Synthesis and evaluation of antimycobacterial activity of 4-phenyl-1,8-naphthyridine derivatives

Article abstract of DOI:10.1016/S0014-827X(98)00094-9

Some 4-phenyl-1,8-naphthyridine derivatives with a piperazino group in the 2- and/or 7-position have been synthesized and evaluated for their tuberculostatic activity. The compounds 1, 6, 10, 17b,c and 19i showed a marked activity against Mycobacterium tuberculosis H₃₇Rv. For this series of compounds, submitted to biological screening, no structure-activity relationship can be deduced.

Full text of DOI:10.1016/S0014-827X(98)00094-9

Il Farmaco 53 (1998) 741–746
Synthesis and evaluation of antimycobacterial activity of
4-phenyl-1,8-naphthyridine derivatives
Pier Luigi Ferrarini a,*, Clementina Manera a, Claudio Mori a, Muwaffag Badawneh b,
Giuseppe Saccomanni a
a Dipartimento di Scienze Farmaceutiche, Uni6ersita` degli Studi di Pisa, 6ia Bonanno 6, 56126 Pisa, Italy
b Philadelphia Uni6ersity, PO Box 1101, Sweileh, Jordan
Received 3 July 1998; accepted 20 October 1998
Abstract
Some 4-phenyl-1,8-naphthyridine derivatives with a piperazino group in the 2- and/or 7-position have been synthesized and
evaluated for their tuberculostatic activity. The compounds 1, 6, 10, 17b,c and 19i showed a marked activity against
Mycobacterium tuberculosis H37Rv. For this series of compounds, submitted to biological screening, no structure–activity
relationship can be deduced. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Tuberculostatic agents; 1,8-Naphthyridines; Piperazino derivatives
1. Introduction
2. Chemistry
Tuberculosis can be considered today as the major
opportunistic emerging infection [1], because of its in-
creasing during the last years.
The carbethoxypiperazino derivative 1, previously
described [7], was converted to compound 2 by alkaline
hydrolysis. The acetyl derivatives 3 and 4 were then
prepared from 1 and 2, respectively, by reaction with
acetic anhydride (Scheme 1, Table 1).
When the hydroxy derivative 5 [7] was treated with
phosphoryl chloride, the chloro derivative 6 was ob-
tained. The acid hydrolysis of this compound gave a
recovery of the starting compound 6 instead of the
chloro derivative 7, whereas by alkaline hydrolysis of 6
the hydroxy derivative 8 was obtained; this was also
prepared by alkaline hydrolysis of 5. Compound 6 was
then treated with sodium methoxide to give, by trans-
esterification, the methoxy derivative 9, and treatment
with a hydroalcoholic solution of sodium hydroxide
gave the corresponding piperazino derivative 10
(Scheme 2, Table 1).
Moreover, it has been reported that only a few
compounds with a bicyclic structure have been synthe-
sized and tested for their antituberculosis activity. In
particular, the preliminary antimycobacterial screening
against Mycobacterium tuberculosis showed that some
compounds, having the quinoline and quinazoline ring
system with morpholino group in the 7-position and
phenyl group in the 2- or 3-position, respectively, pos-
sess tuberculostatic activity [2–6].
These considerations induced us to plan a program
of synthesis and antiinfective screening of a series of
1,8-naphthyridine derivatives, structurally correlated to
quinoline and quinazoline as already mentioned.
In this paper we report the synthesis and the bio-
logical results of some 4-phenyl-1,8-naphthyridine
derivatives.
Attempts of dehalogenation of 6, carried out with
hydrogen at 2 atm in acetic acid in the presence of
sodium acetate using 10% palladium on charcoal as
catalyst at 70°C or in methanol using a Ni-Raney
catalyst at room temperature, gave the corresponding
tetrahydro derivative 11 (Scheme 3, Table 1).
* Corresponding author. Tel.: +39-50-500209; fax: +39-50-40517.
0014-827X/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(98)00094-9

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P.L. Ferrarini et al. / Il Farmaco 53 (1998) 741–746
Table 1
Physical data of 1,8-naphthyridine and 1,2,3,4-tetrahydro-1,8-naphthyridine derivatives
a
Comp.
Ra
R1
Yield (%)
Crystallization solventb
M.p. (°C)
Empirical formula
2
3
4
6
8
NH2
NHCOCH3
Pipz
Cep
Apipz
Cep
Pipz
Cmp
Pipz
Cep
98
93
98
93
97
87
94
85
68
84
90
93
93
78
94
93
98
96
Toluene
Toluene
249–251
127–129
146–149
159–161
207–210
163–166
85–88
142–144
125–128
125–127
112–113
152–153
216–218
173–175
154–157
183–185
115–117
71–74
C18H19N5
C23H25N5O3
C22H23N5O2 · H2O
C21H21N4O2Cl
C18H18N4O
C21H22N4O3
C19H20N4O
C21H26N4O2
C21H22N4O2
C18H22N4
NHCOCH3
Cl
OH
OCH3
OCH3
–
H
–
H
Cl
Cep
Cep
Cep
Pipz
Pipz
Pipz
Ethanol–water
Petroleum ether
Benzene
Benzene/petroleum ether
Petroleum ether
2-Propanol
Petroleum ether
Petroleum ether
Cyclohexane
Ethanol
Toluene
Cyclohexane
Benzene
Toluene
Benzene
9
10
11
12
13
14
16a
17a
17b
17c
18a
18b
18c
Cep
Pipz
Pipz
OCH3
OH
Cep
OCH3
OH
C18H18N4
C15H11N2OCl
C21H22N4O3
C28H34N6O4
C22H24N4O3
C18H18N4O
C22H26N6 · H2O
C19H20N4O
Pipz
OCH3
Petroleum ether
a Pipz, piperazinyl; Cep, 4-carbethoxypiperazinyl; Apipz, 4-acetylpiperazinyl; Cmp, 4-carbomethoxypiperazinyl.
b Petroleum ether 100–140°C was used.
1
The structure of this compound was confirmed by H
NMR spectroscopy; in fact, the 1H NMR spectrum
shows three multiplets at l 2.61, 2.01 and 3.47 due to
H5, H6 and H7, respectively, and a singlet at l 5.72 due
to H3 (Table 2).
When the chloro derivative 6 was allowed to react
with hydrogen in methanol at room temperature and
pressure using 10% palladium on charcoal as catalyst,
compound 12 was obtained (Scheme 3, Table 1). The
1
structure of this compound was again confirmed by H
NMR spectroscopy, with the spectrum of 12 showing
three multiplets at l 8.03, 7.30 and 9.00 due to H5, H6
and H7, respectively (Table 2).
Compounds 11 and 12, when treated with a hydro-
alcoholic solution of sodium hydroxide, gave the corre-
sponding piperazino derivatives 13 and 14, respectively
(Scheme 3, Table 1)
The hydroxy derivative 15 [7] treated with phospho-
ryl chloride at 60°C gave the chloro derivative 16a
(Scheme 4, Table 1).
When the chloro derivatives 16a and 16b [8] were
allowed to react with N-carbethoxypiperazine in sealed
tube at 140°C, the hydroxy derivative 17a and the
dicarbethoxy derivative 17b were obtained, respectively
(Scheme 5, Table 1). Compound 17c was prepared by
reaction of 16a with N-carbethoxypiperazine in toluene
at 80°C (Scheme 5, Table 1). Alkaline hydrolysis of
Scheme 1. (a) Acetic anhydride; (b) 10% aqueous NaOH, ethanol.

P.L. Ferrarini et al. / Il Farmaco 53 (1998) 741–746
743
Scheme 2. (a) POCl3; (b) 20% HCl; (c) 10% aqueous NaOH, ethanol; (d) sodium methoxide.
Scheme 3. (a) H2, 10% Pd/C, CH3COONa, CH3COOH or Ni-Raney, methanol; (b) 10% aqueous NaOH, ethanol; (c) H2, 10% Pd/C, methanol.
carbethoxypiperazino derivatives 17 gave the corre-
sponding compound 18 (Scheme 5, Table 1).
tested in vitro at a concentration of 12.5 mg/ml
against M. tubercolosis H37Rv by a new method re-
cently described by Collins and Franzblau [9]. The
results of the biological evaluation indicate that only
compounds 1, 6, 10, 17b,c and 19i showed a marked
activity against M. tubercolosis H37Rv, whereas the
other compounds tested were found to be slowly ac-
tive or inactive at the assayed concentration (Table
4).
All the synthesized compounds were characterized
by elemental analysis and 1H NMR spectroscopy.
1
The H NMR spectra of the 1,8-naphthyridine deriva-
tives 2–4, 6, 8–10, 16a, 17a–c and 18a–c prepared
show two doublets between l 6.35–7.38 and 7.52–
8.10 due to H6 and H5, respectively, and a singlet
ranging from l 6.48 to 6.95 due to H3 (Table 2).
For this series of compounds, on the basis of the
biological results obtained, the activity does not ap-
pear to be related directly with the substituents
present on the different positions of the 1,8-naph-
thyridine nucleus and, consequently, no structure–ac-
tivity relationship can be deduced.
3. Results and discussion
Some of these new compounds, 1–6, 8–10, 12, 14,
16b and 17–19 (Table 3) previously prepared, were

744
P.L. Ferrarini et al. / Il Farmaco 53 (1998) 741–746
Table 2
1H NMR of 1,8-naphthyridine and tetrahydro-1,8-naphthyridine derivativesa
Comp.
H3(s)
H5
H6
H7
C6H5(m)
Pipzb(m)
Others
2
3
4
6
8
6.63
6.90
6.93
6.95
6.48
6.76
6.76
5.72
7.00
5.80
6.93
7.01
6.30
6.80
6.71
6.30
6.67
6.66
7.83(d)
8.10(d)
8.10(d)
7.96(d)
7.60(d)
7.83(d)
7.90(d)
2.41(m)
8.03(d)
2.50(m)
7.96(d)
8.10(d)
7.55(d)
7.60(d)
7.93(d)
7.52(d)
7.73(d)
7.85(d)
6.53(d)
6.80(d)
6.91(d)
7.10(d)
6.35(d)
6.63(d)
6.63(d)
1.64(m)
7.30(dd)
1.85(m)
7.20(dd)
7.38(d)
6.42(d)
6.92(d)
6.95(d)
6.80(d)
7.30(d)
7.33(d)
–
–
–
–
–
–
–
7.56
7.56
7.56
7.60
7.56
7.55
7.63
7.30
7.56
7.28
7.45
7.56
7.45
7.56
7.53
7.41
7.53
7.50
3.00, 3.83
3.40, 3.75
3.40, 4.00
3.63, 3.87
3.56, 2.74
3.50, 3.75
2.88, 3.69
3.32
3.65, 4.00
3.00, 3.35
3.86, 3.00
–
NH 2.00; NH2 4.96
C2H5 1.33(t), 4.30(q); COCH3 2.23(s); NH 10.25
COCH3 2.16(s); NH 8.70
C2H5 1.33(t), 4.05(q)
NH 2.40
OCH3 3.95(s); CH3 3.75(s)
OCH3 4.20(s)
C2H5 1.33(t), 4.03(q); NH 6.00
C2H5 1.33(t), 4.23(q)
NH 3.35
NH 2.20
OCH3 4.20(s)
C2H5 1.33(t), 4.16(q)
C2H5 1.33(t), 4.16(q)
C2H5 1.33(t), 4.16(q); OCH3 4.26(s)
NH 2.34
9
10
11
12
13
14
16a
17a
17b
17c
18a
18b
18c
3.50(m)
8.90(d)
3.50(m)
8.83(d)
–
–
–
–
–
–
–
3.65
3.00, 3.80
3.50, 3.60
3.00, 3.65
3.00, 3.83
2.80, 3.60
NH 2.20
NH 2.30; OCH3 4.16(s)
a The numeration of the structure of the tetrahydro-1,8-naphthyridine derivatives reported in this table, is used only for their 1H NMR data
on the analogy of that of the 1,8-naphthyridine derivatives.
b Pipz, piperazinyl.
4. Experimental
4.1.1. 7-(4-Carbethoxypiperazin-1-yl)-5-phenyl-1,2,3,4-
tetrahydro-1,8-naphthyridine 11
4.1. Chemistry
1. A solution of 1 mmol of 6 and 2 mmol of anhydrous
sodium acetate in 30 ml of glacial acetic acid was
hydrogenated in presence of 0.2 g of 10% palladium
on charcoal at 2 atm of pressure and at 60°C for 16
h. After cooling, the catalyst was filtered and the
solution was evaporated to dryness in vacuo. The
resulting residue was treated with water, made alka-
line with 10% aqueous sodium hydroxide and ex-
tracted twice with chloroform. The combined
organic extracts were dried (magnesium sulfate) and
evaporated in vacuo to obtain the title compound
11, which was purified by crystallization (Tables 1
and 2).
All compounds were routinely checked for their
structure by IR and H NMR spectroscopy. Melting
1
points were determined using a Ko¨fler hot-stage ap-
1
paratus and were uncorrected. The H NMR spectra
were determined in DMSO-d6 or CDCl3 with TMS as
the internal standard on a Fourier transform spectro-
meter Varian Model CFT 20. Mass spectra were ob-
tained using a Hewlett–Packard 5988A spectrometer
operating at 70 eV. Analytical TLC was carried out on
Merck 0.2 mm precoated silica-gel glass plates (60
F-254) and the location of spots was detected by illumi-
nation with a UV lamp. Flash chromatography was
carried out on silica gel (60 size 0.04–0.063 mm) at low
pressure. Elemental analyses of all synthesized com-
pounds for C, H and N were within 90.4% of the
theoretical values and were performed by our analytical
laboratory.
2. A solution of 1 mmol of 6 in 50 ml of methanol was
hydrogenated in presence of 2 g of Ni-Raney at
room temperature and at atmospheric pressure for
12 h. Compound 11 was then obtained by an
analogous procedure to that reported above.

P.L. Ferrarini et al. / Il Farmaco 53 (1998) 741–746
745
Table 3
4.1.2. 2-(4-Carbethoxypiperazin-1-yl)-4-phenyl-1,8-
naphthyridine 12
1,8-Naphthyridine derivatives previously reported
A solution of 1 mmol of 6 in 50 ml of methanol was
hydrogenated in the presence of 0.2 g of 10% palladium
on charcoal at room temperature and atmospheric pres-
sure for 12 h. The catalyst was filtered and the solvent
was evaporated to dryness in vacuo. The residue ob-
tained was treated with water, made alkaline with 10%
aqueous sodium hydroxide and then extracted twice
with chloroform. The combined organic extracts, dried
(magnesium sulfate) and evaporated to dryness in
vacuo, gave an oil, which was purified by flash chro-
matography eluting with a mixture of ethyl acetate/
petroleum ether (40–70°C)/diethylamine (9:3:0.5) and
then crystallized to give 12 (Tables 1 and 2).
Comp.
R
R1
Ref.
a
b
c
d
e
f
g
h
I
N(CH2CH2OH)2
OH
N(CH2CH2OH)2
N(CH2CH2OH)2
OH
SH
NH2
Cl
NH2
NHCOCH3
OH
N(CH2CH2OH)2
NH2
NH2
OH
NHCOCH3
OCH3
[10]
[8]
[10]
[11]
[8]
[12]
[13]
[13]
[7]
4.1.3. General procedure for the preparation of
7-chloro-4-phenyl-1,8-naphthyridine deri6ati6es 6 and
16a
A solution of 5 mmol of 5 and 15 [7] in 20 ml of
phosphoryl chloride was allowed to react at 80 and
60°C, respectively. The cooled solution was poured into
NH2
crushed ice and the mixture was alkalinized with con-
centrated ammonium hydroxide. The resulting precipi-
tate was collected, washed with water and crystallized
to obtain 6 or 16a (Tables 1 and 2).
4.1.4. 2-(4-Carbomethoxypiperazin-1-yl)-7-methoxy-4-
phenyl-1,8-naphthyridine 9
To a solution of 50 mmol of sodium in 50 ml of
absolute methanol, 5 mmol of 6 were added and the
mixture was refluxed for 5 h and then the solvent was
removed by evaporation in vacuo. The crude residue
was treated with water and then 10% hydrochloric acid
was added until pH 8. The solid obtained was collected,
washed with water and crystallized to give 9 (Tables 1
and 2).
Scheme 4. (a) POCl3.
4.1.5. Preparation of 7-(4-carbethoxypiperazin-1-yl)-
2-hydroxy- and of 2,7-di(4-carbethoxypiperazin-1-yl)-
4-phenyl-1,8-naphthyridines 17a,b
A mixture of 5 mmol of 16a,b and 15 mmol of
N-carbethoxypiperazine was heated in sealed tube at
140°C for 20 h. The crude residue was treated with
water and the solid obtained, collected by filtration and
washed with water, was purified by crystallization to
obtain 17a,b (Tables 1 and 2).
4.1.6. 7-(4-Carbethoxypiperazin-1-yl)-2-methoxy-4-
phenyl-1,8-naphthyridine 17c
A solution of 5 mmol of 16a and 5.5 mmol of
N-carbethoxypiperazine in 30 ml of toluene was kept at
80°C for 24 h. The solvent was evaporated to dryness in
vacuo and the residue was treated with water, filtered
and purified by crystallization to give 17c (Tables 1 and
2).
Scheme 5. (a) N-Carbethoxypiperazine; (b) 10% aqueous NaOH,
ethanol.

746
P.L. Ferrarini et al. / Il Farmaco 53 (1998) 741–746
Table 4
Antimycobacterial in vitro activity of the tested compounds expressed as % inhibition of M. tuberculosis H37Rv at a concentration of 12.5 mg/ml
Comp.
% Inhibition
Comp.
% Inhibition
Comp.
Ref.
% Inhibition
1
2
3
4
5
6
8
9
70
0
0
12
14
0
0
4
19a
19b
19c
19d
19e
19f
19g
19h
19i
[10]
[8]
[10]
[11]
[8]
[12]
[13]
[13]
[7]
15
2
1
0
0
0
0
0
54
16b
17a
17b
17c
18a
18b
18c
0
0
12
71
7
0
67
98
75
77
0
10
34
10
RMPa
a MIC 0.25 mg/ml.
4.1.7. General procedure for the preparation of
substituted 2-, 7- and 2,7-(piperazin-1-yl)-4-phenyl-
1,8-naphthyridines 2, 8, 10, 13, 14 and 18a–c
A solution of 5 mmol of the suitable 1,8-naph-
thyridine derivatives 1, 5, 9, 11, 12 or 17a–c in 20 ml of
ethanol and 20 ml of 10% aqueous sodium hydroxide
was refluxed for 6 h and then concentrated in vacuo to
a small volume. The pH of the solution was adjusted to
8–9 with 10% hydrochloric acid and the solution was
extracted twice with chloroform. The combined extracts
were dried (magnesium sulfate) and evaporated to dry-
ness in vacuo to obtain the piperazin-1-yl derivatives 2,
8, 10, 13, 14 and 18a–c, which were purified by crystal-
lization (Tables 1 and 2).
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by hydrolysis of 6.
4.1.8. General procedure for the preparation of
substituted acetamido-4-phenyl-1,8-naphthyridines 3
and 4
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products were obtained by the following methods. To
obtain 3, the suspension was filtered and washed with
H2O. To obtain 4, the pH of the suspension was made
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The authors wish to thank Dr Joseph Maddry of
Southern Research Institute, Birmingham, AL, USA,
for the TAACF compounds screening program. This
work was supported by grant of the MURST.
.