Full text of DOI:10.1016/S0031-9422(00)89890-8

1
971, Vol. 10, pp. 2425 to 2432.
Press. Printed in England.
XANTHONES OF CANSCORA DECUSSATA
R. K.
and S. GHOSAL
Department of Pharmaceutics, Banaras Hindu University, Varanasi-5, India
(Received 14 October 1970, in revisedform 7 December 1970)
Abstract-The roots of Canscora decussata Schult has been shown to contain sixteen xanthones (I-XVI), six
of which (II, VII, IX, XII, XIII, XVI) are previously unreported in nature. Chemical and spectral methods
and in most cases comparison with authentic synthetic samples established their identity as mangiferin
1
-hydroxy-3,5-dimethoxy- (VII),
(II),
(VIII),
trihydroxy-7-methoxy- (III),
(XI),
(
XIII),
(XIV),
(XII),
(XV), and
methoxy- (IX),
xanthones. In addition, three minor xanthones (IV-VI) have been isolated from the same source and are
partially characterized. Biogenetic and chemotaxonomic significance of the co-occurrence of mangiferin and
the other aforementioned xanthones in a single plant species such as C.
is discussed.
INTRODUCTION
is a small genus of about seven species’ found throughout India
t o an altitude of 4000
largely growing in moist situations. Canscora decussata Schult,
an erect annual plant of height
m, finds use in the indigenous system of medicine for a
variety of The roots are used as laxative, nerve tonic, in tuberculosis and fevers,
while the aerial portions are used in insanity, epilepsy and nervous debility.
No previous phytochemical work has been reported on this genus. The isolation and
identification of several xanthones from the roots of this species constitute the subject of the
present paper.
RESULTS AND DISCUSSION
Preliminary examination of the root extract by TLC showed the presence of a number
of yellow pigments. The assumption on chemotaxonomic grounds that these might be due
to xanthones was supported by their chemical and spectral properties.
Alcohol extraction of a larger sample of the defatted roots afforded a yellow solid,
which was sparingly soluble in
substance indicated it to be a and quickly led to the conclusion that the
compound was mangiferin (I) on the basis of correspondence with IR and UV
solvent. Spectral analyses of
of the compound and its derivatives. The mass spectral data (Table 3) of these
compounds are also consistent with this conclusion.
The alcoholic mother liquor, after separation of mangiferin, gave a syrupy mass from
which the nitrogenous constituents were removed by aqueous acetic acid treatment in the
Part I in the series “Studies on the Chemical Constituents of the Centianaceae”.
J. S.
Flora of Madras, Vol. II, p. 617, Botanical Survey of India, Calcutta (1956).
R. N. CHOPRA, L. NAYAR and I. C. CHOPRA, Glossary of Indian Medicinal Plants, p. 49, C.S.I.R., New
Delhi (1956).
R. C.
F.
R
OBE R T S
,
Rev. 61, 592 (1961).
Tetrahedron 18, 853 (1962).
2
425

2
426
R. K.
and S.
TABLE 1. UV ABSORPTION MAXIMA OF THE XANTHONES OF C. decussata ROOTS
Xanthone
nm (log in
(*Inflection)
2
2
2
42
45
40
260
316
268-270
315
335, 355.
38-240 (sh), 250,
45 308 (4.27).
366 (4.10).
340 (4.06).
337 (3.97).
258
2
2
2
15, 253,
326.
(
VIII)
XIII)
242
262
260
272 sh
263
280-282
313 (4.16).
308
310
330 (4.18).
318
2
2
2
2
40
48
40
53
355 (3.84).
358 (3.61).
330 (4.05).
335 (4.18).
(
255
320
2
240
255
50-252
285
266-268
283
326 (4.22).
332 (3.99).
(
(
XV)
XVI)
(4.22).
TABLE
XANTHONES OF
decussata ROOTS
Methoxyl
protons
_ _ _ _ _
Aromatic protons
H-6 H-5
Xanthone
H-8
H-7
6.77
H-4
6.42
H-2
_
3
.95
7
.79
6.27
6.28
3
.90
7
7
.55
.65
7
.28
6
.43
3
.90, 3.95
6.95
7.20
6.55
6.64,’
6.59
6.28
(
OH-protons
1.61, 11.23)
1
3
.95
6
.63
6.36
Solvents:
*
The signals (in ppm) were recorded from TMS.
usual way. The chloroform-soluble fraction of the aqueous acidic suspension, consisting
of a mixture of xanthones, were separated into three broad fractions (Fractions A-C) by
solvent extractions. The individual entities (II-XVI) were isolated from the above fractions
by preparative chromatography. The characterization of the xanthones is described as
follows in order of their isolation from the fractions (A-C).
Fraction-A, Xanthone II. Xanthone II, m.p.
and a ether The NMR spectrum (Table 2) of the compound showed one
methoxyl (proton absorption at S 3.95). These data suggest that xanthone II is a
methoxy-trihydroxy xanthone. Coupled doublets at S and
two pairs of ortho and aromatic protons. The UV absorption
formed a triacetate
L. M.
1959).
Applications of NMR Spectroscopy in Organic Chemistry, p. 85, Pergamon Press, Oxford
(

Xanthones of Canscora decussata
2427
T
ABLE 3.
OF C.
Molecular ion
Significant peaks
Metastable peak
Xanthone
Found (m/e)
4
2
04 (M-18) (12); 368 (45); 326 (14); 300 (21);
85 (34); 273 (100).
(
I)-Heptaaeetate
716 (18)
674 (38); 632 (98); 590 (84); 572 (36); 523 (92);
94 (100).
4
2
74 274 (100) (100)
246 259 (12); (14); 245 245 (32); (26); 244 231 (25); (8). 231 (11).
274 274
245: 219.0; 245 219
2
72 (100)
257 (18); 243 (23); 242 (12); 229 (7).
272
2
2
72
242:
15.2; 215.5
3
02
287 (16); 273 (21); 272 (8); 259 (34).
317 (12); 303 (42); 302 (22); 304 (5).
302 273 246.8 247
(
IX)
332 (100)
332
32
303
3
2
58 288 (100) (100)
230 273 (8); (12); 229 259 (32); (17); 228 258 (12); (16); 215 245 (7). (29).
258 288
229 202.8 203
2
31.1; 231.5
(
(
XII)
XIII)
318 (100)
304 (100)
303 (8); 289 (12); 275 (17); 274 (5).
289 (20); 275 (24); 274 (16); 261 (46).
304
74.7;
2
The figures in the parenthesis indicate relative abundance of ions.
maxima (Table 1) of the compound indicate a
ether of the xanthone was found to be identical with
The
xanthone. The question remains as to the position of the methoxyl group in the xanthone.
The failure to give positive test and the solubility of the compound in aqueous
sodium carbonate indicate that the methoxyl group is either at C-5 or at C-6 (but not at
C-3). This point was finally settled by mass spectrometric determinations. The abundance
of the species M-29 and M-30 (at
245 and 244) and the absence of any M-15
fragment in its mass spectrum locate the methoxyl at C-6. Xanthones with a
substituent are known’ to produce abundant ion-fragments corresponding to the loss of a
methyl radical while in m-methoxy phenols there has been found virtually no M-15
m-Methoxy phenols display, on the other hand, loss of 29 and 30 mass units from their
molecular ions in one step. Similar anticipated peaks were observed, in the present study,
with other methoxylated xanthones.
ZZZ. Xanthone III, m.p.
ether, and showed one methoxyl group in its NMR spectrum. The UV absorption of the
compound indicates a The methoxyl group in this
xanthone is placed at C-7 on the basis of its solubility in sodium carbonate solution,
formed a triacetate, a
H. D.
B. JACKSO N , H. D.
H. C.
I.
and F.
and F.
Chem.
Chem.
(c), 178 (1966).
(c), 785 (1967).
and D. H. WILLIAMS , Interpretation of Mass Spectra of Organic Com-
pounds, p. 178, Holden-Day, San Francisco (1965).
K. R. MARKHAM , Tetrahedron 21, 3687 (1965); and previous papers.
M. KOMATSU , T.
and M.
Chem. Pharm. Bull.
17, 155 (1969).
S. R. DALAL and R. C. SH AH, Chem. Znd. 140 (1957).

2
428
R. K.
a n d S.
a bu n d a n ce of M-15 (m/e 259) ion-fragment in its mass spectrum, and correspondence of its
m.p. with
Methylation of the xanthone with
diazomethane gave decussatin.
Fraction-B, Xanthones IV,
VI. A fu r th er cr op of xa n th on e III and three other minor
xanthones (IV, V, VI) were isolated from this fraction. While xanthone IV,
showed UV absorption maxima characteristic of
xanthone
(
described later), and xanthone VI, m.p.
showed maxima characteristic of
and showed UV spectrum
pattern, xanthone V had a range in
indicative of a mixture. The structure of these xanthones will be the subject of a later
communication.
Fraction-C, Xanthones
VIII, IX,
XI, XII, XIII. Xanthone VII, m.p.
showed UV absorption spectrum characteristic of a
The insolubility of the compound in aqueous sodium carbonate, abundance of
M-15 species
257) in its mass spectrum, and the positive Gibbs
shown by the
compound suggested its identity with
This conclusion
was confirmed by direct comparison of the compound with an authentic synthetic sample
of the xanthone.
Xanthone VIII,
in all respects.
was found to be identical with decussatin
Xanthone IX, m.p.
formed a monoacetate and showed four
methoxyl groups in its NMR spectrum (12 proton signals at
protons appeared as split doublets at and
The aromatic
and one singlet at
assignable, respectively, to C-4, C-2, and C-5 protons. The UV spectrum of the
compound is also consistent with this assignment. The facile elimination of 30 mass units
from the molecular ion locates more number of methoxyl groups
to th e xanthone
oxygen bridge (e.g. at C-3, C-6 and C-8). The compound was recovered unchanged after
treatment with diazomethane. On the basis of the above data, xanthone IX is identified as
Direct comparison with the
xanthone XIII lends further credence to this conclusion.
ether of
Xanthone X, m.p.
spectrum indicates a
is a monomethoxy-dihydroxyxanthone. The UV
pattern. The methoxyl group is located at C-3
in view of its UV maxima being remained unaffected in ethanolic sodium acetate, its
insolubility in aqueous sodium carbonate, and facile loss of 30 mass units from its molecular
ion. Direct comparison of the xanthone with
their identity.
proved
Xanthone XI, m.p.
is a dihydroxy-dimethoxyxanthone as it formed a
diacetate and a monomethyl ether with diazomethane. The UV absorption and NMR
spectra of the compound showed close similarity to those of xanthone III. On the basis of
these data, together with its negative
and unchanged UV maxima in ethanolic sodium acetate, the xanthone is identified as
The mass fragmentation
test, insolubility in aqueous sodium carbonate,
(
=
of xanthone XI, showing facile loss of both 15 and 30 mass units, is also consonant with this
conclusion. Direct comparison with methylswertianin could not be performed due to
non-availability of the authentic sample. The monomethyl ether of the xanthone was found
to be identical with decussatin.
F . E. KING , T. J .
and L. C. MANNING ,
563 (1957).

Xa n t h on es of Canscora d ecu ssa t a
2429
Xanthone XII, m.p.
is provisionally assigned
xanthone IX structure on the basis of its chemical and spectral properties. The compound
was insoluble in aqueous sodium carbonate, showed positive Gibbs test, and formed a
monomethyl ether identified as xanthone IX. The spectral properties (Tables l-3) of the
compound also support this structure.
Xanthone XIII, m.p.
showed a close similarity in its spectral
properties to xanthone IX. The UV absorption spectrum of the xanthone, except the
bathochromic shift of the longer wavelength band in ethanolic sodium acetate, is almost
identical to that of xanthone IX suggesting the presence of the same pentaoxygenated
pattern in xanthone XIII. The NMR spectrum showed signals due to two methoxyl groups
at
and
and aromatic proton signals at
(H-5),
(H-4),
The corres-
ether was found to be more basic than the parent xanthone on acidic
(H-2). Xanthone XIII is, therefore,
ponding
TLC plates which also
a free
structure for this xanthone.
XV,
The mixture of polyhydroxyxanthones, re-
maining after separation of the above xanthones, could not be isolated directly. Methylation
with diazomethane and preparative chromatography provided separation into three major
compounds, viz.
and
xanthones. Complete demethylation of the individual entities afforded
the corresponding tetra- and pentahydroxy xanthones. The natural mixture of the
hydroxy xanthones was shown to contain these entities (XIV, XV, XVI) by preparative and
co-TLC and from comparison of their individual UV absorption spectrum in neutral and
alkaline solvents.
Although mangiferin (I) occurs in widely divergent
this is the first report of
its occurrence in the Gentianaceae. Further, mangiferin, to the knowledge of the authors,
has not been found to co-occur with other xanthones until this investigation. In view of these
data and the reported significance of the occurrence of mangiferin at species
further investigation about its presence in other Canscora species is warranted. The elabora-
tion of several xanthones based on standard
by further oxydation at C-6 and/or C-8 by a single plant species such as C.
considerable biogenetic and chemotaxonomic interest. Yet another variation in the
oxygenation pattern, e.g. pattern, could be observed in mangiferin
and
patterns, modified
is of
associated with other xanthones in this species. These observations would not only indicate
catholicity of the oxidative enzyme system present in the species but also support a currently
accepted hypothesis’ that xanthones in nature are derived from the direct oxidative coup-
ling of hydroxybenzophenones of the type XVII. The tetra- and the pentaoxygenated
xanthones, primarily found in the
oxidation of the trioxygenated
are, presumably, formed by further
xanthones rather than involving the
or
hydroxylated benzophenone intermediates. In view of this contention, search for the
other common intermediate, viz.
being made in this laboratory.
xanthones, in C. decussatu is currently
G. H . STOUT, E . N. CHRISTENSEN , W. J . BALKENHOL a n d K. L. STE VE NS , Tet r a h ed r on 25, 1961 (1969).
I. CARP ENTER , H. D. L OCKSLEY a n d F . SCH E INMANN .
8, 2013 (1969).
E . C.
a n d J . B. H AR B O R N E , Na t u r e 198,
A. H . WI L L I AMS
,
Nature 202, 824 (1964).
J . R. LE WI S
,
Chem.
373 (1963).

2
430
R. K. CHAUDHUR I and S. GHOSAL
0
OH
0
OH
0
OH
=
=
Me
=
=
Me
H
=
=
Me
=
=
= Me
SCHEME 1 .
EXPERIMENTAL
All
were taken on a
block in open capillary and are uncorrected. UV spectra were recorded
on a Carl Zeiss
mined on
II soectronhotometer in 95
Elmer 137 instrument in
unless otherwise stated. IR spectra were deter-
and only the major bands are quoted. Mass spectra were
determined on AEI. MS-9 instrument operated at 70 e.v. NMR spectra were obtained on Varian A-60
spectrometer. Combustion analyses were performed by the C.D.R.I.,
Separation by column
chromatography was carried out using silica gel
G (Merck). Both neutral and acidic (5
and TLC experiments were done with Kiselgel
chromatoplates were used. Three solvent systems, viz.,
(
4
1 : 5, Solvent 1);
Solvent 2); and
Solvent
were used as developers and vapour was used for the staining purposes.
Extraction of Canscora decussata Roots
Dried and milled roots (1.2 kg), collected from the local area and properly identified (through the
courtesy of the Department of Botany, Banaras Hindu University), were hot extracted in a Soxhlet with
petroleum
and then with
for 30 hr each. The petroleum extract was kept aside for future
investigation.
Z
Concentration of the
extract afforded a pale cream coloured material
from which mangiferin (31
was obtained
(lit.” 269-270”)
Solvent 1); superimposable IR spectra with authentic mangiferin. The
from ethyl acetate-petroleum as needles, 139-141” 141-143”).
The alcoholic mother liquor, after separation of mangiferin, was concentrated to a syrupy liquid and 4
200 ml) added. The mixture was kept at ordinary temperature overnight. The aqueous acidic
treatment with large volume of as coloured
H 0
needles,
for C
(
(
B J HAWTHORNE, N. F.
and Synthetic
S. V. SUNTHAKER and B. D. TILAK),
F. E. KING and J. W.
MORGAN, Recent Progress in the Chemistryo,
Matters and Related Compounds (edited by T. S. G O R E, B. S.
331, Academic Press, New York (1962).
J. D. RAMANATHAN and T. R. SE SHADR I, Tetrahedron 23, 1363 (1967).

Xanthones of Canscora decussata
2431
suspension was extracted with
(3 x 50 ml). The acidic solution was kept aside for further processing
for alkaloids. The CHCl,-soluble neutral fraction upon concentration (to ca. 30 ml) afforded a yellow amor-
phous solid (0.45 g) marked Fraction -A. The chloroform mother liquor was marked Fraction-C.
Separation of Xanthones Present in Fraction-A
The yellow solid
was partially soluble in hot
solution, on evaporation, afforded another solid (0.11 g), m.p.
and (Solvent 2) on neutral chromatoplates. The two components were separated by
the insoluble part was marked Fraction-B.
The
which showed two
spots,
column chromatography using
Xanthone
(4 1.) as the eluent. 100 ml Fractions were collected.
The initial fractions of the eluates gave
trihydroxy-6-methoxyxanthone (62
m.p. 285-287”
which crystallized from alcohol as snuff coloured micro needles,
(Solvent 2);
3300, 1645, 1590, 1512, 1465, 1378, 1360, 1332,
The triacetate crystallized from alcohol as colourless needles, m.p. 191-192”
191-192”).
tion with gave 1-hydroxy-3,5,6-trimethoxyxanthone which crystallized from
as yellow
needles, m.p. and mixed m.p. 181-183”. The corresponding 1-acetyl derivative crystallized from acetone as
colourless needles, m.p. and mixed m.p. 147-148”.
Xanthone ZZZ
The later fractions of the
as yellow needles, m.p.
gave
eluates gave
(
58 mg) which crystallized from
2
93” (lit? 296-299”);
xanthone (= decussatin), m.p. and mixed m.p. 149-151”.
(Solvent 2). Methylation with
Separation of Xanthones Present in Fraction-B
Xanthone ZV. The
solid (0.31 was sparingly soluble in
had m.p. 278-281”; (Solvent 2). The methyl ether (with
as needles, m.p. 170-172”.
fraction was chromatographed using a large volume of as eluent
5 1.). 100 ml Fractions were collected. The first two fractions gave pale yellow micro crystals (25 mg),
The
residue, a snuff coloured solid (15
crystallized from
Xanthone V. The
(
2
45-258”;
255, 268-270, 283
326 and 355-65
Xanthone
The later fractions (6-43) gave a brown solid residue (0.15 g), m.p.
consisting
of two components, R,,
and
(Solvent 2). The two components were separated by fractional
crystallization from
The moderately soluble fraction afforded a further crop of
methoxyxanthone
g), while from the sparingly soluble fraction another xanthone was obtained as pale
0.62; 1670, 1550, 1450, 1327, 1160,
yellow needles (12 mg), m.p.
105, cm-‘.
1
Separation of Xanthones Present in Fraction-C
The residue
g), obtained from this fraction, was taken in benzene and was chromatographed using
(3 1.) and 1.) as eluents. 100 ml Fractions were collected. Each fraction
benzene (3 l.),
was examined by TLC and the fractions found to contain mixtures were rechromatographed for further
separation. The benzene eluates (fractions l-3) yielded a semisolid mass (95
which was
graphed using petroleum-benzene
as eluent.
Xanthone VZZ
Earlier fractions afforded
xanthone (20 mg) which crystallized from benzene as yellow needles, m.p. and mixed m.p. 173-174”
1
74-175”).
Xanthone VZZZ (1-hydroxy-3,7,8-trimethoxyxanthone = decussatin). The middle petroleum-benzene
fractions from the chromatography gave xanthone VIII (28 mg) which crystallized from
as tine yellow
needles, m.p. and mixed m.p. 148-149”. The 1-acetyl derivative crystallized from acetone as colourless
needles, m.p. 167”.
Xanthone
The final petroleum-benzene eluates afforded a
as needles, m.p. 171-172” (Found: C,
yellow amorphous solid (32 mg) which crystallized from
H,
requires: C, 6144; H, 4.82%). The l-acetyl derivative of the xanthone crystallized
from acetone as colourless needles,
(Found: C, 61.21; H, 4.67.
requires: C, 60.95;
H, 4.86%). The benzene eluates (22-28) from Fraction-C gave a straw coloured amorphous solid
which was rechromatographed using benzene as eluent.
Xanthone X
Earlier fractions yielded a yellow crystalline solid
(
30 mg) which recrystallized from alcohol as bright yellow needles,
272”
269-271” and
B. J ACKS ON, H. D. LOCKSLEY and F. SCHEINMANN, Chem.
(c), 178 (1966).
B. J ACKS ON, H. D.
M.
and F. SCHE INMANN, Tetrahedron
M.
(1965).
0
. R.
A. A.
and D. DE B AR R O S
Tetrahedron 22, 1777 (1966).
T. R.
B. R.
P. S.
U. R. RAO and N.
hedron 23, 243 (1967).

2
432
72”)
The methyl ether of the xanthone, formed upon treatment with
R. K. CHAUDHURI and S.
2
(Solvent 3)
1047,
as
crystallized from
needles, m.p.
The residue from the later fractions, a pale yellow solid (158 mg), showed two spots on TLC,
Solvent 3). The two components were separated by fractional crystallization from benzene, the less
polar xanthone being liberally soluble in this solvent.
(
From the liberally benzene soluble fraction was
obtained xanthone XI as pale yellow needles (85 mg), m.p. 191”
585, 1510, 1458, 1367, 1332, 1295, 1250, 1212, 1188, 1170, 1100, 1075, 1038, 875, 830
The diacetate crystallized from acetone as colourless needles, m.p. 208-210” (lit.“’
ether crystallized from as yellow needles, m.p. and mixed
The sparingly soluble fraction in benzene gave
as needles, (Found: C, 60.42; H,
190”);
0.46;
3310, 1655, 1592,
1
The methyl
(decussatin), 148-150”.
a colourless solid (41 mg) which recrystallized from
4
.28
requires: C, 60.38; H,
as cluster of needles,
R,, 0.40. The monomethyl ether of the xanthone crystal-
170-172”. Mixed m.p. with xanthone IX remained undepressed.
eluates (3 showed several spots on TLC. Further identification
lized from
The residue obtained from the
of these constituents is deferred.
The
washings
1.) of the column gave a brown gum (0.54 g) which when triturated with a
small volume of
gave a snuff coloured solid (98 mg).
The snuff coloured solid (98 mg) was taken
as eluent. Earlier fractions gave
requires : C, 59.53 H, 3.94);
in
(2 ml) and rechromatographed using
brown crystals,
290-291” (Found : C, 59.38; H, 3.88.
(
Solvent 2)
3450, 1662, 1578, 1475, 1436, 1362, 1180, 1070,
778, 705 cm-‘.
172”. Mixed m.p.
The monomethyl ether of the xanthone crystallized from benzene as needles,
with xanthone IX remained undepressed. The
less needles, (Found: C, 58.65; H, 4.02.
XZV, XV, The
of the xanthone crystallized from acetone as
requires: C, 58.51; H,
mother liquor, after separation of xanthone XIII,
showed three major spots on acidic chromatoplates. Attempts to separate the components by preparative
failed. The crude mixture of xanthoses was methylated with
The
lated product, on repeated column chromatography using petroleum-benzene as eluent afforded the three
methyl ethers, viz., 1-hydroxy-3,5,6-trimethoxyxanthone (15 mg), m.p. 180-181”;
thoxyxanthone (= decussatin) (21 mg);
(= xanthone IX) (18 mg).
Final purification of the methyl ethers was done on acidic TLC plates. The developing solvent used was
1: 1).
Complete demethylation of the individual methyl ethers with
(
(48
afforded the respective
hydroxyxanthones (XIV, XV, XVI). The natural mixture of the polyhydroxyxanthones was subjected to
TLC using both neutral and acidic chromatoplates. The neutral plates were, however, found to be more
suitable for preparative TLC. The pure components thus obtained were compared with the aforementioned
demethylated products by co-TLC in different solvent systems. The UV absorption maxima of the natural
xanthones and the corresponding markers in alcohol,
were identical.
and
Acknowledgements-We are indebted to Dr. K. R. Markham, Chemistry Division, DSIR,
New
and to Dr. B. C. Das. CNRS. Gif-Sur-Yvette, France.
Kumar, formerly of this Department; for drawing our attention to the
Zealand. to Dr. N. M.
CDRI,
for the spectral data, to Mr.
plant, and to the U.G.C., New Delhi, for the award of a fellowship to the junior author (R.K.C.).