New highly active taxoids from 9β-dihydrobaccatin-9,10-acetals. Part 4

Article abstract of DOI:10.1016/S0968-0896(03)00454-1

It was shown that a new taxane analogue 3, which exhibited both in vitro antitumor activity and in vivo efficacy by both iv and po administration, was prone to be metabolized by human liver microsomes. We identified a major metabolite, M-1, generated by h

Full text of DOI:10.1016/S0968-0896(03)00454-1

Bioorganic & Medicinal Chemistry 11 (2003) 4431–4447
New Highly Active Taxoids from 9ꢀ-Dihydrobaccatin-9,10-
acetals. Part 4
Yasuyuki Takeda,a Kouichi Uoto,a Jun Chiba,a Takao Horiuchi,a Michio Iwahana,b
Ryo Atsumi,c Chiho Ono,c Hirofumi Terasawab and Tsunehiko Sogaa,*
aMedicinal Chemistry Research Laboratory, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13 Kita-Kasai 1-Chome,
Edogawa-ku, Tokyo 134-8630, Japan
bNew Product Research Laboratories III, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13 Kita-Kasai 1-Chome,
Edogawa-ku, Tokyo 134-8630, Japan
cDrug Metabolism & Physicochemical Property Research Laboratory, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center,
16-13 Kita-Kasai 1-Chome, Edogawa-ku, Tokyo 134-8630, Japan
Received 26 March 2003; accepted 30 June 2003
Abstract—It was shown that a new taxane analogue 3, which exhibited both in vitro antitumor activity and in vivo efficacy by both
iv and po administration, was prone to be metabolized by human liver microsomes. We identified a major metabolite, M-1, gen-
erated by human liver microsomes as 20a, a hydroxylated compound at the pyridine ring of 3. To improve the metabolic stability of
3, we designed and synthesized new taxane analogues based on the structure of M-1, and obtained some compounds that main-
tained excellent antitumor activity and were scarcely metabolized by human liver microsomes.
# 2003 Elsevier Ltd. All rights reserved.
Introduction
significantly. On the other hand, modifications at the
position C-7–C-10 regions of the diterpene moiety are
tolerated very well,5 because these regions do not inter-
act directly with tubulin. Under these circumstances, we
focused on the C-7–C-10 region and, as a result, found
that some of the new taxane analogues, 9-b-dihydro-
9,10-O-acetal taxanes, showed activity against several
tumor cell lines stronger than that of docetaxel.6 Fol-
lowing an extensive study, we discovered the compound
3, which exhibited marked in vitro antitumor activity as
well as in vivo efficacy by both iv and po administration
(Fig. 1).7
Paclitaxel (1, Taxol1) was isolated from the bark of the
western yew Taxus brevifolia by Wani et al. in 19711 and
has been shown to be clinically efficacious against sev-
eral tumors that are refractory to other antitumor
drugs. Paclitaxel is an antimitotic agent with a unique
mode of action; it promotes the assembly of stable
microtubules, which cannot be depolymerized by cal-
cium, a variation of temperature, or microtubule-dis-
assembling agents.2 The excellent clinical activity of
paclitaxel prompted intense research aimed at under-
standing the influence of structural modifications of the
paclitaxel molecule on its biological activity and
searching for new analogues with more desirable physi-
cochemical properties and higher potency, such as doc-
etaxel (2, Taxotere1).3 The search for novel taxane
analogues has focused on regions such as the side chain
at the C-13 position, C-2 benzoate and C-4 acetate,
which interact directly with tubulin,4 and the modifi-
cations of such regions influenced the biological activity
During the exploration of the biological property of 3,
however, it was elucidated that the metabolic stability of
3 differed among species; compound 3 was scarcely
metabolized by mouse or dog liver microsomes. On the
other hand, the incubation of 3 with monkey or human
liver microsomes provided the metabolite M-1 rapidly.
Hence, it was considered that the excellent antitumor
efficacy of 3 obtained by both po and iv administration
in mouse might not be assured in the case of oral
administration in humans. For this reason, we started to
prepare taxane analogues that maintained antitumor effi-
cacy but would be less prone to be metabolized (Fig. 2).
*Corresponding author. Tel.: +81-3-3680-0151; fax: +81-3-5696-
8344; e-mail: sogatf7t@daiichipharm.co.jp
0968-0896/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0968-0896(03)00454-1

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Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
Figure 1. Structures of taxane analogues.
and both fragmentation patterns gave product ions at
m/z 130 and 624, which corresponded to the core taxane
ring. Therefore, the core taxane ring was assumed to be
unchanged in M-1. The fragment ions at m/z 183, 209,
and 227 were found in the spectrum of 3, but were not
present in the spectrum of M-1. These were replaced by
new ions at m/z 199, 225, and 243, which were 16 mass
unit greater than the respective corresponding ions.
These results suggested that M-1 is the oxygenated
compound of 3 and that the oxidation occurred on the
pyridine ring moiety. Then, we tried to synthesize the
pyridine N-oxide at first (Fig. 3).
Treating 3 with m-chloroperbenzoic acid (mCPBA) in
CHCl3 afforded the morpholine N-oxide 4 in good yield
but not the pyridine N-oxide (Scheme 1).
Oxidation of 5,7 the precursor of 3, with OsO4 gave the
diol 6; then oxidation with mCPBA afforded the pyri-
dine N-oxide 7. Cleavage of the diol moiety of 7 with
NaIO4 gave the aldehyde, to which the morpholine
moiety was introduced by reductive amination to afford
the targeted pyridine N-oxide 8 (Scheme 2).
As shown by HPLC analysis, the retention time of N-
oxide 8 did not agree with that of M-1. Therefore, it was
assumed that M-1 was oxidized onto the pyridine ring.
Then, we tried to synthesize compounds possessing the
hydroxypyridine rings at the C-13 side chain. The
synthesis of the key b-lactam intermediates (14a, 14b) is
shown in Scheme 3. Protection of the phenol moiety of
9 with benzyl bromide gave the benzyl ether 10, which
was converted to the aldehyde 11a in four steps accord-
ing to a procedure similar to that reported by Blantz
and co-workers.8 The 3-benzyloxypyridyl aldehyde 11b
was synthesized from 12 via the protection followed by
oxidation. Aldehydes 11a and 11b were converted to b-
lactams (13a, 13b) by the method of chiral enolate-imine
cyclocondensation.9,10 Acylations of 13a and 13b were
accomplished with di-tert-butyl dicarbonate [(Boc)2O]
and 4-dimethylaminopyridine (DMAP) to afford the
respective targeted b-lactams (14a, 14b) in high yield.
Figure 2. Remaining rates of docetaxel (upper) and 3 (lower) after
incubation with human, monkey, dog, and mouse liver microsomes.
Figure 3. Mass fragment patterns of 3.
Chemistry
Before beginning to synthesize new taxane analogues,
we tried to identify the structure of M-1. The chemical
structure of M-1 was partially determined by LC/MS/
MSanalysis. As a result of the LC/MSanalysis, M-1
gave a strong signal at m/z 922, that is 16 mass units
greater than the protonated molecular ion (M+H)+ of
3 at m/z 906. Subsequently, LC/MS/MS analysis of 3 at
m/z 906 and that of M-1 at m/z 922 were performed,
The coupling of 167 with the respective b-lactams (14a,
14b) and the subsequent removal of the protecting
group at C-20 were carried out following procedures
similar to those reported by Ojima et al.9 to give the
compounds 18a and 18b. Oxidation of 18a and 18b with
OsO4 followed by cleavage with NaIO4 gave the alde-
hydes, which were converted to the compounds 19a and
19b by reductive amination. Finally, cleavage of the

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4433
Scheme 1. Reagents: (a) mCPBA, CHCl3 (92%).
Scheme 2. Reagents: (a) OsO4, NMO, THF, acetone, H2O (90%); (b) mCPBA, CHCl3 (51%); (c) (1) NalO4, THF, MeOH, H2O; (2) morpholine,
AcOH, NaBH3CN, EtOH (39%).
Scheme 3. Reagents: (a) BnBr, NaH, THF, DMF (82%); (b) (1) mCPBA, CHCl3 (96%); (2) Ac2O (77%); (3) NaOH, EtOH, H2O (75%); (4) MnO2,
CHCl3 (77%); (c) (1) BnBr, KOH, EtOH (66%); (2) MnO2, CHCl3 (73%); (d) (1) LiHMDS, TMSCl, THF; (2) 15, LDA, THF (39% for 13a, 37%
for 13b); (e) (Boc)2O, DMAP, THF (88% for 14a, 83% for 14b).
benzyl moiety of 19a and 19b by catalytic hydrogenation
gave the targeted compounds 20a and 20b (Scheme 4). As
a result of LC/MS/MS analysis, compound 20a was
found to give the same mass fragmentation patterns and
the same retention time in HPLC chromatograms as
those of M-1 generated by human liver microsomes.
Therefore, it was elucidated that the metabolite of 3
produced by human liver microsomes was the com-
pound oxidized onto the 5-position of the pyridine ring
of 3.
therefore considered that the introduction of the sub-
stituent onto the 5-position of the pyridine ring would
not significantly alter the cytotoxicity of 3 but would
effectively block hydroxylation. On this assumption, we
synthesized the taxane analogues possessing the pyri-
dine ring substituted at its 5-position at the C-13 side
chain.
Synthesis of the b-lactams (23a–23f) possessing the pyr-
idine ring with the introduced substituents on their 5-
positions was depicted in Scheme 5. Acylations of chiral
b-lactams (22a–22f) with (Boc)2O afforded the desired
b-lactams (23a–23f) in good yield. The b-lactams (22a–
22f) were derived from the corresponding pyr-
idylaldehydes (21a–21f) in various ways. The b-lactams
(24a, 24d, 24e) were synthesized by the Staudinger
reaction between the imine, which was derived from the
corresponding aldehydes (21a, 21d, 21e) and p-anisidine,
and the ketene derived in situ from 2-acetoxyacetyl
The cytotoxicity of four oxidized compounds (4, 8, 20a,
20b) was compared with those of paclitaxel (1), doc-
etaxel (2), and 3 (Table 1). All compounds, with the
exception of 20a exhibited decreased cytotoxicity.
Although the cytotoxicity of 20a against cancer cell lines
expressing P-glycoprotein (PC-12, PC-6/VCR29-9 and
PC-6/VP1-1) was weak compared with that of 3, 20a
retained the activity against P388 and PC-6. It was

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Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
Scheme 4. Reagents: (a) LiHMDS, b-lactams (90% for 17a, 82% for 17b); (b) TBAF, THF (100% for 18a, 94% for 18b); (c) (1) OsO4, NMO, THF,
acetone, H2O; (2) NaIO4, THF, MeOH, H2O; (3) morpholine, AcOH, NaBH3CN, EtOH (74% for 19a, 69% for 19b); (d) H2, Pd(OH)2, EtOH (64%
for 20a, 84% for 20b).
Table 1. Cytotoxicity and metabolic stability of 7-deoxy-9,10-O-acetal taxane analogues
Compd
Cytotoxicity GI50 (ng/mL)a
Remaining rate (%)b
P388
PC-6
PC-12
PC-6/VCR29-9
PC-6/VP1-1
1
2
3
2.93
0.78
0.18
1.27
0.26
0.26
539
19.1
0.13
455
62.1
2.43
1000
442
19.3
NT
88.7
60.2
4
8
20a
20b
10
4.45
17.1
0.02
7.31
4.12
331
2.66
30.5
>1000
54.3
199
NT
NT
585
NT
NT
NT
NT
NT
42.4
0.05
11.3
40.5
35a
35b
35c
35d
35e
35f
0.06
3.69
0.05
0.14
9.2
0.34
3.97
0.31
0.78
5.84
0.07
0.05
4.66
0.11
0.43
10.5
0.14
0.97
14.6
1.11
4.4
38
1.13
14.1
74.2
13.5
39.3
209
28.8
NT
98.8
87.8
NT
0.16
28.7
87.8
NT, not tested.
aConcentration that inhibited the growth of cells by 50% at 72 h continuous exposure for the five cell lines [mouse leukemia (P388), human lung
cancer cell lines (PC-6 and PC-12), and resistant cancer cell lines (PC-6/VCR29-9 and PC-6/VP1-1)].12
bRemaining rate of the substrate after 5 min of incubation with human liver microsomes.
chloride. Sequential deacetylation and silylation gave
the b-lactams (25a, 25d, 25e). After removal of the p-
methoxyphenyl moieties, the racemic mixtures were
resolved by using a chiral HPLC column to afford the
optically pure b-lactams [(+)-22a, (+)-22d, (+)-22e].
Formation of (+)-27 was achieved via chiral ester-eno-
late imine cyclocondensation utilizing 15 as a chiral
auxiliary and the imine 26 derived from the aldehyde
21b. Finally, the p-methoxyphenyl moiety was removed
with ceric ammonium nitrate (CAN) to afford the
desired b-lactam (+)-22b, whose enantiomeric excess
was 79% ee. Synthesis of (+)-22c was accomplished
according to a published procedure utilizing l-threonine
methyl ester (28) as a chiral auxiliary,11 and its
enantiomeric excess was 54% ee. The b-lactam (+)-
22f,10 possessing the methoxyl group, was synthesized
by following a procedure analogous to that for the pre-
paration of 13a, possessing the benzyloxy group.
The targeted compounds (35a–35f) were synthesized
according to a procedure similar to that described for
the preparation of 19a utilizing 16 and the correspond-
ing b-lactams (23a–23f) (Scheme 6).
Results and Discussion
Activities of the synthetic compounds were evaluated in
cytotoxicity assays against five cell lines (P388, PC-6,
PC-12, PC-6/VCR29-9 and PC-6/VP1-1), and activities
were compared with those of paclitaxel and docetaxel.
The activities of 35a, 35c, and 35f, which possessed,
respectively, a methyl, fluoro, and methoxyl group on
the pyridine ring, were similar to that of 3 against all cell
lines, and 35d possessing the chloro moiety showed
slightly weaker cytotoxicity compared with that of these
three compounds. On the other hand, 35b and 35e,

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4435
Scheme 5. Reagents: (a) (Boc)2O, DMAP, THF (96% for 23a, 92% for 23b, 93% for 23c, 100% for 23d, 99% for 23e, 91% for 23f); (b) (1) 4-
anisidine, Na2SO4, benzene; (2) AcOCH2COCl, Et3N, CH2Cl2 (88% for 24a, 61% for 24d, 23% for 24e); (c) (1) K2CO3, THF, MeOH; (2) TIPSCl,
imidazole, DMF (85% for 25a, 78% for 25d, 36% for 25e); (d) (1) CAN, CH3CN, H2O; (2) Chiralcel OD or AD (27% for 22a, 25% for 22d, 33%
for 22e); (e) 4-anisidine, Na2SO4, benzene (84%); (f) 15, LDA, THF (30%); (g) CAN, CH3CN, H2O (59%); (h) (1) TBDPSCl, imidazole, DMAP,
CH2Cl2; (2) 21c, benzene; (3) AcOCH2COCl, Et3N, CH2Cl2 (72%); (i) TBAF, THF (85%); (j) (1) K2CO3, THF MeOH; (2) TIPSCl, imidazole,
DMF (61%); (k) NaHCO3, KMnO4, acetone, H2O (35%); (l) (1) LiHMDS, TMSCl, THF; (2) 15, LDA, THF (57%).
Scheme 6. Reagents: (a) LiHMDS, b-lactams (80% for 33a, 95% for 33b, 74% for 33c, 71% for 33d, 92% for 33e, 100% for 33f); (b) TBAF, THF
(94% for 34a, 85% for 34b, 99% for 34c, 100% for 34d, 76% for 34e, 91% for 34f); (c) (1) OsO4, NMO, THF, acetone, H2O; (2)NaIO4, THF,
MeOH, H2O; (3) morpholine, AcOH, NaBH3CN, EtOH (58% for 35a, 61% for 35b, 64% for 35c, 77% for 35d, 81% for 35e, 51% for 35f).

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Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
which possessed, respectively, an ethyl and tri-
fluoromethyl group on the pyridine ring, gave sig-
nificantly decreased cytotoxicity. This reduction of
cytotoxicity might be due to a steric hindrance.
and acetonitrile [70:30 (v/v)]; flow rate, 0.2 mL/min;
column temperature, 30 ꢁC; detection, ESI/MS/MS
(positive mode); capillary temperature, 225 or 275 ꢁC;
sheath gas (N2), 70–80 psi; auxiliary gas (N2), 5–10
units; collision energy, ꢂ40 eV; collision gas (Ar), 1.8 m
torr; electron multiplier, 1000 or 1200 V.
The metabolic stability of 35a, 35c, 35d, and 35f, which
all showed nearly the same cytotoxicity as 3, was exam-
ined, and the results were shown as the remaining rate
of substrate after 5 min of incubation with human liver
microsomes. All compounds, except 35a, exhibited good
metabolic stability compared with 3, as we had expec-
ted. Compound 35a possessing a methyl group might be
oxidized at its methyl moiety of the pyridine ring.
Identification of M-1
As a result of the LC/MSanalysis of 8, 20a and 20b, all
samples gave a strong signal at m/z 922, and LC/MS/
MSspectrum of them at m/z 922 gave product ions at
m/z 199, 225, and 243, which were consistent with that
of M-1. The HPLC analysis was performed using two
diverse mobile phases, 0.01 M AcONa (pH 3.8) and
acetonitrile [55:45 (v/v)] (condition A) and 0.01 M
AcONa (pH 5.0) and acetonitrile [50:50 (v/v)] (condi-
tion B) at a constant flow rate of 1.0 mL/min. The
retention times of 3, M-1, 8, 20a and 20b of each mobile
phase were as follows: Condition A; 3 (about 17.2 min),
M-1 (about 9.5 min), 8 (about 6.4 min), 20a (about 9.5
min), 20b (10.3 min). Condition B; 3 (about 27.3 min),
M-1 (about 14.6 min), 8 (about 10.3 min), 20a (about
14.6 min), 20b (about 17.7 min). And the mixture of the
extracts from human liver microsomes and 20a gave a
single peak in both conditions.
In conclusion, to improve the metabolic stability of 3,
we designed and synthesized taxane analogues based on
the structure of M-1, the major metabolite of 3. Some
compounds maintained the strong cytotoxicity and were
scarcely metabolized by human liver microsomes. Fur-
ther study to improve the metabolic stability of 3 is in
progress, and we expect that this study will lead us to
obtain a compound that will exhibit good antitumor
activity not only in mice but also in humans.
Experimental
All chemicals and solvents used in synthesis were
reagent-grade products and were used without addi-
tional purification. The solvent and reagent names are
abbreviated as follows: acetic anhydride (Ac2O), ethyl
acetate (AcOEt), benzyl bromide (BnBr), di-tert-butyl
dicarbonate [(Boc)2O], ceric ammonium nitrate (CAN),
4-dimethylaminopyridine (DMAP), N,N-dimethylform-
amide (DMF), diethyl ether (Et2O), lithium bis(tri-
methylsilyl)amide (LiHMDS), m-chloroperbenzoic acid
(mCPBA), N-methylmorpholine-N-oxide (NMO), tetra-
butylammonium fluoride (TBAF), tert-butyldiphenylsi-
lyl chloride (TBDPSCl), tetrahydrofuran (THF),
triisopropylsilyl chloride (TIPSCl), and trimethylsilyl
chloride (TMSCl). Melting points were obtained on a
Yanaco micro melting point apparatus and are uncor-
rected. NMR spectra were obtained on a JEOL EX-400
spectrometer with tetramethylsilane as an internal stan-
dard. Chemical shifts are reported in parts per million
(ppm, d units). Splitting patterns are designated as s,
singlet; d, doublet; t, triplet; q, quartet; m, multiplet;
and br, broad. Infrared (IR) spectra were obtained on a
Hitachi 270-30 spectrometer with KBr disks. Mass
spectra were recorded on a JEOL AX-505W, or a JMS-
700 spectrometer. Elementary analysis was carried out
with a Perkin-Elmer Model 240C elemental analyzer.
Optical rotations were measured with a Horiba SEPA-
200 polarimeter. Merck Kieselgel 60 (70–230 mesh) was
used for column chromatography. The HPLC system
consisted of a model L-6200, L-6000 system (Hitachi)
with a 717 plus autosampler (Waters), a model L-7400
UV detector (Hitachi), and a 250ꢀ4.6 mm Symmetry
C18 column (Waters) maintained at 30 ꢁC. The condi-
tions for LC/MS/MS were as follows: mass spectro-
metry, TSQ LC/MS/MS system (ThermoQuest); HPLC
system, an Alliance 2690 (Waters); column, 150ꢀ2.1
mm Symmetry C18 (Waters); mobile phase, 0.2% AcOH
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino-N-oxide)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-
(tert-butoxycarbonylamino)-2-hydroxy-3-(2-pyridyl)pro-
pionate (4). To a solution of 3 (100 mg, 0.119 mmol) in
CHCl3 (2 mL) was added mCPBA (21 mg, 0.12 mmol)
with ice cooling, and the mixture was stirred at the same
temperature for 1 h. After saturated aqueous NaHCO3
was added to the reaction mixture, the whole was
extracted with AcOEt. The extract was washed with
brine and dried over Na2SO4. The solvent was removed
under reduced pressure. The residue was purified by
preparative TLC (CHCl3–MeOH=10:1) and lyophi-
lized with 1,4-dioxane to give the title compound (93
mg, 92%) as a white amorphous powder, mp 159–
164 ꢁC. H NMR (CDCl3) d: 1.25 (3H, s), 1.45 (9H, s),
1
1.49 (3H, s), 1.60 (3H, s), 1.74 (3H, s), 1.89–2.04 (3H,
m), 2.20–2.37 (1H, m), 2.47 (3H, s), 2.94 (1H, d, J=5.5
Hz), 3.37–3.78 (8H, m), 4.19 (2H, m), 4.33 (1H, d,
J=8.3 Hz), 4.39–4.48 (2H, m), 4.94 (1H, s), 4.98 (1H, d,
J=2.0 Hz), 5.36 (2H, d, J=8.0 Hz), 5.94–6.00 (2H, m),
6.05 (1H, t-like, J=8.3 Hz), 7.19 (1H, dd, J=2.0, 7.5
Hz), 7.45–7.49 (3H, m), 7.60 (1H, d, J=8.0 Hz), 8.13
(2H, d, J=8.0 Hz), 8.55 (1H, d, J=5.0 Hz); FAB-MS
(m/z): 922 (M+H)+. Anal. calcd for C48H63N3O15 2H2O:
.
C, 60.18; H, 7.05; N, 4.39. Found: C, 60.33; H, 6.93; N,
4.28; IR: 3423, 2971, 1712, 1592, 1569, 1490 cmꢂ1; [a]D26
ꢂ2.9ꢁ (c 0.11, CHCl3).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2,3-dihy-
droxypropylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-
butoxycarbonylamino)-2-hydroxy-3-(2-pyridyl)propionate
(6). To a solution of 5 (40 mg, 0.048 mmol) in a mixture
of THF (1 mL), acetone (1 mL), and H2O (1 mL) were
added NMO (28 mg, 0.24 mmol) and OsO4 (2.5 mg),

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4437
and the mixture was stirred at room temperature for 1
h. After AcOEt and 10% aqueous Na2S2O3 were added
to the reaction mixture, the two layers were separated.
The aqueous layer was extracted with AcOEt, and the
combined organic layer was washed with saturated
aqueous NaHCO3, brine, and dried over Na2SO4. The
solvent was removed under reduced pressure and the
residue was purified by preparative TLC (CHCl3–
MeOH=10:1) to give the title compound (37.5 mg,
90%) as a white amorphous powder. 1H NMR (CDCl3)
d: 1.27 (3H, s), 1.44 (9H, s), 1.50 (3H, s), 1.57 (3H, s),
1.73 (3H, s), 1.84–2.17 (3H, m), 2.36 (3H, s), 2.93 (1H,
d, J=5.4 Hz), 3.75–3.88 (3H, m), 4.20–4.22 (2H, m),
4.32 (1H, d, J=7.8 Hz), 4.84–4.92 (3H, m), 5.28 (2H, d,
J=7.0 Hz), 5.35 (1H, d, J=9.5 Hz), 5.96 (2H, m),
6.10 (1H, br t, J=8.0 Hz), 7.23 (1H, dd, J=2.0, 6.0
Hz), 7.41–7.61 (3H, m), 7.72 (1H, dd, J=2.0, 8.0H),
8.11 (2H, d, J=8.0 Hz), 8.53 (1H, d, J=4.5 Hz); HR-
residue was purified by preparative TLC (CHCl3–
MeOH=10:1) and lyophilized with 1,4-dioxane to give
the title compound (7.5 mg, 39%) as a white amorphous
powder, mp 165–168 ꢁC. 1H NMR (CDCl3) d: 1.27 (3H,
s), 1.41 (9H, s), 1.48 (3H, s), 1.60 (3H, s), 1.80 (3H, s),
1.85–2.11 (2H, m), 2.29–2.31 (1H, m), 2.35 (3H, s),
2.59–2.68 (4H, m), 2.71 (1H, dd, J=5.4, 13.2 Hz), 2.79
(1H, dd, J=4.0, 13.2 Hz), 2.93 (1H, d, J=4.9 Hz), 3.75
(4H, t, J=4.5 Hz), 4.12 (1H, d, J=7.3 Hz), 4.23 (1H, d,
J=8.3 Hz), 4.32 (1H, d, J=8.3 Hz), 4.91 (1H, s), 5.05
(1H, t, J=4.5 Hz), 5.14 (1H, d, J=2.5 Hz), 5.25 (1H, d,
J=7.3 Hz), 5.77 (1H, d, J=9.8 Hz), 6.00 (1H, d, J=4.9
Hz), 6.05 (1H, d, J=8.9 Hz), 6.18 (1H, t, J=8.0 Hz),
7.24–7.28 (1H, m), 7.34 (1H, t, J=7.0 Hz), 7.42–7.49
(3H, m), 7.60 (1H, t, J=7.0 Hz), 8.12 (2H, d, J=8.0
Hz), 8.20 (1H, d, J=7.0 Hz); FAB-MS( m/z): 922
(M+H)+; HR-MScalcd for C 48H64N3O15: 922.4337.
Found, 922.4382; IR: 3430, 2952, 1714, 1602, 1488,
1452, 1432 cmꢂ1; [a]D25 ꢂ22.0ꢁ (c 0.03, CHCl3).
MScalcd for
867.3887.
C
45H59N2O15: 867.3915. Found,
5-Benzyloxy-2-methylpyridine (10). To a suspension of
NaH (60% in oil, 2.05 g, 51.2 mmol) in THF (100 mL)
was added a solution of 9 (5.0 g, 45.8 mmol) in DMF
(50 mL) with ice cooling, and the mixture was stirred at
the same temperature for 30 min. After BnBr (6.0 mL,
50.5 mmol) was added to the reaction mixture, the
whole was stirred overnight at room temperature. To
the reaction mixture was added saturated aqueous
NaHCO3, and the mixture was extracted with AcOEt.
The extract was washed with water, brine, and dried
over Na2SO4. The solvent was removed under reduced
pressure and the residue was chromatographed on silica
gel eluting with n-hexane–AcOEt (2:1). The eluate was
concentrated under reduced pressure to give the title
compound (7.5 g, 82%) as a yellow oil. 1H NMR
(CDCl3) d: 2.49 (3H, s), 5.08 (2H, s), 7.05 (1H, d, J=8.3
Hz), 7.16 (1H, dd, J=2.5, 8.3 Hz), 7.34–7.41 (5H, m),
8.26 (1H, d, J=2.5 Hz).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2,3-dihy-
droxypropylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-
butoxycarbonylamino)-2-hydroxy-3-(2-pyridyl-N-oxide)-
propionate (7). Compound 7 was obtained from 6 as a
white amorphous powder (51%) by following a proce-
dure analogous to that described for the preparation of
4 from 3. 1H NMR (CDCl3) d: 1.27 (3H, s), 1.41 (9H, s),
1.50 (3H, s), 1.58 (3H, s), 1.81 (3H, s), 1.84–2.32 (2H,
m), 2.39 (3H, s), 2.92 (1H, d, J=5.4 Hz), 3.76–3.88 (3H,
m), 4.19–4.24 (2H, m), 4.32 (1H, d, J=7.8 Hz), 4.87–
4.91 (2H, m), 5.15 (1H, s), 5.30–5.36 (2H, m), 5.97 (1H,
d, J=4.0 Hz), 6.19 (1H, t, J=8.0 Hz), 7.23–7.28 (1H,
m), 7.36 (1H, t, J=8.0 Hz), 7.44–7.48 (3H, m), 7.59 (1H,
t, J=8.0 Hz), 8.12 (2H, d, J=8.0 Hz), 8.17 (1H, d,
J=6.5 Hz); HR-MScalcd for C 45H59N2O16: 883.3865.
Found, 883.3840.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-bu-
toxycarbonylamino)-2-hydroxy-3-(2-pyridyl-N-oxide)pro-
pionate (8). To a solution of 7 (19 mg, 0.021 mmol) in a
mixture of THF (1 mL), MeOH (1 mL), and H2O (1
mL) was added NaIO4 (44 mg, 0.21 mmol), and the
mixture was stirred at room temperature for 30 min.
After AcOEt and water were added to the reaction
mixture, the two layers were separated. The aqueous
layer was extracted with AcOEt, and the combined
organic layer was washed with saturated aqueous
NaHCO3, and dried over Na2SO4. The solvent was
removed under reduced pressure and the residue was
dissolved in EtOH (2 mL). To this solution were added
morpholine (0.02 mL, 0.23 mmol), AcOH (0.012 mL,
0.23 mmol), and NaBH3CN (13.5 mg, 0.23 mmol) with
ice cooling, and the mixture was stirred at room tem-
perature for 10 min. After AcOEt, saturated aqueous
NaHCO3, and water were added to the reaction mix-
ture, the two layers were separated. The aqueous layer
was extracted with AcOEt, and the combined organic
layer was washed with brine, and dried over Na2SO4.
The solvent was removed under reduced pressure. The
5-Benzyloxy-2-formylpyridine (11a). (i) To a solution of
10 (7.5 g, 37.6 mmol) in CHCl3 (200 mL) was added
mCPBA (7.14 g, 41.4 mmol) with ice cooling, and the
mixture was stirred at the same temperature for 1 h. To
the reaction mixture was added 5% aqueous Na2CO3
and the whole was extracted with AcOEt. The extract
was washed with brine, and dried over Na2SO4. The
solvent was removed under reduced pressure to give 5-
benzyloxy-2-methylpyridine N-oxide (7.8 g, 96%) as
colorless crystals.
(ii) To Ac2O (39 mL) was added 5-benzyloxy-2-methyl-
pyridine N-oxide (7.8 g, 36.2 mmol) at 80 ꢁC and the
mixture was stirred at 130 ꢁC for 30 min. The reaction
mixture was poured into ice-water and the whole was
stirred at room temperature for 2 h. The mixture was
extracted with AcOEt and the extract was washed with
saturated aqueous NaHCO3, brine, and dried over
Na2SO4. The solvent was removed under reduced pres-
sure and the residue was chromatographed on silica gel
eluting with n-hexane–AcOEt (2:1). The eluate was
concentrated under reduced pressure to give 2-acetoxy-
methyl-5-benzyloxypyridine (7.2 g, 77%) as a yellow
oil.

4438
Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
(iii) To a solution of 2-acetoxymethyl-5-benzyloxypyr-
idine (7.2 g, 28.0 mmol) in a mixture of EtOH (72 mL)
and water (18 mL) was added NaOH (2.0 g, 50 mmol),
and the mixture was stirred under reflux for 1.5 h. After
cooled to room temperature, the reaction mixture was
concentrated under reduced pressure and the residue
was extracted with CHCl3. The extract was washed with
water, and dried over Na2SO4. The solvent was
removed under reduced pressure and the residue was
crystallized from n-hexane–AcOEt. The resulting pre-
cipitate was collected by filtration to give 5-benzyloxy-2-
hydroxymethylpyridine (4.5 g, 75%) as brown crystals.
nBuLi in n-hexane (3.2 mL, 5.0 mmol) at 0 ꢁC. The
solution was stirred at the same temperature for 15 min
and then cooled to ꢂ78 ꢁC. To the mixture was added a
solution of 15 (1.83 g, 4.69 mmol) in THF (5 mL). The
solution was stirred for 2 h followed by addition of a
solution of N-trimethylsilylaldimine, described above.
The mixture was slowly allowed to warm to room tem-
perature and further stirred overnight. After saturated
aqueous NaHCO3 and AcOEt were added to the reac-
tion mixture, the layers were separated. The aqueous
layer was extracted with AcOEt and the combined
extract was washed with water, brine, and dried over
Na2SO4. The solvent was removed under reduced pres-
sure and the residue was chromatographed on silica gel
eluting with n-hexane–AcOEt (2:1). The eluate was
concentrated under reduced pressure to give the title
(iv) To a solution of 5-benzyloxy-2-hydroxymethyl-
pyridine (4.5 g, 20.9 mmol) in CHCl3 (225 mL) was added
MnO2 (22.5 g) and the mixture was stirred under reflux for
5 min. The reaction mixture was filtered through Celite
and the filtrate was concentrated under reduced pressure.
The residue was chromatographed on silica gel eluting
with n-hexane–AcOEt (4:1). The eluate was concentrated
under reduced pressure to give the title compound (3.45 g,
77%) as colorless crystals. 1H NMR (CDCl3) d: 5.21 (2H,
s), 7.34–7.45 (6H, m), 7.95 (1H, d, J=8.8 Hz), 8.50 (1H, d,
J=3.0 Hz), 9.99 (1H, d, J=1.0 Hz).
1
compound (780 mg, 39%) as a yellow oil. H NMR
(CDCl3) d: 0.88–1.00 (21H, m), 4.94 (1H, d, J=4.4 Hz),
5.12 (2H, s), 5.22 (1H, dd, J=2.9, 4.4 Hz), 6.24 (1H, br
s), 7.25–7.43 (7H, m), 8.30 (1H, d, J=2.9 Hz); HR-MS
calcd for C24H35N2O3Si: 427.2417. Found, 427.2390.
(3R, 4S)-4-(3-Benzyloxy-2-pyridyl)-3-triisopropylsilyloxy-
2-azetidinone (13b). Compound 13b was obtained form
11b as a yellow oil (37%) by following a procedure
analogous to that described for the preparation of 13a
from 11a. 1H NMR (CDCl3) d: 0.85–0.99 (21H, m), 5.07
(2H, ABq, J=12.0 Hz), 5.30 (2H, ABq, J=5.0 Hz), 6.35
(1H, br s), 7.15–7.19 (2H, m), 7.34–7.40 (5H, m), 8.23
(1H, dd, J=2.0, 2.5 Hz); HR-MScalcd for
C24H35N2O3Si: 427.2417. Found, 427.2390.
3-Benzyloxy-2-fromylpyridine (11b). (i) To a suspension
of 12 (5.0 g, 26.3 mmol) in EtOH (100 mL) were added
KOH (3.5 g, 53 mmol) and BnBr (3.15 mL, 26.5 mmol),
and the mixture was stirred under reflux for 24 h. After
cooled to room temperature, the reaction mixture was
diluted with water and the whole was extracted with
AcOEt. The extract was washed with water, brine, and
dried over Na2SO4. The solvent was removed under
reduced pressure and the residue was chromatographed
on silica gel eluting with CHCl3–MeOH (20:1). The
eluate was concentrated under reduced pressure to give
3-benzyloxy-2-hydroxymethylpyridine (3.76 g, 66%) as
yellow crystals.
(3R, 4S)-4-(5-Benzyloxy-2-pyridyl)-1-(tert-butoxycarbo-
a
nyl)-3-triisopropylsilyloxy-2-azetidinone (14a). To
solution of 13a (780 mg, 1.83 mmol) and (Boc)2O (0.50
mL, 2.17 mmol) in THF (15.6 mL) was added DMAP
(45 mg, 0.37 mmol) and the mixture was stirred at room
temperature for 1 h. The reaction mixture was con-
centrated under reduced pressure and the residue was
chromatographed on silica gel eluting with n-hexane–
AcOEt (9:1). The eluate was concentrated under
reduced pressure to give the title compound (850 mg,
(ii) To a solution of 3-benzyloxy-2-hydroxymethyl-
pyridine (3.75 g, 17.4 mmol) in CHCl3 (100 mL) was
added MnO2 (15 g) and the mixture was stirred under
reflux for 80 min. The reaction mixture was filtered
through Celite and the filtrate was concentrated under
reduced pressure. The residue was chromatographed on
silica gel eluting with n-hexane–AcOEt (1:1). The eluate
was concentrated under reduced pressure to give the
1
88%) as a colorless syrup. H NMR (CDCl3) d: 0.87–
1.00 (21H, m), 1.42 (9H, s), 5.12 (2H, s), 5.20 (2H, s),
7.25–7.43 (7H, m), 8.33 (1H, d, J=3.0 Hz); HR-MS
calcd for C29H43N2O5Si: 527.2941. Found, 527.2924.
1
title compound (2.7 g, 73%) as a yellow oil. H NMR
(CDCl3) d: 5.26 (2H, s), 7.34–7.47 (7H, m), 8.41 (1H, t,
J=2.5 Hz), 10.40 (1H, s).
(3R, 4S)-4-(3-Benzyloxy-2-pyridyl)-1-(tert-butoxycarbo-
nyl)-3-triisopropylsilyloxy-2-azetidinone (14b). Com-
pound 14b was obtained from 13b as a colorless syrup
(83%) by following a procedure analogous to that
described for the preparation of 14a from 13a. 1H NMR
(CDCl3) d: 0.87–1.01 (21H, m), 1.43 (9H, s), 5.05 (2H,
ABq, J=11.5 Hz), 5.21 (1H, d, J=5.0 Hz), 5.61 (1H, br
s), 7.12–7.19 (2H, m), 7.33–7.42 (5H, m), 8.21 (1H, d,
J=3.0 Hz); HR-MScalcd for C 29H43N2O5Si: 527.2941.
Found, 527.2983.
(3R, 4S)-4-(5-Benzyloxy-2-pyridyl)-3-triisopropylsilyloxy-
2-azetidinone (13a). (i) To a 1.0 M solution of LiHMDS
in THF (5.0 mL, 5.0 mmol) was added a solution of 11a
(1.0 g, 4.69 mmol) in THF (2.5 mL) at ꢂ78 ꢁC, and the
mixture was stirred at the same temperature for 5 min
and then at 0 ꢁC for 30 min. Then, to the reaction mix-
ture was added TMSCl (0.68 mL, 5.51 mmol) and the
mixture was stirred at the same temperature for 30 min
to give a solution of N-trimethylsilylaldimine.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(5-benzyloxy-2-
pyridyl)-3-(tert-butoxycarbonylamino)-2-triisopropylsily-
loxypropionate (17a). To a solution of 16 (100 mg,
(ii) To a solution of diisopropylamine (0.7 mL, 5.0
mmol) in THF (5 mL) was added a 1.58 M solution of

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4439
0.175 mmol) in THF (2 mL) was added LiHMDS
(1.0 M in THF, 0.21 mL, 0.21 mmol) at ꢂ55 ꢁC, and the
mixture was stirred at the same temperature for 30 min.
To the reaction mixture was added a solution of 14a
(140 mg, 0.265 mmol) in THF (2 mL) at ꢂ55 ꢁC, and
the whole was stirred with ice cooling for 30 min. After
saturated aqueous NaHCO3 and AcOEt were added to
the reaction mixture with ice cooling, the two layers
were separated. The aqueous layer was extracted with
AcOEt and the combined organic layer was washed
with brine, and dried over Na2SO4. The solvent was
removed under reduced pressure and the residue was
chromatographed on silica gel eluting with n-hexane–
AcOEt (4:1). The eluate was concentrated under
reduced pressure to give the title compound (157 mg,
82%) as a white amorphous powder. 1H NMR (CDCl3)
d: 0.86–0.93 (21H, m), 1.31 (3H, s), 1.41 (9H, s), 1.52
(3H, s), 1.65 (3H, s), 1.79–2.07 (2H, m), 1.81 (3H, s),
2.26–2.30 (2H, m), 2.50 (3H, s), 2.97 (1H, d, J=5.4 Hz),
4.19–4.22 (2H, m), 4.33 (1H, d, J=7.8 Hz), 4.96 (1H, br
s), 5.12 (2H, s), 5.21 (1H, d, J=6.0 Hz), 5.28 (2H, m),
5.44–5.60 (4H, m), 5.96–6.03 (2H, m), 6.11 (1H, br t,
J=8.0 Hz), 7.20–7.47 (9H, m), 7.57 (1H, t, J=7.8 Hz),
8.13 (2H, d, J=7.8 Hz), 8.31 (1H, d, J=2.5 Hz); HR-
s), 2.93 (1H, d, J=5.4 Hz), 4.17 (1H, d, J=7.0 Hz), 4.21
(1H, d, J=8.3 Hz), 4.32 (1H, d, J=8.3 Hz), 4.77 (1H, br
s), 4.85 (1H, s), 4.92 (1H, s), 5.10 (2H, s), 5.23–5.27 (2H,
m), 5.46 (1H, d, J=10.3 Hz), 5.57 (1H, d, J=17.0 Hz),
5.91 (1H, d, J=10.3 Hz), 5.96–6.02 (2H, m), 6.08 (1H, t,
J=8.0 Hz), 7.28–7.48 (9H, m), 7.59 (1H, t, J=7.8 Hz),
8.12 (2H, d, J=7.8 Hz), 8.28 (1H, d, J=2.5 Hz); HR-
MScalcd for C 52H63N2O14: 939.4279. Found, 939.4293.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(3-benzyloxy-2-
pyridyl)-3-(tert-butoxycarbonylamino)-2-hydroxypropio-
nate (18b). Compound 18b was obtained from 17b as a
white amorphous powder (94%) by following a proce-
dure analogous to that described for the preparation of
1
18a from 17a. H NMR (CDCl3) d: 1.28 (3H, s), 1.40
(9H, s), 1.50 (3H, s), 1.64 (3H, s), 1.86 (3H, s), 1.82–2.24
(5H, m), 2.24 (3H, s), 2.44–2.50 (1H, m), 2.94 (1H, d,
J=5.5 Hz), 4.19–4.23 (2H, m), 4.30 (1H, d, J=8.3 Hz),
4.37 (1H, br s), 4.78 (1H, br s), 4.89 (1H, s), 5.22 (2H, s),
5.25 (1H, d, J=5.9 Hz), 5.32 (1H, d, J=6.0 Hz), 5.46
(1H,d, J=10.5 Hz), 5.68 (1H, d, J=17.0 Hz), 5.83 (1H,
d, J=10.3 Hz), 5.97–6.09 (3H, m), 6.25 (1H, t, J=9.0
Hz), 7.17–7.48 (9H, m), 7.58 (1H, t, J=7.8 Hz), 8.11
(2H, d, J=7.8 Hz), 8.18 (1H, d, J=4.5 Hz); HR-MS
calcd for C52H63N2O14: 939.4279. Found, 939.4351.
MScalcd for
1095.5623.
C 61H83N2O14Si: 1095.5614. Found,
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(3-benzyloxy-2-
pyridyl)-3-(tert-butoxycarbonylamino)-2-triisopropylsily-
loxypropionate (17b). Compound 17b was obtained as a
white amorphous powder (90%) by following a proce-
dure analogous to that described for the preparation of
17a from 16 by replacing 15a with 15b. 1H NMR
(CDCl3) d: 0.86–0.91 (21H, m), 1.36 (3H, s), 1.37 (9H,
s), 1.53 (3H, s), 1.64 (3H, s), 1.75–2.30 (6H, m), 1.79
(3H, s), 2.45 (3H, s), 2.95 (1H, d, J=6.0 Hz), 4.19–4.22
(2H, m), 4.30 (1H, d, J=7.8 Hz), 4.87 (1H, s), 5.12 (1H,
d, J=3.0 Hz), 5.19–5.27 (3H, m), 5.45 (1H, d, J=10.5
Hz), 5.57 (1H, d, J=17.0 Hz), 5.70 (1H, d, J=3.0, 10.0
Hz), 5.95–6.04 (2H, m), 6.13 (1H, d, J=10.0 Hz), 6.19
(1H, br t, J=8.0 Hz), 7.08–7.15 (2H, m), 7.31–7.46 (7H,
m), 7.57 (1H, t, J=7.8 Hz), 8.13–8.17 (3H, m); HR-MS
calcd for C61H83N2O14Si: 1095.5614. Found, 1095.5537.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(5-ben-
zyloxy-2-pyridyl)-3-(tert-butoxycarbonylamino)-2-hydro-
xypropionate (19a). To a solution of 18a (128 mg, 0.136
mmol) in a mixture of THF (1.3 mL), acetone (1.3 mL),
and H2O (1.3 mL) were added NMO (80 mg, 0.68
mmol) and OsO4 (7 mg), and the mixture was stirred at
room temperature for 2.5 h. After AcOEt and 10%
aqueous Na2S2O3 were added to the reaction mixture,
the two layers were separated. The aqueous layer was
extracted with AcOEt, and the combined organic layer
was washed with saturated aqueous NaHCO3, brine,
and dried over Na2SO4. The solvent was removed under
reduced pressure and the residue was dissolved in a
mixture of THF (1.5 mL), MeOH (1.5 mL), and H2O
(1.5 mL). To this solution was added NaIO4 (192 mg,
0.9 mmol) and the mixture was stirred at room tem-
perature for 0.5 h. After AcOEt and water were added
to the reaction mixture, the two layers were separated.
The aqueous layer was extracted with AcOEt, and the
combined organic layer was washed with saturated
aqueous NaHCO3, and dried over Na2SO4. The solvent
was removed under reduced pressure and the residue
was dissolved in EtOH (3 mL). To this solution were
added morpholine (0.079 mL, 0.9 mmol), AcOH (0.051
mL, 0.9 mmol), and NaBH3CN (56 mg, 0.9 mmol), and
the mixture was stirred at room temperature for 15 min.
After AcOEt, saturated aqueous NaHCO3, and water
were added to the reaction mixture, the two layers were
separated. The aqueous layer was extracted with
AcOEt, and the combined organic layer was washed
with brine, and dried over Na2SO4. The solvent was
removed under reduced pressure and the residue was
purified by preparative TLC (CHCl3–MeOH=20:1) to
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(5-benzyloxy-2-
pyridyl)-3-(tert-butoxycarbonylamino)-2-hydroxypropio-
nate (18a). To a solution of 17a (150 mg, 0.137 mmol)
in THF (3 mL) was added TBAF (1.0 M in THF, 0.27
mL, 0.27 mmol) with ice cooling, and the mixture was
stirred at the same temperature for 15 min. After AcOEt
and brine were added to the reaction mixture, the two
layers were separated. The aqueous layer was extracted
with AcOEt and the combined organic layer was dried
over Na2SO4. The solvent was removed under reduced
pressure and the residue was purified by preparative
TLC (n-hexane–AcOEt=1:1) to give the title compound
(128 mg, 100%) as a white amorphous powder. 1H
NMR (CDCl3) d: 1.26 (3H, s), 1.43 (9H, s), 1.49 (3H, s),
1.63 (3H, s), 1.70 (3H, s), 1.83–2.11 (2H, m), 2.34 (3H,

4440
Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
give the title compound (82 mg, 74%) as a white amor-
1
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-but-
oxycarbonylamino)-2-hydroxy-3-(3-hydroxy-2-pyridyl)pro-
pionate (20b). Compound 20b was obtained from 19b as
a white amorphous powder (84%), mp 168–171 ꢁC, by
following a procedure analogous to that described for
phous powder. H NMR (CDCl3) d: 1.26 (3H, s), 1.43
(9H, s), 1.48 (3H, s), 1.60 (3H, s), 1.68 (3H, s), 1.82–2.11
(5H, m), 2.30–2.37 (1H, m), 2.34 (3H, s), 2.58–2.70 (4H,
m), 2.69 (1H, d, J=3.9, 13.5 Hz), 2.77 (1H, d, J=4.9,
13.5 Hz), 2.91 (1H, d, J=5.4 Hz), 3.74 (4H, t, J=4.5
Hz), 4.11 (1H, d, J=7.3 Hz), 4.21 (1H, d, J=8.3 Hz),
4.32 (1H, d, J=8.3 Hz), 4.75 (1H, br s), 4.84 (1H, d,
J=2.0 Hz), 4.92 (1H, s), 5.05 (1H, t, J=4.5 Hz), 5.10
(2H, s), 5.21 (1H, d, J=7.0 Hz), 5.28 (1H, d, J=8.9
Hz), 5.98 (1H, d, J=5.0 Hz), 6.07 (1H, t, J=8.3 Hz),
7.28–7.49 (9H, m), 7.59 (1H, t, J=8.3 Hz), 8.12 (2H, d,
J=8.3 Hz), 8.28 (1H, d, J=2.5 Hz); HR-MScalcd for
C55H70N3O15: 1012.4807. Found, 1012.4884.
1
the preparation of 20a from 19a. H NMR (CDCl3) d:
1.30 (3H, s), 1.43 (9H, s), 1.48 (3H, s), 1.61 (3H, s), 1.77
(3H, s), 1.88–2.31 (5H, m), 2.36 (3H, s), 2.59–2.68 (4H,
m), 2.69 (1H, d, J=3.9, 14.0 Hz), 2.77 (1H, d, J=4.5,
14.0 Hz), 2.94 (1H, d, J=5.5 Hz), 3.74 (4H, t, J=4.5
Hz), 4.13 (1H, d, J=7.3 Hz), 4.21 (1H, d, J=8.3 Hz),
4.34 (1H, d, J=8.3 Hz), 4.92 (1H, s), 4.93 (1H, s), 4.96
(1H, d, J=2.5 Hz), 5.04 (1H, t, J=4.5 Hz), 5.23 (1H, d,
J=7.3 Hz), 5.30 (1H, dd, J=2.5, 8.0 Hz), 5.98 (1H, d,
J=5.5 Hz), 6.17 (1H, t, J=8.3 Hz), 6.48 (1H, d, J=8.0
Hz), 7.19–7.22 (1H, m), 7.30–7.33 (1H, m), 7.48 (2H, t,
J=8.3 Hz), 7.61 (1H, t, J=8.3 Hz), 8.03 (1H, dd, J=1.5,
4.5 Hz), 8.13 (2H, d, J=8.3 Hz); FAB-MS( m/z): 922
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(3-ben-
zyloxy-2-pyridyl)-3-(tert-butoxycarbonylamino)-2-hydro-
xypropionate (19b). Compound 19b was obtained from
18b as a white solid (69%) by following a procedure
analogous to that described for the preparation of 19a
(M+H)+. Anal. calcd for C48H63N3O15 1.25H2O: C,
.
61.04; H, 6.99; N, 4.45. Found: C, 60.91; H, 6.89; N,
4.35; IR : 3411, 2956, 1712, 1600, 1579, 1488, 1452
cmꢂ1; [a]2D3 ꢂ28.0ꢁ (c 0.03, CHCl3).
1
from 18a. H NMR (CDCl3) d: 1.27 (3H, s), 1.40 (9H,
s), 1.48 (3H, s), 1.60 (3H, s), 1.84 (3H, s), 1.82–2.07 (5H,
m), 2.24 (3H, s), 2.42–2.48 (1H, m), 2.58–2.68 (4H, m),
2.69 (1H, d, J=3.9, 14.0 Hz), 2.77 (1H, d, J=4.5, 14.0
Hz), 2.93 (1H, d, J=5.5 Hz), 3.75 (4H, t, J=4.5 Hz),
4.14 (1H, d, J=7.3 Hz), 4.21 (1H, d, J=8.3 Hz), 4.29
(1H, d, J=8.3 Hz), 4.34 (1H, br s), 4.77 (1H, s), 4.88
(1H, s), 5.05 (1H, t, J=4.5 Hz), 5.21 (2H, s), 5.25 (1H,
d, J=8.0 Hz), 5.82 (1H, d, J=8.9 Hz), 5.98 (1H, d,
J=5.0 Hz), 6.07 (1H, t, J=8.3 Hz), 6.24 (1H, d, J=9.0
Hz), 7.17–7.49 (9H, m), 7.58 (1H, t, J=8.3 Hz), 8.10
(2H, d, J=8.3 Hz), 8.17 (1H, d, J=3.5 Hz); HR-MS
calcd for C55H70N3O15: 1012.4807. Found, 1012.4775.
Compounds 23a–f were obtained by following a proce-
dure analogous to that described for the preparation of
14a from 13a by replacing 13a with the corresponding
b-lactams 22a–f.
(3R, 4S)-1-(tert-Butoxycarbonyl)-4-(5-methyl-2-pyridyl)-
3-triisopropylsilyloxy-2-azetidinone (23a). A pale yellow
1
syrup (96%); H NMR (CDCl3) d: 0.87–0.98 (21H, m),
1.43 (9H, s), 2.32 (3H, s), 5.21 (1H, d, J=4.9 Hz), 5.25
(1H, d, J=4.9 Hz), 7.22 (1H, d, J=7.8 Hz), 7.49 (1H, d,
J=7.8 Hz), 8.39 (1H, s); HR-MScalcd for
C23H39N2O4Si: 435.2629. Found, 435.2661.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-but-
oxycarbonylamino)-2-hydroxy-3-(5-hydroxy-2-pyridyl)pro-
pionate (20a). 19a (82 mg, 0.081 mmol) was
hydrogenated over 10% Pd(OH)2 (40 mg) in EtOH (3
mL) at atmospheric pressure for 1 h. The catalyst was
filtered off and the filtrate was concentrated under
reduced pressure. The residue was purified by pre-
parative TLC (CHCl3–MeOH=20:1) and lyophilized
from 1,4-dioxane to give the title compound (48 mg,
64%) as a white amorphous powder, mp 163–165 ꢁC.
1H NMR (CDCl3) d: 1.25 (3H, s), 1.44 (9H, s), 1.48 (3H,
s), 1.59 (3H, s), 1.69 (3H, s), 1.81–2.10 (5H, m), 2.33–
2.36 (1H, m), 2.33 (3H, s), 2.60–2.70 (4H, m), 2.71 (1H,
d, J=3.9, 13.5 Hz), 2.78 (1H, d, J=4.9, 13.5 Hz), 2.90
(1H, d, J=5.4 Hz), 3.75 (4H, t, J=4.5 Hz), 4.11 (1H, d,
J=7.3 Hz), 4.21 (1H, d, J=8.3 Hz), 4.32 (1H, d, J=8.3
Hz), 4.84 (1H, s), 4.92 (1H, s), 5.04 (1H, t, J=4.5 Hz),
5.21–5.26 (2H, m), 5.96–5.98 (2H, m), 6.08 (1H, t,
J=8.3 Hz), 7.05 (1H, dd, J=2.5, 8.3 Hz), 7.19 (1H, d,
J=8.3 Hz),7.47 (2H, t, J=8.3 Hz), 7.60 (1H, t, J=8.3
Hz), 8.02 (1H, d, J=2.5 Hz), 8.12 (2H, d, J=8.3 Hz);
FAB-MS( m/z): 922 (M+H)+. Anal. calcd for
(3R, 4S)-1-(tert-Butoxycarbonyl)-4-(5-ethyl-2-pyridyl)-3-
triisopropylsilyloxy-2-azetidinone (23b).
A
colorless
1
syrup (92%); H NMR (CDCl3) d: 0.86–1.02 (21H, m),
1.22 (3H, t, J=7.3 Hz), 1.43 (9H, s), 2.64 (2H, q, J=7.3
Hz), 5.22 (2H, s), 7.25 (1H, d, J=8.0 Hz), 7.51 (1H, dd,
J=2.0, 8.0 Hz), 8.41 (1H, s); HR-MScalcd for
C24H41N2O4Si: 449.2836. Found, 449.2843.
(3R, 4S)-1-(tert-Butoxycarbonyl)-4-(5-fluoro-2-pyridyl)-
3-triisopropylsilyloxy-2-azetidinone (23c). A colorless
1
syrup (93%); H NMR (CDCl3) d: 0.88–1.01 (21H, m),
1.44 (9H, s), 5.20 (1H, d, J=4.9 Hz), 5.25 (1H, d, J=4.9
Hz), 7.33–7.45 (2H, m), 8.44 (1H, d, J=2.9 Hz); HR-MS
calcd for C22H36FN2O4Si: 439.2428. Found, 439.2400.
(3R, 4S)-1-(tert-Butoxycarbonyl)-4-(5-chloro-2-pyridyl)-
3-triisopropylsilyloxy-2-azetidinone (23d). A colorless
syrup (100%); 1H NMR (CDCl3) d: 0.88–1.02 (21H, m),
1.44 (9H, s), 5.20 (1H, d, J=4.9 Hz), 5.24 (1H, d, J=4.9
Hz), 7.29 (1H, d, J=8.3 Hz), 7.68 (1H, dd, J=8.3 Hz,
2.4 Hz), 8.54 (1H, d, J=2.4 Hz); HR-MScalcd for
C22H36ClN2O4Si: 455.2133. Found, 455.2133.
.
C48H63N3O15 1.25H2O: C, 61.04; H, 6.99; N, 4.45.
Found: C, 61.05; H, 6.97; N, 4.28; IR: 3409, 2960, 1712,
(3R, 4S)-1-(tert-Butoxycarbonyl)-4-(5-trifluoromethyl-2-
pyridyl)-3-triisopropylsilyloxy-2-azetidinone (23e).
1581, 1490, 1454 cmꢂ1; [a]D24 ꢂ13.4ꢁ (c 0.1, CHCl3).
A

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4441
1
colorless syrup (99%); H NMR (CDCl3) d: 0.86–1.00
cooling, and the mixture was stirred at room tempera-
ture for 1 h. To the reaction mixture was added Dowex
50 (H+ form) and the whole was stirred at room tem-
perature for 5 min. The mixture was filtered and the fil-
trate was concentrated under reduced pressure. The
residue was dissolved in DMF (10 mL) and to this
solution were added imidazole (0.73 g, 10.8 mmol) and
TIPSCl (1.15 mL, 5.39 mmol) with ice cooling, and the
mixture was stirred at room temperature for 14 h. The
reaction mixture was poured into ice-water and the
mixture was extracted with Et2O. The extract was
washed with brine, and dried over Na2SO4. The solvent
was removed under reduced pressure and the residue
was chromatographed on silica gel eluting with n-hex-
ane–AcOEt (3:1). The eluate was concentrated under
reduced pressure to give the title compound (1.65 g,
85%) as a white powder. 1H NMR (CDCl3) d: 0.90–1.02
(21H, m), 2.32 (3H, s), 3,74 (3H, s), 5.30 (1H, d, J=4.8
Hz), 5.31 (1H, d, J=4.8 Hz), 6.78–6.79 (2H, m), 7.23–
7.28 (2H, m), 7.43 (1H, dd, J=1.9 Hz, 8.3 Hz), 8.42
(1H, dd, J=1.5 Hz); FAB-MS( m/z): 441 (M+H)+.
Anal. calcd for C25H36N2O3Si: C, 68.14; H, 8.23; N,
6.36. Found: C, 67.99; H, 7.95; N, 6.31.
(21H, m), 1.46 (9H, s), 5.27 (1H, d, J=5.4 Hz), 5.33
(1H, d, J=5.4 Hz), 7.47 (1H, d, J=8.3 Hz), 7.95 (1H, d,
J=8.3 Hz), 8.86 (1H, s); HR-MScalcd for
C23H36F3N2O4Si: 489.2396. Found, 489.2364.
(3R, 4S)-4-(5-Methoxy-2-pyridyl)-1-(tert-butoxycarbo-
nyl)-3-triisopropylsilyloxy-2-azetidinone (23f). A color-
less syrup (91%); H NMR (CDCl3) d: 0.88–1.01 (21H,
m), 1.43 (9H, s), 3.85 (3H, s), 5.18 (1H, d, J=5.8 Hz),
5.24 (1H, d, J=5.8 Hz), 7.18–7.28 (2H, m), 8.27 (1H, d,
J=3.0 Hz); HR-MScalcd for C 23H39N2O5Si: 451.2635.
Found, 451.2635.
1
cis-(ꢃ)-Acetoxy-1-(4-methoxyphenyl)-4-(5-methyl-2-pyr-
idyl)-2-azetidinone (24a). A mixture of 21a (0.79 g, 6.55
mmol), 4-anisidine (0.81 g, 6.62 mmol), and Na2SO4
(2.0 g) in benzene (15 mL) was stirred at room tem-
perature for 1 h. The reaction mixture was filtered and
the filtrate was concentrated under reduced pressure.
The residue was dissolved in CH2Cl2 (25 mL) and to
this solution were added Et3N (1.07 mL, 7.69 mmol)
and 2-acetoxyacetyl chloride (0.57 mL, 5.1 mmol) at
ꢂ78 ꢁC, and the mixture was allowed to come to room
temperature overnight. To the reaction mixture was
added water and the whole was extracted with AcOEt.
The extract was washed with brine, and dried over
Na2SO4. The solvent was removed under reduced pres-
sure and the residue was chromatographed on silica gel
eluting with n-hexane–AcOEt (2:1). The eluate was
concentrated under reduced pressure to give the title
compound (1.5 g, 88%) as a pale orange solid. 1H NMR
(CDCl3) d: 1.77 (3H, s), 2.34 (3H, s), 3,75 (3H, s), 5.45
(1H, d, J=5.0 Hz), 6.09 (1H, d, J=5.0 Hz), 6.80 (2H, m),
7.22 (1H, d, J=7.8 Hz), 7.27 (2H, m), 7.43 (1H, dd, J=1.9
Hz, 8.3 Hz), 8.42 (1H, dd, J=1.5 Hz); FAB-MS( m/z): 327
(M+H)+. Anal. calcd for C18H18N2O4: C, 66.25; H, 5.56;
N, 8.58. Found: C, 66.03; H, 5.55; N, 8.50.
Compounds 25d and 25e were obtained by following a
procedure analogous to that described for the prepara-
tion of 25a from 24a by replacing 24a with the corre-
sponding b-lactams 24d and 24e.
cis-(ꢃ)-4-(5-Chloro-2-pyridyl)-1-(4-methoxyphenyl)-3-
triisopropylsilyloxy-2-azetidinone (25d). Colorless crys-
1
tals (78%); H NMR (CDCl3) d: 0.91–1.02 (21H, m),
3.75 (3H, s), 5.30 (1H, d, J=4.9 Hz), 5.32 (1H, d, J=4.9
Hz), 6.78–6.82 (2H, m), 7.23–7.28 (2H, m), 7.30 (1H, d,
J=8.3 Hz), 7.61 (1H, dd, J=8.3 Hz, 2.4 Hz), 8.57 (1H,
d, J=2.4 Hz); FAB-MS( m/z): 461 (M+H)+; HR-MS
calcd for C24H33ClN2O3Si: 460.1949. Found, 460.1955.
cis-(ꢃ)-1-(4-Methoxyphenyl)-4-(5-trifluoromethyl-2-pyri-
dyl)-3-triisopropylsilyloxy-2-azetidinone (25e). A white
powder (36%); H NMR (CDCl3) d: 0.89–1.02 (21H,
m), 3.75 (3H, s), 5.37 (1H, d, J=4.9 Hz), 5.41 (1H, d,
J=4.9 Hz), 6.81 (2H, d, J=8.8 Hz), 7.25 (2H, d, J=8.8
Hz), 7.47 (1H, d, J=8.3 Hz), 7.86 (1H, dd, J=1.9, 8.3
Hz), 8.88 (1H, s). Anal. calcd for C25H33F3N2O3Si: C,
60.71; H, 6.72; N, 5.66; F, 11.52. Found: C, 60.81; H,
6.81; N, 5.59; F, 11.24.
Compounds 24d and 24e were obtained by following a
procedure analogous to that described for the prepara-
tion of 24a from 21a by replacing 21a with the corre-
sponding b-lactams 21d and 21e.
1
cis-(ꢃ)-Acetoxy-4-(5-chloro-2-pyridyl)-1-(4-methoxyphe-
nyl)-2-azetidinone (24d). Colorless crystals (61%); 1H
NMR (CDCl3) d: 1.81 (3H, s), 3.76 (3H, s), 5.46 (1H, d,
J=5.3 Hz), 6.11 (1H, d, J=5.3 Hz), 6.80–6.84 (2H, m),
7.23–7.27 (2H, m), 7.29 (1H, d, J=8.3 Hz), 7.66 (1H,
dd, J=8.3 Hz, 2.4 Hz), 8.59 (1H, d, J=2.4 Hz); HR-MS
calcd for C17H16ClN2O4: 347.0799. Found, 347.0771.
(3R,4S)-4-(5-Methyl-2-pyridyl)-3-triisopropylsilyloxy-2-
azetidinone (22a). To a solution of 25a (0.98 g, 2.2
mmol) in CH3CN (40 mL) was added a solution of
CAN (3.82 g, 6.6 mmol) in H2O (30 mL) with ice cool-
ing, and the mixture was stirred at the same temperature
for 1.5 h. After saturated aqueous NaHCO3, saturated
aqueous Na2SO3, and AcOEt were added to the reac-
tion mixture, the two layers were separated. The aqu-
eous layer was extracted with AcOEt and the combined
organic layer was washed with brine, and dried over
Na2SO4. The solvent was removed under reduced pres-
sure and the residue was chromatographed on silica gel
eluting with n-hexane–AcOEt (1:1). The eluate was
concentrated under reduced pressure to give the racemic
compound, which was resolved by using a chiral HPLC
cis-(ꢃ)-3-Acetoxy-4-(5-trifluoromethyl-2-pyridyl)-1-(4-
methoxyphenyl)-2-azetidinone (24e). A pale orange solid
1
(23%); H NMR (CDCl3) d: 1.78 (3H, s), 3.77 (3H, s),
5.56 (1H, d, J=5.3 Hz), 6.17 (1H, d, J=5.3 Hz), 6.83
(2H, d, J=8.3 Hz), 7.25 (2H, d, J=8.3 Hz), 7.47 (1H, d,
J=7.8 Hz), 7.93 (1H, d, J=7.8 Hz), 8.91 (1H, s).
cis-(ꢃ)-1-(4-Methoxyphenyl)-4-(5-methyl-2-pyridyl)-3-
triisopropylsilyloxy-2-azetidinone (25a). To a solution of
24a (1.5 g, 4.5 mmol) in a mixture of MeOH (15 mL)
and THF (15 mL) was added K2CO3 (2.5 mg) with ice

4442
Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
column (Daicel Chiralcel OD, with n-hexane–2-propa-
nol [94:6 (v/v)] as the solvent) to give the title compound
(434 mg, 27%) as a white solid. H NMR (CDCl3) d:
0.88–1.01 (21H, m), 2.33 (3H, s), 4.95 (1H, d, J=4.9
Hz), 5.25 (1H, dd, J=2.4, 4.9 Hz), 6.11 (1H, br s), 7.37
(1H, d, J=8.3 Hz), 7.51 (1H, dd, J=1.5, 8.3 Hz), 8.37
(1H, s); FAB-MS( m/z): 335 (M+H)+. Anal. calcd for
C18H30N2O2Si: C, 64.63; H, 9.04; N, 8.37. Found: C,
64.37; H, 8.90; N, 8.16; [a]2D5 +80.8ꢁ (c 1.0, CHCl3).
further stirred overnight. After saturated aqueous
NaHCO3 and AcOEt were added to the reaction mix-
ture, the two layers were separated. The aqueous layer
was extracted with AcOEt and the combined organic
layer was washed with water, brine, and dried over
Na2SO4. The solvent was removed under reduced pres-
sure and the residue was chromatographed on silica gel
eluting with n-hexane–AcOEt (9:1). The eluate was
concentrated under reduced pressure to give the title
1
1
compound (316 mg, 30%) as a yellow oil. H NMR
Compounds 22d and 22e were obtained by following a
procedure analogous to that described for the prepara-
tion of 22a from 25a by replacing 25a with the corre-
sponding b-lactams 25d and 25e. A Daicel Chiralcel AD,
with n-hexane–2-propanol [95:5 (v/v)] as the solvent, was
used for the resolution of (ꢃ)-22d, and a Daicel Chiralcel
OD, with n-hexane–2-propanol [96:4 (v/v)] as the sol-
vent, was used for the resolution of (ꢃ)-22e.
(CDCl3) d: 0.89–1.03 (21H, m), 1.22 (3H, t, J=7.3 Hz),
2.63 (2H, q, J=7.3 Hz), 3.74 (3H, s), 5.31 (2H, s), 6.77–
6.81 (2H, m), 7.25–7.30 (3H, m), 7.45 (1H, dd, J=2.0,
8.0 Hz), 8.44 (1H, d, J=2.0 Hz); HR-MScalcd for
C26H38N2O3Si: 454.2652. Found, 454.2668.
(3R, 4S)-4-(5-Ethyl-2-pyridyl)-3-triisopropylsilyloxy-2-
azetidinone (22b). To a solution of 27 (315 mg, 0.69
mmol) in CH3CN (12.6 mL) was added a solution of
CAN (1.14 g, 2.07 mmol) in H2O (6.3 mL) with ice
cooling, and the mixture was stirred at the same tem-
perature for 10 min. After saturated aqueous NaHCO3,
saturated aqueous Na2SO3, and AcOEt were added to
the reaction mixture, the two layers were separated. The
aqueous layer was extracted with AcOEt and the com-
bined extract was washed with saturated aqueous
NaHCO3, brine, and dried over Na2SO4. The solvent
was removed under reduced pressure and the residue
was chromatographed on silica gel eluting with n-hex-
ane–AcOEt (2:1). The eluate was concentrated under
reduced pressure to give the title compound (143 mg,
59%, 79% ee) as yellow crystals. Enantiomeric purity
was determined by HPLC analysis on a chiral column,
Daicel Chiralcel OD, with n-hexane–2-propanol as the
(3R, 4S)-4-(5-Chloro-2-pyridyl)-3-triisopropylsilyloxy-2-
azetidinone (22d). Colorless crystals (25%); mp: 106–
108 ꢁC; H NMR (CDCl3) d: 0.88–1.01 (21H, m), 4.98
1
(1H, d, J=4.9 Hz), 5.25 (1H, dd, J=4.9 Hz, 3.0 Hz),
6.85 (1H, br s), 7.45 (1H, d, J=8.3 Hz), 7.69 (1H, dd,
J=8.3 Hz, 2.4 Hz), 8.50 (1H, d, J=2.4 Hz); FAB-MS
(m/z): 355 (M+H)+. Anal. calcd for C17H27ClN2O2Si:
C, 57.52; H, 7.67; N, 7.89; Cl, 9.99. Found: C, 57.69; H,
7.65; N, 7.76; Cl, 10.23; IR: 2942, 2865, 1743 cmꢂ1; [a]D23
+93.0ꢁ (c 0.52, EtOH).
(3R, 4S)-4-(5-Trifluoromethyl-2-pyridyl)-3-triisopropylsi-
lyloxy-2-azetidinone (22e). A white solid (33%); 1H
NMR (CDCl3) d: 0.87–1.01 (21H, m), 5.08 (1H, d,
J=4.9 Hz), 5.32 (1H, dd, J=4.9, 3.0 Hz), 6.31 (1H, br
s), 7.63 (1H, d, J=8.3 Hz), 7.94 (1H, d, J=8.3 Hz), 8.83
(1H, s); FAB-MS( m/z): 389 (M+H)+. Anal. calcd for
C18H27F3N2O2Si: C, 55.65; H, 7.00; N, 7.21. Found: C,
55.64; H, 7.06; N, 7.08; [a]2D4 +75.7ꢁ (c 0.17, CHCl3).
1
solvent. H NMR (CDCl3) d: 0.87–1.00 (21H, m), 1.22
(3H, t, J=7.3 Hz), 2.64 (2H, q, J=7.3 Hz), 4.97 (1H, d,
J=4.5 Hz), 5.25 (1H, dd, J=3.0, 4.5 Hz), 6.35 (1H, br
s), 7.39 (1H, d, J=8.0 Hz), 7.53 (1H, dd, J=2.0, 8.0
Hz), 8.30 (1H, d, J=2.0 Hz). Anal. calcd for
C19H32N2O2Si: C, 65.47; H, 9.25; N, 8.04. Found : C,
65.27; H, 9.18; N, 7.94.
N-(4-Methoxyphenyl)-(5-ehtyl-2-pyridyl)methanaldimine
(26). A mixture of 21b (3.0 g, 22.2 mmol), 4-anisidine
(2.75 g, 22.3 mmol), and Na2SO4 (10 g) in benzene (60
mL) was stirred at room temperature for 1 h. The reac-
tion mixture was filtered and the filtrate was con-
centrated under reduced pressure. The residue was
crystallized from n-pentane to give the title compound
Methyl (2S,3R)-2-[(3R,4S)-3-acetoxy-4-(5-fluoro-2-pyri-
dyl)-2-oxo-1-azetidinyl]-3-(tert-butyldiphenylsilyloxy)bu-
tyrate (29), methyl (2S,3R)-2-[(3S,4R)-3-acetoxy-4-(5-
fluoro-2-pyridyl)-2-oxo-1-azetidinyl]-3-(tert-butyldiphenyl-
silyloxy)butyrate (30). To a suspension of 28 (0.5 g, 2.95
mmol) in CH2Cl2 (10 mL) were added imidazole (0.44 g,
6.5 mmol), DMAP (5 mg), and TBDPSCl (0.85 mL, 3.3
mmol), and the mixture was stirred at room tempera-
ture for 72 h. After AcOEt and water were added to the
reaction mixture, the two layers were separated. The
aqueous layer was extracted with AcOEt and the com-
bined organic layer was washed with water, saturated
aqueous NaHCO3, brine, and dried over Na2SO4. The
solvent was removed under reduced pressure and the
residue was dissolved in benzene (20 mL). To this solu-
tion was added 21c (0.37 g, 2.95 mmol) and the mixture
was stirred under reflux for 1 h. Then, the reaction
mixture was concentrated under reduced pressure and
the residue was dissolved in CH2Cl2 (12 mL). To this
solution were added Et3N (0.45 mL, 3.2 mmol) and 2-
acetoxyacetyl chloride (0.35 mL, 3.2 mmol) at ꢂ40 ꢁC
1
(4.5 g, 84%) as yellow crystals. H NMR (CDCl3) d:
1.30 (3H, t, J=7.3 Hz), 2.72 (2H, q, J=7.3 Hz), 3.84
(3H, s), 6.93–6.97 (2H, m), 7.30–7.34 (2H, m), 7.63 (1H,
dd, J=2.0, 8.0 Hz), 8.10 (1H, d, J=8.0 Hz), 8.53 (1H,
d, J=2.0 Hz), 8.61 (1H, s).
(3R,
4S)-4-(5-Ethyl-2-pyridyl)-1-(4-methoxyphenyl)-3-
triisopropylsilyloxy-2-azetidinone (27). To a solution of
diisopropylamine (0.35 mL, 2.5 mmol) in THF (4 mL)
was added a 1.59 M solution of nBuLi in n-hexane (1.57
mL, 2.5 mmol) at 0 ꢁC. The solution was stirred at the
same temperature for 15 min and then cooled to
ꢂ78 ꢁC. To the mixture was added a solution of 15 (0.92
g, 2.35 mmol) in THF (3.5 mL). The solution was stir-
red for 2 h followed by addition of a solution of 26 (565
mg, 2.35 mmol) in THF (3.5 mL). The mixture was
slowly allowed to warm to room temperature and

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4443
and the whole was stirred at ꢂ40 ꢁC to room tempera-
ture overnight. After removal of the solvent, water and
AcOEt were added to the residue and the two layers
were separated. The aqueous layer was extracted with
AcOEt and the combined organic layer was washed
with water, saturated aqueous NH4Cl, saturated aqu-
eous NaHCO3, brine, and dried over Na2SO4. The sol-
vent was removed under reduced pressure and the
residue was chromatographed on silica gel eluting with
n-hexane–AcOEt (3:1). The eluate was concentrated
under reduced pressure to give the mixture of the title
compounds (1.23 g, 72%, 29/30=3.5:1) as a yellow oil.
1H NMR (CDCl3) d: 0.86 (9H, s), 1.07 (3H, d, J=6.4
Hz), 1.74 and 1.76 (total 3H, each s), 3.33 and 3.65
(total 3H, each s), 4.31 and 4.38 (total 1H, each m),
4.45–4.49 (1H, m), 5.41 and 5.67 (total 1H, each d,
J=4.9 Hz), 5.96 and 6.08 (total 1H, each d, J=4.9 Hz),
7.06–7.08 (2H, m), 7.23–7.67 (10H, m), 8.37 and 8.52
(total 1H, each d, J=2.4 Hz).
(3R,4S)-4-(5-Fluoro-2-pyridyl)-3-triisopropylsilyloxy-2-
azetidinone (22c). To a solution of 32 (0.47 g, 1.09
mmol) in a mixture of acetone (9.4 mL) and water (3
mL) were added NaHCO3 (458 mg, 5.45 mmol) and
KMnO4 (181 mg, 1.14 mmol) at ꢂ20 ꢁC, and the mix-
ture was stirred at the same temperature for 20 min. To
the reaction mixture was added water and the whole
was extracted with AcOEt. The extract was washed with
water, saturated aqueous NH4Cl, brine, and dried over
Na2SO4. The solvent was removed under reduced pres-
sure and the residue was chromatographed on silica gel
eluting with n-hexane–AcOEt (2:1). The eluate was
concentrated under reduced pressure to give the title
compound (128 mg, 35%, 54% ee) as colorless crystals.
Enantiomeric purity was determined by HPLC analysis
on a chiral column, Daicel Chiralcel AD, with n-hex-
ane–2-propanol as the solvent. 1H NMR (CDCl3) d:
0.89–1.02 (21H m), 5.00 (1H, d, J=4.9 Hz), 5.26 (1H,
dd, J=2.9, 4.9 Hz), 6.32 (1H, br s), 7.41–7.52 (2H, m),
8.41 (1H, d, J=2.9 Hz). Anal. calcd for
C17H27FN2O2Si: C, 60.32; H, 8.04; N, 8.28; F, 5.61.
Found: C, 60.40; H, 7.97; N, 8.14; F, 5.47.
Methyl
2-[(3R,4S)-3-Acetoxy-4-(5-fluoro-2-pyridyl)-2-
oxo-1-azetidinyl]-2-butenoate (31). To a solution of the
mixture of 29 and 30 (3.5:1) (1.23 g, 2.12 mmol) in THF
(12.3 mL) was added TBAF (1.0 M in THF, 2.25 mL,
2.25 mmol) with ice cooling, and the mixture was stirred
at the same temperature for 15 min. To the reaction
mixture was added saturated aqueous NH4Cl and the
whole was extracted with AcOEt. The extract was
washed with water, brine, and dried over Na2SO4. The
solvent was removed under reduced pressure and the
residue was chromatographed on silica gel eluting with
n-hexane–AcOEt (2:1). The eluate was concentrated
under reduced pressure to give the title compound (0.58
(3R,4S)-4-(5-Methoxy-2-pyridyl)-3-triisopropylsilyloxy-
2-azetidinone (22f). Compound 22f was obtained from
21f as yellow crystals (57%) by following a procedure
analogous to that described for the preparation of 13a
from 11a. 1H NMR (CDCl3) d: 0.89–1.02 (21H, m), 3.86
(3H, s), 4.95 (1H, d, J=4.9 Hz), 5.23 (1H, dd, J=2.4, 4.9
Hz), 6.20 (1H, br s), 7.23 (1H, dd, J=2.9, 8.3 Hz), 7.42
(1H, d, J=8.3 Hz), 8.30 (1H, d, J=2.9 Hz); HR-MS
calcd for C18H31N2O3Si: 351.2104. Found, 351.2138.
1
g, 85%) as a colorless syrup. H NMR (CDCl3) d: 1.80
Compounds 33a–f were obtained by following a proce-
dure analogous to that described for the preparation of
17a from 16 by replacing 14a with the corresponding b-
lactams 23a–f.
(3H, s), 2.12 (3H, d, J=6.8 Hz), 3.75 (3H, s), 5.73 (1H,
d, J=5.4 Hz), 6.02 (1H, d, J=5.4 Hz), 6.95 (1H, q,
J=6.8 Hz), 7.25-7.31 (1H, m), 7.39 (1H, dd, 1H, J=2.9,
8.3 Hz), 8.45 (1H, d, J=2.9 Hz).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-ben-
zoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenylide-
nedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbony-
lamino)-3-(5-methyl-2-pyridyl)-2-triisopropylsilyloxypro-
Methyl 2-[(3R,4S)-4-(5-fluoro-2-pyridyl)-2-oxo-3-triiso-
propylsilyloxy-1-azetidinyl]-2-butenoate (32). To a solu-
tion of 31 (0.57 g, 1.76 mmol) in a mixture of THF (6.75
mL) and MeOH (6.75 mL) was added K2CO3 (15 mg)
and the mixture was stirred at room temperature for 15
min. To the reaction mixture was added Dowex 50 (H+
form) and the mixture was stirred at room temperature
for 5 min. The whole was filtered and the filtrate was
concentrated under reduced pressure. After drying in
vacuo, the residue was dissolved in DMF (6.8 mL) and
to this solution were added imidazole (0.18 g, 2.64
mmol) and TIPSCl (0.56 mL, 2.61 mmol) with ice cool-
ing. The whole was stirred at room temperature for 72 h
and poured into ice-water. The mixture was extracted
with AcOEt and the extract was washed with water,
brine, and dried over Na2SO4. The solvent was removed
under reduced pressure and the residue was chromato-
graphed on silica gel eluting with n-hexane–AcOEt
(4:1). The eluate was concentrated under reduced pres-
sure to give the title compound (0.47 g, 61%) as a col-
1
pionate (33a). A white amorphous powder (80%); H
NMR (CDCl3) d: 0.83–0.93 (21H, m), 1.32 (3H, s), 1.42
(9H, s), 1.52 (3H, s), 1.65 (3H, s), 1.82 (3H, s), 1.59–1.78
(2H, m), 1.87 (1H, s), 2.04–2.13 (1H, m), 2.32 (3H, s),
2.51 (3H, s), 2.26–2.32 (1H, m), 2.97 (1H, d, J=5.4 Hz),
4.20 (1H, d, J=7.8 Hz), 4.22 (1H, d, J=7.3 Hz), 4.33
(1H, d, J=7.8 Hz), 4.96 (1H, br s), 5.21 (1H, d, J=6.4
Hz), 5.28 (1H, d, J=7.3 Hz), 5.44–5.48 (2H, m), 5.58
(1H, d, J=17.1 Hz), 5.78 (1H, s), 5.97–6.00 (2H, m),
6.09 (1H, br t), 7.42–7.46 (3H, m), 7.56 (1H, m), 7.60
(1H, t, J=7.8 Hz), 8.13 (2H, dd, J=1.0, 7.3 Hz), 8.38
(1H, d, J=1.5 Hz); HR-MScalcd for C 55H79N2O13Si:
1003.5351. Found, 1003.5289.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-3-(5-ethyl-2-pyridyl)-2-triisopropylsilyloxypro-
1
orless syrup. H NMR (CDCl3) d: 0.90–1.05 (21H, m),
1
2.04 (3H, d, J=7.3 Hz), 3.73 (3H, s), 5.32 (1H, d, J=4.9
Hz), 5.55 (1H, d, J=4.9 Hz), 6.86 (1H, q, J=7.3 Hz),
7.37–7.40 (2H, m), 8.41 (1H, s).
pionate (33b). A white amorphous powder (95%); H
NMR (CDCl3) d: 0.86–1.05 (21H, m), 1.22 (3H, t,
J=7.5 Hz), 1.32 (3H, s), 1.42 (9H, s), 1.43 (3H, s), 1.65

4444
Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
(3H, s), 1.82 (3H, s), 1.91–1.99 (1H, m), 2.23–2.35 (2H,
m), 2.53 (3H, s), 2.61–2.67 (3H, m), 2.97 (1H, d, J=5.5
Hz), 4.19–4.23 (2H, m), 4.34 (1H, d, J=8 Hz), 4.97 (1H,
s), 5.21 (1H, d, J=5.5 Hz), 5.24–5.31 (2H, m), 5.43–5.60
(3H, m), 5.96–6.05 (2H, m), 6.12 (1H, t, J=8 Hz), 7.24–
7.31 (1H, m), 7.42–7.58 (4H, m), 8.13 (2H, d, J=7 Hz),
8.41 (1H, d, J=2 Hz); HR-MScalcd for
C56H81N2O13Si: 1017.5508. Found, 1017.5532.
nylamino)-3-(5-methoxy-2-pyridyl)-2-triisopropylsilyloxy-
propionate (33f). A white amorphous powder (100%);
1H NMR (CDCl3) d: 0.89–0.95 (21H, m), 1.32 (3H, s),
1.33–1.62 (2H, m), 1.41 (9H, s), 1.52 (3H, s), 1.65 (3H,
s), 1.82 (3H, s), 1.92–2.32 (3H, m), 2.49 (3H, s), 2.98
(1H, d, J=4.9 Hz), 3.85 (3H, s), 4.20 (1H, d, J=7.4
Hz), 4.22 (1H, d, J=6.8 Hz), 4.32 (1H, d, J=8.3 Hz),
4.95 (1H, s), 5.21 (1H, d, J=5.8 Hz), 5.26–5.29 (2H, m),
5.39-5.47 (3H, m), 5.57 (1H, d, J=17.6 Hz), 5.96–6.02
(2H, m), 6.11 (1H, t-like, J=8.3 Hz), 7.15 (H, dd,
J=2.4, 8.8 Hz), 7.31 (1H, d, J=8.8 Hz), 7.44 (2H, t,
J=7.8 Hz), 7.56 (1H, t, J=7.8 Hz), 8.13 (2H, d, J=7.8
Hz), 8.26 (1H, d, J=3.0 Hz); HR-MScalcd for
C55H79N2O14Si: 1019.5301. Found, 1019.5260.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbonyl-
amino)-(5-fluoro-2-pyridyl)-2-triisopropylsilyloxypropio-
nate (33c). A white amorphous powder (74%); 1H
NMR(CDCl3) d: 0.87–0.94 (21H, m), 1.20–1.70 (2H,
m), 1.31 (3H, s), 1.42 (9H, s), 1.52 (3H, s 1.65 (3H, s),
1.82 (3H, s), 1.75–2.07 (2H, m), 2.26–2.32 (2H, m), 2.49
(3H, s), 2.97 (1H, d, J=5.4 Hz), 4.19–4.23 (2H, m), 4.33
(1H, d, J=8 Hz), 4.96 (1H, s), 5.21 (1H, d, J=5.9 Hz),
5.27–5.32 (2H, m), 5.43–5.49 (3H, m), 5.58 (1H, d,
J=17.5 Hz), 5.96–6.04 (2H, m), 6.12 (1H, t, J=8 Hz),
7.36–7.47 (4H, m), 7.57 (1H, t, J=7.3 Hz), 8.13 (2H, d,
J=7.3 Hz), 8.43 (1H, d, J=2.4 Hz); HR-MScalcd for
C54H76FN2O13Si: 1007.5101. Found, 1007.5144.
Compounds 34a–f were obtained by following a proce-
dure analogous to that described for the preparation of
18a from 17a.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-2-hydroxy-3-(5-methyl-2-pyridyl)propionate
(34a). A pale yellow amorphous powder (94%); 1H
NMR (CDCl3) d 1.27 (3H, s), 1.43 (9H, s), 1.49 (3H, s),
1.64 (3H, s), 1.75 (3H, s), 1.59–1.78 (2H, m), 1.88 (1H,
s), 1.91 (1H, m), 2.04–2.13 (2H, m), 2.33 (3H, s), 2.35
(3H, s), 2.33–2.38 (1H, m), 2.94 (1H, d, J=4.9 Hz), 4.19
(1H, d, J=7.3 Hz), 4.22 (1H, d, J=8.3 Hz), 4.33 (1H, d,
J=8.3 Hz), 4.89 (1H, br s), 4.91 (1H, br s), 4.89–4.91
(1H, m), 5.23 (1H, d, J=5.9 Hz), 5.30 (2H, m), 5.46
(1H, d, J=9.8 Hz), 5.58 (1H, d, J=17.1 Hz), 5.92 (1H,
d, J=9.8 Hz), 5.96–6.05 (2H, m), 6.09 (1H, t, J=8.3
Hz), 7.30 (1H, d, J=8.3 Hz), 7.47 (1H, t, J=7.8 Hz),
7.45–7.49 (1H, m), 7.52 (1H, dd, J=1.5, 7.8 Hz), 7.60
(1H, t, J=7.8 Hz), 8.13 (2H, d, J=7.3 Hz), 8.35 (1H, s);
HR-MScalcd for C 46H59N2O13: 847.4017. Found,
847.4095.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyl-
idenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycar-
bonylamino)-3-(5-chloro-2-pyridyl)-2-triisopropylsilyloxy-
propionate (33d). A white amorphous powder (71%); 1H
NMR (CDCl3) d: 0.87–0.94 (21H, m), 1.18–1.69 (2H,
m), 1.31 (3H, s), 1.41 (9H, s), 1.52 (3H, s), 1.65 (3H, s),
1.82 (3H, s), 1.72–2.05 (2H, m), 2.24–2.34 (2H, m), 2.48
(3H, s), 2.97 (1H, d, J=5.4 Hz), 4.19–4.23 (2H, m), 4.33
(1H, d, J=7.8 Hz), 4.95 (1H, s), 5.21 (1H, d, J=5.8 Hz),
5.27–5.31 (2H, m), 5.42–5.47 (3H, m), 5.58 (1H, d, J=17.5
Hz), 5.96–6.04 (2H, m), 6.11 (1H, t, J=8.8 Hz), 7.38 (1H,
d, J=8.3 Hz), 7.44 (2H, t, J=7.3 Hz), 7.57 (1H, t, J=7.3
Hz), 7.65 (1H, dd, J=2.5, 8.3 Hz), 8.13 (2H, d, J=7.3 Hz),
8.53 (1H, d, J=2.5 Hz); HR-MScalcd for
C54H76ClN2O13Si : 1023.4805. Found, 1023.4785.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-3-(5-ethyl-2-pyridyl)-2-hydroxypropionate
(34b). A white amorphous powder (85%); 1H NMR
(CDCl3) d 1.23–1.27 (6H, m), 1.43 (9H, s), 1.50 (3H, s),
1.63 (3H, s), 1.74 (3H, s), 1.84–1.89 (2H, m), 2.03–2.13
(1H, m), 2.32–2.38 (1H, m), 2.35 (3H, s), 2.65 (2H, q,
J=7.5 Hz), 2.93 (1H, d, J=5 Hz), 4.17–4.22 (2H, m),
4.32 (1H, d, J=8.0 Hz), 4.87–4.92 (3H, m), 5.23 (1H, d,
J=6.5 Hz), 5.28–5.33 (2H, m), 5.46 (1H, d, J=10.5 Hz),
5.58 (1H, d, J=7.0 Hz), 5.93–6.05 (3H, m), 6.09 (1H, t,
J=8.0 Hz), 7.32 (1H, d, J=7.5 Hz), 7.46 (1H, t, J=8.0
Hz), 7.48–7.61 (2H, m), 8.11 (2H, d, J=8.0 Hz), 8.37
(1H, s); HR-MScalcd for C 47H61N2O13: 861.4174.
Found, 861.4095.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-3-(5-trifluoromethyl-2-pyridyl)-2-triisopropyl-
silyloxypropionate (33e). A white amorphous powder
1
(92%); H NMR (CDCl3) d: 0.85–0.92 (21H, m), 1.31
(3H, s), 1.43 (9H, s), 1.52 (3H, s), 1.65 (3H, s), 1.83 (3H,
s), 1.60–1.66 (3H, m), 1.92–1.95 (1H, m), 2.04–2.09 (1H,
m), 2.26–2.40 (2H, m), 2.51 (3H, s), 2.98 (1H, d, J=5.4
Hz), 4.19–4.23 (2H, m), 4.34 (1H, d, J=8.3 Hz), 4.96
(1H, s), 5.21 (1H, d, J=5.9 Hz), 5.29 (1H, d, J=6.8
Hz), 5.38 (1H, d, J=9.3 Hz), 5.45–5.51 (3H, m), 5.58
(1H, d, J=17.1 Hz), 5.96–6.05 (2H, m), 6.13 (1H, t,
J=8.8 Hz), 7.45 (2H, t, J=7.8 Hz), 7.55–7.59 (2H, m),
7.93 (1H, d, J=8.3 Hz), 8.13 (2H, d, J=7.3 Hz), 8.86
(1H, s); HR-MScalcd for C 55H76F3N2O13Si: 1057.59.
Found, 1057.5068.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-3-(5-fluoro-2-pyridyl)-2-hydroxypropionate
(34c). A white amorphous powder (99%); 1H NMR
(CDCl3) d: 1.27 (3H, s), 1.20–1.68 (2H, m), 1.44 (9H, s),
1.49 (3H, s), 1.64 (3H, s), 1.74 (3H, s), 1.75–2.05 (2H,
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4445
m), 2.30–2.39 (2H, m), 2.34 (3H, s), 2.93 (1H, d, J=4.9
Hz), 4.18 (1H, d, J=6.8 Hz), 4.23 (1H, d, J=8.3 Hz)
4.33 (1H, d, J=8.3 Hz), 4.62 (1H, d, J=2.5 Hz), 4.90–
4.92 (2H, m), 5.24 (1H, d, J=5.8 Hz), 5.30 (1H, d,
J=6.8 Hz), 5.37 (1H, d, J=9.3 Hz), 5.46 (1H, d,
J=10.2 Hz), 5.58 (1H, d, J=17 Hz), 5.90 (1H, d,
J=10.2 Hz), 5.96–6.05 (2H, m), 6.10 (1H, t, J=7.8 Hz),
7.40–7.49 (4H, m), 7.60 (1H, t, J=7.3 Hz), 8.12 (2H, d,
J=7.3 Hz), 8.41 (1H, s); HR-MScalcd for
C45H56FN2O13: 851.3766. Found, 851.3793.
(2H, t, J=7.8 Hz), 7.60 (1H, t, J=7.8 Hz), 8.13 (2H, d,
J=7.8 Hz), 8.22 (1H, d, J=2.4 Hz); HR-MScalcd for
C46H59N2O14: 863.3966. Found, 863.4012.
Compounds 35a–f were obtained by following a proce-
dure analogous to that described for the preparation of
19a from 18a.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-bu-
toxycarbonylamino)-2-hydroxy-3-(5-methyl-2-pyridyl)pro-
pionate (35a). Colorless small needles (58%), mp 166–
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-3-(5-chloro-2-pyridyl)-2-hydroxypropionate
168 ꢁC. H NMR (CDCl3) d: 1.26 (3H, s), 1.43 (9H, s),
1
1.48 (3H, s), 1.60 (3H, s), 1.74 (3H, s), 1.74–2.13 (6H,
m), 2.33 (3H, s), 2.34 (3H, s), 2.31–2.36 (1H, m), 2.58–
2.68 (4H, m), 2.72 (1H, dd, J=4.9, 13.2 Hz), 2.79 (1H,
dd, J=4.9, 13.2 Hz), 2.93 (1H, d, J=4.9 Hz), 3.74 (4H,
dd, J=4.4, 4.9 Hz), 4.13 (1H, d, J=6.8 Hz), 4.21 (1H,
d, J=8.3 Hz), 4.32 (1H, d, J=8.3 Hz), 4.86 (1H, d,
J=2.0 Hz), 4.86–4.92 (1H, br s), 4.92 (1H, br s), 5.04
(1H, t, J=4.9 Hz), 5.23 (1H, d, J=6.8 Hz), 5.31 (1H, d,
J=9.3 Hz), 5.91 (1H, d, J=9.3 Hz), 5.98 (1H, d, J=4.9
Hz), 6.09 (1H, t, J=8.3 Hz), 7.30 (1H, d, J=8.3 Hz),
7.45–7.53 (1H, t, J=7.3 Hz), 7.60 (1H, t, J=7.3 Hz),
8.12 (2H, d, J=7.3 Hz), 8.35 (1H, s); FAB-MS( m/z):
1
(34d). A white amorphous powder (100%); H NMR
(CDCl3) d: 1.26 (3H, s), 1.22–1.65 (2H, m), 1.43 (9H, s),
1.49 (3H, s), 1.64 (3H, s), 1.74 (3H, s), 1.75–2.09 (2H,
m), 2.30–2.39 (2H, m), 2.33 (3H, s), 2.94 (1H, d, J=4.9
Hz), 4.18 (1H, d, J=5.3 Hz), 4.22 (1H, d, J=8.3 Hz)
4.32 (1H, d, J=8.3 Hz), 4.61 (1H, br s), 4.92 (2H, m),
5.24 (1H, d, J=6.3 Hz), 5.30 (1H, d, J=6.8 Hz), 5.36
(1H, d, J=9.3 Hz), 5.46 (1H, d, J=10.5 Hz), 5.58 (1H,
d, J=17.5 Hz), 5.87 (1H, d, J=9.3 Hz), 5.96–6.05 (2H,
m), 6.11 (1H, t, J=7.8 Hz), 7.39 (1H, d, J=8.3 Hz),
7.47 (2H, t, J=7.3 Hz), 7.60 (1H, t, J=7.3 Hz), 7.69
(1H, dd, J=2.4, 8.3 Hz), 8.12 (2H, d, J=7.3 Hz), 8.51
(1H, d, J=2.4 Hz); HR-MScalcd for C 45H56ClN2O13:
867.3471. Found, 867.3503.
920 (M+H)+. Anal. calcd for C49H65N3O14 0.5H2O: C,
.
63.75; H, 7.16; N, 4.52. Found: C, 63.30; H, 7.16; N,
4.42; IR: 3559, 2952, 1724, 1698, 1602, 1575, 1486, 1452
cmꢂ1; [a]2D3 ꢂ6.8ꢁ (c 0.3, CHCl3).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-2-hydroxy-3-(5-trifluoromethyl-2-pyridyl)pro-
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-bu-
toxycarbonylamino)-3-(5-ethyl-2-pyridyl)-2-hydroxypro-
pionate (35b). A white powder (61%), mp 148–151 ꢁC.
1H NMR (CDCl3) d: 1.23–1.26 (6H, m), 1.43 (9H, s),
1.48 (3H, s), 1.60 (3H, s), 1.72 (3H, s), 1.87–1.90 (2H,
m), 1.98–2.18 (2H, m), 2.31–2.37 (1H, m), 2.35 (3H, s),
2.57–2.68 (6H, m), 2.72 (1H, dd, J=4.9, 13.2 Hz), 2.79
(1H, dd, J=4.9, 13.2 Hz), 3.74 (4H, t, J=4.5 Hz), 4.12
(1H, d, J=7.0 Hz), 4.21 (1H, d, J=8.0 Hz), 4.32 (1H, d,
J=8.0 Hz), 4.86 (1H, d, J=3.5 Hz), 4.92 (1H, s), 5.04
(1H, t, J=4.5 Hz), 5.22 (1H, d, J=7.5 Hz), 5.31 (1H, d,
J=9.0 Hz), 5.92 (1H, d, J=9.0 Hz), 5.98 (1H, d, J=5.0
Hz), 6.09 (1H, t, J=8.0 Hz), 7.32 (1H, d, J=8.0 Hz), 7.47
(2H, t, J=8.0 Hz), 7.54 (1H, dd, J=2.0, 8.0 Hz), 7.60
(1H, t, J=8.0 Hz), 8.12 (1H, d, J=8.0 Hz), 8.36 (1H, s);
FAB-MS( m/z): 934 (M+H)+. Anal. calcd for
1
pionate (34e). A white amorphous powder (76%); H
NMR (CDCl3) d: 1.27 (3H, s), 1.44 (9H, s), 1.49 (3H, s),
1.64 (3H, s), 1.75 (3H, s), 1.60–1.91 (3H, m), 2.04–2.09
(2H, m), 2.33–2.40 (2H, m), 2.34 (3H, s), 2.93 (1H, d,
J=4.9 Hz), 4.18 (1H, d, J=7.3 Hz), 4.23 (1H, d, J=8.3
Hz), 4.33 (1H, d, J=8.3 Hz), 4.65 (1H, br s), 4.92 (1H,
s), 4.98 (1H, s), 5.25 (1H, d, J=6.3 Hz), 5.31 (1H, d,
J=7.8 Hz), 5.46 (1H, d, J=10.8 Hz), 5.58 (1H, d,
J=17.1 Hz), 5.90 (1H, d, J=9.3 Hz), 5.97–6.05 (2H, m),
6.13 (1H, t, J=7.8 Hz), 7.47 (2H, t, J=7.8 Hz), 7.57–
7.62 (2H, m), 7.96 (1H, d, J=7.8 Hz), 8.13 (2H, d,
J=7.8 Hz), 8.84 (1H, s); HR-MScalcd for
C46H55F3N2O13Na: 923.3554. Found, 923.3472.
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-propenyli-
denedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-butoxycarbo-
nylamino)-2-hydroxy-3-(5-methoxy-2-pyridyl)propionate
(34f). A white amorphous powder (91%); 1H NMR
(CDCl3) d: 1.26 (3H, s), 1.43 (9H, s), 1.50 (3H, s), 1.60–
1.91 (3H, m), 1.64 (3H, s), 1.74 (3H, s), 1.91 (1H, s),
2.04–2.16 (2H, m), 2.32–2.37 (1H, m), 2.34 (3H, s), 2.93
(1H, d, J=5.3 Hz), 3.85 (3H, s), 4.18 (1H, d, J=7.3
Hz), 4.22 (1H, d, J=8.3 Hz), 4.33 (1H, d, J=8.3 Hz),
4.79 (1H, br s), 4.85 (1H, br s), 4.92 (1H, br s), 5.23 (1H,
d, J=5.8 Hz), 5.29–5.30 (2H, m), 5.46 (1H, d, J=10.3
Hz), 5.58 (1H, d, J=17.1 Hz), 5.90 (1H, d, J=9.7 Hz),
5.96–6.03 (2H, m), 6.09 (1H, t-like, J=8.4 Hz), 7.22
(1H, dd, J=2.4, 8.8 Hz), 7.34 (1H, d, J=8.8 Hz), 7.47
.
C50H67N3O14 0.75H2O: C, 63.38; H, 7.29; N, 4.43.
Found: C, 63.32; H, 7.28; N, 4.24; IR: 3423, 2964, 1712,
1600, 1571, 1484, 1452 cmꢂ1; [a]D24 ꢂ5.9ꢁ (c 0.15, CHCl3).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-bu-
toxycarbonylamino)-3-(5-fluoro-2-pyridyl)-2-hydroxypro-
pionate (35c). A white powder (64%), mp 148–152 ꢁC.
1H NMR (CDCl3) d: 1.26 (3H, s), 1.20–1.69 (2H, m),
1.43 (9H, s), 1.48 (3H, s), 1.62 (3H, s), 1.72 (3H, s),
1.75–2.02 (2H, m), 2.33 (3H, s), 2.30–2.39 (2H, m),
2.59–2.69 (4H, m), 2.71 (1H, dd, J=5.4, 13.2 Hz), 2.79
(1H, dd, J=3.9, 13.2 Hz), 2.92 (1H, d, J=4.9 Hz), 3.74

4446
Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
(4H, t, J=4.9 Hz), 4.12 (1H, d, J=7.3 Hz), 4.22 (1H, d,
J=8.3 Hz), 4.32 (1H, d, J=8.3 Hz), 4.60 (1H, br s),
4.90–4.92 (2H, m), 5.04 (1H, t, J=4.9 Hz), 5.24 (1H, d,
J=6.8 Hz), 5.36 (1H, d, J=9.3 Hz), 5.89 (1H, d, J=9.8
Hz), 5.99 (1H, d, J=4.9 Hz), 6.09 (1H, t, J=8.0 Hz),
7.42–7.49 (3H, m), 7.60 (1H, t, J=7.3 Hz), 7.60 (1H, t,
J=7.3 Hz), 8.12 (2H, d, J=7.3 Hz), 8.40 (1H, s); FAB-
MS( m/z): 924 (M+H)+. Anal. calcd for
s), 1.48 (3H, s), 1.60 (3H, s), 1.72 (3H, s), 1.78–2.12 (6H,
m), 2.31–2.38 (1H, m), 2.34 (3H, s), 2.58–2.68 (4H, m),
2.71 (1H, dd, J=5.4, 13.2 Hz), 2.79 (1H, dd, J=3.9,
13.2 Hz), 2.93 (1H, d, J=5.3 Hz), 3.75 (4H, t, J=4.9
Hz), 3.86 (3H, s), 4.12 (1H, d, J=7.3 Hz), 4.21 (1H, d,
J=8.3 Hz), 4.33 (1H, d, J=8.3 Hz), 4.76 (1H, br s), 4.85
(1H, br s), 4.92 (1H, s), 5.04 (1H, t, J=4.6 Hz), 5.23
(1H, d, J=6.9 Hz), 5.29 (1H, d, J=8.8 Hz), 5.90 (1H, d,
J=9.3 Hz), 5.98 (1H, d, J=4.9 Hz), 6.08 (1H, t-like,
J=8.3 Hz), 7.22 (1H, dd, J=2.9, 8.8 Hz), 7.34 (1H, d,
J=8.8 Hz), 7.47 (2H, t, J=7.8 Hz), 7.60 (1H, t, J=7.8
Hz), 8.13 (2H, d, J=7.8 Hz), 8.22 (1H, d, J=2.9 Hz),
FAB-MS( m/z): 936 (M+H)+. Anal. calcd for
C49H65N3O15: C, 62.87; H, 7.00; N, 4.49. Found : C,
62.66; H, 7.08; N, 4.28; IR: 3542, 2950, 1729, 1720,
1600, 1581, 1481, 1450 cmꢂ1; [a]D24 ꢂ2.1ꢁ (c 0.77,
CHCl3).
.
C48H62FN3O14 H2O: C, 61.19; H, 6.85; N, 4.46; F, 2.02.
Found: C, 61.16; H, 6.85; N, 4.36; F, 2.05; IR: 3438,
2958, 1716, 1600 cmꢂ1; [a]D25 ꢂ6.7ꢁ (c 0.25, CHCl3).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-bu-
toxycarbonylamino)-3-(5-chloro-2-pyridyl)-2-hydroxypro-
pionate (35d). A white powder (77%), mp 146–150 ꢁC.
1H NMR (CDCl3) d: 1.26 (3H, s), 1.20–1.72 (2H, m),
1.43 (9H, s), 1.48 (3H, s), 1.63 (3H, s), 1.73 (3H, s),
1.75–2.03 (2H, m), 2.33 (3H, s), 2.30–2.38 (2H, m),
2.59–2.69 (4H, m), 2.72 (1H, dd, J=5.4, 13.2 Hz), 2.79
(1H, dd, J=3.9, 13.2 Hz), 2.92 (1H, d, J=4.9 Hz), 3.74
(4H, t, J=4.9 Hz), 4.12 (1H, d, J=7.9 Hz), 4.22 (1H, d,
J=8.8 Hz), 4.32 (1H, d, J=8.8 Hz), 4.59 (1H, br s), 4.91
(2H, m), 5.05 (1H, t, J=4.4 Hz), 5.24 (1H, d, J=6.8
Hz), 5.35 (1H, d, J=9.3 Hz), 5.87 (1H, d, J=9.8 Hz),
5.99 (1H, d, J=4.9 Hz), 6.10 (1H, t, J=8.0 Hz), 7.39
(1H, d, J=8.3 Hz), 7.47 (2H, t, J=7.3 Hz), 7.60 (1H, t,
J=7.3 Hz), 7.69 (1H, dd, J=2.5, 8.3 Hz), 8.12 (2H, d,
J=7.3 Hz), 8.50 (1H, d, J=2.5 Hz); FAB-MS( m/z):
In vitro cytotoxicity. To examine the direct growth-
inhibitory effects of the test compounds against P388
mouse leukemia, PC-6 and PC-12 human non-small cell
lung cancer cell lines, and resistant cell lines PC-6/
VCR29-9 and PC-6/VP1-1, the MTT [3-(4,5-dimethyl-
thiazol-2-yl)-2,5-diphenyl-2H-tetrazolium
bromide]
assay was performed. The concentration giving a
growth inhibition of 50% (GI50) was calculated accord-
ing to a published procedure.13
In vitro metabolic stability. The reaction mixture con-
sisted of 4 mM MgCl2, 10 mM disodium glucose-6-
940 (M+H)+. Anal. calcd for C48H62ClN3O14 H2O: C,
.
phospate,
1
unit/mL glucose-6-phosphate dehy-
60.15; H, 6.73; N, 4.38; Cl, 3.70. Found: C, 60.15; H,
6.74; N, 4.20; Cl, 3.63; IR: 3430, 2956, 1714, 1602 cmꢂ1
drogenase, 1 mM b-NADPH, 10 mM test compound,
and 1 mg protein/mL liver microsomes of each animal
in 0.1 M potassium phosphate buffer (pH 7.4) at a final
volume of 0.5 mL. This mixture was preincubated for 2
min at 37 ꢁC and the reaction was started by the addi-
tion of 10 mL (to the 0.49 mL of mixture) b-NADPH.
After incubation at 37 ꢁC, the reaction was stopped by
adding 1 mL of acetonitrile. After centrifugation, the
supernatant fraction was applied for analysis.
;
[a]2D4 ꢂ3.0ꢁ (c 0.16, CHCl3).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-bu-
toxycarbonylamino)-2-hydroxy-3-(5-trifluoromethyl-2-
pyridyl)propionate (35e). A white powder (81%), mp
148–151 ꢁC. 1H NMR (CDCl3) d: 1.26 (3H, s), 1.44 (9H,
s), 1.48, 1.61, 1.73 (each 3H, all s), 1.63–1.94 (3H, m),
2.03–2.08 (2H, m), 2.34–2.39 (2H, m), 2.34 (3H, s),
2.59–2.68 (4H, m), 2.70–2.82 (2H, m), 2.92 (1H, d,
J=5.3 Hz), 3.75 (4H, t, J=4.4 Hz), 4.12 (1H, d, J=7.3
Hz), 4.23 (1H, d, J=8.3 Hz), 4.33 (1H, d, J=8.3 Hz),
4.62 (1H, br s), 4.91 (1H, s), 4.98 (1H, d, J=1.9 Hz),
5.06 (1H, s), 5.24 (1H, d, J=7.4 Hz), 5.46 (1H, d, J=8.8
Hz), 5.89 (1H, d, J=8.8 Hz), 6.00 (1H, d, J=4.9 Hz),
6.12 (1H, t, J=7.8 Hz), 7.47 (2H, t, J=8.3 Hz), 7.57–
7.62 (2H, m), 7.96 (1H, d, J=8.3 Hz), 8.12 (2H, d,
J=8.3 Hz), 8.83 (1H, s), FAB-MS( m/z): 974 (M+H)+.
References and Notes
1. Wani, M. C.; Taylor, H. L.; Wall, M. E.; Coggon, P.;
MacPhail, A. T. J. Am. Chem. Soc. 1971, 93, 2325.
2. Schiff, P. B.; Fant, J.; Horwitz, S. B. Nature 1979, 277, 665.
3. Gueritte-Voegelein, F.; Guenard, D.; Lavelle, F.; Le Goff,
M.-T.; Mangatal, L.; Potier, P. J. Med. Chem. 1991, 34, 992.
4. For general reviews on taxoid chemistry, see: (a) Suffness,
M., Ed., Taxol1 Science and Applications; CRC: New York,
1995. (b) Georg, I. G., Chen, T. T., Ojima, I., Vyas, D. M.,
Eds., Taxane Anticancer Agents: Basic Science and Current
Status; ACS Symposium Series No. 583; American Chemical
Society: Washington, DC, 1995. (c) Farina, V., Ed., The
Chemistry and Pharmacology of Taxol1 and its Derivatives;
Elsevier: New York, 1995.
5. (a) For review, see: Suffness, M. Annu. Rep. Med. Chem.
1993, 28, 305. (b) Guenard, D.; Gueritte-Voegelein, F.; Potier,
P. Acc. Chem. Res. 1993, 26, 160.
6. Ishiyama, T.; Iimura, S.; Ohsuki, S.; Uoto, K.; Terasawa,
H.; Soga, T. Bioorg. Med. Chem. Lett. 2002, 12, 1083.
7. Takeda, Y.; Yoshino, T.; Uoto, K.; Chiba, J.; Ishiyama, T.;
Iwahana, M.; Jimbo, T.; Tanaka, N.; Terasawa, H.; Soga, T.
Bioorg. Med. Chem. Lett. 2003, 13, 185.
.
Anal. calcd for C49H62F3N3O14 0.75H2O: C, 59.60; H,
6.48; N, 4.25; F, 5.77. Found: C, 59.71; H, 6.65; N, 3.96;
F, 5.47; IR: 3423, 2954, 1712, 1606, 1577, 1488, 1452,
1367 cmꢂ1; [a]D23 ꢂ3.2ꢁ (c 0.4, CHCl3).
(1S, 2S, 3R, 4S, 5R, 8R, 9S, 10R, 13S)-4-Acetoxy-2-
benzoyloxy-5,20-epoxy-1-hydroxy-9,10-[(1S)-2-(morpho-
lino)ethylidenedioxy]tax-11-en-13-yl (2R, 3S)-3-(tert-bu-
toxycarbonylamino)-2-hydroxy-3-(5-methoxy-2-pyridyl)-
propionate (35f). Colorless small needles (51%), mp
160–161 ꢁC. 1H NMR (CDCl3) d: 1.27 (3H, s), 1.43 (9H,

Y. Takeda et al. / Bioorg. Med. Chem. 11 (2003) 4431–4447
4447
8. Blantz, E. J., Jr.; French, F. A.; Doamaral, J. R.; French,
D. A. J. Med. Chem. 1970, 13, 1124.
pound was assumed to be high and/or a kinetic resolution
might occur.
9. Ojima, I.; Habus, I.; Zhao, M.; Zucco, M.; Park, Y. H.;
Sun, C. M.; Brigaud, T. Tetrahedron 1992, 48, 6985.
10. The enantiomeric excess of 13a, 13b and 22f could not be
determined by HPLC analysis with a Chiralcel OD column;
however, from the consideration of good yields at the cou-
pling reaction with 16, the enantiomeric excess of each com-
11. Tennenson, S. M.; Belleau, B. Can. J. Chem. 1980, 58, 1605.
12. PC-6/VCR29-9: PC-6 cell line, which is resistant to Vin-
cristine1. PC-6/VP1-1: PC-6 cell line, which is resistant to VP-
16 (Etoposide1).
13. Ishii, M.; Iwahana, M.; Mitsui, I.; Minami, M.; Imagawa,
S.; Tohgo, A.; Ejima, A. Anticancer Drugs 2000, 11, 353.