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on HSQC and COSY): 169.89 (s, CO); 159.47, 154.71 (2s, C(2), C(6)); 151.34 (s, C(4)); 151.07 (s, C(8));
137.44, 137.28, 137.18, 136.12 (4s); 129.71, 129.40, 129.10, 128.48, 128.44, 128.18, 128.07, 127.96, 127.85, 127.78,
127.52, (several d); 117.17 (s, C(5)); 74.39 (d, C(4')); 74.30 (d, C(2')); 73.79 (d, C(5')); 73.24, 72.58, 71.41
(3t, 3 PhCH2); 69.33 (d, C(1')); 68.48 (t, PhCH2); 67.86 (d, C(3')); 67.17 (t, C(6')); 34.29 (d, Me2CH); 31.58
(t, CH2ÀC(8)); 20.84 (q, MeCO); 19.29 (q, Me2CH). HR-MALDI-MS: 822.3464 (45, [M Na] ,
C46H49N5NaO8 ; calc. 822.3479).
8-[(3-O-Acetyl-2,4,6-tri-O-benzyl-a-d-mannopyranosyl)methyl]-2',3',5'-tri-O-benzoyl-O6-benzyl-N2-(2-
methylpropanoyl)guanosine (21). A soln. of 19 (1.402 g, 1.752 mmol) in MeCN (17 ml) was treated with N,O-
bis(trimethylsilyl)acetamide (0.86 ml, 3.505 mmol), heated to 808 for 25 min, cooled to 238, treated with a soln.
of 1-O-acetyl-2,3,5-tri-O-benzoyl-b-d-ribofuranose (20) (0.972 mg, 1.927 mmol) in MeCN (3 ml), followed by
TMSOTf (0.41ml, 2.277 mmol), stirred at 23 8 for 1h, and heated to 65 8 for 1.5 h. The orange soln. was allowed
to cool to 238, diluted with CH2Cl2 (200 ml), and washed with 50% sat. aq. NaHCO3 soln. The aq. layer was
extracted with CH2Cl2 (2 Â 100 ml). The combined org. extracts were dried and evaporated. FC (silica gel;
cyclohexane/AcOEt, 3 :1) afforded 21 (1.663 g, 76%). Colourless foam. Rf (cyclohexane/acetone 2 :1) 0.40.
25
a 7.6 (c 1.03, CHCl3). IR (neat): 3353w, 3063w, 3032m, 2955w, 2925w, 2870w, 1724s, 1602m, 1496w,
D
1
1452m, 1422m, 1371m, 1314m, 1266s, 1232s, 1178m, 1094s, 1070m, 1026m, 907w. H-NMR (CDCl3, 500 MHz):
8.36 (br. s, exchanges with D2O, NH); 8.00 (dd, J 8.4, 1.3, 2 arom. H); 7.91 (dd, J 8.4, 1.2, 2 arom. H); 7.73
(dd, J 8.4, 1.3, 2 arom. H); 7.61 (dd, J 7.4, 1.6, 2 arom. H); 7.55 (dt, J 7.5, 1.3, 1 arom. H); 7.51 (dt, J 7.5, 1.3,
1arom. H); 7.42 7.11( m, 23 arom. H); 7.05 (dd, J 8.6, 5.3, HÀC(3')); 7.00 (dd, J 6.5, 2.1, 2 arom. H); 6.69
(dd, J 5.3, 1.3, HÀC(2')); 6.50 (d, J 1.4, HÀC(1')); 5.71( d, J 12.1, PhCH); 5.63 (d, J 12.1, PhCH); 5.41
(t, J 3.7, HÀC(3'')); 4.79 4.71( m, HÀC(4'), HAÀC(5')); 4.58 (d, J 11.7, PhCH); 4.59 4.53 (m, HBÀC(5'));
4.41( d, J 11.7, PhCH); 4.37 (s, PhCH2); 4.28 (td, J 9.6, 8.8, 5.3, HÀC(1'')); 4.22 (s, PhCH2); 3.84 (td, J 6.3,
2.9, HÀC(5'')); 3.73 (dd, J 8.2, 3.1, HÀC(2'')); 3.59 (dd, J 4.5, 3.0, HÀC(4'')); 3.53 3.43 (m, HACÀC(8),
2 HÀC(6'')); 3.02 (dd, J 14.8, 9.3, HBCÀC(8)); 3.00 2.86 (br. s, Me2CH); 1.88 (s, MeCO); 1.30, 1.28 (2d, J
6.9, Me2CH). NOEs: irrad. at 6.50 ! 1 % (HÀC(2')), 0.5% (HÀC(4') and HACÀC(8)), 2% (HBCÀC(8)).
13C-NMR (CDCl3, 125 MHz): 175.01 (s, NHCO); 169.85, 166.12, 165.41, 164.99, (4s, 4 CO); 160.04 (s, C(6));
152.71, 151.90, 151.42 (3s, C(2), C(4), C(8)); 137.97, 137.61, 137.58, 136.17 (4s); 133.52 127.28 (several d); 117.27
(s, C(5)); 87.49 (d, C(1')); 78.54 (d, C(4')); 74.47 (d, C(5'')); 74.37 (d, C(2'')); 74.33 (d, C(2')); 74.10 (d, C(4''));
70.84 (d, C(3')); 70.62 (d, C(1'')); 73.04, 72.06, 71.08, 68.85 (4t, 4 PhCH2); 67.49 (t, C(6'')); 67.40 (d, C(3'')); 62.53
(t, C(5')); 36.28 (d, Me2CH); 30.32 (CH2ÀC(1)); 20.88 (q, MeCO); 19.31, 19.27 (2q, Me2CH). HR-MALDI-MS:
1266.4667 (90, [M Na] , C72H69N5NaO15; calc. 1266.4688).
O6-Benzyl-N2-(2-methylpropanoyl)-8-[(2,4,6-tri-O-benzyl-a-d-mannopyranosyl)methyl]guanosine (22). A
soln. of 22 (1.663 g, 1.337 mmol) in CH2Cl2/MeOH 1:1(30 ml) was cooled to 0 8, treated with K2CO3 (0.240 g,
1.737 mmol), and stirred for 80 min at 08 and for 2 h at r.t. The pH of the soln. was adjusted to 6 7 by the
addition of glacial AcOH. Evaporation, co-evaporation with toluene, and FC (silica gel; cyclohexane/acetone/
NH4OH 2 :1:0.01 ! 1:1:0.01) afforded 22 (868 mg, 73%). Colourless solid. Rf (cyclohexane/acetone 1:1) 0.43.
25
D
a À10.9 (c 0.25, CHCl3). IR (neat): 3343w (br.), 3062w, 3030m, 2927m, 2925w, 2872w, 1699w, 1614s,
1592m, 1497m, 1454s, 1427s, 1393m, 1355m, 1234s, 1192m, 1092s, 1071s, 1028m, 907w. 1H-NMR (CDCl3,
500 MHz): 7.76 (br. s, NH); 7.58 7.56 (m, 2 arom. H); 7.37 7.26 (m, 13 arom. H); 7.13 (tt, J 7.3, 1.3, 1 arom.
H); 7.07 (tt, J 7.5, 1.4, 2 arom. H); 6.85 (d, J 6.9, 2 arom. H); 5.98 (d, J 6.5, HÀC(1')); 5.68 (d, J 12.1,
PhCH); 5.63 (d, J 12.1, PhCH); 4.95 (br. d, J 9.0, HOÀC(5')); 4.91(br. s, HOÀC(2')); 4.62 (br. t, J ꢀ 5.9,
HÀC(2')); 4.61 4.53 ( m, 2 PhCH2); 4.50 (dd, J 5.6, 2.2, HÀC(3'); 4.31( d, J 11.3, PhCH); 4.25 (td, J ꢀ 8.9,
2.6, HÀC(1'')); 4.15 (q, J 2.2, HÀC(4')); 4.09 (d, J 11.3, PhCH); 4.11 4.06 (m, HÀC(3''), HÀC(5'')); 3.90
(t, J 10.6, HÀC(6'')); 3.85 (br. d, J 12.6, HÀC(5')); 3.73 (br. t, J ꢀ 10.3, HÀC(5')); 3.68 (dd, J 8.3, 3.0,
HÀC(2'')); 3.52 (dd, J 4.3, 2.5, HÀC(4'')); 3.47 (dd, J 14.4, 3.2, CHAÀC(8)); 3.36 (dd, J 10.7, 3.1,
HÀC(6'')); 3.14 (br. s, HOÀC(3')); 2.95 (dd, J 14.4, 9.5, CHBÀC(8)); 2.83 (sept., J 6.7, Me2CH); 2.50 (br.
s, HOÀC(3'')); 1.31, 1.30 (2d, J 6.9, Me2CH). 13C-NMR (CDCl3, 125 MHz, assignments based on HSQC and
COSY): 178.08 (s, CO); 160.10 (s, C(6)); 152.62, 152.56, 150.61 (3s, C(2), C(4), C(8)); 137.66, 137.04, 136.76,
135.86 (4s); 128.88 127.44 (several d); 117.91 (s, C(5)); 89.74 (d, C(1')); 86.45 (d, C(4')); 76.10 (d, C(2'')); 75.82
(d, C(4'')); 74.26 (d, C(5'')); 72.45 (d, C(2')); 71.69 (d, C(3')); 73.49, 72.43, 71.51, 69.00 (4t, 4 PhCH2); 68.74
(d, C(1'')); 67.63 (t, C(6'')); 66.78 (d, C(3'')); 63.02 (t, C(5')); 36.47 (d, Me2CH); 30.61( t, CH2ÀC(8)); 19.44,
19.33 (2q, Me2CH). HR-MALDI-MS: 912.3780 (90, [M Na] , C49H55N5NaO11; calc. 912.3796).
1-{O6-Benzyl-N2-(2-methylpropanoyl)-8-[(2,4,6-tri-O-benzyl-a-d-mannopyranosyl)methyl]guanin-9-yl}-
2,3-O-isopropylidene-b-d-ribofuranosyluronic Acid (23). A soln. of 22 (0.100 g, 0.112 mmol) and TsOH ¥ H2O
(0.005 g, 0.028 mmol) in acetone (5 ml) was treated with 2,2-dimethoxypropane (0.011 ml, 1.798 mmol), stirred
for 7 h, neutralised (pH 7 8) by the addition of 1m NH4OH soln. in acetone/H2O (3 :7), and filtered, and the