838
Md. J. Uddin et al.
2.4.2.6) was added (300 µg in 2 µL 100 mM sodium phosphate buffer,
pH 6.0) with continued agitation at 37◦C for 4 hours. The reaction was
cooled to room temperature, and water was removed by rotary evaporation.
The resulting residue was purified by flash chromatography using 35:7:1
CHCl3:MeOH:NH4OH resulting in a white solid. The product was recrystal-
lized using 6:1 EtOAc:MeOH to give colorless crystals of 3 (0.59 g, 40%).
1H NMR (400 MHz, D2O) 2.62–2.65 (m, 1H), 2.86–2.88 (m, 1H), 3.81–3.84
(m, 2H), 4.17 (q, 1H), 4.67–4.70 (m, 1H), 6.52 (t, 1H), 8.64 (s, 1H), 8.68 (s,
1H); MS (ESI) m/z (M+H)+ calcd 271.05; found 271.06
Synthesis of 5ꢀ-Dimethoxytrityl 6-chloropurine-2ꢀ-deoxyriboside (4)
To a stirred solution of 3 (174 mg, 0.64 mmol) in dry pyridine
(2.5 mL) was added diiospropylethylamine (168 mg, 0.96 mmol) followed
by dimethoxytrityl chloride (304 mg, 0.9 mmol). The reaction mixture
was stirred at room temperature for 5 hours. Then MeOH (1 mL) was
added with further stirring for 10 minutes. Water (18 mL) was added
and the organic compounds were extracted with CH2Cl2 and washed with
10% K2CO3. The organic layer was dried with Na2SO4 and evaporated in
vacuo, and the residue was purified by flash chromatography using 4:95:1
CHCl3:MeOH:diisopropylethylamine to give the product (4) as a brown
amorphous solid (280 mg, 77%). 1H NMR (400 MHz, DMSO d6) 2.36–2.40
(m, 1H), 2.85–2.89 (m, 1H), 3.12–3.21 (m, 2H), 4.00–4.04 (m, 1H), 4.49–4.52
(m, 1H), 5.40 (d, 1H, OH), 6.47 (t, 1H), 6.50- 6.78 (m, 4H), 7.13–7.21 (m,
7H), 7.27–7.30 (m, 2H), 8.69 (s, 1H), 8.79 (s, 1H); MS (ESI) m/z (M+H)+
calcd 573.18; found 573.20.
Synthesis of 6-Chloropurine-2ꢀ-deoxyriboside 5ꢀ-dimethoxytrityl
3ꢀ-(2-cyanoethyl-N,N-diisopropylamino)phosphoramidite (5)
To a stirred solution of 4 (40 mg, 0.07 mmol) in dry CH2Cl2 (0.5 mL) was
added diisopropylethylamine (13 mg, 0.1 mmol) followed by β-cyanoethyl-
N,N -diisopropylamino-3-chlorophosphoramidite (20 mg, 0.084 mmol). The
reaction mixture was stirred at room temperature for 1 hour. Then EtOAc
(0.5 mL) and water (1 mL) were added, and the organic compounds were
extracted and washed with saturated NaHCO3 and water. The organic layer
was dried with Na2SO4 and evaporated in vacuo, and the residue was purified
by flash chromatography using 49:50:1 EtOAc:n-Hex:triethylamine to give
the product 5 as a colorless gummy mass (86% total). A diastereomerically
pure single isomer was obtained with a silica column using a gradient elution
of EtOAc:n-Hex:TEA (10:89:1 to 30:69:1). Single isomer—1H NMR (400
MHz, DMSO d6) 1.12 (s, 3H), 1.13 (s, 3H), 1.14 (s, 3H), 1.15 (s, 3H),
2.54–2.56 (m, 1H), 2.67 (t, 2H), 3.12–3.14 (m, 1H), 3.22–3.28 (m, 2H),
3.57–3.58 (m, 2H), 3.65–3.68 (m, 2H), 3.71 (s, 3H), 3.72 (s, 3H), 4.18–4.21
(m, 1H), 4.82–4.86 (m, 1H), 6.50–6.52 (m, 1H), 6.74–6.79 (m, 4H), 7.15–7.20