Synthesis and evaluation of 4-quinazolinone compounds as potential antimalarial agents

Article abstract of DOI:10.1016/j.ejmech.2010.05.040

Febrifugine is an alkaloid isolated from Dichroa febrifuga as the active component against Plasmodium falciparum. Adverse side effects have precluded febrifugine as a potential clinical drug. As part of an ongoing malaria chemotherapy project, novel febrifugine analogues were designed and synthesized. Lower toxicity of these newly designed compounds was achieved by reducing or eliminating the tendency to form chemically reactive and toxic intermediates. New compounds possess excellent in vivo antimalarial activity and most of them become less toxic than the natural product febrifugine. Some of the compounds possess a therapeutic index over ten times superior to that of febrifugine and the commonly used antimalarial drug chloroquine. These compounds, as well as the underlying design rationale, may find usefulness in the discovery and development of new antimalarial drugs.

Full text of DOI:10.1016/j.ejmech.2010.05.040

European Journal of Medicinal Chemistry 45 (2010) 3864e3869
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and evaluation of 4-quinazolinone compounds as potential
antimalarial agents
,
a
a
a
b
c
Shuren Zhu a , Joe Wang , Gudise Chandrashekar , Erika Smith , Xianjun Liu , Yongshen Zhang
*
a Radix Pharmaceuticals Inc., 13303 Sunny Brooke PL, Rm 101, Potomac, MD 20854, USA
b True PharmaChem Inc. 270 Baldwin Road, E1, Parsippany, NJ 07054, USA
c Institute of Biochemistry and Cell Biology, SIBS, CAS, 320 Yue Yang Road, Shanghai 200031, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Febrifugine is an alkaloid isolated from Dichroa febrifuga as the active component against Plasmodium
falciparum. Adverse side effects have precluded febrifugine as a potential clinical drug. As part of an
ongoing malaria chemotherapy project, novel febrifugine analogues were designed and synthesized.
Lower toxicity of these newly designed compounds was achieved by reducing or eliminating the
tendency to form chemically reactive and toxic intermediates. New compounds possess excellent in vivo
antimalarial activity and most of them become less toxic than the natural product febrifugine. Some of
the compounds possess a therapeutic index over ten times superior to that of febrifugine and the
commonly used antimalarial drug chloroquine. These compounds, as well as the underlying design
rationale, may find usefulness in the discovery and development of new antimalarial drugs.
Ó 2010 Elsevier Masson SAS. All rights reserved.
Received 4 May 2010
Received in revised form
14 May 2010
Accepted 18 May 2010
Available online 24 May 2010
Keywords:
Drug design
Febrifugine
Malaria chemotherapy
Plasmodium falciparum
1. Introduction
febrifugine as antimalarial agent is initially appealing not only
because of its rapid effect and no drug resistance, but also because
Malaria is the best known protozoal disease. It is one of the most
common infectious diseases in at least 100 tropical and subtropical
countries in Africa, Southeast Asia, and South America [1]. World-
wide, malaria infects 300e600 million people and kills about three
million in a year. While the most powerful general weapon against
malaria would be a long-lasting vaccine, the failure of some vaccine
development indicates that a highly active vaccine is a long way
from reality [2e4]. The increasing prevalence of multiple drug
resistant strains in most malaria endemic areas has significantly
reduced the efficacy of current antimalarial drugs for prophylaxis
and treatment of this disease [5]. Therefore, medicinal agents based
on novel mode of action are required to overcome the emergence of
resistance and to control an ever-increasing number of epidemics
caused by the malaria parasite.
Febrifugine (1) was isolated as the active components against
malaria in the Chinese herb Chang Shan (Dichroa febrifuga Lour)
[6,7], which has been employed by the local people as medicine
against fevers caused by malaria parasites for a long time. Febri-
fugine acts by impairing haemazoin formation required for matu-
ration of the parasite at the trophozoite stage [8]. The use of
of its availability. Subsequent pre-clinical researches have found
that febrifugine possesses adverse side effects. Strong liver toxicity
has precluded febrifugine as a clinical drug [9e11].
Total synthesis and structural modifications of febrifugine have
been made [12e18]. It has been elucidated the essential role played
by the 4-quinazolinone ring and 100-amino group in the appearance
of activity. It is known that febrifugine (1) and isofebrifugine (2) are
in equilibrium when they are in solution (Scheme 1). This equilib-
rium most likely follows a three-step sequence: (i) retro-Michael
reaction (1 / 3); (ii) Michael addition (3 / 4); (iii) hemi-ketal
cyclization (4 / 2). Intermediate 3, as a Michael acceptor, is highly
electrophilic. If half-life of 3 is sufficiently long, then it is very
possible that this electrophile will non-selectively alkylate
biomolecules such as proteins, peptides, DNA, or RNA inside the
host cell, resulting in the observed toxicity.
Febrifugine could be metabolized to the corresponding arene
oxide 5 by cytochrome P-450 enzymes (Scheme 2). When arene
oxide 5 escapes deactivation process by certain enzymes such as
epoxide hydrase or glutathione S-transferase, toxicity can result
because this reactive electrophile will form covalent adducts with
DNA, RNA, proteins, or other biomolecules of the host. Such binding
can cause mutations and result in cell damage. In a recent meta-
bolic study of febrifugine, Oshima and coworkers isolated metab-
olite 6 [16]. This study indicates that arene oxide 5 is most probably
* Corresponding author. Tel.: þ1 301 675 3714; fax: þ1 301 424 1927.
E-mail address: shuren.zhu@gmail.com (S. Zhu).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.05.040

S. Zhu et al. / European Journal of Medicinal Chemistry 45 (2010) 3864e3869
3865
The yield of direct conversion of aldehyde 20 to oxirane 22 by the
Corey-Chaykowsky ylide [21] method was poor. So aldehyde 20
was first converted to alkene 21 under Wittig condition. Although
initial oxidation of alkene 21 by mCPBA to give oxirane 22 was not
successful, the transformation was smooth and high-yielding via
a three-step sequence: (i) dihydroxylation; (ii) tosylation of the
primary alcohol; and (iii) epoxide ring formation facilitated by
potassium carbonate in methanol. 3H-Quinazolin-4-one
condensed with oxirane 22, to furnish corresponding alcohol 23, as
a pair of diastereomers, this follows the methods of Ogasawara et al.
[12]. Compound 23 then underwent TPAP oxidation [22] and
hydrogenolysis, to afford compound 7. The synthesis of compounds
8e18 follows similar route. The respective aromatic moieties are
available from previously published procedures [23e25].
Scheme 1. Febrifugine, isofebrifugine, and the equilibrium mechanism.
3. Results and discussion
Synthesized compounds (7e18) were tested against Plasmodium
falciparum clones W-2, a chloroquine resistant cell line for in vitro
efficacy. All compounds were also evaluated for antimalarial effi-
cacy and toxicity in mouse models. The ED50s (effective dose
leading to 50% reduction in parasitemia), MCDs (minimum clear-
ance dose), and MTDs (maximum tolerated dose) were determined.
The therapeutic indices, which were obtained by using the MCDs as
the effective parameters, were calculated. The data are summarized
in Table 1. All new compounds (7e18) have exhibited comparable
or superior in vitro and in vivo antimalarial activity, as compared to
parent natural product febrifugine. This confirms earlier observa-
tion that it is crucial to possess a planar aromatic ring, a 100-amino
group and C-20, C-300 O-functionality in order to preserve the
excellent antimalarial activity of febrifugine.
a short-lived reactive metabolic intermediate because metabolite 6
would have been derived from intermediate 5 through the rear-
rangement known as NIH shift [19].
As part of an ongoing malaria chemotherapy project in our
laboratory, we undertook the synthesis and antimalarial activity
evaluation of some febrifugine analogues (compounds 7e18, shown
in Fig.1). Lower toxicity of these newly designed compounds will be
achieved by reducing or eliminating the tendency to form chemi-
cally reactive and toxic intermediates. Two strategies are employed:
(I) Blocking the retro-Michael process; (II) Increasing the oxidation
potential of the molecule. In compounds 7e18, the 100-amino group
is now attached to the alpha position of the carbonyl group, elimi-
nating the possibility of retro-Michael reaction. For compounds
8e12, an extra nitrogen atom or a substitution group was also
introduced on the aromatic ring to block the C-5 or C-6 position of
the quinazolinone ring or to increase the oxidation potential of the
molecule. Compounds 13e16 each bear an alkoxyl group on C-300
position of the piperidine ring. These compounds possess increased
lipophilicity. Overall, these compounds closely resemble febrifugine
itself by possessing a planar aromatic ring, a 100-amino group and C-
20, C-300 O-functionality and are therefore expected to possess same
or similar mode of action. Meanwhile, they would be much less
likely to produce toxic intermediates because these compounds are
designed to block the aforementioned unwarranted metabolic
pathway.
Compound 7, where the 100-amino group is now attached to the
alpha position of the carbonyl group, becomes 5 times less toxic as
compared to febrifugine itself. Compounds 8e12 possess an extra
nitrogen atom or an electron-withdrawing group on the aromatic
ring. Those compounds have shown drastically reduced toxicity.
Compounds 13e16 each bears an ethyloxy or benzyloxy group on
C-300 position of the piperidine ring. They also possess excellent
in vitro and in vivo antimalarial activity. The efficacy is comparable
to that of compounds 7, 8, 11 and 12, bearing a free hydroxyl group
on C-300 position of the piperidine ring. It is interesting to note that
the more lipophilic compounds 13e16 have shown slightly
elevated level of toxicity as compared to compounds 7, 8, 11 and 12.
Although the antimalarial efficacy of compounds 17 and 18 is
about the same as that of compound 7, these compounds are
considerably more toxic. Compounds 17 and 18 each possess an
electron-donating methoxy group attached to the C-7 or C-8 of the
aromatic ring and possess even greater tendency to undergo
oxidation than that of compound 7. These biological data further
validate the hypothesis that some oxidized febrifugine metabolites
have contributed to the observed toxicity.
As a comparative study, compounds 17 and 18 were also
designed. These compounds each bear an electron-donating
methoxy group on the C-7 or C-8 position of the aromatic ring.
These compounds have comparable or even greater tendency
to undergo oxidation. Biological data from these compounds
should further validate, or nullify, the hypothesis that some
oxidized febrifugine metabolites have contributed to the observed
toxicity.
In conclusion, novel febrifugine analogues were designed and
synthesized. New compounds possess excellent in vivo antimalarial
activity and most of them become less toxic than the natural
product febrifugine. Some of the compounds (14 and 15) possess
a therapeutic index over ten times superior to that of febrifugine
2. Chemistry
Scheme 3 illustrated the synthesis of compound 7. TPAP/NMO
oxidation of the readily available alcohol 19 [20] gave aldehyde 20.
Scheme 2. Possible febrifugine metabolic pathway.

3866
S. Zhu et al. / European Journal of Medicinal Chemistry 45 (2010) 3864e3869
Fig. 1. Synthesized febrifugine analogues.
and the commonly used antimalarial drug chloroquine. These
compounds, as well as the underlying design rationale, may find
usefulness in the discovery and development of new antimalarial
drugs.
reported as follows: chemical shifts, multiplicity (s ¼ singlet,
d ¼ doublet, t ¼ triplet, q ¼ quartet, qn ¼ quintet, m ¼ multiplet,
and br ¼ broad), coupling constant in Hertz, integration, and
assignment. 13C NMR spectra were recorded in deuteriochloroform,
unless otherwise noted, on a Bruker Avance 600 spectrometer at
the frequency of 150.9 MHz. Chemical shifts are reported in parts
4. Experimental
per million on the
d scale from an internal standard of tetrame-
thylsilane. Combustion analyses were performed by Atlantic
Microlab., Inc. (Norcross, Georgia). All purified compounds possess
a purity of at least 95%. When necessary, solvents and reagents
were dried as follows: ether, tetrahydrofuran, benzene, and toluene
were stored and distilled from sodium benzophenone ketyl;
dichloromethane, triethylamine, pyridine, and hexane were
distilled over calcium hydride. Unless otherwise stated, the
reagents were purchased from Fisher Scientific, Aldrich Chemical
Company, Lancaster, or Fluka, and used as received.
4.1. Chemistry
Melting points were determined on a Mettler FP62 melting
point apparatus and are uncorrected. Unless otherwise noted, all
nonaqueous reactions were performed under an oxygen-free
atmosphere of nitrogen with rigid exclusion of moisture from
reagents and glassware. Analytical thin layer chromatography (TLC)
was performed using EM Reagents 0.25 mm silica gel 60-F plates.
Visualization of the developed chromatogram was performed by
UV absorbance, aqueous potassium permanganate, or ethanolic
anisaldehyde. Liquid chromatography was performed using a force
flow (flash chromatography) of the indicated solvent system on EM
Reagents Silica Gel 60 (70e230 mesh). Preparative TLC was per-
formed using Whatman Silica Gel C8 TLC plates (PLK5F). 1H NMR
spectra were recorded in deuteriochloroform, unless otherwise
noted, on a Bruker Avance 600 spectrometer at the frequency of
600.1 MHz. Chemical shifts are reported in parts per million on the
4.1.1. 3-Benzyloxy-2-formylpiperidine-1-carboxylic acid
benzyl ester (20)
A solution of alcohol 19 (5.5 g) in 25 mL of CH2Cl2 was added
into a stirred slurry of tetrapropylammonium perruthenate (TPAP,
100 mg), N-methyl morpholine N-oxide (NMO, 5.4 g), and groun-
ded molecular sieve (4.5 g) in 30 mL of CH2Cl2 at room temperature.
The reaction completed in 2 h. Solid molecular sieves were filtered
off. The dark liquid was concentrated and loaded directly into
d
scale from an internal standard of tetramethylsilane. Data are
Scheme 3. Synthesis of febrifugine analogues.

S. Zhu et al. / European Journal of Medicinal Chemistry 45 (2010) 3864e3869
3867
Table 1
a rotary evaporator under reduced pressure to furnish the essen-
tially pure diol. Tosyl chloride (TsCl, 2.0 g) was added into a stirred
solution of this diol (3.9 g), triethylamine (Et3N, 2.0 mL) and 4-
dimethylaminopyridine (DMAP, 80 mg) in 30 mL of methylene
chloride (CH2Cl2) in an ice-water bath. The reaction mixture was
then warmed to room temperature and stirred for additional 2 h.
Solvent was evaporated. The resulting slurry was dissolved in ethyl
acetate (40 mL), washed with water (30 mL), then aqueous sodium
bicarbonate (20 mL), and brine (10 mL), dried over anhydrous
sodium sulfate, and evaporated in a rotary evaporator under
reduced pressure to furnish the essentially pure mono-tosylate.
Potassium carbonate (300 mg) was added into a stirred solution of
this mono-tosylate (5.1 g) in 15 mL of methanol at room temper-
ature. After 4 h, reaction mixture was partitioned between ethyl
acetate (30 mL) and water (30 mL), the separated organic layer was
then washed with brine (10 mL), dried over anhydrous sodium
sulfate, and evaporated in a rotary evaporator under reduced
pressure to furnish the crude product. Silica gel flash chromatog-
raphy (10% ethyl acetate in hexanes) furnishes 22 as colorless oil.
Yield: 78% (3 steps). 1H NMR: 7.28e7.20 (m, 10H), 5.47 (m, 2H), 4.75
(m, 2H), 4.63 (m, 1H), 3.57 (m, 2H), 3.34 (m, 1H), 3.05 (m, 1H), 2.69
(m, 2H), 1.74 (m, 2H), 1.61 (m, 2H). 13C NMR: 162.9, 141.1, 138.2,
128.9, 128.1, 127.7, 127.4, 127.2, 126.9, 73.1, 70.9, 68.2, 55.1, 50.5, 47.1,
43.4, 28.9, 21.6. HRESIMS m/z 390.1676 [M þ Na]þ (calcd for
C22H25NNaOþ4 , 390.1681) (100%). Anal. Calcd for C22H25NO4: C,
71.91; H, 6.86; N, 3.81. Found: C, 71.84; H, 6.91; N, 3.85.
Antimalarial efficacy and toxicity evaluationa.
Test
In vitro W2 strain, In vivo P. berghei MCD
MTD
(mg/kg) (mg/kg)
TIb
20
>61
>31
>22
>74
>29
21
76
65
35
5
compounds (IC50, nM)
(ED50, mg/kg)
7
8
9
10
11
12
13
14
15
16
17
18
1.8
2.2
9.4
3.3
6.5
9.2
2.7
7.0
6.5
2.1
1.9
4.8
185
>200
>200
>200
>200
>200
137
160
124
170
66
0.43
1.2
0.61
1.3
0.98
0.49
0.94
1.9
1.7
0.54
1.4
1.7
0.55
0.39
1.0
0.39
0.41
1.2
2.1
3.4
13
8.8
12
40.0
1.6
1.9
54
35
240
6
3
6
Febrifugine
Chloroquine 670
2.5
2.3
4.5
a
Antimalarial activities were determined after oral administration of the
compounds once daily for 4 days to infected mice.
b
Therapeutic indices were calculated as MTD divided by MCD.
a short column of silica gel and eluted with 25% ethyl acetate in
hexanes. Concentration of the eluant under reduced pressure
afforded the corresponding aldehyde 20 as colorless oil. Yield: 92%.
25
[
a]
þ14.2 (c 0.25, CH2Cl2). 1H NMR: 9.82 (s, 1H), 7.30e7.19 (m,
D
10H), 5.67 (s, 2H), 4.81 (d, J ¼ 13.5 Hz, 1H), 4.75 (d, J ¼ 13.5 Hz, 1H),
4.61 (d, J ¼ 6.8 Hz, 1H), 3.44 (m, 2H), 3.29 (m, 1H), 1.69 (m, 2H), 1.55
(m, 2H). 13C NMR: 200.1, 162.4, 140.9, 138.1, 129.1, 128.7, 128.4, 127.6,
127.3, 127.1, 74.1, 73.2, 71.9, 66.7, 49.1, 28.9, 22.4. HRESIMS m/z
376.1532 [M þ Na]þ (calcd for C21H23NNaOþ4 , 376.1525) (100%).
Anal. Calcd for C21H23NO4: C, 71.37; H, 6.56; N, 3.96. Found: C,
71.43; H, 6.54; N, 3.90.
4.1.4. 3-Benzyloxy-2-[1-hydroxy-2-(4-oxo-4H-quinazolin-3-yl)-
ethyl]-piperidine-1-carboxylic acid benzyl ester (23)
Potassium hydride (30% in mineral oil, 1.9 g) was suspended in
25 mL of DMF. It was cooled in an ice-water bath, and solid 3H-
quinazolin-4-one (2.0 g) was added in. After 20 min, a solution of
compound 22 (2.5 g) in 8 mL of DMF was added in. The reaction
mixture was then heated at 80 ꢁC for 12 h under nitrogen atmo-
sphere. It was partitioned between ethyl acetate (50 mL) and water
(50 mL), separated organic layer was washed with water
(3 ꢂ 30 mL), then brine (25 mL), dried over anhydrous sodium
sulfate, and evaporated in a rotary evaporator under reduced
pressure to furnish the crude product. Silica gel flash chromatog-
raphy (60% ethyl acetate in hexanes) furnished 23 as off white solid.
Yield: 82%. MP: 178 ꢁC. 1H NMR: 8.32 (d, J ¼ 7.2 Hz, 1H), 8.26 (s, 1H),
7.75 (m, 2H), 7.44 (m,1H), 7.30e7.26 (m, 10H), 5.47 (m, 2H), 5.09 (br,
1H), 4.80 (m, 2H), 4.29 (m, 1H), 4.12 (m, 1H), 3.87 (m, 2H), 3.61 (m,
2H), 3.19 (m, 1H), 1.86 (m, 2H), 1.59 (m, 2H). 13C NMR: 168.3, 163.2,
158.9, 147.3, 141.1, 138.5, 133.8, 129.1, 128.9, 128.5, 127.8, 127.6, 127.4,
127.1, 127.0, 126.8, 124.8, 76.4, 71.6, 68.5, 66.4, 55.1, 51.7, 47.2, 33.4,
25.8. HRESIMS m/z 536.2156 [M þ Na]þ (calcd for C30H31N3NaO5þ,
536.2161) (100%). Anal. Calcd for C30H31N3O5.HCl: C, 65.51; H, 5.86;
Cl, 6.45; N, 7.64. Found: C, 65.58; H, 5.81; Cl, 6.41; N, 7.68.
4.1.2. 3-Benzyloxy-2-vinylpiperidine-1-carboxylic acid
benzyl ester (21)
The salt Ph3PCHþ3 Iꢀ (7.1 g) was suspended in anhydrous THF
(50 mL). It was cooled to ꢀ20 ꢁC and n-BuLi (11.5 mL, 1.6 M in
hexanes) was slowly added in while the solution was stirred vigor-
ously. 20 min later, a solution of compound 20 (4.9 g) in 10 mL THF
was added in. The resulting solution was allowed to warm up to
ambient temperature and stirred for additional 2 h. The reaction
mixture was quenched by the addition of aqueous NaHCO3 (5 mL),
and then partitioned between ethyl acetate (120 mL) and water
(120 mL). The separated organic layer was washed with brine
(50 mL), dried over anhydrous sodium sulfate, and concentrated in
a rotary evaporator under reduced pressure. Silica gel flash chro-
matography (15% ethyl acetate in hexanes) furnished 21 as colorless
oil. Yield: 82%. [
25
a]
D ꢀ19.1 (c 0.21, CH2Cl2). 1H NMR: 7.28e7.17 (m,
10H), 5.88 (m, 1H), 5.71 (s, 2H), 5.22 (m, 1H), 5.14 (m, 1H), 5.04 (d,
J ¼ 6.6 Hz,1H), 4.84 (d, J ¼ 13.8 Hz,1H), 4.76 (d, J ¼ 13.8 Hz,1H), 3.48
(m, 2H), 3.02 (m, 1H), 1.66 (m, 2H), 1.52 (m, 2H). 13C NMR: 160.8,
141.9, 140.5, 137.9, 129.2, 128.9, 128.5, 127.8, 127.4, 127.0, 115.1, 73.9,
72.2, 71.3, 59.7, 50.1, 29.3, 21.8. HRESIMS m/z 374.1736 [M þ Na]þ
(calcd for C22H25NNaOþ3 , 374.1732) (100%). Anal. Calcd for
C22H25NO3: C, 75.19; H, 7.17; N, 3.99. Found: C, 75.23; H, 7.14; N, 3.92.
4.1.5. 3-[2-(3-Hydroxypiperidin-2-yl)-2-oxoethyl]-3H-quinazolin-
4-one (7)
A solution of compound 23 (2.2 g) in 5 mL of CH2Cl2 was added
into a stirred slurry of TPAP (60 mg), NMO (950 mg), and grounded
molecular sieve (600 mg) in 10 mL of CH2Cl2 at room temperature.
After 1 h, the reaction mixture was loaded directly into a short
column of silica gel and eluted with 5% MeOH/EtOAc. Concentration
of the eluant under reduced pressure afforded the corresponding
ketone. This ketone (2.0 g) was dissolved in 15 mL of 95% EtOH/H2O.
200 mg of 10% Pd on carbon was added in. It was then treated with
hydrogen (60 psi) in a Parr apparatus for 16 h. Solid was filtered off
and the solution was evaporated under vacuum to dryness.
Recrystallization from ethanolewater (with addition of dilute
aqueous HCl solution, 4e5 equiv. of HCl) furnishes compound 7
(HCl salt) as off white crystals. Yield: 74% (two steps). MP:
4.1.3. 3-Benzyloxy-2-oxiranylpiperidine-1-carboxylic acid benzyl
ester (22)
Compound 21 (3.8 g), osmium tetraoxide (OsO4, 4% in water,
0.5 mL), and N-methyl morpholine N-oxide (NMO, 4.0 g) were
dissolved in 25 mL of water and 25 mL of THF. The resulting
heterogeneous solution is stirred vigorously for 3 days at room
temperature. After partition between ethyl acetate (80 mL) and
water (80 mL), the separated organic layer was washed with brine
(30 mL), dried over anhydrous sodium sulfate, and evaporated in

3868
S. Zhu et al. / European Journal of Medicinal Chemistry 45 (2010) 3864e3869
25
187e188 ꢁC. [
a
]
D þ27.1 (c 0.49, EtOH). 1H NMR (CD3OD): 8.32 (s,
1.86 (m, 2H), 1.63 (m, 2H). 13C NMR: 204.4, 165.7, 162.9, 149.6, 135.1,
133.8, 128.6, 128.1, 126.5, 116.2, 71.9, 68.1 51.4, 48.8, 33.6, 23.1.
HRESIMS m/z 378.1038 [M þ Na]þ (calcd for C16H16F3N3NaO3þ,
378.1041) (100%). Anal. Calcd for C16H16F3N3O3.HCl: C, 49.05; H,
4.37; Cl, 9.05; F, 14.55; N, 10.73. Found: C, 49.11; H, 4.35; Cl, 9.01; F,
14.61; N, 10.75.
1H), 8.26 (d, J ¼ 7.2 Hz 1H), 7.77 (dd, J ¼ 7.2, 6.7 Hz, 1H), 7.65 (d,
J ¼ 6.7 Hz, 1H), 7.51 (t, J ¼ 7.2 Hz, 1H), 5.06 (d, J ¼ 16.6 Hz, 1H), 4.92
(d, J ¼ 16.6 Hz, 1H), 3.88 (d, J ¼ 6.6 Hz, 1H), 3.49 (m, 1H), 2.89 (m,
2H), 1.88 (m, 2H), 1.61 (m, 2H). 13C NMR (CD3OD): 205.2, 168.4,
164.1, 148.3, 132.9, 128.5, 127.6, 126.1, 122.3, 72.2, 66.9, 52.9, 46.2,
32.6, 23.5. HRESIMS m/z 310.1162 [M
þ
Na]þ (calcd for
C15H17N3NaOþ3 , 310.1168) (100%). Anal. Calcd for C15H17N3O3.HCl: C,
55.64; H, 5.60; Cl, 10.95; N,12.98. Found: C, 55.60; H, 5.63; Cl, 10.99;
N, 12.89.
4.1.11. 3-[2-(3-Ethoxypiperidin-2-yl)-2-oxoethyl]-3H-quinazolin-4-
one (13)
25
Off white crystals. MP: 169e170 ꢁC. [
a
]
D þ16.8 (c 0.43, EtOH).1H
NMR (CD3OD): 8.34 (s, 1H), 8.29 (d, J ¼ 7.0 Hz 1H), 7.69 (dd, J ¼ 7.0,
6.7 Hz, 1H), 7.61 (d, J ¼ 6.7 Hz, 1H), 7.58 (t, J ¼ 7.2 Hz, 1H), 5.11 (d,
J ¼ 16.9 Hz,1H), 4.95 (d, J ¼ 16.9 Hz,1H), 3.98 (d, J ¼ 6.8 Hz,1H), 3.41
(q, J ¼ 7.1 Hz, 2H), 3.19 (m,1H), 2.87 (m, 2H),1.85(m, 2H),1.59 (m, 2H),
1.17 (t, J ¼ 7.1 Hz, 3H). 13C NMR (CD3OD): 205.9, 167.9, 165.0, 148.7,
133.2, 128.7, 127.4, 126.6, 123.1, 70.3, 68.7, 60.8, 53.4, 47.1, 30.6, 22.9,
15.5. HRESIMS m/z 338.1477 [M þ Na]þ (calcd for C17H21N3NaO3þ,
338.1481) (100%). Anal. Calcd for C17H21N3O3.HCl: C, 58.03; H, 6.30;
Cl, 10.08; N, 11.94. Found: C, 58.10; H, 6.27; Cl, 10.12; N, 11.88.
4.1.6. 3-[2-(3-Hydroxypiperidin-2-yl)-2-oxoethyl]-3H-pyrido[3,2-
d]pyrimidin-4-one (8)
25
Pale yellow crystal. MP: 213e214 ꢁC. [
a
]
D ꢀ29.8 (c 0.45, EtOH).
1H NMR (CD3OD): 8.71 (d, J ¼ 6.9 Hz, 1H), 8.43 (d, J ¼ 6.9 Hz, 1H),
8.29 (s, 1H), 7.72 (t, J ¼ 6.9 Hz, 1H), 5.17 (d, J ¼ 17.1 Hz, 1H), 4.99 (d,
J ¼ 17.1 Hz, 1H), 3.95 (d, J ¼ 6.8 Hz, 1H), 3.61 (m, 1H), 2.95 (m, 2H),
1.91 (m, 2H), 1.57 (m, 2H). 13C NMR: 205.8, 168.9, 162.7, 151.1, 149.4,
142.9, 137.1, 133.7, 71.8, 66.1, 51.5, 46.6, 33.2, 22.8. HRESIMS m/z
311.1115 [M þ Na]þ (calcd for C14H16N4NaO3þ, 311.1120) (100%). Anal.
Calcd for C14H16N4O3.HCl: C, 51.78; H, 5.28; Cl, 10.92; N, 17.25.
Found: C, 51.82; H, 5.26; Cl, 10.88; N, 17.28.
4.1.12. 3-[2-(3-Ethoxypiperidin-2-yl)-2-oxoethyl]-5-fluoro-3H-
quinazolin-4-one (14)
25
White solid. MP: 165e166 ꢁC. [
a
]
ꢀ22.4 (c 0.45, EtOH). 1H
D
4.1.7. 3-[2-(3-Hydroxypiperidin-2-yl)-2-oxoethyl]-3H-pyrido[4,3-
NMR (CD3OD): 8.29 (s,1H), 8.21 (d, J ¼ 7.2 Hz,1H), 7.62 (d, J ¼ 7.2 Hz,
1H), 7.55 (t, J ¼ 7.2 Hz, 1H), 5.03 (d, J ¼ 17.1 Hz, 1H), 4.91 (d,
J ¼ 17.1 Hz, 1H), 3.97 (d, J ¼ 6.8 Hz, 1H), 3.44 (q, J ¼ 6.7 Hz, 2H), 3.31
(m, 1H), 2.83 (m, 2H), 1.91 (m, 2H), 1.60 (m, 2H), 1.16 (t, J ¼ 6.7 Hz,
3H). 13C NMR: 206.2, 167.6, 165.1, 147.3, 140.8, 133.7, 130.8, 128.6,
126.9, 70.1, 68.8, 61.2, 50.9, 49.4, 30.9, 23.6, 15.4. HRESIMS m/z
356.1391 [M þ Na]þ (calcd for C17H20FN3NaOþ3 , 356.1386) (100%).
Anal. Calcd for C17H20FN3O3.HCl: C, 55.21; H, 5.72; Cl, 9.59; F, 5.14;
N, 11.36. Found: C, 55.27; H, 5.69; Cl, 9.63; F, 5.19; N, 11.33.
d]pyrimidin-4-one (9)
25
Pale yellow crystal. MP: 218e219 ꢁC. [
a
]
D þ14.3 (c 0.51, EtOH).
1H NMR (CD3OD): 8.74 (s, 1H), 8.45 (d, J ¼ 7.3 Hz, 1H), 8.29 (s, 1H),
7.89 (d, J ¼ 7.3 Hz, 1H), 5.21 (d, J ¼ 17.4 Hz, 1H), 5.08 (d, J ¼ 17.4 Hz,
1H), 3.91 (d, J ¼ 6.7 Hz, 1H), 3.66 (m, 1H), 2.91 (m, 2H), 1.88 (m, 2H),
1.55 (m, 2H). 13C NMR: 204.6, 168.1, 162.9, 158.4, 153.7, 148.6, 132.5,
129.9, 72.2, 66.4, 50.9, 47.9, 35.1, 23.4. HRESIMS m/z 311.1127
[M þ Na]þ (calcd for C14H16N4NaOþ3 , 311.1120) (100%). Anal. Calcd
for C14H16N4O3.HCl: C, 51.78; H, 5.28; Cl, 10.92; N, 17.25. Found: C,
51.72; H, 5.32; Cl, 10.87; N, 17.30.
4.1.13. 3-[2-(3-Benzyloxypiperidin-2-yl)-2-oxoethyl]-3H-pyrido
[3,2-d]pyrimidin-4-one (15)
25
4.1.8. 3-[2-(3-Hydroxypiperidin-2-yl)-2-oxoethyl]-3H-pyrido[2,3-
Pale yellow crystal. MP: 195e196 ꢁC. [
a
]
D þ22.4 (c 0.47, EtOH).
d]pyrimidin-4-one (10)
1H NMR (CD3OD): 8.69 (d, J ¼ 7.0 Hz, 1H), 8.51 (d, J ¼ 7.0 Hz, 1H),
8.27 (s, 1H), 7.63 (t, J ¼ 7.0 Hz, 1H), 7.29e7.19 (m, 5H), 5.25 (s, 2H),
5.12 (d, J ¼ 17.0 Hz, 1H), 4.94 (d, J ¼ 17.0 Hz, 1H), 4.05 (d, J ¼ 6.8 Hz,
1H), 3.27 (m, 1H), 2.89 (m, 2H), 1.87 (m, 2H), 1.62 (m, 2H). 13C NMR:
206.4, 168.4, 163.1, 151.6, 148.9, 142.5, 137.8, 136.9, 132.9, 128.9,
127.8, 127.1, 72.6, 70.8, 69.0, 50.7, 47.2, 31.2, 22.5. HRESIMS m/z
401.1586 [M þ Na]þ (calcd for C21H22N4NaOþ3 , 401.1590) (100%).
Anal. Calcd for C21H22N4O3.HCl: C, 60.79; H, 5.59; Cl, 8.55; N, 13.50.
Found: C, 60.82; H, 5.55; Cl, 8.58; N, 13.48.
25
Pale yellow needles. MP: 215e216 ꢁC. [
a]
ꢀ18.6 (c 0.42,
D
EtOH). 1H NMR (CD3OD): 8.83 (d, J ¼ 6.8 Hz, 1H), 8.71 (d, J ¼ 6.8 Hz,
1H), 8.35 (s, 1H), 8.15 (t, J ¼ 6.8 Hz, 1H), 5.08 (d, J ¼ 17.1 Hz, 1H), 4.95
(d, J ¼ 17.1 Hz, 1H), 3.96 (d, J ¼ 6.8 Hz, 1H), 3.61 (m, 1H), 2.95 (m,
2H), 1.85 (m, 2H), 1.63 (m, 2H). 13C NMR: 205.8, 170.1, 166.2, 163.9,
151.8, 143.5, 134.0, 130.5, 71.9, 67.0, 51.4, 48.2, 34.7, 22.7. HRESIMS
m/z 311.1117 [M þ Na]þ (calcd for C14H16N4NaOþ3 , 311.1120) (100%).
Anal. Calcd for C14H16N4O3.HCl: C, 51.78; H, 5.28; Cl, 10.92; N, 17.25.
Found: C, 51.83; H, 5.25; Cl, 10.98; N, 17.19.
4.1.14. 3-[2-(3-Benzyloxypiperidin-2-yl)-2-oxoethyl]-5-
4.1.9. 5-Fluoro-3-[2-(3-hydroxypiperidin-2-yl)-2-oxoethyl]-3H-
trifluoromethyl-3H-quinazolin-4-one (16)
25
quinazolin-4-one (11)
White needles. MP: 182e183 ꢁC. [
a
]
D ꢀ22.3 (c 0.42, EtOH). 1H
25
White solid. MP: 172e173 ꢁC. [
a]
D þ24.1 (c 0.5, EtOH). 1H NMR
NMR (CD3OD): 8.24 (s,1H), 7.82 (d, J ¼ 6.9 Hz,1H), 7.71 (d, J ¼ 6.9 Hz,
1H), 7.47 (t, J ¼ 6.9 Hz, 1H), 7.30e7.20 (m, 5H), 5.17 (s, 2H), 5.09 (d,
J ¼ 16.7 Hz,1H), 4.88 (d, J ¼ 16.7 Hz,1H), 3.97 (d, J ¼ 6.7 Hz,1H), 3.25
(m, 1H), 2.91 (m, 2H), 1.83 (m, 2H), 1.57 (m, 2H). 13C NMR: 206.1,
164.9, 161.3,150.0, 137.3, 135.5,131.2,128.9, 128.5, 128.0, 127.6, 127.1,
126.9, 116.5, 73.2, 69.8, 67.8, 51.9, 47.6, 29.7, 23.0. HRESIMS m/z
468.1505 [M þ Na]þ (calcd for C23H22F3N3NaOþ3 , 468.1511) (100%).
Anal. Calcd for C23H22F3N3O3.HCl: C, 57.32; H, 4.81; Cl, 7.36; F, 11.83;
N, 8.72. Found: C, 57.37; H, 4.77; Cl, 7.41; F, 11.75; N, 8.75.
(CD3OD): 8.24 (s, 1H), 8.18 (d, J ¼ 7.2 Hz, 1H), 7.69 (d, J ¼ 7.2 Hz, 1H),
7.51 (t, J ¼ 7.2 Hz, 1H), 5.11 (d, J ¼ 16.9 Hz, 1H), 4.92 (d, J ¼ 16.9 Hz,
1H), 3.89 (d, J ¼ 6.7 Hz, 1H), 3.68 (m, 1H), 2.90 (m, 2H), 1.89 (m, 2H),
1.58 (m, 2H). 13C NMR: 205.8, 167.1, 164.9, 146.1, 141.9, 133.6, 131.4,
128.9, 127.7, 71.3, 67.6 51.8, 49.1, 32.8, 23.4. HRESIMS m/z 328.1068
[M þ Na]þ (calcd for C15H16FN3NaOþ3 , 328.1073) (100%). Anal. Calcd
for C15H16FN3O3.HCl: C, 52.71; H, 5.01; Cl, 10.37; F, 5.56; N, 12.30.
Found: C, 52.67; H, 5.05; Cl, 10.44; F, 5.50; N, 12.28.
4.1.10. 3-[2-(3-Hydroxypiperidin-2-yl)-2-oxoethyl]-5-
4.1.15. 3-[2-(3-Hydroxypiperidin-2-yl)-2-oxoethyl]-7-methoxy-3H-
trifluoromethyl-3H-quinazolin-4-one (12)
quinazolin-4-one (17)
25
25
White solid. MP: 180e181 ꢁC. [
a
]
ꢀ14.5 (c 0.45, EtOH). 1H
White solid. MP: 191e192 ꢁC. [
a
]
þ18.8 (c 0.51, EtOH). 1H
D
D
NMR (CD3OD): 8.19 (s,1H), 7.87 (d, J ¼ 6.9 Hz,1H), 7.69 (d, J ¼ 6.9 Hz,
1H), 7.51 (t, J ¼ 6.9 Hz, 1H), 5.06 (d, J ¼ 16.8 Hz, 1H), 4.84 (d,
J ¼ 16.8 Hz, 1H), 3.93 (d, J ¼ 6.8 Hz, 1H), 3.65 (m, 1H), 2.96 (m, 2H),
NMR (CD3OD): 8.18 (s, 1H), 7.79 (s, 1H), 7.27 (d, J ¼ 7.1 Hz, 1H), 7.33
(d, J ¼ 7.1 Hz, 1H), 5.08 (d, J ¼ 16.8 Hz, 1H), 4.92 (d, J ¼ 16.8 Hz, 1H),
3.81 (s, 3H), 3.78 (d, J ¼ 6.7 Hz, 1H), 3.46 (m, 1H), 2.82 (m, 2H), 1.91

S. Zhu et al. / European Journal of Medicinal Chemistry 45 (2010) 3864e3869
3869
(m, 2H),1.58 (m, 2H). 13C NMR: 206.1,168.4,166.1,162.2,149.1,129.1,
119.4, 113.7, 108.2, 71.1, 65.7, 57.9, 51.9, 46.1, 31.4, 22.6. HRESIMS m/z
340.1281 [M þ Na]þ (calcd for C16H19N3NaOþ4 , 340.1273) (100%).
Anal. Calcd for C16H19N3O4.HCl: C, 54.32; H, 5.70; Cl, 10.02; N, 11.88.
Found: C, 54.33; H, 5.68; Cl, 10.11; N, 11.84.
the responsibility of the authors and does not necessarily represent
the official views of the funding agency.
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4.1.16. 3-[2-(3-Ethoxypiperidin-2-yl)-2-oxoethyl]-8-methoxy-3H-
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25
White needles. MP: 188e183 ꢁC. [
a
]
D ꢀ19.4 (c 0.45, EtOH). 1H
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groups of experimental and control mice were inoculated with this
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candidate antimalarial drugs or with vehicle alone to serve as
negative controls from day 3 to day 10 orally (PO) or subcutaneously
(SC) once a day for eight days. Each experimental group received
a different dose level, with up to 5 different dose groups per
compound. Blood films and body weights were taken on the third
and sixth days post-infection, then at weekly intervals through day
60. Films were Giemsa stained and examined microscopically to
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smear on day 60 were considered cured.
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Acknowledgements
This research was partially supported by a grant from the
National Institutes of Health (AI81308 to S.Z.). The content is solely