Synthesis and biological evaluation of novel isoxazolo[4,3-e]indoles as antibacterial agents

Article abstract of DOI:10.1134/S1068162013020106

The synthesis of a new series of 8-bromo-6-alkyl-1-aryl-6H-isoxazolo[4,3-e] indole derivatives is described. All the newly synthesized compounds were screened for their antibacterial activity against Escherichia coli HB101, Staphylococcus aureus pathogens (methicillin resistant S. aureus and methicillin susceptible S. aureus), Pseudomonas aeruginosa, and Bacillus subtilis; also MIC values of these compounds were determined.

Full text of DOI:10.1134/S1068162013020106

ISSN 1068ꢀ1620, Russian Journal of Bioorganic Chemistry, 2013, Vol. 39, No. 2, pp. 211–214. © Pleiades Publishing, Ltd., 2013.
Synthesis and Biological Evaluation of Novel
Isoxazolo[4,3ꢀe
]indoles as Antibacterial Agents1
Mehdi Pordel2, Amin Abdollahi, and Bahareh Razavi
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Received July 30, 2012; in final form, August 6, 2012
Abstract—The synthesis of a new series of 8ꢀbromoꢀ6ꢀalkylꢀ1ꢀarylꢀ6Hꢀisoxazolo[4,3ꢀe]indole derivatives is
described. All the newly synthesized compounds were screened for their antibacterial activity against Escheriꢀ
chia coli HB101, Staphylococcus aureus pathogens (methicillin resistant S. aureus and methicillin susceptible
S. aureus), Pseudomonas aeruginosa, and Bacillus subtilis; also MIC values of these compounds were deterꢀ
mined.
Keywords: isoxazolo[4,3ꢀe]indole, antibacterial agents, Staphylococcus aureus, MIC
DOI: 10.1134/S1068162013020106
2 1
INTRODUCTION
Based on these facts and in continuation of
research work on the synthesis of bioactive heterocyꢀ
cles [14–17] and evaluation of their biological activiꢀ
ties, we decided to examine the transformation of
Indoles are a pervasive class of compounds found in
abundance in biologically active compounds such as
pharmaceuticals [1, 2], agrochemicals [3] and alkaꢀ
loids [4]. Indole myriad derivatives have, therefore,
3ꢀbromoꢀ1ꢀalkylꢀ5ꢀnitroꢀ1Hꢀindoles to new heteroꢀ
cyclic system isoxazolo[4,3ꢀe]indole by the reaction of
captured the attention of organic synthetic chemists. nucleophilic hydrogen substitution, which may result
in interesting biological activities.
On the other hand, isoxazoles have found continuing
application in medicinal chemistry, several examples
of which have advanced to general medical practice
[5]. As potential new chemical entities advance from
in vitro screening through in vivo study towards cliniꢀ
cal trials, pharmacokinetic properties collectively
RESULTS AND DISCUSSION
The target compounds 8ꢀbromoꢀ6ꢀalkylꢀ1ꢀarylꢀ
6H
ꢀisoxazolo[4,3ꢀ ]indole derivatives (3a ) were
e
–h
referred to as ADMET for Absorption, Distribution, obtained as described in Scheme. The required startꢀ
ing materials 3ꢀbromoꢀ1ꢀalkylꢀ5ꢀnitroꢀ
1Hꢀindoles
Metabolism, Excretion and Toxicity [6, 7] become
important considerations: half of drug attrition can be
attributed to poor ADMET properties. An interesting
facet of the biology of isoxazoles is that one significant
route of metabolism and excretion is Cꢀ5 methyl
hydroxylation [8, 9], mediated by the cytochrome
P450 isoform 3A4 [10], often followed by conjugation
to the glucuronide [11]. The existence of a safe route
for drug metabolism is an important design feature for
potential investigational new drugs containing the isoxꢀ
azole. Combination of the isoxazole moiety with the
indole nucleus may enhance these activities [12, 13].
(
1a ) were prepared by reaction of 5ꢀnitroꢀ1Hꢀ
–
d
indole with bromine [18] and then different alkyl
halides in DMF and KOH [19] using literature methꢀ
ods. The reaction of (1a
2a,b) led to the formation of the new 8ꢀbromoꢀ6ꢀ
alkylꢀ1ꢀarylꢀ ꢀisoxazolo[4,3ꢀ ]indole (3a h) via
–d) with arylacetonitriles
(
6H
e
–
the nucleophilic substitution of hydrogen in basic
EtOH solution in moderate yields (cf. [20–23])
(Scheme). The yield of the reaction was very low when
instead of 3ꢀbromoꢀ1ꢀalkylꢀ5ꢀnitroꢀ
ꢀalkylꢀ5ꢀnitroꢀ ꢀindoles was used in this reaction.
This can be due to the presence of bromine in the
indole ring of compounds (1a ) which are more
1Hꢀindoles (1a–d),
1
1H
–d
1
The article is published in the original.
Corresponding author: phone: 0098ꢀ0511ꢀ8414182; fax: 0098ꢀ
2
electronꢀdeficient than in 1ꢀalkylꢀ5ꢀnitroꢀ
indoles.
1Hꢀ
0511ꢀ8424020; eꢀmail: mehdipordel58@yahoo.com.
211

212
PORDEL et al.
g mL–1) of compounds 3a
–h against methicillinꢀresistant (MRSA) and methicillinꢀsuscepꢀ
Antibacterial activity (MIC,
tible Staphylococcus aureus (MSSA)
µ
Compd.
MRSA
MSSA
Compd.
3f
3g
3h
MRSA
MSSA
(
(
(
(
(
3a
3b
3c
3d
)
)
)
)
22.0
15.7
10.0
17.5
15.3
15.2
10.0
10.0
10.6
15.3
(
(
(
)
10.0
4.3
10.0
4.3
)
)
5.0
5.0
Erythromycin
Cephalexin
32.0
72.0
32.0
4.6
3e)
R'
Br
Br
EtOH, KOH
4 h reflux
O2N
O2N
O2N
O
N
Br
Br2, DMF
RꢀBr
KOH, DMF
N
N
N
CH2CN
R'
H
H
R
N
5ꢀnitroꢀ1
H
ꢀindole
3ꢀbromoꢀ5ꢀnitroꢀ1Hꢀindole
R
1a
–d
2a,
b
3a–h
3a: R = Et, R' = Cl (49%), 3c: R = Bu, R' = Cl (43%),
3e: R = Et, R' = Me (51%), 3g: R = Bu, R' = Me (55%),
3b: R = Et, R' = Cl (45%), 3d: R = isoꢀBu, R' = Cl (55%), 3f: R = Pr, R' = Me (50%), 3h: R = isoꢀBu, R' = Me (60%)
Scheme.
The structural assignments of compounds (3a
–h)
organism will grow in the tube that does not contain
were based on the analytical and spectral data. For enough antimicrobial agents to inhibit growth. For
example, in the 1H NMR spectrum of (3a), there are further confidence, the samples were cultured onto
the doublet signals at
= 9.6 Hz, 1 H)
= 8.5 Hz, 2 H) ppm and singlet signal at 7.85 ppm agent that prevents growth of the test organism, as
δ
7.40 (
J
,
δ
7.47 Petri dishes containing Muller–Hinton agar (18 h at
8.85 37°C). The lowest concentration of the antibacterial
(
J
,
δ
7.57 (
J
= 8.5 Hz, 2 H)
δ
(J
attributed to seven protons of aromatic rings. Moreꢀ detected by lack of visual turbidity (matching the negative
13
over, the C NMR spectrum, molecular ion peak at growth control), is designated the minimum inhibitory
m/z 379 (M
+ + 4) and microanalytical data strongly concentration (MIC). A serial dilution of tested comꢀ
support the tricyclic structure of compound (3a).
pounds (final concentration of 400 to 0.4
g mL–1), were
μ
added to the test bacteria in Mueller–Hinton broth
and were incubated at 37°C for 18 h. Growth was preꢀ
sented in the medium control and was absent from the
inoculum control [25].
ANTIMICROBIAL ACTIVITY
The test compounds listed in table were screened
for the antibacterial activity against Escherichia coli
HB101 (BAꢀ7601C), Staphylococcuse aureus pathoꢀ
gens [methicillin resistant S. aureus (MRSA) and
methicillin susceptible S. aureus (MSSA—ATCC
1112)], Pseudomonas aeruginosa (PTCC 1431), and
Bacillus subtilis (PTCC 1365).
The result indicates that these compounds are only
effective against gram positive bacteria. It has been
observed from the table, all compounds were found to
exhibit considerable antibacterial activities against the
mentioned organisms. These results are compared
with MIC values of Cephalexin (72 and 4.6
and Erythromycin (32 and 32
μ
g mL–1
μ
g mL–1). As the data in
The Minimum inhibitory concentrations (MIC) of
(3a–h) were determined in dilution test tube method,
table display, compound 3g shows the best inhibitory
activity against methicillin resistant S. aureus
(MRSA) and methicillin susceptible S. aureus
(MSSA—ATCC 1112).
which had been introduced by NCCLS (National
Committee for Clinical Laboratory Standards) [24].
For broth dilution methods, in which decreasing conꢀ
centrations of the antimicrobial agents must be tested,
usually prepared in serial two fold dilution of a broth
medium is placed in tubes which will support the growth
of the test microorganism (104 CFU mL–1). After suffiꢀ
CONCLUSIONS
To summarize, we have synthesized some novel
cient incubation (18 h), the tubes are examined for derivatives of isoxazolo[4,3ꢀe]indole and shown them
turbidity, indicating growth of the microorganism. The to be very effective S. aureus growth inhibitors. Such
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 39
No. 2
2013

SYNTHESIS AND BIOLOGICAL EVALUATION
213
compounds would appear to offer a suitable template calcd. for C18H14BrClN2O (389.7): C, 55.48; H, 3.62;
for the design of more powerful antibacterial agents N, 7.19. Found: C, 55.65; H, 3.69; N, 7.02.
and further studies are under way to this end in our labꢀ
8ꢀBromoꢀ6ꢀbutylꢀ1ꢀ(4ꢀchlorophenyl)ꢀ6Hꢀisoxazoꢀ
oratory.
lo[4,3ꢀ
(MeOH), yield (43%), mp: 154–156
(CDCl3) 0.97 (t, = 7.2), 1.33–1.42 (2 H, m), 1.84–
1.91 (2 H, m), 4.21 (2 H, t, = 7.2), 7.41 (1 H, d,
9.6), 7.46 (1 H, d, = 9.6), 7.56 (2 H, d, = 8.5), 7.85
(1 H, s), 8.85 (2 H, d,
= 8.5); 13C NMR (CDCl3):
e]indole (3c) was obtained as yellow needles
1
°
C; H NMR
δ
J
EXPERIMENTAL
J
J =
Melting points were measured on an Electrotherꢀ
J
J
maltypeꢀ9100 meltingꢀpoint apparatus. 1H and
δ
J
δ
13C NMR spectra (
, ppm, J, Hz) were recorded on a
13.23, 20.95, 34.45, 49.56, 94.00, 112.25, 124.57,
127.56, 131.09, 132.92, 132.95, 133.23, 145.87,
Bruker Avance DRXꢀ400 FT spectrometer at
400 MHz for 1H and 100 MHz for 13C using CDCl3 as
148.67, 158.95, 160.20, 164.09; MS (
); Anal. calcd. for C19H16BrClN2O (403.7): C, 56.53;
H, 3.99; N, 6.94. Found: C, 56.43; H, 3.90; N, 7.06.
8ꢀBromoꢀ6ꢀisobutylꢀ1ꢀ(4ꢀchlorophenyl)ꢀ6 ꢀisoxaꢀ
zolo[4,3ꢀ ]indole (3d) was obtained as pale yellow neeꢀ
dles (nꢀhexaneꢀethylꢀacetate), yield (55%), mp: 146–
m/z) 407 (M +
1
13
solvent. The H and C NMR chemical shifts were
referenced to tetramethylsilane (TMS) as internal
standard. The mass spectra were recorded on a Varian
Mat, CHꢀ7 at 70 eV. Elemental analysis was perꢀ
formed on a Thermo Finnigan Flash EA microanaꢀ
lyzer.
The microorganisms S. aureus ATCC 1112 were
purchased from Pasteur Institute of Iran and S. aureus
(methicillin resistant) was isolated from different
specimens which were referred to the Microbiological
Laboratory of Ghaem Hospital of Medical University
of MashhadꢀIran and its methicillin resistance was
tested according to the NCCLS guidelines [24].
4
H
e
1
148
2.23–2.16 (1 H, m), 4.01 (2 H, d,
d, = 9.6), 7.47 (1 H, d, = 9.6), 7.57 (2 H, d,
8.5), 7.85 (1 H, s), 8.85 (2 H, d,
= 8.5 ); 13C NMR
(CDCl3): 20.65, 26.16, 51.89, 93.86, 112.21, 124.54,
127.55, 131.07, 132.90, 132.95, 133.25, 145.86,
148.45, 158.96, 160.21, 164.07; MS ( ) 407 (M +
); Anal. calcd. for C19H16BrClN2O (403.7): C, 56.53;
H, 3.99; N, 6.94. Found: C, 56.41; H, 3.93; N, 7.05.
8ꢀBromoꢀ6ꢀethylꢀ1ꢀ(4ꢀmethylphenyl)ꢀ6 ꢀisoxaꢀ
zolo[4,3ꢀ ]indole (3e) was obtained as pale yellow
needles (EtOH), yield (51%), mp: 151–153
NMR (CDCl3) 1.56 (3 H, t, = 7.3), 2.44 (3 H, s),
4.25 (2 H, q, = 7.3), 7.41 (2 H, d, = 8.0), 7.43 (1 H,
d, = 9.5), 7.47 (1 H, d, = 9.5), 7.86 (1 H, s), 8.77
(2 H, d, 15.25, 21.33,
= 8.0 ); 13C NMR (CDCl3):
°
C; H NMR (CDCl3)
δ
0.98 (6 H, d,
J = 6.5),
J
= 7.2), 7.42 (1 H,
J
J
J =
J
δ
m/z
4
General Procedure for the Synthesis of (3a
–h)
H
from (1a ) and (2a,b
–d
)
e
1
°
C; H
Compounds (1a ) (10 mmol) and (2a,b) (12 mmol)
–d
δ
J
were added with stirring to a solution of KOH (20 g,
357 mmol) in ethanol (80 mL). The mixture was
refluxed with stirring for 4 h, and then poured into
water. The precipitate was collected by filtration,
J
J
J
J
J
δ
42.13, 93.95, 112.22, 124.89, 127.12, 127.76, 129.87,
129.95, 136.11, 145.45, 148.98, 158.33, 160.09,
165.19; MS (m/z) 357 (M + 2); Anal. calcd. for
C18H15BrN2O (355.2): C, 60.86; H, 4.26; N, 7.89.
Found: C, 60.71; H, 4.20; N, 8.00.
washed with water and airꢀdried to give crude (3a–h).
More purification was achieved by crystallization from
suitable solvent such as nꢀhexaneꢀethylꢀacetate,
MeOH or EtOH.
8ꢀBromoꢀ1ꢀ(4ꢀchlorophenyl)ꢀ6ꢀethylꢀ6
lo[4,3ꢀ ]indole (3a) was obtained as pale yellow crysꢀ
tals (EtOH), yield (49%), mp: 151–153
C; 1H NMR
(CDCl3) 1.57 (3 H, t, = 7.3), 4.27 (2 H, q, = 7.3),
7.40 (1 H, d, = 9.6), 7.47 (1 H, d, = 9.6), 7.57 (2 H,
d, = 8.5), 7.85 (1 H, s), 8.85 (2 H, d, = 8.5); 13C
NMR (CDCl3): 15.25, 43.56, 93.89, 112.24, 124.33,
127.45, 131.02, 132.87, 132.95, 133.23, 145.87,
148.55, 158.83, 160.19, 164.17; MS ( ) 379 (
); Anal. calcd. for C17H12BrClN2O (375.6): C, 54.36;
H, 3.22; N, 7.46. Found: C, 54.21; H, 3.18; N, 7.58.
8ꢀBromoꢀ1ꢀ(4ꢀchlorophenyl)ꢀ6ꢀpropylꢀ6 ꢀisoꢀ
xazolo[4,3ꢀ ]indole (3b) was obtained as pale yellow
needles (MeOH), yield (45%), mp: 141–143 C;
1H NMR (CDCl3)
0.98 (3 H, t, = 7.3), 1.95–1.87
(2 H, m), 4.21 (2 H, t, = 7.3), 7.41 (1 H, d, = 9.6), lo[4,3ꢀ
7.46 (1 H, d, = 9.6), 7.56 (2 H, d, = 8.5), 7.85 (1 H, hexaneꢀethylꢀacetate), yield (55%), mp: 136–139
s), 8.85 (2 H, d,
11.23, 27.09, 44.59, 93.75, 112.23, 124.56, 127.56, (2 H, m), 1.84–1.91 (2 H, m), 2.45 (3 H, s), 4.21 (2 H,
131.08, 132.90, 132.96, 133.23, 145.89, 148.63, t, = 7.2), 7.42 (2 H, d, = 8.0), 7.45 (1 H, d, = 9.5),
158.91, 160.23, 164.15; MS ( ) 393 ( + 4); Anal. 7.48 (1 H, d,
Hꢀisoxazoꢀ
8ꢀBromoꢀ1ꢀ(4ꢀmethylphenyl)ꢀ6ꢀpropylꢀ6
lo[4,3ꢀ ]indole 3f) was obtained as pale yellow neeꢀ
dles (MeOH), yield (50%), mp: 146–148
NMR (CDCl3) 0.99 (3 H, t, = 7.3), 1.89–1.98 (2
H, m), 2.45 (3 H, s), 4.19 (2 H, t, = 7.3), 7.41 (2 H,
d, = 8.0), 7.44 (1 H, d, = 9.5), 7.48 (1 H, d,
9.5), 7.87 (1 H, s), 8.76 (2 H, d,
= 8.0 ); 13C NMR
(CDCl3): 11.22, 21.32, 27.07, 44.57, 94.12, 112.13,
124.91, 127.14, 127.76, 129.85, 129.96, 136.10,
145.47, 149.00, 158.31, 160.09, 165.17; MS ( ) 371
M + ); Anal. calcd. for C19H17BrN2O (369.3): C,
Hꢀisoxazoꢀ
e
e
(
°
1
°
C; H
δ
J
J
δ
J
J
J
J
J
J
J
J
J =
δ
J
δ
m
/z
M +
4
m/z
(
2
H
61.80; H, 4.64; N, 7.59. Found: C, 61.94; H, 4.69; N,
7.44.
e
°
δ
J
8ꢀBromoꢀ6ꢀbutylꢀ1ꢀ(4ꢀmethylphenyl)ꢀ6
]indole (3g) was obtained as yellow needles (nꢀ
C;
= 7.2), 1.35–1.45
Hꢀisoxazoꢀ
J
J
e
J
J
°
13
J
= 8.5) ppm; C NMR (CDCl3): 1H NMR (CDCl3)
0.97 (3 H, t, J
δ
δ
J
J
J
m/
z
M
J
= 9.5), 7.86 (1 H, s), 8.77 (2 H, d, J =
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 39
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2013

214
PORDEL et al.
10. Lakehal, F., Dansette, P.M., Becquemont, L., Lasnier, E.,
13.19, 20.81, 21. 33, 34.48,
8.0 );13C NMR (CDCl3):
49.57, 94.11, 112.12, 124.91, 127.19, 127.75, 129.86,
129.97, 136.10, 145.49, 149.04, 158.39, 160.12,
165.16; MS (m/z) 385 (M + 2); Anal. calcd. for
C20H19BrN2O (383.3): C, 62.67; H, 5.00; N, 7.31.
δ
Delelo, R., Balladur, P., Poupon, R., Beaune, P.H., and
Housset, C., Chem. Res. Toxicol., 2001, vol. 14,
pp. 694–701.
11. Zhang, J.Y., Yuan, J.J., Wang, Y.ꢀF., Bible, Jr.R.H., and
Breau, A.P., Drug Metab. Dispos., 2003, vol. 31,
pp. 491–501.
12. Yamuna, E., Kumar, R.A., Zeller, M., and Rajendra
Prasad, K.J., Eur. J. Med. Chem., 2012, vol. 47,
pp. 228–238.
Found: C, 62.49; H, 4.91; N, 7.50.
8ꢀBromoꢀ6ꢀisobutylꢀ1ꢀ(4ꢀmethylphenyl)ꢀ6
lo[4,3ꢀ ]indole (3h) was obtained as pale yellow neeꢀ
dles (MeOH), yield (60%), mp: 156–158
NMR (CDCl3) .97 (6 H, d, = 6.7), 2.21–2.14 (1 H,
m), 2.43 (3 H, s), 4.00 (2 H, d, = 7.2), 7.41 (2 H, d,
= 8.0), 7.45 (1 H, d, = 9.5), 7.47 (1 H, d, = 9.5),
7.87 (1 H, s), 8.76 (2 H, d,
(CDCl3): 20.65, 21.35, 26.16, 51.89, 94.08, 112.11,
124.90, 127.21, 127.80, 129.86, 129.99, 136.11,
145.51, 149.02, 158.39, 160.14, 165.14; MS ( ) 385
M + ); Anal. calcd. for C20H19BrN2O (383.3): C,
Hꢀisoxazoꢀ
e
1
°
C; H
δ
J
13. Pahari, N., Saha, D., Jain, V.K., Jain,B., and Mridha, D.,
J
Int. J. Pharma Sci. Res., 2010, vol. 1, pp. 399–408.
J
J
J
14. Rahimizadeh, M., Pordel, M., Bakavoli, M., Rezaeꢀ
ian, Sh., and Sadeghian, A., World. J. Microbiol. Bioꢀ
technol., 2010, vol. 26, pp. 317–321.
13
J
= 8.0 ); C NMR
δ
15. Sadeghian, H., Sadeghian, A., Pordel, M., Rahimizaꢀ
deh, M., Jahandari, P., Orafaie, A., and Bakavoli, M.,
Med. Chem. Res., 2010, vol. 19, pp. 103–119.
m/z
(
2
62.67; H, 5.00; N, 7.31. Found: C, 62.43; H, 4.93; N,
7.59.
16. Sadeghian, A., Pordel, M., Safdari, H., Fahmidekar, M.A.,
and Sadeghian, H., Med. Chem. Res. (in press).
17. Rahimizadeh, M., Pordel, M., Bakavoli, M., Bakhtiarꢀ
poor, Z., and Orafaie, A., Monatsh. Chem., 2009,
vol. 140, pp. 633–638.
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