Synthesis and structure-activity relationships of nonaromatic taxoids: Effects of alkyl and alkenyl ester groups on cytotoxicity

Article abstract of DOI:10.1021/jm9606711

Several new nonaromatic taxoids are synthesized by means of the β- lactam synthon method. These include taxoids modified with 3-methylbut-2- enoate, 3-methylbutanoate, and cyclohexanecarboxylate groups in place of the benzoate at the C-2 position. In addi

Full text of DOI:10.1021/jm9606711

J . Med. Chem. 1997, 40, 279-285
279
Syn th esis a n d Str u ctu r e-Activity Rela tion sh ip s of Non a r om a tic Ta xoid s:
Effects of Alk yl a n d Alk en yl Ester Gr ou p s on Cytotoxicity
,
†
†
‡
‡
‡
Iwao Ojima,* Scott D. Kuduk, Paula Pera, J ean M. Veith, and Ralph J . Bernacki
Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, and
Department of Experimental Therapeutics, Grace Cancer Drug Center, Roswell Park Cancer Institute,
Elm and Carlton Streets, Buffalo, New York 14263
X
Received September 26, 1996
Several new nonaromatic taxoids are synthesized by means of the â-lactam synthon method.
These include taxoids modified with 3-methylbut-2-enoate, 3-methylbutanoate, and cyclohex-
anecarboxylate groups in place of the benzoate at the C-2 position. In addition, taxoids with
2
-methylprop-1-enyl, 2-methylpropyl, (E)-prop-1-enyl, and cyclohexyl groups at the C-3′ position
are also prepared in combination with the modifications at C-2. The alkyl and alkenyl ester
groups at C-2 displayed pronounced effects on the in vitro cytotoxicity. Two of the fully aliphatic
taxoids possess similar or stronger activity than paclitaxel and docetaxel. It is clear that the
2
-benzoate does not play a unique role, and replacement with the appropriate alkyl and alkenyl
groups provides taxoids with equivalent or superior activity.
In tr od u ction
The naturally occurring antitumor agent paclitaxel1
exception that certain groups, such as thienyl, retained
comparable microtubule assembly properties. Notable
1
0
is the work of Nicolaou who prepared a series of aryl
and heteroaryl analogs as the C-2 position using a ring-
opening reaction of a protected 1,2-carbonate with
organolithium reagents. Once again moieties such as
furyl and thienyl exhibited similar activities to pacli-
taxel, while larger groups showed substantially de-
creased activities. Clearly the size of the aryl or
heteroaryl group at C-3′ and C-2 has prominent effects
on the biological activity of these taxoids.
has shown exceptional efficacy in cancer chemotherapy
and has been approved by the FDA for the treatment
of advanced ovarian cancer and breast cancer as of
December 1992 and April 1994, respectively. Doce-
2
taxel, a semisynthetic analog, has also exhibited sig-
nificant clinical distinction and was approved for the
treatment of breast cancer in May 1996 by the FDA.
These compounds possess a unique mechanism of action
as promoters of tubulin assembly and inhibitors of
microtubule disassembly.3
-5
Saturation of the phenyl rings at the C-3′ position and
However, despite their
1
1
the 2-benzoate has been investigated by us and
potent antitumor activity, these drugs often result in a
1
2,13
others.
In general it has been shown that a cyclo-
number of undesired side effects and are subject to
multidrug resistance (MDR).6 Thus, it is essential to
hexyl group at the C-3′ position or cyclohexanecarbonyl
group at C-2 exhibited weaker cytotoxicity in vitro while
little effect was observed on the tubulin binding ability.
develop new anticancer agents with fewer side effects,
improved pharmacological properties, and activity against
cancers not effectively treated by existing anticancer
drugs.
1
4,15
16,17
We
and others
have reported novel taxoids
containing alkyl and alkenyl groups at the C-3′ position
such as 2-methylprop-1-enyl, 2-methylpropyl, (E)-prop-
1
-enyl, and tert-butyl. These analogs have in most cases
shown superior activity compared to paclitaxel. More
importantly, we have recently reported C-10-modified
3
′-alkyl and 3′-alkenyl taxoids which exhibit exceptional
potency against multidrug resistant cell lines expressing
1
8
the MDR phenotype. However, the replacement of the
-benzoate with simple alkyl and alkenyl esters in
2
conjunction with modifications at the C-3′ position has
not been studied. We report here the synthesis of new
taxoids replacing all phenyl groups of paclitaxel and
docetaxel by alkyl and alkenyl groups and their effects
on cytotoxicity.
Several structure-activity relationship studies have
looked at the effects of the 3′-phenyl and the 2-benzoate
moieties on the biological activity of paclitaxel and its
7
analogs. Multiple reports concerning substituted phen-
yl rings for both C-2 and C-3′ have appeared. With
Ta xoid Syn th esis
8
Alkyl and alkenyl groups such as 2-methylprop-1-
enyl, 2-methylpropyl, (E)-prop-1-enyl, and tert-butyl
were chosen for investigation in place of the phenyl at
the C-2 benzoate position. Several approaches reported
in the literature were attempted,
had its own drawback or was not compatible with our
goal of modifying both C-2 and C-3′ positions. After
these unsuccessful attempts, we decided to use a modi-
fied version of Chen′s method choosing to oxidize the
13-OH to give 13-oxo-7-TES-baccatin III (1) as shown
few exceptions many of these showed substantially
decreased activity. Heteroaromatic groups have also
been included at these positions. The Kansas group has
reported the preparation of several 2-O-heteroaromatic
replacements9 and found that they had detrimental
effects on the activities compared to paclitaxel, with the
7,10,13
but each approach
†
State University of New York at Stony Brook.
Roswell Park Cancer Institute.
Abstract published in Advance ACS Abstracts, J anuary 15, 1997.
1
3
‡
X
10
S0022-2623(96)00671-1 CCC: $14.00 © 1997 American Chemical Society

2
80 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3
Ojima et al.
in Scheme 1. The use of 1 serves as protection for the
C-13 position and also allows the esterification to
proceed under milder conditions as the 2-OH is more
exposed due to a conformational change in the baccatin
core resulting from oxidation of the C-13 position.
Acetylation of 10-deacetyl-13-oxo-7-TES-baccatin III
followed by reduction using Red-Al afforded a 75% yield
of 2. DCC coupling using 3 equiv of dimethylacrylic acid
furnished 3 in 92% yield, and subsequent NaBH4
reduction of the 13-ketone afforded 4a . Esterification
with other acids such as tiglic acid or pivalic acid did
not afford any reaction. Prolonged reaction times and
heating to 65 °C still gave no reaction. This is at-
tributed to the R-methyl substitution on these acids
showing the sensitive steric requirements at this posi-
tion. Hydrogenation of the olefin was carried out to
yield 4b in quantitative fashion using Pd/C in EtOAc
under 1 atm of H2. The 2-(cyclohexylcarbonyl)baccatin
Sch em e 1. Preparation of Baccatin 4
4
c was obtained via hydrogenation of 7-TES-baccatin
1
2
III using the literature procedure.
Coupling reactions were then carried out using meth-
1
9-21
odology developed independently by our group
and
Holton et al.22 Thus treatment of protected baccatins
4
a -c and enantiomerically pure (3R,4S)-1-t-Boc-3-
2
3,24
TIPSO-4-modified-azetidin-2-ones
(5a-d) using LiH-
lung carcinoma), HT-29 (colon carcinoma), MCF7 (mam-
mary carcinoma), and the drug resistant cell line
MCF7-R (mammarian carcinoma 180-fold resistant to
doxorubicin). Results are shown in Table 2 with the
values for paclitaxel, docetaxel, and SB-T-121214 shown
for comparison.
MDS in THF at -40 °C afforded 7-TES-2′-TIPS-
protected taxoids (eq 1). Deprotection using HF/
pyridine produced taxoids 7, 8, 10-12, 14, and 16 in
fair to good yields. Results are summarized in Table 1.
As Table 2 shows, several of the new taxoids exhibit
similar or enhanced activity compared to paclitaxel and
docetaxel. As previously reported, taxoids 7 and 9
bearing cyclohexanecarbonyl groups at the C-2 position
show diminished activity compared to paclitaxel and
docetaxel, particularly for 9. SB-T-1212 exhibits very
potent cytotoxicity, better than docetaxel, particularly
against MCF7 and MCF7-R cell lines. Taxoid 10
bearing 2-methylprop-1-enyl groups at both C-3′ and C-2
is more active than both paclitaxel and docetaxel
showing that a benzoate group at C-2 is not necessary
for strong cytotoxicity in lieu of the appropriate alkyl,
alkenyl, or cyclohexyl group. However, taxoids 11-13
bearing a combination of 2-methylprop-1-enyl and 2-
methylpropyl groups at C-3′ and C-2 were all less active
than 10, showing the considerable sensitivity for the
modification at these positions. It is apparent, however,
from 14-16 that in the case of the 2-cyclohexanecar-
bonyl taxoids, the C-3′ position exerts marked effects
on the activity. In fact, taxoid 14 shows better activity
than docetaxel, especially against the MCF7 and MCF7-R
cell lines. The 3′-(2-methylprop-1-enyl) taxoid 14 is
clearly the most potent of all analogs bearing a 2-cy-
clohexanecarbonyl group, with a significant increase in
activity as compared to 3′-((E)-prop-1-enyl) taxoid 16 as
well as 7 and 9.
Taxoid 9 was prepared in quantitative yield by
reduction of the 3′-phenyl ring of 7 with Pt/C in EtOAc
under 1 atm of H2 in EtOAc for 36 h. Similarly, taxoids
1
3 and 15 were prepared from 12 and 14 via hydroge-
nation over Pd/C under 1 atm of H2 in 24 h. Results
are summarized in eq 2.
While the size of the group at C-3′ exerts marked
effects on the cytotoxicity of the analog, the C-2 sub-
stituent has prominent effects on the biological activity
as well. Whereas a cyclohexanecarbonyl group at C-2
diminishes the activity, the placement of the proper
alkyl or alkenyl group at the C-3′ position brings about
an increase in activity comparable to that of docetaxel.
This is clearly seen from the results for compounds 14-
Biologica l Eva lu a tion of New Ta xoid s
The in vitro cytotoxicity of the new taxoids was
evaluated for potency against several human tumor cell
lines: A121 (ovarian carcinoma), A549 (non-small-cell

Synthesis and SAR of New Nonaromatic Taxoids
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3 281
Ta ble 1. Syntheses of Taxoids through Coupling and Deprotection
a
Isolated two-step yield for coupling and deprotection. b Deprotection was carried out using TBAF/HOAc in THF.
a
Ta ble 2. In Vitro Cytotoxicity (IC50, nM) of Modified Taxoids 7-16
a
The concentration of compound which inhibits 50% of the growth of human tumor cell line: A121 (ovarian carcinoma), A549 (non-
small-cell lung carcinoma), HT-29 (colon carcinoma), MCF7 (mammary carcinoma), and MCF7-R (mammarian carcinoma 180-fold resistant
3
0
to doxorubicin), after 72 h drug exposure.
1
6. A Chem 3D representation of taxoid 10 based on
restrained molecular dynamics is actively underway and
will be reported elsewhere.
2
5-27
the hydrophobic cluster model,
i.e., the dihedral
2
′
2′
3′
3′
angle of H -C -C -H is set to be 180° and energy
minimized, is shown in Figure 1. This conformation
indicates a very strong clustering of the 2-methylprop-
In summary, a series of taxoids with alkyl and alkenyl
modifications at both the C-2 and C-3′ positions have
been prepared and evaluated. It has been shown that
the phenyl of the C-2 benzoate can be replaced by
certain alkyl or alkenyl groups, such as 2-methylpro-
penyl in 10, with the taxoid exhibiting equivalent or
improved activity compared to paclitaxel.
1
-enyl groups at C-2 and C-3′ with the C-4 acetyl
methyl. It appears that a rigid moiety, such as a ring
or olefin, is required at the C-3′ and C-2 positions for
strong activity. When alkyl groups that can freely
rotate such as 2-methylpropyl are introduced at these
positions (taxoids 11-13), the activity is discernibly
reduced. The conformational analysis of these taxoids
based on NMR and molecular modeling including
Exp er im en ta l Section
Gen er a l Meth od s. Melting points were measured with a
Thomas Hoover capillary melting point apparatus and are

2
82 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3
Ojima et al.
2
-Deben zoyl-2-(3-m eth ylbu t-2-en oyl)-7-TES-baccatin III
(
4a ). Compound 3 (70 mg, 0.10 mmol) was dissolved in 4 mL
of MeOH, and 1 mL of THF and NaBH
4
(100 mg, 2.0 mmol)
were added in small portions at 0 °C. The reaction was kept
at 0 °C for 5 h and quenched by addition of 5 mL of saturated
aqueous NH
aqueous layer was extracted with 2 × 20 mL of CH
over MgSO , filtered, and concentrated. Silica gel chromatog-
raphy (hexane:EtOAc ) 2:1) afforded 17 mg (25%) of recovered
and 42 mg of 4a (60%, 80% based on 75% conversion) as a
4
Cl; the mixture was allowed to stir for 5 min. The
2
2
Cl , dried
4
3
1
white film: H NMR (250 MHz, CDCl
.84 (t, J ) 7.8 Hz, 9 H), 0.96 (s, 3 H), 1.08 (s, 3 H), 1.55 (s, 3
H), 1.87 (s, 3 H), 1.57-1.60 (m, 1 H), 2.08-2.12 (m, 1 H), 2.41-
3
) δ 0.48-0.51 (m, 6 H),
0
F igu r e 1. Chem 3D representation of taxoid 10.
2
.52 (m, 1 H), 3.68 (d, J ) 6.3 Hz, 1 H), 4.07 (d, J ) 8.4 Hz, 1
uncorrected. Infrared spectra were recorded on a Perkin-
Elmer Model 1600 FT-IR spectrophotometer with neat samples.
H), 4.36 (d, J ) 8.4 Hz, 1 H), 4.73 (bt, 1 H), 4.87 (d, J ) 9.3
1
13
Hz, 1 H), 5.30 (d, J ) 6.6 Hz, 1 H), 5.60 (bs, 1 H), 6.3 (bs, 1 H);
H, C, and 2D nuclear magnetic resonance (NMR) spectra
1
3
C NMR (63 MHz, CDCl ) δ 5.3, 6.7, 10.0, 14.9, 20.0, 22.7,
3
were measured using a General Electric QE-300 or a Bruker
AC-250 spectrometer using tetramethylsilane as the internal
standard. Optical rotations were measured with a Perkin-
Elmer Model 241 polarimeter. Thin layer chromatography
was performed on Merck DC-alufolien with Kieselgel 60F-254.
Column chromatography was carried out on silica gel 60 (230-
3
8
2
7.3, 38.2, 42.9, 47.4, 58.7, 68.0, 72.3, 73.1, 75.9, 78.3, 80.7,
4.3, 87.4, 103.0, 115.4, 132.7, 144.0, 160.0, 167.4, 169.4, 171.0,
02.4; FAB-HRMS (NBA-NaCl) m/ e 701.3329 (M + Na,
+
35
C H54NO11Si requires 701.3327).
2-Deben zoyl-2-(3-m eth ylbu ta n oyl)-7-TES-ba cca tin III
(4b). Compound 4a (21 mg, 0.031 mmol) was hydrogenated
under 1 atm of H in the presence of 20 mg of 10% Pd/C in 3
4
00 mesh ASTM, Merck). FAB-HRMS were performed at the
UCR Mass Spectrometry Facility, Riverside, CA.
2
Ma ter ia ls. The chemicals were purchased from Aldrich Co.
and Sigma and purified before use by standard methods. THF
was freshly distilled over sodium and benzophenone. 7-(Tri-
ethylsilyl)baccatin III (7-TES) was prepared by the literature
mL of EtOAc. After 22 h the reaction mixture was filtered
through a pipet column of silica gel (EtOAc) and concentrated
1
to afford 21 mg (100%) of 4b as a white film: H NMR (250
MHz, CDCl ) δ 0.52-0.61 (m, 6 H), 0.91 (t, J ) 7.9 Hz, 19 H),
3
2
8
method. (3R,4S)-3-[(Triisopropylsilyl)oxy]-4-(2-methylprop-
-enyl)-1-(tert-butoxycarbonyl)azetidin-2-ones 5 were prepared
0.94 (s, 3 H), 1.00 (d, J ) 3.5 Hz, 6 H), 1.12 (s, 3 H), 1.61 (s, 3
H), 1.78-1.91 (m, 1 H), 2.02-2.27 (m, 4 H), 2.15 (s, 3 H), 2.16
(s, 3 H), 2.45-2.57 (m, 1 H), 3.75 (d, J ) 6.7 Hz, 1 H), 4.15 (d,
J ) 7.9 Hz, 1 H), 4.44 (d, J ) 7.9 Hz, 1 H), 4.79 (bt, J ) 8.2
Hz, 1 H), 4.95 (d, J ) 8.9 Hz, 1 H), 5.46 (d, J ) 6.5 Hz, 1 H),
1
1
4
by literature procedures. 13-Oxo-7-TES-baccatin III (1) was
prepared by the literature method.
-Deben zoyl-13-oxo-7-TES-ba cca tin III (2). To a mix-
1
0
2
6.41 (s, 1 H); 13C NMR (63 MHz, CDCl
) δ 5.3, 6.7, 9.9, 14.9,
ture of 530 mg (0.76 mmol) of 1 in 14 mL of THF at 0 °C was
added dropwise 0.5 mL of Red-Al (Aldrich; 70% wt solution in
toluene). The reaction was monitored by TLC, and Red-Al was
added dropwise until all starting material was consumed,
usually within 1 h. The reaction was quenched by addition of
3
20.0, 20.9, 22.5, 22.6, 25.4, 26.9, 37.2, 37.9, 42.8, 43.9, 47.2,
58.6, 67.9, 72.3, 74.0, 75.8, 76.7, 78.6, 80.6, 84.4, 132.6, 144.0,
169.3, 170.9, 174.3, 202.2; FAB-HRMS (NBA-NaCl) m/ e
+
681.3661 (MH , C35
57
H O11Si requires 681.3670).
1
(
0 mL of a saturated solution of potassium sodium tartrate
Rochelle salt) and the aqueous layer extracted with 2 × 50
mL of Et O. The organic layers were combined, dried over
MgSO , filtered, and concentrated. The crude oil was subjected
to chromatography on silica gel (hexane:EtOAc ) 1:1) to afford
37 mg (75%) of 2 as a clear film: 1H NMR (250 MHz, CDCl
10-Ace t yl-2-(cycloh e xylca r b on yl)-2-d e b e n zoyld oce -
ta xel (7). To a mixture of 16 mg (0.023 mmol) of 4c and 14
mg (0.035 mmol) of 5c in 2 mL of THF was added 0.032 mL of
LiHMDS (1.0 M in THF) at -40 °C. After 20 min the reaction
2
4
was quenched by addition of 10 mL of aqueous NH
aqueous layer was extracted with 2 × 15 mL portions of Et
dried over MgSO , filtered, and concentrated. The crude
4
Cl. The
3
3
)
2
O,
δ 0.55 (q, J ) 7.8 Hz, 6 H), 0.89 (t, J ) 7.8 Hz, 9 H), 1.13 (s,
3
2
4
H), 1.16 (s, 3 H), 1.61 (s, 3 H), 2.01 (s, 3 H), 2.10 (s, 3 H),
.17 (s, 3 H), 2.43 (m, 1 H), 2.54 (d, J ) 19.9 Hz, 1 H), 2.80 (d,
residue was subjected to silica gel chromatography (hexane:
EtOAc ) 1:1) to afford 90 mg (95%) of a white solid. This
material was dissolved in 3 mL of THF, and 2 drops of HOAc
and 0.26 mL of TBAF (1.0 M in THF) were added dropwise.
After 36 h, the solvent was removed, and silica gel chroma-
tography (hexane:EtOAc ) 1:1 to 1:2) afforded 66 mg (98%) of
J ) 19.9 Hz, 1 H), 2.92 (bd, J ) 5.3 Hz, 1 H), 3.53 (d, J ) 6.2
Hz, 1 H), 3.93 (d, J ) 6.2 Hz, 1 H), 3.93 (bt, 1 H), 4.40 (dd, J
)
9.9, 6.8 Hz, 1 H), 4.53 (d, J ) 9.0 Hz, 1 H), 4.61 (d, J ) 9.0
13
Hz, 1 H), 4.88 (d, J ) 9.2 Hz, 1 H); C NMR (63 MHz, CDCl
3
)
7 as a white solid: 1H NMR (250 MHz, CDCl
) δ 0.99 (s, 3 H),
δ 5.2, 6.7, 9.7, 13.5, 18.2, 20.8, 21.6, 32.7, 37.3, 42.7, 43.1, 46.1,
3
5
1
9.5, 72.3, 72.4, 76.1, 77.5, 81.3, 83.8, 140.0, 153.1, 168.9, 170.0,
1.14 (s, 3 H), 1.20-2.43 (m, 14 H), 1.31 (s, 9 H), 1.61 (s, 3 H),
1.73 (s, 3 H), 2.16 (bs, 6 H), 2.40-2.58 (s, 1 H), 3.58 (d, J )
6.9 Hz, 1 H), 4.08 (d, J ) 8.2 Hz, 1 H), 4.40 (d, J ) 8.2 Hz, 1
H), 4.34 (dd, J ) 10.0, 6.6 Hz, 1 H), 4.52 (bs, 1 H), 4.88 (d, J
) 10.0 Hz, 1 H), 5.11 (d, J ) 9.0 Hz, 1 H), 5.28 (bd, J ) 9.0
Hz, 1 H), 5.35 (d, J ) 6.9 Hz, 1 H), 6.09 (t, J ) 8.7 Hz, 1 H),
6.15 (s, 1 H), 7.20-7.33 (m, 5 H). All data are in agreement
with reported literature values.12
+
98.9, 201.2; FAB-HRMS (NBA) m/ e 595.296 (MH , C30
47
H -
NO10Si requires 595.293).
-Deben zoyl-2-(3-m eth ylbu t-2-en oyl)-13-oxo-7-TES-bac-
ca tin III (3). Compound 2 (135 mg, 0.23 mmol), DMAP (83
mg, 0.68 mmol), DCC (140 mg, 0.68 mmol), and dimethyl-
acrylic acid (68 mg, 0.68 mmol) were dissolved in 3 mL of
toluene and allowed to stir overnight. The reaction was
2
quenched with 10 mL of saturated aqueous NaHCO
and the mixture was extracted with 2 × 20 mL of EtOAc, dried
over MgSO , filtered, and concentrated. Silica gel chromatog-
raphy (hexane:EtOAc ) 1:1) afforded 141 mg of 3 (92%) as a
3
solution,
10-Acet yl-2-d eb en zoyl-2-(3-m et h ylb u t -2-en oyl)d oce-
ta xel (8). To a mixture of 30 mg (0.044 mmol) of 4a and 28
mg (0.066 mmol) of 5c in 3 mL of THF was added 0.061 mL of
LiHMDS (1.0 M in THF) at -40 °C. After 20 min the reaction
4
1
white film: H NMR (300 MHz, CDCl
3
) δ 0.56 (q, J ) 7.8 Hz,
was quenched by addition of 10 mL of aqueous NH
aqueous layer was extracted with 2 × 20 mL portions of
EtOAc, dried over MgSO , filtered, and concentrated. The
4
Cl. The
6
1
2
2
H), 0.90 (t, J ) 7.8 Hz, 9 H), 1.15 (s, 3 H), 1.22 (s, 3 H),
.81-1.87 (m, 1 H), 2.06 (s, 3 H), 2.11 (s, 3 H), 2.20 (s, 3 H),
.27-2.54 (m, 1 H), 2.58 (d, J ) 20.1 Hz, 1 H), 2.78 (d, J )
0.1 Hz, 1 H), 3.78 (d, J ) 6.3 Hz, 1 H), 4.13 (d, J ) 8.4 Hz, 1
4
crude residue was subjected to silica gel chromatography
(hexane:EtOAc ) 1:1) to afford 33 mg (70%). A solution of
this material (31 mg, 0.028 mmol) was dissolved in 2 mL of
H), 4.40-4.46 (m, 2 H), 4.90 (d, J ) 7.8 Hz, 1 H), 5.44 (d, J )
.3 Hz, 1 H), 5.63 (bs, 1 H), 6.54 (s, 1 H); 13C NMR (75 MHz,
CDCl ) δ 4.4, 8.3, 12.9, 15.5, 15.6, 16.4, 19.5, 21.3, 22.6, 25.5,
7.8, 32.0, 37.2, 38.3, 41.1, 54.2, 66.1, 67.0, 70.8, 72.9, 75.1,
8.8, 109.5, 135.0, 147.8, 156.2, 161.9, 163.8, 165.1, 193.5,
6
3
pyridine and 2 mL of CH CN, treated with 0.5 mL of HF/
3
pyridine (70% wt solution) at 0 °C, and allowed to warm to
room temperature for 3 h. The reaction was quenched with
10 mL of 1 N HCl, and the mixture was extracted with 2 × 15
2
7
1
+
95.2; HRMS (DCI) m/ e 677.3341 (MH , C30
H
47NO10Si re-
4
mL of EtOAc, dried over MgSO , filtered, and concentrated.
quires 677.3357).
Chromatography on silica gel (hexane:EtOAc ) 1:2) afforded

Synthesis and SAR of New Nonaromatic Taxoids
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3 283
2
0
1
-
1
8 mg (78% and 55%, two-step yield) of 8 as a white film: [R]
D
solid. A solution of this material was dissolved in 1.5 mL of
pyridine and 1.5 mL of CH
3
CN, treated with 0.5 mL of HF/
pyridine (70% wt solution) at 0 °C, and allowed to warm to
room temperature for 3 h. The reaction was quenched with
-1
45.0° (c 0.1, CHCl
3
); IR (CDCl
3
, cm ) 3424, 3036, 2966, 1742,
736, 1731, 1725, 1701, 1660, 1631, 1554, 1378, 1243, 1161;
) δ 1.10 (s, 3 H), 1.24 (s, 3 H), 1.40
s, 9 H), 1.62 (s, 3 H), 1.80 (s, 3 H), 1.96 (s, 3 H), 1.97 (m, 1 H),
.19 (s, 3 H), 2.22 (s, 3 H), 2.24 (s, 3 H), 2.23 (m, 2 H), 2.43 (m,
H), 3.31 (bd, J ) 5.1 Hz, 1 H), 3.68 (bd, J ) 6.5 Hz, 1 H),
.17 (d, J ) 8.4 Hz, 1 H), 4.44 (d, J ) 8.4 Hz, 1 H), 4.37 (m, 1
H), 4.56 (bd, 1 H), 4.95 (m, 2 H), 5.18 (d, J ) 9.5 Hz, 1 H),
.36 (d, J ) 9.8 Hz, 1 H), 5.42 (d, J ) 6.8 Hz, 1 H), 5.68 (bs,
H), 6.09 (bt, 1 H), 6.15 (s, 3 H), 7.30 (m, 5 H); C NMR (63
) δ 9.6, 14.9, 20.6, 20.8, 21.7, 22.6, 26.7, 27.7, 28.2,
5.4, 43.3, 45.8, 56.3, 58.6, 72.1, 72.8, 73.3, 75.7, 76.9, 78.7,
4.5, 115.2, 126.8, 128.1, 133.0, 133.2, 138.4, 142.2, 155.4,
60.6, 167.1, 170.2, 171.3, 172.2, 173.1, 203.8; FAB-HRMS
1
H NMR (250 MHz, CDCl
3
(
10 mL of saturated NaHCO
3
, and the mixture was extracted
, filtered, and
2
1
4
with 2 × 20 mL of EtOAc, dried over MgSO
4
concentrated. Chromatography on silica gel (hexane:EtOAc
) 1:2) afforded 10 mg (53%, two-step yield) of 11 as a white
film: [R]20
-43.4° (c 0.01, CHCl
); H NMR (250 MHz, CDCl
1
)
D
3
3
5
1
δ 0.94 (d, 6 H), 1.09 (s, 3 H), 1.24 (s, 3 H), 1.42 (s, 9 H), 1.63
(s, 3 H), 1.74 (s, 3 H), 1.77 (s, 3 H), 1.86-1.92 (m, 2 H), 2.04-
2.34 (m, 2 H), 2.23 (s, 3 H), 2.24 (s, 3 H), 2.45 (bd, 1 H), 2.50-
2.62 (m, 1 H), 3.31 (d, J ) 7.0 Hz, 1 H), 3.69 (d, J ) 6.6 Hz, 1
H), 4.17-4.21 (m, 2 H), 4.39-4.31 (m, 1 H), 4.48 (d, J ) 8.2
Hz, 1 H), 4.70-4.75 (m, 2 H), 4.97 (d, J ) 8.0 Hz, 1 H), 5.30
1
3
MHz, CDCl
3
3
8
1
+
13
(NBA) m/ e 828.3827 (MH , C43
H
58NO15 requires 828.3806).
(bs, 1 H), 6.13 (t, J ) 8.2 Hz, 1 H), 6.27 (s, 1 H); C NMR (63
1
0-Acet yl-2-(cycloh exylca r b on yl)-3′-cycloh exyl-2-d e-
ben zoyl-3′-d ep h en yld oceta xel (9). Compound 7 (15 mg,
.017 mmol) was hydrogenated under 1 atm of H in the
presence of 20 mg of 5% Pt/C in 3 mL of EtOAc. After 24 h
the reaction mixture was filtered through a pipet column of
silica gel (EtOAc) and concentrated to afford 15 mg (100%) of
3
); H NMR (250
) δ 0.92-2.28 (m, 25 H), 1.05 (s, 3 H), 1.20 (s, 3
H), 1.38 (s, 9 H), 1.66 (s, 3 H), 1.83 (s, 3 H), 2.20 (s, 3 H), 2.28
3
MHz, CDCl ) δ 9.5, 14.9, 18.6, 20.8, 21.6, 22.4, 22.5, 25.3, 25.7,
26.7, 28.3, 35.1, 35.5, 43.2, 43.8, 45.6, 51.6, 58.6, 72.3, 73.7,
74.3, 75.6, 77.2, 79.0, 80.0, 80.7, 120.5, 132.8, 138.0, 142.7,
0
2
155.3, 170.2, 170.8, 171.3, 173.6, 174.2, 203.8; FAB-HRMS
+
(NBA) m/ e 808.4088 (MH , C41
H
62NO15 requires 808.4119).
10-Acet yl-2-d eb en zoyl-3′-d ep h en yl-2-(3-m et h ylb u t -2-
en oyl)-3′-(2-m eth ylp r op yl)d oceta xel (12). To a mixture of
37 mg (0.055 mmol) of 4a and 33 mg (0.082 mmol) of 5b in 2.5
mL of THF was added 0.07 mL of LiHMDS (1.0 M in THF) at
-40 °C. After 20 min the reaction was quenched by addition
2
0
1
9
as a white film: [R]
D
-62.9° (c 0.7, CHCl
MHz, CDCl
3
(
s, 3 H), 2.45 (d, J ) 3.7 Hz, 1 H), 2.46-2.62 (m, 1 H), 3.26 (d,
J ) 5.6 Hz, 1 H), 3.62-3.69 (m, 2 H), 4.16 (d, J ) 8.0 Hz, 1
of 10 mL of aqueous NH
4
Cl. The aqueous layer was extracted
, filtered,
H), 4.35-4.48 (m, 3 H), 4.67 (d, J ) 10.0 Hz, 1 H), 4.96 (d, J
with 2 × 20 mL portions of EtOAc, dried over MgSO
4
)
1
2
2
7
1
8.3 Hz, 1 H), 5.42 (d, J ) 6.9 Hz, 1 H), 6.13 (t, J ) 8.7 Hz,
and concentrated. The crude residue was subjected to silica
gel chromatography (hexane:EtOAc ) 1:1) to afford a white
solid. A solution of this material was dissolved in 1.5 mL of
1
3
3
H), 6.24 (s, 1 H); C NMR (63 MHz, CDCl ) δ 9.5, 14.8, 20.8,
1.8, 22.7, 25.2, 25.5, 25.7, 26.0, 26.2, 26.7, 28.2, 28.5, 29.4,
9.9, 30.1, 35.0, 35.6, 39.1, 43.2, 43.5, 45.4, 57.9, 58.6, 70.2,
2.1, 72.6, 74.4, 75.6, 76.6, 77.2, 79.0, 79.6, 80.8, 132.8, 142.6,
3
pyridine and 1.5 mL of CH CN, treated with 0.5 mL of HF/
pyridine (70% wt solution) at 0 °C, and allowed to warm to
room temperature for 6.5 h. The reaction was quenched with
15 mL of water, and the mixture was extracted with 2 × 15
55.8, 170.1, 170.9, 171.3, 174.8, 177.2, 203.8; FAB-HRMS
68NO15 requires 862.4589).
0-Acet yl-3′-d ep h en yl-2-d eb en zoyl-2-(3-m et h ylb u t -2-
+
(NBA) m/ e 862.4612 (MH , C45
H
1
4
mL of EtOAc, dried over MgSO , filtered, and concentrated.
en oyl)-3′-(2-m eth ylp r op -1-en yl)d oceta xel (10). To a mix-
ture of 30 mg (0.044 mmol) of 4a and 28 mg (0.066 mmol) of
Chromatography on silica gel (hexane:EtOAc ) 1:2) afforded
20
30 mg (68%, two-step yield) of 12 as a white film: [R]
D
-44.0°
1
5
a in 3 mL of THF was added 0.066 mL of LiHMDS (1.0 M in
THF) at -40 °C. After 20 min the reaction was quenched by
addition of 10 mL of aqueous NH Cl. The aqueous layer was
(c 0.75, CHCl ); H NMR (250 MHz, CDCl ) δ 0.92-0.96 (m, 6
3
3
H), 1.10 (s, 3 H), 1.22 (s, 3 H), 1.38 (s, 9 H), 1.62 (s, 3 H), 1.65-
1.69 (m, 1 H), 1.80-1.86 (m, 1 H), 1.84 (s, 3 H), 1.96 (s, 3 H),
2.18 (s, 3 H), 2.22 (s, 3 H), 2.25 (s, 3 H), 2.32-2.60 (m, 3 H),
3.25 (bs, 1 H), 3.67 (d, J ) 6.5 Hz, 1 H), 4.05-4.19 (m, 3 H),
4.36 (dd, J ) 10.6, 6.6 Hz, 1 H), 4.43 (d, J ) 8.4 Hz, 1 H), 4.64
(d, J ) 9.6 Hz, 1 H), 4.95 (d, J ) 8.0 Hz, 1 H), 5.43 (d, J ) 6.6
Hz, 1 H), 5.70 (bs, 1 H), 6.11 (t, J ) 8.6 Hz, 1 H), 6.26 (bs, 1
4
extracted with 2 × 20 mL portions of EtOAc, dried over MgSO
4
,
filtered, and concentrated. The crude residue was subjected
to silica gel chromatography (hexane:EtOAc ) 1:1) to afford
3
3 mg. A solution of this material (25 mg, 0.023 mmol) was
3
dissolved in 1 mL of pyridine and 1 mL of CH CN, treated
H); 13C NMR (63 MHz, CDCl
) δ 9.5, 14.8, 20.6, 20.8, 21.7,
with 0.5 mL of HF/pyridine (70% wt solution) at 0 °C, and
allowed to warm to room temperature for 3 h. The reaction
was quenched with water, and the mixture was extracted with
3
22.0, 22.5, 23.2, 24.6, 26.6, 27.7, 28.2, 35.3, 35.6, 41.2, 43.2,
45.7, 51.4, 58.6, 72.1, 72.7, 73.3, 75.7, 76.8, 79.7, 80.9, 84.5,
2
× 25 mL of EtOAc, dried over MgSO
4
, filtered, and
115.4, 133.0, 142.5, 155.6, 160.3, 167.1, 170.0, 171.2, 174.0,
+
concentrated. Chromatography on silica gel (hexane:EtOAc
203.9; FAB-HRMS (NBA) m/ e 808.4088 (MH , C41
H
62NO15
)
1:2) afforded 15 mg (50%, two-step yield) of 10 as a white
requires 808.4119).
10-Acetyl-2-d eben zoyl-3′-d ep h en yl-2-(3-m eth ylbu ta n -
oyl)-3′-(2-m eth ylp r op yl)d oceta xel (13). Compound 12 (17
2
0
-1
film: [R]
D
-33.3° (c 0.3, CHCl
3
); IR (CDCl
3
, cm ) 3426, 3018,
1
2
3
1
3
3
975, 1636, 1336, 1214; H NMR (250 MHz, CDCl ) δ 1.11 (s,
3
H), 1.24 (s, 3 H), 1.40 (s, 9 H), 1.62 (s, 3 H), 1.73 (s, 3 H),
.76 (s, 3 H), 1.86 (s, 3 H), 1.92 (m, 1 H), 1.96 (s, 3 H), 2.19 (s,
H), 2.22 (s, 3 H), 2.24 (s, 3 H), 2.33 (m, 2 H), 2.54 (m, 1 H),
.69 (d, J ) 6.7 Hz,1 H), 4.38 (dd, J ) 10.5, 7.7 Hz, 1 H), 4.17
2
mg, 0.021 mmol) was hydrogenated under 1 atm of H in the
presence of 20 mg of 10% Pd/C in 3 mL of EtOAc. After 24 h
the reaction mixture was filtered through a pipet column of
silica gel (EtOAc) and concentrated to afford 17 mg (100%) of
2
0
1
(
d, J ) 8.4 Hz, 1 H), 4.44 (d, J ) 8.4 Hz, 1 H), 4.74 (m, 1H),
.96 (d, J ) 9.5 Hz, 1 H), 5.30 (d, J ) 8.2 Hz, 1 H), 5.44 (d, J
6.6 Hz, 1 H), 5.68 (bs, 1 H), 6.12 (t, J ) 8.5 Hz, 1 H), 6.27
13 as a white film: [R]
D
3
-46.0° (c 0.2, CHCl ); H NMR (250
4
MHz, CDCl ) δ 0.92-1.01 (m, 12 H), 1.08 (s, 3 H), 1.22 (s, 3
3
)
H), 1.39 (s, 9 H), 1.60-1.69 (m, 6 H), 1.86 (s, 3 H), 1.78-1.92
(m, 1 H), 2.14-2.36 (m, 4 H), 2.22 (s, 3 H), 2.25 (s, 3 H), 2.45-
2.56 (m, 2 H), 3.67 (d, J ) 6.7 Hz, 1 H), 4.07-4.21 (m, 4 H),
4.38 (bt, 1 H), 4.48 (d, J ) 8.0 Hz, 1 H), 4.59 (d, J ) 9.6 Hz, 1
H), 4.97 (d, J ) 8.2 Hz, 1 H), 5.41 (d, J ) 6.8 Hz, 1 H), 6.10 (t,
1
3
(
bs, 1 H); C NMR (63 MHz, CDCl
3
) δ 9.5, 14.9, 18.6, 20.6,
2
5
8
1
8
0.8, 21.7, 22.4, 25.7, 26.6, 27.7, 28.2, 35.4, 35.6, 43.2, 45.7,
1.5, 58.6, 72.1, 72.5, 73.3, 73.5, 75.7, 76.9, 78.6, 79.9, 80.8,
4.5, 115.3, 120.5, 133.0, 137.1, 142.5, 155.4, 160.4, 167.1,
70.2, 171.2, 173.2, 203.9; FAB-HRMS (NBA-NaCl) m/ e
28.380 (M + Na, C41
J ) 9.2 Hz, 1 H), 6.26 (s, 1 H); 13C NMR (63 MHz, CDCl
) δ
3
+
H
59NO15Na requires 828.387).
9.5, 14.2, 14.9, 20.8, 21.6, 21.9, 22.5, 23.3, 24.7, 25.2, 26.7, 28.2,
34.9, 35.5, 41.2, 43.2, 43.8, 45.5, 51.4, 58.6, 72.1, 72.6, 73.0,
74.3, 75.6, 76.6, 78.9, 79.7, 80.8, 84.5, 132.8, 142.6, 155.6, 170.0,
1
0-Acetyl-2-d eben zoyl-3′-d ep h en yl-3′-(2-m eth ylp r op -1-
en yl)-2-(3-m eth ylbu ta n oyl)d oceta xel (11). To a mixture
of 16 mg (0.023 mmol) of 4b and 14 mg (0.035 mmol) of 5a in
+
171.3, 174.1, 203.8; FAB-HRMS (NBA) m/ e 810.4322 (MH ,
2
mL of THF was added 0.032 mL of LiHMDS (1.0 M in THF)
at -40 °C. After 20 min the reaction was quenched by addition
of 10 mL of aqueous NH Cl. The aqueous layer was extracted
O, dried over MgSO , filtered,
C
41
H
64NO15 requires 810.4276).
10-Acet yl-2-(cycloh exylca r b on yl)-2-d eb en zoyl-3′-d e-
4
p h en yl-3′-(2-m eth ylp r op -1-en yl)d oceta xel (14). To a mix-
ture of 80 mg (0.114 mmol) of 4c and 70 mg (1.71 mmol) of 5a
in 7 mL of THF was added 0.16 mL of LiHMDS (1.0 M in THF)
at -40 °C. After 20 min the reaction was quenched by addition
with 2 × 15 mL portions of Et
2
4
and concentrated. The crude residue was subjected to silica
gel chromatography (hexane:EtOAc ) 1:1) to afford a white

2
84 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 3
Ojima et al.
of 15 mL of aqueous NH
4
Cl. The aqueous layer was extracted
, filtered,
Cytotoxicity Assa y in Vitr o.29 Tumor cell growth inhibi-
tion was dertermined according to the method established by
Skehan et al.30 Human tumor cells (A121 ovarian carcinoma,
HT-29 colon carcinoma, A549 non-small-cell lung carcinoma,
and MCF7 breast carcinoma) were plated at a density of 400
cells/well in 96-well plates and allowed to attach overnight.
These cell lines were maintained in RPMI-1640 medium
(Roswell Park Memmorial Institute growth medium) supple-
mented with 5% fetal bovine serum and 5% Nu serum
(Collaborative Biomedical Product, MA). Taxanes were solu-
bilized in DMSO and further diluted with RPMI-1640 medium.
Triplicate wells were exposed to various treatments. After 72
h incubation, 100 µL of ice-cold 50% trichloroacetic acid (TCA)
was added to each well, and the samples were incubated for 1
h at 4 °C. Plates were then washed five times with water to
remove TCA and serum proteins, and 50 µL of 0.4% sulfor-
hodamine B (SRB) was added to each well. Following a 5 min
incubation, plates were rinsed five times with 0.1% acetic acid
and air-dried. The dye was then solubilized with 10 mM Tris
base (pH 10.5) for 5 min on a gyratory shaker. Optical density
was measured at 570 nm. The IC50 values were then calcu-
lated by fitting the concentration-effect curve data with the
sigmoid-Emax model using nonlinear regression, weighted by
with 2 × 25 mL portions of EtOAc, dried over MgSO
4
and concentrated. The crude residue was subjected to silica
gel chromatography (hexane:EtOAc ) 1:1) to afford 97 mg
(92%). A solution of this material (95 mg, 0.085 mmol) was
3
dissolved in 3 mL of pyridine and 3 mL of CH CN, treated
with 0.5 mL of HF/pyridine (70% wt solution) at 0 °C, and
allowed to warm to room temperature for 3 h. The reaction
was quenched with water, and the mixture was extracted with
2
× 25 mL of EtOAc, dried over MgSO
4
, filtered, and
concentrated. Chromatography on silica gel (hexane:EtOAc
)
1:2) afforded 54 mg (78% and 72%, two-step yield) of 14 as
2
0
1
a white film: [R]
D
3
-40.0° (c 0.75, CHCl ); H NMR (250 MHz,
CDCl ) δ 1.06 (s, 3 H), 1.21 (s, 3 H), 1.25 (m, 2 H), 1.40 (s, 9
3
H), 1.62 (s, 3 H), 1.57-1.80 (m, 4 H), 1.62 (s, 3 H), 1.71 (s, 3
H), 1.85 (s, 3 H), 2.18-2.28 (m, 1 H), 2.21 (s, 3 H), 2.23 (s, 3
H), 2.53 (m, 2 H), 3.43 (d, J ) 6.8 Hz, 1 H), 3.65 (d, J ) 7.0
Hz, 1 H), 4.15 (d, J ) 8.0 Hz, 1 H), 4.45 (d, J ) 8.0 Hz, 1 H),
4
.36 (m, 1 H), 4.70 (m, 1 H), 4.81 (d, J ) 8.5 Hz, 1 H), 4.95 (d,
J ) 8.2 Hz, 1 H), 5.27 (d, J ) 8.5 Hz, 1 H), 5.40 (d, J ) 7.0 Hz,
H), 6.10 (t, J ) 8.6 Hz, 1 H), 6.24 (s, 1 H); 13C NMR (63
MHz, CDCl ) δ 9.4, 14.9, 18.5, 20.8, 21.7, 22.3, 25.1, 25.5, 25.7,
6.6, 28.2, 28.4, 29.3, 35.1, 35.5, 43.1, 43.5, 45.6, 51.6, 58.5,
1
3
2
7
1
3
1
2.1, 73.7, 74.4, 75.6, 79.1, 79.9, 80.7, 84.5, 120.5, 132.7, 137.9,
42.6, 155.4, 170.1, 171.2, 173.0, 177.0, 203.8; FAB-HRMS
the reciprocal of the square of the predicted effect.
+
Ack n ow led gm en t. This research was supported by
grants from the National Institutes of Health (GM417980
to I.O.) and the National Cancer Institute (CA13038 to
R.J .B.). Generous support from Rh oˆ ne-Poulenc Rorer
(
NBA) m/ e 834.4275 (MH , C44
0-Acet yl-2-(cycloh exylca r b on yl)-2-d eb en zoyl-3′-d e-
p h en yl-3′-(2-m eth ylp r op yl)d oceta xel (15). Compound 14
16 mg, 0.019 mmol) was hydrogenated under 1 atm of H in
the presence of 20 mg of 10% Pd/C in 2 mL of EtOAc. After
4 h the reaction mixture was filtered through a pipet column
of silica gel (EtOAc) and concentrated to afford 16 mg (100%)
H63NO15 requires 834.4265).
1
(
2
(I.O.) is also gratefully acknowledged. The authors
2
would like to thank Dr. Ezio Bombardelli, Indena SpA,
for a generous gift of 10-DAB. One of the authors
2
0
1
of 15 as a white film: [R]
D
-43.2° (c 0.1, CHCl
3
); H NMR
(S.D.K.) thanks the U.S. Department of Education for
(
250 MHz, CDCl ) δ 1.06 (s, 3 H), 1.19 (s, 3 H), 1.37 (s, 9 H),
3
1
1
2
.24-1.26 (m, 2 H), 1.61 (s, 3 H), 1.65 (s, 3 H), 1.52-1.86 (m,
a GAANN fellowship.
0 H), 2.03-2.24 (m, 4 H), 2.21 (s, 3 H), 2.24 (s, 3 H), 2.49-
.53 (m, 2 H), 3.24 (d, J ) 6.1 Hz, 1 H), 3.65 (d, J ) 6.9 Hz, 1
Refer en ces
H), 4.12-4.17 (m, 4 H), 4.36 (m, 1 H), 4.46 (d, J ) 8.2 Hz, 1
H), 5.41 (d, J ) 6.9 Hz, 1 H), 6.11 (t, J ) 8.6 Hz, 1 H), 6.24 (s,
1
2
3
7
1
(
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.
1
3
3
H); C NMR (63 MHz, CDCl ) δ 9.5, 14.9, 20.8, 21.8, 22.0,
2.4, 23.0, 23.4, 24.7, 24.9, 25.2, 25.5, 25.7, 28.0, 29.3, 35.1,
5.5, 41.3, 43.1, 43.6, 45.5, 51.4, 58.6, 72.1, 72.5, 73.1, 74.5,
5.6, 79.2, 79.7, 80.9, 84.5, 132.8, 142.5, 155.5, 170.0, 171.2,
(
2) Gu e´ ritte-Voegelein, F.; Mangatal, L.; Gu e´ nard, D.; Potier, P.;
Guilhem, J .; Cesario, M.; Pascard, C. Structure of a Synthetic
Taxol Precursor: N-tert-Butoxycarbonyl-10-deacetyl-N-deben-
zoyltaxol. Acta Crystallogr. 1990, C46, 781-784.
+
73.9, 177.0, 203.8; FAB-HRMS (NBA) m/ e 836.4432 (MH ,
C
43
H
66NO15 requires 836.4472).
0-Acet yl-2-(cycloh exylca r b on yl)-2-d eb en zoyl-3′-d e-
p h en yl-3′-((E)-p r op -1-en yl)d oceta xel (16). To a mixture of
0 mg (0.030 mmol) of 4c and 18 mg (0.045 mmol) of 5d in 3
mL of THF was added 45 µL of LiHMDS (1.0 M in THF) at
40 °C. After 20 min the reaction was quenched by addition
of 10 mL of aqueous NH Cl. The aqueous layer was extracted
, filtered,
(3) Shiff, P. B.; Fant, J .; Horwitz, S. B. Promotion of Microtubule
Assembly in vitro by Taxol. Nature 1979, 277, 665-667.
4) Manfredi, J . J .; Horwitz, S. B. Taxol: an Antimitotic Agent with
1
(
a New Mechanism of Action. Pharmacol. Ther. 1984, 25, 83-
2
1
25.
(5) Ringel, I.; Horwitz, S. B. Studies with RP 56976 (Taxot e` re): A
-
Semisynthetic Analogue of Taxol. J . Natl. Cancer Inst. 1991, 83,
2
88-291.
4
(
6) Verweij, J .; Clavel, M.; Chevalier, B. Paclitaxel (Taxol) and
with 2 × 20 mL portions of EtOAc, dried over MgSO
4
Docetaxel (Taxotere): Not Simply Two of a Kind. Ann. Oncol.
and concentrated. The crude residue was subjected to silica
gel chromatography (hexane:EtOAc ) 1:1) to afford a white
solid. A solution of this material was dissolved in 2 mL of
1
994, 5, 495-505.
(7) Chaudhary, A. G.; Gharpure, M. M.; Rimoldi, J . M.; Chordia,
M. D.; Gunatilaka, A. A. L.; Kingston, D. G. I.; Grover, S.; Lin,
C. M.; Hamel, E. Unexpectedly Facile Hydrolysis of the 2-Ben-
zoate Group of Taxol and Syntheses of Analogs with Increased
Activities. J . Am. Chem. Soc. 1994, 116, 4097-4098.
3
pyridine and 3 mL of CH CN, treated with 0.5 mL of HF/
pyridine (70% wt solution) at 0 °C, and allowed to warm to
room temperature for 3 h. The reaction was quenched with
(
8) Georg, G. I.; Boge, T. C.; Cheruvallath, Z. S.; Clowers, J . S.;
Harriman, G. C. B.; Hepperle, M.; Park, H. The Medicinal
Chemistry of Taxol. In Taxol: Science and Applications; Suff-
ness, M., Ed.; CRC Press: New York, 1995; pp 317-375.
1
0 mL of 1 N HCl, and the mixture was extracted with 2 × 15
mL of EtOAc, dried over MgSO , filtered, and concentrated.
Chromatography on silica gel (hexane:EtOAc ) 1:2) afforded
4
2
0
(9) Georg, G. I.; Harriman, G. C. B.; Ali, S. M.; Datta, A.; Hepperle,
M.; Himes, R. H. Synthesis of 2-O-Heteroaroyl Taxanes: Evalu-
ation of Microtubule Assembly Promotion and Cytotoxicity.
Bioorg. Med. Chem. Lett. 1995, 5, 115-118.
1
7 mg (71%, two-step yield) of 16 as a white film: [R]
D
-48.2°
1
(
(
(
(
c 0.1, CHCl ); H NMR (250 MHz, CDCl ) δ 1.06 (s, 3 H), 1.20
3
3
s, 3 H), 1.26 (m, 2 H), 1.40 (s, 9 H), 1.61 (s, 3 H), 1.56-1.80
m, 4 H), 1.71 (s, 3 H), 1.74 (s, 3 H), 1.84 (s, 3 H), 2.17-2.23
m, 1 H), 2.21 (s, 3 H), 2.26 (s, 3 H), 2.53 (m, 2 H), 3.65 (d, J
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7.0 Hz, 1 H), 4.15 (d, J ) 7.9 Hz, 1 H), 4.46 (d, J ) 7.9 Hz,
H), 4.36 (dd, J ) 10.6, 6.8 Hz, 1 H), 4.53 (m, 1 H), 4.92 (m,
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2
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1
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