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G. Errante et al. / European Journal of Medicinal Chemistry 41 (2006) 773–778
mined (Table 4). The minimum inhibitory concentration (MIC)
values were determined by comparison with amphotericin B as
a standard agent. The data are summarized in Table 5. Most of
these compounds generally showed potent antifungal activities.
Except for Candida albicans, amphotericin B was more active
than all the synthesized compounds, three products (i.e., 6b,
6c, 6d) were very active against the other strains (Candida tro-
picalis, Aspergillus niger, Fusarum oxysporum and Trichophy-
ton tonsurans).
MIC50 of the synthesized molecules against C. albicans
was important in comparison to amphotericin B. MIC50 were
lower than 0.2 μg ml–1 except to 6e which had a MIC50 at
0.3 μg ml–1 for C. tropicalis. For A. niger, T. tonsurans and
F. oxysporum, all MIC50 were lower than 0.2 μg ml–1 except
the MIC50 of 8a and 6e which are 0.3 μg ml–1 and 2 μg ml–1,
respectively.
C. tropicalis and M38-P [12] for A. niger, F. oxysporum and T.
tonsurans. The final concentrations of the antifungal agents
ranged from 0–3 μg ml–1. The inoculi were adjusted to a con-
centration of 4–6 × 105 CFU/ml–1 in RPMI 1640 medium and
an aliquot of 0.1 ml was added to each well of the microdilu-
tion plate which were incubated at 35 °C for C. albicans and
C. tropicalis and at 37 °C for A. niger, F. oxysporum and T.
tonsurans. The plates were read after 48 h with a microplate
spectrophotometer set at 405 nm. MICs were calculated based
on the density of the growth control and were the lowest drug
concentration that resulted in a 50% reduction in growth com-
pared with that of the drug-free growth control. The data are
summarized in Table 5.
4.2. Chemistry
No evident structure-activity relationship seems exist with
these different series.
4.2.1. Materials
Melting points were determined on a Kofler hot-plate melt-
ing point apparatus and were not corrected. Infra-red spectra
were obtained on a PERKING-ELMER FT/IR-1600 instru-
ment. Absorption bands are expressed in cm–1 and only note-
In this work, all synthesized compounds were more active
than amphotericin B against these strains. The inhibition ratio
product: amphotericin B was better than 2:1 for all compounds
except for C. albicans. C. tropicalis is often present in oppor-
tunistic infections such as in HIV, and is known to be a resis-
tant-amphotericin B strain. thus sulfoxide- and sulfide-
quinones can be chosen as candidates to a more extensively
in vivo study. Further investigation is needed to clarify the
mechanism of the antifungical activity.
worthy absorptions are listed. H and 13C NMR spectra were
1
recorded on a BRUKER BZH 200/52 instrument, working at
200 MHz (1H NMR) and 70 MHz (13C NMR). Chemical shifts
are reported in ppm downfield from tetramethylsilane. The
electronic ionization mass spectrometry experiments were per-
formed on a FINNIGAN MAT 95 XL instrument. Compounds
1 and 2 were synthesized with known procedures [7,13].
4. Experimental part
4.2.2. General procedure for the synthesis of disulfide
naphthoquinones 5a–c
4.1. antifungal activity tests
To a solution of naphthoquinone (0.250 mmol) in ethanol
(15 ml) and 0.500 g of celite-KF (celite/KF: 1:1 in weight) was
added a solution of arylsulfide (0.750 mmol). The suspension
was stirred for 2 hours. After filtration the solvent was evapo-
rated and the crude product was crystallized into ethanol
(Table 6).
The stock solution from each molecule was prepared in
DMSO and the final concentration was made in RPMI 1640
medium.
MICs (minimal inhibitory concentrations) of amphotericin
B and the synthesized molecules were calculated by the
NCCLS broth microdilution method [11] for C. albicans and
Table 6
Physico-chemical data of sulfides 5a–d
Compound
5a
X
H
Physico-chemical data
MP (EtOH): 136 °C
IR (KBr): 3435, 1667, 1593, 1498, 1267 cm-1.
1H NMR (DMSOd6): 7.90 (2H) m; 7.15 (2H) m; 7.10 (2H) m.
13C NMR (DMSOd6): 178.1, 147.7, 134.0, 133.8, 132.5, 129.9, 129.1, 127.2, 126.6.
MS: m/z 374 (M+.)
HRMS: calculated for: C22H14S2O2: 374.0435; found: 374.0432.
MP (EtOH): 169 °C
IR (KBr): 2920, 1664, 1649, 1589, 1505, 1491, 1260.
1H NMR (CDCl3): 8.0 (2H) m; 7.6 (2H) m; 7.3 (4H) m; 7.1 (4H) m; 7.5 (6H) s.
13C NMR (CDCl3): 178.8, 148.3, 138.0, 133.6, 132.9, 131.5, 130.2, 129.9, 127.1, 21.2.
MS: m/z 402 (M+).
5b
5c
CH3
HRMS: calculated for: C24H18O2S2 402.0748, found: 402.0742
MP (EtOH): 108 °C
OCH3
IR (KBr): 2942, 1663, 1589, 1491, 1244.
1H NMR (CDCl3): 8.0 (2H) m; 7.6 (2H) m; 7.4 (4H) d (J = 10 Hz); 6.7 (4H) d (J = 10 Hz); 3.8 (6H) s.
13C NMR: 178.9, 159.7, 148.1, 133.8, 133.6, 132.9, 127.0, 124.1, 114.7, 55.3.
MS: m/z 435 (MH+.)
HRMS: calculated for C24H18O4S2H+: 4350725, found: 435.0726.