[CH2:1]1[C:10]2[C:5](=[CH:6][C:7]([C:11]([C@@H:13]3[C@@H:18]([CH3:19])[CH2:17][CH2:16][CH2:15][C:14]3([CH3:21])[CH3:20])=[O:12])=[CH:8][CH:9]=2)[CH2:4][CH2:3][NH:2]1.[CH3:22][Li]>O1CCCC1>[CH2:1]1[C:10]2[C:5](=[CH:6][C:7]([C@@:11]([C@@H:13]3[C@@H:18]([CH3:19])[CH2:17][CH2:16][CH2:15][C:14]3([CH3:20])[CH3:21])([OH:12])[CH3:22])=[CH:8][CH:9]=2)[CH2:4][CH2:3][NH:2]1To a stirred solution of the product of Example 13b (95 mg, 0.33 mmol) in anhydrous tetrahydrofuran (6 mL) under argon at −78° C. was added methyl lithium (1.6 M in diethyl ether) (1.04 mL, 1.66 mmol). The reaction was stirred at −78° C. for 1 hour, after which the reaction was allowed to warm gradually to room temperature and stirring was continued overnight. The reaction was quenched with saturated aqueous ammonium chloride (25 mL) and the organics were extracted with ethyl acetate (25 mL×3). The combined organic phase was washed with brine (40 ml), dried over anhydrous sodium sulfate and concentrated under reduced pressure. Purification of the residue by silica gel column chromatography (eluent: dichloromethane/methanol=50/1->5/1) afforded 30 mg of the impure title compound as a yellow oil which was used directly in the next step. Mass spectrum (ESI +ve) m/z 302 (M+H+).
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