Probing structure/affinity relationships for the Plasmodium falciparum hexose transporter with glucose derivatives

Article abstract of DOI:10.1016/j.bmcl.2005.11.068

A series of 3-O-substituted glucose derivatives was prepared with alkyl, alkenyl, aromatic and ferrocenic substituents; to vary lipophilicity and hydrogen bonding ethylenedioxy and perfluorinated fragments were also introduced. Apparent affinities for the Plasmodium falciparum hexose transporter (PfHT) were determined after heterologous expression in Xenopus oocytes, with highest affinities for compounds with C8-C13 lipophilic chains. As no derivatives show significant affinity for the mammalian glucose transporter (GLUT1), these structure/affinity assays contribute to design of potent PfHT inhibitors and eventual development of antimalarials.

Full text of DOI:10.1016/j.bmcl.2005.11.068

Bioorganic & Medicinal Chemistry Letters 16 (2006) 1267–1271
Probing structure/affinity relationships for the Plasmodium
falciparum hexose transporter with glucose derivatives
Martine Fayolle,a Marina Ionita,a Sanjeev Krishna,b
Christophe Morina,* and Asha Parbhu Patelb
aLaboratoire d’Etudes Dynamiques et Structurales de la Se´lectivite´ (LEDSS), UMR 5616 (IFR 2607),
`
Universite´ Joseph Fourier Grenoble 1, 38402 St Martin d’Heres, France
bSt. George’s University of London, Centre for Infection, Division of Cellular and Molecular Medicine,
Cranmer Terrace, London SW17 ORE, UK
Received 28 October 2005; revised 17 November 2005; accepted 18 November 2005
Available online 19 December 2005
Communicated by Stephen Neidle
Abstract—A series of 3-O-substituted glucose derivatives was prepared with alkyl, alkenyl, aromatic and ferrocenic substituents; to
vary lipophilicity and hydrogen bonding ethylenedioxy and perfluorinated fragments were also introduced. Apparent affinities for
the Plasmodium falciparum hexose transporter (PfHT) were determined after heterologous expression in Xenopus oocytes, with high-
est affinities for compounds with C8–C13 lipophilic chains. As no derivatives show significant affinity for the mammalian glucose
transporter (GLUT1), these structure/affinity assays contribute to design of potent PfHT inhibitors and eventual development of
antimalarials.
ꢀ 2005 Elsevier Ltd. All rights reserved.
In view of the increasing resistance to conventional anti-
malarials, new drugs and new targets are urgently being
sought for malaria.1,2 Plasmodium falciparum depends
on a continuous supply of glucose from its mammalian
host for its energy requirements during asexual replica-
tion. During this stage of its life-cycle, P. falciparum
grows and multiplies within red cells. In comparison
with uninfected red cells, parasites increase utilisation
of glucose by up to 100 times. Delivery of this glucose
to the intraerythrocytic parasite is mediated by PfHT,
a parasite-encoded facilitative transporter that is local-
ised to the region of the parasite plasma membrane.3,4
Heterologous expression of PfHT in Xenopus laevis
oocytes has allowed studies on its substrate specificity
as well as comparisons with the major mammalian hex-
ose transporter, GLUT 1, which is found on the surface
of erythrocytes. Mammalian GLUTs are usually specia-
lised to transport either glucose or fructose, whereas
PfHT can mediate uptake of both substrates. These
studies have also established that some 3-O derivatives
of glucose can selectively inhibit PfHT and rapidly dis-
rupt intraparasitic homeostasis.5 Exposure of parasites
in culture to one derivative (CM3361, see structure 1)
kills parasites in concentrations that do not disrupt host
red cells, validating PfHT as a new drug target and
opening up a new approach to identify antimalarial
agents.2 The aim of this work was to extend our insights
into structure/affinity relationships of substrates that
may interact with PfHT, so that results can be used to
inform improvements in design of antimalarials aimed
at PfHT.
Evidence that 1, a glucose derivative in which an
undecenyl side chain is attached to O-3, inhibits PfHT5
was the starting point from which to explore several
aspects:
• Is the methylene chain of 1 of an optimal length?
• Would reduced compounds (i.e., without double
bonds) retain comparable affinities?
• What would be the effects of changes in the lipophil-
icity/hydrophilicity?
Keywords: Glucose; Carbohydrate transporters; PfHT; Inhibitors;
Malaria.
To address these questions, we have prepared glucose
derivatives of different types (3–17, 21–29, 32–34, 37
*
Corresponding author. E-mail: christophe.morin@ujf-grenoble.fr
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.11.068

1268
M. Fayolle et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1267–1271
and 40) and determined their apparent affinities for
PfHT.
bearing a phenyl group were also prepared: in 21 and 22
at the terminal position, and in 23 on the chain, using
relevant bromides.11,12 Ferrocenyl groups13 were also
introduced (24 and 25) after alkylation of 2 with the
appropriate ferrocenyl bromides,14 which was followed
by cleavage of the acetals (Scheme 1).
3-O-Glucose derivatives can be obtained, as depicted in
general Scheme 1, by alkylation of the sodium salt of
diacetone-D-glucose (2), followed by deprotection of
the acetals. The synthesis of alkyl derivatives 3–116 is
straightforward since the required bromides are com-
mercially available. To obtain the lower (12) and higher
(14 and 15) homologues of 1, it was found advantageous
to mono-alkylate first 2 with a,x-dibromoalkanes and
then to generate the double bond by base-promoted
elimination of the remaining bromide (Scheme 2). For
the synthesis of 13, the alkylating agent was derived7
from commercially available dec-9-en-1-ol. Derivatives
16 and 17 in which the unsaturation lies within the chain
were also considered; to prepare 16, the required bro-
mide was obtained by alkylation8 of dec-1-yne with
1-6-dibromohexane; for the preparation of 17, threo-
aleuritic acid (18) was converted into alkene 19,9 which
was then transformed into x-iodo-ester 2010 (Scheme 3)
with which 2 was alkylated (Scheme 1). Three analogues
To increase the hydrophilicity of the methylene chain,
analogues of 1 (i.e., 26–29) in which one or two oxygen
atoms are in the chain were prepared. 1,7-Heptanediol
was mono-O-allylated and the remaining hydroxyl
group converted into an iodide15 (Scheme 4); its reaction
with 2 was followed by deprotection of the acetals,
which afforded 26. For the synthesis of 27, 2 was first
converted to the hydroxyethyl derivative 30,16 which
was alkylated with x-bromo-hept-1-ene and deprotec-
ted. For the preparation of 28 and 29, since there is an
oxygen atom b to the leaving group,17 triflate 31 was
selected as the alkylating agent and was prepared from
O-allyl-ethylene glycol18 (Scheme 4). Compound 31
was used to alkylate 2 and 30, which afforded 28 and
29, respectively, after acidic cleavage of the acetals.
CH2OH
O
O
1) NaH, RX, DMF
HO
O
OH
OR
OH
2) H +
O
OH
O
1: R = -(CH2)9-CH=CH2
2
Scheme 1. Preparation of 3-O-substituted-D-glucose.
(CH2)n-CH2=CH2
(CH2)n-CH2-CH2-Br
O
O
O
O
O
O
i
ii
2
O
O
O
O
Scheme 2. Reagents and conditions: (i) 1—NaH, DMF; 2—Br-(CH2)n-CH2CH2-Br (1.2 equiv); (ii) K-tert-butylate, THF, 50 ꢁC, 4 h.
(CH2)7-COOH
i
HO-(H2C)6
HO
E
ii
HO-(CH2)6-CH=CH-(CH2)7-COOH
I-(CH2)6-CH=CH-(CH2)7-COOCH3
OH
(+)-18
19
20
Scheme 3. Reagents and conditions: (i) triethylorthoformate see Ref. 9; (ii) 1—CH3COCl–CH3OH—67%; 2—MsCl–Et3N—98%; 3—NaI, acetone,
overnight reflux 94%.
I-(CH2)7-O-CH2-CH=CH2
ii (n=7)
iii (n=2)
i
HO-(CH2)n-OH
HO-(CH2)n-O-CH2-CH=CH2
CF3SO2-O-CH2CH2-O-CH2-CH=CH2
31
Scheme 4. Reagents and conditions: (i) NaH, allyl bromide, see Ref. 15; (ii) 1—TsCl (85%); 2—NaI (90%); (iii) Tf2O (1 equiv), diisopropylethyl
amine (0.95 equiv), CH2Cl2, À20 ꢁC, 57%.

M. Fayolle et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1267–1271
1269
13
In view of the profound changes in lipophilicity and
hydrogen bonding brought about by introduction of
fluorinated fragments,19 fluorinated derivatives were
prepared; 32 and 33 were obtained after the addition20
of perfluorohexyl iodide to alkenyl derivatives (Scheme
5) followed by reduction, whereas 34 was obtained by
acylation of amine 3521,22 with perfluoroheptanoyl chlo-
ride.23 These reactions were followed by cleavage of the
acetals.
(3J–CH@CH– = 15.8 Hz) in the C–1H satellite peaks.25
The saturated analogue 39 was obtained by hydrogena-
tion, and both compounds were submitted to acid treat-
ment, which yielded 37 and 40, respectively.
All the prepared analogues (except for 11, which was not
soluble enough) were tested for their ability to inhibit
uptake of D-glucose mediated by PfHT expressed in
Xenopus oocytes. Apparent inhibitory constants were
derived after curve fitting (Prism, Graphpad v4.0) using
parameters for one-site competition and the table dis-
plays affinities for PfHT.
Finally, the preparation of a Ôdimer’ of 1 (see structure
37 in which two glucose units are linked by a 20-carbon
chain in a symmetrical way) was considered. To obtain
the same, 36 was subjected to cross-metathesis, using
type-II Grubbs catalyst24 which led to 38 (Scheme 6);
the configuration of the double bond was determined
as Z after the observation of a large coupling constant
At the onset of this work, it was known that affinities for
PfHT of Ôshort chain’ analogues of 1 (i.e., O-3 methyl,
ethyl, benzyl and hydroxyethyl derivatives)5 were low
(Ki in the 1–15 mmol range) and even lower compared
O
HO
O(CH2)nCH=CH2
O
O
O(CH2)nCH2CH2C6F13
ii
O
OH
O
O
OH
i
OH
O
O
32 (n = 1)
33 (n = 5)
iii
2
OCH2CH2OH
O
O
iv
O
30
O
HO
OCH2CH2CH2NHCOC6F13
OCH2CH2CH2NH2
O
O
O
v
OH
O
O
OH
OH
35
34
Scheme 5. Reagents and conditions: (i) NaH, Br(CH2)nCH@CH2; (ii) 1—I-C6F13, triphenylphosphine; 2—LAH (n = 1: see Ref. 20); 3—H+; (iii)
1—BrCH2COOC2H5; 2—LAH see Ref. 16; (iv) 1—NaH, DMF, Br-(CH2)3-NH-Cbz—58%; 2—H2, Pd/C; (v) 1—C6F13COCl, Huning’s base,
4 days—43%; 2—H+.
O
O
(CH2)9-A-(CH2)9
O
O
O
O
O
O
(CH2)9-CH2=CH2
O
O
O
O
O
O
O
i
Z
38 A : CH=CH
ii
O
39 A : CH2CH2
iii
O
36
(CH2)9-A-(CH2)9
OH
CH2OH
CH2OH
O
O
OH
Z
O
OH
O
37 A : CH=CH
40 A : CH2CH2
OH
OH
OH
Scheme 6. Reagents and conditions: (i) Grubbs type-II catalyst, CH2Cl2, 40 ꢁC, 48 h—59%; (ii) H2–Pd/C; (iii) H+.

1270
M. Fayolle et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1267–1271
Table 1. Ki/inhibition test for D-glucose uptake of various 3-O-D-
glucose derivatives against PfHT
presumably through the mechanism of increased hydro-
phobicity brought about by fluorinated fragments—
fluorine being a polar hydrophobic element.19 Converse-
ly, it is noteworthy that when hydrophilicity is increased,
as in compounds 26–29 in which an oxygen replaces car-
bon atoms in the chain,26 affinity is also decreased. All
these data show that a C8–C13 lipophilic chain should
be present in the substituent for it to inhibit PfHT-med-
iated glucose uptake in oocytes, which is the main con-
clusion which can be drawn from the affinity
measurements.
Compound R (O-3-substituent)
Kia (mM)
1
3
–(CH2)9–CH@CH2
–(CH2)6–CH3
–(CH2)7CH3
0.053 0.019
<0.5
4
0.030; 0.049b
0.035; 0.032b
0.029; 0.019b
0.023 0.002
0.030 0.008
>0.5
5
–(CH2)8–CH3
–(CH2)9–CH3
6
7
–(CH2)10–CH3
–(CH2)11–CH3
8
9
–(CH2)13–CH3
–(CH2)17–CH3
–(CH2)19–CH3
10
11
12
13
14
15
16
17
21
22
23
24
25
26
27
28
29
32
33
34
37
40
>0.5
c
Importantly, none of the derivatives displayed in the
table inhibited GLUT1 (the ubiquitous human glu-
cose transporter) at concentrations effective against
PfHT and the selectivity of 1 and congeners for
PfHT thus appears to be a salient feature of 3-O-
substituted glucose derivatives. Since the presence of
a C8–C13 lipophilic chain27 correlates with inhibition,
our structure–function analyses of the molecular
requirements for inhibition of the critical hexose
transporter of P. falciparum reinforce the Ôlollypop’
model previously put forward.5 This will hopefully
assist in the design of more potent inhibitors that
can be used as templates for drug design of carbohy-
drate-based antimalarials.
–(CH2)7–CH@CH2
–(CH2)8–CH@CH2
–(CH2)10–CH@CH2
–(CH2)13–CH@CH2
–(CH2)8–X–(CH2)7–COOCH3
0.041 0.002
0.049 0.004
0.036 0.004
0.037 0.009
>0.5
d
e
–(CH2)6–CH@CH–(CH2)7–CH3
–(CH2)5–C6H5
–(CH2)8–C6H5
>0.5
0.072; 0.064b
0.148 0.026
0.081
f
–(CH2)5–C6H4–(CH2)3–CH3
–(CH2)6–Fcg
–(CH2)11–Fcg
>0.5
NI
–(CH2)7–O–CH2–CH@CH2
–(CH2)2–O–(CH2)7–CH@CH2
–(CH2)2–O–CH2–CH@CH2
>0.5
0.590 0.072
>0.5
–(CH2)2–O(–CH2)2–O–CH2–CH@CH2 NI
–(CH2)3–(CF2)5–CF3
–(CH2)7–(CF2)5–CF3
–(CH2)3–NHCO–(CF2)5–CF3
Unsaturated Ôdimer’i
Saturated Ôdimer’i
>0.5
0.13h
NI
0.25; 0.14b
0.56; 0.54b
References and notes
a Values are means of three experiments (standard error of the mean
given) unless otherwise noted.
b Two experiments (i.e., two individual values).
c Too insoluble for assay. NI no inhibition.
d X denotes triple bond.
e Configuration of double bond is E.
f para-Isomer.
g Fc stands for ferrocene.
h Insufficient material to carry out repeats.
i For structures, see Scheme 6.
1. For reviews, see inter alia: (a) Ridley, R. G. Nature 2002,
415, 686; (b) Wiesner, J.; Ortmann, R.; Jomaa, H.;
Schlitzer, M. Angew. Chem., Int. Ed. Engl. 2003, 42,
5274; (c) Go, M.-L. Med. Res. Rev. 2003, 23, 456; (d)
Delhaes, L.; Benoit-Vical, F.; Camus, D.; Capron, M.;
Meunier, B. Drugs 2003, 6, 674; (e) Waters, N. C.; Dow, S.
G.; Kozar, M. P. Expert Opin. Ther. Pat. 2004, 14, 1125;
(f) Staines, H.; Ellory, J. C.; Chibale, K. Comb. Chem.
High Throughput Screening 2005, 8, 81.
2. Joe¨t, T.; Morin, C.; Fischbarg, J.; Louw, A. I.; Eckstein-
Ludwig, U.; Woodrow, C.; Krishna, S. Expert Opin. Ther.
Targets 2003, 7, 593.
with D-glucose; this led us to consider higher homo-
logues and hence the derivatives presented in the Table
1. As affinities in the 20–50 lM range are recorded for
4–7 (alkyl) and 12–15 (alkenyl) C8–C13 derivatives but
not for longer-chain derivatives (i.e., 9–11, 16 and 17),
this clearly shows that the chain length of the substituent
is important. A comparison of compounds with the
same substituent length but differing in the presence of
a terminal double bond (7 vs 1, 5 vs 12, 6 vs 13 and 8
vs 14) shows minimal consequences; however, in the case
of a longer chain (9 vs 15), the affinity is restored when a
terminal double bond is introduced. With regard to Ôdi-
mers’ 37 and 40 (which can be viewed as two hydrophilic
groups linked by a lipophilic chain) there is a ca. 10-fold
decrease in their affinities when compared to that of 1
(the parent compound). The introduction of an aromat-
ic ring, whether in the end position (21 and 22) or not
(23), decreases the affinity as well, whereas the presence
of ferrocenyl groups (24 and 25) results in loss of inhibi-
tion. Perfluorinated derivatives (32 and 34) do not
exhibit interaction with PfHT, or interact poorly (33),
3. Woodrow, C. J.; Penny, J. I.; Krishna, S. J. Biol. Chem.
1999, 274, 7272.
4. Woodrow, C. J.; Burchmore, R. J. S.; Krishna, S. Proc.
Natl. Acad. Sci. U.S.A. 2000, 97, 9931.
5. Joe¨t, T.; Eckstein-Ludwig, U.; Morin, C. Proc. Natl. Acad.
Sci. U.S.A. 2003, 100, 7476.
6. For the preparation of O-3 alkyl glucose, see, for example:
Ikegawa, T.; Irinoda, K.; Saze, K.; Katori, T.; Matsuda, H.;
Ohkawa, M.; Kosik, M. Chem. Pharm. Bull. 1987, 35, 2894.
7. Fryxell, G. E.; Rieke, P. C.; Wood, L. L.; Engelhard, M. H.;
Williford, R. E.; Graff, G. L.; Campbel, A. A.; Wiacek, R.
J.; Lee, L.; Halverson, A. Langmuir 1996, 12, 5064.
8. Kates, M. J.; Schaube, J. H. J. Org. Chem. 1996, 61, 4164.
9. Singh, A. N.; Mhaskar, V. V.; Dev, S. Tetrahedron 1978,
34, 595.
10. For another synthesis, see: Subramanian, G. B. V.; Ahua,
S. Indian J. Chem. 1996, 35B, 724.
11. a,x-Dibromoalkanes with phenyllithium: Spencer, T. A.;
Onafrey, T. J.; Cann, R. O.; Russel, J. S.; Lee, L. E.;
Blanchard, D. E.; Castro, A.; Gu, P.; Jiang, G.; Shechter,
I. J. Org. Chem. 1999, 64, 807.
12. a,x-Dibromoalkanes with p-butylphenylmagnesium bro-
mide: Nishimura, J.; Yamada, N.; Horiuchi, Y.; Ueda, E.;

M. Fayolle et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1267–1271
1271
Onbayashi, A.; Oku, A. Bull. Chem. Soc. Jpn. 1986, 59,
2035.
13. For a review about antimalarials based on ferrocene, see:
Biot, C. Curr. Med. Chem. 2004, 3, 1.
14. Yu, C. J.; Wang, H.; Wang, Y.; Yowanto, H.; Kim, J. C.;
Donilon, L. H.; Tao, C.; Strong, M.; Chong, Y. J. Org.
Chem. 2001, 66, 2937.
15. The intermediate tosylate is a known compound: Toepfer,
A.; Ktretzchmar, G.; Schuth, S.; Sonnetag, M. Bioorg.
Med. Chem. Lett. 1997, 7, 1317.
Valltibera, A. Tetrahedron 2002, 58, 4061; (c) Yu, B.;
Li, B.; Zhang, J.; Hui, Y. Tetrahedron Lett. 1998, 39,
4871.
21. Compound 34 was obtained by alkylation of 2 with N-
benzyloxy-carbonyl-3-bromopropylamine (prepared acc-
ording to Robarge, M. J.; Husbands, S. M.; Kyieltyka, A.;
Brodbeck, R.; Thurkauf, A.; Newman, A. H. J. Med.
Chem. 2001, 44, 3175, ) and reduction.
22. For another preparation, see: Corbett, W. M. J. Chem.
Soc. 1961, 2926.
16. Bignan, G.; Morin, C.; Vidal, M. Carbohydr. Res. 1993,
248, 371.
23. Afzal, J.; Fung, B.-M.; O’Real, E. A. J. Fluorine Chem.
1987, 34, 385.
17. b-Iodo-ethers are reluctant to displacement reactions (see
Ref. 16 and refs. therein) and this peculiar stability has
resulted in their use for radio-labelling; see: (a) Hamant,
S.; Mathieu, J.-P.; Morin, C.; Trimcev, I.; Vidal, M.
Bioorg. Med. Chem. Lett. 1994, 4, 1687; (b) Rossouw, D.
D.; Coenen, H. H. Nucl. Med. Biol. 2003, 30, 373.
18. Lee, G. H.; Choi, E. B.; Lee, E.; Pak, C. S. J. Org. Chem.
1996, 59, 1428.
19. For recent reviews: (a) Biffinger, J. C.; Kim, H. W.;
DiMagno, S. ChemBioChem 2004, 5, 622; (b) Bo¨hm, H.-J.;
Banner, D.; Kansy, M.; Kuhn, B.; Muller, K.; Stahl, U.;
¨
Obst-sander, M. ChemBioChem 2004, 5, 637.
20. (a) Huang, W.-Y.; Zhang, H.-Z. J. Fluorine Chem. 1990,
50, 133; (b) Lumbierres, M.; Moreno-Manas, M.;
24. Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R.
H. J. Am. Chem. Soc. 2003, 125, 11360.
25. In R–13CH@12CH–R, due to the presence of differing
carbon isotopes, the symmetry is disrupted, which
allows the observation of coupling constants. We thank
J. Garcia for theoretical simulation of the spectra of E
and Z isomers.
26. The presence of ethylenedioxy fragments is known to
increase aqueous solubility.
27. Of interest are the recent results (Liu, Y.; Wong, V. K.- W.;
Ko, B. C.-B.; Wong, M.-K.; Che, C.-M. Org. Lett. 2005, 7,
1561), obtained with artemisinin derivatives in which
introduction of lipophilic chains resulted in an up to 200-
fold increase in activities.