Synthesis and antimalarial activity of new isotebuquine analogues

Article abstract of DOI:10.1021/jm061232x

Amodiaquine (AQ) and tebuquine are 4-aminoquinoline antimalarials with Mannich base side chain and are highly effective against chloroquine (CQ)-resistant strains of Plasmodium falciparum. Clinical use of AQ has been severely restricted due to hepatoxicit

Full text of DOI:10.1021/jm061232x

J. Med. Chem. 2007, 50, 889-896
889
Synthesis and Antimalarial Activity of New Isotebuquine Analogues
Olga V. Miroshnikova, Thomas H. Hudson, Lucia Gerena, Dennis E. Kyle, and Ai J. Lin*
DiVision of Experimental Therapeutics, Walter Reed Army Institute of Research, 503 Robert Grant AVenue, SilVer Spring, Maryland 20910
ReceiVed October 20, 2006
Amodiaquine (AQ) and tebuquine are 4-aminoquinoline antimalarials with Mannich base side chain and
are highly effective against chloroquine (CQ)-resistant strains of Plasmodium falciparum. Clinical use of
AQ has been severely restricted due to hepatoxicity and agranulocytosis side effects associated with its
long term use. Lysosomal accumulation and bioactivation to generate reactive quinoneimine metabolite are
implicated to be the cause of the observed AQ toxicities. To avoid the quinoneimine formation and thus the
toxicity, a series of isotebuquine analogues and their Nω-oxides with hydroxy group meta to the amino
rather than in para position of the aniline moiety were prepared. The new Mannich bases are highly active
against both CQ-sensitive (D6) and -resistant (W2 and TM91C235) clones of P. falciparum with IC50 in the
range of 0.3-120 ng/mL. New compounds are1000-fold less toxic (IC50 ) 0.7-6 µg/mL) to mouse
macrophage cell line than to parasite cell lines. Mono-Mannich bases are more active than bis-Mannich
bases. Mono-Mannich base 1a (IC50 ) 0.3 ng/mL) is 20-fold more active than the corresponding
trifluoromethyl analogue 1b. No appreciable difference in either toxicity or efficacy were observed between
the new Mannich bases (m-hydroxyaniline derivatives) 1a or 2a and the corresponding p-hydroxyaniline
derivatives.
Introduction
Malaria is one of the most widespread diseases in many
regions of the world, exposing millions of people to risk of
infection and death. The 4-aminoquinolines such as chloroquine
(CQ) are the most important and widely used class of drugs for
treatment of malaria. Chloroquine has been the drug of choice
for malaria treatment since the early 1950s, providing effective
and safe treatment for millions of Plasmodium falciparum
infected patients a year. Development of drug resistance to
chloroquine in malaria has become a major health concern in
malaria endemic areas, which has prompted a search for
alternative antimalarials against the CQ-resistant strains.1,2 As
a result, several new classes of antimalarial drugs were
developed; none has reached the same status of recognition as
the drug of choice in malaria therapy as CQ.
Amodiaquine (AQ), a new Mannich base 4-aminoquinoline,
is effective against chloroquine-resistant strains of P. falci-
parum.3 However, the clinical use of AQ has been severely
restricted because of the hepatoxicity and agranulocytosis side
effects associated with its long term use.4,5 Recent reports
indicate that AQ was metabolized by cytochrome P-450
oxidation to form reactive quinoneimine metabolite with
subsequent conjugate addition of glutathione or cysteinyl
function of the enzymes.6,7 Lysosomal accumulation and bio-
activation of reactive quinoneimine metabolite are implicated
to be the cause of the observed AQ in vivo toxicity.8,9 To avoid
the quinoneimine metabolite formation, a series of isoquine and
related analogues were reported in the literature.10-12 Isoquine
(IQ) is an analogue of AQ, in which the 4′-hydroxy group on
the aniline ring of AQ is interchanged with a 3′-Mannich base
side chain. IQ was demonstrated to possess higher antimalarial
activity against Plasmodium yoelii than AQ. In contrast to AQ,
IQ was excreted primarily as glucuronide, instead of glutathione
conjugate.10
with a p-chlorophenyl moiety substituted at the 5-position of
the 4-hydroxyaniline side chain of AQ. TQ is significantly more
active than AQ and CQ in both in vitro and in vivo tests.13-15
Similar to AQ, TQ forms active quinoneimine metabolite
(Scheme 1) and consequently develops the same toxic side
effects as AQ in prolonged use.
In this study, we described the synthesis of a series of
isotebuquine analogues with a hydroxy group in meta rather
than para position to the amino group of the aniline moiety.
Unable to produce the toxic quinoneimine metabolite, new
isotebuquine analogues may exhibit similar or better activity
than tebuquine with no or low liver toxicity. In vitro antimalarial
activities of the new compounds were assessed in CQ-sensitive
(D6) and CQ-resistant (W2) cell lines of P. falciparum, and
their in vitro toxicities were measured in a murine monocyte-
like macrophage line J774. Furthermore, in vivo antimalarial
efficacy values against Plasmodium berghei of the new com-
pounds are presented.
Another promising compound from the class of the 4-amino-
quinolines is tebuquine (TQ), which is a biaryl analogue of AQ
Chemistry
The initial step of this work was the synthesis of bis- and
mono-(tert-butylaminomethyl)-5-(7-chloroquinolin-4-ylamino)-
* To whom correspondence should be addressed. Phone: 301-319-9084.
Fax: 301-319-9449. E-mail: ai.lin@na.amedd.army.mil.
10.1021/jm061232x This article not subject to U.S. Copyright. Published 2007 by the American Chemical Society
Published on Web 02/01/2007

890 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 4
MiroshnikoVa et al.
Scheme 1. Biotransformation of Tebuquine by P-450 Oxidation and Further Conjugation with Cysteinyl Function of Enzymes
Scheme 2a
a Reagents and conditions: (i) N-bromosuccinimide, H2SO4, 80 °C; (ii) NaOMe, MeOH, 65 °C, 2 h; (iii) RPhB(OH)2, Pd(PPh3)4, Na2CO3, toluene, EtOH,
reflux, 2 h; (iv) H2, 10% Pd/C, THF, 2 h; (v) BBr3, CH2Cl2, -78 °C, 4 h; (vi) 4,7-dichloroquinoline, EtOH, reflux, 2 h; (vii) t-BuNH2, CH2O, DMF, 3 days.
biphenyl-3-ols, the so-called isotebuquine analogues. The
general approach to prepare the new Mannich bases 1a,b-5a,b
is illustrated in Scheme 2. The intermediate 1-bromo-3,5-
dinitrobenzene (6) was prepared by addition of the N-bromo-
succinimide in small portions to the commercially available
starting material 1,3-dinitrobenzene in sulfuric acid at 80-90
°C.16
3-Bromo-5-nitroanisole (7) was obtained by treatment of 6
with sodium methoxide in absolute methanol.17 The coupling
of bromoanisole 7 with the 4-chlorophenylboronic acid was
achieved using a modified Suzuki method to afford substituted
biaryl compound 8a in a good yield.18 Two types of catalysts
were used in the Suzuki coupling reaction to prepare compounds
8a and 8b. Method A utilized tetrakis-(triphenylphosphine)
palladium(0),18 while method B employed Pd(OAc)2 as a
catalyst (Scheme 3).19 The compound 8a was prepared by
method A, while trifluoromethyl analogue 8b was synthesized
by method B. Both coupling methods A and B were efficient
to prepare the biaryl intermediates when 3,5-dinitro-bromoben-
zene was used. However, when the 1-iodo-3,5-dinitrobenzene

Synthesis of New Isotebuquine Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 4 891
Scheme 3a
reaction mixture gave other analogues, 2 (mono-) and 4 (bis-),
in small yield (7-10%). The yield of compound 5 was
insignificant, isolation of which was possible only in large-scale
synthesis. The products were first separated by column chro-
matography, followed by repeated recrystalization from chlo-
roform and diethyl ether mixture. Purification of products 1 and
4 could not be accomplished by chromatography because of
their similarity in Rf values on TLC under various solvent
systems. However, separation of the products was achieved by
fractional crystallization from methanol.
The structures of all products were characterized by elemental
analysis, mass spectrometry, and 1H and 13C NMR spectroscopy.
As an extension of this work, two Nω-oxide isotebuquine
analogues (13 and 14) were prepared to improve solubility and
therefore enhance the bioavailability of this type of antimalarials.
Synthetic pathway for Nω-oxides was based on the method
developed for the synthesis of isotebuquine derivatives (Scheme
4). Thus, p-chloro-biarylaminophenol 10a was treated with 4,7-
dichloroquinoline 1-oxide13 to provide corresponding 4′-chloro-
5-(7-chloro-1-oxy-quinolin-4-ylamino)-biphenyl-3-ol (12) as
outlined in Scheme 4. Contrary to the synthesis of Mannich
base 1-5, which was rather straightforward, the final step in
the synthesis of the target Nω-oxide 13 and 14 was a challenging
task. In an attempt to apply the same conditions for the Mannich
reaction that has been utilized for the synthesis of regular
isotebuquine analogues 1-5 (3 equiv of tert-butylamine, 4 equiv
of formaldehyde, DMF, room temperature, 3 days), no reaction
was observed. Heating at 100 °C gave a complicated mixture
of high lipophilic byproducts. When the Mannich reaction was
carried out in diluted DMF solution (15 mg/ mL) at 65 °C for
7 days, two new Nω-oxide derivatives, mono- (13) and bis-
Mannich base (14), were obtained in low yield. On scale-up
synthesis, two deoxygenated byproducts, 1a and 3a, were
isolated.
a Reagents and conditions: (i) 4-chlorophenylboronic acid or 4-(trifluo-
romethyl)phenylboronic acid, Pd(PPh3)4, Na2CO3, toluene, EtOH, reflux,
2 h; (ii) 4-(trifluoromethyl)phenylboronic acid, Pd(OAc)2, K2CO3, acetone,
H2O, reflux, 4 h; (iii) NaOMe, MeOH, DMF, 65 °C, 2 h.
was used as a starting material in the Suzuki coupling reaction,
it gave a poorer yield than when 1-bromo-3,5-dinitrobenzene
was used, due to incomplete reaction and tedious purification
procedure.
The reduction of the nitro-group by catalytic hydrogenation
of 8 using palladium on activated carbon afforded the amino-
biphenyl derivatives 9 in a quantitative yield.20 The intermediate
amines obtained were used for the next reaction without further
purification. The boron tribromide-catalyzed demethylation of
9a in dichloromethane solution gave a desired aminophenol 10a
in high yield (70%). The trifluoromethyl-containing analogue
10b was obtained using an alternative reagent, boron tribro-
mide-methylsulfide complex.21
The intermediates 11a and 11b for the synthesis of isotebu-
qine analogues were obtained by treatment of 4,7-dichloro-
quinoline with corresponding biarylaminophenols 11a,b. Intro-
duction of the Mannich base side chain, tert-butylaminomethyl,
into the key intermediate 11 was a challenging task due to low
selectivity of the reaction. When 11a or 11b was subjected to
Mannich reaction in the presence of t-butylamine and 37%
formaldehyde, a mixture consisting of five products was
obtained. The mixture was separated by the use of a silica gel
column followed by fractional crystallization. The product ratio
of this reaction was highly dependent on the ratio of the reagents
used. Formation of bis-Mannich base 3 was favored when the
reaction was conducted using a stoichiometric amount of
reagents, 11, t-buthylamine, and formaldehyde. Doubling the
ratio of the reagents, t-buthylamine and formaldehyde, led to
the formation of both mono-Mannich base 1 as well as bis-
Mannich base 3. Further addition of reagents to the same
1H NMR Studies
Due to poor solubility of some of the final products in CDCl3,
most of the NMR spectra were taken in CD3OD. When
compounds are soluble in both chloroform and methanol, the
spectrum in both solvents, CDCl3 and CD3OD, are reported.
The structure assignments of 1-5 were based on comparison
of their chemical shifts with the key intermediate 11. The
assignment of all protons in compound 11 is straightforward
1
(Table 1). The H NMR spectrum of 11b shows three triplets
for protons Hh, Hi, and Hj of the aminophenol moiety at 6.91,
6.96, and 7.15 ppm, respectively, with small coupling constant
of J ) 1.6 Hz. Two sets of doublets at 7.10 and 8.33 ppm were
attributed to Hb and He of the quinoline ring, and the doublets
at 7.75 and 7.82 ppm were assigned to biaryl protons Hg and
Hf, respectively. The proton chemical shifts of intermediate 11
are informative for the structure determination of its Mannich
Scheme 4a
a Reagents and conditions: (i) 4,7-dichloroquinoline N-oxide, EtOH, reflux, 2 h; (ii) t-BuNH2, CH2O, DMF, 8 days.

892 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 4
MiroshnikoVa et al.
Table 1. 1H NMR Chemical Shifts (δ) for Aromatic Protons of
Isotebuqiune Derivatives (11 and 1-5b) and Their Nω-Oxides (12-14)
in CD3OD Solution
the reaction mixture in nine portions over 1.5 h (one addition every
10 min). The temperature of the mixture was kept at 80-90 °C
during the addition. After the reaction was completed (30 min),
the sulfuric acid solution was poured into ice water. The solid
precipitate was collected, washed with water, and recrystalized from
methanol to give 12.2 g (83%) of the desired product 6 as a pale
yellow crystal, mp 77.2-77.8 °C (lit., 77-78 °C). 1H NMR
(CDCl3): δ 9.03 (t, J ) 2.0 Hz, 1H), 8.73 (d, J ) 2.0 Hz, 2H). 13
C
NMR: 148.85, 132.10, 123.88, 117.72. Anal. (C6H3BrN2O4) C, H,
N.
1-Bromo-3-methoxy-5-nitrobenzene (7).17 To the solution of
compound 6 (12 g, 48.6 mmol) in dry methanol (120 mL) was
added sodium methoxide (3.24 g, 60 mmol). The mixture was boiled
for 2 h and allowed to cool to room temperature. The reaction was
quenched by additional of 1 N solution of HCl, and the mixture
was extracted with dichloromethane (2 × 250 mL). Organic layers
were combined, washed with brine, dried over sodium sulfate,
filtered, and evaporated to dryness in vacuum. The crude product
was purified by flash column chromatography on silica gel, eluting
with a gradient of 2% ethyl acetate in hexane followed by 10-
12% ethyl acetate in hexane to yield 9.25 g (82%) of 7 as a white
solid, mp 86.9 °C (lit., 87.5 °C).17 1H NMR (CDCl3): δ 7.99 (t, J
) 1.83 Hz, 1H), 7.70 (t, J ) 2.2 Hz, 1H), 7.40 (t, J ) 2.2 Hz, 1H),
3.92 (s, 3H). 13C NMR: 160.62, 149.50, 123.92, 123.01, 118.98,
107.78, and 56.20.
4′-Chloro-5-methoxy-3-nitro-biphenyl (8a). Method A. Com-
pound 7 (6.93 g, 30 mmol) and sodium carbonate (30 mL of 2 M
solution) were suspended in a mixture of toluene and ethanol (120
mL, 4:1). To the bilayer mixture were sequentially added 4-chlo-
rophenylboronic acid (5.16 g, 33 mmol) and tetrakis(triphenylphos-
phine) palladium(0) with stirring. The reaction mixture was refluxed
for 2 h under nitrogen atmosphere. On cooling to room temperature,
the solution was poured onto ice water. Solid precipitate formed
was collected, dried, and purified by flash column chromatography
on silica gel eluting with a gradient of 1% ethyl acetate in hexane
followed by 10% ethyl acetate in hexane to give 6.33 g (80%) of
product 8a as a pale yellow solid, mp 131.7 °C. 1H NMR
(CDCl3): δ 8.04 (t, J ) 1.7 Hz, 1H), 7.74 (t, J ) 2.1 Hz, 1H),
7.56 (d, J ) 8.6 Hz, 2H), 7.47 (d, J ) 8.6 Hz, 2H), 7.41 (t, J ) 1.7
Hz, 1H), 3.97 (s, 3H). 13C NMR: 160.53, 149.73, 142.44, 137.17,
134.89, 129.33, 128.41, 119.72, 114.41, 106.85, 56.04. MS (m/z):
264.11 (MH+).
compd Ha Hb Hc Hd He
Hf
Hg Hh
Hi
Hj
11a
1a
2a
3a
4a
11b
1b
2b
3b
4b
5b
12
13
14
8.42 7.07 7.87 7.51 8.31 7.59 7.43 6.84 7.07 6.88
8.38 7.07 7.85 7.49 8.27 7.46 7.37 6.59 6.77 MBa
8.38 6.52 7.90 7.55 8.33 7.59 7.43 MB 7.03 7.00
8.34 6.68 7.87 7.53 8.28 7.47 7.36 MB 6.63 MB
8.42 6.98 7.88 7.51 8.28 7.51 7.33 6.93 MB MB
8.44 7.10 7.90 7.53 8.33 7.82 7.75 6.91 7.15 6.96
8.39 7.08 7.86 7.49 8.28 7.76 7.58 6.61 6.80 MB
8.38 6.53 7.89 7.55 8.33 7.80 7.72 MB 7.08 7.05
8.34 6.61 7.86 7.52 8.27 7.73 7.57 MB 6.67 MB
8.43 6.99 7.89 7.52 8.23 7.52 7.33 6.93 MB MB
8.61 7.32 8.05 7.44 7.93 7.73 7.47 6.64 MB 6.99
8.59 7.00 8.40 7.88 8.61 7.64 7.48 6.88 7.18 7.11
8.35 6.56 8.62 7.78 8.47 7.59 7.42 7.01 7.03 MB
8.33 6.49 8.60 7.76 8.57 7.46 7.34 MB 6.54 MB
a MB ) Mannich base side chain.
base 1-5. Introduction of one or two t-butyl-aminomethyl
substituents into the aminophenol ring of compound 11 caused
dramatic changes in chemical shifts of the surrounding protons.
Distal from Mannich base side chain, proton signals of 7-chlo-
roquinoline moiety, Hd (7.53 ppm), Hc (7.90 ppm), and Ha
(8.44 ppm) were not affected by the introduction of Mannich
base. The chemical shifts of aromatic protons of all new
isotebuquine derivatives are listed in Table 1.
5-Methoxy-3-nitro-4′-trifluoromethyl-biphenyl (8b). Method
B. To the solution of compound 6 (2.7 g, 11.64 mmol) and
4-(trifluoromethyl)phenylboronic acid (2.43 g, 12.80 mmol) in the
mixture of acetone and water (57 mL, 27:30) were added potassium
carbonate (4.0 g, 29.0 mmol) and palladium(II) acetate (100 mg).
The deep black mixture was refluxed for 4 h and allowed to cool
to room temperature. The mixture was extracted with ethyl acetate
(2 × 150 mL), and the organic layer was passed through a layer of
Celite. The solution was dried by Na2SO4 and evaporated in vacuum
to dryness. The residue was purified by flash column chromatog-
raphy on silica gel eluting with a gradient of 2% ethyl acetate in
hexane followed by 10% ethyl acetate in hexane to give 3.2 g (92%)
of the desired product as a pale yellow solid, mp 54.6 °C. 1H NMR
(CDCl3): δ 8.08 (t, J ) 1.6 Hz, 1H), 7.78 (t, J ) 2.1 Hz, 1H),
7.76 (d, J ) 3.0 Hz, 4H), 7.45 (t, J ) 1.6 Hz, 1H), 3.98 (s, 3H).
13C NMR: 160.61, 149.73, 142.17, 130.92, 130.48, 130.05, 129.68,
129.23, 127.56, 126.17, 126.12, 126.07, 126.02, 125.79, 122.19,
120.05, 118.7, 114.65, 107.40, 56.08. MS (m/z): 298.14 (MH+).
4′-Chloro-5-methoxy-biphenyl-3-ylamine (9a). A solution of
8a (6.0 g, 22.75 mmol) with a catalytic amount of 10% palladium
on activated carbon (0.6 g, 10% of the weight) was hydrogenated
in tetrahydrofuran under 40 psi pressure at room temperature for 2
h. The black mixture was passed through a thin layer of Celite,
and the yellow solution was evaporated in vacuum to give 5.10 g
(96%) of crude product as a gum, which was pure enough to be
used for next step synthesis without further purification. A portion
of the mixture was purified to give pure product as a gum. 1H NMR
(CDCl3): δ 7.49 (d, J ) 8.6 Hz, 2H), 7.39 (d, J ) 8.6 Hz, 2H),
6.51 (t, J ) 1.7 Hz, 1H), 6.49 (t, J ) 1.7 Hz, 1H), 6.27 (t, J ) 2.1
The structural assignment for compounds 12-14 was made
using the same approach for the assignment of deoxy analogues
1-5. Compounds 12-14 share the same basic structure with
1-5, thus their NMR spectra are, as expected, similar for the
most part (Table 1).
Experimental Section
Melting points were determined in open capillary tubes on a
Mettler FP62 melting point apparatus (Mettler Toledo, USA) and
are uncorrected. 1H NMR and 13C NMR spectra were recorded using
a Bruker Avance-300 spectrometer (Bruker Instrument, Inc.,
Wilmington, DE) at a frequency of 300.13 MHz. Chemical shifts
are given in ppm (δ) relative to tetramethylsilane (TMS) as internal
standard. Analytical thin-layer chromatography (TLC) was per-
formed using HPLC-HLF normal phase 150 micrometer silica gel
plates or silica gel GF/ UF254, 500 micrometer plates (Analtech,
Newark, DE). Visualization of the developed chromatogram was
performed with UV absorbance or iodine stain. Flash chromatog-
raphy was conducted with silica gel 60 Å (200-400) mesh from
Sigma-Aldrich Co. Solvents and reagents obtained from commercial
sources were used without purification, unless noted. Reactions were
carried out under an inert atmosphere of nitrogen. Elemental analysis
was performed by Atlantic Microlab, Inc. (Norcross, GA). Where
analyses are indicated by symbols of the elements, the analytical
results obtained were within (0.4% of the theoretical values.
1-Bromo-3,5-dinitrobenzene (6).16 1,3-Dinitrobenzene (10 g,
59.5 mmol) was dissolved in concentrated sulfuric acid (60 mL) at
80 °C. N-Bromosuccinimide (14.83 g, 83.3 mmol) was added to

Synthesis of New Isotebuquine Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 4 893
Hz, 1H), 3.84 (s, 3H). 3.78 (br s, 2H). 13C NMR: 161.15, 148.05,
142.33, 139.83, 133.36, 128.75, 128.35, 106.70, 103.30, 100.11,
55.28. MS (m/z): 234.13 (MH+).
5-Methoxy-4′-trifluoromethyl-biphenyl-3-ylamine (9b). Com-
pound 9b was prepared by the same method as described for the
preparation of 9a in a quantitative yield. 1H NMR (CDCl3): δ 7.67
(s, 4H), 6.56 (t, J ) 1.6 Hz, 1H), 6.52 (t, J ) 1.6 Hz, 1H), 31 (t,
J ) 2.1 Hz, 1H). 13C NMR: 161.21, 148.17, 144.93, 142.10,
130.18, 130.03, 129.60, 129.17, 127.38, 126.12, 125.62, 125.58,
125.53, 125.48, 122.52, 118.92, 106.89, 103.57, 100.55, 55.28. MS
(m/z): 268.53 (MH+).
ethanol, and recrystallized from chloroform to give bis-substituted
Mannich base 3 as a pale yellow solid in 40% yield. The
dimethylformamide filtrates were combined and diluted with cool
water (100 mL). The precipitate obtained was collected, washed
with water, and dried. The crude product was purified by silica gel
column chromatography eluting with mixture of CHCl3:EtOAc:
MeOH (10:1:1) to give compounds 2 and 5 which were recrystal-
lized from CHCl3/ether. Fractions, which contained both compounds
1 and 4, were collected and evaporated in vacuum to dryness. The
products were separated by fractional crystallization from methanol
to give first pure 1, and then compound 4, which was recrystallized
from ether.
5-Amino-4′-chloro-biphenyl-3-ol (10a). To a solution of 9a (5.0
g, 21.4 mmol) in dry dichloromethane (60 mL) under a nitrogen
atmosphere at - 78 °C was slowly added a solution of boron
tribromide (1.0 M, 27 mL) in dry dichloromethane. The reaction
mixture was allowed to warm to room temperature and stirred for
4 h. The brown solution was cooled with an ice bath, and to the
solution was slowly added water (100 mL). The organic layer was
separated, and the water layer was extracted twice with dichlo-
romethane. The dichloromethane extracts were combined, washed
successively with saturated sodium bicarbonate solution and water,
dried over Na2SO4, and evaporated to dryness in vacuum. The
residue was purified by flash column chromatography on silica gel
eluting with dichloromethane followed by 5% ethyl acetate in
dichloromethane to give 3.29 g (70%) of 10a as a white solid, mp
6-(tert-Butylaminomethyl)-4′-chloro-5-(7-chloroquinolin-4-
1
ylamino)-biphenyl-3-ol (1a). Yield: 18%, mp >220 °C dec. H
NMR (CD3OD): see Table 1. 13C NMR: 163.48, 150.99, 149.59,
148.88, 143.04, 140.23, 139.57, 135.31, 133.05, 130.82, 128.07,
126.36, 125.23, 123.38, 118.31, 116.00, 112.92, 111.12, 101.76,
52.66, 41.24, 25.85. MS (m/z): 466.0 (MH+). Anal. (C26H25N3-
OCl2‚0.2H2O) C, H, N.
6-(tert-Butylaminomethyl)-5-(7-chloroquinolin-4-ylamino)-4′-
trifluoromethyl-biphenyl-3-ol (1b). Yield: 20%, mp >220 °C dec.
1H NMR (CD3OD): see Table 1. 13C NMR: 163.69, 151.01,
149.56, 148.88, 145.08, 141.82, 140.31, 135.12, 129.47, 129.11,
128.85, 126.36, 125.24, 124.92, 124.87, 124.82, 124.77, 123.38,
118.32, 116.03, 112.74, 111.46, 101.77, 52.54, 41.28, 25.89. MS
(m/z): 250.6 (M + 2H+). Anal. (C27H25N3OClF3) C, H, N.
1
242.7 °C dec. H NMR (CD3OD): δ 7.51 (d, J ) 8.6 Hz, 2H),
7.38 (d, J ) 8.6 Hz, 2H), 6.48 (t, J ) 1.7 Hz, 1H), 6.39 (t, J ) 1.7
Hz, 1H), 6.23 (t, J ) 2.0 Hz, 1H). 13C NMR: 158.30, 149.11,
141.62, 140.27, 132.63, 128.17, 127.89, 105.61, 103.72, 101.53.
MS (m/z): 220.16 (MH+).
4-(tert-Butylaminomethyl)-4′-chloro-5-(7-chloroquinolin-4-
1
ylamino)-biphenyl-3-ol (2a). Yield: 10%, mp >220 °C dec. H
NMR (CD3OD): see Table 1. 13C NMR: 161.52, 151.21, 150.79,
148.89, 141.14, 139.01, 138.42, 135.44, 133.14, 128.53, 127.85,
126.49, 125.36, 123.17, 118.72, 117.94, 114.14, 113.11, 101.35,
52.17, 38.88, 26.29. MS (m/z): 466.0 (MH+). Anal. (C26H25N3-
OCl2) C, H, N.
5-Amino-4′-trifluoromethyl-biphenyl-3-ol (10b).21 To a solu-
tion of compound 9b (2.6 g, 9.73 mmol) in 1,2-dichloroethane (50
mL) was added boron tribromide methyl sulfide complex (10.9 g,
34.05 mmol), and the resulting mixture was refluxed overnight.
The reaction was allowed to cool down to room temperature and
was quenched with water. The organic phase was washed with
saturated sodium bicarbonate solution followed by brine, dried over
sodium sulfate, and evaporated in vacuum to dryness. The residue
was purified using flash chromatography on silica gel eluting with
10% ethyl acetate in chloroform followed by 30% ethyl acetate in
chloroform to give 1.87 g (76%) of 10b as an off-white solid, mp
185.3 °C. 1H NMR (CD3OD): δ 7.71 (d, J ) 4.1 Hz, 4H), 6.54 (s,
1H), 6.46 (s, 1H), 6.28 (s, 1H). 13C NMR: 161.37, 149.29, 145.45,
141.33, 129.61, 129.27, 128.86, 128.43, 126.95, 126.31, 126.28,
125.12, 125.07, 125.02, 124.97, 122.69, 118.16, 105.83, 103.95,
102.02. MS (m/z): 254.19 (MH+).
4-(tert-Butylaminomethyl)-5-(7-chloroquinolin-4-ylamino)-4′-
trifluoromethyl-biphenyl-3-ol (2b). Yield: 10%, mp >200 °C dec.
1H NMR (CD3OD): see Table 1. 13C NMR: 163.80, 161.93,
152.00, 151.22, 150.74, 140.77, 138.93, 135.45, 130.64, 129.28,
126.94, 126.50, 125.43, 125.38, 125.31, 125.26, 123.18, 119.35,
117.63, 114.25, 113.51, 101.36, 52.80, 38.99, 26.29. MS (m/z):
500.0 (MH+). Anal. (C27H25N3OClF3) C, H, N.
4,6-Bis-(tert-butylaminomethyl)-4′-chloro-5-(7-chloroquinolin-
4-ylamino)-biphenyl-3-ol (3a). Yield: 40%, mp >220 °C dec. 1H
NMR (CD3OD): see Table 1. 13C NMR: 160.04, 151.12, 150.43,
148.71, 141.11, 139.38, 137.98, 135.34, 133.04, 130.38, 128.05,
126.49, 125.40, 123.15, 120.15, 118.54, 117.66, 114.98, 101.06,
52.21, 51.48, 41.18, 38.13, 26.76, 26.22. MS (m/z): 551.1 (MH+).
Anal. (C31H36N4OCl2‚1.9H2O) C, H, N.
4,6-Bis-(tert-butylaminomethyl)-5-(7-chloroquinolin-4-ylamino)-
4′-trifluoromethyl-biphenyl-3-ol (3b). Yield: 43%, mp 196 °C.
1H NMR (CD3OD): see Table 1. 13C NMR: 162.32, 151.13,
150.29, 148.73, 144.94, 140.55, 137.99, 135.36, 129.54, 129.31,
128.80, 126.50, 125.24, 124.83, 124.79, 124.75, 124.70, 123.13,
121.15, 119.01, 117.68, 114.92, 101.01, 51.64, 50.89, 41.16, 37.99,
27.07, 26.45. MS (m/z): 293.1 (M+ + 2H). Anal. (C32H36N4OClF3)
C, H, N.
4′-Chloro-5-(7-chloroquinolin-4-ylamino)-biphenyl-3-ol (11a).
A solution of compound 10a (3 g, 13.66 mmol) and 4,7-
dichloroquinoline (2.71 g, 13.66 mmol) in ethanol (35 mL) was
heated at reflux for 2 h. The reaction mixture was allowed to cool
to room temperature. The resulting precipitate was collected, washed
with ethanol, and dried to give 5.1 g (98%) of 11a as a yellow
1
solid, mp >300 °C dec. H NMR (CD3OD): see Table 1. 13C
NMR: 168.66, 150.92, 150.48, 148.81, 141.34, 140.85, 140.53,
135.07, 132.28, 128.17, 127.93, 126.20, 124.86, 123.42, 118.05,
114.80, 113.45, 108.07, 101.42. MS (m/z): 280.9 (MH+). Anal.
(C21H14N2OCl2‚0.4H2O) C, H, N.
2,6-Bis-(tert-butylaminomethyl)-4′-chloro-5-(7-chloroquinolin-
1
4-ylamino)-biphenyl-3-ol (4a). Yield: 7%, mp >250 °C dec. H
5-(7-Chloro-quinolin-4-ylamino)-4′-trifluoromethyl-biphenyl-
3-ol (11b). Compound 11b was prepared by the same procedure
as described for the preparation of 11a in a quantitative yield, mp
260 °C. 1H NMR (CD3OD): as shown in Table 1. 13C NMR:
158.96, 151.11, 149.61, 148.86, 144.48, 142.00, 141.68, 135.43,
129.28, 128.97, 127.16, 126.39, 126.11, 125.40, 125.34, 125.29,
125.24, 123.39, 118.37, 112.88, 110.38, 109.53, 101.96. MS (m/
z): 415.10 (MH+). Anal. (C22H14N2OClF3‚0.9H2O) C, H, N.
General Procedure for Synthesis of Mannich Base. A mixture
of tert-butylamine (23 mmol) and 37% formaline (28 mmol) in
N,N-dimethylformamide (10 mL) was added to a solution of
compound 11 (7 mmol) in N,N-dimethylformamide (30 mL). The
reaction mixture was stirred at room temperature for 3 days. The
resulting precipitate was collected, washed with water followed by
NMR (CD3OD): see Table 1. 13C NMR (CD3OD): 161.73, 151.26,
149.07, 148.93, 141.91, 140.30, 138.05, 135.43, 133.30, 130.65,
128.34, 126.80, 125.25, 125.00, 122.94, 119.56, 118.13, 117.18,
110.90, 101.18, 52.48, 50.29, 41.89, 40.85, 27.44, 26.08. MS (m/
z): 551.1 (MH+). Anal. (C31H36N4OCl2‚0.75H2O) C, H, N.
1H NMR (CDCl3): δ 10.22 (bs, 1H), 8.58 (d, J ) 5.6 Hz, 1H),
8.05 (d, J ) 9.0 Hz, 1H), 8.02 (d, J ) 2.1 Hz, 1H), 7.45 (d, J )
8.6 Hz, 2H), 7.43 (dd, J ) 2.1, 9.0 Hz, 1H), 7.27 (d, J ) 5.6, 1H),
7.12 (d, J ) 8.6 Hz, 2H, s, 1H), 3.62 (s, 2H), 3.36 (s, 2H), 1.12 (s,
9H), 1.05 (s, 9H). 13C NMR (CDCl3): 158.82, 152.16, 150.04,
146.74, 141.15, 140.46, 138.11, 135.01, 133.40, 129.95, 128.70,
128.65, 125.46, 122.48, 119.07, 118.94, 116.20, 107.51, 102.38,
51.31, 50.68, 43.27, 41.84, 28.82, 28.44.

894 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 4
MiroshnikoVa et al.
Table 2. Growth Inhibition of Isoquine Analogues against P.
2,6-Bis-(tert-butylaminomethyl)-5-(7-chloroquinolin-4-ylamino)-
4′-trifluoromethyl-biphenyl-3-ol (4b). Yield: 7%, mp >250 °C
dec. 1H NMR (CD3OD): see Table 1. 13C NMR (CD3OD): 161.46,
151.23, 148.89, 143.60, 141.76, 140.43, 135.44, 129.94, 129.70,
129.26, 126.45, 125.30, 125.04, 124.98, 123.03, 119.22, 118.14,
116.69, 110.94, 101.13, 52.69, 50.19, 41.74, 40.76, 27.19, 25.80.
MS (m/z): 293.1 (M+ + 2H). Anal. (C32H36N4OClF3) C, H, N.
1H NMR (CDCl3): δ 8.58 (d, J ) 5.6 Hz, 1H), 8.03 (m, 2H),
7.74 (d, J ) 8.1 Hz, 2H), 7.44 (dd, J ) 2.1, 9.0 Hz, 1H), 7.73 (d,
J ) 8.1 Hz, 2H), 7.26 (d, J ) 5.6, 1H), 7.14 (s, 1H), 3.59 (s, 2H),
3.32 (s, 2H), 1.10 (s, 9H), 1.02 (s, 9H). 13C NMR (CDCl3): 159.09,
152.05, 149.92, 147.51, 143.59, 141.21, 140.45, 135.25, 130.05,
129.47, 129.10, 128.77, 125.61, 125.56, 125.50, 125.42, 122.47,
118.78, 118.67, 116.05, 107.87, 102.39, 51.39, 50.56, 43.22, 41.74,
28.69, 28.38.
falciparum and Macrophage Line J774 Cell Lines
P. falciparum
(IC50 ng/mL)
macrophage
line J774
compd
(IC50, µg/mL)
D6
W2
TM91C235
1.78
63.0
1a
1b
2a
2b
3a
3b
4a
4b
5b
11a
11b
12
13
14
6.1 ( 0.3
11.6 ( 1.2
1.6 ( 0.3
1.7 ( 0.3
3.6 ( 01
0.75 ( 0.2
2.8 ( 0.3
ND
ND
ND
ND
ND
0.3
7.1
1.4
1.8
2.2
1.9
2.8
1.8
1.2
8.8
15
397
4.3
4.1
1.5
0.4
130.0
1.6
2.1
2.6
2.8
5.3
3.6
1.7
1.8
2.3
2.0
2.5
3.0
73
N/A
140
580
8.8
14.0
22.4
300
2-(tert-Butylaminomethyl)-5-(7-chloroquinolin-4-ylamino)-4′-
trifluoromethyl-biphenyl-3-ol (5b). Yield: 2%, mp >250 °C dec.
1H NMR (CD3OD): see Table 1. 13C NMR (CD3OD): 157.09,
152.71, 150.04, 147.16, 145.67, 143.19, 142.35, 134.51, 130.27,
128.59, 128.50, 128.08, 127.65, 126.63, 125.72, 125.36, 125.33,
123.66, 123.02, 119.92, 118.77, 116.69, 112.31, 107.58, 102.35,
50.83, 41.47, 28.68. MS (m/z): 250.6 (M+ + 2H). Anal. (C27H25N3-
OClF3‚0.25H2O) C, H, N.
>1000
ND
ND
7.2
1.8
9.2
9.1
0.9
8.5
2.3
N/A
31.86
tebuquine-Nω-oxide
tebuquine
chloroquine
0.1
2.96
0.04
143.77
ND
Chulay et al.23 Three P. falciparum malaria parasite clones, from
CDC Indochina III (W-2), CDC Sierra Leone I (D-6), and Southeast
Asia Isolates (TM91C235), were utilized in susceptibility testing.
They were derived by direct visualization and micromanipulation
from patient isolates.24 The W-2 clone is susceptible to mefloquine
(MQ) but resistant to chloroquine (CQ), sulfadoxine, pyrimethamine,
and quinine, whereas the D-6 clone is naturally resistant to MQ
but susceptible to CQ, sulfadoxine, pyrimethamine, and quinine.
The TM91C235 is a multi-drug resistance P. falciparum isolate
from Southeast Asia. Test compounds were initially dissolved in
DMSO and diluted 400-fold in RPMI 1640 culture medium
supplemented with 25 mM Hepes, 32 mM NaHCO3, and 10%
Albumax I (Gibco BRL, Grand Island, NY). These solutions were
subsequently serially diluted 2-fold with a Biomek 1000 (Beckman,
Fullerton, CA) over 11 different concentrations. The parasites were
exposed to serial dilutions of each compound for 48 h and incubated
at 37 °C with 5% O2, 5% CO2, and 90% N2 prior to the addition
of [3H]-hypoxanthine. After a further incubation of 18 h, parasite
DNA was harvested from each microtiter well using Packard
Filtermate 196 Harvester (Meriden, CT) onto glass filters. Uptake
of [3H]-hypoxanthine was measured with a Packard Topcount
Scintillation. Concentration-response data were analyzed by a
nonlinear regression logistic dose response model, and the IC50
values (50% inhibitory concentrations) for each compound were
calculated. The results are shown in Table 2.
(ii) In Vitro Toxicity Assay. Selected compounds were tested
for toxicity in vitro against a subclone (G8) of the murine monocyte-
like macrophage line J774. The cell line was obtained from Dr.
Jose Alunda, Departmento de Sanidad Animal, Facultad de Vet-
erinaria, Universidad Complutense, Madrid, Spain. Murine cells
were maintained in 75 cm2 tissue culture flasks in Dulbecco’s
modified Eagle medium (GIBCO) supplemented with 10% fetal
calf serum, 2 mM l-glutamine 50 µg/mL gentamicin under
humidified 5% CO2/95% air at 37 °C.
Toxicity tests were performed in 96-well tissue culture plates
using an aqueous tetrazolium/formazan system as described.25 Cells
were plated at a density of 1 × 104 cells/well in 100 µL of culture
medium. After 24 h under culture conditions, 10 µL of drug
(experimental) or solvent (control) diluted to the appropriate
concentration in culture medium was added to each well. After the
mixture was incubated for 72 h, 20 µL of a solution containing
3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-
sulfo-phenyl)-2H-tetrazolium, inner salt (MTS), (Technical Bul-
letin: CellTiter 96 AQeousOne Solution Cell Proliferation Assay
Technical Bulletin #TB245, Promega Corporation) was added, and
the plates were cultured for 1 to 2 h at 37 °C. A Spectra MAX
Plus microtiter plate reader (Molecular devices) was used to measure
the optical density (OD) at a wavelength of 490 nm. Solvent control
values were subtracted from experimental values.
1H NMR (CDCl3): δ 8.61 (d, J ) 5.6 Hz, 1H), 8.05 (d, J ) 2.1
Hz, 1H), 7.93 (d, J ) 9.0 Hz, 1H), 7.73 (d, J ) 8.1 Hz, 2H), 7.47
(d, J ) 8.1 Hz, 1H), 7.44 (dd, J ) 2.1 and 9.0 Hz, 1H), 7.32 (d, J
) 5.6, 1H), 6.99 (d, J ) 2.1 Hz, 1H), 6.64 (d, J ) 2.1 Hz, 1H),
3.66 (s, 2H), 1.32 (s, 9H).
4′-Chloro-5-(7-chloro-1-oxy-quinolin-4-ylamino)-biphenyl-3-
ol (12). Compound 12 was prepared by the same method as that
for synthesis of 11a in a quantitative yield starting from 4,7-
1
dichloroquinoline 1-oxide, mp >300 °C dec. H NMR (CD3OD):
δ 8.61 (d, J ) 9.0 Hz, 1H, e), 8.59 (d, J ) 7.3 Hz, 1H), 8.40 (d,
J ) 2.1 Hz, 1H), 7.87 (dd, J ) 2.1, 9.0 Hz, 1H), 7.64 (d, J ) 8.6
Hz, 2H), 7.48 (d, J ) 8.6 Hz, 2H), 7.18 (br s, 1H), 7.11 (br s, 1H),
7.00 (d, J ) 7.3 Hz, 1H), 6.88 (br s, 1H). MS (m/z): 397.2 (MH+).
Anal. (C21H14N2O2Cl2‚0.3H2O) C, H, N.
6-(tert-Butylaminomethyl)-4′-chloro-5-(7-chloro-1-oxy-quino-
lin-4-ylamino)-biphenyl-3-ol (13). To a suspension of compound
12 (4,3 g, 10.83 mmol) in DMF (300 mL) was added tert-
butylamine (2.3 mL, 21.66 mmol) followed by 0.6 mL (21.66
mmol) of 37% formaldehyde. The mixture was heated at 65 °C for
1 day, and another equivalent mole each of tert-butylamine (1.15
mL, 10.83 mmol) and 37% formaldehyde (0.3 mL, 10.83 mmol)
were added. Since tert-butylamine and formaldehyde are volatile,
some of these reagents were lost during the heating, even with a
water-cooling condenser. Over the course of 7 days, an additional
10 equiv of tert-butylamine and 37% formaldehyde were added.
The reaction was cooled to room temperature, and insoluble starting
material was recovered. The solvent was removed in vacuum. The
residue was purified by silica gel column chromatography eluting
with CHCl3:EtOAc:MeOH:NH4OH (10:1:1:0.04) to give crude
product. Recrystallization from EtOAc yielded 0.74 g (14%) of pure
1
final product 13 as a bright yellow solid, mp >250 °C dec. H
NMR (CD3OD): see Table 1. 13C NMR (CD3OD): δ 161.57,
146.72, 141.31, 140.20, 139.23, 138.72, 138.31, 137.99, 133.43,
128.61, 127.96, 127.90, 124.27, 118.87, 118.37, 118.19, 114.10,
113.56, 100.49, 51.93, 38.89, 26.78. MS (m/z): 482 (MH+). Anal.
(C26H25N3O2Cl2‚H2O) C, H, N, Cl
4,6-Bis-(tert-butylaminomethyl)-4′-chloro-5-(7-chloro-1-oxy-
quinolin-4-ylamino)-biphenyl-3-ol (14). Compound 14 was iso-
lated from the same reaction mixture as compound 13. Yield: 25%,
mp >250 °C dec. 1H NMR (CD3OD): see Table 1. 13C NMR (CD3-
OD): δ 167.11, 146.75, 143.16, 140.13, 139.23, 138.53, 138.23,
137.84, 133.51 130.28, 128.29, 127.89, 124.69, 118.21, 118.12,
116.49, 115.84, 114.06, 100.73, 55.48, 55.05, 41.18, 38.98, 24.88.
MS (m/z): 284.17 (M+ + 2H). Anal. (C31H36N4O2Cl2‚0.3H2O) C,
H, N.
Biological Studies. (i) In Vitro Antimalarial Studies. The in
vitro assays were conducted by using a modification of the
semiautomated microdilution technique of Desjardins et al.22 and

Synthesis of New Isotebuquine Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 4 895
Scheme 5
active metabolite, compounds 11a and 11b are expected to act
as chloroquine analogues rather than isoquine analogues and
thus showed cross resistance with CQ. As expected, compounds
with mono- or bis-Mannich base side chains showed no or
minimum cross resistance to chloroquine (Table 2). The results
clearly indicate that the mechanisms of action of the isoquine
and the chloroquine are different, although both are 4-amino-
quinpline derivatives.
In Vivo Antimalarial Activity against P. berghei in Mice.
The three most active compoundss1a, 2a, and 3aswere tested
in mice infected with P. berghei by oral administration
(Thompson test). None showed significant activity on 3-day
treatment with a daily dose up to 192 mg/kg. Likewise, the
N-oxide analogues, 13 and 14, possess only marginal activity
with a minimum active dose of 450 mg/kg. The marginal
efficacy results in Thompson test may be a result of poor oral
bioavailability of these compounds
(iii). Antimalarial Studies against P. berghei in Mice. The in
vivo efficacy of the new compounds was determined in a modified
Thompson test.26,27 This test measures the survivability of mice
and parasite clearance following administration of drug on day 3-5
post infection. In brief, 5 × 106 P. berghei-infected erythrocytes
(KBG-173 strain) were inoculated into the intraperitoneal cavity
of male mice that weighed 24-30 g. By day 3 post-infection,
parasitemia ranged from 1.0 to 3.7%. Each drug, suspended in 0.5%
hydroxyethylcellulose-0.1% Tween 80, was administered orally
(PO) once daily from day 3-5 post-infection. The volume of drug
suspension given depends on the weight of the mouse and the drug
concentration of the suspension. In general, the volume is given at
0.01 mL/gram of body weight.
Five mice were used in each dosage group. Blood films were
taken on day 6 and biweekly for 31 days. Mice blood film negative
on day 31 post-infection were considered cured (C). Compounds
were considered active (A) when the survival time of the treated
mice was greater than twice the control mice, i.e., 12-14 day. Mice
losing >20% of their body weight were sacrificed.
In Vitro Toxicity. Macrophage line J774 was used to assess
the toxicity of the new Mannich base analogues synthesized in
this study (Table 2). The results indicated that the concentration
required to inhibit the normal cell line growth is 1000-fold
higher than that for the inhibition of parasite growth, especially
the chloroquine-sensitive cell line D-6, with therapeutic index
of g1000 and is comparable to that of the positive control drug,
tebuquine and tebuquine Nω-oxide.
Conclusion
Methods for synthesis of isotebuquine analogues and their
Nω-oxides have been developed. New derivatives exhibit
promising in vitro antimalarial activity against both chloroquine-
sensitive (D6) and chloroquine-resistant (W2) clones of P.
falciparum cell growth at a concentration comparable to that
of tebuquine. However, the new isotebuquine analogues showed
only marginal antimalarial activity in the Thompson test against
P. berghei by oral administration. The poor solubility in organic
solvents and water may be partially responsible for the poor
oral activity observed.
Results and Discussion
In Vitro Antimalarial Activity. The antimalarial activity of
the new isotebuquine analogues was assessed against both CQ-
susceptible (D6) and CQ-resistant clones (W2 and TM91C235)
of P. falciparum (Table 2). Tebuquine Nω-oxide and chloroquine
were used as positive control for the study. Chloro derivative
1a (IC50 0.3 ng/mL) is the most active among the compounds
tested and is 20-fold more active than the corresponding
trifluoromethyl analogue 1b. No appreciable difference in
antimalarial activities between chloro (2a-4a) and trifluoro-
methyl (2b-5b) analogues, however, were observed. The new
analogues were better than or equal to tebuquine in growth
inhibition against all three clones of P. falciparum studied. There
appeared no cross resistance with CQ, except 1b. In general,
compounds with mono Mannich base side chain (1a and 2a)
are more active than those with two Mannich base functions
(3a and 4a). It is to be noted that the key intermediates 11a
and 11b which possess no Mannich base side chain are also
highly active against W2 clone in the test, with IC50 of 8.8 and
15 ng/mL, respectively. However, both showed cross resistance
to CQ, with IC50 of 22.4 and 300 ng/mL, respectively, against
D-6, a CQ-resistant cell line. The results are of no surprise from
the structure-activity relationship and mechanism of action
points of view. Structurally, intermediate 11a and 11b are
analogues of CQ, while compounds 1-5 are isotebuquine
analogues.
Acknowledgment. Material has been reviewed by the Walter
Reed Army Institute of Research. There is no objection to its
presentation and/or publications. The opinions or assertions
contained herein are the private views of the author, and they
are not to be construed as official or as reflecting true views of
the Department of the Army or the Department of Defense. Dr.
Miroshnikova gratefully acknowledges the National Research
Council for the NRC Associateship. This research was per-
formed while the author held a National Research Council
Research Associateship Award at the Walter Reed Army
Institute of Research.
Supporting Information Available: Elemental analysis results.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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896 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 4
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