Synthesis and biological evaluation of 11-substituted 6-aminobenzo[c] phenanthridine derivatives, a new class of antitumor agents

Article abstract of DOI:10.1021/jm0490888

The synthesis of 11-substituted 6-amino-11,12-dihydrobenzo[c] phenanthridines and 11-substituted 6-aminobenzo[c]phenanthridines through an efficient method is described. The antiproliferative activity of selected compounds against a wide panel of tumor ce

Full text of DOI:10.1021/jm0490888

2772
J. Med. Chem. 2005, 48, 2772-2777
Synthesis and Biological Evaluation of 11-Substituted
6-Aminobenzo[c]phenanthridine Derivatives, a New Class of Antitumor Agents
Ilka Kock, Dieter Heber, Matthias Weide, Ulrich Wolschendorf, and Bernd Clement*
Department of Pharmaceutical Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel,
Gutenbergstraâe 76, D-24118 Kiel, Germany
Received November 11, 2004
The synthesis of 11-substituted 6-amino-11,12-dihydrobenzo[c]phenanthridines and 11-
substituted 6-aminobenzo[c]phenanthridines through an efficient method is described. The
antiproliferative activity of selected compounds against a wide panel of tumor cell lines was
tested in the in vitro anticancer screening and the in vivo hollow fiber assay of the National
Cancer Institute. Several compounds turned out to exhibit considerable cytotoxicity for tumor
cells. For the study of structure-activity relationships different substituents were introduced
in the 11-position. Compounds with methoxyphenyl substituents tended to show the highest
potency. Several compounds exhibited noteworthy antitumor activity with GI50 values across
all cell lines <1 µM. 6-Amino-11-(3,4,5-trimethoxyphenyl)benzo[c]phenanthridine perchlorate
was the most potent agent in the NCI’s in vivo hollow fiber assay. Most of the tested compounds
showed a remarkable selectivity for leukemia, breast cancer, and prostate cancer.
Introduction
Benzo[c]phenanthridine derivatives are a class of
substances possessing a broad spectrum of pharmaco-
logical activities. In the literature many naturally
occurring alkaloids with the benzo[c]phenanthridine
Figure 1.
ring system and interesting biological properties are
mentioned.1 Fagaronine (Figure 1) is the most impor-
tant representative of this group of alkaloids.2 Antimi-
crobial, antitumoral, cytotoxic, and antileukemic activity
are some of the properties exhibited by fagaronine and
certain other members of this class of alkaloids such as
nitidine, chelerythrine, and sanguinarine.1 Because of
a strong interest in the biological activities associated
with these compounds, the synthesis of benzo[c]phenan-
Figure 2. Chemical structure of the 11-substituted 6-amino-
11,12-dihydrobenzo[c]phenanthridine chlorides (1-31) and the
thridine derivatives and alkaloids of this family occupies
a position of prime importance in heterocyclic chemistry.
Despite the large number of benzo[c]phenanthridine
alkaloids and analogues sythesized, little progress has
been made in preparing compounds with substituents
directly next to the endocyclic nitrogen. In contrast to
synthetic methods already published,3-5 we found a
more efficient synthesis for benzo[c]phenanthridine
derivatives with an exocyclic primary amine group ortho
to the endocyclic nitrogen.6,7 We have reported previ-
ously about the synthesis of the benzo[c]phenanthridine
derivatives 1, 4, 6, 8, 32, and 37 and showed some
preliminary data including cytotoxic properties.7 In this
paper, we present the synthesis of a series of 11-
substituted 6-aminobenzo[c]phenanthridines and cor-
responding dihydro derivatives (Figure 2) as potential
antitumor agents. Selected compounds were evaluated
in terms of their cytotoxicity and antitumor properties
in the in vitro anticancer screening and the in vivo
hollow fiber assay of the National Cancer Institute.
Initial structure-activity relationship (SAR) studies
11-substituted 6-aminobenzo[c]phenanthridine perchlorates
(32-54).
focused on the effects of substitution in the 11-position
of the above-mentioned benzo[c]phenanthridine deriva-
tives.
Chemistry
The synthesis of the 6-amino-11,12-dihydrobenzo[c]-
phenanthridine derivatives 1-31 was accomplished in
a very simple manner by condensation of 2-methylben-
zonitrile with aromatic aldehydes in the presence of the
non-nucleophilic base potassium tert-butylate in 1,3-
dimethyltetrahydropyrimidin-2-one (DMPU) as solvent
and is summarized in Scheme 1.
The broad application of this synthetic pathway
allowed us to synthezise a variety of derivatives with
different substituents in position 11 of the benzo[c]-
phenanthridine ring system.
Dehydrogenation of the resulting dihydro derivatives
upon heating with 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (DDQ) in 1,4-dioxane yielded the corresponding
6-amino-benzo[c]phenanthridines 32-54 (Scheme 2).
Unexpectedly, the 6-amino-11,12-dihydrobenzo[c]-
phenanthridines were the main products when 2 equiv
* To whom correspondence should be addressed. Tel: 049-(0)431-
880 1126. Fax: 049-(0)431-880 1352. E-mail:
pharmazie.uni-kiel.de.
bclement@
10.1021/jm0490888 CCC: $30.25 © 2005 American Chemical Society
Published on Web 03/05/2005

11-Substituted 6-Aminobenzo[c]phenanthridines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8 2773
Scheme 1. Synthesis of the
6-amino-11,12-dihydrobenzo[c]phenanthridine
Derivatives 1-31a
Scheme 4a
a
Reagents: (i) DMPU, potassium tert-butylate.
Table 1. Retention Time Data of Several
6-Amino-11,12-dihydrobenzo[c]phenanthridines
eluent 85/15a
eluent 70/30a
compd
tR1 [min]b
tR2 [min]b
tR1 [min]b
tR2 [min]b
1
8.48
12.31
13.17
10.56
13.70
19.65
21.06
17.72
7.04
7.68
7.97
6.97
9.62
9.14
7.89
9.02
6.79
9.70
9.35
7.24
8.18
7.82
7.28
6.78
6.38
6.06
7.25
10.47
10.63
11.16
9.66
10.12
11.85
9.64
10.59
7.00
11.41
13.66
8.34
10.34
12.06
10.50
10.40
9.04
8.54
13.42
3
4
5
6
17.68-21.14c
8
17.76
12.94
19.12
11.79
23.92
25.39
17.72
24.32
12.8
10
13
14
15
16
17
18
19
20
21
24
25
26
29.44
26.35c
11.28
13.14
12.05
10.99
10.38
9.41
14.08
18.26
21.58
18.34
18.24
15.55
14.36
25.76
a Reagents: (i) DMPU, potassium tert-butylate.
Scheme 2. Synthesis of the
6-aminobenzo[c]phenanthridines 32-54a
8.62
10.81
a Eluent: 85/15 v/v or 70/30 v/v mixture of n-hexane and
i-propanol. b Retention time of the enantiomers 1 and 2. c No
separation of the enantiomers.
Biological Results and Discussion
In Vitro Antitumor Activity. The National Cancer
Institute (NCI) established a primary screen in which
compounds are tested in vitro to determine their growth
inhibitory properties against 60 different human tumor
cell lines organized in subpanels representing mela-
noma, leukemia, and cancers of breast, prostate, lung,
colon, ovary, kidney, and brain. Compounds 7, 8, 10,
13, 17, 27, 30, 31, 33-35, 37, 39, 48 were evaluated in
this Human Tumor Cell Line Screen. The experimental
procedures have been described in detail.9-12 For char-
acterizing the antitumor activity of a compound three
dose response parameters are calculated for each cell
line: The 50% growth-inhibitory concentration (GI50)
describes the concentration of the compound required
to cause 50% inhibition of net cell growth. The total
growth inhibition concentration (TGI) represents the
concentration of the compound resulting in total inhibi-
tion of net cell growth. The 50% lethal concentration
(LC50) indicates the concentration of the compound
leading to 50% net cell death. Values are calculated for
each of these three parameters if the level of effect is
reached. If the effect is not reached or is exceeded, the
value is expressed as greater or less than the maximum
or minimum drug concentration. Averaged values,
designated as meangraph midpoints (MG•MID), are
calculated for each of the mentioned parameters, giving
an averaged activity parameter over all cell lines.
Selective activity of a compound against cancer cell lines
from a special organ is characterized by a high deviation
of the particular cell line parameter compared to the
corresponding MG•MID value.
a Reagents: (i) DDQ, 1,4-dioxane.
Scheme 3a
a
Reagents: (i) DMPU, potassium tert-butylate.
of 2-methylbenzonitrile are used. In the presence of only
1 equiv of 2-methylbenzonitrile, 2-(2-phenylvinyl)ben-
zonitriles (Scheme 3) were formed according to the
method of Takahashi et al.8 Moreover, we could show
that the reaction of an isolated stilbene with 1 equiv of
2-methylbenzonitrile led also to the 6-amino-11,12-
dihydrobenzo[c]phenanthridines (Scheme 4).
The 11-substituted 6-amino-11,12-dihydrobenzo[c]-
phenanthridines were obtained as racemic mixtures.
The separation of the enantiomers was achieved by
high-pressure liquid chromatography using a CHIRA-
CEL-OD as chiral stationary phase. The results of the
analytical HPLC are outlined in Table 1. In all cases
1:1 mixtures of the two enantiomers were detected.

2774 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8
Kock et al.
Table 2. Selected Growth Inhibitory Properties of Tested Compounds in the NCI Cell Line Panel (Representative Data for Leukemia
Cell Lines and the Average GI50 Value over All Cell Lines)
log GI50 [M]a
GI50
compd
CCRF-CEMb
HL-60(TB)b
K-562b
MOLT-4b
RPMI-8226b
MG•MIDc
MG•MID [µM]d
7
-4.75
-5.95
-4.68
-5.58
-5.48
-4.86
-6.06
-5.45
-6.51
-6.54
-6.43
-6.77
-5.01
-5.39
-4.86
-5.15
-5.17
-5.77
-5.38
-5.09
-6.54
-5.26
-6.51
-7.20
-6.42
-7.21
-6.36
-5.35
-5.12
-5.55
-5.37
-6.09
-5.51
-5.79
-6.55
-5.51
-6.66
-7.10
-6.47
-7.34
-5.39
-6.10
-4.81
-5.53
-5.46
-5.58
-5.43
-4.84
-6.20
-5.32
-6.03
-6.43
-6.36
-6.63
-5.92
-5.48
-5.33
-5.62
-5.37
-5.74
-5.55
-5.30
-6.37
-5.48
-6.44
-6.62
-6.54
-6.90
-5.34
-5.55
-4.76
-5.41
-4.67
-5.50
-5.23
-4.92
-6.01
-5.50
-6.17
-6.56
-6.28
-6.74
-4.98
-5.45
16.22
3.89
21.38
3.16
5.89
12.02
0.98
3.16
0.68
0.28
0.52
0.18
10.47
3.55
8
10
13
17
27
30
31
33
34
35
37
39
48
a Log of molar concentration that inhibits 50% net cell growth. b Leukemia cell line. c MG•MID ) meangraph midpoint ) arithmetical
mean value for all tested cell lines. d The average GI50 value over the whole cell line panel.
Table 3. Activity in the in Vivo Hollow Fiber Assay
As indicated in Table 2, all tested compounds dem-
onstrated moderate to remarkable activity in the in vitro
antitumor screening, expressed by MG•MID GI50 val-
ues ranging from 21.38 µM (compound 10) to 0.18 µM
(compound 37). Compounds 30, 33-35, 37 possess
promising growth inhibitory properties with a mean
GI50 across all cell lines < 1 µM. The 3,4-dimethoxyphe-
nyl-substituted derivative 37 is the most active com-
pound with a log MG•MID GI50 value of -6.7, which
is a very good result compared to potent standard
compounds such as doxorubicin (-6.9) and camptothecin
(-7.3).13
compd
total score
ip score
sc score
cell kill
10
13
33
34
35
37
39
20
16
10
28
12
8
10
6
2
14
4
6
6
10
10
8
14
8
2
8
yes
yes
yes
yes
yes
no
14
no
to the tested compound in their patterns of activity
against the panel of 60 cell lines. Similarity in pattern
often indicates similarity in mechanism of action and
molecular structure.14 In this analysis, a Pearson cor-
relation coefficient (PCC) > 0.60 is considered signifi-
cant. COMPARE analysis indicated that the most
growth-inhibitory compounds 33-35, 37 and also com-
pounds 8, 13, 17 shared a response pattern with
antimitotic agents, particularly an interaction with
tubulin, whereas compounds 10 and 39 did not show
correlations with any agents of the NCI database.
Indeed, the derivatives 33 and 34 could be assigned
clearly to the group of agents interacting with tubulin
while the remaining compounds 8, 13, 17, 35, 37
displayed no such strong correlations as the above-
mentioned derivatives. We will try to relate derivatives
33 and 34 to structures that were found in an earlier
study toward identification of antimitotic agents from
the NCI database.15
Initial structure-activity relationship (SAR) studies
focused on the effects of substitution in the 11-position.
Within the dehydro series compounds with methoxy-
phenyl substituents (33-35, 37) showed enhanced
activity compared with those compounds with a furyl
(39) or methylenedioxyphenyl (48) substituent. There-
fore, methoxy groups appeared to be the most favorable
to generate significant antiproliferative acitvity, whereas
introduction of a heterocycle resulted in reduced anti-
tumor potency. For the dihydro series such general
structure-activity relationships could not be found.
However, the 4-hydroxy-3,5-dimethoxyphenyl-substitu-
ed derivative 30 is the most potent one in this series
with a MG•MID GI50 value of 0.98 µM. The derivative
13 (MG•MID GI50: 3.16 µM), bearing a 3,4,5-tri-
methoxyphenyl substituent in the 11-position, was
slightly less potent than 30. These results indicate that
replacement of the methoxy group in the para position
of the phenyl substituent by a hydroxy group produced
an increase of antitumor activity. In contrast to the
dihydro compounds the corresponding dehydro deriva-
tives generally exhibited higher antitumor activity. This
enhanced potency may be explained by the planarity of
the benzo[c]phenanthridine ring system. Accordingly,
DNA intercalation could be assumed as the mechanism
of action for the dehydro derivatives. Most of the
compounds showed selectivity toward cell lines from
leukemia, breast, and prostate subpanel. Cell lines from
lung, ovary, and melanoma subpanel were generally less
sensitive to the compounds.
Among the series of compounds evaluated in the in
vitro screen, derivatives 10, 13, 33-35, 37, 39 were
selected for further in vivo trials.
In Vivo Antitumor Activity. The hollow fiber assay
is used as the initial in vivo experience for compounds
found to have reproducible activity in the in vitro
anticancer drug screen and provides quantitative indices
of drug efficacy.16 The results of the antiproliferative
activity for all tested compounds are listed in Table 3.
Compounds with a combined ip + sc score g20, a sc
score g8 or a net cell kill of one or more cell lines were
considered significantly active.
The derivatives 10 and 34 exhibited a combined ip +
sc score g20, while all compounds except derivative 37
displayed a sc score g8. Indeed, the 3,4,5-trimethoxy-
phenyl-substituted dehydro derivative 34 is the most
potent compound representing the highest score on the
COMPARE Analysis. The patterns of activity of
compounds 8, 10, 13, 17, 33-35, 37, 39 were analyzed
by the COMPARE algorithm. COMPARE searches the
NCI database of screened agents for those most similar

11-Substituted 6-Aminobenzo[c]phenanthridines
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8 2775
Table 4. Yields, Melting Points, and Systematic Names of All Synthesized Compounds
compd
name
yield [%]
mp [°C]
1
6-amino-11,12-dihydro-11-phenylbenzo[c]phenanthridinium chloride
52
81
60
66
49
53
56
57
36
64
29
27
60
30
36
38
62
38
66
43
70
62
53
49
81
38
28
26
23
40
89
50
45
44
51
42
38
48
35
52
41
47
41
57
58
56
42
45
48
13
15
18
4
355
2
6-amino-11,12-dihydro-11-(2-methoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3-methoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-methoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2,3-dimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2,4-dimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2,5-dimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3,4-dimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3,5-dimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2,3,4-trimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2,4,5-trimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2,4,6-trimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3,4,5-trimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2-pyridyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3-pyridyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-pyridyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2-furyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2-thienyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3-bromophenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-chlorophenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-fluorophenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(2-ethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-ethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-methylphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-[4-(2-propyl)phenyl]benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(1-naphthyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3-hydroxy-4-methoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-hydroxy-3-methoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3-hydroxy-2,4-dimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(4-hydroxy-3,5-dimethoxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11,12-dihydro-11-(3,4-methylenedioxyphenyl)benzo[c]phenanthridinium chloride
6-amino-11-phenylbenzo[c]phenanthridinium perchlorate
339
3
288
4
286
5
210
6
205
7
318
8
249
9
308
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
283
298
246
272
238-240
248 (dec)
248
248
232
271 (dec)
263
312
325
273
230
278
265
212
324
327
225 (dec)
293
326
6-amino-11-(2,4-dimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(3,4,5-trimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(2,3,4-trimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(2,3-dimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(3,4-dimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(3-methoxyphenyl)benzo[c]phenanthridinium perchlorate
336
296
289 (dec)
287
290
305
6-amino-11-(2-furyl)benzo[c]phenanthridinium perchlorate
274
6-amino-11-(2-thienyl)benzo[c]phenanthridinium perchlorate
297
6-amino-11-(1-naphthyl)benzo[c]phenanthridinium perchlorate
332
6-amino-11-(4-methylphenyl)benzo[c]phenanthridinium perchlorate
293
6-amino-11-(4-chlorophenyl)benzo[c]phenanthridinium perchlorate
338
6-amino-11-(4-fluorophenyl)benzo[c]phenanthridinium perchlorate
330
6-amino-11-(3-bromophenyl)benzo[c]phenanthridinium perchlorate
286 (dec)
306
6-amino-11-(2,4,5-trimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(2-ethoxyphenyl)benzo[c]phenanthridinium perchlorate
304
6-amino-11-(3,4-methylenedioxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(2,5-dimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(4-ethoxyphenyl)benzo[c]phenanthridinium perchlorate
319
291
305
6-amino-11-(3,5-dimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(2,4,6-trimethoxyphenyl)benzo[c]phenanthridinium perchlorate
6-amino-11-(2-methoxyphenyl)benzo[c]phenanthridinium perchlorate
334
316
341
6-amino-11-(4-methoxyphenyl)benzo[c]phenanthridinium perchlorate
14
328
in vivo assay. Compounds with a trimethoxyphenyl
group in the 11-position (10, 13, 34, 35) contributed to
high antiproliferative activity, whereas compounds bear-
ing a dimethoxyphenyl substituent (33, 37) generally
showed less potency. Therefore, trimethoxyphenyl sub-
stituents in the 11-position seem to be an important
feature leading to higher antitumor potencies. In con-
trast to the in vitro results, the dihydro derivatives 10
and 13 displayed an enhanced activity in this in vivo
study compared with most of the dehydro derivatives.
Planarity of the ring system is apparently not required
to ensure significant cytotoxicity in vivo. Due to these
results the DNA intercalation as a mechanism of action
is rather improbable. In this case it had to be expected
that the dehydro derivatives show stronger effects
related to their planar ring system. The deviating
antitumor activities could be explained by an antimitotic
mechanism for most of the compounds as shown in
COMPARE analysis. Moreover, corresponding to our
derivatives the antimitotic agents colchicin and podo-
phyllotoxin contain trimethoxyphenyl groups. These
trimethoxyphenyl groups interact with a specific region
of tubulin and are able to inhibit polymerization of
tubulin.17 As compounds with a trimethoxyphenyl sub-
stituent were the most potent ones in the in vivo hollow
fiber assay, an antimitotic mechanism of action could
be postulated.
Conclusions
A method for the synthesis of novel benzo[c]phenan-
thridine derivatives was developed. In contrast to other
more complicated methods the compounds were pre-
pared in a simple one step synthesis by the reaction of
2-methylbenzonitrile and aromatic aldehydes. By this

2776 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 8
Kock et al.
bonate and several times with water. The organic layer was
dried over sodium sulfate. After evaporation of the solvent,
perchloric acid (70%) was added with vigorous stirring to
obtain the 11-substituted 6-aminobenzo[c]phenanthridinium
perchlorates. The precipitate was collected, washed with
diethyl ether, and crystallized from methanol.
procedure a series of 6-amino-11,12-dihydrobenzo[c]-
phenanthridines 1-31 was synthesized, showing the
broad applicability of this synthetic method. These
compounds could easily be converted into the corre-
sponding dehydro derivatives 32-54.
Furthermore, the synthesized compounds exhibited
remarkable antitumor activities in in vitro and in vivo
assays. These derivatives are therefore under develop-
ment as potential antitumor agents. Structure-activity
relationships within the dehydro series revealed that
methoxyphenyl substituents in the 11-position lead to
derivatives with enhanced activity. By COMPARE
analysis an interaction with tubulin as antimitotic
mechanism could be postulated. The mechanism of the
antitumor activity is the subject of further investiga-
tions.
Yields, melting points and systematic names of all synthe-
sized compounds are listed in Table 4.
Acknowledgment. The authors thank the Devel-
opmental Therapeutics Program of the National Cancer
Institute, Bethesda, MD, for providing the in vitro and
in vivo antitumor screening data. Special thanks are due
to Dr. Dan Zaharevitz for helpful discussions. We
acknowledge the excellent experimental assistance of
M. Ko¨nig. We also thank Dr. U. Girreser for NMR and
MS spectral experiments. The financial support of the
Fonds der chemischen Industrie is greatly appreciated.
Experimental Section
Supporting Information Available: Spectroscopic data
(1H NMR, 13C NMR, IR, MS) and elemental analysis results.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Melting points were determined with a Bu¨chi 510 melting
point apparatus and on a Thermowar microhotstage and are
reported uncorrected. 1H NMR spectra were obtained on a
Bruker ARX 300 spectrometer at 300 K. Chemical shifts (δ
values) are reported in ppm using TMS as internal standard.
All coupling constants (J values) are quoted in Hz. The
following NMR abbreviations are used: br (broad), s (singlet),
d (doublet), t (triplet), m (unresolved multiplet), Ar (aromatic
proton). IR spectra (as KBr disks) were determined on a
Perkin-Elmer FT-IR 16 PC spectrometer and are expressed
in cm-1. Electron impact mass spectra (70 eV) were recorded
on a Hewlett-Packard 5989 A mass spectrometer. The relative
intensities of the peaks are listed in parentheses. Elemental
analyses were performed by the Microanalytical laboratory of
Ilse Beetz, Kronach, Germany, and were within (0.4% of the
theoretical values unless indicated otherwise. All reagents
were purchased from commercial sources and used without
further purification.
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