Gram-Scale, Stereoselective Synthesis and Biological Evaluation of (+)-Armillariol C

Article abstract of DOI:10.1021/acs.jnatprod.7b00484

Natural products with heteroaromatic cores are ample and widespread in nature, with many compounds exhibiting promising therapeutic properties. (+)-Armillariol C (1a) is a furan-based natural product isolated from Armillaria species. Herein, we report the first enantioselective synthesis of (+)-armillariol C (1a, 79% overall yield), its enantiomer (1b), and four other analogues, on a gram-scale, using microwave-mediated, Suzuki-Miyaura cross-coupling and Sharpless asymmetric dihydroxylation reactions. Compounds were tested for plant- and mycelia-growth regulatory activity, with 1b, 7a, and 7b showing the strongest inhibitory properties in a lettuce assay and 7b and 9b inhibiting Flammulina velutipes.

Full text of DOI:10.1021/acs.jnatprod.7b00484

Note
pubs.acs.org/jnp
Gram-Scale, Stereoselective Synthesis and Biological Evaluation of
(+)-Armillariol C
M. Damoder Reddy,† Hajime Kobori,§ Takumi Mori,‡ Jing Wu,§ Hirokazu Kawagishi,‡,§
and E. Blake Watkins*,†
†Department of Pharmaceutical Sciences, College of Pharmacy, Union University, Jackson, Tennessee 38305, United States
§
‡Faculty of Agriculture and Research Institute of Green Science and Technology, Shizuoka University, 836 Ohya, Suruga-ku,
Shizuoka 422-8529, Japan
S
* Supporting Information
ABSTRACT: Natural products with heteroaromatic cores are ample and widespread in nature, with many compounds
exhibiting promising therapeutic properties. (+)-Armillariol C (1a) is a furan-based natural product isolated from Armillaria
species. Herein, we report the first enantioselective synthesis of (+)-armillariol C (1a, 79% overall yield), its enantiomer (1b),
and four other analogues, on a gram-scale, using microwave-mediated, Suzuki−Miyaura cross-coupling and Sharpless asymmetric
dihydroxylation reactions. Compounds were tested for plant- and mycelia-growth regulatory activity, with 1b, 7a, and 7b showing
the strongest inhibitory properties in a lettuce assay and 7b and 9b inhibiting Flammulina velutipes.
eterocycles are ubiquitous and form the core of many
product and its analogues in sufficient quantities for further
Hagrochemicals and marketed drugs. These compounds biological testing. Our interest in 1a stems from its ability to
hinder plant growth. We envisioned a concise, stereoselective
route to (+)-armillariol C and a variety of analogues that would
permit exploration of this biological property. To the best of
our knowledge there have been no reports on the synthesis of
1a. Herein, we describe the first synthesis of (+)-armillariol C
in a protecting-group-free manner and our initial exploration of
this class of compounds.
Figure 1 outlines a retrosynthetic protocol aimed at the
target molecule. The desired natural product (1a) could be
prepared from conjugated alkene (2) using the Sharpless
asymmetric dihydroxylation methodology. The alkene (2) is
easily accessible from heteroaromatic halide 3 and the
corresponding alkenyl boronic acid derivative via a Suzuki−
Miyaura coupling strategy.
function as insecticides, herbicides, plant-growth regulators,
fungicides, veterinary products, copolymers, and ligands.1,2
Furan is a common constituent encountered in numerous
biologically active heterocyclic scaffolds including natural
products and also serves as a useful building block in several
important reactions such as Diels−Alder and Achmatowicz
reactions, attaining a prominent role in organic synthesis.3
(+)-Armillariol C (1a) is a furan-containing natural product
isolated as a minor component (3.2 mg) from the culture broth
(14 L) of Armillaria sp. (honey fungus), possessing plant-
growth regulatory activity.4 Armillaria sp. comprise edible
mushrooms that display a wide array of biological activity
including anticancer,5,6 anti-inflammatory,7−9 and antioxidant
properties10 and have been used in traditional Chinese
medicine (Tian-ma) to treat hypertension, insomnia, and
dizziness.11,12 Additionally, the genus is responsible for
Armillaria root disease, affecting a myriad of woody plants
including oak, fruit, and nut trees as well as many herbaceous
plants.13 The structure of (+)-armillariol C encompasses a furan
ring with an acetyl group and two asymmetric hydroxy groups
on the aliphatic side chain. The synthesis of 1a represents an
attractive challenge for researchers as a way to make the natural
The preparation of armillariol C (1a) began with the
synthesis of 3 from commercially available 1-(furan-2-yl)ethan-
1-one (4).14 Compound 4 was treated with N-bromosuccini-
mide (NBS) in dimethylformamide (DMF) at room temper-
ature, providing compound 3 in 69% yield.
Received: June 6, 2017
© XXXX American Chemical Society and
American Society of Pharmacognosy
A
DOI: 10.1021/acs.jnatprod.7b00484
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Note
Scheme 1. Synthesis of (+)-Armillariol C (1a) and Its
a
Enantiomer (1b)
Figure 1. Retrosynthetic analysis of target molecule 1a.
a
Reagents and conditions: (a) NBS, DMF, rt, 16 h, 69%; (b) see Table
1; (c) ADmix-α, MeSO2NH2, t-BuOH/H2O (1:1), 0 °C, 24 h, 91%;
(d) ADmix-β, MeSO2NH2, t-BuOH/H2O (1:1), 0 °C, 24 h, 89%.
Initial attempts at the preparation of 2 involved the treatment
of bromofuran 3 with (E)-hept-1-en-1-ylboronic acid (4a)
under palladium-catalyzed conditions,15 which furnished 2 in
78% yield, along with 9% of the furan dimer (2a, entry 1, Table
1). Attempts to improve the yield of the desired alkene 2 and
conditions. Enantiomeric excess was determined using the
method of Bull and James21 (see Experimental Section for
details).
Table 1. Optimization of Reaction Conditions for the
After successful synthesis of armillariol C, we focused on the
synthesis of various analogues. The treatment of 4b with
commercially available 1-(5-bromothiophen-2-yl)ethan-1-one
(5), under Pd-catalyzed and microwave-irradiated conditions,
afforded the corresponding alkene 6 in excellent yield (Scheme
2). Asymmetric dihydroxylation of 6 with ADmix-α and
ADmix-β gave the enantiomeric diols 7a in 90% (>98% ee)
and 7b in 86% yield (>98% ee), respectively.
Suzuki−Miyaura Reaction
Scheme 2. Synthesis of Thiophene Analogues of Armillariol
a
C
reagent (4a/
4b)
time
(h)
yield %
b
entry
1
base/solvent
(2/2a)
4a
4a
4a
4a
4a
t-BuNH2/i-PrOH−H2O
t-BuNH2/i-PrOH−H2O
n-BuNH2/i-PrOH−H2O
EtNH2/i-PrOH−H2O
16
78/9
81/5
56/6
45/8
76/0
c
2
0.5
0.5
0.5
0.5
c
3
c
4
c
5
t-BuNH2/1,4-dioxane−
H2O
6
4b
4b
t-BuNH2/i-PrOH−H2O
t-BuNH2/i-PrOH−H2O
12
83/0
87/0
c
7
0.5
a
Reagents and conditions: bromide 3 (1 mmol), alkenyl borate (4a/
4b) (1.2 mmol), PdCl2(dppf)·CH2Cl2 (0.02 mol %), base (3 mmol),
b
1
solvent (5 mL, 2:1). All products were characterized by H and 13C
a
Reagents and conditions: (a) 4b, PdCl2(dppf)·CH2Cl2, t-BuNH2, i-
c
NMR, IR, and MS. Microwave conditions.
PrOH/H2O (2:1), 100 °C, MW, 30 min, 90%; (b) ADmix-α,
MeSO2NH2, t-BuOH/H2O (1:1), 0 °C, 24 h, 90%; (c) ADmix-β,
MeSO2NH2, t-BuOH/H2O (1:1), 0 °C, 24 h, 86%.
eliminate the production of 2a using bases such as n-BuNH2
and ethylamine and a 1,4-dioxane/water mixture were
unsuccessful (entries 2−5, Table 1). Switching to an alternative
organoboron, alkenyltrifluoroborate 4b proved to be advanta-
geous. Suzuki−Miyaura coupling16−18 of potassium (E)-
trifluoro(hept-1-en-1-yl)borate (4b) with 3 in the presence of
a Pd-catalyst at 100 °C for 12 h under conventional heating
afforded the desired compound 2 in 83% yield as an exclusive
product (entry 6, Table 1).
Likewise, coupling of 4b with 3 under microwave irradiation
gave exclusively 2 in 87% yield after 30 min at 100 °C (entry 7,
Table 1). Sharpless asymmetric dihydroxylation19,20 provided
access to both (+)- and (−)-armillariol C (1a and 1b).
Treatment of 2 with ADmix-α and methanesulfonamide in t-
BuOH-H2O at 0 °C for 24 h gave the anticipated
(+)-armillariol C (1a) in 91% yield and >98% ee (Scheme
1). Similarly, (−)-armillariol C (1b, 89% yield, > 98% ee) was
synthesized by treating 2 with ADmix-β under identical
Additionally, the treatment of 3 with potassium (E)-
trifluoro(styryl)borate (4c) under Pd-catalyzed and micro-
wave-irradiated conditions at 100 °C for 45 min afforded the
heteroaryl alkene 8 in excellent yield (Scheme 3). Finally, 8 was
subjected to ADmix-α and ADmix-β to yield the syn,
enantiomeric diols (9a and 9b, >98% ee) in good yields.
The ability of (+)-armillariol C (1a) and its analogues to
regulate plant growth was determined at a range of
concentrations using lettuce (Figure 2).22 All synthesized
analogues inhibited the growth of lettuce, while analogues 1b,
7a, and 7b showed the strongest inhibition of growth of both
the hypocotyl and root.
Further testing was conducted to determine the ability of the
diols to inhibit the growth of mycelia from Flammulina
velutipes.22 Compounds 7b and 9b inhibited the mycelia growth
of F. velutipes as indicated by the presence of clear zones on
B
DOI: 10.1021/acs.jnatprod.7b00484
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Note
a
Deuterated chloroform was used as the solvent, and spectra were
calibrated against the residual solvent peak (7.24 ppm for 1H and 77.0
ppm for 13C). Chemical shifts (δ) and coupling constants (J) are given
in ppm (parts per million) and Hz (hertz), respectively. The following
abbreviations were used to explain multiplicities: s = singlet, d =
doublet, t = triplet, q = quartet, m = multiplet, bs = broad singlet. Low-
resolution ESI mass spectra were obtained on a Waters Acquity UPLC
H-Class with PDA and SQ mass detectors using a Waters BEH C18 1.7
μm column (2.1 × 50 mm). High-resolution mass spectra were
obtained on a VG 70-70H or LC/MSD trapSL spectrometer operating
at 70 eV using a direct inlet system.
Scheme 3. Synthesis of Analogues of Armillariol C
Synthesis of 1-(5-Bromofuran-2-yl)ethan-1-one (3). To a
stirred solution of 1-(furan-2-yl)ethan-1-one (4, 5 g, 45.4 mmol, 1
equiv) in DMF (50 mL) at 10 °C was added portionwise N-
bromosuccinimide (8.79 g, 49.9 mmol, 1.1 equiv) over a period of 10
min. The mixture was stirred for another 16 h at room temperature
and then poured into ice-cold water (150 mL). The product was
extracted with diethyl ether (100 mL × 3), the combined organic
layers were washed with cold water (100 mL × 2) and brine (100 mL
× 2) and dried over MgSO4, and the solvent was removed in vacuo.
The crude product was purified by flash column chromatography
(silica gel, EtOAc/hexanes, 1:50 to 1:20, Rf = 0.25 in 10% EtOAc in
hexanes) to give the brominated compound 3 in 69% yield as a pale
yellow solid.
Potassium (E)-Trifluoro(hept-1-en-1-yl)borate (4b). To a
solution of 1-heptyne (5.43 mL, 4 g, 41.6 mmol, 1 equiv) in
CH2Cl2 (25 mL) at 0 °C was added dibromoborane dimethyl sulfide
complex (Br2BH·SMe2) (41.6 mL, 41.6 mmol, 1 M in CH2Cl2, 1
equiv). The mixture was stirred at room temperature for 4 h.
Subsequently, the light green solution was added via a double-ended
needle to a mixture of diethyl ether/water (25 mL of diethyl ether and
10 mL of water) at 0 °C. The mixture was stirred at room temperature
for 30 min. The aqueous layer was separated, and the organic phase
was washed with cold water and then brine. The organic phase was
subsequently dried with MgSO4. The solvents were evaporated to
provide (E)-hept-1-en-1-ylboronic acid (4a) as a white solid.
To a solution of the trans-hept-1-en-1-ylboronic acid thus prepared
(4a, 5.3 g) in diethyl ether (60 mL) in a 250 mL plastic beaker/narrow
mouth plastic bottle was added KHF2 (9.08 g, 116 mmol, 2.8 equiv),
followed by slow addition of water (25 mL) over a period of 30 min.
After stirring at room temperature for 3 h, the solution was
concentrated, and the crude material was dissolved in acetone, filtered,
and concentrated. The resulting white solid was purified by dissolving
in hot acetone and precipitating with Et2O, resulting in a white solid
(4b, 5.52 g, 65%).
a
Reagents and conditions: (a) PdCl2(dppf)·CH2Cl2, t-BuNH2, i-
PrOH:H2O (2:1), 100 °C, MW, 45 min, 92%; (b) ADmix-α,
MeSO2NH2, t-BuOH/H2O (1:1), 0 °C, 72 h, 87%; (c) ADmix-β,
MeSO2NH2, t-BuOH/H2O (1:1), 0 °C, 72 h, 88%.
potato dextrose agar (PDA) plates (see Supporting Informa-
tion).
In conclusion, the synthesis of (+)- and (−)-armillariol C
and their analogues using Suzuki−Miyaura cross-coupling and
Sharpless asymmetric dihydroxylation on a gram-scale is
described. (+)-Armillariol C (1a) was synthesized for the first
time and in a two-step protocol from 1-(5-bromofuran-2-
yl)ethan-1-one (3) in 79% overall yield. Additionally, the plant-
and mycelia-growth regulatory activity of the natural product
and its analogues were also investigated, with 1b, 7a, and 7b
showing the strongest inhibitory properties in a lettuce assay
and 7b and 9b inhibiting F. velutipes.
EXPERIMENTAL SECTION
■
General Experimental Procedures. Glassware was dried in an
oven (120 °C), heated under reduced pressure, and cooled under
argon before use. Unless otherwise noted, materials obtained from
commercial suppliers were used without further purification. Reactions
were monitored by thin-layer chromatography on Analtech silica gel
plates using UV light and ceric sulfate or β-naphthol for visualization.
Column chromatography was performed on silica gel (230−400
mesh) using hexanes and ethyl acetate as eluent. Evaporation of
solvents was conducted under reduced pressure at 50 °C. FTIR spectra
were recorded neat on a PerkinElmer Spectrum 65. Specific rotation
values were determined using an Anton-Paar MCP 100 polarimeter.
Microwave reactions were conducted in a Biotage Initiator Classic.
NMR spectra were recorded on a Bruker Avance III 400 NMR
spectrometer at 400 MHz (1H) and 100 MHz (13C), respectively.
General Procedure for the Preparation of trans-Alkenes (2/
6/8). A solution of potassium trans-alkene trifluoroborate (4a/4b/4c)
(6.32 mmol, 1.2 equiv), PdCl2(dppf)·CH2Cl2 (86 mg, 0.106 mmol,
Figure 2. Lettuce growth regulating activity of armillariol C (1a) and analogues against root or hypocotyl. 2,4-Dichlorophenoxyacetic acid (2,4-D)
was used as the positive control. Results are the mean standard deviation (n = 7). The asterisk indicates significant difference from control
(Student’s t test; *, p < 0.05; **, p < 0.01).
C
DOI: 10.1021/acs.jnatprod.7b00484
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Note
21
1
Figure 3. Determination of enantiomeric excess of 1a via H NMR of boronate 10a.
0.02 equiv), 1-(5-bromofuran-2-yl)ethan-1-one (3, 1 g, 5.29 mmol, 1
equiv)/1-(5-bromothiophen-2-yl)ethan-1-one (5, 1 g, 4.88 mmol, 1
equiv), and t-BuNH2 (15.81 mmol, 3 equiv) in i-PrOH/H2O (2:1, 24
mL) was heated at 100 °C under an argon atmosphere for 30 min
under microwave conditions (12 h in the case of conventional heating
on an oil bath), then cooled to room temperature (RT) and diluted
with water (20 mL), followed by extraction of diethyl ether (50 mL ×
2). The organic layers were combined and washed with 1 N HCl (80
mL) and brine (80 mL), dried over MgSO4, and then filtered. The
solvent was removed under vacuum, and the crude product was
purified by silica gel chromatography (eluting with hexanes/ethyl
acetate, 20:1 to 5:1) to afford the corresponding alkene derivative (2/
6/8) in good yields.
(E)-1-(5-(Hept-1-en-1-yl)furan-2-yl)ethan-1-one (2). 1-(5-Bro-
mofuran-2-yl)ethan-1-one (3, 1 g, 5.29 mmol, 1 equiv), potassium (E)-
trifluoro(hept-1-en-1-yl)borate (4b, 1.30 g, 6.32 mmol, 1.2 equiv),
PdCl2(dppf)·CH2Cl2 (86 mg, 0.106 mmol, 0.02 equiv), and t-BuNH2
(1.661 mL, 1.156 g, 15.81 mmol, 3 equiv) in i-PrOH/H2O (2:1, 24
mL), 30 min, 100 °C. After column chromatography (gradient,
hexanes/EtOAc 50:1 to 20:1) 948 mg (87%) of a pale, yellow oil was
obtained.
(E)-1-(5-(Hept-1-en-1-yl)thiophen-2-yl)ethan-1-one (6). 1-(5-
Bromothiophen-2-yl)ethan-1-one (5, 1 g, 4.88 mmol, 1 equiv),
potassium (E)-trifluoro(hept-1-en-1-yl)borate (4b, 1.19 g, 5.85
mmol, 1.2 equiv), PdCl2(dppf)·CH2Cl2 (80 mg, 0.098 mmol, 0.02
equiv), and t-BuNH2 (1.07 g, 14.63 mmol, 3 equiv) in i-PrOH/H2O
(2:1, 24 mL), 30 min, 100 °C. After column chromatography
(gradient, hexanes/EtOAc, 50:1 to 20:1) 975 mg (90%) of a pale,
yellow solid was obtained.
(E)-1-(5-Styrylfuran-2-yl)ethan-1-one (8). 1-(5-Bromofuran-2-
yl)ethan-1-one (3, 1 g, 5.29 mmol, 1 equiv), potassium (E)-
trifluoro(styryl)borate (4c, 1.33 g, 6.35 mmol, 1.2 equiv),
PdCl2(dppf)·CH2Cl2 (86 mg, 0.106 mmol, 0.02 equiv), and t-
BuNH2 (1.161 g, 15.87 mmol, 3 equiv) in i-PrOH/H2O (2:1, 24
mL), 45 min, 100 °C. After column chromatography (gradient,
hexanes/EtOAc, 50:1 to 20:1) 1.03 g (92%) of a pale, yellow solid was
obtained.
mmol, 1 equiv) and ADmix-α (10.0 g, ∼1.4 g for 1 mmol of alkene 2).
The mixture was stirred for 24 h at 0 °C and diluted with brine (40
mL). The product was extracted with ethyl acetate (50 mL × 3). The
combined organic layers were washed with brine (100 mL), dried over
MgSO4, and concentrated. The residue was purified by chromatog-
raphy (hexanes/ethyl acetate, 70:30) to afford (+)-armillariol C (1a)
as a pale, yellow oil (1.59 g) in 91% yield (>98% ee).
(−)-Armillariol C (1b). Following the general procedure used for
the synthesis of (+)-1a: (E)-1-(5-(hept-1-en-1-yl)furan-2-yl)ethan-1-
one (2, 1.5 g, 7.27 mmol, 1 equiv), MeSO2NH2 (692 mg, 7.27 mmol, 1
equiv), ADmix-β (10.0 g, ∼1.4 g for 1 mmol of alkene 2) in t-BuOH/
H2O (1:1, 100 mL), 24 h, 0 °C. After column chromatography
(hexanes/EtOAc, 90:10 to 70:30) 1.55 g (89%) of a pale, yellow oil
was obtained (>98% ee).
(−)-1-(5-((1R,2S)-1,2-Dihydroxyheptyl)thiophen-2-yl)ethan-
1-one (7a). Following the general procedure used for the synthesis of
(+)-1a: (E)-1-(5-(hept-1-en-1-yl)thiophen-2-yl)ethan-1-one (6, 1.5 g,
6.75 mmol, 1 equiv), MeSO2NH2 (642 mg, 5 mmol, 1 equiv), ADmix-
α (9.6 g, ∼1.4 g for 1 mmol of alkene) in t-BuOH/H2O (1:1, 100
mL), 24 h, 0 °C. After column chromatography (hexanes/EtOAc,
90:10 to 70:30) 1.55 g (90%) of a pale, yellow oil was obtained (>98%
ee).
(+)-1-(5-((1S,2R)-1,2-Dihydroxyheptyl)thiophen-2-yl)ethan-
1-one (7b). Following the general procedure used for the synthesis of
(+)-1a: (E)-1-(5-(hept-1-en-1-yl)thiophen-2-yl)ethan-1-one (6, 1.5 g,
6.75 mmol, 1 equiv), MeSO2NH2 (642 mg, 6.75 mmol, 1 equiv),
ADmix-β (9.6 g, ∼1.4 g for 1 mmol of alkene) in t-BuOH/H2O (1:1,
100 mL), 24 h, 0 °C. After column chromatography (gradient,
hexanes/EtOAc, 90:10 to 70:30) 1.49 g (86%) of a pale, yellow oil was
obtained (>98% ee).
(−)-1-(5-((1R,2S)-1,2-Dihydroxy-2-phenylethyl)furan-2-yl)-
ethan-1-one (9a). Following the general procedure used for the
synthesis of (+)-1a: (E)-1-(5-styrylfuran-2-yl)ethan-1-one (8, 1.5 g,
7.07 mmol, 1 equiv), MeSO2NH2 (672 mg, 7.07 mmol, 1 equiv),
ADmix-α (9.90 g, ∼1.4 g for 1 mmol of alkene) in t-BuOH/H2O (1:1,
100 mL), 72 h, 0 °C. After column chromatography (hexanes/EtOAc,
90:10 to 70:30) 1.51 g (87%) of a pale, yellow oil was obtained (>98%
ee).
(+)-1-(5-((1S,2R)-1,2-Dihydroxy-2-phenylethyl)furan-2-yl)-
ethan-1-one (9b). Following the general procedure used for the
synthesis of (+)-1a: (E)-1-(5-styrylfuran-2-yl)ethan-1-one (8, 1.5 g,
7.07 mmol, 1 equiv), MeSO2NH2 (672 mg, 7.07 mmol, 1 equiv),
ADmix-β (9.90 g, ∼1.4 g for 1 mmol of alkene) in t-BuOH/H2O (1:1,
40 mL), 24 h, 0 °C. After column chromatography (hexanes/EtOAc,
1,1′-([2,2′-Bifuran]-5,5′-diyl)bis(ethan-1-one) (2a). The dimer
byproduct was isolated from the reaction of 1-(5-bromofuran-2-
yl)ethan-1-one with alkenyl boronic acids; 15 mg (9% of dimer 2a in
the synthesis of (E)-1-(5-(hept-1-en-1-yl)furan-2-yl)ethan-1-one, 2) of
a pale, yellow solid was obtained.
(+)-Armillariol C (1a). To an ice-cold mixture of (E)-1-(5-(hept-1-
en-1-yl)furan-2-yl)ethan-1-one (2, 1.5 g, 7.27 mmol, 1 equiv), t-BuOH
(50 mL), and H2O (50 mL) were added MeSO2NH2 (692 mg, 7.27
D
DOI: 10.1021/acs.jnatprod.7b00484
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Note
90:10 to 70:30) 1.53 g (88%) of a pale, yellow oil was obtained (>98%
ee).
Chemistry, Biochemistry and Applications, 2nd ed.; Wiley: Chichester,
West Sussex, 2011.
́
General Procedure for the Determination Enantiomeric
Excess.21 The diol (1.0 equiv), 2-formylphenylboronic acid (1.0
equiv), and (S)-(α)-benzylamine (1.0 equiv) were dissolved in CDCl3
under an argon atmosphere. After stirring at RT for 15 min, an aliquot
(2) Lukevits, E.; Demicheva, L. Chem. Heterocycl. Compd. 1993, 29,
243−267.
(3) Reddy, C. R.; Krishna, G.; Reddy, M. D. Org. Biomol. Chem. 2014,
12, 1664−1670.
1
was analyzed by H NMR. The doublet for Ha, multiplet for Hb, or
(4) Kobori, H.; Sekiya, A.; Yasuda, N.; Noguchi, K.; Suzuki, T.; Choi,
J.-H.; Hirai, H.; Kawagishi, H. Tetrahedron Lett. 2013, 54, 5481−5483.
(5) Li, Z.; Wang, Y.; Jiang, B.; Li, W.; Zheng, L.; Yang, X.; Bao, Y.;
Sun, L.; Huang, Y.; Li, Y. J. Ethnopharmacol. 2016, 184, 119−127.
(6) Chen, C.-C.; Kuo, Y.-H.; Cheng, J.-J.; Sung, P.-J.; Ni, C.-L.; Chen,
C.-C.; Shen, C.-C. Molecules 2015, 20, 9994−10003.
(7) Geng, Y.; Zhu, S.; Lu, Z.-M.; Xu, H.-Y.; Cheng, P.; Shi, J.-S.; Xu,
Z.-H. Int. J. Med. Mushrooms 2014, 16, 319−325.
singlet for Hc was utilized to determine enantiomeric excess. Figure 3
shows the resonance peaks for Hb of 10a and 10b. In each instance,
none of the corresponding enantiomer was detected; thus, owing to
1
the limits of H NMR, the enantiomeric excess of each isomer was
reported as >98%.
Bioassay.22 Lettuce seeds were put on filter paper (Advantec No.
2, ϕ 55 mm; Toyo Roshi Kaisha, Japan), soaked in distilled water in a
Petri dish (ϕ 60 × 20 mm), and incubated in a growth chamber under
darkness at 25 °C for 1 day. Each sample was dissolved in 1 mL of
methanol (1, 10−2, 10−4, 10−6, and 10−8 μmol/mL) and then poured
on the filter paper (ϕ 55 mm) in a Petri dish (ϕ 60 × 20 mm). After
the sample-loaded paper had been air-dried, 1 mL of distilled water
was poured on the sample-loaded paper or intact filter paper (control).
The preincubated lettuce seedlings (n = 9 in each Petri dish) were
transferred onto the sample-loaded filter paper or control filter paper
and incubated in a growth chamber under darkness at 25 °C for 3
days. The lengths of the hypocotyl and the root were measured using a
ruler.
(8) Chang, C.-W.; Lur, H.-S.; Lu, M.-K.; Cheng, J.-J. Food Res. Int.
2013, 54, 239−245.
(9) Geng, Y.; Zhu, S.; Cheng, P.; Lu, Z.-M.; Xu, H.-Y.; Shi, J.-S.; Xu,
Z.-H. Phytomedicine 2017, 26, 55−61.
(10) Zhang, S.; Liu, X.; Yan, L.; Zhang, Q.; Zhu, J.; Huang, Na;
Wang, Z. Molecules 2015, 20, 5680−5697.
(11) Chen, Y.-J.; Wu, S.-Y.; Chen, C.-C.; Tsao, Y.-L.; Hsu, N.-C.;
Chou, Y.-C.; Huang, H.-L. J. Funct. Foods 2014, 6, 196−204.
(12) Donatini, B. Phytotherapie 2013, 11, 39−41.
(13) Robinson-Bax, C.; Fox, R. T. V. Mycologist 2002, 16, 21−22.
(14) Ismail, M. A.; Brun, R.; Wenzler, T.; Tanious, F. A.; Wilson, W.
D.; Boykin, D. W. J. Med. Chem. 2004, 47, 3658−3664.
(15) Thimmaiah, M.; Zhang, X.; Fang, S. Tetrahedron Lett. 2008, 49,
5605−5607.
Growth activity against the mycelia of F. velutipes was examined as
follows. The mycelia of F. velutipes were placed onto a PDA plate and
incubated at 25 °C for 1 day in an incubator. Meanwhile, the test
compounds or control solution (in MeOH) was added to autoclaved
paper disks (Advantec ϕ 8 mm; Toyo Roshi Kaisha, Ltd., Japan) and
then air-dried. Each air-dried paper disk containing 1 μmol/paper disk
of the compounds was placed directly onto the incubated plate. Plates
were further incubated at 25 °C for 1−2 weeks. After the incubation,
the inhibitory activity was evaluated by observation of clear zones due
to growth inhibition of mycelia. The observation was repeated in
duplicate for all of the test plates over a period of 2 weeks.
́
(16) Alacid, E.; Najera, C. J. Org. Chem. 2009, 74, 8191−8195.
(17) Molander, G. A.; Bernardi, C. R. J. Org. Chem. 2002, 67, 8424−
8429.
(18) Noreen, M.; Rasool, N.; El Khatib, M.; Molander; Gary, A. J.
Org. Chem. 2014, 79, 7243−7249.
(19) Kobayashi, Y.; Nakano, M.; Kumar, G. B.; Kishihara, K. J. Org.
Chem. 1998, 63, 7505−7515.
(20) Ren, J.; Liu, Y.; Song, L.; Tong, R. Org. Lett. 2014, 16, 2986−
2989.
ASSOCIATED CONTENT
* Supporting Information
(21) Kelly, A. M.; Perez-Fuertes, Y.; Arimori, S.; Bull, S. D.; James, T.
D. Org. Lett. 2006, 8, 1971−1974.
(22) Kobori, H.; Sekiya, A.; Suzuki, T.; Choi, J.-H.; Hirai, H.;
Kawagishi, H. J. Nat. Prod. 2015, 78, 163−167.
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.7b00484.
Physical data, assay results, and copies of 1H and
13C{1H} NMR spectra (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: bwatkins@uu.edu.
ORCID
M. Damoder Reddy: 0000-0002-4000-1548
E. Blake Watkins: 0000-0002-7505-0083
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was funded by Union University. The authors are
grateful for the HRESIMS data provided by D. R. Phillips and
C.-W. Chou [Proteomics and Mass Spectrometry (PAMS)
Facility, NIH grant 1S10RR1028859] at the University of
Georgia, Department of Chemistry, Athens, Georgia.
REFERENCES
■
(1) Pozharskiĭ, A. F.; Katritzky, Alan, R.; Soldatenkov, A. T.
Heterocycles in Life and Society: An Introduction to Heterocyclic
E
DOI: 10.1021/acs.jnatprod.7b00484
J. Nat. Prod. XXXX, XXX, XXX−XXX