Synthesis and antibacterial activity of new lactone 1,4-dihydroquinoline derivatives

Article abstract of DOI:10.1007/s00044-017-2129-x

In this work, a series of lactone 1,4-dihydroquinoline derivatives 4 were efficiently synthesized and characterized by ¹H and ¹³C NMR. The synthesized compounds were evaluated for their in vitro antibacterial activity against the bac

Full text of DOI:10.1007/s00044-017-2129-x

MEDICINAL
CHEMISTRY
RESEARCH
Medicinal Chemistry Research
https://doi.org/10.1007/s00044-017-2129-x
ORIGINAL RESEARCH
Synthesis and antibacterial activity of new lactone 1,4-
dihydroquinoline derivatives
1
Willian P. Gomes1 Ana P. R. Pissurno1 Fernanda A. Santos1
●
●
●
●
Rosangela S. Laurentiz
Vinicius Cristian O. Santos2 Carlos H. G. Martins2
●
Received: 31 August 2017 / Accepted: 22 December 2017
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
In this work, a series of lactone 1,4-dihydroquinoline derivatives 4 were efficiently synthesized and characterized by 1H and
13C NMR. The synthesized compounds were evaluated for their in vitro antibacterial activity against the bacterial strains
Porphyromonas gingivalis, Prevotella nigrescens, Streptococcus mitis, and Streptococcus sanguinis and against
Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium kansasii. The results revealed that the evaluated
compounds were more active against Gram negative bacteria. Compounds 4ba, 4bb, 4bg, 4bi, 4bn, 4ch, and 4ci displayed
moderate antibacterial activity against P. gingivalis. 4bi was the most active compound against the three strains of
Mycobacterium. Based on structure–activity relationship studies, we observed that the presence of a nitro group on the
benzylic ring and a methylenedioxy group on the dihydroquinoline ring enhanced the antibacterial activity of the derivatives.
●
●
Keywords Azo-heterocyclic compounds quinoline derivatives antibacterial activity
Introduction
properties (Teponno et al. 2016). Several studies have
shown that the biological properties of these lignans are
closely related to the nature of ring A, their stereochemistry,
and substituents on the aromatic rings (Antunez-Mojica
et al. 2016). However, little is known about how mod-
ifications in the chemical skeleton of ring B can affect these
properties. The replacement of C7 with nitrogen can greatly
alter these properties, creating new analogs with biological
properties that have not yet been described for this class of
compounds (Fig. 1). These derivatives present two impor-
tant pharmacophoric groups, the lactone and dihy-
droquinoline rings. The lactone ring is present in many
compounds with biological properties (Qiu et al. 2016)
including antimicrobials (Grabarczyk et al. 2013; Mazur
et al. 2016), along with quinoline and dihydroquinoline
rings (Meléndez-Gómez and Kouznetsov 2013; Kharb and
Kaur 2013; Desai et al. 2017).
New quinoline derivatives have been synthesized and
investigated for several biological properties. The position
and type of the substituents on the quinoline and dihy-
droquinoline rings are responsible for the variety of phar-
macological activities that these compounds present,
including antibacterial (El-Essawy and El-Sayed 2013;
Desai et al. 2017), antiplasmodial (Vandekerckhove et al.
2015), antituberculosis (Keri and Patil 2014), antimalarial
(Vandekerckhove and D’hooghe 2015) and anticancer
The combination of pharmacophoric moieties of different
bioactive substances can produce a new hybrid molecule
with improved biological efficacy and affinity, a modified
selectivity profile, and different and/or dual modes of
action, and may reduce undesired side effects (Viegas-
Junior et al. 2007). The combination of lactone and 1,4-
dihydroquinoline rings provides 7-azo synthetic analogs of
aryltetralin lignan lactones. Aryltetralin lignan lactones are
among the various classes of naturally occurring bioactive
molecules that have aroused interest in the area of medicinal
chemistry due to their structural diversity and biological
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s00044-017-2129-x) contains supplementary
material, which is available to authorized users.
* Rosangela S. Laurentiz
rosangela@dfq.feis.unesp.br
1
Department of Physical and Chemistry, Universidade Estadual
Paulista Júlio de Mesquista Filho (UNESP), Ilha Solteria,
São Paulo, Brazil
2
Research Laboratory in Applied Microbiology, Universidade de
Franca, Franca, São Paulo, Brazil

Medicinal Chemistry Research
R
R
Fig. 1 General structure of
dihydroquinoline ring,
aryltetralin lignan lactone and
lactone quinoline derivative
R1
O
O
R2
R3
7'
8'
8
R
R
O
R
O
A
B
7
N
H
N
H
Aryltetralin lignan lactone
Lactone quinoline derivative
Dihydroquinoline ring
O
Scheme 1 Reaction conditions
for obtaining derivatives 4
R2
O
CHO
NH2
1
O
O
MW
EtOH
R1
O
R1
R2
N
H
R2= 3,4-(OCH2O) 3a, 3,4-(OCH3) 3b
3,4,5-(OCH3) 3c, 4-Cl 3d
3-(OCH3)-4OBn 3e, 4-F 3f
4-SCH3 3g; 4-CF3 3h
R1= 3,4,5-OCH3 2a
3,4 OCH2O 2b
3,4- OCH3 2c
4
3,4-(OCH3)2-6-NO2 3i
3-(OCH3)-4-(OH) 3j, 3-(OH) 3k
3-(OCH3) 2l, 3,4-(OH) 3m
3,4-OCH2O-6-NO2 3n
(Spanò et al. 2015). However, there are no reports in the
literature on the antimicrobial activity of lactone dihy-
droquinoline derivatives; therefore we decided to synthesize
these compounds and evaluate their antibacterial activities.
observed depending on the substituent present in the ani-
line. Anilines with electron-withdrawing substituents or
without electron-donating substituents in the meta position
did not react in these conditions. According to the reactional
mechanism proposed herein (Scheme 2), the reaction might
proceed via sequential condensation, addition, cyclization,
and elimination. First, condensation takes place between the
tetronic acid 1 with aromatic aldehydes 3 to afford the
intermediate I. The Michael addition of aniline 2 in I then
furnishes the intermediate product II, which isomerizes to
III.
In the intermediate III, the nucleophilic addition of the
nitrogen in the carbonyl leads to the formation of the
intermediate IV, which then undergoes dehydration to
generate the target derivative 4. In this proposed mechan-
ism, the donating group in the meta position in the aniline
activates the aromatic ring (ortho position at NH2 group) to
attack at intermediate I. The proposed mechanism explains
the low reactivity of anilines with electron-withdrawing, as
well as weakly electron-donating substituents in the para or
ortho positions.
Result and Discussion
Chemistry
The lactone dihydroquinoline derivatives 4 presented in this
paper were prepared via a microwave-assisted reaction
between tetronic acid 1, aniline 2 and aromatic aldehyde 3
in EtOH (Scheme 1). The use of a microwave furnished the
derivatives 4 in high yield and with a shorter reaction time
than the traditional methodology (Frackenpohl et al. 2009).
The reaction was realized with anilines 2a-c and aromatic
aldehydes 3b-n with electron-withdrawing, as well as
electron-donating substituents in different positions on the
aromatic ring (Scheme 1).
Substitution of aldehydes with a nitro group (ortho
position) furnished the derivatives 4 in lower yields, due to
the steric hindrance that the nitro group causes on the car-
bonyl. More pronounced effects on the reaction were
The combination of several anilines and aldehydes
furnished 39 lactone dihydroquinoline derivatives, whose
structures were confirmed by 1H and 13C NMR spectra. The

Medicinal Chemistry Research
R
Scheme 2 Mechanistic proposal
for the formation of 4
R
O
O
CH
O
O
O
O
O
1
OH
O
O
R
I
+
2
H N
2
O
HN
II
O
3
R
O
R
R
R
H
O
O
O
O
R
O
R
O
R
O
H2N
N
H
4
N
HO
H
III
IV
spectral analyses were consistent with the structures pro-
posed and are listed in the supplementary material.
dihydroquinoline ring. Nitro-organic compounds are
reduced by microbial systems and reduced derivatives were
shown to be reactive and to bind to DNA and to proteins
(Shahid et al. 2016). However, the antibacterial effect of
compounds 4bi and 4bn depend not only on the nitro group,
but also on their overall structure and the type of bacteria
evaluated.
Antibacterial activity
The 39 compounds synthesized were evaluated in vitro for
antibacterial activity against Gram negative bacteria, Gram
positive bacteria and mycobacterium strains by the micro-
plate microdilution method using resazurin as an indicator
of microbial activity. The minimum inhibitory concentra-
tion (MIC) values of antibacterial activity are shown in
Table 1. The evaluated compounds were most active against
Gram negative bacteria. P. gingivalis was more sensitive to
the compounds evaluated than P. nigrescence. The sub-
stituents of aniline and aldehyde, such as halogen, methoxy,
trifluormethyl, hydroxy, nitro, and methylthio were varied
to explore the structure–activity relationships between the
lactone dihydroquinoline derivatives. The results of the
evaluation indicated that in the dihydroquinoline ring
methylenedioxy and dimethoxy substituents were more
favorable for antibacterial activity than trimethoxy sub-
stituents. In the benzylic ring, methylenedioxy, dimethoxy,
methylthio, trifluormethyl, and nitro substituents favored
antibacterial activity. Compounds 4ba, 4bb, 4bg, 4bi, 4bn,
4ch, and 4ci showed good antibacterial activity against P.
gingivalis. Only compounds 4ab, 4ae were active against P.
nigrescence. None of the compounds evaluated were active
against Gram positive bacteria. Compound 4bi was the most
active against the three strains of Mycobacterium. Overall,
the most active compounds were 4bi and 4bn, which pos-
sess nitro and electron-donating groups attached to the
benzylic ring and a methylenedioxy group attached to the
Conclusion
Thirty-nine lactone dihydroquinoline derivatives were syn-
thesized and their antibacterial activities against anaerobic
bacteria, aerobic bacteria, and mycobacterium were assayed
using the microplate microdilution method. The presence of
halogen or hydroxyl groups did not enhance their anti-
bacterial activity. The most active compounds were 4bi and
4bn, which possess nitro and electron-donating groups
attached to the benzylic ring and a methylenedioxy group
attached to the dihydroquinoline ring. Therefore, for this
class of compounds the presence of these substituents was
essential for antibacterial activity against P. gingivalis and
Mycobacterium.
Materials and Methods
Chemistry
All chemicals and solvents were purchased from commer-
cial sources and were used as received without further
purification. Microwave irradiation was carried out with a

Medicinal Chemistry Research
Table 1 In vitro antibacterial
activity (MIC µg/mL)
Compounds
G-negative
G-positive
Mycobacterium
P. gingivalis P. nigrescens S. mitis S. sanguinis Tuberculosis Avium
kansasii
4aa
4ab
4ac
4ad
4ae
4af
>200
200
>200
100
>200
>200
>200
>200
200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
200
>2000
>2000
500
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 500
>200
>200
>200
200
200
>200
100
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
2000
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
—
>200
>200
>200
>200
>200
>200
>200
200
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
4ag
4ah
4ai
>200
>200
>200
>200
>200
>200
100
4aj
4am
4an
4ba
4bb
4bc
4bd
4be
4bf
2000
1000
50
>200
>200
>200
>200
200
>200
>200
>200
>200
>200
>200
>200
200
>2000
>2000
>2000
>2000
>2000
>2000
>2000
250
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
200
200
>200
>200
100
4bg
4bh
4bi
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
—
>200
25
250
125
4bj
>200
12,5
>200
>200
>200
>200
200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
—
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
>2000
0.06
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 500
4bn
4ca
4cb
4cc
4cd
4ce
4cf
>200
>200
25
4cg
4ch
4ci
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
>2000 >2000
100
4cn
4cm
Isoniazid
>200
>200
—
>1
1
Chlorhexidine 0.922
—: not tested
0.922
3.68
3.68
—
—
—
Reactor Discover Reflux (CEM Corporation, 300 W).
Reactions were monitored using thin-layer chromatography
(TLC) plates coated with 0.2 mm silica gel 60 F254 (Merck,
Germany). TLC plates were visualized using ultraviolet
per million (δ) relative to DMSO- d6 (39.5 p.p.m.), and J
(coupling constant) values were reported in hertz. The
splitting patterns of protons are described as s (singlet), d
(doublet), dd (doublet of doublets), t (triplet) and m (mul-
tiplet). All melting points were determined on Melting Point
B-540 Buchi apparatus and are uncorrected. The high-
resolution mass spectral data for new compounds were
obtained using Bruker Daltonics—micrOTOF-Q, fitted with
an ESI operating in the positive ion mode.
(UV) irradiation (254 nm). The products were washed with
1
hexane:ethyl acetate (8:2) for purification. Both H and 13
C
NMR spectra were determined on
a Bruker ARX
400 spectrometer in DMSO-d6. Proton chemical shifts in
DMSO-d6 are related to the middle of the residual multiplet
(δ = 2.50). Carbon chemical shifts were reported in parts

Medicinal Chemistry Research
General experimental procedure and
9-(4-chlorophenyl)-6,7,8-trimethoxy-4,9-dihydrofuro[3,4-b]
characterization of synthesized derivatives 4
quinolin-1(3H)-one (4ad)
The mixture of tetronic acid 1 (1.0 mmol), aldehyde 2 (1.0
mmol), and aniline 3 (1.0 mmol) in 2 mL of EtOH was
irradiated at a power of 200 W in an open vessel in a
microwave reactor (reflux temperature of the solvent). The
reaction was monitored using TLC every 3 min and after 15
min the reaction was cooled, the solvent was removed under
vacuum and the solid obtained was washed with hexane-
acetate (8:2).
Yellow solid, yield 81%, mp > 300 °C. 1H NMR (400 MHz,
DMSO-d6): δ (p.p.m.) 9.99 (s, 1H, NH), 7.31 (d, 2H, J =
8.4 Hz), 7.13 (d, 2H, J = 8.4 Hz), 6.39 (s, 1H), 4.96 (s, 1H),
4.90 (d, 1H, J = 15.7 Hz), 4.81 (d, 1H, J = 15.7 Hz), 3.79
(s, 3H), 3.63 (s, 3H), 3.38 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 171.86, 157.79, 152.97, 151.66,
145.76, 137.46, 132.97, 130.46, 129.34, 127.91, 109.47,
95.51, 95.37, 64.92, 60.30, 59.94, 55.63, 34.95. HRMS
(ESI+): m/z [M + Na]+ calculated for C20H18ClNO5Na:
410.0764; found: 410.0755.
9-(benzo[d][1,3]dioxol-5-yl)-6,7,8-trimethoxy-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4aa)
9-(4-(benzyloxy)-3-methoxyphenyl)-6,7,8-trimethoxy-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4ae)
1
Yellow solid, yield 92%, mp 271–273 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.93 (s, 1H, NH), 6.77 (d, 1H,
J = 7.9 Hz), 6.63 (d, 1H, J = 1.7 Hz), 6.54 (dd, 1H, J = 7.9
and 1.7 Hz), 6.38 (s, 1H), 5.94 (d, 1H, J = 0.9 Hz), 5.93 (d,
1H,, J = 0.9 Hz), 4.90 (d, 1H, J = 15.7 Hz), 4.88 (s, 1H),
4.79 (d, 1H, J = 15.7 Hz), 3.79 (s, 3H), 3.64 (s, 3H), 3.42 (s,
3H). 13C NMR (100 MHz, DMSO-d6): δ (p.p.m.) 171.94,
157.59, 152.77, 151.66, 146.84, 145.27, 141.11, 137.47,
132.99, 120.37, 110.05, 108.00, 107.69, 95.92, 95.48,
64.84, 60.31, 60.013, 55.64, 34.92.
1
White solid, yield 85%, mp > 300 °C. H NMR (400 MHz,
DMSO-d6): δ (p.p.m.) 9.89 (s, 1H, NH), 7.43–7.28 (m, 5H),
6.88 (d, 1H, J = 8.3 Hz), 6.83 (d, 1H, J = 2.0 Hz), 6.49 (dd,
1H, J = 8.3 and 2.0 Hz), 6.38 (s, 1H), 5.00 (s, 1H), 4.89 (d,
1H, J = 16.0 Hz), 4.79 (s, 1H, J = 16.0 Hz), 3.79 (s, 3H),
3.71 (s, 3H, 3.64 (s, 3H), 3.38 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 172.03, 157.55, 152.70, 151.69,
148.53, 146.01, 140.18, 137.48, 137.23, 133.06, 128.31,
127.70, 119.38, 113.56, 112.01, 110.07, 96.03, 95.47,
69.97, 64.81, 60.30, 59.94, 55.65, 55.53, 34.78. HRMS
(ESI+): m/z [M + H]+ calculated for C28H28NO7: 490.1857;
found: 490.1849.
9-(3,4-dimethoxyphenyl)-6,7,8-trimethoxy-4,9-dihydrofuro
[3,4-b]quinolin-1(3H)-one (4ab)
White solid, yield 91%, mp 258–260 °C. 1H NMR
(400 MHz, DMSO-d6): δ (p.p.m.) 9.89 (s, 1H, NH),
6.80 (d, 1H, J = 8.2 Hz), 6.80 (d, 1H, J = 1.8 Hz), 6.51
(dd, 1H, J = 1.8 and 8.2 Hz), 6.38 (s, 1H), 4.90 (s, 1H),
4.88 (d, 1H, J = 15.7 Hz), 4.78 (d, 1H, J = 15.7 Hz),
3.78 (s, 3H), 3.68 (s, 3H), 3.67 (s, 3H), 3.63 (s, 3H),
9-(4-fluorophenyl)-6,7,8-trimethoxy-4,9-dihydrofuro[3,4-b]
quinolin-1(3H)-one (4af)
1
White solid, yield 82%, mp > 300 °C. H NMR (400 MHz,
DMSO-d6): δ (p.p.m.) 9.96 (s, 1H, NH), 7.17–7.11 (m, 2H),
7.10–7.03 (m, 2H), 6.39 (s, 1H), 4.96 (s, 1H), 4.89 (d, 1H,
J = 15.7 Hz), 4.81 (d, 1H, J = 15.7 Hz), 3.79 (s, 3H), 3.63
(s, 3H), 3.36 (s, 3H). 13C NMR (100 MHz, DMSO-d6): δ (p.
p.m.) 171.93, 161.69, 159.28, 157.70, 152.89, 151.66,
143.11, 143.08, 137.49, 132.95, 129.26, 129.18, 114.71,
114.50, 109.82, 95.67, 95.51, 64.89, 60.29, 59.91, 55.65,
34.71. HRMS (ESI+): m/z [M + H]+ calculated for
C20H19FNO5: 372.1241; found: 372.1244.
3.39 (s, 3H). 13C NMR (100 MHz, DMSO-d6):
δ
(p.p.m.) 172.12, 157.58, 152.70, 151.67, 148.10, 147.08,
139.68, 137.52, 133.02, 119.42, 111.76, 111.66, 10.13,
99.11, 95.53, 64.87, 64.83, 60.32, 59.98, 55.69, 55.46,
34.70.
6,7,8-trimethoxy-9-(3,4,5-trimethoxyphenyl)-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4ac)
1
Yellow solid, yield 89%, mp 229–231 °C. H NMR (400
6,7,8-trimethoxy-9-(4-(methylthio)phenyl)-4,9-dihydrofuro
MHz, DMSO-d6): δ (p.p.m.) 9.91 (s, 1H, NH), 6.40 (s, 3H),
4.97 (s, 1H), 4.92 (d, 1H, J = 15.6 Hz), 4.79 (d, 1H, J =
15.6 Hz), 3.80 (s, 3H), 3.67 (s, 3H), 3.65 (s, 3H), 3.60 (s,
3H), 3.47 (s, 3H), 3.46 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 172.06, 157.87, 152.78, 152.40,
151.73, 142.48, 136.45, 135.88, 133.15, 109.53, 104.85,
95.72, 95.50, 64.83, 60.32, 60.02, 59.91, 55.74, 55.66,
35.33.
[3,4-b]quinolin-1(3H)-one (4ag)
1
White solid, yield 81%, mp 221–223 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.94 (s, 1H, NH), 7.14 (d, 2H,
J = 8.4 Hz), 7.06 (d, 2H, J = 8.4 Hz), 6.39 (s, 1H), 4.91 (s,
1H), 4.89 (d, 1H, J = 15.8 Hz), 4.80 (d, 1H, J = 15.8 Hz),
3.79 (s, 3H), 3.63 (s, 3H), 3.39 (s, 3H), 2.41 (s, 3H). 13C
NMR (100 MHz, DMSO-d6): δ (p.p.m.) 171.91, 157.64,

Medicinal Chemistry Research
152.81, 151.67, 143.76, 137.46, 135.24, 133.02, 128.09,
125.75, 109.88, 95.75, 95.49, 64.86, 60.30, 59.96, 55.64,
34.87, 14.81. HRMS (ESI+): m/z [M + H]+ calculated for
C21H22SNO5: 400.1211; found: 400.1182.
OH), 7.01 (t, 1H, J = 7.6 Hz), 6.56 (d, 1H, J = 7.6 Hz),
6.54–6.48 (m, 2H), 6.38 (s, 1H), 4.88 (d, 1H, J = 15.7 Hz),
4.86 (s, 1H), 4.79 (d, 1H, J = 15.7 Hz), 3.79 (s, 3H), 3.64 (s,
3H), 3.37 (s, 3H). 13C NMR (100 MHz, DMSO-d6): δ (p.p.
m.) 171.88, 157.58, 156.98, 152.72, 151.70, 148.25,
137.53, 133.13, 128.71, 118.31, 114.56, 112.95, 110.14,
96.00, 95.52, 64.79, 60.30, 59.88, 55.68, 35.22. HRMS
(ESI+): m/z [M + H]+ calculated for C20H20NO6: 370.1284;
found: 370.1286.
6,7,8-trimethoxy-9-(4-(trifluoromethyl)phenyl)-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4ah)
1
White solid, yield 84%, mp > 300 °C. H NMR (400 MHz,
DMSO-d6): δ (p.p.m.) 10.05 (s, 1H, NH), 7.63 (d, 1H, J =
8.2 Hz), 7.34 (d, 1H, J = 8.2 Hz), 6.41 (s, 1H), 5.07 (s, 1H),
4.91 (d, 1H, J = 15.8 Hz), 4.83 (d, 1H, J = 15.8 Hz), 3.80
(s, 3H), 3.62 (s, 3H), 3.77 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 171.82, 157.99, 153.12, 151.65,
151.13, 137.46, 133.01, 128.31, 124.96, 124.93, 109.07,
95.57, 95.02, 64.98, 60.31, 59.89, 55.67, 35.54. HRMS
(ESI+): m/z [M + H]+ calculated for C21H19F3NO5:
422.1209; found: 422.1208.
6,7,8-trimethoxy-9-(3-methoxyphenyl)-4,9-dihydrofuro[3,4-
b]quinolin-1(3H)-one (4al)
1
White solid, yield 92.0%, mp 231–233 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.93 (s, 1H, NH), 7.15 (t, 1H,
J = 8.2 Hz), 6.73–6.69 (m, 1H), 6.67 (brd, 1H, J = 1.4 Hz),
6.68–6.65 (m, 2H), 6.39 (s, 1H), 4.93 (s, 1H), 4.89 (d, 1H,
J = 15.8 Hz), 4.79 (d, 1H, J = 15.8 Hz), 3.79 (s, 3H), 3.69
(s, 3H), 3.36 (s, 3H), 3.38 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 171.89, 158.92, 157.73, 152.80,
151.67, 148.35, 137.50, 133.12, 128.95, 119.82, 113.85,
110.67, 109.84, 95.81, 95.54, 64.83, 60.31, 59.91, 55.68,
54.83, 35.26. HRMS (ESI+): m/z [M + H]+ calculated for
C21H22NO6: 384.1440; found: 384.1441.
9-(4,5-dimethoxy-2-nitrophenyl)-6,7,8-trimethoxy-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4ai)
1
Yellow solid, yield 76%, mp 284–286 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.99 (s, 1H, NH), 7.45 (s, 1H),
6.57 (s, 1H), 6.37 (s, 1H), 6.00 (s, 1H), 4.92 (d, 1H, J = 15.8
Hz), 4.83 (d, 1H, J = 15.8 Hz), 3.81 (s, 3H), 3.78 (s, 3H),
3.65 (s, 3H), 3.60 (s, 3H), 3.40 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 171.50, 158.33, 153.13, 152.42,
151.63, 146.65, 140.13, 137.32, 135.28, 132.87, 112.495,
109.25, 107.24, 95.63, 94.65, 64.96, 60.34, 59.91, 55.92,
55.72, 55.68, 30.00. HRMS (ESI+): m/z [M+H–H2O]+
calculated for C22H21N2O8: 441.1290; found: 441,1283
9-(3,4-dihydroxyphenyl)-6,7,8-trimethoxy-4,9-dihydrofuro
[3,4-b]quinolin-1(3H)-one (4am)
1
White solid, yield 83%, mp 272–274 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.84 (s, 1H, NH), 8.70 (s, 1H,
OH), 8.59 (s, 1H, OH), 6.57 (d, 1H, J = 8.0 Hz), 6.50 (d,
1H, J = 2.1 Hz), 6.38 (dd, 1H, J = 8,0 and 2.1 Hz), 6.36 (s,
1H), 4.86 (d, 1H, J = 15.8 Hz), 4.77 (d, 1H, J = 15.8 Hz),
4.77 (s, 1H), 3.78 (s, 3H), 3.64 (s, 3H). 13C NMR (100
MHz, DMSO-d6): δ (p.p.m.) 171.97, 157.24, 152.53,
151.72, 144.58, 143.38, 138.27, 137.54, 133.04, 118.25,
115.11, 114.91, 110.72, 96.48, 95.47, 64.72, 60.28, 59.94,
55.67, 34.48. HRMS (ESI+): m/z [M + H]+ calculated for
C20H20NO7: 386.1233; found: 386.1221.
9-(4-hydroxy-3-methoxyphenyl)-6,7,8-trimethoxy-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4aj)
1
White solid, yield 80%, mp 216–218 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.86 (s, 1H, NH), 8.72 (brs,
1H, OH), 6.77 (d, 1H, J = 1.9 Hz), 6.62 (d, 1H, J = 8.1 Hz),
6.41 (dd, 1H, J = 8.1 and 1.9 Hz), 6.37 (s, 1H), 4.89 (d, 1H,
J = 15.7 Hz), 4.87 (s, 1H), 4.78 (d, 1H, J = 15.7 Hz), 3.79
(s, 3H), 3.70 (s, 3H), 3.64 (s, 3H), 3.39 (s, 3H). 13C NMR
(100 MHz, DMSO-d6): δ (p.p.m.) 172.06, 157.44, 152.61,
151.70, 146.90, 144.71, 138.25, 137.50, 133.05, 119.75,
115.09, 112.12, 110.39, 96.29, 95.48, 64.78, .28, 59.95,
55.66, 55.63, 34.67. HRMS (ESI+): m/z [M + Na]+ cal-
culated for C21H21NO7Na: 422.1208; found: 422.1212.
6,7,8-trimethoxy-9-(6-nitrobenzo[d][1,3]dioxol-5-yl)-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4an)
1
Orange solid, yield 70%, mp 265–266 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 10.03 (s, 1H, NH), 7.48 (s,
1H), 6.57 (s, 1H), 6.37 (s, 1H), 6.12 (d, 2H, J = 4.7 Hz),
5.94 (s, 1H), 4.93 (d, 1H, J = 15.7), 4.83 (d, 1H, J = 15.7),
3.79 (s, 3H), 3.61 (s, 3H), 3.44 (s, 3H). 13C NMR (100
MHz, DMSO-d6): δ (p.p.m.) 171.35, 158.42, 153.24,
151.58, 151.21, 145.75, 141.38, 137.74, 137.28, 132.76,
109.18, 109.18, 104.17, 103.00, 95.71, 94.48, 65.00, 60.35,
59.92, 30.11. HRMS (ESI+): m/z [M+H-H2O]+ calculated
for C21H17N2O8: 425.0977: found: 425.0953.
9-(3-hydroxyphenyl)-6,7,8-trimethoxy-4,9-dihydrofuro[3,4-
b]quinolin-1(3H)-one (4ak)
1
White solid, yield 81%, mp 263–265 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.90 (s, 1H, NH), 9.19 (s, 1H,

Medicinal Chemistry Research
9-(benzo[d][1,3]dioxol-5-yl)-6,9-dihydro-[1,3]dioxolo[4,5-g]
9-(4-(benzyloxy)-3-methoxyphenyl)- 6,9-dihydro-[1,3]
furo[3,4-b]quinolin-8(5H)-one (4ba)
dioxolo[4,5-g]furo[3,4-b]quinolin-8(5H)-one (4be)
1
1
White solid, yield 86%, mp 288–289 °C. H NMR (400
White solid, yield 84%, mp > 300 °C. H NMR (400 MHz,
MHz, DMSO-d6): δ (p.p.m.) 9.87 (s, 1H, NH), 6.78 (d, 1H,
J = 8.0 Hz), 6.73 (s, 1H), 6.65 (d, 1H, J = 8.0 Hz), 5.95
(brs, 1H), 5.94 (brs, 1H), 5.93 (brs, 1H), 5.89 (brs, 1H), 4.94
(d, 1H, J = 15.76 Hz), 4.83 (d, 1H, J = 15.7 Hz), 4.83 (s,
1H) 13C NMR (100 MHz, DMSO-d6): δ (p.p.m.) 172.56,
158.70, 147.82, 147.00, 146.17, 143.80, 141.75, 130.94,
120.92, 117.27, 110.03, 108.51, 108.40, 101.68, 101.29,
97.79, 94.94, 65.43, 40.09.
DMSO-d6): δ (p.p.m.) 9.85 (s, 1H, NH), 7.45–7.29 (m, 5H),
6.92 (d, 1H, J = 1.9 Hz), 6.90 (d, 1H, J = 8.4 Hz), 6.63 (s,
1H), 6.59 (dd, 1H, J = 8.4 and 1.9 Hz), 6.52 (s, 1H), 5.96
(brs, 1H), 5.90 (brs, 1H), 5.01 (s, 2H), 4.96 (d, 1H, J = 15.7
Hz), 4.85 (d, 1H, J = 15.7 Hz), 4.86 (s, 1H). 13C NMR (100
MHz, DMSO-d6): δ (p.p.m.) 172.12, 158.16, 148.76,
146.36, 146,29, 143.18, 140.17, 137.26, 130.31, 128.36,
127.75, 127.66, 119.36, 116.82, 113.52, 111.73, 109.58,
101.11, 97.20, 94.38, 69.908, 64.86, 55.53, 39.11. HRMS
(ESI+): m/z [M + H]+ calculated for C26H22NO6: 444.1440;
found: 444.1444.
9-(3,4-dimethoxyphenyl)-6,9-dihydro-[1,3]dioxolo[4,5-g]
furo[3,4-b]quinolin-8(5H)-one (4bb)
1
White solid, yield 86%, mp 289–291 °C. H NMR (400
9-(4-fluorphenyl)-6,9-dihydro-[1,3]dioxolo[4,5-g]furo[3,4-b]
quinolin-8(5H)-one (4bf)
MHz, DMSO-d6): δ (p.p.m.) 9.84 (s, 1H, NH), 6.88
(s, 1H), 6.82 (d, 1H, J = 8.5 Hz), 6.62 (brd, 1H), 6.62
(s, 1H), 6.52 (s, 1H), 5.91 (brs, 1H), 5.90 (brs, 1H), 4.96
(d, 1H, J = 15.7 Hz), 4.85 (s, 1H), 4,84 (d, 1H, J = 15.7
Hz), 3.71 (s, 3H), 3.69 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 172.11, 158.12, 148.44, 147.25,
146.34, 143.16, 139,78, 130.30, 119.41, 116.88, 111.86,
111.47, 109,58, 101.10, 97.19, 94.41, 64.85, 55.47, 55.44,
39.10.
1
White solid, yield 81%, mp > 300 °C. H NMR (400 MHz,
DMSO-d6): δ (p.p.m.) 9.90 (s, 1H, NH), 7.24–7.19 (m, 2H),
7.11–7.04 (m, 2H), 6.56 (s, 1H), 6.53 (s, 1H), 5.95 (brs,
1H), 5.90 (brs, 1H), 4.95 (s, 1H), 4.94 (d, 1H, J = 15.6 Hz),
4.85 (d, 1H, J = 15.6 Hz). 13C NMR (100 MHz, DMSO-d6):
δ (p.p.m.) 171.99, 158.24, 146.55, 143.33, 143.08, 143.05,
130.49, 129.29, 129.21, 116.35, 115.04, 114.83, 109.54,
101.19, 97.31, 94.23, 64.93, 38.81. HRMS (ESI+): m/z [M
+ H]+ calculated for C18H13FNO4: 326.0824; found:
326.0828.
9-(3,4,5-triimethoxy)-6,9-dihydro-[1,3]dioxolo[4,5-g]furo
[3,4-b]quinolin-8(5H)-one (4bc)
1
White solid, yield 90%, mp 271–274 °C. H NMR (400
9-(4-(methylthio)phenyl)-6,9-dihydro-[1,3]dioxolo[4,5-g]
MHz, DMSO-d6): δ (p.p.m.) 9.86 (s, 1H, NH), 6.67 (s, 1H),
6.53 (s, 1H), 6.48 (s, 2H), 5.95 (d, 1H, J = 0.7 Hz), 5.90 (d,
1H, J = 0.7 Hz), 4.98 (s, 1H, J = 15.7 Hz), 4.85 (s, 1H),
4.84 (d, 1H, J = 15.7 Hz), 3.70 (s, 6H), 3.60 (s, 3H). 13C
NMR (100 MHz, DMSO-d6): δ (p.p.m.) 172.18, 158.41,
152.74, 146.44, 143.22, 142.68, 136.04, 130.25, 116.50,
109.49, 104.82, 101.24, 101.14, 97.28, 94.14, 64.92, 59.86,
55.82, 39.76.
furo[3,4-b]quinolin-8(5H)-one (4bg)
1
White solid, yield 81%, mp 277–280 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.89 (s, 1H, NH), 7.18–7.12
(m, 4H), 6.56 (s, 1H), 6.53 (s, 1H), 5.96 (brs, 1H), 5.90
(brs, 1H), 4.94 (d, 1H, J = 15.6 Hz), 4.89 (s, 1H), 4.85 (d,
1H, J = 15.6 Hz), 2.43 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 172.02, 158.22, 146.47, 143.75,
143.27, 135.71, 130.42, 128.08, 126.08, 116.48, 109.56,
101.16, 97.27, 94.18, 64.91. HRMS (ESI+): m/z [M + K +
H2O − 2H]+ calculated for C19H16NO5S: 408.0307; found:
408.0324.
9-(4-chlorophenyl)-6,9-dihydro-[1,3]dioxolo[4,5-g]furo[3,4-
b]quinolin-8(5H)-one (4bd)
White solid, yield 80%, mp 290–292 °C. 1H NMR
(400 MHz, DMSO-d6): δ (p.p.m.) 9.93 (s, 1H, NH), 7.33
(d, 2H, J = 8.4 Hz), 7.22 (d, 2H, J = 8.4 Hz), 6.58
(s, 1H), 6.54 (s, 1H), 5.97 (brs, 1H), 5.91 (brs, 1H), 4.96
(s, 1H), 4.96 (d, 1H, J = 15.7 Hz), 4.86 (d, 1H, J = 15.7
Hz). 13C NMR (100 MHz, DMSO-d6): δ (p.p.m.) 171.98,
158.37, 146.61, 145.72, 143.36, 130.90, 130.48, 129.34,
128.24, 116.05, 109.53, 101.22, 97.35, 93.92, 64.97,
38.95.
9-(4-(trifluoromethyl)phenyl)-6,9-dihydro-[1,3]dioxolo[4,5-
g]furo[3,4-b]quinolin-8(5H)-one (4bh)
White solid, yield 88%, mp > 300 °C. 1H NMR (400 MHz,
DMSO-d6): δ (p.p.m.) 9.98 (s, 1H, NH), 7.64 (d, 2H, J =
8.2 Hz), 7.43 (d, 2H, J = 8.2 Hz), 6.58 (s, 1H), 6.57 (s, 1H),
5.97 (brs, 1H), 5.91 (brs, 1H), 5.08 (s, 1H), 4.96 (d, 1H, J
= 15.7 Hz), 4.88 (d, 1H, J = 15.7 Hz). 13C NMR (100

Medicinal Chemistry Research
MHz, DMSO-d6): δ (p.p.m.) 171.95, 158.54, 146.75,
143.45, 130.57, 128.35, 125.29, 125.26, 115.53, 109.54,
101.27, 97.45, 93.70, 65.05, 39.47. HRMS (ESI+): m/z [M
+ Na]+ calculated for C19H13F3NO4Na: 398.0611; found:
398.0609.
9-(benzo[d][1,3]dioxol-5-yl)-6,7-dimethoxy-4,9-dihydrofuro
[3,4-b]quinolin-1(3H)-one (4ca)
1
White solid, yield 91%, mp 287–289 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.85 (s, 1H, NH), 6.79 (d, 1H,
J = 7.9 Hz), 6.73 (d, 1H, J = 1.6 Hz), 6.66 (dd, 1H, J = 7.9
and 1.6 Hz), 6.62 (s, 1H), 6.51 (s, 1H), 5.95 (brs, 1H), 5.94
(brs, 1H), 4.95 (d, 1H, J = 15.5 Hz), 4.87 (s, 1H), 4.84 (d,
1H, J = 15.5 Hz), 3.73 (s, 3H), 3.60 (s, 3H). 13C NMR (100
MHz, DMSO-d6): δ (p.p.m.) 172.15, 158.20, 148.16,
147.19, 145.51, 144.92, 141.15, 129.63, 120.35, 115.44,
113.71, 107.97, 107.85, 100.72, 100.34, 99.46, 64.92,
55.84, 55.43, 38.86.
9-(4,5-dimethoxy-2-nitrophenyl)-6,9-dihydro-[1,3]dioxolo
[4,5-g]furo[3,4-b]quinolin-8(5H)-one (4bi)
1
Yellow solid, yield 69%, mp 243–244 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.96 (s, 1H, NH), 7.43
(s, 1H), 6.71 (s, 1H), 6.57 (s, 1H), 5.97 (brs, 1H), 5.94
(brs, 1H), 5.69 (s, 1H), 4.93 (d, 1H, J = 15.6 Hz), 4,84
(d, 1H, J = 15.6 Hz), 3.83 (s, 3H), 3.71 (s, 3H). 13C NMR
(100 MHz, DMSO-d6): δ (p.p.m.) 171.65, 158.39, 152.68,
147.14, 146.87, 143.56, 140.69, 134.45, 130.86,
115.11, 112.95, 108.86, 107,10, 101.34, 97.63, 93.76,
64.99, 56.01, 55.89, 34.32. HRMS (ESI+): m/z [M + H −
H2O]+ calculated for C20H15N2O7: 395.0872; found:
395.0869.
9-(3,4-dimethoxyphenyl)-6,7-dimethoxy-4,9-dihydrofuro
[3,4-b]quinolin-1(3H)-one (4cb)
1
Yellow solid, yield 90%, mp 228–230 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.82 (s, 1H, NH), 6.89 (d, 1H,
J = 1.9 Hz), 6.1 (d, 1H, J = 8.6 Hz), 6.66 (s, 1H), 6.60 (dd,
1H, J = 8.3 and 1.9 Hz), 6.56 (s, 1H), 4.95 (d, 1H, J = 15.6
Hz), 4.88 (s, 1H), 4.84 (d, 1H, J = 15.6 Hz), 3.73 (s, 3H),
3.71 (s, 3H), 3.69 (s, 3H), 3.60 (s, 3H). 13C NMR (100
MHz, DMSO-d6): δ (p.p.m.) 172.22, 158.18, 148.40,
148.07, 147.16, 144.85, 139.59, 29.62, 119.35, 115.56,
113.78, 111.71, 111.49, 100.29, 94.48, 64.88, 55.83, 55.44,
55.42, 38.74.
9-(4-hydroxy-3-methoxyphenyl)-6,9-dihydro-[1,3]dioxolo
[4,5-g]furo[3,4-b]quinolin-8(5H)-one (4bj)
1
White solid, yield 81%, mp 279–281 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.80 (s, 1H, NH), 8.76 (s, 1H,
OH), 6.84 (d, 1H, J = 1.8 Hz), 6.64 (d, 1H, J = 8.0 Hz),
6.61 (s, 1H), 6.51 (s, 1H), 6.49 (dd, 1H, J = 1.8 and 8.0
Hz), 5.95 (brs, 1H), 5.90 (brs, 1H), 4.94 (d, 1H, J = 15.6
Hz), 4.83 (d, 1H, J = 15.6 Hz), 4.79 (s, 1H), 3.3 (s, 3H).
13C NMR (100 MHz, DMSO-d6): δ (p.p.m.) 172.12,
158.02, 147.24, 146.28, 144.97, 143.14, 38.31, 130.30,
119.72, 117.14, 115.33, 111.89, 109.57, 101.06,
97.15, 94.61, 64.81, 55.63, 39.12. HRMS (ESI+): m/z [M
+ Na]+ calculated for C19H15NO6Na: 376.0791; found
376.0792
6,7-dimethoxy-9-(3,4,5-trimethoxyphenyl)-4,9-dihydrofuro
[3,4-b]quinolin-1(3H)-one (4cc)
1
White solid, yield 92%, mp 236–238 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.83 (s, 1H, NH), 6.85 (s, 1H),
6.73 (s, 1H), 6.52 (s, 1H), 6.50 (s, 1H), 5.00 (d, 1H, J =
15.5 Hz), 4.89 (s, 1H), 4.85 (d, 1H, J = 15.5 Hz), 3.73 (s,
3H), 3.70 (s, 3H), 3.62 (s, 3H), 3.61 (s, 3H). 13C NMR (100
MHz, DMSO-d6): δ (p.p.m.) 17.22, 158.51, 15.70, 148.20,
144.87, 142.49, 135.95, 129.63, 115.17, 113.83, 107.62,
104.78, 100.78, 94.11, 64.94, 59.85, 56.08, 55.99, 55.93,
55.8, 55.45, 18.52.
9-(6-nitrobenzo[d][1,3]dioxol-5-yl)-6,9-dihydro-[1,3]dioxolo
[4,5-g]furo[3,4-b]quinolin-8(5H)-one (4bn)
1
Yellow solid, yield 71%, mp 225–227 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 10.00 (s, 1H, NH), 7.47 (s,
1H), 6.71 (s, 1H), 6.58 (s, 2H), 6.16 (d, 1H, J = 0.8 Hz),
6.14 (d, 1H, J = 0.8 Hz), 5.98 (d, 1H, J = 0.7 Hz), 5.94 (d,
1H, J = 0.7 Hz), 5.62 (s, 1H), 4.92 (d, 1H, J = 15.5 Hz),
4.85 (d, 1H, J = 15.5 Hz). 13C NMR (100 MHz, DMSO-d6):
δ (p.p.m.) 171.62, 158.38, 151.50, 147.00, 146.18, 143.66,
141.87, 136.94, 130.84, 114.89, 109.64, 108.85, 103.84,
103.16, 101.39, 97.68, 93.72, 68.08, 34.15. HRMS (ESI+):
m/z [M + H − H2O]+ calculated for C19H11N2O7:
379.0560; found: 379.0558
9-(4-chlorophenyl)-6,7-dimethoxy-4,9-dihydrofuro[3,4-b]
quinolin-1(3H)-one (4 cd)
1
White solid, yield 81%, mp 265–267 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.88 (s, 1H, NH), 7.31 (d, 2H,
J = 8.4 Hz), 7.21 (d, 2H, J = 8.4 Hz), 6.58 (s, 1H), 6.52 (s,
1H), 4.97 (s, 1H), 4.94 (d, 1H, J = 15.7 Hz), 4.85 (d, 1H, J
= 15.7 Hz), 3.73 (s, 3H), 3.57 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 172.04, 158.34, 148.37, 145.63,
145.08, 130.78, 129.79, 129.35, 128.18, 114.78, 113.83,

Medicinal Chemistry Research
100.52, 94.09, 64.99, 55.89, 55.48, 38.66. HRMS (ESI+):
m/z [M + Na]+ calculated for C19H17ClNO4Na: 380.0659:
found: 380.0661.
J = 8.1 Hz), 7.43 (d, 2H, J = 8.1 Hz), 6.60 (s, 1H), 6.56 (s,
1H), 5.10 (s, 1H), 4.97 (d, 1H, J = 15.7 Hz), 4.87 (d, 1H, J
= 15.7 Hz), 3.75 (s, 3H), 3.58 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 172.02, 158.53, 150.96, 148.49,
145.16, 130.67, 129.88, 128.33, 125.21, 125.18, 114.30,
113.83, 100.61, 93.85, 65.07, 55.88, 55.48, 39.15. HRMS
(ESI+): m/z [M + H]+ calculated for C20H17F3NO4:
392.1104; found: 392.1105.
9-(4-(benzyloxy)-3-methoxyphenyl)-6,7-dimethoxy-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4ce)
1
White solid, yield 92%, mp 232–234 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.80 (s, 1H, NH), 7.44–7.28
(m, 5H), 6.92 (d, 1H, J = 1.9 Hz), 6.89 (d, 1H, J = 8.3 Hz),
6.66 (s, 1H), 6.56 (dd, 1H, J = 8.3 and 1.9 Hz), 6.50 (s, 1H),
4.99 (s, 1H), 4.94 (d, 1H, J = 15.6 Hz), 4.87 (s, 1H), 4.83
(d, 1H, J = 15.6 Hz). 13C NMR (100 MHz, DMSO-d6): δ (p.
p.m.) 172.95, 158.19, 148.81, 148.16, 146.27, 144.92,
140.02, 137.27, 129.70, 128.34, 127.73, 127.68, 119.36,
115.56, 113.93, 113.56, 111.89, 100.41, 94.50, 69.98,
64.89, 55.91, 55.61, 55.48, 38.76. HRMS (ESI+): m/z [M
+ Na]+ calculated for C27H25NO6Na: 482.1571; found:
482.1578.
9-(4,5-dimethoxy-2-nitrophenyl)-6,7-dimethoxy-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4ci)
1
Yellow solid, yield 77%, mp 249–251 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.94 (s, 1H, NH), 7.45
(s, 1H), 6.68 (s, 1H), 6.65 (s, 1H), 6.57 (s, 1H), 5.73 (s,
1H), 4.95 (d, 1H, J = 15.6 Hz), 4.85 (d, 1H, J = 15.6 Hz),
3.83 (s, 3H), 3.76 (s, 3H), 3.70 (s, 3H), 3.57 (s, 3H). 13C
NMR (100 MHz, DMSO-d6): δ (p.p.m.) 171.77, 158.48,
152.61, 148.53, 147.01, 145.11, 140.69, 134.52, 130.04,
113.93, 112.98, 112.75, 107.00, 100.63, 93.87, 65.04,
55.95, 55.83, 55.69, 55.42, 33.81. HRMS (ESI+): m/z
[M + H]+ calculated for C21H21N2O8: 429.1290: found:
429.1297.
9-(4-fluorophenyl)-6,7-dimethoxy-4,9-dihydrofuro[3,4-b]
quinolin-1(3H)-one (4cf)
1
White solid, yield 79%, mp 257–258 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.87 (s, 1H, NH), 7.24–7.20
(m, 2H), 7.11–7.06 (m, 2H), 6.59 (s, 1H), 6.53 (s, 1H), 4.98
(s, 1H), 4.94 (d, 1H, J = 15.6 Hz), 4.85 (d, 1H, J = 15.6
Hz), 3.73 (s, 3H), 3.58 (s, 3H). 13C NMR (100 MHz,
DMSO-d6): δ (p.p.m.) 172.08, 158.24, 1478.31, 145.05,
14.98, 142.95, 129.79, 129.28, 129.20, 115.98, 114.98,
114.77, 113.90, 100.50, 94.35, 64.95, 55.90, 55.49, 38.50.
HRMS (ESI+): m/z [M + H]+ calculated for C19H17FNO4:
342.1136; found: 342.1133.
9-(3,4-dihydroxyphenyl)-6,7-dimethoxy-4,9-dihydrofuro
[3,4-b]quinolin-1(3H)-one (4 cm)
1
White solid, yield 80%, mp 244–246 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.75 (s, 1H, NH), 8.70 (s, 1H,
OH), 8.64 (s, 1H, OH), 6.58 (d, 1H, J = 8.0 HZ), 6.55
(s, 1H), 6.50 (d, 1H, J = 2.0 Hz), 6.49 (s, 1H), 6.46 (dd,
1H, J = 8.0 and 2.0 Hz), 4.89 (d, 1H, J = 15.7 Hz), 4.81
(d, 1H, J = 15.7 Hz), 4.71 (s, 1H), 3.72 (s, 3H), 3.58 (s,
3H). 13C NMR (100 MHz, DMSO-d6): δ (p.p.m.) 172.14,
157.76, 148.06, 144.92, 144.89, 143.63, 138.27, 129.70,
118.19, 116.06, 115.10, 115.03, 113.95, 100.35, 94.98,
64.73, 55.87, 55.49, 38.67. HRMS (ESI+): m/z [M + H +
K]+ calculated for C19H18NO6K: 395.0765; found:
395.0761
6,7,8-trimethoxy-9-(4-(methylthio)phenyl)-4,9-dihydrofuro
[3,4-b]quinolin-1(3H)-one (4cg)
1
White solid, yield 81%, mp 286–287 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.85 (s, 1H, NH), 7.17–7.12
(m, 4H), 6.58 (s, 1H), 6.52 (s, 1H), 4.93 (d, 1H, J = 15.7
Hz), 4.91 (s, 1H), 4.84 (d, 1H, J = 15.7 Hz), 3.73 (s, 3H),
3.58 (s, 3H), 2.42 (s, 3H). 13C NMR (100 MHz, DMSO-d6):
δ (p.p.m.) 172.13, 158.22, 148.25, 145.01, 143.65, 135.55,
129.74, 128.08, 126.03, 115.25, 113.86, 100.47, 94.37,
64.94, 55.89, 55.44, 55.49, 38.74, 14.78. HRMS (ESI+): m/
z [M + H]+ calculated for C20H20NO4S: 370.1106; found:
370.1109.
6,7-dimethoxy-9-(6-nitrobenzo[d][1,3]dioxol-5-yl)-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4cn)
1
Yellow solid, yield 70%, mp 245–246 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.98 (s, 1H, NH), 6.67 (s, 1H),
6.65 (s, 1H), 6.56 (s, 1H), 6.15 (s, 1H), 6.14 (s, 1H), 5.64 (s,
1H), 4.94 (d, 1H, J = 15.6 Hz), 4.87 (d, 1H, J = 15.6 Hz),
3.75 (s, 3H), 3.58(s, 3H). 13C NMR (100 MHz, DMSO-d6):
δ (p.p.m.) 171.74, 158.50, 141.45, 148.63, 146.08, 145.21,
141.84, 137.00, 129.97, 113.75, 112.95, 109.53, 103.88,
103.14, 100.71, 93.78, 65.13, 55.69, 55.45, 33.73. HRMS
(ESI+): m/z [M + H − H2O]+ calculated for C20H15N2O7:
395.0878; found: 395.0872.
6,7-dimethoxy-9-(4-(trifluoromethyl)phenyl)-4,9-
dihydrofuro[3,4-b]quinolin-1(3H)-one (4ch)
1
White solid, yield 82%, mp 255–256 °C. H NMR (400
MHz, DMSO-d6): δ (p.p.m.) 9.95 (s, 1H, NH), 7.64 (d, 2H,

Medicinal Chemistry Research
Biological activity
to 200 μg/mL for the bacteria and from 31.5 to 2000 μg/mL
for Mycobacterium. Microplates (96 wells) were incubated
at 37 °C for 24 h. Thereafter, 30 μL of aqueous resazurin
solution (0.01%) was added to indicate the viability of the
microorganisms. The MIC was determined as the lowest
concentration of the compound capable of inhibiting the
growth of the microorganism. Chlorhexidine was used as
the reference antibiotic at concentrations of 0.115–59.0 μg/
mL in the bioassays for bacteria and isoniazid at con-
centrations of 0.015–1.0 μg/mL for Mycobacterium. Mid-
dlebrook 7H9 broth containing 0.2% DMSO was used as a
negative control.
The antibacterial activity of the derivatives 4 was assessed
against Porphyromonas gingivalis (ATCC 33277), Pre-
votella nigrescens (ATCC 33563), Streptococcus mitis
(ATCC 49456), Streptococcus sanguinis (ATCC 10556),
Mycobacterium tuberculosis (ATCC 27294), Mycobacter-
ium avium (ATCC 25291), and Mycobacterium kansasii
(ATCC 12478).
The minimal inhibitory concentration (MIC) of the
derivatives 4 was determined using the microdilution broth
method in 96-well microplates (Sousa et al. 2015). Samples
were dissolved in dimethyl sulfoxide (DMSO) to a con-
centration of 8000 µg/mL, followed by dilution in tryptic
soy broth (TSB) for aerobic microorganisms and Schaedler
broth (Difco) supplemented which hemin (5.0 g/mL), and
menadione (10.0 g/mL) for anaerobic microorganisms; the
sample concentrations tested ranged from 200 to 0.195 µg/
mL. The final DMSO content was 4% (v/v), and this
solution was used as a negative control. The inoculum was
adjusted for each organism to yield a cell concentration of
5 × 105 colony forming units per mL (CFU/mL), according
to the Clinical and Laboratory Standards Institute (CLSI
2012a) guidelines (CLSI 2012b). The 96-well microplates
containing the aerobic microorganisms were closed with a
sterile plate sealer and incubated aerobically at 37 °C for 24
h. The plates containing the anaerobic microorganisms were
closed with a sterile plate sealer and incubated for 72 h in an
anaerobic chamber, in 5–10% H2, 10% CO2, 80–85% N2
atmosphere, at 36 °C. After that, resazurin (30 µL) in aqu-
eous solution (0.01%) was added to the microplates to
indicate microorganism viability for MIC determination.
Chlorhexidine dihydrochloride (CHD) was used as a posi-
tive control, and the concentrations ranged from 0.115 to
59 µg/mL. Controls were also performed to determine the
sterility of the TSB and Schaedler broths, control culture
(inoculum), CHD, the derivatives 4, and control DMSO.
The MIC values were determined as the lowest concentra-
tion of derivatives 4 capable of inhibiting the growth of the
microorganisms.
For Mycobacterium spp. the antimicrobial activity of the
derivatives 4 was evaluated in vitro using the microplate
microdilution technique (Palomino et al. 2002), using
resazurin as an indicator of microbial activity (REMA-
Resazurin Microtiter Assay), which allowed the determi-
nation of the minimum inhibitory concentration (MIC)
against the microorganisms evaluated. The compounds
were dissolved in dimethyl sulfoxide (DMSO) and serially
diluted in Middlebrook 7H9 broth prior to inoculation, the
final concentration of DMSO being <0.3%. The inoculum
was adjusted to each organism to produce a cellular con-
centration of 108 colony forming units (CFU/mL). The
concentrations of the compounds tested ranged from 0.195
Acknowledgements The authors would like to thank Fundação de
Amparo à Pesquisa do Estado de São Paulo (FAPESP) (Proc. 2014/
07493-5), for their financial support and Coordenacão de Aperfei-
çoamento de Pessoal de Nível Superior (CAPES) for scholarship.
Compliance with Ethical Standards
Conflict of interest The authors declare that they have no conflict of
interest.
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