[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 1 M 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, 1'-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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