Synthesis and biological evaluation of (±)-cryptotanshinone and its simplified analogues as potent CDC25 inhibitors

Article abstract of DOI:10.1016/j.tet.2004.12.033

(±)-Cryptotanshinone and its simplified analogues were synthesized via SmI₂ promoted radical cyclization to construct the furan ring. Analogues 18 and 26 were identified as effective inhibitors of dual specificity protein phosphatase CDC25B which is a key enzyme for cell cycle progression, and they also inhibited growth in A-549 human lung cancer cell line.

Full text of DOI:10.1016/j.tet.2004.12.033

Tetrahedron 61 (2005) 1863–1870
Synthesis and biological evaluation of (G)-cryptotanshinone and
its simplified analogues as potent CDC25 inhibitors
a
a,
Wei Gang Huang,a,b Ying Yan Jiang,a Qian Li,a Jia Li,a, Jing Ya Li, Wei Lu
*
*
and Jun Chao Caia,†
aDepartment of Medicinal Chemistry, Shanghai Institute of Materia Medica, SIBS, Chinese Academy of Sciences, 555, Zuchongzhi Road,
Zhangjiang High-Tech Park, Shanghai 201203, China
bGraduate School of the Chinese Academy of Sciences, Beijing, China
Received 16 August 2004; revised 3 December 2004; accepted 3 December 2004
Available online 22 December 2004
Abstract—(G)-Cryptotanshinone and its simplified analogues were synthesized via SmI2 promoted radical cyclization to construct the furan
ring. Analogues 18 and 26 were identified as effective inhibitors of dual specificity protein phosphatase CDC25B which is a key enzyme for
cell cycle progression, and they also inhibited growth in A-549 human lung cancer cell line.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
attractive drug target for cancer therapy. Over the last few
years, some small molecule CDC25 inhibitors have been
described in the literature.13–28 Some quinones, including
ortho-quinones, displayed inhibitory activity against
CDC25.
Quinones are biologically important compounds, especially
because of their cytotoxic activity and pharmacological
action. Many efficient antineoplastic drugs are quinones
(anthracyline derivatives, mitoxantrone, actinomycin),
quinonoid derivatives (quinolones, genistein, bactracyclin)
or drugs that can easily be converted to quinones by in vivo
oxidation (etoposide).1 The antitumor activities of the
quinones, including naphthoquinone, were revealed more
than three decades ago when the National Cancer Institute
published a report in which 1500 synthetic and natural
quinones were screened for their anticancer activities.2
Many 1,2-naphthoquinones were reported to be cytotoxic
against a number of tumor cell lines.3 Because of their
effectiveness in drug-resistant cells, these agents appear to
hold promise as effective chemotherapeutic agents.3
The rhizome of Salvia miltiorrhiza Bunge, also known as
‘Tanshen’ or ‘Danshen’, is an ancient drug in Chinese
traditional medicine,29 which has been used widely to treat
coronary heart disease, menstrual disorders, miscarriage,
hypertension, and viral hepatitis.30 There have been more
than 50 ortho-quinone diterpenes, called tanshinones,
isolated from Danshen. In our program of high-throughput
screening for CDC25 protein phosphatases inhibitors, the
tanshinones were chosen for evaluation. We found that (K)-
cryptotanshinone (Fig. 1) was a moderate inhibitor of
CDC25B phosphatase (IC50 10.98 mM). Cryptotanshinone
is a typical compound having ortho-quinone skeleton
among these tanshinones. Cryptotanshinone has been
reported to be an effective inhibitor of topoisomerase I31
and exhibit significant cytotoxicity against a number of
cultured human tumor cell lines.32
The dual specificity phosphatases (CDC25), play a pivotal
role in the regulation of the cell cycle by activating cyclin-
dependent kinases (CDK)4 and participating in Raf-1-
mediated cell signaling.5 Three CDC25 homologues exist
in human, CDC25A, CDC25B and CDC25C.4,6–8 Over-
expression of CDC25A and B was observed in a variety of
cancers with a striking association with tumor aggressive-
ness and poor prognosis,9–12 which making CDC25 an
Although there have been many synthetic studies of the
tanshinones,33–39 these synthetic routes are not convenient
for us to further modify these compounds because of the
unavailable materials and harsh reactions. In order to further
study the biological activities of the tanshinonnes, we have
developed a facile strategy to prepare (G)-cryptotanshinone
11 via a SmI2 promoted radical cyclization reaction.40 Using
this strategy, we synthesized new simplified analogues of
Keywords: CDC25 Inhibitor; Cryptotanshinone; Analogues; Antitumor.
* Corresponding author. Tel.: C86 21 50806035; fax: C86 21 50806035;
e-mail: luwei@mail.shcnc.ac.cn
† Prof. Cai J. C. deceased on Sept 10, 2004.
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.12.033

1864
W. G. Huang et al. / Tetrahedron 61 (2005) 1863–1870
Figure 1.
(G)-cryptotanshinone 11 to investigate the structure–
activity relationship as CDC25 inhibitors. The simplified
analogues 18 and 26 demonstrated powerful inhibitory
activity against protein phosphatase CDC25B and cytotoxic
activity against A-549 tumor cell lines.
was treated with NaH and diethyl phosphorochloridate in
dry THF to give aryl diethyl phosphates 2. In the presence of
NiCl2(dppp), compound 3 was obtained via cross-coupling
of 2 with Grignard reagent derived from 1-bromo-4-
methylpent-3-ene.42 Then, cyclization of 3 to 4 proceeded
in excellent yield upon exposure AlCl3 in CH2Cl2 at 0 8C for
30 min39 to finish the building of A ring (Scheme 1).
2. Results and discussion
Then, we built the naphthofuran (D ring) through the SmI2-
initiated radical cyclization reaction.43 The treatment of 4
with BBr3 at 0 8C provided the naphthol 5 in 95%.44
Bromine diluted with carbon tetrachloride was added
dropwise to 5 in carbon tetrachloride at the condition of
Cryptotanshinone is tetracyclic compound, and its B and C
rings are basic naphthalene structure. We use the accessible
5-methoxy-naphthalen-1-ol 141 as starting material. Firstly,
we constructed the A ring of cryptotanshinone. Compound 1
Scheme 1. Reagents and conditions: (a) ClP(O)(OEt)2, NaH, THF; (b) C6H11MgBr, cat. NiCl2 (dppp), Et2O; (c) AlCl3, CH2Cl2, 0 8C; (d) BBr3, CH2Cl2, 0 8C;
(e) Br2, CCl4; (f) allyl bromide, K2CO3, acetone; (g) SmI2, HMPA, THF; (h) HNO3, AcOH, 0 8C; (i) H2, Pd/C, EtOH; (j) Fremy’s salt, 0.06 M NaH2PO4.

W. G. Huang et al. / Tetrahedron 61 (2005) 1863–1870
1865
Scheme 2. Reagents and conditions: (a) Br2, CCl4, 24 h; (b) allyl bromide, K2CO3, acetone; (c) SmI2, HMPA, THF; (d) HNO3, AcOH; (e) H2, Pd/C, EtOH;
(f) Fremy’s salt, 0.06 M NaH2PO4.
ice-water bath to afford 6.41 The desired product 6 was
treated with allyl bromide and K2CO3 to yield allyl ether 7
as colorless oil.45 Conversion of 7 into naphthofuran
compound 8 via SmI2-promoted intramolecular cyclization
was executed in good yield.43
cryptotanshinone without the A ring, was prepared in six
steps with a similar procedure, using 1-naphthol as the
starting material (Scheme 2).
The analogue 26, which possesses a hydroxy group instead
of A ring was synthesized, as shown in Scheme 3. The
intermediate 19 was prepared in four steps in high yield
according to the literature method.48 The reduction of 19
with Na2S2O4 afforded the unstable naphthol 20. Compound
20 was dissolved in acetone immediately, and treated with
allyl bromide and potassium carbonate to give 21. The
protection of another hydroxy group of 21 with a benzyl
group afforded 22 in 51% yield (from 19). The dihydro-
naphthofuran was constructed using a similar procedure as
described above. The catalytic hydrogenation of 23 and the
following oxidation of 24 with AgNO3 in absolute ethanol
After constructing of A and D rings, we need to build ortho-
quinone group to finish our synthesis of (G)-crypto-
tanshinone. By using mild aromatic nitration condition, 8
was smoothly converted into the nitrated derivative 9, which
was catalytically reduced to amine 10.46 Without further
purification, compound 10 was oxidized directly with
Fremy’s salt to give (G)-cryptotanshinone 11 as an orange
needles.47
Compound 18,
a
simplified analogue of (G)-
Scheme 3. Reagents and conditions: (a) Na2S2O4, Et2O/H2O; (b) allyl bromide, K2CO3, acetone; (c) BnBr, K2CO3, acetone; (d) SmI2, HMPA, THF; (e) H2,
Pd/C, EtOAc; (f) AgNO3, absolute EtOH; (g) AlCl3, CH2Cl2.

1866
W. G. Huang et al. / Tetrahedron 61 (2005) 1863–1870
Table 1. CDC25B inhibitory activities of cryptotanshinones and analogues
Compound
(K)-Cryptotanshinone
10.98G1.16
(G)-Cryptotanshinone 11
20.63G1.29
18
25
26
IC50 (mM)
4.96G0.22
O81.89
3.21G0.76
Table 2. Cytotoxic activity against A-549 tumor cell line of cryptotanshinones and analogues
Compound
(K)-Cryptotanshinone
(G)-Cryptotanshinone 11
18
25
26
IC50 (mM)
6.39
8.23
3.65
9.46
2.07
yielded the desired product 25 as orange solid. Compound
26 was prepared by the treatment of 25 with AlCl3 in
CH2Cl2.
4. Experimental
4.1. General
Melting points were taken on Buchi510 apparatus and were
Cryptotanshinones and its analogues were evaluated
for their CDC25B inhibitory activity (Table 1). Natural
(K)-cryptotanshinone, our synthetic (G)-cryptotanshinone
(11) and its analogues 18 and 26 inhibited CDC25B in vitro
with IC50 values from 3.21 to 20.63 mM. Interestingly,
(K)-cryptotanshinone showed a CDC25B inhibitory
activity 2-fold higher than its racemate (11), which proved
that the stereochemistry of the C-3 in furan ring played an
important role in the activity against CDC25B phosphatase.
The absence of the A ring of cryptotanshinone could
increase the activity. The simplified analogues 18 (IC50
4.96 mM), which lack of the A ring, showed a higher
CDC25B inhibitory activity than (G)-cryptotanshinone in
four folds. So the naphthofuran ortho-quinone skeleton
seems necessary for CDC25B inhibitory activity. The
analogue 26, which possesses a hydroxy group instead of
A ring, was the most potent (IC50 3.21 mM). However,
protecting the hydroxy group with a methyl group
(compound 25), led to a complete loss of activity. In
cytotoxic assay, (K)-cryptotanshinone, 11, 18, 25 and 26
were cytotoxic against A-549 tumor cells with IC50 values
of 6.39, 8.23, 3.65, 9.46 and 2.07 mM (Table 2),
respectively. The simplified analogues 18 and 26 also
demonstrated more potent cytotoxic activity against tumor
cells than cryptotanshinones.
1
uncorrected. H and 13C NMR spectra were recorded on
either Gemini-300 or Bruker AM-400. Chemical shifts
(d ppm) were reported for signal center, and coupling
constant J are reported in units of Hz. High-resolution mass
spectra were recorded on Varian MAT-711, MAT-95 or
HT-5989 mass spectrometer. Column chromatography was
performed on 200–300 mesh silica gel. All reagents were
used directly as obtained commercially, unless otherwise
noted.
4.1.1. Phosphoric acid diethyl ester 5-methoxy-naphtha-
len-1-yl ester (2). To a solution of 1 (1.74 g, 10 mmol) in
30 mL of THF at 0 8C was added NaH (80% dispersion in
mineral oil) (0.36 g, 12 mmol). After 30 min, diethyl
phosphorochloridate (1.60 mL, 11 mmol) was added and
stirred for additional 20 min. Water was added and the
mixture was extracted with ethyl acetate. The organic
extracts were washed with water and brine, dried over
MgSO4, and concentrated in vacuo. The crude residue was
purified by column chromatography (petroleum/CH2Cl2/
acetoneZ15:4:1) to afford 2 as a red-brown oil (2.48 g,
1
80%); H NMR (CDCl3, 400 MHz) d 1.32 (t, JZ7.1 Hz,
6H), 3.96 (s, 3H), 4.22 (q, JZ7.1 Hz, 4H), 6.82 (d, JZ
7.7 Hz, 1H), 7.33 (m, 2H), 7.49 (d, JZ7.7 Hz, 1H), 7.72 (d,
JZ8.5 Hz, 1H), 8.07 (d, JZ8.2 Hz, 1H).
4.1.2. 1-Methoxy-5-(4-methyl-pent-3-enyl)-naphthalene
(3). To a mixture of C6H11MgBr (4.8 mmol in 3.6 mL
THF) and NiCl2 (dppp) was added a solution of 2
(1.6 mmol, 0.5 g) in THF (3 mL), and the mixture was
stirred under an atmosphere of nitrogen overnight. The
mixture was poured into ice water and extracted with ethyl
acetate. The organic extract was washed with 1 N HCl and
brine, dried over MgSO4, and concentrated in vacuo. The
crude residue was purified by column chromatography
(petroleum/ethyl acetateZ20:1) to afford 3 as colorless oil
(0.174 g, 45%); 1H NMR (CDCl3, 400 MHz) d 1.58 (s, 3H),
1.71 (s, 3H), 2.47 (m, 2H), 3.11 (t, JZ7.9 Hz, 2H), 4.02 (s,
3H), 5.33 (m, 1H), 6.84 (d, JZ7.5 Hz, 1H), 7.34–7.42 (m,
3H), 7.66 (d, JZ8.6 Hz, 1H), 8.18 (d, JZ8.2 Hz, 1H);
EIMS (m/z): 240 (MC), 171, 158, 143, 128, 115.
3. Conclusion
In summary, we reported a novel synthetic method for
(G)-cryptotanshinone and its new simplified analogs. The
simplified analogues 18 and 26 were identified as micro-
molar inhibitors of CDC25B, and demonstrated powerful
cytotoxic activity against A-549 tumor cell line. The A ring
of cryptotanshinone was not necessary for its CDC25B
inhibitory activity and cytotoxic activity. The stereo-
chemistry of the C-3 in furan ring played an important
role in the activity against CDC25B phosphatase. Thus
these naphthofuran ortho-quinones would serve as
attractive lead molecules of drug development efforts
against the CDC25 phosphatase. The further
investigation of the effect of the stereochemistry of the
C-3 in the analogues on the biological activity is in process
in our laboratory.
4.1.3. 8-Methoxy-1,1-dimethyl-1,2,3,4-tetrahydro-phe-
nanthrene (4). A solution of 3 (2.0 g, 8.33 mmol) in
60 mL of CH2Cl2 was cooled to 0 8C. AlCl3 (1.2 g, 9 mmol)

W. G. Huang et al. / Tetrahedron 61 (2005) 1863–1870
1867
was added in one portion. The solution was stirred at 0 8C
for 30 min and then poured into ice water. The aqueous
phase was separated and extracted with diethyl ether, and
the combined organic phase was washed with water,
saturated NaHCO3 solution and brine, dried over MgSO4,
and concentrated in vacuo. Column chromatography
(petroleum/ethyl acetateZ20:1) furnished 4 as a yellow
oil (1.9 g, 95%); 1H NMR (CDCl3, 400 MHz) d 1.35 (s, 6H),
1.73 (m, 2H), 1.94 (m, 2H), 3.10 (t, JZ6.5 Hz, 3H), 3.98 (s,
3H), 6.78 (d, JZ7.6 Hz, 1H), 7.38 (m, 1H), 7.48 (d, JZ
8.2 Hz, 1H), 7.57 (d, JZ8.2 Hz, 1H), 8.10 (d, JZ9.0 Hz,
1H); EIMS (m/z): 240 (MC), 225, 158, 143, 115; HRMS
calcd for C17H20O 240.1514, found 240.1519.
4.1.7. 1,6,6-Trimethyl-1,2,6,7,8,9-hexahydro-phenan-
thro[1,2-b]furan (8). To a 0.1 M THF solution of SmI2
(40 mL, 2 mmol) and HMPA (2.4 mL, 14 mmol) was added
a solution of 7 (0.317 g, 0.92 mmol) in dry THF at 25 8C.
The solution was stirred under an atmosphere of nitrogen for
3 h. The reaction was quenched with saturated NH4Cl and
extracted with ethyl acetate. The organic extracts were
washed with H2O, 3% Na2S2O3 and brine, dried over
MgSO4, and concentrated in vacuo. The crude product was
purified by column chromatography (petroleum/ethyl
acetateZ20:1) to afford 8 as a colorless oil (0.215 g,
1
88%); H NMR (CDCl3, 400 MHz) d 1.38–1.42 (m, 9H),
1.74–1.78 (m, 2H), 1.93–1.99 (m, 2H), 3.11 (t, JZ6.30 Hz,
2H), 3.73 (m, 1H), 4.30 (dd, JZ7.00, 8.70 Hz, 1H), 4.89 (t,
JZ8.70, 9.00 Hz, 1H), 7.34 (d, JZ8.70 Hz, 1H), 7.45 (d,
JZ8.65 Hz, 1H), 7.51 (d, JZ8.62 Hz, 1H), 7.82 (d, JZ
8.70 Hz, 1H); 13C NMR (CDCl3, 100 MHz) d 155.5, 142.4,
132.9, 130.8, 127.8, 125.6, 124.6, 121.5, 119.2, 115.8, 79.1,
38.8, 37.3, 37.2, 34.2, 31.5, 31.4, 27.2, 19.9, 19.8, 19.6;
EIMS (m/z): 266, 251, 169; HRMS calcd for C19H22O
266.1671, found 266.1662.
4.1.4. 8,8-Dimethyl-5,6,7,8-tetrahydro-phenanthren-1-ol
(5). A solution of 4 (2.0 g, 8.33 mmol) in 40 mL of dry
CH2Cl2 was cooled to 0 8C. BBr3 (3 mL) was added
dropwise. The solution was stirred at 0 8C for 2 h, then
saturated NaHCO3 solution was added slowly. The mixture
was extracted with diethyl ether, and the combined organic
phase was washed with water and brine, dried over MgSO4,
and concentrated in vacuo. Column chromatography
(petroleum/ethyl acetateZ8:1) furnished 5 (1.79 g, 95%);
1H NMR (CDCl3, 400 MHz) d 1.35 (s, 6H), 1.72 (m, 2H),
1.94 (m, 2H), 3.08 (t, JZ6.3 Hz, 2H), 6.76 (d, JZ7.5 Hz,
1H), 7.29 (dd, JZ8.5, 7.5 Hz, 1H), 7.49 (d, JZ7.3 Hz, 1H),
7.55 (d, JZ8.7 Hz, 1H), 7.98 (d, JZ8.8 Hz, 1H); EIMS
(m/z): 226 (MC), 211, 115; HRMS calcd for C16H18O
226.1358, found 226.1354.
4.1.8. 1,6,6-Trimethyl-10-nitro-1,2,6,7,8,9-hexahydro-
phenanthro[1,2-b]furan (9). Compound 8 (0.212 g,
0.8 mmol) and AcOH (0.35 mL) were cooled to 0 8C and
concentrated HNO3 (0.04 mL) was added dropwise. After
this addition, the mixture was placed in the refrigerator at
10 8C for 20 min and then diluted with H2O. The resulting
precipitate was extracted with ethyl acetate. The organic
extracts were washed with H2O and brine, dried over
MgSO4, and concentrated in vacuo. The crude product was
purified by column chromatography (petroleum/ethyl
acetateZ20:1) to afford 9 as yellow oil (0.216 g, 87%);
1H NMR (CDCl3, 400 MHz) d 1.35 (s, 6H), 1.38 (d, JZ
6.87 Hz, 3H), 1.68–1.77 (m, 4H), 2.76 (t, JZ6.05 Hz, 2H),
3.75 (m, 1H), 4.37 (dd, JZ7.14, 8.93 Hz, 1H), 4.96 (dd, JZ
9.07, 9.20 Hz, 1H), 7.59 (d, JZ8.93 Hz, 1H), 7.68 (s, 1H),
7.87 (d, JZ8.93 Hz, 1H); EIMS (m/z): 311, 294, 251;
HRMS calcd for C19H21NO3 311.1521, found 311.1524.
4.1.5. 2-Bromo-8,8-dimethyl-5,6,7,8-tetrahydro-phe-
nanthren-1-ol (6). Compound 5 (1.0 g, 4.42 mmol) was
dissolved in CCl4 and bromine (0.71 g, 4.43 mmol) was
added dropwise at 0 8C. The mixture was stirred for 1 h, and
then 3% Na2S2O3 was added. After being stirred for
additional 10 min, the mixture was extracted with CH2Cl2.
The organic phase was washed sequentially with sodium
thiosulfate, water and brine, dried over MgSO4, and
concentrated in vacuo. The crude residue was purified by
column chromatography (petroleum/ethyl acetateZ15:1) to
4.1.9. (G)-Cryptotanshinone 11. Compound 9 (0.2 g,
0.643 mmol) in EtOH was hydrogenated over 10% Pd/C
(40 mg) for 4.5 h. The catalyst was filtered off and the
solvent was removed in vacuo to give the amine 10. The
crude amine was dissolved in acetone (10 mL) and treated
with Fremy’s salt (550 mg, 2.06 mmol) in 55 mL of 0.06 M
NaH2PO4. The mixture was stirred at room temperature for
30 min and extracted with CH2Cl2. The combined extracts
were washed with water and brine, dried over MgSO4, and
concentrated in vacuo. The crude product was purified by
column chromatography (petroleum/ethyl acetateZ6:1) to
afford 11 as an orange solid (95 mg, 50%), mp 172–173 8C;
1H NMR (CDCl3, 400 MHz) d 1.31 (s, 6H), 1.33 (d, JZ
6.87 Hz, 3H), 1.64–1.67 (m, 2H), 1.76–1.81 (m, 2H), 3.22
(t, JZ6.42 Hz, 2H), 3.60 (m, JZ6.79 Hz, 1H), 4.36 (dd, JZ
6.04, 9.33 Hz, 1H), 4.89 (dd, JZ9.48, 9.48 Hz, 1H), 7.50 (d,
JZ8.10 Hz, 1H), 7.62 (d, JZ8.10 Hz, 1H); 13C NMR
(CDCl3, 100 MHz) d 184.2, 175.6, 170.7, 152.3, 143.6,
132.5, 128.3, 126.2, 122.4, 118.2, 81.4, 37.7, 34.8, 34.5,
31.8 (2C), 29.6, 19.0, 18.8; EIMS (m/z): 296, 253, 171;
HRMS calcd for C19H20O3 296.1412, found 296.1404.
1
afford 6 (1.21 g, 90%) as colorless oil; H NMR (CDCl3,
400 MHz) d 1.34 (s, 6H), 1.72 (m, 2H), 1.93 (m, 2H), 3.05
(t, JZ6.32 Hz, 2H), 5.87 (s, 1H), 7.41 (d, JZ8.79 Hz, 1H),
7.45 (d, JZ9.06 Hz, 1H), 7.50 (d, JZ9.06 Hz, 1H), 8.04 (d,
JZ8.78 Hz, 1H); EIMS (m/z): 306, 304, 291, 289, 210;
HRMS calcd for C16H17OBr 304.0463, found 304.0467.
4.1.6. 8-Allyloxy-7-bromo-1,1-dimethyl-1,2,3,4-tetra-
hydro-phenanthrene (7). K2CO3 (1.98 g, 15.7 mmol) was
added to a solution of 6 (1.2 g, 3.93 mmol) dissolved in
40 mL of acetone. Allyl bromide was added in one portion
and the mixture was stirred at room temperature for 4 h. The
mixture was filtered and concentrated in vacuo. The crude
residue was purified by column chromatography
(petroleum/ethyl acetateZ20:1) to afford 7 as colorless oil
(1.29 g, 95%); 1H NMR (CDCl3, 400 MHz) d 1.36 (s, 6H),
1.72–1.75 (m, 2H), 1.92–1.97 (m, 2H), 3.09 (t, JZ6.42 Hz,
2H), 4.61 (m, 2H), 5.36 (m, 1H), 5.55 (m, 1H), 6.25 (m, 1H),
7.54 (d, JZ8.99 Hz, 1H), 7.57 (d, JZ9.16 Hz, 1H), 7.64 (d,
JZ9.17 Hz, 1H), 7.97 (d, JZ8.98 Hz, 1H); EIMS (m/z):
346, 344, 305, 303, 196; HRMS calcd. for C19H21OBr
344.0776, found 344.0779).
4.1.10. 2-Bromo-1-naphthalenol (13). According to the

1868
W. G. Huang et al. / Tetrahedron 61 (2005) 1863–1870
procedure described above for 6, compound 12 (4.14 g,
28.7 mmol) was converted to 13 (5.314 g, 83%) as white
needles: mp: 46–47 8C; 1H NMR (CDCl3, 400 MHz) d 6.00
(s, 1H), 7.32 (d, JZ8.8 Hz, 1H), 7.47 (d, JZ8.9 Hz, 1H),
7.49–7.54 (m, 2H), 7.78 (m, 1H), 8.24 (m, 1H); EIMS(m/z):
224 (MC), 222 (MC), 143, 144, 114, 115.
acetone, and benzyl bromide (1.915 g, 7.72 mmol) was
added. The mixture was stirred at room temperature for
12 h, filtered with celite, and concentrated in vacuo.
Purification by column chromatography (petroleum/ethyl
acetateZ30:1) afforded 22 (0.785 g, 51% from 19) as
1
colorless oil; H NMR (CDCl3, 400 MHz) d 3.94 (s, 3H),
4.56 (m, 2H), 5.16 (s, 2H), 5.34 (m, 1H), 5.50 (m, 1H), 6.24
(m, 1H), 6.90–7.70 (m, 9H); EIMS (m/z): 400, 398, 307,
227; HRMS calcd for C21H19BrO3 398.0518, found
398.0538.
4.1.11. 1-Allyloxy-2-bromonaphthalene (14). According
to the procedure described above for 7, compound 13
(4.00 g, 17.9 mmol) was converted to 14 (4.615 g, 98%) as a
pale yellow oil; 1H NMR (400 MHz, CDCl3) d 4.65 (d, JZ
5.5 Hz, 2H), 5.35 (dd, JZ10.2, 1.2 Hz, 1H), 5.54 (dd, JZ
17.1, 1.4 Hz, 1H), 6.25 (m, 1H), 7.48–7.62 (m, 4H), 7.84
(dd, JZ6.8, 2.3 Hz, 1H), 8.15 (dd, JZ8.2, 1.8 Hz, 1H);
EIMS (m/z): 264 (MC), 262 (MC), 223, 221, 195, 193, 183,
181, 114.
4.1.16. 5-Benzoxy-6-methoxy-3-methylnaphtho[1,2-
b]furan (23). According to the procedure described above
for 8, compound 22 (0.64 g, 1.60 mmol) was converted to
23 (0.44 g, 85%) as a colorless oil; 1H NMR (CDCl3,
400 MHz) d 1.36 (d, JZ6.87 Hz, 3H), 3.71 (m, 1H), 3.82 (s,
3H), 4.25 (dd, JZ7.83, 8.53 Hz, 1H), 4.85 (dd, JZ8.53,
8.72 Hz, 1H), 5.22 (s, 2H), 6.83–7.57 (m, 9H); EIMS (m/z):
320, 229, 149; HRMS calcd for C21H20O3 320.1412, found
320.1419.
4.1.12. 2,3-Dihydro-3-methylnaphtho[1,2-b]furan (15).
According to the procedure described above for 8,
compound 14 (0.526 g, 2.00 mmol) was converted to 15
(0.360 g, 98%) as a colorless oil; 1H NMR (400 MHz,
CDCl3) d 1.42 (d, JZ6.8 Hz, 3H), 3.75 (m, 1H), 4.32 (dd,
JZ7.4, 8.6 Hz, 1H), 4.92 (dd, JZ9.1, 8.8 Hz, 1H), 7.36 (d,
JZ8.1 Hz, 1H), 7.41–7.52 (m, 3H),7.84 (dd, JZ6.8, 2.7 Hz,
1H), 8.01 (dd, JZ7.8, 2.4 Hz, 1H); EIMS (m/z): 184 (MC),
169, 141, 115.
4.1.17. 2,3-Dihydro-6-methoxy-3-methylnaphtho[1,2-
b]furan-4,5-dione (25). Compound 23 (0.312 g,
1.357 mmol) was dissolved in 20 mL of ethyl acetate, and
hydrogenated over 10% Pd/C (50 mg) overnight. The
catalyst was filtered off, and the solvent was removed in
vacuo to give 24. The crude product 24 was dissolved in
40 mL of absolute ethanol, and powdered AgNO3 (1.454 g,
8.507 mmol) was added. After the mixture had been gently
refluxed for 15 min, water was added to quench the reaction,
followed by an extraction with dichloromethane. The
extracts were washed with water and brine, dried over
MgSO4 concentrated in vacuo. The crude product was
purified by chromatography (petroleum/ethyl acetateZ3:1)
to afford 25 (0.116 g, 50%) as an orange red solid; 1H NMR
(CDCl3, 400 MHz) d 1.37 (d, JZ6.89 Hz, 3H), 3.61 (m,
1H), 3.98 (s, 3H), 4.36 (dd, JZ6.21, 9.23 Hz, 1H), 4.89 (dd,
JZ9.57, 9.57 Hz, 1H), 7.17 (d, JZ8.56 Hz, 1H), 7.27 (d,
JZ7.39 Hz, 1H), 7.59 (dd, JZ7.39, 8.56 Hz, 1H); 13C
NMR (CDCl3, 100 MHz): d 18.5, 34.5, 56.1, 81.1, 116.5,
117.0, 117.5, 119.0, 129.1, 135.8, 161.5, 169.3, 175.2,
180.1; EIMS (m/z): 246, 244, 216, 201, 115; HRMS calcd.
for C14H12O4 244.0736, found 244.0733.
4.1.13. 2,3-Dihydro-3-methy-5-nitronaphtho[1,2-b]furan
(16). According to the procedure described above for 9,
compound 15 (0.360 g, 1.957 mmol) was converted to 16
(0.251 g, 56%) as an orange solid; 1H NMR (CDCl3,
400 MHz) d 1.45 (d, JZ6.9 Hz, 3H), 3.80 (m, 1H), 4.45 (dd,
JZ7.0, 9.1 Hz, 1H), 5.04 (dd, JZ9.1, 9.1 Hz), 7.56 (dd, JZ
8.0, 8.2 Hz, 1H), 7.70 (dd, JZ8.3, 8.8 Hz, 1H), 8.06 (d, JZ
8.4 Hz, 1H), 8.36 (s, 1H), 8.83 (d, JZ9.0 Hz, 1H); EIMS
(m/z): 229 (MC), 214, 199, 168, 139.
4.1.14. 2,3-Dihydro-3-methylnaphtho[1,2-b]furan-4,5-
dione (18). According to the procedure described above
for (G)-cryptotanshinone 11, compound 16 (0.20 g,
0.87 mmol) was converted to 18 (102 mg, 55%) as a red
1
solid; H NMR (CDCl3, 400 MHz) d 1.38 (d, JZ6.7 Hz,
3H), 3.64 (m, 1H), 4.42 (dd, JZ9.31, 9.47 Hz, 1H), 4.93
(dd, JZ9.62, 9.63 Hz, 1H), 7.55–7.66 (m, 3H), 8.08 (m,
1H); 13C NMR (CDCl3, 100 MHz) d 181.3, 175.4, 169.8,
134.6, 131.9, 130.8, 129.4, 127.6, 124.3, 120, 81.5, 34.4,
18.9; EIMS (m/z): 214 (MC), 186, 171; HRMS calcd for
C13H10O3 214.06, found 214.0617.
4.1.18. 2,3-Dihydro-6-hydroxy-3-methylnaphtho[1,2-
b]furan-4,5-dione (26). To the solution of 25 (80 mg,
0.328 mmol) in 10 mL of dry CH2Cl2, was added powdered
AlCl3 (0.660 g, 4.96 mmol) at 0 8C. The mixture was stirred
at 0 8C for 30 min, then at room temperature for 6 h, poured
into ice water, and concentrated hydrochloric acid was
added. The resulting mixture was extracted with ethyl
acetate. The extracts were washed with water and brine,
dried over MgSO4, and concentrated in vacuo. Purification
of the crude product by chromatography (petroleum/ethyl
acetateZ1:1) afforded 26 (74.5 mg, 98%) as a red solid; 1H
NMR (CDCl3, 400 MHz) d 1.40 (d, JZ6.8 Hz, 3H), 3.60
(m, 1H), 4.38 (dd, JZ6.04, 9.34 Hz, 1H), 4.90 (dd, JZ9.62,
9.61 Hz, 1H), 7.12 (d, JZ8.65 Hz, 1H), 7.18 (d, JZ
7.32 Hz, 1H), 7.54 (dd, JZ8.65, 7.28 Hz, 1H), 11.94 (s,
1H); 13C NMR (CDCl3, 100 MHz): d 18.8, 34.8, 81.7,
113.4, 117.6, 120.1, 123.3, 127.4, 137.8, 164.5, 169.4,
175.0, 185.5; EIMS (m/z): 230, 187, 159; HRMS calcd for
C13H10O4 230.0579, found 230.0570.
4.1.15. 1-Allyloxy-4-benzoxy-5-methoxynaohthalene
(22). A suspension of 19 (1.03 g, 3.86 mmol) in 50 mL
diethyl ether was stirred with a freshly prepared solution of
Na2S2O4 (5.00 g, 28.7 mmol) in 50 mL water. After the
mixture was stirred for 30 min, the organic layer was
separated, washed with water and brine, dried over Na2SO4,
and concentrated in vacuo to give 20 as a tan solid. Without
purification, 20 was dissolved in 20 mL of acetone and
K2CO3 (2.92 g, 38.6 mmol) was added. After the suspension
was stirred for several minutes, allyl bromide (0.934 g,
7.72 mmol) was added dropwise. The endpoint of the
reaction was detected by TLC. Then the mixture was
concentrated in vacuo to remove the solvent and remaining
allyl bromide. The residue was dissolved in 20 mL of

W. G. Huang et al. / Tetrahedron 61 (2005) 1863–1870
1869
11. Takemasa, I.; Yamamoto, H.; Sekimoto, M.; Ohue, M.; Noura,
S.; Miyake, Y.; Matsumoto, T.; Aihara, T.; Tomita, N.;
Tamaki, Y.; Sakita, I.; Kikkawa, N.; Matsuura, N.; Shiozaki,
H.; Monden, M. Cancer Res. 2000, 60, 3043–3050.
12. Hernandez, S.; Bessa, X.; Bea, S.; Hernmandez, L.; Nadal, A.;
Mallofre, C.; Muntane, J.; Castells, A.; Fernandez, P. L.;
Cardesa, A.; Campo, E. Lab. Investig. 2001, 81, 465–473.
13. Wu, F. Y. H.; Sun, T. P. Eur. J. Cancer 1999, 35, 1388–1393.
14. Tamura, K.; Rice, R. L.; Wipf, P.; Lazo, J. S. Oncogene 1999,
18, 6989–6996.
4.2. CDC25B inhibition assay
CDC25B phosphatase catalytic domain was expressed with
the Glutathionine S-transferase (GST) and purified by the
GSTrap affinity chromatograph. GST-CDC25B active
enzyme was stored in 50 mM Tris–HCl Ph 8.0, 50 mM
NaCl, 10 mM Glutathionine, 2 mM DTT and 2 mM EDTA
at K80 8C. The typical inhibition assay was carried out in
100 mL system containing 50 mM Tris–HCl PH8.0, 50 mM
NaCl, 2 mM DTT, 2 mM EDTA, 1% glycerol, 10 mM
OMEP, 2% DMSO and 70w100 nM GST-CDC25B. The
reaction was monitored by Victor (Perkin–Elmer; excitation
filter 485 nm and emission filter 530 nm) at the room
temperature.
15. Tamura, K.; Southwick, E. C.; Kerns, J.; Rosi, K.; Carr, B. I.;
Wilcox, C.; Lazo, J. S. Cancer Res. 2000, 60, 1317–1325.
16. Takahashi, M.; Dodo, K.; Sugimoto, Y.; Aoyagi, Y.; Yamada,
Y.; Hashimoto, Y.; Shirai, R. Bioorg. Med. Chem. Lett. 2000,
10, 2571–2574.
17. Peng, H.; Zalkow, L. H.; Abraham, R. T.; Powis, G. J. Med.
Chem. 1998, 41, 4677–4680.
4.3. Cytotoxicity assay
18. Gunasekera, S. P.; McCarthy, P. J.; Kelly-Broger, M.;
Lobkovsky, E.; Clardy, J. J. Am. Chem. Soc. 1996, 118,
8759–8760.
Cytotoxicity assay was performed on human lung cancer
(A-549) cell line. Cells (6000–10,000) in 100 mL culture
medium per well were seeded into 96-well microtest plates
(Falcon, CA). Cells were treated in triplicate with gradient
concentration of test drugs and incubated at 37 8C for 72 h.
The growth inhibitory effect on A-549 cell line was
measured by the Sulforhodamine B (SRB; Sigma, St.
Louis, MO) assay. The drug concentration required for 50%
growth inhibition (IC50) of tumor cells was determined from
the dose-response curve.
19. Blanchard, J. L.; Epstein, D. M.; Boisclair, M. D.; Rudolph, J.;
Pal, K. Bioorg. Med. Chem. Lett. 1999, 9, 2537–2538.
20. Cebula, R. E.; Blanchard, J. L.; Boisclair, M. D.; Mansuri, M.;
Pal, K.; Bockovich, N. J. Bioorg. Med. Chem. Lett. 1997, 7,
2015–2020.
21. Juan, C. C.; Wu, F. Y. Biochem. Biophys. Res. Comm. 1993,
190, 907–913.
22. Rice, R. L.; Rusnak, J. M.; Yokokawa, F.; Messner, D. J.;
Boynton, A. L.; Wipf, P.; Lazo, J. S. Biochemistry 1997, 36,
15965–15974.
Acknowledgements
23. Bergnes, G.; Gilliam, C. L.; Boisclair, M. D.; Blanchard, J. L.;
Blake, K. V.; Epstein, D. M.; Pal, K. Bioorg. Med. Chem. Lett.
1999, 9, 2849–2854.
Financial support from the National Natural Science
Foundation of China (20002005) is gratefully
acknowledged.
24. Peng, H.; Xie, W.; Otterness, D. M.; Cogswell, J. P.;
McConnel, R. T.; Carter, H. L.; Powis, G.; Abraham, R. T.;
Zalkow, L. H. J. Med. Chem. 2001, 44, 834–848.
25. Lazo, J. S.; Aslan, D. C.; Pestell, K. E.; Cooley, K.; Ducruet,
A. P.; Joo, B.; Vogt, A.; Wipf, P. J. Med. Chem. 2001, 44,
4042–4049.
References and notes
26. Lazo, J. S.; Nemoto, K.; Pestell, K. E.; Cooley, K.; Southwick,
E. C.; Mitchell, D. A.; Furey, W.; Gussio, R.; Zaharevitz,
D. W.; Joo, B.; Wipf, P. Mol. Pharmacol. 2002, 61, 720–728.
27. Pu, L.; Amoscato, A. A.; Bier, M. E.; Lazo, J. S. J. Biol. Chem.
2002, 277, 46877–46885.
1. Gantchev, T. G.; Hunting, D. J. Biochem. Biophys. Res.
Commun. 1997, 237, 24–27.
2. Driscoll, J. S.; Hazard, G. F. Jr.; Wood, H. B. Jr.; Goldin, A.
Cancer. Chemother. Rep. 1974, 4, 1–362.
28. Wipf, P.; Joo, B.; Nguyen, T.; Lazo, J. S. Org. Biomol. Chem.
2004, 2, 2173–2174.
3. Dolan, M. E.; Frydman, B.; Thompson, C. B.; Diamond,
A. M.; Garbiras, B. J.; Safa, A. R.; Beck, W. T.; Marton, L. J.
Anti-Cancer Drugs 1998, 9, 437–448.
29. Duke, J. A.; Avensu, E. S. In Medicinal Plants of China, Vol.
2; Reference: Algonac, MI, 1985; p 381.
4. Nilsson, I.; Hoffmann, I. Prog. Cell Cycle Res. 2000, 4,
107–114.
30. Chang, H. M., But, P., Eds.; Pharmacology and Applications
of Chinese Materia Medica; World Science: Singapore, 1986;
Vol. 1, pp 255–268.
5. Xia, K.; Lee, R. S.; Narsimhan, R. P.; Mukhopadhyay, N. K.;
Neel, B. C.; Roberts, T. M. Mol. Cell. Biol. 1999, 19,
4819–4824.
31. Lee, D. S.; Hong, S. D. J. Microbiol. Biotechnol. 1998, 1,
89–91.
6. Galaktionov, K.; Beach, D. Cell 1991, 67, 1181–1194.
7. Sadhu, K.; Reed, S. I.; Richardson, H.; Russell, P. Prog. Natl.
Acad. Sci. U.S.A. 1990, 87, 5139–5143.
32. Ryu, S. Y.; Lee, C. O.; Choi, A. U. Planta Med. 1997, 63,
339–342.
33. Baillie, A. C.; Thomson, R. H. J. Chem. Soc. C 1968, 48–52.
34. Kakisawa, H.; Tateishi, M.; Kusumi, T. Tetrahedron Lett.
1968, 34, 3783–3786.
8. Nagata, A.; Igarashi, M.; Jinno, S.; Suto, K.; Okayama, H. New
Biol. 1991, 3, 959–968.
9. Sasaki, H.; Yukiue, H.; Kobayashi, Y.; Tanahashi, M.;
Moriyama, S.; Nakashima, Y.; Fukai, I.; Kiriyama, M.;
Yamakawa, Y.; Fujii, Y. Cancer Lett. 2001, 173, 187–192.
10. Cangi, M. G.; Gukor, B.; Soung, P.; Signoretti, S.; Moreira, G.
Jr.; Ranashinge, M.; Cady, B.; Pagano, M.; Loda, M. J. Clin.
Investig. 2000, 106, 753–761.
35. Kakisawa, H.; Inouye, Y. J. Chem. Soc., Chem. Commun.
1968, 1327–1328.
36. Inouye, Y.; Kakisawa, H. Bull. Chem. Soc. Jpn 1969, 42,
3318–3323.
37. Lee, J.; Snyder, J. K. J. Am. Chem. Soc. 1989, 111, 1522–1524.

1870
W. G. Huang et al. / Tetrahedron 61 (2005) 1863–1870
38. Lee, J.; Snyder, J. K. J. Org. Chem. 1990, 55, 4995–5008.
39. Danheiser, R. L.; Casebier, D. S.; Firooznia, F. J. Org. Chem.
1995, 60, 8341–8350.
44. Demuynck, M.; Clercq, M. J. Org. Chem. 1979, 44,
4863–4866.
45. Martin, S. F.; Garricon, P. J. J. Org. Chem. 1992, 47,
1513–1518.
40. Jiang, Y. Y.; Li, Q.; Lu, W.; Cai, J. C. Tetrahedron Lett. 2003,
44, 2073–2075.
46. Alves, G. B. C.; Lopes, R. S. C.; Lopes, C. C. Synthesis 1999,
1875–1877.
41. Hannan, R. L.; Barber, R. B.; Rapoport, H. J. Org. Chem.
1979, 44, 2153–2158.
47. Best, T. M.; Wege, D. Aust. J. Chem. 1986, 39, 647–666.
48. Jung, M. E.; Hagenah, J. A. J. Org. Chem. 1987, 52,
1889–1902.
42. Hayashi, T.; Katsuro, Y.; Okamoto, Y.; Kumada, M.
Tetrahedron Lett. 1981, 22, 4449–4452.
43. Inanaga, J.; Ujikawa, O.; Yamaguchi, M. Tetrahedron Lett.
1991, 32, 1737–1740.