Synthesis and cytotoxicity of Methyl-4,8-dihydrobenzo[1,2-b:5,4-b']dithiophene-4,8-dione derivatives

Article abstract of DOI:10.1016/S0968-0896(98)00241-7

2- and 3-Methyl-4,8-dihydrobenzo[1,2-b:5,4-b']dithiophene-4,8-dione and related derivatives were synthesized and evaluated in vitro by NCI against eight cancer types. Compounds 12-15 showed significant activity against melanoma, NCI-H23 non-small cell lung cancer, and MDA-MB-435 and MDA-N breast cancer cell lines; 2-hydroxymethyl-4,8-dihydrobenzo[1,2-b:5,4-b']dithiophene-4,8-dione (13) showed the highest activity against melanoma (mean log GI₅₀=-7.74) and the highest overall potency (mean log GI₅₀=-6.99). Copyright (C) 1999 Published by Elsevier Science Ltd.

Full text of DOI:10.1016/S0968-0896(98)00241-7

Bioorganic & Medicinal Chemistry 7 (1999) 1025±1031
Synthesis and Cytotoxicity of
Methyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione
Derivatives
Yu-Hua Chao,a,b Sheng-Chu Kuo,b,* Kelvin Ku,b I-Ping Chiu,b Chun-Hsiung Wu,b
Anthony Mauger,c Hui-Kang Wanga and Kuo-Hsiung Leea
aNatural Products Laboratory, Division of Medicinal Chemistry and Natural Products, School of Pharmacy CB#7360,
University of North Carolina, Chapel Hill, NC 27599-7360, USA
bGraduate Institute of Pharmaceutical Chemistry, China Medical College, Taichung 400, Taiwan
cDrug Synthesis and Chemistry Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
Received 6 July 1998; accepted 2 October 1998
AbstractÐ2- and 3-Methyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione and related derivatives were synthesized and evaluated
in vitro by NCI against eight cancer types. Compounds 12±15 showed signi®cant activity against melanoma, NCI-H23 non-small cell
lung cancer, and MDA-MB-435 and MDA-N breast cancer cell lines; 2-hydroxymethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-
4,8-dione (13) showed the highest activity against melanoma (mean log GI50= 7.74) and the highest overall potency (mean log
GI50= 6.99). # 1999 Published by Elsevier Science Ltd. All rights reserved.
Introduction
recrystallized from acetic acid to give pure product (8)
as yellow needles in 18% yield. Based on mass spectral
results [m/z (234, M+)] and elemental analysis data, the
molecular formula was determined as C11H6O2S.
However, there are three possible structures (8a, 8b,
and 8) for this compound.
We have previously described the synthesis and potent
antineoplastic activity of 4,8-dihydrobenzo[1,2-b:4,5-b0]-
dithiophene-4,8-dione derivatives (1,2),1,2 and 4,8-di-
hydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione (3)2 deri-
vatives. In this continuing structural modi®cation study,
we now report the synthesis and cytotoxic evaluation of
methyl and substituted methyl derivatives of the latter
compound class.
In the IR spectrum, we found two di€erent carbonyl
1
absorptions at 1640 and 1660 cm 1. In the H NMR
spectrum, a CH3 signal was found at 2.59 ppm, a singlet
was observed at 7.27 ppm, and AB type signals were
1
found at 7.57 and 7.68 ppm. In the H-1H COSY spec-
Synthesis of 2-methyl-4,8-dihydrobenzo[1,2-b:5,4-b0]-
dithiophene-4,8-dione (8) and its derivatives
trum, we observed allylic coupling between the 2-methyl
group and H-3. Accordingly, structure 8a was ruled out.
In the 13C NMR spectrum, we observed two di€erent
carbonyl signals at 173 and 176 ppm; therefore, the car-
bonyl groups are in di€erent chemical environments.
However, from the above data, we still could not
determine if the structure was 8b or 8, and designed
the following chemical transformation experiments.
This compound was oxidized with CrO3 in glacial
acetic acid to give the 2-carboxylic acid product 9,
which was decarboxylated with a suspension of active
copper in quinoline at 190±200 ꢀC to give a 52% yield
of compound 10.
The syntheses of 2-methyl-4,8-dihydrobenzo[1,2-b:5,4-
b0]dithio-phene-4,8-dione (8) derivatives are outlined in
Scheme 1. We used 3-methyl-2-thiophene carboxylic
acid (4) as a starting material. Oxidation of compound 4
to the diacid 5 was accomplished in 45% yield using
potassium permanganate in 15% NaOH. The cyclic
diacylation of 2-methylthiophene (7) using 6 and
AlCl3 a€orded the dione 8 accompanied by small
amounts of other materials. Compound 8 was passed
through a chromatographic column with benzene and
The spectral data (i.e, 1-D and 2-D NMR spectra, mass
spectrum, and elemental analysis) of compound 10 were
compared with data in a published paper,3 proving that
compound 10 is 4,8-dihydrobenzo[1,2-b:5,4-b0]dithio-
Key words: 4,8-Dihydrobenzo[1,2-b:4,5-b0]dithiophene-4,8-diones; 4,8-
dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-diones; antineoplastic activ-
ity; cytotoxicity; structural modi®cation.
*Corresponding author. Tel.: 919 966 1121; fax: 919 966 6919.
0968-0896/99/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(98)00241-7

1026
Y.-H. Chao et al. / Bioorg. Med. Chem. 7 (1999) 1025±1031
phene-4,8-dione. Therefore, 8 is the major product in the
cyclic diacylation reaction and its structure is 2-methyl-
4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione.
data, we con®rmed that this product is 3-methyl-4,8-
dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione (17). In
the presence of a catalytic amount of benzoyl peroxide
and a few drops of hydrobromic acid as an initiator,
compound 17 underwent free radical bromination with
1.5±1.8 equiv of N-bromosuccinimide to a€ord the 2-
Compound 8 is the key intermediate for the preparation
of other anthraquinone derivatives. Oxidation of com-
pound 8 with chromium trioxide in acetic anhydride
under mild conditions (5±10 ꢀC) a€orded the diacetate
intermediate 11. The crude intermediate 11 was hydro-
lyzed with dil H2SO4 to yield 4,8-dihydrobenzo[1,2-
b:5,4-b0]dithiophene-4,8-dione-2-carboxaldehyde (12)
with mp 202±203 ꢀC. Since the direct oxidation of 8
gave 9 only in very low (10%) yield, compound 12
was oxidized with silver nitrate in dioxane to give the
same 2-carboxylic acid (9). Reduction of compound 12
with sodium borohydride in CH3OH gave a 90% yield
of 2-hydroxymethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithio-
phene-4,8-dione (13). Treatment of 13 with acetyl
chloride or thionyl chloride yielded 2-acetoxymethyl-
4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione (14)
in a 92% yield and 2-chloromethyl-4,8-dihydrobenzo-
[1,2-b:5,4-b0]dithiophene-4,8-dione (15) in an 86% yield,
respectively.
1
(bromomethyl) analogue 18. In its H NMR spectrum,
in addition to a CH2 signal at 4.88 ppm, AB type signals
were found at 7.61 and 7.67 ppm, and a singlet was
observed at 7.71 ppm. The 13C NMR spectrum showed
a CH2 signal at 26.5 ppm and two carbonyl carbon sig-
nals at 174 and 175 ppm. The mass spectrum showed
two molecular ion peaks [m/z (312, M+)] and [m/z(314,
M++2)] in a 1:1 ratio, which is characteristic of mono-
bromine substitution, we thus concluded that this
product is 3-bromomethyl-4,8-dihydrobenzo[1,2-b:5,4-
b0]dithiophene-4,8-dione (18). Hydrolysis of compound
18 used silver nitrate in 70% acetone to give a 42% yield
of 3-hydroxymethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithio-
phene-4,8-dione (19).
Results and Discussion
Compounds 8±9, 12±15, 17, and 19 were submitted to
NCI for in vitro testing4±6 against 58 human tumor cell
lines derived from leukemia, small and non-small cell
lung cancers, colon cancer, CNS cancer, melanoma,
ovarian cancer, renal cancer, and breast cancer. All
compounds were active against all cell lines with mean
log GI50 values ranging from 5.18 (compound 9) to
6.99 (compound 13). (Activity is de®ned as
logGI50< 4 where GI50 is the molar concentration
causing 50% cell growth inhibition). Table 1 shows the
biological data in selected cell lines. COMPARE com-
putations4 were performed on all NCI screening data
from the test compounds, and all were negative (Pear-
son correlation coecients <0.6) against the NCI
``Standard Agent'' database. Therefore, these com-
pounds probably act by a mechanism di€ering from
those of the standard agents.
Synthesis of 3-methyl-4,8-dihydrobenzo[1,2-b:5,4-
b0]dithiophene-4,8-dione (17) and its derivatives
The synthesis of derivatives of 3-methyl-4,8-dihydro-
benzo[1,2-b:5,4-b0]dithiophene-4,8-dione (17) is outlined
in Scheme 2. The cyclic diacylation of 3-methylthio-
phene (16) with 6 and AlCl3 a€orded the dione 17 in a
16% yield. Based on mass spectral [m/z (234, M+)] and
elemental analysis data, the molecular formula was
1
determined as C11H6O2S. In its H NMR spectrum, in
addition to a CH3 signal found at 2.58 ppm, a singlet
was observed at 7.31 ppm, and AB type signals were
found at 7.60 and 7.64 ppm. The 13C NMR spectrum
showed a CH3 signal at 16 ppm and two carbonyl car-
bon signals at 174.5 and 175.8 ppm. From the above
The 2-carboxylic acid (9) was less active than either the
2-methyl (8) or 2-carboxaldehyde (12). The 3-methyl
(17) and 3-hydroxymethyl (19) compounds were less
active than the corresponding 2-substituted 8 and 13.
Compounds 13 (2-hydroxymethyl), 14 (2-acetoxymethyl),

Y.-H. Chao et al. / Bioorg. Med. Chem. 7 (1999) 1025±1031
1027
Scheme 1. Synthesis of 2-methyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione (8) and its derivatives.
and 15 (2-chloromethyl) displayed striking potency in
the melanoma cell panel with GI50 values < 8 in sev-
eral cell lines. 2-Hydroxymethyl-4,8-dihydrobenzo[1,2-
b:5,4-b0]dithiophene-4,8-dione (13) had the highest
activity over all cell lines with a mean log GI50 value less
than 6.99. This compound is the most promising can-
didate for further in vivo testing.
and br=broad. Mass spectra (MS) were measured with
HP 5995 GC±MS and JEOL JMS-Hx 110 spectro-
meters. Ultraviolet spectra were recorded on a Shi-
madzu UV-160A spectrophotometer. Elemental
analyses were performed by National Cheng Kung
University and National Chung Hsing University, Tai-
wan. Flash column chromatography was performed on
silica gel (mesh 25±150 mm). Precoated silica gel plates
(Kieselgel 60 F254 0.25 mm, Merck) were used for TLC
analysis.
Synthetic Methods
General experimental procedures
Thiophene-2,3-dicarboxylic acid (5). A stirred solution
of 3-methyl-2-thiophene carboxylic acid (4) (21.3 g,
150 mmol) in 15% NaOH (700 mL) was heated to 70±
80 ꢀC. Potassium permanganate (100 g) was added por-
tionwise over 3 h. Then the mixture was heated to re¯ux
for 3 h, allowed to cool and acidi®ed with excess HCl
(12 M) in an ice bath. The white precipitate was ®ltered,
then was recrystallized from water to give colorless
needles of 5 (mp 270±272 ꢀC) in a 45% yield. IR (KBr):
1700 (CˆO), 3400±3600 (OH) cm 1; 1H NMR (DMSO-
d6): d 7.38 (d, J=5.2 Hz, 1H, H-4), 7.79 (d, J=5.2 Hz,
1H, H-5); 13C NMR (DMSO-d6): d 130.1 (C-4), 130.9
All melting points were determined on a Yanaco MP-
500D apparatus and are uncorrected. IR spectra were
recorded on a Shimadzu IR-440 and Nicolet Impact 400
FT-IR spectrophotometers as KBr pellets. NMR spec-
tra were obtained on Bruker ARX-300 FT-NMR and
Varian VXR-300 FT-NMR spectrometers with tetra-
methylsilane (TMS) as an internal standard. The che-
mical shift values are expressed in d values (parts per
million). The following abbreviations are used: s=sing-
let, d=doublet, t=triplet, q=quartet, m=multiplet,

1028
Y.-H. Chao et al. / Bioorg. Med. Chem. 7 (1999) 1025±1031
Scheme 2. Synthesis of 3-methyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione (17) and its derivatives.
Table 1. Inhibition of in vitro cancer cell lines by compounds 8, 9, 12±15, 17, and 19
Cytotoxicity logGI50(M)a,b
Cell line
8
9
12
13
14
15
17
19
Melanoma
LOXIMVI
MALME-3M
M14
SK-MEL-2
SK-MEL-28
SK-MEL-5
UACC-257
UACC-62
6.89
6.80
6.80
6.44
6.71
6.82
6.74
6.72
5.87
7.57
6.79
7.43
6.74
6.77
7.00
6.78
6.75
<
<
8.00
<
<
<
8.00
<
<
8.00
5.97
6.55
6.25
5.76
5.83
6.24
5.83
5.79
5.50
5.61
6.11
5.83
5.56
6.50
5.91
5.79
<
8.00
5.75
5.68
5.71
5.77
5.70
5.76
7.48
8.00
7.50
8.00
8.00
7.64
7.26
7.42
8.00
7.17
8.00
7.74
7.26
6.79
7.98
8.00
6.93
7.67
7.92
6.74
6.76
<
<
Leukemia
HL-60(TB)
6.48
5.32
6.60
7.14
6.89
7.68
5.61
6.55
Non-small cell lung cancer
NCI-H23
NCI-H522
6.77
6.61
5.68
5.82
6.85
6.24
7.84
6.99
7.82
6.85
7.65
6.77
5.95
5.79
5.76
6.77
Ovarian cancer
OVCAR-3
OVCAR-8
6.28
6.39
4.81
5.37
6.68
6.77
6.74
6.97
6.68
6.79
6.76
6.69
5.77
5.55
5.79
5.61
Breast cancer
HS578T
MDA-MB-435
MDA-N
BT-549
6.38
6.75
6.77
±
5.58
5.76
5.73
6.75
7.73
7.70
±
6.74
7.76
7.75
6.80
7.75
7.73
6.63
7.73
7.74
5.74
6.67
6.53
±
5.72
5.74
5.84
5.76
±
±
±
±
Mean valuec
6.15
5.18
6.50
6.99
6.66
6.59
5.62
5.78
aData obtained from NCI's in vitro disease-oriented tumor cells screen.
bData are an average of at least two testings.
cMean value over all 58 cell lines tested.
(C-5), 136.9 (C-3), 137.3 (C-2), 162.7 C-3-CˆO), 165.3
(C-2-CˆO); MS m/z (relative intensity): 172 (M+, 32),
128 (55), 111 (100); UV lmax (MeOH) nm (log e): 256
(4.01).
dropwise to a stirred suspension of AlCl3 (14.6 g,
109 mmol) in dry 1,2-dichloroethane (50 mL) main-
tained at 4 ꢀC. The mixture was allowed to stir at 4 ꢀC
for 10 min and a solution of 2-methylthiophene (7)
(4.9 g, 50 mmol) in 1,2-dichloroethane (25 mL) was
slowly added. The yellow suspension stirred at room
temperature for 18 h and then was poured into ice and
HCl (50 mL, 2 M). CHCl3 (300 mL) was added and the
mixture was shaken vigorously. The layers were sepa-
rated and the aqueous layer was extracted with CHCl3.
The combined organic portions were washed with satu-
rated NaHCO3 and water, dried over anhydrous
MgSO4, and concentrated to dryness. The resulting yel-
low mixture was puri®ed by column chromatography
Thiophene-2,3-dicarbonyl chloride (6). A stirred suspen-
sion of thiophene-2,3-dicarboxylic acid (5) (8.6 g,
50 mmol) in thionyl chloride (20 mL) was maintained at
re¯ux for 1 h. The dark solution was cooled and the
excess thionyl chloride was removed under reduced
pressure. The residue was treated with two 10 mL por-
tions of dry benzene, followed by the evaporation of
each portion. The tan solid (6) was dried in vacuum for
1 h and used without further puri®cation.
(silica gel, benzene), and
a yellow fraction (Rf
2-Methyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-
dione (8). A solution of the acid chloride (6) obtained
above in dry 1,2-dichloroethane (50 mL) was added
value=0.29 in benzene) was collected. After evapora-
tion, the residue was recrystallized from acetic acid to
give yellow needles of 8 (mp 193±194 ꢀC) in an 18%

Y.-H. Chao et al. / Bioorg. Med. Chem. 7 (1999) 1025±1031
1029
1
yield. IR (KBr): 1600, 1630 (CˆO) cm
;
1H NMR
39.8 mmol). The mixture was stirred for 1 h, then ®ltered
to give red brown metal copper, washed with water and
dried in a desiccator.
(CD2Cl2): d 2.59 (s, 3H, C-2-CH3), 7.27 (s, 1H, H-3),
7.57 (d, J=5.1 Hz, 1H, H-5), 7.68 (d, J=5.1 Hz, 1H, H-
6); 13C NMR (CDCl3): d 16.1 (C-2-CH3), 124.9 (C-3),
126.7 (C-5), 133.2 (C-6), 142.4 (C-4a), 142.6 (C-3a),
143.2 (C-7a), 144.9 (C-8a), 150.1 (C-2), 172.9 (C-4),
176.9 (C-8); MS m/z (relative intensity): 234 (M+, 100),
177 (31); UV lmax (MeOH) nm (log e): 237 (4.31), 293
(4.21); Anal. calcd for C11H6O2S2: C, 56.39; H, 2.58.
Found: C, 56.30; H, 2.65.
2-Formyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-
dione (12). To a suspension of 2-methyl-4,8-dihydro-
benzo[1,2-b:5,4-b0]dithiophene-4,8-dione (8) (3.5 g,
15 mmol) in glacial acetic acid (50 mL) was added
dropwise concd H2SO4 (98%, 2 mL) and CrO3 (4.5 g,
45 mmo1) at 5±10 ꢀC. The mixture was stirred at below
10 ꢀC for 4 h. Then the mixture was poured into ice
water and was extracted with CHCl3. The organic layer
was washed with saturated NaHCO3 and water, dried
over anhydrous MgSO4 and concentrated under
reduced pressure to give crude intermediate 11. EtOH
(95%, 60 mL) and dil. H2SO4 (30%, 40 mL) were added
to 11, and the mixture was maintained at re¯ux for 1 h,
then cooled and poured into ice water. The mixture was
extracted with CHCl3. The organic layer was washed
with saturated NaHCO3 and water, dried, and con-
densed. The residue was puri®ed by column chromato-
graphy (silica gel, benzene) to give yellow 2-formyl-4,8-
dihydro-benzo[1,2-b:5,4-b0]dithiophene-4,8-dione (12)
(mp 202±203 ꢀC) in a 30% yield. IR (KBr): 1650, 1680
4,8-Dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione-2-
carboxylic acid (9). Method I: A suspension of com-
pound 8 (1.2 g, 5.1 mmol) and CrO3 (2 g) in glacial
acetic acid (15 mL) was re¯uxed for 3 h. The remainder
of the CrO3 (1.5 g) was added portionwise over a 5 min
period. The dark solution began to re¯ux vigorously.
Re¯ux was maintained for 4 h after the addition was
completed. The mixture was then poured into cool water.
The resulting precipitate was ®ltered, washed with water
and recrystallized from acetic acid to give yellow needles
of 9 (mp>350ꢀC) in a 10% yield. IR (KBr): 1650, 1660
(CˆO), 2400±3300 (OH) cm 1; H NMR (DMSO-d6): d
1
7.52 (d, J=5.0Hz, 1H, H-5), 7.80 (s, 1H, H-3), 8.14 (d,
J=5.0 Hz, 1H, H-6); 13C NMR (DMSO-d6): d 126.4Â2
(C-3, C-5), 129.6 (C-6), 141.8 (C-4a), 142.4 (C-3a), 143.6
(C-7a), 147.3 (C-8a), 158.0 (C-2), 161.7 (C-2-CˆO),
172.5 (C-4), 174.5 (C-8); MS m/z (relative intensity): 264
(M+, 100), 247 (51); UV lmax (MeOH) nm (log e): 253
(4.28), 293 (4.12); Anal. calcd for C11H4O4S2: C, 49.99;
H, 4.03. Found: C, 50.02; H, 3.88.
1
(CˆO) cm 1; H NMR (CDCl3): d 7.66 (d, J=5.1/Hz,
1H, H-5), 7.76 (d, J=5.1 Hz, 1H, H-6), 8.21 (s, 1H, H-
3), 10.04 (s, 1H, 2-CHO); 13C NMR (CDCl3): d 127.0
(C-3), 132.9 (C-5), 134.9 (C-6), 142.4 (C-4a), 143.0 (C-
3a), 144.6 (C-7a), 148.5 (C-8a), 150.0 (C-2), 172.9 (C-4),
174.9 (C-8), 182.9 (C-2-CˆO); MS m/z (relative inten-
sity): 248 (M+, 22), 247 (100), 219 (5); UV lmax (acet-
onitrile) nm (log e): 244 (4.82), 275 (4.38); Anal. calcd
for C11H4O3S2: C, 53.21; H, 1.62. Found: C, 52.99, H,
1.68.
Method II: To an aqueous solution of 1 mL of NaOH
(0.08 g, 2.0 mmol) was added 1 mL of silver nitrate
(0.14 g, 0.8 mmol) aqueous solution; this mixture was
stirred until a dark brown suspension appeared. Then a
solution of 12 (0.1 g, 0.4 mmol) in 1,4-dioxane (5 mL)
was added, and stirring continued for 30 min at room
temperature until a black metal silver sediment was
produced. The reaction mixture was ®ltered and washed
with hot water several times, then the ®ltrate was acid-
i®ed with concd HCl to form a yellow precipitate. The
precipitate was ®ltered, washed with water, and recrys-
tallized from acetic acid to give yellow needles of 9 (mp
>350 ꢀC) in a 47% yield. The spectral data have been
described above.
2-Hydromethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-
4,8-dione (13). To a suspension of compound 12 (1.2 g,
4.8 mmol) in CH3OH (200 mL) was added sodium bor-
ohydride (0.2 g, 5.2 mmol). The mixture was stirred for
2 h. After acidi®cation with 5% hydrochloric acid solu-
tion, the solution was extracted with CHCl3. The
organic layer was washed with water, dried, and con-
densed. The residue was puri®ed by column chromato-
graphy on silica gel eluting with CHCl3:CH3OH (10:1)
to give 13 as an orange solid (mp 183±184 ꢀC) in a 90%
yield. IR (KBr) 1050 (C-O), 1640 (CˆO), 3300±3500
(OH) cm 1; 1H NMR (DMSO-d6): d 4.76 (d, J=5.4 Hz,
2H, 2-CH2-), 5.99 (t, J=5.4 Hz, OH), 7.42 (s, 1H, H-3),
7.57 (d, J=5.1 Hz, 1H, H-5), 8.09 (d, J=5.1 Hz, 1H, H-
6); 13C NMR (DMSO-d6): d 58.5 (C-2-CH2-), 121.8 (C-
3), 126.3 (C-5), 135.5 (C-6), 141.9 (C-4a), 142.1 (C-3a),
142.3 (C-7a), 144.1 (C-8a), 158.0 (C-2), 172.7 (C-4),
175.6 (C-8); MS m/z (relative intensity): 250 (M+, 100),
221 (24); UV lmax (MeOH) nm (log e): 237 (4.28), 293
(4.18); Anal. calcd for C11H6O3S2: C, 52.79; H, 2.42.
Found: C, 52.79; H, 2.54.
4,8-Dihydrobenzo[1,2-b:5,4-b0]dithiophene-4,8-dione (10).
Compound 9 (0.06 g, 0.22 mmol) and active copper
(25 mg, 0.4 mmol) were added to a hot solution of quin-
oline (5 mL) at 190±200 ꢀC. The mixture was heated at
190±200 ꢀC for 2 h, then 5% HCl (5 mL) was added, and
the resulting mixture was extracted with CHCl3. The
organic layer was separated, washed with saturated
NaHCO3 and water, dried, and evaporated. The residue
was subjected to column chromatography (silica gel,
benzene) to give 10 as a yellow solid (mp 235±237 ꢀC) in
a 52% yield.
2-Acetoxymethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithio-
phene-4,8-dione (14). To a solution of compound 13
(0.3 g, 1.2 mmol) in 1,2-dichloroethane (30 mL) was
added dropwise acetyl chloride (0.2 g, 2.5 mmol). The
mixture was heated at re¯ux for 4 h, then the mixture
was cooled, poured into ice water, and extracted with
Preparation of active copper
To a 80 mL aqueous solution of cupric sulfate pentahy-
drate (10 g, 40.0 mmol) was added Zn powder (2.6 g,

1030
Y.-H. Chao et al. / Bioorg. Med. Chem. 7 (1999) 1025±1031
CHCl3. The organic layer was washed with saturated
NaHCO3 and water, dried, and evaporated. The residue
was puri®ed by column chromatography (silica gel,
CHCl3) to give 14 as a yellow solid (mp 140±141 ꢀC) in a
nm (log e): 245 (4.23), 281 (4.09); Anal. calcd for
C11H6O2S2: C, 56.39; H, 2.58. Found: C, 56.45; H, 2.50.
3-Bromomethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-
4,8-dione (18). To a solution of compound 17 (1.4 g,
6.0 mmol) and benzoyl peroxide (0.1 g, 0.4 mmol) in dry
benzene (30 mL) were added several drops of hydro-
bromic acid. The mixture was re¯uxed for 10 min, then
N-bromosuccinimide (1.2 g, 9.6 mmol) and benzoyl per-
oxide (0.2 g, 0.8 mmol) were added portionwise. Re¯ux
was then continued for 5 h. After ®ltration, the dry
benzene was removed in vacuum. The residue was pur-
i®ed by column chromatography on silica gel eluting
with n-hexane:benzene (1:5) to give 18 as a yellow solid
(mp 179±180 ꢀC) in a 37% yield. IR (KBr): 1650 (CˆO)
92 % yield. IR (KBr): 1240 (C-O), 1600, 1660, 1720
1
(CˆO) cm
;
1H NMR (CDCl3): d 2.11 (s, 3H,
COCH3), 5.25 (s, 2H, 2-CH2-), 7.49 (s, 1H, H-3), 7.55
(d, J=5.1 Hz, 1H, H-5), 7.65 (d, J=5.1 Hz, 1H, H-6);
13C NMR (CDCl3): d 20.6 (C-2-CH3), 60.2 (C-2-CH2-),
126.0 (C-3), 126.7 (C-5), 133.8 (C-6), 142.3 (C-4a), 142.4
(C-3a), 144.5 (C-7a), 144.7 (C-8a), 147.4 (C-2), 170.2 (C-
2-CˆO), 172.8 (C-4), 175.4 (C-8); MS m/z (relative
intensity): 292 (M+, 29), 250 (100), 221 (34); UV lmax
(MeOH) nm (log e ): 237 (4.30), 292 (4.17); Anal. calcd
for C13H8O4S2: C, 53.41; H, 2.76. Found: C, 53.20: H,
2.82.
1
cm 1; H NMR (CDCl3): d 4.89 (s, 2H, 3-CH2-), 7.63
(d, J=4.9 Hz, 1H, H-5), 7.69 (d, J=4.9 Hz, 1H, H-6),
7.73 (s, 1H, H-2); 13C NMR (CDCl3): d 26.5 (C-3-CH2-),
126.4 (C-5), 133.5 (C-2), 133.8 (C-6), 137.6 (C-3a), 140.1
(C-4a), 142.1Â2 (C-7a, C-8a), 148.2 (C-3), 174.3 (C-4),
175.2 (C-8); MS m/z (relative intensity): 314 (M++2,
9), 312 (M+, 9), 233 (100); UV lmax (MeOH) nm (log e):
239 (4.29), 291 (4.17); Anal. calcd for C11H5O2S2Br: C,
42.19; H, 1.61. Found: C, 42.30; H, 1,60.
2-Chloromethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophene-
4,8-dione (15). To a suspension of compound 13 (0.3 g,
1.2 mmol) in dry benzene (30/mL) was added thionyl
chloride (0.4 g, 3.4 mmol). The mixture was heated at
re¯ux for 1 h and the excess thionyl chloride was
removed under reduced pressure. The resulting yellow
mixture was puri®ed by column chromatography on
silica gel eluting with benzene:CHCl3 (10:1) to give 15
as a yellow solid (mp 165±166 ꢀC) in a 86% yield. IR
3-Hydroxymethyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithio-
phene-4,8-dione (19). To an aqueous solution of acet-
one (70%, 65 mL) and silver nitrate (1.4 g, 8.2 mmol)
was added compound 18 (0.6 g, 1.9 mmol). The mixture
was stirred for 2.5 h at 28±30 ꢀC. After ®ltration, the
®ltrate was extracted with diethyl ether. The organic
layer was dried, and evaporated. The residue was pur-
i®ed by column chromatography on silica gel eluting
with CHCl3:CH3OH (12:1) to give 19 as a yellow solid
(mp 139±140 ꢀC) in a 42% yield. IR (KBr): 1275 (C-O),
1650 (CˆO), 3200±3600 (OH) cm 1; 1H NMR (DMSO-
d6): d 5.54 (s, 1H, OH), 5.85 (s, 2H, 3-CH2-), 7.61 (d,
J=5.0 Hz, 1H, H-5), 8.14 (d, J=5.0 Hz, 1H, H-6), 8.24
(s, 1H, H-2); 13C NMR (DMSO-d6): d 68.5 (C-3-CH2-),
126.0 (C-5), 133.3 (C-2), 135.7 (C-6), 135.9Â2 (C-7a, C-
8a), 136.2 (C-4a), 138.2 (C-3a), 141.7 (C-3), 173.9 (C-4),
174.7 (C-8); MS m/z (relative intensity): 250 (M+, 100),
221 (40); UV lmax (MeOH) nm (log e): 237 (4.22), 290
(4.16); Anal. calcd for C11H6O3S2: C, 52.79: H, 2.42.
Found: C, 52.86; H, 2.30.
1
(KBr): 1650 (CˆO) cm 1; H NMR (CDCl3): d 4.77 (s,
2H, CH2), 7.55 (s, IH, H-3), 7.59 (d, J=5.1 Hz, 1H, H-
5), 7.67 (d, J=5.1 Hz, 1H, H-6); 13C NMR (CDCl3): d
39.5 (C-2-CH2-), 126.1 (C-3), 126.8 (C-5), 133.8 (C-6),
142.5Â2 (C-3a, C-4a), 144.5 (C-7a), 144.9 (C-8a), 149.2
(C-2), 172.8 (C-4), 175.5 (C-8); MS m/z (relative inten-
sity): 270 (M++2, 20), 268 (M+, 43), 233 (100); UV
lmax (MeOH) nm (log e): 242 (4.28), 293 (4.16); Anal.
calcd for C11H5O2S2Cl: C, 49.16; H, 1.88. Found: C,
48.98; H, 1.76.
3-Methyl-4,8-dihydrobenzo[1,2-b:5,4-b0]dithiophen-4,8-
dione (17). A solution of the acid chloride (6) obtained
above in dry 1,2-dichloroethane (50 mL) was added
dropwise to a stirred suspension of AlCl3 (14.6 g,
109 mmol) in dry 1,2-dichloroethane (50 mL) main-
tained at 4 ꢀC. The mixture was allowed to stir at 4 ꢀC
for 10 min and a solution of 3-methylthiophene (16)
(4.9 g, 50 mmol) in 1,2-dichloroethane (25 mL) was
slowly added. The yellow suspension was allowed to
stir at room temperature for 18 h and was poured into
ice and HCl (50 mL, 2 M). CHCl3 (300 mL) was added
and the mixture was shaken vigorously. The layers
were separated and the aqueous layer was extracted
with CHCl3. The combined organic portions were
washed with saturated NaHCO3 and water, dried over
anhydrous MgSO4, and concentrated to dryness. The
resulting yellow mixture was puri®ed by column chro-
matography (silica gel, benzene) to give the yellow solid
17 (mp 146±147 ꢀC) in a 16% yield. IR (KBr): 1660
Acknowledgements
This work was supported by grants from the National
Science Council of the Republic of China (S. C. K.) and
the U. S. National Cancer Institute, CA 17625 (K. H. L.).
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(CˆO) cm 1; H NMR (CDCl3): d 2.58 (s, 3H, C-3-
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Y.-H. Chao et al. / Bioorg. Med. Chem. 7 (1999) 1025±1031
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