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D. A. MEGGER AND J. MULLER
2528
Deprotection of 1 with NaOMe. Sodium methoxide (757 mg, 14.0 mmol)
was added to a solution of 1 (2.001 g, 3.875 mmol) in dry methanol (100 mL). The
mixture was stirred for 24 h at ambient temperature under argon and then evapo-
rated to dryness. The residue was purified as described previously to yield compound
3 (865.9 mg, 3.276 mmol, 85%).
Deprotection of 1 with K2CO3. A solution of 1 (91.3 mg, 177 mmol) in dry
methanol (10 mL) was treated with K2CO3 (57.4 mg, 415 mmol) predried at 200 ꢁC.
The resulting suspension was stirred at ambient temperature for 2 h until a clear
solution was formed. The solution was evaporated to dryness, and the residue was
purified as described previously to yield compound 3 (42.0 mg, 159 mmol, 90%).
1-Deaza-6-methoxypurine-N9-b-[2’-deoxy-5’-O-(4,4’-dimethoxytrityl)-
ribonucleoside] (4). Compound 3 (758.3 mg, 2.859 mmol) was co-evaporated with
dry pyridine (2 ꢂ 15 mL) and then dissolved in dry pyridine (15 mL) under argon. To
this solution, catalytic amounts of N,N-dimethyl-4-aminopyridine (2 mg) as well as
4,40-dimethoxytrityl chloride (1.401 g, 4.135 mmol) were added. The reaction mixture
was stirred for 3 h at ambient temperature and then quenched by the addition of
saturated aqueous NaHCO3 solution (15 mL). The mixture was extracted with
dichloromethane (3 ꢂ 50 mL), and the organic extract was dried (Na2SO4) and eva-
porated to dryness. The residue was purified by column chromatography [SiO2,
gradient: A: CH2Cl2 (100)–MeOH (1)–Et3N (1) ! B: CH2Cl2 (95)–MeOH (5)–
1
Et3N (1)], yielding compound 4 (Rf in A ¼ 0.15) (1.328 g, 2.339 mmol, 82%). H
NMR (400 MHz, CDCl3): d=ppm ¼ 8.19 (d, 1H, J ¼ 5.6 Hz, H2); 8.08 (s, 1H, H8);
7.43–7.38 (m, 2H, DMT); 7.32–7.27 (m, 4H, DMT); 7.27–7.21 (m, 2H, DMT);
7.18 (m, 1H, DMT); 6.81–6.75 (m, 4H, DMT); 6.67 (d, 1H, J ¼ 5.6 Hz, H1); 6.58
(pt, 1H, J ¼ 6.5 Hz, H10); 4.62 (m, 1H, H30); 4.17 (m, 1H, H40); 4.09 (s, 3H,
O-Me); 3.76 (s, 6H, DMT); 3.43–3.33 (m, 2H, H50, H500); 2.75 (m, 1H, H20); 2.50
(m, 1H, H200). 13C NMR (101 MHz, CDCl3): d=ppm ¼ 158.5 (DMT); 157.8 (C6);
148.2 (C2); 146.0 (C8); 144.6 (C4); 139.9 (DMT); 135.8 (DMT); 135.7 (DMT);
130.0 (DMT); 128.1 (DMT); 127.8 (DMT); 126.8 (DMT); 125.9 (C5); 113.1
(DMT); 101.7 (C1); 86.4 (DMT); 86.0 (C40); 84.0 (C10); 71.9 (C30); 63.9 (C50); 56.3
(O-Me); 55.1 (DMT); 40.5 (C20). Anal. calcd. for C33H33N3O6 ꢀ MeOH: C, 68.1;
H, 6.2; N, 7.0: Found: C, 68.4; H, 6.8; N, 7.4. MS (MALDI-TOF): calcd. for
C33H34N3O6 (MH)þ: 568: found 568.
1-Deaza-6-methoxypurine-N9-b-[2’-deoxy-3’-O-(2-cyanoethyl)-N,N-
diisopropylphosphoramidite-5’-O-(4,4’-dimethoxytrityl)-ribonucleoside] (5).
N,N-Diisopropylethylamine (735 mL, 4.21 mmol) and 2-cyanoethyl N,N-diisopropyl-
chlorophosphoramidite (525 mL, 3.01 mmol) were added to a solution of 4 (1.193 g,
2.103 mmol) in dry CH2Cl2 (15 mL). The solution was stirred for 30 min at ambient
temperature under argon and then diluted with an aqueous solution of NaHCO3
(5%) (40 mL) and CH2Cl2 (40 mL). The organic layer was separated, and the aque-
ous layer was extracted with CH2Cl2 (2 ꢂ 30 mL). The combined organic layers were
dried (Na2SO4) and evaporated to dryness. The resulting residue was purified by col-
umn chromatography [SiO2, CH2Cl2 (75)–EtOAc (23)–Et3N (2)] to yield the desired
product as a diastereomeric mixture (Rf ¼ 0.55 and 0.40) (895.0 mg, 1.166 mmol,
1
55%). H NMR (200 MHz, CDCl3): d=ppm ¼ 8.20 (d, 1H, J ¼ 5.6 Hz, H2); 8.11 (s,