Corsifurans A-C, 2-arylbenzofurans of presumed stilbenoid origin from Corsinia coriandrina (Hepaticae)

Article abstract of DOI:10.1016/j.phytochem.2004.10.002

Chemical investigation of the diethyl ether extract from Corsinia coriandrina resulted in the identification and synthesis of three 4′,5-O-disubstituted 2-arylbenzofurans as new natural products together with (E)- and (Z)-3,4′-dimethoxystilbene. Chemical

Full text of DOI:10.1016/j.phytochem.2004.10.002

PHYTOCHEMISTRY
Phytochemistry 65 (2004) 3113–3118
www.elsevier.com/locate/phytochem
Corsifurans A–C, 2-arylbenzofurans of presumed stilbenoid
origin from Corsinia coriandrina (Hepaticae)
*
Stephan H. von Reuß , Wilfried A. Ko¨nig
Institut fu¨r Organische Chemie, Universita¨t Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany
Received 24 August 2004; received in revised form 1 October 2004
Abstract
Chemical investigation of the diethyl ether extract from the liverwort Corsinia coriandrina resulted in the isolation of a new
2-arylbenzofuran compound called corsifuran A. The structure was identified by spectroscopic techniques and confirmed by synthe-
sis. Two minor constituents of similar structure, and two related stilbenoids and a bibenzyl were identified by comparison of the
mass spectra and GC retention indices with authentic samples. Due to the similarity in substitution patterns a stilbenoid origin
of the corsifurans is proposed.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Corsinia coriandrina; Liverworts; 2-Arylbenzofurans; Stilbenoids; Structure elucidation; Synthesis
1. Introduction
pathways for 2-arylbenzofuran biogenesis (Fig. 1). The
20,40,6-trioxygenated 2-arylbenzofurans (4) of the Faba-
ceae are considered to be of isoflavonoid origin and derive
from loss of one carbon unit during ring contraction of a
coumestan (3) as shown for the phytoalexin vignafuran
from Vigna unguiculata (Preston et al., 1975; Martin
and Dewick, 1979; Kinoshita, 1997). For the moracin
phytoalexins and related antifungal compounds with a
30,50,6-trioxygenated 2-arylbenzofuran structure (7) ob-
tained from mulberry (Morus sp.) a stilbenoid origin
has been considered (Nomura, 1988) due to the co-occur-
rence of structurally similar resveratrol (5) and oxyresve-
ratrol (6) (Takasugi et al., 1978). Closely related
stilbenoids and 2-arylbenzofurans as well as the corre-
sponding glucosides have also been described from Scho-
enocaulon officinale (Liliaceae) (Kanchanapoom et al.,
2002).
Several 2-arylbenzofurans originating from the phe-
nylpropanoid-polymalonate pathway have previously
been described, mainly from the Fabaceae (Leguminosae)
and Moraceae. A considerable number is known to occur
as phytoalexins, specific stress metabolites produced de
novo in response to microbial or fungal infections as well
as to abiotic factors. These compounds exhibit antifungal
(Carter et al., 1978; Nomura, 1988), antibacterial (Demi-
zu et al., 1988; Tanaka et al., 2003; Erasto et al., 2004), in-
sect feeding deterrent (Russell et al., 1984), free radical
scavenging (Sharma et al., 2001; Erasto et al., 2004), anti-
oxidant (Demizu et al., 1988), cyclooxygenase inhibiting
(Su et al., 2002), and estrogenic activities (Halabalaki
et al., 2000; Collini et al., 2004).
Comparison of the substitution patterns and labelling
experiments have revealed isoflavonoid or stilbenoid
In comparison to flavonoids (2), isoflavonoids (3) and
stilbenoids (8) are very rare in bryophytes, but bibenzyls
and bisbibenzyls are widely distributed among the liver-
worts (Asakawa, 1995, 2004). Nevertheless, licarin A
from Jackiella javanica (Nagashima et al., 1990) and
egonol 2-methylbutanoate from Riccardia multifida
*
Corresponding author. Tel.: +49 40 42838 6088; fax: +49 40 42838
2893.
E-mail address: s.von.reuss@web.de (S.H. von Reuß).
0031-9422/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.phytochem.2004.10.002

3114
S.H. von Reuß, W.A. Ko¨nig / Phytochemistry 65 (2004) 3113–3118
O
HO
OH HO
OH
HO
O
HO
OH
1
2
4
OH
Fabaceae
Moraceae
4'
OH
6
OH
O
HO
HO
O
HO
2'
HO
3
OH
5'
OH
6
O
3'
HO
R
OH
OH
5 (R = H)
7
6 (R = OH)
Corsinia
coriandrina
H CO
3
OCH
3
4'
5
OCH
3
H CO
3
O
8
9
Fig. 1. Biogenetic pathways for 2-arylbenzofurans of phenylpropanoid–polymalonate origin (phenylpropanoid unit drawn bold).
subsp. decrescens (Yoshida et al., 1997), which represent
the only 2-arylbenzofuran compounds reported from the
bryophytes so far, are apparently of neolignan (bisaryl-
propenoid) origin.
We now like to report on the isolation, structure elu-
cidation and synthesis of corsifuran A (9) with a 40,5-
dioxygenated 2-arylbenzofuran skeleton of presumed
stilbenoid origin from the Mediterranean liverwort Cor-
sinia coriandrina.
predominating
molecular
ion
peak
at
m/z = 256 [M]+ and several fragment ion signals of
low intensity, with those at m/z = 241 [M–CH3]+,
m/z = 225 [M–OCH3 ]+ and m/z = 213 [M–CH3–CO]+
indicating a methoxy substituted aromatic structure.
By HRMS, the molecular formula of C16H16O3 with
9 degrees of unsaturation could be established. The
1H NMR spectrum exhibited signals for one 1,4-
disubstituted and one 1,2,4-trisubstituted benzene unit,
two methoxy groups and one anisochoric methylene
group adjacent to a stereogenic methine group (Table
1). Inspection of the H,H-COSY spectrum revealed a
bibenzyl skeleton, whereas the chemical shift of the
stereogenic methine group (dH 5.48) and the aniso-
chrony of the adjacent methylene group (dH 2.90
and 3.09) indicated a 2-(4-methoxyphenyl)-2,3-dihydro-
benzofuran structure with a 5- (or 6-) methoxy substi-
tution, which we name corsifuran A (10).
2. Results and discussion
From the diethyl ether extract of Corsinia coriand-
rina (Spreng.) Lind. (Corsiniaceae), collected in Anda-
lusia, Spain, one unidentified major component (10,
7.1% of the total volatiles) was isolated by a combina-
tion of repeated column chromatography on SiO2
using a n-hexane–diethyl ether gradient and a n-hex-
ane–dichloromethane gradient, followed by preparative
thin-layer chromatography using a n-hexane–ethyl ace-
tate mixture. The mass spectrum exhibited a highly
Two additional minor constituents with similar frag-
mentation patterns, called corsifuran B (11, 1.5%)
(C15H14O3, m/z = 242.0961) and corsifuran C (12,
1.1%) (C16 H14O3, m/z = 254.0965), were tentatively

S.H. von Reuß, W.A. Ko¨nig / Phytochemistry 65 (2004) 3113–3118
3115
Table 1
afforded 5-hydroxy-2-(4-methoxyphenyl)-2,3-dihydro-
benzofuran (11) in moderate yield, which was shown
to be identical to corsifuran B by comparison of the
mass spectra and gas chromatographic retention indices
on different stationary phases. Methylation of 11 af-
1H NMR data for corsifuran A–C in C6D6 (500 MHz, dH in ppm,
integral, multiplicity, J in Hz; assignments made by 1H NMR and
COSY experiments)
1H
Corsifuran
A (10)
Corsifuran
B (11)
Corsifuran
C (12)
1
forded corsifuran A (10), which exhibited MS and H
2
3
5.48 1H t 8.6
2.90 1H
5.44 1H t 8.8
2.84 1H
–
6.61 1H d 0.8
NMR data identical to the natural product isolated
from C. coriandrina. Dehydrogenation of 10 using 2,3-
dichloro-5,6-dicyano-p-benzoquinone (DDQ) in diox-
ane afforded corsifuran C (12) as shown by GC–MS.
In addition, one unidentified minor constituent with a
highly dominating signal for the molecular ion at
m/z = 240 was detected in the diethyl ether extract of
Corsinia coriandrina (13, 1.3% of the total volatiles).
The mass spectrometric fragmentation pattern indicated
a methoxy substituted aromatic compound. HRMS af-
forded the molecular formula C16H16O2 with 9 degrees
of unsaturation and, thus, suggested a dimethoxystil-
bene structure. By comparison with an authentic sample
prepared according to modified literature procedures
(E)-3,40-dimethoxystilbene (13) could be identified in a
liverwort for the first time (Huneck, 1976). Traces of
the isomeric (Z)-3,40-dimethoxystilbene (14, 0.2%) and
3,40-dimethoxybibenzyl (15, 0.1%) were also detected
by GC–MS (Fig. 2).
dd 15.4, 8.5
3.09 1H
dd 15.8, 8.5
3.02 1H
30
–
dd 15.8, 9.1
6.70 1H d 2.8
3.38 3H s
dd 15.8, 9.1
6.45 1H d 2.5
–
4
6.96 1H d 2.5
3.44 3H s
6.84 1H
5-OCH3
6
6.62 1H
6.33 1H
dd 8.5, 2.8
6.83 1H d 8.5
7.20 2H d 8.8
6.75 2H d 8.8
3.28 3H s
dd 8.6, 2.5
6.73 1H d 8.8
7.17 2H d 8.8
6.74 2H d 8.8
3.27 3H s
dd 8.9, 2.5
7
7.30 1H d 8.9
7.75 2H d 8.9
6.79 2H d 8.9
3.27 3H s
2060
3050
40-OCH3
identified as the corresponding O-desmethyl and 2,3-de-
hydro derivatives, respectively.
The 2-(4-methoxyphenyl)-benzofuran skeleton of the
corsifurans and the 5-O-substitution were proven unam-
biguously by synthesis as shown in Fig. 3. Although a
synthetic access to corsifuran A (10) (Gates et al.,
1992) and corsifuran C (12) (Thomas and Bokadia,
1968; Guy and Guette, 1980) has already been de-
scribed, we followed a modification of an alternative lit-
erature procedure (Ohara et al., 2002). Cycloaddition
between 4-methoxystyrene (18) and p-quinone (20) pro-
moted by ferric(III)chloride hexahydrate in acetonitrile
Although corsifuran A and C (10, 12) have previously
been described as synthetic compounds this is the first
report on their identification as natural products. The
unusual 40,5-O-disubstitution of the corsifurans (10–
12) has so far only been described for the corresponding
4
4
3
3
OR
OCH3
4'
4'
2
2
5
6
5
6
H3CO
H3CO
O
O
7
7
12
10 (R = CH3)
11 (R = H)
H3CO
OCH3
OCH3
H3CO
13
14
17
RO
HO
COOH
OR
OH
15 (R = CH3)
16 (R = H)
Fig. 2. 2-Arylbenzofurans (10–12), stilbenoids (13, 14) and bibenzyls (15–17) from Corsinia coriandrina.

3116
S.H. von Reuß, W.A. Ko¨nig / Phytochemistry 65 (2004) 3113–3118
O
OH
a
RO
O
RO
O
20
11 (R = CH3)
21 (R = H)
18 (R = CH3)
19 (R = H)
b
OCH3
OCH3
c
H3CO
H3CO
O
O
12
10
a: FeCl3 x 6 H2O (H3CCN); b: CH3I, K2CO3 (acetone); c: DDQ (dioxane)
Fig. 3. Synthesis of corsifuran A–C (10–12) and previously proposed metabolic pathway of p-coumaric acid in Bacillus megaterium via 19 to 21.
O,O-desmethyl derivative (21), known as a racemic
metabolite of exogenic p-coumaric acid in Bacillus mega-
terium (Torres y Torres and Rosazza, 2001). Due to the
co-occurrence of 4-hydroxystyrene (19), a biogenetic
pathway similar to that of corsifuran B (11) was sug-
gested (Fig. 3), although the origin of the required p-qui-
none (20) remained questionable. In contrast to racemic
21, high enantiopurity of corsifuran A (10) could be
established by enantioselctive GC using an octakis-
CPSil-19 (Chrompack) or Carlo Erba Fractovap 4160
instrument equipped with a 25 m fused silica capillary
column with octakis-(2,6-di-O-methyl-3-O-pentyl)-c-
cyclodextrin in OV-1701 (1:1; w/w). Hydrogen at 0.5
bar inlet pressure was used as carrier gas. Split injection
at 200 ꢁC (split ratio: 1:30); flame ionisation detector at
250 ꢁC. Temp. progr. 50–250 ꢁC at 3 ꢁC/min. Electron
impact (70 eV) GC–MS and GC–HRMS measurements
were carried out on a Hewlett Packard HP 5890 gas
chromatograph equipped with a 25 m CPSil-5 CB
(Chrompack) fused-silica capillary column coupled to
a VG Analytical 70-250S mass spectrometer.
(2,6-di-O-methyl-3-O-pentyl)-c-cyclodextrin
(Ko¨nig, 1987).
column
The similarity in substitution patterns between cor-
sifuran A–C (10, 11, 12), (E)- and (Z)-3,40-dimethoxy-
stilbene (13, 14) and 3,40-dimethoxybibenzyl (15) with
the liverwort-specific dormancy inducing factor lunula-
ric acid (17) and its decarboxylation product lunularin
(16) (Fig. 2), previously isolated from Corsinia coriand-
rina (Gorham, 1977), indicates a common phenylpropa-
noid–polymalonate pathway (Eckermann et al., 2003).
Furthermore, the co-occurrence of 3,40-dimethoxystilbe-
nes (8) suggests a stilbenoid origin for the corsifurans (9)
as shown in Fig. 1. Hence, the A ring of the corsifurans
(9) should originate from the phenylpropanoid unit in
contrast to the oxyresveratrol derived moracins (7) ob-
tained from Moraceae (Fig. 1). Biological tests with
the synthetic compounds and investigation of their
absolute stereochemistry and biogenesis are in progress.
3.1.2. NMR spectroscopy
NMR measurements were carried out with a Bruker
WM 400 instrument for broadband decoupled 13C
NMR and 13C Pendant spectra (100.6 MHz) and with
WM 500 instrument for 1H NMR, H,H-COSY, HMQC
and HMBC spectra (1H: 500.1 MHz, 13C: 125.8 MHz).
Benzene-d6 was used as solvent and TMS served as
internal standard.
3.2. Plant material and extracts
Plant material of Corsinia coriandrina (Spreng.) Lind.
was collected near Tarifa and near St. Bartolomeo,
Andalusia, Spain in March 2003 and April 2004, respec-
tively. The liverworts were identified by Professor R.
Mues, (Universita¨t des Saarlands, Germany) and Dr.
H. Muhle (Universita¨t Ulm, Germany). After careful
cleaning the air dried plant material (10 g) was powdered
under liquid nitrogen and extracted with diethyl ether.
3. Experimental
3.1. General experimental procedures
3.3. Isolation of corsifuran A (10)
3.1.1. GC, GC–MS and GC–HRMS
Gas chromatograms were run using a Carlo Erba
HRGC 5300 Mega instrument equipped with 25 m fused
silica capillary columns with polysiloxanes CPSil-5 and
The crude diethyl ether extract was chromatographed
on silica gel 60 F254 (Merck) using a n-hexane–diethyl

S.H. von Reuß, W.A. Ko¨nig / Phytochemistry 65 (2004) 3113–3118
3117
Table 2
filtered, concentrated and chromatographed on silica
using a n-hexane–ethyl acetate mixture (10/1) to give
140 mg 5-methoxy-2-(4-methoxyphenyl)-2,3-dihydro-
benzofuran (0.55 mmol, 95% yield) identical to the nat-
ural product (10) isolated from C. coriandrina.
5-Methoxy-2-(4-methoxyphenyl)-2,3-dihydrobenzo-
furan. White solid; 1H and 13C NMR data: see Tables 1
and 2, respectively; MS (EI, 70 eV): m/z (%): 256 (100)
[M]+, 241 (6), 225 (2), 213 (3), 198 (4), 181 (4), 171 (2),
165 (2), 148 (6), 141 (3), 128 (4), 115 (6), 91 (3), 77 (5),
55 (8), 51 (6); HRMS m/z = 256.1091 [M]+ (calc. for
C16H16O3: 256.1099).
13C NMR data for corsifuran A–C in C6D6 (100 MHz, dC in ppm,
multiplicity; assignments made by PENDANT, HMQC and HMBC
experiments)
13C
Corsifuran A (10) Corsifuran B (11) Corsifuran C (12)
2
84.3 d
39.1 t
84.3 d
38.9 t
157.6 s
100.7 d
130.9 s
104.0 d
157.1 s
55.1 q
3
3a
4
128.3 s
111.7 d
154.9 s
128.3 s
112.5 d
150.6 s
–
5
5-OCH3 55.6 q
6
113.2 d
109.5 d
154.6 s
134.8 s
127.5 d
114.2 d
159.9 s
114.6 d
109.5 d
154.3 s
134.7 s
127.5 d
114.2 d
159.9 s
54.8 q
113.1 d
112.0 d
150.6 s
124.2 s
127.0 d
114.9 d
160.8 s
55.7 q
7
7a
10
2060
3050
40
3.6. Synthesis of corsifuran C (12)
40-OCH3 54.8 q
A solution of 51 mg 10 (0.2 mmol) in 1 ml dioxane
was treated with 48 mg 2,3-dichloro-5,6-dicyano-p-ben-
zoquinone (0.21 mmol) and heated to 100 ꢁC for 14 h.
Crystals formed after cooling were washed with n-hex-
ane and the combined solution concentrated in vacuum.
The residue was chromatographed on silica (elution with
dichloromethane) to give 48 mg 5-methoxy-2-(4-meth-
oxyphenyl)-benzofuran (0.19 mmol, 95% yield) identical
to the natural product (12) from C. coriandrina.
ether gradient and a n-hexane–dichloromethane gradient,
respectively. Preparative thin-layer chromatography on
glass plates with silica gel 60 F254 (Merck) using a n-hex-
ane–ethyl acetate mixture (10/1, Rf = 0.17, UV detection)
afforded 0.5 mg corsifuran A (0.005% of the dry weight).
5-Methoxy-2-(4-methoxyphenyl)-2,3-dihydrobenzo-
furan. White solid; 1H and 13C NMR data: see Tables 1
and 2, respectively; MS and HRMS data: see Section 3.5.
5-Methoxy-2-(4-methoxyphenyl)-benzofuran.
Off-
white solid; H and 13C NMR data: see Tables 1 and
2, respectively; MS (EI, 70 eV): m/z (%): 254 (100)
[M]+, 239 (44), 223 (2), 211 (18), 196 (5), 183 (7), 168
(20), 152 (10), 139 (16), 127 (7), 114 (6), 63 (7); HRMS
m/z = 254.0965 [M]+ (calc. for C16H14O3: 254.0943).
1
3.4. Synthesis of corsifuran B (11)
A solution of 270 mg p-quinone 20 (2.5 mmol) in 10
ml acetonitrile was treated with 13.5 mg FeCl3 hexahy-
drate (0.05 mmol), and a solution of 335 mg 4-methox-
ystyrene 18 (2.5 mmol) in 1 ml acetonitrile was added
dropwise. After stirring at room temperature for 6 h
the reaction mixture was poured into 15 ml water and
extracted with 2 · 15 ml dichloromethane. The organic
phase was washed with 2 · 25 ml water, dried over so-
dium sulphate and concentrated. Column chromatogra-
phy on silica (elution with dichloromethane) afforded
230 mg 5-hydroxy-2-(4-methoxyphenyl)-2,3-dihydro-
benzofuran (0.95 mmol, 38% yield) identical to the nat-
ural product (11) from C. coriandrina.
Acknowledgements
We thank Dr. V. Sinnwell, Universita¨t Hamburg, for
NMR and Mrs. A. Meiners and Mr. M. Preusse for
GC–MS and GC–HRMS measurements, Professor R.
Mues, Universita¨t des Saarlands, and Dr. H. Muhle,
Universita¨t Ulm, for the identification of the plant mate-
rial and Mr. S. Schmidt-Lehr for technical assistance.
References
5-Hydroxy-2-(4-methoxyphenyl)-2,3-dihydrobenzo-
furan. White solid; 1H and 13C NMR data: see Tables 1
and 2, respectively; MS (EI, 70 eV): m/z (%): 242 (100)
[M]+, 227 (6), 199 (5), 181 (16), 165 (2), 153 (7), 141
(2), 134 (8), 128 (6), 121 (4), 115 (15), 91 (6), 77 (11),
65 (9), 55 (18), 51 (10), 39 (10); HRMS m/z = 242.0961
[M]+ (calc. for C15H14O3: 242.0943).
Asakawa, Y., 1995. Chemical constituents of the bryophytes. Prog.
Chem. Org. Nat. Prod. 65, 1–618.
Asakawa, Y., 2004. Chemosystematics of the Hepaticae. Phytochem-
istry 65, 623–669.
Carter, G.A., Chamberlain, K., Wain, R.L., 1978. The fungitoxicity of
analogs of the phytoalexin 2-(20-methoxy-40-hydroxyphenyl)-6-
methoxybenzofuran (vignafuran). Ann. Appl. Biol. 88, 57–64.
Collini, M.D., Kaufman, D.H., Manas, E.S., Harris, H.E., Henderson,
R.A., Xu, Z.B., Unwalla, R.J., Miller, C.P., 2004. 7-Substituted 2-
phenyl-benzofurans as ERb selective ligands. Bioorg. Med. Chem.
Lett. 14, 4925–4929.
3.5. Synthesis of corsifuran A (10)
A solution of 140 mg 11 (0.58 mmol) in 3 ml acetone
was treated with 0.5 g potassium carbonate and 170 mg
methyl iodide (1.2 mmol). After 12 h, the mixture was
Demizu, S., Kajiyama, K., Takahashi, K., Hiraga, Y., Yamamoto, S.,
Tamura, Y., Okada, K., Kinoshita, T., 1988. Antioxidant and
antimicrobial constituents of licorice: isolation and structure

3118
S.H. von Reuß, W.A. Ko¨nig / Phytochemistry 65 (2004) 3113–3118
elucidation of a new benzofuran derivative. Chem. Pharm. Bull. 36,
3474–3479.
Nagashima, F., Toyota, M., Asakawa, Y., 1990. Terpenoids from
some Japanese liverworts. Phytochemistry 29, 2169–2174.
Nomura, T., 1988. Phenolic compounds of the mulberry tree and
related plants. Prog. Chem. Org. Nat. Prod. 53, 87–201.
Ohara, H., Kiyokane, H., Itoh, T., 2002. Cycloaddition of styrene
derivatives with quinone catalyzed by ferric ion; remarkable
acceleration in an ionic liquid solvent system. Tetrahedron Lett.
43, 3041–3044.
Eckermann, C., Schro¨der, G., Eckermann, S., Strack, D., Schmidt, J.,
Schneider, B., Schro¨der, J., 2003. Stilbencarboxylate biosynthesis: a
new function in the family of chalcone synthase related proteins.
Phytochemistry 62, 271–286.
Erasto, P., Bojase-Moleta, G., Majinda, R.R.T., 2004. Antimicrobial
and antioxidant flavonoids from the root wood of Bolusanthus
speciosus. Phytochemistry 65, 875–880.
Preston, N.W., Chamberlain, K., Skipp, R.A., 1975. A 2-arylbenzofu-
ran phytoalexin from cowpea (Vigna unguiculata). Phytochemistry
14, 1843–1844.
Gates, B.D., Dalidowicz, P., Tebben, A., Wang, S., Swenton, J.S.,
1992. Mechanistic aspects and synthetic applications of the
electrochemical and iodobenzene bis(trifluoroacetate) oxidative
1,3-cycloadditions of phenols and electron-rich styrene derivatives.
J. Org. Chem. 57, 2135–2143.
Russell, G.B., Shaw, G.J., Christmas, P.E., Yates, M.B., Sutherland,
O.R.W., 1984. Two 2-arylbenzofurans as insect feeding deterrents
from sainfoin (Onobrychis viciifolia). Phytochemistry 23, 1417–1420.
Sharma, R., Sharma, A., Shono, T., Takasugi, M., Shirata, A.,
Fujimura, T., Machii, H., 2001. Mulberry moracins: scavengers of
UV stress-generated free radicals. Biosci. Biotechnol. Biochem. 65,
1402–1405.
Gorham, J., 1977. Lunularic acid and related compounds in liverworts,
algae and Hydrangea. Phytochemistry 16, 249–253.
Guy, A., Guette, J.P., 1980. Utilization of polyphosphoric acid in the
presence of a co-solvent. Synthesis, 222–223.
Halabalaki, M., Aligiannis, N., Papoutsi, Z., Mitakou, S., Moutsat-
sou, P., Sekeris, C., Skaltsounis, A.L., 2000. Three new aryl-
obenzofurans from Onobrychis ebenoides and evaluation of their
binding affinity for the estrogen receptor. J. Nat. Prod. 63, 1672–
1674.
Su, B-N., Cuendet, M., Hawthorne, M.E., Kardono, L.B.S., Rswan,
S., Fong, H.H.S., Mahta, R.G., Pezzuto, J.M., Kinghorn, A.D.,
2002. Constituents of the bark and twigs of Artocarpus dadah with
cyclooxygenase inhibitory activity. J. Nat. Prod. 86, 163–169.
Takasugi, M., Munoz, L., Masamune, T., Shirata, A., Takahashi, K.,
1978. Stilbene phytoalexins from diseased mulberry. Chem. Lett.,
1241–1242.
Huneck, S., 1976. Moosinhaltsstoffe XVIII: Synthese von Pellepiphyl-
lin und Lunularin. Tetrahedron 32, 109–113.
Kanchanapoom, T., Suga, K., Kasai, R., Yamasaki, K., Kamel, M.S.,
Mohamed, M.H., 2002. Stilbene and 2-arylbenzofuran glucosides
from the rhizomes of Schoenocaulon officinale. Chem. Pharm. Bull.
50, 863–865.
Tanaka, H., Oh-Uchi, T., Etoh, H., Sako, M., Sato, M., Fukai, T.,
Tateishi, Y., 2003. An arylbenzofuran and four isoflavonoids from
the roots of Erythrina poeppigiana. Phytochemistry 63, 597–602.
Thomas, K.K., Bokadia, M.M., 1968. Cyclodehydration of aryloxyac-
etophenones by polyphosphoric acid: part III. Synthesis of aryl
substituted benzofurans. J. Indian Chem. Soc. 45, 265–269.
Torres y Torres, J.L., Rosazza, J.P.N., 2001. Microbial transforma-
tions of p-coumaric acid by Bacillus megaterium and Curvularia
lunata. J. Nat. Prod. 64, 1408–1414.
Kinoshita, T., 1997. A plausible analogy for biosynthesis of 2-
arylbenzofuran of isoflavonoid origin and its application to
synthesis of vignafuran. Tetrahedron Lett. 38, 259–262.
Ko¨nig, W.A., 1987. The Practice of Enantiomer Separation by
Capillary Gas Chromatography. A. Huthig Verlag, Heidelberg,
¨
Basel, New York.
Yoshida, T., Toyota, M., Asakawa, Y., 1997. Isolation, structure
elucidation, and chemical derivatization of a new cyclic bisbibenzyl
dimer, pusilatin E, from the liverwort Riccardia multifida susp.
decrescens. J. Nat. Prod. 60, 145–147.
Martin, M., Dewick, P.M., 1979. Biosynthesis of the 2-arylbenzofuran
phytoalexin vignafuran from Vigna unguiculata. Phytochemistry
18, 1309–1317.