Orally active docetaxel analogue: Synthesis of 10-deoxy-10-C-morpholinoethyl docetaxel analogues

Article abstract of DOI:10.1016/S0960-894X(00)00682-X

To improve cytotoxicity of 10-deoxy-10-C-morpholinoethyl docetaxel analogues against various tumor cell lines including resistant cells expressing P-glycoprotein (P-gp), we modified the 7-hydroxyl group to hydrophobic groups (methoxy, deoxy, 6,7-olefin, α-F, 7-β-8-β-methano, fluoromethoxy). Among these analogues, the 7-methoxy analogue showed the strongest cytotoxicity. This analogue showed potent activity against B16 melanoma BL6 in vivo by oral administration.

Full text of DOI:10.1016/S0960-894X(00)00682-X

Bioorganic & Medicinal Chemistry Letters 11 (2001) 407±410
Orally Active Docetaxel Analogue:
Synthesis of 10-Deoxy-10-C-morpholinoethyl Docetaxel
Analogues
Shin Iimura, Kouichi Uoto, Satoru Ohsuki, Jun Chiba, Toshiharu Yoshino,
Michio Iwahana, Takeshi Jimbo, Hirofumi Terasawa and Tsunehiko Soga*
New Product Research Laboratories IV, Daiichi Pharmaceutical Co., Ltd., 1-16-13, Kitakasai, Edogawa, Tokyo 134-8630, Japan
Received 19 September 2000; accepted 24 November 2000
AbstractÐTo improve cytotoxicity of 10-deoxy-10-C-morpholinoethyl docetaxel analogues against various tumor cell lines includ-
ing resistant cells expressing P-glycoprotein (P-gp), we modi®ed the 7-hydroxyl group to hydrophobic groups (methoxy, deoxy, 6,7-
ole®n, a-F, 7-b-8-b-methano, ¯uoromethoxy). Among these analogues, the 7-methoxy analogue showed the strongest cytotoxicity.
This analogue showed potent activity against B16 melanoma BL6 in vivo by oral administration. # 2001 Elsevier Science Ltd. All
rights reserved.
Paclitaxel (1, Taxol1)1 and docetaxel (2, Taxotere1)2
are currently considered to be some of the most impor-
tant drugs in cancer chemotherapy. However, their low
water-solubility requires co-injection of a detergent,
Cremophor1 EL or Tween1 80. These detergents fre-
quently cause untoward hypersensitivity reactions, and
patients receiving these drugs require premedication.3
To resolve these problems, we previously described the
synthesis of non-prodrug water-soluble docetaxel ana-
logues, such as 10-O-sec-aminoethyl docetaxel analo-
gues4 and 10-deoxy-10-C-sec-aminoalkyl docetaxel
analogues.5 Among these analogues, 10-deoxy-10-C-
morpholinoethyl docetaxel analogue (3) exhibited
cytotoxicity equal to that of docetaxel (2) (Table 1).
Many patients whose initial response is good go into
relapse because of the development of drug resistance
after treatment.6 To overcome this problem, we mod-
i®ed the 7-hydroxyl group of the 10-C-morpholinoethyl
docetaxel analogue (3) to the groups that have been
reported to be able to improve the cytotoxicity against
cancer cell lines such as methoxy, deoxy, 6,7-ole®n, etc.
We found that the 7-methoxy analogue showed the
most potent activity, regardless of P-gp expression. It
has been reported that the poor oral bioavailability of
docetaxel is caused by P-gp, which is present in the
gastrointestinal tract.7 Consequently, the oral bioavail-
ability of paclitaxel could be increased markedly with P-
gp inhibitors.8 Therefore, a taxane that is a poor sub-
strate of P-gp showed oral bioavailability.9 On the basis
of these observations, the 7-methoxy analogue, a poor
substrate of P-gp, appeared to have good bioavailability
and showed antitumor activity in vivo by oral adminis-
tration. Here we report modi®cation of the 7-hydroxyl
group of 10-deoxy-10-C-morpholinoethyl docetaxel
analogues, and the results of in vivo studies.
However, the cytotoxicity of 3 against drug-resistant
cell lines expressing P-gp was not suciently potent.
Chemistry
Figure 1. Structure of paclitaxel analogues.
10-Deoxy-7-O-methyl-10-C-morpholinoethyl docetaxel
(7) was synthesized from 10-deacetoxy-10-C-morpholi-
noethyl-7,13-O-bis-TES baccatin III (4)5 (Scheme 1).
Selective desilylation and substitution with MTM and
*Corresponding author. Tel.: +81-3-3680-0151; fax: +81-3-5696-
8344; e-mail: sogatf7t@daiichipharm.co.jp
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00682-X

408
S. Iimura et al. / Bioorg. Med. Chem. Lett. 11 (2001) 407±410
following desulfurylation10 gave the key intermediate
(6). Introduction of the phenylisoserine side chain using
protected b-lactam (8)11 as a side-chain precursor and
deprotection using the reported method11 gave 7.12
oxidation, reductive amination, and deprotection gave
12.14
Synthesis of 6,7-dehydro-7,10-di-deoxy-10-C-morpholi-
noethyl docetaxel (15) is described in Scheme 3. The key
intermediate (14) was synthesized from 135 in high
yield.15 14 was converted to 1516 by reactions similar to
those used for preparation of 12.
Synthesis of 7,10-di-deoxy-10-C-morpholinoethyl doc-
etaxel (12) is described in Scheme 2. The key inter-
mediate (11) was synthesized from 913 in the reported
manner.5 Introduction of the phenylisoserine side chain,
Synthesis of 7,10-di-deoxy-7-a-¯uoro-10-C-morpholi-
noethyl docetaxel (18) is described in Scheme 4. The key
intermediate (17) was synthesized from 16 in moderately
high yield.17 Compound 17 was converted to 18.18
Table 1. Cytotoxicity of 10-C-morpholinoethyl docetaxel analogues
modi®ed 7-hydroxyl groupa
7-group
Cytotoxic activity GI50 (ng/mL)b
PC-6
PC-12
PC-6/VCR29-9
2
3
7
12
15
18
21
27
0.408±2.55
1.72
11.7±72.7
21.5
0.756
1.47
0.824
2.55
3.56
39.6±230
76.3
9.01
20.4
18.0
16.2
38.6
40.4
OH
OMe
Deoxy
ole®n
a-F
Methano
OCH2F
0.266
0.761
0.500
0.379
0.873
0.246
1.50
aThe in vitro experiments were performed with three di€erent cell
lines: PC-6, a human small cell lung cancer,23 and its variant, PC-6/
VCR29-9, vincristine-resistant cell line expressing P-gp,24 PC-12, a
human non-small cell lung cancer cell line.23 Determination of GI50
was performed using the MTT assay.25 The cells were exposed con-
tinuously to the test compounds for 72 h.
Scheme 3. Reagents and conditions: (a) cat. p-TsOH, MeOH (75%); (b)
Tf2O, Py (92%); (c) DBU (98%); (d) HF±Py (96%); (e) 8, LiHMDS,
THF (100%); (f) HF±Py (94%); (g) 1) OsO4, N-methylmorpholine N-
oxide, 2) NaIO4, 3) morpholine, AcOH, NaBH3CN (95%).
bGrowth inhibition of 50%: the concentration required to obtain half
of the maximal inhibition for cell growth.
Scheme 1. Reagents and conditions: (a) TsOH, MeOH (71%); (b)
Ac2O, DMSO (42%); (c) Raney-Ni, EtOH, re¯ux (67%); (d) HF±Py
(82%); (e) 8, NaHMDS, THF, 78 ꢀC (72%); (f) HF±Py (82%).
Scheme 4. Reagents and conditions: (a) DAST (50%); (b) HF±Py
(50%); (c) 8, LiHMDS, THF (62%); (d) 1) OsO4, N-methylmorpho-
line N-oxide, 2) NaIO4, 3) morpholine, AcOH, NaBH3CN (51%); (e)
HF±Py (84%).
Scheme 2. Reagents and conditions: (a) hydrazine (53%); (b) CS2,
MeI, n-BuLi (55%); (c) n-Bu3SnH, AIBN, acrolein (30%); (d) NaBH4
(97%); (e) o-nitrophenylseleno cyanide, n-Bu3P (75%); (f) mCPBA
(89%); (g) 8, NaH, THF (94%); (h) 1) OsO4, N-methylmorpholine N-
oxide, 2) NaIO4 (63%); (i) 1) morpholine, H2, Pd±C, 2) HF±Py (47%).
Scheme 5. Reagents and conditions: (a) silica gel, CH3CN±THF,
55 ꢀC (72%); (b) HF±Py (q.y.); (c) 8, LiHMDS, THF (89%); (d) 1)
OsO4, N-methylmorpholine N-oxide, 2) NaIO4, 3) morpholine, AcOH,
NaBH3CN (76%); (e) HF±Py (91%).

S. Iimura et al. / Bioorg. Med. Chem. Lett. 11 (2001) 407±410
409
Synthesis of 7,10-di-deoxy-7-b-8-b-methano-10-C-mor-
pholinoethyl docetaxel (21) is described in Scheme 5.
The key intermediate (20) was synthesized from 19 in
high yield.19 Compound 20 was converted to 21.20
These analogues (7, 12, 15, 18, 21, 27) having a
morpholinoethyl group are more soluble than paclitaxel
and docetaxel in acidic solution.
Synthesis of 10-deoxy-7-O-¯uoromethyl-10-C-morpho-
linoethyl docetaxel (27) is described in Scheme 6. The
key intermediate (26) was synthesized from 22. We
found that oxidative ¯uorination of 7-O-methylthio-
methyl ether (23) using NIS and DAST a€orded
¯uoromethyl ether (24) in good yield.21 The 10-C-alkyl
group was introduced in the reported manner.5 Com-
pound 26 was converted to 27.22
Results and Discussion
Antitumor activities of the 10-deoxy-10-C-morpholi-
noethyl docetaxel analogues modi®ed at the 7-hydroxyl
group were determined in vitro and in vivo. The cyto-
toxicities of 7-modi®ed docetaxel analogues (7, 12, 15,
18, 21, 27) against two human lung cancers and resistant
cell lines expressing P-gp were improved in comparison
with those of 7-hydroxy analogue (3) (Table 1).
Among these analogues, 7-methoxy analogue (7)
showed the most potent cytotoxic activity. We selected
compound 7 as a candidate for further in vivo investi-
gation. To evaluate the antitumor e€ects of compound 7
in vivo, we used B16 melanoma BL6 subcutaneously
implanted into mice, and the activity of 7 was compared
with that of docetaxel (2). Furthermore, we investigated
whether compound 7 exhibits antitumor e€ects by oral
administration or not. Compound 7 showed potent
antitumor e€ects over a wide dose range by both iv and
po administration. However, ®ve of the six mice that
received compound 7 intravenously at 75 mg/kg died
from toxicity. The same dosage by oral administration
exhibited potent antitumor activity with an IR value of
98.3% with body weight loss of only 5.0%. The near
dosage (112.5 mg/kg) by oral administration gave death.
Thus, we considered compound 7 to have excellent oral
bioavailability in mice. In contrast, docetaxel at
600.0 mg/kg given po exhibited no antitumor activity, and
showed no body weight loss. This result clearly showed
that docetaxel has very poor bioavailability (Table 2).
Scheme 6. Reagents and conditions: (a) cat. TsOH, MeOH (80%); (b)
Ac2O, DMSO (49%); (c) NIS, DAST, CH2Cl2, 0 ꢀC (64%); (d) HF±Py
(80%); (e) hydrazine, EtOH (97%); (f) n-BuLi, carbon disul®de,
methyl iodide, THF (91%); (g) acrolein, (TMS)3SiH, AIBN, toluene
(50%); (h) NaBH4, THF (77%); (i) o-nitrophenylseleno cyanide, n-
Bu3P (79%); (j) mCPBA (71%); (k) 8, LiHMDS, THF (92%); (l) HF±
Py (84%); (m) 1) OsO4, N-methylmorpholine N-oxide, 2) NaIO4, 3)
morpholine, AcOH, NaBH3CN (68%).
In conclusion, we synthesized several 10-C-morpholi-
noethyl docetaxel analogues modi®ed at the 7-hydroxyl
group. The 7-methoxy analogue was the most potent of
the analogues prepared and was highly active against
B16 melanoma BL6 by both iv and po administration.
Further investigations of orally active docetaxel analo-
gues will be reported in the near future.
Table 2. Antitumor activity against B16 melanoma BL-6a
Route Dose (mg/kg) IR (%)b BWL max. (%)c Mortality
2
7
iv
po
po
100.0
600.0
112.5
75.0
50.0
33.3
22.2
75.0
50.0
33.3
22.2
95.1
6.2
99
<0
<0
20.0
5.0
1.7
0.9
0/6
0/6
4/6
0/6
0/6
0/6
0/6
5/6
0/6
0/6
0/6
References and Notes
98.3
96.2
82.8
81.7
99.4
98.6
94.4
93.7
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iv
19.2
18.0
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5.7
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12. 1H NMR of 7 (400 MHz, CDCl3) d 1.14 (s, 3H), 1.19 (s, 3H),
1.35 (s, 9H), 1.67 (s, 3H), 1.85 (d, J=1 Hz, 3H), 2.37 (s, 3H), 1.73±
2.75 (m, 12H), 3.25 (s, 3H), 3.68 (m, 4H), 3.93±4.01 (m, 3H), 4.18
(d, J=8 Hz, 1H), 4.30 (d, J=8 Hz, 1H), 4.61 (s, 1H), 4.99 (d,
J=8 Hz, 1H), 5.27 (d, J=10 Hz, 1H), 5.42 (d, J=10 Hz, 1H),
5.63 (d, J=7 Hz, 1H), 6.16 (t, J=8 Hz, 1H), 7.29±7.42 (m, 5H),
7.49 (t, J=8 Hz, 2H), 7.60 (t, J=8 Hz, 1H), 8.10 (d, J=8 Hz, 2H).
13. Chen, S. H.; Huang, S.; Kant, J.; Fairchild, C.; Wei, J.;
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3H), 1.31 (s, 9H), 1.3±1.6 (m, 3H), 1.71 (s, 3H), 1.80 (s, 3H),
1.85±2.05 (m, 2H), 2.1±2.6 (m, 11H), 2.40 (s, 3H), 3.68 (m,
4H), 3.92 (d, J=7 Hz, 1H), 4.08 (t, J=5 Hz, 1H), 4.24 (d,
J=8 Hz, 1H), 4.32 (d, J=8 Hz, 1H), 4.60 (brs, 1H), 4.95 (dd,
J=3 Hz, 10 Hz, 1H), 5.28 (d, J=9 Hz, 1H), 5.37 (d, J=9 Hz,
1H), 5.65 (d, J=7 Hz, 1H), 6.20 (t, J=9 Hz, 1H), 7.31 (t,
J=7 Hz, 1H), 7.37 (d, J=7 Hz, 2H), 7.40 (t, J=7 Hz, 2H), 7.51
(t, J=7 Hz, 2H), 7.61 (t, J=7 Hz, 1H), 8.14 (d, J=7 Hz, 2H).
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3H), 1.33 (s, 9H), 1.45±1.55 (m, 2H), 1.72 (s, 3H), 1.83 (s, 3H),
2.23 (dd, J=8 Hz, 15 Hz, 1H), 2.39 (s, 3H), 2.30±2.60 (m, 8H),
3.68 (t, J=4.7 Hz, 4H), 3.78 (d, J=5 Hz, 7 Hz, 1H), 4.19 (d,
J=7 Hz, 1H), 4.31 (d, J=8 Hz, 1H), 4.42 (d, J=8 Hz, 1H),
4.60 (s, 1H), 5.11 (d, J=6 Hz, 1H), 5.27 (d, J=9 Hz, 1H), 5.41
(d, J=9 Hz, 1H), 5.72 (d, J=10 Hz, 1H), 5.83 (d, J=7 Hz, 1H),
6.02 (dd, J=6 Hz, 10 Hz, 1H), 6.18 (t, J=9 Hz, 1H), 7.51 (t,
J=7 Hz, 2H), 7.62 (t, J=7 Hz, 1H), 8.16 (d, J=7 Hz, 2H).
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3H), 1.33 (s, 9H), 1.68 (s, 3H), 1.77 (s, 3H), 2.40 (s, 3H), 2.14±
2.65 (m, 13H), 3.68 (m, 4H), 4.20±4.24 (m, 2H), 4.33, 4.36
(each d, J=9 Hz, total 2H), 4.52 (dd, J=3 Hz, 47 Hz, 1H),
4.61 (s, 1H), 5.02 (dd, J=2 Hz, 9 Hz, 1H), 5.30 (d, J=10 Hz,
1H), 5.41 (d, J=10 Hz, 1H), 5.74 (d, J=7 Hz, 1H), 6.19 (t,
J=8 Hz, 1H), 7.40±7.42 (m, 5H), 7.51 (t, J=8 Hz, 2H), 7.61 (t,
J=8 Hz, 1H), 8.14 (d, J=8 Hz, 2H).
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1H), 2.12 (m, 1H), 2.20 (m, 1H), 2.39 (m, 4H), 2.43 (m, 6H),
2.55 (m, 1H), 3.71 (m, 4H), 3.75 (m, 1H), 4.04 (d, J=9 Hz,
1H), 4.27 (d, J=7 Hz, 1H), 4.29 (d, J=9 Hz, 1H), 4.60 (brs,
1H), 4.75 (d, J=3 Hz, 1H), 5.29 (m, 1H), 5.35 (d, J=10 Hz,
1H), 5.65 (d, J=7 Hz, 1H), 6.22 (m, 1H), 7.30±7.40 (m, 5H),
7.50 (t, J=8 Hz, 2H), 7.60 (t, J=8 Hz, 1H), 8.16 (d, J=8 Hz,
2H).
21. Experimental procedure of ¯uorination: To a cooled (ice-
water) solution of 7-O-methylthiomethyl-13-O-TES baccatin III
(100 mg, 0.13 mmol) in CH2Cl2, was added N-iodosuccinimide
(45 mg, 0.2 mmol) and DAST (35 mL, 0.20 mmol). Stirring was
continued for 1 h at 0 ꢀC. The reaction mixture was poured
into satd. NaHCO3 and the mixture was stirred vigorously for
5 min. The organic phase was separated and dried over anhy-
drous MgSO4 and evaporated. The residue was puri®ed by
TLC to give 24 as colorless solids (62 mg, 64%).
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2.70 (m, 12H), 3.68 (m, 4H), 4.00±4.06 (m, 2H), 4.19 (d,
J=8 Hz, 1H), 4.31 (d, J=8 Hz, 1H), 4.41 (dd, J=7 Hz, 10 Hz,
1H), 4.60 (s, 1H), 4.96 (d, J=8 Hz, 1H), 5.11 (dd, J=8 Hz, 28
Hz, 1H), 5.22±5.28 (m, 2H), 5.41 (d, J=10 Hz, 1H), 5.65 (d,
J=7 Hz, 1H), 6.17 (t, J=8 Hz, 1H), 7.30±7.42 (m, 5H), 7.49 (t,
J=8 Hz, 2H), 7.61 (t, J=8 Hz, 1H), 8.10 (d, J=8 Hz, 2H).
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