Synthesis and biological evaluation of 1-deoxypaclitaxel analogues

Article abstract of DOI:10.1021/jo981406l

The naturally occurring taxoid baccatin VI has been converted to various 1-deoxypaclitaxel derivatives by selective deacylation followed by attachment of the C-13 side chain. The bioactivities of the resulting analogues were determined in both tubulin polymerization and cytotoxicity assays, and several analogues with activity comparable to that of paclitaxel were discovered. It thus appears that the 1-hydroxyl group is not necessary for the activity of paclitaxel.

Full text of DOI:10.1021/jo981406l

1814
J . Org. Chem. 1999, 64, 1814-1822
Syn th esis a n d Biologica l Eva lu a tion of 1-Deoxyp a clita xel
An a logu es
David G. I. Kingston,* Mahendra D. Chordia, and Prakash G. J agtap
Department of Chemistry, Virginia Polytechnic Institute and State University,
Blacksburg, Virginia 24061-0212
J ingyu Liang
Department of Phytochemistry, China Pharmaceutical University, No. 24 Tong J ia Xiang,
Nanjing 210009, Peoples’ Republic of China
Ya-Ching Shen
Institute of Marine Resources, National Sun Yat-Sen University, Kaohsiung, Taiwan, R.O.C
Byron H. Long, Craig R. Fairchild, and Kathy A. J ohnston
Bristol-Myers Squibb Pharmaceutical Research Institute, P.O. Box 4000, Princeton, New J ersey 05843
Received J uly 20, 1998
The naturally occurring taxoid baccatin VI has been converted to various 1-deoxypaclitaxel
derivatives by selective deacylation followed by attachment of the C-13 side chain. The bioactivities
of the resulting analogues were determined in both tubulin polymerization and cytotoxicity assays,
and several analogues with activity comparable to that of paclitaxel were discovered. It thus appears
that the 1-hydroxyl group is not necessary for the activity of paclitaxel.
In tr od u ction
Interest in the novel diterpenoid paclitaxel (Taxol®) (1)
continues at a high level from chemical, biological, and
clinical viewpoints. First isolated from the bark of the
western yew, Taxus brevifolia,1 its development as a
clinical candidate was slowed by concerns about its
supply and its lack of aqueous solubility. Positive results
in new in vivo models in the mid 1970s and the discovery
of its novel mechanism of action2 greatly increased
interest in the compound, and clinical trials ultimately
demonstrated its clinical effectiveness. It is now approved
for treatment of ovarian and breast cancers, with promise
also for treatment of lung, skin, and head and neck
cancers;3 the paclitaxel analogue docetaxel (2) is also in
clinical use.4
and have led to the general conclusion that the C-13 ester
side chain is essential for activity but that modifications
to the “northern hemisphere” (C-7, C-9, and C-10) have
modest but often beneficial effects on its bioactivity, while
changes to the “southern hemisphere” (C-4, C-2, and the
oxetane ring) can have larger effects on activity, usually
negative but occasionally positive.5 Thus opening of the
oxetane ring leads to loss of activity,6 as does deacety-
lation or deacetoxylation at C-4;7 replacement of the C-4
A large number of structure-activity studies of pacli-
taxel have been carried out, particularly in recent years,
(1) Wani, M. C.; Taylor, H. L.; Wall, M. E.; Coggon, P.; McPhail, A.
T. J . Am. Chem. Soc. 1971, 93, 2325-2327.
(5) (a) Chen, S.-H.; Farina, V. In Taxane Anticancer Agents: Basic
Science and Current Status; Georg, G. I., Chen, T. T., Ojima, I. and,
Vyas, D. M., Eds.; American Chemical Society: Washington, DC, 1994;
ACS Symposium Series Vol. 583; pp 247-261. (b) Georg, G. I.; Boge,
T. C.; Cheruvallath, Z. S.; Clowers, J . S.; Harriman, G. C. B.; Hepperle,
M.; Park, H. In Taxol: Science and Applications; Suffness, M., Ed.;
CRC Press: Boca Raton, FL, 1995; pp 317-375. (c) Kingston, D. G. I.
Pharmacol. Ther. 1991, 52, 1-34. (d) Kingston, D. G. I. Trends
Biotechnol. 1994, 12, 222-227. (e) Kingston, D. G. I. In Taxane
Anticancer Agents: Basic Science and Current Status; Georg, G. I.,
Chen, T. T., Ojima, I., Vyas, D. M., Eds.; American Chemical Society:
Washington, DC, 1994; ACS Symposium Series Vol. 583; pp 203-216.
(f) Kingston, D. G. I. In Paclitaxel in Cancer Treatment; McGuire, W.
P., Rowinsky, E. K., Eds.; Marcel Dekker: New York, Basel, Hong
Kong, 1995; Vol. 8, pp 1-33. (g) Nicolaou, K. C.; Dai, W.-M.; Guy, R.
K. Angew. Chem., Int. Ed. Engl. 1994, 33, 15-44.
(2) (a) Schiff, P. B.; Fant, J .; Horwitz, S. B. Nature 1979, 277, 665-
667. (b) Manfredi, J . J .; Horwitz, S. B. Pharmacol. Ther. 1984, 25, 83-
125.
(3) (a) Arbuck, S. G.; Blaylock, B. A. In Taxol: Science and
Applications; Suffness, M., Ed.; CRC Press: Boca Raton, FL, 1995; pp
379-415. (b) Holmes, F. A.; Kudelka, A. P.; Kavanagh, J . J .; Huber,
M. H.; Ajani, J . A.; Valero, V. In Taxane Anticancer Agents: Basic
Science and Current Status; Georg, G. I., Chen, T. T., Ojima, I., Vyas,
D. M., Eds.; American Chemical Society: Washington, DC, 1994; ACS
Symposium Series Vol. 583; pp 31-57. (c) Donehower, R. C.; Rowinsky,
E. K. Cancer Treat. Rev. 1993, 19 Suppl. C, 63-78. (d) Rowinsky, E.
K.; Donehower, R. C. Paclitaxel (Taxol). New Engl. J . Med. 1995, 1004-
1014.
(4) The early history of the development of paclitaxel has been
reviewed by its discoverers: Wall, M. E.; Wani, M. C. In Economic
and Medicinal Plant Research; Wagner, H., Farnsworth, N. R., Eds.;
Academic Press: Ltd.: London, 1994; Vol. 6, pp 299-322.
(6) Samaranayake, G.; Magri, N. F.; J itrangsri, C.; Kingston, D. G.
I. J . Org. Chem. 1991, 56, 5114-5119.
10.1021/jo981406l CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/10/1999

1-Deoxypaclitaxel Analogues
J . Org. Chem., Vol. 64, No. 6, 1999 1815
acetate with other acyl groups does, however, lead to
restoration or even enhancement of activity.8
Among the analogues of paclitaxel that have been
prepared are several that lack one or more hydroxyl or
acetoxyl groups. Thus analogues have been synthesized
lacking the 2-benzoyloxy group,9,10 lacking the 4-acetoxyl
group,7b lacking the 7-hydroxyl group,11 and lacking the
10-acetoxyl group.12 Despite all the work that has been
done in this area, however, it has not proved possible to
prepare 1-deoxypaclitaxel analogues from paclitaxel;
various attempts to do so by the Barton deoxygenation
method used successfully in other examples led only to
deoxygenation at C-2.9,13
for the activity of paclitaxel,6 it was the crucial starting
material for this work.
The preparation of 1-deoxy analogues of paclitaxel was
an important objective, since the relevance of this func-
tional group to paclitaxel’s activity as an anticancer agent
was unknown, and since introduction of this group
requires additional steps in some synthetic approaches
to paclitaxel.14 Conceivably, if the C-1 hydroxyl group is
not required for activity, or if its removal even enhances
activity, then such a simplified paclitaxel analogue might
be amenable to total synthesis on an industrial scale.
Since direct deoxygenation of paclitaxel appeared to be
an impractical route to the preparation of 1-deoxypacli-
taxel analogues, we elected to make use of the availability
of 1-deoxybaccatin VI (3) as a starting material for the
preparation of selected 1-deoxyanalogues.
Resu lts a n d Discu ssion
The key problem in the conversion of 1-deoxybaccatin
VI (3) to paclitaxel analogues is that of selective deacy-
lation of the 7, 9, 10, and 13 acetoxyl groups (and
especially of the C-13 group) without concomitant deacy-
lation of the C-2 and C-4 acyloxy groups. A similar
situation was faced by Klein in the conversion of 13-
acetyl-9(R)-dihydrobaccatin III (4) to dihydropaclitaxel
analogues17 and was solved by the use of methyllithium,
which gave an 82% yield of the desired 13-deacetyl
derivative of 4. The original mechanism proposed for this
conversion involved a possible complexation of the alkyl-
lithium reagent with the C-1 oxyanion,18 but it was later
proposed that selective deacetylation occurred by a
ketene elimination pathway.17 Other bases have also
been found to be selective for different positions on
paclitaxel. Thus in our work on the debenzoylation of
paclitaxel at the C-2 position we found that phase-
transfer catalysis19 or Triton B20 worked well, while the
reducing agent Red-Al has been found to be effective in
selective debenzoylation of baccatin III derivatives.21
On the other hand, the C-4 acetyl group can be
removed selectively from 7-O-(triethylsilyl)baccatin III by
treatment with potassium tert-butoxide, presumably via
an internal transesterification process.22 We thus elected
to investigate several routes to the selective deacylation
of 1-deoxybaccatin VI.
1-Deoxybaccatin VI (3) was first isolated by one of us
from the heartwood of T. mairei15 and was later reisolated
by another one of us from the same source.16 Since it
contains the oxetane ring system known to be essential
(7) Neidigh, K. A.; Gharpure, M. M.; Rimoldi, J . M.; Kingston, D.
G. I.; J iang, Y. Q.; Hamel, E. Tetrahedron Lett. 1994, 35, 6839-6842.
(b) Chordia, M. D.; Chaudhary, A. G.; Kingston, D. G. I.; J iang, Y. Q.;
Hamel, E. Tetrahedron Lett. 1994, 35, 6843-6846. (c) Datta, A.;
J ayasinghe, L. R.; Georg, G. I. J . Med. Chem. 1994, 37, 4258-
260.
(8) (a) Chen, S.-H.; Kadow, J . F.; Farina, V.; Fairchild, C. R.;
J ohnston, K. A. J . Org. Chem. 1994, 59, 6156-6158. (b) Chen, S.-H.;
Fairchild, C.; Long, B. H. J . Med. Chem. 1995, 38, 2263-2267. (c) Chen,
S.-H.; Wei, J .-M.; Long, B. H.; Fairchild, C. A.; Carboni, J .; Mamber,
S. W.; Rose, W. C.; J ohnston, K.; Casazza, A. M.; Kadow, J . F.; Farina,
V.; Vyas, D.; Doyle, T. W. Bioorg. Med. Chem. Lett. 1995, 5, 2741-
2746. (d) Georg, G. I.; Ali, S. M.; Boge, T. C.; Data, A.; Falborg, L.;
Himes, R. H. Tetrahedron Lett. 1994, 35, 8931-8934.
The first route developed (Scheme 1) proved to be very
efficient for the synthesis of analogues retaining the 7,
9, and 10 acetyl groups. Treatment of 1-deoxybaccatin
VI (3) with Red Al at -20 °C gave 13-deacetyl-1-
deoxybaccatin VI (5a ) in 77% yield, together with 12%
of the 4-deacetyl derivative 5b. The formation of small
amounts of 5b was expected in view of earlier experi-
ence,22a but the amounts formed were acceptable in light
of the good yield of the major product 5a .
(9) Chaudhary, A. G.; Chordia, M. D.; Kingston, D. G. I. J . Org.
Chem. 1995, 60, 3260-3262.
(10) Chen, S.-H.; Wei, J .-M.; Farina, V. Tetrahedron Lett. 1993, 34,
3205-3206.
(11) (a) Chaudhary, A. G.; Rimoldi, J . M.; Kingston, D. G. I. J . Org.
Chem. 1993, 58, 3798-3799. (b) Chen, S.-H.; Huang, S.; Kant, J .;
Fairchild, C.; Wei, J .; Farina, V. J . Org. Chem. 1993, 58, 5028-5029.
(12) (a) Chaudhary, A. G.; Kingston, D. G. I. Tetrahedron Lett. 1993,
34, 4921-4924. (b) Chen, S.-H.; Fairchild, C.; Mamber, S. W.; Farina,
V. J . Org. Chem. 1993, 58, 2927-2928. (c) Chen, S. H.; Wei, J . M.;
Vyas, D. M.; Doyle, T. W.; Farina, V. Tetrahedron Lett. 1993, 34, 6845-
6848. (d) Georg, G. I.; Cheruvallath, Z. S. J . Org. Chem. 1994, 59,
4015-4018. (e) Holton, R. A.; Somoza, C.; Chai, K.-B. Tetrahedron Lett.
1994, 35, 1665-1668.
Conversion of the 13-deacetyl derivative 5a to various
paclitaxel and docetaxel analogues proceeded by the
(13) Chen, S.-H.; Huang, S.; Gao, Q.; Golik, J .; Farina, V. J . Org.
Chem. 1994, 59, 1475-1484.
(17) Klein, L. L.; Li, L.; Maring, C. J .; Yeung, C. M.; Thomas, S. A.;
Grampovnik, D. J .; Plattner, J . J . J . Med. Chem. 1995, 38, 1482-1492.
(18) Klein, L. L. Tetrahedron Lett. 1993, 34, 2047-2050.
(19) 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. J . Am. Chem. Soc. 1994, 116, 4097-4098.
(20) Kingston, D. G. I.; Chaudhary, A. G.; Chordia, M. D.; Gharpure,
M.; Gunatilaka, A. A. L.; Higgs, P. I.; Rimoldi, J . M.; Sanala, L.; J agtap,
P. G.; Giannakakou, P.; J iang, Y. Q.; Lin, C. M.; Hamel, E.; Long, B.
H.; Fairchild, C. R.; J ohnston, K. A. J . Med. Chem. 1998, 41, 3715-
3726.
(21) Chen, S.; Farina, V.; Wei, J .; Long, B.; Fairchild, C.; Mamber,
S. W.; Kadow, J . F.; Vyas, D.; Doyle, T. W. Bioorg. Med. Chem. Lett.
1994, 4, 479-482.
(22) (a) Samaranayake, G.; Neidigh, K. A.; Kingston, D. G. I. J . Nat.
Prod. 1993, 56, 884-898. (b) Datta, A.; J ayasinghe, L. R.; Georg, G. I.
J . Org. Chem. 1994, 59, 4689-4690.
(14) (a) Holton, R. A.; Somoza, C.; Kim, H.-B.; Liang, F.; Biediger,
R. J .; Boatman, P. D.; Shindo, M.; Smith, C. C.; Kim, S.; Nadizadeh,
H.; Suzuki, Y.; Tao, C.; Vu, P.; Tang, S.; Zhang, P.; Murthi, K. K.;
Gentile, L. N.; Liu, J . H. J . Am. Chem. Soc. 1994, 116, 1597-1598. (b)
Holton, R. A.; Kim, H.-B.; Somoza, C.; Liang, F.; Biediger, R. J .;
Boatman, P. D.; Shindo, M.; Smith, C. C.; Kim, S.; Nadizadeh, H.;
Suzuki, Y.; Tao, C.; Vu, P.; Tang, S.; Zhang, P.; Murthi, K. K.; Gentile,
L. N.; Liu, J . H. J . Am. Chem. Soc. 1994, 116, 1599-1600. (c)
Danishefsky, S. J .; Masters, J . J .; Young, W. B.; Link, J . T.; Snyder,
L. B.; Magee, T. V.; J ung, D. K.; Isaacs, R. C. A.; Bornmann, W. G.;
Alaimo, C. A.; Coburn, C. A.; Di Grandi, M. J . J . Am. Chem. Soc. 1996,
118, 2843-2859.
(15) Min, Z. D.; J iang, H.; Liang, J . Y. Acta Pharm. Sin (Yaoxue
Xuebao) 1989, 24, 673-677.
(16) Shen, Y.-C.; Tai, H.-R.; Hsieh, P.-W.; Chen, C.-Y. Chin. Pharm.
J . 1996, 48, 207-217.

1816 J . Org. Chem., Vol. 64, No. 6, 1999
Kingston et al.
Sch em e 1a
Treatment of 3 with Triton B in dichloromethane or
with methanolic sodium hydroxide gave the tris-deacetyl
derivative 9 in good to excellent yield (Scheme 2).
Compound 9 was then selectively protected as its 7,9-
acetonide 10a or its 7,9-benzylidene acetal 10b by treat-
ment with 2-methoxypropene or benzaldehyde in the
presence of acid. Protection of the C-10 hydroxyl group
as its triethylsilyl ether gave the fully protected ana-
logues 11a and 11b, and these could be deacetylated to
the key intermediates 12a and 12b by treatment with
methyllithium at low temperature. The yields of this
selective deacylation step were only modest, but this
route had the advantage already noted of additional
flexibility for the substituents at C-7, 9, and 10.
Treatment of the 13-deacetyl derivatives 12a and 12b
with â-lactams 6b and 6d respectively gave the protected
paclitaxel analogues 13a and 13b, which were depro-
tected in the usual way to give the final products 14a
and 14b (Scheme 2). Attempted deprotection of the acetal
or ketal protecting groups by acidic hydrolysis gave only
poor yields of deprotected products accompanied byprod-
ucts with an opened oxetane ring, and so the ketals 14a
and 14b were evaluated as such for their bioactivity.
After the development of the route described above, we
developed an improved route to the preparation of the 7,
9, 10 trihydroxy analogues that avoided the protection/
deprotection chemistry of Scheme 2. In this route (Scheme
3) the 7,9,10-triacetyl derivative 7b was converted to the
2′-protected 7,9,10-triol 15 with either Triton B in dichlo-
romethane or with methanolic potassium hydroxide.
Deprotection of the TIPS group then gave the triol
derivative 16.
The protected triol 15 was a useful intermediate for
the synthesis of other analogues. Thus reaction with
DMP/acetone in the presence of PPTS, followed by
deprotection at the 2′-position, gave the additional cyclic
ketal 14c. Finally, methylation with methyl iodide in
THF gave the 7-O-methyl ether 17 and the 7-O-methyl-
10-O-methoxybutyl derivative 19, both in low yields.
Compound 19 is presumably formed by initial attack of
THF on methyl iodide to give a methyl oxonium iodide,
which then undergoes nucleophalic attack by the 10-
alkoxide derivative of 15. Presumably small amounts of
other alkylation products related to 17 and 19 were also
formed in the reaction but were not isolated by one
workup procedure.
The bioactivities of the 1-deoxypaclitaxel analogues
8a -8c, 14a -14c, 16, 18, and 20 were determined both
in a tubulin-assembly assay and in a cytotoxicity assay.
The tubulin-assembly assay was carried out with calf
brain tubulin prepared following the procedure of Wil-
liams and Lee,25 and cytotoxicity was determined using
the human colon carcinoma HCT 116 cell line (Table 1).
The general conclusion to emerge from these data is that
the C-1 hydroxyl group of paclitaxel does not have a
major effect on the tubulin assembly activity or cytotox-
icity of paclitaxel. In support of this statement, simple
1-deoxy analogues (excluding those with large substitu-
ents on the “northern hemisphere” such as 14b and 20)
all had tubulin-assembly activity within a factor of 3 of
that of paclitaxel, and most also had a cytotoxicity to HCT
116 cells within a factor of 3.
a
Key: (a) Red Al, THF; 5a , 77%; 5b, 12%; (b) 5a , NaH, THF,
6a -6c, 0 °C- rt, 6a , 77%; 6b, 86%; 6c, 77%; (c) HF/pyridine, -20
°C, 7a , 96%; 7b, 87%; 7c, 96%.
â-lactam chemistry that has been described previously.
The â-lactam derivatives 6a -6c were prepared by lit-
erature methods23 and used to acylate 13-deacetyl-1-
deoxybaccatin VI (5a ); the 2′-silylated 1-deoxypaclitaxel
analogues 7a -7c were prepared by this method in good
yields and were converted to the final analogues 8a -8c
by deprotection of the 2′-hydroxyl group with HF/pyri-
dine.
Although the route described above provided an ef-
ficient means of converting 3 into acetate-protected
1-deoxypaclitaxel analogues, it could not provide deriva-
tives with free hydroxyl groups at the 7, 9, and 10
positions. Since changes in the nature of the substituents
at these positions can affect the bioactivity of the result-
ing analogue in small but nevertheless significant ways,17,24
we desired to develop a route that gave access to free
hydroxyl groups at these positions.
(23) (a) Holton, R. A.; Biediger, R. J .; Boatman, P. D. In Taxol:
Science and Applications; Suffness, M., Ed.; CRC Press: Boca Raton,
FL, 1995; pp 97-121. (b) Ojima, I.; Habus, I.; Zhao, M.; Zucco, M.;
Park, Y. H.; Sun, C. M.; Brigaud, T. Tetrahedron 1992, 48, 6985-7012.
(c) Georg, G. I.; Cheruvallath, Z. S.; Harriman, G. C. B.; Hepperle, M.;
Park, H. Bioorg. Med. Chem. Lett. 1993, 3, 2467-2470.
(24) (a) Mellado, W.; Magri, N. F.; Kingston, D. G. I.; Garcia-Arenas,
R.; Orr, G. A.; Horwitz, S. B. Biochem. Biophys. Res. Commun. 1984,
124, 329-335. (b) Chen, S.-H.; Farina, V. In The Chemistry and
Pharmacology of Taxol and its Derivatives; Farina, V., Ed.; Elsevier
Science B.V.: Amsterdam, 1995; Vol. 22, pp 165-253.
A direct comparison with paclitaxel was not possible,
(25) Williams, R. C., J r.; Lee, J . C. Methods Enzymol. 1982, 85 Pt.
D, 376-385.

1-Deoxypaclitaxel Analogues
J . Org. Chem., Vol. 64, No. 6, 1999 1817
Sch em e 2a
a
Key: (a) Triton B, CH2Cl2, 65% or 1 N NaOH, MeOH, 84%; (b) 2-methoxypropene, PPTS, CH2Cl2, 10a , 55% or PhCHO, CSA, toluene,
10b, 63%; (c) Et3SiCl, Im, CH2Cl2 or DMF, 11a , 74% and 11b, 72%; (d) MeLi, THF, 12a , 63% and 12b, 37%; (e) n-BuLi, THF, 12a , -78
°C; then 6d , yields 13a (23%); NaH, THF, 12b, 0 °C to rt, then 6b, yields 13b (69%) (f) HF-Py, THF, 14a , 99%; 14b, 33%
Sch em e 3a
a
Key: (a) Triton B, CH2Cl2, 42%; or KOH, MeOH, 52%; (b) TBAF, THF, -20 °C, 80%; (c) DMP, TsOH, Me2CO, rt, 97%; (d) TBAF,
THF, -20 °C, 78% (e) MeI, Ag2O, THF, 65 °C, 12h; (f) TBAF, THF, 17, 12%; 18, 15%.
because we did not prepare 1-deoxypaclitaxel itself.
However, 7,9-diacetyl-9(R)-dihydropaclitaxel (21) was
prepared by Klein and his collaborators,17 and our
compound 8a is the 1-deoxy analogue of 21. Although the
data were obtained under different conditions, Klein
reported that compound 21 is slightly more active than
paclitaxel in a tubulin-assembly assay, while compound
8a is slightly less active than paclitaxel. The cytotoxicity
data is even more difficult to compare since different cell
lines were used; in the four cell lines evaluated by Klein,
compound 21 had IC50 values that were, on average, 4.7-,
1.4-, 3.0-, and 2.3-fold greater than those of paclitaxel,
while compound 8a has an IC50 value 11-fold greater than
that of paclitaxel in the one cell line evaluated. Removal
of the C-1 hydroxyl group thus results in a small but
significant loss in both tubulin-assembly activity and
cytotoxicity for 7,9-diacetyl-9(R)-dihydropaclitaxel, and
by extension it is likely that removal of the C-1 hydroxyl
group from paclitaxel itself would also cause a slight
reduction in activity.

1818 J . Org. Chem., Vol. 64, No. 6, 1999
Kingston et al.
Ta ble 1. Bioa ctivity Da ta for 1-Deoxyp a clita xel
An a logu es
8.0 Hz, 1H), 5.84 (m, 1H), 5.98 (d, J ) 11.4 Hz, 1H), 6.15 (d,
J ) 11.1 Hz, 1H), 7.47 (t, J ) 7.4 Hz, 2H), 7.60 (m, 1H), 8.08
(dd, J ) 1.3 and 8.4 Hz, 2H); 13C NMR δ 12.9, 15.1, 20.8, 21.0,
21.4, 22.9, 26.6, 29.7, 30.1, 31.4, 34.6, 37.7, 44.1, 45.8, 47.1,
67.5, 71.4, 71.6, 71.9, 75.5, 81.7, 82.0, 128.6, 129.8, 132.7, 133.5,
142.0, 164.9, 169.1, 169.8, 170.1, 171.7; HRFABMS calcd for
cytotoxicity to HCT116
tubulin data
human colon carcinoma
EC0.01
/
IC50/
no.
EC0.01
EC0.01(PT)a
IC50 (µM)
IC50(PT)a
C
35H44O12 [M + H]+ m/z 679.2730, found 679.2718. 5b: 1H
NMR δ 1.01 (s, 3H), 1.48 (s, 3H), 1.79 (s, 3H), 1.71-2.00 (m,
1H), 2.00 (s, 3H), 2.07 (s, 3H), 2.08 (s, 3H), 2.10 (s, 3H), 2.17
(s, 3H), 2.18-2.22 (m, 2H), 2.40 (m, 1H), 2.62-2.72 (m, 2H),
4.25 (d, J ) 7.7 Hz, 1H), 4.31 (d, J ) 8.0 Hz, 1H), 4.78-4.81
(dd, J ) 2.8 and 8.6 Hz, 1H), 5.29 (m, 1H), 5.65 (m, 1H), 5.91-
5.95 (m, 2H), 6.06 (d, J ) 10.9 Hz, 1H), 7.46 (t, J ) 7.4 Hz,
2H), 7.59 (m, 1H), 8.01 (dd, J ) 1.4 and 8.4 Hz, 2H); 13C NMR
δ 13.1, 16.4, 20.7, 20.9, 21.2, 21.3, 25.5, 27.6, 33.3, 34.1, 37.3,
45.3, 46.4, 47.9, 69.5, 70.6, 71.2, 71.3, 74.9, 75.1, 79.5, 87.0,
128.6, 129.5, 129.7, 133.5, 136.3, 137.8, 164.9, 169.9, 169.2,
169.7, 170.0, 170.1; HRFABMS calcd for C35H44O12 [M + H]+
m/z 679.2730, found 679.2725.
1
8a
8b
8c
5.3 ( 1.1
12.2 ( 4.0
12.0 ( 5.4
18 ( 2
1.0
2.0
2.4
5.8
2.0
0.0018 ( 0.0002
0.0315b
0.0046
0.0047
0.0043
0.0105
0.0022
0.003
1
11.2
2.9
2.7
2.3
6.6
1.2
2.0
14a
9.1 ( 3.7
14b >1000
14c
16
18 >1000
20
21
>200
8.5 ( 3.3
9.1 ( 1.4
1.6
1.8
>200
>0.12
0.0049
>70
12.8 ( 3.3
2.2
2.8
0.9c
0.9-1.8d
a
The EC0.01/EC0.01(PT) and IC50/IC50(PT) values were obtained
by dividing the EC0.01 or IC50 value observed for the analogue by
the EC0.01 or IC50 value observed for paclitaxel in the same run,
and this value varied slightly from run to run; the data thus cannot
be obtained by dividing the observed EC0.01 value by 5.3 or the
7,9-Dia cetyl-9(R)-d ih yd r o-2′-tr ieth ylsilyl-1-d eoxyp a cli-
ta xel (7a ). To a solution of 5a (10.0 mg, 0.015 mmol) and 6a
(9.3 mg, 0.022 mmol) in THF (1.0 mL) was added NaH (7.0
mg, 60% dispersion in mineral oil, 20 equiv) at 0 °C, and the
mixture was allowed to stir at room temperature for 2 h. The
mixture was then quenched with AcOH (0.2 mL) at 0 °C and
diluted with EtOAc (5 mL). This mixture was diluted with
water and extracted with EtOAc (2 × 10 mL), and the organic
layer was washed with a saturated solution of NaHCO3, water,
and brine, followed by drying over Na2SO4. The residue
obtained after evaporation under reduced pressure was puri-
fied by PTLC (silica gel, 500 µm, EtOAc/hexane 1/4) to provide
7a (13.8 mg, 86%): 1H NMR δ 0.38 - 0.51 (m, 6H), 0.78-0.81
(m, 9H), 1.14 (s, 3H), 1.60 (s, 3H), 1.74-1.80 (m, 1H), 1.87 (s,
3H), 1.90-1.92 (m, 1H), 1.97 (s, 3H), 2.02-2.04 (m, 1H), 2.07
(s, 3H), 2.08 (s, 3H), 2.11 (s, 3H), 2.41-2.58 (m, 2H), 2.49 (s,
3H), 3.03 (d, J ) 5.50 Hz, 1H), 4.15 (d, J ) 8.39 Hz, 1H), 4.40
(d, J ) 8.24 Hz, 1H), 4.72 (d, J ) 1.83 Hz, 1H), 4.99 (d, J )
8.39 Hz, 1H), 5.57 (dd, J ) 9.31 and 7.93 Hz, 1H), 5.66 (d, J
) 8.7 Hz, 1H), 5.89 (m, 1H), 5.99-6.04 (m, 2H), 6.24 (d, J )
11.29 Hz, 1H), 7.14 (d, J ) 8.7 Hz, 1H), 7.29-7.51 (m, 10H),
7.60 (t, J ) 7.47 Hz, 1H), 7.74 (d, J ) 7.02 Hz, 2H), 8.07 (d, J
) 7.17 Hz, 2H); 13C NMR (CDCl3) δ 4.4, 6.5, 13.0, 14.4, 20.8,
20.9, 21.4, 23.3, 27.5, 31.4, 34.7, 38.3, 44.1, 45.8, 47.3, 55.6,
71.4, 71.5, 71.9, 74.4, 75.6, 81.4, 83.9, 126.5, 127.0, 127.8, 128.6,
128.7, 129.4, 129.9, 131.7, 133.3, 133.5, 134.3, 138.4, 138.5,
165.0, 167.2, 169.0, 169.3, 170.0, 170.1, 172.0; HRFABMS calcd
for C57H72NO15Si [M + H]+ m/z 1038.4671, found 1038.4657.
3′-N-Deben zoyl-3′-N-ter t-bu toxyca r bon yl-7,9-d ia cetyl-
9(R)-d ih yd r o-2′-tr iisop r op ylsilyl-1-d eoxyp a clita xel (7b).
To a solution of 5a (30 mg, 0.045 mmol) and 6b (23.0 mg, 0.054
mmol) in THF (2.5 mL) was added NaH (23.0 mg, 60%
dispersion in mineral oil, 22 equiv) at 0 °C, and the mixture
was stirred at room temperature for 6 h. The mixture was then
quenched with AcOH (1.0 mL) at 0 °C, diluted with EtOAc (5
mL) and water (5 mL), and extracted with EtOAc (10 mL).
The organic layer was washed with a saturated solution of
NaHCO3, water, and brine and dried over Na2SO4. The residue
obtained after concentration of the organic layer under reduced
pressure was purified by PTLC (silica gel, 1000 µm, EtOAc/
hexane 3/7) to yield 7b (38 mg, 77%): 1H NMR δ 0.90-0.91
(m, 21H), 1.18 (s, 1H), 1.34 (s, 9H), 1.58 (s, 3H), 1.76-1.82
(m, 3H), 1.89 (s, 3H), 1.98 (s, 3H), 2.05 (s, 3H), 2.08 (s, 3H),
2.10 (s, 3H), 2.46 (s, 3H), 2.48-2.56 (m, 2H), 3.34 (d, J ) 5.9
Hz, 1H), 4.14 (d, J ) 8.3 Hz, 1H), 4.41 (d, J ) 8.0 Hz, 1H),
4.81 (d, J ) 1.3 Hz, 1H), 4.98 (d, J ) 8.4 Hz, 1H), 5.24 (d, J )
9.9 Hz, 1H), 5.42 (d, J ) 9.3 Hz, 1H), 5.56-5.61 (dd, J ) 7.9
and 9.6 Hz, 1H), 5.87-5.92 (m, 2H), 6.03 (d, J ) 11.4 Hz, 1H),
6.25 (d, J ) 11.2 Hz, 1H), 7.24-7.36 (m, 5H), 7.47 (t, J ) 7.7
Hz, 2H), 7.59 (m, 1H), 8.08 (dd, J ) 1.2 and 8.4 Hz, 2H); 13C
NMR (CDCl3) d 12.5, 12.6, 12.9, 15.0, 17.8, 17.9, 20.8, 20.9,
21.4, 23.3, 27.7, 28.2, 29.7, 31.4, 34.6, 38.2, 44.1, 45.7, 47.4,
70.8, 71.7, 71.9, 75.4, 75.6, 79.7, 81.4, 84.0, 126.5, 127.6, 128.5,
128.6, 129.5, 129.9, 132.9, 133.5, 165.0, 168.9, 169.2, 169.9,
170.1; HRFABMS calcd for C58H81NO16Si [M + Na]+ m/z
1098.5222, found 1098.5267.
b
observed IC50 value by 0.0018. In the case of 8a the paclitaxel
IC50 value was 0.0028 µM. c ED50/ED50(PT): data from ref 17.
d
Data for human colon adenocarcinoma HT-29 from ref 17.
The analogue 8b was also tested in vivo against the
subcutaneous M109 murine tumor model by the IV route
of administration. It reached a maximum tolerated dose
(MTD) at 20 mg/Kg/injection on a qd5-8 schedule, and
any dose above this was toxic. The delay in the treated
animals as compared with control animals reaching a
tumor size of 1.0 g was 5.5 days; the comparable value
for paclitaxel at its MTD of 40 mg/Kg/injection was 8.8
days.
Exp er im en ta l Section
Gen er a l Meth od s. All chemicals were obtained from
Aldrich Chemical Co. and were used without further purifica-
tion. All anhydrous reactions were performed under argon.
THF was dried over sodium/benzophenone. All reactions were
monitored by TLC (silica gel, GF) and analyzed with UV light
and developed with vanillin spray. 1H NMR spectra were
obtained in CDCl3 at 400 MHz and were assigned by compari-
son of chemical shifts and coupling constants with those of
related compounds and by appropriate 2D NMR techniques;
coupling constants are reported in hertz. 13C NMR spectra
were assigned with the aid of HETCOR and DEPT spectra.
1
Some of the H NMR spectra showed the presence of traces of
ethyl acetate; paclitaxel and its derivative retain ethyl acetate
very tightly, and it cannot be removed completely even on
prolonged treatment in vacuo at 38 °C. Exact mass measure-
ments were performed at the Nebraska Center for Mass
Spectroscopy. Elemental analysis were performed by National
Chemical Consulting, Inc., Tenafly, NJ .
13-Dea cetylba cca tin VI (5a ) a n d 4-Dea cetylba cca tin
VI (5b). Baccatin VI (3) (54 mg, 0.007 mmol) was dissolved in
THF (2 mL); to this solution was added Red-Al (50 µL, 65%
solution in toluene, 0.014 mmol) at -20 °C, and the solution
was stirred for 20 min. The solution was then quenched with
a saturated solution of potassium tartrate (10 mL), and the
reaction mixture was diluted with EtOAc (15 mL). The organic
layer was washed with water and brine and dried over Na2-
SO4. Concentration under reduced pressure furnished a resi-
due which was purified by PTLC (silica gel, 1000 µm, EtOAc/
hexane 1/1) to afford unreacted 3 (6.0 mg), 5a (35 mg, 77% on
the basis of unrecovered starting material), and 5b (5.3 mg,
1
12%). 5a : H NMR δ 1.00 (s, 3H), 1.58 (s, 3H), 1.81 (s, 3H),
1.84-1.98 (m, 2H), 1.98 (s, 3H), 2.09 (s, 3H), 2.10 (s, 3H), 2.21
(s, 3H), 2.28 (s, 3H), 2.48-2.56 (m, 3H), 3.07 (d, J ) 6.1 Hz,
1H), 4.14 (d, J ) 8.2 Hz, 1H), 4.40 (d, J ) 8.4 Hz, 1H), 4.59
(m, 1H), 4.95 (d, J ) 8.7 Hz, 1H), 5.53-5.57 (dd, J ) 9.1 and

1-Deoxypaclitaxel Analogues
J . Org. Chem., Vol. 64, No. 6, 1999 1819
9(R)-Dih yd r o-7,9-d ia cetyl-1-d eoxyp a clita xel (8a ). To a
solution of 7a (11.0 mg, 0.010 mmol) in THF (1 mL) and
pyridine (100 µL) was added HF/pyridine (100 µL), and the
mixture was stirred at room temperature for 30 min. It was
then diluted with EtOAc (5 mL), and the EtOAc layer was
washed succesively with saturated NaHCO3, 0.1 N HCl, again
with saturated NaHCO3, water, and brine, and dried over Na2-
SO4. The residue obtained after evaporation was purified by
PTLC (silica gel, 500 µm, EtOAc/hexane 1/1) to yield 8a (8.11
mg, 87%): 1H NMR δ 1.08 (s, 3H), 1.58 (s, 6H), 1.84 (s, 3H),
1.86-1.90 (m, 2H), 1.96 (s, 3H), 2.00-2.02 (m, 2H), 2.08 (s,
3H), 2.10 (s, 3H), 2.28 (s, 3H), 2.53-2.68 (m, 2H), 2.96 (d, J )
5.80 Hz, 1H), 4.16 (d, J ) 8.09 Hz, 1H), 4.38 (d, J ) 8.24 Hz,
1H), 4.42 (dd, J ) 1.68 and 2.4 Hz, 1H), 4.74 (dd, J ) 2.59
and 2.44 Hz, 1H), 4.96 (d, J ) 8.09 Hz, 1H), 5.47 (dd, J ) 8.70
and 8.39 Hz, 1H), 5.85-5.87 (m, 3H), 5.96 (d, J ) 11.14 Hz,
1H), 6.10 (d, J ) 11.14 Hz, 1H), 7.32-7.51 (m, 10H), 7.60 (t,
J ) 7.47 Hz, 1H), 7.81 (d, J ) 7.05 Hz, 2H), 8.06 (d, J ) 7.18
Hz, 2H); 13C NMR d 13.0, 15.2, 20.7, 20.9, 21.4, 22.6, 26.6, 26.7,
31.3, 34.6, 37.9, 44.0, 46.0, 47.1, 54.3 70.8, 70.9, 71.6, 73.9,
75.4, 82.0, 83.6, 127.0, 127.2, 128.0, 128.6, 128.7, 129.4, 129.7,
131.8, 133.6, 133.8, 134.2, 137.5, 138.5, 164.8, 166.4, 169.0,
169.8, 170.0, 170.9, 171.1; HRFABMS calcd for C51H57NO15 [M
+ Na]+ m/z 946.3625, found 946.3655.
3′-N-Deb en zoyl-N-ter t-b u t oxyca r b on yl-9(R)-d ih yd r o-
7,9-d ia cetyl-1-d eoxyp a clita xel (8b). To a well-stirred solu-
tion of 7b (12.0 mg, 0.011 mmol) in THF (1.2 mL) was added
HF/pyridine (0.3 mL), and the mixture was stirred at room
temperature for 3 h. The mixture was then diluted with EtOAc
(5 mL), and this EtOAc layer was washed successively with
saturated NaHCO3, 0.1 N HCl, again with saturated NaHCO3,
water, and brine. It was then dried over Na2SO4 and concen-
trated under reduced pressure, and the residue obtained was
purified by PTLC (silica gel, 500 µm, EtOAc/hexane 9/11) to
furnish recovered 7b (3.0 mg) and 8b (7.3 mg, 96% on the basis
of unrecovered starting material): 1H NMR δ 1.10 (s, 3H), 1.39
(s, 9H), 1.58 (s, 3H), 1.85 (s, 3H), 1.96-2.40 (m, 3H), 1.96 (s,
3H), 1.98 (s, 3H), 2.08 (s, 3H), 2.10 (s, 3H), 2.24 (s, 3H), 2.48-
2.68 (m, 2H), 2.98 (d, J ) 5.8 Hz, 1H), 4.16 (m, 2H), 4.37 (d, J
) 8.2 Hz, 1H), 4.60 (s, 1H), 4.94 (d, J ) 8.1 Hz, 1H), 5.28 (m,
1H), 5.49 (dd, J ) 9.1 and 8.0 Hz, 1H), 5.63 (d, J ) 9.6 Hz,
1H), 5.86 (m, 2H), 5.97 (d, J ) 11.2 Hz, 1H), 6.14 (d, J ) 11.1
Hz, 1H), 7.26-7.48 (m, 7H), 7.58 (m, 1H), 8.05 (dd, J ) 1.2
and 8.4 Hz, 2H); 13C NMR d 13.0, 20.8, 20.9, 21.4, 22.5, 26.7,
28.3, 31.2, 34.6, 37.9, 44.0, 46.0, 47.2, 71.1, 71.6, 75.5, 77.8,
79.9, 81.9, 83.7, 127.0, 127.7, 128.5, 128.6, 129.5, 129.8, 133.6,
2.28 (s, 3H), 2.52-2.64 (m, 2H), 3.00 (d, J ) 5.79 Hz, 1H),
3.88 (bs, 1H), 4.16 (d, J ) 8.54 Hz, 1H), 4.28-4.30 (dd, J )
2.6 and 4.27 Hz, 1H), 4.39 (d, J ) 8.24 Hz, 1H), 4.82 (m, 1H),
4.97 (d, J ) 7.78 Hz, 1H), 5.02 (d, J ) 9.16 Hz, 1H), 5.24 (d,
J ) 9.00 Hz, 1H), 5.51 (dd, J ) 8.69 and 8.55 Hz, 1H), 5.86-
5.90 (m, 2H), 5.98 (d, J ) 11.14 Hz, 1H), 6.17 (d, J ) 11.14
Hz, 1H), 7.47 (dd, J ) 7.94 and 7.47 Hz, 2H), 7.60 (dd, J )
7.48 and 7.32 Hz, 1H), 8.06 (d, J ) 7.02 Hz, 2H); 13C NMR d
13.0, 15.3, 18.7, 20.8, 20.9, 21.4, 22.4, 25.8, 26.6, 26.8, 28.3,
31.1, 34,6, 37.9, 44.0, 46.0, 47.2, 71.2, 71.7, 73.9, 75.5, 83.7,
120.9, 128.6, 129.5, 129.8, 133.6, 164.9, 168.9, 169.8, 170.1;
HRFABMS calcd for C47H63NO16 [M + H]+ m/z 898.4225, found
898.4219.
7,9,10-Tr id ea cetylba cca tin VI (9). P r oced u r e A. To a
solution of baccatin VI (3) (15.00 mg, 0.021 mmol) in MeOH
(2.0 mL) was added 1 N NaOH (120 µL) at 0 °C, and the
reaction mixture was stirred at room temperature for 4 h. CO2
was bubbled through the reaction mixture, and the residue
obtained after evaporation was purified by PTLC (silica gel,
500 µm, EtOAc/hexane 3/2) to yield 9 (9.00 mg, 84%). P r oce-
d u r e B. To a solution of baccatin VI (3) (50 mg, 0.071 mmol)
in anhydrous CH2Cl2 (1.0 mL) was added benzyltrimethylam-
monium hydroxide (30 µL, 40% w/w solution in MeOH, 0.07
mmol) at 0 °C. The reaction mixture was stirred at room
temperature, and the progress of the reaction was monitored
by TLC until it showed maximum formation of the polar
product. The reaction mixture was diluted with cold CH2Cl2
(5 mL) at 0 °C and quenched with 0.1 N HCl (5 mL). The
organic layer was separated, washed successively with water,
saturated NaHCO3, and brine, and dried over Na2SO4. Con-
centration of the organic layer under reduced pressure gave a
crude residue, which was purified by PTLC (silica gel, 1000
µm, EtOAc/hexane 3/2) to yield unreacted 3 (17 mg), 9 (21.5
mg, 79% on the basis of unrecovered starting material), and a
small amount of a UV-inactive product which was not char-
acterized. 9: 1H NMR δ 1.20 (s, 3H), 1.63-1.69 (m, 1H), 1.76
(s, 3H), 1.79 (s, 3H), 1.85 (s, 3H), 1.88-1.96 (m, 2H), 2.18 (s,
3H), 2.27 (s, 3H), 2.42-2.61 (m, 2H), 2.88 (d, J ) 5.96 Hz,
1H), 3.08 (s, 1H), 3.42 (s, 1H), 4.16 (d, J ) 8.39 Hz, 1H), 4.32-
4.41 (m, 3H), 4.76 (s, 1H), 4.91 (d, J ) 10.38 Hz, 1H), 4.98 (d,
J ) 8.09 Hz, 1H), 5.75 (dd, J ) 2.14 and 5.95 Hz, 1H), 5.96 (d,
J ) 10.5 Hz, 1H), 7.48 (t, J ) 7.94 Hz, 2H), 7.59 (t, J ) 7.32
Hz, 1H), 8.05 (dd, J ) 8.39 and 1.2 Hz, 2H); 13C NMR (CDCl3)
δ 12.5, 14.8, 21.3, 22.8, 26.7, 26.8, 31.7, 38.1, 38.2, 44.1, 44.3,
47.2, 69.3, 71.2, 71.7, 74.5, 78.8, 81.8, 83.9, 128.6, 129.8, 133.5,
135.3, 137.4, 165.0, 169.3, 170.7; HRFABMS calcd for C31H40O10
[M + H]+ m/z 573.2699, found 573.2703.
164.9, 168.9, 169.8, 170.0; HRFABMS calcd for C49H61NO16
Na [M + Na]+ m/z 942.3888, found 942.3883. Anal. Calcd for
49H61NO16: C, 63.97; H, 6.65; N, 1.52. Found: C, 64.21; H,
-
7,9,10-Tr id ea cetylba cca tin VI 7,9-Aceton id e (10a ). To
a solution of 9 (59 mg) in CH2Cl2 (3 mL) were added 2-meth-
oxypropene (10 µL, 1.0 mmol) and pyridinium tosylate (2 mg),
and the resulting solution was stirred at room temperature
for 12 h. After completion of the reaction, it was diluted with
CH2Cl2 (10 mL), washed with a saturated NaHCO3 solution
and brine, and concentrated under vacuo. The residue obtained
was purified by PTLC (silica gel, 1000 µm, EtOAc/hexane 1/3)
to yield 10a (30 mg, 55%): 1H NMR δ 1.11 (s, 3H), 1.48-2.00
(m, 3H), 1.52 (s, 6H), 1.75 (s, 3H), 1.79 (s, 3H), 1.82 (s, 3H),
2.21 (s, 3H), 2.29 (s, 3H), 2.45-2.65 (m, 2H), 2.76 (d, J ) 5.4
Hz, 1H), 4.14 (d, J ) 8.2 Hz, 1H), 4.28-4.39 (m, 2H), 4.58 (d,
J ) 8.5 Hz, 1H), 4.96 (d, J ) 8.7 Hz, 1H), 5.06 (d, J ) 10 Hz,
1H), 5.81 (d, J ) 8.8 Hz, 1H), 6.01 (m, 1H), 7.48 (d, J ) 8.1
C
6.98; N, 1.50.
9(R)-Dih yd r o-7,9-d ia cet yl-3′-d ep h en yl-3′-(3,3-d im et h -
ylp r op en yl)-1-d eoxyp a clit a xel (8c). To a solution of 5a
(10.0 mg, 0.015 mmol) and 6c (5.0 mg, 0.007 mmol) in THF
(0.5 mL) was added NaH (15 mg, 60% dispersion in mineral
oil) at 0 °C, and the mixture allowed to stir at room temper-
ature for 3 h. The mixture was then quenched with AcOH (0.2
mL) at 0 °C and diluted with EtOAc (5 mL). This reaction
mixture was diluted with water and extracted with EtOAc (2
× 10 mL), and the organic layer was washed with a saturated
solution of NaHCO3, water, and brine, followed by drying over
Na2SO4. The residue obtained after evaporation under reduced
pressure was purified by PTLC (silica gel, 500 µm, EtOAc/
hexane 1/4) to provide 9(R)-dihydro-7,9-diacetyl-2′-triethylsilyl-
3′-dephenyl-3′-(3,3-dimethylpropenyl)-1-deoxy taxol (7c, 5.6
mg,77%) which was used directly for the next reaction. To a
solution of 7c (5.0 mg, 0.004 mmol) in THF (1 mL) was added
TBAF (100 µL) at -20 °C, and the mixture was stirred for 10
min. It was then diluted with EtOAc (5 mL), and the EtOAc
layer was washed successively with saturated NaHCO3, 0.1
N HCl, again with saturated NaHCO3, water, and brine and
dried over Na2SO4. The residue obtained after evaporation was
purified by PTLC (silica gel, 500 µm, EtOAc/hexane 1/1) to
yield 8c (4.10 mg, 96%): 1H NMR δ 1.11 (s, 3H), 1.39 (s, 9H),
1.59 (s, 3H), 1.75 (s, 3H), 1.76 (s, 3H), 1.86 (s, 3H), 1.98 (s,
3H), 2.01-2.05 (m, 3H), 2.08 (s, 3H), 2.09 (s, 3H), 2.10 (s, 3H),
Hz, 2H), 7.62 (t, J ) 8.2 Hz, 1H), 8.08 (d, J ) 7.1 Hz, 2H); 13
C
NMR (CDCl3) δ 12.9, 15.3, 21.2, 22.7, 26.2, 26.9, 27.1, 31.7,
36.7, 38.4, 42.0, 42.3, 47.7, 69.4, 71.6, 72.2, 74.5, 76.4, 81.4,
83.7, 84.4, 107.4, 128.5, 129.6, 129.8, 133.2, 133.6, 139.6, 165.0,
169.1, 170.6.
7,9,10-Tr id ea cetylba cca tin VI 7,9-Ben zylid en e Aceta l
(10b). To a solution of 9 (21.5 mg) in toluene (2 mL) were
added camphor sulfonic acid (1 mg), molecular sieves (4A size),
and benzaldehyde (0.2 mL, 1.96 mmol), and the mixture was
stirred at 40 °C for 15 h. The reaction mixture was filtered
through a pad of Celite and washed with EtOAc, and the
organic layer was washed thoroughly with a saturated NaH-
CO3 solution and brine and dried over Na2SO4. The residue
obtained after evaporation was purified by PTLC (silica gel,

1820 J . Org. Chem., Vol. 64, No. 6, 1999
Kingston et al.
1000 µm, EtOAc/hexane 2/3) to yield recovered 9 (5.5 mg) and
10b (12 mg, 63% based on unrecovered starting material): 1H
NMR δ 1.19 (s, 3H), 1.65 (s, 3H), 1.79 (s, 3H), 1.64 (m, 1H),
1.93 (s, 1H), 1.99 (d, J ) 9.3 Hz, 1H), 2.19 (s, 3H), 2.28 (s,
3H), 2.53 (s, 3H), 2.44-2.70 (m, 2H), 2.76 (d, J ) 5.4 Hz, 1H),
4.12 (d, J ) 8.2 Hz, 1H), 4.36 (d, J ) 8.5 Hz, 1H), 4.38 (d, J )
8.9 Hz, 1H), 4.70 (d, J ) 10.1 Hz, 1H), 4.97 (d, J ) 8.7 Hz,
1H), 5.13 (s, 1H), 5.19 d, J ) 10 Hz, 1H), 5.80 (m, 1H), 6.00
(dd, J ) 8.8 and 8.7 Hz, 1H), 6.11 (s, 1H), 7.13-7.27 (m, 3H),
) 1.3 and 8.3 Hz, 2H); 13C NMR δ 5.8, 7.2, 13.8, 15.6, 23.0,
26.6, 27.2, 28.2, 30.7, 31.4, 38.4, 38.7, 42.0, 44.4, 48.1, 67.9,
71.8, 71.9, 74.6, 82.0, 82.6, 84.9, 106.5, 128.6, 129.8, 129.9,
133.4, 133.9, 140.9, 165.1, 172.4; HRFABMS calcd for C38H56O9-
SiLi [M + Li]+ m/z 691.3853, found 691.3847.
7,9,10,13-Tetr a d ea cetyl-10-tr ieth ylsilylba cca tin VI 7,9-
Ben zylid en e Aceta l (12b). To a solution of 11b (16.3 mg,
0.021 mmol) in THF (1.5 mL) was added methyllithium (100
µL, 1.4 M solution in ether, 0.13 mmol) at -78 °C; the solution
was stirred at the same temperature for 15 min. The mixture
was quenched with a buffer solution (pH 7.2) and diluted with
EtOAc (5 mL). The organic layer was washed with water and
brine, dried over Na2SO4, and concentrated under reduced
pressure to give a residue which was purified by PTLC (silica
gel, 500 µm, EtOAc/hexane 1/1) to provide 12b (5.5 mg, 37%):
1H NMR δ 0.68 (q, J ) 8.2 Hz, 6H), 1.02 (t, J ) 8.2 Hz, 9H),
1.55 (s, 3H), 1.68 (s, 3H), 1.75 (s, 3H), 1.91-2.22 (m, 3H), 2.07
(s, 3H), 2.27 (s, 3H), 2.56 (m, 2H), 2.89 (d, J ) 5.6 Hz, 1H),
4.16 (d, J ) 8.2 Hz, 1H), 4.37 (m, 2H), 4.60 (m, 2H), 4.93 (d, J
) 9.1 Hz, 1H), 5.12 (d, J ) 10.3 Hz, 1H), 5.81 (dd, J ) 2.4 and
6.2 Hz, 1H), 5.97 (s, 1H), 7.30-7.62 (m, 8H), 8.08 (dd, J ) 1.2
and 8.4 Hz, 2H); 13C NMR δ 5.9, 7.13, 12.9, 15.9, 23.0, 25.8,
30.5, 31.9, 38.0, 38.6, 42.8, 44.2, 47.6, 67.8, 71.6, 72.8, 82.0,
82.5, 84.9, 102.0, 126.5, 128.4, 128.5, 128.9, 129.8, 133.4, 134.2,
139.0, 142.1, 165.0, 171.9.
10-D e a c e t y l-9(R )-d ih y d r o -10-t r ie t h y ls ily l-2′-t er t -
bu tyldim eth ylsilyl-1-deoxypaclitaxel 7,9-Aceton ide (13a).
To a solution of 12a (20 mg, 0.029 mmol) in THF (1.0 mL)
was added n-butyllithium (20 µL, 2 M solution in the hexane,
0.5 mmol) at -78 °C, followed by the addition of 6d (16 mg,
0.043 mmol) in dry THF (0.2 mL), and the mixture was stirred
at the same temperature for 10 min. The mixture was then
quenched with saturated NH4Cl at -10 °C, diluted with EtOAc
(5 mL), and warmed to room temperature. The mixture was
extracted with EtOAc (2 × 10 mL), and the organic layer was
washed with water and brine and dried over Na2SO4. The
residue obtained after concentration under reduced pressure
was purified by PTLC (silica gel, 1000 µm, EtOAc/hexane 1/4)
to yield 13a (7.2 mg, 23%): 1H NMR δ -0.15 (s, 3Η), 0.01 (s,
3H), 0.65 (q, J ) 8.4 Hz, 6H), 0.82 (s, 9H), 1.00 (t, J ) 8.4 Hz,
9Η), 1.21 (s, 3H), 1.46 (s, 3H), 1.52 (s, 3H), 1.68 (s, 3H), 1.71-
2.00 (m, 3H), 1.84 (s, 3H), 1.86 (s, 3H), 2.38-2.65 (m, 2H), 2.48
(s, 3H), 2.74 (d, J ) 5.8 Hz, 1H), 4.18 (d, J ) 8.4 Hz, 1H), 4.34
(dd, J ) 9.1 and 8.0 Hz, 1H), 4.39 (m, 2H), 4.72 (s, 1H), 4.84
(d, J ) 9.2 Hz, 1H), 4.98 (d, J ) 8.6 Hz, 1H), 5.74 (d, J ) 8.2
Hz, 1H), 5.90 (m, 1H), 6.08 (m, 1H), 7.16 (d, J ) 7.0 Hz, 1H),
7.28-7.55 (m, 10H), 7.62 (t, J ) 8.4 Hz, 1H), 7.78 (d, J ) 8.2
Hz, 2H), 8.09 (dd, J ) 1.3 and 8.4 Hz, 2H); 13C NMR δ -5.8,
-5.2, 5.9, 7.2, 14.0, 14.8, 18.1, 23.4, 25.6, 26.4, 27.2, 27.5, 28.2,
31.7, 38.7, 38.9, 42.2, 44.2, 48.4, 55.6, 71.7, 72.0, 74.2, 74.8,
81.3, 82.6, 84.7, 106.5, 126.5, 127.0, 127.9, 128.6, 128.8, 129.6,
129.9, 131.7, 133.5, 134.2, 134.5, 137.0, 138.4, 165.3, 167.1,
169.6, 171.9; HRFABMS calcd for C60H83NO12Si2Li [M + Li]+
m/z 1073.5605, found 1073.5605.
3′-N-Deben zoyl-3′-N-ter t-bu toxyca r bon yl-10-d ea cetyl-
10-tr ieth ylsilyl-9(R)-d ih yd r o-2′-tr iisop r op ylsilyl-1-d eoxy-
p a clita xel 7,9-Ben zylid en e Aceta l (13b). To a solution of
12b (20 mg, 0.029 mmol) and 6b (5.0 mg, 0.011 mmol) in THF
(1.0 mL) was added NaH (3.5 mg, 60% dispersion in mineral
oil, 20 equiv) at 0 °C, and the mixture was allowed to stir at
room temperature for 2.5 h. The mixture was then quenched
with AcOH (0.2 mL) at 0 °C and diluted with EtOAc (5 mL).
This mixture was then diluted with H2O and extracted with
EtOAc (2 × 10 mL), and the organic layer was washed with
saturated aqueous NaHCO3, water, and brine, followed by
drying over Na2SO4. The residue obtained after evaporation
under reduced pressure was purified by PTLC (silica gel, 500
µm, EtOAc/hexane 1/4) to provide 13b (6.0 mg, 69%): 1H NMR
δ 0.68 (q, J ) 8.2 Hz, 6H), 0.94 (m, 21H), 1.02 (t, J ) 8.2 Hz,
9H), 1.21 (s, 3H), 1.34 (s, 9H), 1.74 (s, 3H), 1.76 (s, 3H), 1.92
(s, 3H), 1.86-2.42 (m, 3H), 2.45 (s, 3H), 2.56 (m, 2H), 2.74 (d,
J ) 5.6 Hz, 1H), 4.15 (d, J ) 8.3 Hz, 1H), 4.36-4.41 (m, 2H),
4.63 (d, J ) 10.2 Hz, 1H), 4.82 (s, 1H), 4.96 (d, J ) 8.8 Hz,
1H), 5.13 (d, J ) 10.2 Hz, 1H), 5.23 (d, J ) 9.7 Hz, 1H), 5.40
(d, J ) 10.5 Hz, 1H), 5.85 (dd, J ) 2.4 and 6.2 Hz, 1H), 5.95
7.40-7.50 (m, 4H), 7.60 (m, 1H), 8.04 (d, J ) 7.1 Hz, 2H); 13
C
NMR (CDCl3) δ 13.1, 15.5, 21.3, 22.7, 26.0, 26.9, 31.7, 36.8,
38.2, 42.0, 42.5, 47.6, 69.4, 71.5, 71.5, 72.1, 81.4, 84.0, 84.4,
101.8, 125.3, 126.1, 128.2, 128.6, 128.6, 128.9, 129.0, 129.3,
129.5, 129.8, 133.0, 133.6, 137.8, 140.4, 165.0, 169.2, 170.6.
7,9,10-Tr id ea cetyl-10-tr ieth ylsilylba cca tin VI 7,9-Ac-
eton id e (11a ). To a solution of 10a (30 mg, 0.049 mmol) in
dry CH2Cl2 (1 mL) was added imidazole (23.3 mg, 0.34 mmol)
followed by Et3SiCl (50 µL, 0.29 mmol). The mixture was
stirred for 2 h at room temperature and diluted with EtOAc
(10 mL). The organic layer was washed with water and brine,
dried over Na2SO4, and concentrated under reduced pressure.
The residue obtained was purified by PTLC (silica gel, 1000
µm, EtOAc/hexane 1/4) to yield 11a (26 mg, 74%): 1H NMR δ
0.65 (q, J ) 8.3 Hz, 6H), 0.99 (t, J ) 8.3 Hz, 9Η), 1.18 (s, 3H),
1.46 (s, 3H), 1.60 (m, 1H), 1.61 (s, 3H), 1.65 (s, 3H), 1.82 (s,
3H), 1.84 (s, 3H), 1.88-1.95 (m, 2H), 2.18 (s, 3H), 2.25 (s, 3H),
2.41-2.65 (m, 2H), 2.70 (d, J ) 5.9 Hz, 1H), 4.13 (d, J ) 8.7
Hz, 1H), 4.29 (t, J ) 8.6 Hz, 1H), 4.31-4.36 (m, 2H), 4.86 (d,
J ) 10.1 Hz, 1H), 4.95 (d, J ) 8.5 Hz, 1H), 5.85 (m, 1H), 5.95
(m, 1H), 7.48 (d, J ) 8.2 Hz, 2H), 7.61 (t, J ) 8.0 Hz, 1H),
8.07 (dd, J ) 1.3 and 8.2 Hz 2H); 13C NMR δ 5.9, 7.12, 13.4,
15.2, 21.2, 22.7, 26.9, 27.0, 27.2, 28.2, 31.5, 38.5, 38.9, 42.6,
44.1, 48.2, 69.5, 71.8, 72.3, 74.2, 76.6, 81.3, 82.5, 84.4, 106.5,
128.6, 129.8, 133.5, 134.5, 137.2, 165.1, 169.2, 170.7; HR-
FABMS calcd for C40H58O11SiLi [M + Li]+ m/z 733.3959, found
733.3960.
7,9,10-Tr id ea cetyl-10-tr ieth ylsilylba cca tin VI 7,9-Ben z-
ylid en e Aceta l (11b). To a solution of 10b (12 mg, 0.018
mmol) in dry DMF (1 mL) were added imidazole (11 mg, 0.16
mmol) and Et3SiCl (15 µL, 0.09 mmol) at room temperature.
The mixture was stirred overnight and diluted with EtOAc
(10 mL). The organic layer was washed with water and brine,
dried over Na2SO4, and concentrated under reduced pressure.
The residue obtained was purified by PTLC (silica gel, 500
µm, EtOAc/hexane 1/3) to yield 11b (10.1 mg, 72%): 1H NMR
δ 0.68 (q, J ) 8.4 Hz, 6H), 1.01 (t, J ) 8.4 Hz, 9H), 1.18 (s,
3H), 1.62 (m, 1H), 1.72 (s, 3H), 1.76 (s, 3H), 1.91 (s, 3H), 2.00
(s, 3H), 2.20 (s, 3H), 2.27 (s, 3H), 2.42-2.60 (m, 2H), 2.71 (d,
J ) 5.9 Hz, 1H), 4.13 (d, J ) 8.7 Hz, 1H), 4.37 (m, 2H), 4.61
(d, J ) 10.5 Hz, 1H), 4.97 (d, J ) 8.5 Hz, 1H), 5.12 (d, J )
10.2 Hz, 1H), 5.81-5.84 (dd, J ) 2.1 and 5.9 Hz, 1H), 5.97 (s,
1H), 5.99 (m, 1H), 7.36-7.61 (m, 8H), 8.06 (dd, J ) 1.3 and
8.5 Hz, 2H); 13C NMR δ 6.0, 7.1, 12.8, 15.5, 21.3, 22.7, 26.2,
26.9, 31.9, 38.4, 38.7, 43.1, 44.1, 47.8, 69.6, 71.6, 72.8, 76.3,
76.4, 81.5, 82.4, 84.7, 102.0, 126.4, 128.4, 128.5, 128.9, 129.8,
133.5, 134.7, 138.7, 138.9, 165.0, 169.3, 170.6.
7,9,10,13-Tetr a d ea cetyl-10-tr ieth ylsilylba cca tin VI 7,9-
Aceton id e (12a ). To a solution of 11a (26 mg, 0.035 mmol)
in THF (1.5 mL) was added methyllithium (75 µL, 1.4 M
solution in ether, 0.06 mmol) at -78 °C, and the resulting
solution was stirred at the same temperature for 10 min. The
mixture was then quenched with saturated NH4Cl, diluted
with EtOAc (5 mL), and warmed to room temperature. The
organic layer was washed with water and brine and dried over
Na2SO4. The residue obtained after concentration of the
organic layer under reduced pressure was purified by PTLC
(silica gel, 500 µm, EtOAc/hexane 1/3) to yield recovered 11a
(10.2 mg) and 12a (9.5 mg, 63% on the basis of unrecovered
11a ): 1H NMR δ 0.66 (q, J ) 8.4 Hz, 6H), 1.00 (t, J ) 8.4 Hz,
9Η), 1.06 (s, 3H), 1.46 (s, 3H), 1.48 (s, 3H), 1.64 (s, 3H), 1.78
(s, 3H), 1.86-1.93 (m, 3H), 2.01 (s, 3H), 2.18 (d, J ) 10.4 Hz,
1H), 2.27 (s, 3H), 2.51-2.59 (m, 2H), 2.79 (d, J ) 5.9 Hz, 1H),
4.16 (d, J ) 8.8 Hz, 1H), 4.28-4.38 (m, 4H), 4.59 (m, 1H), 4.83
(d, J ) 10.4 Hz, 1H), 4.90 (d, J ) 8.4 Hz, 1H), 5.83 (m, 1H),
7.47 (t, J ) 8.4 Hz, 2H), 7.59 (t, J ) 8.3 Hz, 1H), 8.08 (dd, J

1-Deoxypaclitaxel Analogues
J . Org. Chem., Vol. 64, No. 6, 1999 1821
(s, 1H), 7.27-7.60 (m, 13H), 8.08 (dd, J ) 1.2 and 8.4 Hz, 2H);
13C NMR δ 6.0, 7.1, 12.6, 13.0, 15.0, 17.8, 17.9, 23.3, 26.3, 26.8,
28.2, 32.0, 38.6, 38.7, 43.0, 44.0, 48.1, 71.8, 72.7, 72.9, 76.0,
79.8, 81.6, 82.4, 84.9, 102.0, 126.4, 126.6, 127.6, 128.3, 128.5,
128.6, 128.8, 129.6, 129.9, 133.4, 134.1, 138.8, 139.0, 165.2,
169.4, 170.9, 172.3.
8.2 Hz, 1H), 4.35-4.42 (m, 3H), 4.79 (s, 1H), 4.92-4.98 (m,
2H), 5.23 (d, J ) 10.2 Hz, 1H), 5.77 (m, 1H), 5.94 (m, 1H),
7.24-7.36 (m, 5H), 7.47 (t, J ) 7.4 Hz, 2H), 7.59 (m, 1H), 8.05
(dd, J ) 1.3 and 8.5 Hz, 2H); 13C NMR δ 12.6, 14.5, 17.8, 17.9,
23.4, 26.2, 27.5, 28.2, 38.2, 38,5, 43.9, 44.2, 45.9, 47.2, 47.4,
71.7, 71.9, 74.4, 75.5, 78.2, 79.2, 81.8, 84.1, 126.5, 127.6, 128.5,
128.6, 129.6, 129.9, 133.5, 148.6, 167.9, 169.3, 170.1; HR-
FABMS calcd for C52H76NO13 [M + H]+ m/z 950.5085, found
950.5045.
10-Dea cetyl-9(R)-d ih yd r o-1-d eoxyp a clita xel 7,9-Ace-
ton id e (14a ). To a solution of 13a (7.0 mg, 0.006 mmol) in
THF (0.5 mL) and pyridine (100 µL) was added HF/pyridine
(100 µL), and the mixture was stirred at room temperature
for 1.5 h. The mixture was then diluted with EtOAc (5 mL),
and the EtOAc layer was washed succesively with saturated
NaHCO3, 0.1 N HCl, again with saturated NaHCO3, water,
and brine, dried over Na2SO4, and concentrated under reduced
pressure. The residue obtained was purified by PTLC (silica
gel, 500 µm, EtOAc/hexane 1/1) to yield 14a (6.0 mg, 99%):
1H NMR δ 1.16 (s, 3H), 1.52 (s, 6H), 1.56 (s, 3H), 1.69 (s, 3H),
1.78 (s, 3H), 1.81-1.98 (m, 3H), 2.28 (s, 3H), 2.58-2.66 (m,
2H), 2.71 (d, J ) 5.8 Hz, 1H), 3.78 (m, 1H), 4.18 (d, J ) 8.4
Hz, 1H), 4.21 (dd, J ) 9.1 and 8.0 Hz, 1H), 4.36 (m, 2H), 4.54
(d, J ) 10.2 Hz, 1H), 4.78 (m, 1H), 4.96 (m, 2H), 5.81 (m, 1H),
5.85-5.96 (m, 2H), 7.11-7.58 (m, 10H), 7.60 (t, J ) 8.3 Hz,
1H), 7.82 (d, J ) 8.4 Hz, 2H), 8.09 (dd, J ) 1.3 and 8.3 Hz,
2H); 13C NMR δ 13.0, 15.6, 22.6, 25.7, 26.9, 27.0, 31.8, 36.73
38.3, 41.8, 42.6, 47.5, 54.44, 71.1, 71.3, 72.2, 73.8, 74.4, 76.4,
82.2, 83.6, 84.3, 107.5, 127.0, 127.1, 127.3, 128.1, 128.7, 128.9,
129.4, 129.8, 131.8, 133.7, 133.8, 134.3, 138.3, 138.4, 165.0,
166.3, 170.9, 171.3; HRFABMS calcd for C48H55NO12Li [M +
Li]+ m/z 844.3884, found 844.3913.
3′-N-Deben zoyl-3′-N-ter t-bu toxyca r bon yl-10-d ea cetyl-
9(R)-d ih yd r o-1-d eoxyp a clita xel 7,9-Ben zylid en e Aceta l
(14b). To a solution of 13b (6.0 mg, 0.005 mmol) in THF (1.0
mL) was added HF/pyridine (200 µL), and the mixture was
stirred at room temperature for 2 h. The mixture was then
diluted with EtOAc (15 mL), and the EtOAc layer was washed
succesively with saturated NaHCO3, 0.1 N HCl, again with
saturated NaHCO3, water, and brine. It was then dried over
Na2SO4 and concentrated under reduced pressure, and the
residue obtained was purified by PTLC (silica gel, 500 µm,
EtOAc/hexane 9/11) to yield 14b (1.5 mg, 33%): 1H NMR δ
1.16 (s, 3H), 1.39 (s, 9H), 1.65 (s, 3H), 1.78 (s, 3H), 1.79 (s,
3H), 1.91-2.00 (m, 2H), 1.99 (d, J ) 9.0 Hz, 1H),2.25 (s, 3H),
2.62-2.66 (m, 2H), 2.74 (d, J ) 5.3 Hz, 1H), 4.01 (s, 1H), 4.15
(d, J ) 7.6 Hz, 1H), 4.30-4.36 (m, 2H), 4.62-4.68 (m, 2H),
4.93 (d, J ) 9.4 Hz, 1H), 4.96 (d, J ) 10. 9 Hz, 1H), 5.15 (d, J
) 9.6 Hz, 1H), 5.29 (m, 1H), 5.60 (m, 1H), 5.80 (m, 1H), 5.91
(m, 1H), 6.12 (s, 1H), 7.28-7.60 (m, 13H), 8.04 (dd, J ) 1.2
and 8.6 Hz, 2H); HRFABMS calcd for C50H59NO13Li [M + Li]+
m/z 888.4146, found 888.4159.
3′-N-Deben zoyl-3′-N-ter t-bu toxycar bon yl-9(R)-dih ydr o-
10-d ea cet yl-2′-t r iisop r op ylsilyl-1-d eoxyp a clit a xel (15).
P r oced u r e A. To a solution of 7b (26 mg, 0.024 mmol) in
anhydrous CH2Cl2 (1.0 mL) was added benzyltrimethylam-
monium hydroxide (10 µL, 40% w/w solution in methanol,
0.024 mmol) at 0 °C. The reaction mixture was stirred at room
temperature, and the progress of the reaction was monitored
by TLC until a polar spot developed at the base of the
chromatogram. The reaction mixture was then diluted with
cold CH2Cl2 (5 mL) at 0 °C and quenched with 0.1 N HCl (5
mL). The organic layer was separated, washed succesively with
water, saturated NaHCO3, and brine, and dried over Na2SO4.
Concentration of the organic layer under reduced pressure
gave crude residue which was purified by PTLC (silica gel,
1000 µm, MeOH/CH2Cl2 1/24) to furnish recovered 7b (10 mg)
and 15 (6.0 mg, 42% on the basis of unrecovered starting
material). P r oced u r e B. To a solution of 7b (35.00 mg) in
MeOH (2.0 mL) was added 1 N KOH (250 µL) at 0 °C, and the
reaction mixture was stirred at room temperature for 16 h.
CO2 was then bubbled through the reaction mixture, and the
residue obtained after evaporation was purified by PTLC (silica
gel, 500 µm, 4% MeOH/CH2Cl2) to yield unreacted 7b (7.5 mg)
and 15 (12.0 mg, 52% based on unrecovered starting mate-
rial): 1H NMR δ 0.91 (m, 21H), 1.25 (s, 3H), 1.35 (s, 9H), 1.78
(s, 3H), 1.79 (s, 3H), 1.87 (s, 3H), 1.91-2.04 (m, 2H), 2.45 (s,
3H), 2.49-2.61 (m, 2H), 2.91 (d, J ) 5.8 Hz, 1H), 4.17 (d, J )
3′-N-Deben zoyl-3′-N-ter t-bu toxycar bon yl-9(R)-dih ydr o-
10-d ea cetyl-9,10-d ih yd r oxy-1-d eoxyp a clita xel (16). To a
solution of 15 (3.0 mg, 0.003 mmol) in THF (1.0 mL) was added
tetrabutylammonium fluoride (25 µL, 1 M solution in THF)
at -20 °C, and the mixture was stirred at the same temper-
ature for 5 min and then at room temperature for 10 min. The
mixture was then diluted with EtOAc (5 mL), and the EtOAc
layer was washed successively with saturated NaHCO3, water,
and brine and dried over Na2SO4. The residue obtained after
concentration of the organic layer was purified by PTLC (silica
gel, 500 µm, EtOAc/hexane 3/2) to yield 16 (1.9 mg, 80%): 1H
NMR δ 1.19 (s, 3H), 1.39 (s, 9H), 1.68 (s, 3H), 1.76 (s, 3H),
1.80 (s, 3H), 1.86-1.96 (m, 2H), 2.24 (s, 3H), 2.52-2.66 (m,
2H), 2.84 (d, J ) 5.3 Hz, 1H), 4.11 (m,1H), 4.19 (d, J ) 8.5 Hz,
1H), 4.25-4.35 (m, 3H), 4.61 (s, 1H), 4.88(d, J ) 10.2 Hz, 1H),
4.93 (d, J ) 8.3 Hz, 1H), 5.28 (d, J ) 9.4 Hz, 1H), 5.66 (d, J )
9.6 Hz, 1H), 5.76 (m, 1H), 5.87 (m, 1H), 7.27-7.48 (m, 7H),
7.59 (t, J ) 7.4 Hz, 1H), 8.03 (dd, J ) 1.3 and 8.5 Hz, 2H); 13
C
NMR δ 12.5, 15.1, 22.6, 26.7, 28.3, 31.6, 38.2, 43.9, 44.6, 47.2,
55.9, 71.3, 71.4, 74.1, 74.4, 79.0, 83.8, 127.0, 127.8, 128.5, 128.6,
129.5, 133.6, 165.0; HRFABMS calcd for C43H55NO13 [M + H]+
m/z 794.3751, found 794.3740. Anal. Calcd for C52H55NO13: C,
65.06; H, 6.97; N, 1.76. Found: C, 65.09; H, 6.59; N, 1.92.
3′-N-Deben zoyl-3′-N-ter t-bu toxycar bon yl-9(R)-dih ydr o-
10-d ea cetyl-7-O-m eth yl-10-O-(4-m eth oxybu tyl)-1-d eoxy-
p a clita xel (18) a n d 3′-N-Deben zoyl-3′-N-ter t-bu toxyca r -
b on yl-9(R )-d ih yd r o-10-d e a ce t yl-7-O-m e t h yl-1-d e oxy-
p a clita xel (20). To a solution of 15 (20 mg, 0.021 mmol) in
THF (1.0 mL) were added methyl iodide (1 mL) and Ag2O (20
mg), and the mixture was stirred at 65 °C for 16 h. The
reaction mixture was diluted with EtOAc (5 mL), and the
EtOAc layer was washed succesively with buffer solution (pH
7.2), saturated NaHCO3, water, and brine and dried over Na2-
SO4. The residue obtained after concentration of the organic
layer was purified by PTLC (silica gel, 500 µm, EtOAc/hexane
3/2) to yield a mixture of 17 and 19 (4.6 mg) and recovered
starting material (6 mg). This mixture was dissolved in THF
(1 mL), treated with TBAF (50 µL) at -20 °C, and stirred at
the same temperature for 15 min. The residue obtained after
the usual workup was purified by PTLC (silica gel, 500 µm,
2.5%, MeOH/CH2Cl2) to yield 18 (1.6 mg, 12%) and 20 (1.7 mg,
15%).
Com p ou n d 18: 1H NMR δ 1.15 (s, 3H), 1.39 (s, 9H), 1.68
(s, 3H), 1.75 (s, 3H), 1.81 (s, 3H), 1.91-2.04 (m, 3H), 2.10 (s,
3H), 2.16-2.18 (m, 2H), 2.22 (s, 3H), 2.60 (m, 2H), 2.80 (d, J
) 6.11 Hz, 1H), 3.34 (s, 3H), 3.39-3.41 (m, 2H), 3.69-3.71
(m, 2H), 3.72 (s, 3H), 3.99 (d, J ) 10.37 Hz, 1H), 4.17 (m, 1H),
4.33 (d, J ) 8.24 Hz, 1H), 4.61 (m, 1H), 4.68 (d, J ) 10.38 Hz,
1H), 4.93 (d, J ) 8.85 Hz, 1H), 5.58 (m, 1H), 5.73 (m, 1H),
5.89 (m, 1H), 7.29-7.61 (m, 8H), 8.05 (d, J ) 6.71 Hz, 2H);
HRFABMS calcd for C49H68NO14 [M + H]+ m/z 894.4639, found
894.4621.
Com p ou n d 20: 1H NMR δ 1.17 (s, 3H), 1.40 (s, 9H), 1.50-
1.51 (m, 1H), 1.70 (s, 3H), 1.76 (s, 3H), 1.82 (s, 3H), 1.85-1.95
(m, 3H), 2.24 (s, 3H), 2.68 (m, 2H), 2.86 (d, J ) 5.49 Hz, 1H),
3.42 (s, 3H), 3.43 (d, J ) 9.31 Hz, 1H), 3.89 (dd, J ) 9.61 and
7.02 Hz, 1H), 4.20 (d, J ) 8.70 Hz, 1H), 4.34 (d, J ) 8.39 Hz,
1H), 4.61 (m, 1H), 4.70 (d, J ) 10.37 Hz, 1H), 4.96 (d, J )
8.39 Hz, 1H), 5.20 (d, J ) 9.61 Hz, 1H), 5.29 (m, 1H), 5.67 (d,
J ) 9.01 Hz, 1H), 5.85 (m, 1H), 7.28-7.61 (m, 8H), 8.03 (d, J
) 7.17 Hz, 2H); HRFABMS calcd for C44H58NO13 [M + H]+
m/z 808.3908, found 808.3885.
3′-N-Deben zoyl-3′-N-ter t-bu toxyca r bon yl-10-d ea cetyl-
9(R)-d ih yd r o-2′-t r iisop r op ylsilyl-1-d eoxyp a clit a xel 7,9-
Aceton id e (13c). To a solution of 15 (7.0 mg, 0.007 mmol) in
acetone (1 mL) were added dimethoxypropane (200 µL, 1.0

1822 J . Org. Chem., Vol. 64, No. 6, 1999
Kingston et al.
mmol) and pyridinium tosylate (2 mg), and the mixture was
stirred at room temperature for 15 min. After completion of
the reaction, it was diluted with EtOAc (10 mL), washed with
a saturated NaHCO3 solution and brine, and concentrated in
vacuo. The residue obtained was purified by PTLC (silica gel,
1000 µm, EtOAc/hexane 1/3) to yield 13c (7.0 mg, 97%): 1H
NMR δ 0.90 (m, 21H), 1.34 (s, 9H), 1.51 (s, 6H), 1.69 (s, 3H),
1.73-1.85 (m, 2H), 1.81 (s, 3H), 1.88 (s, 3H), 2.04 (s, 3H), 2.09
(m, 1H), 2.44 (s, 3H), 2.59-2.65 (m, 2H), 2.75 (d, J ) 5.95 Hz,
1H), 4.09-4.13 (m, 2H), 4.22-4.38 (m, 2H), 4.58 (d, J ) 10.22
Hz, 1H), 4.79 (m, 1H), 4.94 (d, J ) 8.85 Hz, 1H), 5.03 (d, J )
9.77 Hz, 1H), 5.13 (m, 1H), 5.23 (m, 1H), 5.42 (d, J ) 8.85 Hz,
1H), 5.81 (m, 1H), 5.95 (m,1H), 7.25-7.39 (m, 5H), 7.47 (dd, J
) 7.93 and 7.79 Hz, 2H), 7.59 (t, J ) 7.48 Hz, 1H), 8.07, (d, J
) 7.32 Hz, 2H).
3′-N-Deben zoyl-3′-N-ter t-bu toxyca r bon yl-10-d ea cetyl-
9(R)-d ih yd r o-1-d eoxyp a clita xel 7,9-Aceton id e (14c). To a
solution of 13c (4.5 mg, 0.0045 mmol) in THF (1 mL) was
added TBAF (25 µL) at -20 °C, and the mixture was stirred
at the same temperature for 10 min. The residue obtained after
usual workup was purified by PTLC (silica gel, 500 µm, EtOAc/
hexane 1/1) to yield 14c (2.9 mg, 78%): 1H NMR δ 1.17 (s,
3Η), 1.39 (s, 9H), 1.51 (s, 6H), 1.54 (m, 1H), 1.69 (s, 6H), 1.78
(s, 3H), 1.85-2.00 (m, 3H), 2.23 (s, 3H), 2.57-2.65 (m, 2H),
2.69 (d, J ) 5.34 Hz, 1H), 4.04 (bs, 1H), 4.14 (d, J ) 8.4 Hz,
1H), 4.21-4.25 (dd, J ) 8.09 and 8.24 Hz, 1H), 4.33 (d, J )
8.54 Hz, 1H), 4.52 (d, J ) 10.07 Hz, 1H), 4.61 (m, 1H), 4.90-
4.99 (m, 3H), 5.28 (d, J ) 9.61 Hz, 1H), 5.63 (d, J ) 10.68 Hz,
1H), 5.78-5.80 (dd, J ) 1.83 and 5.99 Hz, 1H), 5.88 (dd, J )
8.69 and 8.55 Hz, 1H), 7.27-7.62 (m, 9H), 8.04 (d, J ) 7.02
Hz, 2H); 13C NMR δ 13.0, 15.6, 22.5, 25.9, 26.3, 26.9, 27.0, 28.3,
31.7, 36.7, 38.4, 41.8, 42.5, 47.6, 55.9, 71.2, 71.6, 72.1, 74.1,
74.4, 79.9, 82.0, 83.7, 84.3, 107.5, 127.0, 127.8, 128.5, 128.6,
129.4, 129.8, 133.7, 138.7, 165.0, 170.7, 171.4; HRFABMS calcd
for C46H59NO13 [M + H]+ m/z 834.4064, found 834.4063. Anal.
Calcd for C46H59NO13: C, 66.28; H, 7.09; N, 1.68. Found: C,
66.46; H, 6.88; N, 1.64.
a modified procedure of Swindell et al.26 These modifications,
in part, result in the expression of tubulin polymerization
potency as an effective concentration for any given compound.
For this method, different compound concentrations in polym-
erization buffer (0.1 M MES, 1 mM EGTA, 0.5 mM MgCl2, pH
6.6) were added to microtubule protein in polymerization
buffer at 37 °C in microcuvette wells of a Beckman (Beckman
Instruments) Model DU 7400 UV spectrophotometer. A final
microtubule protein concentration of 1.0 mg/mL and compound
concentrations of 2.5, 5.0, and 10 µM were used. Initial slopes
of absorbance change measured every 10 s were calculated by
the program accompanying the instrument after initial and
final times of the linear region encompassing at least 3 time
points were manually defined. Under these conditions linear
variances were generally < 10-6, slopes ranged from 0.03 to
0.002 A unit/min, and maximum absorbance was 0.15 A unit.
Effective concentration (EC0.01) is defined as the interpolated
concentration capable of inducing an initial slope of 0.01 A
unit/min and is calculated using the formula EC0.01 ) concen-
tration/slope.
Cytotoxicity Assa ys. Cells of the human colon carcinoma
line HCT116 were grown in 96-well titer plates for 48 h at 37
°C under 5% CO2 in 0.1 mL of medium. The IC50 value was
the drug concentration required to inhibit by 50% the increase
in cell protein. The average IC50 values for paclitaxel in the
experiments presented here were in the range 2.0-2.5 µM.
Ack n ow led gm en t. We are grateful for the financial
support for this work, which was provided by grants
from the National Cancer Institute (CA 69571) and from
Bristol-Myers Squibb Pharmaceutical Research Insti-
tute (all to D.G.I.K.).
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
compounds 8a -8c, 14a -14c, 16, 18, and 20. This material is
available free of charge via the Internet at http://pubs.acs.org.
Tu bu lin Assem bly Assa ys. Twice-cycled microtubule pro-
tein was prepared by following the procedure of Williams and
Lee25 and stored in liquid nitrogen before use. Quantification
of tubulin polymerization potency was accomplished following
J O981406L
(26) Swindell, C. S.; Krauss, N. E.; Horwitz, S. B.; Ringel, I. J . Med.
Chem. 1991, 34, 1176-1184.