5350
H. Kasiganesan et al. / Bioorg. Med. Chem. 17 (2009) 5347–5352
gel flash chromatography (1:9 to 1:4 ethyl acetate/hexanes) to give
4.45 (m, 2H), 4.25–4.21 (m, 1H), 4.16–4.12 (m, 1H), 4.03–3.99
(m, 1H), 3.88–3.83 (m, 1H), 2.15 (s, 3H), 1.03 (s, 9H); 13C NMR
(CDCl3, 100 MHz) d 169.4, 152.0, 151.1, 150.8, 143.8, 143.5,
143.4, 141.2, 135.5, 135.3, 132.5, 132.2, 132.0, 129.7, 127.6,
127.5, 126.9, 124.7, 124.6, 119.9, 88.0, 83.2, 75.4, 66.8, 62.8, 50.9,
47.0, 26.6, 20.5, 19.0; Mass ([M+H]+) 788, ([M+Na]+) 810,
([2M+Na]+) 1597. Anal. Calcd for C43H42ClN5O6Si: C, 65.51; H,
5.37; N, 8.88. Found: C, 65.24; H, 5.54; N, 8.56.
5 as a white solid (3.65 g, 89%). 5: Rf 0.16 (1:4 ethyl acetate/hex-
anes); mp 61–63 °C; ½a D25
ꢂ
ꢃ36.94 (c 0.32, CHCl3); 1H NMR (CDCl3,
400 MHz) d 7.80–7.76 (m, 2H), 7.71–7.69 (m, 4H), 7.63–7.57 (m,
2H), 7.42–7.30 (m, 10H), 5.86 (d, J = 2.9 Hz, 1H), 5.08 (d,
J = 9.6 Hz, 1H), 4.65–4.63 (m, 1H), 4.41 (d, J = 6.8 Hz, 2H), 4.34–
4.28 (m, 1H), 4.22 (t, J = 6.6 Hz, 1H), 3.92–3.88 (m, 1H), 3.87–3.83
(m, 1H), 3.79–3.73 (m, 1H), 2.18 (s, 3H), 2.05 (s, 3H), 1.04 (s, 9H);
13C NMR (CDCl3, 100 MHz) d 155.7, 143.8, 143.7, 141.2, 135.6,
133.2, 133.1, 129.6, 127.7, 127.6, 127.0, 125.0, 119.9, 112.3,
104.2, 80.3, 78.9, 66.9, 62.4, 53.3, 47.1, 26.7, 26.5, 26.3, 19.1; Mass
([M+Na]+) 672. Anal. Calcd for C39H43NO6Si: C, 72.08; H, 6.67; N,
2.16. Found: C, 71.80; H, 6.79; N, 2.10.
3.4. 9-(2-O-Acetyl-3-deoxy-3-fluorenylmethylcarbonylamino-
b-L
-ribofuranosyl)-6-chloropurine (8)
Triethylamine trihydrofluoride (1.6 mL, 9.82 mmol) was added
to a stirring solution of 7 (1.54 g, 1.95 mmol) in anhydrous tetrahy-
drofuran (20 mL) at rt, and the resulting solution was stirred at rt for
24 h, then tlc-grade silica gel was added and volatiles were removed
under reduced pressure. The residue was loaded on a tlc-grade silica
gel column packed with dichloromethane and eluted with a gradient
ofdichloromethane to1:19methanol/dichloromethanetogive8 asa
white solid, containing minor impurities (1.00 g, 93%). A small sam-
ple was purified by preparative silica gel tlc (1:19 methanol/dichlo-
romethane) to give pure 8 as a white solid. Rf 0.16 (1:19 methanol/
3.2. 5-O-tert -Butyldiphenylsilyl-3-deoxy-1,2-diacetyl-3-fluore-
nylmethylcarbonylamino-b-
L-ribofuranose (6)
Sulfuric acid (60 L, 1.13 mmol) was added to a stirring mixture
l
of 5 (3.65 g, 5.62 mmol) in acetic acid (50 mL), and the reaction
was stirred at rt overnight. Acetic anhydride (7.2 mL, 76.17 mmol)
was then added, followed by pyridine (1.7 mL, 21.02 mmol), and
the mixture was stirred at rt for 4 h. Volatiles were evaporated in
vacuo, and the residue was dissolved in dichloromethane
(100 mL), washed with a saturated solution of sodium bicarbonate
(20 mL), water (20 mL) and brine (20 mL). The organic solution was
dried over magnesium sulfate, filtered and concentrated under re-
duced pressure to a crude that was purified by tlc-grade silica gel
flash chromatography (1:4 to 3:7 ethyl acetate/hexanes) to give 6
as a white solid (1.94 g, 50%). Rf 0.46 (3:7 ethyl acetate/hexanes);
dichloromethane); mp 196–197 °C; ½a D22
ꢂ
+35.78 (c 0.34, CHCl3); UV
(MeOH) kmax 264.0, 299.5, 288.5; 1H NMR (CDCl3, 400 MHz) d 8.77
(s, 1H), 8.42 (s, 1H), 7.79–7.75 (m, 2H), 7.59–7.57 (m, 2H), 7.44–
7.38 (m, 2H), 7.35–7.29 (m, 2H), 6.22 (d, J = 2.2 Hz, 1H), 5.54–5.52
(m, 1H), 5.20 (d, J = 8.0 Hz, 1H), 4.87–4.82 (m, 1H), 4.60–4.49 (m,
2H), 4.29–4.19 (m, 3 H), 4.00 (d, J = 12.0 Hz, 1H), 3.76 (d,
J = 12.0 Hz, 1H), 2.11 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 169.5,
156.1, 151.8, 151.3, 150.5, 144.5, 143.4, 141.2, 132.2, 127.7, 126.9,
124.6, 119.9, 88.7, 84.3, 75.5, 66.7, 61.1, 50.5, 47.0, 20.5; Mass
([M+H]+) 550, ([M+Na]+) 572. Anal. Calcd for C27H24ClN5O6: C,
58.97; H, 4.40; N, 12.73. Found: C, 59.05; H, 4.62; N, 12.33.
mp 70–72 °C; ½a 2D6
ꢂ
ꢃ24.43 (c 1.00, CHCl3); 1H NMR (CDCl3,
400 MHz) d 7.79–7.76 (m, 2H), 7.68–7.66 (m, 4H), 7.59–7.55 (m,
2H), 7.44–7.28 (m, 10H), 6.12 (s, 1H), 5.17–5.15 (m, 1H), 4.81–
4.79 (m, 1H), 4.55–4.42 (m, 3H), 4.22 (t, J = 6.6 Hz, 1H), 4.00–3.97
(m, 1H), 3.86 (dd, J = 11.3, 3.0, 1H), 3.71 (dd, J = 11.3, 4.1, 1H),
2.14 (s, 3H), 1.90 (s, 3H), 1.09 (s, 9H); 13C NMR (CDCl3, 100 MHz)
d 170.5, 169.5, 155.5, 143.7, 143.6, 141.3, 135.6, 135.5, 135.2,
130.0, 127.7, 127.7, 127.0, 124.8, 120.0, 97.7, 83.1, 75.7, 66.9,
63.3, 50.7, 47.1, 26.8, 22.9, 20.7, 19.0; Mass ([M+Na]+) 716,
([2M+Na]+) 1409. Anal. Calcd for C40H43NO8Si: C, 69.24; H, 6.25;
N, 2.13. Found: C, 69.00; H, 6.24; N, 2.05.
3.5. 1-(6-Chloro-9H-purin-9-yl)-2-O -acetyl-1,3-dideoxy-3-flu-
orenylmethylcarbonylamino-b-L-ribofuranoic acid (9)
Method A: (Diacetoxyiodo)benzene (770 mg, 2.39 mmol) was
added to a suspension of 8 (600 mg, 1.09 mmol) and 2,2,6,6-tetra-
methyl-1-piperidinyloxy (TEMPO) (43 mg, 0.28 mmol) in 1:1 ace-
tonitrile/water (50 mL), and the resulting mixture was stirred at
rt for 48 h, then diluted with water (100 mL) and extracted with
dichloromethane (3 ꢁ 150 mL). The combined organic extracts
were washed with brine (30 mL), dried over sodium sulfate, fil-
tered and concentrated to a crude that was purified by tlc-grade
silica gel flash chromatography. Elution with dichloromethane to
1:49 methanol/dichloromethane allowed to recover unreacted 8
(140 mg, 25%); subsequent elution with 1:19 to 2:23 methanol/
dichloromethane gave 9 as a yellow solid, containing minor impu-
rities (190 mg, 31%). A small amount of pure 9 was obtain by pre-
parative silica gel tlc (3:17 methanol/dichloromethane, washed
with 2:23 methanol/dichloromethane) as a white solid. Rf 0.44
3.3. 9-(2-O-Acetyl-5-O-tert -butyldiphenylsilyl-3-deoxy-3-flu-
orenylmethylcarbonylamino-b-L-ribofuranosyl)-6-chloropurine
(7)
A mixture of 6-chloropurine (0.67 g, 4.33 mmol) and ammo-
nium sulfate (30 mg, 0.23 mmol) in 1,1,1,3,3,3-hexamethyldisilaz-
ane (30 mL) was refluxed for 3 h, then the solvent was removed in
vacuo at 35–40 °C. A solution of 6 (1.88 g, 2.71 mmol) in anhydrous
acetonitrile (30 mL) was added to the residual solid. The resulting
solution was cooled to 0 °C and trimethylsilyl triflate (0.78 mL,
4.31 mmol) was added, and the reaction was stirred at rt overnight.
The resulting solution was diluted to 100 mL with dichlorometh-
ane and slowly added to an ice-cold saturated solution of sodium
bicarbonate (200 mL). The organic layer was separated and the
aqueous phase was extracted with dichloromethane (2 ꢁ
100 mL). The combined organic extracts were washed with water
(50 mL), brine (50 mL), dried over magnesium sulfate, filtered
and concentrated to a crude that was purified by tlc-grade silica
gel flash chromatography (1:49 methanol/dichloromethane) to
give 7 as a white solid (1.75 g, 82%). Rf 0.14 (1:49 methanol/dichlo-
(3:17 methanol/dichloromethane); mp 198–200 °C (dec.); ½a D22
ꢂ
ꢃ11.43 (c 0.30, CHCl3); UV (MeOH) kmax 264.0, 299.0, 288.5; 1H
NMR (DMSO-d6, 400 MHz) d 9.87 (br s, 1H), 8.80 (s, 1H), 8.20 (d,
J = 8.8 Hz, 1H), 7.89 (d, 2H, J = 7.4 Hz), 7.75–7.72 (m, 3H), 7.42 (t,
2H, J = 7.4 Hz), 7.34 (d, 2H, J = 7.4 Hz), 6.49 (d, J = 4.5 Hz, 1H),
5.60 (t, 1H, J = 4.9 Hz), 4.55–4.49 (m, 1H), 4.36–4.29 (m, 2H),
4.24–4.16 (m, 2H), 1.96 (s, 3H); 13C NMR (DMSO-d6, 100 MHz) d
173.3, 169.3, 155.9, 151.8, 151.5, 149.1, 146.8, 143.9, 143.8,
140.7, 131.3, 127.7, 127.2, 127.1, 125.4, 125.3, 120.2, 120.1, 86.3,
83.5, 75.7, 65.9, 55.4, 46.6, 20.4; Mass ([M+H]+) 564. Anal. Calcd
for C27H22ClN5O7: C, 57.50; H, 3.93; N, 12.42. Found: C, 57.28; H,
3.79; N, 9.42. Method B: Ruthenium(III) chloride monohydrate
(7.5 mg, 0.04 mmol) was added to a vigorously stirred biphasic
heterogeneous mixture of 8 (90 mg, 0.16 mmol) and sodium
romethane); mp 91–93 °C (dec.); ½a D25
ꢃ17.83 (c 0.42, CHCl3); UV
ꢂ
(MeOH) kmax 264.0, 299.0; 1H NMR (CDCl3, 400 MHz) d 8.70 (s,
1H), 8.34 (s, 1H), 7.81–7.78 (m, 2H), 7.68–7.57 (m, 6H), 7.44–
7.36 (m, 4H), 7.35–7.29 (m, 4H), 7.26–7.22 (m, 2H), 6.15 (s, 1H),
5.67–5.64 (m, 1H), 5.12–5.06 (m, 1H), 4.99–4.95 (m, 1H), 4.55–