20-Deoxypseudoisocytidine
1923
(2.21%, H-C(30))=5.12 (2.75%, H-C(10)); 4.36–4.38 (H-C(30)) ! 2.09 (4.86%, Hb-C(20))=
2.33 (1.17%, Ha-C(20))=3.64–3.76 (2.49%, H2-C(50))=3.96–4.00 (2.85%, H-C(40)); 5.12
(H-C(10))! 2.33 (4.83%, Ha-C(20))=3.96–4.00 (2.98%, H-C(40))=7.98 (3.94%, H-C(6));
7.98 (H-C(6)) ! 2.09 (0.84%, Hb-C(20))=3.64–3.76 (0.79%, H2-C(50))=5.12 (4.96%,
13
H-C(10)). C-NMR (75 MHz, CD3OD): 42.09 (t, C(20)); 64.33 (t, C(50)); 74.74,
76.74 (2 d, C(10), C(30)); 89.2 (d, C(40)); 129.66, 130.11 (2 d, Bz); 134.67 (d, C(6)).
HR-MS (FABþ, [M þ H]þ): 332.1261 (calc. 332.1246).
N4-Benzoyl-50-O-(dimethoxytrityl)-20-deoxypseudoisocytidine (5). To a solution
of 4 (76 mg, 0.23 mmol) in dry pyridine (1 mL) was added 4,40-dimethoxytrityl
chloride (94 mg, 0.27 mmol) and DMAP (2.8 mg, 0.02 mmol). Additional portions of
4,40-dimethoxytrityl chloride (39 mg, 0.11 mmol, each) were added in intervals of 1 h
until no more starting material was detected by TLC (total reaction time of 6 h). The
solution was diluted with AcOEt, washed with water, the organic phase dried
(MgSO4) and evaporated. The residue was purified by FC (CH2Cl2=MeOH 2%,
conditioned with 1% Et3N) to give 121 mg (84%, 0.19 mmol) of 5 as a white foam.
1H-NMR (300 MHz, CDCl3): 1.93 (ddd, J1 ¼ 6.3, J2 ¼ 9.2, J3 ¼ 13.2, 1 H, Hb-
C(20)); 2.48 (ddd, J1 ¼ 2.9, J2 ¼ 6.3, J3 ¼ 13.2, 1 H, Ha-C(20)); 3.22 (dd, J1 ¼ 5.3,
J2 ¼ 9.9, 1 H, H-C(50)); 3.31 (dd, J1 ¼ 4.4, J2 ¼ 9.9, 1 H, H-C(50)); 3.78 (s, 6 H, 2
OCH3); 4.04 (m, 1 H, H-C(40)); 4.39 (m, 1 H, H-C(30)); 5.17 (dd, J1 ¼ 6.1,
J2 ¼ 9.0, 1 H, H-C(10)); 6.81–6.84 (m, 4 H, DMT); 7.18–7.33 (m, 7 H, DMT);
7.42–7.45 (m, 2 H, DMT); 7.48–7.53 (m, 2 H, Bz); 7.59–7.64 (m, 1 H, Bz); 7.81 (s,
13
1 H, H-C(6)); 7.93-7.96 (m, 2 H, Bz). C-NMR (75 MHz, CDCl3): 41.16 (t, C(20));
55.20 (q, 2 OCH3); 64.30 (t, C(50)); 73.85, 74.19 (2 d, C(10), C(30)); 85.49 (d, C(40));
113.13, 126.81, 127.82, 127.92 (4 d, DMT); 128.15, 128.95 (2 d, Bz); 130.02,
130.04 (2 d, DMT); 133.57 (d, C(6)); 135.93, 144.73, 158.49 (3 s, DMT). HR-MS
(FABþ, [M þ H]þ): 634.2525 (calc. 634.2553).
N4-Benzoyl-50-O-(dimethoxytrityl)-20-deoxypseudoisocytidine-30-O-(2-cyanoethyl-
N,N-diisopropyl) phosphoramidite (6). To a solution of 5 (107 mg, 0.17 mmol) in dry
THF (4 mL) was added EtNiPr2 (145 mL, 0.84 mmol) followed by 2-cyanoethyl diiso-
propylchlorophosphoramidite (94 mL, 0.42 mmol). After 70 min, 5% aq. NaHCO3
was added and the mixture extracted twice with AcOEt. The combined organic layers
were dried (MgSO4) and evaporated. FC (AcOEt=hexane 6:4, conditioned with 1%
Et3N) gave 107 mg (76%, 0.13 mmol) of 6 as a white foam.
1H-NMR (300 MHz, CDCl3): 1.06–1.33 (m, 12 H, 4 CH3-C); 1.86–1.96 (m, 1 H,
Hb-C(20)); 2.45 (t, J ¼ 5.0, 1 H, -CH2CN); 2.55–2.67 (m, 2 H, Ha-C(20), -CH2CN);
3.21–3.29 (m, 2 H, H-C(50)); 3.778, 3.785 (2 s, 6 H, 2 OCH3); 3.50–3.86 (m, 4 H, 2
H-C(CH3)2, OCH2); 4.18 (m, 1 H, H-C(40)); 4.49 (m, 1 H, H-C(30)); 5.16 (m, 1 H,
H-C(10)); 6.80–6.84 (m, 4 H, DMT); 7.18–7.34 (m, 7 H, DMT); 7.43–7.45 (m, 2 H,
DMT); 7.49–7.53 (m, 2 H, Bz); 7.60–7.63 (m, 1 H, Bz); 7.83, 7.86 (2 s,br, 1 H, H-
C(6)); 7.93–7.95 (m, 2 H, Bz). 13C-NMR (75 MHz, CDCl3): 20.16, 20.34 (2 dt, J(C,P)
¼
6.68, OCH2CH2CN); 24.53, 24.58, 24.63, 24.68 (4 q, 2 (CH3)2CH); 29.68
(t, C(20)); 43.10 (dd, J(C,P) ¼ 5.80, (CH3)2CH); 43.27 (dd, J(C,P) ¼ 6.07, (CH3)2CH);
55.20, 55.21 (2 q, 2 OCH3); 58.25, 58.32 (2 dt, J(C,P) ¼ 18.19, OCH2CH2CN);
63.80, 63.95 (2 t, C(50)); 74.14, 74.20 (2 d, C(10)); 75.19, 75.55 (2 dd, J(C,P) ¼ 17.29,