Maximizing chemical diversity of fungal metabolites: Biogenetically related heptaketides of the endolichenic fungus Corynespora sp. (1)

Article abstract of DOI:10.1021/np900684v

In an attempt to explore the biosynthetic potential of the endolichenic fungus Corynespora sp. BA-10763, its metabolite profiles under several culture conditions were investigated. When cultured in potato dextrose agar, it produced three new heptaketides, 9-O-methylscytalol A (1), 7-desmethylherbarin (2), and 8-hydroxyherbarin (3), together with biogenetically related metabolites scytalol A (4), 8-O-methylfusarubin (5), scorpinone (6), and 8-O-methylbostrycoidin (7), which are new to this organism, and herbarin (8), a metabolite previously encountered in this fungal strain. The use of malt extract agar as the culture medium led to the isolation of 6, 8, 1-hydroxydehydroherbarin (9), and 1-methoxydehydroherbarin (10), which was found to be an artifact formed during the extraction of the culture medium with methanol. The structures of all new compounds were determined by interpretation of their spectroscopic data and chemical interconversions.

Full text of DOI:10.1021/np900684v

1156
J. Nat. Prod. 2010, 73, 1156–1159
Maximizing Chemical Diversity of Fungal Metabolites: Biogenetically Related Heptaketides of
the Endolichenic Fungus Corynespora sp.1
E. M. Kithsiri Wijeratne,† Bharat P. Bashyal,† Malkanthi K. Gunatilaka,§ A. Elizabeth Arnold,§ and A. A. Leslie Gunatilaka*,†
SW Center for Natural Products Research and Commercialization, Office of Arid Lands Studies, College of Agriculture and Life Sciences,
UniVersity of Arizona, 250 E. Valencia Road, Tucson, Arizona 85706-6800, and DiVision of Plant Pathology and Microbiology, School of Plant
Sciences, College of Agriculture and Life Sciences, UniVersity of Arizona, Tucson, Arizona 85721-0036
ReceiVed NoVember 4, 2009
In an attempt to explore the biosynthetic potential of the endolichenic fungus Corynespora sp. BA-10763, its metabolite
profiles under several culture conditions were investigated. When cultured in potato dextrose agar, it produced three
new heptaketides, 9-O-methylscytalol A (1), 7-desmethylherbarin (2), and 8-hydroxyherbarin (3), together with
biogenetically related metabolites scytalol A (4), 8-O-methylfusarubin (5), scorpinone (6), and 8-O-methylbostrycoidin
(7), which are new to this organism, and herbarin (8), a metabolite previously encountered in this fungal strain. The use
of malt extract agar as the culture medium led to the isolation of 6, 8, 1-hydroxydehydroherbarin (9), and
1-methoxydehydroherbarin (10), which was found to be an artifact formed during the extraction of the culture medium
with methanol. The structures of all new compounds were determined by interpretation of their spectroscopic data and
chemical interconversions.
Endosymbiotic microorganisms represent a largely untapped
resource of small-molecule natural products.2 This is especially true
for endolichenic fungi,3 as to date only two reports have described
their secondary metabolites.4,5 This, combined with the potential
to produce a variety of new metabolites from a single strain by
systematic alteration of its cultivation parameters,6 use of elicitors
or enzyme inhibitors to induce or inhibit certain biosynthetic and/
or signal transduction pathways,7 and the feeding of small-molecule
alternative precursors,8 provides new opportunities to maximize
chemical diversity of their metabolites. The approach involving
alteration of culture conditions has been used to release the chemical
diversity of a number of soil-borne fungi and actinomycetes9 and
a fungus of marine origin.10 Recent success in maximizing chemical
diversity of metabolites of plant-associated fungal strains11 prompted
us to investigate the effect of different culture conditions on the
production of metabolites by the endolichenic fungus Corynespora
sp. BA-10763, isolated from the cavern beard lichen, Usnea
caVernosa (Parmeliaceae).4 The genus Corynespora contains over
100 described species of primarily plant-associated fungi with host
species including phylogenetically diverse monocotyledonous and
dicotyledonous angiosperms as well as a small number of non-
flowering vascular plants.12 Known to grow asymptomatically under
some conditions and in some hosts, several host-specific strains of
Corynespora spp. have been explored as agents for biological
control of invasive plants.13 The type species for the genus, C.
cassiicola, is a necrotrophic fungus that has been reported from
more than 70 host plants including economically important crops
such as rubber, cotton, and soybean.14 Only a few reports have
appeared on the chemistry of Corynespora sp. An endophytic strain,
C. cassiicola L36, isolated from Lindenbergia philippensis has been
reported to contain two novel depsidones, corynesidones A and B,
and a diaryl ether, corynether.15 Chemical investigation of an EtOAc
extract of Corynespora sp. BA-10763 derived from the liquid
culture medium, potato dextrose broth (PDB), has led to the
isolation and characterization of herbarin (8), 1-hydroxydehydro-
herbarin (9), and corynesporol (11).4 In an attempt to explore the
biosynthetic potential of this endolichenic fungus, we have inves-
tigated the effect of different culture conditions on the production
of metabolites, and in this paper we report the isolation and structure
elucidation of seven additional, but biosynthetically related hepta-
ketides, 1-7, of which 1-3 are new natural products. 1-Methoxy-
dehydroherbarin (10) encountered in the extract derived from a malt
extract agar (MEA) culture was shown to be an artifact formed
from 9.
Fractionation of the EtOAc extract of a potato dextrose agar
(PDA) culture of Corynespora sp. BA-10763 involving gel
permeation and silica gel column chromatography followed by
normal- and reversed-phase preparative TLC yielded metabolites
1-8. Compound 1 was obtained as an off-white solid that analyzed
for C16H20O6 by a combination of HRFABMS, 13C NMR, and
HSQC data and indicated the molecule to have seven degrees of
unsaturation. Its IR spectrum had absorption bands at 3411 and
1658 cm-1, indicating the presence of OH and R,ꢀ-unsaturated CO
groups. The 1H NMR spectrum of 1 indicated the presence of two
meta-coupled aromatic protons (δ 6.87 and 6.37), a proton attached
to an oxygenated carbon (δ 4.41), two geminally coupled protons
attached to an oxygenated carbon (δ 4.12 and 3.96), two OCH3
groups (δ 3.85 and 3.84), four protons attached to sp3 carbons (δ
2.39-2.28, m), and a CH3 group attached to a quaternary carbon
(δ 1.46). The 13C NMR spectrum of 1, when analyzed in
combination with the HSQC data, showed the presence of a
conjugated ketone carbonyl (δ 194.2), six aromatic carbons, of
which two are oxygenated (δ 164.6 and 162.2) and two are
protonated (δ 102.2 and 98.1), one dioxygenated quaternary carbon
(δ 95.1), one oxymethine carbon (δ 73.0), two OCH3 carbons (δ
55.8 and 55.5), two methylene carbons (δ 59.9 and 38.3), of which
* To whom correspondence should be addressed. Tel: (520) 741-1691.
Fax: (520) 741-0113. E-mail: leslieg@ag.arizona.edu.
† SW Center for Natural Products Research and Commercialization.
§ Division of Plant Pathology and Microbiology, School of Plant
Sciences.
10.1021/np900684v  2010 American Chemical Society and American Society of Pharmacognosy
Published on Web 06/03/2010

Notes
Journal of Natural Products, 2010, Vol. 73, No. 6 1157
6.71, J ) 2.5 Hz), two 1H singlets (δ 6.62 and 6.04), three OCH3
groups (δ 3.94, 3.93, and 3.57), and a CH3 group on an olefinic
carbon (δ 2.11). These data closely resembled those for 1-hydroxy-
dehydroherbarin (9),4 the major difference being due to the presence
of an additional OCH3 group in 10. The chemical shift (δ 3.57) of
the third OCH3 group showed it to be attached to an sp3 carbon
and was therefore placed at C-1. Methylation (Me2SO4/K2CO3/
acetone) of 9 afforded 10, confirming the structure of 10 as
1-methoxydehydroherbarin. The presence of 9 and 10 in the same
extract and the use of MeOH for extraction of the fungal culture
suggested a possible artifactual origin of 10 from 9. Although 9
failed to yield 10 on stirring with MeOH overnight, when MeOH
was replaced with n-BuOH in the extraction process, 10 was found
to be absent in the resulting extract, suggesting that this compound
is an artifact formed from 9 during the extraction of culture medium
with MeOH. However, it is noteworthy that 1-methoxy-9-demeth-
yldehydroherbarin (ascomycone A) has recently been reported as
a genuine metabolite of an unidentified saprophytic ascomycete.20
The ability of the endolichenic fungus Corynespora sp. BA-
10763 to produce new secondary metabolites when grown in
different culture media provides additional support for the notion
that manipulation of culture conditions of endosymbiotic fungi is
a promising approach for the expression of certain silent biosyn-
thetic pathways.6,9-11 Interestingly, all the isolable compounds
encountered were of heptaketide origin and biogenetically related
to each other,21 with differences only in hydroxylation, O-
methylation, and substitution of a nitrogen atom for an oxygen atom
in the O-heterocyclic ring. In addition, the yield of herbarin (8)
was found to be significantly higher when this fungus was cultured
in potato dextrose agar (8.3% of extract weight) compared with
potato dextrose broth (1.7% of extract weight). It is also noteworthy
that 2-azaanthraquinones, scorpinone (6), and 8-O-methylbostry-
coidin (7) are produced in solid media (PDA and MEA), but not
in the liquid medium (PDB) used. This is not surprising, as previous
studies have shown the production of bostrycoidin by Fusarium
solani to be sensitive to the carbon to nitrogen ratio and pH of the
culture conditions.22 We have previously reported the cancer cell
migration inhibitory activity of dehydroherbarin obtained from
herbarin (8) at a noncytotoxic concentration of 5 µM.4 When tested
in this assay and a cancer cell proliferation inhibition (cytotoxicity)
assay using the MTT method,23 compounds 1-10 showed no
significant activity at 5 µM.
Figure 1. Selected HMBC correlations for 3.
one is oxygenated, two methine carbons (δ 47.5 and 40.8), and a
methyl carbon (δ 29.9). The spectroscopic data of this compound
are similar to those of 4, a metabolite occurring in the same extract
(see later) and identified as scytalol A (4). Scytalol A (4), a
modulator of melanin biosynthesis, has previously been reported
from Scytalidium sp. 36-93.16 Methylation of 4 with Me2SO4/
K2CO3/acetone afforded the monomethyl derivative with spectro-
scopic characteristics identical with those of 1, confirming its
structure as 9-O-methylscytalol A.
The molecular formula of 2 was determined as C15H14O6 from
its HRFABMS and 13C NMR data and indicated the molecule to
have nine degrees of unsaturation. Its UV spectrum exhibited
maxima at 445 and 427 nm, characteristic of a pyranonaphtho-
quinone,17 and its IR spectrum showed absorption bands at 3480
and 1656 cm-1, indicating the presence of OH and quinone CO
1
functions. The H NMR data of 2 indicated it to be structurally
related to herbarin (8)4 except for the absence of one of the two
O-methyl groups in 2. Methylation of 2 with CH3I/K2CO3/acetone
afforded its monomethyl derivative, identified as 8, indicating 2 to
contain a phenolic OH group at either C-7 or C-9. Its ability to
undergo methylation under mild conditions (CH3I/K2CO3/acetone/
25 °C) showed the OH in 2 to be located at C-7. Thus, 2 was
identified as 7-desmethylherbarin.
Metabolite 3, obtained as an orange solid, was determined to
have the molecular formula C16H16O7 by a combination of its
HRFABMS, 13C NMR, and HSQC data and indicated the molecule
to have nine degrees of unsaturation. Its UV spectrum showed
characteristic maxima for a pyranonaphthoquinone,17 and its IR
spectrum had absorption bands at 3433 and 1654 cm-1, indicating
the presence of OH and quinone CO functions. The 1H NMR
spectrum of 3 indicated the presence of an aromatic proton (δ 7.40),
two protons attached to an oxygenated carbon (δ 4.64), two OCH3
groups (δ 3.98 and 3.85), two geminally coupled protons (δ 2.77
and 2.48), and a CH3 group attached to a quaternary carbon (δ
1.54). The 13C NMR spectrum of 3 when analyzed in combination
with HSQC data showed the presence of two quinone carbonyls
(δ 182.9 and 182.1), eight aromatic carbons, of which three are
oxygenated (δ 151.1, 147.0, and 144.8) and one is protonated (δ
105.9), one dioxygenated carbon (δ 94.1), two OCH3 carbons (δ
61.4 and 58.0), two methylene carbons, of which one is oxygenated
(δ 56.5), and a methyl carbon (δ 28.8). These data showed close
resemblance to those of herbarin (8)4 except for the presence of an
additional phenolic OH in 3 at C-6 or C-8. In the HMBC spectrum
of 3 (Figure 1) the aromatic proton at δ 7.40 showed a correlation
with the carbonyl carbon at δC 182.9 (C-5), placing this proton at
C-6. It was thus identified as 8-hydroxyherbarin (3).
Experimental Section
General Experimental Procedures. Melting points were determined
with an Electrothermal melting point apparatus. Optical rotations were
measured with a JASCO Dip-370 digital polarimeter using CHCl3 or
MeOH as solvent. UV spectra were recorded on a Shimadzu UV-1601
UV-vis spectrophotometer. IR spectra were recorded on a Shimadzu
FTIR-8300 spectrometer using samples prepared in KBr discs. 1D and
2D NMR spectra were recorded in CDCl3 or acetone-d6 with a Bruker
1
DRX-500 instrument at 500 MHz for H NMR and 125 MHz for 13C
NMR using residual CHCl3 or acetone resonances as internal references.
Low-resolution and high-resolution MS were recorded on Shimadzu
LCMS-QP8000R and JEOL HX110A spectrometers, respectively.
LRP-2 Whatman (catalog no. 4776-001) was used for reversed-phase
(RP) column chromatography. RP-TLC separations were performed
on Merck RP-18 F254S precoated aluminum sheets.
Culturing and Isolation of Metabolites. For secondary metabolite
isolation, the fungus was cultured in 20 T-flasks (800 mL), each
containing 135 mL of PDA coated on five sides of the flasks,
maximizing the surface area for fungal growth (total surface area/flask
ca. 460 cm2). After incubation for 28 days at 28 °C, MeOH (200 mL/
T-flask) was added and the flasks were shaken overnight at 25 °C; the
resulting extract was filtered through Whatman No. 1 filter paper and
a layer of Celite 545. The filtrate was concentrated to ca. 25% of its
original volume by evaporation under reduced pressure and extracted
with EtOAc (3 × 500 mL). The combined organic extracts were
evaporated under reduced pressure to afford the EtOAc extract as a
dark brown solid (1.5 g). The majority (1.49 g) of this was subjected
The remaining metabolites isolated were identified as scytalol
A (4),16 8-O-methylfusarubrin (5),18 scorpinone (6),19 8-O-meth-
ylbostrycoidin (7),18 and herbarin (8)4,17 by comparison of their
experimental and reported physical (mp, UV, MS, and NMR) data.
Separation of an EtOAc extract obtained from the same organism,
cultured in 2% malt extract agar for 14 days, employing gel
permeation and silica gel column chromatography followed by
reversed-phase preparative TLC, yielded scorpinone (6),19 herbarin
(8),4,17 1-hydroxydehydroherbarin (9),4 and 10. The molecular
formula of 10 was determined as C17H16O6 from its HRMS data
and indicated the molecule to have 10 degrees of unsaturation. Its
UV spectrum exhibited maxima at 446 and 422 nm characteristic
of a pyranonaphthoquinone,17 and the H NMR spectrum showed
1
the presence of two meta-coupled aromatic protons (δ 7.26 and

1158 Journal of Natural Products, 2010, Vol. 73, No. 6
Notes
to gel-permeation chromatography over Sephadex LH-20 (50.0 g) made
up in hexanes and eluted with hexanes followed by hexanes-CH2Cl2
(2:1), hexanes-CH2Cl2 (1:1), hexanes-CH2Cl2 (1:2), CH2Cl2,
CH2Cl2-acetone (3:2), CH2Cl2-acetone (1:4), CH2Cl2-MeOH (1:1),
and finally MeOH. Fifteen fractions (60 mL each) were collected and
combined, based on their TLC profiles, to obtain six combined fractions
[F1 (21.8 mg), F2 (22.5 mg), F3-F5 (86.1 mg), F6-F9 (231.1 mg),
F10-F13 (692.6 mg), and F14-F15 (361.3 mg)]. A portion (13.0 mg) of
combined fraction F6-F9 was separated by preparative TLC [eluant:
hexanes-EtOAc (1:9)] to give 6 (5.8 mg, Rf 0.5) and 7 (1.6 mg, Rf
0.3). Combined fraction F10-F13 (300 mg) was chromatographed over
a column of silica gel (10 g) made up in CH2Cl2 and eluted with CH2Cl2
containing increasing amounts of MeOH. A total of 110 fractions (7.5
mL each) were collected, and fractions having similar TLC patterns
were combined to give 10 fractions [A (4.3 mg), B (5.9 mg), C (3.7
mg), D (196.9 mg), E (20.4 mg), F (2.4 mg), G (15.2 mg), H (7.4 mg),
I (2.0 mg), and J (6.2 mg)]. Fraction D (195 mg) was subjected to
column chromatography over LRP-2 (10.0 g) made up in MeOH-H2O
(3:2) and eluted with MeOH-H2O (3:2) followed by MeOH. The first
few fractions from this column were combined to give 8 (33.7 mg),
and the rest of the fractions were combined and subjected to repeated
column chromatography over LRP-2 using CH3CN-H2O (3:7) as eluant
to give additional quantities of 6 (23.8 mg) and 8 (90.2 mg). Fraction
G was further purified by preparative TLC [eluant: i-PrOH-CH2Cl2
(6:94)] to give 5 (11.8 mg, Rf 0.5). A portion (360 mg) of combined
fraction F14-F15 from the first column was chromatographed over a
column of silica gel (25 g) made up in CH2Cl2 and eluted with CH2Cl2
containing increasing amounts of MeOH. A total of 117 fractions (7.0
mL each) were collected, and fractions having similar TLC patterns
were combined to give 10 fractions [K (6.3 mg), L (44.0 mg), M (80.7
mg), N (29.2 mg), O (15.6 mg), P (21.0 mg), Q (2.2 mg), R (5.4 mg),
S (58.5 mg), and T (14.2 mg)]. Fraction O (15.0 mg) was separated on
reversed-phase preparative TLC [eluant: CH3CN-H2O (2:3)] to give
3 (6.7 mg, Rf 0.4). Purification of fraction P (20.0 mg) by silica gel
preparative TLC [eluant: i-PrOH-CH2Cl2 (5:95)] followed by reversed-
phase preparative TLC [eluant: CH3CN-H2O (3:7)] afforded 2 (1.6
mg, Rf 0.5) and 4 (4.5 mg, Rf 0.4). A portion (30 mg) of fraction S was
purified by reversed-phase preparative TLC [eluant: CH3CN-H2O (1:
4)] to yield 1 (20.0 mg, Rf 0.5).
3.98 (3H, s, OCH3), 3.85 (3H, s, OCH3), 2.77 (1H, ddd, J ) 18.7, 2.4,
1.6 Hz, H-4a), 2.48 (1H, dt, J ) 18.7, 3.5 Hz, H-4b), 1.54 (3H, s,
CH3-3); 13C NMR (125 MHz, CDCl3) δ 182.9 (C, C-5), 182.1 (C, C-10),
151.1 (C, C-7), 147.0 (C, C-9), 144.8 (C, C-8), 141.7 (C, C-10a), 137.9
(C, C-4a), 125.6 (C, C-5a), 118.7 (C, C-9a), 105.9 (CH, C-6), 94.1 (C,
C-3), 61.4 (CH3, OCH3-9), 58.0 (CH3, OCH3-7), 56.5 (CH2, C-1), 31.9
(CH2, C-4), 28.8 (CH3, CH3-3); HRFABMS m/z 319.0819 [M - 1]-
(calcd for C16H15O7, 319.0823).
Scytalol A (4): white solid (CH2Cl2-hexanes); mp 166-168 °C
(lit.16 165-169 °C); [R]2D5 +86 (c 1.0, MeOH) [lit.16 +89 (c 0.9,
MeOH)]; 1H NMR and MS data were consistent with reported data.16
Methylation of Scytalol A (4). To a solution of 4 (2 mg) in acetone
(0.2 mL) were added Me2SO4 (10 µL) and K2CO3 (10 mg), and the
mixture was stirred at 80 °C. After 2 h the reaction mixture was filtered,
the filtrate evaporated under reduced pressure, and the product purified
by preparative TLC (8% i-PrOH in CH2Cl2) to afford a product (1.35
mg) that was found to be identical (TLC, [R]D, LC-MS, and 1H NMR)
with 9-O-methylscytalol A (1) obtained above.
8-O-Methylfusarubin (5): red solid; mp 139-140 °C (lit.18a
1
138-139 °C); H NMR and MS data were consistent with reported
data.18
Scorpinone (6): yellow solid (CH2Cl2-hexanes); mp 294-296 °C
(lit.19 295 °C); 1H NMR, 13C NMR, and MS data were consistent with
reported data.19
8-O-Methylbostrycoidin (7): maroon solid (CH2Cl2-hexanes); mp
213-215 °C (lit.18a 215-216 °C); H NMR, 13C NMR, and MS data
1
were consistent with reported data.18
Herbarin (8): yellow solid (CH2Cl2-hexanes); mp 191-193 °C
(lit.4 190-192 °C); 1H NMR and MS data were consistent with reported
data.4,17
Isolation of Metabolites of Corynespora sp. BA-10763 Cultured
in 2% MEA. The fungal strain was cultured in 20 T-flasks (800 mL),
each containing 135 mL of MEA coated on five sides of the flasks
(total surface area/flask ca. 460 cm2). After incubation for 14 days at
28 °C, cultures were processed as for PDA (see above) to afford the
EtOAc extract as a dark brown solid (144 mg). The majority (143 mg)
of this extract was subjected to column chromatography over silica
gel (10 g) made up in CH2Cl2 and eluted with CH2Cl2 containing
increasing amounts of MeOH followed by 100% MeOH. Fifty-six
fractions (7 mL each) were collected, and fractions having similar TLC
patterns were combined to give 12 major fractions (F1-F12). Fraction
2 (F2) was purified by reversed-phase preparative TLC [eluant:
CH3CN-H2O (3:2)] to give 10 (1.4 mg, Rf 0.6). The major fraction
(F6) was separated by reversed-phase preparative TLC [eluant:
CH3CN-H2O (3:2)] to give an additional quantity (1.8 mg) of 10 (Rf
0.4) together with 6 (1.6 mg, Rf 0.3), 8 (6.2 mg, Rf 0.8), and 9 (17.8
mg, Rf 0.7). Fraction 7 (F7) was purified by reversed-phase preparative
TLC [eluant: CH3CN-H2O (3:2)] to give an additional amount of 9
(16.5 mg).
9-O-Methylscytalol A (1): off-white solid (CH2Cl2-hexanes); mp
172-174 °C; [R]2D5 +92 (c 1.1, MeOH); UV (EtOH) λmax (log ε) 309
(3.64), 276 (4.11), 231 (4.10) nm; IR νmax 3411, 1658, 1598, 1569,
1456, 1326, 1218, 1203, 1161, 1051, 1020 cm-1; 1H NMR (500 MHz,
CDCl3) δ 6.87 (1H, dd, J ) 2.2 and 0.8 Hz, H-6), 6.37 (1H, d, J ) 2.2
Hz, H-8), 4.41 (1H, brd, J ) 7.3 Hz, H-5), 4.12 (1H, dd, J ) 11.7 and
4.3 Hz, H-1a), 3.96 (1H, dd, J ) 11.7 and 10.1 Hz, H-1b), 3.85 (3H,
s, OCH3), 3.84 (3H, s, OCH3), 2.39-2.28 (4H, m, H2-4, H-4a and
H-10a), 1.46 (3H, s, CH3-3); 13C NMR (125 MHz, CDCl3) δ 194.2 (C,
C-10), 164.6 (C, C-7), 162.2 (C, C-9), 150.9 (C, C-5a), 114.1 (C, C-9a),
102.2 (CH, C-6), 98.1 (CH, C-8), 95.1 (C, C-3), 73.0 (CH, C-5), 59.9
(CH2, C-1), 55.8 (CH3, OCH3), 55.5 (CH3, OCH3), 47.5 (CH, C-10a),
40.8 (CH, C-4a), 38.3 (CH2, C-4), 29.9 (CH3, Me); HRFABMS m/z
309.1331 [M + 1]+ (calcd for C16H21O6, 309.1333).
1-Hydroxydehydroherbarin (9): orange, amorphous solid; 1H NMR
and MS data were consistent with reported data.4
1-Methoxydehydroherbarin (10): orange solid (CH2Cl2-hexanes);
mp 166-168 °C; UV (EtOH) λmax (log ε) 446 (1.19), 422 (4.10), 336
(4.28), 276 (4.85) nm; IR νmax 1682, 1586, 1320, 1162, 1063 cm-1; 1H
NMR (500 MHz, CDCl3) δ 7.26 (1H, d, J ) 2.5 Hz, H-6), 6.71 (1H,
d, J ) 2.5 Hz, H-8), 6.62 (1H, s. H-4), 6.04 (1H, s, H-1), 3.94 (3H, s,
OMe), 3.93 (3H, s, OMe), 3.57 (3H, s, OMe), 2.11 (3H, s, H-3);
HRFABMS m/z 317.1023 [M + 1]+ (calcd for C17H17O6 317.1020).
7-Desmethylherbarin (2): orange solid (acetone-hexanes); mp
176-178 °C; UV (EtOH) λmax (log ε) 445 (4.01), 427 (3.95), 334 (4.26),
280 (4.94) nm; IR νmax 3480, 1656, 1580, 1567, 1490, 1325, 1230,
1
1170 cm-1; H NMR (500 MHz, acetone-d6) δ 7.12 (1H, d, J ) 2.2
Hz, H-6), 6.78 (1H, d, J ) 2.2 Hz, H-8), 4.54 (2H, m, H-1a and H-1b),
3.87 (3H, s, OCH3), 2.66 (1H, dt, J ) 18.3, 1.8 Hz, H-4a), 2.41 (1H,
dt, J ) 18.3, 3.3 Hz, H-4b), 1.50 (3H, s, CH3-3); 13C NMR (125 MHz,
CDCl3) δ 184.7 (C, C-10), 181.1 (C, C-5), 163.4 (C, C-7 and C-9),
143.9 (C, C-5a), 137.5 (C, C-4a), 136.8 (C, C-10a), 113.1 (C, C-9a),
107.4 (CH, C-6), 105.1 (CH, C-8), 94.4 (C, C-3), 58.7 (CH2, C-1),
56.3 (CH3, OCH3), 32.9 (CH2, C-4), 28.9 (CH3, CH3-3); HRFABMS
m/z 289.0714 [M - 1]- (calcd for C15H13O6, 289.0718).
Acknowledgment. Financial support for this work from the National
Cancer Institute (Grant 5R01CA 90265-07) is gratefully acknowledged.
References and Notes
(1) Studies on Arid Lands Plants and Microorganisms, Part 20. For Part
19, see:Bashyal, B. P.; Gunatilaka, A. A. L. Nat. Prod. Res. 2010,
29, 349–356.
(2) (a) Schmidt, E. W. Nat. Chem. Biol. 2008, 4, 466–473. (b) Miller,
S. J.; Clardy, J. Nat. Chem. 2009, 1, 261–263. (c) Gunatilaka, A. A. L.
J. Nat. Prod. 2006, 69, 509–526. (d) Zhang, H. W.; Song, Y. C.; Tan,
R. X. Nat. Prod. Rep. 2006, 23, 753–771.
(3) Arnold, A. E. Fungal Biol. ReV. 2007, 21, 51–66.
(4) Paranagama, P. A.; Wijeratne, E. M. K.; Burns, A. M.; Marron, M. T.;
Gunatilaka, M. K.; Arnold, A. E.; Gunatilaka, A. A. L. J. Nat. Prod.
2007, 70, 1700–1705.
(5) Ding, G.; Li, Y.; Fu, S.; Liu, S.; Wei, J.; Che, Y. J. Nat. Prod. 2009,
72, 182–186.
Methylation of 7-Desmethylherbarin (2). To a solution of 2 (0.5
mg) in acetone (0.5 mL) were added CH3I (0.05 mL) and K2CO3 (2.0
mg), and the mixture was stirred at 25 °C for 3 h. The reaction mixture
was filtered and evaporated under reduced pressure. The product (0.5
1
mg) formed was shown to be identical (TLC, LC-MS, and H NMR)
with herbarin (8).4,17
8-Hydroxyherbarin (3): orange solid (CH2Cl2-hexanes); mp
163-165 °C; UV (EtOH) λmax (log ε) 375 (3.80), 276 (4.71), 213 (4.69)
nm; IR νmax 3433, 1654, 1589, 1564, 1492, 1330, 1226, 1166 cm-1
;
1H NMR (500 MHz, CDCl3) δ 7.40 (1H, s, H-6), 4.64 (2H, m, H2-1),

Notes
Journal of Natural Products, 2010, Vol. 73, No. 6 1159
(6) Grond, S.; Papastavrou, I.; Zeeck, A. Eur. J. Org. Chem. 2002, 3237–
3242.
(14) Barthe, P.; Pujade-Renaud, V.; Breton, F.; Gargani, D.; Thai, R.;
Roumestand, C.; de Lamotte, F. J. Mol. Biol. 2007, 367, 89–101.
(7) (a) Radman, R.; Saez, T.; Bucke, C.; Keshavarz, T. Biotechnol. Appl.
Biochem. 2003, 37, 91–102. (b) Ariya, B. T.; Bucke, C.; Keshavarz,
T. Biotechnol. Bioeng. 1997, 53, 17–20. (c) Henrickson, J. C.; Hoover,
A. R.; Joyner, P. M.; Cichewicz, R. H. Org. Biomol. Chem. 2009, 7,
435–438. (d) Williams, R. B.; Henrickson, J. C.; Hoover, A. R.; Lee,
A. E.; Cichewicz, R. H. Org. Biomol. Chem. 2008, 6, 1895–1897.
(8) (a) Xu, Y.; Zhan, J.; Wijeratne, E. M. K.; Burns, A. M.; Gunatilaka,
A. A. L.; Molnar, I. J. Nat. Prod. 2007, 70, 1467–1471. (b) Xu, Y.;
Wijeratne, E. M. K.; Espinosa-Artiles, P.; Gunatilaka, A. A. L.; Molnar,
I. ChemBioChem 2009, 10, 345–354.
(9) (a) Puder, C.; Loya, S.; Hizi, A.; Zeeck, A. J. Nat. Prod. 2001, 64,
42–45. (b) Bode, H. B.; Walker, M.; Zeeck, A. Eur. J. Org. Chem.
2000, 3185–3193.
(10) Christian, O. E.; Compton, J.; Christian, K. R.; Mooberry, S. L.;
Valerioate, F. A.; Crews, P. J. Nat. Prod. 2005, 68, 1592–1597.
(11) Paranagama, P. A.; Wijeratne, E. M. K.; Gunatilaka, A. A. L. J. Nat.
Prod. 2007, 70, 1939–1945.
(15) Chomcheon, P; Wiyakrutta, S; Sriubolmas, N.; Ngamrojanavanich,
N; Kengtong, S.; Mahidol, C; Ruchirawat, S.; Kittakoop, P. Phy-
tochemistry 2009, 70, 407–413.
(16) Thines, E.; Anke, H.; Sterner, O. J. Antibiot. 1998, 51, 387–393.
(17) Kadkol, M. V.; Gopalkrishnan, K. S.; Narasimhachari, N. J. Antibiot.
1971, 24, 245–248.
(18) (a) Steyn, P. S.; Wessels, P. L.; Marasas, W. F. O. Tetrahedron 1979,
35, 1551–1555. (b) Gopalakrishnan, S.; Beale, M. H.; Ward, J. L.;
Strange, R. N. Phytochemistry 2005, 66, 1536–1539.
(19) Miljkovic, A.; Mantle, P. G.; William, D. J.; Rassing, B. J. Nat. Prod.
2001, 64, 1251–1253.
(20) Opatz, T.; Kolshorn, H.; Thines, E.; Anke, H. J. Nat. Prod. 2008, 71,
1973–1976.
(21) Parisot, D.; Devys, M.; Babier, M. Microbios 1990, 64, 31–47.
(22) Kurobane, I.; Vining, L. C.; McInnes, A. G.; Gerber, N. N. J. Antibiot.
1980, 33, 1376–1379.
(12) Dixon, L. J.; Schlub, R. L.; Pernezny, K.; Datnoff, L. E. Phytopa-
thology 2009, 99, 1015–1027.
(13) (a) Pereira, J. M.; Barreto, R. W.; Ellison, C. A.; Maffia, L. A. Biol.
Control 2003, 26, 21–31. (b) Onesirosan, P. T.; Arny, D. C.; Durbin,
R. D. Phytopathology 1974, 64, 1364–1367.
(23) Rubinstein, L. V.; Shoemaker, R. H.; Paul, K. D.; Simon, R. M.; Tosini,
S.; Skehan, P.; Sudiero, D. A.; Monks, A.; Boyd, M. R. J. Nat. Cancer
Inst. 1990, 82, 1113–1118.
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