A chalcone and a dihydrochalcone from Uvaria dulcis

Article abstract of DOI:10.1016/S0031-9422(99)00477-X

2',3'-Dihydroxy-4',6'-dimethoxychalcone and the corresponding dihydrochalcone were isolated from the leaves of Uvaria dulcis and characterized by chemical and spectral methods. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0031-9422(99)00477-X

Phytochemistry 53 (2000) 511±513
www.elsevier.com/locate/phytochem
A chalcone and a dihydrochalcone from Uvaria dulcis
Kan Chantraprommaa,*, Yanisa Rat-A-paa, Chatchanok Karalaia,
Vitchu Lojanapiwatanaa, Vatcharee Seechamnanturakitb
aDepartment of Chemistry, Faculty of Science, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand
bScienti®c Equipment Centre, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand
Received 30 April 1999; received in revised form 16 July 1999
Abstract
2',3'-Dihydroxy-4',6'-dimethoxychalcone and the corresponding dihydrochalcone were isolated from the leaves of Uvaria
dulcis and characterized by chemical and spectral methods. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Uvaria dulcis; Annonaceae; Chalcone; Dihydrochalcone; Flavanone
1. Introduction
2. Results and discussion
Hot hexane extract of the leaves of U. dulcis
a€orded a gum which was chromatographed on
silica gel using increasing percentages of chloroform
in hexane to give three compounds. The ®rst, an
oil, MS gave M.W 212 analysing for C14H12O2 was
found to be benzyl benzoate by detailed examination
of IR, NMR, MS spectral data and by comparison
with an authentic sample. The second compound,
mp 124±1268C, was obtained as red crystals and
identi®ed as 2',3'-dihydroxy-4',6'-dimethoxychalcone
1 on the basis of UV, NMR, MS data and chemical
interconversions. The UV spectrum in MeOH supports
a chalcone structure of the compound (Panichpol et
al., 1977; Mabry, Markham & Thomas, 1970), lmax
240, 290 and 346 nm. The lack of a shift in Band II
in NaOAc indicates that the A-ring 4' position is
substituted. A bathochromic shift of Band I in AlCl3
relative to the MeOH spectrum of 34 nm (from 346
to 380 nm) suggests a free hydroxyl group at the
6' position in the A-ring. NMR data establish an
unsubstituted B-ring; a multiplet at d 6.85±7.75 inte-
grating for ®ve aromatic protons which can be
assigned to the B-ring and at d 7.90 to the a- and
The genus Uvaria has been a rich and varied source
of new compounds as is evidenced by the isolation of
alkaloids (Panichpol, Waigh
& Waterman, 1977;
Achenbach & Ro€elsberger, 1979) ¯avonoids (Cole,
Torrance, Wiedhopf, Arora & Bates, 1976; Lasswell &
Hu€ord, 1977; Okorie, 1977; Tammami, Torrance,
Fabela, Wiedhopf & Cole, 1977; Hu€ord, Lasswell,
Hirotsu & Clardy, 1979; Hu€ord & Oguntimcin,
1982), cyclohexene oxides (Holbert et al., 1979;
Schulte, Ganem, Chantrapromma, Kodpinid & Sub-
suansri, 1982) and aromatic oils (Kodpinid, Thebtara-
nonth & Thebtaranonth, 1985). In continuation of our
studies on the genus Uvaria (Holbert et al., 1979;
Schulte et al., 1982; Chantrapromma, Pakawatchai,
Shelton, White & Worapatamasri, 1989), we further
examined the leaves of U. dulcis Dunal. We now
report on the chemical examination of the leaves
which gave a chalcone 1 and its corresponding new
dihydrochalcone 2 together with ¯avanone 3 and ben-
zyl benzoate.
* Corresponding author.
0031-9422/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0031-9422(99)00477-X

512
K. Chantrapromma et al. / Phytochemistry 53 (2000) 511±513
b-protons. One aromatic signal at d 5.91 can be
attributed to a proton at either C-3 or C-5. Two
methoxyl groups at d 3.86 and 3.93 are assigned to
the A Ð ring 4 and 6-positions. The hydrogen-bonded
phenolic-OH at 14.06 in the NMR would then be
placed in the C-2 position, making chalcone 1 a 2-
hydroxychalcone. A strong molecular ion at m/z 300
con®rms the molecular formula of C17H16O5. That the
chalcone contains a 2'-hydroxyl group was con®rmed
by a trace of the ¯avanone 3 were present in all
samples of the chalcone 1, and could be separated by
silica gel TLC as 5,7-dimethoxy-8-hydroxy¯avanone,
an expected cyclization product from the chalcone 1.
Fragments for the chalcone 1 were at m/z 300
(100%), 269 (13%), 223 (22%), 196 (88%), 178
(75%), 150 (66%), 131 (13%), 103 (22%), 77 (44%).
On treatment with acid (1 h 5% aqueous H2SO4)
chalcone 1 gave a pale yellow crystalline ¯avanone 3
(mp 166±1688C), which was identi®ed as 5,7-
dimethoxy-8-hydroxy¯avanone. The ¯avanone 3 was
fully characterized by a combination of spectral data
and X-ray crystallography (Chantrapromma, Seecham-
nanturakit, Pakawatchai, Chantrapromma, Chinnakali
& Fun, 1998).
3. Experimental
3.1. General experimental procedures
All mp's are uncorrected. CC was run on Merck Si
gel 60 (70±230 mesh). TLC was performed on glass
plates precoated with Kieselgel 60 F254 (Merck). MS
were recorded on a Varian Saturn GC/MS 4D spec-
trometer. IR spectra were obtained on a Perkin-Elmer
IR 783 spectrophotometer and UV spectra on a UV-
160 A (SHIMADZU) spectrophotometer. 1H-NMR
were recorded at 60 MHz on a JEOL-PMx 60 and on
a with TMS as an internal standard. Chemical shifts
are quoted in ppm ꢀd). The NOE di€erence spectra
were performed on a Varian INOVA 500 MHz nuclear
magnetic resonance.
The third compound, light yellow crystals, mp
141±1428C gave a brown color with ethanolic FeCl3
indicating the phenolic nature and a negative Shinoda
reaction (Shinoda, 1928) suggesting absence of ¯avone
or ¯avanone nucleus. The molecular formula was
established by MS, m/z 302, C17H18O5. The IR spec-
trum (3480 and 1635 cm 1) indicated the presence of
at least one phenolic hydroxyl group and a conju-
3.2. Plant material
Leaves of U. dulcis were collected at Phrae province,
Thailand, in July 1990. A voucher specimen has been
deposited at the Herbarium of the Forest Institute of
Thailand.
1
gated ketone group. The H-NMR spectrum displayed
ethylene proton signals of an A2B2 system centred at
d 3.05 and 3.35; two methoxyl groups at d 3.84 and
3.95, one proton singlet at d 6.00 and a ®ve proton
multiplet at d 7.01±7.60. It also showed one proton
broad singlet at d 5.10 (lost on deuteration) assignable
to phenolic-OH and a one proton sharp singlet at d
13.80 (exchangeable with D2O) attributable to a
hydrogen bonded phenolic-OH. These data suggested
that this compound is a 2'-hydroxydihydrochalcone
with two methoxyl groups and two hydroxyl groups
on the A-ring. The identi®cation of H-6 of dihydro-
chalcone 2 was determined by NOE di€erence spectra.
Irradiation of the H-6 signal showed a strong enhance-
ment of the two methoxyl groups, thus indicating
that it de®nitely has two methoxyl groups next to
the H-6. In addition, irradiation of 2 at both the
methoxyl signals showed only the enhancement of the
H-6. Dihydrochalcone 2 was also suspected to be a
dihydro derivative of the chalcone 1. Indeed, catalytic
hydrogenation of the chalcone 1 gave 2',3'-dihy-
dro-4',6'-dimethoxydihydrochalcone 2, which was
indistinguishable from the natural product in all
respects.
3.3. Extraction and isolation
The air-dried ground leaves of U. dulcis (800 g) were
extracted with hexane. Evaporation of the hexane
extract in vacuo at 408 yielded a gum (85 g) and chro-
matographed on a column of Si gel (250 g) eluting
with increasing percentages of CHCl3±hexane. Hex-
ane±CHCl3 (9:1) eluted benzylbenzoate (0.07 g). Hex-
ane±CHCl3 (4:1) fraction furnished dihydrochalcone 2
as light yellow crystals mp 141±1428C (0.45 g). UV:
1
1
lmax 208, 240, 290 nm; IR: lmax cm ; 3480, 1635; H-
NMR (CHCl3): d 3.86, 3.93 (2s, 6H, 2xOCH3); 5.97 (s,
1H, 5-Ar-H), 6.85±7.75 (m, 5H, B-ring-H), 7.90 (s, 2H,
a, b-H), 14.06 (s, 1H, 2-OH). MS: m/z 300 (M+,
100%), 269 (12.5%), 223 (21.9%), 207 (12.5%), 197
(18.8%), 196 (87.5%), 178 (75%), 165 (12.5%), 131
(12.5%), 103 (22%), 77 (43.8%). Hexane±CHCl3 (7:3)
eluates a€orded chalcone 1 as red crystal (0.08 g), mp
124±1268. UV: lmax (MeOH): 208, 240, 290 nm; IR:
1
lmax cm 3480, 1680, NMR (CDCl3): d 3.05 (t, 2H,
JAB 7.7 Hz, 2x b-H), 3.35 (t, 2H, JAB 7.7 Hz, 2x a-H),
3.86, 3.93 (2s, 6H, 2xOMe), 5.10 (s, 1H, OH, lost on
deuteration), 5.91 (s, 1H, AR-H), 7.01±7.60 (m, 5H, B-

K. Chantrapromma et al. / Phytochemistry 53 (2000) 511±513
513
ring-H), 13.80 (s, 1H, Ar±OH, disappearing with
D2O). MS: m/z 302 (M+, 37%), 202 (14.8%), 197
(100%), 182 (17%), 105 (10.6%), 91 (37.7%).
Acknowledgements
The authors would like to thank the International
Foundation for Science and Thailand Toray Science
Foundation for ®nancial support of this work.
3.4. Conversion of chalcone 1 to ¯avanone 3
To a solution of chalcone 1 (0.102 g, 0.341 mmol) in
ethanol (5 ml) was added dropwise a solution of 5%
H2SO4 in ethanol (15 ml) in an atmosphere of nitrogen
at 08C, and the mixture was heated under re¯ux for 12
h. The cooled reaction mixture was then evaporated
under reduced pressure to remove the ethanol. The
residue was dissolved in chloroform and the organic
layer was washed with water and brine, and dried
(Na2SO4). Evaporation of the chloroform extract
under reduced pressure a€orded the crude ¯avanone 3
which was puri®ed by preparative TLC with 30%
ethyl acetate in chloroform as eluent. The ®rst band
(Rf = 0.38) yielded ¯avanone 3 (0.053 g, 54%) as pale
yellow crystals, mp 166±1688C. This product was iden-
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