Journal of Chemical Ecology, Vol. 23, No. 7, 1997
ANTIFUNGAL XANTHONES FROM Calophyllum
brasiliensis HEARTWOOD1
RICARDO REYES-CHILPA,*-' MANUEL JIMENEZ-ESTRADA,
and ELIZABETH ESTRADA-MUNIZ
Instituto de Quimica, Universidad National Autonoma de Mexico
Ciudad Universilaria
Coyoacan. 04510 Mexico, DF
(Received October 14, 1996; accepted March 17, 1997)
Abstract—The heartwood of the tropical tree Calophyllum brasiliensis is
known to be highly resistant to fungi and termites. To determine whether
resistance to wood-rotting fungi could be caused by bioactive secondary
metabolites, a chemical and biological study was carried out. Hexane, acetone, methanol, and water extracts were prepared. The yield of the extracts
ranged from 0.04% (hexane) to 4.81% (acetone). Methanol, acetone, and
water extracts (5 mg/ml = 0.5%) inhibited the mycelial growth of the brown
rot fungus Postia placenta by 83%, 59%, and 2 1 % , respectively. Chromatographic separation of the acetone and methanol extracts afforded five
prenylated xanthones: 6-desoxyjacareubin (I), 1,5-dihydroxy-2-(3,3-dimethylallyl)-3-methoxy-xanthone (II), jacareubin ( I I I ) and l,3,5-trihydroxy-2-(3,3dimethylallylj-xanthone (IV) and l,3,5,6-tetrahydroxy-2-(3,3-dimethylallyl)xanthone (V). Xanthones III, IV, and especially V, were the most abundant
constituents of both extracts and inhibited at 0.25 mg/ml the mycelial growth
of P. placenta. Inhibitory activity ranged from 55.5% (V) to 68.8% (III and
IV mixture). Acetylation of xanthones did not induce a sharp change in the
extent of fungistasis compared with parent compounds. The above results
suggest that C. brasiliensis xanthones actually play a defensive role against
wood decay fungi
Key Words—Xanthones, Calophyllum brasiliensis, heartwood, antifungal
activity, Postia placenta, Guttiferae, wood, fungi, extractives.
*To whom correspondence should be addressed.
'Contribution 1264 from Instituto de Quimica, UNAM. Presented in part at the 22nd International
Symposium on Natural Products Chemistry, Mexico City, May 6-7, 1996.
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0098-033l/97/0700-l90l$l2.50/0© 1997 Plenum Publishing Corporation
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REYES-CHILPA, JIMENEZ-ESTRADA, AND ESTRADA-MUNIZ
INTRODUCTION
The genus Calophyllum (Guttiferae) is composed of about 130 species confined
to the warm humid tropics of the world. In the Western Hemisphere, one of the
most widely distributed species is Calophyllum brasiliensis Camb. This large
tree is found in tropical forests from southern Mexico to Brazil. It can reach 40
m in height and 1.3 m diameter at breast height. The timber is used for construction, flooring, and furniture (Chudnoff, 1984, Ortega-Escalona et al., 1991).
Experimental tests indicate that C. brasiliensis heartwood is highly resistant to
the brown rot fungus Lenzites trabea (Torelli, 1982) and to the subterranean
termites Reticulitermes flavipes and Coptotermes formosanus (Carter and
Camargo, 1983); it has also been rated as resistant to the white rot fungus
Coriolus versicolor (Torelli, 1982).
Natural resistance to fungi and termites is primarily attributed to the content
of secondary metabolites present in heartwood, since these compounds frequently exhibit antifungal (Gdmez-Garibay et al., 1990; Scheffer and Cowling,
1966) and antitermitic (McDaniel 1992; Scheffrahn, 1991; Reyes-Chilpa et al.,
1995) properties. In addition, extraction of secondary metabolites with organic
solvents and water renders heartwood susceptible to wood-destroying organisms
(Deon 1983; Reyes-Chilpa et al., 1987). In this paper we report the isolation
of five xanthones (I-V) from Calophyllum brasiliensis heartwood. We also
report the antifungal activity of heartwood extracts and compounds III, IV, and
V against the brown rot fungus Postia placenta.
METHODS AND MATERIALS
Biological Material. Calophyllum brasiliensis heartwood was obtained from
a tree collected in the Lacandona Rain Forest, State of Chiapas, Mexico
(Barcenas-Pazos, 1995). Vouchers and wood samples are deposited at the Institute of Ecology A.C. Herbarium (XAL) in Xalapa, Mexico. Postia placenta
fungus, strain Mad 698, was obtained from the Forest Products Laboratory,
Madison, Wisconsin.
Isolation of Compounds. Heartwood shavings (711.5 g) were extracted at
room temperature with hexane, acetone, methanol, and water. Extracts were
concentrated under reduced pressure. After preparative thin-layer chromatography (pTLC), the hexane extract yielded /3-sitosterol. Part of the acetone extract
(28 g) was subjected to column chromatography (silica gel) eluting with hexane,
acetone, and mixtures of these solvents. Fractions 9-16 eluted with hexancacetone (9:1) yielded a yellow powder (5 mg) that was identified as 6-dcsoxyjacareubin (I) (Figure 1). Fractions 17-20, eluted with hexane-acetone (9: 1),
yielded a yellow powder (12 mg), identified as l,5-dihydroxy-2-(3,3-dimeth-
ANT1FUNGAL XANTHONESs
1903
FIG. 1. Natural and transformed xanthones from Calophyllum brasiliensis heartwood.
ylallyl)-3-methoxyxanthone (II). Fractions 21-24, eluted with hexane-acetone
(8:2), yielded a yellow powder (790 mg) that was further identified as a mixture
of jacareubin (HI) and 2-(3,3-dimethyllallyl)-l,3,5-trihydroxyxanthone (IV).
Preparative TLC of this mixture yielded a pure sample of IV. Fractions 30-43,
eluted with hexane-acetone (7.5:2.5), yielded 2-(3,3-dimethylallyl)-l,3,5,6tetrahydroxyxanthone (V) as a yellow powder (3.3 g).
Part of the methanol extract (2.5 g) was subjected to column chromatography (silica gel) and eluted with hexane, ethyl acetate, and mixtures of these
solvents. Fractions 12-18, eluted with a 9:1 mixture, yielded a mixture of
compounds III and IV (86 mg). Fractions 26-39, eluted with 8:2 mixture,
1904
REYES-CHILPA, JIMENEZ-ESTRADA, AND ESTRADA-MUNIZ
afforded V (516 mg). Structures of compounds were elucidated from their IR,
UV, 'H NMR and MS spectroscopic data.
Transformation of Compounds. Compound V (500 mg) was acetylated with
anhydrous acetic in pyridine at room temperature for 24 hr. The reaction was
stopped with the addition of water giving a solid that was filtered and washed
with 10% HC1 and water. The solid (391 mg, yield 56%) was crystallized from
CH2Cl2/MeOH and identified as 2-(3,3-dimethylallyl)-l-hydroxy-3,5,6-triacetylxanthone (Va). A mixture of III and IV (150 mg) was also acetylated as
previously described, and the reaction products were separated by CC. First
fractions yielded l,3,5-triacetyl-2-(3,3-dimethylallyl)-xanthone (IVa) (8 mg),
while the latter fractions yielded 6 mg of a mixture of triacetyljacareubin (IIIa)
and l',2'-dihydro-5,6-diacetyljacareubin (IIIb).
Bioassays. The effects of extracts (5 mg/ml = 0.5% w/v) and isolated
compounds (0.25 mg/m = 0.025%) on the mycelial growth of the fungus Postia
placenta were examined as described by Reyes-Chilpa et al. (1997). The extracts
were dissolved in acetone, methanol, or water and incorporated into the growth
medium (malt-agar 1.5%). The isolated compounds were dissolved in acetone.
Controls containing each solvent were run simultaneously. Phenol (Sigma) was
also tested in the same way for comparison. Finally, to test whether fungal
metabolism could modify xanthones in vitro, we redissolved agar from plates
with compound V and extracted the solution several times with ethyl acetate.
The organic phase was then subjected to pTLC.
RESULTS
Effects of Extracts
The highest yield of soluble metabolites was obtained with acetone (4.81 %),
while the poorest was achieved with hexane (0.04%) (Table 1). At the concentration tested (5 mg/ml = 0.5% w/v), three extracts showed fungistatic activity
against Postia placenta (Table 1). The methanol extract was the most active,
inhibiting the mycelial growth by 83.6%. Acetone and water extracts were less
active, inhibiting mycelial growth by 59% and 21.9%, respectively. Differences
between extracts were statistically significant. The hexane extract was not tested
because of its low yield.
Compounds Isolated
Chromatographic separation of the acetone and methanol extracts yielded
five prenylated xanthones: 6-desoxyjacareubin (I), l,6-dihydroxy-2(3,3-dimethylallyl)-3-methoxyxanthone (II), jacareubin (III), l,3,5-trihydroxy-2-(3,3dimethylallyl)-xanthone (IV), and l,3,5,6-tetrahydroxy-2-(3,3-dimethylallyl)-
ANTIFUNGAL XANTHONES
1905
TABLE 1. INHIBITION OF Postia placenta MYCELIAL GROWTH BY C. brasiliensis
HEARTWOOD EXTRACTS (5 mg/ml)
Extract
Control
Hexane
Acetone
Methanol
Water
Yield (%)
Growth (cm)"
0.04
4.81
0.92
0.13
4.88 ± 0.16"
nt
2.00 ± 0.00*
0.80 ± 0.14'
3.81 ± 0.06''
Inhibition (%)
0.0 +
nt
59.0 +
83.6 ±
21.9 ±
3.2
0.0
2.8
1.2
"Mean ± standard deviation of three replicates five days after innoculation. Least significant difference > 0.26; values followed by a different letter are significantly different at P = 0.05 (Tukey's
( test), nt: not tested.
xanthone (V). Their 'H NMR data are shown in Table 2. Besides these compounds, spectroscopic evidence also suggested the presence of l',2'-dihydro5,6-diacetyljacareubin (Illb) along with the diacetyl derivative of jacareubin
(IIIa). The mass spectrum of IIIa showed surplus peaks at 412 m/z (19%), 370
(15%), and 328 (31%), which accounted for the molecular ion [C22H20O8] + ,
and the loss of one and two C2H2O fragments, respectively. 'H NMR of IIIa
also suggested residual IIIb, considering two small triplets at 2.7 and 1.85 ppm
assigned to methylene protons at the 1' and 2' positions. The origin of compound
IIIa as a natural product or as an artifact was not determined.
Xanthones III, IV, and especially V were the most common constituents
of both the acetone and methanol extracts. The yields of compound V were
11.7% and 20.6%, respectively; while the mixture of compounds HI and IV
accounted for 2.8% and 3.4%, respectively.
6-Desoxyjacareubin (I). Yellow powder, mp 214-215°C (reported 212214°C; Jackson et al., 1967, 1969). EMIE 70 eV (m/z): 310 M+ (21.3%)
[C18H1405], 295 (100%) [M + -CH 3 ], 257 (4.1%) [M+ -C4H7], 147 (11.5%).
l,5 - Dihydroxy - 2 - (3,3-dimethylallyl) - 3- methoxyxanthone (II).Yellow
powder, mp 254-255°C (reported 242-244°C; Sen et al., 1981). EMIE 70 eV
(m/z): 326 M+ (53.3%) [CI9HI8O5], 311 (41.6%) [M+ -CH 3 J, 283 (73.3%)
[M + -C 3 H 7 ], 271 (100%) [M+ -C4H7], 258 (10%), 241 (11.6%).
/,3,5-Triacetyljacaraubein (IIIa). Yellow powder, mp 169-170°C. UV
X max [MeOH], nm (e): 239 (3496), 292 (3584), 327 (1493). EMIE 70 eV
(m/z): 410 M+ (50%) [C22H18O8], 395 (93%) [M+ -CH3] = A, 353 (97%)
[A-C2H20) + , 311 (100%) [A-2C2H20]+ , 43 (42%) [C2H3O]+ .
l,3,5-Trihydroxy-2-(3,3-dimethylallyl)-x anthone(IV). Yellow powder, m p
288-290°C (reported 280-281 °C; Gunasekera et al., 1977). EMIE 70 eV
1906
REYES-CHILPA, JIMENEZ-ESTRADA, AND ESTRADA-MUNI/.
ANTIFUNGAL XANTHONES
1907
(IM/Z): 312 M+ (55%) [C18H16O5], 297 (35%) [M+-CH3], 269 (60.8%)
[M + -C3H7], 257 (100%) [M+ -C4H7], 244 (10.8%).
l-Hydroxy-2-(3,3-dimethylallyl)-3,5,6-triacetylxanthone
(IVa). Yellow
powder, mp 121-123°C. UV X max [MeOH], nm (e): 360 (6879), 304(17894),
239(60534). IR i>max (KBr): 2925, 1774, 1641, 1614 (C = C), 1436. EMIE 70
eV (m/z): 396 M+ (80.3%) [C22H20O7] + , 353 (51.7%) [M+-C2H3O] = A, 341
(34.8%) [M+-C4H7] = B, 311 (69.6%) [A-C2H3O] + , 299 (100%) [B-C2H3O] + ,
269 (37.5%) [CI5H8O4] + , 257 (66%) [C14H8O4] + , 55 (20%) [C4H7| + , 43 (25%)
[C2H30] + .
l,3,5,6-Tetrahydroxy-2-(3,3-ditnethylallyl)-xanthone (V). Yellow powder,
mp 260-262°C (reported 255-257°C; Jackson et al., 1966). EMIE 70 eV
(m/z): 328 M+ (54%) [C18H,6O6]+ , 313 (30.3%) [M+-CH3|, 285 (66.6%)
[M+-C3H6], 273 (100%) [M+-C4H71, 260 (13.5%)
l-Hydroxy-2-(3,3-dimethylallyl)-3,5,6-triacetylxanthone (Va). Rectangular
yellow prisms, mp 193-196°C. IR v max (CHC13): 2917, 1785, 1649, 1611,
1452, 1373, 1260, 1161, 116, 1087. EMIE 70 eV (m/z): 454 M+ (100%)
[C24H22O9] + , 411 (32.2%) [M+-C2H3O] = A, 399 (44%) [M+ -C4H7j + = B,
368 (60%) [A-C2H30]+ , 357 (68.6%) [B-C2H2O] + , 355 (10.1%), 327 (62.7%),
315 (61.8%), 273 (50%), 272 (32.2%), 69 (15.2%), 43 (33%).
Effects of Xanthones
The natural xanthones III, IV, and V showed fungistatic properties against
P. placenta when tested at 0.25 mg/ml. Phenol showed fungicidal activity at
the same concentration. Differences among the control, xanthones, and phenol
were statistically significant by ANOVA tests (Table 3). Under our conditions,
the natural xanthones exhibit similar inhibitory activity, ranging from 55.8%
(V) to 67.3% (III and IV). Acetylation of xanthones did not induce a sharp
change in the extent of fungistasis compared with parent compounds. At best,
the derivatives showed a 8% increase (Va) or decrease (IIIa and IVa) in activity.
Significant differences among natural and acetylated xanthones could not be
detected (Table 3).
The effect of increasing concentrations of xanthone V on P. placenta growth
was also examined. Concentrations of 0.5 and 1.0 mg/ml inhibited the mycelial
growth by 64.4 and 74.6%, respectively. This last value is significantly different
from the 0.25 mg/ml treatment (Table 3). Inhibition caused by xanthone V at
the highest concentration was not significantly different from phenol at 0.25 mg/
ml. Therefore it seems that V is about four times less potent than phenol. At
the end of the experiments, all the agar plates treated with V were pooled and
extracted to examine if this compound had suffered any transformation. Only
one compound could be reisolated and purified in good yield (71%); it was
identified as V according to 'H NMR data.
REYES-CHILPA, JIMENEZ-ESTRADA, AND ESTRADA-MUNIZ.
1908
TABLE 3. INHIBITION OF Postia placenta MYCELIAL GROWTH BY C, brasiliensis
XANTHONES AND PHENOL"
Compound (mg/ml)
Growth (cm)
Control
V (1.00)
V (0.50)
V (0.25)
IV (0.25)
IIIa and IVa (0.25)
Va (0.25)
III and IV (0.25)
Phenol (0.25)
4.53 ± 0.33"
1.15
1.60
2.00
1.95
1.85
1.68
1.48
0.60
± 0.41M
± 0.14''
± 0.42'"'
± 0.40'"'
± 0.07'"'
± 0.16'1
± 0.28''
± 0.00"'
Inhibition (%)
00.0
74.6
64.6
55.8
56.9
59.1
62.9
67.3
100.0
±
±
±
±
±
±
±
±
±
7.2
9.0
3.0
9.2
8.8
1.5
3.5
6.1
0.0
"Mean of three replicates + standard deviation six days after innoculation. Least significant difference >0.59; values followed by a different letter are significantly different at P = 0.05 (Tukey's
I test).
DISCUSSION
The heartwood of Calophyllum species contains xanthones and neoflavonoids,
while the leaves possess coumarins, benzopyrans, and triterpenes (Ampofo and
Waterman, 1986; Patil et al., 1993). Xanthones isolated from this genus can be
simple or modified, especially with prenyl (3,3-dimethylallyl) -derived substituents. Our results indicate that 2-prenylated xanthones (I, II, HI, IV, and
V) are the main constituents of C. brasiliensis heartwood. All of these compounds exhibit an 1,3,5-trioxygenated substitution pattern. In addition, compound V has an extra hydroxyl on C-6. While compounds I, III, IV, and V
have been previously isolated from other Calophyllum species, compound II
has only been obtained from Garcinia mangosta hulls (Sen et al., 1981). Compound IIIb has not been reported as a natural product; so it is possible that it
could be an artifact produced during the acetylation procedure.
The natural xanthones III, IV, and V showed fungistatic activity against
the brown rot fungus Postia placenta (Table 3). Xanthones III, IV, and especially V, were the most abundant constituents of both the acetone and methanol
extracts. For the heartwood sample here analyzed, these compounds represent
at least 0.65% (w/w). Compound V alone accounts for 0.53%. C. brasiliensis
heartwood resistance against wood decay fungi thus appears to depend mostly
on these compounds, especially V. It was previously reported that 1,3,5,6tetrahydroxyxanthone isolated from Madura pomifera heartwood inhibits the
ANTIFUNGAL XANTHONES
1909
growth of the wood rotting fungi Gleophyllum trabeum and Trametes versicolor
(Schultz et al., 1995). This compound is the biogenetic precursor of V and
showed an IC50 (50% inhibition of radial mycelial growth) greater than 200
ppm with both fungi (Schultz et al., 1995). In our case, compound V, at a
similar concentration (0.25 mg/ml = 250 ppm), inhibited the growth of
P. placenta by 55.8% (Table 3). It is noteworthy that at the same concentration
the antifungal activity of C. brasiliensis heartwood xanthones was lower than
that exhibited by synthetic phenol. Schultz et al. (1995) also observed that
M. pomifera heartwood compounds were less active than commercial fungicides.
Some other xanthones have been shown to be inhibitory to phytopathogenic
fungi. For instance 1,5-dihydroxyxanthone, 6-desoxyjacareubin, 5-hydroxy-lmethoxyxanthone (Rocha et al., 1994), and l,3,5-trihydroxy-2-methoxyxanthone (Pinto et al., 1994) inhibited the growth of Cladosporium curcumerinum.
The former compound was also active against Trichophyton mentagrophytes
(Pinto et al., 1994). On the other hand, four 3-OMe substituted xanthones were
inactive against C. curcumerinum (Rodriguez et al., 1995; Pinto et al., 1994),
suggesting that free hydrogen or hydroxyl at this position might be essential for
antifungal activity. Nevertheless, blocking of hydroxyls (including that on C-3)
by acetylation of V or the mixture of HI and IV did not induce a significant
change in fungistasis as compared with parent compounds (Table 3).
Several xanthones have been recently reported as antioxidants and free
radical scavengers (Minami et al., 1994, 1995). These properties are important
considering that wood degradation by brown rot fungi involves secretion of
fungal H2O2 and its interactions with wood Fe2+ ions (Kirk, 1983). From this
perspective, it is possible to hypothesize that during fungal attack xanthones
could first be oxidized, thus delaying degradation of structural polymers. Preliminary evidence indicates that compound V was not oxidized in vitro by
P. placenta, but the presence of Fe2+ ions was not assured in this system. We
are currently studying oxidative metabolism of V under controlled conditions.
Acknowledgments—Research was supported by grant NI214996 DGAPA-UNAM. The authors
are grateful to Fernando Ortega-Escalona and Guadalupe Barcenas Pazos for providing C. brasilienis
wood, to Dr. Terry Highley for donation of the fungus, and to Dr. Ana Luisa Anaya Lang for her
facilities for culturing it.
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