M. Wang, et al.
Bioorganic & Medicinal Chemistry Letters xxx (xxxx) xxxx
emerge, such as four influenza pandemics worldwide in history:
Spanish influenza in 1918, Asian influenza in 1957, Hong Kong influ-
compounds 7, 10, 14, 17 and several intermediates were first in-
vestigated for their inhibitory effect on IAV A/WSN/33 (H1N1) at
10 μM using the Gaussia luciferase (Gluc) reporter assay in 293T-Gluc
3
–5
enza in 1968, Mexico influenza in 2009.
2
8
Currently, three classes of anti-influenza drugs are available for the
treatment of flu, namely, M2 ion-channel blockers (amantadine and
rimantadine), neuraminidase inhibitors (oseltamivir, zanamivir, per-
cells and the results are shown in Fig. 2. Contrary to our predictions,
the results indicated that all the newly synthesized quinazoline deri-
vatives exhibited a moderate to low inhibition ratio to IAV infection.
According to the result of preliminary screening, the IC50 values of
the selected quinazoline derivatives along with ribavirin for comparison
were summarized in Table 1. Overall, the antiviral activity of these
compounds was equivalent to or weaker than that of the previous in-
dole derivatives. However, some compounds still were identified as
potential anti-IAV agents which deserved further structural modifica-
tion. The selected compounds had potent in vitro anti-IAV activity and
6
amivir and laninamivir octanoate), and RNA polymerase inhibitor
7
(
Favipiravir). Encouragingly, baloxavir marboxil (BXM) has been ap-
proved for the treatment of flu, which inhibits the cap-dependent en-
8
donuclease (CEN). Unfortunately, the M2 ion-channel inhibitors are no
longer recommended for treatment of influenza and NA inhibitors have
several limitations in clinical practice due to their drug resistance and
9
–13
severe side effects.
Therefore, it is still an urgent demand to develop
new antiviral agents for IAV infection with new scaffold and novel
mechanism of action.
showed low cytotoxicity (CC50: > 100 μM) except for 7i (CC50:
64.8 μM). Compared with ribavirin, compounds 10a5, 14c and 17a
(IC50s: 3.70–8.64 μM) showed significantly better activity against IAV
and higher selective indexes (SI > 11.57–27.03). Moreover, the most
active compound 10a5 (IC50: 3.17 ± 0.82 μM) was found to be 4.1-
fold more potent than the reference drug, suggesting that the applica-
tion of quinazoline scaffold in anti-IAV is promising. For the action
mechanism, it may also act on viral RNA transcription and replication,
similar to previous indole compounds, which needs to be further ver-
ified.
1
4,15
In our precious studies,
3-substituted indole derivatives have
been identified as anti-IAV agents with significant activity against A/
WSN/33 (H1N1) virus. We found that these compounds inhibited IAV
replication at the post-entry stage and might target viral RNA tran-
scription and replication. On the other hand, quinazoline is a biologi-
cally imperative scaffold known to be linked with a wide range of
1
6
17
18
pharmacological activities like anticancer, anti-viral, analgesic,
1
9
20
21
anti-inflammatory,
anti-hypertensive,
antitubercular
and anti-
2
2
bacterial activities. It is well-known that bio-isosterism and scaffold
hopping are the strategies for discovering structurally novel com-
As shown in Fig. 2 and Table 1, the anti-IAV activity of the quina-
zoline derivatives in this study depends on both of the groups at the C-2
and C-4 positions. For O-acetamide groups at C-4, the nature of the
substituents greatly influence activity. The introduction of naphthalen-
2-yl (7f), cyclopropyl (7g) and adamantan-1-yl (7j) groups markedly
reduces or even loses activity, which may be attributed to the size of
rigid structures. Compounds with phenyl, benzyl and furfuryl groups
have similar activities, while compounds with thiazol-2-yl (7h) and a 2-
ethoxyl substitution on the benzene ring (7i) show relatively higher
activity. Although a simple SAR is difficult to explore, aromatic ring is
crucial for their anti-IAV effect.
2
3,24
pounds.
However, 2,4-disubstituted quinazoline anti-IAV agents
have not been reported in the literature.
Based on the above facts and as part of our persistent efforts to
develop potential antiviral candidates, we planned to take place of the
indole core with quinazoline scaffold and meanwhile did structural
modifications at the 2-position of the quinazoline core and amide part
of the 4-position (Fig.1). Thus, we designed and synthesized a series of
2
,4-disubstitued quinazoline derivatives and evaluated their anti-IAV
activity in this study, aiming at finding new quinazoline derivatives
with potent anti-IAV activity and facilitate the further development of
these compounds.
In further modifications, we kept phenyl or benzyl groups at the
amide terminal on the C-4 positions and investigated the effect of the
substituent groups at C-2 position. The relative contribution of the
substituents at the C-2 position to activity is as follows: dimethylamino
(10a5) > 3,4-dihydroisoquinolin-2(1H)-yl (10a1 and 10b1) > tetra-
hydro-2H-pyran-4-yl (10a3) > pyrrolidin-1-yl (7a) ≈ diethylamino
(10a4 and 10b2) > 4-methylpiperazin-1-yl (10a2 and 10b3).
On the other hand, switching the sense of the amide group at C-4
(O-ethylamines) leads to some increase in potency compared to O-
acetamides at C-4 (i.e. 14a vs 7g, 14k vs 7b). Surprisingly, introduction
of cyclohexyl (14d) and 4-acetylphenyl (14j) lead to the loss inhibitory
activity. Although there are small differences in activity between the
electron-donating groups and the electron-withdrawing groups on
benzene ring, 4-trifluoromethyl (14c, Table 1) is preferred. For het-
erocyclic groups at C-2 position, 3,4-dihydroisoquinolin-2(1H)-yl
makes more contribution to anti-IAV activity than diethylamino (17a vs
17b vs 17c, Fig.2), while 4-methylpiperazin-1-yl is the lowest (Table 1)
The target compounds 7a–j, 10a–b, 14a–l and 17a–c were syn-
thesized by following the pathway described in Scheme 1. The quina-
zoline core 3 was easily obtained via cyclization of anthranilic acid 1
2
5,26
and urea, and then chlorination.
Nucleophilic substitution of 3 with
27
ethyl glycolate and pyrrolidine successively, and then hydroxlysis
gave 2-((2-(pyrrolidin-1-yl)quinazolin-4-yl)oxy)acetic acid 6. Coupling
of acid 6 with various amines achieved quinazoline derivatives 7a–j.
The hydroxlysis of key intermediate 4 with LiOH, and then amidation
with aniline or benzylamine afforded the amides 9a–b. The chlorine at
the 2-position of 9a–b was substituted with available secondary amines
to provide the target compounds 10a–b. The synthesis of the com-
pounds 14a–l and 17ac were similar to that of 7a–j and 10a–b. The
structures of all the newly synthesized target compounds were con-
1
13
firmed by H NMR, C NMR and HRMS (Supplementary material).
For preliminary screening of anti-IAV candidates, the target
Fig. 1. Design of new quinazoline derivatives.
2
Cen, Shan
