Condensation of D-isoleucine (I) with 4-methoxy-benzenesulfonyl chloride (II) in the presence of Et3N afforded sulfonyl derivative (III), which was subsequently converted to tert-butyl ester (V) upon treatment with dimethylformamide di-tert-butyl acetal (IV). Alkylation of (V) with benzyl bromide and K2CO3 in DMF provided the N-benzyl compound (VI). Then, the tert-butyl ester of (VI) was deprotected with HCl in CH2Cl2, and the resulting carboxylic acid (VII) was condensed with O-tert-butyl hydroxylamine using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide-HCl (EDC) and 1-hydroxybenzotriazole (HOBt) to give the tert-butyl hydroxamate (VIII). The target hydroxamic acid was then obtained by deprotection of (VIII) with HCl in dichloroethane containing one equivalent of EtOH.

Condensation of D-valine (I) with 4-methoxybenzenesulfonyl chloride (II) in the presence of Et3N afforded sulfonyl derivative (III), which was subsequently converted to tert-butyl ester (V) upon treatment with dimethylformamide di-tert-butyl acetal (IV). Alkylation of (V) with 2-picolyl chloride-HCl (VI) and K2CO3 in DMF provided the N-(2-picolyl) compound (VII). Then, the tert-butyl ester of (VII) was deprotected with HCl in CH2Cl2, and the resulting carboxylic acid (VIII) was condensed with O-tert-butyl hydroxylamine using N-(3-dimethylaminopropyl)-N'-ethylcarbo-diimide-HCl (EDC) and 1-hydroxybenzotriazole (HOBt) to give the tert-butyl hydroxamate (IX). The target hydroxamic acid was then obtained by deprotection of (IX) with HCl in dichloroethane containing one equivalent of EtOH.