Bicyclic polyketide lactones from Chinese medicinal ants, Polyrhacis lamellidens

Article abstract of DOI:10.1021/np070558l

Two new bicyclic polyketide lactones, polyrhacitides A (1) and B (2), were isolated from Chinese medicinal ants, Polyrhacis lamellidens, which have been used as an effective therapeutic agent to treat rheumatoid arthritis and hepatitis in China. Their absolute structures were elucidated on the basis of spectroscopic analyses and chemical evidence. The occurrence of polyketides with similar structures in plants of the Lamiaceae, Lauraceae, and Staphyleaceae indicates their significance in the study of chemical ecology.

Full text of DOI:10.1021/np070558l

724
J. Nat. Prod. 2008, 71, 724–727
Bicyclic Polyketide Lactones from Chinese Medicinal Ants, Polyrhacis lamellidens
Zhi-Hong Jiang,*,† Qing-Xiong Yang,† Takashi Tanaka,‡ and Isao Kouno*,‡
School of Chinese Medicine, Hong Kong Baptist UniVersity, Kowloon Tong, Hong Kong, People’s Republic of China, and Department of
Molecular Medicinal Sciences, Graduate School of Biomedical Sciences, Nagasaki UniVersity, Bunkyo-machi 1-14, Nagasaki 852-8521, Japan
ReceiVed October 4, 2007
Two new bicyclic polyketide lactones, polyrhacitides A (1) and B (2), were isolated from Chinese medicinal ants,
Polyrhacis lamellidens, which have been used as an effective therapeutic agent to treat rheumatoid arthritis and hepatitis
in China. Their absolute structures were elucidated on the basis of spectroscopic analyses and chemical evidence. The
occurrence of polyketides with similar structures in plants of the Lamiaceae, Lauraceae, and Staphyleaceae indicates
their significance in the study of chemical ecology.
The Chinese medicinal ant Polyrhacis lamellidens Smith (For-
micidae) is widely distributed in mainland China and has been used
clinically as a folk medicine for treating rheumatoid arthritis and
hepatitis in China.1 We previously investigated the analgesic and anti-
inflammatory effects of ethanol extracts of P. lamellidens and fractions
obtained by solvent partition of the total extracts. The results
demonstrated that extracts of P. lamellidens present remarkable
analgesic and anti-inflammatory activities, which supported the
traditional use of the medicinal ants in the treatment of various diseases
associated with inflammation.2 The diethyl ether fraction was found
to have greater analgesic activity than the crude MeOH extract.2 There
are no reports of chemical studies of the secondary metabolites of this
ant species, although a number of alkaloids3 and peptides4 were isolated
from African and Australian ants. Herein, we describe the isolation
1
Figure 1. H-1H COSY and HMBC correlations in 1 and 2.
and structural determination of polyrhacitides A (1) and B (2), two
novel aliphatic polyketide lactones from the ether fraction of MeOH
extracts of P. lamellidens.
Polyrhacitide A (1) was isolated as optically active ([R]15D +8.3),
colorless needles. The molecular formula was established as
C18H32O5 on the basis of HREIMS ([M - H2O]+, m/z 310.2141)
and 13C NMR data (see Experimental Section). One of three degrees
of unsaturation of 1 was attributed to an ester carbonyl on the basis
of the IR absorption at 1729 cm-1 and the sp2 carbon signal (δ
169.2) in the 13C NMR spectrum. The remaining two degrees of
unstaturation were attributed to two ring units in the molecule
because no other unsaturated carbon signal was observed in the
13C NMR spectrum. The NMR spectra exhibited five oxygenated
methine signals (δC 72.6, 72.3, 72.2, 66.6, 66.0), one methyl group
(δH 0.88; δC 14.1), and 11 methylene signals. Analyses of the cross-
An intramolecular hydrogen bond between the ether oxygen at
C-7 and the OH group at C-9 was deduced from the following
observations. First, the IR absorption at 3315 cm-1 of 1 suggested
the existence of a hydrogen-bonded OH group. Second, the coupling
constants of 10 Hz for JH-8a,H-7 and JH-8a,H-9 and of 3 Hz for JH-8b,H-7
and JH-8b,H-9 indicated a six-membered ring in a chair conformation,
formed by an intramolecular hydrogen bond between 9-OH and
the ether oxygen at C-7. Upon acetylation of 1 to 1a, the values of
JH-8a,H-7, JH-8a,H-9, JH-8b,H-7, and JH-8b,H-9 in the acetylated 1 (1a)
changed to 7, 7, 5, and 5 Hz, respectively (Figure 2), indicating
that the six-membered ring had been disrupted by acetylation of
the C-9 OH group. A six-membered ring with chair conformation
resulted from the intramolecular hydrogen bond, as indicated by
the NOE correlations between Hax-6 (1.64, 1H, ddd, 4, 12, 14) and
Hax-8 (1.73, 1H, dt, 14, 10) and between Heq-6 (2.04, 1H, dd, 4,
14) and Heq-8 (1.58, 1H, dt, 14, 3) observed in the NOESY spectrum
of 1. Therefore, a syn configuration of C-7 and C-9 was established
by the existence of the intramolecular hydrogen bond described
above. This type of intramolecular hydrogen bond was reported in
a synthetic fragment of maitotoxin by Kishi et al.5 The relative
configuration between C-5 and C-7 was also elucidated to be syn
1
peaks in the H-1H COSY spectrum combined with information
from the 1D NMR and HSQC spectra disclosed two partial
structural units, shown by heavy lines in Figure 1. The HMBC
correlation (Figure 1) between H-7 (δ 4.04, 1H, dddd, 3, 4, 10,
12) and C-3 (δ 66.0) demonstrated an ether linkage between C-3
and C-7. Furthermore, both H-2 (δ 2.90, 1H, d, 19; δ 2.82, 1H,
dd, 5, 19) and H-5 (δ 4.89, 1H, ddd, 2, 4, 4) showed HMBC
correlations with carbonyl C-1 (δ 169.2), suggesting a lactone
structure in 1. Finally, the HMBC correlations between the H3-18
signal and C-16 and between H-12 and C-14 revealed a linear alkyl
structure from C-12 to C-18. Taking the unsaturation degrees of 1
into account, both C-9 and C-11 were determined to be hydroxy-
lated. Therefore, compound 1 was characterized as a bicyclic lactone
having a hydroxylated alkyl group attached as shown in Figure 1.
* To whom correspondence should be addressed. Tel: +852-34112906.
Fax: +852-34112461. E-mail: zhjiang@hkbu.edu.hk (Z.-H.J.). Tel: +81-
95-8192432. Fax: +81-95-8192477. E-mail: ikouno@net.nagasaki-u.ac.jp
(I.K.).
† Hong Kong Baptist University.
‡ Nagasaki University.
10.1021/np070558l CCC: $40.75
2008 American Chemical Society and American Society of Pharmacognosy
Published on Web 02/26/2008

Notes
Journal of Natural Products, 2008, Vol. 71, No. 4 725
Figure 2. Acetylation of compounds 1 and 2.
based on an axial orientation of H-7ax (1H, dddd, 3, 4, 10, 12) and
equatorial orientations of both H-5eq (1H, ddd, 2, 4, 4) and H-3eq
(1H, br s) on a six-membered ring (C7-C6-C5-C4-C3-O) with
a chair conformation.
To determine the relative configuration of the 9,11-diol of 1,
the acetonide derivative (1b) of 1 was prepared. The chemical shift
of the acetal carbon and the large difference in chemical shifts of
the two isopropylidene methyl carbons (Figure 3) indicated a syn
relationship between C-9 and C-11.6
Figure 3. Synthesis of the acetonides of polyrhacitides A (1) and
B (2).
(2d, 2e) of the 11,13-syn acetonide (2b) to the modified Mosher’s
method7 led to the conclusion of an R configuration at C-9 (Figure
S1, Supporting Information). Therefore, the absolute configuration
of 2 was determined to be 3S, 5R, 7R, 9R, 11R, and 13R.
Aliphatic polyketides such as 1 and 2 are unusual in ants,
although the aromatic polyketides mellein and 2,4-dihydroxyac-
etophenone were isolated from the Australian ponerine ant.8
Polyrhacitides 1 and 2 have a bicyclic lactone structure in the
molecule formed by intramolecular addition of an OH group to an
R,ꢀ-unsaturated lactone. Similar polyketides having bicyclic lac-
tones, and their precursors, have been isolated from the plants of
Cryptocarya and Ocotea (Lauraceae),9 Syncolostemon (Lami-
aceae),10 Iboza (Lamiaceae),11 and Euscaphis (Staphyleaceae).12
Compound 1 was also converted to 11-mono-(R)- and (S)-MTPA
esters (1c, 1d), 9,11-di-(R)- and (S)-MTPA esters (1e, 1f), and
9-mono-(R)- and (S)-MTPA esters (1g, 1h) for determination of
the absolute configuration. Application of MTPA esters 1c, 1d and
1g, 1h to the modified Mosher’s method,7 respectively, indicated
R-configurations for both C-9 and C-11 in 1 (Figure S1, Supporting
Information). Thus, the absolute configuration of 1 was established
as 3S, 5R, 7R, 9R, 11R.
Polyrhacitide B (2) was isolated as an optically active ([R]15
D
Experimental Section
+7.2), white powder. Its molecular formula (C20H36O6), two carbons
more than 1, was established on the basis of HREIMS ([M -
2H2O]+, m/z 336.2299) and 13C NMR data. Comparison of its NMR
data with those of 1 disclosed that chemical shifts of proton and
carbon signals due to most of the groups were in good agreement
with those of 1, except for additional signals of a methylene and a
hydroxylated methine. Assignment of the NMR signals for 2, with
the aid of 1H-1H COSY, HMQC, and HMBC experiments,
established the gross structure of 2. The intramolecular hydrogen
bond between the C-9 OH and the C-7 oxygen was confirmed on
the basis of analyses of the coupling constants of H-7, H-8, and
H-9 of 2 and its acetylated product 2a.
To determine the relative configurations of the three OH groups
in 2, two acetonide derivatives (2b, 2c) were synthesized (Figure
3). The 13C NMR data of acetal and isopropylidene methyl carbons
in both 2b and 2c indicated a syn relationship between the C-9 and
C-11 as well as C-11 and C-13.6 Application of the MTPA esters
General Experimental Procedures. Melting points were determined
on a micromelting point hot stage apparatus (Yanagimoto) and are
uncorrected. Optical rotations were measured with a JASCO DIP-370
digital polarimeter. IR spectra were recorded on a JASCO FT-IR-230
spectrometer. 1H and 13C NMR spectra were obtained with the following
instruments: Varian Unity plus 500, Varian Gemini 300 at 500 and
300 MHz for 1H and 125 and 75 MHz for 13C, respectively. Coupling
constants are expressed in Hz, and chemical shifts are given on a δ
(ppm) scale with tetramethylsilane as an internal standard. HRESIMS
were recorded on a Q-TOF mass spectrometer (Bruker Daltonics, MA).
EIMS were obtained on a JEOL JMS DX-303 spectrometer. Column
chromatography was performed with Kieselgel 60 (70–230 mesh,
Merck), MCI-gel CHP 20P (75–150 mm, Mitsubish Chemical Co.),
and Chromatorex ODS (100–200 mesh, Fuji Silysia Chemical Ltd.).
TLC was performed on precoated Kiesegal 60 F254 plates (0.2 mm thick,
Merck), and spots were detected by spraying 10% sulfuric acid reagent.
Animal Material. Ants, Polyrhachis lamellidens (2.0 kg), were
purchased from Jinling Ants Therapy Research Center, Nanjing, China.

726 Journal of Natural Products, 2008, Vol. 71, No. 4
Notes
The ants were identified by Professor Jian Wu of Chinese Academy of
Forestry, Beijing, China.
Polyrhacitide B (2): white powder; [R]15D +7.2 (c 0.6, MeOH); IR
(neat) nmax (cm-1) 3450, 3342 (hydrogen-bonded OH), 2925, 2856,
1
1733, 1454, 1328, 1201, 1093 cm-1; H NMR (CDCl3, 500 MHz) δ
Extraction and Isolation. MeOH extracts of the ants (2 kg) were
partitioned between Et2O and H2O. The Et2O layer (90 g) was
fractionated by chromatography over silica gel (CHCl3-MeOH-H2O,
100:0:0–90:10:1–70:30:5). A fraction (16.4 g) eluted with CHCl3-
MeOH-H2O (90:10:1) was further subjected to chromatography over
MCI-gel CHP 20P (0%-100% MeOH). The 80–90% eluent was
chromatographed over silica gel (CHCl3-MeOH-H2O, 100:0:0–90:
10:1) and Chromatorex ODS (60–80% MeOH) to afford polyrhacitide
A (1, 56.2 mg) and polyrhacitide B (2, 19.2 mg).
4.89 (1H, ddd, J ) 2, 4, 4 Hz, H-5), 4.41 (1H, br s, H-3), 4.12 (1H, m,
H-11), 4.10 (1H, dddd, J ) 3, 3, 9, 10 Hz, H-9), 4.04 (1H, dddd, J )
3, 4, 10, 12 Hz, H-7), 3.86 (1H, ddd, J ) 5, 7, 12 Hz, H-13), 2.90 (1H,
d, J ) 19 Hz, H-2a), 2.82 (1H, dd, J ) 5, 19 Hz, H-2b), 2.04 (1H, dd,
J ) 4, 14 Hz, H-6eq), 2.04 (1H, ddd, J ) 2, 4, 14 Hz, H-4a), 1.95
(1H, ddd, J ) 2, 4, 14 Hz, H-4b), 1.73 (1H, dt, J ) 14, 10 Hz, H-8ax),
1.65 (1H, ddd, J ) 4, 12, 14 Hz, H-6ax), 1.61 (1H, m, H-10a), 1.58
(1H, dt, J ) 14, 3 Hz, H-8eq), 1.53 (2H, m, H-12), 1.48 (2H, m, H-10b,
H-14a), 1.41 (1H, m, H-14b), 1.39 (1H, m, H-15b), 1.29 (7H, m, H-15b,
H-16, H-17, H-18, H-19), 0.88 (3H, t, J ) 7 Hz, H-20); 13C NMR
(CDCl3, 125 MHz) δ 169.2 (C, C-1), 73.2 (CH, C-11), 72.5 (CH, C-5),
72.5 (CH, C-13), 72.3 (CH, C-9), 66.9 (CH, C-7), 66.1 (CH, C-3),
43.9 (CH2, C-10), 43.5 (CH2, C-12), 42.8 (CH2, C-8), 38.0 (CH2, C-14),
37.2 (CH2, C-6), 36.5 (CH2, C-2), 31.8 (CH2, C-18), 29.7 (CH2, C-16),
29.5 (CH2, C-4), 29.3 (CH2, C-17), 25.4 (CH2, C-15), 22.7 (CH2, C-19),
14.1 (CH3, C-20); EIMS m/z 372 [M]+, 354 [M - H2O]+, 336 [M -
H2O × 2]+; HREIMS m/z 336.2299 [M - H2O × 2]+ (calcd for
C20H32O4, 336.2301).
Polyrhacitide A (1): colorless needles; mp 65–68 °C; [R]15 +8.3
D
(c 0.6, MeOH); IR (neat) νmax (cm-1) 3421, 3315 (hydrogen-bonded
OH), 2923, 2854, 1729, 1454, 1340, 1201, 1087 cm-1 1H NMR
;
(CDCl3, 500 MHz) δ 4.89 (1H, ddd, J ) 2, 4, 4 Hz, H-5), 4.41 (1H,
br s, H-3), 4.09 (1H, dddd, J ) 3, 3, 9, 10 Hz, H-9), 4.04 (1H, dddd,
J ) 3, 4, 10, 12 Hz, H-7), 3.83 (1H, m, H-11), 2.90 (1H, d, J ) 19 Hz,
H-2a), 2.82 (1H, dd, J ) 5, 19 Hz, H-2b), 2.04 (1H, ddd, J ) 2, 4, 14
Hz, H-4a), 2.04 (1H, dd, J ) 4, 14 Hz, H-6eq), 1.95 (1H, ddd, J ) 2,
4, 14 Hz, H-4b), 1.73 (1H, dt, J ) 14, 10 Hz, H-8ax), 1.64 (1H, ddd,
J ) 4, 12, 14 Hz, H-6ax), 1.58 (1H, J ) dt, 14, 3 Hz, H-8eq), 1.54,
(1H, m, H-10b), 1.52 (1H, m, H-10a), 1.44 (2H, m, H-12), 1.40 (1H,
m, H-13a), 1.29 (7H, m, H-13b, H-14, H-15, H-16, H-17), 0.88 (3H,
t, J ) 7 Hz, H-18); 13C NMR (CDCl3, 125 MHz) δ 169.4 (C, C-1),
72.6 (CH, C-5), 72.3 (CH, C-9), 72.2 (CH, C-11), 66.6 (CH, C-7),
66.0 (CH, C-3), 43.3 (CH2, C-10), 43.0 (CH2, C-8), 37.8 (CH2, C-12),
37.2 (CH2, C-6), 36.4 (CH2, C-2), 31.8 (CH2, C-16), 29.6 (CH2, C-14),
29.5 (CH2, C-4), 29.3 (CH2, C-15), 25.4 (CH2, C-13), 22.6 (CH2, C-17),
14.1 (CH3, C-18); EIMS m/z 328 [M]+, 310 [M - H2O]+; HREIMS
m/z 310.2141 [M - H2O]+ (calcd for C18H30O4, 310.2144).
Acetylation of 2. Compound 2 (1 mg) was acetylated in a manner
similar to that of 1 to give triacetate 2a (1 mg): white powder; [R]20
D
1
+10.4 (c 0.1, CHCl3); H NMR (500 MHz, CDCl3) δ 5.04 (1H, m,
H-9), 4.95 (1H, m, H-11), 4.88 (1H, m, H-13), 4.86 (1H, m, H-5),
4.32 (1H, br s, H-3), 3.88 (1H, J ) 12, 7, 5 Hz, H-7), 2.88 (1H, d, J
) 19 Hz, H-2a), 2.75 (1H, dd, J ) 6, 19 Hz, H-2b), 2.10, 2.04, 2.02
(each 3H, s, acetyls), 1.98, 1.91 (each 1H, m, H2-4), 1.98 (1H, m, H-6a),
1.88 (2H, m, H2-10), 1.85 (2H, dt, J ) 14, 7 Hz, H-8b, H-12b), 1.75
(1H, dt, J ) 14, 6 Hz, H-12a), 1.69 (1H, dt, J ) 14, 5 Hz, H-8a), 1.56
(1H, ddd, J ) 2, 12, 14 Hz, H-6b), 1.52 (1H, m, H-14a), 1.25 (11H,
m, H-14b, H2-15, H2-16, H2-17, H2-18, H2-19), 0.88 (3H, d, J ) 7 Hz,
H3-20); EIMS m/z 498 [M]+ (0.2), 480 [M - H2O]+ (0.5), 438 [M -
Ac - H2O]+ (10), 378 (60), 336 (25), 318 (100), 297 (20), 180 (25),
141 (85); positive HRESIMS m/z 521.2713 (calcd for C26H42O9Na,
521.2721).
Acetylation of 1. A solution of 1 (2 mg) in Ac2O (0.5 mL) and
pyridine (0.5 mL) was kept at room temperature overnight. H2O (5
mL) and Et2O (5 mL) were added to the reaction mixture. The dried
(Na2SO4) Et2O layer was evaporated in Vacuo to give 1a (2 mg): white
1
powder; [R]20 +4.6 (c 0.2, CHCl3); H NMR (500 MHz, CDCl3) δ
D
5.04 (1H, m, H-9), 4.88 (1H, m, H-11), 4.86 (1H, ddd, J ) 2, 4, 4 Hz,
H-5), 4.32 (1H, br s, H-3), 3.88 (1H, ddt, J ) 12, 7, 5 Hz, H-7), 2.88
(1H, d, J ) 19 Hz, H-2a), 2.75 (1H, dd, J ) 6, 19 Hz, H-2b), 2.10,
2.04 (each 3H, s, acetyls), 1.98, 1.91 (each 1H, m, H2-4), 1.98 (1H, m,
H-6a), 1.85 (2H, dt, J ) 14, 7 Hz, H-8b, H-10b), 1.75 (1H, dt, J ) 14,
6 Hz, H-10a), 1.69 (1H, dt, J ) 14, 5 Hz, H-8a), 1.56 (1H, ddd, J )
2, 12, 14 Hz, H-6b), 1.52 (1H, m, H-12a), 1.25 (11H, m, H-12b, H2-
13, H2-14, H2-15, H2-16, H2-17), 0.88 (3H, d, J ) 7 Hz, H3-18); EIMS
m/z 352 [M - Ac - H2O]+ (20), 310 [M - Ac × 2-H2O]+ (50), 292
[M - Ac × 2-H2O × 2]+ (100), 271 (18), 211 (42), 193 (70), 183
(50), 167 (45), 155 (95), 141 (100); positive HRESIMS m/z 435.2321
(calcd for C22H36O7Na, 435.2353).
Acetonides of 2. Compound 2 (12 mg) was treated in the same way
as described for 1 to give a mixture of acetonides 2b and 2c (4:1, 10
1
mg) as a white powder: H NMR (500 MHz, CDCl3) for 2b, δ 4.89
(1H, ddd, J ) 2, 4, 4 Hz, H-5), 4.38 (1H, br s, H-3), 4.09 (1H, m,
H-11), 3.99 (2H, m, H-7, 9), 3.81 (1H, m, H-13), 2.90 (1H, d, J ) 19
Hz, H-2a), 2.78 (1H, dd, J ) 5, 19 Hz, H-2b), 2.08 (1H, m, H-6a),
2.04, 1.94 (each 1H, ddd, J ) 2, 4, 14 Hz, H-4a, H-4b), 1.74 (1H, dt,
J ) 14, 10 Hz, H-8a),1.67 (1H, m, H-10a), 1.64 (1H, m, H-6b), 1.56
(1H, m, H-8b), 1.50 (1H, m, H-12a), 1.48 (1H, m, H-10b), 1.45, 1.38
(each 3H, s, isopropylidene-Me), 1.18 (1H, dt, J ) 20, 12, 12 Hz,
H-12b), 0.88 (3H, t, J ) 7 Hz, H3-20); 13C NMR (75 MHz, CDCl3) for
2b, δ 169.6 (C-1), 98.6 (isopropylidene quaternary carbon), 72.5 (C-
5), 69.0, 68.9, 68.8 (C-9, 11, 13), 66.0 (C-7), 65.2 (C-3), 43.3, 43.0,
37.2, 37.0, 36.5, 36.4 (C-2, 6, 8, 10, 12, 14), 31.9 (C-18), 30.3
(isopropylidene-Me), 29.7, 29.6, 29.3 (C-4, 16, 17), 25.0 (C-15), 22.7
(C-19), 20.0 (isopropylidene-Me), 14.2 (C-20); for 2c: δ 169.7 (C-1),
98.8 (isopropylidene quaternary carbon), 73.0 (C-5), 71.9, 70.5, 62.2
(C-9, 11, 13), 65.8 (C-7), 65.3 (C-3), 42.9, 42.1, 37.7, 37.2, 36.91,
36.87 (C-2, 6, 8, 10, 12, 14), 31.9 (C-18), 30.2 (isopropylidene-Me),
29.8, 29.7, 29.4 (C-4, 16, 17), 25.5 (C-15), 22.7 (C-19), 20.0
(isopropylidene-Me), 14.2 (C-20); MS data for the mixture of 2b and
2c, EIMS m/z 412 [M]+ (2), 397 [M - CH3]+ (98), 336 (10), 297
(10), 209 (15), 155 (30), 141 (80); positive HRESIMS m/z 435.2701
(calcd for C23H40O6Na, 435.2717).
Acetonide of 1. To a solution of 1 (6 mg) in CH2Cl2 (0.5 mL) were
added 2,2-dimethoxypropane (0.1 mL) and pyridinium p-toluene-
sulfonate (2 mg), and the mixture was kept at room temperature
overnight. The solution was subsequently evaporated in Vacuo, and
the residue was purified by silica gel column chromatography (CC)
with n-hexane-EtOAc (3:1–1:1) to yield acetonide 1b (5.5 mg): white
1
powder; [R]20 +6.5 (c 0.6, CHCl3); H NMR (300 MHz, CDCl3) δ
D
4.90 (1H, br s, H-5), 4.35 (1H, br s, H-3), 4.01, 3.81, 3.94 (each 1H,
m, H-7, 9, 11), 2.82 (2H, m, H2-2), 1.37, 1.28 (each 3H, s, isopropy-
lidene-Me), 0.88 (3H, t, J ) 7 Hz, H3-18); 13C NMR (75 MHz, CDCl3)
δ 169.7 (C-1), 98.5 (isopropylidene quaternary carbon), 73.0 (C-5),
65.8 (C-3), 69.0, 65.4, 62.3 (C-7, 9, 11), 42.4, 36.9, 36.8, 36.5 × 2
(C-2, 6, 8, 10, 12), 31.9 (C-16), 30.3 (isopropylidene-Me), 29.9, 29.6,
29.3 (C-4, 14, 15), 25.1 (C-13), 22.7 (C-17), 19.9 (isopropylidene-
Me), 14.2 (C-18); EIMS m/z 368 [M]+ (1), 353 [M - CH3]+ (100),
310 (30), 293 (25), 183 (50), 163 (30), 141 (100); positive HRESIMS
m/z 391.2418 (calcd for C21H36O5Na, 391.2455).
(R)- and (S)-MPTA Esters of 2b. A solution of 2b (3 mg),
dicyclohexylcarbodiimide (6 mg), 4-dimethylaminopyridine (4 mg), and
(R)-(+)-R-methoxy-R-(trifluoromethyl)phenylacetic acid (8 mg) in
CH2Cl2 (1 mL) was kept at room temperature overnight. The resulting
mixture was purified by silica gel CC with n-hexane-EtOAc (3:1–1:
1) to give R-MTPA ester 2d (2.8 mg). Using (S)-(-)-R-methoxy-R-
(trifluoromethyl)phenylacetic acid gave 2e (2.6 mg).
(R)- and (S)-MPTA Esters of 1. A solution of 1 (3.8 mg),
dicyclohexylcarbodiimide (8 mg), 4-dimethylaminopyridine (4 mg), and
(R)-(+)-R-methoxy-R-(trifluoromethyl)phenylacetic acid (9 mg) in
CH2Cl2 (1 mL) was left to stand at room temperature overnight. The
resulting mixture was subjected to silica gel CC with n-hexane-EtOAc
(5:1–2:1) to give 11-mono-(R)-MTPA ester 1c (1.1 mg), 9,11-di-(R)-
MTPA ester 1e (2 mg), and 9-mono-(R)-MTPA ester 1g (0.5 mg). Using
(S)-(-)-R-methoxy-R-(trifluoromethyl)phenylacetic acid gave 11-mono-
(S)-MTPA ester 1d (0.8 mg), 9,11-di-(S)-MTPA ester 1f (2 mg), and
9-mono-(S)-MTPA ester 1h (0.5 mg) (Figure S1, Supporting Informa-
tion).
Acknowledgment. The authors are grateful to Professor Jian Wu
of the Chinese Academy of Forestry for identifying the ant. This
research was supported by Faculty Research Grant of Hong Kong
Baptist University.

Notes
Supporting Information Available: Figure S1, determination of
absolute configurations of 1 and 2 by the modified Mosher’s method.
This material is available free of charge via the Internet at http://
pubs.acs.org.
Journal of Natural Products, 2008, Vol. 71, No. 4 727
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