[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([NH:8][C@H:9]([C:13]([OH:15])=[O:14])[CH:10]([CH3:12])[CH3:11])=[CH:4][CH:3]=1.[CH:16]([O:18][C:19](=O)[CH3:20])=[O:17].C(O)(=O)C.[CH:26]([OH:28])=O>>[CH:16]([N:8]([C:5]1[CH:4]=[CH:3][C:2]([Cl:1])=[CH:7][CH:6]=1)[C@H:9]([C:13]([OH:15])=[O:14])[CH:10]([CH3:12])[CH3:11])=[O:17].[C:19]([C:26]([N:8]([C:5]1[CH:4]=[CH:3][C:2]([Cl:1])=[CH:7][CH:6]=1)[C@H:9]([C:13]([OH:15])=[O:14])[CH:10]([CH3:12])[CH3:11])=[O:28])(=[O:18])[CH3:20]A mixture of the m-phenoxybenzyl ester of N-(4-chlorophenyl)valine (1.22 mmole), acetic formic anhydride in acetic acid (23.8 mmole, 2.1 g) and formic acid (1.5 ml) is stirred overnight at RT under nitrogen. The reaction product is concentrated and then subjected to prep. TLC eluting with 20% ethylacetate/hexane to yield the m-phenoxybenzyl ester of N-formyl,N-(4-chlorophenyl)valine, MS m/e 437 (M+, 8.1), 182 (100).
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