Synthesis of C2-C3′N-linked macrocyclic taxoids. Novel docetaxel analogues with high tubulin activity

Article abstract of DOI:10.1021/jm0497996

Novel C2-C3′N-linked macrocyclic taxoids 4 bearing an aromatic ring at position C2 were synthesized. These compounds, tethered between N3′ and the C2-aromatic ring at the ortho, meta, or para position, were constructed by ring-closing metathesis. The para

Full text of DOI:10.1021/jm0497996

J. Med. Chem. 2004, 47, 5937-5944
5937
Synthesis of C2-C3′N-Linked Macrocyclic Taxoids. Novel Docetaxel Analogues
with High Tubulin Activity
Olivier Querolle, Joe¨lle Dubois,* Sylviane Thoret, Fanny Roussi, Franc¸oise Gue´ritte, and Daniel Gue´nard
Institut de Chimie des Substances Naturelles, CNRS, 91190 Gif sur Yvette, France
Received March 11, 2004
Novel C2-C3′N-linked macrocyclic taxoids 4 bearing an aromatic ring at position C2 were
synthesized. These compounds, tethered between N3′ and the C2-aromatic ring at the ortho,
meta, or para position, were constructed by ring-closing metathesis. The para-substituted
derivatives were unable to stabilize microtubules, whereas the ortho- and meta-substituted
compounds show significant activity in cold-induced microtubule disassembly assay. The meta
derivative 4c is the first C2-C3′-linked cyclic analogue to be equipotent to paclitaxel in this
assay and to show significant cytotoxicity. Computational studies of the conformational behavior
of these compounds indicate that they can adopt several conformations including mainly the
“T-shaped” forms. Docking experiments have shown that the “T-shaped” form is preferred for
a good interaction of these compounds with the â-tubulin binding pocket.
Introduction
The anticancer drugs paclitaxel 1a (Taxol)1 and
docetaxel 1b (Taxotere),2 and their congeners,3 stabilize
microtubular proteins4 by binding to a specific site on
â-tubulin.5,6 During the past 10 years, extensive studies
have been devoted to the elucidation of the bioactive
conformation of the taxoids, i.e. the conformation they
adopt when they are bound to microtubules.
Figure 1.
Conformational analyses, based on X-ray structures
of paclitaxel and docetaxel, NMR, and molecular model-
ing studies, have led to the proposal of two major
conformations for taxoids in which there is a hydropho-
bic collapse between the C2-benzoyl group and the C3′
substituents. The “polar” form, exhibiting hydrophobic
interactions between the C3′-phenyl group and the C2
benzoate, has been identified in the crystal structure
of paclitaxel7 and by NMR in polar solvents.8 On the
other hand, the “nonpolar” conformation where the N3′
substituent is close to the C2 benzoate, has been
observed in the docetaxel solid state9 and by NMR in
apolar solvents.10 More recently, a third conformation
has been calculated using the electron crystallographic
density of tubulin â-sheets11 in conjunction with an
analysis of paclitaxel conformations.12 Contrary to the
former ones, this so-called “T-shaped” structure is
devoid of intramolecular hydrophobic interactions. A few
taxoids with built-in conformational restrictions have
been designed to mimic the presumed bioactive confor-
mations. Macrocyclic taxoids covalently linked between
the C2-benzoyl and the C3′-phenyl groups were designed
to mimic the “polar” form but few of them retain tubulin
assembly activity, and those that do have a lower
activity than that of paclitaxel.13 On the other hand, the
first compounds designed to mimic the T-shaped form
bearing either a constrained C-13 side chain14 or a
tether between the C3′-phenyl and C4-acetyl groups15
have shown cytotoxicity and tubulin interaction. How-
ever, these compounds were not sufficiently constrained
Figure 2.
to allow a definite conclusion. Finally, to mimic the
“nonpolar” form, C2-C3′N-tethered macrocyclic taxoids
have been designed by our team16 and by Ojima’s
group.17 This group has synthesized compounds with
significant cytotoxicity but has reported neither their
tubulin activity nor their conformational behavior.
Therefore, no conclusion on the bioactive conformation
could be drawn from these results.
During the submission of this manuscript, more
constrained C3′Ph-C4-linked macrocyclic taxoids that
actually mimic the T-shaped form have been described
to possess high cytotoxicity and tubulin interaction.18
The authors conclude that the T-shaped form is there-
fore the bioactive conformation of taxoids. The results
* To whom correspondence should be addressed. Phone: 33 (0)1 69
82 30 58. Fax: 33 (0)1 69 07 72 47. E-mail: joelle.dubois@icsn.cnrs-
gif.fr.
10.1021/jm0497996 CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/22/2004

5938 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24
Scheme 1. Retrosynthesis of Compounds 4
Querolle et al.
Scheme 2. Synthesis of Compounds 4a
presented in this paper on C2-C3′N-linked macrocyclic
taxoids corroborate this conclusion.
In the field of “nonpolar” form mimics, we have
synthesized two series of macrocyclic taxoids 2,16a 316b
with C2-C3′N tether (Figure 2). We have found that
the macrocycle ring size is crucial for tubulin activity
as well as the functionalities on the linker. The 22-
membered ring taxoid 3a, bearing a C-C double bond
on the tether, was found to be only 7-fold less active
than paclitaxel on microtubule disassembly assay and
moderately cytotoxic. Molecular modeling studies have
shown that this compound adopts a conformation situ-
ated between the “nonpolar” and T-shaped forms. To get
more insight into the bioactive conformation, it was
important to increase tubulin interaction in our series
of macrocyclic taxoids. We have therefore designed new
compounds that resemble docetaxel more closely by
adding an aromatic ring at the C2 position.
We present, in this paper, the synthesis and biological
evaluation of macrocyclic taxoids 4 bearing a 21-23
membered ring in which the N3′ position is linked to
the ortho-, meta-, or para-position of the C2-aromatic
ring (Figure 2).
Chemistry. The synthesis of compounds 4 has been
realized by using the same strategy as for compounds
3 (Scheme 1). The macrocyclic ring was formed by ring-
closing metathesis on the open chain precursor 5 bear-
ing a C2-allyl benzoate and a C3′N ω-alkenyl chain
which can be obtained from the C2-OH and C3′-NH2
taxoid 6. This derivative is easily obtained from doce-
taxel as previously described.16a
For this series of compounds 4, acylation of the C-3′
amine of 6 was first carried out with 2 equiv of
5-hexenoic or 6-heptenoic acid in the presence of EDCI
and DMAP leading to 7a or 7b16b in good yields (Scheme
2). The subsequent step of the synthesis required the
o-, m-, and p-allylbenzoic acids 8 (o,m,p) that are not
commercially available. A few methods have been
described in the literature to synthesize allylbenzoates
from aryl halides and generally involve a metal in the
reaction such as Ni,19 Zn,20 Pd,21 Co,22 Mg,23 and Mg
with copper catalysis.24 The three allybenzoic acids were
synthesized in 42-59% overall yield according to the
a
(i) EDCI, DMAP, CH2dCH(CH2)nCOOH (2 equiv), CH2Cl2,
rt, 3 h (7a, 79%; 7b, 77%). (ii) 8 (30 equiv), DCC (30 equiv), DMAP
(1 equiv), toluene, 60 °C, 24 h (5a, 54%; 5b, 32%, 5c, 62%; 5d,
72%). (iii) HF/pyridine, pyridine, CH3CN, 0 °C, 1 h then room
temp, 6 h (4a, 46%; 4b, 50%, 4c, 75%; 4d, 43%; 10b, 89%, 10c,
72%; 10d, 65%). (iv) (Cy3P)2Ru(dCHPh)Cl2 (6% mol), CH2Cl2,
reflux, 3 h (9a, 60%; 9b, 77%, 9c, 60%; 9d, 64%).
Knochel procedure24 starting from the commercially
available iodobenzoic acids.
Contrary to our previous results obtained in the
esterification of the C2 hydroxyl group with alkyl
acids,16 the same reaction with allylbenzoic acids 8
proved to be very difficult and a large excess of acid and
DCC was needed to achieve acylation. Such conditions
have already been used by Kingston et al. to realize C2-
OH esterification.25
The major drawback of the reaction with DCC is a
significant side reaction that yields, after formation of
the intermediate O-acylisourea, the N-acylurea via O
to N acyl migration.26 Modifications of the experimental
conditions (coupling reagent, solvent, activation of the
acid) did not improve the yield in the desired compound,

Docetaxel Analogues with High Tubulin Activity
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24 5939
Table 1. Ring-Closure Metathesis Results on Compounds
9a-d
been previously reported for other ortho-substituted
benzoyl analogues.30
compd
n
ring size
yield, %
E/Z
The cytotoxicity of compounds 4c(E), 4c(Z), 4d, and
10d was also evaluated on two other cancer cell lines
(HCT 116 and MCF7) as well as that of compound 3a-
(E) (Figure 2), the most active derivative of our previous
series16b (Table 2). The results clearly show the impor-
tance of the C2-benzoyl group for cytotoxicity since
compound 3a(E) is poorly active, whereas compounds
4 and 10 exhibit significant IC50 values. Compound 10d
is again the most active derivative of this series showing
an IC50 value in the nanomolar range, and the E-isomer
of compound 4c is about 30-fold more cytotoxic than the
Z-isomer. Like docetaxel, these compounds were found
poorly active on a resistant MCF 7 cell line expressing
the P-glycoprotein (data not shown). This result sug-
gests that they are also recognized by this protein.
The cytotoxicity of compounds 4c(E), 4c(Z), 4d, and
10d was also evaluated on two other cancer cell lines
(HCT 116 and MCF7) as well as that of compound 3a-
(E) (Figure 2), the most active derivative of our previous
series16b (Table 2).
The results clearly show the importance of the C2-
benzoyl group for cytotoxicity since compound 3a(E) is
poorly active, whereas compounds 4 and 10 exhibit
significant IC50 values. Compound 10d is again the most
active derivative of this series showing an IC50 value in
the nanomolar range, and the E-isomer of compound 4c
is about 30-fold more cytotoxic than the Z-isomer. Like
docetaxel, these compounds were found poorly active on
a resistant MCF 7 cell line expressing the P-glycoprotein
(data not shown). This result suggests that they are also
recognized by this protein.
The most meaningful result for the elucidation of the
bioactive conformation of taxoids is the activity on cold-
induced microtubule disassembly. As we have hypothe-
sized, the addition of an aromatic ring at position 2
greatly improves tubulin interaction, except for the
para-substituted compounds 4a,b and 10b which do not
interact at all with tubulin. The lack of tubulin activity
of taxoids bearing a para-substituted C2-benzoate has
already been reported for azido, methoxy, or halo
derivatives.25,30,31 The discrepancy between cytotoxicity
and microtubule binding for these para-substituted
compounds deserves additional comments. Though the
taxoid biological activity has been reported to be closely
related to their interaction with microtubules, some
derivatives have already been reported to be cytotoxic
9a
9b
9c
9d
3
4
4
4
22
23
22
21
60
77
60
64
80/20
90/10
65/35
85/15
and the only way to achieve acceptable yields was to
increase the amount of reagents.
Compounds 5a-d were then subjected to ring-closing
metathesis27 using Grubb’s catalyst as previously de-
scribed (Scheme 2).16b Macrocyclic taxoids 9a-d were
obtained in 60-77% yield as an E/Z mixture with a 1.8
1
to 9 ratio, determined by H NMR (Table 1).
The E-isomer was predominantly formed as previ-
ously observed in the synthesis of 21- and 22-membered
macrocycles.16b The E- and Z-isomers were inseparable,
and their configurations were determined by 13C NMR
after examination of the benzylic carbon chemical shift,
that of the E-isomer being about 7 ppm downfield of the
Z-isomer’s. Full deprotection of 9a-d by HF/pyridine
afforded compounds 4a-d in moderate yields. Only the
Z- and E-isomers of the meta derivative 4c were
separated by chromatography. To compare the biological
activities of the macrocyclic taxoids with their open-
chain precursors, compounds 5b-d were also subjected
to HF/pyridine deprotection to afford 10b-d in good
yields (Scheme 2).
Results and Discussion
Biological Evaluation. Macrocyclic taxoids 4a-d
and their acyclic analogues 10b-d were evaluated for
their inhibition of cold-induced microtubule disassem-
bly28 and for their cytotoxicity against the KB cell line29
(Table 2). Though less cytotoxic than docetaxel, these
novel macrocyclic taxoids 4a-d show a significant
activity against KB cell line with a marked increased
cytotoxicity compared to our former aliphatic series 3
(from 10 to 100-fold). Thus, addition of an aromatic ring
at the C2-position is beneficial to activity. This effect is
much more pronounced in the acyclic series where
compounds 10b-d are at least 10-fold more cytotoxic
than their macrocyclic analogues. It is to be noted that
the ortho-substituted compound 10d is only one log less
potent than docetaxel on KB cell line and more active
than the meta derivative 10c, contrary to what have
Table 2. Biological Activities of Compounds 4a-d and 10b-d Compared with Docetaxel 1b and Compound 3b(E)
cytotoxicity against cancer cell lines,
IC50b (µM)
ring
size
microtubule disassembly inhibitory activity
IC50/IC50(paclitaxel)a
compd
n
subst
KB
HCT 116
MCF 7
1b
-
-
-
0.5
0.0003
1.6
0.0022
0.001
4a
3
4
4
4
4
4
4
4
4
para
para
meta
meta
ortho
para
meta
ortho
-
22
23
22
22
21
-
inactive
-
-
4b
inactive
0.28
0.07
0.2
-
-
4c(E)
4c(Z)
4d
1
0.7
8
0.35
>10
2.1
-
1.4
6
0.7
2.4
-
-
0.012
>10
10b
10c
10d
3a(E)
inactive
0.04
0.014
0.0032
8
-
-
22
1
1.2
7.3
-
0.009
>10
a IC50 is the concentration that inhibits 50% of the rate of microtubule disassembly. The ratio IC50/IC50(paclitaxel) gives the activity
with respect to paclitaxel. IC50(paclitaxel) ) 1 µM. b IC50 measures the drug concentration required for the inhibition of 50% cell proliferation
after 72 h of incubation.

5940 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24
Querolle et al.
Figure 3. (a) Superimposition of the nonpolar form of docetaxel (yellow), T-shaped paclitaxel (magenta), and some representative
conformers (cyan) of a) 4c(E), (b) 4d(E) and (c) 4b(E).
but deprived of any interaction with tubulin.16a,32 The
compounds bearing such biological behavior may be
transformed in the cell to more active derivatives either
by hydrolysis of esters in the case of 7-, 9-, or 10-
substituted derivatives32b,c or by biotransformation into
active metabolites. However, these explanations are not
appropriate for the para derivatives 4a,b and 10b and
another mechanism of action must be hypothesized for
these compounds. This would deserve further investiga-
tion and 10b is a good candidate for this study due to
its high cytotoxicity.
Compound 4c(E) is the most active derivative on cold-
induced microtubule disassembly and the first C2-C3′-
linked macrocyclic taxoid equipotent to paclitaxel in this
assay. It is to be noted that this macrocyclic compound
bears the same activity as its acyclic precursor 10c,
proving that the presence of the N3′-C2 tether is not
detrimental to activity and suggesting that the confor-
mational lock induced by the presence of the macrocycle
mimics the bioactive conformation. But, if it is so,
compound 4c(E) should have been more potent than
docetaxel because of the favorable entropic factor
achieved by cyclization. However, the entropic gain may
not be so important because of the presence of many
other easily rotated single bonds in that compound, and
the absence of an increased activity may be due to
unfavorable interactions with the protein. To get further
information, we have studied more extensively the
conformational behavior in solution and in the tubulin
binding site of these derivatives.
Conformational Studies. Compounds 4b, 4c(E),
and 4d were subjected to conformational analysis by
NMR and molecular modeling. As previously reported,16b
the H2′/H3′coupling constant gives a good indication of
the major form present in solution, a low value (<3 Hz)
revealing a major “nonpolar” conformation, whereas a
higher value is the sign of a major “polar” form (>6 Hz).
Unconstrained taxoids show a small JH2′/H3′ (<2 Hz) in
CDCl3 and a larger value (6-8 Hz) in DMSO-d6.33 For
compound 3a, the H2′/H3′ coupling constant was small
in both polar and apolar solvent (<1.5 and 2.5 Hz,
respectively), suggesting a real restricted conformation
with a major “nonpolar” form. For compounds 4b, 4c-
(E), and 4d the coupling constant is still <1.5 Hz in
CDCl3 and it slightly increases to 2, 3.5, and 3 Hz,
respectively, in DMSO-d6. Thus, the conformational
constraint on the C13 side chain has been really
achieved but it is slightly weaker for compounds 4c(E)
and 4d than for 3a and 4b. NMR conformational
analysis (NOESY and ROESY) in polar (DMSO-d6) and
apolar (CDCl3) solvents showed an intense nuclear
Overhauser effect (NOE) between 2′-H and 3′-H, char-
acteristic of a gauche interaction between these two
protons. Other NOE connectivity patterns were very
similar for the three compounds with a slight difference
for 4b that showed strong NOE between 3′-Ph and
4-OAc that was not detected for the two other deriva-
tives and inversely did not exhibit 2′-H/4-OAc NOE
whereas they are present in the spectra of the two other
compounds. Contrary to 4b, 4c(E), and 4d, both con-
nectivities (2′-H/4-OAc and 3′-Ph/4-OAc) were observed
for docetaxel in apolar solvent, suggesting that the
major solution conformation of 4b, 4c(E), and 4d is
somewhat different from the “nonpolar” form.
Molecular dynamic modeling studies were performed
on compounds 4b-d(E) in two different media (vacuum
or H2O) using Sybyl 6.8 software and MMFF94 force
field. For each compound, conformational searching
produced a great number of conformers, and only the
conformers with a trans lactam function have been
considered. No significant differences were observed
between the two media. For the ortho derivative 4d, all
the conformers adopt closely related forms situated
between the “nonpolar” and the “T-shaped” conforma-
tions, the latter being the most frequent (Figure 3b).
For the para compound 4b, two sets of conformers have
been observed, the major one is very similar to that of
the ortho derivative, and the other group bears the 3′-
phenyl group on the other side of the median plane of
the molecule (Figure 3c).
Finally the conformers obtained for the meta deriva-
tive 4c can be classified in three families, two of which
are similar to the para population, and a third group
where the 3′-phenyl group lies in the median plane of
the molecule. It is to be noted that when the phenyl
group lies on the upper side of the macrocycle, it is
located near the benzamide moiety of the T-shaped
paclitaxel (Figure 3a).
Docking experiments of the most representative con-
formers of each compound in the refined model of Râ-
tubulin11 have been realized. None of the 4b conformers
were able to fit the â-tubulin binding pocket. For the
ortho derivative 4d, only “T-shaped” conformers have
led to a good interaction with the binding site, and

Docetaxel Analogues with High Tubulin Activity
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24 5941
Figure 4. (a) Superimposition of two conformers of compound 4c(E) (yellow and magenta) with “T-shaped” paclitaxel (cyan). (b)
The two conformers of compound 4c(E) (yellow and magenta) bound to â-tubulin in globular form (cyan) with π-stacking with
His 229 (green).
finally for the meta compound 4c, two sets of conformers
gave satisfactory docking with the â-tubulin binding site
(Figure 4b). For these conformers, the 3′-phenyl group
occupies either the binding area of the 3′-phenyl or of
the 3′-benzamide, allowing both conformers to be con-
sidered as “T-shaped” forms (Figure 4a).
On these docking models, the binding on â-tubulin is
favored by a π-stacking interaction between the imida-
zolyl moiety of His 229 and the phenyl ring of the
benzoate. This interaction has been depicted in the
model of paclitaxel bound to â-tubulin.11 It should be
mentioned that none of the conformers that resemble
the “nonpolar” form were able to dock in the â-tubulin
binding site.
interaction with the â-tubulin binding pocket for the
ortho- and meta-substituted compounds. The observa-
tion of a possible π-stacking interaction between the
His229-imidazolyl and C2-benzoyl rings as seen with
paclitaxel may explain the increased activity of this
series compared to the former aliphatic ones 2 and 3.
The better docking of “T-shaped” conformers of 4c or
4d with tubulin supports the hypothesis of a “T-shaped”
bioactive conformation of taxoids as suggested by Sny-
der et al.11
Thus two different series of macrocyclic taxoids which
mainly adopt the “T-shaped” form, bearing a tether
either between the C4-acetate and the C3′-phenyl
moiety18 or between the C2-benzoate and the C3′-amine,
have led to the same conclusion on the bioactive
conformation of taxoids. Though these experiments are
based on a 3.5 Å refined structure of tubulin, both
results present evidence of a “T-shaped” conformation
of taxoids when they are bound to microtubules.
It would have been expected that our new macrocyclic
derivatives would be more active than docetaxel if they
mimic the bioactive conformation. However, since our
tether was essentially designed to well-orientate the
different substituents of the C13 side chain, these
compounds keep a relative flexibility that may coun-
terbalance the favorable entropic factor achieved by
cyclization. It should also be noted that the difficulty
with C2,C3′-linked taxoids was to find the right tether
that still allows π-stacking between the benzoate and
the His229 imidazole ring. This also may account for
the lower biological activity of our compounds compared
to the C4-C3′-linked taxoids.18 Even though our 22-
membered-ring macrocycle 4c(E) is at present the most
active compound in this series, the biological activity
may be most likely improved by making some modifica-
tions on the tether, what is under current investigation.
Summary and Conclusions
Seven novel taxoids bearing a C2-aroyl group have
been synthesized including four macrocyclic derivatives.
In agreement with previously reported data, para-
substituted compounds 4a,b and 10b were deprived of
any tubulin interaction. On the other hand, the four
other compounds 4c,d and 10c,d show increased activ-
ity on cold-induced microtubule disassembly compared
to the aliphatic series 2 and 3. Thus, as expected,
introduction of an aromatic ring in the C2-position as
in docetaxel greatly increased tubulin interaction. The
most active derivative, the meta-substituted macrocyclic
taxoid 4c, is equipotent to paclitaxel and to its acyclic
analogue 10c on microtubule stabilization. Though 4c
is less cytotoxic than docetaxel, it is one of the most
potent C2-C3′-linked macrocyclic taxoids so far de-
scribed in the literature with submicromolar IC50 values
on three different cell lines. Examination of the confor-
mational behavior of the macrocyclic taxoids 4b-d has
shown that these compounds, though relatively con-
strained, can adopt several conformations, most of them
being situated between the “nonpolar” and the “T-
shaped” conformations.
Experimental Section
The results obtained from docking experiments are
in good agreement with the biological results, i.e.
inactivity of the para-substituted derivatives and a good
General. 1H and 13C NMR spectra were recorded on a
Bruker AC 300 or AV 300 spectrometer. NOESY and ROESY
spectra have been performed on a Bruker AMX 400 spectro-

5942 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24
Querolle et al.
meter. Chemical shifts are given as δ values and are referenced
to the residual solvent proton or carbon peak, i.e., chloroform
(C1HCl3 ) 7.27 ppm and 13CHCl3 ) 77.14 ppm). The spectra
were fully assigned using COSY, HMQC, and HMBC on a
Bruker AV 300. Mass spectra were obtained on an AQA
Navigator ThermoQuest. High-resolution mass spectra were
performed on a Voyager-, DE STR (PerSeptive Biosystems)
with gentisic acid as matrix and paclitaxel and docetaxel as
internal standards. Merck silica gel 60 (230-400 mesh) was
used for the flash chromatography purification of some com-
pounds. All chemicals were purchased from Fluka, Aldrich,
or Acros and were used without further purification unless
indicated otherwise. Solvents were purchased from SDS.
Toluene and THF were dried and distilled before use. Standard
workup means extraction with a suitable solvent (EtOAc
unless otherwise specified), washing the extract with H2O or
brine, drying over Na2SO4, and evaporation under reduced
pressure. Docetaxel 1b was a gift from Dr. Alain Commerc¸on
(Aventis-Pharma), and compound 6 has been prepared accord-
ing to the previously described procedure.16a Microtubular
proteins were purified from mammalian brain as previously
described.34 Cytotoxicity and microtubule disassembly inhibi-
tion were carried out according to established literature
protocols.28,29
Synthesis of 2-Debenzoyl-2′-O-tert-butyldimethylsilyl-
3′-de-tert-butoxycarbonyl-3′-hex-5-enoyl-7,10-ditriethyl-
silyldocetaxel (7a). Hex-5-enoic acid (6.3 µL, 0.08 mmol, 1.5
equiv) was added to a solution of 6 (50 mg, 0.053 mmol), 1-(3-
dimethylaminopropyl)-3-ethylcarbodiimide (15.2 mg, 0.11 mmol,
1.5 equiv) and DMAP (13 mg, 0.106 mmol, 2 equiv) in CH2Cl2
(0.5 mL). The reaction mixture was stirred at room tempera-
ture for 3 h and then concentrated in vacuo. After standard
workup, the residue was purified by flash chromatography
(CH2Cl2/MeOH, 95/5) to afford pure 2-debenzoyl-2′-O-tert-
butyldimethylsilyl-3′-de-tert-butoxycarbonyl-3′-hex-5-enoyl-
7,10-ditriethylsilyldocetaxel 7a (43.5 mg, 79%) as a white
amorphous solid. 1H NMR (300 MHz, CDCl3) δ ) -0.28 (s, 3H),
-0.07 (s, 3H), 0.49-0.70 (m, 12H), 0.77 (s, 9H), 0.93-1.01 (m,
18H), 1.08 (s, 3H), 1.20 (s, 3H), 1.55 (s, 3H), 1.67-1.78 (m,
2H), 1.78 (s, 3H), 1.83-2.01 (m, 1H), 2.02-2.18 (m, 4H), 2.21-
diluted with EtOAc and filtered over Celite. After standard
workup, the residue was purified by flash chromatography
(heptane/CH2Cl2, 70/30) to afford pure ethyl 3-allylbenzoate
(1.6 g, 77%) as a yellow-brown oil. Analytical data are in
agreement with the literature.21b
(c) 3-Allylbenzoic acid (8m). To an aqueous solution of
sodium hydroxide (2 M, 75 mL) was added an ethanolic
solution of ethyl 3-allylbenzoate (55 mM, 150 mL, 8.2 mmol).
The solution was stirred at room temperature for 3 h, and the
reaction was stopped by addition of an excess of 1 N HCl. After
removal of ethanol, the aqueous layer was extracted three
times with EtOAc. The organic layer was concentrated in
vacuo, and the residue was purified by flash chromatography
(CH2Cl2/MeOH, 97/3) to afford 3-allylbenzoic acid (1.1 g, 83%)
1
as a white amorphous solid. H NMR (300 MHz, CDCl3) δ )
3
3.44 (d, JH,H ) 6.5 Hz, 2 H), 5.03-5.17 (m, 2H), 5.85-6.07
(m, 1H), 7.35-7.50 (m, 2H), 7.87-8.02 (m, 2H).13C NMR (75
MHz, CDCl3) δ ) 39.9, 116.6, 128.2, 128.6, 129.5, 130.3, 134.2,
136.7, 140.6, 172.8. MS (EI): m/z 162 [M•].
In the same manner, 2- and 4-allylbenzoic acids (8o and
8p, respectively) were synthesized (see Supporting Informa-
tion).
General Procedure for the Synthesis of 2-Allylben-
zoyl-2′-O-tert-butyldimethylsilyl-3′-de-tert-butoxycarbo-
nyl-3′-alkenoyl-7,10-ditriethylsilyldocetaxel (5a-d). A
typical procedure is described for the synthesis of 2-m-
allylbenzoyl-2′-O-tert-butyldimethylsilyl-3′-de-tert-butoxycar-
bonyl-3′-heptenoyl-7,10-ditriethylsilyldocetaxel (5c). A solution
of taxoid 7b (100 mg, 0.095 mmol), DCC (577 mg, 2.8 mmol,
30 equiv), and DMAP (11.6 mg, 0.095 mmol, 1 equiv) in
anhydrous toluene (0.4 mL) was stirred at 60 °C for 15 min
before adding 3-allylbenzoic acid 8m (460 mg, 2.8 mmol, 30
equiv). The solution was stirred at 60 °C for 24 h and then
filtered through a Celite/silica gel (1/1) column in EtOAc/
heptane (3/7) and concentrated in vacuo. After standard
workup, the residue was purified by flash chromatography
(heptane/acetone, 92/8 then heptane/acetone, 90/10) to afford
pure 5c (70.8 mg, 62%) as a white amorphous solid: 1H NMR
(300 MHz, CDCl3) δ ) -0.27 (s, 3H), -0.10 (s, 3H), 0.50-0.74
(m, 12H), 0.79 (s, 9H), 0.89-1.09 (m, 18H), 1.24 (s, 6H), 1.29-
1.47 (m, 2H), 1.51-1.65 (m, 2H), 1.69 (s, 3H), 1.86 (s, 3H),
1.86-2.06 (m, 3H), 2.08-2.22 (m, 1H), 2.22-2.30 (m, 2H),
2.32-2.46 (m, 1H), 2.50-2.62 (m, 1H), 2.53 (s, 3H), 3.46 (d,
3JH,H ) 6.5 Hz, 2H), 3.86 (d, 3JH,H ) 7.0 Hz, 1H), 4.20 and 4.30
2.33 (m, 2H), 2.37 (s, 3H), 2.42-2.59 (m, 1H), 3.49 (d, 3JH,H
)
)
3
3
6.5 Hz, 1H), 3.94 (br d, JH,H ) 6.5 Hz, 1H), 4.34 (dd, JH,H
10.5 Hz and 3JH,H ) 6.5 Hz, 1H), 4.49 (br s, 1H), 4.63 and 4.69
(qAB, 3JH,H ) 9.5 Hz, 2H), 4.92 (d, 3JH,H ) 8.5 Hz, 1H), 4.99-
3
5.12 (m, 3H), 5.55 (br d, JH,H ) 9.5 Hz, 1H), 5.67-5.85 (m,
2
3
3
(qAB, JH,H ) 8.5 Hz, 2H), 4.41 (dd, JH,H ) 6.5 Hz and J′H,H
) 11.0 Hz, 1H), 4.56 (br s, 1H), 4.84-5.01 (m, 3H), 5.03-5.22
1H), 6.18 (t, 3JH,H ) 9.0 Hz, 1 H), 6.38 (d, 3JH,H ) 9.5 Hz, 1H),
7.12-7.40 (m, 5H).13C NMR (75 MHz, CDCl3) δ ) -5.8, -5.2,
5.4, 6.1, 7.0, 10.8, 13.7, 18.3, 21.0, 23.4, 25.0, 25.6, 26.5, 33.0,
35,8, 36.0, 37.6, 43.2, 47.0, 54.8, 58.4, 72.4, 72.9, 74.2, 75.1,
75.6, 78.2, 78.6, 82.6, 84.0, 115.8, 126.5, 128.0, 128.7, 133.7,
137.7, 138.0, 138.5, 170.0, 171.6, 172.9, 206.3. MS (ESI+): m/z
1064 [M + Na+].
3
(m, 2H), 5.30 (s, 1H), 5.68 (br d, JH,H ) 9.0 Hz, 1H), 5.64-
5.82 (m, 2H), 5.88-6.04 (m, 1H), 6.22 (t, 3JH,H ) 9.0 Hz, 1 H),
3
6.34 (d, JH,H ) 9.0 Hz, 1H), 7.20-7.48 (m, 7H), 7.96 (br s,
2H). 13C NMR (62.5 MHz, CDCl3) δ ) -5.6, -5.3, 5.4, 6.1, 7.0,
10.6, 13.9, 18.3, 20.9, 23.3, 25.2, 25.6, 26.7, 28.4, 33.4, 35.6,
36.4, 37.5, 40.0, 43.4, 46.7, 55.2, 58.5, 71.9, 72.8, 75.2, 75.4,
76.9, 78.8, 81.4, 84.1, 114.7, 116.6, 126.6, 127.9, 128.1, 128.7,
128.8, 129.5, 130.5, 133.4, 134.2, 136.8, 138.0, 138.5, 138.7,
140.6, 167.1, 170.2, 171.7, 172.2, 205.4. MS (ESI+): m/z 1222
[M + Na+].
Synthesis of compound 7b is described in ref 16b.
General Procedure for the Synthesis of Allylbenzoic
Acids (8). A typical procedure is described for the synthesis
of 3-allylbenzoic acid.
Compounds 5a,b,d were prepared according to this method.
For experimental details and spectral data, see the Supporting
Information.
(a) Ethyl 3-Iodobenzoate. To a solution of 3-iodobenzoic
acid (5 g, 20 mmol) in ethanol (50 mL) was added dropwise
thionyl chloride (2.93 mL, 40 mmol, 2 equiv). The solution was
heated at 60 °C for 4 h, and the reaction mixture was
concentrated in vacuo. After standard workup, the residue was
purified by flash chromatography (heptane/CH2Cl2, 70/30) to
afford pure ethyl 3-iodobenzoate (5.2 g, 93%) as a yellow oil.
Proton NMR and mass spectrometry data are in agreement
with the literature.34 13C NMR (75 MHz, CDCl3) δ )14.4, 61.4,
93.9, 129.8, 130.1, 132.4, 138.5, 141.6, 165.1.
(b) Ethyl 3-Allylbenzoate. To a solution of ethyl 3-iodo-
benzoate (3 g, 10.8 mmol) in dry THF (114 mL) cooled to -40
°C was added dropwise isopropylmagnesium chloride (2 M in
THF, 8.1 mL, 1.5 equiv). The reaction mixture was stirred at
-40 °C for 1 h before adding a daily prepared CuCN, 2LiCl
solution in THF (0.34 M, 32 mL, 10.8 mmol, 1 equiv) followed,
after a further 15 min, by allyl bromide (3.8 mL, 43.2 mmol,
4 equiv). After being stirred for 1 h, the reaction mixture was
General Procedure for the Synthesis of Macrocyclic
Taxoids 9 by Ring-Closure Metathesis. A typical procedure
is described for the synthesis of macrocyclic taxoid 9c. To a
solution of taxoid 5c (69.7 mg, 0.058 mmol) in CH2Cl2 (4 mL)
was added dropwise a solution of bis(tricyclohexylphosphine)-
benzylideneruthenium(IV) dichloride (2.9 mg, 0.0035 mmol)
in CH2Cl2 (1.6 mL). The solution was refluxed for 3 h and
concentrated in vacuo. After standard workup, the residue was
purified by silica gel chromatography (EtOAc/heptane, 75/35)
to afford an inseparable E/Z mixture (65/35) of pure 9c (40.5
mg, 60%) as a white amorphous solid.
9c: 1H NMR (300 MHz, CDCl3) δ ) -0.32 (s, 3H), -0.07 (s,
3H), 0.53-0.79 (m, 21H), 0.90-1.09 (m, 18H), 1.25 (s, 3H), 1.28
(s, 3H), 1.28-1.36 (m, 2H), 1.56-1.76 (m, 2H), 1.70 (s, 3H),
1.81-1.91 (m, 1H), 1.92 (s, 3H), 1.93-2.12 (m, 2H), 2.12-2.42

Docetaxel Analogues with High Tubulin Activity
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24 5943
(m, 4H), 2.48-2.60 (m, 1H), 2.60 (s, 3H), 3.23-3.50 (m, 2H),
3.78-3.91 (m, 1H), 4.14-4.35 (m, 2H), 4.35-4.48 (m, 1H),
4.53-4.64 (br s, 1H), 4.85-4.95 (m, 1H), 5.10-5.55 (m, 2H),
were analyzed using Sybyl 6.8 software, and superimposition
of conformers was based on the backbone atoms of the taxane
core.
Docking experiments on compounds 4b-d-E were realized
using the DOCK software of Sybyl 6.8 with Tripos force field
for minimization.
3
3
5.56-5.85 (m, 3H), 6.24 (d, JH,H ) 9.0 Hz, 1H), 6.40 (t, JH,H
) 9.0 Hz, 1H), 7.22-7.49 (m, 7H), 7.82-8.10 (m, 2H). 13C NMR
(75 MHz, CDCl3) δ (E-isomer) ) -5.9-5.2, 5.4, 6.1, 7.0, 7.1,
10.7, 14.1, 18.3, 21.2, 22.8, 23.3, 25.6, 26.8, 27.1, 30.1, 34.8,
35.7, 37.6, 39.4, 43.5, 47.8, 54.7, 58.7, 70.9, 73.0, 75.2, 75.4,
75.6, 77.0, 79.2, 81.3, 84.3, 126.6, 127.7, 128.7, 129.7, 130.1,
130.5, 133.7, 134.4, 137.7, 138.8, 141.7, 167.6, 171.1, 171.4,
172.2, 205.5. Modifications for the 13C NMR chemical shifts
for the Z-isomer: δ (δ E-isomer) ) 32.3 (39.4), 132.4, 132.6
(130.1, 130.5), 142.8 (141.7). MS (ESI+): m/z 1194 [M + Na+].
Acknowledgment. The authors thank Dr Alain
Commerc¸on (Aventis-Pharma) for a gift of docetaxel.
Christiane Gaspard and Je´roˆme Bignon are acknowl-
edged for cytotoxicity evaluations, Jean-Franc¸ois Gal-
lard and Marie-The´re`se Martin for performing NMR
spectra, and Vincent Gue´rineau for high-resolution
mass spectra.
In the same manner, 9a,b,d were synthesized, see the
Supporting Information
General Procedure for Removal of the Silyl Protect-
ing Groups. A typical procedure is described for the synthesis
of macrocyclic taxoid 4c. To a cooled solution of 9c (25 mg,
0.021 mmol) in pyridine-acetonitrile (7/93, 0.825 mL) was
added dropwise HF/pyridine (70%, 120 µL, 0.85 mmol, 40
equiv) at 0 °C. The solution was stirred for 1 h at 0 °C and
then warmed to room temperature and stirred for additional
6 h at room temperature. The reaction was quenched by
addition of saturated aqueous sodium hydrogenocarbonate (50
mL), and the aqueous layer was extracted three times with
EtOAc (50 mL). After standard workup the crude residue was
purified by silica gel chromatography (CH2Cl2/MeOH, 93/7) to
afford pure 4c-Z (4.3 mg, 24%) and 4c-E (8.9 mg, 50%) as white
amorphous solids.
Supporting Information Available: Experimental de-
tails and characterization data for new compounds 4a,b,d,
5a,b,d, 8p,o, 10b-d, and 11a,b,d. This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(1) Wani, M. C.; Taylor, H. L.; Wall, M. E.; Coggon, P.; McPhail, A.
T. Plant Antitumor Agents VI. The Isolation and Structure of
Taxol, a Novel Antileukemic and Antitumor Agent from Taxus
brevifolia. J. Am. Chem. Soc. 1971, 93, 2325-2327.
(2) Colin, M.; Gue´nard, D.; Gue´ritte-Voegelein, F.; Potier, P. Prepa-
ration of Taxol Derivatives as Antitumor Agents. Eur. Pat.Ap-
pl.EP 253,738 (Cl.C07D305/14), 20 Jan 1988, FR Appl.86/10,400,
17 Jul 1986; Chem. Abstr. 1988, 109, 22762w.
(3) (a) Gue´nard, D.; Gue´ritte-Voegelein, F.; Lavelle, F. Taxoids: A
New Class of Antimitotic Compounds. Curr. Pharm. Des. 1995,
1, 95-112. (b) Baloglu, E.; Kingston, D. G. I. The Taxane
Diterpenoids. J. Nat. Prod. 1999, 62, 1448-1472. (c) Taxus: The
Genus Taxus; Itokawa, H., Lee, K.-H., Eds.; Taylor & Francis
Ltd.: London, 2003.
(4) Schiff, P. B.; Fant, J.; Horwitz, S. B. Promotion of Microtubule
Assembly in vitro by Taxol. Nature 1979, 277, 665-667.
(5) Nogales, E.; Wolff, S. G.; Downing, K. H. Structure of the Râ
Tubulin Dimer by Electron Crystallography. Nature (London)
1998, 391, 199-202.
(6) (a) Rao, S.; Horwitz, S. B.; Ringel, I. Direct Photoaffinity Labeling
of Tubulin with Taxol. J. Natl. Cancer Inst. 1992, 84, 785-788.
(b) Rao, S.; Krauss, N. E.; Heerding, J. M.; Swindell, C. S.;
Ringel, I.; Orr, G. A.; Horwitz, S. B. 3′-(p-Azidobenzamido)taxol
Photolabels the N-Terminal 31 Amino Acids of â-Tubulin. J.
Biol. Chem. 1994, 269, 3132-3134. (c) Dasgupta, D.; Park,;
Harriman, G. C. B.; Georg, G. I.; Himes, R. Synthesis of a
Photoaffinity Taxol Analogue and its Use in Labeling Tubulin.
J. Med. Chem. 1994, 37, 2976-2980. (d) Combeau, C.; Commer-
c¸on, A.; Mioskowski, C.; Rousseau, B.; Aubert, F.; Goeldner, M.
Predominant Labeling of â- over R-Tubulin from Porcine Brain
by a Photoactivable Taxoid Derivative. Biochemistry 1994, 33,
6676-6683. (e) Rao, S.; Orr, G. A.; Chaudhary, A. G.; Kingston,
D. G. I.; Horwitz, S. B. Characterization of the Taxol Binding
Site on the Microtubule. J. Biol. Chem. 1995, 270, 20235-20238.
(f) Loeb, C.; Combeau, C.; Shret-Sabatier, L.; Breton-Gilet, A.;
Faucher, D.; Rousseau, B.; Commerc¸on, A.; Goeldner, M. [3H]
(Azidophenyl)ureido Taxoid Photolabels Peptide Amino Acid
281-304 of R-Tubulin. Biochemistry 1997, 36, 3820-3825.
(7) Mastropaolo, D.; Camerman, A.; Luo, Y.; Brayer, G. D.; Cam-
erman, N. Crystal and Molecular Structure of Paclitaxel (Taxol).
Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 6920-6924.
(8) (a) Vander Velde, D. G.; Georg, G. I.; Grunewald, G. L.; Gunn,
C. W. Mitscher, L. A. A “Hydrophobic Collapse” of Taxol and
Taxotere Solution Conformations in Mixture of Water and
Organis Solvent. J. Am. Chem. Soc. 1993, 115, 11650-11651.
(b) Williams, H. J.; Scott, A. I.; Dieden, R. A.; Swindell, C. S.;
Chirlian, L. E.; Francl, M. M.; Heerding, J. M.; Krausss, N. E.
NMR and Molecular Modelling Study of the Conformation of
Taxol and its Side Chain Methyl Ester in Aqueous and Non-
Aqueous Solution. Tetrahedron 1993, 49, 6545-6560.
4c-E: 1H NMR (300 MHz, CDCl3) δ ) 1.14 (s, 3H), 1.27 (s,
3H), 1.27-1.43 (m, 2H), 1.51-1.65 (m, 2H), 1.78 (s, 3H), 1.88
(s, 3H), 1.88-2.10 (m, 3H), 2.13-2.38 (m, 4H), 2.48 (s, 3H),
3
2.53-2.69 (m, 1H), 3.13 (br s, 1H), 3.38 (d, JH,H ) 5.5 Hz,
3
2H), 3.91 (d, JH,H ) 7.0 Hz, 1H), 4.15-4.30 (m, 2H), 4.34 (d,
3
3JH,H ) 8.5 Hz, 1H), 4.67 (br.s, 1H), 4.94 (d, JH,H ) 9.0 Hz,
1H), 5.18 (s, 1H), 5.24-5.37 (m, 2H), 5.62-5.83 (m, 3H), 6.24
(t, 3JH,H ) 9.0 Hz, 1H), 6.36 (d, 3JH,H ) 9.5 Hz, 1H), 7.30-7.47
(m, 7H), 7.85 (br s, 1H), 8.02 (s, 1H). 13C NMR (62.5 MHz,
CDCl3) δ ) 10.1, 14.6, 20.9, 22.6, 23.5, 26.8, 27.4, 30.8, 35.5,
36.2, 37.2, 39.8, 43.2, 46.5, 53.5, 57.7, 72.2, 72.4, 73.0, 74.5,
74.9, 76.6, 79.2, 81.1, 84.3, 127.1, 128.2, 128.7, 129.0, 129.7,
130.0, 130.8, 134.5, 136.1, 138.3, 141.5, 167.3, 170.7, 172.3,
172.8, 211.5. HRMS (MALDI-TOF): m/z calcd for C46H55-
NO13.Na+ 852.3571, found 852.3587 (∆ ) -1.9 ppm).
4c-Z: 1H NMR (300 MHz, CDCl3) δ ) 1.14 (s, 3H), 1.29 (s,
3H), 1.29-1.49 (m, 2H), 1.50-1.72 (m, 2H), 1.73-1.96 (m, 3H),
1.80 (s, 3H), 1.95 (s, 3H), 2.14-2.38 (m, 3H), 2.40-2.53 (m,
1H), 2.46 (s, 3H), 2.53-2.68 (m, 1H), 3.22 (br s, 1H), 3.35-
3.50 (m, 1H), 3.77-3.90 (m, 1H), 3.94 (d, 3JH,H ) 6.5 Hz, 1H),
3
4.17-4.40 (m, 3H), 4.74 (br.s, 1H), 4.92 (d, JH,H ) 10.0 Hz,
1H), 5.19 (s, 1H), 5.31 (s, 1H), 5.57-5.75 (m, 2H), 5.75-5.88
3
3
(m, 2H), 6.16 (d, JH,H ) 9.5 Hz, 1H), 6.43 (t, JH,H ) 9.0 Hz,
3
1H), 7.30-7.53 (m, 7H), 7.89 (d, JH,H ) 6.5 Hz, 1H), 8.07 (s,
1H). 13C NMR (62.5 MHz, CDCl3) δ ) 10.2, 14.4, 21.4, 22.9,
26.2, 26.7, 27.7, 29.7, 32.4, 35.5, 36.4, 37.0, 43.1, 46.4, 53.5,
57.6, 72.0, 72.4, 72.7, 74.4, 75.3, 77.3, 79.4, 81.0, 84.3, 126.8,
127.3, 128.1, 128.8, 129.4, 130.1, 132.4, 132.8, 135.9, 138.4,
142.1, 167.3, 170.8, 172.1, 173.2, 211.8. HRMS (MALDI-
TOF): m/z calcd for C46H55NO13.Na+ 852.3571, found 852.3556
(∆ ) 1.8 ppm).
In the same manner macrocylic taxoids 4a,b,d were syn-
thesized as the acyclic taxoids 10b-d. For experimental details
and spectral data see the Supporting Information.
Computational Procedures. All calculations were per-
formed on a SiliconGraphics Indigo2 Extreme workstation. All
modelizations were done using Sybyl 6.8 software. The MMFF94
force field was used for minimization and partial charge
calculations, a dielectric constant of 1.0 or 78 being employed.
In all cases A, B, C, and D rings of the taxoids were considered
as an aggregate. Compounds 4b-d were subjected to an
unrestrained molecular dynamics simulation at 1600 K for
20 000 fs. Conformations were sampled every 100 fs during
the simulation. Each of these conformers was minimized and
compared with others with a RMS of 0.3 Å. The structures
(9) Gue´ritte-Voegelein, F.; Gue´nard, D.;. Mangatal, L.; Potier, P.;
Guilhem, J.; Ce´sario, M.; Pascard, C. Structure of a Synthetic
Taxol Precursor: N-tert-Butoxycarbonyl-10-deacetyl-N-deben-
zoyltaxol. Acta Crystallogr. C 1990, 46, 781-784.
(10) Dubois, J.; Gue´nard, D.; Gue´ritte-Voegelein, F.; Guedira, N.;
Potier, P.; Gillet, B.; Beloeil, J.-C. Conformation of Taxotere and
Analogues Determined by NMR Spectroscopy and Molecular
Modeling Studies. Tetrahedron 1993, 49, 6533-6544.
(11) Snyder, J. P.; Nettles, J. H.; Cornett, B.; Downing, K. H.;
Nogales, E. The Binding Conformation of Taxol in â-Tubulin: A
Model Based on Electron Crystallographic Density. Proc. Natl.
Acad. Sci. U.S.A. 2001, 98, 5312-5316.

5944 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24
Querolle et al.
(12) Snyder, J. P.; Nevins, N.; Cicero, D. O.; Jansen, J. The Confor-
mation of Taxol in Chloroform. J. Am. Chem. Soc. 2000, 122,
724-725.
(23) Meyers, A. I.; Temple, D. L., Jr. Synthesis via 2-Oxazolines. III.
The Formation of Substituted Benzoic Acids or Esters Utilizing
the Grignard Reagent of 2-(bromophenyl)-2-oxazolines. J. Am.
Chem. Soc. 1970, 92, 6646-6647.
(24) Boymond, L.; Rottandler, M.; Cahiez, G.; Knochel, P. Preparation
of Highly Functionalized Grignard Reagents by a Iodine-
Magnesium Exchange Reaction and Its Application in Solid-
Phase Synthesis. Angew. Chem., Int. Ed. 1998, 37, 1701-1703.
(25) Chaudary, A. G.; Gharpure, M. M.; Rimoldi, J. M.; Chordia, M.
D.; Gunatilaka, A. A. L.; Kingston, D. G. I. Unexpected Facile
Hydrolysis of the 2-Benzoate Group of Taxol and Syntheses of
Analogues with Increased Activities. J. Am. Chem. Soc. 1994,
116, 4097-4098.
(26) Balcom, B. J.; Petersen, N. O. Solvent Dependence of Carboxylic
Acid Condensations with Dicyclohexylcarbodiimide. J. Org.
Chem. 1989, 54, 1922-1927.
(27) Grubbs, R. H.; Chang, S. Recent Advances in Olefin Metathesis
and its Application in Organic Synthesis. Tetrahedron 1998, 54,
4413-4450.
(28) Lataste, H.; Se´nihl, V.; Wright, M.; Gue´nard, D.; Potier, P.
Relationships between the Structures of Taxol and Baccatin III
Derivatives and their In Vitro Action on the Disassembly of
Mammalian Brain and Physarum Amoebal Microtubules. Proc.
Natl. Acad. Sci. U.S.A. 1984, 81, 4090-4094.
(29) Da Silva, A. D.; Machado, A. S.; Tempeˆte, C.; Robert-Gero, M.
Synthesis and Biological Activity of Methyl-D-Pyranoside De-
rivatives of Mercaptopurine and Mercaptopyrimidine. Eur. J.
Med. Chem. 1994, 29, 149-152.
(30) Kingston, D. G. I.; Chaudary, A. G.; Chordia, M. D.; Gharpure,
M. M.; Gunatilaka, A. A. L.; Higgs, P. I.; Rimoldi, J. M.; Samala,
L.; Jagtap, P. G.; Giannakakou, P.; Jiang, Y. Q.; Lin, C. M.;
Hamel, E.; Long, B. H.; Fairchild, C. R.; Johnston, K. A.
Synthesis and Biological Evaluation of 2-Acyl Analogues of
Paclitaxel (Taxol). J. Med. Chem. 1998, 41, 43715-3726.
(31) He, L.; Jagtap, G. P.; Kingston, D. G. I.; Shen, H. J.; Orr, G. A.;
Horwitz, S. B. A Common Pharmacophore for Taxol and the
Epothilones Based on the Biological Activity of a Taxol Molecule
Lacking a C-13 Side Chain. Biochemistry 2000, 39, 3972-3978.
(32) (a) Merckle´, L.; Dubois, J.; Place, E.; Thoret, S.; Gue´ritte, F.;
Gue´nard, D.; Poupat, C.; Ahond, A.; Potier, P. Semisynthesis of
D-Ring Modified Taxoids: Novel Thia Derivatives of Docetaxel.
J. Org. Chem. 2001, 66, 5058-5065. (b) Cheng, Q.; Oritani, T.;
Horiguchi, T.; Yamada, T.; Mong, Y. Synthesis and Biological
Evaluation of Novel 9-Functional Heterocyclic Coupled 7-Deoxy-
9-Dehydropaclitaxel Analogue. Bioorg. Med. Chem. Lett. 2000,
10, 517-521. (c) Gue´nard, D.; Thoret, S.; Dubois, J.; Adeline,
M.-T.; Wang, Q.; Gue´ritte, F. Effects of the Hydrophobicity of
Taxoids on their Interaction with Tubulin. Bioorg. Med. Chem.
2000, 8, 145-156.
(13) (a) Boge, T. C.; Wu, Z.-J.; Himes, R. H.; Vander Velde, D. G.;
Georg, G. I. Conformationally Restricted Paclitaxel Analogues:
Macrocyclic Mimics of the “Hydrophobic Collapse” Conformation.
Bioorg. Med. Chem. Lett. 1999, 9, 3047-3052. (b) Ojima, I.;
Chakravarty, S.; Inoue, T.; Lin, S.; He, L.; Horwitz, S. B.; Kuduk,
S. D.; Danishefsky, S. J. A Common Pharmacophore for Cyto-
toxic Natural Products that Stabilize Microtubules. Proc. Natl.
Acad. Sci. U.S.A. 1999, 96, 4256-4261. (c) Ojima, I.; Lin, S.;
Inoue, T.; Miller, M. L.; Borella, C. P.; Geng, X.; Walsh, J. J.
Macrocycle Formation by Ring-Closing Metathesis. Application
to the Syntheses of Novel Macrocyclic Taxoids. J. Am. Chem.
Soc. 2000, 122, 5343-5353.
(14) Barboni, L.; Lambertucci, C.; Appendino, G.; Vander Velde, D.
G.; Himes, R. H.; Bombardelli, E.; Wang, M.; Snyder, J. P.
Synthesis and NMR-Driven Conformational Analysis of Taxol
Analogues Conformationally Constrained on the C-13 Side
Chain. J. Med. Chem. 2001, 44, 1576-1587.
(15) Metaferia, B. B.; Hoch, J.; Glass, T. H.; Bane, S. L.; Chatterjee,
S. K.; Snyder, J. P.; Lakdawala, A.; Cornett, B., Kingston, D. G.
I. Synthesis and Biological Evaluation of Novel Macrocyclic
Paclitaxel Analogues. Org. Lett. 2001, 3, 2461-2464.
(16) (a) Querolle, O.; Dubois, J.; Thoret, S.; Dupont, C.; Gue´ritte, F.;
Gue´nard, D. Synthesis of Novel C-2,C-3′N-Linked Macrocyclic
Taxoids with variable Ring Size. Eur. J. Org. Chem. 2003, 542-
550. (b) Querolle, O.; Dubois, J.; Thoret, S.; Roussi, F.; Montiel-
Smith, S.; Gue´ritte, F.; Gue´nard, D. Synthesis of Novel Macro-
cyclic Docetaxel Analogues. Influence of Their Macrocyclic Ring
Size on Tubulin Activity. J. Med. Chem. 2003, 46, 3623-3630.
(17) (a) Ojima, I.; Geng, X.; Lin, S.; Pera, P.; Bernacki, R. J. Design
Synthesis and Biological Activity of Novel C2-C3′ N-Linked
Macrocyclic Taxoids. Bioorg. Med. Chem. Lett. 2002, 12, 349-
352. (b) Geng, X.; Miller, M. L.; Lin, S.; Ojima, I. Synthesis of
Novel C2-C3′N-Linked Macrocyclic Taxoids by Means of Highly
Regioselective Heck Macrocyclization. Org. Lett. 2003, 5, 3733-
3736.
(18) Ganesh, T.; Guza, R. C.; Bane, S.; Ravindra, R.; Shanker, N.;
Lakdawala, A. S.; Snyder, J. P.; Kingston, D. G. I. The Bioactive
Taxol Conformation on â-Tubulin: Experimental Evidence from
Highly Active Constrained Analogues. Proc. Natl. Acad. Sci.
U.S.A. 2004, 101, 10006-10011.
(19) Korte, D. E.; Hegedus, L. S.; Wirth, R. K. Synthesis of Isocou-
marins, Dihydroisocoumarins, and Isoquinolones via π-Allylnick-
el Halide and π-Olefin-Palladium Complexes. J. Org. Chem.
1977, 42, 1329-1336.
(20) Kondo, Y.; Fujinami, M.; Uchiyama, M.; Sakamoto, T. Lithium
Tri-tert-butylzincate as a Chemoselective Metallating Reagent
for Functionalized Organic Halides. J. Chem. Soc., Perkin Trans.
1 1997, 799-800.
(21) Lee, P. H.; Sung, S.; Lee, K. Palladium-Catalyzed Cross-Coupling
Reactions of in Situ Generated Allylindium Reagents with Aryl
Halides. Org. Lett. 2001, 3, 3201-3204.
(33) Jime´nez-Barbero, J.; Amat-Guerri, F.; Snyder, J. P. The Solid
State, Solution and Tubulin-Bound Conformations of Agents that
Promote Microtubule Stabilization Curr. Med. Chem. - Anti-
Cancer Agents 2002, 2, 91-122.
(22) (a) Gomes, P.; Gosmini, C.; Pe´richon, J. Cobalt-Catalyzed Direct
Electrochemical Cross-Coupling between Aryl or Heteroaryl
Halides and Allylic Acetates or Carbonates. J. Org. Chem. 2003,
68, 1142-1145. (b) Gomes, P.; Gosmini, C.; Pe´richon, J. New
Chemical Cross-Coupling between Aryl Halides and Allylic
Acetates Using a Cobalt Catalyst. Org. Lett. 2003, 5, 1043-1045.
(34) Dubois, J.; Le Goff, M.-T.; Gue´ritte-Voegelein, F.; Gue´nard, D.;
Tollon, Y.; Wright, M. Fluorescent and Biotinylated Analogues
of Docetaxel: Synthesis and Biological Evaluation. Bioorg. Med.
Chem. 1995, 3, 1357-1368.
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