4-hydroxy-2-quinolones. 202*. Synthesis, chemical and biological properties of 4-hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3- carboxylic acid alkylamides

Article abstract of DOI:10.1007/s10593-012-0992-4

In continuation of the search for potential analgesics amongst 4-hydroxyquinol-2-one derivatives we have proposed and carried out a preparative method of synthesis of 4-hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3- carboxylic acid alkylamides. It has been shown that bromination of 4-hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid allylamide using an equivalent of molecular bromine occurs with a conventional addition of the halogen to the allyl double bond and not with halocyclization. The results of the study of the analgesic properties of the compounds prepared are presented.

Full text of DOI:10.1007/s10593-012-0992-4

Chemistry of Heterocyclic Compounds, Vol. 48, No. 2, May, 2012 (Russian Original Vol. 48, No. 2, February, 2012)
4-HYDROXY-2-QUINOLONES. 202*. SYNTHESIS,
CHEMICAL AND BIOLOGICAL PROPERTIES
OF 4-HYDROXY-6,7-DIMETHOXY-2-OXO-
1,2-DIHYDROQUINOLINE-3-CARBOXYLIC
ACID ALKYLAMIDES
I. V. Ukrainets1**, O. V. Bevz1, E. V. Mospanova2,
L. V. Savchenkova3, and S. I. Yankovich3
In continuation of the search for potential analgesics amongst 4-hydroxyquinol-2-one derivatives we
have proposed and carried out a preparative method of synthesis of 4-hydroxy-6,7-dimethoxy-2-oxo-
1,2-dihydroquinoline-3-carboxylic acid alkylamides. It has been shown that bromination of 4-hydroxy-
6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid allylamide using an equivalent of
molecular bromine occurs with a conventional addition of the halogen to the allyl double bond and not
with halocyclization. The results of the study of the analgesic properties of the compounds prepared are
presented.
Keywords: 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxamides, amidation, analgesic activity,
bromination.
Pain is one of the most widespread symptoms for which people seek medical advice. Hence, it is not
surprising that analgesic agents are one of the most popular types of medicines [2-4]. Nonetheless, the current
medicinal arsenal of medications of this pharmacological group are regrettably far from perfect [5-7]. For this
reason, the search for substances with the ability to arrest pain and the creation of novel analgesics within
contemporary demands of effectiveness and safety is one of the most important tasks of medicinal chemistry.
Pronounced analgesic properties have recently been discovered in 1-allyl-4-hydroxy-6,7-dimethoxy-
2-oxo-1,2-dihydroquinoline-3-carboxylic acid alkylamides [8]. The chemical modification of these compounds
is undoubtedly of interest for development of this new pharmaceutical direction of 4-hydroxy-2-quinolone
_______
*For Communication 201, see [1].
**To whom correspondence should be addressed, e-mail: uiv@kharkov.ua.
1National University of Pharmacy, 53 Pushkinska St., Kharkiv 61002, Ukraine.
2Institute of Chemical Technology East Ukraine Volodymyr Dahl National University, 31 Lenin St., Rubezhnoe
93003, Ukraine; e-mail: elena_mospanova@list.ru.
3Lugansk State Medicinal University, 1 50 year Lugansk Defense Quarter, Lugansk 91045, Ukraine; e-mail:
slv.05@mail.ru.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 339-346, February, 2012. Original
article submitted February 24, 2011.
320
0009-3122/12/4802-0320©2012 Springer Science+Business Media, Inc.

derivatives. At least the results of such a study can provide the structure-activity relationships theoretically
important for subsequent research. In the case of good luck (an element of chance is always present in similar
studies), it would be quite possible to reveal novel and promising lead structures having practical value in
resolving the problems indicated above.
Many variants of the chemical transformation of 1-allyl-4-hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydro-
quinoline-3-carboxylic acid alkylamides can, of course, be proposed. In our view, however, most rationally is to
start with the simplest one, namely, with the removal of the 1-N-allyl substituent from the basic molecule.
The basis of the whole synthetic scheme is methyl 4-hydroxy-6,7-dimethoxy-2-oxo-1,2-di-
hydroquinoline-3-carboxylate (1), which can be prepared by acylation of the commercially available 4,5-dimethoxy-
methylanthranilate (2) using methyl malonyl chloride (3) in the presence of triethylamine or using monoethyl
malonate (4) in the presence of N,N'-dicyclohexylcarbodiimide with subsequent heterocyclization of the
intermediate anilides 5a,b under base-catalyzed ester condensation. Immediately it should be noted that the use
of sodium methylate in methanol as the main catalyst in the cyclization of ethyl 4,5-dimethoxy-2-[(3-methoxy-
3-oxopropanoyl)amino]benzoate (5b) causes transesterification. Thus, independently of the acylating agent
used, the final reaction product is the same methyl ester 1. Preference should be given, however, to the
monoester 4 since the carbodiimide method ensures not only a higher yield of ester 1, but also such a high
purity (see Experimental) so that no additional purification is needed.
MeO
MeO
COOMe
NH2
COOMe
MeO
MeO
ClOCCH2COOMe 3
or
NHCOCH2COOR
HOOCCH2COOEt 4
2
5a,b
1) MeONa, MeOH
2) HCl, H2O
OH
OH
CONHR1
COOMe
MeO
MeO
MeO
MeO
H2NR1
N
H
O
N
O
H
1
6a–p
OH
OH
O
O
MeO
MeO
MeO
N
Br
Br2
H
6c
Br
N
H
O
MeO
N
H
7
8
5 a R= Me, b R = Et; 6 a R1 = Me, b R1 = Et, c R1 = All, d R1 = Pr, e R1 = 2-Pr, f R1 = Bu,
g R1 = i-Bu, h R1 = C5H11, i R1 = i-C5H11, j R1 = C6H13, k R1 = C7H15, l R1 = C8H17, m R1 = C9H19,
n R1 = C10H21, o R1 = C11H23, p R1 = C12H25
The 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylates are highly reactive [9, 10], therefore, their
conversion to different N-R-amides usually does not cause any difficulty. That is why the problems arising upon
amidation of the dimethoxy-substituted ester 1 using primary alkylamines appeared to be rather unexpected.
Hence, when carrying out the reaction in refluxing DMF (used because of the low solubility of ester 1 in other
organic solvents) a significant amount of the 4-hydroxy-6,7-dimethoxy-1H-quinolin-2-one (7) was found in
addition to the target alkylamides 6. The former was readily identified by the characteristic singlet at 5.59 ppm
for the H-3 proton in the 1H NMR spectrum. This was our first experience of such a marked
321

TABLE 1. Characteristics of Alkylamides 6a-p
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
Mp, °С
(DMF)
Yield,
%
Analgesic
activity*
C
H
N
6a
6b
6c
6d
6e
6f
C13H14N2O5
C14H16N2O5
C15H16N2O5
C15H18N2O5
C15H18N2O5
C16H20N2O5
C16H20N2O5
C17H22N2O5
C17H22N2O5
C18H24N2O5
C19H26N2O5
C20H28N2O5
C21H30N2O5
C22H32N2O5
C23H34N2O5
C24H36N2O5
56.23
56.11
57.62
57.53
59.32
59.21
58.74
58.82
58.90
58.82
60.11
59.99
60.06
59.99
60.94
61.07
61.15
61.07
62.18
62.05
63.09
62.97
63.72
63.81
64.74
64.60
65.40
65.32
65.94
66.01
66.52
66.64
5.15
5.07
5.61
5.52
5.43
5.30
5.81
5.92
5.83
5.92
6.38
6.29
6.35
6.29
6.55
6.63
6.52
6.63
7.01
6.94
7.30
7.23
7.43
7.50
7.85
7.74
8.08
7.97
8.06
8.19
8.30
8.39
9.94
323-325
270-272
276-278
281-283
255-257
242-244
280-282
246-248
259-261
243-245
238-240
234-236
230-232
228-230
225-227
222-224
—
98
96
96
93
88
92
93
90
88
91
85
89
90
86
92
94
—
18.8
22.6
36.5
60.6
24.2
32.9
28.5
25.1
48.1
14.4
43.9
28.5
32.9
35.1
44.3
41.9
35.1
10.07
9.47
9.58
9.14
9.21
9.08
9.15
9.26
9.15
8.85
8.74
8.83
8.74
8.30
8.38
8.27
8.38
7.95
8.04
7.84
7.73
7.36
7.44
7.11
7.17
7.02
6.93
6.58
6.69
6.36
6.48
—
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
Metamizole sodium
—
—
_______
* Decrease in the amount of "acetic acid writhing" when compared with
control, %.
tendency of 3-alkoxycarbonyl-4-hydroxy-2-oxo-1,2-dihydroquinolines to decomposition under rather mild
conditions. It was interesting that the presence in the reaction mixture of the base in the form of alkylamine was
not at all necessary for the loss of the carbomethoxy group from ester 1. It has been found that the
decomposition occurs after refluxing in DMF for only a few minutes (two solvents grades were used: the "pure"
and the anhydrous for peptide synthesis, i.e. practically free from amines and with the water content not more
than 0.02%). It seems doubtful that the effect observed is caused specifically by DMF since a totally similar
transformation of ester 1 occurs in refluxing, dry bromobenzene or xylene.
On the basis of these data it is hard to give an unambiguous explanation of the unusual behavior of
dimethoxy-substituted ester 1 when heated in high boiling solvents.
This problem arising in the preparation of alkylamides 6c-p was solved quite simply. The undesirable
decomposition of ester 1 to quinolone 7 can be avoided by carrying out the amidation at a lower temperature. In
practice, this can be achieved in several ways, e.g. by holding the reaction mixture temperature in the range of
80-100ºC or simply by carrying out the reaction in a refluxing mixture of solvents containing DMF and about
15% methanol.
322

323

As a result, the target alkylamides 6a-p can be prepared in high yields and purity (Table 1). They are all
colorless, crystalline materials with narrow melting point ranges, being moderately soluble in DMF and DMSO
at room temperatures, but virtually insoluble in water. The structure of the compounds synthesized was
confirmed by their 1H NMR spectra (Table 2).
Their ability to exist in different tautomeric forms and thus their far from predictable behavior in
common reactions served as a stimulus for involving 4-hydroxyquinol-2-ones in various chemical processes.
Attention is mostly attracted to reactions, which lead to the effective formation of novel heterocycles.
Bromination of 1-N- and 3-C-allyl-substituted derivatives occurring through halocyclization to oxazolo- [11] or
furoquinolones [12], respectively, can be an example. We have attempted to find out how it is reflected in this
reaction where the allyl and quinolone fragments are separated by a carbamide group by examining the
bromination of 4-hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid allylamide (6c).
The brown color disappears almost immediately after addition of an equivalent of molecular bromine to
the solution of allylamide 6c in glacial acetic acid. After dilution of the reaction mixture with water, a colorless
product has been obtained, which 1H NMR spectrum shows that all of the changes occur exclusively in the allyl
part of the molecule. In other words, the presence of the carbamide bridge between the allyl group and the
4-hydroxyquinolin-2-one ring blocks a potential halocyclization reaction. As a result, the bromination occurs
just as in the classical addition of a halogen to an olefinic bond and ends with the formation of 4-hydroxy-
6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid 2,3-dibromopropylamide (8).
The analgesic properties of the alkylamides 6a-p obtained were studied on the standard "acetic acid
writhing" test [13, 14] reported by us in detail before [15]. Experiments were carried out on non-pedigree white
mice with the weight of 18-23 g by the introduction of the compound orally in the dose of 20 mg/kg. The
classical analgesic metamizole sodium [6] was used as a reference drug by the same administration method in
the dose of 55 mg/kg (corresponding to the ED50 of this compound on the "acetic acid writhing model" [16]).
A comparative analysis of the results of these biological experiments for alkylamides 6a-p (Table 1) and
their allyl-substituted analogs [8] has shown that the removal of the 1-N-allyl fragment undertaken by us, quite
naturally leads in certain cases to some increase in analgesic effects (amides 6d,i,k,n-p) and, conversely, in
others to their decrease (amides 6a,h). However, in our opinion, the observation that complete or at least a
marked loss of activity has not been recorded in a single case is more interesting. Hence, there is every reason to
suggest that a substituent on the quinoline nitrogen atoms has only a weak effect on the analgesic properties of
4-hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid amides. Their biological effect
depends to a much greater extent on the structure of the N-R-amide fragment.
EXPERIMENTAL
1H NMR spectra were recorded on a Varian Mercury VX-200 spectrometer (200 MHz) (alkylamides
6a-p) and on a Varian Mercury-400 spectrometer (400 MHz) (methyl ester 1). DMSO-d6 was used as a solvent
and TMS as internal standard for all compounds. The analysis of purity of the methyl ester 1 samples prepared
by different methods was performed by HPLC on a Waters Alliance 2690 liquid chromatograph with a Waters
PAD 996 photodiode array detector. The chromatographic conditions were: Symmetry C8 (Nova Pak C8)
column, size 3.9150 mm, mobile phase flow rate 1 ml/min, column temperature 40ºC, injection volume 20 l,
and detection wavelength 232 nm. The composition of the mobile phase was 65% acetonitrile and 35% aqueous
ammonium perchlorate solution (5 ml 70% perchloric acid and 25% ammonia solution to pH 2.5-3.0 per 1 l of
the solution).
Methyl 4-Hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylate (1). A. Triethylamine
(1.54 ml, 11 mmol) was added to a solution of methyl 2-amino-4,5-dimethoxybenzoate (2) (2.11 g, 10 mmol) in
CH2Cl2 (20 ml). Methyl malonyl chloride (3) (1.18 ml, 11 mol) was then added dropwise with cooling and
stirring and left at room temperature for 5 h. The reaction mixture was diluted with cold water and vigorously
324

stirred. The organic layer was separated, dried over CaCl2, and the solvent was distilled off (finally under
reduced pressure). The residue of anilide 5a was treated with a solution of sodium methylate (prepared from
metallic sodium (0.69 g, 30 mmol) and absolute MeOH (15 ml)), taken to reflux, and then left for 10-12 h at
room temperature. The reaction mixture was diluted with cold water and acidified with diluted HCl (1:1) to pH
4.5-5.0. The precipitated ester 1 was filtered off, washed with water, and dried. Yield 2.23 g (81%). According
to HPLC, the content of the main substance in the crude product was 93.2%. Mp after recrystallization from
1
MeOH was 245ºC (decomp.). H NMR spectrum, , ppm (J, Hz): 13.94 (1H, s, OH); 11.28 (1H, s, NH); 7.24
(1H, s, H-5); 6.74 (1H, s, H-8); 3.92 (3H, s, OCH3); 3.89 (3H, s, OCH3); 3.85 (3H, s, OCH3). Found, %:
C 55.80; H 4.55; N 4.93. C13H13NO6. Calculated, %: C 55.92; H 4.69; N 5.02.
B. Monoethyl malonate (4) (1.32 g, 10 mmol) was added dropwise with stirring and cooling to a
solution of methyl 2-amino-4,5-dimethoxybenzoate (2) (2.11 g, 10 mmol) and N,N'-dicyclohexylcarbodiimide
(2.06 g, 10 mmol) in CH2Cl2 (30 ml) and left at room temperature for 6-8 h. The precipitated N,N'-dicyclo-
hexylurea was removed by filtration and washed on the filter with CH2Cl2. The solvent from the filtrate was
distilled off on a water bath (finally under reduced pressure). The residue of anilide 5b was treated with the
solution of sodium methylate (prepared from metallic sodium (0.69 g, 30 mmol) and absolute MeOH (15 ml)),
taken to reflux, and left for 10-12 h at room temperature. The cooled reaction mixture was diluted with cold
water (60 ml). A small amount of N,N'-dicyclohexylurea admixture remained as an insoluble material. The
solution was purified using carbon and filtered. The filtrate was acidified with dilute (1:1) HCl to pH 4.5-5.0.
The precipitated ester 1 was filtered off, washed with water, and dried. Yield 2.59 g (93%). The content of the
main product was 99.4%.
1H NMR spectra of the samples of methyl ester 1 prepared by different methods were identical.
4-Hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic Acid Methylamide (6a). A
suspension of methyl ester 1 (2.79 g, 0.01 mol) in DMF (20 ml) was saturated with gaseous methylamine (the
precipitate was rapidly dissolved) and left at room temperature for 3 h. The reaction mixture was diluted with
cold water and acidified with dilute HCl (1:1) to pH 4.5-5.0. The precipitated amide 6a was filtered off, washed
with water, and dried.
Ethylamide 6b was synthesized similarly.
4-Hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic Acid Alkylamides 6c-p
(General Method). The corresponding alkylamine (11 mmol) was added to a mixture of methyl ester 1 (2.79 g,
10 mmol), DMF (30 ml) and MeOH (5 ml) and refluxed for 3 h using a reflux condenser (in the case of the
isopropylamine the reaction time was increased to 6 h). The subsequent treatment of the reaction mixture and
separation of the final product was carried out as in the procedure for compound 6a.
4-Hydroxy-6,7-dimethoxy-1H-quinolin-2-one (7). A solution of 4-hydroxy-6,7-dimethoxy-2-oxo-
1,2-dihydroquinoline-3-carboxylic acid [17] (2.65 g, 0.01 mol) in DMF (15 ml) was refluxed until evolution of
CO2 ceased (about 10 min), cooled, and diluted with cold water. The precipitated quinolinone 7 was filtered off,
1
washed with water, and dried. Yield 2.07 g (94%); mp 403-405ºC (DMF–EtOH, 1:5). H NMR spectrum, ,
ppm (J, Hz): 11.11 (1H, s, OH); 10.95 (1H, s, NH); 7.13 (1H, s, H-5); 6.78 (1H, s, H-8); 5.59 (1H, s, H-3); 3.77
(3H, s, OCH3); 3.75 (3H, s, OCH3). Found, %: C 59.67; H 4.94; N 6.25. C11H11NO4. Calculated, %: C 59.73;
H 5.01; N 6.33.
4-Hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid 2,3-Dibromopropyl-
amide (8). A solution of bromine (0.52 ml, 0.01 mol) in glacial acetic acid (5 ml) was added with vigorous
stirring to a solution of 4-hydroxy-6,7-dimethoxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid allylamide (6c)
(3.04 g, 0.01 mol) in the same solvent (50 ml). The brown color of the bromine disappeared instantly. The
reaction mixture was diluted with cold water and the colorless precipitate of 2,3-dibromopropylamide 8 was
1
filtered off, washed with water, and dried. Yield 3.80 g (82%); mp 255-257ºC (DMF). H NMR spectrum, ,
ppm (J, Hz): 16.63 (1H, s, OH); 11.67 (1H, s, NH); 10.65 (1H, t, J = 6.2, NHCH2); 7.25 (1H, s, H-5); 6.87 (1H,
s, H-8); 4.64 (1H, m, NCH2CH); 3.95 (4H, m, NCH2CH(Br)CH2Br); 3.84 (3H, s, OCH3); 3.80 (3H, s, OCH3).
Found, %: C 38.73; H 3.35; N 5.91. C15H16Br2N2O5. Calculated, %: C 38.82; H 3.47; N 6.04.
325

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