Syntheses and bioactivities of macrocyclic paclitaxel bis-lactones

Article abstract of DOI:10.1016/j.bmc.2004.09.002

Five macrocyclic paclitaxel bis-lactones and their corresponding open chain taxoids were synthesized as models of the tubulin-binding conformation of paclitaxel. Macrocyclic lactones with a 19-21-membered ring underwent isomerization to form smaller rings

Full text of DOI:10.1016/j.bmc.2004.09.002

Bioorganic & Medicinal Chemistry 12(2004) 6147–6161
Syntheses and bioactivities of macrocyclic paclitaxel bis-lactones
Changhui Liu,a Jennifer K. Schilling,a Rudravajhala Ravindra,b
Susan Baneb and David G. I. Kingstona,*
aDepartment of Chemistry, M/C 0212, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
bDepartment of Chemistry, State University of New York, Binghamton, NY 13902, USA
Received 20 August 2004; revised 1 September 2004; accepted 1 September 2004
Available online 28 September 2004
Abstract—Five macrocyclic paclitaxel bis-lactones and their corresponding open chain taxoids were synthesized as models of the
tubulin-binding conformation of paclitaxel. Macrocyclic lactones with a 19–21-membered ring underwent isomerization to form
smaller rings. The lactones were evaluated for cytotoxicity and tubulin-polymerization ability. All five macrocyclic paclitaxel lac-
tones were active, but less so than paclitaxel, while the rearranged macrocyclic lactones and the corresponding open-chain taxoids
were much less active or inactive.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
bound paclitaxel,6,7 while solution NMR studies led to
the identification of three major conformers; a Ônon-
polarÕ form,8,9 a ÔpolarÕ form,10 and a ÔT-taxolÕ form.11
The ÔT-taxolÕ conformation is consistent with the solid
state NMR studies referred to above, and it docks well
into a hydrophobic cleft identified in b-tubulin.12
Paclitaxel (Taxolꢁ, 1) is currently one of the worldÕs
most successful anticancer drugs, and it is used for the
treatment of breast, ovarian, and other cancers.1
O
AcO
OH
O
In order to test these hypotheses, various conformation-
ally restricted paclitaxel analogs have been made,
including analogs with conformationally restricted side
Ph
NH
O
O
H
OBz
O
OAc
chains13,14 and analogs with bridged linkages from the
HO
OH
1
15
C-30 phenyl to the C-2phenyl with both shorter
and
longer16,17 linkers. More recently, a series of macrocyclic
docetaxel analogs was prepared with the bridge from the
C-30 nitrogen to the C-2oxygen. Our group has also
Its anticancer activity comes primarily from its ability to
bind to microtubules and prevent them from undergoing
depolymerization,2 leading ultimately to apoptosis. The
exact nature of the paclitaxel–tubulin interaction is thus
of great interest. It is known that paclitaxel binds pref-
erentially to the b-tubulin unit of the mictrotubule,3,4
and it is probable that it binds to this b-tubulin unit
in a specific binding conformation or in a few closely
related conformations. Several studies have attempted
to elucidate the nature of this bioactive conformation.
Three models have been proposed for it, based primarily
on NMR data, but also including the electron crystallo-
graphic coordinates of polymerized b-tubulin.5 Studies
based on solid state NMR spectroscopy led to the deter-
mination of specific internuclear distances for tubulin-
18
prepared two macrocyclic paclitaxel analogs tethered
from the C-4 position to the side chain C-30 through ring
closing metathesis (RCM) to test the T-taxol hypothe-
sis.19 None of these conformationally restricted paclit-
axel analogs had comparable tubulin assembly activity
to paclitaxel, and the cytotoxicities of even the best ana-
logs were significantly lower than that of paclitaxel.
AcO
O
OH
O
HO
O
H
OBz
O
O
HO
O
O
N
2a n = 1
2b n = 2
2c n = 3
2d n = 4
2e n = 5
H
Keywords: Taxol; Tubulin; Cytotoxicity; Paclitaxel.
*
O
O
Corresponding author. Tel.: +1 5402316570; fax: +1 5402313255;
e-mail: dkingston@vt.edu
n
0968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.09.002

6148
C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
In the proposed T-taxol conformation, the distances be-
tween the two C-13 side chain terminal phenyl rings and
10b was prepared in the same way as 10a. The carboxy-
lic acids with a terminal double bond were not commer-
cially available for the longer chain derivatives 10c–e,
but the corresponding a,x-dicarboxylic acids were avail-
able. It was found that acylation using 7-benzyloxylcar-
bonylheptanoyl chloride worked well, but the product
10e and the starting material could not be separated.
It was possible however to separate pure product after
desilylation with HF-pyridine, and the desired product
(11e) was isolated in good yield. Compounds 11c and
11d were made using the same procedures as for 11e.
After selective acetylation at the C-10 position and selec-
tive silylation at the C-7 position, the fully protected
baccatin analogs (3a–e) were ready for coupling with
the b-lactam.
˚
the C-2phenyl group are approximately 9–10A , and it is
not possible to design a short conformationally directing
tether between these centers. However, the C-4 acetate
methyl is quite close to one edge of the C-30 phenyl moi-
ety in this conformer, indicating a possible conforma-
tional control. A variety of positional isomers and
C30–C4 linkers were modeled as T-Taxol mimics. From
them, we designed and synthesized the analogs 2a–e
linked between the C-30-phenyl group and the C-4 posi-
tion through macrocyclic lactonization. A part of the
motivation for this study was to compare the lactoniza-
tion route to macrocycle formation with the GrubbsÕ
olefin metathesis route used earlier,19 from the perspec-
tive of both synthetic utility and activity of the final
products.
The synthesis of b-lactam (+)-6 was achieved as shown
in Scheme 3. The commercially available aldehyde 8
was first protected as its benzyl ether. The resulting alde-
hyde was reacted with p-anisidine to form the imine,
which subsequently reacted with a ketene generated
from acetoxyacetyl chloride to give the racemic b-lactam
(15). This lactam was then subjected to an enzymatic
resolution using lipase to generate (+)-15 in 48% yield.
A basic deacetylation followed by silyl reprotection
afforded TIPS protected 17 in good yield. Oxidative
deprotection of the PMP group using cerium(IV) ammo-
nium nitrate (CAN) gave 18, which was then treated
with benzoyl chloride to generate the desired b-lactam
6.The coupling between C-4 modified baccatin deriva-
tives (3a–e) and (+)-b-lactam (6) was performed using
standard coupling conditions.23 In Scheme 4, baccatin
derivatives 3a or 3b were first treated with NaH in anhy-
drous THF at 0ꢂC for 5min, and then the b-lactam 6
was added. The reaction generally gave 50–60% yields
of the desired products 19 and 20. The oxidative cleav-
ages of terminal alkenes were carried out using Sharpless
conditions24 to produce two carboxylic acids (21 and
22). After hydrogenolysis, the desired hydroxyl acids
(23 and 24) were obtained in 75–80% yield.
2. Synthesis
Our retrosynthetic analysis of the macrocyclic paclitaxel
lactones 2a–e is shown in Scheme 1. Compounds 2a–e
could be prepared by lactonization of the hydroxyacids
3a–e, which could be prepared from the two key frag-
ments 4a–e and the b-lactam 6; an alternate route would
involve the alkenyl derivatives 5a–e. Compounds 4a–e
can be synthesized through known C-4 deacetylation
and reacylation procedures20 from commercially availa-
ble 10-deacetylbaccatin III (7, 10-DAB), while 6 could
be synthesized through standard b-lactam synthesis21
from 3-hydroxybenzaldehyde (8).
Compounds 3a–e were prepared from 10-DAB (7) as
shown in Scheme 2. The 4-deacetyl 10-DAB analog 9
was made through reported procedures.20 Reacylation
at the C-4 position was first tried using 3-benzyloxylcar-
bonylpropanoyl chloride.22 Unfortunately, this reaction
gave a very low yield and we thus used 4-pentenoyl chlo-
ride to make compound 10a as previously described.19
We planned to use an oxidative cleavage reaction to
convert the terminal double bond into the carboxyl
group necessary for macrolactonization, and compound
The coupling reaction to prepare compounds 28–30 was
performed using LHMDS as base, since the NaH condi-
AcO
AcO
AcO
O
O
O
OH
OTES
OTES
O
O
HO
TIPSO
O
O
O
O
H
OBz
H
OBz
H
OBz
O
O
O
HO
HO
HO
HO
O
O
O
O
N
N
H
2a n = 1
2b n = 2
2c n = 3
2d n = 4
2e n = 5
O
OBn
H
n
O
O
OH
HO
O
4a-e
O
3a-e
n
n
O
or
O
O
HO
AcO
O
OBn
Ph
OH
OTES
H
TIPSO
O
+
O
O
H
H
OBz
HO
HO
OH
HO
N
HO
OBz OAc
O
O
O
8
n
7
6
5a-e
Scheme 1. Retrosynthetic analysis of macrocyclic paclitaxel lactone.

C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
6149
1. LHMDS, 0 oC, THF
0.5h
OTES
O
1. TESCl, imidazole,
DMF, 6h, 90%
2. DMSCl, imidazole
DMF, rt, 99%
O
O
TESO
OTES
TESO
HO
OH
2. acid chloride, 0 oC,
2-3h, 30-70%
3. Red-Al, THF, 0 oC,
45min, 80%
O
O
O
H
O
TESO
H
H
TESO
HO
AcO
OH
OH
DMSO
OBz
DMSO
OBz
OBz
O
10a-e
9
7
R
HF-pyridine/THF
0 oC to rt, overnight,
80-100%
O
O
O
AcO
AcO
HO
TESCl, imidazole
DMF, rt,10-20min,
85-90%
OTES
OH
OH
O
Ac2O, CeCl3, THF, rt, 3h,
90-95%
O
O
O
O
O
H
H
H
HO
HO
HO
OH
OH
OBz
OBz
OHOBz
O
O
R
O
12a-e
COOBn
3a-e
11a-e
R
R
COOBn
3
COOBn
4
e R =
a R =
b R =
d R =
c R =
2
Scheme 2. Synthesis of the baccatin III core (3a–e).
OBn
AcOCH2COCl, TEA,
CH2Cl2, -78 oC to rt
overnight, 60%
O
O
H2NC6H4OCH3,
BnBr,K2CO3,
DMF, rt,
overnight,
100%
MgSO4,
CH2Cl2,
overnight
AcO
O
HO
OBn
OBn
N
N
PMP
O
PMP
N
OBn
13
OH
(-)-16
PMP
47% yield
15 (racemic)
14
8
Lipase PS30
CH3CN/H2O
buffer, pH=7
rt, 7days
+
AcO
HO
TIPSO
TIPSO
O
TIPSO
OBn
OBn
OBn
OBn
OBn
1M KOH/THF
0 oC, 45min, 92%
N
N
N
N
PhCOCl, TEA
DMAP, CH2Cl2
rt, 2h, 90%
NH
CAN, CH3CN/H2O
TIPSCl,
imidazole
DMF, rt, 3h,
95%
Ph
O
O
PMP
O
PMP
PMP
O
0
oC, 1h, 82%
O
(+)-15 48% yield
(+)-18
(+)-6
(+)-17
(+)-16
Scheme 3. Synthesis of (+)-b-lactam 6.
O
O
O
AcO
RuCl3, NaIO4,
CH3CN/CCl4/
H2O
AcO
AcO
OTES
OTES
OTES
Pd-C, H2
,
O
O
O
EtOAc, rt,
2 days,
1. NaH, 0 oC,
rt, 24h,
Ph
NH
O
Ph
NH
O
Ph
NH
O
3a THF, 5 min
75-80%
50-60%
or
H
O
O
H
O
H
O
O
2. (+)-6,
24-48h
50-60%
O
O
O
3b
HO OBz
HO OBz
HO OBz
OTIPS
OTIPS
OTIPS
O
O
O
O
OBn
OBn
OH
21 n = 1
22 n = 2
19 n = 1
20 n = 2
23 n = 1
24 n = 2
n
n
n
HOOC
OTES
HOOC
Scheme 4. Synthesis of the hydroxy acids 23–24.
O
AcO
O
tions gave only complex mixtures. The resulting three
paclitaxel analogs (25–27) were then converted into
hydroxyacids 28–30 by hydrogenolysis (Scheme 5).
1. LHMDS, 0 oC,
THF, 5 min
Ph
NH
O
3c - 3e
H
O
O
O
2. (+)-6,
3-4h
66-90%
HO OBz
OTIPS
O
With five hydroxyacids in hand, we investigated the best
conditions for macrocyclic lactonization, and the Yama-
guchi lactonization strategy was found to work the
best. In general, macrolactonization proceeded well
and gave the desired products in 18–65% yields. As
expected, the yield of the macrolactonization reac-
tion was sensitive to ring size, with yields of 25%
for 31, 18% for 32, and 31–65% for 33–35. These results
OR
n
ROOC
Pd-C, H2,
EtOAc, rt,
3 days,
25 n = 3, R = Bn
26 n = 4, R = Bn
27 n = 5, R = Bn
28 n = 3, R = H
29 n = 4, R = H
30 n = 5, R = H
68-88%
Scheme 5. Synthesis of the hydroxy acids 26–28.

6150
C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
HF-
1. TEA, CH2Cl2,
pyridine or
O
O
OR2
O
O
AcO
AcO
AcO
AcO
OTES
OH
OH
TEA..HF
Yamaguchi's
Reagent,
rt, 0.5 h
O
THF, 0 o
C
to rt, 24h
Ph
NH
O
O
O
+
2. DMAP,
TIPSO
HO
HN
H
O
O
H
O
H
O
H
O
CH2Cl2, rt
0.5 mL/h,
18%-65%
O
O
O
O
OHOBz
OR1
OHOBz
OBz
O
OH
HO OBz
O
n
O
O
O
O
O
O
O
HN
Ph
O
O
O
OH
n
O
Ph
O
O
NH
O
n
n
HOOC
2a n = 1 (23%)
2b n = 2 (13%)
2c n = 3 (43%)
2d n = 4 (90%)
2e n = 5 (91%)
31 n = 1
32 n = 2
33 n = 3
34 n = 4
35 n = 5
O
Ph
23 n = 1, R1 = TIPS, R2 = TES
24 n = 2, R1 = TIPS, R2 = TES
28 n = 3, R1 = TIPS, R2 = TES
29 n = 4, R1 = TIPS, R2 = TES
30 n = 5, R1 = TIPS, R2 = TES
OH
36a n = 1 (49%)
36b n = 2 (51%)
36c n = 3 (45%)
36d n = 4 (<5%)
36e n = 5 (<5%)
37a n = 1, R1 = R2 = H
37b n = 2, R1 = R2 = H
37c n = 3, R1 = R2 = H
37d n = 4, R1 = R2 = H
37e n = 5, R1 = R2 = H
HF-pyridine,
THF, 0 oC to rt,
24h, 75-80%
Scheme 6. Syntheses of the macrocyclic paclitaxel lactones.
Table 1. Cytotoxicity and tubulin-assembly ability of compounds
2a–e, 34a–c, 35a–e
suggested that 31 and 32 might have larger ring strain
than 33–35.
Compound
A2780 IC50 (lM) Tubulin assembly IC50 (lM)
Surprisingly, desilylation of 31–35 under HF-pyridine or
HF-TEA conditions gave two series of products (2a–e
and 36a–e) with the same composition as determined
by HRFABMS. The NMR analysis of these two series
of products showed that 2a–e were the desired products,
while 36a–e were rearranged products with a bridge
from C-4 to C-20, because the chemical shift of C-20 pro-
ton was shifted down field dramatically to suggest an
ester at this position, while the ortho protons at the
C-30 phenyl ring was shifted up field to support a free
hydroxyl group on the phenyl ring (Scheme 6).
Paclitaxel (1)
2a
0.024
18
5.2ND
>21
10
4.21.3
0.5
ND
2b
2c
>30
2.2
2d
2e
36a
36b
36c
37a
37b
37c
37d
37e
>21
2
ND
0
ND
21
>30
ND
ND
ND
>15
20.6
>21
>21
18
>21
>21
The ratio between these two series of products varied
with the ring size. In the formation of 2a and 2b, the ma-
jor products were actually 36a and 36b, which suggests
that the ring strain of 2a and 2b is quite large. This is
consistent with the fact that 31 and 32, the precursors
of 2a and 2b, gave lower yields of macrocycles than pre-
cursors 33–35. On the other hand, compounds 2d and 2e
were the dominant products, and only trace amounts of
36d and 36e could be found by TLC. Compound 36c
was somewhere in between, with 2c and 36c formed in
comparable yields.
open-chain analogs. Bridging can thus be seen as a
way of minimizing unfavorable interactions between
the side chains and tubulin. The second conclusion is
that all the bridged analogs were less active than paclit-
axel itself. The most active compound in both the A2780
assay and the tubulin-assembly assay was compound 2e,
which has a C-4 to C-30-phenyl chain of 10 heavy atoms.
This contrasts with the results from our study of ortho
bridged derivatives described in more detail below,
where compounds with only five heavy atoms provided
the greatest activity.25 The three rearranged macrocyclic
paclitaxel analogs 36a–c and all five open chain paclit-
axel analogs were essentially inactive.
In order to have a better understanding of the bioactiv-
ities for these macrocyclic paclitaxel analogs, we also
prepared a series of the corresponding open chain ana-
logs 37a–e by desilylation of 23–24 and 28–30.
3. Biological results and discussion
One reason that none of the macrocyclic paclitaxel
lactones were as active as paclitaxel may be that the
lactones are not stable, and can rearrange to the
corresponding inactive macrocyclics (36a–c). This is
supported by the fact that the moderately stable com-
pound 2c (IC50 > 2 1lM) was less active than cycloalk-
ene 38, which has a similar length chain between C-4
and the C-30-phenyl; compound 38 had an IC50 value
of 1.23lM in the A2780 assay.19 Both compounds have
the same ring size, and it seems unlikely that the chem-
ical difference between a monolactone and a bis-lactone
The biological activities of paclitaxel and of the macro-
cyclic paclitaxel analogs 2a–e, 36a–c, and the open chain
compounds 37a–e were evaluated in the A2780 ovarian
cancer cell line, and six compounds were also tested for
their tubulin-assembly ability (Table 1).
Two major conclusions emerge from these data. In the
first place, it is significant that all the bridged com-
pounds are more cytotoxic than their corresponding

C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
6151
could account for this activity difference. It is thus pos-
sible that the instability of the lactone 2c with respect to
its inactive isomer 36c accounts for this difference,
although Z-geometry of the double bond might also
be a factor. If the instability of the lactone is the reason
for the reduced activity of 2c, then the relatively good
activity of lactone 2b is surprising, since this is less stable
than 2c. The relatively good activity of the stable analog
2e is also significant, and again supports the hypothesis
that bridged compounds provide an extra measure of
tubulin-binding affinity.
4.2. General procedure for acylation of 4-deacetylbacca-
tins at C-4
To a solution of 1-DMS-7,10,13-triTES-4-deacetyl-10-
deacetylbaccatin III 920 (610mg, 0.676mmol) in dried
THF (5.5mL) at 0ꢂC was added 1M LHMDS
(0.81mL, 0.81mmol). The solution was stirred for
0.5h before 5-hexenoyl chloride (0.879mmol in 0.5mL
THF) was added. The reaction mixture was allowed to
stir at 0ꢂC for 2.5h, and then quenched with saturated
NH4Cl. After diluted with EtOAc, the organic phase
was washed with water, brine, dried over sodium sulfate,
and concentrated in vacuum. The residue was applied to
preparative TLC (30% EtOAc/hexane) to give 10b as a
colorless gum (350mg, 67%) and recovered 9 (140mg,
23%). Compounds 10a19 and 10c–d were prepared
similarly.
O
AcO
OH
O
HO
HN
H
O
O
O
OHOBz
O
O
4.2.1.
1-DMSO-7,10,13-triTES-4-deacetyl-4-(5-hexe-
Ph
O
noyl)-10-deacetylbaccatin III (10b). 1H NMR
(400MHz, CDCl3) d: ꢀ0.28 (3H, d, J = 2.8Hz), 0.08
(3H, d, J = 2.8Hz), 0.57–0.78 (18H, overlapped), 0.96–
1.09 (27H, overlapped), 1.13 (3H, s), 1.21 (3H, s), 1.60
(1H, s), 1.68 (3H, s), 1.86–1.98 (3H, overlapped), 1.99
(3H, d, J = 1.2Hz), 2.19–2.40 (4H, overlapped), 2.49–
2.70 (3H, overlapped), 3.85 (1H, d, J = 6.9Hz), 4.24
(1H, d, J = 8.3Hz), 4.27 (1H, d, J = 8.3Hz), 4.41 (1H,
dd, J = 10.6, 6.6Hz), 4.91 (1H, dd, J = 9.6, 2.0Hz),
4.99 (1H, t, J = 8.4Hz), 5.08–5.17 (2H, overlapped),
5.18 (1H, s), 5.74 (1H, d, J = 6.9Hz), 5.84–5.95 (1H,
m), 7.44–7.50 (2H, m, Ar), 7.56–7.62 (1H, m, Ar),
8.11–8.16 (2H, m, Ar); 13C NMR (100MHz, CDCl3)
d: 0.2, 0.6, 5.0, 5.4, 6.2, 7.1, 7.2, 10.6, 14.6, 21.7, 24.7,
27.6, 33.5, 35.2, 37.6, 39.5, 44.3, 46.8, 58.4, 68.6, 72.9,
75.9, 76.1, 76.9, 81.2, 82.3, 84.4, 115.9, 128.5, 130.3,
130.7, 133.3, 136.2, 137.6, 138.8, 165.5, 172.3, 205.7;
HRFABMS m/z 1021.5504 [M+H+]; calcd for
C53H90O10Si4Na, 1021.5509.
38
Since the completion of this work we have prepared a
series of stable bridged analogs linked through the
ortho position on the C-30 phenyl group to C-4, as
shown for compound 39. Several related bridged
analogs of this type have been made, and some of them
have turned out to have superior activity in several
assays.25 These results support the importance of the
T-conformation for the tubulin-binding activity of
paclitaxel. A macrocyclic paclitaxel lactone with the
same bridge tether would presumably also have good
activity, but the problem of isomerization to an inactive
lactone makes this a less attractive type of derivative for
future work.
AcO
O
OH
4.3. General procedures for deprotection of silyl groups
O
HO
O
H
O
O
To a solution of 1-DMS-7,10,13-triTES-4-deacetyl-4-(5-
hexenoyl)-10-deacetylbaccatin III 10b (350mg, 0.34
mmol) in dried THF (10mL) was added anhydrous
pyridine (2.0mL), then the solution was cooled to
0ꢂC, and HF–pyridine (2.0mL) was added. The reac-
tion mixture was allowed to warm to room temperature,
and stirred for overnight. The reaction mixture was
diluted with EtOAc (100mL), and the organic phase
was washed with sodium bicarbonate, water, brine,
dried over sodium sulfate, and concentrated in vacuum.
The residue was applied to preparative TLC (60%
EtOAc/hexane) to give 11b as a colorless gum (184mg,
88%). Compounds 11a19 and 11c–e were prepared
similarly.
HO
BzO
O
N
H
O
39
4. Experimental
4.1. Materials and instruments
Chemicals were obtained from Aldrich Chemical Co.
and were used without further purification. All solvents
were of reagent grade or HPLC grade. THF was dis-
tilled over sodium/benzophenone, and CH2Cl2 was dis-
1
tilled over calcium hydride. All H NMR spectral data
4.3.1. 4-Deacetyl-4-(5-hexenoyl)-10-deacetylbaccatin III
1
were obtained in CDCl3, CD3OD, or (CD3)2CO on Var-
ian Unity 400 or Varian Inova 400 spectrometer (oper-
ating at 399.951MHz for 1H and 100.578MHz for
13C). Mass spectra were obtained at Analytical Service
in the Department of Chemistry (HRFABMS) Virginia
Tech.
(11b). H NMR (400MHz, CDCl3) d: 1.08 (6H, s), 1.73
(3H, s), 1.78–1.90 (3H, m, overlapped), 2.05 (3H, s),
2.15–2.43 (6H, overlapped), 2.53–2.70 (3H, overlapped),
3.98 (1H, d, J = 7.1Hz), 4.18 (1H, d, J = 8.3Hz), 4.25–
4.36 (3H, overlapped), 4.70–4.87 (1H, m), 4.94 (1H,
dd, J = 9.3, 1.5Hz), 5.05–5.15 (2H, overlapped), 5.26

6152
C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
(1H, s), 5.61 (1H, d, J = 7.1Hz), 5.81–5.92(1H, m),
7.45–7.52(H2 , m, Ar), 7.58–7.64 (1H, m, Ar), 8.08–
8.14 (2H, m, Ar); 13C NMR (100MHz, CDCl3) d: 9.9,
15.2, 19.9, 23.8, 26.8, 33.2, 34.7, 37.0, 38.9, 42.8, 47.2,
57.8, 67.8, 72.1, 75.0, 75.1, 76.8, 79.0, 80.8, 84.5, 115.7,
128.7, 129.5, 130.2, 133.8, 134.7, 137.8, 167.2, 173.3,
211.7; HRFABMS m/z 599.2886 [M+H+]; calcd for
C33H43O10, 599.2856.
211.7; HRFABMS m/z 749.3574 [M+H+]; calcd for
C42H53O12, 749.3537.
4.4. General procedure for selective acetylation of 10-
DAB derivatives at C-10
To a solution of 4-deacetyl-4-(5-hexenoyl)-10-deacetyl-
baccatin III 11b (226mg, 0.38mmol) in dried THF
(3.5mL) was added CeCl3 (10mg, cat.), and then acetic
anhydride (0.55mL, 5.7mmol) was added. After stirring
at room temperature for 3h, the reaction mixture was
diluted with EtOAc (50mL), and then washed with
saturated NaHCO3, brine, and dried with sodium
sulfate. The organic phase was concentrated in vacuum,
and the residue was applied to PTLC (50% EtOAc/hex-
ane) to give 12b as colorless gum (230mg, 95%).
Compounds 12a19 and 12c–e were prepared in similar
procedure.
4.3.2. 4-Deacetyl-4-(5-benzyloxylcarbonylpentanoyl)-10-
deacetylbaccatin III (11c). Colorless gum; 1H NMR
(400MHz, CDCl3) d: 1.09 (6H, s), 1.69–1.90 (9H, over-
lapped), 2.04 (3H, d, J = 1.0Hz), 2.17–2.33 (3H, over-
lapped), 2.41–2.64 (4H, overlapped), 2.68–2.88 (2H,
overlapped), 3.99 (1H, d, J = 7.1Hz), 4.19 (1H, d,
J = 8.5Hz), 4.27–4.36 (3H, overlapped), 4.81 (1H, m),
4.96 (1H, dd, J = 9.3, 1.6Hz), 5.16 (2H, s), 5.27 (1H,
d, J = 1.7Hz), 5.64 (1H, d, J = 7.1Hz), 7.32–7.42 (5H,
m, Ar, overlapped), 7.46–7.53 (2H, m, Ar), 7.58–7.65
(1H, m, Ar), 8.10–8.15 (2H, m, Ar); 13C NMR
(100MHz, CDCl3) d: 9.8, 15.1, 19.8, 23.5, 24.2, 26.7,
33.8, 34.4, 36.9, 38.8, 42.6, 47.1, 57.7, 66.5, 67.6, 72.0,
74.9, 75.0, 76.6, 78.9, 80.7, 84.4, 128.2, 128.4, 128.6,
128.7, 129.4, 130.1, 133.6, 134.5, 135.8, 142.8, 167.1,
172.8, 173.7, 211.7; HRFABMS m/z 721.3218 [M+H+];
calcd for C40H49O12, 721.3224.
4.4.1. 4-Deacetyl-4-(5-hexenoyl)baccatin III (12b). 1H
NMR (400MHz, CDCl3) d: 1.03 (3H, s), 1.05 (3H, s),
1.74–1.84 (3H, overlapped), 1.94–2.00 (4H, overlapped),
2.09–2.29 (7H, overlapped), 2.45–2.82 (5H, overlapped),
3.82(1H, d, J = 7.0Hz), 4.11 (1H, d, J = 8.3Hz), 4.24
(1H, d, J = 8.3Hz), 4.44 (1H, dd, J = 10.2, 7.3Hz),
4.75–4.84 (1H, m), 4.89 (1H, dd, J = 9.4, 1.2Hz), 4.98–
5.09 (2H, overlapped), 5.56 (1H, d, J = 7.0Hz), 5.75–
5.87 (1H, m), 6.27 (1H, s), 7.38–7.46 (2H, m, Ar),
7.52–7.60 (1H, m, Ar), 8.01–8.08 (2H, m, Ar); 13C
NMR (100MHz, CDCl3) d: 9.5, 15.6, 20.0, 21.0, 23.6,
26.9, 33.1, 34.5, 35.6, 39.0, 42.7, 46.2, 58.6, 67.6, 72.3,
75.0, 76.4, 76.5, 79.0, 80.6, 84.7, 115.5, 128.7, 129.4,
130.1, 131.3, 133.7, 137.8, 147.1, 166.9, 171.5, 173.0,
204.4; HRFABMS m/z 641.2967 [M+H+]; calcd for
C35H45O11, 641.2962.
4.3.3. 4-Deacetyl-4-(6-benzyloxylcarbonylhexanoyl)-10-
deacetylbaccatin III (11d). Colorless gum; 1H NMR
(400MHz, CDCl3) d: 1.05 (6H, s), 1.34–1.51 (2H, m),
1.63–1.76 (7H, overlapped), 1.77–1.87 (2H, overlapped),
2.01 (3H, d, J = 1.0Hz), 2.12–2.30 (2H, overlapped),
2.37–2.45 (3H, overlapped), 2.46–2.59 (2H, overlapped),
2.61–2.70 (1H, m), 2.77 (1H, d, J = 4.8Hz), 3.94 (1H, d,
J = 7.1Hz), 4.15 (1H, d, J = 8.3Hz), 4.23–4.33 (3H,
overlapped), 4.76 (1H, m), 4.91 (1H, dd, J = 9.3,
1.5Hz), 5.11 (2H, s), 5.23 (1H, d, J = 1.5Hz), 5.59
(1H, d, J = 7.1Hz), 7.28–7.40 (5H, m, Ar, overlapped),
7.42–7.49 (2H, m, Ar), 7.54–7.60 (1H, m, Ar), 8.06–
8.11 (2H, m, Ar); 13C NMR (100MHz, CDCl3) d:
10.1, 15.3, 20.1, 23.9, 24.7, 26.9, 28.5, 34.2, 34.8, 37.0,
39.0, 42.8, 47.2, 57.9, 66.6, 67.7, 72.2, 75.2, 76.8, 79.1,
80.8, 84.6, 128.4, 128.5, 128.8, 129.6, 130.3, 133.9,
134.6, 136.0, 143.2, 167.2, 173.3, 174.2, 211.9; HRF-
ABMS m/z 735.3356 [M+H+]; calcd for C41H51O12,
735.3381.
4.4.2.
4-Deacetyl-4-(5-benzyloxylcarbonylpentanoyl)-
1
baccatin III (12c). Colorless gum; H NMR (400MHz,
CDCl3) d: 1.12(6H, s), 1.69 (3H, s), 1.72–1.92(6H, over-
lapped), 2.03 (3H, br s), 2.20–2.36 (5H, overlapped),
2.40–2.77 (6H, overlapped), 2.90 (1H, br s), 3.88 (1H,
d, J = 7.1Hz), 4.17 (1H, d, J = 8.4Hz), 4.31 (1H, d,
J = 8.4Hz), 4.51 (1H, m), 4.84 (1H, m), 4.96 (1H, d,
J = 9.2Hz), 5.15 (2H, s), 5.64 (1H, d, J = 7.1Hz), 6.33
(1H, s), 7.32–7.42 (5H, m, Ar, overlapped), 7.46–7.54
(2H, m, Ar), 7.58–7.65 (1H, m, Ar), 8.09–8.14 (2H, m,
Ar); 13C NMR (100MHz, CDCl3) d: 9.5, 15.6, 20.9,
21.0, 23.5, 24.2, 27.0, 33.8, 34.4, 35.6, 38.7, 42.7, 46.3,
58.7, 66.5, 67.7, 72.3, 75.0, 76.3, 76.4, 79.1, 80.7, 84.6,
128.2, 128.4, 128.6, 128.7, 129.4, 130.1, 131.5, 133.7,
135.8, 146.9, 167.1, 171.4, 172.7, 173.7, 204.3; HRF-
ABMS m/z 763.3360 [M+H+]; calcd for C42H51O13,
763.3330.
4.3.4. 4-Deacetyl-4-(7-benzyloxylcarbonylheptanoyl)-10-
deacetylbaccatin III (11e). Colorless gum; 1H NMR
(400MHz, CDCl3) d: 1.08 (6H, s), 1.36–1.50 (4H, over-
lapped), 1.65–1.78 (7H, overlapped), 1.79–1.85 (1H, m),
1.91 (1H, s), 2.05 (3H, s), 2.17–2.32 (2H, overlapped),
2.41 (2H, t, J = 7.3Hz), 2.49–2.71 (4H, overlapped),
2.88 (1H, m), 3.98 (1H, d, J = 7.1Hz), 4.18 (1H, d,
J = 8.3Hz), 4.26–4.38 (3H, overlapped), 4.82 (1H, m),
4.94 (1H, dd, J = 9.4, 1.5Hz), 5.13 (2H, s), 5.27 (1H,
s), 5.62(1H, d, J = 7.1Hz), 7.30–7.41 (5H, m, Ar, over-
lapped), 7.45–7.51 (2H, m, Ar), 7.57–7.63 (1H, m, Ar),
8.09–8.14 (2H, m, Ar); 13C NMR (100MHz, CDCl3)
d: 9.8, 15.0, 19.9, 23.9, 24.5, 26.7, 28.5, 28.6, 34.1,
34.9, 36.8, 38.9, 42.6, 47.0, 57.7, 66.3, 67.5, 72.0, 74.9,
75.0, 76.6, 78.9, 80.6, 84.5, 128.2, 128.3, 128.6, 129.5,
130.1, 133.6, 134.4, 135.9, 143.0, 167.0, 173.2, 174.1,
4.4.3. 4-Deacetyl-4-(6-benzyloxylcarbonylhexanoyl)bacc-
atin III (12d). Colorless gum; 1H NMR (400MHz,
CDCl3) d: 1.10 (3H, s), 1.11 (3H, s), 1.38–1.52(H2 ,
m), 1.68 (3H, s), 1.69–1.81 (4H, overlapped), 1.82–1.90
(1H, m), 1.93 (1H, s), 2.03 (3H, d, J = 1.0Hz), 2.20–
2.35 (5H, overlapped), 2.43 (2H, t, J = 7.5Hz), 2.50–
2.61 (2H, overlapped), 2.63–2.74 (2H, overlapped),
3.00 (1H, d, J = 5.0Hz), 3.87 (1H, d, J = 7.1Hz), 4.17
(1H, d, J = 8.4Hz), 4.30 (1H, d, J = 8.4Hz), 4.50 (1H,

C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
6153
m), 4.83 (1H, m), 4.95 (1H, dd, J = 9.5, 1.6Hz), 5.14
(2H, s), 5.63 (1H, d, J = 7.1Hz), 6.33 (1H, s), 7.32–
7.42(5H, m, Ar, overlapped), 7.45–7.51 (2H, m, Ar),
7.57–7.63 (1H, m, Ar), 8.08–8.14 (2H, m, Ar); 13C
NMR (100MHz, CDCl3): 9.5, 15.5, 20.9, 21.1, 23.6,
24.5, 26.9, 28.2, 34.0, 34.5, 35.6, 38.9, 42.7, 46.2, 58.6,
66.3, 67.6, 72.3, 75.1, 76.3, 76.4, 79.1, 80.6, 84.6, 128.2,
128.3, 128.6, 129.4, 130.1, 131.4, 133.6, 135.9, 147.0,
167.0, 171.4, 173.0, 173.9, 204.3; HRFABMS m/z
777.3447 [M+H+]; calcd for C43H53O13, 777.3486.
4.5.2. 4-Deacetyl-4-(5-benzyloxylcarbonylpentanoyl)-7-
TES-baccatin III (3c). Colorless gum; 1H NMR
(400MHz, CDCl3) d: 0.56–0.66 (6H, m), 0.95 (9H,
t, J = 7.8Hz), 1.06 (3H, s), 1.21 (3H, s), 1.70 (3H,
s), 1.72(1H, s), 1.74–1.93 (6H, overlapped), 2.17 (3H,
d, J = 1.1Hz), 2.20 (3H, s), 2.21–2.34 (2H, over-
lapped), 2.42–2.73 (6H, overlapped), 3.88 (1H, d,
J = 7.0Hz), 4.16 (1H, d, J = 8.4Hz), 4.31 (1H, d,
J = 8.4Hz), 4.52(1H, dd, J = 10.4, 6.7Hz), 4.80 (1H,
m), 4.94 (1H, dd, J = 9.5, 1.6Hz), 5.16 (2H, s), 5.65
(1H, d, J = 7.0Hz), 6.48 (1H, s), 7.32–7.48 (5H, m, Ar,
overlapped), 7.46–7.52(2H, m, Ar), 7.57–7.64 (1H, m,
Ar), 8.10–8.16 (2H, m, Ar); 13C NMR (100MHz,
CDCl3) d: 5.3, 6.7, 10.0, 14.9, 20.2, 21.0, 23.6,
24.3, 26.8, 33.8, 34.7, 37.2, 38.4, 42.8, 47.4, 58.7,
66.4, 67.7, 72.3, 74.8, 75.8, 76.5, 78.8, 80.7, 84.3,
128.2, 128.3, 128.5, 128.6, 129.5, 130.1, 132.4, 133.6,
135.8, 144.4, 167.1, 169.4, 172.5, 173.6, 202.3; HRF-
ABMS m/z 877.4147 [M+H+]; calcd for C48H65O13Si,
877.4194.
4.4.4.
4-Deacetyl-4-(7-benzyloxylcarbonylheptanoyl)-
1
baccatin III (12e). Colorless gum; H NMR (400MHz,
CDCl3) d: 1.07 (3H, s), 1.09 (3H, s), 1.33–1.45 (4H,
overlapped), 1.62–1.75 (7H, overlapped), 1.78–1.88
(2H, overlapped), 2.01 (3H, s), 2.16–2.33 (5H,
overlapped), 2.35–2.41 (2H, m), 2.45–2.68 (4H, over-
lapped), 2.88 (1H, m), 2.96 (1H, br s), 3.84 (1H, d,
J = 7.0Hz), 4.13 (1H, d, J = 8.3Hz), 4.27 (1H,
d, J = 8.3Hz), 4.48 (1H, m), 4.82(1H, m), 4.92(1H,
dd, J = 9.5, 1.6Hz), 5.10 (2H, s), 5.60 (1H, d,
J = 7.0Hz), 6.30 (1H, s), 7.27–7.37 (5H, m, Ar, over-
lapped), 7.41–7.48 (2H, m, Ar), 7.54–7.60 (1H, m, Ar),
8.05–8.11 (2H, m, Ar); 13C NMR (100MHz, CDCl3)
d: 9.7, 15.7, 21.1, 21.3, 23.9, 24.7, 27.1, 28.6, 28.7,
34.3, 34.9, 35.8, 39.1, 42.9, 46.4, 58.8, 66.5, 67.8, 72.5,
75.3, 76.5, 76.6, 79.3, 80.8, 84.9, 128.4, 128.5, 128.8,
129.6, 130.3, 131.5, 133.8, 136.1, 147.3, 167.2, 171.6,
173.3, 174.3, 204.5; HRFABMS m/z 791.3688 [M+H+];
calcd for C44H55O13, 791.3643.
4.5.3. 4-Deacetyl-4-(6-benzyloxylcarbonylhexanoyl)-7-
TES-baccatin III (3d). Colorless gum; 1H NMR
(400MHz, CDCl3) d: 0.53–0.68 (6H, m), 0.95 (9H, t,
J = 7.7Hz), 1.05 (3H, s), 1.20 (3H, s), 1.39–1.55 (2H,
m), 1.70 (3H, s), 1.71–1.93 (6H, overlapped), 2.18 (3H,
s), 2.19 (3H, s), 2.20–2.34 (2H, overlapped), 2.44 (2H,
t, J = 7.2Hz), 2.50–2.70 (3H, overlapped), 2.73 (1H, d,
J = 5.0Hz), 3.88 (1H, d, J = 7.0Hz), 4.16 (1H, d,
J = 8.3Hz), 4.30 (1H, d, J = 8.3Hz), 4.52(1H, dd, J =
10.3, 6.7Hz), 4.79 (1H, m), 4.93 (1H, d, J = 9.2Hz),
5.14 (2H, s), 5.64 (1H, d, J = 7.0Hz), 6.48 (1H, s),
7.31–7.42(5H, m, Ar, overlapped), 7.44–7.51 (2H, m,
Ar), 7.56–7.63 (1H, m, Ar), 8.10–8.16 (2H, m, Ar); 13C
NMR (100MHz, CDCl3) d: 5.3, 6.8, 10.0, 14.9, 20.2,
21.0, 23.8, 24.5, 26.8, 28.4, 34.0, 34.9, 37.3, 38.5, 42.8,
47.3, 58.6, 66.3, 67.7, 72.3, 74.9, 75.9, 76.6, 78.8, 80.7,
84.4, 128.2, 128.3, 128.5, 128.6, 129.5, 130.1, 132.3,
133.6, 135.9, 144.5, 167.0, 169.4, 172.8, 173.8, 202.4;
HRFABMS m/z 891.4338 [M+H+]; calcd for
C49H67O13Si, 891.4351.
4.5. General procedure for selective silylation of baccatin
III derivatives at C-7
To
a solution of 4-deacetyl-4-(5-hexenoyl)baccatin
III12b (230mg, 0.36mmol) in anhydrous DMF (2mL)
was added imidazole (144mg, 2.2mmol) and TESCl
(180lL, 1.1mmol). The reaction mixture was stirring
for 10min, and then diluted with EtOAc (50mL). The
organic phase was washed with water, brine, and
dried with sodium sulfate. After concentrated in
vacuum, the residue was applied to PTLC (30%
EtOAc/hexane) to give 3b as colorless gum (241mg,
89%). Compounds 3a19 and 3c–e were prepared in
similar procedures.
4.5.4.
4-Deacetyl-4-(7-benzyloxylcarbonylheptanoyl)-
7-TES-baccatin III (3e). Colorless gum; 1H NMR
(400MHz, CDCl3) d: 0.56–0.66 (6H, m), 0.95 (9H, t,
J = 7.8Hz), 1.06 (3H, s), 1.21 (3H, s), 1.38–1.50 (4H,
overlapped), 1.67–1.82(8H, overlapped), 1.84–1.93
(2H, overlapped), 2.20 (6H, s), 2.21–2.36 (2H, over-
lapped), 2.42 (2H, t, J = 7.3Hz), 2.51–2.71 (4H, over-
lapped), 3.89 (1H, d, J = 7.0Hz), 4.16 (1H, d,
J = 8.3Hz), 4.31 (1H, d, J = 8.3Hz), 4.53 (1H, dd,
J = 10.4, 6.8Hz), 4.82(1H, m), 4.94 (1H, dd, J = 9.6,
1.3Hz), 5.14 (2H, s), 5.65 (1H, d, J = 7.0Hz), 6.49
(1H, s), 7.31–7.42(5H, m, Ar, overlapped), 7.45–7.51
(2H, m, Ar), 7.58–7.64 (1H, m, Ar), 8.11–8.17 (2H, m,
Ar); 13C NMR (100MHz, CDCl3) d: 5.3, 6.8, 10.0,
14.9, 20.2, 21.0, 24.0, 24.5, 26.8, 28.5, 34.1, 35.2, 37.3,
38.5, 42.8, 47.3, 58.7, 66.3, 67.7, 72.3, 74.9, 75.9, 76.6,
78.8, 80.6, 84.4, 128.2, 128.3, 128.5, 128.6, 129.5,
130.1, 132.4, 133.6, 135.9, 144.5, 167.1, 169.4, 173.0,
173.9, 202.4; HRFABMS m/z 905.4471 [M+H+]; calcd
for C50H69O13Si, 905.4507.
4.5.1. 4-Deacetyl-4-(5-hexenoyl)-7-TES-baccatin III (3b).
Colorless gum; 1H NMR (400MHz, CDCl3) d: 0.52(6H,
m), 0.93 (9H, t, J = 7.9Hz), 1.03 (3H, s), 1.19 (3H, s),
1.68 (3H, s), 1.74 (1H, s), 1.82–1.91 (3H, overlapped),
2.15–2.33 (8H, overlapped), 2.50–2.62 (3H, overlapped),
3.88 (1H, d, J = 7.0Hz), 4.15 (1H, d, J = 8.3Hz), 4.30
(1H, d, J = 8.3Hz), 4.50 (1H, dd, J = 10.5, 6.7Hz),
4.77–4.85 (1H, m), 4.92(1H, dd, J = 9.4, 1.4Hz), 5.04–
5.14 (2H, overlapped), 5.63 (1H, d, J = 7.0Hz), 5.80–
5.92(1H, m), 6.46 (1H, s), 7.44–7.50 (H2 , m, Ar),
7.58–7.64 (1H, m, Ar), 8.09–8.14 (2H, m, Ar); 13C
NMR (100MHz, CDCl3) d: 5.4, 6.8, 10.0, 15.0, 20.2,
21.1, 23.9, 26.9, 33.3, 34.9, 37.4, 38.5, 42.9, 47.4, 58.8,
68.0, 72.4, 74.9, 75.9, 76.7, 78.8, 80.8, 84.5, 115.7,
128.7, 129.5, 130.2, 132.6, 133.7, 137.8, 144.3, 167.1,
169.5, 173.0, 202.5; HRFABMS m/z 755.3873 [M+H+];
calcd for C41H59O11Si, 755.3827.

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C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
4.6. Preparation of racemic b-lactam (15)
165.9; HRFABMS m/z 376.1539 [M+H+]; calcd for
C23H22NO4, 376.1549.
To a solution of m-benzyloxylbenzaldehyde (13) (21.2g,
0.10mol) in anhydrous DCM (250mL) was added p-
anisidine (14.8g, 0.12mol) and anhydrous MgSO4
(12.0g, 0.1mol). After stirring at room temperature for
overnight, the resulting imine 14 solution was filtrated
and used directly. The filtrate was cooled to ꢀ78ꢂC,
and then triethylamine (40.47g, 0.4mol) and acetyloxy-
acetyl chloride (17.75g, 0.13mol) were added. The reac-
tion mixture was then allowed to warm up slowly to
room temperature. After stirring for overnight, the reac-
tion mixture was concentrated under vacuum. The resi-
due was purified by column chromatography (30%
EtOAc/hexane) to give 15 as slightly yellow solid
(25.1g, 60%).
4.8. Preparation of (+)-O-TIPS-b-lactam 17
To a solution of (+)-b-lactam 16 (900mg, 2.4mmol) in
DMF (5mL) was added imidazole (653mg, 9.6mmol)
and TIPSCl (924mg, 4.8mmol). The reaction mixture
was allowed to stir for 3h, and then quenched with
water. The resulting mixture was added EtOAc
(150mL). The combined organic phase was washed with
water, brine, dried with anhydrous sodium sulfate, and
concentrated under vacuum. The residue was purified
by column chromatography (30% EtOAc/hexane) to
give (+)-O-TIPS-b-lactam 17 as white solid (1.21g,
95%).
4.6.1. Cis-2-(3-(benzyloxy)phenyl)-1-(4-methoxyphenyl)-
4-oxoazetidin-3-yl acetate (15). 1H NMR (400MHz,
CDCl3) d: 1.69 (3H, s), 3.76 (3H, s), 5.02(2H, ABq,
J = 12.0Hz), 5.29 (1H, d, J = 4.8Hz), 5.94 (1H, d,
J = 4.8Hz), 6.78–6.83 (2H, m, Ar), 6.87–6.97 (3H, m,
Ar, overlapped), 7.23–7.41 (8H, m, Ar, overlapped);
13C NMR (100MHz, CDCl3): 20.1, 55.6, 61.6, 70.2,
76.5, 114.4, 114.6, 115.6, 119.0, 120.8, 127.7, 128.2,
128.8, 129.9, 130.5, 134.2, 136.8, 156.8, 159.0, 161.5,
169.5; HRFABMS m/z 418.1644 [M+H+]; calcd for
C25H24NO5, 418.1654.
4.8.1.
(3R,4S)-4-(3-(Benzyloxy)phenyl)-1-(4-methoxy-
1
phenyl)-3-TIPS-azetidin-2-one (17). H NMR (400MHz,
CDCl3) d: 0.98–1.14 (21H, overlapped), 3.78 (3H, s),
5.00–5.08 (3H, overlapped), 5.09 (1H, d, J = 4.9Hz),
6.78–6.84 (2H, m, Ar, overlapped), 6.95–7.06 (3H, m,
Ar, overlapped), 7.27–7.45 (8H, m, Ar, overlapped);
13C NMR (100MHz, CDCl3) d: 11.8, 17.6, 17.7, 56.3,
63.2, 70.0, 77.9, 114.3, 114.8, 114.9, 118.7,121.1, 127.5,
127.9, 128.6, 129.3, 131.0, 135.9, 137.0, 156.2, 165.6;
HRFABMS m/z 532.2887 [M+H+]; calcd for
C32H42NO4Si, 532.2883.
4.6.2. Resolution of b-lactam 15. To a solution of racemic
b-lactam (15) (1.0g, 2.4mmol) in CH3CN (5mL) and
phosphate buffer (45mL) was added Lipase PS 30
(1.0g). The reaction mixture was allowed to stir for
7days, and then extracted with EtOAc (3 · 100mL).
The combined organic phase was washed with brine,
dried with anhydrous sodium sulfate, and concentrated
under vacuum. The residue was purified by column
chromatography (30–50% EtOAc/hexane) to give (+)-
lactam acetate 15 (476mg, 48%) and deacetylated (ꢀ)-
lactam 16 (465mg, 47%) both as white solids.
4.9. Preparation of (+)-b-lactam 18
To a solution of (+)-b-lactam 17 (1.21g, 2.3mmol) in
CH3CN (50mL) was added CAN reagent (3.53g in
30mL H2O) at 0ꢂC dropwise in 15min. The reaction
mixture was allowed to stir for another 30min, and
then extracted with EtOAc (3 · 50mL). The combined
organic phase was washed with saturated Na2S2O4,
water, brine, dried with anhydrous sodium sulfate, and
concentrated under vacuum. The residue was purified
by column chromatography (30% EtOAc/hexane) to
give (+)-b-lactam 18 as a yellowish solid (922mg, 96%).
4.7. Preparation of (+)-b-lactam 16
4.9.1. (3R,4S)-4-(3-(Benzyloxy)phenyl)-3-TIPS-azetidin-
2-one (18). H NMR (400MHz, CDCl3) d: 0.89–1.05
1
To a solution of (+)-lactam acetate 15 (1.05g, 2.5mmol)
in THF (100mL) was added 1M KOH (100mL) at 0ꢂC.
The reaction mixture was allowed to stir for 45min, and
then extracted with EtOAc (3 · 100mL). The combined
organic phase was washed with saturated NH4Cl, water,
brine, dried with anhydrous sodium sulfate, and concen-
trated under vacuum. The residue was purified by col-
umn chromatography (50% EtOAc/hexane) to give
(+)-b-lactam 16 as white solid (900mg, 92%).
(21H, overlapped), 4.80 (1H, d, J = 4.7Hz), 5.08 (2H,
ABq, J = 12.4Hz), 5.18 (1H, dd, J = 4.7, 2.7Hz), 6.37
(1H, br s), 6.91–6.98 (2H, m, Ar), 7.00–7.03 (1H, m,
Ar), 7.24–7.30 (2H, m, Ar), 7.32–7.48 (4H, m, Ar, over-
lapped); 13C NMR (100MHz, CDCl3) d: 11.6, 17.5,
17.6, 59.5, 70.0, 80.0, 114.6, 114.8, 120.9, 127.4, 127.9,
128.6, 129.0, 137.0, 138.0, 158.7, 169.9; HRFABMS
m/z 426.2467 [M+H+]; calcd for C25H36NO3Si, 426.2464.
4.7.1. (3R,4S)-4-(3-(Benzyloxy)phenyl)-3-hydroxy-1-(4-
methoxyphenyl)azetidin-2-one
4.10. Preparation of (+)-b-lactam 6
(16).
1H
NMR
(400MHz, (CD3)2CO) d: 3.74 (3H, s), 5.03 (1H, d,
J = 7.7Hz), 5.09 (2H, ABq, J = 11.8Hz), 5.26 (1H, dd,
J = 7.7, 5.2Hz), 5.30 (1H, d, J = 5.2Hz), 6.83–6.88
(2H, m, Ar), 6.95–7.00 (2H, m, Ar), 7.03–7.05 (1H, m,
Ar), 7.27–7.39 (6H, m, Ar, overlapped), 7.42–7.47 (2H,
m, Ar); 13C NMR (100MHz, (CD3)2CO) d: 54.9, 62.5,
69.7, 78.1, 114.2, 114.4, 114.9, 118.5, 120.7, 127.8,
127.9, 128.6, 129.6, 131.6, 137.0, 137.6, 156.4, 159.2,
To a solution of (+)-b-lactam 18 (922mg, 2.2mmol) in
anhydrous DCM (5mL) was added TEA (658mg,
6.5mmol), benzoyl chloride (365mg, 2.6mmol) and
DAMP (50mg, cat.). The reaction mixture was allowed
to stir for 2h, and then diluted with EtOAc (150mL).
The combined organic phase was washed with saturated
NaHCO3, water, brine, dried with anhydrous sodium
sulfate, and concentrated under vacuum. The residue

C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
6155
was purified by column chromatography (20% EtOAc/
hexane) to give (+)-b-lactam 6 as a white solid
(900mg, 90%).
(6H, m), 0.93–1.03 (30H, overlapped), 1.20 (3H, s),
1.25 (3H, s), 1.74 (3H, s), 1.77 (1H, s), 1.84–2.04 (3H,
overlapped), 2.08 (3H, d, J = 1.0Hz), 2.10–2.22 (6H,
overlapped), 2.38–2.47 (1H, m), 2.52–2.69 (2H, over-
lapped), 2.95–3.04 (1H, m), 3.87 (1H, d, J = 7.0Hz),
4.25 (1H, d, J = 8.3Hz), 4.34 (1H, d, J = 8.3Hz), 4.53
(1H, dd, J = 10.6, 6.6Hz), 4.90–4.96 (2H, overlapped),
4.99–5.05 (2H, overlapped), 5.10 (2H, s), 5.67–5.83
(3H, overlapped), 6.21 (1H, t, J = 9.1Hz), 6.50 (1H, s),
6.90–7.12(4H, overlapped), 7.30–7.65 (1H2 , m, Ar,
overlapped), 7.73–7.79 (2H, m, Ar), 8.16–8.21 (2H, m,
Ar); 13C NMR (100MHz, CDCl3) d: 5.3, 6.8, 10.1,
12.6, 14.3, 17.8, 17.9, 20.9, 21.6, 25.0, 26.6, 32.8, 35.4,
35.8, 37.3, 43.4, 46.8, 55.9, 58.4, 70.1, 71.9, 72.2, 74.9,
75.0, 75.5, 76.6, 78.9, 81.1, 84.5, 113.1, 114.5, 115.8,
118.9, 127.0, 127.4, 128.0, 128.5, 128.6, 128.7, 129.3,
129.7, 130.3, 131.7, 133.5, 133.6, 134.0, 136.8, 137.1,
140.1, 140.3, 159.3, 166.8, 167.0, 169.3, 171.9, 172.5,
201.8; HRFABMS m/z 1306.6212 [M+Na+]; calcd for
C73H97NO15Si2Na, 1306.6294.
4.10.1.
(3R,4S)-1-Benzoyl-4-(3-(benzyloxy)phenyl)-3-
TIPS-azetidin-2-one (6). 1H NMR (400MHz, CDCl3)
d: 0.96–1.10 (21H, overlapped), 5.10 (2H, ABq,
J = 11.9Hz), 5.28 (1H, d, J = 6.1Hz), 5.45 (1H, d,
J = 6.1Hz), 6.95–7.00 (1H, m, Ar), 7.04–7.10 (2H, m,
Ar), 7.28–7.70 (9H, m, Ar, overlapped), 8.07–8.12 (2H,
m, Ar); 13C NMR (100MHz, CDCl3) d: 11.7, 17.5,
17.6, 61.1, 70.1, 76.7, 114.7, 114.9, 121.0, 127.4, 128.0,
128.2, 128.6, 129.3, 129.9, 132.1, 133.4, 135.5, 137.1,
158.8, 165.4, 166.3; HRFABMS m/z 529.2638 [M+H+];
calcd for C32H39NO4Si, 529.2648.
4.11. General procedure for coupling of baccatin and the
b-lactam
To a solution of 4-deacetyl-4-(4-pentenoyl)-7-TES-bacc-
atin III 3a (55mg, 0.074mmol) in dried THF (3.6mL) at
0ꢂC was added NaH (40mg, 1.67mmol) and the solu-
tion was stirred for 5min. (+)-b-Lactam 6 (75mg,
0.15mmol in 0.8mL THF) was then added and the reac-
tion was allowed to stir at room temperature for 24h.
The reaction mixture was quenched with saturated
NH4Cl and diluted with EtOAc (30mL), and then
washed with water, brine, and dried with sodium sulfate.
The organic phase was concentrated in vacuo, and the
residue was applied to PTLC (20% EtOAc/hexane) to
give paclitaxel derivative 19 (50mg, 57%). Compounds
20, 25, 26, and 27 were prepared by similar procedures,
except that the last three used LHMDS (1.2equiv) as
base and the reaction only ran for 3–4h.
4.11.3. 4-Deacetyl-4-(5-benzyloxycarbonylpentanoyl)-30-
desphenyl-30-(m-benzyloxyphenyl)-7-TES-20-TIPS-paclit-
axel (25). Colorless gum; H NMR (400MHz, CDCl3)
1
d: 0.52–0.67 (6H, m), 0.90–1.01 (30H, overlapped),
1.18 (3H, s), 1.22 (3H, s), 1.60–1.74 (5H, overlapped),
1.75–1.95 (4H, overlapped), 2.05 (3H, d, J = 1.1Hz),
2.09–2.20 (4H, overlapped), 2.48–2.64 (2H, over-
lapped), 2.95–3.04 (1H, m), 3.83 (1H, d, J = 7.2 Hz),
4.21 (1H, d, J = 8.4Hz), 4.29 (1H, d, J = 8.4Hz), 4.49
(1H, dd, J = 10.5, 6.5Hz), 4.87 (1H, dd, J = 9.5,
1.6Hz), 4.91 (1H, d, J = 1.6Hz), 5.05 (2H, s), 5.06
(2H, s), 5.65–5.72 (2H, overlapped), 6.20 (1H, t,
J = 9.3Hz), 6.46 (1H, s), 6.87 (1H, dd, J = 8.2 ,
2.4Hz), 6.94–7.01 (2H, overlapped), 7.06 (1H, d,
J = 8.9Hz), 7.26–7.42 (13H, m, Ar, overlapped), 7.44–
7.59 (4H, overlapped), 7.70–7.75 (2H, m, Ar), 8.13–
8.18 (2H, m, Ar); 13C NMR (100MHz, CDCl3) d: 5.5,
7.0, 10.4, 12.8, 14.4, 18.0, 18.1, 21.1, 21.9, 24.4, 25.5,
26.8, 33.8, 36.0, 36.1, 37.5, 43.6, 47.0, 56.1, 58.6, 66.4,
70.3, 71.9, 72.5, 75.1, 75.2, 75.7, 76.7, 79.1, 81.4, 84.7,
113.3, 114.6, 119.0, 127.2, 127.6, 128.3, 128.4, 128.5,
128.7, 128.8, 128.9, 129.5, 130.1, 130.5, 132.0, 133.7,
133.8, 134.2, 136.1, 137.0, 140.2, 140.4, 159.5, 167.1,
167.2, 169.6, 172.0, 172.6, 172.9, 202.0; HRFABMS
m/z 1428.6735 [M+Na+]; calcd for C80 H103NO17Si2Na,
1428.6662.
4.11.1.
4-Deacetyl-4-(4-pentenoyl)-30-desphenyl-30-(m-
benzyloxyphenyl)-7-TES-20-TIPS-paclitaxel (19). Color-
less gum; 1H NMR (400MHz, CDCl3) d: 0.57–0.70
(6H, m), 0.94–1.07 (30H, overlapped), 1.21 (3H, s),
1.26 (3H, s), 1.73 (3H, s), 1.87–1.97 (1H, m), 2.07 (3H,
d, J = 1.3Hz), 2.11–2.25 (2H, overlapped), 2.20 (3H,
s), 2.38–2.75 (5H, overlapped), 3.03–3.12 (1H, m), 3.87
(1H, d, J = 7.0Hz), 4.24 (1H, d, J = 8.4Hz), 4.34 (1H,
d, J = 8.4Hz), 4.51 (1H, dd, J = 10.6, 6.7Hz), 4.89–
4.94 (2H, overlapped), 5.03–5.07 (1H, m), 5.10 (2H, s),
5.11–5.17 (1H, m), 5.69 (1H, d, J = 8.9Hz), 5.73 (1H,
d, J = 7.0Hz), 5.81–5.92(1H, m), 6.20 (1H, dt, J = 9.1,
1.3Hz), 6.47 (1H, s), 6.90–7.03 (3H, m, Ar, overlapped),
7.11 (1H, d, J = 8.9Hz), 7.30–7.65 (12H, m, Ar, over-
lapped), 7.74–7.78 (2H, m, Ar), 8.17–8.21 (2H, m, Ar);
13C NMR (100MHz, CDCl3) d: 5.5, 6.9, 10.3, 12.7,
14.4, 18.0, 18.1, 21.0, 21.7, 26.7, 29.9, 35.7, 36.0, 37.4,
43.5, 46.9, 56.1, 58.6, 70.2, 72.1, 72.4, 75.1, 75.2, 75.7,
76.7, 79.0, 81.4, 84.6, 113.3, 114.6, 117.0, 119.1, 127.1,
127.5, 128.2, 128.8, 128.9, 129.0, 129.5, 129.9, 130.4,
131.9, 133.7, 133.8, 134.1, 135.9, 137.0, 140.2, 140.4,
159.4, 167.1, 169.5, 172.0, 172.1, 201.9; HRFABMS
m/z 1292.6179 [M+Na+]; calcd for C72H95NO15Si2Na,
1292.6138.
4.11.4. 4-Deacetyl-4-(6-benzyloxylcarbonylhexanoyl)-30-
desphenyl-30-(m-benzyloxyphenyl)-7-TES-20-TIPS-paclit-
axel (26). Colorless gum; H NMR (400MHz, CDCl3)
1
d: 0.57–0.71 (6H, m), 0.96–1.06 (30H, overlapped),
1.22 (3H, s), 1.27 (3H, s), 1.30–1.44 (2H, m), 1.57–1.71
(2H, m), 1.76 (3H, s), 1.77–2.00 (4H, overlapped), 2.10
(3H, d, J = 1.1Hz), 2.15–2.24 (4H, overlapped), 2.27
(2H, t, J = 7.6Hz), 2.39–2.48 (1H, m), 2.53–2.68 (2H,
overlapped), 2.98–3.07 (1H, m), 3.89 (1H, d,
J = 7.1Hz), 4.27 (1H, d, J = 8.4Hz), 4.34 (1H, d,
J = 8.4Hz), 4.55 (1H, dd, J = 10.4, 6.6Hz), 4.91 (1H,
dd, J = 9.5, 1.6Hz), 4.97 (1H, d, J = 1.6Hz), 5.10 (2H,
s), 5.12 (2H, s), 5.72–5.77 (2H, overlapped), 6.25 (1H,
4.11.2.
4-Deacetyl-4-(5-hexenoyl)-30-desphenyl-30-(m-
benzyloxyphenyl)-7-TES-20-TIPS-paclitaxel (20). Color-
less gum; 1H NMR (400MHz, CDCl3) d: 0.51–0.72
t, J = 9.1Hz), 6.52(1H, s), 6.92(1H, dd, J = 8.3,
2.4Hz), 7.00–7.07 (2H, overlapped), 7.11 (1H, d,

6156
C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
J = 8.9Hz), 7.30–7.46 (13H, m, Ar, overlapped), 7.49–
7.63 (4H, overlapped), 7.75–7.80 (2H, m, Ar), 8.17–
8.23 (2H, m, Ar); 13C NMR (100MHz, CDCl3) d: 5.4,
6.8, 10.2, 12.6, 14.2, 17.8, 17.9, 20.9, 21.7, 24.5, 25.5,
26.6, 28.6, 33.9, 35.9, 36.1, 37.3, 43.4, 46.8, 55.9, 58.5,
66.1, 70.1, 71.8, 72.3, 75.0, 75.5, 76.6, 78.9, 81.1, 84.5,
113.1, 114.5, 118.9, 127.0, 127.4, 128.0, 128.1, 128.2,
128.5, 128.6, 128.7, 129.4, 129.8, 130.3, 131.8, 133.6,
134.0, 136.1, 136.9, 140.1, 140.2, 159.3, 166.8, 167.0,
169.3, 171.8, 172.6, 173.1, 201.7; HRFABMS m/z
m), 2.48–2.58 (1H, m), 2.82–2.96 (3H, overlapped),
3.09–3.18 (1H, m), 3.85 (1H, d, J = 7.1Hz), 4.21 (1H,
d, J = 8.4Hz), 4.30 (1H, d, J = 8.4Hz), 4.50 (1H, dd,
J = 10.6, 6.6Hz), 4.91 (1H, d, J = 1.9Hz), 4.97 (1H,
dd, J = 9.5, 1.7Hz), 5.07 (2H, s), 5.69 (1H, d,
J = 8.8Hz), 5.73 (1H, d, J = 7.1Hz), 6.23 (1H, t,
J = 9.1Hz), 6.47 (1H, s), 6.89–7.01 (3H, m, Ar, over-
lapped), 7.14 (1H, d, J = 8.9Hz), 7.29–7.61 (12H, m,
Ar, overlapped), 7.73–7.77 (2H, m, Ar), 8.11–8.16 (2H,
m, Ar); 13C NMR (100MHz, CDCl3): 5.3, 6.8, 10.2,
12.5, 14.1, 17.8, 17.9, 20.9, 21.8, 26.6, 29.0, 30.9, 35.9,
37.2, 43.4, 46.7, 56.0, 58.5, 70.1, 71.9, 72.2, 74.9, 75.0,
75.5, 76.5, 78.9, 81.7, 84.1, 113.4, 114.3, 118.7, 120.1,
127.0, 127.4, 128.1, 128.6, 128.8, 129.2, 129.9, 130.2,
131.9, 133.6, 133.7, 136.7, 139.9, 140.2, 155.1, 159.2,
167.0, 167.2, 169.3, 171.0, 171.7, 174.5, 201.7; HRF-
ABMS m/z 1310.5851 [M+Na+]; calcd for C71H93NO17-
Si2Na, 1310.5880.
+
1419.6912[M ]; calcd for C81H105NO17Si2, 1419.6921.
4.11.5. 4-Deacetyl-4-(7-benzyloxylcarbonylheptanoyl)-30-
desphenyl-30-(m-benzyloxyphenyl)-7-TES-20-TIPS-paclit-
axel (27). Colorless gum; H NMR (400MHz, CDCl3)
1
d: 0.56–0.71 (6H, m), 0.95–1.05 (30H, overlapped),
1.21 (3H, s), 1.26 (3H, s), 1.28–1.38 (4H, overlapped),
1.52–1.62 (2H, m), 1.75 (3H, s), 1.76–2.00 (4H, over-
lapped), 2.09 (3H, d, J = 1.1Hz), 2.14–2.24 (4H, over-
lapped), 2.29 (2H, t, J = 7.6Hz), 2.39–2.48 (1H, m),
2.53–2.65 (2H, overlapped), 2.96–3.06 (1H, m), 3.88
(1H, d, J = 7.2Hz), 4.26 (1H, d, J = 8.4Hz), 4.33 (1H,
d, J = 8.4Hz), 4.54 (1H, dd, J = 10.5, 6.7Hz), 4.91
(1H, dd, J = 9.5, 1.6Hz), 4.96 (1H, d, J = 1.6Hz), 5.09
(2H, s), 5.13 (2H, s), 5.70–5.76 (2H, overlapped), 6.24
(1H, t, J = 9.1Hz), 6.51 (1H, s), 6.91 (1H, dd, J = 8.3,
2.4Hz), 6.99–7.06 (2H, overlapped), 7.10 (1H, d,
J = 8.9Hz), 7.31–7.48 (13H, m, Ar, overlapped), 7.49–
7.65 (4H, overlapped), 7.74–7.79 (2H, m, Ar), 8.18–
8.23 (2H, m, Ar); 13C NMR (100MHz, CDCl3) d: 5.4,
6.8, 10.2, 12.6, 14.2, 17.8, 17.9, 20.9, 21.7, 24.7, 25.8,
26.6, 28.7, 28.8, 34.1, 35.9, 36.3, 37.3, 43.4, 46.8, 55.9,
58.5, 66.1, 70.1, 71.8, 72.3, 75.0, 75.5, 76.6, 78.9, 81.1,
84.5, 113.1, 114.5, 118.9, 127.0, 127.3, 128.0, 128.1,
128.2, 128.5, 128.6, 128.7, 129.4, 129.7, 130.3, 131.7,
133.5, 133.6, 134.0, 136.1, 136.9, 140.1, 140.2, 159.3,
166.8, 167.0, 169.3, 171.8, 172.7, 173.3, 201.7; HRF-
ABMS m/z 1434.7103 [M+H+]; calcd for C81H105NO17-
Si2, 1434.7156.
4.12.2. 4-Deacetyl-4-(4-carboxybutanoyl)-30-desphenyl-
30-(m-benzyloxyphenyl)-7-TES-20-TIPS-paclitaxel (22).
1
Colorless gum; H NMR (400MHz, CD3OD) d: 0.52–
0.66 (6H, m), 0.94 (9H, t, J = 7.9Hz), 0.97–1.07 (21H,
overlapped), 1.13 (3H, s), 1.19 (3H, s), 1.68 (3H, s),
1.77–1.86 (1H, m), 1.96 (3H, br s), 2.06–2.23 (6H, over-
lapped), 2.29–2.48 (3H, overlapped), 2.51–2.61 (1H, m),
2.70–2.80 (1H, m), 2.94–3.04 (1H, m), 3.84 (1H, d,
J = 7.1Hz), 4.20 (1H, d, J = 8.3Hz), 4.23 (1H, d,
J = 8.3Hz), 4.53 (1H, dd, J = 10.4, 6.7Hz), 4.94–5.00
(2H, overlapped), 5.11 (2H, ABq, J = 12.3Hz), 5.65–
5.72(H2 , overlapped), 6.11 (1H, t,
J = 9.2Hz), 6.47
(1H, s), 6.92–6.98 (1H, m, Ar), 7.08–7.15 (2H, m, over-
lapped), 7.24–7.63 (12H, m, Ar, overlapped), 7.73–7.79
(2H, m, Ar), 8.12–8.18 (2H, m, Ar); 13C NMR
(100MHz, CD3OD) d: 6.3, 7.2, 10.7, 13.8, 15.0, 18.5,
18.6, 20.8, 22.0, 22.4, 27.0, 34.0, 36.5, 36.8, 38.3, 44.7,
48.0, 57.9, 59.7, 71.1, 73.3, 73.8, 76.1, 76.4, 77.0, 77.5,
78.9, 82.4, 85.6, 115.2, 115.8, 120.8, 128.3, 128.5,
128.9, 129.5, 129.7, 129.8, 131.1, 131.2, 131.3, 133.0,
134.5, 135.2, 135.5, 138.6, 140.8, 141.4, 160.6, 167.6,
170.1, 170.8, 173.5, 173.6, 176.3, 204.2; HRFABMS
m/z 1324.6067 [M+Na+]; calcd for C72H95NO17Si2Na,
1324.6036.
4.12. General procedure for oxidative cleavage of double
bond to carboxylic acid
To a solution of 4-deacetyl-4-(4-pentenoyl)-30-desphen-
yl-30-(m-benzyloxyphenyl)-7-TES-20-TIPS-paclitaxel 19
(44mg, 0.035mmol) in H2O/CH3CN/CCl4 (0.9mL/
0.6mL/0.6mL) was added RuCl3 (1mg, cat.) and NaIO4
(75mg, 0.35mmol). After stirring for 24h, the reaction
mixture was quenched with saturated NH4Cl. The aque-
ous phase was extracted with EtOAc (2 · 20mL). The
combined organic phase was washed with water, brine,
and dried with sodium sulfate. After concentrated in
vacuum, the residue was applied to PTLC (35%
EtOAc/hexane) to give 21 as colorless gum (25.9mg,
58%). Compound 22 was prepared by a similar
procedure.
4.13. General procedure for deprotection of benzyl group
using hydrogenolysis
To a solution of 4-deacetyl-4-(3-carboxypropanoyl)-30-
desphenyl-30-(m-benzyloxyphenyl)-7-TES-20-TIPS-paclit-
axel 21 (33mg, 0.026mmol) in EtOAc (10mL) was
added 10% Pd–C (10mg, cat.). The mixture was hydro-
genated at 30psi at room temperature for 48h. The reac-
tion mixture was filtered, and the organic phase was
concentrated in vacuum. The residue was purified by
preparative TLC (70% EtOAc/hexane) to give 23 as col-
orless gum (22.5mg, 73%). Compounds 24, 28, 29, and
30 were prepared by similar procedures.
4.12.1. 4-Deacetyl-4-(3-carboxypropanoyl)-30-desphenyl-
30-(m-benzyloxyphenyl)-7-TES-20-TIPS-paclitaxel (21).
1H NMR (400MHz, CDCl3) d: 0.55–0.65 (6H, m),
0.90–1.03 (30H, overlapped), 1.20 (3H, s), 1.24 (3H, s),
1.72(3H, s), 1.85–1.94 (1H, m), .025 (3H, d,
J = 1.2Hz), 2.09–2.22 (5H, overlapped), 2.33–2.41 (1H,
4.13.1. 4-Deacetyl-4-(3-carboxypropanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-7-TES-20-TIPS-paclitaxel
(23).
1H NMR (400MHz, CDCl3) d: 0.50–0.65 (6H, m),
0.90–0.98 (30H, overlapped), 1.16 (3H, s), 1.22 (3H, s),
1.70 (3H, s), 1.86–1.96 (1H, m), 2.02 (3H, d,

C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
6157
J = 1.0Hz), 2.07–2.20 (4H, overlapped), 2.31–2.41 (1H,
m), 2.46–2.57 (1H, m), 2.75–3.00 (3H, overlapped),
3.11–3.20 (1H, m), 3.85 (1H, d, J = 6.9Hz), 4.24 (1H,
d, J = 8.5Hz), 4.34 (1H, d, J = 8.5Hz), 4.47 (1H, dd,
J = 10.6, 6.6Hz), 4.88 (1H, dd, J = 9.5, 1.5Hz) 4.94
(1H, d, J = 1.7Hz), 5.62(1H, d, J = 9.1Hz), 5.74 (1H,
d, J = 6.9Hz), 6.14 (1H, t, J = 9.2Hz), 6.45 (1H, s),
6.69–6.86 (3H, m, Ar, overlapped), 7.08–7.19 (2H, over-
lapped), 7.32–7.39 (2H, m, Ar), 7.45–7.60 (4H, m, Ar,
overlapped), 7.65–7.71 (2H, m, Ar), 8.10–8.16 (2H, m,
Ar); 13C NMR (100MHz, CDCl3) d: 5.5, 7.0, 10.4,
12.7, 14.4, 18.0, 21.1, 21.9, 26.6, 29.9, 31.3, 35.9, 37.4,
43.6, 46.8, 56.6, 58.7, 72.3, 72.4, 75.2, 75.6, 78.8, 82.0,
84.7, 113.5, 115.4, 117.8, 127.2, 129.0, 129.1, 129.4,
130.1, 130.4, 132.3, 133.6, 133.8, 133.9, 139.2, 140.5,
157.2, 167.3, 168.1, 169.6, 171.5, 172.3, 175.5, 201.9;
HRFABMS m/z 1220.5438 [M+Na+]; calcd for
C64H87NO17Si2Na, 1220.5410.
172.2, 172.6, 202.9; HRFABMS m/z 1226.5916
[M+H+]; calcd for C66H90NO17Si2, 1226.5904.
4.13.4. 4-Deacetyl-4-(6-carboxyhexanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-7-TES-20-TIPS-paclitaxel
(29).
1
Colorless gum; H NMR (400MHz, CD3OD) d: 0.57–
0.72(6H, m), 0.99 (9H, t, J = 8.1Hz), 1.01–1.10 (21H,
overlapped), 1.18 (3H, s), 1.23 (3H, s), 1.42–1.53 (2H,
m), 1.61–1.75 (5H, overlapped), 1.80–1.98 (3H, over-
lapped), 2.03 (3H, d, J = 1.0Hz), 2.18 (3H, s), 2.21–
2.31 (3H, overlapped), 2.43–2.51 (1H, m), 2.57–2.77
(2H, overlapped), 2.94–3.03 (1H, m), 3.90 (1H, d,
J = 7.2Hz), 4.25 (2H, br s), 4.58 (1H, dd, J = 10.5,
6.7Hz), 4.96 (1H, dd, J = 9.7, 1.6Hz), 5.03 (1H, d,
J = 2.7Hz), 5.69–5.74 (2H, overlapped), 6.18 (1H, t,
J = 9.1Hz), 6.51 (1H, s), 6.82(1H, dd, J = 8.1, 2.1Hz),
6.94–6.97 (1H, m, Ar), 7.01 (1H, d, J = 7.8Hz), 7.29
(1H, t, J = 8.1Hz), 7.45–7.70 (6H, m, Ar, overlapped),
7.78–7.83 (2H, m, Ar), 8.17–8.22 (2H, m, Ar); 13C
NMR (100MHz, CD3 OD) d: 4.9, 5.8, 9.4, 12.5, 13.7,
17.1, 17.2, 19.4, 21.0, 24.4, 25.1, 25.6, 28.3, 33.2, 35.5,
35.7, 37.0, 43.4, 46.6, 56.2, 58.3, 71.9, 72.5, 74.8, 75.1,
75.5, 76.2, 77.6, 80.9, 84.4, 114.0, 114.6, 117.7, 126.8,
128.3, 128.4, 129.6, 129.9, 130.0, 131.6, 133.2, 133.9,
134.2, 139.4, 140.0, 157.8, 166.3, 168.6, 169.5, 172.2,
172.7, 175.9, 202.9; HRFABMS m/z 1262.5826
[M+Na+]; calcd for C67H93NO17Si2Na, 1262.5880.
4.13.2. 4-Deacetyl-4-(4-carboxybutanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-7-TES-20-TIPS-paclitaxel
(24).
1
Colorless gum; H NMR (400MHz, CD3OD) d: 0.53–
0.67 (6H, m), 0.91–1.06 (30H, overlapped), 1.13 (3H,
s), 1.18 (3H, s), 1.67 (3H, s), 1.78–1.87 (1H, m), 1.98
(3H, br s), 2.00–2.20 (6H, overlapped), 2.25–2.50 (3H,
overlapped), 2.52–2.63 (1H, m), 2.68–2.79 (1H, m),
2.92–3.04 (1H, m), 3.84 (1H, d, J = 7.0Hz), 4.17–4.26
(2H, overlapped), 4.54 (1H, dd, J = 10.4, 6.7Hz), 4.95–
5.01 (2H, overlapped), 5.62 (1H, d, J = 3.4Hz), 5.67
(1H, d, J = 7.0Hz), 6.08 (1H, t, J = 9.3Hz), 6.47 (1H,
s), 6.71–6.77 (1H, m, Ar), 6.93–7.00 (2H, m, Ar), 7.21–
7.27 (1H, m, Ar), 7.41–7.68 (6H, m, Ar, overlapped),
7.77–7.83 (2H, m, Ar), 8.12–8.18 (2H, m, Ar); 13C
NMR (100MHz, CD3OD) d: 5.1, 6.1, 9.6, 12.7, 13.9,
17.3, 17.4, 19.6, 21.2, 21.7, 25.8, 35.0, 35.5, 35.6, 37.2,
43.6, 46.8, 57.0, 58.5, 72.1, 72.7, 75.0, 75.3, 75.9, 76.4,
77.7, 81.1, 84.6, 114.1, 115.1, 118.1, 127.1, 128.5,
128.7, 129.8, 130.0, 130.1, 131.8, 133.4, 134.0, 134.5,
139.4, 140.3, 158.0, 165.7, 166.5, 168.9, 169.7, 172.6,
172.7, 203.2; HRFABMS m/z 1212.5789 [M+H+]; calcd
for C65H90NO17Si2, 1212.5747.
4.13.5. 4-Deacetyl-4-(7-carboxyheptanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-7-TES-20-TIPS-paclitaxel
(30).
1
Colorless gum; H NMR (400MHz, CD3OD) d: 0.57–
0.72(6H, m), 0.99 (9H, t, J = 8.1Hz), 1.02–1.10 (21H,
overlapped), 1.18 (3H, s), 1.22 (3H, s), 1.34–1.51 (4H,
overlapped), 1.52–1.65 (2H, m), 1.72 (3H, s), 1.79–1.95
(3H, overlapped), 2.03 (3H, d, J = 1.0Hz), 2.18 (3H,
s), 2.19–2.30 (3H, overlapped), 2.44–2.53 (1H, m),
2.56–2.76 (2H, overlapped), 2.94–3.04 (1H, m), 3.91
(1H, d, J = 7.2Hz), 4.25 (2H, ABq, J = 8.6Hz), 4.59
(1H, dd, J = 10.4, 6.6Hz), 4.95 (1H, dd, J = 9.5,
1.7Hz), 5.04 (1H, d, J = 2.5Hz), 5.69–5.75 (2H, over-
lapped), 6.19 (1H, t, J = 9.1Hz), 6.52(1H, s), 7.78–
6.85 (1H, m, Ar), 6.93–6.98 (1H, m, Ar), 7.00 (1H, d,
J = 7.6Hz), 7.28 (1H, t, J = 8.2Hz), 7.45–7.62 (5H, m,
Ar, overlapped), 7.65–7.71 (1H, m, Ar), 7.78–7.83 (2H,
m, Ar), 8.17–8.22 (2H, m, Ar); 13C NMR (100MHz,
CD3OD) d: 4.9, 5.8, 9.4, 12.5, 13.7, 17.1, 17.2, 19.4,
21.0, 24.4, 25.3, 25.6, 28.5, 33.4, 35.5, 35.9, 37.0, 43.4,
46.6, 56.1, 56.2, 58.4, 71.9, 72.4, 74.9, 75.1, 75.5, 76.2,
77.7, 80.9, 84.5, 114.0, 114.6, 117.7, 126.8, 128.4,
129.5, 129.9, 130.0, 131.6, 133.2, 133.9, 134.3, 139.4,
139.5, 140.0, 157.8, 166.3, 168.6, 169.5, 172.2, 172.9,
176.1, 202.9; HRFABMS m/z 1276.5984 [M+Na+];
calcd for C68H95NO17Si2Na, 1276.6037.
4.13.3. 4-Deacetyl-4-(5-carboxypentanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-7-TES-20-TIPS-paclitaxel
(27).
1
Colorless gum; H NMR (400MHz, CD3OD) d: 0.57–
0.72(6H, m), 0.99 (9H, t, J = 7.9Hz), 1.02–1.10 (21H,
overlapped), 1.17 (3H, s), 1.23 (3H, s), 1.72 (3H, s),
1.73–1.99 (5H, overlapped), 2.01 (3H, br s), 2.14–2.26
(4H, overlapped), 2.33–2.50 (3H, overlapped), 2.56–
2.66 (1H, m), 2.69–2.79 (1H, m), 2.96–3.06 (1H, m),
3.90 (1H, d, J = 7.1Hz), 4.26 (2H, ABq, J = 8.3Hz),
4.58 (1H, dd, J = 10.5, 6.8Hz), 4.98 (1H, d,
J = 9.2Hz)5.02 (1H, d, J = 3.0Hz), 5.68–5.76 (2H, over-
lapped), 6.17 (1H, t, J = 9.1Hz), 6.51 (1H, s), 6.80 (1H,
dd, J = 8.1, 2.3Hz), 6.94–6.97 (1H, m, Ar), 7.00 (1H, d,
J = 7.8Hz), 7.30 (1H, t, J = 8.1Hz), 7.45–7.73 (6H, m,
Ar, overlapped), 7.79–7.84 (2H, m, Ar), 8.17–8.23 (2H,
m, Ar); 13C NMR (100MHz, CD3OD) d: 4.9, 5.8, 9.4,
12.5, 13.7, 17.1, 17.2, 19.4, 21.0, 24.1, 24.9, 25.6, 33.1,
35.5, 35.7, 37.0, 43.4, 46.6, 56.3, 58.3, 71.9, 72.5, 74.8,
75.1, 75.5, 76.1, 77.6, 80.9, 84.4, 114.0, 114.7, 117.8,
126.9, 128.3, 128.4, 129.6, 129.9, 130.0, 131.6, 133.2,
133.9, 134.2, 139.3, 140.1, 157.7, 166.3, 168.6, 169.5,
4.14. General procedures for macrolactonization
To a solution of compound 4-deacetyl-4-(3-carboxy-
propanoyl)-30-desphenyl-30-(m-hydroxyphenyl)-7-TES-
20-TIPS-paclitaxel 23 (20.4mg, 0.017mmol) in
anhydrous DCM (1.5mL) was added 2,4,6-trich-
lorobenzoyl chloride (7.9lL, 0.051mmol). After stirring
for 30min, the reaction mixture was transferred into a
syringe. Very slow addition of this mixture through

6158
C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
syringe pump to
a
flask with DMAP (6.4mg,
Ar, overlapped), 7.85–7.91 (2H, m, Ar), 8.14–8.20 (2H,
m, Ar); 13C NMR (100MHz, CDCl3) d: 5.3, 6.7, 10.2,
12.4, 14.0, 17.7, 17.8, 20.9, 21.9, 25.3, 26.7, 27.0, 35.1,
36.1, 36.3, 37.3, 43.4, 47.1, 56.4, 58.5, 71.8, 72.2, 74.9,
75.0, 76.8, 79.0, 81.9, 84.9, 120.1, 120.3, 122.3, 127.1,
128.7, 128.8, 129.3, 130.1, 130.2, 131.9, 133.4, 133.8,
134.0, 140.3, 141.4, 151.7, 166.9, 167.3, 169.3, 171.7,
172.5, 173.1, 201.5; HRFABMS m/z 1230.5566
[M+Na+]; calcd for C66H89NO16Si2Na, 1230.5618.
0.051mmol) in DCM (8.5mL) under stirring. The addi-
tion rate was set to be 0.5mL/h. After addition was over,
the mixture was kept stirring for another hour. The reac-
tion mixture was diluted with DCM (20mL), and then
washed with 0.1N HCl (3 · 20mL), saturated NaHCO3,
brine, and dried with sodium sulfate. The organic phase
was concentrated in vacuum, and the residue was
applied to PTLC (30% EtOAc/hexane) to give 31 as
colorless gum (5.1mg, 25%). Compounds 32–35 were
prepared in similar procedures.
1
4.14.4. Macrocyclic taxoid 34. Colorless gum; H NMR
(400MHz, CDCl3) d: 0.56–0.67 (6H, m), 0.92–1.02
(30H, overlapped), 1.23 (3H, s), 1.26 (3H, s), 1.66–1.80
(5H, overlapped), 1.89–2.11 (9H, overlapped), 2.20
(3H, s), 2.25–2.34 (1H, m), 2.41–2.49 (1H, m), 2.51–
2.79 (4H, overlapped), 2.81–2.91 (1H, m), 3.86 (1H, d,
J = 7.1Hz), 4.26 (1H, d, J = 8.5Hz), 4.37 (1H, d,
J = 8.5Hz), 4.52(1H, dd, J = 10.5, 6.6Hz), 4.85 (1H,
d, J = 1.0Hz), 4.89 (1H, dd, J = 9.6, 1.8Hz), 5.61 (1H,
d, J = 8.4Hz), 5.77 (1H, d, J = 7.1Hz), 6.10 (1H, t,
J = 9.3Hz), 6.49 (1H, s), 6.98–7.03 (1H, m, Ar), 7.17
(1H, dd, J = 8.0, 1.8Hz), 7.21–7.25 (1H, m, Ar), 7.29
(1H, d, J = 8.4Hz), 7.42(1H, t, J = 8.0Hz), 7.47–7.69
(6H, m, Ar, overlapped), 7.83–7.88 (2H, m, Ar), 8.14–
8.19 (2H, m, Ar); 13C NMR (100MHz, CDCl3) d: 5.3,
6.7, 10.2, 12.5, 14.0, 17.7, 17.9, 20.8, 21.8, 24.8, 24.9,
26.7, 28.2, 34.5, 35.8, 35.9, 37.2, 43.4, 46.7, 56.3, 58.4,
72.2, 72.6, 74.9, 75.0, 76.2, 76.5, 78.8, 81.4, 84.6, 119.6,
121.8, 123.2, 127.0, 128.7, 128.8, 129.3, 129.9, 130.1,
131.9, 133.6, 133.7, 134.0, 140.2, 140.6, 151.3, 166.9,
167.4, 169.3, 171.9, 172.3, 201.6; HRFABMS m/z
1244.5759 [M+Na+]; calcd for C67H91NO16Si2Na,
1244.5774.
4.14.1. Macrocyclic taxoid 31. 1H NMR (400MHz,
CDCl3) d: 0.50–0.60 (6H, m), 0.92(9H, t, J = 7.8Hz),
1.13–1.27 (27H, overlapped), 1.29 (3H, s), 1.62–1.71
(5H, overlapped), 1.81–1.90 (1H, m), 2.16 (3H, s),
2.39–2.48 (1H, m), 2.75–3.15 (4H, overlapped), 3.39
(1H, d, J = 7.8Hz), 4.15 (1H, d, J = 8.5Hz), 4.23 (1H,
d, J = 8.5Hz), 4.39 (1H, dd, J = 10.6, 6.5Hz), 4.77–
4.82(H2 , overlapped), 5.63 (1H, d,
J = 7.8Hz), 5.72
(1H, br s), 5.94 (1H, br t, J = 8.7Hz), 6.24 (1H, s),
7.13–7.20 (2H, overlapped), 7.32–7.37 (1H, m, Ar),
7.46–7.80 (8H, m, Ar, overlapped), 7.89–7.95 (2H, m,
Ar), 8.02–8.07 (2H, m, Ar); 13C NMR (100MHz,
CDCl3) d: 5.5, 6.9, 11.0, 12.5, 18.2, 21.1, 28.1, 29.2,
30.5, 36.4, 36.7, 36.98, 36.99, 37.01, 43.5, 47.2, 58.1,
72.1, 73.8, 74.5, 75.9, 76.4, 77.3, 82.0, 84.7, 120.5,
127.4, 128.8, 129.0, 129.5, 130.2, 130.5, 132.3, 132.9,
133.7, 134.09, 134.12, 141.0, 146.3, 152.0, 162.7, 166.6,
167.4, 169.4, 170.6, 201.4; HRFABMS m/z 1202.5312
[M+Na+]; calcd for C64H85NO16Si2Na, 1202.5305.
1
4.14.2. Macrocyclic taxoid 32. Colorless gum; H NMR
(400MHz, CDCl3) d: 0.54–0.68 (6H, m), 0.93–1.12
(30H, overlapped), 1.26 (3H, s), 1.28 (3H, s), 1.65 (3H,
s), 1.75 (3H, s), 1.81 (1H, s), 1.81–2.11 (3H, overlapped),
2.21 (3H, s), 2.23–2.90 (7H, overlapped), 3.79 (1H, br s),
4.27 (1H, d, J = 8.3Hz), 4.39 (1H, d, J = 8.3Hz), 4.51
(1H, dd, J = 10.6, 6.5Hz), 4.78 (1H, br s), 4.87 (1H, d,
J = 9.2Hz), 5.45 (1H, br s), 5.76 (1H, d, J = 7.4Hz),
6.16 (1H, t, J = 9.2Hz), 6.46 (1H, s), 7.13 (1H, d,
J = 8.0Hz), 7.22 (1H, d, J = 7.8Hz), 7.38–7.71 (8H, m,
Ar, overlapped), 7.88 (2H, d, J = 7.8Hz), 8.15 (2H, d,
J = 7.6Hz); 13C NMR (100MHz, CDCl3) d: 5.3, 6.7,
10.4, 12.4, 17.8, 17.9, 20.8, 22.8, 25.1, 26.9, 29.7, 32.6,
36.2, 37.1, 43.4, 47.0, 56.3, 58.3, 68.2, 69.6, 72.2, 74.8,
75.1, 76.5, 81.9, 84.7, 120.1, 120.3, 122.2, 127.1, 128.7,
128.8, 129.2, 130.1, 130.4, 131.9, 133.6, 133.9, 140.1,
140.3, 149.4, 153.0, 166.3, 167.0, 169.3, 171.7, 172.2,
175.2, 201.9; HRFABMS m/z 1216.5433 [M+Na+];
calcd for C65H87NO16Si2Na, 1216.5461.
1
4.14.5. Macrocyclic taxoid 35. Colorless gum; H NMR
(400MHz, CDCl3) d: 0.51–0.64 (6H, m), 0.88–0.98
(30H, overlapped), 1.16 (3H, s), 1.22 (3H, s), 1.60–2.10
(16H, overlapped), 2.16 (3H, s), 2.21–2.30 (1H, m),
2.34–2.74 (5H, overlapped), 2.78–2.88 (1H, m), 3.87
(1H, d, J = 7.0Hz), 4.22 (1H, d, J = 8.5Hz), 4.33 (1H,
d, J = 8.5Hz), 4.48 (1H, dd, J = 10.5, 6.6Hz), 4.80–
4.87 (2H, overlapped), 5.59 (1H, d, J = 8.7Hz), 5.72
(1H, d, J = 7.0Hz), 6.03 (1H, t, J = 9.0Hz), 6.47 (1H,
s), 7.00–7.08 (2H, m, Ar, overlapped), 7.16–7.24 (2H,
m, Ar, overlapped), 7.35–7.67 (7H, m, Ar, overlapped),
7.77–7.83 (2H, m, Ar), 8.10–8.16 (2H, m, Ar); 13C NMR
(100MHz, CDCl3) d: 5.5, 6.9, 10.3, 12.7, 14.4, 18.0, 18.1,
21.1, 21.6, 25.0, 26.7, 27.0, 28.8, 29.5, 34.6, 35.8, 37.2,
37.4, 43.6, 46.8, 56.6, 58.7, 72.4, 73.1, 75.0, 75.3, 75.9,
76.8, 78.7, 81.4, 84.8, 119.7, 122.0, 124.0, 127.2, 128.9,
129.0, 129.5, 130.1, 130.4, 132.1, 133.9, 134.2, 140.3,
140.5, 151.2, 167.1, 167.4, 169.5, 172.3, 172.4, 172.9,
202.0; HRFABMS m/z 1236.6061 [M+H+]; calcd for
C68H94NO16Si2, 1236.6111.
1
4.14.3. Macrocyclic taxoid 33. Colorless gum; H NMR
(400MHz, CDCl3) d: 0.56–0.67 (6H, m), 0.93–1.05
(30H, overlapped), 1.25 (3H, s), 1.26 (3H, s), 1.68–1.80
(5H, overlapped), 1.84–2.13 (6H, overlapped), 2.15–
2.31 (7H, overlapped), 2.41–2.87 (6H, overlapped),
3.90 (1H, d, J = 7.3Hz), 4.28 (1H, d, J = 8.3Hz), 4.34
(1H, d, J = 8.4Hz), 4.50 (1H, dd, J = 10.6, 6.5Hz),
4.76–4.83 (2H, overlapped), 5.53 (1H, d, J = 8.0Hz),
5.76 (1H, d, J = 7.3Hz), 6.13 (1H, t, J = 9.1Hz), 6.50
(1H, s), 7.03–7.12 (2H, m, overlapped), 7.17–7.22 (1H,
m, Ar), 7.40 (2H, t, J = 7.8Hz), 7.47–7.692(6H, m,
4.15. General procedures for desilylation
To a solution of macrocyclic taxoid 31 (6.0mg,
0.005mmol) in dried THF (1.0mL) was added anhy-
drous pyridine (0.2mL), then the solution was cooled
to 0ꢂC, and HF–pyridine (0.2mL) was added. The reac-
tion mixture was allowed to warm to room temperature,
and stirred for overnight. The reaction mixture was

C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
6159
diluted with EtOAc (20mL), and the organic phase was
washed with sodium bicarbonate, water, brine, dried
over sodium sulfate, and concentrated in vacuum. The
residue was applied to preparative TLC (50% EtOAc/
hexane) to give 2a (1.2mg, 26%) and 36a (2.3mg, 49%)
both as colorless gums. Compounds 37a–e were pre-
pared similarly from compounds 23, 24, and 28–30,
while compounds 2b, 36b, 2c, 36c, 2d, and 2e were
prepared from compounds 32–35 by using HF–TEA
instead of HF–pyridine in THF as solvent.
(1H, d, J = 8.5Hz), 4.42(1H, m), 4.64 (1H, br t,
J = 6.5Hz), 4.89 (1H, dd, J = 9.5, 1.8Hz), 5.64 (1H,
dd, J = 7.8, 6.1Hz), 5.72(1H, d, J = 7.4Hz), 6.22 (1H,
t, J = 9.0Hz), 6.24 (1H, s), 7.02–7.08 (1H, m, Ar),
7.14–7.21 (2H, overlapped), 7.28–7.34 (1H, m, Ar),
7.42–7.73 (7H, m, Ar, overlapped), 7.82–7.87 (2H, m,
Ar), 8.12–8.17 (2H, m, Ar); HRFABMS m/z 924.3463
[M+H+]; calcd for C50H54NO16, 924.3443.
4.15.5. Macrocyclic taxoid 36b. Colorless gum; 1H NMR
(400MHz, CDCl3) d: 1.09 (3H, s), 1.29 (3H, s), 1.40 (3H,
d, J = 1.3Hz), 1.68 (1H, s), 1.82(3H, s), 1.85–2.16 (4H,
overlapped), 2.26 (3H, s), 2.27–2.40 (1H, m), 2.48–2.81
(5H, overlapped), 2.91–3.00 (1H, m), 3.58 (1H, d,
J = 7.1Hz), 4.16 (1H, d, J = 8.5Hz), 4.31 (1H, d,
J = 8.5Hz), 4.39 (1H, m), 4.98 (1H, dd, J = 9.6,
1.7Hz), 5.66 (1H, d, J = 7.1Hz), 5.87 (1H, dd, J = 9.4,
3.5Hz), 6.01 (1H, d, J = 3.5Hz), 6.10 (1H, br s), 6.14
(1H, s), 6.42(1H, dt, J = 9.1, 1.3Hz), 6.77–6.81 (1H,
m, Ar), 6.90–6.94 (1H, m, Ar), 6.96–6.99 (1H, m, Ar),
7.23 (1H, t, J = 7.9Hz), 7.50–7.69 (7H, m, Ar, over-
lapped), 7.87–7.92 (2H, m, Ar), 8.05–8.09 (2H, m, Ar);
HRFABMS m/z 924.3410 [M+H+]; calcd for
C50H54NO16, 924.3443.
4.15.1. Macrocyclic taxoid 2a. 1H NMR (400MHz,
CDCl3)d: 1.12(3H, s), 1.92 (3H, s), 1.35 (3H, br s),
1.62–1.69 (1H, m), 1.69 (3H, s), 1.84–1.92 (1H, m),
2.25 (3H, s), 2.47–2.69 (3H, overlapped), 2.83–3.05
(4H, overlapped), 3.48 (1H, d, J = 7.4Hz), 3.79 (1H,
br s), 4.18 (1H, d, J = 8.3Hz), 4.25 (1H, d, J = 8.3Hz),
4.35 (1H, m), 4.53 (1H, br s), 4.83 (1H, dd, J = 9.3,
1.8Hz), 5.47 (1H, m), 5.65 (1H, d, J = 7.4Hz), 6.12
(1H, s), 6.15 (1H, t, J = 9.3Hz), 7.15–7.32(3H, over-
lapped), 7.39–7.62(7H, m, Ar, overlapped), 7.68–7.75
(1H, m, Ar), 7.87–7.91 (2H, m, Ar), 8.00–8.04 (2H, m,
Ar); HRFABMS m/z 910.3317 [M+H+]; calcd for
C49H52NO16, 910.3286.
4.15.2. Macrocyclic taxoid 36a. 1H NMR (400MHz,
CDCl3) d: 1.08 (3H, s), 1.20 (3H, s), 1.39 (3H, d,
J = 1.0Hz), 1.69 (1H, s), 1.71 (3H, s), 1.88–1.96 (1H,
m), 2.01–2.08 (1H, m), 2.13–2.21 (1H, m), 2.25 (3H, s),
2.46–2.56 (2H, overlapped), 2.70–2.79 (2H, overlapped),
3.07–3.24 (2H, overlapped), 3.85 (1H, d, J = 7.6Hz),
4.24 (1H, d, J = 8.6Hz), 4.28 (1H, d, J = 8.6Hz), 4.34
(1H, m), 4.78 (1H, dd, J = 9.7, 1.8Hz), 5.52(1H, d,
J = 3.0Hz), 5.61 (1H, d, J = 7.6Hz), 5.94 (1H, dd,
J = 9.3, 3.0Hz), 6.14 (1H, s), 6.21 (1H, t, J = 8.9Hz),
6.79–6.84 (1H, m, Ar), 6.98–7.03 (2H, overlapped),
7.24–7.28 (1H, m, Ar), 7.49–7.68 (7H, m, Ar, over-
lapped), 7.88–7.94 (2H, m, Ar), 8.11–8.16 (2H, m, Ar);
HRFABMS m/z 910.3295 [M+H+]; calcd for
C49H52NO16, 910.3286.
4.15.6. 4-Deacetyl-4-(4-carboxybutanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-paclitaxel (37b). Colorless gum;
1H NMR (400MHz, CD3OD) d: 1.17 (3H, s), 1.18
(3H, s), 1.68 (3H, s), 1.69–1.87 (2H, overlapped), 1.91
(3H, br s), 2.05–2.18 (3H, overlapped), 2.20 (3H, s),
2.30–2.55 (3H, overlapped), 2.65 (2H, br t, J = 7.8Hz),
3.83 (1H, d, J = 7.2Hz), 4.20 (2H, br s), 4.37 (1H, dd,
J = 10.9, 6.5Hz), 4.69 (1H, d, J = 7.8Hz), 4.96 (1H, d,
J = 9.4Hz), 5.43 (1H, d, J = 7.8Hz), 5.65 (1H, d, J =
7.2Hz), 6.05 (1H, t, J = 9.2Hz), 6.46 (1H, s), 6.68
(1H, dd, J = 8.1, 2.3Hz), 6.97 (1H, d, J = 7.6Hz),
7.04–7.06 (1H, m, Ar), 7.24 (1H, t, J = 7.9Hz), 7.48–
7.74 (6H, m, Ar, overlapped), 7.99–8.04 (2H, m, Ar),
8.09–8.14 (2H, m, Ar); 13C NMR (100MHz, CD3OD)
d: 9.1, 13.2, 19.4, 21.1, 22.2, 25.5, 25.7, 34.8, 35.1,
36.1, 43.2, 46.5, 57.5, 57.8, 70.5, 70.9, 73.8, 74.9, 75.4,
76.1, 77.7, 80.8, 84.8, 114.0, 114.9, 118.5, 127.4, 128.1,
128.5, 129.4, 129.8, 129.9, 131.3, 133.2, 133.4, 134.2,
139.9, 140.9, 157.5, 166.3, 169.3, 169.9, 173.0, 173.2,
203.9; HRFABMS m/z 942.3602 [M+H+]; calcd for
C50H56NO17, 942.3548.
4.15.3. 4-Deacetyl-4-(3-carboxypropanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-paclitaxel (37a). Colorless gum;
1H NMR (400MHz, CD3OD) d: 1.16 (3H, s), 1.18
(3H, s), 1.67 (3H, s), 1.73–1.85 (2H, overlapped), 1.90
(3H, s), 2.06–2.15 (1H, m), 2.16–2.24 (4H, overlapped),
2.42–2.53 (1H, m), 2.60–2.84 (2H, overlapped), 2.86–
2.97 (1H, m), 3.81 (1H, d, J = 7.3Hz), 4.20 (2H, ABq,
J = 8.6Hz), 4.35 (1H, dd, J = 10.9, 6.6Hz), 4.68 (1H,
d, J = 7.3Hz), 5.06 (1H, d, J = 9.1Hz), 5.43 (1H, d,
J = 7.3Hz), 5.65 (1H, d, J = 7.3Hz), 6.08 (1H, t,
J = 9.1Hz), 6.45 (1H, s), 6.69 (1H, dd, J = 8.2, 2.5Hz),
6.93 (1H, d, J = 7.7Hz), 7.02(1H, m, Ar), 7.22(1H, t,
J = 7.9Hz), 7.47–7.73 (6H, m, Ar, overlapped), 7.95–
8.00 (2H, m, Ar), 8.10–8.15 (2H, m, Ar); HRFABMS
m/z 928.3373 [M+H+]; calcd for C49H54NO17, 928.3392.
1
4.15.7. Macrocyclic taxoid 2c. Colorless gum; H NMR
(400MHz, CDCl3) d: 1.17 (3H, s), 1.31 (3H, s), 1.72(3H,
s), 1.82(1H, s), 1.86 (3H, d, J = 1.0Hz), 1.87–2.25 (6H,
overlapped), 2.27 (3H, s), 2.42–2.78 (6H, overlapped),
3.77 (1H, d, J = 7.1Hz), 3.93 (1H, d, J = 6.8Hz), 4.25
(1H, d, J = 8.4Hz), 4.31 (1H, d, J = 8.4Hz), 4.40 (1H,
m), 4.58 (1H, br t, J = 6.1Hz), 4.82(1H, dd, J = 9.6,
1.9Hz), 5.64 (1H, dd, J = 7.9, 5.5Hz), 5.71 (1H, d,
J = 7.1Hz), 6.20 (1H, t, J = 9.2Hz), 6.29 (1H, s), 7.00
(1H, d, J = 7.9Hz), 7.14–7.21 (2H, m, Ar, overlapped),
7.30–7.34 (1H, m, Ar), 7.41–7.72(7H, m, Ar, over-
lapped), 7.80–7.87 (2H, m, Ar), 8.13–8.19 (2H, m, Ar);
13C NMR (100MHz, CDCl3) d: 9.7, 14.4, 20.8, 22.5,
25.1, 26.2, 27.1, 35.0, 35.6, 43.3, 45.8, 56.1, 58.6, 71.6,
72.2, 75.1, 75.5, 76.7, 79.2, 81.6, 84.9, 119.6, 121.2,
124.4, 127.2, 128.7, 128.8, 129.2, 130.2, 130.7, 132.1,
1
4.15.4. Macrocyclic taxoid 2b. Colorless gum; H NMR
(400MHz, CDCl3) d: 1.16 (3H, s), 1.35 (3H, s), 1.73 (3H,
s), 1.79 (3H, s), 1.80 (3H, s), 1.85–1.98 (2H, overlapped),
2.11–2.26 (2H, overlapped), 2.27 (3H, s), 2.42–2.82 (6H,
overlapped), 2.85–2.94 (1H, m), 3.68 (1H, d, J = 7.4Hz),
3.89 (1H, d, J = 7.0Hz), 4.25 (1H, d, J = 8.5Hz), 4.34

6160
C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
132.7, 133.5, 133.8, 139.8, 142.6, 151.6, 167.0, 168.2,
171.3, 172.4, 172.7, 203.5; HRFABMS m/z 938.3671
[M+H+]; calcd for C51H56NO16, 938.3599.
172.9, 203.6; HRFABMS m/z 952.3754 [M+H+]; calcd
for C52H58NO16, 952.3756.
4.15.11. 4-Deacetyl-4-(6-carboxyhexanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-paclitaxel (37d). Colorless gum;
1H NMR (400MHz, CD3OD) d: 1.19 (3H, s), 1.21
(3H, s), 1.37–1.51 (2H, m), 1.62–1.75 (5H, overlapped),
1.76–1.90 (3H, overlapped), 1.95 (3H, d, J = 1.0Hz),
2.02–2.11 (1H, m), 2.16–2.32 (6H, overlapped), 2.45–
2.59 (2H, overlapped), 2.62–2.72 (1H, m), 3.86 (1H, d,
J = 7.2Hz), 4.22 (2H, br s), 4.37 (1H, dd, J = 10.8,
6.6Hz), 4.74 (1H, d, J = 5.4Hz), 4.95 (1H, d,
J = 9.3Hz), 5.58 (1H, d, J = 5.4Hz), 5.68 (1H, d,
J = 7.2Hz), 6.20 (1H, t, J = 9.3Hz), 6.48 (1H, s), 6.75–
6.79 (1H, m, Ar), 6.97–7.02(2H, m, Ar, overlapped),
7.27 (1H, t, J = 8.3Hz), 7.46–7.52(H2 , m, Ar, over-
lapped), 7.54–7.59 (1H, m, Ar), 7.59–7.66 (2H, m, Ar),
7.67–7.74 (1H, m, Ar), 7.89–7.94 (2H, m, Ar), 8.12–
8.18 (2H, m, Ar); 13C NMR (100MHz, CD3OD) d:
9.1, 13.3, 19.4, 21.1, 24.8, 25.3, 25.6, 28.5, 34.9, 35.2,
36.1, 36.2, 43.2, 46.6, 56.2, 57.9, 70.9, 73.0, 74.9, 75.4,
76.2, 77.7, 80.9, 84.8, 114.0, 114.6, 118.2, 127.2, 128.1,
128.4, 129.4, 129.8, 130.0, 131.4, 133.2, 133.4, 134.3,
140.2, 140.9, 157.6, 166.3, 169.5, 169.9, 173.0, 173.3,
174.1, 203.8; HRFABMS m/z 970.3882[M+H +]; calcd
for C52H60NO17, 970.3861.
4.15.8. Macrocyclic taxoid 36c. Colorless gum; 1H NMR
(400MHz, CDCl3) d: 1.08 (3H, s), 1.30 (3H, s), 1.43 (3H,
d, J = 1.1Hz), 1.68 (3H, s), 1.81 (1H, s), 1.86–2.32 (9H,
overlapped), 2.50–2.77 (6H, overlapped), 3.65 (1H, d,
J = 7.2Hz), 4.21 (1H, d, J = 8.6Hz), 4.33 (1H, d,
J = 8.6Hz), 4.39 (1H, m), 4.93 (1H, dd, J = 9.5,
1.9Hz), 5.66 (1H, d, J = 7.2Hz), 5.84 (1H, d,
J = 3.5Hz), 5.94 (1H, dd, J = 9.5, 3.5Hz), 6.14 (1H, s),
6.36 (1H, t, J = 9.1Hz), 6.42(1H, br s), 6.81–6.85 (1H,
m, Ar), 6.94–6.98 (1H, m, Ar), 7.07–7.10 (1H, m, Ar),
7.24 (1H, t, J = 8.4Hz), 7.48–7.68 (7H, m, Ar, over-
lapped), 7.88–7.93 (2H, m, Ar), 8.06–8.11 (2H, m, Ar);
13C NMR (100MHz, CDCl3) d: 9.8, 13.9, 20.8, 22.6,
22.9, 23.0, 27.1, 32.6, 33.7, 35.4, 36.0, 43.2, 45.4, 53.5,
58.3, 71.8, 73.0, 74.2, 75.3, 75.4, 76.3, 79.6, 81.5, 84.5,
114.2, 115.8, 118.4, 127.1, 128.6, 128.9, 129.2, 130.0,
130.2, 132.3, 132.7, 133.3, 133.8, 138.4, 142.1, 156.5,
166.5, 167.0, 169.7, 171.3, 171.4, 172.4, 203.5; HRF-
ABMS m/z 938.3608 [M+H+]; calcd for C51H56NO16,
938.3599.
4.15.9. 4-Deacetyl-4-(5-carboxypentanoyl)-30-desphenyl-
30-(m-hydroxyphenyl)-paclitaxel (37c). Colorless gum;
1H NMR (400MHz, CD3OD) d: 1.18 (3H, s), 1.20
(3H, s), 1.69 (3H, s), 1.70–2.04 (9H, overlapped), 2.20
(3H, s), 2.21–2.74 (6H, overlapped), 3.86 (1H, d,
J = 7.2Hz), 4.22 (2H, br s), 4.37 (1H, dd, J = 10.8,
6.6Hz), 4.72(1H, d, J = 5.8Hz), 4.97 (1H, br d,
J = 9.0Hz), 5.54 (1H, d, J = 5.8Hz), 5.68 (1H, d,
J = 7.2Hz), 6.17 (1H, t, J = 9.2Hz), 6.48 (1H, s), 6.71–
6.77 (1H, m, Ar), 6.96–7.02(2H, m, Ar, overlapped),
7.27 (1H, t, J = 8.0Hz), 7.46–7.74 (6H, m, Ar, over-
lapped), 7.89–7.95 (2H, m, Ar), 8.11–8.16 (2H, m, Ar);
13C NMR (100MHz, CD3OD) d: 9.1, 13.2, 19.4, 21.1,
24.8, 24.9, 25.6, 35.1, 35.3, 36.1, 36.2, 43.2, 46.5, 56.5,
57.8, 70.8, 70.9, 73.3, 74.9, 75.4, 76.2, 77.7, 80.9, 84.8,
114.2, 114.7, 118.2, 127.2, 128.1, 128.4, 129.4, 129.8,
130.0, 131.4, 133.2, 133.5, 134.3, 140.1, 140.8, 157.5,
166.3, 168.9, 169.9, 172.9, 173.2, 203.8; HRFABMS
m/z 956.3688 [M+H+]; calcd for C51H58NO17, 956.3705.
4.15.12. Macrocyclic taxoid 2e. Colorless gum; 1H NMR
(400MHz, CDCl3) d: 1.18 (3H, s), 1.28 (3H, s), 1.60–
2.10 (16H, overlapped), 2.26 (3H, s), 2.30–2.64 (5H,
overlapped), 2.70–2.87 (2H, overlapped), 3.79 (1H, d,
J = 3.8Hz), 3.88 (1H, J = 7.0Hz), 4.26 (1H, d,
J = 8.5Hz), 4.35 (1H, d, J = 8.5Hz), 4.45 (1H, m), 4.67
(1H, br s), 4.87 (1H, dd, J = 9.4, 1.8Hz), 5.70–5.77
(2H, overlapped), 6.21 (1H, t, J = 8.9Hz), 6.32(1H, s),
7.05–7.15 (3H, m, Ar, overlapped), 7.37–7.69 (8H, m,
Ar, overlapped), 7.74–7.80 (2H, m, Ar), 8.13–8.19 (2H,
m, Ar); 13C NMR (100MHz, CDCl3) d: 9.6, 14.7,
20.9, 22.1, 24.9, 26.6, 26.9, 28.5, 29.2, 34.6, 35.6, 35.7,
36.3, 43.3, 45.6, 54.8, 58.6, 72.1, 72.8, 73.4, 75.0, 75.6,
76.5, 78.9, 81.3, 84.8, 120.2, 121.7, 124.1, 127.1, 127.7,
128.8, 129.2, 130.2, 130.3, 132.0, 133.1, 133.7, 133.8,
140.1, 142.1, 151.1, 166.9, 167.3, 171.3, 172.6, 172.9,
173.2, 203.6; HRFABMS m/z 966.3860 [M+H+]; calcd
for C53H60NO16, 966.3912.
4.15.10. Macrocyclic taxoid 2d. Colorless gum; 1H NMR
(400MHz, CDCl3) d: 1.18 (3H, s), 1.31 (3H, s), 1.68–
1.75 (5H, overlapped), 1.85 (3H, s), 1.86–2.10 (6H, over-
lapped), 2.21–2.39 (5H, overlapped), 2.52–2.81 (6H,
overlapped), 3.80 (1H, d, J = 7.2Hz), 3.85 (1H, br s),
4.26 (1H, d, J = 8.5Hz), 4.35 (1H, d, J = 8.5Hz), 4.45
(1H, m), 4.64 (1H, d, J = 2.6Hz), 4.90 (1H, dd,
J = 9.4, 1.7Hz), 5.70–5.77 (2H, overlapped), 6.20 (1H,
t, J = 9.1Hz), 6.30 (1H, s), 7.10–7.20 (3H, m, Ar, over-
lapped), 7.33 (1H, d, J = 8.1Hz), 7.43–7.50 (3H, m,
Ar, overlapped), 7.52–7.60 (3H, m, Ar, overlapped),
7.63–7.70 (1H, m, Ar), 7.78–7.83 (2H, m, Ar), 8.12–
8.18 (2H, m, Ar); 13C NMR (100MHz, CDCl3) d: 9.7,
14.4, 20.9, 22.5, 24.9, 25.2, 27.0, 28.3, 34.5, 35.6, 35.7,
35.9, 43.4, 45.6, 55.1, 58.5, 72.1, 72.5, 74.1, 75.1, 75.5,
76.5, 79.2, 81.5, 84.8, 120.1, 121.7, 123.7, 127.1, 128.7,
128.8, 129.2, 130.1, 130.4, 132.1, 133.0, 133.6, 133.8,
140.1, 142.3, 151.4, 166.9, 167.7, 171.3, 172.4, 172.5,
4.15.13. 4-Deacetyl-4-(7-carboxyheptanoyl)-30-desphen-
yl-30-(m-hydroxyphenyl)-paclitaxel
(37e).
Colorless
gum; 1H NMR (400MHz, CD3OD) d: 1.19 (3H, s),
1.21 (3H, s), 1.31–1.42 (4H, overlapped), 1.52–1.64
(2H, m), 1.70 (3H, s), 1.72–1.92 (3H, overlapped), 1.96
(3H, d, J = 1.1Hz), 2.12–2.29 (6H, overlapped), 2.32–
2.40 (1H, m), 2.46–2.60 (2H, overlapped), 2.68–2.77
(1H, m), 3.88 (1H, d, J = 7.1Hz), 4.21 (1H, d,
J = 8.3Hz), 4.25 (1H, d, J = 8.3Hz), 4.37 (1H, dd,
J = 10.9, 6.5Hz), 4.80 (1H, d, J = 4.4Hz), 4.94 (1H,
d, J = 9.6Hz), 5.65 (1H, d, J = 4.4Hz), 5.69 (1H, d,
J = 7.1Hz), 6.22 (1H, t, J = 9.1Hz), 6.50 (1H, s), 6.76–
6.81 (1H, m, Ar), 6.98–7.05 (2H, m, Ar, overlapped),
7.28 (1H, t, J = 8.0Hz), 7.45–7.73 (6H, m, Ar, over-
lapped), 7.86–7.91 (2H, m, Ar), 8.14–8.20 (2H, m, Ar);
13C NMR (100MHz, CD3OD) d: 9.1, 13.3, 19.4, 21.0,
25.0, 25.1, 25.6, 28.4, 28.7, 35.3, 35.4, 35.5, 36.2, 43.3,

C. Liu et al. / Bioorg. Med. Chem. 12 (2004) 6147–6161
6161
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N.; Potier, P.; Gillet, B.; Betoeil, J.-C. Tetrahedron 1993,
49, 6533–6544.
9. Williams, H. J.; Scott, A. I.; Dieden, R. A.; Swindell, C. S.;
Chirlian, L. E.; Francl, M. M.; Heerding, J. M.; Krauss,
N. E. Tetrahedron 1993, 49, 6545–6560.
10. Vander Velde, D. G.; Georg, G. I.; Grunewald, G. L.;
Gunn, C. W.; Mitscher, L. A. J. Am. Chem. Soc. 1993,
115, 11650–11651.
46.6, 55.7, 57.9, 70.9, 71.1, 72.8, 74.9, 75.4, 76.2, 77.7,
80.9, 84.8, 114.1, 114.5, 118.1, 127.1, 128.2, 128.4,
129.4, 129.8, 130.0, 131.4, 133.2, 133.5, 134.3, 140.1,
140.8, 157.5, 166.3, 168.9, 169.9, 173.0, 173.3, 203.8;
HRFABMS m/z 984.3974 [M+H+]; calcd for
C53H62NO17, 984.4018.
4.16. Cytotoxicity bioassay
11. Snyder, J. P.; Nevins, N.; Cicero, D. O.; Jansen, J. J. Am.
Chem. Soc. 2000, 122, 724–725.
12. Snyder, J. P.; Nettles, J. H.; Cornett, B.; Downing, K. H.;
Nogales, E. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 5312–
5316.
The A2780 ovarian cancer cell line assay was performed
at Virginia Polytechnic Institute and State University as
previously reported.26
13. Barboni, L.; Lambertucci, C.; Appendino, G.; Vander-
Velde, D. G.; Himes, R. H.; Bombardelli, E.; Wang, M.;
Snyder, J. P. J. Med. Chem. 2001, 44, 1576–1587.
14. Liu, C.; Tamm, M.; No¨tzel, M. W.; de Meijere, A.;
Schilling, J. K.; Kingston, D. G. I. Tetrahedron Lett. 2003,
44, 2049–2052.
4.17. Tubulin Assembly Bioassay
Tubulin polymerization bioassays were carried out as
previously described.27
15. Boge, T. C.; Wu, Z.-J.; Himes, R. H.; Vander Velde, D.
G.; Georg, G. I. Bioorg. Med. Chem. Lett. 1999, 9, 3047–
3052.
Acknowledgements
16. Ojima, I.; Chakravarty, S.; Tadashi, I.; Lin, S.; He, L.;
Horwitz, S. B.; Kuduk, S. B.; Danishefsky, S. J. Proc.
Natl. Acad. Sci. U.S.A. 1999, 96, 4256–4261.
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Geng, X.; Walsh, J. J. J. Am. Chem. Soc. 2000, 122, 5343–
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This work was supported by the National Institutes of
Health (Grant CA69571), and we are grateful for this
support. We are also grateful to William Bebout and
Tom Glass in the Departments of Chemistry, Virginia
Polytechnic Institute and State University, for mass
spectroscopic determinations and NMR analysis, and
to Thota Ganesh for helpful discussions.
18. Querolle, O.; Dubois, J.; Thoret, S.; Roussi, F.; Montiel-
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