全 文 ：Received 6 Mar. 2003 Accepted 27 Oct. 2003
Supported by the National Natural Science Foundation of China (39600010) and Teaching and Research Award Program for Outstanding Young
Teachers in Higher Education Institutions of Ministry of Education, China (2000191).
* Author for correspondence. Tel: +86 (0)25 85391289; Fax: +86 (0)25 85301528; E-mail: .
http://www.chineseplantscience.com
.Rapid Communication.
Two New Bis-labdanic Diterpenoids from Alpinia calcarata
KONG Ling-Yi 1, 2 *, QIN Min-Jian 1, NIWA Masatake 2
(1. Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing 210009, China;
2. Faculty of Pharmacy, Meijo University, Nagoya 4688503, Japan)
Abstract: Two novel bis-labdanic diterpenoids named calcaratarin G and calcaratarin H were isolated
from the rhizomes of Alpinia calcarata Rosc. Their structures were elucidated to be a pair of stereoiso-
mers on the basis of the spectral evidence. The 2D NMR techniques including 1H-1H COSY, HMQC, HMBC,
NOESY and HRFABMS were extensively applied to establish the structures.
Key words: Alpinia calcarata ; bis-labdanic diterpenoids; calcaratarin G; calcaratarin H
The labdanic diterpenoids are a class of typical com-
pounds isolated from plants of the genus Alpinia which
are used as traditional herbs in some areas of China and
other countries (Jiangsu College of New Medicine, 1977).
In recent years, more and more labdanic diterpenoids were
isolated from the plants of Zingiberaceae, but the bis-
labdanic diterpenoids are rare in plants. Only two bis-
labdanic diterpenoids, an ester of labda-8 (17), 11, 13-trien-
15-al-16-oic acid and isocoronarin D as well as moldenin
were isolated from Hedychium coronarium (Nakatani et
al., 1994) and Moldenhawera nutans (David et al., 1999),
respectively. We previously reported the isolation and
structure elucidation of several labdanic diterpenoids in-
cluding two bis-labdanic diterpenoids from Alpinia
calcarata (Kong et al., 2000; Kong et al., 2002). In our
continuous studies on the constituents of the plant, two
more novel bis-labdanic diterpenoids, namely calcaratarin
G and calcaratarin H, were isolated and their structures were
established to be a pair of stereoisomers of bis-labdanic
diterpenoids by spectral analyses. This paper describes
the isolation and structural elucidation of those two bis-
labdanic diterpenoids.
1 Results and Discussion
Calcaratarin G (1), colorless oil, was obtained by re-
peated column chromatography, preparative TLC and pre-
parative HPLC. The high resolution FAB mass spectrum
(HRFABMS) gave m/z 619.471 4 for the [M+H]+ ion (calcd.
619.472 6), corresponding to the molecular formula
C41H62O4, which was supported by the 13C-NMR spectrum.
The DEPT spectra confirmed the presence of seven methyls,
one of which was methoxyl group, 16 methylenes, nine
methines and nine quaternary carbons. The 1H-NMR sig-
nals at d 0.87 (3H,s), 0.81 (3H,s), 0.65 (3H,s) and 0.85 (3H,s),
0.78 (3H, s), 0.75 (3H, s) as well as 4.42 (1H, d, J = 1.2 Hz),
4.83 (1H, d, J = 1.2 Hz) and 4.50 (1H, d, J = 1.0 Hz), 4.87 (1H,
d, J = 1.0 Hz) indicated that compound 1 consisted of two
moieties of labdanic diterpenoid, and the signals were as-
signed to the methyl groups of C-18, C-19, C-20 and C-18,
C-19, C-20 as well as the methylene groups of C-17 and C-
17, respectively. The 13C-NMR data, including six methyls
of d 33.61, 21.67, 14.49, 33.58, 21.74, 14.46 and two quater-
nary carbons of d 148.15, 148.03 as well as two methylenes
of d 108.05, 106.56 further provided the evidence of two
moieties of labdanic diterpenoids.
The structures of the sidechains and their linkage posi-
tions of two labdanic diterpenoid moieties were determined
by HMQC and HMBC spectra. In the HMBC spectrum, the
olefinic signal at d 6.54 (1H, t, J = 6.4 Hz, H-12) correlated
with the methylene signal at d 29.18 (C-14) and the alde-
hyde group signal at d 194.76 (C-16). In the HMQC spectrum,
the signal of d 194.76 correlated with the proton signal at d
9.29 (1H, s, H-16). In the HMBC spectrum, the proton signal
of d 9.29 correlated with the methylene signal at d 29.18 (C-
14) and the quaternary carbon signal at 139.05 (C-13). In the
HMQC spectrum, the methine signal at d 109.88 (C-15) cor-
related with the proton signal at d 5.60 (1H, br d, H-15). In
the HMBC spectrum, the proton signal of d 5.60 correlated
with the methylene signal d 29.18 (C-14), the quaternary
carbon signal at d 139.05 (C-13) and the methoxyl signal at
d 54.62 (C-21). The stereochemistry about the double bond
of C-12 and C-13 were deduced by the NOESY spectrum.
Acta Botanica Sinica
植 物 学 报 2004, 46 (2): 159-164
Acta Botanica Sinica 植物学报 Vol.46 No.2 2004160
An obvious NOE correlation between the aldehyde proton
signal at d 9.29 (H-16) and the olefinic signal at d 6.54 (H-12)
showed the stereochemistry to be E configuration.
Accordingly, the structure about the sidechain of one moi-
ety was established.
The structure of another labdanic diterpenoid moiety of
compound 1 was deduced by the combination of HMQC,
HMBC and 1H-1H COSY spectra. In the HMBC spectrum,
the aldehyde proton signal at d 9.91 (1H, s, H-16) correlated
with the quaternary carbon signal at d 138.54 (C-13) and the
methine signal at d 83.34 (C-14). In the HMQC spectrum,
the methine signal of d 83.34 correlated with the proton
signal of d 5.24 (1H, m, H-14). In the HMBC spectrum, the
proton signal of d 5.24 correlated with the two quaternary
carbon signals at d 155.03 (C-12) and d 138.54 (C-13). In the
HMQC spectrum, the methylene signal at d 23.83 (C-15)
correlated with the proton signals at d 2.25 (1H, dddd, J =
13.2, 6.8, 4.4, 1.8 Hz, H-15 a) and d 2.68 (1H, ddd, J = 13.2,
8.6, 4.4 Hz, H-15 b). In the HMBC spectrum, the proton
signal of d 2.68 (H-15 b) correlated with the quaternary
carbon signal at d 155.03 (C-12) as well as an obvious cross
peak between d 22.83 (C-11) and d 2.25 (H-15 a) was
observed. In the 1H-1H COSY spectrum, the weak correla-
tions between the proton signals at d 2.25, 2.68 (H-15 a, 15
b) and d 1.51, 1.72 (H-11a, 11b) were also observed. From
above spectral evidence, and also considering the bioge-
netic pathway of labdanic diterpenoids, it was inferred that
C-15 connecting with C-12 to form a partial structure of
cyclobutene which has rarely been found in plants. The
fragment ion peak at m/z 285 in EIMS also provided the
structural evidence of the moiety. A related compound con-
taining similar structure was isolated from Laurilia
tsugicola (Alberto et al., 1995).
Furthermore, the linkage positions of two labdanic
diterpenoid moieties were further determined by HMBC
spectrum. Two obvious cross peaks between the proton
Table 1 13C-NMR and 1H-NMR data of compound 1
No. C H H (HMBC) No. C H H (HMBC)
1 38.94 α 1.01 ddd (13.2,13.2,4.4) 3β,20 1 39.25 α 1.08 ddd (12.8,12.8,2.8) 3β,20
β 1.63 br d (11.6) β 1.76 br d (12.6)
2 19.34 α 1.46 m 1β 2 19.34 α 1.46 m 1β
β 1.50 ddddd β 1.52 ddddd
(13.2,13.2,13.2,3.6,3.6) (12.8,12.8,12.8,2.8,2.8)
3 42.07 α 1.15 ddd (13.2,13.2,4.4) 1α,1β 3 42.07 α 1.17 ddd (13.2,13.2,4.8) 1α,1β
β 1.41 br d (12.8) β 1.41 br d (12.8)
4 33.58 3α,5,18,19 4 33.58 3α,5,18,19
5 55.49 1.15 dd (12.9,2.4) 1α, 6α,18,19, 20 5 55.55 1.06 dd (12.8,2.8) 1α,6α,18,19,20
6 24.13 α 1.72 m 5,7β 6 24.43 α 1.74 m 5,7β
β 1.37 dddd (12.8,12.8,12.8,4.4) β 1.31 dddd (13.6,13.6,13.6,4.4)
7 37.93 α 2.01 ddd (12.8,12.8,4.8) 5,6α,17a,17b 7 38.22 α 1.94 ddd (13.0,13.0,5.2) 5,6α,17’a,17b
β 2.39 br d (12.8) β 2.39 br d (12.8)
8 148.15 6α,9,11b 8 148.03 6α,9,11’b
9 56.53 1.90 br d (10.4) 17a,17b,20 9 56.80 1.61 br d (10.8) 17’a,17’b,20
10 39.85 1α,9,20 10 39.58 1α,9,20
11 24.68 a 2.43 ddd (14.2,10.6,4.4) 9 11 22.83 a1.51 dd (15.8,3.6) 9, 15α
b 2.65 ddd (15.3,6.2,3.6) b1.72 dd (15.6,10.4)
12 160.04 6.54 dd (6.4,6.4) 11a,11b,14a,14b 12 155.03 14,15β
13 139.05 11b,14b,15,16 13 138.54 14,15α,16
14 29.18 a 2.50 dd (13.8,7.2) 12,15,16 14 83.34 5.24 m 15α,16,15
b 2.84 dd (13.4,4.4)
15 109.88 5.60 br d 21,14 15 23.83 α 2.25 ddd (13.2,6.8,4.4) 11a
β 2.68 ddd (13.2,8.6,4.4)
16 194.76 9.29s 12,14 a 16 186.71 9.91s 14
17 108.05 a 4.42 d (1.2) 9 17 106.56 a 4.50d (1.0) 9
b 4.83 d (1.2) b 4.87d (1.0)
18 33.61 0.87 s 3α,5,19 18 33.58 0.85 s 3α,5,19
19 21.67 0.81 s 3α,5,18 19 21.74 0.78 s 3α,5,18
20 14.49 0.65 s 1α,5,9 20 14.46 0.75 s 1α,5,9
21 54.62 3.32 s 15
The spectral data were recorded in CDCl3 as solvent at 600 MHz for 1H and 150 MHz for 13C. The coupling constants (J) in parentheses
are given in Hz.
KONG Ling-Yi et al.: Two New Bis-labdanic Diterpenoids from Alpinia calcarata 161
signal of d 5.60 (H-15) and the methine signal of d 83.34 (C-
14) as well as between the proton signal of d 5.24 (H-14)
and the methine signal of d 109.88 (C-15) were observed in
the HMBC spectrum. From the chemical shift values of C-
15, H-15 and C-14, H-14, it was known that C-15 and C-14
were linked by an oxygen atom. The relative stereochemis-
tries about the skeletons of two labdanic diterpenoid moi-
eties were identical with those labdanic diterpenoids (Kimbu
et al., 1987; Itokawa et al., 1988; Singh et al., 1991; Sirat,
1994; Sirat et al., 1994; Zhao et al., 1995; Sy and Brown,
1997) isolated from the plants of Zingiberaceae by the
NOESY spectrum analysis. Finally the structure of com-
pound 1 was elucidated as shown in Fig.1. The complete
assignments of 1H- and 13C-NMR data as well as their cor-
relations in HMBC spectrum are listed in Table 1 and the
key NOE correlations in NOESY spectrum are shown in Fig.
2.
Calcaratarin H (2), colorless oil, was obtained by re-
peated column chromatography, preparative TLC and
preparative HPLC. The HRFABMS gave m/z 619.475 6 for
the [M+H]+ ion (calcd. 619.472 6), suggesting the molecular
formula to be C41H62O4. The 1H-NMR signals at d 0.87 (3H,
s), 0.78 (3H,s), 0.75 (3H,s) and 0.85 (3H,s), 0.81 (3H,s), 0.66
(3H,s) as well as 4.45 (1H, br s), 4.85 (1H, br s) and 4.50 (1H,
br s), 4.88 (1H, br s) were the characteristics of bis-labdanic
diterpenoids, and were assigned to the methyl groups of C-
18, C-19, C-20 and C-18, C-19, C-20 as well as the methyl-
ene groups of C-17 and C-17, respectively. The 13C-NMR
data, including six methyls of d 33.65, 21.66, 14.52, 33.56,
21.72, 14.46 as well as two quaternary carbons of d 148.41,
147.66 and two methylenes of d 107.62, 106.66 also pro-
vided the evidence of bis-labdanic diterpenoid.
The 1H-NMR, 13C-NMR, DEPT, 1H-1H COSY, HMQC,
HMBC, EIMS and FABMS of compound 2 were very simi-
lar to that of compound 1, and the molecular formulas of
the two compounds were the same, which indicated
the two compounds to be isomers. It was shown that
Fig.1. The structures of compounds 1 and 2.
Fig.2. The NOE correlations in NOESY spectra of compounds
1 and 2.
Acta Botanica Sinica 植物学报 Vol.46 No.2 2004162
compound 2 also consisted of the same two labdanic
diterpenoid moieties as compound 1 by detailed analyses
of 1D NMR and 2D NMR. About the linkage positions of
two labdanic diterpenoids moieties, an obvious cross peaks
between the proton signal at d 5.71 (H-15) and the methine
signal at d 83.54 (C-14) in HMBC spectrum verified that C-
15 and C-14 were also linked by an oxygen atom. The struc-
tural difference between compounds 2 and 1 was only their
stereochemistry.
The stereochemistry about the double bond of C-12 and
C-13 of compound 2 was E configuration on the basis of an
obvious NOE cross peak between the proton signal at d
6.58 (H-12) and the aldehyde proton signal at d 9.33 (H-16)
in NOESY spectrum. The relative stereochemistries about
skeleton of compound 2 were the same as compound 1
except for C-9 by analyses of 13C-NMR, 1H-NMR and
NOESY spectra. The chemical shift values of C-9 and H-9
were d 55.46 and d 1.54, the chemical shift difference of C-9
between compound 2 and 1 were Dd 1.34, suggesting that
the stereochemistry of C-9 of the two compounds was
different. The relative stereochemistry of C-9 of compound
1 had been determined as 9a H, therefore the relative
stereochemistry of C-9 of compound 2 was established as
9b H. It was further concluded from NOESY spectral
analysis. Accordingly, the structure of calcaratarin H (2) is
elucidated as shown in Fig.1. The complete assignments of
1H- and 13C-NMR data as well as their correlations in HMBC
spectrum are listed in Table 2 and the key NOE correlations
in NOESY spectrum are shown in Fig.2.
The corresponding fraction of EtOH extract of the same
raw materials was analyzed by HPLC. The result showed
the presence of compounds 1 and 2, which provided the
evidence that 1 and 2 are natural products other than
artifacts.
Calcaratarin G (1) and calcaratarin H (2) are the isomers
of two bis-labdanic diterpenoids isolated from the same
Table 2 13C-NMR and 1H-NMR data of compound 2
No. C H H (HMBC) No. C H H(HMBC)
1 39.31 α 1.09 ddd (12.9,12.9,3.6)2α,3β,20 1 39.15 α 0.92 ddd (12.6,12.6,4.2) 2α,3β,20
β 1.76 br d(13.2) β 1.68 br d(12.6)
2 19.34 α 1.47 m 1β 2 19.34 α 1.47 m 1β
β 1.59 ddddd β 1.59 m
(12.8,12.8,12.8,3.2,3.2)
3 42.07 α 1.13 ddd (13.2,13.2,4.2) 1β,18,19 3 42.11 α 1.18 ddd (13.5,13.5,3.6) 1β,18,19
β 1.39 br d (13.2) β 1.41 br d (13.5)
4 33.60 5,18,19 4 33.58 5,18,19
5 55.56 1.13 dd (12.3,3.0) 6α,18,19,20 5 55.56 1.04 dd (12.9,2.4) 6α,18,19,20
6 24.15 α 1.70 m 5 6 24.38 α 1.73 m 5
β 1.30 dddd (13.2,13.2,13.2,4.2) β 1.34 dddd (12.9,12.9,12.9,4.2)
7 37.90 α 2.02 ddd (13.2,13.2,4.8) 17a,17b 7 38.06 α 1.95 ddd (13.1,13.1,5.4) 17a,17b
β 2.42 ddd (13.2,5.4,1.8) β 2.38 ddd (13.1,4.5,2.4)
8 148.41 9,11b 8 147.66 9
9 56.55 1.89 br d (10.8) 7β,17a,17b,20 9 55.46 1.54 br d (10.8) 7β,17a,17b,20
10 39.64 9,20 10 39.63 9,20
11 24.62 a 2.43 ddd (17.2,11.4,5.4) 9 11 21.27 a 1.52 dd (15.9,3.6) 9,15α
b 2.68 ddd (17.2,7.2,3.0) b 1.65 dd (15.9,9.6)
12 159.99 6.58 dd (6.6,6.6) 11a,11b 12 154.80 15α
13 138.83 14b,15,16 13 139.39 16
14 29.17 a 2.56 dd (13.5,6.0) 12,15,16 14 83.54 5.26 m 16,15
b 2.86 dd (13.5,4.2)
15 108.56 5.71 brd(4.2) 21,14 15 23.03 α 2.41 ddd (12.0,6.6,2.4) 11a
β 2.64 ddd (12.0,8.4,8.4)
16 194.68 9.33 s 12 16 186.80 9.85s 14
17 107.62 a 4.45 br s 9 17 106.66 a 4.50 br s 9
b 4.85 br s b 4.88 br s
18 33.65 0.87 s 5,19 18 33.56 0.85 s 5,19
19 21.66 0.78 s 5,18 19 21.72 0.81 s 5,18
20 14.52 0.75 s 5,9 20 14.46 0.66 s 5,9
21 53.87 3.29 s 15
The spectral data were recorded in CDCl3 as solvent at 600 MHz for
1H and 150 MHz for 13C. The coupling constants (J) in parentheses are
given in Hz.
KONG Ling-Yi et al.: Two New Bis-labdanic Diterpenoids from Alpinia calcarata 163
plant by ourselves (Kong et al., 2002), and the structural
differences between the compounds are the stereochemis-
try at C-15 and C-14.
2 Experimental
2.1 General experimental procedures
Optical rotations were taken on a JASCO P-1020 pola-
rimeter (cell length 100 mm). UV spectra were measured on
a JASCO V-560 UV/VIS spectrophotometers (cell length 10
mm). IR spectra were recorded on a JASCO FT/IR-410 infra-
red spectrophotometer. EIMS were measured on a JEOL-
DX-300 mass spectrometer. HRFABMS were measured with
a JEOL HX-110 spectrometer using m-nitrobenzyl alcohol
as a matrix. 1D NMR and 2D NMR spectra were recorded
on a JEOL A-600 spectrometer.
Column chromatography procedures (CC) were per-
formed with BW-820MH silica gel (Fuji silysia Chemical
Ltd.). Preparative TLC was carried out with silica gel 60
F254 0.5 mm (Merck). Analytical TLCs were performed with
silica gel 60 F254 0.25 mm (Merck), the spots were visual-
ized under UV light (254 nm) and further visualized by spray-
ing with 10% molybdic acid and heating of the plates. Pre-
parative HPLC was performed with a JASCO PU-980 intelli-
gent pump, using a PREP-SIL 20 mm× 25 cm column,
equipped with a JASCO UV-970 intelligent UV/VIS detector.
2.2 Plant materials
The rhizomes of Alpinia calcarata Rosc. were collected
in Guangxi Province, China in October 1997. The plants
were identified as A. calcarata by Dr. QIN Min-Jian, De-
partment of Natural Medicinal Chemistry, China Pharma-
ceutical University. A voucher specimen was deposited in
Department of Natural Medicinal Chemistry, China Phar-
maceutical University.
2.3 Extraction and isolation
The dried plant material (2.8 kg) was crushed and ex-
tracted with MeOH three times at room temperature. The
MeOH extract (129 g) was partitioned between EtOAc and
water. The EtOAc solution was concentrated in vacuo to
yield EtOAc extract (88 g). A part of the EtOAc extract (44 g)
was subjected to CC on silica gel (450 g) and then eluted
with hexane, hexane:CHCl3 (10:2), hexane:CHCl3 (10:4) and
CHCl3 to give Frs.1-4, respectively. Fr.4 (17.8 g) was sub-
jected to CC on silica gel (200 g) eluted with a mixture of
hexane and EtOAc. Fr. 4-3 (1.4 g) and Fr. 4-4 (0.9 g) were
obtained from the elution systems of hexane:EtOAc (94:6),
hexane:EtOAc (92:8), respectively. Fr. 4-3 was again sub-
jected to CC on silica gel (65 g), eluted with hexane:EtOAc
(95:5), and further repeated preparative TLC (silica gel,
Merck, 0.5 mm) eluted with hexane:EtOAc (88:12), finally
was purified by preparative HPLC eluted with hexane:2-
propanol (97:3) to give compound 1 (8.9 mg). Fr. 4-4 was
further subjected to CC on silica gel (40 g), eluted with
hexane:EtOAc (94:6), and repeated preparative TLC, eluted
with hexane:EtOAc (85:15), finally was purified by prepara-
tive HPLC eluted with hexane:2-propanol (96:4) to give com-
pound 2 (7.5 mg).
2.4 EtOH extract analysis
The same plant materials were extracted with EtOH three
times at room temperature. The EtOH extract was partitioned
between EtOAc and water. The EtOAc extract was sepa-
rated into four fractions as the same process described in
the section 2.3. Fr. 4 was analyzed by HPLC using a PREP-
SIL column eluted with hexane:2-propanol (97:3), identified
by the authentic samples, and the result showed the exist-
ence of compounds 1 and 2.
2.5 Identification
Compound 1 Colorless oil. [a]27D +24.7°(CHCl3, c
0.25). HRFABMS m/z: 619.471 4 [(M+H)+, C41H63O4], calcd.
619.472 6. UV λmax (CH3CN) nm (logε): 234.0 (4.01). IR
nmax (film) cm-1 : 3 076, 2 928, 2 867, 2 844, 2 723, 1 682, 1 643,
1 561, 1 542, 1 507, 1 457, 1 447, 1 441, 1 387, 1 365, 1225, 1 201,
1 188, 1 159, 1 094, 1 024, 973, 889, 756, 667. EIMS (70 eV)
m/z: 618 (M+), 586, 345, 313, 285, 273, 191, 137, 107, 69. 1H-
NMR (600 MHz, CDCl3): see Table 1. 13C-NMR (150 MHz,
CDCl3): see Table 1.
Compound 2 Colorless oil. [a]27D +77.7°(CHCl3, c
0.38). HRFABMS m/z: 619.475 6 [(M+H)+, C41H63O4], calcd.
619.472 6. UV λmax (CH3CN) nm (logε): 233.5 (4.04). IR
nmax (film) cm-1 : 3 082, 2 927, 2 863, 2 846, 2 717, 1 734, 1 683,
1 644, 1 635, 1 575, 1 558, 1 541, 1 507, 1 457, 1 388, 1 364,
1 343, 1 246, 1 218, 1 191, 1 161, 1 094, 1 020, 890, 757, 667.
EIMS (70 eV) m/z: 618 (M+), 586, 345, 313, 285, 273, 191, 137,
107, 69. 1H-NMR (600 MHz, CDCl3): see Table 2. 13C-NMR
(150 MHz, CDCl3): see Table 2.
Acknowledgements: We are grateful to Dr. Junko ITO
(Meijo University) for the HRFABMS measurements.
References:
Alberto A, Umberta B, Gianluca N, Orso V P. 1995. Isolation and
structure elucidation of tsugicolines A-D, novel protoilludane
sesquiterpenes from Laurilia tsugicola. Tetrahedron, 51:
13357-13364.
David J P, David J M, Yang S W, Cordell G A. 1999. A bis-
labdanic di terpene from Moldenhawera nutans .
Phytochemistry, 50:443-447.
Itokawa H, Yoshimoto S, Morita H. 1988. Diterpenes from the
rhizomes of Alpinia formosana. Phytochemistry, 27:435-438.
Acta Botanica Sinica 植物学报 Vol.46 No.2 2004164
(Managing editor: WANG Wei)
Jiangsu College of New Medicine. 1977. Dictionary of the Tradi-
tional Chinese Medicine. Shanghai: Shanghai Press of Science
and Technology. 169-170.
Kimbu S F, Nagadjui B, Sondengam L B, Njimi T K, Connolly J
D, Fakunle C O. 1987. A new labdane diterpenoid from the
seeds of Aframomum daniellii. J Nat Prod, 50:230-231.
Kong L Y, Qin M J, Niwa M. 2000. Diterpenoids from the rhi-
zomes of Alpinia calcarata. J Nat Prod, 63:939-942.
Kong L Y, Qin M J, Niwa M. 2002. Cytotoxic diterpenoids from
Euphorbia pekinensis. Planta Med, 68:813-817.
Nakatani N, Kikuzaki H, Yamaji H, Yoshio K, Kitora C, Okada
K, Padolina W G. 1994. Labdane diterpenes from rhizomes of
Hedychium coronarium. Phytochemistry, 37:1383-1388.
Singh S, Gray A I, Skelton B W, Waterman P G, White A H. 1991.
(+)-14b-Hydroxylabda-8(17),12-dieno-16,15-lactone [(+)-
isocoronarin-D]: a new diterpene from Hedychium coronarium
(Zingiberaceae). Aust J Chem, 44:1789-1793.
Sirat H M. 1994. Study on the terpenoids of Zingiber ottensii.
Planta Med, 60:497.
Sirat H M, Masri D, Rahman A A. 1994. The distribution of
labdane diterpenes in the Zingiberaceae of Malaisia.
Phytochemistry, 36:699-701.
Sy L K, Brown G D. 1997. Labdane diterpenoids from Alpinia
chinensis. J Nat Prod, 60:904-908.
Zhao Q, Hao X-J,Chen Y-Z,Zou C. 1995. Studies on diterpenoid
constituents of Hedychium forrestii and their cytotoxic activity.
Acta Pharm Sin , 30:119-122. (in Chinese with English
abstract)