New anthracene derivatives from Coussarea macrophylla

Article abstract of DOI:10.1021/np030066i

Five new naturally occurring anthracene derivatives, 1,4,10-trimethoxyanthracene-2-carbaldehyde (1), (1,4,10-trimethoxy-2-anthracen-2-yl)methanol (2), 1,4,8,10-tetramethoxyanthracene-2-carbaldehyde (3), 1,4,10-trimethoxyanthracene-2-carboxylic acid (4), a

Full text of DOI:10.1021/np030066i

© Copyright 2003 by the American Chemical Society and the American Society of Pharmacognosy
Volume 66, Number 7
J uly 2003
Full Papers
New An th r a cen e Der iva tives fr om Cou ssa r ea m a cr oph ylla
Ximena Chiriboga,† Gianluca Gilardoni,‡ Ilaria Magnaghi,‡ Paola Vita Finzi,‡ Giuseppe Zanoni,‡ and
Giovanni Vidari*,‡
Facultad de Ciencias Quimicas, Universidad Central del Ecuador, Quito, Ecuador, and Dipartimento di Chimica Organica,
Universita` di Pavia, Via Taramelli 10, 27100 Pavia, Italy
Received February 17, 2003
Five new naturally occurring anthracene derivatives, 1,4,10-trimethoxyanthracene-2-carbaldehyde (1),
(1,4,10-trimethoxy-2-anthracen-2-yl)methanol (2), 1,4,8,10-tetramethoxyanthracene-2-carbaldehyde (3),
1,4,10-trimethoxyanthracene-2-carboxylic acid (4), and 1,3-dimethoxy-2-methoxymethylanthraquinone (5),
were isolated from Coussarea macrophylla along with three known compounds, 3-hydroxy-1-methoxy-
2-methoxymethylanthraquinone (6), scopoletin, and 3-epi-pomolic acid. The structures of 1-5 were
determined on the basis of analysis of their spectroscopic data and by total synthesis.
About 150 plants of the genus Coussarea grow in Central
and South American countries, between Cuba and the
equatorial regions;1 however, despite the wide occurrence
of Cousarrea species, their secondary metabolites are
almost unknown.2 Coussarea macrophylla Muell. Arg.
(Rubiaceae) is a woody plant, occurring in the tropical
swamp forests of Ecuador. It usually stands upright,
reaching a height of 4 m. Upon cutting, the fruits emanate
a pleasant peppermint fragrance. Although this species is
not used in traditional medicine in Ecuador, during a
general screening of Ecuadorian plants for new bioactive
compounds, we considered this plant worthy of phy-
tochemical investigation.
extract was submitted to extraction with Na2CO3, yielding
a new naturally occurring anthracenecarboxylic acid (4),
along with the known anthraquinone 6.
Resu lts a n d Discu ssion
Compound 1 was detected as a highly yellow fluorescent
spot on TLC plates and gave a molecular ion peak at m/z
296.1046 in the HRMS, which, in accordance with data
obtained from the NMR spectra, corresponded to the
molecular formula C18H16O4. The UV absorption curve
showed multiple absorption maxima between 220 and 450
nm, with those at higher wavelength (>330 nm) being weak
as in anthracene. Four of the 10 hydrogens of the nucleus
were substituted by three methoxy groups [δ 4.07, 4.15,
and 4.20 (3H each, 1s each)] and one formyl group (CHO
The ground bark of C. macrophylla was extracted with
EtOAc, followed by 95% EtOH. The first extract was
partitioned between hexane and MeCN to remove most of
the chlorophylls, and the polar phase was then submitted
to conventional purification procedures, resulting in the
isolation of four new anthracene derivatives (1-3 and 5),
along with scopoletin and 3-epi-pomolic acid. The EtOH
* To whom correspondence should be addressed. Tel: +39-0382-507322.
Fax: +39-0382-507323. E-mail: vidari@chifis.unipv.it.
† Universidad Central del Ecuador.
1
δC 189.1; CHO δ 10.64). The H NMR spectrum displayed
a pattern of four aromatic protons assignable to an unsub-
‡ Universita` di Pavia.
10.1021/np030066i CCC: $25.00
© 2003 American Chemical Society and American Society of Pharmacognosy
Published on Web 06/07/2003

906 J ournal of Natural Products, 2003, Vol. 66, No. 7
Chiriboga et al.
F igu r e 2. Selected NOESY correlations of compounds 3 and 5.
F igu r e 1. Selected HMBC (A) and NOESY (B) correlations of
compound 1.
1
corresponding signal in the H NMR spectrum of 1, due to
the occurrence of an additional oxygen atom at its proxim-
ity (C-8).3 Compound 3 was thus identified as the new
compound 1,4,8,10-tetramethoxyanthracene-2-carbalde-
hyde.
stituted ring of the anthracene moiety. This comprised two
sets of double doublets at δ 8.10 and 8.45, each integrating
for one proton, attributed to H-8 and H-5, respectively, and
a multiplet centered at δ 7.59, integrating for two protons,
assigned to H-6 and H-7. In addition, there were two
singlets at δ 7.05 and 8.65, which were allocated to H-3
and H-9, respectively. The deshielded signals observed for
H-5 and H-9 could be attributed to the occurrence of an
oxygen atom in a peri position (C-10 and C-1, respectively).3
Each carbon atom was correlated to the respective one-
bond linked proton(s) by interpretation of the FGHMQC
NMR spectrum, so that assignment of the structure of 1
was then carried out by interpretation of the FGHMBC
NMR spectrum (Figure 1A). Particularly diagnostic for
establishing the substitution pattern of ring A were the
H-C long-range correlations of the formyl proton at δ 10.64
with the signals of an aromatic methine carbon at δ 96.6
(C-3) and an aromatic MeO-C carbon at δ 158.0 (C-1), and
the correlations of an aromatic proton at δ 7.05 (s, H-3)
with the signals of two carbons each bearing a MeO group
(δ 158.0 and 153.1; C-1 and C-4, respectively). Further, the
aromatic proton at δ 8.65 (s, H-9) showed long-range
correlations with the carbon signals at δ 158.0 (C-1), 123.0
(C-14), and 128.6 (C-8), indicating that this singlet aromatic
proton occurred at C-9 in ring B.
Compound 4 gave a molecular ion peak at m/z 312.1150
by HRMS and showed the same pattern of aromatic protons
and methoxy groups as compound 1; moreover, it gave a
1
methyl ester (4a ; IR: 1737 cm-1; H NMR: δ 3.89 (s, 3H)
for COOMe) upon exposure to diazomethane. These results
firmly established the structure of 4 as the new compound
1,4,10-trimethoxyanthracene-2-carboxylic acid.
Finally, an anthraquinone C18H16O5 (M+: m/z 312) was
obtained, showing two signals of two carbonyl groups at δ
181.0 and 183.1 in the 13C NMR spectrum and two
multiplets and one singlet in the aromatic portion of the
1H NMR spectrum, which were assigned to four protons of
an unsubstituted ring and to an isolated proton, respec-
tively. Three methoxy singlets at δ 3.48, 4.02, and 4.09 and
one methylene signal at δ 4.64, along with NOESY cor-
relations (Figure 2), clearly indicated a 1,2,3-trisubstituted
ring A, with the methoxymethyl group being in the C-2
position. The resulting structure was 1,3-dimethoxy-2-
methoxymethylanthraquinone (5). This compound was
previously obtained by methylation of lucidin4,5 and of
damnacanthol;6 however, it has not yet been reported to
occur in nature. Moreover, spectroscopic data have not been
published so far. To confirm the structure and to secure a
larger amount for biological tests, we completed a short
unambiguous synthesis of 5 (Scheme 1), based on the
reaction, developed by Sammes7 and Biehl,8 of arynes with
3-lithiated phthalides. As anticipated, the synthetic mate-
rial was identical to the natural compound.
These results, as well as other C-H correlations ob-
served between protons in ring A and the respective
carbons, and NOESY correlations (Figure 1B) strongly
supported the proposed structure of 1 as the new compound
1,4,10-trimethoxyanthracene-2-carbaldehyde.
Compound 2 gave a molecular ion at m/z 298.1206 in
the HRMS, which, in accordance with the NMR spectra,
1
Sch em e 1. Synthesis of Anthraquinone 5a
corresponded to the molecular formula C18H18O4. The H
NMR spectrum of compound 2 was similar to that of 1 with
the exception of a singlet peak integrating for two protons
at δ 4.90, representative of a benzylic hydroxymethyl group,
replacing the signal of the formyl proton in 1. Consistent
with the electronic effects exerted by the different substit-
uents at C-2, the singlet aromatic protons H-3 and H-9 of
compound 2 moved upfield with respect to the correspond-
ing signals of 1, whereas the proton pattern in ring A
remained unchanged. Compound 2 was also identical to
the product obtained by reduction of 1 with NaBH4; it was
thus identified as the new compound (1,4,10-trimethoxy-
anthracen-2-yl)methanol.
a
Reagents and conditions: (a) Br2, CHCl3, 0 °C, 80%; (b) BH3, THF,
reflux, 77%; (c) CH(OMe)3, cat. p-TsOH, MeOH, reflux, 78%; (d) 1(3H)-
isobenzofuranone, lithium 2,2,6,6-tetramethylpiperidide, THF, -60 °C, 20
min; then add 10, -40 °C, 15 min, 20 °C, 1 h; (e) air, 15 h, 10% overall
from 10.
The structure of compound 3 contained an additional
OMe group with respect to 1, as indicated by the molecular
ion peak at m/z 326.1156 in the HRMS and an additional
The identity of the known compounds 3-hydroxy-1-
methoxy-2-methoxymethylanthraquinone9-11 (6), scopole-
tin,12 and 3-epi-pomolic acid13 were determined on the basis
of spectroscopic data and comparison with the data in the
literature. They were further confirmed by 2D NMR
spectra. The 13C NMR data of anthraquinone 6 and of 3-epi-
pomolic acid have not been reported in the literature before.
It has been suggested that 2-methoxymethylanthraquino-
nes of type 5 and 6, typical of several Rubiaceae, might be
artifacts formed from the corresponding 2-hydroxymethyl
1
singlet at δ 4.10, integrating for three protons, in the H
NMR spectrum. Consequently, there were five aromatic
1
protons as indicated by the H NMR spectrum, and their
pattern clearly showed that ring C of the anthracene
moiety was monosubstituted by an OMe group which could
be located either at C-5 or at C-8. The substituent was
eventually placed on C-8 on the basis of NOESY evidence
(Figure 2) and the deshielded signal observed at δ 9.10 for
H-9. This proton was shifted downfield compared to the

New Anthracene Derivatives from Coussarea
J ournal of Natural Products, 2003, Vol. 66, No. 7 907
derivatives by contact with methanol.9-11 In the present
investigation, compounds 5 and 6 were not exposed to
MeOH; therefore, we consider the two anthraquinones as
naturally occurring metabolites of C. macrophylla. An-
thracene derivatives 1-4 belong to a rare class of natural
products; as far as we know, oruwal and oruwalol (5- or
8-hydroxyoruwal) are the only related compounds isolated
so far from the plant kingdom and occur in Morinda lucida
Benth., another member of the Rubiaceae.14 The oxidation
pattern of the two groups of anthraquinols is, however,
significantly different; compounds 1-4 exhibit two OMe
substituents at C-1 and C-4 of the anthracene nucleus,
whereas these positions are unsubstituted in oruwal
derivatives. It has been suggested that the isolation of
anthracene derivatives such as oruwal is of biogenetic
interest, since it may indicate the operation of the shikimic
acid-mevalonate pathway15 in the biosynthesis of co-
occurring anthraquinones.14 The isolation of the six com-
pounds 1-6 from C. macrophylla strongly corroborates this
hypothesis and indicates that oxidation of the ring A of
anthracene derivatives may occur at a later step of the
biosynthesis.
Compounds 1, 2, and 5 were tested in standard filter
paper disk assays16 against Staphylococcus aureus and
Escherichia coli; only aldehyde 1 showed an inhibition zone
against S. aureus (inhibition diameter ) 12 mm for 19 µg/
disk). In addition, compounds 1 and 5 were inactive (LC50
> 280 ppm) in the brine shrimp (Artemia salina) lethality
assay.17 By contrast, the triterpene 3-epi-pomolic acid has
been shown by Xu et al. to exhibit a significant anti-HIV-1
protease activity.18 Compounds 3, 4, and 6 were not
obtained in sufficient quantity for testing.
in vacuo to give 9.5 and 2.2 g of oily materials, extracts A and
B, respectively.
Extract A was partitioned between MeCN and hexane to
give 4.5 g of the MeCN extract (A1) and 3.7 g of the hexane
extract (A2) after evaporation in vacuo. A quantity (1.1 g) of
insoluble material (A3) was also recovered. A sample of A1 (4
g) was chromatographed on a silica gel (250 g) column, eluted
with a hexane-EtOAc mixture (gradient of increasing polarity
from 70:30 to 100% EtOAc) followed by EtOAc-MeOH, 4:1.
The eluted fractions (15-20 mL each) were evaluated by TLC
to give nine main fractions, CMA1-1 to CMA1-9.
Chromatography of fraction CMA1-2 (50 mg) on a silica gel
column (3.5 g, hexane-EtOAc, 93:7) yielded 15 mg of com-
pound 1. Chromatography of fraction CMA1-3 (110 mg) on a
silica gel column (10 g, hexane-EtOAc, 95:5) gave 10 major
subfractions, CMA1-3-1 to CMA1-3-10. CMA1-3-5 corresponded
to compound 3, while yellow fine crystals of anthraquinone 5
(4 mg) slowly separated from an EtOAc-hexane solution of
CMA1-3-3 kept at -20 °C. Chromatography of fraction CMA1-4
(216 mg) on two consecutive silica gel columns (15 and 7 g,
respectively), each eluted with hexane-EtOAc mixtures (gra-
dient of increasing polarity from 85:15 to 0:100), afforded 3-epi-
pomolic acid (16.4 mg). Chromatography of fraction CMA1-5
(670 mg) on a silica gel column (50 g, hexane-EtOAc, gradient
of increasing polarity from 40% to 100% EtOAc) yielded 15
mg of compound 2. Chromatography of fraction CMA1-9 (1.18
g) on a silica gel column (70 g, hexane-EtOAc + 1% AcOH,
gradient of increasing EtOAc from 50% to 100%) yielded 12
major subfractions. Separation of fraction CMA1-5-9 (6 mg) on
a
RP-18 column (MeOH-H2O, 4:1) afforded scopoletin
(1.8 mg).
Extract B was dissolved in Et2O (200 mL) and extracted
with four portions (50 mL each) of saturated aqueous Na2CO3.
The basic layers were collected, acidified to pH 2 with 20%
aqueous H2SO4, and extracted with three portions (50 mL
each) of EtOAc. The organic layers were collected, washed with
brine, and dried with anhydrous Na2SO4. Removal of solvent
in vacuo afforded a sticky residue (165 mg), which was
chromatographed on a silica gel (15 g) column. Elution with a
hexane-EtOAc mixture (gradient of increasing polarity from
50:10 to 0:100), followed by an EtOAc-MeOH mixture (gradi-
ent of increasing polarity from 90:10 to 85:15), yielded five
major fractions, CMB-1 to CMB-5. The first one (4.3 mg)
corresponded to anthraquinone 6, while fraction CMB-4 (44.2
mg) was further separated on a silica gel (12 g) column. Elution
with CH2Cl2-EtOAc, 2:1, yielded five subfractions, CMB-4-1
to CMB-4-5. Chromatography of CMB-4-4 (2.8 mg) on a
RP-18 column (eluent: MeCN-H2O, 1:1) finally afforded
compound 4 (0.8 mg).
1,4,10-Tr im eth oxya n th r a cen e-2-ca r ba ld eh yd e (1): pale
yellow crystals (CH2Cl2-hexane); mp 145 °C; UV (EtOH) λmax
(log ꢀ) 243 (4.51), 266 (4.75), 299 (4.44), 360 (3.62), 379 (3.76),
411 (3.75), 433 (3.78) nm; IR (KBr) νmax 1675 (CdO), 1612,
1458, 1400, 1357, 1212, 1143, 1067, 976 cm-1; 1H and 13C NMR
data, see Tables 1 and 2, respectively; EIMS m/z 296 (M+, 100),
281 (72), 253 (24), 238 (20), 221 (6), 209 (15); HREIMS [M+]
m/z 296.1046 (calcd for C18H16O4, 296.1049).
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. Melting points were
determined on a Fisher-J ohns hot-stage apparatus and are
uncorrected. UV (in 95% EtOH) and IR (neat or in mini KBr
disks) spectra were recorded on a Kontron Uvikon 941 and
an FT-IR Perkin-Elmer Paragon 1000 PC spectrometer, re-
spectively. 1H and 13C NMR spectra (CDCl3) were determined
on a Bruker CXP 300 spectrometer at 300 MHz (1H) and 75.47
MHz (13C), respectively. 1H and 13C chemical shifts (δ, ppm)
are relative to residual CHCl3 signals [δH 7.26, δC (central line
of t) 77.1, respectively); the abbreviations s ) singlet, d )
doublet, t ) triplet, q ) quartet, m ) multiplet, and br ) broad
are used throughout; coupling constants (J ) are reported in
Hz. The spectra were interpreted by the aid of the standard
FGCOSY, FGHMBC, and FGHMQC techniques. EIMS and
HREIMS were recorded using a Finnigan MAT 8222 spec-
trometer, with ionization being induced by electron impact at
70 eV. Thin-layer chromatography was performed on silica gel
60 F254 Al sheets (Merck) and RP-18 HPTLC F254 glass-backed
plates (Merck). Compounds were visualized under UV light
(254 and 366 nm) and by spraying with 0.5% vanillin solution
in H2SO4-EtOH (4:1) followed by heating. Flash column
chromatography was performed with Merck Kieselgel 60 (40-
63 µm) and Merck LiChroprep RP-18 (25-40 µm).
P la n t Ma ter ia l. A sample of the bark of C. macrophylla
was collected and identified by one of the authors (X.C.) in
May 1998 in a tropical damp forest at an altitude of 250 m
near the village Santa Ana, in the Provincia de Sucumbios,
district Cascales, Ecuador. The material was dried, ground,
and kept in the dark at room temperature. A voucher speci-
men, registered as Efrain Freire no. 2242, has been deposited
in the Nacional Herbarium of Quito, Ecuador.
Extr a ction a n d Isola tion . The plant material, 750 g of
bark, was extracted with EtOAc (2 L) at room temperature
three times with occasional stirring and filtered. The macerate
was then extracted three times with 96% EtOH (2 L each) for
24 h each time. The extracts were combined and evaporated
(1,4,10-Tr im eth oxya n th r a cen -2-yl)-m eth a n ol (2): pale
yellow crystals (CH2Cl2-hexane); mp 116 °C; UV (EtOH) λmax
(log ꢀ) 244 (4.50), 260 (4.62), 354sh (3.50), 370 (3.72), 384 (3.60),
402sh (3.53) nm; IR (KBr) νmax 3392 (OH), 2916 (C-H), 1621,
1454, 1348, 1137, 1036 cm-1); 1H and 13C NMR data, see Tables
1 and 2, respectively; EIMS m/z 298 (M+, 100), 283 (33), 268
(40), 255 (35), 239 (28), 224 (26), 211 (20); HREIMS [M+] m/z
298.1206 (calcd for C18H18O4, 298.1205).
The same compound was obtained by reduction of aldehyde
1 with NaBH4 according to a standard procedure.19
1,4,8,10-Te t r a m e t h oxya n t h r a ce n e -2-ca r b a ld e h yd e
(3): pale yellow sticky solid; UV (EtOH) λmax (log ꢀ) 238 (4.62),
268 (4.81), 298sh (4.50), 344 (3.76), 364 (3.91), 382 (4.06), 422sh
(4.02), 440 (4.06) nm; IR (film) νmax 2933 (C-H), 1673 (CdO),
1613, 1459, 1353, 1067 cm-1; 1H and 13C NMR data, see Tables
1 and 2, respectively; EIMS m/z 326 (M+, 100), 311 (60), 296
(13), 283 (22), 268 (28), 253 (15); HREIMS [M]+ m/z 326.1156
(calcd for C19H18O5, 326.1154).

908 J ournal of Natural Products, 2003, Vol. 66, No. 7
Chiriboga et al.
Ta ble 1. 1H NMR Data of Compounds 1-5 (CDCl3, 300 MHz)a
proton
1
2
3
4
5
3
7.05 s
6.77 s
7.10 s
6.90 s
4
7.71 s
5
6
7
8
9
15
OMe-1
OMe-3
OMe-4
OMe-8
OMe-10
OMe-15
8.45 (dd, 8.0, 1.5)
7.59 m
7.59 m
8.10 (dd, 8.0, 1.5)
8.65 s
10.64 s
8.38 dd (dd, 8.0, 1.5)
7.50 m
7.50 m
8.01 dd (dd, 8.0, 1.5)
8.42 s
4.93 s
7.98 (br d, 8.0)
7.50 (t, 8.0)
6.87 (br d, 8.0)
8.40 (dd, 8.0, 1.5)
7.66 m
7.66 m
8.10 (dd, 8.0, 1.5)
8.50 s
8.28 m
7.77 m
7.77 m
8.28 m
9.10 s
10.60 s
4.25 s
4.64 s
4.02 s
4.09 s
4.20 s
4.10 s
4.21 s
4.13 s
4.06 s
4.15 s
4.07 s
4.08 s
4.03 s
4.13 s
4.13 s
4.05 s
3.48 s
a
Multiplicities and coupling constants (Hz) in parentheses.
Ta ble 2. 13C NMR Data of Compounds 1-3, 5, and 6 (CDCl3,
37.2 (t, C-22), 37.4 (s, C-4), 40.0 (d, C-20), 40.9 and 41.0 (2s,
C-8 and C-14), 46.8 (d, C-9), 47.6 (s, C-17), 48.7 (d, C-5), 52.6
(d, C-18), 73.0 (s, C-19), 76.1 (d, C-3), 129.4 (d, C-12), 137.7 (s,
C-13), 183.9 (s, C-28). (a-dSignal assignments may be inter-
changed.)
75.47 MHz)a
carbon
1
2
3
5
6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
158.0 s
120.4 s
96.6 d
146.7 s
126.7 s
103.2 d
152.8 s
122.8 d
125.4 d
126.2 d
128.7 d
116.6 d
152.8 s
128.7 s
135.1 s
132.6 s
118.1 s
60.7 t
153.3 s
120.7 s
97.0 d
162.0b
136.8 s
163.3b
s
160.2b
136.8 s
163.0b
s
Syn th esis of 1,3-Dim eth oxy-2-m eth oxym eth yla n th r a -
qu in on e (5). Br2 (2.81 g, 17.6 mmol) was added dropwise to
a solution of commercially available 2,6-dimethoxybenzoic acid
(3 g, 16.5 mmol) in CHCl3 (60 mL) cooled to 0 °C. The mixture
was stirred for 90 min at 0 °C, then saturated aqueous Na2S2O5
was added until decoloration. The two layers were separated,
and the aqueous phase was acidified with 10% HCl and
extracted exhaustively with Et2O. The ether phase was dried
(MgSO4) and evaporated to give 3-bromo-2,6-dimethoxybenzoic
acid (8)20 as a pale yellow crystalline solid (3.44 g, yield ) 80%).
An analytical sample was obtained by recrystallization from
EtOH-H2O: mp 142-145 °C (lit.20 146-148 °C); IR (Nujol)
νmax 2924, 2854, 2630, 1711 (CdO), 1641, 1588, 1465, 1392,
1290, 1258, 1156, 1098, 1000, 911, 841, 804, 759, 714, 667,
s
s
153.1 s
123.4 d
126.1 d
127.1 d
128.6 d
118.9 d
153.8 s
128.4 s
132.7 s
128.4 s
123.0 s
189.1 d
66.0 q
153.0 s
115.0 d
127.2 d
103.3 d
155.9 s
113.8 d
140.0 s
129.5 s
124.3 s
127.7 s
118.0 s
189.1 d
64.1 q
105.3 d
112.4 d
126.6c d
127.4c d
133.1d
d
133.0d
134.6d
d
d
134.3dd
127.1c d
181.0 s
183.1 s
132.4e s
134.8e s
120.0 s
127.3 s
62.6 t
128.1c d
182.2e s
183.5e s
132.5f s
135.1f s
122.5g
127.7g
69.5 t
s
s
OMe-1
OMe-3
OMe-4
OMe-8
OMe-10
OMe-15
62.5 q
63.2 q
58.6 q
62.1 q
1
636 cm-1; H NMR (CDCl3) δ 3.90 (3H, s, OMe), 3.97 (3H, s,
56.2 q
63.7 q
56.2 q
63.5 q
56.1 q
56.7 q
66.6 q
OMe), 6.67 (1H, d, J ) 9.0 Hz, H-5), 7.58 (1H, d, J ) 9.0 Hz,
H-4); anal. C 41.35%, H 3.40%, calcd for C9H9BrO4, C 41.41%,
H 3.47%.
56.4 q
59.3 q
Borane-tetrahydrofuran complex (1.0 M in THF, 6 mL, 6
mmol) was added dropwise by syringe to a solution of
compound 8 (0.59 g, 2.3 mmol) in THF (30 mL) at 0 °C under
an argon atmosphere. After refluxing for 12 h, the solution
was then cooled to 0 °C, and 6 M HCl (3 mL) was added,
followed by 10% aqueous NaOH to basicity.21 The aqueous
phase was extracted exhaustively with Et2O, and the collected
organic layers were dried with MgSO4. Evaporation of the
solvent gave 3-bromo-2,6-dimethoxybenzyl alcohol (9) as a pale
yellow oil (0.43 g, yield ) 77%), which was immediately used
in the following step. An analytical sample was obtained by
filtration on a short silica gel column eluted with 1:1 hexane-
EtOAc: IR (film) νmax 3419 (OH), 3084, 2940, 2838; 1584, 1465,
1410, 1334, 1277, 1230, 1178, 1133, 1098, 1016, 895, 849, 800,
a
Signal multiplicities determined by DEPT experiments.
Assignments with the same superscript in the same column
b-g
may be interchanged.
1,4,10-Tr im eth oxya n th r a cen e-2-ca r boxylic a cid (4):
pale yellow sticky oil; UV (EtOH) λmax (log ꢀ) 226 (4.73), 261
(4.61), 292 (4.35) nm; IR (film) νmax 3200 (OH), 2916 (C-H),
1723 (CdO), 1454, 1234, 1040 cm-1; 1H NMR data, see Table
1; MS data were collected for the corresponding methyl ester
4a , obtained by exposure of 4 to diazomethane: APCIMS m/z
327 [MH]+, 312 [327 - Me]+, 297 [312 - Me]+; HREIMS [M]+
m/z 326.1150 (calcd for C19H18O5, 326.1154).
1,3-Dim et h oxy-2-m et h oxym et h yla n t h r a q u in on e (5):
pale yellow needles (EtOAc-hexane); mp 155-157 °C (lit.
161-162 °C);10 UV (EtOH) λmax (log ꢀ) 202 (4.50), 245 (4.15),
274 (4.59), 334 (3.73), 364 (3.60) nm; IR (KBr) νmax 2907
1
772, 682 cm-1; H NMR (CDCl3) δ 2.40 (1H, br s, OH), 3.87
(3H, s, OMe), 3.89 (3H, s, OMe); 4.78 (2H, s, CH2O), 6.61 (1H,
d, J ) 8.8 Hz, H-5), 7.45 (1H, d, J ) 8.8 Hz, H-4); EIMS m/z
248 (81Br M+, 99), 246 (79Br M+, 100), 231 (80), 214 (75), 201
(30), 185 (15), 167 (20), 157 (10), 134 (40), 124 (20), 119 (15),
100 (20), 92 (20), 77 (50), 63 (55), 51 (35), 43 (8); HREIMS
[M]+ m/z 247.9867 (calcd for C9H1181BrO3, 247.9871).
Trimethyl orthoformate (0.29 g, 2.73 mmol) and catalytic
p-TsOH were added to a solution of compound 9 (0.43 g, 1.74
mmol) in MeOH (30 mL); the resulting solution was refluxed
for 1 h and then cooled to room temperature. Aqueous
Na2CO3 (15 mL; 10%) was added, and most of the MeOH was
evaporated in vacuo. The remaining solution was extracted
with three portions (25 mL each) of Et2O, and the collected
organic layers were dried (anhydrous Na2SO4) and evaporated
in vacuo to yield 3-bromo-2,6-dimethoxybenzyl methyl ether
(10) as a pale yellow oil (0.35 g, yield ) 78%), which was
immediately used in the following step. An analytical sample
was obtained by filtration on a short silica gel column eluted
(C-H), 1668 (CdO), 1574, 1463, 1326, 1283, 1133, 714 cm-1
;
1H and 13C NMR data, see Tables 1 and 2, respectively; EIMS
m/z 312 (M+, 6), 297 (34), 281 (12), 267 (20), 251 (3), 237 (10),
223 (4), 209 (4), 195 (3), 181 (7). Compound 5 was identical to
an authentic synthetic sample (see below).
3-Hyd r oxy-1-m eth oxy-2-m eth oxym eth yla n th r a qu in o-
n e (6): pale yellow needles (EtOAc-hexane); mp 195-198 °C
(lit. 204 °C);9 UV, IR, H NMR, EIMS, consistent with litera-
1
ture values;9,11 13C NMR data, see Table 2.
Scop olet in a n d 3-ep i-P om olic Acid . Scopoletin was
1
identical to an authentic sample. IR, H NMR, and EIMS of
3-epi-pomolic acid were consistent with literature values;13 13
C
NMR (CDCl3) δ 14.9 (q, C-25), 16.1 (q, C-30), 16.8 (q, C-26),
18.2 (t, C-6), 22.1 (q, C-24),a 23.4 (t, C-11), 24.6 (q, C-29),b 25.0
(t, C-16),c 25.2 (t, C-21),c 25.8 (t, C-2),c 27.3 (q, C-27),b 28.0 (t,
C-15), 28.1 (q, C-23),a 32.4 (t, C-7),d 32.7 (t, C-1),d 36.9 (s, C-10),

New Anthracene Derivatives from Coussarea
J ournal of Natural Products, 2003, Vol. 66, No. 7 909
Refer en ces a n d Notes
with 1:1 hexane-EtOAc: IR (film) νmax 3084, 2938, 2838, 1584,
1469, 1409, 1383, 1279, 1230, 1189, 1106, 1017, 990, 951, 902,
(1) Index Kewensis 2.0; Oxford University Press: Oxford, UK, 1997.
(2) Prakash Chaturvedula, V. S.; Schilling, J . K.; J ohnson, R. K.;
Kingston, D. G. I. J . Nat. Prod. 2003, 66, 419-422.
(3) J ackman, L. M.; Sternell, S. Application of Nuclear Magnetic Reso-
nance Spectroscopy in Organic Chemistry, 2nd ed.; Pergamon Press:
Elmsford, NY, 1969; p 81.
(4) J oshi, B. S.; Parkash, N.; Venkataraman, K. J . Sci. Ind. Res. 1955,
14B, 87-92.
(5) Hirose, Y.; Ueno, H.; Iwashita, M.; Kawagishi, E. Chem. Pharm. Bull.
1963, 11, 531-532
(6) Hirose, Y. Chem. Pharm. Bull. 1960, 8, 417-426.
(7) Sammes, P. G.; Dodsworth, D. J . J . Chem. Soc., Chem. Commun.
1979, 33-34.
(8) Zhao, E.; Biehl, E. J . Nat. Prod. 1995, 58, 1970-1974.
(9) Demagos, G. P.; Baltus, W.; Hoefle, G. Z. Naturforsch. 1981, 36B,
1180-1184.
(10) Ferrari, F.; Delle Monache, G.; Alves De Lima, R. Phytochemistry
1985, 24, 2753-2755.
(11) Vidal-Tessier, A. M.; Delaveau, P.; Champion, B. Ann. Pharm. Fr.
1987, 45, 261-267.
(12) Fujioka, T.; Furumi, K.; Fujii, H.; Okabe, H.; Mihashi, K.; Nakano,
Y.; Matsunaga, H.; Katano, M.; Mori, M. Chem. Pharm. Bull. 1999,
47, 96-100.
(13) Pereda-Miranda, R.; Gascon-Figueroa, M. J . Nat. Prod. 1988, 51,
996-998.
(14) Adesogan, E. K. Tetrahedron 1973, 29, 4099-4102.
(15) (a) Thomson, R. H. Naturally Occurring Quinones, 2nd ed.; Academic
Press: New York, 1971. (b) Dewick, P. M. Medicinal Natural
Products. A Biosynthetic Approach, 2nd ed.; J ohn Wiley & Sons: New
York, 2002.
(16) Vanden Berghe, D. A.; Vlietinck, A. J . In Methods in Plant Biochem-
istry; Dey, P. M., Harborne, J . B., Eds.; Academic Press: London,
1991; Vol. 6, pp 47-69.
(17) Meyer, B. N.; Ferrigni, N. R.; Putnam, J . E.; J acobsen, L. B.; Nichols,
D. E.; McLaughlin, J . L. Planta Med. 1982, 45, 31-34.
(18) Xu, H. X.; Zeng, F. Q.; Wan, M.; Sim, K. Y. J . Nat. Prod. 1996, 59,
643-645.
1
800 cm-1; H NMR (CDCl3) δ 3,43 (3H, s, OMe), 3.85 (3H, s,
OMe), 3.90 (3H, s, OMe), 4.54 (2H, s, CH2O), 6.61 (1H, d, J )
9.1 Hz, H-5), 7.47 (1H, d, J ) 9.1 Hz, H-4); EIMS m/z 262
(81Br M+, 49), 260 (79Br M+, 50), 245 (65), 229 (85), 215 (20),
201 (5), 101 (35), 171 (25), 159 (5), 150 (45), 149 (20), 134 (45),
120 (35), 105 (25), 91 (45), 77 (50), 63 (45), 51 (30), 45 (100);
HREIMS [M]+ m/z 262.0031 (calcd for C10H1381BrO3, 262.0028).
BuLi (2.5 M in hexane, 1.25 mL, 3.12 mmol) was added
dropwise by syringe to a solution of dry 2,2,6,6-tetramethylpi-
peridine (0.42 g, 2.97 mmol) in dry THF (3 mL) at -60 °C (CH2-
Cl2-dry ice bath) under an argon atmosphere. The resulting
yellow solution was stirred at -60 °C for 10 min, then a
solution of 1(3H)-isobenzofuranone (0.12 g, 0.89 mmol) in dry
THF (15 mL) was added. The mixture was stirred at -60 °C
for an additional 20 min, during which time it turned yellow-
orange, then warmed to -40 °C. Compound 10 (0.23 g, 0.88
mmol) in dry THF (10 mL) was added by syringe, and the
resulting red solution was stirred at -40 °C for 15 min, then
warmed to room temperature, where stirring was continued
for an additional 1 h. Saturated aqueous NH4Cl was added to
neutrality, and the resulting mixture was stirred for 15 h
under air. THF was evaporated in vacuo, and the remaining
aqueous phase was extracted exhaustively with CH2Cl2. The
organic layer was dried (anhydrous Na2SO4) and evaporated
in vacuo to yield an oily residue. Chromatography on a silica
gel column (20 g; eluent hexane-EtOAc, 3:1) yielded an-
thraquinone 5 (27.5 mg, yield ) 10%), identical (mp, IR, 1H
NMR, 13C NMR) to the natural sample. anal. C 69.30%, H
5.22%, calcd for C18H16O5, C 69.22%, H 5.16%.
(19) Wang, X.; de Silva, S. O.; Reed, J . N.; Billadeau, R.; Griffen, E. J .;
Chan, A.; Snieckus, V. Org. Synth. 1993, 72, 163-172.
(20) Doyle, F. P.; Nayler, H. C.; Waddington, H. R. J .; Hanson, J . C.;
Thomas, G. R. J . Chem. Soc. 1963, 497-506.
Ack n ow led gm en t. The authors thank the Italian MIUR
(Grant COFIN) and the University of Pavia (Grant FAR) for
financial support. We are indebted to Prof. Mariella Mella and
Prof. Giorgio Mellerio, University of Pavia, for recording the
NMR and mass spectra, respectively.
(21) No¨th, H.; Thomas, S. Eur. J . Inorg. Chem. 1999, 1373-1379.
NP030066I