Syntheses and structure - Activity relationships of novel nor-seco taxoids

Article abstract of DOI:10.1021/jo971953r

A series of novel nor-seco taxoids (4a-b, 5a-d, 6), including either a C-13 ester linkage or a C-13 amide linkage, was synthesized by means of the β-lactam synthon method using the coupling of (3R,4S)-1-acyl-β-lactams with properly protected nor-seco baccatin III derivatives (1, 2, 3) as the key step. Nor-seco baccatin III derivatives were prepared through oxidative cleavage of the A ring of 14β-hydroxy-10-deacetylbaccatin III followed by reduction, amination using Mitsunobu conditions, or reductive amination. Nor- seco taxoids with a C-13 ester linkage (4a-b) or a C-13 N-Me amide linkage (6) show reduced cytotoxicity against human cancer cell lines as compared with paclitaxel, but still retain a certain level of activity despite the destruction of the taxane A ring. However, none of the analogues with a C-13 N-H amide linkage (5a-d) exhibit appreciable activity (IC⁵⁰ > 1.0 μM). A restrained molecular dynamics study reveals the inability of 5a-d to attain the proposed bioactive conformation, which accounts for the loss of activity.

Full text of DOI:10.1021/jo971953r

J . Org. Chem. 1998, 63, 1637-1645
1637
Syn th eses a n d Str u ctu r e-Activity Rela tion sh ip s of Novel Nor -seco
Ta xoid s
Iwao Ojima,†,* Songnian Lin,† Subrata Chakravarty,† Ivana Fenoglio,†,‡ Young Hoon Park,†
Chung-Ming Sun,† Giovanni Appendino,‡ 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, Dipartimento di Scienza e Tecnologia del Farmaco, Universita` di Torino, 10125 Torino,
Italy, and Department of Experimental Therapeutics, Grace Cancer Drug Center, Roswell Park Cancer
Institute, Elm and Carlton Streets, Buffalo, New York 14263
Received October 23, 1997
A series of novel nor-seco taxoids (4a -b, 5a -d , 6), including either a C-13 ester linkage or a C-13
amide linkage, was synthesized by means of the â-lactam synthon method using the coupling of
(3R,4S)-1-acyl-â-lactams with properly protected nor-seco baccatin III derivatives (1, 2, 3) as the
key step. Nor-seco baccatin III derivatives were prepared through oxidative cleavage of the A ring
of 14â-hydroxy-10-deacetylbaccatin III followed by reduction, amination using Mitsunobu conditions,
or reductive amination. Nor-seco taxoids with a C-13 ester linkage (4a -b) or a C-13 N-Me amide
linkage (6) show reduced cytotoxicity against human cancer cell lines as compared with paclitaxel,
but still retain a certain level of activity despite the destruction of the taxane A ring. However,
none of the analogues with a C-13 N-H amide linkage (5a -d ) exhibit appreciable activity (IC50
>
1.0 µM). A restrained molecular dynamics study reveals the inability of 5a -d to attain the proposed
bioactive conformation, which accounts for the loss of activity.
Taxol (paclitaxel)1 and Taxote`re (docetaxel)2 are cur-
rently considered to be two of the most exciting drugs in
cancer chemotherapy.3-7 Both paclitaxel and docetaxel8-10
exhibit significant antitumor activity against various
cancers which have not been effectively treated by
existing chemotherapeutic drugs11,12 through their unique
anti-mitotic mechanism of action.13 Paclitaxel was ap-
proved by FDA for the treatment of advanced ovarian
cancer in December 1992 and for the treatment of breast
cancer in April 1994. It is also undergoing clinical trials
for other cancers. Docetaxel was approved by FDA for
the treatment of breast cancer in May 1996 and is
currently undergoing phase II and III clinical trials for
breast and lung cancers worldwide.3,12
The structure-activity relationship (SAR) studies of
paclitaxel and docetaxel have revealed the essential roles
of the N-acylphenylisoserine moiety at the C-13 position,
2-benzoate, 4-acetoxy, and the oxetane ring (D ring) for
their strong antitumor activity.14,15 However, little is
known concerning the role of the A ring of the baccatin
framework.14,15 It is very important to clarify the mini-
mum structural requirements for taxoid antitumor activ-
ity, e.g., binding ability to the tubulin receptor and
cytotoxicity, by looking at the reduced or simplified
structure analogues of paclitaxel. Accordingly, as a part
of our continuing SAR study of paclitaxel and docetaxel
analogues,16-27 we have studied the role of the A ring by
† State University of New York at Stony Brook.
‡ Universita´ di Torino.
§ Roswell Park Cancer Institute.
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Guilhem, J .; Cesario, M.; Pascard, C. Acta Crstallogr. 1990, C46, 781-
784.
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Agents: Basic Science and Current Status; American Chemical Soci-
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C.; Cheruvallath, Z. S.; Datta, A.; Hepperle, M.; Park, H.; HImes, R.
H.; J ayasinghe, L. In Taxane Anticancer Agents: Basic Science and
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American Chemical Society: Washington, DC, 1995; pp 217-232.
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Pera, P.; Bernacki, R. J . J . Med. Chem. 1994, 37, 1408-1410.
(18) Ojima, I.; Fenoglio, I.; Park, Y. H.; Pera, P.; Bernacki, R. J .
Bioorg. Med. Chem. Lett. 1994, 4, 1571-1576.
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Vrignaud, P.; Riou, J . F.; Lavelle, F. J . Med. Chem. 1994, 37, 2602-
2608.
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tions; Suffness, M., Ed.; CRC Press: Boca Raton, 1995; pp 379-415.
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Taxote`re; Stony Brook, NY, May 14-15, 1993; pp Abstracts 23-24.
S0022-3263(97)01953-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/07/1998

1638 J . Org. Chem., Vol. 63, No. 5, 1998
Ojima et al.
Ch a r t 1
Sch em e 1
synthesizing novel nor-seco taxoids in which the A rings
are cleaved but the B, C, and D rings are retained.28
A novel taxane diterpenoid, 14â-hydroxy-10-deacetyl-
baccatin III (14â-OH-DAB) was isolated from the needles
and other parts of Taxus wallichiana Zucc. (Himalayan
yew) in 1992.29 The presence of a cis diol group at the
C-1 and C-14 positions of 14â-OH-DAB allows the oxida-
tive cleavage of the A ring with periodic acid to occur,
giving the corresponding nor-seco-10-deacetylbaccatin III
(1) (Chart 1) after the reduction of the resulting aldehyde.
Novel nor-seco taxoids 4 were synthesized using the nor-
seco-baccatin 1 by means of the â-lactam synthon
method.28 Since it was anticipated that the introduction
of an amide linkage at the C-13 position would rigidify
the conformation of nor-seco taxoids, two 13-amino-nor-
seco-baccatins 2 and 3 were synthesized and coupled with
different isoserine precursors to give another series of
novel nor-seco taxoids 5 and 6. The novel nor-seco
taxoids thus synthesized were assayed for their cytotox-
icity against several human cancer cell lines. We de-
scribe here the syntheses and biological activities of the
novel nor-seco taxoids 4, 5, and 6.
Resu lts a n d Discu ssion
A series of novel nor-seco taxoids (4a -b, 5a -d , 6) was
synthesized from 14â-OH-DAB using highly efficient and
practical coupling protocols based on the â-lactam syn-
thon method.16,30-34 The novel nor-seco baccatin 8 was
synthesized in 92% yield through oxidative cleavage of
the A ring of 14â-OH-DAB with periodic acid (Scheme
1). It is worthy of note that this oxidative cleavage is
realized because of the presence of the hydroxyl group
at C-14, i.e., this type of cleavage is impossible for the
usual 10-deacetylbaccatin III (DAB). The oxidative
cleavage of the A ring gives intermediate 7 bearing a
ketone group at C-1, which immediately reacts with the
hydroxyl group at C-10 in situ to form the hemiketal 8
(Scheme 1).
(21) Ojima, I.; Park, Y. H.; Fenoglio, I.; Duclos, O.; Sun, C.-M.;
Kuduk, S. D.; Zucco, M.; Appendino, G.; Pera, P.; Veith, J . M.; Bernacki,
R. J .; Bissery, M.-C.; Combeau, C.; Vrignaud, P.; Riou, J . F.; Lavelle,
F. In Taxane Anticancer Agents: Basic Science and Current Status;
ACS Symp. Ser. 583; Georg, G. I.; Chen, T. T.; Ojima, I., Vyas, D. M.,
Eds.; American Chemical Society: Washington, DC, 1995; pp 262-
275.
(22) Ojima, I.; Kuduk, S. D.; Slater, J . C.; Gimi, R. H.; Sun, C. M.
Tetrahedron 1996, 52, 209-224.
(23) Ojima, I.; Slater, J . C.; Michaud, E.; Kuduk, S. D.; Bounaud,
P.-Y.; Vrignaud, P.; Bissery, M.-C.; Veith, J .; Pera, P.; Bernacki, R. J .
J . Med. Chem. 1996, 39, 3889-3896.
(24) Ojima, I.; Kuduk, S. D.; Slater, J . C.; Gimi, R. H.; Sun, C. M.;
Chakravarty, S.; Ourevich, M.; Abouabdellah, A.; Bonnet-Delpon, D.;
Be´gue´, J .-P.; Veith, J . M.; Pera, P.; Bernacki, R. J . In Biomedical
Frontiers of Fluorine Chemistry; ACS Symp. Ser. 639; Ojima, I.,
McCarthy, J . R., Welch, J . T., Eds.; American Chemical Society:
Washington, DC, 1996; pp 228-243.
(25) Ojima, I.; Slater, J . S.; Kuduk, S. D.; Takeuchi, C. S.; Gimi, R.
H.; Sun, C.-M.; Park, Y. H.; Pera, P.; Veith, J . M.; Bernacki, R. J . J .
Med. Chem. 1997, 40, 267-278.
(30) Ojima, I.; Habus, I.; Zhao, M.; Zucco, M.; Park, Y. H.; Sun, C.-
M.; Brigaud, T. Tetrahedron 1992, 48, 6985-7012.
(31) Ojima, I.; Zucco, M.; Duclos, O.; Kuduk, S. D.; Sun, C.-M.; Park,
Y. H. Bioorg. Med. Chem. Lett. 1993, 3, 2479-2482.
(32) Ojima, I. In Advances in Asymmetric Synthesis; Hassner, A.,
Ed.; J AI Press: Greenwich, 1995; Vol. 1, pp 95-146.
(33) Ojima, I. Acc. Chem. Res. 1995, 28, 383-389 and references
therein.
(26) Ojima, I.; Kuduk, S. D.; Pera, P.; Veith, J . M.; Bernacki, R. J .
J . Med. Chem. 1997, 40, 279-285.
(27) Ojima, I.; Slater, J . C.; Pera, P.; Veith, J . M.; Abouabdellah,
A.; Be´ge´, J .-P.; Bernacki, R. J . Bioorg. Med. Chem. Lett. 1997, 7, 209-
214.
(28) For a preliminary communication, see: Ojima, I.; Fenoglio, I.;
Park, Y. H.; Sun, C.-M.; Appendino, G.; Pera, P.; Bernacki, R. J . J .
Org. Chem. 1994, 59, 515-517.
(29) Appendino, G.; Gariboldi, P.; Gabetta, B.; Pace, R.; Bombardelli,
E.; Viterbo, D. J . Chem. Soc., Perkins Trans. 1 1992, 2925-2929.
(34) Holton, R. A.; Biediger, R. J .; Boatman, P. D. In Taxol: Science
and Applications; Suffness, M., Ed.; CRC Press: New York, 1995; pp
97-121.

Syntheses and SAR of Novel Nor-Seco Taxoids
J . Org. Chem., Vol. 63, No. 5, 1998 1639
Sch em e 2
Sch em e 4
Sch em e 5
Sch em e 3
Nor-seco taxoids 13a -d bearing a C-13 amide linkage
were synthesized through the ring-opening coupling37 of
N-acyl-â-lactams 12a -d with nor-seco baccatin amine 2.
(3R,4S)-N-Acyl-3-TIPSO-â-lactams (12a -d , TIPS ) tri-
isopropylsilyl) were prepared by the method previously
reported from these laboratories.20,30,31
Protection of the C-7 hydroxyl group of 8 as a trieth-
ylsilyl (TES) ether gave 7-TES-nor-seco-baccatin 9 in 76%
yield (Scheme 2). Reduction of the aldehyde moiety of 9
with sodium cyanoborohydride at pH 6 afforded 7-TES-
nor-seco baccatin alcohol 1 in 86% yield (Scheme 2).
Nor-seco baccatin amine 2 was obtained in two steps
from the nor-seco baccatin alcohol 1 in 80% overall yield
through the Mitsunobu amination reaction (Scheme 3).
Thus, nor-seco baccatin phthalimide 10 was prepared in
90% yield by reacting 1 with triphenylphosphine and
diethyl azodicarboxylate (DEAD) in THF at 45 °C.
Deprotection of phthalimide 10 using excess methyl-
amine35 in ethanol at 55 °C afforded desired 7-TES-13-
amino-nor-seco baccatin 2 in 89% yield. N-methyl-nor-
seco baccatin amine 3 was obtained in 84% yield through
the reductive amination of nor-seco baccatin aldehyde 9
using methylamine and sodium cyanoborohydride (Scheme
4).
The coupling reactions of nor-seco baccatin amine 2
with N-acyl-â-lactams 12a -d 17,30,33 were carried out
under neutral conditions in dichloromethane at 40 °C to
give the coupling products 13a -d in 75-89% yields
(Scheme 6). Deprotection of the 7-TES and 2′-TIPS
groups of 13a -d was carried out using HF/pyridine to
give the desired nor-seco taxoids 5a -d in 80-89% yields
(Scheme 6).
The attempted ring-opening coupling of 3-TIPSO-â-
lactam 12a with N-methyl-nor-seco baccatin amine 3
under the standard conditions (vide supra) resulted in
low conversion and low yield. It is apparent that this is
due to the bulkiness of TIPS group at the C-3 position of
â-lactam 12a 37 as well as N-Me group of nor-seco baccatin
amine 3. Thus, the TIPS group of 12a was removed with
HF/pyridine to afford 3-OH-â-lactam 14a in nearly
quantitative yield. The ring-opening coupling of 3-OH-
â-lactam 14a with nor-seco baccatin amine 3 proceeded
smoothly under the standard conditions to give the
coupling product 15 in 70% yield, which was deprotected
7-TES-nor-seco baccatin alcohol 1, thus obtained, was
coupled with enantiomerically pure N-acyl-3-EEO-â-
lactams 11 (EE ) ethoxyethyl)16,30 using our protocol30,33
to give novel nor-seco paclitaxel 4a and nor-seco docetaxel
4b in fairly good to excellent yields (Scheme 5). It should
be noted that it was impossible to remove 7-TES group
under the standard acidic conditions (0.5% hydrochloric
acid in methanol at room temperature for 36 h).36 This
deprotection was accomplished in excellent yield () 94%)
by using tetra-n-butylammonium fluoride (TBAF) in THF
at -10 °C for 5 min.
(35) Sen, S. E.; Roach, S. L. Synthesis 1995, 756-758.
(36) Denis, J .-N.; Greene, A. E.; Gue´nard, D.; Gue´ritte-Voegelein,
F.; Mangatal, L.; Potier, P. J . Am. Chem. Soc. 1988, 110, 5917-5919.
(37) Ojima, I.; Sun, C. M.; Park, Y. H. J . Org. Chem. 1994, 59, 1249-
1250.

1640 J . Org. Chem., Vol. 63, No. 5, 1998
Ojima et al.
Ta ble 1. In Vitr o Cytotoxicity (IC50, µM)a of n or -seco
Sch em e 6
Ta xoid s
A121
(ovarian) (NSCL)
A549
HT-29
(colon)
MCF-7 MCF7-R
(breast) (breast)
taxoid
paclitaxel
0.0063
0.117
0.131
0.0036
0.133
0.169
0.0036
0.134
0.171
>1.0
0.0017
0.079
0.101
0.300
0.471
0.360
4a
4b
5a
5b
5c
5d
6
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
>1.0
0.535
0.708
0.292
0.200
a
The concentration of compound which inhibits 50% (IC50, µM)
of the growth of human tumor cell line after 72 h drug exposure.39
level cytotoxicity. In contrast to nor-seco taxoids 4a , 4b,
and 6, the nor-seco taxoids with a N-H amide linkage,
5a -d , are all virtually inactive (IC50 > 1.0 µM).
The results obtained in this SAR study clearly indicate
the importance of the A ring for the strong cytotoxicity
of taxoids. However, it is also very important to mention
that two of these reduced-structure analogues, 4a and
4b, retain a certain level of cytotoxicity and their potency
against a drug-resistant human breast cancer cell line
(MCF7-R) is comparable to that of paclitaxel. Replace-
ment of the C-13 ester linkage with an N-H amide
linkage is deleterious to cytotoxicity. Similar findings
have been reported by Chen et al.38 for paclitaxel
analogues bearing an N-H amide linkage. However, the
introduction of N-Me group to the amide linkage, i.e., nor-
seco taxoid 6, recovers cytotoxicity substantially, which
is quite intriguing.
Sch em e 7
To explain the intriguing structure-activity relation-
ships observed, we carried out molecular modeling stud-
ies on the representative analogues 4a (ester linkage),
5a (N-H amide linkage), and 6 (N-Me amide linkage).
We conducted a series of restrained molecular dynamics
(RMD) simulations in a vacuum (Sybyl 6.04) for these
three analogues to investigate their conformational dy-
namism. For each analogue, three simulations were
conducted that maintained the H2′-C2′-C3′-H3′ dihe-
dral angle constant at 180°, 60°, and -60°, respectively.
It has been shown that the value of the H2′-C2′-C3′-
H3′ dihedral angle is an extremely crucial component in
the maintenance of the biologically active conformation
of paclitaxel.40
using HF/pyridine to afford nor-seco taxoid 6 in 83% yield
This RMD study confirmed the greater dynamism of
the phenylisoserine moiety at the C-13 position of the
nor-seco taxoids than that of paclitaxel40 as expected. The
cleavage of the taxane A ring allows for free rotation
around the C12-C13 bond, resulting in different confor-
mations for the phenylisoserine moiety mostly not related
to potentially bioactive conformations of paclitaxel. The
range of movement of the isoserine moiety is demon-
strated in the overlay of the 10 lowest energy structures
for 4a , 5a , and 6 (Figure 1) obtained from the RMD
simulations40 maintaining the H2′-C2′-C3′-H3′ dihe-
dral at 180° (RMD simulations using 124° dihedral angle
gave essentially the same results). We believe this
conformational dynamism is responsible for the lack of
or low activity of the nor-seco taxoids.
(Scheme 7).
The in vitro cytotoxicities of the novel nor-seco taxoids
thus synthesized were evaluated against several human
tumor cell lines, i.e., ovarian (A121), non-small cell lung
(A549), colon (HT-29), breast (MCF7) and the drug-
resistant breast (MCF7-R) cancer cell lines, using the
method developed by Skehan et al.30 Results are sum-
marized in Table 1. The IC50 values of paclitaxel in the
same assay are also shown for comparison.
As Table 1 shows, the nor-seco taxoids with a C-13
ester linkage, 4a and 4b, possess 0.13-0.08 and 0.17-
0.10 µM level IC50 values, respectively, which are 20-40
times weaker activities than that of paclitaxel in the
same cell line assay, but clearly retain a certain level
cytotoxicity. It is worthy of note that 4a and 4b exhibit
IC50 values of 0.47 and 0.36 µM, respectively, against the
doxorubicin-resistant human breast cancer (MCF7-R) cell
line, i.e., 4a and 4b are comparable to paclitaxel. The
nor-seco taxoid 6 bearing a N-Me amide linkage possesses
0.70-0.20 µM level IC50 values, yet still retains a certain
(38) Chen, S. H.; Farina, V.; Vyas, D. M.; Doyle, T. W.; Long, B. H.;
Fairchild, C. J . Org. Chem. 1996, 61, 2065-2070.
(39) Skehan, P.; Streng, R.; Scudierok, D.; Monks, A.; McMahon,
J .; Vistica, D.; Warren, J . T.; Bokesch, H.; Kenney, S.; Boyd, M. R. J .
Nat. Cancer Inst. 1990, 82, 1107-1112.
(40) Ojima, I.; Kuduk, S. D.; Chakravarty, S.; Ourevitch, M.;
Be´gue´,J .-P. J . Am. Chem. Soc. 1997, 119, 5519-5527.

Syntheses and SAR of Novel Nor-Seco Taxoids
J . Org. Chem., Vol. 63, No. 5, 1998 1641
F igu r e 1. Overlay of 10 lowest energy structures obtained in the RMD study of 4a (A), 5a (B), and 6 (C).
F igu r e 2. Overlay of hydrophobic clustering structures for 4a (A), 5a (B), and 6 (C) (shown in black) with the eclipsed conformer
of paclitaxel (gray).40
Although the observed loss of biological activity for 5a
can be ascribed to possible biologically unfavorable
hydrogen bondings involving the amide hydrogen at the
binding site on the microtubules, intrinsic conformational
preferences may well dictate biological activity. Accord-
ingly, we have looked into the structural preference of
each nor-seco taxoid as compared to the hypothetical
bioactive conformations of paclitaxel, i.e., the “hydropho-
bic clustering conformations”.40 We have recently re-
ported the equilibrium of two hydrophobic clustering
conformations (H2′-C2′-C3′-H3′ dihedral angles of 124°
and 180°, respectively) for paclitaxel in aqueous media
based on our “fluorine-probe approach”.40 Thus, we
carried out overlay study of possible hydrophobic cluster-
ing conformations of 4a , 5a , and 6 selected from the
conformations obtained from the RMD study mentioned
above, albeit low dynamic population, with that of
paclitaxel which is predominant in water40 (H2′-C2′-
C3′-H3′ dihedral angles of 124°). Results are shown in
Figure 2.
the C-3′ N-benzoyl group of paclitaxel.42 However, both
the amide analogues, 5a and 6, are restricted to trans
amide conformations that limit the conformational flex-
ibility of the phenylisoserine moiety. The N-H amide
analogue 5a is found to have an extremely strong
preference for a highly extended phenylisoserine moiety.
As Figure 2B clearly shows, the best “hydrophobic
clustering” conformer of 5a has a very poor overlap with
that of paclitaxel at its phenylisoserine moiety. In
contrast to this, the preferred hydrophobic clustering
conformation of the N-Me amide analogue 6 overlaps well
with that of paclitaxel as shown in Figure 2C. The
preference for this conformation for 6 arises from the
absence of steric conflict between the three methyl groups
at the C13-N, C-12, and C-15 positions. This serious
steric conflict is clearly observed when 6 is forced to adopt
the extended conformation of 5a . The overlay study
using the other hydrophobic conformer of paclitaxel
(41) Vander Velde, D. G.; Georg, G. I.; Grunewald, G. L.; Gunn, C.
W.; Mitscher, L. A. J . Am. Chem. Soc. 1993, 115, 11650-11651.
(42) In our previous communication,28 we had proposed a different
model for the biologically active conformation for 4a that was based
on the X-ray crystal structure of docetaxel.2 However, the observation
of hydrophobic clustering conformations in aqueous media provides
more likely models for biological recognition or binding at the active
site.40,41
As Figure 2A indicates, the flexibility of the ester
linkage allows 4a to readily adopt a hydrophobic cluster-
ing conformation that overlaps very well with the C-3′
and C-2 phenyl moieties and, to a certain extent, with

1642 J . Org. Chem., Vol. 63, No. 5, 1998
Ojima et al.
(H2′-C2′-C3′-H3′ dihedral angles of 180°)40,41 led to
essentially the same conclusion. These overlay studies
are consistent with the observed dramatic difference in
the biological activities of 4a , 5a , and 6.
13-For m yl-14-n or -seco-10-d ea cetylba cca tin III (8).
To a solution of 14â-hydroxy-10-deacetylbaccatin III (950
mg, 1.7 mmol) in dioxane (60 mL) was added a solution
of 0.5 N periodic acid in water (8.5 mL, 4.3 mmol). The
mixture was stirred for 12 h, neutralized with aqueous
sodium bicarbonate, and extracted with ethyl acetate.
The combined organic extracts were dried over anhydrous
magnesium sulfate and concentrated in vacuo. The
residue was purified on a silica gel column using hexane/
ethyl acetate (3/2) as the eluant, followed by recrystal-
lization from hexane to give 8 as a white solid (828 mg,
Con clu sion s
A series of novel nor-seco taxoids containing an ester,
an NH amide, or an NMe amide linkage at the C-13
position have been synthesized. Despite the destruction
of the taxane A ring, nor-seco taxoids bearing a C-13 ester
linkage or C-13 N-Me amide linkage retain a certain level
of cytotoxicity against several human cancer cell lines.
However, nor-seco taxoids with a C-13 N-H amide linkage
are found to be inactive (IC50 > 1.0 µM). The reduced
activity of the nor-seco taxoids can be ascribed to the
enhanced conformational flexibility of the phenylisoserine
moiety caused by the loss of the constrained taxane A
ring. The reduced yet significant activity of nor-seco
taxoids 4a (C-13 ester linkage) and 6 (C-13 N-Me amide
linkage) is explained by their ability to adopt the hydro-
phobic clustering conformation of paclitaxel which is
proposed to be responsible for its strong cytotoxicity. On
the contrary, the low-energy hydrophobic clustering
conformation of nor-seco taxoid 5a (C-13 N-H amide
linkage) overlaps poorly with that of paclitaxel, which is
reflected in the loss of activity.
92% yield): mp 190-193 °C; [R]20 -118.8 (c 0.16,
D
1
CHCl3); H NMR (CDCl3) δ 1.36 (s, 3 H), 1.67 (s, 3 H),
1.75 (s, 3 H), 1.78 (s, 3 H), 1.93 (ddd, J ) 14.8, 11.5, 4.2
Hz, 1 H), 2.19 (s, 3 H), 2.47 (ddd, J ) 14.8, 9.7, 5.9 Hz,
1 H), 3.33 (d, J ) 11.2 Hz, 1 H), 4.22 (dd, J ) 11.2, 5.9
Hz, 1 H), 4.27 (d, J ) 8.4 Hz, 1 H), 4.34 (d, J ) 8.4 Hz,
1 H), 4.38 (s, 1 H), 4.78 (s, 1 H), 4.80 (dd, J ) 4.2, 9.7 Hz,
1 H), 5.18 (s, 1 H), 5.90 (d, J ) 11.2 Hz, 1 H), 7.41 (m, 2
H), 7.68 (m, 1 H), 8.40 (m, 2 H), 10.32 (s, 1 H); 13C NMR
(CDCl3) δ 13.1, 13.5, 21.6, 24.2, 29.1, 34.6, 40.8, 48.5, 50.9,
68.7, 74.6, 75.1, 80.3, 83.8, 84.8, 109.2, 128.3, 128.9,
130.3, 132.0, 134.5, 157.3, 168.0, 169.4, 189.1, 211.6.
Anal. Calcd for C28H32O10: C, 63.63; H, 6.10. Found: C,
63.41; H, 6.13.
7-(Tr ieth ylsilyl)-13-for m yl-14-n or -seco-10-deacetyl-
ba cca tin III (9). To a solution of nor-seco baccatin 8
(936 mg, 1.77 mmol) and 4-(dimethylamino)pyridine
(DMAP) (195 mg, 1.60 mmol) in dichloromethane (15 mL)
was added dropwise triethylamine (0.8 mL, 5.8 mmol),
followed by chlorotriethylsilane (0.9 mL, 5.4 mmol) with
stirring at room temperature. The mixture was stirred
for 20 h, quenched with water, and extracted with
chloroform. The combined organic extracts were dried
on anhydrous magnesium sulfate and concentrated in
vacuo to give an oily residue. The crude product was
purified on a silica gel column using petroleum ether
followed by hexane/ethyl acetate (7/3) as the eluant,
followed by recrystallization from hexane to give 9 as a
Exp er im en ta l Section
Gen er a l Meth od s. Melting points are uncorrected.
1H and 13C NMR spectra were measured at 250.13 and
62.90 MHz, respectively, using tetramethylsilane as the
internal standard. Optical rotations were measured at
589 nm. Column chromatography was carried out on
silica gel (230-400 mesh). Elemental analyses were
performed at M-H-W Laboratory, Phoenix, AZ. High-
resolution mass spectra were obtained from the Univer-
sity of California, Riverside Mass Spectrometry Facility,
Riverside, CA.
Ma ter ia ls. The chemicals were purchased from Ald-
rich Co. and Sigma and purified before use by standard
methods. Tetrahydrofuran was freshly distilled under
nitrogen from sodium metal and benzophenone. Dichlo-
romethane was also distilled immediately prior to use
under nitrogen from calcium hydride. (3R,4S)-1-Acyl-
azetidin-2-ones (11a -b, 12a -d , 14a ) were prepared by
the methods previously reported from these laborato-
ries.20,30,31 14â-Hydroxy-10-deacetylbaccatin III was a gift
from Indena, SpA, Italy.
white solid (865 mg, 76% yield): mp 154-155 °C; [R]20
D
-44.4 (c 0.27, CHCl3); 1H NMR (CDCl3) δ 0.75 (m, 6 H),
0.94 (m, 9 H), 1.23 (s, 3 H), 1.70 (s, 3 H), 1.72 (s, 3 H),
1.77 (s, 3 H), 1.95 (ddd, J ) 14.7, 11.5, 4.4 Hz, 1 H), 2.13
(s, 3 H), 2.46 (ddd, J ) 14.7, 9.5, 5.8 Hz, 1 H), 3.33 (d, J
) 11.3 Hz, 1 H), 4.16 (m, 1 H), 4.18 (d, J ) 8.4 Hz, 1 H),
4.48 (d, J ) 8.4 Hz, 1 H), 4.72 (s, 1 H), 4.78 (dd, J ) 9.5,
4.4 Hz, 1 H), 5.15 (s, 1 H), 5.87 (d, J ) 11.3 Hz, 1 H),
7.50 (m, 2 H), 7.61 (m, 1 H), 8.03 (m, 2 H), 10.31 (s, 1 H);
13C NMR (CDCl3) δ 5.8, 6.9, 13.0, 21.7, 24.5, 30.1, 34.8,
41.0, 49.6, 51.0, 68.8, 74.4, 75.5, 80.5, 83.9, 85.0, 109.7,
128.6, 129.6, 129.8, 131.6, 133.5, 157.3, 164.9, 169.6,
189.2, 211.8. Anal. Calcd for C34H46O10Si: C, 63.53; H,
7.21. Found: C, 63.56; H, 7.28.
Molecu la r Mod elin g. Restrained molecular dynam-
ics (RMD) studies and energy minimizations were carried
out using the Tripos force field and Gasteiger-Hu¨ckel
charges on the Sybyl 6.04 molecular modeling platform
(Tripos, Inc.). Three high-temperature dynamics simula-
tions at 900 K were carried out over 100 ps (time step of
1 fs) for each analogue maintaining the H2′-C2′-C3′-
H3′ dihedral angle constant at 180°, 60°, and -60°,
respectively (force penalty ) 0.05 kcal/mol/Å). The
dynamics set was sampled every 2 ps, and each structure
was subjected to a further 2 ps of RMD at 300 K, followed
by minimization using steepest descents and conjugate
gradients, maintaining the same constraints. The result-
ant structures were studied for conformational prefer-
ences, including superimposition with our previously
7-(T r i e t h y ls i ly l)-13-h y d r o x y -14-n o r -s e c o -10-
d ea cetylba cca tin III (1). To a solution of nor-seco
baccatin 9 (88 mg, 0.137 mmol) in methanol (6 mL) was
added a 0.19 M solution of sodium cyanoborohydride in
methanol (3 mL, 0.57 mmol), and the mixture was stirred
at room temperature for 20 min. The pH of the mixture
was maintained at pH 6 with 1 N hydrochloric acid.
Then, a saturated aqueous solution of ammonium chlo-
ride was added to quench the reaction and the reaction
mixture was extracted with chloroform. The combined
organic extracts were dried over anhydrous magnesium
sulfate and concentrated in vacuo. The crude product
was purified on a silica gel column using hexane/ethyl
1
described model for paclitaxel based on the 19F and H
NMR and RMD study of fluorinated analogues.40

Syntheses and SAR of Novel Nor-Seco Taxoids
J . Org. Chem., Vol. 63, No. 5, 1998 1643
acetate (1/1) as the eluant to give 1 as a white solid (76
1.52 (s, 3 H), 1.68 (s, 3 H), 1.73 (s, 3 H), 1.92 (ddd, J )
14.7, 11.2, 4.1 Hz, 1 H), 2.17 (s, 3 H), 2.39-2.52 (m, 1
H), 2.45 (s, 3H), 3.05 (d, J ) 12.1 Hz, 1 H), 3.55 (d, J )
12.8 Hz, 1 H), 3.59 (d, J ) 11.2 Hz, 1 H), 4.12-4.19 (m,
2 H), 4.46 (d, J ) 8.5 Hz, 1 H), 4.80 (dd, J ) 9.5, 3.9 Hz,
1 H), 4.95 (s, 1 H), 5.79 (d, J ) 11.3 Hz, 1 H), 7.45 (m, 2
H), 7.60 (m, 1 H), 8.04 (m, 2 H); 13C NMR (CDCl3) δ 5.8,
6.7, 13.7, 20.0, 21.7, 22.1, 27.6, 34.9, 36.3, 40.5, 48.0, 50.5,
53.2, 69.1, 74.7, 75.4, 80.5, 83.9, 84.7, 109.2, 128.4, 129.7,
129.9, 130.6, 133.2, 137.0, 165.0, 169.9, 213.4. Anal.
Calcd for C35H51O9SiN: C, 63.90; H, 7.81; N, 2.13.
Found: C, 63.98; H, 7.97; N, 2.19.
mg, 86% yield): mp 143-144 °C; [R]20 -42.9 (c 0.07,
D
CHCl3); 1H NMR (CDCl3) δ 0.70 (m, 6 H), 0.87 (m, 9 H),
0.85 (s, 3 H), 1.00 (s, 3 H), 1.52 (s, 3 H), 1.73 (s, 3 H),
1.97 (ddd, J ) 14.6, 11.4, 4.5 Hz, 1 H), 2.23 (s, 3 H), 2.46
(ddd, J ) 14.6, 9.6, 6.0 Hz, 1 H), 3.79 (d, J ) 12.0 Hz, 1
H), 3.87 (d, J ) 11.2 Hz, 1 H), 4.13 (dd, J ) 11.4, 6.0 Hz,
1 H) (H7), 4.19 (d, J ) 8.4 Hz, 1 H), 4.48 (d, J ) 8.4 Hz,
1 H), 4.61 (d, J ) 12.0 Hz, 1 H), 4.77 (dd, J ) 9.6, 4.5 Hz,
1 H), 4.95 (s, 1 H), 5.80 (d, J ) 11.2 Hz, 1 H), 7.39 (m, 2
H), 7.62 (m, 1 H), 8.04 (m, 2 H); 13C NMR (CDCl3) δ 5.8,
6.9, 13.9, 19.3, 22.0, 22.1, 28.2, 34.9, 40.0, 48.3, 50.7, 62.3,
68.8, 74.5, 75.7, 81.4, 84.2, 84.6, 109.1, 128.5, 129.7,
130.4, 133.4, 138.0, 165.0, 171.9, 212.9. Anal. Calcd for
C34H48O10Si: C, 63.33; H, 7.50. Found: C, 63.13; H, 7.49.
7-(Tr ieth ylsilyl)-13-am in o-14-n or -seco-10-deacetyl-
ba cca tin III (2). To a solution of nor-seco baccatin 1
(130 mg, 0.20 mmol), phthalimide (50 mg, 0.34 mmol),
and triphenylphosphine (91 mg, 0.35 mmol) in 13 mL of
anhydrous THF was added dropwise a solution of diethyl
azodicaboxylate (DEAD) (60 µL, 0.38 mmol) in 1.0 mL
THF, and the mixture was stirred at 45 °C for 20 h. The
solvent was removed in vacuo, and the reaction mixture
was purified on a silica gel column using hexane/ethyl
acetate (2/1) as the eluant to give nor-seco baccatin
phthalimide 10 as a white solid (141 mg, 90.4% yield).
To a solution of 10 (141 mg, 0.18 mmol) in ethanol (12
mL) was added an aqueous solution of methylamine (40%
w/w, 0.25 mL, excess), and the mixture was stirred at
55 °C for 22 h. Then the solvent was removed in vacuo,
and the residue was purified on a silica gel column using
methanol/dichloromethane (3/97) as the eluant to give 2
as a white solid (104 mg, 88.7% yield): mp 73-75 °C;
14-Nor -seco-10-d ea cetylba cca tin III 13-[N-Acyl-
(2′R,3′S)-3′-p h en ylisoser in a te] (4a a n d 4b). A typical
procedure is described for the synthesis of 14-nor-seco-
10-deacetylbaccatin III 13-[N-benzoyl-(2′R,3′S)-3′-phe-
nylisoserinate] (4a ). To a solution of 7-TES-nor-seco-
baccatin alcohol 1 (30 mg, 0.046 mmol) and of 3-EEO-1-
benzoyl-â-lactam 11a (31 mg, 0.09 mmol) in THF (1 mL)
was added a 1.0 M solution of sodium hexamethyldisi-
lazide in THF (0.046 mL, 4.6 mmol) at -30 °C over a
period of 10 min. TLC analysis of the reaction mixture
revealed that 1 had been completely consumed. The
reaction mixture was poured into a saturated aqueous
ammonium chloride solution to quench the reaction. The
reaction mixture was extracted with ether and then with
dichloromethane. The combined extracts were washed
with brine, dried over anhydrous sodium sulfate, and
concentrated in vacuo to give an oily residue. The residue
(66 mg) was dissolved in THF (1.5 mL), and 0.5 N
hydrochloric acid (1.5 mL) was added at room tempera-
ture with stirring. After 36 h, ethyl acetate was added
to the reaction mixture and washed with saturated
sodium bicarbonate. The organic layer was dried over
anhydrous sodium sulfate and concentrated in vacuo to
give a white solid. The crude product was purified on a
silica gel column using ethyl acetate/hexane (1/4) as the
eluant to afford 7-TES-4a as a white solid (37 mg, 87%
yield for two steps): mp 105-106 °C; [R]20D -61.6 (c 1.72,
[R]20 -46.4 (c 0.28, CHCl3); 1H NMR (CDCl3) δ 0.67 (m,
D
6 H), 0.83 (m, 9 H), 1.01 (s, 3 H), 1.52 (s, 3 H), 1.67 (s, 3
H), 1.73 (s, 3 H), 1.95 (ddd, J ) 14.7, 11.3, 4.3 Hz, 1 H),
2.20 (s, 3 H), 2.46 (ddd, J ) 14.7, 9.6, 6.0 Hz, 1 H), 3.00
(d, J ) 13.8 Hz, 1 H), 3.68 (d, J ) 11.2 Hz, 1 H), 3.77 (d,
J ) 13.8, 1 H), 4.07-4.24 (m, 2 H), 4.47 (d, J ) 8.1 Hz,
1 H), 4.79 (dd, J ) 9.5, 4.0 Hz, 1 H), 4.93 (s, 1 H), 5.79
(d, J ) 11.2 Hz, 1 H), 7.46 (m, 2 H), 7.60 (m, 1 H), 8.04
(m, 2 H); 13C NMR (CDCl3) δ 5.8, 6.9, 13.8, 19.3, 22.0,
22.2, 27.9, 34.9, 40.3, 43.5, 48.0, 50.6, 69.1, 74.5, 75.6,
80.9, 84.0, 84.6, 109.2, 128.5, 129.8, 133.3, 136.0, 165.0,
170.8, 213.3. Anal. Calcd for C34H49NO9Si: C, 63.43; H,
7.67; N, 2.18. Found: C, 63.51; H, 7.80; N, 2.24.
1
CH2Cl2); H NMR (CDCl3) δ 0.68 (m, 9 H), 0.76 (q, J )
7.0 Hz, 6 H), 0.95 (s, 3 H), 1.42 (s, 3 H), 1.44 (s, 3 H),
1.66 (s, 3 H), 1.88 (ddd, J ) 14.8, 11.1, 3.8 Hz, 1 H), 2.09
(s, 3 H), 2.40 (ddd, J ) 14.8, 9.4, 6.0 Hz, 1 H), 3.43 (d, J
) 11.2 Hz, 1 H), 4.01 (dd, J ) 6.0, 11.1 Hz, 1 H), 4.09 (d,
J ) 8.4 Hz, 1 H), 4.40 (d, J ) 8.4 Hz, 1 H), 4.58 (d, J )
11.5 Hz, 1 H), 4.63 (d, J ) 1.7 Hz, 1 H), 4.71 (dd, J ) 9.4,
3.8 Hz, 1 H), 4.88 (s, 1 H), 4.89 (d, J ) 11.5 Hz, 1 H),
5.72 (m, 1 H), 5.73 (d, J ) 11.1 Hz, 1 H), 7.14 (d, J ) 8.9
Hz, 1 H), 7.18∼7.46 (m, 10 H), 7.53 (t, J ) 7.2 Hz, 1 H),
7.75 (d, J ) 7.2 Hz, 2 H), 7.94 (d, J ) 7.2 Hz, 2 H); 13C
NMR (CDCl3) δ 5.8, 6.9, 13.8, 19.1, 21.9, 22.1, 28.4, 34.9,
40.5, 48.3, 50.7, 55.0, 64.8, 69.1, 74.1, 74.3, 75.5, 80.9,
83.8, 84.6, 109.3, 126.9, 127.0, 127.2, 127.9, 128.5, 128.7,
128.9, 129.8, 131.8, 133.4, 138.6, 141.3, 164.9, 166.6,
170.8, 172.2, 212.9. Anal. Calcd for C50H61O13NSi: C,
65.84; H, 6.74; N, 1.54. Found: C, 66.01; H, 6.90; N, 1.49.
A solution of 7-TES-4a (149 mg, 0.16 mmol) in THF (5
mL) was added a 1.0 M solution of tetra-n-butylammo-
nium fluoride in THF (0.2 mL) at -10 °C for 5 min under
nitrogen. The reaction mixture was poured into water
and extracted with ethyl acetate. The combined organic
extracts were dried over anhydrous sodium sulfate and
concentrated in vacuo. The residue was submitted to a
short column chromatography on silica gel using ethyl
acetate/hexane (1/4) as the eluant to give 4a as a white
solid (120.3 mg, 94% yield): mp 141-142 °C; [R]20D -80.2
7-(Tr ieth ylsilyl)-13-(N-m eth yla m in o)-14-n or -seco-
10-d ea cetylba cca tin III (3). To a solution of nor-seco
baccatin 9 (30 mg, 0.467 mmol) in dry methanol (2 mL)
was added dropwise a 2.0 M solution of methylamine in
THF (0.25 mL) in the presence of anhydrous sodium
sulfate. After the mixture was stirred for 15 min, sodium
cyanoborohydride (8.8 mg, 0.14 mmol) was added quickly
followed by the addition of 0.1 mL of glacial acetic acid,
and the mixture was stirred at room temperature for 9
h. The solvent was removed under reduced pressure, and
water was added to the reaction mixture. The pH of the
solution was adjusted to pH 13 with solid sodium
hydroxide, and the mixture was extracted with dichlo-
romethane. The combined organic extracts were dried
over anhydrous magnesium sulfate and concentrated in
vacuo. The crude product was purified on a silica gel
column using methanol/dichloromethane (5/95) as the
eluant to give 3 as a white solid (26 mg, 84% yield): mp
67-68 °C; [R]20D -34.2 (c 0.38, CHCl3); 1H NMR (CDCl3)
δ 0.65-0.76 (m, 6 H), 0.80-0.89 (m, 9 H), 1.02 (s, 3 H),

1644 J . Org. Chem., Vol. 63, No. 5, 1998
Ojima et al.
(c 0.76, CH2Cl2); 1H NMR (CDCl3) δ 1.15 (s, 3 H), 1.51 (s,
3 H), 1.53 (s, 3 H), 1.74 (s, 3 H), 1.94 (d, J ) 3.7, 11.2,
15.0 Hz, 1 H), 2.24 (s, 3 H), 2.49 (ddd, J ) 15.0, 9.6, 6.1
Hz, 1 H), 3.52 (d, J ) 11.0 Hz, 1 H), 4.15 (dd, J ) 11.2,
6.1 Hz, 1 H), 4.25 (d, J ) 8.3 Hz, 1 H), 4.29 (d, J ) 8.3
Hz, 1 H), 4.71(d, J ) 11.0 Hz, 1 H), 4.73 (d, J ) 1.7 Hz,
1 H), 4.83 (dd, J ) 9.6, 3.7 Hz, 1 H), 4.95 (d, J ) 11.0 Hz,
1 H), 4.98 (s, 1 H), 5.78 (dd, J ) 8.9, 1.7 Hz, 1 H), 5.83
(d, J ) 11.0 Hz, 1 H), 7.20 (d, J ) 8.9 Hz, 1 H), 7.31∼7.55
(m, 10 H), 7.66 (dd, J ) 7.6, 7.2 Hz, 1 H), 7.82 (d, J ) 7.2
Hz, 2 H), 8.12 (d, J ) 7.6 Hz, 2 H); 13C NMR (CDCl3) δ
13.5, 19.0, 21.6, 21.8, 29.7, 34.7, 40.3, 47.2, 50.5, 54.9,
64.8, 69.1, 73.9, 74.5, 75.0, 80.6, 83.7, 84.4, 108.6, 125.8,
127.0, 128.0, 128.7, 130.2, 131.8, 133.9, 134.3, 138.6,
141.3, 166.6, 167.9, 170.6, 172.3, 212.7. Anal. Calcd for
C44H47O13N: C, 66.24; H, 5.94; N, 1.76. Found: C, 66.12;
H, 6.09; N, 1.60.
aqueous saturated copper sulfate solution and water,
dried over anhydrous magnesium sulfate, and concen-
trated in vacuo. The crude product was purified on a
silica gel column using methanol/dichloromethane (3/97)
as the eluant to afford 5 as a white solid (80-91% yields).
14-Nor -seco-10-deacetylbaccatin III 13-[N-ben zoyl-
(2′R,3′S)-3′-p h en ylisoser in a m id e] (5a ): mp 168-170
°C; [R]20
D -130.8 (c 0.13, CHCl3); 1H NMR (CDCl3) δ 1.09
(s, 3 H), 1.28 (s, 9 H), 1.44 (s, 3 H), 1.69 (s, 3 H), 1.93
(ddd, J ) 14.6, 11.4, 4.0 Hz, 1 H), 2.27 (s, 3 H), 2.45 (ddd,
J ) 14.6, 9.5, 6.0 Hz, 1 H), 3.62 (d, J ) 11.0 Hz, 1 H),
3.93-4.02 (m, 3 H), 4.21 (d, J ) 8.2 Hz, 1 H), 4.29 (d, J
) 8.2 Hz, 1 H), 4.62 (s, 1 H), 4.78 (dd, J ) 9.4, 4.1 Hz, 1
H), 4.87 (s, 1 H), 5.71 (d, J ) 6.1 Hz, 1 H), 5.80 (d, J )
11.1 Hz, 1 H), 6.88 (s, 1 H), 7.26-7.30 (m, 3 H), 7.40-
7.53 (m, 7 H), 7.65 (m, 1 H), 7.88 (m, 2 H), 8.10 (m, 2 H),
8.35 (d, J ) 8.0 Hz, 1 H); 13C NMR (CDCl3) δ 13.5, 18.8,
21.6, 21.9, 26.7, 34.7, 39.7, 40.3, 46.9, 50.4, 55.9, 68.8,
73.3, 74.4, 75.1, 80.8, 83.9, 84.4, 108.5, 127.1, 127.2,
127.5, 127.7, 127.9, 128.4, 128.5, 128.7, 130.2, 131.9,
133.7, 134.2, 137.3, 138.5, 167.0, 167.6, 171.2, 172.5,
212.7. Anal. Calcd for C44H48N2O12: C, 66.32; H, 6.07;
N, 3.52. Found: C, 66.19; H, 6.25; N, 3.32.
14-Nor -seco-10-d ea cetylba cca tin III 13-[N-(ter t-
b u t o x y c a r b o n y l)-(2′R ,3′S )-3′-p h e n y li s o s e r i n a -
m id e] (5b): mp 162-164 °C; [R]20D -94.4 (c 0.18, CHCl3);
1H NMR (CDCl3) δ 1.23 (s, 3 H), 1.41-1.49 (m, 15 H),
1.71 (s, 3 H), 1.93 (ddd, J ) 14.5, 11.4, 4.0 Hz, 1 H), 2.27
(s, 3 H), 2.45 (ddd, J ) 14.6, 9.7, 5.9 Hz, 1 H), 3.63 (d, J
) 11.0 Hz, 1H), 3.98-4.16 (m, 4 H), 4.22 (d, J ) 8.2 Hz,
1 H), 4.29 (d, J ) 8.2 Hz, 1 H), 4.47 (s, 1 H), 4.78 (dd, J
) 9.5, 3.9 Hz, 1 H), 4.94 (s, 1 H), 4.98 (br s, 1 H), 5.14 (br
d, J ) 6.3 Hz, 1 H), 5.82 (d, J ) 11.0 Hz, 1 H), 6.05 (br
d, J ) 7.6 Hz, 1 H), 6.68 (br s, 1 H), 7.31-34 (m, 5 H),
7.49 (m, 2 H), 7.65 (m, 1 H), 8.11 (m, 2 H); 13C NMR
(CDCl3) δ 13.6, 19.2, 21.5, 22.0, 26.8, 28.3, 34.7, 39.8, 40.5,
46.9, 50.5, 56.7, 69.0, 74.4, 75.1, 79.9, 81.0, 83.9, 84.4,
108.6, 126.8, 126.9, 127.7, 128.5, 128.7, 130.2, 134.2,
138.5, 155.5, 167.7, 171.5, 171.5, 212.7. Anal. Calcd for
C42H52N2O13: C, 63.62; H, 6.61; N, 3.53. Found: C, 63.49;
H, 6.60; N, 3.38.
In a similar manner, 4b was obtained from nor-seco
baccatin 1 and â-lactam 11b via 7-TES-4b.
7-TES-4b: colorless oil; [R]20 -43.3 (c 1.22, CHCl3);
D
1H NMR (CDCl3) δ 0.73 (m, 9 H), 0.82 (m, 6 H), 1.05 (s,
3 H), 1.42 (s, 9 H), 1.53 (s, 3 H), 1.61 (s, 3 H), 1.75 (s, 3
H), 1.95 (m, 1 H), 2.15 (s, 3 H), 2.49 (m, 1 H), 3.52 (d, J
) 11.2 Hz, 1 H), 3.90 (bs, 1 H), 4.12 (m, 1 H), 4.16 (d, J
) 8.3 Hz, 1 H), 4.47 (d, J ) 8.3 Hz, 1 H), 4.54 (bs, 1 H),
4.74-4.91 (m, 3 H), 4.99 (s, 1 H), 5.25 (bd, J ) 9.5 Hz, 1
H), 5.53 (d, J ) 9.5 Hz, 1 H), 5.81 (d, J ) 11.2 Hz, 1 H),
7.28-7.49 (m, 7 H), 7.60 (m, 1 H), 8.02 (m, 2 H); 13C NMR
(CDCl3) δ 5.8, 6.9, 13.7, 19.0, 21.7, 22.1, 28.3, 29.7, 34.9,
40.5, 48.3, 50.7, 56.3, 64.7, 69.1, 74.2, 74.5, 75.5, 80.8,
83.8, 84.6, 109.3, 125.4, 126.8, 127.7, 128.5, 128.6, 130.0,
133.3, 141.1, 155.1, 164.9, 170.5, 172.3, 213.0. Anal.
Calcd for C48H65NO14Si: C, 63.49; H, 7.21; N, 1.54.
Found: C, 63.38, H, 7.31; N, 1.58.
4b: white solid, mp 119-121 °C; [R]20 -66.7 (c 0.27,
D
1
CHCl3); (CDCl3) δ H NMR (CDCl3) δ 1.15 (s, 3 H), 1.41
(s, 9 H), 1.51 (s, 3 H), 1.62 (s, 3 H), 1.74 (s, 3 H), 1.93 (m,
1 H), 2.20 (s, 3 H), 2.50 (m, 1 H), 3.52 (d, J ) 11.1 Hz, 1
H), 3.80 (bs, 1 H), 4.13-4.23 (m, 2 H), 4.22 (d, J ) 7.7
Hz, 1 H), 4.29 (d, J ) 8.2 Hz, 1 H), 4.54 (s, 1 H), 4.82 (m,
3 H), 5.02 (m, 2 H), 5.25 (m, 1 H), 5.52 (d, J ) 9.4 Hz, 1
H), 5.85 (d, J ) 11.1 Hz, 1 H), 7.28-7.42 (m, 5 H), 7.49
(m, 2 H), 7.65 (m, 1 H), 8.12 (m, 2 H); 13C NMR (CDCl3)
δ 13.5, 19.0, 21.7, 27.3, 28.3, 32.8, 34.7, 40.3, 47.2, 50.5,
56.3, 64.8, 69.0, 74.1, 75.0, 76.9, 78.1, 79.8, 80.5, 83.8,
84.5, 108.8, 126.1, 126.7, 127.8, 128.6, 128.7, 130.2, 134.2,
141.0, 155.1, 167.9, 170.3, 170.9, 212.8. Anal. Calcd for
C42H51NO14: C, 63.55; H, 6.48; N, 1.76. Found: C, 63.59;
H, 6.77; N, 1.64.
Gen er a l P r oced u r e for th e Syn th esis of 14-Nor -
seco-10-d ea cetylba cca tin III 13-[N-Acyl-(2′R,3′S)-
isoser in a m id e] (5a -d ). A mixture of nor-seco baccatin
amine 2 (0.047-0.067 mmol) and â-lactam 12 (0.097-
0.140 mmol, 2.0 equiv) in 3 mL of dichloromethane was
stirred at 40 °C for 20-60 h. Then the solvent was
removed in vacuo, and the residue was purified on a silica
gel column using dichloromethane followed by methanol/
dichloromethane (3/97) as the eluant to afford 13 as a
white solid (75-89% yields). To a solution of 13 in 4 mL
of pyridine/acetonitrile (1/1) was added dropwise HF/
pyridine (70/30, 0.50 mL) at 0 °C, and the mixture was
allowed to warm to room temperature. Then, the mix-
ture was stirred for 27-48 h at 40 °C. The reaction was
quenched with aqueous saturated sodium carbonate
solution, and the reaction mixture was extracted with
ethyl acetate. The combined extracts were washed with
14-Nor -seco-10-d ea cetylba cca tin III 13-[(N-ter t-
bu toxyca r bon yl)-(2′R,3′S)-3′-(2-m eth yl-1-p r op en yl)-
isoser in a m id e] (5c): mp 140-142 °C; [R]20 -96.2 (c
D
1
0.78, CHCl3); H NMR (CDCl3) δ 1.15 (s, 3 H), 1.41 (s, 9
H), 1.47 (s, 3 H), 1.50 (s, 3 H), 1.61 (s, 3 H), 1.72-1.76
(m, 9 H), 1.94 (ddd, J ) 14.7, 11.1, 4.4 Hz, 1 H), 2.29 (s,
3 H), 2.44 (ddd, J ) 15.2, 9.6, 5.9 Hz, 1 H), 3.70 (d, J )
11.0 Hz, 1 H), 4.09-4.24 (m, 6 H), 4.31 (d, J ) 8.2 Hz, 1
H), 4.63 (br s, 1 H), 4.80 (dd, J ) 4.9, 9.5 Hz, 1 H), 4.91-
4.97 (m, 2 H), 5.22-5.29 (m, 2 H), 5.46 (d, J ) 8.2 Hz, 1
H), 5.83 (d, J ) 11.0 Hz, 1 H), 6.95 (br s, 1 H), 7.52 (m,
2 H), 7.65 (m, 1 H), 8.10 (m, 2 H); 13C NMR (CDCl3) δ
13.5, 18.4, 19.1, 21.6, 21.9, 25.8, 26.7, 28.0, 28.3, 34.7,
39.8, 40.4, 47.0, 48.1, 50.5, 51.8, 56.6, 68.9, 74.5, 74.9,
75.2, 79.9, 80.8, 83.9, 84.5, 108.7, 116.7, 120.5, 127.9,
128.5, 128.6, 128.7, 129.7, 130.2, 134.2, 137.5, 138.4,
156.4, 167.7, 171.3, 172.5, 213.0. Anal. Calcd for
C40H54N2O13: C, 62.32; H, 7.06; N, 3.63. Found: C, 62.13;
H, 6.89; N, 3.47.
14-Nor -seco-10-d ea cetylba cca tin III 13-[N-(ter t-
b u t oxyca r b on yl)-(2′R,3′S)-3′-(2-m et h ylp r op yl)iso-
ser in a m id e] (5d ): mp 146-148 °C; [R]20D -95.0 (c 0.20,
1
CHCl3); H NMR (CDCl3) δ 0.93 (d, J ) 2.4 Hz, 3 H),
0.96 (d, J ) 2.4 Hz, 3 H), 1.15 (s, 3 H), 1.41 (s, 9 H), 1.50
(s, 3 H), 1.61 (s, 3 H), 1.73 (s, 3 H), 1.95 (m, 1 H), 2.32 (s,

Syntheses and SAR of Novel Nor-Seco Taxoids
J . Org. Chem., Vol. 63, No. 5, 1998 1645
3 H), 2.46 (m, 1 H), 3.74 (d, J ) 11.0 Hz, 1 H), 3.92 (br s,
1 H), 4.13 (m, 3 H), 4.23 (d, J ) 8.2 Hz, 1 H), 4.31 (d, J
) 8.1 Hz, 1 H), 4.82 (dd, J ) 9.5, 4.9 Hz, 1 H), 4.98 (s, 1
H), 5.07 (bs, 1 H), 5.84 (d, J ) 11.1 Hz, 1 H), 6.99 (br s,
1 H), 7.50 (m, 2 H), 7.66 (m, 1 H), 8.12 (m, 2 H); 13C NMR
(CDCl3) δ 13.6, 19.0, 21.5, 22.0, 22.1, 23.0, 24.9, 26.7, 28.2,
34.7, 39.2, 39.7, 40.5, 47.0, 50.5, 52.0, 68.9, 74.5, 74.6,
74.7, 75.2, 80.0, 80.8, 84.0, 84.5, 108.7, 127.8, 128.6,
128.7, 130.2, 134.2, 138.3, 157.0, 167.7, 171.2, 173.2,
213.0. Anal. Calcd for C40H56N2O13: C, 62.16; H, 7.30;
N, 3.62. Found: C, 62.30; H, 7.46; N, 3.40.
14-Nor -seco-10-d ea cetylba cca tin III 13-(N-Meth -
y l)-13-[N -b e n zo y l-(2′R ,3′S )-3′-p h e n y lis o s e r in a -
m id e] (6). A solution of nor-seco baccatin amine 3 (27.0
mg, 0.041 mmol) and â-lactam 14a (15.5 mg, 0.058 mmol)
in 1.5 mL of dichloromethane was stirred for 24 h at room
temperature. Then the solvent was removed in vacuo,
and the residue was purified on a silica gel column using
hexane/ethyl acetate (1/1) as the eluant to afford 15a as
a white solid (26.5 mg, 70%). To a solution of 15a (26.0
mg, 0.028 mmol) in 3 mL of pyridine/acetonitrile (1/1)
was added dropwise HF/pyridine (70/30, 0.25 mL) at 0
°C, and the mixture was allowed to warm to room
temperature. Then the mixture was stirred at 40 °C for
18 h. The reaction was quenched with aqueous saturated
sodium carbonate solution, the mixture was extracted
with ethyl acetate, and the combined extracts were
washed with aqueous saturated copper sulfate solution
and water, dried over anhydrous magnesium sulfate, and
concentrated in vacuo. The crude product was purified
on a silica gel column using hexane/ethyl acetate (1/2)
as the eluant to afford 6 as a white solid (19.0 mg, 83%
1
yield): mp 158-160 °C; [R]20 -57.5 (c 0.40, CHCl3); H
D
NMR (CDCl3) δ 1.12 (s, 3 H), 1.52 (s, 3 H), 1.55 (s, 3 H),
1.75 (s, 3 H), 1.93 (m, 1 H), 2.25 (s, 3 H), 2.46 (m, 1 H),
3.07 (s, 3 H), 3.43 (d, J ) 11.2 Hz, 1 H), 3.96 (d, J ) 14.9
Hz, 1 H), 4.16-4.26 (m, 2 H), 4.22 (d, J ) 8.8 Hz, 1 H),
4.34 (d, J ) 8.2 Hz, 1 H), 4.43 (d, J ) 5.2 Hz, 1 H), 4.64
(d, J ) 14.8 Hz, 1 H), 4.83 (dd, J ) 9.7, 4.5 Hz, 1 H), 4.92
(d, J ) 3.6 Hz, 1 H), 5.05 (s, 1 H), 5.06 (s, 1 H), 5.68 (d,
J ) 9.1 Hz, 1 H), 5.88 (d, J ) 11.2 Hz, 1 H), 6.95 (d, J )
9.1 Hz, 1 H), 7.32-7.52 (m, 10 H), 7.67 (m, 1 H), 7.75
(m, 2 H), 8.14 (m, 2 H); 13C NMR (CDCl3) δ 13.1, 17.7,
21.7, 21.9, 26.5, 33.8, 34.7, 40.4, 47.0, 48.7, 50.4, 53.1,
69.3, 70.7, 74.8, 75.1, 80.6, 83.7, 84.5, 87.5, 108.8, 126.9,
127.0, 127.9, 128.5, 128.6, 128.67, 128.73, 128.8, 130.3,
131.8, 134.3, 139.0, 139.1, 167.3, 167.9, 169.7, 170.9,
172.1, 213.4; HRMS (FAB, DCM/NBA) m/z calcd for
C45H50N2O12‚H+: 811.3442, found 811.3430.
Ack n ow led gm en t. This research was supported by
a grant from the National Institutes of Health (NIGMS).
Generous support from Indena, SpA, Italy is also
gratefully acknowledged. The authors acknowledge the
university NMR facility at Stony Brook which was
supported by a grant from National Science Foundation
(CHE 9413510).
J O971953R