Substituted dihydronaphthalenes as efflux pump inhibitors of Staphylococcus aureus

Article abstract of DOI:10.1016/j.ejmech.2010.05.006

A new series of 3-(substituted-3,4-dihydronaphthyl)-2-propenoic acid amides has been prepared through convergent synthetic strategies and tested in combination with ciprofloxacin against NorA overexpressing Staphylococcus aureus 1199B as test strain for potentiating of the drug activity. Out of 24 compounds evaluated, 12 compounds potentiated the activity of ciprofloxacin and resulted in 2-16 fold reduction in the MIC (4-0.5 μg/mL) of the drug. The failure of these efflux pump inhibitors (EPIs) to potentiate the activity of ciprofloxacin when tested against NorA knock out S. aureus SA-K1758 established their identity as NorA inhibitors. The structure of all these newly synthesised compounds was confirmed by spectral data. The present communication describes the synthesis, bioevaluation, structure activity relationship and mechanism of action of these EPIs. Design and synthesis of new series of 3-(substituted 3,4-dihydronaphthyl)- propenoic acid amides as efflux pump inhibitors has resulted in the MIC reduction of ciprofloxacin.

Full text of DOI:10.1016/j.ejmech.2010.05.006

European Journal of Medicinal Chemistry 45 (2010) 3607e3616
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Substituted dihydronaphthalenes as efflux pump inhibitors of
Staphylococcus aureus
Niranjan Thota a, Mallepally V. Reddy a, Ashwani Kumar b, Inshad A. Khan b, Payare L. Sangwan a,
,
Nitin P. Kalia b, Jawahir L. Koul a, Surrinder Koul a
*
a Bioorganic Chemistry Division, Indian Institute of Integrative Medicine (CSIR), Canal Road, Jammu Tawi-180001, India
b Clinical Microbiology Unit, Indian Institute of Integrative Medicine (CSIR), Canal Road, Jammu Tawi-180001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of 3-(substituted-3,4-dihydronaphthyl)-2-propenoic acid amides has been prepared
through convergent synthetic strategies and tested in combination with ciprofloxacin against NorA
overexpressing Staphylococcus aureus 1199B as test strain for potentiating of the drug activity. Out of 24
compounds evaluated, 12 compounds potentiated the activity of ciprofloxacin and resulted in 2e16 fold
Received 7 January 2010
Received in revised form
3 May 2010
Accepted 5 May 2010
Available online 12 May 2010
reduction in the MIC (4e0.5 mg/mL) of the drug. The failure of these efflux pump inhibitors (EPIs) to
potentiate the activity of ciprofloxacin when tested against NorA knock out S. aureus SA-K1758 estab-
lished their identity as NorA inhibitors. The structure of all these newly synthesised compounds was
confirmed by spectral data. The present communication describes the synthesis, bioevaluation, structure
activity relationship and mechanism of action of these EPIs.
Keywords:
Bacterial NorA efflux pump inhibitors
Eugenol
Ó 2010 Elsevier Masson SAS. All rights reserved.
Tetralone
Ciprofloxacin
Staphylococcus aureus
Ethidium bromide
1. Introduction
the antiinfective/s and possibly reduce the emergence of target-
based resistance mechanisms. The latter approach would represent
In recent years bacterial resistance to antimicrobial agents has
risen dramatically, resulting in a serious public health problem.
Mechanisms by which this occurs include enzymatic inactivation,
target modification, and reduction of drug accumulation within the
cell by the reduced permeability of the bacterial envelope and/or
extrusion of the drug from the cell by way of membrane-based
efflux proteins [1e5]. Efflux pumps are found in both Gram-positive
and Gram-negative pathogens [6,7]. Some of these efflux pumps
confer multiple-drug resistance (MDR), and the NorA protein of
Staphylococcus aureus is one such pump [8,9]. It belongs to the
major facilitator superfamily (MFS) of transport proteins, one of the
most studied MDR pump, and its substrates include antimicrobial
agents and dyes such as Ciprofloxacin, Norfloxacin, Ethidium
bromide and Acriflavine [10]. Efforts are underway to generate new
antibacterial agents capable of avoiding drug efflux by synthesizing
compounds that are poor pump substrates [11], or alternatively,
identify compounds that reduce or block the efflux pump activity of
a significant advance in antibacterial chemotherapy [12]. These
compounds, called efflux pump inhibitors (EPIs), could be
combined with substrate antimicrobial agents similar to the
b-
lactam- -lactamase combinations already in clinical use [13]. There
b
are ongoing efforts to develop formulations of existing drugs with
EPIs, and one such example is that of an aerosolized ciprofloxacin/
EPI combination for the treatment of cystic fibrosis [14]. The
development of novel bacterial EPIs has been reported by several
groups and many of these compounds are reported to substantially
lower MICs of clinically relevant drugs [15e18]. The present
communication describes the preparation and identification of
potent EPIs, demonstration of their abilities to reduce MICs when
combined with the antibacterial drug ciprofloxacin and the struc-
ture activity relationship (SAR) studies.
2. Results and discussion
2.1. Chemistry
Twenty four compounds (5e10 and 19e36) selected for
biological evaluationwere prepared as described in Schemes 1 and 2.
* Corresponding author. Tel.: þ91 191 2569021; fax: þ91 191 2569333.
E-mail address: skoul@iiim.res.in (S. Koul).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.05.006

3608
MeO
HO
N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
MeO
RO
The synthesis of compounds 5e10 was accomplished by alkylation
MeO
RO
b
a
of naturally occurring plant isolate eugenol 1 and subjecting the
alkylated products 2 and 2a [19] to Vilsmeier reaction to give
formylated products 3 and 3a [20]. Wittig reaction of formylated
products 3 and 3a and subsequent saponification of the products
afforded the acids 3-(3,4-dihydronphthalene)-2-propenoic acids 4
and 4a respectively [21]. The acid chloride of 4 and 4a was allowed to
react with appropriate amines to afford compounds 5e10 in 20%
over all yields (Scheme 1).
O
R = CH3 (2)
1
R = CH3 (3)
R = C3H5 (2a)
R = C3H5 (3a)
c
MeO
RO
MeO
RO
d
OH
O
R1
Compounds 19e23 were prepared via route-A in Scheme 2 by
5-10
R = CH3 (4)
R = C3H5 (4a)
taking
a-tetralone 11 as a starting material and carrying out its
reduction with sodium borohydride followed by Vilsmeier reaction
to give formylated product 13 [22]. Wittig reaction of 13 and
subsequent saponification afforded 3-(3,4-dihydronaphthyl)-2-
propenoic acid 18. Acid chloride of 18 was allowed to condense
with different amines to give compounds 19e23 in 87e92% yields.
Compounds 24e28 were prepared via route-B in Scheme 2 by
Suzuki coupling [23] of compound 14 (obtained by Vilsmeier
reaction of 11 [24]) followed by subjecting the product 15 to
Knoevenagel reaction with malonic acid to afford the acid 18a.
Condensation of acid chloride of 18a with appropriate amines to
afford compounds 24e28 in 70e92% yield.
O
O
H
N
H
N
N
N
R = CH3, R1
=
6
O
O
O
6
5
8
7
O
H
N
N
R = C3H5 , R1
=
O
10
9
Scheme 1. Synthetic methods for the preparation of 5e10: Reagents: (a) RX/K2CO3
(2, 85%; 2a, 81%); (b) DMF/POCl3 (3, 26%; 3a, 23%); (c) (i) P(Ph)3/BrCH2COOEt/NaH/
Benzene; (ii) NaOH/MeOH/HCl (4, 86%; 4a, 60%); (d) SOCl2/DCM; NHR1R2(amines)/
C6H6.
Compounds 29e33 were prepared via route-C in Scheme 2
which involved Grignard reaction of 11 with benzyl halide to
afford compound 16. Vilsmeier reaction of 16 provided formyl
derivative 17, which on Wittig reaction and subsequent hydrolysis
b
e
O
R1
f
a
OH
R
Route-A
13
12
19-23 R = H
24-28 R = Ph
e
c
b
29-33 R = CH2Ph
Route-B
Route-C
OH
11
O
O
g
Cl
O
R
O
14
18 R = H
18a R = Ph
15
d
18b R = CH2Ph
e
b
R1
O
R
HO
34,35 R = H
36
R = Ph
17
16
H
O
O
H
H
N
N
N
N
N
OMe
R = H, R1
=
O
O
O
O
19
21
22
20
23
H
H
N
N
N
N
N
R = Ph, R1
=
O
O
O
=
O
24
N
25
27
26
28
H
N
H
N
R = CH2Ph, R1
O
O
N
N
O
O
O
O
O
29
30
31
33
32
H
R = H, R1
=
N
N
R = Ph, R1
=
N
O
O
O
34
35
36
Scheme 2. Synthetic methods for the preparation of 19e36: Reagents: (a) NaBH4/MeOH, 91%; (b) DMF/POCl3 (13, 96%; 14, 93%; 17, 87%); (c) Phenyl boronic acid, K2CO3/Pd(PPh3)4,
83%; (d) PhCH2Br/Mg/THF, 71.5%; (e) Malonic acid/base/HCl or P(Ph)3/BrCH2COOEt/NaH/Benzene/NaOH/MeOH/HCl, (18, 94.1%; 18a, 70%; 18b, 78%); (f) SOCl2/DCM, NHR1R2
(amines)/C6H6; (g) H2/PdeC.

N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
3609
afforded the acid 18b. Condensation of acid chloride of 18b
with appropriate amines furnished the amides 29e33 in 66e82%
yield.
thereby, that the presence of double bonds is essential for the
exhibition of high EPI activity (Table 1).
In order to establish that these compounds are NorA inhibitors,
we also included S. aureus SA-K1758, in which NorA gene was
knocked out resulting in non- functional NorA protein. Due to the
absence of functional NorA protein, this strain exhibited MIC of
2.2. Bioevaluation studies
0.12 mg/mL, which is 2-fold lower than the MIC of S. aureus 1199
In our earlier studies, we found that in comparison to EPIs such
as 5-(3,4-methylenedioxy-5-yl)-2E,4E-pentadienoic acid amides
(Piperine and its analogues), incorporation of an alkyl group at the
C-4 position of the Piperine improved EPI activity and showed
many fold decrease in the MIC of the drug [25e28]. These obser-
vations prompted us to question the effect of substitution of an
ethyl group at position C-4 on EPI activity if it is fused to the C-6
position of the phenyl ring of the molecule. We found that the
fusion leads to the generation of a dihydronaphthyl ring system
(Fig. 1). Therefore, preparation of 3-(dihydronaphthyl)-propenoic
acid amides and their subsequent evaluation for EPI activity
appeared to be a viable option.
Evaluation of compounds 5e10 in combination with cipro-
floxacin against bacterial pathogens S. aureus 1199 and 1199B
resulted in the identification of compounds 8 and 10 as EPIs specific
to S. aureus 1199B but non-potentiating against the parental
S. aureus 1199 strain, which is not surprising keeping in mind that
S. aureus 1199B is a NorA-overexpressing mutant. Since the
bioevaluation studies revealed low EPI activity of 3-(3,4-dialky-
lated-dihydronaphthalene)-2-propenoic acid amides, (Table 1),
further modifications were attempted in a bid to improve upon the
EPI activity and fifteen more derivatives were synthesized
(wild type). As expected, no change was observed in the MIC
of Ciprofloxacin in the absence or presence of these EPI (Including
the known inhibitors such as Piperine, Reserpine, Verapamil and
Carsonic acid) which conclusively established that these
compounds are NorA inhibitors (Table 1).
The inhibitory mechanism of EPIs was further confirmed by an
efflux inhibition assay using ethidium bromide as the substrate of
NorA efflux pump along with the most potent inhibitor 20, the
inactive EPI 5 (negative control), and the known S. aureus NorA
EPI Reserpine (positive control). These EPIs were tested at their
minimum effective concentration (MEC). All the experiments
were performed in triplicate. Since ethidium bromide fluores-
cences only when it is bound to nucleic acids, NorA mediated
efflux resulted in a rapid decrease in fluorescence. As can be
observed from Fig. 2, only those cells not exposed to EPIs or in
presence of the inactive EPI 5 extruded ethidium bromide,
resulting in a significant decrease in fluorescence over the course
of the assay. The potent inhibitor 20 effectively prevented
ethidium bromide efflux.
3. Conclusion
following route A, B and C with
material (Scheme 2).
a-tetralone 11 as the starting
In conclusion,
a new series of 24 compounds has been
synthesised and several of them identified as potent EPIs capable
of reducing the MIC of Ciprofloxacin by sixteen fold against a NorA-
overexpressing strain of S. aureus. SAR studies revealed that
substituents such as alkyloxy groups in the phenyl ring of the
dihydronaphthyl moiety lower the potentiating activity of the drug
drastically, while substituents such as phenyl and benzyl substit-
uents at C-1position in the partially saturated ring of dihy-
dronaphthyl moiety show marginally better potentiating activity.
Unsubstituted 3-(3,4-dihydronaphthyl)-2-propenoic acid amides
proved to be the most potent EPIs. Unsaturated amides displayed
better activity than their saturated analogs. The fact that the active
EPIs are targeting the NorA protein of S. aureus was confirmed
when these were tested against NorA knock out strain (S. aureus
SA-K1758), where the loss of target was reflected in no change in
the MIC of ciprofloxacin. The inhibitory effect of these EPIs was
further demonstrated by their ability to block the efflux of ethidium
bromide in NorA overexpressing S. aureus strain (1199B).
Compounds capable of potentiating the effect of antimicrobial
agents may allow use of drugs previously discarded as a result of
resistance. They also may prevent the emergence of de novo
resistance by reducing MICs of target organisms. The present study
provided the basis for further development of robust EPIs of
potential clinical importance, an effort which has been initiated in
our laboratory.
The efflux pump inhibitory activity of compounds 19e23 was
tested in combination with ciprofloxacin against S. aureus 1199 and
1199B. Bioevaluation results revealed low potentiating effect
against S. aureus 1199 showing MIC reductions of only two to
fourfold (Table 1), but showed significant EPI activity against S.
aureus SA-1199B. Sixteen fold reduction of the minimum inhibitory
concentration of ciprofloxacin was observed for the compounds 20
and 21 (MIC 0.5
and 22 (MIC 1.0
m
m
g/mL), an eightfold reduction for compounds 19
g/mL), and fourfold reduction for compound 23
(MIC 2.0
24e33 when tested against the test pathogens showed eight fold
MIC reduction for compound 24 (MIC 1.0 g/mL), fourfold for
compound 29 (MIC 2.0 g/mL) and the rest proved to be poor or
mg/mL) against the pathogen S. aureus 1199B. Compounds
m
m
non-potentiator of the antibiotic ciprofloxacin (Table 1). From these
studies, it was observed that replacement of hydrogen atom/s by
methoxy/allyloxy substituents at the 6,7-position of 3,4-dihydro
naphthalene system leads to low activity and/or inactivation of the
EPIs, while molecules without a substitution in the partially satu-
rated ring of the dihydronaphthyl moiety proved to be better
potentiators of ciprofloxacin.
To investigate the role of double bonds on the EPI activity, three
EPIs (compound 19, 20 and 24) were selected and hydrogenated
(H2/Pd/C) (Scheme 2) to give compounds 34e36. Saturation of the
double bonds substantially lowered the potentiating activity of the
EPIs as shown by the very low MIC reduction observed for these
compounds (2 fold) against their unsaturated analogs (19, 20 and
24) where MIC reduction ranged from 8 to 16 fold, emphasizing,
4. Experimental procedure
4.1. Chemistry methods
All reagents for chemical synthesis were obtained from Sigmae
Aldrich. The starting material eugenol was isolated from lemon
grass oil. All the solvents used in reactions were distilled and dried
before use. All reactions were monitored by TLC on 0.25 mm silica
gel 60 F254 plates (E. Merck) using UV light, or ceric sulfate solution
for visualization of the spots. Silica gel 60e120 mesh was used for
R
R
R2
R2
R1
R1
Fig. 1. Proposed model for the synthesis of dihydronaphthalene derivatives.

3610
N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
Table 1
Activity of Ciprofloxacin against S. aureus 1199B, S. aureus 1199 and NorA knock out S. aureus K1758 respectively in combination with synthesized molecules.
S. No.
MECa of EPI
S. aureus 1199B MICb of Cipro. (
m
g/mL)
S. aureus 1199 MICb of Cipro. (
mg/mL)
S. aureus K1758 MICb of Cipro. (
mg/mL)
Without EPI
With EPI
Fold reduction
Without EPI
With EPI
Fold reduction
Without EPI
With EPI
Fold reduction
5
6
7
8
9
10
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
>100
>100
>100
12.5
>100
12.5
25
12.5
25
25
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
4
8
4
1
0.5
0.5
1
2
1
8
8
8
8
2
8
8
8
8
4
4
4
4
2
4
4
0
0
0
2
0
2
8
16
16
8
4
8
0
0
0
0
4
0
0
0
0
2
2
2
2
4
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.12
0.06
0.06
0.25
0.25
0.12
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.12
0.12
0.12
0.12
0
0
0
0
0
0
2
4
4
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0.125
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
25
12.5
>100
>100
>100
>100
25
>100
>100
>100
>100
25
25
25
50
25
25
50
Piperine
Reserpine
Carsonic acid
Verapamil
2
2
The bold values are shown for those compounds which have proved to be active EPIs and those in normal font represent inactive/ least significant.
1. No antibacterial activity of EPIs was observed at 100
g/mL that was the highest concentration tested.
m
2. For determining potentiation of Ciprofloxacin, EPI were tested at concentration range of 50e0.8
m
g/mL.
a
MEC ¼ Minimum effective concentration.
b
MIC ¼ Minimum inhibitory concentration.
column chromatography. 1H NMR and 13C NMR spectra were
recorded on Bruker DPX 200 and 500 instrument using CDCl3 as the
solvent with TMS as internal standard. Mass spectra were recorded
on ESI-esquire 3000 Bruker Daltonics instrument and IR spectra
recorded on Bruker Vector 22 instrument. Melting points were
recorded on Buchi-510 instrument.
4.2. Synthesis
4.2.1. 4-Allyl-1,2-dimethoxy benzene (2)
A solution of eugenol (1) (20 g,121.20 mmol) and CH3I (18 mL) in
dry acetone (100 mL) was refluxed at 60 ꢀC for 24 h. The reaction
mixture reduced to one fourth of its volume on a rotavapor, the
contents cooled and diluted with water (150 mL) and extracted
with ethyl acetate (3 ꢁ 100 mL). The combined organic layer
washed with water (3 ꢁ 50 mL), dried over anhydrous sodium
sulfate and concentrated to give crude product, which on purifi-
cation by column chromatography on silica gel with pet. ether
60e80 ꢀC as an eluent afforded 4-allyl-1,2-dimethoxy benzene (2)
(18.6 g, yield 85.2%) as an oil, Anal. Calcd for C11H14O2: C, 74.13; H,
7.92%. Found: C, 75.03; H, 7.99%. MS (%) Mþþ1 at m/z 179. 1H NMR:
d
3.22 (2H, d, J ¼ 6.6 Hz, AreCH2), 3.83 (6H, br s, 2 ꢁ OCH3),
5.05e5.12 (2H, m, CH]CH2), 5.88e6.04 (1H, m, CH2CH]CH2),
6.69e6.72 (2H, m, 2ꢁ AreH), and 6.85 (1H, d, J ¼ 8.6 Hz, AreH).
4.2.2. 6,7-Dimethoxy-2-formyl-3,4-dihydro-naphthalene (3)
To a chilled solution of 4-allyl-1,2-dimethoxy benzene (2)
(18.0 g, 101.12 mmol) in dry DMF (50 mL), POCl3 (26 mL) was added
dropwise at 0e5 ꢀC for 1 h and the resulting mixture was stirred at
room temperature for 90 h. The reaction mixture was poured into
ice-cold water (150 mL) and pH 7.0 attained by adding 1 N NaOH
solution. The reaction mixture was extracted with ethyl acetate
(5 ꢁ 100 mL) and the combined organic layer washed with water
(3 ꢁ 50 mL), dried over anhydrous sodium sulfate and concentrated
on rotavapour under reduced pressure to give crude product, which
was purified on silica gel column using pet. ether 60e80 ꢀC:ethyl
acetate (4:1) as an eluent to afford 3 (6.4 g, yield 26.1%) as a solid
mp 101e102 ꢀC. Anal. Calcd for C13H14O3: C, 71.54; H, 6.67%. Found:
Fig. 2. Ethidium bromide efflux inhibition assay, S. aureus 1199B. Cells were loaded
with ethidium bromide efflux was allowed to occur in the absence of EPI (control) or in
the presence of EPIs. Each time point represents the mean log10 ꢂSD of three
experiments.
C, 72.44; H, 6.71%. MS (%) Mþ at m/z 218. 1H NMR:
d 2.55 (2H, t,

N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
3611
J ¼ 8.3 Hz, AreCH2CH2), 2.82 (2H, t, J ¼ 8.3 Hz, AreCH2CH2), 3.90
and 3.93 (3H each, s, 2ꢁ OCH3), 6.74 (1H, s, AreH), 6.81 (1H, s,
70.11; H, 7.10; N, 4.31%. MS (%) Mþþ1 at m/z 330. IR (KBr Pellet).
2960, 2926, 1630, 1589, 1455, 1331, 1288, 1259, 1223, 1116, 977, 859,
AreH), 7.20 (1H, s, AreCH]), 9.61 (1H, s, CHO). 13C NMR:
d
19.26,
729 cmꢃ1 1H NMR:
d
2.47 (2H, t, J ¼ 8.2 Hz, AreCH2CH2), 2.82 (2H, t,
26.91, 55.86, 55.97, 111.06, 111.58, 125.06, 132.00, 136.92, 145.98,
147.65, 150.83, and 191.78.
J ¼ 8.2 Hz, AreCH2CH2), 3.31 (4H, br s, eNe(CH2)2), 3.73 (4H, br
s, eOe(CH2)2), 3.82 and 3.89 (3H each, s, 2ꢁOCH3), 6.32 (1H, d,
J ¼ 15.1 Hz, CH]CHCO), 6.66e6.69 (3H, m, 2ꢁ AreH and CH]
4.2.3. 3-(6,7-Dimethoxy-3,4-dihydronaphth-2-yl)-propenoic acid
(4)
CeCH]), 7.66 (1H, d, J ¼ 15.1 Hz, CH]CHCO). 13C NMR:
d 23.19,
27.39, 56.06, 56.12, 66.93 (4ꢁCH2), 111.01, 111.12, 113.76, 126.84,
To a stirring benzene solution of ylide (11.5 g) (prepared from
triphenylphosphine and ethyl bromoacetate) containing sodium
hydride (1.5 g) added benzene solution of 3 (5.5 g, 25.2 mmol) at
0e5 ꢀC for 30 min and stirred the contents for 24 h and an addi-
tional amount of sodium hydride (0.5 g) was added. The reaction
mixture was stirred for 72 h at 40 ꢀC. On cooling, the contents were
diluted with ethyl acetate (100 mL) to quench unused sodium
hydride, and then diluted with water (200 mL), organic layer
separated and the aqueous layer extracted with ethyl acetate
(2 ꢁ 100 mL). The combined organic layer washed with water
(2 ꢁ 50 mL) and concentrated on a rotavapor under reduced
pressure. The crude 3-(6,7-dimethoxy-3,4-dihydronaphth-2-yl)-
propenoiate intermediate obtained was without purification
hydrolysed in 10% methanolic potassium hydroxide solution and
after usual work up, the acid obtained was purified on silica gel
column using pet. ether 60e80 ꢀC:ethyl acetate (3:1) as an eluent to
give compound 4 (5.59 g, yield 85.3%) as a greyish white solid mp
147 ꢀC. Anal. Calcd for C15H16O4: C. 69.22; H, 6.2%. Found: C, 70.12;
H, 6.27%. MS (%) Mþþ1 at m/z 260. IR (KBr Pellet). 3421, 2997, 2935,
1682, 1634, 1538, 1420, 1315, 1237, 1123, 1008, 891, 751, 679 cmꢃ1 1H
127.98, 133.22, 134.34, 145.06, 147.30, 148.59, and 164.3.
4.2.6. 3-(6,7-Dimethoxy-3,4-dihydronaphth-2-yl)-propenoic acid
n-octylamide (7)
This was prepared in 84% yield from 4 and n-octylamine by the
procedure as described for compound 5 as a brown resinous mass.
Anal. Calcd for C23H33NO3: C, 74.36; H, 8.95; N, 3.77%. Found: C,
74.97; H, 9.02; N, 3.81%. MS (%) Mþþ1 at m/z 372. IR (KBr Pellet).
3240, 3039, 2927, 2855, 1644, 1608, 1521, 1438, 1335, 1292, 1239,
1219, 1187, 1033, 899, 861, 824, 760 cmꢃ1 1H NMR:
d 0.88 (3H, t,
J ¼ 6.3 Hz, CH2CH3), 1.22e1.26 (10H, m, eNCH2CH2(CH2)5), 1.54 (2H,
br s, eNCH2CH2), 2.42 (2H, t, J ¼ 8.2 Hz, AreCH2CH2), 2.82 (2H, t,
J ¼ 8.2 Hz, AreCH2CH2), 3.35 (2H, t, J ¼ 6.30 Hz, eNCH2), 3.82 and
3.86 (3H each, s, 2ꢁ OCH3), 5.90 (1H, d, J ¼ 15.2 Hz, CH]CHCO),
6.64e6.68 (3H, m, 2ꢁ AreH and CH]C-CH), 7.41 (1H, d, J ¼ 15.2 Hz,
CH]CHCO). 13C NMR:
d 13.09, 21.63, 22.01, 25.99, 26.10, 26.35,
28.22, 28.69, 30.79, 43.66, 54.98, 55.01, 109.83, 110.01, 116.73,
125.82, 128.91, 132.07, 132.59, 145.07, 147.35, 148.28, and 169.80.
4.2.7. 3-(6,7-Dimethoxy-3,4-dihydronaphth-2-yl)-propenoic acid
isobutyl amide (8)
NMR:
d
2.49 (2H, t, J ¼ 8.2 Hz, AreCH2CH2), 2.84 (2H, t, J ¼ 8.2 Hz,
AreCH2CH2), 3.88 and 3.91 (3H each, s, 2ꢁ OCH3), 5.94 (1H, d,
J ¼ 15.5 Hz, CH]CHCO), 6.71e6.80 (3H, m, 2ꢁ AreH and AreCH]),
This was prepared in 88% yield from 4 and isobutyl amine by the
procedure as described for compound 5 as a red gummy mass. Anal.
Calcd for C19H25NO3: C, 72.35; H, 7.99; N, 4.44%. Found: C 72.99 H
8.08 N 4.49%. MS (%) Mþ þ Na at m/z 338. IR (KBr Pellet). 3067, 2935,
1660, 1599, 1385, 1370, 1217, 1159, 1007, 847, 572 cmꢃ1 1H NMR:
7.56 (1H, d, J ¼ 15.5 Hz, CH]CHCO).13C NMR:
d 22.73, 27.25, 56.03,
56.11, 111.12, 114.68, 126.24, 126.92, 127.72, 133.21, 136.26, 147.62,
148.38, 149.52, and 172.10.
d
0.96 (6H, d, J ¼ 6.3 Hz, CH(CH3)2), 1.53e1.89 (1H, m, CH(CH3)2),
4.2.4. 3-(6,7-Dimethoxy-3,4-dihydronaphth-2-yl)-propenoic acid
piperidide (5)
2.44 (2H, t, J ¼ 8.3 Hz, AreCH2CH2), 2.77 (2H, t, J ¼ 8.3 Hz,
AreCH2CH2), 3.17e3.24 (2H, m, eNCH2), 3.82 and 3.89 (3H each, s,
2ꢁ OCH3), 5.90 (1H, d, J ¼ 15.3 Hz, CH]CHCO), 6.66e6.69 (3H, m,
2ꢁ AreH and CH]CeCH), 7.88 (1H, d, J ¼ 15.3 Hz, CH]CHCO). 13C
To the compound 3-(6,7-dimethoxy-3,4-dihydronaphth-2-yl)-
acrylic acid (4) (500 mg, 1.92 mmol) in dry benzene (50 mL) added
freshly distilled thionyl chloride (2.0 mL excess) and refluxed for
1 h. Excess of thionyl chloride removed under reduced pressure
and the acid chloride reconstituted in benzene and condensed
with benzene solution of piperidine (1.0 mL), the contents stirred
for 30 min. The organic layer washed with water (2 ꢁ 25 mL),
dried over anhydrous sodium sulfate and concentrated on rota-
vapor to give crude product, which was purified on silica gel
column using pet. ether:ethyl acetate (9:1) as an eluent to give the
compound (5) (590 mg, yield 93%) as a brown solid mp 118-119 ꢀC.
Anal. Calcd for C20H25NO3: C, 73.37; H, 7.70; N, 4.28%. Found: C,
74.21; H, 7.78; N, 4.31%. MS (%) Mþþ1 at m/z 328. IR (KBr Pellet).
2998, 2935, 1630, 1587, 1515, 1405, 1236, 1218, 1118, 985, 764,
NMR:
d 20.20, 20.50, 23.21, 27.61, 28.89, 47.21, 56.23, 56.31, 111.24,
111.48, 117.24, 128.59, 129.45, 131.64, 132.15, 143.23, 147.42, 148.29,
and 165.54.
4.2.8. 4-Allyl-(1-allyloxy)-2-methoxybenzene (2a).
This was prepared in 81% yield from 1 and allyl bromide by the
procedure as described for compound 2 as a brown gummy mass.
Anal. Calcd for C13H16O2: C, 76.44; H, 7.90%. Found: C, 76.99; H,
8.08%. MS (%) Mþ þNa at m/z 205. 1H NMR:
d 3.32 (2H, d,
J ¼ 6.64 Hz, AreCH2), 3.85 (3H, s, OCH3), 4.59 (2H, d, J ¼ 6.65 Hz,
OCH2), 5.02e5.12 (2H, m, AreCH2eCH]CH2), 5.23e5.43 (2H, m,
OCH2eCH]CH2), 5.94e6.06 (2H, m, 2ꢁ CH2CH), 6.66e6.79 (2H, m,
2ꢁ AreH), and 6.83 (1H, d, J ¼ 7.8 Hz, AreH).
729 cmꢃ1 1H NMR:
d 1.60 (6H, br s, eNeCH2(CH2)3), 2.47 (2H, t,
J ¼ 8.15 Hz, AreCH2CH2), 2.86 (2H, t, J ¼ 8.15 Hz, AreCH2CH2), 3.59
(4H, br s, eN(CH2)2), 3.82 and 3.88 (3H each, s, 2ꢁ OCH3), 6.39 (1H,
d, J ¼ 15.1 Hz, CH]CHCO), 6.66e6.72 (3H, m, 2ꢁ AreH and CH]
4.2.9. 6-Methoxy-7-allyloxy-2-formyl-3,4-dihydro-naphthalene
(3a)
CeCH), 7.41 (1H, d, J ¼ 15.1 Hz, CH]CHCO). 13C NMR:
d
23.16,
This was prepared in 23% yield from 2a by the procedure as
described for compound 2 as a brown gummy mass. Anal. Calcd for
C15H16O3: C, 73.75; H, 6.60%. Found: C, 74.29; H, 6.88%. MS (%)
24.69, 26.18, 27.08, 27.37, 42.29, 45.28, 55.99, 56.01, 110.85, 111.01,
114.57, 121.87, 124.49, 133.08, 133.43, 143.80, 147.02, 148.44, and
164.44.
M
þ þ Na at m/z 246. 1H NMR:
2.54 (2H, t, J ¼ 8.21 Hz, AreCH2CH2),
d
2.82 (2H, t, J ¼ 8.21 Hz, AreCH2CH2), 3.92 (3H, s, eOCH3), 4.62 (2H,
d, J ¼ 6.64 Hz, eOCH2), 5.28e5.37 (2H, m, CH]CH2), 5.99e6.16 (1H,
m, CH2CH), 6.74 and 6.82 (1H each, s, 2ꢁ AreH), 7.18 (1H, s, AreCH),
4.2.5. 3-(6,7-Dimethoxy-3,4-dihydronaphth-2-yl)-propenoic acid
morpholide (6)
This was prepared in 93% yield from 4 and morpholine by the
procedure as described for compound 5 as a brick red gummy mass.
Anal. Calcd for C19H23NO4: C, 69.28; H, 7.04; N, 4.25%. Found: C,
9.61 (1H, s, eCHO). 13C NMR:
d 28.67, 39.90, 54.84, 68.74, 105.51,
108.14, 117.66, 126.21, 131.30, 131.53, 132.26, 137.73, 148.18, 151.24,
and 191.16.

3612
N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
4.2.10. 3-(6-Methoxy-7-allyloxy-3,4-dihydronaphth-2-yl)-
propenoic acid (4a)
This was prepared in 60% yield from 3a by the procedure as
described for compound 3 as a brick red gummy mass. Anal. Calcd
for C17H18O4: C, 71.31; H, 6.34%. Found: C, 71.79; H, 6.68%. MS (%)
reaction mixture was poured into ice-cold water and pH-7 attained
by adding 0.5N NaOH solution and the reaction mixture extracted
with ethyl acetate. The combined organic layer washed with water,
dried over anhydrous sodium sulfate and evaporated on rotavapor
to give crude product, which was purified on silica gel column using
pet. ether 60e80 ꢀC as an eluent to give 13 (7.2 g, 96.3%) as a pale
yellow solid, mp 107e108 ꢀC. Anal. Calcd for C11H10O: C, 83.53; H,
M
þ þNa at m/z 287. 1H NMR:
2.53 (2H, t, J ¼ 8.21 Hz, AreCH2CH2),
d
2.82 (2H, t, J ¼ 8.21 Hz, AreCH2CH2), 3.92 (3H, s, eOCH3), 4.67 (2H,
d, J ¼ 6.54 Hz, OCH2), 5.28e5.39 (2H, m, CH]CH2), 6.07 (1H, d,
J ¼ 15.14 Hz, CH]CHCO), 6.09e6.16 (1H, m, CH2CH), 6.74 (1H, s,
AreH), 6.85 (1H, s, AreCH), 7.10 (1H, s, AreH), 7.56 (1H, d,
6.37%. Found: C, 84.44; H, 6.41%. 1H NMR:
d
2.56 (2H, t, J ¼ 8.2 Hz,
AreCH2CH2), 2.87 (2H, t, J ¼ 8.2 Hz, AreCH2CH2), 7.18e7.35 (5H, m,
4ꢁ AreH and AreCH), and 9.66 (1H, s, CHO).
J ¼ 15.14 Hz, CH]CHCO).13C NMR:
d 22.63, 27.48, 56.08, 68.59,
111.24, 114.86, 116.63, 117.62, 126.45, 129.85, 131.36, 133.31, 136.48,
140.74, 148.46, 149.64, and 167.26.
4.2.15. 3-(3,4-Dihydronaphth-2-yl)-propenoic acid (18)
To a mixture of 13 (7.0 g, 44.3 mmol) in pyridine (20 mL) and
piperidine (3 mL), malonic acid (9.2 g, 2 eq) was added and the
reaction mixture stirred at room temperature for 52 h and then
heated on water bath for 6 h. The contents cooled and diluted with
water and acidified with 5% HCl solution. The resulting precipitate
filtered, washed with water and crystallized in pet. ether:ethyl
acetate (19:1) to yield 18 (8.1g. 91.4%) as a light brown solid, mp
186e189 ꢀC, Anal. Calcd for C13H12O2: C, 77.98; H, 6.04%. Found; C,
4.2.11. 3-(6-Methoxy-7-allyloxy-3,4-dihydronaphth-2-yl)-
propenoic acid piperidide (9)
This was prepared in 67% yield from 4a and piperidine by the
procedure as described for compound 5 as a yellow semisolid. Anal.
Calcd for C22H27NO3: C, 74.76; H, 7.70%. Found; C, 75.56; H, 7.98; MS
(%) Mþ þNa at m/z 355. 1H NMR:
d 1.60 (6H, br s, eNeCH2(CH2)3),
2.53 (2H, t, J ¼ 8.31 Hz, AreCH2CH2), 2.82 (2H, t, J ¼ 8.31 Hz,
AreCH2CH2), 3.59 (4H, br s, eN(CH2)2), 3.92 (3H, s, eOCH3), 4.67
(2H, d, J ¼ 6.54 Hz, eOCH2), 5.28e5.39 (2H, m, CH]CH2), 6.07 (1H,
d, J ¼ 15.14 Hz, CH]CHCO), 6.09e6.16 (1H, m, CH2 CH), 6.74 (1H, s,
AreH), 6.85 (1H, s, AreCH), 7.10 (1H, s, AreH), 7.56 (1H, d,
78.76; H, 6.11%. MS (%) Mþþ1 at m/z 201. 1H NMR:
d 2.52 (2H, t,
J ¼ 8.24 Hz, AreCH2CH2), 2.92 (2H, t, J ¼ 8.23 Hz, AreCH2CH2), 6.0
(1H, d, J ¼ 15.6 Hz, CH]CHCO), 6.81 (1H, s, AreCH]), 7.14e7.23
(4H, m, 4ꢁ AreH), 7.58 (1H, d, J ¼ 15.6 Hz, CH]CHCO). 13C NMR:
d
20.60, 27.32, 116.56, 126.66, 127.40, 127.55, 128.50, 133.50, 135.30,
J ¼ 15.14 Hz, CH]CHCO).13C NMR:
d
23.21, 24.43, 25.57, 26.56,
135.46, 136.30, 146.94, and 169.80.
27.45, 42.45, 45.38, 55.92, 68.57, 111.19, 114.17, 116.51, 122.37, 126.57,
129.34, 132.53, 133.17, 136.47, 140.06, 147.08, 148.28, and 164.53.
4.2.16. 3-(3,4-Dihydronaphth-2-yl)-propenoic acid piperidide (19)
This was prepared in 87% yield from 18 and piperidine by the
procedure as described for compound 5 as a light brown crystalline
solid, mp 183e184. ꢀC. Anal. Calcd for C18H21NO: C, 80.86; H, 7.92;
N, 5.24%. Found: C, 81.77; H, 7.99; N, 5.28%. MS (%) (Mþþ1) at m/z
268. IR (KBr pellet). 3025, 2928, 1637, 1587, 1438, 1366, 1227, 1192,
4.2.12. 3-(6-Methoxy-7-allyloxy-3,4-dihydronaphth-2-yl)-
propenoic acid isobutyl amide (10)
This was prepared in 88% yield from 4a and isobutyl amine by
the procedure as described for compound 5 as a gummy mass. Anal.
Calcd for C21H27NO3: C, 73.87; H, 7.97; N, 4.10%. Found: C, 74.79; H,
8.08; N, 4.49%. MS (%) Mþ þ Na at m/z 342. IR (KBr Pallet). 3066,
2929, 1669, 1599, 1385, 1370, 1217, 1159, 1007, 847, 572 cmꢃ1 1H
804, 584 cmꢃ1 1H NMR:
d 1.61 (6H, br s, eNeCH2(CH2)3), 2.51 (2H, t,
J ¼ 8.23 Hz, AreCH2CH2), 2.89 (2H, t, J ¼ 8.22 Hz, AreCH2CH2),
3.49e3.63 (4H, m, 2ꢁ eN(CH2), 6.44 (1H, d, J ¼ 15.17 Hz, CH]
CHCO), 6.79 (1H, s, AreCH]), 7.13e7.19 (4H, m, 4ꢁ AreH), 7.51 (1H,
NMR:
d
0.96 (6H, d, J ¼ 6.5 Hz, CH(CH3)2), 1.58e1.88 (1H, m, CH
(CH3)2), 2.44 (2H, t, J ¼ 8.31 Hz, AreCH2CH2), 2.87 (2H, t, J ¼ 8.31 Hz,
AreCH2CH2), 3.18e3.24 (2H, m, eNCH2), 3.87 (3H, s, OCH3), 4.61
(2H, d, J ¼ 6.44 Hz, eOCH2), 5.27e5.38 (2H, m, CH]CH2), 5.90 (1H,
d, J ¼ 15.3 Hz, CH]CHCO), 5.92e6.09 (1H, m, CH]CH2), 6.68e6.71
(3H, m, 2ꢁ AreH and CH]CeCH), 7.58 (1H, d, J ¼ 15.3 Hz, CH]
d, J ¼ 15.17 Hz, CH]CHCO). 13C NMR:
d 23.02, 24.59, 25.55, 26.67,
27.48, 42.38, 45.71, 116.05, 126.62, 127.25, 127.26, 127.90, 133.45,
133.93, 135.77, 135.93, 143.70, and 165.70.
4.2.17. 3-(3,4-Dihydronapth-2-yl)-propenoic acid isobutyl amide
(20)
CHCO). 13C NMR:
d
20.13 (2ꢁCH3), 24.58, 26.96, 28.07, 47.51, 56.32,
68.91, 111.23, 114.16, 116.93, 121.93, 126.71, 129.69, 132.81, 133.14,
136.23, 139.96, 147.21, 148.23, and 164.45.
This was prepared in 92% yield from 18 and isobutyl amine by
the procedure as described for compound 5 as a colourless solid,
mp 141e143 ꢀC. Anal. Calcd for C17H21NO: C, 79.96; H, 8.29; N,
5.49%. Found: C, 80.84; H, 8.33; N, 5.55%. MS (%) (Mþþ1) at m/z 256.
IR (KBr Pellet). 3138, 3011, 2943, 1675, 1610, 1410, 1336, 1310, 1280,
4.2.13. 1,2,3,4-Tetrahydronaphth-1-ol (12)
To a chilled solution of a-tetralone (11) (8.0 g, 54.79 mmol) in
methanol (100 mL), sodium borohydride (500 mg) was added in
small instalments in 2 h maintaining temperature 0e5 ꢀC and after
the completion of the reaction (monitored by TLC), the volume of
the contents was reduced to one fifth, diluted with ice-cold water
and extracted with solvent ether, the organic layer washed with
water and dried over anhydrous sodium sulfate, concentrated on
a rotavapor under reduced pressure to give 12 (7.1 g, 91.3%). as
a colourless viscous mass. Anal. Calcd for C10H12O: C, 81.01; H,
8.16%. Found: C, 82.11; H, 8.21%. MS (%) Mþ þNa at m/z 171. 1H NMR:
1030, 929, 865, 733, 710, 547 cmꢃ1 1H NMR:
d 0.94 (6H, d,
J ¼ 6.70 Hz, CH(CH3)2), 1.59e1.91 (1H, m, CH(CH3)2), 2.47 (2H, t,
J ¼ 8.21 Hz, AreCH2CH2), 2.88 (2H, t, J ¼ 8.21 Hz, AreCH2CH2),
3.17e3.24 (2H, m, eNHCH2), 5.96 (1H, d, J ¼ 15.29 Hz, CH]CHCO),
6.73 (1H, s, AreCH]), 7.12e7.21 (4H, m, 4ꢁ AreH), 7.43 (1H, d,
J ¼ 15.29 Hz, CH]CHCO). 13C NMR:
d
20.06 (2ꢁ CH3), 22.91, 27.45,
28.57, 46.95, 119.33, 126.64, 127.29 (2ꢁ CH), 128.05, 133.81, 133.89,
135.24, 135.96, 142.29, and 166.27.
d
1.55e1.88 (4H, m, AreCH2(CH2)2), 2.86 (2H, br s, AreCH2), 4.66
4.2.18. 3-(3,4-Dihydronaphth-2-yl)-propenoic acid N,N-
diisopropylamide (21)
(1H, br s, AreCHOH), 6.97e7.15 (3H, m, 3ꢁ AreH), 7.25 (1H, d,
J ¼ 8.54 Hz, AreH).
This was prepared in 90% yield from 18 and N,N-diisopropyl
amine by the procedure as described for compound 5 as a gummy
mass. Anal. Calcd for C19H25NO: C, 80.52; H, 8.89; N, 4.90%. Found:
C, 81.43; H, 8.93; N, 4.97%. MS (%) (Mþþ1) at m/z 284. IR (KBr Pellet).
3017, 2968, 1632, 1591, 1438, 1404, 1337, 1208, 1152, 979, 755,
4.2.14. 2-Formyl-3,4-dihydronaphthalene (13)
To a chilled solution of 12 (7 g, 47.3 mmol) in dry DMF (25.0 mL),
POCl3 (12.0 mL) was added drop wise at 0e5 ꢀC for 1 h and the
resulting mixture was stirred at room temperature for 24 h. The
613 cmꢃ1 1H NMR:
d
1.33 (12H, br s, 2ꢁ CH(CH3)2), 2.50 (2H, t,

N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
3613
J ¼ 8.2 Hz, AreCH2CH2), 2.89 (2H, t, J ¼ 8.21 Hz, AreCH2CH2), 3.97
(2H, br s, 2ꢁ N-(CH), 6.39 (1H, d, J ¼ 15.14 Hz, CH]CHCO), 6.68 (1H,
s, AreCH]), 7.09e7.19 (4H, m, 4ꢁ AreH), 7.40 (1H, d, J ¼ 15.14 Hz,
J ¼ 8.23 Hz, AreCH2CH2), 6.86 (1H, d, J ¼ 7.6, AreH), 7.10e7.16
(1H, m, Ar0eH), 7.24e7.33 (3H, m, 3ꢁ AreH), 7.44e7.47 (4H, m,
Ar0eH), and 9.68 (1H, s, CHO).
CH]CHCO). 13C NMR:
d
20.09 (2ꢁ CH3), 20.11 (2ꢁ CH3), 22.94,
27.51, 46.31, 48.72, 119.43, 126.59, 127.53 (2ꢁ CH), 128.11, 133.89,
4.2.23. 3-(1-Phenyl-3,4-dihydronaphth-2-yl)-propenoic acid (18a)
This was prepared in 70% yield from 18 by the procedure as
described for compound 3 as a light brown gummy mass. Anal.
Calcd for C19H16O2: C, 82.58; H, 5.84%. Found: C, 82.62; H, 5.88%. 1H
134.03, 135.31, 135.93, 143.10, and 165.27.
4.2.19. 3-(3,4-Dihydronaphth-2-yl)-propenoic acid p-
methoxyanilide (22)
NMR:
d
2.64 (2H, t, J ¼ 8.23 Hz, AreCH2CH2), 2.90 (2H, t, J ¼ 8.23 Hz,
This was prepared in 92% yield from 18 and p-methoxy aniline
by the procedure as described for compound 5 as a colourless
gummy mass, Anal. Calcd for C20H19NO2: C, 78.66; H, 6.27, N, 4.59%.
Found: C, 78.70; H, 6.29; N, 4.63%. MS (%) Mþþ1 at m/z 306. IR (KBr
Pellet). 3065, 2932, 1650, 1607, 1454, 1411, 1273, 1106, 892, 780,
AreCH2CH2), 5.99 (1H, d, J ¼ 15.7 Hz, CH]CHCO), 6.70 (1H, d,
J ¼ 7.7, AreH), 7.03e7.08 (1H, m, Ar0eH), 7.14e7.21 (3H, m, AreH),
7.38e7.41 (4H, m, Ar0eH), 7.49 (1H, d, J ¼ 15.7 Hz, CH]CHCO). 13C
NMR:
d 21.94, 25.81, 116.64, 123.96, 124.64, 125.13, 125.65, 126.12
(2ꢁ CH), 126.52, 126.29 (2ꢁ CH), 129.91, 133.55, 135.05, 137.11
554 cmꢃ1 1H NMR:
d
2.54 (2H, t, J ¼ 8.21 Hz, AreCH2CH2), 2.88 (2H,
(2ꢁ C), 141.15, and 167.76.
t, J ¼ 8.21 Hz, AreCH2CH2), 3.79 (3H, s, eOCH3), 6.12 (1H, d,
J ¼ 15.16 Hz, CH]CHCO), 6.73 (1H, s, AreCH]), 6.85 (2H, d,
J ¼ 8.9 Hz, 2ꢁ Ar0eH), 7.21e7.29 (4H, m, 4ꢁ AreH), 7.41 (1H, d,
J ¼ 15.16 Hz, CH]CHCO), 7.64 (2H, d, J ¼ 8.9 Hz, 2ꢁ Ar0eH). 13C
4.2.24. 3-(1-Phenyl-3,4-dihydronaphth-2-yl)-propenoic acid
piperidide (24)
This was prepared in 87% yield from 18a and piperidine by the
procedure as described for compound 5 as a brown gummy mass.
Anal. Calcd for C24H25NO: C, 83.93; H, 7.34; N, 4.08%. Found: C,
83.98; H, 7.38; N, 4.09%. MS (%) Mþ at m/z 343. IR (KBr Pellet). 3020,
2959, 2870, 1637, 1586, 1440, 1366, 1143, 1072, 983, 845, 770, 702,
NMR:
d
23.44, 27.92, 55.90, 114.64 (2ꢁ CH), 119.88, 122.06 (2ꢁ CH),
127.18, 127.82, 127.93, 128.71, 132.16, 134.93, 135.08, 135.68, 136.54,
143.88, 157.73, and 166.23.
4.2.20. 3-(3,4-Dihydronaphth-2-yl)-propenoic acid o-methyl
anilide (23)
665, 615 cmꢃ1 1H NMR:
d 1.59 (6H, br s, eNeCH2(CH2)3), 2.64 (2H, t,
J ¼ 8.23 Hz, AreCH2CH2), 2.96 (2H, t, J ¼ 8.23 Hz, AreCH2CH2),
3.49e3.55 (4H, m, eN(CH2)2), 6.43 (1H, d, J ¼ 15.3 Hz, CH]CHCO),
6.70 (1H, d, J ¼ 7.6 Hz, AreH), 7.11e3.16 (1H, m, Ar0eH), 7.18e7.34
This was prepared in 90% yield from 18 and o-methyl aniline by
the procedure as described for compound 5 as a colourless solid,
mp 162e163 ꢀC. Anal. Calcd for C20H19NO: C, 83.01; H, 6.62; N,
4.84%. Found: C, 83.08; H, 6.69; N, 4.88%. MS (%) Mþþ2 at m/z 291.
IR (KBr Pellet). 3237, 2931, 1651, 1609, 1530, 1488, 1403, 1339, 1160,
(8H, m, 3ꢁ AreH, 4ꢁ Ar0eH and CH]CHCO). 13C NMR:
d 24.92,
25.07, 25.99, 28.45, 30.11, 43.56, 47.41, 117.58, 126.81, 127.55, 127.92
(2ꢁ CH), 128.11, 128.77 (2ꢁ CH), 130.85 (2ꢁ CH), 132.28, 136.86,
136.99, 138.40, 141.74, 143.14, and 166.48.
1045, 750, 591 cmꢃ1 1H NMR:
d 2.30 (3H, s, eCH3), 2.51 (2H, t,
J ¼ 8.15 Hz, AreCH2CH2), 2.91 (2H, t, J ¼ 8.15 Hz, AreCH2CH2), 6.12
(1H, d, J ¼ 15.25 Hz, CH]CHCO), 6.78 (1H, s, AreCH]), 7.07e7.25
(8H, m, 4ꢁ AreH and 4ꢁ Ar0eH), 7.56 (1H, d, J ¼ 15.25 Hz, CH]
4.2.25. 3-(1-Phenyl-3,4-dihydronaphth-2-yl)-propenoic acid
isobutyl amide (25)
CHCO). 13C NMR:
d
17.81, 22.94, 27.43, 126.70, 126.78 (2ꢁ CH),
This was prepared in 92% yield from 18a and isobutyl amine by
the procedure as described for compound 5 as a yellowish gummy
mass. Anal. Calcd for C23H25NO: C, 83.34; H, 7.60; N, 4.23%. Found:
C, 83.39; H, 7.66; N, 4.28%. MS (%) Mþþ1 at m/z 332. IR (KBr Pellet).
3024, 2927, 1642, 1604, 1483, 1440, 1368, 1273, 1195, 928, 786, 729,
127.35 (2ꢁ CH), 127.48 (2ꢁ CH), 128.27 (2ꢁ CH), 130.43, 133.70,
134.82, 135.16, 135.80, 136.08, 144.06, and 165.49.
4.2.21. 1-Chloro-2-formyl-3,4-dihydronaphthalene (14)
This was prepared in 93% yield from 11 by the procedure as
described for compound 13 as pale yellow gummy mass. Anal. Calcd
for C11H9ClO: C, 68.58; H, 4.71; Cl, 18.40%. Found: C, 69.04; H, 4.72;
Cl, 18.41%. MS (%) Mþ at m/z 193. 1H NMR: 2.61 (2H, t, J ¼ 8.21 Hz,
AreCH2CH2), 2.85 (2H, t, J ¼ 8.21 Hz, AreCH2CH2), 7.20e7.42 (3H,
m, 3ꢁ AreH), 7.87 (1H, d, J ¼ 6.6 Hz, AreH), 10.39 (1H, s, CHO). 13C
665, 595 cmꢃ1 1H NMR:
d
1.22 (6H, d, J ¼ 6.6 Hz, CH(CH3)2),
1.59e1.71 (1H, m, CH(CH3)2), 2.55 (2H, t, J ¼ 8.21 Hz, AreCH2CH2),
2.87 (2H, t, J ¼ 8.23 Hz, AreCH2CH2), 3.04 (2H, t, J ¼ 6.37 Hz,
eNCH2), 5.92 (1H, d, J ¼ 15.14 Hz, CH]CHCO), 6.62 (1H, d, J ¼ 7.4 Hz,
AreH), 6.91e6.95 (1H, m, Ar0eH), 6.99e7.35 (8H, m, 3ꢁ AreH, 4ꢁ
Ar0eH, CH]CHCO). 13C NMR:
d
20.19 (2ꢁ CH3), 24.46, 28.07, 28.65,
NMR:
d
22.71, 27.64, 125.52, 126.34, 127.77, 129.81, 137.58, 138.33,
47.03, 120.34, 126.50, 127.23, 127.64, 127.68, 127.90, 128.4 (2ꢁ CH),
130.50 (2ꢁ CH), 131.44, 136.40, 136.69, 137.89, 140.12, 143.33, and
166.58.
143.37, 148.91, and 192.64.
4.2.22. 1-Phenyl-2-formyl-3,4-dihydronaphthalene (15)
To Pd(PPh3)4 (0.6 g, 0.52 mmol) was added a deoxygenated
solution of 14 (1.0 g, 5.2 mmol) in DMF (20 mL). This was followed
by addition of a deoxygenated solution of boronic acid (0.952 g,
7.8 mmol) in ethanol (10 mL), and then a deoxygenated solution
of aqueous sodium carbonate (4.41g, 41.6 mmol in 16.2 mL
water). The resultant mixture was heated under reflux under
nitrogen for 4 h. After allowing the mixture to cool to room
temperature, it was quenched with water (75 mL) and the organic
material was then extracted with CH2Cl2 (3 ꢁ 100 mL). The
resultant organic extracts were combined, dried (MgSO4), and
filtered through a celite plug and the excess solvent removed
using a rota vapor. The crude product (an oil) was purified by
column chromatography (30% ethyl acetate/hexane) to afford the
desired product 15 (4.80 g, 83%) as a brown solid, mp 110e111 ꢀC.
Anal. Calcd for C17H14O: C, 87.15; H, 6.02%. Found: C, 87.18; H,
4.2.26. 3-(1-Phenyl-3,4-dihydronaphth-2-yl)-propenoic acid N,N-
diisopropyl amine (26)
This was prepared in 92% yield from 18a and N,N-diisopropyl
amine by the procedure as described for compound 5 as a light
brown gummy mass. Anal. Calcd for C25H29NO: C, 83.52; H, 8.13; N,
3.90%. Found: C, 83.56; H, 8.19; N, 3.99%. MS (%) Mþþ1 at m/z 360.
IR (KBr Pallet). 3059, 2965, 2930, 1632, 1584, 1370, 1260, 1212, 1132,
1072, 1044, 928, 844, 782, 731, 667, 615, 570 cmꢃ1 1H NMR:
d 1.23
(12H, d, J ¼ 6.7 Hz, 2ꢁ CH(CH3)2), 2.57 (2H, t, J ¼ 8.24 Hz,
AreCH2CH2), 2.88 (2H, t, J ¼ 8.24 Hz, AreCH2CH2), 3.67e3.78 (2H,
m, 2ꢁ CH(CH3)2), 6.31 (1H, d, J ¼ 15.3 Hz, CH]CHCO), 6.59 (1H, d,
J ¼ 7.4 Hz, AreH), 6.97e7.07 (1H, m, Ar0eH), 7.09e7.34 (8H, m, 3ꢁ
AreH, 4ꢁ Ar0eH and CH]CHCO). 13C NMR:
21.57 (4ꢁ CH3), 24.95,
d
28.49, 46.18, 48.41, 120.71, 126.79, 127.51, 127.85, 127.93, 128.00,
128.82 (2ꢁ CH), 130.83 (2ꢁ CH), 131.91, 137.36, 137.38, 138.51,
140.28, 143.51, and 166.54.
6.05%. 1H NMR:
d
2.63 (2H, t, J ¼ 8.23 Hz, AreCH2CH2), 2.91 (2H, t,

3614
N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
4.2.27. 3-(1-Phenyl-3,4-dihydronaphth-2-yl)-propenoic acid N,N-
diisobutyl amide (27)
4.2.31. 3-(1-Benzyl-3,4-dihydronaphth-2-yl)-propenoic acid (18b)
To a mixture of 17 (8.5 g, 29.31 mmol) in pyridine (25 mL) and
piperidine (5.0 mL), malonic acid (7.12 g, 2 eq.) was added, and the
reaction mixture stirred at room temperature for 72 h, followed by
heating on water bath for 6 h, and the contents cooled, diluted
with cold water followed by addition of 5% HCl solution. The
precipitate filtered, dried and crystallized from pet. ether:ethyl
acetate (97:3) to yield yellow crystalline compound 18b (7.5g,
78%), Anal. Calcd for C20H18O2: C, 82.73; H, 6.25%. Found: C, 82.78;
This was prepared in 90% yield from 18a and N,N-diisobutyl
amine by the procedure as described for compound 5 as a gummy
mass. Anal. Calcd for C27H33NO: C, 83.68; H, 8.58; N, 3.61%. Found:
C, 83.74; H, 8.62; N, 3.66%. MS (%) Mþþ1 at m/z 388. IR (neat). 3018,
2934, 1633, 1586, 1430, 1352, 1289, 1221, 1160, 1123, 1020, 929, 851,
770, 666, 592 cmꢃ1 1H NMR:
d
0.93 (12H, d, J ¼ 6.3 Hz, 2ꢁ CH
(CH3)2), 1.99e2.06 (2H, m, 2ꢁ eNCH2(CH), 2.69 (2H, t, J ¼ 8.3 Hz,
AreCH2CH2), 3.01 (2H, t, J ¼ 8.3 Hz, AreCH2CH2), 3.22e3.26 (4H, m,
2ꢁ NCH2), 6.48 (1H, d, J ¼ 15.1 Hz, CH]CHCO), 6.74 (1H, d,
J ¼ 7.6 Hz, AreH), 7.03e7.06 (1H, m, Ar0eH), 7.08e7.42 (8H, m,
H, 6.30%. 1H NMR:
d
2.59 (2H, t, J ¼ 8.2 Hz, AreCH2CH2), 2.87 (2H,
t, J ¼ 8.2 Hz, AreCH2CH2), 4.18 (2H, s, AreCH2), 6.11 (1H, d,
J ¼ 15.4 Hz, CH]CHCO), 7.16e7.32 (9H, m, 4ꢁ AreH, 5ꢁ Ar0eH),
3ꢁ AreH, 4ꢁ Ar0eH, CH]CHCO). 13C NMR:
d
20.27 (2ꢁ CH3), 20.43
and 8.06 (1H, d, J ¼ 15.4 Hz, CH]CHCO). 13C NMR:
d 21.52, 25.39,
(2ꢁ CH3), 24.58, 26.96, 28.06, 29.03, 54.91, 56.37, 117.33, 126.42,
127.13, 127.55 (2ꢁ CH), 127.72, 128.38 (2ꢁ CH), 130.43 (2ꢁ CH),
131.81, 136.50, 136.56, 137.90, 141.40, 143.01, and 167.21.
31.18, 115.54, 122.86, 123.54, 124.03, 124.77, 125.27 (2ꢁ CH),
125.42, 125.99 (2ꢁ CH), 129.81, 132.65, 134.95, 137.01 (2ꢁ C),
140.25, and 167.26.
4.2.28. 3-(1-Phenyl-3,4-dihydronaphth-2-yl)-propenoic acid
naphthyl amide (28)
4.2.32. 3-(1-Benzyl-3,4-dihydronaphth-2-yl)-propenoic acid
piperidide (29)
This was prepared in 92% yield from 18a and naphthyl amine by
the procedure as described for compound 5 as a colourless gummy
mass. Anal. Calcd for C29H23NO: C, 86.75; H, 5.77; N, 3.49%. Found:
C, 86.79; H, 5.77; N, 3.56%. MS (%) Mþþ1 at m/z 402. IR (KBr Pellet).
3381, 3057, 2854, 2362, 1648, 1601, 1537, 1499, 1401, 1349, 1295,
This was prepared in 70% yield from 18b and piperidine by the
procedure as described for compound 5 as a light brown gummy
mass. Anal. Calcd for C25H27NO: C, 83.99; H, 7.61; N, 3.92%. Found:
C, 84.08; H, 7.66; N, 3.99%. MS (%) Mþþ1 at m/z 358. IR (KBr pellet)
3060, 2936, 2855, 1715, 1585, 1493, 1366, 1270, 1219, 1138, 1121,
1249, 1021, 765, 699 cmꢃ1 1H NMR:
d
2.67 (2H, t, J ¼ 8.23 Hz,
1076, 969, 852, 752, 622 cmꢃ1 1H NMR:
d 1.59 (6H, br s,
AreCH2CH2), 2.97 (2H, t, J ¼ 8.23 Hz, AreCH2CH2), 6.26 (1H, d,
J ¼ 15.68 Hz, CH]CHCO), 6.77 (1H, d, J ¼ 7.5 Hz, AreH), 7.03e7.06
(1H, m, Ar0eH), 7.08e7.92 (15H, m, 3ꢁ AreH, 4ꢁ Ar0eH, 7ꢁ Ar00eH
eNCH2(CH2)3), 2.59 (2H, t, J ¼ 8.24 Hz, AreCH2CH2), 2.88 (2H, t,
J ¼ 8.24 Hz, AreCH2CH2), 3.47e3.54 (4H, m, 2ꢁ eN(CH2), 4.18 (2H, s,
Ar0eCH2), 6.68 (1H, d, J ¼ 15.07 Hz, CH]CHCO), 7.09e7.30 (9H, m,
4ꢁ AreH and 5ꢁAr0eH), 7.92 (1H, d, J ¼ 15.14 Hz, CH]CHCO). 13C
and CH]CHCO). 13C NMR:
d 23.47, 27.08, 112.53, 119.83, 120.72,
124.60, 125.07, 125.22, 125.54, 126.31, 126.75, 126.76, 127.17, 127.43
(2ꢁ CH), 127.50, 127.63, 129.55 (2ꢁ CH), 130.65, 131.79, 133.44,
133.25, 135.34, 135.92, 136.97, 141.67, 143.28, and 166.62.
NMR: d 23.54, 23.69, 25.65, 27.11, 28.65, 32.71, 42.23, 46.01, 116.78,
124.18, 124.94, 125.57, 126.18, 126.45, 126.90 (2ꢁ CH), 127.53
(2ꢁ CH), 131.11, 131.80, 134.62, 136.13, 136.47, 138.79, and 165.04.
4.2.29. 1-(Benzyl)-tetrahydro-naphth-1-ol (16)
4.2.33. 3-(1-Benzyl-3,4-dihydronaphth-2-yl)-propenoic acid
isobutyl amide (30)
To an ethereal solution of Grignard reagent (prepared from
magnesium metal and benzyl bromide), was added
a
-tetralone
This was prepared in 78% yield from 18b and isobutyl amine by
the procedure as described for compound 5 as a brown solid, mp
174e176 ꢀC. Anal. Calcd for C24H27NO: C, 83.44; H, 7.88; N, 4.05%.
Found: C, 83.91; H, 7.92; N, 4.11%. MS (%) Mþþ1 at m/z 346. IR (KBr
Pellet). 3282, 3026, 2958, 1643, 1603, 1548, 1452, 1368, 1306, 1274,
(15.0g,102.7 mmol) in 1 h and then the reaction mixture worked up
by pouring the contents into 1% aqueous ammonium chloride
solution, the organic layer separated and the aqueous layer
extracted with solvent ether (4 ꢁ 100 mL). The combined organic
layer washed with water (3 ꢁ 20 mL), dried over anhydrous sodium
sulfate, concentrated on rotavapor to give 16 as a gummy mass,
(17.5g, 71.5%), Anal. Calcd for C17H18O: C, 85.67; H, 7.61%. Found: C,
1220, 1119, 1076, 973, 802, 698, 581 cmꢃ1 1H NMR:
d 0.92 (6H, d,
J ¼ 6.6 Hz, 2ꢁ CH(CH3), 1.65e1.83 (1H, m, CH(CH3)2), 2.55 (2H, t,
J ¼ 8.24 Hz, AreCH2CH2), 2.89 (2H, t, J ¼ 8.24 Hz, AreCH2CH2),
3.14e3.20 (2H, m, eNCH2), 4.17 (2H, s, Ar0eCH2), 6.08 (1H, d,
J ¼ 15.13 Hz, CH]CHCO), 7.07e7.30 (9H, m, 4ꢁ AreH and 5ꢁ
85.95; H, 7.69%. 1H NMR:
d 1.61e1.67 (2H, m, C-CH2), 1.79e1.97 (2H,
m, AreCH2CH2), 2.76e2.82 (2H, m, AreCH2), 3.02 and 3.16 (1H each,
d, J ¼ 13.7 Hz, Ar0eCH2), 7.22e7.34 (8H, m, 3ꢁ AreH and 5ꢁ Ar0eH),
and 7.60 (1H, d, J ¼ 6.80 Hz, AreH).
Ar0eH), 7.90 (1H, d, J ¼ 15.13 Hz CH]CHCO). 13C NMR:
d
19.24 (2ꢁ
CH3), 23.53, 27.21, 27.70, 32.81, 46.13, 120.10, 124.35, 125.11, 125.71,
126.32, 126.67, 127.01(2ꢁ CH), 127.62 (2ꢁCH), 131.93, 134.62,
136.30, 137.17, 137.50, 138.85, and 165.57.
4.2.30. 1-Benzyl-2-formyl-3,4-dihydronaphthalene (17)
To a chilled solution of 16 (10 g, 42 mmol) in dry DMF (35 mL),
POCl3 (16.2 mL) was added dropwise at 0e5 ꢀC for 1 h and the
resulting mixture was stirred at room temperature for 45 h. The
reaction mixture was poured into ice-cold water (250 mL) containing
sodium acetate (15 g). The contents were extracted with ethyl acetate
(3 ꢁ100 mL). The organic layer washed with water (3 ꢁ 50 mL), dried
over anhydrous sodium sulfate and concentrated on rotavapor to give
crude product, which was purified on silica gel column using pet.
ether 60e80 ꢀC:ethyl acetate (9:1) as an eluent to give yellowgummy
mass (9.1 g, 87.3%), Anal. Calcd for C18H16O: C, 87.06; H, 6.49%. Found:
4.2.34. 3-(1-Benzyl-3,4-dihydronaphth-2-yl)-propenoic acid N,N-
diisopropylamide (31)
This was prepared in 82% yield from 18b and N,N-diisopropyl
amine by the procedure as described for compound 5 as a light brown
solid, mp 127-130 ꢀC, Anal. Calcd for C26H31NO: C, 83.60; H, 8.37; N,
3.75%. Found: C, 83.66; H, 8.39; N, 4.79%. MS (%) Mþþ1 at m/z 374. IR
(KBr Pellet). 3291, 3061, 2967, 1631, 1582, 1493, 1370, 1281, 1210, 1153,
1076, 1030, 898, 804, 701, 664, 701, 582 cmꢃ1 1H NMR:
d 1.28 (12H, d,
J¼ 6.5Hz,2ꢁ CH(CH3)2), 2.58 (2H, t, J¼ 8.24 Hz, AreCH2CH2), 2.90 (2H,
t, J¼ 8.24 Hz, AreCH2CH2), 3.76e4.02(2H, m,2ꢁCH(CH3)2), 4.17 (2H, s,
Ar0eCH2), 6.55 (1H, d, J ¼ 15.07 Hz, CH]CHCO), 7.08e7.24 (9H, m, 4ꢁ
AreH, and 5ꢁ Ar0eH), 7.89 (1H, d, J ¼ 15.07 Hz CH]CHCO). 13C NMR:
C, 87.08; H, 6.53%. MS (%) Mþ at m/z 248. 1H NMR:
d 2.63 (2H, t,
J ¼ 8.3 Hz, AreCH2CH2), 2.80 (2H, t, J ¼ 8.3 Hz, AreCH2CH2), 4.42 (2H,
s, AreCH2), 7.11e7.42 (8H, m, 3ꢁ AreH, 5ꢁAr0eH), 7.44 (1H, d,
J ¼ 7.61 Hz, AreH), and 10.30 (1H, s, CHO). 13C NMR:
d
20.25, 27.73,
d
19.23 (2ꢁ CH3), 19.28 (2ꢁ CH3), 23.65, 27.16, 32.71, 46.83, 48.21,
32.26, 125.92,126.64, 126.84,127.83 (2ꢁ CH), 128.00,128.88 (2ꢁCH),
117.26, 124.23, 124.93, 125.59, 126.20, 126.45, 126.94 (2ꢁ CH), 127.45
129.98, 135.23, 135.39, 138.89, 139.28, 149.92, and 191.22.
(2ꢁ CH), 131.81, 134.61, 136.22, 136.63, 138.68, 138.79, and 166.21.

N. Thota et al. / European Journal of Medicinal Chemistry 45 (2010) 3607e3616
3615
4.2.35. 3-(1-Benzyl-3,4-dihydronaphth-2-yl)-propenoic acid N,N-
diisobutylamine (32)
4.2.39. 3-(1-Phenyl-1,2,3,4-tetrahydronaphth-2-yl)-propanoic acid
piperidide (36)
This was prepared in 70% yield from 18b and N,N-diisobutyl
amine by the procedure as described for compound 5 as a yellow
solid, mp 146e149 ꢀC, Anal. Calcd for C28H35NO: C, 83.74; H, 8.78; N,
3.49%. Found: C, 83.79; H, 8.79; N, 3.56%. MS (%) Mþþ1 at m/z 402.
IR (KBr Pellet). 3061, 3025, 2928, 1637, 1587, 1465, 1438, 1386, 1297,
1227, 1144, 1120, 1029, 972, 845, 804, 747, 696, 584 cmꢃ1 1H NMR:
This was prepared in 66% yield from 24 by the procedure as
described for compound 34 as a brown gummy mass. Anal. Calcd
for C24H29NO: C, 82.95; H, 8.41; N, 4.03%. Found: C, 83.18; H, 8.58;
N, 4.09% MS (%) Mþþ2 at m/z 349. 1H NMR:
d 1.41e1.71 (10H,
m, eNCH2(CH2)3 and CH(CH2)2), 1.96e2.08 (1H, m, CH(CH2)2), 2.36
(2H, t, J ¼ 9.60 Hz, COCH2), 2.84e2.96 (2H, m, AreCH2), 3.29e3.36
(4H, m, eN(CH2)2), 4.17 (1H, d, J ¼ 5.0 Hz, AreH), and 6.99e7.32,
d
0.91 (12H, d, J ¼ 6.30 Hz, 2ꢁ CH(CH3)2), 1.83e2.04 (2H, m,
2ꢁ NCH2(CH), 2.60 (2H, t, J ¼ 8.3 Hz, AreCH2CH2), 2.88 (2H, t,
J ¼ 8.3 Hz, AreCH2CH2), 3.18e3.28 (4H, m, 2ꢁ NCH2), 4.17 (2H, s,
Ar0eCH2), 6.56 (1H, d, J ¼ 15.13 Hz, CH]CHCO), 7.05e7.22 (9H, m,
4ꢁ AreH, 5ꢁ Ar0eH), 7.91 (1H, d, J ¼ 15.13 Hz, CH]CHCO). 13C NMR:
(9H, m, 4ꢁ AreH, 5ꢁ Ar0eH). 13C NMR:
d 22.14, 23.51, 24.53, 25.52,
28.01, 28.16, 30.27, 37.52, 41.63, 45.71, 48.25, 124.69, 124.95, 125.01,
126.67 (2ꢁ CH), 127.76, 129.29 (2ꢁ CH), 129.59, 135.51, 138.67,
142.14, and 170.38.
d
19.27 (2ꢁ CH3), 19.43 (2ꢁ CH3), 23.58, 25.96, 27.07, 28.03, 32.76,
53.91, 55.37, 117.31, 124.28, 124.98, 125.62, 126.25, 126.51, 126.99
(2ꢁ CH), 127.51 (2ꢁ CH), 131.86, 134.66, 136.27, 136.69, 138.74,
138.85, and 166.27.
4.3. Biology
4.3.1. Determination of minimum effective concentration (MEC) of
the EPIs
4.2.36. 3-(1-Benzyl-3,4-dihydronaphth-2-yl)-propenoic acid 30,40-
methelenedioxy anilide (33)
This was prepared in 70% yield from 18b and 3,4-meth-
elenedioxy aniline by the procedure as described for compound 5
as a colourless gummy mass. Anal. Calcd for C27H23NO3: C, 79.20; H,
5.66; N, 3.42%. Found: C, 79.29; H, 5.69; N, 3.46%. MS (%) Mþ1 at m/z
410. IR (KBr Pellet). 3165, 2926, 1648, 1636, 1558, 1501, 1403, 1205,
The inhibitory potential of the EPIs was tested through the
determination of MEC of these EPIs against S. aureus 1199 (wild
type), S. aureus 1199B (NorA overexpressing) and S. aureus SA
K-1758 (NorA knock out). The MIC of ciprofloxacin was determined
against these cultures in MullereHinton broth in the presence of
increasing amounts of efflux pump inhibitors by broth checker-
board synergy method in microtiter plates using two fold serial
1038, 802, 600 cmꢃ1 1H NMR:
d
2.59 (2H, t, J ¼ 8.3 Hz, AreCH2CH2),
dilutions [29]. Seven serial dilutions of EPIs (50e0.8
tested in combination with ten serial dilutions of ciprofloxacin
(64e0.12
g/mL). The plates were incubated at 37 ꢀC for 24 h, and
mg/mL) were
2.86 (2H, t, J ¼ 8.3 Hz, AreCH2CH2), 4.19 (2H, s, Ar0eCH2), 5.90 (2H,
s, eOCH2O-), 6.16 (1H, d, J ¼ 15.12 Hz, CH]CHCO), 6.74 (1H, d,
J ¼ 8.2 Hz, Ar00eH), 7.10e7.30 (11H, m, 4ꢁ AreH, 5ꢁ Ar0eH and 2ꢁ
m
were read visually after incubation at 37 ꢀC for 24 h. The lowest
concentration well in each row showing no turbidity was recorded
as MIC. The minimal concentration of EPI that produced the
maximal reduction in ciprofloxacin was recorded as MEC [30].
Ar00eH), 8.01 (1H, d, J ¼ 15.12 Hz, CH]CHCO). 13C NMR:
d 23.24,
26.98, 32.57, 101.38, 106.81, 113.03, 117.43, 120.11, 124.19, 124.85,
125.49, 126.36, 126.57, 127.13 (2ꢁ CH), 127.56 (2ꢁ CH), 127.78,
131.76, 134.63, 136.32, 136.65, 138.79, 138.83, 144.02, 147.61, and
166.57.
4.3.2. Efflux mechanism studies
The mechanism of inhibition of bacterial efflux pumps by these
EPIs was determined by the measure of the levels of ethidium
bromide accumulation and efflux in S. aureus 1199B using the
method described by Brenwald and co-workers [31]. The bacterial
4.2.37. 3-(1,2,3,4-Tetrahydronaphth-2-yl)-propanoic acid
piperidide (34)
A mixture of methanolic solution of amide 19 (50 mg) and 5%
PdeC (20 mg) was hydrogenated at 30 psi for 5 h and the contents
were filtered, washed with excess of methanol and concentrated on
a rotavapor at reduced pressure to give crude product which on CC
over silica gel and elution with pet. ether:ethyl acetate (80:20)
afforded compound 34 (77% yield) as a gummy mass, Anal. Calcd for
C18H25NO: C, 79.66; H, 9.28; N, 5.16%. Found: C, 79.95; H, 9.21; N,
suspension was exposed to 2
of the most active EPI (20 at 12.5
5 (50 g/mL) and standard EPI Reserpine (25
m
g/mL ethidium bromide in presence
g/mL concentration), inactive EPI
g/mL) for 30 min at
m
m
m
37 ꢀC. The cells were pelleted down by centrifugation and re-
suspended in fresh buffer. The loss of fluorescence was recorded for
30 min at 5 min interval at excitation and emission wavelengths of
530 and 600 nm in a spectrophotometer (PerkineElmer model
LS50).
5.48%. MS (%) Mþþ1 at m/z 271 1H NMR:
d 1.29e1.74 (10H, m,
eNCH2(CH2)3 and CH(CH2)2), 1.92e1.96 (1H, m, CH(CH2)2), 2.27
(2H, t, J ¼ 7.80 Hz, COCH2), 2.39e2.47 and 2.72e2.85 (4H, m,
2ꢁ AreCH2), 3.20e3.55 (4H, m, 2ꢁ eN(CH2), and 7.05e7.09 (4H, m,
Acknowledgements
4ꢁ AreH). 13C NMR:
d 24.57, 25.57, 26.59, 27.51, 29.06, 30.92, 31.95,
The authors thank Prof. G. W. Kaatz of Wayne State University
School of Medicine, Detroit, Michigan, USA for providing S. aureus
1199, 1199B and SA-K1758.
34.11, 36.00, 42.65, 46.68, 124.43, 125.36, 126.28, 127.86, 133.27,
135.60, and 170.45.
4.2.38. 3-(1,2,3,4-Tetrahydronapth-2-yl)-propanoic acid isobutyl
amide (35)
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This was prepared in 69% yield from 20 by the procedure as
described for compound 34 as a ccolourless gummy mass. Anal.
Calcd for C17H25NO: C, 78.72; H, 9.71; N 5.40%. Found: C, 78.84; H,
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