Tricycloalternarene derivatives from the endophytic fungus Guignardia bidwellii PSU-G11

Article abstract of DOI:10.1016/j.phytol.2011.11.010

Four new tricycloalternarene derivatives, guignarenones A-D (1-4), along with known (6S,9R)-vomifoliol were isolated from the endophytic fungus Guignardia bidwellii PSU-G11. Their structures were determined on the basis of spectroscopic data. The absolute configurations in 1 were assigned using a combination of the modified Mosher's method and NOEDIFF data. Compound 1 displayed mild cytotoxic activity against oral cavity cancer and African green monkey kidney fibroblast (Vero) cell lines.

Full text of DOI:10.1016/j.phytol.2011.11.010

Phytochemistry Letters 5 (2012) 139–143
Contents lists available at ScienceDirect
Phytochemistry Letters
journal homepage: www.elsevier.com/locate/phytol
Tricycloalternarene derivatives from the endophytic fungus
Guignardia bidwellii PSU-G11
b
a
Ubonta Sommart a, Vatcharin Rukachaisirikul a, , Kongkiat Trisuwan , Kwanruthai Tadpetch ,
*
Souwalak Phongpaichit c, Sita Preedanon d, Jariya Sakayaroj d
a Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand
b Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
c Natural Products Research Center and Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand
d National Center for Genetic Engineering and Biotechnology, Thailand Science Park, Klong Luang, Pathumthani 12120, Thailand
A R T I C L E I N F O
A B S T R A C T
Article history:
Four new tricycloalternarene derivatives, guignarenones A–D (1–4), along with known (6S,9R)-vomifoliol
were isolated from the endophytic fungus Guignardia bidwellii PSU-G11. Their structures were
determined on the basis of spectroscopic data. The absolute configurations in 1 were assigned using a
combination of the modified Mosher’s method and NOEDIFF data. Compound 1 displayed mild cytotoxic
activity against oral cavity cancer and African green monkey kidney fibroblast (Vero) cell lines.
ß 2011 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
Received 5 October 2011
Received in revised form 28 November 2011
Accepted 28 November 2011
Available online 9 December 2011
Keywords:
Endophytic fungus
Tricycloalternarene derivatives
Guignardia bidwellii
Guignarenones
Cytotoxic activity
1. Introduction
A (1) were determined by employing a combination of the
modified Mosher’s method (Ohtani et al., 1991) and NOEDIFF data.
The genus Guignardia is a rich source of bioactive natural
products such as isovernin aldehyde (Otomo et al., 1983), (R)-
guignardic acid (Ferreira et al., 2002), and vermistatin (Xia et al.,
2007). As part of our ongoing search for bioactive fungal
metabolites, the endophytic fungus Guignardia bidwellii PSU-G11
was isolated from the leaves of Garcinia hombroniana. The EtOAc
extract from the culture broth was subjected to chemical
investigation. We reported herein the isolation of four new
tricycloalternarene derivatives, guignarenones A–D (1–4), along
with one known metabolite, (6S,9R)-vomifoliol (5) (Yamano and
Ito, 2005) from the culture broth. Their cytotoxic activity against
oral cavity cancer (KB), and African green monkey kidney fibroblast
(Vero) cell lines was examined.
As guignarenones A–D (1–4) were co-metabolites, we proposed
that they would have the same biosynthetic pathway. Conse-
quently, the absolute configurations of rings A and B in 2–4 would
be identical to those of 1. This is the first report on the complete
assignment of the absolute configurations of tricycloalternarenes
using chemical and spectroscopic methods since those of
previously isolated tricycloalternarenes, except for guignardones
A–C (Yaun et al., 2010), have never been determined (Liebermann
et al., 1997; Sugawara et al., 1998; Nussbaum et al., 1999; Qiao
et al., 2007; Yuan et al., 2008). However, the absolute configura-
tions of guignardones A–C were assigned by comparison of their
circular dichroism spectra with the calculated ECD spectra (Yaun
et al., 2010). For the known compound 5, the structure was
confirmed by comparison of the 1H and 13C NMR data as well as the
specific rotation with those previously reported (Yamano and Ito,
2005).
2. Results and discussion
Guignarenone A (1) was obtained as a colorless gum. Its
molecular formula was determined as C22H32O4 by HREIMS,
indicating that 1 had seven degrees of unsaturation. A UV
absorption band at 263 nm was attributed to a conjugated
carbonyl chromophore whereas the IR spectrum showed hydroxyl
and carbonyl absorption bands at 3373 and 1709 cmÀ1, respec-
tively. The 1H NMR spectrum of 1 (Table 1) contained signals for a
Fig. 1 the structures of 1–5 were elucidated by analysis of
spectroscopic data. Their relative congurations were assigned
using NOEDIFF data. The absolute configurations in guignarenone
* Corresponding author. Tel.: +66 74 288 435; fax: +66 74 558 841.
E-mail address: vatcharin.r@psu.ac.th (V. Rukachaisirikul).
1874-3900/$ – see front matter ß 2011 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.phytol.2011.11.010

140
U. Sommart et al. / Phytochemistry Letters 5 (2012) 139–143
Table 1
1H and 13C NMR data for guignarenones A (1) and B (2) (CDCl3,
d ppm).
Position
1
2
dH (J in Hz)
dC
dH (J in Hz)
dC
1
–
194.9
106.0
167.6
65.7
–
–
194.9
105.7
168.3
65.8
–
2
–
–
3
–
–
4
4.24 m
4.27 m
4-OH
5
3.27 d (7.2)
3.25 d (7.0)
2.38 ddd (13.8, 4.8, 3.6)
34.6
2.38 ddd (13.5, 4.5, 4.0)
34.7
2.24 ddd (13.8, 6.6, 5.4)
2.24 ddd (13.5, 7.0, 5.5)
6
7
8
3.70 dd (6.6, 3.6)
3.47 s
79.1
58.4
16.3
3.72 dd (7.0, 4.0)
3.49 s
79.2
58.4
18.7
2.35 m
2.15 m
1.98 m
–
2.68 brd (17.5)
2.28 dd (17.5, 6.5)
1.67 m
9
43.6
87.7
22.4
37.4
50.0
88.9
23.6
38.3
10
11
12
–
1.33 s
1.34 s
2.13 m
1.80 m
1.94 m
1.49 m
2.16 m
–
2.04 m
1.65 m
13
27.9
1.77 m
24.6
1.53 m
14
15
16
48.3
149.8
109.1
2.11 dd (8.0, 7.0)
–
50.0
75.1
22.2
4.76 d (1.5)
4.72 brs
2.07 m
1.95 m
5.07 tm (6.9)
–
1.15, s
17
18
19
20
21
22
33.5
26.6
1.48 m
40.9
22.3
2.00 m
124.0
131.7
25.6
5.12 tm (7.0)
–
124.2
132.2
25.7
1.66, s
1.58, s
1.68 d (0.6)
1.61 s
17.7
17.7
4-methylpent-3-enyl group [
(m), 1.66 (s) and 1.58 (s)], two geminal olefinic protons (
J = 1.5 Hz, and 4.72, brs), two oxymethine protons (
d
5.07 (tm, J = 6.9 Hz), 2.07 (m), 1.95
4.76, d,
4.24, q,
J = 5.7 Hz, and 3.70, dd, J = 6.6 and 3.6 Hz), one hydroxy proton (
3.27, d, J = 7.2 Hz), two coupled methine protons ( 2.16 and 1.98,
each m), two sets of coupled methylene protons ( 2.13, 1.80 and
1.94, 1.49, each 1H, m), two sets of nonequivalent methylene
protons ( 2.38, ddd, J = 13.8, 4.8 and 3.6 Hz, 2.24, ddd, J = 13.8, 6.6
and 5.4 Hz, each 1H, and 2.35, 2.15, each 1H, m), one methoxyl
group ( 3.47, s) and one methyl group (
1.33, s). The 13C NMR
spectrum of 1 displayed three carbons of a fully substituted
-alkoxy- -unsaturated ketone ( 194.9, 167.6 and 106.0), six
carbons of the 4-methylpent-3-enyl unit ( 131.7, 124.0, 33.5,
26.6, 25.6 and 17.7), two carbons of a gem-disubstituted ethylene
(
d
79.1 and 65.7), two methine (
d
48.3 and 43.6), four methylene (
58.4) and one methyl (dC
22.4) carbons. A cyclohexenone having hydroxyl and methoxyl
groups at C-4 (dC 65.7) and C-6 ( 79.1) was established by the
HMBC correlations observed from H-4 ( 4.24) to C-3 ( 167.6) and
C-6, from H2-5 ( 2.38 and 2.24) to C-6 and from H-6 ( 3.70) to C-2
106.0) and C-4 (Fig. 2). The 1H–1H COSY correlations revealed
the connection from H-12 ( 2.13 and 1.80) to H-14 ( 2.16) and
from H-14 to H-9 ( 1.98) (Fig. 2). In addition, the HMBC cross
peaks of H3-11 ( 1.33) with C-9, C-10 ( 87.7) and C-12, and the
d
d
37.4, 34.6, 27.9 and 16.3), one methoxy (d
d
d
d
d
d
d
d
d
d
(
d
d
d
d
d
d
d
d
d
chemical shift of C-10 constructed a cyclopentane with a methyl
group and an oxy substituent at C-10. A tricycloalternarene
skeleton was established on the basis of the 1H–1H COSY
correlations of H-9 (
as the 3J HMBC data from H2-8 to C-1, C-3, C-10 and C-14. The
b
a
,
b
d
d
d 1.98) with H2-8 (d 2.35 and 2.15) as well
(
d
149.8 and 109.1), one oxyquaternary (
d
87.7), two oxymethine
H31C1
OH
O
12
14
10
3
5
21
H3C
7
19
17
8
1
15
OCH3
H31C1
R5
R4
H
O
R3
O
R2
R1
CH3
16
12
14
10
7
3
22
5
R2
R1
17
8
1 R1 + R2 = double bond
2 R1 = CH3, R2 = OH
1
15
16
H3C
H
O
CH3
CH3
H3C
3 R1 = R3 = R4 = H, R2 =
α
-OCH3, R5 =
α-OH
OH
4 R1 + R3 = double bond, R2 = OMe, R4 + R5 = O
OH
O
CH3
5
Fig. 1. Structures of metabolites isolated from the endophytic fungus G. bidwellii PSU-G11.

U. Sommart et al. / Phytochemistry Letters 5 (2012) 139–143
141
11
H3C
HO
O
12
14
3
10
5
19
7
17
8
1
H3C
OCH3
21
15
16
H
O
CH3
22
11
H3C
11
H3C
OH
OH
H
O
O
3
5
12
12
3
5
10
10
21
H3C
21
H3C
H7
OCH3
14
14
17
17
8
19
19
8
7
1
1
15
16
15
16
OCH 3
H
H
O
O
CH3
CH3
22
22
Fig. 2. 1H–1H COSY (
), selected HMBC ( ) and selected NOEDIFF (
) data of 1.
1H–1H COSY and HMBC correlations shown in Fig. 2 constructed
the 4-methylpent-3-enyl unit. This unit was connected to C-15 (dC
149.8) of the gem-disubstituted ethylenyl unit to form a 2-
substituted-6-methyl-1,5-heptadienyl moiety according to the 3J
hydroxyl group on the basis of the chemical shift of C-15. The
absoluteconfigurationsof2 wereproposedtobeidenticaltothoseof
1 on the basis of their identical NOEDIFF data as well as their co-
occurrence. However, the absolute configuration at C-15 remained
unidentified due to inadequate NOEDIFF data. Consequently, 2 was
identified as a new hydrate derivative of 1.
Guignarenone C (3) with the molecular formula C17H24O4 from
HREIMS was obtained as a colorless gum. The UV and IR absorption
bands of 3 were similar to those of 1 and 2. The 1H NMR data (Table
2) were different from those of 1 by the replacement of signals for
the 4-methylpent-3-enyl group in 1 with a singlet signal of a
HMBC correlations of H2-16 (d 4.76 and 4.72) with C-17 (d 33.5) of
the pentenyl unit. This moiety was then attached at C-14 of the
tricycloalternarene skeleton due to the HMBC correlations from
H2-16 to C-14 and from H-9 to C-15.
Irradiation of H-9 enhanced the signal intensity of H-16 (
of the 2-substituted-6-methyl-1,5-heptadienyl unit and H3-11, but
not H-14 ( 2.16), indicating that H-9, H3-11 and the heptadienyl
d 4.72)
d
unit were all cis. Signal enhancement of H-6 upon irradiation of H-4
indicated that 4-OH and 6-OCH3 were placed on the same side of the
molecule. However, these data were inadequate to assign overall
relative configuration of 1. The absolute configuration at C-4 was
determined on the basis of the Mosher’s method using the (S)- and
(R)-MTPA esters (Fig. 3). The differences in the 1H NMR chemical
methyl group (
protons (H3-17) to C-14 (
d
1.67) in 3. The HMBC cross peaks from the methyl
49.0), C-15 ( 145.5) and C-16 ( 111.2)
d
d
d
confirmed the attachment of the methyl group, instead of the 4-
methylpent-3-enyl group, at C-15 in 3. The absolute configurations
in 3 were proposed to be identical to those in 1 based on their
similar specific rotations, NOEDIFF and CD data. Consequently,
guignarenone C would have structure 3.
Guignarenone D (4) was obtained as a colorless gum. The
molecular formula C17H20O4 determined by HREIMS revealed that 4
had four fewer hydrogen atoms than 3. The UV spectrum showed a
shifts between the S- and R-MTPA derivatives (DdH
=
dS
À
dR) near C-
4 (Fig. 3) established the absolute configuration at this position to be
R. Thus, C-6 would have an S configuration. Irradiation of H3-11 of
the S- and R-MTPA derivatives affected signal intensity of the
methoxyl and phenyl protons of the ester moiety in the NOEDIFF
experiments,indicatingthecloseproximityofthismethylgroup and
the ester unit. Consequently, C-10 had R configuration. The absolute
configurations of 1 were then assigned as 4R, 6S, 9S, 10R, and 14R.
Guignarenone B (2) was obtained as a colorless gum with
the molecular formula C22H34O5 from HREIMS. The 1H NMR data
(Table1)weresimilartothoseof1exceptthatsignalsoftwogeminal
maximum absorption band at a longer wavelength (lmax 286 nm)
than that in 1–3, indicating that it possessed a longer conjugated
chromophore. The absorption bands of two typical ketone carbonyl
groups of a 1,4-quinone at 1698 and 1680 cmÀ1, were observed in
the IR spectrum. The 1H NMR data of 4 were similar to those of 3. The
difference was the replacement of signals for H-4, H-6 and H2-5 in 3
byanolefinicprotonsignalofa trisubstituteddoublebond(
4. In addition, the methoxy protons ( 3.82) in 4 resonated at a lower
field. This olefinic proton was attributed to H-5 on the basis of its
HMBC correlations with C-1 ( 181.3), C-3 ( 152.0), C-4 ( 181.3)
and C-6 ( 159.4). The chemical shifts of C-5 ( 104.9) and C-6 as well
as the HMBC correlation from the methoxy protons ( 3.82) to C-6
d5.80)in
olefinic protons in 1 were replaced by a methyl signal (H3-16,
d
1.15)
d
in 2. The location of the methyl group at C-15 (
by the HMBC cross peaks from H3-16 to C-14 (
d
d
75.1) was confirmed
50.0), C-15 and C-17
d
d
d
(d
40.9). The other substituent at this carbon was identified as a
d
d
d
established a double bond at C5–C6 with the methoxyl group at C-6.
These data suggested that the oxymethine carbon, C-4, in 3 was
presumably oxidized to a ketone carbonyl carbon in 4. Signal
-0.24
OR
CH3
-0.08
O
-0.06
+0.01
enhancementofH3-11(d1.36)andH3-17(d1.68)uponirradiationof
-0.04
+0.11
-0.07
H-9 ( 2.00) established the relative configurations of the fused
d
-0.01
-0.01
-0.003
-0.01
-0.01
cyclopentane, identical to those of 1–3. As they were co-metabolites,
the absolute configurations of the fused cyclopentane in 4 were
proposed to be identical to those of 1–3. Thus, 4 was identified as an
oxidized derivative of 3.
H3C
-0.01
OCH3
-0.01
-.0.03
+0.01
H
+0.04
-0.03
O
CH3
-0.01
-0.01
-0.003
Compounds 1 and 3 in sufficient amount were evaluated for
cytotoxic activity against Vero and KB cell lines. Compound 1
displayed mild cytotoxic activity against both KB and Vero cell
1a: R = (S)-MTPA
1b: R = (R)-MTPA
lines with the IC50 values of 138.1 and 136.6
mM, respectively,
Fig. 3. Dd values [Dd (in ppm) = dS
À
d
R] obtained form MTPA esters 1a and 1b.
whereas 3 was inactive against both cell lines.

142
U. Sommart et al. / Phytochemistry Letters 5 (2012) 139–143
Table 2
1H and 13C NMR data for guignarenones C (3) and D (4) (CDCl3,
d ppm).
Position
3
4
dH (J in Hz)
dC
dH (J in Hz)
dC
1
–
194.9
105.9
167.6
65.8
–
–
181.3
113.8
152.0
181.3
–
2
–
–
3
–
–
4
4.26 m
–
4-OH
5
3.27 d (7.5)
–
2.40 ddd (13.8, 4.5, 3.9)
104.9
5.80 s
104.9
2.27 ddd (13.8, 6.6, 5.4)
6
7
8
3.72 dd (6.6, 3.9)
3.49 s
79.2
58.4
16.2
–
159.4
56.3
16.8
3.82s
2.35 m
2.12 m
1.97 m
–
2.53m
2.34m
9
43.3
87.7
22.4
37.5
2.00 m
43.2
88.3
22.7
37.3
10
11
12
–
1.35 s
1.36s
2.13 m
1.79 m
1.92 m
1.54 m
2.21 m
–
2.34m
1.84 ddd (14.5, 14.0, 7.0)
13
27.0
2.00 m
26.9
1.55m
14
15
16
49.0
145.5
111.2
2.24q (9.0)
–
49.1
145.2
111.5
4.74 brt (1.5)
4.65 brs
1.67 s
4.76 qn (1.5)
4.66 qn (1.5)
1.68s
17
19.3
19.2
3. Experimental
purified by silica gel CC using 30% EtOAc-light petroleum to afford
five subfractions. The second subfraction (35.9 mg) was subjected
to silica gel CC using the same method as fraction B2 to give 1
(12.6 mg). Compound 3 (5.7 mg) was obtained from the fourth
subfraction upon purification on silica gel CC eluted with 30%
EtOAc-light petroleum. Subfraction B4 (67.5 mg) was purified
using the same method as fraction B to give three subfractions.
Compounds 2 (1.3 mg) and 4 (1.1 mg) were obtained from the
second subfraction (30.9 mg) after purification by silica gel CC
3.1. General experimental procedures
Optical rotations were measured using
a JASCO P-1020
polarimeter. Ultraviolet (UV) spectra were measured in MeOH on
a SHIMADZU UV-160A spectrophotometer. Infrared spectra (IR)
wererecordedonaPerkinElmer783FTS165FT-IRspectrometer.1H-
and 13C NMR, along with 2D NMR spectra, were recorded on a 300 or
500 MHz Bruker FTNMR Ultra Shield spectrometer. Mass spectra
were obtained on a MAT 95 XL Mass Spectrometer (Thermo
Finnigan). Column chromatography (CC) was carried out on
Sephadex LH-20 or silica gel (Merck) type 100 (70–230 Mesh ASTM).
using
a gradient of EtOAc-light petroleum. Subfraction B5
(33.0 mg) was purified using the same method as the second
subfraction of B4 to afford four subfractions. The second
subfraction contained 5 (1.0 mg).
3.2. Fungal material
3.4. Guignarenone A (1)
The endophytic fungus G. bidwellii PSU-G11 was isolated from
the leaves of G. hombroniana, collected in Songkhla Province,
Thailand, in 2006. This fungus was deposited as PSU-G11 at the
Department of Microbiology, Faculty of Science, Prince of Songkla
University, and as BCC 35873 in the BIOTEC Culture Collection,
National Center for Genetic Engineering and Biotechnology,
Thailand.
Colorless gum; [
263 nm; CD (MeOH) lmax
nm; FT-IR (neat)
a
]
26 + 63 (c 0.76, acetone); UV
l
max(MeOH):
D
(
De): 218 (+8.2), 263 (+48.1), 301 (À9.8)
n
max: 3373, 1709 cmÀ1; 1H NMR (300 MHz, CDCl3)
and 13C NMR (75 MHz, CDCl3) spectra, see Table 1; HREIMS m/z
360.2301 [M]+ (calcd. for C22H32O4, 360.2301).
3.5. Guignarenone B (2)
This endophytic fungus did not produce any conidia or spores.
Thus, it was identified based on the analysis of the DNA sequences
of the internal transcribed spacer (ITS1-5.8S-ITS2) regions of its
ribosomal RNA gene. Its ITS sequence (GenBank accession no
HM049170) matched with four Guignardia sequences from
GenBank comprising Guignardia sp. (AB454311) and G. bidwellii
(AB454268, AB454276 and AB454313) with sequence identity of
93.1%. The endophytic fungus PSU-G11 was then identified as G.
bidwellii.
Colorless gum; [
264 nm; FT-IR (neat)
a
]
n
26 + 55 (c 0.76, acetone); UV
l
max(MeOH):
D
max: 3444, 1703 cmÀ1 1H NMR (500 MHz,
;
CDCl3) and 13C NMR (125 MHz, CDCl3) spectra, see Table 1;
HREIMS m/z 378.2406 [M]+ (calcd. for C22H34O5, 378.2406).
3.6. Guignarenone C (3)
Colorless gum; [
a
]
D
26 + 72 (c 0.76, acetone); UV
l
max(MeOH):
263 nm; CD (MeOH) lmax
(
De): 217 (+2.7), 262 (+60.6), 298
3.3. Extraction and isolation
(À14.9) nm; FT-IR (neat) nmax
: ;
3407, 1709 cmÀ1 1H NMR
(300 MHz, CDCl3) and 13C NMR (75 MHz, CDCl3) spectra, see Table
The broth EtOAc extract (750 mg) was prepared using the same
procedure as previously described (Sommart et al., 2008) and was
subjected to Sephadex LH-20 column chromatography (CC) eluted
with MeOH to give four fractions (A–D). Fraction B (430 mg) was
applied to silica gel CC eluted with a gradient of MeOH–CH2Cl2 to
give six subfractions (B1–B6). Subfraction B2 (170 mg) was further
2; HREIMS m/z 292.1664 [M]+ (calcd. for C17H24O4, 292.1675).
3.7. Guignarenone D (4)
Colorless gum; [
a
]
26 + 45 (c 0.76, acetone); UV
l
max(MeOH):
D
286 nm; FT-IR (neat)
n
max: 1698, 1680 cmÀ1 1H NMR (300 MHz,
;

U. Sommart et al. / Phytochemistry Letters 5 (2012) 139–143
143
CDCl3) and 13C NMR (75 MHz, CDCl3) spectra, see Table 2; HREIMS
m/z 288.1363 [M]+ (calcd. for C17H20O4, 288.1356).
of Songkla University, is gratefully acknowledged for partial
support.
References
3.8. (6S,9R)-Vomifoliol (5)
Ferreira, R.H.K., Heerklotz, J.A., Werner, C. WO 2002017937, 2002.
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Biotechnol. Bioeng. 65, 201–205.
Observed [
MeOH) (Yamano and Ito, 2005).
a] a]
27 + 201.0 (c 0.64, MeOH); [ 23 + 214.10 (c 0.64,
D D
Liebermann, B., Ellinger, R., Gunther, W., Ihn, W., Gallander, H., 1997. Tricycloal-
ternarenes produced by Alternaria alternata related to ACTG-toxins. Phyto-
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3.9. Preparation of MTPA esters of guignarenone A (1)
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To a solution of 1 (2.5 mg) in pyridine (100
mL) and CH2Cl2
(300 L) was added (R)-MTPACl (40 L). The reaction mixture was
m
m
then stirred at room temperature for four days. After removal of
the solvent, the 4-(S)-MTPA ester (1a, 4.30 mg) was obtained.
Compound 1 (2.5 mg) was treated with (S)-MTPACl under the same
conditions as 1a to yield the 4-(R)-MTPA ester (1b, 4.32 mg).
3.10. Cytotoxic assay
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displayed the IC50 values of 2.24 and 0.38
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Acknowledgements
This work was supported by the Bioresources Research
Network (BRN), National Center for Genetic Engineering and
Biotechnology. U. Sommart thanks the Royal Golden Jubilee Ph.D.
Program of the Thailand Research Fund (Grant No. PHD/0232/
2549) and the Center of Excellence for Innovation in Chemistry
(PERCH-CIC) for a scholarship. Finally, the Graduate School, Prince
Yuan, L., Zhao, P.-J., Ma, J., Li, G.-H., Shen, Y.-M., 2008. Tricycloalternarenes A–E: five
new mixed terpenoids from the endophytic fungal strain Alternaria alternata
Ly83. Helv. Chim. Acta 91, 1588–1594.