Diastereoselective reduction of enantiomerically pure 4-oxo alpha-amino acids, available from the reaction of the zinc homoenolate 1 [(S)-N-(tert-butoxycarbonyl)-3-iodozinciolanine benzyl ester] with alpha-functionalised acetyl chlorides in the presence of bis(triphenylphosphine)palladium dichloride, allows the preparation of a variety of 4-hydroxy alpha-amino acid derivatives, including the potential clavalanine precursor 5a and the erythro 4-hydroxyornithine derivative 6f.