Synthesis and antifungal activity of 6,7-bis(arylthio)-quinazoline-5,8- diones and furo[2,3-f]quinazolin-5-ols

Article abstract of DOI:10.1016/j.bmcl.2011.10.099

6,7-Bis(arylthio)-quinazoline-5,8-dione and furo[2,3-f]quinazolin-5-ol derivatives were synthesized and tested for in vitro antifungal activity against Candida, Aspergillus species, and Cryptococcus neoformans. Among them tested, many of furo[2,3-f]quinazolin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-diones showed good antifungal activity. The compounds 4a and 4e completely inhibited the growth of all against Candida and Aspergillus species tested at the MIC level of 12.5 μg/mL. The results suggest that furo[2,3-f]quinazolin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-diones would be promising antifungal agents.

Full text of DOI:10.1016/j.bmcl.2011.10.099

Bioorganic & Medicinal Chemistry Letters 22 (2012) 500–503
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antifungal activity of 6,7-bis(arylthio)-quinazoline-5,8-diones
and furo[2,3-f]quinazolin-5-ols
⇑
Chung-Kyu Ryu , Yang Hui Kim, Hyun Ah Im, Ji Young Kim, Joo Hee Yoon, Aram Kim
College of Pharmacy and Division of Life and Pharmaceutical Sciences, Ewha Womans University, 52 Ewhayeodae-gil, Seodaemun-ku, Seoul 120-750, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
6,7-Bis(arylthio)-quinazoline-5,8-dione and furo[2,3-f]quinazolin-5-ol derivatives were synthesized and
tested for in vitro antifungal activity against Candida, Aspergillus species, and Cryptococcus neoformans.
Among them tested, many of furo[2,3-f]quinazolin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-diones
showed good antifungal activity. The compounds 4a and 4e completely inhibited the growth of all against
Received 25 August 2011
Revised 18 October 2011
Accepted 27 October 2011
Available online 4 November 2011
Candida and Aspergillus species tested at the MIC level of 12.5 lg/mL. The results suggest that furo[2,3-
f]quinazolin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-diones would be promising antifungal agents.
Keywords:
Ó 2011 Elsevier Ltd. All rights reserved.
6,7-Bis(arylthio)-quinazoline-5,8-dione
Furo[2,3-f]quinazolin-5-ol
Antimicrobial compounds
Antifungal
Fungi
Substitution effects
A benzofuran derivative 1, a novel myristoyltransferase inhibitor,
has been reported as antifungal agent1,2 as well as antibacterial
agent3,4 (Fig. 1). N-Myristoyltransferase has been proven to be
essential for the viability of fungi, including medically important
pathogenic fungi, Candida albicans5 and Cryptococcus neoformans6
making it a possible target for the development of antifungal agents
with a novel mode of action.
furo[2,3-f]quinazolin-5-ols 4 could have similar biological activi-
ties with those of quinonoid compounds.
There have not been any reports on furo[2,3-f]quinazolin-5-ols
4 to the best of our knowledge. The presence of aryl, thio, amino
group, or halogen atoms on quinonoid compounds significantly
affects their antifungal activity.9 A variety of furo[2,3-f]quinazo-
In our previous Letters,7 benzofuran-5-ol 2 and furo[2,3-f]quin-
olin-5-ol 3 scaffolds have demonstrated potent antifungal activity
against pathogenic fungi (Fig. 1). Structure–activity relationship
studies from heterocyclic quinonoid compounds indicated that
the number and position of nitrogen (N) atoms substituted in the
heterocyclic ring were considerably important factors to affect
the biological activities.5,6 Generally, increasing the number of sub-
stituent nitrogen atoms in the ring enhances the activities. We
speculated that incorporation of a nitrogen atom into the ring of
the skeleton in compounds 3 would change the physicochemical
properties, and lead to a new pharmacophore furo[2,3-f]quinazo-
lin-5-ols 4 with a different biological profile from scaffolds 3.
Furo[2,3-f]quinazolin-5-ols 4 which would be one of the bioisos-
teres of compounds 3, could metabolize to 5,8-quinolinedione
derivatives with a quinonoid structure in fungi (Fig. 1). Quinonoid
compounds display potent biological properties including anti-
fungal, antimalarial, and antibacterial activity.8 We assumed that
R1
R3
NH2
R1
O
O
R2
N
R2
R4
OH
1: R4 = H
3
2: R4 =OH
R1
R2
R1
O
O
O
R2
N
N
N
R3
N
R3
OH
4
⇑
Corresponding author. Tel.: +82 2 3277 3027; fax: +82 2 3277 3051.
E-mail address: ckryu@ewha.ac.kr (C.-K. Ryu).
Figure 1. Benzofuran, furo[2,3-f]quinolin-5-ol and furo[2,3-f]quinazolin-5-ol
scaffolds.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.10.099

C.-K. Ryu et al. / Bioorg. Med. Chem. Lett. 22 (2012) 500–503
501
R1
N
C
NH2
O
O
O
O
HS
R2
N
O
Cl
Cl
O
C
N
N
O
N
O
O
N
N
Cl
a
b
c
N
S
O
O
OH
8
9
R1
R2
e
d
4a-g: R1, R2= H, X, ...
O
R1
S
S
R2
R3
NH2
N
O
O
O
O
S
N
N
R1
R1
R2
N
O
O
N
S
N
S
R1
OH R1
R3
7n-o: R1 = CH3CH2 or CH3
4h-i: R1 = alkyl
7a-m: R1, R2 , R3= H, X, ..
Scheme 1. Synthesis of furo[2,3-f]quinazolin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-dione derivatives. Reagents and conditions: (a) ethyl cyanoacetate/NH4OH/CeCl3
(0.1 equiv)/EtOH/rt/10 min/51%; (b) arylthiol (1 equiv)/EtOH/reflux/5 h/47–78%; (c) alkylthiol (1 equiv)/EtOH/reflux/5 h/52–66%; (d) arylthiol (2 equiv)/EtOH/reflux/15 h/69
–87%; (e) alkylthiol (2 equiv)/EtOH/reflux/10 h/81–86%.
lin-5-ols 4 with different substituents could exhibit the biological
activities through different actions and sometimes improve upon
the activities.
quently, ethyl 2-(7-halo-5,8-dioxo-5,8-dihydroquinazolin-6-yl)-2-
cyanoacetate (9) was synthesized by regioselective nucleophilic
substitution of compound 8 with 1 equiv of ethyl cyanoacetate
and 0.1 equiv of CeCl3 in the presence of NH4OH according to the
reported method7 with minor modification. 2-Amino-4-arylthio-
5-hydroxyfuro[2,3-f]quinazolines 4a–g were synthesized by
nucleophilic substitution and cyclization of the compound 9 with
appropriate arylthiols in EtOH. To a solution of the compound 9
in EtOH, 1 equiv of arylthiol was added. The mixture was refluxed
for 5 h and concentrated in vacuo. Purification of residual crude
product by column chromatography yielded compounds 4a–g.
Most of these reactions went as expected and had overall high
yields.
Based on this speculation, furo[2,3-f]quinazolin-5-ols 4a–i with
various substituents were designed and synthesized to elucidate
their contribution to the antifungal activity (Scheme 1).
Heterocyclic quinone compounds represent an important class
of biologically active molecules8 and exhibits antifungal activites.9
In our previous reports,10,11 6,7-bis(arylthio)-quinoline-5,8-diones
5 and 6,7-bis(arylthio)-phthalazine-5,8-diones 6 have demon-
strated potent antifungal activity against pathogenic fungi
(Fig. 2). The presence of arylthio moiety to the quinones was con-
siderably important factor to affect their antifungal activity.11,12
We synthesized 6,7-bis(arylthio)-quinazoline-5,8-diones 7 which
could be bioisosteres of quinones 5 and 6 to evaluate their anti-
fungal activity (Scheme 1).
In a similar manner, 4-alkylthio-5-hydroxyfuro[2,3-f]quinazo-
lines 4h–i were synthesized by cyclization of compound 9 with
1 equiv of ethylthiol or 2-mercaptoethanol in EtOH.
The in vitro antifungal activity of new compounds 4 and 7
against pathogenic fungi was determined by the two-fold broth
dilution method. Additional data for antifungal activity are
provided.
Methods for the synthesis of furo[2,3-f]quinazolin-5-ols 4a–i
are shown in Scheme 1 and Table 1. The 6,7-dichloro-quinazo-
line-5,8-dione (8) was prepared from 5,8-dimethoxyquinazoline
according to the known method13 with minor modification. Conse-
The mechanism for the formation of compound 9 involves
Michael-type addition of the anion of ethyl cyanoacetate to qui-
none 8 followed by subsequent dechlorination.7 The substitution
of compound 9 with nucleophilic thiols resulted in the formation
of aromatic hydroquinone system as intermediates and subse-
quent cyclization to compounds 4. The substitution was similar
to the formation of stable aromatic hydroquinone system by the
substitution of thiols on quinones.14
6,7-Bis(arylthio)-quinazoline-5,8-diones 7a–o were synthe-
sized by nucleophilic substitution on compound 8 with 2 equiv
of appropriate arylthiols or alkylthiols according to the known
method.11,12 Most of the substitutions went as expected and had
an overall yield of 69–87%.
O
O
R1
O
O
R1
R2
R3
S
S
R2
R3
S
S
Z
Y
N
The experimental data of representative compounds 4a, 7b, 7n,
and 8 were cited in Ref. 15.
X
N
R1
R2
R1
R2
The synthesized furo[2,3-f]quinazolin-5-ols 4a–i, 6,7-bis(aryl-
thio)-quinazoline-5,8-diones 7a–o, and 5,8-dimethoxyquinazoline
(10) were tested in vitro for their growth inhibitory activity against
pathogenic fungi using the standard method.16 The MIC (minimum
inhibitory concentration) values were determined by comparison
with fluconazole16 and 5-fluorocytosine as standard agents.
As indicated in Table 1, many of furo[2,3-f]quinazolin-5-ols
4a–i and 6,7-bis(arylthio)-quinazoline-5,8-diones 7a–o showed
R3
R3
5: X = N, Y = Z = CH
6: X = CH, Y = Z = N
7
Figure 2. 6,7-Bis(arylthio)-quinones and 6,7-bis(arylthio)-quinazoline-5,8-dione
derivatives.

502
C.-K. Ryu et al. / Bioorg. Med. Chem. Lett. 22 (2012) 500–503
Table 1
Structures and antifungal activity for furo[2,3-f]quinazolin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-diones
Compound
R1
R2
R3
MICa
(l
g/mL)
C. neoformans
C. albicansb
C. tropicalis
C. krusei
A. niger
A. flavus
4a
4b
4c
4d
4e
4f
4g
4h
4i
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
7n
7o
H
H
H
H
F
H
Cl
CH3
CH3CH2
H
H
H
H
H
H
H
CH3
CH3O
Cl
Br
F
F
H
—
—
H
H
H
H
H
CH3
F
CH3
H
F
H
H
H
—
—
—
—
—
—
—
—
—
—
—
—
—
3.2
6.3
6.3
50.0
50.0
25.0
6.3
3.2
12.5
6.3
3.2
6.3
6.3
12.5
3.2
6.3
12.5
6.3
50.0
3.2
12.5
12.5
6.3
6.3
3.2
0.8
3.2
6.3
3.2
12.5
25.0
6.3
3.2
1.6
6.3
12.5
25.0
12.5
3.2
25.0
50.0
25.0
3.2
6.3
12.5
50.0
25.0
6.3
3.2
3.2
3.2
1.6
3.2
3.2
6.3
3.2
6.3
3.2
50.0
50.0
50.0
1.6
25.0
6.3
25.0
25.0
25.0
6.3
25.0
12.5
50.0
6.3
12.5
25.0
12.5
6.3
6.3
6.3
6.3
3.2
12.5
>50.0
>50.0
6.3
50.0
12.5
25.0
12.5
3.2
3.2
6.3
6.3
12.5
12.5
25.0
6.3
12.5
12.5
12.5
25.0
6.3
12.5
50.0
25.0
6.3
12.5
12.5
12.5
1.6
6.3
6.3
12.5
50.0
3.2
1.6
0.8
25.0
6.3
1.6
1.6
12.5
6.3
6.3
50.0
6.3
—
F
CH3O
Cl
Br
CH3
CH3
H
H
H
F
F
H
OH
—
—
—
6.3
12.5
12.5
6.3
3.2
6.3
12.5
6.3
6.3
25.0
25.0
1.6
H
H
H
F
F
H
6.3
12.5
12.5
12.5
25.0
3.2
25.0
25.0
25.0
6.3
12.5
12.5
6.3
25.0
50.0
25.0
6.3
3.2
CH3CH2
CH2CH2OH
—
—
—
12.5
25.0
>50.0
50.0
3.2
10
Fluconazole
5-Fluorocytosine
—
—
3.2
12.5
a
The MIC value was defined as the lowest concentration of the antifungal agent. MIC values were read after 1 day for Candida species and Cryptococcus neoformans, and
2 days for Aspergillus species in 37 °C. The inoculum sizes contained approximately 1 Â 105 cells/mL. Culture media tested were the modified Sabouraud dextrose broth (Difco
Lab.). The final concentration of antifungal agents was between 0.2 and 50.0 lg/mL.
b
Fungi tested: Candida albicans Berkout KCCM 50235, C. tropicalis Berkout KCCM 50662, C. krusei Berkout KCCM 11655, Cryptococcus neoformans KCCM 50564, Aspergillus
niger KCTC 1231, and Aspergillus flavus KCCM 11899.
potent antifungal activity against all tested fungi. Actually, the
activity of compounds 4a and 4e was superior or comparable to
those of 5-fluorocytosine against fungi. The compounds 4a and
4e completely inhibited the growth of all against Candida and
cyclization of compound 9 with appropriate arylthiols or alkylthiols
in EtOH. 6,7-Bis(arylthio)-quinazoline-5,8-diones 7a–o were syn-
thesized by nucleophilic substitution on compound 8 with 2 equiv
of appropriate arylthiols or alkylthiols. Most of these reactions went
as expected and had overall high yields. We have identified a lead
compound that has antifungal activity by screening of our
furo[2,3-f]quinazolin-5-ols 4a–i and 6,7-bis(arylthio)-quinazoline-
5,8-diones 7a–o. Among them tested, many of furo[2,3-f]quinazo-
lin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-diones showed po-
tent antifungal activity. The results suggest that furo[2,3-
f]quinazolin-5-ol and 6,7-bis(arylthio)-quinazoline-5,8-dione scaf-
folds would be promising leads for the development of antifungal
agents. Moreover, the results should encourage the synthesis of
furo[2,3-f]quinazolin-5-ols and 6,7-bis(arylthio)-quinazoline-5,8-
dione analogs for improving antifungal properties.
Aspergillus species tested at the MIC level of 12.5 lg/mL. Many of
compounds 4a–i and 7a–o also was comparable to those of 5-flu-
orocytosine against Candida krusei, Cryptococcus neoformans, and
Aspergillus species. Actually, the activity of compounds 7a or 7h
was superior to those of 5-fluorocytosine against C. neoformans
and Aspergillus flavus.
Generally, the 4-arylthio-furo[2,3-f]quinazolin-5-ols scaffolds
4a–g exhibited potent activity, indicating a correlation that may
offer insight into the mode of action of these compounds. In con-
trast, 4-alkylthio-furo[2,3-f]quinazolin-5-ols scaffolds 4h–i did
not show significant antifungal activity against tested fungi,
although they exhibited good activity against C. neoformans and
A. flavus. 4-Alkylthio-moieties of compounds 4h–i did not improve
significantly their antifungal activity in comparison to 4-arylthio-
compounds 4a–g. 6,7-Bis(arylthio)-quinazoline-5,8-diones 7a–o
exhibited slightly more potent activity than furo[2,3-f]quinazo-
lin-5-ols scaffolds 4a–i. The structure–activity relationship may
not exist between properties of substituents (R1, R2, R3: H, X, Me)
for the 4-arylthio moieties of compounds 4a–g and 7a–m and alkyl
substituents for the compounds 4h–i and 7n–o. In addition, the
nonquinonoid 5,8-dimethoxyquinazoline (10) exhibited no or
poor, if any, antifungal activity. Thus, furo[2,3-f]quinazolin-5-ol
and 6,7-bis(arylthio)quinazoline-5,8-dione moiety could be impor-
tant for the antifungal activity.
References and notes
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In conclusion, ethyl 2-(7-halo-5,8-dioxo-5,8-dihydroquinazolin-
6-yl)-2-cyanoacetate (9) was synthesized by regioselective substi-
tution of 6,7-dichloro-quinazoline-5,8-dione (8) with 1 equiv of
ethyl cyanoacetate and 0.1 equiv of CeCl3 in the presence of NH4OH.
Furo[2,3-f]quinazolin-5-ols scaffolds 4a–i were synthesized by

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with Jeol JMS AX505 WA. Ethyl 2-amino-5-hydroxy-4-(p-tolylthio)furo[2,3-
f]quinazoline-3-carboxylate (4a): violet powder (61%); mp 112–113 °C; 1H
NMR (DMSO-d6) d 1.37 (t, 3H, J = 7.2, CH3), 2.39 (s, 3H, CH3), 4.57 (q, 2H, J = 7.2,
CH2), 7.13–7.16 (m, 2H), 7.33–7.43 (m, 2H), 7.56 (s, 2H, NH2), 9.43 (s, 1H), 9.51
(s, 1H), 9.69 (s, 1H, OH); MS (m/z) 395 (M+). 6,7-Bis(4-
methoxyphenylthio)quinazoline-5,8-dione (7b): yellow green powder (89%);
mp 178–179 °C; 1H NMR (CDCl3) d 7.48 (d, 6H, OCH3), 6.69–6.76 (m, 4H),
7.13–7.17 (m, 4H), 9.32 (s, 1H), 9.74 (s, 1H); MS (m/z) 436 (M+). 6,7-
Bis(ethylthio)quinazoline-5,8-dione (7n): red powder (76%); mp 117–119 °C; 1
H
NMR (DMSO-d6) d 1.25 (t, 6H, J = 7.2, CH3), 3,.28 (q, 4H, J = 7.2, CH2) 9.35 (s, 1H),
9.59 (s, 1H); MS (m/z) 280 (M+). 6,7-Dichloro-5,8-quinazolinedione (8)13: light
yellow crystal (32%); mp 134–135 °C; 1H NMR (CDCl3) d 9.63 (s, 1H), 9.74 (s,
1H; MS) (m/z) 229 (M+).
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545 and were uncorrected. 1H NMR spectra were recorded on Varian Unity
INOVA 400 MHz FT-NMR spectrometer with TMS. Mass spectra were taken
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