Design, synthesis and cytotoxicity evaluation of 1-chloromethyl-5-hydroxy-1,2-dihydro-3H-benz[e]indole (seco-CBI) dimers

Article abstract of DOI:10.1016/S0968-0896(00)00088-2

Three types of 1-chloromethyl-5-hydroxy-1,2-dihydro-3H-benz[e]indole (seco-CBI) dimers were designed, synthesized and evaluated in vitro by NCI against nine types of cancer cells. Biological results showed that the antitumor activities of these seco-CBI dimers were strongly related to the position and length of the linker and generally with potency increasing in the order of C7-C7 dimers (22i-iv)50 values<0.01μM. N3-N3 dimer 25i displayed striking potency against leukemia, CNS cancer, melanoma and prostate cancer cell lines with GI₅₀ values<0.01μM against all the cell lines and showed the highest overall potency of the agents examined (GMG=0.0120μM). Copyright (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0968-0896(00)00088-2

Bioorganic & Medicinal Chemistry 8 (2000) 1607±1617
Design, Synthesis and Cytotoxicity Evaluation of 1-Chloromethyl-
5-hydroxy-1,2-dihydro-3H-benz[e]indole (seco-CBI) Dimers
Guofeng Jia and J. William Lown*
Department of Chemistry, University of Alberta, E3-44 Chemistry Building, Edmonton, AB, Canada T6G 2G2
Received 13 December 1999; accepted 6 March 2000
AbstractÐThree types of 1-chloromethyl-5-hydroxy-1,2-dihydro-3H-benz[e]indole (seco-CBI) dimers were designed, synthesized
and evaluated in vitro by NCI against nine types of cancer cells. Biological results showed that the antitumor activities of these
seco-CBI dimers were strongly related to the position and length of the linker and generally with potency increasing in the order of
C7±C7 dimers (22i±iv) < C7±N3 dimers (28i±iv) < N3±N3 dimers (25i±iv). Compound 28iv showed signi®cant activity against
CCRT-CEM, HL-60 (TB), MOLT-4, and SR leukemia cell lines and the MCF 7 breast cancer cell line with GI50 values < 0.01 mM.
N3±N3 dimer 25i displayed striking potency against leukemia, CNS cancer, melanoma and prostate cancer cell lines with GI50
values < 0.01 mM against all the cell lines and showed the highest overall potency of the agents examined (GMG=0.0120 mM).
# 2000 Elsevier Science Ltd. All rights reserved.
Introduction
and in vivo.8 In fact, many active antitumor agents act
by cross-linking DNA.9 While to date some CPI dimers
have been prepared to examine interstrand cross-linking
of DNA,8 to our knowledge, no attempt has been made
to synthesize 1-chloromethyl-5-hydroxy-1,2-dihydro-
3H-benz[e]indole (seco-CBI) dimers. It is well known
that the activity of the dimeric drug is strongly related
to the length and the position of the linker. In order to
investigate the structure±activity relationships system-
atically, we have designed and synthesized three types of
seco-CBI dimers (i.e., C7±C7, N3±N3 and N3±C7)
which contain two racemic CBI moieties linked from two
positions by a ¯exible methylene chain of variable length.
Sequence-speci®c DNA alkylation has signi®cant
potential for use in molecular biology and human med-
icine. The cyclopropylindole class of antitumor anti-
biotics, exempli®ed by CC-1065 and duocarmycins (Fig.
1), are extremely potent cytotoxins that have engen-
dered great interest both as potential anticancer drugs1
and as targets for synthesis.2 Studies on the mechanism
of cytotoxic action show that these naturally occurring
compounds bind to AT-rich sequences and selectively
alkylate N3 of the 30-adenine in the minor groove of
B-DNA by their cyclopropylindole (CPI) subunits.2a
Many synthetic analogues have been reported in the
search for compounds with better antitumor selectivity
and DNA sequence-speci®c binding properties.3 As a
successful example of modi®cation, Boger ®rst reported
that the simpli®ed moiety, 1,2,9,9a-tetrahydrocyclo-
propa[c]-benz[e]indole-4-one (CBI), and its analogues
were more stable and more potent than the CPI coun-
terparts.4 In our group, attempts have been made to
link CPI5 and CBI6 with pyrrole/imidazole polyamides,
which are well-established DNA minor groove binders,7
in attempts to improve their pharmacological properties
and potencies. Studies have also shown that some syn-
thetic compounds which contain two CPI moieties are
signi®cantly more potent than CC-1065 both in vitro
Results and Discussion
Chemistry
Our strategy of the synthesis of seco-CBI dimers
requires a protected seco-CBI which possesses an active
group at C8 or C7 position. The reports of the synthesis
of 7-methoxy-CBI10 and 7-cyano-CBI11 encouraged us
to design the synthetic methodology of 1-chloromethyl-
5-benzoxy-1,2-dihydro-3H-benz[e]indole (5) shown in
Scheme 1.
Condensation of 4-nitrobenzaldehyde (6) with the
Wadswarth±Horner±Emmons reagent 712 at low tem-
perature provided 8 in 60% yield. Acid-catalyzed
*Corresponding author. Tel.: +1-780-492-3646; fax: +1-780-492-
8231; e-mail: annabelle.wiseman@ualberta.ca
0968-0896/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(00)00088-2

1608
G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
Figure 1. Structures.
Scheme 1. Reagents and conditions: (a) NaH, THF, 60%; (b) 9:1 TFA:H2O, 23 ꢀC, 91%; (c) Ac2O±NaOAc; (d) K2CO3±EtOH, 77% from 9; (e)
BnBR, K2CO3, Cat. Bu4NI, DMF; (f) LiOH, 3:1:1 THF:MeOH:H2O, 99% from 11; (g) DPPa, Et3N, 4 A molecular sieve, t-BuOH, 84%; (h) NIS,
cat. TsOH, 1:1 THF:MeOH, 98%; (i) NaH, ClCHˆCHCH2Cl, cat. Bu4NI, DMF, 83%; (j) N2H4H2O, FeCl3; (k) Fmoc-Cl, Et3N, 86% from 16; (l)
Bu3SnH, AIBN, 78%; (m) Bu4NF, THF, 96%; (n) CH3COCl, Et3N, 92%.

G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
1609
deprotection of 8 a€orded acid 9 in 91% yield.
Although the nitro group is strongly electron-with-
drawing, intramolecular Friedel±Crafts acylation of 9
e€ected by treatment with Ac2O±NaOAc led to 10.
Hydrolysis of the O-acetate 10 a€orded the free phenol
11 (77% overall yield from 9). Protection of the phenol
11 followed by hydrolysis of the ethyl ester 12 cleanly
provided 13 (99% overall yield). Curtius rearrangement
of carboxylic acid 13 employing the Shioiri±Yamada
reagent diphenyl phosphorazidate (DPPA) gave the
carbamate 14, also in good yield (84%). Acid-catalyzed
C4 iodination at room temperature cleanly provided
1513 whose structure was con®rmed by single crystal
X-ray di€raction analysis (Fig. 2). Deprotonation of
carbamate 15, using NaH, followed by alkylation of the
resulting anion with (Z:E)-1,3-dichloropropene in the
presence of phase transfer catalyst Bu4NI gave a
mixture of Z:E isomers of vinyl chloride 16. Selective
reduction of the nitro group of 16 using hydrazine,14
followed by protection of the amino group, provided 18
(86% yield from 16), the desired precursor for the
intramolecular aryl radical cyclization onto a tethered
vinyl chloride.13,15 A deoxygenated solution of 18 in
fresh distilled dry benzene was heated at re¯ux for 15 h
in the presence of tri-n-butyltin hydride and a catalytic
amount of 2,20-azobis(isobutyronitrile) (AIBN) to give
the fully protected bifunctionalized racemic seco-CBI 5
in 78% yield. Although not investigated in detail, no
reaction occurred when nitro compound 16 was treated
under the same conditions as amine 18. Deprotection of
the Fmoc group followed immediately by reaction with
acetyl chloride a€orded 20 almost quantitatively.
Detachment of the Boc group from 20 followed by
coupling with 0.5 molar amount of the appropriate di-
acid chloride (glutaryl dichloride, adipoyl chloride,
pimeloyl chloride, or suberoyl chloride) a€orded 24i±iv
in good yield (66±76%). Hydrogenolysis of 24i±iv
served to remove the benzyl group and provided N3±N3
seco-CBI dimers 25i±iv (HCO2NH4, Pd/C, 72±76%)
(Scheme 3).
Treatment of 23 with glutaric anhydride in the presence
of triethylamine provided acid 26i in good yield (89%)
(Scheme 4). Condensation of agent 23 in the presence of
EDCI with excess amount of the appropriate di-acid
(adipic acid, pimelic acid, or suberic acid) gave acids
26ii±iv in 67±68% yield. Notably, treatment of 23 with
excess di-acid chloride led to a complex mixture, prob-
ably arising from the high activity of the acid chlorides.
Coupling acids 26i±iv with 19 (4 equiv of EDCI, DMF,
23 ꢀC) produced protected seco-CBI dimers 27i±iv in fair
yield (48±62%). Deprotection of benzyl group from 27i±
iv a€orded N3±C7 dimers 28i±iv in good yield (71±77%).
Biological evaluation
Compounds 22i±iv, 25i±iv and 28i±iv were selected by
the US National Cancer Institute (NCI) for evaluation
in an in vitro preclinical antitumor screening program16
against 60 human tumor cell lines derived from leu-
kemia, non-small cell lung cancers, colon cancer, CNS
cancer, melanoma, ovarian cancer, renal cancer, pros-
tate cancer and breast cancer. Selected biological eval-
uation results of compounds 22i±iv, 28i±iv and 25i±iv
are presented in Tables 1±3, respectively, as GI50 values
(the concentration of drug resulting in inhibition of cell
growth to 50% of controls, equivalent to IC50), together
with MGM (the mean graph midpoint).
Coupling 19 with 0.5 equiv of the appropriate di-acid
chloride (glutaryl dichloride, adipoyl chloride, pimeloyl
chloride, or suberoyl chloride) produced benzyl pro-
tected seco-CBI dimers 21i±iv in high yield (80±89%).
Treatment of 21i±iv with ammonium formate in the
presence of Pd/C13 for about 15 min provided C7±C7
seco-CBI dimers 22i±iv in 86±97% yield (Scheme 2).
All compounds were active against almost all cell lines
with MGM value from 41.6 mM (22iii) to 0.0120 mM
(25i) (activity is de®ned as GI50 < 100 mM). In general,
the activity sequence is C7±C7 dimers < C7±N3 dimers
<N3±N3 dimers. Studies have shown that removal of
the linking amide from the CC-1065 analogues would
render the agents incapable of alkylating DNA.17 The
Scheme 2. Reagents and conditions: (a) ClCO(CH2)3COCl, ClCO
(CH2)4COCl, ClCO(CH2)5COCl, or ClCO(CH2)6CO, ClEt3N, THF,
80±89%; (b) HCO2NH4, Pd/C, THF, 86±97%.
Figure 2. ORTEP diagram of compound 15.

1610
G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
Scheme 3. Reagents and conditions: (a) 4 M HCl in dioxane; (b) ClCO(CH2)3COCl, ClCO(CH2)4COCl, ClCO(CH2)5COCl or ClCO(CH2)6COCl,
Et3N, DMF, 66±76%; (c) HCO2NH4, Pd/C, DMF, 72±76%.
Scheme 4. Reagents and conditions: (a) glutaric anhydride, Et3N, THF, 89%; (b) ClCO(CH2)4COCl, ClCO(CH2)5COCl, or ClCO(CH2)6COCl,
Et3N, EDCl, DMF, 67±68%; (c) 19, EDCI, DMF, 48±62%; (d) HCO2NH4, Pd/C, THF, 71±77%.
cytotoxic sequence of these seco-CBI dimers also implies
that the linking N3 amide plays a critically important
role in DNA alkylation.
with MGM values ranging from 0.116 mM for 25ii to
0.0120 mM for 25i. Compound 25i displayed striking
potency in the leukemia, CNS cancer, melanoma,
prostate, and breast cancer cell panels with GI50 values
lower than 0.01 mM in all the cell lines. Compound 25iii
and 25iv selectively inhibited leukemia, CNS cancer and
melanoma with the GI50 values lower than 0.01 mM in
all the cell lines.
Among the C7±C7 dimers, 22i is the most potent com-
pound and the potency decreases with the increasing
length of the linker (22iii and 22iv have almost the same
activities). For the C7±N3 dimers (28i±iv), compound
28iv, which possesses the longest linker (n=6) in the
series, proved to be the most potent with potency
decreasing in the order of 28iv (n=6)>28i (n=3)>28ii
(n=4)>28iii (n=5). Interestingly, compound 28iv
(n=6, GMG=0.0891 mM) was 30Â as potent as com-
pound 28iii (n=5, GMG=2.63 mM) with the only struc-
tural di€erence of one carbon decrease in the linkers.
It was reported that the IC50s of CPI8a and CBI10
monomers against L1210 leukemia cell line were 0.06
and 0.08 mM, respectively. The substituted CBIs, 7-
methoxy-CBI10 and 7-cyano-CBI,11 inhibit L1210 with
the IC50 values of 2000 and 0.09 mM, respectively.
While it is hard to compare the data of dimeric seco-
CBI 28iv and 25i±iv from NCI with the reported data
of these CBI monomers because none of the NCI's cell
lines resembles L1210, the remarkable potencies for
Turning to the N3±N3 dimers, it is evident that this
series of compounds is the most potent set investigated,

G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
1611
Table 1. In vitro cytotoxic potencies (GI50s) of C7±C7 dimers 22i±iv
GI50 (mM)a
Table 2. In vitro cytotoxic potencies (GI50s) of C7±N3 dimers 28i±iv
GI50 (mM)a
Panels/cancer cell lines
22i
22ii
22iii
22iv
Panels/cancer cell lines
28i
28ii
28iii
28iv
Leukemia
CCEF-CEM
HL-60 (TB)
MOLT-4
SR
Leukemia
CCEF-CEM
HL-60 (TB)
MOLT-4
SR
1.53
3.00
0.900
2.20
9.94
Ð
0.27
0.306
1.24
Ð
0.562
0.404
28.8
±
1.42
0.678
0.111
0.193
0.303
0.190
0.0875
0.128
0.313
0.0423
0.0587
<0.0100
<0.0100
<0.0100
<0.0100
0.0945
0.0724
0.0204
Non-small cell lung cancer
HOP-62
NCI-H23
NCI-H460
NCI-H522
Non-small cell lung cancer
HOP-62
NCI-H23
NCI-H460
NCI-H522
11.6
35.5
2.95
1.96
>100
13.1
2.39
>100
>100
24.4
3.43
>100
2.20
1.42
1.71
0.371
2.84
1.37
2.26
0.740
1.57
1.01
0.665
1.05
0.0935
0.0469
0.0234
0.0387
4.67
2.39
5.42
12.3
Colon cancer
COLO 205
HCC-2998
HCT-116
HT 29
Colon cancer
COLO 205
HCC-2998
HCT-116
HT 29
7.64
2.80
5.74
12.9
23.7
7.85
37.8
65.8
7.38
22.8
22.9
3.43
40.4
32.6
1.38
1.08
0.996
1.36
1.57
1.74
2.45
2.69
1.60
1.35
1.65
2.98
0.0928
0.0551
0.0371
0.143
11.0
22.3
CNS cancer
SF-268
SNB-19
U 251
CNS cancer
SF-268
SNB-19
U 251
5.49
20.4
3.30
17.4
31.1
1.95
>100
>100
6.76
>100
0.518
1.13
1.01
1.43
1.81
1.49
1.30
1.33
0.722
0.0399
0.0210
0.0169
57.7
13.4
Melanoma
LOX IMVI
MALME-3M
SK-MEL-2
SK-MEL-5
UACC-257
UACC-62
Melanoma
LOX IMVI
MALME-3M
SK-MEL-2
SK-MEL-5
UACC-257
UACC-62
4.85
11.7
3.33
4.81
5.54
6.48
5.34
15.1
7.31
8.39
69.6
15.9
3.98
>100
72.1
17.3
>100
65.3
57.7
59.6
31.0
15.0
1.14
1.95
1.57
1.68
1.64
1.74
1.56
1.89
2.38
1.54
1.36
2.22
1.30
0.0420
0.103
0.0276
0.0246
0.136
0.780
0.996
0.966
1.19
>100
31.6
1.07
0.0675
Ovarian cancer
IGROV1
OVCAR-3
OVCAR-4
SK-OV-3
Ovarian cancer
IGROV1
OVCAR-3
OVCAR-4
SK-OV-3
16.1
6.48
6.39
27.4
3.88 >100
3.94 >100
>100
92.1
35.2
43.1
1.19
1.05
1.89
1.36
1.42
2.37
3.08
4.39
7.65
1.42
3.61
3.52
0.0505
0.0520
0.232
27.4
>100
>100
>100
0.0557
Renal cancer
786-0
A498
Renal cancer
786-0
A498
2.97
8.08
15.1
0.543
10.1
>100
1.43
24.0
>100
1.42
15.7
>100
1.52
0.993
2.29
2.49
2.01
2.52
1.84
1.56
5.54
0.0578
0.0248
0.129
SN12C
SN12C
Prostate cancer
PC-3
Prostate cancer
PC-3
8.99
10.9
>100
>100
1.61
2.85
2.77
0.0816
Breast cancer
MCF 7
MDA-MB231/ATCC
MDA-MB-435
MDA-N
Breast cancer
MCF 7
MDA-MB231/ATCC
MDA-MB-435
MDA-N
2.23
2.29
2.36 >100
>100 39.9
>100 >100
47.7 36.0
>100
12.1
0.162
1.67
1.01
1.38
1.33
4.04
0.378
2.89
2.10
1.61
1.87
1.12
0.191
2.76
1.70
1.84
1.91
0.735
0.0100
<0.215
0.138
0.134
0.158
0.0946
12.9
4.95
10.9
7.15
4.02
33.8
14.2
19.3
17.4
12.2
BT-549
T 47D
>100
>100
BT-549
T 47D
MGMb
8.71
13.2
41.6
33.1
MGMb
1.74
2.34
2.63
0.0891
aThe cytotoxicity GI50 values are the concentrations corresponding to
50% growth inhibition.
bMean graph midpoint (mM) for growth inhibition against all human
cencer cell lines tested.
aThe cytotoxicity GI50 values are the concentrations corresponding to
50% growth inhibition.
bMean graph midpoint (mM) for growth inhibition against 60 human
cancer cell lines tested.
these seco-CBI dimers against leukemia lines as well as
the other cancer cell lines have clear implications for the
success of our design strategy.
that the antitumor activities of these seco-CBI dimers
were strongly related to the length of the linker and
generally with potency increasing in the order of C7±C7
dimers (22i±iv) < C7±N3 dimers (28i±iv) < N3±N3
dimers (25i±iv). Compound 28iv showed signi®cant
activity against CCRT-CEM, HL-60 (TB), MOLT-4,
and SR leukemia cell lines and MCF 7 breast cancer cell
line with GI50 values < 0.01 mM. N3±N3 dimer 25i dis-
played striking potency in leukemia, CNS cancer, mela-
noma and prostate with GI50 values < 0.01 mM against
all the cell lines and showed the highest overall potency
Conclusions
We have designed and prepared three types of seco-CBI
dimers and all the dimers were selected by the NCI for
evaluation in an in vitro preclinical screening program
against 60 human tumor cell lines. The results showed

1612
G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
Table 3. In vitro cytotoxic potencies (GI50s) of N3±N3 dimers 25i±iv
GI50 (mM)a
modi®ed MS-50 mass spectrometer equipped with a
VG11-250J data system and on a Micromass Zabspec
Hybrid Sector TOF by electrospray. Analytical thin
layer chromatography was performed on silica-coated
plastic plates (silica gel 60 F0254, Merck) and visualized
under UV light. Preparative separations were performed
by ¯ash chromatography on silica gel (Merck, 70±230
or 230±400 mesh). All other solvents were used as
received and were reagent grade where available.
Panels/cancer cell lines
25i
25ii
25iii
25iv
Leukemia
CCEF-CEM
HL-60 (TB)
MOLT-4
SR
<0.0100 <0.0100 <0.0100 <0.0100
<0.0100 <0.0100 <0.0100 <0.0100
<0.0100 <0.0100 <0.0100 <0.0100
<0.0100 <0.0100 <0.0100 <0.0100
Non-small cell lung cancer
HOP-62
NCI-H23
NCI-H460
NCI-H522
<0.0100
<0.0100
<0.0100 <0.0100 <0.0100 <0.0100
0.201 <0.0100 <0.0100
0.0259 <0.0100 <0.0100
tert-Butyl (E)-3-(ethoxycarbonyl)-4-(4-nitrophenyl)-3-but-
enoate (8). To a solution of 7 (32.472 g, 96 mmol) in
20 mL of THF was added NaH (2.451 g, 97 mmol) at
0 ꢀC, and the reaction mixture was stirred for 3 h. The
solution was cooled to 40 ꢀC, 6 (13.59 g, 90 mmol) in
70 mL of THF was added and the mixture was warmed
to 23 ꢀC and stirred for 10 h. The majority of THF was
removed under reduced pressure, and saturated aqueous
NaHCO3 (100 mL) was added. The aqueous layer was
extracted with EtOAc, and the organic layers were
combined, washed with saturated aqueous NaCl, dried
(Na2SO4), and concentrated in vacuo. Chromatography
(SiO2, 20% EtOAc:hexane) provided 8 (18.09 g, 60%
yield) as a pale yellow powder. Mp 116±118 ꢀC. 1H
NMR (CDCl3), d 8.23 (d, J=8.9 Hz, 2H), 7.83 (s, 1H),
7.50 (d, J=8.9 Hz, 2H), 4.28 (q, J=7.2 Hz, 2H), 3.37 (s,
2H), 1.33 (t, J=7.2 Hz, 3H). HR±MS m/z calcd for
C17H21NO6 335.1369, found 335.1372.
<0.0100
0.0576 <0.0100 <0.0100
Colon cancer
COLO 205
HCC-2998
HCT-116
HT 29
<0.0100
0.0166
<0.0100
0.0109
0.116 <0.0100 <0.0100
0.190
0.136 <0.0100 <0.0100
0.334 0.0176 0.0154
0.136 <0.0100
CNS cancer
SF-268
SNB-19
U 251
<0.0100
<0.0100
<0.0100
0.0198 <0.0100 <0.0100
0.0184 <0.0100 <0.0100
0.0299 <0.0100 <0.0100
Melanoma
LOX IMVI
MALME-3M
SK-MEL-2
SK-MEL-5
UACC-257
UACC-62
<0.0100
<0.0100
<0.0100
<0.0100
<0.0100
<0.0100
0.0481 <0.0100 <0.0100
0.205 <0.0100 <0.0100
0.152 <0.0100 <0.0100
0.137 <0.0100 <0.0100
0.146 <0.0100 <0.0100
0.0125 <0.0100 <0.0100
Ovarian cancer
IGROV1
OVCAR-3
OVCAR-4
SK-OV-3
<0.0100
<0.0100
0.0234
0.407
0.249
2.61
0.0192 <0.0100
0.0123 <0.0100
0.150 0.0524
0.0102 <0.0100
(E)-3-(Ethoxycarbonyl)-4-(4-nitrophenyl)-3-butenic acid
(9). A 9:1 mixture of CF3CO2H:H2O (250 mL) at 0 ꢀC
was added to 8 (16.017 g, 47.8 mmol), and the reaction
mixture was warmed to 23 ꢀC and stirred for 4 h. The
reaction mixture was concentrated in vacuo to provide 9
(12.138 g, 91% yield) as a pale yellow powder. Mp 142±
143 ꢀC. 1H NMR (DMSO-d6), d 12.60 (br, 1H), 8.28 (d,
J=9.0 Hz, 2H), 7.82 (s, 1H), 7.67 (d, J=9.0 Hz, 2H),
4.35 (q, J=10.2 Hz, 2H), 3.53 (s, 2H), 1.39 (t, J=
10.2 Hz, 3H). HR±MS m/z calcd for C13H13NO6
279.0743, found 279.0732.
<0.0100
0.351
Renal cancer
786-0
A498
<0.0100
<0.0100
<0.0100
0.0471 <0.0100 <0.0100
0.138 <0.0100 <0.0100
0.182 <0.0100 <0.0100
SN12C
Prostate cancer
PC-3
<0.0100
0.462
0.0193 <0.0100
Breast cancer
MCF 7
<0.0100 <0.0100 <0.0100 <0.0100
MDA-MB231/ATCC
MDA-MB-435
MDA-N
BT-549
T 47D
<0.0100
<0.0100
<0.0100
0.0104
0.299
0.240
0.193
0.281
0.0215
0.0129
0.0142 <0.0100
0.0108 <0.0100
0.0161
0.0120
Ethyl 4-hydroxy-6-nitro-2-naphthalenecarboxylate (11).
A mixture of 9 (13.395 g, 48 mmol) and NaOAc
(4.252 g) in 300 mL of Ac2O was warmed at 70 ꢀC for
12 h. The volatiles were removed in vacuo, and a solu-
tion of the crude (10) and K2CO3 in 300 mL of EtOH
was heated at re¯ux for 4 h. The reaction mixture was
cooled to 0 ꢀC, acidi®ed with the addition of 1 M HCl
(pH 6), and extracted with ether. The organic layers
were combined, washed with saturated aqueous NaCl,
dried (Na2SO4), and concentrated under reduced pres-
sure. Chromatography (SiO2, 25% EtOAc:hexane)
provided 11 (11.206 g, 77% yield) as a yellow powder.
Mp 189±191 ꢀC. 1H NMR (CDCl3), d 9.23 (d, J=
3.8 Hz, 1H), 8.32 (dd, J=3.8, 15.6 Hz, 1H), 8.28 (s, 1H),
8.05 (d, J=15.6 Hz, 1H), 7.63 (s, 1H), 6.16 (s, 1H), 4.60
(q, J=10.1 Hz, 2H), 1.48 (t, J=10.1 Hz, 3H). HR±MS
m/z calcd for C13H11NO4 261.0637, found 261.0635.
<0.0100
0.0166 <0.0100 <0.0100
MGMb
0.0120
0.166 0.0173 0.0151
aThe cytotoxicity GI50 values are the concentrations corresponding to
50% growth inhibition.
bMean graph midpoint (mM) for growth inhibition against 60 human
cancer cell lines tested.
(GMG=0.0120 mM). Some of these seco-CBI dimers
are the most promising candidates and have been selec-
ted for further in vivo testing by the NCI.
Experimental
Melting points were determined using an Electrohome
1
4-Benzyloxy-6-nitro-2-naphthalenecarboxylic acid (13).
A solution of 11 (8.70 g, 33.3 mmol) in dried DMF
(150 mL) under Ar was treated with anhydrous K2CO3
(6.91 g), benzyl bromide (6.84 g, 40 mmol), and Bu4NI
apparatus and are uncorrected. H NMR spectra were
recorded on a Bruker WH-360 spectrometer. High
resolution mass spectra (HR±MS) were recorded on a

G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
1613
(0.5 g). The mixture was stirred at 23 ꢀC for 10 h then
ice-water was added. The solid that precipitated was
collected and the solution of the crude product in THF:
CH3OH:H2O (4:1:1, 290 mL) was treated with LiOH±
H2O (5.544 g, 132 mmol). The suspension was stirred at
23 ꢀC for 4 h before water was added. The solution was
acidi®ed with the addition of 10% aqueous HCl, and
the precipitate was collected and dried to a€orded 13
(10.648 g, 99% yield) as a yellow powder. Mp 157±
159 ꢀC. 1H NMR (DMSO-d6), d 8.97 (m, 1H), 8.35±8.29
(m, 3H), 7.63±7.36 (m, 6H), 5.42 (s, 2H). HR±MS m/z
calcd for C18H13NO5 323.0794, found 323.0792.
6H), 6.22±6.14 (m, 1H), 5.50 (s, 2H), 4.65±4.59 (m, 1H),
4.36±4.30 (m, 1H), 1.29 (s, 9H). HR±MS m/z calcd for
C25H24ClIN2O5 594.0419, found 594.0413.
N-(tert-Butyloxycarbonyl)-N-(3-chloro-2-propen-1-yl)-6-
(9-¯uorenylmethyloxy-carbonylamino)-4-benzyloxy-1-
iodo-2-naphthylamine (18). To a solution of 16 (3.208 g,
5.39 mmol) in MeOH (110 mL) and THF (90 mL) under
Ar, 2.9 g of actived carbon, 0.9 g of FeCl3±6H2O and
1.647 g of N2H4±H2O (95%) were added. The mixture
was heated at re¯ux for 7 h before it was cooled to 23 ꢀC
and ®ltered through Celite. The solvent was removed in
vacuo and a€orded unstable crude amine 17. A solution
of crude 17 in dry THF (50 mL) was treated with Fmoc-
Cl (1.514 g, 5.85 mmol) and DMAP (0.647 g, 5.30 mmol)
at 0 ꢀC. After being stirred for 2 h, the reaction mixture
was concentrated in vacuo. Chromatography (SiO2,
20% EtOAc:hexane) a€orded 18 (3.660 g, 86% yield) as
a white powder. Mp 136±137 ꢀC. 1H NMR (acetone-d6),
d 9.25 (s, 1H), 8.50 (s, 1H), 8.13 (d, J=9.0 Hz, 1H),
7.93±7.86 (m, 3H), 7.78±7.74 (m, 2H), 7.60±7.56 (m,
2H), 7.46±7.28 (m, 7H), 7.02 (s, 1H), 6.28±6.14 (m, 2H),
5.38 (s, 1H), 4.52 (d, J=6.7 Hz, 2H), 4.48±4.39 (m, 1H),
4.32 (t, J=6.7 Hz, 1H), 4.02±3.94 (m, 1H), 1.29 (s, 9H).
HR±ESMS m/z calcd for C40H36N2O5ClINa 809.1255,
found 809.1255 (M+Na+).
N-(tert-Butyloxycarbonyl)-4-benzyloxy-6-nitro-2-naph-
thylamine (14). A solution of 13 (8.250 g, 22.5 mmol) in
freshly distilled dry t-BuOH (800 mL) was treated with
Et3N (2.760 g, 27.3 mmol) and 15 g of activated 4 A
molecular sieves. Diphenyl phosphorazidate (7.726 g,
28.1 mmol) was added, and the reaction mixture was
heated at re¯ux for 15 h. The mixture was cooled to
23 ꢀC, and the solvent was removed under vacuum. The
residue was dissolved in EtOAc, and the organic phase
was washed with 10% aqueous HCl, dried (Na2SO4),
and concentrated in vacuo. Chromatography (SiO2,
20% acetone:hexane) a€orded 14 (8.439 g, 84% yield)
as a yellow powder. Mp 185±186 ꢀC. 1H NMR (CDCl3),
d 9.15 (d, J=4.2 Hz, 1H), 8.21 (dd, J=4.2, 16.2 Hz,
1H), 7.75 (d, J=16.2 Hz, 1H), 7.56±7.39 (m, 6H), 7.18
(d, J=3.6 Hz, 1H), 6.75 (br, 1H), 5.30 (s, 2H), 1.56 (s,
9H). HR±MS m/z calcd for C22H22N2O5 349.1529,
found 349.1528.
5-(Benzyloxy)-3-(tert-butyloxycarbonyl)-1-chloromethyl-
7-(9-¯uorenyl-methyloxycarbonylamino)-1,2-dihydro-3H-
benz[e]indole (5). To
a solution of 18 (12.100 g
15.4 mmol) in dry benzene (1000 mL) were added tri-n-
butyltin hydride (4.55 mL, 18.4 mmol) and AIBN
(0.126 g). After deoxygenation, the reaction mixture was
heated at re¯ux for 4 h and concentrated in vacuo to
give an oily residue. Trituration of the crude oil with
hexanes provided a solid which was collected and
washed with hexanes to give 5 (7.928 g, 78% yield) as a
white powder. Mp 113±115 ꢀC. 1H NMR (acetone-d6), d
9.02 (s, 1H ), 8.38 (s, 1H), 7.88±7.30 (m, 16H), 5.30 (s,
2H), 4.50 (d, J=6.9 Hz, 2H), 4.30 (t, J=6.9 Hz, 1H),
4.22±4.05 (m, 3H), 4.01 (dd, J=3.1, 11.1 Hz, 1H), 3.70
(dd, J=8.4,11.0 Hz, 1H), 1.58 (s, 9H). HR±MS m/z
calcd for C40H37N2O535Cl 660.23907, found 660.23920.
N-(tert-Butyloxycarbonyl)-4-benzyloxy-1-iodo-6-nitro-2-
solution of 14 (4.620 g,
naphthylamine (15).
A
11.7 mmol) in THF (90 mL) and MeOH (90 mL) was
treated with TsOH±H2O (0.135 g) and NIS (2.770 g,
12.3 mmol) at 40 ꢀC under Ar, and the reaction mix-
ture was stirred for 4 h before Et2O (15 mL) was added.
The organic phase was washed with 5% aqueous
NaHCO3 and saturated aqueous NaCl, dried (Na2SO4),
and concentrated in vacuo to provide 15 (5.973 g, 98%
yield) as yellow crystals. Mp 186±188 ꢀC. 1H NMR
(CDCl3), d 9.15 (d, J=4.5 Hz, 1H), 8.28 (s, 1H), 8.26
(dd, J=4.5, 16.2 Hz, 1H), 8.13 (d, J=16.2 Hz, 1H),
7.62±7.43 (m, 5H), 1.56 (s, 9H). HR±MS m/z calcd for
C22H21IN2O5 520.0495, found 520.0496.
5-(Benzyloxy)-3-(tert-butyloxycarbonyl)-1-chloromethyl-
7-amino-1,2-dihydro-3H-benz[e]indole (19). To a solu-
tion of 5 (2.500 g, 3.78 mmol) in THF (130 mL) was
added tetrabutylammonium ¯uoride (2.82 mL, 1.0 M in
THF) and the mixture stirred at 23 ꢀC for 1 h. The sol-
vent was removed in vacuo. Chromatography (SiO2,
50% EtOAc:hexane) a€orded 19 (1.593 g, 96%) as a
N-(tert-Butyloxycarbonyl)-N-(3-chloro-2-propen-1-yl)-4-
benzyloxy-1-iodo-6-nitro-2-naphthylamine (16). A solu-
tion of 15 (3.180 g, 6.11 mmol) in anhydrous DMF
(90 mL) under Ar was treated with NaH (0.232 g, 95%,
9.65 mmol), and the reaction mixture was stirred for 1 h.
The mixture was cooled to 0 ꢀC, and 1,3-dichloro-
propene (2.832 mL, 80%, 24.4 mmol) was added drop-
wise. The solution was stirred overnight. Water was
added, and the aqueous phase was extracted with
EtOAc. The combined organic phases were washed with
saturated aqueous NaCl and dried (Na2SO4), and the
solvent was removed under vacuum. Chromatography
(SiO2, 30% acetone:hexane) a€orded 16 (3.017 g, 83%
ꢀ
1
white powder. Mp 77±78 C. H NMR (acetone-d6), d
7.61±7.56 (m, 4H ), 7.46±7.37 (m, 4H), 7.07 (dd, J=2.4,
8.8 Hz, 1H), 5.23 (s, 2H), 4.82 (br, 2H), 4.19±3.95 (m,
4H), 3.64±3.59 (m, 1H), 1.57 (s, 9H). HR±MS m/z calcd
for C25H27N2O3Cl 438.1710, found 438.1708.
5-(Benzyloxy)-3-(tert-butyloxycarbonyl)-1-chloromethyl-
7-acetylamino-1,2-dihydro-3H-benz[e]indole (20). To a
solution of 19 (0.255 g, 0.582 mmol) in dry THF (30 mL)
were added Et3N (70.6 mg, 0.698 mmol) and AcCl
(50.2 mg, 0.640 mmol) at 0 ꢀC, and the reaction mixture
was stirred for 3 h. The solvent was removed in vacuo.
yield) as a yellow powder. Mp 181±183 ꢀC. H NMR
1
(acetone-d6), d 9.17 (d, J=2.4 Hz, 1H), 8.46 (d, J=
9.3 Hz, 1H), 8.39 (dd, J=2.4, 9.3 Hz, 1H), 7.61±7.35 (m,

1614
G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
Chromatography (SiO2, 60% EtOAc:hexane) a€orded
20 (0.257 g, 92% yield) as a white powder. Mp 101±
General procedure B (preparation of compounds 24i±iv).
Compound 20 was treated with 4 N HCl in dioxane at
0 ꢀC and stirred for 5 h slowly reaching 23 ꢀC. Solvent
was removed and the residue was dried for 1 h in vacuo.
The residue was dissolved in anhydrous DMF, treated
with Et3N and di-acid chloride at 0 ꢀC. After the reac-
tion mixture was stirred at 23 ꢀC for 4 h, the solvent was
removed in vacuo. Flash chromatography (SiO2, hex-
ane±THF) a€orded compounds 24i±iv.
ꢀ
1
103 C. H NMR (DMSO-d6), d 10.09 (s, 1H), 8.33 (s,
1H), 7.84±7.76 (m, 3H), 7.57±7.37 (m, 5H), 5.26 (s, 2H),
4.11±3.97 (m, 4H), 3.82±3.78 (m, 1H), 2.05 (s, 3H), 1.53
(s, 9H). HR±MS m/z calcd for C27H29N2O4Cl 480.1816,
found 480.1813.
General procedure A (preparation of compounds 21i±iv).
A solution of 19 and Et3N in anhydrous THF was
cooled to 0 ꢀC and the di-acid chloride was added
dropwise. The reaction mixture was stirred at 23 ꢀC for
2 h and then evaporated to removed THF. The residue
was puri®ed by ¯ash chromatography (SiO2, hexane±
acetone) to give compounds 21i±iv.
Compound 24i. Prepared according to general procedure
B using 0.2000 g (0.416 mmol) of 20, 8 mL of 4 N HCl in
dioxane, 0.0351 g (0.208 mmol) of glutaryl dichloride,
0.0841 g (0.832 mmol) of Et3N, and 8 mL of DMF to
give 0.1172 g of 24i (66% yield) as a white powder. Mp
ꢀ
1
186±187 C. H NMR (DMSO-d6), d 10.10 (s, 2H), 8.36
(s, 2H), 8.14 (s, 2H), 7.80±7.88 (m, 4H), 7.56±7.33 (m,
10H), 5.24 (s, 4H), 4.38±4.34 (m, 2H), 4.20±4.15 (m, 4H),
4.00±3.96 (m, 2H), 3.85±3.81 (m, 2H), 2.58±2.54 (m, 4H),
2.05 (s, 6H), 1.72±1.71 (m, 2H). ES±MS m/z calcd for C49
H47N4O6Cl2 857.3, found 857.3 (M+H+, 100), 859.2 (70).
Compound 21i. Prepared according to general procedure
A
using 0.2549 g (0.581 mmol) of 19, 0.0617 g
(0.610 mmol) of Et3N, 0.0491 g (0.291 mmol) of glutaryl
dichloride, and 5 mL of THF to give 0.2347 g of 21i
(83% yield) as a white powder. Mp 146±148 ꢀC. 1H
NMR (acetone-d6), d 9.36 (s, 2H), 8.44 (s, 2H), 7.96 (d,
J=9.0 Hz, 2H), 7.75 (d, J=9.0 Hz, 2H), 7.61±7.36 (m,
12H), 5.28 (s, 4H), 4.19±4.07 (m, 6H), 4.02±3.98 (m,
2H), 3.72±3.67 (m, 12H), 2.50 (t, J=7.1 Hz, 4H), 2.10±
2.05 (m, 2H), 1.58 (s, 18H). HR±ESMS m/z calcd for
C55H59N4O8Cl2 973.3710, found 973.3705 (M+H+).
Compound 24ii. Prepared according to general pro-
cedure B using 0.2000 g (0.416 mmol) of 20, 8 mL of 4 N
HCl in dioxane, 0.0381 g (0.208 mmol) of adipoyl
chloride, 0.0841 g (0.832 mmol) of Et3N, and 8 mL of
DMF to give 0.1233 g of 24ii (68% yield) as a white
powder. Mp 183±185 ꢀC. 1H NMR (DMSO-d6), d 10.11
(s, 2H), 8.36 (s, 2H), 8.15 (s, 2H), 7.82±7.79 (m, 4H),
7.56±7.35 (m, 10H), 5.24 (s, 4H), 4.37±4.34 (m, 2H),
4.20±4.16 (m, 4H), 4.01±3.98 (m, 2H), 3.85±3.82 (m,
2H), 2.59±2.54 (m, 4H), 2.05 (s, 6H), 1.74±1.72 (m, 4H).
ES±MS m/z calcd for C50H48N4O6Cl2Na 893.3, found
893.3 (M+Na+, 70), 859.2 (50).
Compound 21ii. Prepared according to general pro-
cedure A using 0.2549 g (0.581 mmol) of 19, 0.0617 g
(0.610 mmol) of Et3N, 0.0533 g (0.291 mmol) of adipoyl
chloride, and 5 mL of THF to give 0.2287 g of 21ii (80%
yield) as a white powder. Mp 133±134 ꢀC. 1H NMR
(DMSO-d6), d 10.04 (s, 2H), 8.33 (s, 2H), 7.82 (d,
J=9.0 Hz, 2H), 7.69 (d, J=9.0 Hz, 2H), 7.54±7.34 (m,
12H), 5.24 (s, 4H), 4.11±3.94 (m, 8H), 3.78±3.69 (m,
2H), 2.38±2.32 (m, 4H), 1.70±1.62 (m, 2H), 1.52 (s, 18H).
HR±ESMS m/z calcd for C56H61N4O8Cl2 987.3866,
found 987.3877 (M+H+).
Compound 24iii. Prepared according to general pro-
cedure B using 0.2000 g (0.416 mmol) of 20, 8 L of 4 N
HCl in dioxane, 0.0410 g (0.208 mmol) of pimeloyl
chloride, 0.0841 g (0.832 mmol) of Et3N, and 8 mL of
DMF to give 0.1227 g of 24iii (67% yield) as a white
powder. Mp 182±183 ꢀC. 1H NMR (DMSO-d6), d 10.11
(s, 2H), 8.36 (s, 2H), 8.15 (s, 2H), 7.83±7.79 (m, 4H),
7.57±7.36 (m, 10H), 5.24 (s, 4H), 4.36±4.34 (m, 2H),
4.20±4.16 (m, 4H), 4.00±3.97 (m, 2H), 3.85±3.83 (m,
2H), 2.57±2.53 (m, 4H), 2.05 (s, 6H), 1.75±1.71 (m, 6H).
ES±MS m/z calcd for C51H51N4O6Cl2 885.3, found
885.3 (M+H+, 100), 887.3 (75).
Compound 21iii. Prepared according to general pro-
cedure A using 0.1905 g (0.434 mmol) of 19, 0.0460 g
(0.456 mmol) of Et3N, 0.0428 g (0.217 mmol) of pimel-
oyl chloride, and 5 mL of THF to give 0.1935 g of 21iii
(89% yield) as a white powder. Mp 130±132 ꢀC. 1H
NMR (DMSO-d6), d 10.04 (s, 2H), 8.32 (s, 2H), 7.83 (d,
J=9.0 Hz, 2H), 7.74 (d, J=9.0 Hz, 2H), 7.54±7.33 (m,
12H), 5.25 (s, 4H), 4.13±3.96 (m, 8H), 3.81±3.78 (m,
2H), 2.34±2.30 (m, 4H), 1.65±1.56 (m, 6H), 1.53 (s, 18H).
HR±ESMS m/z calcd for C57H63N4O8Cl2 1001.4023,
found 1001.4019 (M+H+).
Compound 24iv. Prepared according to general pro-
cedure B using 0.2000 g (0.416 mmol) of 20, 8 mL of 4 N
HCl in dioxane, 0.0439 g (0.208 mmol) of suberoyl
chloride, 0.0841 g (0.832 mmol) of Et3N, and 8 mL of
DMF to give 0.1423 g of 24iv (76% yield) as a white
powder. Mp 184±186 ꢀC. 1H NMR (DMSO-d6), d 10.08
(s, 2H), 8.36 (s, 2H), 8.16 (s, 2H), 7.83±7.78 (m, 4H),
7.56±7.34 (m, 10H), 5.24 (s, 4H), 4.36±4.34 (m, 2H),
4.19±4.16 (m, 4H), 4.02±3.96 (m, 2H), 3.86±3.83 (m,
2H), 2.58±2.53 (m, 4H), 2.06 (s, 6H), 1.76±1.70 (m, 8H).
ES±MS m/z calcd for C52H52N4O6Cl2Na 921.3, found
921.3 (M+Na+, 100), 923.3 (75).
Compound 21iv. Prepared according to general pro-
cedure A using 0.1994 g (0.454 mmol) of 19, 0.0482 g
(0.477 mmol) of Et3N, 0.0479 g (0.227 mmol) of suber-
oyl chloride, and 5 mL of THF to give 0.1892 g of
21iv (82% yield) as a white powder. Mp 129±131 ꢀC. 1H
NMR (DMSO-d6), d 10.03 (s, 2H), 8.33 (s, 2H), 7.84 (d,
J=9.0 Hz, 2H), 7.75 (d, J=9.0 Hz, 2H), 7.54±7.33 (m,
12H), 5.25 (s, 4H), 4.13±3.96 (m, 8H), 3.83±3.78 (m,
2H), 2.33±2.29 (m, 4H), 1.60±1.45 (m, 22H). HR±ESMS
m/z calcd for C58H65N4O8Cl2 1015.4179, found
1015.4179 (M+H+).
Compound 26i. Compound 20 (0.5141 g, 1.069 mmol)
was added to a solution of 4 N HCl in dioxane (20 mL)

G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
1615
at 0 ꢀC under Ar. The reaction mixture was stirred at
23 ꢀC for 5 h before the solvent was removed. After
being dried in vacuo, the residue, Et3N (0.2162 g,
2.138 mmol) and glutaric anhydride (0.1224 g, 1.069
mmol) were dissolved in anhydrous THF (20 mL), and
the reaction mixture was stirred at 23 ꢀC for 12 h then
the solvent was removed in vacuo. Chromatography
(SiO2, 5% MeOH±CH2Cl2) a€orded 26i (0.4722 g, 89%
yield) as a white powder. Mp 213±216 ꢀC. 1H NMR
(DMSO-d6), d 10.12 (s, 1H), 8.37 (s, 1H), 8.14 (s, 1H),
7.82±7.78 (m, 2H), 7.57±7.36 (m, 5H), 5.25 (s, 2H),
4.32±4.30 (m, 1H), 4.15±4.12 (m, 2H), 4.00±3.97 (m,
1H), 3.85±3.82 (m, 1H), 2.57±2.54 (m, 2H), 2.35±2.31
(m, 2H), 2.05 (m, 3H), 1.86±1.80 (m, 2H). ES±MS m/z
calcd for C27H28N2O5Cl 495.2, found 495.2 (M+H+,
100), 497.2 (40).
(s, 2H), 4.34±4.29 (m, 1H), 4.14±4.15 (m, 2H), 4.00±3.98
(m, 1H), 3.83±3.82 (m, 1H), 2.55±2.51 (m, 2H), 2.24±
2.20 (m, 2H), 2.05 (m, 3H), 1.64±1.37 (m, 8H). ES±MS
m/z calcd for C30H33N2O5ClNa 559.3, found 559.3
(M+Na+, 100), 561.3 (34).
General procedure D (preparation of compounds 27i±iv).
A mixture of 26i±iv, 19 and EDCI in DMF was stirred
at 23 ꢀC for 18 h. After DMF was removed in vacuo, the
residue was puri®ed by ¯ash chromatography (SiO2,
hexane±acetone) to a€ord compounds 27i±iv.
Compound 27i. Prepared according to general pro-
cedure D using 0.1000 g (0.202 mmol) of 26i, 0.1419 g
(0.323 mmol) of 19, 0.155 g (0.808 mmol) of EDCI, and
4 mL of DMF to give 0.1147 g of 27i (62% yield) as a
white powder. Mp 155±157 ꢀC. 1H NMR (DMSO-d6), d
10.12 (s, 1H), 10.09 (s, 1H), 8.36 (s, 2H), 8.13 (s, 1H),
7.88±7.74 (m, 5H), 7.56±7.35 (m, 10H), 5.24 (s, 2H), 5.21
(s, 2H), 4.46±4.31 (m, 1H), 4.16±3.96 (m, 7H), 3.84±3.78
(m, 2H), 2.46±2.43 (m, 4H), 2.05 (s, 3H), 1.97±1.93 (m,
2H), 1.53 (s, 9H). ES±MS m/z calcd for C52H53N4O7Cl2
915.3, found 915.3 (M+H+, 30), 917.3 (20).
General procedure C (preparation of compounds 26ii±iv).
Compound 20 was treated with 4 N HCl in dioxane at
0 ꢀC and stirred for 5 h slowly reaching 23 ꢀC. The sol-
vent was removed and the residue was dried for 1 h in
vacuo. The residue was dissolved in anhydrous DMF,
treated with Et3N and di-acid and EDCI at 23 ꢀC. After
the reaction mixture was stirred at 23 ꢀC for 12 h, the
solvent was removed in vacuo. Flash chromatography
(SiO2, hexane±acetone) a€orded compounds 26ii±iv.
Compound 27ii. Prepared according to general pro-
cedure D using 0.0915 g (0.180 mmol) of 26ii, 0.1263 g
(0.288 mmol) of 19, 0.1379 g (0.719 mmol) of EDCI, and
3 mL of DMF to give 0.0929 g of 27ii (56% yield) as a
white powder. Mp 150±153 ꢀC. 1H NMR (DMSO-d6), d
10.11 (s, 1H), 10.08 (s, 1H), 8.36 (s, 2H), 8.13 (s, 1H),
7.85±7.76 (m, 5H), 7.56±7.34 (m, 10H), 5.25 (s, 2H),
5.23 (s, 2H), 4.38±4.25 (m, 1H), 4.16±3.95 (m, 7H),
3.85±3.77 (m, 2H), 2.46±2.43 (m, 4H), 2.05 (s, 3H), 1.74±
1.65 (m, 4H), 1.53 (s, 9H). HR±ESMS m/z calcd for
C53H55N4O7Cl2 929.3448, found 929.3464 (M+H+).
Compound 26ii. Prepared according to general pro-
cedure C using 0.1619 g (0.336 mmol) of 20, 5 mL of 4 N
HCl in dioxane, 0.0374 g (0.370 mmol) of Et3N, 0.1476 g
(1.01 mmol) of adipic acid, 0.1936 g (1.01 mmol) of
EDCI, and 4 mL of DMF to give 0.1172 g of 26ii (68%
yield) as a white powder. Mp 217±220 ꢀC. 1H NMR
(DMSO-d6), d 12.02 (br, 1H), 10.11 (s, 1H), 8.36 (s, 1H),
8.14 (s, 1H), 7.84±7.78 (m, 2H), 7.57±7.34 (m, 5H), 5.24
(s, 2H), 4.33±4.29 (m, 1H), 4.14±4.13 (m, 2H), 4.01±3.97
(m, 1H), 3.84±3.79 (m, 1H), 2.58±2.53 (m, 2H), 2.28±
2.24 (m, 2H), 2.05 (m, 3H), 1.62±1.58 (m, 4H). ES±MS
m/z calcd for C28H30N2O5Cl 509.2, found 509.2
(M+H+, 100), 511.2 (35).
Compound 27iii. Prepared according to general pro-
cedure D using 0.1098 g (0.210 mmol) of 26iii, 0.1474 g
(0.336 mmol) of 19, 0.1610 g (0.839 mmol) of EDCI, and
3 mL of DMF to give 0.1023 g of 27iii (52% yield) as a
white powder. Mp 149±151 ꢀC. 1H NMR (DMSO-d6), d
10.11 (s, 1H), 10.05 (s, 1H), 8.36 (s, 1H), 8.34 (s, 1H),
8.13 (s, 1H), 7.86±7.74 (m, 5H), 7.56±7.35 (m, 10H),
5.24 (s, 2H), 5.22 (s, 2H), 4.36±4.28 (m, 1H), 4.17±3.95
(m, 7H), 3.83±3.75 (m, 2H), 2.42±2.40 (m, 4H), 2.08 (s,
3H), 1.72±1.63 (m, 6H), 1.53 (s, 9H). ES±MS m/z calcd
for C54H57N4O7Cl2 943.3, found 943.3 (M+H+, 100),
945.3 (70).
Compound 26iii. Prepared according to general pro-
cedure C using 0.2000 g (0.416 mmol) of 20, 6 mL of 4 N
HCl in dioxane, 0.0462 g (0.458 mmol) of Et3N, 0.1998 g
(1.25 mmol) of pimelic acid, 0.2390 g (1.25 mmol) of
EDCI, and 4 mL of DMF to give 0.1447 g of 26iii (68%
yield) as a white powder. Mp 199±201 ꢀC. 1H NMR
(DMSO-d6), d 11.98 (br, 1H), 10.11 (s, 1H), 8.37 (s, 1H),
8.14 (s, 1H), 7.82±7.78 (m, 2H), 7.58±7.36 (m, 5H), 5.24
(s, 2H), 4.33±4.29 (m, 1H), 4.16±4.13 (m, 2H), 4.01±3.98
(m, 1H), 3.84±3.81 (m, 1H), 2.54±2.51 (m, 2H), 2.24±
2.20 (m, 2H), 2.05 (m, 3H), 1.63±1.53 (m, 4H), 1.38±1.34
(m, 2H). ES±MS m/z calcd for C29H32N2O5Cl 523.2,
found 523.2 (M+H+, 100), 525.2 (35).
Compound 27iv. Prepared according to general pro-
cedure D using 0.1206 g (0.224 mmol) of 26iv, 0.1577 g
(0.358 mmol) of 19, 0.1722 g (0.896 mmol) of EDCI, and
3 mL of DMF to give 0.1181 g of 27iv (48% yield) as a
white powder. Mp 152±154 ꢀC. 1H NMR (acetone-d6), d
9.36 (s, 2H), 8.44 (s, 2H), 7.97±7.94 (m, 2H), 7.75±7.73
(m, 2H), 7.60±7.35 (m, 12H), 5.28 (s, 4H), 4.19±3.97 (m,
8H), 3.70±3.67 (m, 2H), 2.52±2.48 (m, 4H), 2.05 (s, 3H),
1.59±1.32 (m, 17H). ES±MS m/z calcd for C55H59
N4O7Cl2 943.4, found 957.4 (M+H+, 30), 959.4 (20).
Compound 26iv. Prepared according to general pro-
cedure C using 0.1910 g (0.397 mmol) of 20, 6 mL of 4 N
HCl in dioxane, 0.0441 g (0.437 mmol) of Et3N, 0.208 g
(1.19 mmol) of suberic acid, 0.239 g (1.25 mmol) of
EDCI, and 4 mL of DMF to give 0.1400 g of 26iv (67%
yield) as a white powder. Mp 201±203 ꢀC. 1H NMR
(DMSO-d6), d 11.89 (br, 1H), 10.11 (s, 1H), 8.37 (s, 1H),
8.13 (s, 1H), 7.83±7.78 (m, 2H), 7.58±7.34 (m, 5H), 5.24
General procedure E (deprotection of benzyl group). To
a solution of 21i±iv, 24i±iv, or 27i±iv in THF or DMF
was added 10% Pd/C under Ar. The mixture was cooled

1616
G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
to 0 ꢀC and 10% aqueous ammonium formate was
added. The mixture was stirred at 23 ꢀC until the reac-
tion was complete (TLC). The mixture was then ®ltered
through a pad of Celite, and concentrated in vacuo.
Flash chromatography (SiO2, CH2Cl2±MeOH) a€orded
the ®nal pure compounds.
10% aqueous ammonium formate, 0.06 g of 10% Pd/C,
and 10 mL of DMF to give 0.0624 g of 25ii (76% yield)
as a white powder. Mp > 250 ꢀC. 1H NMR (DMSO-d6)
d: 10.24 (s, 2H), 10.02 (s, 2H), 8.35 (s, 2H), 7.94 (s, 2H),
7.72 (d, J=8.9 Hz, 2H), 7.64 (d, J=8.9 Hz, 2H), 4.34±
4.29 (m, 2H), 4.16±4.10 (m, 4H), 3.98±3.96 (m, 2H),
3.79±3.73 (m, 2H), 2.62±2.53 (m, 4H), 2.06 (s, 6H),
1.65±1.61 (m, 4H). HR±ESMS m/z calcd for C36H37
N4O637Cl2 695.2031, found 695.2045 (M+H+).
Compound 22i. Prepared according to general pro-
cedure E using 0.1768g (0.182mmol) of 21i, 0.826 mL of
10% aqueous ammonium formate, 0.11 g of 10% Pd/C,
and 8 mL of THF to give 0.1279 g of 22i (89% yield) as
Compound 25iii. Prepared according to general pro-
cedure E using 0.0877g (0.099mmol) of 24iii, 0.250 mL of
10% aqueous ammonium formate, 0.05 g of 10% Pd/C,
and 10 mL of DMF to give 0.0510 g of 25iii (73% yield)
as a white powder. Mp > 250 ꢀC. 1H NMR (DMSO-d6)
d: 10.24 (s, 2H), 10.03 (s, 2H), 8.35 (s, 2H), 7.96 (s, 2H),
7.72 (d, J=9.0 Hz, 2H), 7.65 (d, J=9.0 Hz, 2H), 4.35±
4.30 (m, 2H), 4.15±4.04 (m, 4H), 3.98±3.95 (m, 2H),
3.74±3.72 (m, 2H), 2.63±2.53 (m, 4H), 2.06 (s, 6H),
1.60±1.55 (m, 4H), 1.48±1.42 (m, 2H). HR±ESMS m/z
calcd for C37H39N4O6Cl2 705.2247, found 705.2264
(M+H+).
a white powder. Mp 162 ꢀC (dec.). H NMR (DMSO-
1
d6) d: 10.26 (s, 2H), 10.01 (s, 2H), 8.41 (s, 2H), 7.70±7.62
(m, 6H), 4.09±3.65 (m, 10H), 2.42 (t, J=7.2 Hz, 4H),
1.98±1.93 (m, 2H), 1.49 (s, 18H). HR±ESMS m/z calcd
for C41H47N4O8Cl2 793.2771, found 793.2771 (M+H+).
Compound 22ii. Prepared according to general pro-
cedure E using 0.2241 g (0.227 mmol) of 21ii, 1.03 mL of
10% aqueous ammonium formate, 0.15 g of 10% Pd/C,
and 10 mL of THF to give 0.1579 g of 22ii (86% yield)
as a white powder. Mp 159 ꢀC (dec.). 1H NMR
(DMSO-d6) d: 10.25 (s, 2H), 9.98 (s, 2H), 8.34 (s, 2H),
7.70±7.62 (m, 6H), 4.07±3.59 (m, 10H), 2.41±2.36 (m,
4H), 1.69±1.65 (m, 4H), 1.52 (s, 18H). HR±ESMS m/z
calcd for C42H48N4O8Cl2Na 829.2748, found 829.2755
(M+Na+).
Compound 25iv. Prepared according to general pro-
cedure E using 0.0523g (0.058mmol) of 24iv, 0.146 mL of
10% aqueous ammonium formate, 0.03 g of 10% Pd/C,
and 10 mL of DMF to give 0.0301 g of 25iv (72% yield)
as a white powder. Mp > 250 ꢀC. 1H NMR (DMSO-d6)
d: 10.24 (s, 2H), 10.03 (s, 2H), 8.35 (s, 2H), 7.95 (s, 2H),
7.72 (d, J=8.7 Hz, 2H), 7.64 (d, J=8.7 Hz, 2H), 4.32±
4.26 (m, 2H), 4.14±4.05 (m, 4H), 3.99±3.94 (m, 2H),
3.76±3.72 (m, 2H), 2.63±2.52 (m, 4H), 2.07 (s, 6H),
1.66±1.62 (m, 4H), 1.45±1.38 (m, 4H). HR±ESMS m/z
calcd for C38H40N4O6Cl2Na 741.2223, found 741.2239
(M+H+).
Compound 22iii. Prepared according to general pro-
cedure E using 0.1605g (0.160mmol) of 21iii, 0.727 mL of
10% aqueous ammonium formate, 0.10g of 10% Pd/C,
and 8 mL of THF to give 0.1278 g of 22iii (97% yield) as
ꢀ
1
a white powder. Mp 158 C (dec.). H NMR (DMSO-
d6) d: 10.26 (s, 2H), 9.96 (s, 2H), 8.38 (s, 2H), 7.68±7.61
(m, 6H), 4.08±3.65 (m, 10H), 2.34 (t, J=7.2Hz, 4H),
1.68±1.63 (m, 4H), 1.52 (s, 18H), 1.43±1.37 (m, 2H).
HR±ESMS m/z calcd for C43H51N4O8Cl2 821.3084,
found 821.3082 (M+H+).
Compound 28i. Prepared according to general procedure
E using 0.0249 g (0.0272 mmol) of 27i, 0.072 mL of 10%
aqueous ammonium formate, 0.01 g of 10% Pd/C, and
2 mL of THF to give 0.0153 g of 28i (77% yield) as a
Compound 22iv. Prepared according to general pro-
cedure E using 0.1783g (0.176mmol) of 21iv, 0.798 mL of
10% aqueous ammonium formate, 0.10 g of 10% Pd/C,
and 8 mL of THF to give 0.1249 g of 22iv (85% yield) as
white powder. Mp 189 ꢀC (dec.). H NMR (DMSO-d6)
1
d: 10.26 (s, 2H), 10.02 (s, 1H), 10.01 (s, 1H), 8.40 (s,
1H), 8.36 (s, 1H), 7.96 (s, 1H), 7.73±7.63 (m, 5H), 4.33±
4.28 (m, 1H), 4.14±3.90 (m, 7H), 3.78±3.71 (m, 2H),
2.46±2.43 (m, 4H), 2.06 (s, 3H), 1.98±1.93 (m, 2H), 1.53
(s, 9H). HR±ESMS m/z calcd for C38H41N4O7Cl37Cl
737.2323, found 737.2330 (M+H+).
a white powder. Mp 165 ꢀC (dec.). H NMR (DMSO-
1
d6) d: 10.25 (s, 2H), 9.94 (s, 2H), 8.38 (s, 2H), 7.69±7.61
(m, 6H), 4.08±3.69 (m, 10H), 2.33 (t, J=7.3 Hz, 4H),
1.68±1.60 (m, 4H), 1.52 (s, 18H), 1.38±1.34 (m, 4H).
HR±ESMS m/z calcd for C44H53N4O8Cl2 835.3240,
found 835.3244 (M+H+).
Compound 28ii. Prepared according to general pro-
cedure E using 0.0889g (0.0956 mmol) of 27ii, 0.241 mL of
10% aqueous ammonium formate, 0.05 g of 10% Pd/C,
and 8 mL of THF to give 0.0510 g of 28ii (71% yield) as
Compound 25i. Prepared according to general procedure
E using 0.0700 g (0.080 mmol) of 24i, 0.206 mL of 10%
aqueous ammonium formate, 0.04 g of 10% Pd/C, and
10 mL of DMF to give 0.0414 g of 25i (75% yield) as a
a white powder. Mp 212 ꢀC (dec.). H NMR (DMSO-
1
d6) d: 10.25 (s, 1H), 10.23 (s, 1H), 10.01 (s, 1H), 9.98 (s,
1H), 8.38 (s, 1H), 8.34 (s, 1H), 7.94 (s, 1H), 7.71±7.63
(m, 5H), 4.34±4.27 (m, 1H), 4.14±3.94 (m, 7H), 3.78±
3.72 (m, 2H, 2.45±2.32 (m, 4H), 2.06 (s, 3H), 1.78±1.64
(m, 4H), 1.53 (s, 9H). HR±ESMS m/z calcd for
C39H43N4O7Cl2 749.2509, found 749.2496 (M+H+).
white powder. Mp > 250 ꢀC. H NMR (DMSO-d6) d:
1
10.23 (s, 2H), 10.02 (s, 2H), 8.36 (s, 2H), 7.97 (s, 2H),
7.72±7.66 (m, 4H), 4.34±4.26 (m, 2H), 4.18±4.08 (m, 4H),
4.01±3.94 (m, 2H), 3.80±3.72 (m, 2H), 2.70±2.54 (m, 4H),
2.06 (s, 6H), 1.68±1.60 (m, 2H). HR±ESMS m/z calcd
for C35H35N4O6Cl2 677.1934, found 677.1938 (M+H+).
Compound 28iii. Prepared according to general pro-
cedure E using 0.0986g (0.104mmol) of 27iii, 0.263 mL of
10% aqueous ammonium formate, 0.05 g of 10% Pd/C,
Compound 25ii. Prepared according to general pro-
cedure E using 0.1043g (0.120mmol) of 24ii, 0.302 mL of

G. Jia, J. W. Lown / Bioorg. Med. Chem. 8 (2000) 1607±1617
1617
and 8 mL of THF to give 0.0598 g of 28iii (75% yield) as
a white powder. Mp 196 ꢀC (dec.). H NMR (DMSO-
3. (a) Boger, D. L.; Coleman,R. S. J. Am. Chem. Soc. 1988,
110, 4796. (b) Lin, C. H.; Sun, D.; Hurley, H. L. Chem. Res.
Toxicol. 1991, 4, 21. (c) Mitchell, M. A.; Kelly, R. C.; Wic-
nienski, N. A.; Hatzenbuhler, N. T.; Williams, M. G.; Petzold,
G. L.; Slighton, J. L.; Siemeniak, D. R. J. Am. Chem. Soc.
1991, 113, 8994. (d) Kelly, R. C.; Gebhard, I.; Wicknienski,
N.; Aristo€, P. A.; Johnson, P. D.; Martin, D. G. J. Am.
Chem. Soc. 1987, 109, 6837. (e) Boger, D. L.; Yun, W.; Han,
N. Bioorg. Med. Chem. 1995, 3, 1429.
4. (a) Boger, D. L.; Ishizaki, T.; Wysocki, R. J. Jr.; Muck, S.
A. J. Am. Chem. Soc. 1989, 111, 6461. (b) Boger, D. L.; Ishi-
zaki, T. J. Org. Chem. 1990, 55, 5823. (c) Boger, D. L.; Yun,
W.; Teegarden, B. R. J. Org. Chem. 1992, 57, 2873. (d) Boger,
D. L.; Mesini, P.; Tarby, C. M. J. Am. Chem. Soc. 1994, 116,
6461. (e) Boger, D. L.; McKie, J. A. J. Org. Chem. 1995, 60,
1271. (f) Aristo€, P. A.; Johnson, P. D. J. Org. Chem. 1992,
57, 6234. (g) Drost, K. J.; Cava, M. P. J. Org. Chem. 1991, 56,
2240.
1
d6) d: 10.25 (s, 1H), 10.23 (s, 1H), 10.02 (s, 1H), 9.96 (s,
1H), 8.38 (s, 1H), 8.35 (s, 1H), 7.94 (s, 1H), 7.72±7.62
(m, 5H), 4.33±4.27 (m, 1H), 4.13±3.95 (m, 7H), 3.78±
3.72 (m, 2H), 2.44±2.33 (m, 4H), 2.06 (s, 3H), 1.70±1.62
(m, 4H), 1.53 (s, 9H), 1.47±1.41 (m, 2H). HR±ESMS
m/z calcd for C40H45N4O7Cl37Cl 765.2636, found
765.2621 (M+H+).
Compound 28iv. Prepared according to general pro-
cedure E using 0.0975g (0.102mmol) of 27iv, 0.257 mL of
10% aqueous ammonium formate, 0.05 g of 10% Pd/C,
and 10 mL of THF to give 0.0559 g of 28iv (71% yield)
as a white powder. Mp 194 ꢀC (dec.). 1H NMR
(DMSO-d6) d: 10.25 (s, 1H), 10.22 (s, 1H), 10.01 (s, 1H),
9.94 (s, 1H), 8.38 (s, 1H), 8.34 (s, 1H), 7.94 (s, 1H),
7.72±7.63 (m, 5H), 4.30±4.25 (m, 1H), 4.12±3.93 (m,
7H), 3.76±3.72 (m, 2H), 2.45±2.32 (m, 4H), 2.06 (s, 3H),
1.66±1.58 (m, 4H), 1.53 (s, 9H), 1.40±1.34 (m, 4H). HR±
ESMS m/z calcd for C41H47N4O7Cl37Cl 779.2792,
found 779.2792 (M+H+).
5. (a) Fregeau, N. L.; Wang, Y.; Pon, R. T.; Wylie, W. A.;
Lown, J. W. J. Am. Chem. Soc. 1995, 117, 8917. (b) Iida, H.;
Lown, J. W. Recent Res. Devel. in Synth. Org. Chem. 1998, 1,
17.
6. (a) Jia, G.; Iida, H.; Lown, J. W. Heterocyclic Commun.
1998, 4, 557. (b) Jia, G.; Iida, H.; Lown, J. W. Chem. Com-
mun. 1999, 119.
7. Iida, H.; Jia, G.; Lown, J. W. Curr. Opin. Biotechnol. 1999,
10, 29, and references cited therein.
X-ray crystallographic analysis
8. (a) Mitchell, M. A.; Johnson, P. D.; Williams, M. G.;
Aristo€, P. A. J. Am. Chem. Soc. 1989, 111, 6428. (b) Mitchell,
M. A.; Kelly, R. C.; Wicniensky, N. A.; Hatzenbuhler, N. T.;
Williams, M. G.; Petzold, G. L.; Slihgtom, J. L.; Siemieniak,
D. R. J. Am. Chem. Soc. 1991, 113, 8994.
9. Rajski, S. R.; Williams, R. M. Chem. Rev. 1998, 98, 2723.
10. Boger, D. L.; McKie, J. A.; Cai, H.; Cacciari, B.; Baraldi,
P. G. J. Org. Chem. 1996, 61, 1710.
11. Boger, D. L.; Han, N.; Tarby, C. M.; Boyce, C. W.; Cai,
H.; Jin, Q.; Kitos, P. K. J. Org. Chem. 1996, 61, 4894.
12. Owton, W. M.; Gallagher, P. T.; Juan-Montesinos, A.
Synth. Commun. 1993, 23, 2119.
13. Patel, V. F.; Andis, S. L.; Enkeme, J. K.; Kennedy, J. H.;
Mohamadi, F.; Schultz, R. M.; Soose, D. J.; Spees, M. M. J.
Org. Chem. 1997, 62, 8868.
Yellow crystals of 15 were obtained from ethyl acetate.
They were stable without the mother liquor in air and
were selected at room atmosphere for X-ray crystal-
lography. Formula C22H21IN2O5, monoclinic, space
group C2/c, a=16.1690(6), b=19.7813(6), c=14.9515(7)
A, ꢀ=116.755(4), V=4270.2(3)A3, Z=8, graphite-
monochromated Cu Ka radiation (l=1.54178A), ꢁ=
12.09 mm 1, T= 60 ꢀC. Data were collected on a Sie-
mens P4/RA di€ractometer. Calculations were carried
out with the use of programs in the SHELXTL (Version
5.0) package.
Acknowledgements
14. Clive, D. L. J.; Angoh, A. G.; Bennett, S. M. J. Org. Chem.
1987, 52, 1339.
15. Boger, D. L.; Boyce, C. W.; Garbaccio, R. M.; Searcey, M.
Tetrahedron Lett. 1998, 39, 2227.
This research was supported by grants (to J.W.L.) from
the Natural Sciences and Engineering Research Council
of Canada and by the Department of Chemistry, Uni-
versity of Alberta.
16. (a) Monks, A.; Scudiero, D.; Skehan, P.; Shoemaker, R.;
Paull, K.; Vistica, D.; Hose, C.; Langley, J.; Cronise, P.; Vai-
gro-Wol€, A.; Gray-Goodrich, M.; Campbell, H.; Mayo, J.;
Boyd, M. J. Natl. Cancer Inst. 1991, 83, 757. (b) Paull, K. D.;
Shoemaker, R. H.; Monks, A.; Scudiero, D. A.; Rubinstein,
L.; Plowman, J.; Boyd, M. R. J. Natl. Cancer Inst. 1989, 81,
1088. (c) Boyd, M. R.; Paull, K. D.; Rubinstein, L. R. In
Cytotoxic Anticancer Drugs: Models and Concepts for Drug
Discovery. Valeriote, F. A., Corbett, T., Baker, L., Eds.;
Kluwer Academic Publishers: Amsterdam, 1992; pp 11±34.
17. (a) Boger, D. L.; Santillan, Jr., A.; Searcey, M.; Jin, Q. J.
Am. Chem. Soc. 1998, 120, 11554. (b) Boger, D. L.; Santillan,
Jr. A.; Searcey, M.; Jin, Q. J. Org. Chem. 1999, 64, 5241.
References and Notes
1. (a) Reynolds, V. L.; McGovren, J. P.; Hurley, L. H. J.
Antibiot. 1986, 34, 319. (b) Yasuzawa, T.; Muroi, K.; Ichi-
mura, M.; Takahashi, I.; Ogawa, T.; Takahashi, K.; Sano, H.;
Saitoh, Y. Chem. Pharm. Bull. 1995, 43, 378.
2. (a) Boger, D. L.; Johnson, D. S. Angew. Chem., Int. Ed.
Engl. 1996, 35, 1439. (b) Boger, D. L.; Boyce, C. W.; Garbaccio,
R. M.; Goldberg, J. A. Chem. Rev. 1997, 97, 787.