[CH2:1]([O:8][C:9](=[O:20])[NH:10][CH:11]1[CH2:16][CH2:15][CH2:14][CH2:13][CH:12]1[C:17](=[O:19])C)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.O.[OH-].[Li+].Cl.C(OCC)(=[O:27])C>O1CCCC1.O>[CH2:1]([O:8][C:9]([NH:10][CH:11]1[CH2:16][CH2:15][CH2:14][CH2:13][CH:12]1[C:17]([OH:19])=[O:27])=[O:20])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1
The ester of step 1 (26.45 g, 86.62 mmol) was dissolved in 250 mL of tetrahydrofuran and treated with a solution of lithium hydroxide monohydrate (10.65 g, 256 mmol) in 250 mL of water and stirred at ambient temperature for 24 h. The reaction mixture was cooled to 0° C. and neutralized with 300 mL of a 1N HCl solution. Ethyl acetate (400 mL) was added and the organic layer was separated, dried over sodium sulfate, filtered and concentrated to give a crude solid. The product was purified by recrystallizing from ethyl acetate/hexanes to give 19.60 g of a white solid. Yield: 82%, MS: 278 (M+H+), mp=120.1-123.1° C.
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