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Chemical Science
8-Amino-N8-(dimethylaminomethylidene)-50-O-
evaporated to dryness. The residue obtained was extracted with
CH2Cl2 (2 ꢃ 100 mL), washed with water (2 ꢃ 15 mL), brine (10
mL) and dried over anhydrous Na2SO4 and the solvent was
removed under reduced pressure and the residue was puried by
ash column chromatography (n-hexane/ethyl acetate 7/3) to
yield compound 20b as a yellow solid (2.71 g, 88%). 1H NMR (500
MHz, CDCl3) d 7.87 (s, 1H, H-2), 6.16 (t, J ¼ 6.9 Hz, 1H, H-10),
4.74–4.69 (m, 1H, H-30), 3.90–3.86 (m, 1H, H-40), 3.79 (dd, J ¼
10.9, 6.4 Hz, 1H, H-5b0), 3.68 (dd, J ¼ 10.9, 4.6 Hz, 1H, H-5a0), 3.63
(s, 3H, NCH3), 3.18 (pent, J ¼ 6.9 Hz, 1H, H-2b0), 2.15 (ddd, J ¼
10.8, 6.9, 3.9 Hz, 1H, H-2a0), 0.92 (s, 9H, CCH3), 0.85 (s, 9H,
CCH3), 0.11 (s, 6H, SiCH3), 0.02 (s, 3H, SiCH3), ꢁ0.01 (s, 3H,
SiCH3); 13C NMR (125 MHz, CDCl3) d 156.1 (C6), 147.7 (C4), 146.0
(C2), 145.1 (C8), 122.9 (C5), 87.6 (C40), 83.4 (C10), 72.1 (C30), 62.7
(C50), 37.3 (C20), 34.4 (NCH3), 26.0, 25.9 (CCH3), 18.4, 18.1 (CH3C),
ꢁ4.5, ꢁ4.6, ꢁ5.2, ꢁ5.3 (CH3Si); HRMS (ESI+): calcd for
C23H41N7O4Si2 [M + H]+ 536.2831; found 536.2832.
dimethoxytrityl-N1-methyl-20-deoxyinosine (23b)
Reaction of 22b (420 mg, 1.25 mmol) with 4,40-dimethoxytrityl
chloride (465 mg, 1.37 mmol) in dry pyridine (45 mL), in dry
CH2Cl2 (5 mL) was carried out as described for compound 17a
and puried by ash column chromatography (CH2Cl2/MeOH/
TEA 80/2/1) to yield compound 23b (710 mg, 89%) as white
solid. 1H NMR (500 MHz, CDCl3) d 8.68 (s, 1H, N]CH), 7.45 (s,
1H, H-2), 7.41 (d, J ¼ 7.2 Hz, 2H, Ar), 7.31–7.15 (m, 7H, Ar), 6.78–
6.73 (m, 4H, Ar), 6.66 (t, J ¼ 6.9 Hz, 1H, H-10), 4.85–4.80 (m, 1H,
H-30), 4.11–4.06 (m, 1H, H-40), 3.77 (s, 3H, OCH3), 3.76 (s, 3H,
OCH3), 3.54 (s, 3H, NCH3), 3.52–3.45 (m, 1H, H-5b0), 3.32–3.25
(m, 2H, H-2b0, H-5b0), 3.07 (m, 3H, NCH3), 3.02 (m, 3H, NCH3),
2.28 (ddd, J ¼ 12.3, 6.9, 4.5 Hz, 1H, H-2a0); 13C NMR (125 MHz,
CDCl3) d 158.5 (Ar), 157.5 (N]C), 156.7 (C6), 155.4 (C8), 146.9
(C4), 145.0 (Ar), 143.7 (C2), 136.3, 136.1, 130.2, 128.2, 127.8,
126.7 (Ar), 122.8 (C5), 113.1 (Ar), 86.3 (CPh3), 85.5 (C40), 82.6
(C10), 73.6 (C30), 64.6 (C50), 55.3 (OCH3), 40.9 (NCH3), 37.2 (C20),
34.8, 34.1 (NCH3); HRMS (ESI+): calcd for C35H38N6O6 [M + H]+
639.2925; found 639.2926.
8-Amino-N8-(dimethylaminomethylidene)-30-50-O-
di(tertbutyldimethylsilyl)-N1-methyl-20-deoxy-inosine (21b)
The reaction of compound 20b (2.5 g, 4.67 mmol) with NaBH4
(882 mg, 23.33 mmol) in MeOH (26 mL) and then with N,N-
dimethylformamide-dimethylacetal (15 mL) was carried out as
described for compound 21a, and puried by ash column
chromatography (CH2Cl2/MeOH 15/1) to yield yellow solid (1.92
8-Amino-N8-(dimethylaminomethylidene)-50-O-
dimethoxytrityl-N1-methyl-20-deoxyinosine-30-(2-cyanoethyl-
N,N-diisopropyl)phosphoramidite (24b)
The reaction of compound 23b with 1 M bis(diisopropyla-
mino)(2-cyanoethoxy)phosphine (1.18 mL, 1.40 mmol) and 0.45
M 1H-tetrazole (1.45 mL, 0.77 mmol) in CH2Cl2 (25 mL) was
carried out as described for compound 18a and puried by ash
column chromatography (CH2Cl2/MeOH/TEA 40/1/1) to yield
compound 24b (0.380 g, 77%) as white solid. 31P NMR (202 MHz,
CDCl3) d 148.6, 148.2. HRMS (ESI+): calcd for C44H55N8O7P [M +
H]+ 839.4003; found 839.4014.
1
g, 73%). H NMR (500 MHz, DMSO-d6) d 8.56 (s, 1H, CH]N),
8.18 (s, 1H, H-2), 6.47 (t, J ¼ 7.0 Hz, 1H, H-10), 4.71 (dt, J ¼ 6.7,
3.6 Hz, 1H, H-30), 3.80 (dd, J ¼ 10.4, 6.7 Hz, 1H, H-5b0), 3.77–3.72
(m, 1H, H-40), 3.59 (dd, J ¼ 10.4, 4.9, 1H, H-5a0), 3.47 (s, 3H,
NCH3), 3.28–3.21 (m, 1H, H-2b0), 3.15 (s, 3H, NCH3), 3.02 (s, 3H,
NCH3), 2.09 (ddd, J ¼ 10.9, 7.0, 3.6 Hz, 1H, H-2a0), 0.90 (s, 9H,
CCH3) 0.83 (s, 9H, CCH3), 0.11 (s, 6H, SiCH3), ꢁ0.01 (s, 3H,
SiCH3), ꢁ0.03 (s, 3H, SiCH3). 13C NMR (125 MHz, DMSO-d6)
d 157.1 (C]N), 155.7 (C6), 154.6 (C4), 146.8 (C8), 145.5 (C2),
121.7 (C5), 86.3 (C40), 81.9 (C10), 72.5 (C30), 62.8 (C50), 40.2
(NCH3), 36.2 (C20), 34.3 (NCH3), 33.4 (NCH3), 25.7 (CH3), 18.0
(CCH3), 17.7 (CCH3), ꢁ4.6 (SiCH3), ꢁ4.7 (SiCH3). HRMS (ESI+):
calcd for C23H43N5O4Si2 [M + H]+ 565.3348; found 565.3358.
7,8-Dihydro-8-oxo-20-deoxyinosine (3)29
A solution of NaNO2 (516 mg, 7.48 mmol) in (2 mL) of water was
added to a stirred solution of 1 g (3.74 mmol) of compound 5 in
50 mL of 95% aqueous acetic acid. The reaction mixture was
stirred overnight. The solvent was removed under reduced
pressure and the oily residue was puried by ash column
chromatography (CH2CI2/MeOH, 4 : 1) to give 3 (780 mg, 77%)
as a white solid. Spectral and analytical data were in agreement
with previous report.29
8-Amino-N8-(dimethylaminomethylidene)-N1-methyl-20-
deoxyinosine (22b)
The reaction of compound 21b (565 mg, 1.0 mmol) with TBAF
(1 M in THF, 2.2 mL, 2.2 mmol) in THF (10 mL) was carried out
as described for compound 22a and puried by ash column
chromatography (CH2CI2/MeOH, 9 : 1) to give 22b (246 mg,
73%) as a pale yellow solid. 1H NMR (500 MHz, DMSO-d6) d 8.56
(s, 1H, CH]N), 8.21 (s, 1H, H-2), 6.49 (t, J ¼ 6.4 Hz, 1H, H-10),
5.25 (s, 1H, OH), 4.96 (s, 1H, OH), 4.43 (br s, 1H, H-30), 3.81 (br s,
1H, H-40), 3.64 (dd, J ¼ 11.4, 4.6 Hz, 1H, H-5b0), 3.47 (br s, 4H,
NCH3, H-5a0), 3.14 (s, 3H, NCH3), 3.09–2.90 (m, 4H, NCH3, H-
2b0), 2.05 (ddd, J ¼ 8.8, 6.4, 2.0 Hz, 1H, H-2a0); 13C NMR (125
MHz, DMSO-d6) d 157.1 (C]N), 155.5 (C6), 154.4 (C8), 146.5
(C4), 145.6 (C2), 121.7 (C5), 87.5 (C40), 82.5 (C10), 71.3 (C30), 62.3
(C50), 40.3 (NCH3), 37.1 (NCH3), 34.4 (C20), 33.4 (NCH3); HRMS
7,8-Dihydro-50-O-dimethoxytrityl-8-oxo-20-deoxyinosine (25)29
Reaction of compound 3 (350 mg, 1.35 mmol) with 4,40-dime-
thoxytrityl chloride (486 mg, 1.44 mmol) in dry pyridine (70 mL)
was carried out as described for compound 17a and puried by
ash column chromatography (CH2CI2/MeOH/TEA, 95 : 4 : 1) to
give 25 (510 mg, 69%) as a white foam. Spectral and analytical
data were in agreement with previous report.29
7,8-Dihydro-50-O-dimethoxytrityl-8-oxo-20-deoxyinosine-30-
(2-cyanoethyl-N,N-diisopropyl)phosphoramidite (26)29
(ESI+): calcd for C14H20N6O4 [M + Na]+ 359.1438; found The reaction of compound 25 (400 mg, 0.70 mmol) with 1 M
359.1444.
bis(diisopropylamino)(2-cyanoethoxy)phosphine (1.40 mL, 1.40
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Chem. Sci., 2016, 7, 995–1010 | 1007