Synthesis, antitumor and antioxidant evaluation of some new thiazole and thiophene derivatives incorporated coumarin moiety

Article abstract of DOI:10.1007/s00044-011-9610-8

3-Acetylcoumarin (1) was utilized as a key intermediate for the synthesis of 2-aminothiazole derivative 3 via bromination of 1 followed by treatment of the formed acetylbromide 2 with thiourea or via Bignailli reaction of 1. Treatment of 3 with 2 afforded the bis-coumarin 4, whereas, cyanoacetylation of 3 followed by treatment of the formed cyanoacetamide 6 with salicyaldehyde give the bis-coumarin 7. Reaction of 6 with phenyl isothiocyanate in DMF/KOH produced the potassium salt 8, which cyclized with chloroacetyl chloride to give the thiazolidinone 9. Acidification of 8 with HCl afforded the thiocarbamoyl 10, which condensed with 2 in DMF to give the mercapto derivative 12, whereas in DMF/TEA gave the thiophene derivative 13. The thiophenes 15a-c were achieved via treatment of the thiocarbamoyls 14a-c with 2 in DMF/TEA, whereas, in DMF gave the corresponding thiazoles 16a-c. Treatment of the components 17a, b with carbon disulfide in DMF/KOH followed by addition of 2 afforded the dithioacetals 19a, b. Cyclization of 19b under alkaline condition gave the desired thiophene 20. Representative compounds of the synthesized products were evaluated as antitumor and antioxidant agents. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-011-9610-8

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:1062–1070
DOI 10.1007/s00044-011-9610-8
ORIGINAL RESEARCH
Synthesis, antitumor and antioxidant evaluation of some new
thiazole and thiophene derivatives incorporated coumarin moiety
•
Moustafa A. Gouda Moged A. Berghot
•
•
Eman A. Baz Wafaa S. Hamama
Received: 29 October 2010 / Accepted: 18 February 2011 / Published online: 20 March 2011
Ó Springer Science+Business Media, LLC 2011
Abstract 3-Acetylcoumarin (1) was utilized as a key
intermediate for the synthesis of 2-aminothiazole deriva-
tive 3 via bromination of 1 followed by treatment of the
formed acetylbromide 2 with thiourea or via Bignailli
reaction of 1. Treatment of 3 with 2 afforded the bis-cou-
marin 4, whereas, cyanoacetylation of 3 followed by
treatment of the formed cyanoacetamide 6 with salicyal-
dehyde give the bis-coumarin 7. Reaction of 6 with phenyl
isothiocyanate in DMF/KOH produced the potassium salt
8, which cyclized with chloroacetyl chloride to give the
thiazolidinone 9. Acidification of 8 with HCl afforded the
thiocarbamoyl 10, which condensed with 2 in DMF to give
the mercapto derivative 12, whereas in DMF/TEA gave the
thiophene derivative 13. The thiophenes 15a–c were
achieved via treatment of the thiocarbamoyls 14a–c with 2
in DMF/TEA, whereas, in DMF gave the corresponding
thiazoles 16a–c. Treatment of the components 17a, b with
carbon disulfide in DMF/KOH followed by addition of 2
afforded the dithioacetals 19a, b. Cyclization of 19b under
alkaline condition gave the desired thiophene 20. Repre-
sentative compounds of the synthesized products were
evaluated as antitumor and antioxidant agents.
Introduction
Coumarin derivatives constitute an important class of het-
erocyclic compounds with anticoagulant (e.g., warfarin,
acenocoumarol) (Anderson et al., 2002; Tassies et al.,
2002), anticoagulant rodenticide (e.g., brodifacoum, bro-
madiolone) (Stone et al., 1999), insecticide (e.g., couma-
phos) (Weick and Thorn, 2002), and antibacterial (e.g.,
novobiocin, clorobiocin) (Mitscher, 2002; Lafitte et al.,
2002), pharmacological properties. The cytotoxic activities
of coumarin and its known metabolite 7-hydroxycoumarin
were tested in several human tumor cell lines. Both com-
pounds inhibited cell proliferation of a gastric carcinoma
cell line, a colon-carcinoma cell line, a hepatoma-derived
cell line, and a lymphoblastic cell line (Weber et al., 1998).
On the other hand, the thiazoline derivatives have been
reported to exhibit antibacterial and antifungal activities
(Habib and Khali, 1984; Nofal et al., 2002). Furthermore,
thiophene derivatives were found to possess analgesic and
antiinflammatory activities (Russo et al., 1994). The pre-
viously reported works on the synthesis of thiazole deriv-
atives indicated that most of the compounds showed high
antimicrobial (Gouda et al., 2010; Khalil et al., 2009a, b;
Khalil et al., 2010a, b), and analgesic (Abu-Hashem et al.,
2010), activities. In this study the authors report the syn-
thesis, structural determination, and in vitro antioxidant and
antitumor activity of the new 3-substituted coumarins
incorporated thiazole or thiophene moiety.
Keywords Coumarin ꢀ Synthesis ꢀ Antitumor ꢀ
Antioxidant activities
Results and discussion
M. A. Gouda (&) ꢀ M. A. Berghot ꢀ E. A. Baz ꢀ W. S. Hamama
Department of Chemistry, Faculty of Science, Mansoura
University, Mansoura 35516, Egypt
The synthetic procedure adopted to obtain the target
compounds are depicted in Schemes 1, 2, 3, 4, and 5.
The starting compound 3-(2-bromoacetyl)-coumarin (2)
e-mail: dr_mostafa_chem@yahoo.com
123

Med Chem Res (2012) 21:1062–1070
1063
(Siddiqui et al., 2009), was prepared according to the
reported method via bromination of 3-acetyl-coumarin (1)
(Gu¨rsoy and Karali, 2003). Reaction of 2 with thiourea in
refluxing ethanol gave the corresponding 2-amino-4-(3-
coumarinyl)thiazole 3 (Koelsch, 1950).
compound with salicyaldehyde in DMF catalyzed by
piperidine achieved the iminocoumarin 7.
Isothiocyanates have been used as synthetic intermedi-
ates to prepare biologically active heterocyclic compounds
(Mukerjee and Ashare, 1991). The biological and physio-
logical activities of sulfur heterocyclic may be attributed to
the presence of N–C–S fragment characteristic of thiazoles,
In another route, compound 3 was obtained in good
yield via Biganilli Reaction of 3-acetyl coumarin, thiourea,
and iodine. Treatment of 3 with 3-bromoacetyl coumarin 2
in DMF and a basic catalyst led to the corresponding bis-
coumarins 4, while cyanoethylation of 3 with 3,5-dimethyl-
1-cyanoacetyl pyrazole (5) (Gorobets et al., 2004), gave the
cyanoacetamide 6. Knoevenagel condensation of the latter
2
N
DMF/ TEA
12 hrs
O
S
N
O
O
O
4
H3C
3
N
N
CH3
O
NC
O
Br
N
O
Br2 / CHCl3
5
CN
O
4 hrs
Dioxane, 3 hrs
S
N
H
O
O
2
O
6
O
O
S
CHO
OH
H2N-C-NH2
TEA/ DMF
CH3
8 hrs
DMF/ piperidine
4 hrs
O
S
1
S
N
O
NH
H2N-C-NH2
NH2
N
O
O
S
N
O
O
I2, 8 hrs
H
O
3
7
Scheme 1 Synthesis of 3-(2-aminothiazol-4-yl)-2H-chromen-2-one
(3)
Scheme 2 Synthesis of bis-coumarin derivatives 4 and 7
Scheme 3 Reaction of
2-cyano-N-(4-(2-oxo-2H-
chromen-3-yl)thiazol-2-
yl)acetamide (6) with phenyl
isothiocyanate
O
O
Ar
CN
N
H
Cl
Cl
DMF, 12 hrs
Ph
N
S
O
O
9
Ar
CN
KOH
N
6
H
O
PhNCS
12 hrs
PhHN
SK+
Ar
CN
SH
N
HCl
8
H
PhHN
10
2
2
2
DMF
DMF/ TEA
8 hrs
DMF, 4 hrs
O
O
O
Ar
CN
S
Ar
N
CN
NH2
N
Ar
H
N
H
H
O
Ph
N
PhHN
S
PhHN
S
O
O
O
13
O
O
N
O
O
11
Ar=
12
O
O
S
123

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Med Chem Res (2012) 21:1062–1070
view of evaluation of their antitumor and antioxidant
activities. Thus, refluxing of 10 with 2 in DMF catalyzed
by TEA led to the formation of thiophene derivative 13
(Scheme 3).
R
NH2
O
DMF/ TEA
4-7 hrs
O
PhHN
S
O
Furthermore, condensation of 2 with the appropriate
thiocarbamoyl derivatives 14a–c (Augustin and Doelling,
1982; Dawood et al., 1998; Khalil et al., 2009a, b), in DMF
catalyzed by TEA gave the corresponding thiophenes 15a–
c. On the other hand, the thiazole derivatives 16a–c were
obtained via refluxing of 2 with the previously thiocarba-
moyl derivatives 14a–c in DMF (Scheme 4).
15a-c
R
CN
SH
2
R
CN
PhHN
14a-c
Ph
N
S
DMF
4-6 hrs
O
O
16a-c
Oxoketene dithioacetals, especially dimethyl thioacetal
have considerable attention because of their synthetic
importance for the construction of variety of alicyclic,
aromatic, and heterocyclic compounds (Dieter, 1986;
Junjappa et al., 1990). Thus, treatment of 17a, b (Hauser
and Reynolds, 1948; Rinehart and Forbis, 1970), with
carbon disulfide and potassium hydroxide in DMF fol-
lowed by addition of 2, gave the dithioacetal derivatives
19a, b instead of diacetals 18a, b. Cyclization of dithio-
acetal derivative 19b under alkaline conditions gave the
desired thiophene 20 (Scheme 5).
O
O
N
N
NH
N
b; R =
a; R =
c; R =
N
H
S
O
Scheme 4 Reaction of 3-(2-bromoacetyl)-2H-chromen-2-one (2)
with thiocarbamoyl derivatives 14a–c
thiazolines, and thiazolidines (El-Desoky et al., 2002).
Thus, treatment of 6 with phenyl isothiocyanate in dry
DMF in the presence of KOH produced the potassium salt
of thiocarbamoyl derivative 8, which cyclized with chlo-
roacetyl chloride in DMF to give the thiazolidinone
derivative 9, whereas acidification of such potassium salt
yielded the corresponding thiocarbamoyl derivative 10.
Attempting preparation of thiazoline derivative 11 through
the condensation reaction of thiocarbamoyl derivative 10
with 2 in DMF was failed and instead of 11, the authors
obtained the mercaptoacetyl coumarin derivative 12. On
continuation of this study on the synthesis of biologically
interesting heterocyclic molecules containing thiophene
moiety (Khalil et al., 2010a, b; Khalil et al., 2009a, b),
several thiophene derivatives have been synthesized with a
Assignment of the new synthesized compounds was
1
based on elemental analyses, IR, H NMR, Mass Spectra
data (c.f. Exp. Part).
Biological activity
Antitumor activity
Effect of drugs on the viability of Ehrlich ascites cells
(EAC) in vitro
Ten 3-substituted coumarin derivatives were tested for
cytotoxicity against well-known established model EAC in
Scheme 5 Synthesis of
mercaptothiophene derivative
20
O
O
O
O
S
Y
S
X
O
O
i. KOH, CS2, DMF
X
18a, b
Y
ii. 2
iii. dil. HCl
17a, b
Y
X
S
O
O
O
12 hrs
HS
19a, b
19b
5 hrs
i. DMF/TEA
ii. dil. HCl
H
O
O
N
O
a; X =
b; X =
, Y =
, Y =
H2N
CH3
OCH3
N
N
S
S
O
O
CN
HS
S
20
123

Med Chem Res (2012) 21:1062–1070
1065
Table 2 Antioxidant activity assay of 3-substituted coumarin
derivatives
Table 1 In vitro cytotoxicity of 3-substituted coumarin derivatives
(Ehrlich ascites cells dead %)
Compound
No. ABTS
Compound No.
% Dead
ED100 lg/cm3
ED50 lg/cm3
ED25 lg/cm3
Absorbance of samples
%Inhibition
Control of ABTS
0.506
0.081
0.18
0.0
5-FU
6
93
58
37
Ascorbic Acid
83.99
63.58
50.2
8
3.8
2.1
3.1
3.2
3.0
2.9
2.6
3.0
3.0
2.6
1.8
1.3
1.6
1.5
1.7
1.6
1.4
1.6
1.5
1.1
1
7
4.9
7.0
6.8
7.1
5.7
5.6
6.1
5.7
5.4
2
0.248
0.128
0.15
9
3
74.29
70.29
61.38
28.91
23.76
35.44
5.94
12
6
13
7
0.195
0.359
0.385
0.326
0.475
0.504
0.436
0.484
0.476
0.113
15a
15b
15c
16a
16c
9
12
13
15a
15b
15c
16a
16c
20
0.19
Where, ED100, ED50, and ED25 are the effective doses at 25, 50, and
100 ll, respectively, of the compounds used. The dead % refers to the
% of the dead tumor cells and 5-FU is 5-fluorouracil as a well-known
cytotoxic agent
13.66
4.15
5.74
75.64
vitro (Karrer and Rubini, 1965). Results for the ED100
,
ED50, and ED25 values of the active compounds are sum-
marized in Table 1. The data showed clearly that most of
compounds have weak activities except compound 20
which have moderate antitumor activity because of the
presence of both thiazole and thiophene moieties.
On the other hand, compounds 3, 6, and 20 exhibited
high-antioxidant activities compared with the starting
material 1. Thus, it would appear that introducing of thia-
zole, thiophene moieties at the 3-position of the coumarin
enhanced the antioxidant activity, also, the presence of
both thiphene and thiazole groups increases the antioxidant
activity as in the case of compounds 20 (Fig. 1). By
comparing the results obtained from the antioxidant
activity of the investigated compounds with their structures
the authors found that, the following structure activity
relation ships (SARs) were postulated: (i) 2-Aminothiazole
derivative 3 is more potent than compounds 1 and 2 which
may be attributed to the replacement of acetyl or bromo-
acetyl with the aminothiazole moiety. (ii) N-Substituted-2-
aminothiazole 6 is less potent than compound 3 because
of the decrease in aromaticity and conjugation. (iii)
Antioxidant activity assay
The antioxidant activity of the synthesized compounds was
evaluated by Lissi et al., (1999). Some of the 3-substituted
coumarin derivatives exhibited antioxidant activities as
shown in Table 2. Compared with the control (Ascorbic
Acid), the antioxidant potency of compounds 3, 6, and 20
was found to be the highest activities, while compounds 1,
2, and 7 showed a moderate antioxidant activities and the
rest of the tested compounds showed weak activities.
Fig. 1 Comparison of the
results obtained from
antioxidant activity of the
investigated compounds with
their structures (SARs)
N
R
S
N
H
O
O
O
R
O
O
O
NH2
N
3, R= H
O
S
S
O
O
6, R=
7, R=
SH
1, R= CH3, 2, R= CH2Br
O
CN
20
O
NH
123

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Med Chem Res (2012) 21:1062–1070
1
211 (29.1), 145 (38.0), 102 (72.2), 51 (81.0). H NMR
Bis-coumarin 7 is less potent than compound 3 which may
be attributable to slightly solubility. (iv) Compound 20 is
more potent than compound 3 which may be because of the
presence of both thiazole and thiophene moieties or may be
because of oxidation of S–H to S–S.
(DMSO-d6) d: 6.80–8.18 (m, 10H, Ar–H), 8.40 (s, 1H, C4–
H, coumarin).
2-Cyano-N-(4-(2-oxo-2H-chromen-3-yl)
thiazol-2-yl)acetamide (6)
Experimental
A mixture of 3 (0.98 g, 4 mmol) and 3-(3,5-dimethyl-1H-
pyrazol-1-yl)-3-oxopropanenitrile (5) (0.65 g, 4 mmol) in
dioxane (20 ml) was refluxed for 3 h, then cooled and
poured into ice-cold water. The resulting precipitate was
filtered off, washed with water, dried, and recrystallized
from DMF/MeOH (1:3) to give 6; brown crystals; 85.4%
yield, mp 256°C. Analysis: Calcd. for C15H9N3O3S
(311.32): C, 57.87; H, 2.91; N, 13.50; Found C, 57.90; H,
2.97; N, 13.59. IR (cm-1) (KBr): 3382 (NH), 2022 (CN),
1700, 1643 (2C=O), 1604 (C=N). The (–) ESI mass spec-
trum showed one quasi-molecular ion peak at 310 ([M–
H])- pointing 311 as the molecular mass of the compound.
MS (m/z) (I%): 311 (M?, 51.3), 244 (56.6), 211 (42.1), 172
(38.2), 102 (25.0), 68 (100.0). 1H NMR (DMSO-d6) d: 4.05
(s, 2H, CH2), 7.35–8.03 (m, 5H, Ar–H), 8.47 (s, 1H, C4–H,
coumarin), 8.57 (s, 1H, NH).
General
All melting points are in degree centigrade (uncorrected)
and were determined on Gallenkamp electric melting point
apparatus. Elemental analyses were carried out in The
Microanalytical Center (Faculty of Science; Cairo Uni-
versity). IR spectra were recorded (KBr) on a Mattson 5000
FTIR Spectrophotometer in The Microanalytical Center
(Faculty of Science; Mansoura University). 1H NMR
spectra of compounds 9, 10, 13, 15b, 15c, 16a, 16c, and
19a were determined on a Varian XL 200 MHz (Faculty of
Science, Cairo University), while, for compounds 6, 7, 12,
and 16a and 13C NMR spectra were acquired on a JEOL
ECX-400 spectrometer Chemistry department, School of
Engineering and Science University of Jacobs, Bremen,
Germany, operating at 400 MHz. The mass spectra were
recorded on (Kratos, 70 eV) MS equipment and/or a Var-
ian MAT 311 A Spectrometer, in The Microanalytical
Center; (Faculty of Science; Cairo University). High-Res-
olution Mass Spectra (HRMS) were recorded using both a
Bruker HCT ultra and a high-resolution (Bruker Daltonics
micrOTOF) instruments from methanol or dichlorometh-
ane solutions using the positive Electrospray Ionization
Mode (ESI). Biological activities were carried in Pharma-
cognosy Department, Faculty of Pharmacy, Mansoura
University, Mansoura, Egypt.
2-Imino-N-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-
2H-chromene-3-carboxamide (7)
A mixture of 6 (0.31 g, 1 mmol), and salicylaldehyde
(0.12 g, 1 mmol) in dry DMF (10 ml) catalyzed by
piperidine (0.5 ml) was refluxed for 4 h, then cooled and
poured into ice-cold water. The resulting precipitate was
filtered off, dried, and crystallized from DMF/EtOH (3:1)
to afford 7; brown crystals; 80.0% yield, mp 260°C.
Analysis: Calcd. for C22H13N3O4S (415.42): C, 63.61; H,
3.15; N, 10.12; Found C, 63.65; H, 3.21; N, 10.18. IR
(cm-1) (KBr): 3378, 3342 (2NH), 1714 (br, 2C=O), 1606
(C=N). The (?) ESI mass spectrum showed three quasi-
molecular ion peaks at 414 ([M ? H])?, 436 ([M ? Na])?
and 871 ([2 M ? 2Na-H])? pointing 311 as the molecular
mass of the compound. MS (m/z) (I%): 244 (M?-[couma-
rin ? CO], 28.6), 212 (11.9), 156 (11.9), 129 (9.5), 102
3,30-(Imidazo[2,1-b]thiazole-3,6-diyl)bis
(2H-chromen-2-one) (4)
A mixture of 3-(2-aminothiazol-4-yl)-2H-chromen-2-one
(3) (0.49 g, 2 mmol), and 3-(2-bromoacetyl)-2H-chromen-
2-one (2) (0.53 g, 2 mmol) in DMF (15 mL) catalyzed by
TEA (0.5 ml), was heated under reflux for 12 h. The
reaction mixture was left to cool and poured into ice-cold
water. The resulting precipitate was filtered off, dried, and
recrystallized from DMF/MeOH (1:2) to furnish 4; dark
brown powder; 78.3% yield, mp 235°C. Analysis: Calcd.
for C23H12N2O4S (412.42): C, 66.98; H, 2.93; N, 6.79;
Found C, 67.06; H, 2.97; N, 6.85. IR (cm-1) (KBr): 1716
(br, 2CO), 1608 (C=N). MS (m/z) (I%): 442 (M?-[CO2,
H]), 352 (M?-[coumarin ? 2H]), 356 (31.6), 244 (100.0),
1
(38.1), 120 (23.8), 63 (100.0). H NMR (DMSO-d6) d:
7.06–7.63 (m, 11H, Ar–H, NH), 8.42 (s, 1H, C4–H, cou-
marin), 10.35 (br, 1H, NH-C=O).
2-Cyano-N-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-
2-(5-oxo-3-phenyl-thiazolidin-2-ylidene)acetamide (9)
To a cold suspension of finely divided KOH (0.28 g,
5 mmol) in dry DMF (15 ml), cyanoacetamide derivative 6
(1.56 g, 5 mmol) followed by phenyl isothiocyanate
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Med Chem Res (2012) 21:1062–1070
1067
(0.68 g, 5 mmol) were added. The mixture was stirred at
room temperature for 12 h, then cooled again to 0°C,
treated with chloroacetyl chloride (0.56 g, 5 mmol) and
left to stir at room temperature for 12 h. The mixture was
poured into ice-cold water. The resulting precipitate was
filtered off, dried, and crystallized from DMF/EtOH (5:2)
to afford 9; dark brown crystals; 65.0% yield, mp 340°C.
Analysis: Calcd. for C24H14N4O4S2 (486.52): C, 59.25; H,
2.90; N, 11.52; Found C, 59.37; H, 2.94; N, 11.56. IR
(cm-1) (KBr): 3423 (NH), 2206 (CN), 1714, 1647 (br,
3C=O), 1606 (C=N). MS (m/z) (I%): 486 (M?, 1.71), 468
(2.28), 446 (2.24), 395 (8.13), 356 (7.74), 270 (12.35), 244
(100.0), 242 (9.23), 211 (14.27), 174 (55.03), 145 (39.60),
filtered off, dried, and crystallized from benzene/EtOH
(3:1) to give 16a, b and from DMF/EtOH (2:1) to give 12,
16c.
2-Cyano-3-(2-oxo-2-(2-oxo-2H-chromen-3-yl)
ethylthio)-N-(4-(2-oxo-2H-chromen-3-yl)
thiazol-2-yl)-3-(phenylamino)acrylamide (12)
Dark yellow crystals; 68% yield, mp 303–306°C. Reaction
time 4 h; Analysis: Calcd. for C33H20N4O6S2 (632.67): C,
62.65; H, 3.19; N, 8.86; Found C, 62.73; H, 3.22; N, 8.93.
IR (cm-1) (KBr): 3318, 3195 (2NH), 2179 (CN), 1726 (br,
4C=O), 1608 (C=N). The (?) ESI mass spectrum displayed
two quasi-molecular ion peaks at 633 ([M ? H])?,
656([M ? Na])?, and the (–)ESI spectrum showed one
quasi-molecular ion peak at 631 pointing 632 as the
molecular mass. 1H NMR (DMSO-d6) d: 2.47 (s, 2H, CH2–
C=O), 6.64 (s, 1H, NH–Ph), 6.96 (s, 1H, C5–H,), 7.33–8.17
(m, 13H, Ar–H), 8.45 (s, 1H, C4–H, coumarin), 8.47 (s, 1H,
C4–H, coumarin), 10.20 (br, 1H, NH–C=O).
1
135 (5.85), 119 (51.60), 76 (75.10), 50 (73.88). H NMR
(DMSO-d6) d: 3.67 (s, 2H, CH2–C=O), 6.95-8.10 (m, 10H,
Ar–H), 8.34 (br, s, C4–H, coumarin), 10.23 (br, s, NH–
C=O).
2-Cyano-3-mercapto-N-(4-(2-oxo-2H-chromen-3-yl)
thiazol-2-yl)-3-(phenylamino) acrylamide (10)
To a cold suspension of finely divided KOH (0.28 g,
5 mmol) in dry DMF (15 ml), cyanoacetamide derivative 6
(1.56 g, 5 mmol) followed by phenyl isothiocyanate
(0.68 g, 5 mmol) were added. The mixture was stirred at
room temperature for 12 h, and then poured into ice-cold
water and then acidified with 0.1 N HCl to a pH 3–4.
The formed precipitate was filtered off, dried, and crys-
tallized from benzene/EtOH (3:2) to afford 10; yellow
crystals; 70.3% yield, mp 128°C. Analysis: Calcd. for
C22H14N4O3S2 (446.5): C, 59.18; H, 3.16; N, 12.55; Found
C, 59.22; H, 3.25; N, 12.63. IR (cm-1) (KBr): 3197, 3176
(2NH), 2533 (SH), 2187 (CN), 1712 (br, 2C=O). MS (m/z)
(I%): 442 (M?-4H, 2.14), 409 (2.38), 341 (2.32), 293
(4.60), 261 (4.36), 244 (5.17), 228 (9.04), 191 (8.00), 176
(16.09), 164 (11.63), 149 (25.83), 145 (8.01), 135 (58.53),
119 (6.36), 92 (46.70), 85 (78.83), 63 (81.79), 56 (100.0).
1H NMR (DMSO-d6) d: 6.69 (s, 1H, C5–H, thiazole),
7.45–8.08 (m, 9H, Ar–H), 8.53 (s, 1H, C4–H, coumarin),
9.56 (br, 1H, NH), 10.21 (br, 1H, NH–C=O), 11.10 (br, s,
1H, SH).
2-(Benzo[d]thiazol-2-yl)-2-(4-(2-oxo-2H-chromen-3-yl)
-3-phenylthiazol-2(3H)-ylidene) acetonitrile (16a)
Brown crystals; 84% yield, mp 242°C. Reaction time 4.5 h;
Analysis: Calcd. for C27H15N3O2S2 (477.56): C, 67.91; H,
3.17; N, 8.80; Found C, 67.96; H, 3.25; N, 8.83. IR (cm-1
)
(KBr): 2184 (CN), 1718 (C=O), 1602 (C=N). MS (m/z)
(I%): 479 (M? ? 2, 17.71), 477 (M?, 100.0), 460 (1.01),
400 (1.14), 342 (12.28), 248 (46.45), 145 (36.71), 134
1
(9.97), 130 (0.80), 76 (43.80). H NMR (DMSO-d6) d:
7.32–7.38 (m, 10H, Ar–H, C5–H, thiazole), 8.22 (s, 1H,
C4–H, coumarin). 13C NMR (DMSO-d6) d: 166.03 (C=O),
162.08, 158.90, 154.07, 147.74, 137.02, 136.80, 134.04,
133.20, 131.44, 130.43, 129.69, 126.90, 126.74, 123.90,
122.22, 121.80, 120.90, 118.20, 118.46, 117.20, 117.02,
112.70, 69.20.
2-(1H-Benzo[d]imidazol-2-yl)-2-(4-(2-oxo-2H-chromen-
3-yl)-3-phenylthiazol-2(3H)-ylidene)acetonitrile (16b)
Dark green crystals; 90% yield, mp 320°C. Reaction time
4 h; Analysis: Calcd. for C27H16N4O2S (460.51): C, 70.42;
H, 3.50; N, 12.17; Found C, 70.48; H, 3.57; N, 12.23. IR
(cm-1) (KBr): 3264 (NH), 2184 (CN), 1718 (C=O), 1600
(C=N). MS (m/z) (I%): 462 (M? ?2, 11.73), 461 (M? ?1,
37.33), 460 (M?, 100.0), 443 (2.37), 432 (2.16), 415 (1.62),
372 (1.92), 342 (2.54), 288 (2.01), 258 (3.63), 230 (8.16),
205 (2.29), 174 (3.53), 156 (1.87), 145 (5.6), 129 (1.85),
Synthesis of coumarin derivatives 12 and 16a–c
General procedure
To a suspension of 3-(2-bromoacetyl)-2H-chromen-2-one
(2) (0.27 g, 1 mmol) in DMF (15 ml), and thiocarbamoyl
derivatives namely; 10 (0.45 g, 1 mmol), 14a (0.31 g,
1 mmol), 14b (0.29 g, 1 mmol) or 14c (0.52 g, 1 mmol)
was added. The reaction mixture was refluxed for 4–6 h,
then left to cool, poured into ice-cold water and neutralized
with sodium acetate solution. The formed precipitate was
1
115 (2.68), 102 (9.99), 90 (2.93), 77 (18.55). H NMR
(DMSO-d6) d: 6.93–7.46 (m, 9H, Ar–H), 8.20 (s, 1H, C4–
H, coumarin), 9.35 (s, 1H, NH).
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Med Chem Res (2012) 21:1062–1070
3-[1,4-Dioxo-3,4,4a,5,10,10a-hexahydro-1H-5,10-
benzenobenzo[g]-phthalazin-2-yl]-2-[4-(2-oxo-2H-
chromen-3-yl)-3-phenyl-1,3-thiazol-2-(3H)ylidine]-
3-oxo-propiononitrile (16c)
3-(3-Amino-4-(benzo[d]thiazol-2-yl)-5-
(phenylamino)thiophene-2-carbonyl)-2H-chromen-2-one
(15a)
Reaction time 7 h; green crystals; 66% yield, mp 320°C.
Analysis: Calcd. for C27H17N3O3S2 (495.57): C, 65.44; H,
Reddish brown powder; 89% yield, mp 320°C. Reaction
time 6 h; Analysis: Calcd. for C39H24N4O5S (660.7): C,
70.90; H, 3.66; N, 8.48; Found C, 70.84; H, 3.76; N, 8.55.
IR (cm-1) (KBr): 3445 (NH), 2191 (CN), 1726, 1668,
1613 (4C=O). MS (m/z) (I%): 371 (M?-[hexahy-
drobenzenobenzophthalazine moiety], 20.5), 178 (100.0,
anthracene), 77 (24.32). 1H NMR (DMSO-d6) d: 3.4 (s, 2H,
C11–H, C12–H), 4.8 (s, 2H, C9–H, C10–H), 6.96–7.82 (m,
13H, Ar–H), 8.17 (s, 1H, C4–H, coumarin), 11.61 (br, 1H,
NH).
3.46; N, 8.48; Found C, 65.48; H, 3.52; N, 8.56. IR (cm-1
)
(KBr): 3463, 3434 (NH2, NH), 1735 (br, C=O), 1606
(C=N). MS (m/z) (I%): 496 (M? ?1, 2.97), 495 (M?,
12.21), 493 (76.19), 477 (2.27), 460 (8.22), 389 (8.32), 358
(6.08), 329 (2.00), 301 (1.65), 247 (2.5), 230 (4.58), 146
(5.45), 145 (3.7), 108 (7.74), 89 (11.42), 77 (100.0), 69
1
(13.53). H NMR (DMSO-d6) d: 4.99 (br, s, 2H, NH2),
7.15–8.09 (m, 14H, Ar–H, NH), 8.43 (s, 1H, C4–H,
coumarin).
Synthesis of 4-amino-N-(4-(2-oxo-2H-chromen-3-
yl)thiazol-2-yl)-5-(2-oxo-2H-chromene-3-carbonyl)-2-
(phenylamino)thiophene-3-carboxamide (13) and
3-(3-amino-4-aryl-5-(phenylamino)thiophene-2-
carbonyl)-2H-chromen-2-ones 15a–c
3-(3-Amino-4-(1H-benzo[d]imidazol-2-yl)-5-
(phenylamino)thiophene-2-carbonyl)-2H-chromen-2-one
(15b)
Reaction time 5.5 h; pale green powder; 65% yield, mp
320°C. Analysis: Calcd. for C27H18N4O3S (478.52): C, 67.77;
H, 3.79; N, 11.71; Found C, 67.83; H, 3.86; N, 11.75. IR
(cm-1) (KBr): 3342 (br, NH2, 2NH), 1673 (C=O, coumarin),
1691 (C=O). MS (m/z) (I%): 478 (M?, 5.74), 476 (51.2), 460
(9.09), 443 (2.7), 372 (2.76), 238 (14.64), 210 (2.39), 181
(3.34), 156 (3.38), 145 (2.56), 129 (3.88), 118 (4.16), 102
(9.23), 89 (12.15), 65 (13.05), 51 (30.64). 1H NMR (DMSO-
d6) d: 5.78 (br, 2H, NH2), 7.12–8.18 (m, 14H, Ar–H, NH),
8.42 (s, 1H, C4–H, coumarin), 9.75 (s, 1H, NH–Ph).
General procedure
To a suspension of 3-(2-bromoacetyl)-2H-chromen-2-one
(2) (0.27 g, 1 mmol) in DMF (15 ml) catalyzed by TEA
(0.5 ml), and thiocarbamoyl derivatives namely; 10
(0.45 g, 1 mmol), 14a (0.31 g, 1 mmol), 14b (0.29 g,
1 mmol) or 14c (0.52 g, 1 mmol) was added. The reaction
mixture was refluxed for 4–8 h, then cooled and poured
into ice-cold water. The formed precipitate was collected
by filtration, dried, and crystallized from benzene/EtOH
(1:4) to give 13 and 15a–c.
2-[(4-Amino-2-anilino-5-(2-oxo-2H-chromen-3-oyl)-3-
thienyl)carbonyl]-3,4,4a,5,10,10a-hexahydro-1H-5,10-
benzenobenzo[g]-phthalazine-1,4-dione (15c)
4-Amino-N-(4-(2-oxo-2H-chromen-3-yl)thiazol-2-yl)-5-
(2-oxo-2H-chromene-3-carbonyl)-2-
(phenylamino)thiophene-3-carboxamide (13)
Reaction time 4 h; pale green crystals; 83% yield, mp
320°C. Analysis: Calcd. for C39H26N4O6S (678.71): C,
69.02; H, 3.86; N, 8.25; Found C, 69.13; H, 3.94; N, 8.18.
IR (cm-1) (KBr): 3443, 3425 (NH2, H), 1716, 1683, 1642
(4C=O). MS (m/z) (I%): 677 ([M?–H], 0.6), 386 (M?–
[hexahydrobenzenobenzophthalazine moiety], 2.5), 329
(0.6), 275 (0.9), 252 (0.5), 234 (0.7), 225 (1.2), 220 (0.6),
Reaction time 8 h; brown crystals; 63% yield, mp
303–306°C. Analysis: Calcd. for C33H20N4O6S2 (632.67):
C, 62.65; H, 3.19; N, 8.86; Found C, 62.73; H, 3.24; N, 8.95.
IR (cm-1) (KBr): 3334, 3264, 3180 (NH2, 2NH), 1720, 1687,
1639 (3C=O), 1600 (C=N). MS (m/z) (I%): 599 ([M?-SH],
1.3), 504 (1.3), 386 [M?-(aminothiazole, NH2), 50.3], 272
(2.3), 244 (100.0), 211 (17.3), 174 (22.9), 102 (35.9), 76
1
204 (1.1), 195 (0.8), 189 (0.9), 178 (100.0), 76 (20.7). H
NMR (DMSO-d6) d: 3.31 (s, 2H, C11–H, C12–H), 4.85 (s,
2H, C9–H, C10–H), 5.95 (br, 2H, NH2), 7.15–7.80 (m, 13H,
Ar–H), 8.27 (s, 1H, C4–H, coumarin), 9.67 (s, 1H, NH–Ph),
11.82 (br, 1H, NH–C=O).
1
(26.8), 51 (43.1). H NMR (DMSO-d6) d: 6.95–8.13 (m,
16H, NH2, Ar–H), 8.50 (br, 2H, C4–H, coumarin), 9.25 (br,
1H, NH–Ph), 10.82 (br, 1H, C4–H, NH–C=O).
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Med Chem Res (2012) 21:1062–1070
Synthesis of dithioacetal derivatives 19a, b
General procedure
1069
Dark brown powder; 76% yield, mp 180°C. Analysis:
Calcd. for C21H12N2O3S3 (436.53): C, 57.78; H, 2.77; N,
6.42; Found C, 57.84; H, 2.81; N, 6.39. IR (cm-1) (KBr):
3324, 3290 (NH2), 2550 (SH), 1670, 1644 (2CO). MS (m/z)
(I%): 439 (M? ?3, 0.27), 438 (M? ?2, 1.17), 437 (M? ?1,
4.16), 436 (M?, 15.22), 434 (81.39), 433 (100.0), 401
(12.96), 391 (0.87), 369 (5.07), 356 (1.70), 345 (1.42), 334
(0.94), 317 (1.84), 282 (2.30), 272 (1.74), 246 (2.55), 235
(1.37), 217 (11.37), 200 (3.29), 174 (6.59), 159 (2.04), 138
To a cold suspension of finely divided KOH (0.11 g,
2 mmol) in DMF (20 mL), N-(2-methoxyphenyl)-3-ox-
obutanamide (17a) (0.21 g, 1 mmol) or 2-(benzo[d]thiazol-
2-yl)acetonitrile (17b) (0.17 g, 1 mmol) followed by car-
bon disulfide (0.61 g, 8 mmol) were added. The reaction
mixture was stirred for 12 h at 0–5°C, then 3-(2-bromo-
acetyl)-2H-chromen-2-one (2) (0.27 g, 1 mmol) was added
and left to stirred at room temperature for 12 h. The mix-
ture was poured into ice-cold water acidified with dil. HCl.
The obtained precipitate was collected by filtration, dried,
and crystallized from benzene/EtOH (4:3) to give 19a, b.
1
(1.82), 123 (2.50), 108 (3.77), 86 (7.27), 76 (9.48). H
NMR (DMSO-d6) d: 3.71 (br, s, 2H, NH2), 7.22–8.42 (m,
9H, Ar–H, C4–H, coumarin), 9.45 (br, s, 1H, SH).
Biological activity
Antitumor activity
2-(Mercapto(2-oxo-2-(2-oxo-2H-chromen-3-
yl)ethylthio)methylene)-N-(2-methoxyphenyl)-3-
oxobutanamide (19a)
Different concentrations of the tested compounds were
prepared (ED100, ED50, and ED25 lg/ml DMSO). The
amount of DMSO was adjusted to give a final concen-
tration of 0.1%. Ascites fluid was obtained from the
peritoneal cavity of the donor animal from (National
Cancer Institute, Cairo, Egypt) contain Ehrlich cell was as
aseptically aspirated. The cells were grown partially
floating and attach in a suspension culture (RPMI 1660
medium, Sigma Chemical Co. St. Louis, USA), supple-
mented with 10% foetal bovine serum (GIBCO, UK).
They were maintained at 37°C in humidified atmosphere
with 5% CO2 for 2 h. The viability of the cell used in
control experiments (DMSO only without drug) exceeded
95% as determined by microscopically examination using
a hemocytometer and trypan blue stain (stain only the
dead cells).
Yellow powder; 68% yield, mp 212°C. Analysis: Calcd. for
C23H19NO6S2 (469.53): C, 58.83; H, 4.08; N, 2.98; Found
C, 58.87; H, 4.11; N, 3.07. IR (cm-1) (KBr): 2535 (SH),
1725, 1668 (3CO), 1606 (C=N). MS (m/z) (I%): 435.6
(M?–H2S, 0.45), 356 (0.6), 303 (2.85), 249 (4.82), 173
(48.72), 122 (77.93), 108 (100), 88 (62.29). 1H NMR
(DMSO-d6) d: 2.38 (s, 3H, CH3), 3.95 (s, 3H, OCH3), 4.30
(s, 2H, CH2), 5.35 (br, s, 1H, NH), 7.16–8.18 (m, 8H, Ar–
H), 8.40 (s, 1H, C4–H), 9.75 (s, 1H, SH).
2-(Benzo[d]thiazol-2-yl)-3-mercapto-3-(2-oxo-2-(2-oxo-
2H-chromen-3-yl)ethylthio) acrylonitrile (19b)
Orange powder; 73% yield, mp 233–235°C. Analysis:
Calcd. for C21H12N2O3S3 (436.53): C, 57.78; H, 2.77; N,
6.42; Found C, 57.84; H, 2.84; N, 6.52. IR (cm-1) (KBr):
2520 (SH), 2120 (CN), 1731, 1668 (2CO), 1606 (C=N).
MS (m/z) (I%): 434 (M?–2H, 0.14), 324 (2.41), 282 (1.73),
220 (25.28), 173 (100), 146 (13.57), 89 (30.16), 76 (24.25).
1H NMR (DMSO-d6) d: 2.47 (s, 2H, CH2), 7.19–7.93 (m,
8H, Ar–H), 8.45 (s, 1H, C4–H, coumarin), 9.03 (br, s, 1H,
SH).
Antioxidant assay
Antioxidant activity determinations were evaluated from
the bleaching of ABTS derived radical cations. The radical
cation was derived from ABTS [2,20-azino-bis (3-ethyl
benzothiazoline-6-sulfonic acid)] was prepared by reaction
of ABTS (60 ll) with MnO2 (3 ml, 25 mg/ml) in (5 ml)
aqueous buffer solution (pH 7). After shaking the solution
for a few minutes, it was centrifuged and filtered.
3-(3-Amino-4-(benzo[d]thiazol-2-yl)-5-
mercaptothiophene-2-carbonyl)-2H-chromen-2-one (20)
The Absorbance (A control) of the resulting green–blue
solution (ABTS radical solution) was recorded at kmax
734 nm. The absorbance (A test) was measured upon the
addition of (20 ll of 1 mg/ml) solution of the tested sample
in spectroscopic grade MeOH/buffer (1:1 v/v) to the ABTS
solution. The decrease in the absorbance is expressed as %
inhibition which calculated from the Eq. 1.
A suspension of 19b (0.44 g, 1 mmol) in DMF (15 ml)
catalyzed by TEA (0.5 ml) was refluxed for 5 h. The
reaction mixture was left to cool at room temperature,
poured into ice-cold water and treated with conc. HCl. The
produced precipitate was filtered off, dried, and crystallized
from benzene/EtOH (1:2) to afford 20.
123

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Med Chem Res (2012) 21:1062–1070
Khalil AM, Berghot MA, Gouda MA (2009a) Synthesis and
antibacterial activity of some new thiazole and thiophene
derivatives. Eur J Med Chem 44:4434–4440. doi:10.1016/j.
ejmech.2009.06.002
% Inhibition ¼ ½A ðcontrolÞ ꢁ A ðtestÞ= A ðcontrolÞꢂ
ꢃ 100
ð1Þ
Ascorbic acid (20 ll, 2 mM) solution was used as
standard antioxidant (positive control). Blank sample was
run using solvent without ABTS (Table 2).
Khalil AM, Berghot MA, Gouda MA (2009b) Synthesis and
antibacterial activity of some new heterocycles incorporating
phthalazine. Eur J Med Chem 44:4448–4454. doi:10.1016/j.
ejmech.2009.06.003
Khalil AM, Berghot MA, Gouda MA, Abd El-Ghani GE (2010a)
Synthesis and antimicrobial evaluation of some new thiophene
derivatives. Synthetic Commun 40:1658–1669. doi:10.1080/
00397910903161652
Khalil AM, Berghot MA, Gouda MA, Shoeib AI (2010b) Synthesis and
antimicrobial of certain new thiazolidinone, thiazoline, and thio-
phene derivatives. Phosphorus Sulfur Silicon 185:1455–1462. doi:
10.1080/10426500903074858
Acknowledgments The authors thank Dr. Serry A.A. El Bialy for
carrying out the microbiology screening, Department of Pharmaceu-
tical Organic Chemistry, Faculty of Pharmacy, Mansoura University,
Mansoura 35516, Egypt.
References
Koelsch CF (1950) Bromination of 3-Acetocoumarin. J Am Chem
Soc 72(7):2993–2995. doi:10.1021/ja01163a053
Abu-Hashem AA, Gouda MA, Badria FA (2010) Synthesis of some
new pyrimido[20,10:2,3]thiazolo[4,5-b]quinoxaline derivatives as
anti-inflammatory and analgesic agents. Eur J Med Chem
45:1976–1981. doi:10.1016/j.ejmech.2010.01.042
Anderson DM, Shelley S, Crick N, Buraglio M (2002) No effect of
the novel antidiabetic agent nateglinide on the pharmacokinetics
and anticoagulant properties of warfarin in healthy volunteers.
Lafitte D, Lamour V, Tsvetkov PO, Makarov AA, Klich M, Deprez P,
Moras D, Briand C, Gilli R (2002) DNA gyrase interaction with
coumarin-based inhibitors: the role of the hydroxybenzoate
isopentenyl moiety and the 50-methyl group of the noviose.
Biochemistry Biochem 41: 7217–7223. http://www.ncbi.nlm.
nih.gov/pubmed/12044152
Lissi EA, Modak B, Torres R, Escobar J, Urzua A (1999) Total
antioxidant potential of resinous exudates from Heliotropium
species, and a comparison of the ABTS and DPPH methods. Free
Rad Res 30:471–477
J Clin Pharmacol 42: 1358–1365. http://jcp.sagepub.com/
content/42/12/1358.full.pdf?html
Augustin M, Doelling W (1982) Reaction of phenylisothiocyanate
with a-hetaryl nitriles and ketones. J Prakt Chem 324:322–328
Dawood KM, Kandeel ZE, Farag AM (1998) J Chem Res Synop
4:208–209
Dieter RK (1986) a-Oxo ketene dithioacetals and related compounds:
versatile three-carbon synthons. Tetrahedron 42:3029–3096. doi:
10.1016/S0040-4020(01)87376-2
El-Desoky SI, Etman HA, Bondock SB, Fadda AA, Metwally MA
(2002) Utility of isothiocyanates in heterocyclic synthesis. Sulfur
Lett 25:199–205. doi:10.1080/02786110214496
Gorobets NY, Yousefi BH, Belaj F, Kappe CO (2004) Rapid
microwave-assisted solution phase synthesis of substituted
2-pyridone libraries. Tetrahedron 60:8633–8644. doi:10.1016/j.
tet.2004.05.100
Gouda MA, Berghot MA, Abd El-Ghani GE, Khalil AM (2010)
Synthesis and antimicrobial activities of some new thiazole and
pyrazole derivatives based on 4,5,6,7-tetrahydrobenzothiophene
moiety. Eur J Med Chem 45:1338–1345. doi:10.1016/j.ejmech.
2009.12.020
Gu¨rsoy A, Karali N (2003) Synthesis, characterization and primary
antituberculosis activity evaluation of 4-(3-coumarinyl)-3-ben-
zyl-4-thiazolin-2-one Benzylidenehydrazones. Turk J Chem 27:
545–552. http://mistug.tubitak.gov.tr/bdyim/toc.php?dergi=kim
&yilsayi=2003/5
Habib NS, Khali MA (1984) Synthesis and antimicrobial activity of
novel quinazolone derivatives. J Pharm Sci 73:982–985. doi:
10.1002/jps.2600730731
Hauser CR, Reynolds GA (1948) Reactions of b-keto esters with
aromatic amines: syntheses of 2- and 4-hydroxyquinoline
derivatives. J Am Chem Soc 70:2402–2404. doi:10.1021/ja01
187a025
Mitscher LA (2002) Principles of medicinal chemistry. In: Foye WO,
Lemke TL, Williams DA 5th edn. Williams and Wilkins,
Baltimore, pp 819–864
Mukerjee AK, Ashare R (1991) Isothiocyanates in the chemistry of
heterocycles. Chem Rev 91(1):1–24. doi:10.1021/cr00001a001
Nofal ZM, Fahmy HH, Mohamed HS (2002) Synthesis and antimi-
crobial activity of new substituted anilinobenzimidazoles. Arch
Pharmacal Res 25(3):250–257. doi:10.1007/BF02976622
Rinehart KL Jr, Forbis RM (1970) Nybomycin. IV. Total synthesis of
deoxynybomycin. J Am Chem Soc 92(23):6995–6996. doi:
10.1021/ja00726a061
Russo F, Romeo G, Santagati NA, Caruso A, Cutuli V, Amore D
(1994) Synthesis of new thienopyrimidobenzothiazoles and
thienopyrimidobenzoxazoles with analgesic and antiinflamma-
tory properties. Eur J Med Chem 29:569–578. doi:10.1016/
0223-5234(94)90149-X
Siddiqui N, Arshad MF, Khan SA (2009) Synthesis of some new
coumarin incorporated thiazolyl semicarbazones as anticonvul-
sants. Acta Pol Pharm 66(2):161–167
Stone WB, Okoniewski JC, Stedelin JR (1999) Poisoning of wildlife
with anticoagulant rodenticides in New York. J Wildl Dis 35:
187–193. http://www.jwildlifedis.org/cgi/reprint/35/2/187
Tassies D, Freire C, Pijoan J, Maragall S, Monteagudo J, Ordinas A,
Reverter JC (2002) Pharmacogenetics of acenocoumarol: cyto-
chromeP450CYP2C9polymorphisms influencedoserequirements
and stability of anticoagulation. Haematologica 87: 1185–1191.
http://www.haematologica.org/cgi/reprint/87/11/1185
Weber US, Steffen B, Siegers C (1998) Antitumor activities of
coumarin, 7-hydroxy-coumarin and its glucuronide in several
human tumor cell lines. Res Commun Mol Pathol Pharmacol
99:193–206
Junjappa H, Ila H, Asokan CV (1990) a-Oxoketene-S,S-, N,S- and
N,N-acetals: versatile intermediates in organic synthesis. Tetra-
hedron 46:5423–5506. doi:10.1016/S0040-4020(01)87748-6
Karrer K, Rubini JR (1965) On the fate of labelled ehrlich ascites
cells in mice, an autoradiographic study using H3 thymidine.
Medicina et Pharmacologia 13:124–130. doi:10.1159/000135602
Weick J, Thorn RS (2002) Effects of acute sublethal exposure to
coumaphos or diazinon on acquisition and discrimination of odor
stimuli in the honey bee (Hymenoptera: Apidae). J Econ
Entomol 95:227–236. doi:10.1603/0022-0493-95.2.227
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