Isolation and characterization of two new drimanes from Zygogynum baillonii and synthesis of analogues

Article abstract of DOI:10.1016/j.tet.2007.12.022

Two new drimanes were isolated and characterized from the bark of Zygogynum baillonii, an endemic New-Caledonian tree of the Winteraceae family. One of it shows a significant cytotoxic activity. In order to define structure-activity relationships, analogu

Full text of DOI:10.1016/j.tet.2007.12.022

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 2192e2197
www.elsevier.com/locate/tet
Isolation and characterization of two new drimanes from
Zygogynum baillonii and synthesis of analogues
*
Dalia Fomekong Fotsop, Fanny Roussi , Catherine Le Callonec, Hadjira Bousserouel,
´
Marc Litaudon, Franc¸oise Gueritte
Institut de Chimie des Substances Naturelles, UPR 2301 du CNRS, 1 Avenue de la Terrasse, 91198 Gif-Sur-Yvette Cedex, France
Received 29 October 2007; received in revised form 6 December 2007; accepted 10 December 2007
Available online 14 December 2007
Abstract
Two new drimanes were isolated and characterized from the bark of Zygogynum baillonii, an endemic New-Caledonian tree of the Winter-
aceae family. One of it shows a significant cytotoxic activity. In order to define structureeactivity relationships, analogues were synthesized and
their cytotoxicity was evaluated.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
cytotoxicity against HCT-116 human colon carcinoma cells5
and polygodial (3) exhibits antifungal activity (Fig. 1).6,7
In our search to find new cytotoxic compounds, we screened
on KB cell line, a series of 1200 plant extracts prepared from
species belonging to the New-Caledonian biodiversity. This
screening revealed the cytotoxicity of the EtOAc extract of
the bark of Zygogynum baillonii, an endemic New-Caledonian
tree of the Winteraceae family. Bioassay-guided chemical
investigation on this extract led to the isolation of two new
drimane sesquiterpenoids.
HO
O
OH
12
O
11
O
9
6
1
O
OH
NO2
HO
H
H
H
O
2
3
O
1
Figure 1. Some examples of drimane sesquiterpenoids.
Drimane sesquiterpenoids have been discovered sixty years
ago with the isolation1 and the characterization2 of drimenol
(1) from the bark of Drimys winterii Forst. Since then, a large
number of drimanes have been isolated from different families
of plants (for example, Cannellacae, Winteraceae or Polygona-
ceae) and from several fungi.3
In this report, we describe the isolation and characterization
of two new drimanes 4 and 5 from the bark of Z. baillonii, to-
gether with the synthesis and cytotoxic activity of the ana-
logues (Fig. 2).
Drimane sesquiterpenes possess attractive biological proper-
tiesincludingantibacterial, antifungal, antifeedant, and cytotoxic
effects.4 For example, insulicolide A (2) displays significant
O
O
H
15
11
1'
2'
3'
O
O
H
O
O
5'
8'
12
1
4
9
6
6'
7'
O
8
7
2
10
O
4'
9'
5
3
O
O
H
H
OH
14
13
* Corresponding author. Tel.: þ33 (0) 1 69 82 30 13; faxþ 33 (0) 1 69 07 72
5
4
47.
E-mail address: roussi@icsn.cnrs-gif.fr (F. Roussi).
Figure 2. New drimanes from the bark of Zygogynum baillonii.
0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.12.022

D. Fomekong Fotsop et al. / Tetrahedron 64 (2008) 2192e2197
2193
2. Results
The genus Zygogynum consists of some 41 species distrib-
d 123.9 and 165.8, respectively, and confirmed by observation
of long range correlations from H-6 to C-8 and from H-5 to
C-9 in the HMBC spectrum. Finally, correlations of H-5
with H-1 and H3-13 in the NOESY spectrum, allowed us to de-
termine the relative configuration of the asymmetric centers,
that is, the trans orientation of the AB ring junction and the
b position of the trans-cinnamic ester at C-1 (Fig. 3). Thus, the
structure of compound 5 was determined as 1b-O-(p-methoxy-
(E)-cinnamoyl)-bemadienolide.
uted in the west pacific region including Australia, Papua-
New-Guinea, and New-Caledonia. The chemical constituents
of the genus Zygogynum are scarcely known.8 Compound 4
was obtained as a yellowish amorphous powder. Its molecular
formula C25H30O6 was supported by HREIMS of the [MþNa]þ
1
ion peak at m/z 449.1967 (calcd 449.1940). The H and 13C
NMR spectra of 4 were closely related to those of L-b-(p-
methoxy-(E)-cinnamoyl)-polygodial.9 The only structural dif-
ference was the presence of an additional hydroxyl group at
d 1.97 (OH-6). This was confirmed by the presence of an oxy-
gen-bearing methine carbon at d 68.1 (C-6) and a corresponding
proton signal at d 4.66 (m, 1H, H-6). Correlations between H-6
(d 4.66) and H-5 (d 1.41) and H-7 (d 6.83) in the COSY exper-
iment allowed to place the hydroxyl group in position C-6. The
relative configuration of the asymmetric carbons, that is, b posi-
tions of the aldehyde group at C-9 and the trans-cinnamic ester
at C-1, as well as the a position of the hydroxyl group at C-6
could be easily assigned by the NOESY experiment in which
correlations between H-6 (d 4.66) with H3-14 (d 1.15) and
H3-15 (d 1.09), and H-5 (d 1.41) with H-1 (d 4.83), H-9 (d
3.32), and H3-13 (d 1.20) were observed (Fig. 3). On the basis
of these evidences, the structure of compound 4 was determined
as 1b-O-(p-methoxy-(E)-cinnamoyl)-6a-hydroxypolygodial and
was named isodrimanial.
Compound 4 revealed a cytotoxicity on KB cell line with an
IC50 of 0.30 mM whereas 5 was devoid of activity. As compound
4 was available on a gram scale, some structural modifications
were undertaken in order to underline the structureeactivity
relationships.
Compound 4 was first easily epimerized at C-9 in basic
conditions at room temperature to give a 40:60 mixture of sep-
arable 6 9a and 4 9b compounds. The aldehyde functions were
then selectively reduced to give the triol 710 as a single diaste-
reomer (Scheme 1).
O
O
O
O
O
O
a
9
O
O
O
O
H
H
OH
OH
4
4 : 9β 60%
6 : 9α 40%
Compound 5 was obtained as a white amorphous powder.
Its molecular [MþNa]þ ion peak at m/z 431.1858 (calcd
431.1834) by HREIMS, revealed the molecular formula
C25H28O5. Compound 5 was also a p-methoxycinnamoyl de-
rivative as evidenced by the typical signals of H-20, H-30, H-
b
O
O
OH
OH
O
1
50, and H-60 in its H NMR and the signals of C-10eC-70
H
OH
and OMe in its 13C NMR. The presence of an a,b-unsaturated
lactone was readily recognized by signals of quaternary car-
bons at d 171.6, 166.8, and 123.9 in the 13C NMR. This was
supported by a strong absorption band at 1754 cmꢀ1 in the
7
Scheme 1. Reagents and conditions: (a) DMAP, toluene, rt, 50%; (b) NaBH4
(4.6 equiv), MeOH, 0 ꢁC, 33%.
1
IR spectrum. Moreover, examination of the H NMR spectra
In order to oxidize the aldehyde functions, sodium chlorite
and different HOCl scavengers were used. A dioxidation could
be performed on compound 4 with sodium chlorite/H2O2 to
give compound 8 in a nearly quantitative yield (Scheme 2).
A selective mono oxidation could also be performed at C-11
with sodium chlorite/sulfamic acid (Scheme 2). This oxidation
was followed by an intramolecular lactonization on C-12 to
give compound 9 as a single diastereomer. The relative config-
uration of the new asymmetric center could be determined,
thanks to NOE effects between H-12 and H3-15. Compound 9
was then esterified either on C-6 as an acetate (compound 10)
or a bromobenzoate (compound 12) or on C-6 and C-12 as a
diacetate (compound 11).
revealed the presence of signals at d 4.70 (d, J¼18 Hz, 1H,
H-11a) and 4.79 (d, J¼18 Hz, 1H, H-11b) for an oxymethy-
lene group and the presence of signals at d 6.00 (dd, J¼2.3,
9.4 Hz, 1H, H-6) and 6.36 (dd, J¼2.9, 9.4 Hz, 1H, H-7) for
an additional double bond when compared with 4. These struc-
1
tural assignments with the combination of H COSY, HMQC,
HMBC, and NOESY experiments allowed us to determine the
structure of 5. Long range correlations of H-5, H-6, H-7, CH2-
11, Me-13, Me-14, and Me-15 with neighboring carbons were
particularly helpful in determining the structure of the A and B
rings. Assignment of the lactone carbonyl to C-12 was estab-
lished on the basis of the chemical shifts of C-8 and C-9 at
Compound 4 was quite tricky to handle compared with other
polygodial derivatives and was sensitive to acid or basic con-
ditions. For example, in an attempt to mono protect the C-11
aldehyde (APTS, ethylene glycol), we noticed that compound
4 rearranged spontaneously in acidic conditions to give the lac-
tone 5 (NMR and mass spectra identical to those of the natural
compound). This reaction was quantitative with a catalytic
O
OR
H
OR
H
O
O
H
O
H
H
H
OH
Figure 3. Observed NOE for compounds 4 and 5.

2194
D. Fomekong Fotsop et al. / Tetrahedron 64 (2008) 2192e2197
O
O
O
O
12
O
15
H
O
O
b
OH
O
O
O
H
9
OH
H
OH
4
c, d, e
a
O
O
O
O
O
O
OH
H
O
O
OR2
OH
O
O
H
H
OR1
10 R1 = COCH3, R2 = H
OH
8
11 R1 = COCH3, R2 = COCH3
12 R1 = COC6H4Br, R2 = H
Scheme 2. Reagents and conditions: (a) NaClO2 (5 equiv), H2O2 (4 equiv), acetonitrile, rt, 96%; (b) NaClO2 (2 equiv), NH2SO3H (2 equiv), 1,4-dioxane/water
(4:1), 0 ꢁC, 94%; (c) CH3COCl (1.1 equiv), pyridine (1.1 equiv), CH2Cl2, rt, 25%; (d) CH3COCl (3.3 equiv), pyridine (3.3 equiv), CH2Cl2, rt, 31%; (e) DCC
(1.1 equiv), DMAP (0.2 equiv), BrC6H4CO2H (1.1 equiv), toluene, rt, 50%.
O
O
O
O
O
O
R
O
O
O
O
R
O
R
O
H
R
O
R
O
O
H
O
O
O
O
O
+
H
H
H
H
+
OH
O
H
H
4
5
dehydration and hydride transfer
Scheme 3. Reagents and conditions: (a) APTS (0.2 equiv), benzene, reflux, 99%.
amount of APTS in refluxing benzene and was not observed
with polygodial 311 (Scheme 3). The presence of the 6a-OH
plays a crucial role in this rearrangement. Lactone 5 may be
formed by a dehydration process followed by a hydride transfer
in a Tishchenko-type reaction.12 We may emphasis that this
disproportionation reaction may also occur in the plant.
The biological activity of all the new synthesized compounds
6e12 was evaluated on KB cell line. Compound 6 was the only
one to be cytotoxic on KB cells with an IC50 of 4.5 mM. Thus the
presence of the dialdehyde functions was shown essential for
the cytotoxic activity.
(LIT-1275) is deposited in the Herbarium of the Botanical
and Tropical Ecology Department of the IRD Center, Noumea,
New Caledonia.
3.3. Extraction and isolation
The powdered air-dried bark of Z. baillonii (600 g) were ex-
tracted sequentially with heptane (3ꢂ1.5 L), EtOAc (3ꢂ2 L),
and MeOH (3ꢂ1.5 L) at room temperature to afford 4.1 g,
50.6 g, and 25.0 g of heptane, EtOAc, and MeOH extracts,
respectively. EtOAc extract displayed a significant inhibitory
activity for the growth of KB cells (85% inhibition at a concen-
tration of 10 Hg/mL). The EtOAc extract (2ꢂ10 g) was then
subjected to a flash column chromatography on silica (Versa-
PakÔ 40ꢂ150 mm) eluting with heptane/AcOEt/MeOH
(80:20:0 to 0:0:100) to give 14 fractions according to their TLC
profile (fractions 1e14). Fractions 5þ6 (9.57 g) contained com-
pound 4 with a purity over 90% and fractions 7þ8 (0.65 g) con-
tained compound 4 with a purity of 80%. Fraction 6 (310 mg)
was submitted to a silica gel column chromatography using
a gradient of heptane/AcOEt (60:40 to 0:100) to afford com-
pound 4 (156 mg). Fraction 2 (3.49 g) was submitted to a silica
gel column chromatography using a gradient of heptane/AcOEt
(60:40 to 0:100) to give10 fractions (fractions2-1 to 2-10). Frac-
tions 2e4 (1.35 g) were submitted to a flash chromatography on
reversed-phase (VersaPackÔ, C18 Cartridge 40ꢂ75 mm) using
3. Experimental section
3.1. General remarks
All solvents and reagents were purified by standard tech-
niques or used as supplied from commercial sources as appropri-
ate. Flash chromatography was carried out on 230e400 mesh
gel or 70e230 mesh aluminum oxide.
3.2. Plant material
Bark of Z. baillonii were collected in December 2000 in the
high altitude scrubland of ‘Monts Dzumac’, South Province,
New Caledonia, by one of us (M.L.). A voucher specimen

D. Fomekong Fotsop et al. / Tetrahedron 64 (2008) 2192e2197
2195
a gradient mobile phase consisting of H2O/MeCN 50:50 to
3.3.3. 9a-Dialdehyde 6
0:100 at 10 mL/min to give 8 fractions (fractions 2-4-1 to 2-4-
8). Fraction 2-4-3 (138 mg) was finally submitted to a prepara-
tive HPLC (Kromasil C-18 column 250ꢂ21.2 mm, I.D. 5 mm)
using an isocratic mobile phase MeCN/H2O 70:30 at a flow
rate of 21.2 mL minꢀ1 to give 44 mg of compound 5 (tR:
19.0 min).
Compound 4 (50 mg; 0.12 mmol) and DMAP (15 mg;
0.12 mmol) were dissolved in 1 mL of toluene at room temper-
ature. The reaction mixture was stirred for 24 h. Dichlorome-
thane was added and the organic layer was washed with an
aqueous 1 N HCl solution and brine, dried over MgSO4, fil-
tered, and concentrated. The crude product was purified on pre-
parative TLC of silica gel (EtOAc/heptane 1:1) to give pure
compounds 4 (12 mg) and 6 (9 mg). 1H NMR (CDCl3,
300 MHz) d: 1.08 (s, 3H, H-14); 1.12 (s, 3H, H-15); 1.15 (s,
3H, H-13); 1.46 (m, 2H, H-3); 1.57 (d, J¼9.6 Hz, 1H, H-5);
1.77 (m, 2H, H-2); 3.63 (ls, 1H, H-9); 3.83 (s, 3H, OMe);
4.48 (m, 1H, H-6); 4.84 (dd, J¼5.7, 10.5 Hz, 1H, H-1); 6.30
(d, J¼15.9 Hz, 1H, H-20); 6.88 (ls, 1H, H-7); 6.90 (d,
J¼8.7 Hz, 2H, H-6, H0-80); 7.48 (d, J¼8.7 Hz, 2H, H-50, H-
90); 7.66 (d, J¼15.9 Hz, 1H, H-30); 9.44 (s, 1H, H-12); 9.82
(d, J¼1.5 Hz, 1H, H-11). 13C NMR (CDCl3, 75 MHz) d: 17.3
(C-15); 22.6 (C-14); 24.1 (C-2); 33.1 (C-4); 35.5 (C-13);
40.1 (C-3); 44.4 (C-10); 51.3 (C-5); 54.1 (C-9); 55.4 (OMe);
68.0 (C-6); 77.0 (C-1); 114.4 (C-60þC-80); 115.1 (C-20); 126.8
(C-40); 130.0 (C-50þC-90); 139.7 (C-8); 145.4 (C-30); 152.3
(C-7); 161.6 (C-70); 166.3 (C-10); 192.4 (C-12); 201.6 (C-11).
MS (ESIþ, CH2Cl2þMeOH): m/z 449.2 [MþNaþ]. HRESIMS
449.1913 (calcd for C25H30O6Na 449.1940). IR (cmꢀ1): 3440;
2931; 1682; 978. [a]2D5 ꢀ32 (c 0.5, CHCl3).
3.3.1. Isodrimanial 4
Yellowish amorphous powder; 1H NMR (CDCl3, 300 MHz)
d: 1.09 (s, 3H, H-15); 1.15 (s, 3H, H-14); 1.20 (s, 3H, H-13);
1.41 (m, 1H, H-5); 1.53 (m, 1H, H-3); 1.79 (m, 2H, H-2); 1.97
(s, 1H, OH); 3.32 (br s, 1H, H-9); 3.82 (s, 3H, OMe); 4.66 (m,
1H, H-6); 4.83 (dd, J¼11.2 Hz, 3.6 Hz, 1H, H-1); 6.22 (d,
J¼15.9 Hz, 1H, H-20); 6.83 (br s, 1H, H-7); 6.88 (d,
J¼8.6 Hz, 2H, H-60, H-80); 7.47 (d, J¼8.6 Hz, 2H, H-50, H-
90); 7.59 (d, J¼15.9 Hz, 1H, H-30); 9.35 (s, 1H, H-12); 9.75
(d, J¼2.4 Hz, 1H, H-11). 13C NMR (CDCl3, 75 MHz) d:
11.4 (C-15); 22.8 (C-14); 24.0 (C-2); 33.2 (C-4); 35.9 (C-
13); 40.5 (C-3); 44.5 (C-10); 55.4 (OMe); 55.8 (C-5); 58.4
(C-9); 68.1 (C-6); 80.8 (C-1); 114.3 (C-60þC-80); 115.0 (C-
20); 126.8 (C-40); 130.0 (C-50þC-90); 139.7 (C-8); 145.7 (C-30);
153.5 (C-7); 161.6 (C-70); 166.3 (C-10); 192.4 (C-12); 199.9 (C-
11). HRESIMS m/z 449.1967 [MþNa]þ (calcd for C25H30O6Na
449.1940). IR (cmꢀ1): 3443; 2773; 1705; 1662; 1627; 1603;
1158. [a]2D5 þ237 (c 0.3, CH2Cl2).
3.3.4. Triol 7
Compound 4 (150 mg; 0.35 mmol) was dissolved in 3 mL
of anhydrous methanol under argon and the resulting solution
was cooled to 0 ꢁC. Sodium borohydride (48 mg; 1.26 mmol)
was added and the reaction mixture was stirred at 0 ꢁC for 3 h.
Additional NaBH4 (13 mg; 0.35 mmol) was then added. After
one more hour at 0 ꢁC, 1 mL of water was added. Solvent was
evaporated under reduced pressure and the residue was diluted
with ethyl acetate (20 mL) and water (10 mL). The organic
layer was decanted, washed with an aqueous 1 N HCl solution
and brine, dried over MgSO4, filtered, and concentrated. The
crude product was purified by column chromatography on sil-
ica gel (CH2Cl2/MeOH 95:5) to afford the desired compound
(49 mg, 33%). 1H NMR (DMSO-d6, 300 MHz) d: 1.05 (s, 3H,
H-15); 1.08 (s, 3H, H-14); 1.13 (s, 3H, H-13); 1.23 (ls, 1H, H-
5); 1.36 (ls, 2H, H-3); 1.53 (m, 2H, H-2); 1.90 (s, 1H, OH);
2.07 (ls, 1H, H-9); 3.53 (d, J¼4.8 Hz, 1H, H-11); 3.80 (s,
3H, OMe); 3.92 (m, 4H, H-11, H-12, OH-11, OH-12); 4.18
(m, 1H, H-6); 4.44 (d, J¼6.9 Hz, 1H, H-12); 4.69 (ls, 1H,
H-1); 5.63 (ls, 1H, H-7); 6.48 (d, J¼15.9 Hz, 1H, H-20);
6.98 (d, J¼8.4 Hz, 2H, H-6, H0-80); 7.59 (d, J¼8.4 Hz, 2H,
H-5, H0-90); 7.67 (d, J¼15.9 Hz, 1H, H-30). 13C NMR
(DMSO-d6, 75 MHz) d: 11.4 (C-15); 22.6 (C-14); 24.9 (C-
2); 32.9 (C-4); 35.9 (C-13); 40.0 (C-3); 42.2 (C-10); 53.0
(C-9); 55.2 (OMe); 55.3 (C-5); 59.6 (C-11); 63.1 (C-12);
66.4 (C-6); 81.3 (C-1); 114.3 (C-60þC-80); 116.2 (C-20);
126.7 (C-40); 128.9 (C-7); 130.1 (C-50þC-90); 137.4 (C-8);
143.9 (C-30); 161.1 (C-70); 165.8 (C-10). MS (ESIþ, MeOH):
m/z 453.2 [MþNaþ]. HRESIMS 453.2256 (calcd for
C25H34O6Na 453.2253). IR (cmꢀ1): 3283; 2920; 1697; 1146;
978. [a]2D5 ꢀ6 (c 0.3, DMSO).
3.3.2. 1b-O-(p-Methoxy-(E)-cinnamoyl-bemadienolide 5
1
White amorphous powder; H NMR (CDCl3, 300 MHz) d:
1.01 (s, 3H, H-13); 1.07 (s, 3H, H-14); 1.16 (s, 3H, H-15); 1.49
(m, 1H, H-3a); 1.57 (m, 1H, H-3b); 1.78 (m, 1H, H-2a); 1.94
(m, 1H, H-2b); 2.32 (s, 1H, H-5); 3.83 (s, 3H, OMe); 4.70 (d,
J¼18.0 Hz, 1H, H-11a); 4.79 (d, J¼18.0 Hz, 1H, H-11b); 5.03
(dd, J¼4.1, 11.2 Hz, 1H, H-1); 6.00 (dd, J¼2.3, 9.4 Hz, 1H, H-
6); 6.28 (d, J¼15.8 Hz, 1H, H-20); 6.36 (dd, J¼2.9, 9.4 Hz,
1H, H-7); 6.91 (d, J¼8.7 Hz, 2H, H-60, H-80); 7.48 (d,
J¼8.7 Hz, 2H, H-50, H-90); 7.65 (d, J¼15.9 Hz, 1H, H-30).
13C NMR (CDCl3, 75 MHz) d: 11.3 (C-15); 23.0 (C-14);
24.4 (C-2); 32.0 (C-13); 32.8 (C-4); 38.9 (C-3); 42.2 (C-10);
52.2 (C-5); 55.6 (OMe); 69.1 (C-11); 76.6 (C-1); 114.6 (C-
60þC-80); 118.3 (C-7); 114.9 (C-20); 123.9 (C-8); 126.9 (C-40);
130.1 (C-50þC-90); 130.9 (C-6); 145.9 (C-30); 161.9 (C-70);
166.6 (C-10); 166.8 (C-9); 171.6 (C-12). MS (ESIþ,
CH2Cl2þMeOH): m/z 431.2 [MþNa]þ. HRESIMS 431.1834
(calcd for C25H28O8Na 431.1871). IR (cmꢀ1): 2922; 1754;
1703; 1601. [a]2D5ꢀ60 (c 0.5, CHCl3). Compound 4 (20 mg;
0.05 mmol) and APTS (2 mg; 0.01 mmol) were refluxed in
1 mL of benzene for 3 h. Solvent was removed in vacuo.
The crude mixture was diluted with CH2Cl2 (3 mL). The or-
ganic layer was washed with a saturated solution of NaHCO3
and brine, dried over MgSO4, filtered, and evaporated under
reduced pressure. The crude mixture was purified by column
chromatography on aluminum oxide (EtOAc/heptane 15:85)
to afford compound 5 (19 mg, 99%) as a white amorphous
solid. It provided spectral and analytical data identical to those
of the natural product.

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D. Fomekong Fotsop et al. / Tetrahedron 64 (2008) 2192e2197
3.3.5. Diacid 8
washed with brine, dried over MgSO4, and concentrated. The
crude product was purified on preparative TLC of silica gel
(EtOAc/heptane 1:1) to afford pure compound 10 (14 mg,
Sodium phosphate (10 mg; 0.08 mmol) in 0.2 mL of water
and H2O2 (56 mL; 0.64 mmol) were added to a solution of com-
pound 4 (70 mg; 0.16 mmol) and dissolved in 2 mL of acetoni-
trile. Sodium chlorite (93 mg; 0.8 mmol) in 0.5 mL of water
was added dropwise over a period of 15 min. The reaction mix-
ture was stirred for 24 h at room temperature. Solid Na2SO3
(5 mg) was added and the mixture was stirred for 5 min then
acidified by an aqueous solution of 10% HCl. Aqueous layer
was washed three times with CH2Cl2. Combined organic layers
were washed with brine, dried over MgSO4, filtered, and con-
centrated in vacuo. Pure compound 8 was isolated as a white
1
25%). H NMR (CDCl3, 300 MHz) d: 0.89 (s, 3H, H-13);
0.99 (s, 3H, H-14); 1.02 (s, 3H, H-15); 1.44 (m, 2H, H-3);
1.63 (m, 1H, H-2); 1.72 (d, J¼9.3 Hz, 1H, H-5); 1.78 (m, 1H,
H-2); 2.00 (s, 3H, CH3eOAc); 2.62 (d, 1H, H-9); 3.77 (s, 3H,
OMe); 4.77 (dd, J¼4.2, 11.1 Hz, 1H, H-1); 5.62 (m, 1H, H-6);
5.76 (sl, 1H, H-12); 6.20 (d, J¼15.9 Hz, 1H, H-20); 6.59 (t,
J¼3.6 Hz, 1H, H-7); 6.83 (d, J¼8.7 Hz, 2H, H-60, H-80); 7.40
(d, J¼8.7 Hz, 2H, H-50, H-90); 7.52 (d, J¼15.9 Hz, 1H, H-30).
13C NMR (CDCl3, 75 MHz) d: 11.5 (C-15); 21.4 (CH3e
OAc); 22.3 (C-14); 24.3 (C-2); 33.1 (C-13); 33.9 (C-4); 39.9
(C-3); 43.7 (C-10); 53.0 (C-5); 55.4 (OMe); 57.2 (C-9); 69.8
(C-6); 79.3 (C-1); 99.7 (C-12); 114.4 (C-60þC-80); 115.4 (C-
20); 128.6 (C-40); 129.9 (C-50þC-90); 131.6 (C-7); 144.5 (C-
8); 144.6 (C-30); 161.6 (C-70); 166.4 (C-11); 166.7 (C-10);
170.4 (COeOAc). MS (ESIþ, CH2Cl2þMeOH): m/z 507.1
[MþNaþ]. HRESIMS 507.2002 (calcd for C27H32O8Na
507.1995). IR (cmꢀ1): 2968; 1603. [a]D25 þ58 (c 0.7, CHCl3).
1
powder (73 mg; 96%). H NMR (CDCl3, 300 MHz) d: 1.11
(s, 3H, H-15); 1.19 (s, 3H, H-14); 1.30 (s, 3H, H-13); 1.40 (d,
J¼11.0 Hz, 1H, H-5); 1.60 (m, 2H, H-3); 1.81 (m, 2H, H-2);
3.34 (ls, 1H, H-9); 3.74 (s, 3H, OMe); 4.55 (1H, H-6); 4.86
(1H, H-1); 5.45 (ls, 3H, OH); 6.04 (d, J¼15.9 Hz, 1H, H-20);
6.66 (d, J¼8.7 Hz, 2H, H-60, H-80); 6.90 (ls, 1H, H-7); 7.11
(d, J¼8.7 Hz, 2H, H-50, H-90); 7.43 (d, J¼15.6 Hz, 1H, H-30).
MS (ESIꢀ, CH2Cl2þMeOH): m/z 457.2 [MꢀHꢀ]. HRESIMS
457.1835 (calcd for C25H29O8 457.1862). IR (cmꢀ1): 2931;
1697; 1168. [a]D þ34 (c 0.7, CHCl3).
3.3.8. Compound 11
Compound 9 (50 mg; 0.11 mmol), acetyl chloride (27 mL;
0.36 mmol), and dry pyridine (30 mL; 0.36 mmol) were dis-
solved in 1.6 mL of anhydrous CH2Cl2. The reaction mixture
was stirred at room temperature under argon for 24 h then
washed with brine, dried over MgSO4, and concentrated. The
crude product was purified on preparative TLC of silica gel
(EtOAc/heptane 1:1) to afford compounds 11 (18 mg, 31%)
and 10 (5 mg). 1H NMR (CDCl3, 300 MHz) d: 0.89 (s, 3H, H-
15); 0.99 (s, 3H, H-14); 1.06 (s, 3H, H-13); 1.46 (m, 2H, H-3);
1.63 (m, 1H, H-2); 1.74 (d, J¼11.6 Hz, 1H, H-5); 1.80 (s, 3H,
OAc); 1.81 (m, 1H, H-2); 2.00 (s, 3H, OAc); 2.90 (dd, J¼4.6,
9.2 Hz, 1H, H-9); 3.77 (s, 3H, OMe); 4.69 (dd, J¼3.8,
10.8 Hz, 1H, H-1); 5.64 (m, 1H, H-6); 6.09 (d, J¼16.7 Hz, 1H,
H-20); 6.51 (d, J¼7.2 Hz, 1H, H-12); 6.69 (t, J¼5.1 Hz, 1H, H-
7); 6.84 (d, J¼8.2 Hz, 2H, H-60, H-80); 7.41 (d, J¼8.2 Hz, 2H,
H-50, H-90); 7.56 (d, J¼16.7 Hz, 1H, H-30). 13C NMR (CDCl3,
75 MHz) d: 11.0 (C-13); 20.5 (CH3eOAc); 20.8 (CH3eOAc);
22.1 (C-14); 24.1 (C-2); 33.2 (C-4); 33.6 (C-15); 39.9 (C-3);
43.8 (C-10); 52.7 (C-5); 53.9 (C-9); 54.9 (OMe); 69.5 (C-6);
79.8 (C-1); 94.6 (C12); 114.2 (C-60þC-80); 114.7 (C-20); 126.7
(C-40); 129.8 (C-50þC-90); 131.3 (C-7); 136.2 (C-8); 145.8 (C-
30); 161.8 (C-70); 166.3 (C-11); 169.1 (C-10); 170.3 (2 COe
OAc). MS (ESI, CH2Cl2þMeOH): m/z 549.2 [MþNaþ]. HRE-
SIMS 549.2101 (calcd for C29H34O9Na 549.2099). IR (cmꢀ1):
2937; 1778; 1735; 1706. [a]2D5 þ12 (c 0.8, CHCl3).
3.3.6. Monooxidized compound 9
Compound 4 (150 mg; 0.35 mmol) was dissolved in a 4:1
mixture of dioxane and water (3 mL) and cooled to 0 ꢁC. Sulfa-
mic acid (NH2SO3H: 75 mg; 0.77 mmol) and sodium chlorite
(NaClO2: 70 mg; 0.77 mmol) were successively added. The re-
action mixture was stirred for 1 h and diluted with ethyl acetate
(10 mL). A 95:5 mixture of saturated solutions of NaHCO3 and
Na2SO3 (2 mL) was added and the mixture was stirred for
10 min. The organic layer was decanted, washed with brine,
dried over MgSO4, filtered, and concentrated to give a pure yel-
low compound as a single diastereomer (150 mg; 94%), which
was used without further purification. 1H NMR (CDCl3,
300 MHz) d: 0.89 (s, 3H, H-15); 0.98 (s, 3H, H-14); 1.10 (s,
3H, H-13); 1.41 (ls, 1H, H-5); 1.60 (m, 2H, H-3); 1.70 (m,
2H, H-2); 2.50 (ls, 1H, H-9); 2.78 (s, 1H, OH); 3.74 (s, 3H,
OMe); 4.30 (m, 1H, H-6); 4.65 (dd, J¼3.9, 10.8 Hz, 1H, H-
1); 5.70 (ls, 1H, H-12); 5.80 (ls, 1H, eOH); 6.17 (d,
J¼15.9 Hz, 1H, H-20); 6.52 (1H, H-7); 6.79 (d, J¼8.7 Hz,
2H, H-60, H-80); 7.38 (d, J¼8.7 Hz, 2H, H-50, H-90); 7.43 (d,
J¼15.9 Hz, 1H, H-30). 13C NMR (CDCl3, 75 MHz) d: 11.1
(C-15); 22.7 (C-14); 24.4 (C-2); 33.1 (C-4); 35.3 (C-13);
40.4 (C-3); 43.7 (C-10); 55.4 (OMe); 56.5 (C-5); 57.0 (C-9);
67.7 (C-6); 79.9 (C-1); 100.4 (C-12); 114.3 (C-60þC-80); 115.7
(C-20); 127.1 (C-40); 130.1 (C-50þC-90); 135.8 (C-7); 144.5
(C-8); 144.6 (C-30); 161.4 (C-70); 167.1 (C-10); 168.3 (C-11).
MS (ESIþ, CH2Cl2þMeOH): m/z 465.1 [MþNaþ]. HRESIMS
465.1886 (calcd for C25H30O7Na 465.1889). IR (cmꢀ1): 3404;
2931; 1697; 978. [a]2D5 þ13 (c 0.7, CHCl3).
3.3.9. Compound 12
A solution of compound 9(50 mg; 0.11 mmol), 4-bromobenzoic
acid (24 mg; 0.12 mmol), DMAP (2.4 mg; 0.02 mmol), and DCC
(25 mg; 0.12 mmol) in 1 mL of toluene was stirred at room temper-
ature under argon for 48 h. The reaction mixture was filtered and the
solvent was removed under reduced pressure. The crude mixture
was diluted with CH2Cl2 (10 mL). The organic layer was washed
with aqueous 1 M HCl, a saturated solution of NaHCO3, and brine.
The organic layer was dried over MgSO4, filtered, and evaporated
3.3.7. Compound 10
Compound 9 (50 mg; 0.11 mmol), acetyl chloride (9 mL; 0,
12 mmol), and dry pyridine (10 mL; 0.12 mmol) were dis-
solved in 1.6 mL of anhydrous CH2Cl2. The reaction mixture
was stirred at room temperature under argon for 24 h then

D. Fomekong Fotsop et al. / Tetrahedron 64 (2008) 2192e2197
2197
under reduced pressure. The crude mixture was purified by column
chromatography on silica gel (EtOAc/heptane 3:7) to afford com-
1
pound 12 (34 mg, 50%) as a white amorphous solid. H NMR
References and notes
1. Appel, H. H. Scientia (Valparaiso) 1948, 15, 31.
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3. Jansen, B. J. M.; de Groot, A. Nat. Prod. Rep. 1991, 299.
4. Jansen, B. J. M.; de Groot, A. Nat. Prod. Rep. 2004, 449.
(CDCl3, 300 MHz) d: 1.07 (s, 3H, H-15); 1.09 (s, 3H, H-14); 1.15
(s, 3H, H-13); 1.51 (d, J¼9 Hz, 1H, H-5); 1.62 (m, 2H, H-2); 1.83
(2H, H-3); 3.02 (d, J¼5.4 Hz, 1H, H-9); 3.40 (s, 1H, OH); 3.80 (s,
3H, OMe); 4.52 (m, 1H, H-6); 4.72 (dd, J¼3.6, 10.0 Hz, 1H,
H-1); 5.82 (d, J¼15.9 Hz, 1H, H-20); 6.66 (d, J¼5.4 Hz, 1H,
H-12); 6.78 (1H, H-7); 6.81 (d, J¼8.7 Hz, 2H, H-60, H-80); 6.84
(d, J¼15.9 Hz, 1H, H-30); 7.13 (d, J¼8.7 Hz, 2H, H-50, H-90);
7.26 (d, J¼8.7 Hz, 2H, H-400, H-600); 7.46 (d, J¼8.7 Hz, 2H,
H-300, H-700). 13C NMR (CDCl3, 75 MHz) d: 10.9 (C-15); 22.3
(C-14); 24.8 (C-2); 33.7 (C-4); 35.3 (C-13); 40.3 (C-3); 40.3
(C-10); 55.4 (OMe); 56.8 (C-5); 54.1 (C-9); 67.8 (C-6); 80.0
(C-1); 95.2 (C-12); 114.1 (C-60þC-80); 114.2 (C-20); 127.4 (C-
200); 127.6 (C-8); 129.0 (C-40); 129.9 (C-50þC-90); 131.2
(C-400þC-600); 131.5 (C-300þC-700); 136.8 (C-7); 145.4 (C-30);
161.6 (C-70); 164.1 (C-500); 166.1 (C-11); 166.2 (C-10). MS
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647.1318 (calcd for C32H33O8NaBr 647.1256). IR (cmꢀ1):
3325; 2925; 981. [a]2D5 ꢀ223 (c 0.8, CHCl3).
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