Synthesis and physicochemical characterization of novel 6-aminopyrido[3,4-c][1,9]phenanthrolines as aza-analogs of benzo[c] phenanthridines

Article abstract of DOI:10.1016/j.tet.2012.08.047

Based on the 6-aminobenzo[c]phenanthridines, a compound class showing noteworthy antitumor activity, an efficient one-step synthesis consisting of a base-catalyzed condensation of 2 equiv of 4-methylpyridine-3-carbonitrile and various aldehydes causing twofold ring closure is described. The obtained 6-amino-11,12-dihydropyrido[3,4-c][1,9]phenanthrolines could be aromatized with Pd/C at high temperatures to form 6-aminopyrido[3,4-c][1,9]phenanthrolines. All compounds were systematically characterized regarding both lipophilicity and solubility and a high cytotoxic potential was evaluated in preliminary in vitro studies. Compared to formerly described 6-aminobenzo[c]phenanthridines our newly developed phenanthrolines turned out to possess improved drugability, due to significantly increased water-solubility and decreased lipophilicity.

Full text of DOI:10.1016/j.tet.2012.08.047

Tetrahedron 68 (2012) 9105e9112
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Synthesis and physicochemical characterization of novel 6-aminopyrido[3,4-c]
[1,9]phenanthrolines as aza-analogs of benzo[c]phenanthridines
*
Christopher Meier, Joscha Kotthaus, Lars Stenzel, Ulrich Girreser, Dieter Heber, Bernd Clement
Pharmaceutical Institute, Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Gutenbergstraße 76, 24118 Kiel, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 May 2012
Received in revised form 9 August 2012
Accepted 16 August 2012
Available online 28 August 2012
Based on the 6-aminobenzo[c]phenanthridines, a compound class showing noteworthy antitumor ac-
tivity, an efficient one-step synthesis consisting of a base-catalyzed condensation of 2 equiv of 4-
methylpyridine-3-carbonitrile and various aldehydes causing twofold ring closure is described. The
obtained 6-amino-11,12-dihydropyrido[3,4-c][1,9]phenanthrolines could be aromatized with Pd/C at
high temperatures to form 6-aminopyrido[3,4-c][1,9]phenanthrolines. All compounds were systemati-
cally characterized regarding both lipophilicity and solubility and a high cytotoxic potential was evalu-
ated in preliminary in vitro studies. Compared to formerly described 6-aminobenzo[c]phenanthridines
our newly developed phenanthrolines turned out to possess improved drugability, due to significantly
increased water-solubility and decreased lipophilicity.
Keywords:
Pyrido[3,4-c][1,9]phenanthrolines
Benzo[c]phenanthridines
Aza-analog
Ó 2012 Elsevier Ltd. All rights reserved.
Solubility
Heterocycles
Cytotoxicity
12
12
1. Introduction
R 11
R 11
Naturally occurring benzo[c]phenanthridine alkaloids have
been extensively studied in the last decades and are of particular
interest due to their antitumor, antimicrobial, and antiviral prop-
erties.1,2 Regarding the antitumor activity, the alkaloids nitidine and
fagaronine were determined as model compounds for the de-
velopment of DNA topoisomerase I inhibitors with a non campto-
thecin skeleton.3 Current papers set focus on the design of
derivatives containing additional nitrogen atoms in the basic tet-
racyclic ring system and often exhibit an aminoalkyl side chain both
to increase the cytotoxicity and higher the solubility in aqueous
media.4e6 The aza-analogous benzo[c]phenanthridines ARC-111
(Topovale) and its N-monomethyl derivative are presently in clin-
ical trials.3,7
In recent years our laboratory developed an efficient method for
the synthesis of 11-substituted 6-aminobenzo[c]phenanthridines
and corresponding dihydro derivatives (Scheme 1).8,9 The broad
applicability and the simple handling of this procedure allowed us
to prepare a variety of derivatives with different substituents
through condensation of 2 equiv of 2-methyl-benzonitriles with
aromatic aldehydes in the presence of potassium tert-butylate in
1,3-dimethyltetrahydropyrimidin-2-one (DMPU) as solvent.10e12
N3
8 N
N5
N5
6
6
NH2
NH2
Scheme 1. Comparison of 6-aminopyrido[3,4-c][1,9]phenanthro-lines (left) and 6-
aminobenzo[c]phenanthridines (right).
Moreover, applying this novel reaction method we successfully
designed a four-step procedure to provide the benzo[c]phenan-
thridine skeleton.13 Our compounds turned out to exhibit consid-
erable cytotoxicity and antitumor properties in the in vitro
anticancer screening and the in vivo hollow fiber assay of the Na-
tional Cancer Institute, Maryland, USA.13 Derivatives with di- or
trimethoxyphenyl substituents in the 11-position led to com-
pounds with enhanced cytotoxicity showing GI50-values<1
mM
over the whole cell line panel in the 60-tumor-cell-line-screening
of the NCI.14 However, an essential drawback of the 6-aminobenzo
[c]phenanthridines and compounds possessing the benzo[c]phe-
nanthridine skeleton in general that are known so far is their very
poor water solubility limiting the application in test assays as well
as subsequent pharmaceutical use.15 Previous attempts dealing
with the improvement of drugability and thus water solubility were
focused on the modification of the 6-amino-function with basic or
acidic substitutions.16 In this work, we tried to overcome poor
* Corresponding author. Tel.: þ49 431 08801126; fax: þ49 431 8801352; e-mail
address: bclement@pharmazie.uni-kiel.de (B. Clement).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.08.047

9106
C. Meier et al. / Tetrahedron 68 (2012) 9105e9112
water solubility by introducing nitrogen atoms into the skeleton
and decided to apply 4-methylpyridine-3-carbonitrile 2 as a pyri-
dine-analog of 2-methylbenzonitrile as educt. The resulting com-
pounds, 6-aminopyrido[3,4-c][1,9]phenanthrolines and their 11,12-
dihydro derivatives, are novel heterocycles containing 3 nitrogen-
atoms at ring positions 3, 5, and 8, as well as an amino-group at
position 6.
4a: R¼phenyl
4f: R¼3,4,5-trimethoxyphenyl
4h: R¼furyl
4b: R¼3-methoxyphenyl
4d: R¼2,3-dimethoxyphenyl
2.2. Determination of lipophilicity
Lipophilicity (logP) of phenanthroline derivatives wasdwith
exception of the biphenyl derivative 3n (logP: 5.78)ddetermined
to be in the range of 2.34e4.91. The calculated lipophilicities (clogP)
are in accordance to the logP-values determined experimentally for
series 3 and 4 (Table 1). The lowest lipophilicity is observed for the
2. Results & discussion
2.1. Synthesis
The synthesis was carried out using various aldehydes
1
and
nitrogen atmosphere and room temperature, leading to 6-amino-
11,12-dihydropyrido[3,4-c][1,9]phenanthrolines as racemates
2 equiv of 4-methylpyridine-3-carbonitrile 2 under
Table 1
3
Calculated and determined logP values of certain phenanthroline derivatives with
different substituents in 11-position
(Scheme 2). This procedure allows a wide range of different sub-
stituents in position 11 according to the specific aldehydes that
were used. In this connection, aromatic aldehydes afforded the best
yields, but also aliphatic aldehydes as well as para-formaldehyde
could be used.
3
4
R
CH3
Compound
Residue
Yield [%]
55
logPa
clogPa
KO(t-Bu)
O
CN
DMPU
N
2
+
R
H
N
N
NH2
3
3a
3.34
3.34
25-40°C
N2
N
2
1
4a
3b
89
42
d
3.70
3.26
Scheme 2. Synthesis of 11-substituted 6-aminopyrido[3,4-c][1,9]phenanthrolines 3.
3.77
4b
3d
58
33
d
3.62
2.60
Synthesized 6-amino-11,12-dihydropyrido[3,4-c][1,9]phenanthrolines 3aep:
3.74
3a: R¼phenyl
3i: R¼thienyl
3b: R¼3-methoxyphenyl
3c: R¼4-methoxyphenyl
3d: R¼2,3-dimethoxyphenyl
3e: R¼3,5-dimethoxyphenyl
3f: R¼3,4,5-trimethoxyphenyl
3g: R¼2,4,6-trimethoxyphenyl
3h: R¼furyl
3j: R¼3-bromophenyl
3k: R¼4-bromophenyl
3l: R¼3-chlorophenyl
3m: R¼4-fluorophenyl
3n: R¼biphenyl
4d
3e
4e
3f
72
69
d
3.93
3.35
d
2.80
3.35
3.71
2.64
3.00
2.54
2.58
2.52
3o: R¼propyl
3p: R¼H
Raising the temperature up to 80 ꢀC without inert gas we could
determine the 11,12-dehydrogenated type as the main product but
the conversion was not complete. Moreover, dehydrogenation of 3
to obtain the fully aromatic system using DDQ in various sol-
vents8,9,14 failed. Heating the compounds in the presence of 30% Pd/
charcoal without a solvent,17 the results were non-satisfying re-
garding the yields and long reaction times. However, we finally
developed an oxidation method in boiling the 6-amino-11,12-
dihydro-pyrido[3,4-c][1,9]phenanthrolines 3 with Pd (10%)/C in
DMPU for 10e30 min under reflux and nitrogen atmosphere giving
28
75
63
d
2.34
3.94
4.78
d
4f
3g
4g
3h
6-aminopyrido[3,4-c][1,9]-phenanthrolines
4
in good yields
67
2.72
(Scheme 3).
4h
3i
63
54
2.93
2.84
3.09
2.99
R
R
Pd/C
DMPU
N
N
4i
3j
4j
d
19
d
d
3.56
4.21
4.57
N
N
reflux
N2
N
N
NH2
NH2
4.20
d
3
4
Scheme 3. Synthesis of 11-substituted 6-aminopyrido[3,4-c][1,9]-phenanthrolines 4.

C. Meier et al. / Tetrahedron 68 (2012) 9105e9112
9107
bioavailability.15,16 Previous studies determined solubility of several
6-aminobenzo[c]phenanthridines to be in the nanomolar range.16
For example, solubility of the phenanthridine analogues of 3d
Table 1 (continued )
Compound
Residue
Yield [%]
logPa
clogPa
and 3h at pH 7.0 is (16ꢁ2)ꢂ10ꢃ9 mol Lꢃ1 and (66ꢁ5)ꢂ10ꢃ9 mol Lꢃ1
,
respectively.16 In this work, we tried to overcome this fundamental
drawback by incorporating two additional nitrogen atoms into the
aromatic ring systems and investigated solubility at different pH.
Thereby, all compounds showed pH-dependent solubility with
manifestly enhanced solubility especially in acidic media (Fig. 2,
different scaling at the y-axis). On the basis of the significantly
decreased lipophilicities, we also expected improved solubility at
slight acidic and neutral media. At pH 7.4 solubility of 3d and 3h is
3k
4k
3l
37
d
32
d
30
d
28
d
21
d
4.60
d
4.21
4.57
4.06
4.42
3.49
3.85
5.23
5.59
3.36
3.37
4.91
d
4l
determined to be (8ꢁ2)ꢂ10ꢃ6 mol Lꢃ1 and (6.5ꢁ0.8)ꢂ10ꢃ6 mol Lꢃ1
,
respectively. Thus, compared to the data mentioned above, our 6-
aminopyrido[3,4-c][1,9]phenanthrolines 3 show significantly im-
proved solubility.
3m
4m
3n
4n
3o
3.58
d
2.4. Evaluation of drug-likeness in silico
5.78
d
The drug-likeness of all derivatives was evaluated according to
Lipinski’s rule of five to get first hints regarding a possible oral
bioavailability via passive absorption from the intestine. A com-
pound is expected to be oral available if no more than one criteria is
violated: molecular weight below 500 g molꢃ1, number of hydro-
gen bond donors below 5, hydrogen bond acceptors below 10, and
4.65
d
logP not greater than 5.18 However, all 6-amino-11,12-
4o
a
a
dihydropyrido[3,4-c][1,9]phenanthrolines 3 and 4 presented in
this work are anticipated to possess sufficient oral bioavailability,
because all parameters are in accordance to the rule of five.
For comparison logP and clogP are given for classes 3 and 4 (if determined).
3,4,5-trimethoxy derivative 3f (2.34), followed by the furan de-
rivative 3h (2.72), and the thiophene derivative 3i (2.84).
2.5. Cytotoxicity
Moreover, we analogously investigated six 6-aminobenzo[c]-
phenanthridines BP to draw a reasonable conclusion regarding
reduction of lipophilicity. Results demonstrate a considerably de-
creased lipophilicity (mean: 3.58e5.28) compared to the formerly
described BP derivatives (mean: 4.13e6.13). For details see Fig. 1.
To evaluate the biological potential of the 6-amino-pyrido[3,4-c]
[1,9]phenanthrolines 4 and its 11,12-dihydro- derivatives 3 pre-
liminary in vitro cytotoxicity studies were performed by the U.S.
National Cancer Institute (NCI) revealing a high cytotoxic potential.
In the ‘NCI-60 DTP Human Tumor Cell Line Screening’ 60 tumor cell
lines from nine different types of cancer were treated with the
substances to reveal doseeresponse-relations. As one important
parameter determined in the test, the MG_MID (meangraph mid-
point) is the mean of the logarithms of the GI50 values (growth
inhibition 50%) and corresponds to an average response charac-
teristic of all 60 cell lines to the test substance.9
8
Phenathrolines
Phenanthridines
6
Taking the antilogarithm of this value gives the mean of the GI50
values over all cell lines.19 Table 2 indicates a cytostatic activity
(expressed by the GI50-value) for the two compounds 3l (3.80
m
M)
M) comparable to the natural occurring alkaloids
M) and fagaronine (9.48 M) and even better GI50
M) and 4h
and 3o (4.02
nitidine (1.78
m
m
4
2
0
m
-
values for the fully aromatized compounds 4f (0.76
m
(1.74
m
M) were found.20
3. Conclusions
In this work, we successfully designed a novel class of cyto-
statically active 6-amino-11,12-dihydropyrido[3,4-c][1,9]-phenan-
throline derivatives 3. The synthesis used allows a wide range of
different substituents in 11-position that can lead to a large library
of potentially cytostatic substances. These derivatives could be
easily aromatized in good yields to 6-aminopyrido[3,4-c][1,9]phe-
nanthrolines 4 with an optimized oxidation method. First in-
vestigations concerning lipophilicity and solubility show
interesting results indicating a good suitability of this compound
class as a pharmaceutical. Extended studies concerning the cyto-
toxicity are underway bearing promising data. Actual synthetic
strategies in our group are focussed on the variation of the amino
group in 6-position like the linking of (amino)alkyl-side chains or
-
-
-
-
l
l
l-
eny
l
n
a
yl
no-
a
Fur
Me
Pheny
omophen
4-Br 3-Chlor
ph
o
pheny
opheny
Fluor
4-
imethoxy
r
residue at C-11
5-T
4,
3,
Fig. 1. Summary of logP values (3 and BP) determined by HPLC analysis.
2.3. Determination of solubility
We set focus on the solubility of our newly discovered de-
rivatives, because recently published 6-aminobenzo[c]phenan-
thridine derivatives are known to suffer from very poor solubility
that often limits use in test assays and possibly reduces oral

9108
C. Meier et al. / Tetrahedron 68 (2012) 9105e9112
25000
20000
15000
10000
5000
0
2500
pH 2.0
pH 3.0
2000
1500
1000
500
0
3a 3b 3d 3e 3f 3g 3h 3i
3j 3k 3l 3m 3n 3o
3a 3b 3d 3e 3f 3g 3h 3i
3j 3k 3l 3m 3n 3o
600
500
400
300
200
100
0
18
16
14
12
10
8
pH 4.0
pH 7.4
6
4
2
0
3a 3b 3d 3e 3f 3g 3h 3i
3j 3k 3l 3m 3n 3o
3a 3b 3d 3e 3f 3g 3h 3i
3j 3k 3l 3m 3n 3o
Fig. 2. Solubility of phenanthroline derivatives 3 in phosphate buffer at different pH values.
Table 2
Elmer Spectrum 100 FTIR instrument with ATR attachment. Ele-
mental analysis were performed by the Department of Inorganic
Chemistry, Christian-Albrechts-University of Kiel with a CHNS
Analyserr of HEKAtech GmbH, High resolution mass spectra were
recorded on a LTQ Velos Orbitrap mass spectrometer equipped with
a nano electrospray source in positive mode at the Institute of Ex-
perimental Medicine, University Hospital, Kiel.
Cytotoxic activity of phenanthroline derivatives 3 and 4 and selected derivatives
from DTP-60 screening by the NCI20
P
4.07
0.76
1.74
9.48
1.78
Compound
MG_MID
GI50=60 ½ Mꢄ
3.80
m
3l
3o
4f
4h
ꢃ5.42
ꢃ5.39
ꢃ6.12
ꢃ5.76
ꢃ5.02
ꢃ5.75
Fagaronine
Nitidine
4.2. General procedure for the synthesis of the 6-amino-11,12-
dihydropyrido[3,4-c][1,9]phenanthrolines
its removal to obtain the unsubstituted heterocycles. Future studies
will be performed dealing with efficacy to further characterize
these newly identified compounds.
A solution of 1 (2.1 mmol) and 2 (4.2 mmol) in 10 ml DMPU was
added dropwise to KO(t-Bu) (500 mg, 4.4 mmol) in 5 ml DMPU
while the solution was magnetically stirred under N2 at 25e40 ꢀC.
The mixture was stirred for 1e3 h and then hydrolyzed in 80 ml of
ice water. The precipitate formed during hydrolysis was collected
by filtration. The filtrate was extracted with CH2Cl2 (3ꢂ50 ml). The
combined organic extracts were dried (Na2SO4) and concentrated
in vacuo. DMPU was removed by distillation at high vacuum at
100e110 ꢀC. The resulting residue was collected by filtration. The
combined crude products were either recrystallized from MeOH/
CH2Cl2 or, if necessary, purified by column chromatography (silica
gel, CH2Cl2/MeOH (5e20%)).
4. Experimental section
4.1. General
All reactions were carried out in oven-dried glassware. The
solvents (except DMPU) were freshly distilled. All commercial re-
agents were used without purification. Melting points were de-
termined on a Stuart Scientific SMP3 melting-point apparatus, and
are uncorrected. 1H and 13C NMR spectra were recorded on a Bruker
Avance III 300 instrument at 300 K. Chemical shifts are given in
parts per million relative to solvent residual peaks. Mass spectra
were recorded on a Bruker EsquirewLC instrument under ESI
conditions or on a Hewlett Packard MS-Engine 5989 A under EI
conditions (70 eV). IR-spectroscopy was carried out using a Perkin
4.2.1. 6-Amino-11-phenyl-11,12-dihydropyrido[3,4c][1,9]phenan-
throline (3a). The reaction of benzaldehyde (223 mg, 2.1 mmol)
with 2 (500 mg, 4.2 mmol) at room temperature for 3 h afforded
compound 3a. C21H16N4, yield: 373 mg (55%, recrystallized from
MeOH/CH2Cl2); solid; mp 279 ꢀC under decomp.; 1H NMR

C. Meier et al. / Tetrahedron 68 (2012) 9105e9112
9109
2
(300 MHz, DMSO-d6):
d
¼3.15 (d, 1H, H-12a, JH-12a/H-12b¼16.5 Hz),
137.2, 138.1, 141.5, 142.8, 144.0, 145.2, 147.7, 152.5, 156.6, 158.3; IR
(ATR, cmꢃ1): 3415, 3306, 3148, 2929, 1648, 1601, 1453, 1075,
1005; MS (ESI) m/z: 385 ([MþH]þ, 100%), 247 ([Mꢃ2,3-
dimethoxybenzene]þ, 8%), 193 ([Mþ2H]þþ, 57%), 185 (8%), 124
([Mꢃ2,3-dimethoxybenzeneþ2H]þþ, 14%); HRMS (ESI) m/z calcd
for [MþH]þ 385.16589, found 385.16565.
3.54 (dd, 1H, H-12b, 2JH-12b/H-12a¼16.3 Hz, 3JH-12b/H-11¼7.6 Hz), 4.86
3
(d, 1H, H-11, JH-11/H-12b¼7.3 Hz), 7.09 (m, 5H, phenyl), 7.18 (d, 1H,
AreH, 3J¼4.9 Hz), 7.45 (br s, 2H, eNH2), 7.55 (d, 1H, AreH,
3J¼6.0 Hz), 8.39 (d, 1H, AreH, 3J¼4.9 Hz), 8.54 (d, 1H, AreH,
3J¼5.9 Hz), 9.36 (s, 1H, AreH), 9.57 (s, 1H, AreH); 13C NMR (75 MHz,
DMSO-d6):
d
¼35.2 (C-12), 35.9 (C-11), 112.8, 114.1, 115.7, 123.3,
126.3, 127.1 (2C), 128.4 (2C), 129.9, 139.3, 143.0, 144.1, 145.7, 145.9,
147.7, 149.1, 149.6, 157.1; IR (ATR, cmꢃ1): 3330, 3170, 3060, 2902,
1652,1612,1599,1449,1045; MS (ESI) m/z: 325 ([MþH]þ,100%),163
([Mþ2H]þþ, 35%); HRMS (ESI) m/z calcd for [MþH]þ 325.14476,
found 325.14465.
4.2.5. 6-Amino-11-(3,5-dimethoxyphenyl)-11,12-dihydropyrido[3,4-
c]-[1,9]phenanthroline (3e). 3,5-Dimethoxybenzaldehyde (349 mg,
2.1 mmol), rt, 2 h, C23H20N4O2, yield: 557 (69%, recrystallized from
MeOH/CH2Cl2); solid, mp 258 ꢀC; 1H NMR (300 MHz, DMSO-d6):
d
¼3.14 (d, 1H, H-12a, 2JH-12a/H-12b¼16.3 Hz), 3.50 (dd, 1H, H-12b, 2JH-
¼16.2 Hz, 3JH-12b/H-11¼7.6 Hz), 3.56 (s, 6H, 2ꢂ OCH3), 4.77 (d,
12b/H-12a
4.2.2. 6-Amino-11-(3-methoxyphenyl)-11,12-dihydropyrido[3,4c]
[1,9]-phenanthroline (3b). 3-Methoxybenzaldehyde (286 mg,
2.1 mmol), rt, 2.5 h, C22H18N4O, yield: 312 mg (42%, recrystallized
1H, H-11, 3JH-11/H-12b¼7.3 Hz), 6.11 (m, 2H, H-20, H-60, 4J¼2.2 Hz), 6.23
(m, 1H, H-40, 4J¼2.2 Hz), 7.20 (d, 1H, AreH, 3J¼4.9 Hz), 7.46 (br s, 2H,
eNH2), 7.57 (d, 1H, AreH, 3J¼5.9 Hz), 8.41 (d, 1H, AreH, 3J¼4.9 Hz),
8.56 (d, 1H, AreH, 3J¼5.9 Hz), 9.35 (s, 1H, AreH), 9.58 (s, 1H, AreH);
from MeOH/CH2Cl2); solid; mp 259 ꢀC under decomp.; 1H NMR
2
(300 MHz, DMSO-d6):
d
¼3.15 (d, 1H, H-12a, JH-12a/H-12b¼16.4 Hz),
13C NMR (75 MHz, DMSO-d6):
d¼35.0 (C-12), 36.1 (C-11), 54.8 (2C, 2ꢂ
3.52 (dd, 1H, H-12b, 2JH-12b/H-12a¼16.4 Hz, 3JH-12b/H-11¼7.7 Hz), 4.82
(d, 1H, H-11, 3J¼7.6 Hz), 6.46e6.53 (m, 1H, AreH, 3J¼7.8 Hz,
4J¼0.9 Hz), 6.55e6.60 (m, 1H, AreH), 6.61e6.68 (m, 1H, AreH,
3J¼8.1 Hz, 4J¼0.8 Hz), 7.01 (m, 1H, AreH, 3J¼7.9 Hz), 7.19 (d, 1H,
AreH, 3J¼4.9 Hz), 7.45 (br s, 2H, eNH2), 7,56 (d, 1H, AreH,
3J¼5.9 Hz), 8.40 (d, 1H, AreH, 3J¼4.9 Hz), 8.55 (d, 1H, AreH,
3J¼5.9 Hz), 9.35 (s, 1H, AreH), 9.57 (s, 1H, AreH); 13C NMR (75 MHz,
OCH3), 97.3,105.6 (2C, C-20, C-60), 112.7, 114.1, 115.7, 123.3, 130.0, 139.3,
144.3, 145.4, 145.6, 145.9, 147.7, 149.1, 159.6, 157.1, 160.3 (2C, C-30, C-50);
IR (ATR, cmꢃ1): 3325, 3168, 2969, 2828, 1650, 1595, 1452, 1318, 1067.
MS (ESI) m/z: 385 ([MþH]þ,100%), 247 (Mꢃ3,5-dimethoxybenzeneþ,
2%), 193 ([Mþ2H]þþ, 73%); Anal. calcd for C23H20N4O2: C, 71.86; H,
5.24; N, 14.57, found: C, 71.34; H, 5.22; N, 14.43.
DMSO-d6):
d
¼35.1 (C-12), 35.9 (C-11), 54.7 (OCH3), 111.1, 112.7,
4.2.6. 6-Amino-11-(3,4,5-trimethoxyphenyl)-11,12-dihydropyrido[3,4-
c][1,9]phenanthroline (3f). 3,4,5-Trimethoxybenzaldehyde (392 mg,
2.1 mmol), 35 ꢀC, 3 h, C24H22N4O3, yield: 87 mg (28%, silica gel,
113.5, 114.1, 115.7, 119.3, 123.3, 129.4, 129.9,139.3,144.2,144.6, 145.7,
145.9, 147.7, 149.1, 149.6, 157.1, 159.1; IR (ATR, cmꢃ1): 3326, 3170,
3082, 2930, 1651, 1598, 1454, 1061, 821; MS (ESI) m/z: 355 ([MþH]þ,
100%), 178 ([Mþ2H]þþ, 16%), 129 (13%), 124 ([Mꢃ3-methoxy-
benzeneþ2H]þþ, 4%). Anal. calcd for C22H18N4O: C, 74.56; H, 5.12; N,
15.81, found: C, 74.04; H, 4.78; N, 15.75.
CH2Cl2/MeOH (5e20%)), mp 219 ꢀC under decomp.; 1H NMR
2
(300 MHz, DMSO-d6):
d
¼3.18 (d, 1H, H-12a, JH-12a/H-12b¼16.2 Hz),
3
3.53 (s, 6H, 2ꢂ OCH3), 3.57 (s, 3H, OCH3), 4.82 (d, 1H, H-11, JH-11/
¼6.9 Hz), 6.34 (s, 2H, H-20, H-60), 7.26 (d, 1H, AreH, 3J¼4.8 Hz),
H-12b
7.47 (br s, 2H, eNH2), 7.70 (d,1H, AreH, 3J¼5.9 Hz), 8.46 (d,1H, AreH,
3J¼4.8 Hz), 8.62 (d, 1H, AreH, 3J¼5.9 Hz), 9.40 (s, 1H, AreH), 9.62 (s,
1H, AreH). The signal of proton 12b is overlayed by the signals of the
methoxygroups at 3.53e3.57 ppm; 13C NMR (75 MHz, DMSO-d6):
4.2.3. 6-Amino-11-(4-methoxyphenyl)-11,12-dihydropyrido[3,4-c]
[1,9]-phenanthroline (3c). 4-Methoxybenzaldehyde (285 mg,
2.1 mmol), rt, 2.5 h, C22H18N4O, yield: 252 mg (33%, recrystallized
from MeOH/CH2Cl2); solid; mp 282 ꢀC under decomp.; 1H NMR
d
¼35.2 (C-12), 36.2 (C-11), 55.6 (2C, 2ꢂ OCH3), 59.8 (OCH3), 104.5
(300 MHz, DMSO-d6):
d
¼3.09 (d, 1H, H-12a, 2JH-12a/H-12b¼15.8 Hz),
(2C, C-20, C-60), 112.7, 114.5, 115.8, 123.4, 130.0, 136.1, 138.7, 139.4,
144.7, 145.4, 145.8, 147.6, 149.0, 152.5 (2C, C-30, C-50), 157.1; IR (ATR,
cmꢃ1): 3300, 3122, 3006, 2932,1670,1612,1600,1463,1124; MS (ESI)
m/z: 415 ([MþH]þ, 100%), 247 ([Mꢃ3,4,5-trimethoxybenzene]þ, 4%),
3.48 (dd, 1H, H-12b, 2JH-12b/H-12a¼16.1 Hz, 3JH-12b/H-11¼7.9 Hz), 3.58
(s, 3H, OCH3), 4.78 (d, 1H, H-11, 3JH-11/H-12b¼6.8 Hz), 6.66 (m, 2H, H-
30, H-50), 6.87 (m, 2H, H-20, H-60), 7.16 (d, 1H, AreH, 3J¼4.9 Hz), 7.39
(br s, 2H, eNH2), 7.53 (d, 1H, AreH, 3J¼5.7 Hz), 8.38 (d, 1H, AreH,
3J¼4.9 Hz), 8.52 (d, 1H, AreH, 3J¼5.9 Hz), 9.33 (s, 1H, AreH), 9.55
208 ([Mþ2H]þþ, 7%), 124 ([Mꢃ3,4,5-trimethoxybenzeneþ2H]þþ
,
16%); Anal. calcd for C24H22N4O3: C, 69.55; H, 5.35; N,13.52, found: C,
69.18; H, 4.93; N, 13.49.
(s,1H, AreH); 13C NMR (75 MHz, DMSO-d6):
d¼35.1 (C-12), 35.4 (C-
11), 54.8 (OCH3), 112.8, 113.7 (2C), 114.5, 115.7, 123.3, 128.1 (2C),
129.9, 134.8, 129.3, 144.2, 145.7, 145.8, 147.6, 149.0, 149.6, 157.0,
157.7; IR (ATR, cmꢃ1): 3324, 3172, 2950, 2830, 1650, 1456, 1182,
1034; MS (EI) m/z: 354 Mþ (55%), 353 [MꢃH]þ (11%), 247 [Mꢃ4-
methoxy-benzene]þ (100%), 230 (19%), 177 (10%), 155 (8%), 121
(6%). Anal. calcd for C22H18N4O: C, 74.56; H, 5.12; N, 15.81, found: C,
74.89; H, 5.51; N, 15.74.
4.2.7. 6-Amino-11-(2,4,6-trimethoxyphenyl)-11,12-dihydropyrido[3,4-
c][1,9]phenanthroline (3g). 2,4,6-Trimethoxybenzaldehyde (412 mg,
2.1 mmol), 2 h, C24H22N4O3, yield: 547 mg (63%, recrystallized from
MeOH/CH2Cl2); mp 265 ꢀC under decomp.; 1H NMR (300 MHz,
DMSO-d6):
d
¼2.84 (d,1H, H-12a, 2JH-12a/H-12b¼17.0 Hz), 3.43 (br s, 6H,
2
3
2ꢂ OCH3), 3.53 (dd, 1H, H-12b, JH-12b/H-12a¼17.0 Hz, JH-12b/H-
¼10.2 Hz), 3.72 (s, 3H, OCH3), 5.25 (d,1H, H-11, 3JH-11/H-12b¼10.2 Hz),
11
4.2.4. 6-Amino-11-(2,3-dimethoxyphenyl)-11,12-dihydropyrido[3,4-
c]-[1,9]phenanthroline (3d). 2,3-Dimethoxybenzaldehyde (349 mg,
2.1 mmol), rt, 2 h, C23H20N4O2, yield: 492 mg (61% recrystallized
from MeOH/CH2Cl2); solid, mp 268 ꢀC under decomp.; 1H NMR
6.15 (s, 2H, H-30, H-50), 7.17 (d, 1H, AreH, 3J¼4.9 Hz), 7.26 (br s, 2H,
eNH2), 7.52 (d, 1H, AreH, 3J¼5.9 Hz), 8.44 (d, 1H, AreH, 3J¼4.9 Hz),
8.51(d,1H, AreH, 3J¼5.9Hz),9.44(s,1H, AreH), 9.53(s,1H, AreH);13
C
NMR (75 MHz, DMSO-d6):
d
¼24.9 (C-11), 33.5 (C-12), 55.1 (3C, 2ꢂ
(300 MHz, DMSO-d6):
d
¼3.05 (d, 1H, H-12a, 2JH-12a/H-12b¼16.4 Hz),
OCH3, OCH3), 91.1 (2C), 112.2, 112.6, 114.3, 119.4, 124.7, 132.4, 136.4,
137.3, 141.2, 143.1, 143.6, 148.1, 157.5, 158.0, 158.7, 159.9 (2C); IR (ATR,
cmꢃ1): 3115, 3060, 2839, 1655, 1600, 1541, 1413, 1203, 1115; MS (ESI)
m/z: 415 ([MþH]þ, 100%) 247 ([Mꢃ2,4,6-trimethoxybenzene]þ, 6%),
208 ([Mþ2H]þþ, 74%); Anal. calcd for C24H23N4O3$3HCl$1H2O: C,
53.20; H, 5.02; N, 10.34, found: C, 53.25; H, 5.06; N, 10.50.
3.54 (dd, 1H, H-12b, 2JH-12b/H-12a¼16.4 Hz, 3JH-12b/H-11¼8.1 Hz), 3.79
3
(s, 3H, OCH3), 4.02 (s, 3H, OCH3), 5.10 (d, 1H, H-11, JH-11/
¼7.9 Hz), 5.87 (dd, 1H, AreH, 3J¼7.9 Hz, 4J¼1.3 Hz), 6.58 (t, 1H,
H-12b
AreH, 3J¼8.0 Hz), 6.78 (dd, 1H, AreH, 3J¼8.2 Hz, 4J¼1.3 Hz), 7.16
(d, 1H, AreH, 3J¼4.9 Hz), 7.38 (d, 1H, AreH, 3J¼5.9 Hz), 7.43 (br s,
2H, eNH2), 8.39 (d, 1H, AreH, 3J¼4.9 Hz), 8.54 (d, 1H, AreH,
3J¼5.9 Hz), 9.37 (s, 1H, AreH), 9.56 (s, 1H, AreH); 13C NMR
4.2.8. 6-Amino-11-furyl-11,12-dihydropyrido[3,4-c][1,9]phenanthro-
line (3h). Furfural (201 mg, 2.1 mmol), 2 h, C19H14N4O, yield:
441 mg (67%, recrystallized from MeOH/CH2Cl2); solid, mp 267 ꢀC
(75 MHz, DMSO-d6):
d
¼34.9 (C-12), 35.2 (C-11), 55.6 (OCH3), 60.6
(OCH3), 111.9, 113.1, 114.6, 119.1, 119.2, 124.0, 126.8, 131.9, 134.5,

9110
C. Meier et al. / Tetrahedron 68 (2012) 9105e9112
under decomp.; 1H NMR (300 MHz, DMSO-d6):
d
¼3.05 (d, 1H, H-
203 ([Mþ2H]þþ
,
81Br, 100%), 202 ([Mþ2H]þþ
,
79Br, 95%), 193 (5%),
10%). Anal. calcd for
2
2
12a, JH-12a/H-12b¼16.4 Hz), 3.54 (dd, 1H, H-12b, JH-12b/H-
124 ([Mꢃ3-bromobenzeneþ2H]þþ
,
3
¼16.4 Hz, JH-12b/H-11¼8.1 Hz), 4.36 (m, 2H, 3J¼4.0 Hz), 4.92 (m,
C21H15N4Br: C, 62.54; H, 3.75; N, 13.89, found: C, 62.47; H, 3.99; N,
14.17.
12a
1H, 3J¼4.0 Hz), 5.60 (m, 1H, 3J¼3.2 Hz, 4J¼1.9 Hz, 4J¼0.9 Hz), 6.12
(m, 3J¼1.8 Hz), 7.34 (d, 1H, AreH, 3J¼4.9 Hz), 7.39 (m, 1H, 3J¼1.8 Hz,
4J¼0.8 Hz), 7.45 (br s, 2H, eNH2), 7.78 (d, 1H, AreH, 3J¼5.9 Hz), 8.44
(d, 1H, AreH, 3J¼4.9 Hz), 8.62 (d, 1H, AreH, 3J¼5.9 Hz), 9.29 (s, 1H,
4.2.12. 6-Amino-11-(3-chlorophenyl)-11,12-dihydropyrido[3,4-c][1,9-
]-phenanthroline (3l). 3-Chlorbenzaldehyde (295 mg, 2.1 mmol),
2.5 h, C21H15N4Cl, yield: 241 mg (32%, recrystallized from MeOH/
CH2Cl2); solid, mp 307 ꢀC under decomp.; 1H NMR (300 MHz,
AreH), 9.57 (s, 1H, AreH); 13C NMR (75 MHz, DMSO-d6):
d¼30.6 (C-
12), 31.9 (C-11), 106.4, 110.6, 112.9, 113.0, 116.4, 123.5, 123.6, 139.8,
142.4, 145.0, 146.1, 146.4, 148.2, 149.5, 150.1, 156.1, 157.7; IR (ATR,
cmꢃ1): 3325, 3164, 2893,1649,1599, 1508, 1456, 1047, 822; MS (ESI)
m/z: 315 ([MþH]þ, 50%), 218 (100%), 158 ([Mþ2H]þþ, 35%); HRMS
(ESI) m/z calcd for [MþH]þ 315.12403, found 315.12372.
DMSO-d6):
d
¼3.16 (d,1H, H-12a, 2JH-12a/H-12b¼16.4 Hz), 3.53 (dd,1H,
2
3
H-12b, JH-12b/H-12a¼16.4 Hz, JH-12b/H-11¼7.4 Hz), 4.90 (d, 1H, H-11,
3JH-11/H-12b¼7.3 Hz), 6.80e6.90 (m, 1H, AreH), 7.07e7.16 (m, 3H,
AreH), 7.20 (d, 1H, AreH, 3J¼4.9 Hz), 7.51 (br s, 2H, eNH2), 7.56 (d,
1H, AreH, 3J¼6.0 Hz), 8.41 (d, 1H, AreH, 3J¼4.9 Hz), 8.56 (d, 1H,
AreH, 3J¼5.9 Hz), 9.36 (s, 1H, AreH), 9.59 (s, 1H, AreH); 13C NMR
4.2.9. 6-Amino-11-thienyl-11,12-dihydropyrido[3,4-c][1,9]phenan-
throline (3i). Thiophen-2-carbaldehyde (236 mg, 2.1 mmol), 2 h,
(75 MHz, DMSO-d6):
d¼35.4 (C-12), 36.0 (C-11), 113.2, 113.9, 116.0,
C
19H14N4S, yield: 374 mg (54%, recrystallized from MeOH/CH2Cl2);
123.8, 126.2, 127.0, 127.6, 130.3, 130.7, 133.5, 139.7, 144.3, 146.1,
146.3, 146.6, 148.4, 149.6, 150.3, 157.8; IR (ATR, cmꢃ1): 3305, 3121,
2970, 2811, 1666, 1598, 1459, 1375, 820; MS (ESI) m/z: 361 ([MþH]þ,
solid, mp 269 ꢀC under decomp.; 1H NMR (300 MHz, DMSO-d6):
d
¼3.27 (d,1H, H-12a, 2JH-12a/H-12b¼16.2 Hz), 3.51 (dd,1H, H-12b, 2JH-
3
3
¼16.0 Hz, JH-12b/H-11¼6.9 Hz), 5.16 (d, 1H, H-11, JH-11/
37Cl, 35%), 359 ([MþH]þ, 35Cl, 100%), 181 ([Mþ2H]þþ
,
37Cl, 17%), 180
12b/H-12a
¼6.9 Hz), 6.68e6.80 (m, 2H, 3J¼5.2 Hz, 4J¼1.3 Hz), 7.11 (dd, 1H,
([Mþ2H]þþ
,
35Cl, 46%), 124 ([Mꢃ3-chlorobenzeneþ2H]þþ, 7%);
H-12b
3J¼5.2 Hz, 4J¼1.3 Hz), 7.30 (d, 1H, AreH,¼4.9 Hz), 7.45 (br s, 2H,
eNH2), 7.78 (d, 1H, AreH, 3J¼5.9 Hz), 8.44 (d, 1H, AreH, 3J¼4.9 Hz),
8.62 (d, 1H, AreH, 3J¼5.9 Hz), 9.29 (s, 1H, AreH), 9.58 (s, 1H, AreH);
HRMS (ESI) m/z calcd for [MþH]þ, 37Cl: 359.10579, found
359.10526.
13C NMR (75 MHz, DMSO-d6):
d¼31.1 (C-11), 35.8 (C-12), 112.7,
4.2.13. 6-Amino-11-(4-fluorophenyl)-11,12-dihydropyrido[3,4-c][1,9-
]-phenanthroline (3m). 4-Fluorobenzaldehyde (261 mg, 2.1 mmol),
3 h, C21H15N4F, yield: 215 mg (30%, recrystallized from MeOH/
115.6, 119.3, 124.8, 125.3, 126.7, 126.9, 131.4, 138.1, 139.0, 142.3,
142.6, 144.6, 145.1, 146.7, 155.3, 158.4; IR (ATR, cmꢃ1): 3325, 3167,
3070, 2971, 1650, 1598, 1541, 1454, 1043, 825; MS (ESI) m/z: 331
CH2Cl2); solid, mp 286 ꢀC under decomp.; 1H NMR (300 MHz,
([MþH]þ, 100%), 218 (100%), 166 ([Mþ2H]þþ
,
43%), 124
DMSO-d6þ1% acetic-acid-d4):
d
¼3.50 (d, 1H, H-12a, JH-12a/H-
2
([Mꢃthiopheneþ2H]þþ, 14%). HRMS (ESI) m/z calcd for [MþH]þ
¼16.7 Hz), 3.76 (dd, 1H, H-12b, JH-12b/H-12a¼16.9 Hz, JH-12b/H-
2
3
12b
331.10118, found 331.10071.
¼7.5 Hz), 5.09 (d, 1H, H-11, 3JH-11/H-12b¼7.3 Hz), 6.87e6.97 (m, 2H,
11
4
AreH, AA0-part, JHF¼8.8 Hz), 7.02e7.13 (m, 2H, AreH, XX0-part,
3JHF¼8.9 Hz), 7.84 (d, 1H, AreH, 3J¼5.8 Hz), 7.96 (d, 1H, AreH,
3J¼6.6 Hz), 8.66 (d, 1H, AreH, 3J¼6.6 Hz), 8.77 (d, 1H, AreH,
3J¼5.8 Hz), 9.39 (s, 1H, AreH), 9.99 (s, 1H, AreH); 13C NMR (75 MHz,
4.2.10. 6-Amino-11-(3-bromophenyl)-11,12-dihydropyrido[3,4-c][1,9-
]-phenanthroline (3j). 3-Bromobenzaldehyde (389 mg, 2.1 mmol),
3 h, C21H15N4Br, yield: 161 mg (19%, recrystallized from MeOH/
CH2Cl2); solid, mp 268 ꢀC under decomp.; 1H NMR (300 MHz,
DMSO-d6þ1% acetic-acid-d4):
d
¼34.6 (C-11), 35.7 (C-12), 113.0,
DMSO-d6):
d
¼3.15 (d, 1H, H-12a, 2JH-12a/H-12b¼16.3 Hz), 3.53 (dd, 1H,
114.7, 115.1, 115.4, 118.7, 126.2, 129.0, 120.1, 131.4, 137.4, 138.7, 140.1,
142.2, 143.0, 145.1, 154.4, 158.1, 159.4, 162.7; IR (ATR, cmꢃ1): 3333,
3164, 3061, 2888, 1655, 1598, 1508, 1456, 826; MS (ESI) m/z: 343
([MþH]þ, 51%), 172 ([Mþ2H]þþ, 100%), 124 ([Mꢃ4-fluorobenzene
þ2H]þþ, 10%); Anal. calcd for C21H15N4F: C, 73.67; H, 4.42; N,
16.36, found: C, 74.03; H, 4.69; N, 16.69.
2
3
H-12b, JH-12b/H-12a¼16.2 Hz, JH-12b/H-11¼7.4 Hz), 4.89 (d, 1H, H-11,
3JH-11/H-12b¼7.4 Hz), 6.87 (d, 1H, AreH, 3J¼7.7 Hz), 7.05 (t, 1H, AreH,
3J¼7.7 Hz), 7.20 (d, 1H, AreH, 3J¼4.8 Hz), 7.27 (d, 1H, AreH,
3J¼7.7 Hz), 7.29 (s, 1H, AreH), 7.49 (br s, 2H, eNH2), 7.56 (d, 1H,
AreH, 3J¼5.9 Hz), 8.41 (d, 1H, AreH, 3J¼5.0 Hz), 8.56 (d, 1H, AreH,
3J¼5.8 Hz), 9.37 (s, 1H, AreH), 9.59 (s, 1H, AreH); 13C NMR (75 MHz,
DMSO-d6):
d¼35.0 (C-12), 35.5 (C-11), 112.7, 113.4, 115.5, 121.7, 123.3,
4.2.14. 6-Amino-11-(p-biphenyl)-11,12-dihydropyrido[3,4-c][1,9-]phe-
nanthroline (3n). Biphenyl-4-carboxaldehyde (383 mg, 2.1 mmol),
2.5 h, C27H20N4, yield: 235 mg (28%, recrystallized from MeOH/
CH2Cl2); solid, mp 265 ꢀC under decomp.; 1H NMR (300 MHz,
126.1, 129.3, 129.8, 130.0, 130.5, 139.2, 143.8, 145.7, 145.8, 146.1, 147.9,
149.1, 149.8, 157.3; IR (ATR, cmꢃ1): 3325, 3169, 3052, 2969, 1650,
1599, 1457, 1041, 818; MS (ESI) m/z: 405 ([MþH]þ, 81Br, 70%), 403
([MþH]þ, 79Br, 71%), 203 ([Mþ2H]þþ
,
81Br, 94%), 202 ([Mþ2H]þþ
,
DMSO-d6):
d
¼3.21 (d, 1H, H-12a, 2JH-12a/H-12b¼16.3 Hz), 3.57 (dd, 1H,
79Br, 100%), 163 (4%), 157 (10%); Anal. calcd for C21H15N4Br: C, 62.54;
H, 3.75; N, 13.89, found: C, 61.85; H, 3.81; N, 13.39.
H-12b, JH-12b/H-12a¼16.3 Hz, JH-12b/H-11¼7.5 Hz), 4.91 (d, 1H, H-11,
3JH-11/H-12b¼7.4 Hz), 7.08 (m, 2H, AreH, 3J¼8.2 Hz), 7.21 (d, 1H, AreH,
3J¼4.9 Hz) 7.25e7.48 (m, 5H, AreH; br s, 2H, eNH2), 7.51 (m, 2H,
AreH, 3J¼8.1 Hz), 7.59 (d, 1H, AreH, 3J¼5.9 Hz), 8.41 (d, 1H, AreH,
3J¼4.9 Hz), 8.56 (d, 1H, AreH, 3J¼5.9 Hz), 9.39 (s, 1H, AreH), 9.58 (s,
2
3
4.2.11. 6-Amino-11-(4-bromophenyl)-11,12-dihydropyrido[3,4-c][1,9-
]-phenanthroline (3k). 4-Bromobenzaldehyde (389 mg, 2.1 mmol),
3 h, C21H15N4Br, yield: 313 mg (37%, recrystallized from MeOH/
1H, AreH); 13C NMR (75 MHz, DMSO-d6þ1% acetic-acid-d4):
¼34.7
d
CH2Cl2); solid, mp 278 ꢀC under decomp.; 1H NMR (300 MHz,
(C-11), 35.8 (C-12), 113.2, 114.9, 120.0, 126.4 (2C), 127.0 (2C), 127.4,
127.8 (2C), 128.8 (2C), 131.8, 131.9, 137.1, 137.6, 138.9, 139.4,
140.5, 141.5, 143.2, 143.8, 147.3, 156.7, 158.3; IR (ATR, cmꢃ1): 3327,
3029, 2970, 2898, 1652, 1598, 1455, 1044. 821; MS (ESI) m/z: 401
2
DMSO-d6):
d
¼3.12 (d, 1H, H-12a, JH-12a/H-12b¼16.5 Hz), 3.52 (dd,
1H, H-12b, 2JH-12b/H-12a¼16.2 Hz, 3JH-12b/H-11¼7.5 Hz), 4.86 (d, 1H, H-
11, JH-11/H-12b¼7.3 Hz), 6.94 (m, 2H, H-20, H-60, 3J¼8.4 Hz), 7.18 (d,
3
1H, AreH, 3J¼4.9 Hz), 7.31 (m, 2H, H-30, H-50, 3J¼8.4 Hz), 7.48 (br s,
2H, eNH2), 7.53 (d, 1H, AreH, 3J¼6.0 Hz), 8.40 (d, 1H, AreH,
3J¼4.9 Hz), 8.54 (d, 1H, AreH, 3J¼5.9 Hz), 9.36 (s, 1H, AreH), 9.58 (s,
([MþH]þ, 59%), 201 ([Mþ2H]þþ
,
100%), 124 ([Mꢃp-phenyl-
benzeneþ2H]þþ, 8%); HRMS (ESI) m/z calcd for [MþH]þ 401.17606,
found 401.17587.
1H, AreH); 13C NMR (75 MHz, DMSO-d6):
d¼35.0 (C-12), 35.3 (C-
11), 112.7, 113.6, 115.5, 119.5, 123.3, 129.4 (2C), 129.8, 131.2 (2C),
139.2, 142.3, 143.8, 145.8, 146.0, 147.8, 149.1, 149.7, 157.2; IR (ATR,
cmꢃ1): 3327, 3171, 2899, 1649, 1600, 1543, 1456, 1012, 818; MS
(ESI) m/z: 405 ([MþH]þ, 81Br, 64%), 403 ([MþH]þ, 79Br, 63%),
4.2.15. 6-Amino-11-propyl-11,12-dihydropyrido[3,4-c][1,9]phenan-
throline (3o). Butyraldehyde (151 mg, 2.1 mmol), 3 h, C18H18N4,
yield: 128 mg (21%, recrystallized from MeOH/CH2Cl2); solid, mp
231 ꢀC under decomp.; 1H NMR (300 MHz, DMSO-d6):
d
¼0.78 (t,

C. Meier et al. / Tetrahedron 68 (2012) 9105e9112
9111
3H, eCH3, 3J¼6.9 Hz), 1.12e1.48 (m, 4H, eCH2eCH2e), 2.92e3.14
(m, 2H, H-12), 3.42e3.56 (m, 1H, H-11), 7.30 (br s, 2H, eNH2), 7.34
(d, 1H, AreH, 3J¼4.9 Hz), 7.75 (d, 1H, AreH, 3J¼5.9 Hz), 8.46 (d, 1H,
AreH, 3J¼4.9 Hz), 8.64 (d, 1H, AreH, 3J¼5.9 Hz), 9.27 (s, 1H, AreH),
169 (17%). Anal. calcd for C22H16N4O: C, 74.89; H, 4.58; N, 15.90,
found: C, 74.33; H, 4.66; N, 15.57.
4.3.3. 6-Amino-11-(2,3-dimethoxyphenyl)-pyrido[3,4c][1,9]phenan-
throline (4d). The reaction of 3d (200 mg, 0.52 mmol) with
60 mg Pd/C for 10 min afforded compound 4d. C23H18N4O2, yield:
144 mg (72%); solid; mp 231 ꢀC under decomp.; 1H NMR (300 MHz,
9.56 (s, 1H, AreH); 13C NMR (75 MHz, DMSO-d6):
d
¼13.9 (eCH3),
19.9 (eCH2e), 29.9 (C-11), 30.8 (C-12), 35.3 (eCH2e), 112.5, 115.5,
117.1, 123.5, 129.6, 138.9, 144.5, 144.9, 145.7, 147.5, 149.2, 149.5,
156.6; IR (ATR, cmꢃ1): 3325, 3164, 3045, 2953, 2930, 2870, 1651,
1598, 1455, 1043, 821; MS (ESI) m/z: 291 ([MþH]þ, 59%), 146
([Mþ2H]þþ, 25%), 124 ([Mꢃpropane þ2H]þþ, 100%). HRMS (ESI) m/
z calcd for [MþH]þ 291.16041, found 291.16046.
DMSO-d6þ2% DCl in D2O): ¼3.35 (s, 3H, OCH3), 3.91 (s, 3H, OCH3),
d
7.04 (m, 1H, AreH, J¼4.6 Hz), 7.36 (m, 2H, AreH, J¼4.6 Hz), 7.53 (dd,
1H, AreH, 3J¼6.7 Hz, 4J¼0.6 Hz), 7.89 (s, 1H, AreH, H-12), 8.53 (dd,
1H, AreH, 3J¼6.5 Hz, 4J¼0.8 Hz), 8.69 (dd, 1H, AreH, 3J¼6.7 Hz,
4J¼0.6 Hz), 8.93 (dd, 1H, AreH, 3J¼6.5 Hz, 4J¼0.8 Hz), 10.21 (m, 1H,
4.2.16. 6-Amino-11,12-dihydropyrido[3,4-c][1,9]phenanthroline
(3p). Paraformaldehyde (64 mg, 2.1 mmol), 3 h, C15H12N4, yield:
150 mg (29%, silica gel, CH2Cl2/MeOH (5e20%)); solid; mp>310 ꢀC
AreH), 10.23 (m, 1H, AreH); 13C NMR (75 MHz, DMSO-d6):
d¼56.0
(eOCH3), 60.1 (eOCH3), 114.2, 114.4, 114.6, 120.0, 120.8, 123.0, 123.6,
124.2, 125.6, 126.2, 129.0, 134.9, 135.0, 140.6 (2C), 142.1, 142.8, 144.8
(2C), 144.9, 148.1, 153.0, 157.1; IR (ATR, cmꢃ1): 3328, 3163, 2952,
1641, 1606, 1553, 1407, 1267, 1050; MS (ESI) m/z: 383 ([MþH]þ,
100%), 184 (19%), 169 (14%); 163 (13%). HRMS (ESI) m/z calcd for
[MþH]þ 383.15024, found 383.14987.
1H NMR (300 MHz, DMSO-d6):
d
¼3.00 (m, 4H, CH2eCH2), 7.25 (br s,
2H, NH2), 7.31 (d, 1H, AreH, 3J¼4.9 Hz), 7.75 (d, 1H, AreH,
3J¼5.8 Hz), 8.44 (d, 1H, AreH, 3J¼4.9 Hz), 8.62 (d, 1H, AreH,
3J¼5.8 Hz), 9.25 (s, 1H, AreH), 9.54 (s, 1H, AreH).13C NMR (75 MHz,
DMSO-d6):
d¼35.1 (2C), 112.4, 115.6, 122.6, 129.9, 139.2, 145.3, 145.9,
146.3, 147.5, 149.0, 149.2, 155.9, 156.6; IR (ATR, cmꢃ1): 3306, 3136,
1670, 1612, 1568, 1462; MS (EI) m/z:¼248 Mþ (100), 247 [MꢃH]þ
(97), 230 (21). HRMS (ESI) m/z calcd for [MþH]þ 249.11346, found
249.11319.
4.3.4. 6-Amino-11-(3,4,5-trimethoxyphenyl)-pyrido[3,4c][1,9]phe-
nanthroline (4f). The reaction of 3f (200 mg, 0.48 mmol) with
60 mg Pd/C for 10 min afforded compound 4f. C24H20N4O3, yield:
149 mg (75%); solid; mp 246 ꢀC under decomp.; 1H NMR (300 MHz,
DMSO-d6):
d
¼3.73 (s, 6H, 2ꢂ OCH3), 3.79 (s, 3H, eCH3), 6.79 (s, 2H,
4.3. General procedure for the dehydration of the 6-amino-
11,12-dihydropyrido[3,4-c][1,9]phenanthrolines to 6-
aminopyrido-[3,4-c][1,9]phenanthrolines
H-20, H60), 7.18 (d, 1H, AreH, 3J¼6.0 Hz), 7.58 (s, 1H, AreH, H-12),
7.78e7.93 (d, 1H, AreH; br s, 2H, eNH2) 8.46 (d, 1H, AreH,
3J¼6.0 Hz), 8.67 (d,1H, AreH, 3J¼6.1 Hz), 9.68 (br s,1H, AreH),10.33
(br s, 1H, AreH); 13C NMR (75 MHz, DMSO-d6):
d
¼56.1 (2ꢂ OCH3),
200 mg of 3 were dissolved in 5e10 ml of DMPU and Palladium
(10%)/charcoal (30% by weight) was added. The solution was
refluxed under N2 for 10e30 min. The reaction vessel was washed
with 50 ml of CH2Cl2 and the Palladium/charcoal was filtered off.
The filtrate was concentrated in vacuo and DMPU could be removed
by distillation at high vacuum at 90e110 ꢀC. The resulting residue
was collected by filtration and purified via column chromatography
(silica gel, CH2Cl2/MeOH (10%)).
60.3 (OCH3), 106.0 (2C, C-20, C-60), 113.2, 113.8, 118.6, 119.8, 122.4,
123.6, 136.2, 137.4, 138.1, 138.3, 142.3, 145.6, 145.9, 147.2, 148.7,
149.4, 153.4 (2C, C-30, C-50), 156.3; IR (ATR, cmꢃ1): 3330, 3196, 2832,
1644, 1580, 1502, 1462, 1420; MS (EI) m/z: 412 (Mþ, 100%), 397
([MꢃCH3]þ, 31%), 337 (17%), 294 (13%), 283 (10%). Anal. calcd for
C24H20N4O3: C, 69.89; H, 4.89; N, 13.58, found: C, 69.99; H, 5.43; N,
13.75.
4.3.5. 6-Amino-11-furylpyrido[3,4c][1,9]phenanthroline
(4h). The
4.3.1. 6-Amino-11-phenylpyrido[3,4c][1,9]phenanthroline (4a). The
reaction of 3a (200 mg, 0.62 mmol) with 60 mg Pd/C for 10 min
afforded compound 4a. C21H14N4, yield: 178 mg (89%); solid; mp
221 ꢀC under decomp.; 1H NMR (300 MHz, D2Oþ2% DCl in D2O):
reaction of 3h (200 mg, 0.64 mmol) with 60 mg Pd/C for 15 min
afforded compound 4h. C19H12N4O, yield: 126 mg (63%); solid; mp
248 ꢀC under decomp.; 1H NMR (300 MHz, DMSO-d6þ2% DCl in
D2O):
d
¼6.96 (m, 3J¼1.9 Hz), 7.12 (dd, 1H, AreH, 3J¼6.8 Hz,
d
¼7.05e7.11 (m, 2H, AreH), 7.29e7.51 (m, 5H, AreH), 8.02 (d, 1H,
4J¼0.7 Hz), 7.27 (dd, 1H, AreH, 3J¼3.4 Hz, 4J¼0.8 Hz), 8.03 (m, 1H,
3J¼1.8 Hz, 4J¼0.8 Hz), 8.13 (s, 1H, AreH, H-12), 8.54 (dd, 1H,
3J¼6.7 Hz, 4J¼0.8 Hz), 8.88 (dd, 1H, 3J¼6.8 Hz, 4J¼0.6 Hz), 8.97 (dd,
1H, 3J¼6.5 Hz, 4J¼0.8 Hz), 10.11 (m, 1H, AreH), 10.31 (m, 1H, AreH);
AreH, 3J¼6.6 Hz), 8.21 (d, 1H, AreH, 3J¼7.0 Hz), 8.53 (d, 1H, AreH,
3J¼6.6 Hz), 9.55 (s, 1H, AreH), 9.84 (s, 1H, AreH); 13C NMR
(75 MHz, DMSO-d6):
d
¼113.7, 114.5, 123.1, 123.2 (2C), 124.4, 128.2
(3C), 129.8 (2C), 135.0, 136.5, 139.2, 141.4, 142.0, 143.1, 143.8, 148.8,
159.2, 156.8, IR (ATR, cmꢃ1): 3360, 3300, 3049, 1675, 1605, 1560,
1462, 1053, 860; MS (ESI) m/z: 323 ([MþH]þ, 100%), 162
([Mþ2H]þþ, 32%). HRMS (ESI) m/z calcd for [MþH]þ 323.12911,
found 323.12891.
13C NMR (75 MHz, DMSO-d6):
d
¼111.7, 112.5, 113.1, 114.4, 120.9,
121.6,123.6,124.5,135.1,135.3,138.8,141.2,142.1,142.3,143.8,145.3.
149.1, 151.4, 157.2; IR (ATR, cmꢃ1): 3359, 3278, 3049, 2822, 1674,
1610, 1559, 1408, 863; MS (ESI) m/z: 313 ([MþH]þ, 100%), 157
([Mþ2H]þþ, 8%), 143 (6%); HRMS (ESI) m/z calcd for [MþH]þ
313.10838, found 313.10803.
4.3.2. 6-Amino-11-(3-methoxyphenyl)pyrido[3,4c][1,9]phenanthro-
line (4b). The reaction of 3b (200 mg, 0.56 mmol) with 60 mg Pd/C
for 10 min afforded compound 4b. C22H16N4O, yield: 116 mg (58%);
solid; mp 260 ꢀC under decomp.; 1H NMR (300 MHz, DMSO-d6):
4.4. Solubility
1e2 mg were suspended in 100 mM potassium phosphate
buffer (pH 2.0, pH 3.0, pH 4.0, and pH 7.4), shaken for 45 min at
room temperature, and centrifuged twice at 13,000 rpm for 15 min.
Supernatants were analyzed by HPLC and concentrations of the
dissolved compounds were calculated by a calibration of the re-
spective compound in 0.1% TFA in acetonitrile.
d
¼3.79 (s, 3H, OCH3), 6.96e7.03 (m,1H, AreH, 3J¼7.5 Hz, 4J¼0.9 Hz),
7.04e7.07 (m, 1H, AreH), 7.08e7.15 (m, 1H, AreH; d, 1H, AreH,
3J¼5.9 Hz), 7.45 (m, 1H, AreH, 3J¼7.9 Hz), 7.52 (s, 1H, AreH, H-12),
7.78e7.94 (d, 1H, AreH, 3J¼5.9 Hz; br s, 2H, eNH2), 8.38 (d, 1H,
AreH, 3J¼5.9 Hz), 8.67 (d, 1H, AreH, 3J¼6.0 Hz), 9.68 (br s, 1H,
AreH), 10.33 (br s, 1H, AreH); 13C NMR (75 MHz, DMSO-d6þ2% DCl
in D2O):
d
¼55.4, 113.5, 113.6, 115.0, 115.1, 120.5, 121.9, 122.7, 123.4,
4.5. HPLC-analytics
124.4, 130.9, 135.2, 137.7, 141.1, 141.9, 142.5, 143.1, 143.4, 148.1, 149.2,
157.3, 160.0; IR (ATR, cmꢃ1): 3358, 3272, 3047, 1673, 1606, 1559,
1462, 786; MS (ESI) m/z: 353 ([MþH]þ, 100%), 177 ([Mþ2H]þþ, 12%),
We used the Waters Alliance HPLC system consisting of Waters
e2695 XC separation module, Waters 2998 photodiode array

9112
C. Meier et al. / Tetrahedron 68 (2012) 9105e9112
detector, column heater, and Empower 2 software. Compounds
chlorobenzene (2.8), benzophenone (3.2), testosterone (3.2), thy-
mol (3.3), biphenyl (4.0), ketoconazole (4.5), and clotrimazole (6.1).
were separated on a LiChrospherÒ 60 RP-select B (125ꢂ4 mm,
5
m
m) with a C18 guard column (4ꢂ4 mm). The mobile phase
consisted of 0.1% TFA and acetonitrile. The flow rate was set to
4.9. Calculation of lipophilicity (clogP)
1 mL minꢃ1
.
Lipophilicity of all compounds was calculated in their uncharged
state using the software ‘ChemBioDraw Ultra’ (CambridgeSoft,
Cambridge, MA, USA).
4.6. Separation of 6-aminopyrido[3,4-c][1,9]phenanthroline-
derivatives 3
The following gradient was adjusted to ensure separation within
12 min. The acetonitrile percentage was elevated from 26% to 50%
(0e8 min), then reduced to 26% (8e9.5 min), and maintained at
26% for another 2.5 min. The detection wavelength was set to
265 nm. Retention times: 3a: (2.5ꢁ0.1) min; 3b: (2.2ꢁ0.1) min; 3d:
(3.2ꢁ0.1) min; 3e: (3.1ꢁ0.1) min; 3f: (2.2ꢁ0.1) min; 3g: (3.7ꢁ0.1)
min; 3h: (1.7ꢁ0.1) min; 3i: (2.1ꢁ0.1) min; 3j: (3.9ꢁ0.1) min; 3k:
(3.4ꢁ0.1) min; 3l: (3.2ꢁ0.1) min; 3m: (2.8ꢁ0.1) min; 3n:
(5.2ꢁ0.1) min; 3o: (1.6ꢁ0.1) min.
Acknowledgements
Franziska Hohm and Clara Schoeder are gratefully acknowl-
edged for technical assistance. We also thank Dr. Thorsten Overath
for the realization of the HRMS analysis at the Institute for Exper-
imental Medicine, UK-SH, Christian-Albrechts-University of Kiel.
References and notes
1. Simeon, S.; Rios, J. L.; Villar, A. Pharmazie 1989, 44, 593e597.
2. Dvorak, Z.; Kuban, V.; Klejdus, B.; Hlavac, J.; Vicar, J.; Ulrichova, J.; Simanek, V.
Heterocycles 2006, 68, 2403e2422.
4.7. Separation of 6-aminobenzo[c]phenanthridine-de-
rivatives BP
3. Pommier, Y. Nat. Rev. Cancer 2006, 6, 789; Pommier, Y. Chem. Rev. 2009, 109,
789e802.
4. Genes, C.; Lenglet, G.; Depauw, S.; Nhili, R.; Prado, S.; David-Cordonnier, M.-H.;
Michel, S.; Tillequin, F.; Poree, F.-H. Eur. J. Med. Chem. 2011, 46, 2117e2131.
5. Yapi, A.; Debois, N.; Chezal, J.-M.; Chavignon, O.; Teulade, J.-C.; Valentin, A.;
Blache, Y. Eur. J. Med. Chem. 2010, 45, 2854e2859.
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7. Kurtzberg, S.; Roth, S.; Krumbholz, R. Clin. Cancer Res. 2011, 17, 2777e2787.
8. Clement, B.; Weide, M. dt. Patentanmeldung, 195 38 088.6e44, PCT/DE 96/
01958; EP 0873315; US 006030981, 1995.
9. Clement, B.; Weide, M.; Wolschendorf, U.; Kock, I. Angew. Chem., Int. Ed. 2005,
44, 635e638; Angew. Chem. 2005, 117, 641e645.
10. Weide, M. Thesis, Christian-Albrechts-University of Kiel, 1995.
11. Wolschendorf, U. Thesis, Christian-Albrechts-University of Kiel, 2000.
12. z. Nieden, D. Thesis, Christian-Albrechts-University of Kiel, 2007.
13. Kock, I.; Clement, B. Synthesis 2005, 1052e1054.
14. Kock, I.; Heber, D.; Weide, M.; Wolschendorf, U.; Clement, B. J. Med. Chem. 2005,
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16. Zebothsen, I. Thesis, Christian-Albrechts-University of Kiel, 2005.
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2001, 46, 3e26.
Elution was carried out isocratically. The mobile phase con-
tained 40% acetonitrile and the detection wavelength was set to
220 nm. Compounds were eluted within 8 min. Retention times:
BP-1: (4.7ꢁ0.1) min; BP-7: (3.4ꢁ0.1) min; BP-9: (3.7ꢁ0.1) min; BP-
32: (5.1ꢁ0.1) min; BP-34: (6.7ꢁ0.1) min.
4.8. Experimental determination of lipophilicity (logP)
Lipophilicity was determined by using liquid chromatography.
Analytics were carried out on a LiChrospherÒ 100 RP-8 (125ꢂ4 mm,
5
m
m) with a C18 guard column (4ꢂ4 mm) and a mobile phase
consisting of 20 mM potassium phosphate buffer pH 7.4 and
methanol (40/60). A calibration curve was generated by analyzing 9
standard compounds with logP values within the range of 2.5e6.1.
Test compounds were dissolved in the mobile phase in a concen-
tration of 100 mM. All compounds were eluted within 30 min at
a flow rate of 1 mL minꢃ1. Lipophilicity was calculated on the basis
of retention times and calibration curve. The following standard
compounds were used (logP): p-chlorotoluene (2.5), toluene (2.7),
19. Boyd, M. R.; Paull, K. D. Drug Dev. Res. 1995, 34, 91e109.
20. National Cancer Institute, Cancer Screen 10/2009; Data: http://dtp.nci.nih.gov.