J. Nat. Prod. 2000, 63, 104-108
104
New Phloroglucinol Derivatives from Hypericum papuanum
Karin Winkelmann,† Jörg Heilmann,† Oliver Zerbe,† Topul Rali,‡ and Otto Sticher*,†
Department of Pharmacy, Swiss Federal Institute of Technology (ETH) Zurich, CH-8057 Zürich, Switzerland,
and PNG Biodiversity Research PTY Ltd., Port Moresby, Papua New Guinea
Received August 25, 1999
Bioactivity-guided fractionation of the petroleum ether extract of the aerial parts of Hypericum papuanum
led to the isolation of five new tricyclic phloroglucinol derivatives. On the basis of extensive 1D and 2D
NMR experiments as well as MS studies, their structures were elucidated as the C-3 epimers of 8-hydroxy4,4,7-trimethyl-9-(2-methylpropionyl)-3-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-8-ene-10,11-dione (1,
2); the C-3 epimers of 8-hydroxy-4,4,7-trimethyl-9-(2-methylbutyryl)-3-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-8-ene-10,11-dione (3, 4), and 8-hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)-5β-Htricyclo[5.3.1.01,5]undec-8-ene-10,11-dione (5), and their corresponding tautomers (1a, 2a, 3a, 4a, 5a).
Compounds 1/1a-5/5a were named ialibinones A-E, respectively. Compounds 1/1a-4/4a showed
antibacterial activity against Bacillus cereus, Staphylococcus epidermidis, and Micrococcus luteus.
The leaves of Hypericum papuanum Ridley (Guttiferae),
a shrub or woody herb widespread in all mountainous
regions of New Guinea,1 are used in folk medicine for the
treatment of sores.2 In the genus Hypericum many phloroglucinol derivatives with antibiotic properties have been
isolated, of which some are derivatives of the well-known
hyperforin, isolated from Hypericum perforatum L., while
others are phloroglucinol derivatives with filicinic acid
moieties.3-5 Bioactivity-guided fractionation of the petroleum ether extract of the aerial parts of H. papuanum has
led to the isolation of five new phloroglucinol derivatives
with tricyclic structures (1/1a-5/5a), four of which are
active against Bacillus cereus, Staphylococcus epidermidis,
and Micrococcus luteus. No reports concerning the isolation
of similar tricyclic phloroglucinol derivatives from the
family Guttiferae have appeared in the literature so far.
However, structurally related semisynthetic transformation products of the hop constituents humulone and colupulone obtained by oxidation and isomerization have been
described.6,7 In addition, the isolation of aissatone from
Harrisonia abyssinica Oliv. (Simaroubaceae) was published
recently.8
Results and Discussion
The air-dried aerial parts of H. papuanum were extracted successively with petroleum ether, dichloromethane,
methanol, and methanol-water mixtures. The petroleum
ether extract showed antibacterial activity against B.
cereus, S. epidermidis, and M. luteus and was therefore
subjected to repeated vacuum-liquid chromatography
(VLC) and HPLC, which led to the isolation of five new
phloroglucinol derivatives (1/1a-5/5a). All five compounds
were isolated as yellow oils. After being sprayed with
vanillin-sulfuric acid reagent,9 the substances gave turquoise spots by TLC.
The 1H NMR spectrum of 1/1a revealed the presence of
12 methyl groups, eight of which are tertiary (δH 0.85, 0.88,
0.99, 1.00, 1.35, 1.41, 1.78, 1.79, each s) and four secondary
(δH 1.13, d, J ) 6.8 Hz; 1.17, d, J ) 6.8 Hz; 1.17, d, J ) 6.8
Hz; 1.22, d, J ) 6.8 Hz), as well as two septets indicative
of methines in a 2-methylpropionyl side chain (δH 3.96,
sept, J ) 6.8 Hz; 4.03, sept, J ) 6.8 Hz). Furthermore, four
* To whom correspondence should be addressed. Tel.: +41 1 635 6050.
Fax: +41 1 635 6882. E-mail: sticher@pharma.ethz.ch.
†
Swiss Federal Institute of Technology (ETH) Zurich.
‡ PNG Biodiversity PTY, Ltd.
10.1021/np990417m CCC: $19.00
signals indicating terminal methylenes (δH 4.79, 4.81, 4.94,
4.95, each br s) could be detected in addition to a number
of overlapping aliphatic signals in the range of 2.0 to 2.6
ppm. The unusually lowfield shifted signals (δH 18.43,
18.75, each br s) suggested the presence of hydroxyl protons
that participate in rather strong hydrogen bonds (for 1H
NMR data, see Tables 1 and 2).
The 13C NMR showed signals of 42 carbons, which could
be sorted by DEPT experiments into 12 methyl, six meth-
© 2000 American Chemical Society and American Society of Pharmacognosy
Published on Web 12/11/1999
Phloroglucinol Derivatives from Hypericum
Journal of Natural Products, 2000, Vol. 63, No. 1 105
Table 1. 1H NMR Spectral Data of the Preferred Tautomers 1-5 (δ ppm; m; J Hz)a
H
1
2
3
2R
2β
3
2.19 (dd, 13.3, 5.9)
2.51 (t, 13.1)
2.08 (dd, 12.8, 5.9)
2.16 (t, 13.1)
2.54 (dd, 13.5, 7.4)
2.44 (dd, 12.7, 7.2)
2.19 (dd, 13.3, 5.9)
2.50 (t, 13.3)
2.08 (dd, 12.6, 5.7)
5
6R
6β
12
13
14
2′
2.35 (t, 9.6)
1.76 (dd, 13.1, 9.2)
2.24 (dd, 13.1, 9.8)
1.00 (s)
0.85 (s)
1.41 (s)
4.79 (br s)
4.94 (br s)
1.78 (s)
4.03 (sept, 6.8)
1.17b (d, 6.8)
2.30 (dd, 10.2, 5.8)
1.88 (dd, 13.4, 5.8)
2.23 (dd, 13.5, 10.3)
0.60 (s)
0.97 (s)
1.39 (s)
4.79 (br s)
4.98 (br s)
1.79 (s)
4.06 (sept, 6.8)
1.19 (d, 6.8)
1.17b (d, 6.8)
1.15 (d, 6.4)
2.34 (t, 9.6, 9.4)
1.76b (m)
2.24b (m)
1.00 (s)
0.84 (s)
1.41 (s)
4.79 (br s)
4.94 (br s)
1.78 (s)
3.92 (m, 6.9)
1.46 (dd, 13.6, 7.3)
1.72 (dd, 13.7, 7.3)
0.94 (t, 7.4)
1.15 (d, 6.8)
18.77 (br s)
3′
2′′
3′′
4′′
5′′
OH
18.75 (br s)
18.88d(br s)
4
2.14b
(t)
2.53 (dd, 13.0,7.0)
2.44b (m)
2.28 (dd, 10.4, 5.2)
1.87 (dd, 13.1, 5.5)
2.22b(m)
0.59 (s)
0.98 (s)
1.39 (s)
4.80 (br s)
4.97 (br s)
1.79 (s)
3.93 (m, 6.6)
1.44 (m, 13.6, 7.3)
1.72 (m, 13.5, 7.5)
0.95b(m)
1.13 (d, 6.8)
18.85c (br s)
5
2.03b
(m)
2.47b (m)
1.65b (m)
1.71b (m)
2.22b (m)
1.80b (m)
2.22b (m)
0.81 (s)
0.98 (s)
1.39 (s)
4.04 (sept, 6.8)
1.18 (d, 6.7)
1.15 (d, 6.9)
18.84 (br s)
a
The chemical shifts of compounds 1/1a and 2/2a were determined at 600 MHz, in CDCl3. Compounds 3/3a-5/5a were determined at
500 MHz, in CDCl3. b Signals overlapped. c Signal from 1H 300 MHz at 300 K. d Signal from 1H 500 MHz at 295 K.
Table 2. 1H NMR Spectral Data of the Minor Tautomers 1a-5a (δ ppm; m; J Hz)a
H
1a
2a
2R
2β
3
2.26b
(dd, 6.2)
2.54 (t, 13.1)
2.13b
2.26b
5
6R
6β
12
13
14
2′
2.46 (t, 9.6, 8.9)
1.68 (dd, 13.3, 8.5)
2.13 (dd, 13.2, 10.4)
0.99 (s)
0.88 (s)
1.35 (s)
4.81 (br s)
4.95 (br s)
1.79 (s)
3.96 (sept, 6.8)
1.13 (d, 6.8)
2.45 (dd, 10.3, 5.2)
1.79 (dd, 13.9, 5.3)
2.11 (dd, 13.9, 10.4)
0.59 (s)
0.99 (s)
1.33 (s)
4.82 (br s)
5.00 (br s)
1.81 (s)
4.04 (sept, 6.8)
1.19 (d, 6.7)
1.22 (d, 6.8)
1.15 (d, 6.2)
3′
2′′
3′′
4′′
5′′
OH
18.43 (br s)
(m)
2.53 (dd, 12.7, 7.6)
2.50b (dd, 7.4)
18.80d
(br s)
3a
2.24b
(m)
2.54 (t, 13.6)
2.14b (m)
2.45 (m)
1.67 (dd, 13.4, 8.3)
2.13b (m)
0.98 (s)
0.87 (s)
1.35 (s)
4.81 (br s)
4.95 (br s)
1.79 (s)
3.82 (m, 6.9)
1.46 (dd, 13.6, 7.3)
1.72 (dd, 13.7, 7.3)
0.88 (t, 7.4)
1.20 (d, 6.8)
18.44 (br s)
4a
2.23b
(m)
2.53 (dd, 13.0,7.0)
2.48b (m)
2.44 (dd, 10.2, 5.3)
1.76b(m)
2.11b(m)
0.58 (s)
0.97 (s)
1.32 (s)
4.82 (br s)
4.99 (br s)
1.80 (s)
3.90 (m, 6.6)
1.44 (m, 13.6, 7.3)
1.72 (m, 13.5, 7.5)
0.90 (t, 8.7)
1.17 (d, 6.6)
18.79c (br s)
5a
2.13b
(m)
2.47b (m)
1.65b (m)
1.71b (m)
2.37 (dd, 10.4, 5.7)
1.72 (dd, 13.8, 10.4)
2.10 (dd, 13.9, 5.9)
0.78 (s)
1.00 (s)
1.33 (s)
4.02 (sept, 6.8)
1.20 (d, 6.6)
1.14 (d, 7.7)
18.91 (br s)
a
The chemical shifts of compounds 1/1a and 2/2a were determined at 600 MHz, in CDCl3. Compounds 3/3a-5/5a were determined at
500 MHz, in CDCl3. b Signals overlapped. c Signal from 1H 300 MHz at 300 K. d Signal from 1H 500 MHz at 295 K.
ylene, six methine, and 18 quaternary carbons. Six of the
quaternary carbons are ketone carbonyl groups (δC 191.0
s, 194.6 s, 206.1 s, 207.0 s, 207.6 s, 208.6 s) and two are
substituted by enolic hydroxyl groups (δC 200.1 s, 201.6 s)
(for 13C NMR data, see Table 3). The molecular mass of
344 in combination with the 1H and 13C NMR spectra
allowed the establishment of the molecular formula as
C21H28O4. However, doubled 1H and 13C NMR patterns in
a ratio of approximately 1.8:1 (derived from the 1H and 13C
NMR signal intensities) and only one pseudomolecular
peak at m/z 345 [M + H]+ in the positive FABMS allowed
the conclusion that the compound appears in two isomeric
forms, which was later shown to represent the two enol
tautomers 1 and 1a (see below) in solution (CDCl3) in the
ratio mentioned above, with 1 being the preferred tautomer. The HMBC and TOCSY experiments gave evidence
for the presence of two enol tautomers by revealing two
independent networks of correlations between the more
intensive signals on one hand and the less intensive on the
other. The assignment strategy presented below refers to
the preferred tautomeric structure 1. In the first step, the
covalent connectivities of the new compounds were established by analysis of the DQF-COSY spectrum that
revealed spin system A (H3-3′′, H3-4′′, H-2′′) belonging to
the methylpropionyl substituent, spin system B (H2-6, H-5),
and spin system C (H2-2, H-3). Due to the high number of
nonprotonated carbons, HSQC (1H-13C 1J correlated 2D)
and HMBC (1H-13C nJ correlated 2D, n >1) experiments
were utilized extensively to complete the 1H and 13C NMR
assignments. Spin systems B and C are linked through
correlations to the dimethylated quaternary carbon C-4 as
manifested by the HMBC correlations observed between
C-3 and H-5, H3-12, or H3-13 and between C-4 and H2-2,
H-5, or H2-6. Scalar couplings between C-2′ and H-3/H3-3′
and between C-1′ and H-3/H3-3′ confirmed the substitution
of C-3 by a 1-methylvinyl group. HMBC correlations
between C-1′′ and H-2′′, H-3′′, and H-4′′ established the
position of the methylpropionyl side chain. The observed
HMBC correlations of the hydroxyl proton to C-8, C-7, C-9,
and C-2′′ determined the position of the hydroxyl group at
C-8. Interestingly, the correlation between the hydroxyl
proton and C-2′′ is propagated via a strong hydrogen bond
between the hydroxyl proton at C-8 and the ketone carbonyl group at C-1′′ (see Figure 1). Consideration of further
HMBC connectivities (summarized in Figure 1), in conjunction with the conclusions drawn from the 1D NMR
spectra, established the tricyclic structure of the preferred
tautomer 1 as 8-hydroxy-4,4,7-trimethyl-9-(2-methylpro-
106 Journal of Natural Products, 2000, Vol. 63, No. 1
Table 3.
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1′
2′
3′
1′′
2′′
3′′
4′′
5′′
13C
Winkelmann et al.
NMR Spectral Data of Compounds 1/1a-5/5aa
1
72.1 s
25.7 t
54.5 d
42.8 s
55.4 d
33.4 t
61.4 s
201.6 s
109.6 s
191.0 s
206.1 s
24.4 q
25.8 q
12.4 q
143.2 s
113.5 t
23.6 q
208.6 s
34.8 d
18.5 q
19.0 q
1a
67.9 s
24.9 t
54.8 d
43.4 s
57.7 d
33.4 t
65.1 s
194.6 s
109.4 s
200.1 s
207.1 s
24.4 q
25.7 q
13.1 q
143.3 s
113.5 t
23.6 q
207.6 s
34.3 d
18.6 q
19.2 q
2
72.4 s
24.9 t
58.5 d
44.9 s
55.8 d
32.7 t
62.1 s
201.7 s
108.0 s
191.0 s
206.7 s
16.9 q
27.2 q
12.4 q
143.0 s
113.6 t
23.8 q
209.6 s
35.0 d
18.7 q
18.9 q
2a
3
68.3 s
24.2 t
58.7 d
45.2 s
58.2 d
31.1 t
66.2 s
193.6 s
108.0 s
200.3 s
207.2 s
16.5 q
27.2 q
13.1 q
142.8 s
113.8 t
23.7 q
209.1 s
34.7 d
18.8 q
18.9 q
72.4b
s
25.8 t
54.5 d
42.8 s
55.5 d
34.4 t
61.5 s
201.8b s
110.3b s
191.3b s
206.1b s
24.4 q
25.7 q
12.4 q
143.3b s
113.5 t
23.6 q
208.1b s
41.1 d
26.5 t
11.8 q
16.5 q
3a
68.0 s
25.0 t
54.8 d
43.5b s
57.7 d
33.5 t
65.1 s
194.8b s
110.0b s
200.3b s
207.2b s
24.4 q
25.8 q
13.1 q
143.2b s
113.5 t
23.6 q
209.8b s
40.7 d
26.5 t
11.8 q
16.8 q
4
72.5 s
24.9 t
58.4 d
44.9 s
55.7 d
32.7 t
62.2 s
201.9 s
108.4 s
191.1 s
206.8 s
16.9 q
27.2 q
12.4 q
143.0 s
113.6 t
23.8 q
209.3 s
41.3 d
26.5 t
11.8 q
16.4c q
4a
5
5a
68.4 s
24.2 t
58.7 d
45.2 s
58.1 d
31.2 t
66.2 s
193.7 s
108.4 s
200.3 s
207.4 s
16.4c q
27.2 q
13.2 q
142.8 s
113.8 t
23.7 q
208.7 s
41.0 d
26.7 t
11.7 q
16.4c q
75.9b
s
20.6 t
43.2 t
41.8 s
54.7 d
33.3 t
62.3bs
201.7bs
108.4 s
191.2b s
206.6b s
22.3 q
28.2 q
12.4 q
71.3b s
19.8 t
43.2 t
42.2 s
57.2 d
31.7 t
66.5b s
193.9b s
108.1 s
200.2b s
207.3b s
21.6 q
28.1 q
13.2 q
209.4b s
34.9 d
18.6 q
19.0 q
208.9b s
34.6 d
18.7 q
18.9 q
a The chemical shifts of compounds 1/1a-4/4a were determined at 75 MHz, in CDCl . Compound 5/5a was determined at 125 MHz, in
3
CDCl3. Multiplicities were obtained from DEPT135/DEPT90 experiments. b Signals derived from HMBC experiments. c Signals overlapped.
Figure 1. Key long-range (HMBC) correlations of 1.
pionyl)-3β-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-8ene-10,11-dione. The tautomeric form 1a was identified as
10-hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)-3β-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-9-ene-8,11-dione using very similar arguments. The UV spectrum of 1/1a
showed the presence of a chromophore similar to the one
that has been recorded previously for other compounds in
this class with the same tricyclic system,6,7 thereby confirming oxygen substituents at C-8, C-10, and C-11.
Compounds 2/2a, obtained as a yellow oil, are almost
identical to compounds 1/1a, showing a pseudomolecular
peak at m/z 345 [M + H]+ in the positive FABMS, and the
same number of protons and carbons as well as similar
correlations in the 1H-1H COSY spectrum and in direct
(HSQC) and long-range (HMBC) carbon-proton correlation
experiments. It also exists in two enol tautomeric forms,
which have both been characterized. The only difference
from compounds 1/1a is a remarkable upfield shift of C-12
in the 13C NMR spectrum from δ 24.4 ppm (1/1a) to δ 16.9
ppm and to 16.5 ppm in compounds 2/2a. Additionally, the
1H NMR chemical shift of H -12 changed from δ 1.00/0.99
3
ppm to 0.60/0.59 ppm. Most likely, a difference in chemical
shift for only a very few resonances is due to a change in
the relative stereochemistry of the two compounds.
In a second step of the structure-elucidation procedure,
the stereochemistry was established. Each of the compounds 1/1a and 2/2a has four chiral centers at C-1, C-3,
C-5, and C-7. The relative stereochemistry at C-1 and C-7
is constrained by the fact that the bridge between C-1 and
C-7 can only exist in the cis form.7 Because of the rigid
tricyclic ring system, the methyl group H3-14 is fixed below
Figure 2. Selected NOE correlations of 1a.
the plane formed by the two five-membered rings. The
determination of the relative stereochemistry at C-3 and
C-5 was possible with NOESY experiments. In compounds
1/1a and 2/2a NOE cross-peaks between the hydroxyl
proton at C-8 (1/2) and C-10 (1a/2a) and the proton at C-5
indicated the β position of H-5. In the tautomer 1a the
hydroxyl proton at C-10 showed a NOE to the more
downfield-shifted proton of C-2, confirming the β position
of this proton. This proton at C-2 also showed a strong NOE
to the more upfield-shifted proton of C-2′ and to the methyl
group H3-3′, thus establishing the β position of the 1-methylvinyl group at C-3. The β position of the 1-methylvinyl
substituent in 1 was confirmed because the hydroxyl group
at C-8 in compound 1 showed a NOE to the more downfieldshifted proton of C-6, thereby establishing the β position
of this proton. The methyl group H3-12 displayed only a
weak NOE to the β proton at C-6, but a strong NOE to the
R proton of C-6. With H3-12 being in the R position, the
methyl group H3-13 takes the β position, which was well
supported by a strong NOE to H-5. Because the proton at
C-3 showed a strong NOE only to H3-12, H-3 must be in
the R position and the 1-methylvinyl group in the β
position. The NOEs used for the analysis of compound 1a
are summarized in Figure 2. In contrast, in compound 2a,
the R-positioned proton at C-2 showed a NOE to the more
upfield-shifted proton at C-2′, thereby confirming the R
position of the 1-methylvinyl group. The β-positioned
Phloroglucinol Derivatives from Hypericum
methyl group H3-13 showed a strong NOE to H-5 and H-3,
establishing H-3 as β. These observations were confirmed
by NOE signals between the hydroxyl group at C-8 and
the more downfield-shifted proton at C-6 in compound 2.
This β-positioned proton revealed no NOE to the methyl
groups H3-12 and H3-13, whereas the R-positioned one
showed a NOE to H3-12; hence, C-12 is in the R position.
These results led to the conclusion that the compounds 1/1a
and 2/2a are the C-3 epimers of 8-hydroxy-4,4,7-trimethyl9-(2-methylpropionyl)-3-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-8-ene-10,11-dione and 10-hydroxy-4,4,7trimethyl-9-(2-methylpropionyl)-3-(1-methylvinyl)-5β-Htricyclo[5.3.1.01,5]undec-9-ene-8,11-dione, with a 3β-(1methylvinyl) group in compound 1/1a and a 3R-(1-methylvinyl) group in compound 2/2a.
Compounds 3/3a and 4/4a, both isolated separately as
yellow oils, are similar to compounds 1/1a and 2/2a, each
with a pseudomolecular peak at m/z 359 [M + H]+ in the
positive FABMS. The difference of only 14 atomic mass
units compared to compounds 1/1a and 2/2a strongly
indicated the presence of a further methylene group and
established the molecular formula as C22H30O4. A comparison of the corresponding 1D and 2D NMR experiments of
3/3a and 4/4a revealed chemical shifts and correlations in
the tricyclic system identical to those found in 1/1a and
2/2a. However, COSY correlations between H-2′′ and H35′′ or H2-3′′ and between H2-3′′ and H3-4′′ or H-2′′ proved
the replacement of the 2-methylpropionyl group at C-9 by
a 2-methylbutyryl unit. Analysis of NOESY experiments
performed in an analogous manner to substances 1/1a and
2/2a led to the conclusion that the two compounds 3/3a
and 4/4a are C-3-epimers of 8-hydroxy-4,4,7-trimethyl-9(2-methylbutyryl)-3-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-8-ene-10,11-dione and 10-hydroxy-4,4,7-trimethyl9-(2-methylbutyryl)-3-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-9-ene-8,11-dione), with a 3β-(1-methylvinyl) group in compound 3/3a and a 3R-(1-methylvinyl)
group in compound 4/4a.
A fifth substance, again isolated in the form of a yellow
oil, was interpreted by comparing the 1H and 13C NMR
chemical shifts with the corresponding data of compounds
1/1a and 2/2a and by considering the reduction of the
molecular weight by 40 atomic mass units to m/z 304
(EIMS). This reduction indicated the loss of the 1-methylvinyl group at C-3, which was later confirmed by the 2D
NMR (COSY, HSQC, HMBC) data. The NOESY experiment established the β-position of H-5. Again, 5/5a exists
in both tautomeric forms, 8-hydroxy-4,4,7-trimethyl-9-(2methylpropionyl)-5β-H-tricyclo[5.3.1.01,5]undec-8-ene-10,11-dione (5) and 10-hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)-5β-H-tricyclo[5.3.1.01,5]undec-9-ene-8,11-dione
(5a).
Because in all five compounds the same tautomeric form
was preferred, it seems, therefore, that the neighboring
five-membered ring system probably has a destabilizing
effect on the enolic hydroxyl group compared to the methyl
group (C-14).
The five isolates were evaluated for their antibacterial
potential against B. cereus, S. epidermidis, and M. luteus
(Table 4). Compounds 3/3a and 4/4a showed stronger
activity than 1/1a and 2/2a against B. cereus and S.
epidermidis but almost identical effectiveness against M.
luteus. In contrast, compound 5/5a lacked any antibacterial
activity (minimum inhibitory concentration > 256 µg/mL
and 128 µg/mL, respectively). Hence, we conclude that the
1-methylvinyl group at C-3 plays a crucial role for the
antibacterial activity. No difference was observed between
Journal of Natural Products, 2000, Vol. 63, No. 1 107
Table 4. Antibacterial Activities of Compounds 1/1a-5/5a
minimum inhibitory concentration
(MIC) in broth (in µg/mL)
compound
1/1a
2/2a
3/3a
4/4a
5/5a
chloramphenicol
B. cereus
S. epidermidis
M. luteus
(ATCC 10702) (ATCC 12228) (ATCC 9341)
64
64
16
16
> 128
2
64
128
32
32
> 256
4
64
64
64
64
> 128
1
the antibacterial activities of the two corresponding epimers
(1/1a vs 2/2a and 3/3a vs 4/4a).
Experimental Section
General Experimental Procedures. Optical rotations
were recorded with a Perkin-Elmer 241 polarimeter using
CHCl3 as solvent. UV spectra were obtained in ethanol on a
UVIKON 930 spectrophotometer. 13C NMR spectra of 1/1a,
2/2a, 3/3a, and 4/4a were measured at 300 K on a Bruker
AMX-300 spectrometer (operating at 300.13 MHz for 1H and
75.47 MHz for 13C), 1D proton, 1H-1H COSY, 1H-1H TOCSY,
500-ms NOESY, HMBC, and HSQC experiments of compounds
1/1a and 2/2a at 295 K on a Bruker DRX-600 spectrometer
(operating at 600.13 MHz for 1H and 150.92 MHz for 13C). All
other NMR spectra were recorded on a Bruker DRX-500
(operating at 500.13 MHz for 1H and 125.77 MHz for 13C) at
295 K. The spectra were measured in CDCl3 and referenced
against residual CHCl3 in CDCl3 (1H 7.27 ppm) and CDCl3 (13C
δ 77.0 ppm). EIMS were measured on a Hitachi-PerkinElmer-RMUGM mass spectrometer at 70 eV and positive
mode FABMS on a ZAB 2-SEQ spectrometer, using 3-nitrobenzyl alcohol as matrix. HPLC separations were performed
with a Merck-Hitachi L6200A Intelligent Pump connected to
a Rheodyne 7125 Injector, a Merck-Hitachi L-4250 UV/vis
detector, a Merck D-2500 Chromato-Integrator, and a Knauer
HPLC column (Spherisorb 5 ODS II, 5 µm, 250 × 8 mm). Si
gel H & Y (Chromagel, sds), particle size 40-60 µm, and Si
gel for column chromatography (Merck), particle size 15-40
µm, were used for VLC (columns 22 × 7 and 22 × 3 cm,
respectively, vacuum by H2O aspiration). Si gel 60 F254
precoated aluminum sheets (0.2 mm, Merck) and RP18 F254
precoated sheets (0.25 mm, Merck) were used for TLC controls.
All solvents were of HPLC grade.
Plant Material. The aerial parts of Hypericum papuanum
Ridley were collected north of Ialibu, Southern Highlands
Province, Papua New Guinea, in September 1996. The plant
was identified by Paul Katik, National Herbarium, Lae, Papua
New Guinea, and Dr. M. M. J. van Baalgoy, Rijksherbarium,
Leiden, The Netherlands. A voucher specimen is deposited in
the Rijksherbarium (Leiden, The Netherlands) with the identification number ETH 96/34 27-09-96.
Extraction and Isolation. Air-dried and powdered aerial
parts of Hypericum papuanum (2.2 kg) were extracted successively with petroleum ether, dichloromethane, and methanol, as well as 7:3 and 1:1 methanol-water mixtures, respectively, to afford 160 g of petroleum ether-soluble material after
concentration under vacuum. A 46-g quantity of this extract
was applied to VLC over Si gel (40-60 µm), as four separate
portions (5 g, 11 g, 15 g, 15 g). Elution with hexane containing
increasing amounts of ethyl acetate and final washing with
methanol yielded 50 fractions of 180 mL each. Based on the
TLC similarities, identical fractions were combined to give a
total of 16 fractions. Altogether, 1.5 g of recombined VLC
fraction 3 (eluted with hexane-ethyl acetate 98:2) was separated by VLC over Si gel (15-40 µm) using a step gradient
from hexane to ethyl acetate and final washing with methanol.
Based on TLC, the obtained 33 fractions of 100 mL each were
combined to give 12 fractions. The bioactive fractions 10 and
11 (280 mg, eluted with hexane-ethyl acetate 50:50) were
108 Journal of Natural Products, 2000, Vol. 63, No. 1
chosen for further purification. Reversed-phase HPLC purification of the combined fractions 10 and 11 using acetonitrileH2O-trifluoroacetic acid (80:19.5:0.5) as eluent yielded 1/1a
(6.2 mg), 2/2a (14.1 mg), 3/3a (2.2 mg), 4/4a (9.1 mg), and 5/5a
(2.8 mg), each as yellow oil.
Antibacterial Assays. The test organisms were Bacillus
cereus (ATCC 10702, Gram-positive), Staphylococcus epidermidis (ATCC 12228, Gram-positive), and Micrococcus luteus
(ATCC 9341, Gram-positive). Antibacterial assays were carried
out by the doubling dilution method using a modified procedure as described below.10 Bacterial suspensions were obtained
from overnight cultures in nutrient broth (Becton, Dickinson
Co., 11479) cultivated at 37 °C and diluted to approximately
105 cells/mL in fresh medium. The isolated compounds were
dissolved to 1 mg/mL in MeOH as stock solutions. The required
amount of stock solution was pipetted into the wells at the
first column of a 96-well tissue culture plate (Falcon) and dried.
The sample was redissolved in 50 µL DMSO, 50 µL sterile
nutrient broth, and 100 µL dilute culture suspension. Twofold
dilutions were made in 100 µL volumes of dilute bacterial
suspensions. The plates were kept in a moist atmosphere at
37 °C for 20 h. After incubation, 10 µL of 0.25% aqueous
thiazolyl blue tetrazolium bromide was added in each well and
reincubated for 4 h to detect living bacteria as violet turbid
solutions. Chloramphenicol was used as a positive control. All
pure compounds were tested within the range of 256-0.5 µg/
mL.
Ialibinone A (1/1a): 8-Hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)-3β-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec8-ene-10,11-dione (1) and 10-hydroxy-4,4,7-trimethyl-9-(2methylpropionyl)-3β-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-9-ene-8,11-dione (1a), respectively; yellow oil
(6.2 mg); [R]20D -22° (c 0.10, CHCl3); UV (EtOH) λmax (logǫ)
275 (4.13), 236 (sh) (3.78) nm; 1H NMR data, see Tables 1 and
2; 13C NMR spectral data, see Table 3; FABMS (positive) m/z
345.3 [M + H]+; EIMS (CH2Cl2) m/z 344 [M]+ (36), 301 [M C3H7]+ (8), 275 (8), 205 (48), 149 (15).
Ialibinone B (2/2a): 8-Hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)-3R-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec8-ene-10,11-dione (2) and 10-hydroxy-4,4,7-trimethyl-9-(2methylpropionyl)-3R-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec-9-ene-8,11-dione (2a), respectively; yellow oil
(14.1 mg); [R]20D -91° (c 0.10, CHCl3); UV (EtOH) λmax (logǫ)
273 (4.16), 234 (3.87) nm; 1H NMR spectral data, see Tables 1
and 2; 13C NMR spectral data, see Table 3; FABMS (positive)
m/z 345.2 [M + H]+; EIMS (CH2Cl2) m/z 344 [M]+ (31), 301 [M
- C3H7]+ (24), 275 (21), 205 (100), 149 (34).
Ialibinone C (3/3a): 8-Hydroxy-4,4,7-trimethyl-9-(2-methylbutyryl)-3β-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec8-ene-10,11-dione (3) and 10-hydroxy-4,4,7-trimethyl-9-(2methylbutyryl)-3β-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec9-ene-8,11-dione (3a), respectively; yellow oil (2.2 mg); [R]20D
-26° (c 0.10, CHCl3); UV (EtOH) λmax (logǫ) 276 (4.05), 239
Winkelmann et al.
(sh) (3.77) nm; 1H NMR spectral data, see Tables 1 and 2; 13C
NMR spectral data, see Table 3; FABMS (positive) m/z 359.2
[M + H]+; EIMS (CH2Cl2) m/z 358 [M]+ (36), 301 [M - C4H9]+
(7), 289 (9), 205 (42), 149 (15).
Ialibinone D (4/4a): 8-Hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)-3R-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec8-ene-10,11-dione (4) and 10-hydroxy-4,4,7-trimethyl-9-(2methylbutyryl)-3R-(1-methylvinyl)-5β-H-tricyclo[5.3.1.01,5]undec9-ene-8,11-dione (4a), respectively; yellow oil (9.1 mg); [R]20D
-72° (c 0.10, CHCl3); UV (EtOH) λmax (logǫ) 274 (4.07), 238
(sh) (3.80) nm; 1H NMR spectral data, see Tables 1 and 2; 13C
NMR spectral data, see Table 3; FABMS (positive) m/z 359.2
[M + H]+; EIMS (CH2Cl2) m/z 358 [M]+ (15), 301 [M - C4H9]+
(6), 289 (10), 205 (48), 149 (28).
Ialibinone E (5/5a): 8-Hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)-5β-H-tricyclo[5.3.1.01,5]undec-8-ene-10,11-dione (5) and 10-hydroxy-4,4,7-trimethyl-9-(2-methylpropionyl)5β-H-tricyclo[5.3.1.01,5]undec-9-ene-8,11-dione (5a), respectively;
yellow oil (2.8 mg); [R]20D -33° (c 0.10, CHCl3); UV (EtOH)
λmax (logǫ) 281 (3.77), 251 (3.75) nm; 1H NMR spectral data,
see Tables 1 and 2; 13C NMR spectral data, see Table 3; EIMS
(CH2Cl2) m/z 304 [M]+ (54), 261 [M - C3H7]+ (8), 235 (25), 205
(18), 149 (18).
Acknowledgment. This work was supported by the Swiss
National Science Foundation. We thank Paul Katik (National
Herbarium, Lae, Papua New Guinea) and Dr. M. M. J. van
Baalgoy (Rijksherbarium, Leiden, The Netherlands) for identification of the plant material. Thanks are also due to Dr.
Engelbert Zass (ETH Chemistry Department) for performing
literature searches, as well as Mr. Oswald Greter, Mr. R.
Häfliger, and Dr. Walter Amrein (ETH Chemistry Department, Mass Spectral Service) for recording the mass spectra.
References and Notes
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