4
B. Su et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
reagent, PCC etc., proved to be less efficient. Compounds 14, 15 and
16 were prepared by condensation of aldehyde 11 with the corre-
sponding nucleophile hydroxylamine, hydrazine, and methoxyl-
amine in high yields.
phenanthroindolizidines were synthesized and evaluated for their
antiviral activity against TMV systematically for the first time. The
bioassay results indicated that most of these compounds exhibited
good to excellent in vivo anti-TMV activities, of which compounds
4a, 6a, 7a, 11a, 14a, 6b, and 14b, displayed higher or comparable
both in vitro and in vivo antiviral activity compared with
Ningnanmycin, thus emerging as potential inhibitors of plant-
virus. The substituted group at 13a position and the phenan-
threne substitution pattern have great effect on the anti-TMV
activity, demonstrating that the spatial configuration of 13a-H
phenanthroindolizidine alkaloids is not optimal against TMV and
structure optimization at this position is deserving. It was note-
worthy that a hydrogen donor at 13a position may play an essen-
tial role for keeping high activities. Further studies on structural
optimization and mode of action are currently underway in our
laboratory.
To make a judgement of the antiviral potency of 13a-substituet-
ed phenanthroindolizidines (3a–16a, 3b, 4b, 6b, 7b, 10b, and 14b),
the commercial plant virucide Ningnanmycin, Ribavirin, and (+/À)-
tylophorine were used as the controls. The in vitro antiviral assay
results of all of the synthesized compounds were listed in Table 1.
As the control, Ribavirin exhibited 38% and 12.5% inhibitory effect
at 500 l l
g mLÀ1 and 100 g mLÀ1, respectively. All of the synthe-
sized compounds showed higher antiviral activities at both con-
centrations than Ribavirin.
Compared with Ningnanmycin, perhaps the most successful
registered plant virucide, compound 4a exhibited higher activity
at both concentrations. Interestingly, although compounds 3a, 5a,
6a, 7a, 9a, 11a, 14a, 16a, 6b, and 14b showed slightly lower activity
than Ningnanmycin at 500
l
g mLÀ1, they displayed higher inhibi-
Acknowledgments
tory effect at 100
l
g mLÀ1. In other words, these compounds could
still keep much potent antiviral activities in low concentration.
Although the other synthesized 13a-substitueted compounds 8a,
10a, 12a, 13a, 15a, 3b, 4b, 7b, and 10b were less effective than Nin-
gnanmycin, they showed higher or equivalent inhibitory effect
compared with that of representative 13a-H phenanthroindolizi-
dine alkaloid (+/À)-tylophorine. Because all of the synthesized
13a-substitueted phenanthroindolizidines displayed distinguished
in vitro antiviral activity against TMV, further investigates of their
antiviral activity in vivo were deserved.
This work was supported by the National Key Project for Basic
Research (2010CB126106), the National Natural Science Founda-
tion of China (21132003, 21121002, 21372131), and the Special-
ized Research Fund for the Doctoral Program of Higher Education
(20130031110017).
Supplementary data
The in vivo antiviral activity was assayed in three models (pro-
tection, inactivation and curative), and the detailed results were
shown in Table 2. All of the synthesized compounds displayed
good to excellent in vivo inhibitory effect, especially for com-
pounds 4a, 6a, 7a, 11a, 14a, 6b, and 14b, which exhibited higher
or comparable antiviral activity at three models compared with
Ningnanmycin. For inactivation effect and curative effect, com-
pounds 4a, 6a, 7a, 11a, 14a, and 14b showed higher activities at
Supplementary data (experimental details and compound char-
acterization for all synthesized compounds) associated with this
References and notes
both concentrations (500 l l
g mLÀ1 and 100 g mLÀ1) than Nin-
gnanmycin. At these two models, 6b was also more active than
Ningnanmycin at both concentrations, except for curative effect
at 500
11a, 14a, 6b, and 14b displayed higher antiviral activities (from
60.8% to 68.4%) than Ningnanmycin (57.9%) at 500
g mLÀ1, but
slightly lower at 100
g mLÀ1
l
g mLÀ1. In the protection model, compounds 4a, 6a, 7a,
l
l
.
Some important structure and activity relationships were also
observed. 13a-Substituted phenanthroindolizidine analogues 4a,
6a, 7a, 11a and 14a showed much potent inhibitory effect than
the corresponding 13a-H member tylophorine, demonstrating that
the spatial configuration of 13a-H phenanthroindolizidine alka-
loids is not optimal. Compound 4a, with methylene hydroxyl group
at 13a position, displayed much higher antiviral activity than com-
pounds 5a, 6a and 10a. The same tendency was also demonstrated
in other compounds (antiviral effect: 7a > 3a, 14a > 15a, 14a > 16a,
and 14a > 11a), which indicated that a hydrogen donor at 13a posi-
tion may play an important role for keeping high inhibitory effect.
When a methoxyl group was introduced at the C8 position, the
activities decreased for most compounds (antiviral effect:
3a > 3b, 4a > 4b, 7a > 7b, and 10a > 10b), but some showed consid-
erable or slightly higher activities, for example, compound 14b dis-
played higher effect than 14a at 500 l
g mLÀ1. The results indicated
that the methoxy substituent on the phenanthrene unit can also
influence the activity and deserves further investigation in the
future structure modification.
In summary, on the basis of our previous SAR and
antiviral mechanism studies,
a
series of 13a-substituted
Su, Bo
