Anthraquinone derivatives from Heterophyllaea pustulata

Article abstract of DOI:10.1021/np050181o

From the leaves of Heterophyllaea pustulata two new monomeric anthraquinones, heterophylline (1,6-dihydroxy-7-methoxy-2-methylanthraquinone, 1) and pustuline (2-hydroxy-3-methoxy-7-methylanthraquinone, 2), and one new bianthraquinone, (S)-5,5′-bisoranjidiol [(S)-5,5′-bis(1,6-dihydroxy- 2-methylanthraquinone), 3], were isolated. Furthermore, the iridoid glycoside asperuloside and three known flavonoids, quercetin, isoquercitrin, and quercetin-3-O-β-D-glucosyl-6″-acetate, were obtained. The structures were determined by analysis of their spectroscopic data and chemical evidence.

Full text of DOI:10.1021/np050181o

J. Nat. Prod. 2006, 69, 801-803
801
Notes
Anthraquinone Derivatives from Heterophyllaea pustulata
Susana C. Nu´n˜ez Montoya, Alicia M. Agnese, and Jose´ L. Cabrera*
Farmacognosia, Departamento de Farmacia, Facultad de Ciencias Qu´ımicas, UniVersidad Nacional de Co´rdoba, IMBIV-CONICET
(Instituto Multidisciplinario de Biolog´ıa Vegetal-Consejo Nacional de InVestigaciones Cient´ıficas y Te´cnicas), Ciudad UniVersitaria,
5000 Co´rdoba, Argentina
ReceiVed May 26, 2005
From the leaves of Heterophyllaea pustulata two new monomeric anthraquinones, heterophylline (1,6-dihydroxy-7-
methoxy-2-methylanthraquinone, 1) and pustuline (2-hydroxy-3-methoxy-7-methylanthraquinone, 2), and one new
bianthraquinone, (S)-5,5′-bisoranjidiol [(S)-5,5′-bis(1,6-dihydroxy-2-methylanthraquinone), 3], were isolated. Furthermore,
the iridoid glycoside asperuloside and three known flavonoids, quercetin, isoquercitrin, and quercetin-3-O-â-D-glucosyl-
6′′-acetate, were obtained. The structures were determined by analysis of their spectroscopic data and chemical evidence.
Heterophyllaea pustulata Hook. f. (Rubiaceae) is a shrub of 2
to 3 m high, popularly known as “cegadera”. It grows in the Andean
mountain range of the Northwest of Argentina and Bolivia between
2500 and 3000 m of altitude, where it is well known for its toxicity.1
The animals that ingest this plant suffer from dermatitis and
blindness (kerato-conjunctivitis), which are due to a typical
photosensitization reaction, clinically presented without jaundice.2
We have previously demonstrated the antibacterial and antifungal
activity in vitro of different extracts of H. pustulata as well as their
low acute toxicity in vivo.3 The first chemical investigation of these
bioactive extracts showed that the majority of the metabolites were
9,10-anthraquinone aglycones (AQs), among which soranjidiol,
soranjidiol 1-methyl ether, rubiadin, rubiadin 1-methyl ether,
2-hydroxy-3-methylanthraquinone, damnacanthal, and damnacan-
thol were isolated and identified.3 Herein, we report the isolation
and identification of three new anthraquinone derivatives, 1,6-
dihydroxy-7-methoxy-2-methylanthraquinone (heterophylline, 1),
2-hydroxy-3-methoxy-7-methylanthraquinone (pustuline, 2), and
5,5′-bis(1,6-dihydroxy-2-methylanthraquinone) (5,5′-bisoranjidiol,
3), from the benzene leaves extract. In addition, the EtOAc extract
afforded three known flavonoids and an iridoid glycoside. They
were identified by comparison with literature data as quercetin,4-6
isoquercitrin,7,8 quercetin-3-O-â-D-glucosyl-6′′-acetate,5 and asperu-
loside.9-11 The latter compound was previously reported from other
genera of Rubiaceae.12 The structures of the new AQ derivatives,
related to the known soranjidiol, were elucidated on the basis of
analysis of their spectroscopic/spectrometric properties.
and H-8). This spectrum also showed signals for three substituents,
which were assignable to a methyl, an O-methyl group, and a
phenolic hydroxyl peri to the carbonyl group.13 The presence of
this OH in the 1-position was confirmed by an intense IR absorption
band at 1632 cm-1 together with a 13C NMR signal at δ 188.1,
which indicated the presence of a hydrogen-bonded carbonyl group
(C-9).13,14 Regarding the biosynthetic pathway leading to the
anthraquinones in the Rubiaceae,13 it was expected that the methyl
group should be in the 2-position. NOE interactions between the
methyl protons (δ 2.30) and OH-1/H-3 together with COLOC
correlations of the methyl signal at δ 15.7 with H-3/H-4 confirmed
the methyl group at C-2. The placement of the OCH3 at C-7 was
assigned by COLOC correlation of the OCH3 to C-7, which showed
a two-bond correlation with H-8, and this proton was also correlated
with the hydrogen-bonded carbonyl group (C-9 at δ 188.1). In
addition, the OCH3 shows NOE correlation with H-8 (δ 7.56).
Bearing in mind the molecular weight of this compound together
with the fact that hydroxyl groups in 2-, 3-, 6-, or 7-positions (free
Isolation and purification of the compounds from the leaves of
H. pustulata were done by repeated combination of several
chromatographic techniques (Sephadex column, preparative PC, and
preparative TLC). Compounds 1-3, which gave a positive Bor-
trae¨ger test for anthraquinones, were obtained from the benzene
extract. By contrast, the known flavonoids and the iridoid were
isolated from the EtOAc extract.
The HREI mass spectrum of 1 gave a molecular ion at m/z
284.0675 (100%) that suggested the molecular formula C16H12O5
(calcd 284.0685). The 1H NMR spectrum contained signals at-
tributable to four aromatic protons, a pair of doublets (J ) 7.7 Hz)
due to two ortho-positioned aromatic protons (H-3 and H-4), and
a pair of singlets due to two para-positioned aromatic protons (H-5
* To whom correspondence should be addressed. Tel: +54-351-4334163.
Fax: +54-351-4334127. E-mail: jcabrera@dqo.fcq.unc.edu.ar.
10.1021/np050181o CCC: $33.50
© 2006 American Chemical Society and American Society of Pharmacognosy
Published on Web 04/04/2006

802 Journal of Natural Products, 2006, Vol. 69, No. 5
Notes
Table 1. NMR Data (δ in ppm) for 5,5′-Bisoranjidiol (3) and Soranjidiol (4) in DMSO-d6
3
4
position
13Ca
1Hb
position
13Ca
1Hb
NOESYc
COLOC (C)d
1, 1′
2, 2′
3, 3′
4, 4′
4a, 4a′
5, 5′
6, 6′
7, 7′
8, 8′
159.6
133.4
136.9
118.4
131.6
127.1
161.5
125.2
128.6
120.1
187.8
114.4
182.3
132.5
1
2
3
4
4a
5
6
7
8
159.9
134.2
136.8
118.6
131.1
112.5
163.8
124.5
129.8
121.4
187.6
114.7
181.8
135.6
7.34 (d, 7.6)
7.57 (d, 7.6)
7.62 (d, 7.7)
7.68 (d, 7.7)
4
3
1, 2, 4, 4a, 10, 9a, 2-Me
1, 2, 4a, 10
7.49 (d, 2.6)
7
5, 7, 8a, 10
7.36 (d, 8.5)
8.27 (d, 8.5)
7.27 (dd, 2.6, 8.5)
8.14 (d, 8.5)
5, 8
7
7
6, 8a
8a, 8a′
9, 9′
8a
9
9a, 9a′
10, 10′
10a, 10a′
1, 1′-OH
2, 2′-Me
9a
10
10a
1-OH
2-Me
13.18 (s)
2.29 (s)
13.13 (s)
2.32 (s)
15.5
15.6
3
1, 2, 3, 2-Me
a At 50 MHz, referenced to DMSO-d6 at 39.5. b At 200.13 MHz, referenced to DMSO-d6 at 2.54. c NOESY correlations from H to H. d COLOC
correlations from H to C.
OH) are not readily observable in 1H NMR spectra,13 it was possible
to infer that the fourth substituent might be an aromatic hydroxyl.
This was verified by the IR (3344 cm-1, free OH) and EIMS ([M
- OH]+) spectra.14,15 From the above data, compound 1 was
identified as 1,6-dihydroxy-7-methoxy-2-methylanthraquinone (het-
erophylline).
Compound 2 showed a molecular ion [M]+ at m/z 268.0734
(100%) in the HREIMS, consistent with the molecular formula
C16H12O4 (calcd 268.0736). Its 1H NMR spectrum exhibited signals
due to five aromatic protons, two one-proton singlets (H-1 and H-4),
and an ABX pattern for three aromatic protons. This suggested that
the C-ring was substituted in the 2- and 3-positions, whereas the
A-ring had only one substituent, where either the 6- or 7-position
is possible. In addition, signals for three substituents were observed,
a methyl group, an O-methyl group, and a hydroxyl group.13 Only
Figure 1. Molecular drawing of 3.
one medium IR absorption band at 1670 cm-1 indicated that both
carbonyl groups were non-hydrogen-bonded and together with the
band at 3323 cm-1 corroborated a free hydroxyl group.14 The
location of this OH at C-2, adjacent to the O-methyl at C-3, was
established by NOE correlations between OH-2 and H-1/OCH3-3
and between OCH3-3 and H-4/OH-2. The proximity of CH3-7 to
OH-2 was established by the following COLOC interactions:
methyl protons (δ 2.50) with C-7 (δ 144.6), C-7 with H-8 (δ 7.94,
d, J ) 1.4), H-8 with C-9 (δ 181.9), and C-9 with H-1 (δ 7.53, s),
together with a NOE correlation between H-1 and OH-2. On the
other hand, C-10 correlated with H-6 (δ 7.69, dd, J ) 1.4 and 7.9)
and H-4 (δ 7.61, s). Thus, CH3 was unequivocally located at C-7
from 2D NMR experiments. Combinations of these data defined
compound 2 as 2-hydroxy-3-methoxy-7-methylanthraquinone (pus-
tuline).
first time (Table 1). Comparison of the NMR data of 3 and 4 proves
that 3 is a symmetrical dehydro dimer of 4. In the 1H NMR
spectrum of 3, a meta-coupled doublet at δ 7.49 (assigned to H-5
in 4) is absent, showing a C-5, C-5′ anthraquinone linkage. From
the data obtained, it was concluded that compound 3 is 5,5′-bis-
(1,6-dihydroxy-2-methylanthraquinone) (5,5′-bisoranjidiol). Com-
pound 3 possesses axial chirality due to the C5-C5′ biphenyl bond.
The CD spectrum revealed a positive Cotton effect centered at 243
nm, which correlated with an intense π-π* UV absorption. This
indicates (P)-axial chirality, and hence an S-configuration of the
biphenyl bond in 3.18 Figure 1 shows the 3D structure of 3 with
minimized conformational energy, which was generated by AM1
calculation using MOPAC.
Experimental Section
General Experimental Procedures. Melting points were determined
on an Electrothermal 9100 melting point apparatus. The CD spectrum
was recorded on a JASCO Model J-810 spectropolarimeter, which was
calibrated with 10-camphorsulfonic acid. UV spectra were recorded
on a Spectronic Genesis 5 UV-vis spectrophotometer. IR spectra were
obtained with a Nicolet 5-sxc-FTIR infrared spectrophotometer. NMR
spectra were measured on a Bruker AC 200 spectrometer. Chemical
shifts (δ) are reported in ppm relative to TMS as internal standard and
coupling constants (J values) in Hz. EIMS were obtained on a Variant
Mat CH-7A at 70 eV. HRMS were recorded on a VG ZAB2SE (1996)
spectrometer. FABMS were performed on a JEOL JMS-SX/SX102
spectrometer at 6 keV. Column chromatography (CC) was performed
on Sephadex LH-20 (Pharmacia). TLC was performed on precoated
silica gel 60 plates (Merck), and anthraquinones were revealed under
UV light with NH4OH vapors and by spraying the plates with a 10%
KOH solution in EtOH. Paper chromatography (PC) was used to
separate iridoids and flavonoids. These were visualized by using UV
light and NH4OH fumes.
The positive-ion FAB-mass spectrum of 3 showed a pseudo-
molecular ion [M + H]+ peak at m/z 507, which suggested a
bianthraquinone derivative coincident with the molecular formula
C30H18O8 (calcd 506). The number of signals present in the 13C
NMR spectrum of 3 accounted for only half (15 peaks) of the carbon
atoms of the molecule (Table 1). The 1H NMR spectrum suggested
a tetrasubstituted anthraquinone (Table 1) with the presence of an
OH group in the peri position and a methyl group in the 2-position.13
The principal peaks in the IR spectrum indicated a free OH group
as the third substituent and confirmed the existence of a peri-
positioned OH group by the carbonyl group absorptions.14 On the
basis of these data and the high molecular weight, it was suspected
that 3 must be a symmetrical bianthraquinone.16 Reductive cleavage
of 3 with alkaline sodium dithionite17 gave only one product, which
1
was identified as soranjidiol (4) by UV-vis, IR, H NMR, MS,13
and co-chromatography with an authentic sample. The 2D NMR
experiments (NOESY and COLOC) of 4 are recorded here for the

Notes
Plant Material. Leaves of H. pustulata were collected in “La
Almona”, Jujuy Province, Argentina, in April 1996. Plant material was
identified by Prof. Dr. Gloria Barboza (Instituto Multidisciplinario de
Biolog´ıa Vegetal, CONICET-Universidad Nacional de Co´rdoba). A
voucher specimen has been deposited at Museo Bota´nico de Co´rdoba
(U.N.C.) as M.E. La´zzaro s/n, CORD 305.
Extraction and Isolation. Dried and fragmented leaves (387.0 g)
were extracted in a Soxhlet apparatus using solvents of different
polarities in the following order: petrol, benzene, and EtOAc. The
benzene extract (5.04 g) was dissolved in 10% aqueous NaHCO3 and
extracted with CHCl3. The organic extract obtained was evaporated to
dryness, and the residue was dissolved in 1 M NaOH and extracted
with Et2O. The aqueous alkaline extract was acidified with HCl and
extracted with Et2O. Thus, a final ether extract (I) rich in anthraquinones
and without chlorophylls was obtained.19 This extract (I) was submitted
to CC eluted with CHCl3, followed by a gradient of CHCl3-EtOAc
(3:7-7:3) and finally an acetone-EtOAc (3:7-7:3) gradient. The
eluents were monitored by TLC with benzene-EtOAc (8:2) as mobile
phase. Five major fractions were obtained (A-E). From fraction A,
compounds 1 (20.1 mg) and 2 (6.4 mg) were separated by preparative
TLC, developed first with CHCl3 and then with benzene-EtOAc (1:
1). Compound 3 (10.9 mg) was purified from fraction D by preparative
TLC with benzene-EtOAc (1:1) as mobile phase.
Journal of Natural Products, 2006, Vol. 69, No. 5 803
(C-10a), 127.9 (C-4a), 126.6 (C-5), 126.6 (C-9a), 126.4 (C-8), 112.3
(C-1), 108.7 (C-4), 55.9 (OMe-3), 21.2 (Me-7); NOE correlations (H/
H) OH-2/H-1, OMe-3, H-4; H-5/H-6, H-7, Me-7; H-8/H-5, H-6, Me-
7; H-6/H-5, H-8, Me-7; H-4/OMe-3; H-1/OH-2; OMe-3/OH-2, H-4;
Me-7/H-5, H-6, H-8; COLOC correlations (H/C) OH-2/C-1, C-3; H-5/
C-6; H-8/C-6, C-7, C-9, C-10a; H-6/C-5, C-10, C-10a; H-4/C-1, C-3,
C-4a, C-5a, C-9a, C-10; H-1/C-1, C-2, C-3, C-4a, C-9, C-9a; OMe-3/
C-2, OMe-3; Me-7/C-6, C-7, Me-7; EIMS m/z 268 [M]+ (100), 253
[M - CH3]+ (8), 239 [M - COH]+ (20), 225 [M - COCH3]+ (29),
211 [M - COH - CO]+ (5), 197 [M - COCH3 - CO]+ (17), 169 [M
- COCH3 - 2CO]+ (9), 152 [M - COCH3 - 2CO - OH]+ (5), 139
(12), 115 (17); HREIMS m/z 268.0734 (calcd for C16H12O4, 268.0736).
(S)-5,5′-Bisoranjidiol (3): orange amorphous powder (acetone); CD
(c 0.15 mM, MeOH) [θ]243 + 2558; UV (EtOH) λmax (log ꢀ) 251 (sh)
(0.08), 275 (0.07), 287 (sh) (0.07), 416 (sh) (0.04) nm; (EtOH/MeONa)
λmax (log ꢀ) 239 (sh) (0.11), 317 (0.06), 431 (sh) (0.02), 521 (0.04)
nm; (CHCl3) λmax (log ꢀ) 236 (1.36), 272 (1.21), 287 (sh) (0.86), 409
(sh) (0.29), 419 (0.34), 437 (0.32) nm; IR (KBr) νmax 3511 (OH free),
2921, 2847, 1672 (CdO free), 1623 (CdO hydrogen-bonded), 1572,
1
1455, 1430, 1363 cm-1; H NMR and 13C NMR data, see Table 1;
NOE correlations (H/H) Me-2/H-4; H-3/OH-1, H-4; H-7/H-8; positive
FABMS m/z 507 [M + H]+ (calcd for C30H18O8, 506.1).
Acknowledgment. The authors are thankful to S. Gohil (Chemistry
Institute, Uppsala Faculty, Sweden) for measurements of FAB mass
spectra, and to Prof. Dr. G. Barboza (Museo Bota´nico de Co´rdoba,
Fac. Cs. Exactas y Naturales, Universidad Nacional de Co´rdoba,
Argentina) for the identification of the species. This study was supported
by Agencia Co´rdoba Ciencia, SeCyT (UNC), and FONCYT.
The EtOAc extract (15.18 g) was dissolved in H2O and partitioned
with benzene, Et2O (II), and EtOAc (III). The two last extracts (II and
III) were separately subjected to CC eluted with benzene-EtOH (7:3)
and increasing proportions of EtOH up to a 3:7 ratio. From II quercetin
(13.0 mg) was obtained, which was purified by preparative PC using
40% HOAc as mobile phase. III provided isoquercitrin (16.1 mg) and
quercetin-3-O-â-D-glucosyl-6′′-acetate (28.7 mg); the former was
purified by preparative PC with 15% HOAc and the latter by CC using
the identical mobile phase. From the remaining aqueous extract,
asperuloside (6.2 mg) was isolated by CC with EtOH as mobile phase.
It was purified by preparative PC by using 15% HOAc as mobile phase.
Heterophylline (1): yellow crystals (acetone); mp 268-271 °C; UV
(EtOH) λmax (log ꢀ) 287 (1.08), 398 (sh) (0.19), 410 (0.20), 431 (sh)
(0.16) nm; (EtOH/MeONa) λmax (log ꢀ) 302 (0.97), 473 (0.39) nm;
(CHCl3) λmax (log ꢀ) 239 (0.34), 281 (1.17), 302 (sh) (0.35), 348 (sh)
(0.06), 398 (sh) (0.16), 413 (0.17), 431 (sh) (0.13) nm; IR (KBr) νmax
3344 (OH free), 2920, 2849, 1698 (CdO free), 1632 (CdO hydrogen-
References and Notes
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1
bonded), 1562, 1438, 1372 cm-1; H NMR (DMSO-d6, 200 MHz) δ
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12.92 (1H, s, OH-1), 7.65 (1H, d, J ) 7.7, H-4), 7.59 (1H, s, H-5),
7.59 (1H, d, J ) 7.7, H-3), 7.56 (1H, s, H-8), 3.99 (3H, s, OMe-7),
2.30 (3H, s, Me-2); 13C NMR (DMSO-d6, 50 MHz) δ 188.1 (C-9),
180.8 (C-10), 159.8 (C-1), 153.4 (C-7), 152.6 (C-6), 137.0 (C-3), 133.6
(C-2), 131.3 (C-4a), 126.8 (C-8a), 127.5 (C-10a), 118.5 (C-5), 114.9
(C-4), 112.2 (C-9a), 109.0 (C-8), 56.1 (OMe-7), 15.7 (Me-2); NOE
correlations (H/H) OH-1/Me-2, H-3; H-3/OH-1, Me-2; OMe-7/H-8; Me-
2/OH-1, H-3; COLOC correlations (H/C) H-3/C-1, C-2, C-4, C-4a, Me-
2; H-4/C-2, C-4, C-4a; H-5/C-5, C-10; H-8/C-5a, C-6, C-7, C-8, C-8a,
C-9, C-10a; Me-2/Me-2; OMe-7/C-7, OMe-7; EIMS m/z 284 [M]+
(100), 269 [M - CH3]+ (12), 267 [M - OH]+ (5), 255 [M - COH]+
(11), 241 [M - COCH3]+ (19), 213 [M - COCH3 - CO]+ (11), 185
[M - COCH3 - 2CO]+ (6), 157 [M - COCH3 - 3CO]+ (2), 128 [M
- COCH3 - 3CO - COH]+ (9), 115 (4); HREIMS m/z 284.0675 [M]+
(calcd for C16H12O5, 284.0685).
Pustuline (2): yellow-orange needles (acetone); mp 263-266 °C;
UV (EtOH) λmax (log ꢀ) 248 (0.32), 287 (1.02), 338 (sh) (0.09), 386
(sh) (0.04) nm; (EtOH/MeONa) λmax (log ꢀ) 215 (0.47), 251 (0.54),
314 (0.76), 509 (0.08) nm; (CHCl3) λmax (log ꢀ) 245 (sh) (0.29), 281
(1.28), 338 (0.11), 371 (sh) (0.06) nm; IR (KBr) νmax. 3323 (OH free),
2922, 2851, 1670 (CdO free), 1592, 1517, 1462, 1381 cm-1; 1H NMR
(DMSO-d6, 200 MHz) δ 10.71 (1H, s, OH-2), 8.06 (1H, d, J ) 7.9,
H-5), 7.94 (1H, d, J ) 1.4, H-8), 7.69 (1H, dd, J ) 1.4 and 7.9, H-6),
7.61 (1H, s, H-4), 7.53 (1H, s, H-1), 3.99 (3H, s, OMe-3), 2.50 (3H, s,
Me-7); 13C NMR (DMSO-d6, 50 MHz) δ 181.9 (C-9), 181.2 (C-10),
152.8 (C-2), 152.5 (C-3), 144.6 (C-7), 134.6 (C-6), 132.9 (C-8a), 130.9
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NP050181O