[OH-].[NH4+].O[C:4]1[CH:5]=[C:6]([CH:22]=[CH:23][C:24]=1O)[CH2:7][C@@H:8]([C:19]([OH:21])=[O:20])[NH:9][C:10](=[O:18])[CH:11]([CH2:16][SH:17])[C:12]([F:15])([F:14])[F:13].S(=O)(=O)(O)[O-].[K+].CO>O>[F:13][C:12]([F:14])([F:15])[C@@H:11]([CH2:16][SH:17])[C:10]([NH:9][C@@H:8]([CH2:7][CH:6]1[CH2:22][CH2:23][CH2:24][CH2:4][CH2:5]1)[C:19]([OH:21])=[O:20])=[O:18]Concentrated ammonium hydroxide (3.1 mL) was added to a suspension of the title (S) isomer product from part (a) (1.734 g., 4.69 mmol.) in deoxygenated water (3.1 mL) at room temperature. Dissolution occurred almost immediately and the reaction mixture was stirred for 10 minutes at room temperature. The pH was adjusted to 1.5 with saturated potassium bisulfate solution and the mixture was extracted with ethyl acetate (200 mL). The organic layer was washed with brine, dried (MgSO4), and concentrated to a residue which was chromatographed on a 5×15 cm silica gel column. Elution with hexane:ethyl acetate:acetic acid, 80:20:2, concentration of the pure fractions, and coevaporation from heptane afforded a white solid which was triturated with hexane. This solid was dried under high vacuum for 18 hours to afford 1.28 g. of the title (S,S) isomer product; m.p. 141°-143° C., [α]D =+13.6° (c=0.85, methanol).
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