[C:1]([N:4]1[CH2:9][CH2:8][CH2:7][C:6]([CH2:18][CH:19]=[O:20])([CH2:10][C:11]2[CH:16]=[CH:15][C:14]([CH3:17])=[CH:13][CH:12]=2)[CH2:5]1)(=[O:3])[CH3:2].[OH-].[Na+].[CH2:23]([OH:25])[CH3:24]>O.[N+]([O-])([O-])=O.[Ag+]>[C:1]([N:4]1[CH2:9][CH2:8][CH2:7][C:6]([CH2:18][C:19]([O:25][CH2:23][CH3:24])=[O:20])([CH2:10][C:11]2[CH:12]=[CH:13][C:14]([CH3:17])=[CH:15][CH:16]=2)[CH2:5]1)(=[O:3])[CH3:2]Silver nitrate (1.87 g, 11.0 mmol) was dissolved in 3 ml H2O. It was added to a solution of the product from STEP 6 (1.6 g, 5.5 mmol) in 25 ml ethanol. A solution prepared from dissolving NaOH (0.88 g, 22.0 mmol) in 4.0 ml H2O was added dropwise to the silver nitrate solution. The reaction was stirred at 25° C. for 2 h. The reaction was diluted with 15 ml H2O. The ethanol was removed and the resulting residue was extracted with ethyl acetate (2×60 ml). The aqueous extracts were acidified with 1 N aqueous HCl solution to PH=5, and extracted with ethyl acetate (3×100 ml). The organic layer was washed with 15 ml brine, dried with MgSO4, filtered and concentrated to afford a 1.1 g of clean oil. The oil was dissolved in 30 ml ethanol and 15 ml 2M HCl/dioxane. The reaction was stirred at room temperature for 18 h and concentrated. The residue was purified by chromatography (on silica gel, CH2Cl2/MeOH/NH4OH=95/5/0.1) to give 0.88 g of a gummy solid. The 1H NMR spectrum of the product was consistent for the proposed structure.
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