Synthesis, cytotoxic activity, and SAR analysis of the derivatives of taxchinin A and brevifoliol

Article abstract of DOI:10.1016/j.bmc.2008.03.041

Twenty-one derivatives of taxchinin A (1) and brevifoliol (2) were synthesized and evaluated for cytotoxicity against human non-small lung cancer (A549) cell line. Nine derivatives showed potent activity with IC₅₀ values from 0.48 to 6.22 μM. 5

Full text of DOI:10.1016/j.bmc.2008.03.041

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 4860–4871
Synthesis, cytotoxic activity, and SAR analysis of the derivatives
of taxchinin A and brevifoliol
Yu Zhao,a Na Guo,a Li-Guang Lou,b Yu-Wen Cong,c Li-Yan Penga and Qin-Shi Zhaoa,*
aState Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany,
Chinese Academy of Sciences, Kunming 650204, People’s Republic of China
bShanghai Institute of Materia Medica, Shanghai Institute for Biological Science, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
cInstitute of Radiation Medicine, Academy of Military Medical Sciences, Beijing 100850, People’s Republic of China
Received 5 February 2008; revised 14 March 2008; accepted 15 March 2008
Available online 20 March 2008
Abstract—Twenty-one derivatives of taxchinin A (1) and brevifoliol (2) were synthesized and evaluated for cytotoxicity against
human non-small lung cancer (A549) cell line. Nine derivatives showed potent activity with IC50 values from 0.48 to 6.22 lM. 5-
Oxo-13-TBDMS-taxchinin A (11) and 5-oxo-13,15-epoxy-13-epi-taxchinin A (15) are the most potent derivatives, with IC50 at
0.48 and 0.75 lM, respectively. The structure–activity relationship (SAR) of these compounds established that exocyclic unsaturated
ketone at ring C is the key structural element for the activity, while the a,b-unsaturated ketone positioned at ring A has no effect for
the activity. The significant cytotoxicity of derivatives 11 and 15 may be due to the conformational change in the taxane rings. The
3D-QSAR study was conducted on this series of compounds, which provided optimal predictive comparative molecular field (CoM-
FA) model with cross-validated r2 (q2) value of 0.64.
ꢀ 2008 Elsevier Ltd. All rights reserved.
1. Introduction
iol from the leaves and stems of T. chinensis and they
were found to be the most abundant taxoids in the
leaves and stem of this plant (Fig. 1).
Paclitaxel, a well-known antitumor drug with novel
mechanism of action, has spurred the isolation of
more than 400 taxoids from plants of genus Taxus,
of which include large number of 11(15 ! 1)-abeo-tax-
oids with 5/7/6 skeleton.1,2 Most of modification and
study of SAR of taxoids were focused on paclitaxel
and its analogs with 6/8/6 skeleton and an oxetane
ring.3 However, the knowledge base on the modifica-
tion and biological activities of taxoids with 5/7/6 skel-
eton still calls for continuing enrichment. Taxchinin A
(1), isolated from Taxus chinensis, was the first natu-
rally occurring taxoid to be correctly assigned as the
A-nortaxane skeleton,4 although brevifoliol (2) was
the first natural taxoid with the A-nortaxane skeleton
to be isolated from the leaves of T. brevifolia, it was
incorrectly assigned to have a taxa-4(20),11-diene sys-
tem.5 We have also isolated taxchinin A and brevifol-
In the previous publication, brevifoliol was reported to
show cytotoxicity against CaCo2, MCF-7, KB-403,
and COLO-320DM cells.6 And a series of brevifoliol
derivatives were prepared, which included the introduc-
tion of acetyl, troc, N-benzoyl-(20R,30S)-30-phenyl iso-
serine, and TES groups at C-5, C-13. However, all of
this analogs showed little bioactivity.7,8 Taxchinin A
was also reported to have some cytotoxicity against
KB cells,9 but no any modification of taxchinin A could
be traced.
OAc
H
OAc
OAc
OAc
BzO
BzO
19
9
18
10
7
6
8
11
C
4
B
2
12
13
3
5
1
A
OH
OH
14
H
HO
HO
15 OAc
20
16HO
Keywords: Derivatives of taxchinin A and brevifoliol; Synthesis;
Cytotoxicity; SAR.
17
HO
1
2
*
Corresponding author. Tel.: +86 871 5223058; fax: +86 871
5215783; e-mail: qinshizhaosp@yahoo.com
Figure 1. Structure of taxchinin A (1) and brevifoliol (2).
0968-0896/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.03.041

Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
4861
Michael reaction acceptors are the functionalities in
which the olefins or acetylenes conjugated to electron-
withdrawing groups. Michael reaction acceptors are
considered as a class of biological activity molecules, di-
rectly or indirectly involved in the life processes, are reg-
ulators in many signaling pathway in cells, and have
played an important role in chemical biology studies.
One Michael acceptor CRA-3316 developed to treat
Chagas’s disease is in clinical trials.10 Another Michael
acceptor AG7088 (Ruprintrivir) has entered phase II
clinical studies with human as a potential nasally deliv-
ered antirhinoviral agent.11–13 Moreover, Michael
acceptor inhibitors based on the structure of AG7088
drew intense attention in the treatment of SARS (severe
acute respiratory syndrome).14 Now Michael acceptors
are of great medical interest and have great potential
for use as drugs.
cancer (A549) cell line. The SAR on these compounds
was discussed and the CoMFA analysis was performed
using the cytotoxic data. The synthetic procedures and
the biological assay results are also provided herein.
2. Results and discussion
2.1. Synthesis
Synthesis of derivatives of taxchinin A and brevifoliol
(3–23) is shown in Schemes 1 and 2. In Scheme 1, oxida-
tion of 1 with pyridinium dichromate (PDC) in CH2Cl2
for 1 h selectively produced the 13-oxo-taxchinin A (3),
while 5,13-dioxo-taxchinin A (4) could be obtained after
24 h. Compound 2 is very similar to 1 except for the ab-
sence of acetoxy group at C-2, however, the oxidation of
2 with PDC in CH2Cl2 is much different from that of 1.
Oxidation of 2 with PDC for 1 h gave 13-oxo-brevifoliol
(5), whereas 5 accompanying 6 and rearranged product
7 were obtained after 24 h. The rearrangement involving
the PDC oxidation of 2 was first reported, and its mech-
anism was difficult to be explained. All attempts to pre-
pare 5,13-dioxo-brevifoliol were unsuccessful.
Because of the novel skeleton and abundance in the
plant, taxchinin A and brevifoliol were then selected as
the precursors for the synthesis of taxoids with a,b-
unsaturated ketone moiety. And these derivatives, as
the Michael reaction acceptors, are proposed to show
bioactivity. Therefore the derivatives of taxchinin A
and brevifoliol, consisting of the various unsaturated ke-
tones at ring A and ring C, were designed and synthe-
To obtain 5-oxo-taxchinin A (13), strategy of selective pro-
tection of OH-13 was employed. Although attempt to pre-
pare 13-TES derivative with chlorotriethylsilane (TESCl)
gave only 5,13-bis (TES)-taxchinin A (8), 13-TBDMS-tax-
sized.
The
total
21
synthetic
compounds,
accompanying the parent compounds 1 and 2, were sub-
jected to a cytotoxic screening of human non-small lung
OAc
OAc
OAc
OAc
BzO
BzO
O
OTES
H
H
O
TESO
OAc
OAc
OAc
HO
O
HO
OAc
8
4
OAc
OAc
BzO
b
a
c
BzO
d
1
OH
OR2
H
H
R1O
OAc
OAc
HO
HO
3
9 R1 = TBDMS, R2 = H
10 R1 = TBDMS, R2 =TBDMS
OAc
OAc
OAc
BzO
HO
BzO
OAc
OAc
BzO
e
f
9
+
O
O
H
H
O
HO
HO
H
TBDMSO
OAc
OAc
OAc
HO
HO
12
11
13
OAc
OAc
OAc
BzO
OAc
OAc
BzO
BzO
b
a
2
+ 5
O
+
OH
H
O
H
O
H
O
CHO
HO
5
HO
7
HO
6
Scheme 1. Reagents and conditions: (a) PDC, CH2Cl2, 1 h; (b) PDC, CH2Cl2, 24 h; (c) TESCl, pyridine; (d) TBDMSCl, imidazole, DMF; (e) PDC,
CH2Cl2; (f) HF-pyridine, pyridine.

4862
Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
OAc
OAc
BzO
OAc
OAc
OAc
OAc
BzO
BzO
b
a
a
1
2
R
b
H
OH
H
O
OAc
H
CHO
O
O
14 R = α-OH
15 R = =O
17
16
OAc
OAc
OAc
OAc
BzO
BzO
BzO
c
+
O
O
O
H
O
H
O
H
O
OAc
OAc
HO
HO
18
19
4
OAc
OAc
OAc
OAc
OAc
BzO
BzO
BzO
c
+
OH
OH
OAc
OH
H
O
H
20
H
O
O
OAc
3
21
HO
b
d, c
OAc
OAc
BzO
BzO
OAc
OAc
BzO
+
O
H
O
H
O
OTES
CHO
H
22
O
18
23
Scheme 2. Reagents and conditions: (a) TsCl, pyridine; (b) PDC, CH2Cl2; (c) NaH, THF; (d) TESCl, pyridine.
chinin A (9) was obtained, along with the byproduct of
5,13-bis (TBDMS)-taxchinin A (10), by treatment with
tert-butylchlorodimethylsilane (TBDMSCl) in imidazole
and N,N-dimethylformamide (DMF). Further oxidation
of 9 with PDC yielded the 5-oxo-13-TBDMS derivative
11 which was treated with the HF-pyridine in pyridine to
produce the desired 5-oxo taxchinin A (13) accompanying
compound 12 (Scheme 1).
2.2. Cytotoxicity and structure–activity relationship
The cytotoxicity of all compounds (1–23) was evaluated
against A549 cell line, and the anticancer drug cisplatin
(DDP) was used as a reference compound. As shown in
Table 1, nine derivatives exhibited remarkable activity
with IC50 values from 0.48 to 6.22 lM. Taxchinin A
and its 13-oxo derivative 3 showed no activity, while
5,13-dioxo derivative 4 and 5-oxo derivative 13 exhib-
ited potent activity with IC50 values of 1.68 and
3.16 lM, respectively. Moreover, 5,13-bis (TES) deriva-
tive 8, 13-TBDMS derivative 9, and 5,13-bis (TBDMS)
13,15-Epoxy-13-epi-brevifoliol (16) synthesized from 2
was reported,9 which inspired us to prepare 5-oxo-
13,15-epoxy-13-epi-taxchinin A (15) and 5-oxo-13,15-
epoxy-13-epi-brevifoliol. Treatment of 1 and 2 with
tosylchloride (TsCl) yielded 14 and 16, respectively. Fur-
ther oxidation of 14 with PDC afforded desired product
15, while oxidation of 16 gave the unexpected derivative
17 rather than 5-oxo-13,15-epoxy-13-epi-brevifoliol
(Scheme 2).
Table 1. Cytotoxicity of taxchinin A, brevifoliol and their derivatives
against A549 cell linea
Compound
IC50 (lM)
Compounds
IC50 (lM)
1
2
60.50
NA
13
14
3.16
NA
0.75
During our study on the chemistry of 11-(15 ! 1)-abeo-
taxanes, we found that the 2-hydroxyl-isopropyl group
at C-1 of 13-oxo-11-(15 ! 1)-abeo-taxanes could be
eliminated with sodium hydride (NaH) in THF, which
was then employed in our experiment to access more
taxoids with unsaturated ketone unit. Reacting 4 with
NaH in THF, the elimination of 2-hydroxyl-isopropyl
group at C-1 and acetoxy group at C-7 occurred, pro-
ducing 18 and 19. Treatment of 3 with NaH in THF
gave 20 and 21, while treating the 5-TES-13-oxo-taxch-
inin A with NaH yielded 22. Further oxidation of 20
produced 18 and 23 (Scheme 2).
3
91.62
1.68
NA
15
16
4
46.47
6.17
2.80
5
17
18
6
6.22
31.62
87.33
12.39
NA
7
19
20
2.48
8
21.52
80.72
17.37
11.27
2.10
9
21
22
10
11
12
0.48
5.89
23
DDP
a NA, not active; IC50 values greater than 100 lM were considered as
inactive and represented as NA.

Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
4863
derivative 10 showed no activity, but 13-TBDMS-5-oxo
derivative 11 exhibited potent activity with IC50 at
0.48 lM. Compound 14, possessing a C-13 (15) tetrahy-
drofuran ring moiety, exhibited no activity, however, its
5-oxo derivative 15 showed potent activity with IC50 of
0.75 lM.
7.6 Hz; in 15 it is 7.1 Hz, which suggested that 11 and 15
might have the similar conformations which are different
from those of the other derivatives.
2.3. CoMFA analysis
In this study, 18 compounds were employed for the
CoMFA analysis. For 3D-QSAR analyses, 13 com-
pounds (unasterisked molecules in Table 3) were se-
lected as training set for model construction, and the
remaining 5 compounds (asterisked molecules in Table
3) as testing set for model validation.
As taxchinin A and its derivative 3, brevifoliol and its
13-oxo derivative 5 were inactive. When the 5-OH of
brevifoliol was oxidized to carbonyl group (6), it was
found to have activity. Moreover, 13,15-epoxy deriva-
tive 16 showed no activity while its oxidized product
17 exhibited marginal activity.
The inhibition constants were expressed in PIC50 values
(PIC50 = ꢀlog[IC50]) and correlated with the steric and
electrostatic fields (CoMFA) of each compound in train-
ing set. The CoMFA results are summarized in Table 4.
The cross-validation with leave-one-out option and the
SAMPLS program was carried out to obtain the opti-
mal number of components to be used in the final anal-
ysis. After the optimal number of components (four)
was determined, a non-cross-validated analysis was per-
Other derivatives of taxchinin A and brevifoliol, such as
5-oxo-6-ene 12, 5,13-dioxo-1,6-diene 18, and 5,13-dioxo-
6-ene 19, showed moderate to good activity, while com-
pounds 7 and 20–23 without the exocyclic unsaturated
ketone at ring C showed no activity.
These results indicated that exocyclic unsaturated ke-
tone at ring C is the key structural element for the activ-
ity, and all derivatives containing this unit presented
potent activity, while the a,b-unsaturated ketone posi-
tioned at ring A has no effect for the activity. Moreover,
introduction of more double bonds in the molecule gave
no remarkable advantage for the activity, and certain
derivative possessing the unsaturated aldehyde group
at ring C showed weak activity.
Table 3. Predicted activities (PA) from CoMFA models compared
with the experimental activities (EA) and the residues (d)
Compound
EA
CoMFA
PA
d
1
4.22
4.04
5.77
5.21
4.50
4.06
4.91
6.32
5.23
5.50
6.12
4.33
5.21
5.55
5.61
4.67
4.76
4.95
4.14
4.09
5.73
4.80
4.53
4.11
4.87
6.33
5.33
5.06
6.11
4.71
5.24
5.63
5.50
4.49
4.69
4.44
0.08
3
ꢀ0.05
0.04
0.41
4
In addition, it should be noticed that 5-oxo-13-TBDMS-
taxchinin A (11) and 5-oxo-13,15-epoxy-13-epi-taxchi-
nin A (15) are the most potent derivatives among this
series of compounds, with IC50 at 0.48 and 0.75 lM,
respectively, while 5-oxo-taxchinin A (13) showed only
six- and four-fold less active than 11 and 15, with IC50
of 3.16 lM. The significant cytotoxicity of the 5-oxo-
13-substituted taxchinin A 11 and 15 may be due to
the conformational change in the taxane rings as re-
flected in certain key J-coupling. The coupling constant
between H-2 and H-3 is an important descriptor of the
shape of the taxoids, which serves as a reporter of the
dihedral angle along the bottom portion of the B
ring.15–17 Among all obtained taxoids (1–23), only com-
pounds 11 and 15 showed similar coupling constant be-
tween H-2 and H-3 (Table 2). In compound 11 the J2–3 is
6a
7
ꢀ0.03
ꢀ0.05
0.04
8
9
11
12
13a
15
16a
17
18
19
20a
22
23a
ꢀ0.01
ꢀ0.10
0.44
0.01
ꢀ0.38
ꢀ0.03
ꢀ0.08
0.11
0.18
0.07
0.51
a Compounds of the testing set.
Table 4. Summary of results from the CoMFA analyses based on the
training set and all 18 compounds
Table 2. Comparision of the coupling constants between H-2 and H-3
of 11 and 15 in acetone-d6 with those of other obtained taxoids
CoMFA
Compound
J2–3 (Hz)
Compounds
J2–3 (Hz)
Analyses
based on
training set
Analyses
based on all
18 compounds
1
2
9.0
br d
9.2
8.6
br s
8.7
s
13
14
15
16
17
18
19
20
21
22
23
8.2
8.4
7.1
br s
9.5
s
3
PLS statistics
4
q2 (CV correlation coefficient)
N (number of components)
S (stand error of prediction)
r2 (correlation coefficient)
F (F-ratio)
0.642
4
0.540
4
5
6
0.558
0.993
272.663
0.529
0.969
101.627
7
8.2
br s
s
8
9.1
br s
br s
7.6
8.1
9
Field distribution (%)
Steric
Electrostatic
10
11
12
s
39.5
60.5
42.6
57.4
s

4864
Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
A
B
7.00
6.50
6.00
5.50
5.00
4.50
4.00
3.50
7.00
6.50
6.00
5.50
5.00
4.50
4.00
3.50
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
EA
EA
Figure 2. (A) Predicted activities (PA) by CoMFA models versus experimental activities (EA) for the compounds in training set and test set.
,
compounds of the training set; , compounds of the test set. (B) PA by CoMFA models versus EA. The plot report data obtained via a CoMFA
model built using all 18 compounds in Table 3.
Figure 3. (A) CoMFA steric contour plot; green contours indicate regions where bulky groups increase activity, whereas yellow contours indicate
regions where bulky groups decrease activity. (B) CoMFA electrostatic contour plots; blue contours indicate regions where positive charge increases
activity, whereas red contours indicate regions where negative charge increases activity.
formed. The q2 (cross-validated r2 of 0.64), SPRESS
(cross-validated standard error of prediction of 0.56),
r2 (non-cross-validated r2 of 0.99), and F values
(272.66) were computed according to the definitions in
SYBYL. These statistical indexes are reasonably high,
indicating that the CoMFA model has a strong predic-
tive ability. The plots of the experimental results versus
predicted values of 13 studied compounds are shown in
Figure 2A. The relative contribution to this CoMFA
model was 39.5% for the steric field, 60.5% for electro-
static field.
electrostatic nature in the structural features of the dif-
ferent molecules contained in the training set lead to in-
crease or decrease in the activity. The CoMFA steric
field is presented as contour plots in Figure 3A. To aid
in visualization, compound 11 is displayed in the map
as reference structure. A huge sterically favorable region
(Fig. 3A, green contour) is located near the atoms C-13,
C-14, and C-2, suggesting that bulky groups in this area
would increase the cytotoxicity. The yellow region indi-
cates that the bulky substitute near the atoms C-4 and
C-5 is not favorable to the activity. CoMFA electro-
static contour map is shown in Figure 3B. To aid in
visualization, compound 15 is displayed in the map as
reference structure. There is a big blue polyhedron near
the atoms C-14, C-1, C-2, indicating that more positive
charges in this region should play a favorable role in
improving cytotoxicity. There are two small red polyhe-
dra surrounding atom C-5, suggesting that negatively
charged substituents in this area lead to an increase of
cytotoxicity.
To evaluate the predictive ability of this model, we sub-
sequently calculated the PIC50 values for the five com-
pounds in the test set. As it can be seen in Table 3 and
Figure 2A, the calculated values using the constructed
CoMFA model are in good agreement with experimen-
tal data, and the model exhibits a good predictive ability
(r2 = 0.61).
To evaluate whether the results are biased toward the se-
lected training sets, we have also performed additional
CoMFA studies in which all 18 compounds were in-
cluded in analysis. The resulting cross-validated r2 is
0.54, with similar relative contributions of the steric,
electrostatic fields (Table 4 and Fig. 2B).
3. Conclusion
Twenty-one derivatives of taxchinin A and brevifoliol
were synthesized and subjected to the screening of
A549 tumor cell line. Nine derivatives 4, 6, 11–13, 15,
and 17–19 exhibited remarkable activity with IC50 val-
ues from 0.48 to 6.22 lM. The observed SAR of these
The CoMFA result is usually represented as 3D contour
maps. It shows regions where variations of steric and

Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
4865
derivatives is very interesting which shows that exocyclic
unsaturated ketone at ring C is the key structural ele-
ment for the activity, while the a,b-unsaturated ketone
positioned at ring A has no effect for the activity. More-
over, 5-oxo-13-substituted taxchinin A 11 and 15 are the
most potent derivatives among this series of compounds
with IC50 of 0.48 and 0.75 lM, respectively, which may
be due to the conformational change in the taxane rings,
as reflected in the key J-coupling between H-2 and H-3.
Further investigation on the SAR utilizing a CoMFA
method was carried out. The resulting 3D-QSAR model
provides an invaluable tool to design more cytotoxic
compounds. With the employment of all of these results,
further design, synthesis, and cytotoxic evaluation are
ongoing in our laboratory and the results will be re-
ported in due course.
6.5:3.5) to afford 3 (438 mg, 87.8%) as white amorphous
18
D
powder: ½aꢁ 55.8 (c 0.71, CH3OH); UV (CH3OH) kmax
(loge) 233.8 (4.25) nm; IR (KBr) mmax 3413, 2954, 2925,
1744, 1731, 1696, 1453, 1374, 1240, 1113, 1033,
1
719 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 6.05 (1H,
d, J = 9.2 Hz, H-2b), 2.93 (1H, d, J = 9.2 Hz, H-3a),
4.65 (1H, br s, H-5b), 4.82 (1H, t, J = 9.0 Hz, H-7a),
5.08 (1H, d, J = 3.1 Hz, H-9b), 6.08 (1H, d, J = 3.1 Hz,
H-10a), 1.13 (3H, s, H-16), 0.74 (3H, s, H-17), 2.09
(3H, s, H-18), 1.93 (3H, s, H-19), 4.85 (1H, s, H-20a),
5.49 (1H, s, H-20b), 7.97 (2H, d, J = 7.3Hz, Ho-Ph),
7.45 (2H, t, J = 7.6 Hz, Hm-Ph), 7.58 (1H, t, J = 6.9 Hz,
H
p-Ph), 2.04 (3H, s, O2CCH3), 1.89 (3H, s, O2CCH3),
1.86 (3H, s, O2CCH3); 13C NMR (acetone-d6,
100 MHz) d 65.6 (C, C-1), 69.3 (CH, C-2), 46.1 (CH,
C-3), 148.3 (C, C-4), 65.6 (CH, C-5), 36.6 (CH2, C-6),
71.7 (CH, C-7), 44.3 (C, C-8), 75.3 (CH, C-9), 71.4
(CH, C-10), 162.2 (C, C-11), 148.0 (C, C-12), 207.4 (C,
C-13), 45.0 (CH2, C-14), 75.9 (C, C-15), 27.1 (CH3,C-
16), 28.9 (CH3,C-17), 9.4 (CH3, C-18), 15.2 (CH3, C-
19), 114.3 (CH2,C-20), 166.6 (C, O2CC6H5), 131.3 (C,
i-O2CC6H5), 130.4 (CH2, o-O2CC6H5), 129.2 (CH2, m-
O2CC6H5), 133.7 (CH2, p-O2CC6H5), 170.5 (C,
O2CCH3), 170.4 (C, O2CCH3), 170.2 (C, O2CCH3),
21.6 (CH3, O2CCH3), 20.9 (CH3, O2CCH3), 20.7
(CH3, O2CCH3); HRESIMS m/z 635.2466 [M+Na+]
(calcd for C33H40O11Na, 635.2468).
4. Experimental
4.1. General experimental procedures
1H and 13C NMR experiments were performed on a
Bruker AM-400 spectrometer at ambient temperature.
2D NMR spectra were recorded on Bruker DRX-500
NMR instrument. IR spectra were recorded on a Bio-
Rad FTS-135 spectrometer with KBr pellets. UV spec-
tra were obtained on a UV 2401 PC spectrometer.
ESIMS and HRESIMS were taken on a VG Auto
Spec-3000 or on a Finnigan MAT 90 instrument. Melt-
ing points were determined (uncorrected) on an XRC-1
micro melting point apparatus. Optical rotations were
measured with a Horiba SEPA-300 polarimeter. Col-
umn chromatography was performed on silica gel
(Qingdao Marine Chemical Inc., China).
4.3.2. 5,13-Dioxotaxchinin A (4). A solution of taxchinin
A 1 (500 mg, 0.81 mmol) in dichloromethane (40 ml) was
treated with pyridinium dichromate (PDC, 3.68 g,
9.72 mmol) and stirred at room temperature for 24 h.
The reaction mixture was filtered and purified through
the column chromatography (petroleum/ethyl acetate,
7.5:2.5) to afford 4 (382 mg, 77.0%) as white amorphous
18
D
powder: ½aꢁ 151:9ðc 0:77; CH3OHÞ; UV (CH3OH) kmax
4.2. In vitro cytotoxicity assay
(loge) 233.8 (4.25) nm; IR (KBr) mmax 3523, 2943, 2906,
1745, 1707, 1453, 1372, 1238, 1107, 1049, 1028,
1
Exponentially growing human non-small lung cancer
cells (A459, obtained from ATCC, 4 · 104/mL) were,
respectively, made into the 96-well microplate. Cultures
were pre-incubated for 72 h in 37 ꢁC and 5% CO2 incu-
bator. After that, 10 lL controlled or test solution of
compounds (100, 10, 1, and 0.1 lM) was put into each
well and the plate was incubated for an additional
72 h. At the end of exposure, the cells were fixed by
the addition of 50 lL of cold 50% trichloroacetic acid
(TCA) at 4 ꢁC for one hour. After washing with tap
water, cells of each well were stained with a 0.4%
50 lL SRB (sulforhodamin B) solution in 1% acetic acid
for 30 min. Then cultures were rinsed with 1% acetic
acid. At last, 10 mM unbuffered Tris solution (150 lL)
was added to each well. The OD was then read on a
plate reader at a wavelength of 570 nm.
715 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 6.02 (1H,
d, J = 8.6 Hz, H-2b), 3.26 (1H, d, J = 8.6 Hz, H-3a),
5.17 (1H, m, H-7a), 5.27 (1H, br s, H-9b), 6.22 (1H, br
s, H-10a), 1.21 (3H, s, H-16), 0.82 (3H, s, H-17), 2.08
(3H, s, H-18), 1.90 (3H, s, H-19), 5.30 (1H, s, H-20a),
5.87 (1H, s, H-20b), 8.02 (2H, d, J = 7.6 Hz, Ho-Ph), 7.49
(2H, t, J = 7.5 Hz, Hm-Ph), 7.62 (1H, t, J = 7.4 Hz, Hp-
Ph), 2.00 (3H, s, O2CCH3), 1.95 (3H, s, O2CCH3), 1.92
(3H, s, O2CCH3); 13C NMR (acetone-d6, 100 MHz) d
62.5 (C, C-1), 69.6 (CH, C-2), 43.4 (CH, C-3), 144.8 (C,
C-4), 197.9 (C, C-5), 39.2 (CH2, C-6), 71.5 (CH, C-7),
43.9 (C, C-8), 75.1 (CH, C-9), 70.0 (CH, C-10), 162.0
(C, C-11), 147.9 (C, C-12), 206.5 (C, C-13), 44.8 (CH2,
C-14), 75.9 (C, C-15), 27.6 (CH3, C-16), 29.2 (CH3, C-
17), 9.5 (CH3, C-18), 13.6 (CH3, C-19), 128.1 (CH2, C-
20), 166.7 (C, O2CC6H5), 131.3 (C, i-O2CC6H5), 130.5
(d, o-O2CC6H5), 129.3 (CH, m-O2CC6H5), 133.8 (CH,
p-O2CC6H5), 170.3 (C, O2CCH3), 170.2 (C, O2CCH3),
21.9 (CH3, O2CCH3), 20.8 (CH3, O2CCH3), 20.7 (CH3,
O2CCH3); HRESIMS m/z 633.2315 [M+Na+] (calcd for
C33H38O11Na, 633.2311).
4.3. Synthesis
4.3.1. 13-Oxo-taxchinin A (3). A solution of taxchinin A
1 (500 mg, 0.81 mmol) in dichloromethane (40 mL) was
treated with pyridinium dichromate (PDC, 3.68 g,
9.72 mmol) and stirred at room temperature for 1 h.
The reaction mixture was filtered and purified through
the column chromatography (petroleum/ethyl acetate,
4.3.3. 13-Oxo-brevifoliol (5). The title compound was
synthesized from 2 in 85.1% yield by the same procedure
as that for 3: white amorphous powder, (petroleum/

4866
Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
18
ethyl acetate, 7.5:2.5); ½aꢁ 29:7ðc 0:90; MeOHÞ; UV
J = 10.1, 5.9 Hz, H-7a), 5.26 (1H, d, J = 4.5 Hz, H-9b),
6.17 (1H, d, J = 4.5 Hz, H-10a), 0.82 (3H, s, H-16),
1.14 (3H, s, H-17), 1.82 (3H, s, H-18), 1.62 (3H, s, H-
19), 9.43 (1H, s, H-20), 8.01 (2H, d, J = 7.2 Hz, Ho-Ph),
7.47 (2H, t, J = 7.7 Hz, Hm-Ph), 7.60 (1H, t, J = 7.4 Hz,
D
(CH3OH) kmax (loge) 232.2 (4.29) nm; IR (KBr) mmax
3447, 2976, 2937, 1730, 1712, 1630, 1451, 1372, 1260,
1108, 1067, 1028, 748 cmꢀ1 1H NMR (acetone-d6,
;
400 MHz) d 2.86 (1H, br s, H-3a), 4.31 (1H, br s, H-
5b), 5.65 (1H, dd,J = 11.4, 5.1 Hz, H-7a), 6.17 (1H, d,
J = 3.3 Hz, H-9b), 6.69 (1H, d, J = 3.3 Hz, H-10a),
1.19 (3H, s, H-16), 1.36 (3H, s, H-17), 1.89 (3H, s, H-
18), 0.87 (3H, s, H-19), 4.83 (1H, s, H-20a), 5.11 (1H,
s, H-20b), 7.98 (2H, br s, Ho-Ph), 7.48 (2H, t, 7.7, Hm-
Ph), 7.62 (1H, t, 7.2, Hp-Ph), 2.00 (3H, s, O2CCH3) 1.99
(3H, s, O2CCH3); 13C NMR (acetone-d6, 100 MHz) d
59.8 (C, C-1), 28.1 (CH2, C-2), 37.7 (CH, C-3), 151.9
(C, C-4), 72.5 (CH, C-5), 37.2 (CH2, C-6), 70.4 (CH,
C-7), 46.0 (C, C-8), 77.9 (CH, C-9), 71.3 (CH, C-10),
166.5 (C, C-11), 146.9 (C, C-12), 209.7 (C, C-13), 50.3
(CH2, C-14), 75.6 (C, C-15), 27.0 (CH3, C-16), 22.9
(CH3, C-17), 9.1 (CH3, C-18), 13.1 (CH3, C-19), 110.4
(CH2, C-20), 165.0 (C, O2CC6H5), 131.3 (C, i-
O2CC6H5), 130.4 (CH, o-O2CC6H5), 129.6 (CH, m-
O2CC6H5), 134.3 (CH, p-O2CC6H5), 170.3 (C,
O2CCH3), 170.0 (C, O2CCH3), 21.3 (CH3, O2CCH3),
20.9 (CH3, O2CCH3); HRESIMS m/z 577.2429
[M+Na+] (calcd for C31H38O9Na, 577.2413).
H
p-Ph), 1.94 (3H, s, O2CCH3), 1.93 (3H, s, O2CCH3);
13C NMR (acetone-d6, 100 MHz) d 58.9 (C, C-1), 28.5
(CH2, C-2), 35.2 (CH2, C-3), 145.4 (C, C-4), 148.5
(CH, C-5), 27.2 (CH2, C-6), 72.0 (CH, C-7), 44.2 (C,
C-8), 74.6 (CH, C-9), 72.1 (CH, C-10), 166.8 (C, C-
11), 146.3 (C, C-12), 208.0 (C, C-13), 48.7 (CH2, C-
14), 76.0 (C, C-15), 26.3 (CH3, C-16), 27.8 (CH3, C-
17), 9.43 (CH3, C-18), 13.6 (CH3, C-19), 194.5 (CH,
C-20), 164.8 (C, O2CC6H5), 131.8 (C, i-O2CC6H5),
130.5 (d, o-O2CC6H5), 129.2 (CH, m-O2CC6H5), 133.5
(CH, p-O2CC6H5), 170.7 (C, O2CCH3), 170.4 (C,
O2CCH3), 21.0 (CH3, O2CCH3), 20.8 (CH3, O2CCH3);
HRESIMS m/z 575.2251 [M+Na+] (calcd for
C31H36O9Na, 575.2257).
4.3.5. 5,13-Bis (TES) taxchinin A (8). Chlorotriethylsi-
lane (22.06 lL, 0.13 mmol) was added to a solution of
1 (40 mg, 0.065 mmol) in dry pyridine (3 ml). The reac-
tion mixture was stirred at room temperature and mon-
itored by TLC until all starting material was consumed.
The reaction mixture was then diluted with ethyl acetate
and washed with diluted hydrochloric acid and water.
The organic layer was dried (Na2SO4) and evaporated.
The residue was purified by column chromatography
4.3.4. Oxidation of 2 to compounds 5, 6 and 7. Brevifoliol
(2) was treated with pyridinium dichromate (PDC) by
the same procedure as that for 4 to produce the mixture
which was purified through the column chromatography
(petroleum/ethyl acetate, 8:2), affording 5 (8.7%), 6
(18.9%), and 7 (24.4%).
(chloroform/ethyl acetate, 9.5:0.5) to give 8 (40.3 mg,
18
D
73.4%) as colorless oil: ½aꢁ ꢀ 8:8ðc 0:82; CH3OHÞ; UV
(CH3OH) kmax (loge) 201.8 (4.24); IR (KBr) mmax 3572,
2954, 2924, 1739, 1655, 1456, 1372, 1269, 1248, 1091,
4.3.4.1. Compound 6. White amorphous powder:
16
½aꢁ 9:4ðc 0:66; CH3OHÞ; UV (CH3OH) kmax (loge)
1069, 1029, 744, 712 cmꢀ1 1H NMR (acetone-d6,
;
D
201.0 (4.25) nm; IR (KBr) mmax 3420, 2956, 2938, 1757,
1730, 1719, 1641, 1452, 1372, 1239, 1219, 1110,
400 MHz) d 6.03 (1H, d, J = 9.1 Hz, H-2b), 3.58 (1H,
d, J = 9.1 Hz, H-3a), 4.53 (1H, br s, H-5b), 5.63 (1H,
m, H-7a), 6.12 (1H, d, J = 10.4 Hz, H-9b), 6.57 (1H,
d, J = 10.4 Hz, H-10a), 4.63 (1H, m, H-13b), 1.24 (3H,
s, H-16), 1.28 (3H, s, H-17), 2.04 (3H, s, H-18), 1.21
(3H, s, H-19), 4.53 (1H, s, H-20a), 5.12 (1H, s, H-20b),
7.90 (2H, d, J = 6.8 Hz, Ho-Ph), 7.48 (2H, t, J = 7.5 Hz,
1
1025,738, 709 cmꢀ1; H NMR (acetone-d6, 400 MHz) d
2.97 (1H, d, J = 8.7 Hz, H-3a), 6.04 (1H, d,
J = 10.5 Hz, H-6), 7.49 (1H, overlap), 5.97 (1H, d,
J = 10.1 Hz, H-9b), 6.31 (1H, d, J = 10.1 Hz, H-10a),
1.12 (3H, s, H-16), 1.29 (3H, s, H-17), 1.72 (3H, s, H-
18), 1.50 (3H, s, H-19), 5.46 (1H, s, H-20a), 6.06 (1H,
s, H-20b), 8.03 (2H, d, J = 6.7 Hz, Ho-Ph), 7.49 (2H,
overlap, Hm-Ph), 7.63 (1H, t, J = 7.4, Hp-Ph), 2.08 (3H,
s, O2CCH3); 13C NMR (acetone-d6, 100 MHz) d 59.3
(C, C-1), 28.2 (CH2, C-2), 46.5 (CH, C-3), 147.2 (C,
C-4), 189.0 (C, C-5), 129.8 (CH, C-6), 155.3 (CH, C-
7), 44.9 (C, C-8), 76.1 (CH, C-9), 70.7 (CH, C-10),
165.8 (C, C-11), 146.8 (C, C-12), 206.7 (C, C-13), 50.6
(CH2, C-14), 76.3 (C, C-15), 27.6 (CH3, C-16), 27.1
(CH3, C-17), 8.86 (CH3, C-18), 20.6 (CH3, C-19),
118.4 (CH2, C-20), 164.7 (C, O2CC6H5), 130.7 (C, i-
O2CC6H5), 130.6 (CH, o-O2CC6H5), 129.4 (CH, m-
O2CC6H5), 134.2 (CH, p-O2CC6H5), 170.0 (C,
O2CCH3), 21.6 (CH3, O2CCH3); HRESIMS m/z
515.2036 [M+Na+] (calcd for C29H32O7Na, 515.2045).
H
m-Ph), 7.61 (1H, t, J = 7.5 Hz, Hp-Ph), 2.04 (3H, s,
O2CCH3), 2.03 (3H, s, O2CCH3), 2.01 (3H, s,
O2CCH3), 0.68 [12H, J = 7.9 Hz, 2Si(CH2CH3)3], 0.99
[18H, J = 7.9 Hz, 2Si(CH2CH3)3]; 13C NMR (acetone-
d6, 100 MHz) d 68.1 (C, C-1), 68.7 (CH, C-2), 42.6
(CH, C-3), 146.6 (C, C-4), 75.4 (CH, C-5), 39.7 (CH2,
C-6), 69.8 (CH, C-7), 45.8 (C, C-8), 77.1 (CH, C-9),
70.2 (CH, C-10), 133.3 (C, C-11), 153.0 (C, C-12), 77.6
(CH, C-13), 42.1 (CH2, C-14), 76.1 (C, C-15), 26.9
(CH3, C-16), 28.5 (CH3, C-17), 12.3 (CH3, C-18), 14.1
(CH3, C-19), 111.2 (CH2, C-20), 164.9 (C, O2CC6H5),
130.8 (C, i-O2CC6H5), 130.5 (CH, o-O2CC6H5), 129.4
(CH, m-O2CC6H5), 134.0 (CH, p-O2CC6H5), 171.7 (C,
O2CCH3), 170.1 (C, O2CCH3), 169.7 (C, O2CCH3),
20.8 (CH3, O2CCH3), 21.7 (CH3, O2CCH3), 21.4
(CH3, O2CCH3), 5.32 (CH2, SiCH2), 5.13 (CH2, SiCH2),
7.24 (CH3, SiCH2CH3), 7.18 (CH3, SiCH2CH3); HRE-
SIMS m/z 865.4500 [M+Na+] (calcd for C49H70O11Na-
Si2, 865.4354).
4.3.4.2. Compound 7. Yellow amorphous powder:
18
½aꢁ 86:3ðc 0:89; CH3OHÞ; UV (CH3OH) kmax (loge)
D
231.0 (4.28) nm; IR (KBr) mmax 3446, 2973, 2927, 1744,
1725, 1709, 1636, 1585, 1451, 1371, 1245, 1103, 1027,
1
712 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 2.65 (1H,
4.3.6. 13-TBDMS taxchinin A (9) and 5,13-bis (TBDMS)
taxchinin A (10). Compound 1 (400 mg, 0.65 mmol) was
s, H-3a), 6.88 (1H, d, J = 5.8 Hz, H-5), 4.91 (1H, dd,

Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
4867
dissolved in N,N-dimethylformamide (3 mL). To this
solution was added tert-butylchlorodimethylsilane
(589.13 mg, 2.55 mmol) and imidazole (89.6 mg,
1.30 mmol). The reaction mixture was stirred for 5 h at
room temperature when all starting material was con-
sumed. The mixture was diluted with ethyl acetate and
washed with water and brine. The organic layer was
then dried (Na2SO4) and concentrated. The residue
was purified by column chromatography (petroleum/
ethyl acetate, 9:1) to give 9 (110.9 mg, 23%) and10
(120.0 mg, 22%).
13.5(CH3, C-18), 15.1 (CH3, C-19), 113.8 (CH2, C-20),
166.0 (C, O2CC6H5), 131.3 (C, i-O2CC6H5), 130.4
(CH, o-O2CC6H5), 129.3 (CH, m-O2CC6H5), 133.7
(CH, p-O2CC6H5), 171.7 (C, O2CCH3), 170.4 (C,
O2CCH3), 170.0 (C, O2CCH3), 22.0 (CH3, O2CCH3),
20.9 (CH3, O2CCH3), 20.7 (CH3, O2CCH3), ꢀ4.6
(CH3, SiCH3), ꢀ4.5 (CH3, SiCH3), ꢀ4.0 [CH3,
Si(CH3)2C(CH3)3], ꢀ3.8 [CH3, Si(CH3)2C(CH3)3];
HRESIMS m/z 865.4499 [M+Na+] (calcd for
C45H70O11NaSi2, 865.4354).
4.3.7. 5-Oxo-13-TBDMS taxchinin A (11). The title
compound was synthesized from 9 in 88% yield by the
same procedure as that for 3: white amorphous powder,
4.3.6.1. Compound 9. White amorphous powder:
18
½aꢁ 5:7ðc 0:84; CH3OHÞ; UV (CH3OH) kmax (loge)
D
18
201.6 (4.31) nm; IR (KBr) mmax 3459, 2955, 2930, 1739,
1645, 1370, 1247, 1161, 1104, 1066, 1020, 780,
(petroleum/ethyl acetate, 9:1); ½aꢁ 71:2ðc 0:77; CH3OHÞ;
D
UV (MeOH) kmax (loge) 201.6 (4.31) nm; IR (KBr) mmax
3466, 2955, 2930, 1748, 1602, 1365, 1240, 1088, 1027,
1
712 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 5.98 (1H,
1
br s, H-2b), 3.24 (1H, br s, H-3a), 4.20 (1H, m, H-5b),
5.49 (1H, br s, H-7a), 6.09 (1H, br s, H-9b), 6.56 (1H,
br s, H-10a), 4.67 (1H, br s, H-13b), 1.19 (3H, s, H-
16), 1.28 (3H, s, H-17), 2.05 (3H, s, H-18), 1.14 (3H, s,
H-19), 4.48 (1H, s, H-20a), 5.06 (1H, s, H-20b), 7.90
(2H, d, J = 7.0 Hz, Ho-Ph), 7.49 (2H, t, J = 7.6 Hz, Hm-
Ph), 7.61 (1H, t, J = 7.4 Hz, Hp-Ph), 2.08 (3H, s,
O2CCH3), 2.04 (3H, s, O2CCH3), 2.03 (3H, s,
O2CCH3), 0.16 (6H, s, SiCH3), 0.95 (9H, s,
Si(CH3)2C(CH3)3); 13C NMR (acetone-d6, 100 MHz) d
69.9 (C, C-1), 65.8 (CH, C-2), 45.5 (CH, C-3), 147.1
(C, C-4), 71.6 (CH, C-5), 36.7 (CH2, C-6), 70.9 (CH,
C-7), 44.2 (C, C-8), 75.1 (CH, C-9), 71.0 (CH, C-10),
132.3 (C, C-11), 153.6 (C, C-12), 78.6 (CH, C-13), 42.3
(CH2, C-14), 74.5 (C, C-15), 26.2 (CH3, C-16), 28.2
(CH3, C-17), 13.5 (CH3, C-18), 14.1 (CH3, C-19),
113.1 (CH2, C-20), 166.0 (C, O2CC6H5), 131.3 (C, i-
O2CC6H5), 130.4 (CH, o-O2CC6H5), 129.6 (CH, m-
O2CC6H5), 133.8 (CH, p-O2CC6H5), 170.6 (C,
O2CCH3), 170.4 (C, O2CCH3), 170.0 (C, O2CCH3),
21.7 (CH3, O2CCH3), 20.9 (CH3, O2CCH3), 20.7
(CH3, O2CCH3), ꢀ4.6 (CH3, SiCH3), ꢀ4.0 [CH3,
Si(CH3)2C(CH3)3]; HRESIMS m/z 751.3477 [M+Na+]
(calcd for C39H56O11NaSi, 751.3489).
776, 713 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 5.89
(1H, d, J = 7.6 Hz, H-2b), 3.40 (1H, d, J = 7.6 Hz, H-
3a), 5.10 (1H, m, H-7a), 5.19 (1H, br s, H-9b), 6.15
(1H, br s, H-10a), 4.75 (1H, t, J = 6.7 Hz, H-13b), 1.19
(3H, s, H-16), 1.28 (3H, s, H-17), 2.08 (3H, s, H-18),
0.97 (3H, s, H-19), 5.13 (1H, s, H-20a), 5.85 (1H, s, H-
20b), 8.01 (2H, d, J = 7.5 Hz, Ho-Ph), 7.49 (2H, t,
J = 7.7 Hz, Hm-Ph), 7.61 (1H, t, J = 7.4 Hz, Hp-Ph), 1.99
(3H, s, O2CCH3), 1.94 (3H, s, O2CCH3), 1.90 (3H, s,
O2CCH3), 0.17 (6H, s, SiCH3), 0.94 (9H, s,
Si(CH3)2C(CH3)3); 13C NMR (acetone-d6, 100 MHz) d
66.4 (C, C-1), 70.0 (CH, C-2), 42.8 (CH, C-3), 145.6
(C, C-4), 198.0 (C, C-5), 39.2 (CH2, C-6), 71.2 (CH,
C-7), 43.8 (C, C-8), 74.7 (CH, C-9), 70.9 (CH, C-10),
132.4 (C, C-11), 151.8 (C, C-12), 78.9 (CH, C-13), 42.1
(CH2, C-14), 75.5 (C, C-15), 26.2 (CH3, C-16), 28.5
(CH3, C-17), 13.5 (CH3, C-18), 18.5 (CH3, C-19),
126.5 (CH2, C-20), 166.1 (C, O2CC6H5), 131.3 (C, i-
O2CC6H5), 130.5 (CH, o-O2CC6H5), 129.3 (CH, m-
O2CC6H5), 133.7 (CH, p-O2CC6H5), 170.3 (C,
O2CCH3), 170.0 (C, O2CCH3), 170.0 (C, O2CCH3),
22.0 (C, O2CCH3), 20.9 (C, O2CCH3), 20.8 (C,
O2CCH3), ꢀ4.6 (CH3, SiCH3), ꢀ4.0 (CH3,
Si(CH3)2C(CH3)3); HRESIMS m/z 749.3351 [M+Na+]
(calcd for C39H54O11NaSi, 749.3333).
4.3.6.2. Compound 10. White amorphous powder:
18
½aꢁ 9:3ðc 0:97; MeOHÞ; UV (CH3OH) kmax (loge)
4.3.8. Conversion of compound 11 to 12 and 13. A solu-
tion of 11 (60 mg, 0.083 mmol) in tetrahydrofuran was
treated with a 70% solution of hydrogen fluoride in pyr-
idine (0.46 mL) and stirred for 2 h at room temperature.
The reaction mixture was diluted with ethyl acetate and
the reaction was quenched with aqueous sodium bicar-
bonate (10 mL). The organic layer was separated,
washed with aqueous copper(II) sulfate and brine, dried
(Na2SO4), and concentrated. The residue was purified
by column chromatography (petroleum/ethyl acetate,
8:2) to give 12 (16.3 mg, 32%) and 13 (30.0 mg, 45.6%).
D
230.0 (4.27) nm; IR (KBr) mmax 3440, 2956, 2931, 1740,
1
1645, 1370,1246, 1091, 1066, 1030, 777, 711 cmꢀ1; H
NMR (acetone-d6, 400 MHz) d 5.95 (1H, br s H-2b),
3.27 (1H, br s, H-3a), 4.31 (1H, br s, H-5b), 5.49 (1H,
br s, H-7a), 6.08 (1H, br s, H-9b), 6.56 (1H, br s, H-
10a), 4.68 (1H, t, 6.8, H-13b), 1.19 (3H, s, H-16), 1.28
(3H, s, H-17), 2.08 (3H, s, H-18), 1.14 (3H, s, H-19),
4.57 (1H, s, H-20a), 5.13 (1H, s, H-20b), 7.99 (2H, d,
J = 6.9 Hz, Ho-Ph), 7.49 (2H, t, J = 7.6 Hz, Hm-Ph), 7.61
(1H, t, J = 7.4 Hz, Hp-Ph), 1.95 (3H, s, O2CCH3), 1.92
(3H, s, O2CCH3), 1.88 (3H, s, O2CCH3), 0.16 (6H, s,
SiCH3), 0.11 (6H, s, SiCH3), 0.95 (9H, s,
Si(CH3)2C(CH3)3), 0.92 (9H, s, Si(CH3)2C(CH3)3); 13C
NMR (acetone-d6, 100 MHz) d 69.9 (C, C-1), 67.1
(CH, C-2), 45.1 (CH, C-3), 147.8 (C, C-4), 71.4 (CH,
C-5), 37.9 (CH2, C-6), 70.9 (CH, C-7), 44.1 (C, C-8),
74.9 (CH, C-9), 71.1 (CH, C-10), 132.1 (C, C-11),
152.1 (C, C-12), 78.4 (CH, C-13), 42.3 (CH2, C-14),
75.7 (C, C-15), 26.2 (CH3, C-16), 28.2 (CH3, C-17),
18
4.3.8.1. Compound 12. Yellow oil: ½aꢁ 86:3ðc 0:89;
D
CH3OHÞ; UV (CH3OH) kmax (loge) 201.2 (4.25) nm;
IR (KBr) mmax 3443, 2956, 2925, 1744, 1603, 1464,
1
1375, 1241, 1068, 1027, 748, 713 cmꢀ1; H NMR (ace-
tone-d6, 400 MHz) d 5.90 (1H, d, J = 8.1 Hz, H-2b),
3.46 (1H, d, J = 8.1 Hz, H-3a), 5.28 (1H, br s, H-7a),
5.28 (1H, br s, H-9b), 6.17 (1H, br s, H-10a), 4.58
(1H, m, H-13b), 1.17 (3H, s, H-16), 1.28 (3H, s, H-17),

4868
Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
2.08 (3H, s, H-18), 0.93 (3H, s, H-19), 5.17 (1H, s, H-
20a), 5.85 (1H, s, H-20b), 8.01 (2H, d, J = 7.8 Hz, Ho-
Ph), 7.49 (2H, t, J = 7.7 Hz, Hm-Ph), 7.61 (1H, t,
J = 7.4 Hz, Hp-Ph), 1.98 (3H, s, O2CCH3), 1.93 (3H, s,
O2CCH3), 1.89 (3H, s, O2CCH3); 13C NMR (acetone-
d6, 100 MHz) d 65.9 (C, C-1), 70.0 (C, C-2), 42.6 (CH,
C-3), 145.4 (C, C-4), 198.1 (C, C-5), 37.7 (CH2, C-6),
71.3 (CH, C-7), 43.7 (C, C-8), 74.9 (CH, C-9), 70.9
(CH, C-10), 134.1 (C, C-11), 153.0 (C, C-12), 77.7 (C,
C-13), 42.0 (C, C-14), 75.7 (C, C-15), 27.7 (CH3, C-
16), 28.3 (CH3, C-17), 12.0 (CH3, C-18), 14.3 (CH3, C-
19), 127.1 (CH2, C-20), 166.0 (C, O2CC6H5), 131.2 (C,
i-O2CC6H5), 130.5 (CH, o-O2CC6H5), 129.3 (CH, m-
O2CC6H5), 133.8 (CH, p-O2CC6H5), 170.3 (C,
O2CCH3), 170.2 (C, O2CCH3), 170.2 (C, O2CCH3),
22.0 (CH3, O2CCH3), 20.8 (CH3, O2CCH3), 20.0
(CH3, O2CCH3); HRESIMS m/z 635.2466 [M+Na+]
(calcd for C33H40O11Na, 635.2468).
(1H, t, J = 9.1 Hz, H-7a), 4.99 (1H, d, J = 4.3 Hz, H-
9b), 6.26 (1H, d, J = 4.3 Hz, H-10a), 4.37 (1H, br s,
H-13a), 1.28 (3H, s, H-16), 0.87 (3H, s, H-17), 1.87
(3H, s, H-18), 1.63 (3H, s, H-19), 4.83 (1H, s, H-20a),
5.54 (1H, s, H-20b), 8.05 (2H, d, J = 7.6 Hz, Ho-Ph),
7.56 (2H, t, J = 7.7 Hz, Hm-Ph), 7.67 (1H, t, J = 7.4 Hz,
H
p-Ph), 2.05 (3H, s, O2CCH3), 2.03 (3H, s, O2CCH3),
1.95 (3H, s, O2CCH3); 13C NMR (acetone-d6,
100 MHz) d 68.4 (C, C-1), 65.9 (CH, C-2), 47.5 (CH,
C-3), 148.1 (CH2, C-4), 71.7 (CH, C-5), 36.9 (CH2, C-
6), 68.0 (CH, C-7), 43.7 (C, C-8), 74.4 (CH, C-9), 66.8
(CH, C-10), 134.2 (C, C-11), 153.5 (C, C-12), 82.2
(CH, C-13), 48.1 (CH2, C-14), 78.9 (C, C-15), 28.4
(CH3, C-16), 28.0 (CH3, C-17), 14.3 (CH3, C-18), 12.6
(CH3, C-19), 114.0 (CH3, C-20), 165.4 (C, O2CC6H5),
130.2 (C, i-O2CC6H5), 130.4 (CH, o-O2CC6H5), 129.7
(CH, m-O2CC6H5), 134.2 (CH, p-O2CC6H5), 170.7 (C,
O2CCH3), 170.4 (C, O2CCH3), 169.9 (C, O2CCH3),
21.5 (CH3, O2CCH3), 20.9 (CH3, O2CCH3), 20.6
(CH3, O2CCH3); HRESIMS m/z 619.2807 [M+Na+]
(calcd for C33H40O10Na, 619.2519).
4.3.8.2. Compound 13. Yellow amorphous powder:
18
½aꢁ ꢀ 43:7ðc 0:94; CH3OHÞ; UV (CH3OH) kmax (loge)
D
201.2 (4.18) nm; IR (KBr) mmax 3442, 2976, 2937, 1729,
1712, 1634, 1604, 1451, 1372, 1261, 1108, 1067, 1028,
4.3.10. Oxidation of 14 to 15. Compound 15 was synthe-
sized from 14 in 92% yield by the same procedure as that
for 3: yellow amorphous powder, (petroleum/ethyl ace-
1
712 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 6.18 (1H,
d, J = 8.2 Hz, H-2b), 4.06 (1H, d, J = 8.2 Hz, H-3a),
6.06 (1H, d, J = 10.1 Hz, H-6), 7.46 (1H, d,
J = 10.1 Hz, H-7), 6.14 (1H, d, J = 10.7 Hz, H-9b),
6.38 (1H, d, J = 10.7 Hz, H-10a), 4.47 (1H, m, H-13b),
1.19 (3H, q, H-16), 1.29 (3H, q, H-17), 1.82 (3H, q, H-
18), 1.78 (3H, q, H-19), 5.28 (1H, s, H-20a), 5.98 (1H,
s, H-20b), 7.98 (2H, d, J = 7.25 Hz, Ho-Ph), 7.49 (2H, t,
J = 7.7 Hz, Hm-Ph), 7.63 (1H, t, J = 7.4 Hz, Hp-Ph), 2.04
(3H, s, O2CCH3), 2.03 (3H, s, O2CCH3); 13C NMR (ace-
tone-d6, 100 MHz) d 68.1 (C, C-1), 70.4 (CH, C-2), 48.2
(CH, C-3), 144.0 (C, C-4), 189.6 (C, C-5), 129.6 (CH, C-
6), 154.9 (CH, C-7), 44.7 (C, C-8), 75.5 (CH, C-9), 70.7
(CH, C-10), 134.7 (C, C-11), 152.9 (C, C-12), 76.8 (CH,
C-13), 41.7 (CH2, C-14), 76.2 (C, C-15), 27.2 (CH3, C-
16), 28.4 (CH3, C-17), 12.0 (CH3, C-18), 20.5 (CH3, C-
19), 120.2 (CH2, C-20), 165.7 (C, O2CC6H5), 130.6 (C,
i-O2CC6H5), 130.3 (CH, o-O2CC6H5), 129.4 (CH, m-
O2CC6H5), 134.1 (CH, p-O2CC6H5), 171.8 (CH,
O2CCH3), 170.0 (C, O2CCH3), 21.8 (CH3, O2CCH3),
21.5 (CH3, O2CCH3). HRESIMS m/z 575.2270
[M+Na+] (calcd for C31H36O9Na, 575.2257).
18
tate, 7:3); ½aꢁ 51:7ðc 0:87; CH3OHÞ; UV (CH3OH) kmax
D
(log ꢀ) 201.8 (4.19) nm; IR (KBr) mmax 2955, 2925, 1753,
1723, 1678, 1602, 1452, 1374, 1268, 1251, 1094, 1069,
1027, 716 cmꢀ1 1H NMR (acetone-d6, 400 MHz) d
;
5.64 (1H, d, J = 7.1 Hz, H-2b), 3.52 (1H, d, J = 7.1 Hz,
H-3a), 5.19 (1H, m, H-7a), 5.13 (1H, d, J = 4.5 Hz, H-
9b), 6.34 (1H, d, J = 4.5 Hz, H-10a), 4.42 (1H, br s,
H-13a), 1.28 (3H, s, H-16), 0.77 (3H, s, H-17), 1.72
(3H, s, H-18), 1.19 (3H, s, H-19), 5.22 (1H, s, H-20a),
5.92 (1H, s, H-20b), 8.05 (2H, d, J = 7.4 Hz, Ho-Ph),
7.56 (2H, t, J = 7.6 Hz, Hm-Ph), 7.67 (1H, t, J = 7.3 Hz,
H
p-Ph), 2.07 (3H, s, O2CCH3), 2.01 (3H, s, O2CCH3),
1.92 (3H, s, O2CCH3); 13C NMR (acetone-d6,
100 MHz) d 67.9 (C, C-1), 66.7 (CH, C-2), 45.3 (CH,
C-3), 144.3 (C, C-4), 198.1 (C, C-5), 39.4 (CH2, C-6),
70.1 (CH, C-7), 43.1 (C, C-8), 73.7 (CH, C-9), 67.7
(CH, C-10), 133.8 (C, C-11), 152.9 (C, C-12), 47.7
(CH2, C-14), 79.0 (C, C-15), 29.1 (CH3, C-16), 27.7
(CH3, C-17), 13.5 (CH3, C-18), 12.3 (CH3, C-19),
128.2 (CH2, C-20), 165.5 (C, O2CC6H5), 130.4 (C, i-
O2CC6H5), 130.37 (CH, o-O2CC6H5), 129.7 (CH, m-
O2CC6H5), 134.4 (CH, p-O2CC6H5), 170.3 (C,
O2CCH3), 170.2 (C, O2CCH3), 169.9 (C, O2CCH3),
21.7 (CH3, O2CCH3), 20.8 (CH3, O2CCH3), 20.6
(CH3, O2CCH3); HRESIMS m/z 617.2807 [M+Na+]
(calcd for C33H38O10Na, 617.2362).
4.3.9. Conversion of compound 1 to 14. Taxchinin A 1
(100 mg, 0.16 mmol) was dissolved in dry pyridine
(4 mL). To this solution was added p-toluenesulfonyl
chloride (42.6 mg, 0.372 mmol). The reaction mixture
was stirred at room temperature and monitored by
TLC until all starting material was consumed. The reac-
tion mixture was diluted with ethyl acetate, and washed
with diluted hydrochloric acid, water, and brine. The or-
ganic layer was then dried (Na2SO4) and concentrated in
vacuo. The residue was purified by column chromatog-
4.3.11. Conversion of compound 2 to 16. Compound 2
was treated with p-toluenesu- lfonyl chloride by the
same procedure as that for 14 to produce crude mixture
which was purified by column chromatography (petro-
leum/ethyl acetate, 8.5:1.5) to afford starting material 2
raphy (petroleum/ethyl acetate, 8:2) to afford 14
18
D
(50.38 mg, 51.9%) as yellow oil: ½aꢁ ꢀ 1:5ðc 0:72;
(52.1%) and compound 16 (41.2%) as colorless oil:
18
D
CH3OHÞ; UV (CH3OH) kmax (log ꢀ) 201.2 (3.82) nm;
½aꢁ ꢀ 8:5ðc 0:23; CH3OHÞ; UV (CH3OH) kmax (log ꢀ)
IR (KBr) mmax 3424, 2956, 2853, 1743, 1728, 1463,
202.0 (4.18) nm; IR (KBr) mmax 3431, 2954, 2922, 1726,
1
1376, 1243, 1090, 1067, 1027, 718 cmꢀ1; H NMR (ace-
1630, 1463, 1377, 1249, 1111, 1065, 1032, 718 cmꢀ1
;
tone-d6, 400 MHz) d 5.68 (1H, d, J = 8.4 Hz, H-2b), 3.25
(1H, d, J = 8.4 Hz, H-3a), 4.63 (1H, br s, H-5b), 4.87
1H NMR (acetone-d6, 400 MHz) d 3.16 (1H, d,
J = 10.9 Hz, H-3a), 4.37 (1H, s, H-5b), 5.64 (1H, dd,

Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
4869
J = 12.0, 5.6 Hz, H-7a), 5.13 (1H, d, J = 6.1 Hz, H-9b),
6.28 (1H, d, J = 6.1 Hz, H-10a), 4.17 (1H, br s, H-
13a), 1.38 (3H, s, H-16), 0.87 (3H, s, H-17), 1.87 (3H,
s, H-18), 1.19 (3H, s, H-19), 4.93 (1H, s, H-20a), 5.12
(1H, s, H-20b), 8.07 (2H, d, J = 7.8 Hz, Ho-Ph), 7.53
(2H, t, J = 7.6 Hz, Hm-Ph), 7.65 (1H, t, J = 7.4 Hz, Hp-
Ph), 2.04 (3H, s, O2CCH3), 2.03 (3H, s, O2CCH3); 13C
NMR (acetone-d6, 100 MHz) d 62.6 (C, C-1), 23.3
(CH2, C-2), 37.2 (CH, C-3), 153.3 (C, C-4), 73.4 (CH,
C-5), 32.6 (CH2, C-6), 71.4 (CH, C-7), 47.0 (C, C-8),
74.3 (CH, C-9), 68.0 (CH, C-10), 138.2 (C, C-11),
147.7 (C, C-12), 83.3 (CH, C-13), 52.1 (CH2, C-14),
79.8 (C, C-15), 26.8 (CH3, C-16), 26.0 (CH3, C-17),
12.1 (CH3, C-18), 12.0 (CH3, C-19), 111.4 (CH2, C-
20), 165.9 (C, O2CC6H5), 130.8 (C i-O2CC6H5), 130.4
(CH o-O2CC6H5), 129.6 (CH, m-O2CC6H5), 134.1
(CH, p-O2CC6H5), 170.3 (C, O2CCH3), 170.1 (C
O2CCH3), 20.9 (CH3, O2CCH3), 20.6 (CH3, O2CCH3);
HRESIMS m/z 561.2449 [M+Na+] (calcd for
C31H38O8Na, 561.2464).
4.3.13.1. Compound 18. Yellow amorphous powder:
18
½aꢁ ꢀ 99:4ðc 0:75; CH3OHÞ; UV (CH3OH) kmax (loge)
D
201.2 (4.35) nm; IR (KBr) mmax 2956, 2924, 1750, 1726,
1661, 1628, 1452, 1374, 1262, 1221, 1095, 1069, 1027,
1
713 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 6.05 (1H,
s, H-2b), 4.15 (1H, s, H-3a), 5.90 (1H, d, J = 10.2 Hz,
H-6), 6.99 (1H, d, J = 10.2 Hz, H-7), 5.47 (1H, d,
J = 4.7 Hz, H-9b), 6.32 (1H, d, J = 4.7 Hz, H-10a),
1.89 (3H, s, H-15), 1.60 (3H, s, H-16), 5.58 (1H, s, H-
17a), 6.05 (1H, s, H-17b), 7.93 (2H, d, 7.2, Ho-Ph), 7.44
(2H, t, 7.7, Hm-Ph), 7.57 (1H, t, 7.4, Hp-Ph), 1.96 (3H,
s, O2CCH3); 13C NMR (acetone-d6, 100 MHz) d 136.9
(C, C-1), 122.4 (CH, C-2), 46.2 (CH, C-3), 146.5 (C,
C-4), 188.2 (C, C-5), 128.9 (CH, C-6), 158.8 (CH, C-
7), 46.3 (C, C-8), 76.8 (CH, C-9), 70.6 (CH, C-10),
157.9 (C, C-11), 145.2 (C, C-12), 203.3 (C, C-13), 42.3
(CH, C-14), 9.1 (CH3, C-15), 19.3 (CH3, C-16), 120.7
(CH2, C-17), 165.1 (C, O2CC6H5), 129.9 (C, i-
O2CC6H5), 130.5 (CH, o-O2CC6H5), 129.7 (CH, m-
O2CC6H5), 134.6 (CH, p-O2CC6H5), 169.7 (C,
O2CCH3), 20.7 (CH3, O2CCH3); HRESIMS m/z
455.1481 [M+Na+] (calcd for C26H24O6Na, 455.1470).
4.3.12. Oxidation of 16 to 17. Compound 16 was treated
with pyridinium dichromate (PDC) by the same proce-
dure as that for 3 to produce crude mixture which was
purified by column chromatography (petroleum/ethyl
4.3.13.2. Compound 19. Yellow amorphous powder:
15
½aꢁ ꢀ 60:6ðc 0:58; CH3OHÞ; UV (CH3OH) kmax (loge)
D
acetate, 8:2) to afford 17 (50.0%) as light yellow foam:
201.0 (4.42) nm; IR (KBr) mmax 3445, 2925, 1752, 1717,
1679, 1625, 1603, 1451, 1370, 1257, 1281, 1095, 1042,
18
D
½aꢁ 37:8ðc 0:44; CH3OHÞ; UV (CH3OH) kmax (log ꢀ)
1
229 (4.37) nm; IR (KBr) mmax 2973, 2926, 1744, 1723,
1677, 1627, 1451,1369, 1268, 1242, 1094, 1068, 1040,
1026, 753, 712 cmꢀ1; H NMR (acetone-d6, 400 MHz)
d 6.38 (1H, d, J = 8.2 Hz, H-2b), 3.45 (1H, d,
J = 8.2 Hz, H-3a), 6.05 (1H, d, J = 10.1 Hz, H-6), 7.45
(1H, d, J = 10.1 Hz, H-7), 6.31 (1H, d, J = 10.8 Hz, H-
9b), 6.61 (1H, d, J = 10.8 Hz, H-10a), 1.17 (3H, s, H-
16), 1.26 (3H, s, H-17), 1.72 (3H, s, H-18), 1.34 (3H, s,
H-19), 5.29 (1H, s, H-20a), 5.98 (1H, s, H-20b), 8.02
(2H, d, J = 7.3 Hz, Ho-Ph), 7.49 (2H, t, J = 7.8 Hz, Hm-
Ph), 7.65 (1H, t, J = 7.4 Hz, Hp-Ph), 2.15 (3H, s,
O2CCH3), 1.79 (3H, s, O2CCH3); 13C NMR (acetone-
d6, 100 MHz) d 65.0 (C, C-1), 69.6 (CH, C-2), 48.9
(CH, C-3), 143.7 (C, C-4), 189.3 (C, C-5), 130.0 (CH,
C-6), 153.8 (CH, C-7), 44.8 (C, C-8), 75.1 (CH, C-9),
69.9 (CH, C-10), 162.2 (C, C-11), 147.1 (C, C-12),
206.8 (C, C-13), 44.4 (CH2, C-14), 76.1 (C, C-15), 28.0
(CH3, C-16), 28.1 (CH3, C-17), 8.9 (CH3 C-18), 20.5
(CH3, C-19), 120.5 (CH2, C-20), 165.7 (C, O2CC6H5),
130.3 (C, i-O2CC6H5), 130.6 (CH, o-O2CC6H5), 129.5
(CH, m-O2CC6H5), 134.4 (CH, p-O2CC6H5), 171.7 (C,
O2CCH3), 169.9 (C, O2CCH3), 21.8 (CH3, O2CCH3),
21.2 (CH3, O2CCH3). HRESIMS m/z 455.1481
[M+Na+] (calcd for C26H24O6Na, 455.1470).
1027, 712 cmꢀ1 1H NMR (acetone-d6, 400 MHz) d
;
3.26 (1H, d, J = 9.5 Hz, H-3a), 6.86 (1H, br s, H-5),
4.95 (1H, dd, J = 10.0, 5.9 Hz, H-7a), 5.17 (1H, d,
J = 4.8 Hz, H-9b), 6.25 (1H, d, J = 4.8 Hz, H-10a),
4.31 (1H, br s, H-13a), 1.30 (3H, s, H-16), 0.87 (3H, s,
H-17), 1.86 (3H, s, H-18), 1.50 (3H, s, H-19), 9.46
(1H, s, H-20), 8.06 (2H, d, J = 7.5 Hz, Ho-Ph), 7.54
(2H, t, J = 7.3 Hz, Hm-Ph), 7.65 (1H, t, J = 7.1 Hz, Hp-
Ph), 2.04 (3H, s, O2CCH3), 2.18 (3H, s, O2CCH3); 13C
NMR (acetone-d6, 100 MHz) d 64.5 (C, C-1), 22.6
(CH2, C-2), 36.8 (CH, C-3), 144.6 (C, C-4), 146.9 (CH,
C-5), 28.0 (CH2, C-6), 71.1 (CH, C-7), 43.7 (C, C-8),
73.0 (CH, C-9), 67.3 (CH, C-10), 136.6 (C, C-11),
149.5 (C, C-12), 82.4 (CH, C-13), 51.6 (CH2, C-14),
78.1 (C, C-15), 25.8 (CH3, C-16), 25.6 (CH3, C-17),
12.8 (CH3, C-18), 12.1 (CH3, C-19), 193.2 (CH, C-20),
165.7 (C, O2CC6H5), 129.9 (C, i-O2CC6H5), 129.5
(CH, o-O2CC6H5), 128.7 (CH, m-O2CC6H5), 133.3
(CH, p-O2CC6H5), 169.7 (C, O2CCH3), 169.2 (C,
O2CCH3), 19.7 (CH3, O2CCH3); HRESIMS m/z
559.2299 [M+Na+] (calcd for C31H36O8Na, 559.2307).
4.3.14. Conversion of compound 3 to 20 and 21. Com-
pound 3 was treated with sodium hydride by the same
procedure as that for 18 and 19 to produce crude mix-
ture which was purified by column chromatography
(chloroform/ethyl acetate, 8:2) to afford 20 (12.0%)
and compound 21 (27.5%).
4.3.13. Conversion of compound 4 to 18 and 19. Sodium
hydride (52.4 mg, 60%, 1.31 mmol) washed with dry
ethyl ether firstly was stirred in dry tetrahydrofuran
(10 mL). To this mixture was added 4 (200 mg,
0.33 mmol). The reaction mixture was stirred at room
temperature and monitored by TLC until all starting
material was consumed. The mixture was diluted with
ethyl acetate and washed with water and brine. The or-
ganic layer was then dried (NaSO4) and concentrated.
The residue was purified by column chromatography
(chloroform/ethyl acetate, 8:2) to give 18 (44.0 mg,
31%) and 19 (111.6 mg, 62%).
18
4.3.14.1. Compound 20. Yellow oil: ½aꢁ ꢀ 78:2
D
ðc 0:62; CH3OHÞ; UV (CH3OH) kmax (loge) 201.0
(4.39) nm; IR (KBr) mmax 3437, 2925, 1748, 1726, 1704,
1602, 1452, 1370, 1241, 1094, 1069, 1027, 714 cmꢀ1
;
1H NMR (acetone-d6, 400 MHz) d 5.85 (1H, br s,
H-2), 4.25 (1H, d, br s, H-3a), 4.40 (1H, t, J = 2.6 Hz,

4870
Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
H-5b), 5.07 (1H, dd, J = 14.1, 5.1 Hz, H-7a), 5.56 (1H,
d, J = 3.7 Hz, H-9b), 6.30 (1H, d, J = 3.7 Hz, H-10a),
1.82 (3H, s, H-15), 1.10 (3H, s, H-16), 4.98 (1H, s, H-
17a), 5.21 (1H, s, H-17b), 8.05 (2H, d, J = 7.7 Hz, Ho-
Ph), 7.55 (2H, t, J = 7.8 Hz, Hm-Ph), 7.69 (1H, t,
J = 7.4 Hz, Hp-Ph), 2.02 (3H, s, O2CCH3), 2.01 (3H, s,
O2CCH3); 13C NMR (acetone-d6, 100 MHz) d 134.7
(C, C-1), 126.3 (CH, C-2), 42.5 (CH, C-3), 151.0 (C,
C-4), 71.8 (CH, C-5), 35.2 (CH2, C-6), 70.4 (CH, C-7),
46.4 (C, C-8), 72.7 (CH, C-9), 71.2 (CH, C-10), 157.9
(C, C-11), 147.5 (C, C-12), 203.5 (C, C-13), 43.1 (CH2,
C-14), 8.8 (CH3, C-15), 11.4 (CH3, C-16), 112.6 (CH2,
C-17), 165.0 (C, O2CC6H5), 130.1 (C, i-O2CC6H5),
130.5 (CH, o-O2CC6H5), 129.7 (CH, m-O2CC6H5),
134.6 (CH, p-O2CC6H5), 170.0 (C, O2CCH3), 169.6 (C,
O2CCH3), 20.9 (CH3, O2CCH3), 20.7 (CH3, O2CCH3);
HRESIMS m/z 517.1837 [M+Na+] (calcd for
C28H30O8Na, 517.1838).
(3H, s, H-16), 5.00 (1H, s, H-17a), 5.26 (1H, s, H-17b),
8.05 (2H, d, J = 7.8 Hz, Ho-Ph), 7.55 (2H, t, J = 7.9 Hz,
H
m-Ph), 7.69 (1H, t, J = 7.4 Hz, Hp-Ph), 2.04 (2H, s,
O2CCH3), 2.03 (3H, s, O2CCH3), 0.62 (6H, q, 7.9,
SiCH2), 0.97 (9H, t, 7.9, SiCH2CH3); 13C NMR (ace-
tone-d6, 100 MHz) d 134.9 (C, C-1), 126.0 (CH, C-2),
42.4 (CH, C-3), 150.8 (C, C-4), 71.7 (CH, C-5), 36.0
(CH2, C-6), 68.9 (CH, C-7), 46.3 (C, C-8), 73.8 (CH,
C-9), 70.2 (CH, C-10), 157.8 (C, C-11), 147.6 (C, C-
12), 203.5 (C, C-13), 43.0 (CH2, C-14), 8.7 (CH3, C-
15), 11.2 (CH3, C-16), 112.3 (CH2, C-17), 164.9 (C,
O2CC6H5), 129.9 (C, i-O2CC6H5), 130.4 (CH, o-
O2CC6H5), 129.7 (CH, m-O2CC6H5), 134.6 (CH, p-
O2CC6H5), 169.9 (C, O2CCH3), 169.5 (C, O2CCH3),
20.9 (CH3, O2CCH3), 20.7 (CH3, O2CCH3), 5.3 (CH2,
SiCH2), 7.1 (CH3, SiCH2CH3); HRESIMS m/z
631.2695 [M+Na+] (calcd for C34H44O8NaSi, 631.2703).
4.3.16. Compound 23. To a solution of pyridinium chlo-
rochromate (130.90 mg, 0.61 mmol) in dichlorometh-
ane (5 mL) was added 20 (50 mg, 0.10 mmol) in
dichloromethane (3 mL). The mixture was stirred at
room temperature for 6 h. The reaction mixture was
filtered and purified through the column chromatogra-
phy (petroleum ether/ethyl acetate, 8.5:1.5) and con-
centrated to afford 18 (17.49 mg, 17.5%) and 23
(22.51 mg, 45.2%).
18
4.3.14.2. Compound 21. Yellow oil: ½aꢁ ꢀ 8:1ðc 0:62;
D
CH3OHÞ; UV (CH3OH) kmax (loge) 201.0 (4.36) nm; IR
(KBr) mmax 3436, 2926, 1736, 1602, 1451, 1247, 1083,
1
1065, 1026, 712 cmꢀ1; H NMR (acetone-d6, 400 MHz)
d 5.99 (1H, s, H-2), 4.05 (1H, s, H-3a), 4.47 (1H, s, H-
5b), 5.39 (1H, dd, J = 11.9, 5.4 Hz, H-7a), 6.08 (1H, s,
H-9b), 1.79 (3H, s, H-15), 1.04 (3H, s, H-16), 5.10
(1H, s, H-17a), 5.25 (1H, s, H-17b), 8.11 (2H, d,
J = 7.7 Hz, Ho-Ph), 7.57 (2H, t, J = 7.8 Hz, Hm-Ph), 7.70
(1H, t, J = 7.5 Hz, Hp-Ph), 2.04 (3H, s, O2CCH3); 13C
NMR (acetone-d6, 100 MHz) d 133.1 (C, C-1), 124.5
(CH, C-2), 42.7 (CH, C-3), 150.3 (C, C-4), 73.2 (CH,
C-5), 35.9 (CH2, C-6), 74.8 (CH, C-7), 43.6 (C, C-8),
135.8 (CH, C-9), 144.3 (C, C-10), 152.4 (C, C-11),
141.4 (C, C-12), 203.9 (C, C-13), 41.9 (CH2, C-14),
10.3 (CH3, C-15), 13.7 (CH3, C-16), 112.2 (CH2, C-
17), 165.3 (C, O2CC6H5), 130.0 (C, i-O2CC6H5), 130.8
(CH, o-O2CC6H5), 129.8 (CH, m-O2CC6H5), 134.7
(CH, p-O2CC6H5), 170.7 (C, O2CCH3), 21.1 (CH3,
O2CCH3); HRESIMS m/z 457.1618 [M+Na+] (calcd
for C26H26O6Na, 457.1627).
18
D
4.3.16.1. Compound 23. Yellow oil: ½aꢁ ꢀ 17:8
ðc 1:13; CH3OHÞ; UV (CH3OH) kmax (loge) 201.0
(4.19) nm; IR (KBr) mmax 2956, 2925, 1750, 1728, 1707,
1641, 1550, 1453, 1375, 1261, 1100, 1070, 1042, 1025,
1
714 cmꢀ1; H NMR (acetone-d6, 400 MHz) d 5.50 (1H,
s, H-2), 4.06 (1H, s, H-3a), 7.02 (1H, d, J = 5.7 Hz, H-
5), 5.05 (1H, dd, J = 10.6, 5.2 Hz, H-7a), 5.51 (1H, d,
J = 4.2 Hz, H-9b), 6.27 (1H, d, J = 4.2 Hz, H-10a),
1.81 (3H, s, H-15), 1.74 (3H, s, H-16), 9.56 (1H, s, H-
17), 8.05 (2H, d, J = 8.1 Hz, Ho-Ph), 7.56 (2H, t,
J = 7.7 Hz, Hm-Ph), 7.70 (1H, t, J = 7.5 Hz, Hp-Ph), 2.03
(3H, s O2CCH3), 1.96 (3H, s, O2CCH3); 13C NMR (ace-
tone-d6, 100 MHz) d 137.3 (C, C-1), 126.2 (CH, C-2),
39.1 (CH, C-3), 141.2 (C, C-4), 174.6 (CH, C-5), 28.0
(CH2, C-6), 76.8 (CH, C-7), 43.7 (C, C-8), 76.9 (CH,
C-9), 71.5 (CH, C-10), 157.5 (C, C-11), 143.0 (C, C-
12), 203.5 (C, C-13), 40.7 (CH2, C-14), 9.2 (CH3, C-
15), 16.2 (CH3, C-16), 193.5 (CH, C-17), 165.7 (C,
O2CC6H5), 129.9 (C, i-O2CC6H5), 130.7 (CH, o-
O2CC6H5), 129.7 (CH, m-O2CC6H5), 134.7 (CH, p-
O2CC6H5), 170.7 (C, O2CCH3), 170.0 (C, O2CCH3),
21.2 (CH3, O2CCH3), 20.9 (CH3, O2CCH3); HRESIMS
m/z 515.1692 [M+Na+] (calcd for C28H28O8Na,
515.1681).
4.3.15. Compound 22. To a solution of compound 3
(100 mg, 0.16 mmol) in dry pyridine (8 mL) was added
chlorotriethylsilane (41.51 lL, 0.25 mmol) dropwise.
The solution was stirred at room temperature for 12 h
when all starting material was consumed. After dilution
with ethyl acetate, the solution was washed with diluted
hydrochloric acid and water. The organic layer was
dried (Na2SO4) and evaporated. The residue was puri-
fied by column chromatography (chloroform/ethyl ace-
tate, 19.5:0.5) to give 114 mg of crude product
(114 mg). The crude material was dissolved in dry tetra-
hydrofuran, and treated with sodium hydride by the
same procedure as that for 18 and 19 to give compound
4.4. CoMFA
22 in 39.8% yield: white amorphous powder, (chloro-
9.5:0.5);
18
½aꢁ ꢀ 74:3ðc 0:67;
form/ethyl
acetate,
Structures of 18 compounds were built using SYBYL
7.0 molecular modeling software. The structural energy
minimization was performed using standard TRIPOS
D
CH3OHÞ; UV (CH3OH) kmax (loge) 201.2 (4.55) nm;
IR (KBr) mmax 2956, 1753, 1727, 1704, 1638, 1452,
1369, 1234, 1094, 1068, 1027, 1010, 714 cmꢀ1
;
1H
force field and Gasteiger–Huckel charge with an energy
¨
NMR (acetone-d6, 400 MHz) d 5.85 (1H, s, H-2), 4.07
(1H, s, H-3a), 4.49 (1H, br s, H-5b), 5.07 (1H, dd,
J = 11.5, 4.8 Hz, H-7a), 5.55 (1H, J = 3.6 Hz, H-9b),
6.30 (1H, J = 3.6 Hz, H-10a), 1.82 (3H, s, H-15), 1.11
gradient convergence criterion of 0.001 kcal/mol and a
distance-dependent dielectric constant. Systematic con-
formational searches were carried out to find the lowest
energy structures.

Y. Zhao et al. / Bioorg. Med. Chem. 16 (2008) 4860–4871
4871
8. Tremblay, S.; Soucy, C.; Towers, N.; Gunning, P. J.;
Breau, L. J. Nat. Prod. 2004, 67, 838.
9. Kobayashi, J.; Hosoyama, H.; Wang, X. X.; Shigemori,
H.; Koiso, Y.; Iwasaki, S.; Sasaki, T.; Naito, M.; Tsuruo,
T. Bioorg. Med. Chem. Lett. 1997, 7, 393.
Steric and electrostatic interactions were calculated
using an sp3 carbon atom as steric probe and a +1
charge as electrostatic probe with Tripos force field.
˚
The CoMFA grid spacing was 2.0 A in the x, y, and z
directions. The default value of 30 kcal/mol was set as
the maximum steric and electrostatic energy cutoff. Min-
imum-sigma (column filtering) was set to be 2.0 kcal/
mol. The regression analysis was carried out using the
full cross-validated partial least-squares (PLS) method
(leave-one-out) with CoMFA standard options for scal-
ing of variables. The final model (non-cross-validated
conventional analysis) was developed with the optimum
number of components equal to that yielding the highest
q2.
10. Palmer, J. T.; Rasnick, D.; Klaus, J. L.; U.S. Patent
6287840, 2001.
11. Matthews, D. A.; Dragovich, P. S.; Webber, S. E.;
Fuhrman, S. A.; Patick, A. K.; Zalman, L. S.; Hendrick-
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