Poronitins A and B, 4-pyrone and 4-pyridone derivatives from the elephant dung fungus Poronia gigantea

Article abstract of DOI:10.1016/j.tetlet.2012.06.128

New 4-pyrone and 4-pyridone derivatives, poronitins A (1) and B (2), and a new isocoumarin, 3,4-dihydro-6,8-dimethoxy-4-hydroxy-4-methyl-3- methyleneisochromen-1-one (3), were isolated from cultures of the elephant dung fungus, Poronia gigantea. The structures were elucidated on the basis of the NMR and MS data. Poronitin A (1) and known (R)-5-methylmellein were detected in all cultures (4 strains) of P. gigantea, which suggested that these metabolites maybe useful as chemotaxonomic markers.

Full text of DOI:10.1016/j.tetlet.2012.06.128

Tetrahedron Letters 53 (2012) 4848–4851
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Poronitins A and B, 4-pyrone and 4-pyridone derivatives from the elephant
dung fungus Poronia gigantea
⇑
Masahiko Isaka , Somporn Palasarn, Panida Chinthanom, Jiraporn Thongtan, Malipan Sappan,
Sayanh Somrithipol
National Center for Genetic Engineering and Biotechnology (BIOTEC), Thailand Science Park, 113 Phaholyothin Road, 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:
New 4-pyrone and 4-pyridone derivatives, poronitins A (1) and B (2), and a new isocoumarin, 3,4-dihy-
dro-6,8-dimethoxy-4-hydroxy-4-methyl-3-methyleneisochromen-1-one (3), were isolated from cultures
of the elephant dung fungus, Poroniagigantea. The structures were elucidated on the basis of the NMR and
MS data. Poronitin A (1) and known (R)-5-methylmellein were detected in all cultures (4 strains) of P.
gigantea, which suggested that these metabolites maybe useful as chemotaxonomic markers.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 26 April 2012
Revised 13 June 2012
Accepted 27 June 2012
Available online 4 July 2012
Keywords:
Poronia gigantea
Coprophilous fungi
Elephant dung
Chemotaxonomy
Poronia (family: Xylariaceae) is an exclusive coprophilous genus
that is encountered on animal dung only. There have been several
reports of secondary metabolites from Poronia: punctatins (sesqui-
terpenes),3 punctaporonins (sesquiterpenes),4 and (+)-isoepoxy-
don5 from Poronia punctata, and piliformic acid6 from Poronia
piliformis. As part of our research program on novel bioactive com-
pounds from fungal sources in Thailand, we have investigated the
constituents of several coprophilous fungi isolated from elephant
dung samples, primarily due to the interest in this unique ecolog-
ical niche.1 In particular, we focused the chemical analysis on Poro-
nia gigantea, since twelve strains of this species, collected in
various locations in Thailand and deposited in the BIOTEC Culture
Collection, were all isolates from elephant dung samples. Also, in
the first taxonomic report of this species in 1914, the strain type
was isolated from elephant dung in India.7 Chemical studies on
cultures of four independent strains, BCC 2588, BCC 7588, BCC
25650, and BCC 31124,2 led to the isolation of new 4-pyrone and
4-pyridone derivatives, poronitins A (1) and B (2), and a new 3,4-
dihydro-3-methylene-isocoumarin 3.
compounds, (R)-5-methylmellein (4, 25 mg, 3.6 mg/L; ½a D26
ꢂ110,
ꢁ
c 0.51, CHCl3),8,9 5 (7.0 mg),9 and 6 (12 mg).9,10 Compounds 1
(1.3–9.0 mg/L) and 4 (11.2–32.9 mg/L) were also isolated from cul-
tures of three other strains, BCC 7588, BCC 25650, and BCC 31124.
Compound 2 was isolated only from BCC 7588 (4.0 mg, 1.3 mg/L).
5'
CH3
O
O
O
4
3
3'
2'
1'
16
5
H3C
N
H
8
14
4'
15
OH
2
6
R
7
O
1 R = O
2 R = NH
H3CO
O
OH O
8
8a
7
1
O
O
3
9
4
4a
6
H3CO
CH3
5
HO CH3
CH3
10
Poronia gigantea BCC 2588 was fermented in malt extract broth
(MEB, 28 ꢀ 250 mL) at 25 °C for 43 days under static conditions.
The EtOAc extract of the culture filtrate (900 mg) was passed
through a Sephadex LH-20 column (MeOH) and the fractions were
further purified by column chromatography on silica gel (EtOAc/
CH2Cl2) and by preparative HPLC (ODS column, MeCN/H2O) to fur-
nish 1 (2.7 mg, 0.4 mg/L) and 3 (11 mg), together with the known
3
4
OH
O
H3CO
H3CO
O
O
O
O
OH
CH3
O
RO
H3CO
H3CO
CH3
CH
HO
H3C
3
5
6
7 R = CH3
8 R = H
⇑
Corresponding author. Tel.: +66 25646700/3554; fax: +66 25646707.
E-mail address: isaka@biotec.or.th (M. Isaka).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.06.128

M. Isaka et al. / Tetrahedron Letters 53 (2012) 4848–4851
4849
Poronitin A (1) was isolated as a colorless solid. The molecular
O
O
O
formula of 1 was established as C20H23NO6 on the basis of the sodi-
ated quasi-molecular ion peak at m/z 396.1414 (calcd for
1' 16
4
N
H
C
20H23NO6Na, 396.1418) in the HRESI MS.11 The 1H and 13C NMR,
OH
O
O
15
DEPT135, and HMQC spectroscopic data revealed that 1 contained
six sp2 quaternary carbons, two sp2 methines, three trans olefins (J
values, 15.9, 15.3, and 15.2 Hz), an aliphatic methine, three meth-
ylenes, and two methyl groups (Table 1). In addition, the 1H NMR
spectrum showed resonances of two D2O-exchangeable protons
at dH 11.73 (s) and 12.19 (br s). The COSY correlations demon-
strated a linear chain from C-7 to C-14, composed of three trans
olefins (C-7/C-8, C-11/C-12, and C-13/C-14) and two methylenes
(C-9 and C-10). The presence of an isovaleroyl group (C-10–C-50)
was indicated by the COSY correlations and the HMBC correlation
from H2-20 to C-10 (dC 173.5). The 4-pyrone ring was deduced from
HMBC correlations of sp2 methine protons (H-2 and H-5) to sp2
quaternary carbons C-3, C-4, and C-6 (Fig. 1). HMBC correlations
from olefinic protons H-7 and H-8 to C-6, and the correlation from
H-5 to C-7 accomplished the connection of the linear chain to C-6.
The other side of the linear chain was terminated as a carboxylic
acid (dC 168.1, C-15), which was confirmed by the HMBC correla-
tions from H-13 and H-14 to the carboxyl carbon. The remaining
sp2 quaternary carbon at dC 161.4 (C-16) was attached to C-3, as
indicated by the intense HMBC correlation from H-2 and a weak
4J correlation from H-5. HMBC correlation from the downfield NH
(dH 11.73) to C-20 of the isovaleroyl group, and the molecular for-
mula (HRMS) required an imide linkage.
The molecular formula of poronitin B (2) was determined by
HRESI MS as C20H24N2O5.12 The 1H and 13C NMR spectroscopic data
showed close resemblance to 1. The significant differences of the
NMR data were the upfield shifts of H-2 (dH 8.41), C-2 (dC 144.3),
and C-6 (dC 147.5) when compared with 1 (H-2, dH 8.94; C-2, dC
163.5; C-6, dC 163.1). These differences indicated the replacement
of the pyrone oxygen atom in 1 with NH, hence, a 4-pyridone unit
for 2. HMBC correlations found for 2 were similar to those for 1.
Additionally, correlations from the NH (dH 13.09, s) to C-3 and
C-20 further confirmed the imide linkage.
O
1
2
O
O
N
H
OH
N
H
O
Figure 1. Key HMBC correlations present in compounds 1 and 2.
room temperature for 15 h led to a quantitative conversion into 2.
A pure sample of 2 was obtained simply by solvent removal in va-
cuo. A plausible mechanism to account for this transformation is
proposed in Scheme 1. At an early stage of the structure elucida-
tion, we also examined some other chemical transformations of
1. Poronitin A (1, 7.0 mg) was treated with conc. H2SO4 in MeOH
(1:9) (rt, 2 h) with the initial purpose to characterize the free car-
boxylic acid as a methyl ester and to remove the isovaleroyl group
from the main skeleton. Interestingly, the major reaction product
was purified by preparative HPLC and identified as a 3-formyl-2-
pyridone derivative 9 (3.0 mg, 53%)13 (Scheme 2).
A survey of the literature revealed several fungal 4-pyrone and
4-pyridone derivatives structurally related to 1 and 2 (Fig. 2). The
closest known compounds are microsphaerones A and B, isolated
from a sponge-derived fungus Microsphaeropsis sp.,14 differing in
the carboxylic acid chain and the imide acyl group structures.
The corresponding 4-pyridone, microsphaerone C, was later iso-
lated from an endophyte, Diaporthe phaseolorum.15 Himeic acids
A–C, isolated from a marine-derived Aspergillus sp., are side-chain
variants of microsphaerones wherein one of the diene double
bonds (corresponding to C-9/C-10 for 1) is hydrogenated.16 Other
common derivatives are benzyl-substituted carbonarone A,17
The structural relationship of 1 and 2 was confirmed by chem-
ical means. Treatment of 1 with 30% ammonia in DMSO-d6 (1:5) at
Table 1
NMR spectroscopic data for poronitin A (1) and poronitin B (2) in DMSO-d6
Position
Poronitin A (1)a
H Mult. (J in Hz)
8.94, s
Poronitin B (2)b,c
dC
Mult.
HMBC
dC
dH Mult. (J in Hz)
HMBC
2
3
4
5
6
7
8
9
10
11
12
13
163.5
118.8
178.2
113.9
163.1
122.1
141.8
31.8
CH
qC
qC
CH
qC
CH
CH
CH2
CH2
CH
CH
CH
CH
qC
3, 4, 6, 16
144.3
115.9
178.0
116.6
147.5
123.6
138.8
32.0
8.41, s
4, 6, 16
6.61, s
3, 6, 7, 16
6.54, s
3, 6, 7, 16
6.41, d (15.9)
6.77, dd (15.9, 6.7)
2.41, m
6, 9
6
6.31, d (16.1)
6.70, dd (16.1, 6.4)
2.37, m
5, 6, 9
6, 9
8
11, 12
12, 13
10, 11, 13, 14
15
7, 8, 10
8, 9, 11, 12
10, 12, 13
10, 13, 14
11, 15
31.4
2.37, m
31.7
2.35, m
142.9
129.5
144.7
121.1
168.1
161.4
6.23, dt (15.2, 6.4)
6.32, dd (15.2, 10.7)
7.15, dd (15.3, 10.7)
5.82, d (15.3)
12.19, br s
143.0
129.5
144.8
121.1
168.1
163.5
6.24, dt (15.3, 5.8)
6.31, dd (15.3, 10.4)
7.16, dd (15.4, 10.4)
5.81, d (15.4)
12.30, br s
14
12, 15
12, 15
15 (CO2H)
16
NH
10
qC
11.73, s
—
2.60 (d, 7.0)
2.08 (m)
0.92 (d, 6.7)
0.92 (d, 6.7)
20
13.09, s
3, 20
173.5
46.8
24.9
22.7
22.7
qC
CH2
CH
CH3
CH3
174.0
47.1
24.9
22.8
22.8
20
10, 30, 40, 50
20, 40, 50
20, 30, 50
20, 30, 40
2.61 (d, 7.0)
2.08 (m)
0.92 (d, 6.6)
0.92 (d, 6.6)
10, 30, 40, 50
40, 50
20, 30, 50
20, 30, 40
30
40
50
a
b
c
500 MHz for 1H, and 125 MHz for 13C.
400 MHz for 1H, and 100 MHz for 13C.
The second NH resonance for 2 was not observed.

4850
M. Isaka et al. / Tetrahedron Letters 53 (2012) 4848–4851
CH3
O
O
O
H
CH3
O
O
O
O
H3C
N
H
H3C
N
H
O
H2N
:
NH3
1
- H2O
CH3
O
O
O
CH3
O
O
O
2
H
H3C
N
H3C
N
H
H
N
H
O
H2N:
OH
Scheme 1. A plausible mechanism for the transformation of 1 into 2 in the presence of NH3.
The molecular formula of compound 3 was determined by
HRESI MS as C13H14O5.22 NMR spectroscopic data revealed that 3
contained six sp2 quaternary carbons, an exomethylene group (dC
92.3; dH 4.88 and 4.81), a pair of meta-coupled sp2 methines, an
oxy-quaternary carbon (dC 70.7), two methoxy groups, and a
methyl group (Table 2). A 3,4-dihydro-3-methylene-isocoumarin
was deduced on the basis of HMBC correlations. A meta-coupled
methine proton H-5 (dH 6.82, d, J = 1.9 Hz) showed HMBC correla-
tions to C-4, C-4a, C-6, and C-7, while the other methine H-7 (dH
6.43, d, J = 1.9 Hz) exhibited correlations to C-5, C-6, C-8, and C-
8a. In addition, these methines (H-5 and H-7) exhibited weak 4J
correlations to C-1 (dC 158.1). Two methoxy groups were attached
to a benzene ring as confirmed by the HMBC correlations from the
methyl protons at dH 3.92 (3H, s) and 3.90 (3H, s) to C-8 (dC 162.9)
and C-6 (dC 165.8), respectively. To the tertiary alcohol carbon (C-
4) was attached to a methyl group (CH3-10), which was revealed
by the HMBC correlations from H3-10 to C-3, C-4, and C-4a, and
the correlations from 4-OH to C-4 and C-10. NOESY correlations
further supported the planar structure: Ha-9/H3-10, H3-10/H-5,
H-5/6-OCH3, 6-OCH3/H-7, and H-7/8-OCH3. Compound 3 was
therefore identified as 3,4-dihydro-6,8-dimethoxy-4-hydroxy-4-
methyl-3-methyleneisochromen-1-one. This compound is closely
related to known compounds 7 (from Halorosellinia oceanica BCC
5149 and Leptosphaeria sp. KTC 727),23,24 and 8 (from Leptosphaeria
sp. KTC 727).24 Recently, the absolute configurations of 7 and 8,
isolated from Leptosphaeria sp. KTC 727, were determined to be
O
OH
conc. H2SO4
MeOH
1
O
HaN
OCH3
O
:
O
O
O
OH
- H2O
H
OCH3
N
H
O
9
Scheme 2. Transformation of 1 into 9 in concd H2SO4/MeOH.
aspernigrin A,18,19 and pestalamides A and B,20 most frequently iso-
lated from Aspergillus species.21 Although the co-occurrence of the
4-pyrone/4-pyridone from the same fermentation is a rare case,
they should be biogenetically closely related. The smooth transfor-
mation of 1 into 2, as described above (Scheme 1), strongly sug-
gested that the 4-pyridones were derived from the corresponding
4-pyrones. The conversion of the 4-pyrone 1 into the 2-pyridone
9 under acidic conditions (Scheme 2) suggested that carbonarone
B was probably produced by structural rearrangements of the
co-metabolite carbonarone A.17
CH3
O
O
O
O
HO
N
H
O
OH
O
microsphaerone A
O
O
R
O
O
H2N
H2N
OH
R
O
R = O : carbonarone A
R = NH : aspernigrin A
R = O : microsphaerone B
R = NH : microsphaerone C
O
O
OH
CH3
O
O
O
HO
H
N
H
O
N
H
R
R = O : pestalamide A
R = NH : pestalamide B
carbonarone B
Figure 2. 4-Pyridone and 4-pyrone derivatives structurally related to poronitins A and B.

M. Isaka et al. / Tetrahedron Letters 53 (2012) 4848–4851
4851
Table 2
Hywel-Jones, and the living culture was deposited in the BIOTEC Culture
Collection (BCC) on March 31, 2000. Strain BCC 7588 was found in Khao Yai
National Park, Nakhon Nayok Province, by one of the authors (S.S.), and it was
deposited on October 28, 2000. Strain BCC 25650 was found in Khao Yai
National Park, Nakhon Nayok Province, by Ms. Thitiya Boonpratuang, and it
was deposited on June 6, 2007. Strain BCC 31124 was found in UmPhang
wildlife sanctuary, Tak Province, by Mr. Prasert Srikitikulchai, and it was
deposited on November 7, 2008.
NMR spectroscopic data for 3 in CDCl3 (400 MHz for 1H, and 100 MHz for 13C)
Position
dC
Mult.
dH, Mult. (J in Hz)
HMBC
1
3
4
4a
5
6
7
8
8a
9
10
4-OH
6-OCH3
8-OCH3
158.1
159.4
70.7
qC
qC
qC
150.4
99.1
165.8
98.5
162.9
103.3
92.3
qC
CH
qC
CH
qC
qC
3. (a) Anderson, J. R.; Briant, C. E.; Edwards, R. L.; Mabelis, R. P.; Poyser, J. P.;
Spencer, H.; Whalley, A. J. S. J. Chem. Soc., Chem. Commun. 1984, 405–406; (b)
Anderson, J. R.; Edwards, R. L.; Freer, A. A.; Mabelis, R. P.; Poyser, J. P.; Spencer,
H.; Whalley, A. J. S. J. Chem. Soc., Chem. Commun. 1984, 917–919; (c) Poyser, J.
P.; Edwards, R. L.; Anderson, J. R.; Hursthouse, M. B.; Walker, N. P.; Sherdrick, G.
M.; Whalley, A. J. S. J. Antibiot. 1986, 39, 167–169.
4. (a) Anderson, J. R.; Edwards, R. L.; Poyser, J. P.; Whalley, A. J. S. J. Chem. Soc.,
Perkin Trans. 1 1988, 823–831; (b) Edwards, R. L.; Raymond, L.; Maitland, D. J.;
Poyser, J. P.; Whalley, A. J. S. J. Chem. Soc., Perkin Trans. 1 1989, 1939–1941.
5. Gloer, J. B.; Truckenbrod, S. M. Appl. Environ. Microbiol. 1988, 54, 861–864.
6. Culceth, H.; Fuchser, J.; Moss, S. J.; Nieschalk, J.; O’Hagan, D. Tetrahedron Lett.
1998, 39, 1949–1952.
6.82, d (1.9)
6.43, d (1.9)
1, 4, 4a, 6, 7, 8a
5, 6, 8, 8a
CH2
CH3
4.88, s; 4.81, s
1.65, s
2.30, s
3.90, s
3.92, s
3, 4
3, 4, 4a
4, 10
6
30.5
55.7
56.3
CH3
CH3
8
7. Saccardo, P. A. Ann. Mycologici 1914, 12, 282–314.
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9. Sumarah, M. W.; Puniani, E.; Blackwell, B. A.; Miller, J. D. J. Nat. Prod. 2008, 71,
1393–1398.
4R.25 The optical rotation of 2, ½a 2D5
ꢁ
+274 (c 0.15, CHCl3), was the
same sign as (R)-7 [Lit. ½a D27
ꢁ
+96 (c 0.11, CHCl3)]25 and (R)-8 [Lit.
10. The structure of
6 was confirmed by conversion into the methyl ester
derivative (MeI, K2CO3, DMF).9
½
a 2D7 +161 (c 0.19, CHCl3)],25 which suggested the 4R-configuration.
The CD spectrum of 2 showed a similar pattern with the literature
ꢁ
11. Poronitin (1): Colorless solid; mp 221ꢂ223 °C; UV (MeOH) kmax (log
e) 251
(3.61) nm; IR (ATR) mmax 1684, 1656, 1623, 1501, 1410, 1266 cmꢂ1; HRESI MS
m/z 396.1414 [M+Na]+ (calcd for C20H23NO6Na, 396.1418); 1H NMR (500 MHz,
DMSO-d6) and 13C NMR (125 MHz, DMSO-d6) data, see Table 1.
data for (R)-7 and (R)-8.24,25
Poronitin A (1) and B (2) possess a polyene acid chain being dif-
ferent from previously reported 4-pyrone/4-pyridone derivatives.
The polyene conjugation is intercepted by saturation at C-9/C-10.
No side-chain variant, such as 9,10-dehydro-1, was found in any
of the strains of Poronia gigantea. The evidence of production of
compounds 1 and 4 by all the analyzed strains is also noteworthy.
These four strains were collected from three different locations in
Thailand with distances of >400 km from each other.2 The present
results demonstrate the uniqueness and the characteristics of the
secondary metabolites produced by Poronia gigantea, and suggest
that compounds 1 and 4 maybe useful as chemotaxonomic mark-
ers for this species. In these contexts, we are currently planning
further systematic chemical analyses.
12. Poronitin B (2): Colorless solid; mp 234ꢂ236 °C; UV (MeOH) kmax (log
e) 255
(3.84) nm; IR (ATR) m
max 1673, 1619, 1501, 1199 cmꢂ1; HRESI MS m/z 395.1588
[M+Na]+ (calcd for C20H24N2O5Na, 395.1577); 1H NMR (400 MHz, DMSO-d6)
and 13C NMR (100 MHz, DMSO-d6) data, see Table 1
13. Compound 9: Colorless solid; UV (MeCN/H2O = 70:30) kmax 261, 360 nm; IR
(ATR) mmax 1714, 1667, 1646, 1620, 1254 cmꢂ1
; HRESI MS m/z 326.0996
[M+Na]+ (calcd for C16H17NO5Na, 326.0999); 1H NMR (400 MHz, CDCl3) and 13
NMR (100 MHz, CDCl3) data, see Supplementary data.
C
14. Wang, C.-Y.; Wang, B.-G.; Brauers, G.; Guan, H.-S.; Proksch, P.; Ebel, R. J. Nat.
Prod. 2002, 65, 772–775.
15. Sowemimo, A. A.; Edrada-Ebel, R.; Ebel, R.; Proksch, P.; Omobuwajo, O. R.;
Adesanya, S. A. Nat. Prod. Commun. 2008, 3, 1217–1222.
16. Tsukamoto, S.; Hirota, H.; Imachi, M.; Fujimoto, M.; Onuki, H.; Ohta, T.;
Yokosawa, H. Bioorg. Med. Chem. Lett. 2005, 15, 191–194.
17. Zhang, Y.; Zhu, T.; Fang, Y.; Liu, H.; Gu, Q.; Zhu, W. J. Antibiot. 2007, 60, 153–
157.
18. Hiort, J.; Maksimenka, K.; Reichert, M.; Perovic´-Ottostadt, S.; Lin, W. H.; Wray,
V.; Steube, K.; Schaumann, K.; Weber, H.; Proksch, P.; Ebel, R.; Müller, W. E. G.;
Bringmann, G. J. Nat. Prod. 2004, 67, 1532–1543.
Acknowledgments
19. Ye, Y. H.; Zhu, H. L.; Song, Y. C.; Liu, J. Y.; Tan, R. X. J. Nat. Prod. 2005, 68, 1106–
1108.
20. Ding, G.; Jiang, L.; Guo, L.; Chen, X.; Zhang, H.; Che, Y. J. Nat. Prod. 2008, 71,
1861–1865.
21. Henrikson, J. C.; Ellis, T. K.; King, J. B.; Cichewicz, R. H. J. Nat. Prod. 2011, 74,
1959–1964.
Financial support from the Bioresources Research Network,
National Center for Genetic Engineering and Biotechnology
(BIOTEC), is gratefully acknowledged.
22. 3,4-Dihydro-6,8-dimethoxy-4-hydroxy-4-methyl-3-methyleneisochromen-1-
one (3): Colorless solid; mp 138ꢂ139 °C; ½a D25
ꢁ
+274 (c 0.15, CHCl3); UV (MeOH)
Supplementary data
kmax (log e) 221 (4.11), 265 (4.01), 301 (3.83) nm; CD (MeOH) kmax (De) 268
(+13.9), 227 (ꢂ10.0), 206 (+17.3) nm; IR (ATR) mmax 3443, 1724, 1663, 1603,
1220, 1075, 1038 cmꢂ1; HRESI MS m/z 251.0910 [M+H]+ (calcd for C13H15O5,
251.0914); 1H NMR (400 MHz, CDCl3) and 13C NMR (100 MHz, CDCl3) data, see
Table 2
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.06.
128.
23. Chinworrungsee, M.; Kittakoop, P.; Isaka, M.; Chanphen, R.; Tanticharoen, M.;
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References and notes
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Tanticharoen, M., Hyde, K. D., Eds.; BIOTEC: Thailand, 2004; pp 119–128.
2. Poronia gigantea strain BCC 2588 was isolated from an elephant dung sample
collected in Kaen Krachan National Park, Phet Buri Province, by Dr. Nigel L.
25. Tayone, W. C.; Kanamaru, S.; Honda, M.; Tanaka, K.; Nehira, T.; Hashimoto, M.
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