[CH2:1]([O:3][C:4](=[O:20])[C@@H:5]([CH:17]([CH3:19])[CH3:18])[NH:6][S:7]([C:10]1[CH:15]=[CH:14][C:13](F)=[CH:12][CH:11]=1)(=[O:9])=[O:8])[CH3:2].[C:21]1([SH:27])[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=1.C(=O)([O-])[O-].[K+].[K+].O>CN(C)C=O.C(OCC)(=O)C>[CH2:1]([O:3][C:4](=[O:20])[C@@H:5]([CH:17]([CH3:19])[CH3:18])[NH:6][S:7]([C:10]1[CH:15]=[CH:14][C:13]([S:27][C:21]2[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=2)=[CH:12][CH:11]=1)(=[O:9])=[O:8])[CH3:2]
To a solution of 7.76 g (25.6 mmol) of N-[(4-fluorophenyl)sulfonyl]-D-valine ethyl ester from Example 7a in 50 mL of anhydrous dimethylformamide was added 7.8 mL (77 mmol) of thiophenol. After purging with nitrogen for 5 minutes, 10.6 g (77 mmol) of powdered potassium carbonate was added and the reaction heated to 70° C. for 21 hours. The solution was cooled, water and ethyl acetate added and separated. The ethyl acetate layer was washed with saturated sodium bicarbonate, three times with brine, dried with sodium sulfate, filtered and concentrated to afford crude product. This was chromatographed on silica gel using 20% ethyl acetate/hexane to yield 4.2 g of N-[[4-(phenylthio)phenyl]sulfonyl]-D-valine ethyl ester, m/e=400 (M+Li).
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