M. C. Lombard et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1683–1686
1685
Table 1
In vitro antiplasmodial activity and cytotoxicity of synthesized artemisinin hybrids
Compound
D10: IC50 (nM)
SD
Dd2: IC50 (nM)
SD
RI
CHO: IC50
(lM)
SD
SI
9
84.59
21.49
117.76
14.27
30.39
17.25
12.18
14.94
30.72
201.38
28.99
21.54
5.11
2.22
0.13
16.27
2.65
2.71
1.06
1.21
0.05
1.85
19.92
2.70
6.73
0.64
ND
152.80
25.70
183.49
19.75
69.21
30.22
17.12
20.76
68.49
275.99
29.24
157.90
2.09
2.06
1.09
5.68
0.25
2.02
12.22
0.44
3.61
4.19
70.52
3.26
52.70
0.33
ND
2
1
2
1
2
2
1
1
2
1
1
7
0.4
ND
33.04
1.64
37.34
0.17
ND
35.18
3.39
2.75
5.92
ND
3.24
0.08
14.09
0.01
ND
20.14
0.83
0.12
0.88
ND
391
77
317
12
9
1
1
1
1
1
1
1
1
1
a
0
0a
1
1a
ND
2039
279
184
193
ND
80
ND
ND
ND
a
2
2a
3
4
4a
a
a
2.32
ND
ND
0.10
ND
ND
CQ (n = 3)
DHA (n = 4)
Emetine (n = 3)
ND
ND
0.19
0.05
a
Tested as a suspension. n = Number of data sets averaged. Resistance index (RI) = IC50 Dd2/IC50 D10. Selectivity index (SI) = IC50 CHO/ IC50 D10. CHO = Chinese Hamster
Ovarian. SD = standard deviation. ND = not determined.
1
2a, and 14a displayed the best antimalarial activity (Table 1).
References and notes
These compounds showed comparable potency to CQ against
the CQS strain, D10, and were found more potent than CQ
1
2
3
.
.
.
Kaur, K.; Jain, M.; Reddy, R. P.; Jain, R. L. Eur. J. Med. Chem. 2010, 45, 3245.
Meunier, B. Acc. Chem. Res. 2008, 41, 69.
Walsh, J. J.; Coughlan, D.; Heneghan, N.; Gaynor, C.; Bell, A. Bioorg. Med. Chem.
Lett. 2007, 17, 3599.
Varotti, F. d. P.; Botelho, A. C. C.; Andrade, A. A.; De Paula, R. C.; Fagundes, E. M.
S.; Valverde, A.; Mayer, L. M. U.; Mendonca, J. S.; De Souza, M. V. N.; Boechat, N.;
Krettli, A. U. Antimicrob. Agents Chemother. 2008, 52, 3868.
(
IC50 = 157.9 nM) against the CQR strain, Dd2, of P. falciparum,
with IC50 ranging from 17.2 to 38.9 nM. Compounds 12 and
2a displayed the best profile based on both antiplasmodial
4.
1
activity and cytotoxicity. Compounds 11, 11a and 13 showed
good activity against the CQS strain, but were less active against
the CQR strain of P. falciparum—indicated by the resistance index
RI P 2. Compounds 12, 13, and 14 were tested as suspensions in
DMSO, due to insolubility in the medium.
Overall the oxalates had better antiplasmodial activity than
their free base hybrids, presumably due to their better aqueous sol-
ubility in the testing medium. Oxalic acid could also inherit anti-
malarial activity, but also add to the toxicity of a compound.
Slight cytotoxicity was observed with the oxalate salt of compound
5. Dechy-Cabaret, O.; Benoit-Vical, F.; Loup, C.; Robert, A.; Gornitzka, H.;
Bonhoure, A.; Vial, H.; Magnaval, J.; Séguéla, J.; Meunier, B. Chem. Eur. J.
2004, 10, 1625.
6
.
Araújo, N. C. P.; Barton, V.; Jones, M.; Stocks, P. A.; Ward, S. A.; Davies, J.; Bray, P.
G.; Shone, A. E.; Cristiano, M. L. S.; O’Neill, P. M. Bioorg. Med. Chem. Lett. 2009,
19, 2038.
7
8
9
.
.
.
Paitayatat, S.; Tarnchompoo, B.; Thebtaranonth, Y.; Yuthavong, Y. J. Med. Chem.
1997, 40, 633.
Grace, J. M.; Aguilar, A. J.; Trotman, K. M.; Brewer, T. G. Drug Metab. Dispos.
1998, 26, 313.
Li, Y.; Zhu, Y.; Jiang, H.; Pan, J.; Wu, G.; Wu, J.; Shi, Y.; Yang, J.; Wu, B. J. Med.
Chem. 2000, 43, 1635.
1
0 and 10a with a selectivity index (SI) of 12, thus making it the
10. General procedure for the synthesis of9–14. Themethod as describedby Li et al. was
most cytotoxic compound in this series. All other compounds
showed good selectivity towards P. falciparum (SI P 20). The good
used. Particular attention was paid that heating temperature did not exceed 80 °C
which could lead to disubstitution. The residue was extracted with CH
anyinsolubilityoccurred, it was filtered off. Only the relevant peaksfor hybrid10–
4 were notated and as the NMR data for the oxalate salts were a repetition to that
ofthefreebasesonlythelatter’swerereported. IntheMSspectraofcompounds9–
4 the presence of one chlorine atom can be deducedby the presence of twopeaks
ina 3:1 ratio separated by 2 mass units. 1-(7-Chloro-4-(1,2-diaminoethyl)quinolyl)-
-(10b-dihydroartemisinoxy)ethane (9). Yellowish oil. R = 0.46 (DCM/MeOH 9:1).
2 2
Cl and if
activity of some of these compounds against the CQR strain is in
1
agreement with the results from previous studies.5
,20–22
All com-
1
pounds were less active than the antimalarial drug DHA irrespec-
tive of the P. falciparum strain making this a major drawback, but
also merits further very essential investigation especially on how
these hybrids will act in the body whereas the underlying motiva-
tion for a hybrid would come forth.
2
f
0
0
Yield:59%.dH (CDCl )8.44(d, J = 5.3 Hz, 1H,H-2
(d, J = 8.9 Hz, 1H, H-5 ), 7.28 (dd, J = 8.9, 1.9 Hz, 1H, H-6 ), 6.32 (d, J = 5.3 Hz, 1H, H-
3
3
),7.88(d, J = 1.6 Hz,1H,H-8
),7.69
0
0
0
00
), 6.02–5.90 (br s, 1H, H-5 ), 5.33 (s, 1H, H-12), 4.76 (d, J = 3.3 Hz, 1H, H-10), 3.92
0
0
0
0
0
0
(
dt, J = 10.1, 5.0 Hz, 1H, H-1 a), 3.57–3.45 (m, 1H, H-1 b), 3.32–3.23 (m, 2H, H-4 ),
In conclusion, all of the compounds synthesized showed either
higher or comparable potency to that of CQ, with the exception of
hybrids 10 and 14 which were found with lower potency than CQ
against the CQR strain of P. falciparum. Hybrid 12 and its oxalate
salt (12a) possessed the highest antimalarial activity, even though
hybrid 12 was tested as a suspension. These two compounds,
respectively, showed 9- and 7-fold higher activity than CQ against
CQR. The optimum linker could be identified based on the in vitro
activity, as those hybrids inheriting a C-chain with 2/3 Cs and a
C-chain with 3 Cs with a Me-substituent which is present in com-
pound 9, 10 and 12. Therefore it could be deduced that no cyclic
linkers should be included, only chains with 2/3 carbon atoms with
or without Me-substituent.
00 00
.00(t, J = 5.6 Hz, 2H, H-3 ), 2.87–2.75(m, 2H, H-2 ), 2.58(dt, J = 7.7, 5.7 Hz, 1H, H-
3
9), 1.38 (s, J = 12.9 Hz, 3H, 3-Me), 0.82 (d; J = 7.4 Hz, 3H, 9-Me), 0.80 (d; J = 5.5 Hz,
0
0
0
0
3
1
1
H, 6-Me). d
C
(CDCl
3
) 151.79 (C-2 ), 149.87 (C-4 ), 148.83 (C-8a ), 134.74 (C-7 ),
0
0
0
0
28.34 (C-8 ), 125.17 (C-6 ), 121.39 (C-5 ), 117.24 (C-4a ), 104.05 (C-3), 102.00 (C-
0), 99.01 (C-3 ), 87.77 (C-12), 80.84 (C-12a), 67.58 (C-1 ), 52.30 (C-5a), 48.55 (C-
2 ), 47.11 (C-3 ), 43.90 (C-8a), 42.00 (C-4 ), 37.37 (C-6), 36.23 (C-4), 34.36 (C-7),
0.71(C-9),26.05(3-Me),24.48(C-5),24.42(C-8),20.15(6-Me),12.92(9-Me).MS:
0
00
00
0
0
00
3
+
+
m/z:532 (M , 100%), 534 (M +2, 30%). 1-(7-Chloro-4-(1,3-diaminopro pyl)quinolyl)-
-(10b-dihydroartemisinoxy)ethane (10). Yellow oil. R = 0.49 (DCM/MeOH 9:1).
Yield: 35%. dH (CDCl ) 5.38 (s, 1H, H-12), 4.84 (d, J = 3.4 Hz, 1H, H-10), 4.03 (dt,
2
f
3
00 00
a ), 3.60 (dt, J = 10.3, 5.1 Hz, 1H, H-1b ), 3.38 (t, J = 5.9 Hz,
J = 10.4, 5.2 Hz, 1H, H-1
2
0
0
00
00
H, H-5 ), 2.94 (t, J = 5.4 Hz, 2H, H-3 ), 2.87 (t, J = 5.2 Hz, 2H, H-2 ), 1.91 (dt,
00
J = 11.2, 5.6 Hz, 2H, H-4 ), 1.42 (s, 3H, 3-Me), 0.88 (d, J = 7.4 Hz, 3H, 9-Me), 0.87 (d,
J = 5.8 Hz, 3H, 6-Me).d (CDCl )67.79(C-100),49.19(C-200;C-300),43.88(C-500), 27.11
C
3
+
0
0
+
(
C-4 ). MS: m/z: 546 (M , 100%), 548 (M +2, 30%). 1-(7-Chloro-4-(1,4-
diaminophenyl)quinolyl)-2-(10b-dihydroartemisinoxy)ethane (11). Brownish oil.
0
0
R
6
1
f
= 0.57 (DCM/MeOH 9:1). Yield: 35%. d
H
(CDCl
3
) 7.08 (d, J = 8.6 Hz, 2H, H-4 ),
0
0
00
.78(s, 1H, H-7 ),6.64(d, J = 8.7 Hz, 2H, H-5 ),5.36(s, 1H, H-12),4.81(d,J = 3.4 Hz,
0
0
),3.64(ddd, J = 10.4, 6.5, 4.1 Hz,
H, H-10), 4.01(ddd,J = 10.3, 6.2, 4.1 Hz, 1H, H-1
a
Acknowledgements
1H, H-1b00), 3.38–3.25 (m, 2H, H-200), 1.41 (s, 3H, 3-Me), 0.92 (s, 3H, 9-Me), 0.91 (d,
00 00 00
C 3
J = 1.8 Hz, 3H, 6-Me). d (CDCl )146.45 (C-3 ), 128.67(C-6 ), 126.64(C-4 ), 113.82
+ +
00 00 00
C-5 ), 66.95 (C-1 ), 43.85 (C-2 ). MS: m/z: 580 (M , 100%), 582 (M +2, 30%). 1-(7-
(
The authors would like to thank the following: National Research
Foundation (funding), North-West University (funding), Cipla Med-
pro (sample of primaquine), André Joubert (NMR) and Marelize
Ferreira (MS). Special thanks to Drs. Attie Viljoen and Arina Lourens
for their help and support.
Chloro-4-(1,2-diaminopropyl)quinolyl)-2-(10b-dihydroartemisinoxy)ethane (12).
Unable to separate the two isomers, was therefore collected as a mixture. Fluffy
light brown crystals. Mp: 67 °C R
f
= 0.42 (DCM/MeOH 9:1). Yield: 45%. d
H
(CDCl
3
)
0
0
00
5.99(s,1H, H-5 ),5.75(dd, J = 36.6,5.9 Hz, 1H, H-5 ), 5.37–5.33(m, 1H,H-12), 5.29
(
(
s, 1H, H-12), 4.78 (dd, J = 7.4, 4.1 Hz, 1H, H-10), 4.76 (d, J = 3.4 Hz, 1H, H-10), 3.96
00
00
),
ddd, J = 10.3, 7.1, 3.8 Hz, 1H, H-1
a
), 3.90 (ddd, J = 10.5, 6.4, 4.3 Hz, 1H, H-1
a