Pigments of fungi. LXIII Synthesis of (1S,3R)- and (1R,3S)-austrocortilutein and the enantiomeric purity of austrocortilutein in some Australian Dermocybe toadstools

Article abstract of DOI:10.1071/CH99144

The naturally occurring tetrahydroanthraquinones (1S,3R)- and (1R,3S)-austrocortilutein (1b) and (1d), respectively, are synthesized for the first time in enantiomerically pure form by Diels-Alder cycloaddition between the functionalized butadiene derivative (4) and the corresponding monochiral trans-1,3-dihydroxy-1,2,3,4-tetrahydro-5,8-naphthoquinone (5a) or (5b), themselves derived from citramalic acid. Separation of the four stereoisomeric austrocortiluteins by using h.p.l.c. over a chiral stationary phase reveals that the enantiomeric purity of the (1S,3S)-and (1R,3R)-quinones (1a) and (1c) varies from species to species whereas the (1S,3R)-isomer (1b) is, in the five cases examined, enantiomerically pure. CSIRO 2000.

Full text of DOI:10.1071/CH99144

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Aust. J. Chem., 2000, 53, 41–46
Pigments of Fungi. LXIII†
Synthesis of (1S,3R)- and (1R,3S)-Austrocortilutein
and the Enantiomeric Purity of Austrocortilutein
in some Australian Dermocybe Toadstools
Catherine Elsworth,A Melvyn Gill,A,B Evelin RaudiesA and Abilio TenA
A School of Chemistry, The University of Melbourne, Parkville, Vic. 3010.
B Author to whom correspondence should be addressed.
The naturally occurring tetrahydroanthraquinones (1S,3R)- and (1R,3S)-austrocortilutein (1b) and (1d), respectively,
are synthesized for the first time in enantiomerically pure form by Diels–Alder cycloaddition between the func-
tionalized butadiene derivative (4) and the corresponding monochiral trans-1,3-dihydroxy-1,2,3,4-tetrahydro-5,8-
naphthoquinone (5a) or (5b), themselves derived from citramalic acid. Separation of the four stereoisomeric
austrocortiluteins by using h.p.l.c. over a chiral stationary phase reveals that the enantiomeric purity of the (1S,3S)-
and (1R,3R)-quinones (1a) and (1c) varies from species to species whereas the (1S,3R)-isomer (1b) is, in the five
cases examined, enantiomerically pure.
Keywords. Fungi; pigments; toadstools; quinones; Australian; Dermocybe; cycloaddition.
Introduction
Results and Discussion
The Synthesis of (1S,3 R)- and (1 R,3 S)-Austrocortilutein
All four stereoisomers of 1,3,8-trihydroxy-6-methoxy-3-
methyl-1,2,3,4-tetrahydro-9,10-anthraquinone (austrocorti-
lutein) are known as natural products.1 Thus, the (1S,3S)- and
(1S,3R)-diastereoisomers (1a) and (1b) were first isolated
from the Australasian toadstool Dermocybe splendida2 and
have later been found in several other, closely related,
Dermocybe species.1 The (1R,3R)- and (1R,3S)-stereoiso-
mers (1c) and (1d) are less common, being found so far only
in Dermocybe spp. WAT 20934 and WAT 21567,3 respec-
tively.‡ The relative stereochemistry between the C 1 and C 3
hydroxy groups in (1S,3S)-austrocortilutein (1a) was deter-
mined from the 1H n.m.r. spectrum and the absolute config-
uration followed by chemical degradation to the butanolide
(2) and an X-ray crystal structure analysis of the acetonide
derivative.2 The other austrocortiluteins were correlated
directly with (1a) and by way of their 1-deoxy derivatives.2,4
We recently reported the first total synthesis of the
(1S,3S)- and (1R,3R)-austrocortilutein enantiomers (1a) and
(1c) beginning from the (R)- and (S)-enantiomers (3a) and
(3b) of citramalic acid.5 We have now extended this method-
ology to encompass the two remaining natural products in
this series, namely (1S,3R)- and (1R,3S)-austrocortilutein
(1b) and (1d), and have developed a chromatographic
method for determining the stereochemical purity of both the
synthetic and natural compounds.
Our strategy for the synthesis of the trans-1,3-dihydroxy-
tetrahydroanthraquinones (1b) and (1d) is shown in ret-
rosynthetic terms in Scheme 1. Thus, we saw as the final step
in the synthetic process a Diels–Alder cycloaddition between
the silyloxy diene (4) and each of the hitherto unknown
trans-1,3-dihydroxytetahydro-5,8-naphthoquinones (5a) and
(5b). The quinones (5a) and (5b) could themselves arise by
stereoselective reduction and oxidative demethylation of the
corresponding chiral tetralones (6a) and (6b), which could
arise directly from the known cis-1,3-dihydroxytetahydro-
naphthalenes (7a) and (7c).5 Accordingly, the (1R,3R)-dihy-
droxytetrahydronaphthalene (7a) was prepared from
(S)-citramalic acid (3b) precisely as described before.5
Oxidation of the (1R,3R)-diol (7a) in dichloromethane by
using tetrapropylammonium perruthenate6 and 4-methyl-
morpholine N-oxide in the presence of molecular sieves gave
the new (3R)-tetralone (6a), [α]D –15 (c, 1.55 in CHCl3), in
85% yield. Alternatively, and somewhat more efficiently,
oxidation of the diol (7a) with the Dess–Martin periodinane7
in aqueous dichloromethane gave the chiral tetralone (6a) in
88% yield.
The spectroscopic data are in full accord with the tetralone
structure (6a) for the product. Thus, the mass spectrum
shows a molecular ion at m/z 236 that corresponds from
† Part LXII, Aust. J. Chem., 1999, 52, 1115.
‡ The code refers to the accession number under which voucher specimens are held in the herbarium of the Royal Botanic Garden, Edinburgh.
Manuscript received 19 October 1999 © CSIRO 2000 10.1071/CH99144 0004-9425/00/010041

42
C. Elsworth et al.
high-resolution mass measurement and combustion analysis
data to the molecular formula C13H16O4. The infrared spec-
trum of (6a) shows a strong ketone carbonyl stretch at 1670
cm–1 and in the 1H n.m.r. spectrum anAB quartet (J 15.7 Hz),
with components centred at δ 2.71 and 2.77, can be assigned
to the protons of the C 2 methylene group. These data
confirm that the benzylic hydroxy group in (7a) has been
oxidized. The tetralone (6a) is a stable crystalline solid, m.p.
162–164°C, which can be stored at –18°C for several weeks
without significant decomposition.
The next step was to reduce the carbonyl group in the (R)-
tetralone (6a) stereoselectively so as to generate a prepon-
derance of the (1S,3R)-diol (7b). In order to preserve
valuable monochiral intermediates during the optimization
of the conditions necessary to effect this transformation effi-
ciently, we first used the isochiral ketone (6a,b).† Thus,
treatment of the ketone (6a,b) with lithium borohydride in
tetrahydrofuran gave a near quantitative yield of a mixture of
the desired (1S*,3R*)-diol (7b,d) and the (1R*,3R*)-diol
(7a,c) in a ratio of 1: 2. The diastereomeric diols were con-
veniently separated by using flash pad chromatography and
their relative stereochemistry was readily determined from
the respective 1H n.m.r. spectra.2
Scheme 1. Route to the (1S,3R)- and (1R,3S)-austrocortiluteins (1b)
and (1d) from citramalic acid.
A much more satisfactory outcome was obtained when
the tetralone (6a) was exposed to tetramethylammonium
borohydride in the presence of acetic acid.8 Under these con-
ditions tetramethylammonium triacetoxyborohydride is gen-
erated, which is a much more stereoselective reagent than
borohydride itself. Firstly, tetramethylammonium borohy-
dride was prepared in 75% yield by reaction of sodium boro-
hydride with tetramethylammonium hydroxide. Subsequent
treatment of the (R)-tetralone (6a) in a mixture of acetonitrile
and acetic acid (2 : 1) at 0°C with this reagent gave, exclu-
sively, (1S,3R)-1,3-dihydroxy-5,8-dimethoxy-1,2,3,4-tetra-
hydronaphthalene (7b), [α]D +49 (c, 1.53 in CHCl3), in 85%
yield. The mass spectrum of the product (7b) confirmed the
molecular formula C13H18O4 that makes it isomeric with the
(1R,3R)-diol (7a). The trans-relative stereochemistry
between the C 1 and C 3 hydroxy groups in (7b) was evident
from the 1H n.m.r. spectrum and by comparison of it with the
corresponding data from the (1R,3R)-diol (7a).5 Of particu-
lar significance, the axial proton at C 2 in the spectrum of
(7b) appears as a double doublet due to geminal coupling (J
13.5 Hz) to H 2eq and vicinal coupling (J 8.5 Hz) to H 1. The
magnitude of the vicinal coupling constant indicates a trans-
diaxial relationship between H 2ax and H 1 in a preferred
half-chair conformation that places the hydroxy group at C 1
in an equatorial configuration (Fig. 1). The corresponding
proton (H 2ax) in the spectrum of the (1R,3R)-diol (7a)
appears as a double doublet with coupling constants of 14.5
and 5.0 Hz. In support of the structure (7b), the equatorial
proton at C 2 in the spectrum of (7b) appears as a double
doublet of doublets due to geminal coupling with Hax,
vicinal coupling (J 6.8 Hz) with H 1 and W-coupling (J 2.2
Hz) with H 4eq. The hydroxy groups at C 1 and C 3 in (7b)
must therefore be trans-disposed and, with the C 3 stereo-
chemistry inherited from the (R)-tetralone (6a), the absolute
configuration of the product (7b) must be (1S,3R).
† This was prepared in the same way as the (R)-tetralone (6a) starting from isochiral diol (7a,c).5

Pigments of Fungi. LXIII
43
crystallization of the mixture from chloroform gave (1S,3R)-
austrocortilutein (1b) as fine yellow needles, [α]D +293 (c,
0.10 in CHCl3), in 30% yield from (5a). H.p.l.c. analysis (see
below) of (1b) proves that the synthetic material is enan-
tiomerically pure and this, together with other physical, chi-
roptical and spectroscopic data (Experimental section) are in
full accord with the identity of the synthetic quinone (1b) and
(1S,3R)-austrocortilutein as it was isolated from Dermocybe
splendida.2 Since the structure of the natural quinone (1b) is
known unequivocally,2 the (predictable) regiochemical
outcome of the Diels–Alder reaction between (5a) and (4) is
confirmed. This is the first synthesis of (1S,3R)-austrocorti-
lutein (1b) in monochiral form.
We now turned to the last of the four austrocortilutein
stereoisomers, namely, (1R,3S)-austrocortilutein (1d). The
synthesis of the enantiomerically pure (1S,3S)-dihydroxy-
1,2,3,4-tetrahydronaphthalene (7c) from (R)-citramalic acid
(3a) was described before.5 The chemistry connecting the
diol (7c) with (1R,3S)-austrocortilutein (1d) mirrors that dis-
cussed above and need not be reiterated in detail here. The
spectroscopic properties of the individual intermediates
proved to be indistinguishable, with the notable exception of
their specific rotation, with those of their counterparts in the
enantiomeric series.
Briefly, the (1S,3S)-1,3-dihydroxytetrahydronaphthalene
(7c) was oxidized with the Dess–Martin periodinane to the
(S)-tetralone (6b), [α]D +14 (c, 1.53 in CHCl3), reduction of
which with tetramethylammonium borohydride gave the
trans-diol (7d), [α]D –48 (c, 1.56 in CHCl3), in 85% yield.
Oxidative demethylation of (7d) gave (1R,3S)-1,3-di-
hydroxy-1,2,3,4-tetrahydro-5,8-naphthoquinone (5b) as a
yellow gum, [α]D –166 (c, 1.07 in EtOH), which reacted with
1,3-dimethoxy-1-trimethylsilyloxybuta-1,3-diene (4) to give
a mixture of (1R,3S)-austrocortilutein (1d) and its isomer
(9b) in a ratio of 87 : 13, by 1H n.m.r. spectroscopy.
Fractional crystallization of the mixture from chloroform
gave pure (1R,3S)-austrocortilutein (1d) as fine yellow
needles, [α]D –265 (c, 0.18 in CHCl3), that was indistin-
guishable in all respects from the natural product.3
Fig. 1. Preferred half-chair conformation of the tetrahy-
droaromatic ring in the (1S,3R)-diol (7b).
The stereospecificity of the hydride reduction process and
the stereochemistry of the product (7b) can be rationalized in
terms of a mechanism involving chelation control through a
cyclic transition state (Fig. 2) during delivery of hydride to
the re face of the carbonyl group in (6a). Consequently, the
involvement of the C 3 hydroxy group is critical in securing
the required stereochemistry at the developing C 1 stereo-
genic centre.
As a potentially shorter route to trans-diols of the type
(7c) and (7d) we briefly explored the possibility of proceed-
ing directly from the aldehyde (8), the immediate precursor
of the cis-diol (7a), to the trans-diol (7b) by using a
Friedel–Crafts reaction that is sterically rather than chelation
controlled. Unfortunately, exposure of the aldehyde (8) to
both aluminium trichloride and boron trifluoride caused irre-
vocable damage to the molecule and this route was aban-
doned in favour of the oxidation–reduction process.
Oxidative demethylation of the (1S,3R)-tetrahydronaph-
thalene (7b) by using ammonium cerium(IV) nitrate in
aqueous acetonitrile gave (1S,3R)-1,3-dihydroxy-1,2,3,4-
tetrahydro-5,8-naphthoquinone (5a) in good yield as a
yellow gum, [α]D +163 (c, 1.09 in EtOH). High-resolution
mass measurement of the molecular ion at m/z 208 in the
mass spectrum of (5a) confirmed the formula C11H12O4. In
the 1H n.m.r. spectrum of the new quinone (5a) there are no
signals attributable to methoxy resonances while in the 13C
n.m.r. spectrum the carbon atoms of the quinone carbonyl
groups resonate at δ 189.0 and 187.5.
In the next step the (1S,3R)-tetrahydro-5,8-naphtho-
quinone (5a) and 1,3-dimethoxy-1-trimethylsilyloxybuta-
1,3-diene (4)5,9 were stirred together in benzene at room
temperature during 12 h. The mixture of cycloadducts was
diluted with water and stirred in the presence of air for a
further 12 h. The products were separated by chromatogra-
phy and a yellow zone that separated was identified as a
mixture of (1S,3R)-austrocortilutein (1b) and its regioisomer
(9a). The combined yield of the quinones (1b) and (9a) was
47%, with the former predominating in a ratio of 87 : 13 as
determined by integration of the phenolic hydroxy reso-
nances at δ 12.14 (1b) and 12.21 (9a) in the 1H n.m.r. spec-
trum of the mixture. The remainder of the spectrum of (9a) is
very similar to that of (1b), as might be expected. Fractional
The Enantiomeric Purity of Austrocortilutein
The likely biosynthetic progenetor of the austrocorti-
luteins is torosachrysone (10), both enantiomers of which
occur, usually in anisochiral mixtures, in Dermocybe and
Cortinarius.10–13 Consequently, to this point we have been
unsure as to the enantiomeric purity of the various austro-
cortiluteins that occur in Dermocybe. With authentic samples
of austrocortilutein now available in all four stereochemical
modifications we developed a chromatographic method for
their analysis.
We have used two chiral h.p.l.c. systems: the first (A)
employed a Chiralpak OD column (0.46 by 25 cm; Daicel
Chemical Industries) with ethanol/hexane (2 : 3) as eluent,
and the second (B) used a Chiralpak AD column (0.46 by 25
cm; Daicel Chemical Industries) with different combinations
of ethanol and hexane as eluent. The retention times of the
four synthetic austrocortiluteins (1a–d) in both systems A and
B are collected in Table 1. The chromatograms obtained for

44
C. Elsworth et al.
Table 1. H.p.l.c. retention times (min) for the four stereoisomers (1a–d) of austrocortiluteinA
Com-
pound
Retention time
100% EtOH
B
C
System A
System B
2: 3 EtOH/hexane
2: 1 EtOH/hexane
1: 1 EtOH/hexane
(1S,3S)-Austrocortilutein (1a)
(1S,3R)-Austrocortilutein (1b)
(1R,3R)-Austrocortilutein (1c)
(1R,3S)-Austrocortilutein (1d)
18.5
30.9
25.0
18.6
26.2
22.4
32.0
28.5
40.1
26.3
40.1
46.9
49.9
33.4
49.9
62.3
A Conditions are given in the Experimental section. B A Daicel chiralpak OD column was used. C A Daicel chi-
ralpak AD column was used.
the two enantiomeric pairs of synthetic quinones by using
system A are shown in Figs 3a,b. These traces show not only
that each enantiomer is well resolved from its antipode but
also that all synthetic samples are enantiomerically pure at
the levels of detection.
As was mentioned earlier (1S,3S)- and (1S,3R)-austrocor-
tiluteins (1a) and (1b), respectively, were originally isolated
from the ethanolic extracts of Dermocybe splendida2 while
the (1R,3R)- and (1R,3S)-austrocortiluteins (1c) and (1d),
respectively, were obtained from the Australasian
Dermocybe sp. WAT 20934.3 H.p.l.c. analysis of these four
natural products using system B gave the enantiomeric
excesses shown in the first two rows of Table 2. In the final
three rows of Table 2 are the results obtained with samples of
(1S,3S)- and (1S,3R)-austrocortilutein, (1a) and (1b),
recently obtained from three closely related Dermocybe
species collected in Tasmania. The results of the analysis
show that while (1S,3S)-austrocortilutein (1a) from D. splen-
dida is enantiomerically pure, the same pigment from the
Tasmanian species is anisochiral, varying in purity between
48 and 34% e.e. depending on the species. Similarly,
(1R,3R)-austrocortilutein (1c) is present in Dermocybe sp.
WAT 20934 in only 72% e.e. In contrast to the variability
observed in the cis-1,3-diol systems (1a) and (1c), all results
so far obtained with the trans-diastereoisomers (1b) and (1d)
indicate high enantiomeric purity.
Table 2. Stereochemistry and enantiomeric excess (e.e.)A of
austrocortilutein stereoisomers (1a–c) from Dermocybe
Species
Major
diastereoisomer
e.e.
(%)
Minor
diastereoisomer (%)
e.e.
Dermocybe splendida
(1S,3S)
(1R,3R)
(1S,3S)
(1S,3S)
(1S,3S)
100
72
34
36
48
(1S,3R)
(1S,3R)
(1S,3R)
(1S,3R)
(1S,3R)
100
100
100
100
100
Dermocybe sp. WAT 20934
Dermocybe sp. 950426A1
Dermocybe sp. 940417A1
Dermocybe sp. 950509A0
A Determined by h.p.l.c. analysis using system B (see Experimental section).
At this stage and with so few species examined it is not
possible to speculate on the significance, or otherwise, of
these observations. However, it is pertinent to note that, as in
the case of torosachrysone (10) itself,13 these chiral com-
pounds are being formed in some organisms with what is
much less than the level of stereocontrol that one is led to
associate with natural systems.
Fig. 3. H.p.l.c. traces (system A) for: (a) (1S,3S)- and (1R,3R)-austro-
cortilutein (1a) and (1c); (b) (1S,3R)- and (1R,3S)-austrocortilutein (1b)
and (1d).
With a sensitive method now available for determining
the stereochemical composition of these and related pig-

Pigments of Fungi. LXIII
45
(1S,3R)-5,8-Dimethoxy-3-methyl-1,2,3,4-tetrahydronaphthalene-1,3-
diol (7b) and (1R,3S)-5,8-Dimethoxy-3-methyl-1,2,3,4-tetrahydro-
naphthalene-1,3-diol (7d)
ments, we are in a position to examine the extracts of other
related fungi and build up a more extensive picture of the dis-
tribution and stereochemistry of tetrahydroanthraquinones in
Dermocybe and Cortinarius and to evaluate their taxonomic
significance.
Tetramethylammonium borohydride (150 mg, 1.69 mmol) was
added to acetic acid (7 ml) at 18°C.After 10 min, acetonitrile (7 ml) was
added and the mixture was cooled to 0°C. A solution of the (R)-
tetralone (6a) (99.1 mg, 0.416 mmol) in acetonitrile (7 ml) was added
dropwise over 5 min and the reaction mixture was allowed to warm to
room temperature during 18 h. The mixture was diluted with sodium
potassium tartrate (0.5 M, 20 ml) and the products were extracted into
dichloromethane (5×40 ml). The combined extract was washed with
cold dilute sodium hydrogen carbonate (2×40 ml), dried and evapo-
rated and the residue was purified by flash chromatography with ether
as eluent to give the (1S,3R)-diol (7b) (85 mg, 85%) as colourless
needles from ethyl acetate, m.p. 108–110°C {isochiral (7b,d) m.p.
105–107°C} (Found: C, 65.6; H, 7.7. C13H18O4 requires C, 65.5; H,
7.6%), [α]D +49 (c, 1.53 in CHCl3) {the (1R,3S)-diol (7d), [α]D –48 (c,
1.56 in CHCl3)}. νmax 3542, 2961, 1481, 1256 cm–1. δH (300 MHz) 1.39
(3H, s, 3-Me), 1.79 (1H, dd, J 13.5, 8.5 Hz, H2ax), 2.26 (1H, ddd, J
13.5, 6.8, 2.2 Hz, H2eq), 2.66 (1H, d, J 17.5 Hz, H4ax), 2.80 (1H, dd,
J 17.5, 2.2 Hz, H4eq), 3.75 and 3.83 (each 3H, s, 2×OMe), 4.01 (1H,
m, OH), 5.19 (1H, m, H 1), 6.71 (2H, m, H 6, H 7). δC (75 MHz) 30.2,
37.7, 42.7, 55.6, 55.7, 65.2, 69.8, 107.0, 109.1, 124.8, 127.6, 151.7,
151.9. Mass spectrum m/z 238 (M+, 19%), 205 (100), 202 (20), 187
(32), 18 (34).
Experimental
General Methods and Materials
General details are given in Part LXI.14 High-performance liquid
chromatography (h.p.l.c.) was performed on an ISCO model 2350 with
an ISCO UA-6 u.v.–visible detector, an optical flow cell operating at
280 nm and a Spectra-Physics SP 270 integrator. System A used a
Chiralpak OD column (0.46 by 25 cm; 10 µm particle size), while
system B used a Chiralpak AD column (0.46 by 25 cm;10 µm particle
size), both used as purchased from Daicel Chemical Industries, Tokyo.
Dermocybe sp. 950426A1, 940417A1 and 950509A0 were col-
lected by Dr D. A. Ratkowski, School of Agricultural Science, The
University of Tasmania, Hobart. The codes refer to the accession
numbers under which specimens are held in the herbarium in Hobart.
Synthesis of (1S,3R)- and (1R,3S)-Austrocortilutein (1b) and (1d),
Respectively
(R)-3-Hydroxy-5,8-dimethoxy-3-methyl-1,2,3,4-tetrahydronaphthalen-
1-one (6a) and (S)-3-Hydroxy-5,8-dimethoxy-3-methyl-1,2,3,4-
tetrahydronaphthalen-1-one (6b)
Reduction of (6a,b) with Lithium Borohydride
(i) Tetrapropylammonium perruthenate (7.4 mg, 0.021 mmol) was
added in one portion to a mixture of the (1R,3R)-diol (7a) (100 mg, 0.42
mmol), 4-methylmorpholine N-oxide (74 mg, 1.5 equiv.) and powdered
molecular sieves (200 mg, 4 Å) in dichloromethane (4 ml). The sus-
pension was stirred at room temperature for 24 h and filtered through a
pad of silica with ethyl acetate as eluent. The solvents were evaporated
and the residue was purified by using flash pad chromatography with a
gradient solvent system of light petroleum/ether to give the (R)-
tetralone (6a) (84 mg, 85%) as colourless needles from ethyl acetate,
m.p. 162–164°C {isochiral (6a,b) m.p. 157–159°C}, [α]D –15 (c, 1.55
in CHCl3) {the (S)-tetralone (6b) [α]D +14 (c, 1.53 in CHCl3)} (Found:
C, 66.3; H, 6.9. C13H16O4 requires C, 66.1; H, 6.8%). νmax 3479, 2963,
1670, 1586, 1478, 1458, 1433, 1278, 1257, 1072 cm–1. δH (300 MHz)
1.40 (3H, s, 3-Me), 2.00 (1H, m, 3-OH), 2.71 (1H, d, J 15.7 Hz, H 2),
2.77 (1H, d, J 15.7 Hz, H´2), 2.91 (1H, d, J 17.8 Hz, H 4), 3.14 (1H, d,
J 17.8 Hz, H´ 4), 3.79 and 3.84 (each 3H, s, 2×OMe), 6.80 and 6.98
(each 1H, d, J 9.0 Hz, H 6, H 7). δC (75 MHz) 29.2, 37.7, 54.1, 55.9,
56.3, 70.8, 110.5, 116.0, 122.0, 131.5, 150.7, 154.0, 196.3. Mass spec-
trum m/z 236 (M+, 87%), 218 (33), 203 (71), 178 (100), 177 (31), 163
(65), 148 (25), 121 (30), 120 (42), 77 (28).
(ii) A solution of the Dess–Martin periodinane (454 mg, 1.07 mmol)
in dichloromethane (15 ml) was added dropwise to a vigorously stirred
solution of (1R,3R)-diol (7a) (170 mg, 0.714 mmol) and water (19 µl,
1.1 mmol) in dichloromethane (20 ml) over 5 min. The cloudy mixture
was stirred at room temperature for 6 h and poured into saturated
aqueous sodium hydrogen carbonate (30 ml) containing sodium thio-
sulfate (1.5 g) and stirred at room temperature for 20 min. The organic
phase was separated and washed with saturated sodium hydrogen car-
bonate (2×30 ml), water (2×30 ml), dried and evaporated. The residue
was crystallized from ethyl acetate to give the (R)-tetralone (6a) (149
mg, 88%), identical to material described above.
A solution of lithium borohydride in tetrahydrofuran (2 M, 450 µl,
0.9 mmol) was added dropwise to a solution of the isochiral tetralone
(6a,b) (84 mg, 0.36 mmol) in tetrahydrofuran (10 ml). The solution was
stirred at room temperature for 3 h and diluted with ethyl acetate (20 ml)
and water (20 ml). The organic phase was separated and the aqueous
phase was extracted with ethyl acetate (2×30 ml). The combined extract
was evaporated to give a colourless gum that was purified by flash
chromatography, with ether as eluent, to afford a mixture containing the
cis-diol (7a,c) (56 mg, 66%) and the trans-diol (7b,d) (28 mg, 33%),
1
each of which was identical by H n.m.r. spectroscopy with materials
described above.
(1S,3R)-1,3-Dihydroxy-3-methyl-1,2,3,4-tetrahydro-5,8-naphtho-
quinone (5a) and (1R,3S)-1,3-Dihydroxy-3-methyl-1,2,3,4-
tetrahydro-5,8-naphthoquinone (5b)
A solution of ammonium cerium(IV) nitrate (139 mg, 0.254 mmol)
in water (4 ml) was added over 5 min to a solution of the dimethyl ether
(7b) (30.2 mg, 0.127 mmol) in acetonitrile (4 ml). The mixture was
stirred at room temperature for 5 min and diluted with water (20 ml).
The product was extracted into dichloromethane (5×20 ml), dried
(Na2SO4) and evaporated. Gel permeation chromatography (Sephadex
LH-20) of the residue gave the (1S,3R)-naphthoquinone (5a) (18.1 mg,
69%) as a yellow gum (Found: M+•, 208.0733. C11H12O4 requires M+•,
208.0736), [α]D +163 (c, 1.09 in EtOH) {the (1R,3S)-naphthoquinone
(5b), [α]D –166 (c, 1.07 in EtOH)}. δH (300 MHz) 1.42 (3H, s, 3-Me),
1.68 (1H, dd, J 13.4, 9.3 Hz, H 2ax), 2.24 (1H, ddd, J 13.4, 6.6, 2.4 Hz,
H2eq), 2.42 (1H, dd, J 19.5, 2.9 Hz, H 4ax), 2.65 (1H, br d, J 19.5 Hz,
H4eq), 3.46 (1H, s, OH), 5.04 (1H, m, H1), 6.73 (2H, m, Ar–H). δC (75
MHz) 30.5, 36.7, 41.8, 64.5, 69.0, 136.6, 136.7, 140.3, 140.6, 187.5,
189.0. Mass spectrum m/z 208 (M+, 3%), 190 (77), 151 (36), 150 (65),
148 (100), 147 (45).
Tetramethylammonium Borohydride
(1S,3R)-Austrocortilutein (1b) and (1R,3S)-Austrocortilutein (1d)
An aqueous solution of tetramethylammonium hydroxide (25%, 170
ml, 0.47 mol) was added to sodium borohydride (17.6 g, 0.47 mol) and
the mixture was diluted with deionized water and evaporated to
dryness. The colourless solid was suspended in ethanol (95%, 170 ml)
and filtered. The filter cake was suspended in ethanol (70 ml) and fil-
tered; this process was repeated a further 10 times. The product was
dried at 80°C under vacuum (0.1 mmHg) overnight to give tetra-
methylammonium borohydride (31.5 g, 75%) as a colourless micro-
crystalline solid.
A solution of 1,3-dimethoxy-1-trimethylsilyloxybuta-1,3-diene (4)
(21.2 mg, 0.105 mmol) and the napthoquinone (5a) (18.1 mg, 0.087
mmol) in benzene (5 ml) was stirred at room temperature for 12 h.
Water (6 ml) was added and the mixture was stirred vigourously for
12 h in the presence of air. The mixture was diluted with
dichloromethane (25 ml) and washed with water (2×15 ml), dried
(Na2SO4) and evaporated. The residue was purified by flash pad chro-
matography with toluene/ethyl formate/formic acid (50: 49 : 1) to give
a mixture (12.4 mg, 47%) of (1S,3R)-austrocortilutein (1b) and its

46
C. Elsworth et al.
regioisomer (9a) in an 87: 13 ratio. Fractional crystallization from chlo-
roform gave (1S,3R)-austrocortilutein (1b) (7.9 mg, 30%) as orange-
yellow needles, m.p. 162–165°C (lit.2 162–164°C), [α]D +293 (c, 0.10
in CHCl3) [lit.2 +288 (c, 0.10 in CHCl3)] {(1R,3S)-austrocortilutein
(1d), [α]D –265 (c, 0.18 in CHCl3), lit.3 –262 (c, 0.18 in CHCl3)}
(Found: M+•, 304.0946. Calc. for C16H16O6: M+•, 304.0946). λmax 221
(logε 4.49), 270 (4.02), 284sh (3.78), 428 nm (3.46). νmax 1665, 1631,
1596 cm–1. δH (300 MHz) 1.47 (3H, s, 3-Me), 1.75 (1H, dd, J 13.5, 9.1
Hz, H 2ax), 2.31 (1H, ddd, J 13.5, 6.6, 2.6 Hz, H 2eq), 2.55 (1H, dd, J
19.6, 2.5 Hz, H 4ax), 2.80 (1H, ddd, J 19.6, 2.6, 1.8 Hz, H4eq), 3.91
(3H, s, 6-OMe), 4.00 (1H, m, 1-OH), 5.18 (1H, m, H 1), 6.62 (1H, d, J
2.6 Hz, H7), 7.17 (1H, d, J 2.6 Hz, H5), 12.14 (1H, s, peri-OH). Mass
spectrum m/z 304 (M+, 4%), 286 (60), 271 (30), 269 (22), 268 (100).
1H n.m.r. for (9a): δH (300 MHz) 1.47 (3H, s, 3-Me), 1.75 (1H, dd,
J 13.5, 9.1 Hz, H 2ax), 2.31 (1H, ddd, J 13.5, 6.6, 2.6 Hz, H2eq), 2.55
(1H, dd, J 19.6, 2.5 Hz, H 4ax), 2.84 (1H, ddd, J 19.6, 2.6, 1.8 Hz,
H4eq), 3.91 (3H, s, 6-OMe), 4.00 (1H, m, 1-OH), 5.18 (1H, m, H 1),
6.62 (1H, d, J 2.6 Hz, H 7), 7.17 (1H, d, J 2.6 Hz, H5), 12.21 (1H, s,
peri-OH).
940417A1 and 950509A0 were extracted with ethanol and the solvent
was removed in vacuum. The residue was partitioned between ethyl
acetate (20 ml) and water (10 ml) and the organic phase was dried
(Na2SO4) and evaporated. Preparative thin-layer chromatography using
toluene/ethyl formate/formic acid (50: 49: 1) gave two yellow zones
that were analysed further by h.p.l.c. system B. The enantiomeric excess
(e.e.) of each sample is shown in Table 2.
Acknowledgments
E.R. is grateful to the Australian Research Council for the
provision of a Research Assistantship; C.E. and A.T.
received Commonwealth Postgraduate Research Awards.
We thank Dr D. A. Ratkowski for providing the Tasmanian
material and for stimulating discussions.
References
1
Gill, M., Nat. Prod. Rep., 1994, 11, 62.
Gill, M., Smrdel, A. F., Strauch, R. J., and Begley, M. J., J. Chem.
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Soc., Perkin Trans. 1, 1990, 1583.
Gill, M., Gimenez, A., Jhingran, A. G., Smrdel, A. F., and Qureshi,
A., Phytochemistry, 1992, 31, 947.
Gill, M., and Smrdel, A. F., Phytochemistry, 1987, 26, 2999.
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Griffith, W. P., and Ley, S. V., Aldrichimica Acta, 1990, 23, 13.
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H.P.L.C. Experiments
3
Synthetic Quinones (1a–d)
4
Asolution (40 µl) of each of the quinones (1a–d) in ethanol (0.05 mg
ml–1) was chromatographed at room temperature over Chiralpak OD
(system A) and Chiralpak AD (system B) columns by using ethanol or
combinations of ethanol and hexane (Table 1) as eluent at a flow rate of
0.5 ml min–1. Retention times are collected in Table 1; chromatograms
of (1S,3S)- and (1R,3R)-austrocortilutein (1a) and (1c) are shown in
Fig. 3a, while those of (1S,3R)- and (1R,3S)-austrocortilutein (1b) and
(1d) are shown in Fig. 3b.
5
6
7
8
9
10
Fungal Metabolites
Phytochemistry, 1989, 28, 2647.
Eagle, S. N., Gill, M., Saubern, S., and Yu, J., Nat. Prod. Lett., 1993,
2, 151.
Gill, M., Nat. Prod. Rep., 1996, 13, 513.
Gill, M., Saubern, S., and Yu, J., Aust. J. Chem., 2000, in press.
Gill, M., Raudies, E., and Yu, J., Aust. J. Chem., 1999, 52, 989.
Fresh fruit bodies of Dermocybe splendida and Dermocybe sp. WAT
20934 were collected, extracted with ethanol and purified by prepara-
tive thin-layer chromatography as described before.2,3 The yellow
zones corresponding to austrocortilutein were isolated, dissolved in
ethanol (c. 0.05 mg ml–1) and analysed by using h.p.l.c. system B.
Similarly, air-dried specimens (c. 1 g) of Dermocybe sp. 950426A1,
11
12
13
14