[Si]([O:18][CH2:19][C@H:20]1[S:24][CH:23]([N:25]2[CH:33]=[N:32][C:31]3[C:26]2=[N:27][C:28]([NH2:35])=[N:29][C:30]=3[NH2:34])[CH2:22][CH2:21]1)(C(C)(C)C)(C1C=CC=CC=1)C1C=CC=CC=1.C(O)(=O)C.[F-].C([N+](CCCC)(CCCC)CCCC)CCC.O>O1CCCC1.C(OCC)C>[CH:23]1([N:25]2[CH:33]=[N:32][C:31]3[C:26]2=[N:27][C:28]([NH2:35])=[N:29][C:30]=3[NH2:34])[S:24][C@H:20]([CH2:19][OH:18])[CH2:21][CH2:22]1
A mixture of 16 (50 mg, 0.1 mmol), acetic acid (7 μL, 0.12 mmol), and 0.17 mL of 1M tetrabutylammonium fluoride in THF (0.17 mmol) was stirred in 10 mL tetrahydrofuran overnight. Water (2 mL) and 15 mL ethyl ether were added followed by stirring for 5 minutes. The organic phase was extracted with 2 mL water and then the combined aqueous solution was washed with 15 mL ethyl ether. The aqueous extract was concentrated in vacuo to 1 mL and then applied to a 4-mL Dowex 1×4 100-200 (-3OH) column to remove tetrabutylammonium salts by eluting with water followed by 20% aqueous methanol. The solvent was removed in vacuo and the product was recrystallized from ethanol/ethyl acetate to afford 19.5 mg (54%) of 17; mp. 187°-90° C. dec; FAB MS 267 (M+H)+ ; 1H NMR (DMSO-d6) δ 8.0 (s, 1, H-8), 6.68 (br, s, 2, NH2), 5.95 (m, 1, I'-H), 5.71 (brs, 2, NH2), 5.22 (m, 1, 5'-OH), 3.73 (m, 1, 5'-H), 3.57 (m, 2, 4'-H, 5'-H), 2.4 (m, 1, 2'-H), 2.32 (m, 1, 2'-H), 2.12 (m, 1, 3'-H), 1.98 (m, 1, 3'-H).
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