New highly active taxoids from 9beta-dihydrobaccatin-9,10-acetals. Part 3.

Article abstract of DOI:10.1016/S0960-894X(02)00891-0

We synthesized novel water-soluble and orally active taxane analogues, 7-deoxy-9beta-dihydro-9,10-O-acetal taxanes. Cytotoxicities of the synthetic compounds were greater than those of paclitaxel and docetaxel, especially against resistant cancer cell lines expressing P-glycoprotein. In addition, some compounds showed potent antitumor effects against B16 melanoma BL6 in vivo by both iv and po administration.

Full text of DOI:10.1016/S0960-894X(02)00891-0

Bioorganic & Medicinal Chemistry Letters 13 (2003) 185–190
New Highly Active Taxoids from
9ꢀ-Dihydrobaccatin-9,10-acetals. Part 3
Yasuyuki Takeda,a Toshiharu Yoshino,a Kouichi Uoto,a Jun Chiba,a
Takashi Ishiyama,a Michio Iwahana,b Takeshi Jimbo,b Noriko Tanaka,c
Hirofumi Terasawab and Tsunehiko Sogaa,*
aMedicinal Chemistry Research Laboratory, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13 Kita-Kasai 1-Chome,
Edogawa-ku, Tokyo 134-8630, Japan
bNew Product Research Laboratories III, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13 Kita-Kasai 1-Chome,
Edogawa-ku, Tokyo 134-8630, Japan
cNew Product Research Laboratories II, Daiichi Pharmaceutical Co., Ltd., Tokyo R&D Center, 16-13 Kita-Kasai 1-Chome,
Edogawa-ku, Tokyo 134-8630, Japan
Received 13 August 2002; accepted 21 October 2002
Abstract—We synthesized novel water-soluble and orally active taxane analogues, 7-deoxy-9b-dihydro-9,10-O-acetal taxanes.
Cytotoxicities of the synthetic compounds were greater than those of paclitaxel and docetaxel, especially against resistant cancer cell
lines expressing P-glycoprotein. In addition, some compounds showed potent antitumor effects against B16 melanoma BL6 in vivo
by both iv and po administration.
# 2002 Elsevier Science Ltd. All rights reserved.
Introduction
Herein, we report the synthesis and antitumor activity
of these novel taxane analogues (Fig. 1).
Paclitaxel (1, Taxol1)1 and docetaxel (2, Taxotere1)2
are currently considered to be some of the most impor-
tant drugs used in cancer chemotherapy. Although
paclitaxel is currently the agent of choice for the treat-
ment of ovarian, breast, and lung cancer, the lack of
sufficient aqueous solubility (paclitaxel: 0.25 mg/mL,
docetaxel: 6–7 mg/mL)3 was one of the major problems
associated with paclitaxel’s formulation for clinical
applications. To resolve this problem, we previously
synthesized non-prodrug water-soluble docetaxel ana-
logues possessing an amine moiety, exemplified by
compound 3.4 Furthermore, we recently reported new
taxane analogues, 7-deoxy-9b-9,10-O-acetal taxanes
exemplified by compound 4, which showed stronger
activity against several tumor cell lines than that of
paclitaxel and docetaxel.5 As a combination of these
two modifications, we designed a procedure to intro-
duce the morpholine moiety to the acetal region.
Chemistry
The reaction of 55 with acrolein diethyl acetal in the
presence of CSA afforded 9,10-O-acetal 6. The coupling
of 6 with the b-lactam 76 and the subsequent removal of
the protecting group at C-20 were carried out following
procedures similar to those reported by Ojima et al.7 to
give compound 8. Finally, oxidation of 8 with OsO4
followed by cleavage with NaIO4 gave the aldehyde, to
which the morpholine moiety was introduced by reduc-
tive amination to afford the targeted compound 9
(Scheme 1).8
It was reported that the introduction of a methyl group
into the C-20 position of paclitaxel and docetaxel led to
increased cytotoxicity.9 Thus, we tried to apply this
C-13 side chain to our new taxane analogues. According
to a procedure similar to that described for the synthesis
of compound 9, the targeted compound 1210 was
obtained by using b-lactam 109 (Scheme 2).
*Corresponding author. Tel.: +81-3-5696-7473; fax: +81-3-5696-
8723; e-mail: taked8ni@daiichipharm.co.jp
0960-894X/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00891-0

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Y. Takeda et al. / Bioorg. Med. Chem. Lett. 13 (2003) 185–190
In our previous paper, we reported that the 30-(2-pyr-
idyl) analogue 4 showed more potent cytotoxicity than
that of the corresponding 30-phenyl analogue.5 Com-
pound 15,11 possessing a 2-pyridine ring at the C-13 side
chain, was synthesized in a similar manner by using
b-lactam 1312 (Scheme 3).
The synthesis of 30-(2-pyridyl)-20-methyl analogue (20a,
20b) is described in Scheme 4. The key intermediate
b-lactam 17 was synthesized via the ester enolate-imine
cyclocondensation. The reaction of lithium ester enolate
generated in situ from silyloxypropionate 16 with N-tri-
methylsilylaldimine13 gave the racemic cis-b-lactam,
Figure 1. Structures of taxane analogues.
Scheme 1. Reagents and conditions: (a) acrolein diethyl acetal, CSA, THF (47%); (b) (i) 7, NaHMDS, THF; (ii) HF-pyridine, pyridine (34%); (c) (i)
OsO4, NMO, THF, acetone, H2O; (ii) NaIO4, THF, MeOH, H2O; (iii) morpholine, AcOH, NaBH3CN, EtOH (61%).
Scheme 2. Reagents and conditions: (a) (i) 10, LiHMDS, THF; (ii) TBAF, THF (48%); (b) (i) OsO4, NMO, THF, acetone, H2O; (ii) NaIO4, THF,
MeOH, H2O; (iii) morpholine, AcOH, NaBH3CN, EtOH (69%).

Y. Takeda et al. / Bioorg. Med. Chem. Lett. 13 (2003) 185–190
187
which was resolved by using a chiral HPLC column to
Results and Discussion
afford the optically pure cis-b-lactam 17. Acylation of
17 was accomplished with di-tert-butyl dicarbonate or
benzoyl chloride to afford the desired b-lactams (18a,
18b) in good yield. Finally, the reaction of 6 with 18a
and 18b was followed by deprotection to afford the
intermediates 19a and 19b, which were converted to the
targeted compounds 20a and 20b, respectively.14
Activities of the compounds (9, 12, 15, 20a, and 20b)
were evaluated in cytotoxicity assays against five cell
lines (P388, PC-6, PC-12, PC-6/VCR29-9, and PC-6/
VP1-1), and activities were compared with those of
paclitaxel (1) and docetaxel (2). The activities of all the
synthetic compounds were greater than those of pacli-
taxel and docetaxel, especially against the resistant can-
cer cell lines expressing P-glycoprotein (PC-12, PC-6/
VCR29-9, and PC-6/VP1-1). Modifications of the
region between C-7 and C-10 might disrupt the specific
binding of the molecules to P-glycoprotein, resulting in
reduced P-glycoprotein-mediated efflux and increased
activity against resistant cancer cell lines. Among these
The absolute configuration of the acetal moiety was
determined to be S configuration by X-ray analysis
of compound 15, as shown in Figure 2.15 As for C-9
configuration, we had identified it to be S by proton
NMR analysis;5 it was confirmed to be correct by X-ray
analysis.
Scheme 3. Reagents and conditions: (a) (i) 13, LiHMDS, THF; (ii) TBAF, THF (85%); (b) (i) OsO4, NMO, THF, acetone, H2O; (ii) NaIO4, THF,
MeOH, H2O; (iii) morpholine, AcOH, NaBH3CN, EtOH (82%).
Scheme 4. Reagents and conditions: (a) (i) 2-pyridinecarboxaldehyde, LiHMDS, TMS, THF; (ii) 16, LDA, THF; (iii) Chiralcel OD (31%); (b)
(Boc)2O, DMAP, THF or BzCl, Et3N, DMAP, CH2Cl2 (98% for 18a, 98% for 18b); (c) (i) 18a, NaHMDS, THF or 18b, LiHMDS, THF; (ii) TBAF,
THF (25% for 19a, 50% for 19b); (d) (i) OsO4, NMO, THF, acetone, H2O; (ii) NaIO4, THF, MeOH, H2O; (iii) morpholine, AcOH, AcOH,
NaBH3CN, EtOH (83% for 20a, 77% for 20b).

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Y. Takeda et al. / Bioorg. Med. Chem. Lett. 13 (2003) 185–190
Figure 2. ORTEP representation of 15 with four MeOH molecules.
analogues, the compounds possessing a phenyl ring at
the C-13 side chain (9 and 12) showed stronger cyto-
toxicity against P388 compared with the compounds
possessing a pyridine ring (15, 20a and 20b). Replace-
ment of the N-tert-butoxycarbonyl moiety of 20a by the
benzoyl moiety (20b) led to decreased cytotoxicity
(Table 1).
by po administration was narrow. Only at a dose of 12.0
mg/kg, compound 20a showed potent antitumor activ-
ity with an IR value of 92.2% and no body weight loss.
The higher dosage (18.0 mg/kg) resulted in death, and
the lower dosage (8.0 mg/kg) did not exhibit the high
Table 1. Cytotoxicity of 7-deoxy-9,10-O-acetal taxane analogues
We selected compounds 15, 20a, and 20b for further in
vivo investigation, because their possession of a pyridine
ring in addition to a morpholine moiety made them
more soluble in water (Table 2).
Compd
Cytotoxicity GI50 (ng/mL)a
P388 PC-6 PC-12 PC-6/VCR29-9 PC-6/VP1-1
Paclitaxel (1) 2.93 1.27 539
Docetaxel (2) 0.78 0.41 14.9
455
104
1000
958
9
12
15
20a
20b
0.02 0.38
0.02 0.47
0.18 0.39
0.12 0.11
0.19 0.45
0.02
0.07
0.21
0.06
0.57
3.35
14.7
7.16
24.8
6.55
30.4
To evaluate the antitumor effects in vivo, we implanted
B16 melanoma BL6 subcutaneously into mice and
compared the activities of the selected compounds with
that of docetaxel when administered intravenously (iv)
and orally (po). Compound 20a, which showed the most
potent cytotoxicity among these three compounds,
exhibited potent antitumor effects by both iv and po
administration; however, the range of its effective dose
3.37
1.87
1.30
2.54
aConcentration that inhibited the growth of cells by 50% upon 72 h
continuous exposure for the five cell lines [mouse leukemia (P388),
human lung cancer cell lines (PC-6 and PC-12), and resistant cancer
cell lines (PC-6/VCR29-9 and PC-6/VP1-1)].16

Y. Takeda et al. / Bioorg. Med. Chem. Lett. 13 (2003) 185–190
189
Table 2. Estimated water solubility
From the considerations of the cytotoxicity, the anti-
tumor effect, and water-solubility, we estimated that
compound 15 is the most promising candidate for fur-
ther development. Extensive studies to explore the bio-
logical properties of 15 are in progress and will be
reported in due course.
Compd
Solubility (mg/mL)a
Water
JP1 (pH 1.2)
JP2 (pH 6.8)
Docetaxel (2)
9
12
15
20a
20b
<4
<4
<4
14.0
6.0
<4
<4
1200
350
1700
1800
>1800
<4
<4
<4
11
5
<4
Acknowledgements
The authors are greatly indebted to M. Suzuki of the
Discovery Research Laboratory of Daiichi Pharmaceu-
tical Co. Ltd. for performing the X-ray crystal structure
analysis. We also wish to thank Drs. T. Tsuruo, Insti-
tute of Molecular and Cellular Biosciences, University
of Tokyo and I. J. Fidler, the University of Texas M. D.
Andersen Cancer Center for their kind supply of B16
melanoma BL6.
aThe solubility of each compound was determined by using the UV
assay.
antitumor effect. On the other hand, compounds 15 and
20b showed potent antitumor effects over a wide dosage
range by both iv and po administration. Furthermore,
both compounds could be assumed to have good oral
bioavailabilities. Since 15 or 20b administered orally
gave nearly the same antitumor effects and body weight
losses as 2–3-fold amount of those administered intra-
venously. In contrast, docetaxel administered orally
exhibited no antitumor effect and no body weight loss at
a dose of 600 mg/kg, which indicates that docetaxel has
very poor oral bioavailability (Table 3).
References and Notes
1. Wani, M. C.; Taylor, H. L.; Wall, M. E.; Coggon, P.;
McPhail, A. T. J. Am. Chem. Soc. 1971, 93, 2325.
2. Gueritte-Voegelein, F.; Guenard, D.; Lavelle, F.; Le Goff,
M.-T.; Mangatal, L.; Potier, P. J. Med. Chem. 1991, 34, 992.
3. Vyas, D. M.; Wong, H.; Croswell, A. R.; Casazza, A. M.;
Knipe, J. O.; Mamber, S. W.; Doyle, T. W. Bioorg. Med.
Chem. Lett. 1993, 3, 1357.
Table 3. Antitumor activity against B16 melanoma BL6a
4. (a) Uoto, K.; Takenoshita, H.; Yoshino, T.; Hirota, Y.;
Ando, S.; Mitsui, I.; Terasawa, H.; Soga, T. Chem. Pharm.
Bull. 1998, 46, 770. (b) Iimura, S.; Ohsuki, S.; Chiba, J.; Uoto,
K.; Iwahana, M.; Terasawa, H.; Soga, T. Heterocycles 2000,
53, 2719.
Compd
Route
Dose
(mg/kg)
IR
(%)b
BWLmax
(%)c
Mortality
2
po
iv
600.0
100.0
6.2
95.1
<0
<0
0/6
0/6
5. Ishiyama, T.; Iimura, S.; Yoshino, T.; Chiba, J.; Uoto, K.;
Terasawa, H.; Soga, T. Bioorg. Med. Chem. Lett. 2002, 12,
2815.
6. Kant, J.; Schwartz, W. S.; Fairchild, C.; Gao, Q.; Huang,
S.; Long, B. H.; Kadow, J. F.; Langley, D. R.; Farina, V.;
Vyas, D. Tetrahedron Lett. 1996, 37, 6495.
20a
20b
po
18.0
12.0
8.0
98.0
92.2
42.2
18.1
<0
<0
2/6
0/6
0/6
iv
18.0
12.0
—
96.4
—
13.5
6/6
0/6
7. Ojima, I.; Habus, I.; Zhao, M.; Zucco, M.; Park, Y. H.;
Sun, C. M.; Brigaud, T. Tetrahedron 1992, 48, 6985.
8. Spectral data of 9 are as follows: mp: 146–149 ꢀC; 1H NMR
(CDCl3) d: 1.24 (3H, s), 1.40 (9H, s), 1.46 (3H, s), 1.59 (3H, s),
1.63 (3H, s), 1.60–2.15 (5H, m), 2.27 (3H, s), 2.30–2.45 (1H,
m), 2.58–2.94 (6H, m), 2.90 (1H, d, J=4.4 Hz), 3.74 (4H, t,
J=4.8 Hz), 4.09 (1H, d, J=7.4 Hz), 4.23 (1H, d, J=8.8 Hz),
4.31 (1H, d, J=8.8 Hz), 4.50 (1H, br s), 4.62 (1H, s), 4.91 (1H,
s), 5.04 (1H, t, J=3.9 Hz), 5.22 (1H, d, J=7.4 Hz), 5.31 (1H,
d, J=9.3 Hz), 5.70 (1H, d, J=9.3 Hz), 6.05 (1H, d, J=4.4
Hz), 6.05–6.18 (1H, m), 7.20–7.48 (7H, m), 7.60 (1H, t, J=7.3
Hz), 8.11 (2H, d, J=7.3 Hz); FAB-MS (m/z): 905 (M+H)+.
Anal. calcd for C49H64N2O14H2O: C, 63.76; H, 7.21; N, 3.09;
Found: C, 63.74; H, 7.22; N, 3.09; IR (KBr): 3423, 2950, 1712,
1602, 1492, 1452 cmꢁ1; [a]D25 ꢁ14.8ꢀ (c 0.05, CHCl3).
9. Ojima, I.; Sun, C. M.; Zucco, M.; Park, Y. H.; Duclos, O.;
Kuduk, S. Tetrahedron Lett. 1993, 34, 4149.
po
40.5
27.0
18.0
12.0
96.9
91.3
59.7
23.4
4.1
<0
<0
0/6
0/6
0/6
0/6
<0
iv
po
iv
27.0
18.0
12.0
8.0
95.8
89.8
75.4
61.3
2.4
<0
<0
0/6
0/6
0/6
0/6
<0
15
27.0
18.0
12.0
8.0
97.3
93.3
84.9
27.2
4.5
0.3
<0
<0
0/6
0/6
0/6
0/6
18.0
12.0
8.0
95.6
94.4
87.2
62.4
3.7
<0
<0
0/6
0/6
0/6
0/6
5.3
<0
10. Spectral data of 12 are as follows: mp: 160–161 ꢀC; 1H
NMR (CDCl3) d: 1.30 (3H, s), 1.35 (9H, s), 1.47 (3H, s), 1.58
(3H, s), 1.61 (3H, s), 1.63 (3H, s), 1.80–2.15 (5H, m), 2.27 (1H,
dd, J=9.8, 15.1 Hz), 2.44 (3H, s), 2.46–2.83 (6H, m), 2.92 (1H,
d, J=4.8 Hz), 3.61–3.80 (4H, m), 4.10 (1H, d, J=7.3 Hz), 4.25
(1H, d, J=8.3 Hz), 4.32 (1H, d, J=8.3 Hz), 4.92 (1H, s), 4.95–
5.10 (2H, m), 5.20 (1H, d, J=6.4 Hz), 5.70 (1H, d, J=10.3 Hz),
5.98 (1H, d, J=4.8 Hz), 6.20 (1H, t, J=6.8 Hz), 7.20–7.55 (7H,
m), 7.60 (1H, t, J=7.3 Hz), 8.12 (2H, d, J=7.3 Hz); FAB-MS
(m/z): 919 (M+H)+. Anal. calcd for C50H66N2O14ꢂ 0.75H2O:
aCultured B16 melanoma BL6 was kindly provided by Dr. Tsuruo
(Institute of Molecular and Cellular Biosciences, University of Tokyo)
by courtesy of Dr. Fidler (The University of Texas M. D. Andersen
Cancer Center).17 B16 melanoma BL6 cells were subcutaneously
inoculated into C57BL/6 mice (six mice per group) on day 0. Com-
pounds were administered intravenously or orally on day 4 (single
administration). Tumor masses were weighed on day 15.
bIR (%)=(1ꢁTWt/TWc)ꢃ100. TWt, the mean tumor weight of the
treated group. TWc, the mean tumor weight of the control group.
cBWLmax (%), Maximum rate of body weight loss (<0 indicates no
body weight loss).

190
Y. Takeda et al. / Bioorg. Med. Chem. Lett. 13 (2003) 185–190
C, 64.40; H, 7.30; N, 3.00; Found: C, 64.40; H, 7.32; N, 2.86;
IR (KBr): 3430, 2969, 1716, 1602, 1492, 1452, 1367 cmꢁ1; [a]D24
ꢁ13.3ꢀ (c 0.2, CHCl3).
1592, 1490, 1452 cmꢁ1; [a]D25 ꢁ8.7ꢀ (c 0.48, CHCl3). 20b: mp:
160–165 ꢀC; H NMR (CDCl3) d: 1.30 (3H, s), 1.40–2.05 (5H,
1
m), 1.48 (3H, s), 1.51 (3H, s), 1.59 (3H, s), 1.61 (3H, s), 2.13–
2.22 (2H, m), 2.52 (3H, s), 2.53–2.70 (4H, m), 2.71 (1H, dd,
J=5.1, 13.2 Hz), 2.77 (1H, dd, J=3.9, 13.2 Hz), 2.93 (1H, d,
J=5.4 Hz), 3.73 (4H, t, J=4.4 Hz), 4.08 (1H, d, J=7.3 Hz),
4.20 (1H, d, J=8.3 Hz), 4.35 (1H, d, J=8.3 Hz), 4.93 (1H, s),
5.00 (1H, t, J=4.4 Hz), 5.12 (1H, d, J=7.3 Hz), 5.69 (1H, d,
J=9.5 Hz), 5.96 (1H, d, J=5.4 Hz), 5.98 (1H, br s), 6.21 (1H,
br t, J=8.8 Hz), 7.25–7.35 (1H, m), 7.42–7.55 (5H, m), 7.61
(1H, t, J=7.5 Hz), 7.72 (1H, dt, J=1.5, 7.5 Hz), 7.87 (2H, d,
J=7.8 Hz), 7.91 (1H, d, J=7.5 Hz), 8.15 (2H, d, J=7.5 Hz),
8.52 (1H, d, J=4.4 Hz); FAB-MS (m/z): 924 (M+H)+. Anal.
calcd for C51H61N3O13ꢂ 1.25H2O: C, 64.71; H, 6.76; N, 4.44;
Found: C, 64.71; H, 6.78; N, 4.37; IR (KBr): 3421, 2950, 1720,
1664, 1592, 1511, 1482, 1436 cmꢁ1; [a]D25 ꢁ10.4ꢀ (c 0.42,
CHCl3).
11. Spectral data of 15 are as follows: mp: 160–162 ꢀC; 1H
NMR (CDCl3) d: 1.27 (3H, s), 1.30–2.15 (6H, m), 1.43 (9H, s),
1.48 (3H, s), 1.60 (3H, s), 1.73 (3H, s), 2.27–2.38 (1H, m), 2.37
(3H, s), 2.55–2.68 (4H, m), 2.72 (1H, dd, J=5.1, 13.6 Hz), 2.79
(1H, dd, J=3.9, 13.6 Hz), 2.93 (1H, d, J=4.9 Hz), 3.74 (4H, t,
J=4.6 Hz), 4.12 (1H, d, J=7.1 Hz), 4.22 (1H, d, J=8.3 Hz),
4.33 (1H, d, J=8.3 Hz), 4.85 (1H, br s), 4.88–4.95 (2H, m),
5.14 (1H, t, J=4.4 Hz), 5.23 (1H, d, J=7.1 Hz), 5.35 (1H, br
d, J=9.4 Hz), 5.97 (1H, br d, J=9.4 Hz), 5.98 (1H, d, J=4.9
Hz), 6.09 (1H, br t, J=8.3 Hz), 7.23 (1H, dd, J=5.2, 7.1 Hz),
7.42 (1H, d, J=7.8 Hz), 7.47 (2H, t, J=7.8 Hz), 7.60 (1H, t,
J=7.8 Hz), 7.72 (1H, dt, J=1.5, 7.8 Hz), 8.12 (2H, d, J=7.8
Hz), 8.53 (1H, br d, J=5.2 Hz); FAB-MS (m/z): 906
(M+H)+. Anal. calcd for C48H63N3O14: C, 63.63; H, 7.01; N,
4.64; Found: C, 63.62; H, 7.03; N, 4.47; IR (KBr): 2950, 1722,
1689, 1592, 502, 1434, 1365 cmꢁ1; [a]D23 ꢁ5.6ꢀ (c 1.06, CHCl3).
12. Georg, G. I.; Harrima, G. C. B.; Hepperle, M.; Himes,
R. H. Bioorg. Med. Chem. Lett. 1994, 4, 1381.
15. A colorless, prismatic crystal of C52H79N3O18 having
approximate dimensions of 0.30ꢃ0.20ꢃ0.10 mm was grown
from MeOH–MeCN and mounted in a glass capillary. The
lattice parameters and intensities were measured on
a
13. Hart, D. J.; Kanai, K.; Thomas, D. G.; Yang, T.-K. J.
Org. Chem. 1983, 48, 289.
14. Spectral data of 20a and 20b are as follows; 20a: mp: 150–
RIGAKU AFC7R diffractometer with monochromated CuKa
radiation by using the o-2y scan technique. The compound
crystallized in orthorhombic space group P212121 with cell
152 ꢀC; H NMR (CDCl3) d: 1.29 (3H, s), 1.42 (9H, s), 1.48
dimensions a=17.1295 A, b=30.1980 A, c=10.3530 A,
1
˚
˚
˚
3
˚
(3H, s), 1.53 (3H, s), 1.56 (3H, s), 1.59 (3H, s), 1.60–1.80 (1H,
m), 1.83–2.50 (5H, m), 2.51 (3H, s), 2.50–2.84 (6H, m), 2.92
(1H, d, J=5.4 Hz), 3.74 (4H, t, J=4.4 Hz), 4.11 (1H, d, J=6.8
Hz), 4.20 (1H, d, J=8.3 Hz), 4.34 (1H, d, J=8.3 Hz), 4.93
(1H, s), 5.01 (1H, t, J=4.4 Hz), 5.16 (1H, d, J=6.8 Hz), 5.95
(1H, d, J=5.4 Hz), 6.04 (1H, d, J=10.2 Hz), 6.16 (1H, br t,
J=8.8 Hz), 7.20–7.35 (1H, m), 7.40–7.60 (3H, m), 7.60 (1H, t,
J=7.3 Hz), 7.72 (1H, t, J=7.4 Hz), 8.15 (2H, d, J=7.3 Hz),
8.49 (1H, d, J=4.4 Hz); FAB-MS (m/z): 920 (M+H)+. Anal.
calcd for C49H65N3O14ꢂ 1.25H2O: C, 62.44; H, 7.22; N, 4.46;
Found: C, 62.48; H, 7.19; N, 4.45; IR (KBr): 3440, 2973, 1716,
V=5335.4 A . The structure was solved by the direct method
with the program SIR92. After several cycles of refinement,
eight extra peaks of electron density are observed. They were
assigned as four MeOH molecules. For Z=4 and
F.W.=1034.21, the calculated density was 1.28 g/cm3. The
final R value was 0.061.
16. PC-6/VCR29-9: PC-6 cell line, which is resistant to Vin-
cristine1. PC-6/VP1-1: PC-6 cell line, which is resistant to VP-
16 (Etoposide1).
17. Poste, G.; Doll, J.; Hart, I. R.; Fidler, I. J. Cancer Res.
1980, 40, 1636.