Synthesis of novel diazabicycles and their antiprotozoal activities

Article abstract of DOI:10.1071/CH09197

We describe the synthesis of new diaryl substituted diazabicyclo[3.2.1] octanes from diazepanes which were prepared by the reduction of diazepanones. The formation of the bicyclic system was optimized by microwave irradiation and the structures of the new compounds were established by single crystal structure analysis and NMR spectroscopy. All new compounds were tested for their potencies against Plasmodium falciparum K₁ and Trypanosoma b. rhodesiense, the causative organisms of malaria tropica and the East African form of sleeping sickness. CSIRO 2009.

Full text of DOI:10.1071/CH09197

Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2009, 62, 1166–1172
www.publish.csiro.au/journals/ajc
Synthesis of Novel Diazabicycles and their
Antiprotozoal Activities
Volker Wolkinger,A Robert Weis,A Ferdinand Belaj,B Marcel Kaiser,C
Reto Brun,C Robert Saf,D and Werner SeebacherA,E
AInstitute of Pharmaceutical Sciences, Pharmaceutical Chemistry, Karl-Franzens-University,
Universitätsplatz 1, A-8010 Graz, Austria.
BInstitute of Chemistry, Karl-Franzens-University Graz, Heinrichstrasse 28/IV, A-8010 Graz, Austria.
CSwiss Tropical Institute, Socinstrasse 57, CH-4002 Basel, Switzerland.
DInstitute of Chemical Technology of Organic Materials, Erzherzog-Johann University,
Stremayrgasse 26/1, A-8010 Graz, Austria.
ECorresponding author. Email: we.seebacher@uni-graz.at
We describe the synthesis of new diaryl substituted diazabicyclo[3.2.1]octanes from diazepanes which were prepared
by the reduction of diazepanones. The formation of the bicyclic system was optimized by microwave irradiation and
the structures of the new compounds were established by single crystal structure analysis and NMR spectroscopy. All
new compounds were tested for their potencies against Plasmodium falciparum K1 and Trypanosoma b. rhodesiense, the
causative organisms of malaria tropica and the East African form of sleeping sickness.
Manuscript received: 7 April 2009.
Manuscript accepted: 9 June 2009.
Ph
Introduction
Ph
Ph
NH
Ph
Recently we reported the synthesis of diaryl substituted
bicyclo[2.2.2]octane-1,3-diamines1, 2-azabicyclo[3.2.2]nonan-
5-amines 2, and 3-azatricyclo[3.2.2.02,3]nonan-1-amines 3
(Fig. 1).[1,2] These compounds exhibit activities against Plas-
modium falciparum, the causative organism of the most deadly
form of malaria, malaria tropica, and Trypanosoma b. rhode-
siense, the causative organism of the East African form of
sleeping sickness. Enhanced resistance has been observed for
both protozoal organisms, even against newly introduced drugs.
Therefore there is an urgent need for both, new antiplasmodial
and new antitrypanosomal agents.
Compounds 1–3 each contain two nitrogen atoms separated
by 2–3 carbon atoms. In compound 1 both amines are exocyclic,
whereas compounds 2 and 3 each conatin one endocyclic amine.
We have subsequently prepared compounds with a ring struc-
ture containing two endocyclic amines. Because we observed the
necessity of both aromatic residues for the antiprotozoal activ-
ity of bicyclooctane derivatives,[3] we included them in our new
structures. The substitution pattern of the aromatic rings influ-
ences the biological activities of 2.[4] Therefore we prepared
bicycles with differing substitution patterns of the aromatic
residues.
Ph
Ph
NH2
R2N
NH
R2N
R2N
1
2
3
Fig. 1. Structures of bicyclic bases.
H
N
1
Ar
H
N
Ar
Ar
Ar
2
7
6
(ii) NaN3
(i) (CH3)2CO
CH3COONH4
O
3
4
Ar
4a–d
5
H
NH
O
5a–d
O
6a–d
(iii)
H
Ar
Ar
a Ar ꢀ Ph
N
N
1
Ar
Ar
(iv)
b Ar ꢀ 4-CH3Ph
c Ar ꢀ 4-ClPh
d Ar ꢀ 3,4-diClPh
1
8
7
2
2
3
7
6
6
3
4
4
5
N
NH
5
8a–d
7a–d
Scheme 1. Reagents and conditions: (i) refluxing ethanol, 5 min; (ii) conc.
H2SO4, rt; (iii) LiAlH4, ether, reflux, 16 h; (iv) paraformaldehyde, K2CO3,
ethanol, reflux, 16 h.
Results and Discussion
The synthesis started from ammonium acetate, acetone and an
arylaldehyde 4 giving diaryl piperidones 5 via a double Mannich
reaction. The insertion of a second nitrogen was achieved via a
Schmidt reaction[5,6] to afford diaryl[1,4]diazepan-5-ones 6.The
reduction of this compounds with lithium aluminiumhydride led
to diaryl[1,4]diazepanes 7, which were converted to the bicyclic
ring system 8 by reaction with formaldehyde (Scheme 1).
The new compounds were investigated using NMR spec-
troscopy. The overlapping resonances of the two CH and the two
© CSIRO 2009
10.1071/CH09197
0004-9425/09/091166

Synthesis of Novel Diazabicycles
1167
We investigated the course of the reaction under conventional
conditions (reflux, open vessel, 100◦C oil bath temperature) and
the course of the microwave assisted reaction using 60W irra-
diation at 80◦C and at 100◦C. Compound 7a was treated with
paraformaldehyde and potassium carbonate in ethanol, aliquots
were taken, and the ratios of educt to product, as well as the per-
centage yield, determined by integration of the proton signals in
1H NMR spectra (Fig. 5).
Hr
7
Hl
8
8
Ph
1
6
H
3
2
N
1
6
2
H
H
N
7
Hup
H
N
Hdn
H
H
5
N
5
4
4
3
H
H
H
H
Hdn
Obviously, the advantage of the microwave assisted reaction
is the enhanced conversion from 7a to 8a in only a few min-
utes. At 80◦C a transformation to 91% of 8a is observed after
20 min. At longer reaction times, a slight decrease of 8a and an
increase of 7a is observed, and after 300 min some decomposi-
tion products begin to appear in the mixture. The course of the
microwave assisted reaction at 100◦C starts with 58% conver-
sion to 8a and runs parallel to that of the conventional heating
method of boiling ethanol (100◦C oil bath temperature).
However, complete conversions were achieved for the con-
ventional method over night and for the microwave assisted
method in 1 h at 120◦C using 250W irradiation. The solution of
the microwave assisted reaction was colourless after the reaction,
whereas the solution of the conventional reaction was brownish
and an insoluble gum was formed, probably due to polymerized
formaldehyde.
A
B
Fig. 2. Two conformers (A) and (B) of 8a.
Table 1. Observed NOE effects of 8a
Proton-proton
NOE
[%]
Distance
[Å]
H3up-arom. H
H7-H2
H3dn-H7
H8l-H4up
H3dn-H6dn
H8r-H6up
3.8
3.6
3.2
2.7
2.4
1.9
2.058
2.282
2.314
2.300
2.428
2.679
For the sake of comparison of antiprotozoal activities, we
prepared the known bicyclic and tricyclic diamines 9–12 by
Mannich reaction of dibenzylketone, ammonium acetate, and
paraformaldehyde as reported (Fig. 6).[11]
The antitrypanosomal and the antiplasmodial activities of
compounds 6–12 were determined using microplate assays of
T. b. rhodesiense (STIB 900) and the K1 strain of P. falciparum
(resistant to chloroquine and pyrimethamine). Cytotoxicity was
tested with L-6 rat skeletal myoblasts. Melarsoprol and chloro-
quine were used as standards with the results presented in
Table 3.
The diaryl[1,4]diazepan-5-ones 6 show only weak activities,
but a clear trend is observable: The antiprotozoal activities and
the cytotoxicity are in direct proportion to the lipophilicity of
compounds 6. The reduction of the amides 6 to diamines 7
caused a distinct increase of both antiplasmodial and antitry-
panosomal activities. Clearly the second basic centre promotes
these activities. The most promising antiplasmodial compound
in this group is 7a with good activity and low cytotoxicity.
The dichloro-diaryl[1,4]diazepan 7c has the highest antitry-
panosomal potency of all new compounds. The conversion of
diaryl[1,4]diazepanes 7 to bicyclic compounds 8 changed the
biologicalactivitiesonlymarginally.Asobservedforcompounds
7, the 2,7-diphenyl derivative 8a was the most active antiplas-
modial and the dichloro-compound 8c was the most potent
antitrypanosomal agent (Table 3). In the series of 1,3-diaza-
tricyclo[3.3.1.13,7]decan derivatives 9–11, the 9-unsubstituted
diamine 11 shows both antiplasmodial activity and low cytotox-
icity; and therefore promising selectivity.
CH2 groups of the symmetrical educt 5, were replaced by sepa-
rate signals for each CH and CH2 group in the 1H NMR spectra
of the non-symmetrical amides 6.The signal of the amide carbon
disappeared upon reduction to diamines 7, and an additional sig-
nal corresponding to the newly formed CH2 group was observed
in 13C spectra. The 1H resonance for the two corresponding
protons appeared at 3.1 ppm. The ring closure to compounds 8
was detected by the appearence of proton signals of the addi-
tional CH2 group at 3.1 ppm and 3.9 ppm and its corresponding
carbon resonance at 70 ppm; comparable data to that of unsub-
stituted 1,5-diazabicyclo[3.2.1]nonane.[7] Due to the aromatic
substitution, the signals of H2 and H7 are shifted to lower fields
compared with H3, H4, and H6. Evidence of the ring formation
was given by long range couplings from C8 to H2, H4, H6, and
H7 in HMBC spectra. From nuclear Overhauser effect (NOE)
measurements of compound 8a, the through-space couplings
from H3dn to H6dn and H7 indicate a strong preference for con-
formationA versus conformation B (Fig. 2). The observed NOE
effects are listed in Table 1, and compared with the distances
derived from the crystal structure analysis of 8c.
The crystal structure analysis of 8c confirmed our
observations and showed that the compound is 2,7-bis(4-
chlorophenyl)-1,5-diazabicyclo[3.2.1]octane (Figs 3 and 4).
Due to the presence of racemic twinning the substance
is a racemate of R,S- and S,R-configuration of the chiral
molecules. The two phenyl rings are almost co-planar (angle
of 13.44(14)◦ between their normals). Hitherto the structures
of only two 1,5-diazabicyclo[3.2.1]octanes are determined: 4-
(1,5-diazabicyclo[3.2.1]oct-8-yl)-pyridine[8] and 8-(p-anisyl)-
7-phenyl-1,5-diazabicyclo[3.2.1]octan-6-one.[9]
Conclusion
Severalnew2,7-diarylsubstituted, 1,5-diazabicyclo[3.2.1]octanes
have been synthesized from 1,4-diazepanes. The structure of
bicyclic compounds was established by NOE experiments and
single crystal structure analysis. The formation of the bicyclic
ring system was optimized via microwave irradiation and the
course of the reaction compared with that of a conventional
method. All new products were investigated for their in vitro
The formation of bicyclic compounds 8 was optimized for
compound 8a via microwave irradiation. We investigated the
reaction of 7a to 8a at different temperatures from 70 to 120◦C
over 10 min, with highest yields of 8a obtained at 70–80◦C. It
seems that temperatures beyond the boiling point of the mixture
are disadvantageous for this reaction (Table 2).

1168
V. Wolkinger et al.
C174
C174
C73
C72
C73
C72
C74
C75
C74
C75
C71
C7
C71
C76
C76
C6
C6
C7
N5
N5
N1
C2
N1
C2
C8
C8
C4
C4
C26
C3
C26
C25
C3
C21
C21
C25
C24
C124
C22
C23
C22
C23
C24
C124
Fig. 3. Stereoscopic ORTEP[10] plot of 8c showing the atomic numbering scheme. The probability ellipsoids are
drawn at the 50% probability level. Selected distances and angles: N1-C2 1.500(3) Å, N1-C7 1.484(3) Å, N1-C8
1.474(3) Å, N5-C4 1.479(3) Å, N5-C6 1.468(3) Å, N5-C8 1.467(3) Å, C24-Cl24 1.755(3) Å, C74-Cl74 1.752(3) Å;
C2-N1-C7 110.56(19)◦, C2-N1-C8 108.2(2)◦, C7-N1-C8 101.6(2)◦, C4-N5-C6 112.0(2)◦, C4-N5-C8 107.0(2)◦,
C6-N5-C8 101.0(2)◦; C3-C2-C21-C22 9.2(4)◦, N1-C7-C71-C76 0.7(3)◦.
C
C
B
B
0
0
A
A
Fig. 4. Stereoscopic ORTEP[10] plot of the packing of 8c. The atoms are drawn with arbitrary radii.

Synthesis of Novel Diazabicycles
1169
Table 3. Antiprotozoal activitiesA of compounds 6–12
Table 2. Yields of compound 8a at different temperatures
Temp.
[◦C]
% Compound 8a
Comp.
T. b. rhodesiense
IC50 [µM]
P. falciparum K1
IC50 [µM]
Cytotoxicity
L-6 cells IC50 [µM]
After 5 min
After 10 min
6a
6b
6c
6d
7a
7b
7c
7d
8a
8b
8c
8d
9
190.8
171.5
40.99
26.60
13.93
3.09
0.46
1.30
7.26
2.19
16.22
>16.98
>14.92
5.47
>337.9
111.7
60.76
23.48
231.7
40.64
10.15
8.27
88.89
36.59
12.63
12.68
>295.7
>293.7
>309.9
72.70
7.78
70
80
90
100
120
71
85
32
35
16
90
89
86
55
42
1.24
4.64
1.35
1.67
1.05
4.41
1.82
3.06
100
90
80
70
60
50
40
30
20
10
0
1.09
1.63
136.1
>293.7
88.60
15.48
0.0039
>16.43
13.15
1.55
10
11
12
mel
chl
2.10
0.12
188.5
AValues represent the average of four determinations (two determinations
of two independent experiments). chl = chloroquine, mel = melarsoprol.
0
100
200
Min
300
400
of the CDCl3 peak was used as the internal reference (77.0).
Abbreviations are as follows: aromatic H (ArH); aromatic C
(ArC); quaternary aromatic C (ArCq). Signal multiplicities are
abbreviated as follows: s, singlet; d, doublet; dd, doublet of
doublets; ddd, doublet of doublet of doublets; t, triplet; m,
multiplet; br, broad. Coupling constants (J) are reported in
Hertz (Hz). 1H and 13C resonances were assigned using COSY,
Fig. 5. Course of the reaction of 7a to 8a: under conventional conditions
(ꢀ) and microwave assisted at 100◦C (ꢁ) and at 80◦C (ꢂ).
HSQC, and HMBC spectra. H and 13C resonances are num-
1
N
N
H
X
bered as given in the formulae. HRMS was performed on a
Micromass tofspec 3E spectrometer (MALDI), GCT-Premier,
Waters (EI, 70 eV). Crystal structure analysis was performed
on a STOE four circle diffractometer. Microwave assisted reac-
tions were carried out using a CEM Discover/Explorer system,
in sealed 10 mL standard vessels with temperature control. For
column-chromatography (CC), silica gel 60 (Merck 70–230
mesh, pore-diameter 60 Å) was used; TLC was completed using
TLC plates (Merck, silica gel 60 F254 0.2 mm, 200 × 200 mm);
with compounds detected using a UV lamp at 254 nm. Solvents
and reagents were obtained from commercial sources, arylke-
tones 4 from Aldrich and Fluka. 2,6-Diphenylpiperidin-4-one
5a was prepared according to a reported procedure.[12] Com-
pounds 5b–5d were prepared in a similar way and used directly
for further reactions. 2,7-Diphenyl-[1,4]diazepan-5-one 6a was
prepared as reported.[13]
Y
N
HN
12
9 X ꢁ Y ꢀ O
10 X ꢀ H, Y ꢀ OH
11 X ꢀ H, Y ꢀ H
Fig. 6. Structures of compounds 9–12.
activities against P. falciparum K1 and T. b. rhodesiense as
well as for their cytotoxicity using microplate assays. The
2,7-bis(4-chlorophenyl)-[1,4]diazepan showed sub-micromolar
antitrypanosomal activity and will serve as a lead for further
investigations.
General Procedure for the Preparation
of 2,7-Diaryl-1,4-diazepan-5-ones 6
via 2,6-Diarylpiperidin-4-ones 5
Experimental
Materials and Methods
Melting points were obtained on a digital melting point appa-
ratus Electrothermal IA 9200 and are uncorrected. IR spectra
were conducted with an infrared spectrometer system 2000 FT
(Perkin–Elmer). UV/VIS spectra were recorded on a Lambda
17 UV/VIS-spectrometer (Perkin–Elmer), as either CH2Cl2
solutions (bases) or CH3OH solutions (hydrochlorides). NMR
spectra were recorded on a Varian Inova 400 (300 K) with 5 mm
tubes in CDCl3 containing 0.03% TMS. Chemical shifts were
recorded in parts per million (ppm). For 1H spectra, TMS (0.00)
was used an internal standard, for 13C spectra the central peak
Ammonium acetate, acetone, and the corresponding aryl alde-
hyde were dissolved in ethanol and the mixture refluxed until
the colour changed to orange. The mixture was cooled to room
temperature and poured into 100 mL of ether.The formed precip-
itate was filtered off and conc. HCl was added to the filtrate. The
formed2,6-diarylpiperidin-4-onehydrochloride(5·HCl)wasfil-
tered off, recrystallized repeatedly from ethanol/ether (1:10)
and subsequently dried over phosphorous pentoxide. Cold conc.
H2SO4 was poured into an Erlenmeyer flask and the 5·HCl was
addedinportions.Whenthedissolutionwascomplete, NaN3 was

1170
V. Wolkinger et al.
Table 4. Crystal data and structure refinement for 8c
2,7-Bis(4-chlorophenyl)-1,4-diazepan-5-one 6c
Reaction of ammonium acetate (7.7 g, 0.1 mol), acetone
(11.62 g, 0.2 mol), and 4-chlorobenzaldehyde (28.11 g, 0.2 mol)
in ethanol (20 mL) yielded 5c·HCl (6.44 g, 18%). 5c·HCl (2.7 g,
7.57 mmol)reactedinconc. H2SO4 (10 mL)withNaN3 (605 mg,
9.3 mmol) to give a precipitate which was subsequently recrys-
tallized from methanol yielding 6c (2.36 g, 93%), mp 175◦C.
νmax (KBr)/cm−1 3398, 3222, 3083, 1665, 1491, 1464, 1437,
1409, 1362, 1333, 1317, 1176, 1091, 1015, 832, 805, 778,
730. λmax/nm (log ε) 230 (3.996). δH 2.03 (1H, br s, NH),
2.62 (1H d, J = 14.3, H6), 3.05–3.13 (2H, m, H3, H6), 3.60
(1H, ddd, J = 14.1, 9.2, 4.0, H3), 4.01 (1H, d, J = 8.8, H2),
4.12 (1H, d, J = 10.3, H7), 6.09 (1H, br s, NH), 7.26–7.38
(8H, complex m, ArH). δC 47.54 (C6), 50.44 (C3), 58.63 (C7),
64.52 (C2), 127.73, 128.05, 128.86 (ArC), 133.42, 133.70,
140.47, 143.04 (ArCq), 176.31 (C5). HRMS (MALDI): Found:
335.0735. C17H17N2Cl2O requires [M + H]+ 335.0718.
CDC deposition no.
Empirical formula
Formula weight
Crystal description
Crystal size [mm3]
Crystal system
Space group
Unit cell dimensions
a [Å]
b [Å]
716833
C18H18Cl2N2
333.24
Needle, colourless
0.32 × 0.20 × 0.10
Orthorhombic
P 212121
5.9357(9)
9.3627(11)
28.503(3)
1584.0(3)
c [Å]
Volume [Å3]
Z
4
Calc. density [mg m−3
]
1.397
0.407
95
Fine-focus sealed tube
0.71069
ω scans
Abs. coeff. µ [mm−1
Temperature [K]
Radiation source
Wavelength [Å]
Scan type
]
2,7-Bis(3,4-dichlorophenyl)-1,4-diazepan-5-one 6d
Standard reflections
Intensity decay [%]
θ range [◦]
Reflections collected
Reflections unique
3 every 100 reflections
0.0
2.60 to 27.50
3043
2663
2313 with I > 2σ(I)
0.0216
Reaction of ammonium acetate (4.63 g, 60 mmol), acetone
(6.97 g, 120 mmol), and 3,4-dichlorobenzaldehyde (21.06 g,
120 mmol) in ethanol (12 mL) yielded 5d·HCl (5.25 g, 21%).
5d·HCl (1.50 g, 3.52 mmol) reacted in conc. H2SO4 (10 mL)
with NaN3 (0.308 g, 4.74 mmol) to give a precipitate which was
recrystallized from toluene and subsequently from ethanol yield-
ing 6d (1.10 g, 77%). For analytical purposes, the crude product
was purified by CC using CH2Cl2/methanol (9:1) as an eluent.
νmax (KBr)/cm−1 3410, 1671, 1467, 1401, 1353, 1324, 1131,
1030, 820. λmax/nm (log ε) 230 (4.460). δH 2.05 (1H, br s, NH),
2.61 (1H, d, J = 14.7, H6), 3.04–3.14 (2H, m, H3, H6), 3.59 (1H,
ddd, J = 14.1, 9.2, 4.0, H3), 4.00 (1H, d, J = 8.8, H2), 4.10 (1H,
d, J = 10.6, H7), 6.14 (1H, br s, NH), 7.25–7.57 (6H, complex m,
ArH). δC 47.26 (C6), 50.14 (C3), 58.15 (C7), 64.03 (C2), 125.82,
126.11, 128.36, 128.69, 130.74 (ArC), 131.80, 132.07, 132.78,
132.84, 141.76, 144.33 (ArCq), 175.93 (C5). HRMS (MALDI):
Found: 400.9796. C17H13N2Cl4O requires [M − H]− 400.9782.
Sign. unique reflections
R(int)
R(sigma)
0.0583
99.8%
Compl. to ꢀ = 27.5◦
Final R ind. [I > 2σ(I)]
R1
wR2
0.0394
0.0787
R indices (all data)
R1
0.0494
0.0835
1.036
wR2
Goodness-of-fit on F2
General Procedure for the Preparation
of 2,7-Diaryl-1,4-diazepanes 7
addedinportionsof0.1 gwithvigorousstirring.Themixturewas
then poured over crushed ice and basified cautiously with cold
2 M NaOH to pH 8. A white solid separated. After the mixture
was kept over night at room temperature, it was filtered, washed
with water, and dried. It was dissolved in toluene, filtered, and
the solution concentrated for crystallization. The precipitate was
filtered and recrystallized.
The powdered 2,7-diaryl-1,4-diazepan-5-ones 6 were suspended
in stirred, ice cooled dry ether and LiAlH4 added portion wise.
The mixture was refluxed over night in an oil bath, cooled to
room temperature and cautiously quenched with ice water while
cooled and stirred in an ice bath.Then 2 M NaOH was added and
the mixture was extracted 5 times with ether. The organic layers
were combined, washed with water, dried over sodium sulfate,
filtered and solvent evaporated under vacuum, to give yellow
oils. The dihydrochlorides were prepared from a solution of the
base in CH2Cl2 by repeated treatment with an excess of a 2 M
ether solution of HCl. Solvents were evaporated and the residues
recrystallized.
2,7-Bis(4-methylphenyl)-1,4-diazepan-5-one 6b
Reaction of ammonium acetate (7.7 g, 0.1 mol), acetone
(11.6 g, 0.2 mol), and 4-methylbenzaldehyde (24.0 g, 0.2 mol)
in ethanol (20 mL) yielded 5b·HCl (6.24 g, 20%). 5b·HCl
(2.95 g, 9.34 mmol) reacted in conc. H2SO4 (13 mL) with NaN3
(745 mg, 11.5 mmol) giving a precipitate which was recrystal-
lized from methanol yielding 6b (2.20 g, 80%), mp 177◦C. νmax
(KBr)/cm−1 3212, 3088, 2920, 1674, 1511, 1486, 1456, 1430,
1406, 1351, 1320, 1108, 817, 771. λmax/nm (log ε) 229 (3.550),
264 (2.960). δH 2.05 (1H, br s, NH), 2.32 (6H, s, 2CH3), 2.65
(1H, d, J = 14.3, H6), 3.08–3.14 (2H, m, H3, H6), 3.62 (1H,
ddd, J = 14.1, 9.2, 4.2, H3), 3.99 (1H, d, J = 8.8, H2), 4.10
(1H, d, J = 10.3, H7), 6.02 (1H, br s, NH), 7.12–7.32 (8H, com-
plex m, ArH). δC 21.03 (2CH3), 47.77 (C6), 50.75 (C3), 59.11
(C7), 65.01 (C2), 126.24, 126.57, 129.22 (ArC), 137.19, 137.49,
139.42, 141.97 (ArCq), 176.85 (C5). HRMS (MALDI): Found:
295.1805. C19H23N2O requires [M + H]+ 295.1810.
2,7-Diphenyl-1,4-diazepane 7a
Reaction of 6a (1.64 g, 5.48 mmol) with LiAlH4 (836 mg,
22 mmol) in dry ether (70 mL) yielded 7a (1.304 g, 94%) as
a yellow oil which crystallized spontaneously. The dihydrochlo-
ride was recrystallized from ethanol giving colourless crystals,
mp (HCl) 297◦C. νmax (KBr)/cm−1 3341, 3026, 2931, 2827,
1600, 1492, 1452, 1337, 1148, 1134, 1028, 915, 757, 700.
λmax/nm (log ε) 207 (4.270). δH 1.91–2.01 (1H, m, H6), 2.03–
2.11 (1H, m, H6), 2.92 (1H, dd, J = 13.2, 9.9, H3), 3.04–3.20
(3H, m, H3, H5), 3.97 (1H, dd, J = 9.9, 3.7, H2), 4.07 (1H, dd,

Synthesis of Novel Diazabicycles
1171
J = 10.3, 4.4, H7), 7.18–7.41 (10H, complex m, ArH). δC 41.76
(C6), 46.67 (C5), 59.45 (C3), 64.17 (C7), 67.21 (C2), 126.44,
126.79, 126.93, 127.17, 128.40, 128.45 (ArC), 143.65, 146.35
(ArCq). HRMS (MALDI): Found: 253.1644. C17H21N2 requires
[M + H]+ 253.1705.
Na2SO4, and filtered. The solvents were evaporated under vac-
uum and the remaining residue was purified using CC on basic
aluminum oxide with CH2Cl2 as eluent. Fractions containing
compounds 8 were collected and the solvent was removed under
vacuum. The oily residue was recrystallized.
2,7-Bis(4-methylphenyl)-1,4-diazepane 7b
2,7-Diphenyl-1,5-diazabicyclo[3.2.1]octane 8a
Reaction of 6b (1.62 g, 5.48 mmol) with LiAlH4 (836 mg,
22 mmol) in dry ether (70 mL) yielded 7b (1.13 g, 70%). The
dihydrochloride was recrystallized from EtOH giving colour-
less crystals, mp (HCl) 259◦C. νmax (KBr)/cm−1 3417, 2923,
2734, 1616, 1561, 1518, 1456, 1437, 1191, 1055, 811. λmax/nm
(log ε) 210 (4.378). δH 1.76 (2H, br s, NH), 1.89–1.98 (1H, m,
H6), 2.01–2.08 (1H, m, H6), 2.30 (6H, s, 2CH3), 2.90 (1H, dd,
J = 13.4, 9.9, H3), 3.03–3.18 (3H, m, H3, H5), 3.93 (1H, dd,
J = 9.9, 4.0, H2), 4.02 (1H, dd, J = 10.4, 4.2, H7), 7.08–7.29
(8H, complex m, ArH). δC 20.95 (CH3), 20.96 (CH3), 41.75
(C6), 46.65 (C5), 59.48 (C3), 63.99 (C7), 66.97 (C2), 126.35,
126.68, 129.03, 129.07 (ArC), 136.46, 136.72, 140.71, 143.42
(ArCq). HRMS (MALDI): Found: 281.2001. C19H25N2 requires
[M + H]+ 281.2018.
Reaction of 7a (460 mg, 1.8 mmol) and paraformaldehyde
(200 mg, 6.4 mmol) in dry ethanol (10 mL) in the presence of
potassium carbonate (10 mg) yielded 8a (467 mg, 98%).
Microwave-Assisted Reaction for Formation of
2,7-Diphenyl-1,5-diazabicyclo[3.2.1]octane 8a
Reaction of 7a (137 mg, 0.54 mmol) and paraformaldehyde
(40 mg, 1.3 mmol) in dry ethanol (4 mL) in the presence ◦of
potassium carbonate (4 mg), 1 h irradiation at 250W at 120 C
yielded 8a (148 mg, 94%), mp (hexane) 60◦C. νmax (KBr)/cm−1
3432, 3058, 3024, 2943, 2878, 1600, 1493, 1447, 1295, 1260,
1079, 1025, 900, 949, 825, 811, 775, 753, 730, 699. λmax/nm
(log ε) 230 (3.433). δH 1.87 (1H, dd, J = 15.2, 4.6, H3up),
2.25–2.36 (1H, m, H3dn), 2.86–2.96 (2H, m, H4dn, H6up), 3.08
(1H, d, J = 11.0, H8r), 3.28 (1H, ddd, J = 18.3, 13.6, 4.8,
H4up), 3.72 (1H, ddd, J = 11.9, 7.9, 1.6, H6dn), 3.88 (1H, d,
J = 11.0, H8l), 4.10 (1H, d, J = 7.0, H2), 4.61 (1H, br t, J = 6.4,
H7), 7.17–7.65 (10H, complex m, ArH). δC 19.86 (C3), 51.07
(C4), 60.92 (C6), 62.11 (C2), 65.62 (C7), 70.20 (C8), 125.70,
126.11, 126.53, 127.74, 128.11, 128.19 (ArC), 141.48, 143.99
(ArCq). HRMS (MALDI): Found: 265.1706. C18H21N2 requires
[M + H]+ 265.1705.
2,7-Bis(4-chlorophenyl)-1,4-diazepane 7c
Reaction of 6c (1.62 g, 4.8 mmol) with LiAlH4 (836 mg,
22 mmol) in dry ether (70 mL) yielded 7c (1.33 g, 86%). The
dihydrochloride was recrystallized from MeOH giving colour-
less crystals, mp (HCl) 298◦C. νmax (KBr)/cm−1 3424, 2963,
2736, 2684, 2646, 1598, 1550, 1495, 1462, 1426, 1088, 1054,
1016, 997, 824, 722, 691. λmax/nm (log ε) 220 (4.425). δH 1.73
(2H, br s, NH), 1.86–1.95 (1H, m, H6), 2.01–2.08 (1H, m, H6),
2.86 (1H, dd, J = 13.2, 9.5, H3), 3.03–3.17 (3H, m, H3, H5), 3.95
(1H, dd, J = 9.5, 3.8, H2), 4.06 (1H, dd, J = 10.3, 4.0, H7), 7.25–
7.34 (8H, complex m, ArH). δC 41.64 (C6), 46.67 (C5), 59.36
(C3), 62.95 (C7), 66.23 (C2), 127.81, 128.17, 128.59, 128.64
(ArC), 132.59, 132.89, 142.05, 144.80 (ArCq). HRMS (EI+):
Found: 318.0633. C17H16N2Cl2 requires [M − 2H]+ 318.0691.
Found: 262.0193. C14H10NCl2 requires [M]+ 262.0190.
For the determination of reaction progress, the same reac-
tion batch as above was used and 0.2 mL samples were taken
at different times. The solvent was evaporated and the residue
dried in a drying pistol. The residue was dissolved in CDCl3 and
1
the ratios of educt to product were determined using H NMR
integration.
2,7-Bis(4-methylphenyl)-1,5-diazabicyclo[3.2.1]octane 8b
Reaction of 7b (446 mg, 1.59 mmol) with paraformaldehyde
(177 mg, 5.90 mmol) in dry ethanol (10 mL) in the presence
of potassium carbonate (10 mg) yielded 8b (353 mg, 76%), mp
(acetone) 116◦C. νmax (KBr)/cm−1 3442, 2975, 2946, 2875,
1510, 1461, 1448, 1293, 1259, 1081, 1032, 1018, 989, 951, 936,
838, 798, 723. λmax/nm (log ε) 230 (3.758), 266 (3.024). δH 1.90
(1H, dd, J = 15.0, 4.4, H3), 2.31–2.40 (1H, m, H3), 2.34 (3H,
s, CH3), 2.38 (3H, s, CH3), 2.88–2.95 (2H, m, H4, H6), 3.08
(1H, d, J = 11.0, H8), 3.31 (1H, ddd, J = 18.3, 13.6, 4.8, H4),
3.75 (1H, ddd, J =12.8, 7.7, 1.8, H6), 3.90 (1H, d, J = 11.0, H8),
4.12 (1H, d, J = 7.0, H2), 4.63 (1H, br t, J = 6.2, H7), 7.14–7.57
(8H, m, ArH). δC 20.25 (C3), 20.99 (CH3), 21.03 (CH3), 51.40
(C4), 61.31 (C6), 62.19 (C2), 65.67 (C7), 70.32 (C8), 125.89,
127.91, 128.97, 129.04 (ArC), 135.77, 136.25, 138.89, 141.48
(ArCq). HRMS (MALDI): Found: 293.2037. C20H25N2 requires
[M + H]+ 293.2018.
2,7-Bis(3,4-dichlorophenyl)-1,4-diazepane 7d
Reaction of 6d (0.608 g, 1.50 mmol) with LiAlH4 (257 mg,
6.77 mmol) in dry ether (22 mL) yielded 7d (450 mg, 77%). The
dihydrochloride was recrystallized from ethanol giving colour-
less crystals, mp (HCl, decomp.) 275◦C. νmax (KBr)/cm−1 3426,
2962, 2712, 2679, 1549, 1468, 1435, 1412, 1137, 1032, 916, 834,
823, 778. λmax/nm (log ε) 205 (4.787). δH 1.76 (2H, br s, NH),
1.85–1.94 (1H, m, H6), 2.01–2.09 (1H, m, H6), 2.85 (1H, dd,
J = 13.4, 9.3, H3), 3.04–3.16 (3H, m, H3, H5), 3.94 (1H, dd,
J = 9.2, 3.7, H2), 4.05 (1H, dd, J = 10.1, 3.8, H7), 7.20–7.50
(6H, complex m, ArH). δC 41.36 (C6), 46.64 (C5), 59.04 (C3),
62.07 (C7), 66.49 (C2), 125.86, 126.26, 128.44, 128.80, 130.41,
130.47 (ArC), 130.81, 131.12, 132.45, 143.61, 146.34 (ArCq).
HRMS (MALDI): Found: 389.0119. C17H17N2Cl4 requires
[M + H]+ 389.0146.
General Procedure for the Preparation of
2,7-Bis(4-chlorophenyl)-1,5-diazabicyclo[3.2.1]octane 8c
2,7-Diaryl-1,5-diazabicyclo[3.2.1]octanes 8
Reaction of 7c (578 mg, 1.8 mmol) and paraformaldehyde
(200 mg, 6.66 mmol) in dry ethanol (10 mL) in the presence
of potassium carbonate (10 mg) yielded 8c (472 mg, 79%), mp
(ethanol) 126◦C. νmax (KBr)/cm−1 3433, 2967, 2948, 2921,
2875, 1488, 1461, 1398, 1295, 1101, 1082, 1031, 1008, 991,
939, 844, 810, 776, 710. λmax/nm (log ε) 231 (4.031). δH 1.88
(1H, dd, J = 15.4, 4.4, H3), 2.31–2.41 (1H, m, H3), 2.87–2.93
2,7-diaryl-1,4-diazepanes 7 and paraformaldehyde were sus-
pended in dry ethanol and a catalytic amount of potassium
carbonate was added. The mixture was refluxed over night
at 100◦C in an oil bath and the solvent was evaporated. The
remaining residue was repeatedly extracted with ether.The com-
bined organic phases were washed twice with water, dried over

1172
V. Wolkinger et al.
(2H, m, H4, H6), 3.03 (1H, d, J = 11.0, H8), 3.25 (1H, ddd,
J = 18.3, 13.6, 4.6, H4), 3.76 (1H, ddd, J = 11.9, 7.7, 2.2, H6),
3.83 (1H, d, J = 11.0, H8), 4.10 (1H, d, J = 7.0, H2), 4.60
(1H, br t, J = 6.4, H7), 7.29–7.60 (8H, m, ArH). δC 20.04
(C3), 51.06 (C4), 61.19 (C6), 61.78 (C2), 65.26 (C7), 70.34
(C8), 127.30, 128.45, 128.46, 129.32 (ArC), 131.99, 132.56,
140.04, 142.53 (ArCq). HRMS (MALDI): Found: 333.0946.
C18H19N2Cl2 requires [M + H]+ 333.0925.
microtiter plate. Serial drug dilutions were added to the wells.
Then 50 µL of trypanosome suspension (T. b. rhodesiense STIB
900) was added to each well and the plate incubated at 37◦C
under a 5% CO2 atmosphere for 72 h. Alamar Blue (10 µL)
was then added to each well and incubation continued for a fur-
ther 2–4 h. The plate was then read with a Millipore Cytofluor
2300 using an excitation wavelength of 530 nm and emis-
sion wavelength of 590 nm.[17] Fluorescence development was
expressed as percentage of the control, and IC50 values deter-
mined. Cytotoxicity was assessed using the same assay and L-6
cells.
X-Ray Diffraction Data of 8c
All the measurements were performed using graphite-
monochromatized Mo Kα radiation. The structure was solved by
directmethods(SHELXS-97)[14] andrefinedbyfull-matrixleast-
squares techniques against F2 (SHELXL-97).[15] The crystal was
a racemic twin. The refinement was performed using a twin
matrix (−1 0 0 / 0 −1 0 / 0 0 1). No scale factor between the two
twin components was refined in the final refinements because it
did not significantly deviate from 0.5. The non-hydrogen atoms
were refined with anisotropic displacement parameters without
any constraints. The H atoms of the CH2 groups were refined
with common isotropic displacement parameters for the H atoms
of the same group and idealized geometry with approximately
tetrahedral angles and C–H distances of 0.99 Å. The H atoms of
the tertiary C–H groups were included with all X–C–H angles
equal at a C–H distance of 1.00 Å\%A with their isotropic dis-
placement parameters fixed to 1.2 times Ueq of the C atom they
are bonded to. The H atoms of the phenyl rings were put at the
external bisector of the C–C–C angle at a C–H distance of 0.95 Å
and common isotropic displacement parameters were refined for
the H atoms of the same phenyl group. For 205 parameters final R
indices of R1 = 0.0394 and wR2 = 0.0835 (GOF = 1.036) were
obtained (Table 4). The largest peak in a difference Fourier map
In vitro Assay Against Plasmodium falciparum
Antiplasmodial activity was determined using the K1 strain
of P. falciparum (resistant to chloroquine and pyrimethamine).A
modification of the [3H]-hypoxanthine incorporation assay was
used.[18] Briefly, infected human red blood cells in RPMI 1640
medium with 5%Albumax were exposed to serial drug dilutions
in microtiter plates for 48 h.Viability was assessed by measuring
the incorporation of [3H]-hypoxanthine by liquid scintillation
counting 24 h after the addition of the radiolabel. The counts
were expressed as percentage of the control cultures, sigmoidal
inhibition curves were drawn and IC50 values calculated.
References
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[6] H. Wolff, Org. React. 1946, 3, 307.
2,7-Bis(3,4-dichlorophenyl)-1,5-diazabicyclo
[3.2.1]octane 8d
[7] R. W. Alder, E. Heilbronner, E. Honegger, A. B. McEwen, R. E.
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[8] I. L. Karle, K. Britts, Acta Crystallogr. 1966, 21, 532. doi:10.1107/
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[9] B. Alcaide, L. Casarrubios, G. Dominguez, M. A. Sierra, A. Monge,
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[10] C. K. Johnson, ORTEP. Report ORNL-3794. Oak Ridge National
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[11] H. Stetter, J. Schäfer, K. Dieminger, Chem. Ber. 1958, 91, 598.
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[12] T. Ravindran, R. Jeyaraman, R. W. Murray, M. Singh, J. Org. Chem.
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Chem. 1992, 57, 6006. doi:10.1021/JO00048A041
[14] G. M. Sheldrick, SHELXS-97. Program for the Solution of Crystal
Structures. University of Göttingen, Germany, 1997.
[15] G. M. Sheldrick, SHELXL-97. Program for the Refinement of Crystal
Structures. University of Göttingen, Germany, 1997.
Reaction of 7d (215 mg, 0.55 mmol) and paraformaldehyde
(61 mg, 2.0 mmol) in dry ethanol (5 mL) in the presence of potas-
sium carbonate (10 mg) yielded 8d (182 mg, 82%), mp (ethanol)
144◦C. νmax (KBr)/cm−1 2947, 2884, 1470, 1383, 1293, 1263,
1202, 1127, 1084, 1027, 990, 945, 888, 867, 837, 806, 798, 736,
710. λmax/nm (log ε) 231 (4.149), 274 (3.171), 283 (3.116). δH
1.86 (1H, dd, J = 15.4, 4.0, H3), 2.30–2.41 (1H, m, H3), 2.86–
2.93 (2H, m, H4, H6), 3.03 (1H, d, J = 11.4, H8), 3.23 (1H, ddd,
J = 18.1, 13.7, 4.6, H4), 3.76 (1H, dd, J = 12.1, 8.1, H6), 3.83
(1H, d, J = 11.4, H8), 4.08 (1H, d, J = 6.6, H2), 4.56 (1H, br t,
J = 6.2, H7), 7.21–7.72(6H, m,ArH). δC 20.02(C3), 50.86(C4),
61.12 (C6), 61.53 (C2), 64.92 (C7), 70.55 (C8), 125.39, 127.32,
127.87, 129.91, 130.34, 130.41 (ArC), 130.26, 132.43, 132.54,
141.69, 144.14 (ArCq). HRMS (MALDI): Found: 401.0112.
C18H17N2Cl4 requires [M + H]+ 401.0146.
[16] T. Baltz, D. Baltz, C. Giroud, J. Crockett, EMBO J. 1985, 4, 1273.
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[18] H. Matile, J. R. L. Pink, in Immunological Methods (Eds I. Lefkovits,
B. Pernis) 1990, pp. 221–234 (Academic Press: San Diego).
Biological Activities
In vitro Assay Against Trypanosoma b. rhodesiense,
Cytotoxicity
Minimum Essential Medium (50 µL) supplemented accord-
ing to Baltz et al.[16] with 2-mercaptoethanol and 15% heat-
inactivated horse serum was added to each well of a 96-well