Biomimetic transformation and biological activities of globiferin, a terpenoid benzoquinone from Cordia globifera

Article abstract of DOI:10.1021/np9000703

A new 10-membered ring meroterpene (1), named globiferin, was isolated from root extracts of Cordia globifera. Biomimetic transformations of 1 and its derivatives, either by acid cyclization or by Cope rearrangement, provided information relating to the b

Full text of DOI:10.1021/np9000703

J. Nat. Prod. 2009, 72, 861–865
861
Biomimetic Transformation and Biological Activities of Globiferin, a Terpenoid Benzoquinone
from Cordia globifera
†
‡
†
,‡,§
Suppamit Dettrakul, Sanya Surerum, Shuleewan Rajviroongit, and Prasat Kittakoop*
Department of Chemistry, Faculty of Science, Mahidol UniVersity, Bangkok 10400, Thailand, Chulabhorn Research Institute, VibhaVadi-Rangsit
Highway, Laksi, Bangkok 10210, Thailand, and Chemical Biology Program, Chulabhorn Graduate Institute, and the Center for EnVironmental
Health, Toxicology and Management of Chemicals (ETM), VibhaVadi-Rangsit Highway, Laksi, Bangkok 10210, Thailand
ReceiVed February 6, 2009
A new 10-membered ring meroterpene (1), named globiferin, was isolated from root extracts of Cordia globifera.
Biomimetic transformations of 1 and its derivatives, either by acid cyclization or by Cope rearrangement, provided
information relating to the biogenesis of cordiachromes A-C. Globiferin (1) underwent Cope rearrangement upon refluxing
6 6
in xylene and DMSO-d to yield cordiachrome C (3) and cordiaquinol C (4), respectively. Heating in DMSO-d resulted
in an unexpected reduction of a quinone moiety. Globiferin diacetate (1b) cyclized under acidic conditions to give
compounds 10 and 11, respective derivatives of natural cordiachromes B (2) and A (12). The present study indicates
that globiferin (1) is a genuine intermediate for the biosynthesis of cordiachromes in Cordia species. Compounds 1 and
3
exhibited significant antimycobacterial activity, with MIC values of 6.2 and 1.5 µg/mL, respectively. Antimalarial,
antifungal, and cytotoxic activities of 1 and its derivatives were also evaluated.
Plants of the genus Cordia, family Boraginaceae, are native to
tropical America, Africa, and Asia, and they are recognized for
their durability in marine use and general construction, as well as
1
in traditional folk medicine. Compounds isolated from the genus
Cordia have displayed a broad range of biological activities,
2
3
4,5
including antiandrogenic, anti-inflamatory, antifungal,
and
5
larvacidal properties. A number of plants of the genus Cordia,
including C. alba, C. alliodora, C. globosa, C. millenii, and
C. trichotoma, have been chemically examined and yielded
4
,6
7
1
8
8
2,9,10
11
sesquiterpenes, triterpenes,
flavanoids, chromens, quinones,
C. globifera W. W. Smith (Boragi-
5
,12-14
and hydroquinones.
naceae), known in Thai as “Sak Hin”, is found in many parts of
Thailand. Our preliminary study showed that the root extract of C.
globifera possessed antimalarial activity. Chemical exploration of
root extracts of C. globifera led to the identification of several
bioactive compounds, including a new 10-membered terpenoid
benzoquinone, named globiferin (1), and six known compounds,
1
,6
1,8
6
cordiachrome B (2), cordiachrome C (3), cordiaquinol C (4),
alliodorin (5),
6,15
12
3
elaeagin (6), and cordiachromene (7). We found
that globiferin (1) and its derivatives could be biomimetically
transformed to other related natural products, thus providing
information relating to the possible biogenesis of cordiachromes.
Antimalarial, antimycobacterial, antifungal, and cytotoxic activities
of the isolated substances are also reported.
Results and Discussion
Chromatography of a hexane-soluble extract of C. globifera roots
1
,6
on silica gel yielded 1, cordiachrome B (2), and cordiachrome
1
,8
C (3). The MeOH-soluble extract was separated by column
chromatography (on Sephadex LH-20 and silica gel) and semi-
preparative HPLC (reversed-phase C18 column) to afford cor-
6
6,15
12
diaquinol C (4), alliodorin (5),
elaeagin (6), and cordiach-
3
romene (7). The known compounds were identified by analysis
of NMR data and by comparison of spectroscopic data with those
in the literature.
Globiferin (1) possessed a molecular formula of C16
revealed by the ESITOF MS spectrum, showing the accurate mass
18 2
H O , as
+
-1
at m/z 265.1203 [M + Na] . The IR absorption band at 1650 cm
1
3
and the C NMR resonances at δ
C
188.2 and 187.9 indicated the
*
To whom correspondence should be addressed. Tel: +66-86-9755777.
13
presence of a 1,4-benzoquinone unit in 1. Analysis of C and DEPT
NMR data of 1 revealed the presence of two methyl, four methylene,
four methine, and six nonprotonated carbons. The 1H NMR
spectrum of 1 demonstrated resonances of benzoquinone protons,
Fax: +662-5740622, ext. 1513. E-mail: prasatkittakoop@yahoo.com.
†
Department of Chemistry, Mahidol University.
Chulabhorn Research Institute.
Chulabhorn Graduate Institute.
‡
§
1
0.1021/np9000703 CCC: $40.75  2009 American Chemical Society and American Society of Pharmacognosy
Published on Web 04/15/2009

8
62 Journal of Natural Products, 2009, Vol. 72, No. 5
Dettrakul et al.
Scheme 1. Transformations of Globiferin (1) and Its Derivatives
H-2 (δ
.13) and H-11 methines (δ
groups (δ
H
6.80) and H-3 (δ
H
6.76); two olefinic protons of H-7 (δ
5.09); four nonequivalent methylene
1.49 and 1.74).
H
after refluxing 1b in xylene (Scheme 1). NMR data of derivative
4a obtained from Cope rearrangement of 1b were identical to those
from an acetylation of cordiaquinol C (4) (Scheme 1). Previous
studies had demonstrated that trans,trans-cyclodeca-1,5-dienes
underwent Cope rearrangement to give trans-1,2-divinylcyclohexane
derivatives, while cis,trans-cyclodeca-1,5-dienes provided cis-1,2-
5
H
H
1.56-3.65); and two methyl groups (δ
H
It should be noted that broad signals of methylene protons were
1
observed on the H NMR spectrum of 1 (see Supporting Informa-
tion). The 1H- H COSY spectrum of 1 established a partial
structure from H-7 to H-9 and from H-11 to H-12 and also showed
allylic couplings between H-7 and H-15 as well as between H-11
and H-16. The HMBC spectrum of 1 displayed correlations from
H-2 to C-4 and C-13; H-3 to C-1 and C-14; H-7 to C-5 and C-15;
H-11 to C-9, C-12, and C-16; H-15 to C-5, C-6, and C-7; and H-16
to C-9, C-10, and C-11. Unfortunately, no methylene protons
showed HMBC correlations to any carbon; therefore, available
NMR data could not conclusively establish the structure of 1,
particularly of the linkage between the 1,4-benzoquinone unit and
1
19-21
divinylcyclohexane derivatives.
In the present work, globiferin
(1) and its derivatives adopted cis,trans-cyclodeca-1,5-diene sys-
tems, and their Cope rearrangement yielded cis derivatives. Previ-
ously, wigandol acetate (1b) was found to undergo Cope rear-
1
6
rangement by pyrolysis to give compound 4a. It was interesting
to note that Cope rearrangement of 1 in DMSO-d gave cordiaquinol
6
C (4), which was a reduced form of cordiachrome C (3), and that
significant reduction (99%) of 3 to 4 was observed upon heating
in DMSO-d (in an NMR tube) (Scheme 1). Cordiaquinol C (4)
6
the aliphatic part. Compound 1 was reduced by Na
2
S
2
O
4
to its
obtained from chemical transformation was derivatized to 4b and
4c.
1
corresponding 1,4-quinol derivative (1a), whose H NMR spectrum
exhibited, unlike that of 1, sharp methylene signals. The IR
Interestingly, the diacetate 1b could be cyclized under acidic
conditions to give compounds 10 and 11. The mechanistic
transformation from 1b to compounds 10 and 11 possibly involved
protonation of a cis-double bond to provide a tertiary-carbocation,
cyclization of an E-double bond to a tertiary-carbocation while
generating a new tertiary-carbocation, and deprotonation of a
tertiary-carbocation giving rise to exo- and endo-products 10 and
11, respectively. Compounds 10 and 11 are respective derivatives
of cordiachromes B (2) and A (12), which were isolated from
absorption peak at 3318 cm- (OH) and the replacement of the
1
2
quinone carbonyls (δ
carbons (δ
C
188.2 and 187.9) with oxygenated sp
149.1 and 150.3) suggested that the 1,4-benzoquinone
C
unit in 1 was transformed to a 1,4-quinol moiety in 1a. Acetylation
of 1a gave O-diacetate 1b. Analysis of the HMBC spectrum allowed
construction of the gross structure of 1a. The linkage between a
1
,4-quinol unit and an aliphatic part was established by the
following key HMBC correlations: from H-5 to C-4, C-13, and
C-14; from H-12 to C-1, C-13, and C-14. Other important HMBC
correlations were observed from H-2 to C-13; H-3 to C-14; H-7 to
C-5 and C-15; H-9 to C-10 and C-11; H-11 to C-9, C-13, and C-16;
H-15 to C-6 and C-7; and H-16 to C-10 and C-11. On the basis of
these spectroscopic data, the structure of 1a was assigned as shown,
and therefore the structure of globiferin (1) was established
accordingly. The NOESY spectra of 1 and 1a showed the correlation
between H-7 and H-15, suggesting cis-geometry of the C-6/C-7
double bond, while the NOESY correlation between H-12 and H-16
implied trans-geometry of the C-9/C-10 double bond. Globiferin
1
Cordia millenii.
Transformations of globiferin (1) and its derivatives either by
acid cyclization or by Cope rearrangement provide substantial
information on the biogenesis of cordiachromes A-C. In 1973,
Moir and Thomson proposed a biosynthetic pathway to cordiach-
romes A-C via a trans,trans-cyclodecatriene intermediate (i.e.,
1
13), whose structure was coincidently similar to that of globiferin
(1), except for diene geometry. It should be noted that at that time
when Moir and Thomson proposed the biogenesis a natural product
with a cyclodecatriene ring system had not been isolated from
Cordia species. Moir and Thomson proposed that acid cyclization
of a trans,trans-cyclodecatriene intermediate led to the formation
of cordiachromes B (2) and A (12) with cis-stereochemistry, while
a “biogenetic Cope rearrangement” would produce the skeleton of
(
1) was a derivative of wigandol (8), a meroterpenoid previously
16
isolated from the plant Wigandia kunthii. Wigandol (8) was
1
6
previously proposed to possess trans,trans-geometry; however,
its ring system was revised to cis,trans-configuration by a single-
1
7
1
crystal X-ray analysis. It should be noted that flavidulols (i.e.,
cordiachrome C (3). In the past, it was mistakenly perceived that
9
), geranylphenols isolated from the mushroom Lactarius flaVidulus,
Cope rearrangement of a trans,trans-cyclodecatriene would lead
1
8
1,16
also had a structural feature similar to that of globiferin (1).
to the formation of a cis-ring junction,
isomer gave a cis-ring junction.
but in fact, a cis,trans-
Interestingly, the quinones
1
9-21
The chemistry of globiferin (1) and its derivatives provides
insight into the biosynthesis of cordiachromes A-C. Upon heating,
compounds 1 and 1b easily underwent Cope rearrangement.
Refluxing 1 in xylene provided cordiachrome C (3) in 85% yield,
whereas heating 1 in DMSO-d , in an NMR tube, gave cordiaquinol
6
C (4) in 91% yield (Scheme 1). Similar rearrangement was also
observed for O-diacetate 1b, and 4a was obtained in 96% yield
(e.g., cordiachromes A-C) isolated from the Cordia species were
1
,22
obtained as racemic mixtures,
and in the present study, cordi-
achrome B (2), cordiachrome C (3), and cordiaquinol C (4)
exhibited small values of specific rotation, suggesting that they were
likely to be racemates. Previous work suggested that the optically
inactive intermediate (e.g., compound 1) explained why these

Terpenoid Benzoquinone from Cordia globifera
Journal of Natural Products, 2009, Vol. 72, No. 5 863
Table 1. Antimycobacterial, Antimalarial, and Cytotoxic Activities of the Isolated Compounds and Derivatives
antimycobacterial
antimalarial
activity
antifungal
activity
a
b
c
activity
cytotoxic activity (IC50, µg/mL)
d
d
d
d
(
MIC, µg/mL)
(IC50, µg/mL)
(IC50, µg/mL)
Vero
>50
KB
BC-1
NCI-H187
1
2
3
4
4
4
4
5
6
7
6.2
12.5
1.5
25.0
25.0
200
>200
12.5
12.5
12.5
2.1 ( 0.5
1.5 ( 0.2
0.2 ( 0.1
0.3 ( 0.0
0.4 ( 0.1
>20
>20
>20
>20
0.5 ( 0.04
0.4 ( 0.09
0.2 ( 0.06
1.9 ( 0.1
5.1 ( 0.9
>20
7.7 ( 0.1
4.6 ( 0.2
>20
1.7 ( 0.6
1.4 ( 0.4
1.6 ( 0.7
7.3 ( 0.5
>50
6.0 ( 0.5
1.5 ( 0.1
6.9 ( 0.1
8.5 ( 0.6
>20
6.4 ( 0.8
1.8 ( 0.1
3.2 ( 0.2
9.2 ( 0.6
>20
a
b
c
>20
>20
>20
>20
>50
>20
>20
>20
3.1 ( 0.1
3.6 ( 0.1
>20
>20
14.1 ( 1.4
20.0 ( 0.7
>50
12.0 ( 0.2
>20
10.3 ( 0.2
>20
2.2 ( 0.8
6.1 ( 1.1
>20
>20
11.2 ( 0.8
>20
>20
a
b
Standard drugs were rifampicin, isoniazid, and kanamycin, exhibiting respective MIC values of 0.0047, 0.05, and 2.5 µg/mL. The IC50 value of the
reference drug, dihydroartemisinin, was 0.0012 µg/mL. Amphotericin B was the reference compound, exhibiting an IC50 value of 0.08 µg/mL. The
standard drug, ellipticine, exhibited IC50 values toward Vero, KB, BC-1, and NCI-H187 cell lines of 0.4, 0.2, 0.2, and 0.3 µg/mL, respectively.
c
d
1
,22
1,22
quinones were racemates.
Although previous reports,
as well
A voucher specimen (no. CRI 566) was deposited at the Laboratory of
Natural Products, Chulabhorn Research Institute.
Extraction and Isolation. The air-dried roots of C. globifera (2
as the present work, employed mild conditions for extraction and
isolation, racemic cordiachromes were obtained. Accordingly, we
propose that cordiachromes A-C in Cordia species might alter-
natively be formed via a nonenzymatic pathway as guided by the
biomimetic transformations proposed here. The present study
indicates that globiferin (1) is a genuine intermediate for the
biosynthesis of cordiachromes in Cordia species. It should be noted
that the content of globiferin (1) in C. globifera root is relatively
high (0.6 g/2 kg).
kg) were chopped, ground, and extracted with CH
at room temperature. The extract was evaporated to yield a brown,
sticky residue (450 g). The CH Cl extract was then partitioned between
2 2
Cl for three days
2
2
hexane and MeOH, yielding a hexane-soluble extract (150 g) and a
MeOH-soluble extract (250 g). A portion of the hexane-soluble extract
(
1.7 g) was first subjected to silica gel column chromatography eluted
with a gradient of EtOAc-hexane (2 to 10% EtOAc), providing 11
fractions, designated as CA-CL. Fraction CB was chromatographed
on a silica gel flash column, eluted with 2% EtOAc in hexane to afford
The compounds isolated from the root extract of C. globifera,
as well as derivatives, were evaluated for their antimycobacterial,
antimalarial, antifungal, and cytotoxic activities (Table 1). Com-
pounds 1 and 3 exhibited significant antimycobacterial activity, with
respective MIC values of 6.2 and 1.5 µg/mL, while other com-
pounds (2, 4, 4a, 5, 6, and 7) showed weak activity (Table 1).
Compounds 1-4, 4a, 5, and 6 exhibited antimalarial activity against
Plasmodium falciparum with IC50 values ranging from 0.2 to 3.6
µg/mL. Compounds 2, 3, and 7 displayed weak antifungal activity
against the fungus Candida albicans with IC50 ranges of 4.6-11.2
µg/mL. Compounds 2-4, 4a, and 5 showed cytotoxic activity
toward all cell lines tested, while 1 and 6 exhibited activity against
some cell lines. Derivatives 4b and 4c did not show any biological
activity in these tests. It is interesting to note that the products 3
and 4 obtained from Cope rearrangement exhibited better activities
than globiferin (1). While antimycobacterial activity of 3 was
slightly more potent than 1 (6.2 µg/mL for 1 and 1.5 µg/mL for 3),
antimalarial activity of 3 and 4 was significantly improved, 1 order
of magnitude more potent than 1 (Table 1). Compound 3 was active
against the fungus C. albicans (IC50 4.6 µg/mL), whereas 1 was
inactive. Both 3 and 4 were more cytotoxic than 1. Previously,
1
5 subfractions (CB
1
-CB15). Subfractions CB
1
5
-CB were combined
to afford globiferin (1; 614 mg). Fraction CD was subjected to a silica
gel column, eluted with a gradient system of EtOAc in hexane (2 to
20%), to give 1 (45 mg), cordiachrome B (2) (40 mg), and cordiachrome
C (3) (370 mg).
A portion of the MeOH-soluble extract (11.8 g) was separated on a
Sephadex LH-20 column eluted with MeOH to yield to 10 fractions,
designated as MA-MJ. Fraction MD was chromatographed on Sepha-
dex LH-20 (MeOH eluent) to obtain fractions MD
MD5 was fractionated by HPLC (reversed-phase C18 column,
MeCN-H O, 55:45), furnishing cordiachromene (7) (8.3 mg). Fraction
MD was separated on a silica gel column, eluted with 10% EtOAc in
CH Cl
1
-MD15. Fraction
2
8
2
2
, to yield 10 fractions (MD801-MD810). Fraction MD805 was
separated on a Sephadex LH-20 column (MeOH eluent) to afford
cordiaquinol C (4; 6.3 mg). Fraction MD12 was chromatographed on a
silica gel column, eluted with 10% EtOAc in CH
2
2
Cl , yielding alliodorin
(
5; 11.6 mg) and elaeagin (6; 15.3 mg).
Globiferin (1): yellow oil; UV (CHCl
3
) λmax (log ε) 252 (4.1) nm;
-1
1
IR (KBr) νmax 2930, 2858, 1650, 1287, 1444, 846, 755 cm ; H NMR
(
CDCl , 500 MHz) δ 6.80 (1H, d, J ) 9.9 Hz, H-2), 6.76 (1H, d, J )
3
9.9 Hz, H-3), 5.13 (1H, dd, J ) 8.3, 8.3 Hz, H-7), 5.09 (1H, dd, J )
7.3, 9.5 Hz, H-11), 3.64 (1H, br signal, H-12b), 3.32 (1H, br signal,
H-5b), 3.13 (1H, br signal, H-12a), 2.99 (1H, br signal, H-5a), 2.18
(1H, br signal, H-9b), 2.02, (2H, br signal, H-8), 1.74 (1H, br signal,
4,5
metabolites of Cordia species were reported to exhibit antifungal,
22
2
3
5
antiandrogenic, anti-inflamatory, larvacidal, and antileishmanial
activities.
1
3
3
H-9a), 1.74 (3H, s, H-16), 1.49 (3H, s, H-15); C NMR (CDCl , 125
MHz) δ 188.2 (C, C-1), 187.9 (C, C-4), 144.2 (C, C-13), 143.3 (C,
C-14), 137.8 (C, C-6), 136.5 (CH, C-2), 136.2 (CH, C-3), 133.0 (C,
Experimental Section
C-10), 122.8 (CH, C-7), 121.2 (CH, C-11), 38.2 (CH
C-12), 27.3 (CH , C-5), 24.5 (CH , C-8), 23.5 (CH
(CH , C-16); ESITOFMS m/z 265.1203 [M + Na] (calcd for
Na, 265.1204).
Cordiachrome B (2): brown oil; [R]
ESITOFMS m/z, 243.1387 [M + H] (calcd for C16
243.1385). Spectroscopic data of 2 were identical in all respects to
2
, C-9), 27.7 (CH
2
,
General Experimental Procedures. Melting points were measured
with a digital melting point apparatus and are uncorrected. IR spectra
and optical rotations were measured on a Vector 22 (Bruker) spec-
trometer and Jasco P-1030 polarimeter, respectively. UV spectra were
2
2
3
, C-15), and 16.9
+
3
16 18 2
C H O
2
5
D 3
+12.5 (c 0.13, CHCl );
+
1
13
1
1
recorded on a Cary 1E UV-vis spectrophotometer. H, C, H- H
COSY, HMQC, HMBC, NOESY, and DEPT spectra were recorded
on a Bruker Advance 500 D NMR spectrometer, operating at 500 MHz
19 2
H O ,
1
,6
literature data.
Cordiachrome C (3): brown oil; [R]
1
13
26
for H spectra and at 125 MHz for C spectra. ESITOF-MS were
obtained using a Micromass LCT mass spectrometer. Column chro-
matography and preparative TLC were carried out using 60-230 mesh
silica gel.
D
+1.13 (c 0.25, CHCl
ESITOFMS m/z 243.1388 [M + H] (calcd for C16 , 243.1385).
Spectroscopic data of 3 were identical in all respects to literature
3
);
+
19 2
H O
1
,8
data.
Cordiaquinol C (4): off-white solid; mp 264-266 °C; [R]
26
Plant Material. Roots of C. globifera were collected from Nakhon
Sawan Province, Thailand, in August 2002. The plant material was
authenticated by Dr. Nijsiri Ruangrungsi (Department of Pharmacog-
nosy, Faculty of Pharmaceutical Sciences, Chulalongkorn University).
D
+2.1
(c 0.12, acetone); ESITOFMS m/z 243.1391 [M - H] (calcd for
, 243.1385). Spectroscopic data of 4 were identical in all
-
16 19 2
C H O
6
respects to literature data.

8
64 Journal of Natural Products, 2009, Vol. 72, No. 5
Dettrakul et al.
Alliodorin (5): off-white, amorphous solid; ESITOFMS m/z 238.1308
Preparation of Ester 4b. A solution of 4 (40.4 mg, 0.16 mmol) in
dry pyridine (2 mL) was treated with 0.5 mL of benzoyl chloride, and
the solution was stirred at room temperature overnight. Solvent was
removed under reduced pressure, and the residue was dissolved in
EtOAc (5 mL) and washed twice with water. The organic layer was
evaporated to dryness and subjected to a Sephadex LH-20 column
(eluting with MeOH) followed by silica gel column (eluting with 5%
EtOAc in hexane) chromatography to give 4b (25.3 mg, 33.8%): white
+
[
M + Na] (calcd for C16
H
20
O
3
Na, 283.1310). Spectroscopic data of 5
6
,15
were identical in all respects to literature data.
2
6
Elaeagin (6): brown oil: [R]
D
+3.7 (c 0.18, CHCl
m/z 259.1331 [M + H] (calcd for C16 , 259.1334). Spectroscopic
data of 6 were identical in all respects to literature data.
3
); ESITOFMS
+
19 3
H O
1
2
2
6
Cordiachromene (7): brown oil; [R]
D
-10.9 (c 0.095, acetone);
+
ESITOFMS m/z 245.1534 [M + H] (calcd for C16
21 2
H O
, 245.1541).
3
Spectroscopic data of 7 were identical in all respects to literature data.
needles; mp 171-172 °C; UV (CHCl
3
) λmax (log ε) 241 (4.2) nm; IR
Preparation of 1a. An aliquot of 1 (123 mg, 0.50 mmol) in THF (4
(KBr) νmax 2924, 1732, 1638, 1469, 1450, 1314, 1266, 1211, 1083,
-
1 1
mL) was added to a solution of Na
2
S
2
O
4
(8.5 mg, 0.05 mmol) in H
2
O
1063, 1025, 709 cm ; H NMR (CDCl
3
, 500 MHz) δ 8.23 (4 × 1H,
(
1 mL), and the reaction mixture was stirred vigorously for 30 min
until colorless. Aqueous NaHCO was added, and the mixture was
3
m, overlapping signals of H-2′, H-2′′, H-6′, and H-6′′), 7.66 (2 × 1H,
m, overlapping signals of H-4′ and H-4′′), 7.53 (4 × 1H, m, overlapping
signals of H-3′, H-3′′, H-5′, and H-5′′), 7.08 (2 × 1H, s, H-6 and H-7),
5.99 (1H, dd, J ) 11.0, 17.5 Hz, H-14), 5.00 (1H, d, J ) 11.0 Hz,
H-15b), 4.95 (1H, dd, J ) 0.95, 17.3 Hz, H-15a), 4.84 (1H, s, H-12b),
4.75 (1H, s, H-12a), 2.77 (1H, d, J ) 17.3 Hz, H-5b), 2.75 (2H, d, J
) 8.8 Hz, H-8), 2.56 (1H, d, J ) 17.1 Hz, H-5a), 2.38 (1H, d, J ) 8.5
extracted with EtOAc (10 mL × 3). The EtOAc layers were combined,
evaporated, and separated on Sephadex LH-20 (MeOH eluent) to give
1
a (111 mg, 91%): off-white, amorphous solid; λmax (log ε) 204 (4.4)
and 291 (3.7) nm; IR (KBr) νmax 3318, 2964, 2927, 2861, 1617, 1376,
-
1 1
1
(
288, 1183, 798, 747 cm ; H NMR (acetone-d
6
, 500 MHz) δ 7.61
13
1H, br s, 1-OH), 7.63 (1H, br s, 4-OH), 6.59 (1H, d, J ) 8.6 Hz,
3
Hz, H-7), 1.72 (3H, s, H-13), and 1.10 (3H, s, H-16); C NMR (CDCl ,
H-2), 6.57 (1H, d, J ) 8.7 Hz, H-3), 5.23 (1H, dd, J ) 1.8, 13.8 Hz,
H-11), 5.06 (1H, dd, J ) 7.2, 8.4 Hz, H-7), 3.87 (1H, br d, J ) 16.7
Hz, H-12b), 3.42 (1H, d, J ) 13.8 Hz, H-5b), 3.21 (1H, dd, J ) 13.8
and 16.7 Hz, H-12a), 3.20 (1H, d, J ) 13.8 Hz, H-5a), 2.13 (1H, dd,
J ) 5.2, 11.6 Hz, H-9b), 1.96 (2H, m, H-8), 1.79 (3H, s, H-16), 1.70
125 MHz) δ 164.8 (2 × C, C-17 and C-17′), 146.7 (C, C-1), 146.6 (C,
C-4), 146.1 (C, C-11), 141.9 (CH, C-14), 133.7 (2 × CH, C-4′ and
C-4′′), 130.8 (2 × C, C-1′ and C-1′′), 130.3 (4 × CH, C-2′, C-2′′,
C-6′, and C-6′′), 129.5 (C, C-10), 129.4 (C, C-9), 128.7 (4 × CH, C-3′,
C-3′′, C-5′, and C-5′′), 120.0 (CH, C-2), 119.9 (CH, C-3), 113.7 (CH
2
,
,
1
3
(
1H, t, J ) 11.9 Hz, H-9a), 1.59, (3H, s, H-15); C NMR (acetone-d
25 MHz) δ 150.3 (C, C-1), 149.1 (C, C-4), 141.1 (C, C-10), 130.9
C, C-6), 127.6 (C, C-13), 126.5 (C, C-14), 125.1 (CH, C-11), 121.8
CH, C-7), 113.6 (CH, C-2), 113.4 (CH, C-3), 39.1 (CH , C-9), 28.7
, C-16), 17.0
, C-15); ESITOFMS m/z 245.1541 [M + H] (calcd for C16
6
,
C-15), 113.4 (CH
C-5), 27.5 (CH , C-8), 26.2 (CH
ESITOFMS m/z 475.1878 [M + Na] (calcd for C30
2
, C-12), 50.0 (CH, C-7), 37.9 (C, C-6), 37.8 (CH
2
1
2
3
, C-16), and 23.2 (CH
3
, C-13);
28 4
H O Na, 475.1885).
+
(
(
(
(
2
Preparation of Ester 4c. To a solution of 4 (35.4 mg, 0.14 mmol)
in dry pyridine (2 mL) was added 4-bromobenzenesulfonyl chloride
(178.8 mg, 0.7 mmol), and the solution was stirred at room temperature
for 12 h. The solvent was removed under reduced pressure, then the
residue was dissolved in 5 mL of EtOAc and subsequently washed
twice with water. The residue was subjected to Sephadex LH-20 column
chromatography (MeOH eluent) to remove traces of 4-bromobenze-
nesulfonyl chloride and 4-bromobenzenesulfonic acid and was then
purified over silica gel, eluting with 4% EtOAc in hexane to obtain 4c
CH
CH
2 2 2 3
, C-5), 27.8 (CH , C-12), 25.3 (CH , C-8), 22.7 (CH
+
3
H
21
O
2
,
2
45.1531).
Preparation of 1b. Acetic anhydride (0.5 mL) was added to a
solution of 1a (15.4 mg, 0.06 mmol) in pyridine (1.5 mL). The mixture
was stirred at room temperature for 12 h, and the solvent was removed
under reduced pressure. The residue was separated by preparative TLC
(
10% EtOAc in hexane) to yield a yellow liquid (1b, 11.1 mg, 54%);
λ
1
6
max (log ε) 204 (4.4) and 291(3.7) nm; IR (KBr) νmax 2925, 1764,
(38.8 mg, 39.4%): pale pink, amorphous solid; UV (CHCl
(log ε) 242 (4.6) nm; IR (KBr) νmax 3087, 2924, 1575, 1460, 1380,
3
) λmax
-
1
1
469, 1370, 1186, 1041, 895 cm ; H NMR (CDCl
3
, 500 MHz) δ
-
1 1
.94 (1H, d, J ) 8.7 Hz, H-3), 6.90 (1H, d, J ) 8.7 Hz, H-2), 5.18
1091, 822, 784 cm ; H NMR (CDCl
3
, 500 MHz) δ 7.71 (4 × 1H, m,
(
3
1H, d, J ) 13.2 Hz, H-11), 5.12 (1H, br dd, J ) 7.9 and 8.6 Hz, H-7),
.45 (1H, br d, J ) 16.4 Hz, H-12b), 3.33 (1H, dd, J ) 13.2 and 16.4
Hz, H-12a), 3.31 (1H, d, J ) 15.3 Hz, H-5b), 2.98 (1H, d, J ) 15.3
Hz, H-5a), 2.29 (3H, s, CH of acetate), 2.28 (3H, s, CH of acetate),
.13 (1H, dd, J ) 5.7 and 11.5 Hz, H-9b), 2.02 (1H, m, H-8b), 1.92
1H, dd, J ) 10.7, 11.4 Hz, H-8a), 1.72 (2H, s, H-16), and 1.52 (3H,
aromatic protons of 4-bromobenzenesulfonyl group), 7.64 (4 × 1H,
m, aromatic protons of 4-bromobenzenesulfonyl group), 7.03 (1H, d,
J ) 8.9 Hz, H-2), 6.89 (1H, d, J ) 8.9 Hz, H-3), 5.48 (1H, dd, J )
10.9, 17.5 Hz, H-14), 4.86 (1H, d, J ) 10.9, H-15b), 4.81 (1H, s,
H-12b), 4.65 (1H, d, J ) 17.5 Hz, H-15a), 4.51 (1H, s, H-12a), 2.60
(1H, d, J ) 17.6 Hz, H-5b), 2.50 (1H, dt, J ) 10.2, 10.3 Hz, H-8b),
2.24 (1H, d, J ) 17.5 Hz, H-5a), 2.00 (1H, dd, J ) 10.3, 10.7 Hz,
3
3
2
(
1
3
s, H-15); C NMR (CDCl
3
, 125 MHz) δ 169.3 (C, CdO of acetate),
1
3
1
69.2 (C, CdO of acetate), 148.3 (C, C-4), 146.9 (C, C-1), 132.6 (C,
3
H-8a), 1.61 (3H, s, H-13), and 0.97 (3H, s, H-16); C NMR (CDCl ,
C-14), 138.0 (C, C-6), 132.2 (C, C-13), 132.1 (C, C-10), 122.7 (CH,
125 MHz) δ 146.0 (C, C-1), 145.7 (C, C-4), 145.2 (C, C-11), 140.9
(CH, C-14), 134.9 (C, C-1′), 134.8 (C, C-1′′), 132.7 (4 × C, C-3′, C-3′′,
C-5′, and C-5′′), 132.5 (C, C-9), 132.0 (C, C-10), 129.9 (2 × C, C-4′
and C-4′′), 129.7 (4 × C, C-2′, C-2′′, C-6′, and C-6′′), 120.3 (CH,
C-7), 122.2 (CH, C-11), 120.6 (2 × CH, C-2 and C-3), 38.1
(
(
(
CH
CH
CH
2
3
2 2 2
, C-9), 29.3 (CH , C-5), 28.0 (CH , C-12), 24.7 (CH , C-8), 22.8
, C-15), 21.1 (CH
, C-16); ESITOFMS m/z 351.1564 [M + Na] (calcd for
Na, 351.1572).
3 3
of acetate), 20.9 (CH of acetate), and 17.0
+
3
C-2), 120.0 (CH, C-3), 113.7 (CH
2
, C-15), 113.5 (CH
, C-5), 27.3 (CH
, C-13); ESITOFMS m/z 702.9434 [M + Na]
Br Na, 702.9435).
2
, C-12), 49.2
C
22
H
24
O
4
(CH, C-7), 37.6 (C, C-6), 37.5 (CH
2
2
, C-8), 26.0 (CH ,
3
+
Preparation of Ester 4a. Acetic anhydride (0.5 mL) was added to
C-16), and 23.1 (CH
(calcd for C28
3
a solution of 4 (31.1 mg, 0.13 mmol) in dry pyridine (2 mL), and the
mixture was stirred for 12 h at room temperature. Solvent was removed
under reduced pressure, and the residue was dissolved in EtOAc (5
mL) and subsequently washed twice with water. The organic layer was
evaporated to dryness and separated on silica gel eluting with 5% EtOAc
H
26
O
6
S
2
2
Cope Rearrangement of 1 to 4a. A solution of globiferin (1) (17.7
mg) in xylene (2 mL) was heated under reflux for 2 h. After removing
solvent, the residue was separated on a silica gel column (eluting with
2% EtOAc in hexane) to provide cordiachrome C (3) (15.6 mg, 85%).
Cope Rearrangement of 1 to 4. Globiferin (1) (81.9 mg) was
in hexane to provide 4a (13.8 mg, 33%): yellow oil; UV (CHCl
3
) λmax
(
log ε) 241 (3.1) and 260 (2.8) nm; IR (KBr) νmax 3082, 2927, 2855,
6
dissolved in DMSO-d (1.5 mL) in an NMR tube and then heated at
-1
1
1
1
764, 1639, 1470, 1185, 1017, 895 cm ; H NMR (CDCl
3
, 500 MHz)
reflux (189 °C) for 2 h. Progress of the reaction was monitored by H
NMR. Water (5 mL) was added to precipitate, and the resulting solid
was dissolved in acetone and filtered through charcoal. The filtrate was
evaporated to dryness and separated on a Sephadex LH-20 column
(MeOH as eluent) to obtain 4 (75.2 mg, 91%).
δ 6.88 (2 × 1H, s, H-2 and H-3), 5.93 (1H, dd, J ) 10.9, 17.5 Hz,
H-14), 4.97 (1H, dd, J ) 1.2, 10.9 Hz, H-15b), 4.90 (1H, dd, J )
1
5.0, 17.5 Hz, H-15a), 4.88 (1H, s, H-12b), 4.77 (1H, s, H-12a), 2.64
(
1H, d, J ) 17.1 Hz, H-5b), 2.62 (1H, d, J ) 7.9 Hz, H-8), 2.44 (1H,
d, J ) 7.2 Hz, H-5a), 2.33 (1H, dd, J ) 7.3, 7.3 Hz, H-7), 2.30 (3H,
Cope Rearrangement of 1b to 4a. A solution of compound 1b
(11.0 mg) in xylene (2 mL) was heated under reflux for 2 h. Solvent
was removed, and the residue was separated on a Sephadex LH-20
column eluted with MeOH to yield 4a (10.6 mg, 96%).
Transformation of 3 to 4. Cordiachrome C (3) (ca. 25 mg) was
6
dissolved in DMSO-d (0.5 mL) in an NMR tube and then heated at
s, H-18), 2.29 (3H, s, H-20), 1.76 (3H, s, H-13), 1.12 (3H, s, H-16);
1
3
C NMR (CDCl
C, C-1), 146.3 (C, C-4), 146.2 (C, C-11), 141.7 (CH, C-14), 130.4
C, C-10), 129.9 (C, C-9), 119.7 (C, C-3), 113.7 (CH , C-15), 113.4
CH , C-12), 49.9 (CH, C-7), 37.9 (C, C-6), 37.8 (CH , C-5), 27.4 (CH
3
, 125 MHz) δ 169.2 (2 × C, C-17 and C-19), 146.4
(
(
(
2
2
2
2
,
C-8), 26.2 (CH
3
, C-16), 23.3 (CH
3
, C-13), and 20.9 (2 × CH
3
, C-18
reflux (189 °C) for 2 h. Progress of the conversion was monitored by
+
1
and C-20); ESITOFMS m/z 315.1569 [M + Na] (calcd for
H NMR, and it was found that 99% of cordiachrome C (3) was
C
20
H
24
O
4
Na, 351.1572).
converted to cordiaquinol C (4) after heating for 2 h.

Terpenoid Benzoquinone from Cordia globifera
Journal of Natural Products, 2009, Vol. 72, No. 5 865
Acid-Catalyzed Cyclization of 1b. To a solution of compound 1b
also thanks the National Center for Genetic Engineering and Biotech-
nology (BIOTEC) for research facilities and bioassay results. P.K. is
indebted to the Thailand Research Fund (TRF) and the Biodiversity
Research and Training Program (BRT) for financial support. We thank
Dr. Nijsiri Ruangrungsi for the plant identification.
(
26.5 mg, 0.08 mmol) in MeOH (2 mL) was added 25% dilute HCl (3
drops). The reaction mixture was stirred at room temperature for 12 h.
Saturated NaHCO solution was added, and the mixture was extracted
with EtOAc (5 mL × 3). The combined organic layer was washed
with saturated NaCl solution and water, dried over anhydrous MgSO
filtered, and evaporated under reduced pressure. The residue was
purified by HPLC (reversed-phase C18 column, MeCN-H O, 40:60),
furnishing compounds 10 (10.8 mg, 40.7%) and 11 (2.0 mg, 7.6%).
3
4
,
Supporting Information Available: H and 13C spectra of 1, 1a,
1
2
4
b, 4c, 10, and 11. This material is available free of charge via the
Internet at http://pubs.acs.org.
2
6
1
Compound 10: Yellow oil; [R]
CDCl
, 500 MHz) δ 6.87 (2 × 1H, s, overlapping signals of H-2 and
H-3), 4.68 (1H, s, H-15b), 4.42 (1H, s, H-15a), 2.79 (1H, dd, J ) 18.1,
.1 Hz, H-12b), 2.70 (1H, dd, J ) 18.1, 6.4 Hz, H-12a), 2.53 (1H, d,
J ) 16.9 Hz, H-5b), 2.31 (3H, s, CH COO), 2.29 (3H, s, CH COO),
.27 (1H, dd, J ) 13.6 and 5.2 Hz, H-9b), 2.18 (1H, br t, J ) 4.4 Hz,
H-11), 2.07 (1H, d, J ) 16.9 Hz, H-5a), 2.01 (1H, ddd, J ) 13.6, 8.0,
.2 Hz, H-9a), 1.66 (2H, m, H-8), 1.58 (1H, m, H-7b), 1.39 (1H, ddd,
D
+2.1 (c 0.12, MeOH); H NMR
(
3
References and Notes
(
1) Moir, M.; Thomson, R. H. J. Chem. Soc., Perkin Trans. 1 1973, 1352–
357.
4
1
3
3
(
2) Kuroyanagi, M.; Seki, T.; Hayashi, T.; Nagashima, Y.; Kawahara,
N.; Sekita, S.; Satake, M. Chem. Pharm. Bull. 2001, 49, 954–957.
3) Kahn, H. P.; Cossy, J. Tetrahedron Lett. 1999, 8113–8114.
4) Ioset, J. R.; Marston, A.; Gupta, M. P.; Hostettmann, K. J. Nat. Prod.
2000, 63, 424–426.
2
(
(
5
13
J ) 14.9, 10.2, 4.9 Hz, H-7a), and 0.96 (3H, s, H-16); C NMR (CDCl
3
,
1
1
(
(
25 MHz) δ 169.3 (C, CH
46.9 (C, C-4), 146.3 (C, C-1), 129.6 (C, C-14), 128.8 (C, C-13), 119.5
, C-15), 45.1 (CH, C-11), 36.9
, C-9), 33.8 (C, C-6), 31.5 (CH , C-5), 27.3 (CH
, C-12), 23.6 (CH , C-8), 20.9 (CH COO), and 20.8
COO); ESITOFMS m/z 329.1748 [M + H] (calcd for C20
29.1753).
Compound 11: Yellow oil; [R]
CDCl
, 500 MHz) δ 6.88 (2 × 1H, s, H-2 and H-3), 5.23 (1H, d, J )
.9 Hz, H-9), 2.91 (1H, dd, J ) 17.6 and 6.4 Hz, H-12b), 2.47 (1H, d,
3
COO), 169.1 (C, CH
3
COO), 148.8 (C, C-10),
(5) Ioset, J. R.; Marston, A.; Gupta, M. P.; Hostettmann, K. Phytochemistry
2000, 53, 613–617.
(
6) Manners, G. D.; Jurd, L. J. Chem. Soc., Perkin. Trans. 1 1977, 405–
10.
CH, C-3), 119.3 (CH, C-2), 107.9 (CH
CH , C-7), 34.4 (CH
2
4
2
2
2
3
,
(
7) Menezes, J. E. S. A.; Lemos, T. L. G.; Pessoa, O. D. L.; Braz-Filho,
R.; Montenegro, R. C.; Wilke, D. V.; Costa-Lotufo, L. V.; Pessoa,
C.; Moraes, M. O.; Silveira, E. R. Planta. Med. 2005, 71, 54–58.
8) Menezes, J. E. S. A.; Lemos, T. L. G.; Silveira, E. R.; Braz-Filho, R.;
Pessoa, O. D. L. J. Braz. Chem. Soc. 2001, 12, 787–790.
C-16), 24.2 (CH
CH
2
2
3
+
(
3
3
25 4
H O ,
(
2
6
1
D
+5.5 (c 0.08, MeOH); H NMR
(
2
3
(9) Nakamura, N.; Kojima, S.; Lim, Y. A.; Meselhy, M. R.; Hattori, M.;
Gupta, M. P.; Correa, M. Phytochemistry 1997, 46, 1139–1141.
(10) Kuroyanagi, M.; Kawahara, N.; Sekita, S.; Satake, M.; Hayashi, T.;
Takase, Y.; Masuda, K. J. Nat. Prod. 2003, 66, 1307–12.
J ) 16.4 Hz, H-5b), 2.34 (1H, d, J ) 16.4 Hz, H-5a), 2.31 (1H, s,
H-18), 2.30 (2 × 1H, s, H-12a and H-20), 2.03 (2H, m, H-8), 1.85
(
11) Silva, S. A. S.; Rodrigues, M. S. L.; Agra, M. F.; Cunha, E. V. L.;
(
1H, br t, J ) 7.7 Hz, H-11), 1.70 (3H, s, H-15), 1.51 (1H, dd, J )
Barbosa-Filho, J. M.; Silva, M. S. Biochem. Syst. Ecol. 2004, 32, 359–
1
3.5 and 7.8 Hz, H-7b), 1.07 (1H, m, H-7a), and 0.99 (3H, s, H-16);
3
61.
13
C NMR data could not be recorded due to a limited amount of the
(
(
12) Manners, G. D. J. Chem. Soc., Perkin Trans. 1 1983, 39–43.
13) Ioset, J. R.; Marston, A.; Gupta, M.; Hostettmann, K. Phytochemistry
1998, 47, 729–734.
+
material; ESITOFMS m/z 351.1578 [M + Na] (calcd for C20
24 4
H O Na,
3
51.1572).
Antimycobacterial Assay. Antimycobacterial activity was assessed
against Mycobacterium tuberculosis H37Ra using the Microplate Alamar
(14) Yajima, A.; Saitou, F.; Sekimoto, M.; Maetoko, S.; Yabuta, G.
Tetrahedron Lett. 2003, 44, 6925–6918.
2
3
(
(
15) Stevens, K. L.; Jurd, L. Tetrahedron 1976, 32, 665–668.
Blue Assay (MABA). Standard drugs rifampicin, isoniazid, and
kanamycin sulfate were use as the reference compounds (MIC 0.0047,
16) Gomez, F.; Quijano, L.; Calderon, J. S.; Rios, T. Phytochemistry 1980,
1
9, 2202–2203.
0
.05, and 2.5 µg/mL, respectively.).
Antimalarial Assay. Antimalarial activity was evaluated against the
parasite Plasmodium falciparum (K1, multidrug-resistant strain), which
(
17) Toscano, R. A.; Quijano, L.; Gomez, F.; Garcia-Perez, G.; Rios, T.
Acta Crystallogr. 1992, C48, 2000–2002.
(
18) Takahashi, A.; Kusano, G.; Ohta, T.; Nozoe, S. Chem. Pharm. Bull.
was cultured continuously according to the method of Trager and
1
993, 41, 2032–2033.
2
4
Jensen. Quantitative assessment of malarial activity in vitro was
determined by means of microculture radioisotope technique based
(19) Takeda, K.; Tori, K.; Horibe, I.; Ohtsuru, M.; Minato, H. J. Chem.
Soc. (C) 1970, 2697–2703.
2
5
upon the method described by Desjardins et al. An IC50 value of
(20) Takeda, K.; Horibe, I.; Minato, H. J. Chem. Soc. (C) 1970, 2704–
2
707.
0
.0012 µg/mL was observed for the standard compound dihydroarte-
misinin in the same test system.
Antifungal Assay. The isolated compounds were tested for their
(
21) Takeda, K.; Horibe, I. J. Chem. Soc., Perkin Trans. 1 1975, 870–876.
22) Mori, K.; Kawano, M.; Fuchino, H.; Ooi, T.; Satake, M.; Agatsuma,
Y.; Kusumi, T.; Sekita, S. J. Nat. Prod. 2008, 71, 18–21.
(
antifungal activity against Candida albicans using a method modified
(
23) Collins, L.; Franzblau, S. G. Antimicrob. Agents Chemother. 1997, 4,
26
from the soluble formazan assay. The IC50 value of the standard drug
amphotericin B was 0.08 µg/mL.
1
004–1009.
(24) Trager, W.; Jensen, J. B. Science 1976, 193, 673–675.
(25) Desjardins, R. E.; Canfield, C. J.; Haynes, J. D.; Chulay, J. D.
Antimicrob. Agents Chemother. 1979, 16, 710–718.
Cytotoxicity Assay. The cytotoxicity assays against the KB (human
epidermoid carcinoma of the mouth), BC (human breast cancer cells),
NCI-H187 (human small cell lung cancer), and Vero cell lines (African
green monkey kidney fibroblast cells) were evaluated using the
(
26) Scudiero, D.; Shoemaker, R. H.; Paull, K. D.; Monks, A.; Tierney,
S.; Nofziger, T. H.; Currens, M. J.; Seniff, D.; Boyd, M. R. Cancer
Res. 1988, 48, 4827–4833.
27) Skahan, P.; Storeng, R.; Scudiero, D.; Monks, A.; McMahon, J.;
Vistica, D.; Warren, J. T.; Bokesch, H.; Kenny, S.; Boyd, M. R. J. Natl.
Cancer Inst. 1990, 82, 1107–1112.
2
7
colorimetric method as described by Skehan and co-workers. The
reference substance was ellipticine (Table 1).
(
Acknowledgment. S.D. is grateful to the Royal Golden Jubilee Ph.D.
Program and Prof. Y. Thebtaranonth for a student scholarship, and he
NP9000703