Total synthesis of 12-methoxydihydrochelerythrine and anti-tumour activity of its quaternary base: toward an efficient synthetic route for 12-alkoxybenzo[c]phenanthridine bases via naphthoquinone monooxime from 2-benzofuranyl-1-tetralone derivative.

Article abstract of DOI:10.1039/b304216m

A concise total synthesis of 12-methoxydihydrochelerythrine (6), isolated from Bocconia integrifolia, is described. The synthesis features an efficient route to a 12-alkoxybenzo[c]phenanthridine skeleton via naphthoquinone monooxime 11 as a key compound. Starting from 7-methoxy-2-methylbenzo[b]furan (9), 3-aryl-1-tetralone 10 was synthesised, followed by aromatisation to 3-aryl-1-naphthol 17. After oxidative cleavage of the furan ring, basic nitrosation of naphthol 22 gave the naphthoquinone 11. The benzo[c]phenanthridine skeleton was formed by reductive cyclisation of 11. Deoxygenation of the lactam moiety in 23 afforded nor-base 32 and methylation of 32 under reductive conditions gave the target dihydro base 6 (23 steps from benzofuran 9 in 10% overall yield). The corresponding quaternary base 7 showed moderate anti-tumour activity against cancer cell lines; on NCI-H460: IC50 4.5 microM and on MDA-MB-231: IC50 1.2 microM. Introduction of a methoxy group into the 12-position of the benzo[c]phenanthridine skeleton could cause enhanced activity against MDA-MB-231 by comparison of 7 with chelerythrine (35) (IC50 5.3 microM).

Full text of DOI:10.1039/b304216m

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Total synthesis of 12-methoxydihydrochelerythrine and anti-tumour
activity of its quaternary base: toward an efficient synthetic route
for 12-alkoxybenzo[c]phenanthridine bases via naphthoquinone
monooxime from 2-benzofuranyl-1-tetralone derivative
Toshiko Watanabe,*a Yoshiaki Ohashi,a Rie Yoshino,a Naoko Komano,a Miyuki Eguchi,a
Sakiko Maruyamab and Tsutomu Ishikawa*a
a Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi, Inage,
Chiba 263-8522, Japan. E-mail: toshiw@p.chiba-u.ac.jp
b Drug Research Department, R&D Division, Nippon Kayaku Co., Ltd., 31-12 Shimo 3, Kita,
Tokyo 115-8588, Japan
Received 16th April 2003, Accepted 23rd July 2003
First published as an Advance Article on the web 4th August 2003
A concise total synthesis of 12-methoxydihydrochelerythrine (6), isolated from Bocconia integrifolia, is described.
The synthesis features an efficient route to a 12-alkoxybenzo[c]phenanthridine skeleton via naphthoquinone
monooxime 11 as a key compound. Starting from 7-methoxy-2-methylbenzo[b]furan (9), 3-aryl-1-tetralone 10 was
synthesised, followed by aromatisation to 3-aryl-1-naphthol 17. After oxidative cleavage of the furan ring, basic
nitrosation of naphthol 22 gave the naphthoquinone 11. The benzo[c]phenanthridine skeleton was formed by
reductive cyclisation of 11. Deoxygenation of the lactam moiety in 23 afforded nor-base 32 and methylation of 32
under reductive conditions gave the target dihydro base 6 (23 steps from benzofuran 9 in 10% overall yield). The
corresponding quaternary base 7 showed moderate anti-tumour activity against cancer cell lines; on NCI-H460: IC50
4.5 µM and on MDA-MB-231: IC50 1.2 µM. Introduction of a methoxy group into the 12-position of the
benzo[c]phenanthridine skeleton could cause enhanced activity against MDA-MB-231 by comparison of 7 with
chelerythrine (35) (IC50 5.3 µM).
from 7-methoxy-2-methylbenzo[b]furan8 (9) via 3-aryl-1-tetra-
Introduction
lone 10 and naphthoquinone monooxime 11, followed by reduc-
Benzo[c]phenanthridine alkaloids 1, found in Papaveraceous
tive cyclisation to a benzo[c]phenanthridine skeleton.
and Rutaceous plants, have been synthetically approached by
Friedel–Crafts acylation of 9 with homopiperonyloyl chlor-
ide (12) in the presence of SnCl4 afforded a deoxybenzoin
derivative 13. Reformatsky reaction of 13 with ethyl bromo-
acetate and zinc gave the hydroxyester 14. Deoxygenation of
various methods1 in view of their biologically important activ-
ities, such as anti-tumour and DNA-topoisomerase inhibitory
activities.2 We established a general synthetic method for benzo-
[c]phenanthridine alkaloids 1 (Z = H) using 2-aryl-1-tetralones
14 with Et3SiH–CF3COOH followed by alkaline hydrolysis
2 as key intermediates and examined the structure–activity
quantitatively gave an acid 16. Cyclisation of 16 under basic
relationship (SAR) of their antitumour activity.3 An alternative
route, in which an isomeric 3-aryl-1-tetralone 3 played an
conditions (K2CO3 in CH3CN)9 afforded the desired 3-aryl-1-
tetralone 10. The tetralone 10 was aromatised to 1-naphthol 17
important role, has also been explored for 12-alkoxy type
by an acetal exchange reaction with isopropenyl acetate
alkaloids 1 (Z = OMe) such as macarpine4 (4) because of
followed by dehydrogenation with 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ) and basic hydrolysis. The phenolic
function in 17 was protected with a benzyl group. (Scheme 3)
Successive treatment of the benzyl ether 18 with a stoichio-
the difficult application of the general synthetic method.
Recently, Duval and co-workers reported5 the synthesis of a
12-ethoxybenzo[c]phenanthridine base 1 (Z = OEt) via the
isoquinolone derivative 5 (Scheme 1).
metric amount of OsO4 in pyridine and then aqueous Na2SO3
12-Methoxydihydrochelerythrine (6) was isolated from a
afforded the ketoalcohol 19 through an air-oxidation step
South American plant, Bocconia integrifolia (Papaveraceae) by
under basic conditions.10 The ketoalcohol 19 was treated with
Sticher and co-workers6 in 1991 and its structure was elucid-
HIO4 in aqueous dioxane followed by alkaline hydrolysis to give
a salicylic acid 20. Methylation of 20 with Me2SO4 in the
presence of a phase transfer catalyst (PTC) afforded a methyl
ated by NMR spectral data (1H, 13C and NOESY). We tried
to synthesise 6 by a combination of our routes3b,4 for benzo-
[c]phenanthridine alkaloids. In this paper we present the
ester 21.
synthesis of 12-methoxydihydrochelerythrine (6) and the
We 11 have found that basic nitrosation of phenolic com-
pounds with alkyl nitrites, such as isoamyl nitrite (i-AmONO),
resulted in regioselective introduction of a nitrogen function
antitumour activity of its quarternary salt 7 in a line of SAR of
benzo[c]phenanthridine bases. It is noted that Harayama et al.7
reported the first synthesis of 6 by the palladium-catalysed
into their para positions. After reductive deprotection of the
cyclisation of naphthylamide 8 during the course of our
benzyl group in 21, treatment of naphthol 22 with i-AmONO in
synthetic approach.
DMF in the presence of K2CO3 at room temperature followed
by methylation with dimethyl sulfate in a one-pot operation
afforded the desired quinone monooxime 11 (Scheme 4). The
geometry of the O-methyloxime group in 11 was deduced to be
Results and discussion
For elaboration of the 7,8,12-trimethoxy groups in 6 (and 7),
we planned the synthetic strategy outlined in Scheme 2 starting
Z-configuration by nuclear Overhauser effect (NOE) enhance-
ment between the methoxy group and the proton assignable to
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Scheme 1
Fig. 1 Selected NOE enhancements in 11.
Construction of a benzo[c]phenanthridine ring system was
examined under reductive cyclisation of 11. Treatment of 11
with 10% Pd/C–H2 in acetic acid smoothly provided a tetra-
cyclic lactam 23 in quantitative yield, whereas unsuccessful
results were obtained on reduction with NaBH4 or Na2S2O4.
Methylation of 23 with dimethyl sulfate in the presence of PTC
afforded two products (24 and 25) in nearly equal amounts
(Scheme 5). The less polar compound 24 had molecular formula
C22H19NO6 and in the NMR spectra showed four methyl signals
Scheme 2
8-H (δ 8.32) (Fig. 1). We have reported that the same configur-
ation was observed in this type of quinone monooxime toward
the synthesis of macarpine4 (4).
Scheme 3 Reagents and conditions: a, SnCl4, CH2Cl2, Ϫ15 ЊC, 2.5 h, 64%; b, BrCH2CO2Et, Zn, I2, THF, reflux, 0.5 h, 93%; c, Et3SiH, TFA, CH2Cl2,
0 ЊC, 1.5 h, 91%; d, KOH aq., EtOH reflux, 1 h, 100%; e, POCl3, K2CO3, CH3CN, 55 ЊC, 3 h, 81%; f, (i), TsOHؒH2O, isopropenyl accetate, 95 ЊC, 13 h,
(ii), DDQ, rt, 1 h, (iii) NaOHaq, EtOH, 85 ЊC, 1 h, 89%; g, PhCH2Br, K2CO3, DMF, 50 ЊC, 2 h, 91%.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
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the lactam carbonyl group in 23. Therefore, compound 24 was
not the desired N-methylated lactam 26, but an imino ether.
Trials for reductive cleavage of the 6-methoxy group in 24 with
various reagents (LiAlH4, LiBEt3H, Et3SiH–CF3COOH, etc.)
to nor-base 27 resulted in the recovery of the starting material.
The second product 25, obtained as purple prisms, had
molecular formula C21H15NO7. The 1H NMR spectrum showed
three methyl signals at δ 3.95, 4.00 and 4.34 ppm assignable to
methoxy groups. In addition, two carbonyl signals (δ 178.6 and
181.0 ppm) were observed in the 13C NMR, indicating the pres-
ence of an imino ether moiety similar to 24 and an o-quinone
function in 25. The formation of 25 could be explained by air-
oxidation at the α-naphthol function of lactam 23 under basic
conditions followed by methylation, even in an argon atmos-
phere. Structural confirmation of these imino ethers (24 and 25)
was done by 2D-NMR experiments [heteronuclear multiple
quantum coherence (HMQC) and heteronuclear multiple bond
connectivity (HMBC)].
Selective methylation of the phenolic group in lactam 23
was attempted using Me2SO4–K2CO3 or CH2N2; however, the
reaction mixtures were complex on thin-layer chromatography
(TLC). This situation caused us to adopt an alternative route
for removal of the oxygen function at the 6-position in 23 giving
32 (Scheme 6). Mono-acetylation with Ac2O under solvent-free
conditions proceeded smoothly to yield 12-acetoxylactam 28 in
high yield. The acetylated position was confirmed by 2D-NMR
and NOE experiments with comparison to diacetoxylactam 29,
prepared from 23 with the Ac2O-4-(dimethylamino)pyridine
(DMAP)–Et3N system (Fig. 2 and Table 1). However, 28 was
labile under the conditions of trifluoromethanesulfonylation
(triflation) in the next step.
Scheme 4 Reagents and conditions: a, (i) OsO4, pyridine, 30 ЊC, 3 h, (ii)
Na2SO3, EtOH, 75 ЊC, 7 h, 92%; b, (i) HIO4, H2O-dioxane, rt, 24 h, (ii),
NaOHaq., rt, 4 h, 100%; c, Me2SO4, BnNϩBu3ؒClϪ, NaOHaq., benzene,
rt, 3 h, 87%; d, H2, Pd/C, AcOH, rt, 3.5 h, 82%; e, (i) i-C5H11ONO,
K2CO3, DMF, rt, 3.5 h, (ii) Me2SO4, rt, 1.5 h, 86%.
Scheme 6 Reagents and conditions: a, 28: Ac2O, 80 ЊC, 1 d (91%); 30:
(PhCO)2O, 60 ЊC, 14 d, (96%); b, Ac2O, DMAP, 80 ЊC, 11 h then Et3N,
rt, 15 h, (74%); c, Tf2O, iPr2EtN, 0 ЊC, 5 h, 83%; d, Pd(OAc)2, dppp,
Et3SiH, DMF, 60 ЊC, 5 h, 89%.
Thus, mono-benzoylation of 23 was similarly carried out
with benzoic anhydride, leading to the benzoyl lactam 30 in
excellent yield, although a longer reaction time was required
(14 days).12 The benzoylated position in 30 was also confirmed
by 2D-NMR and comparison with the acetate 28. Triflation of
30 followed by reduction with a palladium catalyst [Pd(OAc)2–
1,3-bis(diphenylphosphino)propane (dppp)–Et3SiH] afforded
6-deoxygenated base 32 in high yield.
Scheme 5 Reagents and conditions: a, H2, Pd/C, AcOH, rt, 1.5 h, 95%;
b, Me2SO4, BnNϩBu3ؒClϪ, NaOHaq., CH2Cl2, rt, 1.5 h, 24 (45%), 25
(39%).
assignable to methoxy groups (δH 3.99, 4.03, 4.14 and 4.33;
δC 53.7, 55.6, 57.0 and 61.9). Among them, two methoxy signals
were derived from the starting lactam 23, and one of the
remaining signals should be a 12-methoxy group. One more
methoxy group observed could be formed by O-alkylation on
Alkaline hydrolysis of 32 followed by methylation gave the
desired nor-base 27 in 64% yield. However, difficult isolation of
phenolic imine 33 was observed due to its amphoteric character.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
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Table 1 Selected chemical shifts on 1H NMR of 23, 28 and 29 (400 MHz, CDCl3, δ ppm)
Protons
23
28 (∆δ)a
29 (∆δ)a
C1–H
C11–H
C7–OMe
7.47
7.46
3.83
7.30 (Ϫ0.17)
8.04 (ϩ0.58)
3.82 (Ϫ0.01)
7.24 (Ϫ0.20)
8.08 (ϩ0.62)
4.01 (ϩ0.18)
a The difference was calculated using 23 as a standard.
Scheme 7 Reagents and conditions: a, (i) NaOMe, MeOH, 45 ЊC, 18 h, (ii) Me2SO4, NaBH4, HMPA, 60 ЊC, 11 h, 64%; b, KOH, MeOH, 50 ЊC, 29 h,
67%; c, Me2SO4, K2CO3, DMF, 0 ЊC, 1.5 h, 100%; d, (i) DDQ, NaOHaq., benzene, rt, 20 min, (ii) HClaq., CHCl3, 78%.
Synthetic base 7 showed moderate activities (on NCI-H460:
IC50 4.5 µM and on MDA-MB-231: IC50 1.2 µM), which were
slightly stronger than natural nitidine (34) (IC50: 8.7 and 1.6 µM
respectively) and chelerythrine (35) (IC50: 4.1 and 5.3 µM
respectively), but lower than NK109 (36) (IC50: 0.072 and 0.25
µM respectively), which is a candidate for anti-tumour drug
inhibiting DNA topoisomerase II activity.16 Introduction of a
methoxy group into the 12-position of the benzo[c]phen-
anthridine skeleton could cause enhanced activity against
MDA-MB-231 by comparison of 7 with 35 as in the case of
macarpine (4).4
In summary, we have achieved the total synthesis of 12-
methoxydihydrochelerythrine (6) via naphthoquinone mono-
oxime 11 as a key compound by 23 steps from a benzofuran 9 in
10% overall yield. Though the number of steps is more than
that of Harayama’s synthesis (15 steps, 7% from commercial
tetralone derivative),7 our method may have the potential
for preparing a wide variety of 12-alkoxy derivatives, because
the O-alkylation step for 12-hydroxy group is in the final
stage. This synthetic method could provide an efficient route for
12-alkoxybenzo[c]phenanthridine alkaloids to examine the
SAR of their anti-tumour activity.
Fig. 2 Selected NOE enhancements and HMBC correlations in 28 and
29.
(Scheme 7) Thus, we tried direct conversion of 32 to the target
N-methyldihydrobase 6 in a one-pot operation by application
of our preparation method14 for dihydrobenzo[c]phenan-
thridines from the corresponding nor-bases without isolation
of 33. After methanolysis of 32 with NaOMe followed by
evaporation of the solvent, the residual sodium naphthoxide
was treated with NaBH4 in hexamethylphosphoryltriamide
(HMPA) in the presence of Me2SO4. Double methylation at the
N- and O-functions under reductive conditions as expected,
afforded a dihydrobase 6 in 67% yield. Synthetic 12-methoxydi-
hydrochelerythrine (6) was identical to a sample prepared by
Professor Harayama’s group.7,15 The base 6 was further oxid-
ised to the corresponding quaternary base 7 with DDQ under
basic conditions14 for the testing of anti-tumour activities.
12-Methoxychelerythrine (7) and the related quaternary
bases were examined in human lung cancer cell line NCI-H460
and human breast cancer cell line MDA-MB-231 (Table 2).
Experimental
General
All melting points were measured on a micro melting-point hot
stage, MP-3S (Yanaco) and are uncorrected. Infrared spectra
1
were recorded on a JASCO FT/IR-300E spectrometer. H and
13C NMR spectra were recorded in chloroform-d (CDCl3)
unless otherwise stated, on JEOL JNM GSX-400A, GSX-
500A, and ECP-400 spectrometers with tetramethylsilane as
internal reference. Low-resolution mass spectra were recorded
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
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Table 2 Anti-tumour activities of quaternary benzo[c]phenanthridines against human cancer cells (NCI-H460 and MDA-MB-231)a
IC50/µM
Compound
NCI-H460
MDA-MB-231
7
34
35
36
4.5
8.7
4.1
0.072
1.2
1.6
5.3
0.25
a The anti-tumour activity tests of 7 and NK109 (36) were carried out at the same time, while those of nitidine (34) and chelerythrine (35) were
separately examined.
on a JEOL JMS-AM20 with electron impact (EI) ionisation,
and JEOL JMS-AX500 and JMS-HX 10A with fast atom
bombardment (FAB) ionisation. High-resolution mass spectra
were recorded on JEOL JMS-HX 10A (FAB) and Hitachi M-60
(EI) spectrometers. For column chromatography, silica gel
(particle size: 100 µm) (Fuji Silysia) was used unless otherwise
stated. Tetrahydrofuran (THF) was distilled from sodium
benzophenone ketyl under argon prior to use.
H, s, 2Ј-Me), 2.77 (1 H, d, J 16.2, 2-H), 3.04 (1 H, d, J 13.6, 4-
H), 3.08 (1 H, d, J 16.2, 2-H), 3.11 (1 H, d, J 13.6, 4-H), 3.98 (3
H, s, OMe), 4.01 (2 H, q, J 7.0, OCH2CH3), 4.54 (1 H, s, OH),
5.88 (2 H, s, OCH2O), 6.39 (1 H, d, J 7.8, 6Љ-H), 6.46 (1 H, s, 2Љ-
H), 6.59 (1 H, d, J 8.2, 6Ј-H), 6.62 (1 H, d, J 7.8, 5Љ-H), 6.74
(1 H, s, 3Ј-H) and 6.84 (1 H, d, J 8.2, 5Ј-H); δC (125 MHz) 13.95,
14.00, 43.1, 47.9, 55.9, 60.7, 75.9, 100.7, 103.9, 104.3, 107.6,
111.0, 119.6, 123.6, 127.9, 129.7, 130.3, 144.1, 144.2, 146.1,
147.0, 155.0 and 173.0.
4-(7-Methoxy-2-methylbenzo[b]furanyl)
3,4-methylene-
dioxybenzyl ketone 13. Oxalyl chloride (19.2 mL, 22 mmol) was
added to 3,4-methylenedioxyphenylacetic acid (13.78 g, 77
mmol) under ice-cooling and the mixture was stirred at room
temperature for 3 h. After removal of excess oxalyl chloride
under reduced pressure, the residual acid chloride was dissolved
in dry CH2Cl2 (32 mL). To a solution of acid chloride was
added a solution of benzofuran8 9 (12.41 g, 76 mmol) in dry
CH2Cl2 (100 mL) followed by SnCl4 (36 mL, 0.31 mol) at
Ϫ15 ЊC (ice–sodium chloride bath) and the mixture was stirred
at the same temperature for 2.5 h. The reaction mixture was
poured into water (1 L) and extracted with EtOAc. The organic
layer was washed with saturated NaHCO3 solution, water and
brine, dried (K2CO3), and evaporated in vacuo. The crude yel-
low prisms (25.60 g) were washed with Et2O to afford 13 (15.84
g, 64%) as colourless fine needles (mp 120–121.5 ЊC, Et2O–
hexane) (Found: C, 70.4; H, 4.8. C19H16O5 requires C, 70.4; H,
Ethyl
3-[4-(7-methoxy-2-methylbenzo[b]furanyl)]-4-(3,4-
methylenedioxyphenyl)butyrate 15. To a solution of 14 (1.00 g,
2.42 mmol) in CH2Cl2 (12 mL) was added triethylsilane (1.2
mL, 7.51 mmol) and trifluoroacetic acid (0.75 mL, 9.74 mmol)
at 0 ЊC and the mixture was stirred at the same temperature for
1.5 h. After neutralisation by slow addition of K2CO3 (4.7 g),
insoluble materials were filtered off and washed with CH2Cl2.
The combined organic solution was evaporated in vacuo. The
residual yellow oil was purified by column chromatography
(gradient elution: 100 : 0 0 : 100 hexane–EtOAc) to yield 15
(873 mg, 91%) as a colourless oil; νmax (neat)/cmϪ1: 1735 (C᎐O);
᎐
δH (400 MHz) 1.09 (3 H, t, J 7.0, OCH2CH3), 2.46 (3 H, d, J 1.0,
2Ј-Me), 2.67–2.70 (2 H, m, 2- or 4-H2), 2.83–2.96 (2 H, m, 2- or
4-H2), 3.57 (1 H, m, 3-H), 3.94–4.01 (2 H, m, OCH2CH3), 3.96
(3 H, s, OMe), 5.87 and 5.88 (each 1 H, d, J 1.2, OCH2O), 6.42
(1 H, q, J 1.0, 3Ј-H), 6.48 (1 H, dd, J 8.0, 1.8, 6Љ-H), 6.53 (1 H,
d, J 1.6, 2Љ-H), 6.63 (2 H, d, J 8.0, 6Ј- and 5Љ-H) and 6.84 (1 H,
d, J 8.0, 5Ј-H); δC (125 MHz) 14.04, 14.05, 39.7, 41.2, 41.7, 55.9,
60.2, 100.7, 101.6, 105.2, 107.9, 109.5, 120.7, 122.1, 127.7,
129.4, 133.5, 143.4, 143.5, 145.8, 147.3, 155.2 and 172.4; m/z:
(FAB) 397 (MHϩ) and 261.
5.0%); νmax (Nujol)/cmϪ1 1676 (C᎐O); δH (400 MHz) 2.50 (3 H,
᎐
s, 2Ј-Me), 4.07 (3 H, s, OMe), 4.21 (2 H, s, CH2), 5.93 (2 H, s,
OCH2O), 6.72–6.78 (4 H, m, ArH), 7.20 (1 H, s, 3Ј-H) and 7.84
(1 H, d, J 8.2, 5Ј-H); δC (125 MHz) 14.1, 45.2, 56.2, 100.9, 104.5,
105.0, 108.3, 109.9, 122.1, 122.4, 127.1, 128.8, 131.2, 143.9,
146.4, 147.7, 148.5, 158.3 and 196.7.
3-[4-(7-Methoxy-2-methylbenzo[b]furanyl)]-4-(3,4-methyl-
enedioxyphenyl)butyric acid 16. A mixture of 15 (9.76 g, 24.6
mmol) and 17% aqueous KOH (20 mL, 60.6 mmol) in EtOH
(98 mL) was refluxed for 1 h. The reaction mixture was poured
into water (300 mL) and extracted with Et2O. The aqueous
layer was acidified with concentrated hydrochloric acid to pH 1
and extracted with EtOAc. The organic layer was washed with
water and brine, dried (MgSO4), and evaporated in vacuo to
yield 16 as a yellow oil (9.4 g, quantitatively), which was used
for the next step without purification. νmax (neat)/cmϪ1 3300–
Ethyl 3-hydroxy-3-[4-(7-methoxy-2-methylbenzo[b]furanyl)]-
4-(3,4-methylenedioxyphenyl)butyrate 14. To a stirred suspen-
sion of 13 (5.00 g, 15.4 mmol) and zinc powder (4.94 g, 75.5
mmol) in THF (100 mL) was added iodine (2.40 g, 9.46 mmol)
and ethyl bromoacetate (5.18 g, 30.9 mmol) under reflux, and
the mixture was refluxed for 30 min under an argon atmos-
phere. The reaction mixture was poured into water (180 mL)
and filtered through a Celite pad. The filtrate was extracted
with CHCl3. The organic layer was washed with 1% aqueous KI
solution, water and brine, dried (K2CO3), and evaporated in
vacuo. The residual yellow oil was crystallised and washed with
hexane–Et2O to yield 14 (5.93 g, 93%) as colourless fine needles
(mp 88.5–90 ЊC, EtOH) (Found: C, 67.0; H, 5.6. C23H24O7
requires C, 67.0; H, 5.9%); νmax (Nujol)/cmϪ1 3489 (OH) and
2500 (OH) and 1707 (C᎐O); δ (400 MHz) 2.46 (3 H, s, 2Ј-Me),
᎐
H
2.71–2.73 (2 H, m, 2- or 4-H2), 2.82–2.96 (2 H, m, 2- or 4-H2),
3.53–3.57 (1 H, m, 3-H), 3.96 (3 H, s, OMe), 5.87 and 5.88 (each
1 H, d, J 1.2, OCH2O), 6.40 (1 H, d, J 1.2, 3Ј-H), 6.47 (1 H, dd,
J 8.0, 1.5, 6Љ-H), 6.52 (1 H, d, J 1.5, 2Љ-H), 6.63 (2 H, d, J 8.0,
6Ј- and 5Љ-H) and 6.84 (1 H, d, J 8.0, 5Ј-H); δC (125 MHz) 14.0,
1718 (C᎐O). δ (400 MHz) 1.09 (3 H, t, J 7.0, CH CH3), 2.49 (3
᎐
H
2
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
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39.0, 40.9, 41.6, 55.9, 100.7, 101.5, 105.2, 107.9, 109.5, 120.7,
122.1, 127.3, 129.4, 133.3, 143.56 143.59, 145.9, 147.4, 155.3
and 177.9; m/z: (FAB) 369 (MHϩ).
1-Benzyloxy-3-[4-(2-hydroxy-7-methoxy-2-methyl-3-oxo-2,3-
dihydrobenzo[b]furanyl)]-6,7-methylenedioxynaphthalene 19. To
a solution of 18 (2.55 g, 5.82 mmol) in pyridine (25 mL) was
added OsO4 (1.78 g, 6.98 mmol) and stirred at 30 ЊC for 3 h.
Then a solution of sodium sulfite (8.27 g, 58.2 mmol) in water
(77 mL) and EtOH (38 mL) was added to the reaction mixture
and the mixture was stirred at 75 ЊC for 7 h. The precipitates
were filtered off using Celite and the filtrate was extracted with
EtOAc. The organic layer was washed with saturated cupric
sulfate, water and brine, dried (MgSO4), and evaporated in
vacuo. The residual yellow amorphous solid was purified by
column chromatography (elution gradient 1 : 5 1 : 3 EtOAc–
hexane, then MeOH) to afford 19 as yellow prisms (2.51 g,
92%). Recrystallisation of a portion from Et2O–hexane gave 19
as yellow prisms (mp 171–174 ЊC) (Found: C, 71.4; H, 4.7.
C28H22O7 requires C, 71.5; H, 4.7%); νmax (Nujol)/cmϪ1 3483
3,4-Dihydro-3-[4-(7-methoxy-2-methylbenzo[b]furanyl)]-6,7-
methylenedioxy-1(2H)-naphthalenone 10. To a solution of 16
(1.71 g, 4.63 mmol) in CH3CN (14 mL) was added K2CO3 (1.47
g, 10.6 mmol) and phosphorus oxychloride (2.2 mL, 23.6
mmol) at room temperature and the mixture was stirred at 55
ЊC for 3 h. The reaction mixture was poured into water (120
mL), basified with 10% aqueous NaOH solution to pH 10–11,
and extracted with CHCl3. The organic layer was washed with
water and brine, dried (MgSO4), and evaporated in vacuo. The
residual yellow solid was washed with hexane–Et2O to give 10
as pale yellow prisms (1.31 g, 81%), mp 177–181 ЊC. Recrystal-
lisation of a portion from EtOAc gave colourless prisms (mp
182–184 ЊC) (Found: C, 71.7; H, 5.2. C21H18O5 requires C, 72.0;
H, 5.2%); νmax (Nujol)/cmϪ1 1663 (C᎐O); δ (400 MHz) 2.48
(OH) and 1725 (C᎐O); δH (400 MHz) 1.72 (3 H, s, 2Ј-Me), 3.30
᎐
(1 H, s, 2Ј-OH), 4.00 (3 H, s, OMe), 5.26 (2 H, d, J 1.8,
OCH2Ph), 6.05 (2 H, s, OCH2O), 7.02 (1 H, d, J 1.3, 4-H), 7.11
(1 H, d, J 8.2, 6Ј-H), 7.13 (1 H, s, 5-H), 7.20 (1 H, d, J 8.2, 5Ј-H),
7.26 (1 H, s, 2-H), 7.33–7.54 (5 H, m, CH2Ph) and 7.62 (1 H, s,
8-H); δC (125 MHz) 22.3, 56.3, 70.4, 99.1, 101.0, 103.2, 104.1,
106.4, 115.6, 119.2, 120.1, 122.0, 123.6, 127.5, 127.8, 128.5,
131.3, 132.7, 134.4, 137.3, 145.2, 147.6, 148.1, 153.6, 160.7 and
197.8.
᎐
H
(3 H, s, 2Ј-Me), 2.81–2.98 (2 H, m, 2- or 4-H), 3.09–3.23 (2 H,
m, 2- or 4-H), 3.59–3.65 (1 H, m, 3-H), 4.00 (3 H, s, OMe), 6.02
and 6.03 (each 1 H, d, J 1.0, OCH2O), 6.43 (1 H, s, 3Ј-H), 6.69
(1 H, s, 5-H), 6.71 (1 H, d, J 8.2, 6Ј-H), 6.98 (1 H, d, J 8.2, 5Ј-H)
and 7.53 (1 H, s, 8-H); δC (125 MHz) 14.1, 37.1, 38.5, 44.9, 56.0,
101.3, 101.7, 105.4, 106.3, 108.0, 119.5, 127.0, 127.6, 129.1,
140.5, 143.7, 143.9, 147.2, 152.3, 155.7 and 196.2.
3-[4-(7-Methoxy-2-methylbenzo[b]furanyl)]-6,7-methylene-
dioxy-1-naphthol 17. A solution of 10 (1.17 g, 3.35 mmol) and
p-toluenesulfonic acid monohydrate (99 mg, 0.52 mmol) in iso-
propenyl acetate (18 mL) was stirred at 95 ЊC for 13 h under an
argon atmosphere. Then, DDQ (914 mg, 4.03 mmol) was added
to the reaction mixture and stirred at room temperature for 1 h.
After addition of CH2Cl2 (50 mL) to the reaction mixture, the
organic solution was washed with 1% aqueous NaOH solution
and evaporated in vacuo. The residue was dissolved in EtOH (55
mL) and 5% aqueous NaOH solution (55 mL, 68.8 mmol). The
mixture was stirred at 85 ЊC for 1 h, poured into water (200 ml),
acidified with 10% hydrochloric acid and extracted with CHCl3.
The organic layer was washed with water and brine, dried
(MgSO4), and evaporated in vacuo. The residual brown solid
(1.28 g) was recrystallised from CHCl3–MeOH to afford 17
(1.04 g, 89%) as pale pink prisms (mp 259–262 ЊC); νmax (Nujol)/
cmϪ1 3347 (OH); δH (400 MHz) 2.50 (3 H, s, 2Ј-Me), 4.05 (3 H,
s, OMe), 5.18 (1 H, s, OH), 6.07 (2 H, s, OCH2O), 6.62 (1 H, d
like, J 0.5, 3Ј-H), 6.83 (1 H, d, J 8.2, 6Ј-H), 6.94 (1 H, d, J 1.3,
4-H), 7.14 (1 H, s, 5-H), 7.24 (1 H, d, J 8.2, 5Ј-H), 7.44 (1 H, d,
J 1.3, 2-H) and 7.50 (1 H, s, 8-H). Found (EI): 348.0998 (Mϩ),
C21H16O5 requires 348.0996.
6-[3-(1-Benzyloxy-6,7-methylenedioxynaphthyl)]-2-hydroxy-
3-methoxybenzoic acid 20. To a solution of 19 (305 mg, 0.65
mmol) in dioxane (12 mL) was added a solution of periodic
acid dihydrate (222 mg, 0.97 mmol) in water (1.3 mL) and
dioxane (3.3 mL) and the mixture was stirred at room temper-
ature for 24 h under an argon atmosphere. Then 1% aqueous
NaOH solution (16 mL) was added to the reaction mixture and
the mixture was stirred at room temperature for 4 h. To the
reaction mixture water (30 mL) was added and acidified with
5% hydrochloric acid followed by extraction with EtOAc. The
organic layer was washed with water and brine, dried (MgSO4),
and evaporated in vacuo to give 21 (287 mg, 100%) as a brown
oil, which was used for the next step without further purifi-
cation. νmax (neat)/cmϪ1 3016 (OH) and 1719 (C᎐O); δ (400
᎐
H
MHz) 3.95 (3 H, s, OMe), 5.20 (2 H, s, OCH2Ph), 6.05 (2 H,
s, OCH2O), 6.72 (1 H, s, 4-H), 6.82 (1 H, d, J 8.3, 4Ј-H), 7.04
(1 H, d, J 8.3, 5Ј-H), 7.08 (1 H, s, 5-H), 7.22 (1 H, s, 2-H), 7.35–
7.49 (5 H, m, CH2Ph), 7.63 (1 H, s, 8-H) and 10.83 (1 H, br s,
OH).
Methyl 6-[3-(1-benzyloxy-6,7-methylenedioxynaphthyl)]-2,3-
dimethoxybenzoate 21. To a solution of 20 (2.23 g, 5.02 mmol)
in benzene (200 mL) was added benzyltributylammonium
chloride (1.41 g, 4.52 mmol) and 2% aqueous NaOH solution
(94 mL) followed by dropwise addition of Me2SO4 (2.4 mL,
25.4 mmol), the reaction mixture was stirred at room temper-
ature for 3 h, and poured into 5% aqueous ammonia (35
mL). The mixture was stirred for 1 h and extracted with
EtOAc. The organic layer was washed with 5% aqueous
ammonia, water and brine, dried (K2CO3), and evaporated in
vacuo. The residue was crystallised and washed with hexane–
EtOAc to yield 21 (2.06 g, 87%) as colourless prisms (mp
154–156 ЊC), which were recrystallised from Et2O (Found: C,
70.9; H, 5.2. C28H24O7 requires C, 71.2; H, 5.1%); νmax
(Nujol)/cmϪ1 1739 (C᎐O); δ (400 MHz) 3.63 (3 H, s, CO-
1-Benzyloxy-3-[4-(7-methoxy-2-methylbenzo[b]furanyl)]-6,7-
methylenedioxynaphthalene 18. To a mixture of 17 (695 mg,
2.00 mmol), K2CO3 (554 mg, 4.01 mmol) and DMF (5.6 mL)
was added benzyl bromide (0.29 mL, 2.44 mmol) and the mix-
ture was stirred at 50 ЊC for 2 h. The reaction mixture was
poured into water (20 mL) and extracted with EtOAc. The
organic layer was washed with 2% aqueous NaOH solution,
water and brine, dried (K2CO3), and evaporated in vacuo. The
residual red solid (0.924 g) was washed with hexane–Et2O to
give benzyl ether 18 (793 mg, 91%) as colourless plates (mp
149–152 ЊC, EtOAc–hexane) (Found: C, 76.6; H, 5.05. C28H22O5
requires C, 76.7; H, 5.1%); νmax (Nujol)/cmϪ1 no characteristic
absorption; δH (400 MHz) 2.46 (3 H, s, 2Ј-Me), 4.05 (3 H, s,
OMe), 5.31 (2 H, s, OCH2Ph), 6.06 (2 H, s, OCH2O), 6.29
(1 H, d like, J 0.8, 3Ј-H), 6.82 (1 H, d, J 8.2, 6Ј-H), 6.99 (1 H,
d, J 1.1, 4-H), 7.14 (1 H, s, 5-H), 7.26 (1 H, d, J 8.2, 5Ј-H), 7.26
(1 H, s, 2-H), 7.35–7.53 (5 H, m, –CH2Ph) and 7.66 (1 H, s,
8-H); δC (125 MHz) 14.1, 56.1, 70.1, 99.1, 101.0, 102.5, 103.9,
105.7, 106.0, 118.8, 121.0, 122.5, 127.16, 127.24, 127.8, 128.6,
129.0, 131.9, 136.5, 137.3, 143.8, 144.2, 147.2, 148.2, 153.9 and
155.9.
᎐
H
OMe), 3.93 (3 H, s, ArOMe), 3.94 (3 H, s, ArOMe), 5.20 (2
H, s, OCH2Ph), 6.04 (2 H, s, OCH2O), 6.87 (1 H, d J 1.4,
4-H), 7.03 (1 H, d, J 8.5, 4Ј-H), 7.09 (1 H, s, 5-H), 7.17 (1 H,
d, J 8.5, 5Ј-H), 7.27 (1 H, br s, 2-H), 7.35–7.53 (5 H, m, CH2Ph)
and 7.61 (1 H, s, 8-H); δC (125 MHz) 52.3, 56.1, 61.7, 70.1,
99.0, 101.1, 103.9, 105.4, 113.6, 119.2, 121.2, 125.5, 127.5,
128.0, 128.6, 129.0, 131.6, 132.9, 136.0, 137.0, 146.1, 147.4,
148.3, 151.9, 154.0 and 168.2; m/z: (EI) 472 (Mϩ, 33%) and
147 (100).
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
3029

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Methyl
6-[3-(1-hydroxy-6,7-methylenedioxynaphthyl)]-2,3-
(i)
6,7,8,12-Tetramethoxy-2,3-methylenedioxybenzo[c]-
dimethoxybenzoate 22. To a solution of 21 (2.03 g, 4.29 mmol)
in AcOH (130 mL) was added a solution of 1% palladium–
hydrochloric acid17 (9.5 mL, 0.89 mmol) and activated carbon
(876 mg, 73.0 mmol), and the mixture was hydrogenated at
20 ЊC for 3.5 h. The catalyst was filtered off using Celite. The
filtrate was evaporated in vacuo. The residual orange solid was
washed with Et2O–hexane to afford 22 (1.35 g, 82%) as colour-
less prisms (mp 200–201 ЊC, EtOAc–hexane) (Found: C, 65.7;
H, 4.7. C21H18O7 requires C, 66.0; H, 4.7%); νmax (Nujol)/cmϪ1
phenanthridine 24. 24 (24 mg, 45%) was obtained as less polar
yellow prisms (mp 237–240 ЊC) (Found: C, 67.2; H, 4.8; N, 3.3.
C22H19NO6 requires C, 67.2; H, 4.9; N, 3.6%); νmax (Nujol)/cmϪ1
no characteristic absorption; δH (400 MHz) 3.99 (3 H, s, 7-
OMe), 4.03 (3 H, s, 8-OMe), 4.14 (3 H, s, 12-OMe), 4.33 (3 H, s,
6-OMe), 6.11 (2 H, s, OCH2O), 7.49 (1 H, s, 11-H), 7.52 (1 H, d,
J 9.2, 9-H), 7.65 (1 H, s, 1-H), 8.24 (1 H, d, J 9.2, 10-H) and 8.50
(1 H, s, 4-H); δC (125 MHz) 53.7 (6-OMe), 55.6 (12-OMe), 57.0
(8-OMe), 61.9 (7-OMe), 95.6 (11-C), 99.4 (1-C), 101.2
(OCH2O), 102.1 (4-C), 115.4 (6a-C), 117.5 (10b-C), 117.8 (9-C),
118.6 (10-C), 122.9 (12a-C), 128.9 (4a-C), 131.1 (10a-C), 133.2
(4b-C), 146.5 (7-C), 147.9 (3-C), 148.2 (2-C), 151.6 (8-C), 152.4
(12-C) and 156.4 (6-C); m/z: (EI) 393 (Mϩ, 100%) and 378 (Mϩ–
Me, 30).
3340 (OH) and 1686 (C᎐O); δ (400 MHz) 3.65 (3 H, s, CO-
᎐
H
OMe), 3.92 (3 H, s, ArOMe), 3.93 (3 H, s, ArOMe), 5.49 (1 H, s,
OH), 6.04 (2 H, s, OCH2O), 6.73 (1 H, d, J 1.5, 4-H), 7.01 (1 H,
d, J 8.4, 4Ј-H), 7.07 (1 H, s, 5-H), 7.15 (1 H, d, J 8.4, 5Ј-H), 7.24
(1 H, s, 2-H) and 7.47 (1 H, s, 8-H).
(Z )-Methyl 2,3-dimethoxy-6-[2-(1-methoxyimino-6,7-methyl-
enedioxy-4-oxo-1,4-dihydronaphthyl)]benzoate 11. A mixture of
22 (350 mg, 0.92 mmol) and pulverised K2CO3 (1.27 g, 9.16
mmol) in DMF (3.5 mL) was stirred at room temperature for 20
min under an argon atmosphere. After addition of i-AmONO
(0.21 mL, 1.56 mmol) under ice-cooling, the mixture was stirred
at room temperature for 3.5 h and cooled. After addition of
Me2SO4 (0.11 mL, 1.16 mmol) under ice-cooling, the reaction
mixture was stirred at room temperature for 1.5 h, poured into
5% aqueous ammonia (0.7 mL) and stirred for 1 h. After addi-
tion of water (16 mL) the mixture was extracted with EtOAc.
The organic layer was washed with water and brine, dried
(K2CO3), and evaporated in vacuo. The residual yellow solid was
purified by column chromatography (benzene–EtOAc = 12 : 1)
to give 11 (336 mg, 86%) as yellow prisms (mp 171–173 ЊC,
EtOAc–hexane) (Found: C, 62.1; H, 4.4; N, 3.2. C22H19NO8
(ii)
6,7,8-Trimethoxy-2,3-methylenedioxybenzo[c]phenan-
thridin-11,12-dione 25. 25 (21 mg, 39%) was obtained as more
polar purple prisms (mp > 300 ЊC). νmax (KBr)/cmϪ1 1681 (C᎐O)
᎐
and 1648 (C᎐O); δ (400 MHz) 3.95 (3 H, s, 7-OMe), 4.00 (3 H,
᎐
H
s, 8-OMe), 4.34 (3 H, s, 6-OMe), 6.14 (2 H, s, OCH2O), 7.53
(1 H, s, 1-H), 7.55 (1 H, d, J 9.6, 9-H), 8.06 (1 H, s, 4-H) and
9.24 (1 H, d, J 9.6, 10-H); δC (125 MHz) 55.1 (6-OMe), 56.7
(8-OMe), 61.8 (7-OMe), 102.6 (OCH2O), 107.0 (4-C), 108.4
(1-C), 114.6 (10b-C), 115.6 (6a-C), 121.0 (9-C), 123.3 (10-C),
126.5 (12a-C), 132.1 (10a-C), 135.4 (4a-C), 145.2 (7-C), 149.9
(4b-C), 150.0 (2-C), 152.2 (8-C), 154.4 (3-C), 163.9 (6-C), 178.6
(12-C) and 181.0 (11-C); m/z: (FAB) 394 (MHϩ) and 416
(MNaϩ).
12-Acetoxy-7,8-dimethoxy-2,3-methylenedioxybenzo[c]-
phenanthridin-6(5H)-one 28. A mixture of 23 (51 mg, 0.14
mmol) and acetic anhydride (1 mL) was stirred at room temper-
ature for 2 h, at 50 ЊC for 21 h and then at 80 ЊC for 27 h under
an argon atmosphere. The reaction mixture was washed with
Et2O–hexane to give 28 (51 mg, 91%) as a colorless powder
(mp > 300 ЊC). νmax (Nujol)/cmϪ1 1752 (C᎐O) and 1653 (C᎐O);
δH (400 MHz, DMSO-d6) 2.45 (3 H, s, OCOMe), 3.82 (3 H, s,
7-OMe), 3.92 (3 H, s, 8-OMe), 6.20 (2 H, s, OCH2O), 7.30 (1 H,
s, 1-H), 7.62 (1 H, d, J 9.2, 9-H), 8.04 (1 H, s, 11-H), 8.20 (1 H,
d, J 9.2, 10-H), 8.35 (1 H, s, 4-H) and 11.2 (1 H, s, NH); δC (125
MHz, DMSO-d6) 20.8 (COCH3), 56.2 (8-OMe), 60.9 (7-OMe),
98.6, 99.5, 101.9 (OCH2O), 111.8, 112.2, 118.5, 119.0, 119.2,
119.7, 123.8, 128.9, 129.1, 141.3, 148.4, 148.5, 149.1, 152.3,
159.7 (6-C) and 169.8 (COCH3); m/z: (EI) 407 (Mϩ, 85%), 365
(Mϩ–COMe, 81) and 347 (100).
requires C, 62.1; H, 4.5; N, 3.3%); νmax (Nujol)/cmϪ1 1742 (C᎐O,
᎐
ester) and 1638 (4-C᎐O); δH (400 MHz) 3.66 (3 H, s, COOMe),
᎐
3.93 (6 H, s, OMe × 2), 4.08 (3 H, s, NOMe), 6.12 (2 H, s,
OCH2O), 6.57 (1 H, s, 3-H), 7.01 (1 H, d, J 8.5, 4Ј-H), 7.11 (1 H,
d, J 8.5, 5Ј-H), 7.69 (1 H, s, 5-H) and 8.32 (1 H, s, 8-H); δC (125
MHz) 52.1, 56.0, 61.7, 64.4, 102.2, 106.2, 109.8, 113.3, 124.2,
125.4, 128.3, 128.8, 129.1, 129.3, 145.3, 146.8, 149.4, 151.4,
151.6, 153.5, 166.9 and 183.4.
᎐
᎐
7,8-Dimethoxy-12-hydroxy-2,3-methylenedioxybenzo[c]-
phenanthridin-6(5H)-one 23. To a solution of 11 (252 mg, 0.59
mmol) in AcOH (90 mL) was added 10% palladium–carbon
(50 mg, 0.047 mmol) and the mixture was hydrogenated at room
temperature for 1.5 h under atmospheric pressure. After addi-
tion of CHCl3 (500 mL) the catalyst was filtered off using Celite
and the filtrate was evaporated in vacuo. The yellow residue was
crystallised and washed with Et2O to yield 23 (207 mg, 95%) as
6,12-Diacetoxy-7,8-dimethoxy-2,3-methylenedioxybenzo[c]-
phenanthridine 29. A mixture of 25 (20 mg, 0.055 mmol) and
DMAP (12 mg, 0.098 mmol) in AcOH (0.5 mL, 5.3 mmol) was
stirred at room temperature for 5.5 h, at 50 ЊC for 3.5 h and at
80 ЊC for 1.5 h under argon atmosphere. Triethylamine (0.1 mL,
0.72 mmol) was added to the reaction mixture and the mixture
was stirred at room temperature for 15 h. After addition of
MeOH (1 mL) the solvent was evaporated in vacuo. The residue
was dissolved in EtOAc (10 mL) and the organic layer was
washed with 1 M hydrochloric acid, water, saturated aqueous
NaHCO3 solution, water and brine, dried (MgSO4), and evap-
orated in vacuo. The residual yellow solid (30 mg) was purified
by column chromatography using CHCl3 as an eluent to give 29
(18 mg, 74%) as colourless needles, which were recrystallised
from CHCl3–hexane (mp 230 ЊC, dec.) (Found: C, 64.0; H, 4.35;
N, 3.15. C24H19NO8 requires C, 64.1; H, 4.3; N, 3.1%); νmax
(Nujol)/cmϪ1 1751 (C᎐O); δ (400 MHz) 2.51 (3 H, s, 6-OAc),
yellow prisms (mp > 300 ЊC). νmax (Nujol)/cmϪ1 1654 (C᎐O);
᎐
δH (400 MHz, DMSO-d6) 3.83 (3 H, s, 7-OMe), 3.92 (3 H, s,
8-OMe), 6.17 (2 H, s, OCH2O), 7.46 (1 H, s, 11-H), 7.47 (1 H, s,
1-H), 7.64 (1 H, d, J 9.0, 9-H), 7.96 (1 H, d, J 9.0, 10-H), 8.27
(1 H, s, 4-H), 9.84 (1 H, s, NH) and 11.0 (1 H, s, OH); δC (125
MHz, DMSO-d6) 56.2, 60.9, 99.2, 99.3, 100.2, 101.5, 112.5,
118.4, 119.3, 119.9, 122.0, 124.6, 128.2, 129.2, 147.2, 147.8,
148.2, 149.2, 151.9 and 159.3; Found (FAB) 366.0979 (MHϩ),
C20H16NO6 requires 366.0978.
Methylation of phenolic lactam 23. To a solution of 23 (50
mg, 0.14 mmol) in CH2Cl2 (12 mL) was added 2% aqueous
NaOH solution (4.5 mL), benzyltributylammonium chloride
(86 mg, 0.27 mmol) and Me2SO4 (0.135 mL, 1.42 mmol). The
mixture was stirred at room temperature for 1.5 h, poured into
5% aqueous ammonia (2.85 mL) and stirred at room tem-
perature for 1 h. After addition of water (6 mL) the mixture
was extracted with CHCl3. The organic layer was washed with
brine, dried (K2CO3), and evaporated in vacuo. The purple resi-
due (83 mg) was purified by column chromatography using
CHCl3 as eluent to give two compounds.
᎐
H
2.53 (3 H, s, 12-OAc), 4.01 (3H, s, 7-OMe), 4.04 (3 H, s,
8-OMe), 6.14 (2 H, s, OCH2O), 7.24 (1 H, s, 1-H), 7.60 (1 H, d,
J 9.3, 9-H), 8.08 (1 H, s, 11-H), 8.30 (1 H, d, J 9.3, 10-H) and
8.55 (1 H, s, 4-H); δC (125 MHz) 21.1 (OAc × 2), 56.6 (8-OMe),
62.0 (7-OMe), 98.4 (1-C), 101.6 (OCH2O), 102.8 (4-C), 110.2
(11-C), 115.9 (6a-C), 118.4 (9-C), 119.4 (10-C), 120.4 (10b-C),
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
3030

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123.7 (12a-C), 129.8 (4a-C), 131.2 (10a-C), 136.0 (4b-C), 144.4
(7-C), 145.6 (12-C), 148.9 (2-C), 149.0 (3-C), 151.2 (6-C), 151.4
(8-C), 169.4 (C᎐O) and 169.7 (C᎐O); m/z: (EI) 449 (Mϩ, 48%),
9.75 (1 H, s, 6-H); δC (125 MHz) 56.7, 61.9, 98.6, 101.6, 102.7,
110.5, 118.5, 118.7, 120.2, 121.9, 123.7, 127.7, 128.8, 129.2,
130.4, 130.7, 134.0, 138.2, 145.2, 145.8, 146.4, 148.9, 149.0,
149.6 and 165.3. Found (FAB) 454.1316 (MHϩ), C27H20NO6
requires 454.1291; m/z: (EI) 453 (Mϩ, 39%) and 105 (100).
᎐
᎐
407 (Mϩ–COMe, 63) and 365 (Mϩ-2 × COMe, 100).
12-Benzoyloxy-7,8-dimethoxy-2,3-methylenedioxybenzo[c]-
phenanthridin-6(5H)-one 30. A suspension of 23 (46 mg, 0.13
mmol) and benzoic anhydride (57 mg, 0.25 mmol) in dry
CH2Cl2 (0.3 mL) was stirred at 60 ЊC for 14 days under argon
atmosphere. During the course of reaction, dry CH2Cl2 (0.3
mL) and benzoic anhydride (22 mg, 0.098 mmol) were added
once a day and after 2 days, respectively. The reaction mixture
was diluted with CHCl3 (100 mL). The organic solution was
washed with water, saturated NaHCO3 solution, water, and
brine, dried (Na2SO4), and evaporated in vacuo. The residual
solid was washed with Et2O–EtOAc and then CH2Cl2–hexane
to give 30 (57 mg, 96%) as colourless prisms, which were
recrystallised from CH2Cl2 (mp > 300 ЊC). νmax (Nujol)/cmϪ1
12-Hydroxynorchelerythrine 33. A mixture of 32 (9 mg, 0.019
mmol) and 3% KOH in MeOH (0.5 mL) was stirred at room
temperature for 6 h under argon atmosphere. Additional
3% KOH in MeOH was added twice (50 µL, 0.03 mmol and
0.1 mL, 0.05 mmol) and the whole mixture was stirred at 50 ЊC
for 20 h. The reaction mixture was diluted with water (7 mL)
and extracted with Et2O. The aqueous layer was acidified
(pH 4) with 1 M hydrochloric acid and extracted with CHCl3.
The organic layer was washed with water and brine, dried
(Na2SO4), and evaporated in vacuo to afford 33 (4 mg, 64%) as
yellow prisms, which were used for the next step without further
purification. δH (400 MHz, CDCl3–CD3OD) 4.06 (3 H, s, 7-H),
4.12 (3 H, s, 8-H), 6.14 (2 H, s, OCH2O), 7.57 (1 H, d, J 9.2,
9-H), 7.68 (1 H, s, 11-H), 7.69 (1 H, s, 1-H), 8.26 (1 H, d, J 9.2,
10-H), 8.62 (1 H, s, 4-H) and 9.54 (1 H, s, 6-H); m/z: (EI) 349
(Mϩ, 8.5%), 149 (100) and 105 (95.7).
1734 (C᎐O) and 1647 (NHC᎐O); δ (400 MHz, DMSO-d ) 3.86
᎐
᎐
H
6
(3 H, s, 7-OMe), 3.95 (3 H, s, 8-OMe), 6.22 (2 H, s, OCH2O),
7.20 (1 H, s, 1-H), 7.62 (1 H, d, J 9.0, 9-H), 7.70 (2 H, dd, J 7.2,
7.9, 3Ј- and 5Ј-H), 7.83 (1 H, t, J 7.2, 4Ј-H), 8.26 (1 H, s, 11-H),
8.29 (1 H, d, J 9.0, 10-H), 8.30 (2 H, d, J 7.9, 2Ј- and 6Ј-H), 8.43
(1 H, s, 4-H) and 11.29 (1 H, s, NH); δC (125 MHz, DMSO-d6)
56.2, 60.9, 98.1, 99.7, 102.0, 112.1, 112.3, 118.5, 119.0, 119.4,
119.7, 123.6, 128.8, 128.9, 129.0, 129.3, 130.0, 134.2, 141.3,
148.5, 149.1, 152.3, 159.7 and 165.1; Found (FAB) 470.1231
(MHϩ), C27H20NO7 requires 470.1240; m/z: (EI) 469 (Mϩ,
100%) and 364 (Mϩ–COPh, 83).
12-Methoxynorchelerythrine 27. To a mixture of hydroxy
compound 33 (4 mg, 0.011 mmol) and K2CO3 (21 mg, 0.15
mmol) in DMF (0.5 mL) was added Me2SO4 (10 µL, 0.11
mmol) and the whole mixture was stirred at 0 ЊC for 1.5 h under
argon atmosphere. The reaction mixture was quenched with
aqueous ammonia (0.1 mL), stirred for 1 h, diluted with water
(5 mL) and extracted with EtOAc. The organic layer was
washed with water and brine, dried (Na2SO4), and evaporated
in vacuo. The crude product was washed with Et2O to afford 27
(4 mg, quantitatively) as brown prisms. Purification by column
chromatography (CHCl3–EtOAc = 40 : 1) gave pale orange
prisms (mp 209–210 ЊC). νmax (Nujol)/cmϪ1 no characteristic
absorption; δH (400 MHz) 4.07 (3 H, s, 7-OMe), 4.12 (3 H, s,
8-OMe), 4.18 (3 H, s, 12-OMe), 6.14 (2 H, s, OCH2O), 7.58
(1 H, d, J 9.2, 9-H), 7.60 (1 H, s, 11-H), 7.70 (1 H, s, 1-H), 8.30
(1 H, d, J 9.2, 10-H), 8.69 (1H, s, 4-H) and 9.62 (1H, s, 6-H);
m/z: (EI) 363 (Mϩ, 100%).
12-Benzoyloxy-7,8-dimethoxy-2,3-methylenedioxy-6-trifluoro-
methanesulfonyloxybenzo[c]phenanthridine 31. A mixture of
30 (30 mg, 0.064 mmol), diisopropylethylamine (18 µL, 0.10
mmol) and trifluoromethanesulfonic anhydride (14 µL, 0.083
mmol) in dry CH2Cl2 (13 mL) was stirred at 0 ЊC for 5 h under
argon atmosphere and poured into water (4 mL). The organic
layer was washed with water and brine, dried (Na2SO4), and
evaporated in vacuo. The brown residue was purified by column
chromatography using toluene as an eluant to afford 31 (32 mg,
83%) as colourless prisms, which were recrystallised from
EtOAc (mp 239–241 ЊC) (Found: C, 55.6; H, 3.0; N, 2.25.
C28H18F3NO9S requires C, 55.9; H, 3.0; N, 2.3%); νmax (Nujol)/
cmϪ1 1736 (C᎐O); δ (400 MHz) 4.05 (3 H, s, 7-OMe), 4.10
12-Methoxydihydrochelerythrine 6. To a solution of 32 (30
mg, 0.066 mmol) in anhydrous MeOH (0.4 mL) was added a
solution of sodium methoxide in MeOH (0.8 mL, 0.15 mmol)
and the whole mixture was stirred at 45 ЊC for 18 h under argon
atmosphere. After evaporation of the solvent in vacuo, the resi-
due was dissolved in HMPA (1 mL). To this solution Me2SO4
(0.1 mL, 1.1 mmol) and NaBH4 (40 mg, 1.1 mmol) were added
and the mixture was stirred at 60 ЊC for 1.5 h. Additional
reagents were added as follows: Me2SO4 (0.1 mL, 1.1 mmol)
then NaBH4 (39 mg, 1.0 mmol) with stirring at 60 ЊC for 4.5 h;
Me2SO4 (0.2 mL, 2.1 mmol) and NaBH4 (100 mg, 2.7 mmol)
with stirring at 60 ЊC for 3 h; HMPA (0.5 mL) with stirring at 60
ЊC for 1.5 h. The reaction mixture was quenched with ice–water
and basified with 5% aqueous NaOH solution and extracted
with EtOAc. The organic layer was washed with water and
brine, dried (K2CO3), and evaporated in vacuo. The yellow resi-
due was purified by column chromatography on aluminium
oxide (Merck) (benzene, EtOAc, CHCl3, then CHCl3–MeOH)
to afford 6 (17 mg, 67%) as pale yellow prisms, mp 182–183.5 ЊC
(lit.7 173–174.5 ЊC),18 which were recrystallised from benzene–
MeOH. (Found: C, 69.4; H, 5.7; N, 3.6. C22H21NO5 requires C,
69.6; H, 5.6; N, 3.7%); νmax (KBr)/cmϪ1 no characteristic
absorption; δH (400 MHz) 2.53 (3 H, s, NMe), 3.88 (3 H, s, 7-
OMe), 3.94 (3 H, s, 8-OMe), 4.04 (3 H, s, 12-OMe), 4.27 (2 H, s,
6-H), 6.05 (2 H, s, OCH2O), 6.95 (1 H, d, J 8.4, 9-H), 7.05 (1 H,
s, 11-H), 7.48 (1 H, d, J 8.4, 10-H), 7.55 (1 H, s, 1-H) and 7.65
(1 H, s, 4-H); m/z: (EI) 379 (Mϩ, 100%) and 364 (Mϩ–Me, 61).
This compound was completely identical to the authentic
sample of 6.7
᎐
H
(3 H, s, 8-OMe), 6.14 (2 H, s, OCH2O), 7.31 (1 H, s, 1-H), 7.61
(1 H, d, J 9.3, 9-H), 7.61 (2 H, m, 3Ј- and 5Ј-H), 7.74 (1 H, dt,
J 7.5, 1.3, 4Ј-H), 8.17 (1 H, s, 11-H), 8.27 (1 H, d, J 9.3, 10-H),
8.36 (2 H, dd, J 7.1, 1.3, 2Ј- and 6Ј-H) and 8.40 (1 H, s, 4-H); δC
(125 MHz) 55.6, 61.7, 99.7, 101.8, 102.4, 110.3, 114.5, 118.9,
119.1, 119.3, 121.2, 124.2, 128.9, 129.0, 129.7, 130.4, 131.6,
134.1, 134.7, 144.3, 146.7, 148.4, 149.3, 149.4, 151.9 and 165.1;
m/z: (EI) 601 (Mϩ, 100%).
12-Benzoyloxy-7,8-dimethoxy-2,3-methylenedioxybenzo[c]-
phenanthridine 32. A mixture of 31 (40 mg, 0.066 mmol), pal-
ladium acetate (3 mg, 0.012 mmol) and 1,3-bis(diphenyl-
phosphino)propane (dppp) (5 mg, 0.012 mmol) in DMF (1 mL)
was heated at 60 ЊC for 10 min under argon atmosphere. To this
mixture was added triethylsilane (29 µL, 0.18 mmol) and the
mixture was heated at 60 ЊC for 5 h and diluted with CHCl3 (20
mL). The organic solution was washed with water, saturated
NaHCO3 solution, brine, dried (Na2SO4), and evaporated in
vacuo. The yellow residue was purified by column chromato-
graphy (toluene, CHCl3–EtOAc = 40 : 1, then CHCl3–MeOH)
to afford 32 (27 mg, 89%) as colourless prisms, which were
recrystallisedfromCHCl3–EtOAc(mp249–250ЊC).νmax (Nujol)-
cmϪ1 1735 (C᎐O); δ (400 MHz) 4.06 (3 H, s, 7-OMe), 4.14
᎐
H
(3 H, s, 8-OMe), 6.14 (2 H, s, OCH2O), 7.34 (1 H, s, 1-H), 7.59
(1 H, d, J 9.0, 9-H), 7.62 (2 H, dd, J 7.4, 7.4, 3Ј- and 5Ј-H),
7.74 (1 H, t, J 7.4, 4Ј-H), 8.26 (1 H, s, 11-H), 8.27 (1 H, d, J 9.0,
10-H), 8.39 (2 H, d, J 7.4, 2Ј- and 6Ј- H), 8.78 (1 H, s, 4-H) and
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
3031

View Article Online
(b) V. Simanek in The Alkaloids, ed. A. Brossi, Academic Press, New
York, 1983, vol. 26, p. 185; (c) J. M. Herbert, J. M. Angereau,
J. Gleye and J. P. Maffrand, Biochem. Biophys. Res. Commun., 1990,
172, 993; (d ) S.-D. Fang, L.-K. Wang and S. M. Hecht, J. Org.
Chem., 1993, 58, 5025; (e) C. Vavreckova, I. Gawlik and K. Müller,
Planta Med., 1996, 62, 397; ( f ) T. Schmeller, B. Latz-Bruning and
M. Wink, Phytochemistry, 1997, 44, 257; (g) T. Nakanishi and M.
Suzuki, J. Nat. Prod., 1998, 61, 1263; (h) T. Nakanishi, M. Suzuki,
A. Saimoto and T. Kawabata, J. Nat. Prod., 1999, 62, 864;
(i) F. Fleury, A. Sukhanova, A. Ianoul, J. Devy, I. Kudelina,
O. Duval, A. J. P. Alix, J. C. Jardillier and I. Nabiev, J. Biol. Chem.,
2000, 275, 3501.
3 (a) H. Ishii, Y.-I. Ichikawa, E. Kawanabe, M. Ishikawa, T. Ishikawa,
M. Inomata and A. Hoshi, Chem. Pharm. Bull., 1985, 33, 4139;
(b) H. Ishii, T. Ishikawa, S. Takeda, M. Suzuki and T. Harayama,
Chem. Pharm. Bull., 1992, 40, 2002; T. Ishikawa, A. Takami,
M. Abe, I.-S. Chen, T. Harayama and H. Ishii, Chem. Pharm. Bull.,
1995, 43, 766.
12-Methoxychelerythrine chloride 7. To a solution of 6 (4 mg,
0.011 mmol) in benzene (0.5 mL) was added 5% aqueous
NaOH solution (0.2 mL) and a solution of DDQ (6 mg, 0.025
mmol) in benzene (0.2 mL) and the whole mixture was stirred at
room temperature for 0.5 h. After evaporation of the solvent in
vacuo, the residue was dissolved in water (10 mL) and extracted
with CHCl3. The organic layer was washed with water, dried
(K2CO3), and evaporated to reduce the volume of solvent
(0.5 mL). To this solution 10% hydrochloric acid was added to
yield a yellow precipitate. After co-evaporation with benzene
and MeOH the residual orange solid was washed with Et2O and
hexane–benzene to give 7 (3 mg, 78%) as orange prisms, mp
181–187 ЊC (dec.). δH (500 MHz, CD3OD) 4.14 (3 H, s, OMe),
4.27 (3 H, s, OMe), 4.29 (3 H, s, OMe), 4.97 (3 H, s, NMe), 6.27
(2 H, s, OCH2O), 7.88 (1 H, s, ArH), 7.97 (1 H, s, ArH), 8.16
(1 H, s, ArH), 8.18 (1 H, d, J 9.3, 9- or 10-H), 8.73 (1 H, d, J 9.3,
10- or 9-H) and 9.81 (1 H, s, 6-H). Found (FAB) 378.1316
(Mϩ–Cl), C22H20NO5 requires 378.1342; m/z: 378 (Mϩ–Cl).
4 T. Ishikawa, T. Saito and H. Ishii, Tetrahedron, 1995, 51, 8447.
5 M. A. Lynch, O. Duval, A. Sukhanova, J. Devy, S. P. MacKay,
R. D. Waight and I. Nabiev, Bioorg. Med. Chem. Lett., 2001, 11,
2643.
6 S. M. Oechslin, G. M. König, K. Oechslin-Merkel, A. D. Wright,
A. D. Kinghorn and O. Sticher, J. Nat. Prod., 1991, 54, 519.
7 T. Harayama, T. Akiyama, H. Akamatsu, K. Kawano, H. Abe and
Y. Takeuchi, Synthesis, 2001, 444.
8 T. Ishikawa, K. Nagai, N. Ohkubo and H. Ishii, Heterocycles, 1994,
39, 371.
9 H. Ishii, I.-S. Chen, S. Ueki, T. Masuda, K. Morita and T. Ishikawa,
J. Chem. Soc., Perkin Trans. 1, 1987, 2415.
10 H. Ishii, T. Ishikawa, S. Takeda, S. Ueki and M. Suzuki,
Chem. Pharm. Bull., 1992, 40, 1148.
11 T. Ishikawa, T. Watanabe, H. Tanigawa, T. Saito, K.-I. Kotake,
Y. Ohashi and H. Ishii, J. Org. Chem., 1996, 61, 2774.
12 Unsuccessful selective benzoylations were observed under
different conditions such as the use of benzoyl chloride–Et3N in
CH2Cl2 or benzoic acid–(2-chloro-1,3-dimethylimidazolinium
chloride (DMC)13 in pyridine.
13 T. Isobe and T. Ishikawa, J. Org. Chem., 1999, 64, 6984.
14 H. Ishii, T. Ishikawa, Y.-I. Ichikawa, M. Sakamoto, M. Ishikawa and
T. Takahashi, Chem. Pharm. Bull., 1984, 32, 2984.
In vitro cytotoxicity assay
The cytotoxicity of benzo[c]phenanthridines against human
lung cancer cell line NCI-H460 and human breast cancer cell
line MDA-MB-231 obtained from ATCC (American Type Cul-
ture Collection) was assessed by the methylene blue staining
method. Briefly, 1.5 × 103 NCI-H460 cells/well and 4.0 × 103
MDA-MB-231 cells/well were inoculated into 96-well micro-
plates. Both cells were cultured in RPMI1640 medium sup-
plemented with 10% fetal bovine serum, and 1 mM sodium
pyruvate for NCI-H460 cells. Following overnight culture, seri-
ally diluted samples (0.016, 0.08, 0.4, 2, 10, 50 µg mLϪ1) were
added into the wells. After a 3-day culture, cells were stained
with 0.05% methylene blue dissolved in 10 mM Tris buffer (pH
8.5) for 30 min, and then thoroughly washed with distilled
water. The stained dye was extracted with 3% hydrochloric acid,
and OD660 was measured with microplate reader Benchmark
Plus (Bio-Rad, USA) to determine cell growth inhibition.
15 Sticher and co-workers6 noted that natural 12-methoxy-
dihydrochlerythrine (6) showed [α]20D Ϫ15 (c = 0.2, CHCl3); however,
6 is an achiral compound which should have no optical rotation.
Harayama et al.7 did not comment on this questionable point.
16 (a) T. Nakanishi, A. Masuda, M. Suwa, Y. Akiyama, N. Hoshino-
Abe and M. Suzuki, Bioorg. Med. Chem. Lett., 2000, 10, 2321;
(b) M. Fukuda, M. Inomata, K. Nishio, K. Fukuoka, F. Kanzawa,
H. Arioka, T. Ishida, H. Fukumoto, H. Kurokawa, M. Oka and
N. Saijo, Jpn. J. Cancer Res., 1996, 87, 1086.
Acknowledgements
We would like to thank Professor Takashi Harayama, Faculty
of Pharmaceutical Sciences, Okayama University, for giving us
an authentic sample of 12-methoxydihydrochelerythrine.
17 Anhydrous palladium chloride (1.0 g) was dissolved in concentrated
hydrochloric acid (2.5 mL) and water (6.0 mL). Then, the total
volume of the resulting solution was made up to 60 mL by addition
of water; H. Ishii, E. Kawanabe, K.-I. Harada, T. Deushi, E. Ueda,
T. Watanabe, Y.-I. Ichikawa, M. Sakamoto, T. Ishida, T. Takahashi,
K. Nakajima and T. Ishikawa, Chem. Pharm. Bull., 1983, 31, 3039.
18 No description of the melting point of 6 in ref 6.
Notes and references
1 T. Ishikawa and H. Ishii, Heterocycles, 1999, 50, 627.
2 (a) W. M. Suffiness and G. A. Gordell, in The Alkaloids,
ed. A. Brossi, Academic Press, New York, 1983, vol. 25, p. 178;
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 0 2 4 – 3 0 3 2
3032