Synthesis and evaluation of novel carbamate-substituted flavanone derivatives as potent acetylcholinesterase inhibitors and anti-amnestic agents

Article abstract of DOI:10.1007/s00044-012-0162-3

This study was designed to synthesize and evaluate flavanone derivatives with phenylcarbamate moiety as potent acetylcholinesterase (AChE) inhibitors and anti-amnestic agents for management of AD. The synthesis of carbamate-substituted flavanone derivativ

Full text of DOI:10.1007/s00044-012-0162-3

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:1648–1659
DOI 10.1007/s00044-012-0162-3
ORIGINAL RESEARCH
Synthesis and evaluation of novel carbamate-substituted
flavanone derivatives as potent acetylcholinesterase inhibitors
and anti-amnestic agents
•
Preet Anand Baldev Singh
Received: 20 March 2012 / Accepted: 15 June 2012 / Published online: 1 July 2012
Ó Springer Science+Business Media, LLC 2012
Abstract This study was designed to synthesize and
evaluateflavanone derivatives with phenylcarbamate moiety
as potent acetylcholinesterase (AChE) inhibitors and anti-
amnestic agents for management of AD. The synthesis of
carbamate-substituted flavanone derivatives involved base-
catalysed Claisen-Schmidt condensation reaction of
2-hydroxy acetophenone/2-hydroxy-4,6-dimethoxyaceto-
phenone with differently substituted benzaldehydes to yield
differently substituted chalcones that underwent intra-
molecular oxidative cyclization on refluxing with glacial
acetic acid to yield flavanone compounds. Thereafter,
refluxing of flavanone compounds with phenyl isocyanate in
the presence of petroleum-ether and triethylamine provided
phenyl carbamate-substituted flavanone derivatives. The
synthesized compounds were screened in vitro for AChE
inhibitory activity with donepezil as the standard drug. The
most potent test compound (5f0) was evaluated in vivo for
memory restorative actions in scopolamine (0.4 mg/kg)-
induced amnesia in mice by Morris water maze test. All
the compounds exhibited AChE inhibitory activity with
carbamate substituted 5,7-dimethoxyflavanone derivatives
(5a0–5g0) being the most potent compounds with IC50 rang-
ing from 21.5 1.8 to 9.9 1.6 nM. Compound 5f0 also
ameliorated scopolamine-induced amnesia in mice in terms
of restoration of time spent in target quadrant and escape
latency time. It may be concluded that phenylcarbamate-
substituted 5,7-dimethoxyflavanones may be a promising
structural template for the development of novel AChE
inhibitors in managing amnestic disorders including AD.
Keywords Flavanone ꢀ Carbamate ꢀ
Acetylcholinesterase ꢀ Alzheimer’s disease
Introduction
Alzheimer’s disease (AD), characterised by Alois Alzhei-
mer in 1907, is a progressive neurodegenerative disorder of
the brain and is the most common form of dementia among
the elderly. It affects over 20 million individuals world-
wide and this number will substantially increase in the
future along with the increase of the number of elderly in
the population. Its prevalence increases with age, from
10 % at 65 years to nearly 50 % at 85 years (Bachurin,
2003; Colombres et al., 2004). According to the ‘cholin-
ergic hypothesis’, impairment in the cholinergic function is
of critical importance in AD especially the brain areas
dealing with learning, memory, behaviour and emotional
responses that include the neocortex and the hippocampus.
Brain atrophy is the most obvious clinical finding in AD in
which the levels of acetylcholine (ACh) are decreased due
to its rapid hydrolysis by acetylcholinesterase (AChE)
enzyme (Ladner and Lee, 1998). Furthermore, a broad
range of evidences have shown that enzyme AChE pro-
duces secondary non-cholinergic functions that include
promotion in beta-amyloid (Ab) deposition in the form
senile plaques/neurofibrillary tangles in the brain of
afflicted individuals (Castro and Martinez, 2001; Selkoe
2002; Bartolini et al., 2003; Rees et al., 2003). Thus, AChE
inhibition has been documented as a critical target for the
effective management of AD by an increase in the avail-
ability of ACh in the brain regions and decrease in the Ab
deposition (De Ferrari et al., 2001).
P. Anand ꢀ B. Singh (&)
Department of Chemistry, Punjabi University,
Patiala 147002, Punjab, India
e-mail: baldev.chemistry@gmail.com
Flavonoids are natural phytochemicals that are distrib-
uted in fruits, vegetables and whole grains with a wide
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Med Chem Res (2013) 22:1648–1659
1649
( Carbamate moiety)
range of pharmacological properties including anti-
inflammatory, -tumour, hepatoprotective, anti-viral, -fun-
gal, -microbial and -oxidant (Kim et al., 2004). The studies
have also shown that natural as well as the chemically
synthesised flavonoid analogues exhibit neuroprotective
effects (Wang et al., 2001), AChE inhibitory (Jung and
Park, 2007) along with Ab fibril formation inhibitory
activities (Kim et al., 2005; Zhu et al., 2007). Several
studies have also documented the anti-amnestic and
memory restorative functions of flavonoid derivatives in
different experimental models of amnesia along with pre-
vention/slowing of progressive neurodegeneration in AD
(Richetti et al., 2011). Furthermore, the studies have shown
that addition of different chemical moieties to flavonoid
scaffold such as benzyl piperidine (Shen et al., 2009) and
amino alkyl groups at para and meta positions enhance the
effectiveness of flavonoid nucleus for AChE inhibition
(Sheng et al., 2009).
H C
O
O
O
R
NH
3
N
CH
O
3
rivastigmine with
carbamate moiety
flavanone nucleus
COONHR
O
O
flavanone with carbamate moiety
Fig. 1 Design strategy of carbamate derivatives of flavanone
(3a–3g) and (3a0–3g0), respectively (Lin et al., 2002).
Subsequently, the differently substituted chalcones (3a–3g)
and (3a0–3g0) underwent intra-molecular oxidative cycli-
zation on refluxing with glacial acetic acid to yield flava-
none compounds (4a–4g) and (4a0–4g0), respectively
(Cabrera et al., 2007). Thereafter refluxing of flavanone
compounds (4a–4g) and (4a0–4g0) with phenyl isocyanate
in the presence of petroleum-ether and triethylamine (2 or 3
drops) provided phenyl carbamate-substituted flavanone
derivatives (5a–5g) and (5a0–5g0), respectively.
A number of studies have revealed that carbamate is an
important structural constituent imparting AChE inhibitory
properties. Infact, carbamate is an integral part of clinically
employed AChE inhibitor, rivastigmine. The various
research groups have synthesised carbamate derivatives by
incorporating other chemical moieties to produce potent
AChE inhibitors that included phenyl ring (Lin et al.,
1999), benzopyrano [4,3-b] pyrroles (Bolognesi et al.,
2004), 1,2-phenylalkyl-substituted piperidines (Mustazza
et al., 2002), N-propargylaminoindan and N-propargyl-
phenethylamine (Sterling et al., 2002). Based on these, it
may be proposed that the addition of carbamate moiety to
flavonoid molecule may produce potent AChE inhibitors
(Fig. 1) that in turn may be beneficial for memory resto-
ration in amnesia of diverse aetiology including AD.
Therefore, this study was designed to synthesise novel
carbamate derivatives of flavanone followed by their
screening for AChE inhibitory activity with in vitro testing
along with in vivo evaluation of the most potent AChE
inhibitor for the memory restorative effect in a mice model
of amnesia.
Biological activity
All the synthesized flavanone derivatives were screened for
AChE inhibitory activity in the rat cortex homogenate
using modified Ellman method with donepezil as the
standard AChE inhibitor (Ellmann et al., 1961; Cheng and
Tang, 1998). All the compounds exhibited AChE inhibitory
activity with carbamate substituted 5,7-dimethoxyflava-
none derivatives (5b0–5g0) being the most potent com-
pounds with IC50 ranging from 19.6 1.8 to 9.9 1.6 nM
(Tables 1, 2). Furthermore, the compound 5f0 was found to
be the most potent AChE inhibitor with IC50
9.9 1.6 nM. The replacement of –OH group of ring B of
flavanone scaffold (4a–4g, 4a0–4g0) with the phenyl car-
bamate moiety (5a–5g, 5a0–5g0) led to dramatic increase in
AChE inhibitory activity suggesting phenyl carbamate as
an important moiety that may influence the AChE activity.
The presence of two electron releasing methoxy groups at
5th and 7th position of phenyl ring A of carbamate-
substituted flavanones conferred greater AChE inhibitory
activity in compound 5a0–5g0 as compared to compound
5a–5g without dimethoxy groups at 5th and 7th positions of
carbamate-substituted flavanones. Furthermore, the position
of carbamate moiety linked to ring B of flavanone scaffold
also influenced the AChE inhibitory activity with higher
Results and discussion
Chemistry
The synthesis of carbamate substituted flavanone deriva-
tives is illustrated as a representative case in Figs. 2 and 3.
The base-catalysed Claisen-Schmidt condensation reaction
of 2-hydroxyacetophenone (1) or 2-hydroxy-4,6-dime-
thoxyacetophenone (10) with differently substituted benz-
aldehydes (2a–2g) in the presence of ethyl alcohol and
60 % KOH followed by neutralisation in the presence of
cold acetic acid yielded differently substituted chalcones
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Med Chem Res (2013) 22:1648–1659
Fig. 2 Schematic diagram
describing the steps in the
synthesis of substituted
flavanone derivatives (4a–4g)
and substituted flavanone
derivatives with carbamate
moiety (5a–5g) from
R
O
OH
O
R
OH
+
EtOH, KOH
H
CH
3
°
stirring at 0 C, 1 day
,
R'
R
O
2-hydroxyacetophenone
substituted benzaldehyde
(2a- 2g)
substituted chalcones(3a-3g)
(1)
2-hydroxyacetophenone and
substituted benzaldehyde
refluxing, 72hr
glacial acetic acid
R
COONHC H
6
5
O
O
O
R'
phenylisocyanate
refluxing,15-20 min.
R'
O
substituted flavanones (4a-4g )
substituted
carbamate moiety (5a-5g)
flavanones
with
compound
R
2a
2b
2c
2d
2e
2f
2g
2-OH
3-OH
4-OH
3-OH
4-OH
4-OH
4-OH
NO
R'
H
H
H
4-OMe
3-OMe
3 and 5-OMe
3-OMe and 5-
2
Fig. 3 Schematic diagram
describing the steps in the
synthesis of substituted 5,7-
dimethoxyflavanone derivatives
(4a0–4g0) and substituted 5,7-
dimethoxyflavanone derivatives
with carbamate moiety (5a0–
5g0) from 2-hydroxy-4,6-
R
CH
O
CH
3
3
O
H
R
OH
O
OH
O
EtOH , KOH
°
R'
stirring at 0 C, 1 day
CH
3
+
'
R
O
O
O
H C
H C
3
dimethoxyacetophenone and
substituted benzaldehyde
3
substituted chalcones (3a'-3g' )
substituted benzaldehyde
(2a- 2g)
2-hydroxy-4,6-dimethoxy
acetophenone (1')
glacial acetic acid
refluxing, 72 hr
R
COONHC H
6
5
CH
O
3
H C
3
O
O
O
O
'
R
phenylisocyanate
refluxing, 15_20 min
R'
O
O
O
H C
3
H C
3
substituted flavanones with
carbamate moiety (5a'-5g')
substituted flavanones (4a'-4g' )
compound
2a
2-OH
H
2b
2c
2d
2e
2f
2g
R
3-OH
H
4-OH
H
3-OH
4-OMe
4-OH
4-OH
4-OH
NO
R'
3-OMe
3 and 5-OMe
3-OMe and 5 -
2
potency for compounds with carbamate attached to flava-
none at para position (5e0) as compared to corresponding
compounds with carbamate moiety at meta positions (5d0).
The nature of substituent, i.e. electron releasing/withdrawing
groups attached to ring B of flavanone moiety also influenced
the AChE inhibitory activity. The compound with two
–OCH3 groups (electron releasing) at ring B (5f0, IC50
9.9 1.6 nM) demonstrated higher AChE inhibition as
compared to corresponding compounds with one –OCH3
group (5d0, IC50 16.3 2.1 nM; 5e0, IC50 12.8 1.8 nM)
and –NO2 group (electron withdrawing) (5g0 IC50
18.2 1.9 nM). The compound (5f0) was also evaluated for
memory restoration in scopolamine-induced amnesia in
mice. Administration of scopolamine significantlydecreased
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Med Chem Res (2013) 22:1648–1659
1651
Table 1 AChE inhibitory activity of flavanone derivatives (4a–4g) and flavanone derivatives with carbamate moiety (5a–5g)
COONHC H
R
6
5
O
O
O
R'
R'
O
substituted flavanones with
carbamate moiety (5a-5g)
substituted flavanones (4a-4g )
Sr. no.
Compound
R
R0
–COONHC6H5
(carbamate moiety)
IC50 (nM)
1
4a
20-OH
30-OH
40-OH
30-OH
40-OH
40-OH
40-OH
H
–
149 1.2
147 1.1
145 1.6
140 1.5
138 1.6
131 1.1
144 2.1
39.9 2.5
38.8 1.8
36.7 1.9
27.6 1.2
21.9 1.3
19.3 1.8
30.5 1.2
21.5 3.2
2
4b
H
–
3
4c
H
–
4
4d
40-OMe
30-OMe
30,50-di–OMe
30-OMe and 50-NO2
–
5
4e
–
6
4f
–
7
4g
–
8
5a
–
–
–
–
–
–
–
–
H
ortho
meta
para
meta
para
para
para
–
9
5b
H
10
11
12
13
14
15
5c
H
5d
40-OMe
30-OMe
30,50-di-OMe
30-OMe and 50-NO2
–
5e
5f
5g
Donepezil
day 4 ELT and TSTQ on day 5 indicating an impairment of
memory as assessed on Morris water maze as compared to
normal mice. However, treatment with test compound 5f0
(5 and 10 mg/kg) along with donepezil (25 mg/kg) attenu-
ated scopolamine-induced decrease in day 4 ELT and TSTQ
on day 5 in a significant manner (Table 3; Fig. 4).
respectively. Gly 121 and Gly 122 are important groups of
‘oxy-anionic hole’ which in turn provide hydrogen bond
donors to stabilize tetrahedral transition state of substrate.
Ser 203 is an important constituent of catalytic site lying
˚
deep with in the molecule at the base of an narrow 20 A
deep gorge. The oxygen of other methoxy group attached
to ring B of flavonoid scaffold may show hydrogen bond-
ing with hydroxyl group of Tyr 337 (a constituent of
‘anionic’ sub-site in the gorge and involved in optimally
positioning the ester at the acylation site along with binding
to trimethylammonium choline through p-cation interac-
Molecular docking
To disclose a possible binding mode of compound 5f0 with
human AChE enzyme’s binding pockets, the docking
simulation were performed using the available crystallo-
graphic structure of enzyme (PDB code 1B41) using
Molegro Virtual Docker. The docking simulation revealed
that the enzyme and compound 5f0 interacted through p–p
aromatic interactions and hydrogen bonding (Fig. 5). The
oxygen atom of methoxy group attached to the ring B of
flavonoid may interact with –NH– group of Gly 121; –NH–
of Gly 122 and –OH group of Ser 203 through hydrogen
˚
tions) at the distance of 3.20 A. The heterocyclic oxygen of
ring C of flavonoid scaffold may interact with hydroxyl
group of Tyr 124 (one of the five residues of peripheral
anionic site clustered around the entrance to the active site
˚
gorge) at a distance of 2.89 A. The docking results also
revealed the potential p–p aromatic interactions between
compound 5f0 and amino acid residues of human AChE.
The heterocyclic phenyl C-ring of the compound 5f0 may
show p–p interactions with Phe 338 (constitute ‘anionic
˚
bonding with a distance of 3.46, 3.15 and 2.77 A,
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Med Chem Res (2013) 22:1648–1659
Table 2 AChE inhibitory activity of 5,7-dimethoxyflavanone derivatives (4a0–4g0) and 5,7-dimethoxyflavanone derivatives with carbamate
moiety (5a0–5g0)
R
COONHC H
6
5
H C
3
CH
O
3
O
O
O
O
O
'
R
R'
O
O
H C
3
H C
3
substituted flavanones (4a'-4g' )
substituted flavanones with
carbamate moiety (5a'-5g')
Sr. no.
Compound
R
R0
–COONHC6H5
IC50 (nM)
1
4a0
4b0
4c0
4d0
4e0
4f0
4g0
5a0
5b0
5c0
5d0
5e0
5f0
20-OH
30-OH
40-OH
30-OH
40-OH
40-OH
40-OH
H
H
H
–
120 1.7
119 2.1
118 1.2
114 1.1
112 1.3
107 1.8
116 1.2
21.5 1.3
19.6 1.8
18.8 1.6
16.3 2.1
12.8 1.8
9.9 1.6
18.2 1.9
2
–
3
–
4
40-OMe
30-OMe
3,050-di-OMe
30-OMe and 50-NO2
–
5
–
6
–
7
–
8
–
–
–
–
–
–
–
H
ortho
meta
para
meta
para
para
para
9
H
10
11
12
13
14
H
40-OMe
30-OMe
30,50-di-OMe
30-OMe and 50-NO2
5g0
Table 3 Effect of different interventions on escape latency time (ELT) using Morris water maze for memory evaluation
S. no
Group
Dose
Day 1 ELT
Day 4 ELT
1.
2.
3.
4.
5.
6.
7.
Normal
–
86.2 5.5
89.8 4.8
84.3 2.8
87.5 4.1
83.1 3.9
89.7 3.8
84.8 4.1
37.2 5.2a
79.3 6.3b
72.1 3.6
66.4 5.9
45.4 3.7c
78.7 5.7
52.6 4.0c
Scopolamine
0.4
Compound 5f0 in scopolamine
Compound 5f0 in scopolamine
Compound 5f0 in scopolamine
Vehicle in scopolamine
Donepezil
2 mg/kg (i.p)
5 mg/kg (i.p)
10 mg/kg (i.p)
5 ml/kg (i.p.)
25 mg/kg (i.p.)
Values are expressed as mean SEM for six animals
a
p \ 0.05 vs. day 1 ELT in normal
b
p \ 0.05 vs. day 4 ELT in normal
c
p \ 0.05 vs. day 4 ELT in scopolamine
sub-site’ along with constituents of peripheral anionic site
Tyr 341 and Tyr 72). The phenyl A-ring of flavonoid
scaffold may also show p–p interactions with Phe 295
(a part of acyl pocket, which is responsible for substrate
selectivity by preventing access of other larger members of
choline ester series) and Trp 286 (one of the five residues
of peripheral anionic site clustered around the entrance to
the active site gorge).
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Med Chem Res (2013) 22:1648–1659
1653
Fig. 4 Effect of different
interventions on time spent in
target quadrant (TSTQ), i.e. Q4
in Morris water maze test for
memory evaluation. Values are
expressed as mean SEM for
six animals. Sco scopolamine,
Donel donepezil. a p \ 0.05
versus time spent in other
quadrants (Q1, Q2, Q3) in
normal. b p \ 0.05 versus
TSTQ in normal. c p \ 0.05
versus TSTQ in scopolamine
treated. The data were analysed
using One-way ANOVA
Q1
Q2
Q3
Q4
a
70
60
50
40
30
20
10
0
c
b
o
o
l
o
o
c
co
c
s
a
c
s
sco
s
Sc
m
s
n
r
in
)
in
i
in
)
l in
e
le
ic
No
g
g)
g
/k
k
/k
n
/
h
o
g
g
g
e
D
m
V
followed by Tukey’s multiple
range test
m
m
0
2
5
(
(
'
'
5f
(1
f
f'
5
5
p
m
mp
Co
mp
Co
Co
Fig. 5 The docking view of
compound 5f0 with AChE (PDB
code 1B41) showing five
hydrogen-bond interactions
(shown by broken lines) among
the different amino acid
residues and structural parts of
compound. The different atoms
are shown in different colours,
i.e. nitrogen with blue, oxygen
with red and carbon with white
(Color figure online)
Conclusion
Experimental
A new series of carbamate derivatives of flavanone were
designed and synthesized as AChE inhibitors and anti-
amnestic agents. The results of the present study suggests
that phenylcarbamate substituted 5,7-dimethoxyflavanones
may be a promising structural template for the develop-
ment of novel AChE inhibitors in managing amnesic dis-
orders including AD.
Chemistry
All the reagents and the solvents used were of analytical
grade. Melting points were determined on Gallen–Kamp
apparatus and uncorrected. H1 NMR spectra were recorded
on Bruker Avance II 400 MHz spectrometer in CDCl3 with
TMS (Me4Si) as an internal standard and chemical shifts
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Med Chem Res (2013) 22:1648–1659
were recorded in parts per million (ppm) along with cou-
pling constants (J values) in Hertz. Multiplicities were
designated as singlet (s), doublet (d), triplet (t), quadruplet
(q) and multiplet (m). IR spectra were recorded on a Perkin
Elmer spectrum RX IFT-IR system. Mass spectra were
recorded using Thermo Scientific, LTQ-XL LCMS with
ionization current of 70 eV. Mass spectra (MS) signals
were given in m/z. Elemental analysis (EA) was performed
on an Elementar Analysensysteme GmbH. All the reactions
were monitored using TLC.
J2 = 3.42 Hz, H-2), 3.01 (dd, 1H, J1 = 17.2 and
J2 = 13.70 Hz, H3a), 2.59 (dd, 1H, J1 = 16.7 and
J2 = 3.1 Hz, H3b), 7.51–6.87 (m, 8H, aromatic H), 9.38
(s, 1H, OH); ESI–MS (positive mode) m/z 241 (M ? H)?;
Anal. Cald for C15H12O3: C, 72.88; H, 5.13; O, 18.98.
Found: C, 72.64; H, 5.03; O, 18.68.
2-(4-Hydroxyphenyl)chroman-4-one (4c) Yellow solid,
yield 60.2 %, mp 121–122 °C; IR (Nujol) t 3510, 1678,
1610,1605 1274,1241, 1211,1126 cm-1; H1 NMR (CDCl3,
400 MHz)
d
5.81 (dd, 1H, J1 = 12.48 Hz and
General procedure for the synthesis of substituted
chalcones (3a–3g or 3a0–3g0)
J2 = 3.22 Hz, H-2), 3.03 (dd, 1H, J1 = 16.7 and
J2 = 13.60 Hz, H3a), 2.58 (dd, 1H, J1 = 16.8 and
J2 = 3.1 Hz, H3b), 7.52–6.85 (m, 8H, aromatic H), 9.39
(s, 1H, OH); ESI–MS (positive mode) m/z 241 (M ? H)?;
Anal. Cald for C15H12O3: C, 73.89; H, 5.24; O, 20.98.
Found: C, 72.79; H, 5.21; O, 20.88.
To a solution of 2-hydroxyacetophenone (11 mmol) (1) or
2-hydroxy-4,6-dimethoxyacetophenone(11 mmol) (10) and
substituted benzaldehydes (9 mmol) in absolute ethyl
alcohol (10 ml) was added a 60 % of KOH (10 g) solution
dropwise at 0 °C. The reaction was stirred at 0 °C for
1 day. The cold water was added and the reaction mixture
was neutralised with cold acetic acid. The yellow precipi-
tates were collected, washed with water and recrystallized
from ethyl alcohol to yield substituted chalcones, respec-
tively (3a–3g or 3a0–3g0).
2-(3-Hydroxy-4-methoxyphenyl)chroman-4-one (4d) Yel-
low solid, yield 64.5 %, mp 125–126 °C; IR (Nujol)
t
3508, 1679, 1610,1605 1270,1239, 1211, 1125,
1025 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.81 (dd, 1H,
J1 = 12.44 Hz and J2 = 2.98 Hz, H-2), 3.03 (dd, 1H,
J1 = 16.8 and J2 = 13.62 Hz, H3a), 2.60 (dd, 1H,
J1 = 16.7 and J2 = 3.2 Hz, H3b), 7.53–6.81 (m, 7H, aro-
matic H), 10.01 (s, 1H, OH), 3.83 (s, 3H, 40-OCH3); ESI–
MS (positive mode) m/z 271 (M ? H)?; Anal. Cald for
C16H14O4: C, 71.19; H, 5.22; O, 23.68. Found: C, 70.97; H,
5.18; O, 23.68.
General procedure for the synthesis of substituted
flavanones (4a–4g or 4a0–4g0)
A mixture of the corresponding substituted chalcones
(1 equiv.) (3a–3g or 3a0–3g0) in glacial acetic acid (25 ml/
mmol of substituted chalcones) was refluxed during 72 h.
Thereafter, the mixture was poured into water and extrac-
ted with ethyl acetate (3 9 25 ml). The organic layer was
washed with brine until neutrality and dried with MgSO4
anhydrous. The solvent was evaporated in vacuo to afford
solid product that was recrystallized from ethyl alcohol to
yield flavanones, respectively (4a–4g or 4a0–4g’).
2-(4-Hydroxy-3-methoxyphenyl)chroman-4-one (4e) Yel-
low solid, yield 63.7 %, mp 128–130 °C; IR (Nujol)
t
3520, 1680, 1607,1603 1273,1239, 1213, 1126,
1025 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.82 (dd, 1H,
J1 = 12.40 Hz and J2 = 2.99 Hz, H-2), 3.02 (dd, 1H,
J1 = 16.8 and J2 = 13.70 Hz, H3a), 2.59 (dd, 1H,
J1 = 17.2 and J2 = 2.9 Hz, H3b), 7.54–6.75 (m, 7H, aro-
matic H), 10.00 (s, 1H, OH), 3.82 (s, 3H, 30-OCH3); ESI–
MS (positive mode) m/z 271 (M ? H)?; Anal. Cald for
C16H14O4: C, 71.29; H, 5.10; O, 19.98. Found: C, 70.99; H,
5.01; O, 18.79.
2-(2-Hydroxyphenyl)chroman-4-one (4a) Pale yellow
solid, yield 54.5 %, mp 118–120 °C; IR (Nujol) t 3510,
1680, 1607, 1603, 1273, 1238, 1213 cm-1; H1 NMR
(CDCl3, 400 MHz) d 5.80 (dd, 1H, J1 = 12.48 and
J2 = 3.44 Hz, H-2), 3.03 (dd, 1H, J1 = 16.8 and
J2 = 13.64 Hz, H3a), 2.58 (dd, 1H, J1 = 16.8 and
J2 = 3.2 Hz, H3b), 7.52–6.88 (m, 8H, aromatic H), 9.39
(s, 1H, OH); ESI–MS (positive mode) m/z 241 (M ? H)?;
Anal. Cald for C15H12O3: C, 74.99; H, 5.03; O, 19.98.
Found: C, 74.67; H, 5.02; O, 19.58.
2-(4-Hydroxy-3,5-dimethoxyphenyl)chroman-4-one (4f)
Yellow solid, yield 56.8 %, mp 135–137 °C; IR (Nujol) t
3510, 1681, 1606,1603 1273,1235, 1210, 1026 cm-1; H1
NMR (CDCl3, 400 MHz) d 5.80 (dd, 1H, J1 = 12.80 Hz
and J2 = 3.10 Hz, H-2), 3.01 (dd, 1H, J1 = 17.2 and
J2 = 13.6 Hz, H3a), 2.58 (dd, 1H, J1 = 16.8 and
J2 = 3.1 Hz, H3b), 7.51–6.53 (m, 6H, aromatic H), 9.40
(s, 1H, OH), 3.81 (s, 3H, 30-OCH3), 3.78 (s, 3H, 50-OCH3);
ESI–MS (positive mode) m/z 301 (M ? H)?; Anal. Cald
for C17H16O5: C, 67.29; H, 5.39; O, 25.87. Found: C,
66.67; H, 4.92; O, 24.85.
2-(3-Hydroxyphenyl)chroman-4-one (4b) Yellow solid,
yield 57.8 %, mp 120–122 °C; IR (Nujol) t 3507, 1681,
; 1H NMR
1608,1603 1273,1240, 1210, 1124 cm-1
(CDCl3, 400 MHz) d 5.83 (dd, 1H, J1 = 13.61 Hz and
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2-(4-Hydroxy-3-methoxy
5-nitrophenyl)chroman-4-one
J1 = 16.7 and J2 = 13.60 Hz, H3a), 2.64 (dd, 1H,
J1 = 16.5 and J2 = 3.23 Hz, H3b), 7.37–6.31 (m, 5H,
aromatic H), 10.05 (s, 1H, 30-OH), 3.80 (s, 3H, 5-OCH3),
3.86 (s, 3H, 7-OCH3), 3.83 (s, 3H, 40-OCH3); ESI–MS
(positive mode) m/z 331 (M ? H)?; Anal. Cald for
C18H18O6: C, 65.45; H, 5.50; O, 29.16. Found: C, 64.76; H,
5.22; O, 28.38.
(4g) Yellow solid, yield 55.6 %, mp 133–135 °C; IR
(Nujol) t 3510, 1682, 1607,1603 1274,1239, 1213,1027
cm-1; H1 NMR (CDCl3, 400 MHz) d 5.82 (dd, 1H,
J1 = 12.52 Hz and J2 = 3.12 Hz, H-2), 3.03 (dd, 1H,
J1 = 16.8 and J2 = 13.7 Hz, H3a), 2.80 (dd, 1H, J1 = 17.2
and J2 = 3.2 Hz, H3b), 7.59–6.83 (m, 6H, aromatic H),
9.35 (s, 1H, OH), 3.82 (s, 3H, 30-OCH3); ESI–MS (positive
mode) m/z 316 (M ? H)?; Anal. Cald for C16H13NO6: C,
60.29; H, 4.39; O, 27.78; N, 4.44. Found: C, 60.24; H, 4.25;
O, 26.86; N, 4.35.
2-(4-Hydroxy-3-methoxyphenyl)-5,7-dimethoxychroman-4-
one (4e0) White solid, yield 61.2 %, mp 145–146 °C; IR
(Nujol) t 3519, 1678, 1605,1602 1274,1238, 1211, 1123,
1022 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.81 (dd, 1H,
J1 = 12.44 Hz and J2 = 3.01 Hz, H-2), 3.01 (dd, 1H,
J1 = 16.75 and J2 = 13.68 Hz, H3a), 2.60 (dd, 1H,
J1 = 17.3 and J2 = 2.94 Hz, H3b), 7.32–6.35 (m, 5H,
aromatic H), 10.02 (s, 1H, 40-OH), 3.79 (s, 3H, 5-OCH3),
3.87 (s, 3H, 7-OCH3), 3.82 (s, 3H, 30-OCH3); ESI–MS
(positive mode) m/z 331 (M ? H)?; Anal. Cald for
C18H18O6: C, 65.46; H, 5.48; O, 30.10. Found: C, 64.34; H,
4.72; O, 29.86.
2-(2-Hydroxyphenyl)-5,7-dimethoxychroman-4-one (4a0)
White solid, yield 53.3 %, mp 130–132 °C; IR (Nujol)
t 3511, 1678, 1608, 1604, 1275, 1239, 1214 cm-1; H1
NMR (CDCl3, 400 MHz) d 5.75 (dd, 1H, J1 = 12.45 and
J2 = 3.46 Hz, H-2), 3.02 (dd, 1H, J1 = 16.6 and
J2 = 13.65 Hz, H3a), 2.57 (dd, 1H, J1 = 16.77 and
J2 = 3.15 Hz, H3b), 7.32–6.30 (m, 6H, aromatic H), 9.40
(s, 1H, 20-OH), 3.82 (s, 3H, 5-OCH3), 3.86 (s, 3H,
7-OCH3); ESI–MS (positive mode) m/z 301 (M ? H)?;
Anal. Cald for C17H16O5: C, 67.99; H, 5.37; O, 25.96.
Found: C, 66.77; H, 5.27; O, 25.23.
2-(4-Hydroxy-3,5-dimethoxyphenyl)-5,7-dimethoxychroman-
4-one (4f0) White solid, yield 53.4 %, mp 158–160 °C; IR
(Nujol) t 3511, 1680, 1605,1602 1275,1232, 1205,
1024 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.78 (dd, 1H,
J1 = 12.78 Hz and J2 = 3.12 Hz, H-2), 3.04 (dd, 1H,
J1 = 17.21 and J2 = 13.62 Hz, H3a), 2.59 (dd, 1H,
J1 = 16.79 and J2 = 3.12 Hz, H3b), 7.31–6.34 (m, 4H,
aromatic H), 9.58 (s, 1H, 40-OH), 3.84 (s, 3H, 5-OCH3),
3.88 (s, 3H, 7-OCH3), 3.81 (s, 3H, 30-OCH3), 3.78 (s, 3H,
50-OCH3); ESI–MS (positive mode) m/z 361 (M ? H)?;
Anal. Cald for C19H20O7: C, 63.33; H, 5.59; O, 31.08.
Found: C, 63.32; H, 5.57; O, 31.02.
2-(3-Hydroxyphenyl)-5,7-dimethoxychroman-4-one
(4b0) Colourless solid, yield 55.5 %, mp 134–135 °C; IR
(Nujol) t 3509, 1683, 1605,1601 1274,1237, 1211,
1123 cm-1; 1H NMR (CDCl3, 400 MHz) d 5.85 (dd, 1H,
J1 = 13.63 Hz and J2 = 3.40 Hz, H-2), 3.01 (dd, 1H,
J1 = 17.5 and J2 = 13.65 Hz, H3a), 2.54 (dd, 1H,
J1 = 16.7 and J2 = 3.10 Hz, H3b), 7.38–6.28 (m, 6H,
aromatic H), 9.58 (s, 1H, 30-OH), 3.85 (s, 3H, 5-OCH3),
3.89 (s, 3H, 7-OCH3); ESI–MS (positive mode) m/z 301
(M ? H)?; Anal. Cald for C17H16O5: C, 67.88; H, 5.35; O,
25.95. Found: C, 67.77; H, 5.22; O, 23.58.
2-(4-Hydroxy-3-methoxy-5-nitrophenyl)-5,7-dimethoxychro-
man-4-one (4g0) White solid, yield 55 %, mp 151–
153 °C; IR (Nujol) t 3514, 1680, 1604,1602 1272,1234,
1215,1024 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.81 (dd,
1H, J1 = 12.54 Hz and J2 = 3.11 Hz, H-2), 3.01 (dd, 1H,
J1 = 16.78 and J2 = 13.6 Hz, H3a), 2.81 (dd, 1H,
J1 = 17.4 and J2 = 3.22 Hz, H3b), 7.34–6.29 (m, 4H,
aromatic H), 9.39 (s, 1H, 40-OH), 3.80 (s, 3H, 5-OCH3),
3.86 (s, 3H, 7-OCH3), 3.82 (s, 3H, 30-OCH3); ESI–MS
(positive mode) m/z 376 (M ? H)?; Anal. Cald for
C18H17NO8: C, 57.62; H, 4.56; O, 34.10; N, 3.72. Found:
C, 57.59; H, 4.52; O, 34.05; N, 3.67.
2-(4-Hydroxyphenyl)-5,7-dimethoxychroman-4-one (4c0)
White solid, yield 60 %, mp 136–138 °C; IR (Nujol)
t 3508, 1680, 1611,1605, 1275,1240, 1209,1124 cm-1; H1
NMR (CDCl3, 400 MHz) d 5.82 (dd, 1H, J1 = 12.50 Hz
and J2 = 3.24 Hz, H-2), 3.04 (dd, 1H, J1 = 16.5 and
J2 = 13.58 Hz, H3a), 2.59 (dd, 1H, J1 = 16.78 and
J2 = 3.12 Hz, H3b), 7.35–6.30 (m, 6H, aromatic H), 9.54
(s, 1H, 40-OH), 3.81 (s, 3H, 5-OCH3), 3.84 (s, 3H,
7-OCH3); ESI–MS (positive mode) m/z 301 (M ? H)?;
Anal. Cald for C17H16O5: C, 67.89; H, 5.36; O, 26.01.
Found: C, 67.34; H, 5.01; O, 25.85.
General procedure for the synthesis of flavanone
derivatives with carbamate moiety (5a–5g and 5a0–5g0)
2-(3-Hydroxy-4-methoxyphenyl)-5,7-dimethoxychroman-4-
one (4d0) White solid, yield 59.7 %, mp 140–142 °C; IR
(Nujol) t 3505, 1680, 1608,1604 1269,1240, 1210, 1123,
1020 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.82 (dd, 1H,
J1 = 12.48 Hz and J2 = 3.04 Hz, H-2), 3.01 (dd, 1H,
The dissolved mixture of 0.01 mol of corresponding flav-
anones (4a–4g or 4a0–4g0) and 0.01 mol of phenyl isocy-
anate in 20 ml of petroleum-ether and 2–3 drops of
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2-Methoxy-4-(4-oxochroman-2-yl)phenyl phenylcarbamate
(5e) White solid, yield 61.7 %, mp 143–145 °C; IR
(Nujol) t 3514, 3158, 1763, 1675, 1607, 1602, 1273,1237,
1028 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.40 (dd, 1H,
J1 = 13.61 Hz and J2 = 3.1 Hz, H-2), 2.99 (dd, 1H,
J1 = 16.8 and J2 = 13.52 Hz, H3a), 2.78 (dd, 1H,
J1 = 16.7 and J2 = 3.1 Hz, H3b), 7.76–6.81 (m, 12H,
aromatic H), 8.23 (s, 1H, NH), 3.82 (s, 3H, 30-OCH3); ESI–
MS (positive mode) m/z 390 (M ? H)?; Anal. Cald for
C23H19NO5: C, 70.63; H, 4.90; O, 20.32; N, 3.38. Found:
C, 70.58; H, 4.74; O, 20.29; N, 3.14.
triethylamine was refluxed for 15–20 min. Thereafter, the
reaction mixture was allowed to stand for crystallisation
followed by filtration to get target compounds (5a–5g or
5a0–5g0) which was further recrystallized in ethyl alcohol
till a single spot was observed on TLC plate with solvent
mixture of diethylether:petroleum-ether in 9:1 ratio.
2-(4-Oxochroman-2-yl)phenyl
phenylcarbamate
(5a)
White solid, yield 51.6 %, mp 138–140 °C; IR (Nujol)
t 3510, 3157, 1760, 1680, 1672, 1606,1602 1272,1238,
1212 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.43 (dd, 1H,
J1 = 13.60 Hz and J2 = 2.8 Hz, H-2), 3.01 (dd, 1H,
J1 = 16.7 and J2 = 13.03 Hz, H3a), 2.76 (dd, 1H,
J1 = 16.8 and J2 = 3.2 Hz, H3b), 7.93–6.88 (m, 13H,
aromatic H), 8.40 (s, 1H, NH); ESI–MS (positive mode) m/
z 360 (M ? H)?; Anal. Cald for C22H17NO4: C, 73.53; H,
4.77; O, 17.81; N, 3.90. Found: C, 72.95; H, 4.72; O, 17.78;
N, 3.85.
2,6-Dimethoxy-4-(4-oxochroman-2-yl)phenyl phenylcarba-
mate (5f) White solid, yield 54.9 %, mp 152–154 °C; IR
(Nujol) t 3515,3159, 1760, 1673, 1608,1604 1273,1237,
1027 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.43 (dd, 1H,
J1 = 13.7 Hz and J2 = 3.0 Hz, H-2), 3.02 (dd, 1H,
J1 = 16.8 and J2 = 13.6 Hz, H3a), 2.79 (dd, 1H, J1 = 16.8
and J2 = 2.98 Hz, H3b), 7.70–6.91 (m, 11H, aromatic H),
8.15 (s, 1H, NH), 3.82 (s, 3H, 30-OCH3), 3.78 (s, 3H, 50-
OCH3); ESI–MS (positive mode) m/z 420 (M ? H)?;
Anal. Cald for C24H21NO6: C, 68.63; H, 5.05; O, 22.89; N,
3.34. Found: C, 67.95; H, 4.87; O, 21.78; N, 3.25.
3-(4-Oxochroman-2-yl)phenyl
White solid, yield 53.2 %, mp 143–145° C; IR (Nujol)
3513, 3156, 1762, 1682, 1607,1603 1273,1240,
phenylcarbamate
(5b)
t
1210 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.42 (dd, 1H,
J1 = 13.58 Hz and J2 = 3.1 Hz, H-2), 3.02 (dd, 1H,
J1 = 16.8 and J2 = 13.6 Hz, H3a), 2.79 (dd, 1H, J1 = 16.8
and J2 = 3.1 Hz, H3b), 7.88–6.81 (m, 13H, aromatic H),
8.37 (s, 1H, NH); ESI–MS (positive mode) m/z 360
(M ? H)?; Anal. Cald for C22H17NO4: C, 72.53; H, 4.67;
O, 18.28; N, 3.70. Found: C, 72.48; H, 4.65; O, 18.24; N,
3.61.
2-Methoxy-6-nitro-4-(4-oxochroman-2-yl)phenyl phenylcar-
bamate (5g) White solid, yield 52.7 %, mp 150–152 °C;
IR (Nujol) t 3510,3157, 1761, 1678, 1607,1603 1275,1238,
1026 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.41 (dd, 1H,
J1 = 13.6 Hz and J2 = 2.88 Hz, H-2), 3.03 (dd, 1H,
J1 = 16.8 and J2 = 13.7 Hz, H3a), 2.80 (dd, 1H, J1 = 17.2
and J2 = 3.2 Hz, H3b), 7.86–6.81 (m, 11H, aromatic H),
8.32 (s, 1H, NH), 3.82 (s, 3H, 30-OCH3); ESI–MS (positive
mode) m/z 435 (M ? H)?; Anal. Cald for C23H18N2O7: C,
63.63; H, 4.19; O, 25.32; N, 6.45. Found: C, 62.95; H, 4.05;
O, 24.88; N, 6.39.
4-(4-Oxochroman-2-yl)phenyl
White solid, yield 58.6 %, mp 141–142 °C; IR (Nujol)
3512, 3158, 1761,1673, 1606, 1603 1273,1241,
phenylcarbamate
(5c)
t
1210 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.41 (dd, 1H,
J1 = 13.59 Hz and J2 = 2.9 Hz, H-2), 3.03 (dd, 1H,
J1 = 16.7 and J2 = 13.6 Hz, H3a), 2.80 (dd, 1H, J1 = 16.9
and J2 = 3.2 Hz, H3b), 7.87–6.81 (m, 13H, aromatic H),
8.39 (s, 1H, NH); ESI–MS (positive mode) m/z 360
(M ? H)?; Anal. Cald for C22H17NO4: C, 74.33; H, 3.97; O,
18.28; N, 3.39. Found: C, 73.95; H, 3.78; O, 18.21; N, 3.25.
2-(50-70-Dimethoxy-4-oxochroman-2-yl)phenyl phenylcar-
bamate (5a0) White solid, yield 50.3 %, mp 153–155 °C;
IR (Nujol) t 3503, 3158, 1762, 1682, 1671, 1605,1603
1275,1234, 1211 cm-1; H1 NMR (CDCl3, 400 MHz)
d 5.41 (dd, 1H, J1 = 13.62 Hz and J2 = 2.81 Hz, H-2),
3.03 (dd, 1H, J1 = 16.8 and J2 = 13.5 Hz, H3a), 2.79 (dd,
1H, J1 = 16.7 and J2 = 3.3 Hz, H3b), 7.94–6.29 (m, 11H,
aromatic H), 8.47 (s, 1H, NH), 3.83 (s, 3H, 5-OCH3), 3.85
(s, 3H, 7-OCH3); ESI–MS (positive mode) m/z 420
(M ? H)?; Anal. Cald for C24H21NO6: C, 68.74; H, 5.05;
O, 22.89; N, 3.34. Found: C, 68.55; H, 4.97; O, 22.76; N,
3.15.
2-Methoxy-5-(4-oxochroman-2-yl)phenyl phenylcarbamate
(5d) White solid, yield 60.1 %, mp 146–148 °C; IR
(Nujol) t 3510, 3157, 1763, 1674, 1607,1604 1273,1238,
1027 cm-1; H1 NMR (CDCl3, 400 MHz) d 5.41 (dd, 1H,
J1 = 13.58 Hz and J2 = 2.9 Hz, H-2), 3.01 (dd, 1H,
J1 = 16.8 and J2 = 13.68 Hz, H3a), 2.77 (dd, 1H,
J1 = 17.2 and J2 = 2.9 Hz, H3b), 7.85–6.82 (m, 12H,
aromatic H), 8.12 (s, 1H, NH), 3.81 (s, 3H, 40-OCH3); ESI–
MS (positive mode) m/z 390 (M ? H)?; Anal. Cald for
C23H19NO5: C, 70.33; H, 4.94; O, 20.28; N, 3.46. Found:
C, 70.23; H, 4.72; O, 19.78; N, 3.39.
3-(50-70-Dimethoxy-4-oxochroman-2-yl)phenyl phenylcar-
bamate (5b0) White solid, yield 51.6 %, mp 160–162 °C;
IR (Nujol) t 3510, 3158, 1760, 1681, 1608,1602
1274,1248, 1207 cm-1; H1 NMR (CDCl3, 400 MHz)
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Med Chem Res (2013) 22:1648–1659
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d 5.43 (dd, 1H, J1 = 13.59 Hz and J2 = 3.14 Hz, H-2),
3.01 (dd, 1H, J1 = 16.78 and J2 = 13.5 Hz, H3a), 2.80 (dd,
1H, J1 = 16.7 and J2 = 3.10 Hz, H3b), 8.02–6.35 (m, 11H,
aromatic H), 8.40 (s, 1H, NH), 3.84 (s, 3H, 5-OCH3), 3.87
(s, 3H, 7-OCH3); ESI–MS (positive mode) m/z 420
(M ? H)?; Anal. Cald for C24H21NO6: C, 68.73; H, 5.04;
O, 22.87; N, 3.30. Found: C, 67.95; H, 5.02; O, 22.78; N,
3.12.
H-2), 3.04 (dd, 1H, J1 = 16.84 and J2 = 13.61 Hz, H3a),
2.77 (dd, 1H, J1 = 16.88 and J2 = 3.04 Hz, H3b), 7.88–6.34
(m, 9H, aromatic H), 8.31 (s, 1H, NH), 3.85 (s, 3H, 5-OCH3),
3.90 (s, 3H, 7-OCH3), 3.82 (s, 3H, 30-OCH3), 3.78 (s, 3H, 50-
OCH3); ESI–MS (positive mode) m/z 480 (M ? H)?; Anal.
Cald for C26H25NO8: C, 65.13; H, 5.25; O, 26.68; N, 2.93.
Found: C, 63.97; H, 5.22; O, 25.85; N, 2.91.
2-Methoxy-6-nitro-4-(50,70-dimethoxy-4-oxochroman-2-
yl)phenyl phenylcarbamate (5g0) White solid, yield
51.8 %, mp 174–175 °C; IR (Nujol) t 3505, 3159, 1759,
1678, 1603, 1602, 1275, 1240, 1026 cm-1; H1 NMR (CDCl3,
400 MHz) d 5.40 (dd, 1H, J1 = 13.60 Hz and J2 = 2.99 Hz,
H-2), 3.03 (dd, 1H, J1 = 16.84 and J2 = 13.72 Hz, H3a),
2.85 (dd, 1H, J1 = 17.42 and J2 = 3.24 Hz, H3b), 8.01–6.33
(m, 9H, aromatic H), 8.32 (s, 1H, NH), 3.79 (s, 3H, 5-OCH3),
3.84 (s, 3H, 7-OCH3), 3.82 (s, 3H, 30-OCH3); ESI–MS
(positive mode) m/z 495 (M ? H)?; Anal. Cald for
C25H22N2O9: C, 60.73; H, 4.49; O, 29.14; N, 5.65. Found: C,
60.69; H, 4.42; O, 27.88; N, 5.55.
4-(50-70-Dimethoxy-4-oxochroman-2-yl)phenyl phenylcar-
bamate (5c0) White solid, yield 54.8 %, mp 165–166 °C;
IR (Nujol)
t 3510, 3159, 1760,1674, 1605, 1602
1274,1243, 1204 cm-1; H1 NMR (CDCl3, 400 MHz)
d 5.40 (dd, 1H, J1 = 13.64 Hz and J2 = 2.92 Hz, H-2),
3.04 (dd, 1H, J1 = 16.75 and J2 = 13.62 Hz, H3a), 2.84
(dd, 1H, J1 = 16.8 and J2 = 3.17 Hz, H3b), 7.92–6.32 (m,
11H, aromatic H), 8.38 (s, 1H, NH), 3.79 (s, 3H, 5-OCH3),
3.85 (s, 3H, 7-OCH3); ESI–MS (positive mode) m/z 420
(M ? H)?; Anal. Cald for C24H21NO6: C, 68.72; H, 5.07;
O, 22.88; N, 3.33. Found: C, 68.69; H, 4.73; O, 22.78; N,
3.23.
Biological evaluation
2-Methoxy-5-(50-70-dimethoxy-4-oxochroman-2-yl)phenyl
phenylcarbamate (5d0) White solid, yield 59.9 %, mp
171–172 °C; IR (Nujol) t 3503, 3156, 1761, 1671,
1604,1601 1271,1234, 1025 cm-1; H1 NMR (CDCl3,
400 MHz) d 5.39 (dd, 1H, J1 = 13.53 Hz and J2 = 2.97 Hz,
H-2), 3.02 (dd, 1H, J1 = 16.78 and J2 = 13.69 Hz, H3a),
2.79 (dd, 1H, J1 = 17.1 and J2 = 2.89 Hz, H3b), 7.94–6.35
(m, 10H, aromatic H), 8.32 (s, 1H, NH), 3.82 (s, 3H,
5-OCH3), 3.88 (s, 3H, 7-OCH3), 3.81(s, 3H, 40-OCH3); ESI–
MS (positive mode) m/z 450 (M ? H)?; Anal. Cald for
C25H23NO7: C, 66.80; H, 5.17; O, 24.92; N, 3.10. Found: C,
66.65; H, 4.76; O, 23.78; N, 3.03.
Experimental animals
Swiss albino mice of either sex, weighing 20–25 g were
employed for in vivo evaluation of learning and memory.
The experimental protocol was approved by the Institu-
tional Animal Ethics Committee (IAEC) and the care of the
animals was carried out as per the guidelines of the
Committee for the Purpose of Control and Supervision of
Experiments on Animals (CPCSEA), Ministry of Envi-
ronment and Forest, Government of India (Reg. No.
107/1999/CPCSEA).
2-Methoxy-4-(50-70-dimethoxy-4-oxochroman-2-yl)phenyl
phenylcarbamate (5e0) White solid, yield 58.6 %, mp
169–170 °C; IR (Nujol) t 3505, 3159, 1762, 1674, 1606,
1601, 1274,1236, 1025 cm-1; H1 NMR (CDCl3, 400 MHz)
d 5.38 (dd, 1H, J1 = 13.62 Hz and J2 = 3.12 Hz, H-2),
2.98 (dd, 1H, J1 = 16.7 and J2 = 13.54 Hz, H3a), 2.80 (dd,
1H, J1 = 16.5 and J2 = 3.12 Hz, H3b), 7.96–6.38 (m, 10H,
aromatic H), 8.33 (s, 1H, NH), 3.90 (s, 3H, 5-OCH3), 3.87
(s, 3H, 7-OCH3), 3.82 (s, 3H, 30-OCH3); ESI–MS (positive
mode) m/z 450 (M ? H)?; Anal. Cald for C25H23NO7: C,
66.81; H, 5.18; O, 24.91; N, 3.11. Found: C, 66.71; H, 5.14;
O, 23.78; N, 3.15.
Drugs and chemicals
Scopolamine was dissolved in normal saline and the test
drug was dissolved in 10 % dimethylsulfoxide (DMSO).
All other reagents used in the present study were of ana-
lytical grade and freshly prepared.
In vitro estimation of cholinesterase inhibitory activity
The brain AChE inhibitory activity of the test compounds
was assessed spectrophotometrically at 420 nm (Ellman
et al., 1961). The potency of test compounds were expressed
IC50 with donepezil as the standard AChE inhibitor.
2,6-Dimethoxy-4-(50,70-dimethoxy-4-oxochroman-2-yl)phe-
nyl phenylcarbamate (5f0) White solid, yield 51.2 %, mp
Assessment of learning and memory by Morris water maze
178–179 °C; IR (Nujol)
t 3513,3156, 1760, 1673,
1610,1605, 1274,1240, 1023 cm-1; H1 NMR (CDCl3,
Morris water maze is one of the most commonly used
animal models to test memory (Morris, 1984). It consists of
400 MHz) d 5.40 (dd, 1H, J1 = 13.70 Hz and J2 = 3.05 Hz,
123

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Med Chem Res (2013) 22:1648–1659
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support from UGC New Delhi, India, through the research scheme no.
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