Helvetica Chimica Acta ± Vol. 82 (1999)
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dried (Na2SO4), evaporated, and co-evaporated twice with toluene to yield a brown foam. FC (CH2Cl2/MeOH
95 : 5) gave 10 (6.11 g, 87.3%). Colorless foam. TLC (CH2Cl2/MeOH 95 : 5): Rf 0.56. 1H-NMR (250 MHz,
(D6)DMSO): 12.28 (br. s, NH); 11.72 (br. s, NHBz); 8.35 (s, H C(8)); 8.15 ± 7.42 (m, 20 arom. H); 6.50
(d, 3J(1',2') 4.95, H C(1')); 6.39 (t, H C(2')); 6.21 (t, H C(3')); 4.91 (m, H C(4')); 4.80 (m, 2H C(5')).
13C-NMR (62.9 MHz, (D6)DMSO): 169.02 (NHCO); 165.47, 164.72, 164.47 (CO); 154.98 (C(6)); 148.38
(C(2)); 148.29 (C(4)); 138.72 (C(8)); 133.97, 133.56, 133.18, 132.44, 129.39, 129.30, 129.25, 128.84, 128.80,
128.74, 128.61, 128.47, 128.24 (arom. C); 121.14 (C(5)); 86.03 (C(1')); 79.67 (C(4')); 73.42 (C(2')); 71.44 (C(3'));
63.79 (C(5')). ESI-MS: 700.15 ([M H] ). Anal. calc. for C38H29N5O9 (699.68): C 65.23, H 4.18, N 10.01; found:
C 65.47, H 4.24, N 9.82.
N2,2'-O,3'-O,5'-O-Tetrabenzoyl-6-thioguanosine (11). To a soln. of 10 (1.4 g, 2.0 mmol) in abs. pyridine,
(20 ml), Lawessonꢀs reagent was added (1.62 g, 4.0 mmol) in one portion at r.t. The mixture was heated at reflux
temp. for 6 h. At r.t. pyridine was evaporated, the residue dissolved in CH2Cl2 (40 ml), this soln. washed with 5%
aq. NaHCO3 soln. (60 ml), dried (Na2SO4), and evaporated, and the residue co-evaporated twice with toluene
to yield a yellow foam. FC (CH2Cl2/MeOH 95 :5) gave 11 (1.23 g, 85.6%). Yellow foam. TLC (CH2Cl2/MeOH
95 :5): Rf 0.71. 1H-NMR (250 MHz, (D6)DMSO): 13.61 (br. s, SH); 11.97 (br. s, NHBz); 8.53 (s, H C(8));
8.02 ± 7.42 (m, 20 arom. H); 6.52 (d, 3J(1',2') 4.95, H C(1')); 6.39 (t, H C(2')); 6.20 (t, H C(3')); 4.90
(m, H C(4')); 4.85 (m, 2 H C(5')). 13C-NMR (62.9 MHz, (D6)DMSO): 174.71 (C(6)); 169.25 (NHCO);
165.46, 164.68, 164.47 (CO); 147.73 (C(2)); 144.88 (C(4)); 141.10 (C(8)); 134.03, 133.94, 133.53, 133.32
(arom. C, C(5)); 132.47, 132.20, 129.39, 129.34, 129.22, 128.82, 128.74, 128.61, 128.52, 128.22 (arom. C); 86.10
(C(1')); 79.80 (C(4')); 73.43 (C(2')); 71.41 (C(4')); 63.75 (C(5')). ESI-MS: 716.09 ([M H] ). Anal. calc. for
C38H29N5O8S (715.74): C 63.77, H 4.08, N 9.78; found: C 63.68, H 4.17, N 9.69.
N2-Benzoyl-6-thioguanosine (12). As described for 4, with pyridine (2 ml), MeOH (1 ml), 2m NaOH
(1 ml), and 11 (2.7 g, 3.77 mmol). Recrystallization from EtOH gave 12 (1.25 g, 82.4%). Colorless product. TLC
1
(CH2Cl2/MeOH 8 :2): Rf 0.32. H-NMR (250 MHz, (D6)DMSO): 13.68 (br. s, SH); 12.21 (br. s, NHBz); 8.49
(s, H C(8)); 8.09 ± 7.49 (m, 5 arom. H); 5.90 (d, 3J(1',2') 5.83,
H C(1')); 5.50 (d, OH C(2')); 5.19
(d, OH C(3')); 5.06 (t, OH C(5')); 4.48 (dd, H C(2')); 4.16 (dd, H C(3')); 3.93 (m, H C(4')); 3.61
(m, 2 H C(5')). 13C-NMR (62.9 MHz, (D6)DMSO): 174.20 (C(6)); 167.66 (NHCO); 152.49 (C(2)); 146.98
(C(4)); 139.93 (C(8)); 136.08 (C(5)); 132.43, 131.61, 131.08, 129.22, 128.47, 128.40, 128.22 (arom. C); 87.12
(C(1')); 85.69 (C(4')); 73.74 (C(2')); 70.43 (C(4')); 61.43 (C(5')). ESI-MS: 404.81 ([M H] ).
N-Benzoyl-9-(b-d-ribofuranosyl)-9H-purin-2-amine (13). As described for 5, with 12 (888 mg, 2.2mmol),
boiling H2O (50 ml), and Raney-Ni (4 g). After workup, the residue was dissolved in hot H2O and the soln.
treated with charcoal, filtrated, and cooled down slowly to give 13 (688 mg, 84.2%). Colorless product. TLC
(CH2Cl2/MeOH 8 :2): Rf 0.28. 1H-NMR (250 MHz, (D6)DMSO): 11.09 (s, NH); 9.10 (s, H C(6)); 8.75
(s, H C(8)); 8.00 ± 7.48 (m, 5 arom. H); 6.00 (d, 3J(1',2') 5.73,
H C(1')); 5.53 (d, OH C(2')); 5.23
(d, OH C(3')); 4.99 (t, OH C(5')); 4.69 (dd, H C(2')); 4.21 (m, H C(3')); 3.96 (m, H C(4')); 3.65
(m, 2 H C(5')). 13C-NMR (62.9 MHz, (D6)DMSO): 165.50 (CO); 153.02 (C(2)); 152.03 (C(4)); 148.89
(C(6)); 145.01 (C(8)); 134.30 (C(5)); 131.97, 131.22, 128.23, 128.13 (arom. C); 87.14 (C(1')); 85.86 (C(4')); 73.44
(C(2')); 70.52 (C(3')); 61.13 (C(5')). ESI-MS: 371.87 ([M H] ). Anal. calc. for C17H17N5O9 (371.35): C 54.98,
H 4.16, N 18.86; found: C 54.91, H 4.84, N 18.74.
N-Benzoyl-9-[5'-O-(4,4'-dimethoxytriphenylmethyl)-b-d-ribofuranosyl]-9H-purin-2-amine (14). As de-
scribed for 6, with 13 (743 mg, 2.0 mmol), pyridine (8 ml), 4,4'-dimethoxytriphenylmethyl chloride (744 mg,
2.2 mmol), and pyridine (4 ml) (6 h). Workup with 5% aq. NaHCO3 soln. (30 ml) and CH2Cl2 (2 Â 20 ml) and
FC as described for 6: 14 (1.09 g, 80.9%). Colorless foam. TLC (CH2Cl2/MeOH 95 : 5): Rf 0.37. 1H-NMR
(250 MHz, (D6)DMSO): 9.08 (s, H C(6)); 8.62 (s, H C(8)); 7.92 ± 6.59 (m, 18 arom. H); 6.03 (d, 3J(1',2')
4.48, H C(1')); 5.60 (d, OH C(2')); 5.15 (d, OH C(3')); 4.78 (dd, H C(2')); 4.40 (dd, H C(3')); 4.23
(m, H C(4')); 3.65 (s, 2 MeO); 3.22 (m, 2 H C(5')). 13C-NMR (62.9 MHz, (D6)DMSO): 165.16 (CO);
157.92 ((MeO)2Tr); 153.06 (C(2)); 151.57 (C(4)); 148.91 (C(6)); 145.36 (C(8)); 135.63, 135.47 ((MeO)2Tr);
134.42 (C(5)); 131.98, 131.23, 129.68, 128.30, 128.26, 127.64, 127.55, 126.52, 112.92 ((MeO)2Tr); 88.62 (C(1'));
85.35 ((MeO)2Tr); 84.04 (C(4')); 73.03 (C(2')); 70.67 (C(3')); 64.71 (C(5')); 54.92 (MeO). ESI-MS: 674.53
([M H] ). Anal. calc. for C38H35N5O7 (673.73): C 67.75, H 5.24, N 10.39; found: C 67.22, H 5.29, N 10.36.
N2-Benzoyl-9-{5'-O-(4,4'-dimethoxytriphenylmethyl)-2'-O-[(tert-butyl)dimethylsilyl]-b-d-ribofuranosyl}-9H-
purin-2-amine (15). As described for 7, with 14 (572 mg, 0.85 mmol), pyridine/THF 1:1 (6 ml) AgNO3 (172 mg,
1.015 mmol) and 1m (tert-butyl)dimethylsilyl chloride in THF (1.02 ml): 15 (370 mg, 55.4%). Colorless foam.
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TLC (CH2Cl2/iPrOH 95 :5): Rf 0.51. H-NMR (250 MHz, (D6)DMSO): 10.44 (s, NH); 8.99 (s, H C(6)); 8.47
(s, H C(8)); 7.81 (d, 2 arom. H); 7.62 ± 7.11 (m, 13 arom. H); 6.65 (t, 3 arom. H); 6.08 (d, 3J(1',2') 5.15,
H
C(1')); 5.01 (t, H C(2')); 4.61 (d, OH C(3')); 4.36 (dd, H C(3')); 4.16 (br. s, H C(4')); 3.70 (s, 2 MeO);