Evaluation of Bis-Alkylamidoxime O-Alkylsulfonates as Orally Available Antimalarials

Article abstract of DOI:10.1002/cmdc.201200112

The main threat to controlling malaria is the emerging multidrug resistance of Plasmodiumsp. parasites. Bis-alkylamidines were developed as a potential new chemotherapy that targets plasmodial phospholipid metabolism. Unfortunately, these compounds are not orally available. To solve this absorption issue, we investigated a prodrug strategy based on sulfonate derivatives of alkylamidoximes. A total of 25 sulfonates were synthesized as prodrug candidates of one bis-N-alkylamidine and of six N-substituted bis-C-alkylamidines. Their antimalarial activities were evaluated invitro against P. falciparum and invivo against P. vinckei in mice to define structure-activity relationships. Small alkyl substituents on the sulfonate group of both C-alkyl- and N-alkylamidines led to the best oral antimalarial activities; alkylsulfonate derivatives are chemically transformed into the corresponding alkylamidines.

Full text of DOI:10.1002/cmdc.201200112

MED
DOI: 10.1002/cmdc.201200112
Evaluation of Bis-Alkylamidoxime O-Alkylsulfonates as
Orally Available Antimalarials
Mꢀlissa Degardin,[a] Sharon Wein,[b] Smitha Gouni,[a] Christophe Tran Van Ba,[b] Jean-
Frꢀdꢀric Duckert,[a] Thierry Durand,[a] Roger Escale,[a] Henri Vial,[b] and Yen Vo-Hoang*[a]
The main threat to controlling malaria is the emerging multi-
drug resistance of Plasmodium sp. parasites. Bis-alkylamidines
were developed as a potential new chemotherapy that targets
plasmodial phospholipid metabolism. Unfortunately, these
compounds are not orally available. To solve this absorption
issue, we investigated a prodrug strategy based on sulfonate
derivatives of alkylamidoximes. A total of 25 sulfonates were
synthesized as prodrug candidates of one bis-N-alkylamidine
and of six N-substituted bis-C-alkylamidines. Their antimalarial
activities were evaluated in vitro against P. falciparum and
in vivo against P. vinckei in mice to define structure–activity re-
lationships. Small alkyl substituents on the sulfonate group of
both C-alkyl- and N-alkylamidines led to the best oral antima-
larial activities; alkylsulfonate derivatives are chemically trans-
formed into the corresponding alkylamidines.
Introduction
Malaria is a significant cause of death and illness in children
and adults, particularly in tropical countries. In 2010, there
were an estimated 655000 deaths by malaria and about 216
million cases.[1] Thanks to the Global Malaria Action Plan, 43 of
the 99 countries with ongoing transmission documented de-
creases in the number of malaria cases by more than 50% in
2010 compared with 2000. However, mosquito resistance to in-
secticides and parasite resistance to antimalarial medicines still
pose major threats to achieving global control of malaria.
Indeed, resistance to antimalarial medicines has been docu-
mented for all classes of antimalarials,[2] including artemisinin
derivatives.[3,4]
contain permanent charges, which are the reason for their low
oral bioavailability. Calas and co-workers thus developed bis-al-
kylamidine compounds[8,14] that are bioisosteres of bis-thiazoli-
um salts and are potent antimalarial agents, acting as choline
mimics. Indeed, their two cationic charges are due to the pro-
tonation of the alkylamidine functional group (base with pKa
~12–14). The antimalarial potency of bis-alkylamidines against
the human P. falciparum parasite correlates strongly with their
high pKa values, but their biscationic character also prevents
oral absorption.[8,14] We have explored various approaches over
the past few years to circumvent the physicochemical prob-
lems inherent with bis-alkylamidine compounds and to im-
prove their oral bioavailability. We focused our work on the
design of prodrug candidates, attempting to temporarily mask
the positive charges of bis-alkylamidine derivatives.
The emerging multidrug-resistant strains of Plasmodium par-
asites justify the development of new antimalarial chemothera-
pies. Therefore, Vial and co-workers studied phospholipid me-
tabolism in Plasmodium and identified the effectors of de novo
phosphatidylcholine biosynthesis as promising antimalarial tar-
gets.[5–8] Bis-thiazolium salts were further developed as choline
analogues with potent antimalarial activity and lower toxicity
(Figure 1).[9] This new strategy has been validated, and the lead
compound T3 [now named SAR97276 or Albitiazolium (INN)]
has undergone the clinical trials for the parenteral treatment
of severe malaria.[9–13] These new potent antimalarial agents
Because the use of amidines is limited by their lack of oral
bioavailability, Clement and co-workers studied pentamidine,
an antiparasitic drug with a benzamidine moiety, and originally
developed a prodrug strategy[15,16] based on the neutral benza-
midoxime function.[17,18] Indeed, the cationic charge of benza-
midines is masked by introducing an oxygen atom on the ni-
trogen atom of the amidine function. The resulting benzami-
doximes are therefore less basic and remain unprotonated
[a] Dr. M. Degardin, Dr. S. Gouni, Dr. J.-F. Duckert, Dr. T. Durand, Prof. R. Escale,
Dr. Y. Vo-Hoang
Institut des Biomolecules Max Mousseron
UMR 5247 CNRS-UMI-UMII
Facultꢀ des Sciences Pharmaceutiques et Biologiques
Universitꢀ de Montpellier I
15 avenue Charles Flahault, 34093 Montpellier (France)
E-mail: yen.vo-hoang@univ-montp1.fr
[b] S. Wein, C. Tran Van Ba, Dr. H. Vial
Dynamique Molꢀculaire des Interactions Membranaires
UMR 5235 CNRS-UMII
Figure 1. Lead compounds of bis-thiazolium salts and bis-N-alkylamidines.
Universitꢀ de Montpellier II, 34095 Montpellier (France)
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under physiological conditions. Clement’s research group
showed that reductases in the kidneys, liver, brain, lungs, and
gastrointestinal tract are responsible for the rapid conversion
of the inactive amidoximes to amidines.[19–21] The application of
the amidoxime prodrug strategy to amidine-containing drugs
led to bio-precursors with greater oral bioavailability than their
parent drugs.[22–25] Consistent with these results, we previously
reported that bis-alkylamidoxime derivatives have potent oral
activities thanks to specific O-substituents.[26,27] The bis-methyl-
sulfonate derivatives were able to temporarily mask the basic
character and allowed oral delivery of the bis-alkylamidine
drugs M64 and M34 with the highest antimalarial activities
after oral administration (ED50 p.o.<50 mgkgÀ1).
Figure 3. Targeted prodrug candidates of bis-N-alkylamidines and bis-C-alky-
lamidines.
To the best of our knowledge, no other examples of O-alkyl-
sulfonate amidoximes have been described as prodrug candi-
dates. The bis-alkylamidoxime and corresponding methylsulfo-
nate derivative were investigated as prodrug candidates of
M64, the lead compound of the bis-N-alkylamidine series.[28]
Pharmacokinetic studies in rat and in vitro metabolism by liver
microsomes have shown that both prodrug candidates were
converted into the active drug M64. However, transformation
of the bis-methylsulfonate derivative was too rapid. Indeed, it
is completely converted into M64 after incubation for only
5 min.
Scheme 1. Synthesis of sulfonates in the bis-N-alkylamidine series. Reagents
and conditions: a) sulfonyl chlorides, CHCl3, pyridine, RT, 4 h. (yields 1a–c, e–
h: 60–80%; 1c: 39%).
The aim of this study was to generate new sulfonate deriva-
tives as potential prodrugs in both the bis-N-alkylamidine and
bis-C-alkylamidine series. We have shown that M64 was the
most potent drug in bis-N-alkylamidine series.[29] On the other
hand, bis-N-substituents introduced on bis-C-alkylamidines
could improve in vivo antimalarial potency relative to
M34.[14,30,31] Indeed, the compounds shown in Figure 2[32] re-
which was obtained as previously described.[26] The bis-ami-
doxime 8 reacted with the suitable sulfonyl chloride reagents
in the presence of pyridine to afford the targeted alkylsulfo-
nates 1a–h.[34] These could be prepared with satisfactory yields
(60–80%), except for 1c, presumably because 2-propanesul-
fonyl chloride is more hindered (39% yield).
The targeted sulfonate prodrug candidates 2a–7c of the six
selected bis-C-alkylamidines M38, M40, M42, M44, M45, and
M46 were prepared from the corresponding N-substituted bis-
C-alkylamidoximes 9a–f, analogously to the previously de-
scribed procedure (Scheme 2).[26,27] They were purified by pre-
cipitation in diethyl ether or by silica gel chromatography.
Two different routes were required to generate the N-substi-
tuted bis-C-alkylamidoximes 9a–f. Indeed, the N-monosubsti-
tuted bis-C-alkylamidoximes 9a–d could be prepared as previ-
Figure 2. Modulation of the N-substituents of bis-C-alkylamidines.
vealed IC50 values (drug concentration required to inhibit 50%
parasite growth) lower than 15 nm and/or ED50 values after in-
traperitoneal (i.p.) administration lower than 10 mgkgÀ1 [33]
.
Consequently, we designed sulfonate prodrug candidates of
the N-alkylamidine M64 and of the six selected bis-C-alkylami-
dines M38, M40, M42, M44, M45, and M46, and defined struc-
ture–activity relationships governing their oral antimalarial ac-
tivity (Figure 3).
Results and Discussion
Chemistry
Scheme 2. Synthesis of N-alkylsulfonates in the bis-C-alkylamidine series. Re-
agents and conditions: a) alkylsulfonyl chlorides, pyridine, CHCl3, RT, 4 h.
(yields 41–72%).
The seven sulfonate prodrug candidates of bis-N-alkylamidine
M64 were prepared from bis-N-alkylamidoxime 8 (Scheme 1),
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ously described through N-alkylation of one oxadiazolone.[30]
However, this strategy could afford neither the isopropyl com-
pound 9e in good yield nor the N,N-disubstituted compound
9 f. When we explored alternative access to N-substituted C-al-
kylamidoximes 9e–f,[35] the hydroxyamination of bis-alkylthioa-
mide derivatives did not lead to the expected compounds.[36,37]
On the other hand, the second strategy based on the high re-
activity of bis-hydroximinoyl chloride 12 was successful.[38] The
N-isopropyl and N-pyrrolidinyl bis-C-alkylamidoximes 9e and
9 f were generated in good yields in three steps by starting
from the commercially available 1,14-tetradecanediol 10 and
the corresponding amines (Scheme 3).[39]
378C.[28] This instability may be linked to 1) the the mode of in-
troduction of the alkyl linker on the amidoxime function (on
the carbon atom in the bis-C-alkylamidine series, or on the ni-
trogen atom in the bis-N-alkylamidine series), or 2) the methyl
substituent of the sulfonate group. Here, the influence of this
last parameter was studied by using the model of analogues
of 1a. An aromatic ring or an alkyl chain was introduced onto
the sulfonate group in the bis-N-alkylamidine series, varying
the length, steric bulk, lipophilicity, and electronic effects of
these molecules. These modulations aimed at optimizing the
stability and physicochemical properties, and at enhancing oral
bioavailability and thus oral antimalarial activity. We focused
on lipophilicity, one of the most important parameters. Calcu-
lated ClogP values are listed in the Table 1. As expected, the
longer the alkyl chain, the higher the ClogP value; aromatic
rings also led to enhanced ClogP values.
Table 1. In vitro and in vivo antimalarial activities of O-substituted sulfo-
nate derivatives 1a–h in N-alkylamidine series.
[c]
Compd
R’
LogP[a]
IC50 [nm][b]
ED50 [mgkgÀ1
i.p.
]
p.o.
1a[d]
1b
1c
1d
1e
1 f
Me
Et
iPr
nPr
nBu
nOct
Ph
3.97
5.03
5.73
6.09
7.16
11.41
7.47
6.67
12
12
49
14
2.25
61.5
24.5
41.7
4.7
7.2
5.8
42
60
90
Scheme 3. Synthesis of C-alkylamidoximes 9e and 9 f. Reagents and condi-
tions: a) IBX, DMSO, RT, 4 h; b) NH2OH·HCl, NEt3, EtOH, RT, 16 h (74% over
two steps); c) NCS, anhyd DMF, RT, 1 h; d) 2-propylamine or pyrrolidine, NEt3,
Et2O, RT, 16 h (9e: 81%; 9 f: 82% over two steps).
>5[e]
>5[e]
>180
>180
>180
>180
>180
>20
2.3
>5[e]
1g
1h
2-thiophene
The 1,14-tetradecanediol 10 was first oxidized by freshly pre-
pared 1-hydroxy-1,2-benziodoxol-3(1H)-one 1-oxide (IBX) in
DMSO.[40] The resulting bis-aldehyde was directly condensed
with the hydroxylamine. The generated 1,14-tetradecanediox-
ime 11 reacted with N-chlorosuccinimide (NCS) to prepare the
reactive hydroximinoyl chloride intermediate 12.[41,42] This late
1,14-bis-(N1,N14-dihydroxyimidoyldichloride)tetradecane 12 was
directly coupled with isopropylamine or pyrrolidine.[43] The de-
sired bis-C-alkylamidoximes 9e and 9 f were isolated as their
respective hydrochloride salts owing to purification by re-
versed-phase chromatography. The pure neutral bis-amidox-
imes 9e and 9 f were retrieved after neutralization. As previ-
ously observed for the amidines,[30] the N-methyl- and N-ethyl-
bis-C-alkylamidoximes 9a and 9b could not be obtained by
this strategy. All structures of the synthesized compounds
[a] LogP values were calculated using ACD/LogP DB, Advanced Chemistry
Development Inc. [b] Toward P. falciparum; values are the mean of at
least two independent experiments conducted in duplicate. [c] Antimalar-
ial activities (P. vinckei) were determined after i.p. or p.o. administration
once daily for four days to infected mice (three mice per dose). [d] Com-
pound 1a (M64SMe) was previously described.[26] [e] Toxicity appeared at
higher doses.
The O-substituted sulfonates were evaluated for antimalarial
activity in vitro against the human parasite P. falciparum and
in vivo against P. vinckei in mice. As an initial part, the IC50 and
ED50 values after i.p. or p.o. administration of the seven pro-
drug candidates in the bis-N-alkylamidine series are reported
in Table 1. Results for 1a are also listed as a reference.
The in vitro antimalarial activities were evaluated against
a chloroquine-sensitive P. falciparum strain (Nigerian strain).
The sulfonate derivatives 1a–h constitute a homogeneous
group, showing in vitro antimalarial activities in the low nano-
molar range (IC50: 2–62 nm). For four compounds, the antiplas-
modial activity was moderate (1c: IC50 =49 nm, 1 f: IC50 =
61.5 nm, 1g: IC50 =24.5 nm, 1h: IC50 =41.7 nm). We aimed at
stabilizing the sulfonate moiety by using an aromatic group
(1g and 1h). The introduction of an aromatic ring as well as
a heteroaromatic ring led to decreased antimalarial activity.
With long (octyl) or hindered (isopropyl) alkyl chains, the anti-
malarial activity was also weaker than that of 1a. The antima-
larial potency may be hampered by the steric hindrance of the
1
were consistent with their H and 13C NMR, MS (ESI), and FTIR
characterizations.
Optimization of the sulfonate prodrug strategy
Our main goal was to investigate more extensively the sulfo-
nate prodrug strategy. Indeed, we previously reported that the
bis-O-methylsulfonate derivative 1a (M64SMe) constituted
a new prodrug candidate with an ED50 p.o. value less than
50 mgkgÀ1.[26] This was the first important step to improve the
oral antimalarial activity of the bis-N-alkylamidines. This deriva-
tive 1a was not sufficiently stable in biological media, as it is
totally metabolized into the parent drug M64 after 5 min at
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O-substituent of the sulfonate. The other three substituted O-
sulfonates exhibited potent in vitro antimalarial activities (1b:
IC50 =12 nm, 1d: IC50 =14 nm, 1e: IC50 =2.25 nm) similar to the
one previously described (1a IC50 =12 nm).[26,27] It appears that
small O-substituents afford potent in vitro antiplasmodial activ-
ity.
Optimization of the alkylsulfonate prodrug in the bis-C-alky-
lamidine series
As observed for the N-alkylamidine series, N-substituted bis-C-
alkylamidoximes did not reveal any significant antimalarial ac-
tivity (i.p. or p.o.).[30,45] Indeed, specific O-substituents are likely
needed to improve oral antimalarial activity. Thus, the alkylsul-
fonate derivatives were explored as prodrug candidates in the
bis-C-alkylamidine series. According to the results observed for
orally administered bis-N-alkylamidines, only small aliphatic O-
alkylsulfonates (methyl, ethyl, and isopropyl compounds) were
introduced on bis-C-alkylamidoximes to generate the 18 N-
substituted alkylsulfonates 2a–c, 3a–c, 4a–c, 5a–c, 6a–c, and
7a–c as prodrug candidates of the six selected C-alkylamidines.
The respective IC50 and ED50 values after i.p. or p.o. administra-
tion are listed in Table 2.
The in vivo antimalarial activities were evaluated against the
P. vinckei petteri strain (279BY) in female Swiss mice according
to a modified version of the four-day suppressive test.[7] The
mice (n=3 per dose) were infected on day 0 and were treated
once daily for four consecutive days (days 1–4 post-infection)
by intraperitoneal (i.p.) or oral (p.o.) route (three appropriate
doses). After i.p. administration, no antimalarial activity was de-
tected at the tested doses with compounds sharing long ali-
phatic substituents at the sulfonate group (1d, 1e, and 1 f), al-
though 1d and 1e showed potent in vitro antimalarial activity.
Doses of 1d and 1e higher than 5 mgkgÀ1 could not be used
because toxicity appeared at higher doses; this precluded de-
termination of whether higher doses could be active. For com-
pound 1h with the heteroaromatic ring, no ED50 i.p. could be
determined, but at 5 mgkgÀ1, compound 1h decreased parasi-
temia by 43% relative to control, revealing significant i.p. anti-
malarial activity. Doses higher than 5 mgkgÀ1 could not be
used because of toxicity issues. The presence of a long aliphat-
ic substituent or a heteroaromatic ring greatly increases the
toxicity of the compounds. Notably, the other three sulfonates
1b, 1c, and 1g led to a total clearance of parasitemia, and
ED50 values lower than 8 mgkgÀ1 were recorded, similar to 1a
and the parent drug M64.[44] Thus good in vivo antimalarial po-
tencies are likely afforded by small alkyl or phenyl substituents
on the sulfonate group, shared by compounds 1a, 1b, 1c, and
1g. However, 1c and 1g differ from 1a and 1b, as they they
revealed potent in vivo antimalarial activities, while possessing
moderate in vitro antiplasmodial activity.
Table 2. In vitro and in vivo antimalarial activities of O-alkylsulfonate de-
rivatives 2a–7c in the C-alkylamidine series.
[c]
Compd
R
R’
LogP[a] IC50 [nm][b] ED50 [mgkgÀ1
]
i.p.
p.o.
2a
2b
2c
3a
3b
3c
4a
4b
4c
5a
5b
5c
6a
6b
6c
7a
7b
7c
NHMe
NHMe
NHMe
NHEt
NHEt
NHEt
Me 3.97
12[d]
11[d]
20[d]
7.8[d]
7.5[d]
16[d]
23.5
44
<2
3.05
4.1
<2
<2
<2
>10
>10
>10
2
5.05
8.1
<2
<2
4
44
47
110
41
93
>180
105
>180
>180
130
>180
>180
35
Et
iPr
5.03
5.73
Me 5.03
Et
iPr
6.09
6.79
NH(CH2)2OMe Me 3.99
NH(CH2)2OMe Et
NH(CH2)2OMe iPr
NHBn
NHBn
NHBn
NHiPr
NHiPr
5.05
5.75
Me 7.52
34
15
Et
iPr
8.59
9.28
23.5
44.7
410
465
305
18.5
19
Me 5.73
Et
iPr
6.79
7.48
73
93
>120
>120
>120
NHiPr
Oral administration of 1d, 1e, and 1 f sulfonates resulted in
the detection of no antimalarial activity up to 180 mgkgÀ1, as
observed after i.p. administration. Surprisingly, compound 1g,
which exhibits the best antimalarial activity after i.p. adminis-
tration, is not orally active up to 180 mgkgÀ1. A slight oral
Pyrrolidine
Pyrrolidine
Pyrrolidine
Me 4.3
4
Et
iPr
5.37
6.06
2.2
>5[e]
25.5
[a] LogP values were calculated using ACD/LogP DB, Advanced Chemistry
Development Inc. [b] Toward P. falciparum; values are the mean of at
least two independent experiments conducted in duplicate. [c] Antimalar-
ial activities (P. vinckei) were determined after i.p. or p.o. administration
once daily for four days to infected mice (three mice per dose). [d] Single
value determined in duplicate. [e] Toxicity was observed at higher doses.
effect could be observed with compound 1h at 180 mgkgÀ1
:
parasitemia was decreased by 39% relative to control. On the
other hand, 1a, 1b, and 1c revealed substantial antimalarial
activity after oral administration, unlike M64 alkylamidine, as
a total clearance of parasitemia was observed with these three
compounds. Thus, potent oral antimalarial activities are afford-
ed only by derivatives with the smallest aliphatic substituents
on the O-sulfonate group. These compounds possess the
lowest ClogP values in the series (1a: ClogP=3.97, 1b:
ClogP=5.03, 1c: ClogP=5.73). They may be able to cross the
gastrointestinal tract more efficiently than compounds with
longer aliphatic and aromatic O-substituents (ClogP range: 6–
11.5). The smaller the alkyl chain, the lower the ClogP value
and consequently the better the oral activity. Regarding these
results, methyl, ethyl, and isopropyl groups were selected as
substituents on the sulfonate group applied to prodrug candi-
dates in the bis-C-alkylamidine series.
In contrast to the other compounds of this series, the in vi-
tro antiplasmodial activities of sulfonates 6a–c were weak,
with IC50 values higher than 300 nm for all three (6a: IC50 =
410 nm, 6b: IC50 =465 nm, 6c: IC50 =305 nm). These N-isopro-
pyl derivatives are prodrug candidates of M40. As observed for
the sulfonate derivatives in the N-alkylamidine series, the other
15 compounds 2a–c, 7a–c, 4a–c, 5a–c, and 7a–c form a ho-
mogeneous group with similar IC50 values in the low nanomo-
lar range (IC50: 7–34 nm). O-Isopropylsulfonate derivatives
(group c) showed IC50 values slightly higher than those for the
methyl and ethyl groups, except for 3c and 4c. The IC50 values
of O-sulfonates 2a–c and 3a–c could be determined only once
due to the degradation of sulfonates.
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In vivo, after i.p. administration, all compounds in the bis-C-
alkylamidine series showed substantial antimalarial activities,
with ED50 i.p. values lower than 8 mgkgÀ1, except 4a–c (pro-
drugs of M42). These compounds revealed the weakest anti-
malarial effects. After i.p. administration of 4a, 4b, and 4c at
10 mgkgÀ1, parasitemia decreased by 23, 51, and 57% relative
to control, respectively, and no ED50 value could be deter-
mined. The ED50 i.p. value of the O-isopropyl sulfonate deriva-
tive 7c could not be determined because toxicity appeared at
doses higher than 5 mgkgÀ1. However, i.p. administration of
7c at 5 mgkgÀ1 led to a 25% decrease in parasitemia relative
to control. The other 14 alkylsulfonates 2a–c, 3a–c, 5a–c, 6a–
c, and 7a–b form a homogeneous group, with ED50 i.p. values
lower than 5 mgkgÀ1. Notably, the lower the ClogP value, the
higher the activity of the alkylsulfonate prodrug candidates.
After oral administration of 4b, 4c (prodrugs of M42), 5b
and 5c (prodrugs of M42) at 180 mgkgÀ1, no antimalarial
effect could be observed, and 4a and 5a revealed weak oral
antimalarial activity, with ED50 p.o. values higher than
100 mgkgÀ1. However, if these high (>100 mgkgÀ1) ED50 p.o.
values can be explained by high (>10 mgkgÀ1) ED50 i.p. values
for the prodrug candidates of M42 (4a, 4b, and 4c), this is not
the case for the prodrug candidates of M46 (5a, 5b, and 5c),
the ED50 i.p. values for which are ꢀ8 mgkgÀ1. This apparent
contradiction may be explained by the weaker antimalarial ac-
tivity of the parent drug M46 (ED50 i.p.@20 mgkgÀ1) and/or
the higher ClogP values of the sulfonates 5b and 5c. O-Isopro-
pyl sulfonates 2c, 3c, the M38 prodrug candidates 7a, 7b,
and 7c were also weakly orally potent. Indeed, oral administra-
tion of 7a, 7b, and 7c at 120 mgkgÀ1 decreased parasitemia
in mice by 65, 66, and 76%, respectively, relative to control.
With compounds 2c and 3c administered at 180 mgkgÀ1, par-
asitemia was decreased by 76 and 47%, respectively. Accord-
ing to these results it seems that the prodrug candidates of at
least M46 (5a–c) and M38 (7a–c), and the O-isopropyl sulfo-
nates 2c and 3c possess weak oral bioavailability, although
their ClogP values are not significantly higher than the others.
The weak oral antimalarial activities of the prodrug candidates
of M38 (7a, 7b and 7c) are particularly disappointing, as the
parent drug M38 was the most potent C-alkylamidine.
Figure 4. Oral antimalarial activities of O-methyl (&), ethyl (&), and isopro-
pyl (&) sulfonate prodrug candidates of M64 and of N-substituted C-alkyla-
midines.
be distinguished (1a–c, 2a–c, 3a–c, and 6a–c) according to
the corresponding parent drug M64, M44, M45, and M40. In
each group, the weakest oral activities were obtained with the
compounds bearing the O-isopropyl substituents, and the best
results were attributed to the O-methyl derivatives. These ob-
servations led us to conclude that the oral antimalarial activity
of the alkylsulfonates may depend on the bulkiness of the O-
substituent and the consequent lipophilicity of the com-
pounds. Indeed, the bulkier the O-substituent, the higher the
ClogP value and the weaker the oral activity. Moreover, the
oral antimalarial activities of the four methylsulfonates 1a, 2a,
3a, and 6a are in a similar range (ED50 p.o. between 35 and
44 mgkgÀ1), suggesting that the way the alkyl linker is intro-
duced at the amidoxime function is less important than the O-
alkyl substituent on the sulfonate group. The best oral activity
was observed with 6a (ED50 p.o.=35 mgkgÀ1), while its anti-
malarial activity was moderate in vitro (IC50 =410 nm) and
potent in vivo.
Transformation of the sulfonate prodrug candidates into the
active amidines.
Remarkably, potent oral antimalarial activities were observed
for the other seven O-alkylsulfonates. A total clearance of para-
sitemia could be observed after oral administration of the O-
methylated and ethylated sulfonates 2a, 2b (M44 prodrugs),
3a, and 3b (M45 prodrugs) at 180 mgkgÀ1. Furthermore, para-
sitemia in mice was respectively decreased by 96, 95, and 91%
with 6a, 6b, and 6c (M40 prodrugs).
Compounds 1a, 1b, 1c, 1g, and 2a–c, 3a–c, 5a–c, and 7a–
b all exert their antimalarial activity in the nanomolar range (in
vitro) and with similar ED50 i.p. values (in vivo) as those of the
corresponding bis-cationic bis-alkylamidines M64, M38, M44,
M45, and M46.[33] The most likely explanation is that these pro-
drug candidates are efficiently converted in situ into the corre-
sponding bis-alkylamidine, which is responsible for in vitro an-
tiplasmodial activity.[27] Moreover, our assumption is consistent
with the results obtained in Bressolle’s group.[28] They observed
that 1a was rapidly transformed into M64. We assume that the
desired transformation occurs in biological media for the
seven analogues 1b–h and analogously for the 18 sulfonates
2a–7c in the bis-C-alkylamidine series. The observed IC50 value
would reflect the rapidity of the desired conversion of the pro-
drug candidate into the corresponding drug in vitro, and the
observed ED50 i.p. value would reflect the rate of transforma-
tion into the targeted drug in vivo.
Influence of lipophilicity and steric bulk on oral bioavailabil-
ity and activity
To compare the results of the O-alkylsulfonates as prodrug can-
didates of M64, M44, M45, and M40, the ED50 p.o. values are
presented in Figure 4. These derivatives are represented by dif-
ferent shades according to the three possible O-alkyl substitu-
ents (methyl in white, ethyl in grey, and isopropyl in black).
Four groups of three O-alkylsulfonate prodrug candidates can
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Because no i.p. antimalarial activity could be de-
tected for 1d, 1e, 1 f, 1h, and 4a–c, 7c, it is likely
that their conversion into the corresponding active
drug is not efficient. They may be degraded into me-
tabolites that differ from the targeted molecules M64
or M38. Only small aliphatic or aromatic substituents
on the O-sulfonate group likely permit the efficient
transformation of the prodrug candidates into the
active drug M64. Unfortunately, even with small sub-
stituents on the sulfonate group, M42 was not effi-
ciently produced from its prodrug candidates 4a–c.
The alkylsulfonate conversion may be substrate de-
Figure 5. Possible conversion pathways of M64SMe (1a).
pendent and hampered by the methoxyethyl chain of M42.
The three prodrug candidates 6a–c of M40 constitute
a group of exceptions. They revealed potent i.p. and p.o. anti-
malarial activities while exhibiting very weak in vitro antiplas-
modial activities (IC50 >300 nm). One explanation for this ap-
parent paradox is that the conversion of the prodrug candi-
dates 6a–c into the active M40 occurs efficiently (the antima-
larial activity observed in vivo may be credited to the parent
drug M40), while this conversion occurs less rapidly in vitro.
Compounds 6a–c may be significantly more stable than the
other prodrug candidates (IC50 <50 nm).
The other key point to elucidate is how the sulfonate pro-
drug candidates are converted into the corresponding bis-alky-
lamidine drugs. Knowing that the sulfonates 1a–7c are deriva-
tives of the amidoxime 8, 14a–d, 12, and 13, we assumed at
the beginning, the sulfonate derivatives 2a–7c are prodrug
candidates capable of being transformed into amidoxime 8,
14a–d, 12, and 13, and then reduced into bis-alkylamidines.
However, the parent amidoximes 8, 14a–d, 12, and 13 did not
reveal any antimalarial activity in vitro or in vivo.[30,45] Thus, it is
likely that the alkylsulfonates are not transformed into inactive
amidoximes 8, 14a–d, 12, and 13, but directly into bis-alkyla-
midines M64, M44, M45, M42, M46, M40, and M38.
prodrug candidates of most of bis-alkylamidines (M64, M38,
M42, M44, M45, and M46) are potent in vitro; their transfor-
mation into active bis-alkylamidines likely occurs very rapidly,
except for those of M40, which revealed the weakest in vitro
antiplasmodial potencies. The isopropyl group introduced on
the nitrogen atom of the bis-C-alkylamidine led to the opti-
mized antiplasmodial activity of M40 while imparting the best
stability of the alkylsulfonate prodrug candidates 6a–c and an
efficient conversion into active M40. Because the prodrug can-
didate 6a is the most orally potent, this compound appears to
be the most promising antimalarial agent based on bis-alkyla-
midine choline analogues, potentially working as an alkylsulfo-
nate prodrug.
Conclusions
The main goal of the present study was to investigate the SAR
of the sulfonate prodrug candidates in the bis-N-alkylamidine
and bis-C-alkylamidine series. We wanted to improve the low
stability of 1a in biological media and the oral antimalarial ac-
tivities. We first showed that a small alkyl substituent on the
sulfonate group of prodrug candidates leads to the best oral
antimalarial activities and that the alkylsulfonate prodrug strat-
egy applies to C-alkylamidines as efficiently as it does to N-al-
kylamidines. The optimization of O-substituents on the select-
ed N-substituted C-alkylamidoximes led to orally effective anti-
malarial alkylsulfonates in the N-alkylamidine series, as in C-al-
kylamidine series. According to these results, it appears that
the alkyl substituent on the sulfonate moiety influences the
lipophilicity of the derivatives and their diffusion across biolog-
ical membranes, as well as the rate of conversion of the alkyl-
sulfonate prodrug candidate, whereas the rate of conversion
may be governed by the N-substituents in the bis-C-alkylami-
dine series. Compound 6a revealed the most potent i.p. and
p.o. potencies, as well as improved stability in biological
media. We also came to the conclusion that alkylsulfonate de-
rivatives are directly chemically transformed into the corre-
sponding bis-alkylamidines, the mechanism for which remains
unsolved.
Because the desired conversion of the sulfonate prodrug
candidates into the corresponding alkylamidine drug occurs in
plasma used for in vitro evaluations, it is not likely that sulfo-
nates are enzymatically converted. Indeed, the enzyme systems
(cytochrome P450 reductases) that were predicted to transform
amidoxime derivatives into the corresponding amidines are
not present in the plasma. Moreover, to our knowledge, no
enzyme system present in the plasma is capable of catalyzing
the reduction of sulfonates into amidines. The most likely ex-
planation is that sulfonates are chemically transformed into al-
kylamidines. These assumptions are consistent with the results
of Bressolle’s group[28] for M64 in bis-N-alkylamidine series
(Figure 5), which in analogy may also apply to bis-C-alkylami-
dines. The non-enzymatic transformation of the alkylsulfonate
may consist of a chemical reduction possibly related to the re-
duction of amidoxime tosylates into para-toluenesulfonate
salts of amidines, as reported by Le Berre et al.[46]
There are only few reports on prodrugs designed to rely ex-
clusively on a non-enzymatic activation principle.[47] In this
case, chemical stability issues have to be considered as a priori-
ty, especially when the prodrug candidates are supposed to be
chemically transformed into active drugs.[48] The alkylsulfonate
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Orally Available Bis-Alkylamidoxime O-Alkylsulfonate Antimalarials
MED
[2M+H]+, 264.2 (89) [(M+2H)/2]+, 527.3 (100) [M+H]+; HRMS-ESI
m/z [M+H]+ calcd for C22H47N4O6S2+: 527.2937, found: 527.2938.
Experimental Section
Drug inhibition of in vitro-cultured P. falciparum
1,12-bis-(N,N’-Propylsulfonyloxyacetamidinyl)dodecane
1d:
A chloroquine-sensitive strain of P. falciparum (Nigerian strain)[6]
was asexually cultured in human blood.[49] Compounds were dis-
solved in RPMI 1640 or DMSO (final concentration <0.1%).
Growths of P. falciparum cultures (0.6% initial parasitemia and
1.5% hematocrit) were measured in microtiter plates by
[3H]hypoxanthine incorporation after 48 h incubation with the
compounds to determine the 50% inhibition concentration (IC50),
according to a modified Desjardins test.[6,50]
Using general procedure A, starting from 1,12-bis-(N,N’-hydroxyace-
tamidinyl)dodecane (8) (1 g, 3.18 mmol) and propanesulfonyl chlo-
ride (0.7 mL, 6.37 mmol) affording 1d as a white powder (1.3 g,
75%). Rf =0.63 (CH2Cl2/MeOH 9:1); mp: 68–698C; 1H NMR
(300 MHz, CDCl3): d=5.25 (m, 2H), 3.29 (d, J=7.8 Hz, 4H), 3.10 (q,
J=6.7 Hz, 4H), 1.91 (s, 6H), 1.87 (m, 4H), 1.38 (m, 4H), 1.26 (m,
16H), 1.06 ppm (t, J=7.5 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=
158.0, 60.3, 50.1, 42.9, 30.4, 29.4, 29.3, 29.1, 26.5, 14.4, 14.1,
12.8 ppm; IR: n˜ =1643, 2852, 2923, 3413 cmÀ1; MS (ESI) m/z (%):
264.1 (35) [(M+2H)/2]2+
;
HRMS-ESI m/z [M+H]+ calcd for
C22H47N4O6S2+: 527.2937, found: 527.2943.
In vivo studies
All animal studies followed relevant laws and institutional guide-
lines. They were performed at the Centre d’Elevage et de Condi-
tionnement Experimental des Modꢂles Animaux, Montpellier
(France), under permission number A34370 (Centre National de la
Recherche Scientifique). The in vivo antimalarial activities were
evaluated against the P. vinckei petteri strain (279BY) in female
Swiss mice according to a modified version of the four-day sup-
pressive test.[7] The mice (n=3 per dose) were infected on day 0
and were treated once daily for four consecutive days (days 1–4
post-infection). Drugs and prodrugs were injected in 100 mL vol-
umes of 0.9% NaCl or DMSO by intraperitoneal (i.p.) route, and in
H2O or DMSO by oral (p.o.) route (three appropriate doses). On
day 5, parasitemia levels were monitored in Giemsa-stained blood
smears and by flow cytometry on blood samples.[51]
1,12-bis-(N,N’-Butylsulfonyloxyacetamidinyl)dodecane 1e: Using
general procedure A, starting from 1,12-bis-(N,N’-hydroxyacetamidi-
nyl)dodecane (8) (0.5 g, 1.6 mmol) and butanesulfonyl chloride
(0.5 mg, 3.2 mmol) affording 1e as a colorless oil (0.9 g, 89%). Rf =
0.63 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz, CDCl3): d=5.25 (m,
2H), 3.30 (m, 4H), 3.10 (q, J=6.7 Hz, 4H), 1.91 (s, 6H), 1.81 (m, 4H),
1.49 (m, 8H), 1.26 (m, 16H), 0.93 ppm (t, J=7.3 Hz, 6H); 13C NMR
(75 MHz, CDCl3): d=158.0, 48.1, 42.9, 30.5, 29.4, 29.3, 29.1, 26.5,
25.2, 21.4, 14.4, 13.4 ppm; IR: n˜ =1644, 2852, 2923, 3402 cmÀ1; MS
(ESI) m/z (%): 278.2 (17) [(M+2H)/2]2+, 555.3 (100) [M+H]+;
HRMS-ESI m/z [M+H]+ calcd for C24H51N4O6S2+: 555.3250, found:
555.3242.
1,12-bis-(N,N’-Octylsulfonyloxyacetamidinyl)dodecane 1 f: Using
general procedure A, starting from 1,12-bis-(N,N’-hydroxyacetamidi-
nyl)dodecane (8) (0.5 g, 1.6 mmol) and octanesulfonyl chloride
(0.62 mL, 3.2 mmol) affording 1 f as a white powder (0.55 g, 70%).
Rf =0.63 (CH2Cl2/MeOH 9:1); mp: 82–838C; 1H NMR (300 MHz,
CDCl3): d=5.24 (m, 2H), 3.29 (t, J=7.9 Hz, 4H), 3.19 (q, J=6.7 Hz,
4H), 1.91 (s, 6H), 1.82 (m, 4H), 1.51 (m, 12H), 1.41 (m, 12H), 1.26
(m, 16H), 0.86 ppm (t, J=6.5 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=
158.0, 60.3, 50.1, 42.9, 30.4, 29.4, 29.3, 29.1, 26.5, 14.4, 14.1,
12.8 ppm; IR: n˜ =1636, 2849, 2926, 3388 cmÀ1; MS (ESI) m/z (%):
334.2 (24) [(M+2H)/2]2+, 667.3 (100) [M+H]+; HRMS-ESI m/z [M+
H]+ calcd for C32H67N4O6S2+: 667.4502, found: 667.4508.
Chemistry
General procedure A: synthesis of sulfonate derivatives: To a so-
lution of amidoxime derivative (1 equiv) in CHCl3 cooled at 08C
was added pyridine (2.5 equiv). A solution of sulfonyl chloride de-
rivative (2.5 equiv) in CHCl3 was added to the medium. The reac-
tion was stirred at room temperature for 4 h. After completion, the
reaction was quenched with H2O. The organic layer was washed
with brine, dried over MgSO4, filtered, and concentrated under re-
duced pressure. The residue was subjected to silica gel column
chromatography twice with a step gradient of MeOH (0–1%) in
CH2Cl2 to afford the desired sulfonate derivative.
1,12-bis-(N,N’-Phenylsulfonyloxyacetamidinyl)dodecane
1g:
Using general procedure A, starting from 1,12-bis-(N,N’-hydroxyace-
tamidinyl)dodecane (8) (1 g, 3.18 mmol) and benzenesulfonyl chlo-
ride (0.8 mL, 6.37 mmol) affording 1g as a white powder (1.53 g,
80%). Rf =0.63 (CH2Cl2/MeOH 9:1); mp: 108–1098C; 1H NMR
(300 MHz, CDCl3): d=8.00 (d, J=3.6 Hz, 4H), 7.62 (m, 4H), 7.52 (m,
4H), 5.25 (m, 2H), 3.22 (d, J=6.7 Hz, 4H), 3.10 (q, J=6.4 Hz, 4H),
1.91 (s, 6H), 1.51 (m, 4H), 1.26 ppm (m, 16H); 13C NMR (75 MHz,
CDCl3): d=158.1, 136.1, 133.4, 42.8, 30.4, 29.4, 29.3, 29.1, 26.5, 14.4,
ppm; IR: n˜ =1639, 2854, 2931, 3388 cmÀ1; MS (ESI) m/z (%): 298.1
(38) [(M+2H)/2]2+, 595.1 (100) [M+H]+; HRMS-ESI m/z [M+H]+
calcd for C28H43N4O6S2+: 595.2624, found: 595.2618.
1,12-bis-(N,N’-Ethylsulfonyloxyacetamidinyl)dodecane 1b: Using
general procedure A, starting from 1,12-bis-(N,N’-hydroxyacetamidi-
nyl)dodecane (8) (1 g, 3.18 mmol) and ethanesulfonyl chloride
(0.6 mL, 6.37 mmol) affording 1b as a white powder (0.95 g, 60%).
Rf =0.63 (CH2Cl2/MeOH 9:1); mp: 56–578C; 1H NMR (300 MHz,
CDCl3): d=5.25 (m, 2H), 3.3 (q, J=7.5 Hz, 4H), 3.12 (q, J=6.7 Hz,
4H), 1.91 (s, 6H), 1.51 (m, 4H), 1.38 (m, 6H), 1.25 ppm (m, 16H);
13C NMR (75 MHz, CDCl3): d=158.1, 30.4, 29.4, 29.3, 29.1, 26.5, 14.4,
8 ppm; IR: n˜ =1630, 2854, 2926, 3376 cmÀ1; MS (ESI) m/z (%): 250
(18) [(M+2H)/2]+, 499 (100) [M+H]+; HRMS-ESI m/z [M+H]+
calcd for C22H43N4O6S2+: 499.2624, found: 499.2632.
1,12-bis-(N,N’-2-Thiophenylsulfonyloxyacetamidinyl)dodecane
1h: Using general procedure A, starting from 1,12-bis-(N,N’-hydrox-
yacetamidinyl)dodecane (8) (1 g, 3.18 mmol) and 2-thiophenesul-
fonyl chloride (1.18 g, 6.37 mmol) affording 1h as a white powder
(1.3 g, 68%). Rf =0.63 (CH2Cl2/MeOH 9:1) mp: 85–868C; 1H NMR
(300 MHz, CDCl3): d=7.79 (m, 1H), 7.68 (m, 1H), 7.11 (m, 1H), 5.20
(m, 2H), 3.08 (q, J=6.7 Hz, 4H), 1.86 (s, 6H), 1.48 (m, 4H),
1.26 ppm (m, 16H); 13C NMR (75 MHz, CDCl3): d=158.3, 134.6,
133.5, 127.0, 42.9, 29.4, 29.3, 29.1, 26.8, 26.5, 14.3 ppm; IR: n˜ =
1626, 2852, 2922, 3402 cmÀ1; MS (ESI) m/z (%): 304.1 (38) [(M+
1,12-bis-(N,N’-2-Propylsulfonyloxyacetamidinyl)dodecane
1c:
Using general procedure A, starting from 1,12-bis-(N,N’-hydroxyace-
tamidinyl)dodecane (8) (1 g, 3.18 mmol) and 2-propanesulfonyl
chloride (0.7 mL, 6.37 mmol) affording 1c as a colorless oil (0.65 g,
39%). Rf =0.63 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz, CDCl3): d=
5.25 (m, 2H), 3.78 (m, 2H), 3.11 (q, J=6.7 Hz, 4H), 1.92 (s, 6H), 1.49
(m, 4H), 1.41 (m, 12H), 1.25 ppm (m, 16H); 13C NMR (75 MHz,
CDCl3): d=158.0, 49.7, 30.5, 29.4, 29.3, 29.1, 26.5, 16.3, 14.4 ppm;
IR: n˜ =1632, 2854, 2926, 3381 cmÀ1; MS (ESI) m/z (%): 1053.6 (11)
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2H)/2]2+, 607.1 (100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for
1,12-bis-(N-Isopropyl-N’-hydroxyamidinyl)dodecane 9e: Using
general procedure B, starting from 1,14-tetradecanedial dioxime
(11) (7.7 g, 30.0 mmol) and 2-iodopropylamine (9.5 mL,
110.0 mmol) affording 9e as a beige powder (8.9 g, 81% over two
steps). Rf =0.30 (CH2Cl2/MeOH 9:1); mp: 78–798C; 1H NMR
(300 MHz, MeOD): d=3.64 (hept, J=4.8 Hz, 2H), 2.18 (t, J=7.6 Hz,
4H), 1.54 (m, 4H), 1.31 (m, 16H), 1.18 ppm (m, 12H); 13C NMR
(75 MHz, MeOD): d=157.5, 44.9, 30.7, 30.6, 30.4, 30.3, 29.5, 28.8,
24.7 ppm; IR: n˜ =1662, 2851, 2917, 3143, 3418 cmÀ1; MS (ESI) m/z
C24H39N4O6S2+: 607.1752, found: 607.1745.
1,14-Tetradecanedial dioxime 11: A mixture of 1-hydroxy-1,2-ben-
ziodoxol-3-(1H)-one 1-oxide (IBX) (34.5 g, 123.3 mmol) in DMSO
(200 mL) was cooled with an ice bath. 1,14-Tetradecanediol (9.5 g,
41,1 mmol) was added. The solution was stirred at room tempera-
ture for 5 h. Cold H2O (500 mL) was added to the medium. The
formed solid was filtered and washed with H2O (3ꢃ50 mL). The
solid was solubilized with EtOAc (500 mL). This organic layer was
washed with brine (2ꢃ400 mL), dried over MgSO4, filtered, and
evaporated to give 1,14-tetradodecanedial as an oil becoming
a white powder under high vacuum (8.7 g, crude). This was used
directly in next step without further purification: Rf =0.50 (cHex/
(%): 741 (12) [2M+H]+, 371 (85) [M+H]+, 186 (100) [(M+2H)/2]2+
;
HRMS-ESI m/z [M+H]+ calcd for C20H43N4O2+: 371.3386, found:
371.3394.
1,12-bis-(N-Pyrrolidinyl-N’-hydroxyamidinyl)dodecane 9 f: Using
general procedure B, starting from 1,14-tetradecanedial dioxime
(11) (3.15 g, 9.7 mmol) and pyrrolidine (3.2 mL, 38.70 mmol) afford-
ing 9 f as a beige powder (3.36 g, 82% over two steps). Rf =0.46
1
EtOAc 7:3); H NMR (300 MHz, [D6]DMSO): d=9.76 (s, 2H), 2.39 (m,
4H), 1.61 (m, 4H), 1.24 ppm (m, 16H); 13C NMR (75 MHz,
[D6]DMSO): d=202.8, 43.8, 29.4, 29.3, 29.2, 29.0, 21.9 ppm; IR: n˜ =
1710, 2848, 2912 cmÀ1; MS (ESI) m/z (%): 227.2 (100) [M+H]+;
HRMS-ESI m/z [M+H]+ calcd for C14H27O2: 227.2011, found:
227.2015. Hydroxylamine hydrochloride (13.4 g, 192.8 mmol) was
added to a solution of 1,14-tetradecanedial (8.7 g, 38.6 mmol) and
anhydrous pyridine (21.6 mL, 268.6 mmol) in anhydrous EtOH
(200 mL). The reaction was held at reflux overnight. After comple-
tion, the solvents were evaporated, and the solid obtained was
washed with H2O (3ꢃ50 mL), MeOH, and Et2O to yield 11 as
a white powder (7.7 g, 74% over two steps): Rf =0.64 (CH2Cl2/
MeOH 9:1); 1H NMR (300 MHz, [D6]DMSO): d=10.66 (s, 2H, OH),
6.62 (t, J=5.4 Hz, 2H), 2.50 (m, 4H), 1.39 (m, 4H), 1.25 ppm (m,
16H); 13C NMR (75 MHz, [D6]DMSO): d=153.3, 29.0, 28.9, 28.7, 28.5,
25.6, 24.5 ppm; MS (ESI) m/z (%): 257 (100) [M+H]+; HRMS-ESI m/z
[M+H]+ calcd for C14H28N2O2+: 257.2229, found: 257.2232.
1
(CH2Cl2/MeOH 9:1); mp: 125–1268C; H NMR (300 MHz, MeOD): d=
3.24 (m, 8H), 2.51 (t, J=7.9 Hz, 4H), 1.88 (m, 8H), 1.57 (m, 4H),
1.33 ppm (m, 16H); 13C NMR (75 MHz, MeOD): d=163.7, 47.7, 30.8,
30.7, 30.6, 30.4, 27.3, 27.2, 26.0 ppm; IR: n˜ =1627, 2853, 2923,
3258 cmÀ1; MS (ESI) m/z (%): 789 (6) [2M+H]+, 395 (41) [M+H]+,
198 (100) [(M+2H)/2]2+
;
HRMS-ESI m/z [M+H]+ calcd for
C22H43N4O2+: 395.3386, found: 395.3395.
1,12-bis-(N-Methanesulfonyloxy-N’-methylamidinyl)dodecane
2a: Using general procedure A, starting from 1,12-bis-(N-hydroxy-
N’-methylamidinyl)dodecane (9a) (0.53 g,1.7 mmol) and methane-
sulfonyl chloride (0.33 mL, 4.2 mmol) affording 2a as a white
powder (0.32 g, 41%). Rf =0.78 (CH2Cl2/MeOH 9:1); mp: 90–918C;
1H NMR (300 MHz, CDCl3): d=5.22 (m, 2H), 3.11 (s, 6H), 2.87 (d, J=
5.2 Hz, 6H), 2.24 (t, J=7.8 Hz, 4H), 1.59 (m, 4H), 1.27–1.36 ppm (m,
16H); 13C NMR (75 MHz, CDCl3): d=161.8, 36.0, 29.6, 29.5, 29.3,
28.1, 26.2 ppm; IR: n˜ =1633, 2854, 2927, 3401 cmÀ1; MS (ESI) m/z
(%): 236 (7) [(M+2H)/2]+, 941 (41) [2M+H]+, 471 (100) [M+H]+;
HRMS-ESI m/z [M+H]+ calcd for C18H39N4O6S2+: 471.2311, found:
471.2326.
General procedure B: synthesis of amidoxime derivatives: To
a solution of 1,14-tetradecanedial dioxime (11) (1 equiv) in anhy-
drous DMF at 08C under N2 atmosphere was added dropwise a so-
lution of N-chlorosuccinimide (2.4 equiv) in anhydrous DMF. The re-
action was stirred at room temperature for 1 h and then quenched
with cold H2O. Extractions with Et2O were carried out, then the
combined organic layers were washed with brine. After separation,
the organic layer was dried over MgSO4, filtered, and concentrated
under reduced pressure to afford 1,14-bis-(N1,N14-dihydroxyimidoyl-
dichloride)tetradecane (12) as a white powder (90%, crude). This
crude was directly used in the next step without further purifica-
tion: Rf =0.22 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz, MeOD): d=
2.46 (t, J=7.3 Hz, 4H), 1.63 (m, 4H), 1.30 ppm (m, 16H); 13C NMR
(75 MHz, [D6]DMSO): d=162.8, 36.5, 29.3, 29.2, 28.9, 28.3,
26.1 ppm; IR: n˜ =1635, 2848, 2916, 3273 cmÀ1. To a solution of 12
(1 equiv) in anhydrous Et2O at 08C was simultaneously slowly
added Et3N (5 equiv) and 2-iodopropylamine (4 equiv). The reaction
was stirred at room temperature overnight. After completion, the
solvents were removed under reduced pressure. The residue was
taken up in H2O, and CH2Cl2 extractions were carried out. After sep-
aration of the layers, the combined organic layers were washed
with brine, dried over MgSO4, filtered, and evaporated. The remain-
ing residue was taken up in MeOH. An aqueous solution of 37%
HCl was added. The solution was stirred at room temperature for
15 min, and then the solvents were evaporated. The crude product
was subjected to reversed-phase column chromatography with
a step gradient of MeOH (0–30%) in H2O pH 3. The isolated HCl
salt was taken up in MeOH (50 mL) and neutralized by the addition
of a solution of MeONa (5m) in MeOH until pH>7/pH<8. The sol-
vents were then evaporated to afford the desired amidoxime deriv-
ative.
1,12-bis-(N-Ethanesulfonyloxy-N’-methylamidinyl)dodecane 2b:
Using general procedure A, starting from 1,12-bis-(N-hydroxy-N’-
methylamidinyl)dodecane (9a) (0.5 g, 1.6 mmol) and ethanesulfon-
yl chloride (0.38 mL, 4.0 mmol) affording 2b as a colorless oil
(0.459 g, 58%). Rf =0.78 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz,
CDCl3): d=5.23 (m, 2H), 3.33 (q, J=7.4 Hz, 4H), 2.87 (d, J=5.2 Hz,
6H), 2.24 (t, J=7.7 Hz, 4H), 1.59 (m, 4H), 1.39 (t, J=7.4 Hz, 6H),
1.26–1.42 ppm (m, 16H); 13C NMR (75 MHz, CDCl3): d=161.6, 43.1,
29.6, 29.5, 29.2, 28.0, 26.2, 8.1 ppm; IR: n˜ =1632, 2854, 2926,
3401 cmÀ1; MS (ESI) m/z (%): 250 (12) [(M+2H)/2]+, 997 (56) [2M+
H]+, 499 (100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for
C20H43N4O6S2+: 499.2624, found: 499.2633.
1,12-bis-(N-Isopropanesulfonyloxy-N’-methylamidinyl)dodecane
2c: Using general procedure A, starting from 1,12-bis-(N-hydroxy-
N’-methylamidinyl)dodecane (9a) (0.5 g, 1.6 mmol) and 2-propane-
sulfonyl chloride (0.45 mL, 4.0 mmol) affording 2c as a colorless oil
(0.392 g, 50%). Rf =0.78 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz,
CDCl3): d=5.24 (m, 2H), 3.77 (hept, J=6.9 Hz, 2H), 2.87 (d, J=
5.1 Hz, 6H), 2.23 (t, J=7.7 Hz, 4H), 1.58 (m, 4H), 1.42 (t, J=6.9 Hz,
6H), 1.26–1.43 ppm (m, 16H); 13C NMR (75 MHz, CDCl3): d=161.6,
50.0, 29.7, 29.6, 29.3, 28.1, 26.3, 16.6 ppm; IR: n˜ =1632, 2854, 2926,
3399 cmÀ1; MS (ESI) m/z (%): 1053 (7) [2M+H]+, 264 (22) [(M+
2H)/2]+, 527 (100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for
C22H47N4O6S2+: 527.2937, found: 527.2947.
1,12-bis-(N-Ethyl-N’-methanesulfonyloxyamidinyl)dodecane 3a:
Using general procedure A, starting from 1,12-bis-(N-ethyl-N’-hy-
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Orally Available Bis-Alkylamidoxime O-Alkylsulfonate Antimalarials
MED
droxyamidinyl)dodecane (9b) (0.6 g, 1.8 mmol) and methanesul-
fonyl chloride (0.34 mL, 4.4 mmol) affording 3a as a white powder
(0.539 g, 62%). Rf =0.78 (CH2Cl2/MeOH 9:1); mp: 42–438C; H NMR
1,12-bis-(N-2-Methoxyethyl-N’-2-propanesulfonyloxyamidinyl)-
dodecane 4c: Using general procedure A, starting from 1,12-bis-
1
(N-hydroxy-N’-2-methoxyethylamidinyl)dodecane
(9c)
(1.0 g,
(300 MHz, CDCl3): d=5.10 (m, 2H), 3.20 (m 4H), 3.12 (s, 6H), 2.24
(t, J=7.7 Hz, 4H), 1.59 (m, 4H), 1.27 (m, 16H), 1.20 ppm (t, J=
7.2 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=160.9, 37.5, 36.1, 29.6,
2.5 mmol) and 2-propanesulfonyl chloride (0.7 mL, 6.2 mmol) af-
fording 4c as a colorless oil (1.0 g, 67%). Rf =0.76 (CH2Cl2/MeOH
9:1); 1H NMR (300 MHz, CDCl3): d=5.45 (m, 2H), 3.77 (hept, J=
6.9 Hz, 2H), 3.46 (t, J=5.2 Hz, 4H), 3.36 (s, 6H), 3.32 (m, 4H), 2.24
(t, J=7.7 Hz, 4H), 1.57 (m, 4H), 1.43 (d, J=6.9 Hz, 6H), 1.26–
1.39 ppm (m, 16H); 13C NMR (75 MHz, CDCl3): d=160.3, 71.7, 59.0,
49.8, 42.4, 29.5, 29.4, 29.1, 28.3, 26.3, 16.4 ppm; IR: n˜ =1628, 2854,
29.3, 19.7, 28.4, 26.5, 16.0 ppm; IR: n˜ =1615, 2853, 2924 3290 cmÀ1
;
MS (ESI) m/z (%): 250 (14) [(M+2H)/2]+, 997 (17) [2M+H]+, 499
(100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for C20H43N4O6S2
:
+
499.2624, found: 499.2637.
2926, 3421 cmÀ1; MS (ESI) m/z (%): 308 (30) [(M+2H)/2]+, 615
(100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for C26H55N4O8S2
:
+
1,12-bis-(N-Ethanesulfonyloxy-N’-ethylamidinyl)dodecane
3b:
Using general procedure A, starting from 1,12-bis-(N-ethyl-N’-hy-
droxyamidinyl)dodecane (9b) (0.6 g, 1.8 mmol) and ethanesulfonyl
chloride (0.42 mL, 4.4 mmol) affording 3b as a white powder
615.3461, found: 615.3457.
1,12-bis-(N-Benzyl-N’-methanesulfonyloxyamidinyl)dodecane 5a:
Using general procedure A, starting from 1,12-bis-(N-benzyl-N’-hy-
droxyamidinyl)dodecane (9d) (0.7 g, 1.5 mmol) and methanesul-
fonyl chloride (0.29 mL, 3.8 mmol) affording 5a as a colorless oil
(0.471 g, 50%). Rf =0.83 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz,
CDCl3): d=7.24–7.39 (m, 10H), 5.59 (m, 2H), 4.36 (d, J=6.2 Hz,
4H), 3.13 (s, 6H), 2.27 (t, J=7.7 Hz, 4H), 1.60 (m, 4H), 1.24–
1.36 ppm (m, 16H); 13C NMR (75 MHz, CDCl3): d=161.1, 137.7,
129.1, 128.1, 127.0, 46.5, 36.1, 29.6, 29.5, 29.3, 28.4, 26.5 ppm; IR:
n˜ =1627, 2854, 2926, 3397 cmÀ1; MS (ESI) m/z (%): 312 (11) [(M+
1
(0.665 g, 72%). Rf =0.86 (CH2Cl2/MeOH 9:1); mp: 25–268C; H NMR
(300 MHz, CDCl3): d=5.10 (m, 2H), 3.35 (q, J=7.4 Hz, 4H), 3.20 (m,
4H), 2.20 (t, J=7.7 Hz, 4H), 1.55 (m, 4H), 1.39 (t, J=7.4 Hz, 6H),
1.26–1.40 (m, 16H), 1.21 ppm (t, J=7.2 Hz, 6H); 13C NMR (75 MHz,
CDCl3): d=160.8, 43.1, 37.5, 29.7, 29.6, 29.3, 28.4, 26.5, 16.0,
8.2 ppm; IR: n˜ =1628, 2854, 2926, 3384 cmÀ1; MS (ESI) m/z (%): 264
(15) [(M+2H)/2]+, 1053 (25) [2M+H]+, 527 (100) [M+H]+; HRMS-
ESI m/z [M+H]+ calcd for C22H47N4O6S2
: 527.2937, found:
+
527.2950.
2H)/2]2+, 529 (35) [(M-CH3SO3)+H]2+, 623 (100) [M+H]+; HRMS-
ESI m/z [M+H]+ calcd for C30H47N4O6S2
+
: 623.2937, found:
1,12-bis-(N-Ethyl-N’-2-propanesulfonyloxyamidinyl)dodecane 3c:
Using general procedure A, starting from 1,12-bis-(N-ethyl-N’-hy-
droxyamidinyl)dodecane (9b) (0.6 g, 1.8 mmol) and 2-propanesul-
fonyl chloride (0.49 mL, 4.4 mmol) affording 3c as a colorless oil
(0.588 g, 61%). Rf =0.86 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz,
CDCl3): d=5.10 (m, 2H), 3.77 (hept, J=6.9 Hz, 2H), 3.19 (m, 4H),
2.21 (t, J=7.7 Hz, 4H), 1.59 (m, 4H), 1.42 (d, J=6.9 Hz, 6H), 1.25–
1.36 (m, 16H), 1.20 ppm (t, J=7.2 Hz, 6H); 13C NMR (75 MHz,
CDCl3): d=160.8, 50.0, 37.5, 29.7, 29.6, 29.3, 28.4, 26.6, 16.5, 16.0,
ppm; IR: n˜ =1628, 2854, 2926, 3383 cmÀ1; MS (ESI) m/z (%): 1109
623.2944.
1,12-bis-(N-Ethanesulfonyloxy-N’-benzylamidinyl)dodecane 5b:
Using general procedure A, starting from 1,12-bis-(N-benzyl-N’-hy-
droxyamidinyl)dodecane (9d) (0.7 g, 1.5 mmol) and ethanesulfonyl
chloride (0.36 mL, 3.8 mmol) affording 5b as
a colorless oil
(0.696 g, 71%). Rf =0.83 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz,
CDCl3): d=7.24–7.40 (m, 10H), 5.58 (m, 2H), 4.36 (d, J=6.2 Hz,
4H), 3.36 (q, J=7.4 Hz, 4H), 2.27 (t, J=7.7 Hz, 4H), 1.60 (m, 4H),
1.4 (t, J=7.4 Hz, 6H), 1.24–1.43 ppm (m, 16H); 13C NMR (75 MHz,
CDCl3): d=160.8, 137.4, 128.9, 127.9, 126.8, 46.3, 43.0, 29.4, 29.3,
29.1, 28.2, 26.3, 8.0 ppm; IR: n˜ =1626, 2854, 2926, 3393 cmÀ1; MS
(ESI) m/z (%): 326 (13) [(M+2H)/2]+, 651 (100) [M+H]+; HRMS-ESI
m/z [M+H]+ calcd for C32H51N4O6S2+: 651.3250, found: 651.3251.
(13) [2M+H]+, 278 (15) [(M+2H)/2]+, 555 (100) [M+H]+; HRMS-
ESI m/z [M+H]+ calcd for C24H51N4O6S2
: 555.3250, found:
+
555.3250.
1,12-bis-(N-Methanesulfonyloxy-N’-2-methoxyethylamidinyl)do-
decane 4a: Using general procedure A, starting from 1,12-bis-(N-
1,12-bis-(N-2-Propanesulfonyloxy-N’-benzylamidinyl)dodecane
5c: Using general procedure A, starting from 1,12-bis-(N-benzyl-N’-
hydroxyamidinyl)dodecane (9d) (0.7 g, 1.5 mmol) and 2-propane-
sulfonyl chloride (0.42 mL, 3.8 mmol) affording 5c as a white
powder (0.55 g, 55%). Rf =0.83 (CH2Cl2/MeOH 9:1); mp: 95–968C;
1H NMR (300 MHz, CDCl3): d=7.24–7.34 (m, 10H), 5.59 (m, 2H),
4.36 (d, J=6.1 Hz, 4H), 3.80 (hept, J=6.9 Hz, 4H), 2.26 (t, J=7.6 Hz,
4H), 1.60 (m, 4H), 1.40 (d, J=6.9 Hz, 6H), 1.24–1.44 ppm (m, 16H);
13C NMR (75 MHz, CDCl3): d=160.9, 137.7, 129.2, 128.1, 127.0, 50.1,
46.5, 29.7, 29.6, 29.3, 28.5, 26.6, 16.6 ppm; IR: n˜ =1629, 2849, 2923,
3390 cmÀ1; MS (ESI) m/z (%): 340 (13) [(M+2H)/2]+, 679 (100) [M+
H]+; HRMS-ESI m/z [M+H]+ calcd for C34H55N4O6S2+: 679.3563,
found: 679.3558.
hydroxy-N’-2-methoxyethylamidinyl)dodecane
(9c)
(0.5 g,
1.2 mmol) and methanesulfonyl chloride (0.24 mL, 3.1 mmol) af-
fording 4a as a white powder (0.34 g, 49%). Rf =0.76 (CH2Cl2/
MeOH 9:1); mp: 77–788C; 1H NMR (300 MHz, CDCl3): d=5.44 (m,
2H), 3.46 (t, J=5.1 Hz, 4H), 3.37 (s, 6H), 3.32 (m, 6H), 3.12 (s, 6H),
2.25 (t, J=7.8 Hz, 4H), 1.58 (m, 4H), 1.26–1.42 ppm (m, 16H);
13C NMR (75 MHz, CDCl3): d=160.7, 71.6, 59.2, 42.6, 36.1, 29.7, 29.6,
29.3, 28.5, 26.5 ppm; IR: n˜ =1629, 2854, 2926, 3387 cmÀ1; MS (ESI)
m/z (%): 280 (25) [(M+2H)/2]+, 559 (100) [M+H]+; HRMS-ESI m/z
[M+H]+ calcd for C22H47N4O8S2+: 559.2835, found: 559.2844.
1,12-bis-(N-Ethanesulfonyloxy-N’-2-methoxyethylamidinyl)dode-
cane 4b: Using general procedure A, starting from 1,12-bis-(N-hy-
droxy-N’-2-methoxyethylamidinyl)dodecane (9c) (0.5 g, 1.2 mmol)
and ethanesulfonyl chloride (0.30 mL, 3.1 mmol) affording 4b as
a colorless oil (0.38 g, 52%). Rf =0.76 (CH2Cl2/MeOH 9:1); 1H NMR
(300 MHz, CDCl3): d=5.46 (m, 2H), 3.46 (t, J=5.2 Hz, 4H), 3.37 (s,
6H), 3.32 (m, 8H), 2.25 (t, J=7.8 Hz, 4H), 1.57 (m, 4H), 1.40 (t, J=
7.4 Hz, 6H), 1.26–1.42 ppm (m, 16H); 13C NMR (75 MHz, CDCl3): d=
160.6, 71.6, 59.1, 43.1, 42.5, 29.6, 29.5, 29.2, 28.5, 26.4, 8.2 ppm; IR:
n˜ =1628, 2854, 2925, 3388 cmÀ1; MS (ESI) m/z (%): 294 (56) [(M+
2H)/2]+, 587 (100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for
C24H51N4O8S2+: 587.3148, found: 587.3154.
1,12-bis-(N-Methanesulfonyloxy-N’-2-propylamidinyl)dodecane
6a: Using general procedure A, starting from 1,12-bis(N-hydroxy-
N’-2-propylamidinyl)dodecane (9e) (0.5 g, 1.35 mmol) and metha-
nesulfonyl chloride (0.261 mL, 3.37 mmol) affording 6a as a color-
less oil (0.37 g, 52%). Rf =0.85 (CH2Cl2/MeOH 95:5); 1H NMR
(300 MHz, CDCl3): d=4.95 (m, 2H), 3.59 (m, 2H), 3.08 (s, 6H), 2.2 (t,
J=6.4 Hz 4H), 1.56 (m, 4H), 1.23 (m, 16H), 1.16 ppm (d, J=6.5 Hz,
12H); 13C NMR (75 MHz, CDCl3): d=159.8, 44.5, 35.8, 29.4, 29.3,
29.1, 28.9, 28.3, 26.9, 24.5 ppm; IR: n˜ =1637, 2855, 2927,
3275 cmÀ1; MS (ESI) m/z (%): 264 (7) [(M+2H)/2]+, 527 (91) [M+
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H]+; HRMS-ESI m/z [M+H]+ calcd for C22H47N4O6S2+: 527.2937,
found: 527.2945.
Acknowledgements
This work was supported by the European Community Integrated
Project AntiMal (LSHP-CT-2005-018834), MNERT, CNRS, Universitꢀ
Montpellier 1, and Sanofi–Aventis. We are grateful to Marjorie
Maynadier (Universitꢀ de Montpellier II, France) for her assistance
in testing the compounds.
1,12-bis-(N-Ethanesulfonyloxy-N’-2-propylamidinyl)dodecane
6b: Using general procedure A, starting from 1,12-bis-(N-hydroxy-
N’-2-propylamidinyl)dodecane (9e) (0.5 g, 1.4 mmol) and ethane-
sulfonyl chloride (0.32 mL, 3.4 mmol) affording 6b as a colorless oil
(0.46 g, 61%). Rf =0.86 (CH2Cl2/MeOH 9:1); 1H NMR (300 MHz,
CDCl3): d=5.01 (m, 2H), 3.61 (m, 2H), 3.34 (q, J=7.4 Hz, 4H), 2.23
(t, J=7.7 Hz, 4H), 1.58 (m, 4H), 1.26–1.41 (m, 22H), 1.20 ppm (d,
J=6.4 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=160.0, 44.7, 43.1, 24.5,
29.7, 29.6, 29.3, 28.5, 27.0, 8.2 ppm; IR: n˜ =1637, 2854, 2926,
3279 cmÀ1; MS (ESI) m/z (%): 224.2 (17) [([MÀCH3CH2SO3]+2H)/
2]2+, 339.4 (20) [(MÀ2CH3CH2SO3)+H]+, 555.4 (20) [M+H]+, 170.2
(85) [([MÀ2CH3CH2SO3]+2H)/2]2+, 447.4 (100) [(MÀCH3CH2SO3)+
H]+; HRMS-ESI m/z [M+H]+ calcd for C24H51N4O6S2+: 555.3250,
found: 555.3277.
Keywords: antimalarial activity · phospholipids · structure-
activity relationships · parasitemia · prodrugs
[1] World Malaria Report 2010, World Health Organization, Geneva (Switzer-
land), 2009, http://www.who.int/malaria/world_;malaria_report_2010/
en/index.html (accessed April 10, 2012).
[2] Global Report on Antimalarial Efficacy and Drug Resistance 2000–2010,
World Health Organization, Geneva (Switzerland), 2010, http://
www.who.int/malaria/publications/atoz/9789241500470/en/index.html
(accessed April 10, 2012).
1,12-bis-(N-2-Propanesulfonyloxy-N’-2-propylamidinyl)dodecane
6c: Using general procedure A, starting from 1,12-bis-(N-hydroxy-
N’-2-propylamidinyl)dodecane (9e) (0.2 g, 0.5 mmol) and 2-pro-
panesulfonyl chloride (0.15 mL, 1.4 mmol) affording 6c as a color-
less oil (0.15 g, 48%). Rf =0.86 (CH2Cl2/MeOH 9:1); 1H NMR
(300 MHz, CDCl3): d=5.00 (m, 2H), 3.75 (hept, J=6.8 Hz, 2H), 3.59
(m, 4H), 2.20 (t, J=7.7 Hz, 4H), 1.55 (m, 4H), 1.20–1.40 ppm (m,
28H); 13C NMR (75 MHz, CDCl3): d=159.7, 49.7, 44.5, 29.5, 29.4,
29.1, 28.3, 26.0, 24.3, 16.3 ppm; IR: n˜ =1637, 2854, 2926,
3279 cmÀ1; MS (ESI) m/z (%): 292.2 (16) [(M+2H)/2]2+, 461.4 (71)
[(MÀ(CH3)2CHSO3)+H]+, 583.4 (100) [M+H]+; HRMS-ESI m/z [M+
H]+ calcd for C26H55N4O6S2+: 583.3563, found: 583.3542.
[3] N. J. White, Lancet 2010, 376, 2051.
[4] A. M. Dondorp, F. Nosten, P. Yi, D. Das, A. P. Phyo, J. Tarning, K. M. Lwin,
F. Ariey, W. Hanpithakpong, S. J. Lee, P. Ringwald, K. Silamut, M.
Imwong, K. Chotivanich, P. Lim, T. Herdman, S. S. An, S. Yeung, P. Sin-
ghasivanon, N. P. Day, N. Lindegardh, D. Socheat, N. J. White, N. Engl. J.
Med. 2009, 361, 455.
[5] M. L. Ancelin, M. Calas, J. Bompart, G. Cordina, D. Martin, M. Ben Bari, T.
Jei, P. Druilhe, H. J. Vial, Blood 1998, 91, 1426.
[6] M. L. Ancelin, M. Calas, V. Vidal-Sailhan, S. Herbute, P. Ringwald, H. J.
Vial, Antimicrob. Agents Chemother. 2003, 47, 2590.
[7] M. L. Ancelin, M. Calas, A. Bonhoure, S. Herbute, H. J. Vial, Antimicrob.
Agents Chemother. 2003, 47, 2598.
[8] H. Vial, M. Calas, R. Escale, V. Vidal, F. Bressolle, M. L. Ancelin, (CNRS)
WO/2004/009068, 2004.
[9] A. Hamzꢀ, E. Rubi, P. Arnal, M. Boisbrun, C. Carcel, X. Salom-Roig, M.
Maynadier, S. Wein, H. Vial, M. Calas, J. Med. Chem. 2005, 48, 3639.
[10] M. Calas, M. L. Ancelin, G. Cordina, P. Portefaix, G. Piquet, V. Vidal-Sail-
han, H. Vial, J. Med. Chem. 2000, 43, 505.
[11] H. J. Vial, S. Wein, C. Farenc, C. Kocken, O. Nicolas, M. L. Ancelin, F. Bres-
solle, A. Thomas, M. Calas, Proc. Natl. Acad. Sci. USA 2004, 101, 15458.
[12] K. Wengelnik, V. Vidal, M. L. Ancelin, A. M. Cathiard, J. L. Morgat, C. H.
Kocken, M. Calas, S. Herrera, A. W. Thomas, H. J. Vial, Science 2002, 295,
1311.
1,12-bis-(N-Methanesulfonyloxy-N’-pyrrolidinylamidinyl)dode-
cane 7a: Using general procedure A, starting from 1,12-bis-(N-hy-
droxy-N’-pyrrolidinylamidinyl)dodecane (9 f) (0.3 g, 0.76 mmol) and
methanesulfonyl chloride (0.15 mL, 1.90 mmol) affording 7a as
a colorless oil (0.2 g, 47%). Rf =0.87 (CH2Cl2/MeOH 95:5); 1H NMR
(300 MHz, CDCl3): d=3.40 (m, 2H), 3.09 (m, 8H), 2.48 (t, J=8.7 Hz,
4H), 1.89 (m, 8H), 1.80 (m, 4H), 1.41 (m, 12H), 1.16 ppm (m, 16H);
13C NMR (75 MHz, CDCl3): d=166.7, 46.9, 35.7, 29.7, 29.6, 29.5, 29.2,
26.3, 25.2 ppm; IR: n˜ =1627, 2854, 2926, 3279 cmÀ1; MS (ESI) m/z
(%): 551.3 (100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for
C24H47N4O6S2+: 551.2932, found: 551.2943.
1,12-bis-(N-Ethanesulfonyloxy-N’-pyrrolidinylamidinyl)dodecane
7b: Using general procedure A, starting from 1,12-bis-(N-hydroxy-
N’-pyrrolidinylamidinyl)dodecane (9 f) (0.3 g, 0.76 mmol) and etha-
nesulfonyl chloride (0.18 mL, 1.90 mmol) affording 7b as a colorless
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61.
1
oil (0.242 g, 55%). Rf =0.74 (CH2Cl2/MeOH 95:5); H NMR (300 MHz,
CDCl3): d=5.10 (m, 2H), 3.40 (m, 2H), 3.09 (m, 8H), 2.48 (t, J=
8.7 Hz, 4H), 1.89 (m, 8H), 1.87 (m, 4H), 1.39 (m, 12H), 1.25 ppm (m,
16H); 13C NMR (75 MHz, CDCl3): d=166.4, 46.7, 45.7, 24.7–
29.7 ppm; IR: n˜ =1627, 2854, 2926, 3279 cmÀ1; MS (ESI) m/z (%):
579.3 (100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for
C26H51N4O6S2+: 579.3245, found: 579.3259.
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33, 1740.
1,12-bis-(N-2-Propanesulfonyloxy-N’-pyrrolidinylamidinyl)dode-
cane 7c: Using general procedure A, starting from 1,12-bis-(N-hy-
droxy-N’-pyrrolidinylamidinyl)dodecane (9 f) (0.3 g, 0.76 mmol) and
2-propanesulfonyl chloride (0.21 mL, 1.9 mmol) affording 7c as
a colorless oil (0.2 g, 42%). Rf =0.74 (CH2Cl2/MeOH 95:1); 1H NMR
(300 MHz, CDCl3): d=3.79 (m, 2H), 3.29 (m, 8H), 2.48 (t, J=8.7 Hz,
4H), 1.89 (m, 8H), 1.52 (m, 4H), 1.41 (d, J=6.9 Hz, 12H), 1.25 ppm
(m, 16H), 13C NMR (75 MHz, CDCl3): d=166.5, 49.6, 46.9, 16.6–
29.8 ppm; IR: n˜ =1637, 2855, 2927, 3279 cmÀ1; MS (ESI) m/z (%):
607.9 (100) [M+H]+; HRMS-ESI m/z [M+H]+ calcd for
C28H55N4O6S2+: 607.8890, found: 607.8896.
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These are not the final page numbers!

Orally Available Bis-Alkylamidoxime O-Alkylsulfonate Antimalarials
MED
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L. L. Bostrom, J. Liu, C. A. Higley, F. W. Rankin, A. E. Tobin, G. Emmett,
G. K. Lalka, J. Y. Sze, S. V. D. Meo, S. A. Mousa, M. J. Thoolen, A. L. Raca-
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[32] M40: 1H NMR (300 MHz, CD3OD): d=1.24 (d, J=6.5 Hz, 12H), 1.20–1.45
(m, 16H), 1.65 (m, 4H), 2.14 (q, J=7.9 Hz, 4H), 3.78 ppm (hept, J=
6.5 Hz, 4H); 13C NMR (75 MHz, CD3OD): d=20.0, 27.2, 28.4, 28.8, 29.1,
29.2, 32.8, 44.5, 166.8 ppm; MS (ESI) m/z (%): 339 (100) [M+H]+. M40:
1H NMR (300 MHz, CD3OD): d=1.24 (d, J=6.5 Hz, 12H), 1.20–1.45 (m,
16H), 1.65 (m, 4H), 2.14 (q, J=7.9 Hz, 4H), 3.78 ppm (hept, J=6.5 Hz,
4H); 13C NMR (75 MHz, CD3OD): d=20.0, 27.2, 28.4, 28.8, 29.1, 29.2,
32.8, 44.5, 166.8 ppm; MS (ESI) m/z (%): 339 (100) [M+H]+.
[44] M64: IC50 =9.3 nm, ED50 i.p.=3.1 mgkgÀ1, ED50 p.o.>200 mgkgÀ1
.
[45] M40AH: IC50 =5850 nm, ED50 i.p.>10 mgkgÀ1, ED50 p.o.>90 mgkgÀ1
.
M38AH: IC50 =67.5 nm, ED50 i.p.=5 mgkgÀ1, ED50 p.o.>90 mgkgÀ1
[46] A. Le Berre, C. Renault, C. R. Acad. Sci. 1964, 259, 176.
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[33] M34: IC50 =0.3 nm; M44: IC50 =14.4 nm; M45: IC50 =9.4 nm, ED50 i.p.=
6.3 mgkgÀ1
;
M42: IC50 =9.2 nm, ED50 i.p.=8 mgkgÀ1
;
M46: IC50
4.6 nm; M40: IC50 =31 nm, ED50 i.p.=4.1 mgkgÀ1; M38: IC50 =0.75 nm,
ED50 i.p.=1.3 mgkgÀ1
=
.
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Received: February 28, 2012
Revised: April 3, 2012
Published online on && &&, 0000
ChemMedChem 0000, 00, 1 – 12
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
&
11
&
ÞÞ
These are not the final page numbers!

FULL PAPERS
M. Degardin, S. Wein, S. Gouni,
C. Tran Van Ba, J.-F. Duckert, T. Durand,
R. Escale, H. Vial, Y. Vo-Hoang*
Improved bioavailability: Bis-alkylami-
dines were originally developed as po-
tential new antimalarial agents that
target phospholipid metabolism, but
these compounds are not orally bio-
available. To solve this issue, 25 sulfo-
nates were investigated as prodrug can-
didates. Their antimalarial activities were
evaluated in vitro and in vivo to define
structure–activity relationships.
&& – &&
Evaluation of Bis-Alkylamidoxime O-
Alkylsulfonates as Orally Available
Antimalarials
&12
&
www.chemmedchem.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 0000, 00, 1 – 12
ÝÝ
These are not the final page numbers!