H. Xu, et al.
Bioorganic&MedicinalChemistryLettersxxx(xxxx)xxxx
Table 1
The antifungal activity of the target compounds A1–A14.
Compd.
X
R
MIC90 (μg/mL)
C.alb
C.neo
C.zey
C.alb(sc5314) A.f
> 128 > 128
A1
H
F
F
F
F
F
F
2-C2H5
2,5-di-CH3
2-C2H5
3-Br
> 128
> 128
> 128
> 128
16
> 128
> 128
> 128
A2
8
4
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 128
A3
8
8
A4
16
> 128 64
A5
4-OC2H5
2-Cl
8
32
16
4
2
A6
8
16
8
A7
3,5-di-Cl
> 128
> 128
64
> 128
> 128
A8
CH3 2,5-di-CH3 64
> 128 64
> 128 32
A9
CH3 2-Cl
64
64
A10
A11
A12
A13
A14
FCZ
CH3 4-OC2H5
CH3 2-C2H5
CH3 3-Br
64
32
> 128
16
8
64
4
64
> 128
> 128
64
> 128
> 128
8
> 128
> 128
16
> 128
CH3 3,5-di-Cl
> 128
CH3
–
H
–
4
1
2
1
2
Scheme 4. Synthetic routes of target compounds.
Abbreviations: C.alb., Candida albicans(CPCC400616); C.neo., Cryptococcus
neoformans(CGMCC2.3161); C.zey., Candida zeylanoides(CGMCC2.3739); A.f.,
Aspergillus fumigatus(CGMCC 3.7795); C.alb(sc5314), fluconazole-sensitive
strains of Candida albicans. FCZ, Fluconazole. Values are the average of three
independent experiments. Relative errors are generally within 5–10%.
The synthesis of key intermediates 11a–11h was illustrated in
Scheme 2. 10a–10h were obtained by reacting 8a–8h and phenyl
chloroformate (9) in the pyridine. Compounds 10a–10h were treated
with hydrazine hydrate to afford key intermediates 11a–11h.
The synthesis of key intermediates 15a–15f was illustrated in
Scheme 3. Intermediates 13a–13f were obtained via an addition reac-
tion between aniline or ammonium hydroxide and carbon disulfide in
the ammonia medium. Then the addition of sodium chloroacetate to
reaction mixture resulted in the generation of intermediates 14a–14f.
Subsequently, the intermediates 14a–14f reacted with hydrazine hy-
drate to yield key intermediates 15a–15f.
group, the antifungal activities were decreased. When the R sub-
stituent group was an electron-withdrawing group, the antifungal
activity decreased. In addition, the antifungal activities were de-
creased as the number of electron-withdrawing groups increases.
ii) Compared to the selenochroman-4-ones, most compounds of series
B and C showed improved antifungal activities against Candida al-
bicans, Cryptococcus neoformans, Candida zeylanoides and sensitive
Candida albicans. In addition, the relationship among the sub-
stituents at the 6-position of the benzene ring was also investigated.
When the substituent was a fluorine atom on the 6-position of the
The general synthetic strategies for the formation of the target
compounds are shown in Scheme 4. The target compounds 2,3-dihydro-
tively obtained by the condensation reaction of the intermediates 7a–7c
with 11a–11h or 15a–15f in good yields (25–85%).
series
B compounds, the activities against Candida albicans,
Cryptococcus neoformans and Candida zeylanoides could be sig-
nificantly enhanced. If the fluorine atom was replaced by a methyl
group, the antifungal activity decreases significantly. The R sub-
stituent group was the benzene, the compounds had the strongest
antifungal activity against strain SC5314. When the number of
electron-donating substituent was increased, the antifungal activ-
ities were decreased. For the test strain, the substitution of electron
donating group on the thiosulphonyl benzene ring has little effect
on the antifungal activity.
The in vitro antifungal activity of the target compounds was mea-
sured by means of the minimal inhibitory concentrations (MIC90) with
fluconazole as the control drug. Test fungal strains were obtained from
American Type Culture Collection (strain SC5314 of C.alb.), China
Pharmaceutical Culture Collection (Candida albicans CPCC400616),
China General Microbiological Culture Collection Center (Cryptococcus
neoformans CGMCC2.3161, Aspergillus fumigatus CGMCC3.7795 and
Candida zeylanoides CGMCC2.3739) or were clinical isolates (flucona-
zole-resistant strains 100, 103, 17# and CaR of C.alb.). The in vitro
antifungal activity of target compounds was determined by the micro-
broth dilution method in 96-well plates according to the CLSI M27-A3
guidelines.22 The results are summarized in Tables 1 and 2. The activity
data of the intermediates is shown in Table 3.
iii) And even more obviously, the inhibition activities of series B on
Candida albicans are significantly better than that of series A and C.
In addition, Compounds B3, B8, B12 and C2 inhibited Candida al-
bicans significantly stronger than fluconazole. Compound C1 in-
hibited Candida zeylanoides and Cryptococcus neoformans more
strongly than fluconazole. The series B and C inhibited the grown of
Cryptococcus neoformans more strongly than the series A.
The structure-activity relationship (SAR) was evaluated as follows:
Due to the unique antifungal mechanism of azole antifungal drugs
and the wide clinical application, the phenomenon of drug resistance is
becoming more and more serious. Many Candida albicans resistant to
fluconazole have been found and isolated clinically. Therefore, evalu-
ating the antifungal activities of compounds against fluconazole-re-
sistant strains is a key step in the development of innovative drugs. The
potent compounds B3, B8, B9, C1 and C2 were selected to evaluate
their antifungal activity against fluconazole-resistant strains of C. albi-
cans (strain100, strain103, strain 17# and strain CaR). The results are
summarized in Table 4. Compound B8 shows excellent antifungal ac-
B8 against strain 100, strain 103, strain 17# and strain CaR reached
i) Most compounds of series A showed weak antifungal activities
against Candida albicans, Cryptococcus neoformans, Candida zeyla-
noides and sensitive Candida albicans except strain SC5314. What is
gratifying is that hybrid molecules A2–A6 hold better antifungal
activities against Candida albicans compared with selenochroman-4-
ones. Compounds A5, A6 and A11 produced antifungal activity
against Candida zeylanoides that selenochroman-4-ones does not
possess. Meanwhile, the relationship between various substituents
on the 6-position of benzene ring were investigated. When the
substituent on the 6-position of benzene ring was a fluorine atom,
the antifungal activity against the strain SC5314 is enhanced. When
the 6-position was unsubstituted or substituted with a methyl
3