Structural modifications of quinolone-3-carboxylic acids with anti-HIV activity

Article abstract of DOI:10.1016/j.bmc.2011.06.020

A series of new quinolone-3-carboxylic acids featuring a hydroxyl group at C-5 position were synthesized and evaluated for their in vitro activity against HIV in C8166 cell culture. All the compounds showed anti-HIV-1 activity with low micromolar to submi

Full text of DOI:10.1016/j.bmc.2011.06.020

Bioorganic & Medicinal Chemistry 19 (2011) 5039–5045
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Structural modifications of quinolone-3-carboxylic acids with anti-HIV activity
Qiu-Qin He a, Shuang-Xi Gu a, Jia Liu b, Hai-Qiu Wu a, Xuan Zhang c, Liu-Meng Yang c, Yong-Tang Zheng c,
Fen-Er Chen a,d,
⇑
a Department of Chemistry, Fudan University, Shanghai 200433, PR China
b Department of Medicinal Chemistry, School of Pharmacy, Second Millitary Medical University, Shanghai 200433, PR China
c Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences & Yunnan Province, Kunming Institute of Zoology, Chinese Academy of Sciences,
Kunming 650223, PR China
d Institute of Biomedical Science, Fudan University, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new quinolone-3-carboxylic acids featuring a hydroxyl group at C-5 position were synthe-
sized and evaluated for their in vitro activity against HIV in C8166 cell culture. All the compounds
showed anti-HIV-1 activity with low micromolar to submicromolar EC50 values. The most active com-
Received 10 April 2011
Revised 5 June 2011
Accepted 8 June 2011
Available online 15 July 2011
pound 2k exhibited activity against wild-type HIV-1 with an EC50 value of 0.13 lV. Preliminary struc-
ture–activity relationship of the newly synthesized quinolone analogues was also investigated. Further
docking study revealed that the anti-HIV activity of these compounds might involve a two-metal che-
lating mechanism.
Keywords:
HIV
Integrase inhibitor
Quinolone-3-carboxylic acids
Two-metal chelating mechanism
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
with methanol to afford benzoic ester 4. The Negishi cross-
coupling of 4 with 3-chloro-2-flurobenzylzinc bromide in the
Since its discovery in 2006, quinolone-3-carboxylic acids be-
lieved as one-metal chelating inhibitors of HIV-1 integrase (IN),
have attracted a great deal of attention due to their high activity
and favorable pharmacokinetic property.1 Considerable structural
modifications of quinolones focused on N-1, C-6, 7 and 8 position,
have been introduced in order to obtain more potent and selective
IN inhibitors. These efforts have led to the identification of many
new quinolone or quinolone-like 3-carboxylic acids such as
4-oxoquinoline 3-carboxylic acids and 4-oxonaphthyridine 3-car-
boxylic acids with high anti-HIV activity (1a,b, Fig. 1).1,2 However,
chemical modifications at C-5 position are scarce.2 This paper
described a series of new 5-hydroxylquinolone-3-carboxylic acids
(2a–k, Fig. 1) in an attempt to investigate whether the introduction
of OH at C-5 position would provide an additional metal binding
site and result in an improved activity against HIV-1.
presence of Pd(PPh3)4 in THF/toluene and subsequent hydrolysis
of the resulting coupling product 5 with satd aq LiOH yielded
benzoic acid 6. Treatment of the carbonyl diimidazole (CDI) actived
6 with potassium methylmalonate and anhydrous MgCl2 produced
b-ketoester 7. Condensation of 7 with N,N-dimethylformamide
dimethyl acetal (DMFDMA) and followed by substitution with
O
OH
O
OH
R3
R2
R3'
R2'
O
O
N
N
N
R1
R1'
4-oxoquinoline 3-carboxylic acids
1a
4-oxonaphthyridine 3-carboxylic acids
1b
2. Chemistry
F
OH
O
OH
Cl
O
The synthesis of the target compounds 2a–k is outlined in
Scheme 1. The iodination of 2,6-difluorobenzoic acid with
N-iodobutanimide (NIS) in concd H2SO4 gave the corresponding
aryl iodide 3, which was subjected to acid-catalyzed esterification
N
R
5-hydroxylquinolone-3-carboxylic acids
2a-k
⇑
Corresponding author. Tel.: +86 21 65643809; fax: +86 21 65643811.
E-mail address: rfchen@fudan.edu.cn (F.-E. Chen).
Figure 1. The structures of quinolone-3-carboxylic acids.
0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.06.020

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Q.-Q. He et al. / Bioorg. Med. Chem. 19 (2011) 5039–5045
F
O
F
F
O
F
F
O
F
c
b
I
I
a
OH
O
OH
3
4
F
F
O
F
F
F
O
d
e
Cl
Cl
Cl
Cl
Cl
O
OH
F
5
6
F
F
F
O
F
O
O
F
F
O
F
O
N
g
f
O
O
7
8
F
O
F
F
F
O
O
h
Cl
O
O
NH
R
N
R
9a-k
10a-k
F
F
O
O
F
OH
O
O
Cl
j
Cl
i
OH
OH
10a-j
N
R
N
R
2a-j
11a-j
F
O
O
N
O
F
OH
O
N
O
Cl
l
Cl
k
OH
OH
10k
OH
OH
2k
11k
Scheme 1. Reagents and conditions: (a) NIS, concd H2SO4, 0 °C, 3.5 h; (b) MeOH, SOCl2, reflux, 3 h; (c) (1) 3-chloro-2-flurobenzyl bromide, Zn, 1,2-dibromoethane,
chlorotrimethylsilane, THF, 60 °C, 1 h, (2) Pd(PPh3)4, toluene, reflux, overnight; (d) satd aq LiOH, THF, 50 °C, 3 h; (e) (1) CDI, THF, rt, 2 h; (2) potassium methylmalonate, MgCl2,
THF, 60 °C, overnight; (f) DMFDMA, THF, 50 °C, 3 h; (g) aliphatic amines, THF, 50 °C, 5–10 min; (h) DBU, DMF, 60–90 °C, overnight; (i) satd aq LiOH, dioxane, 50 °C, 3 h; (j)
12.5 M NaOH, dioxane, 80 °C, 1–2 d. (k) MeONa, MeOH, reflux, 20 h. (l) 2 M BBr3, CH2Cl2, ꢀ40 °C to rt, overnight.
appropriate aliphatic amines led to acrylates 9a–k, which were
then cyclized using DBU as a base to furnish quinolone esters
10a–k. The target compounds 2a–j were obtained from 10a–j by
ester hydrolysis and subsequent 5-OH incorporation under basic
conditions. The target compound 2k was synthesized from 10k
by methoxylation with sodium methoxide and subsequent
demethylation with BBr3.
being in phase III trials,4 was included as reference compound.
The cytotoxicity and antiviral activities of these compounds are
listed in Table 1.
All of the target compounds 2a–k exhibited anti-HIV-1 activity
with low micromolar to submicromolar EC50 values in infected
C8166 cells. Compounds 2a–c bearing a straight alkyl chain of var-
iable length showed significant decrease in activity with the length
of the chain. The replacement of straight chain alkyl group of 2b
with branched ones (2e–g) led to an improvement of antiviral
activity. The compound 2k, characterized by a hydroxymethyl
moiety at the 1S-position of the isobutyl group, appeared to be
the most active one against HIV-1. The compounds with N-substi-
tuted cyclic groups 2h, 2i were more active than the corresponding
ones with linear or branched moieties 2a, 2c, and 2d. The com-
pound 2g with t-butyl group displayed no significant cytotoxicity
3. Results and discussion
3.1. Biological evaluation
The synthesized compounds 2a–k were evaluated by 3-(4,5-
dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) as-
say3 for cytotoxicity and antiviral activity in C8166 cells infected
with the wild-type HIV-1 (LAI strain IIIB). Elviltegravir, currently
with a CC50 of 400.17 lM.

Q.-Q. He et al. / Bioorg. Med. Chem. 19 (2011) 5039–5045
5041
Table 1
Anti-HIV-1 activity and cytotoxicity of compounds 2a–k in C8166 cellsa
4. Conclusion
b
c
Compd
R
EC50
(lM)
CC50
(l
M)
SId
In conclusion, we designed and synthesized a series of new 5-
hydroxylquinolone-3-carboxylic acids. All the target compounds
exhibited anti-HIV-1 activity with low micromolar to submicrom-
olar EC50 values in infected C8166 cells. The most active com-
pound 2k exhibited activity against wild-type HIV-1 with an
2a
2b
2c
2d
2e
2f
2g
2h
n-Propyl
n-Butyl
n-Pentyl
i-Propyl
i-Butyl
s-Butyl
2.79
8.09
23.54
4.44
3.47
1.83
4.53
2.01
3.87
2.81
0.13
24.17
19.95
39.93
26.49
19.53
30.72
400.17
39.12
12.41
17.37
125.03
17.20
8.66
2.47
1.70
5.97
5.63
16.79
88.34
19.46
3.21
EC50 value of 0.13 lV. Further docking study revealed that the
anti-HIV activity of these compounds might involve a two-metal
chelating mechanism. However, in all cases, the measured activi-
ties were lower than that of Elvitegravir. This might be due to the
introduction of C-5 hydroxyl group resulting in unfavorable phys-
icochemical property or the lack of the influence of C-7 methoxyl
group which together with N-1 hydroxyalkyl moiety could lead to
a synergistic improvement of antiviral activity.1 Further studies
are ongoing to clarify the structure–activity relationship for this
quinolone series.
t-Butyl
Cyclopropyl
Cyclopentyl
Cyclohexyl
2i
2j
2k
6.18
961.77
81904.76
Elvitegravir
0.00021
a
All data represent mean values from at least two separate experiments.
EC50: compound concentration required to protect the cell against viral cyto-
b
pathogenicity by 50% in C8166 cells.
c
CC50: compound concentration that decreases the normal uninfected C8166 cell
viability by 50%.
d
SI: selectivity index; ratio CC50/EC50
.
5. Experimental
5.1. General procedures
Melting points were measured on a WRS-1 digital melting
point apparatus and are uncorrected. 1H NMR and 13C NMR spec-
tra on a Brucker AV 400 MHz spectrometer were recorded in
CDCl3. Chemical shifts are reported in d (ppm) units relative to
the internal standard tetramethylsilane (TMS). Mass spectra were
obtained on an Agilent MS/5975 mass spectrometer. All chemicals
and solvents used were of reagent grade and were purified and
dried by standard methods before use. All air-sensitive reactions
were run under a nitrogen atmosphere. All the reactions were
monitored by TLC on pre-coated silica gel G plates at 254 nm
under a UV lamp using ethyl acetate/hexane as eluents. Flash
chromatography separations were obtained on silica gel (300–
400 mesh).
5.2. 2,6-Difluoro-3-iodobenzoic acid (3)
Figure 2. Binding model of compound 2k in the active site of new homoly model of
HIV-1 IN.
To a solution of 2,6-difluorobenzoic acid (1.58 g, 10.0 mmol) in
concd H2SO4 (25 mL) was added NIS (2.25 g, 10.0 mmol) portion-
wise at 0 °C. After being stirred at 0 °C for 3.5 h, the mixture was
poured onto crushed ice (10 g), and 3% Na2SO3 (10 mL) was added.
The resulting slurry was stirred at 0 °C for 1 h, filtered, washed by
water, dried to give the compound 3 as a white solid (2.05 g, 72%):
1H NMR (CDCl3) d 6.78–6.82 (t, 1H, J = 8.4 Hz, ArH), 7.78–7.83 (m,
1H, ArH); GC–MS: 240 [Mꢀ44]+.
3.2. Molecular modeling calculations
In an attempt to determine the interaction between the hydro-
xyl group at C-5 position and HIV-1 IN, molecular docking study
was performed.
Crystallographic analysis of inhibitors bound to the HIV IN/viral
DNA complex continues to be a daunting challenge. Nevertheless,
the recently reported crystal structures of DNA-bound retroviral
IN5 made it possible to model the HIV-1 intasome. The model of
the HIV-1 catalytic core domain (CCD)/viral DNA complex was
homology constructed using Discovery Studio 2.5 based on the ori-
ginal X-ray crystal structures of IN from prototype foamy virus
(PFV) (pdb: 3OYA). Compound 2k, as a representative of the target
molecules, was docked into the HIV IN core domain using AUTODOCK
4.0 program. The docking result suggested that the C-5 hydroxyl,
together with 4-ketone and 3-carboxylate in compound 2k could
form a two-Mg2+ chelation with HIV-1 IN as shown in Figure 2.
The binding mode of 2k in the active site of IN showed that C-6
5.3. Methyl 2,6-difluoro-3-iodobenzoate (4)
To a mixture of 2,6-difluoro-3-iodobenzoic acid 3 (2.84 g,
10.0 mmol) in methanol (30 mL) was added SOCl2 (0.1 mL)
dropwise at 0 °C. After being stirred at reflux for 3 h, the mixture
was concentrated under reduced pressure. The residue was puri-
fied by column chromatography (silica gel, petroleum ether/ethyl
acetate 15:1 to 10:1, v/v) to give the desired compound 4 as a
white solid (2.75 g, 92%): mp 54–55 °C (lit.6 mp 53–55 °C);
1H NMR (CDCl3) d 3.95 (s, 3H, CH3), 6.78–6.82 (t, 1H, J = 8.4 Hz,
ArH), 7.78–7.83 (m, 1H, ArH); 13C NMR (CDCl3) d 53.10, 75.42,
75.46, 75.69, 75.73 (dd, JC –F = 4.2, J0 = 26.8 Hz), 111.49, 111.69,
substituted benzyl group and quinolone ring exhibit p–p stacking
C—F
111.89 (t, JC–F = 19.8 Hz), 113.81, 113.84, 114.03, 114.07
interaction with C16 and A17, respectively. No interaction could be
detected between the hydroxyalkyl group on N-1 of 2k and IN,
which indicates that this part of the molecule might contribute
to favorable physicochemical properties of 2K and lead to an
improvement in antiviral activity.
(dd, JC –F = 3.9, J0 = 22.4 Hz), 141.42, 141.45, 141.51, 141.54 (dd,
C—F
JC –F = 3.1, J0 = 9.4 Hz), 157.99, 158.05, 160.52, 160.58 (dd, JC
–
C—F
F = 6.2, J0 = 252.6 Hz), 159.48, 159.53, 162.04, 162.09 (dd, JC–
F = 5.1, J0C—F= 256.2 Hz), 161.16; GC–MS: 298 M+.
C—F

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Q.-Q. He et al. / Bioorg. Med. Chem. 19 (2011) 5039–5045
5.4. Methyl 3-(3-chloro-2-fluorobenzyl)-2,6-difluorobenzoate
(5)
2H, CH2), 4.03 (s, 2H, CH2), 6.91–6.96 (m, 1H, ArH), 7.02–7.12 (m,
2H, ArH), 728–7.34 (m, 2H, ArH); Enol form 1H NMR (CDCl3) d
3.83 (s, 1.3H, CH3), 4.03 (s, 0.9H, CH2), 5.44 (s, 0.4H, OH), 6.89–
6.96 (m, 0.4H, ArH), 7.02–7.12 (m, 0.9H, ArH), 7.21–7.34 (m,
0.9H, ArH), 12.31 (s, 0.4H, CH); MS (ESI) m/z 357 [M+H]+.
Under N2, zinc powder (156 mg, 2.4 mmol) was suspended in
THF (5 mL), then 1,2-dibromoethane (catalytic amount) and tri-
methylsilyl chloride (catalytic amount) were added at 60 °C. After
being stirred for 30 min, a solution of 3-chloro-2-fluorobenzyl bro-
mide (488 mg, 2.2 mmol) in THF (3 mL) was added dropwise at
60 °C. The mixture was stirred for further 1 h to give the solution
of 3-chloro-2-fluorobenzylzinc bromide. To a mixture of methyl
2,6-difluoro-3-iodobenzoate 4 (596 mg, 2.0 mmol) and Pd(PPh3)4
(13 mg, 0.011 mmmol) in toluene (10 mL) was added the above
solution of 3-chloro-2-fluorobenzylzinc bromide dropwise at
60 °C under N2. After completion of the addition, the mixture
was heated under reflux overnight. After allowing the mixture to
cool, toluene (15 mL) and 20% aqueous NH4Cl solution (10 mL)
were added to the reaction solution, and the mixture was stirred
and partitioned. The organic layer was washed twice with 20%
aqueous NH4Cl solution (5 mL) and twice with satd NaHCO3
(5 mL), then dried over anhydrous MgSO4. After filtration, the fil-
trate was concentrated under reduced pressure. The residue was
purified by column chromatography (silica gel, petroleum ether/
ethyl acetate 40:1 to 25:1, v/v) to give the desired compound 5
as a colorless oil (290 mg, 46%): 1H NMR (CDCl3): d 3.95 (s, 3H,
CH3), 4.00 (s, 2H, CH2), 6.87–6.92 (td, 1H, J = 8.8, J00 = 1.6 Hz, ArH),
6.99–7.03 (m, 1H, ArH), 7.05–7.09 (m, 1H, ArH), 7.24–7.30 (m,
2H, ArH); 13C NMR (CDCl3): d 27.82, 27.85, 27.88 (t, JC–F = 3.2 Hz),
52.79, 110.74, 110.93, 111.11 (t, JC–F = 18.6 Hz), 111.77, 111.81,
5.7. Methyl 2-(3-(3-chloro-2-fluorobenzyl)-2,6-difluorobenzoyl)
-3-(dimethylamino)acrylate (8)
A mixture of methyl 3-(3-(3-chloro-2-fluorobenzyl)-2,6-difluo-
rophenyl)-3-oxopropanoate 7 (320 mg, 0.9 mmol) and DMFMDA
(129 mg, 1.1 mmol) in THF (10 mL) was heated at 50 °C for 3 h.
The reaction mixture was cooled to room temperature and then
concentrated under reduced pressure. The residue was used di-
rectly for the next step without further purification.
5.8. General procedure for the preparation of 9a–j
A mixture of 2-(3-(3-Chloro-2-fluorobenzyl)-2,6-dif uoroben-
zoyl)-3-(dimethylamino)acrylate 8 (618 mg, 1.5 mmol) and appro-
priate aliphatic amines (1.8 mmol) in THF (15 mL) was stirred at
50 °C for 5–10 min and then concentrated under reduced pressure.
The resulting residue 9a–j was used directly for the next step with-
out further purification.
5.9. General procedure for the preparation of 10a–j
A mixture of 9a–j (1.5 mmol) and DBU (2.3 mmol) in DMF
(10 mL) was stirred at 60–90 °C overnight, then cooled down and
poured into ice-water. The mixture was extracted by dichloro-
methane (5 mL ꢂ 3). The combined organic solution was washed
with brine (5 mL ꢂ 2), dried over MgSO4 and concentrated under
reduced pressure. The residue was purified by column chromatog-
raphy (silica gel, petroleum ether/ethyl acetate 5:1 to 3:1, v/v) to
give the desired compound 10a–j.
111.99, 112.03 (dd, JC–F = 4.1, J0 = 21.7 Hz), 121.12, 121.30 (d, J
C—F
C–F = 17.9 Hz), 122.71, 122.75, 122.87, 122.91 (dd, JC–F = 3.9,
J0C—F = 16.1 Hz), 124.65, 124.70 (d, JC–F = 4.6 Hz), 127.48, 127.63 (d,
JC–F = 15.5 Hz), 129.16, 129.20 (d, JC–F = 3.9 Hz), 129.23, 133.51,
133.57, 133.59, 133.66 (dd, JC–F = 6.5, J0C—F = 8.7 Hz), 155.15,
157.62 (d, JC–F = 246.7 Hz), 157.04, 157.10, 159.58, 159.64 (dd, JC–
F = 6.2, J0 = 254.6 Hz), 158.04, 158.10, 160.58, 160.64 (dd, JC–
F = 6.1, J0C—F= 253.9 Hz), 162.07; MS (ESI) m/z 337 [M+Na]+.
C—F
5.9.1. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-4-oxo-1-
propyl-1,4-dihydroquinoline-3-carboxylate (10a)
5.5. 3-(3-Chloro-2-fluorobenzyl)-2,6-difluorobenzoic acid (6)
Yield 54%. 1H NMR (CDCl3) d 1.02–1.06 (t, 3H, J = 7.2 Hz, CH3),
1.89–1.95 (m, 2H, CH2), 3.94 (s, 3H, OCH3), 4.08–4.12 (t, 2H,
J = 7.2 Hz, CH2), 4.13 (s, 2H, CH2), 7.01–7.05 (t, 1H, J = 8.0 Hz,
ArH), 7.14–7.16 (d, 1H, J = 9.2 Hz, ArH), 7.18–7.21 (m, 1H, ArH),
7.28–7.31 (m, 1H, ArH), 7.49–7.53 (m, 1H, ArH), 8.41 (s, 1H, CH).
To a solution of methyl 3-(3-chloro-2-fluorobenzyl)-2,6-dif-
luorobenzoate 5 (315 mg, 1.0 mmol) in THF (8 mL) was added satd
aq LiOH (5 mL). After being stirred at 50 °C for 3 h, the mixture was
cooled, poured into ice-water and acidified with 4 M HCl to pH ꢁ2.
The precipitate was filtered off, washed by water, and dried to af-
ford 6 as a white solid. This crude was used directly for the next
step without further purification.
5.9.2. Methyl 6-(3-chloro-2-fluorobenzyl)-1-butyl-5-fluoro-4-
oxo-1,4-dihydroquinoline-3-carboxylate (10b)
Yield 61%. 1H NMR (CDCl3) d 0.97–1.00 (t, 3H, J = 7.2 Hz, CH3),
1.37–1.45 (m, 2H, CH2), 1.80–1.85 (m, 2H, CH2), 3.91 (s, 3H,
OCH3), 4.08–4.12 (t, 2H, J = 7.4 Hz, CH2), 4.10 (s, 2H, CH2), 6.98–
7.02 (t, 1H, J = 8.0 Hz, ArH), 7.12–7.14 (d, 1H, J = 9.2 Hz, ArH),
7.16–7.19 (m, 1H, ArH), 7.24–7.28 (m, 1H, ArH), 7.46–7.50 (m,
1H, ArH), 8.37 (s, 1H, CH).
5.6. Methyl 3-(3-(3-chloro-2-fluorobenzyl)-2,6-difluorophenyl)-
3-oxo-propanoate (7)
To a suspension of CDI (389 mg, 2.4 mmol) in THF (5 mL) was
added a solution of 3-(3-chloro-2-fluorobenzyl)-2,6-difluoroben-
zoic acid 6 (602 mg, 2.0 mmol) in THF (5 mL) dropwise, the
mixture was stirred at rt for 2 h. After a mixture of potassium
3-methoxy-3-oxopropanoate (374 mg, 2.4 mmol) and MgCl2
(228 mg, 2.4 mmol) in THF (10 mL) stirring at 50 °C for 2 h was
added the above solution. The resulting mixture was stirred at
50 °C overnight, filtrated. The filtrate was diluted with water
(5 mL) and acidified with 4 M HCl to pH 5ꢁ6. The mixture was ex-
tracted with ethyl acetate (15 mL) and washed with water (5 mL),
satd aq NaHCO3 (5 mL), and brine (5 mL), then dried over MgSO4.
After filtration, the filtrate was concentrated under reduced pres-
sure. The residue was purified by column chromatography (silica
gel, petroleum ether/ethyl acetate 20:1 to 15:1, v/v) to give the de-
sired compound 7 as a colorless oil (320 mg, 45%): keto form/enol
form = 2.3:1; keto form 1H NMR (CDCl3) d 3.75 (s, 3H, CH3), 3.95 (s,
5.9.3. Methyl 6-(3-chloro-2-fluorobenzyl)-1-butyl-5-fluoro-4-
oxo-1,4-dihydroquinoline-3-carboxylate (10c)
Yield 63%. 1H NMR (CDCl3) d 0.91–0.94 (t, 3H, J = 6.8 Hz, CH3),
1.37–1.39 (m, 4H, 2CH2), 1.84–1.86 (m, 2H, CH2), 3.92 (s, 3H,
OCH3), 4.09–4.13 (t, 2H, J = 7.4 Hz, CH2), 4.11 (s, 2H, CH2), 7.00–
7.04 (t, 1H, J = 8.0 Hz, ArH), 7.13–7.15 (d, 1H, J = 9.2 Hz, ArH),
7.16–7.20 (m, 1H, ArH), 7.26–7.29 (m, 1H, ArH), 7.47–7.50 (m,
1H, ArH), 8.38 (s, 1H, CH).
5.9.4. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-iso-propyl
-4-oxo-1,4-dihydroquinoline-3-carboxylate (10d)
Yield 62%. 1H NMR (CDCl3) d 1.56–1.57 (d, 6H, J = 6.4 Hz, 2CH3),
3.90 (s, 3H, OCH3), 4.09 (s, 2H, CH2), 4.77–4.80 (m, 1H, CH),

Q.-Q. He et al. / Bioorg. Med. Chem. 19 (2011) 5039–5045
5043
6.96–7.00 (t, 1H, J = 8.0 Hz, ArH), 7.13–7.17 (m, 1H, ArH), 7.22–7.29
(m, 2H, ArH), 7.45–7.47 (m, 1H, ArH), 8.53 (s, 1H, CH).
4 M HCl to pH ꢁ2. The resulting precipitate was collected by filtra-
tion, washed by water, and then dried to give the crude desired
compound 11a–j. This crude was used directly for the next step
without further purification.
5.9.5. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-iso-butyl-
4-oxo-1,4-dihydroquinoline-3-carboxylate (10e)
Yield 71%. 1H NMR (CDCl3) d 0.95–0.96 (d, 6H, J = 6.4 Hz, 2CH3),
2.16–2.23 (m, 1H, CH), 3.86 (s, 3H, OCH3), 3.86–3.88 (d, 2H,
J = 8.4 Hz, CH2), 4.05 (s, 2H, CH2), 6.95–6.99 (t, 1H, J = 8.0 Hz,
ArH), 7.07–7.09 (d, 1H, J = 8.8 Hz, ArH), 7.11–7.15 (m, 1H, ArH),
7.21–7.25 (m, 1H, ArH), 7.40–7.44 (m, 1H, ArH), 8.29 (s, 1H, CH).
5.11. (S)-6-(3-Chloro-2-fluorobenzyl)-1-(1-hydroxy-3-
methylbutan-2-yl)-5-methoxy-4-oxo-1,4-dihydroquinoline-3-
carboxylic acid (11k)
To a solution of MeONa (2.16 g, 40 mmol) in methanol (20 mL)
was added 10k (450 mg, 1.0 mmol) and one drop of water. After
being stirred at reflux for 20 h, the mixture was cooled, poured into
ice-water and acidified with 4 M HCl to pH ꢁ2, extracted by dichlo-
romethane (10 mL ꢂ 3) and concentrated. The residue was purified
by column chromatography (silica gel, dichloromethane/methanol
60:1 to 40:1, v/v) to give the desired compound 11k as a white so-
lid (390 mg, 87%): 1H NMR (CDCl3) d 0.82–0.84 (d, 3H, J = 6.4 Hz,
CH3), 1.20–1.22 (d, 3H, J = 6.8 Hz, CH3), 2.44–2.46 (m, 1H, CH),
3.48–3.53 (m, 1H, OH), 3.94 (s, 3H, OCH3), 4.13–4.22 (m, 4H,
2CH2), 4.52–4.53 (m, 1H, CH), 7.01–7.05 (dd, 1H, J = J0 = 8.0 Hz,
ArH), 7.13–7.16 (m, 1H, ArH), 7.28–7.31 (m, 1H, ArH), 7.51–7.53
(d, 1H, J = 9.2 Hz, ArH), 7.60–7.62 (d, 1H, J = 9.2 Hz, ArH), 8.86 (s,
1H, CH), 15.80 (s, 1H, COOH).
5.9.6. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-sec-butyl-
4-oxo-1,4-dihydroquinoline-3-carboxylate (10f)
Yield 68%. 1H NMR (CDCl3) d 1.82–1.92 (m, 6H, 2CH3), 2.23–2.26
(m, 2H, CH2), 3.87 (s, 3H, OCH3), 4.05 (s, 2H, CH2), 4.78–4.81 (m,
1H, CH), 6.94–6.98 (t, 1H, J = 8.0 Hz, ArH), 7.10–7.14 (m, 1H,
ArH), 7.20–7.24 (m, 1H, ArH), 7.29–7.31 (d, 1H, J = 8.8 Hz, ArH),
7.41–7.45 (m, 1H, ArH), 8.48 (s, 1H, CH).
5.9.7. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-tert-butyl-
4-oxo-1,4-dihydroquinoline-3-carboxylate (10g)
Yield 57%. 1H NMR (CDCl3) d 1.84 (s, 9H, 3CH3), 3.91 (s, 3H,
OCH3), 4.10 (s, 2H, CH2), 6.99–7.03 (t, 1H, J = 8.0 Hz, ArH), 7.17–
7.20 (m, 1H, ArH), 7.24–7.29 (m, 1H, ArH), 7.41–7.45 (m, 1H,
ArH), 7.59–7.61 (d, 1H, J = 8.8 Hz, ArH), 8.80 (s, 1H, CH).
5.12. General procedure for the preparation of 2a–j
5.9.8. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-
cyclopropyl-4-oxo-1,4-dihydroquinoline-3-carboxylate (10h)
Yield 45%. 1H NMR (CDCl3) d 1.10–1.14 (m, 2H, CH2), 1.28–1.35
(m, 2H, CH2), 3.38–3.43 (m, 1H, CH), 3.92 (s, 3H, OCH3), 4.12 (s, 2H,
CH2), 7.00–7.04 (t, 1H, J = 8.0 Hz, ArH), 7.17–7.20 (m, 1H, ArH),
7.26–7.30 (m, 1H, ArH), 7.50–7.54 (m, 1H, ArH), 7.65–7.67 (d, 1H,
J = 8.8 Hz, ArH), 8.52 (s, 1H, CH).
To a solution of 12.5 N NaOH (5 mL) in dioxane (8 mL) was
added 11a–j (1.2 mmol). After being stirred at 80 °C for 1 to 2 days,
the mixture was cooled, poured into water and acidified with 4 M
HCl to pH ꢁ2, then extracted by dichloromethane (5 mL ꢂ 3). The
combined organic solution was washed with water (5 mL ꢂ 2),
dried over MgSO4 and concentrated under reduced pressure. The
residue was purified by column chromatography (silica gel, dichlo-
romethane) to afford the desired compound 2a–j.
5.9.9. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-
cyclopentyl-4-oxo-1,4-dihydroquinoline-3-carboxylate (10i)
Yield 55%. 1H NMR (CDCl3) d 1.87–1.99 (m, 6H, 3CH2), 2.28–2.33
(m, 2H, CH2), 3.94 (s, 3H, OCH3), 4.13 (s, 2H, CH2), 4.82–4.85 (m,
1H, CH), 7.00–7.04 (t, 1H, J = 8.0 Hz, ArH), 7.17–7.21 (m, 1H,
ArH), 7.26–7.30 (m, 1H, ArH), 7.33–7.36 (d, 1H, J = 8.8 Hz, ArH),
7.49–7.53 (m, 1H, ArH), 8.55 (s, 1H, CH).
5.12.1. 6-(3-Chloro-2-fluorobenzyl)-5-hydroxy-4-oxo-1-propyl-
1,4-dihydroquinoline-3-carboxylic acid (2a)
Yield 45%. Mp 207–209 °C; 1H NMR (CDCl3) d 1.01–1.04 (t, 3H,
J = 7.4 Hz, CH3), 1.93–1.98 (m, 2H, CH2), 4.10 (s, 2H, CH2), 4.19–
4.22 (t, 2H, J = 7.4 Hz, CH2), 6.92–6.94 (d, 1H, J = 8.4 Hz, ArH),
6.99–7.02 (t, 1H, J = 8.0 Hz, ArH), 7.21–7.28 (m, 2H, ArH), 7.57–
7.59 (d, 1H, J = 8.4 Hz, ArH), 8.68 (s, 1H, CH), 13.35 (s, 1H, OH),
13.70 (s, 1H, COOH); 13C NMR (CDCl3): d = 10.98, 22.02, 28.36,
28.38 (d, JC–F = 2.5 Hz), 56.93, 105.43, 107.13, 113.42, 120.93,
121.11 (d, JC–F = 18.0 Hz), 123.17, 124.46, 124.51 (d, JC–F = 4.6 Hz),
128.32, 128.48 (d, JC–F = 15.5 Hz), 128.85, 129.78, 129.82 (d, J
5.9.10. Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-
cyclohexyl-4-oxo-1,4-dihydroquinoline-3-carboxylate (10j)
Yield 50%. 1H NMR (CDCl3) d 1.25–1.85 (m, 4H, 2CH2), 2.00–2.14
(m, 4H, 2CH2), 3.90 (s, 3H, OCH3), 4.09 (s, 2H, CH2), 4.24–4.31 (m,
1H, CH), 6.97–7.01 (t, 1H, J = 8.0 Hz, ArH), 7.14–7.17 (m, 1H,
ArH), 7.24–7.26 (m, 2H, ArH), 7.45–7.49 (m, 1H, ArH), 8.54 (s, 1H,
CH).
C–F = 4.0 Hz), 136.78, 138.88, 148.83, 155.34, 157.80 (d,
J
C–F = 246.0 Hz), 160.00, 165.92, 181.62. MS (ESI) m/z 390 [M+H]+.
Anal. Calcd for C20H17ClFNO4: C, 61.62; H, 4.40; N, 3.59. Found:
C, 61.37; H, 4.64; N, 3.81.
5.9.11. (S)-Methyl 6-(3-chloro-2-fluorobenzyl)-5-fluoro-1-
(1-hydroxy-3-methylbutan-2-yl)-4-oxo-1,4-dihydroquinoline-
3-carboxylate (10k)
5.12.2. 6-(3-Chloro-2-fluorobenzyl)-1-butyl-5-hydroxy-4-oxo-
1,4-dihydro quinoline-3-carboxylic acid (2b)
Yield 62%. 1H NMR (CDCl3) d 0.74–0.76 (d, 3H, J = 6.8 Hz, CH3),
1.22–1.23 (d, 3H, J = 6.0 Hz, CH3), 2.52–2.57 (m, 1H, CH), 3.72–
3.90 (m, 2H, CH2), 3.82 (s, 3H, OCH3), 4.13–4.18 (m, 2H, CH2),
4.28–4.32 (m, 1H, CH), 5.38–5.41 (t, 1H, J = 6.8 Hz, OH), 6.93–6.97
(dd, 1H, J = J0 = 8.0 Hz, ArH), 6.99–7.02 (m, 1H, ArH), 7.22–7.25
(m, 1H, ArH), 7.34–7.37 (d, 1H, J = 8.8 Hz, ArH), 7.39–7.43 (m, 1H,
ArH), 8.59 (s, 1H, CH).
Yield 41%. Mp 190–192 °C; 1H NMR (CDCl3) d 0.97–1.01 (t, 3H,
J = 7.4 Hz, CH3), 1.38–1.48 (m, 2H, CH2), 1.85–1.92 (m, 2H, CH2),
4.10 (s, 2H, CH2), 4.22–4.25 (t, 2H, J = 7.4 Hz, CH2), 6.93–6.95 (d,
1H, J = 8.8 Hz, ArH), 6.99–7.03 (t, 1H, J = 8.0 Hz, ArH), 7.21–7.28
(m, 2H, ArH), 7.56–7.59 (d, 1H, J = 8.8 Hz, ArH), 8.67 (s, 1H, CH),
13.34 (s, 1H, OH), 13.71 (s, 1H, COOH); 13C NMR (100 MHz,
CDCl3-d3): d 13.53, 19.91, 28.38, 28.41 (d, JC–F = 2.4 Hz), 30.66,
55.32, 105.42, 107.18, 113.44, 120.92, 121.11 (d, JC–F = 18.3 Hz),
123.17, 124.47, 124.52 (d, JC–F = 4.6 Hz), 128.32, 128.47 (d, J
C–F = 15.4 Hz), 128.87, 129.80, 129.84 (d, JC–F = 3.8 Hz), 136.78,
138.88, 148.76, 155.34, 157.80 (d, JC–F = 246.0 Hz), 160.01, 165.97,
181.61; MS (ESI) m/z 404 [M+H]+. Anal. Calcd for C21H19ClFNO4:
C, 62.46; H, 4.74; N, 3.47. Found: C, 62.24; H, 5.02; N, 3.21.
5.10. General procedure for the preparation of 11a–j
To a solution of satd aq LiOH (5 mL) in dioxane (8 mL) was
added 10a–j (1.2 mmol). After being stirred at 50 °C for 3 h, the
mixture was cooled, poured into ice-water and acidified with

5044
Q.-Q. He et al. / Bioorg. Med. Chem. 19 (2011) 5039–5045
5.12.3. 6-(3-Chloro-2-fluorobenzyl)-5-hydroxy-4-oxo-1-pentyl-
1,4-dihydro quinoline-3-carboxylic acid (2c)
7.28 (m, 2H, ArH), 7.38–7.40 (d, 1H, J = 8.8 Hz, ArH), 7.51–7.53 (d,
1H, J = 9.2 Hz, ArH), 9.06 (s, 1H, CH), 13.74 (s, 2H, OH, COOH); 13C
NMR (CDCl3) d 28.24, 28.27 (d, JC–F = 2.8 Hz), 30.68, 65.49, 106.42,
109.84, 114.50, 120.92, 121.10 (d, JC–F = 18.0 Hz), 122.79, 124.47,
124.51 (d, JC–F = 4.5 Hz), 128.35, 128.51 (d, JC–F = 15.5 Hz), 128.84,
129.86, 129.90 (d, JC–F = 3.8 Hz), 135.03, 138.97, 146.07, 155.37,
157.83 (d, JC–F = 246.3 Hz), 160.46, 166.40, 181.21; MS (ESI) m/z
404 [M+H]+. Anal. Calcd for C21H19ClFNO4: C, 62.46; H, 4.74; N,
3.47. Found: C, 62.67; H, 4.52; N, 3.28.
Yield 32%. Mp: 185–187 °C; 1H NMR (CDCl3) d 0.90–0.93 (t, 3H,
J = 6.8 Hz, CH3), 1.37–1.39 (m, 4H, 2CH2), 1.88–1.92 (m, 2H, CH2),
4.09 (s, 2H, CH2), 4.21–4.25 (t, 2H, J = 7.6 Hz, CH2), 6.92–6.94 (d,
1H, J = 8.8 Hz, ArH), 6.98–7.02 (t, 1H, J = 8.0 Hz, ArH), 7.21–7.27
(m, 2H, ArH), 7.56–7.58 (d, 1H, J = 8.8 Hz, ArH), 8.67 (s, 1H, CH),
13.31 (s, 1H, OH), 13.68 (s, 1H, COOH); 13C NMR (CDCl3) d 13.84,
22.18, 28.35, 28.38 (d, JC–F = 2.8 Hz), 28.43, 28.67, 55.55, 105.45,
107.15, 113.40, 120.91, 121.09 (d, JC–F = 18.0 Hz), 123.13, 124.47,
124.51 (d, JC–F = 4.7 Hz), 128.32, 128.47 (d, JC–F = 15.5 Hz), 128.85,
129.79, 129.83 (d, JC–F = 4.0 Hz), 136.77, 138.87, 148.76, 155.33,
157.79 (d, JC–F = 246.0 Hz), 159.97, 165.94, 181.57; MS (ESI) m/z
418 [M+H]+. Anal. Calcd for C22H21ClFNO4: C, 63.24; H, 5.07; N,
3.35. Found: C, 63.01; H, 5.29; N, 3.08.
5.12.8. 6-(3-Chloro-2-fluorobenzyl)-1-cyclopropyl-5-hydroxy-4-
oxo-1,4-dihydroquinoline-3-carboxylic acid (2h)
Yield 32%. Mp: 208–209 °C; 1H NMR (CDCl3) d 1.20–1.21 (m, 2H,
CH2), 1.40–1.41 (m, 2H, CH2), 3.54–3.56 (m, 1H, CH), 4.13 (s, 2H,
CH2), 7.01–7.05 (t, 1H, J = 8.0 Hz, ArH), 7.23–7.28 (m, 2H, ArH),
7.42–7.44 (d, 1H, J = 8.4 Hz, ArH), 7.62–7.64 (d, 1H, J = 8.4 Hz,
ArH), 8.84 (s, 1H, CH), 13.20 (s, 1H, OH), 13.70 (s, 1H, COOH); 13C
NMR (CDCl3) d 8.23, 28.41, 28.43 (d, JC–F = 2.4 Hz), 36.01, 106.27,
107.23, 112.80, 120.92, 121.11 (d, JC–F = 18.2 Hz), 123.32, 124.46,
124.51 (d, JC–F = 4.4 Hz), 128.37, 128.53 (d, JC–F = 15.5 Hz), 128.85,
129.76, 129.80 (d, JC–F = 4.0 Hz), 136.78, 140.61, 148.64, 155.34,
157.80 (d, JC–F = 246.0 Hz), 159.66, 165.82, 181.14; MS (ESI) m/z
388 [M+H]+. Anal. Calcd for C20H15ClFNO4: C, 61.94; H, 3.90; N,
3.61. Found: C, 61.74; H, 4.19; N, 3.38.
5.12.4. 6-(3-Chloro-2-fluorobenzyl)-5-hydroxy-1-isopropyl-4-
oxo-1,4-dihydroquinoline-3-carboxylic acid (2d)
Yield 43%. Mp: 190–192 °C; 1H NMR (CDCl3) d 1.62–1.64 (d, 6H,
J = 6.8 Hz, 2CH3), 4.10 (s, 2H, CH2), 4.90–4.97 (m, 1H, CH), 6.98–
7.02 (t, 1H, J = 7.6 Hz, ArH), 7.06–7.08 (d, 1H, J = 8.8 Hz, ArH),
7.21–7.28 (m, 2H, ArH), 7.57–7.59 (d, 1H, J = 8.8 Hz,ArH), 8.83 (s,
1H, CH), 13.49 (s, 1H, OH), 13.75 (s, 1H, COOH); 13C NMR (CDCl3)
d 22.16, 28.35, 28.38 (d, JC–F = 2.9 Hz), 53.01, 104.74, 107.42,
113.49, 120.91, 121.10 (d, JC–F = 18.2 Hz), 123.05, 124.46, 124.50
(d, JC–F = 4.6 Hz), 128.36, 128.51 (d, JC–F = 15.4 Hz), 128.84, 129.77,
129.81 (d, JC–F = 4.0 Hz), 136.72, 139.37, 144.14, 155.34, 157.80
(d, JC–F = 245.9 Hz), 160.23, 166.10, 181.33; MS (ESI) m/z 390
[M+H]+. Anal. Calcd for C20H17ClFNO4: C, 61.62; H, 4.40; N, 3.59.
Found: C, 61.87; H, 4.12; N, 3.86.
5.12.9. 6-(3-Chloro-2-fluorobenzyl)-1-cyclopentyl-5-hydroxy-4-
oxo-1,4-dihydroquinoline-3-carboxylic acid (2i)
Yield 30%. Mp: 170–171 °C; 1H NMR (CDCl3): d 1.86–2.03
(m, 6H, 3CH2), 2.31–2.38 (m, 2H, CH2), 4.10 (s, 2H, CH2),
4.92–4.98 (m, 1H, CH), 6.98–7.02 (t, 1H, J = 8.0 Hz, ArH), 7.10–
7.12 (d, 1H, J = 8.8 Hz, ArH), 7.20–7.28 (m, 2H, ArH), 7.56–7.58
(d, 1H, J = 8.8 Hz, ArH), 8.79 (s, 1H, CH), 13.47 (s, 1H, OH), 13.74
(s, 1H, COOH); 13C NMR (CDCl3) d 23.69, 28.33, 28.36 (d, J
C–F = 2.8 Hz), 32.41, 63.21, 105.67, 107.03, 113.45, 120.90, 121.08
(d, JC–F = 18.0 Hz), 123.05, 124.45, 124.50 (d, JC–F = 4.7 Hz), 128.37,
128.53 (d, JC–F = 15.4 Hz), 128.82, 129.76, 129.80 (d, JC–F = 4.0 Hz),
136.55, 136.57 (d, JC–F = 1.6 Hz), 139.91, 144.47, 155.32, 157.79
(d, JC–F = 246.2 Hz), 160.01, 166.09, 181.28; MS (ESI) m/z 416
[M+H]+. Anal. Calcd for C22H19ClFNO4: C, 63.54; H, 4.61; N, 3.37.
Found: C, 63.31; H, 4.85; N, 3.58.
5.12.5. 6-(3-Chloro-2-fluorobenzyl)-5-hydroxy-1-isobutyl-4-
oxo-1,4-dihydroquinoline-3-carboxylic acid (2e)
Yield 41%. Mp: 195–196 °C; 1H NMR (CDCl3) d 0.99–1.01 (d, 6H,
J = 6.8 Hz, 2CH3), 2.26–2.32 (m, 1H, CH), 4.02–4.04 (d, 2H, J = 7.6
Hz, CH2), 4.09 (s, 2H, CH2), 6.89–6.92 (d, 1H, J = 8.8 Hz, ArH), 6.98–
7.02 (t, 1H, J = 8.0 Hz, ArH), 7.21–7.27 (m, 2H, ArH), 7.55–7.57 (d,
1H, J = 8.8 Hz, ArH), 8.62 (s, 1H, CH), 13.33 (s, 1H, OH), 13.68 (s, 1H,
COOH); 13C NMR (CDCl3): d = 19.80, 27.39, 28.36, 28.39 (d, JC–F=2.8
Hz), 28.39, 62.65, 105.66, 106.89, 113.39, 120.92, 121.10 (d, J
C–F = 17.9 Hz), 123.17, 124.47, 124.51 (d, JC–F = 4.6 Hz), 128.30,
128.46 (d, JC–F = 15.4 Hz), 128.86, 129.80, 129.84 (d, JC–F = 3.9 Hz),
136.69, 139.04, 149.15, 155.34, 157.80 (d, JC–F = 246.1 Hz), 159.95,
165.88, 181.63; MS (ESI) m/z 404 [M+H]+. Anal. Calcd for C21H19
ClFNO4: C, 62.46; H, 4.74; N, 3.47. Found: C, 62.25; H, 4.51; N, 3.66.
5.12.10. 6-(3-Chloro-2-fluorobenzyl)-1-cyclohexyl-5-hydroxy-4-
oxo-1,4-dihydroquinoline-3-carboxylic acid (2j)
Yield 31%. Mp: 178–179 °C; 1H NMR (CDCl3) d 1.25–2.19 (m,
10H, 5CH2), 4.08 (s, 2H, CH2), 4.41–4.47 (m, 1H, CH), 6.97–7.01
(t, 1H, J = 8.0 Hz, ArH), 7.04–7.06 (d, 1H, J = 8.8 Hz, ArH), 7.19–
7.26 (m, 2H, ArH), 7.55–7.57 (d, 1H, J = 8.8 Hz, ArH), 8.81 (s, 1H,
CH), 13.46 (s, 1H, OH), 13.74 (s, 1H, COOH); 13C NMR (CDCl3) d
25.14, 25.84, 28.36, 28.37 (d, JC–F = 1.7 Hz), 32.82, 61.08, 104.74,
107.24, 113.52, 120.91, 121.09 (d, JC–F = 17.9 Hz), 122.97, 124.45,
124.49 (d, JC–F = 4.6 Hz), 128.39, 128.54 (d, JC–F = 15.4 Hz), 128.82,
129.76, 129.80 (d, JC–F = 3.9 Hz), 136.61, 139.39, 144.65, 155.33,
157.79 (d, JC–F = 246.0 Hz),160.19, 166.15, 181.24; MS (ESI) m/z
430 [M+H]+. Anal. Calcd for C23H21ClFNO4: C, 64.26; H, 4.92; N,
3.26. Found: C, 64.03; H, 4.69; N, 3.52.
5.12.6. 6-(3-Chloro-2-fluorobenzyl)-1-sec-butyl-5-hydroxy-4-
oxo-1,4-dihydroquinoline-3-carboxylic acid (2f)
Yield 40%. Mp: 161–163 °C; 1H NMR (CDCl3) d 0.94–0.97 (t, 3H,
J = 7.2 Hz, CH3), 1.59–1.60 (d, 3H, J = 6.8 Hz, CH3), 1.91–2.02 (m, 2H,
CH2), 4.10 (s, 2H, CH2), 4.67–4.72 (m, 1H, CH), 6.98–7.02 (t, 1H,
J = 8.0 Hz, ArH), 7.05–7.07 (d, 1H, J = 8.8 Hz, ArH), 7.21–7.27 (m,
2H, ArH), 7.56–7.58 (d, 1H, J = 8.4 Hz, ArH), 8.75 (s, 1H, CH),
13.50 (s, 1H, OH), 13.75 (s, 1H, COOH); 13C NMR (CDCl3) d 10.48,
20.13, 28.35, 28.38 (d, JC-F = 2.8 Hz), 29.06, 67.11, 104.67, 107.41,
113.50, 120.91, 121.09 (d, JC–F = 18.0 Hz), 122.99, 124.45, 124.50
(d, JC–F = 4.7 Hz), 128.36, 128.51 (d, JC–F = 15.4 Hz), 128.84, 129.79,
129.83 (d, JC–F = 4.0 Hz), 136.69, 136.71 (d, JC–F = 2.0 Hz), 139.82,
145.67, 155.34, 157.80 (d, JC–F = 246.0 Hz), 160.21, 166.06,
181.27; MS (ESI) m/z 404 [M+H]+. Anal. Calcd for C21H19ClFNO4:
C, 62.46; H, 4.74; N, 3.47. Found: C, 62.71; H, 4.98; N, 3.25.
5.12.11. (S)-6-(3-Chloro-2-fluorobenzyl)-5-hydroxy-1-(1-
hydroxy-3-methylbutan-2-yl)-4-oxo-1,4-dihydroquinoline-3-
carboxylic acid (2k)
To a solution of 11k (224 mg, 0.5 mmol) in dichloromethane
(10 mL) was added BBr3 (2 M, 5.0 mmol) dropwise at ꢀ40 °C. After
being stirred for 1 h, the mixture was allowed to warm to rt and
stirred overnight. Ice-water (5 mL) was added dropwise to the
reaction solution. The resulting mixture was extracted by dichloro-
methane (10 mL ꢂ 3), washed with cold 5% aqueous NaHCO3 solu-
tion (5 mL), dried and concentrated. The residue was purified by
5.12.7. 6-(3-Chloro-2-fluorobenzyl)-1-tert-butyl-5-hydroxy-4-
oxo-1,4-dihydroquinoline-3-carboxylic acid (2g)
Yield 31%. Mp: 234–235 °C; 1H NMR (CDCl3) d 1.90 (s, 9H,
3CH3), 4.10 (s, 2H, CH2), 6.99–7.03 (t, 1H, J = 7.6 Hz, ArH), 7.23–

Q.-Q. He et al. / Bioorg. Med. Chem. 19 (2011) 5039–5045
5045
column chromatography (silica gel, dichloromethane/methanol
(20872018), from Chinese Academy of Sciences (KSCX2-YW-R-
185), from the Eleventh Five-Year Key Scientific and Technological
Program of China (2009ZX09501-029), and from National Basic Re-
search Program of China (2009CB5223006).
60:1 to 50:1, v/v) to give the desired compound 2k as a colorless
oil (53 mg, 24%): ½a D20
ꢃ
¼ ꢀ24:8 (c 0.5, CHCl3), 1H NMR (CDCl3) d
0.80–0.82 (d, 3H, J = 6.8 Hz, CH3), 1.18–1.19 (d, 3H, J = 6.4 Hz,
CH3), 2.44–2.49 (m, 1H, CH), 3.37–3.38 (m, 1H, OH), 4.06–4.20
(m, 4H, 2CH2), 4.43–4.45 (m, 1H, CH), 7.01–7.07 (dd, 1H,
J = J0 = 8.0 Hz, ArH), 7.07–7.09 (d, 1H, J = 8.8 Hz, ArH), 7.24–7.26
(m, 2H, ArH), 7.55–7.57 (d, 1H, J = 8.8 Hz, ArH), 8.85 (s, 1H, CH),
13.37 (s, 1H, OH), 13.78 (s, 1H, COOH); 13C NMR (CDCl3) d 19.51,
19.69, 28.31, 28.33 (d, JC–F = 2.6 Hz), 29.42, 61.10, 68.03, 105.01,
106.49, 113.32, 120.90, 121.08 (d, JC–F = 18.1 Hz), 123.00, 124.45,
124.49 (d, JC–F = 4.5 Hz), 128.36, 128.51 (d, JC–F = 15.5 Hz), 128.81,
129.78, 129.82 (d, JC–F = 4.0 Hz), 136.79, 140.95, 146.27, 155.35,
157.81 (d, JC–F = 245.9 Hz),160.05, 166.93, 181.12; MS (ESI) m/z
434 [M+H]+. Anal. Calcd for C22H21ClFNO5: C, 60.90; H, 4.88; N,
3.23. Found: C, 60.72; H, 5.16; N, 3.55.
References and notes
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Acknowledgments
This project was funded by China Postdoctoral Science Founda-
tion (20100470625). The work was also supported in part by grant
from the National Natural Science Foundation of China
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