Synthesis and NMR studies of novel chromone-2-carboxamide derivatives

Article abstract of DOI:10.1002/mrc.3937

Chromones are heterocyclic compounds of natural or synthetic origin that possess relevant pharmacological activities. Versatile functionalization of the chromone nucleus allows attaining of a chemical diversity suitable to perform structure-activity relationships in drug discovery and development programs. Accordingly, the synthesis and identification of novel chromone carboxamide derivatives with electron-donating and electron-withdrawing substituents in different positions of the exocyclic ring are reported in this work. Their complete structural characterization was performed using one-dimensional and two-dimensional resonance techniques. The data acquired are useful for a prompt analysis of related compounds that encompass our integrated medicinal chemistry sketch. Copyright

Full text of DOI:10.1002/mrc.3937

MRC Letters
Received: 5 November 2012
Revised: 23 December 2012
Accepted: 17 January 2013
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/mrc.3937
Synthesis and NMR studies of novel chromone-
2-carboxamide derivatives
Alexandra Gaspar,a,b Fernando Cagide,a Elias Quezada,a Joana Reis,a
Eugenio Uriarteb and Fernanda Borgesa*
Chromones are heterocyclic compounds of natural or synthetic origin that possess relevant pharmacological activities. Versatile
functionalization of the chromone nucleus allows attaining of a chemical diversity suitable to perform structure–activity relation-
ships in drug discovery and development programs. Accordingly, the synthesis and identification of novel chromone carboxamide
derivatives with electron-donating and electron-withdrawing substituents in different positions of the exocyclic ring are reported in
this work. Their complete structural characterization was performed using one-dimensional and two-dimensional resonance techni-
ques. The data acquired are useful for a prompt analysis of related compounds that encompass our integrated medicinal chemistry
sketch. Copyright © 2013 John Wiley & Sons, Ltd.
1
Keywords: synthesis; chromone carboxamides; H NMR; 13C NMR; HMQC; HMBC
Method A
Introduction
To a solution of chromone-2-carboxylic acid (1.1 mmol) in
Chromones are benzannulated oxygen-containing heterocyclic
dimethylformamide (1.5 ml), phosphoryl chloride (POCl3; 1 mmol)
compounds widely distributed in nature that have a g-pyrone
was added. The mixture was stirred at room temperature for
ring. In fact, the chemical core of chromone has an important
30 min with the in situ formation of the corresponding acyl
place in the realm of natural products, in synthetic organic chem-
chloride. Then, the aromatic amine with the pretended aromatic
istry, and in drug discovery programs because of its particular
pattern was added. The system was heated to 160 ꢀC for 5 min in
structural features and diverse pharmacological properties. The
a microwave apparatus, and the mixture was poured into a
importance of the chromone nucleus is well recognized not only
beaker, and water was added. The formed solid was filtered
by the development of new and improved synthetic methods [1,2]
and purified by recrystallization (CH2Cl2/n-hexane).
but also by their application in medicinal chemistry programs.[3]
N-(2-Methoxyphenyl)-4-oxo-4H-benzopyran-2-carboxamide (1):
The chromone scaffold has emerged as a privileged structure
+
•
Yield 90%; EIMS (m/z): 295 (M , 100), 266 (20), 191 (41), 89 (35)
for drug discovery because of the versatile pharmacological pro-
57 (3).
file and good drug-like properties.[3,4] Besides anti-asthmatic,
N-(3-Methoxyphenyl)-4-oxo-4H-benzopyran-2-carboxamide (2)
anti-inflammatory, anticoagulant, anticancer, and antimicrobial
+
•
Yield 65%; EIMS (m/z): 295 (M , 15), 294 (100), 266 (13), 89 (2),
activities, their application for neurodegenerative diseases, such
57 (8).
as Parkinson, was recently highlighted.[3–5] In fact, the versatile
N-(2-Bromophenyl)-4-oxo-4H-benzopyran-2-carboxamide (4)
functionalization of chromone allows attaining chemical diversity
+
•
Yield 45%; EIMS (m/z): 345 (M + 2, 8), 344 (6), 343 (M , 8), 342
(4), 264 (100), 121 (8), 89 (40), 63 (8).
N-(3-Bromophenyl)-4-oxo-4H-benzopyran-2-carboxamide (5)
Yield 60%; EIMS (m/z): 345 (M + 2, 22), 344 (100), 343 (M , 22),
suitable in either improving the pharmacological profile or dis-
covering new biological applications. Therefore, in a continuation
of our previous studies in the development of novel small-mole-
+
•
cule agents to address the therapeutic needs of neurodegenera-
342 (100), 316 (14), 314 (15), 89 (32), 63 (6).
tive diseases,[6] the synthesis of novel chromone carboxamide
derivatives with electron-donating and electron-withdrawing
substituents in different positions of the exocyclic ring (Fig. 1)
Method B
To a solution of the chromone-2-carboxylic acid (1mmol) in
dimethylformamide (2.5ml) at 4ꢀC was added a solution of benzo-
triazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate
was performed. The selected compounds were appropriate for
a complete identification by 1D and 2D NMR techniques and
for data extrapolation for other chromone derivatives of our
library, speeding up the structure–activity studies of the medici-
nal chemistry program.
*
Correspondence to: Fernanda Borges, Departamento de Química e Bioquímica,
Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre 687, 4169-007
Porto, Portugal. E-mail: fborges@fc.up.pt
Experimental
a CIQUP/Departamento de Química
e Bioquímica Faculdade de Ciências,
Synthesis
Universidade do Porto, Porto, 4169-007, Portugal
The chromone derivatives were synthesized by two synthetic
approaches, previously developed by our group.[5,6]
b Departamento de Química Orgánica, Facultad de Farmacia, Universidad de
Santiago de Compostela, 15782, Santiago de Compostela, Spain
Magn. Reson. Chem. (2013)
Copyright © 2013 John Wiley & Sons, Ltd.

A. Gaspar et al.
Figure 1. Structure of the chromone carboxamide derivatives.
(1mmol) in CH2Cl2 (2.5ml). The mixture was kept in an ice bath and
stirred for 30 min. Then, the substituted aromatic amine was added,
and the mixture was allowed to warm up to room temperature. The
reaction was kept with stirring for 4 h. Work-up of the crude mate-
rial was performed by a liquid–liquid extraction (CH2Cl2), followed
by flash chromatography (CH2Cl2/MeOH) and final purification by
recrystallization (ethyl acetate/n-hexane).
an attempt to accelerate the synthetic process by the application
of a microwave-assisted process via acyl chloride. In this methodol-
ogy, the formation of the acyl chloride intermediate was attained
by the reaction of the chromone-2-carboxylic acid, with phospho-
rus oxychloride. The chromone carboxamide was synthesized by
taking advantage of a microwave reactor involving a condensation
reaction between the previously mentioned intermediate and the
aniline derivative. On the other hand, method B is based on the
activation of the carboxylic acid function under mild reaction
conditions using the coupling reagent benzotriazol-1-yl-oxytripyr-
rolidinophosphonium hexafluorophosphate. The in situ generated
intermediate reacts with the appropriate aniline derivative, giving
rise to the target chromone. It is noteworthy that the microwave-
assisted reaction of the products was finished in a short time with
a low-price reagent and easier work-up.
N-(4-Methoxyphenyl)-4-oxo-4H-benzopyran-2-carboxamide (3)
+
•
Yield 85%; EIMS (m/z): 296 (14), 295 (M , 100), 294 (30), 266 (15),
173 (13), 145 (10), 122 (68), 95 (17), 89 (22), 71 (10), 69 (11), 57 (15).
N-(4-Bromophenyl)-4-oxo-4H-benzopyran-2-carboxamide (6)
+
•
Yield 70%; EIMS (m/z): 345 (M + 2, 48), 344 (38), 343 (M , 49),
342 (28), 145 (20), 89 (100), 63 (21).
NMR spectroscopy
The complete structural characterization of the six synthesized
compounds was achieved by the combined use of 1D and 2D
NMR techniques, such as HMQC and HMBC. The 1H and 13C
chemical shifts (d) and coupling constants, obtained for 1–6
(Fig. 1) as well as the HMBC 13C–1H correlations, allowing
unambiguous assignments of all carbons and hydrogen atoms,
are depicted in Tables 1 and 2.
1H and 13C NMR spectra of the samples, approximately 10%
solutions in deuterated dimethyl sulfoxide, were recorded at room
temperature in 5-mm-outer-diameter tubes. TMS was used as inter-
nal standard, and chemical shifts are expressed in parts per million
(d) and J in hertz. 1D 13C NMR was recorded on a Bruker AMX 500
(Billerica, MA) NMR spectrometer operating at 125.77 MHz, typically
with a 30ꢀ pulse flip angle, a pulse repetition time of 4.8s, and a
spectral width of 31.250Hz with 32K data points. For the DEPT
sequence, the width of the 90ꢀ pulse for 13C was 4 ms, and that of
The structure of 1 (Fig. 1) was assigned through a detailed
analysis of 2D NMR experiments. The signals of the protons at
carbons 3 and 5–8 were easily assigned by their chemical shift
(d), multiplicities, and direct correlation (HMQC) between the
protons and their direct attached carbons. H-5 disclosed a long-
range correlation (HMBC) with C-7 and with two quaternary car-
bons at d = 155.48 and 177.73 ppm. These signals were attributed
to carbons 8a and 4, respectively, because of their distinct chem-
ical environment. H-8 displayed a direct correlation with C-6, C-
8a, and a quaternary carbon at d = 124.11 ppm that was assigned
to C-4a. From the HMBC experiments, it was verified that the H-3
signal shows a long-range correlation with those of C-4, C-4a, and
also two carbons, one at d = 155.86 ppm, assigned to C-9, and the
other at d = 157.82 ppm, assigned to C-2. The data were con-
firmed by a long-range correlation between the N–H proton
and a tertiary carbon at d = 124.27 ppm, assigned to C-60, and a
quaternary carbon at d = 151.75 ppm, assigned to C-20 and with
C-2. Furthermore, the C-20 chemical shift assignment was also
confirmed by a long-range interaction with the methoxyl pro-
tons. H-60 exhibits a correlation with the quaternary carbon C-20,
a tertiary carbon at d = 127.21 ppm, assigned to C-40, and a qua-
ternary carbon d = 125.73 ppm, assigned to C-10. Finally, the 13C
1
the 90ꢀ pulse for H was 9.5ms; the delay 2JC,H was set to 3.5 ms.
One-bond HMQC spectra were recorded on a Bruker AMX 500
spectrometer using a pulse sequence that allowed gradient selec-
tion (Bruker programs INV4GS and INVGSLPLRND). The spectra
were collected in the t1 domain in 256 experiments with 2K data
points and spectral widths of 5.050 and 27.669 Hz in the F2 (1H)
and F1 (13C) dimensions, respectively. The relaxation delay D1 was
set to 2 s. The data were processed using sine-bell weighting
functions in both dimensions.
EIMS were carried out on a VG AutoSpec (Fison, Ipswich,
United Kingdom) instrument; the data are reported as m/z
(percentage of relative intensity of the most important fragments).
Microwave-assisted synthesis was executed in a BiotageW
Initiator Microwave Synthesizer (Uppsala, Sweden).
Results and Discussion
The chromone carboxamides were obtained following the syn-
thetic strategies outlined in Scheme 1. Briefly, method A includes
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Magn. Reson. Chem. (2013)

Structural elucidation of chromone-2-carboxamides
O
O
COOH
Method B
Method A
rt /30 min
4ºC/30 min
DMF
O
O
O
COCl
N
O
O
P
N
N
Aniline derivative
160ºC/ 5 min
Aniline derivative
rt/ 4 h
CONH
O
O
R
R= OCH3 or Br
Scheme 1. Synthetic strategies used for the obtention of chromone carboxamide derivatives.
NMR signal carbons at d = 112.04 and 120.90 were assigned to
C-30 and C-50, respectively. This was performed on the basis of
HMBC data that indicate a long-range correlation of the H-5 with
C-10 and C-30. Moreover, for H-30, a long-range correlation be-
tween the tertiary carbon C-50 and the quaternary carbons C-10
and C-20 was observed.
9), was assigned by the same approach as described for 1. The
methyl protons exhibit a long-range interaction with a carbon
at d = 159.93 ppm, which was assigned to C-30. The 13C NMR
signal detected at d = 107.20 ppm was readily attributed to C-20
by the HMQC experiments. By analysis of the HMBC results, it
was observed that H-20 correlates with the quaternary carbon
C-30 and a quaternary carbon with d = 139.17 ppm, assigned to
C10. In addition, a correlation was detected for the H-20 with
The structure of 2 (Fig. 1), particularly the carbons of the
chromone carboxamide structure (2, 3, 4, 4a, 5, 6, 7, 8, 8a, and
Table 1. 1H and 13C chemical shifts and HMBC correlations for 1–3
1
2
3
1Ha
13C
HMBCb
1Ha
13C
HMBCb
1Ha
13C
HMBCb
2
—
157.82
111.41
177.73
124.11
125.43
126.62
135.53
119.42
155.48
155.86
125.73
151.75
112.04
127.21
120.90
124.27
56.34
—
—
158.17
111.54
177.76
124.15
125.39
126.59
135.50
119.49
155.60
156.08
139.17
107.20
159.93
110.93
130.10
113.68
55.58
—
—
157.75
111.35
177.77
124.14
125.39
126.55
135.47
119.45
155.62
156.31
130.94
123.15
114.40
156.87
114.40
123.15
55.68
—
3
6.92 (s)
—
C2, C4, C4a, C9
—
6.96 (s)
—
C2, C4, C4a, C9
—
6.94 (s)
—
C2, C4, C4a, C9
—
4
4a
5
—
—
—
—
—
—
8.07 (d, 7.8)
7.55 (m)
7.90 (m)
7.82 (m)
—
C4, C7, C8a
C4a, C8
C5, C8a
C4a, C6, C8a
—
8.06 (d, 7.8)
7.55 (m)
7.91 (m)
7.84 (d, 7.8)
—
C4, C7, C8a
C4a, C8
C5, C8a
C4a, C6, C8a
—
8.06 (d, 8.8)
7.54 (m)
7.91 (m)
7.82 (d, 8.8)
—
C4, C7, C8a
C4a, C8
C5, C8a
C4a, C6, C8a
—
6
7
8
8a
9
10
20
30
40
50
60
CH3O
NH
—
—
—
—
—
—
—
—
—
—
C10, C30, C40, C60
—
C20, C30, C60
C10, C30
C10, C20, C40
C30
—
—
—
—
7.45 (s)
—
7.70 (d, 8.8)
6.97 (d, 8.8)
—
C10, C40, C60
C10, C40, C50
—
C10, C30, C40
C10, C20, C40
C40
7.14 (d, 7.8)
7.24 (m)
7.00 (m)
7.82 (m)
3.88 (s)
10.01 (br)
C10, C20, C50
C20, C60
C10, C30
C10, C20, C40
C20
6.77 (d, 8.8)
7.31 (m)
7.39 (d, 8.8)
3.76 (s)
10.68 (br)
6.97 (d, 8.8)
7.70 (d, 8.8)
3.75 (s)
10.64 (br)
—
C2, C20, C60
—
C2, C20, C60
—
C2, C20, C60
aChemical shifts d in parts per million (multiplicity, J in hertz); solvent: dimethyl sulfoxide.
bCarbons coupled to the corresponding H atom.
Magn. Reson. Chem. (2013)
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A. Gaspar et al.
Table 2. 1H and 13C chemical shifts and HMBC correlations for 4–6
4
5
6
1Ha
13C
HMBCb
1Ha
13C
HMBCb
1Ha
13C
HMBCb
2
—
158.47
111.69
177.68
124.14
125.47
126.69
135.66
119.38
155.54
155.59
135.49
120.61
128.78
129.20
128.88
133.35
—
—
—
158.43
111.73
177.72
124.15
125.43
126.65
135.59
119.44
155.57
155.73
139.62
123.83
121.93
128.01
131.32
120.26
—
—
-
158.32
111.66
177.73
124.15
125.41
126.62
135.56
119.47
155.60
155.91
137.43
123.43
132.16
117.30
132.16
123.43
—
—
3
6.95 (s)
—
C2, C4, C4a, C9
—
6.97 (s)
—
C2, C4, C4a, C9
—
6.97 (s)
—
C2, C4, C4a, C9
—
4
4a
5
—
—
—
—
—
—
8.08 (d, 8.8)
7.56 (m)
7.91 (m)
7.80 (d, 8.8)
—
C4, C7, C8a
C4a, C8
C5, C8a
C4a, C6, C8a
—
8.07 (m)
7.55 (m)
7.92 (m)
7.81 (m)
—
C4, C7, C8a
C4a, C8
C5, C8a
C4a, C6, C8a
—
8.07 (d, 7.8)
7.55 (m)
7.92 (m)
7.83 (d, 7.8)
—
C4, C7, C8a
C4a, C8
C5, C8a
C4a, C6, C8a
—
6
7
8
8a
9
—
—
—
—
—
—
10
20
30
40
50
60
NH
—
—
—
—
C10, C30, C40, C60
—
C20, C30, C60
C10, C30
C10, C20, C40
C2, C20, C60
—
—
—
—
8.07 (m)
—
7.78 (d, 8.8)
7.60 (d, 8.8)
—
C10, C40, C60
C10, C40, C50
—
C10, C30, C40
C10, C20, C40
C2, C20, C60
7.64 (d, 8.8)
7.29 (m)
7.47 (m)
7.76 (d, 8.8)
10.66 (br)
C10, C20, C50
C20, C60
C10, C30
C10, C20, C40
C2, C20, C60
7.38 (m)
7.38 (m)
7.81 (m)
10.83 (br)
7.60 (d, 8.8)
7.78 (d, 8.8)
10.84 (br)
aChemical shifts d in parts per million (multiplicity, J in hertz) ; solvent: dimethyl sulfoxide.
bCarbons coupled to the corresponding H atom.
two tertiary carbons with d = 110.93 ppm and d = 113.68 ppm that
were easily assigned to C-40 and C-60, respectively. This was based
on the chemical shifts and multiplicities of the protons directly
linked to these carbons and the direct HMQC correlation with those
carbons atoms. Finally, the signal observed at d = 130.10 ppm was
assigned to C50 according to their directly attached proton.
The structural similarity of 3 (Fig. 1) compared with 1 and 2
allows an unambiguous interpretation of the NMR data. However,
the presence of the methoxyl group in the para-position at the exo-
cyclic aromatic ring causes chemical shift changes, due to inductive
and resonance effects, confirmed by 2D NMR experiments. The pro-
tons of the methoxyl group display a long-range correlation with a
quaternary carbon at d = 156.87 ppm that was assigned to C-40. So,
the 1H NMR signal at d = 6.97 ppm was assigned to H-30/H-50, two
chemically equivalent protons, as it has a long-range correlation
with C-40. Likewise, the chemically equivalent protons H-20/H-60
are located at d = 7.70 in the NMR spectra.
reaction, the target compounds were obtained in a shorter time with
a low-price reagent and easier work-up. The compounds were fur-
ther characterized by 1D and 2D NMR techniques that allowed full
NMR signal assignments. The acquired data constitute a valuable
database for the unambiguous identification of the chromone library
developed with the aim of our medicinal chemistry program.
Acknowledgements
The authors thank the Foundation for Science and Technology
(FCT), Portugal (PTDC/QUI-QUI/113687/2009), for support through
FCT grants to A. Gaspar (SFRH/BD/43531/2008), F. Cagide (SFRH/
BPD/74491/2010), and E. Quezada (SFRH/BPD/74596/2010).
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Conclusions
Novel chromone carboxamide derivatives with electron-donating
and electron-withdrawing substituents in different positions of the
exocyclic ring were obtained in moderate to high yields by either
classic or microwave reactions. However, in the microwave-assisted
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