The esterification of D-leucine (I) with benzyl alcohol and HCl gives the corresponding ester (II), which is N-benzylated by reductocondensation with benzaldehyde and sodium cyanoborohydride yielding N-benzyl-D-leucine benzyl ester (III). The condensation of (III) with methyl phenyl phosphinyl chloride (IV) by means of N-methylmorpholine in dichloromethane affords the phosphinylamino derivative (V), which is treated with H2 over Pd/C in methanol to give N-benzyl-N-[methyl(phenyl)phosphinyl]-D-leucine (VI). The condensation of (VI) with O-benzylhydroxylamine (VII) by means of 1-[3-(dimethylamino) propyl]-3-ethylcarbodiimide (DEC) and HOBT in DMF yields the N-benzyl hydroxamic acid (VIII) as a diastereomeric mixture that is separated by flash chromatography providing the diastereomer (IX). Finally, this compound is deprotected by hydrogenation with H2 over Pd/C in methanol.

The esterification of D-leucine (I) with benzyl alcohol and HCl gives the corresponding ester (II), which is N-benzylated by reductocondensation with benzaldehyde and sodium cyanoborohydride yielding N-benzyl-D-leucine benzyl ester (III). The condensation of (III) with methyl phenyl phosphinyl chloride (IV) by means of N-methylmorpholine in dichloromethane affords the phosphinylamino derivative (V), which is treated with H2 over Pd/C in methanol to give N-benzyl-N-[methyl(phenyl)phosphinyl]-D-leucine (VI). The condensation of (VI) with O-benzylhydroxylamine (VII) by means of 1-[3-(dimethylamino) propyl]-3-ethylcarbodiimide (DEC) and HOBT in DMF yields the N-benzyl hydroxamic acid (VIII) as a diastereomeric mixture that is separated by flash chromatography providing the diastereomer (IX). Finally, this compound is deprotected by hydrogenation with H2 over Pd/C in methanol.