Highly Efficient Chiral-Pool Synthesis of (2S,4R)-4-Hydroxyornithine

A concise synthesis of the amino acid (2S,4R)-4-hydroxyornithine is described. Starting from diprotected l-aspartic acid, the scaffold of the target compound is constructed in a three-step approach:  an efficient α-nitroketone formation through acylation of nitromethane is followed by a diastereoselective reduction of the resulting ketone. In the last step, the nitro group is reduced to furnish the (2S,4R)-4-hydroxyornithine scaffold. This new approach to the title compound offers advantages to the synthetic pathways previously described.