1.1. mannich reaction of coumarins: 3shodhganga.inflibnet.ac.in/bitstream/10603/20757/14/8...mannich...
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Chapter I
1
1. INTRODUCTION
Coumarins are a group of naturally occurring lactones with wide ranging
biological activities and benzimidazoles have been recognized as privileged
structures in the field of drug discovery. The work in this chapter involves a
study of Mannich reaction of 2-(4'-coumarinomethyl) benzimidazoles and
hence a brief survey of literature on this reaction which has been reported on
both the ring systems is presented.
1.1. Mannich reaction of Coumarins:
First report on Mannich reaction of coumarins was by Robertson et al [1], who
have found that the reaction of 4-hydroxy coumarin 1 with primary amines and
formaldehyde resulted in the formation of 3-aminomethyl-4-hydroxycoumarins
2 in analytically pure crystalline state. But attempts to prepare the compounds
from paraformaldehyde and amine hydrochlorides did not give Mannich base
2, instead 3,3'-methylenebis-4-hydroxy coumarin 3 was obtained as the
exclusive product.
O
OH
OO
OH
O O
OH
O
CH2
OO
OH
CH2 N
R
R'Paraformaldehyde/
amine hydrochloride
HN
R'
R
HCHO
12 3
Similarly, Mannich reaction of 3-hydroxy coumarin 4 with formaldehyde and
primary or secondary amines resulted in 4-N,N-dialkylaminomethyl-3-hydroxy
coumarins 5 [2].
O O O OHN
R'
R
HCHO
OH OH
NR
R'
4 5
Chapter I
2
Reaction of 7-hydroxy-4-methyl coumarins 6 with aniline/benzyl amine
resulted in the formation of oxazino-4-methyl coumarins 7 or 7-hydroxy-8-
substituted aminomethyl-4-methylcoumarins 8, depending upon whether two
equivalents or one equivalent of formaldehyde was employed [3].
O O O O
CH3
R'
HOO O
CH3
R'
HO O
N
R'
CH3
R'
NH
R''
CH2O+R''-NH2 2CH2O+R''-NH2
6 78
Kontogiorgis and Hadjipavlou-Litina [4] showed that Mannich bases 10, 11 of
7-hydroxy coumarin 9, act as potent anti-inflammatory agents.
O O O OHOO OHO O
N
CH3
N
R'2
CH2O+R1R2-NH 2CH2O+CH3-NH2
R1
R1= H, R2= Aryl, isopropyl, pentyl etcR1&R2 =
N N O N NH
9 1011
Recently it has been observed that Mannich bases 13 derived from 7-hydroxy
coumarins 12 act as good anti-viral agents [5].
O O
R'
HOO O
R'
HO
NR2
R'= H,CH3
NR2= secondary amines
NHR2, HCHO
12 13
Chapter I
3
Garazd et al [6] explored the reactivity of hydroxyl coumarins towards
Mannich reaction, where in 7-hydroxy 14 and 5-hydroxy-4-phenylcoumarins
15 were reacted with number of 1,1-diaminomethanes to give 8-
dialkylaminomethyl-7-hydroxy-4-phenylcoumarins 16 and dialkylaminomethyl
7-hydroxy-4-phenyl coumarins 17.
O OHO O OHO
NR''R'
R
R= H, Cl, Et, Pr
14 16
O O
OH
O O
OH
H3C H3C
N
R''
R'
15 17
Further, Mannich reaction of 7-hydroxy-4-phenyl coumarins 14 with amino
acids and one equivalent of formaldehyde produced 7-hydroxy-8-(N-
aminoacyl)methyl-4-phenyl coumarins 18.
O OHO
O OHO
NH
ROH
O
NH2CHRCOOH
CH2O
14 18
Chapter I
4
Atul Kumar et al [7] developed an efficient non-ionic surfactant catalysed
multi component synthesis of benzylamino coumarins 19 from secondary
amines, aromatic aldehyde and 4-hydroxy coumarin 1 via a Mannich type
reaction in water.
O O
OH
O O
OH
O O
OH
OO
OH
N
O
H
R
H N
R1
R1
R1R1
Organic solvent
Watertrtion x-100
R
R
1 20
19
8-bromo-7-methyl-9H-pyrano[2,3-e]-benzo-1,4-oxazine-2,9-dione 21 was
allowed to undergo Mannich reaction using different secondary amines, namely
diethylamine, piperidine and/or methylpiparazine in the presence of
paraformaldehyde to give the corresponding 8-bromo-7-methyl-3-substituted
9H-pyrano-1,4-oxazinones 22 [8].
OO
NH
O
O
Br
CH3
OO
NH
O
O
Br
CH3
R
R= N(C2H5)2, N N N CH3
HCHO
Sec amine
21 22
Chapter I
5
Ni et al [9] synthesized coumarin-based dyes 24 via the introduction of
functionalised amino methyl group at the 8th
position of ethyl 7-hydroxy-2-oxo-
2H-chromene-3-carboxylate derivatives 23 and studied the relationship
between the structures, the conformations and also measured the quantum
yields of synthesized dyes.
O
X
HO O
O
O
O
X
HO O
O
O
NR2
HCHO, R2NH
CH3CN/H2O,reflux
X= H, F, Cl, Br
R2NH= HN HN N HN N OCH3, ,
23 24
Bolakatti et al [10] synthesized coumarinyl Mannich bases 26 by reacting
3-acetyl coumarin 25 with various substituted secondary amines in presence of
paraformaldehyde. These compounds showed encouraging analgesic and
antipyretic activities.
O O
O
CH3
O O
O
NR1
R2
Paraformaldehyde
NH
R1
R2
R1 & R2 = Diethyl, piperidyl, etc
25 26
1.2. Mannich reaction of Benzimidazoles
Equimolar amounts of benzimidazole 27, formaldehyde, and piperidine
resulted in the formation of of 1-(piperidinomethy1) benzimidazole 28 in 97%
yield [11]. Attempts to use primary amines or higher aldehydes in place of
formaldehyde in the reaction were unsuccessful.
Chapter I
6
NH
N
HNN
N
N
HCHO+ +
27 28
Reaction of 2(3H)-Benzimidazolone/thione 29 with formaldehyde and anilines
resulted in the formation of 1,3-bis(anilinomethyl) benzimidazolones/thiones
30, by a double Mannich reaction at the ring nitrogens [12].
NH
HN
X 2HCHO
NH2
+ + 2
N
NX
NH
NH
X= S,O29 30
Jesudason et al [13] synthesized Mannich bases of benzimidazoles which were
found to possess good anti-inflammatory activity and exhibit high in vitro
bovine corneal permeability as well.
NH
NR1
N
NR1
R2
R2H
HCHO
R1= H, CH3, CH=CH-C6H5
R2= N(CH3)2, N(C2H5)2, N(C6H5)2, N N O
3132
,
Reaction of 2-mercaptobenzimidazole 33 with alkyl/arylalkyl amines and two
equivalents of formaldehyde in presence of ethanol resulted in the formation of
thiadiazinobenzimidazoles 34 [14].
Chapter I
7
N
HN
N
NS
N
R
SH
RNH2/excess CH2O,
EtOH, reflux
R= CH3, CH3CH2, CH(CH3)2, benzyl, C5H4N
33 34
Mannich bases of 2-ethylbenzimidazole 35 were found to exhibit potent
anti -inflammatory and analgesic activities [15].
NH
N CH3
N
N CH3
N
R2
R1
HCl, HCHO,
R1 = R2= Secondary aminesR1 & R2= Primary aromatic amines
NH
R2
R1
35 36
In the light of the interesting chemistry associated with these moieties and the
biological activity of the resulting compounds, it was thought of great interest
to attempt the reaction of aromatic primary amine and formaldehyde on a
molecular system, which contains both coumarin and benzimidazole ring
systems, is described in the next section.
2. PRESENT WORK
Work carried out during the present investigation has been described in
Scheme 1. Reaction of coumarin-4-acetic acids [16] 1 with o-phenylene
diamine 2 using anhydrous phosphoric acid as condensing medium afforded
benzimidazoles 3. (Scheme 1) Anhydrous phosphoric acid was used for
condensation since coumarin-4-acetic acids were insoluble in 4 N HCl and
hence the N-heterocyclisation could not be achieved under the Philip’s aqueous
HCl conditions. Reactants were mixed well and heated in anhydrous
phosphoric acid on an oil bath at 170-180 °C for 4 hours. The contents were
poured into ice cold water and then basified with liquor ammonia. The
resulting solid was filtered and washed with water, dried and recrystallised to
Chapter I
8
obtain the pure product. Further, compounds 3 were refluxed with equimolar
quantities of primary amines and excess of aqueous formalin (37%) in presence
of ethanol for 10 hours, the reaction mixture was concentrated to half and
cooled in ice, solid separated was filtered and washed with cold ethanol with a
view to obtain the Mannich bases 4 expected in this reaction. The actual
products obtained in this reaction corresponded to structure 6, the formation of
which has been explained by a second N-hydroxymethylation on the secondary
amine 4 followed by an intramolecular attack of enolate 5A leading to a C-C
bond formation. This is supported by spectroscopic data for the compounds.
Chapter I
9
O
COOH
O
NH2
NH2O O
N
HN
O O
N
NNH
O O
N
NN
O O
NN
NH
R'
R
R'
R
R'
R
R
R
1 2 3 (a,b)
4
5
6 (a-o)
Anhy.H3PO4
-H2O
HO H
H CH2O/37%
NH2
R'
CH2O/37%
O O
N
NN
R'
R
HO
H
H
5A
(Expected Mannich base)
(Obtained products)
Scheme 1: Synthesis of Tetrahydro Pyrimido Benzimidazolyl Coumarins.
Chapter I
10
3. RESULTS AND DISCUSSION
Formation of benzimidazole coumarin conjugates 3 was well supported by
spectral data. In the IR spectrum, compound 3a ( R= 6-CH3 ) exhibited a sharp
band at 3311 cm-1
due to N-H stretching of benzimidazole and lactone carbonyl
was observed at 1725cm-1
. In 1H-NMR the N-C4-CH2 protons of coumarin
appeared as a singlet at 4.47 ppm and C3-H appeared as a singlet at 6.43 δ ppm
and N-H proton at 12.39 ppm (Spectrum No. 2) which was found to be D2O
exchangeable. The molecular ion peak was observed at m/z 290 (Spectrum No.
1). Further, compounds 3 were refluxed with excess of aqueous formalin (37%)
with a view to obtain secondary amines 4 which are the Mannich bases
expected in this reaction.
Spectral data of the product obtained did not correspond to structure 4. IR
spectrum did not show any peak around 3300 cm-1
and the 1H-NMR did not
indicate any exchangeable NH and the singlet due to N-CH2 protons around
4.50 ppm was also absent. The mass spectrum showed a higher molecular ion
peak exceeding by 12 mass units.
It was apparent that the secondary amine 4 was undergoing a
N-hydroxymethylation leading to tertiary amine 5. In the next step,
deprotonation of the C4-CH2 by the tertiary nitrogen generates an enolate
stabilized carbanion 5A which can attack the N-CH2OH to form a C-C bond
followed by a simultaneous dehydration, leading to compounds 6.
Similar reactions involving second hydroxymethylation is supported by earlier
reports. Formation of oxazino coumarins has been reported (Scheme 2) in the
Mannich reaction of 7-hydroxy-4-methyl coumarins which involved a second
N-hydroxymethylation followed by an intramolecular attack by the C-7
hydroxyl group [3]. Reaction of N-benzyl anilines possessing ortho-hydroxyl
group, with formaldehyde has also resulted in the formation of oxazinones
[17,18]. Formation of C-C and N-C bond in this sequence has been of current
interest. Mannich reaction of iminium salts and ketones has led to the synthesis
Chapter I
11
of piperidones via the intermediacy of β-aminoketones [19]. Present report
illustrates a rare C-C bond forming reaction between the N-hydroxymethylated
product and an enolate stabilized C4-CH2 function attached to the coumarin
ring. Reactivity of the C4- methylene group of coumarin has been demonstrated
by our earlier work related to the reactions of ortho substituted
4-aryloxymethyl coumarins leading to the formation of 4-2' benzo [b] furanyl
coumarins [20], 2,3- dihydrobenzofuranols [21] and the corresponding
arylamines [22,23].
O O O O
CH3
R'
HO O O
CH3
R'
HO O
N
R'
CH3
R"
NH
R''
CH2O+R''-NH2 CH2O
Scheme 2: Second hydroxymethylation in Mannich reaction.
Proposed structure 6 for the products obtained is supported by spectral data. In
the 13
C- NMR, compound 6h exhibited four upfield signals at 21.47, 36.98,
51.05 and 60.72 ppm which agreed with the proposition of a second N-
hydroxymethylation (Spectrum No. 6). In its mass spectrum compound 6h
exhibited molecular ion peak at m/z 407 (Spectrum No. 3). In the 1H- NMR
(Spectrum Nos. 4&5) the prochiral methylene protons flanked between two
nitrogens (-N-CH2-N-) appeared as two doublets in the region of 5.80-6.06
ppm (J = 12.0 Hz). The N-CH2 and coumarin C4-H show AMX pattern of
splitting. The diastereotopic N-CH2 protons appear upfield at 4.41 and 4.05
ppm in the form of four lines for each proton due to geminal (J = 14.0 Hz) and
vicinal coupling (J = 8.8 Hz and 5.6 Hz) with the C-4 proton. The C-4 proton at
4.95 ppm in turn gives two 3JC-H values (5.6 Hz and 8.0 Hz). Further HETCOR
spectrum (Spectrum No. 8) confirmed that the two doublet of doublets at 4.05
and 4.41 ppm each corresponding to one proton correlated to one carbon at
51.05 ppm, and a doublet of doublet at 4.95 corresponding to one proton
correlated to the peak at 36.98 ppm, and two doublets at 5.81 and 6.06
corresponding to one proton each correlated to one carbon at 60.72 ppm.
Chapter I
12
Further 13
C-DEPT (Spectrum no. 7) confirmed that peaks at 51.05 and 60.72
ppm are due to carbons of methylene groups and peak at 36.98 ppm is due to
C-4 carbon. A singlet at 2.41 ppm corresponds to C7-CH3 of coumarin which
correlated with 13
C-signal at 21.47 ppm (Fig. 1). Aromatic protons resonated
between 6.87-7.82 ppm. Similarly all the compounds synthesized have been
confirmed by spectral data.
Fig. 1: 13
C-1H Correlations observed for the -N-CH2-N-CH2-, C4-CH- fragment
(6h).
From the above discussions it is quite clear that the attempted Mannich reaction
on benzimidazole coumarin conjugates 3 has resulted in the formation of 4-(2-
phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-2H-
chromen-2-ones 6.
Mass Spectral Fragmentation for compound 6h
The molecular ion (I) can undergo a 1, 3-(C, N) prototopic shift to (IA) which
can then undergo a retro-Diels alder fragmentation to a high yielding odd-
electron ion (II). Ion (II) still possessing coumarin can expel carbon monoxide
and a H-radical leading to a benzofuran derivative (III) at m/z 273.
Another route for the molecular ion is the probable expulsion of a N-phenyl
aziridine by two 1,3-H shifts leading to a moderately strong odd-electron-ion
(IV) (40%) at m/z 290, which can yield a benzofuran derivative (V) by the
expulsion of carbon monoxide. Expulsion of carbon monoxide is usually
observed in the fragmentation of coumarins (Scheme 3).
O
NN
N
O
H
H H
H
H
60.72
5.81 6.06
4.05
4.4151.05
36.984.98
H3C
Chapter I
13
O O
NN
NH
H3C O O
NN
NH
H3C
H H
Retro Diels Alder
O O
HN
N
H3C
H2C
-CO-H
N
N+
H3C
H2C
O
HH
H
H
O O
HN
N
H3C
H
H
N
+
-CO
HN
N
H3C O
H
H
m/z=407(M+)
(28 %)m/z=302 (72%)
m/z=273( 38%)
m/z=262 (30%)
m/z=290 (40%)
(I)
(IA) (II)
(III)
(V)
Scheme 3: Mass spectral fragmentation of compound 6h.
PHARMACOLOGY
Some of the selected compounds were subjected to pharmacological
evaluation in albino mice. In the in vivo acute toxicity experiments, all the
compounds showed LD50 values around 2000 mg/kg body weight.
The anti-inflammatory activity was evaluated at the dose of 200 mg/kg body
weight by the Carrageenan induced paw edema method. Experimental results
ar presented in Table 1, indicating the changes in paw volumes, percent
inhibition of inflammation monitored over a period of five hours. Relation
between the observed inhibition (%) varying with time is depicted in Fig. 2.
Chapter I
14
Table 1: Paw volume (% inhibition) at different time intervals.
Entry Entry 0 HOUR 1 HOUR 2 HOUR 3 HOUR 4 HOUR 5 HOUR
Control Control 1.042±0.042 1.047±0.042 1.18±0.048 1.21±0.047 1.245±0.091 1.245±0.078
Phenyl
butazone
R R’ Phenyl
butazone
1.043±0.023
(-0.095)
0.95±0.054
(9.26)
0.761±0.078***
(35.59)
0.687±0.062***
(43.22)
0.59±0.068***
(52.61)
0.52±0.035***
(58.23)
6a 6-CH3 H 6a 1.051±0.054
(-0.869)
1.011±0.023
(3.43)
0.91±0.019
(22.88)
0.88±0.094*
(27.27)
0.85±0.058**
(31.72)
0.78±0.074**
(37.34)
6b 6-CH3 4-CH
3 6b 1.017±0.051
(2.39)
1.00±0.043
(4.48)
0.78±0.033**
(33.89)
0.753±0.076**
(37.76)
0.71±0.067**
(42.97)
0.65±0.045**
(47.79)
6c 6-CH3 4-OCH
3 6c 1.024±0.076
(1.72)
1.034±0.062
(1.24)
0.958±0.037
(18.81)
0.93±0.076*
(23.14)
0.91±0.045*
(26.90)
0.85±0.041**
(31.72)
6d 6-CH3 3-CH
3 6d 1.046±0.032
(-0.38)
0.97±0.043
(7.3)
0.763±0.047***
(35.33)
0.75±0.083***
(38.01)
0.69±0.073***
(44.57)
0.63±0.051***
(49.39)
6e 6-CH3 3,4-CH
3 6e 1.072±0.013
(-2.87)
1.034±0..043
(1.21)
0.921±0.054
(21.94)
0.915±0.045**
(24.38)
0.87±0.076**
(30.12)
0.83±0.051**
(33.33)
6f 6-CH3 2,3-CH
3 6f 1.035±0.043
(0.67)
1.023±0.076
(2.29)
0.811±0.052**
(31.27)
0.79±0.046**
(34.71)
0.75±0.042**
(39.75)
0.71±0.054**
(42.97)
6g 6-CH3 4-Cl 6g 1.043±0.032
(0.095)
1.039±0.033
(0.76)
0.946±0.065
(19.83)
0.931±0.061*
(23.05)
0.91±0.031*
(26.90)
0.86±0.024**
(30.92)
6h 7-CH3 H 6h 1.049±0.024
(-0.7)
1.041±0.076
(0.57)
0.914±0.066
(22.59)
0.910±0.036*
(24.79)
0.870±0.024**
(30.12)
0.82±0.027**
(34.13)
6i
7-CH3 4-OCH3 6i
1.035±0.023
(0.67)
1.00±0.045
(4.481)
0.77±0.035**
(34.74)
0.73±0.046***
(39.66)
0.70±0.062***
(43.77)
0.64±0.035***
(48.59)
6j 7-CH3 4-CH3 6j 1.064±0.038
(-2.11)
1.02±0.037
(2.57)
0.77±0.05**
(34.74)
0.69±0.034***
(42.97)
0.61±0.062***
51.00)
0.59±0.053***
(52.61)
RESULTS ARE EXPRESSED IN MEAN± SEM, ANOVA FOLLOWED BY DUNNET T TEST, SIGNIFICANT P<0.05*, P<0.01**, P<0.001***
Chapter I
15
There was gradual increase in edema paw volume in rats in control
(carrageenan treated group) showing its maximum value at 4 h. The result
showed significant anti-inflammatory activity (p< 0.001) by treated
compounds. Maximum percent inhibition of paw edema volume in all
compounds was found at 5 h (Fig. 2). Most of the compounds 6a-6j have
shown considerable inhibition of inflammation (P< 0.01) which is depicted in
Table 1. Amongst tested compound 6j showed maximum inhibition of paw
edema (52.61%) where as phenyl butazone as reference drug showed inhibition
(58.23%) at 5h.
Fig. 2: The graph of % inhibition of paw edema vs. time.
Structure activity relation studies (SAR): have shown that the p-methoxy
group was most effective amongst the four groups in the aryl amino moiety.
Accordingly compound 6b (R= 6-CH3 and R'= 4-CH3), 6d (R= 6-CH3 and
R'= 3-CH3) and 6h (R= 7-CH3 and R'= 4-CH3) showed 47.79, 49.39 and
48.59% inhibition of inflammation at the end of 5 hours. The p-chloro
substitution in the form of compound 6g was found to be the least active
compound in the series with the inhibition of 30.72%. The combination of CH3
and p-OCH3 group was found to be most effective in the case of compound 6j
where in a maximum inhibition of 52.61% was observed; however, its
equivalent 6c was less effective. It is also important to see that there was no
-10
0
10
20
30
40
50
60
0 2 4 6
Phenyl
butazone
6a
6b
6c
6d
6e
% I
nh
ibit
ion
Time in hours
Chapter I
16
quick onset of action because the activity observed at the end of second hour
was only 18%, where as in case of 6j it was 34.74%. Compounds 6a, 6e, 6g
and 6h were also found to be less effective at the end of second hour. The
present studies have shown that the most active compound was 6j.
Table 2: Correlation of anti-inflammatory activity with calculated molecular
parameters.
Compound Log P Polar surface
area (2D)
van der Waal’s
(3D) Surface
area
% inhibition
(at 5th
hour)
6a 5.35 47.36 551.73 37.34
6b 5.86 47.79 584.26 47.79
6c 5.19 56.59 600.45 31.72
6d 5.86 47.36 584.54 49.39
6e 5.86 47.36 584.54 33.33
6f 6.38 47.36 615.99 42.97
6g 5.95 47.36 568.07 30.92
6h 5.35 47.36 551.76 34.13
6i 5.86 47.43 584.19 48.59
6j 5.19 56.59 600.38 52.61
Calculations of molecular and partitioning parameters [24] (Table 2) reveals
that the substituents did not lead to significant variation in the polar surface
area of the compounds. Log P values expectedly are more sensitive to the
substituents. A combination of Log P and higher 3D surface area which can be
found in 6j resulted in the best activity observed during the present work.
Other compounds like 6b, 6d and 6h also exhibit a fair agreement with this
proposition. Less activity observed in the case of 6c emphasizes orientation of
the groups in coumarin and aryl moieties.
Chapter I
17
Sp
ectr
um
No
. 1:
Mas
s S
pec
tru
m o
f C
om
po
un
d 3
a.
Chapter I
18
So
lven
t: D
MS
O-d
6
Sp
ectr
um
No.
2:
1H
NM
R o
f C
om
po
un
d 3
a.
Chapter I
19
Sp
ectr
um
No.
3:
Mas
s S
pec
trum
of
Com
pou
nd
6h
.
Chapter I
20
Solv
ent:
DM
SO
-d6
M+
Sp
ectr
um
No
. 4
: 1H
NM
R o
f C
om
po
und
6h
.
Chapter I
21
Solv
ent:
DM
SO
-d6
Sp
ectr
um
No
. 5
: 1H
NM
R o
f C
om
po
un
d 6
h (
Ex
pan
sion
).
Chapter I
22
So
lven
t: D
MS
O-d
6
Sp
ectr
um
No
. 6
: 1
3C
-NM
R o
f C
om
po
un
d 6
h.
Chapter I
23
Solv
ent:
DM
SO
-d6
Sp
ectr
um
No.
7:
13C
-DE
PT
NM
R o
f C
om
po
un
d 6
h.
Chapter I
24
Spectrum No. 8: 1H-13C HETCOR NMR of Compound 6h.
O
NN
N
O
H
H H
H
H
60.72
5.81 6.06
4.05
4.4151.05
36.984.98
H3C
Chapter I
25
4. EXPERIMENTAL
Melting points were determined in open capillaries and are uncorrected. IR
spectra (KBr disc) were recorded on a Nicolet-5700 FT-IR spectrophotometer.
1H-NMR spectra were recorded on Bruker 300 MHz and 400 MHz
spectrometers using CDCl3 and DMSO-d6 as solvents and TMS as an internal
standard. The chemical shifts are expressed in δ ppm. Mass spectra were
recorded using Shimadzu GCMS-QP2010S. Elemental analyses was carried
out using Hereaus CHN rapid analyzer. Purity of the compounds was checked
by TLC.
Synthesis of coumarin-4-acetic acids 2:
Coumarin-4-acetic acids have been synthesized by literature method [20] by
the cyclization of phenols and citric acid monohydrate using sulfuric acid as the
cyclising agent.
General procedure: Synthesis of 4-((1H-benzo[d]imidazol-2-yl) methyl)-
2H-chromen-2-ones 3:
Substituted coumarin-4-acetic acid (0.01M) and o-phenylene diamine (0.011M)
were mixed with 25 mL of anhydrous phosphoric acid and heated in an oil bath
at 170-180 °C for four hours and cooled, resulting thick syrupy liquid is added
carefully to ice cold water and stirred well. Solid separated was basified
carefully using 25% liquor ammonia till basic. Solid separated was washed
with water and then 5% sodium carbonate solution to remove unreacted
o-phenylene diamine. Then the solid was again washed with water and dried
and recrystallised using ethanol.
Chapter I
26
4-((1H-benzo[d]imidazol-2-yl) methyl)-6-methyl-2H-chromen-2-one 3a:
Off white solid, yield: 65%, mp= 248-50 °C
(ethanol), FT-IR (KBr) cm-1
: 1725 (C=O);
3311 (N-H); 1H-NMR (DMSO, 300 MHz,
TMS) δ ppm: 2.33 (s, 3H, C6- CH3 of
coumarin), 4.46 (s, 2H, C4-CH2), 6.43 (s, 1H,
C3-H coumarin), 7.16 (dd, 2H, J = 3.0, 6.0 Hz,
C5- C6-H benzimidazole), 7.31 (d, 1H, J = 9.0 Hz, C8-H coumarin), 7.43 (d,
1H, J = 9.0 Hz, C7- H coumarin), 7.51 (dd, 2H, J = 3.0, 6.0 Hz C4-, C7-H
benzimidazole), 7.68 (s, 1H, C5-H coumarin), 12.39 (s, 1H, N-H, D2O
exchangeable), 13
C-NMR (DMSO, 75 MHz, TMS) δ ppm: 21.36, 32.21,
116.59, 116.76, 117.29, 119.29, 122.60, 125.84, 125.93, 133.86, 134.56,
151.32, 152.21, 152.24, 160.80; MS (m/z)= (M+) 290 (79%); Anal. Calcd for
C18H14N2O2 (%): C, 74.47; H, 4.86; N, 9.65. Found: C, 74.50; H, 4.83; N, 9.64.
4-((1H-benzo[d]imidazol-2-yl) methyl)-7-methyl-2H-chromen-2-one 3b:
Off white solid, yield: 60%, mp= 215-17 °C
(Ethanol), FT-IR (KBr) cm-1
: 1699 (C=O),
3249 (N-H); 1H-NMR (DMSO 300 MHz,
TMS) δ ppm: 2.38 (s, 3H, C7- CH3 of
coumarin), 4.45 (s, 2H, C4-CH2), 6.42 (s, 1H,
C3-H of coumarin), 7.14 (m, 3H, Ar-H), 7.26
(s, 1H, Ar-H), 7.49 (bs, 2H, Ar-H ), 7.73 (d, 1H, J = 9.0 Hz, Ar-H), 12.37 (s,
1H, N-H, D2O exchangeable), MS (m/z)= (M+) 290 (75%); Anal. Calcd for
C18H14N2O2 (%): C, 74.47; H, 4.86; N, 9.65, Found: C, 74.45;H, 4.84; N, 9.68.
O O
N
HN
H3C
O O
N
HN
H3C
Chapter I
27
General Procedure: 4-(2-phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-2H-chromen-2-one 6:
4-((1H-benzo[d]imidazol-2-yl)methyl)-6-methyl-2H-chromen-2-one 3 (0.001
M) was dissolved in 25 mL of absolute alcohol and substituted aromatic amine
(0.001 M) and formalin (0.0025 M) were added and refluxed at 80-90 °C for
10 h and completion of the reaction was monitored by TLC. Then the reaction
mixture was filtered and filtrate was concentrated to three by fourth of its
original volume and cooled and the solid separated was filtered and washed
with cold ethanol. Recrystallisation was done using appropriate solvent.
4-(2-phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-
methyl-2H-chromen-2-one 6a:
White solid, yield: 60%, mp= 252-54 °C
(DMF), FT-IR (KBr) cm-1
: 1718 (C=O); 1H-
NMR (DMSO, 300 MHz, TMS) δ ppm: 2.37
(s, 3H, C6-CH3 coumarin), 4.08 (dd, 1H,
3JH-H = 9.0 Hz,
2JH-H= 15.0 Hz, -N-CH2-), 4.41
(dd, 1H, 3JH-H = 6.0 Hz,
2JH-H = 15.0 Hz, -N-
CH2-), 5.00 (t, 1H, C4-H), 5.82, 6.05 (2d, each,
1H, J = 12.0 Hz, -N-CH2-N-), 6.20 (s, 1H, C3-H coumarin), 6.91 (t, 1H, Ar-H),
7.13 (d, 2H, J = 9.0 Hz, Ar-H), 7.23-7.34 (m, 4H, Ar-H), 7.37 (d, 1H, J = 9.0
Hz, Ar-H), 7.50 (d, 1H, J = 9.0 Hz, Ar-H), 7.57 (d, 1H, J = 9.0 Hz, Ar-H), 7.61
(s, 1H, Ar-H), 7.84 (d, 1H, J = 6.0 Hz, Ar-H), MS (m/z)= (M-C6H5NH2)+
314
(6%); Anal. Calcd for C26H21N3O2 (%): C, 76.64; H, 5.19; N, 10.31, Found: C
76.62; H, 5.22; N, 10.34.
O O
NN
NH
H3C
Chapter I
28
4-(2-p-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-
methyl-2H-chromen-2-one 6b:
Pale yellow solid, yield: 50%, mp= 232-34
°C (Ethanol), FT-IR (KBr) cm-1
: 1722
(C=O); 1H-NMR (CDCl3, 300 MHz, TMS),
δ ppm: 2.31 (s, 3H, p-tolyl CH3), 2.41 (s,
3H, C6-CH3 of coumarin), 3.86 (m, 1H, -N-
CH2-), 4.31 (m, 1H, -N-CH2-), 4.89 (m, 1H,
C4-H), 5.62, 5.70 (2d, each, 1H, J = 12.0
Hz, -N-CH2-N-), 6.27 (s, 1H, C3-H coumarin), 6.88 (d, 2H, J = 9.0 Hz, Ar-H),
7.12 (d, 2H, J = 9.0 Hz, Ar-H), 7.30 (s, 2H, Ar-H), 7.39 (m, 3H, Ar-H), 7.51 (d,
1H, J = 9.0 Hz, Ar-H), 7.77 (d, 1H, J = 6.0 Hz, Ar-H), 13
C-NMR (DMSO, 100
MHz, TMS) δ ppm: 20.01, 20.55, 35.87, 51.07, 60.47, 110.28, 115.58, 116.67,
116.77, 117.88, 118.79, 122.08, 124.55, 129.42, 129.68, 129.81, 132.78,
133.02, 133.88, 142.16, 144.50, 149.43, 151.41, 153.83, 159.68; MS (m/z)=
(M+) 421 (65%); Anal. Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N,9.97,
Found; C 76.96; H, 5.46; N, 10.01.
4-(2-(4-methoxyphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]
pyrimidin-4-yl) -6-methyl-2H-chromen-2-one 6c:
Pale yellow solid, yield: 48%, mp= 210-
12 °C (Ethanol), FT-IR (KBr) cm-1
: 1726
(C=O); 1H-NMR (DMSO, 400 MHz,
TMS) δ ppm: 2.48 (s, 3H, C6-CH3
coumarin), 3.66 (s, 3H, O-CH3 p-
anisidine), 3.95 (dd, 1H, 3JH-H = 8.4 Hz,
2JH-H = 13.6 Hz, -N-CH2-), 4.28 (dd, 1H,
3JH-H = 5.6,
2JH-H = 13.6 Hz, -N-CH2-), 4.93 (dd,
1H,
3JH-H = 5.6, 8.0 Hz, C4-H),
5.72, 5.89 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.18 (s, 1H, C3-H
coumarin), 6.83 (d, 2H, J = 9.2 Hz, Ar-H), 7.03 (d, 2H, J = 9.2 Hz, Ar-H), 7.20
O O
NN
NH
H3C
H3C
O O
NN
NH
H3C
H3CO
Chapter I
29
(t, 1H, J = 8.0 Hz, Ar-H), 7.29 (t, 1H, J = 8.0 Hz, Ar-H), 7.35 (d, 1H, J =
8.4Hz, Ar-H), 7.47 (dd, 1H, J = 1.6, 8.4 Hz, Ar-H), 7.56 (d, 2H, J = 8.0 Hz, Ar-
H) 7.79 (d, 1H, J = 8.0 Hz, Ar-H); MS (m/z)= (M+) 437 (6%); Anal. Calcd for
C27H23N3O3 (%): C, 74. 12; H, 5.30; N, 9.60, Found: C 74.15; H, 5.32; N, 9.56.
4-(2-m-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-
methyl-2H-chromen-2-one 6d:
Pale yellow solid, yield: 54%, mp= 215-27 °C
(Ethanol), FT-IR (KBr) cm-1
: 1719 (C=O); 1H-
NMR (DMSO 300 MHz, TMS) δ ppm: 2.22
(s, 3H, CH3 m-tolyl), 2.38 (s, 3H, C6- CH3
coumarin), 4.05 (m, 1H, -N-CH2-), 4.38 (m,
1H, -N-CH2-), 5.00 (m, 1H, C4-H), 5.78, 6.03
(2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.19
(s, 1H, C3-H coumarin), 6.70 (d, 1H, J = 7.2 Hz, Ar-H), 6.90 (d, 1H, J = 8.4
Hz, Ar-H), 6.97 (s, 1H, Ar-H), 7.14 (t, 1H, J =7.5 Hz, Ar-H), 7.23-7.39 (m,
3H, Ar-H), 7.51 (d, 1H, J = 8.4 Hz, Ar-H), 7.57 (t, 1H, J = 7.8 Hz, Ar-H), 7.62
(s, 1H, Ar-H), 7.83 (d, 1H, J = 7.5 Hz, Ar-H); MS (m/z)= (M+) 421 (12%);
Anal. Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N, 9.97, Found: C, 76.96;
H, 5.51; N, 10.00.
4-(2-(3,4-dimethylphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6e:
Pale yellow solid, yield: 50%; mp= 234-
36 °C (Ethanol), FT-IR (KBr) cm-1
: 1727
(C=O); 1H-NMR (CDCl3, 300 MHz, TMS)
δ ppm: 2.19 (s, 6H, 2-CH3 amine), 2.38 (s,
3H, C6-CH3 coumarin), 3.77 (m, 1H, -N-
CH2), 4.28 (m, 1H, -N-CH2-), 4.89 (m, 1H,
O O
NN
NH
H3C
CH3
O O
NN
NH
H3C
CH3
H3C
Chapter I
30
NH), 5.58, 5.67 (2d, each, 1H, J = 11.1 Hz, -N-CH2-N-), 6.26 (s, 1H, C3-H
coumarin), 6.67 (d, 1H, J = 8.1 Hz, Ar-H), 6.78 (s, 1H, Ar-H), 7.02 (d, 1H, J =
8.1 Hz, Ar-H), 7.26-7.37 (m, 5H, Ar-H), 7.48 (d, 1H, J = 6.3 Hz, Ar-H), 7.76
(d, 1H, J = 6.9 Hz, Ar-H), 13
C-NMR (DMSO, 100 MHz, TMS) δ ppm: 18.36,
19.72, 20.56, 35.90, 51.02, 60.44, 110.28, 113.83, 115.55, 116.78, 117.90,
118.00, 118.78, 122.06, 124.48, 128.48, 130.24, 132.82, 133.00, 133.86,
137.13, 142.14, 144.70, 149.43, 151.40, 153.71, 159.66; MS (m/z)= (M+) 435
(12%); Anal. Calcd for C28H25N3O2 (%): C, 77.22; H, 5.79; N, 9.65, Found: C,
77.18; H, 5.75; N, 9.69.
4-(2-(2,3-dimethylyphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6f:
Pale yellow solid, yield: 53%, mp= 254-56 °C
(Ethanol), FT-IR (KBr) cm-1
: 1718 (C=O);
1H-NMR (DMSO, 400 MHz, TMS) δ ppm:
2.15, 2.21 (2s, each, 3H, 2-CH3 amine), 2.33
(s, 3H, C6-CH3 coumarin), 3.69 (dd, 1H, 3JH-H
= 6.8 Hz, 2JH-H = 13.0 Hz, -N-CH2-), 3.89 (dd,
1H, 3JH-H = 5.6,
2JH-H = 13.0 Hz, -N-CH2-),
5.03 (t, 1H,
3JH-H = 5.6 Hz, C4-H), 5.37, 5.52 (2d, each, 1H, J = 10.8 Hz, -N-
CH2-N-), 6.14 (s, 1H, C3-H coumarin), 6.94 (d, 1H, J = 8.0 Hz, Ar-H), 6.98 (d,
1H, J = 6.8 Hz , Ar-H), 7.05 (t, 1H, J = 7.6Hz, Ar-H), 7.24 (pd, 2H, J = 1.2, 7.6
Hz, Ar-H), 7.34 (d, 1H, J = 8.4 Hz, Ar-H), 7.46 (dd,1H, J = 1.6, 8.4 Hz, Ar-H),
7.57 (s, 1H, Ar-H), 7.60 (d, 1H, J = 8.4 Hz, Ar-H), 7.69 (d, 1H, J = 8.4 Hz,
Ar-H); MS (m/z)= (M+) 435 (8%); Anal. Calcd for C28H25N3O2 (%): C, 77.22;
H, 5.79; N, 9.65, Found; C, 76.25; H, 5.82; N, 9.68.
O O
NN
NH
H3C
CH3
CH3
Chapter I
31
4-(2-(4-chlorophenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6g:
Pale yellow solid, yield: 51%, mp= 222-24
°C (Ethanol), FT-IR (KBr) cm-1
: 1724
(C=O); 1H-NMR (DMSO, 400 MHz, TMS)
δ ppm: 2.36 (s, 3H, 6-CH3 coumarin), 4.06
(dd, 1H, 3JH-H = 8.4 Hz,
2JH-H = 14.0 Hz,
-CH2-N-), 4.40 (dd, 1H, 3JH-H = 5.2,
2JH-H =
14.0 Hz, -CH2-N-), 5.00 (dd, 1H,
3JH-H = 5.6,
8Hz, C4-H), 5.79, 6.02 (2d, each, J = 10.8 Hz, 1H, -N-CH2-N-), 6.19 (s, 1H,
C3-H coumarin), 7.14 (d, 2H, J = 8.8 Hz, Ar-H), 7.20-7.31 (m, 4H, Ar-H), 7.36
(d, 1H, J = 8.4 Hz, Ar-H), 7.47 (d, 1H, J = 8.4 Hz, Ar-H) 7.55 (d, 1H, J = 8.0
Hz, Ar-H), 7.62 (s, 1H, Ar-H), 7.80 (d, 1H, J = 7.6 Hz, Ar-H); MS (m/z)= (M+)
441 (21%), (M+2)+
443 (7%); Anal. Calcd for C26H20ClN3O2 (%): C, 70.67; H,
4.56; N, 9.51, Found; C, 70.71; H, 4.60; N, 9.48.
4-(2-phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-7-
methyl-2H-chromen-2-one 6h:
White solid, yield: 57%, mp= 156-58 °C
(Ethanol), FT-IR (KBr) cm-1
: 1712 (C=O); 1H-
NMR (DMSO 400 MHz, TMS) δ ppm: 2.41
(s, 3H, C7-CH3 coumarin), 4.05 (dd, 1H, 3JH-H
= 8.8 Hz, 2JH-H = 14.0 Hz, -N-CH2- ), 4.41 (dd,
1H, 3JH-H = 5.6,
2JH-H = 14.0 Hz, -N-CH2-),
4.95 (dd, 1H,
3JH-H = 5.6, 8.0 Hz, C4-H), 5.80, 6.06 (2d, each, 1H, J = 12.0 Hz,
-N-CH2-N-), 6.20 (s, 1H, C3-H coumarin), 6.87 (t, 1H, J = 7.2 Hz, Ar-H), 7.11
(d, 2H, J = 8.0 Hz, Ar-H), 7.17 (d, 1H, J = 10.0 Hz, Ar-H), 7.21-7.31 (m, 5H,
Ar-H), 7.53 (d, 1H, J = 8.0 Hz, Ar-H), 7.60 (d, 1H, J = 6.4 Hz, Ar-H), 7.82 (d,
1H, J = 8.0 Hz, Ar-H); 13
C-NMR (DMSO, 100 MHz, TMS) δ ppm: 20.93,
36.46, 50.54, 60.20, 110.30, 114.73, 115.67, 116.40, 116.98,118.77, 120.66,
122.06, 124.79, 125.67, 129.39, 132.76, 142.14, 142.95,146.76, 149.35,
O O
NN
NH
H3C
Cl
O O
NN
NH
H3C
Chapter I
32
153.40, 153.81, 159.70, MS (m/z)= (M+) 407 (27%); Anal. Calcd for
C26H21N3O2 (%): C,76.64; H, 5.19; N, 10. 31, Found: C, 76.61; H, 5.23; N,
10.29.
4-(2-p-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-7-
methyl-2H-chromen-2-one 6i:
Pale yellow solid, yield: 58%, mp= 218-20
°C (Ethanol), FT-IR (KBr) cm-1
: 1731
(C=O); 1H NMR (CDCl3, 300 MHz, TMS),
δ ppm: 2.30 (s, 3H, CH3 p-tolyl), 2.46 (s,
3H, C7- CH3 coumarin), 3.88 (m, 1H, -N-
CH2-), 4.29 (m, 1H, -N-CH2-), 4.85 (m, 1H,
C4-H), 5.69 (m, 2H, -N-CH2-N-), 6.21 (s,
1H, C3-H coumarin), 6.86 (d, 2H, Ar-H), 7.11 (m, 3H, Ar-H), 7.19 (s, 1H, Ar-
H), 7.28-7.37 (m, 3H, Ar-H), 7.51 (d, 1H, Ar-H), 7.77 (d, 1H, Ar-H); 13
C-NMR
(DMSO 100 MHz, TMS) δ ppm: 20.01, 20.95, 36.34, 50.97, 60.46, 110.31,
114.74, 115.69, 116.66, 117.00, 118.76, 122.06, 124.78, 125.69, 129.66,
129.84, 132.77, 142.13, 142.95, 144.42, 149.38, 153.42, 153.84, 159.74, MS
(m/z)= (M+) 421 (60%); Anal Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N,
9.97, Found; C, 76.97; H, 5.48; N, 9.94.
4-(2-(4-methoxyphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-7-methyl-2H-chromen-2-one 6j:
Pale yellow solid, yield: 57%, mp= 200-
02 °C (Ethanol), FT-IR (KBr) cm-1
: 1725
(C=O); 1H NMR (DMSO, 400 MHz,
TMS) δ ppm: 2.41 (s, 3H, C7-CH3
coumarin), 3.66 (s, 3H, OCH3 p-
anisidine), 3.95 (dd, 1H, 3JH-H = 8.0 Hz,
2JH-H = 16.0 Hz, -N-CH2-), 4.29 (dd, 1H,
3JH-H = 4.0 Hz,
2JH-H = 14.0 Hz, -N-CH2-), 4.90 (dd,
1H,
3JH-H = 4.0, 8.0 Hz, C4-
O O
NN
NH
H3C
H3C
O O
NN
NH
H3C
H3CO
Chapter I
33
H), 5.72, 5.93 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.21 (s, 1H, C3-H
coumarin), 6.83 (d, 2H, J = 8.0 Hz, Ar-H), 7.03 (d, 2H, J = 8.0 Hz, Ar-H), 7.18
(t, 1H, J = 8.0 Hz, Ar-H), 7.22 (d, 1H, J = 8.0 Hz, Ar-H), 7.29 (t, 2H, J = 8.0
Hz, Ar-H), 7.54 (d, 2H, J = 8.0 Hz, Ar-H), 7.79 (d, 1H, J = 8.4 Hz, Ar-H); MS
(m/z)= (M+) 437 (15%); Anal. Calcd for C27H23N3O3 (%): C, 74.12; H, 5.30; N,
9.60, Found: C, 74.09; H, 5.31; N, 9.63.
4-(2-(3,4-dimethylphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-7-methyl-2H-chromen-2-one 6k:
Pale yellow solid, yield: 60%, mp= 240-
42 °C (Ethanol), FT-IR (KBr) cm-1
: 1727
(C=O); 1H NMR (DMSO 400 MHz, TMS)
δ ppm: 2.08, 2.11 (2s, each, 3H, 2CH3-
amine), 2.41 (s, 3H, C7-CH3 coumarin),
3.98 (dd, 1H, -N-CH2-, 3JH-H = 8.8 Hz,
2JH-H
= 14.0 Hz), 4.33 (dd, 1H, 3JH-H = 5.6,
2JH-H
= 14.0 Hz, -N-CH2-), 4.92 (dd, 1H, 3JH-H = 5.6, 8.8 Hz, C4-H), 5.73, 6.00 (2d,
each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.19 (s, 1H, C3-H coumarin), 6.80 (dd,
1H, J = 2.4, 8.2 Hz, Ar-H), 6.92 (d, 1H, J = 2.4 Hz, Ar-H), 6.97 (d, 1H, J = 8.4
Hz, Ar-H), 7.17 (d,1H, J = 8.4 Hz, Ar-H), 7.22 (d, 1H, J = 8.0 Hz, Ar-H), 7.29
(t, 2H, Ar-H), 7.53 (d, 1H, J = 8.0 Hz, Ar-H), 7.57 (d, 1H, J = 6.0 Hz, Ar-H),
7.81 (d, 1H, J = 8.0 Hz, Ar-H); 13
C-NMR (DMSO, 100 MHz, TMS) δ ppm:
18.36, 19.72, 20.95, 36.21, 50.76, 60.60, 110.55, 113.91, 114.81, 115.66,
117.01, 118.01, 118.39, 122.37, 122.42, 124.73, 125.69, 128.55, 130.27,
132.58, 137.12, 141.15, 143.00, 144.61, 149.36, 153.41, 153.50, 159.69; MS
(m/z)= (M+) 435 (12%); Anal. Calcd for C28H25N3O2 (%): C, 77.22; H, 5.79; N,
9.65, Found: C, 77.25; H, 5.82; N, 9.69.
O O
NN
NH
H3C
CH3
H3C
Chapter I
34
4-(2-m-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-7-
methyl-2H-chromen-2-one 6l:
Pale yellow solid, yield: 45%, mp= 199-200
°C (Ethanol), FT-IR (KBr) cm-1
1723 (C=O);
1H-NMR (DMSO 400 MHz, TMS) 2.21 (s,
3H, -CH3 m-tolyl) 2.42 (s, 3H, C6-CH3
coumarin), 4.04 (dd, 1H, 3JH-H = 8.0,
2JH-H =
14.0 Hz, -N-CH2-), 4.34 (dd, 1H, 3JH-H = 4.0
Hz, 2JH-H = 14.0 Hz, -N-CH2-), 4.95 (dd, 1H,
3JH-H = 4.0 Hz, 8.0 Hz, C4-H), 5.77, 6.03 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-
), 6.19 (s, 1H, C3-H coumarin), 6.69 (d, 1H, J = 8.0 Hz, Ar-H), 6.89 (d, 1H, J =
8.0 Hz, Ar-H), 6.95 (s, 1H, Ar-H), 7.11 (t, 1H, J = 8.0 Hz, Ar-H), 7.20 (t, 1H, J
= 8.0 Hz, Ar-H), 7.21 (t, 1H, J = 8.0 Hz, Ar-H), 7.27-7.31 (m, 2H, Ar-H), 7.54
(d, 1H, J = 8.0 Hz, Ar-H), 7.60 (d, 1H, Ar-H), 7.82 (d, 1H, J = 8.0 Hz, Ar-H);
MS (m/z)= (M+H)+ 422(97%); Anal. C27H23N3O2 (%): C, 76.94; H, 5.50; N,
9.97, Found: C, 76.90; H, 5.46; N, 9.94.
4-(2-(4-chlorophenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-7-methyl-2H-chromen-2-one 6m:
Off white solid, yield: 52%, mp= 169-70 °C
(Ethanol), FT-IR (KBr) cm-1
: 1716 (C=O);
1H NMR (DMSO, 400 MHz, TMS) δ ppm:
2.42 (s, 3H, C7-CH3 coumarin), 4.05 (dd, 1H,
3JH-H = 8.0 Hz,
2JH-H = 12.0 Hz, -CH2-N-),
4.40 (dd, 1H, 3JH-H = 4.0 Hz,
2JH-H = 12.0 Hz,
-CH2-N-), 4.96 (dd, 1H,
3JH-H = 4.0, 8.0 Hz,
C4-H), 5.79, 6.07 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.23 (s, 1H, C3-H
coumarin), 7.14-7.19 (m, 3H, Ar-H), 7.22 (d, 1H, J = 8.0 Hz, Ar-H), 7.26-7.31
(m, 4H, Ar-H), 7.53 (d, 1H, J = 8.0 Hz, Ar-H), 7.61 (d, 1H, J = 4.0 Hz, Ar-H),
O O
NN
NH
H3C
CH3
O O
NN
NH
H3C
Cl
Chapter I
35
7.81 (d, 1H, J = 8.0 Hz, Ar-H); 13
C-NMR (DMSO, 100 MHz, TMS) δ ppm:
20.96, 36.39, 50.44, 60.13, 110.35, 114.79, 115.69, 116.98, 118.08, 118.80,
122.11, 124.36, 124.99, 125.69, 129.13, 132.76, 142.15, 142.99, 145.76,
149.35, 153.41, 153.76, 159.72; MS (m/z)= (M+H) +
442 (97%), (M+2+H) +
444 (28%); Anal. Calcd for C26H20ClN3O2 (%): C, 70.67; H, 4.56; N, 9.5,
Found: C, 70.64; H, 4.53; N, 9. 54.
4-(2-(4-bromophenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-
c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6n:
Off white solid, yield: 53%, mp= 233-35 °C
(Ethanol), FT-IR (KBr) cm-1
: 1722 (C=O),
1H- NMR (DMSO, 400 MHz, TMS) δ ppm:
2.37 (s, 3H, C6-CH3 coumarin), 4.07 (dd, 1H
3JH-H = 8.4Hz,
2JH-H = 14.0 Hz, -CH2-N-),
4.40 (dd, 1H, 3JH-H = 5.6,
2JH-H = 14.0 Hz,-
CH2-N-), 5.02 (dd, 1H,
3JH-H = 5.6, 8.4 Hz,
C4-H), 5.81, 6.04 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.22 (s, 1H, C3-H
coumarin), 7.11 (d, 2H, J = 9.2 Hz, Ar-H), 7.22 (t, 1H, J = 7.6 Hz, Ar-H), 7.30
(t, 1H, J = 8.0 Hz, Ar-H), 7.36-7.39 (m, 3H, Ar-H), 7.50 (d, 1H, J = 8.4 Hz, Ar-
H), 7.59 (d, 1H, J = 8.4 Hz, Ar-H), 7.65 (s, 1H, Ar-H), 7.82 (d,1H, J = 8.0 Hz,
Ar-H), 13
C-NMR (DMSO, 100 MHz, TMS) δ ppm: 20.52, 35.88, 50.30, 60.01,
110.30, 112.04, 115.60, 116.71, 117.91, 118.40, 118.80, 122.11, 124.79,
131.95, 132.73, 133.04, 133.88, 142.15, 146.21, 149.43, 151.39, 153.81,
159.65, MS (m/z)= (M+H) +
486 (93%), (M+2+H) +
, 488 (90%); Anal. Calcd
for C26H20BrN3O2 (%): C, 64.21; H, 4.14; N, 8.64, Found: C, 64.18; H,4.22; N,
8.65.
O O
NN
NH
Br
H3C
Chapter I
36
4-(2-o-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-
methyl-2H-chromen-2-one 6o:
Off white coloured solid, yield: 49%,
mp=241-42 °C (Ethanol), FT-IR (KBr) cm-1
:
1723 (C=O); 1H-NMR (DMSO, 400 MHz,
TMS) δ ppm: 2.25 (s, 3H, CH3 o-toluidine),
2.35 (s, 3H, 6- CH3 coumarin), 3.71 (dd, 1H,
3JH-H = 6.8 Hz,
2JH-H = 13.0 Hz, -N-CH2-), 3.99
(dd, 1H, 3JH-H = 5.2 Hz,
2JH-H = 13.0 Hz, -N-
CH2-), 5.19 (m, 1H, C4-H), 5.56, 5.63 (2d, each, 1H, -N-CH2-N-, J = 11.0 Hz),
6.29 (s, 1H, C3-H coumarin), 7.08-7.25 (m, 4H, Ar-H), 7.36-7.44 (m, 3H, Ar-
H), 7.49 (d, 1H, J = 8.4 Hz, Ar-H), 7.62 (s, 1H, Ar-H), 7.71 (d, 1H, J = 7.6 Hz,
Ar-H), 7.85 (d, 1H, J = 7.2 Hz, Ar-H); MS (m/z)= (M+H)+ 422(87%); Anal.
Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N, 9.97, Found: C, 76.97; H,
5.48; N, 9.95.
PHARMACOLOGY
Acute oral toxicity:
Healthy young mice of either sex weighing 22-30 g were used for acute
toxicity study [25] to determine LD50 of test compounds. Each group contained
three animals. The temperature in the experimental room was maintained
around 25 °C. Lighting was natural; sequence being 12 hours dark, 12 hours
light cycle. The conventional laboratory diet was fed with adequate supply of
drinking water. The animals were randomly selected, marked to permit
individual identification and kept in polypropylene cages for one week prior to
dosing, in order for them to acclimatize to laboratory conditions. The test
compounds were prepared as a suspension by triturating with water and 1%
tween 80. The test compounds were administered in a single dose by using a
mice oral feeding needle. Prior to dosing, animals were kept for 12 hours
fasting. The animals were then weighed and test compounds were
O O
NN
NH
H3C
CH3
Chapter I
37
administered. After the administration of dose, food was withheld for a further
3-4 hours. In each step three animals were used in each group. Study began at
50 mg/kg body weight and was continued till 2000 mg/kg body weight.
Observations:
Animals were observed initially after dosing atleast once during the first 30
minutes, periodically during the first 24 hours, with special attention given
during the first 4 hours. In above case, death was observed within first 24
hours. Additional observations like changes in skin, fur, eyes, mucous
membranes, respiratory, circulatory, autonomic, central nervous system,
somatomotor activity and behavior pattern were also noted. Attention was also
given to observation of tremors and convulsions. No tremors and convulsions
were observed upon inspection and a post mortem examination revealed no
hemorrhagic spots.
Evaluation of carrageenan induced inflammation:
Acute inflammation was induced by injecting 0.1 ml of (1%) carrageenan
into plantar surface of rat hind paw [26]. The test samples and
phenylbutazone (100 mg/kg, orally) as reference agent were administered
60 min before carrageenan injection. The paw volumes were measured at 0,
1, 2, 3, 4 and 5 h, using mercury plethysmometer. The mean changes in
injected paw edema, with respect to initial paw volume, were calculated on
respective hours and percentage inhibition of paw edema with respect to
untreated group was calculated using following formula:
i = [1- (∆VTreated/ ∆VControl)] X 100
where, I = % inhibition of paw edema
∆VTreated = Mean change in paw volume of treated rat.
∆VControl = Mean change in paw volume of treated rat.
Chapter I
38
5. CONCLUSIONS
In conclusion, we have observed an unexpected C-C bond formation in the
Mannich reaction of formaldehyde and primary amines of methylene bridged
4-2'-benzimidazolyl coumarins leading to a serendipitous synthesis of 4-(2-
phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-2H-
chromen-2- ones. The synthesized compounds have been confirmed by spectral
methods. Compounds 6b, 6d, 6h and 6j exhibited good anti-inflammatory
activity, amongst which 6j was found to be most potent.
Chapter I
39
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Chapter I
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