Potent antitumor activity of synthetic 1,2-naphthoquinones and 1,4-naphthoquinones

Article abstract of DOI:10.1016/S0968-0896(03)00226-8

Rhinacanthone (1) and two 1,2-pyranonaphthoquinones (2,3) were synthesized and found to show very potent cytotoxicity against three cancer cell lines (KB, HeLa and HepG₂) with IC₅₀ values of 0.92-9.63 μM, whereas the corresponding hydroxylated derivative 4 had reduced cytotoxicity (IC₅₀ values of 7.61-24.13 μM). Three 1,2-furanonaphthoquinone derivatives (5-7) were also synthesized with similar cytotoxicity as 1,2-pyranonaphthoquinones. In comparison to 1,2-naphthoquinones, six 1,4-naphthoquinones derivatives fused with pyran ring (8-10) and furan ring (11-13) were synthesized and they showed less cytotoxicity or inactive to the cancer cell lines. Moreover, compound 13 had significant cytotoxicity against HeLa cell line (IC₅₀ value of 9.25 μM) while it showed no toxic to vero cell.

Full text of DOI:10.1016/S0968-0896(03)00226-8

Bioorganic & Medicinal Chemistry 11 (2003) 3179–3191
Potent Antitumor Activity of Synthetic 1,2-Naphthoquinones
and 1,4-Naphthoquinones
Ngampong Kongkathip,a,* Boonsong Kongkathip,a Pongpun Siripong,b Chak Sangma,a
Suwaporn Luangkamin,a Momad Niyomdecha,a Suppachai Pattanapa,a
Suratsawadee Piyaviriyagulb and Palangpon Kongsaereec
aNatural Products and Organic Synthesis Research Unit, Department of Chemistry, Faculty of Science,
Kasetsart University, Bangkok 10900, Thailand
bNatural Products Research Section, Research Division, National Cancer Institute, Bangkok 10400, Thailand
cDepartment of Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
Received 4 January 2003; accepted 31 March 2003
Abstract—Rhinacanthone (1) and two 1,2-pyranonaphthoquinones (2,3) were synthesized and found to show very potent cyto-
toxicity against three cancer cell lines (KB, HeLa and HepG2) with IC50 values of 0.92–9.63 mM, whereas the corresponding
hydroxylated derivative 4 had reduced cytotoxicity (IC50 values of 7.61–24.13 mM). Three 1,2-furanonaphthoquinone derivatives
(5–7) were also synthesized with similar cytotoxicity as 1,2-pyranonaphthoquinones. In comparison to 1,2-naphthoquinones, six
1,4-naphthoquinones derivatives fused with pyran ring (8–10) and furan ring (11–13) were synthesized and they showed less cyto-
toxicity or inactive to the cancer cell lines. Moreover, compound 13 had significant cytotoxicity against HeLa cell line (IC50 value of
9.25 mM) while it showed no toxic to vero cell.
# 2003 Elsevier Science Ltd. All rights reserved.
Introduction
Therefore, rhinacanthone (1), three 1,2-pyranonaphtho
quinones (2–4), three 1,2-furanonaphthoquinones (5–7),
three 1,4-pyranonaphthoquinones (8–10) and three
1,4-furanonaphthoquinones (11–13) were synthesized,
all in high yield for cytotoxicity evaluation.1ꢀ12
Rhinacanthone (1)1ꢀ5 (3,4-dihydro-3,3-dimethyl-2H-
naphtho[1,2-b]pyran-5,6-dione) was first isolated from
the shrub, Rhinacanthus nasutus, which is used in Thai
folk medicines for the treatment of cancer, hepatitis,
skin diseases such as athletes foot. It has also been
reported to has antifungal activity4 against Pyricularie
oryzae. Moreover, rhinacanthone (1) has been reported
antitumor activity1 against Dalton’s ascitic lymphoma.
Rhinacanthone (1) has 1,2-pyranonaphthoquinone
structure. Our group has also done extraction and iso-
lation of cytotoxic constituents from the plant but very
limited amounts of active compounds were obtained.
So it was desirable to synthesize more rhinacanthone
derivatives, other 1,2-naphthoquinone derivatives related
to rhinacanthone and some 1,4-naphthoquinone deriva-
tives in order to compare the bioactivity of the systems.
*Corresponding author. Tel.: +66-2-942-8900x211; fax: +66-2-942-
8900x102; e-mail: fscinpk@ku.ac.th
0968-0896/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0968-0896(03)00226-8

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N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
1). After methylation of compound 14 by methyl iodide
and then reduction of the resultant methyl ester (15)
with lithium aluminium hydride, the hydroxy methyl
naphthol ether (16) was obtained in 91% yield. Bromi-
nation of compound 16 using phosphorous tribromide
and then alkylation of the resulting bromide (17) by
methyl isobutylate gave compound 18. Demethylation
of compound 18 to obtain lactone (19) could be done
Synthesis of pyranonaphthoquinones
Synthesis of rhinacanthone (1) and compound 8 were
achieved starting from 1-hydroxy-2-naphthoic acid (14)
via 1-naphthol derivative (20) (Scheme 1). The yields of
all steps involved were very high. Derivatives, com-
pounds 2 and 9 without methyl substitution on C-3 and
compounds 3 and 10 with one methyl group on C-3,
were also prepared as shown in Scheme 2 via O-allyl-
ation of 1-naphthol and Claisen rearrangement.
Hydroxypyrano-naphthoquinone (4) was achieved by
C-alkylation of lawsone (35) and then epoxidation
(Scheme 3).
Synthesis of furanonaphthoquinones
Furanonaphthoquinone derivatives (5), (6), (11) and (12)
were synthesized by C-allylation of lawsone and then
cyclization by acid (Scheme 3). Also, furanonaphtho-
quinones (7) and (13) were accessed from C-alkylation of
lawsone by a-bromoacetate ethyl ester followed by
reduction and then cyclization by concentrated acid as
shown in Scheme 4. Variation of acid concentration with
water was also used for the cyclization.
Results and Discussion
Chemistry
Rhinacanthone (1) and compound 8 were prepared
starting from 1-hydroxy-2-naphthoic acid (14) (Scheme
Scheme 2. (a) (i)
, K2CO3, reflux, 3 h; (ii)
, K2CO3,
ꢁ
-
.
reflux, 20 h; (b) 180 C, DMF, 6 h; (c) BH3 THF and then H2O2/OH ;
(d) Fremy’s salt, MeOH–DMF, 1 M NaOAc, rt, 12 h; (e) DDQ,
p-TsOH, benzene, reflux, 20 min; (f) 1% aq NaOH, reflux, 2 h; (g) 20%
aq H2SO4, reflux.
Scheme 1. (a) Mel, K2CO3, reflux, 12 h; (b) LiAlH4, dry ether, rt,
1.5 h; (c) PBr3, dry hexane–CH2Cl2 (1:1), rt 6 h; (d) LDA, methyl iso-
butylate, ꢀ78 ꢁC, 2 h; (e) AlCl3, chlorobenzene, reflux, 4 h; (f) LiAlH4,
dry ether, rt 2 h; (g) Fremy’s salt, MeOH–DMF, 1 M NaOAc, rt 12 h;
(h) DDQ, p-TsOH, benzene, reflux, 20 min; (i) 1% aq NaOH, reflux,
2 h; (j) 20% aq H2SO4, reflux, 5 h.
Scheme 3. (a) (i) R=H;
, K2CO3, DMF, reflux, 3 h; (ii)
R=Me; , K2CO3, Kl, DMF, reflux, 3 h; (b) concd H2SO4,
0 ꢁC to rt, 30 min; (c) 20% aq H2SO4, reflux 5 h; (d) m-CPBA, CH2Cl2,
0ꢁ–rt, 24 h.

N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
3181
obtained in high yield (81%). This may be caused by
heterogeneous reaction conditions, where enolates like the
anion formed (A) was not very soluble in solution
(Scheme 5). In Scheme 3, compound 4 was obtained by
oxidation of compound 36 using m-chloroperbenzoic acid
in dichloromethane. Similarly in Scheme 4, C-alkylation
of lawsone by a-bromoacetate ethyl ester in DMF resulted
in compound 38 and reduction of the ester function of 38
provided quinone (39) followed by cyclization using 20%
aqueous sulfuric acid to afford 1,4-naphthoquinone (13)
in 54% yield whereas using concentrated sulfuric acid,
compound 7 was obtained in 45% yield.
Scheme 4. (a)
, Li2CO3, DMF, reflux, 3 h; (b) NaBH4,
Compounds 36 and 37 were cyclized to furano-1,2-
naphthoquinone (5 and 6) by concentrated sulfuric acid
at 0 ꢁC to room temperature in 61 and 70% yield,
respectively22 (Scheme 3). With respect to cyclization of
olefinic alcohols (36 and 37), using 20% aqueous sulfu-
ric acid, it was found that the 1,4-naphthoquinone pro-
ducts (11 and 12) were obtained instead.15 It seemed
that the mechanism of using concentrated sulfuric acid
(H2SO4) is different from using aqueous sulfuric acid.
The mechanism of concentrated H2SO4 action may be
mediated by tautomerization of protonated naphtho-
quinone (B) as shown in Scheme 6 whereas using
MeOH, reflux, 7 h; (c) concd H2SO4, 0 ꢁC; (d) 20% aq H2SO4, reflux,
5 h.
using trimethyl silyl chloride13 or aluminium chloride in
chlorobenzene.10 After reduction of the lactone (19) by
lithium aluminium hydride to give naphthol alcohol
(20), oxidation of the alcohol (20) was done by Fremy’s
salt14 to obtain the mixture of naphthoquinones 21 and
22 and then cyclization by dichlorodicyanobenzo-
quinone (DDQ) to yield rhinacanthone (1). Then
hydrolysis of compound 1 with base gave 1,4- naphtho-
quinone (23) which was recyclized by acid to afford
compound 8.12,15
Another four pyranonaphthoquinones16ꢀ20 (2), (3), (9)
and (10) were accessed from 1-naphthol in five steps
(Scheme 2) which are easier, milder and shorter steps
than that of the synthesis of rhinacanthone (1) and
compound 8. O-Allylation of 1-naphthol (CH2¼CH-
CH2–Br, K2CO3) gave O-allyl-1-naphthol ether (25) in
86% yield. Claisen rearrangement of the allyl ether (25)
(180 ꢁC, DMF) gave 2-allyl-1-naphthol (27) (82%).
Compound 27 was converted to alcohol (29) (71%) by
hydroboration and then hydrogen peroxide oxidation in
sodium hydroxide solution. Finally, oxidation of the
naphthol (29) to compound 31 and then cyclization
using the same reagent as for the preparation of the
rhinacanthone and compound 8, the pyranonaphtho-
quinone (2) and (9) were obtained in 95 and 89% yield,
respectively. Similarly, pyrano naphthoquinones (3) and
(10) were prepared by analogous routes in 95 and 89%
yield, respectively, and 2-methyl allyl chloride was used
for O-allylation instead of allyl bromide.
Scheme 5.
Furanonaphthoquinones17,21,22 (5) and (6) were synthe-
sized in only two steps (C-allylation and cyclization)
from lawsone (35) which could be isolated from the
shrub, Lawsonia inermis.23 C-Allylation of lawsone
(allyl bromide, K2CO3, DMF) gave allyl lawsone (36) in
81% yield (Scheme 3). It was found that solvent effected
the C-allylation. Firstly, C-allylation of lawsone was
tried by refluxing with allyl bromide and potassium
carbonate in acetone, but no C-allylated lawsone was
obtained. Only O-allylated product (35%) occurred
together with the starting material. Use of ethanol gave
only 6% of the C-allylated product together with
O-allyated product (32%). However, when N,N-dimethyl-
formamide (DMF) was used as a solvent the reaction
mixture became milky and the C-allylated product was
Scheme 6.

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N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
pyran ring instead, reduced the cytotoxicity (IC50 value
about 6.90–24.13 mM). However, all 1,2-pyranon-
aphthoquinones (1–4) showed potent cytotoxicity
against cancer cell lines. This result is in agreement with
the report that reduction of lipophilicity by hydroxyl
group caused lower cytotoxicity.25 It means that the
1,2-pyranonaphthoquinone skeleton plays an important
role for the activity. In the same way, a similar skeleton
with 1,2-furanonaphthoquinone (5–7) still showed
strong cytotoxicity against all cancer cell lines (KB,
HeLa and HepG2). When the 1,2-naphthoquinone was
changed to 1,4-naphthoquinone as shown in Table 1 (8–
13), the cytotoxicity was reduced or was insignificant in
accordance with the results reported by De Moura25
and Goulart26 groups who observed that the trypanoci-
dal activity of 1,2-quinones is higher than that of the
corresponding 1,4-quinones. This means that 1,2-naph-
thoquinone is an important functional group for bio-
activity. Regarding normal cells, it was found as usual
that compounds 1–7, 11–12 showed cytotoxicity to Vero
cell similar to that in cancer cell lines. Interestingly,
compound 13 was inactive to normal cells with IC50
value of 84.15 mM whereas it showed strong cytotoxicity
against HeLa cancer cell lines with the IC50 values of
9.25 mM. This result suggests that compound 13 might
be modified as a cancer drug for treatment of cervical
cancers without any harm to normal cells and agrees
with Thai folk medicine which recommends the plant
(R. nasutus) for the treatment of cervical cancer.
Scheme 7.
aqueous H2SO4, protonation of the double bond at the
side chain may be faster than protonation of the car-
bonyl group of naphthoquinone and then the hydroxy
group at C-3 position attacked the carbocation straight
away (Scheme 7).
Bioactivity
There was a report1 that rhinacanthone showed sig-
nificant inhibition against Daton’s ascitic lymphoma
(DAL) in Swiss albino mice. With respect to rhina-
canthone activity, all pyranonaphthoquinones (1–4, 8–
10) and furanonaphthoquinones (5–7, 11–13) were
evaluated against human cancer cell lines which are KB
(human epidermoid carcinoma), HeLa (human cervical
carcinoma) and HepG2 (human hepatocellular carci-
noma) cell lines employing the MTT colorimetric
method.24 The results of their cytotoxicities are shown
in Table 1.
Furthermore, many chemotherapeutic agents have been
reported to exert their antitumor effects by inducing
apoptosis of cancer cells.27 For example, b-lapachone
(3,4-dihydro-2,2-dimethyl-2H-naphthol[1,2-b]pyran-5,6-
dione), a naturally occurring 1,2-naphthoquinone which
is structurally related to rhinacanthone was proved to
be a novel anticancer drug. It was shown to induce cell-
cycle arrest and apoptosis in various human cancer cells
by inhibiting the DNA topoisomerase I and II.27,28
From Table 1, compounds 2 and 3 with 1,2-pyrano
naphthoquinone skeleton, with one and without methyl
group on C-2 of pyran ring, showed better cytotoxicity
against KB, HeLa and HepG2 cells with IC50 values in
the range of 0.92–3.22 mM. Whereas this skeleton with
dimethyl groups (1) or hydroxy group (4) on C-2 of
Rhinacanthone
(1), (3,4-dihydro-2,2-dimethyl-2H-
naphtho[1,2-b]pyran-5,6-dione) may effect the human
cancer cells by the same action as b-lapachone. How-
ever, the potential antineoplastic mechanisms of rhina-
canthone and its active analogues which were
synthesized in this study is still unknown. Apoptosis-
inducing mechanisms of these active compounds are
being investigated in detail. Since, rhinacanthone has
been found to have antitumor activity against Dalton’s
ascitic lymphoma in mice,1 the inhibitory effects of
active analogues in in vivo tumor models are being fur-
ther determined.
Table 1. Cytotoxicity of compounds 1–13 against human carcinoma
cell lines (KB, HeLa and HepG2)and vero cell line
Compd
Cancer cell lines IC50 (mM)a
KB HeLa HepG2
Vero cella
IC50 (mM)
1
2
3
4
5
6
7
8
9
10
11
12
9.63Æ1.421
3.22Æ0.224
2.37Æ0.289
24.13Æ1.474
2.24Æ0.241
2.71Æ0.453
3.05Æ0.195
7.15Æ0.814 6.90Æ0.620 7.52Æ0.169
0.92Æ0.248 1.07Æ0.276 2.76Æ0.117
1.10Æ0.254 2.10Æ0.579 2.37Æ0.101
7.83Æ0.726 7.61Æ0.600 7.74Æ0.578
2.46Æ0.171 2.41Æ0.158 2.28Æ0.509
2.52Æ0.477 2.66Æ0.149 2.48Æ0.252
2.85Æ0.210 3.00Æ0.040 2.90Æ0.140
In addition, we have also done computer docking to
simulate how rhinacanthone (1) and its analogues (2–
13) might bind to topoisomerase II, the target enzyme
of rhinacanthone, using the AUTODOCK29 and
PASS30 program (Fig. 1).
38.55Æ7.235 23.30Æ1.950 20.83Æ0.690 55.08Æ9.661
47.52Æ13.107 9.95Æ0.920 22.62Æ0.780 29.44Æ1.748
59.65Æ6.649 17.89Æ3.579 24.30Æ2.228 65.04Æ3.303
10.31Æ1.202
10.89Æ1.276
18.10Æ3.760
0.033
7.59Æ0.816 7.59Æ0.767 7.81Æ0.329
7.56Æ0.748 8.64Æ0.257 8.50Æ0.191
9.25Æ0.420 26.15Æ1.435 84.15Æ7.360
13
Adriamycinb
0.33
0.40
23.94Æ6.243
First, we used the program PASS to predict the poten-
tial binding sites of topoisomerase II (1AB4 obtained
from the PDB database). Then the result from PASS
program was verified by allowing the known drug,
adriamycin (doxorubicin), to dock onto the enzyme
KB, human epidermoid carcinoma; HeLa, human cervical carcinoma;
HepG2, human hepatocellular carcinoma; Vero cell line, African green
monkey kidney cell.
aThe results are the average mean of six replicate determinationsÆSD.
bUsed as reference.

N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
3183
Figure 1. Binding areas of adriamycin (in red wire-framed structures)
to 1AB4 (gray spiral) as proposed by AUTODOCK and potential
binding sites (colored balls) as predicted by PASS.
Figure 3. Different manner of binding of rhinacanthone (red) and
compound 13 (yellow) as predicted by PASS.
using the AUTODOCK program. The area, commonly
predicted by the two programs, is our proposed binding
site in the green ball area as shown in Figure 1.
1,4-naphthoquinone, bind in different way. For exam-
ple, rhinacanthone (1), 1,2-naphthoquinone, and com-
pound 13, 1,4-naphthoquinone, dock at the same
binding site but in different manner (Fig. 3).
The AUTODOCK and PASS were verified using the
known drug, adriamycin (doxorubicin), to see how this
drug could bind to topoisomerase II. The sites predicted
by docking and PASS were used as a guideline for
rhinacanthone and other naphthoquinones (Fig. 2). It
was found that all compounds (1–13) showing various
activities tended to bind to the same binding site as
adriamycin (Fig. 2); however, some compounds with
less or no activity at all also bind to the same site in
most cases. However, after a close look into the mode
of binding, the highly or moderately active and less
active compounds appear to bind in a different manner
as shown in Figure 2. The two sets of our synthetic
compounds which are 1,2-naphthoquinone and
In conclusion, these preliminary results show that 1,2-
and 1,4-naphthoquinones fused with furan or pyran
ring are important groups for cytotoxicity to cancer cell
lines, with 1,2-naphthoquinones having better activity.
Experimental
General remarks
Melting points were determined on a Fisher-John
apparatus and are uncorrected. The IRspectra were
recorded on a FTIRPerkin–Elmer System 2000. Mass
spectral data were obtained on the GCMS-QP-5050A.
Nuclear magnetic resonance spectra were recorded at
400 MHz on a Brucker Advance DPX-400. Chemical
shifts are given in parts per million (d) downfield from
tetramethylsilane (TMS) as internal standard. Coupling
constants are given in Hertz (Hz). The following abbre-
viations are used: s=singlet, d=doublet, t=triplet,
q=quartet, m=multiplet, br s=broad singlet,
dd=double doublet, dt=double triplet. Column chro-
matography was performed with flash silica gel (Merck
9385).
Methyl 1-methoxy-2-naphthoate (15). A mixture of
1-hydroxy-2-naphthoic acid (10 g, 0.053 mol), potassium
carbonate (29 g, 0.21 mol), acetone (200 mL) and iodo-
methane (15 mL, 0.24 mol) were stirred and refluxed for
13 h. Then the reaction mixture was cooled to room
temperature, filtered and washed with acetone. The fil-
trate was concentrated in vacuo, then dichloromethane
was added, washed with water, dried over anhydrous
sodium sulfate, filtered and concentrated in vacuo. The
residue was purified by column chromatography eluting
Figure 2. The picture shows how adriamycin (red and grey stick) and
test compounds (in colors) dock at the binding site predicted by PASS.

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N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
with 49:1 v/v hexane–ethyl acetate to afford the product
15 (84%) as a colorless oil.2 IR(neat) cm ꢀ1: 3059, 1720
hexamethylphosphoramide (HMPA) (0.6 mL) and dry
THF (2 mL) was added dropwise to the reaction mix-
ture at the same temperature. After stirring for 2 h at
ꢀ78 ꢁC, the reaction mixture was quenched with satu-
rated ammonium chloride solution and then extracted
with diethyl ether (3Â50 mL). The combined organic
phase was washed with water and brine, dried over
anhydrous sodium sulfate, filtered and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 49:1 v/v hexane–ethyl acetate to
afford the product 18 as a colorless solid; mp 99–
100 ꢁC.2 IR(KBr) cm ꢀ1: 2965, 1733 and 1193. 1H NMR
(CDCl3) d: 1.20 (s, 6H, 2ÂCH3), 3.08 (s, 2H, CH2), 3.70
(s, 3H, CO2CH3), 3.90 (s, 3H, OCH3), 7.18 (d, 1H,
J=8.4 Hz, ArH), 7.4–7.55 (m, 3H, ArH), 7.80 (d, 1H,
J=7.8 Hz, ArH) and 8.05 (d, 1H, J=7.8 Hz, ArH).13C
1
and 1076. H NMR(CDCl ) d: 3.98 (s, 3H, CO2CH3),
3
4.07 (s, 3H, OCH3), 7.57 (m, 2H, ArH), 7.61 (d, 1H,
J=8.7 Hz, ArH), 7.84 (m, 1H, ArH), 7.86 (d, 1H,
J=8.7 Hz, ArH) and 8.28 (m, 1H, ArH). 13C NMR
(CDCl3) d: 52.9 (CH3O), 64.0 (OCH3), 124.2 (2C),
127.1, 127.3, 128.5, 128.9 (CH arom), 119.8, 129.2,
137.4, 158.9 (C arom) and 167.3 (OC¼O). MS m/z (%):
216 (M+, 95), 185 (100), 170 (36), 127 (57) and 114 (74).
2-Hydroxymethyl-(1-methoxynaphthalene) (16). To a
stirred and ice-cooled suspension of lithium aluminium
hydride (1.7 g, 0.046 mol) in dry diethyl ether (30 mL)
was added dropwise a solution of compound 15 (5 g,
0.023 mol) in dry diethyl ether (20 mL). After stirring for
2 h at room temperature, the reaction mixture was
quenched with ethyl acetate and water, then extracted
with diethyl ether (3Â100 mL). The combined organic
phase was washed with water and brine, filtered and
concentrated in vacuo. The residue was purified by col-
umn chromatography eluting with 9:1 v/v hexane–ethyl
acetate to afford product 16 (91%) as a colorless amor-
NMR(CDCl ) d: 24.0 (2ÂCH3), 38.9 (CH2), 42.9 (C),
3
50.8 (CH3O), 60.6 (CH3O), 121.2, 122.4, 124.6, 124.8,
126.9, 128.3 (CH arom), 125.4, 126.9, 133.2, 153.6 (C
arom) and 177.3 (OC¼O). MS m/z (%): 272 (M+, 17),
171 (100), 128 (34) and 115 (26).
3,4-Dihydro-3,3-dimethyl-2H-naphtho[1,2-b]pyran-2-one
(19). A mixture of compound 18 (0.8 g, 2.9 mmol) and
powdered aluminium chloride (0.78 g, 5.8 mmol) in dry
redistilled chlorobenzene (20 mL) were refluxed for 4 h.
The solution was cooled to room temperature and
poured into 10% hydrochloric acid (60 mL), then
extracted with diethyl ether (3Â30 mL). The combined
organic phase was washed with water, dried over an-
hydrous sodium sulfate, filtered and concentrated in
vacuo. Then chlorobenzene was removed by distillation
under reduced pressure. The resulting residue was pur-
ified by column chromatography, eluting with 49:1 v/v
hexane–ethyl acetate to afford the product 19 (83%) as
a colorless amorphous powder, mp 123–124 ꢁC.2 IR
(KBr) cmꢀ1: 2974, 1759, 1383 and 1111. 1H NMR
(CDCl3) d: 1.30 (s, 6H, 2ÂCH3), 2.90 (s, 2H, CH2), 7.17
(d, 1H, J=8.3 Hz, ArH), 7.46 (m, 2H, ArH), 7.53 (d,
1H, J=8.3 Hz, ArH), 7.76 (m, 1H, ArH) and 8.18 (m,
phous powder, mp 70–71 ꢁC.2 IR(KBr) cm ꢀ1: 3196,
1
1570, 1365 and 1053. H NMR(CDCl ) d: 2.20 (br s,
3
1H, OH), 4.00 (s, 3H, OCH3), 4.90 (s, 2H, OCH2), 7.56
(m, 3H, ArH), 7.63 (d, 1H, J=8.4 Hz, ArH), 7.83 (dd,
1H, J=7.5 Hz, J=1.3 Hz, ArH) and 8.10 (dd, 1H,
J=7.9 Hz, J=0.9 Hz, ArH). 13C NMR(CDCl ) d: 61.4
3
(OCH3), 63.3 (OCH2), 122.7, 125.1, 126.7, 126.8, 127.3,
128.7 (CH arom), 128.4, 129.6, 135.4 and 154.3 (C
arom). MS m/z (%): 188 (M+, 71), 156 (39), 127 (100)
and 115 (72).
2-Bromomethyl-1-methoxynaphthalene (17). To a stirred
solution of compound 16 (2 g, 0.01 mol) in dry hexane–
dichloromethane (1:1) (15 mL), phosphorus tribromide
(1 M in dichloromethane, 20 mL, 0.02 mol) was added
dropwise. After stirring for 6 h at room temperature,
water was added, then the mixture was neutralised with
saturated sodium hydrogen carbonate and extracted
with dichloromethane (3Â50 mL). The combined
organic phase was washed with water and brine, dried
over anhydrous sodium sulfate, filtered and con-
centrated in vacuo. The product 17 was obtained as a
colorless solid in quantitative yield, mp 65–66 ꢁC.2 IR
(KBr) cmꢀ1: 2940, 1570, 1366 and 1078. 1H NMR
(CDCl3) d: 4.00 (s, 3H, OCH3), 4.70 (s, 2H, CH2Br),
7.41 (d, 1H, J=8.4 Hz, ArH), 7.47 (m, 2H, ArH), 7.57
(d, 1H, J=8.4 Hz, ArH), 7.78 (m, 1H, ArH) and 8.07
1H, ArH). 13C NMR(CDCl ) d: 25.5 (2ÂCH3), 37.8
3
(C), 39.4 (CH2), 121.7, 124.5, 126.5, 127.0, 127.1, 128.2
(CH arom), 117.1, 123.9, 134.1, 146.8 (C arom) and
174.3 (OC¼O). MS m/z (%): 226 (M+, 61), 198 (65),
183 (100), 155 (40) and 128 (57).
2-(3-Hydroxy-2,2-dimethylpropyl)-1-hydroxy naphthalene
(20). To a stirred and ice-cooled suspension of lithium
aluminium hydride (0.34 g, 9 mmol) in dry tetra-
hydrofuran (10 mL), a solution of compound 19 (0.97 g,
4 mmol) in dry tetrahydrofuran (5 mL) was added
dropwise. After stirring for 2 h at room temperature, the
reaction mixture was quenched with ethyl acetate and
water, then extracted with diethyl ether (3Â40 mL). The
combined organic phase was washed with water and
brine, dried over anhydrous sodium sulfate, filtered and
concentrated in vacuo to give the product 20 (98%) as a
colorless amorphous powder, mp 123–124 ꢁC.2 IR
(KBr) cmꢀ1: 3363, 2955, 1386 and 1079. 1H NMR
(CDCl3) d: 1.04 (s, 6H, 2ÂCH3), 2.45 (br s, 1H, OH),
2.77 (s, 2H, CH2), 3.25 (s, 2H, CH2O), 7.16 (d, 1H,
J=8.4 Hz, ArH), 7.34 (d, 1H, J=8.4 Hz, ArH), 7.46 (m,
2H, ArH), 7.76 (m, 1H, ArH), 8.30 (m, 1H, ArH) and
(m, 1H, ArH). 13C NMR(CDCl ) d: 29.1 (CH2), 63.1
3
(OCH3), 123.1, 125.4, 127.0, 127.5, 128.6, 128.8 (CH
arom), 128.5, 128.6, 135.8 and 155.0 (C arom). MS m/z
(%): 252 (M++1, 7), 250 (7), 171 (100), 128 (86) and
115 (47).
2-(2,2-Dimethyl-3-methylpropanoate)-1-methoxy naphtha-
lene (18). To a stirred solution of diisopropylamine
(0.56 mL, 4 mmol) and n-BuLi (1.6 M in cyclohexane,
2.5 mL, 4 mmol) in dry tetrahydrofuran (THF) (5 mL)
at 0 ꢁC, methyl isobutyrate (0.34 mL, 3 mmol) was
added dropwise at ꢀ78 ꢁC and stirring was continued
for 1 h. A solution of compound 17 (0.4 g, 1.6 mmol) in

N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
3185
8.53 (br s, 1H, OH). 13C NMR(CDCl 3) d: 25.8
(2ÂCH3), 37.3 (C), 39.0 (CH2), 69.8 (CH2O), 119.6,
123.1, 125.6, 126.3, 127.8, 131.4 (CH arom), 118.2,
126.1, 134.3 and 151.5 (C arom). MS m/z (%): 230
(M+, 28), 183 (16), 157 (100) and 128 (76).
2-Hydroxy-3-(3-hydroxy-2,2-dimethylpropyl)-1,4-naphtho-
quinone (23). The solution of compound 1 (0.5 g,
2.1 mmol) in 1% aqueous sodium hydroxide solution
(12 mL, 3.1 mmol) was refluxed for 2 h. Then the reac-
tion mixture was cooled to room temperature and acid-
ified with acetic acid, extracted with dichloromethane
(3Â50 mL). The combined organic phase was washed
with water and brine, dried over anhydrous sodium
sulfate, filtered and concentrated in vacuo. The residue
was recrystallized from hexane–dichloromethane to give
the product 23 (86%) as a yellow amorphous powder,
mp 144–145 ꢁC.4 IR(KBr) cm ꢀ1: 3418, 1672, 1482 and
1216. 1H NMR(CDCl 3) d: 1.00 (s, 6H, 2ÂCH3), 2.60 (s,
2H, CH2), 3.10 (s, 2H, CH2O), 3.70 (br s, 1H, OH), 7.74
(dt, 1H, J=7.5 Hz, J=1.4 Hz, ArH), 7.76 (br s, 1H,
OH), 7.8 (dt, 1H, J=7.5 Hz, J=1.4 Hz, ArH), 8.12 (dd,
1H, J=7.5 Hz, J=0.96 Hz, ArH) and 8.16 (dd, 1H,
J=7.5 Hz, J=0.96 Hz, ArH). 13C NMR(CDCl 3) d: 25.9
(2ÂCH3), 31.3 (CH2), 39.2 (C), 70.5 (CH2O), 126.9,
127.8, 133.9, 135.7 (CH arom), 122.5, 130.1, 133.4,
155.8 (C), 181.5 and 187.0 (C¼O). MS m/z (%): 260
(M+, 2), 230 (77), 188 (100), 160 (35), and 77 (76).
2-(3-Hydroxy-2,2-dimethylpropyl)-1,4-naphthoquinone
(21) and 1,4-naphthoquinone-2-spiro-20-(40,40-dimethyl-
tetrahydrofuran) (22). To a stirred solution of com-
pound 20 (1 g, 4 mmol) in methanol–dimethylformamide
(MeOH–DMF) (3:1) (64 mL) was added a solution of
Fremy’s salt (8 g, 30 mmol) in water (260 mL) and 1 M
aqueous sodium acetate solution (6.6 mL). After stirring
for 14 h at room temperature, the reaction mixture was
extracted with diethyl ether (3Â50 mL). The combined
organic phase was washed with water and brine, dried
over anhydrous sodium sulfate and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 17:3 v/v hexane–ethyl acetate to
afford the product 21 (76%) as a yellow solid and pro-
duct 22 (19%) as a yellow oil.2 Compound 21: mp 81–
82 ꢁC. IR(KBr) cm ꢀ1: 3420, 1663, 1589 and 1293. H
1
NMR(CDCl 3) d: 0.90 (s, 6H, 2ÂCH3), 2.50 (s, 2H,
CH2), 3.10 (s, 2H, OCH2), 6.76 (s, 1H, CH¼), 7.69 (m,
2H, ArH), 8.01 (m, 1H, ArH) and 8.05 (m, 1H, ArH).
3,4-Dihydro-3,3-dimethyl-2H-naphtho[2,3-b]pyran-5,10-
dione (8). 20% Aqueous sulfuric acid (50 mL) was
added to the solution of compound 23 (50 mg,
0.2 mmol) in dichloromethane (1 mL) at room tempera-
ture. After the reaction mixture was refluxed for 5 h,
cool water was added to the reaction mixture and
extracted with chloroform (3Â50 mL). The combined
organic phase was washed with water, dried over anhy-
drous sodium sulfate, filtered and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 19:1 v/v hexane–ethyl acetate to
afford the product 8 (86%) as yellow needles, mp 146–
148 C.4 IR(KBr) cm ꢀ1: 1683, 1672, 1589 and 1202. H
NMR(CDCl 3) d: 1.08 (s, 6H, 2ÂCH3), 2.41 (s, 2H,
CH2), 3.92 (s, 2H, OCH2), 7.70 (dt, 1H, J=7.4 Hz,
J=1.6 Hz, ArH), 7.76 (dt, 1H, J=7.4 Hz, J=1.6 Hz,
ArH), 8.10 (dd, 1H, J=7.0 Hz, J=2.0 Hz, ArH) and
8.13 (dd, 1H, J=7.0 Hz, J=2.0 Hz, ArH). 13C NMR
(CDCl3) d: 25.6 (2ÂCH3), 28.6 (C), 33.1 (CH2), 77.1
(OCH2), 126.7, 127.0, 133.7, 134.6 (CH arom), 121.6,
131.5, 132.8, 155.0 (C), 180.2 and 185.2 (C¼O). MS m/z
(%): 242 (M+, 88), 214 (44), 102 (52), 76 (100) and 41
(77). HRMS calcd for C15H14O3 (M+H) 243.1021,
found 243.1024.
13C NMR(CDCl ) d: 25.5 (2ÂCH3), 37.7 (CH2), 38.2
3
(C), 70.3 (CH2O), 126.7, 127.7, 134.4, 134.7, 139.0
(CH), 132.6, 132.8, 149.5 (C), 185.3 and 187.3 (C¼O).
MS m/z (%) 244 (M+, 8), 214 (40), 172 (100), 144 (47)
and 115 (80). Compound 22: IR(nujol) cm ꢀ1: 3070,
1
1700, 1600 and 1300. H NMR(CDCl ) d: 1.10 (s, 3H,
3
CH3), 1.20 (s, 3H, CH3), 1.60 and 2.40 (2Âd, 2Â1H,
J=13 Hz, CH2), 3.20 and 3.30 (2Âd, 2Â1H, J=16 Hz,
CH2O), 3.60 and 3.70 (2Âd, 2Â1H, J=8.5 Hz,
CH2CO), 7.76 (m, 2H, ArH), 8.06 (m, 1H, ArH) and
8.12 (m, 1H, ArH). 13C NMR(CDCl 3) d: 26.2 (CH3), 28.4
(CH3), 41.4 (C), 47.1 (CH2), 51.7 (CH2), 81.3 (CH2O),
86.8 (C), 127.2, 128.4, 134.7, 135.0 (CH arom), 135.0,
135.8 (C arom), 194.6 and 195.6 (C¼O). MS m/z (%): 244
(M+, 67), 201 (57), 146 (67), 104 (83) and 76 (100).
ꢁ
1
3,4-Dihydro-3,3-dimethyl-2H-naphtho[1,2-b]pyran-5,6-
dione (1). A mixture of compound 21 and 22 (0.6 g,
2.6 mmol),
dichlorodicyanobenzoquinone
(DDQ)
(0.87 g, 3.8 mmol) and p-toluenesulfonic acid mono-
hydrate (0.05 g, 0.26 mmol) in dry benzene (8 mL) were
stirred for 30 min under refluxed, cooled to room tem-
perature and filtered, then washed with dichloro-
methane and concentrated in vacuo. The residue was
filtered through aluminium oxide to afford the product
1 (92%) as an orange amorphous powder, mp 151–
1-Allyloxy-naphthalene (25). A mixture of 1-naphthol
(0.5 g, 3.5 mmol), allyl bromide (0.33 mL, 3.9 mmol) and
potassium carbonate (0.48 g, 3.5 mmol) in acetone
(10 mL) were refluxed for 2 h, the reaction mixture was
cooled to room temperature, filtered and washed with
acetone. The combined organic phase was concentrated
in vacuo, then diethyl ether (50 mL) was added, washed
with water (3Â20 mL), dried over anhydrous sodium
sulfate, filtered and concentrated in vacuo. The residue
was purified by column chromatography eluting with
hexane to afford the product 25 (86%) as a colorless
ꢁ
152 C.2 IR(KBr) cm ꢀ1: 1696, 1640, 1599 and 1293. H
NMR(CDCl 3) d: 1.00 (s, 6H, 2ÂCH3), 2.30 (s, 2H,
CH2), 3.90 (s, 2H, CH2O), 7.45 (dt, 1H, J=7.6 Hz,
J=1.1 Hz, ArH), 7.59 (dt, 1H, J=7.6 Hz, J=1.4 Hz,
ArH), 7.76 (dd, 1H, J=7.8 Hz, J=0.6 Hz, ArH) and
8.01 (dd, 1H, J=7.6 Hz, J=0.9 Hz, ArH). 13C NMR
(CDCl3) d: 25.5 (2ÂCH3), 28.6 (C), 32.6 (CH2), 77.8
(CH2O), 124.8, 129.4, 131.4, 135.6 (CH arom), 113.9,
130.5, 132.5, 162.7 (C), 179.7 and 180.3 (C¼O). MS m/z
(%): 242 (M+, 4), 214 (21), 159 (50), and 56 (100). Anal.
calcd for C15H14O3: C, 74.36; H, 5.82. Found: C, 74.19;
H, 5.86.
1
1
oil.16,18 IR(neat) cm ꢀ1: 1580, 1400 and 1269. H NMR
(CDCl3) d: 4.73 (d, 2H, J=5.0 Hz, CH2O), 5.35 (dd, 1H,
J=10.0 Hz, J=1.0 Hz, CH2 ¼CH), 5.55 (dd, 1H,
J=17.0 Hz, J=1.0 Hz, CH2 ¼CH), 6.20 (m, 1H,

3186
N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
ꢀCH¼CH2), 6.82 (d, 1H, J=7.5 Hz, ArH), 7.38 (m,
1H, ArH), 7.45 (d, 1H, J=8.2 Hz, ArH), 7.50 (m, 2H,
ArH), 7.80 (m, 1H, ArH) and 8.35 (m, 1H, ArH). 13C
(d, 1H, J=8.3 Hz, ArH), 7.42 (d, 1H, J=8.3 Hz, ArH),
7.50 (m, 2H, ArH), 7.80 (m, 1H, ArH) and 8.22 (m, 1H,
ArH). 13C NMR(CDCl ) d: 22.0 (CH3), 40.7 (CH2),
3
NMR(CDCl ) d: 69.9 (OCH2), 105.7 (CH2¼), 118.0,
112.8 (CH2¼), 120.2, 121.6, 125.2, 125.8, 127.5, 129.0
(CH arom), 117.6, 124.9, 133.8, 150.1 (C arom), 144.7
(C). MS m/z (%): 198 (M+, 70), 183 (63), 155 (52) and
128 (100).
3
121.0, 122.8, 125.8, 126.4, 127.0, 128.1, 134.0 (CH),
127.0, 135.2, 155.0 (C arom). MS m/z (%): 184 (M+,
70), 143 (72) and 113 (100).
1-(2-Methyl-allyloxy)-naphthalene (26). A mixture of
1-naphthol (0.5 g, 3.5 mmol), 3-chloro-2-methyl-1-pro-
pene (0.4 mL, 4.2 mmol) and potassium carbonate
(0.48 g, 3.5 mmol) in acetone (10 mL) were refluxed for
24 h. The reaction mixture was cooled to room tem-
perature, filtered and washed with acetone. The com-
bined organic phase was concentrated in vacuo, then
diethyl ether (50 mL) was added, washed with water
(3Â20 mL), dried over anhydrous sodium sulfate, fil-
tered and concentrated in vacuo. The residue was pur-
ified by column chromatography eluting with hexane to
afford the product 26 (65%) as a colourless oil.18 IR
(neat) cmꢀ1: 3054, 1579, 1398 and 1101. 1H NMR
(CDCl3) d: 2.00 (s, 3H, Me), 4.65 (s, 2H, CH2O), 5.10
and 5.30 (2Âs, 2Â1H, CH2¼), 6.86 (d, 1H, J=7.5 Hz,
ArH), 7.40 (m, 1H, ArH), 7.48 (d, 1H, J=7.6 Hz, ArH),
7.54 (m, 2H, ArH), 7.85 (m, 1H, ArH) and 8.39 (m, 1H,
2-(3-Hydroxy-propyl)-naphthalen-1-ol (29). A 1 M solu-
tion of borane in tetrahydrofuran (7.4 mL, 7.4 mmol)
was added dropwise to a stirred solution compound (27)
(1.36 g, 7.4 mmol) in anhydrous tetrahydrofuran
(15 mL) at room temperature under nitrogen. After
stirring at room temperature for 4 h, water (0.74 mL)
was added dropwise, followed by 3 M sodium hydroxide
(1 mL). Then hydrogen peroxide (40%, 1 mL) was
added at such a rate that the temperature of the reaction
mixture stayed between 30 and 50 ꢁC. Following the
addition, stirring was continued for 4 h at room tem-
perature. Diethyl ether (15 mL) was added to the reac-
tion mixture, washed with brine and water. After drying
over anhydrous sodium sulfate, filtered and con-
centrated in vacuo, the residue was purified by column
chromatography eluting with 9:1 v/v hexane–ethyl ace-
tate to afford the product 29 (71%) as a colorless
amorphous powder, mp 86–87 ꢁC. IR(KBr) cm ꢀ1: 3481,
1513 and 1272. 1H NMR(CDCl 3) d: 1.95 (m, 2H, CH2),
2.95 (t, 2H, J=6.4 Hz, CH2), 3.65 (t, 2H, J=5.7 Hz,
CH2O), 7.20 (d, 1H, J=8.3 Hz, ArH), 7.37 (d, 1H,
J=8.3 Hz, ArH), 7.45 (m, 2H, ArH), 7.75 (dd, 1H,
J=7.4 Hz, J=1.5 Hz, ArH) and 8.25 (dd, 1H,
ArH). 13C NMR(CDCl ) d: 19.5 (CH3), 71.7 (OCH2),
3
104.9 (CH2¼), 112.5, 120.2, 122.0, 125.1, 125.8, 126.3,
127.4 (CH arom), 126.3, 135.3, 154.3 (C arom), 141.7
(C). MS m/z (%): 198 (M+, 77), 183 (56), 143 (63) and
115 (100).
2-Allyl-naphthalen-1-ol (27). The allyl ether (25) (0.4 g)
in N,N-dimethylformamide (4 mL) was heated for 6 h at
180 ꢁC. Then the reaction mixture was cooled to room
temperature, water was added and extracted with die-
thyl ether (3Â20 mL). The organic phase was washed
with water, dried over anhydrous sodium sulfate, fil-
tered and concentrated in vacuo. The residue was pur-
ified by column chromatography eluting with 49:1 v/v
hexane–dichloromethane to afford the product 27
J=8.9 Hz, J=1.5 Hz, ArH). 13C NMR(CDCl ) d: 25.0
3
(CH2), 31.5 (CH2), 60.5 (CH2O), 120.2, 122.3, 125.2,
125.7, 127.5, 128.8 (CH arom), 119.8, 125.4, 134.0 and
150.5 (C arom). MS m/z (%): 202 (M+, 98), 184 (99),
156 (69) and 128 (100). Anal. calcd for C13H14O2: C,
77.20; H, 6.98. Found: C, 77.41; H, 6.79.
2-(3-Hydroxy-2-methyl-propyl)-naphthalen-1-ol (30). A
1 M solution of borane in tetrahydrofuran (1.3 mL,
1.3 mmol) was added dropwise to a stirred solution of
(28) (0.25 g, 1.3 mmol) in anhydrous tetrahydrofuran
(10 mL) at room temperature under nitrogen. After
stirring at room temperature for 4 h, water (0.13 mL)
was added dropwise followed by 3 M NaOH (0.2 mL).
Then hydrogen peroxide (40%, 0.2 mL) was added at
such a rate that the temperature of the reaction mixture
stayed between 30 and 50 ꢁC. Following the addition,
stirring was continued for 4 h at room temperature.
Diethyl ether (15 mL) was added to the reaction mix-
ture, washed with brine and water. After drying over
anhydrous sodium sulfate, filtered and concentrated in
vacuo, the residue was purified by column chromato-
graphy eluting with 9:1 v/v hexane–ethyl acetate to
afford the product 30 (96%) as a colorless amorphous
powder, mp 89–90 ꢁC. IR(KBr) cm ꢀ1: 3376, 1384 and
1016. 1H NMR(CDCl 3) d: 1.08 (d, 3H, J=7.0 Hz,
CH3), 2.10 (m, 1H, CH), 2.40 (br s, 1H, OH), 2.90 (m,
2H, CH2), 3.38 (dd, 1H, J=10.3 Hz, J=6.9 Hz, CH2O),
3.60 (dd, 1H, J=10.3 Hz, J=3.9 Hz, CH2O), 7.21 (d,
1H, J=8.3 Hz, ArH), 7.40 (d, 1H, J=8.3 Hz, ArH),
7.48 (m, 2H, ArH), 7.80 (m, 1H, ArH), 8.15 (br s, 1H,
(82%) as a colorless oil.16 IR(neat) cm ꢀ1: 3509, 1289
1
and 1265. H NMR(CDCl ) d: 3.56 (d, 2H, J=6.2 Hz,
3
CH2), 5.23 (m, 2H, CH2 ¼CH), 5.54 (s, 1H, OH), 6.67
(m, 1H, CH2 ¼CH), 7.21 (d, 1H, J=8.3 Hz, ArH), 7.40
(d, 1H, J=8.3 Hz, ArH), 7.45 (m, 2H, ArH), 7.77 (m,
1H, ArH) and 8.16 (m, 1H, ArH). 13C NMR(CDCl 3) d:
36.4 (CH2), 117.7 (CH2¼), 121.0, 122.0, 126.0, 126.4,
128.2, 129, 136.8 (CH), 118.4, 125.5, 134.4, 150.3 (C
arom). MS m/z (%): 184 (M+, 100), 169 (32), 141 (45),
128 (63) and 115 (38).
2-(2-Methylallyl)-naphthalen-1-ol (28). The allyl ether
(26) (0.4 g) in N,N-dimethylformamide (4 mL) was
heated for 6 h at 180 ꢁC. Then the reaction mixture was
cooled to room temperature, water was added and
extracted with diethyl ether. The organic phase was
washed with water, dried over anhydrous sodium sul-
fate, filtered and concentrated in vacuo. The residue was
purified by column chromatography eluting with 49:1 v/
v hexane–dichloromethane to afford the product 28
(93%) as a colorless oil.20 IR(neat) cm ꢀ1: 3489, 1657
and 1266; 1H NMR(CDCl 3) d: 1.80 (s, 3H, Me), 3.58 (s,
2H, CH2), 5.03 (s, 2H, CH2¼), 5.82 (s, 1H, OH), 7.24
OH) and 8.30 (m, 1H, ArH). 13C NMR(CDCl ) d: 17.5
3

N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
3187
(CH3), 32.5 (CH2), 36.0 (CH), 65.7 (CH2O), 119.5,
122.2, 125.1, 125.8, 127.5, 129.8 (CH arom), 118.9,
125.7, 133.8 and 150.5 (C arom). MS m/z (%): 216
(M+, 62), 198 (40), 183 (44), 157 (94), 128 (100). Anal.
calcd for C14H16O2: C, 77.75; H, 7.46. Found: C, 77.66;
H, 7.43.
1564 and 1258. 1H NMR(CDCl 3) d: 2.05 (m, 2H, CH2),
2.55 (t, 2H, J=6.4 Hz, CH2), 4.45 (t, 2H, J=5.2 Hz,
CH2O), 7.52 (t, 1H, J=7.7 Hz, ArH), 7.65 (t, 1H,
J=7.7 Hz, ArH), 7.80 (d, 1H, J=7.8 Hz, ArH) and 8.07
(d, 1H, J=8.1 Hz, ArH). 13C NMR(CDCl 3) d: 18.5
(CH2), 21.4 (CH2), 69.0 (CH2O), 124.6, 129.2, 131.3,
135.5 (CH arom), 114.8, 130.6, 132.9, 163.7 (C), 179.2
and 180.2 (C¼O). MS m/z (%): 214 (M+, 21), 186 (75),
158 (63), 130(71), 102 (69) and 76 (100). Anal. calcd for
C13H10O3: C, 72.89; H, 4.71. Found: C, 72.71; H, 4.99.
2-(3-Hydroxy-propyl)-[1,4]-naphthoquinone (31). To a
stirred solution of compound (29) (0.2 g, 0.99 mmol) in
methanol-dimethylformamide (MeOH–DMF) (3:1)
(13 mL) was added a solution of Fremy’s salt (2.7 g) in
water 52 mL and 1 M aqueous sodium acetate solution
(1.44 mL). After stirring for 8 h at room temperature,
the reaction mixture was extracted with diethyl ether
(3Â20 mL). The combined organic phase was washed
with water and brine, dried over anhydrous sodium
sulfate and concentrated in vacuo. The residue was
purified by column chromatography eluting with 4:1 v/v
hexane–ethyl acetate to afford the product 31 (71%) as
a yellow solid, mp 66–67 ꢁC. IR(KBr) cm ꢀ1: 3249, 1663
and 1305. 1H NMR(CDCl 3) d: 1.85 (m, 2H, CH2), 1.95
(br s, 1H, OH), 2.65 (t, 2H, J=7.6 Hz, CH2), 3.70 (t,
2H, J=6.1 Hz, CH2O), 6.80 (s, 1H, CH¼), 7.70 (m, 2H,
ArH) and 8.05 (m, 2H, ArH). 13C NMR(CDCl 3) d: 26.6
(CH2), 31.8 (CH2), 62.3 (CH2O), 126.7, 127.3, 134.3,
134.4, 135.9 (CH), 132.7, 132.8, 152.0 (C), 185.7 and
186.1 (C¼O). MS m/z (%): 216 (M+, 32), 188 (51), 128
(61) and 76 (100). Anal. calcd for C13H12O3: C, 72.21;
H, 5.59 Found: C, 72.17; H, 5.59.
3-Methyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione
(3). A mixture of compound 32 (0.2 g, 0.87 mmol),
dichlorodicyanobenzoquinone (DDQ) (0.3 g, 1.3 mmol)
and p-toluenesulfonic acid monohydrate (0.016 g,
0.08 mmol) in dry benzene (4 mL) were stirred for
20 min under refluxed and cooled to room temperature,
filtered, washed with dichloromethane and concentrated
in vacuo. The residue was filtered through aluminium
oxide to afford the product 3 (95%) as an orange
amorphous powder, mp 148–149 ꢁC. IR(KBr) cm
:
ꢀ1
1
1688, 1645, 1256 and 1168. H NMR(CDCl ) d: 1.03
3
(d, 3H, J=6.5 Hz, CH3), 2.00 (m, 1H, CH2), 2.07 (m,
1H, CH), 2.70 (m, 1H, CH2), 3.81 (m, 1H, CH2O), 4.37
(m, 1H, CH2O), 7.43 (m, 1H, ArH), 7.57 (m, 1H, ArH),
7.71 (m, 1H, ArH) and 7.98 (m, 1H, ArH). 13C NMR
(CDCl3) d: 17.3 (CH3), 26.5 (CH), 26.6 (CH2), 74.0
(CH2O), 124.7, 129.3, 131.3, 135.5 (CH arom), 114.2,
130.5, 132.7, 163.3 (C), 179.3 and 180.3 (C¼O). MS m/z
(%): 228 (M+, 3), 200 (100), 185 (71), 158 (58) and 102
(70). Anal. calcd for C14H12O3: C, 73.67; H, 5.30.
Found: C, 73.61; H, 5.40.
2-(3-Hydroxy-2-methyl-propyl)-[1,4]-naphthoquinone (32).
To
a
stirred solution of compound 30 (0.2 g,
0.92 mmol) in MeOH–DMF (3:1) (13 mL) was added a
solution of Fremy’s salt (2.5 g) in water 50 mL and 1 M
aqueous sodium acetate solution (1.3 mL). After stirring
for 13 h at room temperature, the reaction mixture was
extracted with diethyl ether (3 30 mL). The combined
organic phase was washed with water and brine, dried
over anhydrous sodium sulfate and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 5:1 v/v hexane–ethyl acetate to
3-Hydroxy-2-(3-hydroxypropyl)-1,4-naphthoquinone (33).
The solution of compound (2) (0.2 g, 0.93 mmol) in 1%
aqueous sodium hydroxide solution (6 mL) was refluxed
for 2 h. Then the reaction mixture was cooled to room
temperature and acidified with acetic acid, extracted
with dichloromethane (3Â30 mL). The combined
organic phase was washed with water, dried over an-
hydrous sodium sulfate, filtered and concentrated in
vacuo. The residue was recrystallized from hexane–di-
chloromethane to give the product 33 (86%) as a yellow
afford the product 32 (85%) as a yellow oil. IR(neat)
1
cmꢀ1: 3403, 1662, 1589 and 1029. H NMR(CDCl ) d:
3
amorphous powder, mp 106–107 ꢁC. IR(KBr) cm
:
ꢀ1
0.95 (d, 3H, J=6.8 Hz, CH3), 1.99 (m, 1H, CH), 2.09
(br s, 1H, OH), 2.38 and 2.72 (2Âm, 2Â1H, CH2), 3.43
and 3.51 (2Âm, 2Â1H, CH2O), 6.80 (s, 1H, CH¼), 7.71
(m, 2H, ArH) and 8.05 (m, 2H, ArH). 13C NMR
(CDCl3) d: 17.3 (CH3), 33.8 (CH2), 36.4 (CH), 67.5
(CH2O), 126.7, 127.4, 134.3, 134.5, 137.1 (CH), 132.7,
132.8, 150.8 (C), 185.6 and 186.4 (C¼O). MS m/z (%):
230 (M+, 18), 212 (64), 197 (100) and 115 (84). HRMS
calcd for C14H14O3 (M+Na) 253.0841, found 253.0848.
1
3342, 1640, 1638, 1365 and 1272. H NMR(CDCl ) d:
3
1.81 (m, 2H, CH2), 2.70 (t, 2H, J=7.0 Hz, CH2), 3.60 (t,
2H, J=6.0 Hz, CH2O), 7.69 (m, 2H, ArH) and 8.06 (m,
2H, ArH). 13C NMR(CDCl 3) d: 19.6 (CH2), 31.3
(CH2), 62.1 (CH2O), 126.8, 127.5, 133.7, 135.6 (CH
arom), 124.3, 130.1, 133.3, 154.4 (C), 181.7 and 186.0
(C¼O). MS m/z (%): 232 (M+, 36), 214 (97), 188 (77),
105 (65) and 77 (100). Anal. calcd for C13H12O4: C,
67.23; H, 5.21. Found: C, 67.15; H, 5.27.
3,4-Dihydro-2H-naphtho-[1,2-b]pyran-5,6-dione (2).
A
mixture of compound 31 (0.2 g, 0.9 mmol), dichloro-
dicyanobenzoquinone (DDQ) (0.3 g, 1.4 mmol) and
p-toluenesulfonic acid monohydrate (0.02 g, 0.09 mmol)
in dry benzene (4 mL) were stirred for 30 min under
refluxed and cooled to room temperature, filtered,
washed with dichloromethane and concentrate in vacuo.
The residue was filtered through aluminium oxide to
afford the product 2 (95%) as an orange amorphous
powder, mp 184–185 ꢁC.6 IR(KBr) cm ꢀ1: 1687, 1642,
3-Hydroxy-2-(3-hydroxy-2-methylpropyl)-1,4-naphtho-
quinone (34). The solution of compound 3 (0.1 g,
0.44 mmol) was refluxed in 1% aqueous sodium
hydroxide solution (2.7 mL) for 2 h. Then the reaction
mixture was cooled to room temperature, acidified with
acetic acid, extracted with dichloromethane (3Â30 mL).
The combined organic phase was washed with water,
dried over anhydrous sodium sulfate, filtered and con-
centrated in vacuo. The residue was recrystallized from

3188
N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
hexane–dichloromethane to give the product 34 (94%)
as a yellow amorphous powder, mp 146–147 ꢁC. IR
(KBr) cmꢀ1: 3485, 1656, 1371 and 1215. 1H NMR
(CDCl3) d: 0.96 (d, 3H, J=6.8 Hz, CH3), 1.60 (br s, 2H,
2ÂOH), 1.95 (m, 1H, CH), 2.58 (m, 2H, CH2), 3.36 (m,
2H, CH2O), 7.67 (m, 2H, ArH) and 8.04 (m, 2H, ArH).
13C NMR(CDCl 3) d: 17.8 (CH3), 26.7 (CH2), 36.3
(CH), 67.2 (CH2O), 126.9, 127.6, 133.8, 135.6 (CH
arom), 123.5, 130.1, 133.4, 154.6 (C), 181.7 and 186.3
(C¼O). MS m/z (%): 246 (M+, 200), 216 (75), 188 (80),
105 (73) and 77 (100). HRMS calcd for C14H14O4
(M+H) 247.0970, found 247.0966.
2-Allyl-3-hydroxy-1,4-naphthoquinone (36). A solution
of lawsone (35) (2.0 g, 11.5 mmol) in dimethylforma-
mide (15 mL) was added to the potassium carbonate
(1.6 g, 11.5 mmol) in dimethylformamide (50 mL) and
stirring for 15min at room temperature. Allyl bromide
(3.5 g, 28.7mmol) in dimethylformamide (5 mL) was
added dropwise over 15min and stirring was continued
for 15min at the same temperature. After the reaction
mixture was refluxed for 3 h, then the reaction mixture
was cooled to room temperature, filtered and dichloro-
methane (30 mL) was added, then washed with water
(5Â25mL), dried over anhydrous sodium sulfate, filtered
and concentrated in vacuo. The residue was purified by
column chromatography eluting with 9:1v/v hexane–ethyl
acetate to afford the product 36 (81%) and recrystalized
from hexane–dichloromethane to give yellow needles, mp
112–113 ꢁC.25 IR(KBr) cm ꢀ1: 3362, 1648, 1600 and 1227.
3,4-Dihydro-2H-naphtho[2,3-b]pyran-5,10-dione (9). 20%
aqueous sulfuric acid (10 mL) was added to the solution
of compound 33 (40 mg, 0.17 mmol) in dichloromethane
(1 mL) at room temperature. After the reaction mixture
was refluxed for 5 h, cool-water (3Â30 mL) was added
to the reaction mixture and extracted with chloroform.
The combined organic phase was washed with water,
dried over anhydrous sodium sulfate, filtered and con-
centrated in vacuo. The residue was purified by column
chromatography eluting with 19:1 v/v hexane–ethyl
acetate to afford the product 9 (89%) and recrystalized
from hexane–dichloromethane to give yellow needles,
1H NMR(CDCl ) d: 3.31 (d, 2H, J=4.5 Hz, CH2), 5.00
3
(dd, 1H, J=10 Hz, J=1.4 Hz, CH2¼), 5.11 (dd, 1H,
J=17 Hz, J=1.4 Hz, CH2¼), 5.88 (m, 1H, CH¼), 7.25 (br
s, 1H, OH), 7.64 (dt, 1H, J=7.5Hz, J=1.0Hz, ArH), 7.71
(dt, 1H, J=7.5Hz, J=1.0Hz, ArH), 8.03 (dd, 1H,
J=7.6Hz, J=1.3 Hz, ArH) and 8.08 (dd, 1H, J=1.3Hz,
J=7.6Hz, ArH). 13C NMR(CDCl 3) d: 27.7 (CH2), 122.0
(CH2¼), 126.4, 127.1, 129.6, 133.0, 133.2 (CH), 116.6,
133.9, 135.2, 153.3 (C), 181.7 and 184.4 (C¼O). MS m/z
(%): 214 (M+, 64), 129 (78), 115 (100) and 77 (95).
mp 216–218 ꢁC.6 IR(KBr) cm ꢀ1: 2948, 1672, 1638 and
1
1187. H NMR(CDCl ) d: 2.05 (m, 2H, CH2), 2.63 (t,
3
2H, J=6.3 Hz, CH2), 4.36 (t, 2H, J=5.3 Hz, CH2O),
7.69 (dt, 1H, J=7.4 Hz, J=1.6 Hz, ArH), 7.73 (dt, 1H,
J=7.4 Hz, J=1.6 Hz, ArH), 8.09 (dd, 1H, J=1.1 Hz,
J=6.8 Hz, ArH) and 8.11 (dd, 1H, J=6.8 Hz,
J=1.1 Hz, ArH). 13C NMR(CDCl 3) d: 19.0 (CH2), 21.1
(CH2), 68.3 (CH2O), 126.7, 126.9, 133.3, 134.6 (CH
arom), 122.3, 131.5, 132.6, 156.1 (C), 180.3, 184.8
(C¼O). MS m/z (%): 214 (M+, 100), 129 (42), 104 (53)
and 76 (99). HRMS calcd for C13H10O3 (M+H)
215.0708, found 215.0705.
2-Hydroxy-3-(2-methyl-2-propenyl)-1,4-naphthoquinone
(37). A solution of lawsone (35) (2.0 g, 11.5 mmol) in
dimethylformamide (15 mL) was added to the potas-
sium carbonate (1.6 g, 11.5mmol) in dimethylformamide
(50 mL) and stirring for 15min at room temperature.
3-Chloro-2-methyl-1-propene (2.1 g, 23.0 mmol) in di-
methylformamide (5 mL) was added dropwise over
15 min and stirring was continued for 15 min at the
same temperature. After the reaction mixture was
refluxed for 3 h, then the reaction mixture was cooled to
room temperature, filtered and added dichloromethane
(30 mL), then washed with water (5Â25 mL), dried over
anhydrous sodium sulfate, filtered and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 9:1 v/v hexane–ethyl acetate to
afford the product 37 (59%) and recrystalized from
hexane–dichloromethane to give yellow needles, mp
3,4-Dihydro-3-methyl-2H-naphtho[2,3-b]pyran-5,10-dione
(10). 20% Aqueous sulfuric acid (70 mL) was added to
the solution of compound 34 (500 mg, 0.2 mmol) in di-
chloromethane (2 mL) at room temperature. After the
reaction mixture was refluxed for 5 h, cool-water was
added to the reaction mixture and extracted with
chloroform (3Â50 mL). The combined organic phase
was washed with water, dried over anhydrous sodium
sulfate, filtered and concentrated in vacuo. The residue
was purified by column chromatography eluting with
19:1 v/v hexane–ethyl acetate to afford the product 10
(89%) and recrystalized from hexane–dichloromethane
126–126.5 ꢁC.31 IR(KBr) cm ꢀ1: 3351, 1646, 1593 and
1
1228. H NMR(CDCl ) d: 1.75 (s, 3H, CH3), 3.27 (s,
3
2H, CH2), 4.68 (d, 1H, J=1.8 Hz, CH2¼), 4.73 (d, 1H,
J=1.4 Hz, CH2¼), 7.35 (s, 1H, OH), 7.64 (dt, 1H,
J=7.5 Hz, J=1.4 Hz, ArH), 7.71 (dt, 1H, J=7.5 Hz,
J=1.4 Hz, ArH), 8.06 (dd, 1H, J=7.6 Hz, J=1.4 Hz,
ArH) and 8.08 (dd, 1H, J=1.4 Hz, J=7.6 Hz, ArH).
13C NMR(CDCl 3) d: 23.7 (CH3), 31.7 (CH2), 112.1
(CH2¼), 126.8, 127.6, 133.6, 135.6 (CH arom), 122.5,
130.5, 133.5, 142.7, 154.2 (C ), 182.1 and 185.0 (C¼O).
MS m/z (%): 228 (M+, 100), 213 (75) and 77 (34).
to give yellow needles, mp 167–168 ꢁC.31 IR(KBr)
1
cmꢀ1: 2963, 1675, 1638 and 1239. H NMR(CDCl ) d:
3
1.13 (d, 3H, J=6.4 Hz, CH3), 2.15 (m, 2H, CH2), 2.84
(m, 1H, CH), 3.80 and 4.41 (2Âm, 2Â1H, OCH2), 7.70
(dt, 1H, J=7.5 Hz, J=1.6 Hz, ArH), 7.73 (dt, 1H,
J=7.5 Hz, J=1.6 Hz, ArH), 8.10 (dd, 1H, J=7.5 Hz,
J=2.0 Hz, ArH) and 8.12 (dd, 1H, J=7.5 Hz,
J=2.0 Hz, ArH). 13C NMR(CDCl 3) d: 17.4 (CH3), 26.2
(CH2), 28.1 (CH), 73.3 (CH2O), 126.7, 126.9, 133.7,
134.6 (CH arom), 121.8, 131.6, 132.7, 155.7 (C), 180.3,
184.9 (C¼O). MS m/z (%): 228 (M+, 60), 200 (49), 102
(51) and 76 (100). HRMS calcd for C14H12O3
(M+NH4) 246.1130, found 246.1128.
2,3-Dihydro-2-methylnaphthol[1,2-b]furan-4,5-dione 6).
A solution of 2-allyl-3-hydroxy-1,4-naphthoquinone
(36) (1 g, 4.7 mmol) in dichloromethane (5 mL) was
added dropwise to concentrated sulfuric acid (25 mL) at
0 ꢁC. After stirring for 30–45 min at 0 ꢁC, the reaction
mixture was quenched with ice-water, and extracted

N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
3189
with dichloromethane (3Â30 mL). The combined
organic phase was washed with water, dried over an-
hydrous sodium sulfate, filtered and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 17:3 v/v hexane–ethyl acetate to
afford the product 6 (70%) and recrystalized from hex-
ane–dichloromethane to give red needles, mp 126–
126.5 ꢁC. IR(KBr) cm ꢀ1: 1690, 1645 and 1158. 1H
2,3-Dihydro-2-methylnaphtho[2,3-b]furan-4,9-dione (12).
20% Aqueous sulfuric acid (40 mL) was added to the
solution of compound 36 (200 mg, 0.93 mmol) in di-
chloromethane (2 mL) at room temperature. After the
reaction mixture was refluxed for 5 h, cool water was
added to the reaction mixture and extracted with
chloroform (3Â50 mL). The combined organic phase
was washed with water, dried over anhydrous sodium
sulfate, filtered and concentrated in vacuo. The residue
was purified by column chromatography eluting with
19:1 v/v hexane–ethyl acetate to afford the product 12
(75%) and recrystalized from hexane–dichloromethane
NMR(CDCl ) d: 1.52 (d, 3H, J=3.2 Hz, CH3), 2.68
3
(dd, 1H, J=7.6 Hz, J=7.2 Hz, CH2), 3.22 (dd, 1H,
J=7.6 Hz, J=9.2 Hz, CH2), 5.20 (m, 1H, O–CH), 7.52
(m, 1H, ArH), 7.58 (m, 2H, ArH) and 8.01 (m, 1H,
ArH). 13C NMR(CDCl ) d: 22.2 (CH3), 33.7 (CH2),
to give yellow needles, mp 166.5–167 ꢁC.9 IR(KBr)
3
1
84.9 (CH), 124.7, 127.9, 129.6, 131.0 (CH arom), 115.4,
132.1, 134.7, 169.9 (C), 175.8 and 181.5 (C¼O). MS m/z
(%): 214 (M+), 186 (100), 158 (39) and 129 (29). HRMS
calcd for C13H10O3 (M) 214.0624, found 214.0630.
cmꢀ1: 1683, 1645, 1593 and 1194. H NMR(CDCl ) d:
3
1.50 (d, 3H, J=6.4 Hz, CH3), 2.74 (dd, 1H, J=16.9 Hz,
J=7.8 Hz, CH2), 3.28 (dd, 1H, J=16.9 Hz, J=10.2 Hz,
CH2), 5.13 (m, 1H, CH), 7.60 (dt, 1H, J=7.4 Hz,
J=1.5 Hz, ArH), 7.65 (dt, 1H, J=7.4 Hz, J=1.5 Hz,
ArH), 7.99 (dd, 1H, J=1.7 Hz, J=3.4 Hz, ArH) and
8.01 (dd, 1H, J=1.7 Hz, J=3.4Hz, ArH). 13C NMR
(CDCl3) d: 22.5 (CH3), 35.0 (CH2), 83.7 (CH), 126.6,
126.9, 133.5, 134.8 (CH arom), 124.5, 132.1, 133.7, 160.5
(C), 178.7 and 183.0 (C¼O). MS m/z (%): 214 (M+, 84),
129 (50), 15 (50), 104 (67) and 76 (100). HRMS calcd for
C13H10O3 (M+H) 215.0708, found 215.0704.
2,3-Dihydro-2,2-dimethylnaphtho[1,2-b]furan-4,5-dione
(5). A solution of compound 37 (1 g, 4.4 mmol) in di-
chloromethane (5 mL) was added dropwise to con-
centrated sulfuric acid (25 mL) at 0 ꢁC. After stirring for
30–45 min at 0 ꢁC, the reaction mixture was quenched
with ice-water, and extracted with dichloromethane
(3Â30 mL). The combined organic phase was washed
with water, dried over anhydrous sodium sulfate, fil-
tered and concentrated in vacuo. The residue was pur-
ified by column chromatography eluting with 17:3 v/v
hexane–ethyl acetate to afford the product 5 (61%) and
recrystalized from hexane–dichloromethane to give red
needles, mp 170–171 ꢁC.8 IR(KBr) cm ꢀ1: 1694, 1642,
1403 and 1276. 1H NMR(CDCl 3) d: 1.54 (s, 6H,
2ÂCH3), 2.89 (s, 2H, CH2), 7.51 (m, 1H, ArH), 7.57 (m,
2H, ArH) and 8.01 (m, 1H, ArH). 13C NMR(CDCl 3) d:
28.6 (2ÂCH3), 39.5 (CH2), 93.9 (C), 124.8, 128.1, 129.5,
131.1 (CH arom), 115.2, 132.1, 134.6, 169.0 (C), 175.9
and 181.5 (C¼O). MS m/z (%): 228 (M+, 83), 186
(100), 158 (38) and 129 (30). Anal. calcd for C14H12O3:
C, 73.67; H, 5.30. Found: C, 73.69; H, 5.30.
3,4-Dihydro- 2-hydroxy -2H -naphtho[1,2-b]pyran-5,6-
dione (4). A solution of m-chloroperbenzoic acid (0.2 g,
1.1 mmol) in dichloromethane (2 mL) was added drop-
wise to the solution of 2-allyl-3-hydroxy-1,4-naphtho-
quinone (36) (0.2 g, 0.93 mmol) in dichloromethane
(2 mL) at 0 ꢁC. After the reaction mixture was stirred for
24 h, then the reaction mixture was filtered and di-
chloromethane (50 mL) was added, then washed with
water (3Â20 mL), dried over anhydrous sodium sulfate,
filtered and concentrated in vacuo. The residue was
purified by column chromatography eluting with 7:3 v/v
hexane–ethyl acetate to afford the product 4 (30%) and
recrystalized from hexane–ethyl acetate to give red nee-
dles, mp 197–199 ꢁC. IR(KBr) cm ꢀ1: 3470, 1609 and
1
2,3-Dihydro-2,2-dimethylnaphtho[2,3-b]furan-4,9-dione
(11). 20% Aqueous sulfuric acid (50 mL) was added to
the solution of compound 37 (360 mg, 1.58 mmol) in
dichloromethane (2 mL) at room temperature. After the
reaction mixture was refluxed for 5 h, cool water was
added to the reaction mixture and extracted with
chloroform (3Â50 mL). The combined organic phase
was washed with water, dried over anhydrous sodium
sulfate, filtered and concentrated in vacuo. The residue
was purified by column chromatography eluting with
19:1 v/v hexane–ethyl acetate to afford the product 11
(86%) and recrystalized from hexane–dichloromethane
1277. H NMR(CDCl ) d: 2.78 (dd, 1H, J=15.3 Hz,
3
J=7.4 Hz, CH2), 2.93 (dd, 1H, J=10.2 Hz, J=15.3 Hz,
CH2), 3.58 (dd, 1H, J=12.3 Hz, J=5.1 Hz, OCH2), 3.70
(dd, 1H, J=12.3 Hz, J=3.1 Hz, OCH2), 4.66 (br s, 1H,
OH), 5.00 (m, 1H, CH), 7.38 (dt, 1H, J=7.5 Hz,
J=1.4 Hz, ArH), 7.46 (dt, 1H, J=7.5 Hz, J=1.4 Hz,
ArH), 7.50 (dd, 1H, J=7.5 Hz, J=1.4 Hz, ArH), 7.82
(d, 1H, J=7.6 Hz, ArH). 13C NMR(CDCl 3) d: 28.3
(CH2), 63.8 (CHOH), 88.7 (CH2O), 125.2, 129.5, 132.3,
135.0 (CH arom), 116.0, 127.9, 131.0, 170.7 (C), 175.6
and 181.7 (C¼O). LCMS 253 (M++Na). HRMS calcd
for C13H10O4 (M+Na) 253.0477, found 253.0477.
to give yellow needles, mp 184–184.5 ꢁC.8 IR(KBr)
1
cmꢀ1: 1675, 1634, 1440 and 1206. H NMR(CDCl ) d:
2-(Ethylacetylate)-3-hydroxy-1,4-naphthoquinone (38). A
solution
3
1.61 (s, 6H, 2ÂCH3), 3.02 (s, 2H, CH2), 7.68 (dt, 1H,
J=6.0 Hz, J=1.5 Hz, ArH), 7.73 (dt, 1H, J=6.0 Hz,
J=1.5 Hz, ArH), 8.08 (dd, 1H, J=5.6 Hz, J=1.4 Hz,
ArH) and 8.10 (dd, 1H, J=1.4 Hz, J=5.6 Hz, ArH).
of
2-hydroxy-1,4-naphthoquinone
(35)
(200 mg, 1.2 mmol) in DMF (1 mL) was added to
lithium carbonate (100 mg, 1.2 mmol) in dimethylfor-
mamide (5 mL) at room temperature and stirring was
continued for 15 min at room temperature, ethyl bro-
moacetate (380 mg, 2.3 mmol) in DMF (1 mL) was
added dropwise over 5 min and stirring was continued
for 15 min at room temperature. After the reaction
mixture was refluxed for 3 h, then the reaction mixture
13C NMR(CDCl ) d: 29.0 (2ÂCH3), 40.7 (CH2), 92.6
3
(C), 126.5, 126.8, 133.4, 134.7 (CH arom), 124.0, 132.2,
133.7, 178.9 (C), 189.5 and 183.1 (C¼O). MS m/z (%):
228 (M+, 35), 200 (60), 104 (49) and 76 (100). HRMS
calcd for C14H12O3 (M+H) 229.0864, found 229.0864.

3190
N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
was cooled to room temperature, and dichloromethane
(3 mL) was added, then washed with water (5Â10 mL),
dried over anhydrous sodium sulfate, filtered and con-
centrated in vacuo. The residue was purified by column
chromatography eluting with 2:1:1 v/v/v hexane–ethyl
acetate–chloroform to afford the product 38 (40%) and
recrystalized from hexane–ethyl acetate to give brown
2,3-Dihydronaphtho[2,3-b]furan-4,9-dione (13). 20%
Aqueous sulfuric acid (10 mL) was added to the solution
of compound 39 (25 mg, 0.11 mmol) in dichloromethane
(0.5 mL) at room temperature. After the reaction mix-
ture was refluxed for 5 h, cool water was added to the
reaction mixture and extracted with chloroform
(3Â10 mL). The combined organic phase was washed
with water, dried over anhydrous sodium sulfate, fil-
tered and concentrated in vacuo. The residue was pur-
ified by column chromatography eluting with 19:1 v/v
hexane–ethyl acetate to afford the product 13 (54%)
and recrystalized from hexane–dichloromethane to give
yellow needles, mp 214–216 ꢁC.9 IR(KBr) cm ꢀ1: 1675,
1403 and 1052. 1H NMR(CDCl 3) d: 3.25 (t, 2H,
J=9.9 Hz, CH2), 4.83 (t, 2H, J=9.9 Hz, OCH2), 7.70
(dt, 1H, J=7.5 Hz, J=1.5 Hz, ArH), 7.75 (dt, 1H,
J=7.5 Hz, J=1.5 Hz, ArH) and 8.10 (dd, 2H,
needles, mp 157–158 ꢁC.32 IR(KBr) cm ꢀ1: 3239, 1731,
1
1671, 1475 and 1049. H NMR(CDCl ) d: 1.29 (t, 3H,
3
J=7.2 Hz, CH3), 3.68 (s, 2H, CH2), 4.20 (q, 2H,
J=7.2 Hz, CH2O), 7.73 (dt, 1H, J=6.1 Hz, J=1.4 Hz,
ArH), 7.80 (dt, 1H, J=6.1 Hz, J=1.4 Hz, ArH), 8.13
(dd, 1H, J=6.1 Hz, J=1.4 Hz, ArH) and 8.16 (dd, 1H,
J=6.1 Hz, J=1.4 Hz, ArH). 13C NMR(CDCl ) d: 14.8
3
(CH3), 29.6 (CH2), 61.8 (OCH2), 126.9, 127.5, 133.7,
135.7 (CH arom), 117.6, 130.1, 133.2, 154.8 (C), 170.7,
181.8 and 184.5 (C¼O). MS m/z (%): 260 (M+, 9), 232
(52), 187 (100), 159 (96) and 105 (65).
J=7.5 Hz, J=1.5 Hz, ArH). 13C NMR(CDCl ) d: 28.0
3
(CH2), 73.9 (CH2O), 126.7, 126.9, 133.6, 134.8 (CH
arom), 125.1, 132.1, 133.6, 161.4 (C), 178.7 and 183.0
(C¼O). LC/MS 223 (M+Na). HRMS calcd for
C12H8O3 (M+Na) 223.0371, found 223.0398.
2-Hydroxy-3-(2-hydroxyethyl)-1,4-naphthoquinone (39).
Sodium borohydride (100 mg, 2.6 mmol) was added to
the solution of compound 38 (100 mg, 0.38 mmol) in
ethanol (5 mL) at 0 ꢁC. After the reaction mixture was
refluxed for 7 h, then the reaction mixture was cooled to
room temperature, the solution was poured into cool-
water (10 mL), acidified with 1% aqueous sulfuric acid
and extracted with chloroform (3Â5 mL), dried over
anhydrous sodium sulfate, filtered and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 1:1 hexane–ethyl acetate to afford the
product 39 (48%) and recrystalized from hexane–ethyl
acetate to give yellow needles, mp 148–149 ꢁC.7 IR(KBr)
cmꢀ1: 3500, 1672, 1638, 1433 and 1068. 1H NMR(CDCl 3)
d: 2.95 (t, 2H, J=6.1Hz, CH2), 3.90 (t, 2H, J=6.1Hz,
OCH2), 7.72 (dt, 1H, J=7.5 Hz, J=1.4 Hz, ArH), 7.79 (dt,
1H, J=7.5 Hz, J=1.4 Hz, ArH), 8.12 (dd, 1H, J=7.7 Hz,
J=1.3 Hz, ArH) and 8.15 (dd, 1H, J=7.7 Hz, J=1.3 Hz,
ArH). 13C NMR (CDCl3) d: 27.6 (CH2), 62.2 (CH2O),
126.9, 127.5, 133.8, 135.6 (CH arom), 121.9, 130.1, 133.4,
154.8 (C), 181.8 and 186.1 (C¼O). MS m/z (%): 218 (M+,
57), 188 (96), 160 (82), 105 (82) and 77 (100).
Cytotoxicity assay
By MTT colorimetric method. Compounds 1–13 were
subjected to cytotoxic evaluation against KB (human
epidermoid carcinoma), HeLa (human cervical carci-
noma) and HepG2 (human hepatocellular carcinoma)
cell lines employing the colorimetric method.24 Adria-
mycin was used as the reference substance which exhi-
bits activity against KB, HeLa and HepG2 cell lines.
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium
bromide (Sigma Chemical Co., USA) was dissolved in
saline to make the concentration of 5 mg/mL as a stock
solution. Cancer cells (3Â103 cells) suspended in 100 mg/
well of MEM medium containing 10% fetal calf serum
(FCS, Gibco BRL, Life Technologies, NY, USA) were
seeded onto a 96-well culture plate (Costar, Corning
Incorporated, NY 14831, USA). After 24 h pre-incu-
bation at 37 ꢁC in a humidified atmosphere of 5% CO2/
95% air to allow cells attachment, various concentra-
tions of test solution (10 mL/well) as listed in Table 1
were added and then incubated for 48 h under the above
condition. At the end of the incubation, 10 mL of tetra-
zolium reagent was added into each well and then incu-
bated at 37 ꢁC for 4 h. The supernatant was decanted,
and DMSO (100 mL/well) was added to allow formosan
solubilization. The optical density (OD) of each well
was detected by a Microplate reader (Bio-Rad, Bench-
mark Microplate reader) at 550 nm and for correction at
595 nm. Each determination represents the average
means of six replicates. The 50% inhibition concen-
tration (IC50) was determined by curve fitting.
2,3-Dihydronaphtho[1,2-b]furan-4,5-dione (7). A solution
of compound 39 (25 mg, 0.11 mmol) in dichloromethane
(0.5 mL) was added dropwise to concentrated sulfuric
acid (3 mL) at 0 ꢁC. After stirring for 30–45 min at 0 ꢁC,
the reaction mixture was quenched with ice-water, and
extracted with dichloromethane (3Â3 mL). The com-
bined organic phase was washed with water, dried over
anhydrous sodium sulfate, filtered and concentrated in
vacuo. The residue was purified by column chromato-
graphy eluting with 17:3 v/v hexane–ethyl acetate to
afford the product 7 (45%) and recrystalized from hex-
ane–dichloromethane to give red needles, mp 227–
229 ꢁC.7 IR(KBr) cm ꢀ1: 1687, 1638, 1407 and 1079. H
1
NMR(CDCl ) d: 3.18 (t, 2H, J=9.2 Hz, CH2), 4.90 (t,
3
2H, J=9.2 Hz, OCH2), 7.60 (m, 1H, ArH), 7.68 (m, 2H,
ArH) and 8.10 (m, 1H, ArH). 13C NMR(CDCl 3) d: 27.0
(CH2), 75.4 (CH2O), 125.1, 130.0, 132.6, 135.2 (CH
arom), 116.2, 128.0, 131.2, 171.3 (C), 176.0 and 181.8
(C¼O). MS m/z (%): 200 (M+, 12), 172 (100), 144 (36)
and 115 (52). HRMS calcd for C12H8O3 (M) 200.0473,
found 200.0465.
Acknowledgements
This work was supported by the Thailand Research
Fund (TRF) under the Royal Golden Jubilee Project,
the National Research Council of Thailand (NRCT)
and Kasetsart University Institute (KURDI). The

N. Kongkathip et al. / Bioorg. Med. Chem. 11 (2003) 3179–3191
3191
Biodiversity Research and Training Program (BRT) is
acknowledged for supporting in part of bioactivity tests
and carrying out the HRMS measurements. We also
thank Professor Walter Taylor of Sydney University,
Australia for proof reading of the manuscript.
Trippe, A. J.; Appelt, K.; Davies, J. F., II; Wu, B. W.; Musick,
L. J. Med. Chem. 1996, 39, 2781.
17. House, H. O. Modern Synthetic Reactions, 2nd ed.;
Benjamin, Inc., Menlo Park, California, 1972; p 492.
18. Boddy, I. K.; Cambie, R. C.; Dixon, G.; Rutledge, P. S.;
Woodgate, P. D. Aust. J. Chem. 1983, 36, 803.
19. Anisimova, E. A.; Mitrasov, Y. N.; Kormachev, V. V.
Russ. J. Gen. Chem. 1995, 65, 356.
20. Krohn, K.; Bernhard, S. Synthesis 1996, 699.
21. Sun, J. S.; Geiser, A. H.; Frydman, B. Tetrahedron Lett.
1998, 39, 8221.
22. Schaffner-Sabba, K.; Schmidt-Ruppin, K. H.; Wehrli, W.;
Schnerch, A. R.; Wasley, J. W. F. J. Med. Chem. 1984, 27, 990.
23. Afzal, M.; Al-Oriquat, G.; Al-Hassan, J. M.; Muhammad,
N. Heterocycles 1984, 22, 813.
24. Skehan, P.; Storeng, R.; Scudiero, D.; Monks, A.;
McMahon, J.; Vistica, D.; Warren, J. T.; Bokesch, H.; Ken-
ney, S.; Boyd, M. R. J. Natl. Cancer. Inst. 1990, 82, 1107.
25. De Moura, K. C. G.; Emery, F. S.; Neves-Pinto, C.;
Pinto, M. F. R.; Dantas, A. P.; Salomao, K.; De Castro, S. L.;
Pinto, A. V. J. Braz. Chem. Soc. 2001, 12, 325.
26. Goulart, M. O. F.; Zani, C. L.; Tonholo, J.; Freitas, L. R.;
Abreu, F. C.; Oliveira, A. B.; Raslan, D. S.; Starling, S.;
Chiari, E. Bioorg. Med. Chem. Lett. 1997, 7, 2043.
27. Wuerzberger, S. M.; Pink, J. J.; Planchon, S. M.; Byers,
K. L.; Bornmann, W. O.; Boothman, D. A. Cancer Res. 1998,
58, 1876.
References and Notes
1. Thirumurugan, R. S.; Kavimani, S.; Srivastava, R. S. Biol.
Pharm. Bull. 2000, 23, 1438.
2. Kuwahara, S.; Nemoto, A.; Hiramatsu, A. Agric. Biol.
Chem. 1991, 55, 2909.
3. Kodama, O.; Ichikawa, H.; Akatsuka, T. J. Nat. Prod.
1993, 56, 292.
4. Kuwahara, S.; Awai, N.; Kodama, O. J. Nat. Prod. 1995,
58, 1455.
5. Awai, N.; Kuwahara, S.; Kodama, O.; Santisopasri, V.
Biosci. Biotech. Biochem. 1995, 59, 1999.
6. Machatzke, H.; Vaughan, W. R.; Warren, C. L.; White,
G. R. J. Pharm. Sci. 1967, 56, 86.
7. Gupta, R. B.; Franck, R. W. Synlett. 1990, 355.
8. Senboku, H.; Kajizuka, Y.; Kobayashi, K.; Tokuda, M.;
Suginone, H. Heterocycles 1997, 44, 341.
9. Godbole, H. M.; Ranade, A. A.; Joseph, A. R.; Paradkar,
M. V. Synth. Commun. 2000, 30, 2951.
10. Kobayashi, K.; Shimizu, H.; Sasaki, A.; Suginome, H.
J. Org. Chem. 1993, 58, 4614.
28. Krishnan, P.; Bastow, K. F. Biochem. Pharmacol. 2000,
60, 1367.
11. Suginome, H.; Sakurai, H.; Sasaki, A.; Takeuchi, H.;
Kobayashi, K. Tetrahedron 1994, 50, 8293.
12. Kongkathip, N.; Kongkathip, B.; Luangkamin, S.;
Niyomdecha, M.; Siripong, P.; Piyaviriyagul, S. Thailand
Patent 073725, 2002.
13. Ahmad, F. B. H.; Bruce, J. M. Synth. Commun. 1996, 26,
1263.
14. Zimmer, H.; Lankin, D. C.; Horgan, S. W. Chem. Rev.
1971, 71, 229.
29. Morris, G. M.; Goodsell, D. S.; Huey, R.; Hart, W. E.; Hal-
liday, S.; Belew, R.; Olson, A. J. AutoDock: Automated Docking
of Flexible Ligands to Receptors, Version 3.0.3, The Scripps
Research Institute, Molecular Graphics Laboratory, Department
of Molecular Biology: Mail Drop MB-5, USA, 1999; p 1.
30. Brady, G. P.; Stouten, P. F. W. First Prediction and
Visualization of Protein Binding Pockets with PASS; DuPont
Parmaceuticals Company: Italy; p 1.
31. Maruyama, K.; Matano, Y. Bull. Chem. Soc. Jpn. 1989,
62, 3877.
32. Jynichi, K.; Katsumi, Y.; Kouji, N.; Akira, T. Chem.
Pharm. Bull. 1997, 45, 1579.
15. Cassis, R.; Tapia, R.; Valderrama, J. J. Heterocyclic.
Chem. 1982, 19, 381.
16. Reich, S. H.; Melnick, M.; Pino, M. J.; Fuhry, M. A. M.;