New synthesis of 5-amino-4-hydroxy-2,6-dimethylheptanoic acid, a hydroxyethylene isostere of the Val-Ala dipeptide

Two stereoisomers of the title compound have been synthesized from the methyl ester of N-Boc L-valine. The aminoester was initially converted into an α′-amino α,β-unsaturated ketone via a phosphonoketone and a Horner–Emmons olefination with acetaldehyde. Hydrocyanation of the enone with diethylaluminium cyanide and functional group conversions gave the hydroxyaminoacids protected as oxazolidines or as lactones.