2336
R.S.F. Silva et al. / European Journal of Medicinal Chemistry 44 (2009) 2334e2337
M. tuberculosis. Recently quinoxalinic and phenazinic com-
pounds had emerged as prototype anti-tubercular drugs [13e
5.1. General procedure for the synthesis of 4, 5, 7, 10
1
6]. The activities against M. tuberculosis of the compounds
To a solution of 1 mmol of substrates (3, 6, or 9) in 40 ml of
chloroform, 20 ml of solution of hydrogen peroxide (30% v/v)
was added, followed by 20 ml of acetic anhydride. The bi-
phasic system has stirred at room temperature for 24 h. The or-
ganic phase was separated and consecutively washed with
a solution of Na S O 5% (2 ꢀ 50 ml), followed by a solution
synthesized in the present work are shown in Table 1.
The oxidation of 3 furnished two compounds: macrolide 4
and a-hydroxy-ketone 5, both already described in the litera-
ture, prepared by MCPBA oxidation [9]. Quinoxaline 6 gave
7
7
tone, but with a low yield [11]. The bromine-N-oxide, macro-
lactone 10, was obtained with 33% yield, three times higher
than that obtained by MCPBA oxidation [10].
The peracetic acid oxidation allowed to synthesize 13 with
good yield (70%). The reaction with MCPBA or ozone did not
allow this synthesis. MCBBA oxidation of 12 gave only its
phenazine-N-oxide [17], while the ozonolysis gave a complex
mixture of products. Except for 4, the peracetic acid oxidation,
described here, was a more effective methodology for the syn-
thesis of these macrolides. MCPBA oxidation gave in all cases
a complex mixture of products, thus making it very hard to
isolate these productions.
with 68% yield. We have already reported the synthesis of
by MCPBA oxidation with its corresponding a-hydroxy-ke-
2
2 3
of Na CO 5% (2 ꢀ 50 ml). The organic phase then was dried
2
3
over anhydrous Na SO , filtered and evaporated under vac-
2 4
uum. In each case, the solid residues were submitted to col-
umn chromatography over silica gel and eluted with
mixtures of hexaneeethyl acetate with increasing gradient of
polarity. The unreacted substrate was recovered in all cases
with a hexaneeethyl acetate mixture at 2%. The macrolac-
tones were eluted from the column with a mixture containing
10% of ethyl acetate. In the oxidative reaction of phenazine 3
polar compound 5 was eluted in a polarity corresponding to
40% of ethyl acetate.
5.2. Synthesis of new compound 13 (7,7-dimethyl-7,8-
Initial assays against M. tuberculosis were performed at
00 mg/mL, the MIC 90 was then determined for the most ac-
dihydrobenzo[3,4]oxonino[6,7-b]quinoxaline-5,9-dione)
1
tive. The lactone 4 turned out to display an MIC of 0.62 mg/
mL, which is better than that the MIC of rifampicin (1.0 mg/
mL), one of the standard drugs used in TB chemotherapy.
To a solution of 300 mg (1 mmol) of 12 in 40 ml of chloro-
form, 20 ml of solution of hydrogen peroxide (30% v/v) was
added, followed by 20 ml of acetic anhydride. The biphasic
system has stirred at room temperature for 24 h. The organic
phase was separated and consecutively washed with a solution
of Na S O 5% (2 ꢀ 50 ml), followed by a solution of Na CO
4
. Conclusion
2
2
3
2
3
The level of antimycobacterial activity of macrolactone 4 is
5% (2 ꢀ 50 ml). The organic phase then was dried over anhy-
2 4
of interest which justifies laboratory test for citotoxical activ-
ity. The current rise of M. tuberculosis strains resistant to the
current treatments is a major concern. We hope that our initial
results may provide a lead toward the design of an original
drug which would remain active on these resistant strains.
drous Na SO , filtered and evaporated under vacuum. The
solid residue was submitted to column chromatography over
silica gel and eluted with mixtures of hexane/ethyl acetate
with increasing gradient of polarity. The unreacted substrate
was recovered with a hexaneeethyl acetate mixture at 2%.
The macrolactone 13 was eluted from the column with a mix-
ture containing 10% of ethyl acetate, 232 mg yielding 70%.
5
. Experimental protocols
ꢁ
1
Coumpound 13: colorless crystals, mp: 192 C; H NMR
00 MHz [CDCl , d (ppm), J (Hz)] d: 8.22 (m, 1H), 8.13
4
The NMR experiments were performed in a Bruker
3
(
m, 1H), 8.08 (dd, J ¼ 7.8 Hz, J ¼ 0.8 Hz, 1H), 7.93 (dd,
AVANCE DRX-400 instrument, using deuterochloroform as
solvent, and TMS as internal standard. Infrared spectra were
recorded on a PerkineElmer FT-IR Spectrometer. For elemen-
tal analysis, a PerkineElmer CHN 2400 was used.
J ¼ 7.7 Hz, J ¼ 1.2 Hz, 1H), 7.86 (m, 2H), 7.73 (td,
J ¼ 12.1 Hz, J ¼ 7.5 Hz, J ¼ 1.2 Hz, 1H), 7.56 (td,
J ¼ 7.5 Hz, J ¼ 7.5 Hz, J ¼ 1.2 Hz, 1H), 3.91 (d,
J ¼ 14.5 Hz, 1H), 3.48 (d, J ¼ 15.5 Hz, 1H), 1.95 (s, 3H),
The physical and spectroscopic data of compounds 4, 5, 7
and 10 are in accordance with the ones described in the litera-
ture [6e8]. The new compound 13 had its structure deduced by
1
3
1
1
1
1
8
.02 (s, 3H); C NMR 100 MHz (CDCl ) d: 200.05 (s),
3
68.21 (s), 153.03 (s), 150.52 (s), 142.01 (s), 138.21 (s),
36.52 (s), 133.47 (d), 133.01 (d), 132.98 (s), 131.15 (d),
30.80 (d), 130.31 (d), 129.91 (d), 129.63 (d), 128.79 (d)
2.88 (s), 51.86 (t), 30.55 (q), 30.12 (q); Anal. calcd:
1
13
physical methods ( H, C NMR, IR) and elementary analysis.
Table 1
Antimycobacterial activity of the compounds 4, 5, 7, 10 and 13
C H N O : C 72.28, H 4.85, N 8.43; Found: C 72.21, H
20 16 2 3
4.91, N 8.40.
Compounds
M. tuberculosys, MIC (mg/mL)
4
7
0.62
50
5.3. Antimicobacterial activity
1
1
5
0
3
25
100
To test its antimicobacterial activity, the primary screening
ꢂ1
Resistant
1.0
was conducted at 100.0 mg mL
(
against M. tuberculosis
ATCC 27294 H Rv) in BACTEC12B medium using the
Rifampicin
37