2ꢁ-O-Photocaged Ribonucleoside Phosphoramidites
123
1H), 7.44 (s, 1H), 7.37–7.33 (m, 2H), 7.07–7.04 (m, 3H), 6.76 (s, 1H),
6.07 (d, J = 7.3 Hz, 1H), 5.03 (d, J = 12.8 Hz, 1H), 4.96–4.93 (m, 3H),
4.71–4.65 (m, 2H), 4.40 (s, 1H), 3.99 (dd, J = 1.5, 13.0 Hz, 1H), 3.87 (s,
3H), 3.82 (s, 3H), 3.81 (dd, J = 1.5, 13.0 Hz, 1H); 13C NMR (CDCl3) δ
167.3, 157.1, 153.1, 152.0, 150.4, 149.1, 148.5, 143.7, 140.2, 129.9, 129.7,
126.7, 123.8, 115.0, 114.6, 111.4, 108.1, 89.1, 88.1, 81.2, 70.7, 70.1, 68.3,
65.1, 63.1, 56.5, 56.4; HRMS calcd for C27H29N6O10 [MH+] 597.1940, found
597.1937.
2ꢁ-O-(o-Nitrobenzyl)-N4-phenoxyacetylcytidine (5c).[19] 2ꢁ-O-(o-Nitro-
benzyl)cytidine (4c)[15] (3.58 g, 9.46 mmol) was dried by co-evaporation
with dry pyridine (3 × 100 mL) under vacuum and resuspended in dry
pyridine (180 mL) under argon. Chlorotrimethylsilane (9.0 mL) was added
to the suspension at 0◦C. After the mixture was stirred at rt for 45 minutes, a
solution of phenoxyacetyl chloride (2.00 mL, 14.4 mmol) and 1,2,4-triazole
(0.980 g, 14.3 mmol) in pyridine-acetonitrile (120 mL, 1:1) was slowly
added. After the mixture was stirred at 55◦C overnight, it was cooled to rt,
and the reaction was quenched by addition of H2O (10 mL). After stirring
for 5 minutes, concentrated aqueous NH4OH (6.5 mL) was added at 0◦C,
and the mixture was stirred for 30 minutes. The solvent was removed, and
the crude product was purified by silica gel chromatography, eluting with
3–5% MeOH in CH2Cl2 to give 5c[19] (3.44 g, 71% yield) as a yellow foam.
1H NMR (DMSO-d6) δ 11.04 (s, 1H), 8.51 (d, 1H, J = 7.5 Hz), 8.08 (dd,
1H, J = 1.3, 8.2 Hz), 7.94 (d, 1H, J = 7.7 Hz), 7.77 (m, 1H), 7.57 (m, 1H),
7.35–7.25 (m, 2H), 7.11 (d, 1H, J = 7.5 Hz), 6.96 (m, 1H), 6.92 (m, 2H),
5.94 (d, 1H, J = 2.4 Hz), 5.34 (d, 1H, J = 6.7 Hz), 5.25 (t, 1H, J = 5.0 Hz),
5.15 (s, 2H), 4.83 (s, 2H), 4.12 (m, 1H), 4.15 (s, 1H), 4.03–3.95 (m, 3H),
3.79 (m, 1H), 3.64 (m, 1H); HRMS calcd for C24H25N4O9 [MH+] 513.1622,
found 513.1621.
5ꢁ-O-(Dimethoxytrityl)-2ꢁ-O-(4,5-dimethoxy-2-nitrobenzyl)-N6-phenoxy-
acetyladenosine (6a). According to the procedure described for the
synthesis of 2a, compound 6a was prepared by the reaction of 5a (797 mg,
1.34 mmol) with DMTrCl (1.25 g, 4.02 mmol) in dry pyridine at rt overnight.
Silica gel chromatography (1% methanol in dichloromethane containing
0.5% triethylamine) of the crude product yielded 6a (864 mg, 72% yield)
1
as a yellow foam. H NMR (CDCl3) δ 9.47 (brs, 1H), 8.66 (s, 1H), 8.26 (s,
1H), 7.59 (s, 1H), 7.44–6.81 (m, 19H), 6.30 (d, J = 4.1 Hz, 1H), 5.24 (d, J =
14.0 Hz, 1H), 5.08 (d, J = 14.0 Hz, 1H), 4.86 (s, 2H), 4.74 (t, J = 4.6 Hz,
1H), 4.57 (t, J = 4.9 Hz, 1H), 4.32 (m, 1H), 3.96 (s, 3H), 3.91 (s, 3H), 3.78
(s, 6H), 3.57 (dd, J = 3.2, 10.8 Hz, 1H), 3.46 (dd, J = 4.1, 10.7 Hz, 1H), 2.92
(b, 1H); 13C NMR (CDCl3) δ 158.7, 157.1, 153.6, 152.6, 151.4, 148.4, 148.3,
144.5, 141.9, 140.1, 135.62, 135.60, 130.2, 130.0, 128.2, 128.0, 127.8, 127.1,
123.2, 122.5, 115.0, 113.3, 110.6, 108.2, 87.1, 86.9, 84.3, 81.9, 70.1, 69.8,