Synthesis and antitumor activity of 6- and 2-(1-substituted-thio-4-methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-diones

Article abstract of DOI:10.1016/j.ejmech.2008.09.039

In an attempt to develop potent and selective antitumor agents, a series of 6- and 2-(1-substituted-thio-4-methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-diones were designed and synthesized. The cytotoxicities of these compounds were evaluated in vitro

Full text of DOI:10.1016/j.ejmech.2008.09.039

European Journal of Medicinal Chemistry 44 (2009) 1410–1414
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antitumor activity of 6- and 2-(1-substituted-thio-4-
methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-diones
,
,
Li-Ming Zhao a b, Tian-Pei Xie c, Yu-Qin He c, De-Feng Xu a, Shao-Shun Li a
*
a School of Pharmacy, Shanghai Jiaotong University, 800 Dongchuan Road, Shanghai 200240, China
b School of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou, Jiangsu 221116, China
c Shanghai Standard Biotech Co., Ltd., 1011 Halei Road, Shanghai 201203, China
a r t i c l e i n f o
a b s t r a c t
Article history:
In an attempt to develop potent and selective antitumor agents, a series of 6- and 2-(1-substituted-thio-
4-methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-diones were designed and synthesized. The
cytotoxicities of these compounds were evaluated in vitro against BEL-7402, HT-29 and SPC-A1 cell lines.
The pharmacological results showed that most of the prepared compounds displayed the excellent
selective cytotoxicity toward HT-29 cells. From the structure–activity relationships we may conclude that
the introduction of a thioether functional group at the 10-position in the side chain of shikonin is
associated with an increase in cytotoxicity.
Received 24 April 2008
Received in revised form
18 September 2008
Accepted 18 September 2008
Available online 7 October 2008
Keywords:
Shikonin derivatives
Synthesis
Ó 2008 Elsevier Masson SAS. All rights reserved.
Antitumor activity
Structure–activity relationship
1. Introduction
Thioether functional groups are known to contribute to the
enhancement of the antitumor activity [8,9]. Combining the
Many clinically successful anticancer drugs are either natural
products or have been developed from naturally occurring lead
compounds, such as taxol, topotecan, irinotecan and vinblastine.
Shikonin was isolated from the root of Lithospermum erythrorhizon.
Closely related derivatives have been attracting much attention in
view of their interesting antitumor activities [1–4]. A number of
shikonin derivatives have been prepared and studied as to their
tumor inhibitory potency. Most modifications to shikonin were
focused on the hydroxyl group of side chain. For instance, Ahn et al.
[5] and Plyta et al. [6] reported that acetylshikonin possessed more
potent topoisomerase I inhibitory activity than shikonin. Lu et al.
[7] synthesized a series of acylshikonin as antitumor agents and
concluded that suitable modification of the side chain of shikonin
would produce better telomerase inhibitors.
inherent antitumor activity of the shikonin and the functional group
in one structure was expected to produce more active compounds.
Many of the existing results indicate that the dimethylation of
naphthazarin ring will benefit the antitumor activities of quinones.
For example, 5,8-dimethoxy-1,4-naphthoquinone was found to be
less toxic and more active than naphthazarin ring [10,11]. So in
this study, we designed and synthesized a series of 6- and 2-
substituted-5,8-dimethoxy-1,4-naphthoquinone derivatives con-
taining sulfur including thiol esters and thioethers to screen their
antitumor activity against different cancer cell lines in vitro in order
to get more potent and selective agents.
2. Chemistry
However, the shikonin derivatives prepared in the past were
only some oxygen-containing acylshikonin derivatives. To this date
there have been no reports on the sulfur-containing acylshikonin
derivatives. To give a further insight into the antitumor activity, we
introduced sulfur atom in place of oxygen atom into side chain of
shikonin to synthesize sulfur-containing acylshikonin derivatives.
The preparation of target compounds is illustrated in Scheme 1.
1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-en-1-ol
2 was prepared using 1,4,5,8-tetramethoxynaphthalene-2-carbal-
dehyde 1 as starting material according to the procedure reported
by our group previously [12]. Refluxing compound 2 with thiourea
in ethanol in the presence of hydrobromic acid, followed by basic
hydrolysis and neutralization with hydrochloric acid, subsequently
formed thiol 3 [13].
* Corresponding author. School of Chemistry and Chemical Engineering, Xuzhou
Normal University, Xuzhou, Jiangsu 221116, China Tel.: þ86 21 34204775; fax: þ86
21 34204776.
Thereafter, alkylation of thiol 3 with various alkyl halides under
basic conditions gave substituted thioethers 4–6. The etherification
by using alkyl halide and potassium carbonate was first carried out
E-mail address: ssli@sjtu.edu.cn (S.-S. Li).
0223-5234/$ – see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.09.039

L.-M. Zhao et al. / European Journal of Medicinal Chemistry 44 (2009) 1410–1414
1411
Scheme 1. Reagents and conditions: (i) prenyl bromide/Zn/HMPA, 130 ꢀC, 10 h, N2; (ii) 48% HBr/thiourea/EtOH, reflux, 1 h, then hydrolyze with 40% NaOH, N2; (iii) RBr/NaOH/EtOH,
reflux, 4 h, N2; (iv) DCC/DMAP/CH2Cl2/, rt, 12 h; (v) CAN/CH3CN/H2O, rt, 0.5 h.
in anhydrous DMF [14], however, invariably low yields of ether are
obtained after refluxing for long periods. Nevertheless, the reaction
proceeded smoothly until consumption of the starting material
when using an ethanol/H2O (1:1) mixture as solvent in the pres-
ence of sodium hydroxide.
they were less potent than shikonin. It could be concluded that the
cytotoxicity of the tested compound against HT-29 was higher than
BEL-7402 and SPC-A1 cell lines, reflecting the excellent selectivity
for a particular human colorectal cancer cell type.
The cytotoxicities of the resulting shikonin derivatives appeared
to be related to the nature of the leaving group at the 10-position in
the side chain, which was in agreement with the cytotoxic mech-
anism reported [19]. It has been observed from Table 1 that most of
the shikonin derivatives with thioether moieties have higher
cytotoxicity than those with thiol ester groups. However, there
were some exception, such as 17a < 19a in SPC-A1 cell line. Among
15a–17b bearing thioether moieties, the IC50 of 15a and 15b against
Next, we turned our attention to the introduction of various
carboxylic acids to compound 3. Different experimental conditions
were examined, that is, dicyclohexylcarbodiimide (DCC)/4-dime-
thylaminopyridine (DMAP) activation [15], triphenylphosphine/N-
bromo succinimide activation [16] and direct condensation with
acid chloride/triethylamine. The attempt using the triphenylphos-
phine/NBS activation failed to give any product, possibly due to the
greater steric bulk of thiol and the intermediate triphenylphos-
phonium bromide preventing the nucleophilic attack. When
treating compound 3 with acid chloride in the presence of trie-
thylamine, the reaction occurred in very low yield. However, when
it was performed in anhydrous dichloromethane using DCC/DMAP
as the coupling agent, the coupling reaction occurred in very high
yield. So substituted thiol esters 7–14 were synthesized by acyl-
ating with various carboxylic acids in the presence of DCC and
DMAP at room temperature.
HT-29 is 8.4 mM and 6.9 mM, respectively, which is superior to
Table 1
Cytotoxicity of shikonin derivatives against BEL-7402, HT-29 and SPC-A1 cell lines
O
O
O
O
O
O
S
S
O
O
R
R
15b-25b
15a - 25a
Compounds
R
IC50
(m
M)
Finally, thioethers 4–6 were further transformed to
6-(1-(alkylthio)-4-methylpent-3-enyl)-5,8-dimethoxynaphthalene-
1,4-dione 15a and 2-(1-(alkylthio)-4-methylpent-3-enyl)-5,8-
dimethoxynaphthalene-1,4-dione 15b derivatives by oxidative
demethylation with cerium(IV) ammonium nitrate (CAN) [17].
Meanwhile, the methyl group elimination of thiol esters 7–14 was
accomplished using the same procedure and reagents as thioethers
4–6.
BEL-7402
HT-29
SPC-A1
15a
15b
16a
16b
17a
17b
18a
Ethyl
Ethyl
24.2
86.4
47.0
62.6
61.7
19.4
84.3
64.6
96.5
85.2
87.7
>100
80.5
55.8
59.8
8.4
6.9
19.5
18.2
42.2
24.4
>100
71.2
Propyl
Propyl
Pentyl
Pentyl
Acetyl
39.7
19.8
11.8
16.8
27.8
43.2
40.5
29.3
30.8
33.4
16.9
11.9
23.9
88.3
23.2
15.3
22.5
23.0
82.4
75.4
16.7
67.9
17.4
18b
19a
Acetyl
Propionyl
Propionyl
Butyryl
Butyryl
(E)-But-2-enoyl
(E)-But-2-enoyl
Isobutyryl
19.4
35.2
78.3
43.9
59.1
17.6
3. Results and discussion
19b
20a
20b
21a
21b
22a
22b
23a
23b
24a
24b
25a
25b
Shikonin
The in vitro cytotoxicities of the shikonin derivatives against
BEL-7402, HT-29 and SPC-A1 were evaluated by the standard MTT
assay [18] using shikonin as a positive control. Antitumor potency
of the compounds was indicated by IC50 values that were calculated
by linear regression analysis of the concentration–response curves
obtained for each compound. Data are reported in Table 1.
As shown in Table 1, while most of prepared compounds showed
potent inhibitory effects on HT-29 cell lines, and the potencies of
some compounds were better or comparative to the lead
compound shikonin, some compounds showed moderate cyto-
toxicity against BEL-7402 and SPC-A1 cancer cell lines, although
39.8
51.4
Isobutyryl
>100
97.9
4-Methylpent-3-enoyl
4-Methylpent-3-enoyl
Hexanoyl
Hexanoyl
2-Methoxybenzoyl
2-Methoxybenzoyl
>100
>100
93.8
89.4
93.2
>100
18.1
>100
>100
>100
>100
>100
54.5
Data represent the mean values of three independent determinations.

1412
L.-M. Zhao et al. / European Journal of Medicinal Chemistry 44 (2009) 1410–1414
shikonin (IC50 ¼ 16.7
m
M). Within the series 18a–25b bearing thiol
alkaline pH by careful addition of 40% NaOH (10 ml) under nitrogen
and heated to reflux for 2 h. The reaction mixture was cooled to
room temperature and acidified with 6 M hydrochloric acid and
then extracted with CH2Cl2 (3 ꢁ15 ml). The combined organic layer
was washed with brine, dried over Mg2SO4 and concentrated in
vacuo. The residual oil was purified by flash chromatography on
silica gel (diethylether:hexane ¼ 1:5) to give 1-(1,4,5,8-tetrame-
thoxynaphthalen-7-yl)-4-methylpent-3-ene-1-thiol 3 (0.79 g, 87%
ester moieties, the great majority of compounds displayed lower
activity than shikonin. The results indicated that the introduction of
thioether functional group at the 10-position in the side chain of
shikonin facilitates the increase of their cytotoxic activities, while
thiol ester functional group was unfavorable.
For HT-29 cell line, most of the prepared compounds showed
potent inhibitory activities with the IC50 values lower than 20
mM,
which were slightly lower than those of shikonin (IC50 ¼ 16.7
mM).
yield) as brown yellow oil. 1H NMR (CDCl3)
d: 7.01 (s, 1H), 6.81 (d,
While thiol esters with aliphatic acetic to butyric acid showed
a slightly decreased cytotoxic activity compared with shikonin,
thiol esters of aromatic acid faced considerable loss of cytotoxicity.
A similar tendency was observed against BEL-7402 and SPC-A1
cells. For example, compounds 18a–20b were approximately 2-fold
2H), 5.23 (t, J ¼ 7.2 Hz, 1H), 4.54 (t, J ¼ 7.2 Hz, 1H), 3.98 (s, 3H), 3.94
(s, 3H), 3.91 (s, 3H), 3.76 (s, 3H), 2.62 (m, 2H), 1.71 (s, 3H), 1.68 (s,
3H).
less active with the IC50 values of 27.8, 43.2, 40.5, 29.3, 30.8, 33.4
than lead compound shikonin (IC50 ¼ 16.7 M) against HT-29.
However, the aromatic thiol esters 25a and 25b were significantly
less potent with the IC50 values of greater than 75.4 M in all cell
lines. The data indicated that the introduction of aromatic thiol
esters in the side chain might result in the loss of cytotoxicity. Also,
the size of the ester chain and whether it was saturated could affect
the toxicity of target compounds. For instance, compound 21b
m
M
5.4. General procedure for preparation of alkyl(1-(1,4,5,8-
tetramethoxynaphthalen-7-yl)-4-methylpent-3-enyl)sulfanes (4–6)
m
m
To a solution of 1-(1,4,5,8-tetramethoxynaphthalen-7-yl)-4-
methylpent-3-ene-1-thiol 3 (0.50 mmol) in ethanol (10 ml) were
added alkyl halide (0.60 mmol) and KI (0.05 mmol), followed by
immediate addition of 40% aqueous NaOH (0.5 ml). The reaction
mixture was refluxed for 4 h under nitrogen atmosphere, and then
ethanol was removed under reduced pressure, extracted with
CH2Cl2, dried over Mg2SO4 and concentrated in vacuo. The residue
was purified by flash chromatography on silica gel to afford 4–6 as
light yellow oil.
containing double bond (IC50 ¼ 11.9
m
M) was approximately 3-fold
more cytotoxic than saturated compound 20b (IC50 ¼ 33.4
mM)
against the HT-29 cell line. Similarly, the hexanoyl derivative 24b
was significantly less potent than acetyl derivative 18b at killing
human liver cancer cell (IC50 > 100
mM vs IC50 ¼ 64.6
mM).
5.4.1. Ethyl(1-(1,4,5,8-tetramethoxynaphthalen-7-yl)-4-
4. Conclusion
methylpent-3-enyl)sulfane (4)
Yield 75%. 1H NMR (CDCl3)
d: 7.06 (s, 1H,), 6.83 (d, 2H), 5.14 (t,
In summary, we have designed and synthesized twenty-two
sulfur-containing shikonin derivatives, and evaluated their anti-
tumor activities against three cancer cell lines. Most of the prepared
compounds displayed the selective toxicity toward HT-29 cell line.
From the structure–activity relationships we may conclude that the
introduction of thioether functional group at the 10-position in the
side chain of shikonin is associated with enhanced cytotoxic
activity. This study may provide valuable information for further
designing more potent anticancer agents.
J ¼ 7.5 Hz, 1H), 4.66 (t, J ¼ 7.5 Hz, 1H), 3.95 (s, 3H), 3.93 (s, 3H), 3.90
(s, 3H), 3.72 (s, 3H), 2.58 (q, 2H), 2.35 (m, 2H), 1.61 (s, 3H), 1.57 (s,
3H), 1.13 (t, J ¼ 7.2 Hz, 3H).
5.4.2. Propyl(1-(1,4,5,8-tetramethoxynaphthalen-7-yl)-4-
methylpent-3-enyl)sulfane (5)
Yield 81%. 1H NMR (CDCl3)
d: 7.08 (s, 1H), 6.83 (d, 2H), 5.14 (t,
J ¼ 7.2 Hz, 1H), 4.63 (t, J ¼ 6.9 Hz, 1H), 3.95 (s, 3H), 3.93 (s, 3H), 3.91
(s, 3H), 3.72 (s, 3H), 2.58 (t, 2H), 2.31 (m, 2H), 1.61 (s, 3H), 1.56 (s,
3H), 1.47 (m, 2H), 0.86 (t, J ¼ 7.2 Hz, 3H).
5. Experimental protocols
5.4.3. Phenyl(1-(1,4,5,8-tetramethoxynaphthalen-7-yl)-4-
5.1. Chemistry
methylpent-3-enyl)sulfane (6)
Yield 82%. 1H NMR (CDCl3)
d: 7.08 (s, 1H), 6.84 (d, 2H), 5.16 (t,
Reagents and solvents were obtained from commercial
suppliers. Solvents were dried and purified using standard tech-
niques. All reactions involving air or moisture sensitive reagents or
intermediates were performed under nitrogen. 1H NMR spectra
were recorded on a Mercuryplus 300 spectrometer. Mass spectra
were recorded on a Shimadzu LCMS-2010EV mass spectrometer.
J ¼ 7.5 Hz, 1H), 4.64 (t, J ¼ 7.5 Hz, 1H), 3.97 (s, 3H), 3.94 (s, 3H), 3.92
(s, 3H), 3.73 (s, 3H), 2.59 (m, 2H), 2.35 (m, 2H), 1.63 (s, 3H), 1.57 (s,
3H), 1.48 (m, 2H), 1.22 (m, 4H), 0.82 (t, J ¼ 7.2 Hz, 3H).
5.5. General procedure for preparation of 1-(1,4,5,8-
tetramethoxynaphthalen-7-yl)-4-methylpent-3-enyl thioates (7–14)
5.2. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-en-
1-ol (2)
To a solution of 1-(1,4,5,8-tetramethoxynaphthalen-7-yl)-4-
methylpent-3-ene-1-thiol
3 (0.50 mmol) and carboxylic acid
1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-en-
1-ol 2 was obtained as recently described procedure [12].
(0.60 mmol) in CH2Cl2 (10 ml) were added DCC (0.75 mmol) and
DMAP (0.25 mmol). After stirring overnight at room temperature
under nitrogen atmosphere, the reaction mixture was filtered,
concentrated, redissolved in ether, filtered once more, and
concentrated in vacuo. The residual oil was purified by flash chro-
matography to afford 7–14 as light yellow oil.
5.3. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-ene-
1-thiol (3)
1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-en-
1-ol
2
(0.87 g, 0.025 mol), thiourea (0.38 g, 0.005 mol), 48%
5.5.1. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-
hydrobromic acid (0.56 ml) and ethanol (30 ml) were refluxed for
1 h. After cooling to room temperature, the reaction mixture was
concentrated. Ether (20 ml) and distilled water (20 ml) were
poured into the residue. The aqueous layer was then brought to
enyl ethanethioate (7)
Yield 94%. 1H NMR (CDCl3)
d
: 6.81 (m, 3H), 5.29 (t, J ¼ 7.2 Hz,1H),
5.05 (t, J ¼ 7.2 Hz, 1H), 3.92 (s, 6H), 3.88 (s, 3H), 3.78 (s, 3H), 2.69 (m,
2H), 2.31 (s, 3H), 1.59 (s, 6H).

L.-M. Zhao et al. / European Journal of Medicinal Chemistry 44 (2009) 1410–1414
1413
5.5.2. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-
1H), 4.51 (t, J ¼ 7.5 Hz, 1H), 3.95 (s, 3H), 3.79 (s, 3H), 2.53 (m, 2H),
2.39 (q, 2H), 1.69 (s, 3H), 1.54 (s, 3H), 1.20 (t, 3H). ESI-MS: 383.10
(M þ Na)þ.
enyl propanethioate (8)
Yield 92%. 1H NMR (CDCl3)
d
: 6.80 (m, 3H), 5.30 (t, J ¼ 7.2 Hz,1H),
5.05 (t, J ¼ 7.2 Hz,1H), 3.92 (s, 6H), 3.88 (s, 3H), 3.78 (s, 3H,), 2.70 (m,
Compound 15b. Yield 35%, red oil. 1H NMR (CDCl3)
d: 7.30 (s, 2H,
2H), 2.54 (q, J ¼ 7.2 Hz, 2H), 1.58 (s, 6H), 1.15 (t, J ¼ 7.2 Hz, 3H).
benzene ring H), 6.79 (s, 1H, quinone ring H), 5.10 (t, J ¼ 6.6 Hz, 1H),
4.18 (t, J ¼ 6.9 Hz, 1H), 3.95 (s, 6H), 2.60 (m, 2H), 2.48 (q, 2H), 1.64 (s,
3H), 1.57 (s, 3H), 1.20 (t, 3H).
5.5.3. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-
enyl butanethioate (9)
Yield 92%. 1H NMR (CDCl3)
d
: 6.82 (m, 3H), 5.32 (t, J ¼ 6.9 Hz,1H),
5.6.2. 6-(1-(Propylthio)-4-methylpent-3-enyl)-5,8-
5.07 (t, J ¼ 6.9 Hz,1H), 3.92 (s, 6H), 3.88 (s, 3H), 3.79 (s, 3H), 2.68 (m,
2H), 2.51 (t, J ¼ 7.2 Hz, 2H), 1.69 (q, J ¼ 7.2 Hz, 2H), 1.59 (s, 6H), 0.93
(t, J ¼ 7.2 Hz, 3H).
dimethoxynaphthalene-1,4-dione (16a) and 2-(1-(propylthio)-4-
methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-dione (16b)
Compound 16a. Yield 20%, yellow oil. 1H NMR (CDCl3)
d: 7.57 (s,
1H, benzene ring H), 6.78 (s, 2H, quinone ring H), 5.10 (t, J ¼ 7.5 Hz,
1H), 4.48 (t, J ¼ 6.9 Hz, 1H), 3.99 (s, 3H), 3.82 (s, 3H), 2.55 (t, 2H),
2.38 (m, 2H), 1.73 (m, 2H),1.64 (s, 3H), 1.54 (s, 3H), 0.92 (t, J ¼ 7.2 Hz,
3H).
5.5.4. (E)-1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-
3-enyl but-2-enethioate (10)
Yield 87%. 1H NMR (CDCl3)
d
: 6.91 (dd, J ¼ 15.5 Hz, J ¼ 6.9 Hz,
1H), 6.84 (s, 1H), 6.82 (s, 2H), 6.11 (dd, J ¼ 15.5 Hz, J ¼ 2.1 Hz, 1H),
5.38 (t, J ¼ 6.9 Hz, 1H), 5.07 (t, J ¼ 6.9 Hz, 1H), 3.92 (s, 6H), 3.88 (s,
3H), 3.79 (s, 3H), 2.72 (m, 2H), 1.85 (dd, J ¼ 6.9 Hz, J ¼ 2.1 Hz, 3H),
1.59 (s, 6H).
Compound 16b. Yield 41%, red oil. 1H NMR (CDCl3)
d: 7.30 (s, 2H,
benzene ring H), 6.79 (s, 1H, quinone ring H), 5.10 (t, J ¼ 7.2 Hz, 1H),
4.16 (t, J ¼ 7.2 Hz, 1H), 3.96 (s, 6H), 2.45 (m, 4H), 1.64 (s, 3H), 1.55 (s,
3H), 0.92 (t, J ¼ 7.2 Hz, 3H). ESI-MS: 397.10 (M þ Na)þ.
5.5.5. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-
5.6.3. 6-(1-(Pentylthio)-4-methylpent-3-enyl)-5,8-
enyl 2-methylpropanethioate (11)
dimethoxynaphthalene-1,4-dione (17a) and 2-(1-(pentylthio)-4-
methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-dione (17b)
Yield 90%. 1H NMR (CDCl3)
d
: 6.82 (m, 3H), 5.29 (t, J ¼ 6.9 Hz,1H),
5.07 (t, J ¼ 6.9 Hz, 1H), 3.93 (s, 6H), 3.89 (s, 3H), 3.76 (s, 3H), 2.70 (m,
Compound 17a. Yield 19%, yellow oil. 1H NMR (CDCl3)
d: 7.56 (s,
2H), 1.19 (d, J ¼ 6.6 Hz, 6H), 1.15 (d, J ¼ 6.6 Hz, 3H).
1H, benzene ring H), 6.78 (s, 2H, quinone ring H), 5.10 (t, J ¼ 7.5 Hz,
1H), 4.48 (t, J ¼ 7.5 Hz, 1H), 3.99 (s, 3H), 3.82 (s, 3H), 2.54 (t, 2H),
2.39 (m, 2H),1.64 (s, 3H), 1.54 (s, 3H),1.28 (m, 6H), 0.84 (t, J ¼ 7.2 Hz,
3H). ESI-MS: 417.05 (M þ Na)þ.
5.5.6. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-
enyl 4-methylpent-3-ene-thioate (12)
Yield 89%. 1H NMR (CDCl3)
d
: 6.81 (m, 3H), 5.28 (m, 2H), 5.05 (t,
Compound 17b. Yield 33%, red oil. 1H NMR (CDCl3)
d: 7.30 (s, 2H,
J ¼ 6.0 Hz, 1H), 3.92 (s, 6H), 3.88 (s, 3H), 3.80 (s, 3H), 3.23 (d,
benzene ring H), 6.79 (s, 1H, quinone ring H), 5.11 (t, J ¼ 6.9 Hz, 1H),
4.16 (t, J ¼ 7.2 Hz, 1H), 3.95 (s, 6H), 2.46 (m, 4H), 1.64 (s, 3H), 1.57 (s,
3H), 1.26 (m, 6H), 0.84 (t, J ¼ 7.2 Hz, 3H).
J ¼ 6.6 Hz, 2H), 2.68 (m, 2H), 1.73 (s, 3H), 1.63 (s, 3H), 1.59 (s, 6H).
5.5.7. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-
enyl hexanethioate (13)
5.7. General procedure for preparation of 1-(1,4-dihydro-5,8-
dimethoxy-1,4-dioxonaphthalen-6-yl)-4-methylpent-3-enyl
thioates (18a–25a) and 1-(1,4-dihydro-5,8-dimethoxy-1,4-
dioxonaphthalen-2-yl)-4-methylpent-3-enyl thioates (18b–25b)
Yield 88%. 1H NMR (CDCl3)
d
: 6.82 (m, 3H), 5.31 (t, J ¼ 7.2 Hz,1H),
5.07 (t, J ¼ 7.2 Hz, 1H), 3.93 (s, 6H), 3.89 (s, 3H), 3.79 (s, 3H), 2.68 (m,
2H, CH2), 2.52 (t, J ¼ 7.2 Hz, 2H), 1.61 (s, 6H), 1.32 (m, 6H), 0.90 (t,
J ¼ 7.2 Hz, 3H).
Compounds 18a–25a and 18b–25b were synthesized with the
same method used for the preparation of compounds 15a–17a and
15b–15b using 1-(1,4,5,8-tetramethoxynaphthalen-7-yl)-4-meth-
ylpent-3-enyl thioate 7–14 instead of alkyl(1-(1,4,5,8-tetrame-
thoxynaphthalen-7-yl)-4-methylpent-3-enyl)sulfane 4–6.
5.5.8. 1-(1,4,5,8-Tetramethoxynaphthalen-7-yl)-4-methylpent-3-
enyl 2-methoxybenzothioate (14)
Yield 94%. 1H NMR (CDCl3)
d: 7.76 (d, J ¼ 7.5 Hz, 1H), 7.44 (t,
J ¼ 7.5 Hz, 1H), 6.97 (t, J ¼ 7.5 Hz, 2H), 6.93 (s, 1H), 6.83 (s, 2H), 5.51
(t, J ¼ 6.6 Hz, 1H), 5.13 (t, J ¼ 6.3 Hz, 1H), 3.94 (s, 6H), 3.91 (s, 3H),
3.88 (s, 3H), 3.84 (s, 3H), 2.81 (m, 2H), 1.62 (s, 3H), 1.60 (s, 3H).
5.7.1. 1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-yl)-4-
methylpent-3-enyl ethanethioate (18a) and 1-(1,4-dihydro-5,8-
dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enyl
ethanethioate (18b)
5.6. General procedure for preparation of 6-(1-(alkylthio)-4-
methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-diones
(15a–17a) and 2-(1-(alkylthio)-4-methylpent-3-enyl)-5,8-
dimethoxynaphthalene-1,4-diones (15b–17b)
Compound 18a. Yield 35%, yellow oil. 1H NMR (CDCl3)
d: 7.30 (s,
1H, benzene ring H), 6.77 (s, 2H, quinone ring H), 5.03 (m, 2H), 3.96
(s, 3H), 3.90 (s, 3H), 2.61 (t, 2H), 2.31 (s, 3H), 1.63 (s, 3H), 1.55 (s, 3H).
ESI-MS: 397.05 (M þ Na)þ.
To a solution of alkyl(1-(1,4,5,8-tetramethoxynaphthalen-7-yl)-
4-methylpent-3-enyl)sulfane 4–6 (0.20 mmol) in acetonitrile
(3 ml) was added dropwise a solution of CAN (0.50 mmol) in water
(2 ml). The reaction mixture was stirred at room temperature for
10 min, then diluted with water and extracted with CH2Cl2, washed
with brine, dried over with Mg2SO4, and concentrated. The residual
oil was purified by preparative TLC to afford 15a–17a as yellow oil
and 15b–17b as red oil.
Compound 18b. Yield 30%, red oil. 1H NMR (CDCl3)
d: 7.28 (s, 2H,
benzene ring H), 6.75 (s, 1H, quinone ring H), 5.04 (t, J ¼ 7.2 Hz, 1H),
4.67 (t, J ¼ 7.2 Hz, 1H), 3.96 (s, 3H), 3.94 (s, 3H), 2.57 (m, 2H), 2.28 (s,
3H), 1.64 (s, 3H), 1.57 (s, 3H).
5.7.2. 1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-yl)-4-
methylpent-3-enyl propanethioate (19a) and 1-(1,4-dihydro-5,8-
dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enyl
propanethioate (19b)
5.6.1. 6-(1-(Ethylthio)-4-methylpent-3-enyl)-5,8-
dimethoxynaphthalene-1,4-dione (15a) and 2-(1-(ethylthio)-4-
methylpent-3-enyl)-5,8-dimethoxynaphthalene-1,4-dione (15b)
Compound 19a. Yield 36%, yellow oil. 1H NMR (CDCl3)
d: 7.31 (s,
1H, benzene ring H), 6.78 (s, 2H, quinone ring H), 5.05 (m, 2H), 3.96
(s, 3H), 3.91 (s, 3H), 2.59 (m, 4H), 1.64 (s, 3H), 1.55 (s, 3H), 1.15 (t,
J ¼ 7.2 Hz, 3H). ESI-MS: 411.10 (M þ Na)þ.
Compound 15a. Yield 18%, yellow oil. 1H NMR (CDCl3)
d: 7.54 (s,
1H, benzene ring H), 6.77 (s, 2H, quinone ring H), 5.08 (t, J ¼ 6.0 Hz,

1414
L.-M. Zhao et al. / European Journal of Medicinal Chemistry 44 (2009) 1410–1414
Compound 19b. Yield 28%, red oil. 1H NMR (CDCl3)
d
: 7.29 (s, 2H,
5.7.7. 1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-yl)-4-
methylpent-3-enyl hexanethioate (24a) and 1-(1,4-dihydro-5,8-
dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enyl
hexanethioate (24b)
benzene ring H), 6.75 (s, 1H, quinone ring H), 5.04 (t, J ¼ 7.2 Hz, 1H),
4.69 (t, J ¼ 7.2 Hz, 1H), 3.95 (s, 3H), 3.94 (s, 3H), 2.53 (m, 4H), 1.63 (s,
3H), 1.57 (s, 3H), 1.13 (t, J ¼ 7.2 Hz, 3H).
Compound 24a. Yield 39%, yellow oil. 1H NMR (CDCl3)
d: 7.31 (s,
5.7.3. 1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-yl)-4-
methylpent-3-enyl butanethioate (20a) and 1-(1,4-dihydro-5,8-
dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enyl
butanethioate (20b)
1H, benzene ring H), 6.77 (s, 2H, quinone ring H), 5.05 (m, 2H), 3.96
(s, 3H), 3.91 (s, 3H), 2.60 (m, 2H), 2.52 (t, J ¼ 7.2 Hz, 2H), 1.64 (s, 3H),
1.55 (s, 3H), 1.31 (m, 6H), 0.89 (t, J ¼ 7.2 Hz, 3H). ESI-MS: 453.10
(M þ Na)þ.
Compound 20a. Yield 37%, yellow oil.1HNMR (CDCl3)
d: 7.31 (s,1H,
Compound 24b. Yield 23%, red oil. 1H NMR (CDCl3)
d: 7.30 (s, 2H,
benzene ring H), 6.77 (s, 2H, quinone ring H), 5.06 (m, 2H), 3.95 (s,
3H), 3.90(s, 3H), 2.60(m, 2H), 2.51 (t, J ¼ 6.6 Hz, 2H), 2.60(m, 2H),1.67
(m, 5H),1.54 (s, 3H), 0.92 (t, J ¼ 7.2 Hz, 3H). ESI-MS: 425.05 (M þ Na)þ.
benzene ring H), 6.75 (s, 1H, quinone ring H), 5.04 (t, J ¼ 7.5 Hz, 1H),
4.68 (t, J ¼ 7.5 Hz, 1H), 3.95 (s, 3H), 3.94 (s, 3H), 2.55 (m, 2H), 2.48 (t,
J ¼ 7.2 Hz, 2H), 1.64 (s, 3H), 1.56 (s, 3H), 1.26 (m, 6H), 0.86 (t,
J ¼ 7.2 Hz, 3H).
Compound 20b. Yield 28%, red oil. 1H NMR (CDCl3)
d: 7.29 (s, 2H,
benzene ring H), 6.75 (s, 1H, quinone ring H), 5.04 (t, J ¼ 7.5 Hz, 1H),
4.69 (t, J ¼ 7.2 Hz, 1H), 3.95 (s, 3H), 3.94 (s, 3H), 2.50 (m, 2H), 2.47 (t,
J ¼ 6.9 Hz, 2H), 1.65 (m, 5H), 1.56 (s, 3H), 0.90 (t, J ¼ 7.5 Hz, 3H).
5.7.8. 1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-yl)-4-
methylpent-3-enyl 2-methoxybenzothioate (25a) and 1-(1,4-
dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-
3-enyl 2-methoxybenzothioate (25b)
5.7.4. (2E)-1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-
yl)-4-methylpent-3-enyl but-2-enethioate (21a) and (2E)-1-(1,4-
dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-
3-enyl but-2-enethioate (21b)
Compound 25a. Yield 36%, yellow oil. 1H NMR (CDCl3)
d: 7.74 (d,
J ¼ 7.8 Hz, 1H), 7.46 (t, J ¼ 7.8 Hz, 1H), 7.43 (s, 1H, benzene ring H),
6.98 (t, J ¼ 7.8 Hz, 2H), 6.77 (s, 2H, quinone ring H), 5.25 (t,
J ¼ 7.2 Hz, 1H), 5.10 (t, J ¼ 7.2 Hz, 1H), 3.96 (s, 6H), 3.90 (s, 3H), 2.71
(m, 2H), 1.64 (s, 3H), 1.58 (s, 3H).
Compound 21a. Yield 43%, yellow oil. 1H NMR (CDCl3)
d: 7.34 (s,
1H, benzene ring H), 6.90 (dd, J ¼ 15.5 Hz, J ¼ 6.9 Hz, 1H), 6.77 (s,
2H, quinone ring H), 6.09 (dd, J ¼ 15.5 Hz, J ¼ 1.8 Hz, 1H), 5.13 (t,
J ¼ 7.2 Hz, 1H), 5.05 (t, J ¼ 7.2 Hz, 1H), 3.96 (s, 3H), 3.92 (s, 3H), 2.63
(m, 2H), 1.87 (dd, J ¼ 7.2 Hz, J ¼ 1.8 Hz, 3H), 1.63 (s, 3H), 1.55 (s, 3H).
ESI-MS: 423.05 (M þ Na)þ.
Compound 25b. Yield 27%, red oil. 1H NMR (CDCl3)
d: 7.74 (d,
J ¼ 7.5 Hz, 1H), 7.44 (t, J ¼ 7.5 Hz, 1H), 7.28 (s, 2H, benzene ring H),
6.95 (t, J ¼ 7.5 Hz, 2H), 6.87 (s, 1H, quinone ring H), 5.12 (t,
J ¼ 6.9 Hz, 1H), 4.90 (t, J ¼ 6.9 Hz, 1H), 3.95 (s, 3H), 3.93 (s, 3H), 3.90
(s, 3H), 2.67 (m, 2H), 1.64 (s, 3H), 1.59 (s, 3H). ESI-MS: 489.10
(M þ Na)þ.
Compound 21b. Yield 30%, red oil. 1H NMR (CDCl3)
d: 7.29 (s, 2H,
benzene ring H), 6.87 (dd, J ¼ 15.3 Hz, J ¼ 6.9 Hz, 1H), 6.77 (s, 1H,
quinone ring H), 6.06 (dd, J ¼ 15.3 Hz, J ¼ 1.8 Hz, 1H), 5.05 (t,
J ¼ 7.2 Hz, 1H), 4.74 (t, J ¼ 7.2 Hz, 1H), 3.94 (s, 3H), 3.93 (s, 3H), 2.61
(m, 2H), 1.84 (dd, J ¼ 7.2 Hz, J ¼ 1.8 Hz, 3H), 1.63 (s, 3H), 1.56 (s, 3H).
References
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5.7.5. 1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-yl)-4-
methylpent-3-enyl 2-methylpropanethioate (22a) and 1-(1,4-
dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-
3-enyl 2-methylpropanethioate (22b)
Compound 22a. Yield 39%, yellow oil. 1H NMR (CDCl3)
d: 7.32 (s,
1H, benzene ring H), 6.77 (s, 2H, quinone ring H), 5.05 (m, 2H), 3.96
(s, 3H), 3.91 (s, 3H), 2.72 (m, 1H), 2.60 (m, 2H), 1.63 (s, 3H), 1.55 (s,
3H), 1.18 (d, J ¼ 7.2 Hz, 3H), 1.15 (d, J ¼ 7.2 Hz, 3H).
Compound 22b. Yield 28%, red oil. 1H NMR (CDCl3)
d: 7.29 (s, 2H,
benzene ring H), 6.75 (s, 1H, quinone ring H), 5.04 (t, J ¼ 7.5 Hz, 1H),
4.67 (t, J ¼ 7.2 Hz, 1H), 3.95 (s, 3H), 3.94 (s, 3H), 2.68 (m, 1H), 2.56
(m, 2H), 1.63 (s, 3H), 1.56 (s, 3H), 1.15 (d, J ¼ 7.2 Hz, 3H), 1.13 (d,
J ¼ 7.2 Hz, 3H). ESI-MS: 425.05 (M þ Na)þ.
[8] W. Huang, M.Z. Liu, Y. Li, Y. Tan, G.F. Yang, Bioorg. Med. Chem. 15 (2007)
5191–5197.
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5.7.6. 1-(1,4-Dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-6-yl)-4-
methylpent-3-enyl 4-methylpent-3-enethioate (23a) and 1-(1,4-
dihydro-5,8-dimethoxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-
3-enyl 4-methylpent-3-enethioate (23b)
Compound 23a. Yield 36%, yellow oil. 1H NMR (CDCl3)
d: 7.30 (s,1H,
benzene ring H), 6.76 (s, 2H, quinone ring H), 5.23 (t, J ¼ 7.5 Hz, 1H),
5.03 (m, 2H), 3.95 (s, 3H), 3.89 (s, 3H), 3.21 (d, J ¼ 7.5 Hz, 2H), 2.60 (m,
2H), 1.74 (s, 3H), 1.63 (s, 6H), 1.54 (s, 3H). ESI-MS: 451.10 (M þ Na)þ.
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Compound 23b. Yield 27%, red oil. 1H NMR (CDCl3)
d: 7.29 (s, 2H,
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benzene ring H), 6.74 (s, 1H, quinone ring H), 5.23 (t, J ¼ 7.2 Hz, 1H),
5.03 (t, J ¼ 7.2 Hz, 1H), 4.66 (t, J ¼ 7.2 Hz, 1H), 3.95 (s, 3H), 3.94 (s,
3H), 3.18 (d, J ¼ 7.5 Hz, 2H), 2.56 (m, 2H), 1.73 (s, 3H), 1.62 (s, 6H),
1.56 (s, 3H).