Kumar et al.
side 14r (10.61 g, 24.3 mmol) was coevaporated with anhydrous
pyridine (2 × 75 mL) and dissolved in a mixture of anhydrous
CH2Cl2 (240 mL) and anhydrous pyridine (8 mL, 98.9 mmol).
Trifluoroacetic anhydride (6.8 mL, 48.9 mmol) was added dropwise
over 5 min at 0 °C. The reaction mixture was warmed to room
temperature and stirred for 100 min, whereupon crushed ice (50
mL) was added. The reaction mixture was diluted with CH2Cl2 (150
mL) and washed with saturated aqueous NaHCO3 (2 × 70 mL).
The organic phase was evaporated to dryness and coevaporated
with toluene to give the crude trifluoroacetamide-protected nucleo-
side [Rf ) 0.5 (10% i-PrOH in CHCl3, v/v), MALDI-HRMS m/z
556.0960 ([M + Na]+, C21H22F3N3O8S‚Na+, Calcd 556.0972)] as
a white powder, which was used in the next step without further
purification. To a solution of the crude trifluoroacetamide-protected
nucleoside in 1,4-dioxane (240 mL) were added potassium acetate
(7.13 g, 72.7 mmol) and 18-crown-6 (6.40 g, 24.2 mmol), and the
reaction mixture was stirred at 80 °C for 13 h. The reaction mixture
was cooled to room temperature, concentrated to 1/5 volume, and
diluted with H2O (50 mL) and EtOAc (350 mL). The phases were
separated, and the organic phase was washed with brine (2 × 100
mL) and evaporated to dryness to afford the crude acylated product
[Rf ) 0.6 (10% i-PrOH in CHCl3, v/v), MALDI-HRMS m/z
520.1293 ([M + Na]+, C22H22F3N3O7‚Na+, Calcd 520.1302)] as a
white solid material, which was used in the next step without further
purification. The crude acylated nucleoside was dissolved in
saturated NH3/MeOH (250 mL) and stirred at room temperature
for 15 h, whereupon the reaction mixture was evaporated to dryness.
The resulting residue was purified by silica gel column chroma-
tography (0-5% i-PrOH in CH2Cl2, v/v) to give a rotameric mixture
ex, J ) 5.9 Hz, 5′-OHA+B), 4.67 (br s, 1.7H, H2′A), 4.53 (m, 1H,
H3′B), 4.45-4.48 (m, 2.7H, H2′B, H3′A), 4.04-4.10 (d, 1.7H, J )
11.0 Hz, H5′′A), 3.66-3.83 (m, 8.1H, 2 × H5′A+B, H5′′A, H5′′B),
3.57 (d, 1H, J ) 12.4 Hz, H5′′B), 1.78 (d, 3H, J ) 0.9 Hz, CH3-B),
1.76 (d, 5.1H, J ) 0.9 Hz, CH3-A); 13C NMR (DMSO-d6) δ 163.7,
163.6, 154.4-155.8 (m, 2 × COCF3), 150.1, 149.9, 134.05, 133.98,
115.7 (q, J ) 289 Hz, CF3), 115.6 (q, J ) 289 Hz, CF3), 108.6,
108.3, 90.6, 89.2, 85.1, 84.4, 72.0, 70.0, 64.6, 62.3, 57.4, 57.3, 52.7,
52.6, 12.0, 11.7.
(1S,3R,4S,7R)-1-(4,4′-Dimethoxytrityloxymethyl)-7-hydroxy-
3-(thymin-1-yl)-2-oxa-5-azabicyclo[2.2.1]heptane (18). Method
A from 17: see the Supporting Information. Method B from 19:
diol 19 (5.14 g, 14.1 mmol) was coevaporated with anhydrous
pyridine (2 × 50 mL) and redissolved in anhydrous pyridine (200
mL). To this was added 4,4′-dimethoxytrityl chloride (DMTrCl,
7.15 g, 21.10 mmol) and DMAP (0.87 g, 7.12 mmol), and the
reaction mixture was stirred at room temperature for 20 h,
whereupon it was evaporated to dryness. The resulting residue was
taken up in EtOAc (200 mL), and the organic phase was washed
sequentially with saturated aqueous NaHCO3 (75 mL) and brine
(2 × 75 mL). The organic phase was evaporated to dryness and
coevaporated with toluene (2 × 50 mL) to give the crude O5′-
tritylated alcohol (∼12 g) [Rf ) 0.5 (10% MeOH in CH2Cl2, v/v),
MALDI-HRMS m/z 690.2034 ([M + Na]+, C34H32F3N3O8S‚Na+,
Calcd 690.2008)] as a white powder, which was used in the next
step without further purification. Aqueous NaOH (2.0 M, 22 mL,
44.0 mmol) was added to an ice-cold solution of the crude O5′-
tritylated alcohol (∼12 g) in a mixture of absolute EtOH and
pyridine (240 mL, 3:1, v/v). The reaction mixture was warmed to
room temperature and stirred for 4 h, whereupon it was evaporated
to dryness and coevaporated with toluene (2 × 75 mL). The
resulting residue was purified by silica gel column chromatography80
(0-5% MeOH in CH2Cl2, v/v) to afford amino alcohol 18 (6.50 g,
81% over two steps) as a white solid material. Rf ) 0.3 (10% MeOH
in CH2Cl2, v/v), MALDI-HRMS m/z 594.2211 ([M + Na]+,
C32H33N3O7‚Na+, Calcd 594.2192); 1H NMR (DMSO-d6) δ 11.28
(s, 1H, ex, NH), 7.57 (s, 1H, H6), 7.21-7.46 (m, 9H, Ar), 6.88-
6.93 (d, 4H, J ) 9.2 Hz, Ar), 5.90 (d, 1H, J ) 1.5 Hz, H1′), 5.58
(d, 1H, ex, J ) 4.6 Hz, 3′-OH), 4.26 (d, 1H, J ) 4.6 Hz, H3′),
3.74 (s, 6H, 2 × CH3O), 3.34 (d, 1H, H2′ overlapping with H2O),
3.25-3.29 (d, 1H, J ) 10.8 Hz, H5′),81 3.19-3.24 (d, 1H, J )
10.8 Hz, H5′), 3.03-3.08 (d, 1H, J ) 10.3 Hz, H5′′), 2.94-2.99
(d, 1H, J ) 10.3 Hz, H5′′), 1.84 (s, 3H, CH3); 13C NMR (DMSO-
d6) δ 163.8, 158.0, 150.3, 144.8, 136.5 (C6), 135.4 (Ar), 135.3
(Ar), 129.7 (Ar), 127.7 (Ar), 127.6 (Ar), 126.6 (Ar), 113.1 (Ar),
106.9, 89.5, 85.8 (C1′), 85.1, 73.4 (C3′), 61.5 (C2′), 60.7 (C5′),
1
(∼1:1.3 by H NMR) of nucleoside 15 (7.12 g, 64% over three
steps) as a white solid material. Physical data for the mixture of
rotamers: Rf ) 0.3 (10% i-PrOH in CHCl3, v/v); MALDI-HRMS
m/z 478.1174 ([M + Na]+, C20H20F3N3O6‚Na+, Calcd 478.1196);
1H NMR (DMSO-d6)79 δ 11.40 (s, 2.3H, ex, NHA+B), 7.60 (d, 1.3H,
J ) 0.8 Hz, H6A), 7.47 (d, 1H, J ) 0.8 Hz, H6B), 7.25-7.40 (m,
11.5H, PhA+B), 6.08 (d, 1H, J ) 1.8 Hz, H1′B), 6.04 (d, 1.3H, J )
1.5 Hz, H1′A), 5.21 (ap t, 2.3H, ex, J ) 5.9 Hz, 5′-OHA+B), 4.92
(br s, 1.3H, H2′A), 4.84 (br s, 1H, H2′B), 3.61-4.74 (m, 16.1H,
H3′A+B, H5′A+B, H5′′A+B, CH2PhA+B), 1.78 (d, 3H, J ) 0.8 Hz,
CH3-B), 1.76 (d, 3.9H, J ) 0.8 Hz, CH3-A); 13C NMR (DMSO-d6)
δ 163.6, 163.5, 155.2 (q, J ) 36.6 Hz, COCF3), 155.0 (q, J ) 36.6
Hz, COCF3), 150.1, 149.9, 137.5 (C6), 137.3 (C6), 134.0, 133.9,
128.2, 127.6, 127.2, 115.6 (q, J ) 289 Hz, CF3), 115.5 (q, J ) 288
Hz, CF3), 108.7, 108.4, 89.7, 88.3, 85.1 (C1′A), 84.5 (C1′B), 78.8,
76.9, 71.3, 62.1 (C2′B), 60.6 (C2′A), 57.1, 56.9, 53.1, 52.9, 11.9,
11.7. Anal. Calcd for C20H20F3N3O6: C, 52.75; H, 4.43; N, 9.23.
1
Found: C, 53.17; H, 4.19; N, 9.07. Calcd with /16 i-PrOH: C,
54.9 (CH3O), 50.6 (C5′′), 12.4 (CH3). Anal. Calcd for C32H33N3O7‚
10
52.81; H, 4.50; N, 9.15.
/ H2O: C, 65.94; H, 5.92; N, 7.21. Found: C, 66.33; H, 5.66;
16
(1S,3R,4S,7R)-7-Hydroxy-1-hydroxymethyl-3-(thymin-1-yl)-
5-trifluroacetyl-2-oxa-5-azabicyclo[2.2.1]heptane (19). Nucleo-
side 15 (8.28 g, 18.2 mmol) was coevaporated with anhydrous 1,2-
dichloroethane (2 × 50 mL), suspended in anhydrous CH2Cl2 (230
mL), and cooled to -70 °C. To this was added BCl3 (1.0 M in
hexanes, 91 mL, 91.0 mmol) over 20 min. The reaction mixture
was warmed to room temperature and stirred for 20 h, whereupon
it was evaporated to dryness and coevaporated with toluene (3 ×
100 mL). The resulting residue was purified by silica gel column
chromatography (0-8% MeOH in CH2Cl2, v/v) to give a rotameric
mixture (∼1:1.7 by 1H NMR) of diol 19 (5.14 g, 77%) as a white
solid material. Physical data for the mixture of rotamers: Rf ) 0.4
(20% MeOH in CHCl3, v/v); MALDI-HRMS m/z 388.0727 ([M
+ Na]+, C13H14F3N3O6‚Na+, Calcd 388.0711); 1H NMR (DMSO-
d6)79 δ 11.34 (br s, 2.7H, ex, NHA+B), 7.56 (d, 1.7H, J ) 0.9 Hz,
H6A), 7.44 (d, 1H, J ) 0.9 Hz, H6B), 6.28 (d, 1H, ex, J ) 4.0 Hz,
3′-OHB), 6.25 (d, 1.7H, ex, J ) 4.0 Hz, 3′-OHA), 6.06 (d, 1H, J )
1.5 Hz, H1′B), 6.04 (d, 1.7H, J ) 1.5 Hz, H1′A), 5.08 (ap t, 2.7H,
N, 6.81.
(1S,3R,4S,7R)-1-(4,4′-Dimethoxytrityloxymethyl)-5-(9′-fluoren-
ylmethoxycarbonyl)-7-hydroxy-3-(thymin-1-yl)-2-oxa-5-azabicyclo[2.2.1]-
heptane (20). To an ice-cold suspension of amino alcohol 18 (0.25
g, 0.44 mmol) in saturated aqueous NaHCO3 (2 mL) and 1,4-
dioxane (2 mL) was added 9′-fluorenylmethyl chloroformate
(FmocCl, 125 mg, 0.48 mmol). After stirring for 3 h at room
temperature, the reaction mixture was diluted with H2O (10 mL)
and EtOAc (35 mL). The phases were separated, and the aqueous
phase was extracted with EtOAc (3 × 35 mL). The combined
organic phase was evaporated to dryness, and the resulting residue
was purified by silica gel column chromatography (20-80% EtOAc
in petroleum ether, v/v)80 to afford a rotameric mixture (∼1:1.2 by
1H NMR) of nucleoside 20 (0.28 g, 81%) as a white solid material.
Physical data of rotamers: Rf ) 0.6 (5% MeOH in CH2Cl2, v/v),
(80) During purification of this compound the silica gel chromatography
column was initially packed using an eluent containing either Et3N or
pyridine (1%, v/v).
(79) The integral of the H1′-signal of the least predominant rotamer
(termed B) is set to 1.0.
(81) Assignments of 1H NMR signals of H5′ and H5′′, and of the
corresponding 13C signals, may in principle be interchanged.
4200 J. Org. Chem., Vol. 71, No. 11, 2006