Synthesis and antifungal activities of 5/6-arylamino-4,7-dioxobenzothiazoles

Article abstract of DOI:10.1016/S0960-894X(00)00301-2

5/6-Arylamino-4,7-dioxobenzothiazoles were synthesized and tested for in vitro antifungal activities against pathogenic fungi. Most of the tested 4,7-dioxobenzothiazoles exhibited potent antifungal activites against Candida species and Aspergillus niger (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00301-2

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1589±1591
Synthesis and Antifungal Activities of 5/6-arylamino-4,7-
dioxobenzothiazoles
Chung-Kyu Ryu,a,* Hye-Young Kang,a Yu-Jin Yi,a Keun-Hwa Shina
and Byung-Hoon Leeb
aCollege of Pharmacy, Ewha Womans University, Seodaemun-ku, Seoul 120±750, South Korea
bCollege of Pharmacy, Wonkwang University, Iksan, Chonbuk 570±749, South Korea
Received 21 March 2000; accepted 11 May 2000
AbstractÐ5/6-Arylamino-4,7-dioxobenzothiazoles were synthesized and tested for in vitro antifungal activities against pathogenic
fungi. Most of the tested 4,7-dioxobenzothiazoles exhibited potent antifungal activities against Candida species and Aspergillus
niger # 2000 Elsevier Science Ltd. All rights reserved.
Due to an increase of invasive mycoses in immunocom-
promised patients and frequent accounts of resistance
there has been a renewed interest in antifungal agents
with novel mode of action.1
and 4a±4k in comparison with their cytoxic potential
(Scheme 1 and Table 1).
Chemistry
Quinones such as 5-n-undecyl-6-hydroxy-4,7-dioxo-
benzothiazole (UHDBT, 1) and 7-alkyl-6-hydroxy-5,8-
quinolinediones blockade a mitochondrial electron trans-
port in Saccaromyces cerevisiae.2 The UHDBT inhibits a
ubiquinol-cytochrome c reductase in S. cerevisiae.3 In
previous report,4,5 6-arylamino-7-chloro-5,8-quinoline-
diones 2 have demonstrated potent antifungal activities
against pathogenic fungi. The arylamino-substituents of
quinones 2 sometimes improve the activities.5 From this
information, 6-arylamino-4,7-dioxobenzothiazoles 3 and
5-arylamino-2-methyl-4,7-dioxobenzothiazoles 4, which
would be bioisosteres of quinones 2, were synthesized for
evaluation of their antifungal activities (Fig. 1).
A method for the synthesis of the 4,7-dioxobenzothiazoles
3a±3f and 4a±4k (Table 1) is shown in Scheme 1. 6-Meth-
oxy-7-aminobenzothiazole (5) was prepared according to
the known method.6 Oxidation of the compound 5 with
Fremy's salt (potassium nitrosodisulfonate) gave 6-
methoxy-4,7-dioxobenzothiazole (6) in about 70% yield.
The 6-arylamino-4,7-dioxobenzothiazoles 3a±3f were
prepared from the compound 6. The 6-arylamino-4,7-
dioxobenzothiazoles 3a±3f were formed by regioselective
nucleophilic substitution of the compound 6 with the
appropriate arylamines in the presence of CeCl3. The
The UHDBT (1), one of 4,7-dioxobenzothiazole com-
pounds, has been reported as inhibitors of mitochondrial
cytochrome complex in malaria,6 yeast,7 bacteria8 and
mammalians.9 Also, the other 4,7-dioxobenzothiazole
derivatives exhibited inhibitory activities of mitochondrial
cytochrome complex bc in mammalians10 and cytotoxic
activities against cancer cell lines.11 However, the anti-
fungal activities of the 4,7-dioxobenzothiazole classes
against pathogenic fungi have not been reported.
Therefore, we describe herein the antifungal activities of
5/6-arylamino-4,7-dioxobenzothiazole derivatives 3a±3f
*Corresponding author. Tel.: +82-2-3277-2027; fax: +82-2-3277-
3051; e-mail: ckryu@mm.ewha.ac.kr
Figure 1. 5,8-Quinolinedione and 4,7-dioxobenzothiazole derivatives.
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00301-2

1590
C.-K. Ryu et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1589±1591
Scheme 1. Synthesis of 5/6-arylamino-4,7-dioxobenzothiazoles. Reagents and conditions: (a) Fremy's salt (2 equiv) in 0.3 M NaH2PO4/acetone/rt/1
h/67%; (b) arylamine (1 equiv)/CeCl3 (0.5 equiv)/EtOH/re¯ux/5 h/80±95%; (c) arylamine (1 equiv)/EtOH/re¯ux/5 h/75±95%.
Table 1. Structures and in vitro antifungal and cytotoxic activities for 5/6-arylamino-4,7-dioxobenzothiazoles
Compounds
R1
R2
MICa (mg/mL)
C. tropicalis
IC50 (mg/mL)
C. albicansb
C. krusei
A. niger
Cytotoxicity for HepG2c
3a
3b
3c
3d
3e
3f
4a
4b
4c
4d
4e
4f
4g
4h
4i
H
H
F
H
H
H
H
H
H
H
H
H
H
H
F
H
12.5
12.5
12.5
12.5
12.5
12.5
6.3
3.2
12.5
6.3
6.3
6.3
12.5
12.5
12.5
12.5
1.6
6.3
25
1.6
6.3
12.5
0.8
6.3
6.3
0.8
0.4
25
6.3
3.2
3.2
25
6.3
3.2
0.4
3.2
25
1.6
3.2
3.2
25
12.5
6.3
6.3
3.2
12.5
50
3.2
3.2
1.6
12.5
3.2
3.2
12.5
3.2
6.3
12.5
1.6
6.3
6.3
12.5
12.5
12.5
12.5
25
12.5
1.6
NT
14.7
17.9
100>
16.4
23.6
100>
1.5
1.6
3.4
1.2
4.9
100>
100>
22.0
5.7
15.0
4.8
NTd
NT
Cl
OCH2CH3
OCF3
H
F
Cl
CH3
OCH2CH3
CF3
OCF3
n-C6H13
H
3.2
12.5
12.5
12.5
12.5
12.5
12.5
50
25
3.2
NT
H
Cl
Br
CH3
4j
4k
6
H
CH3
7
25
50
NT
Flucytosine
Cisplatin
3.2
NT
NT
0.33
aMIC was de®ned as the lowest concentration of the agent at which there was no visible colonial growth. MIC values were read after 1 day for
Candida species and 2 days for A. niger in 30 ꢀC. The inoculum sizes contained approximately 1Â105 CFU/mL. Culture media tested were the
modi®ed Sabouraud dextrose agar (Difco Lab.). The ®nal concentration of antifungal agents was between 0.4 and 100 mg/mL.
bFungi tested: Candida albicans ATCC 10231, C. tropicalis ATCC 28775, C. krusei ATCC 749 and Aspergillus niger KCTC 1231.
cCytotoxicity evaluation for HepG2 (hepatocarcinoma from ATCC): according to MTT assay.13
dNT=not tested.
nucleophilic displacement of the 6-methoxy group with
the amines produced the 4,7-dioxobenzothiazoles 3a±3f.
Most of these substitutions went as expected and had
overall high yields of 80±95%.
concentration) values were determined by comparison
with ¯ucytosine12 as a fungicidal standard agent. As indi-
cated in the Table 1, the 6-arylamino-4,7-dioxobenzothia-
zoles 3a±3f showed generally potent antifungal activities
against all tested fungal species. However, the activities
against many fungi were less potent than those of ¯ucyto-
sine. Most of the 5-arylamino-2-methyl-4,7-dioxobenzo-
thiazoles 4a±4k showed potent antifungal activities against
all tested fungal species, and the activity against C. tropi-
calis was prominent. All compounds tested had more
potent antifungal activities against C. tropicalis than ¯u-
cytosine. Actually, the activities of compounds 4b, 4d and
4e were superior or comparable to those of ¯ucytosine
against many tested fungi. The 4,7-dioxobenzothiazoles
4b and 4e completely inhibited the growth of all fungal
species tested at 6.3 mg/mL. The cytotoxic potential of
compounds 3 and 4 was determined in human cancer
In a similar manner, the 5-arylamino -2- methyl- 4,7 -
dioxobenzothiazoles 4a±4k were prepared by regiose-
lective nucleophilic substitutions of the 5-methoxy-2-
methyl-4,7-dioxobenzothiazole (7) with the appropriate
arylamines according to previously reported method.11
Biological Activities
The quinones 3 and 4 were tested in vitro for their
growth inhibitory activities against pathogenic fungi by
the standard method.12 The MIC (minimum inhibitory

C.-K. Ryu et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1589±1591
1591
cell HepG2 by the MTT assay according to the protocol
References and Notes
as described previously.13 Cisplatin was used as a cyto-
toxic reference agent. As indicated in Table 1, some 4,7-
dioxobenzothiazoles 3 and 4 showed very weak or even
no cytotoxicities.14 Among the quinones tested, the com-
pounds 3c, 3e, 3f, 4f, 4g and 4h showed the selectivity, in
that they possess potent antifungal activities without
cytotoxicities in mammalian cells.
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891 and references therein.
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10 (5), 461; in this paper, we have reported the physical data
and cytotoxicities of ®ve compounds 4±4e.
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Medicine (4th ed.); Lorian, V., Ed.; Williams and Wilkins:
Baltimore, 1996; pp 176±211.
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14. Unpublished data; we also tested cytotoxicities of the 4,7-
dioxobenzothiazoles 3 and 4 against human tumor cell lines
such as A 549 (human lung carcinoma) and Col 1 (human
colon carcinoma). Among the quinones tested, the compounds
3c, 3e, 3f, 4f, 4g and 4h showed no cytotoxic activities.
In contrast, the compounds 4a, 4b, 4d and 4e showed
both potent cytotoxic and antifungal activities.11
In terms of structure±activity relationship, the 5-aryla-
mino-4,7-dioxobenzothiazoles 4a±4k showed, in general,
more potent antifungal activities than the 6-arylamino-
4,7-dioxobenzothiazoles skeletons 3a±3f. However, the
compounds 3a±3f exhibited relatively more selective
activities than the compounds 4a±4k. In addition, the
4,7-dioxobenzothiazoles 6 and 7 without an arylamino
group exhibited the poor antifungal activities. Thus, 5/6-
arylamino groups of quinones 3 and 4 partially improve
the antifungal activities. The structure±activity relation-
ship may not exist between properties of substituents (R1
and R2) of 5/6-arylamino moiety of compounds 3a±3f
and 4a±4k.
In conclusion, the results of this study suggest that 5/6-
arylamino-4,7-dioxobenzothiazoles would be potent anti-
fungal agents. Moreover, the results should encourage the
synthesis of 4,7-dioxobenzothiazoles analogues for
improving antifungal properties.
Acknowledgements
This research was supported by the Brain Korea 21 Pro-
ject and the MOST through National R&D Program
(97-N6-01-01-A-18) for Women's Universities.