Synthesis and antitumor activity of 2-(m-substituted-benzoyl)baccatin III analogs from taxinine

Article abstract of DOI:10.1016/S0040-4020(03)00048-6

2-m-Azidobenzoyl and 2-m-chlorobenzoyl baccatin III analogs were prepared from taxinine, a major component in Japanese yew leaves. In this study, a novel acetyl migration from 13- to 4-hydroxyl group was observed. The antitumor activity of these compounds

Full text of DOI:10.1016/S0040-4020(03)00048-6

Tetrahedron 59 (2003) 1529–1538
Synthesis and antitumor activity of
2-(m-substituted-benzoyl)baccatin III analogs from taxinine
†
Tohru Horiguchi, Takayuki Oritani and Hiromasa Kiyota
*
Division of Life Science, Graduate School of Agricultural Science, Tohoku University, 1-1, Tsutsumidori-Amamiya, Aoba, Sendai,
Miyagi 9818555, Japan
Received 27 August 2002; revised 7 January 2003; accepted 7 January 2003
Abstract—2-m-Azidobenzoyl and 2-m-chlorobenzoyl baccatin III analogs were prepared from taxinine, a major component in Japanese yew
leaves. In this study, a novel acetyl migration from 13- to 4-hydroxyl group was observed. The antitumor activity of these compounds was
evaluated. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
The methods to synthesize 2-(m-substituted-benzoyl)-1,7-
dideoxybaccatin III analogs from taxinine 3,5 a major taxoid
component in Japanese yew leaves, and the evaluation of
their antitumor activity is reported herein (Fig. 1).
Taxol 1, first isolated from the Pacific yew tree Taxus
brevifolia,1–3 is a powerful therapeutic drug for cancer
chemotherapy. It exhibits remarkably high cytotoxicity and
strong antitumor activity against different cancers resistant
to existing anticancer drugs. Most works have focused on
the structure-activity relationships (SAR)2a,e of 1 and have
revealed that top of the diterpene moiety, C7, C9 and C10,
tolerate a wide variety of substituents, while the C2
benzoyloxy group and C4 acetoxy group with the oxetane
are essential for the biological activity. In addition the side
chain at C13 also has been shown to be essential for
biological activity, although it has been reported that 2-(m-
azidobenzoyl)baccatin III 2b has taxol-like activity.4 To
obtain more information about SAR, we undertook a
synthesis of 2b analogs.
2. Results and discussion
Deoxygenation of the 1-hydroxyl group of 2a had been
reported to be a difficult procedure,6 thus we selected
taxinine 3 as a starting material (Scheme 1).
In an attempt to construct an oxetane moiety on 3, treatment
of 5-decinnamoyltaxinine5c with OsO4 and NMO in THF
was tried. Although only an exo double bond was
dihydroxylated, the reaction gave an inseparable mixture
of 2-O-acetate and 20-O-acetate. This was due to an
Figure 1.
Keywords: taxol; antitumor activity; taxinine; m-azidobenzoyl.
*
Corresponding author. Tel.: þ81-22-717-8785; fax: þ81-22-717-8783; e-mail: kiyota@biochem.tohoku.ac.jp
†
Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA.
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00048-6

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T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
Scheme 1. Modification of taxinine.
intramolecular acetyl migration from the 2-position to a
newly formed 20-hydroxyl group. Thus 3 was converted to
the 2,5-diol 4 by the known methods.5 The 5-hydroxyl
group was selectively protected as TBS ether with TBSOTf
and 2,6-lutidine at 2208C giving alcohol 5. Attempts to
protect the 2-hydroxyl group as TBS ether or MTM ether
were unsuccessful and protection as Bn ether (with BnCl,
NaH, TBAI, 408C) was low yielding (40%). Finally, the
2-hydroxyl group could be protected as ethoxyethyl ether
(EE) quantitatively. The TBS group was removed under
alkaline conditions to give 6 in a quantitative yield. As the
2-hydroxyl group was protected by a non-migrating group,
the exo olefin was dihydroxylated and the newly formed
primary hydroxyl group was selectively protected as TBS
ether. Then the secondary hydroxyl group at C5 was
mesylated, the TBS group was removed and oxetane ring
was formed according to Potier’s procedure to give 8.7
With 8 in hand, conditions to remove the EE group were
investigated (Table 1). Under strongly acidic conditions
(entries 3–5), the newly formed 2-hydroxyl group of 9
attacked the oxetane ring to form a furan ring (10).8 Under
mildly acidic condition (entry 2), 9 was obtained in a 32%
yield.
Benzoylation of the 2-hydroxyl group of 9 was then tried.
The attempt to introduce a 2,4-cyclic carbodiester using
carbonyl diimidazole and pyridine (cat.) in CH2Cl2 at
2208C in order to utilize a PhLi-cleavage resulted in
immediate isomerization to 10.9 Reaction of 9 with
Table 1. Deprotection of the 2-EE group
Entry
Conditions
9 (%)
10
Recovery 8
1
2
3
4
5
AcOH–THF–H2O (1/1/1), rt, 3 h
AcOH–THF–H2O (1/1/2), rt, 8 h
PPTS, MeOH, rt, 24 h
0.3% HCl–MeOH, 08C, 25 min
2.5% HCl–MeOH, 08C, 4 min
–
32
Trace
Trace
Trace
–
100
8
–
15
–
32
63
74
61
Scheme 2.

T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
1531
Scheme 3.
Scheme 4.
PhCOOH and DCC10 gave the expected 2-O-benzoate 11,
but furan 12 was also formed (Scheme 2).
used on 8, to give 18 in a good yield. It is noteworthy that
relative to the reaction on 8, the yield of a furan by-product
19 was decreased. This improvement may be due to a
conformational change, that is, the distance between
generated 2-hydroxyl and C20 in compound 18 became
longer than that of compound 9; or the steric hindrance
caused by the 4-O-acetyl group. This tendency was also
Next, although acetylation of the 4-hydroxyl group of 11
under a variety of conditions (1.1 equiv. DMAP, 20 equiv.
Ac2O, Py, 508C), (10 equiv. LiHMDS, DMF, 08C, 30 min,
then 1 equiv. AcBr) etc., were examined, only the starting
material was recovered. The acetylation was also tried for
9,10-dihydroxyl or diacetyl derivatives (13, 14 and 15) in
which the conformational rigidity could be eased, however,
acetylation at 4-position did not occur (Scheme 3).
Finally, the 4-hydroxyl of compound 8 could be acetylated
with acetyl chloride after treatment with LiHMDS to give
16 in a low yield, and enol acetate 17 as a by-product
(Scheme 4).
This improvement of reactivity might be due to the smaller
ethoxyethyl substituent at C2 of 8 relative to the benzoyl
group of 11. Treatment of 17 with K2CO3 in MeOH
regenerated the enone 8, and surprisingly, the reaction also
gave acetate 16 through the acetyl migration from the 13-
hydroxyl to the 4-hydroxyl. The proportion of the migration
to the hydrolysis product increased from 65/32 at rt to 94/6
at 08C (Scheme 4). This migration between the 13-hydroxyl
and the 4-hydroxyl was reasonable for the possible
conformation in which 13-hydroxyl locates close to the
˚
4-hydroxyl in the molecular model analysis [3.46 A from
4-oxygen to 13-O-acetyl carbonyl carbon at the 3rd stable
conformational model of 17 (pc spartan pro 1.0.7 MM2
software)]. This base-catalyzed intramolecular acetyl
transfer between the 13-hydroxyl and the 4-hydroxyl is a
first example and interesting from a view point of an acetate
origin on the 4-acetoxy oxetane biosynthesis.2a,c,11
The EE group of 16 was removed under the same condition
Scheme 5.

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T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
observed in the next reaction; m-N3-Bz and m-Cl-Bz group
were introduced to the compound 18 to give the compounds
20a and 20b, respectively, as a sole product without any
production of the corresponding furan compounds
(Scheme 5). These final compounds bear least functionali-
ties for the antitumor activity without C1–OH group:
essential 2-m-substituted benzoyloxy and 4-acetoxy groups,
and D-oxetane ring. As the oxygen functionalities at 7, 9 and
10-positions were known to be dispensable for the activity,
the 9,10-acetonide moiety were not modified further.
otherwise noted, TMS as an internal standard). Mass spectra
were recorded on a JEOL JMS-700 mass spectrometer.
Optical rotation values were measured on a HORIBA
SEPA-300 polarimeter. IR spectra were recorded on JASCO
IR-Report-100. Merck silica gel 60 (70–230 mesh) was
used for column chromatography and Merck silica gel 60
F254 was used for preparative thin-layer chromatography
(PTLC).
3.2. Materials: isolation of taxinine
The antitumor activity of synthesized taxoids (20a and 20b)
was evaluated as a function of inhibition of tumor cell
growth using a panel screening coupled with a drug
sensitivity database, based on the methods of National
Cancer Institute.12 We employed these acetonide com-
pounds because the 9,10-positions were reported to be
impartinent to the activity. The screening was accomplished
using a sulforhodamine-B assay in 38 human tumor cell
lines and mouse P388 leukemia cells. Disappointingly, both
compounds exhibited only weak activities. Average con-
centration required for 50% growth inhibition (GI50) was
48 mm for 20a and 62 mm for 20b. Even in the most
effective result, GI50 was 22 mm for 20a to SF-268 and
26 mm for 20b to SNB-75. IC50 value of 2b, drug
concentration that inhibits cell division of A549 by 50%
after 72 h, was reported as a value of 68 nm (0.068 mm);
while GI50 values, those after 48 h, were .100 mM for 20a
and 67 mm for 20b. The differential growth inhibitions were
also too weak to guess the mode of action of these
compounds by the COMPARE analysis. The reason why
these compounds display a reduced activity than 2b is as yet
unclear, but it would be due to the less solubility of 20a and
20b with the less number of hydroxyl groups than 2b.
The needles of the Japanese yew collected in Sendai or
Hokkaido, Japan was dried at rt for 1 month and cut into
pieces by GARDEN SHEDDER HG-1500 (Sanyo metal Co.
L.T.D). The rough powder was immersed into MeOH for 2
weeks. The organic layer was filtered by the mixture of
Celite and Carbon powder (5/1) and the filtrate was
concentrated in vacuo. The residue was dissolved into
EtOAc and washed with saturated NaCl solution of 1%
NaOH and brine, dried over Na2SO4 and concentrated in
vacuo. The residue was chromatographed on column
chromatography (EtOAc/hexane, 1/2), yielding crude taxi-
nine (Rf¼0.45). The crude was purified by recrystallization
(EtOH or EtOAc) to give pure taxinine (ca. 2 g/kg flesh
leaves).
3.2.1. Selective protection at 5-OH of diol 4 as TBS ether
5; 20-t-butyldimethylsilyloxy-9a,10b-isopropyliden-
dioxy-4 (20),11-taxadien-13-one (5). To a solution of 4
(927 mg, 2.38 mmol) and 2,6-lutidine (510 mg, 4.76 mmol)
in dry CHCl3 (3 ml) was added TBSOTf (942 mg,
3.57 mmol) at 2208C. After stirring for 2 h, the mixture
was diluted with CHCl3 (30 ml). The reaction mixture was
washed with aqueous NaHCO3, aqueous NH4Cl and brine.
The organic layer was dried over Na2SO4 and concentrated
in vacuo. The residue was purified by chromatography
(EtOAc/hexane, 1/2), yielding 5 (1086 mg, 2.21 mmol,
92%) as amorphous solid; [a]2D0¼þ81 (c 0.013, CHCl3); 1H
NMR (300 MHz), d¼0.01 (s, 3H, Me2Si), 0.03 (s, 3H,
Me2Si), 0.86 (s, 9H, tBuSi), 1.02 (s, 3H, 19-Me), 1.22 (m,
2H), 1.22 (s, 3H, 17-Me), 1.43 (s, 3H, Me2CO2), 1.49 (s, 3H,
Me2CO2), 1.55–1.70 (m, 2H), 1.66 (s, 3H, 16-Me), 2.06 (s,
3H, 18-Me), 2.20 (d, J¼19.8 Hz, 1H, 14a-H), 2.20 (m, 1H,
OH), 2.40 (dd, J¼2.5, 7.1 Hz, 1H, 1-H), 2.78 (dd, J¼7.1,
19.8 Hz, 1H, 14b-H), 3.13 (d, J¼6.6 Hz, 1H, 3-H), 4.20 (m,
2H, 9-H and 2-H), 4.23 (m, 1H, 5-H), 4.92 (d, J¼9.3 Hz,
1H, 10-H), 5.10 (s, 1H, 20-H), 5.23 (s, 1H, 20-H); IR (KBr)
cm21: 3600–3200 (s, O–H), 3000–2800 (s), 1660 (s,
CvO), 1470 (m), 1460 (m), 1443 (m), 1405 (m), 1380 (s),
1370 (s), 1340 (w), 1305 (w), 1280 (w), 1250 (s), 1230 (s),
1200 (s), 1160 (s), 1140 (s), 1120 (s), 1060 (s), 1040 (w),
1020 (w), 950 (s), 920 (s), 870 (s), 850 (s), 830 (s), 780 (s),
730 (s), 700 (w), 670 (w); 13C NMR (125 MHz, CDCl3),
d¼199.71, 150.28, 148.65, 137.91, 113.42, 107.70, 82.01,
76.95, 75.50, 68.01, 51.25, 43.34, 41.32, 38.07, 37.89,
36.21, 32.58, 27.27, 26.81, 26.24, 26.03, 24.48, 18.78,
17.64, 14.17, 24.47, 24.89; HR-FAB-MS, calcd for
C29H49O5Si (MH)þ m/z 505.3346, found 505.3346.
In conclusion, 1,7-dideoxybacacatin III derivatives have
been conveniently prepared in 12 steps in ca. 2.0% overall
yield from readily available taxinine, a major taxoid
component in Japanese yew leaves. In this study, a novel
acetyl migration from 13- to 4-hydroxyl group was
observed.
Although these analogs did not show any expected
biological activity, the synthetic methodology described
here and better understanding chemical reactivity of taxoids
would be useful for the preparation of the candidates of
biogenetic intermediates of taxol. Among eight oxygen
functionalities on taxol, the hydroxyls at C7 and C1 is
presumed to be introduced biogenetically at later stage.13
Since 1,7-dideoxybaccatin III derivatives exist little in
nature and is very difficult to prepare through deoxygenation
of baccatin III 2a,6 this approach from taxinine would be
able to apply for the labeled 1,7-dideoxybaccatin III
derivatives.
3. Experimental
3.1. General
3.2.2. 2a-Ethoxyethoxy-5a-hydroxy-9a,10b-isopropyl-
idendioxy-4 (20),11-taxadien-13-one (6). To a solution of
5 (300 mg, 0.0589 mmol) and p-toluenesulfonic acid (cat.)
in THF (2 ml) was slowly added ethyl vinyl ether (0.280 ml,
1H and 13C NMR spectra were recorded on a Varian UNITY
INOVA 500 and GEMINI 2000 spectrometers (300 and
1
500 MHz for H and 125 MHz for 13C in CDCl3 unless

T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
1533
2.95 mmol) at rt After being stirred for 2 h, the reaction
mixture was diluted with EtOAc (30 ml) and the organic
layer was washed with aqueous NaHCO3 and brine. The
organic layer was dried over Na2SO4, and concentrated in
vacuo. The residue was filtered by carbon powder, yielding
a crude compound (340 mg, 0.583 mmol, 99%). To the
compound (340 mg, 0.583 mmol) in EtOH (1 ml) was
added KOH [5.89 mmol, in EtOH (20 ml)]. The reaction
mixture was stirred at rt for 6 h and was condensed in vacuo.
The residue was diluted with CHCl3. To the mixture was
added carefully AcOH [0.330 ml, 5.76 mmol in H2O
(10 ml)] at 08C and the organic layer was washed with
aqueous NaHCO3 and brine. The organic layer was dried
over Na2SO4 and concentrated in vacuo. The residue was
purified by chromatography (EtOAc/hexane, 1/2), yielding
(s, CvO), 1470 (m), 1440 (s), 1370 (s), 1340 (s), 1300 (m),
1270 (m), 1230 (s), 1200 (s), 1160 (s), 1140 (s), 1120 (s),
1080 (s), 1050 (s), 1030 (s), 940 (m), 920 (m), 870 (s), 830
(m), 810 (m), 790 (m), 750 (s), 690 (s). Anal. calcd for
C27H44O8: C, 65.30; H, 8.93. Found: C, 64.75; H, 8.33.
3.3. Construction of oxetane ring from 7a to 8a
3.3.1. Silylation of 7a to 7b; 20-t-butyldimethylsilyloxy-
2a-ethoxyethoxy-4a,5a-dihydroxy-9a,10b-isopropyl-
idendioxy-11-taxen-13-one (7b). To a solution of 7a
(599 mg, 1.21 mmol) in DMF (2 ml) were added imidazole
(163 mg, 2.40 mmol) and TBDMSCl (274 mg, 1.82 mmol).
After being stirred for 3 h at rt, the mixture was diluted with
EtOAc (30 ml). To the mixture was carefully added aqueous
NaHCO3 at 08C. The organic layer was washed with brine
and concentrated in vacuo. The residue was purified by
chromatography (EtOAc/hexane, 1/3), yielding 7b (605 mg,
0.992 mmol, 82%) as amorphous solid; 1H NMR
(300 MHz), d¼0.01–0.09 (m, 6H, Me2Si), 0.88 and 0.89
(s, each 4.5H, tBuSi),01.01 and 1.06 (s, each 1.5H, 19-Me),
1.18–1.28 (m, 3H, 4 -Me; and m, 1.5H, 20-Me), 1.33 (d,
J¼5.2 Hz, 1.5H, 20-Me), 1.42 (s, 3H, Me2CO2), 1.48 (s, 3H,
Me2CO2), 1.50–1.63 (m, 2H),1.61 and 1.62 (s, each 1.5H,
16-Me), 1.65–1.82 (m, 2.5H), 2.03 (s, 3H, 18-Me), 2.10 (m,
0.5H, 1-H), 2.42–2.63 (m, 2H, 3-H and OH), 2.72 (dd,
J¼8.0, 18.7 Hz, 14b-H), 3.27 (d, J¼18.7 Hz, 0.5H, 14a-H),
3.34 (d, J¼18.7 Hz, 0.5H, 14a-H), 3.46–3.58 (m, 3H, 30-H
and other), 3.60 (m, 1H, 5-H), 3.89 (d, J¼9.6 Hz, 1H), 3.99
(dd, J¼2.2, 4.4 Hz, 0.5H, 2-H), 4.13 and 4.14 (d, J¼9.1 Hz,
each 0.5H, 9-H or 10-H), 4.19 (dd, J¼2.5, 4.7 Hz, 0.5H,
2-H), 4.40 (d, J¼9.9 Hz, 1H, 9-H or 10-H), 4.55 and 4.70 (q,
J¼5.2 Hz, each 0.5H, 10-H), 4.83 (d, J¼9.1 Hz, 1H, 9-H or
10-H); IR (neat) cm21: 3600–3300 (s, O–H), 1670 (s,
CvO), 1450 (m), 1370 (s), 1230 (s), 1160 (s), 1120 (s),
1080 (s), 1020 (s), 1000 (s), 930 (m), 870 (s), 830 (s), 770
(m). Anal. calcd for C33H58O8Si: C, 64.88; H, 9.57. Found:
C, 64.81; H, 9.57.
1
6 quantitatively as amorphous solid; H NMR (300 MHz),
d¼1.02 and 1.07 (s, each 1.5H, 19-Me), 1.20 and 1.22 (s,
each 1.5H, 17-Me), 1.23 and 1.24 (t, J¼7.1 Hz, 0each 1.5H,
40-Me), 1.31 and 1.34 (d, J¼5.5 Hz, each 1.5H, 2 -Me), 1.45
(s, 3H, Me2CO2), 1.56–1.63 (m, 2H), 1.71–1.82 (m, 2H),
2.08 and 2.09 (s, each 1.5H, 18-Me), 2.20 and 2.52 (d,
J¼7.1 Hz, each 0.5H, 3-H), 2.32 and 2.35 (d, J¼10.4 Hz,
each 0.5H, 14-H), 2.72 and 2.82 (dd, J¼7.1, 19.8 Hz, 0each
0.5H, 14-H), 3.20 (m, 1H, 1-H), 3.49–3.61 (m, 2H, 3 -H),
4.13 (m, 1H, 5-H), 4.25 and 4.16 (m, each 0.5H, 2-H), 4.19
and 4.21 (d, J¼5.8 Hz, each 0.5H, 9- or 10-H), 4.64 and 4.70
(q, J¼5.2 Hz, each 0.5H, 10-H), 4.92 and 4.93 (d, J¼5.5 Hz,
each 0.5H, 9- or 10-H), 5.11, 5.16, 5.29, and 5.65 (m, each
0.5H, 20-H); IR (KBr) cm21: 3600–3200 (s, O–H), 1670 (s,
CvO), 1450 (m), 1370 (s), 1230 (s), 1200 (s), 1040 (s), 870
(m), 810 (m). Anal. calcd for C27H42O6: C, 70.10; H, 9.15.
Found: C, 69.71; H, 9.15.
The pair of diastereomers of 6, 7a, 7b, 7c, 7d, 8, 16 and 17
could not be separated from each other.
3.2.3. Dihydroxylation of 6 to 7a; 2a-ethoxyethoxy-
4a,5a,20-trihydroxy-9a,10b-isopropylidendioxy-11-
taxen-13-one (7a). To a solution of 6 (439 mg, 0.949 mmol)
in THF/H2O (2 ml/1 ml) were added N-methylmorpholine
N-oxide (1300 mg, 11.1 mmol) and OsO4 (0.0197 mmol in
t-BuOH, 9.60 ml) at 08C. After being stirred for 2 days,
Na2S2O4 (200 mg) was added to the mixture. After being
stirred for additional 1 h, the mixture was diluted with
EtOAc (40 ml) and the organic layer was washed with
aqueous NH4Cl and brine. The organic layer was dried over
Na2SO4 and concentrated in vacuo. The residue was purified
by chromatography (EtOAc/hexane, 1/2), yielding 7a
3.3.2. Mesylation of 7b to 7c; 20-t-butyldimethylsilyloxy-
2a-ethoxyethoxy-4a-hydroxy-9a,10b-isopropyliden-
dioxy-5a-methanesulfonyloxy-11-taxen-13-one (7c). To a
solution of 7b (605 mg, 0.992 mmol) in pyridine (3 ml) at
08C was added MsCl (1.98 mmol, 227 mg). The reaction
mixture was stirred for 24 h at rt, after which time EtOAc
(15 ml) was added. To the mixture, aqueous NaHCO3 was
added at 08C. The mixture was stirred for 6 h at 08C. The
organic layer was washed with brine, H2O, aqueous CuSO4,
H2O and brine. The organic layer was dried over Na2SO4
and concentrated in vacuo. The residue was purified by
chromatography (EtOAc/hexane, 1/2), yielding 7d (589 mg,
0.855 mmol, 86%) as amorphous solid; 1H NMR
(300 MHz), d¼0.07 (s, 6H, Me2Si), 0.85 (s, 9H, tBuSi),
1.07 and 1.92 (s, each 1.5H, 19-Me), 1.170–1.27 (m, 6H,
40-Me, 17-Me), 1.028 (d, 1.5H, J¼5.2 Hz, 2 -Me), 1.35 (d,
1.5H, J¼5.0 Hz, 2 -Me), 1.41 (s, 3H, Me2CO2), 1.47 (s, 3H,
Me2CO2), 1.50–1.70 (m, 1H), 1.61 and 1.63 (s, each 1.5H,
16-Me), 1.80–2.00 (m, 3H), 2.09 (s, 3H, 18-Me), 2.14 and
2.52 (m, each 0.5H, H-1), 2.46 and 2.47 (d, J¼4.4 Hz, each
0.5H, 3-H), 2.74 (dd, J¼7.1, 19.5 Hz, 0.5H, 14b-H), 2.80
(dd, J¼7.1, 19.8 Hz, 0.5H, 14b-H), 2.98 and 2.99 (s, each
1.5H, MeSO3), 3.15 (d, J¼19.8 Hz, 0.5H, 14a-H), 3.17 (d,
J¼19.5 Hz, 0.5H, 14a-H), 3.34 and 3.36, (s, each 0.5H,
1
(433 mg, 0.869 mmol, 92%) as amorphous solid; H NMR
(300 MHz), d¼1.03 and 1.08 (s, each 1.5H, 19-Me), 1.20–
1.30 (m, 6H, 17-Me, 40-Me), 1.35 (d, J¼4.9 Hz, 1.5H,
20-Me), 1.41 (d, J¼4.9 Hz, 1.5H, 20-Me), 1.42 (s, 3H,
Me2CO2), 1.47 (s, 3H, Me2CO2), 1.50–1.63 (m, 2H), 1.65–
1.82 (m, 2H), 2.04 (s, 3H, 18-Me), 2.56 (s, 0.5H, OH), 2.68
(s, 0.5H, OH), 2.82 (s, 0.5H, OH), 2.84 (s, 0.5H, OH), 2.86
and 2.93 (d, J¼4.7 Hz, each 0.5H, 3-H), 2.65–2.84 (m, 2H,
14-H), 2.22 and 2.59 (m, each 0.5H, 1-H), 3.49 (m, 0.5H,
20-H), 3.51–3.61 (m, 2H, 30-H; and 0.5H, H-20), 3.56 (m,
1H, 9- or 10-H), 3.64 (m, 0.5H, 20-H), 3.80 (m, 1H, 5-H),
3.96 (s, 0.5H, OH), 4.05 (s, 0.5H, OH), 4.34 (m, 0.5H, 2-H),
4.67 (q, J¼5.2 Hz, each 0.5H, 10-H), 4.83 (d, J¼9.3 Hz, 1H,
9- or 10-H), 5.50 (q, J¼5.0 Hz, each 0.5H, 10-H), 4.10 (m,
0.5H, 20-H); IR (NaCl) cm21: 3600–3200 (s, O–H), 1660

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T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
4-OH), 3.40–3.60 (m, 2H, 30-H), 3.72 (d, J¼10.7 Hz, 1H),
3.91 (d, J¼11.0 Hz, 0.5H), 4.00 (dd, J¼2.2, 4.4 Hz, 0.5H,
H-2), 4.13 (d, J¼9.34 Hz, 1H), 4.20 (dd, J¼2.2, 4.4 Hz,
0.5H, 2-H), 4.32 (d, J¼011.0 Hz, 0.5H), 4.56 and 4.69 (q,
J¼5.2 Hz, each 0.5H, 1 -H), 4.80 (d, J¼9.1 Hz, 1H, 9- or
10-H), 4.88 (m, 1H, H-5); IR (neat) cm21: 3600–3400 (s,
O–H), 1670 (s, CvO), 1370 (s), 1350 (s), 1250 (m), 1230
(m), 1200 (m), 1170 (s), 1150 (m), 1080 (s), 1040 (s), 1010
(m), 1000 (m), 970 (m), 960 (m), 930 (s), 900 (m), 840 (s),
770 (m), 750 (m). Anal. calcd for C34H60O10SSi: C, 59.27;
H, 8.78. Found: C, 59.18; H, 8.78.
(m), 750 (m). Anal. calcd for C27H42O7: C, 67.76; H, 8.84.
Found: C, 67.47; H, 9.02.
3.3.5. Deprotection of ethoxyethyl group: 5b,20-epoxy-
2a,4a-dihydroxy-9a,10b-isopropylidendioxy-11-taxen-
13-one (9) and 2a,20-epoxy-4a,5a-dihydroxy-9a,10b-
isopropylidendioxy-11-taxen-13-one (10). Compound 8
(243 mg, 0.507 mmol) was dissolved in a mixture of
HOAc/THF/H2O (2 ml/2 ml/4 ml). After being stirred for
24 h at rt, the mixture was diluted with EtOAc (50 ml). The
organic layer was washed with aqueous NaHCO3, aqueous
NH4Cl, and brine. The organic layer was dried over Na2SO4
and concentrated in vacuo. The residue was purified by
chromatography (CHCl3/MeOH, 20/1), yielding 9 (66.0 mg,
0.163 mmol, 32%) as amorphous solid, 10 (65.0 mg,
0.160 mmol, 32%) as amorphous solid, and recovered 8
(19.0 mg, 0.039 mmol, 8.0%).
3.3.3. Desilylation of 7c to 7d; 2a-ethoxyethoxy-4a,20-
dihydroxy-9a,10b-isopropylidendioxy-5a-methane-
sulfonyloxy-11-taxen-13-one (7d). To a solution of 7c
(589 mg, 0.855 mmol) in THF (2 ml) at 08C was added
tetra-n-butylammonium fluoride (1.0 ml, 1.0 mmol in THF).
The reaction mixture was stirred for 1 h at rt, after which
time EtOAc (50 ml) was added. The mixture was washed
with aqueous NH4Cl and brine. The organic layer was dried
over Na2SO4 and was concentrated in vacuo. The residue
was purified by chromatography (EtOAc/hexane, 1/2),
yielding 7d (447 mg, 0.778 mmol, 91%) as amorphous
solid; 1H NMR (300 MHz), d¼01.06 and 1.12 (s, each 1.5H,
19-Me), 1.21–1.29 (m, 3H, 4 -Me), 1.25 (s, 3H, 17-Me),
1.33 (d, 1.5H, J¼5.0 Hz, 20-Me), 1.38 (d, J¼5.0 Hz, 1.5H,
20-Me), 1.30–1.50 (m, 1H), 1.41 (s, 3H, Me2CO2), 1.47 (s,
3H, Me2CO2), 1.50–1.70 (m, 2H), 1.57 and 1.62 (s, each
1.5H, 16-Me), 1.80–2.00 (m, 2H), 2.10 (s, 3H, 18-Me),
2.50–2.64 (m, 1H), 2.70–2.90 (m, 2H), 2.98 and 2.99 (s,
each 1.5H, MeSO3), 2.38, 2.52, 3.97, and 4.08 (m, each
0.5H, OH), 3.42–3.61 (m, 4H, 30-H, 9-H or 10-H, and 20-
H), 4.13 (m, 0.5H, 1H, H-20), 4.13 (dd, J¼2.5, 9.1 Hz, 0.5H,
2-H), 4.26 (m, 0.5H, H-20), 4.32 (m, 0.5H, H-2), 4.64 and
4.76 (q, J¼5.2 Hz, each 0.5H, 10-H), 4.82 (d, J¼9.3 Hz, 1H,
9-H or 10-H), 4.94 (m, 1H, 5-H); IR (KBr) cm21: 3600–
3200 (s, O–H), 1640 (s, CvO), 1370 (m), 1320 (s), 1230
(m), 1160 (s), 1080 (m), 1050 (s), 1040 (s), 990 (m), 920 (s),
990 (m); HR-FAB-MS, calcd for C28H46O10SNa (MNa)þ
m/z 597.2707, found 597.2704.
1
Compound 9 (oxetanol). H NMR (300 MHz), d¼1.22 (s,
3H, 19-Me), 1.15–1.35 (m, 1H, 7-H), 1.43 (s, 3H, Me2CO2),
1.49 (s, 3H, Me2CO2), 1.66 (s, 3H, 16-Me), 1.65–1.75 (m,
1H, 6-H), 1.75–1.85 (m, 1H, 7-H), 1.78 (d, 1H, J¼5.2 Hz,
3-H), 1.9–2.0 (m, 1H, 6-H), 1.92 (s, 3H, 18-Me), 2.28 (m,
1H, 1-H), 2.75 (m, 1H, OH), 2.75 (m, 2H, 14-H), 3.83 (m,
1H, OH), 4.27 (d, J¼9.6 Hz, 1H, 9-H), 4.30 (m, 1H, 2-H),
4.36 (d, J¼8.5 Hz, 20-H), 4.78 (d, J¼8.5 Hz, 1-H, 20-H),
4.70 (m, 1H, 5-H), 4.64 (d, J¼9.3 Hz, 1H, 10-H); IR (NaCl)
cm21: 3600–3200 (s, O–H), 1710 (m), 1650 (m), 1450 (m),
1370 (m), 1230 (m), 1170 (m), 1050 (m), 870 (m); HR-
FAB-MS, calcd for C25H35O6 (MþH)þ m/z 448.2432,
found 448.2436.
1
Compound 10 (furanol). H NMR (300 MHz), d¼1.20 (s,
6H, 17-Me and 19-Me), 1.35–1.45 (m, 1H, 7-H), 1.43 (s,
3H, Me2CO2), 1.46 (s, 3H, Me2CO2), 1.60 (s, 3H, 16-Me),
1.65–1.75 (m, 1H, 6-H), 1.75–1.85 (m, 1H, 7-H), 1.9–2.0
(m, 1H, 6-H), 1.88 (s, 3H, 18-Me), 2.00 (d, 1H, J¼5.5 Hz,
3-H), 2.40 (dd, 1H, J¼3.3, 6.9 Hz, 1-H), 2.45 (m, 2H, OH),
2.65 (dd, 1H, J¼6.9, 19.7 Hz, 14b-H), 3.03 (d, 1H,
J¼20.0 Hz, 14a-H), 3.66 (d, 1H, J¼11.4 Hz, 20-H), 3.75
(d, 1H, J¼11.4 Hz, 20-H), 4.05 (t, 1H, J¼6.5 Hz, 5-H), 4.22
(d, 1H, J¼9.6 Hz, 9-H), 4.39 (dd, 1H, J¼3.9, 4.7 Hz, 2-H),
4.53 (d, 1H, J¼9.3 Hz, 10-H); IR (NaCl) cm21: 3200–3600
(s, OH), 1800 (s), 1760 (s), 1670 (s), 1640 (s), 1390 (w),
1370 (w), 1260 (w), 1230 (s), 1210 (s), 1180 (s), 1080 (s),
1040 (s), 1000 (s), 1000 (s), 870 (w), 760 (w); HR-FAB-MS,
calcd for C25H35O6 (MþH)þ m/z 448.2432, found
448.2437.
3.3.4. Construction of oxetane ring: 7d to 8; 5b,20-
epoxy-2a-ethoxyethoxy-4a-hydroxy-9a,10b-isopropyl-
idendioxy-11-taxen-13-one (8). To a solution of 7d
(447 mg, 0.778 mmol) in toluene (4 ml) was added DBU
(3.89 mmol, 0.580 ml). The mixture was stirred at reflux
temperature for 1 h, after which time EtOAc (50 ml) was
added. The mixture was washed with aqueous NH4Cl,
aqueous NaHCO3 and brine. The organic layer was dried
over Na2SO4 and concentrated in vacuo. The residue was
purified by chromatography (EtOAc/hexane, 1/2), yielding
8 (243 mg, 0.507 mmol, 65%) as amorphous solid; 1H NMR
(300 MHz), d¼1.08–1.32 (m, 7H, 19-Me, 40-Me, 7-H), 1.22
(s, 3H, 17-Me), 1.43 (s, 3H, Me2CO2), 1.50 (s, 3H,
Me2CO2), 1.51 (s, 3H, 20-Me) 1.65 and 1.67 (s, each 1.5H,
16-Me), 1.82 (d, J¼3.5 Hz, 1H), 1.92 (s, 3H, 18-Me), 1.92–
2.26 (m, 3H), 2.22 (m, 0.5H, 1-H), 2.60 (m, 0.5H, 1-H), 2.70
(m, 2H, 14-H), 02.93 and 3.00 (s, each 0.5H, 4-OH), 3.45–
3.60 (m, 2H, 3 -H), 4.10 (dd, J¼2.5, 5.0 Hz, 0.5H, 2-H),
4.20–4.38 (m, 3H), 4.55 (d, J¼8.0 Hz, 0.5H), 4.57–4.77
(m, 2.5H), 4.89 (d, J¼8.0 Hz, 0.5H); IR (neat) cm21: 3600–
3200 (m, O–H), 1670 (s, CvO), 1450 (m), 1380 (m), 1220
(m), 1170 (s), 1090 (m), 1050 (s), 1000 (m), 970 (m), 870
3.3.6. Benzoylation of 9 to 11 and 12; 2a-benzoyloxy-
5b,20-epoxy-4a-hydroxy-9a,10b-isopropylidendioxy-
11-taxen-13-one (11) and 5b-benzoyloxy-2a,20-epoxy-
4a-hydroxy-9a,10b-isopropylidendioxy-11-taxen-13-
one (12). To a solution of 9 (105 mg, 0.259 mmol), benzoic
acid (633 mg, 5.18 mmol), and DMAP (632 mg,
5.18 mmol) in dry CH3CN (10 ml) at 08C was added DCC
[1067 mg, 5.18 mmol in dry CH3CN (10 ml)]. After being
stirring for 24 h, EtOAc (50 ml) was added to the mixture.
The organic layer was washed with the solution of HCl (1N,
25 ml), brine, aqueous NaHCO3 and brine. The organic
layer was dried over Na2SO4 and concentrated in vacuo.
The residue was purified by chromatography (CHCl3/
MeOH, 25/1), yielding 11 (86.0 mg, 0.168 mmol, 65%) as

T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
1535
amorphous solid and 12 (31.0 mg, 0.0608 mmol, 24%) as
amorphous solid.
as amorphous solid, and recovered 11 (5.3 mg, 0.010 mmol,
15%); [a]2D0¼þ26 (c 0.0097, MeOH); 1H NMR (300 MHz,
CD3OD), d¼1.06 (dt, J¼12.9, 6.6 Hz, 1H, 7-H), 1.15 (s, 3H,
19-Me), 1.41 (s, 3H, 17-Me), 1.70–1.90 (m, 1H), 1.72 (s,
3H, 16-Me), 1.87 (s, 3H, 18-Me), 2.00–2.20 (m, 3H), 2.35
(d, J¼5.2 Hz, 1H, 3-H), 2.63 (dd, J¼6.8, 19.8 Hz, 1H, 14-
H), 3.40 (d, J¼19.5 Hz, 1H, 14-H), 4.12 (d, J¼9.3 Hz, 1H,
20-H), 4.21 (s, 2H, H-9 and H-10), 4.61 (d, J¼9.6 Hz, 1H,
20-H), 4.69 (dd, J¼2.5, 8.8 Hz, 1H, 5-H), 5.81 (m, 1H), 7.47
(m, 2H, arom.), 7.62 (m, 1H, arom.), 8.01 (d, J¼1.2 Hz, 2H,
arom.); IR (neat) cm21: 3200–3600 (s, O–H), 1710 (s,
CvO), 1660 (s, CvO), 1260 (s), 1090 (w), 1050 (w), 705
(m), 1020 (m), 970 (w), 920 (w); HR-FAB-MS, calcd for
C27H34O7 Mþ m/z 470.2302, found 470.2307.
Compound 11. [a]D20¼þ39 (c 0.017, CHCl3); 1H NMR
(300 MHz), d¼1.25 (m, 1H, H-7), 1.25 (s, 3H, Me-19), 1.43
(s, 3H, Me2CO2), 1.44 (s, 3H, Me2CO2), 1.57 (s, 3H, 17-
Me), 1.50–1.70 (m, 1H), 1.80 (s, 3H, 16-Me), 1.85–2.20
(m, 2H), 1.93 (s, 3H, 18-Me), 2.14 (d, J¼5.0 Hz, 3-H), 2.21
(d, J¼2.5 Hz, 1H, 1-H), 2.77 (dd, J¼7.2, 19.8 Hz, 14b-H),
3.25 (d, J¼19.8 Hz, 1H, 14a-H), 4.19 (d, J¼8.2 Hz, 1H, 20-
H), 4.37 (d, J¼8.2 Hz, 1H, 20-H), 4.46 (d, J¼9.3 Hz, 1H, 9
or 10-H), 4.74 (m, 1H, 5-H), 4.75 (d, J¼9.3 Hz, 9 or 10-H),
7.45 (m, 2H, arom.), 7.57 (m, 1H, arom.), 8.01 (dd, J¼8.2,
1.1 Hz, 2H, arom.); IR (neat) cm21; 3400 (s, O–H), 1710 (s,
CvO), 1450 (s, CvO), 1360 (m), 1310 (m), 1050 (s) 1040
(m), 1020 (m), 980 (m), 860 (m), 710 (m); HR-EI-MS, calcd
for C30H39O7 (MþH)þ m/z 511.2694, found 511.2698.
3.5.2. Acetylation of 13 to 14; 9a,10b-diacetoxy-2a-
benzoyloxy-5b,20-epoxy-4a-hydroxy-11-taxen-13-one
(14). To a solution of 11 (19.5 mg, 0.0347 mmol) and
DMAP (cat.) in dry pyridine (0.4 ml) was added Ac2O
(50 ml). After the mixture was stirred for 24 h, EtOAc
(20 ml) was added. The organic layer was washed with
brine, H2O, aqueous CuSO4, H2O and brine. The organic
layer was dried over Na2SO4 and concentrated in vacuo,
yielding 14 (22.7 mg, 0.0347 mmol, quantitative) as
Compound 12. [a]2D0¼þ120 (c 0.0095, CHCl3); H NMR
1
(300 MHz), d¼1.20–1.40 (m, 1H, 7-H), 1.29 (s, 3H, 17-Me
or 19-Me), 1.30 (s, 3H, 17-Me or 19-Me), 1.47 (s, 3H,
Me2CO2), 1.50 (s, 3H, Me2CO2), 1.64 (s, 3H, 16-Me),
1.91–2.00 (m, 2H), 1.96 (s, 3H, 18-Me), 2.20 (m, 2H), 2.42
(m, 1H), 2.68 (dd, J¼7.1, 19.5 Hz, 1H, 14b-H), 3.19 (m, 2H,
14a-H, 4-OH), 3.59 (d, J¼10.0 Hz, 1H, 20-H), 3.64 (d,
J¼9.8 Hz, 1H, 20-H), 4.29 (d, J¼9.5 Hz, 1H, 9- or 10-H),
4.32 (m, 1H, 2-H), 4.64 (d, J¼9.5 Hz, 1H, 9- or 10-H), 5.27
(m, 1H, 5-H), 7.47 (m, 2H, arom.), 7.62 (m, 1H, arom.), 8.01
(d, J¼1.2 Hz, 2H, arom.); HR-FAB-MS, calcd for
C30H38O7Na (MþNa)þ m/z 533.2513, found 533.2519.
amorphous solid; [a]2D0¼þ14 (c 0.011, CHCl3); H NMR
1
(300 MHz), d¼1.15 (m, 1H, 7-H), 1.17 (s, 3H, 19-Me), 1.26
(s, 3H, 17-Me), 1.41 (s, 3H, 16-Me), 1.50–1.70 (m, 2H),
1.85 (s, 3H, 18-Me), 2.09 (s, 3H, MeCO), 2.10 (m, 1H), 2.12
(s, 3H, MeCO), 2.24 (dd, J¼6.9, 2.7 Hz, 1H, H-1), 2.46 (d,
J¼5.2 Hz, 1H, 3-H), 2.76 (m, 1H, OH), 2.76 (dd, J¼6.9,
19.8 Hz, 1H, 14-H), 3.40 (d, J¼19.5 Hz, 1H, 14-H), 4.19 (d,
J¼8.3 Hz, 1H, 20-H), 4.36 (d, J¼8.5 Hz, 1H, H-20), 4.72
(dd, J¼3.0, 9.3 Hz, 1H, 5-H), 5.93 (dd, J¼2.5, 5.5 Hz, 1H,
2-H), 5.98 (d, 2H, J¼5.5 Hz, 9-H and 10-H), 7.47 (m, 2H,
arom.), 7.62 (m, 1H, arom.), 8.01 (d, J¼1.2 Hz, 2H, arom.);
IR (neat) cm21: 3200–3600 (s, O–H), 1710 (s, CvO), 1660
(s, CvO), 1260 (s), 1090 (w), 1050 (w), 705 (m), 1020 (m),
970 (w), 920 (w); HR-FAB-MS, calcd for C31H39O9 Mþ m/z
555.2591, found 555.2588.
3.4. Trial for acetylation of 11 (method 1)
To a solution of 11 (65.0 mg, 0.127 mmol) in THF (1.0 ml),
was added LiHMDS (0.170 ml, 0.170 mmol) at 08C. After
being stirred for 30 min, AcCl (3.1 mg, 0.042 mmol) was
added. The mixture was stirred for 1 h, after which time,
EtOAc (30 ml) was added. The mixture was washed with
brine. The organic layer was dried over Na2SO4 and
concentrated in vacuo, almost all 11 (62.0 mg, 0.122 mmol,
95%) was recovered.
3.6. Trial for acetylation of 14
3.5. Trial for acetylation of 11 (method 2)
To a solution of 14 (11.7 mg, 0.0211 mmol) in THF
(0.5 ml), was added LiHMDS (32 ml, 0.032 mmol) at 08C.
After being stirred for 30 min, AcCl (3.3 mg, 0.042 mmol)
was added and the mixture was stirred for 1 h. After which
time, the mixture was diluted with EtOAc (20 ml). The
mixture was washed with brine. The organic layer was dried
over Na2SO4 and concentrated in vacuo to recover 14.
To a solution of 11 (4.0 mg, 0.0078 mmol) and DMAP
(8.0 mg, 0.065 mmol) in dry pyridine (0.5 ml) was added
Ac2O (20 ml). After the mixture was stirred for 24 h at 508C,
EtOAc (20 ml) was added. The organic layer was washed
with brine, H2O, aqueous CuSO4, H2O and brine. The
organic layer was dried over Na2SO4 and concentrated in
vacuo, almost all 11 was recovered and no acetylated
compound was obtained.
3.6.1. Reduction of 14; 9a,10b-diacetoxy-4a,20-epoxy-
2a-ethoxyethoxy-11-taxene-13b-ol (15). A stirred suspen-
sion of 14 (22.0 mg, 0.0396 mmol) in dry MeOH (1.5 ml)
was treated with CeCl3 (44.0 mg, 0.179 mmol) followed by,
portionwise, NaBH4 (90.0 mg, 2.38 mmol). After 25 min,
acetone (1 ml) was added and stirring was continued for
additional 15 min. The crude reaction product was isolated
with Et2O in usual manner and purified by chromatography
(CHCl3/MeOH, 20/1), yielding pure b-alcohol 15 (7.7 mg,
0.014 mmol, 34%) and the inseparable mixture of two
compounds (8.7 mg).
3.5.1. Deprotection of isopropylidene group; 2a-benzoyl-
oxy-5a,20-epoxy-4a,9a,10b-trihydroxy-11-taxen-13-
one (13). Compound 11 (34.5 mg, 0.0675 mmol) was
dissolved in
a mixture of AcOH/THF/H2O (2 ml/
0.5 ml/1 ml). After being stirred for 29 h at 528C, the
mixture was diluted with EtOAc (50 ml). The organic layer
was washed with aqueous NaHCO3 and brine. The organic
layer was dried over Na2SO4 and concentrated in vacuo.
The residue was purified by chromatography (CHCl3/
MeOH, 20/1), yielding 13 (21.0 mg, 0.0446 mmol, 66%)
1
Compound 15. [a]2D0¼þ4.9 (c 0.0061, CHCl3); H NMR

1536
T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
(300 MHz), d¼1.30 (m, 1H, 7-H), 1.31 (s, 3H, 19-Me), 1.30
(s, 3H, 17-Me), 1.50–1.60 (m, 1H), 1.78 (s, 3H, 16-Me),
1.80–2.00 (m, 2H), 2.03 (s, 3H, Me-18), 2.04 (s, 3H,
MeCO), 2.10 (s, 3H, MeCO), 2.00–2.20 (m, 2H), 2.29 (d,
J¼5.8 Hz, 1H, 3-H), 2.50 (m, 1H, 14-H), 2.70 (m, 1H,
4-OH), 4.18 (d, J¼8.2 Hz, 1H, 20-H), 4.19 (d, J¼7.7 Hz,
1H, 20-H), 4.30 (dd, J¼8.5, 4.1 Hz, 1H, 13-H), 4.76 (m, 1H,
5-H), 5.90 (m, 1H, 2-H), 5.93 (s, 2H, 9- and 10-H), 7.47 (m,
2H, arom.), 7.60 (m, 1H, arom.), 7.98 (d, J¼1.3 Hz, 2H,
arom.); IR (neat) cm21: 3200–3600 (s, O–H), 1740 (s,
CvO), 1710 (s, CvO), 1450 (w), 1370 (s), 1310 (w), 1270
(s), 1240 (s), 1150 (w), 1100 (s), 1060 (m), 1020 (s), 970
(m), 710 (s); FAB-MS, m/z (MþH–H2O)þ 539.
(d, J¼8.8 Hz, 0.5H), 4.95 (m, 1H, 5-H), 5.39 and 5.47 (d,
J¼6.1 Hz, each 0.5H, 14-H). HR-FAB-MS, calcd for
C29H44O8 (MþH)þ m/z 520.3034, found 520.3037.
3.7. Migration of Ac group from 13-OH to 4-OH
To a solution of 17 (28.0 mg, 0.0539 mmol) in MeOH
(1 ml), was added K2CO3 (20.0 mg, 0.145 mmol) at rt After
being stirred for 30 min, the mixture was diluted with
EtOAc (20 ml). The mixture was washed with aqueous
NH4Cl and brine, The organic layer was dried over Na2SO4
and concentrated in vacuo. The residue was purified by
chromatography (hexane/EtOAc, 2/1), yielding 16
(13.0 mg, 0.0250 mmol, 46%) and 8 (7.0 mg, 0.015 mmol,
28%).
3.6.2. Acetylation of 8 to 16 and 17; 4a-acetoxy-5b,20-
epoxy-2-ethoxyethoxy-9a,10b-isopropylidendioxy-11-
taxen-13-one (16) and 4a,13-diacetoxy-5b,20-epoxy-2a-
ethoxyethoxy-9a,10b-isopropylidendioxy-11,13-taxa-
diene (17). To a solution of 8 (92.0 mg, 0.192 mmol) in
THF (1 ml), was added LiHMDS (0.230 ml of 1 M solution
in THF, 0.230 mmol) at 08C. After being stirred for 30 min,
AcCl (18 mg, 0.23 mmol) was added and the mixture was
stirred for 1 h. The mixture was diluted with EtOAc (20 ml).
The organic layer was washed with brine. The organic layer
was dried over Na2SO4 and concentrated in vacuo, yielding
16 (26.0 mg, 0.050 mmol, 26%) as amorphous solid, 17
(26.0 mg, 0.050 mmol, 26%) and recovered 8 (34.0 mg,
0.0710 mmol, 34%).
The same reaction was carried out for 17 (219 mg,
0.422 mmol) at 08C, yielding 16 (147 mg, 0.283 mmol,
67%) and 8 (8.4 mg, 0.018 mmol, 4%).
3.7.1. Deprotection of ethoxyethyl group; 4a-acetoxy-
5b,20-epoxy-2a-hydroxy-9a,10b-isopropylidendioxy-
11-taxen-13-one (18) and 4a-acetoxy-2a,20-epoxy-5b-
hydroxy-9a,10b-isopropylidendioxy-11-taxene-13-one
(19). Compound 16 (243 mg, 0.507 mmol) was dissolved in
a mixture of AcOH/THF/H2O (1 ml/1 ml/2 ml). After being
stirred for 50 h at rt, the mixture was diluted with EtOAc
(30 ml). The organic layer was washed with aqueous
NH4Cl, aqueous NaHCO3 and brine. The organic layer
was dried over Na2SO4 and concentrated in vacuo. The
residue was purified by chromatography (CHCl3/MeOH,
20/1), yielding 18 (40.0 mg, 0.0890 mmol, 52%) and 19
(17.0 mg, 0.0378 mmol, 19%).
Compound 16. 1H NMR (300 MHz), d¼1.20–1.30 (m, 7H,
19-Me, 40-Me, 7-H), 1.43 (s, 3H, 16-Me), 1.48 (s, 3H,
Me2CO2), 1.49 (s, 3H, Me2CO2), 1.50 and 1.52 (s, each
1.5H, 20-Me), 1.63 and 1.65 (s, each 1.5H, 17-Me), 1.65–
1.70 (m, 1H), 1.80–1.90 (m, 1H), 2.00 and 2.03 (s, each
1.5H, MeCO), 2.14–2.26 (m, 1H), 2.19 (dd, J¼2.5, 7.1 Hz,
0.5H, 1-H), 2.35 (d, J¼20.1 Hz, 0.5H, 14-H), 2.38 (d,
J¼20.1 Hz, 0.5H, 14-H), 2.49 (d, J¼4.1 Hz, 0.5H, 3-H),
2.54 (d, J¼5.0 Hz, 0.5H, 3-H), 2.62 (dd, J¼2.5, 6.8 Hz,
0.5H, 1-H), 2.66 (dd, J¼6.9, 20.3 Hz, 0.5H, 14-H), 2.73 (dd,
J¼6.9, 20.1 Hz, 0.5H, 14-H), 3.40–3.60 (m, 2H, 30-H), 4.01
(dd, J¼2.5, 5.0 Hz, 0.5H, 2-H), 4.27 (dd, J¼2.8, 5.5 Hz,
0.5H, 2-H), 4.51 and 4.60 (q, J¼5.0, 5.2 Hz, each 0.5H, 10-H),
4.70 (dd, J¼1.7, 9.3 Hz, 1H, H-5); IR (neat) cm21: 1720 (s,
CvO), 1670 (s, CvO), 1450 (m), 1360 (s), 1220 (s), 1170 (s),
1050 (s), 980 (s), 870 (m), 450 (s); HR-FAB-MS, calcd for
C29H44O8 (MþH)þ m/z 520.3034, found 520.3037.
Compound 18 (oxetanol). [a]2D0¼þ54 (c 0.0035, CHCl3); 1H
NMR (300 MHz), d¼1.24–1.30 (m, 1H, 7-H), 1.25 (s, 3H,
19-Me), 1.91 (m, 1H, 6-H), 1.56 and 1.68 (s, each 3H, 16- or
17-Me), 1.46 (s, 3H, Me2CO2), 1.51 (s, 3H, Me2CO2), 1.94
(s, 3H, 18-Me), 2.08 (s, 3H, MeCO), 2.10 (m, 1H, 6-H), 2.19
(d, J¼19.8 Hz, 1H, 14-H), 2.20–2.30 (m, 2H, 1-H and 7-H),
2.50 (d, J¼5.1 Hz, 1H, 3-H), 2.82 (dd, J¼6.8, 19.8 Hz, 1H,
14-H), 4.27 (d, J¼9.5 Hz, 1H), 4.34 (m, 1H, H-2), 4.55 (d,
J¼8.8 Hz, 1H), 4.65 (d, J¼8.8 Hz, 1H), 4.73 (d, J¼9.3 Hz,
1H), 4.97 (d, J¼8.0 Hz, 1H, H-5); IR (neat) cm21: 3600–
3200 (m, O–H), 1730 (s, CvO), 1670 (s, CvO), 1460 (m),
1370 (s), 1230 (s), 1200 (m), 1170 (m), 1050 (s), 1030 (s),
1000 (m), 970 (m), 780 (m), 660 (m); HR-FAB-MS, calcd
for C25H36O7 (MþH)þ m/z 448.2459, found 448.2461.
Compound 19 (furanol). [a]2D0¼þ77 (c 0.0087, CHCl3); 1H
NMR (300 MHz), d¼1.18–1.23 (m, 1H, H-7), 1.18 (s, 3H,
19-Me), 1.32 (s, 3H, 17-Me), 1.44 and 1.48 (s, each 3H,
Me2CO2), 1.64 (s, 3H, 16-Me), 1.91 (s, 3H, 18-Me), 1.97
(m, 1H), 2.01 (s, 3H, MeCO), 2.20–2.02 (m, 2H), 2.40 (m,
2H), 2.70 (m, 2H), 3.68 (d, J¼11.3 Hz, 4-OH), 4.10 (s, 2H,
H-20), 4.31 (d, J¼9.6 Hz, 1H, 9- or 10-H), 4.38–4.31 (m,
2H, 2-H, 5-H), 4.59 (d, J¼9.6 Hz, 1H, 9- or 10-H); IR (neat)
cm21: 3600–3200 (m, O–H), 3000–2800 (m), 1730 (s,
CvO), 1670 (s, CvO), 1650 (s, CvO), 1450 (w), 1390
(s),1370 (s), 1230 (s),1220 (s), 1170 (m), 1065 (s), 1050 (s),
1040 (s), 1020 (s), 1000 (m), 970 (w), 950 (w), 940 (w), 780
(m); HR-FAB-MS, calcd for C25H36O7 (MþH)þ m/z
448.2459, found 448.2462.
3.6.3. 13-Acetoxy-5b,20-epoxy-2a-ethoxyethoxy-9,10-
isopropylidendioxy-11,13-taxadien-4-ol (17). 1H NMR
(300 MHz), d¼1.22–1.27 (m, 6H, 19-Me and 40-Me),
1.43 (s, 3H, Me2CO2), 1.44 (m, 1H, 6- or 7-H), 1.44 and
1.45 (s, each 1.5H, 20-Me), 1.47 and 1.48 (s, each1.5H,
Me2CO2), 1.52 and 1.61 (s, 1.5H, 17-Me), 1.74 and 1.75 (s,
each 1.5H, Me-16), 1.86 (m, 1H, 6- or 7-H), 2.01 (m, 1H, 6-
or 7-H), 2.05 (m, 1H, 6-H), 2.06 (m, 0.5H, 1-H), 2.07 and
2.09 (s, each 1.5H, Ac), 2.19 and 2.20 (s, each 1.5H,
18-Me), 2.20 (m, 1H, 3-H), 02.51 (dd, J¼2.7, 6.1 Hz, 0.5H,
1-H), 3.50–3.60 (m, 2H, 3 -H), 4.01 (dd, J¼2.7, 4.9 Hz,
0.5H, 2-H), 4.21 (d, J¼9.3 Hz, 0.5H), 4.22 (d, J¼9.3 Hz,
0.5H), 4.27 (dd, J¼2.9, 5.1 Hz, 1H, 2-H), 4.35 (d, J¼8.3 Hz,
0.5H), 4.45 (d, J¼8.8 Hz, 0.5H), 4.50 (d, J¼8.3 Hz, 0.5H),
4.57 (q, J¼4.9 Hz, 1H, 10-H), 4.59 (d, J¼9.3 Hz, 0.5H), 4.60
(d, J¼9.3 Hz, 0.5H), 4.63 (q, J¼5.1 Hz, 0.5H, 10-H), 4.84

T. Horiguchi et al. / Tetrahedron 59 (2003) 1529–1538
1537
3.7.2. Introduction of m-N3-benzoyl and m-chloro-
benzoyl group: 4a-acetoxy-2a-(m-azido-benzoyloxy)-
5b,20-epoxy-9a,10b-isopropylidendioxy-11-taxene-13-
one (20a). To a solution of 18 (39.0 mg, 0.0868 mmol) in
dry CH3CN (10 ml), m-N3-benzoic acid (200 mg,
1.64 mmol), DMAP (200 mg, 1.64 mmol) and DCC
(338 mg, 1.64 mmol) were added at 08C. After being
stirring for 24 h at rt, EtOAc (50 ml) was added. The
mixture was washed with solution of HCl (1N, 25 ml),
brine, aqueous NaHCO3 and brine. The organic layer was
dried over Na2SO4 and concentrated in vacuo. The residue
was purified by chromatography (CHCl3/MeOH, 27/1; and
hexane/EtOAc, 7/2), yielding 20a (44.0 mg, 0.0795 mmol,
92%) as amorphous solid: [a]2D0¼þ110 (c 0.021, CHCl3);
1H NMR (500 MHz), d¼1.23 (s, 3H, Me-19), 1.47 (s, 3H,
Me2CO2), 1.55 (s, 3H, Me2CO2), 1.55 (s, 3H, Me-17), 1.56
(m, 1H, 7-H), 1.83 (s, 3H, Me-16), 1.87 (m, 1H, 6-H), 1.98
(s, 3H, Me-18), 2.13 (dd, 1H, J¼7.6, 13.7 Hz, 7-H), 2.18 (s,
3H, MeCO), 2.25 (dd, J¼2.4, 6.8 Hz, 1H, 1-H), 2.28 (dd,
J¼9.0, 16.6 Hz, 1H, 6-H), 2.44 (d, J¼19.8 Hz, 1H, 14a-H),
2.80 (dd, J¼6.8, 20.0 Hz, 1H, 14b-H), 2.84 (d, 1H,
J¼5.9 Hz, 3-H), 4.12 (dd, J¼1.0, 8.3 Hz, 1H, 20-H), 4.40
(d, J¼8.1 Hz, 1H, 20-H), 4.44 (d, J¼9.2 Hz, 1H, 9-H), 4.77
(d, J¼9.5 Hz, 1H, 10-H), 4.98 (d, 1H, J¼8.1 Hz, 5-H), 5.85
(dd, J¼2.7, 5.9 Hz, 1H, 2-H), 7.25 (ddd, 1H, J¼1.0, 2.4,
8.1 Hz, arom.), 7.48 (dd, 1H, J¼7.8, 8.1 Hz, arom.), 7.76
(dd, 1H, J¼1.7, 2.0 Hz, arom.), 7.85 (dt, 1H, J¼7.8, 1.2 Hz,
arom.); 13C NMR (125 MHz), d¼198.10 (C-13), 169.85
(MeCO), 163.99 (N3–PhCO), 152.70 (C-11), 140.84
(arom.) 139.47 (C-12), 131.11 (arom.), 130.16 (arom.),
126.20 (arom.), 124.30 (arom.), 119.69 (arom.), 108.01
(Me2CO2), 85.22 (C-5), 82.35 (C-4), 81.25 (C-9), 76.20
(C-20), 75.48 (C-10), 71.00 (C-2), 47.46 (C-1), 41.58 (C-3),
38.91 (C-8), 38.49 (C-15), 38.04 (C-17), 35.41 (C-14),
27.24 (Me2CO2), 27.03 (C-6), 26.76 (Me2CO2), 26.55 (C-7),
24.36 (C-16), 21.85 (4-Ac), 16.46 (C-19), 14.12 (18-Me);
IR (neat) cm21: 2940, 2120 (s, N3), 1720 (s, CvO), 1670 (s,
CvO), 1580 (m), 1520 (w), 1480 (w), 1440 (w), 1300 (s),
1230 (s), 1170 (m), 1100 (m), 1050 (s), 1020 (s), 990 (m),
940 (w), 890 (w), 880 (w), 810 (w), 760 (s), 670 (m); HR-
FAB-MS, calcd for C32H40N3O8 (MþH)þ m/z 594.2813,
found 594.2814.
126.20 (arom.), 124.30 (arom.), 119.69 (arom.), 108.02
(Me2CO2), 85.20 (C-5), 82.36 (C-4), 81.24 (C-9), 76.16
(C-20), 75.48 (C-10), 71.06 (C-2), 47.48 (C-1), 41.60 (C-3),
38.91 (C-8), 38.48 (C-15), 38.06 (C-17), 35.42 (C-14),
27.25 (Me2CO2), 27.04 (C-6), 26.77 (Me2CO2), 26.58 (C-7),
24.40 (C-16), 21.84 (4-Ac), 16.48 (C-19), 14.12 (18-Me);
IR (neat) cm21: 2940 (m), 1720 (s, CvO), 1670 (s, CvO),
1570 (w), 1530 (w), 1450 (w), 1420 (w), 1370 (m), 1320
(w), 1290 (m), 1230 (w), 1170 (m), 1120 (m), 1100 (m),
1070 (m), 1050 (s), 1020 (m), 990 (m), 970 (w), 940 (w),
890 (w), 880 (w), 810 (w), 760 (s), 670 (m); HR-FAB-MS,
calcd for C32H39O8Cl Mþ m/z 586.2302, found 586.2330.
Acknowledgements
We thank Dr Takao Yamori (Cancer Chemotherapy Center,
Japanese Foundation for Cancer Research) for evaluation of
biological activity of compounds 20a and 20b.
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