The Structure of Chalybaeizanic Acid and Quaesitic Acid, Two New Lichen Depsidones Related to Salazinic Acid

Article abstract of DOI:10.1071/CH99056

The depsidones chalybaeizanic acid (1,4,10-trihydroxy-8-methyl-3,7-dioxo-1,3-dihydro-7H-isobenzofuro[4,5-b][1,4]benzodioxepin-5,11-dicarbaldehyde) (4) and quaesitic acid (11-formyl-1,4,10-trihydroxy-8-methyl-3,7-dioxo-1,3-dihydro-7H-isobenzofuro[4,5-b][1,4]benzodioxepin-5-methyl hydrogen fumarate) (5) have been isolated from the lichens Xanthoparmelia amphianthoides and Hypotrachyna quaesita respectively, and their structures determined by a combination of spectroscopic evidence, partial synthesis, derivatization or degradation reactions.

Full text of DOI:10.1071/CH99056

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Volume 52, 1999
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Aust. J. Chem., 1999, 52, 713–715
.
The Structure of Chalybaeizanic Acid and Quaesitic Acid,
Two New Lichen Depsidones Related to Salazinic Acid
John A. Elix and Judith H. Wardlaw
Department of Chemistry, The Faculties, Australian National University,
Canberra, A.C.T. 0200.
The depsidones chalybaeizanic acid (1,4,10-trihydroxy-8-methyl-3,7-dioxo-1,3-dihydro-7H -isobenzofuro-
[
4,5-b][1,4]benzodioxepin-5,11-dicarbaldehyde) (4) and quaesitic acid (11-formyl-1,4,10-trihydroxy-8-
methyl-3,7-dioxo-1,3-dihydro-7H -isobenzofuro[4,5-b][1,4]benzodioxepin-5-methyl hydrogen fumarate) (5)
have been isolated from the lichens Xanthoparmelia amphixanthoides and Hypotrachyna quaesita
respectively, and their structures determined by a combination of spectroscopic evidence, partial
synthesis, derivatization or degradation reactions.
1
The continuation of our phytochemical survey of
lichens has led to the identi�cation of a further two
The similarities of the H n.m.r. and mass spectra of
(2) and (4) were thus not surprising.
1
depsidones from several species. These compounds
have been characterized by the normal spectroscopic
techniques from which their respective structures have
been deduced.
The structure of chalybaeizanic acid (4) was ulti-
mately established by synthesis and derivatization.
Oxidation of salazinic acid (2) with pyridinium dichro-
mate under mild conditions led to the formation of
chalybaeizanic acid (4), albeit mixed with unreacted
salazinic acid (2). The properties [thin-layer chromato-
graphy (t.l.c.), high-performance liquid chromatogra-
phy (h.p.l.c.), ultraviolet absorption (u.v.)] of this
synthetic sample of chalybaeizanic acid (4) were found
to be identical to those of the natural material.
Acetylation of a mixture of salazinic acid (2) and
chalybaeizanic acid (4) by treatment with acetic anhy-
dride and sulfuric acid led to the formation of the
expected salazinic acid hexaacetate (8) and chaly-
baeizanic acid heptaacetate (9).
Chalybaeizanic Acid (4)
In his monographic study of the lichen genus
2
Xanthoparmelia, Mason Hale observed that X. chaly-
baeizans produced �ve major phenolic metabolites.
This included the common cortical dibenzofuran usnic
acid, together with the �-orcinol depsidones norstictic
acid (1), salazinic acid (2), and consalazinic acid (3)
together with the ‘chalybaeizans unknown’, a compound
we have called chalybaeizanic acid. Although Hale
detected this unknown in a number of Xanthoparmelia
species by microchemical methods he did not isolate
it nor elucidate its structure.
Chalybaeizanic acid (4) is a further representative of
the �-orcinol depsidones, and may arise biosynthetically
by selective oxidation of the co-occurring salazinic acid
3,4
Recently we have undertaken a larger scale extraction
of Xanthoparmelia amphixanthoides (Stein. & Zahlbr.)
Hale which contains the same �ve metabolites as X.
chalybaeizans, and followed this by fractional crystal-
lization of the extract. This led to the isolation of
chalybaeizanic acid (4), the structure of which followed
initially from the spectroscopic properties.
(
2).
Quaesitic Acid (5)
5
In 1986 Kurokawa reported the new lichen species
Parmelia quaesita Kurok. (Hypotrachyna quaesita
(
Kurok.) DePriest & B. Hale) which contained the com-
mon cortical depsides atranorin and chloroatranorin,
the �-orcinol depsidone fumarprotocetraric acid (11),
together with an unknown which he termed quaesitic
acid. Although Kurokawa detected the compound by
microchemical methods he did not attempt to isolate it
nor elucidate its structure. Analytical h.p.l.c. indicated
that the major metabolites detected by Kurokawa were
accompanied by minor amounts of salazinic acid (2) and
protocetraric acid (10). Recently, we have undertaken
a larger scale extraction of H. quaesita and followed
1
In particular, the H n.m.r. spectrum showed a
C-methyl resonance (� 2�52), an aromatic proton
signal overlapping a methine proton resonance (6�87),
a methine proton (7�01), two aldehyde proton signals
(
10�43, 10�63) and two intramolecularly hydrogen-
bonded hydroxy signals (12�31, 13�42). High-resolution
mass measurement on the molecular ion established that
the molecular formula of (4) was C18H10O10, whereas
that of the co-occurring salazinic acid is C18H12O10.
Manuscript received 10 May 1999
᭧ CSIRO 1999
10.1071/CH99056
0004-9425/99/070713$ 05.00

7
14
Short Communications
1
Table 1.
H n.m.r. data (�) for �-orcinol depsidones
Spectra were recorded at 300 MHz
A
B
B
A
C
A
Proton(s)
(10)
(11)
(1)
(2)
(4)
(5)
1
6
-Me
-Me
2�47
2�67
—
4�81
6�75
10�72
2�54
2�66
—
5�37
6�77
10�78
2�46
—
2�50
—
7�01
4�92
6�83
10�64
2�52
—
2�53
—
6�78
5�40
6�78
10�23
HC(OH)O
CH2O
ArH
6�90
7�01
—
—
6�86
10�48
6�87
10�63
CHO
1
0�43
OH
—
—
—
12�28
12�31
—
1
3�42
—
(
9
E)-CH=CH
-Me
—
6�74
—
2�22
—
—
6�76
—
—
A
B
C
Spectrum run in (CD3)2CO.
Spectrum run in (CD3)2SO.
Spectrum run in CDCl3.
this by fractional crystallization and preparative t.l.c.
of the extract. This led to the isolation of quaesitic
acid (5), the structure of which followed initially from
its spectroscopic properties.
overlapping a methine proton resonance (6�78), an
aldehyde proton (10�23), a two-proton singlet (5�40)
due to the benzyloxy group and another two-proton
singlet (6�76) assigned to alkene protons. This spec-
1
1
In particular, the H n.m.r. spectrum showed a C-
trum showed similarities with the H n.m.r. spectra
methyl resonance (� 2�54), an aromatic proton signal
of fumarprotocetraric acid (11) and salazinic acid (2),
both cometabolites of quaesitic acid (Table 1).
Although the mass spectrum of quaesitic acid did
not show a molecular ion, the observed fragmentation
pattern was very similar to that exhibited by galbinic
6
acid (6). This combination of spectroscopic data was
consistent with structure (5) for quaesitic acid.
The structure of quaesitic acid (5) was ultimately
established by degradation. Inadvertent methanolysis
of quaesitic acid (5), by storing a methanolic solution
of this compound at room temperature, e� ciently
converted (5) into salazinic acid �-methyl ether (7)
and fumaric acid, the former establishing the core
�
-orcinol depsidone structure of quaesitic acid.
Quaesitic acid (5) is the second �-orcinol depsidone
known in which biosynthesis has involved secondary
side-chain esteri�cation by fumaric acid.
Experimental
The general experimental details have been described
7
previously.
Extraction of Xanthoparmelia amphixanthoides (Stein. &
Zahlbr.) Hale
The lichen material was collected on sandstone, Rooiberg
Pass, 19 km from Vanwyksdorp towards Calitzorp, Cape
Province, Republic of South Africa, F. Brusse 4900 (CANB).
The lichen material (4�3 g) was dried and extracted with
anhydrous ether in a Soxhlet extractor for 24 h. This pro-
cedure was then repeated with anhydrous acetone. After
concentration, the extract from the latter yielded a colourless
1
solid (39 mg), which t.l.c., h.p.l.c. and H n.m.r. analyses
revealed was approximately a 1 : 1 mixture of salazinic acid (2)
and chalybaeizanic acid (4). Fractional crystallization of this
mixture from aqueous acetone a�orded salazinic acid (2) (5 mg,
�
8
�
1
(
�2%) as colourless needles, m.p. 265 (dec.) (lit. 260–280
1
dec.)), identical with authentic material (t.l.c., h.p.l.c.,
H
n.m.r., u.v., mass spectrum). The mother liquor so obtained
was enriched in chalybaeizanic acid (4) (2�6 mg, 0�6%), which
on concentration crystallized in colourless microcrystals, m.p.

Short Communications
715
�
+�
>
M
�
300 (dec.) (Found:
M
, 386�0274. C18H10O10 requires
(71 mg) shown by t.l.c. to comprise a mixture of atranorin,
chloroatranorin, fumarprotocetraric acid (11), quaesitic acid
(5) and traces of salazinic acid (2) and protocetraric acid
(10). The residue was puri�ed by repeated preparative layer
chromatography over silica gel with toluene–acetic acid (85 : 15)
as eluent. Three major bands developed. The faster moving
band containing atranorin and chloroatranorin was discarded.
+
�
, 386�0274). The homogeneity of this compound was con-
1
rmed by h.p.l.c. and H n.m.r. spectroscopy. Mass spectrum:
m/z 386 (M, 24%), 341 (30), 340 (28), 312 (34), 199 (24), 179
56), 177 (16), 152 (48), 151 (62), 149 (34), 57 (100). Standard
t.l.c. RF values:
Standard h.p.l.c. values:
(
9,10
RF (A) 0�11; RF (B) 0�05; RF (C) 0�10.
6,11
Rt 17�90 min; RI 0�10.
The second band a�orded fumarprotocetraric acid (11) (2�0 mg,
1
Oxidation of Salazinic Acid (2)
0
�4%), identical (t.l.c., h.p.l.c., u.v., H n.m.r.) with authentic
material. The third band yielded quaesitic acid (5) (6�4 mg,
A solution of salazinic acid (2) (100 mg, 0�26 mmol) in
�
1
�4%), which crystallized from acetone in colourless microcrys-
N,N -dimethylformamide (10 ml) was cooled to 0 and stirred
�
tals, m.p. >350 (dec.) (Found: C, 54�0; H, 3�0. C22H14O13
requires C, 54�3; H, 2�9%). Mass spectrum: m/z 305 (14%),
while pyridinium dichromate (121 mg, 0�32 mmol) was added.
�
The mixture was stirred for a further 1 h at 0 , then poured
2
05 (23), 149 (19), 139 (11), 137 (13), 126 (21), 124 (18), 113
into water (200 ml) and extracted with ethyl acetate. The
combined organic extract was washed with water, brine and
dried (MgSO4). The residue (22 mg) obtained on evaporation
of the solvent was analysed by t.l.c., h.p.l.c. and ultraviolet
spectroscopy. This con�rmed that the residue comprised a
mixture of salazinic acid (c. 85%) and chalybaeizanic acid (4)
(
(
15), 112 (14), 111 (34), 110 (13), 109 (27), 99 (15), 98 (14), 97
52), 96 (19), 95 (38), 57 (100). Standard t.l.c. RF values:
9
,10
RF (A) 0�06; RF (B) 0�09; RF (C) 0�06. Standard h.p.l.c.
6,11
values:
Rt 18�47 min; RI 0�10.
Methanolysis of Quaesitic Acid (5)
(
c. 15%) with identical RF and Rt values and an identical ultra-
violet absorption spectrum with the natural material isolated
above.
A solution of quaesitic acid (5) (1 mg) in anhydrous methanol
was permitted to stand at room temperature for 48 h. After this
time no quaesitic acid could be detected by h.p.l.c. analysis—
Acetylation of Mixture of Salazinic Acid (2) and
Chalybaeizanic Acid (4)
13
instead the presence of salazinic acid 5-�-methyl ether (6)
and fumaric acid was con�rmed by comparison with authentic
samples (h.p.l.c., u.v.). No maleic acid was detected. On evap-
oration of the solvent this product composition was con�rmed
by comparative t.l.c. in three independent solvent systems.
The mixture of depsidones (2) and (4) (50 mg) was stirred in
a solution of acetic anhydride (1�5 ml) and concentrated sulfuric
acid (1 drop) at room temperature for 19�5 h. Water (15 ml)
was then added and the solution stirred at room temperature
for a further 3�5 h. The precipitate which formed was �ltered,
washed with water, and dried, to give the crude product
Acknowledgment
We thank the Australian Research Council for
generous �nancial support.
(
60 mg). The crude material was puri�ed by preparative layer
chromatography over silica gel with 35–40% ethyl acetate–light
petroleum as eluent. Two major bands developed.
References
The faster moving band a�orded hexaacetylsalazinic acid
1
(
20 mg), which crystallized from ethanol in colourless prisms,
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W., Aust. J. Chem., 1999, 52, 717.
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Elix, J. A., and Wardlaw, J. H., Aust. J. Chem., 1997, 50,
�
12
�
m.p. 173–174 (lit. 178 ). This material was identical with
authentic
n.m.r.).
12
1
2
hexaacetylsalazinic acid (8) (t.l.c., h.p.l.c.,
H
3
4
The slower moving band yielded heptaacetylchalybaeizanic
�
5
acid (9) (11 mg) as a colourless solid, m.p. >340 (Found: C,
5
1
6
4�0; H, 4�0. C32H28O19 requires C, 53�6; H, 3�9%).
H
n.m.r. (CDCl3) � 2�08, 2�14, 2�15, 2�17, 2�22, 2�36, 2�45,
�58, 8s, Me; 6�95, s, ArH; 7�88, s, H 1; 7�97, 7�98, 2s, ArCH.
Mass spectrum: m/z 674 (M � CH2CO, 0�1%), 614 (8), 572
30), 512 (28), 470 (74), 454 (16), 453 (16), 428 (50), 412 (30),
7
2
1
145.
8
(
4
3
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11 (49), 410 (76), 386 (40), 370 (34), 369 (44), 368 (100),
41 (21), 340 (55), 339 (20), 312 (12), 300 (28), 299 (30), 221
15), 179 (20), 177 (14).
9
0
1
(
Extraction of Hypotrachyna quaesita (Kurok.) DePriest &
B. Hale
1
1
1
1
2
3
The lichen material was collected on a fallen tree branch in
disturbed Nothofagus forest, Mount Kaindi, Morobe Province,
Papua New Guinea, H. Streimann 33165 (CANB).
The lichen material (0�45 g) was dried and extracted with
anhydrous ether for 42 h, and then extracted with acetone for
4
8 h. Evaporation of the combined solvent a�orded a residue