Meroterpenoid pigments from Albatrellus flettii (basidiomycetes)

Article abstract of DOI:10.1002/ejoc.200601022

The pigments responsible for the blue colour of the North American polypore Albatrellus flettii have been isolated and their structures elucidated by spectroscopic methods. Albatrellin, a dimeric meroterpenoid with a furylbenzoquinone chromophore, is acco

Full text of DOI:10.1002/ejoc.200601022

FULL PAPER
DOI: 10.1002/ejoc.200601022
Meroterpenoid Pigments from Albatrellus flettii (Basidiomycetes)
Barbara Koch[a][‡] and Wolfgang Steglich*[b]
Dedicated to Professor Conrad Hans Eugster on the occasion of his 85th birthday
Keywords: Natural products / Meroterpenoids / Mushrooms / Quinones / Furans
The pigments responsible for the blue colour of the North
American polypore Albatrellus flettii have been isolated and
their structures elucidated by spectroscopic methods. Alba-
trellin, a dimeric meroterpenoid with a furylbenzoquinone
chromophore, is accompanied by its 16-hydroxy and 16-oxo
derivatives. The latter has recently been described as gri-
folone B from a Japanese collection of A. caeruleoporus.
Based on the idea that albatrellin is formed in nature by oxi-
dative coupling of a grifolinquinone with the furan derivative
cristatin, the blue pigment was synthesized in vitro. The re-
action could be applied to the synthesis of several analogues.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
Results and Discussion
Mushrooms of the genus Albatrellus (Aphyllophorales)
contain meroterpenoids with various biological activities.
Grifolin (1)[1] and neogrifolin (2)[1b] are the most common
metabolites of this type to which other compounds like cris-
tatic acid (3)[2] are closely related.
Isolation and Structural Elucidation of the Pigments
Freshly collected fruit bodies of A. flettii were peeled and
the blue skins from 1.5 kg of fungi extracted with methanol.
TLC of the extract on silica gel revealed the presence of
three violet-blue pigments A, B, and C according to increas-
ing polarity. In addition two colourless compounds were
identified as grifolin (1) and neogrifolin (2). The pigments
were enriched by chromatography of the crude extract on
Sephadex LH-20, followed by flash chromatography of the
coloured fractions on silica gel. Separation of the individual
pigments was achieved by centrifugal thin layer chromatog-
raphy to yield 12.5 mg of pigment A, 6 mg of pigment B,
and 1.3 mg of pigment C. In a separate workup the meth-
anol extract from lyophilized fruit bodies was distributed
between water and chloroform. Repeated flash chromatog-
raphy of the organic phase on silica gel with hexanes/EtOAc
yielded grifolin (1, 0.9% of dry weight) and neogrifolin (2,
0.2%), identified by comparison with authentic samples.[1b]
Solutions of the pigments in chloroform or dichloro-
methane resemble blue ink; in methanol they appear more
violet. According to the great similarity of their UV/Vis
spectra with maxima in the range of λmax = 272–274, 395–
397, and 530–535 nm (in MeOH) all three pigments must
contain the same chromophore. Pigment A, named albatrel-
lin, exhibits a molecular ion peak at m/z = 680.4061 in the
high-resolution EI-MS, corresponding to the molecular for-
mula C44H56O6. This indicates that the pigment is a dehy-
dro dimer of grifolin or neogrifolin (C22H32O2) containing
two additional oxygen atoms and two more double-bond
equivalents. Intensive [M+ + H] and [M+ + 2 H] peaks and
Some years ago, we became attracted by the beautiful
velvet-blue colour shown by the fruit bodies of A. flettii
Morse ex Pouzar, a species occurring in the Pacific West of
North America[3] and in West China.[4] Other species with
remarkable blue and greenish tints are A. caeruleoporus
(Peck) Pouzar and A. cristatus (Schaeff.) Kotl. & Pouzar
(German: Grüner Kammporling), respectively. In this pub-
lication we describe the structural elucidation of the pig-
ments from A. flettii.[5]
[a] Kekulé-Institut für Organische Chemie und Biochemie der Uni-
versität Bonn
Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
[b] Department Chemie, Ludwig-Maximilians-Universität
München,
Butenandtstr. 5–13 (F), 81377 München, Germany
Fax: +49-89-2180-77756
E-mail: wos@cup.uni-muenchen.de
[‡] New address: Bayer CropScience AG, BCS-D-MEF, Geb.6650,
40789 Monheim, Germany
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B. Koch, W. Steglich
FULL PAPER
a strong IR absorption at 1650 cm–1 are characteristic for a
quinone system.
The 13C NMR spectrum of albatrellin exhibits 40 signals
and in addition two signals, each representing two identical
carbon atoms. According to the DEPT spectrum, 9 methyl,
8 methylene, 8 methine, and 19 quaternary carbon atoms
1
are present. The H-coupled 13C NMR spectrum of alba-
trellin allows to identify partial structure A, which corre-
sponds to cristatin (8),[2] the decarboxylation product of cri-
static acid (3). Notable are the singlet for the 15Ј-furan pro-
ton at δH = 6.17 ppm (δC = 110.9 ppm), a multiplet for the
12Ј-methylene protons at δH = 1.64 ppm (δC = 110.9 ppm),
and a multiplet at δH = 6.00 ppm (δC = 114.1 ppm), charac-
teristic for the deshielded methine proton at the terminal
isobutenyl residue. In addition, the methylresorcinol ex-
plains the formation of a strong benzyl ion peak at m/z =
carbon signal suffers the expected downfield shift from δC
= 39.7 ppm in 4 to δC = 55.1 ppm (δH = 3.00). Pigment 5
is identical with grifolinone B, a metabolite recently isolated
by Asakawa et al.[6] from a Japanese collection of A. caeru-
leoporus. Interestingly, the monomeric 16-oxogrifolin (gri-
folinone A) was also found in this species. Both compounds
inhibit the nitric oxide production in RAW 264.7 cells. The
biological activity of albatrellin is unknown.
1
137 in the EI-MS. Since in the H NMR spectrum of alba-
trellin the signal for the furan α-proton is missing, partial
structure A must be connected through position 21Ј to the
rest of the molecule (Figure 1).
The most polar pigment C of A. flettii C44H56O7, pos-
sesses one more oxygen atom than albatrellin. The presence
of a hydroxy group is indicated by an intense [M+ – H2O]
ion peak in the high-resolution EI-MS (m/z = 678) and
NMRspectroscopicdata,whichrevealthepresenceofa(CH3)2-
C=CHCHOHCH2– moiety. Noteworthy is the methine sig-
nal at δH = 4.39 ppm (δC = 65.7 ppm), which appears as
triplet of doublets (J = 8.5, 4.5 Hz) due to 3J couplings with
the neighbouring CH2 and CH protons. Since all the other
signals agree with those of albatrellin, pigment C must pos-
sess the structure of a 16-hydroxyalbatrellin (6). The limited
amount of material as well as the intense colour of this
compound prohibited the determination of the chiroptical
properties.
Figure 1. Partial structures A and B for albatrellin (arrows indicate
1
selected couplings from the H-coupled 13C NMR spectrum).
The remaining NMR signals of albatrellin can be as-
signed to a 1,4-benzoquinone moiety carrying an intact far-
nesyl chain as well as a methyl and a hydroxy substituent.
In the 1H-coupled 13C NMR spectrum the quinone car-
bonyl signal at δC = 185.2 ppm and the signal of the carbon
atom carrying the enolic OH group at δC = 150.5 ppm ap-
Biomimetic Synthesis of Albatrellin and Some of Its
Analogues
3
pear as triplets with JH,C = 4.5 and 5 Hz, respectively, due
to coupling with the signals of the methylene protons of the
attached farnesyl residue. Similarly, the signals of the sec-
The structure of albatrellin (4), (Scheme 1) suggests its
ond quinone carbonyl group at δC = 184.1 ppm and a car- formation from two components, one derived from grifolin
bon atom at δC = 135.5 ppm are split into quadruplets with (1) and the other from cristatic acid (3). To prove this idea
3JH,C = 4 and 5 Hz, respectively, by interaction with the experimentally, we prepared the unknown hydroxyquinone
neighbouring methyl substituent. Considering the two re- 7 from grifolin by treatment with potassium nitrosodisul-
2
maining carbon signals at δC = 120.0 ppm (t, JC,H
=
fonate (Fremy’s salt).[7] Cristatin (8) was obtained by ther-
6.5 Hz) and δC = 137.5 ppm (m) allows the completion of mal decarboxylation of cristatic acid (3).[2] On stirring a 2:1
the benzoquinone ring as depicted in partial structure B. mixture of 7 and 8 in dichloromethane at room tempera-
Combining both partial structures at positions 21Ј and 6 ture, the solution gradually turned blue and, after two
leads to formula 4 for albatrellin, which is supported by weeks, albatrellin could be isolated in 30% yield. Since each
COSY and COLOC experiments.
of the starting materials, grifolin (1)[8] and cristatic acid
In pigment B, C44H54O7, one of the methylene groups of (3),[9] have already been prepared by total syntheses, this
albatrellin (4) has been transformed into a keto group. Its constitutes a formal total synthesis of albatrellin.
position is indicated by the EI-MS, in which the base peak
Similarly, the reaction of quinone 7 with cristatic acid (3)
at m/z = 83 (C5H7O) can be explained by α-cleavage from yielded 32% of 4Ј-carboxyalbatrellin (9). The latter is rather
a terminal (CH3)2C=CHCOCH2– unit. This leads to the unstable and suffers easy decarboxylation to albatrellin (4)
structure of 16-oxoalbatrellin (5) for this pigment, which is even on standing in the refrigerator. Reaction of 2-hydroxy-
supported by the NMR spectroscopic data. In the 13C 3,6-dimethyl-1,4-benzoquinone (10)[10] with cristatin (8) af-
NMR spectrum of 5, the signal of the additional CO group forded the coupling product 11 in 22% yield. On the other
appears at δC = 200.3 ppm, and the neighbouring methylene hand, reaction of the benzoquinones 7 or 10 with 2-isobut-
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Meroterpenoid Pigments from Albatrellus flettii (Basidiomycetes)
FULL PAPER
conjugated furan chromophore[12] and not from a charge
transfer interaction of the quinone with the remote resor-
cinol group.
Experimental Section
General: Evaporation of the solvents was performed under reduced
pressure using a rotary evaporator. Column chromatography: Silica
gel 60 (Merck), Sephadex LH-20 (Pharmacia). Analytical TLC: Sil-
ica gel 60 F254 aluminium foils (Merck); solvent system A (v/v):
hexanes/EtOAc, 5:1; B: toluene/HCO2Et/HCO2H, 10:5:3; C:
CH2Cl2/MeOH, 20:1; D: CH2Cl2; E: hexanes/EtOAc, 10:2. Prepar-
ative centrifugal TLC: Chromatotron 7924T (Harrison Research),
silica gel/CaSO4 plates, 1–4 mm. UV: Varian Cary 17 spectropho-
tometer. IR: Perkin–Elmer 1420. NMR: Bruker instruments AC
600, WM 400, AC 200 and WH 90, in CDCl3 and [D6]acetone with
the solvent peak as internal standard. Multiplets due to 1J(C,H)
couplings are indicated by capital letters. EI-MS: A.E.I. MS 50
with data system DS 50, direct inlet (DI) at 70 eV and 180 °C.
2-Hydroxy-3,6-dimethyl-1,4-benzoquinone (10)[10,17] was prepared
from 2,5-dimethylbenzoquinone via 1,2,4-triacetoxy-3,6-dimeth-
ylbenzene and 3,6-dimethylbenzene-1,2,4-triol according to litera-
ture procedures.[5] 2-(1-Acetoxy-2-methylpropyl)furan was ob-
tained from 2-(1-hydroxy-2-methylpropyl)furan[11a] in 75% yield by
treatment with acetic anhydride/pyridine in the presence of a cata-
lytic amount of DMAP. Cristatic acid (3) was isolated from A. cris-
tatus.[2]
Scheme 1. Synthesis of albatrellin (4).
enylfuran (12)[11] furnished the corresponding furylqui-
nones 13 and 14 only in 3 and 1.5% yield, respectively. This
reflects the importance of the additional alkyl chain at the
furan ring for the coupling reaction.[12] Experiments to en-
hance the reaction rate by adding Lewis acid catalysts such
as BF3, ZnCl2, AlCl3 or traces of HCl or AcOH were un-
successful[13] and caused the formation of uncharacterized
green “polymers” due to the instability of cristatic acid (3)
under acidic conditions.[2] The addition of oxidizing agents
such as DDQ,[14] useful for the quinone–furan coupling in
simple cases, is known to convert ortho-polyprenylated phe-
nols into the corresponding chromenes.[15]
Mushrooms: A. flettii was collected in September 1987 near Bam-
field, Vancouver Island, Canada.
Isolation Procedure: The caps of fresh fruit bodies of A. flettii
(1500 g) were peeled and the blue skins extracted with MeOH.
Concentration of the extracts yielded a brownish black residue
(2.99 g), which was divided into two portions and prepurified by
gel chromatography on two Sephadex LH-20 columns with MeOH
as eluent. Three coloured fractions were obtained, which were
flash-chromatographed on silica gel (hexanes/EtOAc, 5:1) to re-
move 1 and 2. The separation of the three very similar pigments
was achieved by repeated centrifugal TLC chromatography on sil-
ica gel (hexanes/EtOAc, 7:1, 5:1, 2:1, and CH2Cl2/MeOH, 20:1).
Final purification of each fraction with Sephadex LH-20 (eluent
CHCl3/MeOH, 1:1) yielded pigments 4 (12.5 mg), 5 (6.6 mg), and
6 (1.3 mg) as dark blue, glass-like solidified oils. For the isolation
of 1 and 2, dried fruit bodies (25.5 g) of A. flettii were powdered
and extracted with MeOH (2ϫ250 mL). The combined extracts
were concentrated under reduced pressure, and the resulting residue
was triturated with water (20 mL) to remove mannitol. Extraction
of the mixture with CHCl3 and concentration of the organic phases
yielded
a residue (0.92 g), which was prepurified by flash
chromatography on silica gel (hexanes/EtOAc, 5:2, stepwise gradi-
ent to 100% EtOAc). Rechromatography of the grifolin/neogrifolin
fractions yielded the pure compounds. Grifolin (1): 0.24 g (0.94%
of dry weight), Rf (TLC) = 0.71 (hexanes/EtOAc, 10:3), 0.80 (sol-
vent system B). The TLC spot turns carmine-red within a few days,
with anisaldehyde/H2SO4 blue-violet, and with sulfovanillin blue,
finally blue-green. Neogrifolin (2): 0.05 g (0.2% of dry weight), Rf
(TLC) = 0.35 (hexanes/EtOAc, 10:3), 0.59 (solvent system B). The
TLC spot turns yellowish red within a few days, with anisaldehyde/
H2SO4 blue-violet, and with sulfovanillin blue, finally green-brown.
Compounds 1 and 2 were identified by direct comparison with au-
thentic samples.[2]
The reaction between activated benzoquinones and fu-
rans has been thoroughly investigated by Eugster and co-
workers.[16] More recently, Valderrama et al.[3] discovered
that nonactivated quinones can be coupled with furans in
acetic acid. In the case of cristatin (8), this coupling occurs
even in dichloromethane without proton catalysis through
enhancement of the nucleophilicity at the furan ring by the
isobutenyl substituent.
All coupling products including the simplest derivative
14 are blue and exhibit UV spectra similar to those of the
albatrellins. This indicates that the colour originates from
Albatrellin (4): Rf (TLC) = 0.56 (system A), 0.71 (system B). UV/
electronic interactions between the benzoquinone and the Vis (MeOH): λmax (logε) = 274 (4.45), 397 (3.56), 535 (3.50) nm.
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B. Koch, W. Steglich
FULL PAPER
IR (KBr): ν = 3420 (s), 2960 (sh), 2920 (s), 2860 (sh), 1650 (s),
16-Hydroxyalbatrellin (6): Rf (TLC) = 0.29 (system A), 0.50 (system
˜
1600 (m), 1430 (m), 1370 (m), 1310 (s), 1240 (m), 1160 (w), 1050 B). UV/Vis (MeOH): λmax (εrel) = 273 (1.0), 395 (0.17), 530 (0.09
(m), 980 (w), 820 (w) cm–1. 1H NMR (600 MHz, CDCl3): δ = 1.54 sh) nm. 1H NMR (600 MHz, CDCl3): δ = 1.54 (s, 3 H, 21-H), 1.61
(s, 3 H, 21-H), 1.56 (s, 3 H, 20-H), 1.64 (tt, J = 6.5 Hz, 2 H, 12Ј- (s, 3 H, 20-H), 1.64 (m, 2 H, 12Ј-H), 1.66 (d, J = 1.5 Hz, 19-H),
H), 1.65 (s, 3 H, 19-H), 1.72 (s, 3 H, 22-H), 1.75 (s, 3 H, 22Ј-H),
1.89 (s, 3 H, 19Ј-H), 1.95 (s, 3 H, 20Ј-H), 1.90–2.05 (m, 10 H, 11-
H, 12-H, 15-H, 16-H, 11Ј-H), 2.02 (s, 3 H, 7-H), 2.18 (s, 3 H, 7Ј-
H), 2.21 (t, J = 7.5 Hz, 2 H, H-13Ј), 3.16 (d, J = 7 Hz, 2 H, 8-H),
1.70 (d, J = 1.5 Hz, 3 H, 22-H), 1.75 (s, 3 H, 22Ј-H), 1.88 (s, 3 H,
19Ј-H), 1.95 (s, 3 H, 20Ј-H), 1.97 (m, 4 H, 11-H, 11Ј-H), 2.02 (s, 3
H, 7-H), 2.00–2.10 (m, 4 H, 12-H, 15-H), 2.17 (s, 3 H, 7Ј-H), 2.18
(m, 2 H, H-13Ј), 3.15 (d, J = 7 Hz, 2 H, 8-H), 3.30 (d, J = 7 Hz, 2
3.32 (d, J = 7 Hz, 2 H, 8Ј-H), 4.92 (br. s, 2 OH), 5.05 (tm, J = H, 8Ј-H), 4.39 (td, J = 8, 4.5 Hz, 16-H), 5.15 (m, 4 H, 17-H, 13-H,
7 Hz, 2 H, 13-H, 17-H), 5.14 (tm, J = 7 Hz, 1 H, 9-H), 5.17 (tm, J 9Ј-H, 9-H), 5.32 (s, OH), 6.00 (sept, J = 1.5 Hz, 1 H, 17Ј-H), 6.18
= 7 Hz, 1 H, 9Ј-H), 6.00 (m, 1 H, 17Ј-H), 6.17 (s, 1 H, 15Ј-H), 6.18
(s, 2 H, 4Ј-H, 6Ј-H), 7.03 (br. s, 1 OH) ppm. 1H-coupled 13C NMR
(150 MHz, CDCl3): δ = 13.5 (Q, J = 130 Hz, C-7), 16.0 (Qm*, C-
(s, 1 H, 15Ј-H), 6.18 (s, 2 H, 4Ј-H, 6Ј-H), 7.05 (br. s, 1 H, OH)
ppm. 13C NMR (150 MHz, CDCl3): δ = 13.4 (C-7), 16.0–16.1 (C-
21, C-22, C-22Ј), 18.2 (C-20), 20.3 (C-20Ј), 21.1 (C-7Ј), 22.1 (C-8Ј),
21), 16.1 (Qm*, C-22), 16.2 (Qm*, C-22Ј), 17.7 (Qm*, C-20), 20.3 22.2 (C-8), 25.3 (C-13Ј), 25.8 (C-19), 26.4 (C-12), 27.3 (C-19Ј), 27.8
(Qm, J = 121 Hz, C-20Ј), 21.0 (Qt, J = 126, 5 Hz, C-7Ј), 22.1 (Td, (C-12Ј), 39.2 (C-11Ј), 39.5 (C-11), 48.1 (C-15), 65.7 (C-16), 108.8
J = 127, 4 Hz, C-8Ј), 22.3 (Td, J = 130, 4 Hz, C-8), 25.4 (Tm, J =
127 Hz, C-13Ј), 25.7 (Qm, J = 125 Hz, C-19), 26.5 (Tm*, C-12), 120.3 (CH), 122.4 (CH), 127.2 (CH), 128.7 (CH), 131.2 (Cq), 131.5
26.7 (Tm*, C-16), 27.2 (Q*, C-19Ј), 27.8 (Tm, J = 128 Hz, C-12Ј), (Cq), 134.4 (Cq), 135.0 (Cq), 135.5 (Cq), 136.7 (Cq), 137.3 (Cq),
39.1 (Tm*, C-11Ј), 39.67 (Tm*, C-15), 39.72 (Tm*, C-11), 108.9 137.4 (Cq), 137.5 (C-5Ј), 140.5 (C-21Ј), 150.6 (C-3), 154.8 (C-1Ј, C-
(C-4Ј, C-6Ј), 110.5 (C-2Ј), 111.0 (C-15Ј), 114.1 (C-17Ј), 119.8 (Cq),
(Dquint, J = 158, 6 Hz, C-4Ј, C-6Ј), 110.3 (m, C-2Ј), 110.9 (Dm, J
= 171 Hz, C-15Ј), 114.1 (Dsept, J = 154, 6 Hz, C-17Ј), 119.6 (Dm,
J = 155 Hz, C-9), 120.0 (t, J = 6.5 Hz, C-2), 122.1 (Dm, J = 152 Hz,
C-9Ј), 124.1 (Dm, J = 151 Hz, C-13), 124.4 (Dm, J = 151 Hz, C-
17), 131.1 (m, C-18), 131.3 (m, C-14Ј), 135.0 (m, C-14), 135.5 (q,
3Ј, C-16Ј), 184.1 (C-4), 185.2 (C-1) ppm. EI MS: m/z (%) = 696
(3.4) [M+], 680 (31.8) [M+ + 2 H –H2O], 679 (26.6) [M+ + H –
H2O], 678 (57.6) [M+ – H2O], 529 (18.1) [M+ – C11H19O], 203 (10.8)
[C13H15O2], 191 (6.3), 175 (62.0) [C11H11O2], 137 (100) [C8H9O2],
83 (75.6) [C5H7O]. HR EI-MS: calcd. for C44H56O7 696.4025;
J = 5.5 Hz, C-6), 137.1 (m, C-10), 137.3 (m, C-18Ј), 137.4 (m, C- found 696.4006.
5Ј), 137.5 (m, C-5), 137.9 (m, C-10Ј), 140.3 (m, C-21Ј), 150.5 (t, J
2-Farnesyl-3-hydroxy-5-methyl-1,4-benzoquinone (7): A solution of
= 5 Hz, C-3), 154.7 (m, C-1Ј, C-3Ј), 154.9 (d, J = 10 Hz, C-16Ј),
184.1 (q, J = 4 Hz, C-4), 185.2 (t, J = 4.5 Hz, C-1) ppm; * signals
overlapping. EI MS: m/z (%) = 682 (14.5), 681 (37.2), 680 (78.1)
[M+], 597 (5.9) [M+ – C5H7O], 191.1795 (8.3) [C14H23], 191.1061
(15.0) [C12H15O2], 177 (11.8) [C11H13O2], 175 (32.7) [C11H11O2],
163 (10.1) [C10H11O2], 149 (9.4) [C9H9O2], 137 (100) [C8H9O2], 83
(19.8) [C5H7O], 69 (41.6) [C5H9]. HR EI-MS: calcd. for C44H56O6
680.4077; found 680.4061.
1 (100 mg, 0.31 mmol) in acetone (10 mL) was treated with a solu-
tion of potassium nitrosodisulfonate (483 mg, 1.8 mmol) in the
minimum amount of water. The mixture was buffered with 0.6 
aqueous KH2PO4 (57 mL) and the resulting turbidity removed by
addition of acetone. After 16 h of stirring at room temperature in
the dark, the reaction was complete. Removal of the acetone under
reduced pressure, extraction of the remaining aqueous phase with
CHCl3 (1ϫ100 mL, 2ϫ200 mL) and concentration of the dried
(Na2SO4) combined extracts yielded the crude product, which was
purified by flash chromatography with hexanes/EtOAc (10:2). 7
(76 mg, 73%) was obtained as a yellow solid. Rf (TLC) = 0.71
(system E). UV/Vis (MeOH): λmax (logε) = 264 (4.17), 312 (sh,
16-Oxoalbatrellin, Grifolinone B (5): Rf (TLC) = 0.42 (system A),
0.57 (system B). UV/Vis (MeOH): λmax (logε) = 272 (4.37), 395
(4.02), 533 (3.92) nm. IR (KBr): ν = 3400 (s, br.), 2920 (s), 2860
˜
4.20), 403 (4.12) nm. IR (KBr): ν = 3480 (s), 2970 (m), 2910 (m),
˜
(sh), 1650 (s), 1620 (s), 1440 (m), 1350 (m), 1310 (s), 1235 (m), 1165
(w), 1090 (w), 1050 (m), 985 (w), 820 (w) cm–1. 1H NMR
(600 MHz, CDCl3): δ = 1.55 (s, 3 H, 21-H), 1.65 (m, 2 H, 12Ј-H),
1.70 (s, 3 H, 22-H), 1.74 (s, 3 H, 22Ј-H), 1.86 (s, 3 H, 19Ј-H), 1.88
(s, 3 H, 19-H), 1.95 (s, 3 H, 20Ј-H), 1.95–2.07 (m, 6 H, 11-H, 12-
H, 11Ј-H), 2.03 (s, 3 H, 7-H), 2.13 (s, 3 H, 20-H), 2.16 (s, 3 H, 7Ј-
H), 2.19 (t, J = 7.5 Hz, 2 H, 13Ј-H), 3.00 (s, 2 H, 15-H), 3.15 (d, J
= 7 Hz, 2 H, 8-H), 3.31 (d, J = 7 Hz, 2 H, 8Ј-H), 5.14 (tm, J =
7 Hz, 1 H, 9-H), 5.16 (tm, J = 7 Hz, 1 H, 9Ј-H), 5.18 (tm, J = 7 Hz,
13-H), 6.00 (m, 1 H, 17Ј-H), 6.09 (sept, J ≈ 1 Hz, 1 H, 17-H), 6.17
(s, 1 H, 15Ј-H), 6.19 (s, 2 H, 4Ј-H, 6Ј-H) ppm. 13C NMR (150 MHz,
CDCl3): δ = 13.4 (C-7), 16.0 (C-22), 16.2 (C-22Ј), 16.4 (C-21), 20.3
(C-20Ј), 20.8 (C-20), 21.1 (C-7Ј), 22.1 (C-8Ј), 22.2 (C-8), 25.4 (C-
13Ј), 26.7 (C-12), 27.3 (C-19Ј), 27.76 (C-19), 27.84 (C-12Ј), 39.2 (C-
11Ј), 39.3 (C-11), 55.2 (C-15), 108.8 (C-4Ј, C-6Ј), 110.5 (C-2Ј), 111.1
(C-15Ј), 114.1 (C-17Ј), 119.6 (C-2), 119.9 (C-9), 122.4 (C-9Ј), 123.0
(C-17), 128.8 (C-14), 129.3 (C-13), 131.3 (C-14Ј), 135.5 (C-6), 136.3
(C-10), 136.9 (C-10Ј), 137.3 (C-5Ј), 137.37 (C-18Ј), 137.40 (C-5),
141.4 (C-21Ј), 150.6 (C-3), 154.8 (C-16Ј), 154.9 (C-1Ј, C-3Ј), 156.4
(C-18), 184.1 (C-4), 185.2 (C-1), 200.3 (C-16) ppm. EI MS: m/z (%)
= 696 (65.2), 695 (31.7), 694 (67.7) [M+], 613 (9.7) [M+ + 2 H –
C5H7O], 612 (5.0) [M+ + H – C5H7O], 611 (5.9) [M+ – C5H7O],
2850 (m), 1655 (s), 1630 (s), 1615 (s), 1445 (w), 1390 (m), 1370 (s),
1335 (m), 1305 (s), 1210 (s), 1175 (m), 1080 (w), 1055 (m), 890 (m)
cm–1. 1H NMR (200 MHz, CDCl3): δ = 1.55, 1.57 (each s, 3 H, 20-
H, 21-H), 1.65 (dm, J = 1.4 Hz, 3 H, 19-H), 1.72 (dm, J = 1.4 Hz,
3 H, 22-H), 1.85–2.07 (m, 8 H, 11-H, 12-H, 15-H, 16-H), 2.03 (d,
J = 1.7 Hz, 3 H, 7-H), 3.12 (dm, J = 7.5, 0.75 Hz, 3 H, 8-H), 5.05
(tq, J = 6.7, 1.4 Hz, 2 H, 13-H, 17-H), 5.11 (tq, J = 7.3, 1.4 Hz, 1
1
H, 9-H), 6.48 (q, J = 1.7 Hz, 1 H, 6-H), 6.92 (s, 1 OH) ppm. H-
coupled 13C NMR (50 MHz, CDCl3): δ = 14.9 (Qd, J = 129.5,
5.6 Hz, C-7), 16.1 (Qsext§, J = 125, 4 Hz, C-21), 16.2 (Qsext§, J =
125, 4 Hz, C-22), 17.7 (Qsext, J = 125, 4 Hz, C-20), 21.9 (Td, J =
129.5, 4 Hz, C-8), 25.8 (Q*, J ≈ 127 Hz, C-19), 26.5, 26.8 (each
Tm§, J = 128 Hz, C-12, C-16), 39.7 (Tm*, J = 127 Hz, 2 C, C-11,
C-15), 119.6 (Dm, J = 155.2 Hz, C-9), 120.4 (m, J = 6.5 Hz, C-2),
124.1, 124.4 (each Dm*, J ≈ 150 Hz, 2 C, C-13, C-17), 131.3 (sept,
J = 5.9 Hz, C-18), 135.1 (m, C-14), 135.3 (Dq, J = 164.8, 5.9 Hz,
C-6), 137.2 (m, C-10), 141.0 (q, J = 6.9 Hz, C-5), 150.8 (“q”, J =
4.8 Hz, C-3), 184.3 (ddq, J = 11.2, 4, 4 Hz, C-4), 187.4 (t, J =
4.8 Hz, C-1) ppm; * overlapping signals; § signals exchangeable. EI
MS: m/z (%) = 344 (3.0), 343 (1.6), 392 (4.7) [M+], 191 (53.7), 153
(38.1), 69 (100).
529 (18.4) [M+ – C11H17O], 203 (4.1) [C13H15O2], 175 (64.2) 2-(2-Methylpropenyl)furan (12): 2-(1-Acetoxy-2-methylpropyl)furan
[C11H11O2], 137 (66.1) [C8H9O2], 83 (100) [C5H7O]. HR EI-MS:
calcd. for C44H54O7 694.3870; found 694.3866.
(5 g, 27.4 mmol) was evaporated with a Kugelrohr apparatus at
75 °C and pyrolyzed by flash vacuum thermolysis (FVT) at 500 °C
1634
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 1631–1635

Meroterpenoid Pigments from Albatrellus flettii (Basidiomycetes)
FULL PAPER
under 10–3 mbar. The products were collected in a cool trap, dis-
solved in n-pentane and, for removal of the AcOH, extracted with
saturated aqueous NaHCO3. Evaporation of the solvent yielded 12
as a colourless oil (0.57 g, 17%), which quickly turns brown on air,
on Sephadex LH-20. Violet-blue solidified oil. Rf (TLC) = 0.82
(system B), 0.89 (system D). UV/Vis (MeOH): λmax (logε) = 282
(4.21), 373 (3.66), 530 (3.57) nm. H NMR (400 MHz, CDCl3): δ
= 1.94 (br. s, 3 H), 1.95, 2.03, 2.37 (each s, 3 H), 6.12 (br. “s”, 1
H), 6.39 (d, J = 3.7 Hz, 1 H), 7.14 (s, OH), 7.31 (d, J = 3.7 Hz, 1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 8.4, 13.3, 20.7, 27.5,
111.4, 114.3, 116.3, 122.6, 131.1, 132.3, 139.5, 146.4, 151.2, 156.4,
1
1
b.p. 155–156 °C. Rf (TLC) = 0.79 (n-pentane). H NMR (90 MHz,
CDCl3): δ = 1.87, 1.96 (each br. s, 3 H), 6.06 (m, 1 H, 6-H), 6.15
(d, J = 11 Hz, 1 H, 3-H), 6.37 (dd, J = 11, 6 Hz, 1 H, 4-H), 7.35
(d, J = 6 Hz, 1 H, 5-H) ppm. 13C NMR (22 MHz, CDCl3): δ = 183.5, 186.7 ppm. EI MS: m/z (%) = 274 (11.9), 272 (100) [M+],
20.1 (C-8), 27.0 (C-9), 107.2 (C-3), 111.0 (C-4), 114.5 (C-6), 135.3 191 (88), 83 (78). HR EI-MS: calcd. C16H16O4 272.1049; found
(C-7), 140.5 (C-5), 153.8 (C-2) ppm. EI MS: m/z (%) = 122 (100)
[M+], 107 (56.6), 93 (19.9), 91 (22.3), 81 (22.8), 79 (37.8), 77 (40.6).
HR EI-MS: calcd. C8H10O 122.0732; found 122.0732.
272.1049.
Acknowledgments
General Procedure for the Synthesis of 4 and Analogues: A solution
of the quinone (0.5 mmol) and the corresponding furan
(0.25 mmol) was stirred in CH2Cl2 or CHCl3 (50 mL) at room tem-
perature in the dark for three weeks. After removal of the solvent
under reduced pressure, the dark brown residue was purified either
by flash chromatography on silica gel with CH2Cl2/MeOH (4:
100:1; 9: 20:1) or by gel chromatography on Sephadex LH-20 with
MeOH.
This work was financially supported by the Bundesministerium für
Bildung und Forschung and the Fonds der Chemischen Industrie.
We thank Dr. Bert Steffan and Dr. Ingrid Josten for NMR experi-
ments, Dr. Fritz Hansske, Biofrontera Heidelberg, for his help in
collecting Albatrellus flettii and Prof. A. Bresinsky, Regensburg, for
identifying the species.
Albatrellin (4): Obtained from 7 and 8 in 30.2% yield according to
the general procedure. All spectroscopic data derived from 4 are in
agreement with those of the natural compound.
[1] a) T. Goto, H. Kakisawa, Y. Hirata, Tetrahedron 1963, 19,
2079–2083; b) H. Besl, G. Höfle, B. Jendrny, E. Jägers, W. Steg-
lich, Chem. Ber. 1977, 110, 3770–3776; c) I. Vrkoc, M. Budes-
˘ˇ
ˇ
4Ј-Carboxyalbatrellin (9): Obtained from 7 and 3 in 32% yield ac-
cording to the general procedure. Dark blue solidified oil, soluble
in CHCl3 with ink-blue and in MeOH with violet colour. 9 un-
dergoes slow decarboxylation to 4 even in the refrigerator. Rf
(TLC) = 0.43 (system A), 0.59 (system B). UV/Vis (MeOH): λmax
(logε) = 268 (4.34), 392 (4.29), 530 (4.22) nm. 1H NMR (600 MHz,
CDCl3): δ = 1.54, 1.57 (each s, 3 H), 1.65 (m, J = 6.5 Hz, 2 H),
1.65, 1.70, 1.75, 1.88, 1.95 (each s, 3 H), 1.90–2.02 (m, 10 H), 2.01
(s, 3 H), 2.20 (t, J = 7.5 Hz, 2 H), 3.16, 3.35 (each d, J = 7 Hz, 2
H), 5.04 (t, J = 7 Hz, 2 H), 5.14, 5.16 (each t, J = 7 Hz, 1 H), 6.00
(br. s, 1 H), 6.18 (s, 1 H), 6.20 (s, 1 H) ppm. EI MS: m/z (%) = 680
(100) [M+ – CO2], 597 (17.2), 177 (50.9), 137 (87.5), 83 (75), 69
(37.5), 44 (75.0).
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164–168.
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Model Compound 11: Obtained from quinone 10 and 8 according
to the general procedure. Yield 22% after purification by flash
chromatography (SiO2, CH2Cl2/MeOH, 20:1). Dark blue solidified
oil. Rf (TLC) = 0.58 (system B), 0.60 (system C). UV/Vis (MeOH):
λmax (logε) = 275 (4.12), 388 (3.30), 530 (3.24) nm. 1H NMR
(200 MHz, CDCl3): δ = 1.65 (m, J = 7 Hz, 2 H), 1.76, 1.89 (each
s, 3 H), 1.96 (s, 6 H), ≈ 2.00 (m, 2 H), 2.03, 2.19 (each s, 3 H), 2.22
(t, J = 7.5 Hz, 2 H), 3.32 (d, J = 7.2 Hz, 2 H), 5.17 (tm, J = 7.2 Hz,
1 H), 6.01 (sept, J = 1.5 Hz, 1 H), 6.19 (s, 3 H) ppm. EI MS: m/z
(%) = 492 (56.5), 491 (7.9), 490 (25.0) [M+], 409 (26.5), 283 (31.6),
259 (37.7), 217 (30.6), 175 (100), 137 (100), 83 (67.3). HR EI-MS:
calcd. C30H34O6 490.2355; found 490.2359.
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Bull. Chem. Soc. Jpn. 1994, 67, 1178–1185 and literature cited
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Model Compound 13: Obtained from 7 and furan 12 according to
the general procedure. Yield 3% after purification by flash
chromatography (SiO2, CH2Cl2). Dark blue solidified oil. Rf (TLC)
= 0.93 (system B). UV/Vis (MeOH): λmax (logε) = 286 (4.32), 380
1
(3.73), 534 (3.70) nm. H NMR (200 MHz, CDCl3): δ = 1.56 (br.,
6 H), 1.65, 1.75 (each d, J = 1.3 Hz, 3 H), 1.90–2.10 (m, 8 H), 1.94,
2.02, 2.35 (each s, 3 H), 3.15 (d, J = 6.6 Hz, 2 H), 5.05 (m, 2 H),
5.14 (t, J = 6.6 Hz, 1 H), 6.12 (m, 1 H), 6.38, 7.32 (each d, J =
4.2 Hz, 1 H) ppm. EI MS: m/z (%) = 462 (81.4) [M+], 326 (11.6),
311 (100), 272 (17.4), 191 (22.6), 175 (27.3), 137 (81.3). HR EI-MS:
calcd. C30H38O4 462.2770; found 462.2805.
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Lett. 1987, 393–396.
Model Compound 14: Obtained from 10 and 12 by refluxing the
Received: November 27, 2006
components in CHCl3 for 16 h. Yield 1.4% after chromatography
Published Online: February 14, 2007
Eur. J. Org. Chem. 2007, 1631–1635
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1635