Synthesis of quinoline dicarboxylic esters as biocompatible fluorescent tags

Article abstract of DOI:10.1021/jo301652j

A series of dicarboxylic quinoline derivatives bearing electron-releasing or -withdrawing substituents have been synthesized using mono- or/and biphasic methodologies. By controlling the regioselectivity of addition into our electrophilic intermediate, we also characterized by which mechanism the Doebner-Miller cyclization step occurred. As anticipated, electronreleasing substituents induce a red shift of the low-energy absorption allowing excitation in the visible region. In addition, by playing on the strength and position of the electron-releasing substituents, chromophore having interesting fluorescent properties such as large Stoke shifts, good fluorescent quantum yields, emission in the visible green-yellow region and reasonable two-photon absorption in the NIR region have been obtained. These small-size fluorophores, which can be made water-soluble and have been shown to be non-toxic, can be hetero- and/or polyfunctionalized and thus represent promising key units for fluorescence-based physiological experiments with low background interactions.

Full text of DOI:10.1021/jo301652j

Article
pubs.acs.org/joc
Synthesis of Quinoline Dicarboxylic Esters as Biocompatible
Fluorescent Tags
Younes Laras,† Vincent Hugues,‡ Yogesh Chandrasekaran,‡ Mireille Blanchard-Desce,‡
Francine C. Acher,† and Nicolas Pietrancosta*,†
†Universite
‡Universite
́
́
Paris Descartes, Sorbonne Paris Cite,
́
Centre National de la Recherche Scientifique, UMR 8601, F-75006 Paris, France
Bordeaux, ISM, Centre National de la Recherche Scientifique, UMR 5255, F-33400 Talence, France
S
* Supporting Information
ABSTRACT: A series of dicarboxylic quinoline derivatives bearing electron-releasing or -withdrawing substituents have been
synthesized using mono- or/and biphasic methodologies. By controlling the regioselectivity of addition into our electrophilic
intermediate, we also characterized by which mechanism the Doebner−Miller cyclization step occurred. As anticipated, electron-
releasing substituents induce a red shift of the low-energy absorption allowing excitation in the visible region. In addition, by
playing on the strength and position of the electron-releasing substituents, chromophore having interesting fluorescent properties
such as large Stoke shifts, good fluorescent quantum yields, emission in the visible green-yellow region and reasonable two-
photon absorption in the NIR region have been obtained. These small-size fluorophores, which can be made water-soluble and
have been shown to be non-toxic, can be hetero- and/or polyfunctionalized and thus represent promising key units for
fluorescence-based physiological experiments with low background interactions.
nisms and strategies: Conrad−Limpach−Knorr,11,12 Skraub−
INTRODUCTION
■
Doebner−Von Miller,13−15 Frielaender,16,17 halogen medi-
ated,18 copper catalyzed19 or miscellaneous.14,20 Classical
Skraup procedure involves the use of a large amount of sulfuric
acid at high temperature. Other methods are not fully
satisfactory with regards to yields, reaction conditions, and
operational simplicity. The Doebner−Miller method allows
mild conditions, but yields remain low and reactions involve
tedious isolation procedures from complex reaction mix-
tures.13−15 In this context, we present herein an improved
methodology that allows generating a large range of derivatives
which are liable for further derivatization. Their absorption and
fluorescent properties, as well as biocompatibility, have been
studied in order to identify the most promising structures as
fluorescent tags.
Fluorescent probes and among them quinoline-based structures
play a crucial role in bioimaging studies.1,2 The use of
fluorescent dyes easily functionalizable and compatible with
biological experiments represents a key feature for physiological
research.3,4 Recent elaborated studies used coumarin or
quinoline scaffolds as central caged or fluorescent chemical
cores to investigate small endogenous molecule functions.5−8
These experiments remain limited and are highly dependent on
both intrinsic biological activity and fluorescent properties of
fluorophore (low tissue penetration, probe biological side
effects, decrease of natural function of studied molecules when
labeled, etc.). The use of small and biological inactive
fluorophore coupled to the molecule of interest appears crucial
to observe both its localization and its function in physiological
conditions.9,10
To be efficient, these fluorescent probes should be
biocompatible (i.e., have low side effects at typical concen-
trations used for bioapplications) and have optimal fluorescent
properties. In this context, quinolines appear quite attractive
due to their relative synthetic versatility. The quinoline
heterocyclic scaffold allows facile introduction of substituents
and subsequent tuning of physicochemical properties of
molecules (fluorescence, solubility, etc.). Synthesis of sub-
stituted quinolines have been reported using various mecha-
RESULTS AND DISCUSSION
■
Synthesis. Here, we report the Doebner−Miller synthesis
and fluorescent properties of a novel series of quinoline
dicarboxylic esters generated in improved synthetic conditions
and better yields compare with those previously described.21−23
To synthetize our series of compounds, we selected two
Received: August 19, 2012
Published: August 29, 2012
© 2012 American Chemical Society
8294
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
Scheme 1. Synthetic Methodology Used for Quinoline Diester (3) Synthesis Using Monophasic (A) or Biphasic (B) Methods
*
Specific conditions used for these compounds.
Table 1. Yields of Quinoline Cyclization Step
a
a
yields (%)
yields (%)
entry
R
method A
method B
entry
R
method A
method B
3a
3b
3c
3d
3e
3f
H
47
55
20
3e
8
11
32
48
5
3l
6-OH
7-OH
8-OH
13
8
34
20
6-Me
7-Me
3m
3n
3o
3p
3q
3r
30
39
21
46
30
60
23
32
10
6-NH2
6-OMe
28
6-NHCOCF3
6-NHMe
6-N(Me)2
7-N(Me)2
6-N(Et)2
6-NO2
−
−
−
−
−
−
nr
7-OMe
33
15
25
23
15
33
nr
8-OMe
13
3g
3h
3i
8-OBn
1
3s
5-Me; 8-OH
5-Me; 8-OBoc
6-CO2H
−
traces
3t
3j
3u
−
3k
7-NO2
a
nr, no reaction; dashes, not experimented.
synthetic conditions, using either classical TFA as Brøn
acid, or biphasic phosphomolybdic acid and sodium dodecyl
sulfate (SDS) as surfactant (Scheme 1).
́
sted
is substituted in this position 7 (3c, 3m, 3p) and yields the
attempted product in very low proportion. In contrast, even if
reaction with 7-subltituted aniline remained difficult with both
methodologies, method B gives the corresponding product in
better yield and with less side product. Indeed, when m-
aminoaniline was condensed with intermediate 2, Method B
provided the desired product 3d whereas Method A gave only
the side compound 3e.
Altogether, these results led us to investigate the influence of
various parameters involved in the cyclization mechanism (e.g.,
amine pKa, regioselectivity). Predicted pKa values of anilines
with SPARC24,25 confirmed that no correlation could be
evidenced between basicity and condensation yield (data not
shown). Indeed, starting with anilines having distant pKa’s (R =
NO2 and R = OMe) gave the corresponding quinolines 3j and
3o with similar yields (33 and 39%, respectively).
Ketoglutaric acid is first diesterified in the presence of thionyl
chloride in ethanol. The unsaturated ester 2 is then generated
in two successive steps, alpha bromination of ketone followed
by elimination of HBr. The three steps give only the E-isomer
of 2 in very good global yield (80%). Intermediate 2 is then
condensed with various anilines using classical method A or/
and biphasic method B leading to the desired quinolines 3.
As shown in Table 1, yields of the condensation step
remained low and appeared to be highly dependent on the
substituent position present in the aniline. Surprisingly,
electron-donating or electron-withdrawing groups did not
impact the cyclization. For example, compounds with
substituents at position 6, 3j (R = NO2), 3o (R = OMe) or
3u (R = CO2H) afforded similar yields, respectively 33, 39 and
32%. On the other hand, the effect of group position is crucial
when using Method A and B and highlights that position 7 is
notably unfavorable compared to the others (compounds 3l−n
or 3o−q or 3b,c). Nevertheless, we could underline that the
classical methodology (Method A) is less efficient when aniline
Regarding the cyclization, two different reaction mechanisms
have been postulated for the first step in the literature. The
aniline may attack either directly the ketone group to form the
imine intermediate26 or through a 1−4 Michael addition
leading to the corresponding enolate adduct.14
8295
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
Scheme 2. Cyclization Mechanism of Quinoline Diester
To confirm their propositions, authors succeeded in isolating
each key intermediate (imine or enolate). The mechanism
appears to be correlated to both electrophilic character of the
unsaturated moiety and the nucleophilicity of the amine.14,26 In
order to clarify this question, we decided to replace the α-keto-
ester of our electrophilic intermediate by a α-keto benzyl amide
7. This reactant, when condensed with m-N,N dimethylamino
aniline led to a quinoline unsymetrically substituted on the two
carbonyl groups (3v) (Scheme 2). Surprisingly, while authors
previously characterized an imine adduct for similar quinolines,
our cyclization is 1−4 Michael addition mediated according to
the C4 benzamide position in compound 3v (Supporting
Information). It can be noted that even if the reaction appears
difficult and incomplete, no enolate intermediate as expected
for our 1−4 Michael addition or, of course, any imine adduct
(C2 benzamide attack intermediate) have been isolated.14
Biocompatibility. To confirm the potentiality of these
structures as a multifunctionalizable and biocompatible scaffold,
we performed solubility and cytoxicity assays of two monoacid
derivatives 4p and 4v. (Scheme 3) These were obtained by
basic treatment of compounds 3p and 3v with 1 equiv of
sodium hydroxide in THF.23 Regioselectivity of the depro-
tection was characterized by 1D and 2D NMR (Section 2,
Supporting Information). It allows the access to a free acid that
may be subsequently functionalized by a reactive group
(hydroxyl, amine, thiol or halide) present on the bioactive
compounds of interest.6−8 Compounds 4p and 4v exhibited
high aqueous solubility up to 50 mM compared to the poor
solubility of compounds 3a−v. In addition, no cytotoxic effects
were observed even at 1 mM in cell culture.
Photophysical Properties. In order to assess the
potentialities of newly synthesized quinoline derivatives as
fluorescent probes, their photophysical properties were
investigated in ethanol or pure water (for water-soluble
compounds) solutions. All compounds show significant
absorption in UV−visible range and, in some cases,
fluorescence emission depending on the nature and position
of the substituents on the quinoline ring (Table 2).
Compounds 3a−c, 3j and 3u, which bear alkyl or electron-
withdrawing groups in the sixth (or seventh) position, show a
medium intensity absorption band in the UV region and almost
no fluorescence. In contrast, diester derivatives 3d, 3f−i, 3l−s
bearing electron-donating (ED) substituents instead show
medium intensity absorption band in the near UV region or
blue-visible region as a result of the bathochromic shift induced
by ED substituents while their fluorescence strongly depends
on the ED substituents’ strength and positions. When the ED
groups are in the sixth or eighth position, significant
fluorescence is obtained, whereas the substitution on the
seventh position leads to a sizable reduction of the fluorescence
quantum yield. Comparison of chromophores 3o−r (as well as
3l−n and 3g,h) indicate that the sixth position substitution
leads to the strongest absorption and emission, as clearly
exemplified in Figure 1A,B, whereas the eighth position
substitution induces a major bathochromic shift of the emission
band (which is shifted to the green-yellow region). Replace-
ment of O-alkyl by OH induces a marked hypochromic and
slight bathochromic shift of absorption, as well as a red shift
and significant reduction of fluorescence except for the eighth
position substitution (Table 2). As illustrated in Figure 2C,D,
Scheme 3. Classical and Regioselective Deprotection of
Compounds 3p and 3v
8296
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
Table 2. Photophysical Properties and Two-Photon Absorption of New Quinoline Derivatives
a
b
d
max
max
max
max
entry
R
λabs (nm) εmax (103 M−1 cm−1
)
λem (nm) Stokes shift (cm−1
)
Φ
(%)
λTPA (nm) σ2 (GM)
3a
3b
3c
3d
3e
3f
H
319
330
321
421
346
429
443
430
453
304
364
373
369
355
362
368
366
369
312
316
426
349
403
3.5
4.7
4.8
5.6
3.4
420
417
422
537
436
539
564
541
561
/
7 500
6 300
7 500
5 100
6 000
4 800
4 800
4 800
4 200
/
0.6
2.2
1.9
/
/
/
/
b
b
6-Me
7-Me
/
/
c
6-NH2
40
34
47
820
/
10.5
/
b
6-NHCOCF3
6-NHMe
6-N(Me)2
7-N(Me)2
6-N(Et)2
6-NO2
c
11
12
5.0
840
920
840
920
/
11
12
13
20.5
/
c
3g
3h
3i
59.5
c
41
c
9.5
9.3
6.4
1.7
0.7
8.2
2.8
1.4
1.7
2.0
2.6
3.5
2.3
3.9
1.7
49
3j
/
b
3l
6-OH
466
474
527
441
451
526
512
528
505
/
6 000
5 700
8 100
5 500
5 500
8 200
7 800
8 200
12 200
/
16
/
/
b
3m
3n
3o
3p
3q
3r
3s
3t
7-OH
0.7
/
/
c
8-OH
17
/
/
b
6-OMe
53
/
/
b
c
7-OMe
9.8 , 9.9
/
/
bc
,
8-OMe
17
20
26
22
/
/
/
b
c
8-OBn
/
/
5-Me; 8-OH
5-Me; 8-OBoc
6-CO2H
7-N(Me)2
7-OMe
/
/
c
/
/
3u
3v
/
/
c
586
462
603
6 400
5 100
7 100
6
/
/
e
c
c
4p
e
15
/
/
4v (sodium Salt)
7-N(Me)2
1.3
/
/
a
b
c
d
e
Fluorescence quantum yield. Standard: quinine bisulfate. Standard: fluorescein. GM = 10−50 cm4 s photon −1. In water.
Figure 1. Effect of substitution position: Absorption (A) and emission (B) spectra of quinoline derivatives 3o−q in ethanol. Effect of substituent
donating strength: Absorption (C) and emission (D) spectra of quinoline derivatives 3f, 3g, 3o.
increasing the ED strength of the substituents in the sixth
position induces a red-shift of both absorption and emission.
The same stands for substitution by ED groups in the seventh
position, with additional marked hyperchromic effect and
fluorescence enhancement, as indicated by comparison of 3h
and 3p characteristics (Table 2). As a result, substitution by
strong ED groups (such as NR2) in the seventh position also
leads to strong fluorescence. Interestingly, investigation of the
fluorescence properties of biocompatible water-soluble deriva-
tives 4p and 4v (Table 2) provides evidence that ester-acid
quinoline derivatives are indeed promising fluorescent tags for
biomolecules. Indeed compound 4p shows a 50% fluorescence
enhancement in water as compared to its diester precursor 3p
in ethanol. In contrast, comparison of 3h, 3v (in ethanol) and
4v (in water) fluorescence reveals that the benzamide
connection has deleterious effect on fluorescence.
Hence the ester linkage in the fourth position should be
preferred to amide linkage for grafting the new quinoline tags
on biomolecules. On the basis of the above results, the newly
synthesized diester quinoline derivatives bearing strong ED
substituents in the sixth or seventh position were selected as the
most promising as fluorescent tags for biomolecules.
Comparisons with structures already described give also
information and highlight the potentiality of our structures. For
example, when in the second position, the ester of compounds
3o−q was replaced by a sulfonyl group (−SO2Me), the less
functionalizable resulting quinolines showed similar quantum
yields of 69 vs 53, 19 vs 10, and 5 vs 17%, respectively, for
8297
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
Figure 2. Two-photon absorption data in absolute ethanol for quinoline 3i, 3h, 3g and 3f (solid lines indicate rescaled one-photon absorption).
methoxy group in position sixth, seventh, and eighth.27 Another
example has been described by Ito et al. with an analogue of 3g
(where the ester in the fourth position was replaced by a
hydroxyl group). The quantum yield of this derivative (6%) is
one log lower than with our structure (60%).28 Other studies
showed as for our structures that electron-withdrawing
substituent induced a loss of fluorescence.29−32
Two-Photon Absorption Properties. In order to assess
the interest of these red-shifted fluorescent derivatives as
potential probes for biphotonic imaging, we have investigated
their TPA responses in the spectral region of interest for
bioimaging (i.e., 700−1000 nm region) by measuring their two-
photon excited fluorescence in solution.33 These small-size
chromophores show a broad TPA band located in the 750−
1000 nm region, which matches the low-energy one-photon
absorption band, indicating that the lowest one-photon excited
state is also two-photon allowed (Figure 2).
We note that chromophores 3g and 3h, which bear identical
ED substituent in the sixth or seventh position, show similar
TPA maximum cross-section (12 and 13 GM, respectively), but
the TPA band of compound 3g is red-shifted in agreement with
the bathochromic shift of the one-photon absorption (Table 2).
On the other hand, slight increase of ED strength (3d → 3f →
3g → 3i) induces either a red-shift of the TPA bands (3d → 3f
→ 3g) or a marked increase (by almost a factor of 2) for 3g →
3i. As a result, chromophore 3i has a TPA maximum action
cross-section at 920 nm, which is about 2 orders of magnitude
larger than that of flavines34,35 (i.e., common endogenous
chromophores having the largest TPA action maximum cross
sections in the NIR region). We stress that this is not the case
for one-photon excitation in the near UV−visible region;
flavines having larger maximum absorption coefficient than the
quinoline derivatives investigated in the present work. This
indicates that two-photon excitation would allow more selective
excitation of the newly synthesized fluorescent derivatives in
biological conditions thanks to the large contrast between their
two-photon absorption cross-section and that of endogenous
fluorophores.36
CONCLUSION
■
The present study has demonstrated that the implemented
synthetic methodologies (classical or biphasic) give access to a
large variety of substituted quinoline diesters in reasonable to
good yields. Moreover, the elucidation of cyclization mecha-
nism allows the control of substitution either in the phenyl or
in the heterocyclic ring of quinolines, paving the way to a wide
range of substitutions.
Compounds 3f−3i, which bear a strong ED substituent in
the sixth or seventh position, represent promising moieties for
use as new fluorescent tags for monitoring of biomolecules due
to their reduced size, suitable fluorescence, much larger TPA
cross sections than endogenous chromophores at 900 nm,
biocompatibility and possibility for heterofunctionalization. We
are currently investigating this route.
EXPERIMENTAL SECTION
■
Materials and Methods. All air-sensitive manipulations were
performed under a positive pressure of nitrogen or argon using
standard Schlenk line. Solvents were degassed prior to use when
necessary. THF was freshly distilled before use. Column chromatog-
raphy was conducted on silica gel 60. NMR spectra were recorded on a
250 or 500 MHz (1H frequency) spectrometer. Chemical shifts are
reported using tetramethylsilane or the residual solvent peak as
internal reference for 1H or for 13C. Product visualization was achieved
with 2% (w/v) ninhydrin in ethanol. Thin layer chromatography
(TLC) system for routine monitoring the course of certain reactions
and confirming the purity of analytical samples employed aluminum-
backed silica gel plates: cyclohexane/ethyl acetate or CH2Cl2/MeOH
were used as developing solvents, and detection of spots was made by
UV light and/or by iodine vapors.
8298
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
trifluoroacetamido)quinoline-2,4-dicarboxylate which was chromato-
graphed (cyclohexane/EtOAc, 3:1) to isolate a orange amorphous
1
solid (yield method A, 8% (31 mg): H NMR (δ, ppm) (CDCl3, 250
MHz) 9.18 (d, J = 2.4 Hz, 1H), 8.71 (s, 1H), 8.38 (d, J = 9.5 Hz, 1H),
8.15 (dd, J= 9.5, 2.4 Hz, 1H), 4.70 (brs, 1H), 4.58 (q, J = 7.2 Hz, 2H),
4.55 (q, J = 7.2 Hz, 2H), 1.51 (t, J = 7.2 Hz, 6H); 13C NMR (δ, ppm)
(CDCl3, 250 MHz) 165.6, 164.8, 147.9, 155.3 (d, J = 37.9 Hz), 146.7,
136.8, 135.9, 132.8, 127.0, 124.0, 123.5, 115.7 (d, J = 288.9 Hz), 115.4,
62.8, 62.6, 14.5, 14.4; HRMS (ESI) calcd. for C17H16F3N2O5 [M + H]
385.1011, found 385.1013.
General Procedure for the Synthesis of Quinoline-2,4-
dicarboxylic Acid Diethyl Ester. Method A. A mixture of diethyl
2-ketoglutaconate 2 (2.0 mmol) and aniline (1.0 mmol) in 2 mL of
TFA was stirred at reflux for 18−24 h; after TFA removal by
evaporation, the residue was dissolved in 20 mL of AcOEt, and the
solution was washed with 5 mL of saturated aqueous NaHCO3, dried
over anhydrous MgSO4, filtered, and evaporated under reduced
pressure. The desired products were purified by flash chromatography
on silica gel (cyclohexane/ethyl acetate).
Method B. Phosphomolybdic acid (0.02 mmol) and sodium
dodecylsulfate (0.02 mmol) were dissolved in water (5 mL). A
solution of aniline (1.0 mmol) and diethyl 2-ketoglutaconate 2 (1.5
mmol) in CH2Cl2 (5 mL) was then added to the previous mixture and
vigorously stirred at 80 °C for 18 h. After completion of the reaction,
the lower layer was separated and slighly basified using sodium
bicarbonate solution, and the product was extracted with ethyl acetate.
The organic layer was dried over sodium sulfate and concentrated to
get a crude product, which was further purified by column
chromatography over silica gel.
Diethyl 6-(methylamino)quinoline-2,4-dicarboxylate (3f). N-
Methyl-p-phenylenediamine dihydrochloride affords the correspond-
ing quinoline-2,4-dicarboxylic acid diethyl ester, which was chromato-
graphed (cyclohexane/EtOAc, 2:1) to isolate a red amorphous solid
1
(yield method A, 15% (45 mg)): H NMR (δ, ppm) (CDCl3, 250
MHz) 8.60 (s, 1H), 8.16 (d, J = 9.2 Hz, 1H), 7.78 (d, J = 2.4 Hz, 1H),
7.20−7.23 (m, 1H), 4.52 (q, J = 7.2 Hz, 2H), 4.49 (q, J = 7.2 Hz, 2H),
3.00 (s, 3H), 1.47 (t, J = 7.2 Hz, 6H); 13C NMR (δ, ppm) (CDCl3,
250 MHz) 166.2, 164.9, 150.5, 143.5, 141.0, 132.0, 131.6, 129.83,
123.6, 123.1, 99.8, 62.3, 61.8, 30.3, 14.5, 14.4; HRMS (ESI) calcd. for
C16H19N2O4 [M + H] 303.1345, found 303.1340.
Diethyl 6-(dimethylamino)quinoline-2,4-dicarboxylate (3g). 4-
(Dimethylamino)aniline affords the corresponding quinoline-2,4-
dicarboxylic acid diethyl ester, which was chromatographed (cyclo-
hexane/EtOAc, 5:1) to isolate a orange amorphous solid (yield
Diethyl quinoline-2,4-dicarboxylate (3a). Aniline affords the
unsubstituted quinoline-2,4-dicarboxylic acid diethyl ester, which was
chromatographed (cyclohexane/EtOAc, 6:1) to isolate a light beige
amorphous solid (yield method A, 47% (128 mg); method B, 11% (30
1
method A, 25% (79 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz)
8.59 (s, 1H), 8.14 (d, J = 9.4 Hz, 1H), 7.89 (d, J = 2.6 Hz, 1H), 7.39
(dd, J= 9.4, 2.6 Hz, 1H), 4.51 (q, J = 7.2 Hz, 2H), 4.46 (q, J = 7.2 Hz,
2H), 3.14 (s, 6H), 1.46 (t, J = 7.2 Hz, 3H), 1.45 (t, J = 7.2 Hz, 3H);
13C NMR (δ, ppm) (CDCl3, 250 MHz) 166.6, 165.6, 151.1, 143.3,
142.1, 132.6, 131.5, 129.0, 123.8, 119.7, 101.9, 62.1, 61.9, 40.6 (2C),
14.6, 14.5; HRMS (ESI) calcd. for C17H21N2O4 [M + H] 317.1501,
found 317.1496.
Diethyl 7-(dimethylamino)quinoline-2,4-dicarboxylate (3h). N,N-
Dimethyl-1,3-phenylenediamine dihydrochloride affords the corre-
sponding quinoline-2,4-dicarboxylic acid diethyl ester, which was
chromatographed (cyclohexane/EtOAc, 5:1) to isolate a brown
amorphous solid (yield method A, 23% (72 mg)): 1H NMR (δ,
ppm) (CDCl3, 250 MHz) 8.57 (d, J = 9.6 Hz, 1H), 8.25 (s, 1H),
7.24−7.30 (m, 2H), 4.49 (q, J = 7.2 Hz, 2H), 4.43 (q, J = 7.2 Hz, 2H),
3.04 (s, 6H), 1.42 (t, J = 7.2 Hz, 3H), 1.40 (t, J = 7.2 Hz, 3H); 13C
NMR (δ, ppm) (CDCl3, 250 MHz) 166.3, 165.3, 151.3, 150.8, 147.9,
135.9, 126.0, 119.8, 119.0, 117.9, 107.7, 62.3, 61.9, 40.3 (2C), 14.5,
14.4. ; HRMS (ESI) calcd. for C17H21N2O4 [M + H] 317.1501, found
317.1494.
1
mg)): H NMR (δ, ppm) (CDCl3, 250 MHz) 8.78 (d, J = 8.2 Hz,
1H), 8.61 (s, 1H), 8.34 (d, J = 8.2 Hz, 1H), 7.67−7.83 (m, 2H), 4.55
(q, J = 7.2 Hz, 2H), 4.50 (q, J = 7.2 Hz, 2H), 1.47 (t, J = 7.2 Hz, 3H),
1.45 (t, J = 7.2 Hz, 3H); 13C NMR (δ, ppm) (CDCl3, 250 MHz)
165.9, 165.0, 148.7, 148.0, 136.8, 131.4, 130.6, 130.3, 126.4, 125.7,
122.2, 62.7, 62.3, 14.5, 14.4; HRMS (ESI) calcd. for C15H16NO4 [M +
H] 274.1079, found 274.1072.
Diethyl 6-methylquinoline-2,4-dicarboxylate (3b). 4-Methylani-
line affords the corresponding quinoline-2,4-dicarboxylic acid diethyl
ester, which was chromatographed (cyclohexane/EtOAc, 5:1) to
isolate a yellow amorphous solid (yield method A, 55% (158 mg);
1
method B, 32% (92 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz)
8.61 (s, 1H), 8.59 (brs, 1H), 8.27 (d, J = 8.7 Hz, 1H), 7.67 (dd, J = 8.7,
2 Hz, 1H), 4.58 (q, J = 7.2 Hz, 2H), 4.53 (q, J = 7.2 Hz, 2H), 2.61 (s,
3H), 1.50 (t, J = 7.2 Hz, 3H), 1.49 (t, J = 7.2 Hz, 3H); 13C NMR (δ,
ppm) (CDCl3, 250 MHz) 165.8, 164.9, 147.2, 146.7, 140.9, 135.6,
132.8, 130.8, 126.4, 124.3, 122.1, 62.4, 62.0, 22.3, 14.4, 14.3; HRMS
(ESI) calcd. for C16H18NO4 [M + H] 288.1236, found 288.1238.
Diethyl 7-methylquinoline-2,4-dicarboxylate (3c). 3-Methylaniline
affords the corresponding quinoline-2,4-dicarboxylic acid diethyl ester,
which was chromatographed (cyclohexane/EtOAc, 4:1) to isolate a
yellow amorphous solid. (yield method A, 20% (57 mg); method B,
Diethyl 6-(diethylamino)quinoline-2,4-dicarboxylate (3i). N,N-
Diethyl-p-phenylenediamine affords the corresponding quinoline-2,4-
dicarboxylic acid diethyl ester, which was chromatographed (cyclo-
hexane/EtOAc, 5:1) to isolate a orange amorphous solid (yield
1
method A, 15% (51 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz)
1
8.60 (s, 1H), 8.14 (d, J = 9.5 Hz, 1H), 7.96 (d, J = 2.3 Hz, 1H), 7.38
(dd, J= 9.5, 2.3 Hz, 1H), 4.53 (q, J = 7.2 Hz, 2H), 4.48 (q, J = 1.45 =
7.2 Hz, 2H), 3.55 (q, J = 7.2 Hz, 4H), 1.47 (t, J = 7.2 Hz, 3H), 1.45 (t,
J = 7.2 Hz, 3H), 1.28 (t, J = 7.2 Hz, 6H); 13C NMR (δ, ppm) (CDCl3,
250 MHz) 166.6, 165.6, 148.7, 143.3, 141.8, 132.8, 132.1, 129.3, 123.8,
119.6, 101.5, 62.0, 61.6, 45.2 (2C), 14.6, 14.5, 12.7 (2C); HRMS (ESI)
calcd. for C19H25N2O4 [M + H] 345.1814, found 345.1807.
Diethyl 6-nitroquinoline-2,4-dicarboxylate (3j). 4-Nitroaniline
affords the corresponding quinoline-2,4-dicarboxylic acid diethyl
ester, which was chromatographed (cyclohexane/EtOAc, 9:1) to
isolate a orange amorphous solid (yield method A, 33% (105 mg)): 1H
NMR (δ, ppm) (CDCl3, 500 MHz) 9.84 (d, J = 2.4 Hz, 1H), 8.77 (s,
1H), 8.55 (dd, J = 9.4, 2.4 Hz, 1H), 8.47 (d, 9.4 Hz, 1H), 4.59 (q, J =
7.2 Hz, 2H), 4.57 (q, J = 7.2 Hz, 2H), 1.52 (t, 7.2 Hz, 3H), 1.50 (t, J =
7.2 Hz, 3H); 13C NMR (δ, ppm) (CDCl3, 500 MHz) 164.7, 164.2,
151.3, 150.4, 148.0, 138.3, 133.1, 125.5, 123.9 (2C), 123.8, 63.1, 63.0,
14.4, 14.3; HRMS (ESI) calcd. for C15H15N2O6 [M + H] 319.0930,
found 319.0936.
48% (138 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz) 8.70 (d, J =
8.7, 1H), 8.58 (s, 1H), 8.17 (s, 1H), 7.58 (dd, J = 8.7, 1.3 Hz, 1H),
4.57 (q, J = 7.2 Hz, 2H), 4.51 (q, J = 7.2 Hz, 2H), 2.58 (s, 3H), 1.50 (t,
J = 7.2 Hz, 3H), 1.48 (t, J = 7.2 Hz, 3H); 13C NMR (δ, ppm) (CDCl3,
250 MHz) 165.9, 165.0, 148.9, 147.8, 141.2, 136.4, 132.7, 130.2, 125.2,
124.5, 121.5, 62.6, 62.2, 21.8, 14.5, 14.4; HRMS (ESI) calcd. for
C16H18NO4 [M + H] 288.1236, found 288.1231.
Diethyl 6-aminoquinoline-2,4-dicarboxylate (3d). 1-4-Phenyl-
enediamine affords the diethyl 6-aminoquinoline-2,4-dicarboxylate
which was chromatographed (cyclohexane/EtOAc, 4:1) to isolate a
yellow amorphous solid (yield method B, 5% (14.4 mg)): 1H NMR (δ,
ppm) (CDCl3, 250 MHz) 8.59 (s, 1H), 8.12 (d, J = 9.1 Hz, 1H), 7.98
(d, J = 2.5 Hz, 1H), 7.22 (dd, J = 9.1, 2.6 Hz, 1H), 4.54 (q, J = 7.0 Hz,
2H), 4.48 (q, J = 7.0 Hz, 2H), 4.35 (brs, 2H), 1.48 (t, J = 7.1 Hz, 3H),
1.46 (t, J = 7.1 Hz, 3H); 13C NMR (δ, ppm) (CDCl3, 250 MHz)
166.3, 165.4, 148.5, 144.3, 143.2, 133.1, 132.3, 129.0, 123.4, 122.4,
104.6, 62.2, 61.8, 14.6, 14.5; HRMS (ESI) calcd. for C15H17N2O4 [M +
H] 289.1188, found 289.1180.
Diethyl 6-hydroxyquinoline-2,4-dicarboxylate (3l). 4-Hydroxyani-
line affords the corresponding quinoline-2,4-dicarboxylic acid diethyl
Diethyl 6-(2,2,2-trifluoroacetamido)quinoline-2,4-dicarboxylate
(3e). 1-4-Phenylenediamine affords the diethyl 6-(2,2,2-
8299
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
ester, which was chromatographed (cyclohexane/EtOAc, 2:1) to
isolate a light yellow amorphous solid (yield method A, 13% (37 mg);
method B, 34% (98 mg)): H NMR (δ, ppm) (CD3OD, 250 MHz)
8.48 (s, 1H), 8.18−8.03 (m, 2H), 7.43 (dd, J = 9.3, 2.7 Hz, 1H), 4.50
(q, J = 7.1 Hz, 2H), 4.49 (q, J = 7.1 Hz, 2H), 1.47 (t, J = 7.1 Hz, 6H);
13C NMR (δ, ppm) (MeOD, 250 MHz) 166.9, 166.0, 161.0, 145.3,
145.0, 135.1, 133.1, 129.7, 124.72, 123.4, 107.6, 63.2, 63.0, 14.6, 14.5;
HRMS (ESI) calcd. for C15H16NO5 [M + H] 290.1028, found
290.1028.
Hz, 1H), 7.56−7.62 (m, 3H), 7.32−7.43 (m, 3H), 7.19 (d, J = 7.9 Hz,
1H), 5.44 (s, 2H), 4.56 (q, J = 7.2 Hz, 2H), 4.50 (q, J = 7.2 Hz, 2H),
1.46−1.52 (m, 6H); 13C NMR (δ, ppm) (CDCl3, 250 MHz) 165.9,
165.1, 155.4, 146.6, 141.3, 136.5, 136.5, 130.7, 128.6 (2C), 127.9,
127.6, 127.2 (2C), 122.5, 117.6, 111.2, 71.2, 62.3, 62.2, 14.3, 14.3;
HRMS (ESI) calcd. for C22H22NO5 [M + H] 380.1498, found
380.1494.
1
Diethyl 8-hydroxy-5-methylquinoline-2,4-dicarboxylate (3s). To
a solution of diethyl 8-(tert-butoxycarbonyloxy)-5-methylquinoline-
2,4-dicarboxylate (3t) (1 mmol) in CH2Cl2 was added piperidine (2
mmol). The reaction mixture was stirred at room temperature for 18
h, and then the solvent was evaporated, and the residue was filtered
through a pad of silica gel (cyclohexane/EtOAc, 2:1). The solvent was
Diethyl 7-hydroxyquinoline-2,4-dicarboxylate (3m). 3-Hydroxya-
niline affords the corresponding quinoline-2,4-dicarboxylic acid diethyl
ester, which was chromatographed (cyclohexane/EtOAc, 1:1) to
isolate a yellow amorphous solid (yield method A, 8% (23 mg);
1
1
evaporated to give a yellow oil (yield 60%, 182 mg): H NMR (δ,
method B, 20% (58 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz)
ppm) (CDCl3, 250 MHz) 8.48 (brs, 1H), 8.13 (s, 1H), 7.42 (d, J = 7.8
Hz, 1H), 7.17 (d, J = 7.8 Hz, 1H), 4.52 (q, J = 7.2 Hz, 2H), 4.52 (q, J
= 7.2 Hz, 2H), 2.53 (s, 3H), 1.48 (t, J = 7.2 Hz, 3H), 1.45 (t, J = 7.2
Hz, 3H); 13C NMR (δ, ppm) (CDCl3, 250 MHz) 169.2, 164.3, 151.9,
144.4, 140.9, 138.9, 133.3, 124.4, 123.8, 120.5, 111.1, 62.7, 62.4, 20.5,
14.5, 14.2; HRMS (ESI) calcd. for C16H18NO5 [M + H] 304.1185,
found 304.1181.
8.35 (s, 1H), 8.27 (d, J = 9.3 Hz, 1H), 7.57 (d, J = 1.7, 1H), 6.94 (dd, J
= 9.3, 1.7 Hz, 1H), 4.58 (q, J = 7.2 Hz, 2H), 4.36 (q, J = 7.2 Hz, 2H),
1.57 (t, J = 7.2 Hz, 3H), 1.15 (t, J = 7.2 Hz, 3H); 13C NMR (δ, ppm)
(CDCl3, 250 MHz) 165.5, 164.2, 159.9, 148.9, 146.04, 136.8, 126.7,
123.3, 120.8, 119.2, 109.7, 62.6, 62.2, 14.4, 14.0; HRMS (ESI) calcd.
for C15H16NO5 [M + H] 290.1028, found 290.1031.
Diethyl 8-hydroxyquinoline-2,4-dicarboxylate (3n). 2-Aminophe-
nol affords the corresponding quinoline-2,4-dicarboxylic acid diethyl
ester, which was chromatographed (cyclohexane/EtOAc, 5:1) to
isolate a orange amorphous solid (yield method A, 30% (86 mg);
Diethyl 8-(tert-butoxycarbonyloxy)-5-methylquinoline-2,4-dicar-
boxylate (3t). A solution of 2-amino-4-methylphenol (1.0 mmol) and
diethyl 2-ketoglutaconate (2.0 mmol) in 2 mL of TFA was stirred at
reflux for 24 h, after which TFA was distilled off. The residue was
dissolved in 20 mL of EtOAc, and the solution was washed with 5 mL
of saturated aqueous NaHCO3, dried over anhydrous MgSO4, filtered,
and evaporated under reduced pressure. The crude product (yellow
oil) was used in the next step without purification. The residue (1.0
mmol) was solubilized in anhydrous CH2Cl2 (10 mL), and both 4-
dimethylaminopyridine (1.2 mmol) and di-tert-butyl dicarbonate (1.0
mmol) were added at 0 °C under nitrogen. The mixture was first
stirred for 5 min at 0 °C and then for 18 h at room temperature. The
reaction mixture was evaporated under reduced pressure, and the
residue was purified through a silica gel column (cyclohexane/EtOAc,
1
method B, 10% (29 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz)
8.63 (s, 1H), 8.24 (d, J = 8.7 Hz, 1H), 7.66 (t, J = 8.2 Hz, 1H), 7.26 (d,
J = 7.7 Hz, 1H), 4.53 (dd, J=14.2, 7.2 Hz, 2H), 4.51 (d, J=14.3, 7.2 Hz,
2H), 1.48 (t, J = 7.2 Hz, 3H), 1.47 (t, J=7.2 Hz, 3H); 13C NMR (δ,
ppm) (CDCl3, 250 MHz) 165.7, 164.5, 153.5, 145.2, 139.0, 136.7,
132.1, 126.9, 123.0, 116.1, 111.3, 62.5, 62.3, 14.5, 14.4; HRMS (ESI)
calcd. for C15H16NO5 [M + H] 290.1028, found 290.1025.
Diethyl 6-methoxyquinoline-2,4-dicarboxylate (3o). p-Anisidine
affords the corresponding quinoline-2,4-dicarboxylic acid diethyl ester,
which was chromatographed (cyclohexane/EtOAc, 6:1) to isolate a
light beige amorphous solid (yield method A, 39% (118 mg); method
1
1
5:1) to yield 190 mg (23%) of 3t as a yellow amorphous solid: H
B, 28% (85 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz) 8.67 (s,
NMR (δ, ppm) (CDCl3, 250 MHz) 8.16 (s, 1H), 7.45−7.53 (m, 2H),
4.52 (q, J = 7.2 Hz, 2H), 4.49 (q, J = 7.2 Hz, 2H), 2.61 (s, 3H), 1.60
(s, 9H), 1.45 (t, 7.2 Hz, 3H), 1.45 (t, J = 7.2 Hz, 3H); 13C NMR (δ,
ppm) (CDCl3, 250 MHz) 169.0, 164.6, 152.0, 147.0, 146.9, 141.9,
140.8, 132.1, 131.3, 125.1, 121.7, 120.6, 83.7, 62.7, 62.3, 27.8 (3C),
21.1, 14.5, 14.1; HRMS (ESI) calcd. for C21H26NO7 [M + H]
404.1709, found 404.1713.
1H), 8.21−8.226 (m, 2H), 7.45 (dd, J = 9.3, 2.8 Hz, 1H), 4.56 (q, J =
7.2 Hz, 2H), 4.51 (q, J = 7.2 Hz, 2H), 3.98 (s, 3H), 1.49 (t, 7.2 Hz,
3H), 1.48 (t, J = 7.2 Hz, 3H); 13C NMR (δ, ppm) (CDCl3, 250 MHz)
166.0, 165.1, 161.1, 145.2, 145.0, 133.8, 132.8, 128.5, 123.9, 123.1,
103.1, 62.4, 62.0, 55.8, 14.5, 14.4; HRMS (ESI) calcd. for C16H18NO5
[M + H] 304.1185, found 304.1179.
Diethyl 7-methoxyquinoline-2,4-dicarboxylate (3p). m-Anisidine
affords the corresponding quinoline-2,4-dicarboxylic acid diethyl ester,
which was chromatographed (cyclohexane/EtOAc, 4:1) to isolate a
brown amorphous solid (yield method A, 21% (63 mg); method B,
2,4-Bis(ethoxycarbonyl)quinoline-6-carboxylic acid (3u). 4-Ami-
nobenzoic acid affords the corresponding quinoline-2,4-dicarboxylic
acid diethyl ester, which was chromatographed (CH2Cl2/MeOH,
9.5:0.5) to isolate an orange amorphous solid (yield method A, 32%
1
33% (100 mg)): H NMR (δ, ppm) (CDCl3, 250 MHz) 8.71 (d, J =
1
(101 mg)): H NMR (δ, ppm) (DMSO-d6, 500 MHz) 9.28 (s, 1H),
9.2 Hz, 1H), 8.50 (s, 1H), 7.69 (brs, 1H), 7.39 (dd, J = 9.5, 2.6 Hz,
1H), 4.57 (q, J = 7.2 Hz, 2H), 4.51 (q, J = 7.2 Hz, 2H), 4.97 (s, 3H),
1.49 (t, 7.2 Hz, 3H), 1.45 (t, J = 7.2 Hz, 3H); 13C NMR (δ, ppm)
(CDCl3, 250 MHz) 165.9, 165.0, 161.3, 150.7, 148.0, 136.5, 126.6,
123.9, 121.9, 120.1, 108.6, 62.6, 62.2, 55.9, 14.5, 14.4; HRMS (ESI)
calcd. for C16H18NO5 [M + H] 304.1185, found 304.1188.
8.42−8.44 (m, 2H), 8.25 (m, 1H), 4.46−4.52 (m, 4H), 1.39−1.43(m,
6H); 13C NMR (δ, ppm) (DMSO-d6, 500 MHz) 169.0, 165.0, 164.1,
148.8, 148.4, 137.2, 131.1, 130.1, 126.9, 126.2, 124.6, 121.4, 62.1, 61.9,
14.2, 14.1; HRMS (ESI) calcd. for C16H16NO6 [M + H] 318.0978,
found 318.0973.
4-(Ethoxycarbonyl)-7-methoxyquinoline-2-carboxylic acid (4p).
To a solution of diethyl 7-methoxyquinoline-2,4-dicarboxylate (3p)
(275 mg, 1 mmol) in of THF/H2O (5:5, 10 mL) was added NaOH
(40 mg, 1 mmol). The reaction mixture was monitored with TLC
(cyclohexane/EtOAc, 5:5). After the completion of reaction, the
sovent was evaporated, and the crude residue was purified by
preparative RP-HPLC (Preparative C18 column, λ 240 nm, solvent
system: H2O (A), CH3CN (B), 8 mL/min, gradient: 0′-5′: 80% (A)/
20% (B); 20′-30′: 80% (A)/20% (B); 40′-60′: 80% (A)/20% (B)) to
yield a light yellow amorphous solid 4-(ethoxycarbonyl)-7-methox-
yquinoline-2-carboxylic acid (30%, 82 mg): 1H NMR (δ, ppm) (D2O,
250 MHz) 8.25 (d, J = 9.2 Hz, 1H), 8.17 (s, 1H), 7.36 (d, J= 2.7 Hz,
1H), 7.23 (dd, J = 9.4, 2.7 Hz, 1H), 4.54 (q, J = 7.2 Hz, 2H), 3.98 (s,
3H), 1.49 (t, J = 7.2 Hz, 3H); 13C NMR (δ, ppm) (D2O, 500 MHz)
172.1, 168.6, 161.4, 154.4, 149.6, 137.5, 127.0, 122.6, 121.0, 120.1,
107.8, 64.1, 56.5, 14.2; HRMS (ESI) calcd. for C14H14NO5 [M + H]
276.0872, found 276.0866.
Diethyl 8-methoxyquinoline-2,4-dicarboxylate (3q). 2-Methoxya-
niline affords the corresponding quinoline-2,4-dicarboxylic acid diethyl
ester, which was chromatographed (cyclohexane/EtOAc, 2:1) to
isolate a light yellow amorphous solid (yield method A, 46% (139
1
mg); method B, 13% (39 mg)): H NMR (δ, ppm) (CDCl3, 250
MHz) 8.66 (s, 1H), 8.33 (dd, J = 8.8, 0.6 Hz, 1H), 7.67 (dd, J = 8.8,
7.8 Hz, 1H), 7.13 (dd, J = 7.8, 0.6 Hz, 1H), 4.54 (q, J = 7.0 Hz, 2H),
4.51 (q, J = 7.0 Hz, 2H), 4.09 (s, 3H), 1.50 (t, J = 7.0 Hz, 3H), 1.45 (t,
J = 7.0 Hz, 3H); 13C NMR (δ, ppm) (CDCl3, 250 MHz) 165.9, 165.1,
156.3, 146.5, 140.8, 136.6, 130.9, 127.6, 122.8, 117.1, 108.4, 62.7, 62.3,
56.3, 14.4, 14.4; HRMS (ESI) calcd. for C16H18NO5 [M + H]
304.1185, found 304.1182.
Diethyl 8-(benzyloxy)quinoline-2,4-dicarboxylate (3r). 2-Benzy-
loxyaniline affords the corresponding quinoline-2,4-dicarboxylic acid
diethyl ester, which was chromatographed (cyclohexane/EtOAc, 8:1)
to isolate a yellow amorphous solid (yield method A, 30% (113 mg)):
1H NMR (δ, ppm) (CDCl3, 250 MHz) 8.67 (s, 1H), 8.36 (d, J = 8.2
8300
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
Methyl 4-(benzylcarbamoyl)-7-(dimethylamino)quinoline-2-car-
boxylate (3v). Methyl 5-(benzylamino)-4,5-dioxopent-2-enoate (7).
Dimethyl 2-oxoglutarate (174 mg, 1.0 mmol) was dissolved in 2 M
benzylamine in THF (5 mL, 1.5 mmol) and stirred for 6 h at room
temperature. The solvent was then evaporated in vacuo, and the
remaining oily residue was purified by column chromatography
(cyclohexane/EtOAc, 1:3), affording 206 mg (82%) of methyl 5-
(benzylamino)-4,5-dioxopentanoate as a colorless oil (6): 1H NMR (δ,
ppm) (CDCl3, 250 MHz) 7.26−7.32 (m, 5H), 4.48 (d, J = 6.1 Hz,
2H), 3.68 (s, 3H), 3.27 (t, J = 6.5 Hz, 2H), 2.65 (t, J = 6.5 Hz, 2H). To
a solution of methyl 5-(benzylamino)-4,5-dioxopentanoate (250 mg,
1.0 mmol)) dissolved in 15 mL of CH2Cl2 was added bromine (0.077
mL, 1.5 mmol) dissolved in 1 mL of CH2Cl2. The solution was stirred
at 35 °C for 18 h, after which the solvent and residual HBr were
evaporated to yield methyl 5-(benzylamino)-3-bromo-4,5-dioxopenta-
noate as an yellow oil (yield, quantitative): 1H NMR (δ, ppm)
(CDCl3, 250 MHz) 7.21−7.23 (m, 5H), 5.56 (dd, J = 9.2, 6.0 Hz, 1H),
4.43 (d, J= 6.1 Hz, 2H), 3.59 (s, 3H), 3.22 (dd, J = 17.2, 9.2 Hz, 1 H),
3.02 (dd, J = 17.2, 6.1 Hz). Triethylamine (2.0 mmol, 0.278 mL) was
added to a solution of 5-(benzylamino)-3-bromo-4,5-dioxopentanoate
(327 mg, 1 mmol) in 10 mL of diethyl ether. After being stirred for 6
h, the solvent was then evaporated in vacuo, and the oily residue was
purified by column chromatography (cyclohexane/EtOAc, 4:1),
affording the methyl 5-(benzylamino)-4,5-dioxopent-2-enoate as a
yellow amorphous solid (7) (61%, 151 mg): 1H NMR (δ, ppm)
(CDCl3, 250 MHz) 8.00 (d, J = 16.4 Hz, 1H), 7.30−7.32 (m, 5H),
7.04 (d, J = 16.4 Hz, 1H), 4.51 (d, J = 6.1 Hz, 2H), 3.83 (s, 3H); 13C
NMR (δ, ppm) (CDCl3, 250 MHz) 185.5, 165.4, 159.9, 135.1, 133.0,
128.9 (2C), 128.0, 127.9 (2C), 127.9, 52.6, 43.6.
Methyl 4-(benzylcarbamoyl)-7-(dimethylamino)quinoline-2-car-
boxylate (3v). A mixture of methyl 5-(benzylamino)-4,5-dioxopent-2-
enoate 7 (1.5 mmol) and N,N-dimethyl-1,3-phenylenediamine
dihydrochloride (1.0 mmol) in 3 mL of TFA affords the corresponding
quinoline-2,4-dicarboxylic acid diethyl ester, which was chromato-
graphed (cyclohexane/EtOAc, 3:1) to isolate an orange amorphous
solid (yield 19%, 69 mg): 1H NMR (δ, ppm) (CDCl3, 500 MHz) 8.12
(d, J = 10 Hz, 1H), 7.83 (s, 1H), 7.20−7.41 (m, 7H), 6.75 (brs, 1H),
4.72 (d, J = 5.6 Hz, 2H), 4.01 (s, 3H), 3.08 (s, 6H); 13C NMR (δ,
ppm) (CDCl3, 250 MHz) 167.2, 165.9, 151.7, 150.3, 147.5, 142.3,
137.8, 129.0 (2C), 128.2 (2C)., 127.9, 125.9, 119.3, 118.3, 114.3,
107.5, 53.2, 44.3, 40.4 (2C); HRMS (ESI) calcd. for C21H22N3O3 [M
+ H] 364.1661, found 364.1659.
4-(Benzylcarbamoyl)-7-(dimethylamino)quinoline-2-carboxylic
acid (4v). To a solution of methyl 4-(benzylcarbamoyl)-7-
(dimethylamino)quinoline-2-carboxylate (3v) (100 mg, 0.28 mmol)
in of THF/H2O (5:5, 10 mL) was added NaOH (7 mg, 0.28 mmol).
The reaction mixture was monitored with TLC (cyclohexane/EtOAc,
1:1). The solvent was removed under reduced pressure, the solid was
washed with chloroform (20 mL), dissolved in water (3 mL) and then
acidified with 0.1 N HCl solution to give a yellow precipitate. The
precipitate was filtered to give 4v (68%, 66 mg) as a yellow amorphous
solid: 1H NMR (δ, ppm) (DMSO-d6, 500 MHz) 9.36 (brs, 1H), 7.95
(d, J = 9.3 Hz, 1H), 7.92 (s, 1H), 7.46−7.34 (m, 5H), 7.31−7.23 (m,
2H), 4.53 (d, J = 5.5 Hz, 2H), 3.02 (s, 6H); 13C NMR (δ, ppm)
(DMSO-d6, 250 MHz) 167.9, 167.5, 157.3, 150.7, 149.2, 141.4, 139.5,
128.3 (2C), 127.2 (2C), 126.8, 125.3, 116.9, 116.5, 115.3, 107.6, 42.5,
39.8 (2C); HRMS (ESI) calcd. for C20H20N3O3 [M + H] 350.1505,
found 350.1503.
Photophysical Properties. Emission spectra were obtained using
a spectrofluorometer, for each compound at λex = λmax (abs) with Aλex
= 0.1 to minimize internal absorption. Fluorescence quantum yields
were measured on samples at rt; fluorescein in 0.1 N NaOH (Φ = 0.90
at λexc = 470 nm)37,38 and quinine bisulfate in 1 N H2SO4 (Φ = 0.54 at
λexc = 347 nm) were used as standards depending on the emission
spectral range.
980 nm) according to the experimental protocol established by Xu and
Webb,39,40 and using the appropriate solvent-related refractive index
corrections.41 The quadratic dependence of the fluorescence intensity
on the excitation intensity was verified for all investigated compounds
and wavelengths, indicating that the measurements were carried out in
intensity regimes in which saturation or photodegradation did not
occur. Measurements were conducted using excitation sources
delivering fs pulses. This is preferred in order to avoid excited state
absorption during the pulse duration, a phenomenon that has been
shown to lead to overestimated TPA cross-section values. To span the
700−980 nm range, a Nd:YLF-pumped Ti:sapphire oscillator was used
generating 150 fs pulses at a 76 MHz rate. To span the 1000−1400 nm
range, an OPO (PP-BBO) was added to the setup to collect and
modulate the output signal of the Ti:sapphire oscillator. The excitation
was focused into the cuvette through a microscope objective (10X, NA
0.25). The fluorescence was detected in epifluorescence mode via a
dichroic mirror and a barrier filter by a compact CCD spectrometer.
Total fluorescence intensities were obtained by integrating the
corrected emission.
ASSOCIATED CONTENT
■
S
* Supporting Information
Nuclear magnetic resonance spectra 1D and 2D for new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: Nicolas.pietrancosta@parisdescartes.fr.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by a grant from Agence Nationale
pour la Recherche (Grant 2010 ANR-10-MALZ-105 and ANR-
10-BLAN-1436). We thank Paris Descartes University for YL
fellowship and financial support. MBD thanks the Conseil
Reg
d’excellence).
́
ional d’Aquitaine for financial support (chaire d’accueil
REFERENCES
■
(1) Sheng, R. L.; Wang, P. F.; Gao, Y. H.; Wu, Y.; Liu, W. M.; Ma, J.
J.; Li, H. P.; Wu, S. K. Org. Lett. 2008, 10, 5015.
(2) Jung, H. S.; Kwon, P. S.; Lee, J. W.; Kim, J. I.; Hong, C. S.; Kim, J.
W.; Yan, S. H.; Lee, J. Y.; Lee, J. H.; Joo, T.; Kim, J. S. J. Am. Chem.
Soc. 2009, 131, 2008.
(3) Wu, C. Y.; Wei, J. J.; Tian, D. H.; Feng, Y.; Miller, R. H.; Wang,
Y. M. J. Med. Chem. 2008, 51, 6682.
(4) Wang, C. N.; Wu, C. Y.; Zhu, J. Q.; Miller, R. H.; Wang, Y. M. J.
Med. Chem. 2011, 54, 2331.
(5) Kantevari, S.; Matsuzaki, M.; Kanemoto, Y.; Kasai, H.; Ellis-
Davies, G. C. R. Nat. Methods 2010, 7, 123.
(6) Gordo, J.; Avo, J.; Parola, A. J.; Lima, J. C.; Pereira, A.; Branco, P.
S. Org. Lett. 2011, 13, 5112.
(7) Jones, G.; Jackson, W. R.; Choi, C.; Bergmark, W. R. J. Phys.
Chem. 1985, 89, 294.
(8) Koefod, R. S.; Mann, K. R. Inorg. Chem. 1989, 28, 2285.
(9) Textor, J.; Peixoto, A.; Henrickson, S. E.; Sinn, M.; von Andrian,
U. H.; Westermann, J. Proc. Natl. Acad. Sci. U. S. A. 2011, 108, 12401.
(10) McDole, K.; Xiong, Y.; Iglesias, P. A.; Zheng, Y. X. Dev. Biol.
2011, 355, 239.
(11) Curran, A. C. W. J. Chem. Soc., Perkin Trans. 1 1976, 975.
(12) Misani, F.; Bogert, M. T. J. Org. Chem. 1945, 10, 347.
(13) Sakai, N.; Aoki, D.; Hamajima, T.; Konakahara, T. Tetrahedron
Lett. 2006, 47, 1261.
Two-photon absorption cross sections (σ2) were obtained by
measuring the two-photon excited fluorescence (TPEF) cross sections
(σ2ϕ) and fluorescence emission quantum yield (Φ). TPEF cross
sections of 10−4 M solutions were measured relative to known
reference compounds fluorescein in 0.01 M aqueous NaOH for 700−
8301
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302

The Journal of Organic Chemistry
Article
(14) Wu, Y. C.; Liu, L.; Li, H. J.; Wang, D.; Chen, Y. J. J. Org. Chem.
2006, 71, 6592.
(15) Eisch, J. J.; Dluzniewski, T. J. Org. Chem. 1989, 54, 1269.
(16) Ryabukhin, S. V.; Naumchik, V. S.; Plaskon, A. S.; Grygorenko,
O. O.; Tomachev, A. A. J. Org. Chem. 2011, 76, 5774.
(17) Gladiali, S.; Chelucci, G.; Mudadu, M. S.; Gastaut, M. A.;
Thummel, R. P. J. Org. Chem. 2001, 66, 400.
(18) Zhang, X. X.; Yao, T. L.; Campo, M. A.; Larock, R. C.
Tetrahedron 2010, 66, 1177.
(19) Li, X. J.; Mao, Z. J.; Wang, Y. G.; Chen, W. X.; Lin, X. F.
Tetrahedron 2011, 67, 3858.
(20) Chaskar, A.; Padalkar, V.; Phatangare, K.; Langi, B.; Shah, C.
Synth. Commun. 2010, 40, 2336.
(21) Corey, E. J.; Tramontano, A. J. Am. Chem. Soc. 1981, 103, 5599.
(22) Itoh, S.; Kato, J.; Inoue, T.; Kitamura, Y.; Komatsu, M.; Ohshiro,
Y. Synthesis 1987, 1067.
(23) Carling, R. W.; Leeson, P. D.; Moseley, A. M.; Baker, R.; Foster,
A. C.; Grimwood, S.; Kemp, J. A.; Marshall, G. R. J. Med. Chem. 1992,
35, 1942.
(24) Hilal, S. H.; Karickhoff, S. W.; Carreira, L. A. Quant. Struct.-Act.
Relat. 1995, 14, 348.
(25) Hilal, S. H.; Karickhoff, S. W.; Carreira, L. A. QSAR Comb. Sci.
2003, 22, 565.
(26) Denmark, S. E.; Venkatraman, S. J. Org. Chem. 2006, 71, 1668.
(27) Yoshida, T.; Moriyama, Y.; Nakano, S. Chem. Pharm. Bull. 1992,
40, 1322.
(28) Ito, H.; Matsuoka, M.; Ueda, Y.; Takuma, M.; Kudo, Y.; Iguchi,
K. Tetrahedron 2009, 65, 4235.
(29) Mashraqui, S. H.; Betkar, R.; Chandiramani, M.; Estarellas, C.;
Frontera, A. New J. Chem. 2011, 35, 57.
(30) Piechowska, J.; Gryko, D. T. J. Org. Chem. 2011, 76, 10220.
(31) Xue, L.; Liu, Q.; Jiang, H. Org. Lett. 2009, 11, 3454.
(32) Nosova, E.; Trashakhova, T.; Ustyugov, V.; Mochul’skaya, N.;
Valova, M.; Lipunova, G.; Charushin, V. Russ. Chem. Bull. 2011, 60,
942.
(33) Xu, C.; Zipfel, W.; Shear, J. B.; Williams, R. M.; Webb, W. W.
Proc. Natl. Acad. Sci. U. S. A. 1996, 93, 10763.
(34) Huang, S. H.; Heikal, A. A.; Webb, W. W. Mol. Biol. Cell 2000,
11, 126a.
(35) Huang, S.; Heikal, A. A.; Webb, W. W. Biophys. J. 2000, 78,
443a.
(36) Robin, A. C.; Gmouh, S.; Mongin, O.; Jouikov, V.; Werts, M. H.
V.; Gautier, C.; Slama-Schwok, A.; Blanchard-Desce, M. Chem.
Commun. 2007, 1334.
(37) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991.
(38) Eaton, D. F. Pure Appl. Chem. 1988, 60, 1107.
(39) Xu, C.; Webb, W. W. J. Opt. Soc. Am. B 1996, 13, 481.
(40) Albota, M. A.; Xu, C.; Webb, W. W. Appl. Opt. 1998, 37, 7352.
(41) Werts, M. H. V.; Nerambourg, N.; Pelegry, D.; Le Grand, Y.;
Blanchard-Desce, M. Photochem. Photobiol. Sci. 2005, 4, 531.
8302
dx.doi.org/10.1021/jo301652j | J. Org. Chem. 2012, 77, 8294−8302