Synthesis and biological evaluation of conformationally flexible as well as restricted dimers of monastrol and related dihydropyrimidones

Article abstract of DOI:10.1016/j.ejmech.2011.04.048

A series of conformationally flexible and restricted dimers of monastrol as well as related dihydropyrimidones have been synthesized by employing one-pot Biginelli multicomponent reaction. These dimers have been evaluated for cytotoxic potency against sel

Full text of DOI:10.1016/j.ejmech.2011.04.048

European Journal of Medicinal Chemistry 46 (2011) 3274e3281
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European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and biological evaluation of conformationally flexible as well as
restricted dimers of monastrol and related dihydropyrimidones
,
a
a
a
a
b
Ahmed Kamal a , M. Shaheer Malik , Shaik Bajee , Shaik Azeeza , Shaikh Faazil , Sistla Ramakrishna ,
*
V.G.M. Naidu b, M.V.P.S. Vishnuwardhan b
a Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 607, India
b Division of Pharmacology, Indian Institute of Chemical Technology, Hyderabad 500 607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of conformationally flexible and restricted dimers of monastrol as well as related dihydropyr-
imidones have been synthesized by employing one-pot Biginelli multicomponent reaction. These dimers
have been evaluated for cytotoxic potency against selected human cancer cell lines and some of the
compounds have exhibited more cytotoxic potency than the parent monastrol. Further, the DNA binding
ability by thermal denaturation studies and antimicrobial activities of these compounds are also
discussed.
Received 13 December 2010
Received in revised form
19 April 2011
Accepted 19 April 2011
Available online 5 May 2011
Ó 2011 Elsevier Masson SAS. All rights reserved.
Keywords:
Monastrol
Dihydropyrimidones
Dimers
Anticancer
Antimicrobial
DNA binding ability
1. Introduction
By the end of last century a structurally simple DHPM, monas-
trol (1) has been identified on screening a large library of diverse
With the discovery of multicomponent reaction, the dihy-
dropyrimidin-(1H)-ones (DHPM’s) were reported for the first time
by Biginelli over a century ago [1]. The multifunctionalized dihy-
small molecules, as a novel cell permeable molecule that causes
mitotic arrest by blocking bipolar mitotic spindle in mammalian
cells (Fig. 1) [6]. Monastrol is the first Eg5 inhibitor to be identified
dropyrimidinones scaffold represents
a
class of heterocylic
with an IC50 value of 14 mM causing a specific and reversible cell
compounds with significant pharmacological efficiency and are
receiving considerable amount of interest. They exhibit a diverse
pharmacological profile like calcium channel blockade, a1a-adre-
noreceptor antagonism, antibacterial, antifungal and other related
properties [2,3]. From natural marine sources, several alkaloids
containing the dihydropyrimidine core unit have been isolated
such as batzelladine alkaloids, which are found to be potent HIV gp-
120-CD4 inhibitors [4]. With the advent of combinatorial synthesis,
which is particularly useful for multicomponent reactions like
Biginelli condensation, diverse DHMPs libraries have been
synthesized and subjected to high throughtput screening for bio-
logical activity [5].
cycle block. It is considered as a new lead in anticancer drug
development as it specifically inhibits mitotic kinesin Eg5 motor
protein. The antimitotic activity of monastrol itself is not very high
and this does not warrant it as a drug candidate [7]. Therefore the
development of more potent, specific, cell permeable monastrol
analogues with enhanced kinesin inhibitory and anti-proliferative
properties has been carried out in recent years with encouraging
results [8] and necessitates more studies in this potential cancer
drug development area.
In continuation of our research endeavors on the development
of new agents based on heterocyclic scaffolds with enhanced bio-
logical effects [9], it is considered of interest to synthesize the
dimers of dihydropyrimidone scaffold and evaluate their biological
properties. Moreover as the DHPMs exhibits a diverse pharmaco-
logical profile, dimers of monastrol and related dihydropyr-
imidones with flexible alkyl chain spacers of varying length and
conformationally restricted spacers with unsaturation (cis and
* Corresponding author. Tel.: þ91 40 27193157; fax: þ91 40 27193189.
E-mail address: ahmedkamal@iict.res.in (A. Kamal).
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.04.048

A. Kamal et al. / European Journal of Medicinal Chemistry 46 (2011) 3274e3281
3275
position) by introducing amide functionality. The naturally occur-
ring amino acid proline has been utilized in the introduction of
amide functionality as it is present in many natural and synthetic
compounds which exhibits anti-proliferative activity. The required
OH
O
O
NH
b-ketoamide intermediate has been prepared starting from
L
-proline by trans-acetoacetylation of methylated proline with tert-
N
H
S
butyl acetoacetate. The symmetric dimers of monastrol 9aee are
synthesized by cyclocondensation of the substituted dibenzalde-
hyde 4aee, thiourea 6 and ethyl acetoacetate 7 by employing
cerium chloride in acetonitrile under reflux condition in good
1
Fig. 1. Structure of Monastrol.
yields. The use of
b-ketoamide 8 in the Biginelli condensation
provides the asymmetric dimers 10aee (Scheme 2).
trans) have been designed and synthesized. The dimers with flex-
ible alkyl chain bridge are intended to assume different intercon-
vertible conformations, whereas the dimers with unsaturated
spacers shows reduced conformational flexibility. Further the
cytotoxic potency, DNA binding ability and antimicrobial properties
of these dimers have been evaluated.
The symmetric dimers of dihydropyrimidones 11aee are also
synthesized by cerium chloride catalyzed condensation of
substituted dibenzaldehydes 5aee, ethyl acetoacetate 7 and thio-
urea 6 under refluxing acetonitrile in good yields. Similarly, the
asymmetric dimers of monastrol related dihydropyrimidones
(12aee) are synthesized by the same Biginelli protocol with
ketoamide 8 in good to acceptable yields (Scheme 3).
b-
2. Chemistry
The key intermediates (4aee, 5aee) required for the synthesis of
dimers of monastrol and related dihydropyrimidones have been
prepared by the condensation of the corresponding substituted
aromatic benzaldehyde with dibromo aliphatic compounds. The
3. Pharmacology
3.1. Cytotoxicity assay
condensation of the 3-hydroxy aldehyde
2
with dibromo
The synthesized dimers (9e12aee) have been evaluated for
their in vitro cytotoxicity in selected human cancer cell lines of
breast (MCF-7), colon (Colo-205, HT-29), skin (A431), and lung
cancer (A549). The in vitro cytotoxic activity of the compounds has
been tested in triplicates and determined by MTT cell proliferative
assay based on mitochondrial reduction of yellow MTT tetrazolium
to a highly coloured blue formazan product [12]. The human tumor
cell lines of the cancer screening panel are grown in DMEM
medium (for A431, Colo-205), RPMI medium (for A549) and MEM
medium (for MCF-7) supplemented with 10% fetal bovine serum
compounds (1, 3-dibromo propane, 1, 4-dibromobutane, 1, 5-
dibromo pentane, cis-1, 4-dichlorobutane and trans-1, 4-dibromo-
butane) provides the substituted dibenzaldehydes 4aee (Scheme 1).
The condensation is carried out under reflux condition employing
anhydrous potassium carbonate as base in acetonitrile. The use of
potassium iodide salt as catalyst has provided the intermediates
4aee in good yields. The synthesis of the intermediates 5aee is
carried out with vanillin (3) under similar conditions in good yields.
The substituted dibenzaldehydes (4aee and 5aee) have been
utilized to synthesize the dimers by employing Biginelli reaction.
The Biginelli condensation is an important multicomponent reac-
tion (MCR), inwhich the product is assembled according toa cascade
of elementary chemical reactions [10]. The MCR approach is
considered as a powerful synthetic tool for preparing target mole-
cules of biological relevance in an efficient manner. The MCRs can
provide products with the diversity needed for the discovery of new
lead compounds or lead optimization employing combinatorial
chemistry techniques [11]. This aspect of multicomponent approach
for the synthesis of dimers of monastrol and related dihydropyr-
imidone employing Biginelli condensation protocol is exploited in
the present study. The substituted dibenzaldehydes 4aee and 5aee
are subjected to Bignelli condensation with thiourea 6 and 1,3-
and 2 mM L
-glutamine. The cultures are incubated at 37 ꢀC, 5% CO2,
95% air and 100% relative humidity for 24 h prior to addition of
experimental compounds. For a typical screening experiment,
1 ꢁ 104 cells counted by Tryptan blue exclusion dye method are
incubated with a series of concentration (200,100, 50, 25 and 10 mg/
mL) of the compounds in a 96 well micro titer plates for 48 h at
37 ꢀC in RPMI/DMEM/MEM with 10% FBS medium. The viability of
the cells is measured by adding 10
PBS) to each well containing 90 l of fresh serum free media. The
plates are incubated at 37 ꢀC for 4 h, followed by replacing the
media with 200
l of DMSO and again incubated for 10 min at 37 ꢀC.
ml of MTT reagent (5 mg/mL in
m
m
The absorbance is measured on a spectrophotometer (SpectraMax,
Molecular devices) at 570 nm wavelength. The mean percent of cell
viability relative to that of untreated cells is estimated from data of
three individual experiments. Finally, the IC50 value of each
compound is calculated by curve fitting method.
dicarbonyl ester (ethyl acetoacetate 7) as well as
b-ketoamide 8.
In the present investigation, structural modification on the
monastrol backbone has been carried out at the ester moiety (C-5
OH
O
O
( )n
i
CHO
2
CHO
OMe
CHO
OMe
4a-e
a
b
c
d
e
n
3
4
5
OH
OMe
O
O
( )n
i
OHC
CHO
CHO
3
5a-e
Scheme 1. Synthesis of substituted dibenzaldehydes (4aee, 5aee). Reagents and conditions: (i) Dibromo compound, and. K2CO3, cat. KI, CH3CN.

3276
A. Kamal et al. / European Journal of Medicinal Chemistry 46 (2011) 3274e3281
OEt
S
O
O
( )n
i
HN
O
HN
O
NH
4a-e
+
O
O
( )n
S
N
H
CHO
NH2
CHO
O
S
O
OEt
9a-e
H2N
O
6
7
O
O
CO2Me
O
( )n
N
S
HN
O
HN
O
NH
N
4a-e
i
O
CHO
O
CHO
H2N
+
( )n
S
N
H
O
CO2Me
S
+
N
NH2
10a-e
MeO2C
8
6
a
b
c
d
e
n
3
4
5
Scheme 2. Synthesis of dimers of monastrol (9aee, 10aee). Reagents and conditions: (i) CeCl3.7H2O, CH3CN.
3.2. Thermal denaturation studies
the dry inoculums 6 mm diameter wells are prepared with the help
of sterilized cork borer. Finally, different concentration of test
The thermal denaturation studies for determining the DNA
binding ability of dimers with dihydropyrimidine ring system have
been investigated with duplex form of DNA from calf thymus (CT-
DNA) following reported procedure [13]. Working solutions in
aqueous buffer (10 mM NaH2PO4/Na2HPO4, 1 mM Na2EDTA, pH
compounds (50e100 mg/mL) are prepared by dissolving in dimethyl
sulfoxide (DMSO) and introduced into duplicate wells. The plates
are incubated at 37 ꢀC for 18 h. Subsequently, the plates are
examined for bacterial growth inhibition and the inhibition zone
diameter (IZD) is measured to the nearest millimeter. The standard
antibiotic, ciprofloxacin is used as positive control and DMSO is
used as negative control.
7.00) containing CT-DNA (100
mM in phosphate) and the dimer
compounds (20 M) are prepared by addition of concentrated
m
compound solutions in DMSO to obtain a fixed [Compd]/[DNA]
molar ratio of 1:5. The resulting DNA-ligand solutions are incubated
for 0 and 18 h at 37 ꢀC, followed by monitoring at 260 nm using
a BeckmaneCoulter DU 800 spectrophotometer fitted with high
performance temperature controller by heating applied at 1 ꢀC
minꢂ1 in the 40e90 ꢀC range.
4. Results and discussion
4.1. In vitro cytotoxic activity
The dimers of monastrol (9aee, 10aee) and related dihy-
dropyrimidones (11aee, 12aee) have been evaluated for their
in vitro cytotoxicity in selected human cancer cell lines of breast
(MCF-7), colon (Colo-205, HT-29), skin (A431), and lung cancer
(A549) by using MTT cell proliferative assay. Table 1 reveals the
cytotoxic activity of symmetric (9aee) and asymmetric dimers
(10aee) of monastrol expressed in half maximal inhibitory
concentration (IC50) in microgram per milliliter. Almost all the
dimers of monastrol did not show any significant activity against
3.3. Antimicrobial assay
The antibacterial screening of the synthesized dimers have been
determined by the well diffusion method. First, three to five iden-
tical colonies from cultured agar plates are inoculated into a 5 mL of
nutrient medium in culture tube. The culture tubes are incubated
and the turbidity of each bacterial suspension is adjusted to reach
an optical comparison to that of a 0.5 McFarland standard; resulting
in a suspension containing approximately 1 ꢁ 108 CFU/mL. Then,
Mueller-Hinton agar plates are inoculated by streaking with
a sterilized swab over the entire sterile agar surface twice to ensure
even distribution of the inoculums and the rim of the agar is also
swabbed. The plates are allowed to dry at room temperature and on
the HT-29 cancer cell line (IC50 value >200 mg/mL). Some encour-
aging activities are shown by the dimers particularly for the cell
lines Colo-205 and A431. The most cytotoxic effect is shown on
MCF-7 cell line and the monastrol dimer 9d and 10e exhibit
moderate cytotoxic activity against this cell line with an IC50 value
around 50
mg/mL, whereas the dimer 10c exhibited IC50 value of
OMe
OMe
R
O
O
O
( )n
OMe
OMe
H
N
S
O
O
i
( )n
+ 6 + 7/8
HN
S
NH
O
R
NH
OHC
CHO
5a-e
R = -OEt 11a-e
a
b
c
d
e
O
12a-e
n
3
4
5
R =
N
O
Scheme 3. Synthesis of dimers of monastrol related dihydropyrimidones (11aee, 12aee). Reagents and conditions: (i) CeCl3.7H2O, CH3CN.

A. Kamal et al. / European Journal of Medicinal Chemistry 46 (2011) 3274e3281
3277
Table 1
Table 3
IC50 valuesa (in
lines.
m
g/mL) for dimers 9aee and 10aee in selected human cancer cell
Thermal denaturation data with CT-DNA.
Compound
[Compd.]:[DNA] Molar ratioa
D
Tm (ꢀC)b after
incubation at
Compound
MCF-7b
A431c
Colo-205d
A549e
37 ꢀC
9a
9b
9c
9d
16
186
178
49
175
175
128
34
76
>200
74
190
185
190
148
159
183
96
144
>200
190
120
>200
>200
154
>200
175
>200
184
>200
148
0 h
18 h
9a
9e
10d
10e
11e
12d
12e
Monastrol
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:5
0.2
2.5
3.0
2.1
2.8
3.8
2.5
0.1
0.1
2.5
3.1
2.5
3.2
4.1
2.8
0.0
64
9e
>200
>200
154
71
180
10a
10b
10c
10d
10e
Monastrol
156
54
45
127
164
53
118
a
For CT-DNA alone at pH 7.00 ꢃ 0.01, Tm ¼ 69.2ꢀC ꢃ 0.01 (mean value from 10
a
50% Inhibitory concentrations and the values are mean of three determinations.
separation determinations), all
D
Tm values are ꢃ 0.01e0.02.
b
c
Breast cancer.
Skin cancer.
Colon cancer.
Lung cancer.
b
For a 1:5 M ratio of [Compd.]/[DNA], where CT-DNA concentration ¼ 100
and ligand concentration ¼ 20 M in aqueous sodium phosphate buffer [10 mM
sodium phosphate þ 1 mM EDTA, pH 7.00 ꢃ 0.01].
mM
m
d
e
studies with CT-DNA and the increase in melting temperature
Tm) for each compound was examined at 0 and 18 h incubation at
34
mg/mL. Amongst the series of dimers of monastrol the
(D
compound 9a, with three carbon alkyl spacing and an ester group
at the C5 position of the pyrimidine ring, is found to be the most
active displaying an IC50 value of 16 mg/mL against MCF-7 cell line.
37 ꢀC. Among the compounds investigated, some of the dimers
elevated the helix melting temperature of CT-DNA and are shown
in Table 3. It is interesting to note that the conformationally
restricted dimers with cis and trans double bond have specifically
exhibited an increase in helix melting temperature of CT-DNA. The
It is interesting to note that some of the compounds in the series are
more potent than monastrol, the parent structure and the dimer 9a
is almost 3 times more potent than monastrol against MCF cell line.
During the completion of this present investigation, bis(dihy-
dropyrimidinone)benzenes have been reported to possess weak to
moderate cytotoxic potency [14].
The cytotoxic activity of symmetric (11aee) and asymmetric
dimers (12aee) ofmonastrol related dihydropyrimidones is shownin
Table 2. Similar to the dimers of monastrol, these dimers have shown
negligible activity against the tested cell lines of colon (HT-29). The
compound 12d has shown more affinity to DNA with a D
Tm of 3.8 ꢀC
at 0 h and 4.1 ꢀC after 18 h of incubation. Interestingly, the parent
compound monastrol showed no increase in DNA melting
temperature.
4.3. Antibacterial and antifungal activity
The multi-drug resistance to clinically available antibiotics
against bacterial and fungal pathogens is a frequently emerging
challenge resulting in efforts to design new chemical entities with
improved properties. The dihydropyrimidinones scaffold is well
known to possess antimicrobial activity [2], therefore these new
conformationally varying dimers of DHPM are also tested for
antibacterial activity against a panel of Gram-positive bacteria like
Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis
and Gram-negative bacteria such as Escherichia coli, Klebsiella
pneumoniae, and Pseudomonas aeruginosa. Whereas the antifungal
activity is evaluated against Candida albicans (MTCC 227). The
inhibitory zones (in mm) have been determined by using agar well
method (cup plate method) and the tests are performed in dupli-
cates. Most of the compounds have exhibited poor antibacterial
activity and some of the dimers which have exhibited moderate
activity are shown in Table 4. Further, the fungus C. albicans (MTCC
227) have been found to be resistant and the dimers have shown no
zone of inhibitions.
dimers 11e and 12a have shown an IC50 value of 90 mg/mL against
colo-205 cell line. Amongst the series, the dimers with trans unsat-
urated spacer (11e and 12e) are found to be active as they exhibit an
IC50 value of 35 mg/mLand34mg/mLagainstMCF-7andA431celllines,
respectively. Similar to dimers of monastrol, some compounds in this
series have also shown more cytotoxic potency than
monastrol. Compound 11a is found to be 2 times more potent than
monastrol against MCF cell line exhibiting an IC50 value of 22 mg/mL.
4.2. Thermal denaturation studies
The DNA binding ability of these conformationally flexible and
restricted dimers has been investigated by thermal denaturation
Table 2
IC50 valuesa (in
lines.
mg/mL) for dimers 11aee and 12aee in selected human cancer cell
Compound
MCF-7b
A431c
Colo-205d
A549e
11a
11b
11c
11d
11e
12a
12b
12c
22
178
180
84
66
185
124
170
185
165
190
125
183
34
49
>200
113
120
90
116
>200
>200
>200
165
180
>200
150
5. Conclusion
In summary, we have synthesized a series of conformationally
flexible and restricted dimers of monastrol as well as related
dihydropyrimidones by employing Biginelli cyclocondensation
reaction. These dimers have been evaluated for different biological
properties such as cytotoxic potency, antimicrobial activity and
DNA binding ability. The dimers showed moderate to good cyto-
toxic potency against selected human cancer cell lines and
compounds 9a, 10c, 11a, 11e and 12e are more potent than mon-
astrol. In addition, few of the compounds have exhibited moderate
DNA binding affinity, however no significant antimicrobial activity
has been observed.
35
140
169
55
175
60
92
154
142
>200
69
12d
12e
Monastrol
>200
158
118
45
53
164
a
50% Inhibitory concentrations and the values are mean of three determinations.
b
c
Breast cancer.
Skin cancer.
Colon cancer.
Lung cancer.
d
e

3278
A. Kamal et al. / European Journal of Medicinal Chemistry 46 (2011) 3274e3281
Table 4
Preliminary antibacterial activity of selected dimers against Gram-positive and negative bacteria at 100 mg/mL concentration (zone of inhibition in mm).
Compounda
S. aureus
S. epidermidis
B. substilis
E. Coli
K. pneumonia
P. aeroginosa
9a
9d
9e
10d
11b
11c
11d
CIPc
10
15
8
15
15
12
18
17
12
10
18
35
8
10
12
12
15
8
20
8
5
8
8
3
5
10
-
12
12
18
15
12
10
12
10
10
12
35
9
13
19 (10)b
12
20 (12)b
15
13
33
25
38
a
Bacteria are resistant to the compound at 50 mg/mL concentration.
Zone of inhibition 50 mg/mL concentration.
Ciprofloxacin used as standard.
b
c
6. Experimental protocols
6.2.2. 3-[4-(3-Formylphenoxy)butoxy]benzaldehyde (4b)
Yield: 74%; mp 49e50 ꢀC; IR (KBr): 2926, 1692, 1586, 1263 cmꢂ1
1H NMR (300 MHz, CDCl3):
1.96e2.08 (4H, m), 4.05e4.16 (4H, m),
;
6.1. Material and methods
d
7.08e7.18 (2H, m), 7.32e7.47 (6H, m), 9.95 (2H, s); ESIMS (m/z): 299
[M þ H]þ, 321 [M þ Na]þ; Anal. Calcd for C18H18O4: C, 72.47; H, 6.08.
Found: C, 72.43; H, 6.10%.
Reactions were monitored by TLC, performed on silica gel glass
plates containing 60 F-254 and visualization onTLC was achieved by
UV light or iodine indicator. Column chromatography was per-
formed with Merck (Navi Mumbai, India) 60e120 mesh silica gel.
Infrared (IR) spectra are recorded on PerkineElmer model 683 or
1310 spectrometers with sodium chloride optics. 1H NMR spectra
were recorded on Gemini (200 MHz) (Varian Inc, Palo Alto, CA, USA)
or [Avance (300 MHz); Bruker, Fallanden, Switzerland] instruments.
Chemical shifts (d) are reported in ppm, downfield from internal
TMS standard. ESI spectra were recorded on Micro mass, Quattro LC
using ESIþ software with capillary voltage of 3.98 kV and ESI mode
positive ion trap detector. Elemental analyses were performed on an
elemental analyzer (Model: VARIO EL, Elementar,Hanau, Germany).
Melting points were determined with an Electrothermal melting
point apparatus and are uncorrected. Starting materials and
reagents were commercially available, purchased from SigmaAl-
drich (St Louis, MO, USA), Lancaster (Alfa Aesar, Johnson Matthey Co,
Ward Hill, MA, USA) and Spectrochem Pvt Ltd (Mumbai, India).
6.2.3. 3-[5-(3-Formylphenoxy)pentyl]oxybenzaldehyde (4c)
Yield: 75%; mp 55e57 ꢀC; IR (KBr): 2927, 1688, 1581,
1266 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.56e1.78 (2H, m),
1.82e2.00 (4H, m), 4.06 (4H, t, J ¼ 6.6 Hz), 7.10e7.21 (2H, m),
7.33e7.48 (6H, m), 9.96 (2H, s); ESIMS (m/z): 313 [M þ H]þ, 335
[M þ Na]þ; Anal. Calcd for C19H20O4: C, 73.06; H, 6.45. Found: C,
73.01; H, 6.42%.
6.2.4. 3-[(Z)-4-(3-Formylphenoxy)-2-butenyl]oxybenzaldehyde (4d)
Yield: 68%; mp 57e59 ꢀC; IR (KBr): 2954, 1703, 1589, 1269 cmꢂ1
;
1H NMR (300 MHz, CDCl3):
d 4.69e4.80 (4H, m), 5.91e6.01 (2H, m),
7.12e7.20 (2H, m), 7.33e7.48 (6H, m), 9.95 (2H, s); ESIMS (m/z): 297
[M þ H]þ, 319 [M þ Na]þ; Anal. Calcd for C18H16O4: C, 72.96; H, 5.44.
Found: C, 72.95; H, 5.43%.
6.2.5. 3-[(E)-4-(3-Formylphenoxy)-2-butenyl]oxybenzaldehyde (4e)
Yield: 65%; mp 89e91 ꢀC; IR (KBr): 2949, 1701, 1586, 1266 cmꢂ1
;
6.2. General procedure for the synthesis of substituted
dibenzaldehydes (4aee and 5aee)
1H NMR (300 MHz, CDCl3):
d 4.58e4.69 (4H, m), 6.03e6.13 (2H, m),
7.10e7.21 (2H, m), 7.31e7.49 (6H, m), 9.94 (2H, s); ESIMS (m/z): 297
[M þ H]þ, 319 [M þ Na]þ; Anal. Calcd for C18H16O4: C, 72.96; H, 5.44.
Found: C, 72.93; H, 5.46%.
To a stirred solution of 3-hydroxy benzaldehyde or vanillin
(20 mmol) in 25e30 mL of acetonitrile, anhydrous potassium
carbonate (60 mmol), dibromo compound (6.5 mmol) and potas-
sium iodide (2 mmol) were added. The resulting reaction mixture
was stirred under reflux at 90 ꢀC for 48 h, followed by filtration of
potassium carbonate over celite pad and washed with ethyl acetate.
The filtrate was removed under reduced pressure and the residue
obtained was re-dissolved in ethyl acetate. The organic layer was
washed with 5% NaOH solution, followed by brine solution and
dried over anhydrous Na2SO4. The solvent was removed under
reduced pressure and the residue was purified by column chro-
matography to give substituted dibenzaldehydes 4aee and 5aee in
65e74% yields.
6.2.6. 4-[3-(4-Formyl-2-methoxyphenoxy)propoxy]-3-methoxy-
benzaldehyde (5a)
Yield: 70%; mp 140e142 ꢀC; IR (KBr): 2925, 1680, 1587, 1263,
1133 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 2.41e2.51 (2H, m,
J ¼ 6.0 Hz), 3.94 (6H, s), 4.36 (4H, t, J ¼ 6.0 Hz), 7.05 (2H, d,
J ¼ 8.3 Hz), 7.41e7.48 (4H, m), 9.87 (2H, s); ESIMS (m/z): 345
[M þ H]þ, 367 [M þ Na]þ; Anal. Calcd for C19H20O6: C, 66.27; H,
5.85. Found: C, 66.26; H, 5.81%.
6.2.7. 4-[4-(4-Formyl-2-methoxyphenoxy)butoxy]-3-methoxy-
benzaldehyde (5b)
6.2.1. 3-[3-(3-Formylphenoxy)propoxy]benzaldehyde (4a)
Yield: 71%; mp 150e153 ꢀC; IR (KBr): 2929, 1685, 1586, 1261,
Prepared from 3-hydroxy benzaldehyde 2 (2.44 g, 20 mmol), 1,3
dibromo propane (0.66 mL, 6.5 mmol), anhydrous potassium
carbonate (8.29 g, 60 mmol) and potassium iodide (0.3 g, 2 mmol)
by following the above general procedure to provide 2.05 g of the
substituted dibenzaldehyde 4a as white coloured solid. Yield: 72%;
1130 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.88e2.02 (4H, m), 3.93
(6H, s), 4.26 (4H, t, J ¼ 6.6 Hz), 7.01 (2H, d, J ¼ 7.3 Hz), 7.40e7.47 (4H,
m), 9.86 (2H, s); ESIMS (m/z): 359 [M þ H]þ, 381 [M þ Na]þ; Anal.
Calcd for C20H22O6: C, 67.03; H, 6.19. Found: C, 67.05; H, 6.15%.
mp 48e50 ꢀC; IR (KBr): 2927, 1696, 1587, 1264 cmꢂ1
;
1H NMR
2.16e2.30 (2H, m), 4.06e4.17 (4H, m),
6.2.8. 4-[5-(4-Formyl-2-methoxyphenoxy)pentyl]oxy-3-methoxy-
benzaldehyde (5c)
(300 MHz, CDCl3):
d
7.09e7.16 (2H, m), 7.31e7.46 (6H, m), 9.95 (2H, s); ESIMS (m/z): 285
[M þ H]þ, 307 [M þ Na]þ; Anal. Calcd for C17H16O4: C, 71.82; H, 5.67.
Found: C, 71.80; H, 5.65%.
Yield: 73%; mp 107e110 ꢀC; IR (KBr): 2930, 1681, 1586, 1265,
1129 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.69e1.79 (2H, m),

A. Kamal et al. / European Journal of Medicinal Chemistry 46 (2011) 3274e3281
3279
1.90e2.08 (4H, m), 3.92 (6H, s), 4.15 (4H, t, J ¼ 6.6 Hz), 6.97 (2H, d,
6.3.3. Ethyl 4-3-[(5-3-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]phenoxypentyl)oxy]phenyl-6-
methyl-2-thioxo-1,2,3,4-tetrahydro-5-pyrimidinecarboxylate (9c)
J ¼ 7.3 Hz), 7.38e7.49 (4H, m), 9.85 (2H, s); ESIMS (m/z): 373
[M þ H]þ, 395 [M þ Na]þ;Anal. Calcd for C21H24O6: C, 67.73; H, 6.50.
Found: C, 67.71; H, 6.48%.
Yield: 72%; mp 258e260 ꢀC; IR (KBr): 3324, 3189, 2968, 1668,
159, 1492 cmꢂ1 1H NMR (200 MHz, DMSO-d6):
; d 1.18 (6H, t,
J ¼ 6.9 Hz, J ¼ 6.6 Hz), 1.56e1.94 (6H, m), 2.35 (6H, s), 3.97 (4H, t,
J ¼ 6.1 Hz, J ¼ 6.9 Hz), 4.07 (4H, q, J ¼ 7.6 Hz, J ¼ 6.9 Hz), 5.27 (2H,
d, J ¼ 3.0 Hz), 6.74e6.91 (6H, m), 7.14e7.25 (2H, m), 9.34 (2H, d,
J ¼ 3.0 Hz), 9.97 (2H, s); 13C NMR (100 MHz; DMSO-d6): 14.21,15.55,
22.29, 26.06, 57.45, 60.29, 68.26, 107.94, 112.16, 115.55, 118.56,
128.34, 142.73, 158.71, 166.45, 172.42, 174.23; ESIMS (m/z): 653
[M þ H]þ, 675 [M þ Na]þ; Anal. Calcd for C33H40N4O6S2: C, 60.72; H,
6.18; N, 8.58. Found: C, 60.70; H, 6.15; N, 8.54%.
6.2.9. 4-[(Z)-4-(4-Formyl-2-methoxyphenoxy)-2-butenyl]oxy-3-
methoxy benzaldehyde (5d)
Yield: 65%; mp 113e114 ꢀC; IR (KBr): 2942, 1688, 1581, 1265,
1132 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 3.93 (6H, s), 4.88 (4H, d,
J ¼ 2.9 Hz), 5.98 (2H, t, J ¼ 2.9 Hz), 6.98 (2H, d, J ¼ 8.05), 7.38e7.45
(4H, m), 9.85 (2H, s); ESIMS (m/z): 379 [M þ Na]þ; Anal. Calcd for
C20H20O6: C, 67.41; H, 5.66. Found: C, 67.42; H, 5.64%.
6.2.10. (E)-4-(4-Formyl-2-methoxyphenoxy)-2-butenyl]oxy-3-
methoxy benzaldehyde (5e)
6.3.4. Ethyl 4-3-[((Z)-4-3-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetra hydro-4-pyrimidinyl]phenoxy-2-butenyl)oxy]phenyl-
6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-pyrimidinecarboxylate (9d)
Yield: 64%; mp 256e258 ꢀC; IR (KBr): 3308, 3175, 2984,1665,1575,
Yield: 63%; mp 160e162 ꢀC; IR (KBr): 2940, 1686, 1582, 1266,
1130 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 3.87 (6H, s), 4.69e4.75
(4H, m), 6.11e6.19 (2H, m), 7.12 (2H, d, J ¼ 8.0 Hz), 7.36e7.52 (4H,
m), 9.82 (2H, s); ESIMS (m/z): 357 [M þ H]þ, 379 [M þ Na]þ; Anal.
Calcd for C20H20O6: C, 67.41; H, 5.66. Found: C, 67.43; H, 5.62%.
1482 cmꢂ1;1HNMR(200MHz, DMSO-d6):
d
1.16 (6H, t, J¼ 7.4 Hz), 2.32
(6H, s), 4.06(4H, q, J¼ 7.4 Hz, J¼ 6.6Hz), 4.64e4.73(4H,m), 5.22(2H, d,
J ¼ 3.0 Hz), 5.86e5.94 (2H, m), 6.80e6.90 (6H, m), 7.15e7.22 (2H, m),
9.53 (2H, d, J ¼ 3.0 Hz), 10.18 (2H, s); 13C NMR (100 MHz; DMSO-d6):
14.11, 15.59, 57.39, 58.02, 60.34, 67.87, 108.01, 112.01, 115.24, 118.49,
128. 42, 129. 90, 142.97, 158.75, 166.58, 172.42, 174.26; ESIMS (m/z):
637 [M þ H]þ, 659 [M þ Na]þ;Anal. Calcd for C32H36N4O6S2: C, 60.36;
H, 5.70; N, 8.80. Found: C, 60.34; H, 5.67; N, 8.78%.
6.3. General procedure for the synthesis of dimers of monastrol
(9aee and 10aee)
A solution of substituted dibenzaldehydes 4aee (1 mmol), 1,3-
dicarbonyl ester or amide (7 or 8) (2 mmol), and thiourea 6 (4 mmol)
in acetonitrile (10 mL) was heated under reflux (85e90 ꢀC) overnight
in the presence of cerium (III) chloride heptahydrate (35 mol %)
under nitrogen. The reaction mixture after being cooled to room
temperature was poured into crushed ice and stirred for 5e10 min.
The solid separated was filtered under suction, washed with ice-cold
water (20 mL) and some of the products were purified on column
chromatography to afford dimers of monastrol 9a-e and 10a-e in
60e70% yields.
6.3.5. Ethyl 4-3-[((E)-4-3-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetra hydro-4-pyrimidinyl]phenoxy-2-butenyl)oxy]phenyl-
6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-pyrimidinecarboxylate (9e)
Yield: 65%; mp 238e240 ꢀC; IR (KBr): 3193, 2983, 1713, 1587,
1485 cmꢂ1; 1H NMR (200 MHz, DMSO-d6):
d
1.17 (6H, t, J ¼ 7.4 Hz,
J ¼ 6.6 Hz), 2.33 (6H, s), 4.05 (4H, q, J ¼ 7.4 Hz, J ¼ 6.6 Hz), 4.55e4.61
(4H,m), 5.12 (2H, d, J ¼ 3.6 Hz), 6.02e6.10 (2H, m), 6.78e6.89 (6H,
m), 7.16e7.24 (2H, m), 9.53 (2H, d, J ¼ 3.7 Hz), 10.19 (2H, s); ESIMS
(m/z): 637 [M þ H]þ, 659 [M þ Na]þ; Anal. Calcd for C32H36N4O6S2:
C, 60.36; H, 5.70; N, 8.80. Found: C, 60.33; H, 5.66; N, 8.81%.
6.3.1. Ethyl 4-[3-(3-3-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]phenoxypropoxy)phenyl]-6-
methyl-2-thioxo-1,2,3,4-tetrahydro-5-pyrimidinecarboxylate (9a)
Prepared from substituted dibenzaldehyde 4a (0.28 g, 1 mmol),
ethyl acetoacetate 7 (0.26 mL, 2 mmol) and thiourea 6 (0.11 g,
2 mmol) by following the above general procedure to provide 0.43 g
of the dimer 9a as white coloured solid. Yield: 70%; mp 250e252 ꢀC;
6.3.6. Methyl (2S)-1-[4-(3-3-[3-(5-[(2S)-2-(methoxycarbonyl)
tetrahydro-1H-1-pyrrolyl] carbonyl-6-methyl-2-thioxo-1,2,3,4-
tetrahydro-4-pyrimidinyl) phenoxy]propoxyphenyl)-6-methyl-2-
thioxo-1,2,3,4-tetrahydro-5-pyrimidinyl] carbonyltetrahydro-1H-2-
pyrrolecarboxylate (10a)
IR (KBr): 3175, 2986, 1709, 1596, 1472 cmꢂ1
;
1H NMR (200 MHz,
1.17 (6H, t, J ¼ 7.3 Hz), 2.16e2.30 (2H, m), 2.32 (6H, s),
Yield: 69%; mp 186e188 ꢀC; IR (KBr): 3201, 2953, 1743, 1605,
1440 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.85e2.16 (10H, m), 1.96
DMSO-d6):
d
3.97e4.21 (8H, m), 5.21 (2H, d, J ¼ 2.9 Hz), 6.78e6.89 (6H, m),
7.16e7.26 (2H, m), 9.54 (2H, s), 10.17 (2H, s); 13C NMR (100 MHz;
DMSO-d6): 14.21, 15.58, 29.78, 57.42, 60.33, 65.08, 107.96, 112.11,
115.60, 118.52, 128.35, 142.79, 158.73, 166.45, 172.41, 174.29; ESIMS
(m/z): 625 [M þ H]þ, 647 [M þ Na]þ; Anal. Calcd for C31H36N4O6S2: C,
59.60; H, 5.81; N, 8.97. Found: C, 59.62; H, 5.80; N, 8.94%.
and 1.97 (6H, s), 3.10e3.19 (4H, m), 3.71 and 3.72 (6H, s), 4.01e4.11
(4H, m), 4.31e4.45 (2H, m), 5.24 and 5.32 (2H, s), 6.70e6.96 (6H,
m), 7.15e7.23 (2H, m), 7.53 and 7.62 (2H, s), 8.18 and 8.23 (2H, s);
HRMS (ESI) m/z calcd for C39H46N6O8NaS2 [M þ Na]þ, 813.2716;
found, 813.2697; Anal. Calcd for for C39H46N6O8S2: C, 59.22; H,
5.86; N, 10.63. Found: C, 59.20; H, 5.85; N, 10.60%.
6.3.2. Ethyl 4-[3-(4-3-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]phenoxybutoxy)phenyl]-6-
methyl-2-thioxo-1,2,3,4-tetrahydro-5-pyrimidinecarboxylate (9b)
6.3.7. Methyl(2S)-1-[4-(3-4-[3-(5-[(2S)-2-(methoxycarbonyl)
tetrahydro-1H-1-pyrrolyl]carbonyl-6-methyl-2-thioxo-1,2,3,4-
tetrahydro-4-pyrimidinyl) phenoxy]butoxyphenyl)-6-methyl-2-
thioxo-1,2,3,4-tetrahydro-5-pyrimidinyl] carbonyltetrahydro-1H-2-
pyrrolecarboxylate (10b)
Yield: 72%; mp 257e258 ꢀC; IR (KBr): 3195, 2982, 1714, 1589,
1
1485 cmꢂ1; H NMR (200 MHz, DMSO-d6):
d
1.18 (6H, t, J ¼ 7.4 Hz,
J ¼ 6.6 Hz),1.90e2.01 (4H, m), 2.33 (6H, s), 3.96e4.13 (8H, m), 5.25 (2H,
d, J ¼ 3.7 Hz), 6.75e6.89 (6H, m), 7.15e7.25 (2H, m), 9.45 (2H, d,
J ¼ 3.7 Hz), 10.08 (2H, s); 13C NMR (100 MHz; DMSO-d6): 14.20, 15.55,
26.08, 57.47, 60.31, 68.25, 107.92, 112.17, 115.58, 118.55, 128.31, 142.75,
158.72, 166.47, 172.44, 174.25; ESIMS (m/z): 639 [M þ H]þ, 661
[M þ Na]þ; Anal. Calcd for C32H38N4O6S2: C, 60.17; H, 6.00; N, 8.77.
Found: C, 60.12; H, 5.98; N, 8.74%.
Yield: 65%; mp 150e151 ꢀC; IR (KBr): 3195, 2952, 1744, 1605,
1440 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.54e1.86 (4H, m),
1.93e2.10 (8H, m), 1.96 and 1.97 (6H, s), 3.11e3.20 (4H, m), 3.71 and
3.72 (6H, s), 3.97e4.08 (4H, m), 4.32e4.44 (2H, m), 5.23 and 5.31
(2H, s), 6.72e6.96 (6H, m), 7.16e7.24 (2H, m), 7.50 and 7.62 (2H, s),
8.15 and 8.22 (2H, s); 13C NMR (100 MHz; DMSO-d6): 15.22, 22.71,

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A. Kamal et al. / European Journal of Medicinal Chemistry 46 (2011) 3274e3281
26.12, 29.01, 45.92, 51.21, 56.45, 59.52, 68.09, 107.62, 112.29, 115.75,
118.54, 129.48, 143.12, 157.52, 159.03, 171.28, 172.48, 175.03; ESIMS
(m/z): 806 [M þ H]þ, 828 [M þ Na]þ; Anal. Calcd for C40H48N6O8S2:
C, 59.68; H, 6.01; N, 10.44. Found: C, 59.65; H, 6.03; N, 10.41%.
6.4.1. Ethyl-4-[4-(3-4-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]-2-methoxyphenoxypropoxy)-3-
methoxyphenyl]-6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-
pyrimidinecarboxylate (11a)
Prepared from substituted dibenzaldehyde 5a (0.34 g, 1 mmol),
ethyl acetoacetate 7 (0.26 mL, 2 mmol) and thiourea 6 (0.30 g,
4 mmol) by following the above general procedure to provide 0.46 g
of the dimer 11a as light yellow coloured solid. Yield: 68%; mp
6.3.8. Methyl (2S)-1-(4-[3-(5-[3-(5-[(2S)-2-(methoxycarbonyl)
tetrahydro-1H-1-pyrrolyl]carbonyl-6-methyl-2-thioxo-1,2,3,4-
tetrahydro-4-pyrimidinyl) phenoxy]pentyloxy)phenyl]-6-methyl-2-
thioxo-1,2,3,4-tetrahydro-5-pyrimidinylcarbonyl) tetrahydro-1H-2-
pyrrolecarboxylate (10c)
180e182 ꢀC; IR (KBr): 3198, 2954, 1716, 1570, 1464 cmꢂ1
;
1H NMR
(300 MHz, CDCl3):
d
1.19 (6H, t, J ¼ 7.2 Hz), 2.18e2.29 (2H, m), 2.38
Yield: 70%; mp 168e170 ꢀC; IR (KBr): 3197, 2952, 1743, 1603,
(6H, s), 3.80 (6H, s), 4.01e4.39 (8H, m), 5.28e5.40 (2H, m), 6.50e6.89
(6H, m), 8.08 (2H, s), 8.42 (2H, s); 13C NMR (100 MHz; DMSO-d6):
14.22, 15.52, 29.74, 56.21, 57.44, 60.37, 65.10, 107.94, 112.14, 115.62,
118.49, 128.34, 142.81, 158.74, 166.44, 172.40, 174.31; ESIMS (m/z):
686 [M þ H]þ, 708 [M þ Na]þ; Anal. Calcd for C33H40N4O8S2: C, 57.88;
H, 5.89; N, 8.18. Found: C, 57.85; H, 5.87; N, 8.15%.
1440 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.68e2.17 (14H, m), 1.95
and 1.97 (6H, s), 3.12e3.20 (4H, m), 3.69 and 3.70 (6H, s), 3.98e4.09
(4H, m), 4.29e4.42 (2H, m), 5.21 and 5.30 (2H, s), 6.71e6.96 (6H,
m), 7.14e7.23 (2H, m), 7.51 and 7.61 (2H, s), 8.16 and 8.21 (2H, s); 13C
NMR (100 MHz; DMSO-d6): 15.21, 22.28, 22.70, 26.12, 29.04, 45.91,
51.22, 56.45, 59.54, 68.11, 107.61, 112.30, 115.76, 118.53, 129.48,
143.13, 157.54, 159.01, 171.25, 172.45, 175.05; ESIMS (m/z): 820
[M þ H]þ, 842 [M þ Na]þ; Anal. Calcd for C41H50N6O8S2: C, 60.13; H,
6.15; N, 10.26. Found: C, 60.11; H, 6.12; N, 10.22%.
6.4.2. Ethyl-4-[4-(4-4-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]-2-methoxyphenoxybutoxy)-3-
methoxyphenyl]-6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-
pyrimidinecarboxylate (11b)
6.3.9. Methyl-(2S)-1-(4-[3-((Z)-4-[3-(5-[(2S)-2-(methoxycarbonyl)
tetrahydro-1H-1-pyrrolyl]carbonyl-6-methyl-2-thioxo-1,2,3,4-
tetrahydro-4-pyrimidinyl) phenoxy]-2-butenyloxy)phenyl]-6-
methyl-2-thioxo-1,2,3,4-tetrahydro-5-pyrimidinylcarbonyl)
tetrahydro-1H-2-pyrrolecarboxylate (10d)
Yield: 70%; mp 145e147 ꢀC; IR (KBr): 3195, 2941, 1710, 1566,
1465 cmꢂ1
;
1H NMR (300 MHz, CDCl3):
d
1.18 (6H, t, J ¼ 7.3 Hz),
1.91e2.13 (4H, m), 2.37 (6H, s), 3.76 (6H, s), 3.98e4.29 (8H, m),
5.29e5.39 (2H, m), 6.56e6.87 (6H, m), 8.01 (2H, s), 8.26 (2H, s); 13C
NMR (100 MHz; DMSO-d6): 14.22, 15.52, 26.12, 56.23, 57.42, 60.35,
68.28, 107.93, 112.15, 115.60, 118.52, 128.32, 142.83, 158.74, 166.42,
172.39, 174.33; ESIMS (m/z): 700 [M þ H]þ; Anal. Calcd for
C34H42N4O8S2: C, 58.44; H, 6.06; N, 8.02. Found: C, 58.41; H, 6.04; N,
8.00%.
Yield: 67%; mp 182e184 ꢀC; IR (KBr): 3196, 2928, 1744,
1604, 1440 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.87 and 1.98
(6H, s), 1.98e2.10 (8H, m), 3.10e3.22 (4H, m), 3.71 and 3.73 (6H, s),
4.32e4.44(2H, m), 4.56e4.68 (4H, m), 5.25and 5.33(2H, s), 6.01e6.12
(2H, m), 6.80e6.97 (6H, m), 7.20e7.26 (2H, m), 7.53 and 7.63 (2H, s),
8.20 and 8.21 (2H, s); HRMS (ESI) m/z calcd for C40H46N6O8NaS2
[M þ Na]þ, 825.2716; found, 825.2693; Anal. Calcd for C40H46N6O8S2:
C, 59.83; H, 5.77; N, 10.47. Found: C, 59.85; H, 5.75; N, 10.45%.
6.4.3. Ethyl-4-4-[(5-4-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]-2-methoxyphenoxypentyl)oxy]-
3-methoxyphenyl-6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-
pyrimidinecarboxylate (11c)
6.3.10. Methyl-(2S)-1-(4-[3-((E)-4-[3-(5-[(2S)-2-(methoxycarbo-
nyl)tetrahydro-1H-1-pyrrolyl]carbonyl-6-methyl-2-thioxo-1,2,3,4-
tetrahydro-4-pyrimidinyl) phenoxy]-2-butenyloxy)phenyl]-6-
methyl-2-thioxo-1,2,3,4-tetrahydro-5-pyrimidinylcarbonyl)
tetrahydro-1H-2-pyrrolecarboxylate (10e)
Yield: 68%; mp 137e139 ꢀC; IR (KBr): 3196, 2952, 1712, 1572,
1463 cmꢂ1 1H NMR (200 MHz, CDCl3):
; d 1.11e1.26 (6H, m),
1.63e1.99 (6H, m), 2.37 (6H, s), 3.73 (6H, s). 3.96e4.21 (8H, m),
5.34e5.41 (2H, m), 6.71e6.91 (6H, m), 7.86 (2H, s), 8.13 (2H, s);
HRMS (ESI) m/z calcd for C35H44N4O8NaS2 [M þ Na]þ, 735.2498;
found, 735.2527; Anal. Calcd for C35H44N4O8S2: C, 58.97; H, 6.22; N,
7.86. Found: C, 58.95; H, 6.19; N, 7.83%.
Yield: 60%; mp 155e157 ꢀC; IR (KBr): 3195, 2930, 1746, 1604,
1440 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.88 and 1.96 (6H, s),
1.95e2.18 (8H, m), 3.09e3.21 (4H, m), 3.70 and 3.71 (6H, s), 4.34e4.43
(2H, m), 4.57e4.67 (4H, m), 5.21 and 5.31 (2H, s), 6.01e6.09 (2H, m),
6.79e6.97 (6H, m), 7.19e7.24 (2H, m), 7.51 and 7.66 (2H, s), 8.19 and
8.23 (2H, s); 13C NMR (100 MHz; DMSO-d6): 15.25, 22.69, 29.04,
45.94, 51.19, 56.44, 59.53, 71.65,107.66,112.32, 115.73,118.52, 129.45,
143.13, 157.55, 159.01, 171.34, 172.50, 175.07; ESIMS (m/z): 804
[M þ H]þ, 826 [M þ Na]þ; Anal. Calcd for C40H46N6O8S2: C, 59.83; H,
5.77; N, 10.47. Found: C, 59.85; H, 5.72; N, 10.43%.
6.4.4. Ethyl 4-4-[((Z)-4-4-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]-2-methoxyphenoxy-2-butenyl)
oxy]-3-methoxy phenyl-6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-
pyrimidinecarboxylate (11d)
Yield: 65%; mp 135e137 ꢀC; IR (KBr): 3187, 2975, 1698, 1565,
1458 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.19e1.29 (6H, m), 3.36
and 3.37 (6H, s), 3.77 and 3.81 (6H, s), 4.08e4.19 (4H, m), 4.73e4.89
(4H, m), 5.39 (1H, d, J ¼ 3.21 Hz), 5.42 (1H, d, J ¼ 3.77 Hz), 5.83e5.90
(2H, m), 6.64e6.77 (6H, m), 8.04 and 8.21 (2H, s), 8.53 and 8.78 (2H,
s); ESIMS (m/z): 698 [M þ H]þ; Anal. Calcd for C34H40N4O8S2: C,
58.60; H, 5.79; N, 8.04. Found: C, 58.55; H, 5.75; N, 8.01%.
6.4. General procedure for the synthesis of dimers of monastrol
related dihydropyrimidone (11aee and 12aee)
A solution of substituted dibenzaldehydes 5aee (1 mmol), 1,3-
dicarbonyl ester or amide (7 or 8) (2 mmol), and thiourea 6
(4 mmol) in acetonitrile (10 mL) was heated under reflux
(85e90 ꢀC) overnight in the presence of cerium (III) chloride hep-
tahydrate (35 mol %) under nitrogen. The reaction mixture after
being cooled to room temperature was poured into crushed ice and
stirred for 5e10 min. The solid separated was filtered under suction,
washed with ice-cold water (20 mL) and some of the products were
purified on column chromatography to afford dimers of monastrol
11aee and 12aee in 58e70% yields.
6.4.5. Ethyl 4-4-[((E)-4-4-[5-(ethoxycarbonyl)-6-methyl-2-thioxo-
1,2,3,4-tetrahydro-4-pyrimidinyl]-2-methoxyphenoxy-2-butenyl)
oxy]-3-methoxy phenyl-6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-
pyrimidinecarboxylate (11e)
Yield: 64%; mp 145e147 ꢀC; IR (KBr): 3188, 2973, 1701, 1568,
1460 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.19e1.29 (6H, m), 3.25
and 3.38 (6H, s), 3.83 and 3.84 (6H, s), 4.08e4.21 (4H, m), 4.61e4.77
(4H, m), 5.39 (1H, d, J ¼ 3.02 Hz), 5.43 (1H, d, J ¼ 3.77 Hz), 5.93e5.99
(2H, m), 6.69e6.86 (6H, m), 7.84 and 7.95 (2H, s), 8.31 and 8.75 (2H,

A. Kamal et al. / European Journal of Medicinal Chemistry 46 (2011) 3274e3281
3281
s); 13C NMR (100 MHz; DMSO-d6): 14.22, 15.54, 56.25, 57.42, 60.33,
6.4.10. Methyl (2S)-1-((4-(3-methoxy-4-(((E)-4-(2-methoxy-4-(5-
71.65, 107.95, 112.13, 115.62, 118.54, 128.29, 142.79, 158.71, 166.40,
172.41, 174.29; ESIMS (m/z): 698 [M þ H]þ, 719 [M þ Na]þ; Anal.
Calcd for C34H40N4O8S2: C, 58.60; H, 5.79; N, 8.04. Found: C, 58.57;
H, 5.74; N, 8.02%.
(((2S)-2-(methoxycarbonyl)tetrahydro-1H-1-pyrrolyl)carbonyl)-6-
methyl-2-thioxo-1,2,3,4-tetra hydro-4-pyrimidinyl)phenoxy)-2-
butenyl)oxy)phenyl)-6-methyl-2-thioxo-1,2, 3,4-tetrahydro-5-
pyrimidinyl) carbonyltetrahydro-1H-2-pyrrolecarboxylate (12e)
Yield: 60%; mp 168e170 ꢀC; IR (KBr): 3205, 2948, 1738, 1610,
6.4.6. Methyl (2S)-1-[4-(3-methoxy-4-3-[2-methoxy-4-(5-[(2S)-2-
(methoxy carbonyl) tetrahydro-1H-1-pyrrolyl]carbonyl-6-methyl-
2-thioxo-1,2,3,4-tetra hydro-4-pyrimidinyl)phenoxy]propoxyph-
enyl)-6-methyl-2-thioxo-1,2,3,4-tetra hydro-5-pyrimidinyl]
carbonyltetrahydro-1H-2-pyrrolecarboxylate (12a)
1444 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.90 and 1.96 (6H, s),
1.96e2.19 (8H, m), 3.13e3.32 (4H, m), 3.69 and 3.78 (6H, s), 3.82
and 3.88 (6H, s), 4.28e4.44 (2H, m), 4.70e4.85 (4H, m), 5.25 and
5.48 (2H, s), 5.88e5.12 (2H, m), 6.65e6.94 (6H, m), 7.81 and 7.91
(2H, s), 8.13 and 8.21 (2H, s); 13C NMR (100 MHz; DMSO-d6): 15.32,
22.59, 29.21, 46.14, 51.80, 56.01, 58.37, 71.71, 107.55, 112.36, 115.85,
118.31, 129.17, 143.51, 158.01, 159.09, 171.72, 172.34, 175.13; ESI-MS
Yield: 65%; mp 148e150 ꢀC; IR (KBr): 3210, 2960, 1745, 1612,
1442 cmꢂ1 1H NMR (300 MHz, CDCl3):
; d 1.80e2.20 (10H, m), 1.94
and 1.99 (6H, s), 2.99e3.29 (4H, m), 3.69 and 3.70 (6H, s), 3.81 and
3.82 (6H, s), 3.99e4.10 (4H, m), 4.33e4.44 (2H, m), 5.24 and 5.31
(2H, s), 6.74e6.94 (6H, m), 7.49 and 7.56 (2H, s), 7.74 and 7.86 (2H,
s); 13C NMR (100 MHz; DMSO-d6): 15.29, 22.54, 29.23, 29.69, 46.11,
51.76, 56.07, 58.36, 65.16, 107.53, 112.32, 115.81, 118.26, 143.56,
158.09, 159.12, 171.69, 172.31, 175.15; ESIMS (m/z): 852 [M þ H]þ,
874 [M þ Na]þ; Anal. Calcd for for C41H50N6O10S2: C, 57.87; H, 5.92;
N, 9.88. Found: C, 57.85; H, 5.91; N, 9.87%.
(m/z): 864 [M
þ
H]þ, 886 [M
þ
Na]þ;Anal. Calcd for for
C42H50N6O10S2: C, 58.45; H, 5.84; N, 9.74. Found: C, 58.46; H, 5.83;
N, 9.74%.
Acknowledgments
Authors (MSM, SB, SA and SF) are thankful to CSIR, New Delhi for
the award of research fellowship.
References
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; d 1.68e2.18 (12H, m), 1.92
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(((2S)-2-(methoxy carbonyl)tetrahydro-1H-1-pyrrolyl)carbonyl)-6-
methyl-2-thioxo-1,2,3,4-tetra hydro-4-pyrimidinyl)phenoxy)pentyl)
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d 1.620e2.19 (14H, m), 1.91
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(2H, s), 6.72e6.93 (6H, m), 7.48 and 7.57 (2H, s), 7.74 and 7.89 (2H,
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(((2S)-2-(methoxycarbonyl)tetrahydro-1H-1-pyrrolyl)carbonyl)-6-
methyl-2-thioxo-1,2,3,4-tetrahydro-4-pyrimidinyl)phenoxy)-2-
butenyl)oxy)phenyl)-6-methyl-2-thioxo-1,2,3,4-tetrahydro-5-
pyrimidinyl) carbonyltetrahydro-1H-2-pyrrolecarboxylate (12d)
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1.97e2.18 (8H, m), 3.14e3.34 (4H, m), 3.71 and 3.80 (6H, s), 3.82 and
3.88 (6H, s), 4.28e4.44 (2H, m), 4.69e4.87 (4H, m), 5.22 and 5.44 (2H,
s), 5.79e5.91 (2H, m), 6.68e6.98 (6H, m), 7.84 and 7.90 (2H, s), 8.11
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885.2927; found, 885.2957; Anal. Calcd for for C42H50N6O10S2:
C, 58.45; H, 5.84; N, 9.74. Found: C, 58.46; H, 5.83; N, 9.74%.
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