C([S:4][CH2:5][CH:6]([C:18]([F:21])([F:20])[F:19])[C:7]([NH:9][C@H:10]([C:15]([OH:17])=[O:16])[CH2:11][CH:12]([CH3:14])[CH3:13])=[O:8])(=O)C.S([O-])(O)(=O)=O.[K+].C(OCC)(=O)C>[OH-].[NH4+].O.CO.C(O)(=O)C.CCCCCC>[F:19][C:18]([F:20])([F:21])[CH:6]([CH2:5][SH:4])[C:7]([NH:9][C@H:10]([C:15]([OH:17])=[O:16])[CH2:11][CH:12]([CH3:14])[CH3:13])=[O:8]
A suspension of the product of Example 18 (2.3 g., 6.98 mmol.) in 4.45 mL of concentrated ammonium hydroxide and 10 mL of water was stirred at room temperature under argon for 8 minutes. The resulting clear solution was acidified with 5% potassium hydrogen sulfate solution to pH 2 and extracted with 100 mL of ethyl acetate followed by 3×75 mL of additional extractions. The combined ethyl acetate extract was washed with 100 mL of brine, dried (MgSO4) and evaporated to give 1.94 g. of an off-white solid. Flash chromatography on 200 g. of silica gel eluting with ethyl acetate:hexanes:acetic acid, 100:100:1 afforded 1.72 g. of the title isomer A product as a white crystalline solid, m.p. 143°-145° C., TLC Rf =0.38 (100:50:1 ethyl acetate:hexane:acetic acid), [α]D =-62.2° (c=1.00, methanol).
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