10.1002/cmdc.201700579
ChemMedChem
FULL PAPER
from the filtrate under reduced pressure. The residue was submitted to
column chromatography over silica gel. Evaporation of the eluate
obtained with ethyl acetate-hexane (3:7 v/v) left a white amorphous
powder (689 mg, 35%), that started melting at 152 C and was
completely molten at 185 C; Rf 0.66 (hexane-ethyl acetate 7:3); 1H NMR
(600 MHz, CDCl3) (ppm): 5.77 (d, J = 9.9 Hz, 1H, H-10), 5.41 (s, 1H, H-
12), 5.34 (d, J = 4.1 Hz, 1H, H-6”), 4.62 - 4.57 (m, 1H, H-3”), 2.74 – 2.50
(m, 4H, H-2’, H-3’), 2.37 - 2.32 (m, J = 3.2 Hz, 1H, H-14”), 2.29 - 2.28 (m,
J = 7.1 Hz, 1H, H-8a), 1.41 (s, 3H, H-13), 0.98 (s, 3H, H-19”), 0.94 (d, J =
6.1 Hz, 3H, H-14), 0.88 (d, J = 6.5 Hz, 3H, H-15), 0.85 (d, J = 1.8 Hz, 3H,
H-21”), 0.82 (dd, J = 2.6, 2.9 Hz, 6H, H-26”, H-27”), 0.65 (s, 1H, H-18”);
13C NMR (151 MHz, CDCl3): 171.47 (C-4’), 171.19 (C-1’), 139.57 (C-5”),
122.65 (C-6”), 104.44 (C-3), 92.08 (C-10), 91.47 (C-12), 80.10 (C-12a),
74.33 (C-3”), 51.53 (C-5a), 49.97 (C-9”), 45.20 (C-8a), 42.27 (C-13”),
39.69 (C-24”), 31.86 (C-6), 18.68 (C-21”), 12.06 (C-15), 11.82 (C18”); IR
max cm-1: 2949, 2895, 2867, 2847, 1761, 1714, 1467, 1458, 1374; MS:
m/z: calcd for C46H72O8Na +: 775.5125 [M+Na]+ ; found: 775.5192.
max cm-1: 2930, 2864, 1690, 1429, 1379, 1246, 1195, 1127, 1110; MS:
m/z: calcd for C47H77N2O6+: 765.5782 [M+H]+ ; found: 765.5678.
Next, cholesterol was converted into the acid chlorides 12 and 13 as
follows. Cholesterol (1000 mg, 2.59 mmol) was dissolved in
dichloromethane (20 mL) and triethylamine (541 µL, 5.18 mmol, 2 eq.).
To this mixture the acid chloride (5.18 mmol, 2 eq.) was added and the
reaction mixture was left to stir at room temperature overnight. The
reaction mixture was quenched with saturated NaHCO3 (20 mL) and the
crude mixture extracted with dichloromethane (3 x 20 mL). The extracts
were combined and dried over MgSO4. After filtration to remove MgSO4
the filtrate was concentrated under reduced pressure to leave the crude
product. To a solution of 10 (1050 mg, 2.98 mmol) in THF (10 mL) under
reflux (65 °C) was added triethylamine (286 µL, 2.05 mmol, 1.3 eq.)
followed by a solution of the crude product from the previous step in THF
(10 mL). The reaction mixture was left to stir for 24 h and was quenched
with saturated aqueous NaHCO3 (20 mL). The crude mixture was
extracted with diethyl ether (3 x 20 mL) and combined extracts were
dried over MgSO4. Following filtration to remove MgSO4 the filtrate was
concentrated under reduced pressure and submitted to column
chromatography over silica gel. Elution with ethyl acetate-hexane (v/v)
column chromatography gave pure product. This method was used for
synthesis of the conjugates 14, 15 and 17 as described below.
Preparation of C-10 N-linked artemisinin-cholesterol conjugates (Scheme
2)
Compound 10. To a suspension of DHA (1000 mg, 3.52 mmol) in
toluene (10 mL) under a nitrogen atmosphere was added DMSO (25.1 µL,
0.35 mmol, 0.1 eq.) and this was followed by dropwise addition of oxalyl
chloride (350 µL, 1.13 eq.). The reaction mixture was left to stir for 1 h at
room temperature and then was added directly to a solution of piperazine
(1500 mg, 5 eq.) in dichloromethane (10 mL). The resulting mixture was
stirred overnight at room temperature under nitrogen, and then quenched
with saturated aqueous NaHCO3 (20 mL), and extracted with ethyl
acetate (3 x 20 mL). The extracts were combined and dried over MgSO4.
After filtration, the solvent was removed by evaporation under reduced
pressure to leave the crude product that was submitted to column
chromatography. Elution with methanol-dichloromethane (1:9 v/v) and
evaporation of the eluate gave the intermediate 10 as cream white solid
(743 mg, 60%), mp 163.6 – 163.7 C; 1H NMR (600 MHz, CDCl3)
(ppm): 5.20 (s, 1H, H-12), 3.92 (d, J = 10.2 Hz, 1H, H-10), 3.07 - 2.80 (m,
4H, H-5’, H-3’), 2.68 - 2.61 (m, 4H, H-6’, H-2’), 2.55 - 2.46 (m, 1H, H-8a),
2.27 (td, J = 14.0, 3.9 Hz, 2H, H-4), 1.98 - 1.89 (m, 2H, H-7), 1.32 (s, 3H,
Compound 14. The product obtained from the reaction of chloroacetyl
chloride with cholesterol, compound 12, was treated with compound 10
according to the method described above. The product was purified by
chromatography with ethyl acetate-hexane (2.5:7.5, v/v) to give a light-
purple amorphous solid (743 mg, 32.0%), that started to melt at 145 C
and was completely molten at 203 C; Rf 0.49 (hexane-ethyl acetate
1
7.5:2.5); H NMR (600 MHz, CDCl3) (ppm): 5.34 (d, J = 3.7 Hz, 1H, H-
6”), 5.24 (s, 1H, H-12), 4.64 (s, 1H, H-3”), 4.03 (d, J = 9.9 Hz, 1H, H-10),
3.29 (s, 2H, H-6’), 3.21 (s, 2H, H-7’), 3.15 – 3.05 (m, 2H, H-5’, H-3’), 2.90
– 2.73 (m, 2H, H-2’), 1.34 (s, 3H, H-13), 0.98 (s, 3H, H-19”), 0.91 (d, J =
6.2 Hz, 3H, H-14), 0.88 (d, J = 6.5 Hz, 3H, H-15), 0.83 (dd, J = 6.6, 2.7
Hz, 6H, H-26”, H-27”), 0.79 (d, J = 6.6 Hz, 3H, H-21”), 0.64 (s, 3H, H-
18”); 13C NMR (151 MHz, CDCl3) (ppm): 139.37 (C-5”), 122.84 (C-6”),
103.94 (C-3), 91.51 (C-10), 90.41 (C-12), 80.25 (C-12a), 74.82 (C-3”),
56.63 (C-14”), 56.08 (C-17”), 51.62 (C-5a), 49.94 (C-6’, C-2’), 45.79 (C-
13”), 23.79 (C-23”), 22.79 (C-26”, C-27”), 20.26 (C-14), 19.27 (C-19”),
18.68 (C-21”), 13.39 (C-15), 11.82 (C-18”); IR (ATR) max cm-1: 3422,
2931, 2867, 1743, 1450, 1376, 1208, 1176, 1128; MS: m/z: calcd for
C48H79N2O6+: 779.5938 [M+H]+ ; found: 779.5897.
H-13), 0.88 (d, J = 6.3 Hz, 3H, H-14), 0.73 (d, J = 7.3 Hz, 3H, H-15); 13
C
NMR (151 MHz, CDCl3) (ppm): 103.96 (C-3), 91.64 (C-10), 91.06 (C-
12), 80.34 (C-12a), 51.74 (C-5a), 50.70 (C-6’, C-2’), 45.84 - 45.69 (C-5’,
C-3’), 26.02 (C-13), 24.78 (C-5), 21.67 (C-7), 20.31 (C-14), 13.45 (C-15);
IR max cm-1: 3261, 2926, 2869, 2839, 1738, 1453, 1408, 1375, 1349;
MS: m/z: calcd for C19H33N2O4+: 353.2440 [M+H]+ ; found: 353.2469.
Compound 15. The product obtained from the reaction of bromohexanoyl
chloride with cholesterol, compound 13, was treated with compound 10
as described above. The crude product was purified by chromatography
with ethyl acetate-hexane (1:9, v/v) to give a cream-white amorphous
solid (144 mg, 5.79%) that started softening at 121 °C and was complete-
ly molten at 171 °C; Rf 0.32 (hexane-ethyl acetate 9:1) 1H NMR (600
MHz, CDCl3) (ppm): 5.34 (d, J = 4.0 Hz, 1H, H-6’’’), 5.24 (s, 1H, H-12),
4.61 – 4.54 (m, 1H, H-3’’’), 4.06 (d, J = 9.4 Hz, 1H, H-10), 2.54 – 2.51 (m,
2H, H-1”), 2.33 – 2.24 (m, 2H, H-5”), 1.33 (s, 3H, H-13), 1.25 – 1.20 (m,
2H, H-8), 0.99 (s, 3H, H-15), 0.92 (d, J = 6.3 Hz, 3H, H-14), 0.88 (d, J =
6.5 Hz, 3H, H-19’’’), 0.83 (dd, J = 6.6, 2.7 Hz, 6H, H-26’’’, H-27’’’), 0.76 (d,
J = 7.1 Hz, 3H, H-21’’’), 0.65 (s, 3H, H-18’’’); 13C NMR (151 MHz, CDCl3)
(ppm): 139.64 (C-5’’’), 122.59 (C-6’’’), 103.95 (C-3), 91.40 (C-10), 80.28
(C-12a), 73.83 (C-3’’’), 56.65 (C-1’), 56.08 (C-17’’’), 51.58 (C-5a), 49.98
(C-5’), 45.72 (C-8a), 42.27 (C-13’’’), 22.53 (C-26’’’, C-27’’’), 20.25 (C-14),
19.29 (C-19’’’), 18.68 (C-15), 13.39 (C-21’’’), 11.82 (C-18’’’); IR (ATR)
Compound 11. To a stirred solution of 10 (740 mg, 2.09 mmol) and
triethylamine (344 µl, 2.72 mmol, 1.2 eq.) in dichloromethane (10 mL)
under a nitrogen atmosphere was added a solution of cholesteryl
chloroformate (1030 mg, 2.72 mmol, 1.2 eq.) in dichloromethane (5 mL).
The reaction mixture was stirred overnight and was then quenched with
saturated aqueous NaHCO3 (20 mL). The crude mixture was extracted
with dichloromethane (3 x 20 mL) and the extracts were combined and
dried over MgSO4. After filtration to remove MgSO4 the filtrate was con-
centrated under reduced pressure to leave the crude product that was
submitted to column chromatography over silica gel. Elution with ethyl
acetate-hexane (2:8 v/v) gave the product as a white amorphous powder
1
(688 mg, 43%), mp 169-172 C; Rf 0.55 (hexane-ethyl acetate, 2:8); H
NMR (600 MHz, CDCl3) (ppm): 5.34 (d, J = 2.3 Hz, 1H, H-6”), 5.25 (s,
1H, H-12), 4.45 – 4.48 (m, 1H, H-3”), 4.00 (d, J = 8.5 Hz, 1H, H-10), 3.44
- 3.40 (m, 2H, H-5’), 2.88 – 2.96 (m, 2H, H-3’), 2.63 – 2.52 (m, 4H, H-6’,
H-2’), 1.62 (s, 3H, H-13), 1.36 (s, 3H, H-15), 0.99 (s, 3H, H-19”), 0.92 (d,
J = 6.1 Hz, 3H, H-14), 0.89 (d, J = 6.5 Hz, 3H, H-21”), 0.84 (dd, J = 6.6,
2.8 Hz, 6H, H-26”, H-27”), 0.65 (s, 3H, H-18”); 13C NMR (151 MHz,
CDCl3) (ppm): 154.97 (C-7’), 140.07 (C-5”), 122.36 (C-6”), 103.84 (C-3),
91.79 (C-10), 90.75 (C-12), 80.26 (C-12a), 74.64 (C-3”), 56.65 (C-14”),
56.08 (C-17”), 45.80 (C-5’, C-3’), 44.05 (C-8a), 42.28 (C-13”), 20.25 (C-
14), 19.34 (C-19”), 18.68 (C-21”), 13.46 (C-15), 11.82 (C-18”); IR (ATR)
max cm-1: 2927, 2864, 1732, 1460, 1444, 1375, 1322, 1236, 1188, 1173;
MS: m/z: calcd for C52H87N2O6+: 835.6564 [M+H]+ ; found: 835.6573.
Compound 17. DMSO (25.1 µL, 0.35 mmol, 0.1 eq.) was added to a
suspension of DHA (1000 mg, 3.52 mmol) in toluene (10 mL) under an
inert atmosphere at room temperature. Oxalyl chloride (350 µL, 1.13 eq.)
was added dropwise to the resulting solution. The reaction mixture was
left to stir for 1 h at room temperature and then transferred into a solution
7
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