L.-F. Zhu et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
3
Br
Br
Br
a
b
c
COOH
COOH
O
MeO
d
MeO
MeO
CHO
OH
OMe
1
2
3
5
4
1
Br
3
e
g
f
2'
3'
Br-
N
O
O
8
R
OMe
OMe
OMe OMe
4'
OMe
7-1 7-36
-
4
5
6
h
Br
I
I
g
i
N
N
CHO
Br-
Br-
OAc
OH
OH
9-1
8
9-2
j
I
I
I
k
N
Br-
l
N
N
OR'
9-3, 9-4
OH
OR'
11-1, 11-2
10
R = H, F, Cl, Br, I, NO2, CF3, CN, OMe, OH, CH3; R' = Et, Bn
Scheme 1. Synthetic route of compounds 7-x and 9-x. Reagents and conditions: (a) Br2, dry CH2Cl2; (b) NaBH4, I2, dry THF, 40 °C; (c) (HCHO)n, TFA, 0 °C to rt; (d) n-BuLi, dry
THF, ꢀ78 °C; (e) DDQ, dry MeOH, dry CH2Cl2; (f) TMSBr, Bu4NBr, dry toluene, 80 °C; (g) Ar-NH2, dioxane; (h) BBr3, dry CH2Cl2, ꢀ78 °C, rt overnight; (i) acetic anhydride;
(j) NaBH4, MeOH; (k) NaH, alkyl halide, dry DMF; (l) I2, ethanol, reflux.
their similar structures. In the NMR spectra, 7-x and 9-x
showed one singlet signal in the range of dH 9.19–9.65 and dC
161.5–168.1 ppm due to the iminium moiety (C@N+), and signals
of one CH2CH2 moiety at dH ca. 3.4 (2H, t, J = ca. 7.8 Hz) and ca.
4.4 (2H, t, J = ca. 7.8 Hz). Additionally, 7-x also showed signals of
one methoxyl group at dH ca. 4.05 (3H, s) and dC ca. 57.5. Compared
with 7-11, 9-x showed less signals of one methoxyl group in the 1H
and 13C NMR spectra, while 9-2, 9-3 and 9-4 showed additional
signals of one acetyl, one ethoxy and one benzyloxy group,
respectively. All the compounds showed a characteristic ion peak
at m/z [MꢀBr]+ in positive ESI-MS or HRMS spectra. The presence
of bromide anion was confirmed by ion peaks at m/z [79Br]ꢀ and
EC50 values of <10
and V. mali. For F. solani, ten out of the compounds showed EC50
M. A similar case was observed for three com-
pounds (7-6, 7-32, 9-4) for F. graminearum and two compounds
(7-32, 7-34) for V. mali. Among the compounds, 7-6 gave the high-
lM were more active than TBZ against F. solani
values of 610
l
est activities against F. solani and F. graminearum [EC50 = 1.81
(0.64 g/mL), 7.88 M (2.78
est activity against V. mali, with an EC50 value of 8.71
(4.15 g/mL).
l
M
l
l
l
g/mL)], whereas 7-34 had the high-
lM
l
Based on the EC50 values in Table 1, it was concluded that both
substitution patterns of the C-ring and the type of 8-OR on the A-ring
significantly influenced the activity of the compounds (Fig. 2). By
comparison with 7-1 (R = H), it was found that the introduction of
electron-donating groups like –CH3, –OCH3 or –OH (7-22–7-30) to
the C ring always leads to a decrease of the activity in all cases
(Table 1). On the contrary, in most cases, the presence of electron-
withdrawing groups like halogen atoms, –CF3, –NO2 or –CN on the
C-ring is able to increase the activity. It was worth noting that
the effect of halogen atoms or –NO2 is obviously related with its type
and position. Unlike the cases of 20- or 30-substituted isomers, 40-F
and 40-Cl isomers (7-4, 7-7) gave the decreased activities in most
cases relative to 7-1 (Table 1). In contrast, for Br- or I-substituted
compounds (7-8–7-13), almost all the position isomers showed
the increased activity in all cases. The presence of 40-NO2 (7-21) is
able to significantly increase the activity, whereas the presence of
20-NO2 (7-20) leads to the dramatic decrease of the activity.
Comparison of the activities of compounds 7-32–7-36 and 7-1
showed that the presence of two halogen atoms also increases
the activity against in all cases. However, when compared
with the corresponding mono-halogenated compounds, the effect
of the second halogen atom on the activity varies with its type
and substitution position. For example, 20,40-dichlorinated
compound had the higher activity than the corresponding 20- or
40-chlorinated compounds (7-32 vs 7-5, 7-7). A similar case was
also observed for 20,40-dibrominated compound (7-34 vs. 7-8,
7-10). But the opposite case was observed for 30,50-diCl combina-
tion (7-33 vs. 7-6). Both 20-F-40-Br and 20-F-40-I combinations
reduce the activity, relative to 20-F substitution, but increase the
activity, relative to 40-Br or 40-I substitution.
[
81Br]ꢀ in negative ESI-MS spectra.
According to the mycelia growth rate method,11 compounds 7-x
and 9-x were screened for antifungal activities in vitro at 150
lM
(ca. 50 g/mL) against three plant pathogenic fungi. Thiabendazole
l
(TBZ), and azoxystrobin (ASB), two commercial fungicides, were
used as positive controls. Sanguinarine (SA), chelerythrine (CH)
and MYN were used as reference controls. The results were listed
in Table 1.
The data in Table 1 clearly showed that most of the test com-
pounds presented the inhibition activity in varying degrees against
each of the tested fungi. For each of the fungi, the vast majority of
the compounds displayed the medium to high activity with inhibi-
tion rates of 50–100%, superior to ASB. Some of the compounds
were more active than TBZ, SA and CH against part or all of the
fungi. Generally, the order of susceptibility of the three strains
of fungi to the target compounds is Fusarium solani > V. mali >
Fusarium graminearum.
In order to explore the antifungal potential in more detail and
the structure–activity relationship, the compounds with the inhibi-
tion rates of >80% in Table 1 were subjected to median effective
concentrations (EC50) assay. TBZ was used as a positive control,
and SA, CH and 2-(2-iodophenyl)-3,4-dihydroisoquinolin-2-ium
bromide (MYN) were used as reference controls. The results were
shown in Table 1.
The results in Table 1 showed that the vast majority of the
tested compounds presented EC50 values of <20
lM for all the
fungi, much lower than SA and CH. Part of the compounds with
Zhu, Li-Fei
