N-Alkylation of N-Boc-O-benzylhydroxylamine (1) with benzyl 4-bromobutyrate (2) in DMF gave N,O-bisprotected benzyl 4-hydroxyamino-butyrate (3), which was converted into 4-benzyloxyamino-butyric acid benzyl ester (4) with TFA in methylene chloride. Treatment of 4 with formic acid/acetic anhydride or various acid chlorides followed by catalytic hydrogenation led to 4-(N-acyl-N-hydroxyamino)-butyric acids 6.