Practical synthesis of the high-quality antitumor agent KW-2189 from duocarmycin B2 using a facile one-pot synthesis of an intermediate

Article abstract of DOI:10.1021/op980038k

A facile and large-scale preparation process of a potent antitumor agent KW-2189 (2), derived from the antitumor antibiotic duocarmycin B2 (1), has been developed. This new synthetic route required three steps: (i) one-pot carbamoylation and subsequent reduction, (ii) Wagner-Meerwein rearrangement of the methoxycarbonyl group for the production of the pyrrole compound 6, and (iii) formation of the hydrobromide salt 2. The key strategic improvement was to obtain good quality hydroxy compound 4 in a reasonable yield without isolation of the unstable keto intermediate 3a. During commercial-scale production at a scale of about 50 g, this strategy provided high-quality KW-2189 (2) in a 55% overall yield from 1. Potential degradation compounds 7-9 were also synthesized and shown to be absent in the KW-2189 (2) prepared.

Full text of DOI:10.1021/op980038k

Organic Process Research & Development 1998, 2, 344−350
Articles
Practical Synthesis of the High-Quality Antitumor Agent KW-2189 from
Duocarmycin B2 Using a Facile One-Pot Synthesis of an Intermediate
Masahiko Kinugawa,† Satoru Nagamura,‡,1 Akihiko Sakaguchi,† Yoshiaki Masuda,† Hiromitsu Saito,‡,2
Takehiro Ogasa,*,† and Masaji Kasai†
Sakai Research Laboratories, Kyowa Hakko Kogyo Co., Ltd., 1-1-53, Takasu-cho, Sakai, Osaka 590, Japan, and Tokyo
Research Laboratories, Kyowa Hakko Kogyo Co., Ltd., 3-3-6, Asahimachi, Machida, Tokyo 194, Japan
Abstract:
A facile and large-scale preparation process of a potent
antitumor agent KW-2189 (2), derived from the antitumor
antibiotic duocarmycin B2 (1), has been developed. This new
synthetic route required three steps: (i) one-pot carbamoylation
and subsequent reduction, (ii) Wagner-Meerwein rearrange-
ment of the methoxycarbonyl group for the production of the
pyrrole compound 6, and (iii) formation of the hydrobromide
salt 2. The key strategic improvement was to obtain good
quality hydroxy compound 4 in a reasonable yield without
isolation of the unstable keto intermediate 3a. During com-
mercial-scale production at a scale of about 50 g, this strategy
provided high-quality KW-2189 (2) in a 55% overall yield from
1. Potential degradation compounds 7-9 were also synthesized
and shown to be absent in the KW-2189 (2) prepared.
Introduction
Figure 1. Structure of duocarmycins isolated from Strepto-
myces.
Duocarmycins (DUMs) (Figure 1) are a new class of
antitumor antibiotics isolated from Streptomyces species
which show antitumor activity against murine lymphocytic
P388 transplanted in CDF1 mice and murine Sarcoma 180
in ddY mice.3-9 With the aim of enhancing and broadening
the spectrum of antitumor activity and improving their
solubility or stability,10-13 a series of analogues have been
† Sakai Research Laboratories.
‡ Tokyo Research Laboratories.
(1) Present address: Technical Research Laboratories, Kyowa Hakko Kogyo
Co., Ltd., 1-1, Kyowamachi, Hofu, Yamaguchi 747, Japan.
(2) Present address: Fuji Plant, Kyowa Hakko Kogyo Co., Ltd., 1188,
Shimotogari, Nagaizumi-cho, Shizuoka 411, Japan.
(3) Takahashi, I.; Takahashi, K.; Ichimura, M.; Morimoto, M.; Asano, K.;
Kawamoto, I.; Tomita, F.; Nakano, H. J. Antibiot. 1988, 41, 1915.
(4) Ichimura, M.; Muroi, K.; Asano, K.; Kawamoto, I.; Tomita, F.; Morimoto,
M.; Nakano, H. J. Antibiot. 1988, 41, 1285.
(5) Ogawa, T.; Ichimura, M.; Katsumata, S.; Morimoto, M.; Takahashi, K. J.
Antibiot. 1989, 42, 1299.
(6) Ichimura, M.; Ogawa, T.; Takahashi, K.; Kobayashi, E.; Kawamoto, I.;
Yasuzawa, T.; Takahashi, I.; Nakano, H. J. Antibiot. 1990, 43, 1037.
(7) Yasuzawa, T.; Iida, T.; Muroi, K.; Ichimura, M.; Takahashi, K.; Sano, H.
Chem. Pharm. Bull. 1988, 36, 3728.
Figure 2. Structure of KW-2189.
synthesized from duocarmycin B2 (1, DUMB2), which was
more efficiently isolated than other natural DUMs. Among
these analogues, KW-2189 (2) (Figure 2) displays a remark-
ably effective and broad spectrum of activities in vivo against
various human xenografts including LC-6 (lung), St-4
(stomach), and Co-3 (colon).14 KW-2189 (2) also possesses
(11) Nagamura, S.; Kanda, Y.; Kobayashi, E.; Gomi, K.; Saito, H. Chem. Pharm.
Bull. 1995, 43, 1530.
(12) Nagamura, S.; Kanda, Y.; Asai, A.; Kobayashi, E.; Gomi, K.; Saito, H.
Chem. Pharm. Bull. 1996, 44, 933.
(13) Nagamura, S.; Asai, A.; Kanda, Y.; Kobayashi, E.; Gomi, K.; Saito, H.
Chem. Pharm. Bull. 1996, 44, 1723.
(14) Kobayashi, E.; Okamoto, A.; Asada, M.; Okabe, M.; Nagamura, S.; Asai,
A.; Saito, H.; Gomi, K.; Hirata, T. Cancer Res. 1994, 54, 2404.
(8) Yasuzawa, T.; Saitoh, Y.; Ichimura, M.; Takahashi, I.; Sano, H. J. Antibiot.
1991, 44, 445.
(9) Yasuzawa, T.; Muroi, K.; Ichimura, M.; Takahashi, I.; Ogawa, T.; Takahashi,
K.; Sano, H.; Saitoh, Y. Chem. Pharm. Bull. 1995, 43, 378.
(10) Gomi, K.; Kobayashi, E.; Miyoshi, K.; Ashizawa, T.; Okamoto, A.; Ogawa,
T.; Katsumata, S.; Mihara, A.; Okabe, M.; Hirata, T. Jpn. J. Cancer Res.
1992, 83, 113.
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Vol. 2, No. 6, 1998 / Organic Process Research & Development
10.1021/op980038k CCC: $15.00 © 1998 American Chemical Society and Royal Society of Chemistry
Published on Web 08/21/1998

Scheme 1. Synthesis of KW-2189
Table 1. Solvent effects on the NaBH4 reduction of 3aa
improved stability and solubility in water (10 mg/mL) and
has consequently been selected for clinical development.
Under basic conditions, the starting material 1 is easily
converted to duocarmycin A (DUMA), followed by decom-
position.13 Consequently, the reported synthetic method of
2 required seven steps (24% overall yield) including tedious
protection-deprotection procedures of the phenolic hydroxy
group of 1 with the tert-butyldimethylsilyl group. For
commercial production, more efficient procedures for large-
scale operation were required. Our synthetic approach
avoided protective group chemistry and proceeded by direct
carbamoylation of the phenolic hydroxy group of 1, followed
by reduction and rearrangement to 2, as shown in Scheme
1. The carbamoyl group might have been unstable under
the reduction conditions with sodium borohydride and the
subsequent acid treatment, but if this strategy could be
followed, this synthetic pathway would not need a protecting
group such as the silyl moiety. We report an improved and
straightforward synthesis of KW-2189 (2).
yield (%)c
solvent
MeOH
allyl alcohol
i-PrOH
n-PrOH
PhCH2OH
DMF
time (h)b
4a
4b
5
2.0
1.0
5.0
4.0
1.5
4.0
4.0
57
71
31
31
57
16
24
22
6
9
6
4
11
7
10
8
26
18
15
12
14
THF
a All reactions were carried out under ice-cooling using a 3.0 M amount of
NaBH4 (based on 3a). b All reactions were quenched after disappearance of 3a
in HPLC analyses. c Determined by HPLC analyses. Other byproducts have not
been identified.
used, selectivity was reduced and the undesirable diols 517
were formed (Table 1). The stereochemistries of compounds
4a and 4b at C8 were confirmed by NMR studies.18
During further studies on scale-up, it was found that the
intermediate 3a was degraded to the corresponding exo-
methylene compound 7 in the isolation (Scheme 2).19
Generally speaking, the yield of the reaction went down on
scale-up; the stability of the product might be responsible.
Compound 3a was unstable in highly concentrated solution
even at 20 °C and was presumed to easily convert to 7 in
the evaporation process of the workup (Figure 3). The
dehydrobromination was thought to be caused by the
Results and Discussion
DUMB2 (1) was almost quantitatively converted into the
carbamate 3a using N-methylpiperazinecarbonyl chloride
(Scheme 1).15 Sodium borohydride was then used for a
selective reduction of the carbonyl group at C8 of compound
3a. With regard to solvents, this reduction was carried out
in best yield and stereoselectivity in ice-cold allyl alcohol
when the 8R-hydroxy compound 4a was obtained as the
major product in 71% yield.16 When other solvents were
(17) Diols 5 are the mixture of 8R- and 8â-hydroxy compounds. They are not
separated by the various analytical methods such as HPLC and TLC
analyses.
(18) More intense NOEs between 8-H and 7-CH3 and between 8-H and 1-CH2-
Br were observed in 4b than in 4a, indicating that the stereochemistry of
8-H is â-face in 4a and R-face in 4b.
(19) For an example, a suspension of 1 (2.0 g) was carried out using the similar
procedure described in the Experimental Section; 3a was obtained in 65%
yield and the yield of 7 was 34%.
(15) Fujii, T.; Oka, K.; Ueda, M.; Tomino, K.; Shigematsu, S. JP. 1951, 4929;
Chem. Abstr. 1953, 47, 9369.
(16) To our knowledge, sodium borohydride reduction using allyl alcohol as
reaction solvent has not been investigated.
Vol. 2, No. 6, 1998 / Organic Process Research & Development
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345

Scheme 2. A series of degradation compounds 7-9
Table 2. Acid-catalyzed rearrangement of 4
conditions
temp
(°C)
time
yield of 6
acida
solvent
(h)b
(%)c
CSAd
ClCH2CH2Cl
toluene
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
50
50
50
50
25
50
2.5
2.5
1.5
3.0
1.5
1.0
83
72
82
86
81
85
CSAd
TsOH‚H2O
CH3SO3H
CF3SO3H
BF3‚Et2O
a A 3 M amount of acid was used (based on 4). b All reactions were quenched
after disappearance of 4 in HPLC analyses. c Isolated yield. d (()-10-Camphor-
sulfonic acid.
was stirred at 25 °C until the carbamoylation was complete.
The mixture was then cooled, and sodium borohydride was
added intermittently to the reaction mixture, until 3 disap-
peared completely and converted to 4. This one-pot proce-
dure accounted for the high isolated yield and quality
improvement to the key intermediate 4. The undesirable exo-
methylene compound 8 was detected at less than 0.2% in
the isolated 4.20 In a typical experiment, 31.8 g of 4 (4a
and 4b) was obtained from 30 g of 1 (91% yield, 4a 87%,
4b 4%). This result was critical to the successful scale-up
of the synthesis of KW-2189.
The Wagner-Meerwein rearrangement of 4 is the most
important route to KW-2189, and up to now this acid-
catalyzed rearrangement has been investigated using silyl-
protected DUMB2.13 Lewis acids such as aluminum chloride
and boron trifluoride etherate were more effective than
p-toluenesulfonic acid and methanesulfonic acid.12 In our
hands, the Lewis acid, boron trifluoride etherate, was
effective, and Brønsted acids were also shown to be useful
for the rearrangement (Table 2). On balance, we selected
methanesulfonic acid as the most convenient reagent, because
of the high yield, easy workup, and environmental concerns.
Thus, 4 [a mixture of 4a and 4b (ca. 19:1)] was treated with
methansulfonic acid in 1,2-dichloroethane to give 6 in an
86% yield.21
The free base 6 was finally converted to the corresponding
hydrobromide salt 2 by treating it with 48% hydrobromic
acid in a mixture of acetone and methanol when the salt 2
was precipitated from the reaction mixture and isolated easily
by filtration (88% yield). A trace amount of 9 generated by
acidic rearrangement of 8 was present in the reaction mixture,
but was completely removed in the filtrates. To remove a
small amount of residual acetone (approximately 2000 ppm),
compound 2 was crystallized from aqueous ethanol (84%
yield, more than 99.5% purity by HPLC22).
Figure 3. Stabilities of 3a in highly concentrated solution.
Legend: (a) determined by HPLC analyses (see Experimental
Section), at 0 °C (b), 20 °C (O), and 35 °C (0).
N-methylpiperazine fragment of 3a. Thus, the degradation
accelerated in line with the amount of triethylamine used.
Decreasing the basicity of the reaction mixture by the
addition of acids improved the stability of 3a and as a result
the corresponding hydrochloride salt 3b, which was prepared
from 3a with hydrogen chloride in ethanol, was quite stable
in the same concentrated solution even at 35 °C. However,
the solubility of 3b in chloroform which had been selected
as the most appropriate solvent for the extraction of 3a from
the reaction mixture, was very low (less than 1 mg/mL) and
the crystallization trials did not succeed as well.
Conclusions
The procedure for the commercial production of high
quality KW-2189 has been developed. The synthesis was
Therefore, we decided to pursue a straightforward syn-
thesis of 4 using the hydrochloride salt of N-methylpipera-
zinecarbonyl chloride without isolation of 3b by telescoping
in the reduction of the carbonyl group at C8. N-Methylpip-
erazinecarbonyl chloride hydrochloride was added to 1 in
allyl alcohol in the presence of pyridine, and the mixture
(20) The compound 4 is more stable than 3a and the degradation product 8 was
not increased even at the high concentration during the workup evaporation
process. The compound 8 was obtained from 4a only using a strong base
such as DBU (Scheme 2).
(21) The rearrangement rate of 4b was faster than that of 4a. The 3-OH group
of 4b appears to be pseudo axial and well overlapped with π-electrons of
the aromatic ring, so that the elimination proceeded more easily than in 4a.
(22) Compound 9 was not detectable in the final compound 2 by HPLC analyses.
346
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Vol. 2, No. 6, 1998 / Organic Process Research & Development

accomplished in three steps from DUMB2 (1) in 55% overall
yield. The improvement in the yield significantly contributed
to reduce the quantity of the starting material. It needed
less than half of the natural DUMB2 (1) compared with the
preliminary method.13 Despite the lower yield, we should
select toluene as the reaction solvent instead of 1,2-
dichloroethane before launch (Table 2). The degradation
compounds 7-9 (Scheme 2) were also synthesized and
shown to be absent from the KW-2189 (2) prepared by this
procedure.
Hz, 1H), 3.64 (br s, 2H), 3.76 (br s, 2H), 3.78 (s, 3H), 3.92
(s, 3H), 3.94 (s, 3H), 4.04 (dd, J ) 10.1, 3.3 Hz, 1H), 4.08
(s, 3H), 4.25 (m, 1H), 4.59 (dd, J ) 10.8, 4.5 Hz, 1H), 4.63
(br d, J ) 9.3 Hz, 1H), 5.48 (br s, 1H), 6.87 (s, 1H), 6.94
(d, J ) 2.3 Hz, 1H), 8.45 (s, 1H), 9.32 (br s, 1H); IR (KBr)
υ ) 2940, 1710, 1621, 1521, 1493, 1430, 1385, 1289, 1231,
1049, 1002 cm-1; SIMS 716, 714 (M + H)+.
Methyl (1S,7R)-1-(Bromomethyl)-7-methyl-5-[(4-me-
thylpiperazinyl)carbonyloxy]-8-oxo-3-[(5,6,7-trimethoxy-
2-indolyl)carbonyl]-1,2,7,8-tetrahydro-3H-pyrrolo[3,2-e]-
indole-7-carboxylate Hydrochloride (3b). A solution of
3a (29 mg, 0.041 mmol) in EtOH (1.5 mL) was treated with
anhydrous 5.8 M HCl in EtOH (0.01 mL) at 0 °C for 1 h.
The resulting mixture was poured into Et2O (30 mL), and
the whole was vigorously stirred at 0 °C for 1 h. The
resulting precipitate was collected by filtration and dried
under reduced pressure to afford 3b as a bright yellow
Experimental Section
General. 1H and 13C NMR spectra were recorded at 270
MHz on a JEOL JNM-GX270 and 300 MHz on a JEOL
JNM-GX300 spectrometers, and signals are given in ppm
using TMS as an internal standard. IR spectra were recorded
on a Shimadzu FTIR-4300 spectrophotometer. SIMS spectra
were recorded on a Hitachi M-80B mass spectrometer.
HRFABMS were recorded on a JEOL JMS SX-102 mass
spectrometer. Elemental analyses were performed using a
Yanaco MT-3 CHN apparatus. For column chromatography,
silica gel (SiO2, Wako C-200) was used. All reagents and
solvents were of commercial quality.
1
solid: 16 mg (53%); mp 183-195 °C; H NMR (DMSO-
d6) δ ) 1.51 (s, 3H, 7-CH3), 2.83 (s, 3H, N-CH3), 3.24 (br
s, 4H, N-(CH2)2), 3.42 (br s, 4H, N-(CH2)2), 3.64 (s, 3H,
CO2CH3*), 3.79 (s, 3H, 5′-OCH3*), 3.81 (s, 3H, 6′-OCH3*),
3.90 (dd, J ) 10.0, 6.7 Hz, 1H, 1-CHHBr), 3.93 (s, 3H, 7′-
OCH3*), 3.97 (dd, J ) 10.0, 3.1 Hz, 1H, 1-CHHBr), 4.20
(m, 1H, 1-H), 4.34 (dd, J ) 10.4, 4.4 Hz, 1H, 2-H), 4.68 (t,
J ) 10.4 Hz, 1H, 2-H), 5.75 (s, 1H, 6-NH), 6.96 (s, 1H,
4′-H), 7.00 (d, J ) 2.2 Hz, 1H, 3′-H), 7.83 (br s, 1H, HCl),
8.30 (s, 1H, 4-H), 11.35 (br s, 1H, 1′-NH) {assignments with
an asterisk may be interchanged}; 13C NMR (DMSO-d6) δ
) 20.1 (q), 36.5 (t), 41.2 (d), 42.1 (q), 43.9 (t, 2C), 51.7 (t,
2C), 53.0 (q), 54.9 (t), 56.0 (q), 61.0 (q), 61.1 (q), 71.0 (s),
98.0 (d), 106.1 (d), 115.2 (s), 120.3 (d), 123.2 (s), 125.3 (s),
127.1 (s), 130.6 (s), 135.5 (s), 135.9 (s), 139.0 (s), 139.9
(s), 149.2 (s), 151.5 (s), 151.6 (s), 159.6 (s), 168.9 (s), 197.5
(s); IR (KBr) υ ) 2930, 1718, 1617, 1522, 1492, 1457, 1430,
1387, 1308, 1234, 1170, 1109 cm-1; HRFABMS calcd for
C32H3679BrN5O9 m/z 714.1775 (M + H)+, found 714.1794.
Methyl (1S,7R,8R)-1-(Bromomethyl)-8-hydroxy-7-meth-
yl-5-[(4-methylpiperazinyl)carbonyloxy]-3-[(5,6,7-tri-meth-
oxy-2-indolyl)carbonyl]-1,2,7,8-tetrahydro-3H-pyrrolo-
[3,2-e]indole-7-carboxylate (4a). To a suspension of 1 (30.0
g, 51.0 mmol) in allyl alcohol (600 mL) and pyridine (41.2
mL) was added N-methylpiperazinecarbonyl chloride hy-
drochloride (19.3 g, 96.9 mmol), and the mixture was stirred
for 4 h at 25 °C. After cooling to -5 to 0 °C, the reaction
mixture was treated with NaBH4 (25.0 g, 663 mmol), and
then the mixture was stirred for 3.5 h at the same temperature.
After the reaction, the pH of the mixture was adjusted to
pH 6.95 with citric acid buffer solution (0.2 M, pH 1.9, 900
mL), and the quenched mixture was extracted with EtOAc
(300 mL). The organic layer was washed with saturated
brine (each 300 mL) twice and dried under reduced pressure,
and the resulting residue was purified by column chroma-
tography (silica gel, CHCl3/MeOH as eluents, initially 96:4
then 90:10) to afford 4a as a slightly yellow solid: 31.8 g
(87%); mp 200-205 °C (dec); 1H NMR (CDCl3/TMS) δ )
1.57 (s, 3H, 7-CH3), 2.17 (s, 1H, 8-OH), 2.34 (s, 3H, N-CH3),
2.47 (br s, 4H, N-(CH2)2), 3.43 (dd, J ) 10.3, 10.2 Hz, 1H,
1-CHHBr), 3.58 (br s, 2H, N-CH2), 3.69 (br s, 2H, N-CH2),
HPLC Analyses. The yields of 4a, 4b, and 5 in Table 1
and the stability of 3a in Figure 3 were estimated using the
following conditions: detector, ultraviolet absorption pho-
tometer (wavelength 330 nm); column, GL Sciences Inc.
UNISIL PACK 5C18-250A; mobile phase, a mixture of 0.05
M phosphate buffer (pH 5.9) and CH3CN (1:1); flow rate,
1.0 mL/min; column temperature, 35 °C; tR (min), 2 and 6
(38), 3a and 3b (21), 4a (9.7), 4b (9.0), 5 (5.7), 7 (20), 8
(8.2), 9 (30).
Stability in Highly Concentrated Solutions (Figure 3).
From the organic layer in the workup process for the
synthesis of 3a (described below), 1.0 mL of solution was
exactly weighed out and evaporated to a concentration of
200 mg/mL under reduced pressure and maintained at the
corresponding measured temperature. The time-course sta-
bility of 3a was determined by HPLC analyses using
1-nitronaphthalene as the internal standard. In this stability
test of 3a, the only detected degradation product was 7.
Compounds 3b and 4 were not degraded at 35 °C in the
same procedures for 3a.
Methyl (1S,7R)-1-(Bromomethyl)-7-methyl-5-[(4-me-
thylpiperazinyl)carbonyloxy]-8-oxo-3-[(5,6,7-trimethoxy-
2-indolyl)carbonyl]-1,2,7,8-tetrahydro-3H-pyrrolo[3,2-e]-
indole-7-carboxylate (3a). To a suspension of 1 (DUMB2,
100 mg, 0.17 mmol) in CH2Cl2 (2.0 mL) and pyridine (0.14
mL) was added N-methylpiperazinecarbonyl chloride (55 mg,
0.34 mmol), and the mixture was stirred for 2.5 h at 25 °C.
After being quenched with aqueous phosphate buffer (0.05
M, pH 5.9, 5.0 mL), the mixture was extracted with CHCl3
(5.0 mL). The organic layer was washed with saturated brine
(5.0 mL) and dried over Na2SO4, and the filtrate was dried
under reduced pressure. The resulting residue was purified
by column chromatography (silica gel, 95:5 CHCl3/MeOH
as an eluent) to afford 3a as a yellow solid: 120 mg (99%);
mp 185-190 °C (dec); 1H NMR (CDCl3/TMS) δ ) 1.69 (s,
3H), 2.37 (s, 3H), 2.52 (br s, 4H), 3.61 (dd, J ) 10.1, 8.9
Vol. 2, No. 6, 1998 / Organic Process Research & Development
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347

3.73 (s, 3H, CO2CH3*), 3.89 (s, 3H, 5′-OCH3*), ca. 3.9 (m,
1H, 1-H), 3.94 (s, 3H, 6′-OCH3*), 4.06 (s, 3H, 7′-OCH3*),
4.12 (dd, 1H, J ) 10.3, 3.1 Hz, 1-CHHBr), 4.50 (dd, J )
10.6, 8.7 Hz, 1H, 2-H), 4.56 (dd, J ) 10.6, 4.6 Hz, 1H, 2-H),
4.79 (s, 1H, 6-NH), 5.33 (s, 1H, 8-H), 6.86 (s, 1H, 4′-H),
6.90 (d, J ) 2.2 Hz, 1H, 3′-H), 8.03 (s, 1H, 4-H), 9.48 (s,
1H, NH) {assignments with an asterisk may be inter-
changed}; 13C NMR (CDCl3/TMS): δ ) 18.9 (q), 36.2 (t),
42.9 (d), 43.9 (t), 44.4 (t), 46.0 (q), 53.0 (q), 54.5 (t), 54.5
(t), 55.8 (t), 56.3 (q), 61.1 (q), 61.5 (q), 71.8 (s), 75.3 (d),
97.7 (d), 106.2 (d), 113.7 (d), 123.7 (s), 125.4 (s), 126.7 (s),
126.9 (s), 129.9 (s), 135.9 (s), 137.6 (s), 138.8 (s), 139.3
(s), 140.4 (s), 150.1 (s), 152.6 (s), 159.4 (s), 175.6 (s); IR
(KBr) υ ) 1709, 1623, 1522, 1482, 1428, 1387, 1311, 1227,
1151, 1114, 1050 cm-1; SIMS 718, 716 (M + H)+;
HRFABMS calcd for C32H3879BrN5O9 m/z 716.1931 (M +
H)+, found 716.1932.
Methyl (1S,7R,8S)-1-(Bromomethyl)-8-hydroxy-7-meth-
yl-5-[(4-methylpiperazinyl)carbonyloxy]-3-[(5,6,7-tri-meth-
oxy-2-indolyl)carbonyl]-1,2,7,8-tetrahydro-3H-pyrrolo-
[3,2-e]indole-7-carboxylate (4b). To a solution of 3a (72
mg, 0.10 mmol) in MeOH (3.0 mL) was added NaBH4 (11
mg, 0.30 mmol), and the mixture was stirred for 2 h at 0
°C. After being quenched with aqueous phosphate buffer
(0.05 M, pH 5.9, 5.0 mL), the mixture was extracted with
EtOAc (5.0 mL each) three times. The organic layer was
washed with saturated brine (5.0 mL) and dried over Na2-
SO4, and the filtrate was dried under reduced pressure. The
resulting residue was purified by column chromatography
(silica gel, 95:5 CHCl3/MeOH as an eluent) to afford 4a [49
mg (70%)] and a fraction containing compound 4b. The
latter was further purified by HPLC (ODS, 50:50 CH3CN/
H2O as an eluent) to give 4b as a slightly yellow solid: 10
mg (14%); 1H NMR (CDCl3/TMS) δ ) 1.53 (s, 3H, 7-CH3),
2.32 (s, 3H, N-CH3), 2.44 (br s, 4H, N-(CH2)2), 3.54 (dd, J
) 10.4, 10.0 Hz, 1H, 1-CHHBr), 3.64 (br s, 4H, N-CH2),
3.76 (dd, 1H, J ) 10.4, 3.1 Hz, 1-CHHBr), 3.84 (s, 3H, CO2-
CH3*), 3.85 (s, 3H, 5′-OCH3*), ca. 3.9 (1H, 8-OH), ca. 4.0
(m, 1H, 1-H), 3.93 (s, 3H, 6′-OCH3*), 4.04 (s, 3H, 7′-
OCH3*), 4.38 (dd, J ) 10.7, 5.0 Hz, 1H, 2-H), 4.49 (dd, J
) 10.7, 9.2 Hz, 1H, 2-H), 4.71 (s, 1H, 6-NH), 5.06 (s, 1H,
8-H), 6.83 (s, 1H, 4′-H), 6.86 (d, J ) 2.2 Hz, 1H, 3′-H),
8.10 (s, 1H, 4-H), 9.36 (s, 1H, NH) {assignments with an
asterisk may be interchanged}; 13C NMR (CDCl3/TMS) δ
) 23.9 (q), 34.2 (t), 41.6 (d), 44.2 (t, 2C), 46.1 (q), 52.7 (q),
54.5 (t, 2C), 55.5 (t), 56.3 (q), 61.1 (q), 61.5 (q), 72.2 (s),
79.7 (d), 97.7 (d), 106.3 (d), 113.6 (d), 123.7 (s), 125.3 (s),
126.1 (s), 126.3 (s), 129.9 (s), 136.5 (s), 137.8 (s), 138.8
(s), 138.8 (s), 140.4 (s), 150.1 (s), 152.7 (s), 159.3 (s), 173.4
(s); IR (KBr) υ ) 1716, 1625, 1527, 1458, 1435, 1314, 1232,
1114 cm-1; SIMS 718, 716 (M + H)+; HRFABMS calcd
for C32H3879BrN5O9 m/z 716.1931 (M + H)+, found 716.1944.
(1S,7R)-1-(Bromomethyl)-8-hydroxy-7-(hydroxymethyl)-
7-methyl-5-[(4-methylpiperazinyl)carbonyloxy]-3-[(5,6,7-
trimethoxy-2-indolyl)carbonyl]-1,2,7,8-tetrahydro-3H-
pyrrolo[3,2-e]indole (5). To a solution of 3a (143 mg, 0.20
mmol) in MeOH (6.0 mL) was added NaBH4 (22 mg, 0.60
mmol), and the mixture was stirred for 2 h at 0 °C. After
being quenched with aqueous phosphate buffer (0.05 M, pH
5.9, 5.0 mL), the mixture was extracted with EtOAc (10.0
mL each) three times. The organic layer was washed with
saturated brine (10.0 mL) and dried over Na2SO4, and the
filtrate was dried under reduced pressure. The resulting
residue was purified by column chromatography (silica gel,
90:10 CHCl3/MeOH as an eluent) to afford 5 as a slightly
1
yellow solid: 14 mg (10%); H NMR (CDCl3/TMS) δ )
1.29 (s, 3H, 7-CH3), 2.35 (s, 3H, N-CH3), 2.53 (br, 4H,
N-(CH2)2), 3.31 (br, 1H, 1-CHHBr), 3.35 (s, 2H, 7-CH2O),
3.50 (br, 2H, N-CH2), 3.57 (br, 2H, N-CH2), 3.86 (s, 3H,
5′-OCH3*), ca. 3.9 (m, 1H, 1-H), 3.92 (s, 3H, 6′-OCH3*),
4.04 (s, 3H, 7′-OCH3*), 4.14 (br, 1H, 1-CHHBr), 4.44 (br,
2H, 2-H2), 4.79 (s, 1H, 8-H), 6.83 (s, 1H, 4′-H), 6.85 (br,
1H, 3′-H), 8.14 (s, 1H, 4-H), 9.74 (s, 1H, 1′-NH) {assign-
ments with an asterisk may be interchanged}; 13C NMR
(CDCl3/TMS) δ ) 17.1 (q), 36.4 (t), 42.8 (d), 43.8 (t), 44.2
(t), 45.9 (q), 54.3 (t, 2C), 55.8 (t), 56.1 (q), 61.0 (q), 61.4
(q), 67.1 (t), 68.5 (s), 74.6 (d), 97.6 (d), 106.2 (d), 112.7
(d), 123.5 (s), 125.3 (s), 127.1 (s), 128.9 (s), 129.8 (s), 135.8
(s), 136.9 (s), 138.7 (s), 138.8 (s), 140.2 (s), 149.9 (s), 152.6
(s), 159.4 (s); IR (KBr) υ ) 3350, 1700, 1445, 1225, 1232
cm-1; SIMS 690, 688 (M + H)+; HRFABMS calcd for
C31H3879BrN5O8 m/z 688.1982 (M + H)+, found: 688.1982.
Methyl (7R)-7-Methyl-1-methylene-5-[(4-methylpiper-
azinyl)carbonyloxy]-8-oxo-3-[(5,6,7-trimethoxy-2-indolyl)-
carbonyl]-1,2,7,8-tetrahydro-3H-pyrrolo[3,2-e]indole-7-
carboxylate (7). To a solution of 3a (72 mg, 0.10 mmol)
in CH2Cl2 (2.0 mL) was added Et3N (0.042 mL, 0.30 mmol),
and the mixture was stirred for 10 h at 25 °C. After being
quenched with aqueous phosphate buffer (0.05 M, pH 5.9,
5.0 mL), the mixture was extracted with CHCl3 (5.0 mL).
The organic layer was washed with saturated brine (5.0 mL)
and dried over Na2SO4, and the filtrate was dried under
reduced pressure. The resulting residue was purified by
column chromatography (silica gel, 95:5 CHCl3/MeOH as
1
an eluent) to afford 7 as a yellow solid: 57 mg (90%); H
NMR (CDCl3/TMS) δ ) 1.70 (s, 3H, 7-CH3), 2.37 (s, 3H,
N-CH3), 2.52 (br, 4H, N-(CH2)2), 3.64 (br, 2H, N-CH2), 3.76
(br, 2H, N-CH2), 3.79 (s, 3H, CO2CH3*), 3.91 (s, 3H, 5′-
OCH3*), 3.94 (s, 3H, 6′-OCH3*), 4.07 (s, 3H, 7′-OCH3*),
5.14 (s, 2H, 2-H2), 5.48 (s, 1H, 6-NH), 5.49 (br, 1H, 1-CHH),
6.86 (s, 1H, 4′-H), 6.94 (d, J ) 2.2 Hz, 1H, 3′-H), 6.98 (br,
1H, 1-CHH), 8.65 (s, 1H, 4-H), 9.39 (s, 1H, 1′-NH)
{assignments with an asterisk may be interchanged}; 13C
NMR (CDCl3/TMS) δ ) 22.2 (q), 44.2 (t), 44.7 (t), 46.1
(q), 53.6 (q), 54.5 (t), 54.6 (t), 55.8 (t), 56.3 (q), 61.1 (q),
61.5 (q), 70.7 (s), 97.7 (d), 106.5 (d), 111.3 (t), 116.4 (s),
120.4 (d), 123.8 (s), 125.6 (s), 126.5 (s), 129.5 (s), 138.2
(s), 138.6 (s), 138.7 (s), 140.5 (s), 141.3 (s), 150.2 (s), 152.1
(s), 152.2 (s), 158.9 (s), 169.5 (s), 196.6 (s); IR (KBr) υ )
1702, 1616, 1491, 1441, 1229 cm-1; SIMS 634 (M + H)+;
HRFABMS calcd for C32H35N5O9 m/z 634.2513 (M + H)+,
found: 634.2508.
Methyl (7R,8R)-8-Hydroxy-7-methyl-1-methylene-5-
[(4-methylpiperazinyl)carbonyloxy]-3-[(5,6,7-trimethoxy-
2-indolyl)carbonyl]-1,2,7,8-tetrahydro-3H-pyrrolo[3,2-e]-
indole-7-carboxylate (8). To a solution of 7 (63 mg, 0.10
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mmol) in allyl alcohol (3.0 mL) was added NaBH4 (8 mg,
0.20 mmol), and the mixture was stirred for 5 h at 0 °C.
After being quenched with aqueous phosphate buffer (0.05
M, pH 5.9, 5.0 mL), the mixture was extracted with EtOAc
(5.0 mL each) three times. The organic layer was washed
with saturated brine (5.0 mL) and dried over Na2SO4, and
the filtrate was dried under reduced pressure. The resulting
residue was purified by column chromatography (silica gel,
95:5 CHCl3/MeOH as an eluent) to afford 8 as a slightly
yellow solid: 38 mg (60%). Another synthetic method is
described below. To a solution of 4a (72 mg, 0.10 mmol)
in CH2Cl2 (3.0 mL) was added DBU (0.030 mL, 0.20 mmol),
and the mixture was stirred for 10 h at 25 °C. After being
quenched with aqueous phosphate buffer (0.05 M, pH 5.9,
5.0 mL), the mixture was extracted with CHCl3 (5.0 mL).
The organic layer was washed with saturated brine (5.0 mL)
and dried over Na2SO4, and the filtrate was dried under
reduced pressure. The resulting residue was purified by
column chromatography (silica gel, 95:5 CHCl3/MeOH as
an eluent) to afford 8 as a slightly yellow solid: 57 mg
Hz, 1H, 3′-H), 8.12 (s, 1H, 4-H), 9.41 (s, 2H, 6-NH and
1′-NH) {assignments with an asterisk may be interchanged};
13C NMR (CDCl3/TMS): δ ) 15.0 (q), 36.6 (t), 44.3 (t),
44.5 (d), 44.8 (t), 46.1 (q), 51.2 (q), 54.5 (t), 54.7 (t), 55.4
(t), 56.3 (q), 61.1 (q), 61.5 (q), 97.8 (d), 104.3 (s), 106.4 (d,
2C), 120.1 (s), 123.7 (s), 124.5 (s), 125.4 (s), 125.6 (s), 130.1
(s), 136.2 (s), 138.7 (s), 138.9 (s), 140.5 (s), 146.6 (s), 150.1
(s), 153.3 (s), 160.0 (s), 165.4 (s). IR (KBr) υ ) 2944, 1698,
1491, 1410, 1313, 1217, 1110 cm-1; SIMS 700, 698 (M +
H)+; HRFABMS calcd for C32H3679BrN5O8 m/z 698.1825 (M
+ H)+, found 698.1812.
Methyl (1S)-1-(Bromomethyl)-7-methyl-5-[(4-meth-
ylpiperazinyl)carbonyloxy]-3-[(5,6,7-trimethoxy-2-indolyl)-
carbonyl]-1,2-dihydro-3H-pyrrolo[3,2-e]indole-8-carbox-
ylate hydrobromide (2, KW-2189). To a solution of 6 (56.3
g, 80.6 mmol) in acetone (500 mL) and MeOH (2,250 mL)
was added 48% hydrobromic acid (13.8 mL, 121 mmol),
and the mixture was stirred for 7 h at 25 °C and for 9 h
under ice-cooling. The precipitated crystals were filtered,
washed with cold MeOH/EtOH mixture (1:1) (300 mL), and
dried under vacuum to afford semi-purified 2: 55.3 g (88%).
The semi-purified 2 (52.4 g, 67.2 mmol) was further purified
by recrystallization from aqueous EtOH (2,830 mL) and
drying under vacuum to afford 2 as a light yellow crystalline
powder: 44.0 g (84% from semi-purified 2); mp 252 °C
(dec); 1H NMR (DMSO-d6/TMS) δ ) 2.70 (br s, 3H, 7-CH3),
2.89 (br s, 3H, N-CH3), 3.26 (br s, 4H, N-(CH2)2), 3.40 (br
s, 1H, 1-CHHBr), 3.53 (br s, 4H, N-(CH2)2), 3.80 (br s, 1H,
1-CHHBr), 3.81 (s, 3H, 6′-OCH3*), 3.82 (s, 3H, 5′-OCH3*),
3.86 (s, 3H, CO2CH3*), 3.96 (s, 3H, 7′-OCH3*), 4.44 (br d,
J ) 10.9 Hz, 1H, 2-H), 4.48 (m, J ) 8.6, 2.8 Hz, 1H, 1-H),
4.65 (dd, J ) 10.9, 8.6 Hz, 1H, 2-H), 6.98 (s, 1H, 4′-H),
7.02 (br d, J ) 2.3 Hz, 1H, 3′-H), 7.94 (br s, 1H, 4-H), 10.0
(br s, 1H, HBr), 11.24 (br s, 1H, 1′-NH), 12.02 (br s, 1H,
6-NH) {assignments with an asterisk may be interchanged};
13C NMR (DMSO-d6/TMS) δ ) 14.5 (q), 38.2 (t), 41.0 (t,
2C), 42.5 (q), 43.0 (d), 50.9 (q), 52.2 (t, 2C), 55.4 (t), 56.1
(q), 61.0 (q), 61.1 (q), 98.2 (d), 103.3 (s), 105.8 (d), 106.0
(d), 119.6 (s), 123.2 (s), 123.9 (s), 125.2 (s), 125.6 (s), 131.2
(s), 135.6 (s), 138.2 (s), 139.0 (s), 139.8 (s), 146.8 (s), 149.3
(s), 152.1 (s), 160.0 (s), 165.0 (s); IR (KBr) υ ) 3460, 2947,
2550, 1718, 1410, 1219, 746 cm-1; UV λmax (CH3OH) nm
(ꢀ) 331 (4010); [R]20D ) -27.9° (c 1.5, CHCl3); SIMS 698
(M + H)+. Anal. Calcd for C32H36BrN5O8‚HBr: C, 49.31;
H, 4.89; N, 8.96. Found: C, 49.31; H, 4.78; N, 8.98.
Methyl 1,7-Dimethyl-5-[(4-methylpiperazinyl)carbo-
nyloxy]-3-[(5,6,7-trimethoxy-2-indolyl)carbonyl]-3H-pyr-
rolo[3,2-e]indole-8-carboxylate (9). Acidic rearrange-
ment of 8 (32 mg, 0.050 mmol) with MeSO3H (0.008
mL,0.125 mmol) was carried out in ClCH2CH2Cl (1.2 mL)
at 50 °C to afford 9 in a manner similar to the synthesis of
6. Compound 9 was isolated and purified by column
chromatography (silica gel, 95:5 CHCl3/MeOH as an eluent)
as a slightly yellow solid: 21 mg (69%); 1H NMR (DMSO-
d6/TMS) δ ) 2.28 (s, 3H, CH3), 2.33 (s, 3H, CH3), 2.49 (br,
4H, N-(CH2)2), 2.60 (s, 3H, N-CH3), 3.51 (br, 2H, N-CH2),
3.76 (br, 2H, N-CH2), 3.85 (s, 3H, 6′-OCH3*), 3.85 (s, 3H,
5′-OCH3*), 3.85 (s, 3H, CO2CH3*), 3.99 (s, 3H, 7′-OCH3*),
1
(90%); H NMR (CDCl3/TMS) δ ) 1.65 (s, 3H, 7-CH3),
2.33 (s, 3H, N-CH3), 2.44 (br, 4H, N-(CH2)2), 3.53 (br, 4H,
N-(CH2)2), 3.72 (s, 3H, CO2CH3), 3.77 (s, 3H, 5′-OCH3*),
3.93 (s, 3H, 6′-OCH3*), 4.04 (s, 3H, 7′-OCH3*), 4.81 (d, J
) 15.6 Hz, 1H, 2-H), 4.86 (s, 1H, 6-NH), 4.92 (d, J ) 14.7
Hz, 1H, 2-H), 5.21 (br, 1H, 1-CHH), 5.47 (s, 1H, 8-H), 5.72
(br, 1H, 1-CHH), 6.77 (s, 1H, 4′-H), 6.80 (d, J ) 2.2 Hz,
1H, 3′-H), 8.27 (s, 1H, 4-H), 9.38 (s, 1H, 1′-NH) {assign-
ments with an asterisk may be interchanged}; 13C NMR
(CDCl3/TMS) δ ) 19.1 (q), 44.1 (t, 2C), 46.1 (q), 53.0 (q),
54.5 (t, 2C), 55.6 (t), 56.1 (q), 61.1 (q), 61.5 (q), 71.6 (s),
75.0 (d), 97.5 (d), 106.4 (d), 106.5 (t), 114.1 (d), 123.8 (s),
124.1 (s), 124.5 (s), 125.3 (s), 139.7 (s), 136.5 (s), 138.8
(s), 139.1 (s), 140.1 (s), 140.2 (s), 140.3 (s), 150.0 (s), 152.7
(s), 158.6 (s), 176.0 (s); IR (KBr) υ ) 3440, 1718, 1617,
1455, 1235 cm-1; SIMS 636 (M + H)+; HRFABMS calcd
for C32H37N5O9 m/z 636.2670 (M + H)+, found 636.2666.
Methyl (1S)-1-(Bromomethyl)-7-methyl-5-[(4-meth-
ylpiperazinyl)carbonyloxy]-3-[(5,6,7-trimethoxy-2-indolyl)-
carbonyl]-1,2-dihydro-3H-pyrrolo[3,2-e]indole-8-carbox-
ylate (6). To a solution of 4 (30.0 g, 41.9 mmol) in
ClCH2CH2Cl (1,200 mL) was added MeSO3H (6.80 mL, 105
mmol), and the mixture was stirred for 5 h at 50 °C. After
cooling, the reaction mixture was quenched with saturated
NaHCO3 (600 mL) and extracted with CHCl3 (300 mL). The
organic layer was washed with saturated brine (300 mL) and
dried over Na2SO4, and the filtrate was dried under reduced
pressure, the resulting residue was purified by column
chromatography (silica gel, 95:5 CHCl3/MeOH as an eluent)
to afford 6 as a slightly yellow solid: 25.3 g (86%); mp
1
160-163 °C; H NMR (CDCl3/TMS) δ ) 2.39 (s, 3H,
7-CH3), 2.56 (br s, 4H, N-(CH2)2), 2.60 (s, 3H, N-CH3), 3.21
(br d, J ) 9.6 Hz, 1H, 1-CHHBr), 3.63 (br s, 2H, N-CH2),
3.67 (br s, 2H, N-CH2), 3.79 (dd, J ) 9.6, 2.2 Hz, 1H,
1-CHHBr), 3.91 (s, 3H, CO2CH3*), 3.95 (s, 3H, 5′-OCH3*),
3.95 (s, 3H, 6′-OCH3*), 4.07 (s, 3H, 7′-OCH3*), 4.49 (dd, J
) 10.4, 8.8 Hz, 1H, 2-H), 4.57 (m, 1H, 1-H), 4.74 (dd, J )
10.4, 1.2 Hz, 1H, 2-H), 6.89 (s, 1H, 4′-H), 6.99 (d, J ) 2.3
Vol. 2, No. 6, 1998 / Organic Process Research & Development
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349

7.03 (s, 1H, 4′-H), 7.14 (s, 1H, 2-H), 7.74 (s, 1H, 3′-H),
8.04 (s, 1H, 4-H), 11.81 (s, 1H, NH), 12.00 (s, 1H, NH)
{assignments with an asterisk may be interchanged}; 13C
NMR (DMSO-d6/TMS) δ ) 13.0 (q), 13.4 (q), 43.8 (t), 44.2
(t), 45.8 (q), 51.1 (q), 54.1 (t, 2C), 55.9 (q), 61.0 (q), 61.1
(q), 98.2 (d), 103.8 (d), 106.4 (s), 110.3 (d), 117.7 (s), 119.0
(s), 120.1 (s), 122.9 (s), 124.8 (s), 125.5 (s), 126.8 (s), 129.4
(s), 131.0 (s), 134.3 (s), 139.1 (s), 140.1 (s), 140.6 (s), 149.5
(s), 152.9 (s), 160.2 (s), 166.7 (s); IR (KBr) υ ) 1701, 1419,
1207 cm-1; SIMS 618 (M + H)+; HRFABMS calcd for
C32H35N5O8 m/z 618.2564 (M + H)+, found 618.2563.
Received for review April 27, 1998.
OP980038K
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