Miniolins A-C, novel isomeric furanones induced by epigenetic manipulation of Penicillium minioluteum

Article abstract of DOI:10.1039/c4ra11712c

Cultivation of Penicillium minioluteum with azacitidine, a DNA methyltransferase inhibitor, led to the isolation of a novel type of aspertetronin dimer, named miniolins A-C (1-3), along with their precursor aspertetronin A (4). The structures of 1-3 were elucidated by extensive spectroscopic methods, and the absolute configurations were assigned by the chiral HPLC analysis of chemical degradation products and electronic circular dichroism associated with the TDDFT computational method (CAM-B3LYP/TZVP). The miniolins showed moderate cytotoxic activity against Hela cell lines. This journal is

Full text of DOI:10.1039/c4ra11712c

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Miniolins A–C, novel isomeric furanones induced
by epigenetic manipulation of Penicillium
minioluteum†
Cite this: RSC Adv., 2015, 5, 2185
*
Hao-Yu Tang,‡ Qiang Zhang,‡ Yu-Qi Gao, An-Ling Zhang and Jin-Ming Gao
Cultivation of Penicillium minioluteum with azacitidine, a DNA methyltransferase inhibitor, led to the
isolation of a novel type of aspertetronin dimer, named miniolins A–C (1–3), along with their precursor
aspertetronin A (4). The structures of 1–3 were elucidated by extensive spectroscopic methods, and the
absolute configurations were assigned by the chiral HPLC analysis of chemical degradation products and
electronic circular dichroism associated with the TDDFT computational method (CAM-B3LYP/TZVP). The
miniolins showed moderate cytotoxic activity against Hela cell lines.
Received 3rd October 2014
Accepted 13th November 2014
DOI: 10.1039/c4ra11712c
www.rsc.org/advances
precursor (+)-(E,E)-(S)-aspertetronin A (4),16,17 which was origi-
nally isolated from various Aspergillus sp.18–20
Introduction
Fungi are unique organisms capable of producing pharmaceu-
tically useful compounds, as exemplied by penicillin, cyclo-
sporine and lovastatin.1,2 In the current post-genomic era, many
microorganisms have been found to harbor signicant
numbers of biosynthetic pathways to secondary metabolites,
such as Aspergillus oryzae3 and A. fumigatus.4 However, many
natural-product-encoding gene clusters in microorganisms are
silent under common culture conditions. Nevertheless, only a
few of their small molecule products have been detected in the
laboratory.5 Thus, in recent years, multiple techniques have
been developed to sidestep transcriptional roadblocks and
enhance product diversity via silent biosynthetic pathways. To
date, chemical approaches targeting histone and DNA post-
translational processes have shown great potential for rationally
directing the activation of silent gene clusters.6,7 The epigenetic
manipulation of fungal gene expression by small molecules,
DNA methyl transferase and/or histone deacetylase (HDAC)
inhibitors inuences secondary metabolism in the fungus and
is an appropriate method for exploring novel fungal metabolites
prepared through cryptic biosynthetic pathways.8–11
Results and discussion
Miniolin A (1) was obtained as a colorless oil ([a]2D1 ꢀ85.3 (c0.13,
CHCl3)). Its molecular formula (C32H40O8) was deduced from
HRESIMS at m/z 553.2865 [M + H]+ (calcd. 553.2796), indicating
13 degrees of unsaturation. The 13C NMR and DEPT spectra
(Table 1) revealed 32 carbon signals, including eight methyls
(including two oxygenated), three methylenes, ten methines
(including nine unsaturated) and eleven quaternary carbons;
among these, seven double bonds and four carbonyl groups are
found. Apart from the eleven degrees due to the unsaturated
bonds, the remaining two degrees implied that 1 possesses two
rings in the molecule. Inspection of the signals in the 1D NMR
and MS spectra suggested an aspertetronin A-derived dimer
skeleton with a characteristic furan-3(2H)-one moiety (dC 192.4,
107.6, 198.0, 91.3).16
In our ongoing search for novel bioactives from fungi,12–15 we
found that the addition of azacitidine, a DNA methyltransferase
inhibitor, to the culture medium of Penicillium minioluteum
signicantly enhanced the production and diversity of small
molecule metabolites (Fig. S1†), leading to three new poly-
ketidefuranones, named miniolins A, B and C (1–3), and their
College of Science, Northwest A&F University, Yangling 712100, Shaanxi, China.
E-mail: jinminggao@nwsuaf.edu.cn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra11712c
Extensive analysis of the 2D NMR spectra (HSQC, 1H–1H
COSY, and HMBC) further established the connectivities among
‡ H.-Y. Tang and Q. Zhang contributed equally.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2185–2190 | 2185

View Article Online
RSC Advances
Paper
Table 1 13C (125 MHz) and 1H (500 MHz) NMR data of 1–3 in CDCl3
a
1
2
3
dC
dH
dC
dH
dC
dH
1
2
3
4
5
6
7
14.1
1.91, d (7.2)
6.29, q (7.2)
14.2
1.91, d (7.2)
6.30, q (7.2)
15.3
1.65, d (6.9)
5.98, mb
137.8
132.6
192.4
107.6
198.0
91.3
137.3
133.0
192.0
107.7
197.9
91.4
130.6
134.3
191.1
109.2
198.1
91.4
8
9
125.5
131.8
127.6
139.5
25.6
13.2
162.8
22.2
51.6
19.4
31.4
35.7
5.52, d (15.4)
125.3
132.4
127.7
139.7
25.6
13.2
162.9
22.4
51.6
18.7
31.2
36.5
5.52, d (15.4)
6.26, dd (15.4, 10.4)
5.95, dd (15.7, 10.4)
5.80, mb
125.3
132.2
127.6
139.7
25.7
13.3
162.2
22.5
51.7
18.9
36.7
37.1
5.51, d (15.4)
6.27, dd (15.4, 10.4)
5.96, dd (15.1, 10.4)
5.78, mb
6.32, dd (15.4, 10.4)
5.98, dd (14.8, 10.4)
5.79, dt (14.8, 7.0)
2.10, mb
10
11
12
13
14
15
16
10
20
30
2.10, mb
2.09, mb
1.00, t (7.0)
0.99, t (7.4)
0.99, t (7.2)
1.53, s
3.74, s
1.30, d (6.9)
3.60, m
3.16, dd (14.2, 7.2)
3.46, dd (14.2, 8.5)
1.50, s
3.76, s
1.24, d (6.9)
3.56, m
3.28, dd (13.6, 7.5)
3.36, dd (13.6, 8.2)
1.51, s
3.78, s
1.18, d (6.6)
3.17, mb
3.17, mb
3.29, dd (10.7, 7.2)
40
196.1
107.3
198.6
90.9
125.9
131.8
127.8
139.4
25.6
196.5
107.3
198.6
90.8
125.7
131.9
127.9
139.3
25.6
196.5
107.3
198.4
91.3
125.4
132.1
127.7
139.6
25.7
50
60
70
80
5.59, d (15.4)
5.61, d (15.4)
6.34, d (15.4, 10.4)
6.01, dd (15.7, 10.4)
5.83, mb
5.59, d (15.4)
6.32, dd (15.4, 10.4)
6.00, dd (14.8, 10.4)
5.81, mb
90
6.25, dd (15.4, 10.4)
5.97, dd (15.1, 10.4)
5.85, dt (15.1, 7.0)
2.10, mb
100
110
120
130
140
150
160
2.10, mb
0.99, t (7.4)
2.09, mb
0.99, t (7.2)
13.2
163.2
22.5
1.00, t (7.0)
13.2
163.1
22.7
13.2
163.1
22.6
1.64, s
3.79, s
1.59, s
3.81, s
1.61, s
3.80, s
51.5
51.5
51.6
a
dH multi, (J in Hz). b Overlapped.
the substituents and the furan-3(2H)-one moieties. Four frag- methyl ester attached to the central core at C-5. Similar HMBC
ments (a–d, in Fig. 1) were deduced from COSY interaction correlations of the other monomer suggested the same frag-
pairs. Further detailed HMBC analysis conrmed the connec- ments (c, d, and a furan-3(2H)-one moiety, Fig. 1). Furthermore,
tivities of fragments a–d and the two furan-3(2H)-one moieties. the HMBC correlations of H-10/C-3, and H-30/C-3 revealed that
The HMBC correlations of CH3-15/C-6, 7, 8 indicated that the two monomers were connected between C-20 and C-3. These
moiety a, H3C-15 and the carbonyl at C-6 were connected by the data led to the planar structure of miniolin A (1).
oxygen-bearing quaternary carbon C-7. The HMBC correlations
The geometry of the four double bonds on the two diene side
of H-1/C-3 and H-2/C-4 indicated the connectivity of unit b to C- chains was determined by NOESY correlations and coupling
4 through C-3. The HMBC correlation of CH3-16/C-14 suggests a constants. The large vicinal coupling constants (15.4 Hz of H-8
and H-9 and H-80 and 90, 14.8 of H-10 and H-11, and 15.1 Hz of
H-100 and H-110) and the NOESY correlations of H-9/H-11 and H-
90/H-110 (Fig. 2) conrmed the all-trans geometry of the double
bonds on C-8, C-10, C-80 and C-100. Furthermore, the NOE
signals of H-1/H-20 suggested an E-geometry of the D2 olen.
However, the relative congurations of the three chiral centers
(C-7, 20 and 70) in 1 could not be deduced from NOE correlations
because of the high exibility of the compound.
HR ESIMS data of miniolins B (2) and C (3) suggested they
possess the same molecular formula as miniolin A (1). The
similar NMR data of all the miniolins indicated they are
stereoisomeric. The 1D and 2D NMR data of 2 were very similar
Fig. 1 Selected COSY and HMBC correlations of 1.
2186 | RSC Adv., 2015, 5, 2185–2190
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Scheme 1 Oxidative cleavages of 1–3 to methylsuccinic acids.
Fig. 2 Key NOESY correlations of 1.
addition, the presence of the methylsuccinic acids also sup-
ported the linkage between C-20 and C-3 in 1–3.
to those of 1 (Table 1 and Fig. 3), which indicated both
compounds share the same planar structure with E-geometry
The absolute congurations of the oxygen-bearing quater-
nary centers C-7 and C-70 in 1–3 were biogenetically related to
those of 4 (Scheme 2). Compound 4 showed the same signs of
optical rotation ([a]2D1 +209.8, c0.13 in CHCl3) as those reported
for both synthetic ([a]2D0 +166.1, c0.55 in CHCl3 (ref. 16)) and
natural ([a]D +133, c0.30 in CHCl3 (ref. 19)) aspertetronin A,
disclosing its 7S-conguration. The congurations of C-7 and C-
70 in 1–3 were also proposed to be S, thus revealing the same
chirality.
The stereochemistry of 1 and 4 was further corroborated by
their CD spectra. In recent years, TDDFT has become a powerful
tool to provide highly precise CD curves.24 Comparison of the
theoretical CD curve with the experimental spectrum provides a
convenient approach to identify absolute conguration for trace
and non-crystalline natural products.25–27 However, for exible
molecules, it is still difficult to obtain highly accurate results in
a limited time period, since the exibility leads to conforma-
tions that are too numerous to be favorable for calculations. In
order to balance accuracy and computational time, we utilized
an economical molecular force eld (MMFF94S) in Conex 6.7
(ref. 28) to acquire meaningful conformers, followed by DFT
optimizations at the B3LYP/6-31G* level for 1 and B3LYP/6-
31+G(d,p) for 4 in Gaussian 09.29 Theoretical CD curves were
for all double bonds. Compound 3 also had similar 1H and 13
C
NMR data (Table 1) and COSY and HMBC correlations (Fig. 3) to
those of 1, with only one exception, the NOESY correlations of
H-2/H-20, which indicated an Z-geometry of the D2 olen in 3. As
with compound 1, we were unable to employ NOE data to assign
stereochemistry of the chiral centers in 2 and 3 due to their high
exibilities.
The absolute congurations of the chiral centers (C-7, C-20,
and C-70) in 1–3 were assigned by chiral HPLC analysis of their
chemical degradation products and ECD spectra. To determine
the chirality at C-20 in 1–3, we performed an oxidative cleavage
reaction21,22 to remove unrelated branches as nonchiral mixed
organic acids and to obtain products with retention of the
stereochemistry of C-20, as shown in Scheme 1. Unexpectedly,
oxidation of 1–3 with RuO4 (ref. 23) produced only 20-methyl-
succinic acid, which was identied by LC/ESI-MS2 analysis
(Fig. S2†). The absolute stereochemistry of the 20-methyl-
succinic acid was assigned by chiral HPLC analysis on the basis
of comparing the tR with those of standard S- or R-methyl-
succinic acid (Fig. 4). Therefore, the absolute conguration of C-
20 in 1 was assigned as S, while that of both 2 and 3 was R. In
Fig. 3 Selected 2D NMR correlations of 2 and 3.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2185–2190 | 2187

View Article Online
RSC Advances
Paper
Fig. 5 Calculated and experimental CD spectra of 1–4.
show a wide range of bioactivities, such as phytotoxic32 and DNA
polymerase inhibitory effects.33 To the best of our knowledge,
miniolins A–C (1–3) represent the rst instances of asperte-
tronin dimers in nature. Particularly, it should be pointed out
that the originally proposed structures of gregatins A–D and
Fig. 4 Chiral analysis of the resulting methylsuccinic acids on a
aspertetronins A and B have been revised twice by Burghart-Stoll
CHIRALPAK AD-H chiral column.
16,17
¨
and Bruckner through total synthesis.
Biogenetically, aspertetronin A (4) is the precursor of mini-
olins A–C (1–3), which were envisioned to be biosynthesized via
polyketide pathways. However, they were not articial products
obtained during the purication procedures, but were produced
by fermentation (Fig. S1†). A plausible biogenetic pathway for
miniolins A–C (1–3) is proposed in Scheme 2. The precursor
aspertetronin A (4) is epoxidized by NADP+, followed by a ring
opening to form a carbonium (ii), which undergoes an addition
reaction with another molecule of 4 to generate the 20-epi-
intermediate (iii). Hydriding of iii then yields iv, followed by
elimination of the 2-hydroxyl group to afford the title
compounds 1–3.
The cytotoxicity of 1–4 was evaluated against Hela cell lines
by SRB colorimetric assay, with etoposide as the positive
control. Compounds 1–3 displayed moderate inhibition with
IC50 values of 33.3, 28.7, and 21.4 mM, respectively, while 4 was
non-cytotoxic.
calculated by the TDDFT method at the CAM-B3LYP/TZVP level
and simulated using SpecDis30 according to Boltzmann distri-
butions. The resulting calculated CD spectra of (S)-4 matched
well with its experimental CD spectra (Fig. 5), which provided
another certication of the conguration of C-7 and C-70 in the
monomer and dimers. The similarity in the CD spectra of the
dimers (1–3) indicates that the congurations of chiral C-2 do
not have a great inuence on the CD Cotton effects. Thus, 1 was
selected to have CD calculation performed (CAM-B3LYP/TZVP)
to check the entire absolute conguration assignments.
Accordingly, the calculated CD curve showed a positive Cotton
effect for the n–p* transition of the furan-3(2H)-one moiety and
conjugated alkene around the crossover point at 265 nm, cor-
responding to the experimental positive Cotton effects observed
around 260 nm. Thus, the entire absolute structures of 1–3 were
established as (ꢀ)-(7S,20S,70S)-1, (ꢀ)-(7S,20R,70S)-2, and
(ꢀ)-(7S,20R,70S)-3.
Members of the furanone structural class of natural
oxygenated heterocycles have been reported from fungi of the
genera Cephalosporium (for example, gregatins and graminin A),
Aspergillus (aspertetronins, huaspenones A and B),18–20 Penicil-
lium (penicilliol) and Paraconiothyrium (graminin B),31 and they
Experimental
General procedures
UV spectra were obtained using a Thermo Scientic Evolution
300 UV-vis spectrophotometer. IR spectra were recorded on a
Bruker Tensor 27 spectrophotometer with KBr disks. Optical
Scheme 2 Plausible biosynthetic pathway of 1–3.
2188 | RSC Adv., 2015, 5, 2185–2190
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
rotations were measured on a Rudolph Autopol III automatic (ꢀ21.3), 260 (ꢀ3.0), 270 (ꢀ5.0), 318 (+3.0) nm; IR (KBr) vmax
polarimeter. CD spectra were obtained on a Chirascan CD 3444, 2958, 2922, 2852, 1732, 1716, 1703, 1685, 1651, 1635,
spectrometer. ESI-MS was performed on a Thermo Fisher LTQ 1458, 1116 cmꢀ1 1H NMR and 13C NMR data, see Table 1;
;
Fleet instrument spectrometer. HR ESIMS was performed on an ESIMS m/z 553.00 [M + H]+; HRESIMS m/z 553.2865 [M + H]+
Agilent 6520 Accurate-Mass Q-TOF LC/MS spectrometer. 1D and (calcd. for C32H40O8H [M + H]+ 553.2796).
2D NMR spectra were recorded on a Bruker AVANCE III (500
Miniolin B (2). Colorless oil; [a]2D1 ꢀ103.7 (c0.1, CHCl3); UV
MHz) instrument. Chemical shis were recorded using the (MeCN) lmax (log 3) 233 nm (3.48); CD (MeCN) lmax (D3) 244
solvent residual peak as the internal standard. High perfor- (ꢀ21.3), 260 (ꢀ3.0), 270 (ꢀ5.0), 318 (+3.0) nm; IR (KBr) vmax
mance liquid chromatography (HPLC) analysis and semi- 3446, 2956, 2922, 2850, 1716, 1651, 1579, 1560, 1440, 1384
preparation was performed on a Waters 1525 instrument cmꢀ1 1H NMR and 13C NMR data, see Table 1; ESIMS m/z
;
(Waters Corp.). Chiral separation was performed on a CHIR- 552.97 [M + H]+; HRESIMS m/z 553.2826 [M + H]+ (calcd. For
ALPAK AD-H column. Column chromatography was performed
on silica gel (90–150 mm; Qingdao Marine Chemical Inc.,
C
32H40O8H [M + H]+ 553.2796).
Miniolin C (3). Colorless oil; [a]2D1 ꢀ106.2 (c0.05, CHCl3); UV
Qingdao, China), MCI gel (75–150 mm; Mitsubishi Chemical (MeCN) lmax (log 3) 195 nm (5.58); CD (MeCN) lmax (D3) 244
Corp., Tokyo, Japan), Sephadex LH-20 (40–70 mm; Amersham (ꢀ21.3), 260 (ꢀ3.0), 270 (ꢀ5.0), 318 (+3.0) nm; IR (KBr) vmax
Pharmacia Biotech AB, Uppsala, Sweden), and Lichroprep RP-18 3446, 2954, 2920, 2850, 1733, 1706, 1703, 1651, 1577, 1458, 1377
gel (40–63 mm; Merck, Darmstadt, Germany). GF254 plates cmꢀ1 1H NMR and 13C NMR data, see Table 1; ESIMS m/z
;
(Qingdao Marine Chemical Inc.) were used for thin-layer chro- 552.64 [M + H]+; HRESIMS m/z 553.2810 [M + H]+ (calcd. for
matography (TLC).
C
32H40O8H [M + H]+ 553.2796).
Aspertetronin A (4). Colorless oil; [a]2D1 +209.8 (c0.13, CHCl3);
UV (MeCN) lmax (log 3) 231 (4.09) nm; CD (MeCN) lmax (D3) 228
(ꢀ18.6), 251 (+7.1), 270 (+7.4), nm; IR (KBr) vmax 3423, 2962,
1743, 1706, 1645, 1438, 1132, 991, 788 cmꢀ1; 1H NMR (400 MHz,
CDCl3) d (multi, J in Hz) 2.06 (H3-1, dd, 6.8, 1.4 Hz), 7.20 (H-2,
dq, 15.7, 6.8 Hz), 7.33 (H-3, dq, 15.7, 1.4 Hz), 5.57 (H-8, d,
15.4 Hz), 6.27 (H-9, dd, 15.4, 10.3 Hz), 5.97 (H-10, dd, 15.1, 10.3
Hz), 5.80 (H-11, dt, 15.1, 6.5 Hz), 2.10 (H2-12, dq, 7.4, 6.5 Hz),
0.99 (H3-13, t, 7.4 Hz), 1.54 (H3-15, s), 3.84 (H3-16, s); 13C NMR
(100 MHz, CDCl3) d (in ppm) 19.3 (C-1), 144.6 (C-2), 120.8 (C-3),
185.2 (C-4), 103.7 (C-5), 198.3 (C-6), 90.4 (C-7), 126.1 (C-8), 131.5
(C-9), 127.8 (C-10), 139.2 (C-11), 25.6 (C-12), 13.2 (C-13), 163.5
(C-14), 22.5 (C-15), 51.5 (C-16); ESIMS m/z 277.00 [M + H]+.
Fungal material, extraction, and isolation
Penicillium minioluteum was purchased from China General
Microbiological Culture Collection Center (CGMCC, no.
3.5723). The fungus was incubated in potato dextrose agar
(PDA) at 25 ꢁC for 4 days. For the cultural media tests, one piece
(approximately 7 mm2) of mycelium was inoculated aseptically
into three 500 mL Erlenmeyer asks containing 150 mL of
potato dextrose (PD) liquid medium with 500 mM 5-azacitidine
(AZA) as a chemical epigenetic modier. The asks were then
cultured at 27 ꢂ 0.5 ꢁC for 10 days with shaking at 150 rpm. As a
parallel control, another three asks of medium excluding AZA
were cultured under the same conditions. Ethyl acetate (EtOAc)
extracts of the cultures and the controls were compared by
HPLC with an Agilent TC-C18 column (250 ꢃ 4.6 mm). The
Oxidative cleavage reactions and chiral HPLC analysis
results (Fig. S1†) showed that 5-azacitidine enriched the diver- Compounds
1 (2.1 mg), 2 (1.9 mg) and 3 (1.5 mg)
sity of the metabolites. For the scale-up of metabolite produc- were, respectively, treated with 50 eq. NaIO4 and 2.2% mol
tion, a seed mycelium of the fungus was inoculated into 150 RuCl3$xH2O in the solvent system H2O/CH3CN/AcOEt (3 : 2 : 2).
Erlenmeyer asks containing 22.5 L of potato dextrose (PD) The mixture was stirred for 4 h at room temperature. Aer
liquid medium in total, and cultured under the tested addition of 0.5 mL 1 N HCl for the suppression of methyl-
conditions.
succinic acid ionization, the mixture was extracted with water
saturated n-butyl alcohol (3 ꢃ 1.0 mL). The combined organic
extracts were dried over MgSO4. The resulting products and
reference methylsuccinic acid were carried forward for
comparative analysis on a Thermo LCQ Fleet LC/MS with an
Agilent TC-18 column (250 ꢃ 4.6 mm) and CHIRALPAK AD-H
column (250 ꢃ 4.6 mm). tR and MS/MS data were collected.
Extraction, isolation and purication
The cultures of P. minioluteum were extracted with petroleum
ether (PE) to yield 2.0 g of residue. The residue was fractionated
by silica ash chromatography eluted with a PE-EtOAc gradient
to give four fractions (Fr. 1–Fr. 4). Fr. 2 (70 mg) was subjected to
PTLC with a developing solvent of CHCl3–acetone (50 : 1) to
yield compound 1 (9 mg) and a mixture (32 mg). The latter was
Computational method
then separated on a semi-preparative HPLC C18 column A preliminary conformational search was performed in Conex
(Thermo BDS Hypersil 250 ꢃ 10 mm) and eluted with 75% 6.7 using an MMFF94S force eld. Conformers with 3 kcal
MeCN to yield compounds 2 (1.9 mg) and 3 (3.2 mg). Fr. 3 was molꢀ1 were saved and further optimized using the Gaussian 09
chromatographed on a Sephadex LH-20 gel column, then soware package at the B3LYP/6-31+G(d,p) level for compound
puried on a HPLC C18 semi-preparative column with 75% 4 and the B3LYP/6-31G* level for 1. The stable conformers with
MeOH as eluent to afford 4 (8 mg).
distributions greater than 1% and without imaginary frequen-
Miniolin A (1). Colorless oil; [a]2D1 ꢀ85.3 (c0.13, CHCl3); UV cies were submitted for ECD calculation by the TDDFT (CAM-
(MeCN) lmax (log 3) 231 nm (4.27); CD (MeCN) lmax (D3) 244 B3LYP/TZVP) method associated with the CPCM solvent
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 2185–2190 | 2189

View Article Online
RSC Advances
Paper
model in MeCN. The excitation energies (E), oscillator strength 17 H. Burghart-Stoll and R. Brückner, Org. Lett., 2011, 13, 2730.
(f), and rotatory strength of the lowest 30 excited states were 18 K. Kotayashi and T. Ui, Tetrahedron Lett., 1975, 16, 4119.
calculated. The ECD spectra of different conformers were 19 J. A. Ballantine, V. Ferrito, C. H. Hassall and V. I. P. Jones, J.
simulated using SpecDis with a half bandwidth of 0.5 eV. The
Chem. Soc. C, 1969, 56.
nal ECD spectra were generated according to the Boltzmann- 20 Z.-J. Zhan, J.-P. Jin, Y.-M. Ying and W.-G. Shan, Helv. Chim.
calculated distribution of each conformer.
Acta, 2011, 94, 1454.
21 N. U. Sata, S. Wada, S. Matsunaga, S. Watabe, R. W. M. van
Soest and N. Fusetani, J. Org. Chem., 1999, 64, 2331.
22 S. Matsunaga, P. Liu, C. A. Celatka, J. S. Panek and
N. Fusetani, J. Am. Chem. Soc., 1999, 121, 5605.
23 S. Rup, M. Sindt and N. Oget, Tetrahedron Lett., 2010, 51,
3123.
Acknowledgements
We are grateful to Dr Shigeki Matsunaga of the University of
Tokyo for kind suggestions about absolute conguration. This
work is nancially supported from the National Natural Science
Foundation of China (no. 31371886, 21102114).
24 L. Goerigk and S. Grimme, J. Phys. Chem. A, 2009, 113, 767.
25 X. Lin, S. Ji, X. Qiao, H. Hu, N. Chen, Y. Dong, Y. Huang,
D. Guo, P. Tu and M. Ye, J. Org. Chem., 2013, 78, 11835.
26 H.-J. Zhang, J. Luo, S.-M. Shan, X.-B. Wang, J.-G. Luo,
M.-H. Yang and L.-Y. Kong, Org. Lett., 2013, 15, 5512.
27 A. E. Nugroho and H. Morita, J. Nat. Med., 2014, 68, 1.
28 Conex 6.7, Conex Corp., Tokyo Yokohama, Japan, 2010.
29 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J. J. A. Montgomery,
J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N. J. Millam,
M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
F. Dannenberg, J. B. Foresman, J. V. Ortiz, J. Cioslowski
and D. J. Fox, Gaussian 09 revision D.01, Gaussian Inc.,
Wallingford CT, 2013.
Notes and references
1 A. Evidente, A. Kornienko, A. Cimmino, A. Andol,
F. Lefranc, V. Mathieu and R. Kiss, Nat. Prod. Rep., 2014,
31, 617.
2 J.-M. Gao, S.-X. Yang and J.-C. Qin, Chem. Rev., 2013, 113,
4755.
3 M. Machida, K. Asai, M. Sano, T. Tanaka, T. Kumagai,
G. Terai, K.-I. Kusumoto, T. Arima, O. Akita and
Y. Kashiwagi, Nature, 2005, 438, 1157.
4 W. C. Nierman, A. Pain, M. J. Anderson, J. R. Wortman,
H. S. Kim, J. Arroyo, M. Berriman, K. Abe, D. B. Archer and
C. Bermejo, Nature, 2005, 438, 1151.
5 S. Kroken, N. L. Glass, J. W. Taylor, O. C. Yoder and
B. G. Turgeon, Proc. Natl. Acad. Sci. U. S. A., 2003, 100, 15670.
6 R. H. Cichewicz, Nat. Prod. Rep., 2010, 27, 11.
7 E. K. Shwab, J. W. Bok, M. Tribus, J. Galehr, S. Graessle and
N. P. Keller, Eukaryotic Cell, 2007, 6, 1656.
8 T. Asai, Y.-M. Chung, H. Sakurai, T. Ozeki, F.-R. Chang,
K. Yamashita and Y. Oshima, Org. Lett., 2012, 14, 513.
9 T. Asai, D. Luo, Y. Obara, T. Taniguchi, K. Monde,
K. Yamashita and Y. Oshima, Tetrahedron Lett., 2012, 53,
2239.
10 T. Asai, T. Yamamoto, N. Shirata, T. Taniguchi, K. Monde,
I. Fujii, K. Gomi and Y. Oshima, Org. Lett., 2013, 15, 3346.
11 T. Asai, S. Morita, N. Shirata, T. Taniguchi, K. Monde,
H. Sakurai, T. Ozeki and Y. Oshima, Org. Lett., 2012, 14,
5456.
30 T. Bruhn, A. Schaumloeffel, Y. Hemberger and
G. Bringmann, Chirality, 2013, 25, 243.
´
31 C. Almeida, N. El Aouad, J. Martin, I. Perez-Victoriatn,
´
´
V. Gonzalez-Menendez, G. Platas, M. de la Cruz,
M. C. Monteiro, N. de Pedro, G. F. Bills, F. Vicente,
O. Genilloud and F. Reyes, J. Antibiot., 2014, 67, 421.
32 S. Tanaka, N. Kondo and S. Naito, J. Gen. Plant Pathol., 2007,
73, 242.
12 H. Li, J. Xiao, Y.-Q. Gao, J. Tang, A.-L. Zhang and J.-M. Gao, J.
Agric. Food Chem., 2014, 62, 3734.
13 J. Xiao, Q. Zhang, Y.-Q. Gao, J.-J. Tang, A.-L. Zhang and
J.-M. Gao, J. Agric. Food Chem., 2014, 62, 3584.
14 Q. Zhang, S.-Q. Wang, H.-Y. Tang, X.-J. Li, L. Zhang, J. Xiao,
Y.-Q. Gao, A.-L. Zhang and J.-M. Gao, J. Agric. Food Chem.,
2013, 61, 11447.
33 T. Kimura, T. Takeuchi, Y. Kumamoto-Yonezawa, E. Ohashi,
H. Ohmori, C. Masutani, F. Hanaoka, F. Sugawara,
H. Yoshida and Y. Mizushina, Bioorg. Med. Chem., 2009,
17, 1811.
15 X.-J. Li, Q. Zhang, A.-L. Zhang and J.-M. Gao, J. Agric. Food
Chem., 2012, 60, 3424.
¨
16 H. Burghart-Stoll and R. Bruckner, Eur. J. Org. Chem., 2012,
2012, 3978.
2190 | RSC Adv., 2015, 5, 2185–2190
This journal is © The Royal Society of Chemistry 2015