Article
(1R,3R,4R,7S)-7-(tert-Butyldimethylsilyloxy)-1-[1-(S)-(4,40-di-
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 23 8317
washed with brine, dried (Na2SO4), and concentrated. Purifica-
tion by column chromatography (silica gel, eluting with 50-
60% ethyl acetate in hexanes) provided the desired nucleoside
phosphoramidite.
(1R,3R,4R,7S)-7-[2-Cyanoethoxy(diisopropylamino)phos-
phinoxy]-1-[1-(S)-(4,40-dimethoxytrityloxy)ethyl]-3-(uracil-1-yl)-
2,5-dioxabicyclo[2.2.1]heptane (27). 27 was prepared according
to the general procedure using 24 (0.14 g, 0.24 mmol) to provide
27 (0.16 g, 87%). 31P NMR (121 MHz, CDCl3) δ: 149.1, 148.5.
HRMS (QTOF) calcd for C41H48N4O9P, 771.3159; found
771.3180.
(1R,3R,4R,7S)-7-[2-Cyanoethoxy(diisopropylamino)phos-
phinoxy]-1-[1-(R)-(4,40-dimethoxytrityloxy)ethyl]-3-(uracil-1-yl)-
2,5-dioxabicyclo[2.2.1]heptane (28). 28 was prepared according
to the general procedure, using 26 (0.18 g, 0.31 mmol) to provide
28 (0.2 g, 81%). 31P NMR (121 MHz, CDCl3) δ: 149.4, 148.6.
methoxytrityloxy)ethyl]-3-(uracil-1-yl)-2,5-dioxabicyclo[2.2.1]-
heptane (23). 23 was prepared according to the general proce-
dure using 21 (0.5 g, 1.3 mmol) to provide 23 (0.82 g, 91%). 1H
NMR (300 MHz, CDCl3) δ: 9.19 (br s, 1 H), 8.10 (d, J = 8.1 Hz,
1 H), 7.50-7.18 (m, 9 H), 6.89-6.75 (m, 4 H), 5.74-5.63 (m, 2
H), 4.34 (s, 1 H), 4.25 (s, 1 H), 3.86 (d, J = 7.5 Hz, 1 H), 3.80 (d,
J = 2.1 Hz, 6 H), 3.72 (dd, J = 7.1, 9.9 Hz, 2 H), 0.96 (d, J = 6.4
Hz, 3 H), 0.77 (s, 9 H), 0.04 (s, 3 H), -0.10 (s, 3 H). 13C NMR
(75 MHz, CDCl3) δ: 163.4, 158.7, 149.7, 146.2, 139.5, 136.4,
136.3, 130.5, 128.3, 127.7, 127.0, 120.1, 113.0, 101.6, 91.8, 87.2,
86.4, 79.1, 72.0, 71.0, 66.1, 55.2, 25.5, 17.9, 17.8, -4.4, -4.9.
ESI-MS [M þ Na]þ calcd 709.3; found 709.2. HRMS (QTOF)
calcd for C38H46N2O8SiNa, 709.2921; found 709.2912.
(1R,3R,4R,7S)-7-[tert-Butyldimethylsilyloxy]-1-[1-(R)-(4,40-di-
methoxytrityloxyethyl]-3-(uracil-1-yl)-2,5-dioxabicyclo[2.2.1]-
heptane (24). 24 was prepared according to the general proce-
dure using 22 (0.19 g, 0.5 mmol) to provide 24 (0.27 g, 95%).
1H NMR (300 MHz, CDCl3) δ: 8.42-8.31 (m, 1 H), 7.60 (d,
J = 8.3 Hz, 1 H), 7.52-7.44 (m, 2 H), 7.43-7.14 (m, 7 H), 6.81
(d, J = 8.9 Hz, 4 H), 5.61 (s, 1 H), 5.59-5.52 (m, 1 H), 4.24 (s,
1 H), 3.96 (d, J = 7.9 Hz, 1 H), 3.84 (s, 1 H), 3.78 (s, 6 H), 3.69
(d, J = 8.1 Hz, 1 H), 3.58 (m, 1 H), 1.11 (d, J = 6.6 Hz, 3 H),
0.78 (s, 9 H), 0.00 (s, 3 H), -0.02 (s, 3 H). 13C NMR (75 MHz,
CDCl3) δ: 162.7, 158.6, 149.4, 146.3, 138.8, 136.3, 136.2,
130.3, 130.3, 127.9, 127.8, 126.8, 113.1, 113.1, 101.8, 91.5,
87.7, 86.7, 79.5, 73.3, 71.8, 67.1, 55.2, 25.5, 17.8, 17.5, -4.7, -5.1.
ESI-MS [M þ Na]þ calcd 709.3; found 709.2.
Acknowledgment. We thank Dr. Karsten Schmidt for
HRMS measurements.
Supporting Information Available: General experimental pro-
cedures for synthesis of 29, 30, 31, and R- and S-50-Me-LNA
1
cytosine phosphoramidites; H and 13C NMR spectra for all
new compounds; 31P NMR spectra for phosphoramidites;
analytical data for oligonucleotides. This material is available
References
General Procedure for Deprotecting 30O-TBDMS Group. A
solution of tetrabutylammonium fluoride (1.2 equiv, 1 M in
THF) was added to a solution of nucleoside (1 equiv) in THF
(0.3 M). After being stirred at room temperature for 16 h, the
mixture was diluted with ethyl acetate and the organic layer was
washed with water, brine, dried (Na2SO4), and concentrated.
Purification by column chromatography (silica gel, eluting with
30-40% acetone in dichloromethane) provided the 30-depro-
tected nucleoside.
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(1R,3R,4R,7S)-1-[1-(S)-(4,40-Dimethoxytrityloxy)ethyl]-7-
hydroxy-3-(uracil-1-yl)-2,5-dioxabicyclo[2.2.1]heptane (25). 25
was prepared according to the general procedure using 23
(0.2 g, 0.29 mmol) to provide 25 (0.15 g, 88%). 1H NMR (300
MHz, CDCl3) δ: 9.72 (br s, 1 H), 8.00 (d, J = 8.1 Hz, 1 H),
7.54-7.34 (m, 6 H), 7.33-7.15 (m, 3 H), 6.84 (dd, J = 1.2, 8.8
Hz, 4 H), 5.66 (d, J = 8.1 Hz, 1 H), 5.60 (s, 1 H), 4.36 (s, 1 H),
4.01 (d, J = 4.5 Hz, 1 H), 3.83-3.73 (m, 2 H), 3.80 (s, 6H), 3.65
(d, J = 7.9 Hz, 1 H), 2.45 (d, J = 4.9 Hz, 1 H), 1.04 (d, J = 6.4
Hz, 3 H). 13C NMR (75 MHz, CDCl3) δ: 163.9, 158.7, 158.7,
149.9, 145.9, 139.5, 136.2, 136.1, 130.6, 128.3, 127.8, 127.0,
113.1, 113.1, 101.6, 91.3, 87.0, 86.8, 79.3, 71.6, 70.3, 65.4, 55.3,
55.2, 18.2. ESI-MS [M þ Na]þ calcd 595.2; found 595.2.
(1R,3R,4R,7S)-1-[1-(R)-(4,40-Dimethoxytrityloxy)ethyl]-7-
hydroxy-3-(uracil-1-yl)-2,5-dioxabicyclo[2.2.1]heptane (26). 26
was prepared according to the general procedure, using 24
(0.26 g, 0.4 mmol) to provide 26 (0.20 g, 90%). 1H NMR (300
MHz, CDCl3) δ: 9.05-8.91 (m, 1 H), 7.52-7.46 (m, 2 H),
7.45-7.35 (m, 4 H), 7.32-7.16 (m, 4 H), 6.88-6.80 (m, 4 H),
5.57 (s, 1 H), 5.53 (d, J = 8.1 Hz, 1 H), 4.35 (s, 1 H), 3.99 (q, J =
8.5 Hz, 2 H), 3.79 (s, 6 H), 3.78-3.69 (m, 2 H), 2.94 (br s, 1 H),
1.17 (d, J = 6.6 Hz, 3 H). 13C NMR (75 MHz, CDCl3) δ: 163.1,
158.8, 158.7, 149.6, 145.8, 138.6, 136.0, 135.8, 130.3, 130.3,
128.0, 127.9, 127.0, 113.3, 113.2, 101.7, 89.8, 87.4, 86.9, 79.8,
71.9, 71.5, 67.9, 55.3, 18.2. ESI-MS [M þ Na]þ calcd 595.2; found
595.2. HRMS (QTOF) calcd for C32H32N2O8Na, 595.2056;
found 595.2055.
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General Procedure for Preparation of Nucleoside Phosphor-
amidites. 2-Cyanoethyl N,N0-tetraisopropylphosphoramidite
(1.5 equiv) was added to a solution of nucleoside (1 equiv),
tetrazole (0.8 equiv), and N-methylimidazole (0.25 equiv) in
DMF (0.2 M). After being stirred for 8 h at room temperature,
the mixture was poured into EtOAc and the organic phase was
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