 [M–C7H5]
? (12), 171 [M–CH(OH)–
CH2COOMe]? (28); NMR data (CDCl3, 90 MHz); Roots of Leuzea carthamoides DC (syn. Rhaponticum carthamoides Willd.
Iljin) (family: Asteraceae) (Szendrei et al. 1984)
206 Phytochem Rev (2016) 15:197–220
123
Table 2 Naturally occurring thiophene: group-II: bithiophene
30. 5-Acetyl-2,20-bithiophene
mp 59–60 �C; UV kmax (CH3OH): 254, 365 nm; NMR data (CDCl3, 500 and 125 MHz); Roots of Echinops latifolius Tausch.
(family: Asteraceae) (Wang et al. 2008)
31. 5-(4-Hydroxybut-1-ynyl)-2,20-bithiophene
UV kmax (CH3OH): 254, 365 nm; NMR data (CDCl3, 500 and 125 MHz); Roots of Echinops latifolius Tausch. (family:
Asteraceae) (Wang et al. 2008)
32. BBT; 5-(But-3-en-1-ynyl)-2,20-bithiophene
UV kmax (CH3OH): 254, 365 nm; NMR data (CDCl3, 500 and 125 MHz); Roots of Echinops latifolius Tausch. (family:
Asteraceae) (Margl et al. 2001; Wang et al. 2008)
33. 5-(3-Acetoxy -4-isovaleroyloxybut-1-ynyl-2,20-bithiophene
mp 94–95 �C; UV kmax (CH3OH): 254, 365 nm; NMR data (CDCl3, 500 and 125 MHz); Roots of Echinops latifolius Tausch.
(family: Asteraceae) (Wang et al. 2008)
34. 5-(3-Hydroxmethyl-3-isovaleroyloxyprop-1-ynyl)-2,20-bithiophene
Phytochem Rev (2016) 15:197–220 207
123
Table 2 continued
Yellow oil; [a]D -9.0 (c 0.001, CHCl3); HRMS: m/z 334.0696 (calcd. for C17H18O3S2, 334.0671); ESIMS m/z (rel. int.): 357.0
[M?Na]? (9.0), 358.0 [M?H?Na]? (1.7), 359.0 [M?2H?Na]? (1.1), 360.2 [M?3H?Na]? (0.3), 254.8 [M?Na-102]?
(100.0); NMR data (CDCl3, 300 and 75 MHz); Roots of Echinops latifolius Tausch. (family: Asteraceae) (Wang et al. 2006)
35. Grijisone A: 5-[(4-Isovaleroyloxy) buta-1-onyl]-2,20-bithiophene
Yellow powder (CDCl3); mp 62.3-62.7 �C; UV (MeOH) kmax (log e): 375 (4.3), 262 (3.2), 220 (3.6) nm; IR (KBr) mmax: 1729,1655, 839, 801, 717 cm-1; HREIMS m/z: 336.0838 [M]? (calcd. for C17H20O3S2, 336.0854); EIMS m/z (rel. int.): 336.1 (100),
337.1 (19.8), 338.0 (10.4), 166 (4.3); NMR data (CDCl3, 600 and 150 MHz); Roots of Echinops grijissi Hance (family:
Asteraceae) (Zhang et al. 2008)
36. 5-(3,4-Diacetoxy-l-butynyl)-2,20-bithiophene
Yellow oil; EIMS m/z (rel. int.): 334 [M]? (25); 274 [M–AcOH]? (l), 232 (49, 95 (4), 73 (5), 43 (100); C16H14O4S2; NMR data
(CDCl3, 200 MHz); Roots of Tagetes patula L. (family: Asteraceae) (Menelaou et al. 1991)
37. 50-Methyl-[5-(4-acetoxy-1-butynyl)]-2,20-bithiophene
Yellow oil; ESIMS m/z (rel. int.): 291 [M?H]? (10), 301 (26), 245 (33), 229 (73), 313 [M?Na]? (100); NMR data (CDCl3, 300
and 75 MHz); Aerial parts of Porophyllum ruderale (Jacq.) (family: Asteraceae) (Takahashi et al. 2013, 2011)
38. Methyl-5-[4-(3-methyl-1-oxobutoxy)-1-butynyl]-2,20-bithiophene
Yellow needle-like crystals; UV kmax (Et2O): 347.2 nm; EIMS m/z (rel. int. %): 245.7 [M]? (94.6), 228.8 (70), 216.8 (100);
HREIMS m/z: 246.0155 (C13H10OS2); NMR (CDCl3, 300 and 75 MHz); Roots of Tagetes patula L. (family: Asteraceae) (Bano
et al. 2002)
208 Phytochem Rev (2016) 15:197–220
123
Table 2 continued
39. Methyl-5-[4-(3-methyl-1-oxobutoxy)-1-butynyl]-2,20-bithiophene
Yellowish oil; UV kmax (Et2O): 339 nm (e 26,726); IR (CCl4) mmax: 2850 (C–H stretching), 2300 (C:C), 1717 (ester carbonyl),
1600 (C=C) cm-1; HREIMS m/z (rel. int.): 332.0903 M]? (C18H20O2S2) (19), 230.0186 [M–C5H10O2]? (100), 217 (9), 197 (5),
115 (7), 102 (4); NMR (CDCl3, 300 and 75 MHz); Roots of Tagetes patula L. (family: Asteraceae) (Bano et al. 2002)
40. Grijisyne A; 5-[2-[4-(5-Propyneylthiophen-2-yl)buta-1,3-diynyl]cyclobutaneyl]ethynyl]-2,20-bithiophene
Yellow powder; mp 134.2–135.0 �C; UV (MeOH) kmax (log e): 340.4 (4.2), 250.6 (3.5) nm; IR (KBr) mmax: 2192, 796, 836,674 cm-1; HREIMS m/z: 412.0429 [M]? (calcd. for C25H16S3, 412.0414); EIMS m/z: 413.0 (100), 414.0 (28.5), 415.1 (12.9),
166 (5.6); NMR data (CDCl3, 600 and 150 MHz); Roots of Echinops grijissi Hance (family: Asteraceae) (Zhang et al. 2008)
41. Cardopatine
Yellow plates; mp 123-125 �C; UV (MeOH) kmax (log e): 340.0 (4.82), 242.0 (4.33) nm; [a]D; IR (KBr) mmax: 840 (2-thienyl), 810(thiophen-2,5-diyl) cm-1; EIMS: m/z (rel. int.): 432 (9) 216.0 (100), 171 (13), 95 (6); NMR data (CDCl3, 400 and 100 MHz);
Stem and leaves of Echinops latifolius Tausch. (family: Asteraceae) (Selva et al. 1978; Zhang et al. 2007)
42. Isodopatine
Light yellow plates; mp 79–80 �C; UV (MeOH) kmax (log e): 340.0 (4.82), 242.0 (4.33) nm; IR (KBr) mmax: 840 (2-thienyl), 810
(thiophen-2,5-diyl) cm-1; EIMS: m/z (rel. int.): 432 (12), 216.0 (100), 171 (13), 95 (7); NMR data (CDCl3, 300 and 75 MHz);
Stem and leaves of Echinops latifolius Tausch. (family: Asteraceae) (Selva et al. 1978; Zhang et al. 2007)
Phytochem Rev (2016) 15:197–220 209
123
of plant. For example, no thiophenes can be found in the
shoots of achenes, with bithienyls and traces of 5-(but-
3-en-1-ynyl)-2,20-bithiophene (BBT) being identified
as the major chemicals in this case. a-Terthienyl, whichcan be found in the root of corresponding plants but not
in the shoots, and accumulates in flowers. Despite many
experiments, it remains to be shown whether thiophene
metabolites originate exclusively in the roots, and that
specific thiophenes are preferentially accumulated in
the different parts of the plant, or whether enzymatic
components of the thiophene pathway are expressed in a
tissue-specific manner. It has been reported that methyl
cleavage occurs prior to the formation of the second
thiophene ring (Minto and Blacklock 2008).
Methods for separation of thiophenes
Thiophenes extraction and purification
To allow for the exclusive extraction and isolation of
only thiophene-containing compounds, the plant ma-
terials were extracted with a 1:1 (v/v) mixture of EtOH
andH2O. The resulting thiopheneswere then separated
by partitioning them between a 1:1 (v/v) mixture of n-
hexane and tert-butylmethylether (Jacobs et al. 1995).
The individual layers were collected and the organic
solventswere evaporated under a stream ofN2 gas. The
resulting mixture of thiophenes mixture was then
dissolved in EtOH and purified by preparative HPLC
over an octadecylsilane (C18) reversed-phase column,
using 72–85 % acetonitrile or 70–85 % MeOH as an
eluent (Downum et al. 1984). The compounds eluted
from the column were detected using a UV spec-
trophotometer with a detection range of 320–350 nm
(Jin et al. 2008; Norton et al. 1985; Tosi et al. 1991).
Normal phase HPLC analyses were conducted using a
95:5 (v/v) mixture of n-hexane and dioxane as the
eluent (Szarka et al. 2006, 2007). HPLC was used to
identify and quantify the different thiophene-contain-
ing compounds (Camm et al. 1975; Croes et al. 1989).
Thiophenes can generally be isolated by the extrac-
tion of plant materials with EtOH or MeOH, and the
resulting thiophenes can then be further purified by
partitioning the alcohol extract between n-hexane or pet
ether (PE). The n-hexane or PE fraction can then be
subjected to purification by column chromatography
using n-hexane:EtOAc or PE:acetone as the eluent with
a gradient elution system. The isolated compounds can
then be further purified by preparative HPLC.
Another method for the isolation and purification of
thiophenes is the direct extraction of plant materials
with n-hexane or PE. The resulting extracts can be
purified by column chromatography over silica gel
eluting with an n-hexane:EtOAc or PE:acetone gradi-
ent, followed by preparative HPLC.
Table 2 continued
43. Xanthopappin C; 1,2-Bis[5-(E)-hept-5-ene-1,3-diynylthiophen-2-yl]-2-hydroxypentane-1,4-dione
Brown oil; [a]D 0 (c 0.085, acetone); UV kmax (CH3OH) (log e): 215 (4.72), 269 (4.83), 353 (4.52) nm; EIMS m/z: 456 [M]? (4),
398 [M–CH3COCH3]? (17), 370 [M–CH3COCH3–H2O]
? (9), 257 [M–HCOC4H2SC:CC:CCH=CHCH3]? (25), 200
[HCOC4H2SC:CC:CCH=CHCH3]? (18), 199 [HCOC4H2SC:CC:CCH=CHCH3–H]
? (100), 171 (6); HRTOFMS m/z:
479.0737 [M?Na]?(calcd. for C27H20O3NaS2, 479.0751); NMR data (CDCl3, 500 and 125 MHz); The stems and roots of
Xanthopappus subacaulis C. Winkl (family: Asteraceae) (Tian et al. 2006)
210 Phytochem Rev (2016) 15:197–220
123
Table 3 Naturally occurring thiophene: group-III: terthiophene
44. a-Terthiophene
Colourless needles; mp 91–92 �C; IR (KBr) mmax: 3434, 2931, 2862, 1637, 1460, 1378, 1240, 1050, 1021, 969, 958, 837,
800 cm-1; C12H8S3; NMR data (Acetone-d6, 500 and 125 MHz); Roots of Echinops grijissii Hance (family: Asteraceae) (Liu
et al. 2002)
45. 5-Acetyl-a-terthiophene
Yellow crystals; mp 135–1378 �C; C14H10S3O; IR (KBr) mmax: 2919, 2850, 1731, 1636 cm-1; EIMS m/z: 290 [M]?, 275 [M–
CH3]?, 247 [M–CH3CO]
?, 203, 138; NMR data (Acetone-d6, 500 and 125 MHz); Roots of Echinops grijisii Hance (family:
Asteraceae) (Liu et al. 2002)
46. 5-Chloro-a-terthiophene
Yellow crystals; mp 129–130 �C; C12H7S3Cl; IR (KBr) mmax: 2914, 1586, 1422, 833, 788, 686 cm-1; EIMS m/z: 284 [M?2]?,
282 [M]?, 247 [M–Cl]?, 237, 214, 203, 141, 127, 102, 93; NMR data (Acetone-d6, 500 and 125 MHz); Roots of Echinops
grijisii Hance (family: Asteraceae) (Liu et al. 2002)
47. 5,50 0-Dichloro-a-terthiophene
Yellow crystals; mp 134–135 �C; C12H6S3Cl2; IR (KBr) mmax: 2914, 1427, 849, 787 cm-1; EIMS m/z: 320 [M?4]?, 318 [M?2]?,
316 [M]?, 281 [M–Cl]?, 246 [M–2Cl]?, 237, 201, 158, 145, 119; NMR data (Acetone-d6, 500 and 125 MHz); Roots of
Echinops grijisii Hance (family: Asteraceae) (Liu et al. 2002)
48. 5-Methyl-2,20:50,20 0-terthiophene
Viscous yellow oil; ESIMS m/z (rel. int.): 185 (15), 229 (25), 263 [M?H]? (36), 262 (100); NMR data (CDCl3, 300 and 75 MHz);
Aerial parts of Porophyllum ruderale (family: Asteraceae) (Takahashi et al. 2013, 2011)
Phytochem Rev (2016) 15:197–220 211
123
TLC chromatography and detection of thiophenes
The following solvent systems were used for TLC
analysis: PE:acetone (99:1), PE, PE:diethyl ether
(90:10), and n-hexane:dioxane:n-BuOH (75:25:1)
(Margl et al. 2001). Thiophenes can be detected on a
TLC plate by their characteristic fluorescence under
long wave UV light or by their reaction with one of the
following TLC stains:
1. Vanillin spray reagent (0.5 g vanillin ? 9 mL
95 % EtOH ? 0.5 mL conc. H2SO4 ? 3 drops
glacial acetic acid (Picman et al. 1980).
2. Isatin spray reagent (0.4 % isatin in conc. H2SO4)
(Curtis and Phillips 1962).
Structural elucidation of the thiophenes
Nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance spectroscopy (NMR) is
one the most powerful techniques available for
investigating the structural properties of different
molecules. One of the main applications of NMR in
thiophene research is the structural elucidation of
novel compounds based on their 1D (1H, 13C and
DEPT) and 2D (1H–1H COSY, HSQC/HMQC and
HMBC) NMR data (Tables 1, 2, 3, 4, 5). The
connectivities of the different atoms present in the
thiophenes isolated in the current study were estab-
lished by NOE and ROESY experiments to determine
the stereochemistries of the different thiophenes.
Mass spectroscopy (MS)
Mass spectroscopy has been used as an effective
method for the identification and quantitative deter-
mination of thiophenes. The mass spectra of sulfur-
containing compounds generally contain a series of
characteristic fragments, including [M]?, [M?H]?
and [M?2H]? (corresponding to 4.5 % of the inten-
sity of theM?�ion). Electrospray ionization (ESI) mass
spectrometry generally gives [M?H]? and [M?Na]±
ions for sulfur-containing compounds. It is noteworthy
that sulfur can be lost from the M?� ions of sulfur-
containing compounds together with neighboring C
atoms as CHS fragments. These fragments would
appear with m/z values of 45 (CHS?) and 44 (CS?�),
and can be used as indicators for the presence of sulfur
(Pretsch et al. 2009).
Table 3 continued
49. Ecliptal; 5-Formyl-a-terthiophene
mp 144–145 �C; EIMS m/z: 276 [M]?; NMR data (CDCl3, 300 and 75 MHz); Herbs of Eclipta alba Hassk (family: Asteraceae)
(Das and Chakravarty 1991; Yuan et al. 2007)
Table 4 Naturally occurring thiophene: group-IV: quinquethiophene
50. 5-Methyl-2, 20,50, 20 0,50 0,20 0 0,50 0 0,20 0 0-quinquethiophene
Brown needles; mp 215–216 �C; UV (MeOH) kmax: 334, 387 nm; IR (KBr) mmax: 2870, 1600 cm-1; HRESIMS m/z: 427.6611
[M?H]? (calcd. for C21H15S5, 427.6609); 428.6613 [M?2H]? (calcd. for C21H16S5, 428.6609); NMR data (CDCl3, 500 and
125 MHz); Leaves of Tagetes minuta L. (family Asteraceae) (Al-Musayeib et al. 2014)
212 Phytochem Rev (2016) 15:197–220
123
Table 5 Naturally occurring thiophene: group-V: miscellaneous
51. Echinothiophenegenol; 5-Hydroxy-6-[(1E,3E)-6-hydroxy-1,3-hexadienyl]-2-hydroxymethyl-thieno[2,3-e]-isobenzofuran-8(6H)-one
Pale yellow powder; IR (KBr) mmax: 3436, 1697, 1467 cm-1; ESIMS m/z: 332 [M?H]?; HRESIMS m/z: 331.0643 [M–H]-
(calcd. 331.0640); NMR data (DMSO-d6, 600 and 150 MHz); Roots of Echinops grijissii Hance (family: Asteraceae) (Zhanga
et al. 2009)
52. Echinothiophene; 5-O-b-D-glucopyranosyl-6-[(1E,3E)-6-hydroxy-1,3-hexadienyl]-2-hydroxymethyl-thieno[2,3-e]-isobenzofuran-8(6H)-one
Phytochem Rev (2016) 15:197–220 213
123
Biological activity
Despite the unique nature of their chemical structures
relative to the many other different classes of naturally
occurring compounds, thiophenes have not yet been
well studied in terms of their potential pharmaco-
logical activities. Several naturally occurring thio-
phenes and thiophene-rich extracts have exhibited a
variety of different biological effects, including
antimicrobial, cytotoxic, chemo-preventive, photo-
toxic, insecticidal, herbicidal, and anti-leishmanial
activities.
Antimicrobial activities
Some of the thiophenes isolated in the current study
exhibited antibacterial, antifungal and antiviral ac-
tivities towards a variety of different microorganisms.
Saha et al. (2013) reported that the isolation of a
thiophene-rich extract from Tagetes minuta exhibited
moderate antifungal activity towards several soil
borne and foliar plant pathogens, including
Rhizoctonia solani, Sclerotinia sclerotiorum, and
Sclertium rolfsii. These results therefore indicated
that Tagetes minuta could be used as a potential
candidate for the production of natural fungicides.
Furthermore, the methanol extract of Tagetes patula
exhibited a dose dependent anti-fungal activity to-
wards several phytopathogenic fungi, including Botry-
tis cinerea, Fusarium moniliforme, and Pythium
ultimum. It is noteworthy that the methanol extract
of Tagetes patula exhibited much stronger antifungal
activity when it was used in light than it did in the dark.
The enhanced antifungal activity of the extract in the
presence of light could be attributed to light-induced
changes in the fungal cell membranes involving the
production of free radicals, which could result in the
premature aging of the fungal mycelia (Mares et al.
2004).
Compound 3, which was isolated from Xanthopap-
pus subcaulis, exhibited potent antibacterial activity
against Bacillus subtilis with an MIC of 7.25 lg/mL.
In contrast, the corresponding erythro isomer 4
exhibited broad spectrum antibacterial activity
Table 5 continued
Pale-yellowish needles; mp 214–216 �C (dec); IR (KBr) mmax: 3421, 2924, 1750, 1645, 1094, 1056 cm-1; UV kmax (MeOH) (log
e): 254 (4.94), 319 (4.10) nm; HRFABMS m/z: 495.1339 [M?H]? (D0.0022 of the calcd.) and m/z: 517.1147 [M?Na]?
(D0.0010 of the calcd.) (C23H26O10S); NMR data (DMSO-d6, 500 and 125 MHz); Roots of Echinops grijissii Hance (family:
Asteraceae) (Koike et al. 1999)
214 Phytochem Rev (2016) 15:197–220
123
towards Escherichia coli, B. cereus, Staphylococcus
aureus, and Erwinia carotovora with MIC values of
12.5, 15.5, 7.2, and 7.2 lg/mL, respectively. Several
other chlorinated derivatives (8–11), which were
isolated from the same plant, exhibited only moderate
activity towards E. coli, B. cereus, S. aureus, E.
carotovora, and B. subtilis (Zhang et al. 2014).
Compound 5, which was isolated from the chloroform
extract of Chrysanthemum coronarium, exhibited
moderate antimicrobial activity towards B. subtilis,
Pseudomonus aeruginosa, Candida albicans and
Trichophyton mentagrophytes (Ragasa et al. 1997).
Compound 7 was isolated from Balsamorhiza sagit-
tata, which is a plant native to Northwestern America.
This plant has been reported as a folk medicine
because of its antibacterial and antifungal activities,
and compound 7 exhibited significant activities again-
st B. subtilis, S. aureus and S. aureus SA0017, which is
a methicillin-resistant strain of S. aureus. The an-
tibacterial activity of compound 7 towards a variety of
different bacteria was enhanced when the experiments
were conducted in the presence of UV-A light
Fig. 2 Biosynthesis of
different thiophenes
Phytochem Rev (2016) 15:197–220 215
123
(Matsuura et al. 1996). Furthermore, the antibacterial
activity of compound 7 was confirmed by Kundu and
Chatterjee (2013), who reported that this compound
exhibited MIC values in the range of 25–100 lg/mL
towards six different strains of S. aureus. The authors
of this study also conducted a series of mechanistic
studies with compound 7, which revealed that this
compound exhibited bacteriostatic effects. Further-
more, compound 7 was determined to be a DNA
polymerase inhibitor, as confirmed by agarose gel
electrophoresis (Kundu and Chatterjee 2013). Com-
pound 17 was isolated from Leuzea carthamoides, and
exhibited significant broad spectrum antifungal ac-
tivity towards a variety of different fungal strains, with
Trichophyton mentagrophytes var. mentagrophytes,
Absidia corymbifera and Candida tropicalis being
particularly sensitive to this compound (Chobot et al.
2003).
Thiophenes 18, 27, 31, 32, 36, 40 and 44 were
identified in the dichloromethane extract of Echinops
ritro using an antifungal/biological activity guided
approach. Compounds 18, 31 and 44 exhibited the
most potent antifungal activities of the seven different
compounds towards a variety of different plant
A BFig. 3 The two distinct
proposals for the biogenesis
of acetylenic bonds
Fig. 4 Sulfur addition to
polyacetylenes
216 Phytochem Rev (2016) 15:197–220
123
pathogens, including Colletotrichum acutatum, Col-
letotrichum fragrariae and Colletotrichum gloeospo-
rioides at concentrations in the range of 3–30 lM.
Compound 44 appeared to be relatively selective
towards Colletotrichum species, exhibiting a high
level of activity against C. gloeosporioides (IC50\1.6 lM), whilst showing only moderate levels of
activity towards C. acutatum and C. fragariae with
IC50 values of 3.0 and 4.9 lM, respectively. Com-
pound 18 appeared to demonstrate selective antifungal
activity towards Phomopsis species, with moderate
activities towards Phomopsis obscurans (IC50 = 2.9 -
lM) and Phomopsis viticola (IC50\ 1.6 lM). Fur-
thermore, compound 18 exhibited a high level of
activity towards Fusarium oxysporum with an IC50 of
9.5 lM. The high activity of compound 18 is
particularly interesting because very few chemicals
have been reported to inhibit the activity of F.
oxysporum with IC50 values of\30 lM (Fokialakis
et al. 2006).
Compound 49 showed promising inhibitory activity
towards HIV-1 protease with an IC50 value of 58 lM,
but did not show any activity towards HIV-1 integrase
(Tewtrakul et al. 2007). It is noteworthy that com-
pound 44 exhibited a dose-dependent inhibitory
activity towards HIV in the presence of UV-A light
(320–400 nm), but no activity in the presence of
visible light or in the dark. However, compound 44 did
not exhibit any activity towards poliovirus or cox-
sackievirus (Hudson et al. 1993).
Compounds 44, 48, and 49 exhibited photo-induced
inhibitory activity towards the growth of S. aureus. It
is noteworthy that the unsubstituted 2,20:50,200-terthio-phene (44) was the only one of these three compounds
to exhibit inhibitory activity towards E. coli with an
MIC value of 0.62 lg/mL. Furthermore, none of these
three compounds exhibited inhibitory activity towards
P. aeruginosa (Ciofalo et al. 1996).
Antiparasitic activity
Compounds 37 and 48 exhibited antileishmanial
activity towards the promastigote and axenic forms
of Leishmania amazonensis with IC50 values of 7.7
and 21.3 lg/mL, and 19.0 and 28.7 lg/mL, respec-
tively (Takahashi et al. 2011). Both of these com-
pounds were shown to be highly selective towards
intracellular amastigotes with minimal toxicity to-
wards human cells. Furthermore, changes in the
mitochondrial membrane were observed in promastig-
otes treated with compound 37, as well variations in
the morphological characteristics of the cells (Taka-
hashi et al. 2013).
Compound 44 also exhibited significant nematici-
dal activity when it was irradiated with near UV light.
The nematicidal activity of this compound was
attributed to the liberation of reactive oxygen species
from the compound upon UV irradiation (Bakker et al.
1979).
Phototoxic, insecticidal, and herbicidal effects
There is a growing interest in the discovery of
phototoxic phytochemicals, especially those charac-
terized by significant increases in their activities
following exposure to light. These compounds are
mainly used as insecticides, herbicides and antimicro-
bial agents. Thiophenes are a class of natural products
that have been extensively studied in terms of their
phototoxic effects.
The herbicidal activity of a-terthienyl (44) was
assessed in pot and field trials by Lambert et al. (1991).
The results of this study revealed that compound 44
acted as a contact herbicide in corn and broad leaf
weeds with IC50 values in the range of 15–29 kg ha-1.
Compounds 2, 9, 16, 17, 28 and 43 showed photo-
activated insecticidal activity towards the fourth
instar-larvae of the Asian tiger mosquito with LC50
values of 0.71, 0.53, 0.30, 4.2, 0.66, and 0.95 lg/mL,
respectively. In the absence of light, the LC50 values of
compounds 2, 16, 17, 28 and 43 were [10 lg/mL,
while that of compound 9 was 5.1 lg/mL. These
results demonstrated that the irradiation of compounds
2, 16, 17, 28 and 43with light led to 14.1-, 15.2-, 10.5-,
33.3- and 2.4-fold increases in their activity, respec-
tively, as well as a 9.6-fold increase in the activity of 9.
The photo-activated insecticidal effects of these
compounds were attributed to light dependent toxicity
mechanisms involving the photo-oxidation of insect
targets resulting in membrane damage, enzyme inac-
tivation, cell death and other biological loss of
function mechanisms (Tian et al. 2006).
Compound 17was isolated from the roots of Leuzea
carthamoides and exhibited potent phototoxic effects
in histidine photo-oxidation, Artemia salina and
Tubifex assays compared with the known phototoxic
agent xanthotoxin. The higher activity of 17 towards
A. salina could be attributed to the release of singlet
Phytochem Rev (2016) 15:197–220 217
123
oxygen from 17 following its irradiation with light
rather than the release of a superoxide anion, as is the
case with xanthotoxin. A. salina is much more
sensitive to singlet oxygen than it is to superoxide
anion radicals, which explains the higher activity of 17
towards A. salina compared with xanthotoxin (Chobot
et al. 2003).
Cytotoxic effect
Several thiophenes were screened to determine their
cytotoxic effects against a wide range of human cancer
cell lines. The marine sponge-derived thiophene 1
exhibited weak cytotoxicity towards Vero cells
(African green monkey kidney cells) with an IC50
value of 31 lM (Pedpradab and Suwanborirux 2011).
Compounds 35 and 40, which were isolated from the
roots of Echinops grijisii, were evaluated in terms of
their cytotoxic activity towards a variety of different
cancer cell lines, including HL-60, K562 and MCF-7
cells. Compound 35 exhibited moderate activities
against HL60 and K562 cells, with IC50 values of
21.1 and 25.2 lg/mL, respectively. Compound 40 also
exhibited moderate levels of activity against HL60,
K562, and MCF-7 cells, with IC50 values of 19.6, 18.9
and 28.7 lg/mL (Zhang et al. 2008). Compounds 25,
32, 33, 36, 40, and 43were also isolated fromEchinops
grijisii and screened for their cytotoxic activity against
HepG2, K562, HL60, and MCF-7 cells. Compound 36
exhibit a high level of activity towards HL60 andK562
cells with IC50 values of 12 lg/mL), while 33 showed
potent activity towards K562 cells (IC50 = 7 lg/mL).
Jin et al. (2008) reported that most thiophenes are
cytotoxic after UV irradiation. The UV light-mediated
cytotoxicity of thiophenes has been attributed to them
being highly conjugated and becoming increasingly
unstable under UV irradiation conditions. The irra-
diation of these compounds with UV light would
therefore result in the liberation of free radicals that
would attack the cells. However, the main interest of
the authors of this particular study was the structure
activity relationships of compounds that exhibited
cytotoxic activity in the absence of light. The authors
reported that the introduction of an acyl substituent as a
side chain was essential to the cytotoxic activity of
these compounds, especially in the non-radiated
bithiophenes.
Thiophenes have also been reported to exhibit a
variety of other activities, including antimutagenic
and chemopreventive effects. Compound 5 was
investigated in terms of its antimutagenic effects
using a micronucleus test. At a dose of 8 mg/kg bwt,
compound 5 reduced the number of micronucleated
polychromatic erythrocytes by 66.5 % (Ragasa et al.
1997). Compound 21 was reported to possess potent
NAD(P)H: quinine oxidoreductase 1 (NQO1) induc-
ing activity in murine Hepa1c1c7 cells. The maximum
induction of this compound was 3.3-fold greater than
that of 40-bromoflavone (positive control) at a con-
centration of 40 lM. As a phase 2 detoxifying enzyme
inducer, the mechanism of action of compound 21was
investigated to determine whether it was monofunc-
tional (i.e., progressing through the Keap1-Nrf2
pathway) or bifunctional (i.e., progressing through
the aryl hydrocarbon receptor-xenobiotic response
element pathway). The study concluded that com-
pound 21 was acting in a mono-functional manner
though the activation of the Keap1-Nrf2 pathway (Shi
et al. 2010).
Conclusions
Thiophenes are a class of heterocyclic aromatic
compounds that fulfill all the requirements for being
lead compounds in a number of different therapeutic
areas. Compounds belonging to this class possess a
variety of different chemical compositions, and have
been reported to exhibit a wide range of biological
activities. In this review, we have described the
biosynthetic pathways, spectral data, sources and
biological activities of 52 different thiophenes.
Conflict of interest The authors declare that they have no
conflicts of interest.
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